Polyimide resin, polyimide varnish, and polyimide film

Abstract

A polyimide resin comprising constituent units A, which are derived from tetracarboxylic dianhydrides, and constituent unit B, which is derived from a diamine, wherein the constituent units A comprise constituent unit (A1), which is derived from 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) and constituent unit (A2), which is derived from 1,2,4,5-cyclohexanetetracarboxlic dianhydride.

Description

Technical Field

[0001] The present invention relates to polyimide resins, polyimide varnishes, and polyimide films.

Background Art

[0002] Polyimide resins are obtained from, for example, aromatic tetracarboxylic acid anhydrides and aromatic diamines, and generally have excellent heat resistance, chemical resistance, mechanical properties, and electrical properties due to the rigidity of the molecules, 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 the above applications, it is particularly important to have transparency, and studies have been made to improve the transparency of polyimide resins.

[0003] Patent Document 1 discloses a polyimide having TAHMBP or the like as a structural unit in order to improve transparency, heat resistance, solvent processability, etc.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, especially in applications such as displays and front panels for protecting them, highly elastic polyimide resins are required as an alternative to conventionally used glass materials. However, conventional highly elastic polyimide resins have problems such as poor transparency. Recently, it has also been used as a display or protective plate of a smartphone having a folding structure. Therefore, while having high elasticity, flexibility is also required, and properties such as the property of recovering the shape after the polyimide film is deformed and the elongation of the film are also necessary. Therefore, a polyimide resin having these properties has been desired. That is, the problem to be solved by the present invention is to provide a polyimide resin capable of forming a film that achieves both high elasticity and transparency, and is excellent in deformation recovery and elongation while having high elasticity, and a polyimide film that achieves both high elasticity and transparency and is excellent in deformation recovery and elongation.

Means for Solving the Problems

[0006] As a result of intensive studies, the inventors have found that a polyimide resin having structural units derived from specific two tetracarboxylic dianhydrides can achieve both high elasticity and transparency, and can form a film that is excellent in deformation recovery and elongation while having high elasticity, and thus have reached 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, wherein 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 a compound represented by the following formula (a2).

Chemical formula

Chemical formula

[0008] According to the present invention, there can be provided a polyimide resin capable of forming a film that achieves both high elasticity and transparency, is highly elastic, and is excellent in deformation recovery and elongation, a polyimide varnish containing the polyimide resin, and a polyimide film that achieves both high elasticity and transparency and is excellent in deformation recovery and elongation. [Brief Description of the Drawings]

[0009]

Figure 1

[0010] [Polyimide Resin] The polyimide resin of the present invention is a polyimide resin having a constitutional unit A derived from a tetracarboxylic dianhydride and a constitutional unit B derived from a diamine, 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 a compound represented by the following formula (a2). [Chemical formula] Hereinafter, the polyimide resin of the present invention will be described.

[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 in the polyimide resin. The structural unit A includes a structural unit (A1) derived from the compound represented by the formula (a1) and a structural unit (A2) represented by the formula (a2).

[0012] The compound represented by the formula (a1) is 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (TMPBP-TME). By the structural unit A including the structural unit (A1), the elastic modulus of the obtained polyimide resin is improved.

[0013] The compound represented by the formula (a2) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA). By the structural unit A including the structural unit (A2), the transparency can be improved while maintaining the elastic modulus, and the elongation can also be improved. Thus, having the structural units derived from the above two tetracarboxylic dianhydrides enables both high elasticity and transparency, and excellent deformation recovery and elongation. Although the reason is not clear, it is considered to be due to the rigidity of the ester group and the transparency of the alicyclic compound.

[0014] The proportion of structural unit (A1) to structural unit A is preferably 20 to 90 mol%, more preferably 20 to 80 mol%, still more preferably 30 to 80 mol%, even more preferably 50 to 80 mol%, even more preferably 50 to 70 mol%, and even more preferably 55 to 65 mol%. The proportion of structural unit (A2) to structural unit A is preferably 10 to 80 mol%, more preferably 20 to 80 mol%, still more preferably 20 to 70 mol%, even more preferably 20 to 50 mol%, even more preferably 30 to 50 mol%, and even more preferably 35 to 45 mol%.

