EP0154217A2 - Monofilament and bristles from acrylonitrile homo or copolymers and process for manufacturing them - Google Patents

Abstract

Monofils and bristles which comprise at least 90% by weight of acrylonitrile units and have a linear density of more than 2.5 tex possess a relative solution viscosity of 1.7 to 6.0, a tear strength of at least 20 cN/tex and an initial modulus of more than 700 cN/tex. The manufacturing process is distinguished by a wet stretch of the spun filaments by at least 1:4, drying under tension and a subsequent hot stretch of at least 1:2, the overall stretch being at least 1:8, preferably 1:10 to 1:20. The monofils and bristles according to the invention are suitable in particular for producing filament-reinforced composite materials.

Description

The invention relates to monofilaments and bristles made of polyacrylonitrile or polyacrylonitrile copolymers which are predominantly composed of acrylonitrile building blocks and whose titers are higher than 2.5 tex, their strength is greater than 20 cN / tex and their initial modulus is greater than 700 cN / tex - based on 100 % Stretch - is.

In the present invention, the shaped products were termed monofilament in the case of endless material and bristles in the case of short-cut material in order to clarify that it is not textile threads or fibers in the usual sense, but rather structures with diameters of more than 0.05 to approx 0.2 mm, corresponding to a single titer of more than 2.5 tex to about 30 tex. According to the invention, it is not necessary that the monofilaments have been spun from nozzles with only one nozzle hole. Manufacturing processes for bristles and monofilaments are largely the same, so we shall speak below to simplify filaments, provided that both monofilaments and bristles can be meant.

German Offenlegungsschrift 3,027,844 describes high-modulus threads and fibers made of polyacrylonitrile, the initial modulus of which is higher than 1300 cN / tex. The titers described in the examples of this preliminary literature are between 1.7 and 3.6 dtex. The titer range from about 1.5 to 15 dtex specified in the text limits the titer range to the usual range of textile spun threads and fibers, which usually ranges from 20 dtex in some cases to 20 dtex and exceptionally up to 25 dtex with a single titer of 15 dtex. This preliminary literature cannot do anything can be seen that would have caused the expert to significantly exceed the titer range and to leave the field of textile staple fibers and threads.

Spinning such coarse-titer filaments is associated with a number of difficulties. For example, DE-PS 2 658 179 describes a process in which filaments with individual titers of 2 to 8 tex can be produced by a special dry spinning. The filaments obtained, however, only have strengths of 15 to 17 cN / tex. They could only be stretched 1: 2.5 times, the elongation at break was very high (e.g. 97%). The areas of use for such shaped structures are the production of synthetic hair and awning hair for imitation fur. Nothing can be inferred from this preliminary literature that is directed towards the production of high-modulus filaments.

The production of filaments that are as similar as possible to natural human hair is also the subject of German Offenlegungsschrift 2,434,488. According to the teaching of this preliminary literature, filaments in the titer range from 2 to 7 tex are produced by a wet spinning process. The total stretching of 1: 6 takes place in two stages in the wet state. No physical-physical values of the filaments produced can be derived from the examples in this preliminary literature. However, reworking has shown that the method according to DE _- OS 2 434 488 can at best produce filaments which have an initial modulus below 600 cN / tex. As described in detail in the comparative example below, it was not possible to achieve the specified final titer of the filaments without at the same time allowing significant shrinkage during the drying process. Such shrinkage generally lowers the tensile strength of filaments, increases the elongation at break and, in particular, lowers the initial modulus.

So there was still the task of producing monofilaments and bristles from acrylonitrile polymers, which are characterized by good tear strength and in particular by a high initial modulus. A manufacturing process had to be found by which such filaments could be produced.

Textile fibers and threads made of polymers with a high content of acrylonitrile units are usually produced by a solution spinning process. In the spinning process, the solvent, which usually makes up more than 70% of the thread emerging from the nozzle, has to be removed and the thread-forming polymer has to be compressed into a compact thread. The removal of the solvent and the production of a compact thread are more difficult to solve, the thicker the diameter of the spun filament.

Surprisingly, it was found that it is possible to produce monofilaments and bristles from homo- or copolymers of acrylonitrile by a solution spinning process and then spinning them in a coagulation bath, the filaments obtained having a coarse titer above 2.5 tex being high Mark starting module. It is known that the initial module, as a measure of the force absorption of a filament at low elongation, is much more sensitive to defects in the filament structure than, for example, the tensile strength. Nevertheless, such filaments with initial moduli of e.g. Generate 1500 or 1700 cN / tex. The high stretchability of the coarse-titer filaments spun from a solution was also surprising. For example, a filament drawn out of the nozzle with a calculated titer of 215 tex (based on the thread-forming substance) - or 1200 tex, based on the spinning material used - could be 16.7-fold to a final titer of 12.9 tex be stretched.

