CN114245809B - Polyimide resin composition, polyimide varnish and polyimide film - Google Patents

Abstract

A polyimide resin composition comprising a polyimide resin and a crosslinking agent having at least 2 oxazolyl groups, wherein the polyimide resin has a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from diamine, the structural unit A comprises a structural unit (A-1) derived from CpODA, the structural unit B comprises a structural unit (B-1) derived from TFMB, and a structural unit (B-2) derived from a specific compound represented by 3, 5-DABA.

Description

Polyimide resin composition, polyimide varnish and polyimide film

Technical Field

The invention relates to a polyimide resin composition, a polyimide varnish and a polyimide film.

Background technique

Generally, polyimide resin has excellent heat resistance, and therefore various applications thereof are being studied in the fields of electrical/electronic components, etc. For example, in order to make the device lighter and more flexible, it is expected that the glass substrate used in image display devices such as liquid crystal displays and OLED displays will be replaced with a plastic substrate, and research is being promoted on polyimide films suitable as the plastic substrate. The polyimide films for such applications are required to be colorless and transparent.

When a varnish applied on a glass support or silicon wafer is heated and cured to form a polyimide film, residual stress is generated in the polyimide film. If the residual stress of the polyimide film is large, the glass support or silicon wafer may warp, so the polyimide film is also required to reduce the residual stress.

However, in order to be suitable for substrates, polyimide films not only have colorless transparency and low residual stress, but also have chemical resistance (e.g., acid resistance, alkali resistance, and solvent resistance). For example, when polyimide films are used as substrates for forming ITO (Indium Tin Oxide) films, polyimide films are required to have resistance to acids used in etching of ITO films. If the acid resistance of polyimide films is insufficient, there is a concern that the film may turn yellow and the colorless transparency may be impaired.

In addition, in the cleaning of a support such as a glass plate used in the manufacture of a polyimide film (a support coated with a polyimide varnish), an alkali aqueous solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is mainly used. Cleaning with an alkali aqueous solution may be performed in a state where a polyimide film is formed on a support such as a glass plate. Therefore, the polyimide film is also required to have resistance to alkali.

Furthermore, in the process of forming various electronic circuits such as TFTs on polyimide films, organic solvents such as NMP are sometimes used, and polyimide films are also required to have resistance to organic solvents.

On the other hand, after the polyimide resin composition is processed into a polyimide film, it is necessary to clean the pipes and devices used in coating, etc. In order to fully clean the device, the polyimide resin composition is also required to be soluble in the cleaning liquid used (for example, "OK73 thinner" manufactured by Tokyo Ohka Industry Co., Ltd., various organic solvents such as NMP), and requires two contradictory properties: solvent resistance and cleaning properties.

As a polyimide resin providing a thin film with low residual stress, Patent Document 1 discloses a polyimide resin synthesized using 4,4'-oxydiphthalic dianhydride as a tetracarboxylic acid component and α,ω-aminopropyl polydimethylsiloxane having a number average molecular weight of 1000 and 4,4'-diaminodiphenyl ether as diamine components.

Patent Document 2 discloses a polyimide resin composition comprising a polyimide resin having a carboxyl group and a crosslinking agent having at least two oxazole groups, and states that a film having good transparency and high hardness can be formed using the polyimide resin composition.

However, there is no description about chemical resistance and cleaning properties in Patent Document 1. In addition, in Patent Document 2, resistance to solvent (N,N-dimethylacetamide) is not evaluated, and cleaning properties and residual stress are not studied at all.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2005-232383

Patent Document 2: Japanese Patent Application Publication No. 2016-222797

Summary of the invention

Problem that the invention aims to solve

As described above, polyimide films are required to have colorless transparency, low residual stress, and chemical resistance, but it is not easy to improve these properties while maintaining excellent heat resistance.

The problem to be solved by the present invention is to provide a polyimide resin composition capable of forming a film having excellent heat resistance, colorless transparency, chemical resistance and cleaning properties and low residual stress, as well as a polyimide varnish and a polyimide film comprising the polyimide resin composition.

Solutions for solving problems

The present inventors have found that a polyimide resin composition containing a polyimide resin having a combination of specific structural units and a specific cross-linking agent can solve the above-mentioned problems, thereby completing the invention.

That is, the present invention relates to the following <1> to <11>.

<1> A polyimide resin composition comprising a polyimide resin and a crosslinking agent having at least two oxazole groups,

The polyimide resin comprises a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from diamine, wherein the structural unit A comprises a structural unit (A-1) derived from a compound represented by the following formula (a-1), and the structural unit B comprises a structural unit (B-1) derived from a compound represented by the following formula (b-1) and a structural unit (B-2) derived from a compound represented by the following formula (b-2).

(In formula (b-2), X is a single bond, a substituted or unsubstituted alkylene group, a carbonyl group, an ether group, a group represented by the following formula (b-2-i), or a group represented by the following formula (b-2-ii), p is an integer of 0 to 2, m1 is an integer of 0 to 4, and m2 is an integer of 0 to 4. When p is 0, m1 is an integer of 1 to 4.)

(In formula (b-2-i), m3 is an integer of 0 to 5; in formula (b-2-ii), m4 is an integer of 0 to 5. It should be noted that when m1+m2+m3+m4 is 1 or more and p is 2, the two Xs and the two m2 to m4 are independently selected.)

<2> The polyimide resin composition according to <1> above, wherein the structural unit (B-2) is a structural unit (B-21) derived from a compound represented by the following formula (b-21).

<3> The polyimide resin composition according to <1> or <2>, wherein the ratio of the structural unit (A-1) in the structural unit A is 40 mol% or more.

<4> The polyimide resin composition according to any one of <1> to <3>, wherein the ratio of the structural unit (B-1) in the structural unit B is 35 to 95 mol%,

The ratio of the structural unit (B-2) in the structural unit B is 5 to 65 mol%.

<5> The polyimide resin composition according to any one of <1> to <4>, wherein the structural unit A further includes a structural unit (A-2) derived from a compound represented by the following formula (a-2).

<6> The polyimide resin composition according to any one of <1> to <5>, wherein the structural unit A further includes a structural unit (A-3) derived from silicone modified with acid anhydrides at both ends.

<7> The polyimide resin composition according to any one of <1> to <6>, wherein the crosslinking agent is a compound including an aromatic ring or an aromatic heterocyclic ring to which at least two oxazolyl groups are bonded.

<8> The polyimide resin composition according to any one of <1> to <7>, wherein the crosslinking agent is a compound including a benzene ring to which at least two oxazolyl groups are bonded.

<9> The polyimide resin composition according to any one of <1> to <8>, wherein the crosslinking agent is 1,3-bis(4,5-dihydro-2-oxazolyl)benzene.

