Aromatic polyimide powder for molding, molding using the same, and method for improving mechanical strength of molding

Abstract

Provided is an aromatic polyimide powder that is for a molded body, that contains volatile components in an amount of 0.50-5.00 mass% with respect to 100 mass% of the aromatic polyimide powder at 25°C, and that provides, when being molded, an aromatic polyimide molded body having a flexural strength of 60 MPa or more.

Description

[Technical Field]

[0001] The present invention relates to a polyimide powder for moldings having improved mechanical properties, a molded body using the same, and a method for improving the mechanical strength of a molded body. [Background technology]

[0002] Aromatic polyimides, obtained from aromatic tetracarboxylic acid components and aromatic diamine components as primary raw materials, have excellent properties such as heat resistance, mechanical strength, electrical properties, and solvent resistance, and are widely used as materials for electrical and electronic components, etc. Among these, aromatic polyimide powder processed into powder form can be filled into a mold and pressed to obtain desired molded products, and is therefore widely used as a material for manufacturing parts for industrial manufacturing equipment.

[0003] In recent years, efforts have been made to enhance the functionality of aromatic polyimide powders in order to further expand their range of applications while taking advantage of their properties. For example, techniques for mixing polyimide powders with various materials have been developed. Patent Document 1 discloses a technique for mixing polyimide powders with conductive carbon to obtain molded bodies for use in electrical and electronic components. Patent Document 2 discloses a technique for mixing polyimide powders with an inorganic fibrous filler and a solid lubricant to impart wear resistance and mechanical strength. Furthermore, Patent Document 3 discloses a technique for mixing polyimide powders with fluorine-containing resin powders to improve the handleability of the polyimide powder.

[0004] However, mixing with additives or resins other than the polyimide powder reduces the content of the polyimide powder relatively, and as a result, the inherent properties of the polyimide powder cannot be fully exhibited.

[0005] To solve these problems, methods of chemically modifying polyimide powder are being adopted. For example, Patent Document 4 discloses the use of a soluble polyimide. Also, Patent Document 5 discloses a method of incorporating a fluorine functional group such as a 2-hydroxy-1,1,1,3,3,3-hexafluoroisopropyl group. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-016222 [Patent Document 2] Japanese Patent Publication No. 62-0132960 [Patent Document 3] International Publication No. 2015 / 005271 [Patent Document 4] Japanese Patent Application Publication No. 2019-059835 [Patent Document 5] Japanese Patent Application Publication No. 2019-089998 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when a soluble polyimide such as that described in Patent Document 4 is used, the solvent resistance of the resulting molded article is impaired, making it difficult for the polyimide's functions to be fully exhibited. Similarly, when a fluorine functional group is introduced as described in Patent Document 5, the solubility of the polyimide powder in solvents is improved, resulting in a deterioration in the solvent resistance of the resulting molded article. Therefore, conventionally known methods do not fully exhibit the properties of aromatic polyimide powder, and in particular, tend to impair solvent resistance and mechanical properties.

[0008] The present invention solves the above-mentioned problems. Through trial and error to improve mechanical properties without compromising solvent resistance, the inventors surprisingly discovered a correlation between the amount of volatile components in an aromatic polyimide powder and the mechanical properties of an aromatic polyimide molded article. Therefore, an object of the present invention is to provide an aromatic polyimide powder that can fully utilize the properties of the aromatic polyimide powder to the fullest. In particular, an object of the present invention is to provide an aromatic polyimide powder that can be molded into an aromatic polyimide molded article with excellent mechanical properties. Another object of the present invention is to provide a method for improving the mechanical properties of an aromatic polyimide molded article, thereby obtaining a molded article with excellent mechanical properties. [Means for solving the problem]

[0009] The present invention particularly relates to the following items: 1. An aromatic polyimide powder for use in moldings, wherein the content of volatile components contained in the aromatic polyimide powder for use in moldings is 0.50 to 5.00 mass % relative to 100 mass % of the aromatic polyimide powder at 25° C. The aromatic polyimide powder for use in moldings of the present invention is preferably such that the bending strength of an aromatic polyimide molding obtained by molding the aromatic polyimide powder for use in moldings of the present invention is 60 MPa or more. 2. A method for producing an aromatic polyimide powder for use in molded bodies according to 1.1, comprising a volatile component adjustment step of adjusting the total proportion of volatile components in the aromatic polyimide powder to within the range of 0.50 to 5.00 mass% relative to 100 mass% of the aromatic polyimide powder at 25°C. 3. A method for producing an aromatic polyimide powder for molding, wherein the volatile component adjustment step according to 2 includes a washing step and / or a drying step. 4. A method for producing an aromatic polyimide powder for molding, wherein the cleaning step according to 4.3 includes a cleaning step using alcohol. 5. An aromatic polyimide molded article having a bending strength of 60 MPa or more, obtained by molding the aromatic polyimide powder for moldings according to 1. 6. A method for improving the mechanical strength of an aromatic polyimide molded body, comprising adjusting the content of volatile components contained in the aromatic polyimide powder as a raw material to 0.50 to 5.00 mass% relative to 100 mass% of the aromatic polyimide powder at 25°C. [Effects of the Invention]

[0010] The present invention can provide an aromatic polyimide powder and a method for producing the same that can realize aromatic polyimide molded articles with excellent mechanical properties without deteriorating solvent resistance. Furthermore, it can provide a method for improving the mechanical properties of aromatic polyimide molded articles. According to the present invention, by the simple method of adjusting the content of volatile components, it is possible to obtain an aromatic polyimide powder that can significantly improve the mechanical strength of molded articles, which can be said to be an industrially groundbreaking invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Aromatic polyimide powder for molding> First, the aromatic polyimide powder for moldings of the present invention will be described. The aromatic polyimide powder for moldings of the present invention contains 0.50 to 5.00 mass% of volatile components. Here, "volatile components" refers to components that volatilize in a temperature range of 50 to 350°C. The present invention is characterized in that the volatile components are contained in an amount of 0.50 to 5.00 mass% relative to 100 mass% of the aromatic polyimide powder at 25°C. That is, for example, if the amount of components that volatilize in a temperature range of 50 to 350°C is 1.00 mass%, the aromatic polyimide powder for moldings will be composed of 99.00 mass% of components that do not volatilize in a temperature range of 50 to 350°C, which are primarily composed of aromatic polyimide powder, and 1.00 mass% of components that volatilize in a temperature range of 50 to 350°C.

