Method for producing polyimide varnish

Abstract

Disclosed is a method for producing a polyimide varnish, the method including a step for imidizing a tetracarboxylic acid dianhydride that contains a compound represented by formula (a1) and a compound represented by formula (a2) and a diamine that contains a compound represented by formula (b1) in the presence of a base catalyst and an organic solvent that includes a lactone-based solvent. According to the method for producing a polyimide varnish, there can be obtained a polyimide varnish which contains a solvent-soluble polyimide resin, and with which it is possible to obtain a polyimide film that has a high elastic modulus and excellent colorless transparency.

Description

Polyimide varnish manufacturing method

[0001] The present invention relates to a method for producing a polyimide varnish.

[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, polyimide resins have been increasingly used as optical and electronic materials, particularly as materials for image display devices, and colorless transparency has become a requirement. However, conventional polyimide resins 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] In addition to the above-mentioned problems, because they can form films without reactions, solvent-soluble polyimide resins and polyimide varnishes dissolved in solvents are in demand, especially as raw materials for optical materials and electronic materials. Fluorinated polyimides can improve colorlessness and transparency and 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. Under these circumstances, the use of perfluoroalkyl compounds and polyfluoroalkyl compounds in electronic components may be restricted. Simply improving colorless transparency can be achieved by using aliphatic or alicyclic raw materials. However, this results in a deterioration in mechanical properties, which are extremely important performance characteristics, making it difficult to achieve both colorless transparency and mechanical properties in a polyimide resin. Therefore, a polyimide resin that is excellent in both colorless transparency and mechanical properties without using PFAS as a raw material has been sought. Furthermore, polyimides are generally insoluble in solvents and must be formed into a film at the polyamic acid precursor stage, making it difficult to control the imidization rate and polymer properties. As mentioned above, solvent-soluble polyimide resins are sought. However, polyimide resins containing many aromatic rings to improve mechanical properties have the problem of reduced solubility in solvents, making it difficult to obtain a homogeneous varnish. The present invention has been made in light of these circumstances, and an object of the present invention is to provide a method for producing a polyimide varnish containing a solvent-soluble polyimide resin, which can produce a polyimide film having a high elastic modulus and excellent colorless transparency.

[0005] The present inventors have found that the above-mentioned problems can be solved by a method that uses a specific tetracarboxylic dianhydride and a diamine as raw materials and includes a step of imidizing them in the presence of a specific catalyst and a solvent, and have thus completed the present invention.

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

[20] : [1] A method for producing a polyimide varnish, comprising a step of imidizing a tetracarboxylic dianhydride containing a compound represented by the following formula (a1) and a compound represented by the following formula (a2), and a diamine containing a compound represented by the following formula (b1), in the presence of a base catalyst and an organic solvent containing a lactone-based solvent. [2] The method for producing a polyimide varnish according to [1] above, wherein neither the tetracarboxylic dianhydride nor the diamine contains the following structural element (c): (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.) [3] The method for producing a polyimide varnish according to the above [1] or [2], wherein the diamine 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.) [4] A method for producing a polyimide varnish according to the above item [3], wherein 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 is 50 mol % or less. [5] A method for producing a polyimide varnish according to the above item [3] or [4], wherein the molar ratio of the compound represented by formula (b1) in structural unit B 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) in the diamine, [(b1) / ((b2)+(b3)+(b4)+(b5)+(b6)], is 50 / 50 to 99 / 1. [6] The method for producing a polyimide varnish according to any one of [1] to [5] above, wherein the amount of the base catalyst is 100 mol % or less relative to the amount of the tetracarboxylic dianhydride, and the base catalyst is at least one selected from the group consisting of triethylamine and triethylenediamine. [7] The method for producing a polyimide varnish according to any one of [1] to [6] above, wherein the lactone solvent is γ-butyrolactone. [8] The method for producing a polyimide varnish according to any one of [1] to [7] above, wherein the compound represented by formula (a1) contains 30% or more of a compound represented by the following formula (a11): [9] The method for producing a polyimide varnish according to any one of [1] to [8] above, wherein the ratio of the compound represented by formula (a2) in the tetracarboxylic dianhydride is 27 mol % or less.

[10] The method for producing a polyimide varnish according to any one of [1] to [9] above, wherein the ratio of the compound represented by formula (a1) in the tetracarboxylic dianhydride is 10 to 99 mol %.

[11] The method for producing a polyimide varnish according to any one of [1] to

[10] above, wherein the molar ratio [(a1) / (a2)] of the compound represented by formula (a1) to the compound represented by formula (a2) in the tetracarboxylic dianhydride is 73 / 27 to 99 / 1.

[12] The method for producing a polyimide varnish according to any one of [1] to

[11] above, wherein the ratio of the compound represented by formula (b1) in the diamine is 40 to 100 mol %.

[13] The method for producing a polyimide varnish according to any one of [1] to

[12] above, further comprising the step of adding an organic solvent.

[14] A polyimide varnish obtained by the manufacturing method described in any one of [1] to

[13] above.

