Method for producing polyimide film

Abstract

A method for producing a polyimide film, which is a method for producing a polyimide film formed by a polyimide resin, wherein the polyimide resin has: a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from diamine, wherein the structural unit A includes: a structural unit derived from alicyclic tetracarboxylic dianhydride, and the structural unit B includes: a structural unit (B1) derived from a compound represented by the following general formula (b1), wherein the production method is as follows: a polyimide varnish prepared by dissolving the polyimide resin in an organic solvent is applied to a support, the organic solvent is removed at 60 to 140° C. to form a self-supporting film, the self-supporting film is peeled off from the support, the ends of the self-supporting film are fixed, and the film is calcined at a temperature exceeding the glass transition temperature of the polyimide resin and at a temperature not higher than 50° C. higher than the glass transition temperature of the polyimide resin. (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted by fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted by fluorine, -S-, -SO-, -SO 2 ‑, ‑O‑, or ‑CO‑. )

Description

Technical Field

[0001] The invention relates to a method for producing a polyimide film. Background Art

[0002] Various uses of polyimide resins in the fields of electrical / electronic components are being studied. For example, glass substrates are used in image display devices such as liquid crystal displays and OLED displays, but it is expected to be replaced with plastic substrates for the purpose of lightweight and flexible devices. Research on polyimide films suitable as such plastic substrates is being promoted. Polyimide films for such uses are required to be colorless and transparent.

[0003] Furthermore, as required properties of the polyimide film, a small phase difference due to birefringence and a low retardation are required.

[0004] Patent Document 1 discloses, as a polyimide resin providing a thin film with reduced birefringence, a polyimide resin obtained by using a diamine (eg, metaphenylenediamine) in which at least one of the amino groups of the diamine is bonded at a meta position to the main chain.

[0005] Patent document 2 discloses a polyimide resin as a polyimide resin for providing a film having excellent heat resistance, transmittance, low linear expansion coefficient and low retardation, which comprises: a tetracarboxylic acid residue and a diamine residue of a specific structure, and a tetracarboxylic acid residue and / or a diamine residue having a curved portion. Specifically, a polyimide resin obtained by using 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biscyclohexanetetracarboxylic dianhydride, pyromellitic anhydride, 2,2'-bis(trifluoromethyl)benzidine, and 4,4'-diaminodiphenyl sulfone is disclosed.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 8-134211

[0009] Patent Document 2: International Publication No. 2015 / 125895 Summary of the invention

[0010] Problem that the invention aims to solve

[0011] As mentioned above, good optical properties such as colorless transparency are required for polyimide films. In particular, recently, the performance requirements for display applications of electronic equipment have also increased, and films with high optical isotropy are particularly required. However, the raw materials used in polyimide films are limited to diamines and tetracarboxylic dianhydride, etc., and the molecular structure is limited. Therefore, the necessity of improving performance according to manufacturing conditions, etc. has gradually arisen. That is, a method for manufacturing a polyimide film that maintains high colorless transparency while improving optical isotropy is sought.

[0012] Therefore, an object of the present invention is to provide a method for producing a polyimide film capable of obtaining a polyimide film that maintains high colorless transparency and is particularly excellent in optical isotropy.

[0013] Solutions for solving problems

[0014] The present inventors have found that the above-mentioned problems can be solved by forming a thin film from a varnish containing a polyimide resin having a specific combination of structural units by a specific drying method and a baking method, and have thus completed the invention.

[0015] That is, the present invention relates to the following [1] to

[12] .

[0016] [1] A method for producing a polyimide film, which is a method for producing a polyimide film formed from a polyimide resin, wherein the polyimide resin has: a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from diamine, the structural unit A includes: a structural unit derived from alicyclic tetracarboxylic dianhydride, and the structural unit B includes: a structural unit (B1) derived from a compound represented by the following general formula (b1), the production method is as follows: a polyimide varnish prepared by dissolving the polyimide resin in an organic solvent is applied to a support, the organic solvent is removed at 60 to 140°C to form a self-supporting film, the self-supporting film is peeled off from the support, the ends of the self-supporting film are fixed, and the film is calcined at a temperature exceeding the glass transition temperature of the polyimide resin and at a temperature not higher than 50°C higher than the glass transition temperature of the polyimide resin.

[0017]

[0018] (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted by fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted by fluorine, -S-, -SO-, -SO 2 -, -O- or -CO-. )

[0019] [2] The method for producing a polyimide film according to [1] above, wherein the thickness of the obtained polyimide film is 5 to 100 μm.

[0020] [3] The method for producing a polyimide film according to [1] or [2], wherein the calcination is performed for 5 to 60 minutes.

[0021] [4] The method for producing a polyimide film according to any one of [1] to [3] above, wherein the calcination temperature is 190 to 360°C.

[0022] [5] The method for producing a polyimide film according to any one of [1] to [4], wherein the structural unit A includes a structural unit (A1) derived from a compound represented by the following formula (a1).

[0023]

[0024] [6] A method for producing a polyimide film according to any one of the above [1] to [5], wherein the structural unit B further includes a structural unit (B2), and the structural unit (B2) is at least one selected from the group consisting of a structural unit (B21) derived from a compound represented by the following general formula (b21), a structural unit (B22) derived from a compound represented by the following general formula (b22), and a structural unit (B23) derived from a compound represented by the following general formula (b23).

[0025]

[0026] (Where X 2 ~X 7 Each independently represents a single bond, an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, -S-, -SO-, -SO 2 -, -O- or -CO-. )

[0027] [7] The method for producing a polyimide film according to [6] above, wherein the molar ratio of the structural unit (B1) to the structural unit (B2) [(B1) / (B2)] is 40 / 60 to 80 / 20.

[0028] [8] The method for producing a polyimide film according to any one of [1] to [7], further comprising: a structural unit (B3) derived from a compound represented by the following general formula (b3).

[0029]

[0030] (In formula (b3), Z 1 and Z 2 Each independently represents a divalent aliphatic group or a divalent aromatic group which may contain an oxygen atom, and R 1 and R 2Each independently represents a monovalent aromatic group or a monovalent aliphatic group, and R 3 and R 4 Each independently represents a monovalent aliphatic group, R 5 and R 6 Each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer greater than 1, and the sum of m and n represents an integer of 2 to 1000.

[0031] [9] The method for producing a polyimide film according to [8], wherein the R 1 and R 2 is phenyl, R 3 and R 4 It is methyl.

[0032]

[10] A method for producing a polyimide film according to any one of the above [1] to [9], which comprises the following steps: imidizing a tetracarboxylic acid component providing a structural unit A derived from tetracarboxylic dianhydride and a diamine component providing a structural unit B derived from diamine in the presence of a base catalyst and an organic solvent, and adding an organic solvent as needed to obtain a polyimide varnish.

[0033]

[11] A method for producing a polyimide film according to any one of the above [1] to

[10] , wherein the structural unit (B1) is at least one structural unit selected from the group consisting of a structural unit (B11) derived from a compound represented by the following general formula (b11) and a structural unit (B12) derived from a compound represented by the following formula (b12).

[0034]

[0035] (In formula (b11), R 1 and R 2 Each independently represents a methyl group or a trifluoromethyl group. )

[0036]

[12] A method for producing a polyimide film according to any one of the above [6] to

[11] , wherein the structural unit (B2) comprises: at least one structural unit selected from the group consisting of a structural unit derived from a compound represented by the following formula (b211), a structural unit derived from a compound represented by the following formula (b212), a structural unit derived from a compound represented by the following formula (b213), and a structural unit derived from a compound represented by the following formula (b231).

[0037]

[0038] Effects of the Invention

[0039] According to the present invention, there can be provided a method for producing a polyimide film capable of obtaining a polyimide film which maintains high colorless transparency and is particularly excellent in optical isotropy. DETAILED DESCRIPTION

[0040] [Method for producing polyimide film]

[0041] The method for producing a polyimide film of the present invention is a method for producing a polyimide film formed by a polyimide resin, wherein the polyimide resin has: a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from diamine, wherein the structural unit A includes: a structural unit derived from alicyclic tetracarboxylic dianhydride, and the structural unit B includes: a structural unit (B1) derived from a compound represented by the following general formula (b1). The production method is as follows: a polyimide varnish prepared by dissolving the polyimide resin in an organic solvent is applied to a support, the organic solvent is removed at 60 to 140° C. to form a self-supporting film, the self-supporting film is peeled off from the support, the ends of the self-supporting film are fixed, and the film is calcined at a temperature exceeding the glass transition temperature of the polyimide resin and below a temperature 50° C. higher than the glass transition temperature of the polyimide resin.

