EP0013889A1 - Continuous process for the manufacture of filaments or fibres from synthetic polymers of low solubility - Google Patents

Abstract

The invention relates to a process for the continuous production of synthetic non-discolored filaments and fibers from a filament forming synthetic polymer being difficultly soluble in an organic polar solvent particularly polyacrylonitrile polymers which process comprises preparing a suspension of said polymer and said solvent at room temperature and subsequently heating the suspension thus formed for at least 3 minutes to at least 130 DEG C., and filtering the clear spinning solution formed without intermediate cooling, homogenizing and spinning it immediately afterwards into filaments.

Description

A large number of processes are known for the production of spinnable solutions from polymerization products, such as, for example, polyacrylonitrile, for the production of synthetic threads and fibers. For example, acrylonitrile polymers can be dissolved in dimethylformamide or another polar organic solvent, such as dimethylacetamide, dimethyl sulfoxide, etc., with stirring at 70-90 ° C., then filtered and spun into threads. For technical reasons, large boilers are mostly used here, which leads to raw clay damage to the spinning solutions with longer spinning times. In the case of less soluble polymers, for example those with a high K value, or specialty polymers without plasticizing, comonomer constituents, for example acrylonitrile homopolymers, must the solution temperatures are generally increased considerably in order to obtain spinnable, bulb-free and jellyfish-free and, above all, viscosity-stable solutions. This additional temperature load on the spinning solution creates major problems with regard to the raw clay and the raw clay constancy over a longer spinning period. There has been no shortage of proposals to overcome these problems. Roughly speaking, the suggestions can be divided into two groups. One group consists of additives that are added to the spinning solution in order to have a positive influence on the raw shade, viscosity behavior and spinnability. The other group is a special procedure for the preparation of homogeneous spinning solutions.

From this group, the German patent application P 4152 29b, 3/65 should be particularly emphasized, in which a process is proposed in which the comminuted polymer is slurried in solvent and the slurry after being transferred to a heating zone to a temperature (for example 150 ^° C.) brings, in which the solvent has a noticeably dissolving effect on the polymer and the resulting clear, colorless solution spins into threads. In this process, the solution formed in the heating zone is not "kept at an elevated temperature for a substantial time" in order to avoid damage to the color of the solution. According to claim 2 and the examples, this means a duration of approximately 40 seconds.

As experiments with poorly soluble polymers have shown, this process of polymer slurry with subsequent transfer to a heating zone is still the most suitable, however, despite improved raw clay, numerous spinning problems in the form of fluctuations in titre and sticking were also found, so that use of this material, e.g. in the silk sector, with its many texturing steps, led to difficulties. There were increased capillary breaks, postponements and bristles.

It has now been found that sparingly soluble polymers can be processed in a continuous dissolving and spinning process to give threads or fibers which have a good raw tone, the disadvantages described no longer occurring when the sparingly soluble polymers which are used for spinning are combined with the spinning solvent to be used pastes, the suspension is heated for at least 3 minutes, but preferably 5 minutes, to at least 130 ° C., but preferably 150 ° C., and this still inhomogeneous solution is converted into a homogeneous, clear, viscosity-stable spinning solution with a good raw tone, filtered and immediately thereafter feeds the spinneret.

The invention therefore relates to a process for the continuous production of synthetic non-discolored threads and fibers from thread-forming synthetic polymers which are sparingly soluble in organic polar solvents by producing a suspension of polymer and solvent at room temperature and then heating this suspension, which is characterized in that the suspension is heated to at least 130 ° C for at least 3 minutes, the resulting clear spinning solution is homogenized without intermediate cooling, filtered and immediately spun into threads.

Poorly soluble polymers were understood according to the invention to mean those with K values of 90 and above. Acrylonitrile polymers with at least 85% by weight of acrylonitrile fractions, particularly acrylonitrile homopolymers, are particularly preferred.

Suitable solvents are the polar organic solvents customary for this technique, especially dimethylformamide.

The spinning solutions, which are preferably homogenized using static mixers, preferably have a solids content of 24 to 30.5% by weight.

Normally, according to the prior art, the spinning solvent, for example dimethylformamide, is mixed with the polymer solid, for example PAN powder, via a pasting device, the resulting clear, yellow solution is discharged into an intermediate vessel, brought to the desired temperature in a secondary solvent and into a venting vessel is pressed. A pump then conveys the spinning solution into a spinning kettle, from where it is conveyed through a filter to the spinning machine. A detailed description of such a PAN dissolving system is dealt with by F. Fourne, for example in chemical fibers, May 21, 1971, page 372. Compared to the conventional dissolving process described, the process found has the great advantage that large batches cannot be dissolved in boilers and pump around. At high boiler or after-dissolver heater temperatures, which are necessary to produce stable spinning solutions because of the poor solubility of certain polymers, large raw clay damage occurs due to the long spinning times and the resulting long residence times of the spinning solutions at high temperatures. In the process found, however, only as much spinning solution is produced as is actually used immediately. As already mentioned, it has been shown that the use of a high temperature alone is not sufficient to produce viscosity-stable spinning solutions. The dwell time of the spinning solution also plays an important role in these polymers. As can be seen from viscosity measurements, the residence time of, for example, acrylonitrile homopolymers with a K value of 90 and more at a spinning solution concentration of approximately 25% must be at least 3 minutes, but preferably 5 minutes, in order to obtain viscosity-stable solutions. With increasing concentration of the spinning solution, the dwell time of the spinning solution at high temperatures of 130 ° C. and more must be extended accordingly.