[15] The polyimide varnish described in

[14] above, containing 20% ​​by mass or more of gamma-butyrolactone based on the total amount of the polyimide varnish.

[16] The polyimide varnish described in

[14] or

[15] above, wherein the polyimide varnish has a YI of 40 or less, a total light transmittance of 80% or more, and a haze of 10% or less, as measured at 23°C in a cell with a 10 mm light path length.

[17] A method for manufacturing a polyimide film, comprising: a coating step of applying the polyimide varnish described in any one of

[14] to

[16] above onto 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.

[18] A polyimide film obtained by the manufacturing method described in

[17] above.

[19] The polyimide film according to

[18] , wherein the polyimide film has a YI of 7.5 or less, a total light transmittance of 80% or more, a haze of 1.0% or less, and a tensile modulus of 3.7 GPa or more when measured in accordance with JIS K7127 under the conditions of a test piece of 50 μm × 10 mm × 120 mm, a tensile speed of 20 mm / min, and a chuck distance of 50 mm, when the thickness is 50 μm.

[20] The polyimide film according to

[18] or

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

[0007] According to the present invention, a method for producing a polyimide varnish can be provided that can produce a polyimide film having a high elastic modulus and excellent colorless transparency. Furthermore, according to the present invention, a polyimide varnish containing a solvent-soluble polyimide resin can be produced. Therefore, the polyimide varnish produced by the production method of the present invention is useful as a raw material for optical materials and electronic materials, particularly display materials, and the resulting polyimide film is useful as an optical material and electronic material, particularly display materials. Furthermore, according to the production method of the present invention, a polyimide resin, polyimide varnish, and polyimide film having the above properties can be produced without using raw materials containing a perfluoroalkyl structure or a polyfluoroalkyl structure.

[0008] [Method for Producing Polyimide Varnish] The method for producing a polyimide varnish of the present invention includes a step of imidizing a tetracarboxylic dianhydride containing a compound represented by the following formula (a1) and a compound represented by the following formula (a2), and a diamine containing a compound represented by the following formula (b1), in the presence of a base catalyst and an organic solvent containing a lactone-based solvent.

[0009] The polyimide varnish produced by the method of the present invention can produce a polyimide film having a high elastic modulus and excellent colorless transparency. The reason why the method of the present invention produces a polyimide varnish containing a solvent-soluble polyimide resin is unclear, but it is thought to be as follows: The polyimide resin constituting the resulting polyimide film is thought to have excellent colorless transparency and solubility due to the presence of an alicyclic cyclohexane structure. Furthermore, the high elastic modulus is thought to be due to the rigid structure of a substituted biphenyl structure. Furthermore, the imide ring adjacent to the cyclobutane structure is thought to have good packing, and the inclusion of a small amount of this structure is thought to result in a high elastic modulus while maintaining the above-mentioned performance. Furthermore, imidization of such a polyimide resin in the presence of a base catalyst and an organic solvent containing a lactone-based solvent is thought to significantly improve solvent solubility. As described above, the polyimide varnish produced by the method of the present invention is thought to produce a polyimide film having a high elastic modulus and being soluble in a solvent. Furthermore, the method of the present invention is thought to produce a polyimide varnish containing a solvent-soluble polyimide resin.

[0010] In the method for producing a polyimide varnish of the present invention, it is preferable that neither the tetracarboxylic dianhydride nor the diamine contains the following structural element (c). By containing the following structural element (c), the raw material and the resulting polyimide film (polyimide resin) may fall under the category of a perfluoroalkyl compound or a polyfluoroalkyl compound (PFAS). According to the production method of the present invention, it is possible to obtain a polyimide resin that has a high elastic modulus, excellent colorless transparency, and is soluble in a solvent, and a polyimide film that has a high elastic modulus and excellent colorless transparency, even without using a raw material containing a perfluoroalkyl structure or a polyfluoroalkyl structure. (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.)

[0011] <Imidization Step> The method for producing a polyimide varnish of the present invention 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.

[0012] (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 include the following structural element (c): (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.) When the tetracarboxylic dianhydride contains the compound represented by formula (a1) and the compound represented by formula (a2), the elastic modulus of the polyimide film can be increased and colorless transparency can be improved without containing the perfluoroalkyl structure or polyfluoroalkyl structure represented by structural element (c). In addition, the solvent solubility of the polyimide resin contained in the varnish can be improved.

[0013] The compound represented by formula (a1) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA). When the tetracarboxylic dianhydride contains the compound represented by formula (a1), the transparency of the polyimide film (polyimide resin) can be improved. In addition, the solvent solubility of the polyimide resin can also be improved.

[0014] The compound represented by formula (a1) preferably contains 30% or more of 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.

[0015] The compound represented by formula (a2) is 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA). When the tetracarboxylic dianhydride contains the compound represented by formula (a2), the elastic modulus of the polyimide film (polyimide resin) can be particularly increased.