The invention therefore relates to monofilaments and bristles made of homo- or copolymers of acrylonitrile which consist of at least 90% by weight of acrylonitrile building blocks and have a titer of more than 2.5 tex. These filaments are characterized in that they have a tensile strength of at least 20 cN / tex, preferably more than 23 cN / tex and an initial modulus, based on 100% elongation, of more than 700 cN / tex. The polymer required for this should have a relative viscosity, measured as a solution of 0.5 g in 100 ml of dimethylformamide at 20 ° C., of 1.7 to 6.0. The filaments according to the invention preferably have a titer of more than 2.5 to about 30 tex. Arithmetically, assuming a circular cross section, this corresponds to diameter values of approx. 0.052 to 0.180 mm. Further features that are the subject of the subclaims, but are discussed below in connection with possible uses of such monofilaments and bristles.

The monofilaments and bristles according to the invention are particularly suitable for the production of filament-reinforced composite materials. Compared to the use of fibers and threads from the textile sector, ie with titers below 25, generally below 15 dtex, the filaments according to the invention and in particular the bristles according to the invention can be mixed into the materials to be reinforced in a much simpler, more homogeneous and in higher concentration. The mixtures produced in this way are characterized, for example, by lower viscosities and better flow behavior. The preferred titer and cut lengths of the filaments according to the invention depend very much on the intended area of use and the required amount of use in the composite material. For example, the use of bristles with a titre of 8 to 20 tex in concrete mixes leads to a considerable reduction in the formation of cracks hardened concrete parts, it increases elasticity, reduces brittleness and increases fracture energy considerably. Similar advantages can be observed with sprayed concrete, mortar and a wide variety of plasters reinforced with bristles according to the invention.

In the case of plastics (e.g. polypropylene), bristles in the titer range from 3 to 10 tex produce particularly good reinforcement results. For example, increased impact strength - in contrast to the results when using glass fibers - is maintained even at low temperatures. The same titer range leads e.g. when used in sealing compounds based on polymer bitumen for particularly high dimensional stability.

The optimal titer of the bristles is very significantly influenced by the amount of bristles used, the admixing technique and, in the case of solids, by the grain size distribution of the material to be reinforced. The strengths of the filaments according to the invention are in each case above 20 cN / tex and preferably in the range from 25 to 60 cN / tex. The initial moduli of the filaments according to the invention must be over 700, preferably over 800, preferably between 1000 and 1800 cN / tex. Cutting lengths of e.g. 0.5 to 30 mm, in other areas of application of the bristles cutting lengths from 100 to 150 mm. The short cutting lengths of the bristles in the area of 1 to 2 mm or less should preferably be used in a mixture with filaments with a longer cutting length. The short cutting lengths, however, can fundamentally improve the rheological behavior of, for example, building adhesives and tile adhesives.

If the monofilaments or bristles according to the invention are used in alkaline or aggressive media which expect the filament raw material to be influenced leave, the use of a higher molecular weight polymer, which is preferably made up of more than 99 wt .-% of acrylonitrile building blocks, is advantageous, since the filaments produced therefrom are significantly more resistant to aggressive media than corresponding filaments made from raw materials with a higher copolymer content.

The invention is also based on a method for producing the monofilaments or bristles by a wet spinning process, in which in addition to wet drawing, hot drawing must be carried out after drying. The process according to the invention is characterized in that the pilaments are stretched at least 1: 4 before, during or after the washing, dried under tension, but if appropriate with low shrinkage, and then at least one hot stretching at temperatures of at least 120 ° C and a stretch ratio of at least 1: 2 are subjected. The effective total drawing of the threads should be at least 1: 8, preferably 1:10 to 1:20. The hot stretching is preferably a stretching in the dry-hot state, the amount of heat required being transferred by contacting surface radiators or hot rollers.