[0042]

[0043] (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted by fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted by fluorine, -S-, -SO-, -SO 2 -, -O- or -CO-. )

[0044] <Polyimide resin>

[0045] The polyimide resin used in the method for producing a polyimide film of the present invention comprises a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein the structural unit A comprises a structural unit derived from an alicyclic tetracarboxylic dianhydride, and the structural unit B comprises a structural unit (B1) derived from a compound represented by the following general formula (b1).

[0046]

[0047] (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted by fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted by fluorine, -S-, -SO-, -SO 2 -, -O- or -CO-. )

[0048] (Structural unit A)

[0049] Structural unit A is a structural unit derived from tetracarboxylic dianhydride that accounts for a portion of the polyimide resin, and includes a structural unit derived from alicyclic tetracarboxylic dianhydride. Structural unit A includes a structural unit derived from alicyclic tetracarboxylic dianhydride, thereby improving the colorless transparency and optical isotropy of the film.

[0050] The alicyclic tetracarboxylic dianhydride is preferably at least one selected from the group consisting of alicyclic tetracarboxylic dianhydrides such as 1,2,4,5-cyclohexanetetracarboxylic dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and dicyclohexyltetracarboxylic dianhydride.

[0051] Among them, 1,2,4,5-cyclohexanetetracarboxylic dianhydride and norbornane-2-spiro-α-cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride listed below are more preferred.

[0052] The structural unit A preferably contains at least one structural unit selected from the group consisting of 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 more preferably contains a structural unit (A1) derived from a compound represented by the following formula (a1).

[0053]

[0054] The compound represented by formula (a1) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride.

[0055] The structural unit A includes the structural unit (A1), thereby improving the colorless transparency and optical isotropy of the film.

[0056] The compound represented by formula (a2) is norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride. When structural unit A contains structural unit (A2), the colorless transparency of the film is further improved.

[0057] The structural unit A may include both the structural unit (A1) and the structural unit (A2), but preferably includes either the structural unit (A1) or the structural unit (A2), and more preferably includes the structural unit (A1).

[0058] When the structural unit A contains the structural unit (A1) and the structural unit (A2), the total ratio of the structural units (A1) and (A2) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural units (A1) and (A2) is not particularly limited, that is, it is 100 mol%, and the total ratio of the structural units (A1) and (A2) is 100 mol% or less.

[0059] When the structural unit A contains the structural unit (A1), the ratio of the structural unit (A1) in the structural unit A is preferably 45 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the ratio is not particularly limited, that is, when it is 100 mol%, the ratio of the structural unit (A1) in the structural unit A is 100 mol% or less.

[0060] When the structural unit A contains the structural unit (A2), the ratio of the structural unit (A2) in the structural unit A is preferably 45 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the ratio is not particularly limited, that is, when it is 100 mol%, the ratio of the structural unit (A2) in the structural unit A is 100 mol% or less.

[0061] The structural unit A may further include a structural unit (A3) derived from a compound represented by the following formula (a3). From the viewpoint of improving the colorless transparency of the film, the structural unit (A3) derived from a compound represented by the formula (a3) ​​is preferably included.

[0062]

[0063] The compound represented by formula (a3) ​​is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.

[0064] When the structural unit A contains the structural unit (A3), the ratio of the structural unit (A3) in the structural unit A is preferably 55 mol% or less, more preferably 30 mol% or less, and preferably 1 mol% or more.

[0065] When the structural unit A includes the structural unit (A3), the structural unit A preferably includes the structural unit (A1) and the structural unit (A3), and more preferably consists of the structural unit (A1) and the structural unit (A3).

[0066] The structural unit A may also contain structural units other than the structural units derived from the alicyclic tetracarboxylic dianhydride and the structural units (A1) to (A3) as long as the effects of the present invention are not impaired. The tetracarboxylic dianhydride providing such a structural unit is not particularly limited, and examples thereof include aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-biphenyl tetracarboxylic dianhydride, and 2,2',3,3'-biphenyl tetracarboxylic dianhydride; and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butane tetracarboxylic dianhydride.

[0067] It should be noted that, in the present 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 and no aromatic ring, and aliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring.

[0068] The structural unit contained in the structural unit A may be one kind or two or more kinds.

[0069] The structural unit A preferably does not contain any structural unit other than the structural units (A1) to (A3).

[0070] (Structural unit B)

[0071] The structural unit B is a structural unit derived from diamine that accounts for the polyimide resin, and includes a structural unit (B1) derived from a compound represented by the following general formula (b1). The inclusion of the structural unit (B1) provides excellent colorless transparency and optical isotropy.

[0072]

[0073] (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted by fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted by fluorine, -S-, -SO-, -SO 2 -, -O- or -CO-. )

[0074] [Structural unit (B1)]

[0075] The structural unit (B1) is a structural unit derived from the compound represented by the aforementioned general formula (b1), and is preferably at least one structural unit selected from the group consisting of a structural unit (B11) derived from a compound represented by the following general formula (b11) and a structural unit (B12) derived from a compound represented by the following formula (b12).

[0076]

[0077] In formula (b11), R 1 and R 2 Each independently represents a methyl group or a trifluoromethyl group.

[0078] The compound represented by formula (b11) is 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) or 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP),

[0079] The compound represented by formula (b12) is 4,4′-bis(4-aminophenoxy)biphenyl (BODA).

[0080] The structural unit B preferably includes at least one structural unit selected from the group consisting of structural units (B11) and (B12), and the structural unit B more preferably includes the structural unit (B11).

[0081] The structural unit B may contain both the structural units (B11) and (B12), but preferably contains one of the structural units (B11) and (B12). That is, the structural unit B preferably contains the structural unit (B11) or the structural unit (B12).

[0082] The structural unit B contains the structural unit (B1), thereby improving the colorless transparency and optical isotropy of the film. The structural unit (B1) may be one kind or two or more kinds.

[0083] [Other structural units optionally contained in structural unit B]

[0084] The structural unit B may contain structural units other than the structural unit (B1). The diamine providing such a structural unit is not particularly limited, but preferably contains a structural unit (B2), wherein the structural unit (B2) is at least one selected from the group consisting of a structural unit (B21) derived from a compound represented by the following general formula (b21), a structural unit (B22) derived from a compound represented by the following general formula (b22), and a structural unit (B23) derived from a compound represented by the following general formula (b23).

[0085] In addition, it is preferred that the structural unit (B3) derived from a compound represented by the following general formula (b3) is contained.

[0086]

[0087] In formulas (b21), (b22) and (b23), X 2 ~X 7Each independently represents a single bond, an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, -S-, -SO-, -SO 2 -, -O- or -CO-.

[0088] In formula (b3), Z 1 and Z 2 Each independently represents a divalent aliphatic group or a divalent aromatic group which may contain an oxygen atom, and R 1 and R 2 Each independently represents a monovalent aromatic group or a monovalent aliphatic group, and R 3 and R 4 Each independently represents a monovalent aliphatic group, R 5 and R 6 Each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer greater than 1, and the sum of m and n represents an integer of 2 to 1,000.

[0089] The structural unit (B2) is at least one structural unit selected from the group consisting of a structural unit (B21) derived from a compound represented by the following general formula (b21), a structural unit (B22) derived from a compound represented by the following general formula (b22), and a structural unit (B23) derived from a compound represented by the following general formula (b23).

[0090]

[0091] In formulas (b21), (b22) and (b23), X 2 ~X 7 Each independently represents a single bond, an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, -S-, -SO-, -SO 2 -, -O- or -CO-.

[0092] The compound represented by the general formula (b21) is 2 and X 3 The three benzene rings are connected, and there is an X bonded to the 1,3 positions of the central benzene ring. 2 and X 3 The compound represented by the general formula (b22) is obtained by X 4 and X 5 The three benzene rings are connected, and there is an X bonded to the 1,2 position of the central benzene ring. 4 and X 5 The compound represented by the general formula (b23) is obtained by X 6 and X 7 The three benzene rings are connected, and there is an X bonded to the 1,4 positions of the central benzene ring. 6 and X 7By having such a structure, a film having excellent colorless transparency and optical isotropy can be formed.

