Ink composition, a method for preparing the ink composition and use thereof, a water soluble resin and use thereof in an ink composition

Abstract

The invention relates to a latex ink composition, the latex ink composition comprising a water soluble resin. The invention further relates to a water soluble resin suitable for a latex ink composition, the water soluble resin comprising a backbone and a stabilizing group, wherein the stabilizing group is capable of forming hydrogen bonds. The invention further relates to the use of a water soluble resin in a latex ink composition.

Claims

1. An ink composition comprising: a. water; b. a water dispersible resin; c. a colorant; d. a water soluble resin, the water soluble resin comprising a water soluble backbone and a stabilizing group, the water soluble backbone comprising a polyethyleneglycol chain, a polypropyleneglycol chain or a polyethyleneglycol-propyleneglycol chain, the stabilizing group comprising a 2-pyrrolidone moiety or a salicylic acid moiety, the stabilizing group being capable of forming intermolecular hydrogen-bonds, wherein the stabilizing group is coupled to the water soluble backbone via a bridging group, the bridging group being selected from the group consisting of an amide bridging group, a urethane bridging group, a carbamate bridging group and an ester bridging group.

2. The ink composition according to claim 1, wherein the water soluble resin is able to form a matrix upon evaporation of water, in which matrix the water dispersible resin and the colorant are stabilized.

3. The ink composition according to claim 1, wherein the water soluble resin is substantially non-crystalline.

4. A method for preparing an ink composition according to claim 1, the method comprising the steps of: providing a water soluble resin, the water soluble resin comprising a water soluble backbone and a stabilizing group, the water soluble backbone comprising a polyethyleneglycol chain, a polypropyleneglycol chain or a polyethyleneglycol-propyleneglycol chain, the stabilizing group comprising a 2-pyrrolidone moiety or a salicylic acid moiety, the stabilizing group being capable of forming intermolecular hydrogen-bonds, wherein the stabilizing group is coupled to the water soluble backbone via a bridging group, the bridging group being selected from the group consisting of an amide bridging group, a urethane bridging group, a carbamate bridging group and an ester bridging group; providing water; providing a colorant; providing a dispersion comprising the water dispersible resin; and mixing the water soluble resin, the water, the colorant and the dispersion of the water dispersible resin.

5. A method for printing an image onto an image receiving medium, the method comprises the step of: i. applying droplets of a fluid onto the image receiving medium, wherein the fluid is an ink composition according to claim 1.

6. A water soluble resin comprising a water soluble backbone and a stabilizing group, the water soluble backbone comprising a polyethyleneglycol chain, a polypropyleneglycol chain or a polyethyleneglycol-propyleneglycol chain, the stabilizing group comprising a 2-pyrrolidone moiety or a salicylic acid moiety, wherein the stabilizing group is coupled to the water soluble backbone via a bridging group, the bridging group being selected from the group consisting of an amide bridging group, a urethane bridging group, a carbamate bridging group and an ester bridging group.

7. A method for preparing a water soluble resin according to claim 6, the method comprising the steps of: a. providing a water soluble resin backbone precursor, the water soluble resin backbone precursor comprising a water soluble backbone, the water soluble backbone comprising a polyethyleneglycol chain, a polypropyleneglycol chain or a polyethyleneglycol-propyleneglycol chain; b. providing a stabilizing group precursor, the stabilizing group precursor comprising a stabilizing group, the stabilizing group comprising a 2-pyrrolidone moiety or a salicylic acid moiety; c. coupling the water soluble resin backbone precursor and the stabilizing group precursor, thereby forming the water soluble resin, wherein the stabilizing group is coupled to the water soluble backbone via a bridging group, the bridging group being selected from the group consisting of an amide bridging group, a urethane bridging group, a carbamate bridging group and an ester bridging group.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given herein below and accompanying schematic drawings which are given by way of illustration only and are not limitative of the invention, and wherein:

(2) FIG. 1 shows a schematic representation of an inkjet printing system.

(3) FIG. 2 shows a schematic representation of an inkjet marking device: A) and B) assembly of inkjet heads; C) detailed view of a part of the assembly of inkjet heads.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) In the drawings, same reference numerals refer to same elements.

