WO1994025649A1

WO1994025649A1 - Modified polyimide fibres, process for producing the same and their uses

Info

Publication number: WO1994025649A1
Application number: PCT/EP1993/001018
Authority: WO
Inventors: Tamara Kurmangazievna Musina; Sinaida Grigorjevna Opric; Aleksandr Michajlovic^¿ S^¿C^¿ETININ; Aleksandr Ivanovic^¿ ANDREJAS^¿IN; Nikolaj Malinin
Original assignee: Pion Ag
Priority date: 1993-04-27
Filing date: 1993-04-27
Publication date: 1994-11-10

Abstract

Modified polyimide fibres have a set of characteristic parameters, among which a statistical cation exchange capacity (covering capacity) in a range from 3 to 4.5 mVal/g, an oxygen index (LOI value) in a range from 40 to 80 % and a breaking strength from 50 to 160 cN/tex. According to a process for producing modified polyimide fibres, polyamide acid fibres produced in a manner known per se are thermochemically processed at high temperature in the presence of a modifying agent in the form of an acid compound applied on the fibres, so as to transform them into fixed modified polyimide fibres. These fibres are used as reinforcing fibres, in textile materials suitable for producing articles of clothing, and when associated with other textile materials, such as cotton fabrics, also for producing multilayered fabrics for protective clothing.

Description

Modified polyimide fibers, processes for their production and their uses

The invention relates to high-temperature-resistant modified aromatic polyimide fibers, processes for their production and preferred uses of these modified polyimide fibers.

Fibers made of polyimides, in particular aromatic polyimides, have long been known from the prior art. One process for the production of polyimide fibers consists in first starting from selected monomers (tetracarboxylic acids and diamines or diisocyanates)

Produces solutions of polyamic acids, spins them into polyamide acid fibers and then converts the polyamide acid fibers obtained into polyimide fibers. Regarding the relevant prior art, reference is made, for example, to DE-A-2442 203, DE-A-28 29 811, DE-A-32 12 384,

US-A-3,179,614, US-A-3,415,782 and the prior art cited in the cited documents.

To supplement the disclosure of the present application with regard to the process steps which are assumed to be known per se in the present application and to the media used in these process steps known per se and to the process conditions refer in particular to DE-A-28 29 811, to which express reference is hereby made.

Such processes, which form the narrower prior art, are to be distinguished from other processes for the production of polyimide fibers, in which, as in EP-A-119 185 and EP-A-481 953, a solution of the finished polyimide is assumed or in which fibers from certain polyimides are produced by melt spinning, as described in EP-A-291 801.

Certain handi grades of polyimide fibers for special applications are already available in various countries, and an overview of the polyimide fibers produced in the former Soviet Union under the name "Arimid" has recently been published in: Textile Res.J. 63 (2), pp. 99-103 (1993).

The subject of the present patent application are polyimide fibers which are improved compared to the prior art and which, owing to a special modification during their production, once again have significantly improved properties, both with regard to their high temperature resistance and flame resistance and also with regard to their strength and other properties, and methods of making such fibers and their preferred uses.

The polyimides according to the invention have, as parameters which enable them to be distinguished from the prior art, the fiber parameters which can be gathered from patent claim 1, namely a statistical cation exchange capacity (occupancy capacity) in the range from 3 to 4.5 meq / g and an oxygen index (LOI- Value) in the range of 40 to 80% and a tensile strength of 50 to 160 cN / tex.

Preferred fibers also have an elasticity modulus in the range from 1500 kg / mm ² to 23000 kg / mm ² ,

The preferred polyimide fibers according to the invention are completely aromatic polyimides of the general formula

in which Q represents a radical which is derived from one or more tetracarboxylic acids which are selected from pyromellitic acid, diphenyltetracarboxylic acid, diphenyl oxide tetracarboxylic acid, benzophenone tetracarboxylic acid, hydroquinone bis (3,4-dicarboxyphenyl) ether, resorcinol bis (3,4-dicarboxyphenyl) ether or p-phenylene-bis-trimellitate, and

R stands for a radical which is derived from one or more diamines which are selected from p-phenylenediamine, m-phenylenediamine, a diaminodiphenylmethane, a diaminodiphenyl oxide, 4,4'-diaminodiphenyl, 4,4'-diamino-p terphenyl, 2,7-diaminofluorene, 2,7-diaminofluorenone and 2,8-diaminophenoxazine, polyimides being preferred in which Q is derived from one of the tetracarboxylic acids pyromellitic acid, 3,3 ', 4, 4'-diphenyltetracarboxylic acid, 3,3 ', 4,4'-benzophenonetetracarboxylic acid and 3,3', 4,4'-diphenyloxide tetracarboxylic acid and R is derived from p-phenylenediamine, m-phenylenediamine,

4,4'-diaminodiphenyl oxide and 4,4'-diaminodiphenylmethane. Polyimides from all of the monomer units mentioned are known per se.

