TWI849136B - Polyimide resin and its manufacturing method, and polyimide film and its manufacturing method - Google Patents

Abstract

The polyimide resin of the present invention has a structure derived from an acid dianhydride and a structure derived from a diamine. As the diamine, the diamine contains 40 mol% to 100 mol% of fluoroalkyl-substituted benzidine relative to 100 mol% of the total amount of the diamines. As the acid dianhydride, the acid dianhydride represented by the general formula (1) contains 40 mol% to 85 mol% and the acid dianhydride having a cyclobutane structure contains 15 mol% to 60 mol% relative to 100 mol% of the total amount of the acid dianhydrides. In the general formula (1), R ¹ to R ⁸ are independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a perfluoroalkyl group having 1 to 20 carbon atoms, and at least one of R ¹ to R ⁴ and at least one of R ⁵ to R ⁸ are an alkyl group having 1 to 20 carbon atoms, or a perfluoroalkyl group having 1 to 20 carbon atoms.

Description

Polyimide resin and its manufacturing method, and polyimide film and its manufacturing method

The present invention relates to a polyimide resin and a manufacturing method thereof, a polyimide solution, and a polyimide film and a manufacturing method thereof.

In order to achieve lightweight or flexible display devices such as smartphones, polyimide films are being studied as a substitute for glass, which was previously used as a substrate or surface protective material. Conventional polyimide is colored yellow or brown and does not show solubility in organic solvents, but by introducing alicyclic structures or fluoroalkyl groups, low-coloring polyimide can be obtained (for example, Patent Document 1). [Prior Art Document] [Patent Document]

[Patent document 1] Japanese Patent Publication No. 2006-282884

[The problem the invention is trying to solve]

The polyimide film obtained from the polyimide resin of Patent Document 1 has insufficient mechanical strength for use in a cover window disposed on the outer surface of a device. The purpose of the present invention is to provide a polyimide resin and a polyimide film that are soluble in a low-boiling point solvent such as dichloromethane and have excellent transparency and mechanical strength. [Technical means to solve the problem]

The polyimide resin of one embodiment of the present invention has a structure derived from an acid dianhydride and a structure derived from a diamine. The acid dianhydride includes an acid dianhydride represented by the general formula (1) and an acid dianhydride having a cyclobutane structure. The diamine includes benzidine substituted with a fluoroalkyl group.

[Chemistry 1]

In the general formula (1), ^R1 to ^R8 are independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a perfluoroalkyl group having 1 to 20 carbon atoms, and at least one of ^R1 to ^R4 and at least one of ^R5 to ^R8 are an alkyl group having 1 to 20 carbon atoms, or a fluoroalkyl group having 1 to 20 carbon atoms.

The amount of the acid dianhydride represented by the general formula (1) is preferably 40 to 85 mol% relative to 100 mol% of the total amount of the acid dianhydride. The amount of the acid dianhydride having a cyclobutane structure is preferably 15 to 60 mol% relative to 100 mol% of the total amount of the acid dianhydride. The amount of the fluoroalkyl-substituted benzidine is preferably 40 to 100 mol% relative to 100 mol% of the total amount of the diamine.

As specific examples of the acid dianhydride represented by the general formula (1), there can be mentioned compounds represented by the formula (2).

[Chemistry 2]

As a specific example of the acid dianhydride containing a cyclobutane structure, 1,2,3,4-cyclobutanetetracarboxylic dianhydride can be cited. As a specific example of the benzidine substituted with a fluoroalkyl group, 2,2'-bis(trifluoromethyl)benzidine can be cited.

The polyimide may also contain an acid dianhydride component or a diamine component other than the above. Examples of acid dianhydrides other than the above include 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride. Examples of diamines other than the above include diaminodiphenylsulfone.

A polyimide solution is prepared by dissolving a polyimide resin in a solvent, the polyimide solution is coated on a substrate, and the solvent is removed to obtain a polyimide film. A low boiling point solvent such as dichloromethane is preferably used as a solvent for dissolving polyimide.

The thickness of the polyimide film can be 40 μm or more. The yellowness of the polyimide film can be 3.0 or less, the tensile modulus can be 5.0 GPa or more, and the pencil hardness can be H or more. [Effects of the invention]

The polyimide resin of the present invention is soluble in low-boiling-point solvents such as methylene chloride, and the residual solvent is reduced without heating at a high temperature, so a polyimide film with higher transparency can be obtained. The polyimide resin of the present invention is soluble in low-boiling-point solvents such as methylene chloride, and the residual solvent is reduced without heating at a high temperature, so a polyimide film with higher transparency can be obtained. The polyimide film of the present invention has high mechanical strength and high transparency even when the film thickness is large, so it can be used as a substrate material or cover window material for a display.

[Polyimide resin] Polyimide is generally obtained by dehydrating and cyclizing a polyamic acid obtained by reacting tetracarboxylic dianhydride (hereinafter sometimes simply described as "acid dianhydride") with a diamine. That is, polyimide has a structure derived from an acid dianhydride and a structure derived from a diamine. The polyimide resin of the present invention contains an ester-containing acid dianhydride (bis(trimellitic acid) anhydride) and an acid dianhydride having an alicyclic structure as an acid dianhydride component, and contains fluoroalkyl-substituted benzidine as a diamine component.

<Acid dianhydride> The polyimide of the present invention comprises an ester-containing acid dianhydride represented by the following general formula (1) and an alicyclic acid dianhydride having a cyclobutane structure as the acid dianhydride.

[Chemistry 3]

In the general formula (1), R ¹ to R ⁸ are independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a fluoroalkyl group having 1 to 20 carbon atoms. At least one of R ¹ to R ⁴ is a substituent other than a hydrogen atom, and at least one of R ⁵ to R ⁸ is a substituent other than a hydrogen atom (i.e., an alkyl group having 1 to 20 carbon atoms or a fluoroalkyl group having 1 to 20 carbon atoms).

