Polyimide resin

Abstract

This polyimide resin has structural units A each derived from a tetracarboxylic dianhydride and structural units B each derived from a diamine. The structural units A include a structural unit (A1) derived from a compound represented by formula (a1) and a structural unit (A2) derived from a compound represented by formula (a2). The structural units B include a structural unit (B1) derived from a compound represented by formula (b1). The proportion of the structural unit (A2) in the structural units A is 27 mol% or less. The polyimide resin does not include a structural element (c). (In formula (c), X represents a fluorine atom, a hydrogen atom, or a carbon atom.)

Description

Polyimide resin

[0001] The present invention relates to a polyimide resin.

[0002] Polyimide resins are generally obtained by polycondensation of aromatic tetracarboxylic acid anhydrides and aromatic diamines. Due to their structure, polyimide resins possess molecular rigidity, resonance stabilization, and strong chemical bonds. Therefore, polyimide resins have excellent heat resistance, chemical resistance, mechanical properties, and electrical characteristics, and are widely used in fields such as molding materials, composite materials, electrical and electronic components, optical materials, displays, and aerospace. In recent years, polyimides have increasingly been used as materials for image display devices, among other optical and electronic materials, and properties such as colorless transparency and solvent solubility of polyimide resins have become increasingly important. However, conventional polyimides often have problems, such as high haze values ​​and yellow indexes (YI). To address this problem, Patent Document 1, for example, proposes a film comprising a fluorinated polyimide layer having a total haze value of 4 or less, a yellow index of 3 or less, and a total light transmittance of 90% or more.

[0003] JP 2016-027146 A

[0004] Fluorinated polyimides can improve colorlessness and transparency and can improve solubility, but some compounds belonging to the group of perfluoroalkyl compounds and polyfluoroalkyl compounds (PFAS; perfluoroalkyl substances and polyfluoroalkyl substances) are restricted substances in the European REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) regulations due to concerns about environmental impact and health hazards, and these regulations are expected to become stricter in the future. Against this background, the use of perfluoroalkyl compounds and polyfluoroalkyl compounds in electronic components may be restricted. If transparency is simply to be improved, it can also be improved by using aliphatic raw materials, alicyclic raw materials, etc. However, the mechanical properties are reduced, making it difficult to achieve both transparency and mechanical properties in polyimide resins, and a polyimide resin that is excellent in both transparency and mechanical properties without falling under the category of PFAS has been sought. The present invention has been made in view of this situation, and an object of the present invention is to provide a polyimide resin that is excellent in transparency, has a high elastic modulus and high strength, is also excellent in elongation, and is soluble in solvents. In particular, an object of the present invention is to provide a polyimide resin that has the above properties without containing a perfluoroalkyl structure or a polyfluoroalkyl structure.

[0005] The present inventors have discovered that a polyimide resin containing a specific combination of structural units can solve the above problems, and have completed the present invention.

[0006] That is, the present invention relates to the following items [1] to

[12] : [1] A polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein structural unit A contains a structural unit (A1) derived from a compound represented by formula (a1) below and a structural unit (A2) derived from a compound represented by formula (a2) below, and structural unit B contains a structural unit (B1) derived from a compound represented by formula (b1) below, wherein the proportion of structural unit (A2) in structural unit A is 27 mol % or less, and the polyimide resin does not contain the following structural element (c): (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.) [2] The polyimide resin according to [1] above, wherein the proportion of the structural unit (A1) in the structural unit A is 10 to 99 mol %. [3] The polyimide resin according to [1] or [2] above, wherein the molar ratio of the structural unit (A1) to the structural unit (A2) in the structural unit A [(A1) / (A2)] is 73 / 27 to 99 / 1. [4] The polyimide resin according to any one of [1] to [3] above, wherein the proportion of the structural unit (B1) in the structural unit B is 40 to 100 mol %. [5] The polyimide resin according to any one of [1] to [4] above, wherein the structural unit B further comprises at least one selected from the group consisting of a structural unit (B2) derived from a compound represented by the following formula (b2), a structural unit (B3) derived from a compound represented by the following formula (b3), a structural unit (B4) derived from a compound represented by the following formula (b4), a structural unit (B5) derived from a compound represented by the following formula (b5), and a structural unit (B6) derived from a compound represented by the following formula (b6): (In formula (b6), each R is independently a hydrogen atom or a methyl group, Y is a divalent group containing an aromatic ring and having 12 to 30 carbon atoms, and n is 0 or 1.) [6] The polyimide resin according to item [5] above, wherein the total proportion of structural units (B2), (B3), (B4), (B5), and (B6) within structural unit B is 50 mol % or less. [7] The polyimide resin according to item [5] above, wherein the molar ratio of structural unit (B1) to the total of structural units (B2), (B3), (B4), (B5), and (B6) within structural unit B, [(B1) / ((B2)+(B3)+(B4)+(B5)+(B6)], is 50 / 50 to 99 / 1. [8] The polyimide resin according to any one of [1] to [7] above, wherein the proportion of trans structures derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride contained in the structural unit (A1) is 30 mol % or more within the structural unit (A1). [9] A polyimide varnish obtained by dissolving the polyimide resin according to any one of [1] to [8] above in an organic solvent.

[10] A polyimide film comprising the polyimide resin according to any one of [1] to [8] above.

[11] The polyimide film according to

[10] above, having a thickness of 50 μm, a YI of 7.5 or less, a total light transmittance of 80% or more, a haze of 1.0% or less, a tensile elongation at break of 5% or more in a tensile test conducted under conditions of 23°C and 50% RH, with a test piece of 50 μm x 10 mm x 120 mm, a tensile speed of 20 mm / min, and a chuck distance of 50 mm, and a tensile modulus of elasticity of 3.7 GPa or more calculated as the slope of the stress-strain curve obtained by the tensile test in the section from 0.1 mm to 0.5 mm strain by the least squares method.

[12] The polyimide film according to

[10] or

[11] above, having a thickness of 5 to 100 μm.

[0007] The present invention provides a polyimide resin that is excellent in transparency, has a high modulus of elasticity and high strength, yet is also excellent in elongation, and is soluble in solvents. In particular, a polyimide resin having these properties can be provided without containing a perfluoroalkyl structure or a polyfluoroalkyl structure. Therefore, the polyimide resin of the present invention is useful as an optical material or an electronic material, particularly as a display material.

[0008] [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, wherein the structural unit A contains 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 contains a structural unit (B1) derived from a compound represented by the following formula (b1), the proportion of the structural unit (A2) in the structural unit A is 27 mol % or less, and the polyimide resin does not contain the following structural element (c): The polyimide resin of the present invention has excellent transparency, a high elastic modulus and high strength, and also excellent elongation, and is soluble in a solvent. (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.)

[0009] The reasons why the polyimide resin of the present invention has excellent transparency, a high modulus of elasticity and high strength, yet excellent elongation, and is soluble in solvents are not clear, but are thought to be as follows: It is believed that the polyimide resin of the present invention has excellent transparency, excellent solubility, and good elongation due to the inclusion of a cyclohexane structure, which is an alicyclic structure. It is also believed that the polyimide resin of the present invention has a high modulus of elasticity, high strength, and good elongation due to the inclusion of a rigid structure, a substituted biphenyl structure. Furthermore, it is believed that the imide ring adjacent to the cyclobutane structure has good packing, and the inclusion of a small amount of this structure is thought to result in a high modulus of elasticity, high strength, and good elongation while maintaining the above-mentioned performance. From the above, it is believed that the polyimide resin of the present invention has excellent transparency, a high modulus of elasticity and high strength, yet excellent elongation, and is soluble in solvents.

[0010] <Structural Unit A> The structural unit A is a structural unit derived from a tetracarboxylic dianhydride that accounts for a proportion of 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), and the proportion of the structural unit (A2) in the structural unit A is 27 mol % or less. Furthermore, the structural unit A does not include the following structural element (c): (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.) When the structural unit A contains the structural unit (A1) and the structural unit (A2), the transparency of the polyimide resin can be improved, while the elastic modulus and strength can be increased, elongation can be improved, and solvent solubility can be improved, without including the perfluoroalkyl structure or polyfluoroalkyl structure represented by the structural element (c).

[0011] The compound represented by formula (a1) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA). By including the structural unit (A1) in the structural unit A, the transparency of the polyimide resin can be improved, and the elongation can also be improved. In addition, the solvent solubility can also be improved.

