JP7517342B2 - Polyimide resin composition, polyimide varnish and polyimide film - Google Patents

Description

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

In general, polyimide resins have excellent heat resistance, and various applications in the fields of electrical and electronic components are being considered. For example, it is desirable to replace the glass substrates used in image display devices such as liquid crystal displays and OLED displays with plastic substrates in order to make the devices lighter and more flexible, and research is being conducted on polyimide films suitable for such plastic substrates. Polyimide films for such applications are required to be colorless and transparent.

When a varnish applied to 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 in the polyimide film is large, the glass support or silicon wafer may warp, so there is a demand for reducing the residual stress in the polyimide film.

However, for a polyimide film to be suitable as a substrate, not only colorless transparency and low residual stress but also chemical resistance (e.g., acid resistance, alkali resistance, solvent resistance) are important physical properties. For example, when a polyimide film is used as a substrate for forming an ITO (Indium Tin Oxide) film, the polyimide film must be resistant to the acid used to etch the ITO film. If the acid resistance of the polyimide film is insufficient, the film may turn yellow and lose its colorless transparency.

In addition, alkaline aqueous solutions such as aqueous sodium hydroxide and aqueous potassium hydroxide are mainly used to clean supports such as glass plates used in the production of polyimide films (supports on which polyimide varnish is applied). Cleaning with an aqueous alkaline solution may also be performed when a polyimide film has been formed on a support such as a glass plate. Therefore, polyimide films are also required to be resistant to alkali.

Furthermore, organic solvents such as NMP may be used in the process of forming various electronic circuits such as TFTs on polyimide films, and polyimide films are also required to be resistant 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 equipment used for coating, etc. In order to thoroughly clean the equipment, the polyimide resin composition is also required to be soluble in the cleaning solution used (for example, "OK73 Thinner" manufactured by Tokyo Ohka Kogyo Co., Ltd., various organic solvents such as NMP), and the conflicting properties of solvent resistance and cleanability are required.

Patent Document 1 discloses a polyimide resin that provides a film with low residual stress, which is synthesized using 4,4'-oxydiphthalic dianhydride as the tetracarboxylic acid component and α,ω-aminopropylpolydimethylsiloxane having a number average molecular weight of 1000 and 4,4'-diaminodiphenyl ether as the diamine components.

Patent Document 2 discloses a polyimide resin composition containing a polyimide resin having a carboxyl group and a crosslinking agent having at least two oxazolyl groups, and states that the polyimide resin composition makes it possible to form a film having good transparency and high hardness.

However, Patent Document 1 does not mention anything about chemical resistance or cleanability. Furthermore, Patent Document 2 does not evaluate resistance to solvents (N,N-dimethylacetamide), and does not consider cleanability or residual stress.

JP 2005-232383 A JP 2016-222797 A

As described above, polyimide films are required to be colorless and transparent, have low residual stress, and are chemically resistant. However, it is not easy to improve these properties while maintaining excellent heat resistance.
An object of the present invention is to provide a polyimide resin composition which is excellent in heat resistance, colorless transparency, chemical resistance and cleanability and is capable of forming a film having low residual stress, as well as a polyimide varnish and a polyimide film each containing the polyimide resin composition.

The inventors discovered that a polyimide resin composition containing a polyimide resin having a specific combination of structural units and a specific crosslinking agent can solve the above problems, and thus completed the invention.

（式（ｂ－２）中、Ｘは単結合、置換若しくは無置換のアルキレン基、カルボニル基、エーテル基、下記式（ｂ－２－ｉ）で表される基、又は下記式（ｂ－２－ｉｉ）で表される基であり、ｐは０～２の整数であり、ｍ１は０～４の整数であり、ｍ２は０～４の整数である。ただし、ｐが０の場合、ｍ１は１～４の整数である。）

（式（ｂ－２－ｉ）中、ｍ３は０～５の整数であり；式（ｂ－２－ｉｉ）中、ｍ４は０～５の整数である。なお、ｍ１＋ｍ２＋ｍ３＋ｍ４は１以上であり、ｐが２の場合、２つのＸ及び２つのｍ２～ｍ４のそれぞれは独立して選択される。）
＜２＞ 構成単位（Ｂ－２）が、下記式（ｂ－２１）で表される化合物に由来する構成単位（Ｂ－２１）である、上記＜１＞に記載のポリイミド樹脂組成物。

