JPH0455613B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing polyimide molded articles, particularly fibers or films, having excellent heat resistance and mechanical properties. More specifically, the present invention relates to a method for industrially producing polyimide fibers, films, etc. suitable for uses such as heat-resistant protective clothing, resin or metal reinforcement, etc. by wet molding polyamic acid. BACKGROUND OF THE INVENTION Polyimide has conventionally been known to be useful as a raw material for fibers, films, and other molded products with excellent heat resistance, mechanical properties, electrical properties, and weather resistance. For example, polyimide produced from 4,4'-diaminodiphenyl ether and pyromellitic dianhydride provides a film with excellent heat resistance, and is widely used for electrical insulation purposes. In the field of heat-resistant fibers, polyimide fibers having relatively rigid skeletons have been reported in recent years. For example, Japanese Patent Publication No. 57-37687 discloses that a polyamic acid solution is spun into an aqueous solution of monohydric, dihydric, or trihydric alcohol, a mixture thereof, or a polar solvent, and the resulting gel fiber is stretched, dried, and heat treated. The invention describes the production of flame-resistant, high-strength, high-modulus fibers. Also,
The Journal of the Japan Institute of Textile Technology, 40, T-480 (1984) describes a method of producing spinnerets obtained by performing wet spinning in the same manner as in the above invention using a spinning dope whose wet coagulability was improved by ring-closing a portion of polyamic acid into polyimide. It is described that a polyimide fiber with even better mechanical properties can be obtained by immersing a filamentous body in an acetic anhydride/pyridine system to promote imidization, and heat-treating it after drying. As mentioned in the latter explanation, high strength
In order to obtain a high modulus fiber, it is desirable that the polymer has as high a degree of polymerization as possible in the final fiber stage. Polyamic acids generally have poor hydrolysis resistance. Among them, some polyamic acids with ether bonds introduced into the main chain have relatively good hydrolyzability, but polyamic acids that can be used as precursors for polyimide with a rod-like skeleton have poor hydrolysis resistance. Particularly inferior. Therefore, in order to produce fibers with good mechanical properties, it is necessary to prepare a polymer with as high a degree of polymerization as possible during the polymerization process, and it is also possible to reduce the degree of polymerization during the molding process. It is necessary to suppress the In both of the above prior art techniques, an aqueous coagulation bath is used, and even though it is possible to slow down the hydrolysis rate by controlling the spinning temperature, etc., the degree of polymerization of the polymer in the spun yarn inevitably decreases. is coming. As a non-aqueous coagulation bath, it has been reported in a laboratory that a system in which acetic anhydride is mixed with an aromatic hydrocarbon such as toluene is used as a ring-closing bath. In this system, hydrolysis by water and the like is avoided. However, in order to remove the polymerization solvent, acetic anhydride, and acetic acid, wet molding using an aqueous coagulation bath is ultimately applied, which is incompatible with the water remaining in the fibers. Aromatic hydrocarbons often cause problems during wet molding. Also,
When dry molding is applied, it is required to be equipped with an explosion-proof spinning device that has extremely low leakage of solvent. OBJECT OF THE INVENTION The present invention aims to solve the above-mentioned drawbacks of the prior art.
When molding products such as films, hydrolysis of the polymer can be suppressed as much as possible during the molding process.
