COMPOSITIONS AND METHODS FOR INDIGO DYEING

Abstract

Methods for obtaining indigo dyed yarns with controlled ring dyeing are provided. Systems and devices for yarn indigo dyeing resulting in dyed yarns with homogenous color intensity are also provided.

Claims

1.-24. (canceled)

25. A system for dyeing yarns, comprising: a dyeing bath configured to hold a dyeing solution comprising an indigo composition; at least one yarns delivery system for directing yarns into and inside the dyeing bath; and at least one a solution reduction unit, located after the yarns exit from the dyeing bath and configured to reduce a solution pick-up to at most 100%, wherein the solution pick-up is the percentage of the solution picked up by a cotton yarn exiting the dyeing bath, from the weight of the cotton yarn.

26. The system of claim 25, wherein the dyeing bath comprises at least one US unit.

27. The system of claim 25, wherein the yarns delivery system, comprises: a plurality of delivery units, and wherein each delivery unit comprises two or more delivery rollers configured to direct a portion of the yarns into and inside a dyeing bath.

28. The system of claim 27, wherein each delivery unit is assembled such that each portion of the yarns enters the dyeing bath at a different location.

29. The system of claim 27, further comprising a plurality of squeezing pairs of rollers, wherein each pair of rollers is configured to receive and squeeze the portion of the years from a corresponding delivery unit.

30. The system of claim 27, wherein a distance between each two neighboring yarns rolling on at least one roller from the two or more rollers, of each delivery unit, is in a width of at least one yarn.

31. The system of claim 25, wherein the yarns delivery system, comprises: at least two rollers having a wavy curvature, characterized by varying diameters along the roller's length, and wherein the rollers are assembled consecutively in the yarns' transport direction.

32. The system of claim 31, wherein the rollers are assembled prior to entering a dyeing bath.

33. The system of claim 31, wherein the rollers are assembled after the dyeing bath.

34. The system of claim 31, wherein the wavy curvature has a harmonic curvature.

35. The system of claim 34, wherein the wavy curvature has an irregular harmonic curvature.

36. The system of claim 31, wherein a first roller has a harmonic curvature characterized by a first harmonic frequency, and wherein the first harmonic frequency is determined based on a distance between the first roller and a following second roller.

37. The system of claim 31, wherein the harmonic curvature of each roller is characterized by a harmonic frequency, and wherein the harmonic frequency of each roller depends on the harmonic frequencies of the other rollers.

38. The system of claim 31, comprising: a first roller having a first wavy curvature; and a second roller having a second wavy curvature, wherein a ratio between an average diameter of the first roller and an average diameter of the second roller is at least 1.5.

39. The system of claim 38, wherein the first roller is assembled prior to the second roller in the yarns' transport direction.

40. The system of claim 31, comprising at least 3 rollers.

41. The system of claim 25, wherein the solution reduction unit comprises a blower configured to blow air on the yarns.

42. The system of claim 25, wherein the solution reduction unit comprises a suction unit configured to suck the solution from the yarns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0085] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[0086] FIGS. 1A-1D present images of ring dyeing of yarn at different ultrasound wave frequencies. FIG. 1A 25 kHz, FIG. 1B 40 kHz, FIG. 1C 80 kHz and FIG. 1D 100 kHz.

[0087] FIG. 2 presents a flow chart of the dyeing method of the invention.

[0088] FIGS. 3A-3B presents illustrations of: dyeing method of the invention (FIG. 3A) and traditional indigo dyeing process (FIG. 3B).

[0089] FIG. 4 presents images of denim fabrics woven from the yarns dyed following an exemplary dyeing method of the invention (right). The fabric was subjected to enzyme (middle) and bleach (left) washes.

[0090] FIGS. 5A, 5B, 5C, and 5D are a block-diagram and illustrations of wet sonication systems which can be applied along with the method of the invention.

[0091] FIGS. 5E and 5F are illustrations of delivery systems which can be applied along with the method of the invention.

[0092] FIG. 5G is an illustration of a for dyeing yarns with a solution reduction unit which can be applied along with the method of the invention.

[0093] FIGS. 6A-6B present an image (6A) and a graph (6B) demonstrating a schematic distribution of the indigo along a cross-section of yarns dyed by the traditional indigo dyeing.

[0094] FIGS. 7A-7B present an image (7A) and a graph (7B) demonstrating a schematic distribution of the indigo along a cross-section of yarns dyed by one cycle of sonication-assisted indigo dyeing (Method 1).

[0095] FIGS. 8A-8B present an image (8A) and a graph (8B) demonstrating a schematic distribution of the indigo along a cross-section of yarns dyed by one cycle of sonication-assisted indigo dyeing (Method 2). FIG. 8A shows an inner region (A) with low indigo concentration, and an outer region (B) with high indigo concentration.

[0096] FIGS. 9A-9B present images of indigo dyed yarns after sizing in a composition containing a sizing agent (9A) and similar yarns after sizing in a composition containing the sizing agent and 1% w/w indigo nanoparticles (9B) demonstrating increased color depth at the yarn's rim.

[0097] FIGS. 10A-10B present images of indigo dyed yarns with pre-wetting (10A) and without pre-wetting (10B).

DETAILED DESCRIPTION

[0098] The present invention in some embodiments thereof, is directed to an indigo ring dyeing process(es) mimicking the gradual indigo distribution profile along the cross section of the dyed yarn, as obtained during traditional indigo dyeing process.

[0099] In another embodiment, the present invention is directed to specific elements (e.g., transducer plates, yarn delivery system elements, etc.) in the indigo dyeing system, configured for inducing dyeing homogeneity within a batch of indigo dyed yarns.

Indigo Ring dyeing

[0100] Denim yarns are characterized by ring dyeing effect, i.e. only external fibers of the yarns are intensively dyed and fiber of the inner core are almost not dyed. That makes a cross-section of the yarn look like dyed ring (peripheral portion of the yarn) around almost white core (weakly dyed or undyed center), see FIG. 6A. The creation of the desired worn denim looks is based on this phenomenon and low affinity of indigo to the yarn.

[0101] Traditionally, ring dyeing effect is achieved by use of very diluted dyestuff, short immersion of the yarns to the dyebath, multiple dipping (for dyestuff, such as leuco-indigo, uptake) and skyeing (for dyestuff oxidation and fixation) steps, and, in case of indigo dyeing, pH control which has a profound effect on diffusion speed of leuco-indigo.

[0102] A typical, ring dyeing effect of the traditional indigo dyed yarns is schematically demonstrated in FIG. 6B. As shown in FIG. 6B, the indigo ring is characterized by high indigo concentration at yarn outer shell leading to a significantly more dark shade at the outer diameter, whereas indigo concentration gradually decreases towards the core of the yarn which is practically undyed or contains very low concentration of indigo. The ring dyeing percentage of the traditional indigo dyed yarns is about 75-90%.

[0103] In contrast to the traditional dyeing, a single dyeing step of sonication/cavitation assisted indigo dyeing process disclosed in WO 2024/038442 results in a ring pattern exemplified in FIGS. 7A-B. As shown in FIG. 7B, the indigo ring is characterized by uniform distribution and high concentration of indigo along the entire dyed region within the yarn. Near the inner diameter of the indigo ring, the concentration is abruptly decreases towards undyed inner core. In this case, the ring dyeing percentage is about 30-50%.

[0104] Here, the ring dyeing % is defined as R2/R1, wherein R1 is the total yarn radius, and R2 is the radius of undyed inner core. The terms undyed inner core and undyed core are used herein interchangeably and refer to an almost white or slightly dyed core. Usually, a color depth value (L) in L*a*b or L*C*h color space of the undyed core is between 40 and 60.

[0105] In order to mimic a unique appearance of the traditional denim, the inventors have developed alternative dyeing process, resulting in yarns exhibiting both ring dyeing % and indigo distribution profile similar to indigo dyed yarns obtained by traditional indigo dyeing.

Manufacturing Process

[0106] In one aspect of the invention, there is provided a method for ring indigo dyeing of a yarn comprising: [0107] (i) dipping a plurality of dry yarns into an aqueous composition, to obtain wet yarns; [0108] (ii) dipping the wet yarns into a dyeing composition comprising a plurality of indigo nanoparticles; thereby obtaining indigo ring dyed yarns; wherein the dyeing composition is as disclosed below.

Method 1

[0109] In another aspect of the invention, there is provided a method for yarn indigo dyeing comprising: [0110] (i) dipping a plurality of dry yarns into an aqueous composition, to obtain wet yarns; [0111] (ii) dipping the wet yarns into a dyeing composition to obtained indigo soaked yarns; and [0112] (iii) subjecting the indigo soaked yarns to acoustic waves suitable for inducing a cavitation; thereby obtaining indigo ring dyed yarns.

[0113] In some embodiments, the dyeing composition is as described below. In some embodiments, the subjecting is performed while the indigo soaked yarns are within an aqueous composition (i.e., within the aqueous composition as described below, or the dyeing composition). In some embodiments, the steps (ii) and (iii) are performed simultaneously or subsequently.

[0114] In another aspect of the invention, there is provided a method for yarn indigo dyeing comprising: [0115] (i) dipping a plurality of dry yarns into an aqueous composition, to obtain wet yarns; [0116] (ii) dipping the wet yarns into a dyeing composition; and [0117] (iii) subjecting the wet yarns in contact with the dyeing composition to acoustic waves suitable for inducing a cavitation; thereby obtaining indigo ring dyed yarns.

[0118] In some embodiments, the dyeing composition is characterized by a surface tension above a critical surface tension of the wet yarns. In some embodiments, the cavitation is characterized by cavitation bubbles having an average size between 1 um and 200 um, as disclosed below. In some embodiments, the dyeing composition comprises a plurality of indigo nanoparticles and is characterized by a surface tension above a critical surface tension of the wet yarns.

[0119] In some embodiments, dipping step (i) also referred to herein as pre-wetting step is performed in a pre-wetting bath (e.g., comprising the aqueous composition as disclosed hereinbelow). In some embodiments, the pre-wetting the substrate, wherein the preliminary step is performed prior to performing the dyeing step (ii).

[0120] In some embodiments, dipping step is performed by contacting dry yarns with the aqueous composition for a time period sufficient for obtaining wet yarns. In some embodiments, contacting comprises any process suitable for wetting of dry yarns. In some embodiments, contacting is by dipping, immersing, coating, spraying, spray coating (warm or cold), flow coating, dip coating, extrusion coating, transfer coating, electrospinning, printing, and spin coating or any combination thereof.

[0121] In some embodiments, the term dry yarns refers to yarns which have been stored at ambient conditions and have not been wetted by a liquid. In some embodiments, the moisture content of the dry yarns substantially originates from the moisture absorbed during the manufacturing process, and/or during storage. One skilled artisan will appreciate that a moisture content of dry yarns may vary, depending on the physico-chemical characteristic of the yarns (e.g., chemical composition of the yarns) and/or on the storage conditions. Usually, a moisture content of the dry yarns is less than 10% w/w. In some embodiments, the dry yarns are undyed yarns.

[0122] In some embodiments, wet yarns are fully wetted or partially wetted yarns.

[0123] In contrast, the wet yarns have a significantly greater moisture content than dry yarns. In some embodiments, the moisture content of the wet yarns is greater by at least 10%, at least 30%, at least 50%, at least 100%, at least 150%, at least 200%, than a moisture content of the dry yarns. In some embodiments, the moisture content of the wet yarns is between 5 and 300%, between 5 and 10%, between 10 and 300%, between 15 and 300%, between 20 and 300%, between 20 and 30%, between 25 and 300%, between 30 and 50%, between 50 and 100%, between 100 and 150%, between 150 and 200%, between 250 and 300% w/w, including any range between.

[0124] In some embodiments, the moisture content is sufficient for guiding the ultrasonic waves and/or cavitation inside the plurality of yarns in contact with indigo nanoparticles. In some embodiments, the moisture content is sufficient for sonication-assisted impregnation of the wet yarns with indigo particles, so as to result in dyed yarns with a predefined indigo loading.

[0125] In some embodiments, the yarn comprises or consists essentially of a synthetic or a natural material.

[0126] The material of the yarns is not particularly limited, and examples include natural fibers such as cotton, linen, silk, hemp, bamboo, kapok, modal, ramie, cellulose, rubber and wool; semi-synthetic material such as rayon, viscose, and acetylated cellulose; synthetic material such as polyamide (e.g., Nylon), synthetic rubber, polyester (e.g. PET, PBT, PHT, PTT), polyurethane, polyacrylate, nanofibers, modacryl, modified cellulose and a polyolefin (e.g., polyethylene, polypropylene, etc.), including any composite and any mixture or blend thereof.

[0127] The yarn may be an untreated yarn, encompassing for example natural yarns devoid of pretreatment processes, such as desizing, bleaching or scouring, etc. Untreated yarn may be a hydrophobic (i.e., unscoured) yarn. In some embodiments, the untreated yarn is a hydrophobic yarn comprising a natural material (e.g., cotton, wool, silk, linen, etc.).

[0128] The yarn may be a pre-treated yarn, i.e., a natural yarn subjected to a pre-treatment process. Pre-treatment encompasses but is not limited to: bleaching, desizing, scouring, mercerization, bottoming dyeing, hydrophobization, or any combination thereof. Hydrophobization treatment is known in the art and includes for example water repellency treatment, moisture anti-wicking treatment, etc.

[0129] Untreated yarn can be defined using capillary diffusion coefficient of the yarns (D). The inventors have determined the D value of the untreated substrate to be below 0.1, or below 0.01 measured upon contacting the yarn with an aqueous composition (e.g., an indigo-based dyeing composition disclosed herein). A value of D for a specific yarn and a specific aqueous composition can be determined based on a wicking curve, such as disclosed in Ferrero, F., Periolatto, M. (2015). Modification of surface energy and wetting of textile fibers. Wetting and wettability, 139-168.

[0130] In some embodiments, the untreated yarn characterized by D value below 0.1, below about 0.08, below about 0.05, below about 0.03, below about 0.01, below about 0.008, below about 0.005, including any range between. In some embodiments, the untreated yarn is characterized by absorption height (h) above 1 mm, when measured 100 second upon immersion of the yarn into the aqueous composition. Absorption height (h) of a yarn can be determined as described in Ferrero et. al.

[0131] In some embodiments, dipping step is performed by continuously delivering dry yarns through the aqueous composition. In some embodiments, delivering is performed by a delivery system generating a continuous movement of yarns entering the aqueous composition and/or the dyeing composition. In some embodiments, the continuous movement is characterized by an average delivery speed of the yarns of between 5 and 50m/min, including any range between. In some embodiments, the method of the invention is performed at a temperature of the aqueous composition and/or the dyeing composition ranging between 10 and 60 C., between 15 and 40 C., between 15 and 30 C., including any range between.

[0132] In some embodiments, the aqueous composition is water. In some embodiments, the aqueous composition is in aqueous solution or an aqueous dispersion comprising a salt, a buffer, an additional agent and/or the plurality of indigo nanoparticles, or any combination thereof. In some embodiments, the aqueous composition comprises the composition disclosed herein.

[0133] In some embodiments, the additional agent (also used herein as additive) is selected from a surfactant, a wetting agent, an antifoaming agent, a leveling agent, a cationization agent, a migration inhibitor, a fixing agent, binder, gloss agent, blooming agent, pH modifier, conductivity modifier, rheology modifier, an antibacterial agent or any combination thereof.

[0134] In some embodiments, a weight concentration of the additional agent within the aqueous composition is between 0.01 and 10%, between 0.01% and 0.1%, between 0.01% and 1%, between 0.1% and 1%, between 0.1% and 5%, between 0.2% and 5%, between 0.5% and 10%, or between 0.1% and 10%, including any range in between.

