Technical area

[0001] This invention relates to a method for reducing the pilling behaviour of a fabric containing or consisting of man-made cellulosic fibers, in particular modal or lyocell fibers.

Prior art

[0002] Lyocell fibres, which are solvent-spun cellulose fibres, not regenerated cellulose fibres (see ISO 2076:1999 (E)), were introduced commercially relatively recently. Lyocell fibres have a tendency to fibrillate during vigorous dyeing and finishing processes, and much effort has been put into controlling this phenomenon. In particular, treatments have been developed to remove the relatively long protruding fibre ends which are formed in the first stage of the fibrillation process (so-called "primary fibrillation") and which otherwise produce a hairy effect, often matted, on the surface of the fabric and thus disfigure its appearance. On the other hand, the development of the shorter fibrils which are formed in the fibrillation process (so-called "secondary fibrillation") is encouraged. These shorter fibrils create a surface finish which is characterized as being "clean", in the sense of being substantially free from a hairy effect, and as having a soft touch imparted by the shorter fibrils on the fabric surface and which is referred to as a "soft-touch finish". When the shorter fibrils are sufficiently developed, the soft touch of the fabric surface is more pronounced and the soft-touch finish is referred to as a "peach-touch finish". Examples of such treatments for lyocell fabrics are described in WO 95/30043, WO 97/30204, and GB 2314568.

[0003] Modal fibres are defined in International Standard ISO 2076:1999 (E) and are high wet-modulus, high breaking- strength regenerated cellulose fibres produced using particular viscose and regeneration bath compositions which allow greater molecular orientation during stretch coagulation of the fibres. Another regenerated cellulose fibre of the modal type, again with high wet modulus and high breaking strength, is known as a polynosic fibre and was developed in Japan by the Tachikawa Company. Both modal and polynosic fibres are often referred to as high wet-modulus (HWM) fibres because that is their significant characteristic compared with ordinary viscose fibres.

[0004] Of the modal-type regenerated cellulose fibres, modal fibres themselves are less susceptible to fibrillation than lyocell fibres. Although fibrillation can be induced in such modal fibres by vigorous processing, controlling the fibrillation to produce the desired clean, soft-touch finish to a commercially acceptable standard has proved difficult. Polynosic fibres fibrillate more easily than modal fibres but, again, controlling the fibrillation to produce the desired surface finish is difficult.

[0005] The staple fibre yarns used may comprise just man-made cellulosic fibres or a blend of man-made cellulosic fibres with one or more other fibre types such as cotton, linen, polyester and nylon. Furthermore, the fabrics may additionally include yarns which do not incorporate man-made cellulosic fibres, for example yarns of the other fibre types referred to and blends thereof.

[0006] It is known that fibrils can be removed from lyocell fabrics by conventional resin-finishing treatments (hereinafter also referred to as “resin treatment”), for example using an N-methylol resin such as dihydroxydimethylolethyleneurea (DHDMEU). Such resin treatments, however, serve to remove both primary and secondary fibrils and tend to suppress all subsequent fibrillation.

[0007] It is also known that a peachskin finish can be obtained by wet processing to induce primary fibrillation, removing the primary fibrils by enzymatic treatment with a cellulase, followed by further wet processing to induce secondary fibrillation. This is a lengthy and expensive process, and disposal of enzyme-containing liquors may pose environmental problems.

[0008] WO 03/062515 A2 discloses a process for producing a dyed and finished modal fabric having a clean, soft-touch surface finish by carrying out the steps of dyeing, washing and drying the fabric using vigorous action on the fabric in at least one of the steps, wherein before the dyeing step is carried out, the fabric is evenly impregnated with an aqueous solution of an acid or acid donor and is then heat treated in a gaseous atmosphere to activate the action of the acid or acid donor, whereby the dyed and finished fabric has a clean, soft-touch surface finish free from long fibrils and visible crease marks. In particular, the soft-touch finish achieved may be a peach-touch finish. According to WO 03/062515 A2 the fabric is impregnated with a solution of an acid, preferably a weak acid at a pH of greater than about 3, and subsequently heat- treated at a temperature of between 120°C and 220°C, preferably 140°C and 200°C for 0.5 to 5 minutes. Thereafter it is dyed, washed and dried.