If such solutions are spun, titer fluctuations usually still occur, which occur in the end product in the form of bristles. In order to avoid these difficulties, intensive mixing of the spinning solution before or after the filtration has proven to be particularly suitable. Usable aggregates are, for example Static mixing elements in the form of combs, honeycomb grids, lamellas or spirals, whereby usually several elements are rotated 90 ° against each other, arranged one behind the other. An embodiment in which the mixing element is arranged directly in front of the spinneret has proven to be particularly favorable. In this way, intensive homogenization and good heat exchange as well as optimal concentration, viscosity and temperature compensation are achieved.

Suitable units for rapid solution preparation are, for example, double-walled tubes which are heated with steam at a pressure of about 3-5 bar, so that the temperature of the solution at the tube outlet is 130-150 ° C. Depending on the number of spinning positions and the spinning solution throughput, this embodiment of a heating device can be structurally dimensioned such that corresponding dwell times of at least 3 minutes can be set. In the following examples, the viscosity of the spinning solutions is expressed in falling ball seconds (measured according to K. Jost, Rheologica Acta, Volume 1, No. 2 to 3, (1958), page 303). Unless otherwise noted, parts and percentages relate to weight.

The determination of the physical quantities mentioned above was carried out as described below.

Determination of the color number:

A 5% solution of the corresponding fiber sample in dimethylformamide is prepared by treatment at 100 ° C. for 30 minutes. The mixture is then cooled to room temperature and, if it is still slightly cloudy, the solution is centrifuged off and measured in a 1 cm cuvette at 420 nm in comparison with pure DMF using the Elko II device from Zeiss. A color number up to approx. 0.25 visually represents bright white fibers. Color numbers from about 0.25 to about 0.35 represent a yellowish cream to cream-colored raw tone and color numbers above 0.35 stand for a light yellow to lemon-colored appearance of the fibers.

Assessment of the spinning pattern

100 cross-sectional images are made of each spinning test and the number of titre fluctuations and bonds per 1000 capillaries is determined. With more than approx. 5 titer fluctuations per 1000 capillaries, capillary cracks and postponements usually occur during the stretching process, which leads to bristles and fluffy material. Furthermore, a strong tendency to wrap is observed on the stretching units, which gives rise to frequent production disruptions.

Examples 1-5

75.5 kg of dimethylformamide are introduced with 24.5 kg of acrylonitrile homopolymer having a K value of 91 according to Fikentscher in a kettle at room temperature and the suspension is pumped via a gear pump into a spinning kettle equipped with a stirrer. The suspension, which has a solids concentration of 24.5% by weight, is then heated in a 60 cm long double-walled tube with an inner diameter of 8 cm using steam at a pressure of 4.0 bar. The temperature of the solution at the tube outlet is 150 ° C and the dwell time in the tube is 8 minutes. After leaving the heating device, the spinning solution is filtered, passed through a tube which is equipped with a plurality of mixing combs, and then dry-spun from a 96-hole nozzle according to procedures which are known in the art. The spun material with a titre of 1670 dtex is then drawn on a draw twister 1: 9.6 times over hot godets at 150 ° C. Perfect running behavior, without capillary cracks. Fiber strength 4.2 centinewton / dtex, elongation at break 11%. Cross-sectional microscopic images show no fluctuations in titre and sticking. The fibers with a final titer of 2.8 dtex have T- and Y-shaped cross-sections and look optically bright white. Color number = 0.238.

Wie man der Tabelle 1 entnehmen kann, werden auch mit hochkonzentrierten Spinnlösungen aus Acrylnitrilhomopolymerisat gute Verarbeitungseigenschaften unter Änderung der Querschnittsstruktur erzielt. Der Rohton ist in allen Fällen optisch gesehen hellweiß.Table 1 below shows further experiments with acrylonitrile homopolymer of different solids concentration. All polymers were as described in Example 1, spun into fibers with a final titer of 2.8 dtex and textured. The texturing was smooth in all cases.

As can be seen from Table 1, good processing properties are achieved even with highly concentrated spinning solutions made of acrylonitrile homopolymer, while changing the cross-sectional structure. The raw tone is optically bright white in all cases.

