NONWOVEN CELLULOSE FIBER FABRIC WITH FIBER DIAMETER DISTRIBUTION

Abstract

A nonwoven cellulose fiber fabric directly manufactured from lyocell spinning solution, wherein the fabric comprises a network of substantially endless fibers differing concerning fiber diameter so that a ratio between a largest fiber diameter and a smallest fiber diameter is more than 1.5.

Claims

1. A nonwoven cellulose fiber fabric, in particular directly manufactured from lyocell spinning solution, wherein the fabric comprises a network of substantially endless fibers differing concerning fiber diameter so that a ratio between a largest fiber diameter and a smallest fiber diameter is more than 1.5.

2. The fabric according to claim 1, comprising at least one of the following features: different sections of the same fiber differ concerning fiber diameter so that a ratio between a largest fiber diameter of this fiber and a smallest fiber diameter of this fiber is more than 1.5; different fibers differ concerning fiber diameter so that a ratio between a largest fiber diameter of one of the fibers and a smallest fiber diameter of another one of the fibers is more than 1.5.

3. The fabric according to claim 1, wherein different ones of the fibers are located at least partially in different distinguishable layers.

4. The fabric according to claim 3, comprising at least one of the following features: fibers of different layers are integrally connected at least one merging position between the layers; different ones of the fibers being located at least partially in different layers differ concerning fiber diameter, in particular differ concerning an averaged fiber diameter; fibers of different layers have the same fiber diameter, in particular have substantially the same averaged fiber diameter; fibers of different layers provide different functionality, wherein the different functionality in particular comprises at least one of the group consisting of different wicking, anisotropic behavior, different liquid absorbing capability, different cleanability, different roughness, different smoothness, and different stability.

5. The fabric according to claim 1, wherein at least 80 mass percent of the fibers have an average fiber diameter in a range between 3 m and 40 m, in particular between 3 m and 15 m.

6. The fabric according to claim 1, wherein the fibers have a copper content of less than 5 ppm and/or have a nickel content of less than 2 ppm.

7. The fabric according to claim 1, wherein the fabric has an oil absorbing capability of at least 500 mass percent, in particular at least 800 mass percent, more particularly at least 1000 mass percent, preferably at least 1500 mass percent.

8. The fabric according to claim 1, wherein the fabric comprises fibers differing concerning fiber diameter so that a ratio between a largest fiber diameter and a smallest fiber diameter is more than 2.5, in particular more than 4.

9. The fabric according to claim 1, wherein at least some of the fibers are mutually aligned side-by-side at least over a portion of their length to form a superordinate fiber structure having a larger diameter than the individual fibers of the superordinate fiber structure.

10. A method of manufacturing nonwoven cellulose fiber fabric directly from lyocell spinning solution, wherein the method comprises extruding the lyocell spinning solution through at least one jet with orifices supported by a gas flow into a coagulation fluid atmosphere to thereby form substantially endless fibers; collecting the fibers on a fiber support unit to thereby form the fabric; adjusting process parameters so that the fibers differ concerning fiber diameter so that a ratio between a largest fiber diameter and a smallest fiber diameter is more than 1.5.

11. The method according to claim 10, comprising at least one of the following features: wherein adjusting the process parameters for adjusting fiber diameter comprises adjusting coagulation conditions for the fibers, in particular adjusting an amount of coagulation fluid interacting with the lyocell spinning solution; wherein adjusting the process parameters for adjusting fiber diameter comprises serially arranging multiple jets of orifices with different properties along a movable fiber support unit, in particular having different properties in terms of at least one of the group consisting of different orifice diameters, different speed of gas flow, different amounts of gas flow, and different gas flow pressure.

12. The method according to claim 10, wherein the method further comprises further processing the fibers and/or the fabric in situ after collection on the fiber support unit, in particular by at least one of the group consisting of hydro-entanglement, needle punching, impregnation, steam treatment with a pressurized steam, gas treatment with a pressurized gas, and calendering.

13. A device for manufacturing nonwoven cellulose fiber fabric directly from lyocell spinning solution, wherein the device comprises: at least one jet with orifices configured for extruding the lyocell spinning solution supported by a gas flow; a coagulation unit configured for providing a coagulation fluid atmosphere for the extruded lyocell spinning solution to thereby form substantially endless fibers; a fiber support unit configured for collecting the fibers to thereby form the fabric; a control unit configured for adjusting process parameters so that the fibers differ concerning fiber diameter so that a ratio between a largest fiber diameter and a smallest fiber diameter is more than 1.5.

14. A method of using a nonwoven cellulose fiber fabric according to claim 1 for at least one of the group consisting of a wipe, a dryer sheet, a filter, a hygiene product, a medical application product, a geotextile, agrotextile, clothing, a product for building technology, an automotive product, a furnishing, an industrial product, a product related to beauty, leisure, sports or travel, and a product related to school or office.

15. A product or composite, comprising a fabric according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited:

[0054] FIG. 1 illustrates a device for manufacturing nonwoven cellulose fiber fabric which is directly formed from lyocell spinning solution being coagulated by a coagulation fluid according to an exemplary embodiment of the invention.

[0055] FIG. 2 to FIG. 4 show experimentally captured images of nonwoven cellulose fiber fabric according to an exemplary embodiment of the invention in which merging of individual fibers has been accomplished by a specific process control.

[0056] FIG. 5 and FIG. 6 show experimentally captured images of nonwoven cellulose fiber fabric according to an exemplary embodiment of the invention in which swelling of fibers has been accomplished, wherein FIG. 5 shows the fiber fabric in a dry non-swollen state and FIG. 6 shows the fiber fabric in a humid swollen state.

[0057] FIG. 7 shows an experimentally captured image of nonwoven cellulose fiber fabric according to an exemplary embodiment of the invention in which formation of two superposed layers of fibers has been accomplished by a specific process implementing two serial bars of nozzles.

[0058] FIG. 8 shows a schematic image of a fiber of a nonwoven cellulose fiber fabric according to an exemplary embodiment of the invention, wherein the shown fiber has sections of different fiber thicknesses.

[0059] FIG. 9 shows a schematic image of interconnected fibers of a nonwoven cellulose fiber fabric according to another exemplary embodiment of the invention, wherein different ones of the shown fibers have different fiber thicknesses.