[0016] 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, even more preferably 23 mol% or less, and still 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%, even more preferably 15 to 25 mol%, still more preferably 15 to 23 mol%, and still 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 obtained polyimide film (polyimide resin) and also to provide it with a high elastic modulus.

[0017] 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, the transparency of the resulting polyimide resin can be improved while also achieving a high elastic modulus.

[0018] The ratio of the compound represented by formula (a1) in the tetracarboxylic dianhydride is preferably 10 to 99.5 mol%, more preferably 10 to 99 mol%, even more preferably 50 to 99 mol%, still 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 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 a high elastic modulus. The total ratio of the compound represented by formula (a1) and the compound represented by formula (a2) in the tetracarboxylic 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 dianhydride may consist only of the compound represented by formula (a1) and the compound represented by formula (a2), and it is even more preferable that the tetracarboxylic dianhydride consists only of the compound represented by formula (a1) and the compound represented by formula (a2). In other words, the total ratio of the compound represented by formula (a1) and the compound represented by formula (a2) in the tetracarboxylic dianhydride may be 100 mol%, and it is even more preferable that it is 100 mol%.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] (Diamine) The diamine includes a compound represented by the following formula (b1): Furthermore, it is preferable that the diamine does not include the following structural element (c). (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.)

[0023] By including a compound represented by formula (b1) in the diamine, the polyimide resin can maintain its colorless transparency and solvent solubility while increasing its elastic modulus without including the perfluoroalkyl or polyfluoroalkyl structure represented by structural element (c). The compound represented by formula (b1) is 2,2'-dimethylbenzidine (mTB).

[0024] 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%, still more preferably 85 to 100 mol%, and still more preferably 85 to 95 mol%. The ratio of the compound represented by formula (b1) in the diamine may be 100 mol%, or the diamine may consist solely of the compound represented by formula (b1).

[0025] 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.)

[0026] 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 compound represented by formula (b3), 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 still more preferably, it includes a compound represented by formula (b6).

[0027] The compound represented by formula (b2) is diaminodiphenyl sulfone. 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 colorless transparency of the polyimide resin can be improved.

[0028] The compound represented by formula (b3) is octafluorobenzidine (8FBZ). When the diamine contains the compound represented by formula (b3), the elastic modulus of the polyimide resin can be improved.

[0029] The compound represented by formula (b4) is 2,3,5,6-tetrafluorobenzene-1,4-diamine. When the diamine contains the compound represented by formula (b4), the elastic modulus of the polyimide resin can be improved.

[0030] The compound represented by formula (b5) is 2,4,5,6-tetrafluorobenzene-1,3-diamine. When the diamine contains the compound represented by formula (b5), the elastic modulus of the polyimide resin can be improved.

[0031] 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, 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). When the diamine contains 4,4'-diaminobenzanilide (DABA) among the compounds represented by formula (b6), the colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus.

[0032] 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).

[0033] 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 colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus. 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 colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus. 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 colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus. 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 colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus. As described above, when the diamine contains a compound represented by formula (b6), the colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus.

[0034] 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 colorless transparency of the obtained polyimide resin while maintaining a high elastic modulus.

[0035] 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 colorless transparency of the obtained polyimide resin while maintaining a high elastic modulus.

[0036] 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).

[0037] 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).

[0038] 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.

[0039] 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.

[0040] (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.

[0041] 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 %, still 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.

[0042] 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.

[0043] 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 %.

[0044] The amount of the base catalyst used in this step relative to the amount of diamine is preferably the same as the amount relative to the amount of tetracarboxylic dianhydride. Thus, the amount of the base catalyst used in this step relative to the amounts of the tetracarboxylic dianhydride and the diamine 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 %, still more preferably 10 to 60 mol %, still more preferably 30 to 60 mol %, and still more preferably 40 to 60 mol %.

[0045] 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.

[0046] 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."

[0047] (Organic Solvent) The organic solvent used in this step 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.

[0048] 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.

[0049] 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, with N,N-dimethylacetamide being preferred. 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.

[0050] 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.

[0051] When the organic solvent contains both a lactone solvent and an amide solvent, the proportion of trans-isomers derived from (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride can be increased. When the organic solvent contains both a lactone solvent and an amide solvent, the mass ratio of the lactone solvent to the amide solvent [lactone solvent / amide solvent] in the organic solvent is preferably 50 / 50 to 99 / 1, more preferably 60 / 40 to 99 / 1, even more preferably 60 / 40 to 97 / 3, still more preferably 70 / 30 to 95 / 5, even more preferably 70 / 30 to 90 / 10, still more preferably 70 / 30 to 85 / 15, and still more preferably 75 / 25 to 85 / 15.

[0052] (Imidization Conditions) The method for producing a polyimide varnish of the present invention includes a step of imidizing the tetracarboxylic dianhydride and the diamine in the presence of the base catalyst and the organic solvent, and it is preferable to carry out the imidization reaction under the following conditions:

[0053] 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.