• Acrylamid, Acrylsäure und deren Ester, Methacrylnitril, Methacrylamid, Methacrylsäure und deren Ester und entsprechende an der Methylgruppe substituierte Verbindungen, Vinylester und -äther wie Vinylacetat, Vinylstearat, Vinylbutyläther, Halogenessigsäurevinylester wie Bromessigsäurevinylester, Dichloressigsäurevinylester, Trichloressigsäurevinylester, Styrol, Maleinimid, Vinylhalogenide wie z.B. Vinylchlorid, Vinylylidenchlorid, Vinylbromid sowie Sulfonatgruppen tragende ungesättigte Verbindungen usw.

The precipitation or solution polymers prepared by the customary process can be used as polymer raw materials. Depending on the requirements for the areas of application, both homo- and copolymers of acrylonitrile can be used. The purity of the monomers used should be as high as possible. Suitable comonomers are all unsaturated compounds copolymerizable with acrylonitrile, of which the following should be mentioned here, for example:

• Acrylamide, acrylic acid and its esters, methacrylonitrile, methacrylamide, methacrylic acid and their esters and corresponding compounds substituted on the methyl group, vinyl esters and ethers such as vinyl acetate, vinyl stearate, vinyl butyl ether, haloacetic acid vinyl esters such as bromoacetic acid vinyl ester, dichloroacetic acid vinyl esters, trichloroacetic acid halide, vinyl malides, such as vinyl chloride, maleinate, vinyl halide, such as vinyl chloride, vinyl acetate, malic acid, vinyl halide, such as vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, vinyl chloride, for example, trichloroacetic acid, vinyl halide, such as vinyl chloride , Vinyllylidene chloride, vinyl bromide and sulfonate-bearing unsaturated compounds etc.

Polymers can be used whose relative solution viscosities, measured as 0.5% dimethylformamide solutions at 20 ° C., are in the range from 1.7 to 6.0. Typically, higher molecular weight polymers result in filaments with better physical properties. For their production, however, a considerably larger amount of solvent must be used and recovered, as a result of which the production costs of such filaments are increased considerably. Good results under economic conditions are achieved with polymers which are in a viscosity range of approximately 1.85 to 3.5; polymers in the viscosity range between 2.5 and 3) 5 give particularly good results.

When producing the spinning solutions, the dissolving conditions are to be selected so that the most homogeneous, gel particle-free spinning solutions are obtained. Scattered light measurements using a laser as the light source are particularly suitable for checking the quality of the spinning solution. Only flawless spinning solutions which show very low scattered light values enable the high draws required according to the invention. The spinning solutions can be used both continuously and discontinuously. Inorganic or organic additives, such as matting agents, stabilizers, flame retardants, etc., can be incorporated into the spinning solutions. Additives such as CaC0 ₃ or Si0 ₂ in a concentration of 1 to 20% that influence the surface structure are also suitable.

The spinning process according to the invention is distinguished by a high effective total drawing of at least 1: 8. When determining the effective total drawing, only the wet drawing before, during or after the washing process and the hot drawing are taken into account, but a contraction of the filaments is deducted.

The so-called nozzle warpage is not included in the values of the total stretching; rather, the fresh spun filaments that are obtained after a wet spinning process are classified as undrawn material. The effective total stretching should be at least 1: 8 by the method according to the invention. Effective total draw ratios of 1:10 to 1:20 are preferred. The method according to the invention can be carried out on conventional filament spinning plants. The required effective total stretching takes place in several stages, first the spun filaments are wet-drawn before, during or after washing out the residual solvent content in one or gradually in several hot baths at least in a ratio of 1: 4. The temperature of the stretching bath media, which generally consist of mixtures of water and the aprotic solvent used, should be kept as high as possible. Temperatures a little below the boiling point of the bath liquid are preferred. However, baths that contain other stretching bath media are also possible, e.g. Glycol or glycerin, if appropriate also in mixtures with the polymer solvent, at which stretching temperatures above 100 ° C. can also be selected.

After stretching and washing out the residual solvent content, the filaments are prepared in a preparation bath and then freed as much as possible of adhering water by the action of rotating pairs of press rollers. The preparation applied in the preparation bath can - the stretching behavior of the filaments. It should therefore be selected from known preparation mixtures that shows the lowest possible thread friction.

Following the preparations, the filaments obtained are dried under tension on hot rollers.

A small amount of shrinkage, which often proves to be advantageous for the subsequent stretching, can be permitted on drying; When setting the shrinkage, however, care must be taken that the cables always run under tension over the drying rollers. The temperatures of the rollers should be chosen so that the cable leaves the dryer with a very low residual moisture content of less than 1%. Temperatures of the drying rollers of 140 to 240 ° C have proven to be particularly favorable, but this does not exclude the use of higher or lower temperatures. It is also possible to dry on the rollers at stepped temperatures.

