Polyimide film manufacturing method

Abstract

A method for producing a polyimide film formed of a polyimide resin that has a constitutional unit A derived from a tetracarboxylic dianhydride and a constitutional unit B derived from a diamine, the constitutional unit A including a constitutional unit derived from an alicyclic tetracarboxylic dianhydride, the constitutional unit B including a constitutional unit (B1) derived from a compound represented by general formula (b1), the method comprising: applying on a support a polyimide varnish obtained by dissolving said polyimide resin in an organic solvent; removing the organic solvent at 60-140°C to obtain a self-supporting film; detaching the self-supporting film from the support; fixing an end of the self-supporting film; and baking the film at a temperature that is higher than the glass transition temperature of the polyimide resin and that is at most 50°C higher than the glass transition temperature of the polyimide resin. (In formula (b1), X1 represents a single bond, an alkylene group optionally substituted with fluorine and having 1-5 carbon atoms, an alkylidene group optionally substituted with fluorine and having 2-5 carbon atoms, -S-, -SO-, -SO2-, -O-, or -CO-.)

Description

[Technical Field]

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

[0002] Various applications of polyimide resins are being considered in the fields of electrical and electronic components. For example, glass substrates are used in image display devices such as liquid crystal displays and OLED displays, but it is desirable to replace them with plastic substrates in order to make devices lighter and more flexible. Research is ongoing into polyimide films suitable for such plastic substrates. Polyimide films for such applications must be colorless and transparent. Furthermore, polyimide films are required to have a small phase difference due to birefringence and low retardation.

[0003] Patent Document 1 discloses a polyimide resin obtained using a diamine (e.g., metaphenylenediamine) in which at least one of the amino groups of the diamine is bonded to the meta position relative to the main chain, as a polyimide resin that provides a film with reduced birefringence. Patent Document 2 discloses a polyimide resin containing tetracarboxylic acid residues and diamine residues of a specific structure, and tetracarboxylic acid residues and / or diamine residues having bending portions, as a polyimide resin that provides a film excellent in heat resistance, transmittance, low linear expansion coefficient, and low retardation. Specifically, the document discloses a polyimide resin obtained using 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-bicyclohexanetetracarboxylic acid dianhydride, pyromellitic anhydride, 2,2'-bis(trifluoromethyl)benzidine, and 4,4'-diaminodiphenyl sulfone. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-134211 [Patent Document 2] International Publication No. 2015 / 125895 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, polyimide films are required to have good optical properties, such as colorless transparency. Recently, the performance requirements for electronic device display applications have increased, and films with particularly high optical isotropy are in demand. However, the raw materials used for polyimide films are limited to diamines and tetracarboxylic dianhydrides, and the molecular structure is therefore limited. This has created a need for improving performance through the manufacturing conditions, etc. In other words, there has been a need for a manufacturing method for polyimide films that improves optical isotropy while maintaining high colorless transparency. Therefore, an object of the present invention is to provide a method for producing a polyimide film, which can provide a polyimide film that is particularly excellent in optical isotropy while maintaining high colorless transparency. [Means for solving the problem]

[0006] The present inventors discovered that the above-mentioned problems can be solved by forming a varnish containing a polyimide resin having a specific combination of structural units into a film using a specific drying method or baking method, and thus completed the invention.

[0007] That is, the present invention relates to the following [1] to

[12] . [1] A method for producing a polyimide film made of a polyimide resin, the polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein structural unit A includes a structural unit derived from an alicyclic tetracarboxylic dianhydride, and structural unit B includes a structural unit (B1) derived from a compound represented by the following general formula (b1): a polyimide varnish formed 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, edges of the self-supporting film are fixed, and the self-supporting film is baked at a temperature that exceeds the glass transition temperature of the polyimide resin and is not higher than 50°C higher than the glass transition temperature of the polyimide resin. [ka] (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted with fluorine, -S-, -SO-, -SO2-, -O- or -CO-. [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. [3] The method for producing a polyimide film according to [1] or [2] above, wherein the baking time is 5 to 60 minutes. [4] The method for producing a polyimide film according to any one of [1] to [3] above, wherein the baking temperature is 190 to 360°C. [5] The method for producing a polyimide film according to any one of [1] to [4] above, wherein the structural unit A includes a structural unit (A1) derived from a compound represented by the following formula (a1): [ka] [6] The method for producing a polyimide film according to any one of the above items [1] to [5], wherein the structural unit B further comprises at least one structural unit (B2) 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): [ka] (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-, -SO2-, -O- or -CO-. [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. [8] The method for producing a polyimide film according to any one of the above [1] to [7], further comprising a structural unit (B3) derived from a compound represented by the following general formula (b3): [ka] (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, R 3 and R 4 each independently represents a monovalent aliphatic group, and R 5 and R 6 each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represents an integer of 1 or more, and the sum of m and n represents an integer of 2 to 1000. [9] R 1 and R 2 is a phenyl group, and R 3 and R 4is a methyl group.

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

[11] The 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): [ka] (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 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): [ka] [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing a polyimide film, which can obtain a polyimide film that is particularly excellent in optical isotropy while maintaining high colorless transparency. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Polyimide film manufacturing method] The method for producing a polyimide film of the present invention is a method for producing a polyimide film made of a polyimide resin, wherein the polyimide resin has a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein structural unit A includes a structural unit derived from an alicyclic tetracarboxylic dianhydride, and structural unit B includes a structural unit (B1) derived from a compound represented by the following general formula (b1): a polyimide varnish obtained 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 from the support, edges of the self-supporting film are fixed, and the self-supporting film is baked at a temperature that exceeds the glass transition temperature of the polyimide resin and is not higher than 50°C higher than the glass transition temperature of the polyimide resin. [ka] (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted with fluorine, -S-, -SO-, -SO2-, -O- or -CO-.

[0010] <Polyimide resin> The polyimide resin used in the method for producing a polyimide film of the present invention has a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, in which the structural unit A contains a structural unit derived from an alicyclic tetracarboxylic dianhydride, and the structural unit B contains a structural unit (B1) derived from a compound represented by the following general formula (b1): [ka] (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted with fluorine, -S-, -SO-, -SO2-, -O- or -CO-.

[0011] (Structural unit A) The structural unit A is a structural unit derived from a tetracarboxylic dianhydride contained in the polyimide resin, and includes a structural unit derived from an alicyclic tetracarboxylic dianhydride. By including a structural unit derived from an alicyclic tetracarboxylic dianhydride in the structural unit A, the colorless transparency and optical isotropy of the film can be improved. 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. Among these, 1,2,4,5-cyclohexanetetracarboxylic dianhydride and norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride are more preferred.