[0012] The structural unit (A1) preferably contains a trans structure derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride. The trans structure derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride refers to a structure represented by the following formula (1) in the skeleton of the polyimide resin. The structure represented by the following formula (2) is a cis structure and is not included in the trans structure. The raw material for obtaining the structure represented by formula (1) is preferably (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride, but is not limited to (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride. Raw materials other than (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride, such as (1S,2R,4S,5R)-cyclohexanetetracarboxylic dianhydride having a cis structure, may also be used. That is, the structure of formula (1) is a trans structure derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride. The proportion of trans structures derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride contained in the structural unit (A1) is preferably 30 mol% or more within the structural unit (A1). The proportion of trans structures derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride contained in the structural unit (A1) is preferably 35 to 100 mol%, more preferably 40 to 100 mol%, even more preferably 50 to 100 mol%, still more preferably 55 to 100 mol%, even more preferably 60 to 100 mol%, still more preferably 70 to 100 mol%, still more preferably 75 to 100 mol%, and still more preferably The structural unit (A1) may be composed exclusively of a trans structure derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride, and it is even more preferred that the structural unit (A1) is composed exclusively of a trans structure derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride. The structural unit (A1) containing a trans structure improves the transparency of the resulting polyimide resin and increases its modulus of elasticity and strength. In other words, the proportion of the structure of formula (1) contained in the structural unit (A1) is preferably 30 mol % or more of the structural unit (A1).The proportion of the structure of formula (1) contained in the structural unit (A1) is more preferably 35 to 100 mol%, even more preferably 40 to 100 mol%, even more preferably 50 to 100 mol%, even more preferably 55 to 100 mol%, even more preferably 60 to 100 mol%, even more preferably 70 to 100 mol%, even more preferably 75 to 100 mol%, even more preferably 80 to 100 mol%, even more preferably 85 to 100 mol%, even more preferably 90 to 100 mol%, and even more preferably 95 to 100 mol%. The structural unit (A1) may consist solely of the structure of formula (1), and it is even more preferable that the structural unit (A1) consists solely of the structure of formula (1). By including a trans structure in the structural unit (A1), the transparency of the resulting polyimide resin can be improved, and the elastic modulus and strength can be increased.

[0013] The compound represented by formula (a2) is 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA). When the structural unit A contains the structural unit (A2), the elastic modulus of the polyimide resin can be particularly increased.

[0014] The proportion of the structural unit (A2) in the structural unit A is 27 mol% or less. The proportion of the structural unit (A2) in the structural unit A is preferably 25 mol% or less, more preferably 23 mol% or less, and even more preferably 22 mol% or less. The lower limit for the proportion of the structural unit (A2) in the structural unit A is preferably 0.5 mol% or more. The proportion of the structural unit (A2) in the structural unit A is preferably 0.5 to 27 mol%, more preferably 1 to 27 mol%, even more preferably 3 to 27 mol%, still more preferably 5 to 27 mol%, even more preferably 10 to 27 mol%, still more preferably 10 to 25 mol%, even more preferably 15 to 25 mol%, still more preferably 15 to 23 mol%, and even more preferably 15 to 22 mol%. By ensuring that the proportion of the structural unit (A2) in the structural unit A is within the above range, it is possible to improve the transparency of the resulting polyimide resin, while simultaneously achieving a high modulus of elasticity and strength as well as excellent elongation.

[0015] The molar ratio of the structural unit (A1) to the structural unit (A2) in the structural unit A [(A1) / (A2)] is preferably 73 / 27 to 99 / 1, more preferably 73 / 27 to 97 / 3, even more preferably 73 / 27 to 95 / 5, still more preferably 73 / 27 to 90 / 10, still more preferably 75 / 25 to 90 / 10, still more preferably 75 / 25 to 85 / 15, still more preferably 77 / 23 to 85 / 15, and still more preferably 78 / 22 to 85 / 15. By achieving this molar ratio, it is possible to improve the transparency of the resulting polyimide resin while simultaneously achieving a high modulus of elasticity, strength, and excellent elongation.

[0016] The proportion of the structural unit (A1) in the structural unit A is preferably 99.5 mol% or less, more preferably 10 to 99.5 mol%, even more preferably 10 to 99 mol%, even more preferably 50 to 99 mol%, even more preferably 73 to 99 mol%, even more preferably 73 to 97 mol%, even more preferably 73 to 95 mol%, even more preferably 73 to 90 mol%, even more preferably 75 to 90 mol%, even more preferably 75 to 85 mol%, even more preferably 77 to 85 mol%, and even more preferably 78 to 85 mol%. By setting the proportion of the structural unit (A1) in the structural unit A within the above range, it is possible to improve the transparency of the resulting polyimide resin while achieving both high elastic modulus and strength and excellent elongation. The total proportion of the structural unit (A1) and the structural unit (A2) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and preferably 100 mol% or less. The structural unit A may be composed only of the structural unit (A1) and the structural unit (A2), and it is even more preferable that the structural unit A be composed only of the structural unit (A1) and the structural unit (A2). In other words, the total proportion of the structural unit (A1) and the structural unit (A2) in the structural unit A may be 100 mol%, and it is even more preferable that it is 100 mol%.

[0017] The structural unit A may contain a structural unit other than the structural unit (A1) and the structural unit (A2). The tetracarboxylic acid dianhydride that provides such a structural unit is not particularly limited, but examples include aromatic tetracarboxylic acid dianhydrides excluding the compounds represented by formula (a1) and excluding the compounds represented by formula (a2), alicyclic tetracarboxylic acid dianhydrides, and aliphatic tetracarboxylic acid dianhydrides.

[0018] Examples of aromatic tetracarboxylic dianhydrides other than the above compounds include 4,4'-oxydiphthalic anhydride (ODPA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), hydroquinone diphthalic anhydride (HQDEA), ethylene glycol bis(trimellitate) dianhydride (TMEG), 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (TMPBP-TME), and 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride.

[0019] Examples of alicyclic tetracarboxylic dianhydrides include cyclohexane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, 3,3',4,4'-bicyclohexyltetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, decahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic dianhydride (DNDA), 5,5'-(1,4-phenylene)-bis[hexahydro-4,7-methanoisobenzofuran-1,3-dione], 5,5'-bis-2-norbol ene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5',6,6'-tetracarboxylic acid anhydride (CpODA), 2,2-propylidene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, oxy-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, bicyclo[2.2.2]octane-2,3:5,6-tetracarboxylic acid dianhydride (BODA), bicyclo[4.4.0]decane-2,3,6,7-tetracarboxylic acid dianhydride, and the like. Examples of aliphatic tetracarboxylic dianhydrides include 1,2,3,4-butanetetracarboxylic dianhydride. In this specification, aromatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more aromatic rings, alicyclic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more alicyclic rings but no aromatic rings, and aliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring. The structural unit A may optionally contain one type of structural unit, or two or more types of structural units.

[0020] <Structural Unit B> The structural unit B is a structural unit derived from a diamine contained in a polyimide resin. The structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1). In addition, the structural unit B does not include the following structural element (c). (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.)

[0021] By including the structural unit (B1) in the structural unit B, it is possible to increase the elastic modulus and strength of the polyimide resin while maintaining the transparency and solvent solubility without including the perfluoroalkyl structure or polyfluoroalkyl structure represented by the structural element (c). The compound represented by formula (b1) is 2,2'-dimethylbenzidine (mTB).

[0022] The proportion of the structural unit (B1) in the structural unit B is preferably 40 to 100 mol%, more preferably 50 to 100 mol%, even more preferably 70 to 100 mol%, still more preferably 80 to 100 mol%, even more preferably 85 to 100 mol%, and still more preferably 85 to 95 mol%. The proportion of the structural unit (B1) in the structural unit B may be 100 mol%, or the structural unit B may consist solely of the structural unit (B1).

[0023] The structural unit B may consist solely of the structural unit (B1), or may include a structural unit other than the structural unit (B1). Preferably, however, the structural unit other than the structural unit (B1) further includes at least one structural unit selected from the group consisting of a structural unit (B2) derived from a compound represented by the following formula (b2), a structural unit (B3) derived from a compound represented by the following formula (b3), a structural unit (B4) derived from a compound represented by the following formula (b4), a structural unit (B5) derived from a compound represented by the following formula (b5), and a structural unit (B6) derived from a compound represented by the following formula (b6). (In formula (b6), each R is independently a hydrogen atom or a methyl group, Y is a divalent group containing an aromatic ring and having 12 to 30 carbon atoms, and n is 0 or 1.)

[0024] The structural unit B preferably includes at least one selected from the group consisting of the structural unit (B2) derived from a compound represented by formula (b2), the structural unit (B3) derived from a compound represented by formula (b3), the structural unit (B4) derived from a compound represented by formula (b4), the structural unit (B5) derived from a compound represented by formula (b5), and the structural unit (B6) derived from a compound represented by formula (b6); more preferably, it includes at least one selected from the group consisting of the structural unit (B2) derived from a compound represented by formula (b2), the structural unit (B3) derived from a compound represented by formula (b3), and the structural unit (B6) derived from a compound represented by formula (b6); even more preferably, it includes at least one selected from the group consisting of the structural unit (B2) derived from a compound represented by formula (b2), and the structural unit (B6) derived from a compound represented by formula (b6); and even more preferably, it includes the structural unit (B6) derived from a compound represented by formula (b6).

[0025] The compound represented by formula (b2) is diaminodiphenyl sulfone. Examples of compounds represented by formula (b2) include 4,4'-diaminodiphenyl sulfone (4,4'-DDS), in which both amino groups are located at the 4-position, and 3,3'-diaminodiphenyl sulfone (3,3'-DDS), in which both amino groups are located at the 3-position, with 4,4'-diaminodiphenyl sulfone (4,4'-DDS) being preferred. When structural unit B contains structural unit (B2), the transparency of the polyimide resin can be improved.

[0026] The compound represented by formula (b3) is octafluorobenzidine (8FBZ). When the structural unit B contains the structural unit (B3), the elastic modulus and elongation of the polyimide resin can be improved.

[0027] The compound represented by formula (b4) is 2,3,5,6-tetrafluorobenzene-1,4-diamine. When the structural unit B contains the structural unit (B4), the elastic modulus and elongation of the polyimide resin can be improved.

[0028] The compound represented by formula (b5) is 2,4,5,6-tetrafluorobenzene-1,3-diamine. When the structural unit B contains the structural unit (B5), the elastic modulus and elongation of the polyimide resin can be improved.

