KR20230005349A - spun-dyed cellulose fibers - Google Patents

Abstract

The present invention is a cellulosic fiber containing incorporated indigo pigment in oxidized form, wherein the fiber is produced according to the Modal process and has a tenacity (conditioned) of at least 29 cN/tex and a wettability according to BISFA of at least 5 cN/tex/%. It relates to cellulosic fibers, which exhibit modulus. The invention also relates to the manufacture of such fibers and the use of such fibers in fabrics.

Description

spun-dyed cellulose fibers

The present invention is a cellulosic fiber containing incorporated indigo pigment in oxidized form, wherein the fiber is made according to the Modal process and has a tenacity (conditioned) measured according to BISFA of at least 29 cN/tex and an elongation of at least 5 at 5% elongation. Cellulose fibers exhibiting a wet modulus measured according to BISFA in cN/tex/%. The present invention also relates to the manufacture of these fibers and the use of these fibers in fabrics and garments (shoes, etc.).

Natural or man-made cellulosic fibers and articles made therefrom, such as yarns or fabrics, can be dyed using a number of dye classes. The most common type of dye used is reactive, where the dye reacts chemically with hydroxyl groups on the cellulose molecules that make up the fiber. This creates covalent bonds that give this type of dye high fastness properties. Reactive dyes are the most common because they provide a high degree of fastness and a full shade range. In addition to reactive dyes, cellulosic fibers can be colored with other dye types such as direct, vat or sulfur dyes.

One of the most important vat dyes is indigo (CI vat blue 1). Indigo is used to color yarns that are subsequently used to make indigo denim fabric. The spun warp yarn is first made into beams and then dyed with indigo (CI Vat Blue 1) before weaving into fabric. The manufacture of the yarn is usually a simple scouring to remove any impurities, but may include such chemical treatment as caustic soda treatment. Indigo can be applied by a number of methods but by application to the yarn through a Rope or Slasher application.

Since indigo dye is insoluble in water, it is first converted to a soluble, so-called "leuco" form using an alkali reduction system using sodium hydroxide and sodium dithionite. Since this leuco indigo has a low substantivity to cellulose, only a pale depth can be obtained by an exhaust dyeing procedure. Thus, indigo is applied in a series of dips with intermediate pressing and atmospheric oxidation. By repeating the process, the dye is applied to the substrate layer by layer to provide a deep dyeing with relatively low rubbing fastness.

In rope dyeing, the cellulose warp yarns are extended along a range in the form of a rope. A yarn group is typically 300 to 400 ends called ropes or cables. In slasher dyeing, the warp yarns are flat and individually elongated and arranged parallel to each other. Indigo can also be dyed batchwise or in fabric form, usually continuously. Batch dyeing of yarn hanks can be done on the beck with repeated short dips followed by squeezing and atmospheric oxidation, but this application is much less common.

The most common denim is derived from colored warp yarns while the weft yarns are left white. As a result of warp faced twill weaving, one side of the textile is dominated by blue warp yarns and the other side is dominated by white weft yarns. The indigo dyeing process, in which the core of the warp yarn remains white, creates denim's signature fading characteristic.

Other vat dyes and sulfur dyes may also be used to color the yarn or fabric.

Dyes used to color cellulosic fibers and articles made therefrom generally cannot be used to color fibers (eg viscose, modal) during the fiber spinning process. It has been found that the incorporation of reactive dyes into the dopes used to make lyocell fibers has a negative effect on process stability and is not acceptable for process safety reasons.

Indigo-dyed denim has some properties that are disadvantageous to some extent and some requirements (which are actually very welcome by others): Since the dye is only on the outer surface of the cotton fibers, its fastness to rubbing and washing is quite poor. . Denim articles exhibit a wash down effect by losing indigo after washing and washing treatment (bleaching, oxidation, etc.).

Denim laundry uses a variety of methods to give denim fabric a variety of effects, such as a bleached, worn, and faded look. Historically, bleaching chemicals such as hydrogen peroxide, hypochlorite and permanganate have been mainly used. Recent sustainable options for denim washing are laser and ozone treatments. The laser light sublimates the dye on the surface of the fabric, revealing a specific design pattern as well as giving it a faded and used look. Ozone gas is used to bleach denim garments through its high oxidation potential.

Another very big drawback is the dyeing process for normal denim products: dyeing with indigo is carried out on yarn. Not only is this process very expensive, but it also potentially pollutes the environment, especially the wastewater of the dyeing room.