[0054] 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 introduced is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, per mol of the tetracarboxylic acid component. 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 these 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] <Step of Adding Organic Solvent> The polyimide varnish production method of the present invention may further include a step of adding an organic solvent as an optional step. Because the imidization reaction described above is carried out in an organic solvent, the polyimide resin can be obtained as a solution. Therefore, the obtained solution may be used as a polyimide varnish as is. By further adding an organic solvent to the solution, a polyimide varnish with the desired concentration, viscosity, and solvent composition can be obtained. The organic solvent used in this step is the same as the organic solvent used in the imidization step described above. Among these, at least one selected from the group consisting of lactone solvents and amide solvents is preferred, with amide solvents being more preferred. Specifically, the organic solvent used in this step is more preferably at least one selected from the group consisting of γ-butyrolactone (GBL) and N,N-dimethylacetamide, with N,N-dimethylacetamide being even more preferred. The addition of an amide solvent can adjust the viscosity of the resulting varnish to a low level. The organic solvent contained in the resulting polyimide varnish is preferably adjusted to 20% by mass or more, more preferably 20 to 90% by mass, even more preferably 20 to 70% by mass, 20 to 60% by mass, even more preferably 20 to 50% by mass, even more preferably 30 to 50% by mass, and even more preferably 30 to 45% by mass, relative to the total amount of the polyimide varnish. Furthermore, the organic solvent contained in the resulting polyimide varnish is preferably adjusted to 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, and even more preferably 35 to 50% by mass.

[0059] As the organic solvent contained in the polyimide varnish, it is preferable to adjust the amide solvent to 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. Furthermore, as the organic solvent contained in the polyimide varnish, it is preferable to adjust the amide solvent to 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.

[0060] [Polyimide Varnish] The polyimide varnish of the present invention is a polyimide varnish obtained by the above-described production method. The polyimide varnish is obtained by dissolving a polyimide resin 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.

[0061] The organic solvent contained in the polyimide varnish is the same as the organic solvent used in the imidization step and the organic solvent addition step described above. Among these, the organic solvent contained in the polyimide varnish is preferably at least one selected from the group consisting of lactone solvents and amide solvents, with lactone solvents being more preferred. It is even more preferred that the polyimide varnish contains both lactone solvents and amide solvents. The organic solvent contained in the polyimide varnish is more preferably at least one selected from the group consisting of γ-butyrolactone (GBL) and N,N-dimethylacetamide, with γ-butyrolactone (GBL) being even more preferred. It is even more preferred that the polyimide varnish contains both γ-butyrolactone (GBL) and N,N-dimethylacetamide. The inclusion of the above solvents improves the solubility and coatability of the polyimide resin. The polyimide varnish may contain only γ-butyrolactone as the organic solvent contained in the polyimide varnish, 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 polyimide varnish preferably contains γ-butyrolactone as the organic solvent contained in the polyimide varnish 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.

[0062] The polyimide varnish preferably contains an amide solvent as an organic 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, even more preferably 40 to 60% by mass, based on the total amount of the polyimide varnish. The polyimide varnish preferably contains an amide solvent as an organic 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.

[0063] The polyimide resin contained in the polyimide varnish obtained by the above production method is solvent-soluble, and therefore can be a highly concentrated varnish that is stable at room temperature. The polyimide varnish of the present invention preferably contains 5 to 40 mass %, more preferably 8 to 30 mass %, and even more preferably 10 to 20 mass % of polyimide resin. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, more preferably 1 to 100 Pa·s. The viscosity of the polyimide varnish is a value measured at 25°C using an E-type viscometer.

[0064] The polyimide varnish of the present invention preferably has the following physical properties. The following physical properties are suitable as properties of a polyimide varnish used in producing a polyimide film, and are not limited to the composition. However, they are preferably measured for a polyimide varnish containing 15% by mass of polyimide resin. If the following physical properties are measured for a polyimide varnish containing 15% by mass of polyimide resin, a polyimide film having the excellent properties described below can be obtained from the polyimide varnish. The polyimide varnish of the present invention preferably has a YI of 40 or less, a total light transmittance of 80% or more, and a haze of 10% or less, as measured at 23°C in a cell with a light path length of 10 mm. These properties will be described in more detail below.

[0065] The YI measured at 23°C in a cell having an optical path length of 10 mm is preferably 40 or less, more preferably 30 or less, even more preferably 20 or less, still more preferably 16 or less, still more preferably 13 or less, and still more preferably 11 or less.

[0066] The total light transmittance measured at 23°C in a cell having an optical path length of 10 mm is preferably 80% or more, more preferably 85% or more, even more preferably 90% or more, still more preferably 93% or more, and still more preferably 95% or more.

[0067] The haze measured at 23°C in a cell with an optical path length of 10 mm is preferably 10% or less, more preferably 2.0% or less, even more preferably 1.0% or less, still more preferably 0.5% or less, and even more preferably 0.3% or less. The above-mentioned physical property values ​​in the present invention can be specifically measured by the method described in the Examples. The polyimide varnish of the present invention has the properties described above, and the polyimide resin contained in the varnish has excellent solvent solubility.

