A plurality of man-made cellulosic fibers, a method for its manufacture and its use

Abstract

This invention relates to a plurality of man-made cellulosic fibers of the same fiber titer, composed of at least 3 different fiber fractions, wherein each fiber fraction shows a uniform fiber length and that one of these fiber fractions (the "homogeneous portion") represents between 40 and 80% by weight of the plurality and shows a fiber length of between 20 and 30mm. Furthermore, this invention relates to a method for producing such a plurality of cellulosic man- made fibers wherein all fiber fractions were passed through the same wet-cut aftertreatment stage. Last but not least this invention relates to the use of such fiber plurality for the manufacture of fabrics with nature-like appearance.

Description

[0001] Lenzing AG, PL0831-WO

[0002] A plurality of man-made cellulosic fibers, a method for its manufacture and its use

[0003] This invention relates to a plurality of man-made cellulosic fibers of the same fiber titer, composed of at least 3 different fiber fractions, wherein each fiber fraction shows a uniform fiber length and that one of these fiber fractions represents between 40% and 80% by weight of the plurality and shows a fiber length of between 20 and 30mm. Furthermore, this invention relates to a method for producing such a plurality of cellulosic man-made fibers wherein all fiber fractions were passed through the same wet-cut aftertreatment stage. Last but not least this invention relates to the use of such fiber plurality for the manufacture of fabrics with nature-like appearance.

[0004] Prior Art

[0005] The production of cellulosic synthetic fibres is carried out on a larger scale using the viscose process or the more recent lyocell process. These "manmade" cellulose fibers are known under the generic names viscose, modal and lyocell, with the definitions being defined by the BISFA (Bureau for the International Standardisation of Man-Made-Fibers).

[0006] The production of staple fibres is usually carried out according to known methods on a spinning machine with several spinning positions by spinning a spinning dope through spinnerets into a precipitation bath. The spun filaments are pulled off as a spun filament tow with the help of a drawing device and fed into a cutting device before or after further treatment steps. There, the filament tow is cut into uniform “staples” with a precisely defined length, i.e. a staple is a composite of very many fibers of the same length. During a nonwoven after- treatment, these staples are transformed into a homogeneous fibre fleece, which is washed, coated with a fiber finish preparation and dried. In the case of tow after-treatment, the filament tow is treated before cutting and, if necessary, crimped.

[0007] Usually, the same types of fibres are produced on a spinning machine and delivered in bale form to the further processor, mostly a yam spinning plant or a nonwoven roll good manufacturer. Lenzing AG, PL0831-WO

[0008] For the purposes of this invention, a fiber type is understood to be fibers with the same fineness (i.e. with the same titer) and the same cutting length as well as the same generic type according to BISFA. A typical commercially available fiber type has e.g. 38mm cut length and a titer of 1 ,3dtex.

[0009] One of the major fabric types used for garments is denim that is traditionally made purely or at least mostly of cotton fibers, being cellulosic. However, as cotton has some disadvantages regarding sustainability, other fibers are more and more intended to be used for denim. Besides elastane, mostly man-made cellulosic fibers are of interest for this application, as they offer the same wear comfort as cotton, due to the same chemical nature as cotton. Man-made cellulosic fibers are mostly staple fibers made according to the viscose, modal or lyocell process. However, staple fibers due to their homogeneous fiber length give to the fabric and the final garment an appearance different than cotton fibers.

[0010] It is well known to produce staple fibres with different cutting lengths. US 3,901 ,015 concerns a process for cutting multifilaments into staple fibres with variable cutting lengths. Its purpose is to produce pluralities of fibers intended to imitate the appearance of wool. The applied technology consists of crimping the filament tow and thereafter pass it to a horizontal blade. This shall result in a continuous fiber length spectrum according to the description in US 3,901 ,015. According to the examples the resulting pluralities of fibers show fiber length spectra of from 15-20mm up to 60-100mm. Furthermore, due to the applied technology the fiber length distribution will be random and cannot be controlled exactly.

