Method for producing polyimide varnish

Abstract

A method for producing a polyimide varnish in which one or more types of tetracarboxylic dianhydrides and one or more types of diamines are polycondensed in an organic solvent at a reaction temperature of 160-220 DEG C to obtain a reaction solution, and the reaction is stopped by adding a solvent for dilution and lowering the temperature of the reaction solution from the reaction temperature to 120 DEG C at a rate of 4 DEG C / min or more. According to the present invention, it is possible to provide a method for producing a polyimide varnish with which it is possible to obtain a varnish which contains a solvent-soluble polyimide and which is free from discoloration and has excellent colourlessness.

Description

Technical Field

[0001] The invention relates to a method for preparing polyimide varnish. Background Art

[0002] Polyimide resins have excellent mechanical properties and heat resistance, and therefore various applications have been studied in the fields of electrical and electronic components. For example, it is expected that glass substrates used in image display devices such as liquid crystal displays and OLED displays will be replaced with polyimide film substrates, and polyimide resins that meet the performance requirements of optical materials have been developed.

[0003] As a raw material for easily producing a polyimide molded body represented by such a polyimide film, a varnish which is a solution of a polyimide soluble in a solvent is used. In order to improve the performance of the obtained polyimide molded body, polyimide varnishes are also studied.

[0004] For example, Patent Document 1 discloses a solvent-soluble alicyclic polyimide copolymer and a varnish obtained by imidizing a combination of 1,2,4,5-cyclohexanetetracarboxylic dianhydride, a specific dicarboxylic anhydride, and a specific alicyclic diamine at a specific charging ratio for the purpose of improving heat resistance, transparency, and toughness.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-045054 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] The varnish of the polyimide soluble in solvent is excellent in formability as mentioned above. In addition, polyimide resin has excellent property as mentioned above, but easily produces coloring such as yellowing when manufacturing. Recently, owing to also being used for optical material as mentioned above, higher colorlessness is required. Therefore, it is required to obtain the method for the varnish comprising the polyimide of solvent soluble type and excellent colorlessness.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a polyimide varnish which contains a solvent-soluble polyimide and is free of color and has excellent colorlessness.

[0011] Solutions for solving problems

[0012] The present inventors have found that the above-mentioned problems can be solved by polycondensing tetracarboxylic dianhydride and diamine in an organic solvent at a specific temperature in the production of a polyimide varnish, and then adding a diluting solvent to lower the temperature under specific conditions to stop the reaction, thereby completing the invention.

[0013] That is, the present invention relates to the following [1] to [9].

[0014] [1] A method for producing a polyimide varnish, wherein one or more tetracarboxylic dianhydrides and one or more diamines are subjected to polycondensation in an organic solvent at a reaction temperature of 160 to 220°C to obtain a reaction solution, and the reaction is terminated by adding a diluting solvent to reduce the temperature of the reaction solution from the reaction temperature to 120°C at a rate of 4°C / min or more.

[0015] [2] The method for producing a polyimide varnish according to [1], wherein the time required for the temperature of the reaction solution to reach 120° C. is 12 minutes or less from the start of adding the dilution solvent.

[0016] [3] The method for producing a polyimide varnish according to [1] or [2], wherein the dilution solvent is at least one selected from the group consisting of γ-butyrolactone, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.

[0017] [4] The method for producing a polyimide varnish according to any one of [1] to [3], wherein the temperature of the dilution solvent during the addition is 50° C. or lower.

[0018] [5] The method for producing a polyimide varnish according to any one of [1] to [4], wherein the tetracarboxylic dianhydride contains a compound represented by the following formula (1).

[0019]

[0020] [6] The method for producing a polyimide varnish according to any one of [1] to [5], wherein the diamine contains a compound represented by the following formula (2).

[0021]

[0022] [7] The method for producing a polyimide varnish according to any one of [1] to [6], wherein the diamine comprises a compound represented by the following formula (3).

[0023]

[0024] [8] The method for producing a polyimide varnish according to any one of [1] to [7], wherein the organic solvent used in the polycondensation reaction is at least one selected from the group consisting of γ-butyrolactone, N,N-dimethylacetamide and N-methyl-2-pyrrolidone.

[0025] [9] The method for producing a polyimide varnish according to [6] or [8], wherein the diamine further comprises a compound represented by the following formula (3), and the molar ratio [(2) / (3)] of the compound represented by formula (2) to the compound represented by formula (3) is 20 / 80 to 80 / 20.