[0068] 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, antifoaming agents, fluorescent brightening agents, crosslinking agents, polymerization initiators, and photosensitizers, as long as the required properties of the polyimide resin and polyimide film are not impaired. Next, suitable polyimide resins to be contained in the polyimide varnish will be described.

[0069] <Polyimide Resin> The polyimide resin contained in the polyimide varnish of the present invention preferably has a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine. More preferably, 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), and the structural unit B contains a structural unit (B1) derived from a compound represented by the following formula (b1). Since the polyimide resin is contained in the polyimide varnish of the present invention, it is contained in the resulting polyimide film and is colorless and transparent, has a high elastic modulus, and is soluble in solvents.

[0070] (Structural Unit A) The structural unit A is a structural unit derived from a tetracarboxylic dianhydride contained in a 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). Furthermore, it is preferable that 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 colorless transparency of the polyimide resin can be improved, while the elastic modulus can be increased and the solvent solubility can be improved, without including the perfluoroalkyl structure or polyfluoroalkyl structure represented by the structural element (c).

[0071] The compound represented by formula (a1) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA). When the structural unit A contains the structural unit (A1), the transparency of the polyimide resin can be improved. In addition, the solvent solubility can also be improved.

[0072] 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). There is no upper limit, but it is preferably 80 mol % or less. By including a trans structure in the structural unit (A1), the transparency of the resulting polyimide resin can be improved, and the elastic modulus can be increased.

[0073] 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.

[0074] The proportion of the structural unit (A2) in the structural unit A is preferably 27 mol% or less, more preferably 25 mol% or less, even more preferably 23 mol% or less, and even more preferably 22 mol% or less. The lower limit of 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%, even more preferably 5 to 27 mol%, even more preferably 10 to 27 mol%, even more preferably 10 to 25 mol%, even more preferably 15 to 25 mol%, even more preferably 15 to 23 mol%, and even more preferably 15 to 22 mol%. By setting the proportion of the structural unit (A2) in the structural unit A within the above range, the transparency of the resulting polyimide resin can be improved while achieving a high elastic modulus.

[0075] 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, the transparency of the resulting polyimide resin can be improved while also achieving a high elastic modulus.

[0076] The proportion of the structural unit (A1) in the structural unit A is preferably 10 to 99.5 mol%, 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 ensuring that the proportion of the structural unit (A1) in the structural unit A falls within the above range, the resulting polyimide resin can have a high elastic modulus while improving its transparency. 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, and it is even more preferable that it is, 100 mol%.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] (Structural Unit B) The structural unit B is a structural unit derived from a diamine contained in a polyimide resin. The structural unit B contains a structural unit (B1) derived from a compound represented by the following formula (b1). It is also preferable that the structural unit B does not contain the following structural element (c). (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.)

[0081] By including the structural unit (B1) in the structural unit B, it is possible to increase the elastic modulus of the polyimide resin while maintaining the colorless 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).

[0082] 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).

[0083] 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.)

[0084] 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).

[0085] 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 colorless transparency of the polyimide resin can be improved.

[0086] The compound represented by formula (b3) is octafluorobenzidine (8FBZ). When the structural unit B includes the structural unit (B3), the elastic modulus of the polyimide resin can be improved.

[0087] The compound represented by formula (b4) is 2,3,5,6-tetrafluorobenzene-1,4-diamine. When the structural unit B includes the structural unit (B4), the elastic modulus of the polyimide resin can be improved.

[0088] The compound represented by formula (b5) is 2,4,5,6-tetrafluorobenzene-1,3-diamine. When the structural unit B includes the structural unit (B5), the elastic modulus of the polyimide resin can be improved.

[0089] 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 colorless transparency of the polyimide resin while maintaining a high elastic modulus.

[0090] 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 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), more preferably at least one selected from the group consisting of compounds represented by the following formula (b61), compounds represented by the following formula (b62), and compounds represented by the following formula (b63), even more preferably at least one selected from the group consisting of compounds represented by the following formula (b61) and compounds represented by the following formula (b63), and still more preferably at least one selected from the group consisting of compounds represented by the following formula (b61) and compounds represented by the following formula (b63), and still more preferably a compound represented by formula (b61).

[0091] 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 colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus. 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), the colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus. 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), the colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus. 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), the colorless transparency of the polyimide resin can be improved while maintaining a high elastic modulus. As described above, by including the structural unit (B6) in the structural unit B, it is possible to improve the colorless transparency of the polyimide resin while maintaining a high elastic modulus.

[0092] 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%, still 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 colorless transparency of the resulting polyimide resin can be improved while maintaining a high elastic modulus.

[0093] 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) relative to the total of the structural units (B2), (B3), (B4), (B5), and (B6) in the structural unit B is within the above range, the colorless transparency of the obtained polyimide resin can be improved while maintaining a high elastic modulus.

[0094] 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).

[0095] 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).

[0096] 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.

[0097] 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.