[0011] A device for trapezoidal cuts of spin cables is known from US 4,006,277. The disclosed technology comprises a cutting wheel with blades mounted in distinct angles with respect to the filament tow direction. This results in a continuous fiber length spectrum. According to the description fiber length spectra of e.g. 1 ,5 to 3inches, 2,5 to 5inches or 4-6inches are possible. Obviously broader fiber length spectra are not possible by this technology because of the limited angle variation possibilities for the blades. Lenzing AG, PL0831-WO

[0012] The utility model AT 002 422 U2 concerns a cutting device for the production of staple fibres with variable cut lengths. Its purpose is to imitate the fiber length spectrum of natural cotton. For this purpose the AT 002 422 U2 suggests to produce a plurality of fibers with fiber lengths of between 40 and 120mm.

[0013] US 2019 / 0024266 A1 discloses a method of producing a yam having the look and feel of natural fibers by blending man-made fibers with noils of man-made or natural fibers. Such noils are the short fibers removed during the combing of a textile fiber and may have a length of between 4 and 38mm. They are often separately spun into yarn and show a continuous fiber length spectrum. Such fiber compositions may vary in their fiber length distribution and hence in their yarn spinning behaviour in a manner that is not acceptable for a reliable yam spinning process and further for the production of fabrics with homogeneous appearance.

[0014] US 4,466,237 discloses a synthetic yam which comprises fibers of different lengths. At least three groups of synthetic fibers are present in this yam, with the fibers within each group being substantially uniform in length. The purpose is to resemble the characteristics of natural fiber-containing yams such as cotton or wool containing yams.

[0015] In summary the prior art documents suggest either compositions of mere synthetic fibers or compositions containing or even consisting of fibrous compounds with continuous fiber length spectra, which are either manufactured by complicated or unreliable methods or are of varying composition, i.e. unreproducible. Synthetic fiber compositions show a reduced comfort for the wearer of the garment produced thereof. Complicated or unreproducible methods cause unreliable production processes and therefore are undesirable in the textile industry.

[0016] Problem

[0017] In view of this prior art the problem to be solved consisted in providing a fiber plurality with a reproducible composition that can be used for fabrics with Lenzing AG, PL0831-WO nature-like appearance and providing high comfort for the wearer, as well as a reliable, simple method for the manufacture of such fiber plurality.

[0018] Description

[0019] This problem could be solved by a plurality of man-made cellulosic fibers of the same fiber titer, composed of at least 3 different fiber fractions, wherein each fiber fraction shows a uniform fiber length and wherein one of these fiber fractions (the “homogeneous portion”) represents between 40 and 80% by weight, preferably between 45 and 70% by weight, of the plurality and shows a fiber length of between 20 and 30mm. The term “uniform fiber length” shall mean that all fibers contained in one fraction have an identical length. I.e. the length of all the fibers of the “homogeneous portion” is identical and either 20mm only or 30mm only or one value only within this range. Man-made cellulosic fibers according to the invention generally include viscose, modal, lyocell, cupro and cellulose carbamate fibers. Even more preferably the homogeneous portion represents between 45 and 60% by weight of the fiber plurality. The homogeneous portion may preferably show a uniform fiber length (in the meaning as outlined above) of between 26 and 30mm.

[0020] In a preferred embodiment of the present invention each of the remaining fiber fractions (altogether hereinafter also called the “vario-cut portion”) in the fiber plurality show a uniform fiber length of between 10 and 30mm and the fiber lengths within the vario-cut portion are always in a range of not more than 10mm difference. This means that the fiber length of the longest fiber fraction in a vario-cut portion has to be at most 10mm longer than the fiber length of the shortest fiber fraction in that vario-cut portion. Again, the term “uniform fiber length” shall mean that all fibers contained in one fraction have an identical length. For example, if the longest fibers in the vario-cut portion have a length of 21mm, then the shortest fiber fractions shall have a length of least 11 mm. It was found in the course of the invention that a range of at most 10mm will still result in reliably spinnable yarns. If the range would be greater this could cause problems during yarn spinning and then the desired naturelike appearance of fabrics containing the fiber plurality according to the invention may be not achieved. However, if the range of fiber length in the Lenzing AG, PL0831-WO vario-cut portion would be less than 5mm, then the desired nature-like appearance of fabrics containing the fiber plurality according to the invention may be not achieved. Hence, the fiber lengths within the vario-cut portion preferably shall always be in a range of 5mm or more. Fibers shorter than 5mm should not be contained in the vario-cut portion, otherwise such portions could not be spun properly. For the same reason yams should not contain more than 30% by weight of short vario-cut portion (with length of between 11 and 21mm).

