JPH02269156A - Novel dope for shaping - Google Patents

Abstract

PURPOSE:To provide a shaping dope exhibiting a stream birefringence property and giving polyimide shaped products having excellent heat resistance and mechanical characteristics by dissolving a polyimide having a specific structure in sulfuric acid and/or methane sulfonic acid. CONSTITUTION:(A) Pyromellitic acid (derivative) and 2,2'-dimethylbenzidine (derivative) are reacted with each other at a temperature of <=80 deg.C in a solvent and subsequently heated or treated with an imidizing agent (e.g. acetic anhydride) to prepare a polyimide comprising the structural units of the formula and having an intrinsic viscosity of >=1, preferably >=1.5, (at 35 deg.C, in sulfuric acid), which is dissolved in (B) sulfuric acid (having a concentration of >=98% and containing <=30% of fuming sulfuric acid) and/or methane sulfonic acid to provide a novel shaping dope having a concentration of >=5wt.%, preferably >=8wt.%, and exhibiting a stream birefringence property.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a molding stock solution useful for producing polyimide molded articles with excellent heat resistance and mechanical properties, particularly fibers, films, and pulp-like particles. The present invention relates to a novel molding dope exhibiting flow birefringence.

(Conventional technology) Conventionally, polyimide has excellent heat resistance, mechanical properties, electrical properties,
It is known to be useful as a raw material for fibers, films, and other molded products with excellent weather resistance. For example, 4,
Polyimides produced from 4'-diaminodiphenyl ether and pyromellitic dianhydride provide films with excellent heat resistance and are widely used in electrical insulation applications.

In addition, in the field of heat-resistant fibers and films, aramid fibers, synthetic papers, polyimide films, etc. are used, but with the advancement of advanced materials for space and aircraft applications, they are becoming more heat-resistant. In recent years, there has been a demand for materials with mechanical properties such as high strength, high strength, and high modulus.

In the field of heat-resistant fibers, polyimide fibers having relatively rigid skeletons have been reported in recent years.

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. describes a technique for producing flame-resistant, high-strength, and high-modulus fibers. Also, Journal of the Japan Textile Society, 40, T-480<198
4+ and Japanese Unexamined Patent Publication No. 59-157319, etc., a spinning dope with improved wet coagulability is obtained by ring-closing a part of polyamic acid into polyimide, and a filament obtained by wet spinning the same. It is described that polyimide fibers with excellent mechanical properties can be obtained by immersing the fiber in an acetic anhydride/pyridine system to promote imidization, and then heat-treating the fiber after drying. However, the mechanical properties of fibers obtained by either method do not reach a level that is satisfactory as high-performance fibers. This is because -a is a polymer with a rigid skeleton and when high mechanical properties are obtained by solution molding, the molding dope has fluid birefringence, as typified by the manufacturing method of poly-p-phenylene terephthalamide. Furthermore, it is an important condition to exhibit optical anisotropy. This is because the polymer molecular chains form an aggregate structure called a domain, which creates a state in which they are highly oriented before molding, and as a result, it is possible to obtain a molded product in which orientation is highly promoted. be. In the case of rigid skeleton polyimide, the polyamic acid dope for molding has fluid birefringence,
Furthermore, not only does it not exhibit optical anisotropy, but even if the final polyimide is rigid, the polyamic acid that is the precursor for its molding is as follows (Ar is a rigid skeleton diamine residue). ) It has a skeleton in which a p-oriented body as in (1) and an m-oriented body as in (2) coexist, and therefore the polymer molecular chain is not straight but in a bent wire-like state. Therefore, it is difficult to promote orientation during molding, and the resulting mechanical properties do not exhibit satisfactory values. On the other hand, JP-A-60-65112
As shown in the above publications, a method has been proposed in which the polyimide skeleton is made somewhat flexible to obtain solvent-soluble polyimide, and this is molded to obtain high-strength fibers. Therefore, high modulus cannot be achieved.

(Objective of the Invention) The main object of the present invention is to solve the problems of the prior art as described above, and to produce polyimide molded articles with excellent heat resistance and mechanical properties, especially fibers, film bulb-shaped particles, etc. The object of the present invention is to provide a new molding dope useful for molding, especially a polyimide molding dope that exhibits unprecedented flow birefringence and is highly oriented during molding.