[0098] (Structure and Properties of Polyimide Resin) The polyimide resin preferably does not contain the following structural element (c). (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.)

[0099] The structural element (c) in the present invention will be described in detail below. The structural element (c) in the polyimide resin, polyimide varnish, polyimide varnish production method, and polyimide film of the present invention has the same meaning. CF other than X in formula (c) 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 preferably does not have any structural unit derived from the following tetracarboxylic dianhydride or any structural unit derived from the following diamine.

[0100] 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).

[0101] 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).

[0102] 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.

[0103] 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, it is preferable that 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, it may be 100% by mass, and the polyimide resin may be composed only of polyimide chains.

[0104] [Method for Producing Polyimide Film] The method for producing a polyimide film of the present invention 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, preferably 220°C or higher. The polyimide film obtained by the method for producing a polyimide film of the present invention contains the polyimide resin. Therefore, the polyimide film does not contain a perfluoroalkyl structure or a polyfluoroalkyl structure, has excellent colorless transparency, and has a high elastic modulus.

[0105] <Coating Step> The coating step is a step in which a polyimide varnish is applied to 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; a glass plate or plastic film is more preferred, and a plastic film is even 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, and these methods can be applied without any particular limitations. A glass rod or a 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] <Primary Drying Step> The primary drying step is a step in which the coating film is dried and peeled off from the support to obtain a self-supporting film. Primary drying is a step in which a portion of the organic solvent is removed to obtain a self-supporting film, and the organic solvent is removed by heating the coating film on the support. The temperature when removing the organic solvent 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] <Secondary Drying Step> 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, still 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 simultaneously achieved. 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] [Polyimide Film] The polyimide film of the present invention is a polyimide film obtained by the above-described production method. Therefore, the polyimide film of the present invention does not contain a perfluoroalkyl structure or a polyfluoroalkyl structure, and has excellent colorless transparency and a high elastic modulus. Note that polyimide films obtained using the polyimide varnish as a raw material are also included in the present invention. Such polyimide films may be obtained by any method, but are preferably obtained by the above-described production method, and by obtaining them by the above-described production method, the above-described performance can be further improved.

[0109] The polyimide film of the present invention preferably has the following physical properties. When the polyimide film has a thickness of 50 μm, 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, and a tensile modulus of 3.7 GPa or more, calculated as the slope of the least squares method in the section from 0.1 mm to 0.5 mm in strain in a stress-strain curve obtained by a tensile test performed under conditions of 23°C and 50% RH, with a test piece of 50 μm × 10 mm × 120 mm, a tensile speed of 20 mm / min, and a chuck distance of 50 mm. These properties will be explained in more detail below.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] The polyimide film of the present invention contains the polyimide resin, does not contain a perfluoroalkyl structure or a polyfluoroalkyl structure, and has excellent colorless transparency and a high elastic modulus. 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.

[0115] 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.

[0116] The polyimide film of the present invention has the excellent properties described above and is therefore particularly suitable for use as an optical material or electronic material, particularly as a display material.

[0117] 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.

[0118] [Evaluation of Polyimide Resin Structure and Polyimide Varnish] The structure of the polyimide resin obtained in the Examples and Comparative Examples and the polyimide varnish were analyzed and evaluated by the methods described below.

[0119] (1) Varnish Viscosity The viscosity of the varnish was measured at 23°C using an E-type viscometer (TVE-25H model, manufactured by Toki Sangyo Co., Ltd.). The solids concentration of the varnish (concentration of the polyimide resin) was 15% by mass or 20% by mass, as shown in Tables 1 and 2. The unit of the measured viscosity is mPa s.

[0120] (2) Total Light Transmittance, Yellow Index (YI), and Haze A polyimide varnish was placed in a 10 mm square quartz glass cell to serve as a test sample, which was measured at 23° C. under the following conditions: Total light transmittance was measured in accordance with JIS K7361-1:1997, YI in accordance with ASTM E313-05 (D light source, 65°), and haze in accordance with JIS K7136:2000, all of which were measured using a color and turbidity simultaneous measuring instrument (COH7700, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0121] [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.

[0122] (1) Ratio of trans structure derived from cyclohexanetetracarboxylic dianhydride (HPMDA) (HPMDA trans structure ratio) The ratio of trans structure derived from cyclohexanetetracarboxylic dianhydride in a polyimide resin is determined by the ratio of the trans structure of the polyimide resin (polyimide film). １ The following calculation was made by measuring the H-NMR spectrum. １ H-NMR spectrum measurement was performed using an NMR spectrophotometer (ASCEnd ＴＭ Measurement 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.

[0123] 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

[0124] (2) Polyimide Film Thickness The thickness of the polyimide film was measured using a micrometer manufactured by Mitutoyo Corporation.

[0125] (3) Tensile Modulus and Tensile Strength The tensile modulus and tensile strength were measured in accordance with JIS K7127:1999 using a tensile tester "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd. The chuck distance was 50 mm, the test piece size was 10 mm 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 modulus of elasticity of the polyimide film (polyimide resin) and the more preferable it is. Furthermore, the higher the tensile strength value, the more preferable the polyimide film (polyimide resin) is and the more excellent its strength is.