[0060] FIG. 10 shows a schematic image of fibers of a nonwoven cellulose fiber fabric according to still another exemplary embodiment of the invention, wherein different ones of the shown fibers have different fiber thicknesses and two of the shown fibers are integrally interconnected along a merging line to form a superordinate fiber structure.

[0061] FIG. 11 shows a schematic image of a nonwoven cellulose fiber fabric according to still another exemplary embodiment of the invention composed of two stacked and merged layers of interconnected fibers having different fiber thicknesses.

[0062] FIG. 12 illustrates a part of a device for manufacturing nonwoven cellulose fiber fabric composed of two stacked layers of endless cellulose fiber webs according to an exemplary embodiment of the invention.

[0063] FIG. 13 and FIG. 14 show experimentally captured images of nonwoven cellulose fiber fabric according to an exemplary embodiment of the invention in which different fibers in different fiber sections have substantially different diameters.

[0064] FIG. 15 shows a schematic image of nonwoven cellulose fiber fabric according to an exemplary embodiment of the invention composed of three stacked layers with different diameters of fibers.

DETAILED DESCRIPTION OF THE DRAWINGS

[0065] The illustrations in the drawings are schematic. In different drawings similar or identical elements are provided with the same reference labels.

[0066] FIG. 1 illustrates a device 100 according to an exemplary embodiment of the invention for manufacturing nonwoven cellulose fiber fabric 102 which is directly formed from lyocell spinning solution 104. The latter is at least partly coagulated by a coagulation fluid 106 to be converted into partly-formed cellulose fibers 108. By the device 100, a lyocell solution blowing process according to an exemplary embodiment of the invention may be carried out. In the context of the present application, the term lyocell solution-blowing process may particularly encompass processes which can result in essentially endless filaments or fibers 108 of a discrete length or mixtures of endless filaments and fibers of discrete length being obtained. As further described below, nozzles each having an orifice 126 are provided through which cellulose solution or lyocell spinning solution 104 is ejected together with a gas stream or gas flow 146 for manufacturing the nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention.

[0067] As can be taken from FIG. 1, wood pulp 110, other cellulose-based feedstock or the like may be supplied to a storage tank 114 via a metering unit 113. Water from a water container 112 is also supplied to the storage tank 114 via metering unit 113. Thus, the metering unit 113, under control of a control unit 140 described below in further detail, may define relative amounts of water and wood pulp 110 to be supplied to the storage tank 114. A solvent (such as N-methyl-morpholine, NMMO) accommodated in a solvent container 116 may be concentrated in a concentration unit 118 and may then be mixed with the mixture of water and wood pulp 110 or other cellulose-based feedstock with definable relative amounts in a mixing unit 119. Also the mixing unit 119 can be controlled by the control unit 140. Thereby, the water-wood pulp 110 medium is dissolved in the concentrated solvent in a dissolving unit 120 with adjustable relative amounts, thereby obtaining lyocell spinning solution 104. The aqueous lyocell spinning solution 104 can be a honey-viscous medium composed of (for instance 5 mass % to 15 mass %) cellulose comprising wood pulp 110 and (for instance 85 mass % to 95 mass %) solvent.

[0068] The lyocell spinning solution 104 is forwarded to a fiber formation unit 124 (which may be embodied as or which may comprise a number of spinning beams or jets 122). For instance, the number of orifices 126 of the jets 122 may be larger than 50, in particular larger than 100. In one embodiment, all orifices 126 of a fiber formation unit 124 (which may comprise a number of spinnerets or jets 122) of orifices 126 of the jets 122 may have the same size and/or shape. Alternatively, size and/or shape of different orifices 126 of one jet 122 and/or orifices 126 of different jets 122 (which may be arranged serially for forming a multilayer fabric) may be different.

[0069] When the lyocell spinning solution 104 passes through the orifices 126 of the jets 122, it is divided into a plurality of parallel strands of lyocell spinning solution 104. A vertically oriented gas flow, i.e. being oriented substantially parallel to spinning direction, forces the lyocell spinning solution 104 to transform into increasingly long and thin strands which can be adjusted by changing the process conditions under control of control unit 140. The gas flow may accelerate the lyocell spinning solution 104 along at least a part of its way from the orifices 126 to a fiber support unit 132.

[0070] While the lyocell spinning solution 104 moves through the jets 122 and further downward, the long and thin strands of the lyocell spinning solution 104 interact with non-solvent coagulation fluid 106. The coagulation fluid 106 is advantageously embodied as a vapor mist, for instance an aqueous mist. Process relevant properties of the coagulation fluid 106 are controlled by one or more coagulation units 128, providing the coagulation fluid 106 with adjustable properties. The coagulation units 128 are controlled, in turn, by control unit 140. Preferably, respective coagulation units 128 are provided between the individual nozzles or orifices 126 for individually adjusting properties of respective layers of fabric 102 being produced. Preferably, each jet 122 may have two assigned coagulation units 128, one from each side. The individual jets 122 can thus be provided with individual portions of lyocell spinning solution 104 which may also be adjusted to have different controllable properties of different layers of manufactured fabric 102.

[0071] When interacting with the coagulation fluid 106 (such as water), the solvent concentration of the lyocell spinning solution 104 is reduced, so that the cellulose of the former e.g. wood pulp 110 (or other feedstock) is at least partly coagulated as long and thin cellulose fibers 108 (which may still contain residual solvent and water).

[0072] During or after initial formation of the individual cellulose fibers 108 from the extruded lyocell spinning solution 104, the cellulose fibers 108 are deposited on fiber support unit 132, which is here embodied as a conveyor belt with a planar fiber accommodation surface. The cellulose fibers 108 form a nonwoven cellulose fiber fabric 102 (illustrated only schematically in FIG. 1). The nonwoven cellulose fiber fabric 102 is composed of continuous and substantially endless filaments or fibers 108.

[0073] Although not shown in FIG. 1, the solvent of the lyocell spinning solution 104 removed in coagulation by the coagulation unit 128 and in washing in a washing unit 180 can be at least partially recycled.