(Containing ester-based acid dianhydride) The content of the acid dianhydride represented by the general formula (1) is 40 to 85 mol%, preferably 40 to 80 mol%, more preferably 40 to 75 mol%, and may be 45 to 70 mol% or 50 to 65 mol% in the total amount of the acid dianhydride component of 100 mol%. When the content of the acid dianhydride represented by the general formula (1) is within the above range, during the polymerization reaction of polyamide acid or the imidization reaction in the solution, significant viscosity increase or gelation can be suppressed, and the solubility of the polyimide resin in low-boiling point solvents can be ensured. In addition, when the content of the acid dianhydride represented by the general formula (1) is within the above range, the mechanical strength of the polyimide film tends to be improved.

The acid dianhydride represented by the general formula (1) is an ester of trimellitic anhydride and a biphenol having a substituent. Since the acid dianhydride represented by the general formula (1) has a biphenyl structure, the ultraviolet resistance of the polyimide is improved, and the decrease in transparency (increase in yellowness YI) accompanying ultraviolet irradiation tends to be suppressed.

The substituents R ¹ to R ⁸ in the general formula (1) are independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a fluoroalkyl group having 1 to 20 carbon atoms. Specific examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, n-hexyl, and cyclohexyl. Examples of the fluoroalkyl group include monofluoromethyl, difluoromethyl, trifluoromethyl, and pentafluoroethyl. Among the fluoroalkyl groups, perfluoroalkyl groups such as trifluoromethyl and pentafluoroethyl are preferred.

In the general formula (1), at least one of R ¹ to R ⁴ is a substituent other than a hydrogen atom, and at least one of R ⁵ to R ⁸ is a substituent other than a hydrogen atom. Preferably, at least one of R ² and R ³ , and at least one of R ⁶ and R ⁷ are substituents other than a hydrogen atom. If these are substituents other than a hydrogen atom, the bonds between the two benzene rings of biphenyl are twisted due to steric hindrance, thereby reducing the planarity of the π-conjugation, thereby causing the absorption end wavelength to shift to a short wavelength, and the coloring of the polyimide tends to decrease.

In the general formula (1), preferably ^R2 and ^R6 are methyl groups, and ^R3 and ^R7 are hydrogen atoms. Among them, preferably ^R1 , ^R4 , ^R5 and ^R8 are methyl groups, and the bis(1,3-dioxy-1,3-dihydroisobenzofuran-5-carboxylic acid) 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diester (TAHMBP) represented by the following formula (2) is used.

[Chemistry 4]

(Acid dianhydride containing cyclobutane structure) The content of acid dianhydride having cyclobutane structure is 15-60 mol%, preferably 15-50 mol%, and more preferably 15-40 mol% in the total amount of acid dianhydride components of 100 mol%. When the content of acid dianhydride having cyclobutane structure is 15 mol% or more, the mechanical strength of polyimide film tends to be improved, and when the content of acid dianhydride having cyclobutane structure is 60 mol% or less, the solubility of polyimide resin in low boiling point solvents tends to be improved.

Specific examples of the acid dianhydride having a cyclobutane structure include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,4-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dipropyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,4-dipropyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, cyclobutane-1,2:3,4-bis(tetramethylene)-1,2,3,4-tetracarboxylic dianhydride, etc. Among them, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) is preferred.

(Other acid dianhydrides) As long as the solubility in low-boiling point solvents such as dichloromethane is not impaired and the properties such as transparency or mechanical strength are not impaired, other acid dihydrate components other than the above may also be used in combination. Examples of acid dianhydrides other than the above include fluorine-containing aromatic acid dianhydrides such as 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, and 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-hexafluoropropane dianhydride. As other acid dianhydrides, there can be mentioned 3,3',4,4'-biphenyltetracarboxylic dianhydride, p-phenylene bis(trimellitic) dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, 1,1'-biscyclohexane-3,3',4,4'-tetracarboxylic-3,4:3',4'-dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2, 2-Bis(2,3-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,3-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]phthalic dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride Alkanedianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl} dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl} dianhydride, 4,4'-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4'-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl} dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl} dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl} dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl} dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl} dianhydride bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 2,2-bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, and the like.

For example, as the acid dianhydride, in addition to the acid dianhydride represented by the general formula (1) and the acid dianhydride having a cyclobutane structure, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA) or 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) is used, whereby the solubility in low boiling point solvents such as dichloromethane is maintained and the mechanical strength of the polyimide film tends to be improved. In particular, when 6FDA is used, the transparency of the polyimide film tends to be improved. The content of 6FDA in the total amount of 100 mol% of the acid dianhydride component is preferably 5 mol% or more, more preferably 10 mol% or more, and can also be 15 mol% or more. The content of BPDA in the total amount of 100 mol % of the acid dianhydride component may be 5 mol % or more, 10 mol % or more, or 15 mol % or more.

The content of acid dianhydrides other than the acid dianhydride represented by the general formula (1) and the acid dianhydride having a cyclobutane structure is preferably 40 mol% or less in the total amount of 100 mol% of the acid dianhydride components. The content of 6FDA is preferably 25 mol% or less and the content of BPDA is preferably 25 mol% or less in the total amount of 100 mol% of the acid dianhydride components.

<Diamine> (Fluoroalkyl-substituted benzidine) The polyimide of the present invention contains fluoroalkyl-substituted benzidine as a diamine component. The content of fluoroalkyl-substituted benzidine in the total 100 mol% of the diamine components is 40 to 100 mol%, preferably 60 mol% or more, and more preferably 70 mol% or more. If the content of fluoroalkyl-substituted benzidine is 40 mol% or more, the coloring of the polyimide film is suppressed, and the pencil hardness or elastic modulus tends to be increased.