[0012] The content of "volatile components" can be measured by known analytical methods such as thermogravimetric analysis. For example, in thermogravimetric analysis, a predetermined amount of aromatic polyimide powder is heated to a temperature exceeding 350°C at a rate of 20°C / min, the total amount of volatile components volatilized at 50°C to 350°C is measured, and the proportion of this total amount relative to the predetermined amount of aromatic polyimide powder is calculated. Note that the weight of the aromatic polyimide powder refers to the weight measured at 25°C. However, other analytical methods may be used as long as they can measure the amount of components volatilized in the temperature range of 50 to 350°C.

[0013] Such volatile components may include, for example, monomer components such as aromatic diamine components or aromatic tetracarboxylic acid components, residual solvents, additives, moisture, and further modified or decomposed products of these components due to heating, but the types thereof are not limited. In other words, in the present invention, the type of volatile component is not important, but the amount of volatile component is technically important.

[0014] The aromatic polyimide powder for molded articles of the present invention has a content of components that volatilize in a temperature range of 50 to 350°C. From the viewpoints of the mechanical properties of the molded articles and the handleability of the powder, the lower limit is preferably 1.00% by mass or more, more preferably 1.50% by mass or more, and particularly preferably 2.00% by mass or more. Similarly, the upper limit is preferably 4.30% by mass or less, more preferably 4.00% by mass or less, and particularly preferably 3.00% by mass or less.

[0015] The aromatic polyimide powder for molded bodies of the present invention may have any content of components that volatilize in a temperature range of 50 to 350°C within the above range. However, from the viewpoint of further improving the mechanical properties of molded bodies and the handleability of the powder, the content of components that volatilize in a temperature range of 150 to 350°C is preferably 75.0 to 99.0 mass%, where the content of components that volatilize in a temperature range of 50 to 350°C is taken as 100 mass%, with the lower limit being more preferably 80.0 mass% or more, and particularly preferably 90.0 mass% or more, and the upper limit being more preferably 98.0 mass% or less, and particularly preferably 97.0 mass% or less. Similarly, from the viewpoint of further improving the mechanical properties of the molded body and the handleability of the powder, when the content of components that volatilize in a temperature range of 50 to 350°C is taken as 100 mass%, the content of components that volatilize in a temperature range of 150 to 250°C is preferably 50.0 to 80.0 mass%, with the lower limit being more preferably 55.0 mass% or more, and particularly preferably 60.0 mass% or more, and the upper limit being more preferably 75.0 mass% or less, and particularly preferably 70.0 mass% or less.

[0016] The size of the aromatic polyimide powder for molding of the present invention is not particularly limited, but from the viewpoint of the mechanical properties of the molded body and the handleability of the powder, the average particle diameter is preferably 5 to 20 μm. Here, the average particle diameter referred to in the present invention refers to a value measured using a laser diffraction / scattering particle size distribution analyzer. Furthermore, the shape of the aromatic polyimide powder for molding is also not particularly limited as long as the effects of the present invention are achieved.

[0017] The aromatic polyimide powder for molding of the present invention preferably contains, as a main component, an aromatic polyimide containing a repeating unit represented by the following chemical formula (II): The method for producing the aromatic polyimide powder will be described later.

[0018] [ka] (In the formula, X1 represents one or more tetravalent groups obtained by removing a carboxyl group from a tetracarboxylic acid having an aromatic ring, and Y1 represents one or more divalent groups obtained by removing an amino group from a diamine having an aromatic ring.)

[0019] In the above X1, a tetravalent group having no substituent on the aromatic ring is preferred, and a tetravalent group represented by any of the chemical formulae (III) to (VII) is particularly preferred.

[0020] [ka] (wherein Z1 is a direct bond or the following divalent group:

[0021] [ka] In the formula, W1 is a divalent organic group, W2 and W3 are each independently an amide bond, an ester bond, or a carbonyl bond, and W4 is an organic group containing an aromatic ring.

[0022] Specific examples of W1 include aliphatic hydrocarbon groups having 2 to 24 carbon atoms and aromatic hydrocarbon groups having 6 to 24 carbon atoms.

[0023] Specific examples of W4 include aromatic hydrocarbon groups having 6 to 24 carbon atoms.

[0024] Examples of compounds used as raw materials for forming the tetravalent groups represented by chemical formulas (III) to (VII) (sometimes referred to as "aromatic tetracarboxylic acid components") include compounds derived from aromatic tetracarboxylic acid dianhydrides such as 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 2,2',3,3'-biphenyltetracarboxylic acid dianhydride, pyromellitic dianhydride, benzophenonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic dianhydride, diphenylsulfonetetracarboxylic acid dianhydride, p-terphenyltetracarboxylic acid dianhydride, and m-terphenyltetracarboxylic acid dianhydride. From the viewpoint of the solvent resistance and mechanical properties of the aromatic polyimide molded article, tetravalent groups derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, diphenylsulfonetetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, or m-terphenyltetracarboxylic dianhydride are more preferred, and those derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride or 2,3,3',4'-biphenyltetracarboxylic dianhydride are particularly preferred. These aromatic tetracarboxylic acid components may be used alone or in combination.

[0025] Furthermore, a tetracarboxylic acid component having a substituent on the aromatic ring can be used in combination, provided that the effect of the present invention is not impaired. For example, halogen-substituted tetracarboxylic acid dianhydrides such as 5,5'-[2,2,2-trifluoro-1-[3-(trifluoromethyl)phenyl]ethylidene]diphthalic anhydride, 5,5'-[2,2,3,3,3-pentafluoro-1-(trifluoromethyl)pyropyridene]diphthalic anhydride, 1H-difuro[3,4-b:3',4'-i]xanthene-1,3,7,9(11H)-tetrone, 5,5'-oxybis[4,6,7-trifluoro-pyromellitic anhydride], 3,6-bis(trifluoromethyl)pyromellitic dianhydride, 4-(trifluoromethyl)pyromellitic dianhydride, 1,4-difluoropyromellitic dianhydride, and 1,4-bis(3,4-dicarboxytrifluorophenoxy)tetrafluorobenzene dianhydride can be mentioned. These tetracarboxylic acid components can be used alone or in combination of two or more, and may be selected appropriately in consideration of the desired properties. The tetracarboxylic acid component having a substituent on an aromatic ring preferably accounts for less than 5 mol% of all tetracarboxylic acid components.