The polyimide fibers according to the invention can be known from known polyimide fibers from the above-mentioned building blocks in addition to the parameters selected above in the sense of a Description by "product-by-process" can be distinguished, namely in that they are obtainable by a special thermochemical treatment in which a modifier is used in the polyamide acid fiber, which is produced in a manner known per se, prior to its thermal treatment Form of a non-volatile acid compound is applied and the thermal treatment takes place in the presence of this applied modifier.

The basic process which enables the production of modified polyimide fibers which are improved in the sense of the present invention accordingly relates to a process in which a polyamic acid fiber is obtained, which in a manner known per se by wet spinning a solution of the corresponding polyamic acid in a polar aprotic organic solvent was obtained in a precipitation bath, for conversion into a polyimide fiber, a thermal treatment in the presence of a modifier in the form of a sufficiently non-volatile acid compound. When the term "fiber" is used in connection with the present invention, this term is usually synonymous with the term "monofilament" or "monofilament yarn" or "thread", unless it is clear from the particular situation Context.

Preferred embodiments of this method are given in claims 9 to 12 or are described below.

Owing to the improved properties of the polyimide fibers according to the invention, particularly advantageous uses are claimed in claims 13 to 17 or are also explained in more detail below.

According to the present invention, modified polyimide fibers with improved properties are described, which fibers are known per se from the prior art represent aromatic polyimides, but differ from them by a total of physical and chemical fiber properties. A property of these fibers, which is the result of the special thermochemical treatment process used for their production and which is particularly suitable for distinguishing them from most other polyimide fibers, is a certain cation exchange capacity of the polyimide fibers according to the invention, which can be expressed as H ^* cation exchange capacity in the Range from 3 to 4.5 meq / g (mgram equivalent per g; val / kg), without the use of monomers in the preparation of the polyimide fibers according to the invention which have, for example, sulfonic acid or phosphonic acid or other side groups, such as those for synthetic Cation exchange materials are typical.

The polyimide fibers according to the invention also have values for the oxygen index (LOI) in a range which is in the upper limit range of known polyimide fibers or is even significantly better. At the same time, the strength and the modulus of elasticity, which are frequently limited in the case of polyimide fibers, are also improved, so that the polyimide fibers according to the invention achieve values with these properties which place them in the class of high-strength fibers.

At the same time, the polyimide fibers according to the invention have a distinctly textile character and can advantageously be processed into textiles which are very similar to "normal" textiles in terms of their wearing comfort.

The polyimide fibers according to the invention are produced from polyamic acid fibers which are based on known processes suitable for the purposes of the present invention for polymerizing tetracarboxylic acids and diamines or diisocyanates with the formation of Has obtained polyamic acid solutions as spinning solutions and their wet spinning using suitable precipitation baths known per se. The polyimide fibers according to the invention obtain their special properties in particular through a thermochemical treatment coupled with the imidization stage, in which catalytically active acid compounds are used, especially at the elevated temperatures of the treatment, sufficiently non-volatile inorganic acid compounds.

These non-volatile acid compounds can be inorganic, but also organic in nature, but they must not be volatile or, at least at the initial temperatures of the subsequent thermal treatment, not be evaporable. Ortho-phosphoric acid and its derivatives and condensation products such as pyrophosphoric acid can be mentioned as preferred examples of such acid compounds. In addition, sulfuric acid and - under certain circumstances - hydrochloric acid can also be used.

Because of their many physical and mechanical parameters, the polyimide fibers according to the invention fall within the range of currently industrially produced synthetic fibers, but differ from most of these synthetic fibers in that they are extraordinarily stable at high temperatures (300 to 400 ° C.) space over extended Zeit¬ as well as at temperatures up to 1000 ^β C for short periods.

The fibers have a high resistance to the action of an open flame in an environment with an increased oxygen content (LOI values of 40 to 80%, in particular 50 to 75%). In this context, it is particularly important that the flames do not in any way produce smoke or release harmful substances. Thus, fabrics based on the polyimide fibers according to the invention retain up to two minutes of exposure to the flame of a propane burner, the temperature of which is 1200 ° C., and its textile structure and are only destroyed by a subsequent external mechanical exposure.

The polyimide fibers according to the invention, like many polyimide fibers in general, also have the property of maintaining their elastic properties and strength properties even at very low temperatures, down to temperatures of the liquid nitrogen.

