WO1997027244A1

WO1997027244A1 - Polyimide composite material powder and the manufacturing method thereof

Info

Publication number: WO1997027244A1
Application number: PCT/US1997/001269
Authority: WO
Inventors: Mitsuru Nakano
Original assignee: E.I. Du Pont De Nemours And Company; Dupont Kabushiki Kaisha; Toyota Jidosha Kabushiki Kaisha
Priority date: 1996-01-29
Filing date: 1997-01-29
Publication date: 1997-07-31
Also published as: JPH09208822A; JP3651711B2

Abstract

To provide a type of polyimide composite material powder, which has the clay mineral dispersed uniformly in the polyimide molding and has excellent dimensional stability, as well as its manufacturing method.

Description

IΠLE

POLYIMIDE COMPOSITE MATERIAL POWDER AND THE MANUFACTURING METHOD THEREOF BACKGROUND OF THE INVENTION

This invention pertains to a type of polyimide composite material powder and its manufacturing method. More specifically, this invention pertains to the powder feedstock for manufacturing polyimide composite material molding, which has clay minerals dispersed in polyimide resin and has excellent dimensional stability as a main feature, as well as its manufacturing method.

BRIEF DESCRIPTION OF THE RELATED ARTS Polyimide has excellent thermal properties, mechanical properties, electrical insulating properties, high chemical resistance, etc., and is used in manufacturing film, flexible printed boards, insulators for motors, electric cable coating materials, etc. However, in the practical application, it has the disadvantage of high gas permeability and a high thermal expansion coefficient.

For the polyimide molding, Japanese Laid-Open Patent Publication (Kokai) No. Hei 1-292035 (1989) discloses a manufacturing method characterized by the following facts: as a laminated polymer of polyimide, polyamic acid is prepared in a basic solvent (pyridine or β-picoline); then, polyamic acid is brought in contact with a poor solvent (acetone) for polyamic acid to precipitate to form fine low-crystalline polyamic acid powder; subsequently, the obtained powder is processed in a thermal ring-closing reaction to form polyimide powder, which is then subjected to compressive/sintering molding to form a resin molding. It has been disclosed that the wear resistance can be improved by adding a carboneous substance, such as graphite, as a filler to the polyimide powder. However, there is yet no description ofthe addition of other inorganic fillers to improve the characteristics of the resin.

On the other hand, as far as the polyimide composite material is concerned, Japanese Laid-Open Patent Publication (Kokai) No. Hei 4-33955 (1992) discloses the following method: polyamic acid as an intermediate polymer of polyimide and clay converted to organic form by organic onium ions is uniformly blended in an aprotic polar solvent (such as N,N- dimethylacetamide, N-methylpyrrolidone), and the liquid mixture is cast to form a polyamic acid film; for the obtained polyamic acid film, a thermal ring-closing reaction is performed to form a polyimide film with organociay minerals dispersed uniformly in it.

In the aforementioned manufacturing method of polyimide molding disclosed in the Japanese Laid-Open Patent Publication (Kokai) No.

Hei 1-292035 (1989), when the organociay is blended with the polyamic acid solution in a basic solvent, coagulation takes place for the organociay, so the organociay cannot be dispersed uniformly in the polyimide matrix, and there is no way to form the desired polyimide composite material having a high dimensional stability. This is because, although the organociay can be dispersed uniformly in an aprotic polar solvent, it cannot be dispersed uniformly in a basic solvent.

In the precipitation method, a liquid mixture of polyamic acid and organociay is prepared using an aprotic polar solvent that can uniformly disperse the organociay, and powder is precipitated from the liquid mixture. However, the powder is not appropriate for molding of polyimide, because the solubility of the aprotic polar solvent to the polyamic acid is higher than to the basic solvent.

The purpose of this invention is to solve the problems of the aforementioned conventional method by providing a type of composite material powder with clay mineral dispersed uniformly in the polyimide molding and having high dimensional stability, as well as its manufacturing method.

