EP0019870B1 - Filaments and fibres of acrylonitrile copolymer blends, and process for manufacturing them - Google Patents

Abstract

The invention relates to flame-retarding filaments and fibers and a process for the manufacture thereof. The filament-forming substance is a mixture of from 20 to 70 weight % of an acrylonitrile copolymer A containing at least 80 weight % of acrylonitrile units and from 0.3 to 20 weight % of other units copolymerizable with acrylonitrile, and from 80 to 30 weight % of an acrylonitrile copolymer B containing from 50 to 75 weight % of acrylonitrile units, from 25 to 45 weight % of vinyl chloride and/or vinylidene chloride units and from 0 to 5 weight % of other units copolymerizable with acrylonitrile. The filaments and fibers have a boil-off shrinkage of at least 20% and a knot strength of at least 10 cN/tex and are obtained by spinning the turbid solutions of the copolymer mixture, which however do not separate into components, in an aprotic solvent, and drawing of the filaments in a moderate ratio.

Description

The invention relates to flame-retardant acrylic threads and fibers which, in addition to high shrinkage, in particular have low brittleness, and processes for their production. The thread-forming substance of these threads and fibers consists of a mixture of different acrylonitrile copolymers which do not form a homogeneous solution in the aprotic solvents used for spinning, but also do not separate.

It is known to produce acrylic fibers with high shrinkage values. Such a method is described, for example, in German Offenlegungsschrift 2 532 120. Such high shrinkage threads can then be obtained by fixing the non-stretched spun threads instead of steam and then stretching them by a factor of 1: 3.5 to 1: 5.0. However, high-shrinkage fibers produced in this way have a high degree of brittleness, which leads to considerable difficulties in the further processing of the fibers and thus to a reduced usability. In addition, these acrylic fibers have no flame-retardant properties.

It is also known that threads made from copolymers of acrylonitrile have a sharply increasing shrinkage value with increasing content of vinyl chloride or vinylidene chloride building blocks. Since such comonomer constituents can impart flame-retardant properties to the threads and fibers, there has been no lack of attempts to improve the usability of the fibers from such copolymers.

For example, fibers are known which e.g. consist of a polymer with 60% acrylonitrile and 40% vinyl chloride, have a shrinkage of more than 30% and also have good knot strength. The major disadvantage of these fibers made from such copolymers, however, is that they have a temperature resistance that is too low and that the shrinkage values are very dependent on the treatment temperature. If such threads are shrunk out, for example, by treatment in boiling water, a subsequent heat treatment leads to further severe shrinkage even at slightly higher temperatures. At temperatures around 150 ° C, the shrinkage is generally so great that a fiber structure can no longer be recognized. For example, it is impossible to use such threads or fibers for the manufacture of carpets because they do not survive the temperatures necessary for the application of the back coating.

It is possible to improve the usability of such threads made of acrylonitrile-vinyl chloride / vinylidene chloride copolymers in terms of textile technology by using mixtures of different acrylonitrile copolymers in which one component consists largely of polyacrylonitrile and the other component predominantly consists of polyvinyl chloride or polyvinylidene chloride. By using such mixtures it is possible to overcome the disadvantages of threads made from acrylonitrile-vinyl halide copolymers, e.g. Reduce adhesive temperatures below 150 ° C, low thermal stability, sensitivity to common solvents, etc. When using mixtures of different copolymers for the production of acrylic fibers, it is observed at the same time that the tendency of such fibers to shrink is significantly reduced.

Another problem arises in the production of spinning solutions from various types of acrylonitrile copolymers, which is referred to as the incompatibility of the copolymers. For example, if the various copolymers are individually dissolved in dimethylformamide, turbidity or even segregation often occurs when the two copolymer spinning solutions are mixed. It was long held that such an incompatibility of the copolymers in the spinning solution should also have negative consequences for the quality of the threads and fibers produced therefrom. A whole series of proposals can be found in the literature, such as this incompatibility, for example by adding solvent-containing copolymers (German design specification 1,279,889), by using graft polymers (US Pat. No. 2,763,631) or by selecting certain mixing ranges of selected copolymer compositions and by special design the polymerization conditions (German design specification 1 569153) can be lifted again.

With a suitable selection of the copolymers and the mixing ratios, the properties of the threads and fibers obtained in this way can approach those of polyacrylonitrile threads. Such threads can again have a higher softening temperature and lower sensitivity to solvents, for example, but their shrinkage values are also low.