Moreover, it is an object of the present invention to provide a method for manufacturing a polyimide molded article having good moldability. Structure of the Invention The above-mentioned object is to use a liquid bath consisting essentially of acetic acid and/or acetic anhydride as a coagulation bath when producing molded articles such as fibers and films by wet-molding a polyamic acid solution. This is achieved by the method for producing a polyimide molded article of the present invention, which is characterized by the following. Hereinafter, each step of the manufacturing method of the present invention will be explained in detail. (A) Preparation of polyamic acid solution The method for preparing the polyamic acid solution that will be the stock solution for molding is to carry out solution polymerization of a combination of monomers mainly consisting of aromatic diamine and aromatic tetracarboxylic acid dianhydride. There are two methods: a solution polymerization method that directly obtains a polyamic acid solution, and a method that redissolves the prepared and isolated polymer in an appropriate solvent. Although any method can be adopted in the method of the present invention,
The former method is industrially preferred. Methods for preparing polyamic acids by solution polymerization are already known. US Pat. No. 3,179,614 gives examples of various aromatic diamines, tetracarboxylic anhydrides, and polymerization solvents. In addition, regarding the combination to obtain a polyamic acid having a relatively rod-like skeleton to which the method of the present invention is particularly applicable,
JP-A No. 55-16925, No. 58-185624, No. 59-
No. 157319, described in the official gazette. Phenyl diamines used as raw materials for preparing the polyamic acid solution used in the method of the present invention,
Examples of tetracarboxylic diacid anhydrides and functional derivatives thereof include the following. (a) Phenylene diamines (a-1) Para-type (coaxial type, parallel axis type) diamine: Para-phenylene diamine (and one or more lower alkyl group, lower alkoxy group, halogeno group in its aromatic ring) , those containing non-reactive functional groups such as lower carbalkoxy groups and nitro groups; the same applies to the following diamines), benzidine, 4,
4″-diamine-paraterphenyl, 2,7-diaminefluorenone, 2,8-diaminephenoxatin, 1,4-, 1,5- or 2,6-naphthylenediamine. (a-2) Non-paraterphenyl Type diamine: Metaphenylenediamine (and those containing one or more non-reactive functional groups such as lower alkyl group, lower alkoxy group, halogeno group, lower carboalkoxy group, nitro group, etc. in the aromatic ring; below) (a-3) Diamine in which two or more phenylene groups are bonded through one or more atoms: H ₂ N-Ar(-X-Ar)-nNH ₂ In the above formula, Ar is a phenylene group, and X is It is a divalent group selected from the following atomic bonds: -O-, -S-, -SO ₂ -, -CS-, -NH-, -NR-, (R is an alkyl group having 5 or less carbon atoms) Atomic bond: -N=N-, -N=CH-, -N=CR-, -C=C-, -C=C-, -NH-CO-, -O-CO-, -NH-SO-, Atomic bonds: -NH-CO-NH-, -CO-NH-NH-, Typical examples of such diamines As, 3,3
-,3,4'- or 4,4'-diaminodiphenyl ether, 3,3-,3,4- or 4,4'-diaminophenyl thioether, 3,3-,3,4'- or 4 , 4'-diaminodiphenylmethane, 3,3-
Mention may be made of 3,4'- or 4,4'-diaminodiphenylsulfone and 3,3-,3,4'- or 4,4'-benzophenone diamine. In addition, as an example of aromatic diamines in which three or more phenylene groups are bonded to one atom, JP-A-59-
Various conventionally known diamines described in JP 170122 and the like can also be used. (b) Diacid anhydride Pyromellitic diacid anhydride, 3,3',4,4'-
Diphenyltetracarboxylic acid anhydride, 2,
3,3'4'-diphenyltetracarboxylic diacid anhydride, 3,3',4,4'-diphenyloxytetracarboxylic diacid anhydride, 3,3',4,4'-benzophene Nontetracarboxylic diacid anhydride, 3,3',
4,4'-diphenylsulfonetetracarboxylic diacid anhydride, 3,3',4,4'-diphenylalkylenetetracarboxylic diacid anhydride, 3,3',4,
4'-Diphenylsulfonetetracarboxylic diacid anhydride, bis(3,4-dicarboxyphenyl ether) hydroquinone diacid anhydride, bis(3,
4-Dicarboxyphenyl ether) resorcinol diacid anhydride, paraphenyl-bis-trimellitic diacid anhydride. (c) Functional derivatives Dialkyl esters of tetracarboxylic acids (methyl, ethyl, octyl, etc.), salts of tetracarboxylic acids. Among the above-mentioned reaction components, a combination of para-oriented phenylene diamines and pyromellitic dianhydride is preferred. Further, as a solvent used as a polymerization solvent in a polyamic acid polymerization reaction or a solvent used when redissolving a polymerized polyamic acid, the following amide-based solvents are suitable. N,N,N',N'-tetramethylurea (TMU),
N,N-dimethylacetamide (DMAC), N,
N-diethylacetamide (DEAC), N,N-
Dimethylpropionamide (DMPR), N,N-
Dimethylbutyramide (NMBA), N,N-dimethylisobutyramide (NMIB), N-methylpyrrolidone-2 (NMP), N-ethylpyrrolidone-
2 (NEP), N-methylcaprolactam (NMC),
N,N-dimethylmethoxyacetamide, N-acetylpyrrolidine (NAPR), N-acetylpiperidine, N-methylpiperidone-2 (NMPD),
