IMPROVEMENTS RELATING TO THE COLD-ALKALI PROCESS FOR THE PRODUCTION OF REGENERATED CELLULOSIC FIBERS

Abstract

A method and a production facility for producing regenerated cellulosic fibers. A spinning solution is extruded into a coagulation bath which contains a salt and preferably an alkali. The spinning solution comprises cellulose dissolved in an aqueous solvent comprising NaOH and ZnO and the coagulation bath has a pH-value of at least seven. The processing facility comprises a cutter to cut the fiber tow in an undried state into cut fibers, a fleece-forming device for suspending the cut fibers and collecting them in form of a non-woven fiber layer, and at least on pressing device for pressing the non-woven fiber layer, thereby imposing a natural crimp on the fibers.

Claims

1. A method for producing regenerated cellulosic fibers including extruding a spinning solution into a coagulation bath which contains a salt and preferably an alkali to produce a fiber tow, the spinning solution comprising cellulose dissolved in an aqueous solvent comprising NaOH and ZnO, the coagulation bath having a pH-value of at least seven, the method comprising the following steps of: cutting the fiber tow in an undried state into cut fibers; suspending the cut fibers and collecting them in form of a non-woven fiber layer, and pressing the non-woven fiber layer, thereby imposing a natural crimp on the fibers.

2. The method according to claim 1, further comprising the steps of: stretching the fibers in the fiber tow to a final cellulose specific diameter, and orienting the fibers in the fiber tow to a final state before being cut in an undried state.

3. The method according to claim 1, further comprising the steps of: after leaving the coagulation bath, routing the fiber tow into at least one conditioning bath, the conditioning bath comprising between about 10 percent and about 30 percent per weight a salt to facilitate a further coagulation of the spinning solution, the conditioning bath preferably being fluidly separated from a downstream washing line; and stretching the fibers in the fiber tow to a final cellulose specific diameter and orienting the fibers in the fiber towy to a final state in the at least one conditioning bath.

4. The method according to claim 3, wherein the coagulation bath and the conditioning bath are fluidly connected and wherein a temperature of the coagulation bath and a temperature of the conditioning bath are independently controlled.

5. The method according to claim 3, further comprising the steps of: routing the fiber tow through a washing line, the washing line comprising at least one washing step and being configured downstream of the at least one conditioning bath; and keeping a tension of the fiber tow and a cellulose specific diameter of the fibers constant in the washing line.

6. The method according to claim 1, further comprising at least one of the following steps: washing the fiber tow or the non-woven fiber layer; neutralizing the fiber tow or the non-woven fiber layer with an acidic liquid, wherein the acidic liquid is one of diluted acetic acid, lactic acid, and sulphuric acid; bleaching the fiber tow or the non-woven fiber layer; applying a crosslinking agent to the fiber tow or the non-woven fiber layer; applying a finishing agent onto the fiber tow or the non-woven fiber layer; drying the non-woven fiber layer; and pressing the fiber tow or the non-woven fiber layer before and/or after any other processing step.

7. The method according to claim 1, further comprising at least one of opening the non-woven fiber layer to loosen up and/or at least partially separate the fibers.

8. A processing facility for producing regenerated cellulosic fibers including a spinneret for extruding a spinning solution into a coagulation bath which contains a salt and preferably an alkali to produce a fiber tow, the spinning solution comprising cellulose dissolved in an aqueous solvent comprising NaOH and ZnO, the coagulation bath having a pH-value of at least seven, the processing facility comprising: a cutter configured to cut the fiber tow in an undried state into cut fibers; a fleece-forming device configured to suspend the cut fibers and collect the cut fibers in a non-woven fiber layer; and at least once pressing device configured to squeeze the non-woven fiber layer to pose a natural crimp on the cut fibers.

9. The processing facility according to claim 8, wherein the processing facility further comprises at least one stretching device for configured to stretch the fibers in the fiber tow to a final cellulose specific diameter and orient cellulose in the fibers to a final state.

10. The processing facility according to claim 8, further comprising: at least one conditioning bath downstream of the coagulation bath, the conditioning bath being fluidly separated from a downstream washing line; and at least one stretching device configured to stretch the fibers in the fiber tow to a final cellulose specific diameter and orient cellulose in the fibers to a final state within the at least one conditioning bath.