<10> A polyimide varnish obtained by dissolving the polyimide resin composition according to any one of <1> to <9> in an organic solvent.

<11> A polyimide film obtained by crosslinking the polyimide resin in the polyimide resin composition according to any one of <1> to <9> above with the crosslinking agent.

Effects of the Invention

According to the present invention, a thin film having excellent heat resistance, colorless transparency, chemical resistance and cleaning properties and low residual stress can be formed.

Detailed ways

[Polyimide resin composition]

The polyimide resin composition of the present invention comprises a polyimide resin and a crosslinking agent. The polyimide resin and the crosslinking agent in the present invention are described below.

<Polyimide resin>

The polyimide resin of the present invention comprises a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein the structural unit A comprises a structural unit (A-1) derived from a compound represented by the following formula (a-1), and the structural unit B comprises a structural unit (B-1) derived from a compound represented by the following formula (b-1) and a structural unit (B-2) derived from a compound represented by the following formula (b-2).

(In formula (b-2), X is a single bond, a substituted or unsubstituted alkylene group, a carbonyl group, an ether group, a group represented by the following formula (b-2-i), or a group represented by the following formula (b-2-ii), p is an integer of 0 to 2, m1 is an integer of 0 to 4, and m2 is an integer of 0 to 4. When p is 0, m1 is an integer of 1 to 4.)

(In formula (b-2-i), m3 is an integer of 0 to 5; in formula (b-2-ii), m4 is an integer of 0 to 5. It should be noted that when m1+m2+m3+m4 is 1 or more and p is 2, the two Xs and the two m2 to m4 are independently selected.)

(Structural unit A)

The structural unit A is a structural unit derived from tetracarboxylic dianhydride in the polyimide resin, and contains a structural unit (A-1) derived from a compound represented by the following formula (a-1).

The compound represented by formula (a-1) is norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride. By making the structural unit A contain the structural unit (A-1), the colorless transparency and heat resistance of the film are improved.

The ratio of the structural unit (A-1) in the structural unit A is preferably 40 mol% or more, more preferably 50 mol% or more, and further preferably 60 mol% or more. The upper limit of the ratio of the structural unit (A-1) is not particularly limited, that is, 100 mol%. The structural unit A may also contain only the structural unit (A-1).

The structural unit A may contain structural units other than the structural unit (A-1).

The structural unit A preferably contains a structural unit (A-2) derived from a compound represented by the following formula (a-2) in addition to the structural unit (A-1).

The compound represented by formula (a-2) is biphenyltetracarboxylic dianhydride (BPDA), and specific examples thereof include 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) represented by the following formula (a-2s), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA) represented by the following formula (a-2a), and 2,2',3,3'-biphenyltetracarboxylic dianhydride (i-BPDA) represented by the following formula (a-2i). 3,3',4,4'-biphenyltetracarboxylic dianhydride is preferred because it can reduce the residual stress of the polyimide film of the present invention.

When the structural unit A contains the structural unit (A-1) and the structural unit (A-2), the ratio of the structural unit (A-1) in the structural unit A is preferably 40 to 95 mol%, more preferably 50 to 90 mol%, and further preferably 55 to 85 mol%. The ratio of the structural unit (A-2) in the structural unit A is preferably 5 to 60 mol%, more preferably 10 to 50 mol%, and further preferably 15 to 45 mol%.

The total ratio of the structural units (A-1) and (A-2) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural units (A-1) and (A-2) is not particularly limited, that is, 100 mol%. The structural unit A may also contain only the structural unit (A-1) and the structural unit (A-2).

When the structural unit A further contains the structural unit (A-2), the residual stress is further reduced.

In addition, by making the structural unit A further contain the structural unit (A-2), the light transmittance of the film at a wavelength of 308nm is reduced. In recent years, as a method for peeling the support body and the resin film in a support body laminated with a resin film, a laser lift-off process called laser lift-off (LLO) has attracted much attention. The smaller the light transmittance at a wavelength of 308nm, the better the laser lift-off property based on the XeCl excimer laser at a wavelength of 308nm.

The structural unit A preferably contains a structural unit (A-3) derived from silicone modified with acid anhydrides at both ends in addition to the structural unit (A-1).

As the silicone modified with anhydride at both ends, a compound represented by the following formula (a-3) is preferred.

(In formula (a-3),

R ¹ to R ⁶ are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms,

^L1 and ^L2 are each independently a single bond or a divalent hydrocarbon group having 1 to 20 carbon atoms,

^Z1 and ^Z2 are each independently a trivalent hydrocarbon group having 1 to 20 carbon atoms,

n is 1 to 200. )

In the formula (a-3), R ¹ to R ⁶ are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms.

Examples of the monovalent hydrocarbon group having 1 to 20 carbon atoms include alkyl groups having 1 to 20 carbon atoms, cycloalkyl groups having 3 to 20 carbon atoms, aryl groups having 6 to 20 carbon atoms, aralkyl groups having 7 to 20 carbon atoms, and alkenyl groups having 2 to 20 carbon atoms.

As the alkyl group having 1 to 20 carbon atoms, an alkyl group having 1 to 10 carbon atoms is preferred, and examples thereof include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl and hexyl. As the cycloalkyl group having 3 to 20 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms is preferred, and examples thereof include cyclopentyl and cyclohexyl. As the aryl group having 6 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms is preferred, and examples thereof include phenyl and naphthyl. As the aralkyl group having 7 to 20 carbon atoms, an aralkyl group having 7 to 10 carbon atoms is preferred, and examples thereof include benzyl and phenethyl. As the alkenyl group having 2 to 20 carbon atoms, an alkenyl group having 2 to 10 carbon atoms is preferred, and examples thereof include vinyl, allyl, propenyl, isopropenyl and butenyl.

R ¹ to R ⁶ are each independently preferably selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, and an alkenyl group having 2 to 20 carbon atoms; more preferably selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, and an alkenyl group having 2 to 10 carbon atoms; further preferably selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an alkenyl group having 2 to 10 carbon atoms; particularly preferably selected from the group consisting of a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a hexyl group, a phenyl group, a naphthyl group, a vinyl group, an allyl group, a propenyl group, an isopropenyl group, and a butenyl group; and most preferably selected from the group consisting of a methyl group, an ethyl group, a phenyl group, and a vinyl group.

In the formula (a-3), ^L1 and ^L2 are each independently a single bond or a divalent hydrocarbon group having 1 to 20 carbon atoms.

Examples of the divalent hydrocarbon group having 1 to 20 carbon atoms include an alkylene group having 1 to 20 carbon atoms, a cycloalkylene group having 3 to 20 carbon atoms, and an arylene group having 6 to 20 carbon atoms.