(5) A printing process in which the inks according to the present invention may be suitably used is described with reference to the appended drawings shown in FIG. 1 and FIG. 2A-C. FIGS. 1 and 2A-C show schematic representations of an inkjet printing system and an inkjet marking device, respectively.

(6) In FIG. 1 a sheet of a receiving medium P is shown. The image receiving medium P may be composed of e.g. paper, cardboard, label stock, coated paper, plastic, machine coated paper or textile. Alternatively, the receiving medium may be a medium in web form (not shown). The medium, P, is transported in a direction for conveyance as indicated by arrows 50 and 51 and with the aid of transportation mechanism 12. Transportation mechanism 12 may be a driven belt system comprising one (as shown in FIG. 1) or more belts. Alternatively, one or more of these belts may be exchanged for one or more drums. A transportation mechanism may be suitably configured depending on the requirements (e.g. sheet registration accuracy) of the sheet transportation in each step of the printing process and may hence comprise one or more driven belts and/or one or more drums. For a proper conveyance of the sheets of receiving medium, the sheets need to be fixed to the transportation mechanism. The way of fixation is not particularly limited and may be selected from electrostatic fixation, mechanical fixation (e.g. clamping) and vacuum fixation. Of these, vacuum fixation is preferred.

(7) The printing process as described below comprises of the following steps: media pre-treatment, image formation, drying and fixing and optionally post treatment.

(8) FIG. 1 shows that the sheet of receiving medium P may be conveyed to and passed through a first pre-treatment module 13, which module may comprise a preheater, for example a radiation heater, a corona/plasma treatment unit, a gaseous acid treatment unit or a combination of any of the above. Optionally and subsequently, a predetermined quantity of the pre-treatment liquid is applied on the surface of the receiving medium P at pre-treatment liquid applying member 14. Specifically, the pre-treatment liquid is provided from storage tank 15 of the pre-treatment liquid to the pre-treatment liquid applying member 14 composed of double rolls 16 and 17. Each surface of the double rolls may be covered with a porous resin material such as sponge. After providing the pre-treatment liquid to auxiliary roll 16 first, the pre-treatment liquid is transferred to main roll 17, and a predetermined quantity is applied on the surface of the receiving medium P. Subsequently, the image receiving medium P on which the pre-treatment liquid was supplied may optionally be heated and dried by drying member 18 which is composed of a drying heater installed at the downstream position of the pre-treatment liquid applying member 14 in order to decrease the quantity of the water content in the pre-treatment liquid to a predetermined range. It is preferable to decrease the water content in an amount of 1.0 weight % to 30 weight % based on the total water content in the provided pre-treatment liquid provided on the receiving medium P.

(9) To prevent the transportation mechanism 12 being contaminated with pre-treatment liquid, a cleaning unit (not shown) may be installed and/or the transportation mechanism may be comprised multiple belts or drums as described above. The latter measure prevents contamination of the upstream parts of the transportation mechanism, in particular of the transportation mechanism in the printing region.

(10) Image Formation

(11) Image formation is performed in such a manner that, employing an inkjet printer loaded with inkjet inks, ink droplets are ejected from the inkjet heads based on the digital signals onto a print medium. The inkjet inks may be ink jet inks according to the present invention.

(12) Although both single pass inkjet printing and multi pass (i.e. scanning) inkjet printing may be used for image formation, single pass inkjet printing is preferably used since it is effective to perform high-speed printing. Single pass inkjet printing is an inkjet recording method with which ink droplets are deposited onto the receiving medium to form all pixels of the image by a single passage of a receiving medium underneath an inkjet marking module.

(13) In FIG. 1, 11 represents an inkjet marking module comprising four inkjet marking devices, indicated with 111, 112, 113 and 114, each arranged to eject an ink of a different color (e.g. Cyan, Magenta, Yellow and black). The nozzle pitch of each head is e.g. about 360 dpi. In the present invention, “dpi” indicates a dot number per 2.54 cm.