[0012] The structural unit A preferably includes 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 includes a structural unit (A1) derived from a compound represented by the following formula (a1). [ka]

[0013] The compound represented by formula (a1) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride. When the structural unit A contains the structural unit (A1), the colorless transparency and optical isotropy of the film can be improved.

[0014] The compound represented by formula (a2) is norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid dianhydride. When structural unit A contains structural unit (A2), the colorless transparency of the film is further improved.

[0015] The structural unit A may contain both the structural unit (A1) and the structural unit (A2), but preferably contains either the structural unit (A1) or the structural unit (A2), and more preferably contains the structural unit (A1).

[0016] When the structural unit A contains the structural unit (A1) and the structural unit (A2), the total proportion of the structural units (A1) and (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 particularly preferably 99 mol% or more. There is no particular upper limit for the total proportion of the structural units (A1) and (A2); in other words, the upper limit is 100 mol%, and the total proportion of the structural units (A1) and (A2) is 100 mol% or less.

[0017] When the structural unit A contains the structural unit (A1), the proportion of the structural unit (A1) in the structural unit A is preferably 45 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. There is no upper limit to this proportion, i.e., it is 100 mol%, and the proportion of the structural unit (A1) in the structural unit A is 100 mol% or less. When the structural unit A contains the structural unit (A2), the proportion of the structural unit (A2) in the structural unit A is preferably 45 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. There is no upper limit to this proportion, i.e., it is 100 mol%, and the proportion of the structural unit (A2) in the structural unit A is 100 mol% or less.

[0018] The structural unit A may further include a structural unit (A3) derived from a compound represented by the following formula (a3), and from the viewpoint of improving the colorless transparency of the film, it preferably includes the structural unit (A3) derived from a compound represented by formula (a3). [ka]

[0019] The compound represented by formula (a3) is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.

[0020] When the structural unit A contains the structural unit (A3), the proportion of the structural unit (A3) within the structural unit A is preferably no more than 55 mol %, more preferably no more than 30 mol %, and is preferably at least 1 mol %. When the structural unit A contains the structural unit (A3), the structural unit A preferably contains the structural unit (A1) and the structural unit (A3), and more preferably consists of the structural unit (A1) and the structural unit (A3).

[0021] The structural unit A may contain structural units derived from the alicyclic tetracarboxylic dianhydride and structural units other than the structural units (A1) to (A3), provided that the effects of the present invention are not impaired. Tetracarboxylic dianhydrides that provide such structural units are not particularly limited, and examples thereof include aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, and 2,2',3,3'-biphenyltetracarboxylic dianhydride; and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride. In this specification, aromatic tetracarboxylic acid dianhydride means a tetracarboxylic acid dianhydride containing one or more aromatic rings, alicyclic tetracarboxylic acid dianhydride means a tetracarboxylic acid dianhydride containing one or more alicyclic rings but no aromatic rings, and aliphatic tetracarboxylic acid dianhydride means a tetracarboxylic acid dianhydride containing neither an aromatic ring nor an alicyclic ring. The structural unit contained in the structural unit A may be one type, or two or more types. It is preferable that the structural unit A does not contain any structural units other than the structural units (A1) to (A3).

[0022] (Structural unit B) The structural unit B is a structural unit derived from a diamine contained in the polyimide resin, and includes a structural unit (B1) derived from a compound represented by the following general formula (b1): By including the structural unit (B1), the polyimide resin has excellent colorless transparency and optical isotropy. [ka] (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted with fluorine, -S-, -SO-, -SO2-, -O- or -CO-.

[0023] [Structural unit (B1)] The structural unit (B1) is a structural unit derived from a compound represented by the general formula (b1) above, 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):

[0024] [ka]

[0025] In formula (b11), R 1 and R 2each independently represents a methyl group or a trifluoromethyl group.

[0026] 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), The compound represented by formula (b12) is 4,4'-bis(4-aminophenoxy)biphenyl (BODA).

[0027] The structural unit B preferably contains at least one structural unit selected from the group consisting of the structural units (B11) and (B12), and of these, it is more preferable that the structural unit B contains the structural unit (B11). The structural unit B may contain both the structural units (B11) and (B12), but preferably contains one of the structural units (B11) or (B12). In other words, it is preferable that the structural unit B contains either the structural unit (B11) or the structural unit (B12).

[0028] The colorless transparency and optical isotropy of the film can be improved by including the structural unit (B1) in the structural unit B. The structural unit (B1) may be one type, or two or more types.

[0029] [Other structural units that may be included in structural unit B] The structural unit B may contain a structural unit other than the structural unit (B1). The diamine that provides such a structural unit is not particularly limited, but it is preferable that the diamine contain at least one structural unit (B2) selected from the group consisting of the structural unit (B21) derived from a compound represented by the following general formula (b21), the structural unit (B22) derived from a compound represented by the following general formula (b22), and the structural unit (B23) derived from a compound represented by the following general formula (b23). It is also preferable to include a structural unit (B3) derived from a compound represented by the following general formula (b3).

[0030] [ka]

[0031] 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-, -SO2-, -O- or -CO-. 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, R 3 and R 4 each independently represents a monovalent aliphatic group, and R 5 and R 6 each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represents an integer of 1 or more, and the sum of m and n represents an integer of 2 to 1,000.

[0032] 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).

[0033] [ka]

[0034] 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-, -SO2-, -O- or -CO-.

[0035] The compound represented by general formula (b21) is X 2 and X3 Three benzene rings are connected via X, and the central benzene ring has X at the 1,3 positions. 2 and X 3 The compound represented by general formula (b22) has a skeleton to which X 4 and X 5 Three benzene rings are connected via X at the 1st and 2nd positions of the central benzene ring. 4 and X 5 The compound represented by general formula (b23) has a skeleton to which X 6 and X 7 Three benzene rings are connected via X at the 1,4 positions of the central benzene ring. 6 and X 7 By having such a structure, it is possible to form a film that is excellent in colorless transparency and optical isotropy.

