OPTICALLY TRANSPARENT WET NONWOVEN CELLULOSE FIBER FABRIC

Abstract

A nonwoven cellulose fiber fabric, in particular directly manufactured from lyocell spinning solution, wherein the fabric comprises a network of substantially endless fibers, wherein different ones of the fibers are located at least partially in different distinguishable interconnected layers, and wherein the fabric is optically transparent when wet.

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 wherein different ones of the fibers are located at least partially in different distinguishable interconnected layers, and wherein the fabric is optically transparent when wet.

2. The fabric according to claim 1, wherein the fabric is optically opaque, in particular with an optical gray value of lower than 85, when completely dry.

3. The fabric according to claim 1, wherein the fabric has an optical gray value of at least 90, in particular of at least 100, when wet.

4. The fabric according to claim 1, wherein the fabric is optically transparent when being wet to such a degree that a mass ratio between a mass of moisture, in particular water, in an interior of the fabric and a mass of the fibers is at least 3, in particular is at least 5, more particularly is at least 7.

5. The fabric according to claim 1, comprising at least one of the following features: wherein fibers of a respective layer are integrally merged at at least one merging position within said layer; wherein fibers of different layers are integrally merged at at least one merging position between said layers.

6. The fabric according to claim 5, comprising at least one of the following features: wherein the merging between the different layers is adjusted so that pulling on the layers in opposite directions results in a separation of the fabric at an interface between the different layers; wherein the merging is adjusted so that a merging-based connection force between the different layers is smaller than a merging based connection force within a respective one of the different layers.

7. The fabric according to claim 1, comprising a permanently opaque marker being optically visible through at least a part of the fabric when a moisture content of the fabric is above a predetermined threshold value and being optically invisible through at least a part of the fabric when the moisture content of the fabric is below the predetermined threshold value, in particular when the fabric is dry.

8. The fabric according to claim 1, comprising at least one of the following features: comprising at least three interconnected layers composed at least of two opposing cover layers between which an intermediate layer is embedded, wherein an active agent is accommodated in the intermediate layer and is releasable via at least one of the cover layers towards an environment; wherein an adhesion force between the distinguishable interconnected layers is smaller than an adhesion force within a respective one of the layers; wherein an average diameter of the fibers of a respective layer is different from an average diameter of the fibers of a respective other layer; wherein an interconnection between the layers is accomplished without separate binder or glue material; wherein an interconnection between fibers within a respective one of the layers is accomplished without separate binder or glue material; wherein the endless fibers have an amount of fiber ends per volume of less than 10,000 ends/cm.sup.3, in particular less than 5,000 ends/cm.sup.3; wherein at least 50%, in particular at least 80%, of the fibers have a cross sectional shape having a roundness of more than 60%, in particular of more than 80%; wherein the fabric is configured so that a wicking speed is at least 0.25 g water/g fabric/s; wherein at least 80 mass percent of the fibers have an average fiber diameter in a range between 1 m and 40 m, in particular between 3 m and 15 m; wherein the fabric is configured as a lotion delivery system; wherein the fiber network is tailored to control at least one function or property, in particular in terms of at least one of the group consisting of wicking, anisotropic behavior, oil retention, water retention, cleanability, and roughness.

9. 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.

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 different ones of the fibers are located at least partially in different distinguishable interconnected layers, and so that the fabric is optically transparent when wet.

11. 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, and calendering.

12. 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 different ones of the fibers are located at least partially in different distinguishable interconnected layers, and so that the fabric is optically transparent when wet.

13. The device according to claim 12, comprising a further jet with orifices configured for extruding further lyocell spinning solution supported by a further gas flow, the further jet being arranged downstream of the jet, and wherein the jet is configured for forming one of the layers and the further jet is configured for forming another one of the layers on top of the layer.

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, an 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

[0072] The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited:

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] FIG. 8 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 average fiber diameter.

[0078] FIG. 9 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.

[0079] FIG. 10 shows a schematic image of nonwoven cellulose fiber fabric according to an exemplary embodiment of the invention composed of three stacked layers with different average diameters of fibers.

[0080] FIG. 11 shows a schematic image of nonwoven cellulose fiber fabric according to an exemplary embodiment of the invention composed of three stacked layers and configured as lotion delivery system with a marker visually indicating a user progress of active agent release.

