EP0119185B1 - Method for the preparation of highly fire-retarding, heat-resisting polyimide fibres - Google Patents

Description

The invention relates to a method for producing flame-retardant, high-temperature-resistant polyimide fibers by the dry spinning method from a solution in aprotic organic solvents.

Heat-resistant polymers have been known for a long time. They contain aromatic groups in their molecular chains, so that highly conjugated binding systems are created which are essential for high temperature resistance. Examples of this are aromatic polyamides and polyimides, in which the temperature resistance could be significantly increased by substituting the aliphatic chain with benzene residues.

An obstacle to the technical application of these compounds is the fact that they are generally neither soluble nor meltable in solvents. As with other plastics, they cannot be shaped by extrusion, melt spinning, dry spinning, wet spinning or similar processes.

In order to avoid these difficulties, it has been proposed to first produce a polyamic acid by condensing a tetracarboxylic acid dianhydride with a diamine under relatively mild conditions, in which the respective amine group only reacts with one of the two available carboxyl groups of the anhydride. This polyamic acid is soluble and films, films or fibers can be formed from its solutions. The solvent is then removed from these products by heating and the reaction to the polyimide is carried out by further heating.

However, this procedure has serious disadvantages in that the intermediate stage is very sensitive to hydrolytic degradation and in the final condensation to the polyimide water is released again, which can only escape from the interior of the shaped bodies (films, films, fibers) by diffusion. If this reaction is carried out too quickly, the resulting water vapor forms cavities in the interior of the moldings which are harmful to the properties of use.

Another known proposal for the production of flame-retardant, high-temperature-resistant polymers can be found in DE-C-2143 080. The mixed polyimides described therein are soluble in polar, aprotic organic solvents, such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide. The polymers are prepared by the solution codification of benzophenonetetracarboxylic acid dianhydride with a mixture of tolylene diisocyanate and diphenylmethane diisocyanate in one of the aforementioned solvents. The polymer can be processed directly from the solutions. DE-A-2 442 203 further describes that fibers can be produced from the solutions, in particular by wet spinning, the fiber cross section being able to be designed differently by selecting the spinning bath. When using water with varying proportions of polar aprotic solvent (e.g. dimethylformamide, dimethylacetamide, N-methylpyrrolidone or similar) the fiber cross section is round or elliptical. When using z. B. Glycerin in the precipitation bath pseudo hollow fibers with a narrow longitudinal slot and a serrated outside. With regard to dry spinning, DE-A-2442 203 only contains general information without any statement about the fiber properties that can be achieved.

The production of polyimide fibers by the dry spinning process from solutions, which polymers, formed from benzophenonetetracarboxylic acid dianhydride and a mixture of tolylene diisocyanate and diphenylmethane diisocyanate. included, has therefore not yet been satisfactorily resolved. As a result of the saving in coagulation baths and the easier recovery of the spinning solvents in dry spinning, fiber production using the dry spinning method is also more economical from the point of view of economy than using wet spinning.

It has also already been proposed to impart a desired lobed or serrated cross section to dry or melt spinning of synthetic textile fibers by using nozzle holes with a corresponding cross section, for example in the shape of a star. So z. It is described, for example, in DE-A-3 040 970 that cross-section-modified acrylic fibers can be obtained by the dry spinning process by means of a special geometric design of the nozzle holes - by means of so-called profile nozzle holes. Apart from the difficult and expensive manufacture of the complicated nozzle openings, there is also the disadvantage that such nozzles corrode much more quickly than nozzles with a round cross section. Nevertheless, this disadvantage was accepted in order to obtain better performance properties of the fibers, in particular an improvement in the soiling behavior, an increase in the color brilliance, the achievement of a pleasant grip and an improvement in the loss of goods in textile applications.

Usually round fiber holes are obtained when using round nozzle holes in melt spinning and dumbbell-shaped fiber cross-sections when spinning solutions. Thus, no other result was to be expected when using polyimide solutions in a conventional dry spinning process.