[0074] While being transported along the fiber support unit 132, the nonwoven cellulose fiber fabric 102 can be washed by washing unit 180 supplying wash liquor to remove residual solvent and may then be dried. It can be further processed by an optional but advantageous further processing unit 134. For instance, such a further processing may involve hydro-entanglement, needle punching, impregnation, steam treatment with a pressurized steam, calendering, etc.

[0075] The fiber support unit 132 may also transport the nonwoven cellulose fiber fabric 102 to a winder 136 on which the nonwoven cellulose fiber fabric 102 may be collected as a substantially endless sheet. The nonwoven cellulose fiber fabric 102 may then be shipped as roll-good to an entity manufacturing products such as wipes or textiles based on the nonwoven cellulose fiber fabric 102.

[0076] As indicated in FIG. 1, the described process may be controlled by control unit 140 (such as a processor, part of a processor, or a plurality of processors). The control unit 140 is configured for controlling operation of the various units shown in FIG. 1, in particular one or more of the metering unit 113, the mixing unit 119, the fiber formation unit 124, the coagulation unit(s) 128, the further processing unit 134, the dissolution unit 120, the washing unit 118, etc. Thus, the control unit 140 (for instance by executing computer executable program code, and/or by executing control commands defined by a user) may precisely and flexibly define the process parameters according to which the nonwoven cellulose fiber fabric 102 is manufactured. Design parameters in this context are air flow along the orifices 126, properties of the coagulation fluid 106, drive speed of the fiber support unit 132, composition, temperature and/or pressure of the lyocell spinning solution 104, etc. Additional design parameters which may be adjusted for adjusting the properties of the nonwoven cellulose fiber fabric 102 are number and/or mutual distance and/or geometric arrangement of the orifices 126, chemical composition and degree of concentration of the lyocell spinning solution 104, etc. Thereby, the properties of the nonwoven cellulose fiber fabric 102 may be properly adjusted, as described below. Such adjustable properties (see below detailed description) may involve one or more of the following properties: diameter and/or diameter distribution of the fibers 108, amount and/or regions of merging between fibers 108, a purity level of the fibers 108, properties of a multilayer fabric 102, optical properties of the fabric 102, fluid retention and/or fluid release properties of the fabric 102, mechanical stability of the fabric 102, smoothness of a surface of the fabric 102, cross-sectional shape of the fibers 108, etc.

[0077] Although not shown, each spinning jet 122 may comprise a polymer solution inlet via which the lyocell spinning solution 104 is supplied to the jet 122. Via an air inlet, a gas flow 146 can be applied to the lyocell spinning solution 104. Starting from an interaction chamber in an interior of the jet 122 and delimited by a jet casing, the lyocell spinning solution 104 moves or is accelerated (by the gas flow 146 pulling the lyocell spinning solution 104 downwardly) downwardly through a respective orifice 126 and is laterally narrowed under the influence of the gas flow 146 so that continuously tapering cellulose filaments or cellulose fibers 108 are formed when the lyocell spinning solution 104 moves downwardly together with the gas flow 146 in the environment of the coagulation fluid 106.

[0078] Thus, processes involved in the manufacturing method described by reference to FIG. 1 may include that the lyocell spinning solution 104, which may also be denoted as cellulose solution is shaped to form liquid strands or latent filaments, which are drawn by the gas flow 146 and significantly decreased in diameter and increased in length. Partial coagulation of latent filaments or fibers 108 (or preforms thereof) by coagulation fluid 106 prior to or during web formation on the fiber support unit 132 may also be involved. The filaments or fibers 108 are formed into web like fabric 102, washed, dried and may be further processed (see further processing unit 134), as required. The filaments or fibers 108 may for instance be collected, for example on a rotating drum or belt, whereby a web is formed.

[0079] As a result of the described manufacturing process and in particular the choice of solvent used, the fibers 108 have a copper content of less than 5 ppm and have a nickel content of less than 2 ppm. This advantageously improves purity of the fabric 102.

[0080] The lyocell solution blown web (i.e. the nonwoven cellulose fiber fabric 102) according to exemplary embodiments of the invention preferably exhibits one or more of the following properties:

(i) The dry weight of the web is from 5 to 300 g/m.sup.2, preferably 10-80 g/m.sup.2
(ii) The thickness of the web according to the standard WSP120.6 respectively DIN29073 (in particular in the latest version as in force at the priority date of the present patent application) is from 0.05 to 10.0 mm, preferably 0.1 to 2.5 mm
(iii) The specific tenacity of the web in MD according to EN29073-3, respectively ISO9073-3 (in particular in the latest version as in force at the priority date of the present patent application) ranges from 0.1 to 3.0 Nm.sup.2/g, preferably from 0.4 to 2.3 Nm.sup.2/g
(iv) The average elongation of the web according to EN29073-3, respectively ISO9073-3 (in particular in the latest version as in force at the priority date of the present patent application) ranges from 0.5 to 100%, preferably from 4 to 50%.
(v) The MD/CD tenacity ratio of the web is from 1 to 12
(vi) The water retention of the web according to DIN 53814 (in particular in the latest version as in force at the priority date of the present patent application) is from 1 to 250%, preferably 30 to 150%
(vii) The water holding capacity of the web according to DIN 53923 (in particular in the latest version as in force at the priority date of the present patent application) ranges from 90 to 2000%, preferably 400 to 1100%.
(viii) Metal residue levels of copper content of less than 5 ppm and nickel content of less than 2 ppm, according to the standards EN 15587-2 for the substrate decomposition and EN 17294-2 for the ICP-MS analysis (in particular in the latest version as in force at the priority date of the present patent application)

[0081] Most preferably, the lyocell solution-blown web exhibits all of said properties (i) to (viii) mentioned above.