SUMMARY OF THE INVENTION The polyimide composite material powder comprises fine clay minerals and polyimide covering the fine clay minerals. The composite material powder is manufactured in the following operation steps: a blending step, in which a first liquid made ofthe intermediate polymer of polyimide and a solvent for dissolving the intermediate polymer, and a second liquid made of a clay mineral and a dispersion medium which can disperse the clay mineral and is miscible with the aforementioned first liquid, wherein the clay mineral is finely dispersed and held in the dispersion medium, to form a liquid mixture; and a pulverizing operation step, in which the aforementioned liquid mixture is subjected to spray drying to form a polyimide-clay mineral composite material powder in the form of fine powder with the clay mineral dispersed in it uniformly. The polyimide composite material powder of this invention is characterized by the fact that it is composed of fine clay minerals and polyimide covering the fine clay minerals.

This invention also provides a manufacturing method of he polyimide composite material powder comprising the following operation steps: a blending step, in which a first liquid made ofthe intermediate polymer of polyimide and a solvent for dissolving the intermediate polymer, and a second liquid made of a clay mineral and a dispersion medium which can finely disperse and hold the clay mineral and is miscible to the aforementioned first liquid to form a liquid mixture and a pulverizing operation step, in which the aforementioned liquid mixture is subjected to spray drying to form a polyimide- clay mineral composite material powder in the form of fine powder with the clay minerals uniformly dispersed in it.

The polyimide composite material powder can be used as a feed powder feedstock that can easily form the molding, which has the fine clay mineral dispersed uniformly in polyimide so that the thermal expansion coefficient is small.

DETAILED DESCRIPTION OF THE INVENTION Based on the finding that the pyridine solution of polyamic acid is soluble in water and that the clay minerals can be dispersed uniformly in water, it is possible to blend the pyridine solution of polyamic acid and the aqueous dispersion ofthe clay minerals to form a uniform slurry. As the slurry is subjected to spray drying, it is possible to form the fine powder for polyimide molding in which the clay minerals are blended in a uniform state. In this way, this invention was reached.

The clay minerals used in this invention are preferably the laminated clay minerals. Examples ofthe laminated clay minerals that can be used include montmorillonite, saponite, beidellite, stevensite, and other smectite clay minerals; vermiculite, halloysite, swelling type mica, etc. For the laminated clay minerals, the cationic exchange capacity is preferably about 50-300 mEq/100 g. If the cationic exchange capacity is over 300 mEq/100 g, the interlayer binding strength ofthe laminated clay mineral becomes too high, and interlayer expansion becomes difficult, hence the dispersability deteriorates. On the other hand, if it is lower than 50 mEq/100 g, the affinity with polyimide is insufficient. For the fine clay mineral, the grain size should be in the range of 0.1 -100 μm, or preferably in the range of 1-20 μm. For the fine clay mineral grains with the aforementioned size, a flake shape is preferred. If the grain size is larger than 100 μm, the specific surface area is too small to form a good molding in the compressive/sintering molding. On the other hand, if the grain size is smaller than 0.1 μm, the fine clay mineral grains are too small to have good operability in molding. More specifically, for the fine clay mineral, laminated clay minerals with grains having 5 or less layers are preferred, and the laminated clay mineral that can be peeled to single-layer clay mineral grains is most preferred. If the total amount of the clay mineral is 100%, the amount ofthe laminated clay mineral having 5 or less layers should be 50% or more, or preferably 70% or more.

The intermediate polymer of polyimide used in this invention is prepared in a polycondensation reaction between diamine and acid dianhydride, and, as its feedstock monomers, any acid anhydride and diamine as the conventional polyimide raw materials can be used. For example, examples of the acid anhydride include pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, etc. Examples of diamines include 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, p- phenylenediamine, m-phenylenediamine, etc.

The intermediate polymer of polyimide may be homopolymerized to form homopolymer. It may be copolymerized with several types of monomers to form a copolymer. It is possible to perform copolymerization for dicarboxylic acid, diol, their derivatives, etc., and to make use ofthe product as the intermediate polymer of polyamidoimide, polyesteramidoimide, and polyesterimide.