[0093] From the viewpoint of forming a thin film having a low retardation, X in the general formulae (b21), (b22) and (b23) is 2 ~X 7 Each independently preferably represents an alkylidene group having 3 to 5 carbon atoms, -SO 2 -, or -O-, more preferably represents an alkylidene group having 3 to 5 carbon atoms, or -O-, further preferably represents an isopropylidene group, or -O-, further preferably represents an isopropylidene group.

[0094] X in the general formula (b21) 2 and X 3 They may have different groups, but are preferably the same groups. Similarly, X in the general formula (b22) 4 and X 5 They may have different groups, preferably the same groups. X in the general formula (b23) 6 and X 7 They may have different groups, but are preferably the same groups.

[0095] The amino groups in the general formulae (b21), (b22) and (b23) are preferably 2 ~X 7 Any of them is bonded to the para position or meta position of the benzene ring.

[0096] The structural unit (B2) preferably includes at least one selected from the group consisting of a structural unit (B21) derived from a compound represented by the above-mentioned general formula (b21) and a structural unit (B23) derived from a compound represented by the above-mentioned general formula (b23), and more preferably includes a structural unit (B21) derived from a compound represented by the above-mentioned general formula (b21).

[0097] From the viewpoint of improving optical isotropy, when the structural unit (B2) includes the structural unit (B21), the structural unit (B1) preferably includes the structural unit (B11), and when the structural unit (B2) includes the structural unit (B23), the structural unit (B1) preferably includes the structural unit (B12).

[0098] The structural unit (B21) derived from the compound represented by the above general formula (b21) preferably includes at least one structural unit selected from the group consisting of a structural unit derived from a compound represented by the following formula (b211), a structural unit derived from a compound represented by the following formula (b212), and a structural unit derived from a compound represented by the following formula (b213). That is, the structural unit (B2) preferably includes at least one structural unit selected from the group consisting of a structural unit derived from a compound represented by the following formula (b211), a structural unit derived from a compound represented by the following formula (b212), a structural unit derived from a compound represented by the following formula (b213), and a structural unit derived from a compound represented by the following formula (b231).

[0099]

[0100] The compound represented by formula (b211) is 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene (BisAM),

[0101] The compound represented by formula (b212) is 1,3-bis(4-aminophenoxy)benzene,

[0102] The compound represented by formula (b213) is 1,3-bis(3-aminophenoxy)benzene.

[0103] Among the compounds represented by formula (b211) to formula (b213), at least one compound selected from the group consisting of the compound represented by formula (b211) and the compound represented by formula (b212) is preferred, and the compound represented by formula (b211) is more preferred.

[0104] The structural unit (B23) derived from the compound represented by the above general formula (b23) preferably includes a structural unit derived from a compound represented by the following formula (b231).

[0105]

[0106] The compound represented by formula (b231) is 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene (BisAP).

[0107] The structural unit (B3) is a structural unit derived from a compound represented by the following general formula (b3).

[0108]

[0109] In formula (b3), Z 1 and Z 2 Each independently represents a divalent aliphatic group or a divalent aromatic group which may contain an oxygen atom, and R 1 and R 2Each independently represents a monovalent aromatic group or a monovalent aliphatic group, and R 3 and R 4 Each independently represents a monovalent aliphatic group, R 5 and R 6 Each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer greater than 1, and the sum of m and n represents an integer of 2 to 1,000.

[0110] It should be noted that in formula (b3), two or more different repeating units described in [] may be repeated in any form and order, whether random, alternating or block-like, regardless of the order of [].

[0111] In formula (b3), Z 1 and Z 2 The divalent aliphatic group or divalent aromatic group in the formula (I) may be substituted with a fluorine atom. Examples of the divalent aliphatic group include a divalent saturated or unsaturated aliphatic group having 1 to 20 carbon atoms and an aliphatic group containing an oxygen atom. The divalent aliphatic group preferably has 3 to 20 carbon atoms.

[0112] Examples of the divalent saturated aliphatic group include alkylene groups having 1 to 20 carbon atoms, such as methylene, ethylene, propylene, trimethylene, tetramethylene, hexamethylene, octamethylene, decamethylene, and dodecamethylene.

[0113] Examples of the divalent unsaturated aliphatic group include alkenylene groups having 2 to 20 carbon atoms, such as vinylene groups, propenylene groups, and alkenylene groups having an unsaturated double bond at the terminal.

[0114] Examples of the aliphatic group containing an oxygen atom include an alkyleneoxy group and an aliphatic group having an ether bond.

[0115] Examples of the alkyleneoxy group include a propyleneoxy group and a trimethyleneoxy group.

[0116] Examples of the divalent aromatic group include an arylene group having 6 to 20 carbon atoms and an aralkylene group having 7 to 20 carbon atoms. 1 and Z 2 Specific examples of the arylene group having 6 to 20 carbon atoms include o-phenylene, m-phenylene, p-phenylene, 4,4′-biphenylene, and 2,6-naphthylene.

[0117] As Z 1 and Z 2 , particularly preferably trimethylene and p-phenylene, more preferably trimethylene.

[0118] In formula (b3), as R 1 ~R6 The monovalent aliphatic group in the formula (a) may be a monovalent saturated or unsaturated aliphatic group. As the monovalent saturated aliphatic group, an alkyl group having 1 to 22 carbon atoms may be mentioned, such as methyl, ethyl, propyl, etc. As the monovalent unsaturated aliphatic group, an alkenyl group having 2 to 22 carbon atoms may be mentioned, such as vinyl, propenyl, etc. These groups may be substituted with fluorine atoms.

[0119] As R of formula (b3) 1 , R 2 , R 5 and R 6 Examples of the monovalent aromatic group in include an aryl group having 6 to 20 carbon atoms, an aryl group having 7 to 30 carbon atoms and substituted by an alkyl group, and an aralkyl group having 7 to 30 carbon atoms. The monovalent aromatic group is preferably an aryl group, and more preferably a phenyl group.

[0120] Preferred R 1 and R 2 At least one of them is a monovalent aromatic group, and more preferably R 1 and R 2 are all monovalent aromatic groups, and R 1 and R 2 All are phenyl.

[0121] As R 3 and R 4 , preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group.

[0122] As R 5 and R 6 , preferably a monovalent aliphatic group, more preferably a methyl group.

[0123] As described above, among the compounds represented by the general formula (b3), the compounds represented by the following formula (b31) are preferred.

[0124]

[0125] (In formula (b31), m and n have the same meanings as m and n in formula (b3), and the preferred ranges are also the same.)

[0126] In formula (b3) and formula (b31), m represents the number of repetitions of siloxane units to which at least one monovalent aromatic group is bonded, and n represents the number of repetitions of siloxane units to which a monovalent aliphatic group is bonded.

[0127] In formula (b3) and formula (b31), m and n each independently represent an integer greater than 1, and the sum of m and n (m+n) represents an integer of 2 to 1000. The sum of m and n preferably represents an integer of 3 to 500, more preferably 3 to 100, and even more preferably 3 to 50.

[0128] The ratio of m / n in the formula (b3) and the formula (b31) is preferably 5 / 95 to 50 / 50, more preferably 10 / 90 to 40 / 60, and further preferably 20 / 80 to 30 / 70.

[0129] The functional group equivalent (amine equivalent) of the compound represented by formula (b3) is preferably 150 to 5000 g / mol, more preferably 400 to 4000 g / mol, and further preferably 500 to 3000 g / mol.

[0130] In addition, the functional group equivalent refers to the mass of the compound represented by formula (b3) per 1 mol of the functional group (amino group).

[0131] Among the compounds represented by the general formula (b3), those available as commercial products include "X-22-9409", "X-22-1660B", "X-22-161A", and "X-22-161B" manufactured by Shin-Etsu Chemical Co., Ltd.

[0132] The structural unit B contains the structural unit (B3), thereby improving the colorless transparency, optical isotropy and flexibility of the film.