After drying, the spinning tow is stretched again using at least twice its length using dry heat. This stretching can also take place in one or more stages. The heating of the cable can be carried out according to the methods customary in the art, e.g. by rotating hot rollers, by contact via hot plates, in a hot air duct or by radiation, in particular infrared radiation. Gradual stretching, in which different heating methods are used, can also be used. Such combinations are always particularly advantageous when stretching from or between hot rolls in the first stretching stage and using one of the three other methods described in the second stage. The drawing temperatures are influenced by the type of polymer used and in part by the previous drawing and the drying conditions. Drying temperatures in the range from about 120 to 250 ° C. are generally suitable.

After stretching, the filaments are cooled in a conventional manner and either wound up to form continuous material or cut into bristles with the desired cutting length using known methods. If the application requires it, a special preparation, e.g. improves the spreadability or adhesion in a composite material to which monofilaments or bristles are applied.

The following examples are intended to illustrate the invention. Unless otherwise stated, percentages and parts are by weight.

Example 1:

A 19% solution of a polymer of 99.3% acrylonitrile and 0.7% methyl acrylate of relative viscosity (measured as a solution of 0.5 g in 100 ml of dimethylformamide at 20 ° C.), of 3.0 was passed through a nozzle with 1000 holes, hole diameter 0.12 mm in a coagulation bath with 43.8% dimethylformamide (DMF) and 56.2% water at 40 ° C, pulled vertically upwards from the nozzle at 6.3 m / min, then in two Baths with 33% DMF and 67 water at boiling temperature stretched to 29 m / min, washed with hot water in countercurrent, allowing shrinkage to 27 m / min, then finished and on hot drums at 170 °, 190 ° and briefly Dried 230 ° C, cooled to 180 ° C and stretched over heated plates at 180 ° C to 74 m / min. The effective total drawing was 1: 11.7. The filaments obtained had the following properties:

The measured values were recorded with an Instron tensile tester, model 1122. The clamping length was 200 mm, the expansion took place at a speed of 100% of the clamping length per minute. The initial modulus was determined in the stretch range 0.1-0.3%.

Example 2:

A spinning mass; as described in Example 1, was pressed through a nozzle with 500 holes, hole diameter 0.15 mm, into a precipitation bath of 43% DMF and 57% water at 34 ° C. The resulting sheet was withdrawn vertically from the nozzle at 6.3 m / min, in two successive troughs, which were filled with a mixture of 40% DMF and 60% water, stretched to 27 m / min at boiling temperature, in hot water in Countercurrent washed, finished, dried at 170, 190 and briefly 230 ° C to then first be stretched at 180 ° C to 40 m / min and then over hot plates at 180 ° C to 78 m / min. The total effective stretching was 1: 12.4. The filaments obtained had the following properties:

Example 3:

An 18% spinning mass of a polymer according to Example 1 was pressed through a nozzle with 10 holes, hole diameter 0.3 mm into a precipitation bath of 40% DMF and 60% water at 39 ° C. The filaments were drawn off from the nozzle at 4.5 m / min, drawn to 22.5 m / min in two baths with 60% DMF and 40% water at 95 ° C., washed in hot water and after passing through an anti-aging bath 2 duos at temperatures of 150 and 190 ° C below

Tension dried. With a third duo heated to 190 ° C, the filaments were stretched to 42 m / min and then drawn off from this duo at 67.0 m / min. The total draw was 1: 14.9.

The filaments showed the following properties:

Example 4:

A spinning mass as described in Example 3 was drawn off through a 10-hole nozzle with a hole diameter of 0.5 mm into a _{precipitation} bath consisting of 38% DMF and 62% water at 30 ° C. at 4.5 m / min and then stretched in two tubs with 58% DMF and 42% water at 95 ° C to 22.5 _{m /} min, washed with hot water, finished, dried on 3 duos at 150, 160 and 180 ° C, with a fourth duo , which was heated to 190 ° C, stretched to 32.2 m / min and drawn off from this duo at 75 m / min. The _G esamtverstreckung was 1: 16.7. The threads obtained in this way had the following properties:

Example 5:

A dope as described in Example 3 was spun, wet drawn, washed and finished under the conditions of Example 4. The drying took place on 3 duos with a surface temperature of 150, 160 and 180 ° C. The cable was stretched to 42 m / min with a duo heated to 205 ° C. and pulled off from this duo at 59 m / min (total stretching 1: 13.1). The filaments obtained had the following values:

