EP0091567A2 - Process for the manufacture of thermostable fibres and yarns - Google Patents

Abstract

The invention relates to continuous processes for the production of synthetic threads and fibers made of acrylonitrile which are insoluble in dimethylformamide and which have a weight loss of at most 20, preferably 15% when heated to 400 ° C., by spinning appropriate polymer solutions, continuous treatment of the thread strands obtained before the first drying or heating with an aqueous solution containing copper (I) ions, heat setting of the copper content and heating of the strands to 200 to 350 ° C.

Description

The invention relates to continuous processes for producing synthetic threads and fibers insoluble in N, N-dimethylformamide from acrylonitrile polymers, which have a weight loss of at most 20%, preferably 15%, when heated to 400 ° C.

Conventional polyacrylonitrile threads and fibers have a weight loss of approx. 30 to 40% under these conditions and largely lose their textile technology properties.

Until now, fibers with a similarly low weight loss could only be obtained by a separate preoxidation, as is known for the production of carbon fibers.

This pre-oxidation, which is usually very time-consuming and costly, cannot be combined continuously with the production process of the starting threads.

There has been no shortage of attempts, in particular in recent years, to shorten the preoxidation time by using heavy metal salts as catalysts. For example, impregnation of the polyacrylonitrile threads or fibers with a copper (II) chloride solution has been proposed.

However, even under these conditions, as described in JP-OS 49 035 629, the pre-oxidation time is still 3 hours.

The treatment of acrylic fibers with copper (I) salts to achieve dyeability with acid dyes was only used in the beginning of acrylic fiber processing as a so-called cupro ion dyeing process. A summary of this work is, for example, by Rath et al. in " _M elliand Textilberichte" 38 (1957), pages 431 to 435 and 538 to 542. More recently, JP-OS 51-90387 has described the aftertreatment of moldings with copper (I) salts with the aim of catalyzing the preoxidation during the thermal stabilization of these products.

When copper (I) salts are reacted with polymers containing acrylonitrile building blocks, a cupro-ion complex is formed with the nitrile groups of the polyacrylonitrile. However, the subsequent conversion of copper (I) salts with shaped structures made of polyacrylonitrile is extremely complex and, due to the instability of the copper (I) salts in aqueous solutions, in particular at elevated temperatures, cannot be regulated reproducibly. The treatment of polyacrylonitrile powders with solutions of copper (I) salts leads to products which are insoluble in the known solvents for polyacrylonitrile or which form gel-like, non-spinnable masses in the course of the solution attempts. If, for example, copper (I) salts are added to a finished spinning solution, the spinning solution begins to gel and can no longer be spun without interference, while the extrusion of spinning masses containing copper (I) salts into injection molded articles may not yet be hindered.

So there was still the task of making threads and fibers from organic polymers simple, continuous lier way to produce, which have the properties of the threads obtained by protracted pre-oxidation or even exceed these properties.

Surprisingly, it was found that it is possible to produce synthetic fibers and threads insoluble in dimethylformamide from acrylonitrile polymers with increased thermostability if the polymers usually spun into strands or cables during their production process before the first drying or a first temperature treatment continuously above 100 ° C. are treated with an aqueous solution containing copper (I) ions, the copper content in the strands or cables is fixed at the same time or by subsequent heating to temperatures above 60, preferably above 100 ° C., and the strands or cables open during or after drying Temperatures of 200 to 350 ° C are heated. With this process, the copper (I) ions are absorbed within seconds and can therefore be integrated into the production process of threads and fibers containing acrylonitrile without difficulty. It does not matter whether the threads were produced using a dry or wet spinning process. The copper (I) ions are naturally particularly easily absorbed with wet-spun threads; However, it is also possible to load dry-spun threads which still contain solvent within the washing process or post-treatment process with copper (I) ions. Depending on the desired amount of copper (I) ions taken up, the treatment can be carried out before, during or after the washing of the strands or cables. The copper (I) content in the threads can of course also be influenced by the length of the exposure time and the concentration in the bath liquid.