[0036] X in general formulae (b21), (b22) and (b23) 2 ~X 7 From the viewpoint of forming a film with excellent low retardation, each independently preferably represents an alkylidene group having 3 to 5 carbon atoms, -SO2-, or -O-, more preferably represents an alkylidene group having 3 to 5 carbon atoms or -O-, even more preferably represents an isopropylidene group or -O-, and still more preferably represents an isopropylidene group. X in general formula (b21) 2 and X 3 may each have a different group, but preferably have the same group. 4 and X 5 may each have a different group, but preferably have the same group, and X 6 and X 7 may each have a different group, but preferably have the same group. The amino groups in the general formulae (b21), (b22) and (b23) are bonded to the benzene ring to which each amino group is bonded. 2 ~X 7It is preferable that the benzene ring is bonded to either of the above at the para or meta position.

[0037] The structural unit (B2) preferably includes at least one selected from the group consisting of the structural unit (B21) derived from a compound represented by the above general formula (b21) and the structural unit (B23) derived from a compound represented by the above general formula (b23), and more preferably includes the structural unit (B21) derived from a compound represented by the above general formula (b21). From the viewpoint of improving optical isotropy, when the structural unit (B2) contains the structural unit (B21), it is preferable that the structural unit (B1) contains the structural unit (B11), and when the structural unit (B2) contains the structural unit (B23), it is preferable that the structural unit (B1) contains the structural unit (B12).

[0038] The structural unit (B21) derived from a compound represented by the above general formula (b21) preferably comprises at least one structural unit selected from the group consisting of structural units derived from a compound represented by the following formula (b211), structural units derived from a compound represented by the following formula (b212), and structural units derived from a compound represented by the following formula (b213). In other words, the structural unit (B2) preferably comprises at least one structural unit selected from the group consisting of structural units derived from a compound represented by the following formula (b211), structural units derived from a compound represented by the following formula (b212), structural units derived from a compound represented by the following formula (b213), and structural units derived from a compound represented by the following formula (b231).

[0039] [ka]

[0040] The compound represented by formula (b211) is 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene (BisAM), The compound represented by formula (b212) is 1,3-bis(4-aminophenoxy)benzene, The compound represented by formula (b213) is 1,3-bis(3-aminophenoxy)benzene.

[0041] Of the compounds represented by formulas (b211) to (b213), at least one compound selected from the group consisting of compounds represented by formula (b211) and compounds represented by formula (b212) is preferred, and a compound represented by formula (b211) is more preferred.

[0042] 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).

[0043] [ka]

[0044] The compound represented by formula (b231) is 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene (BisAP).

[0045] The structural unit (B3) is a structural unit derived from a compound represented by the following general formula (b3).

[0046] [ka]

[0047] 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, R 3 and R 4 each independently represents a monovalent aliphatic group, and R 5 and R 6 each independently represents a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represents an integer of 1 or more, and the sum of m and n represents an integer of 2 to 1,000. In formula (b3), the two or more different repeating units described in [ ] may be repeated in any form and order of random, alternating, or block, regardless of the order of [ ].

[0048] In formula (b3), Z 1 and Z 2 The divalent aliphatic group or divalent aromatic group in 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. 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. 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. Examples of the aliphatic group containing an oxygen atom include an alkyleneoxy group and an aliphatic group having an ether bond. Examples of the alkyleneoxy group include a propyleneoxy group and a trimethyleneoxy group. 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. Z 1 and Z 2 Specific examples of the arylene group having 6 to 20 carbon atoms in the formula include an o-phenylene group, an m-phenylene group, a p-phenylene group, a 4,4'-biphenylylene group, and a 2,6-naphthylene group. Z 1 and Z 2 As the alkyl group, a trimethylene group and a p-phenylene group are particularly preferred, and a trimethylene group is more preferred.

[0049] In formula (b3), R 1 ~R 6The monovalent aliphatic group in the formula (I) includes a monovalent saturated or unsaturated aliphatic group. Examples of the monovalent saturated aliphatic group include an alkyl group having 1 to 22 carbon atoms, such as a methyl group, an ethyl group, and a propyl group. Examples of the monovalent unsaturated aliphatic group include an alkenyl group having 2 to 22 carbon atoms, such as a vinyl group and a propenyl group. These groups may be substituted with a fluorine atom. R in equation (b3) 1 , R 2 , R 5 and R 6 Examples of the monovalent aromatic group in the formula (I) include an aryl group having 6 to 20 carbon atoms, an aryl group having 7 to 30 carbon atoms and substituted with an alkyl group, and an aralkyl group having 7 to 30 carbon atoms. As the monovalent aromatic group, an aryl group is preferred, and a phenyl group is more preferred. R 1 and R 2 At least one of R is preferably a monovalent aromatic group. 1 and R 2 are more preferably both monovalent aromatic groups, and R 1 and R 2 More preferably, both are phenyl groups. R 3 and R 4 As the alkyl group, an alkyl group having 1 to 6 carbon atoms is preferred, and a methyl group is more preferred. R 5 and R 6 As the alkyl group, a monovalent aliphatic group is preferred, and a methyl group is more preferred.

[0050] As described above, among the compounds represented by the above general formula (b3), the compound represented by the following formula (b31) is preferred.

[0051] [ka] (In formula (b31), m and n have the same meanings as m and n in formula (b3), respectively, and the preferred ranges are also the same.)

[0052] 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 in formula (b3) and formula (b31) represents the number of repetitions of siloxane units to which a monovalent aliphatic group is bonded. In formula (b3) and formula (b31), m and n each independently represent an integer of 1 or greater, and the sum of m and n (m+n) represents an integer of 2 to 1000. The sum of m and n is preferably an integer of 3 to 500, more preferably an integer of 3 to 100, and even more preferably an integer of 3 to 50. 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 even more preferably 20 / 80 to 30 / 70.

[0053] The functional group equivalent (amine equivalent) of the compound represented by formula (b3) is preferably 150 to 5,000 g / mol, more preferably 400 to 4,000 g / mol, and even more preferably 500 to 3,000 g / mol. The functional group equivalent weight means the mass of the compound represented by formula (b3) per mole of the functional group (amino group).

[0054] Among the compounds represented by the general formula (b3) above, commercially available products include "X-22-9409," "X-22-1660B," "X-22-161A," and "X-22-161B," manufactured by Shin-Etsu Chemical Co., Ltd.

[0055] When the structural unit B includes the structural unit (B3), the colorless transparency, optical isotropy, and flexibility of the film can be improved.

