Polyimide resin, polyimide varnish and polyimide film

Abstract

A polyimide resin having a constituent unit A derived from a tetracarboxylic acid dianhydride and a constituent unit B derived from a diamine, wherein the constituent unit A includes a constituent unit (A1) derived from a compound represented by formula (a1) and a constituent unit (A2) derived from a compound represented by formula (a2), and the constituent unit B includes a constituent unit (B1) derived from a compound represented by formula (b1) and at least one constituent unit (B2) selected from the group consisting of a constituent unit (B21) derived from a compound represent by formula (b21) and a constituent unit (B22) derived from a compound represented by formula (b22).

Description

[Technical field]

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

[0002] Various applications of polyimide resins are being considered in the fields of electric and electronic components, etc. For example, it is desirable to replace glass substrates used in image display devices such as liquid crystal displays and OLED displays with plastic substrates in order to make the devices lighter and more flexible, and research is being conducted on polyimide films suitable for such plastic substrates. Films used in image display devices are required to have various optical properties. For example, when light emitted from a display element is emitted through a plastic substrate, the plastic substrate is required to be colorless and transparent.

[0003] In order to satisfy the above-mentioned performance requirements, polyimide resins with various compositions have been developed. For example, Patent Document 1 discloses a polyimide film containing a structure consisting of a combination of 3,3'-diaminodiphenylsulfone and another specific diamine as a diamine component, with the aim of obtaining a polyimide film that contains a polyamide having good solubility in a solvent and excellent processability, is colorless and transparent, and has excellent toughness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 158825 Summary of the Invention [Problem to be solved by the invention]

[0005] In addition to being colorless and transparent, when the retardation film or polarizing plate is used in applications in which light passes through, such as liquid crystal displays and touch panels, high optical isotropy (i.e., low Rth) is particularly required. Furthermore, polyimide films with high chemical resistance are also required. For example, when a varnish for forming a resin layer (e.g., a color filter or resist) is applied to a polyimide film to form the resin layer on the polyimide film, the polyimide film is required to have resistance to the solvent contained in the varnish. If the solvent resistance of the polyimide film is insufficient, the film may dissolve or swell, making it useless as a substrate. However, in order to ensure the optical properties as described above, the polyimide film must be in the form of a solution when it is produced, and it has been difficult to achieve both of these properties. In addition, when a polyimide film is used as a substrate, there is a process of peeling the polyimide film from the support after the circuit is formed. In this process, the polyimide film is required to have a certain degree of toughness, i.e., good elongation, in order to facilitate the process and prevent breakage during peeling. Thus, there has been a demand for a polyimide resin capable of giving a polyimide film having excellent elongation and chemical resistance while maintaining the optical properties, particularly optical isotropy, of the resulting polyimide film. [Means for solving the problem]

[0006] The present inventors discovered that a polyimide resin containing a combination of structural units derived from two specific types of tetracarboxylic dianhydrides and structural units derived from two specific types of diamines can solve the above-mentioned problems, and thus completed the invention.

[0007] That is, the present invention provides the following <1> ~ <5> Regarding. <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), and the structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1), and at least one structural unit (B2) selected from the group consisting of a structural unit (B21) derived from a compound represented by the following formula (b21), and a structural unit (B22) derived from a compound represented by the following formula (b22). [ka] <2> The ratio of the structural unit (A1) in the structural unit A is 30 to 90 mol %, and the ratio of the structural unit (A2) in the structural unit B is 10 to 70 mol %. <1> The polyimide resin according to claim 1. <3> The ratio of the structural unit (B1) in the structural unit B is 5 to 80 mol %, and the ratio of the structural unit (B2) in the structural unit B is 20 to 95 mol %. <1> or <2> The polyimide resin according to claim 1. <4> the above <1> ~ <3> 2. A polyimide varnish obtained by dissolving the polyimide resin according to any one of 1 to 11 in an organic solvent. <5> the above <1> ~ <3> 13. A polyimide film comprising the polyimide resin according to claim 12. Effect of the Invention

[0008] According to the present invention, it is possible to provide a polyimide resin and a polyimide varnish which are capable of forming a film having excellent optical isotropy as well as excellent elongation and chemical resistance, and a polyimide film having excellent optical isotropy as well as excellent elongation and chemical resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Polyimide resin] The polyimide resin of the present invention is a polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, in which the structural unit A includes a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from a compound represented by the following formula (a2), and the structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1), and at least one structural unit (B2) selected from the group consisting of a structural unit (B21) derived from a compound represented by the following formula (b21), and a structural unit (B22) derived from a compound represented by the following formula (b22).