The uptake of the copper (I) ions from a bath or from a spray zone at room temperature is largely reversible, which means that the copper content can be reduced by the following washes can be removed. For this reason, it is necessary to fix the copper content in the fiber. This fixation can be carried out by a temperature treatment above about 60 ° C., preferably above 85 ° C., or by a drying process in which correspondingly high temperatures are usually exceeded. Naturally, not only the temperature used, but also the dwell time of the threads or cables is important for the fixing process. While the fixation, for example, requires longer dwell times at 65 ° C., at temperatures above 100 ° C., only times of one minute or possibly a few seconds are required for the same effect. In contrast to the uptake of the copper (I) ions from aqueous solutions at room temperature, fixation of the copper (I) ions in the polymer molecule is observed at the same time when using bath temperatures from about 60 ° C. If, for example, the copper (I) bath is kept at the boiling temperature, the copper (I) ions are absorbed and fixed at the same time. A disadvantage of this process, however, is that the stability of aqueous solutions containing copper (I) ions generally decreases significantly with temperature, and the controllability of the uptake of copper ions is usually made noticeably more difficult.

After such a temperature treatment or fixation, the copper (I) content can no longer be washed out; it can be assumed that the copper (I) ions have been complexly incorporated into the polyacrylonitrile under these conditions.

A common procedure consists in pulling the cable or the strands through a copper (I) ion-containing bath and, after the excess bath liquid has been largely squeezed out, for example via hot godets of, for example, 100 ° C. surface temperature. Then, if desired, a further wash can be provided to remove copper salts adhering to the surface etc. from the threads, in order to then apply a customary preparation to the threads or cables in a subsequent bath before they are finally dried.

However, it is also possible to treat the cables with a copper (I) ion solution immediately before the first drying and to fix them with drying. In this case, the threads have superficially non-complexly bonded copper compounds that can be detached on first contact with water. Instead of using heated godets or rollers, it is also possible to carry out the temperature treatment to fix the copper content in a steam atmosphere, for example at temperatures above 95 ° C. or using infrared radiators or by passing over a contact heat path.

• Die gewünschte Lösung kann durch Auflösung von Kupfer(I)-Salzen, zum Beispiel cuCl, in Wasser erfolgen, wobei es wegen der schlechten Löslichkeit dieser Salze von Vorteil ist, diese Lösungen in 20 bis 50 %igen Natriumchloridlösungen zu bereiten.

The treatment medium is in all cases an aqueous solution of copper (I) salts. There are various ways of producing such a solution. The following options are mentioned as examples:

• The desired solution can be obtained by dissolving copper (I) salts, for example cuCl, in water, and because of the poor solubility of these salts it is advantageous to prepare these solutions in 20 to 50% sodium chloride solutions.

Furthermore, a copper (I) ion solution can be produced directly by electrolytic reduction of copper (II) solutions or by heating copper (II) salt solutions in the presence of metallic copper, the copper being added in the form of a powder or by electrolysis can be generated.

In addition, the solution can be prepared by mixing a copper (II) salt solution with a reducing agent.

The copper salt CuSO ₄ x 5 H ₂ 0 has proven to be particularly favorable as the usual copper (II) salt.

Of the many possible reducing agents proved Aldehyde sulfoxylates, and in particular the sodium salt of hydroxymethanesulfinic acid, are particularly advantageous since high copper (I) ion concentrations with good stability can be obtained with this system. The stability can additionally be increased by suitable complexing agents. The low temperatures required for the aqueous solutions make a significant contribution to the stability of the copper (I) solutions. In contrast to the old cuproion process, which was carried out at cooking temperature, a temperature close to room temperature is sufficient in almost all cases. If necessary, temperatures slightly above room temperature, i.e. from 25 to 30 ° C, for example, can be used, since here the constant temperature of the bath can be ensured by the simplest technical means. If desired, however, it is also possible to work at higher temperatures, for example 60 to 95 ° C.

Since the stability of copper (I) solutions is only guaranteed for shorter times even at room temperature, the following procedure has proven to be particularly favorable.

A copper (II) salt solution in water and an aqueous solution containing the reducing agent are metered separately into the bath near the entry point of the cable and mixed in the bath. This ensures that fresh copper (I) solution is applied to the cable. Cable and bath liquid move in direct current, excess bath liquid, which is expediently largely used up, is drawn out of the tub near the cable outlet and returned, for example, after refreshing.

The concentration of copper (I) ions can vary within wide limits depending on the desired fiber properties.