The alkylene group having 1 to 20 carbon atoms is preferably an alkylene group having 1 to 10 carbon atoms, and examples thereof include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, and a hexylene group.

The cycloalkylene group having 3 to 20 carbon atoms is preferably a cycloalkylene group having 3 to 10 carbon atoms, and examples thereof include cyclobutylene, cyclopentylene, cyclohexylene, and cycloheptylene.

The arylene group having 6 to 20 carbon atoms is preferably an arylene group having 6 to 10 carbon atoms, and examples thereof include a phenylene group and a naphthylene group.

^L1 and ^L2 are each independently preferably selected from the group consisting of a single bond, an alkylene group having 1 to 20 carbon atoms, a cycloalkylene group having 3 to 20 carbon atoms, and an arylene group having 6 to 20 carbon atoms; more preferably selected from the group consisting of a single bond, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, and an arylene group having 6 to 10 carbon atoms; further preferably selected from the group consisting of a single bond, an alkylene group having 1 to 10 carbon atoms, and an arylene group having 6 to 10 carbon atoms; particularly preferably selected from the group consisting of a single bond, a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a phenylene group, and a naphthylene group; and most preferably selected from the group consisting of a single bond, a methylene group, an ethylene group, a propylene group, and a phenylene group.

In the formula (a-3), ^Z1 and ^Z2 are each independently a trivalent hydrocarbon group having 1 to 20 carbon atoms.

^Z1 and ^Z2 are each independently preferably selected from the group consisting of a group represented by the following formula (a-3-i), a group represented by the following formula (a-3-ii), a group represented by the following formula (a-3-iii) and a group represented by the following formula (a-3-iv).

The group represented by formula (a-3-i) is a succinic acid residue, the group represented by formula (a-3-ii) is a phthalic acid residue, the group represented by formula (a-3-iii) is a 2,3-norbornene dicarboxylic acid residue, and the group represented by formula (a-3-iv) is a 5-norbornene-2,3-dicarboxylic acid residue. It should be noted that in formulas (a-3-i) to (a-3-iv), "*" represents a bonding position.

n in formula (a-3) is 1 to 200. n is preferably 3 to 150, more preferably 5 to 120.

Examples of commercially available silicone modified with anhydride at both ends include "X22-168AS", "X22-168A", "X22-168B", and "X22-168-P5-8" manufactured by Shin-Etsu Chemical Co., Ltd. and "DMS-Z21" manufactured by Gelest Corporation.

When the structural unit A contains the structural unit (A-1) and the structural unit (A-3), the ratio of the structural unit (A-1) in the structural unit A is preferably 50 to 99 mol%, more preferably 60 to 98 mol%, and further preferably 70 to 97 mol%. The ratio of the structural unit (A-3) in the structural unit A is preferably 1 to 50 mol%, more preferably 2 to 40 mol%, and further preferably 3 to 30 mol%.

The total ratio of the structural units (A-1) and (A-3) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural units (A-1) and (A-3) is not particularly limited, that is, 100 mol%. The structural unit A may also contain only the structural unit (A-1) and the structural unit (A-3).

When the structural unit A further contains the structural unit (A-3), the colorless transparency can be improved while maintaining the residual stress of the film at a low level.

Furthermore, it is preferred that the structural unit A contains both the structural unit (A-2) and the structural unit (A-3) in addition to the structural unit (A-1).

When the structural unit A contains the structural unit (A-1), the structural unit (A-2) and the structural unit (A-3), the ratio of the structural unit (A-1) in the structural unit A is preferably 50 to 90 mol%, more preferably 60 to 85 mol%, and further preferably 65 to 80 mol%. The ratio of the structural unit (A-2) in the structural unit A is preferably 5 to 30 mol%, more preferably 5 to 25 mol%, and further preferably 5 to 20 mol%. The ratio of the structural unit (A-3) in the structural unit A is preferably 1 to 25 mol%, more preferably 2 to 20 mol%, and further preferably 3 to 15 mol%.

The total ratio of the structural units (A-1) to (A-3) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural units (A-1) to (A-3) is not particularly limited, that is, 100 mol%. The structural unit A may also contain only the structural unit (A-1), the structural unit (A-2) and the structural unit (A-3).

Structural units other than the structural unit (A-1) optionally included in the structural unit A are not limited to the structural units (A-2) and (A-3). There are no particular limitations on the tetracarboxylic dianhydride that provides such an optional structural unit, and examples thereof include aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride, 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride and 4,4'-(hexafluoroisopropylidene)phthalic anhydride; alicyclic tetracarboxylic dianhydrides such as 1,2,3,4-cyclobutane tetracarboxylic dianhydride and 1,2,4,5-cyclohexane tetracarboxylic dianhydride (except the compound represented by formula (a-1)); and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butane tetracarboxylic dianhydride.

It should be noted that, in the present specification, aromatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more aromatic rings, alicyclic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more alicyclic rings and no aromatic ring, and aliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring.

The structural unit other than the structural unit (A-1) which may be contained in the structural unit A may be one kind or two or more kinds.

(Structural unit B)

Structural unit B is a structural unit derived from diamine in the polyimide resin, and includes a structural unit (B-1) derived from a compound represented by the following formula (b-1) and a structural unit (B-2) derived from a compound represented by the following formula (b-2).

(In formula (b-2), X is a single bond, a substituted or unsubstituted alkylene group, a carbonyl group, an ether group, a group represented by the following formula (b-2-i), or a group represented by the following formula (b-2-ii), p is an integer of 0 to 2, m1 is an integer of 0 to 4, and m2 is an integer of 0 to 4. When p is 0, m1 is an integer of 1 to 4.)

(In formula (b-2-i), m3 is an integer of 0 to 5; in formula (b-2-ii), m4 is an integer of 0 to 5. It should be noted that when m1+m2+m3+m4 is 1 or more and p is 2, the two Xs and the two m2 to m4 are independently selected.)

In addition, in formula (b-2-i) and (b-2-ii), "*" represents a bonding position.

The compound represented by formula (b-1) is 2,2'-bis(trifluoromethyl)benzidine. When structural unit B contains structural unit (B-1), the colorless transparency of the film is improved and the residual stress is reduced.

Specific examples of the compound represented by the formula (b-2) include compounds represented by the following formulae (b-21) to (b-27).

Specific examples of the compound represented by the formula (b-21) include a compound represented by the following formula (b-211), that is, 3,5-diaminobenzoic acid.

The structural unit (B-2) is preferably a structural unit (B-21) derived from a compound represented by the formula (b-21), and more preferably a structural unit (B-211) derived from a compound represented by the formula (b-211).

When the structural unit B contains the structural unit (B-2), the heat resistance of the film is improved.

The ratio of the structural unit (B-1) in the structural unit B is preferably 35 to 95 mol %, more preferably 40 to 90 mol %, further preferably 45 to 85 mol %.

