JPH0999491A - Production of polymer molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain a larger molding by performing the molding of a non-thermoplastic polymer requiring extremely high pressure heretofore under lower pressure. SOLUTION: A powder of a non-thermoplastic polymer is molded by a discharge plasma sintering method to obtain a densely molded non-thermoplastic polymer molding under surprising low pressure as compared with a conventional compression molding method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polymer molded body, and more particularly to a method for producing a polymer molded body which enables simple molding of a non-thermoplastic polymer at a lower pressure.

[0002]

2. Description of the Related Art Organic polymers can be roughly classified into three types, that is, thermoplastic polymers, thermosetting polymers and non-thermoplastic polymers, each of which has the following characteristics and problems. are doing.

That is, a thermoplastic polymer has a melting point or a softening point, and when it is heated to a certain temperature or higher, it becomes fluid and can be molded by various methods. However, the fact that it exhibits thermoplasticity means that it softens even after molding at this temperature or higher, and it cannot be used in applications requiring heat resistance.

Further, thermosetting polymers such as epoxy resins are originally composed of so-called oligomers of relatively low molecular weight, which are once melted by heating and then reacted with a reactive group at the end of the molecular chain or in the molecular chain. In many cases, the polymer is three-dimensionally polymerized and becomes insoluble or has a high softening point. In this case, high dimensional accuracy is required because the viscosity becomes extremely low in the molten state during the process, dimensional change occurs in the process of polymerizing, that is, curing reaction, and in some cases volatile matter is generated by the reaction. It is unsuitable for use in such molded products.

On the other hand, although the non-thermoplastic polymer is basically a linear polymer similar to the thermoplastic polymer,
It is characterized by not having a softening point because it has a high symmetry and linearity of the molecule, contains a group with a high polarizability, and has a high cohesive force between the molecules. At the same time, it has a feature that it is mainly composed of an aromatic ring or a nitrogen-containing heterocyclic ring and has a high decomposition initiation temperature. Therefore, it has very high heat resistance and can be used in a wide range of applications. However, this non-thermoplastic polymer is difficult to mold because it does not soften due to heat. As a method of molding such a non-thermoplastic polymer, a method of compressing and molding the polymer into fine powder has been proposed.

[0006]

However, in the molding of this non-thermoplastic polymer, the polymer is packed as a fine powder in a mold and pressed at high temperature under high pressure or molded, or heated at high pressure and then heated. With conventional molding methods such as processing,
There was a problem that the larger the molded product, the higher the pressure required, and the larger the equipment.

Therefore, the present inventors have solved the above-mentioned conventional problems and made it possible to perform molding of a non-thermoplastic polymer, which required a very high pressure, at a lower pressure, thereby simplifying a larger molded body. As a result of intensive studies aimed at providing a method for obtaining the above-mentioned method, a conventional compression molding method was applied by applying the spark plasma sintering method, which was conventionally applied to metals, to the molding of non-thermoplastic polymers. The present inventors have found that a non-thermoplastic polymer can be densely molded at a surprisingly low pressure as compared with the above, and have reached the present invention.

[0008]

The gist of the method for producing a polymer molded body according to the present invention is to mold a powder of a non-thermoplastic polymer using a discharge plasma sintering method.

In the method for producing a polymer molded body, the non-thermoplastic polymer is an aromatic polyimide.

Further, the aromatic polyimide is composed of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride.

The aromatic polyimide is composed of a phenylenediamine and an acid dianhydride having one or more aromatic rings.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A method for producing a polymer molded body according to the present invention is characterized in that a powder of a non-thermoplastic polymer is molded by using a discharge plasma sintering method. It is possible to obtain a densely molded non-thermoplastic polymer molding at a surprisingly low pressure as compared with the molding method.

