Polyimide resin, polyimide varnish and polyimide film

Abstract

A polyimide resin that has structural units A derived from tetracarboxylic acid dianhydride and structural units B derived from diamine, said structural units A containing structural units (A1) derived from 9,9-bis(3,4-dicarboxyphenyl)fluorene acid dianhydride and structural units (A2) derived from aliphatic tetracarboxylic acid dianhydride, and said structural units B containing structural units (B1) derived from 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane.

Description

[Technical Field]

[0001] The present invention relates to a polyimide resin, a polyimide varnish, and a polyimide film. [Background technology]

[0002] Polyimide resins are obtained from aromatic tetracarboxylic acid anhydrides and aromatic diamines, and generally have excellent heat resistance, chemical resistance, mechanical properties, and electrical characteristics due to their molecular rigidity, resonance stabilization, and strong chemical bonds. Therefore, they are widely used in fields such as molding materials, composite materials, electrical and electronic components, optical materials, displays, and aerospace. In particular, glass materials have traditionally been used for electrical and electronic components, optical materials, displays, etc., but taking advantage of their flexibility, applications to flexible devices are also being considered.

[0003] For example, Patent Document 1 discloses a composition for forming a flexible device substrate, which contains a polyimide, which is a reaction product of a tetracarboxylic dianhydride component containing an alicyclic tetracarboxylic dianhydride and a diamine component containing a fluorine-containing aromatic diamine, and an organic solvent, for the purpose of improving heat resistance, retardation, flexibility, and transparency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 097143 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the application of polyimide resins has progressed, particularly in displays and their protective front panels, and polyimide resins with good mechanical strength, i.e., high strength and high elastic modulus, are required to replace the glass materials that have been used conventionally. However, conventional high-strength polyimide resins often have problems such as insufficient flexibility and poor colorless transparency. Recently, polyimide films have also been used for displays and protective plates in smartphones with folding structures, so they are required to be strong yet also more flexible, and they also need to have the ability to recover their shape after being deformed. Therefore, a polyimide resin having these properties has been desired. In other words, the problem to be solved by the present invention is to provide a polyimide resin that can form a film that has both mechanical properties and colorless transparency, and that is high in strength and also has excellent deformation recovery properties, and to provide a polyimide film that has both mechanical properties and colorless transparency, and that is high in strength and also has excellent deformation recovery properties. [Means for solving the problem]

[0006] As a result of extensive research, the inventors have found that a polyimide resin containing a specific combination of structural units can solve the above problems, and have arrived at the present invention.

[0007] That is, the present invention relates to the following [1] to [8]. [1] A polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, A polyimide resin, wherein the structural unit A comprises a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from an aliphatic tetracarboxylic dianhydride, and the structural unit B comprises a structural unit (B1) derived from a compound represented by the following formula (b1): [ka] [2] The polyimide resin according to [1] above, wherein the structural unit (A2) is a structural unit derived from an alicyclic tetracarboxylic dianhydride. [3] The polyimide resin according to [1] or [2] above, wherein the structural unit (A2) is at least one selected from the group consisting of a structural unit (A2-1) derived from a compound represented by the following formula (a2-1), a structural unit (A2-2) derived from a compound represented by the following formula (a2-2), and a structural unit (A2-3) derived from a compound represented by the following formula (a2-3): [ka] [4] The polyimide resin according to any one of [1] to [3] above, wherein the proportion of the structural unit (B1) relative to the structural unit B is 30 mol % or more. [5] The polyimide resin according to any one of [1] to [4] above, wherein the proportion of the structural unit (A1) relative to the structural unit A is 50 to 90 mol %. [6] The polyimide resin according to any one of the above [1] to [5], wherein the structural unit (A2) is a structural unit (A2-2) derived from a compound represented by the following formula (a2-2): [ka] [7] A polyimide varnish obtained by dissolving the polyimide resin according to any one of the above [1] to [6] in an organic solvent. [8] A polyimide film comprising the polyimide resin according to any one of [1] to [6] above. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a polyimide resin that can form a film that has both mechanical properties and colorless transparency and is high in strength and excellent in deformation recovery; a polyimide varnish containing the polyimide resin; and a polyimide film that has both mechanical properties and colorless transparency and is high in strength and excellent in deformation recovery. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a conceptual diagram showing a method for measuring the deformation recovery of a polyimide film. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Polyimide resin] The polyimide resin of the present invention is a polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, in which the structural unit A includes a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from an aliphatic tetracarboxylic dianhydride, and the structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1): [ka] The polyimide resin of the present invention will be described below.