[0010] [ka]

[0011] Although the reason why the polyimide resin of the present invention has excellent elongation and chemical resistance while maintaining optical isotropy is not clear, it is believed that the polyimide resin of the present invention has excellent optical isotropy as well as excellent elongation and chemical resistance because it has an appropriate ratio of alicyclic structures, aromatic structures, and ether structures and sulfonyl structures.

[0012] <Structural unit A> The structural unit A is a structural unit derived from a tetracarboxylic dianhydride contained in the polyimide resin. The structural unit A includes a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from a compound represented by the following formula (a2).

[0013] [ka]

[0014] The compound represented by formula (a1) is 4,4'-oxydiphthalic anhydride. When the structural unit A contains the structural unit (A1), chemical resistance and elongation can be improved. The compound represented by formula (a2) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride. When the structural unit A contains the structural unit (A2), the solubility of the resulting polyimide resin in a varnish can be increased, while the transparency and optical isotropy can be improved.

[0015] The proportion of the structural unit (A1) in the structural unit A is preferably from 30 to 90 mol %, more preferably from 35 to 70 mol %, and even more preferably from 40 to 60 mol %. The proportion of the structural unit (A2) in the structural unit A is preferably from 10 to 70 mol %, more preferably from 30 to 65 mol %, and even more preferably from 40 to 60 mol %. The total ratio of the structural units (A1) and (A2) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. There is no particular upper limit, and the total ratio of the structural units (A1) and (A2) in the structural unit A is 100 mol% or less. The structural unit A may be composed of only the structural unit (A1) and the structural unit (A2). From the viewpoint of improving optical isotropy and chemical resistance, the molar ratio of the structural unit (A1) to the structural unit (A2) in the structural unit A [(A1) / (A2)] is preferably 30 / 70 to 90 / 10, more preferably 35 / 65 to 70 / 30, and even more preferably 40 / 60 to 60 / 40.

[0016] The structural unit A may contain a structural unit other than the structural unit (A1) and the structural unit (A2). The tetracarboxylic dianhydride that gives such a structural unit is not particularly limited, but examples thereof include aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (excluding the compound represented by formula (a1)); 1,2,3,4-cyclobutanetetracarboxylic dianhydride; alicyclic tetracarboxylic acid dianhydrides such as norbornane-2-spiro-α-cyclopentanone-α'-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic acid dianhydride and 5,5′-bis-2-norbornene-5,5′,6,6′-tetracarboxylic acid-5,5′,6,6′-dianhydride (excluding the compound represented by formula (a2)); and aliphatic tetracarboxylic acid dianhydrides such as 1,2,3,4-butanetetracarboxylic acid dianhydride. In this specification, the term "aromatic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing one or more aromatic rings, the term "alicyclic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing one or more alicyclic rings but no aromatic rings, and the term "aliphatic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing neither an aromatic ring nor an alicyclic ring. The structural unit optionally contained in the structural unit A may be of one type, or of two or more types.

[0017] <Structural unit B> The structural unit B is a structural unit derived from a diamine contained in the polyimide resin. The structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1), and at least one structural unit (B2) selected from the group consisting of a structural unit (B21) derived from a compound represented by the following formula (b21), and a structural unit (B22) derived from a compound represented by the following formula (b22).

[0018] [ka]

[0019] The compound represented by formula (b1) is bis[(aminophenoxy)phenyl]sulfone, and specific examples include bis[4-(4-aminophenoxy)phenyl]sulfone represented by the following formula (b1a) and bis[4-(3-aminophenoxy)phenyl]sulfone represented by the following formula (b1b). When the structural unit B contains the structural unit (B1), the elongation and chemical resistance of the film can be improved, and further, the heat resistance and optical isotropy can be improved.

[0020] [ka]

[0021] The compound represented by formula (b21) is bis(aminomethyl)cyclohexane, and specific examples thereof include 1,3-bis(aminomethyl)cyclohexane represented by the following formula (b21a) and 1,4-bis(aminomethyl)cyclohexane represented by the following formula (b21b).

[0022] [ka]

[0023] The cis:trans ratio of the compound represented by formula (b21) is preferably 0:100 to 80:20, more preferably 0.1:99.9 to 70:30, even more preferably 0.5:99.5 to 60:40, and even more preferably 1:99 to 20:80, from the viewpoints of organic solvent resistance and heat resistance.

[0024] The compound represented by formula (b22) is bis(aminomethyl)norbornane. Formula (b22) represents an isomer mixture, and the compound represented by formula (b22) can be obtained as an isomer mixture. When the structural unit B contains the structural unit (B2), the transparency and optical isotropy of the film can be improved.

