GB2091769A - Process for de-sizing and bleaching woven fabrics - Google Patents

Abstract

A process for de-sizing and bleaching fabrics in a single operation which process comprises treating the fabric in a bath comprising sodium chlorite, a base, an activating agent, and an enzymatic preparation including a starch-degrading enzyme and a surfactant.

Description

SPECIFICATION Process for de-sizing and bleaching woven fabrics This invention relates to a process for de-sizing and bleaching in a single operation woven fabrics or similar materials based on textile fibres.

It is known that the treatment of fabrics made of cellulose fibres, by dyeing, printing and otherfinishing treatments, generally comprises the operations of de-sizing, boiling off, bleaching and, optionally mercerising.

The purpose of de-sizing is to remove the sizing products previously applied to the warp threads to improve their properties on the loom, and any sizing material which may have been applied to the weft threads.

The sizing products applied to the threads before weaving may be based either on starch dispersions alone or in admixture with starches which may have been subjected to chemical treatments, or may be based on polyvinyl alcohol derivatives, polyacrylate derivatives or etherified cellulose.

The sizing products may be retained in the fabric in varying amounts, depending on the drying temperature, and twisting of the threads and the texture of the fabric.

The presence of such products makes it impossible to obtain a uniform, solid colour shade during dyeing and printing with many dyes, and this means that the sizing products have to be eliminated before the dyeing or printing operations can be carried out.

For some fabrics intended for white garments or other white articles, the removal of the size is also desirable to ensure that the treated goods are pleasant and supple to the touch.

De-sizing is generally effected by impregnation in a bath of enzymes and surfactant heated to a temperature of from 60"C to 75"C. The impregnated fabric may either be left to stand or steamed at a temperature of 100"C. It is then washed at 95 C, then at 60"C, and optionally in running water.

Boiling off, which is designed to saponify the greases in the cotton and solubilise the ligneous residues, is effected in a caustic soda medium at a temperature of from 100 C to 140"C.

The purpose of bleaching isto oxidisethe impurities which are a part of the unbleached or already boiled off cotton, linen or any other cellulose fibre. In virtually every case, bleaching is carried out with oxidising agents such as hydrogen peroxide, alkali peroxides and per-salts, peracetic acid, sodium hypochlorite and sodium chlorite.

The operations of de-sizing, boiling off and bleaching are generally carried out in an aqueous medium, with heat. Each operation is followed by hot and cold washes, resulting in considerable water and energy consumption.

The aim of the present invention is to reduce the number of operations for the preparation of fabric based on cellulose fibres, either alone or mixed with other cellulose fibres or with other regenerated or chemical fibres, such as viscoses, polyamides and polyesters; the present invention further provides a new process in which de-sizing and bleaching are combined in a single operation.

The process of de-sizing and bleaching in a single operation according to this invention is carried out in a bath containing sodium chlorite, a base such as sodium hydroxide, optionally an activating agent, and an enzymatic preparation which includes a starch-degrading enzyme and a surfactant.

An enzymatic preparation suitable for use in accordance with the invention is for example the preparation which is described in German Patent Application P 2909396.7, and which consists of an intimate mixture of a starch-degrading enzyme, such as amylase, and a non-ionic surfactant chosen from alkoyl and alkaryl oxalkoylates in water. An appropriate enzymatic composition is for example composed of 10 to 40 parts of aqueous enzymatic preparation and 10 to 60 parts of a non-ionic surfactant.

Particularly good results are obtained when using an enzymatic preparation sold underthetradename Enzylase C by Messrs DIAMALT.

The process is preferably carried out using the following steps: 1) Impregnating the fabric in the de-sizing and bleaching bath; squeezing out, so as to leave in the fabric only the quantity of liquor necessary for the reaction. This is generally from 60 to 120% of the weight of dry fabric, depending on the fabric in question.

2) Steaming, to bring the fabric to the desired reaction temperature, generally from 20 to 1 20"C.