[0011] [Structural unit A] The structural unit A contained in the polyimide of the present invention is a structural unit derived from a tetracarboxylic dianhydride contained in the polyimide resin. The structural unit A includes a structural unit (A1) derived from a compound represented by the above formula (a1) and a structural unit (A2) derived from an aliphatic tetracarboxylic dianhydride.

[0012] The compound represented by the formula (a1) is 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF). When the structural unit A contains the structural unit (A1), the mechanical strength of the resulting polyimide resin is improved.

[0013] The structural unit (A2) is a structural unit derived from an aliphatic tetracarboxylic dianhydride, and preferably contains a structural unit derived from an alicyclic tetracarboxylic dianhydride, and more preferably contains a structural unit derived from a tetracarboxylic dianhydride having an alicyclic ring with 4 to 25 carbon atoms. By containing a structural unit derived from a tetracarboxylic dianhydride having an alicyclic ring, the deformation recovery property and colorless transparency are improved while maintaining mechanical strength. In this specification, an aliphatic tetracarboxylic acid dianhydride refers to a tetracarboxylic acid dianhydride that does not contain an aromatic ring, and an alicyclic tetracarboxylic acid dianhydride refers to an aliphatic tetracarboxylic acid dianhydride that contains one or more alicyclic rings. Here, the term "alicyclic" refers to a cyclic hydrocarbon structure, excluding aromatic rings, in which carbon atoms are bonded in a ring, and the number of carbon atoms in the alicyclic ring refers to the number of carbon atoms constituting the ring.

[0014] Specific 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, and positional isomers thereof. Specific examples of aliphatic tetracarboxylic dianhydrides other than alicyclic tetracarboxylic dianhydrides include 1,2,3,4-butanetetracarboxylic dianhydride.

[0015] Among these, the structural unit (A2) derived from an aliphatic tetracarboxylic dianhydride preferably includes at least one selected from the structural unit (A2-1) derived from a compound represented by the following formula (a2-1), the structural unit (A2-2) derived from a compound represented by the following formula (a2-2), and the structural unit (A2-3) derived from a compound represented by the following formula (a2-3), and more preferably includes the structural unit (A2-2) derived from a compound represented by the following formula (a2-2). Furthermore, the structural unit (A2) derived from an aliphatic tetracarboxylic dianhydride is preferably at least one selected from the structural unit (A2-1) derived from a compound represented by the following formula (a2-1), the structural unit (A2-2) derived from a compound represented by the following formula (a2-2), and the structural unit (A2-3) derived from a compound represented by the following formula (a2-3), and more preferably the structural unit (A2-2) derived from a compound represented by the following formula (a2-2). [ka] The compound represented by the formula (a2-1) is 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA). The compound represented by the formula (a2-2) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA). The compound represented by the formula (a2-3) is norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride (CpODA). When the structural unit A includes the structural unit (A2), the mechanical strength is maintained while the deformation recovery property and colorless transparency are improved. Thus, since the structural unit A derived from a tetracarboxylic dianhydride contains the structural units (A1) and (A2), the polyimide resin and polyimide film of the present invention achieve both mechanical properties and colorless transparency, and have high strength while also excellent deformation recovery. Although the reason for this is not clear, it is thought to be due to the rigidity of the fluorene group and the flexibility of the aliphatic compound.

[0016] The proportion of the structural unit (A1) relative to the structural unit A is preferably 30 to 90 mol %, more preferably 40 to 90 mol %, even more preferably 50 to 90 mol %, and still more preferably 50 to 80 mol %. The proportion of the structural unit (A2) relative to the structural unit A is preferably 10 to 70 mol %, more preferably 10 to 60 mol %, even more preferably 10 to 50 mol %, and still more preferably 20 to 50 mol %.

[0017] The total proportion of the structural unit (A1) and the structural unit (A2) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. There are no particular upper limits for the total proportion of the structural unit (A1) and the structural unit (A2), and it is 100 mol% or less. The structural unit A may be composed only of the structural unit (A1) and the structural unit (A2).