[0025] The proportion of the structural unit (B1) in the structural unit B is preferably from 5 to 80 mol %, more preferably from 10 to 70 mol %, and even more preferably from 30 to 60 mol %. The proportion of the structural unit (B2) in the structural units B is preferably from 20 to 95 mol %, more preferably from 30 to 90 mol %, and even more preferably from 40 to 70 mol %. The total ratio of the structural units (B1) and (B2) in the structural unit B is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. There is no particular upper limit, and the total ratio of the structural units (B1) and (B2) in the structural unit B is 100 mol% or less. The structural unit B may be composed of only the structural unit (B1) and the structural unit (B2). The molar ratio of the structural unit (B1) to the structural unit (B2) in the structural unit B [(B1) / (B2)] is preferably 5 / 95 to 80 / 20, more preferably 10 / 90 to 70 / 30, and even more preferably 30 / 70 to 60 / 40, from the viewpoint of improving optical isotropy and chemical resistance. Also, from the viewpoint of heat resistance and elongation, it is preferably 25 / 75 to 80 / 20, more preferably 35 / 65 to 65 / 35, even more preferably 35 / 65 to 55 / 45, and even more preferably 35 / 65 to 45 / 55.

[0026] The structural unit B may contain a structural unit other than the structural unit (B1) and the structural unit (B2). Diamines that provide such structural units are not particularly limited, but include 1,4-phenylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenyl ether, 4,4'-diamino-2,2'-bistrifluoromethyldiphenyl ether, 4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-inden-5-amine, α,α'-bis(4-aminophenyl) )-1,4-diisopropylbenzene, N,N'-bis(4-aminophenyl)terephthalamide, 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, and other aromatic diamines (excluding the compound represented by formula (b1)); alicyclic diamines (excluding the compounds represented by formula (b21) and formula (b22)); and aliphatic diamines such as ethylenediamine and hexamethylenediamine. In this specification, an aromatic diamine refers to a diamine containing one or more aromatic rings, an alicyclic diamine refers to a diamine containing one or more alicyclic rings but no aromatic rings, and an aliphatic diamine refers to a diamine containing neither an aromatic ring nor an alicyclic ring. The structural unit optionally contained in the structural unit B may be of one type, or of two or more types.

[0027] <Characteristics of polyimide resin> From the viewpoint of the mechanical strength of the resulting polyimide film, the weight-average molecular weight of the polyimide resin is preferably 5,000 to 300,000. The weight-average molecular weight of the polyimide resin can be determined, for example, from a standard polymethyl methacrylate (PMMA)-equivalent value measured by gel filtration chromatography.

[0028] The polyimide resin may contain a structure other than a polyimide chain (a structure formed by imide bonding between a structural unit A and a structural unit B). Examples of structures other than a polyimide chain that can be contained in a polyimide resin include a structure containing an amide bond. The polyimide resin preferably contains a polyimide chain (a structure formed by imide bonding of structural unit A and structural unit B) as a main structure. Therefore, the ratio of the polyimide chain in the polyimide resin is preferably 50 mass % or more, more preferably 70 mass % or more, even more preferably 90 mass % or more, particularly preferably 99 mass % or more, and 100 mol % or less. The polyimide resin may be composed of only polyimide chains.

[0029] The polyimide resin composition of the present invention containing the above polyimide resin can form a film excellent in optical isotropy, elongation and chemical resistance, and the suitable physical properties of the film are as follows.

[0030] The total light transmittance, when made into a film having a thickness of 10 μm, is preferably 88% or more, more preferably 88.5% or more, and further preferably 89% or more. The yellow index (YI) when made into a film having a thickness of 10 μm is preferably 5.0 or less, more preferably 3.0 or less, even more preferably 2.5 or less, and still more preferably 2.0 or less. The absolute value of the thickness retardation (Rth) is preferably 70 nm or less, more preferably 50 nm or less, even more preferably 35 nm or less, still more preferably 30 nm or less, and even more preferably 20 nm or less, when the film has a thickness of 10 μm.

[0031] Furthermore, a film that can be formed using the polyimide resin has good mechanical properties and heat resistance, and has the following preferable physical properties. The tensile strength is preferably 70 MPa or more, more preferably 90 MPa or more, and further preferably 100 MPa or more. The tensile modulus is preferably 1.5 GPa or more, more preferably 2.0 GPa or more, even more preferably 2.5 GPa or more, and still more preferably 2.7 GPa or more. The tensile elongation at break is preferably 8% or more, more preferably 10% or more, even more preferably 15% or more, and still more preferably 20% or more. The glass transition temperature (Tg) is preferably 200° C. or higher, more preferably 230° C. or higher, and further preferably 250° C. or higher. The above-mentioned physical properties in the present invention can be specifically measured by the methods described in the Examples.

