Polyimide resin, polyimide varnish, and polyimide film

Abstract

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 (A-1) derived from a compound represented by formula (a-1) and a structural unit (A-2) derived from a compound represented by formula (a-2), and the structural unit B includes a structural unit (B-1) derived from a compound represented by formula (b-1).

Description

Technical Field

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

Background Art

[0002] Polyimide resins are being considered for various uses in fields such as electric and electronic components. For example, it is desired to replace the glass substrate used in image display devices such as liquid crystal displays and OLED displays with a plastic substrate for the purpose of reducing the weight and making the device flexible, and research on polyimide films suitable as such a plastic substrate is underway. Polyimide films for such applications are required to have colorless transparency.

[0003] In image display devices such as liquid crystal displays and OLED displays, thin film transistors (TFTs) are used as pixel switching elements. Polycrystalline silicon (polysilicon), which has excellent crystallinity, has a higher electron mobility than amorphous silicon, so the TFT characteristics are significantly improved. One method of forming a polysilicon film is the excimer laser annealing (ELA) method. The dehydrogenation process of amorphous silicon in this method is a high-temperature process. Therefore, in order to form a polysilicon film on a polyimide film as a plastic substrate, the polyimide film is required to have high heat resistance (i.e., a high glass transition temperature). Furthermore, in a high-temperature state, there is a risk that organic compounds (outgases) volatilized from the substrate material itself will have a serious adverse effect on the elements. Therefore, the polyimide film is also required to have high thermal stability to suppress the generation of outgases as much as possible up to a high temperature range.

[0004] Also, when a polyimide film is formed by heat-curing a varnish applied on a glass support or a silicon wafer, residual stress is generated in the polyimide film. If the residual stress in the polyimide film is large, there is a problem that the glass support or the silicon wafer is warped, so reduction of the residual stress is also required for the polyimide film. Patent Document 1 discloses a polyimide resin that provides a film with low residual stress. The polyimide resin is synthesized using 4,4'-oxydiphthalic dianhydride as the tetracarboxylic acid component and α,ω-aminopropylpolydimethylsiloxane with a number average molecular weight of 1000 and 4,4'-diaminodiphenyl ether as the diamine components. [Prior Art Document] [Patent Document]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-232383 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] As described above, various properties are required for polyimide films, but it is not easy to satisfy these properties simultaneously. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a polyimide resin capable of forming a film excellent in colorless transparency, heat resistance, and thermal stability and having further low residual stress, a method for producing the same, a polyimide varnish containing the polyimide resin, and a polyimide film. [Means for Solving the Problems]

[0007] The inventors of the present invention have found that a polyimide resin containing a specific combination of structural units can solve the above problems, and have completed the invention.

[0008] That is, the present invention relates to the following [1] to [9]. [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 (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2). A polyimide resin in which the structural unit B includes a structural unit (B-1) derived from a compound represented by the following formula (b-1). [Chemical formula]

[0009] [2] The ratio of the structural unit (A-1) in the structural unit A is 40 to 95 mol%, The polyimide resin according to [1] above, wherein the ratio of the structural unit (A-2) in the structural unit A is 5 to 60 mol%. [3] The polyimide resin according to [1] or [2] above, wherein the ratio of the structural unit (B-1) in the structural unit B is 50 mol% or more. [4] The polyimide resin according to any one of [1] to [3] above, wherein the structural unit B further includes a structural unit derived from 9,9-bis(4-aminophenyl)fluorene. [5] The polyimide resin according to any one of [1] to [4] above, wherein the ratio [(A-1) / (A-2)] (mol / mol) of the structural unit (A-1) to the structural unit (A-2) is 25 / 75 to 95 / 5. [6] A method for producing a polyimide resin, comprising subjecting a tetracarboxylic acid component containing the compound represented by the above formula (a-1) and the compound represented by the above formula (a-2) and a diamine component containing the compound represented by the above formula (b-1) to an imidization reaction by heating in the presence of a reaction solvent. [7] The method for producing a polyimide resin according to [6] above, wherein the reaction solvent is at least one selected from the group consisting of an amide-based solvent and a lactone-based solvent. [8] A polyimide varnish obtained by dissolving the polyimide resin according to any one of [1] to [5] above in an organic solvent. [9] A polyimide film containing the polyimide resin according to any one of [1] to [5] above.

Advantages of the Invention

[0010] According to the present invention, a film excellent in colorless transparency, heat resistance, and thermal stability and having a lower residual stress can be formed.