(Structure of the Invention) That is, the present invention provides a dope prepared by dissolving a polyimide whose main structural unit is represented by the following formula (I) in sulfuric acid and/or methanesulfonic acid, and the dope exhibits flow birefringence. This is a new molding dope characterized by the following.

The polyimide comprising the structural unit represented by the above formula (I>) used in the present invention is produced by a method of reacting pyromellitic acid or a derivative thereof with 2,2'-dimethylbenzidine or a derivative thereof.

For example, it is easy to produce polyamic acid by reacting pyromellitic anhydride and 2,2'-dimethylbenzidine in a solvent, and then imidizing it by heating or using a chemical imidizing agent such as acetic anhydride. can be manufactured. but,
It goes without saying that the object of the present application can be achieved even if the product is produced by other methods, such as a method using diester dichloride of pyromellitic acid or a method using a diisocyanate derived from 2,2'-dimethylbenzidine. Nor.

Regarding the reaction solvent when producing such polyimide,
It dissolves the raw material monomers as mentioned above, is substantially non-reactive with them, and preferably has an intrinsic viscosity of at least 61
, 0 or more, more preferably 1.degree.

For example, 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 (NM
P), N-ethylpyrrolidone-2 (NEP), N-methylcaprolactam (NMC), N,N-dimethylmethoxyacetamide, N-acetylpyrrolidine (NAP)
R), N-acetylbiperidine, N-methylpiperidone-2 (NMPD), N,N'-dimethylethyleneurea, N,N'-dimethylpropyleneurea, N,N.

Amide solvents such as N', N'-tetramethylmalonamide and N-acetylpyrrolidone, p-chlorophenol,
Phenol, m-cresol, p-cresol, 2.4
- Phenolic solvents such as dichlorophenol or mixtures thereof can be mentioned. The polymer is produced in the same manner as the usual solution polymerization method in the above-mentioned solvent in which the monomer is dehydrated. The reaction temperature at this time is generally 80
℃ or lower, preferably 60℃ or lower. If the temperature is too high, a hydrolysis reaction may occur, which is not preferable.

Also, the concentration at this time is 1 to 20 wt as monomer concentration.
% is preferable.

The polymer thus obtained is generally polyamic acid or polyamide ester, which is a precursor of polyimide. In the present invention, such a polyimide precursor needs to be further reacted and used as a polyimide.

Any conventionally known method may be used to form the imide, and the -a method includes a heating method and a chemical method, both of which can be employed. Here, the heating method refers to a method in which a precursor is heated to 100°C or higher, preferably 150°C or higher to form an imide, and the chemical method refers to a method in which a precursor is formed into an imide using a chemical dehydrating agent such as acetic anhydride. It's a method.

In addition, in such an imidization reaction, heating conditions for too long tend to deteriorate the solubility of the resulting polymer in the solvent, so the heating conditions must be selected appropriately. Even if an insoluble portion is present, most of it can be dissolved in a small amount. Therefore, by separating the insoluble portion, for example, by separating it in a furnace, a molding dope without any problems can be obtained. Further, as the polyimide precursor, polyamide ester is preferable because it tends to be more soluble than polyamide acid.

In addition, since polyimide precursors are usually obtained in the form of a solution, if imidization is directly performed by a chemical method or a heating method, the polyimide is obtained in the form of a slurry.

In order to separate the precursor or polyimide from such a precursor solution or polyimide mixture, a generally well-known method such as mixing with water or other poor solvent may be used as is. Further, either of the separation operation and the imidization operation may be performed first. The polyimide thus obtained is usually in powder form, but may be in any other form.

Note that it is used after being dried before being used for the next dissolution operation.

The polyimide used in the present invention is produced as described above, and usually has a polyimide of 1.0 or more, preferably 1.
．． It is preferable to have an intrinsic viscosity of 5 or more, more preferably 2.0 or more. Note that the intrinsic viscosity here is 35°C.
This is a value measured in sulfuric acid.

In the present invention, such a polyimide is dissolved in sulfuric acid and/or methanesulfonic acid to obtain the dope of the present invention having flow birefringence.

The sulfuric acid used in the present invention has a concentration of 98% or more and contains up to 30% fuming sulfuric acid.

In particular, one method that is preferable is to bring the dissolved solution into a state in which almost no water is present. Further, it is preferable that the amount of water in methanesulfonic acid is as low as possible. Such sulfuric acid and methanesulfonic acid may be used in combination.