[0032] <Method of manufacturing polyimide resin> The polyimide resin of the present invention can be produced by reacting a tetracarboxylic acid component containing a compound which provides the above-mentioned structural unit (A1) and a compound which provides the above-mentioned structural unit (A2) with a diamine component containing a compound which provides the above-mentioned structural unit (B1) and a compound which provides the above-mentioned structural unit (B2).

[0033] Compounds that provide the structural unit (A1) include, but are not limited to, compounds represented by formula (a1), and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids (i.e., 4,4'-oxydiphthalic acid) corresponding to the tetracarboxylic dianhydride represented by formula (a1), and alkyl esters of the tetracarboxylic acid. Among these, the tetracarboxylic dianhydride represented by formula (a1) is preferred. Similarly, examples of compounds that provide the structural unit (A2) include, but are not limited to, compounds represented by formula (a2), and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids (i.e., 1,2,4,5-cyclohexanetetracarboxylic acid) corresponding to the tetracarboxylic dianhydride represented by formula (a2), and alkyl esters of the tetracarboxylic acid. Among these, the tetracarboxylic dianhydride represented by formula (a2) is preferred.

[0034] The tetracarboxylic acid component contains a compound that provides the structural unit (A1) in an amount of preferably from 30 to 90 mol %, more preferably from 35 to 70 mol %, and even more preferably from 40 to 60 mol %. The tetracarboxylic acid component contains a compound that provides the structural unit (A2) in an amount of preferably from 10 to 70 mol %, more preferably from 30 to 65 mol %, and even more preferably from 40 to 60 mol %. The tetracarboxylic acid component contains a compound that gives the structural unit (A1) and a compound that gives the structural unit (A2) in a total amount of preferably 50 mol % or more, more preferably 70 mol % or more, and more preferably 90 mol % or more. There is no particular upper limit, and the tetracarboxylic acid component contains a compound that gives the structural unit (A1) and a compound that gives the structural unit (A2) in a total amount of 100 mol % or less. The tetracarboxylic acid component may be composed only of a compound that gives the structural unit (A1) and a compound that gives the structural unit (A2). The molar ratio of the compound that provides the structural unit (A1) to the compound that provides the structural unit (A2) in the tetracarboxylic acid component [(A1) / (A2)] is preferably 30 / 70 to 90 / 10, more preferably 35 / 65 to 70 / 30, and even more preferably 40 / 60 to 60 / 40.

[0035] The tetracarboxylic acid component may contain any compound other than the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2). Such optional compounds include the above-mentioned aromatic tetracarboxylic acid dianhydrides, alicyclic tetracarboxylic acid dianhydrides, and aliphatic tetracarboxylic acid dianhydrides, as well as derivatives thereof (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.). The compound optionally contained in the tetracarboxylic acid component may be one type or two or more types.

[0036] Compounds that provide the structural unit (B1) include compounds represented by formula (b1), but are not limited thereto, and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compounds represented by formula (b1). Compounds that provide the structural unit (B1) are preferably compounds represented by formula (b1) (i.e., diamines). Similarly, examples of compounds that provide the structural unit (B2) include compounds represented by formula (b21) and compounds represented by formula (b22), but are not limited thereto, and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compound represented by formula (b21) and diisocyanates corresponding to the compound represented by formula (b22). Compounds that provide the structural unit (B2) are preferably compounds represented by formula (b21) and compounds represented by formula (b22) (i.e., diamines).

[0037] The diamine component contains a compound that provides the structural unit (B1) in an amount of preferably 5 to 80 mol %, more preferably 10 to 70 mol %, and even more preferably 30 to 60 mol %. The diamine component contains a compound that provides the structural unit (B2) in an amount of preferably from 20 to 95 mol %, more preferably from 30 to 90 mol %, and even more preferably from 40 to 70 mol %. The diamine component contains a compound that gives the structural unit (B1) and a compound that gives the structural unit (B2) in a total amount of preferably 50 mol% or more, more preferably 70 mol% or more, and more preferably 90 mol% or more. There is no particular upper limit, and the tetracarboxylic acid component contains a compound that gives the structural unit (B1) and a compound that gives the structural unit (B2) in a total amount of 100 mol% or less. The tetracarboxylic acid component may be composed only of a compound that gives the structural unit (B1) and a compound that gives the structural unit (B2). The molar ratio [(B1) / (B2)] of the compound providing the structural unit (B1) to the compound providing the structural unit (B2) in the diamine component is preferably 5 / 95 to 80 / 20, more preferably 10 / 90 to 70 / 30, and even more preferably 30 / 70 to 60 / 40, from the viewpoint of improving optical isotropy and chemical resistance. Also, from the viewpoint of heat resistance and elongation, it is preferably 25 / 75 to 80 / 20, more preferably 35 / 65 to 65 / 35, even more preferably 35 / 65 to 55 / 45, and even more preferably 35 / 65 to 45 / 55.