[0135] In some embodiments, the aqueous composition comprises the plurality of indigo nanoparticle at a weight concentration between 0.01 and 10%, between 0.01% and 0.1%, between 0.01% and 1%, between 0.1% and 1%, between 0.1% and 5%, between 0.2% and 5%, between 0.5% and 10%, or between 0.1% and 10%, including any range in between.

[0136] In some embodiments, wet yarns are partially wetted yarns, such that only an outer portion of each yarn is wetted, wherein the core of the yarns remains dry (i.e., ring-patterned wetting). In some embodiments, the ring-patterned wetting is obtained by controlling the cavitation parameters, so as to generate cavitation bubbles with a predetermined average size, as disclosed herein. In some embodiments, a wetting depth of the ring-patterned wetting predetermines the penetration depth of indigo nanoparticles during the dyeing step.

[0137] In some embodiments, dipping step (ii) (also referred to herein as dyeing step) is performed by a single step of contacting the wet yarns with the dyeing composition comprising a plurality of indigo nanoparticles. In some embodiments, contacting is performed by any one of the methods disclosed above for step (i). In some embodiments, dipping step (ii) comprises a single dipping cycle. In some embodiments, the method of the invention comprises a single dyeing cycle.

[0138] In some embodiments, dyeing step consist of contacting the wet yarns with the dyeing composition. In some embodiments, dyeing step is performed without applying acoustic waves. Inventors have successfully performed indigo-dyeing of substrates by using a pre-wetting step, followed by dip dyeing step without application of ultrasound/cavitation.

[0139] In some embodiments, dyeing step comprises dipping the wet yarns into the dyeing composition; and subjecting the wet yarns in contact with the dyeing composition to acoustic waves suitable for inducing cavitation; thereby obtaining indigo ring dyed yarns.

[0140] In some embodiments, the dyeing step comprises contacting at least a portion of the wet yarns with the dyeing composition, wherein the dyeing composition is characterized by a surface tension above a critical surface tension of the substrate; and subjecting the wet yarns in contact with the dyeing composition to acoustic waves suitable for inducing cavitation; thereby obtaining the indigo ring dyed yarns; and wherein the cavitation is characterized cavitation bubbles having an average size between 1 um and 200 um, or between 3 and 150 um. In some embodiments, contacting at least a portion of the wet yarns with the dyeing composition and subjecting to acoustic waves are performed simultaneously, or subsequently. In some embodiments, subjecting is performed while the wet yarns are at least partially immersed into the dyeing composition.

[0141] In some embodiments, acoustic waves suitable for inducing cavitation are characterized by a frequency between 15 KHz and about 1.5 MHz; between 15 KHz and about 500 KHz, between 15 KHz and about 300 KHz, between 10 KHz and 2000 KHz, between about 20 KHz and about 1000 KHz, including any range between.

[0142] In some embodiments, acoustic waves suitable for inducing cavitation are generated via an acoustic source, wherein the input power of the acoustic source is between 30 and 2000 W. In some embodiments, acoustic waves suitable for inducing cavitation w are characterized by (i) a frequency between about 15 KHz and about 500 KHz, and (ii) intensity corresponding to input power of the source of between 30 and 2000 W.

[0143] In some embodiments, dyeing step comprises controlling the penetration depth of the indigo nanoparticles into the yarn (i.e. the thickness of the ring-like pattern and consequently the ring dyeing %) within a predetermined range. In some embodiments, the average penetration depth (R) of the indigo nanoparticles into the indigo ring dyed yarns ranges between 0.4 and 0.15, between 0.3 and 0.15, between 0.35 and 0.15, between 0.4 and 0.1, between 0.3 and 0.2 of a cross section of the indigo ring dyed yarns (R1), including any range between.

[0144] In some embodiments, the indigo ring dyed yarns obtained according to the above disclosed method (Method 1) are characterized by ring dyeing between 60 and 90%, between 60 and 85%, between 65 and 85%, between 65 and 80%, between 65 and 75%, between 60 and 80%, including any range between. The ring dyeing % disclosed herein refers to an average value, wherein the value R2 (and consequently the value of R) for each yarn is determined visually.

[0145] In some embodiments, the indigo ring dyed yarns obtained according to the above disclosed method (Method 1) are characterized by average ring dyeing % as disclosed above, and by a deviation from the average ring dyeing % of below 30%, below 20%, or below 10% including any range between. As exemplified in Example 5, the prewetting step contributes to high uniformity of the ring dyeing % within the batch of dyed yarns.

[0146] Without being bound to any specific theory, it is postulated that the wetting of the yarn by the water-born indigo nanoparticles is dependent on its hydrophobic or hydrophilic nature. This might not be consistent along the same yarn or might be variable between yarn to yarn. This can influence the depth of particle penetration (color ring), and its control. To improve this, a primary surface wetting can be applied using a pre-wetting step. Now, when the yarn will enter the dyeing bath, the wetting capabilities of the yarn itself are not relevant and the penetration of the indigo particles to the yarn using the controlled cavitation field will be more uniform.

[0147] The indigo ring dyed yarns obtained according to Method 1 are characterized by a ring pattern exemplified in FIGS. 7A-B.

[0148] In some embodiments, the predetermined range of the penetration depth is between 1 and about 200 um, between 3 and about 200 um, between 3 and about 150 um, between 3 and about 50 um, between 3 and about 10 um, between 5 and about 100 um, between 5 and about 50 um, including any range between. The penetration depth may vary depending on the cross-section of the yarn. The indigo ring dyed yarns obtained according to Method 1 are characterized by uniform penetration depth R, and each yarn is further characterized by a uniform distribution of indigo particles in the entire ring (e.g., uniform color depth of the ring in radial direction, determined by visual inspection).

[0149] In some embodiments, the penetration depth is predetermined by the average size of the cavitation bubbles. In some embodiments, the average size of the cavitation bubbles is between 3 um and 150 um, between 3 um and 100 um, between 3 um and 50 um, between 5 um and 150 um, between 7 um and 150 um, between 10 um and 150 um, including any range in between. The inventors have observed that the frequency between 20 and about 200 KHz generates cavitation bubbles with an average size between 3 um and 150 um.

[0150] In some embodiments, controlling the penetration depth is by varying the intensity and/or frequency of the acoustic waves, so as to obtain cavitation bubbles with a predetermined average size, wherein the penetration depth is almost equal (e.g., the penetration depth varies from the predetermined average size by up to 30%, up to 20%, up to 10%, including any rang between).

[0151] In some embodiments, a w/w concentration of the plurality of indigo nanoparticles in the dyeing composition is between 1 and 30% w/w, between 1 and 15% w/w, between 1 and 10% w/w, between 2 and 10% w/w, between 1 and 5% w/w, including any range between.

[0152] In some embodiments, the amount of the indigo nanoparticles in the dyeing composition is sufficient for obtaining a predefined loading of the indigo within the indigo dyed yarns. In some embodiments, the predefined loading is sufficient for obtaining a color depth of the dyed yarns as disclosed above. In some embodiments, the predefined loading is predetermined by a moisture content of the wet yarns. In some embodiments, the moisture content and/or distribution along yarn's cross section determines the predefined loading and/or distribution of the indigo particles within the dyed yarn.

[0153] In some embodiments, Method 1 further comprises performing any one of the steps comprising drying, fixating and/or sizing, as disclosed herein below.

Method 2

[0154] In another aspect of the invention, there is provided a method for yarn indigo dyeing comprising: [0155] dipping a plurality of dry yarns into a first dyeing composition to obtain wet yarns; [0156] dipping the wet yarns into a second dyeing composition, thereby obtaining indigo ring dyed yarns; [0157] wherein the first dyeing composition and the second dyeing composition are characterized by a surface tension above a critical surface tension of the plurality of dry yarns; and wherein the first dyeing composition and the second dyeing composition comprise a plurality of indigo nanoparticles.

[0158] In another aspect of the invention, there is provided a method for yarn indigo dyeing comprising: [0159] (i) dipping a plurality of dry yarns into a first dyeing composition to obtain wet yarns, and subjecting the wet yarns to acoustic waves suitable for inducing a cavitation; [0160] (ii) dipping the wet yarns into a second dyeing composition; and subjecting the wet yarns to acoustic waves suitable for inducing a cavitation; thereby obtaining indigo ring dyed yarns; wherein: [0161] the cavitation is characterized by cavitation bubbles having an average size between 1 um and 200 um; [0162] the first dyeing composition and the second dyeing composition are characterized by a surface tension above a critical surface tension of the plurality of dry yarns; and wherein the first dyeing composition and the second dyeing composition are aqueous dispersions comprising a plurality of indigo nanoparticles dispersed therewithin. In some embodiments, the step (i) comprises subjecting the wet yarns in contact with the first dyeing composition to acoustic waves. In some embodiments, the step (ii) comprises subjecting the wet yarns in contact with the second dyeing composition to acoustic waves.

[0163] In another aspect of the invention, there is provided a method for yarn indigo dyeing comprising: [0164] dipping a plurality of dry yarns into a first dyeing composition to obtain wet yarns, and subjecting the wet yarns in contact with the first dyeing composition to acoustic waves suitable for inducing a cavitation; [0165] dipping the wet yarns into a second dyeing composition; and subjecting the wet yarns in contact with the dyeing composition to acoustic waves suitable for inducing a cavitation; [0166] thereby obtaining indigo ring dyed yarns; wherein: [0167] the cavitation is characterized by cavitation bubbles having an average size between 1 um and 200 um; [0168] the first dyeing composition and the second dyeing composition are characterized by a surface tension above a critical surface tension of the plurality of dry yarns; and wherein the first dyeing composition and the second dyeing composition are aqueous dispersions comprising a plurality of indigo nanoparticles dispersed therewithin.

[0169] In some embodiments, the first dyeing composition and the second dyeing composition are as described hereinbelow (see Dyeing composition section). In some embodiments, the first dyeing composition and the second dyeing composition independently comprise the plurality of indigo nanoparticles dispersed therewithin, and further comprise the dispersant, and optionally the additional agent, wherein the chemical composition and the concentration/ratio of the dispersant and optionally of the additional agent in the 1.sup.st and 2.sup.nd dyeing compositions are as described hereinbelow (see Dyeing composition section).

[0170] and wherein a concentration of the indigo nanoparticles within the first dyeing composition is at least 1.5, at least 2, at least 5, at least 3, or between 1.2 and 10, between 1.2 and 20 times lower than a concentration of the indigo nanoparticles within the second dyeing composition.

[0171] In some embodiments, the first dipping step and the second dipping step are performed as disclosed above, and further comprising simultaneous application of acoustic waves to induce cavitation in the first dyeing composition and in the second dyeing composition. In some embodiments, the acoustic waves applied during the first dipping step and the second dipping step are as disclosed above. In some embodiments, the first dipping step and the second dipping step are performed under conditions suitable for inducing a ring-patterned dyeing of the yarns.

[0172] In some embodiments, the frequency and/or intensity of the acoustic waves in the first dipping step and/or in the second dipping step is selected based on the predetermined dyeing depth. In some embodiments, the predetermined dyeing depth is controlled by selecting cavitations parameters suitable for obtaining cavitation bubbles with a specific average size, which is substantially equivalent to the predetermined dyeing depth.

[0173] In some embodiments, the frequency and/or intensity of the acoustic waves in the first dipping step and/or in the second dipping step are substantially the same or different.

[0174] In some embodiments, a concentration of the indigo nanoparticles in the first dyeing composition is between 0.1 and 0.7% w/w, between 0.1 and 0.5% w/w, between 0.2 and 0.7% w/w, between 0.2 and 0.6% w/w, including any range between.

[0175] In some embodiments, a concentration of the indigo nanoparticles in the second dyeing composition is between 1 and 30% w/w, between 1 and 15% w/w, between 1 and 10% w/w, between 2 and 10% w/w, between 1 and 5% w/w, including any range between.

[0176] In some embodiments, the first dipping step is performed to obtain dyed yarns characterized by a first L value ranging between about 22 and 24.

[0177] In some embodiments, the second dipping step is performed to obtain dyed yarns characterized by a second L value, wherein the second L value is at least 5%, at least 10%, at least 20%, at least 30%, at least 50%, at least 70%, or between 5 and 100%, between 5 and 70%, between 10 and 70% lower than the first L value, including any range between.

[0178] In some embodiments, the second L value is in a range between 13 and 21.

[0179] The first L value and the second L value are average values are determined separately after the first dipping step and after the second dipping step, respectively. L values of the dyed yarns are determined by LAB method disclosed in the Examples section.

[0180] In some embodiments, the average penetration depth (R) of the indigo nanoparticles into the indigo ring dyed yarn obtained according to Method 2 ranges between 0.65 and 0.2, between 0.6 and 0.2, between 0.55 and 0.2, between 0.5 and 0.3, between 0.6 and 0.3 of a cross section of the indigo ring dyed yarn (R1), including any range between.

[0181] In some embodiments, the indigo ring dyed yarns obtained according to Method 2 are characterized by ring dyeing between 35 and 80%, between 60 and 85%, between 65 and 85%, between 65 and 80%, between 65 and 75%, between 60 and 80%, including any range between.

[0182] The indigo ring dyed yarns obtained according to Method 2 are characterized by a ring pattern exemplified in FIGS. 8A-B. As demonstrated in FIG. 8A the indigo ring dyed yarn comprises an inner region (A) enclosing a substantially undyed core, and an outer region (B) enclosing the inner region (A). As further demonstrated in FIG. 8A A has significantly lower indigo concentration (and color density) compared to B, in-line with the first and second L values disclosed above.

[0183] In some embodiments, the indigo ring dyed yarns obtained according to Method 2 are characterized by substantially uniform indigo concentration in the outer region (B) and in the inner region (A), as determined by visual inspection (see FIGS. 8A-B).

[0184] In some embodiments, subjecting or exposing the wet yarns in contact with the dyeing composition to acoustic waves (i.e., the dyeing step of Method 1 or the 1.sup.st/2.sup.nd dipping step of Method 2) is performed by providing the wet yarns in operable communication with solid vibrating element. In some embodiments, the solid vibrating element is composed essentially of a source of ultrasonic waves, or a source of acoustic waves suitable for inducing cavitation. In some embodiments, the solid vibrating element comprises a source of acoustic waves and at least one contact surface for being in contact with the substrate. The terms solid vibrating element and source of acoustic waves suitable for inducing cavitation are used herein interchangeably. The terms acoustic waves suitable for inducing cavitation and acoustic waves are used herein interchangeably and encompass any acoustic waves in wavelength range suitable for inducing cavitation in an aqueous composition (e.g., water, the aqueous composition of the invention, or any other aqueous solution or dispersion, optionally wherein the aqueous composition is devoid of an organic solvent). In some embodiments, the acoustic waves encompass any sonic/ultrasonic waves. In some embodiments, the acoustic waves encompass any sonic/ultrasonic waves are as disclosed above.

[0185] In some embodiments, the source of acoustic/ultrasonic waves (also referred to herein as the source) refers to any apparatus or system configured for generating ultrasonic and/or acoustic waves. Various sources are known in the art (e.g., acoustic transducer). Optionally, the can provide between 30 to 150 W of acoustic waves per 100 cm.sup.2 of a treated substrate.

[0186] In some embodiments, the contact surface is in operable communication with the source. In some embodiments, the contact surface is configured to receive the acoustic waves from the source. In some embodiments, the contact surface is configured to transmit or transfer the acoustic waves. In some embodiments, the contact surface is configured to transmit or transfer the acoustic waves to the wet substrate in contact therewith. In some embodiments, the contact surface is permeable to acoustic waves.

[0187] In some embodiments, the contact surface is located in close proximity to the source. In some embodiments, the contact surface is in contact with the source. In some embodiments, the contact surface is operably coupled to the source, such as via a medium (e.g., a liquid) capable of transferring ultrasonic waves from the source to the contact surface. In some embodiments, the substrate is located in close proximity to the solid vibrating element. In some embodiments, at least a portion of the substrate is in contact with the contact surface. In some embodiments, the term close proximity encompasses a predetermined distance is as disclosed below.