Examples of the fluoroalkyl-substituted benzidine include 2,2'-dimethylbenzidine, 2-fluorobenzidine, 3-fluorobenzidine, 2,3-difluorobenzidine, 2,5-difluorobenzidine, 2,6-difluorobenzidine, 2,3,5-trifluorobenzidine, 2,3,6-trifluorobenzidine, 2,3,5,6-tetrafluorobenzidine, 2,2'-difluorobenzidine, 3,3'-difluorobenzidine, 2,3'-difluorobenzidine, 2,2',3-trifluorobenzidine, 2,3,3'- Trifluorobenzidine, 2,2',5-trifluorobenzidine, 2,2',6-trifluorobenzidine, 2,3',5-trifluorobenzidine, 2,3',6,-trifluorobenzidine, 2,2',3,3'-tetrafluorobenzidine, 2,2',5,5'-tetrafluorobenzidine, 2,2',6,6'-tetrafluorobenzidine, 2,2',3,3',6,6'-hexafluorobenzidine, 2,2',3,3',5,5',6,6'-octafluorobenzidine, 2-(trifluoromethyl)benzidine, 3-(Trifluoromethyl)benzidine, 2,3-bis(trifluoromethyl)benzidine, 2,5-bis(trifluoromethyl)benzidine, 2,6-bis(trifluoromethyl)benzidine, 2,3,5-tris(trifluoromethyl)benzidine, 2,3,6-tris(trifluoromethyl)benzidine, 2,3,5,6-tetrakis(trifluoromethyl)benzidine, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-bis(trifluoromethyl)benzidine, 2,3'-bis(trifluoromethyl)benzidine, 2,2',3- Bis(trifluoromethyl)benzidine, 2,3,3'-tris(trifluoromethyl)benzidine, 2,2',5-tris(trifluoromethyl)benzidine, 2,2',6-tris(trifluoromethyl)benzidine, 2,3',5-tris(trifluoromethyl)benzidine, 2,3',6,-tris(trifluoromethyl)benzidine, 2,2',3,3'-tetrakis(trifluoromethyl)benzidine, 2,2',5,5'-tetrakis(trifluoromethyl)benzidine, 2,2',6,6'-tetrakis(trifluoromethyl)benzidine, and the like.

Among them, fluoroalkyl-substituted benzidine having a fluoroalkyl group at the 2-position of biphenyl is preferred, and 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as "TFMB") is particularly preferred. By having fluoroalkyl groups at the 2-position and 2'-position of biphenyl, in addition to the reduction of the π electron density due to the electron-withdrawing property of the fluoroalkyl group, the steric hindrance of the fluoroalkyl group causes the bond between the two benzene rings of biphenyl to twist and reduce the planarity of the π conjugation, thereby causing the absorption end wavelength to shift to a short wavelength, which can reduce the coloring of the polyimide.

(Other diamines) Diamines other than those mentioned above may be used in combination as long as the solubility in low-boiling-point solvents such as dichloromethane is not impaired and the properties such as transparency or mechanical strength are not impaired. Examples of diamines other than fluoroalkyl-substituted benzidine include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 3,4 ...3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 3,3'-diamino Aminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 9,9-bis(4-aminophenyl)fluorene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-bis(3-aminophenyl)propane, 2,2-di (4-aminophenyl) propane, 2-(3-aminophenyl)-2-(4-aminophenyl) propane, 1,1-bis(3-aminophenyl)-1-phenylethane, 1,1-bis(4-aminophenyl)-1-phenylethane, 1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy) Benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminobenzyl)benzene, 1,3-bis(4-aminobenzyl)benzene, 1,4-bis(3-aminobenzyl)benzene, 1,4-bis(4-aminobenzyl)benzene, 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-aminobenzyl)benzene 1,4-Bis(3-amino-α,α-dimethylbenzyl)benzene, 1,4-Bis(4-amino-α,α-dimethylbenzyl)benzene, 2,6-Bis(3-aminophenoxy)benzonitrile, 2,6-Bis(3-aminophenoxy)pyridine, 4,4'-Bis(3-aminophenoxy)biphenyl, 4,4'-Bis(4-aminophenoxy)biphenyl, bis[ 4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]sulfide 2,2-Bis[4-(3-aminophenoxy)phenyl]propane, 2,2-Bis[4-(4-aminophenoxy)phenyl]propane, 1,3-Bis[4-(3-aminophenoxy)benzyl]benzene, 1,3-Bis[4-(4-aminophenoxy)benzyl]benzene, 1,4-Bis[4-(3-aminophenoxy)benzyl]benzene, 1,4-Bis[ 4-(4-aminophenoxy)benzyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene Benzene, 4,4'-bis[4-(4-aminophenoxy)benzyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl sulfone, 3,3'-diamino- 4,4'-diphenoxybenzophenone, 3,3'-diamino-4,4'-diphenyloxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-phenyloxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiandene, 6,6'-bis(4-aminophenoxy)-3, 3,3',3'-Tetramethyl-1,1'-spirobiandene, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, α,ω-bis(3-aminobutyl)polydimethylsiloxane, bis(aminomethyl)ether, bis(2-aminoethyl)ether, bis(3-aminopropyl) ether, bis(2-aminomethoxy)ethyl]ether, bis[2-(2-aminoethoxy)ethyl]ether, bis[2-(3-aminopropoxy)ethyl]ether, 1,2-bis(aminomethoxy)ethane, 1,2-bis(2-aminoethoxy)ethane, 1,2-bis[2-(aminomethoxy)ethoxy]ethane, 1,2-bis[2-(2-aminoethoxy)ethoxy]ethane, ethylene glycol Bis(3-aminopropyl)ether, diethylene glycol bis(3-aminopropyl)ether, triethylene glycol bis(3-aminopropyl)ether, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diamino Undecane, 1,12-diaminododecane, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, trans-1,4-diaminocyclohexane, 1,2-bis(2-aminoethyl)cyclohexane, 1,3-bis(2-aminoethyl)cyclohexane, 1,4-bis(2-aminoethyl)cyclohexane, bis(4-aminocyclohexyl)methane, 2,6-bis( 1,4-Diamino-2-fluorobenzene, 1,4-Diamino-2,3-difluorobenzene, 1,4-Diamino-2,5-difluorobenzene, 1,4-Diamino-2,6-difluorobenzene, 1,4-Diamino-2,3,5-trifluorobenzene, 1,4-Diamino-2,3,5,6 -tetrafluorobenzene, 1,4-diamino-2-(trifluoromethyl)benzene, 1,4-diamino-2,3-bis(trifluoromethyl)benzene, 1,4-diamino-2,5-bis(trifluoromethyl)benzene, 1,4-diamino-2,6-bis(trifluoromethyl)benzene, 1,4-diamino-2,3,5-tris(trifluoromethyl)benzene, 1,4-diamino-2,3,5,6-tetrakis(trifluoromethyl)benzene.