11. The processing facility according to claim 10, wherein the coagulation bath and the conditioning bath are fluidly connected and wherein a temperature of the coagulation bath and a temperature of the conditioning bath independently controlled.

12. The processing facility according to claim 8, further comprising a washing line through which the fiber tow is routed, the washing line comprising at least one washing step, wherein the washing line is configured downstream of at least one conditioning bath, and wherein a tension of the fiber tow and a cellulose specific diameter of the fibers are preferably kept essentially-constant in the washing line.

13. The processing facility according to claim 8, further comprising at least one treatment facility comprising at least one of: at least one washing device configured to wash the fiber tow or the non-woven fiber layer; at least one further pressing device configured to the fiber tow or the non-woven fiber layer; a neutralizer configured to neutralize the cut or uncut fibers with an acidic liquid; a bleaching facility configured to bleach the cut or uncut fibers; a crosslinking facility configured to apply a crosslinking agent to the cut or uncut fibers, a finishing facility configured to apply a finishing agent; to the cut or uncut fibers, an opener configured to open the non-woven fiber layer to loosen up and/or at least partially separate the cut fibers; and a dryer, configured to dry the cut fibers.

14. A regenerated cellulosic fiber, produced in a processing facility including a spinneret for extruding a spinning solution into a coagulation bath which contains a salt and preferably an alkali to produce a fiber tow, the spinning solution comprising cellulose dissolved in an aqueous solvent comprising NaOH and ZnO, the coagulation bath having a pH-value of at least seven, the processing facility further comprising a cutter configured to cut the fiber tow in dried state into cut fibers; a fleece-forming device configured to s be cut fibers and collect them in form of a non-woven fiber layer and at least one pressing device configured to squeeze the non-woven fiber layer to impose a natural crimp on the cut fibers.

15. A product comprising a regenerated cellulosic fiber produced in a processing facility including a spinneret for extruding a spinning solution into a coagulation bath which contains a salt and preferably an alkali to produce a fiber tow, the spinng solution comprising cellulose dissolved in an aqueous solvent comprising NaOH and ZnO, the coagulation bath having a pH-value of at least seven the processing facility further comprising a cutter configured to cut the fiber tow in an undried state into cut fibers; a fleece-forming device configured to suspend the cut fibers and collect them in form of a non-woven fiber layer; and at least one pressing device configured to squeeze the non-woven fiber layer to impose a natural crimp on the cut fibers.

16. The product according to claim 15, wherein the product is selected from a list consisting of: yarns, fabrics, textiles, home textiles, garments, nonwovens, hygiene products, upholstery, or technical applications.

17. A regenerated cellulosic fiber, produced by a method including extruding a spinning solution into a coagulation bath which contains a salt and preferably an alkali to produce a fiber tow, the spinning solution comprising cellulose dissolved in an aqueous solvent comprising NaOH and ZnO, the coagulation bath having a pH-value of at least seven, the method further comprising the steps of cutting the fiber tow in an undried state into cut fibers; suspending the cut fibers and collecting them in form of a non-woven fiber layer; and pressing the non-woven fiber layer, thereby imposing a natural crimp on the fibers.

18. A product comprising a regenerated cellulosic fiber produced by a method including extruding a spinning solution into a coagulation bath which contains a salt and preferably an alkali to produce a fiber tow, the spinning solution comprising cellulose dissolved in an aqueous solvent comprising NaOH and ZnO, the coagulation bath having a pH-value of at least seven, the method further comprising cutting the fiber tow in an undried state into cut fibers; suspending the cut fibers and collecting them in form of a non-woven fiber layer; and pressing the non-woven fiber layer, thereby imposing a natural crimp on the fibers.

19. The product according to claim 18, wherein the product is selected from a list comprising yarns, fabrics, textiles, home textiles, garments, nonwovens, hygiene products, upholstery, and technical applications.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Reference is now made more particularly to the drawings, which illustrate the best presently known mode of carrying out the present disclosure and wherein similar reference characters indicate the same parts throughout the views.

[0065] FIG. 1 is a schematic and exemplified representation of a fiber production process according to the present disclosure focusing on the spinning dope preparation and

[0066] FIG. 2 is a schematic and exemplified representation of processing facility according to the present disclosure focusing on the post-processing of the spun fibers.