＜３＞ 構成単位Ａ中における構成単位（Ａ－１）の比率が４０モル％以上である、上記＜１＞又は＜２＞に記載のポリイミド樹脂組成物。
＜４＞ 構成単位Ｂ中における構成単位（Ｂ－１）の比率が３５～９５モル％であり、
構成単位Ｂ中における構成単位（Ｂ－２）の比率が５～６５モル％である、上記＜１＞～＜３＞のいずれか１つに記載のポリイミド樹脂組成物。
＜５＞ 構成単位Ａが、下記式（ａ－２）で表される化合物に由来する構成単位（Ａ－２）を更に含む、上記＜１＞～＜４＞のいずれか１つに記載のポリイミド樹脂組成物。

＜６＞ 構成単位Ａが、両末端酸無水物変性シリコーンに由来する構成単位（Ａ－３）を更に含む、上記＜１＞～＜５＞のいずれか１つに記載のポリイミド樹脂組成物。
＜７＞ 前記架橋剤が、少なくとも２つのオキサゾリル基が結合した芳香環又は芳香族複素環を含む化合物である、上記＜１＞～＜６＞のいずれか１つに記載のポリイミド樹脂組成物。
＜８＞ 前記架橋剤が、少なくとも２つのオキサゾリル基が結合したベンゼン環を含む化合物である、上記＜１＞～＜７＞のいずれか１つに記載のポリイミド樹脂組成物。
＜９＞ 前記架橋剤が、１，３－ビス（４，５－ジヒドロ－２－オキサゾリル）ベンゼンである、上記＜１＞～＜８＞のいずれか１つに記載のポリイミド樹脂組成物。
＜１０＞ 上記＜１＞～＜９＞のいずれか１つに記載のポリイミド樹脂組成物が有機溶媒に溶解してなるポリイミドワニス。
＜１１＞ 上記＜１＞～＜９＞のいずれか１つに記載のポリイミド樹脂組成物中の前記ポリイミド樹脂が前記架橋剤により架橋されてなる、ポリイミドフィルム。 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 oxazolyl groups,
The polyimide resin composition is a polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein the structural unit A includes a structural unit (A-1) derived from a compound represented by the following formula (a-1), and the structural unit B 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. However, 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. Note that, m1+m2+m3+m4 is 1 or more, and when p is 2, each of the two Xs and the two m2 to m4 is independently selected.)
<2> The polyimide resin composition according to the above <1>, in which 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 the above <1> or <2>, wherein the ratio of the structural unit (A-1) in the structural unit A is 40 mol % or more.
<4> The ratio of the structural unit (B-1) in the structural unit B is 35 to 95 mol %,
The polyimide resin composition according to any one of the above <1> to <3>, wherein 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 the above <1> to <4>, in which the structural unit A further contains 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 the above <1> to <5>, in which the structural unit A further contains a structural unit (A-3) derived from a silicone modified with an acid anhydride at both ends.
<7> The polyimide resin composition according to any one of <1> to <6> above, wherein the crosslinking agent is a compound containing an aromatic ring or an aromatic heterocycle having at least two oxazolyl groups bonded thereto.
<8> The polyimide resin composition according to any one of <1> to <7> above, wherein the crosslinking agent is a compound containing a benzene ring having at least two oxazolyl groups bonded thereto.
<9> The polyimide resin composition according to any one of <1> to <8> above, 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> above 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.

According to the present invention, it is possible to form a film that has excellent heat resistance, colorless transparency, chemical resistance and cleanability, and also has low residual stress.

[Polyimide resin composition]
The polyimide resin composition of the present invention contains a polyimide resin and a crosslinking agent. The polyimide resin and the crosslinking agent in the present invention will be described below.