[0021] Preferably the homogeneous portion of the fiber plurality according to the invention shows the longest fiber length within the fiber plurality.

[0022] In a preferred embodiment of the present invention the fiber plurality is a fiber bale, i.e. it is in the form of a fiber bale. This embodiment may alternatively be described as a fiber bale wherein the fibers of this bale have a composition according to the fiber plurality of the invention as described above. Fiber bales are the most common packing unit for textile staple fibers. However, the plurality of fibers according to the invention may also be packed into sacks or into boxes like cardboard boxes. Such fiber plurality according to the invention, i.e. in the form of a fiber bale or in the form of the content of a sack or a box, may show a weight of between 100 and 500kg, preferably between 250 and 400kg.

[0023] In a preferred embodiment of the present invention all fibers in the fiber plurality are of the same generic fiber type, according to the BISFA definition. In particular they may be lyocell, viscose or modal fibers. These BISFA definitions of the generic fiber types can be found in the “Terminology of manmade fibers”, 2009 Edition, published by the organization BISFA (International Bureau for the Standardization Of Man-Made Fibers). However, in another possible embodiment of the present invention the fibers of the homogeneous portion and the vario-cut portion may be of different generic fiber types. For example one of these portions may consist of lyocell fibers and the other portion may consist of modal fibers. Lenzing AG, PL0831-WO

[0024] Another object of the present invention consists in providing a method for producing a plurality of cellulosic man-made fibers according to known methods on spinning machines with several spinning positions by spinning a spinning dope through spinnerets into a precipitation bath. The spun filaments are pulled off as a spun filament tow with the help of a drawing device and are fed into a cutting device. The plurality of cellulosic man-made fibers is of substantially the same generic fiber type and the same fiber titer, composed of at least 3 different fiber fractions, wherein all fiber fractions were passed in parallel through the same wet-cut aftertreatment stage. The term “same wetcut aftertreatment stage” according to the present invention shall mean that all fibers were cut in a never-dried state and all after cutting were combined on the same aftertreatment stage where all the fibers jointly were washed and bleached. In a preferred embodiment of the method according to the invention the homogeneous fiber portion and the vario-cut fiber portion are spun and cutted on separate fiber spinning lines and combined thereafter on the same aftertreatment stage.

[0025] In the method according to the invention the vario-cut fiber portion is preferably produced by providing the fiber tow at constant speed to a filament cutting device with rotating blades and the rotating blades of this cutting device are preferably mounted on the filament cutting device in distinct angles corresponding to the fiber fraction lengths of the fiber plurality. Mounting the blades in appropriate angles is one of the means to determine the fiber lengths in the vario-cut portion. The other means to determine the fiber lengths is the rotating speed of the rotating blades and the speed of the tow provided. In state-of-the-art cutting devices driven by electric motors the rotating speed will mostly be controlled by a frequency converter.

[0026] Still another object of the present invention consists in the use of the fiber plurality according to the invention as described above for the manufacture of fabrics with nature-like appearance, wherein between 15 and 50 % (w / w) of a fiber plurality according to claim 1 are blended with other man-made cellulosic fibers in order to spin a yarn and that yarn is woven or knitted to make the fabrics with nature-like appearance. This use could also be denoted as a method. “Nature-like appearance” in relation to the present invention shall Lenzing AG, PL0831-WO mean an uneven appearance that is usually generated by the use of natural fibers like cotton or hemp that are naturally grown and therefore show various individual fiber lengths. Surprisingly it was found that a fiber plurality according to the present invention, used for the manufacture of a fabric, is able to mimicking the natural fiber fabric / surface appearance. Possible fabric types may be fabrics with denim-like construction, but also e.g. other plain weave or knit fabrics.