DETAILED DESCRIPTION OF THE DRAWINGS

[0067] The following description of technology is merely exemplary in nature of the subject matter, manufacture and use of one or more inventions, and is not intended to limit the scope, application, or uses of any specific invention claimed in this application or in such other applications as may be filed claiming priority to this application, or patents issuing therefrom. The following definitions and non-limiting guidelines must be considered in reviewing the description of the technology set forth herein.

[0068] In the following detailed description numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be understood by those skilled in the art that the present disclosure may be practiced without these specific details. For example, the present disclosure is not limited in scope to the particular type of industry application depicted in the figures. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present disclosure.

[0069] The headings and sub-headings used herein are intended only for general organization of topics within the present disclosure and are not intended to limit the disclosure of the technology or any aspect thereof. In particular, subject matter disclosed in the Background may include novel technology and may not constitute a recitation of prior art. Subject matter disclosed in the Summary is not an exhaustive or complete disclosure of the entire scope of the technology or any embodiments thereof. Classification or discussion of a material within a section of this specification as having a particular utility is made for convenience, and no inference should be drawn that the material must necessarily or solely function in accordance with its classification herein when it is used in any given composition.

[0070] The citation of references herein does not constitute an admission that those references are prior art or have any relevance to the patentability of the technology disclosed herein. All references cited in the Detailed Description section of this specification are hereby incorporated by reference in their entirety.

[0071] FIG. 1 shows a flowchart representing an exemplary fiber production process according to the present disclosure. The diagram is a simplified representation and shows the process in a schematized manner.

[0072] The process can be sectioned into the following basic steps, which are denoted in with roman numbers in FIG. 1:

I. Supplying the Raw Material

[0073] For the process according to the present disclosure a broad range of possible cellulosic raw materials can be used. Generally, the intrinsic viscosity and the degree of polymerization of the cellulose used as a raw material is lower than it is common for the viscose- or lyocell-process. For example, dissolving pulp (kraft or sulphite) with an intrinsic viscosity (measured in Cuen, according to SCAN-CM 15:99) of about 200 mL/g to 700 mL/g (degree of polymerization DP of 500 to 1900), preferably between about 250 and about 400 mL/g (DP or 600 to 950) can be used. Further, recycling pulp or cotton linters (preferably having the same DP as stated above) can be used. The recycling pulp can, for example, be derived from wastepaper, recycled viscose textile material, recycled modal textile material, recycled lyocell textile material an/or recycled cotton fiber textile material. Blends of pulps of different origin, such as blends of virgin wood pulp with recycling pulp, are possible and may be even desirable.

[0074] In FIG. 1 a staple of dissolving pulp 1 is exemplarily depicted as the raw material

II. Pretreatment of the Raw Material

[0075] The cellulosic raw material can be subjected to a pretreatment, wherein the degree of polymerization is adjusted to a desired DP to adjust the viscosity of the spinning dope to a value that allows for filtering and spinning. The pretreatment can comprise subjecting the raw material to an acidic pulp treatment, wherein the DP-value is mainly influenced by the duration of the pretreatment and the concentration of the acid. In other cases, the pretreatment can be omitted, if the DP-value is already at the desired value. For example, pulp derived from cellulosic regenerate fibers may have a DP that allows for a direct dissolution without a pretreatment.

[0076] In a more specific example, an acidic pulp treatment with 1-10 percent per weight sulfuric acid at 50? ? C. to 95? C. for a duration from 5 min to 2 h can be used as a pretreatment. As the profitability of the process is reduced by a long duration of this treatment step, it is generally preferable to minimize the duration of the pretreatment as far as possible. The person skilled in the art, who is aware of the teachings of this disclosure is able to find suitable parameters and optimize them without undue burden.

[0077] The pretreatment further comprises washing the cellulosic material with water and pressing to reduce moisture content, e.g., to about 50 percent per weight of the cellulosic material.

[0078] In FIG. 1 a source for a pretreatment chemical 2, e.g., sulfuric acid, and a pretreatment vessel 3 are exemplarily depicted. After the pretreatment in pretreatment vessel 3 the cellulosic material can be squeezed and washed to reduce the amount of acid that is transported to the next step.