If the copper (I) solution is produced by reducing copper (II) compounds, then the reducing agent is use at least in the stoichiometric amount. A slight excess is preferably used in order to avoid the presence of copper (II) salts. In contrast to the copper (I) compounds, the copper (II) ions cannot be bound in a complex manner by the polymer molecules, so they are washed out during subsequent washes and pollute the waste water. A large excess of reducing agents generally has no further advantages. Rather, there is a risk that the copper (I) compound is further reduced to metallic copper, that it can then no longer be incorporated into the threads or fibers.

An exception here seems to be the aldehyde sulfoxylates, in which even a larger excess at room temperature does not increase the copper deposition.

The processes customary in the art for the production of polyacrylonitrile fibers and filaments can be used for the process according to the invention. As already mentioned above, there are particular advantages with the wet spinning process, since in general the diffusion of the copper (I) ions into the wet-spun threads is easier than with dry-spun threads.

The copper (I) ion solution can be applied to the cables or thread strands by various known methods, for example by passing the cables or strands through a bath. However, it is also possible to apply the solution by spraying or the like. It is advantageous to squeeze the fiber cables or strands as far as possible before and after the treatment with the aqueous copper (I) ion solution. It can thus be ensured _that the carry-over of the copper ions into and other baths does not lead to an unnecessary dilution of the copper (I) ions. treatment bath remains within tolerable limits. Of course, it is advantageous if measures are taken which ensure good and uniform penetration of a thread cable or strand in the treatment liquor. For example, cables should be so wide in the loading treatment bath that a depletion of the copper ion concentration or a delayed penetration with the treatment bath inside the cable should be neglected if possible.

As already stated above, it is necessary to fix the copper (I) ions in the thread or fiber material by means of a thermal treatment. Only after heating to temperatures above 60 ° C., preferably above approximately 100 ° C., does the desired complex formation occur within a short time, and the copper compounds can then no longer be removed from the treated thread material by washing. For subsequent washing after the heat treatment. of course, the amount of copper compounds that was on the surface of the thread material and could not be fixed is washed off.

The acrylonitrile-containing polymers used are understood to be those polymers which are composed of more than 50%, preferably more than 85%, of acrylonitrile units. Particularly good results have been obtained with polyacrylonitriles which are composed of at least 98% acrylonitrile units. Other copolymer components that can be considered are, for example, acrylic acid, methacrylic acid and their esters and amides, vinyl acetate, vinyl chloride, vinylidene chloride, vinylidene cyanide or other unsaturated compounds copolymerizable with acrylonitrile.

The desired good thermal stability ensure the yarns or fibers produced, after drying, if appropriate, also be carried out together with the drying, a further _T empera- turbehandlung that erfolgen.soll at 200 to 350 ° C, preferably between 250 and 330 ° C. It is necessary to keep the threads under tension, preferably even to subject them to a slight additional stretching. The threads can be heated to these temperatures by known, conventional methods, such as For example, multiple routing over heated godets, use of infrared radiators or guiding over a contact heat path.

As a result of this high-temperature treatment under tension, the treated strands or cables have in general become discolored and have dark brown to black shades. The thermal stability of the threads obtained was examined with the aid of thermo-gravimetric analysis. The Thermoanalyzer 2 from Mettler Instrumente AG, Greifensee, Zurich, was used as the measuring device. The samples were heated to 400 ° C. with a heating program of 10 ° C./min and an air flow of 5 l / h and the weight loss was then determined. The threads thus continuously produced show a weight loss of only a maximum of 20%, preferably less than 15%, in the case of such heating to 400.degree. They can be converted into pre-oxidized fibers or thread strands within a few minutes, which can then be subjected to a carbonization process above 700 ° C.

Due to the good thermal resistance, such threads and fibers are particularly suitable for technical purposes, such as filter material for hot gas filtration, for the production of protective clothing and the like, and as reinforcing fibers or threads for inorganic and organic materials such as e.g. as asbestos substitute e.g. in friction linings or the like. In addition, it is possible to make the products obtained practically non-flammable by further temperature treatment in the de-energized state. This temperature treatment generally causes the threads treated in this way to crimp.

