EP0061117B1 - Fixed polyacrylonitrile filaments and fibres, and process for preparing them - Google Patents

Abstract

The invention relates to filaments and fibers spun from at least 98% by weight of polyacrylonitrile and relative viscosities of between 2.5 and 6.0 which have tensile strengths of more than 50 cN/tex with an elongation at break of at most 15% and a shrinkage at the boil of less than 5% and to a process for their production which comprises at least 2 stretching stages with a minimum stretching ratio of 1:9 as well as a concluding setting stage in which the filaments are treated without shrinkage in dry heat at 170 DEG to 280 DEG C. Such filaments and fibers are distinguished by an increased resistance to swelling and hydrolysis and they are particularly suitable for reinforcing organic and inorganic materials.

Description

The invention relates to threads and fibers made of polyacrylonitrile. whose thread-forming substance consists of at least 98% by weight of acrylonitrile building blocks and has a high average molecular weight. A special drawing and fixing process can be used to obtain threads and fibers which show increased resistance to swelling and hydrolysis processes, even at elevated temperatures.

It is known to subject polyacrylonitrile thread cables to multi-stage stretching in order to obtain threads or fibers which, owing to their initial modulus values, should be particularly suitable for technical fields of application. For example, DE-A-2 851 273 describes a process in which the threads are drawn further directly after wet drawing in a “steam pressure drawing zone” at temperatures of 110 to 40 ° C. under the action of saturated steam under pressure. A similar stretching process at elevated temperatures under water vapor pressure is also described in DD-A-135.509. In compliance with special conditions, it was possible to obtain initial moduli up to about 1200 cN / tex. For example, it was necessary to spin out particularly fine titers or to use a specially prepared solution polymer.

In EP-A-0 044 534 (filing date July 16, 1981, priority July 23, 1980 DE), threads and fibers made of acrylonitrile polymers are already claimed, the thread-forming substance of which is 70 to 100% by weight, preferably at least 90 or even 99 % By weight is made up of acrylonitrile building blocks and these threads or fibers have an initial modulus of more than 1300 cN / tex, based on 100% elongation, and possibly a tensile strength of at least 50 cN / tex with an elongation at break of max. Should have 15%.

Such threads can be obtained by spinning a solution of thread-forming polymer and solvent either by a dry spinning process or using a precipitation bath of solvent and water. After a wet drawing, preferably at temperatures a little below the boiling point of the bath liquid and a washing treatment, the spun threads are then dried on hot rollers under tension, possibly with a low degree of shrinkage, and then subjected to a contact drawing of at least 1: 1.5. The effective total drawing of the threads should be at least 1: 9, preferably 1:10 to 1:25.

Such fibers and threads can be used with great success in technical fields of application, for example for the production of filters and filter fabrics, for use as a base fabric for the production of coated fabrics and in particular also for reinforcing organic and inorganic materials.

Especially in the production of such fiber-reinforced composites, however, it was found that the threads and fibers for reinforcement no longer show optimal properties when temperatures of approximately 100 ° C. in an anhydrous medium, and temperatures of approximately 80 ° C. in an aqueous medium during the production of the Composites are exceeded. It can be assumed that under these conditions structural changes occur in the fibers which make them more sensitive to the attack of the solvent in the setting composite of the monomers and other primarily low molecular weight components or which make them more sensitive to a hydrolytic attack Presence of water in the manufacture of fiber reinforced composites. Such sensitivity can be observed, for example, if the fiber-reinforced composite materials have hydraulically setting binders, i. that is, the aqueous phase reacts alkaline. It is believed that the action of the solvent residues and monomers leads in particular to swelling at higher temperatures and also the reinforcing properties of the threads, i. H. in particular their initial modulus and fiber strength are reduced.

It was therefore still the task to develop polyacrylonitrile fibers, in particular for technical fields of application, whose good physical properties can also be maintained above 100 ° C. in an anhydrous medium. Maintain above 80 ° C in water-containing media.