[0009] GB2314568 A discloses a method of finishing lyocell fabric, wherein the fabric is dyed under conventional conditions on a machine selected from the group consisting of a jet-dyeing machine, a garment drum dyeing machine, a garment drum washing machine and a wet-tumbling machine, wherein prior to the dyeing step the fabric is processed in the said machine in contact with an aqueous solution of an acid. The fabric is preferably a woven fabric but may be a knitted fabric. The fabric may be processed in rope or garment form. The acid is preferably a strong mineral acid, such as hydrochloric acid or particularly sulphuric acid. The concentration of acid in the solution is often in the range from 0.5 to 15, preferably from 1 to 5, grams per litre. The temperature of the acid solution may range from ambient to the boil; elevated temperatures in the range from 60 to 95°C may be preferred. The circulation time through the acid solution preferably shall be in the range from 30 to 120 minutes. After the acid treatment a vigorous treatment has to be applied to induce primary fibrillation, i.e. long fibrils, remove these such long fibrils and induce secondary fibrillation to obtain the peach skin handle. Overall this is a lengthy, complicated process.

[0010] All known methods described above are damaging the man-made cellulosic fibers in a way which requires that they have to be blended with other fiber types, preferably cotton, or requires a chemical treatment such as resination or crosslinking. Furthermore, they are difficult to control because slight variations of processing temperature and processing time result in either not sufficient treatment or heavy damaging of the fibers. While it would be highly desirable to have fabrics made of 100% man-made cellulosic fibers which are not crosslinked or resin-treated, e.g. for underwear, this was not available up to now for the reasons as outlined above.

Disclosure of the invention

[0011] Thus there is a need for fabrics made of or containing significant amounts of pilling-free man-made cellulosic fibers which are not crosslinked or resin-treated. [0012] The present invention provides for a method for reducing the pilling behaviour of a fabric containing or consisting of man-made cellulosic fibers, wherein said fabric is treated by the following sequence: a. Impregnation of the fabric with an aqueous liquor containing at least one kind of acid for a period of 1 to 20 min at between 10 and 30°C (preferably for 2 to 10 min at between 15 and 28°C, even more preferred for 2 to 6 min at between 15 and 28°C), b. Steaming of the impregnated fabric for a period of 2 to 20 min at between 90 and 105°C (preferably for 2 to 8 min at between 95 and 104°C), c. Washing the fabric neutral.

[0013] The method can be performed on conventional textile processing machines after appropriate, however only minor modification. By the method according to the invention a pilling grade of equal or higher than 3 can be achieved. In particular a pilling grade of more than 3 may be achieved, or even at least 4 or higher. For the purposes of the present invention pilling grade shall be understood as a pilling grade determined according to the Swiss Standard SN 198525:1990, using reference photographs. According to this standard the highest possible pilling grade is 5, i.e. defining the upper limit. Up to now such pilling grades of fabrics containing man-made cellulosic fibers can be only achieved by crosslinking or resination of the fabric. Preferably the acids used are non-volatile or low-volatile, in order not to harm the workers and the equipment used. Such acids are e.g. sulfuric acid, phosphoric acid, oxalic acid and polyacrylic acid. However such pollution can also be avoided by a housing of the treatment device. Preferably the acid is one that does not damage the material of the machines, which are used for performing the method. Usually such material is a stainless steel, as defined e.g. in EN 10020 and EN 10027. Commonly used stainless steels are also identified as 1.4301, 1.4541, 1.4307, 1.4401, 1.4571 and 1.4404.