N,N'-dimethylethyleneurea, N,N'-dimethylpropyleneurea, N,N,N',N'-tetramethylmalonamide, N-acetylpyrrolidone. In the method of the present invention, the above-mentioned polyamic acid solution may be directly used as a molding stock solution for forming such as spinning or film forming, but the polyamic acid solution may be subjected to a reaction treatment in advance or at the same time as forming to ring-close a part of the polyamide. It is also possible to use a material instead of polyimide. It is also known that a solution in which part or all of polyamide is replaced with polyimide exhibits good coagulation properties in an aqueous coagulation bath (see the above-mentioned Journal of the Japan Institute of Textile Science and Technology,
40, T-480). This (partial) chemical ring closure method to improve coagulation properties can also be preferably applied to the method of the present invention. This reaction can be roughly divided into a thermal ring-closing method and a chemical ring-closing method. In the thermal ring-closing method, the water generated by the reaction hydrolyzes the remaining polyamic acid, reducing the substantial degree of polymerization of the polymer. Chemical ring closure methods are preferably used. As an imidizing agent that can be used for chemical ring closure, a combination of an acid anhydride and a tertiary amine as a reaction catalyst can generally be preferably used. In general, the stock solution conditions for stock solution stability and coagulability are often contradictory; for example, as the rigidity of the polymer skeleton increases, the polymer concentration increases, and the ring closure rate increases, coagulability improves but the stability of the stock solution deteriorates. It is on the way. Therefore, the ring closure rate must be selected in consideration of the balance between the stability and coagulability of the stock solution. Note that copolymers have better solution stability than their homopolymers, so
It is also possible to ensure a ring closure rate necessary to exhibit better coagulability; for example, the chemical ring closure rate can be set to about 15 to 30 mol%. Acid anhydrides used for chemical ring closure include aliphatic acid anhydrides such as acetic anhydride and propionic anhydride;
Aromatic acid anhydrides such as benzoic anhydride (including those having a substituent on the benzene ring), nicotinic anhydride, isonicotinic anhydride, picolinic anhydride, quinolinic anhydride, cinchomelic anhydride, pyrazine-
Examples include acid anhydrides having tertiary nitrogen in the molecule, such as 2, 3, 5, 6, and tetracarboxylic acid anhydrides. Examples of tertiary amines used as reaction catalysts include pyridine, quinoline, isoquinoline, 2-methylpyridine, dimethylaniline, diethylaniline, and trialkylamines. Among these combinations of acid anhydrides and tertiary amines, a combination of acetic anhydride and pyridine is particularly preferred. A polyamic acid/polyimide solution partially subjected to a ring-closing reaction as described above is also included in the concept of a polyamic acid solution used as a stock solution for molding in the present invention. The stock solution for molding may further contain colorants, if necessary.
It may also contain additives such as a dissipating agent and a filler. (B) Wet molding In the method of the present invention, when the above stock solution is wet molded to form a molded article such as a fiber, tape, ribbon, film, etc., a liquid consisting essentially of acetic acid, acetic anhydride, or a mixture thereof is used as a coagulation bath. Use a bath. When the above-mentioned stock solution is combined with this coagulation bath and wet-molded, it exhibits extremely good coagulation properties and can be made into a molded article with excellent physical properties. In the method of the present invention, a mixed system containing acetic acid, acetic anhydride, and a solvent non-reactive with acetic acid and/or acetic anhydride, such as an amide solvent, is used as a coagulation bath, if necessary, to improve coagulation properties or speed up coagulation. It can also be controlled. In addition to the above-mentioned amide solvent, ether, halogenated hydrocarbon, water, alcohol, etc. can be selected as the type of such additive solvent, but the amount added is 50% by weight or less, preferably 30% by weight or less. . Further, the above-mentioned tertiary amine may be included in the coagulation bath. In the method of the present invention, it is important to use a coagulation bath with the above composition, but the guidelines for selecting a specific suitable coagulation bath composition for producing fibers by wet spinning are summarized as follows. . (b) In general, acetic acid shows better coagulability than acetic anhydride. Therefore, when using a stock solution that already has good coagulability, use a coagulation bath consisting only of acetic anhydride or acetic acid with a high composition ratio of acetic anhydride. - It is preferable to use a coagulation bath consisting of a mixed system of acetic anhydride. (b) By mixing an amide solvent, which can also be used as a polymerization solvent, into the coagulation bath at a constant ratio, the coagulation rate is reduced. Therefore, it is possible to provide a sufficient spinning draft during the coagulation period to thin the yarn or pre-orient it. Also,