In the heat treatment after drying at temperatures of 200 to 350 ° C, the residence time of the thread material at these temperatures naturally also plays a role. Generally, residence times from a few seconds to a few minutes are required to achieve the desired one To achieve effect. In any case, the temperature treatment is so short that it can be integrated into a continuous thread or fiber manufacturing process. If it is not necessary to remove the copper compounds adhering to the surface of the threads or cables, it is possible to combine the copper fixing process with drying and the subsequent heat treatment.

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

example 1

A 17% solution of polyacrylonitrile in dimethylformamide was spun in a known manner using the wet spinning process. The polyacrylonitrile used consisted of 99.5% acrylonitrile building blocks and 0.5% methyl acrylate building blocks and had a relative viscosity of 2.9. The relative viscosity was determined in solutions containing 0.5 g of polymer in 100 ml of N, N-dimethylformamide, measuring temperature 25 ° C. The temperature of the spinning solution was 90 ° C. A 300 perforated nozzle with a bore diameter of 80 µm was used.

This spinning solution was spun in a spinning bath of 50% N, N-dimethylformamide (DMF) and 50% water at 50 ° C. and drawn off from the precipitation bath at a speed of 7 m / min, followed by a wet drawing at 60 ° C. in the ratio 1: 2.31 in a bath consisting of 60% DMF and 40% water, and then washed with water at 30 ° C solvent-free. After the wash, the sliver was squeezed to remove most of the water and passed through a trough containing an aqueous solution of 100 g CuSO ₄ x 5 H ₂ 0 per liter and 20 g per liter of the sodium salt of hydroxymethanesulfinic acid. This treatment bath also contained the necessary fiber preparation. Residence time in this bath about 1.5 seconds.

The treatment solution was supplemented by continuous metering of an aqueous solution of 200 g / 1 CuSO ₄ × 5 H ₂ O and an aqueous solution of 40 g / 1 of the sodium salt of hydroxymethanesulfinic acid *. The two solutions were mixed shortly before entering the treatment tub.

^* Formula: CH ₂ SO ₂ Na x 2 H ₂ 0

After passing through the tub, the sliver was squeezed off again and then dried on two heating godets at 130 ° C (contact time 7 seconds) and then on two heating godets at 170 ° C (contact time 14 seconds) subjected to a stretching of 1: 1.85 and on one another godet of 250 ° C (contact time 9 seconds) one Subsequent stretching of 1: 1.61 and then brought to the reel via a cold take-off device. The brown-black discolored threads had a strength of 25 cN / dtex, an elongation of 7.8% and an initial modulus of 1000 cN / tex of the single thread titer was 3.0 dtex. The thermal stability of these fibers was measured using the Mettler Thermoanalyzer 2. A weight loss of 12% up to a heating temperature of 400 ° C. was found in the threads produced according to this example. A correspondingly produced fiber, which, however, was not subjected to treatment with a copper (I) salt solution, showed a weight loss of 33% according to this measurement technique.

Heating the threads or fibers obtained to 300 ° C. without tension for a period of 2 hours resulted in an incombustible fiber which had good crimp.

Example 2

A polymer solution, as described in Example 1, was spun through a 600 hole nozzle with a hole diameter of 60 μm into a precipitation bath consisting of 61% DMF and 39% water. The temperature of the precipitation bath was 50 ° C. The freshly spun threads were withdrawn from the coagulation bath at a speed of 6 m / min, subjected to wet drawing at 98 ° C. of 1: 4.86 in a bath which consisted of 62% DMF and 38% water, and then with water washed solvent-free at 80 ° C. After the washing process, the sliver was squeezed to remove a large part of the water and passed through a trough which contained an aqueous solution of 75 g / 1 CuSO ₄ x 5 H ₂ 0 and 50 g / l of the sodium salt of hydroxymethanesulfinic acid * and a conventional fiber preparation . The solution was supplemented by continuous metering of an aqueous solution of 150 g / 1 CuSO ₄ x 5 H ₂ 0 with an aqueous solution of 100.g / 1 of the sodium salt of hydroxymethanesulfinic acid. The two solutions were mixed shortly before entering the treatment tub. The copper sulfate solution used to (formula CH ₂ SO ₂ Na x 2 H ₂ O)

Reinforcement was used also contained the fiber preparation.