[0082] As described, the process to produce the nonwoven cellulose fiber fabric 102 preferably comprises:

(a) Extruding a solution comprising cellulose dissolved in NMMO (see reference numeral 104) through the orifices 126 of at least one jet 122, thereby forming filaments of lyocell spinning solution 104
(b) Stretching said filaments of lyocell spinning solution 104 by a gaseous stream (see reference numeral 146)
(c) Contacting said filaments with a vapor mist (see reference numeral 106), preferably containing water, thereby at least partly precipitating said fibers 108. Consequently, the filaments or fibers 108 are at least partly precipitated before forming web or nonwoven cellulose fiber fabric 102.
(d) Collecting and precipitating said filaments or fibers 108 in order to form a web or nonwoven cellulose fiber fabric 102
(e) Removing solvent in wash line (see washing unit 180)
(f) Optionally bonding via hydro-entanglement, needle punching, etc. (see further processing unit 134)
(g) Drying and roll collection

[0083] Constituents of the nonwoven cellulose fiber fabric 102 may be bonded by merging, intermingling, hydrogen bonding, physical bonding such as hydroentanglement or needle punching, and/or chemical bonding.

[0084] In order to be further processed, the nonwoven cellulose fiber fabric 102 may be combined with one or more layers of the same and/or other materials, such as (not shown) layers of synthetic polymers, cellulosic fluff pulp, nonwoven webs of cellulose or synthetic polymer fibers, bicomponent fibers, webs of cellulose pulp, such as airlaid or wetlaid pulp, webs or fabrics of high tenacity fibers, hydrophobic materials, high performance fibers (such as temperature resistant materials or flame retardant materials), layers imparting changed mechanical properties to the final products (such as Polypropylene or Polyester layers), biodegradable materials (e.g. films, fibers or webs from Polylactic acid), and/or high bulk materials.

[0085] It is also possible to combine several distinguishable layers of nonwoven cellulose fiber fabric 102, see for instance FIG. 7.

[0086] The nonwoven cellulose fiber fabric 102 may essentially consist of cellulose alone. Alternatively, the nonwoven cellulose fiber fabric 102 may comprise a mixture of cellulose and one or more other fiber materials. The nonwoven cellulose fiber fabric 102, furthermore, may comprise a bicomponent fiber material. The fiber material in the nonwoven cellulose fiber fabric 102 may at least partly comprise a modifying substance. The modifying substance may be selected from, for example, the group consisting of a polymeric resin, an inorganic resin, inorganic pigments, antibacterial products, nanoparticles, lotions, fire-retardant products, absorbency-improving additives, such as superabsorbent resins, ion-exchange resins, carbon compounds such as active carbon, graphite, carbon for electrical conductivity, X-ray contrast substances, luminescent pigments, and dye stuffs.

[0087] Concluding, the cellulose nonwoven web or nonwoven cellulose fiber fabric 102 manufactured directly from the lyocell spinning solution 104 allows access to value added web performance which is not possible via staple fiber route. This includes the possibility to form uniform lightweight webs, to manufacture microfiber products, and to manufacture continuous filaments or fibers 108 forming a web. Moreover, compared to webs from staple fibers, several manufacturing procedures are no longer required. Moreover, nonwoven cellulose fiber fabric 102 according to exemplary embodiments of the invention is biodegradable and manufactured from sustainably sourced raw material (i.e. wood pulp 110 or the like). Furthermore, it has advantages in terms of purity and absorbency. Beyond this, it has an adjustable mechanical strength, stiffness and softness. Furthermore, nonwoven cellulose fiber fabric 102 according to exemplary embodiments of the invention may be manufactured with low weight per area (for instance 10 to 30 g/m.sup.2). Very fine filaments down to a diameter of not more than 5 m, in particular not more than 3 m, can be manufactured with this technology. Furthermore, nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention may be formed with a wide range of web aesthetics, for instance in a flat crispy film-like way, in a paper-like way, or in a soft flexible textile-like way. By adapting the process parameters of the described process, it is furthermore possible to precisely adjust stiffness and mechanical rigidity or flexibility and softness of the nonwoven cellulose fiber fabric 102. This can be adjusted for instance by adjusting a number of merging positions, the number of layers, or by after-treatment (such as needle punch, hydro-entanglement and/or calendering). It is in particular possible to manufacture the nonwoven cellulose fiber fabric 102 with a relatively low basis weight of down to 10 g/m.sup.2 or lower, to obtain filaments or fibers 108 with a very small diameter (for instance of down to 3 to 5 m, or less), etc.

[0088] FIG. 2, FIG. 3 and FIG. 4 show experimentally captured images of nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention in which merging of individual fibers 108 has been accomplished by a corresponding process control. The oval markers in FIG. 2 to FIG. 4 show such merging regions where multiple fibers 108 are integrally connected to one another. At such merging points, two or more fibers 108 may be interconnected to form an integral structure.

[0089] FIG. 5 and FIG. 6 show experimentally captured images of nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention in which swelling of fibers 108 has been accomplished, wherein FIG. 5 shows the fiber fabric 102 in a dry non-swollen state and FIG. 6 shows the fiber fabric 102 in a humid swollen state. The pore diameters can be measured in both states of FIG. 5 and FIG. 6 and can be compared to one another. When calculating an average value of 30 measurements, a decrease of the pore size by swelling of the fibers 108 in an aqueous medium up to 47% of their initial diameter could be determined.

[0090] FIG. 7 shows an experimentally captured image of nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention in which formation of two superposed layers 200, 202 of fibers 108 has been accomplished by a corresponding process design, i.e. a serial arrangement of multiple spinnerets. The two separate, but connected layers 200, 202 are indicated by a horizontal line in FIG. 7. For instance, an n-layer fabric 102 (n2) can be manufactured by serially arranging n spinnerets or jets 122 along the machine direction.

[0091] Specific exemplary embodiments of the invention will be described in the following in more detail:

[0092] FIG. 8 shows a schematic image of a fiber 108 of a nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention. The shown fiber 108 has sections of different fiber thicknesses d and D>d. More specifically, the embodiment of FIG. 8 provides a nonwoven cellulose fiber fabric 102 directly manufactured from lyocell spinning solution 104, wherein the fabric 102 comprises fiber 108 differing concerning fiber diameter by several 100% in relation to smallest diameter d. Thus, an intra-fiber thickness variation is present in FIG. 8.

[0093] FIG. 9 shows a schematic image of interconnected fibers 108 of a nonwoven cellulose fiber fabric 102 according to another exemplary embodiment of the invention. According to FIG. 9, different ones of the shown three fibers 108 have different fiber thicknesses d and D>d. According to FIG. 9, different fibers 108 differ concerning fiber diameter by several 100% in relation to smallest diameter d. In particular, a ratio D:d may be significantly higher than 1.5. Thus, an inter-fiber thickness variation between different fibers 108 is present in FIG. 8, in addition to an intra-fiber thickness variation of the individual fibers 108.