[0029] In formula (b6), each R is independently a hydrogen atom or a methyl group, Y is a divalent group containing an aromatic ring and having 12 to 30 carbon atoms, and n is 0 or 1. Each R is independently a hydrogen atom or a methyl group, but is preferably a hydrogen atom, and more preferably both R are hydrogen atoms. n is 0 or 1, and preferably 0. In formula (b6), when both R are hydrogen atoms and n is 0, the compound represented by formula (b6) is 4,4'-diaminobenzanilide (DABA). By including a structural unit B derived from 4,4'-diaminobenzanilide (DABA) from the structural unit (B6), it is possible to improve the transparency and elongation of the polyimide resin while maintaining its high elastic modulus and strength.

[0030] In formula (b6), when n is 1, the compound represented by formula (b6) contains Y, which is a divalent group having 12 to 30 carbon atoms. Y is a divalent group containing an aromatic ring and having 12 to 30 carbon atoms, and is preferably a divalent group containing an aromatic ring and having 12 to 26 carbon atoms. Among the compounds represented by formula (b6), preferred compounds when n is 1 include compounds represented by the following formula (b61), compounds represented by the following formula (b62), compounds represented by the following formula (b63), and compounds represented by the following formula (b64). The compound represented by formula (b6) is preferably at least one selected from the group consisting of a compound represented by the following formula (b61), a compound represented by the following formula (b62), a compound represented by the following formula (b63), and a compound represented by the following formula (b64), more preferably at least one selected from the group consisting of a compound represented by the following formula (b61), a compound represented by the following formula (b62), and a compound represented by the following formula (b63), even more preferably at least one selected from the group consisting of a compound represented by the following formula (b61) and a compound represented by the following formula (b63), and still more preferably a compound represented by formula (b61).

[0031] The compound represented by formula (b61) is N,N'-(2,2'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis[4-amino-3-methylbenzamide] (AMB-mTOL). When the structural unit B contains a structural unit derived from the compound represented by formula (b61) among the structural units (B6), the transparency and elongation of the polyimide resin can be improved while maintaining a high elastic modulus and strength. The compound represented by formula (b62) is N,N'-[(octahydro-1,3,5,7-tetraoxobenzo[1,2-c:4,5-c']dipyrrole-2,6(1H,3H)-diyl)bis(3-methoxy-4,1-phenylene)]bis[4-amino-benzamide] (AB-MP-HPMDI). When the structural unit B contains a structural unit derived from the compound represented by formula (b62) among the structural units (B6), it is possible to improve the transparency and elongation of the polyimide resin while maintaining its high elastic modulus and strength. The compound represented by formula (b63) is N,N'-(2,2'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis[4-amino-benzamide] (AB-mTOL). When the structural unit B contains a structural unit derived from the compound represented by formula (b63) among the structural units (B6), it is possible to improve the transparency and elongation of the polyimide resin while maintaining its high elastic modulus and strength. The compound represented by formula (b64) is N,N'-(oxydi-4,1-phenylene)bis[4-amino-benzamide] (AB-44ODA). When the structural unit B contains a structural unit derived from the compound represented by formula (b64) among the structural units (B6), it is possible to improve the transparency and elongation of the polyimide resin while maintaining its high elastic modulus and strength. As described above, by including the structural unit (B6) in the structural unit B, it is possible to improve the transparency and elongation of the polyimide resin while maintaining the high elastic modulus and strength of the polyimide resin.

[0032] The total ratio of the structural units (B2), (B3), (B4), (B5), and (B6) in the structural unit B is preferably 50 mol% or less. The total ratio of the structural units (B2), (B3), (B4), (B5), and (B6) in the structural unit B is more preferably 1 to 50 mol%, even more preferably 1 to 40 mol%, even more preferably 1 to 30 mol%, even more preferably 3 to 25 mol%, even more preferably 3 to 20 mol%, even more preferably 5 to 20 mol%, and even more preferably 5 to 15 mol%. By setting the total ratio of the structural units (B2), (B3), (B4), (B5), and (B6) in the structural unit B within the above range, the transparency and elongation of the resulting polyimide resin can be improved while maintaining a high elastic modulus and strength.

[0033] Within the structural unit B, the molar ratio of the structural unit (B1) to the total of the structural units (B2), (B3), (B4), (B5), and (B6) [(B1) / ((B2)+(B3)+(B4)+(B5)+(B6))] is preferably 50 / 50 to 99 / 1, more preferably 60 / 40 to 99 / 1, even more preferably 70 / 30 to 99 / 1, still more preferably 75 / 25 to 97 / 3, even more preferably 80 / 20 to 97 / 3, still more preferably 80 / 20 to 95 / 5, and still more preferably 85 / 15 to 95 / 5. By ensuring that the molar ratio of the structural unit (B1) to the total of the structural units (B2), (B3), (B4), (B5), and (B6) in the structural unit B is within the above range, the transparency and elongation of the obtained polyimide resin can be improved while maintaining a high elastic modulus and strength.

[0034] The total proportion of the structural units (B1), (B2), (B3), (B4), (B5), and (B6) in the structural unit B is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and preferably 100 mol% or less. The structural units contained in the structural unit B may be only the structural unit (B1), the structural unit (B2), the structural unit (B3), the structural unit (B4), the structural unit (B5), and the structural unit (B6).

[0035] The structural unit B may contain structural units other than the structural unit (B1), the structural unit (B2), the structural unit (B3), the structural unit (B4), the structural unit (B5), and the structural unit (B6). Diamines that provide such structural units are not particularly limited, and examples include aromatic diamines, alicyclic diamines, and aliphatic diamines, excluding compounds represented by formula (b1), excluding compounds represented by formula (b2), excluding compounds represented by formula (b3), excluding compounds represented by formula (b4), excluding compounds represented by formula (b5), and excluding compounds represented by formula (b6).

[0036] Examples of aromatic diamines other than the above compounds include bis(4-aminophenyl)terephthalate (APTP), 1,4-bis(4-aminobenzoyloxy)benzene, 4,4'-diaminodiphenyl ether (4,4'-ODA), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (DDM), 9,9-bis(4-aminophenyl)fluorene (BAFL), 4,4'-diaminobiphenyl (benzidine), 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diaminodiphenyl sulfide, and 4,4'-diaminodiphenylmethane (DDM). benzophenone, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 5-amino-1,3,3-trimethyl-1-(4-aminophenyl)-indan (5-TMDM), 6-amino-1,3,3-trimethyl-1-(4-aminophenyl)-indan (6-TMDM), 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene (BisAM), 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene (BisAP) ), 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl (BODA), 1,1-bis[4-(4-aminophenoxy)phenyl]cyclohexane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, bis[4-(3-aminophenoxy)phenyl]ketone, biphenyl bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4-diaminobenzanilide, 4-aminophenyl 4-aminobenzoate, and 3,4-diaminobenzanilide.

[0037] Examples of alicyclic diamines include 1,3-bis(aminomethyl)cyclohexane (1,3-BAC), 1,4-bis(aminomethyl)cyclohexane, 1,3-cyclohexyldiamine, 1,4-cyclohexyldiamine, isophoronediamine, bis(aminomethyl)norbornane, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexyl ether, and 2,2-bis(4-aminocyclohexyl)propane. Examples of aliphatic diamines include ethylenediamine and hexamethylenediamine. In this specification, aromatic diamine refers to a diamine containing one or more aromatic rings, alicyclic diamine refers to a diamine containing one or more alicyclic rings but no aromatic rings, and aliphatic diamine refers to a diamine containing neither an aromatic ring nor an alicyclic ring. The structural unit optionally contained in structural unit B may be one type, or two or more types.

[0038] <Structure and Properties of Polyimide Resin> The polyimide resin of the present invention does not contain the following structural element (c). (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.)

[0039] The structural element (c) in the present invention will be explained in detail below. The structural element (c) in the polyimide resin, the production method thereof, the polyimide varnish, and the polyimide film of the present invention all have the same meaning. ２The carbon atom bonded to the group is a secondary carbon, a tertiary carbon, or a quaternary carbon, and may be a carbon atom constituting an aromatic ring, or may be substituted with a hydrogen atom or an atom other than a carbon atom. Examples of atoms other than a hydrogen atom or a carbon atom include halogen, nitrogen atom, and oxygen atom. When X is a carbon atom, the carbon atom represented by X is a primary carbon, secondary carbon, tertiary carbon, or quaternary carbon, and may be a carbon atom constituting an aromatic ring, or may be substituted with a hydrogen atom or an atom other than a carbon atom. Examples of atoms other than a hydrogen atom or a carbon atom include halogen, nitrogen atom, and oxygen atom. The structural element (c) is a perfluoroalkyl structure or a polyfluoroalkyl structure. Examples of polyimide resins containing the above structural element include polyimide resins having a structural unit derived from the following tetracarboxylic dianhydride and a structural unit derived from the following diamine. In other words, the polyimide resin of the present invention does not have any structural unit derived from the following tetracarboxylic dianhydride or any structural unit derived from the following diamine.

[0040] Examples of the tetracarboxylic dianhydride include 9,9-bis(trifluoromethyl)-9H-xanthene-2,3,6,7-tetracarboxylic dianhydride (6FCDA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA).

[0041] Examples of the diamine include 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-TFMB), 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-5,5'-diaminobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane (HFDA), 2,2-bis(3-amino-4-methylphenyl)hexafluoropropane, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP).