Modes for Carrying Out the Invention

[0011] [Polyimide Resin] The polyimide resin of the present invention 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 (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2), and the structural unit B includes a structural unit (B-1) derived from a compound represented by the following formula (b-1).

Chemical formula

[0012] <Structural Unit A> The structural unit A is a structural unit derived from a tetracarboxylic dianhydride in the polyimide resin, and includes a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2).

Chemical formula

[0013] The compound represented by the formula (a-1) is 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride. By the structural unit A including the structural unit (A-1), the colorless transparency, heat resistance, and thermal stability of the film are improved.

[0014] The compound represented by formula (a-2) is biphenyltetracarboxylic dianhydride (BPDA), and specific examples thereof include 3,3’,4,4’-biphenyltetracarboxylic dianhydride (s-BPDA) represented by the following formula (a-2s), 2,3,3’,4’-biphenyltetracarboxylic dianhydride (a-BPDA) represented by the following formula (a-2a), and 2,2’,3,3’-biphenyltetracarboxylic dianhydride (i-BPDA) represented by the following formula (a-2i). [Chemical formula]

[0015] By including the structural unit A containing the structural unit (A-2), the heat resistance and thermal stability of the film are improved, and the residual stress is reduced.

[0016] The ratio of the structural unit (A-1) in the structural unit A is preferably 25 to 95 mol%, more preferably 30 to 90 mol%, still more preferably 35 to 85 mol%, even more preferably 40 to 80 mol%, and particularly preferably 50 to 80 mol%. The ratio of the structural unit (A-2) in the structural unit A is preferably 5 to 75 mol%, more preferably 10 to 70 mol%, still more preferably 15 to 65 mol%, even more preferably 20 to 60 mol%, and particularly preferably 20 to 50 mol%. Also, the ratio [(A-1) / (A-2)] (mol / mol) of the structural unit (A-1) to the structural unit (A-2) is preferably 25 / 75 to 95 / 5, more preferably 30 / 70 to 90 / 10, still more preferably 35 / 65 to 85 / 15, even more preferably 40 / 60 to 80 / 20, and particularly preferably 50 / 80 to 50 / 20. The total ratio of constitutional units (A-1) and (A-2) in constitutional unit A is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of constitutional units (A-1) and (A-2) is not particularly limited, that is, it is 100 mol%. Constitutional unit A may consist only of constitutional unit (A-1) and constitutional unit (A-2).

[0017] Constitutional unit A may contain constitutional units other than constitutional units (A-1) and (A-2). The tetracarboxylic dianhydride that gives such a constitutional unit is not particularly limited, but aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (however, excluding the compounds represented by formula (a-1) and formula (a-2)); alicyclic tetracarboxylic dianhydrides such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride; and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride. In the present 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. The constitutional units other than constitutional units (A-1) and (A-2) optionally contained in constitutional unit A may be one kind or two or more kinds.

[0018] <Constitutional unit B> Constitutional unit B is a constitutional unit derived from diamine in the polyimide resin and contains constitutional unit (B-1) derived from the compound represented by the following formula (b-1).

Chemical formula

[0019] The compound represented by the formula (b-1) is 2,2'-bis(trifluoromethyl)benzidine. By including the structural unit (B-1) in the structural unit B, the colorless transparency, heat resistance, and thermal stability of the film are improved, and the residual stress is reduced.

[0020] The ratio of the structural unit (B-1) in the structural unit B is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the ratio of the structural unit (B-1) is not particularly limited, that is, it is 100 mol%. The structural unit B may consist only of the structural unit (B-1).

[0021] Constituent unit B may contain constituent units other than constituent unit (B-1). The diamine that provides such a constituent unit is not particularly limited, but examples include aromatic diamines such as 1,4-phenylenediamine, p-xylylenediamine, 3,5-diaminobenzoic acid, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminodiphenyl sulfone, 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, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, and 9,9-bis(4-aminophenyl)fluorene (excluding the compound represented by formula (b-1)); alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine. Among these, aromatic diamines are preferred, and 9,9-bis(4-aminophenyl)fluorene is more preferred. 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. The constituent units other than constituent unit (B-1) optionally contained in constituent unit B may be one kind or two or more kinds.

[0022] The number average molecular weight of the polyimide resin of the present invention is preferably 5,000 to 300,000, more preferably 5,000 to 100,000, from the viewpoint of the mechanical strength of the obtained polyimide film. The number average molecular weight of the polyimide resin can be determined, for example, from the standard polymethyl methacrylate (PMMA) conversion value by gel filtration chromatography measurement.