[0038] The diamine component may contain any compound other than the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2). Such optional compounds include the aromatic, cycloaliphatic, and aliphatic diamines described above, as well as their derivatives (such as diisocyanates). The compound optionally contained in the diamine component may be one type or two or more types.

[0039] In the production of the polyimide resin of the present invention, the ratio of the amount of the tetracarboxylic acid component and the diamine component used in the production of the polyimide resin is preferably 0.9 to 1.1 mol of the diamine component per 1 mol of the tetracarboxylic acid component.

[0040] In addition, in the production of the polyimide resin of the present invention, a terminal blocking agent may be used in addition to the above-mentioned tetracarboxylic acid component and diamine component. As the terminal blocking agent, monoamines or dicarboxylic acids are preferred. The amount of the terminal blocking agent to be introduced is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, per 1 mol 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, and 4-methylaniline, and benzylamine and aniline are preferred. As the dicarboxylic acid terminal blocking agent, dicarboxylic acids are preferred, and a part of them may be ring-closed. Examples 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, and 4-cyclohexene-1,2-dicarboxylic acid, and preferably phthalic acid and phthalic anhydride.

[0041] The method for reacting the tetracarboxylic acid component and the diamine component is not particularly limited, and any known method can be used. Specific reaction methods include: (1) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the mixture is stirred at 10 to 110°C for 0.5 to 30 hours, and then the temperature is raised to carry out the imidization reaction; (2) a method in which a diamine component and a reaction solvent are charged into a reactor and dissolved, and then the tetracarboxylic acid component is charged, and the mixture is stirred at 10 to 110°C for 0.5 to 30 hours as necessary, and then the temperature is raised to carry out the imidization reaction; and (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the temperature is immediately raised to carry out the imidization reaction.

[0042] 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. Examples of the solvent include aprotic solvents, phenolic solvents, ether solvents, and carbonate solvents.

[0043] Specific examples of aprotic solvents include amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), N-methylcaprolactam, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone-based solvents such as γ-butyrolactone (GBL) and γ-valerolactone; phosphorus-containing amide-based solvents such as hexamethylphosphoric amide and hexamethylphosphine triamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and sulfolane; ketone-based solvents such as acetone, cyclohexanone, and methylcyclohexanone; amine-based solvents such as picoline and pyridine; and ester-based solvents such as 2-methoxy-1-methylethyl acetate.

[0044] Specific examples of phenol-based solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol. Specific examples of ether solvents include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, and 1,4-dioxane. Specific examples of carbonate solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate. Among the above reaction solvents, aprotic solvents are preferred, amide solvents and lactone solvents are more preferred, and lactone solvents are even more preferred. The above reaction solvents may be used alone or in combination of two or more.

[0045] In the imidization reaction, it is preferable to carry out the reaction while removing water generated during the production using a Dean-Stark apparatus, etc. By carrying out such an operation, it is possible to further increase the degree of polymerization and the imidization rate.

[0046] In the above imidization reaction, a known imidization catalyst can be used, such as a base catalyst or an acid catalyst. Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine (TEA), tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, and N,N-diethylaniline; and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogencarbonate, and sodium hydrogencarbonate. Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, oxybenzoic acid, terephthalic acid, benzenesulfonic acid, paratoluenesulfonic acid, naphthalenesulfonic acid, etc. The above imidization catalysts may be used alone or in combination of two or more kinds. Among the above, from the viewpoint of ease of handling, it is preferable to use a base catalyst, it is more preferable to use an organic base catalyst, and it is even more preferable to use triethylamine.

[0047] The temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C., from the viewpoints of reaction rate and suppression of gelation, etc. The reaction time is preferably 0.5 to 10 hours after the start of distillation of the produced water.