[0026]

[0027] Effects of the Invention

[0028] According to the present invention, there can be provided a method for producing a polyimide varnish which contains a solvent-soluble polyimide and is free of color and has excellent colorlessness. DETAILED DESCRIPTION

[0029] [Method for producing polyimide varnish]

[0030] The method for producing a polyimide varnish of the present invention comprises the steps of polycondensing one or more tetracarboxylic dianhydrides and one or more diamines in an organic solvent at a reaction temperature of 160 to 220° C. to obtain a reaction liquid, and then adding a diluting solvent to reduce the temperature of the reaction liquid from the reaction temperature to 120° C. at a rate of 4° C. / min or more to stop the reaction.

[0031] <Polycondensation process>

[0032] The method for producing a polyimide varnish of the present invention firstly polycondenses one or more tetracarboxylic dianhydrides and one or more diamines in an organic solvent at a reaction temperature of 160 to 220° C. to obtain a reaction liquid.

[0033] The reaction liquid contains the polyimide after polycondensation. The polycondensation continues until the reaction is stopped in the next step, but the reaction is stopped quickly by adding a diluting solvent in the next step, so the polyimide obtained in this step is substantially the polyimide contained in the finally obtained polyimide varnish.

[0034] (Tetracarboxylic dianhydride)

[0035] The tetracarboxylic dianhydride used for polycondensation in this step is not particularly limited, but preferably contains alicyclic tetracarboxylic dianhydride, and more preferably contains a compound represented by the following formula (1). In addition, the tetracarboxylic dianhydride used for polycondensation in this step is preferably alicyclic tetracarboxylic dianhydride, and more preferably a compound represented by the following formula (1).

[0036] The ratio of the compound represented by the following formula (1) in the tetracarboxylic dianhydride used in this step is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and further preferably 95 mol% or more. The upper limit of the ratio of the compound represented by the following formula (1) is not particularly limited, and can be 100 mol% or less.

[0037]

[0038] Examples of the alicyclic tetracarboxylic dianhydride include 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, dicyclohexyltetracarboxylic dianhydride, 5,5'-(1,4-phenylene)-bis[hexahydro-4,7-methanoisobenzofuran-1,3-dione], 5,5'-bis-2-norbornene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride, and positional isomers thereof.

[0039] Among them, 1,2,4,5-cyclohexanetetracarboxylic dianhydride which is a compound represented by the above formula (1) is preferred.

[0040] By using alicyclic tetracarboxylic dianhydride, the obtained polyimide is soluble in solvent, has no coloration, and has excellent colorlessness. In particular, by using the compound represented by the above formula (1), the obtained polyimide is soluble in solvent, has no coloration, and has extremely excellent colorlessness.

[0041] As tetracarboxylic dianhydride, tetracarboxylic dianhydride other than alicyclic tetracarboxylic dianhydride may be contained. Such tetracarboxylic dianhydride is not particularly limited, and examples thereof include aromatic tetracarboxylic dianhydride and aliphatic tetracarboxylic dianhydride.

[0042] Examples of the aromatic tetracarboxylic dianhydride include biphenyltetracarboxylic dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, pyromellitic dianhydride, 3,3',4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 2,2',3,3'-benzophenonetetracarboxylic dianhydride.

[0043] As aliphatic tetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride etc. are mentioned.

[0044] The tetracarboxylic dianhydride may be one or more types, and may be one type or two or more types.

[0045] It should be noted that, in the present specification, aromatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more aromatic rings, alicyclic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more alicyclic rings and no aromatic ring, and aliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring.

[0046] (Diamine)

[0047] The diamine used for polycondensation in this step is not particularly limited, but preferably contains an aromatic diamine, more preferably contains at least one selected from the group consisting of a compound represented by the following formula (2) and a compound represented by the following formula (3), and further preferably contains a compound represented by the following formula (2) and a compound represented by the following formula (3). In addition, the diamine used for polycondensation in this step is preferably an aromatic diamine, more preferably a compound represented by the following formula (2) and a compound represented by the following formula (3).

[0048] The total ratio of the compound represented by the following formula (2) and the compound represented by the following formula (3) in the diamine used in this step is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and further preferably 95 mol% or more. The upper limit of the total ratio of the compound represented by the following formula (2) and the compound represented by the following formula (3) is not particularly limited, and can be 100 mol% or less.