[0081] FIG. 12 shows how a roundness of fibers having a cross-section deviating from a circular cross-section can be calculated as a ratio between an inscribed circle and a circumscribed circle of the cross-section of the fiber according to an exemplary embodiment of the invention.

[0082] FIG. 13 is a diagram illustrating optical gray value of a nonwoven cellulose fiber fabric according to an exemplary embodiment of the invention in a wet state.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0083] The illustrations in the drawings are schematic. In different drawings similar or identical elements are provided with the same reference labels.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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 is to a fiber support unit 132.

[0088] 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.

[0089] 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).

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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)

[0099] Most preferably, the lyocell solution-blown web exhibits all of said properties (i) to (viii) mentioned above.

[0100] 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

[0101] 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.

[0102] 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.

[0103] It is also possible to combine several distinguishable layers of nonwoven cellulose fiber fabric 102, see for instance FIG. 7.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] Specific exemplary embodiments of the invention will be described in the following in more detail:

[0110] FIG. 8 shows a schematic cross sectional view of a nonwoven cellulose fiber fabric 102 according to an 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. 8). 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). Fibers 108 of the respective layers 200, 202 are also merged at merging positions 204, compare the lower two details of FIG. 8. 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. 8). 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.

[0111] Merging properties may be adjusted to obtain desired properties. For instance, a number of merging points 204 per volume of fabric 102 may be adjusted separately within the respective one of the layers 200, 202 and/or between the layers 200, 202. This can be done by adjusting the coagulation properties (in particular coagulation of filaments of lyocell spinning solution 104 upstream of the fiber accommodation surface of the fiber support unit 132, coagulation of filaments of lyocell spinning solution 104 after lay down of the filaments on the fiber accommodation surface of the fiber support unit 132, etc.). The merging between the different layers 200, 202 may be adjusted so that pulling on the layers 200, 202 in opposite directions results in a separation of the fabric 102 at an interface between the different layers 200, 202. In other words, a merging-based connection force between the different layers 200, 202 may be adjusted to be smaller than a merging based connection force within a respective one of the different layers 200, 202.

[0112] The fibers 108 located in the different layers 200, 202 and being formed with different average diameter and different merging properties 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 holding capability, different water absorbing and holding capability, different cleanability, different mechanical properties and/or different roughness.

[0113] The mentioned functionalization may also involve an adaptation of the manufactured nonwoven cellulose fiber fabric 102 as an optical switch which can be transformed between a dry optically opaque state and a wet optically transparent state by the mere supply of water, an aqueous solution, oil, etc., or a liquid removal procedure (for instance drying the fabric 102 by evaporating liquid therein by heating). Since the fabric 102 can be manufactured in a very pure way, i.e. consisting substantially of cellulose with low contamination with impurities, the optical transparency in the wet state is quite pronounced. By promoting liquid absorbing capability and by adjusting a high wicking speed, a high optical transparency in the liquid soaked state of the fabric 102 and a quick switch between different light transmissivity conditions of the fabric 102 can be accomplished. Process parameters which can be adjusted for that purpose are for instance adjusting a high degree of roundness of the fibers 108, accomplishing inter-fiber and intra-fiber interconnection by integrally forming cellulose merging positions 204, suppressing impurities (in particular heavy metal impurities) of the fabric 102, etc. For instance, it is also possible that the process parameters of the manufacturing process of producing fabric 102 shown in FIG. 8 are adjusted so that the endless fibers 108 have an amount of fiber ends per volume of not more than 5,000 ends/cm.sup.3 in a fabric having a density of 0.1 t/m.sup.3. Since also free fiber ends in an interior of fabric 102 may serve as scattering centers for light, the strong reduction of the amount of such free fiber ends (in particular compared with staple fibers) further promotes optical transmissivity in the wet state of the fabric 102. For instance, the process parameters during manufacturing the fabric 102 may be adjusted so that a wicking speed is at least 0.025 g/s. Thus, liquid such as water may rapidly enter fabric 102, may rapidly spread across fiber 102, and may also be quickly removed therefrom (in terms of a drying procedure, which may be promoted by heating fabric 102 to an elevated temperature).