[0042] From the viewpoint of the mechanical strength of the resulting polyimide film, the number average molecular weight of the polyimide resin is preferably 5,000 to 300,000. The number average molecular weight of the polyimide resin can be determined, for example, by gel permeation chromatography measurement using a standard polymethyl methacrylate (PMMA) equivalent.

[0043] The polyimide resin may contain a structure other than a polyimide chain (a structure formed by imide bonding between structural unit A and structural unit B). Examples of structures other than polyimide chains that can be contained in a polyimide resin include structures containing amide bonds. However, structures other than polyimide chains do not contain structural element (c). It is preferable that the polyimide resin contains a polyimide chain (a structure formed by imide bonding between structural unit A and structural unit B) as the main structure. Therefore, the proportion of polyimide chains in the polyimide resin is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 99% by mass or more. It is also preferably 100% by mass or less. Even more preferably, the polyimide resin may be composed of only polyimide chains.

[0044] <Method for Producing Polyimide Resin> The method for producing the polyimide resin of the present invention is not particularly limited, but a method for obtaining a polyimide resin by reacting a tetracarboxylic dianhydride that provides the above-mentioned structural unit A with a diamine that provides the above-mentioned structural unit B is preferred. According to this method, a polyimide resin is obtained directly from a tetracarboxylic dianhydride and a diamine. Among these, the following production method is preferred. A preferred method for producing a polyimide resin includes a step of imidizing a tetracarboxylic dianhydride containing a compound represented by formula (a1) and a compound represented by formula (a2) with a diamine containing a compound represented by formula (b1) in the presence of a base catalyst and an organic solvent containing a lactone-based solvent. A preferred production method is described below.

[0045] (Tetracarboxylic acid dianhydride) The tetracarboxylic acid dianhydride includes a compound represented by the following formula (a1) and a compound represented by the following formula (a2): In addition, it is preferable that the tetracarboxylic acid dianhydride does not contain the following structural element (c): (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.) When the tetracarboxylic acid dianhydride contains a compound represented by formula (a1) and a compound represented by formula (a2), the transparency of the polyimide film (polyimide resin) can be improved, while the elastic modulus and strength can be increased, elongation can be improved, and solvent solubility can be improved, without containing the perfluoroalkyl structure or polyfluoroalkyl structure represented by structural element (c).

[0046] When the tetracarboxylic dianhydride contains the compound represented by formula (a1), the transparency of the polyimide film (polyimide resin) can be improved, and the elongation and solvent solubility can also be improved.

[0047] The compound represented by formula (a1) preferably contains a compound represented by the following formula (a11). The compound represented by the following formula (a11) is (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride. (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride has a trans structure. The compound represented by the following formula (a12) has a cis structure and is not included in the compounds represented by the following formula (a11). The ratio of the compound represented by formula (a1) contained in the compound represented by formula (a1) is preferably 30 mol% or more in the compound represented by formula (a1). The ratio of the compound represented by formula (a1) contained in the compound represented by formula (a1) is preferably 30 to 100 mol%, more preferably 35 to 100 mol%, even more preferably 50 to 100 mol%, even more preferably 60 to 100 mol%, even more preferably 70 to 100 mol%, even more preferably 80 to 100 mol%, even more preferably 90 to 100 mol%, even more preferably 95 to 100 mol%, and may be 100 mol%, and even more preferably 100 mol%. The compound represented by formula (a1) may consist solely of the compound represented by formula (a11), and it is even more preferable that the compound represented by formula (a1) consists solely of the compound represented by formula (a11). When the compound represented by formula (a1) contains the compound represented by formula (a11), the transparency of the obtained polyimide film (polyimide resin) can be improved and the elastic modulus can be increased. Note that even when only the compound represented by formula (a12) is used as the compound represented by formula (a1), a trans structure can be introduced into the obtained polyimide resin depending on the production conditions, but using the compound represented by formula (a11) is preferable because it can more reliably introduce a trans structure into the obtained polyimide resin.

[0048] When the tetracarboxylic dianhydride contains the compound represented by formula (a2), the elastic modulus of the polyimide film (polyimide resin) can be particularly increased.

[0049] The ratio of the compound represented by formula (a2) in the tetracarboxylic dianhydride is preferably 27 mol% or less. The ratio of the compound represented by formula (a2) in the tetracarboxylic dianhydride is more preferably 25 mol% or less, more preferably 23 mol% or less, and even more preferably 22 mol% or less. The lower limit of the ratio of the compound represented by formula (a2) in the tetracarboxylic dianhydride is preferably 0.5 mol% or more. The ratio of the compound represented by formula (a2) in the tetracarboxylic dianhydride is preferably 0.5 to 27 mol%, more preferably 1 to 27 mol%, even more preferably 3 to 27 mol%, still more preferably 5 to 27 mol%, even more preferably 10 to 27 mol%, still more preferably 10 to 25 mol%, still more preferably 15 to 25 mol%, still more preferably 15 to 23 mol%, and even more preferably 15 to 22 mol%. By setting the ratio of the compound represented by formula (a2) in the tetracarboxylic dianhydride within the above range, it is possible to improve the transparency of the resulting polyimide film (polyimide resin), while simultaneously achieving high elastic modulus and strength as well as excellent elongation.

[0050] The molar ratio of the compound represented by formula (a1) to the compound represented by formula (a2) in the tetracarboxylic dianhydride [(a1) / (a2)] is preferably 73 / 27 to 99 / 1, more preferably 73 / 27 to 97 / 3, even more preferably 73 / 27 to 95 / 5, still more preferably 73 / 27 to 90 / 10, still more preferably 75 / 25 to 90 / 10, still more preferably 75 / 25 to 85 / 15, still more preferably 77 / 23 to 85 / 15, and still more preferably 78 / 22 to 85 / 15. By setting the molar ratio within this range, it is possible to improve the transparency of the resulting polyimide resin while simultaneously achieving high elastic modulus, strength, and excellent elongation.

[0051] The ratio of the compound represented by formula (a1) in the tetracarboxylic dianhydride is preferably 99.5 mol% or less, more preferably 10 to 99.5 mol%, even more preferably 10 to 99 mol%, still more preferably 50 to 99 mol%, still more preferably 73 to 99 mol%, even more preferably 73 to 97 mol%, still more preferably 73 to 95 mol%, still more preferably 73 to 90 mol%, still more preferably 75 to 90 mol%, still more preferably 75 to 85 mol%, still more preferably 77 to 85 mol%, and still more preferably 78 to 85 mol%. By setting the ratio of the compound represented by formula (a1) in the tetracarboxylic dianhydride within the above range, the transparency of the resulting polyimide resin can be improved, while achieving both high elastic modulus and strength and excellent elongation. The total ratio of the compound represented by formula (a1) and the compound represented by formula (a2) in the tetracarboxylic acid dianhydride is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 90 mol % or more, and preferably 100 mol % or less. The tetracarboxylic acid dianhydride may consist only of the compound represented by formula (a1) and the compound represented by formula (a2), and it is preferred that the tetracarboxylic acid dianhydride consist only of the compound represented by formula (a1) and the compound represented by formula (a2).

[0052] The tetracarboxylic acid dianhydride may include a tetracarboxylic acid dianhydride other than the compound represented by formula (a1) and the compound represented by formula (a2). Such a tetracarboxylic acid dianhydride is not particularly limited, but examples thereof include aromatic tetracarboxylic acid dianhydrides excluding the compound represented by formula (a1) and the compound represented by formula (a2), alicyclic tetracarboxylic acid dianhydrides, and aliphatic tetracarboxylic acid dianhydrides.

[0053] Examples of aromatic tetracarboxylic dianhydrides other than the above compounds include 4,4'-oxydiphthalic anhydride (ODPA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), hydroquinone diphthalic anhydride (HQDEA), ethylene glycol bis(trimellitate) dianhydride (TMEG), 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (TMPBP-TME), and 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride.

[0054] Examples of alicyclic tetracarboxylic dianhydrides include cyclohexane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, 3,3',4,4'-bicyclohexyltetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, decahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic dianhydride (DNDA), 5,5'-(1,4-phenylene)-bis[hexahydro-4,7-methanoisobenzofuran-1,3-dione], 5,5'-bis-2-norbol ene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5',6,6'-tetracarboxylic acid anhydride (CpODA), 2,2-propylidene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, oxy-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, bicyclo[2.2.2]octane-2,3:5,6-tetracarboxylic acid dianhydride (BODA), bicyclo[4.4.0]decane-2,3,6,7-tetracarboxylic acid dianhydride, and the like. Examples of aliphatic tetracarboxylic dianhydrides include 1,2,3,4-butanetetracarboxylic dianhydride. In this specification, aromatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more aromatic rings, alicyclic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more alicyclic rings but no aromatic rings, and aliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring. The optionally contained tetracarboxylic dianhydride may be one type or two or more types.

[0055] (Diamine) The diamine contains a structural unit (B1) derived from a compound represented by the following formula (b1): Furthermore, it is preferable that the diamine does not contain the following structural element (c). (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.)

[0056] When the diamine contains a compound represented by formula (b1), the polyimide resin can have an increased elastic modulus and strength while maintaining its transparency and solvent solubility, without containing a perfluoroalkyl structure or polyfluoroalkyl structure represented by the structural element (c).

[0057] The ratio of the compound represented by formula (b1) in the diamine is preferably 40 to 100 mol%, more preferably 50 to 100 mol%, even more preferably 70 to 100 mol%, still more preferably 80 to 100 mol%, even more preferably 85 to 100 mol%, and still more preferably 85 to 95 mol%. The diamine may consist solely of the compound represented by formula (b1).