The coexistence of an amide solvent often contributes to improving coagulation properties. (c) Since the coagulation bath contains a chemical ring-closing agent that converts polyamic acid into polyimide, it is both a coagulation bath and a reaction bath. Therefore, in order to ensure as good coagulation as possible, acetic acid with good coagulability is used as the first bath for spinning, and then acetic anhydride (or acetic anhydride/acetic acid mixed system) is used as the second bath. When used thereafter, coagulation can be completed while the chemical ring-closing reaction is progressing, and the spun yarn in a gel state can be stretched to improve orientation. (d) The ring-closing rate can be controlled by controlling the convection time in the reaction bath, the bath temperature, the presence or absence of a reaction catalyst, etc. Furthermore, the ring closure rate can be controlled relatively freely depending on the purpose. Therefore, the above reaction bath conditions should be selected appropriately in a system in which a yarn with some unclosed ring portion remaining will be highly oriented in the subsequent drawing process and exhibit high mechanical properties, rather than an unheat-treated yarn with 100 mol% ring closure. Thus, a spun yarn with a desired ring closure rate can be obtained. In the coagulation bath, as mentioned above, an amide solvent and a third
It is permissible to contain a class amine, etc., but the presence of water causes hydrolysis, so it is necessary to be substantially anhydrous. When performing wet molding according to the method of the present invention, a conventionally known wet molding apparatus can be used. Further, in the case of wet spinning, various wet spinning methods such as horizontal or vertical normal wet spinning, dry jet wet spinning, and falling tension spinning can be applied. Additionally, flow tubes and other techniques can be applied as needed. (C) Post-treatment (solvent removal, heat treatment, etc.) It is desirable to remove the polymerization solvent, chemical ring-closing agent or its by-products, catalyst, etc. contained in the molded product immediately after wet molding before heat treatment. There are dry methods and/or wet methods for removing the solvent. In the dry method, in addition to drying under normal pressure, reduced pressure, ventilation, etc., the solvent can also be removed by heating. In the method of the present invention, the solvent can be removed by a wet method. According to the observations of the present inventors, when polyamic acid undergoes ring closure and turns into polyimide, in most cases, the polymer and the amide solvent undergo phase separation, resulting in a composition consisting mostly of polymer. Therefore, in molded bodies that have undergone sufficient ring closure, the solvent is often already separated and removed spontaneously, so it is possible to easily remove the adhering solvent and a small amount of impregnating solvent by washing with water or other operations. It is. Of course, when washing with water, it is necessary that the ring closure treatment is completed to such an extent that hydrolysis due to contact with water does not become a problem. Therefore, in the method of the present invention, the phase separation phenomenon accompanying the ring-closing reaction described above is effectively caused to improve the orientation of the molded product (e.g., spun yarn), and ultimately to the heat-treated product finally obtained. It is also possible to improve mechanical properties. That is, when the phase separation phenomenon begins, the molded body is stretched in a coagulation bath, a reaction bath, air, etc., and stretching orientation can be performed simultaneously with phase separation, which makes orientation fixation more advantageous. This molded article can be made to exhibit even better heat resistance and mechanical properties by subjecting it to heat treatment as necessary. Heat treatment can usually be carried out at a temperature range of 200 to 600°C under tension or non-tension.
The preferred mode of heat treatment varies depending on the polymer skeleton and composition of the fiber, but it is heated at 350 to 550°C in air.
Good results are often obtained by treating under tension. In addition, in the case of heat treatment under an inert atmosphere such as nitrogen or argon, preferable results are often obtained at higher temperatures such as 450 to 600°C. Effects of the Invention According to the method of the present invention as described above, useful polyimide molded bodies can be produced by wet molding by suitably combining and selecting various factors such as polymer skeleton and composition, coagulation bath composition and conditions, etc. You can.
In particular, the method of the present invention skillfully avoids a decrease in performance due to a decrease in the degree of polymerization due to hydrolysis, so the performance of the obtained molded article is extremely high. The fibers obtained by the method of the present invention are useful as heat-resistant fibers and as high strength/high modulus fibers in the field of rubber reinforcement or resin reinforcement for insulating cloth, filter cloth, tires, etc. The film is also useful in fields such as electrical insulation and printed wiring boards. Examples Hereinafter, the present invention will be explained with reference to Examples. In addition, in the examples, the intrinsic viscosity (ηinh) is determined by the polymer concentration.