[0056] The structural unit B may contain structural units other than the structural units (B1) to (B3). Diamines that provide such structural units are not particularly limited, but include 1,4-phenylenediamine, p-xylylenediamine, 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-(4-aminophenyl) aromatic diamines such as 2,3-dihydro-1,3,3-trimethyl-1H-inden-5-amine, N,N'-bis(4-aminophenyl)terephthalamide, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, and 9,9-bis(4-aminophenyl)fluorene, and 1,4-bis(4-aminophenoxy)benzene; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine. In this specification, aromatic diamine means a diamine containing one or more aromatic rings, alicyclic diamine means a diamine containing one or more alicyclic rings but no aromatic rings, and aliphatic diamine means a diamine containing neither an aromatic ring nor an alicyclic ring. The structural units other than the structural units (B1) to (B3) optionally contained in the structural unit B may be of one type, or may be of two or more types.

[0057] [Configuration of structural unit B] When the structural unit B contains the structural unit (B1) and the structural unit (B2), the total proportion 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, even more preferably 90 mol% or more, and even more preferably 95 mol% or more. There are no particular limitations on the upper limit of the total proportion of the structural unit (B1) and the structural unit (B2), but it is preferably 100 mol%, and the total proportion of the structural unit (B1) and the structural unit (B2) in the structural unit B is 100 mol% or less. It is even more preferable that the structural unit B consists only of the structural unit (B1) and the structural unit (B2).

[0058] When the structural unit B comprises 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, even more preferably 45 / 55 to 70 / 30, still more preferably 45 / 55 to 65 / 35, even more preferably 45 / 55 to 60 / 40, and even more preferably 45 / 55 to 55 / 45.

[0059] When the structural unit B contains the structural unit (B1) and the structural unit (B3), the total proportion 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, even more preferably 90 mol% or more, and even more preferably 95 mol% or more. There are no particular limitations on the upper limit of the total proportion of the structural unit (B1) and the structural unit (B3), but it is preferably 100 mol%, and the total proportion of the structural unit (B1) and the structural unit (B3) in the structural unit B is 100 mol% or less. It is even more preferable that the structural unit B consists only of the structural unit (B1) and the structural unit (B3).

[0060] When the structural unit B comprises 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, even more preferably 60 / 40 to 90 / 10, and still more preferably 70 / 30 to 90 / 10.

[0061] When the structural unit B contains the structural unit (B1), the structural unit (B2), and the structural unit (B3), the total proportion 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, even more preferably 90 mol% or more, and even more preferably 95 mol% or more. There are no particular limitations on the upper limit of the total proportion of the structural unit (B1), the structural unit (B2), and the structural unit (B3), but it is preferably 100 mol%, and the total proportion 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 even more preferable that the structural unit B consists only of the structural unit (B1), the structural unit (B2), and the structural unit (B3).

[0062] When the structural unit B comprises 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 when the structural unit B comprises 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%, even more preferably 1 to 30 mass%, and still more preferably 1 to 20 mass%.

[0063] (Physical properties of polyimide resin, etc.) The number-average molecular weight of the polyimide resin used in the production method of the present invention is preferably 5,000 to 200,000 from the viewpoint of the mechanical strength of the resulting polyimide film. The number-average molecular weight of the polyimide resin can be determined, for example, from a standard polymethyl methacrylate (PMMA) equivalent value measured by gel permeation chromatography.

[0064] The polyimide resin used in the production method of the present invention may contain a structure other than a polyimide chain (a structure formed by imide bonding between the structural unit A and the structural unit B). Examples of structures other than polyimide chains that can be contained in the polyimide resin include structures containing amide bonds. The polyimide resin used in the production 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 the main structure. Therefore, the proportion of polyimide chains in the polyimide resin used in the production method of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 99% by mass or more. Alternatively, it may be 100% by mass or less.

[0065] By using the polyimide resin of the present invention, a film having particularly excellent optical isotropy can be formed, and the preferred physical properties of the film are as follows. The total light transmittance of a 30 μm thick film is preferably 79% or more, more preferably 85% or more, even more preferably 88% or more, and still more preferably 89% or more. When formed into a film having a thickness of 30 μm, the haze is preferably 0.6% or less, more preferably 0.4% or less, even more preferably 0.3% or less, and even more preferably 0.2% or less. The yellow index (YI) of the resulting film having a thickness of 30 μm is preferably 31 or less, more preferably 7 or less, even more preferably 3 or less, and even more preferably 2 or less. The in-plane retardation (Re) of a 30 μm thick film is preferably 10 nm or less, more preferably 8 nm or less, even more preferably 6 nm or less, still more preferably 5 nm or less, and even more preferably 4 nm or less. The thickness retardation (Rth) of a 30 μm thick film is preferably 30 nm or less, more preferably 28 nm or less, even more preferably 25 nm or less, still more preferably 15 nm or less, and even more preferably 10 nm or less. The above-mentioned physical property values in the present invention can be specifically measured by the methods described in the examples.

[0066] <Method of manufacturing polyimide resin> The polyimide resin of the present invention can be produced by reacting a tetracarboxylic acid component, which is a compound that provides the above-mentioned structural unit A, with a diamine component that includes a compound that provides the above-mentioned structural unit (B1).

[0067] The compound that provides the structural unit A preferably includes an alicyclic tetracarboxylic acid dianhydride. Examples of compounds that provide structural units derived from alicyclic tetracarboxylic dianhydrides include, but are not limited to, alicyclic tetracarboxylic dianhydrides, and may also be derivatives thereof as long as they provide the same structural units. Examples of such derivatives include tetracarboxylic acids corresponding to the alicyclic tetracarboxylic dianhydrides and alkyl esters of the tetracarboxylic acids. Preferred compounds that provide structural units derived from alicyclic tetracarboxylic dianhydrides are alicyclic tetracarboxylic dianhydrides. As compounds that provide structural units derived from alicyclic tetracarboxylic dianhydrides, compounds that provide structural units (A1) and compounds that provide structural units (A2) are preferred. Examples of compounds that provide the structural unit (A1) include compounds represented by formula (a1), but are not limited thereto and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic acid dianhydrides represented by formula (a1) and alkyl esters of such tetracarboxylic acids. Compounds that provide the structural unit (A1) are preferably compounds represented by formula (a1) (i.e., dianhydrides). Similarly, examples of compounds that provide the structural unit (A2) include, but are not limited to, compounds represented by formula (a2), and derivatives thereof may also be used as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic acid dianhydrides represented by formula (a2) and alkyl esters of such tetracarboxylic acids. Compounds represented by formula (a2) (i.e., dianhydrides) are preferred as compounds that provide the structural unit (A2).