3) Depositing the fabric by rolling up or folding into pleasts in a J-Box, U-Box, carpet machine... for a time which may vary from a few minutes to several hours.

The treatment is followed by washing at 90 95"C, 60"C and then a cold wash. The washing bath at 90"C - 95"C may advantageously contain added alkaline components, caustic soda, sodium carbonate, trisodium phosphate and surface-active detergents.

One of the advantages of the process according to the invention is that it does away with a wet desizing operation carried out at a minimum temperature of 60 -650C, and several washing baths at temperatures of 90" - 95"C.

The use of the process also does away with a "wet on wet" impregnation, i.e. wet fabric being put in a bath containing the bleaching products. It is known that this treatment involves a number of procedures: preparation of a more concentrated bath, maintaining the impregnation bath at a constant level and concentration, which requires either manual checking or automatic adjustment.

To avoid "wet on wet" impregnation, some users adopt the procedure of an intermediate passage over a drying tenter, which involves the use of expensive equipment and a substantial energy consumption, particularly heat.

The use of the process according to the invention therefore results in major savings in water, steam, labour and investment costs.

The characteristics of the fabric thus treated are excellent: a high degree of whiteness, virtually total elimination of the size, instant hydrophilism, a satisfactory degree of polymerisation.

The following Examples illustrate the invention without restricting it.

EXAMPLE 1 A cotton fabric weighing 138 gim2, width 150 cm, reflcstance 49.6%, measured with an ELREPHO ZEISS reflectometer, no. 8 filter, waveiength 457 nonme. res, size content 7.85%, starch content 4%, intended to be printed with reactive dyes, was impregnatcd directly after being woven, in a bath contain.ng: 25% by weight sodium chlorite 80 mill Activating agent UG 45 15 gll Enzylase C 10 gll Ukanil 1036, detergent wetting agent 0.5 mIll Sodium hydroxide is added to give a pH of 9.2 - 9.5.

The fabric, impregnated with 106% of its weight of bath liquor, is heated to 95"C by steaming.

It is rolled up in a heat-insulated chamber, where it continues to react at 950C for 1 hour 30 minutes.

Afterthistime, it is unrolled and rinsed continu ousiy in a series of vats: the first contains water heated to 95"C; the second contains water heated to 95"C and sodium carbonate: 3-5 girl; the third contains water at 600C; the fourth contains cold water.

After drying, the fabric has the following characteristics: Reflectance (ELREPHO ZEISS) 82.8% Residual starch content 0.16% Instant hydrophilism.

EXAMPLE 2 A particularly grey and rough basket-weave cotton fabric which normally requires a de-sizing treatment and two bleaching treatments was singed and then subjected to de-sizing and bleaching, in a single operation.

The fabric,150 cm wide, weighing 180 g per m2, had a reflectance of 49.5% and a starch content of 7.25%.

It was impregnated in a bath containing: 25% by weight sodium chlorite 90 mIll Activating agent UG 45 18 g/l Enzylase C 10 g/l Ukanil 1036 1 ml/l Sodium hydroxide is added to give a pH of 9.2 - 9.5.

The fabric is moved at a speed of 70 metres per minute and picks up 94.5% of its own weight of the bath liquor. It is heated to 850C by passing it into a steamer and is then rolled up in an insulated chamber.

After 21 hours' reaction at 85"C, it is unrolled and then washed continuously under the conditions described in Example 1.

After drying, the bleached fabric has the following characteristics: ELREPHO reflectance 80.1% Residual starch content 0.18% Subsequent dyeing with reactive dyes gives excellent results.

EXAMPLE 3 A Hacabah cotton fabric, unbleached reflectance 52.8%, starch content 6.60%, was treated, immediately after being woven, in a bath containing: Sodium hypochlorite expressed as 100% NaClO2 27 g/l Activating agent UG 45 14 g/l Enzylase C 10 gll Ukanil 1036 0.5 ml/l Sodium hydroxide is added to adjust the pH to 9.2 9.5.

