GB2118478A - Filaments, yarns and fibres based on polyvinyl chloride - Google Patents

Abstract

The present invention relates to filaments, yarns and fibres consisting of 75 to 92% of polyvinyl chloride and 8 to 25% by weight of acrylic polymer. After shrinkage in boiling water, the said filaments, yarns and fibres possess a tenacity of at least 20 cN/tex, preferably at least 25 cN/tex, an elongation less than 60%, preferably less than 50%, and a residual shrinkage in boiling water less than 5%, preferably below 2%. These filaments are obtained by wet spinning, double stretching, stabilization under tension, and free shrinkage. They can be used for the production of woven and 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 process for their production The present invention relates to filaments, yarns, fibres and other similar articles made of at least 75% by weight of ordinary polyvinyl chloride and up to 25% by weight of acrylic polymer.

Fibres based on polyvinyl chloride are valued in the textile field because of certain particular properties such as non-flammabiity, negative triboelectricity, resistance to light, chemical inertness and thermal, accoustic and electrical insulating power. 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 80"C, because this is the least expensive process, is a predominantly atactic polymer having a glass transition temperature (Tg) of the order of 65-85"C. Thus, the yarns and fibres obtained from atactic polyvinyl chloride by itself have, after stretching and stabilisation and 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 customary 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 polymerisation carried out at temperatures below 0 C and falling to -60 C 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 90 -100 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 06.07.1973, 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.

To improve the dissolution of syndiotactic polyvinyl chloride, attempts have been made to mix it with 5 to 50% by weight of polyacrylonitrile so as to obtain stable solutions at high temperature. However, a mixture of this type does not solve the problem of the cost price of syndiotactic polyvinyl chloride.

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 preponderant proportion of ordinary polyvinyl chloride and possessing good mechanical characteristics, in particular both a good tenacity and an elongation which is not excessive, associated with a low residual shrinkage, and also a good dimensional stability, which yarns and fibres are capable of being dyed by the process of dyeing at the boil, by adding a small amount of acrylic polymer to ordinary polyvinyl chloride by means of a continuous industrial process, that is to say under advantageous economic conditions.

More particularly, the present invention relates to filaments, yarns and fibres consisting of 75 to 92% by weight of ordinary polyvinyl chloride and 8 to 25% by weight of acrylic polymer, and possessing, after shrinkage in boiling water, a tenacity of at least 20 cN/tex up to about 38 cN/tex, an elongation at break of less than 60% and a residual shrinkage in boiling water of less than 5%.

Preferably, the tenacity is at least 25 cN/tex, the elongation at break is less than 50% and the shrinkage in saturated steam at 10500 is less than or equal to 10%.

The present invention also relates to a process for the production of yarns and fibres based on 75 to 92% by weight of polyvinyl chloride and 8 to 25% of an acrylic polymer, which consists in spinning a solution having a polymer concentration of between 15 and 30%, preferably of 20 to 25%, into a coagulating bath containing from 65 to 90% by weight of dimethylformamide and 35 to 10% by weight of water, preferably 75 to 90% by weight of dimethylformamide and 25 to 10% by weight of water, kept at a temperature of between 0 and 15"C, in carrying out a first stretching of the filaments in a water/dimethylformamide medium, preferably at between 20 and 50"C, in a ratio of between 2 and 4 X, in washing the said filaments and in stretching the filaments again in an aqueous fluid medium, at a temperature above 90"C, in a ratio of between 3 and 5 X, the overall stretching ratio being between 6 and 10 X; the filaments are subsequently sized and then subjected to stabilisation under tension in an aqueous fluid medium at a temperature greater than or equal to 10000, and then to shrinkage in the free state in an aqueous fluid medium at a temperature greater than or equal to 1000C.