[0015] The total ratio of structural unit (A1) and structural unit (A2) in structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more. The upper limit of the total ratio of structural unit (A1) and structural unit (A2) is not particularly limited and is 100 mol% or less. Structural unit A may consist only of structural unit (A1) and structural unit (A2).

[0016] The molar ratio [(A1):(A2)] of structural unit (A1) and structural unit (A2) in structural unit A is preferably 20:80 to 90:10, more preferably 20:80 to 80:20, still more preferably 30:70 to 80:20, even more preferably 50:50 to 80:20, even more preferably 50:50 to 70:30, and even more preferably 55:45 to 65:35, from the viewpoints of improving modulus of elasticity, elongation, transparency, and deformation recovery.

[0017] The polyimide resin of the present invention may contain, as structural units other than the above structural unit (A1) and structural unit (A2) in structural unit A, structural units derived from a compound represented by the above formula (a1) and a tetracarboxylic dianhydride other than the compound represented by the above formula (a2), as long as the effects of the present invention are not impaired. The tetracarboxylic dianhydrides other than the compound represented by the above formula (a1) and the compound represented by the above formula (a2) are not particularly limited, but include aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride, 2,3,5,6-toluene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride; alicyclic tetracarboxylic dianhydrides such as 1,2,4,5-cyclopentane tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, dicyclohexyltetracarboxylic dianhydride or their positional isomers; and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-pentanetetracarboxylic dianhydride. These can be used alone or in combination of two or more.

[0018] In this specification, the aromatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing one or more aromatic rings, the alicyclic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing one or more alicyclic rings and no aromatic rings, and the aliphatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring.

[0019] [Structural unit B] The structural unit B contained in the polyimide of the present invention is a structural unit derived from a diamine. There is no limitation on the structural unit derived from the diamine contained in the structural unit B, but the following preferred structural units will be described.

[0020] The structural unit B contained in the polyimide of the present invention preferably contains a structural unit (B1) derived from a compound represented by the following general formula (b1). By containing the structural unit (B1), the elastic modulus, elongation, transparency and deformation recovery property are improved. [Chemical formula] (In the formula (b1), X is a single bond or an oxygen atom.)

[0021] The constitutional unit (B1) preferably contains at least one constitutional unit selected from the group consisting of a constitutional unit (B11) derived from a compound represented by the following formula (b11) and a constitutional unit (B12) derived from a compound represented by the following formula (b12). From the viewpoints of transparency, elastic modulus, and colorlessness, it is more preferable to contain the constitutional unit (B11) derived from the compound represented by the following formula (b11). Further, from the viewpoint of elongation, it is more preferable to contain the constitutional unit (B12) derived from the compound represented by the following formula (b12). The constitutional unit (B1) may contain only one of the constitutional unit (B11) or the constitutional unit (B12), or may contain both of them.

[0022]

Chemical formula

[0023] The compound represented by the formula (b11) is 2,2'-bis(trifluoromethyl)benzidine (TFMB).

[0024] The compound represented by the formula (b12) is 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA).

[0025] The ratio of the constitutional unit (B1) to the constitutional unit B is preferably 30 mol% or more, more preferably 40 mol% or more, still more preferably 50 mol% or more, even more preferably 70 mol% or more, and even more preferably 85 mol% or more. Further, the upper limit value of the ratio of the constitutional unit (B1) is not particularly limited and is 100 mol% or less.

[0026] The constitutional unit B may contain a constitutional unit (B2) derived from a compound represented by the following formula (b2). From the viewpoint of improving the elastic modulus, it is preferable to contain the constitutional unit (B2) derived from the compound represented by the following formula (b2).

Chemical formula

[0027] From the viewpoints of transparency and deformation recovery property, the proportion of the constitutional unit (B2) relative to the constitutional unit B is preferably 50 mol% or less, more preferably 40 mol% or less, still more preferably 30 mol% or less. It may be 15 mol% or less. The lower limit of the proportion of the constitutional unit (B2) is not particularly limited and is 0 mol% or more, but from the viewpoint of improving the elastic modulus, it is preferably 5 mol% or more.

[0028] When the constitutional unit B contains the constitutional unit (B1) and the constitutional unit (B2), the total ratio of the constitutional unit (B1) and the constitutional unit (B2) in the constitutional unit B is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more. The upper limit of the total ratio of the constitutional units (B1) and (B2) is not particularly limited and is 100 mol% or less. The constitutional unit B may consist only of the constitutional unit (B1) and the constitutional unit (B2).