[0018] The molar ratio of the structural unit (A1) to the structural unit (A2) in the structural unit A [(A1) / (A2)] is preferably 20 / 80 to 90 / 10, more preferably 30 / 70 to 90 / 10, even more preferably 40 / 60 to 80 / 20, and still more preferably 50 / 50 to 70 / 30, from the viewpoint of improving mechanical properties, colorless transparency, and deformation recovery. In particular, from the viewpoint of improving deformation recovery at high temperatures, the ratio is preferably 40 / 60 to 80 / 20, more preferably 40 / 60 to 70 / 30, and even more preferably 40 / 60 to 60 / 40.

[0019] The polyimide resin of the present invention may contain, within the structural unit A, a structural unit derived from a tetracarboxylic dianhydride other than the structural unit (A1) and the structural unit (A2), as long as the effects of the present invention are not impaired. The tetracarboxylic acid dianhydride that provides a structural unit other than the structural unit (A1) and the structural unit (A2) is not particularly limited, but examples include aromatic tetracarboxylic acid dianhydrides such as pyromellitic anhydride, 2,3,5,6-toluenetetracarboxylic acid dianhydride, and 1,4,5,8-naphthalenetetracarboxylic acid dianhydride. These can be used alone or in combination of two or more.

[0020] In this specification, the aromatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing one or more aromatic rings.

[0021] [Structural unit B] The structural unit B contained in the polyimide of the present invention is a structural unit derived from a diamine. The structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1). [ka]

[0022] The compound represented by the formula (b1) is 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP). When the structural unit B includes the structural unit (B1), the mechanical strength of the resulting polyimide resin can be improved while maintaining its colorless transparency.

[0023] The proportion of the structural unit (B1) relative to the structural unit B is preferably 20 mol % or more, more preferably 30 mol % or more, even more preferably 40 mol % or more, and even more preferably 50 mol % or more. Particularly from the viewpoint of improving the elongation of the resulting polyimide film, the content is even more preferably 70 mol % or more, and even more preferably 90 mol % or more. There is no particular upper limit to the proportion of the structural unit (B1), but it is up to 100 mol %. The structural unit B may consist solely of the structural unit (B1).

[0024] The polyimide resin of the present invention may contain, in the structural unit B, a structural unit derived from a diamine other than the compound represented by the general formula (b1) above, as a structural unit other than the structural unit (B1) above, as long as the effects of the present invention are not impaired. Diamines other than the compound represented by the general formula (b1) are not particularly limited, but examples thereof include 3,5-diaminobenzoic acid (3,5-DABA), bis[4-(3-aminophenoxy)phenyl]sulfone (BAPS-M), 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA), 1,4-phenylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenylmethane, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 2,2-bis(4-aminophenyl)hexafluoropropane, and the like. Examples of suitable diamines include aromatic diamines such as benzene, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-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; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; aliphatic diamines such as ethylenediamine and hexamethylenediamine; and modified silicone diamines. These can be used alone or in combination of two or more. Among these, from the viewpoint of achieving high strength and improving deformation recovery at high temperatures, at least one selected from the group consisting of 3,5-diaminobenzoic acid (3,5-DABA), bis[4-(3-aminophenoxy)phenyl]sulfone (BAPS-M), and 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA) is preferred.

[0025] In this specification, aromatic diamine means a diamine containing one or more aromatic rings, aliphatic diamine means a diamine containing no aromatic rings, and alicyclic diamine means an aliphatic diamine containing one or more alicyclic rings.

[0026] [Properties of polyimide resin] From the viewpoint of the mechanical strength of the resulting polyimide film, the number average molecular weight of the polyimide resin of the present invention is preferably 5,000 to 100,000. The number average molecular weight of the polyimide resin can be measured by gel filtration chromatography or the like.

[0027] The polyimide resin of the present invention may further contain various additives, such as antioxidants, light stabilizers, surfactants, flame retardants, plasticizers, and polymer compounds other than the polyimide resins, as long as the effects of the present invention are not impaired. Examples of the polymer compound include polyimides other than the polyimide resin of the present invention, polycarbonates, polystyrenes, polyamides, polyamideimides, polyesters such as polyethylene terephthalate, polyethersulfones, polycarboxylic acids, polyacetals, polyphenylene ethers, polysulfones, polybutylenes, polypropylenes, polyacrylamides, and polyvinyl chlorides.

[0028] [Method for producing polyimide resin] The polyimide resin of the present invention can be produced by reacting a tetracarboxylic acid component containing a compound that provides the structural unit (A1) and a compound that provides the structural unit (A2) with a diamine component that contains a compound that provides the structural unit (B1).