[0188] In some embodiments, the dyeing step of Method 1 and/or each of the dipping steps of Method 2 is performed while the yarns are immersed into the dyeing composition within the sonication unit. In some embodiments, the sonication unit comprising at least one first source of acoustic/ultrasonic waves (also termed herein as the first source) and a sonication bath; and optionally at least one second source of acoustic/ultrasonic waves (also termed herein as the second source) and a delivery system configured to continuously deliver the substrate into and throughout the sonication bath such that a predetermined distance is formed between the substrate and the first source and optionally the second source, wherein the predetermined distance is as disclosed below (i.e. a distance of between about 0.1 and about 1.0 times of acoustic wavelength emitted by the source).

[0189] In some embodiments, the sonication bath is a container configured to hold a liquid volume of a dyeing composition sufficient for immersion of the substrate therewithin. In some embodiments, the first source and optionally the second source is in operable communication with the substrate. In some embodiments, the first source and optionally the second source is in contact with the dyeing composition. In some embodiments, the first source and optionally the second source is located within the sonication bath. In some embodiments, the first source and optionally the second source is within the sonication bath so that upon filling the sonication bath with the dyeing composition the first source and optionally the second source are in liquid communication with each other and with the yarns (i.e., immersed within the liquid volume of the dyeing composition). In some embodiments, the first source and the second source face the opposite surfaces of the yarns.

[0190] In some embodiments, the sonication unit further comprises a pre-wetting bath located upstream to the sonication bath and is configured to contain the aqueous composition. In some embodiments, the pre-wetting bath is adopted for immersion of the yarns.

[0191] In some embodiments, the delivery system is configured to continuously deliver the yarns into a pre-wetting bath (prior to delivering thereof into the sonication bath), and continuously deliver the yarns from the pre-wetting bath to the sonication bath. In some embodiments, the delivery system may include a conveyor configured to continuously convey yarns, for example, using a plurality of rollers configured to deliver yarns inside the sonication bath such that a predetermined distance is formed between the yarns and first sonotrode, and/or between the yarns and any one of the plurality of sonotrodes.

[0192] Reference is now made to FIG. 5A which is a block diagram of a yarns' dyeing system, also referred herein as a wet sonication system according to some embodiments of the invention. A use of systems 100 or any of the components of the system, and units according to some embodiments of the invention together with any one of the methods and/or process disclosed herein may result in a uniform dyeing of the yarns (e.g., uniform distribution of indigo inside the yarn), specifically in comparison to standard methods.

[0193] Yarn's dyeing system 100 may include at least one delivery system 30/110a and/or 110b (disclosed and discussed with respect to FIGS. 5B-5F respectively). Delivery system 30/110a/110b may be configured to passively direct and deliver a plurality of yarns 5 into a dyeing bath 21, also refers herein as, a sonication bath 21. In some embodiments, dyeing/sonication bath 21 may include one or more US units 20. In some embodiments, system 100 may further include a solution reduction unit 121, located after yarns 5 exit from dyeing bath 21 and configured to reduce a solution pick-up, as illustrated and discussed with respect to FIG. 5G, herein below.

[0194] In some embodiments, dyeing system 100 may further include a controller 101 that is configured to control controllable aspects of dyeing system 100. Controller 101 may include a computing device (e.g., a chip, a processor, etc.), a memory and a communication unit. Controller 101 may be configured to execute and/or supervise methods according to some embodiments of the invention. For example, controller 101 may control the speed of the yarn progression, the power provided to US units 20, the air blowing and/or suction provided by solution reduction unit 121, and the like.

[0195] Reference is now made to FIGS. 5B, 5C, and 5D which are illustrations of a wet sonication systems (or sonoboxes) according to some embodiments of the invention. A wet sonication/yarns dyeing system 100 may include a sonication unit 20 that may include at least one first sonotrode 22 and a sonication bath 21. In some embodiments, sonication unit 20 may further include at least one of: at least one second sonotrode 24 (illustrated in FIGS. 5B and 5C) and optionally at least one reflector 26 (illustrated in FIG. 5D). In some embodiments, the sonication unit 20 is devoid of a reflector. In some embodiments, the wet sonication systems comprises a plurality of sonotrodes. In some embodiments, the sonotrodes are located within the sonication bath 21. In some embodiments, the sonotrodes are fully or partially immersed within the aqueous composition.

[0196] In some embodiments, the system comprises a plurality of sonotrodes, wherein the plurality of sonotrodes or sources (e.g., the first source 22 and the second source 24) are located at opposed sides of the fabric, as illustrated in FIGS. 5B and 5C.

[0197] In some embodiments, sonication bath 21 is configured to hold a liquid volume. In some embodiments, the liquid volume is sufficient for sonicating the fabric. In some embodiments, the dimensions of the sonication bath 21 and/or the pre-wetting bath (length, width, height dimensions) and/or the volume thereof are sufficient for immersing at least a portion of the fabric within the liquid volume included within the sonication bath 21.

[0198] In some embodiments, sonication bath 21 may include an aqueous composition comprising indigo nanoparticles. In some embodiments, the aqueous composition may include a dispersion of indigo nanoparticles. In some embodiments, the aqueous composition may include the indigo nanoparticle dispersion and at least one of: a wetting agent and a wicking agent.

[0199] In some embodiments, sources 22 and 24 may be similar or different. In the nonlimiting example illustrated in FIGS. 5B-5D sonotrodes 22 and 24 are rectangular plates. In some embodiments, sources 22 and 24 can provide between 30 to 150 W per 100 cm.sup.2 of a treated substrate 5 (e.g., yarns).

[0200] In some embodiments, reflector 26 includes any material (e.g., metal) that can reflect back US waves inside a sonication bath.

[0201] System 100 may further include a delivery system 30 configured to deliver substrate (i.e., yarns) 5 to and from sonication bath 21. Delivery system 30 may include a conveyor configured to continuously convey substrate 5, for example, using a plurality of rollers 35 configured to deliver substrate 5 inside sonication bath 21 such that a predetermined distance is formed between the fabric and first sonotrode 22, and/or between the fabric and any one of the plurality of sonotrodes, wherein the predetermined distance is as disclosed herein.

[0202] In some embodiments, the first source 22 faces a first surface of the fabric, and the second source 24 faces a second surface of the fabric. In some embodiments, the delivery system 30 is configured to deliver fabric between the first source 22 and the second source 24. In some embodiments, the plurality of sources located at both sides of fabric delivered by the delivery system 30, induce uniform impregnation or embedding of the dye nanoparticles into the first surface and into the second surface of the fabric. In some embodiments, the delivery system 30, is configured to deliver fabric between the first source 22 and the second source 24 so that the predetermined distance is formed between the fabric and first source 22 and between the fabric and second source 24. In some embodiments, the first source 22 and the second source 24 are opposed to each other. In some embodiments, the first source 22 and the second source 24 are distant from each other along the propagation direction of the fabric.

[0203] In some embodiments, reflector 26 is optionally located at the predetermined distance 6 from first source 22, and delivery system 30 directs substrate 5 between reflector 26 and source 22, as illustrated in FIG. 5C. The system may be operated without the reflector. It is postulated that the fabric reflects almost the entire ultrasound waves applied thereto.

[0204] In some embodiments, second source 24 is located at the predetermined distance from the fabric, and delivery system 30 directs substrate 5 between first and second sources 22 and 24, as illustrated in FIGS. 5B and 5D.

[0205] In some embodiments, delivery system 30 may further be configured to deliver yarns 5 into a prewetting step, which may be performed in sonication bath 21, as illustrated in FIGS. 5C and 5D or into the pre-wetting bath 10, illustrated in FIG. 5B. In such case, system 100 may further include pre-wetting bath 10 and delivery system 30 may continuously deliver substrate 5 from the pre-wetting bath to the sonication bath 21.

[0206] In some embodiments, pre-wetting bath 10 is in operable communication with the sonication bath 21. In some embodiments, pre-wetting bath 10 is in fluid communication with the sonication bath 21.

[0207] In some embodiments, pre-wetting bath 10 is configured to hold a liquid volume. In some embodiments, the liquid volume is sufficient for sonicating the fabric. In some embodiments, the dimensions of pre-wetting bath 10 (length, width, height dimensions) and/or the volume thereof are sufficient for immersing at least a portion of the fabric within the liquid volume included within the pre-wetting bath 10. In some embodiments, pre-wetting bath 10 is adopted for immersion of the fabric. In some embodiments, pre-wetting bath 10 contains first and/or second source(s) 22 and 24.

[0208] In some embodiments, any one of system 100 of FIGS. 5B-5D may include solution reduction unit 121 discussed with respect to FIG. 5G.

[0209] Reference is now made to FIGS. 5E and 5F which are illustrations of yarn delivery systems for a yarn dyeing system according to some embodiments of the invention and which can be applied along with the method of the invention. The aim of both yarns delivery systems is to prevent the coalescence of neighboring yarns at the exit from dyeing bath 21. Each one of yarn delivery systems 110a and 110b solves this problem using a different approach. System 110a, illustrated in FIG. 5E, may include at least two rollers 111 having a wavy curvature, characterized by varying diameters along the roller's length. In some embodiments, rollers 111 are assembled consecutively in the yarns' transport direction, indicated by the arrows in FIGS. 5B-5D and 5F-5G.

[0210] The angular velocity of shaped roller 111 is defined by the average linear speed of all yarn 5 the drive it, assuming the warping angle is sufficiently high. The average speed R represents in most cases (average (r(x)), where r(x) is the radius at the x location. This means that a yarn that has a potential to run faster will have an increased tension, while the one with less potential will have a lower tension. This means that a yarn that is in the peak area (high r(x)) will tend to shift to the valley area (lower r(x)).

[0211] In some embodiments, the wavy curvature of roller 111 may have a harmonic curvature. In some embodiments, the wavy curvature of roller 111 may have an irregular harmonic curvature. In some embodiments, the irregular harmonic curvature may result from summing harmonic curvature and an irregular noise.

[0212] In some embodiments, a series of multiple rollers 111 may create a superposition of the yarn density effect that will accumulate to white noise. Adding a phase shift to each roller 111 and fabricating each roller 111 in a different diameter may ensure that the white noise-mechanical scrambler will act as a transient in time and will not cause a constant disturbance. The location of these rollers are either before the dye bath, inside the dye bath, or near the squeeze roller.

[0213] In some embodiments, the different roller 111 in system 110a may differ in the average diameter (or radius), the wavy curvatures (e.g., two different harmonic frequencies, phase shift, noise, etc.) or both.

[0214] For example, system 110a may include a first roller 111 having a harmonic curvature characterized by a first harmonic frequency, and wherein the first harmonic frequency is determined based on a distance between first roller 111 and a following second roller 111. In some embodiments, the harmonic curvature of each roller 111 is characterized by a harmonic frequency, and wherein the harmonic frequency of each roller depends on the harmonic frequencies of the other rollers.

[0215] In another nonlimiting example, yarns delivery system 110a may include: a first roller 111 having a first wavy curvature; and a second roller 111 having a second wavy curvature. In some embodiments, a ratio between an average diameter of the first roller and an average diameter of the second roller is at least 1.5, for example, at least 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.5, 3 or more. In some embodiments, the first roller is assembled prior to the second roller in the yarns' transport direction.

[0216] In yet another nonlimiting example, yarns delivery system 110a may include three or more rollers 111. In some embodiments, at least some of the three or more roller 111 may be different or similar.

[0217] Yarns delivery system 110b, illustrated in FIG. 5F may include a plurality of delivery units (e.g., units 112 and 116) each is configured to deliver a portion of the yarns, therefore broadening the distances between two neighboring yarns and avoiding coalescence.

[0218] As should be understood by the one skilled in the art the two delivery units 112 and 116 illustrated in FIG. 5F are given as an example only, and the invention may include any number of delivery units, for example, 2, 3, 4, and more. In some embodiments, delivery units 112 and 116 may each include two or more delivery rollers configured to direct a portion of the yarns into and inside a dyeing bath. In the nonlimiting example illustrated in FIG. 5F, delivery unit 112 may include three delivery rollers 113a, 113b, and 113c configured to direct a first portion 5a of yarns 5, and delivery unit 116 may include two delivery rollers 117a and 117b configured to direct a second portion 5b of the yarns 5.

[0219] In some embodiments, each delivery unit is assembled, for example, in system 100, such that each portion 5a and 5b of yarns 5 enters dyeing bath 21 at a different location A and B.

[0220] In some embodiments, yarns delivery system 110b may further include a plurality of squeezing pairs of rollers 114 and 118, wherein each pair of rollers 114 and 118 is configured to receive and squeeze the portion 5a or 5b of the yarns from a corresponding delivery unit 112 and 116. In some embodiments, squeezing pairs of rollers 114 and 118 may include a piston for applying squeezing force on pairs 114 and 118.

[0221] In some embodiments, a distance between each two neighboring yarns 5 rolling on at least one roller 113a, 113b, and 113c, 117a, and 117b is in a width of at least one yarn. This may ensure that upon exiting of any portion of yarns 5 from dyeing bath 21, coalescence between neighboring yarns is avoided.

[0222] Reference is now made to FIG. 5G which is an illustration of another system 100 for dyeing cotton yarns according to some embodiments of the invention. System 100 may include at least a dyeing bath 21 configured to hold a solution (e.g., indigo solution) and a solution reduction unit 121, located after yarns 5 exit from dyeing bath 21 and configured to reduce a solution pick-up to at most 100%. A used herein the solution pick-up is defined as the percentage of the solution picked up by a cotton yarn exiting the dyeing bath, from the weight of the cotton yarn. As known to the one skilled in the art at 120% and some time at least 300% solution is picked up by the cotton yarn exiting the dyeing bath.

[0223] In some embodiments, the solution pick-up is an excess droplet of solution that are attached to the yarn and accumulate the lower portion of the yarn, when the yarn exits dyeing bath 21, due to gravitational process. If not evacuated this excess solution may cause an uneven dyeing for yarns 5, for example, a nonuniform distribution of indigo across the yarn.

[0224] Therefore, system 100 may include one or more of the two following solution reduction unit 121. In the first nonlimiting example, solution reduction unit 121 may include a blower configured to blow air on the yarns. In some embodiments, the blower may gently blow away the excess solution without drying the yarns, such that the solution pick-up is reduced to at most 100%. The blower may include, at least one of, compressor, a pressurized gas tank, a pressurized gas source (e.g., pipeline) and a nozzle for blowing the air/gas over the yarns. In some embodiments, controller 101 may control the blower to provide a controlled amount of air, which may reduce the pick-up to at most 100%, but not lower, thereby avoiding drying the yarns.

[0225] In a second nonlimiting example, solution reduction unit 121 may include a suction unit configured to suck the solution from the yarns. The suction unit may include any type of pumps, for example, piston pumps, electromagnetic pumps, positive-displacement pumps, impulse pumps, velocity pumps, gravity pumps, valveless pumps and the like. The suction unit may further include an inlet positioned in proximity to the yarns for collecting the excess solution. In some embodiments, controller 101 may control the suction unit to reduce the pick-up to at most 100%, but not lower, thereby avoiding drying the yarns.

[0226] In some embodiments, the step (ii) comprises applying to the wet substrate acoustic waves under appropriate conditions, while the wet substrate is in operable communication with the source of acoustic waves. In some embodiments, operable communication comprises the wet substrate (or a portion thereof) located in close proximity to the source. In some embodiments, operable communication comprises the wet substrate (or a portion thereof) in contact with the source of acoustic waves or with the contact surface.