[0029] The polyimide resin of the present invention may contain, as constitutional units other than the constitutional unit (B1) and the constitutional unit (B2) in the constitutional unit B, constitutional units derived from a compound represented by the general formula (b1) and a diamine other than the compound represented by the formula (b2), as long as the effects of the present invention are not impaired. The diamines other than the compound represented by the general formula (b1) and the compound represented by the formula (b2) are not particularly limited, but include 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, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-indene-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 aromatic diamines such as 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.

[0030] In the present specification, the aromatic diamine means a diamine containing one or more aromatic rings, the alicyclic diamine means a diamine containing one or more alicyclic rings and no aromatic rings, and the aliphatic diamine means a diamine containing neither an aromatic ring nor an alicyclic ring.

[0031] [Properties of Polyimide Resin, etc.] From the viewpoint of the mechanical strength of the obtained 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.

[0032] The polyimide resin of the present invention may be further mixed with various additives as long as the effects of the present invention are not impaired. Examples of the additives include antioxidants, light stabilizers, surfactants, flame retardants, plasticizers, and polymer compounds other than the polyimide resin. Examples of the polymer compound include polyimides other than the polyimide resin of the present invention, polycarbonates, polystyrenes, polyamides, polyamide-imides, polyesters such as polyethylene terephthalate, polyethersulfones, polycarboxylic acids, polyacetals, polyphenylene ethers, polysulfones, polybutylene, polypropylene, polyacrylamide, and polyvinyl chloride.

[0033] 〔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 above-described structural unit (A1) and a compound that provides the structural unit (A2) with a diamine component.

[0034] Examples of the compound that provides the structural unit (A1) include, but are not limited to, the compound represented by the formula (a1), and derivatives thereof may be used as long as they provide the same structural unit. Examples of the derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydrides represented by the formula (a1) and alkyl esters of the tetracarboxylic acids. As the compound that provides the structural unit (A1), the compound represented by the formula (a1) (i.e., dianhydride) is preferred. Similarly, examples of the compound that provides the structural unit (A2) include, but are not limited to, the compound represented by the formula (a2), and derivatives thereof may be used as long as they provide the same structural unit. Examples of the derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydrides represented by the formula (a2) and alkyl esters of the tetracarboxylic acids. As the compound that provides the structural unit (A-2), the compound represented by the formula (a2) (i.e., dianhydride) is preferred.

[0035] The tetracarboxylic acid component preferably contains a compound that provides a structural unit (A1) in an amount of 20 to 90 mol%, more preferably 20 to 80 mol%, still more preferably 30 to 80 mol%, even more preferably 50 to 80 mol%, even more preferably 50 to 70 mol%, and even more preferably 55 to 65 mol%. The tetracarboxylic acid component preferably contains a compound that provides a structural unit (A2) in an amount of 10 to 80 mol%, more preferably 20 to 80 mol%, still more preferably 20 to 70 mol%, even more preferably 20 to 50 mol%, even more preferably 30 to 50 mol%, and even more preferably 35 to 45 mol%.

[0036] The total content ratio of the compound that provides a structural unit (A1) and the compound that provides a structural unit (A2) in the total tetracarboxylic acid component is preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more. The upper limit value of the total content ratio of the compound that provides a structural unit (A1) and the compound that provides a structural unit (A2) is not particularly limited and is 100 mol% or less. The tetracarboxylic acid component may consist only of the compound that provides a structural unit (A1) and the compound that provides a structural unit (A2).

[0037] The molar ratio [(A1):(A2)] of the compound that provides a structural unit (A1) and the compound that provides a structural unit (A2) in the tetracarboxylic acid component is preferably 20:80 to 90:10, more preferably 20:80 to 80:20, still more preferably 30:70 to 80:20, even more preferably 50:50 to 80:20, even more preferably 50:50 to 70:30, and even more preferably 55:45 to 65:35 from the viewpoint of improving the elastic modulus and transparency.