A solution to this problem has been to incorporate indigo pigments of natural or synthetic origin in an oxidized, ie blue form, or other dye type that mimics the color and laundry wash-down of indigo into viscose fibers during spinning. Such fibers are marketed under the term "Viscose Indigo". However, viscose indigo has relatively low mechanical strength, especially in the wet state. Thus, viscose indigo fibers are generally blended with significant amounts of polyester fibers. Garments made using these blended yarns present some significant disadvantages: due to the high content of synthetic fibers, wearing comfort is reduced compared to garments composed of 100% cellulosic fibres. In addition, the polyester fiber component may also need to be dyed; These fiber types require a different type of dye that is not suitable for cellulose.

assignment

In view of this prior art, the problem to be solved consisted in providing a fiber that was suitable for creating a denim look, but exhibited improved friction fastness while providing good wear comfort to garments made therefrom.

Described

An object of the present invention is a cellulosic fiber containing incorporated indigo pigment in oxidized form, the fiber being produced according to the Modal process and also with a "breaking force" measured according to BISFA of at least 29 cN/tex. Tenacity (conditioned), which is called, to provide a fiber that exhibits a wet modulus measured according to BISFA of at least 5 cN/tex/% at 5% elongation. Both properties are measured according to methods as described in the BISFA brochure ("Testing methods viscose, modal, lyocell and acetate staoke fibers and tows", 2004 edition). In a preferred embodiment of the invention, the fibers according to the invention fulfill the requirements for modal fibers according to BISFA (see BISFA Terminology, 2009 edition), including that these mechanical properties depend on the potency of the fibers. This means that a 1.3 dtex fiber according to the present invention will exhibit a tenacity (conditioned) of at least 31.4 cN/tex and a wet modulus (wet) of at least 4.39 cN/tex/% at 5% elongation. A 1.5 dtex fiber according to the present invention will exhibit a tenacity (conditioned) of at least 30.61 cN/tex and a wet modulus (wet) of at least 4.8 cN/tex/% at 5% elongation.

Preferably, the indigo pigment contains a very low content of aniline, less than 50 ppm, preferably less than 25 ppm and even more preferably less than 20 ppm.

Preferably, the fiber according to the present invention contains 0.5 to 4.0% (w/w), particularly preferably 1.8 to 3.0% (w/w) of indigo pigment relative to the total weight of the bone dry fiber. contain A lower indigo pigment content will not provide a sufficiently deep color of the fiber and a higher indigo pigment content will reduce the mechanical strength of the fiber.

The fibers can be made by a process analogous to the FR pigment incorporation cellulosic fiber process as disclosed in AT 287905 B as follows: 4-7% cellulose, 5-10% NaOH, 36-42% (with cellulose Viscose with a content of carbon disulfide (relative to cellulose) and a modifier of 1 to 5% (relative to cellulose) was prepared. It has a radial gamma value of 50 to 68 and a radial viscosity of 50 to 120 ballfall seconds; and an alkali ratio (= cellulose concentration/alkali content) of the prepared viscose from 0.7 to 1.5. Indigo pigment with a very low aniline content in oxidized form is used in an amount of from 0.5 to 4.0% (w/w) of indigo pigment, particularly preferably from 1.8 to 3.0% (w/w) of fiber, relative to the total weight of the bone dry fibers. were incorporated during spinning in the form of a pigment masterbatch dispersion in an amount suitable to obtain the final concentration of Indigo-containing viscose was extruded through a spinneret into a spinning bath exhibiting a temperature of 34-48° C. and the following spinning bath concentrations: H ₂ SO ₄ = 68-90 g/L, Na ₂ SO ₄ = 90-160 g/L l, ZnS0 ₄ = 30 to 65 g/l. The coagulated yarn was drawn from the spinning bath at a speed of 15 to 60 m/min. The coagulated, drawn yarn was further thoroughly washed and cut into staple fibers, with a titer of 1.3 dtex and a length of 38 mm. For purposes of this patent's examples, this fiber is referred to below as "Modal Indigo".

According to the present invention, the indigo pigment is incorporated within the entire cross-section of the fiber. That is, micrographs of fiber cross-sections show pigments distributed over the entire area of the cross-section, whereas conventionally dyed cellulosic fibers show indigo pigments only on the outer surface of the fibers. Surprisingly, the bleeding rate of indigo pigments in the fibers according to the invention is significantly lower than that of indigo pigments in viscose indigo.