Like other known polyimide fibers, the fibers are also stable to radioactive radiation and UV radiation (for example, the mechanical properties do not change after 200 hours of exposure to a UV source (PRK-2) in air, and when exposed to ionizing electron radiation with a total dose of 1000 billion, they lose no more than 20% of their initial strength).

A particularly interesting property of the polyimide fibers according to the invention also consists in the fact that, like other known polyimide fibers, they deform almost completely elastically, even at elevated temperatures.

There are also medium-frequency dielectrics in the fibers, which work from low to high temperatures. Their dielectric constant is in the range from 3 to 3.5 and their resistivity in the range from 10 ¹⁷ to 10 ¹⁸ Ohm.cm.

The fibers are stable against acids, organic solvents and fats and oils, but are attacked by bases.

The properties mentioned enable the polyimide fibers according to the invention to be used in the traditional ones Areas of application of polyimide fibers, as there are uses in apparatus which are exposed to high temperatures or ionizing radiation, as reinforcing fibers or fabrics for various synthetic resin or plastic objects and other composite materials, whereby they are characterized by a high lightness with good at the same time Characterize reinforcement properties even at high temperatures.

The polyimide fibers according to the invention are outstandingly suitable for the production of any textile fabrics, including plush or fur-like textiles, and because of their high temperature resistance they are particularly suitable for protective work clothing and as clothing for pilots and racing drivers or also for military use and are suitable for space travel.

In the technical field, polyimides are used for the production of filter materials for hot gases and aggressive liquids as well as for the production of electrical insulation, for thermal insulation and for the production of fabrics where elasticity is important both at low and high temperatures and / or which must be resistant to irradiation with ultraviolet light or with cosmic radiation.

Examples

Preferred polyamide fibers according to the invention, which are aromatic polyimide fibers of the above general formulas, are produced from polyamide acids which are produced in principle by known processes by a process which proceeds as follows:

By reacting the selected starting monomers, solutions of the corresponding polyamic acids in polar aprotic solvents, in particular in solvents of the amide type (dimethylacetamide, dimethylformamide, N-methylpyrrolidone), and from these polyamic acid solutions at a content of 5 to 35% by weight polyamic acids can be prepared by wet spinning in a conventional coagulation bath polyamic acid fibers.

As is known in principle from the prior art, the production of the polyamide fibers according to the invention is also carried out in such a way that the freshly formed polyamide acid fibers after leaving the precipitation bath at temperatures in the room temperature range, in particular at 20 ° C., in the plasticized state The fibers are then washed to remove solvent residues.

In order to obtain polyimide fibers (monofilament yarns) according to the invention from such polyamic acid fibers, the fiber surface is now preferably treated with an acid catalyst in liquid or dissolved or solid form, and the fibers are dried. The acid catalyst is used in an amount in the range from 0.3 to 3.5% by weight, based on the weight of the polymer fiber.

The acid compound used as modifier is an acid compound which does not evaporate at least at the initial temperatures of the subsequent chemical treatment, it being possible in principle to use a number of different acid compounds successfully. With good success ortho-phosphoric acid is used to produce the polyimide fiber according to the invention. However, other acids, preferably cheap inorganic acids such as pyrophosphoric acid or sulfuric acid, can also be used.

The dried polyamic acid fibers (monofilaments) with the applied modifier in the form of the above Acid compounds are then drawn through a tubular heating device with an inert gas atmosphere at a speed in the range from 20 to 100 m / min and under a tension, which is preferably in the range of about 10 cN / tex, and further stretched, wherein the heater at the input of preferably a temperature of about 270 C and ^β may have a temperature of about 630 ° C at the exit. In this case, are preferably in a first stage temperatures Wandt reasonable 270-320 ° C, and then to fix the fibers Tempera¬ structures 450-610 ^β C. At this stage can, however, isolated cases even higher temperatures are used in Ein¬.

The fibers are then cooled in the customary manner and, if appropriate, also spun into a yarn in a manner known per se like other known polyimide fibers.

The properties of three different polyimide fibers (monofilament yarns) according to the invention are given in the table below with a metric number of 34 (29.4 tex), all of the polyimide fibers having been subjected to a thermochemical treatment in the sense of the present invention. Similarly, finer monofilaments with metric numbers of 45, 70 and 90 (22.2, 14.3 and 11.1 tex) were spun from the polyimides 1 and 2.

The polyimides 1 and 2 in the table are each polyimides based on pyromellitic acid and 4,4-

Diaminodiphenyl ether, where their different physical characteristics result from slightly different conditions in the thermochemical treatment in the presence of the modifier.