[0094] FIG. 10 shows a schematic image of fibers 108 of a nonwoven cellulose fiber fabric 102 according to still another exemplary embodiment of the invention, wherein two of the shown fibers 108 are integrally interconnected along a merging line (see reference numeral 204) to form a superordinate fiber structure 206. FIG. 10 also includes a cross-sectional view of the superordinate fiber structure 206 showing that is it is formed by two fibers 108 being integrally connected at reference numeral 204. Thus, the above two fibers 108 are aligned side-by-side to form a superordinate fiber structure 206 having a larger diameter than the separate third fiber 108 in the lower part of FIG. 10.

[0095] FIG. 11 shows a schematic cross sectional view of a nonwoven cellulose fiber fabric 102 according to still another exemplary embodiment of the invention composed of two stacked and merged layers 200, 202 of interconnected fibers 108 having different fiber thicknesses d and D>d (see the lower two details of FIG. 11). More specifically, different ones of the fibers 108 being located in the different layers 200, 202 differ concerning an averaged fiber diameter (i.e. averaged over the fibers 108 of the respective layer 200, 202). A further detail of the interface between the layers 200, 202 is shown as well, where a merging point 204 is visible which integrally couples fibers 108 of both layers 200, 202 at the interface for increasing stability of the fabric 102 at the interface (see the upper detail of FIG. 11). Additionally, different ones of the fibers 108 being located in the different layers 200, 202 are integrally connected at at least one respective merging position 204. The fibers 108 located in the different layers 200, 202 and being formed with different average diameter may be provided with different functionalities. Such different functionalities may be supported by the different average diameters, but may also be further promoted by a respective coating or the like. Such different functionalities may for instance be a different behavior in terms of wicking, anisotropic behavior, different oil absorbing capability, different water absorbing capability, different cleanability, and/or different roughness.

[0096] FIG. 12 illustrates a part of a device 100 for manufacturing nonwoven cellulose fiber fabric 102 composed of two stacked layers 200, 202 of endless cellulose fibers 108 according to an exemplary embodiment of the invention. A difference between the device 100 shown in FIG. 12 and the device 100 shown in FIG. 1 is that the device 100 according to FIG. 12 comprises two serially aligned jets 122 and respectively assigned coagulation units 128, as described above. In view of the movable fiber accommodation surface of the conveyor belt-type fiber support unit 132, the upstream jet 122 on the left-hand side of FIG. 12 produces layer 202. Layer 200 is produced by the downstream jet 122 (see right hand side of FIG. 12) and is attached to an upper main surface of the previously formed layer 202 so that a double layer 200, 202 of fabric 102 is obtained.

[0097] According to FIG. 12, the control unit 140 (controlling the jets 122 and the coagulation units 128) is configured for adjusting process parameters so that the fibers 108 of the different layers 200, 202 differ concerning fiber diameter by more than 50% in relation to a smallest diameter (see for example FIG. 11). Adjusting the fiber diameters of the fibers 108 of the layers 200, 202 by the control unit 140 may comprise adjusting an amount of coagulation fluid 106 interacting with the lyocell spinning solution 104. Additionally, the embodiment of FIG. 12 adjusts the process parameters for adjusting fiber diameter by serially arranging multiple jets 122 with orifices 126 (optionally with different properties) along the movable fiber support unit 132. For instance, such different properties may be different orifice 126 diameters, different speed of gas flow 146, different amounts of gas flow 146, and/or different gas flow 146 pressure. Although not shown in FIG. 12, it is possible to further process the fibers 108 after collection on the fiber support unit 132 by liquid jet compression, needling, and/or impregnating.

[0098] Still referring to the embodiment illustrated in FIG. 12, one or more further nozzle bars or jets 122 may be provided and may be arranged serially along a transport direction of fiber support unit 132. The multiple jets 122 may be arranged so that further layer 200 of fibers 108 may be deposited on top of the previously formed layer 202, preferably before the coagulation or curing process of the fibers 108 of the layer 202 and/or of the layer 200 is fully completed, which may trigger merging. When properly adjusting the process parameters, this may have advantageous effects in terms of the properties of a multilayer fabric 102:

[0099] On the one hand, the first deposited layer 202 may be laid on a transport band such as a conveyor belt as fiber support unit 132. In such an embodiment, the fiber support unit 132 may be embodied as an ordered structure of a release mechanism and air suction openings (not shown). In the statistical distribution of filaments of fibers 108, this may have the effect that a higher material concentration can be found in the regions in which no airflow is present. Such a (in particular microscopic) material density variation can be considered as a perforation from a mechanical point of view which functions as a distortion (in particular due to its tendency of suppressing patterns) of the homogeneity of the nonwoven cellulose fiber fabric 102. At the position where the gas flow or a liquid flow (for instance water) penetrates through the nonwoven cellulose fiber fabric 102, pores may be formed in the nonwoven cellulose fiber fabric 102. By such a fluid flow (wherein the fluid can be a gas or a liquid), the tear strength of the manufactured nonwoven cellulose fiber fabric 102 may be increased. Without wishing to be bound to a specific theory, it is presently believed that the second layer 200 can be considered as a reinforcement of the first layer 202, which compensates the homogeneity reduction of the layer 202. This increase of the mechanical stability can be further improved by fiber diameter variation (in particular inter-fiber diameter variation and/or intra-fiber longitudinal diameter variation of the individual fibers 108). When exerting deeper (in particular punctual) pressure (for instance provided by air or water), the cross-sectional shape of a fiber 108 can be further intentionally distorted, which may advantageously result in a further increased mechanical stability.

[0100] On the other hand, intended merging between fibers 108 of the fabric 102 according to FIG. 12 can be triggered so as to further increase the mechanical stability of the fabric 102. In this context, merging may be a supported contact point adhesion of contacting filaments of fibers 108, in particular prior to the completion of a coagulation process of one or both of the fibers 108 being merged. For instance, merging may be promoted by increasing a contact pressure by a fluid flow (for instance a flow of air or water). By taking this measure, the strength of the coagulation on the one hand between filaments or fibers 108 of one of the layers 200, 202 and/or on the other hand between the layers 200, 202 may be increased.