Another aspect of the invention is the use of the fibers according to the invention as described above for the manufacture of fabrics (knit, woven, seamless, etc.) having a denim appearance provided by a washing effect such as laser and ozone. . Preferably, these colored fibers are used in the warp yarns, while the ecru (i.e., undyed) fibers are used in the weft yarns of the woven fabric to mimic conventional denim fabrics.

To achieve different aesthetics and wearing comfort for consumers, these colored fibers may be used in weft yarns, while the warp yarns may contain conventional indigo-dyed cellulosic fibers. In these products, the indigo-colored modal fibers are on the skin side by bringing the modal fiber's softness, i.e., comfort. Wash-down of the warp side will behave differently than using a light brown (ie, undyed) fiber which causes a darker shade on the warp side.

Preferably, this fabric is a textile fabric with a denim appearance containing from 40 to 100% (w/w) of the fibers according to the invention as described above.

In a preferred embodiment of the present invention, the fabric exhibits a friction fastness according to ISO 105-X12:2016 of 4.0 to 5.0. Typically, yarn-dyed denim exhibits a rub fastness of about 3.0.

ISO 3759에 따른 수축 시험에서 5.0% 미만의 수축을 나타낼 수 있다.In a preferred embodiment of the present invention, the fabric is a woven fabric. Preferably, such fabrics contain from 80 to 100% (w/w), preferably from 95 to 100% (w/w) of the fibers according to the invention in the warp yarns. This will result in a typical denim look, especially in twill weaves where one side of the textile is dominated by blue warp yarns and the other side is dominated by white weft yarns. These fabrics are washed and cleaned according to ISO 6330.

Shrinkage tests according to ISO 3759 may show less than 5.0% shrinkage.

ISO 3759에 따른 수축 시험에서 12.0% 미만의 수축률을 나타낸다.In another preferred embodiment of the present invention, it is a knit fabric. Preferably, these fabrics are washed and washed according to ISO 6330.

Shows less than 12.0% shrinkage in the shrinkage test according to ISO 3759.

Another aspect of the present invention is a process for making a fiber according to the present invention as described above comprising the following steps:

a. preparing a modal spinning solution;

b. preparing an indigo pigment in oxidized form;

c. adding indigo pigment to the modal spinning solution;

d. Extruding the solution of step c into a coagulation bath according to the modal spinning process.

Pigments used in the process of the present invention can be prepared, for example, according to WO 2004/024826 A2. For example, conventional modal spinning conditions as described in patent AT287905B or WO 2011/026159 A1 may be applied.

Preferably the indigo pigment is added to the Modal spinning solution in the form of a masterbatch, and the indigo pigment content has, for example, 20% (w/w) in the masterbatch suspension. For example, when using a masterbatch containing 20% (w/w) indigo pigment to obtain 0.5 to 4.0% (w/w) of indigo pigment in the final fiber, 2.7 to 20.0% (w/w) w), a masterbatch suspension of (for dissolved cellulose) should be added to the modal spinning solution.

Surprisingly, it has been found that the fibers according to the present invention additionally have a much lower bleeding rate than other spun-dyed modal fibers. The bleeding rate of modal indigo is also lower than that of viscose indigo, but the mechanical textile properties are much higher for modal fibers compared to viscose fibers.

Also surprisingly, the indigo pigment in oxidized form retains its conventional blue color very stably when incorporated into the cellulosic man-made fiber according to the invention, although the dye is applied on cotton, for example by conventional denim indigo dyeing. found to be very sensitive to oxidation.

denim washing

Typically, a hypochlorite bleaching treatment applied commercially in denim washing (e.g., 2 g/L soda, 3 g/L sodium hypochlorite; 30 °C for 30 minutes, warm and cold rinse, 40 °C for 30 minutes 0.8 g /l H ₂ O ₂ dechlorination, warm and cold rinse) as well as strong peroxide bleaching treatment (eg 4 g/l peroxide, 4 g/l NaOH, 90 °C for 30 min, then neutralization (1 In the case of g/L acetic acid)), little effect was observed.

Increasing the hypochlorite concentration (4 g/L sodium hypochlorite, 40° C., 10 min, followed by neutralization (3 g/L sodium thiosulfate, 30° C., 10 min)) may provide some effect. However, this treatment is not recommended considering the large amount of chemicals used to achieve very little effect on the product.

However, denim washing conditions using permanganate (e.g., 4 g/L potassium permanganate, 40°C, 10 minutes, followed by neutralization (2 g/L metabisulphite, 40°C, 10 minutes)) It was very effective in removing indigo from dyed modal indigo products.