The dope of the present invention is obtained by dissolving the above-mentioned polyimide in the above-mentioned solvent, and the concentration is 5% by weight or more,
The concentration should preferably be 8% by weight or more, so that the dope exhibits flow birefringence. Note that since this concentration varies depending on the molecular weight of the polyimide, etc., it cannot necessarily be determined unambiguously. This flow birefringence can be confirmed simply by sandwiching the dope between two glass plates placed between orthogonal polarizing plates and observing the change from dark field to bright field when a slight abrasion deformation is applied. Naturally, this also includes the case where a bright field appears under static conditions after sliding deformation.

It can also be confirmed using a piston-type viscometer that extrudes the dope through a small hole, and when exhibiting flow birefringence, the viscosity does not decrease even if the load is increased if the load applied to the piston exceeds a certain value. In some cases, the phenomenon of becoming higher occurs.

The dope of the present invention described in detail above has excellent moldability and can be molded into fibers, film pulp-like particles, etc. by a wet method or a dry jet wet method.

(Operations and Effects of the Invention) In the case of the rigid skeleton polyimide targeted by the present invention, -m does not have a solvent to be dissolved, and even if it can be dissolved, the solution is so concentrated that it exhibits flow birefringence. It was never imagined that this could be achieved. However, from the polyimide used in the present invention, a highly concentrated dope exhibiting flow birefringence can be formed.

This dope forms a highly oriented state during molding,
Therefore, it becomes possible to obtain a polyimide molded article with excellent heat resistance and mechanical properties. In particular, the fiber spun from the dope of the present invention can be used as a heat-resistant fiber and as a high-strength/high-modulus fiber in fields such as robes, belts, insulating cloth, R cloth, honeycomb structure materials, and rubber products such as tires. It can be widely used in the fields of thermosetting or thermoplastic resin reinforcing materials, as well as protective clothing.

(Example) The present invention will be described below with reference to Examples. In the examples, the intrinsic viscosity (IV>) was measured in 100% sulfuric acid at 35°C.

Example 1 Pyromellitic anhydride (PMDA) and methanol were mixed and reacted, and then the methanol was distilled to dryness and dimethyl ester was refluxed in thionyl chloride. After cooling the obtained reaction product, the precipitate was filtered, and the acid chloride obtained by recrystallizing with toluene was found to be 2,5-dicarbomethoxyterephthalic acid chloride (A) as a result of NMR1 infrared analysis. It was confirmed.

2,2'-
Add 4.83 g of dimethylbenzidine to 150 ml of the above solvent.
The mixture was dissolved in a stream of dry nitrogen. This amine solution was kept at -10°C by external cooling and the above acid chloride (A) was added in 7.
31g was added to cause a polymerization reaction.

When the acid chloride (A) was completely dissolved and the solution gradually became viscous, 5 ml of pyridine was added and the temperature was lowered to 50 ml.
When the temperature was raised to 0.degree. C., the reaction proceeded rapidly, the solution became viscous, and some polymers were observed to precipitate. Stirring was further continued for 2 hours to complete the polymerization reaction. After the reaction was completed, the temperature was returned to room temperature and the mixture was poured into a large amount of methanol to precipitate a polymer.

The obtained polymer is separated, further washed with methanol and acetone, and then vacuum dried.

This polymer was heat treated at 200°C for 1 hour. The obtained polymer was almost completely converted to imide, as determined by the measurement results of infrared absorption spectrum. The intrinsic viscosity measured by dissolving this polymer in 100% sulfuric acid prepared using concentrated sulfuric acid and fuming sulfuric acid was 1.80.

The physical properties of the above polymer dissolved in 100% sulfuric acid at various concentrations are shown in the table.

In the table, "flow birefringence" indicates whether the obtained solution was observed under crossed nicols using a microscope and light transmission was observed during slight abrasion deformation, and viscosity was determined by observing the obtained solution under crossed nicol conditions using a Koka type flow tester. The values are shown when dope is flowed out from a hole with a hole diameter of 0.7 mm and a length of 10 mm.

Claims (1)

[Claims] (1) A dope made by dissolving a polyimide whose main structural unit is represented by the following formula (I) in sulfuric acid and/or methanesulfonic acid, for new molding, characterized in that the dope exhibits flow birefringence. Dope. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I)