[0023] The polyimide resin of the present invention may contain a structure other than the polyimide chain (a structure in which structural unit A and structural unit B are imide-bonded). Examples of the structure other than the polyimide chain that can be contained in the polyimide resin include a structure containing an amide bond. The polyimide resin of the present invention preferably contains a polyimide chain (a structure in which structural unit A and structural unit B are imide-bonded) as the main structure. Therefore, the ratio of the polyimide chain in the polyimide resin of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and particularly preferably 99% by mass or more.

[0024] By using the polyimide resin of the present invention, a film excellent in colorless transparency, heat resistance, and thermal stability and having a lower residual stress can be formed, and the preferable physical property values of the film are as follows. The total light transmittance is preferably 85% or more, more preferably 87% or more, still more preferably 88% or more, when the film has a thickness of 10 μm. The yellow index (YI) is preferably 5.0 or less, more preferably 4.0 or less, still more preferably 3.5 or less, when the film has a thickness of 10 μm. The glass transition temperature (Tg) is preferably 370°C or higher, more preferably 380°C or higher, still more preferably 400°C or higher. The weight loss rate at 450°C is preferably 1.00% or less, more preferably 0.80% or less, still more preferably 0.50% or less. The weight loss rate at 480 °C is preferably 3.00% or less, more preferably 2.50% or less, and still more preferably 2.00% or less. The residual stress is preferably 40.0 MPa or less, more preferably 35.0 MPa or less, and still more preferably 30.0 MPa or less.

[0025] The film that can be formed by using the polyimide resin of the present invention also has good mechanical properties and has the following suitable physical property values. The tensile modulus is preferably 2.5 GPa or more, more preferably 3.0 GPa or more, and still more preferably 3.5 GPa or more. The tensile strength is preferably 70 MPa or more, more preferably 90 MPa or more, and still more preferably 100 MPa or more. In addition, the above physical property values in the present invention can be specifically measured by the method described in the examples.

[0026] [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 structural unit (A-1) and a compound that provides the above structural unit (A-2) with a diamine component containing a compound that provides the above structural unit (B-1). A more specific method for producing the polyimide resin of the present invention is to perform an imidization reaction by heating a tetracarboxylic acid component containing a compound that provides structural unit A and a diamine component containing a compound that provides structural unit (B-1) in the presence of a reaction solvent. That is, an imidization reaction is performed by heating a tetracarboxylic acid component containing a compound represented by formula (a-1) and a compound represented by formula (a-2) and a diamine component containing a compound represented by formula (b-1) in the presence of a reaction solvent.

[0027] Examples of the compound that provides the structural unit (A-1) include, but are not limited to, the compound represented by the formula (a-1), and derivatives thereof may also be used as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydride represented by the formula (a-1) and alkyl esters of the tetracarboxylic acids. As the compound that provides the structural unit (A-1), the compound represented by the formula (a-1) (i.e., dianhydride) is preferred. Similarly, examples of the compound that provides the structural unit (A-2) include, but are not limited to, the compound represented by the formula (a-2), and derivatives thereof may also be used as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydride represented by the formula (a-2) and alkyl esters of the tetracarboxylic acids. As the compound that provides the structural unit (A-2), the compound represented by the formula (a-2) (i.e., dianhydride) is preferred.

[0028] The tetracarboxylic acid component preferably contains 25 to 95 mol%, more preferably 30 to 90 mol%, still more preferably 35 to 85 mol%, even more preferably 40 to 80 mol%, and particularly preferably 50 to 80 mol% of the compound that provides the structural unit (A-1). The tetracarboxylic acid component preferably contains 5 to 75 mol%, more preferably 10 to 70 mol%, still more preferably 15 to 65 mol%, even more preferably 20 to 60 mol%, and particularly preferably 20 to 50 mol% of the compound that provides the structural unit (A-2). The tetracarboxylic acid component preferably contains 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more, and particularly preferably 99 mol% or more in total of the compound that provides the structural unit (A-1) and the compound that provides the structural unit (A-2). The upper limit value of the total content of the compound that provides the structural unit (A-1) and the compound that provides the structural unit (A-2) is not particularly limited, i.e., it is 100 mol%. The tetracarboxylic acid component may consist only of the compound that provides the structural unit (A-1) and the compound that provides the structural unit (A-2).