[0114] The multilayer nonwoven cellulose fiber fabric 102 according to FIG. 8 can be directly manufactured from lyocell spinning solution 104 using the device 100 and corresponding manufacturing method described below referring to FIG. 9. Advantageously, the partial heavy metal contaminations of the fibers 108 of the fabric 102 according to FIG. 8 are not more than 10 ppm for each individual chemical heavy metal element (i.e. not more than 10 ppm for iron, not more than 10 ppm for zinc, not more than 10 ppm for cadmium, etc.). Beyond this, an overall or entire heavy metals content of fabric 102 summed up for all heavy metal chemical elements together (i.e. in particular for Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Cd, Sn, W, Pb, Bi) is not more than 30 ppm. Apart from this, the fibers 108 have a copper content of less than 5 ppm and have a nickel content of less than 2 ppm. This is a consequence of the operating fluids (in particular lyocell spinning solution 104, coagulation fluid 106, washing liquor, gas flow 146, etc.) which are used during the manufacturing process and which may be substantially free of heavy metal sources such as copper salt. As a result of this design of the manufacturing process, the fibers 108 may be of high quality. The absence of any mentionable heavy metal impurities in the manufacturing process prevents highly undesired decomposition of involved media (in particular of the lyocell spinning solution 104) and therefore allows to obtain highly reproducible and highly pure cellulose fabric 102.

[0115] As a result of the above described manufacturing method and the corresponding properties of the fabric 102, the fabric 102 is optically transparent when being loaded with liquid, but can be converted into an optically opaque state by drying (i.e. by removing liquid from an interior of the fabric). This procedure is reversible and can be repeated multiple times. More specifically, the fabric 102 may be provided with an optical gray value of at least 90 (i.e. 90 or above), or even at least 100, when wet. In the opaque dry state of the fabric 102, the interior of the fabric 102 is substantially free of liquid such as water. In the opaque dry state of the fabric 102, the gray value may be below 85, in particular below 80. In other words, the fabric may be optically opaque (in particular with an optical gray value of lower than 85) when completely dry. The mentioned gray values corresponding to a scale from 0 to 255 and are measured in transmission geometry. In the optically transparent wet state of the fabric 102, a liquid such as water has entered into the fibers 108 (which results in fiber swelling) as well as in gaps between the fibers 108 in an interior of the fabric 100. In particular, the fabric 102 may be rendered optically transparent when being wet to such a degree that a mass ratio between a mass of moisture in an interior of the fabric 102 and a mass of the dry fibers 108 is above 3.

[0116] FIG. 9 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. 9 and the device 100 shown in FIG. 1 is that the device 100 according to FIG. 9 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. 9 produces layer 202. Layer 200 is produced by the downstream jet 122 (see right hand side of FIG. 9) 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.

[0117] According to FIG. 9, 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. 8). 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. 9 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. 9, it is possible to further process the fibers 108 after collection on the fiber support unit 132 by hydroentangling, needling, and/or impregnating.

[0118] In particular, the device 100 shown in FIG. 9, when compared to the device 100 shown in FIG. 1, comprises a further jet 122 with orifices 126 configured for extruding further lyocell spinning solution 104 supported by a further gas flow 146. As can be taken from FIG. 9, the further jet 122 is arranged downstream of the jet 122. The jet 122 is configured for forming one of the layers 202, and the further jet 122 is configured for forming another one of the layers 200 upon the layer 202. The geometry shown in FIG. 9 allows to freely and independently adjust the properties of the fibers 108 and the corresponding layer 200, 202, also in terms of adjusting its optical properties. Hence, 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:

[0119] The device 100 according to FIG. 9, which is configured for the manufacture of multilayer fabric 102, implements a high number of process parameters which can be used for designing optically relevant properties 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.

[0120] With device 100 according to FIG. 9, 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.

[0121] 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. All this can be obtained for a fabric 102 having a very low heavy metals content due to the adjusted lack of heavy metal sources along the process line.

[0122] FIG. 10 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. 10, an intermediate sandwich layer 200 has significantly smaller diameters of fibers 108 than the two exterior layers 200, 202 above and below.

[0123] The multilayer fabric 102 shown in FIG. 10 is particularly appropriate for applications such as medical appliances, agricultural textiles, cosmetic application, etc. For instance, an active substance or a lotion 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.

[0124] In another application, the multilayer fabric 102 shown in FIG. 10 may be used as facial mask, industrial wipe, etc., 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 average diameters of the fibers 108 of the respective layer 200, 200, 202 may be used as a design parameter for adjusting these functions. In particular, the multilayer fabric 102 shown in FIG. 10 may be configured as a lotion delivery system.