It has now surprisingly been found threads and fibers made of acrylonitrile polymers, the thread-forming substance of which is composed of at least 98% by weight of acrylonitrile units, the relative viscosity of the thread-forming substance (measured as a 0.5% by weight solution in dimethylformamide at 25 ° C. ) is between 2.5 and 6.0. The fibers and threads have tensile strengths of more than 50 cN / tex with a boiling shrinkage of less than 5% and an elongation at break of at most 15% and in which the initial modulus after an aqueous alkaline treatment at 90 ° C. for 24 hours is greater than 900 cN / tex, based on 100% elongation.

A method is suitable for producing such threads, in which the threads drawn off from the nozzle, obtained by a wet or dry spinning process, are wet drawn before or after washing, dried under tension on hot rollers and under the action of dry heat at 140 to 200 ° C. are post-stretched, with a post-drawing of at least 1 1.5 the total drawing is at least 1: 9 and the threads after post-drawing are fixed without the approval of shrinkage by exposure to dry heat at 170 to 280 ° C, preferably 180 to 250 ° C .

The necessity of a fixation treatment is surprising, since it is generally known that the fiber strength and the initial modulus decrease and the elongation values decrease with such a fixation treatment increase. It is also known that such a fixing treatment usually facilitates the diffusion of low molecular weight compounds into the interior of the fiber. For example, it is known that fixed fibers take up dyes considerably faster than the corresponding unfixed threads or fibers. However, if threads and fibers, the thread-forming substance of which has the required composition and the high relative viscosity, are drawn and fixed by the process according to the invention, they show better reinforcing effects if the composite materials are exposed to high temperatures for several hours during production than comparable unfixed fibers , even if their initial module is higher.

The better reinforcement effects could be achieved with organic composite systems, e.g. B. based on epoxy resins or unsaturated polyester resins as well as in inorganic systems with hydraulic binders.

To characterize this novel property of the threads and fibers according to the invention, the change in the physical properties in a Portland cement filtrate at higher temperatures and an exposure time over several hours was selected. Such a filtrate shows a number of advantages that cannot be achieved in a test with organic substances. A slight swelling and hydrolytic attack on the fibers occurs under the influence of the Portland cement filtrate. The fibers to be tested can be separated from the filtrate in a simple manner, while preparation from hardening masses on an organic basis can give rise to considerable errors. The use of pure monomer mixtures, e.g. B. prevented by the addition of inhibitors of the polymerization leads to concentration and diffusion ratios that do not correspond to practice.

• 1. Die fadenbildende Substanz muß zu wenigstens 98, vorzugsweise 99 Gew.-% aus Acrylnitrilbausteinen bestehen.
• 2. Die relative Viskosität der fadenbildenden Substanz muß zwischen 2,5 und 6,0, vorzugsweise zwischen 2,6 und 3,5 liegen.
• 3. Die Gesamtverstreckung der von der Düse abgezogenen Fäden muß mindestens 1 : 9 betragen, wobei die Verstreckung in eine Naßverstreckung in heißen Bädern und in eine Nachverstreckung nach dem Trocknen aufgeteilt ist und die Nachverstreckung unter trockener Hitze mit einem Verstreckverhältnis von mindestens 1 : 1,5 erfolgen muß.
• 4. Nach der abschließenden Verstreckung unter trockener Hitze müssen die Fäden durch Anwendung von trockener Hitze ohne Zulassung eines Schrumpfes fixiert werden. Die dabei benötigten Temperaturen liegen im Bereich von 170 bis 280, vorzugsweise 180 bis 250 °C.