III. Preparation of the Spinning Dope

[0079] To prepare the spinning dope (also called spinning solution), the wet and pretreated pulp is first cooled to about 0? C. (while freezing of the pulp should be avoided), and an aqueous solvent comprising NaOH and ZnO is prepared. Preferably the solvent is adjusted to provide a spinning solution comprising 5 to 10 percent per weight NaOH and 0.8 to 3 percent per weight ZnO. The solvent is cooled down to a process temperature, which preferably lies between ?5? C. and ?10? C.

[0080] The pulp and the solvent are blended to dissolve the cellulose in the solvent. To improve the processability, the preparation of the spinning dope comprises a mixing step followed by a homogenization step. During the mixing step the blend is mixed with a high shear stress, which can be done in a high-shear mixer. This high shear stress mixing is preferably only performed for a rather short period of time, for example the mixing can be done for 1-2 minutes. In the following homogenization step the blend is agitated with a lower shear intensity. The homogenization step can last longer than the mixing step, for example about 5 minutes.

[0081] During both the mixing and the homogenization step the temperature of the mixture is controlled, especially cooled. Preferably the temperature is kept below 0? C. The process temperature should never exceed 5? C., as the solution could then thicken and be irrecoverably lost.

[0082] The so prepared spinning solution is then filtered and de-aerated. For example, the spinning dope can be filtrated at least twice via a KK filter (Kolben-Korb-Filter, Lenzing Technik) with a mesh size of 15 micrometer.

[0083] For the de-aeration the spinning solution is exposed to reduced pressure. This step is per-se known from the viscose process. Other techniques for filtering and de-aerating the dope that can be used are known to the person skilled in the art.

[0084] The prepared spinning dope should be free of voids, have a homogenous consistency and a proper viscosity that allows for an extrusion in the spinneret used in the following extrusion step.

[0085] In a preferred embodiment the ballfall-viscosity of the spinning dope should be in the range of about 30 to 200 s. The ballfall-viscosity can be measured according to DIN 53015-2019. The viscosity of the spinning dope can be adjusted by several different means. For example, the viscosity can be adjusted by altering the DP-value of the cellulose, by changing the composition of the solvent and/or the concentration of the cellulose in the spin dope. For example, the concentration of the cellulose can be in the range of about 4 percent per weight to about 12 percent per weight, particularly in the range of about 5 percent per weight to about 8 percent per weight preferably about 6 percent to about 7 percent per weight.

[0086] The specific parameters of the mixing, homogenization and filtering steps can be found by the person skilled in the art, who is aware of the current disclosure, by routine work and experimentation.

[0087] In FIG. 1 a chemical repository 4 for the storage of the ingredients of the solvent, a solvent cooling device 5 for the cooling of at least parts of the solvent, a pulp cooling device 6, a mixing vessel 7 and a de-aerating filter 8 are exemplarily depicted. The mixing vessel 7 is provided with a cooling jacket 9.

IV. Extrusion into the Coagulation Bath

[0088] The spinning dope can be extruded through a nozzle directly into a coagulation bath. In case additives are added to the spinning dope, the dope can be homogenized via a static mixer to incorporate additives. Before the extrusion step, the dope can preferably be tempered to spinning temperature, for example to a temperature in the range of from 5? C. to 30? C. For fiber production, a straightforward approach could be to use as the extrusion nozzle a spinneret comprising, for example, up to 150 cups with a diameter of 12.5 to 16 mm, comprising up to 3000 holes with a diameter of about 40 to 75 micrometers, which corresponds to dimensions as they are known per se and commonly used in connection with the viscose spinning process. Nonetheless, it was surprisingly found that in connection with the cold-alkali process broader diameters can improve process stability and facilitate the coagulation and stretching of the fibers. According to the present disclosure it is therefore suggested to use a spinneret comprising holes with a diameter of about 80-120 ?m, preferably between 90 and 110 ?m. For example, in an industrial scale production plant one spinneret could comprise up to 150 cups with a diameter of 12.5 to 16 mm, comprising about 600 to 1400 holes with a diameter of about 80-120 ?m, preferably between 90 and 110 ?m. The relatively thick diameter of the spinning holes causes different course of coagulation, i.e., that the freshly extruded fibers first only coagulate at the outer surface, while the middle of the fiber stays in a liquid state for a longer time. This allows for a higher stretching and the stretching conditions can be uphold in a more stable way.