[0049]

[0050] Examples of the aromatic diamine include 4,4'-bis(4-aminophenoxy)biphenyl, α,α'-bis(4-aminophenyl)-1,3-diisopropylbenzene, 1-(4-aminophenyl)-1,3,3-trimethylphenylindaneamine, 4-aminophenyl-4-aminobenzoate, 2,2'-bis(trifluoromethyl)benzidine, 3,5-diaminobenzoic acid, 9,9-bis(4-aminophenyl)fluorene, 1,4-phenylenediamine, p-phenylenediamine, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'- Diaminodiphenylmethane, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-H-inden-5-amine, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, N,N'-bis(4-aminophenyl)terephthalamide, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 1,4-bis(4-aminophenoxy)benzene, etc.

[0051] Among them, at least one selected from the group consisting of 4,4′-bis(4-aminophenoxy)biphenyl as the compound represented by the above formula (2) and α,α′-bis(4-aminophenyl)-1,3-diisopropylbenzene as the compound represented by the above formula (3) is preferred.

[0052] By using an aromatic diamine, the obtained polyimide is soluble in a solvent, has no coloration, and has excellent colorlessness. In particular, by using any one or both of the compound represented by the aforementioned formula (2) and the compound represented by the aforementioned formula (3), the obtained polyimide is soluble in a solvent, has no coloration, and has extremely excellent colorlessness.

[0053] When both the compound represented by the above formula (2) and the compound represented by the above formula (3) are used as the diamine for polycondensation in this step, the molar ratio [(2) / (3)] of the compound represented by the above formula (2) to the compound represented by the above formula (3) is preferably 20 / 80 to 80 / 20, more preferably 30 / 70 to 70 / 30, and even more preferably 40 / 60 to 60 / 40.

[0054] The diamine used for polycondensation in this step may contain diamines other than aromatic diamines. Such diamines are not particularly limited, and examples thereof include alicyclic diamines and aliphatic diamines.

[0055] As alicyclic diamine, 1, 3- bis (aminomethyl) cyclohexane, 1, 4- bis (aminomethyl) cyclohexane, etc. are mentioned.

[0056] Examples of the aliphatic diamine include ethylenediamine and hexamethylenediamine.

[0057] In this step, the diamine to be subjected to polycondensation may be one or more types, and may be one type or two or more types.

[0058] In the present specification, aromatic diamine refers to a diamine containing one or more aromatic rings, alicyclic diamine refers to a diamine containing one or more alicyclic rings and no aromatic ring, and aliphatic diamine refers to a diamine containing neither an aromatic ring nor an alicyclic ring.

[0059] (Polycondensation reaction)

[0060] This step is a step of polycondensing one or more tetracarboxylic dianhydrides and one or more diamines in an organic solvent at a reaction temperature of 160 to 220° C. to obtain a reaction liquid. The polycondensation reaction in this step is preferably performed as follows.

[0061] The polycondensation reaction in this step is carried out in an organic solvent.

[0062] The organic solvent used in the polycondensation reaction may be any solvent that can dissolve the generated polyimide, and examples thereof include aprotic solvents, phenolic solvents, etheric solvents, carbonate solvents, etc., and preferably at least one selected from the group consisting of aprotic solvents, phenolic solvents, etheric solvents and carbonate solvents.

[0063] Specific examples of the aprotic solvent include amide solvents such as cyclic amides and chain amides, phosphorus-containing amide solvents, sulfur-containing solvents, ketone solvents, and ester solvents including cyclic esters.

[0064] Wherein, the organic solvent preferably comprises at least one selected from the group consisting of cyclic amide, chain amide and cyclic ester, more preferably comprises at least one selected from the group consisting of chain amide and cyclic ester, and further preferably comprises chain amide and cyclic ester. In addition, the organic solvent is preferably at least one selected from the group consisting of cyclic amide, chain amide and cyclic ester, more preferably at least one selected from the group consisting of chain amide and cyclic ester, and further preferably chain amide and cyclic ester.

[0065] Examples of the cyclic amide include N-methyl-2-pyrrolidone, N-methylcaprolactam, and 1,3-dimethylimidazolidinone, and N-methyl-2-pyrrolidone is preferred.

[0066] Examples of the chain amide include N,N-dimethylformamide, N,N-dimethylacetamide, and tetramethylurea.

[0067] Examples of the cyclic ester include γ-butyrolactone and γ-valerolactone.

[0068] As other ester solvents, acetic acid (2-methoxy-1-methylethyl ester) and the like can be mentioned.

[0069] Examples of the phosphorus-containing amide solvent include hexamethylphosphoramide and hexamethylphosphorus triamide.

[0070] Examples of the sulfur-containing solvent include dimethyl sulfone, dimethyl sulfoxide, and sulfolane.