[0029] Examples of compounds that provide the structural unit (A1) include compounds represented by formula (a1), but are not limited thereto and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic acid dianhydrides represented by formula (a1) and alkyl esters of such tetracarboxylic acids. Compounds that provide the structural unit (A1) are preferably compounds represented by formula (a1) (i.e., dianhydrides). Similarly, compounds that provide the structural unit (A2) include aliphatic tetracarboxylic dianhydrides, preferably alicyclic tetracarboxylic dianhydrides, and more preferably compounds represented by formula (a2-1), (a2-2), or (a2-3). However, the present invention is not limited to these, and derivatives thereof may also be used as long as they provide the same structural unit. Derivatives of the compounds represented by formula (a2-1), (a2-2), or (a2-3) include tetracarboxylic acids corresponding to the tetracarboxylic dianhydrides represented by formula (a2-1), (a2-2), or (a2-3), and alkyl esters of these tetracarboxylic acids. Compounds that provide the structural unit (A2) are preferably compounds represented by formula (a2-1), (a2-2), or (a2-3) (i.e., dianhydrides).

[0030] The tetracarboxylic acid component preferably contains 30 to 90 mol %, more preferably 40 to 90 mol %, even more preferably 50 to 90 mol %, and still more preferably 50 to 80 mol % of the compound that provides the structural unit (A1). The tetracarboxylic acid component preferably contains 10 to 70 mol %, more preferably 10 to 60 mol %, even more preferably 10 to 50 mol %, and even more preferably 20 to 50 mol % of the compound that provides the structural unit (A2).

[0031] The total content of the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2) is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more, of the total tetracarboxylic acid component. There are no particular limitations on the upper limit of the total content of the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2), and it is 100 mol% or less. The tetracarboxylic acid component may consist solely of the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2).

[0032] The molar ratio of the compound that provides the structural unit (A1) to the compound that provides the structural unit (A2) in the tetracarboxylic acid component [(A1) / (A2)] is preferably 20 / 80 to 90 / 10, more preferably 30 / 70 to 90 / 10, even more preferably 40 / 60 to 80 / 20, and still more preferably 50 / 50 to 70 / 30, from the viewpoint of improving mechanical properties, colorless transparency, and deformation recovery. In particular, from the viewpoint of improving deformation recovery at high temperatures, the ratio is preferably 40 / 60 to 80 / 20, more preferably 40 / 60 to 70 / 30, and even more preferably 40 / 60 to 60 / 40.

[0033] The tetracarboxylic acid component may contain compounds other than the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2). Examples of such compounds include the above-mentioned aromatic tetracarboxylic acid dianhydrides and derivatives thereof (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.). The compound optionally contained in the tetracarboxylic acid component (that is, a compound other than the compound that provides the structural unit (A1) and the structural unit (A2)) may be one type, or two or more types.

[0034] Compounds that provide the structural unit (B1) include, but are not limited to, compounds represented by formula (b1), and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the diamines represented by formula (b1). Compounds that provide the structural unit (B1) are preferably compounds represented by formula (b1) (i.e., diamines).

[0035] The diamine component preferably contains 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, and even more preferably 50 mol% or more of the compound that provides the structural unit (B1). From the viewpoint of improving the elongation of the resulting polyimide film, the content is even more preferably 70 mol% or more, and even more preferably 90 mol% or more. Furthermore, the upper limit of the proportion of the compound that provides the structural unit (B1) is not particularly limited, and is 100 mol% or less. The diamine component may consist solely of the compound that provides the structural unit (B1).

[0036] The diamine component may contain compounds other than the compound that provides the structural unit (B1), and examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, aliphatic diamines, modified silicone diamines, and derivatives thereof (diisocyanates, etc.). The compound optionally contained in the diamine component (that is, a compound other than the compound that provides the structural unit (B1)) may be one type, or two or more types.

[0037] When producing the polyimide resin according to the present invention, the ratio of the amount of the tetracarboxylic acid component to the amount of the diamine component charged is preferably 0.9 to 1.1 moles of the diamine component per mole of the tetracarboxylic acid component.