The object of the invention is to produce fibers from flame-retardant, high-temperature-resistant polyimide polymers according to the dry spinning method, which have improved performance properties, in particular an irregular fiber cross-section, which, with the same basis weight as fibers of round cross-section, ensure much better coverage, a pleasant feel and a high level To have shine.

wobei R teilweise als eine Gruppe der Formel

und der Rest als eine Gruppe der Formel

vorliegt, erfindungsgemäss dadurch gelöst, dass der Trockenspinnprozess in einem Spinnschacht durchgeführt wird, wobei eine 20 bis 40%ige Lösung des Polyimids aus Düsen mit rundem Querschnitt, Lochzahlen von 20 bis 800 und einem Düsenlochdurchmesser von 100 bis 300 µm versponnen wird, eine Spritzgeschwindigkeit zwischen 20 und 100 m/min, eine Abzugsgeschwindigkeit zwischen 100 und 800 m/min, eine Spinngasmenge zwischen 40 und 100 m²/h unter Normalbedingungen und eine Spinngastemperatur zwischen 200 und 350 °C angewendet werden, die dabei erhaltenen Schachtkabel mit einem Restlösungsmittelgehalt von 5 bis 25 Gew.% - bezogen auf den Polymerfeststoff - und mit einem Einzelfilamenttiter zwischen 3,5 und 35 dtex in heissem Wasser gewaschen, dann auf einen Feuchtigkeitsgehalt von weniger als 5% getrocknet, anschliessend hochtemperaturverstreckt und gegebenenfalls gekräuselt und zu Stapelfasern geschnitten werden.This object is achieved in a process of the type defined at the outset, starting from polyimide polymers with a composition of the general formula

where R is partially as a group of formula

and the rest as a group of the formula

is present, solved according to the invention in that the dry spinning process is carried out in a spinning shaft, a 20 to 40% solution of the polyimide being spun from nozzles with a round cross-section, number of holes from 20 to 800 and a nozzle hole diameter from 100 to 300 μm, an injection speed between 20 and 100 m / min, a take-off speed between 100 and 800 m / min, a spinning gas quantity between 40 and 100 m ² / h under normal conditions and a spinning gas temperature between 200 and 350 ° C are used, the shaft cables obtained with a residual solvent content of 5 up to 25% by weight - based on the polymer solid - and washed with a single filament titer between 3.5 and 35 dtex in hot water, then dried to a moisture content of less than 5%, then stretched at high temperature and optionally crimped and cut into staple fibers.

As is known, the preparation of the polymers can be carried out by reacting benzophenonetetracarboxylic acid dianhydride, tolylene diisocyanate and diphenylmethane diisocyanate in an aprotic organic solvent, giving a solution of the polymer. However, the solid powdery polymer can also be brought into solution continuously or discontinuously in an aprotic solvent such as dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide, preferably dimethylformamide. The dissolving temperature is chosen between 30 and 120 ° C, preferably a solution with a content between 25 and 35 wt.% Is prepared. The solution obtained is degassed, can be filtered one or more times and is fed to the spinning head of a dry spinning device via a spinning pump.

The individual shaft output can expediently be between 20 and 400 kg fiber / d, preferably between 150 and 300 kg / d.

Depending on the design of the system, several spinning shafts can be combined to form a so-called "spinning machine _" .

The technical design of the spinning head, the spinning shaft or the entire spinning machine can be similar to that which is common in the dry spinning of acrylic fibers.

In compliance with the specified spinning conditions, according to the invention, in dry spinning from round nozzles, completely lobed and irregularly toothed fiber cross sections are obtained in a completely surprising manner.

1 shows typical fiber cross sections of a shaft cable obtained in this way.