[0125] As mentioned above, an exemplary embodiment of the invention provides a nonwoven cellulose fiber fabric 102 with a very low contamination with heavy metal elements. This is promoted on the one hand by the above described configuration of lyocell spinning solution 104 and other media used along the production line which are by themselves substantially heavy metal element free. Simultaneously, also the hardware configuration of the device 100 may be configured so that substantially no re-contamination of the processed lyocell spinning solution 104 and the manufactured fibers 108 with heavy metal impurities occurs along the line. Thus, a biocompatible and biodegradable nonwoven cellulose fiber fabric 102 may be obtained.

[0126] In particular, also integral interconnection of fibers 108 of the fabric 102 by the formation of merging points 204 on the basis of lyocell spinning solution 104 (rather than by a separate adhesive or binder made of one or more additional materials) contributes significantly to the purity of the manufactured fabric 102. Thus, no highly disturbing heavy metals comprising connection points of separate adhesive or binder material need to be formed as a result of the process flow described referring to FIG. 1 and FIG. 9. The formation of merging positions 204 between fibers 108 of the fabric 102 can be accomplished by merely bringing filaments of lyocell spinning solution 104 in direct physical contact with one another prior to coagulation, i.e. before precipitation of solid fibers 108. This allows to obtain pure cellulose fabric 102 without additional adhesive material, with a precisely adjustable (in particular a strong) inter-fiber connection, with a moderate bulk density, and with very low residual amount of heavy metal elements and compounds. Thereby, a fabric 102 can be obtained which advantageously has a low environmental impact and which is not harmful to health for a user.

[0127] By the described cellulose filament production on the basis of lyocell spinning solution 104 it can be ensured that no production related heavy metal impurities accumulate in the manufactured fabric 102. This is particularly advantageous for post processing of such fabric 102 and when a correspondingly manufactured product gets into contact with human beings or natural organisms. The opportunity to manufacture nonwoven cellulose fiber fabric 102 with low heavy metal content (in particular low copper content) by a corresponding process control allows to prevent copper-based inhibiting or even toxic effects on microorganisms. Moreover, toxicity of copper may be reinforced by other heavy metals such as Hg, Sn, Cd. Thus, not only the low copper content, but also the low entire or overall heavy metal content of the fabric 102 manufactured with the above described manufacturing method is advantageous.

[0128] Moreover, wherein biodegradable nonwoven cellulose fiber fabric 102 decomposes after use, non-biodegradable heavy metal content thereof will not decompose and will therefore accumulate. Thus, fabric 102 according to an exemplary embodiment of the invention being poor in terms of heavy metal content is particularly appropriate for biodegradation after use without mentionable ecological footprint.

[0129] FIG. 11 shows a schematic image of nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention composed of three stacked layers 200, 201, 202 and configured as lotion delivery system. For instance, the fabric 102 of FIG. 11 may be configured for delivering a cosmetic or medical lotion.

[0130] The product shown in a cross-sectional view of FIG. 11 and being manufactured on the basis of a fabric 102 is composed of here exactly three interconnected layers 200, 201, 202. Between two opposing liquid permeable (in view of pores defined between the networked fibers 108) cover layers 200, 202, an intermediate layer 201 is sandwiched and embedded. An active agent 272 (such as a pharmaceutically active agent or a cosmetically active agent) is accommodated and retained in the intermediate layer 201. The active agent 272 is accommodated in cavities 274 (only one is shown) of the fiber network of layer 201 between several fibers 108 and may be held or retained in the tiny cavity 274 under the influence of capillary forces. The cavity 274 is in fluid communication with pores 260 which are also delimited between fibers 108 and serve as fluidic channels or conduits within the fabric 102. For instance triggered by a mechanical impact (such as squeezing of the fabric 102 shown in FIG. 11 by applying a manual pressing force on the fabric 102 by a user), the active agent 272 can be released from the cavities 274 in the intermediate layer 201. From there, the active agent 272 can be released from the central intermediate layer 201 via a respective one of the cover layers 200, 202 towards an environment. Such an environment may for instance be the face skin of a user (not shown) onto which the fabric 102 may be attached, for instance if the shown product is a face mask.