[0101] The device 100 according to FIG. 12, which is configured for the manufacture of multilayer fabric 102, implements a high number of process parameters which can be used for designing shape and/or diameter or diameter distribution of the fibers 108 as well as of fiber layers 200, 202. This is the result of the serial arrangement of multiple jets 122, each of which being operable with individually adjustable process parameters.

[0102] With device 100 according to FIG. 12, it is in particular possible to manufacture a fabric 102 composed of at least two layers 200, 202 (preferably more than two layers). The fibers 108 of the different layers 200, 202 may have different values of average diameter and may be formed in one continuous process. By taking this measure, a highly efficient production of the nonwoven cellulose fiber fabric 102 can be ensured, which in particular allows to transfer the obtained multilayer fabric 102 in one transport procedure to a destination for further processing.

[0103] By the defined layer separation of a multilayer fabric 102, it is also possible to later separate the multilayer fabric 102 into the different individual layers 200, 202 or into different multilayer sections. According to exemplary embodiments of the invention, both intra-layer adhesion of the fibers 108 of one layer 200, 202 as well as inter-layer adhesion of the fibers 108 between adjacent layers 200, 202 (for instance by merging and/or by friction generating contact) may be properly and individually adjusted. A corresponding separate control for each layer 200, 202 individually may be in particular obtained when the process parameters are adjusted so that coagulation or curing of the fibers 108 of one layer 202 is already completed when the other layer 200 of fibers 108 is placed on top thereof.

[0104] FIG. 13 and FIG. 14 show experimentally captured images of nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention in which different fibers 108 in different fiber sections have substantially different diameters. The embodiment of FIG. 13 shows a tight and dense web or fabric 102 with a high capillary suction capability. The embodiment of FIG. 14 shows different variations of diameter/titer and shape of fibers 108 of a fabric 102. This involves twists, thickness variations within one and the same fiber 108, different fiber diameters as well as coagulated parallel fibers 108.

[0105] FIG. 15 shows a schematic image of nonwoven cellulose fiber fabric 102 according to another exemplary embodiment of the invention composed of three stacked layers 202, 200, 200 with different diameters of fibers 108. According to FIG. 15, an intermediate sandwich layer 200 has significantly smaller diameters of fibers 108 than the two exterior layers 200, 202 above and below.

[0106] The multilayer fabric 102 shown in FIG. 15 is particularly appropriate for applications such as medical appliances, agricultural textiles, etc. For instance, an active substance may be stored in the inner layer 200 showing a high capillary action. The exterior layers 200, 202 may be designed in terms of rigidity and surface haptic. This is advantageous for cleaning and medical applications. For agricultural applications, the fiber layer design may be specifically configured in terms of evaporation properties and/or root penetration.

[0107] In another application, the multilayer fabric 102 shown in FIG. 15 may be used as facial mask, wherein the central layer 200 may have a specifically pronounced fluid retaining capability. The cover layers 200, 202 may be configured for adjusting fluid release properties. The diameters of the fibers 108 of the respective layer 200, 200, 202 may be used as a design parameter for adjusting these functions.

[0108] According to exemplary embodiments, fiber diameter variations in nonwoven cellulose fiber fabric 102 are adjusted in a manufacturing process and may be used for setting desired product properties as a functionalization. In particular, such a functionalization as a result of adjusted fiber diameter variations may be used for improving mechanical robustness of the manufactured nonwoven cellulose fiber fabric 102. Highly advantageously, the fibers 108 of the nonwoven cellulose fiber fabric 102 showing diameter variations may be endless fibers 108.

[0109] Due to the described manufacturing process, is also possible to obtain the fiber diameter variations in the nonwoven cellulose fiber fabric 102 with an extremely small concentration of heavy metal impurities, in particular what concerns copper and nickel. Nickel for example is known to involve a risk of allergic reactions by users. Such risks may be significantly reduced when keeping the concentration of heavy metal impurities, in particular from nickel, very small. These small concentrations of heavy metal impurities are the result of the formation of the fabric 102 on the basis of a lyocell spinning solution 104 and its ingredients. Therefore, a highly pure cellulose fiber network may be obtained with very small concentration of impurities. Hence, by the described filament production according to the lyocell manufacturing architecture, no process related heavy metal contents of significant amounts are in the readily manufactured fabric 102. This is in particular advantageous to achieve compatibility with post processing requirements and is in particular advantageous when the readily manufactured fabric 102 comes into contact with human beings and/or natural organisms.

[0110] With the nonwoven cellulose fiber fabric 102 with pronounced fiber diameter variation according to an exemplary embodiment of the invention, a higher mechanical stability may be obtained for a given grammage (i.e. weight per area of sheet like fabric 102), or a reduced grammage may be obtained at the same mechanical stability.

[0111] By the method of manufacturing nonwoven cellulose fiber fabric 102 as described above, the fiber formation unit 124 may use a nozzle bar (see jet 122) for forming filaments or fibers 108. These filaments or fibers 108 are then stretched under the influence of a gas flow 146, i.e. rendered long and thin, and are laid down on a transport apparatus such as fiber support unit 132. The formation of merging points between filament fiber 108 and filament fiber 108 can then be promoted by air turbulence or vorticity applied during stretching the fibers 108 or a (for instance still uncured or not yet fully coagulated) preform thereof. Additionally or alternatively, it is also possible to form the merging points between the various fibers 108 or preforms thereof when laying them down on the fiber support unit 132. During this stretching process, there is a large random controlled variability of the generated filament jet. During such a process, the self-organizing properties of a possible parallel air and water flow can be problematic in view of the large number of individual filaments of fibers 108. Undesired pattern formation by mechanical interference, which can be generated by an air flow in a transition region between laminar and turbulent flow can be suppressed or even eliminated by triggering significant fiber diameter variations of the manufactured nonwoven cellulose fiber fabric 102 by a corresponding adjustment of the process parameters. In this context, it may be sufficient that only individual filaments of fibers 108 are slightly modified. By taking this measure, the harmony of detailed parameters as required for pronounced self-organization may be intentionally distorted and the random character of the resulting filament diameter distribution can be increased. The result is a nonwoven cellulose fiber fabric 102 with a high mechanical stability.