Although the individual filaments have roughly the same fiber titer, the cross-sections are irregular and have - to use alphabetical letters as a comparison - strongly profiled shapes such as W, U, C, Y, E, V, T, X.These fiber cross-sectional shapes, which also apply to the The following fiber aftertreatment is not a property that has long been desired by textile technicians and which brings about the improvement in use properties mentioned above. The typical fiber bundle cross sections shown in FIG. 1 do not change when different numbers of nozzle holes are used, provided that the nozzle holes are only round. The same typical cross-sectional shapes were obtained when using 100-hole nozzles as well as 200, 400, 600 and 800-hole nozzles.

The shaft cables obtained in the manner described by means of dry spinning, spooled in between or deposited in cans are advantageously washed with water at a speed of 2 to 20 m / min at first at temperatures of 80 to 100 ° C. for the aftertreatment, then previved, using a sieve drum or calender dryer dried at temperatures between 120 and 300 ° C until the cable moisture after the dryer is less than 5%, the cable tape is then stretched in one or more stages in a ratio of 1: 2 to 1:10 at temperatures between 315 to 450 ° C, then post-finished with a conventional preparation, crimped in a compression crimping machine at room temperature and finally cut into staple fibers or, in the case of the production of continuous filaments, wound up after the stretching process.

The fibers are freed of residual solvent by intensive washing with hot water. Preavivation involves the application of a commercially available antistatic in order to be able to pass the sliver through the dryer without any problems. Maintaining the moisture content of less than 5% after drying is important in order to carry out the subsequent high-temperature drawing without difficulty can. This high temperature drawing is carried out either over heated rolls, a heating table or over a hot air oven, and it can be carried out in one or more stages. Maintaining temperatures between 315 and 450 ° C during stretching is necessary because of the high glass transition point of the polyimide fibers (about 315 ° C).

Despite the high glass transition point of the polymers, a satisfactory crimp can be applied with conventional stuffer box crimping machines at temperatures <100 ° C, which enables the later processing of the staple fibers on conventional textile machines. The re-finishing takes place by means of commercially available finishing agents for synthetic fibers, which can have a cationic and / or anionic and / or non-ionic character. The point in time of the re-activation does not necessarily have to be after the high-temperature stretching, but can also be selected after the crimping. The cutting into staple fibers is done with commercially available cutting machines. In the case of the production of continuous yarns, the cable strips with the desired cable thickness are passed separately through the aftertreatment system and are wound up on spools after the high-temperature stretching and possibly after-aging.

Die nach dem erfindungsgemässen Verfahren hergestellten, trockengesponnenen Polyimidfasern zeichnen sich durch folgende Eigenschaften aus:

• - Schwerentflammbarkeit: die Fasern besitzen einen LOI (Limiting Oxygen Index) nach ASTM D-2863 von >33% 0₂.
• - Die Fasern schmelzen nicht, sondern zersetzen sich bei Temperaturen > 450 °C.
• - Thermostabilität: die bisherigen Messungen zeigen,, dass die nach obigem Verfahren hergestellten Polyimidfasern Dauertemperaturbelastungen bis 260°C standhalten, ohne ihre Fasereigenschaften merklich einzubüssen. - Textilmechanische Faserdaten:
• - ausgezeichnetes Arbeitsvermögen; (ein typisches Kraft/Dehnungs-Diagramm ist in Fig. 2 dargestellt)
• - sehr gute Knoten- und Schlingenfestigkeit;
• - niedriger Faserschrumpf in kochendem Wasser « 0,5%);
• - unregelmässiger, gelappter bzw. gezähnter Faserquerschnitt;
• - begrenztes Wasseraufnahmevermögen;
• - hoher Glanz;
• - angenehmer, wollähnlicher Griff:
• - Endfasertiter variabel von 0,6 bis 10 dtex.
• - Farbe: die natürliche Farbe der nach obigem Verfahren hergestellten Polyimidfaser ist goldgelb.