(14) An inkjet marking device for use in single pass inkjet printing, 111, 112, 113, 114, has a length, L, of at least the width of the desired printing range, indicated with double arrow 52, the printing range being perpendicular to the media transport direction, indicated with arrows 50 and 51. The inkjet marking device may comprise a single print head having a length of at least the width of said desired printing range. The inkjet marking device may also be constructed by combining two or more inkjet heads, such that the combined lengths of the individual inkjet heads cover the entire width of the printing range. Such a constructed inkjet marking device is also termed a page wide array (PWA) of print heads. FIG. 2A shows an inkjet marking device 111 (112, 113, 114 may be identical) comprising 7 individual inkjet heads (201, 202, 203, 204, 205, 206, 207) which are arranged in two parallel rows, a first row comprising four inkjet heads (201-204) and a second row comprising three inkjet heads (205-207) which are arranged in a staggered configuration with respect to the inkjet heads of the first row. The staggered arrangement provides a page wide array of nozzles which are substantially equidistant in the length direction of the inkjet marking device. The staggered configuration may also provide a redundancy of nozzles in the area where the inkjet heads of the first row and the second row overlap, see 70 in FIG. 2B. Staggering may further be used to decrease the nozzle pitch (hence increasing the print resolution) in the length direction of the inkjet marking device, e.g. by arranging the second row of inkjet heads such that the positions of the nozzles of the inkjet heads of the second row are shifted in the length direction of the inkjet marking device by half the nozzle pitch, the nozzle pitch being the distance between adjacent nozzles in an inkjet head, d.sub.nozzle (see FIG. 2C, which represents a detailed view of 80 in FIG. 2B). The resolution may be further increased by using more rows of inkjet heads, each of which are arranged such that the positions of the nozzles of each row are shifted in the length direction with respect to the positions of the nozzles of all other rows.

(15) In image formation by ejecting an ink, an inkjet head (i.e. print head) employed may be either an on-demand type or a continuous type inkjet head. As an ink ejection system, there may be usable either the electric-mechanical conversion system (e.g., a single-cavity type, a double-cavity type, a bender type, a piston type, a shear mode type, or a shared wall type), or an electric-thermal conversion system (e.g., a thermal inkjet type, or a Bubble Jet type (registered trade name)). Among them, it is preferable to use a piezo type inkjet recording head which has nozzles of a diameter of 30 μm or less in the current image forming method.

(16) FIG. 1 shows that after pre-treatment, the receiving medium P is conveyed to upstream part of the inkjet marking module 11. Then, image formation is carried out by each color ink ejecting from each inkjet marking device 111, 112, 113 and 114 arranged so that the whole width of the image receiving medium P is covered.

(17) Optionally, the image formation may be carried out while the receiving medium is temperature controlled. For this purpose a temperature control device 19 may be arranged to control the temperature of the surface of the transportation mechanism (e.g. belt or drum) underneath the inkjet marking module 11. The temperature control device 19 may be used to control the surface temperature of the receiving medium P, for example in the range of 10° C. to 100° C. The temperature control device 19 may comprise heaters, such as radiation heaters, and a cooling means, for example a cold blast, in order to control the surface temperature of the receiving medium within said range. Subsequently and while printing, the receiving medium P is conveyed to the down stream part of the inkjet marking module 11.

(18) Drying and Fixing

(19) After an image has been formed on the receiving medium, the prints have to be dried and the image has to be fixed onto the receiving medium. Drying comprises the evaporation of solvents, in particular those solvents that have poor absorption characteristics with respect to the selected receiving medium.

(20) FIG. 1 schematically shows a drying and fixing unit 20, which may comprise a heater, for example a radiation heater. After an image has been formed, the print is conveyed to and passed through the drying and fixing unit 20. The print is heated such that solvents present in the printed image, to a large extent water, evaporate. The speed of evaporation and hence drying may be enhanced by increasing the air refresh rate in the drying and fixing unit 20. Simultaneously, film formation of the ink occurs, because the prints are heated to a temperature above the minimum film formation temperature (MFFT). The residence time of the print in the drying and fixing unit 20 and the temperature at which the drying and fixing unit 20 operates are optimized, such that when the print leaves the drying and fixing unit 20 a dry and robust print has been obtained. As described above, the transportation mechanism 12 in the fixing and drying unit 20 may be separated from the transportation mechanism of the pre-treatment and printing section of the printing apparatus and may comprise a belt or a drum.