[0026] Furthermore, in the above Y1, a divalent group having no substituent on the aromatic ring is preferred, and in particular, divalent groups represented by chemical formulas (IX) to (X) are particularly preferred.

[0027] [ka] (wherein Z2 is a direct bond or the following divalent group:

[0028] [ka] In the formula (XII), W5 to W 13 each independently represents a direct bond or a divalent group represented by formula (XI).

[0029] Compounds used as raw materials for forming chemical formulas (IX) to (X) (sometimes referred to as "aromatic diamine components") include, for example, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenylmethane, and from the viewpoint of the solvent resistance of the aromatic polyimide molded article, it is more preferable to use p-phenylenediamine or 4,4'-diaminodiphenyl ether, and from the viewpoint of the solvent resistance and mechanical properties of the aromatic polyimide molded article, it is even more preferable to use p-phenylenediamine. These aromatic diamine components can be used alone or in combination of two or more.

[0030] Furthermore, diamine components having a substituent on the aromatic ring can be used in combination, provided that the effects of the present invention are not impaired. Examples include halogen-substituted diamines such as 2,4-toluenediamine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, bis(4-amino-3-carboxyphenyl)methane, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,3,5,6-tetrafluoro-1,4-diaminobenzene, 2,4,5,6-tetrafluoro-1,3-diaminobenzene, 2,3,5,6-tetrafluoro-1,4-benzene(dimethanamine), 2,2'-difluoro(1,1'-biphenyl)-4,4'-diamine, 4,4'-diaminooctafluorobiphenyl, and 4,4'-oxybis(2,3,5,6-tetrafluoroaniline). These diamine components can be used alone or in combination, and can be selected appropriately based on the desired properties. The diamine component having a substituent on the aromatic ring preferably accounts for less than 5 mol % of all diamine components.

[0031] <Method for producing aromatic polyimide powder for molding> Next, a method for producing the aromatic polyimide powder for use in moldings of the present invention will be described with reference to a representative example. The method for producing the aromatic polyimide powder for use in moldings of the present invention is not particularly limited as long as the volatile component content can be adjusted to 0.50 to 5.00 mass %, but from the viewpoint of ease of adjusting the volatile component, an aromatic tetracarboxylic acid component and an aromatic diamine component are used as raw materials (hereinafter collectively referred to as "monomer components") to form an aromatic polyimide via a polyamic acid, and then a step of adjusting the volatile component is carried out, followed by powdering, whereby the aromatic polyimide powder for use in moldings can be produced.

[0032] First, the step of forming the polyamic acid will be described. The polyamic acid preferably contains a repeating unit represented by the following chemical formula (I).

[0033] [ka] (In the formula, A is one or more tetravalent groups obtained by removing a carboxyl group from an aromatic tetracarboxylic acid, and B is one or more divalent groups obtained by removing an amino group from an aromatic diamine.)

[0034] In the above A, a tetravalent group having no substituent on the aromatic ring is preferred, and in particular, a tetravalent group represented by the above-mentioned chemical formulas (III) to (VII) is preferred.

[0035] Examples of compounds used as raw materials for forming the tetravalent groups represented by chemical formulas (III) to (VII) (sometimes referred to as "aromatic tetracarboxylic acid components") include compounds derived from aromatic tetracarboxylic acid dianhydrides such as 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 2,2',3,3'-biphenyltetracarboxylic acid dianhydride, pyromellitic dianhydride, benzophenonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic dianhydride, diphenylsulfonetetracarboxylic acid dianhydride, p-terphenyltetracarboxylic acid dianhydride, and m-terphenyltetracarboxylic acid dianhydride. From the viewpoint of the solvent resistance and mechanical properties of the aromatic polyimide molded article, tetravalent groups derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, diphenylsulfonetetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, or m-terphenyltetracarboxylic dianhydride are more preferred, and those derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride or 2,3,3',4'-biphenyltetracarboxylic dianhydride are particularly preferred. These aromatic tetracarboxylic acid components may be used alone or in combination.

[0036] Furthermore, a tetracarboxylic acid component having a substituent on the aromatic ring can be used in combination, provided that the effect of the present invention is not impaired. For example, halogen-substituted tetracarboxylic acid dianhydrides such as 5,5'-[2,2,2-trifluoro-1-[3-(trifluoromethyl)phenyl]ethylidene]diphthalic anhydride, 5,5'-[2,2,3,3,3-pentafluoro-1-(trifluoromethyl)pyropyridene]diphthalic anhydride, 1H-difuro[3,4-b:3',4'-i]xanthene-1,3,7,9(11H)-tetrone, 5,5'-oxybis[4,6,7-trifluoro-pyromellitic anhydride], 3,6-bis(trifluoromethyl)pyromellitic dianhydride, 4-(trifluoromethyl)pyromellitic dianhydride, 1,4-difluoropyromellitic dianhydride, and 1,4-bis(3,4-dicarboxytrifluorophenoxy)tetrafluorobenzene dianhydride can be mentioned. These tetracarboxylic acid components can be used alone or in combination of two or more, and may be selected appropriately in consideration of the desired properties. The tetracarboxylic acid component having a substituent on an aromatic ring preferably accounts for less than 5 mol% of all tetracarboxylic acid components.

[0037] Furthermore, in the above B, a divalent group having no substituent on the aromatic ring is preferred, and in particular, the divalent groups represented by the above chemical formulae (IX) to (X) are particularly preferred.

[0038] Compounds used as raw materials for forming chemical formulas (IX) to (X) (sometimes referred to as "aromatic diamine components") include, for example, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenylmethane, and from the viewpoint of the solvent resistance of the aromatic polyimide molded article, it is more preferable to use p-phenylenediamine or 4,4'-diaminodiphenyl ether, and from the viewpoint of the solvent resistance and mechanical properties of the aromatic polyimide molded article, it is even more preferable to use p-phenylenediamine. These aromatic diamine components can be used alone or in combination of two or more.