[0071] Examples of the ketone solvent include acetone, methyl ethyl ketone, cyclohexanone, and methylcyclohexanone.

[0072] Specific examples of the phenolic solvent include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol.

[0073] Specific examples of the ether solvent include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, and 1,4-dioxane.

[0074] Specific examples of the carbonate-based solvent include diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate.

[0075] Among these specific organic solvents, the organic solvent preferably contains at least one selected from the group consisting of γ-butyrolactone, N,N-dimethylacetamide and N-methyl-2-pyrrolidone, more preferably contains at least one selected from the group consisting of γ-butyrolactone and N,N-dimethylacetamide, and preferably contains γ-butyrolactone and N,N-dimethylacetamide. In addition, the organic solvent is preferably at least one selected from the group consisting of γ-butyrolactone, N,N-dimethylacetamide and N-methyl-2-pyrrolidone, more preferably at least one selected from the group consisting of γ-butyrolactone and N,N-dimethylacetamide, and further preferably γ-butyrolactone and N,N-dimethylacetamide.

[0076] The above organic solvents can be used alone or in combination of two or more.

[0077] In this step, the method for polycondensing tetracarboxylic dianhydride and diamine is not particularly limited, and a known method can be used.

[0078] Specific reaction methods include: (1) a method in which a solution containing a diamine and an organic solvent and tetracarboxylic dianhydride are added to a reactor, stirred at 10 to 110° C. for 0.5 to 30 hours as required, and then the temperature is raised to carry out a polycondensation reaction; (2) a method in which a solution containing a diamine and an organic solvent and tetracarboxylic dianhydride are added to a reactor, and the temperature is immediately raised to carry out a polycondensation reaction.

[0079] In this step, the charging amount ratio of tetracarboxylic dianhydride and diamine used for the production of the polyimide resin is preferably 0.9 to 1.1 mol of diamine per 1 mol of tetracarboxylic dianhydride.

[0080] In the polycondensation reaction, water is generated by imidization, so it is preferable to carry out the reaction while removing the water generated during the production using a Dean-Stark apparatus, etc. By carrying out such an operation, the degree of polymerization and the imidization ratio can be further increased.

[0081] In the above-mentioned imidization reaction, a known imidization catalyst can be used. Examples of the imidization catalyst include a base catalyst and an acid catalyst.

[0082] Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-methylpyridine, β-methylpyridine, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, and N,N-diethylaniline; and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogen carbonate, and sodium hydrogen carbonate.

[0083] Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, hydroxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid. The imidization catalysts may be used alone or in combination of two or more.

[0084] Among the above, from the viewpoint of operability, a base catalyst is preferred, an organic base catalyst is more preferred, at least one selected from triethylamine and triethylenediamine is further preferred, and triethylamine is further preferred.

[0085] The reaction temperature of the polycondensation reaction in the polycondensation step is 160 to 220° C. From the viewpoint of reaction rate and suppression of gelation, it is preferably 160 to 250° C., more preferably 160 to 230° C., and even more preferably 170 to 200° C. The reaction time is preferably 0.5 to 10 hours after the distillation of generated water starts.

[0086] In addition, the polycondensation step is preferably performed under an inert gas atmosphere such as nitrogen.

[0087] The concentration of the polyimide in the obtained reaction liquid is usually in the range of 1 to 50% by mass, preferably 3 to 35% by mass, and more preferably 5 to 30% by mass.

[0088] From the viewpoint of the mechanical properties of the obtained polyimide, the weight average molecular weight (Mw) of the polyimide obtained in this process is 200,000 or more, preferably 300,000 or more, and more preferably 400,000 or more. In addition, there is no upper limit, preferably 1,000,000 or less, more preferably 700,000 or less. In addition, from the same viewpoint, the number average molecular weight is preferably 50,000 to 500,000. It should be noted that the weight average molecular weight and number average molecular weight of the polyimide can be obtained by using the standard polystyrene (PS) conversion value measured based on gel filtration chromatography.

[0089] In this polycondensation step, a terminal blocking agent may be used in addition to the above-mentioned tetracarboxylic dianhydride and diamine.

[0090] As the end-capping agent, monoamines or dicarboxylic acids are preferred. The amount of the end-capping agent introduced is preferably 0.0001 to 0.1 moles, particularly preferably 0.001 to 0.06 moles, relative to 1 mole of the tetracarboxylic acid component. As the monoamine end-capping agent, methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline, etc. are preferred. Among them, benzylamine and aniline can be used appropriately. As a dicarboxylic acid end-capping agent, dicarboxylic acids are preferred, and a part of them can also be closed-loop. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenone dicarboxylic acid, 3,4-benzophenone dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. are recommended. Among them, phthalic acid and phthalic anhydride can be used appropriately.