[0068] When the tetracarboxylic acid component contains a compound that provides the structural unit (A1) and a compound that provides the structural unit (A2), the total content of the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2) is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. There is no particular upper limit on the total content of the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2); that is, the upper limit is 100 mol%, and this content is 100 mol% or less. The tetracarboxylic acid component may consist only of the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2).

[0069] When the tetracarboxylic acid component contains a compound that provides the structural unit (A1) or a compound that provides the structural unit (A2), the compound that provides the structural unit (A1) or the compound that provides the structural unit (A2) preferably accounts for 45 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more of the compound that provides the structural unit (A1). There is no upper limit to the content of the compound that provides the structural unit (A1) or the compound that provides the structural unit (A2), and the upper limit is 100 mol%, i.e., the upper limit is 100 mol%. The tetracarboxylic acid component may consist solely of the compound that provides the structural unit (A1) or the compound that provides the structural unit (A2), and preferably consists solely of the compound that provides the structural unit (A1).

[0070] The tetracarboxylic acid component may include a compound that provides the structural unit (A3) described above. Compounds that provide the structural unit (A3) include, but are not limited to, compounds represented by general formula (a3), and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic acid dianhydrides represented by general formula (a3) and alkyl esters of such tetracarboxylic acids. Compounds that provide the structural unit (A3) are preferably compounds represented by general formula (a3) (i.e., dianhydrides).

[0071] When the tetracarboxylic acid component contains a compound that provides the 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 that provides the structural unit (A3).When the tetracarboxylic acid component contains a compound that provides the structural unit (A3), it is preferable that the tetracarboxylic acid component consists only of the compound that provides the structural unit (A1) and the compound that provides the structural unit (A3).

[0072] The tetracarboxylic acid component may include a compound other than the alicyclic tetracarboxylic acid dianhydride, the compound that provides the structural unit (A1), the compound that provides the structural unit (A2), and the compound that provides the structural unit (A3). Examples of such compounds include the above-mentioned aromatic tetracarboxylic acid dianhydrides and aliphatic tetracarboxylic acid dianhydrides, as well as derivatives thereof (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.). The tetracarboxylic acid component may contain one kind of compound or two or more kinds of compounds.

[0073] Compounds that provide the structural unit (B1) include compounds represented by general formula (b11), which provide the structural unit (B11), and compounds represented by general formula (b12), which provide the structural unit (B12). However, the compound is not limited to these and may also be a derivative thereof, as long as it provides the same structural unit. Examples of such derivatives include diamines represented by general formula (b11) and diisocyanates corresponding to diamines represented by general formula (b12). The compound that provides the structural unit (B1) is preferably at least one compound (i.e., a diamine) selected from the group consisting of compounds represented by general formula (b11) and compounds represented by general formula (b12).

[0074] 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). In other words, it is preferable for the structural unit B to contain a compound that provides the structural unit (B11) or a compound that provides the structural unit (B12).

[0075] The diamine component may include a compound that provides the above-mentioned structural unit (B2). Compounds that provide the structural unit (B2) include compounds represented by general formula (b21), compounds represented by general formula (b22), and compounds represented by general formula (b23), but are not limited to these and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the diamines represented by general formula (b21), diisocyanates corresponding to the diamines represented by general formula (b22), and diisocyanates corresponding to the diamines represented by general formula (b23). The compound that provides the structural unit (B2) is preferably at least one compound (i.e., a diamine) selected from the group consisting of compounds represented by general formula (b21), compounds represented by general formula (b22), and compounds represented by general formula (b23).

[0076] The compound that provides the structural unit (B2) preferably includes a compound represented by general formula (b21) or a compound represented by general formula (b23), and more preferably includes a compound represented by general formula (b21). The compound represented by general formula (b21) preferably includes at least one compound selected from the group consisting of compounds represented by formula (b211), compounds represented by formula (b212), and compounds represented by formula (b213), more preferably includes at least one compound selected from the group consisting of compounds represented by formula (b211) and compounds represented by formula (b212), and particularly preferably includes a compound represented by formula (b211). As the compound represented by general formula (b23), a compound represented by formula (b231) is preferred.

[0077] The diamine component may include a compound that provides the above-mentioned structural unit (B3). Compounds that provide the structural unit (B3) include, but are not limited to, compounds represented by general formula (b3), and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compounds represented by general formula (b3). Compounds that provide the structural unit (B3) are preferably compounds represented by general formula (b3) (i.e., diamines). The compound that provides the structural unit (B3) is preferably a compound represented by general formula (b3), and more preferably includes a compound represented by formula (b31).

[0078] When the diamine component contains a compound that provides the structural unit (B1) and a compound that provides the structural unit (B2), the total content of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2) is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. There is no particular upper limit on the total content of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2), i.e., 100 mol%. The diamine component may consist solely of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2).

[0079] When the diamine component contains a compound that provides the structural unit (B1) and a compound that provides the structural unit (B2), the molar ratio of the compound that provides the structural unit (B1) to the compound that provides the structural unit (B2) [(B1) / (B2)] is preferably 40 / 60 to 80 / 20, more preferably 45 / 55 to 75 / 25, even more preferably 45 / 55 to 70 / 30, still more preferably 45 / 55 to 65 / 35, even more preferably 45 / 55 to 60 / 40, and even more preferably 45 / 55 to 55 / 45.

[0080] When the diamine component contains a compound that provides the structural unit (B1) and a compound that provides the structural unit (B3), the total content of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B3) is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. There is no particular upper limit on the total content of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B3); that is, the upper limit is 100 mol%, and this content is 100 mol% or less. The diamine acid component may consist only of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B3).

[0081] When the diamine component contains a compound that provides the structural unit (B1) and a compound that provides the structural unit (B3), the molar ratio of the compound that provides the structural unit (B1) to the compound that provides the structural unit (B3) [(B1) / (B3)] is preferably 40 / 60 to 99 / 1, more preferably 50 / 50 to 95 / 5, even more preferably 60 / 40 to 90 / 10, and still more preferably 70 / 30 to 90 / 10.