[0133] The structural unit B may contain structural units other than the structural units (B1) to (B3). The diamines that provide such structural units are not particularly limited, and examples thereof include 1,4-phenylenediamine, p-phenylenediamine, 3,5-diaminobenzoic acid, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobenzanilide, 3,4'-diaminodiphenyl ether, 1-( Aromatic diamines such as 1,4-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 9,9-bis(4-aminophenyl)fluorene, and 1,4-bis(4-aminophenoxy)benzene; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine.

[0134] 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 and no aromatic ring, and aliphatic diamine refers to a diamine containing neither an aromatic ring nor an alicyclic ring.

[0135] The structural unit other than the structural units (B1) to (B3) optionally contained in the structural unit B may be one kind or two or more kinds.

[0136] [Composition of structural unit B]

[0137] When the structural unit B contains the structural unit (B1) and the structural unit (B2), the ratio of the total of the structural unit (B1) and the structural unit (B2) in the structural unit B is preferably 70 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, and further preferably 95 mol% or more. The upper limit of the ratio of the total of the structural unit (B1) and the structural unit (B2) is not particularly limited, but is preferably 100 mol%, and the ratio of the total of the structural unit (B1) and the structural unit (B2) in the structural unit B is 100 mol% or less. It is further preferred that the structural unit B consists only of the structural unit (B1) and the structural unit (B2).

[0138] When the structural unit B contains the structural unit (B1) and the structural unit (B2), the molar ratio of the structural unit (B1) to the structural unit (B2) [(B1) / (B2)] is preferably 40 / 60 to 80 / 20, more preferably 45 / 55 to 75 / 25, further preferably 45 / 55 to 70 / 30, further preferably 45 / 55 to 65 / 35, further preferably 45 / 55 to 60 / 40, further preferably 45 / 55 to 55 / 45.

[0139] When the structural unit B contains the structural unit (B1) and the structural unit (B3), the ratio of the total of the structural unit (B1) and the structural unit (B3) in the structural unit B is preferably 70 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, and further preferably 95 mol% or more. The upper limit of the ratio of the total of the structural unit (B1) and the structural unit (B3) is not particularly limited, but is preferably 100 mol%, and the ratio of the total of the structural unit (B1) and the structural unit (B3) in the structural unit B is 100 mol% or less. It is further preferred that the structural unit B consists only of the structural unit (B1) and the structural unit (B3).

[0140] When the structural unit B contains the structural unit (B1) and the structural unit (B3), the molar ratio of the structural unit (B1) to the structural unit (B3) [(B1) / (B3)] is preferably 40 / 60 to 99 / 1, more preferably 50 / 50 to 95 / 5, further preferably 60 / 40 to 90 / 10, and further preferably 70 / 30 to 90 / 10.

[0141] When the structural unit B contains the structural unit (B1), the structural unit (B2) and the structural unit (B3), the ratio of the total of the structural unit (B1), the structural unit (B2) and the structural unit (B3) in the structural unit B is preferably 70 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, and further preferably 95 mol% or more. The upper limit of the ratio of the total of the structural unit (B1), the structural unit (B2) and the structural unit (B3) is not particularly limited, but is preferably 100 mol%, and the ratio of the total of the structural unit (B1), the structural unit (B2) and the structural unit (B3) in the structural unit B is 100 mol% or less. It is further preferred that the structural unit B consists only of the structural unit (B1), the structural unit (B2) and the structural unit (B3).

[0142] When the structural unit B includes the structural unit (B1), the structural unit (B2) and the structural unit (B3), the molar ratio of the structural unit (B1) to the structural unit (B2) [(B1) / (B2)] is the same as that in the case where the structural unit B includes the structural unit (B1) and the structural unit (B2), and the content of the structural unit (B3) in the structural unit B is preferably 1 to 50 mass %, more preferably 1 to 40 mass %, further preferably 1 to 30 mass %, and further preferably 1 to 20 mass %.

[0143] (Physical properties of polyimide resin, etc.)

[0144] From the viewpoint of mechanical strength of the obtained polyimide film, the number average molecular weight of the polyimide resin used in the production method of the present invention is preferably 5000 to 200000. The number average molecular weight of the polyimide resin can be determined, for example, from a standard polymethyl methacrylate (PMMA) conversion value measured by gel filtration chromatography.

[0145] The polyimide resin used in the production method of the present invention may contain structures other than the polyimide chain (structure formed by imide bonding of structural unit A and structural unit B). Examples of structures other than the polyimide chain that may be contained in the polyimide resin include structures containing amide bonds.

[0146] The polyimide resin used in the manufacturing method of the present invention preferably contains a polyimide chain (a structure formed by imide bonding of structural unit A and structural unit B) as a main structure. Therefore, the ratio of the polyimide chain in the polyimide resin used in the manufacturing method of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 90% by mass or more, and particularly preferably 99% by mass or more. In addition, it can be 100% by mass or less.

[0147] By using the polyimide resin of the present invention, a film having particularly excellent optical isotropy can be formed, and suitable physical property values ​​of the film are as follows.

[0148] When formed into a thin film with a thickness of 30 μm, the total light transmittance is preferably 79% or more, more preferably 85% or more, further preferably 88% or more, and further preferably 89% or more.

[0149] When formed into a thin film with a thickness of 30 μm, the haze is preferably 0.6% or less, more preferably 0.4% or less, further preferably 0.3% or less, and further preferably 0.2% or less.

[0150] When formed into a thin film having a thickness of 30 μm, the yellowness index (YI) is preferably 31 or less, more preferably 7 or less, further preferably 3 or less, and further preferably 2 or less.

[0151] When a thin film having a thickness of 30 μm is formed, the in-plane retardation (Re) is preferably 10 nm or less, more preferably 8 nm or less, further preferably 6 nm or less, further preferably 5 nm or less, further preferably 4 nm or less.

[0152] When a thin film having a thickness of 30 μm is formed, the thickness retardation (Rth) is preferably 30 nm or less, more preferably 28 nm or less, further preferably 25 nm or less, further preferably 15 nm or less, further preferably 10 nm or less.

[0153] It should be noted that the above-mentioned physical property values ​​in the present invention can be specifically measured by the methods described in Examples.

[0154] <Method for producing polyimide resin>

[0155] The polyimide resin of the present invention can be produced by reacting a tetracarboxylic acid component which is a compound providing the structural unit A and a diamine component containing a compound providing the structural unit (B1).

[0156] As the compound providing the structural unit A, it is preferred to contain alicyclic tetracarboxylic dianhydride.

[0157] As a compound providing a structural unit derived from alicyclic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride can be cited, but it is not limited thereto, and its derivatives can also be provided within the scope of providing the same structural unit. As the derivative, tetracarboxylic acids corresponding to alicyclic tetracarboxylic dianhydride and alkyl esters of the tetracarboxylic acids can be cited. As a compound providing a structural unit derived from alicyclic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride is preferred.

[0158] As the compound which provides the structural unit derived from alicyclic tetracarboxylic dianhydride, a compound which provides the structural unit (A1) and a compound which provides the structural unit (A2) are preferred.

[0159] As the compound providing the structural unit (A1), the compound shown in formula (a1) can be cited, but it is not limited thereto, and its derivative can also be provided within the scope of providing the same structural unit. As the derivative, tetracarboxylic acid corresponding to the tetracarboxylic dianhydride shown in formula (a1) and the alkyl ester of the tetracarboxylic acid can be cited. As the compound providing the structural unit (A1), the compound shown in formula (a1) (i.e., dianhydride) is preferred.

[0160] Similarly, as the compound providing structural unit (A2), the compound shown in formula (a2) can be cited, but it is not limited thereto, and it can also be its derivative within the scope of providing the same structural unit. As the derivative, tetracarboxylic acid corresponding to the tetracarboxylic dianhydride shown in formula (a2) and the alkyl ester of the tetracarboxylic acid can be cited. As the compound providing structural unit (A2), the compound shown in formula (a2) (i.e., dianhydride) is preferred.

[0161] When the tetracarboxylic acid component includes a compound providing a structural unit (A1) and a compound providing a structural unit (A2), the total preferably includes 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more of the compound providing a structural unit (A1) and the compound providing a structural unit (A2). The upper limit of the total content of the compound providing a structural unit (A1) and the compound providing a structural unit (A2) is not particularly limited, that is, 100 mol%, and the content is 100 mol% or less. The tetracarboxylic acid component can be composed only of a compound providing a structural unit (A1) and a compound providing a structural unit (A2).