The ratio of the structural unit (B-2) in the structural unit B is preferably 5 to 65 mol %, more preferably 10 to 60 mol %, further preferably 15 to 55 mol %.

The total ratio of the structural units (B-1) and (B-2) in the structural unit B is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural units (B-1) and (B-2) is not particularly limited, that is, 100 mol%. The structural unit B may also contain only the structural unit (B-1) and the structural unit (B-2).

The structural unit B may contain structural units other than the structural units (B-1) and (B-2). The diamines that provide such structural units are not particularly limited, and examples thereof include 1,4-phenylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-inden-5-amine, α,α'-bis(4-aminophenyl)-1,4-diisocyanate, and α-(4-aminophenyl)-1,4-diisocyanate. Aromatic diamines such as propylbenzene, N,N'-bis(4-aminophenyl)terephthalamide, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane and 9,9-bis(4-aminophenyl)fluorene (except the compound represented by formula (b-1) and the compound represented by formula (b-2)); alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine.

In the present specification, aromatic diamine refers to a diamine containing one or more aromatic rings, alicyclic diamine refers to a diamine containing one or more alicyclic rings and no aromatic ring, and aliphatic diamine refers to a diamine containing neither an aromatic ring nor an alicyclic ring.

The structural unit other than the structural units (B-1) and (B-2) optionally contained in the structural unit B may be one kind or two or more kinds.

From the viewpoint of mechanical strength of the obtained polyimide film, the number average molecular weight of the polyimide resin is preferably 5000 to 100000. The number average molecular weight of the polyimide resin can be determined, for example, from a standard polymethyl methacrylate (PMMA) conversion value measured by gel filtration chromatography.

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

The polyimide resin preferably contains a polyimide chain (a structure formed by imide bonding of structural unit A and structural unit B) as a main structure. Therefore, the ratio of the polyimide chain in the polyimide resin is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 90% by mass or more, and particularly preferably 99% by mass or more.

The polyimide resin composition of the present invention including the above-mentioned polyimide resin can form a film having excellent heat resistance, colorless transparency, chemical resistance and cleaning properties and low residual stress. The film has the following suitable physical property values.

The glass transition temperature (Tg) is preferably 380°C or higher, more preferably 400°C or higher, and further preferably 450°C or higher.

The total light transmittance is preferably 88% or more, more preferably 89% or more, and even more preferably 90% or more when used as a film with a thickness of 10 μm.

The yellowness index (YI) is preferably 5.0 or less, more preferably 4.0, and even more preferably 3.0 or less when used as a film having a thickness of 10 μm.

The residual stress is preferably 25.0 MPa, more preferably 24.0 MPa, and further preferably 22.0 MPa or less.

In addition, by using a polyimide resin in which the structural unit A further includes the structural unit (A-2), which is one embodiment of the polyimide resin, a film having excellent laser peelability can be formed. The preferred physical property values of the film are as follows.

The light transmittance at a wavelength of 308 nm is preferably 0.8% or less, more preferably 0.6% or less, and even more preferably 0.4% or less when formed into a thin film with a thickness of 10 μm.

Furthermore, the thin film formed using the polyimide resin described above also has good mechanical properties and has the following suitable physical property values.

The tensile modulus is preferably 2.0 GPa or more, more preferably 3.0 GPa or more, and further preferably 4.0 GPa or more.

The tensile strength is preferably 80 MPa or more, more preferably 100 MPa or more, and further preferably 120 MPa or more.

In addition, the above-mentioned physical property values in the present invention can be specifically measured by the methods described in Examples.

<Method for producing polyimide resin>

In the present invention, the polyimide resin can be produced by reacting a tetracarboxylic acid component containing a compound providing the structural unit (A-1) with a diamine component containing a compound providing the structural unit (B-1) and a compound providing the structural unit (B-2).

As the compound providing the structural unit (A-1), the compound shown in formula (a-1) can be cited, but it is not limited thereto, and its derivatives can also be provided within the scope of providing the same structural unit. As the derivative, the tetracarboxylic acid corresponding to the tetracarboxylic dianhydride shown in formula (a-1) (i.e., norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid) and the alkyl ester of the tetracarboxylic acid can be cited. As the compound providing the structural unit (A-1), the compound shown in formula (a-1) (i.e., dianhydride) is preferred.

The tetracarboxylic acid component preferably contains 40 mol% or more, more preferably 50 mol% or more, and further preferably 60 mol% or more of the compound providing the structural unit (A-1). The upper limit of the content of the compound providing the structural unit (A-1) is not particularly limited, that is, 100 mol%. The tetracarboxylic acid component may also contain only the compound providing the structural unit (A-1).

The tetracarboxylic acid component may contain compounds other than the compound which provides structural unit (A-1).

It is preferred that the tetracarboxylic acid component contains a compound providing the structural unit (A-2) in addition to the compound providing the structural unit (A-1).

As the compound providing the structural unit (A-2), the compound shown in formula (a-2) can be cited, but it is not limited thereto, and its derivative can also be provided within the scope of providing the same structural unit. As the derivative, tetracarboxylic acid corresponding to the tetracarboxylic dianhydride shown in formula (a-2) and the alkyl ester of the tetracarboxylic acid can be cited. As the compound providing the structural unit (A-2), the compound shown in formula (a-2) (i.e., dianhydride) is preferred.

When the tetracarboxylic acid component contains a compound providing the structural unit (A-1) and a compound providing the structural unit (A-2), the tetracarboxylic acid component preferably contains 40 to 95 mol%, more preferably 50 to 90 mol%, and further preferably 55 to 85 mol% of the compound providing the structural unit (A-1), and preferably contains 5 to 60 mol%, more preferably 10 to 50 mol%, and further preferably 15 to 45 mol% of the compound providing the structural unit (A-2).

The tetracarboxylic acid component contains a compound providing a structural unit (A-1) and a compound providing a structural unit (A-2) in a total amount of preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total content of the compound providing a structural unit (A-1) and the compound providing a structural unit (A-2) is not particularly limited, that is, 100 mol%. The tetracarboxylic acid component may also contain only a compound providing a structural unit (A-1) and a compound providing a structural unit (A-2).

It is preferred that the tetracarboxylic acid component contains a compound providing the structural unit (A-3) in addition to the compound providing the structural unit (A-1).

As the compound providing the structural unit (A-3), an anhydride-modified silicone at both ends (for example, a compound represented by formula (a-3)) can be cited, but it is not limited thereto and can be a derivative thereof within the scope of providing the same structural unit. As the derivative, a tetracarboxylic acid corresponding to the anhydride-modified silicone at both ends and an alkyl ester of the tetracarboxylic acid can be cited. As the compound providing the structural unit (A-3), an anhydride-modified silicone at both ends (i.e., a dianhydride) is preferred.