The following requirements are necessary for the production of the threads and fibers according to the invention:

• 1. The thread-forming substance must consist of at least 98, preferably 99% by weight of acrylonitrile building blocks.
• 2. The relative viscosity of the thread-forming substance must be between 2.5 and 6.0, preferably between 2.6 and 3.5.
• 3. The total draw of the threads drawn off from the nozzle must be at least 1: 9, the draw being divided into a wet draw in hot baths and a post-draw after drying and the post-draw under dry heat with a draw ratio of at least 1: 1, 5 must be done.
• 4. After the final stretching under dry heat, the threads must be fixed by applying dry heat without allowing shrinkage. The temperatures required are in the range from 170 to 280, preferably 180 to 250 ° C.

Under these conditions, threads and fibers are obtained which have high tensile strengths of 50 to 100 cN / tex, preferably 55 to 80 cN / tex, low boiling shrinkage of less than 5%, preferably less than 3% and elongations at break of up to 15 , preferably a maximum of 12%. The fibers and threads obtained also have excellent stability against the action of swelling and hydrolytically attacking media. After a 24-hour treatment in a 90 ° C, aqueous alkaline medium, produced by extracting 150 g of Portland cement with 1 liter of water, and then washing and drying, the fibers still have an initial modulus of at least 900 cN / tex, preferably of at least 1 000 cN / tex, based on 100% elongation. The threads and fibers tested in this way shrink by less than 5% during this hot wet alkali treatment.

The best reinforcement properties are shown by fibers that do not shrink by more than 1% under these hot wet alkali conditions. This result is also surprising, since it was previously assumed that at least some of the reinforcing effects observed in composite materials are based on the fact that the fibers used in the setting or polymerization process should preferably have a higher shrinkage, which leads to a kind of prestressing of the composite material and thus to leads to better consolidation.

The threads and fibers according to the invention are particularly suitable as reinforcing threads or fibers or in the form of woven, knitted or non-woven fabrics for the production of reinforced organic or inorganic materials. These products are particularly advantageous for the production of hydraulic binder-containing products with a fine cavity structure. But they are also suitable for the production of filters or filter fabrics or as a base fabric for the production of coated fabrics.

The invention is also based on a process for the production of fibers and threads by a wet or dry spinning process, the wet stretching of the spun threads being able to take place before, during or after the washing treatment, the threads then being dried and then subjected to hot stretching. The process according to the invention is characterized in that the threads are optionally dried in cable or strand form on hot rollers under tension and then subjected to a contact stretching of at least 1 1.5, the effective total stretching having to be at least 1: 9. Under a contact stretching, the stretching in the dry hot state, e.g. B. be understood by using panel radiators.

After the contact has been drawn, the threads are fixed by exposure to dry heat. This can be done, for example, on rotating hot rollers, on irons, in a hot air duct or by infrared radiation.

The precipitation or solution polymers prepared by the customary processes 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 highest possible purity should be ensured for the monomers used. Suitable comonomers are all unsaturated compounds copolymerizable with acrylonitrile.

Polymers can be used whose relative solution viscosities - measured in 0.5% dimethylformamide solutions - are in the range from 2.5 to 6.0. Particularly good results under economic conditions are achieved with polymers which are in a viscosity range from about 2.6 to 3.5.

The polymers used should preferably have a content of at least about 99% by weight of acrylonitrile units.

When producing the spinning solutions, the dissolving conditions must 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 prepared both continuously and discontinuously. In the spinning solution, inorganic or organic additives can be incorporated, such as. B. Niating agents, stabilizers, flame retardants, etc.

The spinning process according to the invention is characterized by a high effective total drawing of at least 1: 9. When determining the effective total drawing, only the wet drawing and the contact drawing are taken into account, but a shrinkage of the threads is deducted. The so-called nozzle warpage is not included in the values of the total draw, the fresh spun threads that are obtained after a dry or wet spinning process are rather classified as undrawn material. The effective total drawing should be at least 1: 9 by the method according to the invention. Effective total draw ratios of 1:10 to 1:25 are preferred.