The following table clearly summarizes the conditions to be observed in the individual stages in the process according to the invention:

The dry-spun polyimide fibers produced by the process according to the invention are distinguished by the following properties:

• Flame retardancy: the fibers have an LOI (Limiting Oxygen Index) according to ASTM D-2863 of> 33% 0 ₂ .
• - The fibers do not melt, but decompose at temperatures> 450 ° C.
• - Thermostability: the previous measurements show, that the polyimide fibers manufactured according to the above process can withstand permanent temperature loads of up to 260 ° C without noticeably losing their fiber properties. - Textile mechanical fiber data:
• - excellent work ability; (a typical force / strain diagram is shown in Fig. 2)
• - very good knot and loop strength;
• - low fiber shrinkage in boiling water «0.5%);
• - irregular, lobed or serrated fiber cross-section;
• - limited water absorption;
• - high gloss;
• - pleasant, wool-like feel:
• - Final fiber titer variable from 0.6 to 10 dtex.
• - Color: the natural color of the polyimide fiber produced by the above process is golden yellow.

The process according to the invention is explained in more detail in the following examples:

Example 1:

9 kg of polyimide of the general formula (I) are dissolved in 24.3 kg of dimethylformamide for 30 minutes at a temperature of 30 ° C. with stirring in a container. The mixture is then converted into a spinning solution by heating at 60 ° C. for 40 minutes, degassed at a pressure of 507 mbar, filtered and fed to the spinning head of a dry spinning shaft via a gear pump. The spinning is carried out via a 240-hole nozzle, the nozzle hole shape is circular and has a hole diameter of 175 µm. The spinning solution temperature is 70 ° C before entering the nozzle package. The spinning gas temperature at the height of the nozzle package is 295 ° C and at the end of the 8 m long spinning shaft is 115 ° C, the amount of spinning gas is 60 m ³ / h (based on normal conditions). The shaft output is set to 150 kg fiber / d. The spun material with a total titer of 2640 dtex, which has a residual DMF content of 15% by weight, based on polymer solids, is collected on spools and folded into a cable band with a total titer of 184800 dtex. The cable band is then washed in water at 90 ° C, provided with an antistatic finish in a dip tank, dried at 180 ° C using a sieve drum dryer and then stretched over a heating bracket in a ratio of 1: 5. The surface temperature of the heating bracket is 380 ° C. The stretched cable tape is provided with a mixture of cationic / nonionic preparation, crimped in a stuffer box at room temperature and cut into staple fibers of 40 mm in length. The fibers, which have a final titer of 2.2 dtex, have a strength of 28 cN / tex, the fiber elongation is 34%, the loop strength 15 cN / tex, the knot strength 20 cN / tex, the boiling shrinkage is 0.4%.

The fibers have a pronounced lobed or serrated shape in cross section (as shown in FIG. 1) and the LOI value, measured on a knitted stocking with a weight per unit area of 150 g / m ² , is 37% 0 ₂ . If the fibers are exposed to a temperature of 260 ° C for a period of 250 hours, the specified fiber data will not change, ie the fiber is thermostable at the specified temperature. The water absorption of the fibers is 20 ° C and 65% relative humidity 2.7%.

Example 2:

11 kg of polyimide of the composition described in Example 1 are dissolved in 25 kg of dimethylformamide for 40 min at a temperature of 50 ° C. with stirring in a container. The mixture is then converted into a 31.5% spinning solution by heating at 80 ° C. for one hour, degassed at a pressure of 467 mbar, filtered and fed to the spinning head of a dry spinning shaft via a gear pump. The spinning takes place via a 600-hole nozzle, the nozzle hole shape is circular and has a hole diameter of 150 µm. The spinning solution temperature is 90 ° C before entering the nozzle package. The spinning gas temperature at the height of the nozzle pack is 320 ° C and at the end of the spinning shaft 120 ° C, the amount of spinning gas is 70 m ³ / h (based on normal conditions). The shaft output is set to 200 kg fiber / d. The spun material with a total titre of 7140 dtex, which has a residual DMF content of 17% by weight, based on polymer solids, is collected on spools and folded into a cable band with a total titre of 357,000 dtex. As described in Example 1, the cable band is washed, pre-treated, dried and then stretched in two stages over heated rollers. The total stretch ratio is 1: 7, the surface temperature of the heated rolls is 340 ° C. The cable tape is crimped at room temperature in a compression crimping chamber, then treated with a nonionic finishing agent by spraying and cut into staple fibers.