[0126] (4) Total Light Transmittance, Yellow Index (YI), and Haze Total light transmittance was measured in accordance with JIS K7361-1:1997, YI in accordance with ASTM E313-05 (D light source, 65°), and haze in accordance with JIS K7136:2000, all of which were measured using a color and turbidity simultaneous measuring instrument (COH7700, manufactured by Nippon Denshoku Industries Co., Ltd.). The higher 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). The smaller the haze value, the more excellent the colorless transparency of the polyimide film (polyimide resin).

[0127] <Abbreviations for Components, etc.> The tetracarboxylic acid components and diamine components used in the examples and comparative examples, and their abbreviations, are as follows.

[0128] (Tetracarboxylic acid components) HPMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (compound represented by formula (a1), ratio of the content of the compound represented by formula (a11) to the content of the compound represented by formula (a12) [(a11) / (a12)] = 0 / 100, manufactured by Mitsubishi Gas Chemical Company, Inc.) trans-HPMDA: (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride (compound represented by formula (a11), ratio of the content of the compound represented by formula (a11) to the content of the compound represented by formula (a12) [(a11) / (a12)] = 100 / 0) CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride (compound represented by formula (a2)) BPDA: biphenyltetracarboxylic dianhydride

[0129] (Diamine Components) mTB: 2,2'-dimethylbenzidine (compound represented by formula (b1), manufactured by Seika Corporation) DABA: 4,4'-diaminobenzanilide (compound represented by formula (b6), n = 0, R each represents a hydrogen atom, 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)) 4,4'-DDS: 4,4'-diaminodiphenyl sulfone (compound represented by formula (b2), amino groups are both at 4-position)

[0130] 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

[0131] <Production of Polyimide Resin, Polyimide Varnish, and Polyimide Film> Example 1 Into a 300 mL five-neck round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark stirrer equipped with a condenser, a thermometer, and a glass end cap, 15.20 g (0.0715 mol) of diamine mTB and 1.81 g (0.0079 mol) of DABA, and 64.2 g of GBL as a solvent were placed, and the system was heated to a temperature of 70°C under a nitrogen atmosphere and stirred at 200 rpm to obtain a solution. To this solution, 14.26 g (0.0636 mol) of tetracarboxylic dianhydride HPMDA and 3.12 g (0.0159 mol) of CBDA, and 8.0 g of GBL as a solvent were added all at once, followed by 4.02 g (0.0397 mol) of TEA as an imidization catalyst, 0.45 g (0.0040 mol) of TEDA, and GBL as a solvent. The amount of solvent at the start of the reaction was adjusted so that the concentration of the resulting polyimide resin was 30% by mass. The reaction system was heated with a mantle heater, and the temperature in the reaction system was raised to a reaction temperature of 190 ° C. over approximately 20 minutes. While collecting the distilled components, the reaction temperature was maintained at 190 ° C. and refluxed for 1.3 hours to obtain a solution containing a polyimide resin. DMAc was added as a solvent to adjust the solids concentration to 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 evaluation results of the varnish are shown in Table 1. The resulting polyimide varnish was then applied to a PET (polyethylene terephthalate) substrate and dried on a hot plate at 60°C for 20 minutes as primary drying, then at 80°C for 20 minutes, and then at 100°C for 30 minutes. After peeling from the PET substrate, the coating was heated in a hot air dryer under an air atmosphere at 220°C for 20 minutes to evaporate the solvent, yielding a polyimide film. The film's physical properties and evaluation results are shown in Table 1.

[0132] Examples 2 to 9 and Comparative Examples 1 to 7 In Example 1, the types and amounts of the diamine, tetracarboxylic dianhydride, and imidization catalyst were changed to the raw materials shown in Table 1 or Table 2, respectively. The type of solvent was changed to the solvent shown in Table 1 or Table 2. The amount of solvent at the start of the reaction was adjusted so that the concentration of the resulting polyimide resin would be the concentration shown in Table 1 or Table 2. A polyimide varnish containing a polyimide resin was obtained in the same manner as in Example 1, except that the reaction temperature was changed to the temperature shown in Table 1 or Table 2. The evaluation results of the varnish are shown in Table 1 or Table 2. Note that, in order to produce all Examples and Comparative Examples under similar conditions, the concentration during the reaction was set higher for compositions in which the polymerization reaction did not proceed easily. In Comparative Example 2, the concentration during the reaction was adjusted in stages. The reaction temperature (reflux temperature) was also adjusted based on the boiling point of the polymerization solvent. Furthermore, a polyimide film was obtained in the same manner as in Example 1, except that the temperature and time of the primary drying and the temperature and time of the secondary drying were changed to the temperatures and times shown in Table 1 or Table 2, respectively. The physical properties and evaluation results of the film are shown in Table 1 or Table 2. In the varnishes of Comparative Examples 2 and 4, the resin was not completely dissolved, and the varnish was non-uniform, failing to provide a homogeneous film. The varnish of Comparative Example 3 had an extremely low viscosity, failing to provide a homogeneous film. Therefore, it was not possible to measure and evaluate the physical properties.