The method according to the invention can be carried out on conventional thread or fiber spinning systems. New techniques that were not previously common are not required. In particular, it is not necessary to use a special drawing chamber in which the threads, for. B. exposed in cable form to the action of steam under pressure. The process is characterized by high total draw values of the freshly spun threads, whereby an effective minimum draw of 900% is required. This effective total drawing takes place in several stages. First, the threads are stretched wet before or after washing out the residual solvent content in one or gradually in several hot baths. The temperature of the stretching bath media, which generally consist of mixtures of water and the solvent, should be kept as high as possible. Temperatures a little below the boiling point of the bath liquid are preferred. However, baths which contain other stretching bath media are also possible, e.g. B. glycol or glycerin, optionally in a mixture with the polymer solvent, at which stretching temperatures above 100 ° C can be selected. After stretching and washing out the residual solvent content, which can also be washed out first and then stretched, the threads 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 influence the stretching behavior of the threads. It should therefore be selected from known preparation mixtures that shows a low thread-thread friction.

The threads are then dried under tension on hot rollers. When drying, a small amount of shrinkage, which often proves to be advantageous for the subsequent stretching, can be permitted; When setting the shrinkage, however, care must be taken that the cables always run under tension over the drying rollers. The temperature 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 in the range from 140 to 200 ° C. have proven particularly favorable for these rolls, 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 spun tow is stretched again using dry heat at least 1.5 times its length. The stretching can also take place in one or more stages. The heating of the cable can be done according to the usual methods in the art, e.g. B. by rotating hot rollers, by contact over hot plates, in a hot air duct or by radiation, especially infrared radiation. Gradual stretching, in which different heating methods are used, can also be used.

The drawing temperatures are influenced by the type of polymer used and in part by the previous drawing and the drying conditions. A temperature range of about 120 to 250 ° C. is generally suitable, and the range of 140 to 200 ° C. is particularly favorable.

After stretching, the threads are exposed to dry heat at temperatures of 170 to 280, preferably 180 to 250 ° C fixed without approval of shrinkage. The fixation can be done according to the usual methods in the art, for. B. by rotating hot rollers, by contact with hot plates, in a hot air duct or by radiation, especially by infrared radiation.

After fixation, the threads are cooled, either wound up into continuous material by known methods or cut into fibers with the desired cutting length. If required by the field of application, a special preparation can be applied to the threads or fibers before or after cutting.

The selection of the temperatures and the residence time of the threads during fixing can have a significant influence on the physical properties of the threads treated in this way and on their resistance to swelling and / or hydrolytically active substances. The optimal conditions in individual cases can, however, be determined by simple tests. They are influenced, for example, by the titer of the individual filaments, the total thread thickness, the quality of the contact with the heated surfaces, etc. Under the conditions of Example 4, optimal values at temperatures of the first duo of 190 ° C. and 230 to 250 ° C. for the second duo and residence times of in total about 40 seconds were observed on the surfaces of the rolls.

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

example 1

A polymer of 99.4% acrylonitrile and 0.6% methyl acrylate was continuously dissolved in a 17% spinning solution in dimethylformamide, filtered and degassed. From this spinning solution, 351 g / min were pressed through a 2500 hole nozzle, hole diameter 0.06 mm, into a precipitation bath which contained 56% dimethylformamide (DMF) and 44% water and was 50 ° C. warm. The threads obtained were drawn off the nozzle at 6.5 m / min, drawn in baths containing 56% DMF and 44% water at 98 ° to six times their length and then washed. When washing in hot water, 9% shrinkage was allowed. After passing through an Aviva bath, the threads were dried at 165 ° C. and stretched 2.4 times their length in several stages at 180 ° C. The total draw was 1: 13.1.

The individual filaments produced in this way had the following properties:

Threads with these properties were fixed after the second drawing over hot plates with a surface temperature of 230 ° C. while keeping their length constant. After fixing, the individual filaments had the following properties.