[0227] In some embodiments, operable communication comprises bonding the wet substrate (or a portion thereof) to the contact surface. In some embodiments, bonding comprises fixating the wet substrate at a predefined location on the contact surface. In some embodiments, bonding is by applying a pressure to the wet substrate, thereby contacting the wet substrate (or a portion thereof) with the source of ultrasonic waves or with the contact surface. In some embodiments, bonding is by providing a fixating device to the wet substrate. In some embodiments, bonding comprises delivering the substrate via the delivery system at the predetermined distance from the source.

[0228] In some embodiments, the substrate is in contact with a plurality of contact surfaces. In some embodiments, at least two surfaces of the substrate are independently in contact with the contact surface (wherein the contact surface is the same or different). In some embodiments, at least two surfaces of the substrate are independently in contact with a contact surface, wherein each contact surface is independently in operable communication with a source of ultrasonic waves.

[0229] In some embodiments, the contact surface is substantially dry. In some embodiments, the contact surface is not immersed within a liquid (e.g., the dispersion, as disclosed herein).

[0230] In some embodiments, the contact surface is attached to the source (i.e., a source of acoustic waves such as acoustic transducer). In some embodiments, the contact surface is at a predetermined distance from the source (i.e., acoustic transducer). In some embodiments, the predetermined distance is between the distal end of the source and the contact surface. In some embodiments, the predetermined distance is from 0.1 mm to 10 cm, from 0.1 to 1 mm, from 1 to 10 mm, from 1 to 10 cm, including any range between. In some embodiments, predetermined distance is equivalent to a distance of between about 0.1 and about 1.0 times (such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, or between about 0.4 and about 0.6 times, between about 0.1 and about 0.6 times, between about 0.2 and about 1 times, between about 0.3 and about 0.8 times, between 0.3 and 0.7, between 0.4 and 0.8 times) of acoustic wavelength emitted by the source, including any range between.

[0231] The acoustic wavelength may be calculated from the corresponding frequency of acoustic waves emitted by the source, taking into account the velocity of sound in an aqueous solution. In some embodiments, the predetermined distance is 5-40 mm, between 5 and 35 mm, between about 5 and about 40 mm, between about 5 and about 30 mm, for example, 5, 10 mm, 15 mm, 20 mm, 30 mm, 40 mm including any value in between.

[0232] In some embodiments, the contact surface is an inner surface of a container. In some embodiments, the container comprises at least one wall defining a lumen. In some embodiments, the wall comprises an outer surface facing an ambient and an inner surface. In some embodiments, the inner surface faces the lumen.

[0233] In some embodiments, the wet substrate is located within the lumen, and at least a portion of the wet substrate is in contact with the inner surface of the container. In some embodiments, the container is immersed within a liquid. In some embodiments, the container is immersed within an ultrasonic bath.

[0234] In some embodiments, the appropriate conditions comprise applying ultrasonic waves for a time period sufficient for stably binding or embedding indigo on or within the textile substrate. In some embodiments, the method of the invention comprises applying an ultrasonic waves for a time period of at least 1 second(s), at least 3s, at least 10s, at least 30s, at least 60s, at least 2 minutes (m), at least 3m, at least 10m, at least 30m, including any range or value therebetween. It should be appreciated that exact application time depends on the input power of the source, and/or on the frequency and/or intensity of the ultrasonic waves applied to the wet substrate.

[0235] In some embodiments, appropriate conditions comprise applying the ultrasonic waves, while the wet substrate is at least partially immersed within the dispersion disclosed herein.

[0236] In some embodiments, appropriate conditions further comprise providing the wet substrate to a temperature of at least 10 C., at least 20 C., at least 30 C., at least 40 C., at least 50 C., at least 60 C., at least 70 C., including any range or value therebetween. In some embodiments, the temperature is above the melting point of the solvent. In some embodiments, the temperature is below the boiling point of the solvent.

[0237] In some embodiments, the temperature is less than the boiling point of the solvent of the dispersion (e.g., water and/or a polar organic solvent).

[0238] In some embodiments, appropriate conditions comprise a frequency of the ultrasonic waves of between 15 KHz and 10 MHz, between 10 KHz and 1000 KHz, between 10 KHz and 2000 KHz, between 15 KHz and 400 KHz, between 20 KHz and 30 KHz, between 30 KHz and 40 KHz, between 40 KHz and 60 KHz, between 60 KHz and 100 KHz, between 100 KHz and 400 KHz, including any range or value therebetween.

[0239] In some embodiments, appropriate conditions comprise an input power of the source between 30 and 2000 W, between 50 and 2000 W, between 30 and 200 W, between 50 and 100 W, between 50 and 500 W, between 50 and 1000 W, between 100 and 2000 W, between 100 and 1000 W, including any range or value therebetween.

[0240] In some embodiments, appropriate conditions comprise at least one of: (i) a time period of at least 2 seconds, (ii) a frequency of between 15 KHz and 1000 KHz, (iii) an input power of the source between 30 and 2000 W, and (iv) a temperature of at least 20 C., or a combination of i-iv.

[0241] In some embodiments, appropriate conditions comprise a power of the ultrasonic waves of at least 10 W/m.sup.2, at least 20 W/m.sup.2, at least 50 W/m.sup.2, at least 100 W/m.sup.2, at least 500 W/m.sup.2, at least 1000 W/m.sup.2, at least 10.000 W/m.sup.2, at least 100.000 W/m.sup.2, at least 1 MW/m.sup.2, including any range or value therebetween. In some embodiments, the step (ii) comprises subjecting the wet substrate to cavitation under appropriate conditions, wherein at least a portion of the wet substrate (or the entire wet substrate) is immersed within the dispersion.

[0242] In some embodiments, the dyeing step of Method 1 and/or each of the dipping steps of Method 2 is performed while the wet yarns are subjected to cavitation. In some embodiments, the appropriate conditions for cavitation comprises conditions sufficient for generating the cavitation bubbles within a predetermined range suitable for indigo embedding into the substrate. In some embodiments, the predetermined range of the cavitation bubbles comprises an average bubble size of between 3 um and 150 um, between 3 um and 100 um, between 3 um and 50 um, between 5 um and 150 um, between 7 um and 150 um, between 10 um and 150 um, including any range in between.

[0243] Non-limiting examples of methods for inducing cavitation include but are not limited to: vibration, acoustic cavitation, liquid jetting, etc.

[0244] Acoustic cavitation occurs whenever a liquid is subjected to sufficiently intense sound or ultrasound (that is, sound with frequencies of roughly 20 kHz to 10 MHz). When sound passes through a liquid, it consists of expansion (negative-pressure) waves and compression (positive-pressure) waves. If the intensity of the sound field is high enough, it can cause the formation, growth, and rapid recompression of vapor bubbles in the liquid. The implosive bubble collapse generates localized heating, a pressure pulse, and associated localized high-energy transfer. Increasing the ultrasound frequency decreases the sound wavelength and increases the density of the vapor bubbles. Increasing the ultrasound intensity causes faster growth of the vapor bubbles and increases the intensity of the pressure pulses. Thus, the use of higher ultrasound frequency while keeping the same accumulative intensity can cause smaller vapor bubbles with lower distance between them. Their collapse will enable a more uniform pressure pulses field. The intensity variation controls the vapor bubble growth rate and changes the pressure pulses field, as well. As the pressure pulses field controls the depth of penetration of the nano indigo particles to the yarn, changing the ultrasound frequency and intensity controls this penetration and obviously controls the generation of the colored ring.

[0245] In some embodiments, controlling the cavitation bubbles within a predetermined range is by operating the cavitation source under suitable conditions, wherein the suitable conditions comprise controlling cavitations parameters (such as frequency, and/or intensity of the acoustic waves). In some embodiments, suitable conditions comprise controlling the time period of subjecting the substrate to cavitation field.

[0246] In some embodiments, suitable conditions comprise a frequency of acoustic waves between 15 KHz and 10 MHz, between 15 KHz and 500 KHz, between 15 KHz and 1000 KHz, between 15 KHz and 300 KHz, between 15 KHz and 250 KHz, including any range between. In some embodiments, the intensity of the acoustic waves refers to an input power of the source of between 30 and 2000 W. In some embodiments, the frequency and/or intensity of the acoustic waves is selected based on the predetermined wetting depth. In some embodiments, the predetermined wetting depth is controlled by selecting cavitations parameters suitable for obtaining cavitation bubbles with a predetermined average size. In some embodiments, the predetermined wetting depth is substantially equivalent to the predetermined average size of the cavitation bubbles.

[0247] In some embodiments, the predetermined average size of the cavitation bubbles is between 3 um and 150 um, between 3 um and 100 um, between 3 um and 50 um, between 5 um and 150 um, between 7 um and 150 um, between 10 um and 150 um, including any range in between. The inventors have observed that the frequency between 20 and about 200 KHz generates cavitation bubbles with an average size between 3 um and 150 um.

[0248] In some embodiments, the dyeing step of Method 1 and/or each of the dipping steps of Method 2 is performed is performed once (i.e., the method of the invention includes a single dyeing cycle). In some embodiments, the dyeing step is performed twice.

[0249] In some embodiments, the method is for embedding an effective amount of indigo on or within the yarns. In some embodiments, the method is for obtaining dyed yarns having a predefined loading of indigo, wherein loading refers to a weight portion of indigo relative to the entire weight of the dyed yarns.

[0250] In some embodiments, the dyed yarns are characterized by indigo loading after a single dyeing cycle of at least 0.5%, at least 1%, at least 1.5%, at least 2%, at least 2.5%, and between 0.5 and 10%, between 0.5 and 5%, between 2 and 4%, including any range or value in between. The inventors have observed that this method allows to obtain a dark shade with 2-4 weight % of indigo loading in single pass of the textile substrate through the sonication-assisted dyebath (i.e., during the dyeing step of Method 1 or the 2.sup.nd dipping step of Method 2).

[0251] In some embodiments, the method of the invention further comprises a step of drying the indigo dyed yarns. In some embodiments, drying comprises exposing wet indigo dyed yarns to a thermal radiation, thereby providing thereof to a temperature of between 4 and 200 C., between 8 and 100 C., between 10 and 150 C., between 15 and 200 C., including any range or value therebetween. In some embodiments, drying further comprises preliminary step of squeezing the wet indigo dyed yarns.

[0252] In some embodiments, drying is performed by convection drying, such as by applying a hot gas stream to the dyed yarns. In some embodiments, drying is performed by cold drying, such as by applying a de-humidified gas stream to the wet indigo dyed yarns. In some embodiments, drying is performed by infrared (IR) drying. In some embodiments, drying is performed by microwave drying. In some embodiments, drying comprises vacuum drying. Generally, the drying method and exact drying conditions selected will depend upon, among other things, chemical and physical properties of the yarns material.

[0253] As opposed to the traditional indigo dyeing process, no oxidation treatment is necessary in the process disclosed herein. Fixing agent can be used to improve rubbing or washing fastness, if needed.

[0254] In some embodiments, the method further comprises a step of contacting the indigo dyed yarns with a composition comprising fixing agent, wherein contacting is as described hereinabove.

[0255] In some embodiments, the method further comprises a sizing step comprising contacting (or dipping) the indigo dyed yarns with a sizing composition comprising a sizing agent, wherein contacting is as described hereinabove. In some embodiments, contacting/dipping is as described hereinabove. In some embodiments, sizing step is performed on dry yarns. In some embodiments, sizing step is performed after drying step. In some embodiments, sizing step is devoid of subjecting the yarns in contact with the sizing composition to acoustic waves.

[0256] In some embodiments, the sizing composition further comprises the plurality of indigo nanoparticles. In some embodiments, a concentration of the plurality of indigo nanoparticles in the sizing composition is between 0.5 and 10% w/w, between 0.5 and 5% w/w, between 0.5 and 7% w/w, between 1 and 10% w/w, between 1 and 5% w/w, including any range between.

[0257] In some embodiments, the sizing composition further comprises a dispersant and optionally the additional agent, wherein a w/w ratio between the dispersant and the plurality of indigo nanoparticles is as described herein. In some embodiments, the sizing composition comprises or consists essentially of the sizing agent and the composition, as disclosed herein.

[0258] In some embodiments, the sizing composition is characterized by a viscosity between 30 and 1000 cP, between 50 and 1000 cP, between 50 and 500 cP at 25 C., including any range between.

[0259] Non-limiting examples of sizing agents include but are not limited to: chitosan, pectin, polyvinyl alcohol, polyacrylates carbomethylcellulose, starch, wax, gelatine, or any combination thereof.

[0260] In some embodiments, sizing step comprises dipping the indigo ring dyed yarns into the sizing composition, thereby obtaining sized yarns characterized by a color depth value (L) in L*a*b or L*C*h color space being by at least 5%, at least 10%, at least 15%, at least 20%, at least 50% lower than L of the indigo ring dyed yarns before the sizing step.

[0261] To improve ring dyeing shape and color depth, indigo dispersion at different concentrations can be introduced into the sizing bath. Sized yarns are characterized by increased color depth (L), compared to unsized yarns. Since no acoustic waves are applied at the sizing step, the penetration depth of the indigo particles is quite low. Accordingly, the vast majority of the additional indigo particles embedded during the sizing step are located close to is the outer diameter of the yarn.

[0262] Thus, the sized yarns are characterized by low color depth close to the core and by a gradual/stepwise increase of the blue shade along the yarn radius, with a maximum concentration of indigo nanoparticles at the outer diameter of the yarn (see FIGS. 9A-B).

[0263] In some embodiments, the terms predefined loading, loading, and effective amount are used herein interchangeably, and refer to a specific w/w concentration, or a concentration range of indigo within the indigo dyed yarns, wherein the w/w concentration or the concentration range is it least sufficient for providing any one of: a predetermined color, a predetermined color intensity, a predetermined color strength, a predetermined light fastness, including any combination thereof.

[0264] In some embodiments, the method of the invention is substantially devoid of the application of a reducing agent. The method of the invention enables achieving the desired indigo loading (as reflected by a desired L*a*b value) in a single dyeing cycle, whereas traditional indigo dyeing methods require a plurality of repetitive leuco-indigo dyeing and reduction cycles. In some embodiments, the method of the invention is devoid of washing during the dyeing process (except washing after substrate pre-treatment). In some embodiments, the method of the invention is devoid of post-dyeing washing step. In contrast, traditional indigo dyeing methods requires at least one step of washing before the dyeing process (a wash step between scouring and dyeing, then multiple dyeing steps, then 1-3 washes after last dyeing).

[0265] In some embodiments, the indigo ring dyed yarns obtained by the method of the invention are characterized by an average L value between 13 and 21.

[0266] In some embodiments, the indigo ring dyed yarns obtained by the method of the invention and using the system/yarns delivery system disclosed herein are characterized by color homogeneity, or color uniformity. The term color homogeneity refers to uniform color intensity/color distribution within the surface of a single batch of dyed yarns, as determined visually.

[0267] In some embodiments, upon at least 10 successive laundry test cycles the indigo dyed yarns are characterized by a color difference AE below 2, below 1, below 0.9, below 0.8, below 0.6, below 0.5, below 0.3, between 0.3 and 1, between 0.5 and 1, including any value in between, wherein E is in L*a*b or L*C*h color space as calculated according to CIE76, CIE94, CIEDE2000 or CMC 1:c (1984) formulas, and wherein the laundry test is performed according to ISO 6330 laundry test.

[0268] Reference is now made to FIG. 2 which is a flowchart representing an exemplary method of dyeing a substrate according to some embodiments of the invention. First, the method comprises contacting (e.g., dipping) a substrate/yarn (i.e., treated, or untreated substrate/yarn) with an aqueous composition or with the composition to obtain a wet substrate/yarn (step 130).

[0269] Further, the method comprises contacting (e.g., dipping) the wet substrate/yarn with the dyeing composition to obtain a dyed substrate/yarn, and subjecting the dyed substrate/yarn to ultrasound waves or cavitation (step 140), thereby obtaining a dyed substrate/yarn.