[0048] [Polyimide varnish] The polyimide varnish of the present invention is obtained by dissolving the polyimide resin of the present invention in an organic solvent. That is, the polyimide varnish of the present invention contains the polyimide resin of the present invention and an organic solvent, and the polyimide resin is dissolved in the organic solvent. The organic solvent is not particularly limited as long as it dissolves the polyimide resin. However, it is preferable to use the above-mentioned compounds as reaction solvents used in the production of the polyimide resin, either alone or in combination of two or more kinds. The polyimide varnish of the present invention may be a polyimide solution itself in which a polyimide resin obtained by a polymerization method is dissolved in a reaction solvent, or may be a polyimide solution diluted with an additional solvent.

[0049] Since the polyimide resin of the present invention has solvent solubility, it can be made into a highly concentrated varnish that is stable at room temperature. The polyimide varnish of the present invention preferably contains 5 to 40 mass %, more preferably 5 to 20 mass %, of the polyimide resin of the present invention. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, more preferably 1 to 100 Pa·s. The viscosity of the polyimide varnish is a 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, UV stabilizers, surfactants, leveling agents, defoamers, fluorescent brightening agents, crosslinking agents, polymerization initiators, and photosensitizers, as long as the additives do 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 any known method can be applied.

[0050] [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 optical isotropy, peelability and chemical resistance. The suitable physical properties of the polyimide film of the present invention are as described above under <Characteristics of polyimide resin>. The method for producing the polyimide film of the present invention is not particularly limited, and a known method can be used. For example, the polyimide varnish of the present invention is applied to a smooth support such as a glass plate, a metal plate, or a plastic plate, or formed into a film, and then organic solvents such as a reaction solvent and a dilution solvent contained in the varnish are removed by heating.

[0051] Examples of the coating method include known coating methods such as spin coating, slit coating, and blade coating, and spin coating and slit coating are preferred. Among these, slit coating is more preferred from the viewpoint of controlling intermolecular orientation and improving chemical resistance, and from the viewpoint of workability. A method for removing the organic solvent contained in the varnish by heating is preferably to evaporate the organic solvent at a temperature of 150°C or less to make it tack-free, and then to dry it at a temperature equal to or higher than the boiling point of the organic solvent used (not particularly limited, but preferably 200 to 500°C). It is also preferable to dry it in an air atmosphere or a nitrogen atmosphere. The pressure of the drying atmosphere may be reduced pressure, normal pressure, or increased pressure. The method for peeling off the polyimide film formed on the support from the support is not particularly limited, but a mechanical peel-off method, a laser lift-off method, or the like can be used.

[0052] The polyimide film of the present invention can also be produced by using a polyamic acid varnish prepared by dissolving a 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 gives the above-mentioned structural unit (A1) and a compound that gives the above-mentioned structural unit (A2), and a diamine component containing a compound that gives the above-mentioned structural unit (B1) and a compound that gives the above-mentioned structural unit (B2). The polyamic acid is imidized (dehydration ring closure) to obtain the polyimide resin of the present invention, which is the final product. 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 production of the polyimide film of the present invention, the polyamic acid varnish may be a polyamic acid solution itself obtained by subjecting a tetracarboxylic acid component and a diamine component to a polyaddition reaction in a reaction solvent, or may be a polyamic acid solution diluted with an additional solvent.

[0053] The method for producing a polyimide film using the polyamic acid varnish is not particularly limited, and a known method can be used. For example, the polyamic acid varnish is applied to a smooth support such as a glass plate, a metal plate, or a plastic plate, or formed into a film, and the organic solvent contained in the varnish, such as a reaction solvent or a dilution solvent, is removed by heating to obtain a polyamic acid film, and the polyamic acid in the polyamic acid film is imidized by heating, thereby producing a polyimide film. The heating temperature when the polyamic acid varnish is dried to obtain a polyamic acid film is preferably 50 to 120° C. The heating temperature when the polyamic acid is imidized by heating is preferably 200 to 400° C. The imidization method is not limited to thermal imidization, and chemical imidization can also be applied.

[0054] The thickness of the polyimide film of the present invention can be appropriately selected depending on the application, etc., but is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, even 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 free-standing film becomes possible. The thickness of the polyimide film can be easily controlled by adjusting the solids concentration and viscosity of the polyimide varnish.

[0055] The polyimide film of the present invention is suitably used as a film for various members such as color filters, flexible displays, semiconductor parts, optical members, etc. The polyimide film of the present invention is particularly suitably used as a substrate for image display devices such as liquid crystal displays and OLED displays. EXAMPLES

[0056] The present invention will be specifically described below with reference to examples, although the present invention is not limited to these examples in any way.

[0057] <Film properties and evaluation> The physical properties of the films obtained in the examples and comparative examples were measured by the methods shown below.