[0039] Furthermore, diamine components having a substituent on the aromatic ring can be used in combination, provided that the effects of the present invention are not impaired. Examples include halogen-substituted diamines such as 2,4-toluenediamine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, bis(4-amino-3-carboxyphenyl)methane, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,3,5,6-tetrafluoro-1,4-diaminobenzene, 2,4,5,6-tetrafluoro-1,3-diaminobenzene, 2,3,5,6-tetrafluoro-1,4-benzene(dimethanamine), 2,2'-difluoro(1,1'-biphenyl)-4,4'-diamine, 4,4'-diaminooctafluorobiphenyl, and 4,4'-oxybis(2,3,5,6-tetrafluoroaniline). These diamine components can be used alone or in combination, and can be selected appropriately based on the desired properties. The diamine component having a substituent on the aromatic ring preferably accounts for less than 5 mol % of all diamine components.

[0040] Such polyamic acid can be prepared by reacting an aromatic tetracarboxylic acid component and an aromatic diamine component in approximately equimolar amounts in a solvent, optionally with heating, until the desired viscosity (or molecular weight) is achieved. In the present invention, "approximately equimolar" refers to a molar ratio of the aromatic tetracarboxylic acid component to the aromatic diamine component of approximately 0.90 to 1.10, preferably approximately 0.95 to 1.05. The monomer components for forming the polyamic acid can be mainly composed of the aromatic tetracarboxylic acid component and the aromatic diamine component.

[0041] The solvent that can be used in this production method is not particularly limited, and any known solvent used in the production of polyamic acid can be selected and used. For example, from the viewpoint of solubility of the monomer components or polyamic acid, it is preferable to use at least one nitrogen-containing solvent. Furthermore, from the viewpoint of ease of control of the amount of volatile components, a solvent with a boiling point of 100°C or higher is preferable. Examples of such solvents include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,1,3,3-tetramethylurea, 1,3-dimethyl-2-imidazolidinone, N,N-dimethylisobutyramide, and N,N-dimethylpropionamide.

[0042] The polyamic acid can be produced by adding the monomer components and the solvent to a reaction vessel equipped with a stirrer and then stirring. The order of adding these raw materials is not particularly limited. For example, a predetermined amount of the aromatic diamine component may be dissolved in the solvent and then the aromatic tetracarboxylic acid component may be added. Alternatively, the aromatic tetracarboxylic acid component may be dissolved in the solvent and then the aromatic diamine component may be added. Alternatively, the aromatic tetracarboxylic acid component and the aromatic diamine component may be added alternately. If necessary, additives such as known reaction catalysts may be added at any timing.

[0043] The reaction temperature is not particularly limited, but is preferably 0 to 100°C, more preferably 10 to 90°C, and even more preferably 20 to 70°C. By adjusting the reaction temperature within the above range, it is possible to produce an aromatic polyimide powder with little variation in coloration and mechanical properties. The temperature may be constant or may be increased or decreased as appropriate.

[0044] <Formation of aromatic polyimide> The aromatic polyimide can be formed by utilizing known reactions such as a thermal imidization reaction carried out by heating a polyamic acid solution or a chemical imidization reaction carried out using an imidizing agent. These imidization reactions are preferably carried out in an inert gas atmosphere by flowing in an inert gas such as nitrogen gas or argon gas.

[0045] The reaction temperature for the thermal imidization reaction can be appropriately set depending on the type of monomer component and the solvent used, but it is usually preferable to carry out the reaction in the range of 130 to 230°C, and more preferably in the range of 140 to 190°C.

[0046] The imidizing agent used in the chemical imidization reaction can be a carboxylic acid anhydride such as acetic anhydride, propionic anhydride, succinic anhydride, phthalic anhydride, or benzoic anhydride. Acetic anhydride is preferred from the viewpoints of cost and ease of removal after the reaction. The catalyst added during the formation of the polyamic acid may be used as is, or it may be added anew or additionally after the formation of the polyamic acid. The equivalent weight of the imidizing agent used is equal to or greater than the equivalent weight of the amide bond in the polyamic acid used in the chemical imidization reaction, preferably 1.1 to 5 times, and more preferably 1.5 to 4 times, the equivalent weight of the amide bond. Using a slight excess of the imidizing agent relative to the amide bond allows the imidization reaction to be carried out efficiently even at relatively low temperatures.

[0047] From the viewpoint of reducing variations in the physical properties of molded articles, the aromatic polyimide (powder) preferably has an imidization rate of 95% or more, more preferably 98% or more. The imidization rate can be measured by infrared spectroscopy according to a conventional method.

[0048] <Formation of aromatic polyimide powder> Finally, the process for producing an aromatic polyimide powder will be described. When an aromatic polyimide is formed from a polyamic acid solution as described above, the aromatic polyimide precipitates as an insoluble matter in the solution system. The powder precipitated in the system is filtered out from the solution, and then subjected to a volatile component adjustment process to obtain an aromatic polyimide powder.

[0049] The volatile component adjusting step is not particularly limited as long as it can adjust the volatile components of the aromatic polyimide powder, but preferably includes a washing step and / or a drying step. To increase the efficiency of the washing step and / or the drying step, it is preferable to form an aromatic polyimide powder having a particle size close to the desired size in advance. For example, the imidization reaction may be carried out while stirring, or a pulverization treatment may be added after the aromatic polyimide is formed. Naturally, a combination of these steps may also be used.

[0050] The method for washing the aromatic polyimide powder is not particularly limited, and any known method can be appropriately selected for the washing step. From the viewpoint of ease of operation, the washing method can be appropriately selected, such as a method in which the aromatic polyimide powder is filtered and then the aromatic polyimide powder remaining on the filter is rinsed with a washing liquid, or a method in which the aromatic polyimide powder obtained by filtration is placed in a separately prepared container, a washing liquid is added thereto, and then the mixture is stirred to wash.

[0051] The cleaning liquid used in the cleaning step is not particularly limited as long as it does not dissolve the aromatic polyimide powder, but hydrophilic solvents such as water and alcohol are preferred.