[0162] When the tetracarboxylic acid component includes a compound providing a structural unit (A1) or a compound providing a structural unit (A2), it is preferably included in an amount of 45 mol% or more, more preferably 70 mol% or more, and further preferably 90 mol% or more of a compound providing a structural unit (A1) or a compound providing a structural unit (A2). The upper limit of the content of the compound providing a structural unit (A1) or the compound providing a structural unit (A2) is not limited, that is, 100 mol%, and the content is 100 mol% or less. The tetracarboxylic acid component can be composed only of a compound providing a structural unit (A1) or a compound providing a structural unit (A2), and is preferably composed only of a compound providing a structural unit (A1).

[0163] The tetracarboxylic acid component may contain a compound that provides the above-mentioned structural unit (A3).

[0164] As the compound providing the structural unit (A3), the compound shown in the general formula (a3) ​​can be cited, but it is not limited thereto, and its derivative can also be provided within the scope of providing the same structural unit. As the derivative, the tetracarboxylic acid corresponding to the tetracarboxylic dianhydride shown in the general formula (a3) ​​and the alkyl ester of the tetracarboxylic acid can be cited. As the compound providing the structural unit (A3), the compound shown in the general formula (a3) ​​(i.e., dianhydride) is preferred.

[0165] When the tetracarboxylic acid component contains a compound providing structural unit (A3), it preferably contains 55 mol% or less, more preferably 30 mol% or less, and preferably 1 mol% or more of the compound providing structural unit (A3). When the tetracarboxylic acid component contains a compound providing structural unit (A3), it is preferably composed only of a compound providing structural unit (A1) and a compound providing structural unit (A3).

[0166] The tetracarboxylic acid component may contain compounds other than the aforementioned alicyclic tetracarboxylic dianhydride, the compound providing the structural unit (A1), the compound providing the structural unit (A2), and the compound providing the structural unit (A3). Examples of such compounds include the aforementioned aromatic tetracarboxylic dianhydride, aliphatic tetracarboxylic dianhydride, and derivatives thereof (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.).

[0167] The compound contained in the tetracarboxylic acid component may be one kind or two or more kinds.

[0168] As the compound providing the structural unit (B1), the compound providing the structural unit (B11), i.e., the compound represented by the general formula (b11), and the compound providing the structural unit (B12), i.e., the compound represented by the general formula (b12), can be cited, but it is not limited thereto, and its derivatives can also be provided within the scope of providing the same structural unit. As the derivative, diisocyanates corresponding to the diamine represented by the general formula (b11) and the diamine represented by the general formula (b12) can be cited. As the compound providing the structural unit (B1), it is preferred to select at least one compound (i.e., diamine) from the group consisting of the compound represented by the general formula (b11) and the compound represented by the general formula (b12).

[0169] The diamine component may contain a compound that provides two or more of the structural units (B11) and (B12), but preferably contains a compound that provides one of the structural units (B11) and (B12). That is, the structural unit B preferably contains a compound that provides the structural unit (B11) or a compound that provides the structural unit (B12).

[0170] The diamine component may contain a compound that provides the above-mentioned structural unit (B2).

[0171] As the compound providing the structural unit (B2), the compound shown in the general formula (b21), the compound shown in the general formula (b22), and the compound shown in the general formula (b23) can be cited, but it is not limited thereto, and its derivatives can also be provided within the scope of providing the same structural unit. As the derivative, the diisocyanate corresponding to the diamine shown in the general formula (b21), the diisocyanate corresponding to the diamine shown in the general formula (b22), and the diisocyanate corresponding to the diamine shown in the general formula (b23) can be cited. As the compound providing the structural unit (B2), it is preferred to be selected from at least one compound (i.e., diamine) in the group consisting of the compound shown in the general formula (b21), the compound shown in the general formula (b22), and the compound shown in the general formula (b23).

[0172] As the compound providing the structural unit (B2), it is preferred to include a compound represented by the general formula (b21) or a compound represented by the general formula (b23), and it is more preferred to include a compound represented by the general formula (b21).

[0173] As the compound represented by the general formula (b21), it is more preferred to contain at least one compound selected from the group consisting of the compound represented by the formula (b211), the compound represented by the formula (b212), and the compound represented by the formula (b213), and it is further preferred to contain at least one compound selected from the group consisting of the compound represented by the formula (b211) and the compound represented by the formula (b212), and the compound represented by the formula (b211) is particularly preferred.

[0174] As the compound represented by the general formula (b23), a compound represented by the formula (b231) is preferred.

[0175] The diamine component may contain a compound that provides the above-mentioned structural unit (B3).

[0176] As the compound providing the structural unit (B3), the compound shown in the general formula (b3) can be cited, but it is not limited thereto, and its derivative can also be provided within the scope of providing the same structural unit. As the derivative, the diisocyanate corresponding to the compound shown in the general formula (b3) can be cited. As the compound providing the structural unit (B3), the compound shown in the general formula (b3) (i.e., diamine) is preferred.

[0177] The compound providing the structural unit (B3) is preferably a compound represented by the general formula (b3), and more preferably includes a compound represented by the formula (b31).

[0178] When the diamine component includes a compound providing structural unit (B1) and a compound providing structural unit (B2), the total content of the compound providing structural unit (B1) and the compound providing structural unit (B2) is preferably 70 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, and particularly preferably 95 mol% or more. The upper limit of the total content of the compound providing structural unit (B1) and the compound providing structural unit (B2) is not particularly limited, that is, 100 mol%. The diamine component may be composed only of the compound providing structural unit (B1) and the compound providing structural unit (B2).

[0179] When the diamine component contains a compound providing the structural unit (B1) and a compound providing the structural unit (B2), the molar ratio of the compound providing the structural unit (B1) to the compound providing the structural unit (B2) [(B1) / (B2)] is preferably 40 / 60 to 80 / 20, more preferably 45 / 55 to 75 / 25, further preferably 45 / 55 to 70 / 30, further preferably 45 / 55 to 65 / 35, further preferably 45 / 55 to 60 / 40, further preferably 45 / 55 to 55 / 45.

[0180] When the diamine component includes a compound providing the structural unit (B1) and a compound providing the structural unit (B3), the total amount of the compound providing the structural unit (B1) and the compound providing the structural unit (B3) is preferably 70 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, and particularly preferably 95 mol% or more. The upper limit of the total content of the compound providing the structural unit (B1) and the compound providing the structural unit (B3) is not particularly limited, that is, 100 mol%, and the content is 100 mol% or less. The diamine component may be composed only of the compound providing the structural unit (B1) and the compound providing the structural unit (B3).

[0181] When the diamine component contains a compound providing the structural unit (B1) and a compound providing the structural unit (B3), the molar ratio of the compound providing the structural unit (B1) to the compound providing the structural unit (B3) [(B1) / (B3)] is preferably 40 / 60 to 99 / 1, more preferably 50 / 50 to 95 / 5, further preferably 60 / 40 to 90 / 10, and further preferably 70 / 30 to 90 / 10.

[0182] When the diamine component includes a compound providing a structural unit (B1), a compound providing a structural unit (B2), and a compound providing a structural unit (B3), the total amount of the compound providing a structural unit (B1), a compound providing a structural unit (B2), and a compound providing a structural unit (B3) is preferably 70 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, and particularly preferably 95 mol% or more. The upper limit of the total content of the compound providing a structural unit (B1), a compound providing a structural unit (B2), and a compound providing a structural unit (B3) is not particularly limited, that is, 100 mol%, and the content is 100 mol% or less. The diamine component may be composed only of a compound providing a structural unit (B1), a compound providing a structural unit (B2), and a compound providing a structural unit (B3).

[0183] When the diamine component contains a compound providing structural unit (B1), a compound providing structural unit (B2), and a compound providing structural unit (B3), the molar ratio of the compound providing structural unit (B1) to the compound providing structural unit (B2) [(B1) / (B2)] is the same as in the case where the diamine component contains a compound providing structural unit (B1) and a compound providing structural unit (B2), and the content of the compound providing structural unit (B3) in the diamine component is preferably 1 to 50% by mass, more preferably 1 to 40% by mass, further preferably 1 to 30% by mass, and further preferably 1 to 20% by mass.