[0038] When producing the polyimide resin of the present invention, a terminal blocking agent may be used in addition to the tetracarboxylic acid component and the diamine component. Monoamines or dicarboxylic acids are preferred as terminal blocking agents. The amount of terminal blocking agent to be introduced is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, per mol of the tetracarboxylic acid component. Preferred monoamine terminal blocking agents include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, and 4-methylaniline. Of these, benzylamine and aniline are more preferred. Preferred dicarboxylic acid terminal blocking agents are dicarboxylic acids, some of which may be ring-closed. Preferred dicarboxylic acids include phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclohexane-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. Of these, phthalic acid and phthalic anhydride are more preferred.

[0039] There are no particular limitations on the method for reacting the tetracarboxylic acid component and the diamine component, and any known method can be used. Specific reaction methods include: (1) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the mixture is stirred at 10 to 110°C for 0.5 to 30 hours, and then the temperature is raised to carry out the imidization reaction; (2) a method in which a diamine component and a reaction solvent are charged into a reactor and dissolved, and then the tetracarboxylic acid component is charged, and the mixture is stirred at 10 to 110°C for 0.5 to 30 hours as needed, and then the temperature is raised to carry out the imidization reaction; and (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the temperature is immediately raised to carry out the imidization reaction.

[0040] The reaction solvent used in the production of the polyimide resin may be any solvent that does not inhibit the imidization reaction and can dissolve the resulting polyimide resin, such as aprotic solvents, phenolic solvents, ether solvents, and carbonate solvents.

[0041] Specific examples of aprotic solvents include amide solvents such as N,N-dimethylisobutylamide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone solvents such as γ-butyrolactone and γ-valerolactone; phosphorus-containing amide solvents such as hexamethylphosphoric amide and hexamethylphosphine triamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and sulfolane; ketone solvents such as acetone, cyclohexanone, and methylcyclohexane; amine solvents such as picoline and pyridine; and ester solvents such as 2-methoxy-1-methylethyl acetate.

[0042] Specific examples of phenol-based solvents 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. Specific examples of ether solvents 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. Specific examples of carbonate solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate. Among the above reaction solvents, amide-based solvents and lactone-based solvents are preferred. The above reaction solvents may be used alone or in combination of two or more.

[0043] The imidization reaction is preferably carried out while removing water generated during the production using a Dean-Stark apparatus, etc. By performing such an operation, the degree of polymerization and the imidization rate can be further increased.

[0044] In the imidization reaction, a known imidization catalyst can be used, such as a base catalyst or an acid catalyst. Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, tripropylamine, tributylamine, imidazole, N,N-dimethylaniline, and N,N-diethylaniline; and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogencarbonate, and sodium hydrogencarbonate. Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, oxybenzoic acid, terephthalic acid, benzenesulfonic acid, paratoluenesulfonic acid, naphthalenesulfonic acid, etc. The above imidization catalysts may be used alone or in combination of two or more. Of the above, from the viewpoint of ease of handling, it is preferable to use a base catalyst, more preferable to use an organic base catalyst, and even more preferable to use triethylamine.

[0045] When the above catalyst is used, the temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 190° C., and even more preferably 180 to 190° C., from the viewpoint of the reaction rate and suppression of gelation, etc. The reaction time is preferably 0.5 to 10 hours after the start of distillation of the produced water. When no catalyst is used, the temperature for the imidization reaction is preferably 200 to 350°C.

[0046] [Polyimide varnish] The polyimide varnish of the present invention is obtained by dissolving the polyimide resin of the present invention in an organic solvent. That is, the polyimide varnish of the present invention contains the polyimide resin of the present invention and an organic solvent, and the polyimide resin is dissolved in the organic solvent. The organic solvent is not particularly limited as long as it dissolves the polyimide resin, but it is preferable to use the compounds described above as reaction solvents used in the production of polyimide resins, either alone or in combination of two or more. The polyimide varnish of the present invention preferably contains 5 to 60 mass %, more preferably 5 to 45 mass %, of the polyimide resin of the present invention. The viscosity of the polyimide varnish is preferably 0.1 to 200 Pa·s, more preferably 0.5 to 150 Pa·s.

[0047] [Polyimide film] The polyimide film of the present invention contains the above-mentioned polyimide resin, and preferably consists of the above-mentioned polyimide resin. That is, the polyimide resin has a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein the structural unit A includes a structural unit (A1) derived from a compound represented by formula (a1) and a structural unit (A2) derived from an aliphatic tetracarboxylic dianhydride, and the structural unit B includes a structural unit (B1) derived from a compound represented by formula (b1). By containing such a polyimide resin, the polyimide film of the present invention achieves both mechanical properties and colorless transparency, and is excellent in deformation recovery while having high strength.