[0038] The tetracarboxylic acid component may contain compounds other than the compound providing the structural unit (A1) and the compound providing the structural unit (A2), and examples of such compounds include the above-mentioned aromatic tetracarboxylic dianhydrides, alicyclic tetracarboxylic dianhydrides, and aliphatic tetracarboxylic dianhydrides, as well as their derivatives (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.). The compound optionally contained in the tetracarboxylic acid component (i.e., a compound other than the compound providing the structural unit (A1) and the compound providing the structural unit (A2)) may be one kind or two or more kinds.

[0039] The diamine component is not limited, but preferably contains the compound providing the above-mentioned structural unit (B1). Examples of the compound providing the structural unit (B1) include, but are not limited to, the compound represented by the formula (b1), and derivatives thereof may also be used as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the diamine represented by the formula (b1). The compound providing the structural unit (B1) is preferably the compound represented by the formula (b1) (i.e., diamine).

[0040] The diamine component preferably contains 30 mol% or more, more preferably 40 mol% or more, still more preferably 50 mol%, even more preferably 70 mol% or more, and even more preferably 85 mol% or more of the compound providing the structural unit (B1). Also, the upper limit value of the proportion of the compound providing the structural unit (B1) is not particularly limited and is 100 mol% or less.

[0041] The diamine component may contain the compound providing the structural unit (B2), and from the viewpoint of improving the elastic modulus, it is preferable to contain the compound providing the structural unit (B2). Examples of the compound that provides the structural unit (B2) include, but are not limited to, the compound represented by formula (b2), and derivatives thereof may also be used as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the diamines represented by formula (b2). As the compound that provides the structural unit (B2), the compound represented by formula (b2) (i.e., diamine) is preferred.

[0042] The total content ratio of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2) is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more in all the diamine components. The upper limit value of the total content ratio of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2) is not particularly limited and is 100 mol% or less. The diamine component may consist only of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2).

[0043] The diamine component may contain compounds other than the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2). Examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, aliphatic diamines, modified silicone diamines, and their derivatives (such as diisocyanates). The compound optionally contained in the diamine component (i.e., a compound other than the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2)) may be one kind or two or more kinds.

[0044] When producing the polyimide resin according to the present invention, the charging amount ratio of the tetracarboxylic acid component to the diamine component is preferably such that the diamine component is 0.9 to 1.1 mol with respect to 1 mol of the tetracarboxylic acid component.

[0045] When producing the polyimide resin of the present invention, in addition to the tetracarboxylic acid component and the diamine component, a terminal blocking agent may be used. Monamines or dicarboxylic acids are preferred as the terminal blocking agent. The charged amount of the introduced terminal blocking agent is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, per 1 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, 4-methylaniline, etc. Among these, benzylamine and aniline are more preferred. Dicarboxylic acids are preferred as the dicarboxylic acid terminal blocking agent, and a part of them 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. Among these, phthalic acid and phthalic anhydride are more preferred.

[0046] There is no particular limitation on the method for reacting the aforementioned tetracarboxylic acid component and diamine component, and known methods can be used. Specific reaction methods include: (1) charging the tetracarboxylic acid component, diamine component, and reaction solvent into a reactor, stirring at 10 to 110 °C for 0.5 to 30 hours, and then raising the temperature to carry out the imidization reaction; (2) charging the diamine component and reaction solvent into a reactor and dissolving them, then charging the tetracarboxylic acid component, stirring at 10 to 110 °C for 0.5 to 30 hours as necessary, and then raising the temperature to carry out the imidization reaction; (3) charging the tetracarboxylic acid component, diamine component, and reaction solvent into a reactor and immediately raising the temperature to carry out the imidization reaction, etc.

[0047] 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. For example, aprotic solvents, phenolic solvents, ether solvents, carbonate solvents, etc. can be mentioned.

[0048] Specific examples of aprotic solvents include amide solvents such as N,N-dimethylisobutyramide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone, tetramethylurea, etc.; lactone solvents such as γ-butyrolactone, γ-valerolactone, etc.; phosphorus-containing amide solvents such as hexamethylphosphoric amide, hexamethylphosphine triamide, etc.; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, sulfolane, etc.; ketone solvents such as acetone, cyclohexanone, methylcyclohexane, etc.; amine solvents such as picoline, pyridine, etc.; ester solvents such as (2-methoxy-1-methylethyl) acetate, etc.