(21) Post Treatment

(22) To increase the print robustness or other properties of a print, such as gloss level, the print may be post treated, which is an optional step in the printing process. For example, the prints may be post treated by laminating the prints. Alternatively, the post-treatment step comprises a step of applying (e.g. by jetting) a post-treatment liquid onto the surface of the coating layer, onto which the inkjet ink has been applied, so as to form a transparent protective layer on the printed recording medium.

(23) Hitherto, the printing process was described such that the image formation step was performed in-line with the pre-treatment step (e.g. application of an (aqueous) pre-treatment liquid) and a drying and fixing step, all performed by the same apparatus (see FIG. 1). However, the printing process is not restricted to the above-mentioned embodiment. A method in which two or more machines are connected through a belt conveyor, drum conveyor or a roller, and the step of applying a pre-treatment liquid, the (optional) step of drying a coating solution, the step of ejecting an inkjet ink to form an image and the step or drying an fixing the printed image are performed. It is, however, preferable to carry out image formation with the above defined in-line image forming method.

Experiments and Examples

(24) Materials

(25) Polypropylene glycol (M.sub.n≈425 gram/mole) was obtained from Sigma Aldrich. Jeffamine D-230 and Jeffamine EDR-176 were obtained from Huntsman. 2-pyrrolidone-5-carboxylic acid, salicylic acid and xylene were obtained from Sigma Aldrich. As pigment, Pro-Jet™ Black APD 1000 was used. This pigment was obtained from Fujifilm as an aqueous pigment dispersion. As water dispersible resin, Neocryl™ A-1127 was used. Neocryl™ A-1127 is an acrylic resin and is obtained from DSM Neoresins as an aqueous emulsion.

(26) Syringe filters were obtained from VWR. The syringe filters have nylon membrane, the membrane having a pore size of 0.45 μm.

(27) All materials were used as obtained, unless stated otherwise.

(28) Methods

(29) Stability of Ink Composition

(30) 5 mL of an ink composition were filled into a 5 mL luer lock syringe provided with a syringe filter. The ink was passed through the filter. When the color of the ink composition does not change upon filtration, and no visible residue of colorant is left on the syringe filter, the ink composition is considered stable. When filtration yield a colorless liquid, and the syringe filter is colored after the filtration, the ink composition is considered instable.

(31) Re-Dispersing Ink Composition

(32) 3 Grams of the ink composition was weighted into an aluminum dish having a diameter of 5 cm and was dried at room temperature under atmospheric pressure for 16 hours. After drying, the residue is transferred to a glass flask and an amount of solvent, equal to the amount of solvent evaporated from the ink composition, was added to the residue. The solvent is the solvent used in the ink composition, thus water or a water/co-solvent mixture was used. The mixture was stirred at ambient temperature for one hour. In case no homogeneous mixture was obtained, the ink is considered not re-dispersible. In case a homogeneous mixture was obtained, the ink is considered re-dispersible. The stability of the re-dispersible ink was tested using the stability test for ink jet ink compositions described above.

(33) Stability of Re-Dissolved Ink Composition

(34) 5 mL of a re-dispersed ink composition were filled into a 5 mL luer lock syringe provided with a syringe filter having a nylon membrane, the membrane having a pore size of 0.45 μm. The re-dispersed ink was passed through the membrane. When the color of the ink composition does not change upon filtration, and no visible traces of colorant are left on the syringe filter, the re-dispersed ink composition is considered stable. When filtration yield a colorless liquid, and the syringe filter is colored after the filtration, the re-dispersed ink composition is considered instable.

(35) Water-Resistance of Prints Made Using Ink Composition

(36) The ink composition was applied onto a vinyl substrate (8 cm*15 cm) by rodcoating to yield a 8 μm thick layer of the ink composition on the substrate. The substrates, having the ink composition applied thereon are dried; either at low temperature or at high temperature. Drying at low temperature was carried out by letting the substrates dry at room temperature at ambient pressure for 1-4 h. Drying at high temperature was carried out by letting the substrates dry in an oven at 60° C.-80° C. for 5-15 min., at ambient pressure. The water-resistance of the inkjet ink image on the substrate was tested by rinsing the substrate with water. When the inkjet ink image was removed upon rinsing with water, the print was considered not water-resistant. When the inkjet ink image was not removed upon rinsing with water, the print was considered water-resistant.