[0082] When the diamine component contains a compound that provides the structural unit (B1), a compound that provides the structural unit (B2), and a compound that provides the structural unit (B3), the total content of the compound that provides the structural unit (B1), the compound that provides the structural unit (B2), and the compound that provides the structural unit (B3) is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. There is no particular upper limit to the total content of the compound that provides the structural unit (B1), the compound that provides the structural unit (B2), and the compound that provides the structural unit (B3); that is, the upper limit is 100 mol%, and this content is 100 mol% or less. The diamine acid component may consist solely of the compound that provides the structural unit (B1), the compound that provides the structural unit (B2), and the compound that provides the structural unit (B3).

[0083] When the diamine component contains a compound that provides the structural unit (B1), a compound that provides the structural unit (B2), and a compound that provides the structural unit (B3), the molar ratio of the compound that provides the structural unit (B1) to the compound that provides the structural unit (B2) [(B1) / (B2)] is the same as when the diamine component contains a compound that provides the structural unit (B1) and a compound that provides the structural unit (B2), and the content of the compound that provides the structural unit (B3) in the diamine component is preferably 1 to 50 mass%, more preferably 1 to 40 mass%, even more preferably 1 to 30 mass%, and still more preferably 1 to 20 mass%.

[0084] The diamine component may contain compounds other than the compound that provides the structural unit (B1), the compound that provides the structural unit (B2), and the compound that provides the structural unit (B3). Examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, as well as derivatives thereof (diisocyanates, etc.). The compounds optionally contained in the diamine component other than the compound that provides the structural unit (B1), the compound that provides the structural unit (B2), and the compound that provides the structural unit (B3) may be one type, or two or more types.

[0085] In the present invention, the ratio of the amount of the tetracarboxylic acid component to the amount of the diamine component used in producing the polyimide resin is preferably 0.9 to 1.1 moles of the diamine component per mole of the tetracarboxylic acid component.

[0086] In the present invention, in addition to the tetracarboxylic acid component and diamine component, a terminal blocking agent may be used in the production of the polyimide resin. Monoamines or dicarboxylic acids are preferred as terminal blocking agents. The amount of terminal blocking agent to be introduced is preferably 0.0001 to 0.1 mol, particularly preferably 0.001 to 0.06 mol, per mol of the tetracarboxylic acid component. Examples of monoamine terminal blocking agents that are recommended include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, and 4-methylaniline. Of these, benzylamine and aniline are preferred. Dicarboxylic acids are preferred as dicarboxylic acid terminal blocking agents, and some of these may be ring-closed. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. are recommended. Of these, phthalic acid and phthalic anhydride are preferably used.

[0087] There are no particular limitations on the method for reacting the tetracarboxylic acid component and the diamine component, and any known method can be used. Specific reaction methods include: (1) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the mixture is stirred at 0 to 80°C for 0.5 to 30 hours, and then the temperature is raised to carry out the imidization reaction; (2) a method in which a diamine component and a reaction solvent are charged into a reactor and dissolved, and then the tetracarboxylic acid component is charged, and the mixture is stirred at 0 to 80°C for 0.5 to 30 hours as needed, and then the temperature is raised to carry out the imidization reaction; and (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the temperature is immediately raised to carry out the imidization reaction.

[0088] The reaction solvent used in the production of the polyimide resin may be any solvent that does not inhibit the imidization reaction and can dissolve the resulting polyimide, such as aprotic solvents, phenolic solvents, ether solvents, and carbonate solvents.

[0089] 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 hexamethylphosphoric amide and hexamethylphosphine triamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and sulfolane; 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.

[0090] Specific examples of phenol-based solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol. Specific examples of ether solvents include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, and 1,4-dioxane. Specific examples of carbonate solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate. Among the above reaction solvents, amide-based solvents and lactone-based solvents are preferred. The above reaction solvents may be used alone or in combination of two or more.

[0091] 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.

[0092] In the imidization reaction, a known imidization catalyst can be used, such as a base catalyst or an acid catalyst. Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, and N,N-diethylaniline; and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogencarbonate, and sodium hydrogencarbonate. Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, oxybenzoic acid, terephthalic acid, benzenesulfonic acid, paratoluenesulfonic acid, naphthalenesulfonic acid, etc. The above imidization catalysts may be used alone or in combination of two or more. Among the above, from the viewpoint of ease of handling, it is preferable to use a base catalyst, it is more preferable to use an organic base catalyst, it is even more preferable to use one or more selected from triethylamine and triethylenediamine, and it is particularly preferable to use triethylamine.

[0093] 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.

[0094] <Polyimide varnish> 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.

[0095] The organic solvent is not particularly limited as long as it dissolves the polyimide resin, but it is preferable to use the compounds described above as reaction solvents used in the production of polyimide resins, either alone or in combination of two or more. 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 solution diluted by further adding an organic solvent. The polyimide varnish used in the production method of the present invention may be prepared by dissolving a polyimide resin in a low-boiling solvent having a boiling point of 130°C or less. By using such a low-boiling solvent as the organic solvent, the heating temperature during production of the polyimide film described below can be reduced. Examples of such low-boiling solvents include carbon tetrachloride, dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran, and acetone, with dichloromethane being preferred.

[0096] The polyimide resin is solvent-soluble, allowing it to be made into a highly concentrated varnish that is stable at room temperature. The polyimide varnish of the present invention preferably contains 5 to 40 mass % of the polyimide resin, more preferably 10 to 30 mass %. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, 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. The polyimide varnish used in the production method of the present invention may also contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, UV stabilizers, surfactants, leveling agents, antifoaming agents, fluorescent brightening agents, crosslinking agents, polymerization initiators, and photosensitizers, as long as the additives do not impair the required properties of the polyimide film obtained by the production method of the present invention. The method for producing the polyimide varnish used in the production method of the present invention is not particularly limited, and known methods can be applied.

[0097] <Production of Polyimide Film> The method for producing a polyimide film of the present invention is a method for producing a polyimide film made from the above-mentioned polyimide resin, which comprises applying the above-mentioned polyimide varnish to a support, removing the organic solvent contained in the varnish at 60 to 140°C to form a self-supporting film, peeling the self-supporting film from the support, fixing the edges of the self-supporting film, and baking at a temperature that exceeds the glass transition temperature of the polyimide resin and is not higher than 50°C higher than the glass transition temperature of the polyimide resin. 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 more specifically, more preferably includes a step of imidizing a tetracarboxylic acid component that provides the structural unit A derived from a tetracarboxylic dianhydride and a diamine component that provides the structural unit B derived from a diamine in the presence of a base catalyst and an organic solvent, and optionally adding an organic solvent to obtain a polyimide varnish. The tetracarboxylic acid component, diamine component, base catalyst, and organic solvent used in the imidization and polyimide varnish production steps include those described in the above section <Method for producing polyimide resin>, and the same applies to suitable tetracarboxylic acid components, diamine components, base catalysts, and organic solvents.