[0270] The method may further comprise an optional step of drying the dyed substrate/yarn (step 150), thereby obtaining a dried substrate/yarn. The method may further comprise a step of contacting the dried substrate/yarn with a sizing composition (step 160) and optionally drying, thereby obtaining the sized substrate/yarn. The sizing composition of step 160 may further contain indigo nanoparticles, the dispersant and optionally an additional agent disclosed herein.

[0271] Optionally, the method may comprise a preliminary step performed prior to dyeing step. The preliminary step may comprise pretreating an untreated (pristine) substrate by any of: scouring, desizing, bleaching, mercerizing, bottoming dyeing, hydrophobization and subsequently may comprise a washing step (step 120), thereby obtaining a treated substrate.

[0272] Reference is now made to FIG. 3B which is an illustration of traditional indigo dyeing process. The traditional indigo dyeing process 11 comprises: a beam creel unit 100, wherein the substrate (e.g., yarn) is loaded; a scouring unit, which includes a scouring bath 200, a washing bath(s) 230. The scouring bath 200 and washing bath(s) 230 correspond to step 120 of the flowchart. The traditional indigo dyeing process 11 further includes a steamer 220; a dyeing unit 300, which comprises five leuco-indigo dyeing baths 340, 342, 344, 346 and 348 containing a leuco-indigo solution along with toxic reducing agents (dyeing step), and a steamer 350. Subsequently, traditional indigo dyeing process 11 includes a washing bath 380 for performing a post-dyeing wash; an accumulator unit 400; a drying unit 500 (drying step); a sizing unit 600; an additional drying unit 700 (additional drying step), a separation unit 800, which separates the substrate from one another; and a beam winder unit 900.

[0273] Traditional dyeing comprises numerous dyeing baths (usually 6-12), and requires numerous sequential dyeing cycles. In addition, traditional dyeing requires a washing step (before dyeing, after pre-treatment, especially for cotton substrate), and furthermore an additional washing step after dyeing before drying the dyed substrate. Traditional dyeing further requires a step of post-dyeing oxidation of the leuco-indigo, which is tedious, time consuming and in addition the shade of the dyed substrate may vary from one cycle to another.

[0274] Reference is now made to FIG. 3A which is an illustration of the indigo dyeing process according to some embodiments of the invention. The dyeing method of the invention optionally comprises: a beam creel unit 10, wherein the substrate is loaded; optionally a scouring unit, which includes a scouring bath 20, a washing bath 28, and optionally a steamer 24 (corresponding to optional preliminary step 120 of the flow chart); a dyeing unit 30, which comprises a single dyeing bath comprising the aqueous dyeing composition and a source of ultrasonic waves/cavitation (corresponding to step 130 of the flow chart). Subsequently, the dyeing method comprises a drying unit 35, to perform drying step after the dyeing step. Further, the dyeing method comprises an accumulator unit 40; a drying unit 50 (corresponding to step 140 of the flow chart); a sizing unit 60 and an additional drying unit 70 (corresponding to step 150 of the flow chart), a separation unit 80, which separates the substrate from one another; and a beam winder unit 90.

[0275] Thus the method/system of the invention does not require a pre-treatment and a post-dyeing wash step, and operates only a single dyeing bath (so that the substrate dyeing can be accomplished in a single dyeing cycle).

[0276] Cavitation is a phenomena formation of vapor bubbles within a liquid at low-pressure regions that occur in places where the liquid has been accelerated to high velocities. Subsequent implosions of the bubbles create areas of elevated temperature and pressure. Cavitation allows to incorporate water-based dyestuff into relatively hydrophobic substrate. Ultrasonication is a convenient way to induce cavitation in liquid. It is also known to the skilled in art how sonication parameters affect the cavitation bubbles. So, size of the bubbles depends on sonication frequency and amount of the appearing bubbles depends on sonication power.

[0277] The inventors were surprised to find that depth of penetration of the liquid into substrate can be tuned by sonication frequency (the higher, the less penetration) and, to much less extent, amplitude (the lower, the less penetration). The observed phenomena apparently is caused by different pressure generated by implosion of the bubbles of different size.

[0278] The inventors have found that sonication-induced cavitation significantly improves wettability of the unscoured textile substrate (specifically, raw cotton yarns) without any pre-treatment, and allows direct dyeing of the dry, unscoured textile.

[0279] Ultrasonication-induced cavitation bubbles' size depends primarily on sonication frequency. Number of bubbles' per volume of liquid depends both on frequency and acoustic power of sonication. The higher the sonication frequency is, the smaller cavitation bubbles it induces. Thus, if the same sonication power is maintained, higher frequency sonication will induce higher amount of smaller cavitation bubbles. The energy needed to induce cavitation bubbles equals to energy released in bubble's implosion and depends on its size. Implosion of the smaller bubbles releases less energy than implosion of large ones.

[0280] The more powerful implosions and higher their amount of them lead to the deeper penetration of the liquid into the textile substrate. Thus, tuning of the sonication frequency, power and exposure time allows to control depth of dyestuff penetration into the yarns, providing control over ring dyeing effect.

Dyeing Composition

[0281] According to one aspect of the invention, there is provided a composition comprising a plurality of indigo nanoparticles and a dispersant; wherein the plurality of indigo nanoparticles is characterized by an average particle size of below 500 nm, such as between 10 nm and 480 nm, between 50 and 480, between 50 and 450, between 50 and 400, between 55 and 450 nm, between 55 and 400, between 55 and 300, between 55 and 250, between 60 and 250, or between 60 and 300, including any range between.

[0282] As used herein, the term average particle size refers to the median particle size on an intensity basis value obtained by laser diffraction particle size analyzers such as DLS.

[0283] As used herein, the term indigo solely refers to:

##STR00001##

[0284] Furthermore, the term indigo nanoparticles, as used herein consist essentially of indigo (e.g. between 90-100%, between 95-100% by dry weight of the nanoparticles consist of indigo). In some embodiments, the indigo nanoparticles are devoid of indigo derivatives (such as leucoindigo, indigo-disulfonate, etc.)

[0285] In some embodiments, a weight content of the plurality of indigo nanoparticles within the composition is between 0.1% and 99%, between 0.1% and 30%, between 0.1% and 10%, between 1% and 30%, between 1% and 10%, between 1% and 20%, between 30% and 40%, between 30% and 50%, between 30% and 60%, between 30% and 70%, between 30% and 80%, or between 30% and 90%, including any range in between.

[0286] In some embodiments, the plurality of indigo nanoparticles is characterized by an average particle size between about 50 and about 450 nm, between 50 and 400 nm, between 50 and 350 nm, between 50 and 300 nm, between 60 and 300 nm, between 60 and 250 nm, between 60 and 220 nm, between 50 and 300 nm, between 50 and 250 nm, between 50 and 220 nm, between 80 and 300 nm, between 80 and 250 nm, between 80 and 200 nm, between 80 and 150 nm, between 90 and 300 nm, between 90 and 250 nm, between 90 and 200 nm, between 90 and 150 nm, between 100 and 150 nm, or between 100 and 250 nm, including any range between, as determined by DLS. In some embodiments, the plurality of indigo nanoparticles is characterized by a polydispersity index between about 0.2 and about 0.35, between about 0.1 and about 0.35, between about 0.22 and 0.3, or between about 0.2 and 0.3, including any range between, as determined by DLS.

[0287] In some embodiments, the plurality of indigo nanoparticles is characterized by a D90 below 500 nm, below 400, or below 350 nm, as determined by DLS.

[0288] Without being bound to any particular theory, it is postulated that indigo particles with an average particle size above 500 nm, are inferior in terms of indigo dyeing of the substrate, according to the method of the invention. More details are provided in Example 3.

[0289] In some embodiments, the plurality of indigo nanoparticles has a spheric geometry or shape. In some embodiments, the plurality of indigo nanoparticles has an inflated or deflated shape. In some embodiments, the plurality of indigo nanoparticles is devoid of any characteristic geometry or shape. In some embodiments, the plurality of indigo nanoparticles has a spherical shape, a quasi-spherical shape, a cubic shape, a semi-cubic shape, a quasi-elliptical sphere, a deflated shape, a concave shape, an irregular shape, or any combination thereof. One skilled in the art will appreciate that the exact shape of each of the plurality of particles may differ from one particle to another. Moreover, the exact shape of the plurality of indigo nanoparticles may be derived from any of the geometric forms listed above, so that the shape of the particle does not perfectly fit a specific geometrical form. One skilled in the art will appreciate that the exact shape of the nanoparticle may have substantial deviations (such as at least 5%, at least 10%, or at least 20% deviation) from a specific geometrical shape (e.g., a cube or a sphere).

[0290] In some embodiments, the plurality of indigo nanoparticles comprises or consist essentially of indigo in a crystalline state. In some embodiments, the plurality of indigo nanoparticles consists essentially of indigo in an amorphous state.

[0291] In some embodiments, the indigo nanoparticles are obtained by milling or grinding a bulk indigo material. In some embodiments, prior to milling or grinding, the bulk indigo material is mixed with the dispersant, wherein the dispersant is as described herein.

[0292] In some embodiments, the dispersant is a water-soluble polymeric dispersant. In some embodiments, water-soluble dispersant, is selected from: a cationic dispersant, anionic dispersant, or non-ionic dispersant, including any combination thereof. In some embodiments, the dispersant includes a single dispersant specie. In some embodiments, the dispersant includes a plurality of chemically distinct dispersant species.

[0293] The dispersant may be a polymeric dispersant or a non-polymeric dispersant (i.e., a small molecule-based dispersant). Non-limiting examples of polymeric dispersants include but are not limited to: acrylate-based block copolymers (e.g., polyacrylamides, polyacrylates, alkylol ammonium salts of acrylates, etc.), polyurethanes, styrene-based copolymers (e.g., styrene maleic acid copolymers, styrene maleic anhydride copolymers, etc.), glycol-based polymers (e.g., polyglycols, carboxyl polyglycol copolymers, etc.), polyethers, phosphated alkoxylated polymers, oleo epoxide (alkylene oxide) block-copolymers, alkyol ammonium salts of carboxylic acids, salts of carboxylic acids, polyoxyethylene ethers of carboxylic acids, alkylphenol alkoxylates, alkoxylated acetylene polyols, acetylene diol surfactants, fluorinated surfactants, sulfosuccinates, alkoxylated alcohols, siloxane gemini surfactants; alkylphenol alkoxylates, alkoxylated acetylene polyols, acetylene diol surfactants, fluorinated surfactants, sulfosuccinates, alkoxylated alcohols, siloxane gemini surfactantor any combination thereof. In some embodiments, the dispersant is devoid of polyethyleneglycol. In some embodiments, the polymeric dispersant is devoid of polyurethanes.

[0294] In some embodiments, the polymeric dispersant is, selected from: Tego series of Evonik (such as Tego 655), Dispex and Efka series of BASF (such as Dispex Ultra 4575, Dispex Ultra 4290, Efka 4585, Efka FA4671), Triton series of DOW, Edaplan series of Munzig, DISPERBYK and BYKJET series of Altana (such DISPERBYK 2015, BYKJET 9151, Solsperse series of Lubrizol (such as Solsperse 1700, Solsperse 20000)

[0295] Additional examples of dispersants include but are not limited to limited to: cationic, anionic, and/or non-ionic surfactant such as alkoxylated fatty acid, glucosyl dialkyl ether, polysorbate, span, tween, triton, triton X-100, quaternary ammonium salts such as benzalkonium chloride, benzethonium chloride, and cetylpyridinium chloride, pyridinium salts, ethoxylated castor oil, alkyl benzene sulfonate, alcohol ether sulfate, secondary alkane sulfonates and alkyl sulfates, a salt of a fatty acid or a substituted fatty acid including any combination thereof including any mixture or a copolymer thereof.

[0296] In some embodiments, the composition consists essentially of the plurality of indigo nanoparticles and the polymeric dispersant, and optionally of one or more additive(s) disclosed herein.

[0297] In some embodiments, the composition is in a form of a solid (or solid composition). Non-limiting examples of solid compositions include but are not limited to powder, capsules, granules, or flakes. In some embodiments, the composition is a powder. In some embodiments, the solid composition is dispersible. In some embodiments, by adding a predetermined amount of an aqueous carrier to the solid composition a dispersion is obtained, wherein the predetermined amount is so as to obtain a stable dispersion, as disclosed hereinbelow. In some embodiments, weight ratio between the plurality of indigo nanoparticles and the polymeric dispersant is so that upon addition of the predetermined amount of an aqueous carrier to the solid composition a dispersion is obtained, and wherein the dispersion is characterized by a predetermined surface tension above the surface tension of the substrate (for example: a surface tension of at least 28 dyn.Math.cm.sup.1, at least 30 dyn.Math.cm.sup.1, at least 35 dyn.Math.cm.sup.1, at least 40 dyn.Math.cm.sup.1, including any range or value in between). A skilled artisan will appreciate that the predetermined surface tension of the dispersion may vary, based on the surface tension of the substrate to be dyed with the composition of the invention. Accordingly, the weight ratio between the plurality of indigo nanoparticles and the polymeric dispersant in the solid composition may be selected so as to obtain the predetermined surface tension of the dispersion.

[0298] It is advantageous to maintain the surface tension (e.g., by varying the amount/type of the dispersant, or by adding an appropriate amount of a surfactant) of the dyeing composition above the predetermined surface tension value as disclosed above, to obtain ring dyeing. When the surface tension was below the predetermined surface tension value, an almost uniform penetration of the indigo nanoparticles inside the dyed fiber has been observed (so that no ring dyeing has been obtained).

[0299] In some embodiments, a weight ratio between the dispersant and the plurality of indigo nanoparticles within the composition is between 2:1 and 0.001:1, between 2:1 and 0.01:1, between 2:1 and 0.1:1, between 2:1 and 1:1, between 1:1 and 0.001:1, between 0.1:1 and 0.001:1, between 0.5:1 and 0.001:1, between 0.01:1 and 0.001:1, including any range between. In some embodiments, a weight ratio between the plurality of indigo nanoparticles and the dispersant within the composition is between 0.5:1 and 0.05:1.

[0300] In some embodiments, the composition further comprises an aqueous carrier. In some embodiments, the composition comprising the aqueous carrier (also referred to herein as dispersion) is in a form of a dispersion. The terms dispersion, and dyeing composition are used herein interchangeably.

[0301] In some embodiments, a weight percentage of the aqueous carrier within the dispersion is sufficient to form a stable dispersion. In some embodiments, a weight percentage of the aqueous carrier within the dispersion is the predetermined amount required to form a stable dispersion. In some embodiments, the weight percentage of the aqueous carrier within the dispersion is between 85% and 99%, between 85% and 95%, between 85% and 90%, or between 90% and 99%, including any range between.

[0302] In some embodiments, the dispersion is characterized by a surface tension of at least 28 dyncm.sup.1, at least 30 dyncm.sup.1, at least 35 dyncm.sup.1, at least 40 dyncm.sup.1, including any range or value in between.

[0303] In some embodiments, the dispersion is characterized by viscosity between 2 cP and 50 cP, between 3 cP and 10 cP, between 3 cP and 20 cP, between 3 cP and 30 cP, between 3 cP and 40 cP at 25 C.

[0304] In some embodiments, the weight percentage of the dispersant within the dyeing composition is between about 1 and about 30%, between about 1 and about 20%, between about 1.5 and about 20%, including any range in between.