It is possible to use a basic solvent as the solvent for dissolving the intermediate polymer of polyimide used in this invention. The basic solvent is a solvent having the property of accepting protons (H⁺). For the solvent, its functional groups should not react with the monomer to form a polyimide.

Examples ofthe solvents include pyridine, β-picoline, triethylamine, etc. The basic solvent dissolves the polyamic acid forming the raw material, polyamic acid ofthe intermediate polymer is formed, and the solution state of the intermediate polymer is maintained. When the solvent is blended with the dispersion medium, to be explained later, it is miscible with the dispersion medium, and, it should be able to dissolve the intermediate polyimide polymer even in the miscible state.

The dispersion medium used in this invention is a medium that can disperse the fine clay minerals well. It is preferred that the dispersion medium be able to enter between the layers ofthe laminated clay mineral to disperse it into flakes. Water is the optimum dispersion medium for this purpose. It is also possible to use alcohol, carboxylic acids, etc., which are capable of dispersing the laminated clay mineral to flakes in a stable manner without condensation of the laminated clay mineral, although their function in forming flakes ofthe laminated clay mineral is less significant.

When the dispersion medium is blended with the solution ofthe intermediate polymer of polyimide, it is necessary to maintain the solution in a molecular state free of precipitation ofthe intermediate polymer.

In the mixing step in the manufacturing method ofthe polyimide composite material powder of this invention, the first liquid and the second liquid are mixed to form a liquid mixture. The first liquid is a solution ofthe intermediate polymer of polyimide in the aforementioned solvent. If the intermediate polymer is dissolved in a solvent for solution polymerization, the obtained solution after polymerization may be used directly as the first liquid. Also, the first liquid may be prepared by dissolving the intermediate polymer in the aforementioned solvent.

The second liquid can be prepared by dispersing the aforementioned clay mineral in the aforementioned dispersion medium. Dispersion may be performed using a stirrer. The first liquid and the second liquid is blended. It is preferred that forcible stirring be performed by a stirrer after blending to form a slurry. For example, pyridine may be used as the basic solvent, and water may be used as the dispersion medium. In this case, pyridine and water are uniformly blended, and a blending solvent of water is formed for dissolving the polyamic acid. It is believed that polyamic acid can form a type of complex with pyridine ofthe basic solvent. Consequently, polyamic acid is dissolved in the basic solvent, and the clay mineral can be dispersed uniformly in the smallest units (molecular level) in a liquid mixture of water and a basic solvent.

In the pulverizing operation step, the spray drying method is adopted. In this case, the liquid mixture is sprayed into liquid droplets, and the liquid is evaporated in this state. In this way, the polyimide composite material powder of this invention can be obtained. The clay mineral can be uniformly dispersed stably in the smallest units (molecular level) in a liquid mixture of water and basic solvent. Consequently, as the liquid mixture is subjected to spray drying, the solvent alone is removed, while the clay mineral is maintained in the 5 molecular-level dispersion state in polyimide. In this state, the fine polyimide composite material powder can be isolated.

After pulverizing, heating may be performed to promote the ring-closing polymerization ofthe polyamic acid ofthe intermediate polymer. The ring- closing polymerization is performed in a nonoxidative atmosphere by heating at l o 150-400°C for 0.1-20 h. Also, no change in the dispersion state of the clay mineral takes place due to the ring-closing reaction ofthe polyamic acid.

The polyimide composite material powder of this invention comprises fine clay minerals and polyimide covering the fine clay minerals. The powder may contain multigrain fine clay minerals. In this case, it is possible to have

15 each clay mineral grain separately dispersed in polyimide.

The polyimide composite material powder is a type of fine powder appropriate for compressive/sintering molding. The grain size ofthe powder should be in the range of 0.1 - 100 μm, or preferably in the range of 1 -20 μm. If the grain size is larger than 100 μm, the specific area is too small to form a good

20 molding in the compressive/sintering molding. On the other hand, if the grain size is smaller than 0.1 μm, the fine clay mineral grains are too small to have a good handling properties in molding.