Here, the non-thermoplastic polymer in the present invention means, for example, a substance whose definite melting point or softening point is difficult to detect by TMA or a dynamic viscoelasticity measuring device, or fluidity which can be detected. It means that it does not cause softening to the extent that it appears, and that the melting point and softening point are sufficiently high temperatures of 400 ° C or higher and the softening point and the decomposition point are close to each other, which makes thermal molding difficult by conventional molding methods. . Specifically, examples of the non-thermoplastic polymer include aromatic polyimide, aromatic polyamide, various aromatic ladder polymers, or aromatic thiazole 5-membered ring, aromatic oxazole 5-membered ring, aromatic imidazole 5-membered ring. Examples thereof include polymers having a ring and having high symmetry / rigidity of the molecule and exhibiting non-thermoplasticity, and copolymers and blends thereof.

Among them, the aromatic polyimide exhibits particularly excellent properties even when formed into a molded product because of the excellent heat resistance, chemical resistance, mechanical properties and electrical properties of the resin itself. Furthermore, not only the performance of the obtained molded body is excellent,
The effect of the manufacturing method of the present invention is particularly remarkable. That is, in order to obtain a molded body of aromatic polyimide, a pressure of 500 MPa is usually required in the compression molding method, whereas according to the present invention, molding can be performed at a pressure of about 20 to 50 MPa.

Further, a wholly aromatic polyimide having a molecular structure which does not include an aliphatic chain and is composed of only aromatic rings or aromatic rings and a bonding group which does not cut off electron delocalization of the aromatic rings is preferable. Especially as a wholly aromatic polyimide, one consisting of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether shows a well-balanced characteristic such as electrical / thermal characteristics and slidability, and is industrially used. Especially useful. Also useful are polyimides consisting of phenylenediamines and acid dianhydrides having one or more aromatic rings.

There are no particular restrictions on the method for producing the aromatic polyimide powder, and any method may be used. Specifically, for example, a stoichiometric or more stoichiometric dehydrating agent is added to a solution of a polyamic acid obtained from an aromatic diamine and an aromatic tetracarboxylic dianhydride by a conventionally known method, and the temperature of the solution is raised. The mixture is left to stir with stirring, and the polyimide powder precipitated in the reaction solution is filtered, washed and dried to obtain a thermal imidization method, or the polyamic acid solution is mixed with a stoichiometric or more dehydrating agent. A catalytic amount of a tertiary amine is added, the mixture is stirred at room temperature for several hours, and the reaction solution is dropped into a poor solvent such as methanol or water to expose the polyimide in the form of threads or lumps, and then dried and crushed. Examples thereof include chemical imidization methods.

The size of the non-thermoplastic polymer powder is not limited, but the smaller the particle size, the more precise the molding. It is preferably 100 μm or less, more preferably 30 μm or less, still more preferably 10 μm or less.

By the way, the discharge plasma sintering method is a method in which hot pressing is performed by directly energizing a graphite mold as a resistor. Specifically, the graphite mold is filled with a powder of a non-thermoplastic polymer, and Pressurizing at -50 MPa, then depressurizing the molding atmosphere, that is, the inside of the sintering furnace, and using the graphite mold as a resistor, a voltage value of 0.1 to 20 V, preferably 1 to 5 V, 10
3000A, preferably with a current value of 100-1000A,
By repeating ON and OFF in ms (millisecond) unit, plasma is generated and sintered. At this time, the temperature in the sintering furnace is raised to a predetermined temperature. When raising the temperature, it takes about 1 to 15 minutes to reach the maximum temperature, and the maximum temperature is held for 1 to 30 minutes. After that, it is cooled and taken out from the mold.

At this time, the maximum temperature at the time of sintering is within a range in which the resin is not decomposed, and it is necessary to experimentally find the maximum temperature at which sufficiently dense molding can be performed. In addition to the graphite type, a cemented carbide type such as WC and a die steel type can be used.

At this time, it is preferable that the sintering furnace is depressurized before the sintering as described above and the sintering is also performed under the reduced pressure. This is because oxygen and water may adversely affect metals and polymers in the air, and the generation of plasma in the mold may be hindered, which may prevent precise molding. It is also possible to carry out in an inert gas for the same reason.