When the tetracarboxylic acid component contains a compound providing the structural unit (A-1) and a compound providing the structural unit (A-3), the tetracarboxylic acid component preferably contains 50 to 99 mol%, more preferably 60 to 98 mol%, and further preferably 70 to 97 mol% of the compound providing the structural unit (A-1), and preferably contains 1 to 50 mol%, more preferably 2 to 40 mol%, and further preferably 3 to 30 mol% of the compound providing the structural unit (A-3).

The tetracarboxylic acid component contains a compound providing a structural unit (A-1) and a compound providing a structural unit (A-3) in a total amount of preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total content of the compound providing a structural unit (A-1) and the compound providing a structural unit (A-3) is not particularly limited, that is, 100 mol%. The tetracarboxylic acid component may also contain only a compound providing a structural unit (A-1) and a compound providing a structural unit (A-3).

It is preferred that the tetracarboxylic acid component contains both of a compound providing a structural unit (A-2) and a compound providing a structural unit (A-3) in addition to the compound providing the structural unit (A-1).

When the tetracarboxylic acid component contains a compound providing a structural unit (A-1), a compound providing a structural unit (A-2), and a compound providing a structural unit (A-3), the tetracarboxylic acid component preferably contains 50 to 90 mol%, more preferably 60 to 85 mol%, and further preferably 65 to 80 mol% of the compound providing the structural unit (A-1), preferably 5 to 30 mol%, more preferably 5 to 25 mol%, and further preferably 5 to 20 mol% of the compound providing the structural unit (A-2), and preferably 1 to 25 mol%, more preferably 2 to 20 mol%, and further preferably 3 to 15 mol% of the compound providing the structural unit (A-3).

The tetracarboxylic acid component contains a compound providing a structural unit (A-1), a compound providing a structural unit (A-2), and a compound providing a structural unit (A-3), preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total content of the compound providing a structural unit (A-1), the compound providing a structural unit (A-2), and the compound providing a structural unit (A-3) is not particularly limited, that is, 100 mol%. The tetracarboxylic acid component may also contain only a compound providing a structural unit (A-1), a compound providing a structural unit (A-2), and a compound providing a structural unit (A-3).

The compounds other than the compounds providing structural unit (A-1) optionally included in the tetracarboxylic acid component are not limited to the compounds providing structural unit (A-2) and the compounds providing structural unit (A-3). As such optional compounds, the above-mentioned aromatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride and aliphatic tetracarboxylic dianhydride and their derivatives (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.) can be cited.

The compound other than the compound which provides the structural unit (A-1) which is optionally contained in the tetracarboxylic acid component may be one kind or two or more kinds.

As the compound providing the structural unit (B-1), the compound shown in formula (b-1) can be cited, but it is not limited thereto, and its derivative can also be provided within the scope of providing the same structural unit. As the derivative, a diisocyanate corresponding to the diamine shown in formula (b-1) can be cited. As the compound providing the structural unit (B-1), the compound shown in formula (b-1) (i.e., diamine) is preferred.

Similarly, as a compound providing a structural unit (B-2), a compound shown in formula (b-2) can be cited, but it is not limited thereto, and a derivative thereof can also be cited within the scope of providing the same structural unit. As the derivative, a diisocyanate corresponding to the diamine shown in formula (b-2) can be cited. As a compound providing a structural unit (B-2), a compound shown in formula (b-2) (i.e., a diamine) is preferred.

The diamine component preferably contains 35 to 95 mol %, more preferably 40 to 90 mol %, and even more preferably 45 to 85 mol % of the compound providing the structural unit (B-1).

The diamine component preferably contains 5 to 65 mol%, more preferably 10 to 60 mol%, and even more preferably 15 to 55 mol% of the compound providing the structural unit (B-2).

The diamine component contains a compound providing a structural unit (B-1) and a compound providing a structural unit (B-2) in a total amount of preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total content of the compound providing a structural unit (B-1) and the compound providing a structural unit (B-2) is not particularly limited, that is, 100 mol%. The diamine component may also contain only a compound providing a structural unit (B-1) and a compound providing a structural unit (B-2).

The diamine component may contain compounds other than the compound providing the structural unit (B-1) and the compound providing the structural unit (B-2), and examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, aliphatic diamines, and derivatives thereof (such as diisocyanates).

The compound other than the compound providing the structural unit (B-1) and the compound providing the structural unit (B-2) which may be contained in the diamine component may be one kind or two or more kinds.

In the present invention, regarding the charging amount ratio of the tetracarboxylic acid component and the diamine component used for production of the polyimide resin, the diamine component is preferably 0.9 to 1.1 mol per 1 mol of the tetracarboxylic acid component.

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

The method for reacting the above-mentioned tetracarboxylic acid component and the diamine component is not particularly limited, and a 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 placed in a reactor, stirred at room temperature to 80° C. for 0.5 to 30 hours, and then the temperature is raised to carry out an imidization reaction; (2) a method in which a diamine component and a reaction solvent are placed in a reactor and dissolved, and then a tetracarboxylic acid component is placed in the reactor, and stirred at room temperature to 80° C. for 0.5 to 30 hours as required, and then the temperature is raised to carry out an imidization reaction; (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are placed in a reactor, and the temperature is immediately raised to carry out an imidization reaction.

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 generated polyimide, and examples thereof include aprotic solvents, phenolic solvents, etheric solvents, and carbonate-based solvents.

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

Specific examples of the phenolic solvent include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol.

Specific examples of the ether solvent include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, and 1,4-dioxane.

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

Among the above reaction solvents, amide solvents or lactone solvents are preferred. In addition, the above reaction solvents may be used alone or in combination of two or more.

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

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

Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine (TEA), tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, and N,N-diethylaniline; and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogen carbonate, and sodium hydrogen carbonate.

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

From the viewpoint of handling properties, among the above, it is preferred to use a base catalyst, more preferred to use an organic base catalyst, further preferred to use triethylamine, and particularly preferred to use triethylamine and triethylenediamine in combination.

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

<Crosslinking agent>

In the present invention, the crosslinking agent has at least two oxazolyl groups. That is, the crosslinking agent in the present invention is a polyfunctional oxazoline compound having two or more oxazolyl groups (oxazoline rings) in the molecule.

The oxazolyl group is reactive with the carboxyl group, and when the carboxyl group reacts with the oxazolyl group, an amide ester bond is formed as shown below. This reaction is particularly easy to proceed when heated to 80°C or higher.

Since the polyimide resin contained in the polyimide resin composition of the present invention has a carboxyl group, when the polyimide resin composition of the present invention is heated, the polyimide resins are cross-linked with the aid of a cross-linking agent to form a cross-linked polyimide resin. For this reason, the chemical resistance of the film is improved.