[0091] <Reaction Stopping Step>

[0092] In the method for producing a polyimide varnish of the present invention, the polycondensation reaction is stopped by adding a diluting solvent to reduce the temperature of the reaction solution from the reaction temperature to 120° C. at a rate of 4° C. / min or more. That is, in order to stop the polycondensation in the polycondensation step, a diluting solvent is added to reduce the temperature from the reaction temperature of 160 to 220° C. to 120° C.

[0093] Hereinafter, this step will be described as a reaction stopping step.

[0094] The dilution solvent used in this step can dissolve the generated polyimide, and the organic solvent used in the polycondensation reaction can be appropriately used. Specifically, aprotic solvents, phenolic solvents, ether solvents, carbonate solvents, etc. can be listed, preferably at least one selected from the group consisting of aprotic solvents, phenolic solvents, ether solvents and carbonate solvents.

[0095] Specific examples of the aprotic solvent include amide solvents such as cyclic amides and chain amides, phosphorus-containing amide solvents, sulfur-containing solvents, ketone solvents, and ester solvents including cyclic esters.

[0096] Wherein, the dilution solvent preferably comprises at least one selected from the group consisting of cyclic amide, chain amide and cyclic ester, more preferably comprises at least one selected from the group consisting of chain amide and cyclic ester, and further preferably comprises chain amide. In addition, the dilution solvent is preferably at least one selected from the group consisting of cyclic amide, chain amide and cyclic ester, more preferably at least one selected from the group consisting of chain amide and cyclic ester, and further preferably chain amide.

[0097] Examples of the cyclic amide include N-methyl-2-pyrrolidone, N-methylcaprolactam, and 1,3-dimethylimidazolidinone, and N-methyl-2-pyrrolidone is preferred.

[0098] Examples of the chain amide include N,N-dimethylformamide, N,N-dimethylacetamide, and tetramethylurea.

[0099] Examples of the cyclic ester include γ-butyrolactone and γ-valerolactone.

[0100] As other ester solvents, acetic acid (2-methoxy-1-methylethyl ester) and the like can be mentioned.

[0101] Examples of the phosphorus-containing amide solvent include hexamethylphosphoramide and hexamethylphosphorus triamide.

[0102] Examples of the sulfur-containing solvent include dimethyl sulfone, dimethyl sulfoxide, and sulfolane.

[0103] Examples of the ketone solvent include acetone, methyl ethyl ketone, cyclohexanone, and methylcyclohexanone.

[0104] Specific examples of the phenolic solvent include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol.

[0105] Specific examples of the ether solvent include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, and 1,4-dioxane.

[0106] Specific examples of the carbonate-based solvent include diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate.

[0107] Among these specific dilution solvents, the dilution solvent preferably contains at least one selected from the group consisting of γ-butyrolactone, N,N-dimethylacetamide and N-methyl-2-pyrrolidone, more preferably contains at least one selected from the group consisting of γ-butyrolactone and N,N-dimethylacetamide, and preferably contains N,N-dimethylacetamide. In addition, the dilution solvent is preferably at least one selected from the group consisting of γ-butyrolactone, N,N-dimethylacetamide and N-methyl-2-pyrrolidone, more preferably at least one selected from the group consisting of γ-butyrolactone and N,N-dimethylacetamide, and further preferably N,N-dimethylacetamide.

[0108] The above-mentioned dilution solvents may be used alone or in combination of two or more.

[0109] At the time of being added to the reaction solution obtained in the polycondensation reaction, the temperature of the dilution solvent is preferably 50°C or less. By keeping the temperature of the dilution solvent low, the temperature of the reaction solution can be effectively lowered, and the reaction can be stopped quickly. At the time of being added to the reaction solution obtained in the polycondensation reaction, the temperature of the dilution solvent is more preferably 40°C or less, further preferably 30°C or less, and further preferably 25°C or less. There is no lower limit, but it is usually 0°C or more.

[0110] The rate of decrease (cooling rate) of the temperature of the reaction solution when the reaction is stopped by the input of the dilution solvent is 4°C / minute or more. By rapidly reducing the temperature of the reaction solution, a varnish containing a solvent-soluble polyimide and having excellent colorlessness and colorlessness can be obtained. The rate of decrease (cooling rate) of the temperature of the reaction solution when the reaction is stopped by the input of the dilution solvent is preferably 5°C / minute or more, more preferably 7°C / minute or more, further preferably 8°C / minute or more, and further preferably 9°C / minute or more. There is no upper limit, usually 30°C / minute or less.