（式（ｂ－２）中、Ｘは単結合、置換若しくは無置換のアルキレン基、カルボニル基、エーテル基、下記式（ｂ－２－ｉ）で表される基、又は下記式（ｂ－２－ｉｉ）で表される基であり、ｐは０～２の整数であり、ｍ１は０～４の整数であり、ｍ２は０～４の整数である。ただし、ｐが０の場合、ｍ１は１～４の整数である。）

（式（ｂ－２－ｉ）中、ｍ３は０～５の整数であり；式（ｂ－２－ｉｉ）中、ｍ４は０～５の整数である。なお、ｍ１＋ｍ２＋ｍ３＋ｍ４は１以上であり、ｐが２の場合、２つのＸ及び２つのｍ２～ｍ４のそれぞれは独立して選択される。） <Polyimide resin>
The polyimide resin of the present invention has a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, in which the structural unit A contains a structural unit (A-1) derived from a compound represented by the following formula (a-1), and the structural unit B contains 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. However, 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. Note that, m1+m2+m3+m4 is 1 or more, and when p is 2, each of the two Xs and the two m2 to m4 is independently selected.)

(Structural unit A)
The structural unit A is a structural unit derived from a tetracarboxylic dianhydride contained in a polyimide resin, and includes 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. When structural unit A contains structural unit (A-1), the colorless transparency and heat resistance of the film are improved.

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

The structural unit A may contain a structural unit other than the structural unit (A-1).
It is preferable that the structural unit A further contains, in addition to the structural unit (A-1), a structural unit (A-2) derived from a compound represented by the following formula (a-2).

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 even more preferably 55 to 85 mol %, and 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 even more 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, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. There is no particular upper limit to the total ratio of the structural units (A-1) and (A-2), that is, it is 100 mol%. The structural unit A may be composed of 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.
Furthermore, by further including the structural unit (A-2) in the structural unit A, the light transmittance of the film at a wavelength of 308 nm is reduced. In recent years, a laser peeling process called laser lift-off (LLO) has been attracting attention as a method for peeling a resin film from a support on which a resin film is laminated. The smaller the light transmittance at a wavelength of 308 nm, the better the laser peelability with a XeCl excimer laser at a wavelength of 308 nm.

（式（ａ－３）中、
Ｒ¹～Ｒ⁶は、それぞれ独立して、炭素数１～２０の一価の炭化水素基であり、
Ｌ¹及びＬ²は、それぞれ独立して、単結合又は炭素数１～２０の二価の炭化水素基であり、
Ｚ¹及びＺ²は、それぞれ独立して、炭素数１～２０の三価の炭化水素基であり、
ｎは、１～２００である。） In addition to the structural unit (A-1), the structural unit A preferably further contains a structural unit (A-3) derived from a silicone modified with an acid anhydride at both ends.
The silicone modified with acid anhydrides at both ends is preferably a compound represented by the following formula (a-3).

(In formula (a-3),
R ¹ to R ⁶ are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms;
L ¹ and L ² each independently represent a single bond or a divalent hydrocarbon group having 1 to 20 carbon atoms;
^Z1 and ^Z2 each independently represent a trivalent hydrocarbon group having 1 to 20 carbon atoms;
n is 1 to 200.

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

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; and even 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. It is 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 t-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 it is most preferably selected from the group consisting of a methyl group, an ethyl group, a phenyl group, and a vinyl group.

In formula (a-3), L ¹ and L ² each independently represent 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.
As the alkylene group having 1 to 20 carbon atoms, an alkylene group having 1 to 10 carbon atoms is preferable, and examples thereof include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, and a hexylene group.
As the cycloalkylene group having 3 to 20 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms is preferable, and examples thereof include a cyclobutylene group, a cyclopentylene group, a cyclohexylene group, and a cycloheptylene group.
As the arylene group having 6 to 20 carbon atoms, an arylene group having 6 to 10 carbon atoms is preferable, and examples thereof include a phenylene group and a naphthylene group.

L ¹ and L ² 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; even more 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; 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 formula (a-3), Z ¹ and Z ² 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-norbornanedicarboxylic acid residue, and the group represented by formula (a-3-iv) is a 5-norbornene-2,3-dicarboxylic acid residue. In formulas (a-3-i) to (a-3-iv), "*" indicates the bond position.

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

Commercially available silicones modified with acid anhydrides 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 Pharmaceuticals.