[0058] The diamine may consist solely of the compound represented by formula (b1), or may contain a diamine other than the compound represented by formula (b1). Preferably, the diamine other than the compound represented by formula (b1) further contains at least one selected from the group consisting of a compound represented by the following formula (b2), a compound represented by the following formula (b3), a compound represented by the following formula (b4), a compound represented by the following formula (b5), and a compound represented by the following formula (b6). (In formula (b6), each R is independently a hydrogen atom or a methyl group, Y is a divalent group containing an aromatic ring and having 12 to 30 carbon atoms, and n is 0 or 1.)

[0059] The diamine preferably includes at least one selected from the group consisting of a compound represented by formula (b2), a compound represented by formula (b3), a compound represented by formula (b4), a compound represented by formula (b5), and a compound represented by formula (b6); more preferably, it includes at least one selected from the group consisting of a compound represented by formula (b2), a structural unit (B3) derived from a compound represented by formula (b3) below, and a compound represented by formula (b6); even more preferably, it includes at least one selected from the group consisting of a compound represented by formula (b2) and a compound represented by formula (b6); and even more preferably, it includes a compound represented by formula (b6).

[0060] Examples of the compound represented by formula (b2) include 4,4'-diaminodiphenyl sulfone (4,4'-DDS) in which both amino groups are located at the 4-position, and 3,3'-diaminodiphenyl sulfone (3,3'-DDS) in which both amino groups are located at the 3-position, with 4,4'-diaminodiphenyl sulfone (4,4'-DDS) being preferred. When the diamine contains the compound represented by formula (b2), the transparency of the polyimide resin can be improved.

[0061] When the diamine contains the compound represented by formula (b3), the elastic modulus, strength and elongation of the polyimide resin can be improved.

[0062] When the diamine contains the compound represented by formula (b4), the elastic modulus, strength, and elongation of the polyimide resin can be improved.

[0063] When the diamine contains the compound represented by formula (b5), the elastic modulus, strength, and elongation of the polyimide resin can be improved.

[0064] In formula (b6), R is independently a hydrogen atom or a methyl group, Y is a divalent group containing an aromatic ring and having 12 to 30 carbon atoms, and n is 0 or 1. R is independently a hydrogen atom or a methyl group, preferably a hydrogen atom, and more preferably both R are hydrogen atoms. n is 0 or 1, and preferably 0. In formula (b6), when both R are hydrogen atoms and n is 0, the compound represented by formula (b6) is 4,4'-diaminobenzanilide (DABA). When the diamine contains a structural unit derived from 4,4'-diaminobenzanilide (DABA) among the compounds represented by formula (b6), it is possible to improve the colorless transparency and elongation while maintaining the high elastic modulus and strength of the polyimide resin.

[0065] In formula (b6), when n is 1, the compound represented by formula (b6) contains Y, which is a divalent group having 12 to 30 carbon atoms. Y is a divalent group containing an aromatic ring and having 12 to 30 carbon atoms, and is preferably a divalent group containing an aromatic ring and having 12 to 26 carbon atoms. Among the compounds represented by formula (b6), preferred compounds when n is 1 include compounds represented by the following formula (b61), compounds represented by the following formula (b62), compounds represented by the following formula (b63), and compounds represented by the following formula (b64). The compound represented by formula (b6) is preferably at least one selected from the group consisting of a compound represented by the following formula (b61), a compound represented by the following formula (b62), a compound represented by the following formula (b63), and a compound represented by the following formula (b64), more preferably at least one selected from the group consisting of a compound represented by the following formula (b61), a compound represented by the following formula (b62), and a compound represented by the following formula (b63), even more preferably at least one selected from the group consisting of a compound represented by the following formula (b61) and a compound represented by the following formula (b63), and still more preferably a compound represented by formula (b61).

[0066] The compound represented by formula (b61) is N,N'-(2,2'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis[4-amino-3-methylbenzamide] (AMB-mTOL). When the diamine contains a compound represented by formula (b61), the transparency and elongation of the polyimide resin can be improved while maintaining a high elastic modulus and strength. The compound represented by formula (b62) is N,N'-[(octahydro-1,3,5,7-tetraoxobenzo[1,2-c:4,5-c']dipyrrole-2,6(1H,3H)-diyl)bis(3-methoxy-4,1-phenylene)]bis[4-amino-benzamide] (AB-MP-HPMDI). When the diamine contains a compound represented by formula (b62), the transparency and elongation of the polyimide resin can be improved while maintaining a high elastic modulus and strength. The compound represented by formula (b63) is N,N'-(2,2'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis[4-amino-benzamide] (AB-mTOL). When the diamine contains a compound represented by formula (b63), the transparency and elongation of the polyimide resin can be improved while maintaining a high elastic modulus and strength. The compound represented by formula (b64) is N,N'-(oxydi-4,1-phenylene)bis[4-amino-benzamide] (AB-44ODA). When the diamine contains a compound represented by formula (b64), the transparency and elongation of the polyimide resin can be improved while maintaining a high elastic modulus and strength. As described above, when the diamine contains a compound represented by formula (b6), the transparency and elongation of the polyimide resin can be improved while maintaining a high elastic modulus and strength.

[0067] The total ratio of the compounds represented by formula (b2), (b3), (b4), (b5), and (b6) in the diamine is preferably 50 mol% or less. The total ratio of the compounds represented by formula (b2), (b3), (b4), (b5), and (b6) in the diamine is more preferably 1 to 50 mol%, even more preferably 1 to 40 mol%, still more preferably 1 to 30 mol%, still more preferably 3 to 25 mol%, still more preferably 3 to 20 mol%, still more preferably 5 to 20 mol%, and still more preferably 5 to 15 mol%. By setting the total ratio of the compound represented by formula (b2), the compound represented by formula (b3), the compound represented by formula (b4), the compound represented by formula (b5), and the compound represented by formula (b6) in the diamine within the above range, it is possible to improve the transparency and elongation of the obtained polyimide resin while maintaining high elastic modulus and strength.

[0068] In the diamine, the molar ratio of the compound represented by formula (b1) to the total of the compound represented by formula (b2), the compound represented by formula (b3), the compound represented by formula (b4), the compound represented by formula (b5), and the compound represented by formula (b6) [(b1) / ((b2)+(b3)+(b4)+(b5)+(b6))] is preferably 50 / 50 to 99 / 1, more preferably 60 / 40 to 99 / 1, even more preferably 70 / 30 to 99 / 1, still more preferably 75 / 25 to 97 / 3, still more preferably 80 / 20 to 97 / 3, still more preferably 80 / 20 to 95 / 5, and still more preferably 85 / 15 to 95 / 5. By setting the molar ratio of the compound represented by formula (b1) to the total of the compounds represented by formula (b2), (b3), (b4), (b5), and (b6) in the diamine within the above range, it is possible to improve the transparency and elongation of the obtained polyimide resin while maintaining high elastic modulus and strength.

[0069] The total ratio of the compounds represented by formula (b1), (b2), (b3), (b4), (b5), and (b6) in the diamine is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and preferably 100 mol% or less. The diamine may consist solely of the compounds represented by formula (b1), (b2), (b3), (b4), (b5), and (b6).

[0070] The diamine may include a diamine other than the compounds represented by formula (b1), (b2), (b3), (b4), (b5), and (b6). Such diamines are not particularly limited, but include aromatic diamines, alicyclic diamines, and aliphatic diamines excluding the compounds represented by formula (b1), (b2), (b3), (b4), (b5), and (b6).

[0071] Examples of aromatic diamines other than the above compounds include bis(4-aminophenyl)terephthalate (APTP), 1,4-bis(4-aminobenzoyloxy)benzene, 4,4'-diaminodiphenyl ether (4,4'-ODA), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (DDM), 9,9-bis(4-aminophenyl)fluorene (BAFL), 4,4'-diaminobiphenyl (benzidine), 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diaminodiphenyl sulfide, and 4,4'-diaminodiphenylmethane (DDM). benzophenone, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 5-amino-1,3,3-trimethyl-1-(4-aminophenyl)-indan (5-TMDM), 6-amino-1,3,3-trimethyl-1-(4-aminophenyl)-indan (6-TMDM), 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene (BisAM), 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene (BisAP) ), 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl (BODA), 1,1-bis[4-(4-aminophenoxy)phenyl]cyclohexane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, bis[4-(3-aminophenoxy)phenyl]ketone, biphenyl bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4-diaminobenzanilide, 4-aminophenyl 4-aminobenzoate, and 3,4-diaminobenzanilide.

[0072] Examples of alicyclic diamines include 1,3-bis(aminomethyl)cyclohexane (1,3-BAC), 1,4-bis(aminomethyl)cyclohexane, 1,3-cyclohexyldiamine, 1,4-cyclohexyldiamine, isophoronediamine, bis(aminomethyl)norbornane, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexyl ether, and 2,2-bis(4-aminocyclohexyl)propane. Examples of aliphatic diamines include ethylenediamine and hexamethylenediamine. In this specification, aromatic diamine refers to a diamine containing one or more aromatic rings, alicyclic diamine refers to a diamine containing one or more alicyclic rings but no aromatic rings, and aliphatic diamine refers to a diamine containing neither an aromatic ring nor an alicyclic ring. The optionally contained diamine may be one type or two or more types.