In recent years it has been recognized that it is also possible to spin acrylonitrile copolymers that are incompatible with one another from solutions. For example, German Offenlegungsschrift 2,340,463 describes non-flammable fibers made from two acrylonitrile-vinylidene chloride copolymers which, however, have only a slight shrinkage. The same also applies to threads which, according to German Offenlegungsschrift 1,669,566, consist of a thread-forming polymer mixture, preferably more than 90% of this mixture consisting of polyacrylonitrile and less than 10% of polyvinyl chloride or a corresponding copolymer. Threads and fibers are also obtained here that show only low shrinkage values.

So there was still the task of producing flame retardant threads and fibers from acrylonitrile copolymers, which are characterized by high shrinkage with low brittleness and which also above the triggering temperature over a larger temperature range of z. B. 140-190 ° C away, have no significant additional shrinkage and are suitable for the production of flame-retardant articles.

Surprisingly, it has been found that threads and fibers with such a broad spectrum of properties can be produced if at least two acrylonitrile copolymers of different compositions, at least one of which contains halogen, are spun together from a solution, the polymers in the solvents used being incompatible with one another. The thread-forming substance of these threads and fibers consists of a mixture of 20-70% by weight of an acrylonitrile copolymer A, which consists of at least 80% by weight of acrylonitrile units and 0.3-20% by weight of other units copolymerizable with acrylonitrile is built up and 80-30 wt .-% of an acrylonitrile copolymer B, 50-75 wt .-% of acrylonitrile units, 25-45 wt .-% of vinyl chloride and / or vinylidene chloride units and 0-5 wt .-% is composed of other units copolymerizable with acrylonitrile. The threads and fibers according to the invention are distinguished by a high boiling shrinkage of 20% and more and a knot strength of more than 10 cN / tex. The thread-forming substance is non-homogeneously soluble in N, N-dimethylformamide as a 24% by weight solution.

Threads and fibers in which the mixture of copolymers A and B is in a weight ratio of 40:60 to 60:40 are preferred.

The threads and fibers according to the invention preferably have a boiling shrinkage of more than 30% and a knot strength of more than 12 or even more than 15 cN / tex. A particularly favorable property of the threads and fibers according to the invention is that the shrinkage value shows only a slight dependence on the shrinking temperature. If, for example, the threads or fibers according to the invention, shrinkage is triggered by a temperature treatment with saturated steam at 110 ° C, the threads, however, in a subsequent further processing stage, temperatures of e.g. Exposed to 120 or 140 ° C, the additional shrinkage caused by the higher temperature above the release temperature is very low. In contrast, fibers made from a homogeneous copolymer with a comparable halogen content show strongly increasing shrinkage values at such a temperature increase, which can lead to the complete dissolution of the fiber structure.

The acrylonitrile copolymers A and B are said to be composed of acrylonitrile units and, in the case of the copolymer B, additionally of vinyl chloride and / or vinylidene chloride units and furthermore have other units copolymerizable with acrylonitrile. Examples of suitable comonomers of acrylonitrile are: acrylic, α-chloroacrylic and methacrylic acid or their esters or amides, for. B. methyl methacrylate, acrylic acid methyl ester, acrylamide, methacrylonitrile, vinyl ketones such as e.g. Methyl vinyl ketone and vinyl carboxylates such as e.g. Vinyl acetate, other compounds containing the vinyl group such as e.g. Vinylsulfonic acid, allyl- and methallylsulfonic acid, ethylene-a, ß-dicarboxylic acids and their anhydrides or derivatives, styrenes, vinyl-substituted tertiary heterocyclic amines such as vinylpyridines and vinylimidazoles and vinylhalogen compounds such as vinyl chloride, vinylidene chloride, vinyl bromide etc.

In the case of the other monomers copolymerizable with acrylonitrile for the preparation of the copolymer B, vinyl chloride and vinylidene chloride are by definition to be excluded in this context.

Non-homogeneously soluble means the incompatibility of the copolymers used in the mixture. This incompatibility of the polymers can already be seen with the naked eye from the cloudiness of the corresponding solutions. A quantitative statement regarding the grading of the incompatibility of different copolymers is only possible with the help of spectrophotometric methods. A suitable method of determination consists in producing a 24% solution 213 of the copolymer mixture or the fibers produced therefrom in N, N = dimethylformamide. This solution is measured against air in a 1 cm glass cuvette using the Beckmann DB-GT spectrophotometer, the absorption (measuring range 0 to 2A) being determined at 850 nm. Corresponding measured values obtained using this measurement method are mentioned in the examples. An incompatibility or a solution that is no longer homogeneous is always present under the selected measurement conditions, provided that an absorption value> 0.20 is found.