[0133]

[0134]

[0135] As shown in Table 1, the polyimide films (polyimide resins) obtained using the polyimide varnishes of the Examples have a high tensile modulus. Furthermore, the polyimide resins (polyimide films) of the Examples have a high total light transmittance, a small YI, and particularly excellent haze. On the other hand, as shown in Table 2, the polyimide varnishes of the Comparative Examples have poor solvent solubility of the polyimide resin contained in the varnish, and either a film could not be obtained, or even if a film was obtained, it did not satisfy all of the above-mentioned performance requirements. From this, it can be seen that the method for producing a polyimide varnish of the present invention can produce a polyimide varnish that has a high modulus and can produce a polyimide film that is colorless and transparent. Furthermore, it can be seen that the production method of the present invention can produce a polyimide film having the above-mentioned properties without using raw materials containing a perfluoroalkyl structure or a polyfluoroalkyl structure.

Claims

1. A method for producing a polyimide varnish, comprising a step of imidizing a tetracarboxylic dianhydride containing a compound represented by the following formula (a1) and a compound represented by the following formula (a2), and a diamine containing a compound represented by the following formula (b1), in the presence of a base catalyst and an organic solvent containing a lactone-based solvent.

2. The method for producing a polyimide varnish according to claim 1, wherein neither the tetracarboxylic dianhydride nor the diamine contains the following structural element (c): (In formula (c), X is a fluorine atom, a hydrogen atom, or a carbon atom.) 3. A method for producing a polyimide varnish according to claim 1 or 2, wherein the diamine further comprises 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.) 4. The method for producing a polyimide varnish according to claim 3, wherein 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 is 50 mol % or less.

5. A method for producing a polyimide varnish according to claim 3 or 4, wherein in the structural unit B, the molar ratio of the compound represented by formula (b1) to the sum of the compounds represented by formula (b2), (b3), (b4), (b5) and (b6) in the diamine [(b1) / ((b2)+(b3)+(b4)+(b5)+(b6)] is 50 / 50 to 99 / 1.

6. A method for producing a polyimide varnish according to any one of claims 1 to 5, wherein the amount of the base catalyst is 100 mol % or less relative to the amount of the tetracarboxylic dianhydride, and the base catalyst is at least one selected from the group consisting of triethylamine and triethylenediamine.

7. The method for producing a polyimide varnish according to any one of claims 1 to 6, wherein the lactone solvent is γ-butyrolactone.

8. A method for producing a polyimide varnish according to any one of claims 1 to 7, wherein the compound represented by formula (a1) contains 30% or more of a compound represented by the following formula (a11):

9. A method for producing a polyimide varnish according to any one of claims 1 to 8, wherein the ratio of the compound represented by formula (a2) in the tetracarboxylic dianhydride is 27 mol % or less.

10. A method for producing a polyimide varnish according to any one of claims 1 to 9, wherein the ratio of the compound represented by formula (a1) in the tetracarboxylic dianhydride is 10 to 99 mol %.

11. A method for producing a polyimide varnish according to any one of claims 1 to 10, wherein the molar ratio of the compound represented by formula (a1) to the compound represented by formula (a2) in the tetracarboxylic dianhydride [(a1) / (a2)] is 73 / 27 to 99 / 1.

12. A method for producing a polyimide varnish according to any one of claims 1 to 11, wherein the ratio of the compound represented by formula (b1) in the diamine is 40 to 100 mol %.

13. The method for producing a polyimide varnish according to any one of claims 1 to 12, further comprising the step of adding an organic solvent.

14. A polyimide varnish obtained by the method according to any one of claims 1 to 13.

15. The polyimide varnish according to claim 14, which contains 20 mass% or more of γ-butyrolactone based on the total amount of the polyimide varnish.

16. A polyimide varnish according to claim 14 or 15, in which the polyimide varnish has a YI of 40 or less, a total light transmittance of 80% or more, and a haze of 10% or less, as measured at 23°C in a cell having an optical path length of 10 mm.

17. A method for producing a polyimide film, comprising: a coating step of applying the polyimide varnish according to any one of claims 14 to 16 onto a support to obtain a coating film; a primary drying step of drying the coating film and peeling it off 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.

18. A polyimide film obtained by the method according to claim 17.

19. The polyimide film according to claim 18, which has a YI of 7.5 or less, a total light transmittance of 80% or more, a haze of 1.0% or less when made 50 μm thick, and a tensile modulus of elasticity of 3.7 GPa or more when measured in accordance with JIS K7127 under conditions of a test piece of 50 μm × 10 mm × 120 mm, a tensile speed of 20 mm / min, and a chuck distance of 50 mm.

20. The polyimide film according to claim 18 or 19, having a thickness of 5 to 100 μm.

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