[0048] The method for producing the polyimide film of the present invention is not particularly limited, and any known method can be used, such as a method in which a solution containing the polyimide resin of the present invention or a solution containing the polyimide resin of the present invention and the various additives described above is applied to a smooth support such as a glass plate, a metal plate, or a plastic, or formed into a film, and then solvent components such as organic solvents contained in the solution are removed.

[0049] The polyimide resin-containing solution may be a polyimide resin solution obtained by polymerization. Alternatively, the polyimide resin solution may be a mixture of at least one compound selected from the compounds listed above as a solvent in which the polyimide resin dissolves. By adjusting the solids concentration and viscosity of the polyimide resin-containing solution as described above, the thickness of the polyimide film of the present invention can be easily controlled.

[0050] A release agent may be applied to the surface of the support as needed. The following method is preferred as a method for applying a solution containing the polyimide resin or the polyimide resin composition to the support and then heating to evaporate the solvent component. That is, it is preferred to evaporate the solvent at a temperature of 120°C or less to form a self-supporting film, peel the self-supporting film from the support, fix the edges of the self-supporting film, and dry at a temperature of the boiling point of the solvent component used and 350°C or less to produce a polyimide film. Drying under a nitrogen atmosphere is also preferred. The pressure of the drying atmosphere may be reduced, normal, or increased.

[0051] The thickness of the polyimide film of the present invention can be appropriately selected depending on the application, etc., but is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, and even more preferably 10 to 80 μm. A thickness of 1 to 250 μm enables practical use as a free-standing film.

[0052] The polyimide film containing the polyimide resin of the present invention is suitably used as a film for various members such as color filters, flexible displays, semiconductor parts, and optical members. [Example]

[0053] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0054] The physical properties of the polyimide films obtained in the following Examples and Comparative Examples were measured by the following methods. (1) Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation. (2) Tensile strength and tensile modulus The measurement was performed in accordance with JIS K7127 using a tensile tester "Strograph VG1E" manufactured by Toyo Seiki Co., Ltd. (3) Tensile elongation at break The tensile elongation at break was measured by a tensile test (measurement of elongation) in accordance with JIS K 7127. Test pieces having a width of 10 mm and a thickness of 10 to 70 μm were used. (4) Total light transmittance (evaluation of transparency) Measurements were performed in accordance with ASTM E313-05 using a color and turbidity simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd. (5) Yellow Index (YI) (evaluation of colorlessness) Measurements were performed in accordance with ASTM E313-05 using a color and turbidity simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd. (5) Deformation recovery As shown in Figure 1(a), polyimide film 1 cut to a size of 10 mm wide x 100 mm long was fixed with a jig at an R of 3 mm and left to stand for 24 hours or 100 hours under conditions of 65°C and 90% relative humidity, or 70°C and dry conditions. The jig was then removed and the film was left to stand for 170 hours at 23°C and 50% relative humidity. The deformation recovery was evaluated by measuring the angle θ of the film's return, as shown in Figure 1(b). Note that a smaller measured angle indicates better deformation recovery, and a smaller value is preferable.

[0055] [Example 1] A 300 mL five-neck round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark apparatus equipped with a condenser, a thermometer, and a glass end cap was charged with 27.66 g (0.053 mol) of 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (manufactured by Seika Corporation, hereinafter referred to as HFBAPP) as a diamine component, 44.8 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation, hereinafter referred to as GBL) as an organic solvent, and 2.70 g of triethylamine (manufactured by Kanto Chemical Co., Inc., hereinafter referred to as TEA) as an imidization catalyst, and the mixture was stirred at 150 rpm under a nitrogen atmosphere at a system temperature of 70°C to obtain a solution. To this mixture, 12.23 g (0.027 mol) of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (manufactured by JFE Chemical Corporation, hereinafter referred to as BPAF) and 5.98 g (0.027 mol) of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Company, Inc., hereinafter referred to as HPMDA) were added as tetracarboxylic acid components, and 24.1 g of GBL were added all at once. The mixture was then heated with a mantle heater, and the temperature in the reaction system was raised to 190 °C over approximately 20 minutes. The distilled components were collected, and the reaction system was refluxed for 2 hours while maintaining the temperature at 190 °C, while adjusting the rotation speed according to the increase in viscosity. A polyimide solution was then obtained by cooling the reaction system to 120 °C. N,N-dimethylacetamide (manufactured by Mitsubishi Gas Chemical Company, Inc., hereinafter referred to as DMAc) was then added to achieve the desired solids concentration, and the mixture was further stirred for approximately 3 hours to homogenize, yielding a polyimide varnish (A) with a solids concentration of 20.0% by mass.