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 even more preferably 70 to 97 mol %, and 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 even more 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, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. There is no particular upper limit to the total ratio of the structural units (A-1) and (A-3), that is, it is 100 mol%. The structural unit A may be composed of only the structural unit (A-1) and the structural unit (A-3).

By including structural unit A further containing structural unit (A-3), the colorless transparency of the film can be improved while maintaining low residual stress.

It is also preferable that the structural unit A further 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 even more 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 even more preferably 5 to 20 mol%, and 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 even more 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, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. There is no particular upper limit to the total ratio of the structural units (A-1) to (A-3), that is, it is 100 mol%. The structural unit A may be composed of only the structural unit (A-1), the structural unit (A-2), and the structural unit (A-3).

The structural units other than the structural unit (A-1) optionally contained in the structural unit A are not limited to the structural units (A-2) and (A-3). The tetracarboxylic acid dianhydride that gives such an optional structural unit is not particularly limited, but examples thereof include aromatic tetracarboxylic acid dianhydrides such as pyromellitic dianhydride, 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride; alicyclic tetracarboxylic acid dianhydrides such as 1,2,3,4-cyclobutane tetracarboxylic acid dianhydride and 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride (excluding the compound represented by formula (a-1)); and aliphatic tetracarboxylic acid dianhydrides such as 1,2,3,4-butane tetracarboxylic acid dianhydride.
In this specification, the term "aromatic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing one or more aromatic rings, the term "alicyclic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing one or more alicyclic rings but no aromatic rings, and the term "aliphatic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing neither an aromatic ring nor an alicyclic ring.
The structural unit other than the structural unit (A-1) optionally contained in the structural unit A may be of one type, or of two or more types.

（式（ｂ－２）中、Ｘは単結合、置換若しくは無置換のアルキレン基、カルボニル基、エーテル基、下記式（ｂ－２－ｉ）で表される基、又は下記式（ｂ－２－ｉｉ）で表される基であり、ｐは０～２の整数であり、ｍ１は０～４の整数であり、ｍ２は０～４の整数である。ただし、ｐが０の場合、ｍ１は１～４の整数である。）

（式（ｂ－２－ｉ）中、ｍ３は０～５の整数であり；式（ｂ－２－ｉｉ）中、ｍ４は０～５の整数である。なお、ｍ１＋ｍ２＋ｍ３＋ｍ４は１以上であり、ｐが２の場合、２つのＸ及び２つのｍ２～ｍ４のそれぞれは独立して選択される。）
なお、式（ｂ－２－ｉ）及び（ｂ－２－ｉｉ）中、「＊」は結合位置を示す。 (Structural unit B)
The structural unit B is a structural unit derived from a diamine contained in a 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. However, 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. Note that, m1+m2+m3+m4 is 1 or more, and when p is 2, each of the two Xs and the two m2 to m4 is independently selected.)
In the formulae (b-2-i) and (b-2-ii), "*" indicates the bond 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 residual stress is reduced.

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

A specific example of the compound represented by formula (b-21) is the 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 formula (b-21), and more preferably a structural unit (B-211) derived from a compound represented by formula (b-211).

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

The proportion of the structural unit (B-1) in the structural unit B is preferably from 35 to 95 mol %, more preferably from 40 to 90 mol %, and even more preferably from 45 to 85 mol %.
The proportion of the structural unit (B-2) in the structural unit B is preferably from 5 to 65 mol %, more preferably from 10 to 60 mol %, and even more preferably from 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, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. There is no particular upper limit to the total ratio of the structural units (B-1) and (B-2), that is, it is 100 mol%. The structural unit B may be composed of only the structural unit (B-1) and the structural unit (B-2).

The structural unit B may contain a structural unit other than the structural units (B-1) and (B-2). Diamines that provide such structural units are not particularly limited, but 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-diisopropylbenzene, N, Examples of the diamine include aromatic diamines (excluding the compounds represented by formula (b-1) and formula (b-2)) such as 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; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine.
In this specification, an aromatic diamine means a diamine containing one or more aromatic rings, an alicyclic diamine means a diamine containing one or more alicyclic rings but no aromatic rings, and an aliphatic diamine means a diamine containing neither an aromatic ring nor an alicyclic ring.
The structural units other than the structural units (B-1) and (B-2) optionally contained in the structural unit B may be of one type, or of two or more types.