[0305] In some embodiments, a weight percentage of the plurality of indigo nanoparticles within the dispersion is between 0.1% and 30%, between 0.1% and 10%, between 1% and 30%, between 1% and 10%, between 1% and 20%, between 1% and 5%, between 1% and 8%, between 2% and 30%, between 5% and 20%, between 5% and 30%, including any range in between. In some embodiments, a weight percentage of the plurality of indigo nanoparticles within the dispersion is between 0.1% and 10%, between 0.1% and 1%, between 0.1% and 5%, between 1% and 10%, between 2% and 10%, between 4% and 10%, between 5% and 10% including any range in between. Based on extensive experiments the inventors have arrived at the above-mentioned weight concentration of indigo nanoparticles in the dispersion as being suitable for efficient dyeing of various substrates. A skilled artisan will appreciate that the exact concentration of indigo nanoparticles may vary based on: (i) the amount of repetitive dyeing cycles using in the dyeing process; and (ii) on the desired shade (predetermined by the indigo loading) of the dyed substrate.

[0306] In some embodiments, the dyeing composition is stable for at least 1 h, at least 5 h, at least 10 h, at least 24 h, at least 1 d, at least 5 d, at least 10 d, at least 30 d, or at least 2 months, including any range between.

[0307] The term stable refers to the composition that encompasses dispersion stability. In some embodiments, a stable dispersion is substantially devoid of precipitation. Precipitation may be determined visually or by DLS. Furthermore, the dispersion stability is determined under ambient conditions, such as a temperature (i.e., between 5 and 40 C.), and exposure to the ambient atmosphere. In some embodiments, dispersion stability is characterized by an average size distribution that is essentially similar to the average size distribution of the composition of the invention. As used here the term essentially similar refers to having at most 5%, at most 10%, at most 15%, including any range or value in between, difference in the value of the average particle size.

[0308] In some embodiments, the composition (i.e., solid composition or dispersion) further comprises an additional agent (also used herein as additive). In some embodiments, the additional agent affects the mechanical and physical properties of the composition of the invention.

[0309] In some embodiments, the dry weight concentration of the additional agent within the composition is between 0.01 and 10%, between 0.01% and 0.1%, between 0.01% and 1%, between 0.1% and 1%, between 0.1% and 5%, between 0.2% and 5%, between 0.5% and 10%, or between 0.1% and 10%, including any range in between.

[0310] In some embodiments, the additional agent is selected from a wetting agent, an antifoaming agent, a leveling agent, a cationization agent, a migration inhibitor, a fixing agent, binder, surfactant, gloss agent, blooming agent, pH modifier, conductivity modifier, rheology modifier, an antibacterial agent including any combination thereof or any combination thereof.

[0311] In some embodiments, the composition consists essentially of the indigo nanoparticles, the polymeric dispersant and the surfactant (and optionally further comprises the additive), wherein the weight ratio between the dispersant and the surfactant within the composition is so as to obtain the predetermined surface tension, as disclosed above. In some embodiments, the chemical nature and/or concentration of the dispersant is selected to obtain the predetermined surface tension of the dispersion. In some embodiments, the fixing agent enhances the adhesion between the plurality of indigo particles and a textile substrate/fiber by non-covalent bonding of the fixing agent to the substrate, such as by electrostatic interactions. In some embodiments the fixing agent forms a film on the surface of the substrate comprising the nanoparticles embedded therewithin. In some embodiments, the dry weight concentration of the fixing agent within the dispersion is between 0.1% and 10%, between 0.5% and 3%, between 0.5% and 5%, between 0.5% and 10%, between 1% and 5%, between 1% and 10%, including any range in between.

[0312] Non-limiting examples of the fixing agent include but are not limited to, polycations (cationic oligomers/polymers), polyamines, polysaccharides (e.g., alginic acid, alginate, cellulose, gum, etc.), proteins (e.g., soy protein), amine compounds (e.g., trialkyl amine, diethylenetriamine, epichlorohydrin, dimethyl diallyl ammonium chloride, diallylamine etc.), phosphonium cations, epoxy, formaldehyde and tertiary sulphonium groups including any combination thereof.

[0313] In some embodiments, the composition consists essentially of the indigo nanoparticles, the polymeric dispersant, and the fixing agent.

[0314] In some embodiments, the binder enhances the adhesion between the plurality of indigo particles and the substrate by forming a polymer film on top of the dyed substrate, thereby embedding the indigo nanoparticles and enhancing the affinity of indigo particles to the substrate.

[0315] In some embodiments, the dry weight percentage of the binder within the composition is between 0.1% to 10%, including any range in between.

[0316] In some embodiments, the binder comprises a resin, such as acrylate resin, urethane resin, acrylonitrile resin, epoxy resin including any mixture thereof.

[0317] In some embodiments, the composition further comprises a co-solvent. In some embodiments, the co-solvent is characterized by a flash point of at least 170 C. The following co-solvents may be used without any limitation to these: glycerol, polyethylene glycol, and mono-, di-tri-propylene glycol, wherein the PEG has a molecular weight that ranges from 200 Dalton to 1000 Dalton.

[0318] In some embodiments, the composition is a textile substrate (fibers, yarn, textile) dyeing composition. In some embodiments, dyeing is by embedment of the plurality of indigo nanoparticles on or within a substrate (e.g., textile substrate, textile fiber, yarn, etc.) in need of dyeing. In some embodiments, embedment is by non-covalent interaction (e.g., physical interactions, electrostatic interaction, etc.). In some embodiments, dyeing is by ultrasonication and/or cavitation process, such as disclosed hereinbelow. In some embodiments, the composition is a sonication textile substrate indigo dyeing composition. In some embodiments, the composition is a cavitation textile substrate indigo dyeing composition.

[0319] The terms plurality of indigo nanoparticles and indigo nanoparticle(s) are used herein interchangeably and refer to indigo nanoparticles in a solid composition or dyeing composition. In contrast, the term indigo particles refer to indigo on or with the dyed substrate (e.g. embedded into the substrate, as disclosed herein).

Dyed Substrate

[0320] According to one aspect, there is provided indigo dyed yarns comprising one or more yarn(s) in contact with a plurality of indigo particles (also referred to herein as indigo particles) embedded on or within each yarn. According to another aspect, there is provided indigo dyed substrate comprising the indigo dyed yarns disclosed above.

[0321] In some embodiments, the substrate is or comprises a fibrous substrate. In some embodiments, the substrate comprises any one of: a textile fiber, a yarn, a textile substrate, or any combination thereof. In some embodiments, the substrate disclosed herein encompasses a textile fiber, a yarn, a textile substrate, or any combination thereof further in contact with an additional pigment and/or a dye, and/or a nanoparticle, other than indigo. In some embodiments, the substrate disclosed herein is solely in contact with the indigo particles.

[0322] In some embodiments, the textile substrate comprises a plurality of fibers or a plurality of yarns. In some embodiments, the fibers or yarns are in contact with each other. In some embodiments, the fibers or yarns are in a form of a mat. In some embodiments, the textile substrate is a fibrous substrate. In some embodiments, the textile substrate is a woven or a non-woven textile substrate. In some embodiments, each yarn comprises a plurality of fibers. As used herein, the terms fiber and textile fiber are used herein interchangeably.

[0323] In some embodiments, the textile substrate of the invention is selected from a knitted textile substrate, a woven textile substrate, and a non-woven textile substrate, including any combination thereof.

[0324] In some embodiments, the textile substrate of the invention is a textile fabric, the textile fabric is a woven fabric, a knitted fabric, or a uniaxial or multiaxial composite. If the textile substrate is a woven textile substrate, the term woven refers to any type of weave, such as plain weave, satin weave, panama weave, twill weave, and the like.

[0325] In some embodiments, the substrate (such as a textile substrate) has an outer surface and an inner surface, wherein the outer surface is configured to face an ambient and/or is referred to an exterior layer. In some embodiments, the outer surface and the inner surface are the same or different. In some embodiments, the outer surface is an indigo dyed surface. In some embodiments, the outer surface is in contact with the indigo particles. In some embodiments, the inner surface is an undyed surface. In some embodiments, the inner surface of the textile substrate is substantially devoid of indigo particles, or any other particles such as a dye, a pigment, etc., in contact therewith.

[0326] In some embodiments, the textile substrate is a single-layer substrate. In some embodiments, the textile substrate comprises a plurality of layers.

[0327] In some embodiments, the substrate is an untreated substrate (e.g., devoid of post-manufacturing processing such as bleaching, scouring, etc.). In some embodiments, the substrate is a pre-treated substrate, wherein pre-treatment refers to any treatment process performed on the substrate prior to dyeing thereof (such as bleaching, desizing, scouring, mercerization, bottoming dyeing, hydrophobization etc.). In some embodiments, the untreated substrate is a hydrophobic substrate (i.e., unscoured substrate). In some embodiments, the untreated substrate is a hydrophobic substrate comprising natural yarns (e.g., cotton, wool, silk, linen, etc.).

[0328] In some embodiments, the substrate is a hydrophobized substrate. Hydrophobization treatment is known in the art and includes for example water repellency treatment, moisture anti-wicking treatment, etc.

[0329] In some embodiments, the substrate is a hydrophobic substrate. In some embodiments, the hydrophobic substrate is characterized by a water contact angle above 90, above 90, above 100, above 120, above 130, or between 9 and 170, between 10 and 170, between 10 and 160, between 9 and 150, including any range between.

[0330] In some embodiments, the substrate is a hydrophilic substrate characterized by a water contact angle below 90. In some embodiments, the hydrophilic substrate is a pretreated substrate (e.g., a scoured substrate).

[0331] In some embodiments, the indigo particles are embedded on or within the outer surface of the fiber, of the yarn, of the textile substrate, or any combination thereof. In some embodiments, the indigo particles are embedded between the adjacent fibers or yarns within the textile substrate. In some embodiments, the indigo particles are embedded on top of the fibers or yarns within the textile substrate. In some embodiments, the indigo particles are embedded on top of the fibers or yarns, and between the adjacent fibers or yarns within the textile substrate. In some embodiments, the textile substrate is stably bound to the indigo particles, wherein stable is described herein. In some embodiments, the substrate is fully or partially coated by the indigo particles.

[0332] In some embodiments, between 30 and 99.9%, between 30 and 40%, between 30 and 50%, between 30 and 80%, between 30 and 90%, between 50 and 99.9%, between 50 and 90%, between 50 and 80%, between 30 and 70%, between 30 and 60%, between 60 and 99.9%, between 60 and 90%, between 70 and 99.9%, between 70 and 90%, between 50 and 70%, between 70 and 80%, between 80 and 99.9%, between 80 and 90%, between 90 and 95%, between 95 and 97%, between 97 and 99.9%, of the substrate surface is in contact with the indigo particles, including any range between. In some embodiments, the entire surface of the substrate is in contact with the indigo particles.

[0333] In some embodiments, the indigo particles are distributed in a form of a coating layer on top of the substrate. In some embodiments, the coating layer has a substantially homogenous thickness ranging between about 40 nm and about 1000 nm, about 40 nm and about 800 nm, about 100 nm and about 1000 nm, about 100 nm and about 500 nm, including any range between. In some embodiments, the term layer, refers to a substantially homogeneous substance of substantially uniform-thickness. In some embodiments, the term layer, refers to a layer of indigo particles of substantially uniform-thickness.

[0334] In some embodiments, the indigo particles form a plurality of agglomerates or clusters on top of the outer surface of the substrate. In some embodiments, the indigo particles are distributed in a form of a homogenous coating on top of the substrate. In some embodiments, the outer surface of the substrate is in contact with the indigo particles. In some embodiments, the outer surface of the textile substrate is bound to the indigo particles.

[0335] In another aspect of the invention, there is provided an indigo dyed substrate comprising a substrate in contact with indigo particles embedded on or within the outer surface of the substrate, wherein the indigo particles comprise spherical indigo particles, as disclosed herein, wherein the spherical indigo particles are in a form of a homogenous layer characterized by a substantially uniform thickness ranging between about 40 nm and about 1000 nm, about 40 nm, and about 800 nm, about 100 nm and about 1000 nm, about 100 nm and about 500 nm, including any range between. In some embodiments, the indigo dyed substrate is substantially devoid of elongated indigo particles. In some embodiments, the spherical indigo particles are embedded on and/or within the surface of the substrate. In some embodiments, the above disclosed indigo dyed substrate (e.g., comprising a uniform layer of spherical particles) is obtained by contacting the composition with the substrate (e.g., by dipping or spraying, etc.), subjected to cavitation (without applying ultrasonic waves). In some embodiments, it is further postulated that the application of ultrasonic waves subsequently or during the coating process induces formation of elongated particles (or increases a length dimension thereof).

[0336] In some embodiments, the indigo particles are in contact with or embedded into substrate. In some embodiments, the indigo particles are in contact with the textile fiber. In some embodiments, the indigo dyed yarns of the invention are ring-dyed yarns.

[0337] In some embodiments, the penetration depth of the indigo nanoparticles into the ring-dyed yarn (i.e., the thickness of the ring-like pattern) is between 1 and about 200 um, between 3 and about 200 um, between 3 and about 150 um, including any range between. In some embodiments, the penetration depth is predetermined by the average size of the cavitation bubbles generated during the dyeing process. In some embodiments, a predetermined penetration depth (i.e., between 1 and about 200 um) is modified/controlled by varying the cavitation/ultrasonication conditions (e.g. intensity and/or frequency of the acoustic waves) required for generation of the cavitation bubbles with predetermined average size. In some embodiments, the core of the ring-dyed yarn is substantially devoid of indigo particles (e.g., retains the color of the undyed yarn).

[0338] Ring dyed yarn may comprise indigo nanoparticles adjacent to the external portion of the yarn. Ring dyed yarns may comprise indigo nanoparticles and surface active agent. The article of the invention (e.g. ring dyed fabric) may comprise or consists essentially of, comprising weft and warp yarns, at least portion of which (warp only, weft only, or both) comprised of ring dyed yarns. The thickness of the outer ring may range from about 5 percent to 100% of a total thickness of the yarn.

[0339] In some embodiments, the indigo particles are in contact with or embedded into at least a portion of the plurality of yarns composing the textile substrate.

[0340] In some embodiments, the indigo particles are embedded or impregnated into the fiber, into the yarn and/or into the textile substrate. In some embodiments, the indigo dyed substrate comprises indigo particles embedded or impregnated into the fiber, into the yarn, and/or into the textile substrate by applying ultrasonic waves (e.g., having a suitable frequency and/or input power of the ultrasonic source, and being applied for a sufficient time) for embedding the indigo particles into at least a portion of the substrate (i.e., fiber, yarn, or textile substrate). In some embodiments, the indigo dyed substrate of the invention comprises the indigo particles embedded or impregnated into the fiber, the yarn, and/or into the textile substrate.

[0341] In some embodiments, a weight ratio between the indigo particles and the substrate (pristine fiber, pristine yarn or pristine textile substrate) within the indigo dyed substrate of the invention is between 0.2:1 and 0.001:1, between 0.1:1 and 0.001:1, between 0.15:1 and 0.001:1, between 0.05:1 and 0.001:1, between 0.01:1 and 0.001:1, including any range between.

[0342] In some embodiments, the indigo dyed substrate of the invention further comprises the dispersant and optionally the surfactant. In some embodiments, the dispersant and optionally the surfactant is in contact with the indigo particle and/or with the substrate. In some embodiments, a weight ratio between the dispersant and the indigo particles within the indigo dyed substrate is between 2:1 and 0.001:1, between 2:1 and 0.01:1, between 2:1 and 0.1:1, between 2:1 and 1:1, between 1:1 and 0.001:1, between 0.1:1 and 0.001:1, between 0.5:1 and 0.001:1, between 0.01:1 and 0.001:1, including any range between.

[0343] In some embodiments, the surfactant and/or dispersant are as disclosed herein.

[0344] In some embodiments, the indigo dyed substrate of the invention further comprises an additive, wherein the additive is as described hereinabove. In some embodiments, the additive is selected from (i) a binder, (ii) a fixing agent, or both (i) and (ii). In some embodiments, the indigo dyed substrate of the invention consists essentially of indigo particles, a binder and optionally of at least one of a fixing agent, a surface active agent, or any combination thereof. In some embodiments, the binder and the fixing agent are as disclosed herein. In some embodiments, the additive further comprises a sizing agent.