For example, when diaminodiphenyl sulfone is used as the diamine in addition to fluoroalkyl-substituted benzidine, the solubility or transparency of the polyimide resin in the solvent may be improved. Among diaminodiphenyl sulfones, 3,3'-diaminodiphenyl sulfone (3,3'-DDS) and 4,4'-diaminodiphenyl sulfone (4,4'-DDS) are preferred. 3,3'-DDS and 4,4'-DDS may also be used together.

The content of diaminodiphenyl sulfone relative to 100 mol% of the total amount of diamine is preferably 3 mol% or more, more preferably 5 mol% or more, and may be 8 mol% or more or 10 mol% or more. From the perspective of the mechanical strength of the polyimide resin, the content of diaminodiphenyl sulfone relative to 100 mol% of the total amount of diamine is preferably 40 mol% or less, more preferably 30 mol% or less.

<Composition of polyimide> As described above, the polyimide of the present invention contains an acid dianhydride represented by the general formula (1) and an acid dianhydride having a cyclobutane structure as an acid dianhydride component, and contains a fluoroalkyl-substituted benzidine as a diamine. The acid dianhydride represented by the general formula (1) is preferably TAMBP represented by the formula (2), the acid dianhydride containing a cyclobutane structure is preferably CBDA, and the benzidine substituted by a fluoroalkyl group is preferably TFMB. The polyimide may further contain 6FDA and/or BPDA as an acid dianhydride component, and may further contain 3,3'-DDS and/or 4,4'-DDS as a diamine component.

In the total amount of 100 mol % of the acid dianhydride components, the amount of TahmbP is more preferably 40 to 85 mol %, and the amount of CBDA is more preferably 15 to 60 mol %. Furthermore, from the viewpoint of improving the solubility of the polyimide resin or improving the transparency of the film, it is preferred to contain 25 mol % or less of 6FDA and/or BPDA as the acid dianhydride components.

The amount of TFMB is preferably 40 to 100 mol%, more preferably 70 to 95 mol%, based on 100 mol% of the total amount of the diamine component. In addition, it is preferred that 5 to 30 mol% of 3,3'-DDS or 4,4'-DDS is contained as the diamine component.

Since the polyimide of the above composition has a high solubility in low boiling point solvents such as dichloromethane, it is easy to reduce the residual solvent amount of the polyimide membrane, and can produce a polyimide membrane with high transmittance, low yellowness, and high mechanical strength.

[Production method of polyimide resin] The production method of polyimide resin is not particularly limited. Preferably, a method is a method in which a diamine and an acid dianhydride are reacted in a solvent to prepare a polyimide as a precursor of polyimide, and the polyimide is imidized by dehydration and cyclization of the polyimide. For example, an imidization catalyst and a dehydrating agent are added to a polyimide solution to dehydrate and close the polyimide ring, thereby obtaining a polyimide solution. The polyimide solution is mixed with a poor solvent for polyimide to precipitate the polyimide resin, and solid-liquid separation is performed to obtain a polyimide resin.

<Preparation of polyamide> By reacting acid dianhydride and diamine in a solvent, a polyamide solution is obtained. The polymerization of polyamide can be carried out without particular limitation using an organic solvent that can dissolve diamine and acid dianhydride as raw materials and polyamide as a polymerization product. Specific examples of the organic solvent include urea-based solvents such as methyl urea and N,N-dimethylethyl urea; sulfonium-based solvents such as dimethyl sulfoxide, diphenyl sulfone and tetramethyl sulfone; amide-based solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N,N'-diethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone and hexamethylphosphoric acid triamide; halogenated alkane-based solvents such as chloroform and dichloromethane; aromatic hydrocarbon-based solvents such as benzene and toluene, and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether and p-cresol methyl ether. These solvents may be used alone or in combination of two or more. Among these, N,N-dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone may be preferably used due to their excellent polymerization reactivity and solubility of polyamide.

The polymerization of polyamide is carried out by dissolving diamine and dianhydride in an organic solvent. The solid content concentration of the polyamide solution (the added concentration of diamine and dianhydride in the reaction solution) is usually about 5 to 40% by weight, preferably 10 to 30% by weight. The dianhydride and diamine are preferably used in equimolar amounts (95:105 to 105:95). If one component is excessive, the molecular weight of polyamide and polyimide may not be sufficiently increased, and the mechanical strength of the polyimide film may be reduced.

The reaction temperature is not particularly limited, but is preferably 0°C or higher and 80°C or lower, and more preferably 20°C or higher and 45°C or lower. By setting the temperature to 0°C or higher, the decrease in reaction rate can be suppressed, and the polymerization reaction can be carried out in a relatively short time. In addition, by setting the temperature to 80°C or lower, the decrease in polymerization degree caused by the ring opening of the acid dianhydride component can be suppressed.

The order of adding diamine and dianhydride to the organic solvent (reaction system) in the polymerization of polyamide is not particularly limited. The arrangement of monomer components (structures derived from dianhydride and structures derived from diamine) in polyamide and polyimide can be random or block.

After dissolving or dispersing in an organic solvent in the form of a slurry any one of the total amount of diamine or the total amount of acid dianhydride, the other is added to obtain a random polyamide. For example, diamine is dissolved or dispersed in an organic solvent in the form of a slurry to prepare a diamine solution, and the acid dianhydride is added to the diamine solution. Diamine can also be added to a solution prepared by dissolving the acid dianhydride in an organic polar solvent. Multiple acid dianhydrides and diamines can be added at once or in multiple times. Diamine and acid dianhydride can be added in a solid state or in a state of being dissolved or dispersed in an organic solvent in the form of a slurry.