[0111] In addition, the time until the temperature of the reaction solution reaches 120° C. when the reaction is stopped by the addition of the diluting solvent is preferably less than 1 hour from the start of the addition of the diluting solvent, more preferably less than 30 minutes, further preferably less than 12 minutes, and further preferably less than 10 minutes. Since the temperature of the reaction solution drops rapidly, a varnish containing a solvent-soluble polyimide and having excellent colorlessness and colorlessness can be obtained. The lower limit is not limited, but is usually more than 5 minutes.

[0112] Until the temperature of the reaction liquid reaches 120°C, a diluting solvent is added to reduce the temperature at a rate of 4°C / min or more. After reaching 120°C, further solvent may be added as needed. Thereafter, there is no limitation on the temperature of the reaction liquid as long as it is below 120°C.

[0113] The diluted solution obtained in this step has polyimide uniformly dissolved therein, and the polyimide concentration (solid content) is preferably 5 to 40% by mass, more preferably 10 to 30% by mass. The viscosity (25° C.) of the polyimide solution is preferably 1 to 200 Pa·s, more preferably 1 to 100 Pa·s.

[0114] Since the solution obtained in this step contains polyimide, it can be used as a polyimide varnish as it is, and the concentration can be adjusted by adding or removing an organic solvent.

[0115] (Polyimide)

[0116] The solution obtained in this step contains a polyimide. The polyimide contains a structural unit derived from the above-mentioned tetracarboxylic dianhydride and a structural unit derived from the above-mentioned diamine.

[0117] Specifically, the polyimide preferably comprises a structural unit derived from an alicyclic tetracarboxylic dianhydride, and more preferably comprises a structural unit derived from a compound represented by the following formula (1). The ratio of the structural unit derived from the compound represented by the following formula (1) in the structural unit derived from the tetracarboxylic dianhydride is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and further preferably 95 mol% or more. The upper limit of the ratio of the structural unit derived from the compound represented by the following formula (1) is not particularly limited, and can be 100 mol% or less.

[0118]

[0119] By including the compound represented by the above formula (1), the obtained polyimide is soluble in a solvent and has no coloration and is extremely excellent in colorlessness.

[0120] As the structural unit derived from tetracarboxylic dianhydride, the structural unit derived from tetracarboxylic dianhydride other than the structural unit derived from alicyclic tetracarboxylic dianhydride may also be included. As such a structural unit derived from tetracarboxylic dianhydride, there is no particular limitation, and the structural unit derived from aromatic tetracarboxylic dianhydride and the structural unit derived from aliphatic tetracarboxylic dianhydride can be listed.

[0121] The structural unit derived from tetracarboxylic dianhydride may be one or more types, and may be one type or two or more types.

[0122] The polyimide preferably contains a structural unit derived from an aromatic diamine, more preferably contains at least one selected from the group consisting of a structural unit derived from a compound represented by the following formula (2) and a structural unit derived from a compound represented by the following formula (3), and further preferably contains a structural unit derived from a compound represented by the following formula (2) and a structural unit derived from a compound represented by the following formula (3). The total ratio of the structural unit derived from the compound represented by the following formula (2) and the structural unit derived from the compound represented by the following formula (3) in the structural unit derived from the diamine is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and further preferably 95 mol% or more. The upper limit of the total ratio of the structural unit derived from the compound represented by the following formula (2) and the structural unit derived from the compound represented by the following formula (3) is not particularly limited, and it can be 100 mol% or less.

[0123]

[0124] By containing either or both of the structural unit derived from the compound represented by the above formula (2) and the structural unit derived from the compound represented by the above formula (3), the polyimide is soluble in a solvent and has no color and is extremely excellent in colorlessness.

[0125] When the compound comprises both structural units derived from the compound represented by the aforementioned formula (2) and structural units derived from the compound represented by the aforementioned formula (3), the molar ratio of the structural units derived from the compound represented by the aforementioned formula (2) to the structural units derived from the compound represented by the aforementioned formula (3) [(2) / (3)] is preferably 20 / 80 to 80 / 20, more preferably 30 / 70 to 70 / 30, and further preferably 40 / 60 to 60 / 40.

[0126] The structural unit derived from diamine may contain a structural unit derived from diamine other than the structural unit derived from aromatic diamine. Such a structural unit derived from diamine is not particularly limited, and examples thereof include a structural unit derived from alicyclic diamine and a structural unit derived from aliphatic diamine.