The cross-linking agent is not particularly limited as long as it is a polyfunctional oxazoline compound having two or more oxazolyl groups in the molecule. Specific examples thereof include 1,3-bis(4,5-dihydro-2-oxazolyl)benzene, 1,4-bis(4,5-dihydro-2-oxazolyl)benzene, 2,2'-bis(2-oxazoline), K-2010E, K-2020E, K-2030E manufactured by Nippon Shokubai Co., Ltd., 2,6-bis(4-isopropyl-2-oxazolin-2-yl)pyridine, 2,6-bis(4-phenyl-2-oxazolin-2-yl)pyridine, 2,2'-isopropylidenebis(4-phenyl-2-oxazoline), and 2,2'-isopropylidenebis(4-tert-butyl-2-oxazoline).

The cross-linking agent is preferably a compound containing an aromatic ring or aromatic heterocyclic ring to which at least two oxazolyl groups are bonded, more preferably a compound containing a benzene ring or pyridine ring to which at least two oxazolyl groups are bonded, further preferably a compound containing a benzene ring to which at least two oxazolyl groups are bonded, and particularly preferably 1,3-bis(4,5-dihydro-2-oxazolyl)benzene.

The cross-linking agent may be used alone or in combination of two or more.

The polyimide resin composition of the present invention preferably contains a polyimide resin and a crosslinking agent in a ratio such that the molar ratio of the oxazole group in the crosslinking agent to the carboxyl group in the polyimide resin (oxazole group/carboxyl group) is in the range of 1/8 to 1/0.5. The molar ratio is more preferably 1/6 to 1/1, and further preferably 1/4 to 1/2.

It should be noted that the above-mentioned molar ratio refers to the molar ratio of the oxazole group contained in the crosslinking agent to the carboxyl group contained in the compound providing the structural unit (B-1) used in the production of the polyimide resin, and is calculated based on the added amount of the crosslinking agent and the added amount of the compound providing the structural unit (B-1).

[Polyimide varnish]

A preferred embodiment of the polyimide resin composition of the present invention includes a polyimide resin composition (hereinafter also referred to as “polyimide varnish”) containing an organic solvent in addition to the polyimide resin and the crosslinking agent, and in which the polyimide resin is dissolved.

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

The polyimide varnish may be prepared by adding a crosslinking agent to a solution obtained by dissolving a polyimide resin obtained by a polymerization method in a reaction solvent, or by adding a diluting solvent and a crosslinking agent to the solution.

The polyimide varnish preferably contains 5 to 40% by mass, more preferably 7 to 30% by mass, and even more preferably 8 to 20% by mass of a polyimide resin. The viscosity of the polyimide varnish is preferably 50 to 5000 Pa·s, more preferably 100 to 4000 Pa·s, and even more preferably 300 to 3500 Pa·s. The viscosity of the polyimide varnish is a value measured at 25° C. using an E-type viscometer.

In addition, the polyimide varnish of the present invention may also contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, ultraviolet stabilizers, surfactants, leveling agents, defoaming agents, fluorescent brighteners, crosslinking agents, polymerization initiators, and photosensitizers within the range that the required properties of the polyimide film are not impaired.

The method for producing the polyimide varnish of the present invention is not particularly limited, and a known method can be applied.

[Polyimide film]

The polyimide film of the present invention is formed by crosslinking the above-mentioned polyimide resin contained in the polyimide resin composition of the present invention through the above-mentioned crosslinking agent. That is, the polyimide film of the present invention contains a crosslinked polyimide resin as a crosslinked product formed by the crosslinking agent between polyimide resins. Therefore, the polyimide film of the present invention has excellent heat resistance, colorless transparency and chemical resistance, and further has low residual stress. The suitable physical property values of the polyimide film of the present invention are as described above.

The method for producing the polyimide film of the present invention is not particularly limited as long as it includes a step of crosslinking at a temperature (preferably above 80°C, more preferably above 100°C, and further preferably above 150°C) at which the polyimide resin and the crosslinking agent undergo a crosslinking reaction. For example, a method in which the polyimide varnish is coated on a smooth support such as a glass plate, a metal plate, or a plastic, or is formed into a film and then heated. By this heat treatment, the polyimide resin in the polyimide varnish can undergo a crosslinking reaction with the crosslinking agent, and organic solvents such as a reaction solvent and a diluting solvent contained in the polyimide varnish can be removed. If necessary, a release agent can also be applied in advance on the surface of the aforementioned support.

As a heat treatment, the following method is preferred. That is, it is preferred to first evaporate the organic solvent at a temperature below 120°C, and then further dry it at a temperature above the boiling point of the organic solvent to produce a polyimide film. In addition, it is preferred to dry it under a nitrogen atmosphere. The pressure of the drying atmosphere can be reduced pressure, normal pressure, or pressurized. By drying at two stages of temperature, a film with a smooth and defect-free film surface can be obtained. In addition, the drying temperature of the second stage is not particularly limited, and is preferably 200 to 450°C, more preferably 300 to 430°C, and particularly preferably 350 to 400°C. By drying at this temperature range, the transparency/yellowness index of the film becomes good, and good solvent resistance can be obtained.

The polyimide film of the present invention can also be produced using a polyamic acid varnish in which a polyamic acid and a cross-linking agent are dissolved in an organic solvent.

The polyamic acid contained in the polyamic acid varnish is a precursor of the polyimide resin in the present invention, which is a product of a polyaddition reaction of a tetracarboxylic acid component containing a compound providing the structural unit (A-1) and a diamine component containing a compound providing the structural unit (B-1) and a compound providing the structural unit (B-2). By imidizing (dehydration ring closure) the polyamic acid, a polyimide resin can be obtained.

As the organic solvent contained in the polyamic acid varnish, the organic solvent contained in the polyimide varnish of the present invention can be used.

In the present invention, the polyamic acid varnish may be a polyamic acid solution itself obtained by subjecting a tetracarboxylic acid component containing a compound providing the structural unit (A-1) and a diamine component containing a compound providing the structural unit (B-1) and a compound providing the structural unit (B-2) to a polyaddition reaction in a reaction solvent, or a polyamic acid solution obtained by further adding a diluting solvent to the polyamic acid solution.

In the method for making polyimide film using polyamic acid varnish, as long as it is included in the process of crosslinking at a temperature (preferably above 80°C, more preferably above 100°C, more preferably above 150°C) at which polyimide resin and a crosslinking agent can undergo a crosslinking reaction, there is no particular restriction, and known methods can be used. For example, polyamic acid varnish is coated on a smooth support such as a glass plate, a metal plate, plastics, or is formed into a film-like shape, and organic solvents such as a reaction solvent and a diluting solvent contained in the varnish are removed by heating to obtain a polyamic acid film, and the polyamic acid in the polyamic acid film is imidized by heating, and then the polyimide resin and the crosslinking agent are reacted and crosslinked, thus polyimide film can be manufactured.