The fibers, which have a final titer of 1.7 dtex, have a strength of 30 cN / tex, the fiber elongation is 30%, the boiling shrinkage is 0.45%.

The fibers show in cross section the characteristic shape shown in FIG. 1 or described in Example 1.

Example 3:

A 25% solution of polyimide (composition see example 1) in DMF, which was obtained in the polycondensation reaction, is filtered and filled directly into the degassing container. The further treatment of the solution is as in Example 1. The solution is spun using a 240-hole nozzle, the nozzle hole shape is circular and has a hole diameter of 175 _kt m. The spinning solution temperature is 60 ° C before entering the nozzle pack. The spinning gas temperature at the level of the nozzle package is 260 ° C and at the end of the spinning shaft 110 ° C, the amount of spinning gas is 55 m ³ / h (based on normal conditions). The shaft output is set to 130 kg fiber / d. The spun material with a total titre of 6240 dtex, which has a residual DMF content of 20% by weight, based on polymer solids, is collected on bobbins and several bobbins are submitted to the aftertreatment process. The individual cable tapes, each with a total titer of 6240 dtex, are passed through the post-treatment process separately, i.e. washed, pre-aged and dried. The drawing takes place in one step in a hot air oven, the drawing ratio be carries 1: 4.7. The air temperature during stretching is 420 ° C. The stretched cable tapes are then individually wound on cross-wound bobbins as an endless filament bundle. The individual filaments, which have a final titer of 5.5 dtex, have a strength of 24 cN / tex, the fiber elongation is 40%, the boiling shrinkage is 0.3%.

The filaments show in cross section the characteristic shape shown in FIG. 1.

Claims (3)

1. Method of producing non-flammable, high-temperature resistant polyimide fibres having a composition of the general formula

wherein R is present partly as a group of the formula

and partly as a group of the formula

by dry-spinning of a solution in aprotic organic solvents, characterised in that dry-spinning is carried out in a spinning column, wherein a 20 to 40% solution of the polyimide is spun from spinnerets having circular orifices, orifice numbers ranging from 20 to 800 and orifice diameters of from 100 to 300 pm, an extrusion speed of between 20 and 100 m/min, a take-up speed of between 100 and 800 m/min, an amount of spin gas of between 40 and 100 m³/h (based on standard conditions), and a spin gas temperature of between 200 and 350 °C are used, the thus obtained fibre tows leaving the spinning column, having a residual solvent content of 5 to 25% by weight - based on the dry polymer - and a single filament titer of between 3.5 and 35 dtex, are washed in hot water, then dried to a moisture content of less than 5%, subsequently drawn at high-temperature and, if desired, crimped and cut into staple fibres.

2. Method according to claim 1, characterised in that the fibre tows obtained, wound on spools or stored in cans, for aftertreatment, are first washed in water at take-in speeds of from 2 to 20 m/min at temperatures of between 80 and 100°C, are then pre-finished, dried in a perforated cylinder or cal- ander drier at temperatures of between 120 and 300°C, until the moisture content after the drier amounts to less than 5%, the tow is subsequently drawn in one or several steps at a ratio of from 1:1 to 1:10 at temperatures of between 315 and 450 °C, is then post-finished with a conventional preparation, is crimped in a stuffer box crimping machine at room temperature, and finally cut into staple fibres or, in the case of producing continuous filaments, is wound on spools after the drawing procedure.

3. Method according to 1 or both of claims 1 and 2, characterised in that a solution of the polyimide in dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone or preferably in dimethylformamide is spun.

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