[0058] (1) Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

[0059] (2) Tensile strength, tensile modulus, and tensile elongation at break (evaluation of elongation) The tensile strength, tensile modulus and tensile elongation at break were measured in accordance with JIS K7127:1999 using a tensile tester "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd. The chuck distance was 50 mm, the test piece size was 10 mm × 70 mm, and the test speed was 20 mm / min.

[0060] (3) Glass transition temperature (Tg) Using a thermomechanical analyzer "TMA / SS6100" manufactured by Hitachi High-Tech Science Corporation, the specimen was heated to a temperature sufficient to remove the residual stress under the following conditions: sample size 2mm x 20mm, load 0.1N, and heating rate 10℃ / min in tensile mode, and then cooled to room temperature. The specimen elongation was then measured under the same conditions as in the treatment for removing the residual stress, and the point at which an inflection point in the elongation was observed was determined as the glass transition temperature.

[0061] (4) Total light transmittance and yellow index (YI) The total light transmittance and YI were measured in accordance with JIS K7136 using a color / turbidity simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.

[0062] (5) Hayes The measurements were performed in accordance with JIS K7361-1 using a color and turbidity simultaneous measuring device "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.

[0063] (6) Thickness retardation (Rth) (evaluation of optical isotropy) The thickness retardation (Rth) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The thickness retardation value was measured at a measurement wavelength of 590 nm. Rth is expressed by the following formula, where the maximum in-plane refractive index of the polyimide film is nx, the minimum is ny, the refractive index in the thickness direction is nz, and the thickness of the film is d. Rth = [{(nx + ny) / 2}-nz] × d It should be noted that Rth converted to 10 μm is Rth when the value of d is set to 10 μm.

[0064] (7) Solvent resistance (PGMEA resistance) (evaluation of chemical resistance) The polyimide film formed on the glass plate was immersed in a solvent at room temperature to check whether there was any change in the film surface. The solvent used was propylene glycol monomethyl ether acetate (PGMEA). The evaluation criteria for solvent resistance were as follows. A: There was no change on the film surface. B: The film surface was cracked or dissolved.

[0065] <Abbreviations for ingredients, etc.> The tetracarboxylic acid components and diamine components used in the examples and comparative examples, and their abbreviations, are as follows:

[0066] (Tetracarboxylic acid component) ODPA: 4,4'-oxydiphthalic anhydride (manufactured by Manac Corporation; compound represented by formula (a1)) HPMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (a2))

[0067] (Diamine component) BAPS: bis[4-(4-aminophenoxy)phenyl]sulfone (manufactured by Seika Corporation; compound represented by formula (b1a)) M-BAPS: bis[4-(3-aminophenoxy)phenyl]sulfone (manufactured by Seika Corporation; compound represented by formula (b1b) 1,3-BAC: 1,3-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (b21a)) 1,4-BAC: 1,4-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (b21b); trans ratio 40%) 1,4-BACT: 1,4-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (b21b); trans ratio 85%) 3,3'-DDS: 3,3'-diaminodiphenyl sulfone (Seika Corporation)

[0068] <Production of polyimide resin, varnish and polyimide film> Example 1 Into a 500 mL five-neck round-bottom flask equipped with a stainless steel half-moon shaped stirring blade, a nitrogen inlet tube, a Dean-Stark equipped with a cooling tube, a thermometer, and a glass end cap, 8.650 g (0.020 mol) of BAPS, 11.380 g (0.080 mol) of 1,4-BACT, and 45.710 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were placed, 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, 15.511 g (0.050 mol) of ODPA, 11.209 g (0.050 mol) of HPMDA, and 11.427 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once, and then 0.506 g of triethylamine (manufactured by Kanto Chemical Co., Ltd.) was added as an imidization catalyst, and the reaction system was heated with a mantle heater and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 190° C. and refluxed for 2 hours while adjusting the rotation speed according to the increase in viscosity. Thereafter, 187.350 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) was added so that the solid content concentration was 15% by mass, and the temperature inside the reaction system was cooled to 100° C., after which the mixture was further stirred for about 1 hour for homogenization to obtain a polyimide varnish. The resulting polyimide varnish was then applied onto a glass plate by spin coating, held on a hot plate at 80°C for 20 minutes, and then heated in an air atmosphere in a hot air dryer at 260°C for 30 minutes to evaporate the solvent and obtain a film.