[0089] The coagulation bath comprises an alkali, preferably NaOH, and a salt, preferably sodium carbonate, Na.sub.2CO.sub.3, or sodium sulfate, Na.sub.2SO.sub.4. As an example, the coagulation bath can comprise from 10 percent per weight to 30 percent per weight Na.sub.2CO.sub.3 or Na.sub.2SO.sub.4 and from 0 to 3 percent per weight NaOH, preferably from 0.1 to 3% and still more preferred from 0.2 to 0.7 percent per weight NaOH. In a specific example the coagulation bath can comprise about 22 percent per weight Na.sub.2CO.sub.3 and about 0.5 percent per weight NaOH. The temperature of the coagulation bath can, for example, be adjusted to between 10? C. and 30? C., and preferably be tempered at about 20? C.

[0090] The optimal distance, that the freshly extruded fiber travels through the coagulation bath (i.e., the coagulation bath distance) depends, inter alia, on the extrusion speed, the pull-off speed, the composition and consistency of the spinning dope, the composition of the coagulation bath and the temperature. Without being restricted to these values, under most parameter conditions the optimal coagulation bath distance may be found within a range from about 10 cm to about 100 cm. Preferred values for the coagulation bath distance range from about 15 cm to about 60 cm.

[0091] The fiber tow is drawn out of the coagulation bath to a transporting section, which can comprise several godets and/or pulleys that transport the fiber tow through a series of post-processing stages. The pull-off force that is exerted on the freshly extruded fibers can be regulated by the extrusion speed and the speed of the first transporting unit (or godet), which preferably can be positioned outside of the coagulation bath. Due to the pull-off force, which is exerted on the freshly extruded fibers by the first transporting unit, the fibers get stretched already inside the coagulation bath. Further stretching steps can be during the following post processing of the fibers.

[0092] In FIG. 1 a coagulation bath 10 comprising a coagulation liquid 11, a spinneret 12 and a first godet 13 are exemplarily depicted. The spinneret 12 extrudes a number of fibers 14 (corresponding to the number of holes of the spinneret 12) into the coagulation liquid 11. The freshly extruded fibers 14 are gathered together into a fiber tow 15 by the first godet 13. By adjusting the extrusion speed at the spinneret 12 and the speed of the godet 13 the amount of stretching, that is done directly after extrusion within the coagulation bath 10 can be set. Although an inclined angle of the spinneret 12 (and the freshly extruded fibers 14) is shown in FIG. 1, the skilled practitioner, who is aware of the current teaching, is able to apply other spinning configurations that are per se known in the field, e.g., from viscose production.

V. Post-Processing of the Fiber Tow

[0093] As it is used throughout this disclosure, the term post-processing encompasses all processing steps that are performed on the extruded fibers after they have been withdrawn from the coagulation bath. Post-processing steps can be applied to the fiber tow while it is transported on the transporting unit. Additionally, the fiber tow can be cut in a cutting apparatus and further post-processing steps can be performed on the cut fibers.

[0094] In FIG. 1 the post-processing is only schematically represented by the respective reference sign V.

[0095] Post-processing of the fibers can comprise, but are not restricted to, any combination of one or more of the following steps: [0096] washing of the fiber tow and/or the cut fibers, [0097] squeezing the fiber tow and/or the cut fibers to reduce the amount of liquid therein, [0098] neutralizing the fiber tow and/or the cut fibers with an acidic liquid, [0099] bleaching the fiber tow and/or the cut fibers, [0100] crosslinking the fiber tow and/or the cut fibers by applying a crosslinking agent on the fibers, [0101] applying a finishing agent (soft finish) to the fibers of the fiber tow and/or the cut fibers, [0102] drying the cut fibers.

[0103] Immediately after the fibers in the fiber tow have been withdrawn from the coagulation bath, they already have been stretched to a certain extent, but may not have reached their final elongation (and final cellulose specific diameter).

[0104] In a different approach, several successive stretching steps during the post-processing can be implemented. For example, a counter current flow washing can be implemented in the post processing, wherein the fibers in the fiber tow are being incrementally stretched during and/or in-between the several washing steps until they have reached their final extension.