The spinning process required for the production of the threads and fibers according to the invention differs significantly from the previously known processes for the production of high-shrinkage fibers from polyacrylonitrile or corresponding copolymers. It has been found that the high-shrinkage threads according to the invention do not require steam fixation before or after drying, as described, for example, in German Offenlegungsschrift 2,532,120 in their manufacture. This significantly simplifies the manufacturing process.

This process, which is new for shrink threads and fibers, essentially consists of the following work steps. Two copolymers of acrylonitrile A and B which are incompatible in solution are mixed in the desired ratio. This mixture is in an aprotic solvent, preferably in dimethylformamide or dimethylacetamide, in a stirred kettle Spinning solution of usual concentration dissolved. Usual concentrations of such spinning solutions are generally above 20% by weight; in the examples below, 24% by weight solutions were used. The spinning solution can also be prepared from the mixture of the copolymers by first dissolving the individual copolymers separately, then mixing this solution with the aid of a dynamic or static mixer to give the desired combination.

A solution prepared in this way is pressed through spinnerets after the usual degassing and safety filtration with the aid of a spinning pump. It is advisable to warm the spinning solution to elevated temperatures before spinning. Depending on the spinning process used, the thread formation then takes place either by diffusion of a portion of the solvent molecules into the surrounding gas space during the dry spinning process or into the aqueous precipitation bath, which usually also contains a higher percentage of the solvent used in addition to water.

The freshly spun threads, which usually still contain a relatively large percentage of the polymer solvent, are subjected to wet drawing after solidification in the spinning bath or in the heating shaft in the dry spinning process. The hiding place, which preferably also contains large amounts of solvent in addition to water, should have a temperature of 40--9O ⁰ C. The threads are drawn in a ratio of 1: 1 to 1: 2.5, preferably 1: 1.2 to 1: 1.7. This stretching is followed by the usual washing and finishing of the threads with surface-active agents, the so-called finish. It is advantageous to allow the threads to shrink slightly during this washing and finishing treatment. A shrinkage of up to 15% has proven to be advantageous. Subsequently, the threads are dried at temperatures below 150 ^° C., preferably without further shrinkage, and then subjected to post-stretching from 1: 1.2 to 1: 4, preferably 1: 1.5 to 1: 2.3, under the action of a heating unit stretched. The total stretching, ie the effect of the wet stretching and the post-stretching together, should be in the range from 1: 1.5 to 1: 4, preferably 1: 2 to 1: 3.

The post-stretching takes place without the action of steam on the dried threads. The use of so-called contact heating sections has proven particularly advantageous. The heater temperature should be between 120 and 180 ° C, preferably 130 to 150 ° C.

The threads and fibers treated in this way can then be subjected to customary further treatment steps, such as e.g. mechanical crimping, cutting into staple fibers, etc.

The threads or fibers obtained are flame-retardant due to their halogen content. They are characterized by high shrinkage, very low brittleness and very good temperature resistance. Fibers according to the invention, when mixed with normal shrinking fibers, give yarns which can have a particularly high bulk. The flame-retardant effect of the high-shrinkage fibers according to the invention are retained in the case of fiber mixtures in particular if the non-shrinking fibers of this mixture are also correspondingly flame-retardant.

The examples described below are intended to illustrate the invention. Unless otherwise stated, quantities and percentages relate to weight units.

Examples 1 to 14

The following copolymers were used in the examples described below.

These copolymers were dissolved individually and in mixtures in N, N-dimethylformamide or N, N-dimethylacetamide to form 24% solutions. Each solution prepared in this way was heated to 60 ° C. and spun with the aid of a spinning pump through a spinneret with 300 holes and a hole diameter of 80 μm into a precipitation bath which consisted of 49% water and 51% dimethylformamide. The temperature of the coagulation bath was 69 ° C. The spun tow obtained was withdrawn from the nozzle at 13 m / min and drawn in a drawing bath in a ratio of 1: 1.45. The composition of the draw bath was 64% dimethylformamide and 36% water, the temperature was 80 ° C. The cable stretched in this way was then washed and finished in further baths by known processes, with a total shrinkage of 10% being permitted in these processes. The cable was then dried on a drum dryer without further shrinkage at 135 ° C.