[0056] Next, polyimide varnish (A) was applied to a PET substrate and held at 60°C for 20 minutes, 80°C for 20 minutes, and 100°C for 30 minutes to evaporate the solvent, yielding a self-supporting, transparent, primary dried film. The film was then fixed to a stainless steel frame and dried at 220°C in an air atmosphere for 20 minutes to remove the solvent, yielding a polyimide film. The measurement and evaluation results of physical properties are shown in Table 1.

[0057] [Example 2] A polyimide varnish (B) with a solids concentration of 15.0 mass% was obtained in the same manner as in Example 1, except that the amount of HFBAPP was 24.25 g (0.047 mol), 1.78 g (0.012 mol) of 3,5-diaminobenzoic acid (manufactured by Nippon Junyaku Ryohin Co., Ltd., hereinafter referred to as 3,5-DABA) was added, the amount of TEA was changed to 0.296 g, the amount of BPAF was changed to 13.40 g (0.029 mol), and the amount of HPMDA was changed to 6.55 g (0.029 mol). Using the obtained polyimide varnish (B), a polyimide film was obtained in the same manner as in Example 1. The measurement results and evaluation results of physical properties are shown in Table 1.

[0058] [Example 3] The amount of HFBAPP was 14.58 g (0.028 mol), bis[4-(3-aminophenoxy)phenyl]sulfone (manufactured by Seika Corporation, hereinafter referred to as BAPS-M) was added at 12.16 g (0.028 mol), the amount of TEA was changed to 0.296 g, the amount of BPAF was changed to 12.89 g (0.028 mol), and the amount of HPMDA was changed to 6.31 g (0.028 mol). Except for this, a polyimide varnish (C) having a solids concentration of 18.5 mass% was obtained in the same manner as in Example 1. Using the obtained polyimide varnish (C), a film was obtained in the same manner as in Example 1. The measurement results and evaluation results of physical properties are shown in Table 1.

[0059] [Example 4] A polyimide varnish (D) having a solids concentration of 18.5% by mass was obtained in the same manner as in Example 1, except that the amount of HFBAPP was 19.15 g (0.037 mol), 12.42 g (0.037 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (manufactured by ChinaTech Chemical (Taijin) Co., Ltd., hereinafter referred to as 6FODA) was added, the amount of TEA was changed to 0.296 g, the amount of BPAF was changed to 16.93 g (0.037 mol), and the amount of HPMDA was changed to 8.28 g (0.037 mol). Using the obtained polyimide varnish (D), a film was obtained in the same manner as in Example 1. The measurement results and evaluation results of physical properties are shown in Table 1.

[0060] [Example 5] A polyimide varnish (E) having a solids concentration of 18.5 mass% was obtained in the same manner as in Example 4, except that the amount of HFBAPP was changed to 12.08 g (0.023 mol), the amount of 6FODA to 18.28 g (0.054 mol), the amount of BPAF to 17.80 g (0.039 mol), and the amount of HPMDA to 8.70 g (0.039 mol). A film was obtained using the obtained polyimide varnish (E) in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[0061] [Example 6] A polyimide varnish (F) having a solids concentration of 18.5 mass% was obtained in the same manner as in Example 4, except that the amount of HFBAPP was changed to 18.19 g (0.035 mol), the amount of 6FODA to 11.79 g (0.035 mol), the amount of BPAF to 22.51 g (0.049 mol), and the amount of HPMDA to 4.72 g (0.021 mol). A film was obtained using the obtained polyimide varnish (F) in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[0062] [Example 7] A polyimide varnish (G) with a solids concentration of 20.0 mass % was obtained in the same manner as in Example 1, except that the amount of HFBAPP was changed to 33.49 g (0.065 mol), the amount of BPAF was changed to 14.81 g (0.032 mol), HPMDA was not used, and 12.42 g (0.032 mol) of norbornane-2-spiro-α-cyclopentanone-α'-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (manufactured by JXTG Nippon Oil & Energy Corporation, hereinafter referred to as CpODA) was added. A film was obtained using the obtained polyimide varnish (G) in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[0063] [Comparative Example 1] A polyimide varnish (H) having a solids concentration of 18.5 mass% was obtained in the same manner as in Example 1, except that the amount of HFBAPP was changed to 30.52 g (0.059 mol), the amount of TEA was changed to 0.298 g, the amount of BPAF was changed to 26.98 g (0.059 mol), and HPMDA was not used. A film was obtained using the obtained polyimide varnish (H) in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[0064] Comparative Example 2 A polyimide varnish was prepared in the same manner as in Example 2, except that the amount of HFBAPP was 39.23 g (0.076 mol), the amount of 3,5-DABA was 2.88 g (0.019 mol), BPAF was not used, and the amount of HPMDA was changed to 21.20 g (0.095 mol), to obtain a polyimide varnish (I) with a solids concentration of 20 mass%. A film was obtained using the obtained polyimide varnish (I) in the same manner as in Example 1.