The heating temperature when the polyamic acid varnish is dried to obtain a polyamic acid film is preferably 50 to 120° C. The heating temperature when the polyamic acid is imidized by heating is preferably 200 to 400° C.

It should be noted that the imidization method is not limited to thermal imidization, and chemical imidization may also be applied.

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

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

The polyimide film of the present invention can be suitably used as a film for various members such as color filters, flexible displays, semiconductor components, optical members, etc. The polyimide film of the present invention can be particularly suitably used as a substrate for image display devices such as liquid crystal displays and OLED displays.

Example

The present invention will be specifically described below using examples, but the present invention is not limited to these examples.

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

(1) Solid content concentration

The solid content concentration of the varnish was measured by heating the sample at 320° C. for 120 minutes using a small electric furnace “MMF-1” manufactured by AS ONE CORPORATION, and calculating the solid content concentration from the difference in mass of the sample before and after heating.

(2) Film thickness

The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

(3) Total light transmittance, yellow index (YI)

The total light transmittance and YI were measured in accordance with JIS K7105:1997 using a color/turbidity simultaneous measuring device "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.

(4) Glass transition temperature (Tg)

Using a thermomechanical analyzer "TMA/SS6100" manufactured by Hitachi High-Tech Science Co., Ltd., the residual stress was removed by heating to a temperature at which the residual stress can be sufficiently removed under the conditions of a sample size of 2 mm × 20 mm, a load of 0.1 N, and a heating rate of 10°C/min in the tensile mode, and then cooling to room temperature. Thereafter, the elongation of the test piece was measured under the same conditions as the treatment for removing the residual stress, and the inflection point of the elongation was confirmed as the glass transition temperature.

(5) Residual stress

Using the residual stress measuring device "FLX-2320" manufactured by KLA-Tencor Corporation, a 4-inch silicon wafer with a thickness of 525μm±25μm, whose "warpage" was previously measured, was coated with polyimide varnish or polyamic acid varnish using a spin coater and pre-baked. After that, a heat curing treatment was performed at 350-400°C for 30 minutes in a nitrogen atmosphere using a hot air dryer to produce a silicon wafer with a polyimide film having a thickness of 8-15μm after curing. The warpage of the wafer was measured using the aforementioned residual stress measuring device, and the residual stress generated between the silicon wafer and the polyimide film was evaluated.

(6) Tensile modulus and tensile strength

The tensile modulus and tensile strength were measured in accordance with JIS K7127 using a tensile tester "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd. The distance between chucks was 50 mm, the test piece size was 10 mm×50 mm, and the test speed was 20 mm/min.

(7) Solvent resistance 1 (PGMEA)

A solvent was dropped onto a polyimide film formed on a glass plate at room temperature to confirm whether there was any change on the film surface. Propylene glycol monomethyl ether acetate (PGMEA) was used as the solvent.

The evaluation criteria of solvent resistance are as follows.

○: No change on the film surface.

△: There are slight cracks on the film surface.

×: There are cracks on the film surface or the film surface is dissolved.

(8) Solvent resistance 2 (NMP)

The polyimide film formed on the glass plate was peeled off and immersed in N-methyl-2-pyrrolidone (NMP) at room temperature for 60 minutes. The evaluation criteria are as follows.

○: The film did not dissolve and maintained its shape.

×: The film was dissolved and failed to maintain its shape.

(9) Cleanability

N-methyl-2-pyrrolidone and the polyimide varnish were mixed and checked at room temperature to see whether they were uniformly mixed. The evaluation criteria for cleaning properties were as follows.

○: The polyimide varnish and the NMP mixed liquid are uniformly mixed.

×: The polyimide varnish and the NMP mixed liquid were not uniformly mixed, and precipitates were generated.

The tetracarboxylic acid component and the diamine component used in the Examples and Comparative Examples and their abbreviations are as follows.

<Tetracarboxylic acid component>

CpODA: Norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride (manufactured by JX Energy Co., Ltd.; compound represented by formula (a-1))

s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Corporation; compound represented by formula (a-2))

<Diamine>

TFMB: 2,2'-bis(trifluoromethyl)benzidine (manufactured by Wakayama Seika Industries, Ltd.; compound represented by formula (b-1))

3,5-DABA: 3,5-diaminobenzoic acid (manufactured by Japan Junryo Pharmaceutical Co., Ltd.; compound represented by formula (b-2))

<Crosslinking agent>

1,3-PBO: 1,3-bis(4,5-dihydro-2-oxazolyl)benzene (manufactured by Mikuni Pharmaceutical Industry Co., Ltd.)

<Others>

GBL: γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation)

TEA: triethylamine (manufactured by Kanto Chemical Co., Ltd.)

Example 1

In a 1 L five-necked round-bottom flask equipped with a stainless steel half-moon-shaped stirring blade, a nitrogen inlet tube, a Dean-Stark apparatus with a condenser, a thermometer, and glass end caps, 25.619 g (0.080 mol) of TFMB, 3.043 g (0.020 mol) of 3,5-DABA, and 161.040 g of GBL were added, and the mixture was stirred at a temperature of 70° C. in a nitrogen atmosphere at a rotation speed of 150 rpm to obtain a solution.

After adding 38.438 g (0.100 mol) of CpODA and 20.130 g of GBL to the solution, 0.506 g of TEA and 0.056 g of triethylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.) as an imidization catalyst were added, and the temperature in the reaction system was raised to 190° C. in about 20 minutes by heating with a hooded heater. The components removed by distillation were collected, and the rotation speed was adjusted according to the increase in viscosity, and the temperature in the reaction system was maintained at 190° C. and refluxed for 2 hours.

Then, GBL was added to a solid content concentration of 10% by mass, and the temperature in the reaction system was cooled to 120° C., followed by stirring for about 1 hour to make it homogenous. Then, 0.167 g of 1,3-PBO (0.25 mol % relative to 1 mol % of 3,5-DABA) was added to 100 g of the obtained varnish, and stirred for 30 minutes to make it homogenous, thereby obtaining a polyimide varnish.

Then, the polyimide varnish obtained by coating the silicon wafer was applied to a glass plate by spin coating, maintained at 80°C for 20 minutes on a hot plate, and then heated at 400°C for 30 minutes in a hot air dryer under a nitrogen atmosphere to evaporate the solvent, thereby obtaining a film with a thickness of 10 μm.