[0014] Preferably the acid shows a pKs-value of equal or lower than 3.0. In case of polyprotonic acids, i.e. if more than one proton may dissociate, such as phosphoric acid, the first pKs-value, i.e. that of the first proton to dissociate shall be equal or lower than 3.0. The weaker the acid the longer the treatment time required. Sulfuric acid is particularly preferred for the method of the invention. A concentration of between 1.0 and 10.0 % sulfuric acid is preferred, more preferred between 1.2% and 7.0 %, even more preferred - especially if the cellulosic fibers are lyocell fibers - between 1.2 % and 3.5 %.

[0015] Generally for the present invention applies that if a concentration is given in then this means “weight-%”.

[0016] While the present invention will mainly be applied to fabrics containing or consisting of staple fibers, the teaching of the invention applies to endless filaments made according to the lyocell or modal process, as well. Therefore, for the purposes of the present invention, the term “fiber” means staple fibers as well as filaments.

[0017] The fabric containing or consisting of man-made cellulosic fibers may contain between 10% and 100% of man-made cellulosic fibers. Preferably the fabric may contain at least 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or even 95% of man-made cellulosic fibers. The remainder may be natural fibers like cotton and/or synthetic fibers like polyester, polyamide, elasthan fibers and/or other synthetic fibers.

[0018] In a preferred embodiment of the present invention the steaming of the impregnated fabric is done by a pad steam process. A pad steam process is preferred because it can be well controlled.

[0019] Preferably the man-made cellulosic fibers are lyocell fibers. In a preferred embodiment of the present invention the temperature and duration of the impregnation step, the concentration of the impregnation liquor and the temperature and duration of the steaming step are controlled in a way which results in fibers with an elongation at break (conditioned) of between 2.9 % and 5.0 %, preferably between 3.0 % and 5.0 %. The elongation at break (conditioned) was measured according to the commonly known method as described e.g. in the BISFA Booklet “Testing methods viscose, modal, lyocell and acetate staple fibres and tows”, Edition 2004. This feature was found surprisingly because no direct correlation between the elongation of a fiber and the pilling behavior of the fabric containing this fiber was known or even expected in the state of the art.

[0020] In another preferred embodiment of the present invention the man-made cellulosic fibers are modal fibers. A successful treatment of modal fibers requires a slightly higher acid concentration than the treatment of lyocell fibers, if the duration of the treatment is the same. Preferably the washing step c. of the method according to the invention is followed by an enzyme treatment as the step d.. Enzyme treatments of cellulosic fibers are generally known to the expert. However in the past it was only known that enzymes work not or only after impracticably long processing times. Now it was found that suitable enzymes are specific cellulase types, treatment times of between 30 and 60 min and pH values - depending on the specific enzyme used - of between 5.5 and 6.5. The enzyme activity then will be stopped by heating the mixture at a temperature of 80°C or even more for at least 10 min. Preferably the whole treatment should be done while applying vigorous action, thereby causing friction on the fabric by a suitable device, e.g. a garment dyeing machine (e.g. of the brand “T upesa”), followed by drying in a tumbler. Alternatively the enzyme treatment, washing and drying can be done in rope form in a jet dyeing machine (e.g. of manufacturer THEN, type Airflow).

[0021] For fabrics containing modal fibers preferably the temperature and duration of the impregnation step, the concentration of the impregnation liquor, the temperature and duration of the steaming step and the pH-value and the duration of the enzyme treatment are controlled in a way results in fibers with an elongation at break (conditioned) of between 6.0 % and 9.0 %. The elongation at break (conditioned) was measured according to the commonly known method as described e.g. in the BISFA Booklet “Testing methods viscose, modal, lyocell and acetate staple fibres and tows”, Edition 2004. This feature was found surprisingly because no direct correlation between the elongation of a fiber and the pilling behavior of the fabric containing this fiber was known or even expected in the state of the art.

[0022] Another aspect of the present invention is a fabric containing or consisting of lyocell fibers showing an elongation at break (conditioned) of between 2.9 % and 5.0 % for the manufacture of a fabric with a pilling grade of equal or higher than 3, that was not crosslinked or resin-treated. Preferably the pilling grade is higher than 3, in particular at least 4 or higher.