[0112] In an embodiment, it is possible that the titer of the fibers 108 of the nonwoven cellulose fiber fabric 102 is intentionally distorted by a large amount of significant fiber diameter differences. For instance, very thin fibers 108 may allow to achieve a proper capillarity between neighbored fibers 108. A mixing with thicker fibers 108 may result in an increased stiffness, roughness and/or rigidity.

[0113] The combination of different titers according to an exemplary embodiment of the invention can be achieved by a thickness variation of endless fibers 108 along the length of one respective fiber 108 (for instance by a periodic pressure and/or velocity change induced by the stretching gas flow 146 during fiber formation). On the other hand, this can also be achieved by forming fibers with varying fiber thicknesses as a result of the use of varying diameters of the orifices 126 of the nozzle. A further possibility of forming fibers 108 with significant variations of the diameter is the adjustment of the coagulation process for layers 200, 202 with different titers. Yet another exemplary embodiment of the invention forms fibers 108 with fiber diameter variations by a coagulation of parallel aligned fibers 108 which combine or merge to thereby form a thicker superordinate fiber structure 206 connected along an oblong merging line.

[0114] In particular in the scenario of a dense nonwoven cellulose fiber fabric 102, a diameter variation along the individual endless fibers 108 contributes to a larger stability of the entire fabric 102 by the effect that even a relatively small adhesion serves as springy buffer for thickness variations in the case of pulling forces.

[0115] According to an exemplary embodiment of the invention, variations of the diameters of the fibers can also be used for influencing or adjusting the wicking speed (i.e. the speed according to which a liquid enters into the fabric). Descriptively speaking, very thin fibers will react on entering fluid in a different way than thicker fibers.

[0116] By fiber diameter variations along large extensions of the fibers 108 it is possible to obtain a desired friction based clamping effect in the fabric 102. This may result in a self-inhibiting effect (in a similar way as in case of a conical tool reception). Such an effect may already be obtained in the event of relatively small deviations of the diameter distribution compared to a constant diameter. The thereby created cone can form an inhibiting system together with another fiber (for instance in a cone on cone geometry or in a cone on cylinder geometry). Another clamping effect may also be generated by an arbitrary winding of one fiber 108 around another fiber 108. It may be also advantageous when one fiber 108 penetrates a through hole of a bail of another fiber 108, in particular when the first mentioned fiber 108 has a varying diameter along its length. In such a scenario, a further reinforcement is obtained despite of a relatively high initial elasticity. This has also a positive impact on the entire rigidity of the fabric 102.

[0117] The mentioned measures and/or other measures for triggering fiber diameter variations can be implemented individually or can be combined. For instance, fiber diameter variations in a range between 1:1.1 and 1:1000 can be adjusted. This allows to combine many different diameters.

[0118] The high mechanical stability of fabric 102 according to exemplary embodiments of the invention is also promoted by the use of endless fibers 108 made of cellulose, because endless fibers 108 (in comparison to staple fibers having a typical length of 38 mm) intrinsically involve a lower number of disturbing transitions, so that already the individual endless fiber 108 has a higher mechanical stability. By the provision of cellulose fibers 108 obtained from a lyocell architecture, it is possible to form the fabric 102 from highly pure fibers 108 which may for instance have a process related heavy metal content of less than 10 ppm for each individual chemical element. This may prevent a mechanical weakening of the fibers 108, since this high degree of purity suppresses the tendency of inclusion of contaminants or impurities in the fiber 108.

[0119] A design of a carrier grid, carrier web or other kind of carrier structures may allow to further refine the control of the mechanical stability of the formed fabric 102 in such a way that, as a result of water induced merging, a force transmission and force balancing structure similar to bionic structures may be obtained. Such kind of structures are capable of receiving significantly larger forces than conventional cellulose fabric.

[0120] Different layer thicknesses in multilayer fabric 102 and/or fiber diameter variations within the nonwoven cellulose fiber fabric 102 may also allow to obtain a mechanical damping effect and/or an adjustment of an expressed overall elasticity of the readily manufactured nonwoven cellulose fiber fabric 102. This may for instance be advantageous for applications of the fabric 102 used as a package for mechanically protecting a packaged good.

[0121] For applications with required haptic properties, it is possible to combine specific basic properties of a fabric 102 (for instance a specific liquid management) with a haptically adapted (in particular soft) cover layer. In particular the opportunity of fiber diameter variations allows the combination of different functional properties of the nonwoven cellulose fiber fabric 102 according to exemplary embodiments of the invention (for instance swelling capability, hydrophilic property, oleophilic property, wicking, liquid retaining property).

[0122] In an experimental analysis, very good results in terms of mechanical reinforcement have been obtained with fiber diameters below 70 m, in particular in a range between 3 m and 30 m.

[0123] Wherein analyzing and manufacturing nonwoven cellulose fiber fabric 102 with fiber diameter variations, it turned out that this concept allows to significantly improve cleanability (which may be advantageous for cleaning sheets or wipes). Moreover, the fabric 102 can be laid on a surface of a face (which may comprise non-planar features such as in particular wrinkles, rounding) smoother and with better contact (this may be advantageous for applications such as face masks). Furthermore, smoothness of the fabric 102 can be precisely controlled. Beyond this, reception zones or solid particles can be precisely formed on the fabric 102.

[0124] What concerns the amount of the distribution of the fiber thickness, already moderate fiber diameter variations of 50% (i.e. largest diameter divided by smallest diameter times 100% minus 100%) have turned out to be sufficient in order to prevent patterns formed by self-organization effects of endless fibers 108 in the production process. Such small diameter variations can be manufactured very easily by slightly differing diameters when generating the endless fiber 108 from the lyocell spinning solution 104 or by blowing with variations in the transition region between laminar and turbulent flow.