[0069] Example 2 A polyimide varnish having a solid content concentration of 15% by mass was obtained in the same manner as in Example 1, except that the amount of 1,4-BACT was changed from 11.380 g (0.080 mol) to 9.958 g (0.070 mol) and the amount of BAPS was changed from 8.650 g (0.020 mol) to 12.975 g (0.030 mol). A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0070] Example 3 A polyimide varnish having a solid content concentration of 15% by mass was obtained in the same manner as in Example 1, except that the amount of 1,4-BACT was changed from 11.380 g (0.080 mol) to 8.535 g (0.060 mol) and the amount of BAPS was changed from 8.650 g (0.020 mol) to 17.300 g (0.040 mol). A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0071] Example 4 A polyimide varnish having a solid content concentration of 15 mass% was obtained in the same manner as in Example 1, except that the amount of 1,4-BACT was changed from 11.380 g (0.080 mol) to 7.113 g (0.050 mol) and the amount of BAPS was changed from 8.650 g (0.020 mol) to 21.625 g (0.050 mol). A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0072] Example 5 A polyimide varnish having a solid content concentration of 15 mass % was obtained in the same manner as in Example 4, except that 7.113 g (0.050 mol) of 1,4-BACT was changed to 7.113 g (0.050 mol) of 1,4-BAC. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0073] Example 6 A polyimide varnish having a solid content concentration of 15 mass % was obtained in the same manner as in Example 4, except that 7.113 g (0.050 mol) of 1,4-BACT was changed to 7.113 g (0.050 mol) of 1,3-BAC. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0074] Example 7 A polyimide varnish having a solid content concentration of 15 mass% was obtained in the same manner as in Example 4, except that 7.113 g (0.050 mol) of 1,4-BACT was changed to 7.713 g (0.050 mol) of bis(aminomethyl)norbornane (isomer mixture: manufactured by Tokyo Chemical Industry Co., Ltd.; compound represented by formula (b22)). A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0075] Example 8 A polyimide varnish having a solid content concentration of 15 mass % was obtained in the same manner as in Example 4, except that 21.625 g (0.050 mol) of BAPS was changed to 21.625 g (0.050 mol) of M-BAPS. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0076] Comparative Example 1 A polyimide varnish having a solid content concentration of 20 mass % was obtained in the same manner as in Example 4, except that 21.625 g (0.050 mol) of BAPS was changed to 12.415 g (0.050 mol) of 3,3'-DDS. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0077] Comparative Example 2 A polyimide varnish having a solids concentration of 20% by mass was obtained in the same manner as in Example 1, except that the amount of BAPS was changed from 8.650 g (0.020 mol) to 43.249 g (0.100 mol), the amount of HPMDA was changed from 11.209 g (0.050 mol) to 22.417 g (0.100 mol), and ODPA and 1,4-BACT were not used. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0078] Comparative Example 3 A polyimide varnish having a solids concentration of 20% by mass was obtained in the same manner as in Example 8, except that the amount of M-BAPS was changed from 21.625 g (0.050 mol) to 43.249 g (0.100 mol), the amount of HPMDA was changed from 11.209 g (0.050 mol) to 22.417 g (0.100 mol), and ODPA and 1,4-BACT were not used. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish.

[0079] The polyimide films obtained in the examples and comparative examples were subjected to the above-mentioned physical property measurements and evaluations. The results are shown in Table 1.

[0080] [Table 1]

[0081] As shown in Table 1, the polyimide films of the Examples have good optical isotropy, and are also excellent in toughness and chemical resistance. Comparative Example 1 has good optical isotropy and chemical resistance, but poor elongation. Comparative Example 2 has poor optical isotropy, chemical resistance, and elongation. Comparative Example 3 has good optical isotropy, but poor elongation and chemical resistance. Therefore, a polyimide film produced by using ODPA or HPMDA as the tetracarboxylic acid component and BAPS or M-BAPS and an alicyclic diamine such as 1,3-BAC, 1,4-BAC, or 1,4-BACT as the diamine component in combination therewith has excellent optical isotropy, chemical resistance, and elongation, and can be suitably used as a plastic substrate for liquid crystal displays, OLED displays, touch panels, and the like.

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 structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1), and at least one structural unit (B2) selected from the group consisting of a structural unit (B21) derived from a compound represented by the following formula (b21), and a structural unit (B22) derived from a compound represented by the following formula (b22): the ratio of the structural unit (A1) in the structural unit A is 30 to 90 mol %, and the ratio of the structural unit (A2) in the structural unit A is 10 to 70 mol %, A polyimide resin in which the proportion of the structural unit (B1) in the structural unit B is 5 to 80 mol %, and the proportion of the structural unit (B2) in the structural unit B is 20 to 95 mol %. 【Chemistry 1】

2. A polyimide varnish obtained by dissolving the polyimide resin according to claim 1 in an organic solvent.

3. A polyimide film comprising the polyimide resin according to claim 1.

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