Example 6 (comparison)

Analogous amounts of dimethylformamide and acrylonitrile homopolymer, as described in Example 1, are pasted in a screw and the slurry of solution is fed into a kettle. There, the slurry is heated to 90 ^° C. with stirring for 3 hours, a solution which is not yet completely homogeneous being formed. This can be seen from the undissolved particles and jellyfish still present in the solution, so that the solution appears optically cloudy when viewed through. This unfinished solution is then heated to 120 ° C until the solution is no longer visually cloudy. After 30 minutes the solution is then filtered and spun directly as described in Example 1 _/ into threads with a total titer of 1670 dtex. In the subsequent stretching test on the stretch twisting machine, capillary breaks and tendency to wrap are repeatedly determined. Spinning image: titre fluctuations 11-12 per 1000 capillaries, no gluing. The fibers with a final titer of 2.8 dtex look optically cream-colored to light yellow. Color number = 0.360.

Examples 7-14 (Examples 7, 8, 12, 13, 14 are comparative examples)

An analogous spinning solution was produced as described in Example 1, but the residence time of the spinning solution in the heating device was shortened by changing the throughput. The amount of spinning solution conveyed was dimensioned such that a residence time of 60 seconds in the heating device after leaving the heatable tube was achieved. The solution was then again as described in Example 1, filtered, homogenized and spun into 1670 dtex threads. No processing was possible during the subsequent stretch test on the stretch twisting machine. Capillary breaks occurred constantly. Spinning image: titre fluctuations 16-17 per 1000 capillaries, bonds 1-2 per 1000 capillaries. The fibers look optically bright white, but have thick and thin spots along the individual capillaries, which can also be determined manually in the form of nodules. Color number = 0.109.

Wie man der Tabelle 2 entnehmen kann, ist der Rohton der Fasern in allen Fällen gut und verbessert sich mit abnehmender Temperaturbelastung. Die Spinnlösung sollte jedoch mindestens 3 Minuten lang auf 130°C gebracht werden, um viskositätsstabile Lösungen zu erreichen. Nur so ist ein einwandfreier Lauf auf der Strechzwirnmaschine möglich.The following Table 2 lists further tests varying the residence time and the temperature of the spinning solution in the heating device described in Example 1. In addition to the throughput, the dwell time of the spinning solution was also changed via the number of heating devices used. In all cases, a spinning solution with the chem. Composition and concentration used as explained in Example 1.

As can be seen from Table 2, the raw tone of the fibers is good in all cases and improves with decreasing temperature load. However, the spinning solution should be brought to 130 ° C for at least 3 minutes in order to achieve viscosity-stable solutions. This is the only way to ensure trouble-free running on the streching machine.

Examples 15-19 (comparison)

An analogous spinning solution as described in Example 1 was prepared, filtered and spun, but the static mixing device consisting of several mixing combs was dispensed with. The 1670 dtex spinning material was then drawn 1: 9.6 times on the drawing twister. There were repeated capillary cracks and tendency to wrap on the cops. Spinning pattern: 8-9 titre fluctuations per 1000 capillaries, bonds 3-4. The fibers had a good raw tone corresponding to Example 1. Color number = 0.203.

Wie aus Tabelle 3 hervorgeht, verschlechtert sich das Spinnbild (Zunahme von Titerschwankungen, Verklebungen und Borsten) mit zunehmender Polymerfeststoffkonzentration. Unter Weglassung der statischen Mischkämme ist praktisch keine Verarbeitung auf der Streckzwirnmaschine mehr zu erreichen. (Starke Wickelneigung, Kapillarbrüche, flusiges Material).Table 3 below shows further tests with different solids concentrations. All of the polymers were spun into fibers with a total titer of 1670 dtex, as mentioned in Example 15, and then drawn on a stretching machine 1: 9.6 times on a trial basis.

As can be seen from Table 3, the spinning pattern (increase in titre fluctuations, bonds and bristles) deteriorates with increasing polymer solids concentration. With the omission of the static mixing combs, virtually no processing on the draw twisting machine can be achieved. (Strong tendency to wrap, capillary breaks, fluffy material).

Claims (5)

1) Process for the continuous production of synthetic non-discolored threads and fibers from thread-forming synthetic polymers which are sparingly soluble in organic polar solvents by preparing a suspension of polymer and solvent at room temperature and then heating this suspension, characterized in that the suspension is at least 3 minutes at least Heated to 130 ° C, the resulting clear spinning solution was filtered without intermediate cooling, homogenized and immediately spun into threads. 2) Process according to claim 1, characterized in that acrylonitrile homopolymers or copolymers with K values of 90 and above are used as the sparingly soluble polymers. 3) Process according to claims 1 and 2, characterized in that dimethylformamide is used as solvent. 4) Process according to claims 1 to 3, characterized in that the spinning solutions used have solid concentrations of 24 to 30.5% by weight. 5) Method according to claims 1 to 4, characterized in that the homogenization takes place via static mixers.