PROCESS FOR IMPROVING THE TOUCH AND DRAPING CHARACTERISTICS OF TEXTILE PRODUCTS BASED ON POLYESTER

Abstract: A process for improving the touch and draping char­ acteristics of polyester-based textile products by controlled and discontinuous hot treatment with an aqueous solution of a hydrox­ ide of an alkaline metal containing a hydrolysis accelerator, selected from cetyl-trimethyl-ammonium bromide, lauryl dimethyl-benzyl-ammonium chloride, trimethyl-stearyl-­ ammonium methyl sulphate and dimethyl-ethyl-coco-ammonium­ ethyl sulfphate- in which the hydroxide amount of alkaline metal contained in the aqueous medium is adjusted as a function of the textile product weight loss to be obtained in the ratio 1 : 2.4 and in which the ratio: textile product weight/ aqueous solution volume ranges from 1:5 to 1:100.

Description: This invention relates to a process for improving the touch and draping characteristics of textile products based on polyester. The term "textile products based on polyester" as used herein covers threads, filaments, staple fibres, yarns, multi­ filament threads, either texturized or plain, and textiles, including non-woven fabrics, knitted yarns, non-laddering fab­ rics, fabrics for curtains etc., consisting of polyester or containing at least 50% of polyester and less than 50% of other natural, man-made or synthetic products. The term "polyester", as used in the present specifica­ tion and in the appended claims, denotes polymers preferably containing, in their recurring unit, the terephthalic group and being capable of forming fibres. Such polyesters are preparable by polycondensation of a glycol having the general formula: HO-(CH₂) n -OH, wherein n is an integer from 2 to 10, with an aromatic dicarb­ oxylic acid of formula: in which R₁ and R₂ represent the radical -(CH₂) m - in which m is zero or an integer from 1 to 4. Other copolymerizable bifunctional compounds may be incorporated in amounts up to 15% by weight. In order to improve the touch and draping characte­ ristics of textiles or textile products based on polyester it has been suggested, in GB-A-652,948, to subject such tex­ tiles to a heat treatment with an aqueous solution of an al­ kali metal hydroxide, in particular caustic soda or potash. Said treatment causes a weight loss of the fabric due to the dissolution of the polyester from the filament surface by hydrolysis. Said weight loss can be determined by weighing the dry textile before and after the treatment with the alka­ line solution. In practice, the treatment of a textile product based on polyester fibres with an alkaline solution for the purpose mentioned above involves, however, several problems, particu­ larly when the process is carried out on a commercial scale. In fact, in order to obtain a significant weight loss of the fabric and thus a sensible improvement of the touch and draping characteristics, it is necessary to employ highly concentrated solutions and/or very long periods of time and/or high temperatures. Under these conditions it is very difficult to control the hydrolysis step and as a consequence thereof the treatment with an alkali metal hydroxide does not afford reproducible results. In order to overcome the above drawbacks it has been suggested to add various substances which act as hydrolysis accelerators to the alkaline solution. Suitable hydrolysis accelerators may be quaternary am­ monium salts, preferably selected from cetyl-trimethylammonium bromide and lauryl-dimethyl-benzyl-ammonium chloride, or an ammonium sulphate selected from tri-methyl-stearyl-ammonium-­ methylsulphate and di-methyl-ethyl-coco-ammonium-ethylsulphate. The treatment with the alkaline solution containing one of the above accelerators can be carried out either dis­ continuously, for example in a jigger, jet or reel vat, or continuously, for example by padding and heat treatment with an air-vapour mixture. However, even if a solution of an alkali metal hydroxide is employed in the presence of a hydrolysis accelerator, the results are not satisfactory since the corresponding process still is not sufficiently reliable in terms of reproducibili­ ty. GB-A-922406 describes a process for treating crimped oriented synthetic polymer filaments or fibres (made, among others, of polyester), before heat-setting the crimp to reduce residual shrinkage in boiling water for one minute to less than 1%, with a chemical agent (among others sodium hydroxide) under conditions such that the filaments or fibres are weakened) at intervals corresponding to the apexes of their crimp by the uniform application of the chemical agent. US-A-4,370,143 is directed to a process for imparting improved soil-release, moisture-wicking, soil-redeposition, and anti-static properties to a polyester fabric wherein said fabric is immersed in an alkaline bath, the pH of the alkaline bath is adjusted to a value of 5.5 or less and a certain type of polyester copolymer is added to said bath. It is an object of the present invention to provide a process free from the drawbacks cited hereinbefore. More particularly, the object of the present invention is to provide a process for the discontinuous treatment of textile products based on polyester which permits to obtain both uniformity and reproducibility of the treatment. It has now been found that this and still other objects are achieved by a process for improving the touch and draping characteristics of textile products based on at least 50% of polyester by discontinuous heat treatment with an aqueous so­ lution of an alkali metal hydroxide containing a hydrolysis accelerator, wherein the amount of the alkali metal hydroxide contained in the solution is adjusted as a function of the desired weight loss of the textile product so as to result in a weight ratio of 1 (amount of alkali metal hydroxide) :2.4 (weight loss), and wherein the ratio: weight of the starting textile product (in kg) /volume of aqueous solution (in 1) ranges from 1:5 to 1:100. The amount of hydrolysis accelerator is not critical in the process of the present invention, although higher amounts than 0.5 g/l of solution are preferred. Said amounts vary as a function of temperature and treatment time and can range from 1 to 10 g/l for a temperature range of from 140° to 60°C and a treatment time of from 30 to 240 minutes. The process of the present invention can be conducted in any discontinuously operating device, such as a jigger, jet, reel vat etc. In order to optimize the mechanical characteristics of the textile articles obtained by the process of the present invention it is preferable, in most cases, to subject the tex­ tile product, prior to the treatment with the solution of an alkali-metal hydroxide, to a scouring and heat-setting opera­ tion. Heat-setting is conducted in dry hot air at a tempera­ ture of from 160 to 220°C. The characteristics of the textile product obtained can be optimized also by subjecting said product to washing with an alkaline solution, subsequent to the treatment with the solution of an alkali metal hydroxide and prior to an op­ tional neutralization treatment. The process of the present invention permits to obtain predetermined results, which are perfectly reproducible and independent of count and structure of the treated textile pro­ duct. The present invention is further illustrated by the following examples, which are given for merely illustrative purposes. EXAMPLE 1 100 kg of a shuttle fabric weighing 100 g/m², consisting in warp and weft of polyethylene terephthalate yarn having a count of 50/36 dtex, was immersed,after scouring and heat setting at 190°C in a Rameuse for 30 seconds, into a jet con­ taining 2000 l of an aqueous solution of 10 kg of hydrated sodium hydroxide and 4 kg of dimethyl-benzyl-laurylammonium chloride, prepared at 50°C. The fabric was kept in said solu­ tion at 110°C for 60 minutes. Subsequently it was cooled, the solution was discharged and the fabric was repeatedly washed, neutralized with diluted acetic acid and air-dried at 110°C. The final weight of the fabric was 76 kg, which corresponded to a weight loss of 24%. The touch and draping characteristics of the thus trea­ ted fabric were exactly like those of a corresponding silk fabric. EXAMPLE 2 The same results as in example 1 as regards weight loss as well as touch and draping characteristics were obtained by treating, under the conditions described in example 1, shuttle fabrics made from polyethylene terephthalate yarn and having hte following counts: 33/10 dtex, 33/24 dtex, 50/10 dtex, 50/48 dtex, 78/36 dtex, 110/48 dtex, 167/30 dtex and 167/72 dtex; or circular knitted fabrics or non-ladding fab­ rics produced from polyethylene terephthalate yarns having the above counts. EXAMPLE 3 The same results as regards weight loss, touch and dra­ ping characteristics as in example 1 were obtained by varying, in the process of example 1, the treatment temperature from 60 minutes to 240 minutes or by changing the amount of accele­ rator from 2 g/l to 1 g/l or to 5 g/l.