Example 2

A polyimide varnish was prepared in the same manner as in Example 1 except that the amount of TFMB was changed to 27.220 g (0.085 mol) and the amount of 3,5-DABA was changed to 2.282 g (0.015 mol) to obtain a polyimide varnish having a solid content concentration of 10% by mass.

Using the obtained polyimide varnish, a film was produced by the same method as in Example 1 except that the drying temperature in the second step was changed to the conditions described in Table 1, thereby obtaining a film having a thickness of 9 μm.

Example 3

In a 1 L five-necked round-bottom flask equipped with a stainless steel half-moon-shaped stirring blade, a nitrogen inlet tube, a Dean-Stark apparatus with a condenser, a thermometer, and glass end caps, 25.619 g (0.080 mol) of TFMB, 3.043 g (0.020 mol) of 3,5-DABA, and 156.713 g of GBL were added, and the mixture was stirred at a temperature of 70° C. in a nitrogen atmosphere at a rotation speed of 150 rpm to obtain a solution.

After adding 30.750 g (0.08 mol) of CpODA, 5.884 g (0.02 mol) of s-BPDA and 39.178 g of GBL together with 0.506 g of TEA as an imidization catalyst and 0.056 g of triethylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.), the reaction system was heated with a hooded heater to raise the temperature to 190° C. over about 20 minutes. The components removed by distillation were collected, the rotation speed was adjusted according to the increase in viscosity, and the temperature in the reaction system was maintained at 190° C. and refluxed for 2 hours.

Then, GBL was added so that the solid content concentration became 10 mass %, and the temperature in the reaction system was cooled to 120° C., and then stirred for about 1 hour to make it uniform. Then, 0.173 g of 1,3-PBO (0.25 mol % relative to 1 mol % of 3,5-DABA) was added, and stirred for 30 minutes to make it uniform, thereby obtaining a polyimide varnish with a solid content concentration of 10 mass %.

The polyimide varnish obtained by coating the silicon wafer was then spin-coated on a glass plate and maintained at 80°C for 30 minutes on a hot plate. Thereafter, the solvent was evaporated by heating at 350°C for 20 minutes in a hot air dryer under a nitrogen atmosphere to obtain a film with a thickness of 10 μm.

Example 4

A polyimide varnish having a solid content concentration of 10% by mass was obtained by preparing a polyimide varnish in the same manner as in Example 3 except that the amount of TFMB was changed to 28.822 g (0.090 mol) and the amount of 3,5-DABA was changed to 1.522 g (0.010 mol).

Using the obtained polyimide varnish, a thin film was produced by the same method as in Example 3 to obtain a thin film having a thickness of 10 μm.

Example 5

A polyimide varnish having a solid content concentration of 10% by mass was obtained by preparing a polyimide varnish in the same manner as in Example 1 except that the amount of TFMB was changed to 17.933 g (0.070 mol) and the amount of 3,5-DABA was changed to 3.652 g (0.030 mol).

A thin film was produced by the same method as in Example 3 using the obtained polyimide varnish to obtain a thin film having a thickness of 9 μm.

Comparative Example 1

A polyimide varnish having a solid content concentration of 10% by mass was prepared in the same manner as in Example 1 except that 1,3-PBO was not added. A film was prepared in the same manner as in Example 1 using the obtained polyimide varnish to obtain a film having a thickness of 10 μm.

Comparative Example 2

A polyimide varnish having a solid content concentration of 10% by mass was prepared in the same manner as in Example 2 except that 1,3-PBO was not added. A film was prepared in the same manner as in Example 1 using the obtained polyimide varnish to obtain a film having a thickness of 10 μm.

Comparative Example 3

A polyimide varnish having a solid content concentration of 10% by mass was prepared in the same manner as in Example 3 except that 1,3-PBO was not added. A film was prepared in the same manner as in Example 1 using the obtained polyimide varnish to obtain a film having a thickness of 10 μm.

The obtained film was subjected to the above-mentioned evaluation. The results are shown in Table 1.

[Table 1]

Table 1

As shown in Table 1, the polyimide films of Examples 1 to 5 were excellent in heat resistance and colorless transparency, had low residual stress, were excellent in chemical resistance, and were also good in cleaning properties. On the other hand, the polyimide films of Comparative Examples were poor in solvent resistance.

Claims (10)

1. A polyimide resin composition comprising a polyimide resin and a crosslinking agent having at least two oxazole groups, The polyimide resin comprises a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from diamine, wherein the structural unit A comprises a structural unit (A-1) derived from a compound represented by the following formula (a-1), and the structural unit B comprises a structural unit (B-1) derived from a compound represented by the following formula (b-1) and a structural unit (B-2) derived from a compound represented by the following formula (b-2), The ratio of the structural unit (B-1) in the structural unit B is 80 to 95 mol%. The ratio of the structural unit (B-2) in the structural unit B is 5 to 20 mol%. In formula (b-2), X is a single bond, a substituted or unsubstituted alkylene group, a carbonyl group, an ether group, a group represented by the following formula (b-2-i), or a group represented by the following formula (b-2-ii), p is an integer of 0 to 2, m1 is an integer of 0 to 4, and m2 is an integer of 0 to 4, wherein when p is 0, m1 is an integer of 1 to 4, In formula (b-2-i), m3 is an integer from 0 to 5; in formula (b-2-ii), m4 is an integer from 0 to 5, wherein m1+m2+m3+m4 is greater than or equal to 1, and when p is 2, 2 Xs and 2 m2 to m4 are selected independently. 2. The polyimide resin composition according to claim 1, wherein the structural unit (B-2) is a structural unit (B-21) derived from a compound represented by the following formula (b-21), 3 . The polyimide resin composition according to claim 1 , wherein the ratio of the structural unit (A-1) in the structural unit A is 40 mol % or more. 4. The polyimide resin composition according to claim 1 or 2, wherein the structural unit A further comprises a structural unit (A-2) derived from a compound represented by the following formula (a-2): The polyimide resin composition according to claim 1 or 2, wherein the structural unit A further comprises a structural unit (A-3) derived from silicone modified with anhydride at both ends. 6 . The polyimide resin composition according to claim 1 , wherein the crosslinking agent is a compound including an aromatic ring or an aromatic heterocyclic ring to which at least two oxazole groups are bonded. 7 . The polyimide resin composition according to claim 1 , wherein the crosslinking agent is a compound including a benzene ring to which at least two oxazole groups are bonded. 8 . The polyimide resin composition according to claim 1 , wherein the crosslinking agent is 1,3-bis(4,5-dihydro-2-oxazolyl)benzene. 9 . A polyimide varnish, wherein the polyimide resin composition according to claim 1 is dissolved in an organic solvent. 10 . A polyimide film, wherein the polyimide resin in the polyimide resin composition according to claim 1 is cross-linked with the cross-linking agent.