The term "ordinary polyvinyl chloride" is understood as meaning essentially polyvinyl chloride having a glass transition temperature which is generally between 65 and 85"C, 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 0 C and more generally of between 20 and 60"C 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 term "acrylic polymer" is understood as meaning polymers containing at least 85% by weight of acrylonitrile and up to 15% by weight of units derived from one or more ethylenic monomers which can be copolymerised with acrylonitrile, such as vinylic compounds, for example vinyl chloride and acetate, acrylic or methacrylic acids, acid esters and acid amides, methacrylonitrile, compounds containing a carboxylic acid group, such as itaconic acid, or containing a sulphonic acid group, such as vinylsulphonic compounds, allylsulphonic and methallylsulphonic acids, sulphonated aromatic derivatives, styrenesulphonic and vinyloxyarenesulphonic acids, vinylic derivatives of the basic type, such as vinylpyridine and its alkylated derivatives, vinyl dialkylamine ethers, and the like. However, acrylonitrile copolymers will be used in preference to the homopolymer.

While retaining the advantageous properties of polyvinyl chloride fibres, in particular the non-flammability and the insulating power, the filaments, yarns and fibres according to the present invention surprisingly possess very advantageous mechanical characteristics, even with a small amount of acrylic polymer of less than 25%: after shrinkage in boiling water, they have a tenacity of at least 20 cN/tex, preferably of at least 25 cN/tex, and an elongation at break of less than 60%, preferably of less than 50%, these two characteristics only being important when associated with a residual shrinkage in boiling water of less than 5%, preferably of less than 2%.

Furthermore, the yarns and fibres have a dimensional stability in steam at 105 C which is such that their residual shrinkage is less than 7%.

The yarns and fibres according to the present invention are obtained in the following manner: the two polymers are first introduced cold into dimethylformamide, in the desired proportions, and then the solution is stirred and heated to a temperature of at least 80 C, the total polymer concentration of the solution being between 15 and 30%, preferably between 20 and 25%.The solution thus obtained is spun into a coagulating bath consisting of 65 to 90% by weight of dimethylformamide and 35 to 10% by weight of water, kept at a low temperature which is generally between 0 and 15"C, preferably between Sand 1000. The filaments are then stretched a first time in a medium consisting of dimethylformamide and water, generally in proportions of 30-70% to 70-30% by weight, by passage over suitable rollers or through a tank, in a ratio of 2 to 4 X, preferably at between 10 and 50 C, the stretching ratio being the higher, the higher the temperature, and are then washed, generally in a counter-current of water, at ambient temperature in a horizontal tank.During the washing, they can be subjected to a small degree of controlled shrinkage, simply by adjusting the rollers.

The filaments are stretched again in an aqueous fluid medium, at a temperature of at least 90"C, preferably in a bath of boiling water, if appropriate in a tube, in a ratio of between 3 and 5 X, and are then sized in the usual manner.

They are then subjected to stabilisation under tension in an aqueous fluid medium at a temperature greater than or equal to 100 C; this can be carried out either by passage through a bath of boiling water, or by stabilisation in pressurised steam for 1 to 3 seconds at a temperature of between 105 and 1 30"C.

The filaments are then shrunk in an aqueous fluid medium at a temperature of between 98OC and 130"C.

The free shrinkage can be carried out in boiling water for a variable period of time, for example at least 10 minutes, generally from 10 to 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 10500 and 130"C and are simultaneously shrunk and crimped, which permits a better subsequent textile workability. Likewise, in the case where the shrinkage is carried out in boiling water, this is preferably preceded by mechanical crimping using any known process, for the same purpose of facilitating the subsequent workability.

All the operations from dissolution 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 which follow, the tenacity and elongation values are measured 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 - Firstly, 4 parts by weight of a copolymer consisting of 91.4% by weight of acrylonitrile, 7.75% of methyl methacrylate and 0.85% of sodium methallysulphonate, and then 16 parts of atactic polyvinyl chloride, are introduced into dimethylformamide kept at about 5"C, so as to give a solution having a total polymer concentration of 20% by weight: this solution is subsequently heated to 85 C and then spun through a spinneret possessing 2,750 orifices into a coagulating bath kept at 8"C and containing 85% by weight of dimethylformamide and 15% of water. The filaments pass through a second tank kept at 35"C and containing 35% by weight of dimethylformamide and 65% of water, where they are subjected to stretching in a ratio of 3 X.After washing in a counter-current of water, they are subjected to a further stretching in a ratio of 3 X in a tank of boiling water, and are then sized.