As far as the composition ofthe polyimide composite material powder is concerned, with respect to the total amount ofthe polyimide composite material

25 powder 100 wt%, the amount of polyimide is preferably in the range of 50-99.99 parts by weight, and the amount of the clay mineral is preferably in the range of 0.01-50 parts by weight. If the amount of polyimide is less than 50 parts by weight, and the amount ofthe clay minerals is over 50 parts by weight, the amount ofthe clay minerals is too large in the composite material.

30 Consequently, the excellent mechanical properties and surface smoothness of polyimide are degraded. On the other hand, if the amount ofthe clay mineral is less than 0.01 parts by weight, the effect of addition ofthe clay mineral cannot be displayed. This is undesired.

As the polyimide composite material powder is formed by spray drying,

35 even when ring-closing reaction is performed, the resin still can maintain a low crystallinity. This has been confirmed by the fact that, in X-ray diffraction, no significant peak ofthe polyimide crystal was observed in the range of 2Θ = 10-35°.

In addition to polyimide and clay minerals, if needed, the polyimide composite material powder of this invention may also contain polyether ketone, polysulfone, polyamidoimide, etc., as well as resins other than polyimide in appropriate amounts to prepare for the desired properties and characteristics. Depending on the purpose, it is also possible to add pigments and dyes, glass fibers, metal fibers, metal flakes, carbon fibers, and other reinforcing materials and fillers, thermal stabilizers, oxidation inhibitors, UV inhibitors, optical stabilizers, lubricants, plasticizers, static inhibitors, fire retarding agents, etc.

The polyimide composite material powder of this invention is prepared by blending the first liquid ofthe intermediate polymer of polyimide and the second liquid of a dispersion ofthe clay mineral to form a slurry-like mixture solution with the clay mineral dispersed uniformly in it, followed by spray drying ofthe slurry-like mixture solution directly. Consequently, it is possible to maintain the clay mineral in the molecular-level dispersion state in the polyimide matrix. Then, by compressing and sintering molding ofthe obtained polyimide composite material powder, it is possible to form a polyimide resin molded article with clay mineral dispersed uniformly in it and with high dimensional stability.

As a laminated clay mineral with 5 or less layers is used, it is possible to realize uniform dispersion in the slurry-like mixture solution, and to form a composite material powder with even more significant effect of addition ofthe clay mineral.

As a manufacturing method ofthe polyimide composite material powder of this invention, the first liquid prepared by dissolving the intermediate polymer of polyimide in a basic solvent and a second liquid prepared by dispersing the clay mineral in water are mixed with each other, and the mixture solution is subjected to spray drying directly. The solvent alone is removed, the clay minerals are dispersed in the slurry and are present in the intermediate polymer of polyamic acid, and the obtained fine powder ofthe polyimide composite material has a low crystallinity and is appropriate for manufacturing molded articles. Consequently, it is possible to use the prepared polyimide composite material powder as a raw material for molding the polyimide-clay mineral composite material with the clay mineral dispersed uniformly in it.

In addition, by mixing the first liquid prepared from the basic solvent of the polyamic acid forming the intermediate polymer, and a second liquid with 5 the clay mineral dispersed in it, it is possible to form a stable slurry with the clay mineral blended in it uniformly without precipitating the intermediate polymer. Consequently, even in the case of spray drying, phase separation still does not take place, and it is possible to easily obtain the fine powder with clay mineral dispersed uniformly in polyamic acid. 0 When a laminated clay mineral with at least 50% made of grains having

5 or less layers is used as the clay mineral, it is possible to increase the dispersability in the resin matrix. Consequently, there is no need to specifically form the organociay mineral for addition. During sintering molding, no deterioration takes place due to the organic substance used for forming the 5 organociay, and it is possible to add the clay mineral in the polyimide matrix with a high filling rate.

For the polyimide composite material powder, the clay mineral is dispersed uniformly in the resin matrix. Consequently, when compressing/sintering molding is performed, the linear expansion coefficient in o the direction peφendicular to the compressing molding direction can be reduced by up to over 70%, and it is possible to increase the dimensional stability.