[0052] The alcohol used as the cleaning liquid is not particularly limited, but from the viewpoint of removing the solvent, imidizing agent, etc. contained in the aromatic polyimide powder, alcohols having a total carbon number of 5 or less, such as methanol, ethanol, and isopropyl alcohol, are preferred, with isopropyl alcohol being particularly preferred. Furthermore, from the viewpoint of controlling volatile components, the cleaning liquid used may be selected to have a boiling point of 150°C or less, more preferably 100°C or less. These cleaning liquids can be used alone or, if necessary, mixed with other cleaning liquids.

[0053] Although there is no particular limitation on the amount of washing liquid relative to the aromatic polyimide powder, from the viewpoint of industrial productivity, it is preferably 10 times or less the mass of the aromatic polyimide powder immediately after filtration. The amount of washing liquid relative to the aromatic polyimide powder referred to here is the amount of washing liquid used in one washing.

[0054] The drying step of the aromatic polyimide powder can be carried out at any temperature, but from the viewpoint of suppressing decomposition of the aromatic polyimide powder, the temperature is preferably 400° C. or lower, more preferably 350° C. or lower, even more preferably 300° C. or lower, and particularly preferably 200° C. or lower. The lower limit temperature can be set to preferably 80° C. or higher, more preferably 100° C. or higher, and particularly preferably 110° C. or higher.

[0055] The drying of the aromatic polyimide powder may be carried out under normal pressure or under reduced pressure. It may also be carried out under the atmosphere or under an inert gas atmosphere, but is preferably carried out under an inert gas atmosphere from the viewpoint of suppressing decomposition of the aromatic polyimide powder. It may also be carried out under a mixed atmosphere of the atmosphere and an inert gas, or may be carried out under the atmosphere and then under an inert gas atmosphere, or may be carried out under an inert gas atmosphere and then under the atmosphere.

[0056] The drying time may be adjusted appropriately taking into consideration the content of volatile components. However, from the viewpoint of suppressing decomposition of the aromatic polyimide powder and industrial productivity, the drying time is preferably within 36 hours, more preferably within 24 hours, and particularly preferably within 18 hours. The lower limit of the drying time is not particularly limited, but is preferably 30 minutes or more, more preferably 1 hour or more.

[0057] The washing step and / or drying step may be repeated multiple times, or the washing step and the drying step may be repeated alternately. When the washing step or the drying step is included multiple times, the washing step or the drying step does not need to be performed under the same conditions, and the conditions can be changed as appropriate. For example, in the washing step, the type of washing liquid or the amount of washing liquid relative to the aromatic polyimide powder may be changed, and in the drying step, the drying temperature, drying time, etc. may be changed.

[0058] In general, the primary focus of washing and / or drying processes is to eliminate volatile components as much as possible, not only for polyimide powders but also for other resin powders. However, in the present invention, the volatile component adjustment process, including the washing and / or drying process, differs in that the volatile component content is adjusted to 0.5 to 5.0 mass%. Therefore, to distinguish it from the general washing and / or drying process, it is referred to as the volatile component adjustment process in the present invention. For example, in the industrial production of aromatic polyimide powders, the production facilities are large-scale and large amounts of raw materials are used, so it is expected that aromatic polyimide powders with a volatile component content of less than 0.5 mass% may be obtained in whole or in part. Such aromatic polyimide powders with a volatile component content of less than 0.5 mass% can be adjusted to 0.5 to 5.0 mass% by spraying a desired amount of the organic solvent or the like. In other words, the volatile component adjustment process is a concept that encompasses not only a process for reducing the volatile component content but also a process for increasing the volatile component content. To reiterate, the volatile component adjustment step is a step of adjusting the content of volatile components to 0.5 to 5.0 mass%. In addition to the organic solvents described above, various organic solvents such as acetone, methyl ethyl ketone, toluene, methanol, ethanol, isopropyl alcohol, ethyl benzoate, ethylene glycol, and propylene glycol can be used as the organic solvent to be sprayed. After spraying the organic solvent, drying may be performed as necessary. Furthermore, a method of adjusting the content of volatile components by mixing the aromatic polyimide powder with the organic solvent described above and drying the mixture may also be employed.

[0059] <Aromatic polyimide molded article and method for producing the same> The aromatic polyimide molded article of the present invention is obtained by molding the aromatic polyimide powder for molding of the present invention described above, and has mechanical properties such as a bending strength of 60 MPa or more. Here, the bending strength referred to in the present invention is the average value calculated by measuring the breaking strength of a molded article molded under the following conditions (n=10 times) using a bending strength tester. After filling the powder into a powder molding machine, the powder is broken at room temperature by 6000 kgf / cm. 2The molded article is then uniaxially molded at a pressure of 1000 kJ / min to form a rectangular parallelepiped shape measuring 5 mm wide, 40 mm long, and 4 mm thick. This rectangular parallelepiped shape is then subjected to pressureless firing at 400°C in an air atmosphere to produce a molded article. The molded article thus produced is measured using a bending strength tester at a test speed of 0.5 mm / min, and the strength at break is taken as the breaking strength. The bending strength is preferably 62 MPa or more, more preferably 64 MPa or more, and even more preferably 65 MPa or more. The conditions for pressureless firing are not particularly limited, but a typical condition is to heat the material at 400°C in an air atmosphere at a temperature of 10°C / min, hold the material at 50°C for 30 minutes, then heat the material again at 10°C / min, hold the material at 200°C for 1 hour, then heat the material at 10°C / min, and hold the material at 400°C for 15 minutes. The molding time for uniaxial molding is typically 1 minute.

[0060] In order to achieve such bending strength, the aromatic polyimide powder of the present invention can be used without any particular limitation on its manufacturing method. It is sufficient to use the aromatic polyimide powder of the present invention in a state in which the volatile component content is within the above-mentioned range for the production of a molded product. For example, the aromatic polyimide powder of the present invention can be filled into a mold and then heated and compressed by applying pressure and heat simultaneously or separately. That is, the aromatic polyimide molded product of the present invention may also be a sintered aromatic polyimide molded product molded and sintered by heating and compression. Such heating temperature and pressure conditions depend on the molding equipment, and ranges suitable for the equipment can be selected as desired. In particular, the manufacturing method of the present invention allows the aromatic polyimide to fully exhibit its heat resistance by containing a volatile component content within a specific range. As a result, molding is possible even at temperatures above 300°C, and even at temperatures above 400°C, the molded product can exhibit the desired mechanical strength without deterioration in appearance or cracking. The upper limit of the heating temperature is preferably 600°C or less, more preferably 550°C or less, and particularly preferably 500°C or less.