They are then set under tension in the presence of pressurised steam for two seconds at a temperature of 120"C, before being shrunk in a bath of boiling water for 20 minutes. The characteristics of the filaments obtained are collated in the table below.

B - A solution of pure atactic polyvinyl chloride having a concentration of 20% by weight is prepared and spun in the manner indicated above. The filaments obtained are then treated in the manner indicated under A.

The characteristics of the filaments obtained are collated in the table below.

Example 1A A Example 1 B tenacity, cN/tex 28 18 elongation, % 50 60 residual shrinkage, % (boiling water) < 5 < 5 gauge per strand, dtex 2.0 2.0 residual shrinkage in saturated steam at 1050C,% 8 24 Example 2 Firstly, two parts by weight of a copolymer consisting of 91.4% by weight of acrylonitrile, 7.75% of methyl ethacrylate and 0.85% of sodium methallylsulphonate, and then 18 parts of afactic polyvinyl chloride, are introduced into dimethylformamide kept at about 5"C: this gives a solution having a total polymer concentration of 20% by weight.This solution is subsequently heated to 850C and then spun through a spinneret possessing 2,750 orifices into a coagulating bath kept at 80C and containing 85% by weight of dimethylformamide and 15% of water.

The filaments pass through a second tank kept at 350C and containing 35% by weight of dimethylformamide and 65% of water, where they are subjected to stretching in a ratio of 2.5 X. They are subsequently washed in a counter-current of water at ambient temperature and then stretched again in a bath of boiling water in a ratio of 3.52 X, and sized. They are set under tension in a bath of boiling water before being shrunk, again in a bath of boiling water, for 20 minutes.

The filaments thus obtained possess the following characteristics: tenacity, cN/tex 21 elongaton, % 55 residual shrinkage, % (boiling water) < 5 gauge per strand, dtex 1.63 residual shrinkage in saturated steam at 105 C, % 10

Claims (14)

1. Filaments, yarns and fibres comprising 75 to 92% by weight of polyvinyl chloride and 8 to 25% by weight of acrylic polymer, and having, after shrinkage in boiling water, a residual shrinkage in boiling water of less than 5%, a tenacity of at least 20 cN/tex, and an elongation at break of less than 60%.

2. Filaments, yarns and fibres according to Claim 1, having a residual shrinkage of less than 2%, measured in boiling water.

3. Filaments, yarns and fibres according to Claim 1 or 2, having a tenacity of at least 25 cN/tex.

4. Filaments, yarns and fibres according to Claim 1,2 or 3, having an elongation at break of less than 50%.

5. Filaments, yarns and fibres according to any of Claims 1 to 4, having a shrinkage in saturated steam at 105"C of less than 10%.

6. 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 15 and 30% into a coagulating bath consisting of 65 to 90% by weight of dimethylformamide and 10 to 35% by weight of water 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 4 X, washing and again stretching the filaments in an aqueous fluid medium at a temperature above 90"C in a ratio between 3 and 5 X, the overall stretching ratio being between 6 and 10 X, sizing the filaments, and subjecting them to a stabilization treatment under tension in an aqueous fluid medium at a temperature greater than or equal to 100"C, and finally shrinking the filaments in the free state in an aqueous medium at a temperature of at least 100 C.

7. Process according to Claim 6 in which the first stretching is effected in a medium comprising 30 to 70% by weight of dimethylformamide and 70 to 30% of water.

8. Process according to Claim 6 or 7 in which the first stretching is effected at a temperature of 10 to 50"C.

9. Process according to any of Claims 6 to 8 in which the second stretching is effected in a bath of boiling water.

10. Process according to any of Claims 6 to 9 in which the stabilization treatment is effected in a bath of boiling water.

11. Process according to any of Claims 6 to 9 in which the stabilization treatment is effected in the presence of pressurized steam for 1 to 3 seconds at a temperature between 105 and 130 C.

12. Process according to any of Claims 6 to 11 in which the free shrinking treatment is carried out in boiling water for at least 10 minutes.

13. Process according to Claim 6 substantially as described in the Example.

14. Filaments, yarns and fibres as claimed in Claim 1 when produced by the process of any of Claims 6 to 13.