JPH06887A - Method for molding aromatic polyimide resin - Google Patents

Abstract

PURPOSE:To obtain a large-sized homogenous aromatic polyimide resin molded product by filling a rubber mold with an aromatic polyimide resin and applying static water pressure to the rubber mold in a liquid to form a green compact and baking the green compact under an inert gas atmosphere or vacuum. CONSTITUTION:Since it is necessary to equally packing a rubber mold with a raw material powder, a raw material processed into a granular state is pref. used. The molding pressure at the time of static water pressure molding is pref. 1-10ton/cm<2>. The rubber mold to be used is pref. composed of a rubber material having high elongation and low elastic modulus so as to withstand the reduction of volume at the time of static pressure molding because the compression ratio of a raw material resin is large. By performing this static water pressure molding, the density distribution of an obtained green compact becomes uniform and, when the green compact is baked under a controlled condition, the green compact is not cracked during a baking process. Further, a homogenous molded product can be obtained because of uniform density distribution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method excellent in molding a large and homogeneous aromatic polyimide resin molded article.

[0002]

2. Description of the Related Art Polyimide resin has excellent heat resistance,
Due to mechanical properties, sliding properties, etc., demand has rapidly increased in recent years in the electric / electronic device industry, automobile industry, aviation / space industry, office equipment industry, and the like. Since aromatic polyimide resins do not have a clear melting point,
The methods used for molding thermoplastic resins such as injection molding and extrusion molding cannot be performed, and the compression molding and transfer molding used for molding thermosetting resins cannot be performed. Therefore, in molding an aromatic polyimide resin, as is known in Japanese Examined Patent Publication No. 49-5737, resin powder is put in a mold and compressed uniaxially to mold a green compact. It was usual to make a molded product by a free sintering method in which the resin grain interfaces are joined by heating in an inert gas atmosphere such as.

Here, the aromatic polyimide resin is bulky, and the apparent density of the powder is about 0.13 to 0.15 g /
It is as low as cc. Further, in order to obtain a molded product having sufficient strength, it is usually necessary to set the density of the molded product to 1.3 g / cc or more, so that the compression ratio is about 10 times. This is 10
The height of the powder is 100 mm, in other words, the depth of the mold is 100 mm to make a molded product of mm. This is very important, and a mold for molding a plate material having a thickness of 50 mm requires a depth of 500 mm. Further, when a molded article of aromatic polyimide resin is produced by a conventional method, high pressure is required when molding a green compact. According to our study result, a surface pressure of 1 ton / cm ² or more is required.
This, for example, when molding rectangular plate having a width 200 × length 200 mm, the projected area becomes 400 cm ^2, if the molding pressure and 3 ton / cm ^2, is 1200ton press machine for molding the rectangular plate is necessary.

Therefore, a large mold and a press machine are required to mold a large thickness or a large projected area. Further, when the filling of the raw material powder is non-uniform or when molding a molded product having a large thickness, the pressure is not evenly applied, and it is difficult to make the density of each part of the green compact uniform. In addition, a long pipe-shaped product has a limited press stroke and is difficult to form. A method for molding a long product of an aromatic polyimide resin is disclosed in JP-A-55-867.
Although there is a molding method using ram extrusion disclosed in JP-A No. 31 and JP-A-56-28839, it is difficult to obtain a good molded product because a defective fusion portion is generated in a discontinuous portion of raw material supply.

[0005]

Therefore, an object of the present invention is to establish a method for molding a large and homogeneous aromatic polyimide resin molded article.

[0006]

The present invention includes: Aromatic polyimide characterized by filling an aromatic polyimide resin in a rubber mold, forming a green compact by applying hydrostatic pressure in a liquid, and then firing the green compact in an inert gas atmosphere or in a vacuum. Method for molding group polyimide resin. 2. 2. The method for molding an aromatic polyimide resin as described in 1 above, wherein the aromatic polyimide resin is granular. 3. The method for molding an aromatic polyimide resin as described in 1 or 2 above, wherein the hydrostatic pressure is 1 to 10 ton / cm ² . 4. The method for molding an aromatic polyimide resin according to the above 1 or 2 or 3, wherein the material of the rubber mold is one or more elastomers selected from silicone rubber, polyurethane resin, NBR and SBR. By doing so, the purpose is achieved.