The number average molecular weight of the polyimide resin is preferably 5,000 to 100,000 from the viewpoint of the mechanical strength of the resulting polyimide film. The number average molecular weight of the polyimide resin can be determined, for example, from a standard polymethyl methacrylate (PMMA) equivalent value measured by gel filtration chromatography.

The polyimide resin may contain a structure other than a polyimide chain (a structure formed by imide bonding between a structural unit A and a structural unit B). Examples of structures other than a polyimide chain that can be contained in the polyimide resin include a structure containing an amide bond.
The polyimide resin preferably contains, as a main structure, a polyimide chain (a structure formed by imide bonding between structural unit A and structural unit B). 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, even more preferably 90% by mass or more, and particularly preferably 99% by mass or more.

The polyimide resin composition of the present invention containing the above polyimide resin can form a film that is excellent in heat resistance, colorless transparency, chemical resistance and cleanability, and further has low residual stress, and the preferred physical properties of the film are as follows:

The glass transition temperature (Tg) is preferably 380° C. or higher, more preferably 400° C. or higher, and even more preferably 450° C. or higher.
The total light transmittance, when made into a film having a thickness of 10 μm, is preferably 88% or more, more preferably 89% or more, and further preferably 90% or more.
The yellow index (YI) when made into a film having a thickness of 10 μm is preferably 5.0 or less, more preferably 4.0 or less, and further preferably 3.0 or less.
The residual stress is preferably 25.0 MPa or less, more preferably 24.0 MPa or less, and further preferably 22.0 MPa or less.

Furthermore, by using a polyimide resin in which the structural unit A further contains the structural unit (A-2), which is one embodiment of the polyimide resin, a film that is even more excellent in laser peelability can be formed, and the suitable 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 made into a film having a thickness of 10 μm.

Furthermore, a film that can be formed using the polyimide resin has good mechanical properties and the following preferable physical properties.
The tensile modulus is preferably 2.0 GPa or more, more preferably 3.0 GPa or more, and even more 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.
The above-mentioned physical properties in the present invention can be specifically measured by the methods described in the Examples.

<Method of producing polyimide resin>
In the present invention, the polyimide resin can be produced by reacting a tetracarboxylic acid component containing a compound that provides the above-mentioned structural unit (A-1) with a diamine component containing a compound that provides the above-mentioned structural unit (B-1) and a compound that provides the above-mentioned structural unit (B-2).

Compounds that provide the structural unit (A-1) include, but are not limited to, compounds represented by formula (a-1), and may be derivatives thereof as long as they provide the same structural unit. Such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydride represented by formula (a-1) (i.e., norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic acid), and alkyl esters of the tetracarboxylic acid. Compounds that provide the structural unit (A-1) are preferably compounds represented by formula (a-1) (i.e., dianhydrides).

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

The tetracarboxylic acid component may contain a compound other than the compound that provides the structural unit (A-1).
It is preferred that the tetracarboxylic acid component further contains a compound that provides the structural unit (A-2), in addition to the compound that provides the structural unit (A-1).
Compounds that provide the structural unit (A-2) include, but are not limited to, compounds represented by formula (a-2), and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydride represented by formula (a-2) and alkyl esters of the tetracarboxylic acid. Compounds that provide the structural unit (A-2) are preferably compounds represented by formula (a-2) (i.e., dianhydrides).

When the tetracarboxylic acid component contains a compound that provides the structural unit (A-1) and a compound that provides the structural unit (A-2), the tetracarboxylic acid component preferably contains 40 to 95 mol %, more preferably 50 to 90 mol %, and even more preferably 55 to 85 mol %, of the compound that provides the structural unit (A-1), and preferably contains 5 to 60 mol %, more preferably 10 to 50 mol %, and even more preferably 15 to 45 mol % of the compound that provides the structural unit (A-2).
The tetracarboxylic acid component contains, in total, the compound that gives the structural unit (A-1) and the compound that gives the structural unit (A-2), preferably at least 50 mol%, more preferably at least 70 mol%, even more preferably at least 90 mol%, and particularly preferably at least 99 mol%. There is no particular upper limit on the total content of the compound that gives the structural unit (A-1) and the compound that gives the structural unit (A-2), that is, it is 100 mol%. The tetracarboxylic acid component may consist only of the compound that gives the structural unit (A-1) and the compound that gives the structural unit (A-2).