[0065] Comparative Example 3 A polyimide varnish (J) with a solids concentration of 20.0 mass% was obtained in the same manner as in Example 1, except that HFBAPP was not used, 29.81 g (0.093 mol) of 2,2'-bis(trifluoromethyl)benzidine (manufactured by Wakayama Seika Kogyo Co., Ltd., hereinafter referred to as TFMB) was used, the amount of TEA was changed to 0.471 g, the amount of BPAF was changed to 21.34 g (0.047 mol), and the amount of HPMDA was changed to 10.43 g (0.047 mol). A film was obtained using the obtained polyimide varnish (J) in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[0066] Comparative Example 4 A polyimide varnish (K) with a solids concentration of 20.0 mass% was obtained in the same manner as in Example 1, except that the amount of HFBAPP was changed to 29.96 g (0.058 mol), 8.22 g (0.058 mol) of 1,4-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc., hereinafter referred to as 1,4-BACT) was added, BPAF was not used, and the amount of HPMDA was changed to 25.91 g (0.116 mol). Using the obtained polyimide varnish (K), a film was obtained in the same manner as in Example 1. The measurement results and evaluation results of physical properties are shown in Table 1.

[0067] Comparative Example 5 A polyimide varnish (L) with a solids concentration of 20.0 mass% was obtained in the same manner as in Example 1, except that the amount of HFBAPP was 24.64 g (0.048 mol), the amount of TEA was changed to 0.481 g, 17.41 g (0.048 mol) of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (manufactured by Wakayama Seika Kogyo Co., Ltd., hereinafter referred to as DABPAF) was added, BPAF was not used, and the amount of HPMDA was changed to 21.31 g (0.095 mol). Using the obtained polyimide varnish (L), a film was obtained in the same manner as in Example 1. The measurement results and evaluation results of physical properties are shown in Table 1.

[0068] [Table 1]

[0069] It can be seen from Table 1 that the polyimide films of Examples 1 to 7 have both mechanical properties and colorless transparency, and are high in strength while also exhibiting excellent deformation recovery under both high humidity and dry conditions.

Claims

1. A polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, A polyimide resin in which the structural unit A comprises a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from an aliphatic tetracarboxylic dianhydride, the structural unit B comprises a structural unit (B1) derived from a compound represented by the following formula (b1), and the structural unit (A2) is at least one selected from the group consisting of a structural unit (A2-1) derived from a compound represented by the following formula (a2-1), a structural unit (A2-2) derived from a compound represented by the following formula (a2-2), and a structural unit (A2-3) derived from a compound represented by the following formula (a2-3): 【Chemistry 1】 【change】

2. 2. The polyimide resin according to claim 1, wherein the proportion of the structural unit (B1) relative to the structural unit B is 30 mol % or more.

3. 3. The polyimide resin according to claim 1, wherein the proportion of the structural unit (A1) relative to the structural unit A is 50 to 90 mol %.

4. The polyimide resin according to any one of claims 1 to 3, wherein the structural unit (A2) is a structural unit (A2-2) derived from a compound represented by the following formula (a2-2): 【Chemistry 2】

5. A polyimide varnish obtained by dissolving the polyimide resin according to any one of claims 1 to 4 in an organic solvent.

6. A polyimide film comprising the polyimide resin according to any one of claims 1 to 4.

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