Claims: 1. Process for improving the touch and draping characteristics of textile products based on at least 50% of polyester by discontinuous heat treatment with an aqueous solution of an alkali metal hydroxide containing a hydrolysis accelerator, characterized in that the amount of alkali metal hydroxide contained in the solution is adjusted as a function of the desired weight loss of the textile product so as to result in a weight ratio alkali metal hydroxide/desired weight loss of 1:2.4 and that the ratio:weight of the starting textile product (in kg) to volume of said aqueous solution (in liter) ranges from 1:5 to 1:100. 2. Process according to claim 1, wherein the amount of hydro­ lysis accelerator is higher than 0.5 g/l of solution. 3. Process according to claim 2, wherein the amount of hydro­ lysis accelerator ranges from 1 to 10 g/l. 4. Process according to any of the preceding claims, in which the treatment is conducted at a temperature ranging from 140° to 60°C for 30 to 240 minutes. 5. Process according to any of the preceding claims, in which the hydrolysis accelerator is selected from cetyl-trimethyl-­ ammonium bromide, lauryl-dimethyl-benzyl-ammonium chloride, trimethyl-stearyl-ammonium methyl sulphate and dimethyl­ ethyl-coco-ammonium-ethyl sulphate.

Inventors: BORGIS, ROBERTO, HONORATI, GIORGIO
Applicants: MONTEFIBRE S.P.A.
Application year: 1986
Main classification: D06M11
IPC codes: D06M13, D06M11