[0345] In some embodiments, a weight ratio between the additive and the substrate (pristine substrate or indigo dyed substrate) is between 0.0001:1 and 0.2:1, between 0.0001:1 and 0.01:1, between 0.0001:1 and 0.1:1, between 0.001:1 and 0.2:1, between 0.01:1 and 0.2:1, including any range between.

[0346] In some embodiments, the indigo dyed substrate comprises indigo particles stably bound to the substrate (pristine textile fiber, pristine yarn, pristine textile substrate). In some embodiments, the indigo particles are stably bound to the substrate by non-covalent interaction and/or covalent interaction.

[0347] In some embodiments, the term stably bound refers to the capability of the indigo dyed substrate of the invention to maintain at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, between 50 and 99%, between 50 and 95%, between 50 and 90%, between 60 and 99%, between 70 and 99%, between 50 and 70%, between 80 and 99%, between 80 and 95% of the initial loading of the indigo particles upon at least 5, at least 10, at least 20, at least 30, at least 50, at least 100 successive laundry test cycles, including any range between. In some embodiments, the laundry test is performed according to ISO 6330 laundry test. In some embodiments, the term stably bound refers to bleaching and/or abrasion stability of the indigo dyed substrate, as determined by conventional tests known in the textile industry.

[0348] In some embodiments, the indigo particles content can be determined spectrophotometrically (e.g., by color difference in L*a*b and L*C*h color space, as disclosed below), as compared to the initial loading, which refers to the weight percentage of indigo particles relative to the pristine substrate. The term initial loading refers to the indigo particles loading immediately after the dyeing process (or upon a washing cycle after the dyeing).

[0349] In some embodiments, the indigo dyed substrate has a uniform color intensity/color distribution. In some embodiments, the indigo dyed substrate is characterized by a color difference E below 2, below 1, below 0.9, below 0.8, below 0.6, below 0.5, below 0.3, between 0.3 and 1, between 0.5 and 1, including any value in between, wherein E is in L*a*b or L*C*h color space as calculated according to CIE76, CIE94, CIEDE2000 or CMC 1:c (1984) formulas. In some embodiments, the above disclosed color difference of the indigo dyed substrate is upon at least 10 successive laundry test cycles, wherein the laundry test is performed according to ISO 6330 laundry test.

[0350] In some embodiments, the dyed substrate is substantially devoid of a reducing agent trace amounts. The term reducing agent encompasses any sulfur-based indigo reducing agents and derivatives thereof, such as sulfite, sulfide, sulfate, bisulfite, metabisulfite, dithionite, thiosulfate, including any combination thereof. In some embodiments, the term trace amounts refers to a weight content of the reducing agent in the dyed substrate of between 1 ppm and 0.5%, between 1 ppm and 0.1%, between 1 ppm and 1000 ppm, including any range between. In some embodiments, the term trace amounts refers to a weight content of the reducing agent above the weight concentration of the same reducing agent in the pristine (non-dyed) substrate. In some embodiments, the article of the invention is substantially devoid of a reducing agent, such as an indigo reducing agent (e.g., dithionite, including any salt thereof). In some embodiments, the article of the invention is devoid of trace amounts of indigo reducing agent (e.g., dithionite, including any salt thereof).

[0351] In some embodiments, the dyed substrate of the invention is characterized by a sodium, potassium, and/or calcium weight content (including salts thereof, such as hydroxides) that is similar (i.e., not more than 10% greater Na-, K-, and/or Ca-content) to the undyed substrate. In some embodiments, the Na-content of the dyed substrate of the invention is between 0.07 and 0.1%, in contrast, indigo dyed substrates obtained by traditional indigo dyeing methods have a significantly greater sodium content (such as between 0.3 and 1% w/w, which is almost 10 times greater than the Na-content of the substrate of the invention).

Article

[0352] In another aspect, there is provided an indigo dyed textile substrate comprising or consisting essentially of (i) the indigo dyed fibers disclosed herein, (ii) indigo dyed yarns disclosed herein, or of both (i) and (ii).

[0353] In another aspect, there is provided an article comprising the indigo dyed textile substrate, wherein the indigo dyed textile substrate comprises or consists essentially of (i) the indigo dyed fibers disclosed herein, (ii) indigo dyed yarns disclosed herein, or of both (i) and (ii). In some embodiments, the indigo dyed textile substrate is an ultrasonically dyed textile substrate. In some embodiments, the indigo dyed textile substrate is a cavitation dyed textile substrate.

[0354] In some embodiments, a weight ratio between the indigo particles and the textile substrate within the article of the invention is between 1:10.000 and 1:5, between 1:1.000 and 1:5, between 1:100 and 1:5, between 1:10.000 and 1:10, between 1:1.000 and 1:10, between 1:10.000 and 1:100, between 1:10.000 and 1:1000, including any range between.

[0355] In some embodiments, the article of the invention is characterized by a loading of the indigo particles relative to the surface area of the textile substrate ranging between 0.1 and 20 g/m.sup.2, between 0.1 and 0.2 g/m.sup.2, between 0.1 and 2 g/m.sup.2, between 0.1 and 5 g/m.sup.2, between 0.1 and 10 g/m.sup.2, between 0.2 and 0.5 g/m.sup.2, between 0.5 and 0.8 g/m.sup.2, between 0.8 and 1 g/m.sup.2, between 1 and 1.5 g/m.sup.2, between 1.5 and 2 g/m.sup.2, between 1 and 20 g/m.sup.2, between 1 and 10 g/m.sup.2, between 10 and 20 g/m.sup.2, including any range therebetween.

[0356] In some embodiments, the article of the invention is characterized by indigo loading (relative to the dry weight of the dyed substrate) of between 0.5 and 10%, between about 0.5 and about 5%, between 0.5 and 1%, between 0.5 and 3%, between 1 and 5%, between 1 and 8%, between 2 and 10%, between 2 and 8%, between 5 and 10%, between 3 and 6%, including any range in between.

[0357] In some embodiments, the article of the invention is at least partially dyed by indigo particles. In some embodiments, between 10 and 99.9%, between 10 and 50%, between 50 and 99.9%, between 10 and 30%, between 30 and 99.9%, between 50 and 99.9%, between 70 and 99.9% of the outer surface of the substrate or of the article comprising thereof, is in contact with the indigo particles, as disclosed herein.

[0358] In some embodiments, the article of the invention (e.g., in a form of a garment) comprising the indigo dyed substrate (e.g., a yarn or a textile substrate), is characterized by indigo particles stably bound to the substrate.

[0359] In some embodiments, the article of the invention (e.g., the indigo dyed textile substrate, the indigo dyed textile fiber, or the indigo dyed yarn) is stable at a temperature up to 200 C., including any range or value therebetween, wherein stable refers to a stable bonding of the indigo particle to the substrate, as disclosed herein.

[0360] In some embodiments, the article of the invention is stable upon successive washings cycles. In some embodiments, the article of the invention is stable upon successive washings and drying cycles. In some embodiments, the washings and drying cycles are performed under regular conditions (e.g., a temperature of up to 60 C., or up to 90 C., and/or application of standard laundry detergents).

[0361] In some embodiments, the article of the invention is stable upon at least 3, at least 5, at least 7, at least 10, at least 15, at least 20, at least 30, at least 50 laundry test cycles, including any range between. In some embodiments, the laundry test stability is assessed via a standard ISO 6330 laundry test.

[0362] In some embodiments, the article of the invention maintains at least 50%, at least 55%, at least 60%, at least 70%, of the initial loading of the plurality of indigo particles, upon at least 10 successive laundry test cycles, wherein the laundry test is performed according to ISO 6330 laundry test, including any range or value in between.

[0363] In some embodiments, the article of the invention is characterized by a substantially homogenous dyeing on the outer surface of the article. In some embodiments, the outer surface of the article is characterized by a substantially uniform color intensity and/or uniform color distribution across the indigo dyed substrate. In some embodiments, the outer surface of the article (or an indigo dyed portion thereof) is characterized by a uniform color intensity/color distribution. In some embodiments, the outer surface of the article is characterized by a color difference E below 2, below 1, below 0.9, below 0.8, below 0.6, below 0.5, below 0.3, between 0.3 and 1, between 0.5 and 1, including any value in between, wherein E is in L*a*b or L*C*h color space as calculated according to CIE76, CIE94, CIEDE2000 or CMC 1:c (1984) formulas.

[0364] In one embodiment, the indigo dyed article is compatible with a denim finishing process. Ring dyed yarns and textile made of them (including denim for denim apparel such as jeans) demonstrating ability to lose dyestuff and dyed fiber of outer portion of the yarns upon exposure to denim finishing, creates a finishing pattern on a surface of the garment (denim washes).

[0365] In one embodiment, the denim finishing process includes but is not limited to: Desizing washhigh temperature, detergents, can be with amylase; Stone wash with pumice stones; Enzyme wash (cellulase, peroxidase); Bleach: calcium or sodium hypochlorite, PP; Ozone, laser washes; Sand blasting.

[0366] In some embodiments, the article is substantially devoid of trace amounts of a reducing agent. In some embodiments, the article of the invention is devoid of trace amounts of indigo reducing agent (e.g., dithionite, including any salt thereof).

[0367] In some embodiments, the article of the invention is characterized by a sodium, potassium, and/or calcium weight content that is similar (i.e., not more than 10% greater Na-, K-, and/or Ca-content) to the undyed article. In some embodiments, the Na-content of the article is between 0.07 and 0.1%, in contrast, indigo dyed articles obtained by traditional indigo dyeing methods have a significantly greater sodium content (such as between 0.3 and 1% w/w, which is almost 10 times greater than the Na-content of the substrate of the invention).

[0368] In some embodiments, the indigo particles are in a form of a layer or agglomerates on top of the outer surface of the indigo dyed substrate, or of the article of the invention. In some embodiments, the indigo particles are homogenously distributed on the outer surface of the indigo dyed substrate, or of the article of the invention. In some embodiments, the indigo particles are in a form of a pattern on the outer surface of the indigo dyed substrate, or of the article of the invention.

[0369] In some embodiments, the article of the invention is manufactured according to a method disclosed herein.

[0370] In some embodiments, the article of the invention is stable for at least 12 months, for at least 15 months, for at least 18 months, for at least 20 months, at least 24 months at a temperature range as disclosed hereinabove, and upon exposure thereof to the ambient conditions (comprising inter alia ambient atmosphere, UV radiation, etc.).

[0371] As used herein the term stable refers to the capability of the article of the invention to substantially maintain its structural and/or mechanical integrity, and to substantially maintain its initial loading of the indigo particles, as described hereinabove.

[0372] In some embodiments, the article according to some embodiments of the present invention can be used for the preparation of clothing, bedding, and the like such as side fabric for down, coats, blousons, windbreakers, blouses, dress shirts, skirts, slacks, gloves, hats, mattress sheets, mattress covers, curtains, or tents.

[0373] In some embodiments, the article of the invention is or comprises a textile product. Non-limiting examples of textile products include but are not limited to: apparel, carpets, rugs, towels, curtains, sheets, twine, clothing, bedding, and the like such as side fabric for down, coats, blousons, windbreakers, blouses, dress shirts, skirts, slacks, gloves, hats, mattress sheets, mattress covers, curtains, or tents, furniture upholstery and automotive upholstery, or any combination thereof.

[0374] In some embodiments, the substrate is textile fiber, yarn, woven or non-woven or knitted fabric, or garment.

[0375] In some embodiments, the substrate is textile yarn. In some embodiments, the yarn is a warp yarn for denim. The term textile yarn includes, but not limited to the ring spun or open-end yarns consisting of cotton, Lycra bamboo, Tencel, modal, viscose, polyester, a polyamide (e.g. Nylon), linen, wool, kapok, ramie, cellulose, acetylated cellulose, polyurethane, polyacrylate, rubber, modacryl, polypropylene, a polyolefin (e.g. polyethylene, polypropylene, etc.), a nanofiber, hemp, rayon and silk or any combination thereof. Yarns count is Ne (Number English) is from 4.0 to 30.0, from 5.5 to 12.5.

General

[0376] As used herein the term about refers to +10%.

[0377] The terms comprises, comprising, includes, including, having and their conjugates mean including but not limited to.

[0378] The term consisting of means including and limited to.

[0379] The term consisting essentially of means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure. Specifically, the term consisting essentially of means that at least 90%, at least 95%, at least 97%, at least 99%, at least 99.9% of the composition or of the article is composed of the ingredients listed herein, including any range or value therebetween.

[0380] The word exemplary is used herein to mean serving as an example, instance or illustration. Any embodiment described as exemplary is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.

[0381] The word optionally is used herein to mean is provided in some embodiments and not provided in other embodiments. Any particular embodiment of the invention may include a plurality of optional features unless such features conflict.

[0382] The term enhancing is by at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 80%, at least 100%, at least 150%, at least 200%, at least 250%, at least 300%, including any range or value therebetween.

[0383] As used herein, the singular form a, an and the include plural references unless the context clearly dictates otherwise. For example, the term a compound or at least one compound may include a plurality of compounds, including mixtures thereof.

[0384] Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0385] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases ranging/ranges between a first indicate number and a second indicate number and ranging/ranges from a first indicate number to a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0386] As used herein the term substantially refers at least 60%, at least 70%, at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, at least 99%, at least 99.9%, including any rage or value therebetween. In some embodiments, the terms substantially and the term consisting essentially of are used herein interchangeably.

[0387] As used herein the term method refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the chemical, pharmacological, biological, biochemical and medical arts.

[0388] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0389] Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples. Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non-limiting fashion.

EXAMPLES

[0390] Denim is an extremely popular textile material due to its unique ability to fade, creating used look desired in fashion industry. This fabric consists of dyed warp and white weft, which give the denim its characteristic salt and pepper pattern. A faded look can be achieved due to the ring dyeing of warp yarns-meaning that only the external part of the yarn is dyed, whereas the core stays white. Various washing techniques are used to remove the dyed layers of the yarn revealing its white core.

[0391] Indigo is traditionally used for denim dyeing. Indigo dye is the most popular dye of vat dyes, however indigo is not soluble in water and to be dissolved for dyeing it need to be reduced by reduction agent (such as sodium dithionite or glucose) in basic condition (usually achieved by addition of soda caustic). The dyebaths (vats) are unstable on air due to the oxidation by atmospheric oxygen and requires addition of the reducing agent to maintain dye in its soluble reduced form.

[0392] Textile substrate is immersed into solution of the reduced dye, absorbs that solution, and subsequently removed from the solution and exposed to air and/or hot steam for oxidation of the dyestuff into its insoluble form. The insoluble form of dye forms particles on the surface of the textile. Process is repeated a few times to achieve desired depth of shade.

[0393] The particles do not form chemical bonds with the substrate. Lack of affinity of those particles to the substrate leads to the poor resistance to washes and abrasion, which, being a defect for other dyes, is a unique feature of indigo dyed textile. Poor resistance to washes and abrasion in combination with ring dyeing allows to create faded, vintage look of the garments made of such textile.

[0394] Destuff inevitably degrades due to exposure to air, whilst accumulating salts deteriorate quality of dyeing. Due to the limited affinity of indigo to cellulose, dyestuff instability on air and a need for the ring dyeing effect, the dyeing is carried out by multiple dipping (8-12 baths) in diluted solutions. Large amount of dyebaths and washing bath before and after dyeing results in massive, energy-demanding production lines.

[0395] Since indigo does not form chemical bonds with textile, binder (resins) are required to fix pigment on the substrate. Comparing to the traditional pigments dyeing, our method does not require thermal curing. Fixing agents can be used to improve rubbing or washing fastness, if needed. Binders, however, can also be used if the dyestuff should be fixed to level constraining further wash down, for creation of various effect on the garment (such as jeans crease), or if pigments dyeing is done on the same substrate (for example, in so called pigment wash of denim).