[0029] The tetracarboxylic acid component may include compounds other than the compound providing the structural unit (A-1) and the compound providing the structural unit (A-2). 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 compounds other than the compound providing the structural unit (A-1) and the compound providing the structural unit (A-2) that are optionally contained in the tetracarboxylic acid component may be one kind or two or more kinds.

[0030] Examples of the compound providing the structural unit (B-1) include, but are not limited to, the compound represented by formula (b-1), 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 formula (b-1). As the compound providing the structural unit (B-1), the compound represented by formula (b-1) (i.e., diamine) is preferred.

[0031] The diamine component preferably contains 50 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more of the compound providing the structural unit (B-1). The upper limit of the content of the compound providing the structural unit (B-1) is not particularly limited, that is, it is 100 mol%. The diamine component may consist only of the compound providing the structural unit (B-1).

[0032] The diamine component may include compounds other than the compound providing the structural unit (B-1). Examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, as well as their derivatives (diisocyanates, etc.). The compounds other than the compound providing the structural unit (B-1) that are optionally contained in the diamine component may be one kind or two or more kinds.

[0033] In the present invention, the charge ratio of the tetracarboxylic acid component to the diamine component used in the production of the polyimide resin is preferably 0.9 to 1.1 moles of the diamine component per 1 mole of the tetracarboxylic acid component.

[0034] Further, in the present invention, in the production of the polyimide resin, in addition to the aforementioned tetracarboxylic acid component and diamine component, a terminal blocking agent may be used. As the terminal blocking agent, monoamines or dicarboxylic acids are preferred. The charged amount of the introduced terminal blocking agent is preferably 0.0001 to 0.1 moles, particularly preferably 0.001 to 0.06 moles, per 1 mole of the tetracarboxylic acid component. Examples of the monoamine terminal blocking agent 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 can be preferably used. As the dicarboxylic acid terminal blocking agent, dicarboxylic acids are preferred, and a part of them may be ring-closed. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. are recommended. Among these, phthalic acid and phthalic anhydride can be preferably used.

[0035] There is no particular limitation on the method for reacting the aforementioned tetracarboxylic acid component and diamine component, and known methods can be used. As specific reaction methods, there are: (1) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, stirred at room temperature to 80 °C for 0.5 to 30 hours, and then the temperature is raised to carry out an imidization reaction; (2) a method in which a diamine component and a reaction solvent are charged into a reactor and dissolved, then a tetracarboxylic acid component is charged, stirred at room temperature to 80 °C for 0.5 to 30 hours as necessary, and then the temperature is raised to carry out an imidization reaction; (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 an imidization reaction, etc.

[0036] The reaction solvent used in the production of the polyimide resin may be any one that does not inhibit the imidization reaction and can dissolve the resulting polyimide. For example, aprotic solvents, phenolic solvents, ether solvents, carbonate solvents, etc. can be mentioned.

[0037] Specific examples of aprotic solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone, tetramethylurea; lactone solvents such as γ-butyrolactone, γ-valerolactone; phosphorus-containing amide solvents such as hexamethylphosphoric amide, hexamethylphosphine triamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, sulfolane; ketone solvents such as acetone, cyclohexanone, methylcyclohexanone; amine solvents such as picoline, pyridine; ester solvents such as (2-methoxy-1-methylethyl) acetate, etc.

[0038] 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 the 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, and the like. Specific examples of the carbonate solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, and the like. Among the above reaction solvents, amide solvents and / or lactone solvents are preferred, and lactone solvents are more preferred. Further, the above reaction solvents may be used alone or in combination of two or more. When using a mixture of two or more solvents, it is particularly preferable to use a mixture of an amide solvent and a lactone solvent.

[0039] 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.

[0040] 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, triethylenediamine, 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, still more preferably triethylamine, and particularly preferably a combination of triethylamine and triethylenediamine.

[0041] From the viewpoints of reaction rate and suppression of gelation, etc., the temperature of the imidization reaction is preferably 120 to 250°C, more preferably 160 to 200°C. Further, the reaction time is preferably 0.5 to 10 hours after the start of distillation of the generated water.

[0042] [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 one in which the polyimide resin is soluble and is not particularly limited, but 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 may be the polyimide solution itself in which the polyimide resin obtained by the polymerization method is dissolved in the reaction solvent, or may be obtained by further adding a diluting solvent to the polyimide solution.