[0131] Advantageously, the fabric 102 according to FIG. 11 may be provided with a permanently opaque marker 250. In the shown embodiment, the marker 250 may be printed on an interface surface of layer 201 or layer 202. Alternatively, the marker at 250 may also be printed on an exterior surface of the fabric 102, preferably a surface of the fabric 102 attached to the destination of the active agent 272 (for instance a face of a user). The marker 250 is optically visible from an exterior of the fabric 102 when the fabric 102 is optically transparent, as indicated in FIG. 11 showing a light source 210 emitting light 212 being reflected partially by the fabric 102 so as to be visible by a user's eye 214. When the active agent 272 is released from the intermediate layer 201 towards the face skin of the user, a moisture content of the fabric 102 is continuously reduced so that the fabric 102 turns from the wet optically transparent state into a dry optically opaque state. The latter occurs when the moisture content of the fabric 102 falls below a predetermined threshold value since the fabric 102 has dried out due to the continued release of the active agent 272. When the fabric 102 turns into the opaque state, the marker 250 may be no longer visible for the user, since the light 212 is no longer capable of propagating up to the marker 250. When the marker 250 provides a corresponding instruction to a user (such as release of active agent is not yet completeddo not yet remove fabric), loss of visibility of the marker 250 indicates to the user that the fabric 102 may now be removed from the face skin.

[0132] Reference is now made to FIG. 12. Preferably, at least 80% of the fibers 108 have a cross sectional shape having a roundness of more than 90%. Thus, it is preferred for a high optical transmissivity in the wet state of fiber fabric 102 that the fibers 108 are as round as possible, i.e. ideally assume a circular cylindrical shape. This corresponds to a circular cross-section of the fibers 108. It is believed that deviations from the circular cross-sectional shape act as optical irregularities, promote undesired scattering of visible electromagnetic radiation and therefore deteriorate optical transmissivity of the fabric 102 in the wet state. For this reason, it is advantageous when the process parameters of the manufacturing method of manufacturing fabric 102 are adjusted so that the deviation of the cross section of the fibers from a circular cross-section is as small as possible. This can for instance be promoted by truly circular orifices 126, an adjusted gas flow 146 around filaments of lyocell spinning solution 104, adjusted coagulation conditions, a homogeneous viscosity of the lyocell spinning solution 104, etc.

[0133] FIG. 12 shows how a value of roundness of fibers 108 having a cross-section deviating from a circular cross-section can be calculated as the ratio between an inscribed circle 280 and a circumscribed circle 282 of the cross-section of the fiber 108 according to an exemplary embodiment of the invention.

[0134] The minimum circumscribed circle 282 is defined as the smallest circle which encloses whole of the roundness profile of the cross-section of the fiber 108 illustrated in FIG. 12. The maximum inscribed circle 280 is defined as the largest circle that can be inscribed inside the roundness profile of the cross-section of the fiber 108 illustrated in FIG. 12. In the context of the present application, roundness can be defined as a ratio between a radius r of the inscribed circle 280 divided by a radius R of the circumscribed surface 282. Roundness may be indicated by a resulting percentage value. In the present example, R2r and the roundness of the fiber 108 is therefore approximately 0.5 or 50%. For comparison, a circular cylindrical fiber 108 fulfills the condition R=r and has a roundness of one or 100%.

[0135] FIG. 13 is a diagram 290 illustrating optical gray value of a nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention in a wet state. The diagram 290 has an abscissa 292 along which gray values are plotted from 0 to 255. Furthermore, the diagram 290 has an ordinate 294 indicating a respective number of pixels per gray value.

[0136] The characteristic shown in diagram 290 and being indicative of an optical transparency of the investigated fabric 102 has been experimentally obtained by analyzing a fabric 102 material with a grammage of 38 g/m.sup.2 which has been investigated for its wet transparency.

[0137] The test method was as follows. The wetted sample (10 fold loaded with water, equilibrium time 10 min) was put on an optically transparent plastic foil and on a defined light source with light shining through the sample. With software analysis the gray value of each pixel was measured.

[0138] The gray value at the received maximum pixel number is a value for transparency, respective opacity of the fabric. The higher the gray value the higher the transparency.