In addition, after spraying a 20 g/L potassium permanganate solution and drying in air (or at 80° C. in a stenter frame dryer), a sodium dithionite solution (1 to 4 g/L) at 40° C. for 20 minutes The effect of topical bleaching with potassium permanganate by washing the fabric gave significantly visible results.

Also, ozone treatment (50% G2 Lab machine, ozone gas concentration: 45 gr/Nm3, 15 min, 30 min or 45 min) and laser marking (using a machine from Jeanologia), e.g. 40 to 150 tpx (per pixel) time) gave significant visual results for the fibers according to the invention.

home laundry

Conventional home-launder washing (water and detergent) of denim articles causes the indigo dye to be lost from the fabric in that a faded appearance appears after each wash cycle. Thus, conventional denim products do not have color retention after home-launder washing.

The indigo dye captured in the spun-dyed modal indigo fiber is not lost during home laundry washing. Our study showed that 30 home-launder washes did not cause color loss in a spun-dyed modal indigo garment, thus demonstrating color retention. For the home-laundry washing test, a commercial home-laundry detergent (Fewa Color) was used, and spun-dyed modal indigo garments (knit and woven) were washed at 40° C. and flat or tumble dried.

A faded, wash-down or similar appearance of spun-dyed modal indigo products can only be provided by commercial denim washes (laser, ozone, permanganate, etc.). This garment effect/appearance will be maintained throughout the consumer life of the garment as the indigo is not removed by home-launder washing. This characteristic distinguishes indigo spun-dyed modal products from commercially available dyed indigo dyed products.

Preferred uses of the fibers according to the invention are:

● denim-type woven fabric structures, in particular denim fabrics having an areal weight greater than 100 g/m 2 ;

● weave-type fabric structures, especially lightweight fabrics for shirting, dresses, etc., having an areal weight greater than 80 g/m2;

● Knitwear including seamless materials, in particular tops, bottoms and underwear, as well as other garments, shoes, bags, etc. made of or containing textile fabrics.

In all these applications, modal indigo outperforms viscose indigo due to its lower shrinkage and higher strength. In all these applications, the low bleeding tendency of the fibers according to the present invention can be advantageous.

The invention will now be illustrated by examples. These examples do not limit the scope of the present invention in any way. The present invention also includes any other implementations based on the same inventive concept.

Example

Example 1 : Preparation of Indigo-Containing Spun-Dyeed Modal Fibers:

Incorporated cellulosic fibers were prepared by a process analogous to the FR pigment incorporated cellulosic fiber process as disclosed in AT 287905 B as follows:

A viscose was prepared with a content of 6% cellulose, 7% NaOH, 39% (relative to cellulose) carbon disulfide and 3% (relative to cellulose) modifier. It exhibited a radial gamma value of 57 and a radial viscosity of 80 ball-pole seconds. During spinning in the form of a pigment masterbatch containing 20% (w/w) of an indigo pigment with a very low aniline content in oxidized form, of 2.3% (w/w) relative to the cellulose content of the spinning solution. got mixed up Indigo-containing viscose was extruded through a spinning nozzle into a spinning bath exhibiting a temperature of 38° C. and the following spinning bath concentrations: H ₂ SO ₄ = 72 g/L, Na ₂ SO ₄ = 120 g/L, ZnSO ₄ = 60 g/l. The coagulated yarn was drawn from the spinning bath at a speed of 45 m/min. The coagulated, drawn yarn was further thoroughly washed and cut into staple fibers with a titer of 1.58 dtex and a length of 38 mm. The tenacity (conditioned) was 32.1 cN/tex and the wet modulus (wet) was 5.5 cN/tex/% at 5% elongation. The elongation at break was 15.5%. All mechanical properties were measured according to the methods described in the BISFA brochure ["Testing methods viscose, modal, lyocell and tows", 2004 edition]. For purposes of the examples of this patent, these fibers are hereinafter referred to as "modal indigo".

Example 2 : Characteristics of Fabrics Containing the Fibers According to the Invention and Characteristics thereof

Three fabrics were prepared using the fibers of Example 1 as follows; Yarns of the fibers were spun by a rotor yarn spinning machine:

2.a.: Jeans bottom weight fabric

● Warp: Modal indigo yarn, Ne 11

● Weft yarn: cotton/elastane (98%/2%) yarn, Ne 15

● 3/1 RHT fabric configuration; 7 ends/cm, 20 picks/cm

2.b.: shirting weight fabric

● Warp: Modal indigo yarn, Ne 24/1

● Weft: Cotton, Ne 15

● 2/1 RHT fabric configuration; 185 gsm

2.c.: Knit upper fabric

● Modal indigo yarn Ne 24

• single jersey fabric construction with 2% elastane; 185 gsm

This fabric was tested for several properties as follows:

Friction fastness was measured according to ISO 105-X12:2016 (1 = worst; 5 = best); See Table 1:

Table 1:

Both fabrics with fibers according to the present invention exhibited very good friction fastness properties.