[0043] Since the polyimide resin of the present invention has solvent solubility, a high-concentration varnish stable at room temperature can be obtained. The polyimide varnish of the present invention preferably contains 5 to 40% by mass of the polyimide resin of the present invention, more preferably 5 to 30% by mass, and still more preferably 10 to 30% by mass. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, more preferably 1 to 150 Pa·s, and still more preferably 5 to 150 Pa·s. The viscosity of the polyimide varnish is the value measured at 25°C using an E-type viscometer. In addition, the polyimide varnish of the present invention may contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, ultraviolet stabilizers, surfactants, leveling agents, defoaming agents, fluorescent brighteners, crosslinking agents, polymerization initiators, and photosensitizers within a range that does not impair the required properties of the polyimide film. The method for producing the polyimide varnish of the present invention is not particularly limited, and known methods can be applied.

[0044] [Polyimide Film] The polyimide film of the present invention contains the polyimide resin of the present invention. Therefore, the polyimide film of the present invention is excellent in colorless transparency, heat resistance, and thermal stability, and further has low residual stress. The suitable physical property values of the polyimide film of the present invention are as described above. The method for producing the polyimide film of the present invention is not particularly limited, and known methods can be used. For example, the polyimide varnish of the present invention is applied onto a smooth support such as a glass plate, a metal plate, or a plastic, or formed into a film shape, and then an organic solvent such as a reaction solvent or a diluting solvent contained in the varnish is removed by heating. The surface of the support may be coated with a release agent in advance if necessary. As a method for removing the organic solvent contained in the varnish by heating, the following method is preferable. That is, after evaporating the organic solvent at a temperature of 120°C or lower to form a self-supporting film, the self-supporting film is peeled off from the support, the end of the self-supporting film is fixed, and it is preferably dried at a temperature above the boiling point of the used organic solvent to produce a 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. The heating temperature when drying the self-supporting film to produce a polyimide film is not particularly limited, but is preferably 200 to 500°C, and more preferably 200 to 400°C.

[0045] In addition, the polyimide film of the present invention can also be produced using a polyamic acid varnish obtained by dissolving polyamic acid in an organic solvent. The polyamic acid contained in the polyamic acid varnish is a precursor of the polyimide resin of the present invention, and is a product of a polyaddition reaction between a tetracarboxylic acid component containing a compound that provides the above structural unit (A-1) and a compound that provides the above structural unit (A-2) and a diamine component containing a compound that provides the above structural unit (B-1). By imidizing (dehydration ring closure) this polyamic acid, the polyimide resin of the present invention, which is the final product, can be obtained. As the organic solvent contained in the polyamic acid varnish, the organic solvent contained in the polyimide varnish of the present invention can be used. In the present invention, the polyamic acid varnish may be the polyamic acid solution itself obtained by subjecting a tetracarboxylic acid component containing a compound that provides the above structural unit (A-1) and a compound that provides the above structural unit (A-2) and a diamine component containing a compound that provides the above structural unit (B-1) to a polyaddition reaction in a reaction solvent, or may be the one obtained by further adding a diluting solvent to the polyamic acid solution.

[0046] There is no particular limitation on the method for producing a polyimide film using the polyamic acid varnish, and a known method can be used. For example, the polyamic acid varnish is applied onto a smooth support such as a glass plate, a metal plate, or a plastic, or formed into a film shape, and the organic solvents such as the reaction solvent and the diluting solvent contained in the varnish are removed by heating to obtain a polyamic acid film, and the polyamic acid in the polyamic acid film is imidized by heating to produce a polyimide film. The heating temperature when drying the polyamic acid varnish to obtain a polyamic acid film is preferably 50 to 120°C. The heating temperature when imidizing the polyamic acid by heating is preferably 200 to 500°C, more preferably 200 to 480°C, still more preferably 200 to 450°C, and even more preferably 200 to 400°C. Note that the method of imidization is not limited to thermal imidization, and chemical imidization can also be applied.

[0047] The thickness of the polyimide film of the present invention can be appropriately selected according to the intended use and the like, but is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, still more preferably 8 to 80 μm, and even more preferably 10 to 80 μm. When the thickness is 1 to 250 μm, practical use as a self-supporting film becomes possible. The thickness of the polyimide film can be easily controlled by adjusting the solid content concentration and viscosity of the polyimide varnish.

[0048] The polyimide film of the present invention is suitably used as a film for various members such as color filters, flexible displays, semiconductor components, and optical members. The polyimide film of the present invention is particularly preferably used as a substrate for image display devices such as liquid crystal displays and OLED displays.