[0139] The instruments and conditions used were: [0140] Camera: Olympus Color View 2 BW 1040772=(802880 Pixel) [0141] Light source: Volpi Intralux 6000-1 [0142] Lens: Pentax 12 mm [0143] Cold light board: Fostec [0144] Software: Olympus Analysis auto [0145] Shutter speed: 20 ms [0146] Aperture: 4 [0147] Picture width: 90.5 mm

[0148] According to an exemplary embodiment of the invention, an optically transparent multilayer nonwoven cellulose fiber fabric 102 is provided. The optical transmissivity or translucency is high in a wet state of the fabric 102. Such a high wet transmissivity or translucency can be obtained by manufacturing highly pure cellulose fabric 102 of endless fibers 108 with a purely cellulose-based integral merging between different layers 200, 202. In order to manufacture such a fabric 102, it is possible to use a nozzle bar for generating filaments of lyocell spinning solution 104, which filaments are then stretched and laid down on a fiber support unit 132. The formation of fiber-to-fiber adhering merging positions 204 may be promoted by gas turbulence during the stretching procedure (so that the filaments get into physically contact prior to coagulation or precipitation of fibers 108) and/or during laydown on the fiber support unit 132. By providing at least one additional nozzle bar or jet 122 (compare FIG. 9), a further layer 200 of fibers 108 may be laid down on the previously formed layer 202 of fibers 108, preferably before the fibers 108 of at least one of the interconnected layers 200, 202 had already completed coagulation and precipitation. Thereby, integral merging positions 204 or merging points of cellulose are formed interconnecting fibers 108 within the respective layer 200, 202 and between different layers 200, 202. This procedure at the same time may allow to maintain a proper separation between the different layers 200, 202. The so manufactured fabric 102 shows a pronounced optical transparency in a wet or moisture filled condition of the fabric 102. A proper adjustment of the process parameters of such a manufacturing process allows to prevent impurities to be introduced in the fabric 102 and may prevent optically less favored cross-sectional shapes of the fibers 108 (i.e. to promote a circular round cross-sectional shape rather than a flat or irregular cross-section of the fibers 108).

[0149] The fact that the manufacturing process described referring to FIG. 1 and FIG. 9 allows to obtain a fabric 102 being substantially free of heavy metal contents and other impurities promotes the proper optical transmission characteristic of the wet fabric 102. This also promotes a homogeneous intrinsic construction of the fibers 108 having an additionally positive impact on the optical transparency in the wet condition. A corresponding product is moreover biodegradable and biocompatible, in particular appropriate for being brought in contact with human beings and other natural organisms.

[0150] Surprisingly, the nonwoven cellulose fiber fabric 102 according to an exemplary embodiment is optically transparent in the wet state despite of the multilayer configuration. In particular an interface plane between different layers 200, 202 of such a fabric 102 is in general a source of undesired light scattering and optical diffusing. Integral merging of the layers 200, 202 rather than interconnecting them with a separate adhesive glue or the like provides a substantially uniform and homogeneous fabric 102 with nevertheless visually distinguishable and separately configurable layers 200, 202. Hence, merging can be controlled by controlling timing of laydown of the filaments or fibers 108 and/or of the various layers 200, 202 on top of each other, preferably before completing coagulation. By appropriate timing parameters, a similar filament coupling may be obtained between the distinguishable layers 200, 202 as within a respective layer 200, 202.

[0151] By the use of endless fibers 108 it can be ensured that only a minor number of free fiber ends (as occur in a high number in staple fibers) is present within the fabric 102. This increases the optical homogeneity and provides a larger optical transparency in the wet state.

[0152] Heavy metal additives have the capability of reducing optical transparency already in very small amounts. For instance, a heavy metal compound comprising cobalt may already cause a blue color in a concentration significantly below 100 ppm. By manufacturing the fibers 108 substantially without heavy metal contamination, the optical transparency in the wet state may be further promoted.

[0153] A multi-layer multi-functionality fabric 102 according to an exemplary embodiment of the invention may result from a separate functionalization of different layers 200, 202. The fabric 102 made of endless cellulose fibers 108 offers a particularly high number of material properties and geometric properties which can be used for adjusting the fabric 102 to obtain a certain function.