[0127] The structural unit derived from diamine may be one or more types, and may be one type or two or more types.

[0128] [Polyimide varnish]

[0129] Provided is a method for producing a polyimide varnish, wherein the polyimide varnish obtained by the above-mentioned production method contains a solvent-soluble polyimide, and the production method can obtain a varnish with no coloration and excellent colorlessness.

[0130] The polyimide varnish contains polyimide and an organic solvent.

[0131] As the polyimide, the above-mentioned polyimide is preferable.

[0132] The organic solvent contained in the polyimide varnish is the same as the organic solvent used in the polycondensation step or the reaction stopping step. The solution obtained in the reaction stopping step can be used directly as the polyimide varnish, and the solution obtained in the reaction stopping step can be used directly as the polyimide varnish by adjusting the polyimide concentration (solid content) suitable for the polyimide varnish in the reaction stopping step.

[0133] The polyimide varnish has polyimide uniformly dissolved therein, and the polyimide concentration (solid content) thereof is preferably 5 to 40% by mass, more preferably 10 to 30% by mass. The viscosity (25° C.) of the polyimide varnish is preferably 1 to 200 Pa·s, more preferably 1 to 100 Pa·s.

[0134] The polyimide varnish may contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, ultraviolet stabilizers, surfactants, leveling agents, defoamers, fluorescent whitening agents, crosslinking agents, polymerization initiators, and photosensitizers within a range that does not impair the effects of the present invention.

[0135] The polyimide varnish obtained by the production method of the present invention is suitable for use as a raw material for various components such as color filters, flexible displays, semiconductor components, optical components, etc. The polyimide varnish obtained by the production method of the present invention is particularly suitable for use as a raw material for image display devices such as liquid crystal displays and OLED displays.

[0136] Example

[0137] The present invention is specifically described below by way of examples, but the present invention is not limited by these examples.

[0138] Evaluation of the varnishes obtained in Examples and Comparative Examples was performed by the following methods.

[0139] (1) Yellowness Index (Yellowness, YI)

[0140] The yellowness (YI) of the polyimide varnish obtained in the examples and comparative examples was measured by placing the polyimide varnish in a measuring cell having a cell length (measurement thickness) of 10 mm using a color / turbidity simultaneous measuring device "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd. The smaller the yellowness (YI), the better the colorlessness. For the polyimide varnish used for the measurement of the yellowness (YI), N,N-dimethylacetamide was added as a diluting solvent, and after confirming that it became uniform, the polyimide varnish was stored at room temperature (25°C) for 16 hours.

[0141] <Manufacturing of polyimide varnish>

[0142] Example 1

[0143] Into a 2 L 5-necked glass round-bottom flask equipped with a stainless steel half-moon-shaped stirring blade, a nitrogen inlet pipe, a Dean-Stark equipped with a cooling tube, a thermometer, and glass end caps were charged 113.751 g (0.331 mol) of α,α'-bis(4-aminophenyl)-1,3-diisopropylbenzene (a compound represented by the formula (3), manufactured by MITSUI FINE CHEMICALS, INC.), 121.330 g (0.331 mol) of 4,4'-bis(4-aminophenoxy)biphenyl (a compound represented by the formula (2), manufactured by Wakayama Seika Industries, Ltd.), and 460.6 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation), and the mixture was stirred at 100 rpm at a temperature of 70°C in a nitrogen atmosphere to obtain a solution. 148.254 g (0.661 mol) of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (a compound represented by formula (1), manufactured by Mitsubishi Gas Chemical Co., Ltd.), 115.15 g of N,N-dimethylacetamide (manufactured by Mitsubishi Gas Chemical Co., Ltd.), and 3.35 g of triethylamine (manufactured by Kanto Chemical Co., Ltd.) as a catalyst were added thereto, and then heated in an oil bath to raise the temperature in the reaction system to 180° C. The components removed by distillation were collected, and the temperature in the reaction system was maintained at 180° C. for 5 hours to carry out a polycondensation reaction to obtain a reaction liquid.

[0144] N,N-dimethylacetamide at 25°C was added to the obtained reaction solution at 180°C, while the temperature in the reaction system was lowered at a rate of 10°C / min, so that the temperature of the reaction solution became 120°C. The amount of N,N-dimethylacetamide added was adjusted to obtain a uniform polyimide varnish having a solid content concentration of 20% by mass. The evaluation results of the obtained polyimide varnish are shown in Table 1.