Example 6:

A 26% spinning mass of a polymer composed of 93.5% by weight of acrylonitrile, 6% of methyl acrylate and 0.5% of sodium methallylsulfonate, which had a relative viscosity of 1.92, was passed through a 10-hole nozzle with a hole diameter of 0.5 mm pressed into a precipitation bath consisting of 30% DMF and 70% water at 32 ° C. The threads were withdrawn from the nozzle at 3.5 m / min, drawn in two subsequent baths of 60% DMF and 40% water at 95 ° C. to 22.6 m / min, washed in hot water at 80 ° C. and finished and dried on 4 duos at 135, 150, 165 and 170 ° C. The speeds of the individual duos were: 22.5; 24.8; 24.5 and 22.5 m / min. The threads from the last duo were drawn off at 48.0 m / min, which means that the effective total drawing was 1: 13.7. The filaments obtained had the following properties:

Example 7 (comparison)

This example represents a reworking of the essential details of Example 1 of DE-OS 2 434 488. A 22% solution of a polymer of 93.6% by weight acrylonitrile, 5.8% by weight methyl acrylate and 0.6% Sodium methallylsulfonate in DMF was spun through a 10 hole nozzle, hole diameter 0.3 mm, nozzle diameter 20 mm into a precipitation bath of 55% DMF and 45% water at 20 ° C.

The spraying speed of the spinning mass was set to 6.0 m / min and the threads were drawn off the nozzle at 4.8 m / min (delay: 0.8). In a bath with 50% DHF and 50% water at 90 ° C, the filaments were drawn to 24 m / min, washed with hot water in countercurrent, post-drawn in water at boiling temperature to 28.8 m / min, finished and without approval from Shrink dried. The effective total drawing was 1: 6, as in the cited example of the previous literature. Filaments with the following properties were found under these conditions:

The initial modulus was determined in the range from 0.3 to 0.5% elongation, since the values were in the range from 0.1 to 0.3% lower. The titer value resulted from the individual capillary values averaged from all 10 capillaries. It was not possible in this way to achieve a titer of 4 tex. For this reason, the spinning test of Example 7 was repeated, but now the threads, after drying at 180 ° C., were wound up at 27.0 m / min. The following physical values resulted under these conditions:

Here too, the initial modulus was determined from the 0.3 to 0.5% elongation range.

Even with this variant it was not yet possible to achieve a titer of 4.0 tex. It can be assumed that in the process according to Example 1 of DE-OS 2 434 488, even a larger shrinkage was permitted than stated above. However, this means that the threads of Example 1 certainly had an even lower tensile strength and in particular the initial modulus must have been clearly below 500 cN / tex.

Claims (6)

1. monofilaments and bristles of homo- or copolymers of acrylonitrile, which consist of at least 90% by weight of acrylonitrile building blocks and have a titer of more than 2.5 tex, characterized in that the polymer has a relative viscosity, measured as a solution of 0 , 5 g in 100 ml of dimethylformamide at 90 ° C, from 1.7 to 6.0 and the monofilaments and bristles have a tensile strength of at least 20 cN / tex and an initial modulus, based on 100% elongation, of more than 700 cN / have tex. 2. monofilaments and bristles according to claim 1, characterized in that the titer of the monofilaments and bristles is at values above 2.5 to about 30 tex. 3. monofilaments and bristles according to claim 1 or 2, characterized in that the relative viscosity of the acrylonitrile polymer is between 2.5 and 3.5. 4. Monofilaments and bristles according to one of the preceding claims, characterized in that the initial module is 800 to 1800, preferably 1000 to 1800 cN / tex. 5. Monofilaments and bristles according to one of the preceding claims, characterized in that the thread-forming substance consists of at least 99% by weight of acrylonitrile building blocks. 6. Process for the production of monofilaments and bristles according to one of the preceding claims by producing a spinning solution of the polymer in an aprotic solvent, spinning in a precipitation bath, wet drawing of the filaments obtained and subsequent drying, characterized in that the filaments are drawn before, during or after the washing at least in a ratio of 1: 4, under tension, but if necessary with the approval of low shrinkage, and then subjected to at least one hot drawing at temperatures above 120 ° C. with a drawing ratio of at least 1: 2 , the effective total drawing being at least 1: 8, preferably 1:10 to 1:20.