Experiment 1

(37) Production of Water Soluble Resin (2)

(38) 100 gr of 2-pyrrolidone-5-carboxylic acid (0.78 mole) and 94 gr of Jeffamine D-230 (0.82. mole, 1.05 eq) were weighted and put in a 500 mL glass round-bottom flask. 40 mL of xylene was added to the mixture. The round-bottom flask was equipped with Dean-Stark equipment and provided with a nitrogen atmosphere. The mixture was heated to reflux temperature. When a temperature of about 150° C. was reached, a homogeneous mixture was obtained. The mixture was allowed to react at reflux temperature for 24 hours. During the reaction time, the water formed was removed via the Dean Stark equipment. After the mixture has reacted at reflux temperature for 24 hours, the mixture was allowed to cool down and the solvent was removed under reduced pressure and a resin was obtained. The resin was transferred into an aluminium dish and dried for 16 h in an over at a temperature of 150° C. and a pressure of 5*10.sup.−2 mbar. The prepared resin 2 is a transparent glassy material.

(39) Several other resins in accordance with the present invention (3-5) were synthesized in a similar way as describes above, by combining the desired amounts of backbone precursor and a carboxylic acid into the round-bottom flask equipped with a Dean-Stark trap, in experiment 2-4, respectively.

(40) TABLE-US-00002 TABLE 2 water soluble resins Exp resin backbone precursor carboxylic acid 1 2 Jeffamine D230 2-pyrrolidone-5-carboxylic acid 2 3 Jeffamine D230 salicylic acid 3 4 Jeffamine EDR-176 2-pyrrolidone-5-carboxylic acid 4 5 Polypropylene glycol 2-pyrrolidone-5-carboxylic acid

Example 1

(41) Preparation of an Ink Composition (10)

(42) 10 grams of water soluble resin 2 was weighted and 60 grams of de-mineralized water was added. The mixture was stirred. Subsequently, the emulsion containing Neocryl™ A-1127 was added. Then, the aqueous dispersion of Pro-Jet™ Black APD 1000 was added. The amounts of emulsion containing Neocryl™ A-1127 and dispersion containing Pro-Jet™ Black APD 1000 that were added were such, that the resulting ink composition 10 comprised 10 wt % of water soluble resin 2, 5 wt % of pigment Pro-Jet™ Black APD 1000 and 10 wt % of Neocryl™ A-1127 water dispersible resin, wherein the weight percentages were based on the weight of the total ink composition 10. If necessary, water was added to obtain an ink composition comprising the desired amounts of the components.

Example 2

(43) Preparation of an Ink Composition (20)

(44) 10 grams of water soluble resin 2 was weighted and 20 grams of 2-pyrrolidone was added. The mixture was stirred, and 1 g of Dynol 607 was added to the homogeneous mixture. Subsequently, the emulsion containing Neocryl™ A-1127 was added. Then, the aqueous dispersion of Pro-Jet™ Black APD 1000 was added. The amounts of emulsion containing Neocryl™ A-1127 and dispersion containing Pro-Jet™ Black APD 1000 that were added were such, that the resulting ink composition 20 comprised 10 wt % of water soluble resin 2, 4 wt % of pigment Pro-Jet™ Black APD 1000 and 5 wt % of Neocryl™ A-1127 water dispersible resin, wherein the weight percentages were based on the weight of the total ink composition 20. If necessary, water was added to obtain an ink composition comprising the desired amounts of the components.

Comparative Example 1

(45) 30 grams of the Neocryl™ A-1127 emulsion was weighted. To the water dispersible resin emulsion, the aqueous dispersion of Pro-Jet™ Black APD 1000 was added, as well as de-mineralized water. The amounts of dispersion containing Pro-Jet™ Black APD 1000 and water that were added were such, that the resulting ink composition CE1 comprised 5 wt % of pigment Pro-Jet™ Black APD 1000 and 10 wt % of Neocryl™ A-1127 water dispersible resin, wherein the weight percentages were based on the weight of the total ink composition CE1.