[0061] Similarly, the pressure may be selected from an optimum range suited to the manufacturing equipment. From the viewpoint of improving the mechanical properties of the aromatic polyimide molded article and suppressing the occurrence of cracks in the aromatic polyimide molded article, it is preferably 4000 kgf / cm. 2 More preferably, 5000 kgf / cm 2 More than 5500 kgf / cm, particularly preferably 2 or more, preferably 7000 kgf / cm 2 Less than 6500 kgf / cm, more preferably 2 The heating and compression molding time in the heating and compression molding is preferably 10 minutes or more, more preferably 40 minutes or more, preferably 100 minutes or less, and more preferably 60 minutes or less. Furthermore, it is preferable that the heating and compression molded product be cooled in the mold at a rate of 5 to 10°C / min, from the viewpoints of improving the mechanical properties of the aromatic polyimide molded product and suppressing the occurrence of cracks in the aromatic polyimide molded product. On the other hand, the compression molding time in the compression molding at room temperature is preferably 30 seconds or more, more preferably 1 minute or more, preferably 10 minutes or less, and more preferably 5 minutes or less.

[0062] The aromatic polyimide molded article of the present invention can also be produced by compression molding at room temperature under the above-mentioned pressure, followed by sintering without compression. That is, the aromatic polyimide molded article of the present invention may be a sintered aromatic polyimide molded article that has been molded and then sintered. In this case, the sintering temperature is preferably 300°C or higher, more preferably 350°C or higher, and particularly preferably 400°C or higher, from the viewpoint of the mechanical properties of the aromatic polyimide molded article, and is preferably 600°C or lower, more preferably 550°C or lower, and particularly preferably 500°C or lower. When sintering without compression, the sintering time is preferably 60 minutes or higher, more preferably 120 minutes or higher, preferably 240 minutes or lower, and more preferably 180 minutes or lower. The sintered molded article is preferably cooled at a rate of 5 to 10°C / min, from the viewpoint of improving the mechanical properties of the aromatic polyimide molded article and suppressing the occurrence of cracks in the molded article.

[0063] When sintering is performed without compression, the sintering temperature may be set to the above-mentioned temperature, but the heating rate during sintering is preferably 5°C / min or more, more preferably 10°C / min or more, and preferably 30°C / min or less, and more preferably 20°C / min or less. When sintering is performed without compression, a temperature holding treatment may be performed during the heating process. The temperature holding treatment may be performed once or multiple times during the heating process. For example, when the temperature holding treatment is performed three times, the holding temperature in the second temperature holding treatment is preferably 100°C or more, more preferably 150°C or more, and preferably 250°C or less, and more preferably 200°C or less, and the holding time is preferably 10 minutes or more, more preferably 30 minutes or more, and preferably 120 minutes or less, and more preferably 60 minutes or less. Furthermore, the holding temperature in the third temperature holding treatment is preferably 350°C or higher, more preferably 400°C or higher, preferably 550°C or lower, more preferably 500°C or lower, and the holding time is preferably 5 minutes or higher, more preferably 15 minutes or higher, preferably 60 minutes or lower, more preferably 30 minutes or lower.

[0064] Furthermore, when producing the aromatic polyimide molded article, any filler can be mixed with the aromatic polyimide powder. There are no particular limitations on the filler used, and examples include inorganic fillers such as glass fiber, ceramic fiber, boron fiber, glass beads, whiskers, diamond powder, alumina, silica, natural mica, synthetic mica, alumina, carbon black, silver powder, copper powder, aluminum powder, nickel powder, metal fiber, ceramic fiber, whiskers, silicon carbide, silicon oxide, alumina, magnesium powder, titanium powder, carbon fiber, and graphite, as well as organic fillers such as fluorine-containing resin and aramid fiber. These fillers can be used alone or in combination of two or more.

[0065] The amount of filler used can be selected depending on the application, but can be, for example, in the range of 1 to 50 mass % based on the weight of the aromatic polyimide powder.

[0066] In the above-mentioned heat compression molding, examples of the apparatus for producing the aromatic polyimide molded article include a four-column hydraulic press, a high-pressure hot press, and a WIP apparatus. The preform is preferably formed by a method using, for example, a wet-cleaning-in-place (WIP), a dry-cleaning-in-place (DIP), a high-pressure press, a hydraulic press, a rotary press, or a tablet machine. The aromatic polyimide molded article of this invention can also be produced by applying the above-mentioned heat compression molding method to a sheet-like laminate.

[0067] As described above, the aromatic polyimide powder of the present invention can fully exhibit the properties of aromatic polyimides and is therefore applicable to a variety of production methods under a wide range of conditions, making it highly valuable for industrial use. In particular, the aromatic polyimide powder can exhibit excellent mechanical properties even when subjected to a method of compression molding at room temperature under the above-mentioned pressure followed by sintering under non-compression (so-called direct forming). Therefore, according to the present invention, aromatic polyimide molded articles having various shapes can be produced with high productivity.

[0068] The aromatic polyimide molded article obtained by the present invention can be suitably used as pins, guides, evaluation sockets, vacuum pads, etc. for semiconductor manufacturing related equipment; bushings, seal rings, trust washers, bearing retainers, piston rings, lock nut inserts, etc. for automotive and aerospace applications; and bearing sleeves, roller bushings, piston rings, etc. for industrial machinery related equipment. [Example]

[0069] EXAMPLES The present invention will be explained in more detail below with reference to Examples, Comparative Examples, and Reference Examples, but the present invention is not limited to these.

[0070] The measurement methods used in the following examples are shown below.