Examples

[0049] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited by these examples. The solid content concentration of the varnishes obtained in the examples and comparative examples and the physical properties of the films were measured by the following methods.

[0050] (1) Solid content concentration The solid content concentration of the varnish was calculated from the mass difference of the sample before and after heating the sample at 320 ° C. for 120 min in a small electric furnace “MMF-1” manufactured by AS ONE Corporation. (2) Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation. (3) Total light transmittance, yellow index (YI) (evaluation of colorless transparency) The total light transmittance and YI were measured in accordance with JIS K7361-1: 1997 using a color and turbidity simultaneous measuring instrument “COH400” manufactured by Nippon Denshoku Industries Co., Ltd. The closer the total light transmittance is to 100%, and the smaller the value of YI, the better the colorless transparency. (4) Glass transition temperature (Tg) (evaluation of heat resistance) Using a thermomechanical analyzer "TMA / SS6100" manufactured by Hitachi High-Tech Science Corporation, the temperature was raised to a temperature sufficient to remove the residual stress under the conditions of a sample size of 2 mm × 20 mm, a load of 0.1 N, and a heating rate of 10 °C / min in the tensile mode to remove the residual stress, and then cooled to room temperature. Thereafter, the measurement of the specimen elongation was carried out under the same conditions as the treatment for removing the residual stress, and the point where the inflection point of the elongation was observed was determined as the glass transition temperature. The higher the value of Tg, the better the heat resistance. (5) Weight loss rate at 450 °C and 480 °C (evaluation of thermal stability) A differential thermal and thermogravimetric simultaneous measurement apparatus "TG / DTA6200" manufactured by Hitachi High-Tech Science Corporation was used. The sample was heated from 40 °C to a predetermined temperature (450 °C or 480 °C) at a heating rate of 10 °C / min and held at that temperature for 1 hour. The ratio of the weight decreased during the 1-hour holding at 450 °C to the weight before the 1-hour holding was defined as the weight loss rate at 450 °C, and the ratio of the weight decreased during the 1-hour holding at 480 °C to the weight before the 1-hour holding was defined as the weight loss rate at 480 °C. The higher the value of each weight loss temperature, the better the thermal stability. (6) Residual stress Using a residual stress measurement apparatus "FLX-2320" manufactured by KLA-Tencor Corporation, polyimide varnish or polyamic acid varnish was applied onto a 4-inch silicon wafer with a thickness of 525 μm ± 25 μm, on which the "warp amount" had been measured in advance, using a spin coater and pre-baked. Thereafter, a heat curing treatment at 400 °C for 1 hour was carried out under a nitrogen atmosphere using a hot air dryer to produce a silicon wafer with a polyimide film having a film thickness of 8 to 20 μm after curing. The warp amount of this wafer was measured using the aforementioned residual stress measurement apparatus, and the residual stress generated between the silicon wafer and the polyimide film was evaluated. The smaller the value of the residual stress, the better. (7) Tensile modulus of elasticity and tensile strength The tensile modulus of elasticity and tensile strength were measured in accordance with JIS K7127 using a tensile testing machine "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd.

[0051] The tetracarboxylic acid components and diamine components used in the examples and comparative examples, and their abbreviations are as follows. <Tetracarboxylic acid component> BPAF: 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride (manufactured by JFE Chemical Corporation; compound represented by formula (a-1)) BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Corporation; compound represented by formula (a-2)) HPMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Company, Inc.) <Diamine component> TFMB: 2,2'-bis(trifluoromethyl)benzidine (manufactured by Wakayama Seika Kogyo Co., Ltd.; compound represented by formula (b-1)) BAFL: 9,9-bis(4-aminophenyl)fluorene (manufactured by Taoka Chemical Industry Co., Ltd.)

[0052] <Example 1> Into a 1 L five-necked 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, 32.024 g (0.100 mol) of TFMB and 89.499 g of N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation) were charged, and the mixture was stirred at a system temperature of 70 °C under a nitrogen atmosphere at a rotation speed of 150 rpm to obtain a solution. To this solution, 36.674 g (0.080 mol) of BPAF, 5.884 g (0.020 mol) of BPDA, and 22.375 g of N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation) were added all at once. Then, 0.506 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) was charged as an imidization catalyst, and the mixture was heated with a mantle heater to raise the temperature inside the reaction system 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 3 hours. Thereafter, 526.935 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) was added, and after cooling the temperature inside the reaction system to 120 °C, the mixture was further stirred for about 3 hours for homogenization to obtain a polyimide varnish having a solid content concentration of 10.0 mass%. Subsequently, the obtained polyimide varnish was applied onto a glass plate and then onto a silicon wafer, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes under a nitrogen atmosphere to evaporate the solvent, obtaining a film with a thickness of 8 μm. The results are shown in Table 1.