(46) Comparison Experiments

(47) Stability of the Ink Composition

(48) In a first comparison experiment, the stability of the ink compositions 10 and 20 is compared to the stability of ink composition CE1. The stability was tested as described above and the results are summarized in table 3.

(49) TABLE-US-00003 TABLE 3 10 20 CE1 stability of ink composition Stable Stable Stable

(50) Both the ink compositions according to the present invention (ink compositions 10 and 20), as well as the ink composition according to the comparative example (CE1) are stable, when they have not yet dried.

(51) Re-Dispersing Ink Composition

(52) The ink compositions were dried at ambient temperature, as described above, and their re-dispersibility was investigated. The result are summarized in table 4.

(53) TABLE-US-00004 TABLE 4 10 20 CE1 re-dispersibility re-dispersible re-dispersible not re-dispersible

(54) The ink according to the present invention (ink compositions 10 and 20) is re-dispersible, whereas the ink according to the comparative example (CE1) is not re-dispersible. Thus, when water has been removed from ink composition 10 or 20, addition of water to the solid residue may result in re-dispersion of the solid residue in water. Therefore, the dispersion of the solid components of ink compositions 10 and 20 is considered reversible. The ability to disperse reversibly is believed to be provided by the water soluble resin comprising the stabilizing group. The ink composition CE1 does not show reversible dispersion of the solid components of the ink composition.

(55) Stability of Re-Dispersed Ink Composition

(56) The stability of the ink compositions after they have been re-dispersed was tested. The results are summarized in table 5. Since the ink composition CE1 showed not to be re-dispersible (or re-dissolvable), the stability of the re-dispersed CE1 ink composition could not be investigated.

(57) TABLE-US-00005 TABLE 5 10 20 CE1 stability of re-dispersed ink Stable Stable not tested composition

(58) The ink compositions 10 and 20, which are ink compositions according to the present invention, were stable after re-dispersion of the ink. Thus, the ink components are of the ink compositions 10 and 20, according to the present invention, are not only reversibly dispersible, the resulting re-dispersed ink composition is also a stable dispersion. Therefore, the ink composition may be suited to be used as an ink after re-dispersion.

(59) Water-Resistance of Prints Made Using Ink Composition

(60) The water-resistance of prints made using ink composition was tested as described above. Prints were made by applying the ink compositions 10 and 20 onto a receiving medium by rodcoating. Two samples were investigated for each ink composition. In one sample, the ink composition (10, 20 resp.) was dried at room temperature after the ink was applied onto the receiving medium. In the second sample, the ink composition (10, 20 resp.) was dried at elevated temperature after the ink was applied onto the receiving medium. The results are summarized in table 6.

(61) TABLE-US-00006 TABLE 6 dried at room dried at high temperature temperature water-resistance of print made not-water-resistant water-resistant using ink composition 10 water-resistance of print made not-water-resistant water-resistant using ink composition 20

(62) When the ink was dried at room temperature after the ink composition had been applied onto the receiving medium, the ink applied onto the receiving medium was removed upon rinsing the receiving medium with water, for both ink composition 10 and 20. When the ink was dried at elevated temperature instead, the print made using ink composition was water-resistant, for both ink composition 10 and 20. Thus, when the print is dried at high temperature (fused), the print becomes water-resistant. On the other hand, when the print is not dried at high temperature, the print made using an ink composition according to the present invention is not water-resistant.

(63) When an ink compositions according to the present invention (10, 20) is compared to compositions not in accordance with the present invention (comparative example CE1), it is clear that the ink composition according to the present invention is able to be effectively re-dispersed after drying at room temperature and that the ink composition can become water-resistant upon drying at elevated temperatures. The ink compositions not in accordance with the present invention, on the other hand, cannot be effectively re-dispersed after drying at room temperature.

(64) Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually and appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination and any combination of such claims are herewith disclosed. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language).