[0073] (Base 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 bicarbonate, and sodium bicarbonate. The above base catalysts may be used alone or in combination of two or more. Of the above, from the viewpoint of handleability, organic base catalysts are more preferred, and at least one selected from the group consisting of triethylamine and triethylenediamine is even more preferred, and it is even more preferred to use both triethylamine and triethylenediamine.

[0074] The amount of the base catalyst used in this step is preferably 100 mol% or less, more preferably 1 to 100 mol%, even more preferably 1 to 60 mol%, still more preferably 5 to 60 mol%, even more preferably 10 to 60 mol%, still more preferably 30 to 60 mol%, and still more preferably 40 to 60 mol% relative to the amount of the tetracarboxylic dianhydride. In order to increase the proportion of trans structures derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride in the structural unit (A1) derived from the compound represented by formula (a1) in the resulting polyimide resin, the amount of the base catalyst used is preferably at least 30 mol% relative to the amount of the tetracarboxylic dianhydride.

[0075] The amount of triethylamine used in this step is preferably 100 mol% or less, more preferably 1 to 90 mol%, even more preferably 1 to 60 mol%, still more preferably 5 to 60 mol%, still more preferably 10 to 60 mol%, still more preferably 10 to 55 mol%, still more preferably 30 to 55 mol%, and still more preferably 40 to 55 mol%, relative to the amount of the tetracarboxylic dianhydride.

[0076] When both triethylamine and triethylenediamine are used, the amount of triethylenediamine relative to the amount of the tetracarboxylic dianhydride is preferably 50 mol % or less, more preferably 1 to 50 mol %, even more preferably 1 to 20 mol %, still more preferably 1 to 10 mol %, still more preferably 1 to 7 mol %, still more preferably 1 to 6 mol %, still more preferably 2 to 6 mol %, and still more preferably 3 to 6 mol %.

[0077] The amount of the base catalyst used in this step is preferably the same relative to the amount of diamine as the amount relative to the amount of tetracarboxylic dianhydride. Therefore, the amount of the base catalyst used in this step is preferably 100 mol% or less, more preferably 1 to 100 mol%, even more preferably 1 to 60 mol%, still more preferably 5 to 60 mol%, even more preferably 10 to 60 mol%, still more preferably 30 to 60 mol%, and still more preferably 40 to 60 mol% relative to the amounts of the tetracarboxylic dianhydride and the diamine. In order to increase the proportion of trans structures derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride in the structural unit (A1) derived from the compound represented by formula (a1) in the resulting polyimide resin, the amount of the base catalyst used is preferably at least 30 mol% or more relative to the amounts of the tetracarboxylic dianhydride and the diamine.

[0078] The amount of triethylamine used in this step is preferably 100 mol% or less, more preferably 1 to 90 mol%, even more preferably 1 to 60 mol%, still more preferably 5 to 60 mol%, still more preferably 10 to 60 mol%, still more preferably 10 to 55 mol%, still more preferably 30 to 55 mol%, and still more preferably 40 to 55 mol%, based on the amount of the tetracarboxylic dianhydride and the diamine.

[0079] When both triethylamine and triethylenediamine are used, the amount of triethylenediamine is preferably 50 mol % or less, more preferably 1 to 50 mol %, even more preferably 1 to 20 mol %, still more preferably 1 to 10 mol %, still more preferably 1 to 7 mol %, still more preferably 1 to 6 mol %, still more preferably 2 to 6 mol %, and still more preferably 3 to 6 mol % relative to the amounts of the tetracarboxylic dianhydride and the diamine. Note that "relative to the amounts of the tetracarboxylic dianhydride and the diamine" means "relative to the amount of the tetracarboxylic dianhydride and the diamine, and similarly relative to the amount of the diamine."

[0080] (Organic Solvent) The organic solvent used in the present production method preferably contains a lactone solvent. Examples of lactone solvents include γ-butyrolactone (GBL) and γ-valerolactone, with γ-butyrolactone (GBL) being preferred. The ratio of the lactone solvent contained in the organic solvent is preferably 10 to 100% by mass, more preferably 30 to 100% by mass, even more preferably 50 to 100% by mass, still more preferably 70 to 100% by mass, even more preferably 90 to 100% by mass, still more preferably 95 to 100% by mass, and even more preferably 99 to 100% by mass, relative to the total amount of organic solvent. The organic solvent may consist solely of the lactone solvent.

[0081] The organic solvent may include an organic solvent other than a lactone-based solvent, and examples of such an organic solvent include, but are not limited to, aprotic solvents other than lactone-based solvents, phenol-based solvents, and the like.

[0082] Examples of aprotic solvents other than lactone solvents include amide solvents, glycol solvents, phosphorus-containing amide solvents, sulfur-containing solvents, ketone solvents, amine solvents, ester solvents, ether solvents, and carbonate solvents. Examples of amide solvents include N,N-dimethylformamide, N,N-dimethylacetamide, N-methylcaprolactam, 1,3-dimethylimidazolidinone, tetramethylurea, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide. Examples of glycol solvents include diethylene glycol dimethyl ether, triethylene glycol, and triethylene glycol dimethyl ether. Examples of phosphorus-containing amide solvents include hexamethylphosphoric amide and hexamethylphosphine triamide. Examples of sulfur-containing solvents include dimethyl sulfone, dimethyl sulfoxide, and sulfolane. Examples of ketone solvents include acetone, cyclopentanone, cyclohexanone, and methylcyclohexanone. Examples of amine solvents include picoline and pyridine. Examples of ester solvents include 2-methoxy-1-methylethyl acetate. 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. Examples of carbonate solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate.

[0083] 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. Among the organic solvents other than the lactone-based solvents, aprotic solvents are preferred, and amide solvents are more preferred. The organic solvents listed above may be used alone or in combination.

[0084] By including an amide solvent in addition to a lactone solvent in the organic solvent, the proportion of trans structures derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride in the structural unit (A1) derived from the compound represented by formula (a1) in the resulting polyimide resin can be increased. Examples of lactone solvents include γ-butyrolactone (GBL) and γ-valerolactone, with γ-butyrolactone (GBL) being preferred. Examples of amide solvents include N,N-dimethylformamide, N,N-dimethylacetamide, N-methylcaprolactam, 1,3-dimethylimidazolidinone, tetramethylurea, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide, with N,N-dimethylacetamide being preferred.

[0085] (Imidization Conditions) The present production method includes a step of imidizing the tetracarboxylic dianhydride and the diamine in the presence of the base catalyst and the organic solvent, and the imidization reaction is preferably carried out under the following conditions.

[0086] In this step, the ratio of the amount of tetracarboxylic dianhydride to the amount of diamine charged is preferably 0.9 to 1.1 moles of diamine per mole of tetracarboxylic dianhydride.

[0087] In addition to the tetracarboxylic dianhydride and diamine, a terminal blocking agent may also be used in this step. Monoamines or dicarboxylic acids are preferred as terminal blocking agents. The amount of terminal blocking agent to be introduced is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, per mol of tetracarboxylic dianhydride. Examples of monoamine terminal blocking agents include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, and 4-methylaniline, with benzylamine and aniline being preferred. Dicarboxylic acids are preferred as dicarboxylic acid terminal blocking agents, and a portion of the dicarboxylic acid 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, with phthalic acid and phthalic anhydride being preferred.

[0088] The method for reacting the tetracarboxylic dianhydride with the diamine is not particularly limited, and known methods can be used. Specific reaction methods include (1) a method in which the tetracarboxylic dianhydride, the diamine, and the organic solvent are charged into a reactor, stirred at 0 to 80°C for 0.5 to 30 hours, and then heated to carry out the imidization reaction, (2) a method in which the diamine and the organic solvent are charged into a reactor and dissolved, and then the tetracarboxylic dianhydride is charged, stirred at 0 to 80°C for 0.5 to 30 hours as needed, and then heated to carry out the imidization reaction, and (3) a method in which the tetracarboxylic dianhydride, the diamine, and the organic solvent are charged into a reactor, and immediately heated to carry out the imidization reaction.

[0089] The imidization reaction is preferably carried out while removing water generated during the production using a Dean-Stark apparatus, etc. By performing such an operation, the degree of polymerization and the imidization rate can be further increased.

[0090] The temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C., from the viewpoint of the reaction rate and suppression of gelation, etc. The reaction time is preferably 0.5 to 10 hours after the start of distillation of the produced water.

[0091] [Polyimide Varnish] The polyimide varnish of the present invention is obtained by dissolving the polyimide resin of the present invention in an organic solvent. That is, the polyimide varnish of the present invention contains the polyimide resin of the present invention and an organic solvent, and the polyimide resin is dissolved in the organic solvent. The organic solvent is not particularly limited as long as it dissolves the polyimide resin, but it is preferable to use the above-mentioned compounds as organic solvents used in the production of polyimide resins, either alone or in a mixture of two or more. The polyimide varnish of the present invention may be a solution of the polyimide resin obtained by polymerization and imidization in an organic solvent as described above, or may be a solution obtained by diluting the polyimide solution by further adding an organic solvent.

[0092] Because the polyimide resin of the present invention is solvent-soluble, 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% by mass, more preferably 8 to 30% by mass, and even more preferably 10 to 20% by 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 measured at 25°C using an E-type viscometer. The polyimide varnish of the present invention may also contain various additives, such as inorganic fillers, adhesion promoters, release agents, flame retardants, UV stabilizers, antioxidants, surfactants, leveling agents, defoamers, fluorescent brighteners, crosslinking agents, polymerization initiators, and photosensitizers, as long as the required properties of the polyimide resin and polyimide film are not impaired. The method for producing the polyimide varnish of the present invention is not particularly limited, and known methods can be used.