Wash fastness was measured according to ISO 105-C10:2006. The fabric was washed with each white side. White modal fabrics and dyes were evaluated on a color scale (1 = worst fastness; 5 = best fastness); See Table 2:

Table 2:

Both fabrics with fibers according to the present invention showed very good wash fastness properties.

ISO 3759:2011에 따라 측정하였다. 시험된 직조 패브릭은 모달 인디고를 갖는 실시예 2.a의 데님 패브릭 및 모달 인디고 대신에 비스코스 인디고를 함유한 것을 제외하고 동일한 방식으로 제조된 데님 패브릭이었다. 시험된 니트 패브릭은 모달 인디고를 갖는 실시예 2.c의 패브릭 및 모달 인디고 대신에 비스코스 인디고를 함유한 것을 제외하고 동일한 방식으로 제조된 니트 패브릭이다. 표 3은 본 발명에 따른 모달 인디고 섬유를 함유하는 패브릭이 비스코스 인디고를 사용하여 제조된 비교 가능한 패브릭보다 유의하게 더 낮은 수축률을 나타낸다는 것을 보여준다. Shrinkage after washing of the sample according to ISO 6330:2012

Measured according to ISO 3759:2011. The woven fabrics tested were the denim fabric of Example 2.a with modal indigo and the denim fabric made in the same manner except containing viscose indigo instead of modal indigo. The knit fabric tested is the fabric of Example 2.c with modal indigo and the knit fabric made in the same manner except that it contains viscose indigo instead of modal indigo. Table 3 shows that fabrics containing modal indigo fibers according to the present invention exhibit significantly lower shrinkage than comparable fabrics made using viscose indigo.

Table 3:

Example 3 : Yarn Tenacity After Denim Bleaching Process Compared to Viscose Indigo

Modal indigo fibers according to the present invention were compared with commercially available viscose indigo fibers (obtained from Lenzing Aktiengesellschaft, Lenzing/Austria). The yarn was spun using a Quickspin machine, ie by a rotor spinning process. Yarn tenacity was measured before and after treatment with permanganate in aqueous solution according to the following conditions: potassium permanganate concentration 4 g/l, 40° C. for 10 min, followed by 2 g/l disodium metabi at 40° C. for 10 min. Neutralize with sulfite. Table 4 shows that the modal indigo exhibits satisfactory mechanical properties even after permanganate bleaching, although the viscose indigo deteriorated so much that yarn strength and yarn elongation could not be measured (yarn tearing when clamped).

Table 4:

Example 4 : Testing fibers for bleeding

A Labomat device with a 500 mL-tube operating at a rotational speed of 20 rpm was used. 200 ml of deionized water was measured in a graduated cylinder and heated to 85° C. in a Labomat device. 5 g of fiber was added. The Labomat temperature was raised to 98°C as quickly as possible. The sample was treated at 98°C for 5 minutes and then cooled to 70°C as quickly as possible. The liquid was transferred to a 100 ml beaker and allowed to cool to room temperature (i.e., 20° C.) while manually removing the fibers.

Two methods were applied to the resulting liquid to evaluate bleeding:

- Photometric evaluation of absorption at a wavelength of 480 nm in the resulting liquid.

- turbidity measurement using a turbidimeter according to ISO 7027-1:2016; Results are given as [NTU] = Nephelometric Turbidity Unit.

For each measurement, a test tube filled with pure water is required as a blank standard. The fibers tested were:

Modal indigo was obtained according to Example 1. Viscose Indigo, Viscose Black (spun dyed) and Modal Black (spun dyed) were obtained as commercially available products from Lenzing Aktiengesellschaft in Lenzing/Austria. All fibers used were staple fibers with a titer of 1,3 to 1,7 dtex and a cut length of 38 to 39 mm.

Table 5:

The results (Table 5) show that conventional to indigo pigment conversion in spun dyed viscose fibers results in higher bleeding, whereas conventional to indigo pigment conversion in spun dyed modal fibers is surprisingly significantly reduced. shows that it causes bleeding. This is particularly surprising since the basic chemistry of both processes (formation of cellulose xanthogenate and subsequent coagulation and regeneration of cellulose) is the same.