According to such a method for producing a polymer molded body according to the present invention, a non-thermoplastic polymer which is difficult to mold because it does not soften by heat but has a very high heat resistance is extremely low. It can be molded by pressure, and even a relatively large molded body can be easily processed. And the molded body obtained by such a method is excellent in denseness,
It is a strong material that does not easily chip.

Among them, aromatic polyimide is 20 to 50M.
It becomes possible to mold with Pa, and the effect of the manufacturing method of the present invention is particularly remarkable. Although the polyimide molded body exhibits very excellent slidability even when used alone, it is possible to uniformly mix a filler in a certain ratio in order to obtain higher slidability. As the filler, graphite, polytetrafluoroethylene, molybdenum disulfide, spherical silicone or the like is preferably used.

Although the embodiments of the method for producing a polymer molded product according to the present invention have been described above, the present invention is not limited to these embodiments, and the present invention is within the scope of the present invention. Therefore, various improvements, changes and modifications can be made based on the knowledge of those skilled in the art.

[0024]

EXAMPLES The present invention will be specifically described below by showing examples using aromatic polyimide, but the present invention is not limited to these examples.

Example First, as a method for producing the aromatic polyimide powder used in the present invention, N, N-dimethylacetamide (hereinafter, DMAc) was used under a nitrogen stream.
And ) And pyridine in a mixed solution (volume ratio 1: 1)
Then, to obtain a polyamic acid solution from the same molar amount of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride, and continue heating and stirring the resulting polyamic acid solution, the polyimide becomes insoluble powder Has been deposited as. After allowing to cool, the powder obtained by filtration is repeatedly washed and filtered in the order of DMAc and methanol, and further, under nitrogen,
Heat treatment was carried out at 200 ° C. for 20 hours to complete imidization and drying to obtain an aromatic polyimide powder having an average particle diameter of 30 μm.

Next, about 3 g of the obtained aromatic polyimide powder was put into a cylindrical graphite mold having an inner diameter of 2 cm to obtain 50 M.
Pressure was applied at Pa, then the molding atmosphere was depressurized to about 5 Pa, a current of 1.5 V and 200 A was applied, and spark plasma sintering was performed. At this time, the temperature raising step is from room temperature to 4
The temperature was raised to 00 ° C over 6 minutes, further increased to 420 ° C over 2 minutes, and then maintained at 420 ° C for 10 minutes. Thereafter, the temperature was returned to room temperature over about 30 minutes, and then the product was taken out from the mold to obtain a polyimide molded body. When the molded body obtained as described above was observed with a microscope, a dense molded state was confirmed. In addition, it was a strong material that was not easily chipped.

[Comparative Example] The same average particle diameter 30 μm as in the example
About 3 g of aromatic polyimide powder of m was charged into a cylindrical graphite mold having an inner diameter of 2 cm and pressurized at 50 MPa, then the molding atmosphere was decompressed to about 5 Pa, and the temperature was raised under the same conditions as in Example without energization. Then, a polyimide molded body was obtained. But,
The obtained molded product had poor compactness and was brittle enough to be chipped by a human nail.

[0028]

According to the manufacturing method of the present invention, it is possible to mold a non-thermoplastic polymer, particularly a polyimide, at a low pressure, and therefore, a large-sized processing machine as in the prior art is not required. As a result, a relatively large non-thermoplastic polymer molding can be easily processed. The molded product thus obtained has excellent heat resistance and wear resistance, and is useful for mechanical parts such as sliding members, automobile parts, office equipment parts, and electric / electronic parts.

Claims (4)

[Claims] 1. A method for producing a polymer molded body, which comprises molding a non-thermoplastic polymer powder using a discharge plasma sintering method. 2. The method for producing a polymer molded body according to claim 1, wherein the non-thermoplastic polymer is an aromatic polyimide. 3. The method for producing a polymer molding according to claim 2, wherein the aromatic polyimide is composed of 4,4′-diaminodiphenyl ether and pyromellitic dianhydride. 4. The method for producing a polymer molded body according to claim 2, wherein the aromatic polyimide is composed of phenylenediamines and an acid dianhydride having one or more aromatic rings.