[0093] The organic solvent is not particularly limited as long as it dissolves the polyimide resin, but it is preferable to use the compounds described above as organic solvents used in producing the polyimide resin, either alone or in combination of two or more. Among these, at least one selected from the group consisting of lactone solvents and amide solvents is preferred, lactone solvents are more preferred, and a solvent containing both a lactone solvent and an amide solvent is even more preferred. At least one selected from the group consisting of γ-butyrolactone (GBL) and N,N-dimethylacetamide is more preferred, γ-butyrolactone (GBL) is even more preferred, and a solvent containing both γ-butyrolactone (GBL) and N,N-dimethylacetamide is even more preferred. The inclusion of such a solvent improves the solubility and coatability of the polyimide resin. The organic solvent contained in the polyimide varnish may contain only γ-butyrolactone, but the polyimide varnish preferably contains γ-butyrolactone in an amount of 20% by mass or more, more preferably 20 to 90% by mass, even more preferably 20 to 70% by mass, even more preferably 20 to 60% by mass, even more preferably 20 to 50% by mass, even more preferably 30 to 50% by mass, even more preferably 30 to 45% by mass, based on the total amount of the polyimide varnish. Furthermore, the organic solvent contained in the polyimide varnish preferably contains γ-butyrolactone in an amount of 30% by mass or more, more preferably 30 to 95% by mass, even more preferably 30 to 80% by mass, even more preferably 30 to 70% by mass, even more preferably 35 to 60% by mass, even more preferably 35 to 50% by mass.

[0094] The polyimide varnish preferably contains an amide solvent in an amount of 1% by mass or more, more preferably 5 to 70% by mass, even more preferably 20 to 70% by mass, even more preferably 25 to 70% by mass, even more preferably 35 to 70% by mass, even more preferably 35 to 60% by mass, and even more preferably 40 to 60% by mass, based on the total amount of the polyimide varnish. Furthermore, the organic solvent contained in the polyimide varnish preferably contains an amide solvent in an amount of 1% by mass or more, more preferably 5 to 70% by mass, even more preferably 20 to 70% by mass, even more preferably 30 to 70% by mass, even more preferably 40 to 65% by mass, and even more preferably 50 to 65% by mass, based on the total amount of the organic solvent.

[0095] [Polyimide Film] The polyimide film of the present invention contains the polyimide resin described above. Therefore, the polyimide film of the present invention does not contain a perfluoroalkyl structure or a polyfluoroalkyl structure, and is excellent in colorless transparency, high elastic modulus, and elongation.

[0096] The polyimide film of the present invention preferably has the following physical properties: when made 50 μm thick, the polyimide film of the present invention preferably has a YI of 7.5 or less, a total light transmittance of 80% or more, a haze of 1.0% or less, a tensile elongation at break of 5% or more in a tensile test conducted under conditions of 23°C and 50% RH, with a test piece of 50 μm x 10 mm x 120 mm, a tensile speed of 20 mm / min, and a chuck distance of 50 mm, and a tensile modulus of elasticity of 3.7 GPa or more, calculated as the slope of the stress-strain curve obtained from the tensile test by the least squares method in the section from 0.1 mm to 0.5 mm strain. These properties will be explained in more detail below.

[0097] When the thickness is 50 μm, the YI is preferably 7.5 or less, more preferably 7.2 or less, even more preferably 5.0 or less, still more preferably 4.0 or less, and even more preferably 3.0 or less.

[0098] The total light transmittance when the thickness is 50 μm is preferably 80% or more, more preferably 85% or more, even more preferably 86% or more, still more preferably 87% or more, and still more preferably 88% or more.

[0099] The haze when the thickness is 50 μm is preferably 1.0% or less, more preferably 0.9% or less, even more preferably 0.6% or less, still more preferably 0.5% or less, and even more preferably 0.4% or less.

[0100] The tensile elongation at break in a tensile test conducted under conditions of an environment of 23°C and 50% RH, a test piece of 50 μm × 10 mm × 120 mm, a tensile speed of 20 mm / min, and a chuck distance of 50 mm is preferably 5% or more, more preferably 6% or more, even more preferably 7% or more, still more preferably 8% or more, still more preferably 9% or more, still more preferably 10% or more, and still more preferably 11% or more.

[0101] The tensile modulus, calculated as the slope of the least squares method in the section from 0.1 mm to 0.5 mm of strain in a stress-strain curve obtained by a tensile test performed under conditions of 23°C, 50% RH, a test piece of 50 μm × 10 mm × 120 mm, a tensile speed of 20 mm / min, and a chuck distance of 50 mm, is preferably 3.7 GPa or more, more preferably 3.8 GPa or more, even more preferably 3.9 GPa or more, and still more preferably 4.0 GPa or more. The above-mentioned physical property values ​​in the present invention can be specifically measured by the methods described in the Examples.

[0102] The polyimide film of the present invention contains the polyimide resin described above, but does not contain a perfluoroalkyl or polyfluoroalkyl structure, and has excellent colorless transparency, a high elastic modulus, and excellent elongation. Therefore, the polyimide film of the present invention is suitable for use as an optical material or an electronic material, particularly as a display material.

[0103] The thickness of the polyimide film of the present invention is not particularly limited, but is preferably 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 film thickness is within the above range, it can be suitably used as an optical material or electronic material, particularly as a display material. The thickness of the polyimide film can be easily controlled by adjusting the solids concentration and viscosity of the varnish.

[0104] <Method for Producing Polyimide Film> 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 film can be obtained by applying a polyimide varnish to a support and drying the applied film. Among these methods, the following production method is preferred. That is, a preferred method for producing a polyimide film includes a coating step of applying the polyimide varnish to a support to obtain a coating film, a primary drying step of drying the coating film and peeling it from the support to obtain a self-supporting film, and a secondary drying step of drying the self-supporting film at 210°C or higher, preferably 220°C or higher.

[0105] The coating step is a step of applying a polyimide varnish onto a support to obtain a coating film. The support is preferably a glass plate, metal plate, metal drum, metal belt, or plastic film having a smooth surface, with a glass plate or plastic film being more preferred. From the viewpoint of improving productivity, it is preferable to use an endless support such as a metal drum or metal belt, or a long plastic film, as the support, and produce a polyimide film by a roll-to-roll method. Examples of coating methods include known coating methods such as spin coating, slit coating, blade coating, and die coating. A glass rod or coater may also be used. The coating thickness is preferably 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, in terms of the thickness of the polyimide film after drying. If necessary, a release agent may be applied to the surface of the support in advance.

[0106] The primary drying step is a step of drying the coating film and peeling it off from the support to obtain a self-supporting film. Primary drying is a step of removing a portion of the organic solvent to obtain a self-supporting film, and the organic solvent is removed by heating the coating film on the support. The temperature during organic solvent removal is preferably 50 to 140°C, more preferably 50 to 120°C. To prevent prolonged heating, the temperature may be gradually increased. In this case, the first temperature is preferably 50 to 90°C, more preferably 50 to 70°C. The final temperature is preferably 80 to 140°C, more preferably 90 to 120°C. The organic solvent is preferably removed under a nitrogen atmosphere. The organic solvent may be removed under reduced pressure, normal pressure, or increased pressure. The resulting film is peeled off from the support. The film after peeling is self-supporting.

[0107] The secondary drying step is a step of drying the self-supporting film at 210°C or higher. The edges of the self-supporting film obtained in the previous step are fixed and dried at 210°C or higher. The secondary drying temperature is preferably 210 to 300°C, more preferably 210 to 280°C, even more preferably 210 to 260°C, even more preferably 220 to 260°C, and even more preferably 220 to 240°C. By setting the secondary drying temperature within the above range, the elastic modulus can be increased, and colorless transparency and a high elastic modulus can be achieved at the same time. Secondary drying is preferably performed under a nitrogen atmosphere. Secondary drying may be performed under reduced pressure, normal pressure, or increased pressure. The secondary drying time can be adjusted appropriately depending on the temperature, but is preferably 3 to 60 minutes, more preferably 5 to 60 minutes, even more preferably 5 to 30 minutes, and even more preferably 5 to 20 minutes. From the viewpoint of further improving colorless transparency, the drying time is preferably 3 to 30 minutes, more preferably 3 to 20 minutes, even more preferably 3 to 15 minutes, and even more preferably 5 to 15 minutes. On the other hand, from the viewpoint of further improving the elastic modulus, the drying time is more preferably 10 to 50 minutes, even more preferably 15 to 40 minutes, and even more preferably 17 to 28 minutes. After secondary drying, the film is cooled, but annealing may also be performed.

[0108] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples in any way.

[0109] [Structure of Polyimide Resin] The structure of the polyimide resins obtained in the examples and comparative examples was analyzed by the following method.

[0110] (1) Ratio of trans structure derived from cyclohexanetetracarboxylic dianhydride The ratio of trans structure derived from cyclohexanetetracarboxylic dianhydride in a polyimide resin is １ The following calculation was made by measuring the H-NMR spectrum. １ H-NMR spectrum measurement was performed using an NMR spectrophotometer (ASCEnd ＴＭMeasurement was performed using a polyimide resin solution in deuterated dimethyl sulfoxide (Bruker Corporation No. 500). The ratio of trans-type structures derived from cyclohexanetetracarboxylic dianhydride was calculated from the integral value of the peak derived from the cyclohexanetetracarboxylic acid moiety shown below.