[0145] Example 2

[0146] A polycondensation reaction was carried out in the same manner as in Example 1 to obtain a reaction liquid.

[0147] N,N-dimethylacetamide at 25°C was added to the obtained reaction solution at 180°C, while the temperature in the reaction system was lowered at a rate of 7.2°C / min, so that the temperature of the reaction solution became 120°C. The amount of N,N-dimethylacetamide added was adjusted to obtain a uniform polyimide varnish having a solid content concentration of 20% by mass. The evaluation results of the obtained polyimide varnish are shown in Table 1.

[0148] Example 3

[0149] A polycondensation reaction was carried out in the same manner as in Example 1 to obtain a reaction liquid.

[0150] N,N-dimethylacetamide at 25°C was added to the obtained reaction solution at 180°C, while the temperature in the reaction system was lowered at a rate of 5.1°C / min, so that the temperature of the reaction solution became 120°C. The amount of N,N-dimethylacetamide added was adjusted to obtain a uniform polyimide varnish having a solid content concentration of 20% by mass. The evaluation results of the obtained polyimide varnish are shown in Table 1.

[0151] Comparative Example 1

[0152] A polycondensation reaction was carried out in the same manner as in Example 1 to obtain a reaction liquid.

[0153] To the obtained reaction solution at 180°C, N,N-dimethylacetamide at a temperature of 25°C was added while the temperature in the reaction system was lowered at a rate of 1.3°C / min, so that the temperature of the reaction solution became 120°C. The amount of N,N-dimethylacetamide added was adjusted to obtain a uniform polyimide varnish having a solid content concentration of 20% by mass. The evaluation results of the obtained polyimide varnish are shown in Table 1.

[0154] Comparative Example 2

[0155] A polycondensation reaction was carried out in the same manner as in Example 1 to obtain a reaction liquid.

[0156] To the obtained reaction solution at 180°C, N,N-dimethylacetamide at 25°C was added while the temperature in the reaction system was lowered at a rate of 3.5°C / min, so that the temperature of the reaction solution became 120°C. The amount of N,N-dimethylacetamide added was adjusted to obtain a uniform polyimide varnish having a solid content concentration of 20% by mass. The evaluation results of the obtained polyimide varnish are shown in Table 1.

[0157] [Table 1]

[0158] Table 1

[0159]

[0160] *) Regarding the reaction solvent and the dilution solvent, GBL is γ-butyrolactone and DMAc is N,N-dimethylacetamide.

[0161] As shown in Table 1, it can be seen that the polyimide varnish obtained by the production method of the present invention is uniform and has low yellowness, and therefore contains a solvent-soluble polyimide, is non-colored, and has excellent colorlessness. Therefore, the polyimide varnish obtained by the production method of the present invention can be used for applications such as materials for image display devices.

Claims

1. A method for producing a polyimide varnish, wherein: One or more tetracarboxylic dianhydrides and one or more diamines are polycondensed in an organic solvent at a reaction temperature of 160 to 220° C. to obtain a reaction solution, and a diluting solvent is added to reduce the temperature of the reaction solution from the reaction temperature to 120° C. at a rate of 4° C. / min or more to stop the reaction.

2. The method for producing a polyimide varnish according to claim 1, wherein: The time required for the temperature of the reaction solution to reach 120° C. is 12 minutes or less from the start of adding the diluting solvent.

3. The method for producing a polyimide varnish according to claim 1 or 2, wherein: The dilution solvent is at least one selected from the group consisting of γ-butyrolactone, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.

4. The method for producing a polyimide varnish according to claim 1 or 2, wherein: The temperature of the dilution solvent during introduction is 50° C. or lower.

5. The method for producing a polyimide varnish according to claim 1 or 2, wherein: The tetracarboxylic dianhydride comprises a compound represented by the following formula (1):

6. The method for producing a polyimide varnish according to claim 1 or 2, wherein: The diamine comprises a compound represented by the following formula (2):

7. The method for producing a polyimide varnish according to claim 1 or 2, wherein: The diamine comprises a compound represented by the following formula (3):

8. The method for producing a polyimide varnish according to claim 1 or 2, wherein: The organic solvent used in the polycondensation reaction is at least one selected from the group consisting of γ-butyrolactone, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.

9. The method for producing a polyimide varnish according to claim 6, wherein: The diamine further comprises a compound represented by the following formula (3), and the molar ratio [(2) / (3)] of the compound represented by formula (2) to the compound represented by formula (3) is 20 / 80 to 80 / 20,

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