[0049] Specific examples of phenolic solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, etc. 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, 1,4-dioxane, etc. Specific examples of carbonate solvents also include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, etc. Among the above reaction solvents, amide solvents or lactone solvents are preferred. Also, the above reaction solvents may be used alone or in a mixture of two or more.

[0050] In the imidization reaction, it is preferable to carry out the reaction while removing the water generated during production using a Dean-Stark apparatus or the like. By performing such an operation, the degree of polymerization and the imidization rate can be further increased.

[0051] In the above imidization reaction, a known imidization catalyst can be used. Examples of the imidization catalyst include 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, N,N-diethylaniline, and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogen carbonate, and sodium hydrogen carbonate. Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methyl benzoic acid, oxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, and the like. The above imidization catalysts may be used alone or in combination of two or more. Among the above, from the viewpoint of handleability, it is preferable to use a base catalyst, more preferably an organic base catalyst, and even more preferably triethylamine.

[0052] When using the above catalyst, 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 viewpoints of reaction rate and suppression of gelation and the like. The reaction time is preferably 0.5 to 10 hours after the start of distillation of the generated water. In addition, when no catalyst is used, the temperature of the imidization reaction is preferably 200 to 350 °C.

[0053] [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 may be any solvent in which the polyimide resin can dissolve and is not particularly limited. However, it is preferable to use the above-described compounds alone or in combination of two or more as the reaction solvent used in the production of the polyimide resin. The polyimide varnish of the present invention preferably contains 5 to 60% by mass, more preferably 5 to 45% by 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.

[0054] [Polyimide Film] The polyimide film of the present invention contains the above polyimide resin. That is, it has a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, and 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 a compound represented by the following formula (a2), and contains a polyimide resin. By including such a polyimide resin, the polyimide film of the present invention achieves both high elasticity and transparency and is also excellent in deformation recovery.

[0055] There is no particular limitation on the method for producing the polyimide film of the present invention, and known methods can be used. For example, a solution containing the polyimide resin of the present invention, or a solution containing the polyimide resin of the present invention and various additives described above is applied onto a smooth support such as a glass plate, a metal plate, or plastic, or formed into a film shape, and then a solvent component such as an organic solvent contained in the solution is removed.

[0056] The solution containing the polyimide resin may be the polyimide resin solution obtained by the polymerization method itself. Alternatively, it may be a mixture obtained by mixing at least one selected from the compounds exemplified above as a solvent in which the polyimide resin is dissolved with the polyimide resin solution. By adjusting the solid content concentration and viscosity of the solution containing the polyimide resin as described above, the thickness of the polyimide film of the present invention can be easily controlled.

[0057] A release agent may be applied to the surface of the support as necessary. As a method of applying the solution containing the polyimide resin or the polyimide resin composition to the support and then heating to evaporate the solvent component, the following method is preferable. That is, it is preferable to evaporate the solvent at a temperature of 120°C or lower to obtain a self-supporting film, then peel the self-supporting film from the support, fix the end of the self-supporting film, and dry at a temperature of 350°C or lower and above the boiling point of the solvent component used to produce the polyimide film. Further, it is preferable to dry in a nitrogen atmosphere. The pressure of the drying atmosphere may be any of reduced pressure, normal pressure, and increased pressure.

[0058] The thickness of the polyimide film of the present invention can be appropriately selected according to the use and the like, but is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, and still more preferably 10 to 80 μm. When the thickness is 1 to 250 μm, practical use as a self-supporting film becomes possible. In the present invention, a polyimide film having a total light transmittance of preferably 85% or more, more preferably 88% or more, and still more preferably 89% or more at a thickness of 50 μm can be obtained. In the present invention, a polyimide film having a yellow index (YI value) of preferably 8.0 or less, more preferably 7.5 or less, still more preferably 6.0 or less, and even more preferably 4.0 or less can be obtained. The total light transmittance and YI value of the polyimide film can be specifically measured by the method described in the examples.

[0059] 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 components, and optical members.

Example

[0060] The present invention will be specifically described below with reference to the following examples. However, the present invention is not limited by these examples.