[0184] The diamine component may contain compounds other than the compound providing the structural unit (B1), the compound providing the structural unit (B2) and the compound providing the structural unit (B3), and examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, and their derivatives (diisocyanates, etc.).

[0185] The compound other than the compound providing the structural unit (B1), the compound providing the structural unit (B2), and the compound providing the structural unit (B3) which is optionally contained in the diamine component may be one kind or two or more kinds.

[0186] In the present invention, the charging amount ratio of the tetracarboxylic acid component and the diamine component used for producing the polyimide resin is preferably 0.9 to 1.1 mol of the diamine component relative to 1 mol of the tetracarboxylic acid component.

[0187] In addition, in the present invention, when manufacturing the polyimide resin, in addition to the aforementioned tetracarboxylic acid component and diamine component, an end-capping agent can also be used. As the end-capping agent, monoamines or dicarboxylic acids are preferred. The amount of the introduced end-capping agent is preferably 0.0001 to 0.1 moles, particularly preferably 0.001 to 0.06 moles, relative to 1 mole of the tetracarboxylic acid component. As monoamine end-capping agents, for example, methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline, etc. are recommended. Among them, benzylamine and aniline can be suitably used. As dicarboxylic acid end-capping agents, dicarboxylic acids are preferred, and a part of them can be ring-closed. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenone dicarboxylic acid, 3,4-benzophenone dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. are recommended. Among them, phthalic acid and phthalic anhydride can be preferably used.

[0188] The method for reacting the tetracarboxylic acid component and the diamine component is not particularly limited, and a known method can be used.

[0189] Specific reaction methods include: method (1), in which a tetracarboxylic acid component, a diamine component and a reaction solvent are added to a reactor, stirred at 0 to 80° C. for 0.5 to 30 hours, and then heated to carry out an imidization reaction; method (2), in which a diamine component and a reaction solvent are added to a reactor to dissolve them, and then a tetracarboxylic acid component is added, and stirred at 0 to 80° C. for 0.5 to 30 hours as required, and then heated to carry out an imidization reaction; method (3), in which a tetracarboxylic acid component, a diamine component and a reaction solvent are added to a reactor, and then the temperature is immediately raised to carry out an imidization reaction; etc.

[0190] The reaction solvent used in the production of the polyimide resin may be any solvent as long as it does not inhibit the imidization reaction and can dissolve the generated polyimide, and examples thereof include aprotic solvents, phenolic solvents, etheric solvents, carbonate solvents, and the like.

[0191] Specific examples of aprotic solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone solvents such as γ-butyrolactone and γ-valerolactone; phosphorus-containing amide solvents such as hexamethylphosphoramide and hexamethylphosphinetriamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and cyclopentane; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methylcyclohexanone; amine solvents such as picoline and pyridine; and ester solvents such as (2-methoxy-1-methylethyl)acetate.

[0192] Specific examples of the phenolic solvent 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.

[0193] Specific examples of the ether solvent 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.

[0194] Specific examples of the carbonate-based solvent include diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate.

[0195] Among the above reaction solvents, amide solvents or lactone solvents are preferred. The above reaction solvents may be used alone or in combination of two or more.

[0196] In the imidization reaction, it is preferred to use a Dean-Stark water trap apparatus or the like to carry out the reaction while removing water generated during the production. By carrying out such an operation, the degree of polymerization and the imidization ratio can be further increased.

[0197] In the above-mentioned imidization reaction, a known imidization catalyst can be used. Examples of the imidization catalyst include a base catalyst and an acid catalyst.

[0198] Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-methylpyridine, β-methylpyridine, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, 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 hydrogen carbonate, and sodium hydrogen carbonate.

[0199] Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, hydroxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid. The imidization catalysts described above may be used alone or in combination of two or more.

[0200] Among the above, from the viewpoint of operability, it is preferred to use a base catalyst, more preferably to use an organic base catalyst, further preferably to use one or more selected from triethylamine and triethylenediamine, and particularly preferably to use triethylamine.

[0201] From the viewpoint of reaction rate and suppression of gelation, the temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C. The reaction time is preferably 0.5 to 10 hours after the start of distillation of generated water.

[0202] <Polyimide varnish>

[0203] The polyimide varnish used in the production method of the present invention is obtained by dissolving the polyimide resin in an organic solvent. That is, the polyimide varnish used in the production method of the present invention contains the polyimide resin and an organic solvent, and the polyimide resin is dissolved in the organic solvent.

[0204] The organic solvent is not particularly limited as long as it can dissolve the polyimide resin, and it is preferred to use the above compounds alone or in combination of two or more as a reaction solvent used in the production of the polyimide resin.

[0205] The polyimide varnish used in the production method of the present invention may be a polyimide solution itself in which a polyimide resin obtained by a polymerization method is dissolved in a reaction solvent, or may be a polyimide varnish obtained by further adding an organic solvent to the polyimide solution and diluting the polyimide solution.

[0206] The polyimide varnish used in the manufacturing method of the present invention may be a polyimide resin dissolved in a low boiling point solvent having a boiling point of 130° C. or less. By using the low boiling point solvent as an organic solvent, the heating temperature during the manufacture of the polyimide film described later can be reduced. Examples of the low boiling point solvent include carbon tetrachloride, dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran, acetone, etc., among which dichloromethane is preferred.

[0207] The polyimide resin has solvent solubility, and therefore, a high-concentration varnish that is stable at room temperature can be formed. The polyimide varnish of the present invention preferably contains 5 to 40% by mass of the polyimide resin, and more preferably contains 10 to 30% by mass. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, and more preferably 5 to 150 Pa·s. The viscosity of the polyimide varnish is a value measured at 25°C using an E-type viscometer.

[0208] In addition, the polyimide varnish used in the manufacturing method of the present invention may contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, ultraviolet stabilizers, surfactants, leveling agents, defoaming agents, fluorescent whitening agents, crosslinking agents, polymerization initiators, and photosensitizers within the range that does not impair the required properties of the polyimide film obtained by the manufacturing method of the present invention.

[0209] The method for producing the polyimide varnish used in the production method of the present invention is not particularly limited, and a known method can be applied.

[0210] <Manufacturing of polyimide film>

[0211] The method for producing a polyimide film of the present invention is a method for producing a polyimide film formed by the above-mentioned polyimide resin, and the production method is as follows: the above-mentioned polyimide varnish is coated on a support, the organic solvent contained in the varnish is removed at 60 to 140° C. to form a self-supporting film, the self-supporting film is peeled off from the support, the ends of the self-supporting film are fixed, and the film is calcined at a temperature exceeding the glass transition temperature of the polyimide resin and below a temperature 50° C. higher than the glass transition temperature of the polyimide resin.

[0212] That is, the method for producing a polyimide film of the present invention preferably includes a step of obtaining the above-mentioned polyimide varnish, and specifically, more preferably includes the following step: imidizing a tetracarboxylic acid component providing a structural unit A derived from tetracarboxylic dianhydride and a diamine component providing a structural unit B derived from diamine in the presence of a base catalyst and an organic solvent, and adding an organic solvent as needed to obtain a polyimide varnish.

[0213] The tetracarboxylic acid component, diamine component, base catalyst and organic solvent used in the above-mentioned imidization and polyimide varnish obtaining step include those described in the above-mentioned <Method for producing polyimide resin>, and suitable tetracarboxylic acid components, diamine components, base catalysts and organic solvents are also the same.

[0214] Examples of a method for coating the polyimide varnish on a support include a method of coating the polyimide varnish on a smooth support such as a glass plate, a metal plate, or plastic. A glass rod, a coater, or the like can be used for coating.

[0215] The coating is preferably performed so that the thickness of the film after drying becomes preferably 1 to 250 μm, more preferably 5 to 100 μm, and further preferably 10 to 80 μm.

[0216] The surface of the support may be coated with a release agent in advance as necessary.

[0217] Then, the organic solvent contained in the varnish is removed at 60 to 140° C. to form a self-supporting film, and the self-supporting film is peeled off from the support.

[0218] The temperature when removing the organic solvent contained in the varnish is 60 to 140° C., preferably 80 to 120° C. The removal of the organic solvent is preferably performed under a nitrogen atmosphere. The removal of the organic solvent may be performed under reduced pressure, normal pressure, or increased pressure.

[0219] The obtained film is peeled off from the support body. The peeled film has self-supporting properties.

