GB2117314A - Polyvinyl chloride/cellulose acetate filaments - Google Patents

Abstract

The present invention relates to filaments, yarns and fibres consisting of 70% to 92% of polyvinyl chloride and 8 to 30% by weight of cellulose acetate, and to the process for their production. After shrinkage in boiling water, the said yarns and fibres have a tenacity of at least 20 cN/tex, preferably of at least 23 cN/tex, an elongation of less than 60%, preferably of less than 50%, an absorption capacity of at least 50%, preferably of at least 70%, and a shrinkage in boiling water and in steam at 105 DEG C of less than 5%. They are obtained by wet spinning, double stretching, stabilisation under tension and free shrinkage. The yarns and fibres according to the invention can be used for the production of woven fabrics, knitted fabrics and the like, which are capable of being dyed at the boil.

Description

SPECIFICATION Filaments, yarns and fibres based on polyvinyl chloride and the process for their production The present invention relates to filaments, yarns, fibres and other similar articles made of synthetic material, which consist of at least 70% by weight of ordinary polyvinyl chloride and up to 30% by weight of cellulose acetate.

Fibres based on polyvinyl chloride are valued in the textile field because of certain particular properties such as non-flammability, negative triboelectricity, resistance to light and chemical and electrical inertness. However, ordinary polyvinyl chloride, prepared by the process most commonly used, that is to say under the action of heat at temperatures of between 0 and 800 C, because this is the least expensive process, is a predominantly atactic polymer having a glass transition temperature (Tg) of the order of 65850C.Thus, the yarns and fibres obtained from atactic polyvinyl chloride by itself have, after stretching and setting, but before shrinkage, adequate mechanical properties for their textile conversion, but the finished articles have an excessively high shrinkage, which can be as much as 30%; if they are subjected at this stage to a shrinkage treatment, the mechanical properties which they then possess are insufficient to avoid restretching during textile conversion, which results in a shrinkage which is too large to allow these fibres to be dyed "at the boil", that is to say by a dyeing process at 980C.

With the aim of improving the properties of fibres based on polyvinyl chloride, new polymers have been developed from vinyl chloride by a technique based on the polymerisation carried out at temperatures below OOC and falling to -600C or even lower, in the presence of suitable catalysts which are effective at these low temperatures.

These new polymers, of predominantly syndiotactic structure, have a glass transition temperature (Tg) which is generally above 900-- 1 OO"C, which gives the yarns and fibres obtained a better heat resistance and considerably improved properties compared with the textile products derived from ordinary polyvinyl chloride.

French Application No. 2,161,084, published on 06.07.1 973, illustrates fibres based on this type of polymer and having good mechanical properties. However, a low-temperature polymerisation process of this type is an extremely expensive process which considerably increases the cost price of the fibres and makes their industrial production much less advantageous.

It has also been proposed, according to French Patent 1,359,178, to improve fibres and yarns based on polyvinyl chloride (PVC) by mixing ordinary polyvinyl chloride with post-chlorinated polyvinyl chloride. This solution, which indeed makes it possible to obtain yarns and fibres having better mechanical characteristics, is also a solution which is the more expensive industrially, the greater the proportion of post-chlorinated polyvinyl chloride added.

It has now been found that it is possible to obtain yarns and fibres containing a major proportion of ordinary polyvinyl chloride and possessing good mechanical characteristics, in particular a good tenacity, a relatively low elongation and a low residual shrinkage at the same time, enabling such yarns and fibres to be dyed at the boil after textile conversion, by adding a minor amount of cellulose acetate. Such yarns and fibres can furthermore be obtained by an economical and industrial continuous process.

More particularly, the present invention relates to filaments, yarns and fibres consisting of 70 to 92% by weight of ordinary polyvinyl chloride and 8 to 30% of cellulose acetate, and having, after shrinkage in boiling water, a tenacity of at least 20 cN/tex up to about 30 cN/tex, an elongation of less than 60% and a residual shrinkage in boiling water of less than 5%.