[0125] In a further embodiment, different functionalizations in one and the same nonwoven cellulose fiber fabric 102 may be created. Such different functionalization may be obtained by fiber diameter variation as well. For instance, fibers 108 of different diameters can be appropriately combined during the production process:

[0126] In a first variant, it is possible to provide an appropriate amount of sufficiently thick filaments or fibers 108 within one volume element so that the desired mechanical robustness can be obtained. Additionally, thinner filaments or fibers 108 can be implemented as a fine-meshed matrix in the same volume element, which can for example be adapted to in terms of providing a specific function (for instance detention of impurities). The fine-meshed matrix may for instance be configured to provide the desired function by adjusting fiber diameter, degree of network formation, number of merging point, etc. Such a top-down design can for instance be advantageous when rigidity is important and when an additional function is desired which can be provided by the thinner fibers 108.

[0127] In a second variant, it is possible to provide such an amount of thin fibers 108 within one volume element that the cleaning, detention, embedding and/or filter requirements concerning the final product are complied with. The remaining desired mechanical stability can then be provided by supplementing thicker fibers 108 so that the desired mechanical minimum load requirements can be fulfilled. Such a bottom-up design can for instance be advantageous when certain criteria (such as a maximum number of pores per fabric area) shall not be exceeded.

[0128] In an exemplary embodiment of the invention, fibers 108 of different diameters or diameter distribution may be interconnected by merging them, as described above.

[0129] In a further embodiment, it is possible to achieve an improved mixing or reinforcing of basic properties when using endless fibers 108 (in contrast to staple fibers). The reason for this is that such an architecture makes it possible that thick static fiber portions with high contribution in terms of mechanical stability may transit into thinner fiber portions. By fixing of a fiber 108 at one or more merging points, the one or more merging points may define the position of the first fail. When the number of fiber transitions from thick to thin, or vice versa, it increased, also the robustness of the thin fibers 108 is increased.

[0130] In a further embodiment, fiber diameter variations may be manufactured by coagulation of parallel fibers 108. In such an embodiment, a very high merging degree can be obtained, so that a high degree of diameter variations is possible. It has been surprisingly found that, by taking this measure, high values of smoothness could be obtained, and on the other hand very low values of visible linting was achievable. Without wishing to be bound to a specific theory, it is presently believed that a high amount of thin fibers 108 in the nonwoven cellulose fiber fabric 102 results in an overall high smoothness without pronounced linting.

[0131] In yet another exemplary embodiment of the invention, a nonwoven cellulose fiber fabric 102 is obtained which has a significant capability of receiving oil. This can be obtained by the described relatively high homogeneity and a correspondingly obtainable equal cavity formation. On the other hand, mechanical stability is created by the thick fibers 108. This prevents the cavities from collapsing. Thus, the combination of very thick fibers 108 with very thin fibers 108 allows to obtain a mechanically robust oil storing capillary system.

[0132] In another exemplary embodiment of the invention, the nonwoven cellulose fiber fabric 102 is used for a biodegradable product. After biodegradation, no binder material or adhesive material remains. In particular, no significant amount of heavy metals forms part of such a biodegradable product.

[0133] In the another exemplary embodiment of the invention with fiber diameter variations between layers 200, 202 of a multilayer fabric 102, it is possible to form or create a gradient of fluids retaining capability and/or fluid distribution capability. For instance, this may allow to properly design an acquisition distribution layer (ADL), as implemented in female hygiene products, incontinence products, etc. Such an acquisition distribution layer may be configured to accumulate fluid as quick as possible and to forward it to a subsequent layer. In the subsequent layer, the fluid can then be spatially distributed and can be forwarded to a core layer (absorbent core).

[0134] Summarizing, in particular one or more of the following adjustments may be made: [0135] a low homogeneous titer may allow to obtain a high smoothness of the fabric 102 [0136] multilayer fabric 102 with small titer and relatively small velocity may allow to obtain a high fabric thickness at a small fabric density [0137] equal absorption curves of the functionalized layers can allow to obtain a homogeneous humidity and fluid accommodation behavior, as well as a homogenous behavior in terms of fluid release [0138] the described connection of layers 200, 202 of fabric 102 allows to design products with low linting upon layer separation [0139] by separating layers 200, 202 of a multilayer fabric 102, many medical, agricultural, personal care functions may be precisely adjusted [0140] it is also possible to differently functionalize single layers 200, 202 so that products with anisotropic properties are obtained (for instance for wicking, oil accommodation, water accommodation, cleanability, roughness).

[0141] Finally, it should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The words comprising and comprises, and the like, do not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0142] In the following, examples for producing variations in the merging factor are described and visualized in the table below. Different merging factors in the cellulose fiber fabric may be achieved by varying the coagulation spray flow while using a constant spinning solution (i.e. a spinning solution with a constant consistency), in particular a Lyocell spinning solution, and a constant gas flow (e.g. air throughput). Hereby, a relationship between the coagulation spray flow and the merging factor, i.e. a trend of merging behaviour (the higher the coagulation spray flow, the lower the merging factor), may be observed. MD denotes hereby the machine direction, and CD denotes the cross direction.

TABLE-US-00001 Specific Hand Fmax Fmax Coagulation Merging MD CD Total cond. cond. Sample spray flow Factor [mN [mN [mN MD CD ID l/h % m.sup.2/g] m.sup.2/g] m.sup.2/g] [N] [N] 1.0 10 9.20 n n n 45.6 10.0 1.1 60 5.65 48.8 38.1 43.4 43.6 33.4 1.2 100 3.29 31.1 23.6 27.3 37.8 29.4 1.3 140 2.93 36.5 17.3 26.9 31.8 24.9 1.4 180 2.48 17.5 16.4 16.9 26.9 20.9 1.5 220 2.34 19.1 13.6 16.3 22.7 21.0 1.6 260 1.98 15.2 11.9 13.6 22.8 20.4 1.7 350 0.75 2.2 2.0 2.1 22.4 19.2

[0143] The softness (described by the known Specific Hand measuring technique, measured with a so-called Handle-O-Meter on the basis of the nonwoven standard WSP90.3, in particular the latest version as in force at the priority date of the present patent application) may follow the above described trend of merging. The tenacity (described by Fmax), for example according to EN29073-3, respectively ISO9073-3, in particular the latest version as in force at the priority date of the present patent application, may also follow the described trend of merging. Thus, the softness and the tenacity of the resulting nonwoven cellulose fiber fabric may be adjusted in accordance with the degree of merging (as specified by the merging factor).