[0071] <Amount of volatile components> Approximately 20 mg of aromatic polyimide powder was used as a test sample, and the temperature was raised from 25°C to 700°C at a rate of 20°C / min in a nitrogen atmosphere using a thermogravimetric measuring device. The weight loss rate from 50 to 350°C was calculated from the resulting weight curve. The weight loss rates from 150 to 250°C and from 150 to 350°C were also calculated.

[0072] <Average particle size> About 20 mg of aromatic polyimide powder was used as a test sample, and the average particle size was measured using a laser diffraction / scattering particle size distribution analyzer.

[0073] <Bending strength> Aromatic polyimide powder was compressed in a powder molding machine at room temperature under a pressure of 6000 kgf / cm 2 The aromatic polyimide molded article was then subjected to uniaxial molding at a pressure of 100 kJ / min for 1 minute to obtain an aromatic polyimide molded article having a width of 5 mm, a length of 40 mm, and a thickness of 4 mm. The aromatic polyimide molded article was then subjected to pressureless baking in an air atmosphere under the specified temperature conditions described below, and then its bending strength was measured at a test speed of 0.5 mm / min using a bending strength tester. Ten measurements were performed, and the average value was taken as the bending strength.

[0074] The abbreviations for the compounds used in the following examples are as follows: s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride a-BPDA: 2,3,3',4'-biphenyltetracarboxylic dianhydride PMDA: 1,2,4,5-benzenetetracarboxylic dianhydride ODPA: 4,4'-oxydiphthalic dianhydride PPD: Paraphenylenediamine NMP: N-methyl-2-pyrrolidone IPA: Isopropyl alcohol

[0075] <Preparation of aromatic polyimide powder A> 240.00 g of NMP was added as a solvent, and 28.56 g of s-BPDA, 2.15 g of a-BPDA, and 11.29 g of PPD were added and dissolved by stirring. The temperature was then raised to 50°C to carry out polymerization, yielding a polyamic acid solution. The temperature was then further raised to 190°C to carry out an imidization reaction, resulting in the precipitation of an aromatic polyimide powder. The precipitated powder was filtered, washed four times with IPA, and dried at 100°C under a reduced pressure of 2 kPa for 24 hours to obtain aromatic polyimide powder A. The amount of volatile components in the resulting aromatic polyimide powder A (the content of components volatile in the temperature range of 50 to 350°C, hereinafter the same) was 1.03% by mass. In addition, the content of components that volatilize in the temperature range of 150 to 350°C was 0.99 mass% (96.1 mass% of the total volatile components), and the content of components that volatilize in the temperature range of 150 to 250°C was 0.61 mass% (59.2 mass% of the total volatile components).

[0076] <Preparation of aromatic polyimide powder B> An aromatic polyimide powder was precipitated in the same manner as in the preparation of aromatic polyimide powder A, and the precipitated powder was filtered off, washed four times with IPA, and then dried at 120°C for 2 hours under a nitrogen atmosphere to obtain aromatic polyimide powder B. The amount of volatile components in the obtained aromatic polyimide powder B was 1.50% by mass. The content of components volatilizing in the temperature range of 150 to 350°C was 1.23% by mass (82.0% by mass of the total volatile components), and the content of components volatilizing in the temperature range of 150 to 250°C was 0.78% by mass (52.0% by mass of the total volatile components).

[0077] <Preparation of aromatic polyimide powder C> An aromatic polyimide powder was precipitated in the same manner as in the preparation of aromatic polyimide powder A, and the precipitated powder was filtered off, washed three times with IPA, and then dried at 120°C for 2 hours under a nitrogen atmosphere to obtain aromatic polyimide powder C. The amount of volatile components in the obtained aromatic polyimide powder C was 2.10% by mass. The content of components volatilizing in the temperature range of 150 to 350°C was 1.97% by mass (93.8% by mass of the total volatile components), and the content of components volatilizing in the temperature range of 150 to 250°C was 1.51% by mass (71.9% by mass of the total volatile components).

[0078] <Preparation of aromatic polyimide powder D> An aromatic polyimide powder was precipitated in the same manner as in the preparation of aromatic polyimide powder A, and the precipitated powder was filtered off, washed twice with IPA, and then dried at 120°C for 2 hours under a nitrogen atmosphere to obtain aromatic polyimide powder D. The amount of volatile components in the obtained aromatic polyimide powder D was 4.23% by mass. The content of components volatilizing in the temperature range of 150 to 350°C was 3.27% by mass (77.3% by mass of the total volatile components), and the content of components volatilizing in the temperature range of 150 to 250°C was 2.81% by mass (66.4% by mass of the total volatile components).

[0079] <Preparation of aromatic polyimide powder E> An aromatic polyimide powder was precipitated in the same manner as in the preparation of aromatic polyimide powder A, and the precipitated powder was filtered off, washed four times with IPA, and then dried at 260°C for 8 hours in a nitrogen atmosphere to obtain aromatic polyimide powder E. The amount of volatile components in the obtained aromatic polyimide powder E was 0.08% by mass.

[0080] <Preparation of aromatic polyimide powder F> An aromatic polyimide powder was precipitated in the same manner as in the preparation of aromatic polyimide powder A, and the precipitated powder was filtered off, washed four times with IPA, and then dried at 250°C under a reduced pressure of 2 kPa for 24 hours to obtain aromatic polyimide powder F. The amount of volatile components in the obtained aromatic polyimide powder F was 0.20% by mass.

[0081] <Preparation of aromatic polyimide powder G> An aromatic polyimide powder was precipitated in the same manner as in the preparation of aromatic polyimide powder A, and the precipitated powder was filtered off, washed four times with IPA, and then dried at 225°C under a reduced pressure of 2 kPa for 18 hours to obtain aromatic polyimide powder G. The amount of volatile components in the obtained aromatic polyimide powder G was 0.49% by mass.

[0082] <Preparation of aromatic polyimide powder H> An aromatic polyimide powder was precipitated in the same manner as in the preparation of aromatic polyimide powder A, and the precipitated powder was filtered off, washed once with IPA, and then dried at 100°C under a reduced pressure of 2 kPa for 24 hours to obtain aromatic polyimide powder H. The amount of volatile components in the obtained aromatic polyimide powder H was 5.62% by mass.