In general, they have a tenacity of at least 23 cN/tex, an elongation of less than 50%, a dimensional stability in saturated steam at 1050C of less than 5% and an absorption capacity according to the DIN Standard Specification of more than 50%, generally of more than 70%.

The present invention also relates to a process for the production of yarns and fibres containing 8 to 30% of cellulose acetate and 70 to 92% of polyvinyl chloride, which consists in spinning a solution having a polymer concentration of between 1 5 and 30% by weight into a coagulating bath containing 60 to 80% by weight of dimethylformamide and 20 to 40% of water, kept at low temperature, preferably at between 0 and 200C.The filaments are then subjected to a first stretching, which is carried out in a medium consisting of water and dimethylformamide, in a ratio of between 2 and 4x, preferably at a temperature which can be between about 5 and 400 C. The filaments are subsequently washed, generally with water, then stretched again in an aqueous fluid medium at a temperature above 900C, in a ratio of 2 to 4x, the total stretching ratio being between 4 and 11 x, sized, stabilized under tension in an aqueous fluid medium at a temperature greater than or equal to 1 OOOC, and then shrunk in the free state in an aqueous fluid medium at a temperature equal to or greater than 1000C.

The term "ordinary polyvinyl chloride" is understood as meaning essentially polyvinyl chloride having a glass transition temperature which is generally between 65 and 850C, and consisting predominantly of the atactic isomeric form. A polymer of this type is most commonly obtained in the least expensive manner by known techniques of polymerisation in bulk, in suspension or in emulsion, at temperatures generally above OOC, more generally of between 20 and 600C or even higher.

The expression "polyvinyl chloride" is also understood as meaning copolymers containing at least 95% (by weight) of vinyl chloride such as defined above, copolymerised with compounds containing an ethylenic double bond, such as vinyl acetate, vinylic and (meth)acrylic esters and ethers, acrylonitrile, and olefines such as ethylene.

The expression "cellulose acetate" is understood as meaning both the so-called secondary acetate and the triacetate, that is to say, in practice, a cellulose acetate in which the degree of substitution of the alcohol groups by the acetyl groups is between 1.8 and 3 per glucose unit (combined acetic acid level of between 45.68% and 62.5%).

Surprisingly, the yarns and fibres according to the present invention possess mechanical properties and a dimensional stability which are superior to those of the yarns and fibres derived from each of the constituents by itself. In particular, after shrinkage in boiling water, they have a tenacity of at least 20 cN/tex, preferably of at least 23 cN/tex, and an elongation of less than 60%, preferably of less than 50%, these two factors being essentially associated with a residual shrinkage in boiling water of less than 5%, more generally of less than 3%.

In fact, the tenacity and elongation values can only be of real significance when associated with the residual shrinkage, because, before the final shrinkage treatment, these two characteristics are at a higher level, but the residual shrinkage then remains much too large for it to be possible to convert such fibres while retaining advantageous textile properties.

Before carrying out the spinning operation, the solutions are prepared in the following manner: firstly, a dilute solution of cellulose acetate in dimethylformamide is prepared at ambient temperature, with stirring, and the polyvinyl chloride is then preferably added in powder form, with vigorous stirring, the temperature of the solution being lowered to less than 1 00C.

The solutions, having a concentration of between 1 5 and 30% by weight, preferably of 18 to 25%, are first heated to 800C until dissolution is complete, and then spun into an aqueous bath of dimethylformamide in which the proportions of dimethylformamide and water by weight vary from 60 to 80% of dimethylformamide and from 40 to 20% of water, the coagulating bath being kept at a temperature of between 0 and 200 C.

The filaments are taken up and subjected to a first stretching in a medium consisting of water and dimethylformamide in proportions of 30/70 to 70/30, in a ratio of between 2 and 4x, for example by passage over associated rollers or through a bath, at a temperature which can range from about 5 to 400 C, the value of the stretching ratio obviously depending on the medium and the temperature.

In particular, the stretching ratio is the higher, the higher the temperature.

The filaments are then washed with water, generally in counter-current, at a temperature which can vary from ambient temperature to 600 C, and stretched a second time in an aqueous fluid medium for example in a bath of boiling water or in a tube, in a ratio of between 2 and 4x, the overall stretching ratio being between 4 and 11 x.