The polyimide 3 also differs chemically from the poly-amide 1 and 2 in that two others are known per se The above monomers were used to prepare the polyamic acid.

table

Physico-mechanical properties of polyimide fiber games according to the invention

Parameters polyimide 1 polyimide 2 polyimide 3 yarns ^* yarns ^* yarn

Metric number (tex) 34 (29.4) 34 (29.4) 34 (29.4)

Strength, cN / tex 50-60 70-80 160

Elongation at break,% 6-18. 8-10 3-4

Modulus of elasticity, kg / mm ² 945-1000 1500 12000 thermal resistance,

% Strength after

300 ^β C / 100h 70-80 85-90 70-80 400 ^β C / 20h 48 55 54

Thermal conductivity, W / m. ^β C 0.077 0.067

LOI value,% 50 60-65 70-75

Density, g / cm ³ 1.43 1.43 1.55

Moisture absorption at 65% relative humidity,% 1.0 1.5 1.2

Shrinkage in hot water,% 0 0 0

Shrinkage in air, 300 ° C,% <5 <5 <1

Smoke development,% <1 <1 _. <1

Strength at - 196 ° C cN / text 80-90 90-100 195-200 In the table, "strength" stands for the tensile strength, measured in the usual way with a dynamometer.

The percentage residual strengths given under "thermal resistance" after the thermal treatments under the specified conditions in a thermostatted chamber correspond to the following concrete strength values (in cN / tex) for the three polyimides 1, 2 and 3 in the order of the table : (for 300 ^β C / 100h) 35-48; 59.5-72; 112-128; (for 400 ^β C / 20h) 24-28.8; 37.1-42.4; 86.4.

The polyimides according to the invention also have cation exchange capacitances in the range from 3 to 4.5 meq / g ascertained potentiometrically (inflection point of the curve of the potentiometric titration).

It is believed that this property is due to acid residues of the modifying agent bound to the fiber during the thermal treatment, the presence of which e.g. also leads to the excellent LOI values.

Usage example

For the production of protective clothing e.g. In the form of a combination for pilots, seafarers, rescue teams, firefighters or for workers and welders who have the possibility of coming into contact with open fire during their work, a laminate is used in which an outer layer made of a fabric ¬ be of polyimide fibers according to the invention is combined with at least one inner layer made of cotton.

The outer layer of the polyimide fabric leads to the fact that one is in a combination of such

Laminate can temporarily stay in a fire zone, at temperatures around 800 ° C without the protective clothing catching fire or losing its mechanical cohesion. The outer layer is vapor-permeable and prevents the development of smoke or gas from the fabric.

The at least one inner layer made of cotton increases comfort and forms a warming layer that also dissipates sweat and body heat. To a certain extent, this task can be such

Inner layer can also be taken over by a cotton underwear worn under the combination.

Instead of a single cotton inner layer, several inner layers can also be provided, one or more of which can also consist of cotton-polyimide blended fabrics. In addition to the polyimide outer layer, one or more polyimide inner layers can also be provided.

Such protective clothing ensures reliable protection of the skin of the wearer of the combination, even in the event of brief contact with an open fire.

Since the polyimides according to the invention have the property of binding a certain amount of flue gases or other toxic gases and thereby acting as a filter, they also increase safety and wearing comfort in this way.

The use of polyimide outer layers, in particular those made from a polyimide according to the invention, leads to a significant increase in the maximum operating temperatures compared to similar protective clothing. The textile character of the polyimide material also enables such a combination to be worn as normal work clothing. Due to the high strength and temperature resistance, polyimide wastes in the production of polyimide textiles or also polyimide fibers and filaments recovered from worn-out old textiles can be used for other uses without disposal problems, for example uses as reinforcing materials for different types of composite materials or for building materials. When incorporated into building boards, for example, polyimide fibers, of course also polyimide fibers recovered from old clothing, can replace glass fibers as reinforcing materials without impairing fire safety. This also leads to considerable weight savings, since polyimide bevels are much lighter than glass fibers with the same strength.

The separation of the polyimide fibers from laminates, composites or blended fabrics is e.g. using their high temperature resistance possible without difficulty.

Claims

1. High-temperature-resistant modified aromatic polyamide fiber, characterized by a statistical cation exchange capacity (occupancy capacity) in the range from 3 to 4.5 meq / g as well as an oxygen index (LOI value) in the range from 40 to 80% and a tensile strength of 50 to 160 cN / tex.

2. Polyimide fiber according to claim 1, further characterized by a modulus of elasticity in the range from 1500 kg / mm ² to 23000 kg / mm ² .