[0023] A further aspect of the present invention is the use of lyocell fibers showing an elongation at break (conditioned) of between 2.9 % and 5.0 %, available by the method of the invention as described above, for the manufacture of a fabric with a pilling grade of equal or higher than 3, wherein the fabric is not treated by crosslinking or resin treatment. Preferably the pilling grade is higher than 3, in particular at least 4 or higher.

[0024] Yet another aspect of the present invention is a fabric containing or consisting of modal fibers showing an elongation at break (conditioned) of between 6.0 % and 9.0 % for the manufacture of a fabric with a pilling grade of equal or higher than

3, that shows no crosslinking or resin treatment. Preferably the pilling grade is higher than 3, in particular at least 4 or higher.

[0025] Therefore a further aspect of the present invention is the use of modal fibers showing an elongation at break (conditioned) of between 6.0 % and 9.0 %, available by the method of the invention as described above, for the manufacture of a fabric with a pilling grade of equal or higher than 3, wherein the fabric is not treated by crosslinking or resin treatment. Preferably the pilling grade is higher than 3, in particular at least 4 or higher.

Examples [0026] The following examples further describe and demonstrate embodiments within the scope of the present invention. The examples are given solely for the purpose of illustration and are not to be construed as limitations of the present invention, as many variations thereof are possible without departing from the spirit and scope of the invention. [0027] Tenacity at break (conditioned) - (“FFk”), and elongation at break

(conditioned) - (“FDk”) - were measured according to the BISFA Booklet “Testing methods viscose, modal, lyocell and acetate staple fibres and tows”, Edition 2004.

[0028] Pilling grade was determined according to the Swiss Standard SN

198525:1990, using reference photographs. Grade 1 means very severe pilling while grade 5 means no pilling. From a commercial point of view grade 4 is acceptable and grade 5 is excellent, while grade 3 or lower means unacceptable appearance. Pilling grade was evaluated on the dried fabrics after the finish treatment, and again on some of the fabrics after the washing test.

Example 1: Lyocell fabrics [0029] The following knitted fabric was used: Interlock fabric made of an Nm 50/1 Ring yarn made of 100% lyocell staple fibers, 38mm/1.3 dtex (origin of the fibers: Lenzing Aktiengesellschaft, Austria).

[0030] For desizing the greige fabrics, the fabrics were prewashed for 20 minutes at 80°C using a lye with the following composition: 1.0 g/l Kieralon JET, 1.0 g/l sodium carbonate, 1.0 g/l Albaflow FFA, 1.0 g/l Persoftal L. Thereafter the fabrics were rinsed warm (10 min at 55°C) and cold (10 min at 20°C) with water.

[0031] Thereafter the fabrics were treated with acid according to the invention as follows: On a foulard the fabric was impregnated with 60 weight-% of a solution containing 1.5 weight-% resp. 3.0 weight-% sulfuric acid for a duration of 3 min at room temperature (25°C). Thereafter the impregnated fabric was steamed in a steamer for 3 min at 102°C with saturated steam. Thereafter it was rinsed warm (10 min at 55°C) and cold (10 min, 20°C).

[0032] Thereafter the fabrics were dyed in a laboratory dying machine (garment dyeing machine brand “T upesa”) with a liquor ratio of 1 : 10 (1 part fabric, 10 parts water, all by weight) as follows: Dyeing was done either with enzyme or without enzyme (see Table 1 below). All other steps were done identically for all samples. The dyeing liquor had 30°C and was adjusted to a pH 6 within 5 min. Then sodium sulfate (Glauber’s salt) was added to achieve a concentration of 55 g/l. 15 min later 2.5% dye stuff Levafix blue CA was added within 30 min at a pH of 6 (the percentage refers to the fabric weight). Subsequently 2% Lava Cell NSB was added at pH 6 (the percentage refers to the fabric weight). For dyeing without enzyme, at this stage no enzyme was added. 20 min later the temperature was increased within 30 min up to 60°C. At this stage sodium carbonate was added within 20 min to achieve a concentration of 2.8 g/l. Then further sodium carbonate was added within 20min to achieve a total concentration of 14 g/l. For the next 30 min everything was kept constant, then the temperature was reduced to 40°C within 10min.