After passing through the tub, the sliver was squeezed off again and then dried on 2 heating godets at 190 ° C. (contact time 7 seconds) and then subjected to a drawing of 1: 1.54 on 2 heating godets at 310 ° C. The cable was then heated on 2 further godets with a surface temperature of 310 and 330 ° C. and then brought to the reel by means of a cold take-off device, again stretching by 1: 1.06. The pure contact times of the treated cable at 310 ° C were 50 seconds and at 330 ° C 15.7 seconds. The dark-colored individual filaments of the treated cable showed a weight loss of up to 400 ° C of 7%. The other technical textile data was

Titer 1.5 dtex

Strength: 23 cN / tex

Starting module 1160 cN / tex

Elongation 7%

All details of the initial module refer to an elongation value of 100%.

Example 3

A spinning was carried out in accordance with Example 2, but the fiber cable treated with the copper solution was subjected to a further wash at 80 ° C. and a preparation after drying at 190 ° (contact time 11 seconds) and then a second drying at 190 ° C. (Contact time 11 seconds).

The cable was then passed over 4 godets which were heated to a surface temperature of 310, 310, 310 and 330 °. The contact time of the cable at 310 ° C was 61 seconds at 330 ° C 18 seconds. During the high temperature treatment, the fibers were subjected to a drawing of 1: 1.25. The thread material obtained was subjected to thermogravimetric analysis and showed a weight loss on heating of up to 400 ° C. of less than 10%. The textile data found was

Titre 3.3 dtex

Strength 30 cN / tex

Elongation 11%

Initial module 811 cN / tex The fibers or thread strands obtained were subjected to carbonization at temperatures above 700 ° C. after a greatly shortened preoxidation, as is used for the production of carbon fibers. The pre-oxidation time for these cable harnesses was less than 7 minutes and thus only a small fraction of the time otherwise required.

Example 4

Thread cables corresponding to 3 were produced and these samples were then subjected to heating in a drying cabinet at 250 ° C. for 120 minutes without tension. Fibers with good crimp that were non-flammable were obtained. After this treatment, the fibers had the following textile values

Titer 3.5 dtex

Strength 30 cN / tex

Elongation 13%

Starting module 800 cN / tex.

Claims (8)

1. A process for the production of synthetic fibers and threads insoluble in N, N-dimethylformamide from acrylonitrile polymers with increased thermal stability, characterized in that a solution of a polymer which consists of more than 50% by weight of acrylonitrile units, according to a known dry or wet-spinning process is spun into thread strands or cables, which, however, are continuously treated with an aqueous solution containing copper (I) ions before the first drying or a temperature treatment above 100 ° C., the copper content in the strands or cables simultaneously or is fixed by subsequent heating to temperatures above 60, preferably above 100 ° C and the strands or cables are heated to temperatures of 200 to 350 ° C during or after drying. 2. The method according to claim 1, characterized in that the copper (I) ion-containing solution has about room temperature. 3. The method according to claim 1 or 2, characterized in that the temperature treatment is carried out during or after drying at 250 to 330 ° C. 4. The method according to any one of the preceding claims, characterized in that the fixing of the copper content and the drying or drying and the subsequent temperature treatment or all three heat treatments are carried out as a common process step. 5. The method according to any one of the preceding claims, characterized in that the copper (I) ion concentration of the treatment solution 0.1 to 50 g / l, preferred is 0.5 to 30 g / 1. 6. The method according to any one of the preceding claims, characterized in that the thread strands or cables after the continuous treatment with a solution containing copper (I) ions and extensive stripping and / or squeezing the excess solution, first a temperature treatment above 60, preferably Be subjected to above 100 ° C, in order to then be subjected to further washing processes, preparation and drying with subsequent thermal treatment. 7. The method according to any one of the preceding claims, characterized in that the solution containing copper (I) ions is produced or refreshed continuously by mixing a solution containing copper (II) ions with an aqueous solution containing a reducing agent, the reducing agent must be added at least in the stoichiometric ratio. 8. The method according to claim 7, characterized in that a solution containing copper (II) ions contains a solution of copper (II) sulfate in water and as a reducing agent solution contains a solution of an aldehyde sulfoxylate, preferably the sodium salt of hydroxymethanesulfinic acid, in Water is used.