After sizing in the usual manner, the filaments are stabilised under tension in an aqueous fluid medium at a temperature greater than or equal to 1000C. The stabilisation can be carried out, for example, by passage through a bath of boiling water or by stabilisation in the presence of pressurised steam for 1 to 3 seconds at a temperature of between 105 and 1 300C.

The free shrinkage is then carried out in an aqueous fluid medium, such as boiling water, for at least 10 minutes, preferably at least 20 minutes, or in saturated steam, for example by passage through a nozzle such as described in French Patent No.83/329-1,289,491. In a nozzle of this type, the filaments are treated with saturated steam at a temperature of between 105 and 1 300C and are simultaneously shrunk and crimped, which facilitates the subsequent textile conversion.

Likewise, when the shrinkage is carried out in boiling water, this is preferably preceded by mechanical crimping using any known process.

The yarns and fibres thus obtained possess better mechanical characteristics than fibres of pure polyvinyl chloride and fibres of pure cellulose acetate, in particular a better tenacity, a lower elongation associated with a good residual shrinkage, a better dimensional stability to heat treatment, which enables such fibres to be dyed at the boil, a good dyeing affinity for plastosoluble dyestuffs and, in particular, an excellent absorption capacity according to DIN Standard Specification 53,814, even for a small proportion of cellulose acetate, which is a totally surprising feature.

All the operations from the dissolution of the polymers onwards can be carried out continuously and hence under conditions which can easily be achieved industrially and which are economically advantageous.

The dissolved polymers spun according to the present Application can contain customary additives such as stabilisers, fluorescent brighteners, pigments, dyestuffs, plasticisers capable of improving some of their properties, such as colour, dyeing affinity, electrical resistivity, and the like.

A process of this type makes it possible to obtain, at an advantageous price, filaments which are capable of undergoing all the textile operations appropriate to the finishing of the filaments, and of being used, by themselves or blended with other yarns, for the production of woven fabrics, knitted fabrics, non-woven articles and the like, which can undergo the usual washing and dry-cleaning treatments under appropriate conditions without subsequent shrinkage.

The examples which follow, in which the parts are understood to be by weight, are given by way of indication, but do not limit the invention.

In the examples, the tenacity and elongation measurements are carried out by means of an instrument known commercially under the name Instron, by measurement of the maximum force which a sample can withstand relative to its gauge, this force being measured at constant elongation gradient.

Example 1 A 10% strength by weight solution of cellulose acetate (acetic acid level: 54.8%--degree of polymerisation (DP) of the order of 1 80 to 190) in dimethylformamide is prepared at ambient temperature, with stirring for 1 hour 30 minutes.

Atactic polyvinyl chloride (DP of the order of 900) is added to this solution, cooled to 50C, with vigorous stirring, in an amount such that the solution contains: 20% by weight of cellulose acetate, relative to the total amount of polymer, and 20% by weight of polymers, relative to the total solution.

This solution is then heated for 1 hour at 850C.

with stirring, and spun through a spinneret possessing 3,000 holes of diameter 0.12 mm, into a coagulating bath of dimethyl-formamide and water in a weight ratio of 68/32, kept at 80C.

The filaments are then stretched in an aqueous bath containing 35% of dimethylformamide, kept at 350C, in a ratio of 3x. They are subsequently washed in countercurrent at ambient temperature and then stretched again in a bath of boiling water, in a ratio of 3 x, and sized.

The filaments are subject to setting in a tube in the presence of pressurized steam at 1 200C for 2 seconds, and then to shrinkage in boiling water for 20 minutes.