[0061] 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 modulus (evaluation of elasticity), tensile strength The measurement was carried out in accordance with JIS K7127 using a tensile tester "Strograph VG1E" manufactured by Toyo Seiki Co., Ltd. (3) Elongation at break (evaluation of elongation) The elongation at break was determined by a tensile test (measurement of elongation rate) in accordance with JIS K7127. Test pieces with a width of 10 mm and a thickness of 10 - 70 μm were used. (4) Total light transmittance (evaluation of transparency), YI value The measurement was carried out in accordance with ASTM E313-05 using a color and haze simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd. (5) Deformation recovery As shown in Fig. 1(a), the polyimide film 1 cut into a width of 10 mm and a length of 100 mm was fixed to a jig with R = 3 mm and left standing at 65 °C and a relative humidity of 90% for 24 hours. Then, after removing the jig at 23 °C and a relative humidity of 50% and leaving it standing for 2 hours, the deformation recovery was evaluated by measuring the angle θ shown in Fig. 1(b) of the film's return. Note that the smaller the measured angle, the better the deformation recovery, and a smaller numerical value is preferred.

[0062] [Example 1] A 300 mL five-neck round-bottom flask equipped with a stainless-steel semi-circular stirring blade, a nitrogen inlet tube, a Dean-Stark apparatus with a cooling tube, a thermometer, and a glass end cap was charged with 18.76 g (0.059 mol) of 2,2'-bis(trifluoromethyl)benzidine (manufactured by Wakayama Seika Kogyo Co., Ltd., a compound represented by formula (b11), hereinafter referred to as TFMB) as a diamine component, 85.8 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation, hereinafter referred to as GBL) as an organic solvent, and 0.296 g of triethylamine (manufactured by Kanto Chemical Co., Inc., hereinafter referred to as TEA) as an imidization catalyst. The mixture was stirred at 70 °C under a nitrogen atmosphere at a rotation speed of 150 rpm to obtain a solution. To this, 5.25 g (0.023 mol) of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Company, Inc., a compound represented by formula (a2), hereinafter referred to as HPMDA) and 21.75 g (0.035 mol) of 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (manufactured by Honshu Chemical Industry Co., Ltd., a compound represented by formula (a1), hereinafter referred to as TMPBP-TME), both as tetracarboxylic acid components, and 21.3 g of GBL were added all at once. Then, the mixture was heated with a mantle heater, and the temperature inside the reaction system was raised to 190 °C over about 20 minutes. The components to be distilled off were collected, and while adjusting the rotation speed according to the increase in viscosity, the temperature inside the reaction system was maintained at 190 °C and refluxed for 2 hours to obtain a polyimide solution. Thereafter, when the temperature inside the reaction system was cooled to 120 °C, N,N-dimethylacetamide (manufactured by Mitsubishi Gas Chemical Company, Inc.) was added to reach a predetermined solid content concentration, and the mixture was further stirred for about 3 hours to homogenize it, obtaining a polyimide varnish (A) with a solid content concentration of 15.0 mass%.

[0063] Subsequently, the polyimide varnish (A) was applied onto a glass substrate and held at 60 °C for 20 minutes, 80 °C for 20 minutes, and 100 °C for 30 minutes to volatilize the solvent, obtaining a transparent primary dried film having self-supporting properties. Further, the film was fixed to a stainless-steel frame and dried at 220 °C in an air atmosphere for 20 minutes to remove the solvent, obtaining a polyimide film. The measurement results and evaluation results of the physical properties are shown in Table 1.

[0064] [Example 2] The amount of TFMB was changed to 17.27 g (0.054 mol), 0.91 g (0.0060 mol) of 3,5-diaminobenzoic acid (manufactured by Nippon Pure Chemical Co., Ltd., the compound represented by formula (b2), hereinafter 3,5-DABA) was added, and the amount of HPMDA was 5.37 g (0.024 mol). A polyimide varnish (B) with a solid content concentration of 15.0% by mass was obtained in the same manner as in Example 1, except that the amount of TMPBP-TME was changed to 22.23 g (0.036 mol). Using the obtained polyimide varnish (B), a polyimide film was obtained in the same manner as in Example 1. The measurement results of physical properties and the evaluation results are shown in Table 1.