This is a value measured at 30°C at 0.5g/dl. Example 1 (Preparation of spinning dope) 2.69 g of paraphenylenediamine was dissolved in 150 ml of N-methylpyrrolidone (NMP) dehydrated with molecular sieves in a stream of dry nitrogen. After externally cooling this amine solution with ice water, 5.47 g of pyromellitic anhydride was added to cause a polymerization reaction.
The viscosity of the mixed solution gradually increased. A portion of the obtained polymerization solution was taken out, diluted to a concentration of 0.5 g/dl, and ηinh was measured to be 3.2. Acetic anhydride and pyridine equivalent to chemically ring-closing 17.5 mol% of the polymer in the obtained polymerization solution were added to obtain a viscous polyamic acid/polyimide solution. (Wet spinning) The solution obtained by the above method is degassed under reduced pressure, and the pore size is
It was passed through a 0.3 mm nozzle with 3 holes into a coagulation bath consisting of 9 parts acetic acid, 1 part acetic anhydride, and 0.5 parts pyridine.
Dry jet wet spinning was carried out under the conditions of a discharge speed of 5 m/min and an air gap of 20 mm. After passing about 1 m through a coagulation bath, it was passed through a reaction bath (7 parts of acetic anhydride, 3 parts of pyridine) at 20 to 70°C and wound up, sufficiently imidized, and then washed with water and dried. Single yarn diameter D (μm) / strength T (Kg/mm ² ) / elongation E after dry yarn is heat treated at 480℃ under tension
(%)/modulus Y (Kg/mm ² ) was as follows. D/T/E/M=36/42/2.1/8500 Example 2 Paraphenylenediamine (PPDA) and 3,4'-
Diaminodiphenyl ether (3,4'-ODA)
A copolyimide fiber was obtained by dry jet wet spinning in the same manner as in Example 1 using a spinning stock solution prepared by polymerizing mixed diamine consisting of the following and pyromellitic anhydride (PMDA) in the same manner as in Example 1. In this experiment, the copolymerization ratio of PPDA and 3,4'-ODA was varied and the results are shown in the table below.

[Table] Example 3 Paraphenylenediamine (PPDA) and 3,3'-
A spinning dope was prepared from a mixed diamine consisting of dimethylbenzidine (OTLD) and pyromellitic anhydride (PMDA) in the same manner as in Example 1, and the performance of the copolyimide fiber obtained by dry jet wet spinning is shown in the table below. .

[Table] Example 4 The solution obtained in Example 1 was degassed and filtered under reduced pressure,
It was cast on a glass plate using a doctor knife with a thickness of 500 μm, and immersed and coagulated in a coagulation bath consisting of 9 parts acetic acid, 1 part acetic anhydride, and 0.5 parts pyridine. Then, it was immersed in a reaction bath (7 parts of acetic anhydride, 3 parts of pyridine) to be sufficiently imidized, washed with water, fixed to a metal frame, and then dried. Thickness t (μ
m)/strength T (Kg/mm ² )/elongation E (%)/modulus Y (Kg/mm ² ) were as follows: t/T/E/M=23/19/3.6/8500 Example 5 In the same manner as in Example 1, 50 mol% of paraphenylenediamine, 2-chloroparaphenylenediamine
A polyamic acid solution having a polymer concentration of 5.5% by weight was prepared by reacting a diamine component consisting of 25% by mole and 25% by mole of 3,3'-dichlorobenzidine with pyromellitic anhydride. Acetic anhydride and pyridine were added to this solution so that the chemical ring closure rate was 25 mol%. This spinning stock solution was spun in the same manner as in Example 1, except that a coagulation bath consisting of 9.5 parts acetic anhydride and 0.5 parts pyridine was used. Single yarn diameter D (μm) / strength T (Kg/mm ² ) / elongation E after dry yarn is heat treated at 500℃ under tension
(%)/modulus Y (Kg/mm ² ) was as follows: D/T/E/M=25/56/2.8/13000

Claims (1)

[Claims] 1. A liquid bath consisting essentially of acetic acid and/or acetic anhydride is used as a coagulation bath when manufacturing molded articles such as fibers and films by wet molding a polyamic acid solution. A method for producing a polyimide molded article. 2. The manufacturing method according to claim 1, wherein the polyamic acid solution is prepared by solution polymerizing an aromatic diamine and an aromatic tetracarboxylic anhydride. 3. The manufacturing method according to claim 1, wherein the polyamic acid solution contains an acid anhydride and a tertiary amine. 4. The production method according to claim 1, wherein the coagulation bath contains an amide solvent and/or a tertiary amine.