The details will be described below. The present invention is to fill a rubber mold with an aromatic polyimide resin, form a green compact by applying hydrostatic pressure in a liquid, and then fire the green compact in an inert gas atmosphere or in a vacuum. It is a characteristic method for molding an aromatic polyimide resin. As the method for producing the aromatic polyimide resin used in the present invention, known methods can be used. For example, the details are disclosed in JP-B-39-22196, but aromatic tetracarboxylic acid dianhydride and aromatic diamine or aromatic diisocyanate are used, for example, N-methylpyrrolidone, N, N-dimethylacetamide. It can be produced by reacting in an organic polar solvent such as diglyme, and then subjecting the obtained polyamic acid to ring closure with a dehydrated imide.

Specific examples of the aromatic tetracarboxylic dianhydride used here include pyromellitic dianhydride, 3,
3 ', 4,4'-benzophenone tetracarboxylic acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3 ', 4'-biphenyltetracarboxylic acid dianhydride 1,2 ', 3,3'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-diphenylethertetracarboxylic dianhydride, 3,3 ',
4,4′-Diphenylsulfone tetracarboxylic acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane Dianhydride, 1,2,
5,6-naphthalene tetracarboxylic acid dianhydride, 2,
3,6,7-naphthalenetetracarboxylic acid dianhydride,
1,4,5,8-naphthalene tetracarboxylic acid dianhydride and the like can be mentioned. Further, these acid dianhydrides can also be used in the form of derivatives such as carboxylic acids, esters and acid chlorides.

Specific examples of aromatic diamines and aromatic diisocyanates include p-phenylenediamine and m-.
Phenylenediamine, 2-chloro-p-phenylenediamine, benzidine, 2-chlorobenzidine, 4,4'-
Diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4 '
-Diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ketone, 3,3'-diaminodiphenyl ketone, 4,4'-
Diaminodiphenyl sulfide, 4,4'-diaminoterphenyl, 1,4-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene,
1,3-bis (3-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] sulfone,
Bis [4- (4-aminophenoxy) phenyl] ketone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoro Propane, 4,4'-
Bis (4-aminophenoxy) biphenyl, 4,4'-
Examples thereof include bis (3-aminophenoxy) biphenyl and the like, and diisocyanates thereof.

Among them, the preferred aromatic polyimide resin is
A polyimide having the following structure, which is obtained from pyromellitic dianhydride and 4,4′-diaminodiphenyl ether.

[Chemical 1]

Here, those in which the imide group portion remains in the state of the amino acid which is the ring-closing precursor thereof are also included. Further, the polyimide resin used in the present invention may be mixed with various fillers as necessary to impart desired properties, and examples of such fillers include graphite, fluororesin, and disulfide. Examples thereof include molybdenum, boron nitride, glass fiber, carbon fiber, aramid fiber, potassium titanate fiber, aluminum, silver, copper, lead and various metal oxides.

A method for molding a green compact by hydrostatic pressure using a rubber mold used in the present invention is a method used in some fields as a cold isostatic pressing (CIP) method. is there. This hydrostatic forming method is mainly used for forming ceramics, and is rarely used for forming large materials such as sintered metals and plastics. In some cases, polytetrafluoroethylene is formed, especially in cylindrical form. It was only used to get the goods. The reason why this hydrostatic molding method is not adopted for the molding of large plastic materials is that ordinary plastics can be extruded, injection molded, and compression molded. This is because the product has excellent physical properties such as strength, hardness, and density.

On the other hand, in the aromatic polyimide resin,
Since there is no melting point, extrusion molding and injection molding are difficult,
In the compression molding, as described above, a very large press machine is required, and there is a problem that the density of the molded product is not uniform. Also, JP-A-55-867
Various additional tests were conducted on the ram extrusion molding method disclosed in JP-A No. 31-31868 and JP-A-56-28839, but a good product could not be molded. The present invention, under such circumstances, was found as a result of various examinations of a method for molding an aromatic polyimide resin molded article having good performance, in which a green compact is molded by hydrostatic pressure, and then the green compact is formed. We have found that baking the body can solve these problems.

The points of selection for facilitating the achievement of this object are as follows. (1) It is necessary to evenly pack the raw material powder in the rubber mold. Therefore, it is preferable to use a raw material processed into a granular form. The average particle size of the granules is 100-1000 μm
Is preferable, and more preferably 250 to 500 μm. (2) molding pressure is preferably from 1~6ton / cm ^2, more preferably from 2~4ton / cm ^2. (3) Since the rubber mold to be used has a large compression ratio of the aromatic polyimide resin, it is preferable to use a rubber material having a large elongation and a low elastic modulus so as to withstand the volume reduction during the hydrostatic molding. Further, if the mold releasability is not good, the resin compact adheres to the rubber mold during depressurization, causing cracks and chips.