Polyimide composite material powder may be used alone or as a mixture with other components to form the feed material for molding. Examples ofthe other components include polyimide resin, polyamide resin, and other synthetic 5 resins, clay mineral powders, and other inorganic fillers, glass fibers, whiskers, and other reinforcing materials.

EXAMPLES In the following, this invention will be explained in more detail with o reference to application examples.

Application Example 1

60.07 g (0.3 mol) of diaminodiphenyl ether were dissolved in 1126.6 g of pyridine. Subsequently, 65.1 1 g (0.2985 mol) of pyromellitic anhydride were 5 added, followed by stirring at room temperature for about 1 h. The polymerization reaction takes place while heat is generated, forming polyamic acid as an intermediate polymer of polyimide (10 wt% pyridine solution). This solution was taken as the first liquid.

On the other hand, 10.89 g of Na montmorillonite (Kunipia F, product of Kunimine Kogyo K.K.) were added to 5007 g of water, followed by vigorous stirring for 1 h in a homogenizer (with the dispersion prepared such that the final clay content in the resin powder became 8 wt%) to form an aqueous dispersion of montmorillonite, which was taken as the second liquid.

The aqueous dispersion of montmorillonite as the second liquid was added into the aforementioned pyridine solution of polyamic acid as the first liquid, and the mixture was stirred forcibly to form a uniform mixture slurry.

The mixture slurry is processed using the spray drying method to form fine powder. In this case, the spraying conditions were selected as follows. Spray apparatus: spray drier using organic solvent, Model GS-31 (product of Yamato Kagaku K.K.); spray method: 2-fluid nozzle method; hot air temperature: 160°C; air and nozzle pressure: 1 kg/cm ; atmosphere: dry nitrogen (with oxygen concentration of 0.8%)

For the clay-mineral-containing polyamic acid powder prepared under the aforementioned conditions, observation was made on an optical microscope, and the grain size was found to be 1-20 μm. The content ofthe clay mineral (montmorillonite) in the powder was determined using ash residue method. It was found that the content ofthe clay was identical to the loading amount.

Ash residue method: 0.1 g ofthe polyamic acid powder containing the clay mineral was loaded in a crucible, and was heated on a gas burner for 3 h. In this case, all of the organic substances in the powder burned off, and only the clay mineral was left. Consequently, the amount of the inorganic substances in the polyamic acid powder can be determined.

The obtained powder was dried in vacuum at 160°C for 15 h, and the polyamic acid powder was converted to the fine powder ofthe polyimide composite material by the ring-closing reaction.

In the X-ray diffraction measurement for the obtained clay-containing polyimide powder, no significant diffraction peak was observed in the angle range of 2Θ = 10-35°. This indicated that a low-crystalline polyimide powder was obtained. Subsequently, 10 g ofthe powder were subjected to compressing/sintering molding in a resistance-heating type vacuum-pressing hot press (FVPHP-R-10, product of Fuji Denpa Kogyo K.K.).

In this case, 10 g ofthe powder sample were loaded in a 40-mm-diameter cylindrical mold, followed by evacuating for 5 min at room temperature, followed by gradually increasing the pressure to 200 atm, and then heating to 400°C at 10°C/min. After keeping in this state for 2 h, the pressure was released, followed by natural cooling. The molding was removed when the temperature ofthe mold dropped below 100°C. The molding was then observed on a transmission electron microscope (TEM). It was found that the clay mineral was uniformly dispersed in units of a single or several layers in polyimide.

In order to measure the linear expansion coefficient ofthe molding, a specimen measuring 5 mm in length, 5 mm in width, and 15 mm in thickness was cut out from the aforementioned molding. Also, measurement was performed in the thickness direction ofthe specimen set in agreement with the direction peφendicular to the compression molding direction. The conditions of measurement ofthe linear expansion coefficient are as follows.

Measurement apparatus: thermal stress/strain measurement apparatus (DT-30, product of Shimadzu Coφ.)

Range of temperature: room temperature - 300°C; heating rate: 2°C/min; load: 500 mg

The measurement data ofthe linear expansion coefficient are as follows:

Table 1.