The fabric, ravelling at a rate of 85 metres per minute, was impregnated with 102% of its weight of bath liquor and steamed at 95" - 98 C. The fabric was rolled up and kept for two hours at a temperature of 90" - 92"C. It was then subjected to washes at 90"C with the addition of sodium carbonate, at 600C and then in the cold. After drying, the bleached fabric had the following characteristics: Reflectance 77% Residual starch content 0.15% Instant hydrophilism.

The conventional treatment usually comprises de-sizing by impregnation in a bath heated to 65"C, then leaving the fabric in a heat-insulated chamber, followed by washing at 95C - 60"C, and then by a cold wash. The fabric is dried on a tenter, and then bleached by impregnation. It is then steamed at 95"C, stored at 85"C for 22 hours, and finally washed at 95"C - 60"C and then in a cold wash.

EXAMPLE 4 A cream linen-cotton mixture, with unbleached cotton warp threads and cream linen weft, cm wide, weighing 525 g per m2, starch content 5.70%, was singed then treated as follows: Impregnation in a bath containing, per 800 litres: 25% sodium chlorite 105 i Activating agent UG 45 18.4 kg Enzylase C 8.0 kg Ukanil 1036 1.61 Sodium hydroxide is added to give a pH of 9.2 - 9.5.

The linenlcotton mixture, impregnated at a speed of 40 -45 metres/minute, picks up 75% of its weight of bath liquor, passes into a steamer heated to 90"C and is then left rolled up in a chamber maintained at 85 -90 for3 hours.

It is then washed at 90 metreslminute under conditions analogous to those described above.

After drying, the fabric has the following characteristics: Reflectance 79% Residual starch content 0.56% Instant hydrophilism EXAMPLE 5 A 65/35 polyesterlcotton poplin, weight 130 glum2, unbleached reflectance 69.4% was impregnated at 98"C with its own weight of: Sodium chlorite, 25% of its weight 33 mIll Activating agent UG 45 7 gll Enzylase C 10 gIl Ukanil 1036 0.5 ml/l Sodium hydroxide is added to give a pH of 9.2-9.5.

The fabric was steamed at 98"C, then kept at this temperature for 12 hours.

It was then washed in water at 95"C with 3 gll of NaCOa, then in water at 60 C and finally in a cold wash.

After drying, the bleached fabric has the following characteristics: Reflectance 83.2% Residual starch content 0% Instant hydrophilism EXAMPLE 6 A cotton sheet fabric intended to be printed, width 240 cm, weight 318 g per running metre, reflectance 59.4% starch content 7.82% of the weight of the fabric, was treated in a bath containing: Enzylase C 10 gel Ukanil 1036 0.5 mIll The bath is heated to 1000C for 55 minutes, then cooled to 70"C, and the following are added: 25% sodium chlorite, expressed as 100% NaCIO2 3 g/l Activating agent UG 45 1.2 g/l Formic acid for pH 4.

This is heated for 30 minutes to 100"C and maintained at 1 OO"C for 30 minutes. The fabric is drained, then rinsed hot and cold and dried on a tenter.

The fabric thus de-sized and bleached has the following characteristics: Reflectance 80.3% Starch content 0 Instant hydrophilism.

Claims (5)

1. A process for de-sizing and bleaching fabrics in a single operation which process comprises treating the fabric in a bath comprising sodium chlorite, a base, an activating agent, and an enzymatic preparation including a starch-degrading enzyme and a surfactant.

2. A process according to Claim 1, wherein the enzymatic preparation comprises 10 to 40 parts aqueous enzymatic preparation and 10 to 60 parts of a non-ionic surfactant.

3. A process according to Claim 1 or 2, wherein the enzymatic preparation is Enzylase C.

4. A process according to Claim 1 substantially as hereinbefore described in Example 1,2 or3.

5. A de-sized and bleached fabric whenever obtained by a process as claimed in any one of the preceding claims.