Taking these points into consideration, when the aromatic polyimide resin is hydrostatically molded, the density distribution of the obtained green compact is uniform, and if it is subsequently fired under a well-controlled condition, the density unevenness is caused. There is no residual stress due to strain and there is no cracking during the firing process. In addition, since the density distribution is uniform, the physical properties such as strength, surface hardness, and coefficient of thermal expansion are also uniform, the quality is uniform, and a material preferable as a product can be produced.

The present invention will be described in more detail with reference to the following examples. The aromatic polyimide resin used is an aromatic polyimide resin having the following structure.

[Chemical 2]

[0017]

Example 1 110 g of granules of an aromatic polyimide resin having an average particle diameter of 250 to 500 μm was filled in a rubber mold made of NBR, and a hydrostatic pressure of 3 ton / cm ² was applied and held for 1 minute to form a green compact. did. This green compact was fired in a nitrogen gas atmosphere at a maximum temperature of 400 ° C., and then cut into a round bar of φ30 × 100 mm.

[0018]

Example 2 1800 g of aromatic polyimide resin granules having an average particle size of 120 to 800 μm were filled in a silicone rubber mold, and a hydrostatic pressure of 5 ton / cm ² was applied and held for 1 minute to form a green compact. did. This green compact was fired in the same manner as in Example 1 and then cut into a round bar of φ80 × 250 mm.

[0019]

Example 3 Granules (average particle size 250 to 10) obtained by blending aromatic polyimide resin with 30% graphite (manufactured by Nippon Graphite Co., Ltd.)
(100 μm) 120 g was molded in the same manner as in Example 1, fired, and then cut into a round bar of φ30 × 100 mm.

[0020]

[Comparative Example 1] 120 g of the granules used in Example 1 were filled in a mold, and 2.5 ton /
A compacting pressure of cm ² was applied and held for 1 minute to form a green compact. This green compact was fired in the same manner as in Example 1 to obtain φ50 × 5
A 0 mm round bar was used.

[0021]

Comparative Example 2 50 g of the granules used in Example 3 were filled in a mold and 3 ton / cm ² by a floating die method.
Molding pressure was applied and held for 1 minute to mold a green compact. This green compact is fired in the same manner as in Example 1 to obtain φ30 × 50 mm
It was a round bar.

Examples 1 to 3 and Comparative Example 1 described above,
The surface hardness of each part in the length direction was measured for the molded product of No. 2. The results are shown in Fig. 1. As can be seen from FIG. 1, in Comparative Examples 1 and 2 which are press-molded products, the hardness of the central portion is low, and the hardness is higher near the ends. On the other hand, in Examples 1 to 3 which are molded products according to the method of the present invention, the hardness is substantially constant over the entire length direction. This indicates that the molded article produced by the method of the present invention utilizing the CIP method has a very high homogeneity.

[0023]

As is clear from the examples and comparative examples, the molding method of the present invention is excellent in molding a homogeneous aromatic polyimide resin molded article. Therefore, it is useful as a method for molding a large-sized material of an aromatic polyimide resin, and has excellent industrial effects.

[0024]

[Brief description of drawings]

FIG. 1 is a hardness chart of each part of a round bar obtained in Examples 1 to 3 and Comparative Examples 1 and 2.

[0025]

[Explanation of symbols]

 None.

Claims (4)

[Claims] 1. A rubber mold is filled with an aromatic polyimide resin,
A method for molding an aromatic polyimide resin, comprising molding a green compact by applying hydrostatic pressure in a liquid, and then firing the green compact in an inert gas atmosphere or in a vacuum. 2. The method for molding an aromatic polyimide resin according to claim 1, wherein the aromatic polyimide resin is granular. 3. The method for molding an aromatic polyimide resin according to claim 1 or ² , wherein the hydrostatic pressure is 1 to 10 ton / cm ² . 4. The aromatic compound according to claim 1, wherein the material of the rubber mold is one or more elastomers selected from silicone rubber, polyurethane resin, NBR and SBR. Molding method for polyimide resin.