By adjusting the order of monomer addition, various physical properties of the resulting polyimide can also be controlled. For example, (A) among a plurality of acid dianhydrides and diamines, a specific acid dianhydride is first reacted with a diamine to form a chain segment (oligomer) having a structural unit (repeating unit) formed by a specific acid dianhydride and a diamine bonded together. After the oligomer is adjusted, (B) the remaining portion of the diamine and acid dianhydride is added and further reacted (post-polymerization) to obtain a polyamide containing a block structure in the molecule. By subjecting the polyamide to imidization, a polyamide containing a continuous block of structural units formed by a specific diamine and a specific acid dianhydride bonded together in the molecular structure is obtained. When polyimide has a block structure, the mechanical strength or heat resistance of the polyimide film tends to be improved.

In the above step (A), either the dianhydride or the diamine is reacted in excess to form an anhydride-terminated or amine-terminated oligomer. The amount of the dianhydride and the diamine added in the preparation of the oligomer is preferably 70-95 mol%, more preferably 75-90 mol%, relative to the total amount added (the total amount of (A) and (B) added).

In the preparation of oligomers, if the amount of diamine added is greater than the amount of acid dianhydride added, an amine-terminated oligomer is generated. When preparing an amine-terminated oligomer, the amount of diamine added is preferably 1.01 to 1.25 times, more preferably 1.03 to 1.2 times, and further preferably 1.05 to 1.18 times the amount of acid dianhydride added in terms of molar ratio. The closer the ratio of the two is to 1, the greater the molecular weight of the oligomer tends to be.

In the preparation of the oligomer, it is preferred to include fluoroalkyl-substituted benzidine such as TFMB as the diamine, and include acid dianhydrides represented by the general formula (1) such as TAMBP and acid dianhydrides containing a cyclobutane structure such as CBDA as the acid dianhydrides. In particular, it is preferred to use only fluoroalkyl-substituted benzidine as the diamine. By adjusting the composition of the oligomer, that is, the block structure, the mechanical strength of the polyimide film tends to be improved.

In step (B), the remaining portion of diamine and acid dianhydride is added in an equal molar amount (95:105 to 105:95) to react the end of the oligomer prepared in step (A) with the monomer added in step (B) to obtain a polyamide with an alternating block structure. By subjecting the polyamide to imidization, a polyimide having a continuous block of structural units formed by bonding a specific diamine and a specific acid dianhydride in the molecular structure is obtained.

In step (B), the remaining acid dianhydride and diamine may be added simultaneously or sequentially. Alternatively, an oligomer obtained by reacting the remaining acid dianhydride with diamine in advance may be added to the oligomer solution prepared in (A).

<Imidization> Polyimide is obtained by dehydration and cyclization of polyamide. The chemical imidization method of adding a dehydrating agent and an imidization catalyst to the polyamide solution is applicable to the imidization in the solution. In order to promote the progress of imidization, the polyamide solution can also be heated.

As the imidization catalyst, a tertiary amine can be used. As the tertiary amine, a heterocyclic tertiary amine is preferred. Specific examples of the heterocyclic tertiary amine include pyridine, picoline, quinoline, isoquinoline, etc. As the dehydrating agent, a carboxylic anhydride can be used, and specifically, acetic anhydride, propionic anhydride, butyric anhydride, benzoic anhydride, trifluoroacetic anhydride, etc. can be mentioned. The amount of the imidization catalyst added is preferably 0.5 to 5.0 times the molar equivalent relative to the amide group of the polyamide, more preferably 0.7 to 2.5 times the molar equivalent, and further preferably 0.8 to 2.0 times the molar equivalent. The amount of the dehydrating agent added is preferably 0.5 to 10.0 times the molar equivalent of the amide group of the polyamide, more preferably 0.7 to 5.0 times the molar equivalent, and further preferably 0.8 to 3.0 times the molar equivalent.

<Precipitation of polyimide resin> The polyimide solution obtained by imidization of polyamide can also be used directly as a coating for film formation, but it is better to temporarily precipitate the polyimide resin in the form of a solid. By precipitating the polyimide resin in the form of a solid, impurities or residual monomer components generated during the polymerization of polyamide, dehydrating agents, imidization catalysts, etc. can be washed and removed. Therefore, a polyimide film with excellent transparency or mechanical properties can be obtained.

By mixing the polyimide solution with a poor solvent, the polyimide resin is precipitated. The poor solvent is a poor solvent for the polyimide resin, preferably a solvent that is miscible with the solvent that dissolves the polyimide resin, and examples thereof include water and alcohols. Examples of alcohols include methanol, ethanol, isopropanol, ethylene glycol, triethylene glycol, 2-butanol, 2-hexanol, cyclopentanol, cyclohexanol, phenol, tert-butanol, and the like. In terms of the difficulty in causing ring opening of the polyimide, alcohols such as isopropanol, 2-butanol, 2-pentanol, phenol, cyclopentanol, cyclohexanol, and tert-butanol are preferred, and isopropanol is particularly preferred.

[Polyimide film] A polyimide solution (film-forming coating) obtained by dissolving a polyimide resin in an organic solvent is applied to a substrate, and the solvent is dried and removed to produce a polyimide film.

The organic solvent for dissolving the polyimide resin is not particularly limited as long as it can dissolve the above-mentioned polyimide resin. From the perspective of easy drying and removal of the solvent, which can reduce the amount of residual solvent in the polyimide film, low-boiling point solvents such as dichloromethane, methyl acetate, tetrahydrofuran, acetone, and 1,3-dioxacyclopentane are preferred, and dichloromethane is particularly preferred. As described above, by setting the composition ratio of the acid dianhydride component and the diamine component within a specified range, a polyimide that shows high solubility in low-boiling point solvents such as dichloromethane can be obtained.

The solid content concentration of the polyimide solution can be appropriately set according to the molecular weight of the polyimide, the thickness of the film, the film-forming environment, etc. The solid content concentration is preferably 5 to 30% by weight, more preferably 8 to 20% by weight.