The filaments obtained possess the following characteristics: gauge per strand (dtex) 3 tenacity (cN/tex) 22 elongation (%) 43 residual shrinkage (boiling water) (%) 3 comfort index (water retention capacity according to DIN Standard Specification 53,814 in 9/0) 74 shrinkage in saturated steam at 1050C(%) 3.5 shrinkage in saturated steam at 1150C(%) 7.5 Example 2 Firstly, a solution of cellulose acetate in dimethylformamide is prepared in the manner indicated in Example 1, and the polyvinyl chloride is then added in the presence of 3 parts per 1 ,000 of a stabiliser (relative to the polymer, the total polymer concentration being 20% by weight and the proportion of cellulose acetate, relative to the total weight of polymer, being 20%.Dissolution is carried out at 850C for 60 minutes, with stirring, and the solution is spun through a spinneret possessing 3,000 holes of diameter 0.12 mm.

into a coagulating bath, kept at 80C, consisting of 7% by weight of dimethylformamide and 30% of water.

The filaments are then stretched in a bath, kept at 35"C, consisting of dimethylformamide and water in a weight ratio of 35/65, in a ratio of 3x, washed in a counter-current of water, stretched in a second bath containing boiling water, in a ratio of 3x, and sized; the filaments are stabilised in the presence of pressurised steam at a temperature of 1 200C for 2 seconds and then shrunk in a bath of boiling water at 1000C for 20 minutes.

The filaments obtained possess the following characteristics: gauge per strand (dtex) 2.60 tenacity (cN/tex) 23 elongation (%) 43.5 residual shrinkage (boiling water) (%) 3 comfort index (water retention capacity according to DIN Standard Specification 53,814 in %) 63 shrinkage in saturated steam at 105 C (%) 3.5

Claims (14)

Claims

1. Filaments, yarns and fibres comprising 70 to 92% by weight of polyvinyl chloride and 8 to 30% by weight of cellulose acetate, and having, after shrinkage in boiling water, a tenacity of at least 20 cN/tex, an elongation at break of less than 60%, and a residual shrinkage in boiling water of less than 5%.

2. Filaments, yarns and fibres according to Claim 1, having a shrinkage in saturated steam at 1050C of less than 5%.

3. Filaments, yarns and fibres according to Claim 1, having a residual shrinkage in boiling water of less than 3%.

4. Filaments, yarns and fibres according to Claim 1, 2 or 3 having a tenacity of at least 23 cN/tex.

5. Filaments, yarns and fibres according to any of Claims 1 to 4 having an elongation of less than 50%.

6. Filaments, yarns and fibres according to any of Claims 1 to 5 having an absorption capacity according to DIN Standard Specification 53,814 of at least 50%.

7. Process for the production of filaments, yarns and fibres according to Claim 1, which comprises spinning a solution of the said polymers having a concentration of between 1 5 and 30% into a coagulating bath consisting of water and dimethylformamide in proportions by weight of between 60/80 and 20/40, kept at a temperature of between 0 and 15"C, stretching the filaments in a medium of water and dimethylformamide in a ratio of between 2 and 4x, washing and again stretching the filaments in an aqueous fluid medium at a temperature above 900C in a ratio of between 2 and 4x, the overall stretching ratio being between 6 and 11 x, sizing the filaments, subjecting them to a stabilisation treatment under tension in an aqueous fluid medium at a temperature equal to or greater than 1000C, and finally shrinking the filaments in the free state in an aqueous fluid medium at a temperature equal to or greater than 1000C.

8. Process according to Claim 7, in which the first stretching is carried out at a temperature of between 20 and 500C in a bath consisting of 30 to 70% by weight of dimethylformamide and 70 to 30% by weight of water.

9. Process according to Claim 7 or 8, in which the second stretching is carried out in a bath of boiling water.

10. Process according to Claim 7, 8 or 9, in which the stabilisation treatment under tension is carried out in a bath of boiling water.

11. Process according to Claim 7, 8 or 9 in which the stabilisation treatment is carried out in the presence of pressurised steam for 1 to 3 seconds at a temperature of between 105 and 1300C.

12. Process according to any of Claims 7 to 11, in which the free shrinkage treatment is carried out in boiling water for at least 10 minutes.

1 3. Process according to Claim 7 substantially as described in Example 1 or 2.

14. Filaments, yarns and fibres as claimed in Claim 1 when produced by the process of any of Claims 7 to 13.