[0065] [Example 3] The amount of TFMB was changed to 19.56 g (0.061 mol), the amount of 3,5-DABA was changed to 1.03 g (0.0068 mol), the amount of HPMDA was 9.13 g (0.041 mol), and the amount of TMPBP-TME was changed to 16.79 g (0.027 mol). A polyimide varnish (C) with a solid content concentration of 15.0% by 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 of physical properties and the evaluation results are shown in Table 1.

[0066] [Example 4] The amount of TFMB was changed to 22.56 g (0.070 mol), 1.19 g (0.0078 mol) of 3,5-DABA was added, the amount of HPMDA was 14.04 g (0.063 mol), and the amount of TMPBP-TME was changed to 9.68 g (0.016 mol). A polyimide varnish (D) with a solid content concentration of 15.0% by mass was obtained in the same manner as in Example 1. Using the obtained polyimide varnish (D), a film was obtained in the same manner as in Example 1. The measurement results of physical properties and the evaluation results are shown in Table 1.

[0067] [Example 5] TFMB was changed to 19.44 g (0.058 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (manufactured by ChinaTech Chemical (Taijin) Co., Ltd., a compound represented by the formula (b12), hereinafter 6FODA), and the amount of HPMDA was changed to 5.18 g (0.023 mol) and the amount of TMPBP-TME was changed to 21.46 g (0.035 mol). Otherwise, in the same manner as in Example 1, a polyimide varnish (E) having a solid content concentration of 15.0 mass% was obtained. Using the obtained polyimide varnish (E), a film was obtained in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[0068] [Example 6] TFMB was changed to 17.79 g (0.053 mol) of 6FODA, 0.90 g (0.0059 mol) of 3,5-DABA was added, and the amount of HPMDA was changed to 5.27 g (0.024 mol) and the amount of TMPBP-TME was changed to 21.82 g (0.035 mol). Otherwise, in the same manner as in Example 1, a polyimide varnish (F) having a solid content concentration of 15.0 mass% was obtained. Using the obtained polyimide varnish (F), a film was obtained in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[0069] [Comparative Example 1] TFMB was changed to 15.96 g (0.050 mol), HPMDA was not used, and the amount of TMPBP-TME was changed to 30.83 g (0.050 mol). Otherwise, in the same manner as in Example 1, a polyimide varnish (G) having a solid content concentration of 15.0 mass% was obtained. Using the obtained polyimide varnish (G), a film was obtained in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[0070] [Comparative Example 2] The polyimide varnish was prepared in the same manner as in Example 1, except that the amount of TFMB was changed to 37.75 g (0.12 mol), TMPBP-TME was not used, and the amount of HPMDA was changed to 26.43 g (0.12 mol), and a polyimide varnish (H) with a solid content concentration of 20% by mass was obtained. Using the obtained polyimide varnish (H), a film was obtained in the same manner as in Example 1.

[0071] [Comparative Example 3] A polyimide varnish (I) with a solid content concentration of 20% by mass was obtained in the same manner as in Example 1, except that 6FODA was used instead of TFMB at 38.44 g (0.11 mol), TMPBP-TME was not used, and the amount of HPMDA was changed to 25.63 g (0.11 mol). Using the obtained polyimide varnish (I), a film was obtained in the same manner as in Example 1. The measurement results of physical properties and the evaluation results are shown in Table 1.

[0072]

Table 1

[0073] It can be seen from Table 1 that the polyimide films of Examples 1 to 6 achieve both transparency and elastic modulus, and also have excellent deformation recovery and elongation rates.

Claims

1. A polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, 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 a compound represented by the following formula (a2), The ratio of the structural unit (A1) to the structural unit A is 20 to 65 mol%, A polyimide resin in which the ratio of the structural unit (A2) to the structural unit A is 35 to 80 mol%. 【Chemical Formula 1】

2. The polyimide resin according to claim 1, wherein the structural unit B includes a structural unit (B1) derived from a compound represented by the following general formula (b1). 【Chemical Formula 2】 (In formula (b1), X is a single bond or an oxygen atom.)

3. The polyimide resin according to claim 1 or 2, wherein the structural unit B further includes a structural unit (B2) derived from a compound represented by the following formula (b2). 【Chemical Formula 3】

4. The polyimide resin according to claim 2, wherein the ratio of the structural unit (B1) to the structural unit B is 70 mol% or more.

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 containing the polyimide resin according to any one of claims 1 to 4.

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