The polyimide solution may also contain resin components or additives other than polyimide. Examples of additives include ultraviolet absorbers, crosslinking agents, dyes, surfactants, leveling agents, plasticizers, microparticles, etc. The content of the polyimide resin relative to 100 parts by weight of the solid content of the polyimide solution (film-forming coating) is preferably 60 parts by weight or more, more preferably 70 parts by weight or more, and further preferably 80 parts by weight or more.

As a method for coating the polyimide solution on a substrate, a known method can be used, for example, coating can be performed by a rod coater or a notched wheel coater. As a substrate for coating the polyimide solution, a glass substrate, a metal substrate such as SUS (Steel Use Stainless Steel), a metal roller, a metal belt, a plastic film, etc. can be used. From the viewpoint of improving productivity, it is preferable to use an annular support such as a metal roller, a metal belt, or a long plastic film as a support, and manufacture the film by roll-to-roll. When a plastic film is used as a support, a material that is insoluble in the solvent of the film-forming coating may be appropriately selected. As the plastic material, polyethylene terephthalate, polycarbonate, polyacrylate, polyethylene naphthalate, etc. may be used.

It is preferred to heat the solvent when drying it. The heating temperature is not particularly limited, but from the viewpoint of suppressing coloration, it is preferably 200°C or less, and more preferably 180°C or less. When drying the solvent, the heating temperature may be increased in stages. The solvent may also be dried under reduced pressure. The polyimide resin described above is soluble in low-boiling-point solvents such as dichloromethane, so the residual solvent can be easily reduced even when heated at 200°C or less.

The residual solvent amount of the polyimide film (the mass of the solvent contained in the film relative to the mass of the film) is preferably 1.5% or less, and more preferably 1.0% or less. If the residual solvent amount is within this range, the mechanical strength of the polyimide film tends to be improved.

The thickness of the polyimide film is not particularly limited and can be appropriately set according to the application. The thickness of the polyimide film is, for example, about 5 to 100 μm. In applications requiring impact resistance such as cover window materials for displays, the thickness of the polyimide film is preferably 30 μm or more, more preferably 35 μm or more, and further preferably 40 μm or more. The polyimide film of the present invention has excellent transparency even when the film thickness is 40 μm or more. From the perspective of maintaining excellent transparency, the thickness of the polyimide film is preferably 90 μm or less, and more preferably 85 μm or less.

[Characteristics of polyimide film] The yellowness index (YI) of the polyimide film is preferably 3.0 or less, and more preferably 2.5 or less. When the yellowness index is 3.0 or less, the film is not colored yellow and can be preferably used as a film for display, etc.

The total light transmittance of the polyimide film is preferably 80% or more, more preferably 85% or more. Furthermore, the light transmittance of the polyimide film at a wavelength of 400 nm is preferably 35% or more, further preferably 40% or more. The tensile modulus of elasticity of the polyimide film is preferably 4.9 GPa or more, more preferably 5.0 GPa or more, further preferably 5.2 GPa or more.

From the viewpoint of preventing film damage caused by contact with the roll during roll-to-roll conveyance or contact between the films during winding, the pencil hardness of the polyimide film is preferably HB or higher, more preferably F or higher. When the polyimide film is used for a cover window of a display, etc., since scratch resistance from external contact is required, the pencil hardness of the polyimide film is preferably H or higher.

[Application of polyimide film] The polyimide film of the present invention has low yellowness and high transparency, and can be preferably used as a display material. In particular, the polyimide film with high mechanical strength can be applied to surface components such as cover windows of displays. When the polyimide film of the present invention is actually used, an antistatic layer, an easy-to-adhesive layer, a hard coating layer, an anti-reflection layer, etc. can be set on the surface. [Example]

Hereinafter, the present invention will be specifically described based on embodiments and comparative examples. In addition, the present invention is not limited to the following embodiments.

[Preparation of polyamide solution] <Polymerization of random bodies: Examples 3, 10-12, Comparative Examples 1, 7, 8> In a separable flask, N,N-dimethylformamide was added as a solvent. While stirring under a nitrogen atmosphere, a diamine and anhydride in a molar ratio shown in Composition A of Table 1 were added. The mixture was stirred for 5 hours under a nitrogen atmosphere to obtain a polyamide solution having a solid content concentration of 18%.

<Polymerization of block body: Examples 1, 2, 4 to 9, Comparative Examples 2 to 6> In a separable flask, N,N-dimethylformamide was added as a solvent, and diamine and dianhydride in the molar ratio shown in composition A of Table 1 were added while stirring under a nitrogen atmosphere. The mixture was stirred for 10 hours under a nitrogen atmosphere to synthesize an oligomer. Subsequently, diamine and dianhydride were added in the molar ratio shown in composition B of Table 1, and polymerization was performed after stirring for a specified time under a nitrogen atmosphere to obtain a polyamide solution with a solid content concentration of 18%.

The abbreviations of the raw material monomers shown in Table 1 are as follows. TMHQ: p-phenylene trimellitic dianhydride TAHMBP: bis(1,3-dihydroxy-1,3-dihydroisobenzofuran-5-carboxylic acid) 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diester 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride TFMB: 2,2'-bis(trifluoromethyl)benzidine 3,3'-DDS: 3,3'-diaminodiphenyl sulfonate 4,4'-DDS: 4,4'-diaminodiphenyl sulfonate

[Imidization, monoisocyanation of polyimide resin, and preparation of polyimide solution] 5.5 g of pyridine as an imidization catalyst was added to 100 g of polyimide solution to make it completely dispersed, and then 8 g of acetic anhydride was added and stirred at 90°C for 3 hours to carry out imidization. For the solution that did not gel, 100 g of 2-propanol (hereinafter referred to as "IPA") was added dropwise at a rate of 2 to 3 drops/second while stirring the solution cooled to room temperature to precipitate polyimide. Furthermore, 150 g of IPA was added, stirred for about 30 minutes, and then vacuum filtered using a Kiriyama funnel. The obtained solid was washed with 100 g of IPA. After the cleaning operation was repeated 6 times, the polyimide resin was obtained by drying in a vacuum oven set at 120°C for 8 hours. In addition, in Comparative Examples 1 to 5, the viscosity of the solution increased rapidly during the imidization and gelled, so the polyimide solution could not be obtained. Therefore, in these comparative examples, the subsequent operation and evaluation were not carried out.