[0053] <Example 2> A polyimide varnish was prepared in the same manner as in Example 1, except that the amount of BPAF was changed from 36.674 g (0.080 mol) to 27.506 g (0.060 mol), and the amount of BPDA was changed from 5.884 g (0.020 mol) to 11.769 g (0.040 mol), obtaining a polyimide varnish with a solid content concentration of 10.0 mass%. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1, obtaining a film with a thickness of 9 μm. The results are shown in Table 1.

[0054] <Example 3> A polyimide varnish was prepared in the same manner as in Example 1, except that the amount of BPAF was changed from 36.674 g (0.080 mol) to 18.337 g (0.040 mol), the amount of BPDA was changed from 5.884 g (0.020 mol) to 17.653 g (0.060 mol), and the diluting solvent after 3 hours of reaction was changed from γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) to N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation), obtaining a polyimide varnish with a solid content concentration of 10.0 mass%. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1, obtaining a film with a thickness of 10 μm. The results are shown in Table 1.

[0055] <Example 4> The amount of BPAF was changed from 36.674 g (0.080 mol) to 22.921 g (0.050 mol), the amount of BPDA was changed from 5.884 g (0.020 mol) to 14.711 g (0.050 mol), the amount of TFMB was changed from 32.024 g (0.100 mol) to 16.012 g (0.050 mol), 17.423 g (0.050 mol) of BAFL was added, and the synthetic solvent was changed from N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation) to γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation). A polyimide varnish was prepared in the same manner as in Example 1, and a polyimide varnish with a solid content concentration of 10.0 mass% was obtained. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1, and a film with a thickness of 9.5 μm was obtained. The results are shown in Table 1.

[0056] <Example 5> The amount of BPAF was changed from 36.674 g (0.080 mol) to 22.921 g (0.050 mol), the amount of BPDA was changed from 5.884 g (0.020 mol) to 14.711 g (0.050 mol), the amount of TFMB was changed from 32.024 g (0.100 mol) to 25.619 g (0.080 mol), 6.969 g (0.020 mol) of BAFL was added, and the synthetic solvent was changed from N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation) to γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation). A polyimide varnish was prepared in the same manner as in Example 1, and a polyimide varnish with a solid content concentration of 10.0 mass% was obtained. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1, and a film with a thickness of 9 μm was obtained. The results are shown in Table 1.

[0057] <Comparative Example 1> The amount of BPAF was changed from 36.674 g (0.080 mol) to 45.843 g (0.100 mol), and a polyimide varnish was prepared in the same manner as in Example 1 except that BPDA was not added, and a polyimide varnish with a solid content concentration of 10.0 mass% was obtained. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1, and a film with a thickness of 9 μm was obtained. The results are shown in Table 1.

[0058] <Comparative Example 2> BPAF was changed from 36.674 g (0.080 mol) to 22.417 g (0.100 mol), and BPDA was changed from 5.884 g (0.020 mol) to HPMDA 22.417 g (0.100 mol). A polyimide varnish was prepared in the same manner as in Example 1 except that the synthesis solvent was changed from N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation) to γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation), and a polyimide varnish with a solid content concentration of 10.0% by mass was obtained. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1, and a film with a thickness of 9 μm was obtained. The results are shown in Table 1.

[0059] <Comparative Example 3> The amount of BPAF was changed from 36.674 g (0.080 mol) to 22.922 g (0.050 mol), 11.209 g (0.050 mol) of HPMDA was added, BPDA was not added, and a polyimide varnish was prepared in the same manner as in Example 1 except that the synthesis solvent was changed from N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation) to γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation), and a polyimide varnish with a solid content concentration of 10.0% by mass was obtained. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1, and a film with a thickness of 15 μm was obtained. The results are shown in Table 1.