[0111] １ H NMR (DMSO-d ６ A = integrated value of the peak in the range of δ 2.179 ppm to δ 2.279 ppm (trans-cyclohexanetetracarboxylic acid protons (3-position, 6-position), 4H) B = integrated value of the peak in the range of δ 2.279 ppm to δ 2.391 ppm (cis-cyclohexanetetracarboxylic acid protons (3-position, 6-position), 4H) Ratio of trans structure (mol%) = A / (A + B) × 100

[0112] [Evaluation of Polyimide Film (Polyimide Resin)] The physical properties of the polyimide films (polyimide resin) obtained in the Examples and Comparative Examples were measured and evaluated by the methods described below.

[0113] (1) Polyimide Film Thickness The thickness of the polyimide film was measured using a micrometer manufactured by Mitutoyo Corporation.

[0114] (2) Tensile Modulus, Tensile Strength, and Tensile Elongation at Break The tensile modulus, tensile strength, and tensile elongation at break were measured in accordance with JIS K7127:1999 using a tensile testing machine "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd. The chuck distance was 50 mm, the test piece size was 10 mm x 120 mm, the test speed (tensile speed) was 20 mm / min, and the measurement temperature was 23°C. The tensile modulus was calculated as the slope of the stress-strain curve obtained by the tensile test in the section from 0.1 mm to 0.5 mm strain using the least squares method. The higher the tensile modulus value, the higher the polyimide film (polyimide resin) is, and the more preferable it is. The higher the tensile strength value, the better the strength of the polyimide film (polyimide resin), and the more preferable it is. Furthermore, the higher the tensile elongation value, the better the elongation of the polyimide film (polyimide resin), and the more preferable it is.

[0115] (3) Haze, Total Light Transmittance, and Yellow Index (YI) Haze was measured in accordance with JIS K7136:2000, total light transmittance in accordance with JIS K7361-1:1997, and YI in accordance with ASTM E313-05 (D light source, 65°), all of which were measured using a color and turbidity simultaneous measuring instrument (COH7700, manufactured by Nippon Denshoku Industries Co., Ltd.). The smaller the haze value, the more excellent the transparency of the polyimide film (polyimide resin). The larger the total light transmittance value, the more excellent the transparency of the polyimide film (polyimide resin). The smaller the YI value of the polyimide film, the more excellent the colorlessness of the polyimide film (polyimide resin).

[0116] <Abbreviations for Components, etc.> The tetracarboxylic dianhydrides and diamines used in the examples and comparative examples, and their abbreviations, are as follows.

[0117] (Tetracarboxylic acid dianhydrides) HPMDA: 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride (compound represented by formula (a1), manufactured by Mitsubishi Gas Chemical Company, Inc.) CBDA: 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (compound represented by formula (a2))

[0118] (Diamines) mTB: 2,2'-dimethylbenzidine (compound represented by formula (b1), manufactured by Seika Corporation) 4,4'-DDS: 4,4'-diaminodiphenyl sulfone (compound represented by formula (b2), amino groups are both at 4-position) 3,3'-DDS: 3,3'-diaminodiphenyl sulfone (compound represented by formula (b2), amino groups are both at 3-position, manufactured by Seika Corporation) 8FBZ: octafluorobenzidine (compound represented by formula (b3)) DABA: 4,4'-diaminobenzanilide (compound represented by formula (b6), n = 0, R are both hydrogen atoms, manufactured by Seika Corporation) AMB-mTOL: N,N'-(2,2'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis[4-amino-3-methylbenzamide] (compound represented by formula (b61))

[0119] The abbreviations for the solvents and catalysts used in the examples and comparative examples are as follows: GBL: γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) DMAc: N,N-dimethylacetamide TEA: triethylamine (manufactured by Kanto Chemical Co., Ltd.) TEDA: triethylenediamine

[0120] Example 1: A 500 mL five-necked round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark condenser, a thermometer, and a glass end cap was charged with 16.938 g (0.0798 mol) of diamine mTB and 64.17 g of GBL. The mixture was stirred at 200 rpm under a nitrogen atmosphere at a system temperature of 70° C. to obtain a solution. To this solution were added 14.308 g (0.0638 mol) of tetracarboxylic dianhydrides HPMDA, 3.129 g (0.0160 mol) of CBDA, and 8.02 g of GBL all at once, followed by the addition of 4.04 g (0.0399 mol) of TEA and 0.447 g (0.0040 mol) of TEDA as imidization catalysts and GBL as solvent. The reaction system was heated using a mantle heater, and the temperature was raised to 190°C over approximately 20 minutes. While collecting the distilled components, the reaction system was maintained at 190°C and refluxed for 1 hour, yielding a solution containing a polyimide resin. DMAc was added to achieve a solids concentration of 15% by mass, and the reaction system was cooled to 50°C to obtain a polyimide varnish containing a polyimide resin. (Solvent composition (by mass) in the varnish: GBL / DMAc = 38 / 47) The resulting polyimide varnish was then applied to a PET (polyethylene terephthalate) substrate, heated on a hot plate for 20 minutes at 60°C, then heated at 80°C for 20 minutes, and then heated in a hot air dryer at 220°C for 20 minutes in an air atmosphere to evaporate the solvent, yielding a polyimide film. The film's physical properties and evaluation results are shown in Table 1.

[0121] Examples 2 to 7 and Comparative Examples 1 to 5 Polyimide varnishes containing polyimide resins were obtained in the same manner as in Example 1, except that the types and amounts of diamines and tetracarboxylic dianhydrides in Example 1 were changed to the types and amounts of diamines and tetracarboxylic dianhydrides shown in Table 1. Furthermore, polyimide films were obtained in the same manner as in Example 1. The physical properties and evaluation results of the films are shown in Table 1.

[0122]

[0123] As shown in Table 1, the polyimide resins (polyimide films) of the Examples not only have a high tensile modulus but also a high tensile strength, yet also have a high tensile elongation at break, demonstrating excellent mechanical properties. Furthermore, the polyimide resins (polyimide films) of the Examples are particularly excellent in haze, and in addition, have a high total light transmittance. This demonstrates that the polyimide resins of the present invention are excellent in transparency, have high modulus and strength, and also excel in elongation. Furthermore, since the polyimide resins of the present invention are dissolved in a solvent as a varnish, they are soluble in the solvent. In particular, the polyimide resins of the present invention possess the above properties despite not containing a perfluoroalkyl structure or a polyfluoroalkyl structure.

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 structural unit A comprises a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from a compound represented by the following formula (a2), structural unit B comprises a structural unit (B1) derived from a compound represented by the following formula (b1), the ratio of structural unit (A2) in structural unit A is 27 mol % or less, and the polyimide resin does not contain the following structural element (c). (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.) 2. The polyimide resin according to claim 1, wherein the ratio of the structural unit (A1) in the structural unit A is 10 to 99 mol %.

3. The polyimide resin according to claim 1 or 2, wherein the molar ratio of the structural unit (A1) to the structural unit (A2) in the structural unit A [(A1) / (A2)] is from 73 / 27 to 99 / 1.

4. The polyimide resin according to any one of claims 1 to 3, wherein the ratio of the structural unit (B1) in the structural unit B is 40 to 100 mol %.

5. The polyimide resin according to any one of claims 1 to 4, wherein the structural unit B further comprises at least one selected from the group consisting of a structural unit (B2) derived from a compound represented by the following formula (b2), a structural unit (B3) derived from a compound represented by the following formula (b3), a structural unit (B4) derived from a compound represented by the following formula (b4), a structural unit (B5) derived from a compound represented by the following formula (b5), and a structural unit (B6) derived from a compound represented by the following formula (b6): (In formula (b6), each R is independently a hydrogen atom or a methyl group, Y is a divalent group containing an aromatic ring and having 12 to 30 carbon atoms, and n is 0 or 1.) 6. The polyimide resin according to claim 5, wherein the total ratio of the structural units (B2), (B3), (B4), (B5) and (B6) in the structural unit B is 50 mol % or less.

7. The polyimide resin according to claim 5 or 6, wherein in the structural unit B, the molar ratio of the structural unit (B1) to the total of the structural units (B2), (B3), (B4), (B5) and (B6) [(B1) / ((B2)+(B3)+(B4)+(B5)+(B6)] is 50 / 50 to 99 / 1.

8. The polyimide resin according to any one of claims 1 to 7, wherein the ratio of trans structures derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride contained in the structural unit (A1) is 30 mol % or more in the structural unit (A1).

9. A polyimide varnish obtained by dissolving the polyimide resin according to any one of claims 1 to 8 in an organic solvent.

10. A polyimide film comprising the polyimide resin according to any one of claims 1 to 8.

11. The polyimide film according to claim 10, wherein, when the film has a thickness of 50 μm, the YI is 7.5 or less, the total light transmittance is 80% or more, the haze is 1.0% or less, the tensile elongation at break is 5% or more in a tensile test performed under conditions of 23°C, 50% RH, a test piece of 50 μm × 10 mm × 120 mm, a tensile speed of 20 mm / min, and a chuck distance of 50 mm, and the tensile modulus of elasticity calculated as the slope of the stress-strain curve obtained by the tensile test in the section from 0.1 mm to 0.5 mm strain by the least squares method is 3.7 GPa or more.

12. The polyimide film according to claim 10 or 11, which has a thickness of 5 to 100 μm.

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