The values in parentheses are relative values with respect to the linear expansion coefficient measurement value for the sample of polyimide free of clay in the comparative example. That is, 0.82 indicates that the thermal expansion coefficient ofthe molding prepared from the polyimide composite material powder in this application example is 0.82 times the thermal expansion coefficient of the molding of polyimide alone free of clay. That is, by using the polyimide composite material powder prepared in this application example, for the obtained molding, the linear expansion coefficient can be reduced to 18%.

Application Example 2

Except that the amount of Na montmorillonite was changed to 31.30 g, the same procedure for forming the hybrid sample (preparation ofthe slurry, spray drying, compressing/sintering molding) as in Application Example 1 was adopted in this case (the clay content was 20 wt% in this application example). The obtained clay-containing polyimide composite material powder was a fine power with size of 1-20 μm and having a low crystallinity. It contained the same amount of clay mineral as what was loaded. TEM observation ofthe molding indicated that the clay mineral was dispersed uniformly at the molecular level in polyimide. The linear expansion coefficient was measured in the same way as in Application Example 1. The results are as follows:

Table 2.

It can be seen that the linear expansion coefficient was significantly reduced.

Application Example 3

Except that the Na montmorillonite used in Application Example 1 was replaced by Na tetrasihcic mica (swelling-type mica ME100T2, product of Cope Chemical Co.), the same procedure for forming the hybrid sample (preparation of the slurry, spray drying, compressing/sintering molding) as in Application Example 1 was adopted in this case (the clay content was 8 wt% in this application example). The obtained clay-containing polyimide composite material powder was a fine powder with size of 1 -20 μm and having a low crystallinity. It contained the same amount of clay mineral as what was loaded. TEM observation of the molding indicated that the clay mineral was dispersed uniformly at the molecular level in polyimide. The linear expansion coefficient was measured in the same way as in Application Example 1. The results are as follows:

Table 3.

Temperature Coefficient of Linear Expansion Range (°C) (μm/m-°C)

30-100 25.5 (0.70)

100-200 32.2 (0.78)

200-300 33.6 (0.68)

It can be seen that the linear expansion coefficient was significantly reduced. Application Example 4

Except that the Na montmorillonite used in Application Example 1 was replaced by Na tetrasihcic mica (swelling-type mica DM Green A, product of Topi Kogyo K.K.), the same procedure for forming the hybrid sample (preparation of the slurry, spray drying, compressing/sintering molding) as in Application Example 1 was adopted in this case (the clay content was 8 wt% in this application example). The obtained clay-containing polyimide composite material powder was fine powder with size of 1 -20 μm and having a low crystallinity. It contained the same amount of clay mineral as what was loaded. TEM observation on the molding indicated that the clay mineral was dispersed uniformly at the molecular level in polyimide. The linear expansion coefficient was measured in the same way as in Application Example 1. The results are as follows:

Table 4.

It can be seen that the linear expansion coefficient was significantly reduced.

Application Example 5

Except that the amount of Na tetrasihcic mica (swelling type mica ME100T2, product of Cope Chemical Co.) was changed to 31.30 g, the same procedure for forming the hybrid sample (preparation ofthe slurry, spray drying, compressing/sintering molding) as in Application Example 3 was adopted in this case (the clay content was 20 wt% in this application example). The obtained clay-containing polyimide composite material powder was a fine powder with size of 1-20 μm and having a low crystallinity. It contained the same amount of clay mineral as what was loaded. TEM observation ofthe molding indicated that the clay mineral was dispersed uniformly at the molecular level in polyimide. The linear expansion coefficient was measured in the same way as in Application Example 1. The results are as follows:

Table 5.

Temperature Coefficient of Linear Expansion Range (°C) (μm/m-°C)

30-100 16.6 (0.45)

100-200 21.9 (0.53)

200-300 24.9 (0.50)

It can be seen that the linear expansion coefficient was significantly reduced.