[0098] The method for applying the polyimide varnish to a support includes applying the polyimide varnish to a smooth support such as a glass plate, a metal plate, a plastic plate, etc. A glass rod, a coater, etc. can be used for application. The coating thickness is preferably 1 to 250 μm, more preferably 5 to 100 μm, and even more preferably 10 to 80 μm, in terms of film thickness after drying. If necessary, a release agent may be applied to the surface of the support in advance.

[0099] Next, the organic solvent contained in the varnish is removed at 60 to 140° C. to form a self-supporting film, which is then peeled off from the support. The temperature for removing the organic solvent contained in the varnish is 60 to 140° C., preferably 80 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, and after peeling, the film has self-supporting properties.

[0100] The edges of the obtained self-supporting film are fixed, and the film is baked at a temperature that is higher than the glass transition temperature of the polyimide resin and is not higher than 50° C. than the glass transition temperature of the polyimide resin. For example, if the glass transition temperature of the polyimide resin is 300°C, the polyimide film is baked at a temperature above 300°C and not higher than 350°C in the method for producing the polyimide film of the present invention. In the present invention, even if the baking temperature falls outside the above range for a short period of time, this is also included within the scope of the present invention, provided that the effects of the present invention are not impaired. For example, the baking temperature may exceed a temperature 50°C higher than the glass transition temperature of the polyimide resin for 5% or less of the total baking time. Hereinafter, the glass transition temperature of the polyimide resin is defined as (Tg), and the temperature that is X°C higher than the glass transition temperature of the polyimide resin is indicated as (Tg+X°C).

[0101] The baking temperature is a temperature above the glass transition temperature (Tg) of the polyimide resin and not higher than 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, even more preferably a temperature 7°C higher than the glass transition temperature of the polyimide resin (Tg + 7°C) or higher, and even more preferably a temperature 10°C higher than the glass transition temperature of the polyimide resin (Tg + 10°C) or higher. Furthermore, the temperature is preferably not more than 40°C higher than the glass transition temperature of the polyimide resin (Tg + 40°C), more preferably not more than 30°C higher than the glass transition temperature of the polyimide resin (Tg + 30°C), even more preferably not more than 20°C higher than the glass transition temperature of the polyimide resin (Tg + 20°C), and even more preferably not more than 15°C higher than the glass transition temperature of the polyimide resin (Tg + 15°C). By baking within the above temperature range, a polyimide film having excellent colorless transparency and optical isotropy can be obtained.

[0102] Furthermore, particularly from the viewpoint of further improving optical isotropy, the temperature is even more preferably at least 15°C higher than the glass transition temperature of the polyimide resin (Tg + 15°C), even more preferably at least 20°C higher than the glass transition temperature of the polyimide resin (Tg + 20°C), and even more preferably at least 25°C higher than the glass transition temperature of the polyimide resin (Tg + 25°C). On the other hand, particularly from the viewpoint of further improving colorless transparency, the temperature is even more preferably not more than a temperature 15°C higher than the glass transition temperature of the polyimide resin (Tg + 15°C), even more preferably not more than a temperature 10°C higher than the glass transition temperature of the polyimide resin (Tg + 10°C), and even more preferably not more than a temperature 5°C higher than the glass transition temperature of the polyimide resin (Tg + 5°C).

[0103] In addition, in view of the glass transition temperature of the polyimide preferably used in the production method of the present invention, the baking temperature is preferably 190 to 360°C, more preferably 200 to 350°C, even more preferably 230 to 320°C, still more preferably 240 to 300°C, and even more preferably 240 to 280°C. The firing is preferably carried out in a nitrogen atmosphere, and may be carried out under reduced pressure, normal pressure, or elevated pressure. The baking time 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. Furthermore, from the viewpoint of further improving colorless transparency, the 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 optical isotropy, the time is more preferably from 10 to 50 minutes, even more preferably from 15 to 40 minutes, and even more preferably from 17 to 28 minutes. The baking time starts when the target temperature, which is 3 to 50°C higher than the glass transition temperature of the polyimide resin, is reached, and ends when the temperature is lowered by cooling or weakening the heating and falls below the target temperature by 1°C or more. If there are multiple target temperatures within the range, the total time for all of them is the baking time.

[0104] In the method for producing a polyimide film of the present invention, after baking under the above conditions, it is preferable to cool or anneal the film, and it is more preferable to cool the film.

[0105] The cooling is preferably carried out by gradually cooling from the firing temperature to room temperature (for example, 25°C). Annealing is preferably carried out at a temperature lower than the firing temperature, more preferably at a temperature lower than 10°C lower than the firing temperature, even more preferably at a temperature lower than 30°C lower than the firing temperature, and even more preferably at a temperature lower than 50°C lower than the firing temperature.

[0106] The thickness of the polyimide film of the present invention can be appropriately selected depending on the application, etc., but is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, and even more preferably 10 to 80 μm. A thickness of 1 to 250 μm enables practical use as a free-standing film. The thickness of the polyimide film can be easily controlled by adjusting the solid content and viscosity of the polyimide varnish.

[0107] The polyimide film obtained by the production method of the present invention is suitably used as a film for various components such as color filters, flexible displays, semiconductor components, optical members, etc. The polyimide film of the present invention is particularly suitably used as a substrate for image display devices such as liquid crystal displays and OLED displays. [Example]

[0108] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples in any way. The solid content of the varnishes and the physical properties of the films obtained in the examples and comparative examples were measured by the methods described below.

[0109] (1) Solid content concentration The solid content of the varnish was measured by heating the sample at 280°C for 120 minutes in a small electric furnace "MMF-1" manufactured by AS ONE Corporation, and calculating the mass difference between the sample before and after heating. (2) Glass transition temperature (Tg) of polyimide resin The glass transition temperature of the polyimide resin was measured in accordance with JIS K7121 using a differential scanning calorimeter "DSC 7000X" manufactured by Hitachi High-Tech Science Corporation. DSC measurements were performed at a heating rate of 10°C / min to obtain a DSC curve. The glass transition temperature was determined according to the method described in JIS K7121 as the point where a line equidistant in the vertical direction from the line extending each baseline (high-temperature baseline and low-temperature baseline) in the DSC curve intersects with the curve of the stepwise change in the glass transition (midpoint glass transition temperature).