[0220] The end portion of the obtained self-supporting film is fixed and baked at a temperature exceeding the glass transition temperature of the polyimide resin and at a temperature not higher than 50° C. higher than the glass transition temperature of the polyimide resin.

[0221] For example, if the glass transition temperature of the polyimide resin is 300° C., in the method for producing the polyimide film of the present invention, calcination is performed at a temperature exceeding 300° C. and 350° C. or lower.

[0222] In the present invention, even if the calcination temperature deviates from the above range for a short period of time, it is also included in the present invention within the range that does not impair the effect of the present invention. For example, it can be mentioned that the calcination temperature exceeds the temperature 50°C higher than the glass transition temperature of the polyimide resin within a range of 5% or less of the total calcination time.

[0223] Hereinafter, the glass transition temperature of the polyimide resin is represented by (Tg), and the temperature higher by X° C. than the glass transition temperature of the polyimide resin is represented by (Tg+X° C.).

[0224] The temperature for calcining is a temperature exceeding the glass transition temperature (Tg) of the polyimide resin and below a temperature 50°C higher than the glass transition temperature of the polyimide resin (Tg+50°C), preferably a temperature 3°C higher than the glass transition temperature of the polyimide resin (Tg+3°C) or higher, more preferably a temperature 5°C higher than the glass transition temperature of the polyimide resin (Tg+5°C) or higher, further preferably a temperature 7°C higher than the glass transition temperature of the polyimide resin (Tg+7°C) or higher, and further preferably a temperature 10°C higher than the glass transition temperature of the polyimide resin (Tg+10°C) or higher. In addition, it is preferably a temperature below the temperature 40°C higher than the glass transition temperature of the polyimide resin (Tg+40°C), more preferably a temperature below the temperature 30°C higher than the glass transition temperature of the polyimide resin (Tg+30°C), further preferably a temperature below the temperature 20°C higher than the glass transition temperature of the polyimide resin (Tg+20°C), and further preferably a temperature below the temperature 15°C higher than the glass transition temperature of the polyimide resin (Tg+15°C).

[0225] By calcining within the above temperature range, a polyimide film having colorlessness, transparency and excellent optical isotropy can be obtained.

[0226] Furthermore, from the viewpoint of further improving optical isotropy in particular, a temperature that is 15°C higher than the glass transition temperature of the polyimide resin (Tg+15°C) or higher, a temperature that is 20°C higher than the glass transition temperature of the polyimide resin (Tg+20°C) or higher, and a temperature that is 25°C higher than the glass transition temperature of the polyimide resin (Tg+25°C) or higher is more preferably used.

[0227] On the other hand, from the viewpoint of further improving the colorless transparency, in particular, it is further preferred that the temperature is 15°C higher than the glass transition temperature of the polyimide resin (Tg+15°C) or lower, further preferred that the temperature is 10°C higher than the glass transition temperature of the polyimide resin (Tg+10°C) or lower, and further preferred that the temperature is 5°C higher than the glass transition temperature of the polyimide resin (Tg+5°C) or lower.

[0228] The glass transition temperature of the polyimide preferably used in the production method of the present invention and the calcination temperature are preferably 190 to 360°C, more preferably 200 to 350°C, further preferably 230 to 320°C, further preferably 240 to 300°C, further preferably 240 to 280°C.

[0229] The calcination is preferably carried out in a nitrogen atmosphere. The calcination may be carried out under any pressure of reduced pressure, normal pressure or increased pressure.

[0230] The calcination time is preferably 3 to 60 minutes, more preferably 5 to 60 minutes, further preferably 5 to 30 minutes, and further preferably 5 to 20 minutes.

[0231] Furthermore, from the viewpoint of further improving colorless transparency, the time is preferably 3 to 30 minutes, more preferably 3 to 20 minutes, further preferably 3 to 15 minutes, and still further preferably 5 to 15 minutes.

[0232] On the other hand, from the viewpoint of further improving the optical isotropy, the time is more preferably 10 to 50 minutes, further preferably 15 to 40 minutes, and still further preferably 17 to 28 minutes.

[0233] It should be noted that the calcination time starts from the time when the target temperature is reached at a temperature 3 to 50°C higher than the glass transition temperature of the polyimide resin, and ends at the time when the temperature is lowered by 1°C or more by cooling or reducing the heating. In addition, when there are multiple target temperatures within the above range, the total time of these target temperatures is taken as the calcination time.

[0234] In the method for producing a polyimide film of the present invention, after calcining under the above conditions, cooling is preferably performed or annealing is performed, and cooling is more preferably performed.

[0235] The cooling is preferably a method of slowly cooling from the calcination temperature to room temperature (eg, 25° C.).

[0236] Annealing is preferably performed at a temperature lower than the temperature at which calcination is performed, more preferably at a temperature lower than 10°C lower than the temperature at which calcination is performed, further preferably at a temperature lower than 30°C lower than the temperature at which calcination is performed, and further preferably at a temperature lower than 50°C lower than the temperature at which calcination is performed.

[0237] The thickness of the polyimide film of the present invention can be appropriately selected depending on the application, and is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, and even more preferably 10 to 80 μm. When the thickness is 1 to 250 μm, it can be practically used as a self-supporting film.

[0238] The thickness of the polyimide film can be easily controlled by adjusting the solid content concentration and viscosity of the polyimide varnish.

[0239] The polyimide film obtained by the production method of the present invention is suitable for use as a film for various components such as color filters, flexible displays, semiconductor components, optical components, etc. The polyimide film of the present invention is particularly suitable for use as a substrate for image display devices such as liquid crystal displays and OLED displays.

[0240] Example

[0241] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[0242] The solid content concentration of the varnishes obtained in Examples and Comparative Examples and various physical properties of the thin films were measured by the methods shown below.

[0243] (1) Solid content concentration

[0244] The solid content concentration of the varnish was measured by heating a sample at 280° C. for 120 minutes in a small electric furnace “MMF-1” manufactured by AS ONE CORPORATION and calculating the solid content concentration from the difference in mass of the sample before and after heating.

[0245] (2) Glass transition temperature (Tg) of polyimide resin

[0246] The glass transition temperature of the polyimide resin is measured as follows: using a differential scanning calorimeter device "DSC 7000X" manufactured by Hitachi High-Tech Science Co., Ltd., according to JIS K7121. DSC measurement is performed under the condition of a heating rate of 10°C / min to obtain a DSC curve. The glass transition temperature is set as follows: according to the method described in JIS K7121, the straight line extending from each baseline (high temperature side baseline and low temperature side baseline) in the aforementioned DSC curve is set to the point where the straight line located at an equal distance along the vertical axis direction and the curve of the step-shaped change part of the glass transition intersects (the midpoint glass transition temperature).

[0247] (3) Film thickness

[0248] The film thickness was measured using a micrometer manufactured by Mitutoyo Co., Ltd.

[0249] (4) Total light transmittance, haze, yellowness index (YI) (evaluation of colorless transparency)

[0250] The total light transmittance, haze, and YI were measured using a color / turbidity simultaneous measuring device "COH7700" manufactured by Nippon Denshoku Industries, Ltd.

[0251] The total light transmittance was measured in accordance with JIS K7361-1:1997, the haze was measured in accordance with JIS K7136:2000, and the YI was measured in accordance with ASTM E313-05.

[0252] (5) In-plane retardation (Re) (Evaluation of optical isotropy)

[0253] The in-plane retardation (Re) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The value of the in-plane phase difference at a measurement wavelength of 590 nm was measured.

[0254] (6) Thickness phase difference (Rth) (Evaluation of optical isotropy)

[0255] The thickness phase difference (Rth) is measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The value of the thickness phase difference is measured at a measurement wavelength of 550nm. It should be noted that when the maximum refractive index in the plane of the polyimide film is set to nx, the minimum is set to ny, the refractive index in the thickness direction is set to nz, and the thickness of the film is set to d, Rth is represented by the following formula.

[0256] Rth=[{(nx+ny) / 2}-nz]×d

[0257] The tetracarboxylic acid component and the diamine component used in Examples and Comparative Examples, and their abbreviations and the like are as follows.