Application Example 6

Except that the amount of Na tetrasihcic mica (swelling-type mica DM Green A, product of Topi Kogyo K.K.) was changed to 31.30 g, the same procedure for forming the hybrid sample (preparation ofthe slurry, spray drying, compressing/sintering molding) as in Application Example 4 was adopted in this case (the clay content was 20 wt% in this application example). The obtained clay-containing polyimide composite material powder was a fine powder with size of 1-20 μm and having a low crystallinity. It contained the same amount of clay mineral as what was loaded. TEM observation ofthe molding indicated that the clay mineral was uniformly dispersed at the molecular level in the polyimide. The linear expansion coefficient was measured in the same way as in Application Example 1. The results are as follows:

Table 6.

It can be seen that the linear expansion coefficient was significantly reduced. Application Example 7

Except that the amount of Na tetrasihcic mica (swelling type mica DM Green A, product of Topi Kogyo K.K.) was changed to 83.33 g, the same procedure for forming the hybrid sample (preparation ofthe slurry, spray drying, compressing/sintering molding) as in Application Example 4 was adopted in this case (the clay content was 40 wt% in this application example). The obtained clay-containing polyimide composite material powder was a fine powder with size of 1 -20 μm and having a low crystallinity. It contained the same amount of clay mineral as what was loaded. TEM observation ofthe molding indicated that the clay mineral was dispersed uniformly at the molecular level in polyimide. The linear expansion coefficient was measured in the same way as in Application Example 1. The results are as follows:

Table 7.

It can be seen that the linear expansion coefficient was significantly reduced.

Comparative Example Except that 5007 g of water free of the clay mineral were added to pyridine solution of polyamic acid, the same procedure for forming the hybrid sample (preparation ofthe slurry, spray drying, compressing/sintering molding) as in Application Example 1 was adopted in this case. The obtained polyimide powder was a fine powder with size of 1-20 μm and having a low crystallinity. The linear expansion coefficient was measured in the same way as in Application Example 1. The results are as follows: Table 8.

Temperature Coefficient of Linear Expansion Range (°C) (μm/m-°C)

30-100 36.9

100-200 41.0

200-300 50.3

It can be seen that the linear expansion coefficients in the Application Examples are all lower than in the Comparative Example, and the moldings of the Application Examples have excellent dimensional stability.

Claims

CLAIMS:

1. A polyimide composite material powder comprising a fine clay mineral and a polyimide covering said fine clay minerals. 5

2. The polyimide composite material powder of Claim 1 , wherein the fine clay minerals further comprises laminated clay minerals; and, if the total amount of the laminated clay minerals is 100%, at least 50% of the laminated clay minerals have 5 layers or less.

3. The polyimide composite material powder of Claim 1, further 0 comprising a laminated clay mineral such that if the total amount ofthe laminated clay mineral is 100%, at least 50% of the laminated clay mineral have a single layer.

4. A polyimide intermediate polymer composite material powder comprising a fine clay mineral and a polyimide intermediate polymer prior to s the ring closing reaction, wherein said polyimide intermediate polymer covers said fine clay minerals.

5. A method for manufacturing a polyimide composite material powder comprising the following steps:

(a) forming a first liquid which comprises a polyimide intermediate 0 polymer and solvent capable of dissolving said polyimide intermediate polymer;

(b) forming a second liquid which comprises a fine clay mineral and a dispersion medium which is miscible with said first liquid, wherein said fine clay minerals are dispersed and held in said 5 dispersion medium;

(c) mixing said first liquid with said second liquid to form a liquid mixture;

(d) pulverizing a polyimide composite material wherein said liquid mixture is spray dryed in the form of a fine powder with the fine o clay minerals dispersed in polyimide uniformly.

6. The manufacturing method of Claim 5, wherein said dispersion medium is water, said solvent is a basic solvent, and said fine clay mineral is a laminated clay mineral.

7. The manufacturing method of Claim 5, further comprising a ring-closing imidation step, which occurs after said pulverizing operation step, in which said polyamic acid is heated and is at least partially imidized.

8. A polyimide composite material molded article produced by molding the polyimide composite material powder cited in any of Claims 1-3, or a mixture ofthe same with another composition.

9. A method for manufacturing a polyimide composite material molded article comprising the step of compressing and sintering a polyimide composite material powder cited in Claim 5 or 7.