[0033] Thereafter the dyed fabric was rinsed warm (55°C/10min) and cold (20°C/10min), neutralized with 1 ml/l acetic acid 60% for 15 min at 40°C, rinsed warm (55°C/10min) and cold (20°C/10min), soaped with 1 g/l Kieralon JET for 20 min at 90°C; rinsed warm (10 min at 55°C) and cold (10min, 20°C) ) . [0034] Thereafter a finish was applied: 2% Evosoft VNI for 20 min at 40°C and pH 6. Finally the dyed fabric was dried in a tumbler.

[0035] For the washing test the fabrics were washed 5 times at 40°C with intermediate tumbling according to the DIN EN ISO 6330 (February 2013) standard to imitate household washing conditions. Specific conditions were: Type A frontloading machine, Type III - 100 % Polyester, liquid household detergent, drying in a drying oven at 40°C.

[0036] The properties of the treated fabrics are described in Table 1. They show that the best results are obtained using 3.0 weight-% sulfuric acid. All acid-treated fabrics show an excellent washing behavior as can be derived from the pilling grade after washing. Enzymatic treatments give no further improvement in case of lyocell fibers and only would increase the treatment costs. However further increasing the acid concentration will damage the fabric to an unacceptable extent.

[0037] Table 1:

Pilling

Titer FFk FDk Pilling

Example Fiber Treatment grade dtex cN/tex % grade

(washed)

1.1 Lyocell Dyeing 1.29 35,0 9,6 1

1.2 Lyocell Dyeing + enzyme 1.30 29.5 7,5 3

1.3 Lyocell Acid 1 .5% + dyeing 1 ,26 22.6 4,9 4 5

Acid 1 .5% + dyeing + 5

1.4 Lyocell 1.29 18,8 4,4 4 enzyme

1.5 Lyocell Acid 3.0 % + dyeing 1 ,25 20.1 3,8 5 5

Acid 3.0 % + dyeing + 5

1.6 Lyocell 1.30 17.1 3,6 5 enzyme Example 2: Modal fabrics

[0038] The following knitted fabric was used: Interlock knitted fabric (greige) made of an Nm 50/1 Ring yarn, containing 100% modal fibers (38mm/1.3 dtex) (origin of the fibers: Lenzing Aktiengesellschaft, Austria)

[0039] These fabrics were prewashed in the same way as in Example 1. The acid treatment according to the invention was done in the same way as in Example 1. Thereafter a dyeing step with resp. without enzymatic treatment was applied in the same way as in Example 1. The finishing and washing were also done in the same way as described in Example 1.

[0040] The properties of the treated fabrics are described in Table 2. They show that the best results are obtained using 3.0 weight-% sulfuric acid plus enzymatic treatment in case of modal fibers. Acid or enzyme treatment alone or with 1.5% acid give no sufficient results. The combination of acid treatment and additional enzymatic treatment therefore is needed in case of modal fibers, at least as long as the acid concentration is 3.0% or lower.

[0041] These effects are even more visible after washing: While the washing behavior is even improved by an acid treatment with 3% sulfuric acid, the pilling grade (washed) after the treatments with less or no acid is worse.

[0042] Table 2:

Pilling

Titer FFk FDk Pilling

Example Fiber Treatment grade dtex cN/tex % grade

(washed)

2.1 Modal Dyeing 1 ,30 28,7 10,9 4 3

2.2 Modal Dyeing + enzyme 1 ,36 28,4 10,8 3

2.3 Modal Acid 1 .5% + dyeing 1 ,31 24,0 8,6 2 1-2

Modal Acid 1 .5% + dyeing 4

2.4 23,3 8,6

+ enzyme

2.5 Modal Acid 3.0 % + dyeing 1 ,34 22,6 8,7 3-4 4

Modal Acid 3.0 % + dyeing

2.6 1 ,27 23,0 8,5 5 + enzyme