[0258] <Tetracarboxylic acid component>

[0259] HPMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Co., Ltd.; compound represented by formula (a1))

[0260] <Diamine component>

[0261] BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (manufactured by Wakayama Seika Industries, Ltd., a compound represented by formula (b11))

[0262] BODA: 4,4'-bis(4-aminophenoxy)biphenyl (compound represented by formula (b12))

[0263] BisAM: 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene (manufactured by Mitsui Chemical Fine Co., Ltd., a compound represented by formula (b211))

[0264] BisAP: 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene (compound represented by formula (b231))

[0265] The details of the solvents and catalysts used in Examples and Comparative Examples are as follows.

[0266] γ-Butyrolactone (Mitsubishi Chemical Corporation)

[0267] N,N-dimethylacetamide (manufactured by Mitsubishi Gas Chemical Co., Ltd.)

[0268] Triethylamine (manufactured by Kanto Chemical Co., Ltd.)

[0269] <Example 1>

[0270] A 0.3L five-necked glass round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet pipe, a Dean-Stark trap equipped with a condenser, a thermometer, and a glass end cap was used as a reaction apparatus. In the round-bottom flask, 20.534g (0.050 mol) of BAPP, 17.289g (0.050 mol) of BisAM, 49.1g of γ-butyrolactone, and 10.13g of triethylamine as a catalyst were placed. Then, the temperature was raised to 80°C while stirring at 150 rpm under a nitrogen atmosphere to obtain a solution. After 22.439g (0.100 mol) of HPMDA and 11.1g of γ-butyrolactone were added to the solution, the solution was heated in a hooded heater, and the temperature in the reaction system was raised to 190°C in about 20 minutes. The components removed by distillation were collected, and the temperature in the reaction system was maintained at 190°C for 7 hours. After adding 166.1 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a uniform polyimide varnish (1) having a solid content concentration of 20% by mass.

[0271] Next, the obtained polyimide varnish (1) was applied on a PET substrate and maintained at 100°C for 20 minutes to volatilize the solvent, thereby obtaining a self-supporting colorless and transparent primary dried film. The film was further fixed to a stainless steel frame and baked at 255°C in an air atmosphere for 20 minutes to obtain a film. The evaluation results of the polyimide film are shown in Table 1.

[0272] <Examples 2 to 4 and Comparative Examples 1 and 2>

[0273] The polyimide varnish (1) obtained by the method described in Example 1 was applied to a PET substrate and maintained at 100°C for 20 minutes to volatilize the solvent, thereby obtaining a self-supporting colorless and transparent primary dried film. The film was further fixed to a stainless steel frame and baked at the baking temperature (210 to 320°C) described in Table 1 in an air atmosphere for 20 minutes to obtain a film. The evaluation results of these polyimide films are shown in Table 1.

[0274] [Table 1]

[0275] Table 1

[0276]

[0277] <Examples 5 to 7 and Comparative Example 3>

[0278] In Example 1, except that the amount of BAPP was changed from 20.534 g (0.050 mol) to 24.641 g (0.060 mol), and the amount of BisAM was changed from 17.289 g (0.050 mol) to 13.831 g (0.040 mol), a uniform polyimide varnish (2) having a solid content concentration of 20% by mass was obtained in the same manner as in Example 1.

[0279] Next, the obtained polyimide varnish (2) was applied on a PET substrate and maintained at 100°C for 20 minutes to volatilize the solvent, thereby obtaining a self-supporting colorless and transparent primary dried film. The film was further fixed to a stainless steel frame and baked at the baking temperature (210°C or 260°C) listed in Table 2, in an air atmosphere, and for the baking time (15 to 30 minutes) listed in Table 2, thereby obtaining a film. The evaluation results of these polyimide films are shown in Table 2.

[0280] <Example 8 and Comparative Example 4>

[0281] In Example 1, except that BAPP and BisAM were changed to BODA18.440 g (0.050 mol) and BisAP17.290 g (0.050 mol), a uniform polyimide varnish (3) having a solid content concentration of 20% by mass was obtained in the same manner as in Example 1.

[0282] Next, the obtained polyimide varnish (3) was applied on a PET substrate and maintained at 100°C for 20 minutes to volatilize the solvent, thereby obtaining a self-supporting colorless and transparent primary dried film. The film was further fixed to a stainless steel frame and baked at the baking temperature (330°C or 260°C) listed in Table 2 in an air atmosphere for 10 minutes to obtain a film. The evaluation results of these polyimide films are shown in Table 2.

[0283] [Table 2]

[0284] Table 2

[0285]

[0286] As shown in Tables 1 and 2, it can be seen that the polyimide film obtained by the production method of the example is particularly excellent in optical isotropy and also excellent in colorless transparency.

Claims

1. A method for producing a polyimide film, which is a method for producing a polyimide film formed from a polyimide resin. The polyimide resin comprises a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from diamine. The structural unit A comprises: a structural unit derived from an alicyclic tetracarboxylic dianhydride, The structural unit B comprises: a structural unit (B1) derived from a compound represented by the following general formula (b1), The manufacturing method is as follows: applying a polyimide varnish prepared by dissolving the polyimide resin in an organic solvent onto a support, removing the organic solvent at 60 to 140° C. to form a self-supporting film, peeling the self-supporting film from the support, fixing the ends of the self-supporting film, and baking at a temperature exceeding the glass transition temperature of the polyimide resin and at a temperature 10° C. or less higher than the glass transition temperature of the polyimide resin, In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted by fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted by fluorine, -S-, -SO-, -SO 2 -, -O- or -CO-.

2. The method for producing a polyimide film according to claim 1, in, The obtained polyimide film has a thickness of 5 to 100 μm.

3. The method for producing a polyimide film according to claim 1 or 2, in, The calcination time is 5 to 60 minutes.

4. The method for producing a polyimide film according to claim 1 or 2, in, The calcination temperature is 190 to 360°C.

5. The method for producing a polyimide film according to claim 1 or 2, in, The structural unit A comprises: a structural unit (A1) derived from a compound represented by the following formula (a1), 6. The method for producing a polyimide film according to claim 1 or 2, in, The structural unit B further includes a structural unit (B2), wherein the structural unit (B2) is at least one selected from the group consisting of a structural unit (B21) derived from a compound represented by the following general formula (b21), a structural unit (B22) derived from a compound represented by the following general formula (b22), and a structural unit (B23) derived from a compound represented by the following general formula (b23), In the formula, X 2 ~X 7 Each independently represents a single bond, an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, -S-, -SO-, -SO 2 -, -O- or -CO-.

7. The method for producing a polyimide film according to claim 6, in, The molar ratio of the structural unit (B1) to the structural unit (B2) [(B1) / (B2)] is 40 / 60 to 80 / 20.

8. The method for producing a polyimide film according to claim 1 or 2, in, It also contains: a structural unit (B3) derived from a compound represented by the following general formula (b3), In formula (b3), Z 1 and Z 2 Each independently represents a divalent aliphatic group or a divalent aromatic group which may contain an oxygen atom, and R 1 and R 2 Each independently represents a monovalent aromatic group or a monovalent aliphatic group, and R 3 and R 4 Each independently represents a monovalent aliphatic group, R 5 and R 6 Each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer greater than 1, and the sum of m and n represents an integer of 2 to 1,000.

9. The method for producing a polyimide film according to claim 8, in, The R 1 and R 2 is phenyl, R 3 and R 4 It is methyl.

10. The method for producing a polyimide film according to claim 1 or 2, comprising the step of imidizing a tetracarboxylic acid component providing a structural unit A derived from tetracarboxylic dianhydride and a diamine component providing a structural unit B derived from diamine in the presence of a base catalyst and an organic solvent, and adding an organic solvent as needed to obtain a polyimide varnish.

11. The method for producing a polyimide film according to claim 1 or 2, in, The structural unit (B1) is at least one structural unit selected from the group consisting of a structural unit (B11) derived from a compound represented by the following general formula (b11) and a structural unit (B12) derived from a compound represented by the following formula (b12), In formula (b11), R 1 and R 2 Each independently represents a methyl group or a trifluoromethyl group.

12. The method for producing a polyimide film according to claim 6, in, The structural unit (B2) comprises at least one structural unit selected from the group consisting of a structural unit derived from a compound represented by the following formula (b211), a structural unit derived from a compound represented by the following formula (b212), a structural unit derived from a compound represented by the following formula (b213), and a structural unit derived from a compound represented by the following formula (b231),

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