[0154] In an exemplary embodiment, a fast reacting liquid display system can be provided (for instance for cosmetic applications or the like), which allows to distinguish visually clearly and unambiguously between wet and dry. Simultaneously, such a reaction can be obtained very fast. This is for instance of high advantage for applications such as splash masks, i.e. face masks having a short application time. By the use of cellulose fibers 108, the hydrophilic property of the cellulose material may accelerate effects connected with capillary forces, in particular fast wetting characteristic and pronounced wicking speed. This results in a quick accommodation of humidity in the fabric 102, which, in turn, results in a quick formation of a transparent state. Moreover, the use of endless cellulose fibers 108 allows to obtain an improved transparency for light in the visible range when the respective nonwoven cellulose fiber fabric 102 is brought in interaction with moisture. As compared to staple fibers, endless fibers 108 do not suffer significantly from disturbing fiber transitions and free fiber ends.

[0155] Under consideration of the refraction index of the (substantially colorless) cellulose of about 1.47 to 1.49 (depending on the frequency) as compared to a refraction index of water of about 1.33, the number of transitions between cellulose material and water in the wet fabric 102 should be kept as small as possible to obtain a high optical transmissivity. Each transition can cause undesired diffusion or refraction of light which reduces the transmitted light intensity. It has turned out that the formation of the fibers 108 with a cross-sectional shape being exactly or at least approximately circular results in a lower loss of light energy compared to flat or irregular cross-sections of fibers 108.

[0156] In yet another exemplary embodiment (which can be used advantageously for agricultural applications), endless cellulose fibers 108 may be used for accomplishing a fast transport of moisture along a fiber 108. In the framework of a fabric 102 composed of multiple of such endless fibers 108, this results in a very rapid liquid spreading along a two-dimensional area. In addition, the use of endless cellulose fibers 108 allows to obtain an improved transparency for light in the visible range when the fabric 102 is humidified. In view of this rapid and efficient response of the transparency in the presence of moisture, it is possible to create self-controlled biological systems. Agricultural issues such as undesired drying can be inspected automatically using a fabric 102 according to an exemplary embodiment of the invention. Since the fabric 102 turns from an optically transparent condition into an opaque condition when an excessive amount of moisture is released from the fabric 102, a need of additional water can be detected optically by inspecting the fabric 102, and new moisture can be delivered to the fabric 102 if a change of the optical transmissivity is detected.

[0157] In yet another exemplary embodiment, a fabric 102 may be used also for the agricultural application described in the following: sun light activates color pigments in fruits which thereby change color. In particular, the sun induced enzymatic decomposition of tanning agent and fruit acids may be influenced by adjusting transmissivity of a fabric 102 covering fruits or plants. Therefore, humidity may be supplied to such a fabric 102 for switching sunlight on for a fruit or plant. By properly positioning such a fabric 102 also sunlight reflection properties may be controlled. In case of wet, the optical transmissivity of the fabric 102 may direct the sunlight into the ground. In case of dry, the opaque property of the fabric 102 may reflect the sunlight to thereby influence maturation processes. For the example of fruits, maturation by light may be controlled in such a way that at high irradiation power, compounds in the fluid being instable with respect to light and oxygen can be decomposed for supporting the maturation process. Further functional mechanisms which can be influenced by taking this measure are related to photo-oxidation.

[0158] A nonwoven cellulose fiber fabric 102 according to an exemplary embodiment of the invention may be also used for the following cosmetic application related for instance to face masks, more particularly to splash masks. For such applications, a quickly reacting liquid display system is desired which visually distinguishes clearly and unambiguously between dry and wet. In particular when using endless cellulose fibers 108 with a diameter range between 5 m and 20 m, a thin sheet like nonwoven cellulose fiber fabric 102 can be manufactured which nevertheless has a high retention capability for a liquid and provides for a high delivery rate of an active agent 274. By this thin geometry in combination with a high liquid storage capability, it is possible to optically visualize the different operation states wet and dry of the face mask. In particular, on the backside of the foil of fabric 102 a text such as Please wait, active agent is released may be printed as a marker 250 which is no longer readable when the fabric 102 has dried (since the fabric 102 then turns opaque).

[0159] Summarizing, in particular one or more of the following adjustments may be made according to exemplary embodiments of the invention: [0160] a low homogeneous fiber diameter may allow to obtain a high smoothness of the fabric 102 [0161] multilayer fabric 102 with low fiber diameter may allow to obtain a high fabric thickness at a low fabric density [0162] 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 [0163] the described connection of layers 200, 202 of fabric 102 allows to design products with low linting upon layer separation [0164] 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).

[0165] 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.

[0166] 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

[0167] 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).