[0396] Cotton fibers are naturally covered by oils, waxes, pectines and other hydrophobic organic materials, which make quality dyeing impossible. Traditional dyeing requires scouring (cleaning with NaOH, wetting and detergent agent) of the yarns prior to dyeing, making the yarn hydrophilic and wettable by water-based dyestuff. However, hydrophilicity of the yarns leads to easy diffusion of the dyestuff into the yarn's core, deteriorating ring dyeing effect.

[0397] Attempts on optimization of the scouring process have been made to improve the ring dyeing by performing gentle scouring to avoid thorough cleaning of the yarn's core. However, scouring or mercerization prior to dyeing remains necessary in traditional indigo dyeing.

[0398] Multiple attempts to adopt pigments dyeing to denim yarns have been made so far. However, they do not provide ring dyeing effect. Ring dyeing effect can be achieved by shock drying of the yarns to induce dyestuff migration towards external portion of the yarn. These methods require use of polymeric binders (polyacrylates or polyurethanes) and high temperature curing (above 130 C., usually above 150 C.) for the pigment fixation in the polymer matrix.

[0399] Advantageously, the method of the invention in some embodiments thereof is directed to the application of sonication-induced cavitation during dyeing and/or pre-wetting step(s), which significantly improves wettability of the unscoured textile substrate (specifically, raw cotton yarns) without any pre-treatment, and allows direct dyeing of the dry, unscoured textile.

[0400] Indigo and leuco-indigo have low affinity to textile substrate. Besides that, the textile substrate (such as the most common substrate for the indigo dyeing-cotton), is naturally covered by waxes, pectines and other organic materials, which constrain its wettability with water-based dyestuff. Therefore, in a traditional dyeing process cleaning pretreatment of the substrate is required to assure dyeability of the substrate. Such pretreatment (scouring or mercerization) is made by mixture of caustic soda, detergent and wetting agent.

[0401] In the method disclosed herein, no scouring is required to obtain an efficient dyeing of the substrate. Cavitation provides wetting of the substrate and adhesion of the indigo nanoparticles to the yarns in the sonication affected areas. Yarns can be subjected to the additional pre-treatment with hydrophobic or anti-wicking (blocking capillary movement) materials, constraining dyeing in areas not subjected to sonication and improving ring dyeing effect (i.e. decreasing dyestuff penetration depth). This approach allows to use high concentration of dyestuff (up to 30%), and dye only external part of the yarns (ring dyeing effect), since yarn's core is not wetted and stays unaffected by process.

[0402] Nevertheless, scoured or mercerized yarns can be utilized in the process disclosed herein.

Example 1

Nanoparticles Preparation.

[0403] Indigo nanoparticles were obtained by milling in the presence of different dispersant, exemplary procedure is presented: indigo nanoparticles were obtained by milling 100 g indigo pigment in the bead mill with 0.3 mm beads in presence of the 125 g BASF Dispex 4575 dispersing agent (40% active material), 0.3 g of Agitan 701 anti-foaming agent and 775 g of water. Obtained dispersion contains aggregates with intensity-weighted average hydrodynamic size of 202 nm (PDI 0.36). SEM image reveals that aggregates consist of 25+7 nm nanoparticles. Additional dispersants that were successfully implemented during the milling process and/or for stabilization of the dispersion are as follows:

Ultrasonication Dyeing.

1. Plate Transducer as a Source of the Ultrasonic Energy.

[0404] Dyeing was performed in the sonoboxdyeing bath with two ultrasonic plate transducers in two opposite walls of the bath (such as disclosed in greater details in U.S. 63/348,109, which is incorporated herein by reference in its entirety). Sonobox was filled with the formulation containing 1, 2, 5 or 10 wt. % of indigo nanoparticles for different final shades.

[0405] 100% cotton fabrics were placed into the sonobox at the equal distance between the transducers, fabric surface parallel to the plates and sonication immediately has been applied by one or both transducers for 2 and 5 s. Frequency of the ultrasonic generator was 25 kHz. Alternatively, samples without ultrasonication applied were prepared for comparison.

[0406] In another example, fabric was first prewetted in the dyeing bath for 2 or 5 s without ultrasonication applied and then subjected to the ultrasonication. Prewetting of the dry fabric allows to increase overall dye uptake and remove entrapped air from the fabric.

[0407] In another example, 100% cotton fabric was first scoured, washed with water, padded to uptake of 70 or 100% and then subjected to dyeing, with or without prewetting step. In some examples fabrics were padded to 70 or 100% dye uptake after sonication. In some examples yarns were used for dyeing, being fixed on the holder parallel to the transducers plates with a distance of 0.5-2 mm between yarns. In some examples dyeing formulations contained additive of 0.1% of acetic acid and 0.1% of chitosan as leveling and thickening agent. After dyeing fabrics or yarns were thermally cured at 180 C., washed with water and dried at 150, 65 or 25 C.

[0408] Although it is possible to dye fabrics without ultrasonication, only by dipping fabrics into a dyeing formulation containing 1 wt. % of indigo nanoparticles, Sample, dyed with ultrasonication has significantly darker shade and less dyeing defects.

2. 40 kHzUltrasonic Bath

[0409] Ultrasonication dyeing can also be performed with use of the 40 kHz ultrasonic generator. Glass container was placed at 1 cm distance from bottom transducer of the ultrasonic bath and filled with the dispersion containing 1 wt. % of indigo nanoparticles. 100% cotton fabrics were placed into the container for 5 s for prewetting and then were subjected to ultrasonication for 5 s. Fabrics were fixed in the container by metal ring weight. Alternatively, fabric was submerged into the container without sonication for 10 s. Fabrics were dried and thermally cured at 180 C., washed with water and dried at 150 C. FIG. 6 demonstrates fabrics dyed without and with sonication applied.

[0410] Color measurements of the dyed yarns have been performed according to LAB method:

[0411] A typical color spectrophotometer (TS7600 Grating Spectrophotometer) was used to obtain the CIELAB and CIELCH measurements. Colorimeters were developed under the standardization of the Commission Internationale de l'Eclairage (CIE), an international authority on light and color, as an objective color quantification tool that represents human color vision.

[0412] Briefly, the fabric sample is placed under a calibrated spectrophotometer and the measurement is obtained to give all the values: L, a, b, c, and h.

Example 2

[0413] The inventors tested dispersions containing indigo nanoparticles with different average particle size. Exemplary dispersions containing indigo nanoparticles with an average particle size of 500 nm (control) and 150 nm, respectively were prepared and further utilized for ultrasonication assisted dyeing of cotton pads, as described above.

[0414] Indigo particles with an average size of 500 nm were highly inferior to smaller particles, and resulted in an undesired brownish color of the dyed pad (which is attributed to a significantly lower indigo loading).

[0415] Control Cotton pad is characterized by an L*a*b values of L 66.2, a 3.8, b 9.8. In contrast, cotton pads dyed with indigo particles having an average size of 150 nm, show a uniform blue indigo color with L*a*b values of L 27.7, a 2.3, b 10.9.

[0416] Furthermore, various concentrations of the indigo nanoparticles (i.e. between 0.1 and 20% w/w) have been successfully implemented for ultrasound/cavitation assisted dyeing process of the invention. For example, a concentration of at least 1% w/w is required for an efficient dyeing after a single cycle. A skilled artisan will appreciate that the actual concentration may vary, depending on the desired shade of the dyed substate. Furthermore, even by using dispersions with low nanoparticles concentration (between 0.1 and 0.5%) may result in an efficient dyeing when implementing repetitive dyeing cycles.

[0417] Furthermore, the inventors prepared various dispersions of indigo nanoparticles with an average particle size ranging between 60 nm and 500 nm using different dispersants. Stable dispersions were obtained using the following dispersants: BASF Dispex 4290, BASF Dispex 4575, Triton X-100, Tween 80, DISPERBYK 2015, BYKJET 9151, Evonik Tego 655.

[0418] Surprisingly, the inventors obtained high indigo loading of up to 5-6% w/w after a single dyeing cycle.

[0419] In addition, different compositions of the invention were formulated based on some embodiments of the invention comprising various additives, such as binders, surfactant, and/or fixing agents. Exemplary compositions are summarized below. [0420] Wetting agents: Biolite RW-150 of Avco, Metolat 364 of Munzig. [0421] Binders: Denimcol Binder-RE NEU of CHT, Impranil DL 2077 of Covestro.

[0422] Exemplary ultrasonication conditions for yarn dyeing are as follows: [0423] Sonication of 25, 28, 40, 80, 100, 200 kHz and power of 20, 350, 540, 700 and 1000 W was used for the textile substrate/yarn dyeing experiments.

[0424] Exemplary cavitation parameters implemented for textile dyeing are as follows: Cavitation with the resonance size of the cavitation bubble between 150 um and 15 um was utilized for the textile dyeing experiments.

[0425] The inventors additionally examined the weight percentage of sodium cations on a dyed substrate. Interestingly, the amount of sodium in dyed substrates according to the invention are at most 0.099% (which is even lower than the original Na content of the pristine substrate). In contrast, dyed substrates obtained by traditional indigo dyeing exhibited significantly higher Na content (up to 9 times higher Na content). The results are summarized in Table 1.

TABLE-US-00001 TABLE 1 No. of post-dyeing Sample Na, wt. % wash steps Raw cotton 0.123 0 Traditional 1 0.315 3 Italy Traditional 2 0.996 3 Turkey Sonovia 1 (present invention) 0.072 0 Sonovia 2(present invention) 0.091 0 Sonovia 3 (present invention) 0.098 0 Sonovia 4 (present invention) 0.099 0

Example 3

[0426] The inventors surprisingly observed that penetration depth of the indigo nanoparticles into the yarns substrate depends on the cavitation parameters. 100% raw cotton 10 Ne yarns were placed into the sonobox filled by dispersion of 150 nm indigo nanoparticles at the equal distance between the transducers and sonication immediately has been applied by one of the transducers plates. Yarns were subjected to sonication of 25, 40, 80 and 100 kHz for 5 s. Penetration depth of the dyestuff was 173 um in the yarns when treated with 100 kHz, 486 um when treated with 80 kHz, 898 um when treated with 40 kHz and 15018 um when treated with 25 kHz (FIGS. 1A-D).

Example 4

[0427] 100% raw cotton yarns were dyed in the slasher machine by the indigo dispersion containing indigo nanoparticles of the medium size of 150 nm wherein the dyeing process consisted of steps 130, 140 and 150 of the flowchart at the FIG. 2. After the exposure to the sonication in the dyebath yarns were dried at 110 C. In some examples yarns were dried at 80 C. Yarns were sized after the dyeing and drying. 3/1 twill fabric was woven from the sized yarns. The resulting fabric was consequently subjected to desizing wash (amylase, 55 C., 15 min), enzyme wash (cellulase 0.9%, 55 C., 60 min), and bleach wash (sodium hypochlorite 0.2%, 55 C., 15 min), FIG. 4. The washes resulted in increase of L (lightness) and C (chroma) values of the colors of the fabrics in CIELCH color space. The L value was 20.8, 21.4, 22.3 and 32, correspondingly. The C value was 7.3, 8.6, 10.8 and 13.2, correspondingly.

Example 5

[0428] General procedure for ring dyeing according to Method 1 disclosed above.

Pre-Wetting:

[0429] Dry undyed cotton yarns were continuously delivered into a pre-wet bath containing water to obtain wet yarns.

Dyeing:

[0430] Dyeing was performed in the dyeing bath containing a dyeing composition (1-10% w/w indigo particles with an average size of 70 nm and 500 and 1-20% w/w of a dispersant (e.g. BASF Dispex 4575, Triton X-100, Tween 80, Evonik Tego 655) and equipped with ultrasonic transducers.

[0431] After exiting the wet pre-wet bath, wet yarns were continuously delivered via a delivery system (e.g. as schematically presented in FIGS. 5E-F) into the dyeing bath, while operating the ultrasonic transducers (frequency 25 kHz and power of 350 W).

[0432] After drying of the wet yarns, the L value of the dyed yarns was determined to be 13-21.

[0433] The resulting yarns showed a uniform ring dyeing of 70% (see FIGS. 7A-B).

[0434] For comparison, similar batch of dyed yarns was prepared as described above, without the pre-wetting step. The resulting yarns showed wide variation of ring dyeing %. In addition, dyed yarns without pre-wetting has insufficient color uniformity and color depth, as compared to dyed yarns obtained by Method 1 (see FIGS. 10A-B).

[0435] General procedure for ring dyeing according to Method 2 disclosed above.

1.SUP.st .Dipping:

[0436] 1.sup.st dipping was performed in a first dyeing bath containing a dilute indigo dispersion (0.1-0.7 indigo particles, and dispersant, see above) and equipped with ultrasonic transducers. Dry undyed cotton yarns were continuously delivered into the first dyeing bath while operating the ultrasonic transducers (frequency 25 kHz and power of 350 W). The resulting yarns had low concentration in deep ring dyed area and were characterized by L value of 22-24.

2.SUP.nd .Dipping:

[0437] 2.sup.nd dipping was performed in a second dyeing bath containing a concentrated indigo dispersion (1-10% w/w indigo particles with an average size of 70 nm and 500 and 1-20% w/w of a dispersant) equipped with ultrasonic transducers. Wet yarns from the 1.sup.st dipping step were continuously delivered via a delivery system (e.g. as schematically presented in FIGS. 5E-F) into the second dyeing bath while operating the ultrasonic transducers (frequency 25 kHz and power of 350 W). The resulting yarns had high indigo concentration at the outer ring dyed area, and were characterized by L value of 13-21.

[0438] Indigo dyed yarns obtained by Method 2 showed a uniform ring dyeing of 70% (see FIGS. 8A-B).

[0439] To improve ring dyeing shape and color depth, dry dyed yarns of Method 1 or Method 2 were subjected to a sizing step, containing the indigo dispersion in the sizing composition. Sizing is the last step in the indigo dyeing process and allows to achieve a final indigo coating layer on the yarns. Subjecting the dyed yarns to indigo dispersion in the sizing composition increases the color depth (L) of the yarn as well as results in a modulated ring dyeing; wherein the inner core of the yarn is white, and the blue shade increases along the yarn radius.

[0440] In addition, sizing step allows for: [0441] dry-on-wet application of indigo to increase color depth; [0442] high viscosity of the sizing composition (about 50 cP or more) as indigo carrier ensures minimal capillary penetration and thin ring dyeing shape; and [0443] using lower concentrations of indigo in the pre-wet and dyeing step to create a gradual ring dyeing profile.

[0444] L values of yarns subjected to a conventional sizing and sizing with indigo dispersion were determined. The resulting L values (presented in table below) show a significant decrease (=higher color depth) after indigo-based sizing.

TABLE-US-00002 L Clean Sizing 34 Sizing + indigo 32

[0445] The inventors observed high color homogeneity (determined visually) of yarns dyed by Method 1 or by Method 2, wherein dyeing was performed by using the exemplary system for dyeing yarns of the invention (see FIGS. 5A-5G).

[0446] It is postulated that the entire components of the system for dyeing yarns disclosed herein (see FIG. 5A) representing a general assembly of such system, which in combination with the method of the invention results in uniform indigo dyeing of the yarns to obtain both uniform ring dyeing and color homogeneity within the batch of dyed yarns.

[0447] In particular, a combination of (i) the yarn delivery system configured to avoid coalescence between the neighboring yarns (see a non-limiting illustration in FIGS. 5E and 5F) with (ii) the solution reduction unit (see a non-limiting illustration in FIG. 5E) configured to reduce a pick-up of the wet yarn thus preventing non-uniform indigo absorption due to excess of indigo particles on the wet yarns, contributes to color homogeneity of the indigo dyed yarns according to the methods disclosed herein. This result is highly surprising, in light of a single dyeing step implemented in the method of the invention.