9 g of dichloromethane (DCM) was added to 1 g of the polyimide resin obtained above, and after stirring at room temperature for 12 hours, the DCM solubility of the polyimide resin was evaluated by visually confirming the presence of dissolved residues. Those that obtained a visually transparent solution were considered DCM "soluble", and those that confirmed dissolved residues in the form of solid components were considered DCM "insoluble". In addition, those that gelled during imidization were recorded as "gelled" in Table 1.

[Preparation of polyimide film] The polyimide resin was dissolved in dichloromethane (hereinafter referred to as "DCM") to obtain a polyimide solution having a solid content concentration of 10 wt%. The polyimide solution was applied to an alkali-free glass plate using a rod coater, and the solvent was removed by heating at 40°C for 60 minutes, 80°C for 30 minutes, 150°C for 30 minutes, and 170°C for 30 minutes in an atmosphere to obtain a polyimide film having the thickness shown in Table 1. Furthermore, since the polyimide resin of Comparative Example 8 was not soluble in DCM, a polyimide solution prepared by dissolving the polyimide resin in methyl ethyl ketone (MEK) was used to prepare the membrane.

[Evaluation of polyimide film] (Tensile elastic modulus) Measurement was performed using the "AUTOGRAPH AGS-X" manufactured by Shimadzu Corporation under the following conditions. Sample measurement range: width 10 mm, distance between fixtures 100 mm, tensile speed: 20.0 mm/min, measurement temperature: 23°C. The sample was left to stand for 1 day at 23°C/55%RH and humidified.

(Yellowness) Using a 3 cm square sample, the yellowness (YI) was measured using the spectrophotometer "SC-P" manufactured by Suga Test Instruments.

(Pencil hardness) The pencil hardness of the film is measured using the JIS K-5600-5-4 "Pencil scratch test".

(Transmittance at 400 nm) Use the UV-visible spectrophotometer "V-560" manufactured by JASCO Corporation to measure the transmittance of the film at 300 to 800 nm and read the transmittance at a wavelength of 400 nm.

(Total light transmittance) Measured using the haze meter "HZ-V3" manufactured by Suga Test Instruments, using the method described in JIS K7361-1.

(Residual solvent amount) Use about 8.9 g of 1,3-dioxolane as a solvent, dissolve about 0.1 g of polyimide membrane and about 1 g of diethylene glycol butyl methyl ether (DEGBME) as an internal standard substance, and prepare a sample for measurement. The solution is measured using a gas chromatograph (GC, manufactured by Shimadzu Corporation), and the residual solvent amount (DCM or MEK) contained in the polyimide membrane is calculated from the GC peak area and the preparation concentration.

Table 1 shows the composition of the polyimide resin of the above-mentioned Examples and Comparative Examples (the molar ratio of the amount of dianhydride and diamine added in the polymerization of polyamide acid), the solubility in DCM, the solvent used for film formation, and the evaluation results of the polyimide film.

[Table 1] Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 Embodiment 7 Embodiment 8 Embodiment 9 Embodiment 10 Embodiment 11 Embodiment 12 Comparison Example 1 Comparison Example 2 Comparison Example 3 Comparison Example 4 Comparison Example 5 Comparative Example 6 Comparison Example 7 Comparative Example 8 Polymer sequence Block Block No rules Block Block Block Block Block Block No rules No rules No rules No rules Block Block Block Block Block No rules No rules Composition A Diamine TFMB 90 90 90 90 90 90 90 90 90 90 100 70 100 90 90 60 90 100 100 70 3,3'-DDS - 3.3 10 - - - - - 3.3 10 - 30 - - - - - - - 30 Acid dianhydride TAHMBP 50 50 50 50 45 50 50 40 40 40 70 70 50 50 35 25 - 45 100 - TMH - - - - - - - - - - - - - - - - 50 - - - BPDA - - - - 15 15 15 20 20 20 15 15 40 30 30 25 15 25 - CBDA 30 30 30 30 20 15 15 20 20 20 15 15 10 - 15 - 15 - - 60 6FDA - - 20 - - - - - - 20 40 B Diamine TFMB - - - - - - - - 10 10 10 - 3,3'-DDS 10 6.7 - 10 10 - 10 6.7 - - 30 10 - 4,4'-DDS - - 10 - - 10 - - - - - - - Acid dianhydride 6FDA 20 20 20 20 20 20 20 20 20 20 50 20 30 DCM solubility Soluble Soluble Soluble Soluble Soluble Soluble Soluble Soluble Soluble Soluble Soluble Soluble Gel Gel Gel Gel Gel Soluble Soluble Insoluble Film making solvent DCM DCM DCM DCM DCM DCM DCM DCM DCM DCM DCM DCM DCM DCM MEK Membrane properties Film thickness mm 56 54 50 50 50 49 51 50 50 50 54 55 54 50 49 Tensile modulus GPa 5.7 5.5 5.1 5.6 5.2 5.4 5.2 5.6 5.2 5.0 5.3 5.0 4.6 4.8 4.1 Pencil hardness - 4H 4H 4H 4H 4H 4H 4H 4H 4H 3H 4H 3H 3H 4H 3H YI - 2.3 2.3 2.1 2.3 2.2 2.5 2.4 2.3 2.3 2.2 2.8 2.7 2.7 2.6 1.9 Transmittance at 400 nm % 58.2 60.3 62.1 60.4 52.5 51.9 51.1 50.0 51.1 51.7 45.7 46.6 45.1 51.2 81.7 Total light transmittance % 89.5 89.8 89.5 89.5 89.5 89.3 89.3 89.2 89.2 89.3 89.1 88.8 89.1 89.2 91.0 Residual solvent amount % ND ND 0.1 0.2 ND ND 0.2 ND 0.1 0.2 ND 0.1 0.6 0.1 2.8

As shown in Table 1, it can be seen that in Examples 1 to 12, the polyimide exhibits DCM solubility, and the polyimide film exhibits a tensile elastic modulus of more than 5 GPa, and can have both excellent mechanical strength and transparency.