[0105] According to another approach, the fiber tow can be led into a conditioning bath comprising from 10 percent per weight to 30 percent per weight a salt that facilitates a further coagulation of the spinning solution, the conditioning bath preferably being fluidly separated from any downstream washing facilities and stretched to essentially the final cellulose specific diameter of the fibers and oriented to essentially their final state within the conditioning bath. The conditioning bath can comprise a coagulation liquid that is similar or identical to the coagulation bath liquid. The coagulation speed in the conditioning bath can be adjusted by the temperature of the liquid therein, which preferably can be controlled independently from the coagulation bath.

[0106] Following the second bath, the fiber tow can be washed in a downstream washing line, where no additional stretching is applied to the fiber.

[0107] As the case may be (and according to the technical requirements), other post-processing steps can be arranged in the processing line according to any technically useful configuration.

[0108] FIG. 2 is a schematic block-diagram showing an exemplary configuration of a post-processing facility for treating a fiber-tow which is produced according to the current disclosure, e.g., by the facility depicted in FIG. 1.

[0109] Fibers 14 are extruded by a spinneret 12 into a coagulation liquid 11 within a coagulation bath 10 and gathered together into a fiber tow 15 by the first godet 13 (similar to FIG. 1). From the first godet 13 the fiber tow is directed to a second godet 18. Between the first godet 13 and the second godet 18 the fiber tow 15 is diverted via a guide 16, e.g., a roller, bar or the like, and submerged into a conditioning bath 17 containing a coagulation liquid 11. The coagulation liquid can be identical or similar to the coagulation liquid 11 in the coagulation bath 10. Preferably the coagulation liquid 11 in the coagulation bath 10 and the coagulation liquid 11 in the conditioning bath 17 are circulated in a common fluid cycle. Preferably the temperature of the coagulation liquid 11 in the conditioning bath 17 can be controlled independently from the temperature of the coagulation liquid 11 in the coagulation bath 10. Generally, a higher temperature is preferred for the coagulation liquid 11 in the conditioning bath 17. For example, the temperature of the coagulation liquid 11 in the coagulation bath 10 can be adjusted to a value between about 10? C. and about 20? C. and the temperature of the coagulation liquid 11 in the conditioning bath 17 can be adjusted to a value between about 20? C. and about 40? C.

[0110] Between the first godet 13 and the second godet 18 and essentially within the conditioning bath 17 the fibers in the fiber tow are stretched to essentially their final cellulose specific diameter and oriented to essentially their final state.

[0111] In FIG. 2 only one conditioning bath is shown. Nonetheless it would be possible to install more than one conditioning bath, for example two successive conditioning baths or a series of consecutive conditioning baths. Preferably the conditioning baths share the same fluid circuit with the coagulation bath and have an essentially identical or at least similar content of salt and/or alkali. The temperatures of the conditioning baths can either be the same or controlled independently, as the case may be. Depending on the configuration, the fibers can, for example, be stretched in a cascading style, i.e., consecutive conditioning baths have an increasing stretching rate. The fibers could also be stretched to essentially their final state in an upstream conditioning bath (or several upstream conditioning baths) and than be further coagulated and fixated within one (ore more) downstream conditioning bath(s) with constant speed and stretch. The person skilled in the art and having knowledge of the teachings disclosed herein is able to optimize the number of conditioning baths, their temperatures and extension rated by routine tests and experiments without deviating from the scope of the current disclosure. The fiber parameters, such as tensile strength, elongation, crystallinity etc., can so be optimized in a methodical manner.

[0112] From the second godet 18 the fiber tow 15 is directed to a washing line 19 which can comprise several washing steps which are exemplarily depicted in FIG. 2 as washing steps 20 and 20. As the case may be, the washing line 19 can also comprise only one washing step 20 or any number of washing steps exceeding two. Further, any washing techniques for washing fiber tows, that are known per se in the art, can be used for in the washing line 19.

[0113] The transporting means for the fiber tow, such as rollers and godets or the like, in the washing line are operated at a constant speed so that the tension is kept essentially constant and no further stretching of the fibers in the fiber tow occurs. This also keeps the orientation of the fibers essentially at the state they were when leaving the second godet 18 after the stretching within the conditioning bath.

[0114] After the washing line 19 the fiber tow 15 is directed to a cutter 21, which cuts the fiber tow into staple fibers 22. During the washing steps 20 the consistency of the fibers has sufficiently settled so that the fibers essentially keep their cellulose specific diameter, elongation and orientation even if they are cut in wet or never-dried state. Therefore, it is not necessary to dry the fiber tow 15 before cutting, which can reduce costs and allows for the implementation of more efficient post-processing steps.