The fixed and, as a comparison, the unfixed fibers were each treated for 24 hours with a cement filtrate, made from 150 g of Portland cement and 1 liter of water, at different temperatures. The aqueous cement extract had a pH of approximately 11.6. After the treatment, the tested filaments were briefly rinsed with water and air-dried at room temperature. Force expansion diagrams were then recorded on the individual filaments at an elongation rate of 100% / min and the initial moduli were determined.

During the treatment at 90 ° C the fixed fibers shrank by 3%, the unfixed ones by 12.5%.

Example 2

Analogously to Example 1, fibers with a single titer of 1.3 dtex were spun. The total draw had to be reduced to 1: 12.3. The fibers obtained were fixed at 230 ° C. The following fiber data were obtained:

Example 3 (comparison)

A polymer was spun according to Example 1, but consisting of 95% acrylonitrile and 5% methyl acrylate. With these threads, the stretching had to be reduced somewhat after drying, so that the total stretching was only 1: 11.7. The unfixed fibers had an initial modulus of 1,340 cN / tex, those fixed at 230 ° C an initial modulus of 1,020 cN / tex. After a 24-hour treatment at 90 ° C. in the Portland cement filtrate described, the unfixed fiber had an initial modulus of 720 cN / tex and the fixed one an initial modulus of 740 cN / tex. After this treatment, both fibers had a slightly sticky surface in the moist state, which suggests that the fibers had already been slightly saponified in the hot, alkaline medium.

Example 4

1,700 g of a polymer composed of 99.2% acrylonitrile and 0.8% methyl acrylate were batchwise dissolved in 8,300 g of DMF. After filtering and degassing this spinning solution, 15.1 g / min were pressed through a nozzle with 100 holes, hole diameter 0.075 mm, into a precipitation bath consisting of 50% DMF and 50% water at 50 ° C. The threads obtained were drawn off from the precipitation bath at 5.5 m / min and drawn to 29.3 m / min in a drawing bath composed of 60% DMF and 40% water at 99 ° C. The threads were then washed, finished and dried on 2 duos with surface temperatures of 140 and 185 ° C with a .shrinkage of 0.6 m / min. The threads were drawn from the second duo at 33.3 m / min and stretched over 4 hot plates at temperatures of 150, 160, 160 and 175 ° C. to 91.9 m / min. The total draw was therefore 1: 16.5.

These threads were then fixed on 2 heated duos with the exclusion of shrinkage. The diameter of the duos was 180 mm, the threads were passed 42 times around the 1st and 39 times around the 2nd duo. The properties of the individual filaments of the threads obtained as a function of the fixing temperatures used before and after 24 hours of treatment in a 90 ° C. aqueous cement filtrate have been summarized in the following table. The titer of the filaments was 2.8 dtex in each case.
(See table on page 7 f.)

Claims (2)

1. Filaments or fibers of acrylonitrile polymers, wherein their filament-forming substance is composed to a least 98 % by weight of acrylonitrile units and the relative viscosity of which (measured on a 0,5 % by weight strength solution in dimethylformamide at 25 °C) is within a range between 2.5 and 6.5, the filaments or fibers having a tenside strength of more than 50 cN/tex. a shrinkage at the boil of less than 5 %, an elongation at break of a most 15 % and an initial modulus, calculated on 100 % elongation, greater than 900 cN/tex after an aqueous alkaline treatment at 90 °C for 24 yours.

2. A process for the production of filaments and fibers as claimed in claim 1, characterized in that the filaments drawn from the jet, received by a wet or dry spinning method, are wet-stretched before or after the wash, drying them under tension on hot rolls and afterstretching them at 140 to 200 °C under the action of dry heat, the after-stretch ratio being at least 1 1.5 with the total stretch ratio being at least 1 : 9 and after the after-stretch setting the filaments with shrink prevention at 170 to 280 °C, preferably 180 to 250 °C by the action of dry heat.