The subsequent post-stretching was carried out in a ratio of 1: 1.8. The cable was in Brought into contact with a heater that had a surface temperature of 135 ° C. The individual filaments of the cable were then crimped in a known manner and then cut into staple fibers.

The changes made in the individual examples and the measured values on the spinning solution and the threads produced are summarized in Table 2 below.

As can be seen from Table 2, under the chosen spinning conditions it is possible to produce threads from pure copolymers that show high boiling shrinkage values. However, the knot strength of such threads is very low. Such threads are therefore difficult to process. In contrast, when using mixtures of copolymers which are incompatible in solution (absorption of the spinning solution> 0.2), knot strengths are always found which are greater than 10 cN / tex and often even greater than 12 cN / tex. If a mixing ratio of 40:60 to 60:40 is used, even knot strengths of 15 and more cN / tex can be achieved.

Example 15

Fibers of Example 6 were spun into a yarn and processed into a woven carpet with a pile weight of 850 g / m ² . Such a carpet was tested for flammability in accordance with DIN 54332. The measured values obtained are summarized in Table 3 below.

A carpet made of this material meets the requirements of the DIN standard, it is flame retardant.

Examples 16-30

Based on Examples 1 to 14, a 24% spinning solution in dimethylformamide of copolymers a and b was prepared in a ratio of 1: 1 and through a spinneret with 300 holes, hole diameter 80 pm into a precipitation bath with 51% dimethylformamide and 49% water injected. The temperature of the precipitation bath was 70 ° C. The threads were drawn from the precipitation bath at a speed of 13.5 m / min and drawn in a drawing bath with 64% dimethylformamide and 36% water. Then washed in water with partial approval of shrinkage, finished, dried on godets and stretched on a contact heater. The wet drawing, the temperature of the drawing and washing baths, the wet shrinking, the post-drawing, the temperature of the contact heater during the post-drawing and the total drawing were varied. The exact values are summarized in Table 4. This table also contains the boiling shrinkage values of the threads thus obtained and, in some selected cases, also the knot strength of these threads. The results of Examples 16 to 30 show that there is an optimum range both for the value of the wet stretching and for the post-stretching in the method according to the invention and that in particular the temperature of the heater during the post-stretching has a considerable influence on the size of the cooking shrinkage and possibly also on the knot strength.

Claims (7)

1. Filaments or fibers of mixtures of two acrylonitrile copolymers, characterized in that the filament-forming substanze consists of a mixture of from 20 to 70 weight % of an acrylonitrile copolymer A containing at least 80 weight % of acrylonitrile units and from 0.3 to 20 weight % of other units copolymerizable with acrylonitrile, and from 80 to 30 weight % of an acrylonitrile copolymer B containing from 50 to 75 weight % of acrylonitrile units, from 25 to 45 weight % of vinyl chloride and/ or vinylidene chloride units and from 0 to 5 weight % of other units copolymerizable with acrylonitrile; the filaments having a boil-off shrinkage of 20% and more and a knot strength of more than 10 cN/tex, and the filament-forming substance is not homogeneously soluble as a 24 weight % solution in N,N-dimethyl formamide.

2. The filaments and fibers as claimed in Claim 1, wherein the filament-forming substance is a mixture of copolymers A and B in a weight ratio of from 40:60 to 60:40.

3. The filaments and fibers as claimed in Claims 1 and 2 having a boil-off shrinkage of more than 30% and a knot strength of more than 12 cN/tex.

4. A process for the manufacture of filaments and fibers as claimed in one of the previous Claims by wet or dry spinning and subsequent wet drawing, washing, finishing, drying and after-drawing, characterized in that it comprises dissolving a mixture of the corresponding acrylonitrile copolymers in an aprotic solvent to form a turbid spinning solution, drawing the filaments obtained by spinning and containing still an amount of solvent in a bath containing water and solvent at temperatures of from 40 to 90°C by the factor of 1:1 to 1:2.5, allowing a shrinkage of up to 15% in the subsequent washing and finishing steps, drying the filaments without allowing further shrinkage at temperatures of preferably below 150°C, and subjecting them subsequently to an after-drawing in a ratio of from 1:1.2 to 1:4 over a heater at a temperature of from 120 to 180 °C; the total drawing ratio of the filaments being from 1:1,5 to 1:4.

5. The process as claimed in Claim 4, wherein the wet drawing ratio is from 1:1.2 to 1:1.7, the ratio of after-drawing on a contact heater having a surface temperature of from 130 to 150 °C is from 1:1.5 to 1:2.3, and the total drawing ratio is from 1:2 to 1:3.