[0027] The invention will now be illustrated by examples. These examples are not limiting the scope of the invention in any way. The invention includes also any other embodiments which are based on the same inventive concept

[0028] Examples

[0029] A plurality of lyocell fibers with the composition shown in Table 1 was produced using two conventional lyocell staple fiber lines and wet cut. The filaments of both fiber lines were extruded and stretched in a way to give a final titer of 1 ,7dtex. The filament tow of fiber line 1 was cut by a conventional fiber cutter to a length of 28 mm homogeneously. The filament tow of fiber line 2 was provided to a “vario-cut” fiber cutter at constant speed. The rotating blade of this vario-cut fiber cutter was driven by an electric motor with the rotating speed being controlled by a frequency converter according to a program ensuring the composition of fibers with a length of between 11 and 21 mm according to Table 1 . The cut fibers from both fiber lines were brought together at the beginning of the same wet-cut aftertreatment stage and jointly passed through that aftertreatment stage where the fibers were washed and bleached and thereafter dried and pressed to obtain a fiber bale.

[0030] Lenzing AG, PL0831-WO

[0031] Table 1 :

[0032] The fibers of that fiber bale were afterwards opened by a conventional fiber opener, blended with 70% by weight of conventional lyocell fibers (1 ,3dtex, 38mm) and spun into yams of Nm 10 and Nm 17. These yams generally were more uneven with more thick places and thin places in the yam compared to yams made merely of the conventional lyocell fibers. The yams according to the invention were used to weave denim fabrics of 2 / 1 twill construction.

[0033] These denim fabrics showed an appearance close to denim fabrics of the same construction made from 100% cotton yam. According to these positive findings it may also be recommendable to use the yams with up to 50% by weight of the fiber plurality according to the invention only in the warp direction of denim fabrics.

Claims

Lenzing AG, PL0831-WOClaims1. A plurality of man-made cellulosic fibers of the same fiber titer, composed of at least 3 different fiber fractions, characterized in that each fiber fraction shows a uniform fiber length and that one of these fiber fractions (the “homogeneous portion”) represents between 40 and 80% by weight of the plurality and shows a fiber length of between 20 and 30mm.

2. The fiber plurality according to claim 1 wherein each of the remaining fiber fractions (altogether the “vario-cut portion”) in the fiber plurality show a uniform fiber length of between 10 and 30mm and wherein the fiber lengths within the vario-cut portion are always in a range of not more than 10mm difference.

3. The fiber plurality according to claim 1 , wherein the homogeneous portion shows the longest fiber length within the fiber plurality.

4. The fiber plurality according to claim 1 , which is a fiber bale.

5. The fiber plurality according to claim 1 , which shows a weight of between 100 and 500kg, preferably between 250 and 400kg.

6. The fiber plurality according to claim 1 , wherein all fibers are of the same generic fiber type.

7. A method for producing a plurality of cellulosic man-made fibers of the same fiber titer, composed of at least 3 different fiber fractions, characterized in that all fiber fractions were passed through the same wet-cut aftertreatment stage.

8. The method according to claim 7, wherein the vario-cut fiber portion is produced by providing the fiber tow at constant speed to a filament cutting device with rotating blades and the rotating blades of this cutting device are mounted in distinct angles corresponding to the fiber fraction lengths of the fiber plurality.

9. Use of the fiber plurality of claim 1 for the manufacture of fabrics with nature-like appearance, wherein between 15 and 50% by weight of a fiber plurality according to claim 1 is blended with other man-made cellulosic fibers to spin a yam and that yam is woven or knitted to make the fabrics with nature-like appearance.

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