[0110] (3) Film Thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation. (4) Total light transmittance, haze, yellow index (YI) (evaluation of colorless transparency) The total light transmittance, haze, and YI were measured using a color and turbidity simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd. 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.

[0111] (5) In-plane retardation (Re) (evaluation of optical isotropy) The in-plane retardation (Re) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The in-plane phase difference value was measured at a measurement wavelength of 590 nm. (6) Thickness retardation (Rth) (evaluation of optical isotropy) The thickness retardation (Rth) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The thickness retardation value was measured at a measurement wavelength of 550 nm. Rth is expressed by the following formula, where nx is the maximum in-plane refractive index of the polyimide film, ny is the minimum, nz is the refractive index in the thickness direction, and d is the thickness of the film. Rth=[{(nx+ny) / 2}-nz]×d

[0112] The tetracarboxylic acid components and diamine components used in the examples and comparative examples, as well as their abbreviations, are as follows: <Tetracarboxylic acid component> HPMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (a1)) <Diamine component> BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (manufactured by Wakayama Seika Kogyo Co., Ltd., a compound represented by formula (b11)) BODA: 4,4'-bis(4-aminophenoxy)biphenyl (compound represented by formula (b12)) BisAM: 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene (manufactured by Mitsui Fine Chemicals, Inc., a compound represented by formula (b211)) BisAP: 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene (compound represented by formula (b231))

[0113] Details of the solvents and catalysts used in the examples and comparative examples are as follows. γ-butyrolactone (Mitsubishi Chemical Corporation) N,N-Dimethylacetamide (Mitsubishi Gas Chemical Company, Inc.) Triethylamine (Kanto Chemical Co., Ltd.)

[0114] Example 1 A 0.3 L five-neck glass round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet, a Dean-Stark apparatus equipped with a condenser, a thermometer, and a glass end cap was used as the reaction apparatus. 20.534 g (0.050 mol) of BAPP, 17.289 g (0.050 mol) of BisAM, 49.1 g of γ-butyrolactone, and 10.13 g of triethylamine as a catalyst were added to the round-bottom flask. The mixture was then heated to 80°C under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. 22.439 g (0.100 mol) of HPMDA and 11.1 g of γ-butyrolactone were added in one portion to this solution, followed by heating with a mantle heater. The temperature in the reaction system was raised to 190°C over approximately 20 minutes. The distilled components 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 homogeneous polyimide varnish (1) with a solid content of 20% by mass.

[0115] The resulting polyimide varnish (1) was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and baked at 255°C in air for 20 minutes to obtain a film. The evaluation results of this polyimide film are shown in Table 1.

[0116] <Examples 2 to 4 and Comparative Examples 1 and 2> Polyimide varnish (1) obtained by the method described in Example 1 was applied to a PET substrate and held at 100°C for 20 minutes to volatilize the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and baked in an air atmosphere for 20 minutes at the baking temperature (210-320°C) shown in Table 1, yielding a film. The evaluation results of these polyimide films are shown in Table 1.

[0117] [Table 1]

[0118] <Examples 5 to 7 and Comparative Example 3> A homogeneous polyimide varnish (2) having a solid content concentration of 20% by mass was obtained in the same manner as 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).

[0119] The resulting polyimide varnish (2) was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and baked in an air atmosphere at the baking temperature (210°C or 260°C) shown in Table 2 for the baking time (15 to 30 minutes) shown in Table 2, yielding a film. The evaluation results of these polyimide films are shown in Table 2.

[0120] <Example 8 and Comparative Example 4> A homogeneous polyimide varnish (3) having a solid content concentration of 20 mass % was obtained in the same manner as in Example 1, except that BAPP and BisAM in Example 1 were changed to 18.440 g (0.050 mol) of BODA and 17.290 g (0.050 mol) of BisAP.

[0121] The resulting polyimide varnish (3) was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and baked for 10 minutes in an air atmosphere at the baking temperature (330°C or 260°C) shown in Table 2. The evaluation results of these polyimide films are shown in Table 2.

[0122] [Table 2]

[0123] As shown in Tables 1 and 2, the polyimide films obtained by the manufacturing methods of the examples are particularly excellent in optical isotropy and colorless transparency.

Claims

1. A method for producing a polyimide film made of a polyimide resin, comprising: the polyimide resin has a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, the structural unit A includes a structural unit derived from an alicyclic tetracarboxylic dianhydride, The structural unit B includes a structural unit (B1) derived from a compound represented by the following general formula (b1): A method for producing a polyimide film includes applying a polyimide varnish obtained 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 edges of the self-supporting film, and baking the self-supporting film at a temperature that exceeds the glass transition temperature of the polyimide resin and is not higher than 10°C higher than the glass transition temperature of the polyimide resin. 【Chemical 1】 (In formula (b1), X 1 represents a single bond, an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, an alkylidene group having 2 to 5 carbon atoms which may be substituted with fluorine, -S-, -SO-, -SO 2 represents -, -O- or -CO-.)

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

3. 3. The method for producing a polyimide film according to claim 1, wherein the baking time is 5 to 60 minutes.

4. The method for producing a polyimide film according to any one of claims 1 to 3, wherein the baking temperature is 190 to 360°C.

5. The method for producing a polyimide film according to any one of claims 1 to 4, wherein the structural unit A includes a structural unit (A1) derived from a compound represented by the following formula (a1): 【Chemistry 2】

6. The method for producing a polyimide film according to any one of claims 1 to 5, wherein the structural unit B further comprises at least one structural unit (B2) 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): 【Chemistry 3】 (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 represents -, -O- or -CO-.)

7. 7. The method for producing a polyimide film according to claim 6, wherein 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 any one of claims 1 to 7, further comprising a structural unit (B3) derived from a compound represented by the following general formula (b3): 【Chemistry 4】 (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, 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 represents an integer of 1 or more, and the sum of m and n represents an integer of 2 to 1000.

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

10. 10. The method for producing a polyimide film according to claim 1, comprising the steps of: imidizing a tetracarboxylic acid component that provides the structural unit A derived from a tetracarboxylic dianhydride and a diamine component that provides the structural unit B derived from a diamine in the presence of a base catalyst and an organic solvent; and optionally adding an organic solvent to obtain a polyimide varnish.

11. The method for producing a polyimide film according to any one of claims 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): 【Chemistry 5】 (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 any one of claims 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): 【Chemistry 6】

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