In Comparative Example 1, in which the amount of CBDA relative to the total amount of the acid dianhydride was 10 mol%, the solvent solubility of the polyimide was low, and the solution gelled during imidization, so that the polyimide resin could not be isolated. In Comparative Example 2, in which no CBDA was used, and Comparative Example 3, in which the amount of TAMBP was 35 mol%, and Comparative Example 4, in which the amount of TAMBP was 25 mol%, gelled during imidization, similarly to Comparative Example 1.

In Comparative Example 5, in which TMHQ, which is a trimellitic acid dianhydride ester, is used as the acid dianhydride, gelation also occurs during imidization. From the comparison between Example 6 and Comparative Example 5, it can be seen that the polyimide having a structure derived from TAMBP, which is an acid dianhydride having a substituent on the benzene ring of biphenyl, has excellent solvent solubility.

In Comparative Example 8 using a combination of CBDA and 6FDA as an acid dianhydride, although gelation did not occur during imidization, the isolated polyimide did not show DCM solubility. The polyimide film of Comparative Example 8 obtained by using MEK as a solvent for film formation showed excellent transparency, but the tensile elastic modulus was 4.1 GPa, and the mechanical strength was inferior to that of the embodiment. In addition, in Comparative Example 8, the residual solvent amount of MEK was 2.8%, which was larger than that of other examples using DCM. In Comparative Example 8, since DCM, which is a low-boiling point solvent, cannot be used, it is difficult to obtain a polyimide membrane with a small amount of residual solvent. Reducing the amount of residual solvent requires extending the heating time, and the productivity of the polyimide membrane is difficult to improve.

In Comparative Examples 6 and 7, although CBDA was not used as the dianhydride, the introduction ratio of TAMBP and 6FDA was increased, thereby obtaining a polyimide resin soluble in DCM. However, the tensile elastic modulus of the polyimide films of Comparative Examples 6 and 7 was lower than 5 GPa, and the mechanical strength was insufficient.

From the above results, it can be seen that the polyimide containing fluoroalkyl-substituted benzidine as the diamine component, the ester of diphenol having a substituent on the benzene ring and trimellitic acid dianhydride, and the acid dianhydride having a cyclobutane structure as the acid dianhydride in a specified ratio is soluble in a low boiling point solvent such as DCM. Therefore, a film with a small amount of residual solvent can be easily prepared, and it can have both the mechanical properties and transparency of the polyimide film.

From the comparison between Examples 1 and 2 and Example 3, and the comparison between Examples 8 and 9 and Example 10, it can be seen that the polyimide having a block structure shows a higher elastic modulus than the polyimide having a random structure of the same composition. In particular, in Examples 1 and 8 in which a block containing only TFMB as a diamine component is formed, it can be seen that the tensile elastic modulus of the polyimide film tends to be improved.

Claims (14)

A polyimide resin having a structure derived from an acid dianhydride and a structure derived from a diamine, wherein the diamine comprises 40-100 mol% of fluoroalkyl-substituted benzidine relative to 100 mol% of the total amount of the diamines, and the acid dianhydride comprises 40-65 mol% of an acid dianhydride represented by the general formula (1), 15-60 mol% of an acid dianhydride having a cyclobutane structure, and at least one selected from the group consisting of 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride relative to 100 mol% of the total amount of the acid dianhydrides.

In the general formula (1), R ¹ to R ⁸ are independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a perfluoroalkyl group having 1 to 20 carbon atoms, and at least one of R ¹ to R ⁴ and at least one of R ⁵ to R ⁸ are an alkyl group having 1 to 20 carbon atoms, or a fluoroalkyl group having 1 to 20 carbon atoms. The polyimide resin of claim 1, wherein the acid dianhydride represented by the general formula (1) is a compound represented by the formula (2), [Chemical 2]

As in the polyimide resin of claim 1 or 2, the acid dianhydride having a cyclobutane structure is 1,2,3,4-cyclobutane tetracarboxylic dianhydride. The polyimide resin of claim 1 or 2, wherein the fluoroalkyl-substituted benzidine is 2,2'-bis(trifluoromethyl)benzidine. The polyimide resin of claim 1 or 2, wherein the diamine further comprises 5 to 40 mol% of diaminodiphenylsulfone. A method for producing a polyimide resin, which is a method for producing a polyimide resin as claimed in any one of claims 1 to 5, wherein the diamine and the acid dianhydride are reacted in a solvent to prepare a polyimide solution, a dehydrating agent and an imidization catalyst are added to the polyimide solution to imidize the polyimide. A method for producing a polyimide resin as claimed in claim 6, wherein a polyimide solution in which polyimide is dissolved in an organic solvent is further mixed with a poor solvent for polyimide to precipitate the polyimide resin. A method for producing a polyimide resin as claimed in claim 6 or 7, wherein in the preparation of the polyamide solution, (A) either an acid dianhydride or a diamine is reacted in excess to adjust the oligomers at the acid anhydride end or the amine end, and (B) the remaining diamine and the acid dianhydride are added in an equimolar amount to perform post-polymerization. A method for producing a polyimide resin as claimed in claim 6 or 7, wherein in the preparation of the polyamide acid solution, one of the total amount of the diamine and the total amount of the dianhydride is dissolved or dispersed in an organic solvent, and then the other is added. A polyimide film comprising a polyimide resin as claimed in any one of claims 1 to 5. For example, the polyimide film of claim 10 has a tensile modulus of 5.0 GPa or more. For example, the polyimide film of claim 10 or 11 has a pencil hardness of H or above. For the polyimide film in claim 10 or 11, the yellowness is below 3.0. A method for manufacturing a polyimide film, which comprises applying a polyimide solution prepared by dissolving a polyimide resin as described in any one of claims 1 to 5 in a solvent containing dichloromethane onto a substrate, and removing the solvent.