[0115] In the lower part of FIG. 2 an exemplary post-processing facility for the cut staple fibers is shown. The cut staple fibers are transported (or fall) from the cutter 21 to a fleece-forming device 23 having a basin 24 filled with a liquid, e.g., water, and a conveyer belt 25. The conveyer belt 25 is permeable to liquid and a current is maintained in the basin that transports the fibers that are suspended in the liquid of the basin to the conveyer belt 25, where they are collected and form a non-woven fiber layer 26 on the top surface of the conveyer belt 25. The surface of the conveyor belt is tilted and transports the newly formed non-woven fiber layer 26 out of the liquid and to further transport equipment (which is, for reasons of conciseness, not shown in FIG. 2). The freshly cut staple fibers 22 should be regularly distributed across the width of the fleece-forming device 23 so that the non-woven fiber layer 26 has a uniform width and consistency.

[0116] After leaving the fleece-forming device 23, the non-woven fiber layer 26 is squeezed in a first pressing device 27a to remove some of the liquid in the non-woven fiber layer 26. Several further pressing devices 27b to 27e can be arranged downstream between several processing steps. Especially the first pressing device 27a, but also the other pressing devices, create a natural crimp on the fibers in the non-woven fiber layer which is preferable for many fiber appliances.

[0117] The post-processing that is performed on the non-woven fiber layer 26, as it is shown in FIG. 2, comprises a neutralizer 28, a bleaching facility 29, a crosslinking facility 30, a finishing facility 31, an opener 32, a dryer 33 and a baling press 34.

[0118] In the neutralizer 28 the fibers that may still contain residues of alkali are neutralized with an acidic liquid, which can be selected from a list comprising diluted acetic acid, lactic acid, sulphuric acid or the like. Depending on the specific processing conditions, a neutralizing step may not always be necessary.

[0119] The fibers in the non-woven fiber layer 26 are then bleached in bleaching facility 29. If appropriate, a further washing step (not shown in FIG. 2) can be implemented between the neutralizer 28 and the bleaching facility 29. The used water of this (and any other) washing step can be forwarded to upstream washing steps and/or the cutter 21 of the washing line 19 in the form of a countercurrent washing system.

[0120] In the crosslinking facility 30 a crosslinking agent can be applied to the fibers in order to reduce fibrillation of the fibers and improve the processing and handling of the fibers in the textile chain.

[0121] In the finishing facility 31 a finishing agent or soft finish can be applied to the fibers.

[0122] After dewatering the non-woven fiber layer 26 in the pressing device 27e the non-woven fiber layer 26 is fed into an opener 32, which loosens and opens the structure of the fiber layer 26 to improve the drying efficiency in the following dryer 33 and also to improve the further processing of the finished staple fibers.

[0123] The preferred embodiments of the disclosure have been described above to explain the principles of the present disclosure and its practical application to thereby enable others skilled in the art to utilize the present disclosure. However, as various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the present disclosure, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings, including all materials expressly incorporated by reference herein, shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present disclosure should not be limited by the above-described exemplary embodiment but should be defined only in accordance with the following claims appended hereto and their equivalents.

REFERENCE SIGNS

[0124] dissolving pulp 1 [0125] source for a pretreatment chemical 2 [0126] pretreatment vessel 3 [0127] chemical repository 4 [0128] solvent cooling device 5 [0129] pulp cooling device 6 [0130] mixing vessel 7 [0131] de-aerating filter 8 [0132] cooling jacket 9 [0133] coagulation bath 10 [0134] coagulation liquid 11 [0135] spinneret 12 [0136] first godet 13 [0137] fibers 14 [0138] fiber tow 15 [0139] guide 16 [0140] conditioning bath 17 [0141] second godet 18 [0142] washing line 19 [0143] washing step 20 [0144] cutter 21 [0145] staple fibers 22 [0146] fleece-forming device 23 [0147] basin 24 [0148] conveyer belt 25 [0149] non-woven fiber layer 26 [0150] pressing device 27 [0151] neutralizer 28 [0152] bleaching facility 29 [0153] crosslinking facility 30 [0154] finishing facility 31 [0155] opener 32 [0156] dryer 33 [0157] baling press 34