3. Polyimide fiber according to one of claims 1 or 2, characterized in that sie.as polyimide is a fully aromatic polyimide of the general formula

contains, in which Q represents a radical which is derived from one or more tetracarboxylic acids which are selected from pyromellitic acid, diphenyltetracarboxylic acid, diphenyloxide tetracarboxylic acid, benzophenonetetracarboxylic acid, hydroquinone bis (3,4-dicarboxyphenyl) ether, resorcinol bis- (3,4-dicarboxyphenyl) ether or p-phenylene-bis-trimelli¬ tat, and

R represents a radical which is derived from one or more diamines which are selected from p-phenylenediamine, m-phenylenediamine, a diaminodiphenylmethane, a diaminodiphenyloxide, 4,4'-diaminodiphenyl, 4,4'-diamino -p- terphenyl, 2, 7-diaminofluorene, 2,7-diaminofluorenone and 2, 8-diaminophenoxazine.

4. polyimide fiber according to claim 3, characterized in that Q is derived from one of the tetracarboxylic acids

Pyromellitic acid, 3,3 ', 4,4'-diphenyltetracarboxylic acid, 3,3', 4,4'-benzophenonetetracarboxylic acid and 3,3 ', 4,4'-diphenyloxide tetracarboxylic acid and R is derived from p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl oxide and 4,4'-diaminodiphenylmethane.

5. polyimide fiber according to any one of claims 1 to 4, characterized in that it is obtainable by known wet spinning a solution of a corresponding polyamic acid in a polar aprotic organic

Solvent in a precipitation bath, stretching the polyamic acid fiber obtained in the plasticized state and transferring the dried polyamic acid fiber obtained by thermal treatment at elevated temperature into a polyimide fiber, a modifier in the form of a non-volatile acid compound being applied to the polyamic acid fiber prior to its thermal treatment and the thermal treatment in the presence of the applied modifier.

6. Polyimide fiber according to one of claims 1 to 5, characterized in that it is obtainable by a process according to claim 5, in which the thermal treatment in two stages at temperatures in the range from 270 to 610 ° C under an inert gas atmosphere he follows.

7. polyimide fiber according to any one of claims 1 to 6, characterized in that it is obtainable by a process according to claim 5, in which the non-volatile acid compound is applied to the polyamic acid fiber in the form of a solution or in solid form.

8. A process for the production of modified aromatic polyimide fibers with improved high temperature strength and flame resistance, characterized in that a polyamic acid fiber obtained in a precipitation bath in a manner known per se by wet spinning a solution of the corresponding polyamic acid in a polar aprotic organic solvent was subjected to a thermal treatment in the presence of 0.3 to 3.5% by weight, based on the weight of the dry polyamic acid fiber, of a modifier applied to the fiber in the form of an acid compound for conversion into a polyimide fiber.

9. The method according to claim 8, characterized in that one applies the non-volatile acid compound following the stretching and before drying in liquid or dissolved form on the polyamic acid fiber.

10. The method according to claim 8, characterized in that the non-volatile acid compound is applied in solid form to a stretched, washed and dried polyamide acid fiber.

11. The method according to any one of claims 8 to 10, characterized in that the ortho acid compound is

Phosphoric acid used.

12. The method according to any one of claims 8 to 11, characterized in that one carries out the thermal treatment under tension in a tubular heating device with an inert gas atmosphere in which the temperature at the outlet of the heating device is 250 to 400 ° C higher than at the entrance.

13. The method according to any one of claims 8 to 11, characterized in that one carries out the thermal treatment in the presence of the modifier in two stages, wherein temperatures in the range from 270 to 320 ° C are used in the first stage and temperatures in the range from 450 to 610 ° C are used in the second stage.

14. Use of a modified polyimide fiber according to one of claims 1 to 7 or the product of a method according to one of claims 8 to 13 for the production of textile fabrics for the production of clothing.

15. Use of a modified polyimide fiber according to claim 14 for the production of woven fabrics for the manufacture of protective clothing.

16. Use of a modified polyimide fiber according to claim 14 for the production of multilayer fabrics in which at least the outer layer consists of a fabric of the polyimide fiber.

17. Use of a modified polyimide fiber for the production of multilayer materials, in which at least the outer layer consists of a fabric of the polyimide fiber, according to claim 16, wherein the outer layer of the fabric of the polyimide fiber is combined with at least one further layer, which consists of a material that is selected from cotton, a cotton-polyimide blend and a rubber coating.

18. Use of a polyimide fiber according to one of claims 1 to 7 or the product of a method according to one of claims 8 to 13 as reinforcing material for plastic products and building materials.