Example 5 : Sustainability evaluation based on theoretical model

To evaluate the sustainability of the present invention, it was compared with three conventional denim dyeing methods. The three conventional methods compared are hereinafter referred to as Methods A, B and C.

The comparison was made by sustainability expert consulting firm GAVILAN AD using expert software developed by Archroma called 'One Way'. This expert system provides full control over the resources (water, energy, CO2 produced, etc.) required to operate each piece of equipment (padder, washing box, pre-dryer, drying can, stenter, etc.) in the application process. It has an embedded database with information. This expert program also calculates indirect resource requirements (eg energy by type of fuel for the boiler, heating system for the application box - direct/indirect steam, power required for the engine, etc.). “owf” means “by fiber weight”.

The assumptions for methods A, B and C were as follows:

4 ways, i.e. . Methods involving modal indigo processing according to the present invention, general assumptions for all

- Length of dyed warp yarn: 10000 m

- Weight: 2190 kg

- Type of denim article: lightweight (7 Oz/Yd², i.e. approximately 235 g/m²)

- 25 °C for all process steps

- Methods A-B-C involve yarn spinning prior to indigo dyeing, whereas the spun-dyed modal indigo fiber according to the present invention involves yarn spinning after indigo spun-dying of the fiber.

Additional assumptions for Method A (conventional indigo yarn dyeing) were as follows:

- Concentration of indigo (standard commercial form of granulated indigo): 4% owf (dark tone)

- Indigo yarn dyeing process is pre-wet, warm rinse (2 boxes), cold rinse (1 box), indigo dyeing (6 boxes), rinse (3 boxes).

Additional assumptions for Method B (pre-reduced indigo yarn dyeing) were as follows:

- 4% owf (dark tone) for liquid indigo pre-reduced under nitrogen gas to prevent oxidation

- Indigo yarn dyeing process is pre-wet, warm rinse (2 boxes), cold rinse (1 box), indigo dyeing (3 boxes), rinse (3 boxes).

Additional assumptions for method C (low water consumption sulfur dyeing) were as follows:

- Concentration of non-indigo dye adjusted for both laboratory and bulk comparative staining: 12% pre-reduced sulfur dye

- The application of non-indigo dyes considers a pre-mercerization step instead of the usual pre-wetting for indigo.

- mercerizing, warm rinse (2 boxes), sulfur dye (2 boxes), fixation bath (2 boxes), rinse (3 boxes)

When the method for producing spun-dyed modal indigo fibers according to the present invention is compared with other dyeing methods A to C, the method according to the present invention has significant savings in water, chemicals, electricity, heat and wastewater (see Table 6). : Savings achieved with indigo spun-dyed modal according to the present invention compared to methods A, B and C). The heat energy normally required to dry the dyed yarn is not required for modal indigo fibers.

table 6

Claims (11)

A cellulosic fiber containing incorporated indigo pigment in oxidized form, said fiber being prepared according to a modal process, said cellulosic fiber having a tenacity (conditioned) of at least 29 cN/tex ), characterized in that it exhibits a wet modulus according to BISFA of at least 5 cN/tex/%. The fiber of claim 1 wherein the indigo pigment is incorporated within the entire cross-section of the fiber. Use of the fibers according to claim 1 for the production of a fabric having a denim appearance. A textile fabric with a denim appearance, characterized in that it contains 40 to 100% (w/w) of the fibers according to claim 1 . 5. The fabric of claim 4 exhibiting a rub fastness according to ISO 105-X12:2016 of 4.0 to 5.0. 5. The fabric according to claim 4, which is a woven fabric. 7. The fabric according to claim 6, which contains from 80 to 100% (w/w), preferably from 95 to 100% (w/w) of the fibers according to claim 1 in the warp. According to claim 6, washing according to ISO 6330 and

A fabric that exhibits a shrinkage of less than 5.0% in a shrinkage test according to ISO 3759. 5. The fabric of claim 4 which is a knit fabric. 10. The process according to claim 9, wherein washing according to ISO 6330 and

A fabric that exhibits a shrinkage of less than 12.0% in a shrinkage test according to ISO 3759. A method for producing the fiber according to claim 1,
a. Preparing a Modal spinning solution;
b. preparing an indigo pigment in oxidized form;
c. adding the indigo pigment to the modal spinning solution;
d. and extruding the solution of step c into a coagulation bath according to a modal spinning process.