[0060] <Comparative Example 4> Into a 1 L five-necked round-bottom flask equipped with a stainless steel semi-circular stirring blade, a nitrogen inlet tube, a Dean-Stark with a cooling tube, a thermometer, and a glass end cap, 32.024 g (0.100 mol) of TFMB and 196.627 g of N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation) were charged, and the mixture was stirred at a system temperature of 50 °C under a nitrogen atmosphere at a rotation speed of 150 rpm to obtain a solution. To this solution, 294.22 g (0.100 mol) of BPDA and 49.157 g of N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation) were charged all at once, and the mixture was stirred for 7 hours while maintaining the temperature at 50 °C with a mantle heater. Subsequently, 307.230 g of N-methylpyrrolidone (manufactured by Mitsubishi Chemical Corporation) was added, and the mixture was further stirred for about 3 hours for homogenization to obtain a polyamic acid varnish with a solid content concentration of 10% by mass. Subsequently, the obtained polyamic acid varnish was applied onto a glass plate and a silicon wafer, held at 80°C for 20 minutes on a hot plate, and then heated at 400°C for 30 minutes in a hot air dryer under a nitrogen atmosphere to evaporate the solvent and further thermally imidize it, obtaining a film with a thickness of 12 μm. The results are shown in Table 1.

[0061]

Table 1

[0062] As shown in Table 1, the polyimide films of Examples 1 to 5 produced using specific tetracarboxylic acid components and specific diamine components were excellent in colorless transparency, heat resistance, and thermal stability, and furthermore had low residual stress. On the other hand, the polyimide film of Comparative Example 1 produced using only BPAF without using BPAF and BPDA in combination as the tetracarboxylic acid component had a large residual stress as compared with the polyimide films of Examples 1 to 5. The polyimide film of Comparative Example 4 produced using only BPDA without using BPAF and BPDA in combination as the tetracarboxylic acid component was inferior in colorless transparency because of a large YI and inferior in heat resistance because of a low Tg as compared with the polyimide films of Examples 1 to 5. The polyimide film of Comparative Example 2 produced using only HPMDA as the tetracarboxylic acid component was inferior in heat resistance because of a low Tg, inferior in thermal stability because of large weight loss rates at 450°C and 480°C, and had a large residual stress as compared with the polyimide films of Examples 1 to 5. The polyimide film of Comparative Example 3 produced using BPAF and HPMDA in combination as the tetracarboxylic acid component was inferior in thermal stability because of large weight loss rates at 450°C and 480°C and had a large residual stress as compared with the polyimide films of Examples 1 to 5.

Claims

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 (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2), the structural unit B consists of a structural unit (B-1) derived from a compound represented by the following formula (b-1), or consists of a structural unit (B-1) and a structural unit derived from 9,9-bis(4-aminophenyl)fluorene, the ratio of the structural unit (A-1) in the structural unit A is 40 to 60 mol%, the ratio of the structural unit (A-2) in the structural unit A is 40 to 60 mol%, and the charge amount ratio of the tetracarboxylic acid component to the diamine component used in the production of the polyimide resin is 1 to 1.1 mol of the diamine component per 1 mol of the tetracarboxylic acid component. A polyimide resin. 【Chemical 1】

2. The polyimide resin according to claim 1, wherein the ratio of the structural unit (B-1) in the structural unit B is 50 mol% or more.

3. The polyimide resin according to claim 1 or 2, wherein the ratio [(A-1) / (A-2)] (mol / mol) of the structural unit (A-1) to the structural unit (A-2) is 40 / 60 to 60 / 40.

4. A method for producing a polyimide resin, comprising heating a tetracarboxylic acid component containing a compound represented by the following formula (a-1) and a compound represented by the following formula (a-2) and a diamine component consisting of a compound represented by the following formula (b-1) or consisting of a compound represented by the following formula (b-1) and 9,9-bis(4-aminophenyl)fluorene in the presence of a reaction solvent to carry out an imidization reaction, wherein the ratio of the compound represented by the following formula (a-1) in the tetracarboxylic acid component is 40 to 60 mol%, the ratio of the compound represented by the following formula (a-2) in the tetracarboxylic acid component is 40 to 60 mol%, and the charge amount ratio of the tetracarboxylic acid component to the diamine component is 1 to 1.1 mol of the diamine component per 1 mol of the tetracarboxylic acid component. A method for producing a polyimide resin. 【Chemical Formula 2】

5. The method for producing a polyimide resin according to claim 4, wherein the reaction solvent is at least one selected from the group consisting of an amide-based solvent and a lactone-based solvent.

6. A polyimide varnish obtained by dissolving the polyimide resin according to any one of claims 1 to 3 in an organic solvent.

7. A polyimide film comprising the polyimide resin according to any one of claims 1 to 3.

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