[0083] <Preparation of aromatic polyimide powder I> An aromatic polyimide powder was precipitated in the same manner as in the preparation of aromatic polyimide powder A, and the precipitated powder was filtered off, washed once with IPA, and then dried at 120°C for 2 hours in a nitrogen atmosphere to obtain aromatic polyimide powder I. The amount of volatile components in the obtained aromatic polyimide powder I was 10.49% by mass.

[0084] <Preparation of aromatic polyimide powder J> An aromatic polyimide powder was precipitated in the same manner as in the preparation of aromatic polyimide powder A, and the precipitated powder was filtered and then dried at 120°C for 2 hours in a nitrogen atmosphere to obtain aromatic polyimide powder J. The amount of volatile components in the obtained aromatic polyimide powder J was 50.00% by mass.

[0085] <Preparation of aromatic polyimide powder K> 7 g of aromatic polyimide powder A obtained by the above method was prepared, and 1 g of ethyl benzoate and 29 g of acetone were added and stirred. The aromatic polyimide powder to which ethyl benzoate and acetone had been added was then dried at 120°C for 2 hours in a nitrogen atmosphere to obtain aromatic polyimide powder K. The amount of volatile components in the obtained aromatic polyimide powder K was 0.98 mass%.

[0086] <Preparation of aromatic polyimide powder L> 6 g of aromatic polyimide powder A obtained by the above method was prepared, and 1 g of NMP and 29 g of acetone were added and stirred. Next, the aromatic polyimide powder to which NMP and acetone had been added was dried at 120°C for 2 hours under a nitrogen atmosphere to obtain aromatic polyimide powder L. The amount of volatile components in the obtained aromatic polyimide powder L was 4.13 mass%.

[0087] Example 1 The obtained aromatic polyimide powder A was filled into a mold and compressed at room temperature under 6000 kgf / cm using a powder molding machine. 2 The resulting aromatic polyimide molded article was uniaxially molded at a pressure of 0.05 mm for 1 minute to obtain an aromatic polyimide molded article measuring 5 mm wide, 40 mm long, and 4 mm thick. The resulting aromatic polyimide molded article was calcined at 400°C in an air atmosphere without pressure, and then its bending strength was evaluated. The results are shown in Table 1. The specific calcination conditions were as follows: the temperature was increased at a rate of 10°C / min, held at 50°C for 30 minutes, then increased again at a rate of 10°C / min, held at 200°C for 1 hour, then increased at a rate of 10°C / min, held at 400°C for 15 minutes, and then cooled at a rate of 10°C / min.

[0088] <Example 2> An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder B was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 1.

[0089] Example 3 An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder C was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 1.

[0090] Example 4 An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder D was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 1.

[0091] <Comparative Example 1> An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder E was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 2.

[0092] <Comparative Example 2> An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder F was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 2.

[0093] <Comparative Example 3> An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder G was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 2.

[0094] <Comparative Example 4> An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder H was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 2.

[0095] <Comparative Example 5> An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder I was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 2.

[0096] <Comparative Example 6> Molding was attempted in the same manner as in Example 1, except that aromatic polyimide powder J was used instead of aromatic polyimide powder A, but molding did not go well (molding was impossible).

[0097] <Example 5> An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder K was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 3.

[0098] Example 6 An aromatic polyimide molded article was obtained in the same manner as in Example 1, except that aromatic polyimide powder L was used instead of aromatic polyimide powder A. The flexural strength of the obtained aromatic polyimide molded article was evaluated. The results are shown in Table 3.

[0099] Example 7 Aromatic polyimide powder A was uniaxially molded to obtain an aromatic polyimide molded article measuring 5 mm in width, 40 mm in length, and 4 mm in thickness in the same manner as in Example 1. The obtained molded article was then subjected to pressureless baking in an air atmosphere under the conditions shown in Table 4, and the bending strength was evaluated. The obtained results are shown in Table 4.

[0100] Example 8 Aromatic polyimide powder A was uniaxially molded to obtain an aromatic polyimide molded article measuring 5 mm in width, 40 mm in length, and 4 mm in thickness in the same manner as in Example 1. The obtained molded article was then subjected to pressureless baking in an air atmosphere under the conditions shown in Table 4, and the bending strength was evaluated. The obtained results are shown in Table 4.

[0101] [Table 1]

[0102] [Table 2]

[0103] [Table 3]

[0104] [Table 4]

[0105] When the solvent resistance of the obtained molded bodies was evaluated, the molded bodies obtained by molding the aromatic polyimide powders of Examples 1 to 8 had excellent solvent resistance equivalent to that of the molded bodies obtained by molding the aromatic polyimide powders of Comparative Examples 1 to 3, which had a low content of volatile components. On the other hand, the solvent resistance deteriorated as the content of volatile components increased. [Industrial Applicability]

[0106] The aromatic polyimide powder of the present invention can provide an aromatic polyimide molded article having excellent mechanical properties without deteriorating solvent resistance, and can also provide a method for improving the mechanical strength of an aromatic polyimide molded article.

Claims

1. A method for producing an aromatic polyimide molded article having a bending strength of 60 MPa or more, the method comprising molding an aromatic polyimide powder for molding, the aromatic polyimide powder containing, as a main component, an aromatic polyimide containing units derived from 2,3,3',4'-biphenyltetracarboxylic dianhydride, the content of volatile components contained in the aromatic polyimide powder for molding is 0.50 to 5.00 mass% relative to 100 mass% of the aromatic polyimide powder at 25°C; The aromatic polyimide powder is heated at room temperature under a pressure of 4000 to 7000 kgf / cm ２ and then sintering the resulting mixture without compression to obtain the aromatic polyimide molded article.

2. A method for improving the mechanical strength of an aromatic polyimide molded article containing, as a main component, an aromatic polyimide containing units derived from 2,3,3',4'-biphenyltetracarboxylic dianhydride, the aromatic polyimide molded article being obtained by subjecting an aromatic polyimide powder as a raw material to a pressure of 4000 to 7000 kgf / cm at room temperature. ２ and then sintering the resulting product without compression, and the content of volatile components contained in the aromatic polyimide powder as a raw material is adjusted to 0.50 to 5.00 mass % relative to 100 mass % of the aromatic polyimide powder at 25°C.

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