It is preferred that the tetracarboxylic acid component further contains a compound that provides the structural unit (A-3), in addition to the compound that provides the structural unit (A-1).
Examples of compounds that provide the structural unit (A-3) include silicones modified with acid anhydrides at both ends (for example, compounds represented by formula (a-3)), but are not limited thereto, and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the silicones modified with acid anhydrides at both ends and alkyl esters of the tetracarboxylic acids. Examples of compounds that provide the structural unit (A-3) are silicones modified with acid anhydrides at both ends (i.e., dianhydrides).

When the tetracarboxylic acid component contains a compound that provides the structural unit (A-1) and a compound that provides the structural unit (A-3), the tetracarboxylic acid component preferably contains 50 to 99 mol %, more preferably 60 to 98 mol %, and even more preferably 70 to 97 mol %, of the compound that provides the structural unit (A-1), and preferably contains 1 to 50 mol %, more preferably 2 to 40 mol %, and even more preferably 3 to 30 mol %, of the compound that provides the structural unit (A-3).
The tetracarboxylic acid component preferably contains at least 50 mol %, more preferably at least 70 mol %, even more preferably at least 90 mol %, and particularly preferably at least 99 mol % of the compound that provides the structural unit (A-1) and the compound that provides the structural unit (A-3). There is no particular upper limit on the total content of the compound that provides the structural unit (A-1) and the compound that provides the structural unit (A-3), that is, it is 100 mol %. The tetracarboxylic acid component may consist only of the compound that provides the structural unit (A-1) and the compound that provides the structural unit (A-3).

It is also preferred that the tetracarboxylic acid component further contains, in addition to the compound that provides the structural unit (A-1), both a compound that provides the structural unit (A-2) and a compound that provides the structural unit (A-3).
When the tetracarboxylic acid component contains a compound which provides the structural unit (A-1), a compound which provides the structural unit (A-2), and a compound which provides the structural unit (A-3), the tetracarboxylic acid component preferably contains 50 to 90 mol %, more preferably 60 to 85 mol %, and even more preferably 65 to 80 mol %, of the compound which provides the structural unit (A-1), preferably contains 5 to 30 mol %, more preferably 5 to 25 mol %, and even more preferably 5 to 20 mol %, of the compound which provides the structural unit (A-3), and preferably contains 1 to 25 mol %, more preferably 2 to 20 mol %, and even more preferably 3 to 15 mol % of the compound which provides the structural unit (A-3).
The tetracarboxylic acid component preferably contains at least 50 mol%, more preferably at least 70 mol%, even more preferably at least 90 mol%, and particularly preferably at least 99 mol% of the compound that gives the structural unit (A-1), the compound that gives the structural unit (A-2), and the compound that gives the structural unit (A-3). There is no particular upper limit to the total content of the compound that gives the structural unit (A-1), the compound that gives the structural unit (A-2), and the compound that gives the structural unit (A-3), that is, it is 100 mol%. The tetracarboxylic acid component may be composed only of the compound that gives the structural unit (A-1), the compound that gives the structural unit (A-2), and the compound that gives the structural unit (A-3).

Compounds other than the compound that provides the structural unit (A-1) that are optionally contained in the tetracarboxylic acid component are not limited to the compounds that provide the structural unit (A-2) and the compounds that provide the structural unit (A-3). Examples of such optional compounds include the above-mentioned aromatic tetracarboxylic acid dianhydrides, alicyclic tetracarboxylic acid dianhydrides, and aliphatic tetracarboxylic acid dianhydrides, as well as derivatives thereof (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.).
The compound other than the compound which gives the structural unit (A-1) optionally contained in the tetracarboxylic acid component may be one type or two or more types.

Compounds that provide the structural unit (B-1) include, but are not limited to, compounds represented by formula (b-1), and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the diamines represented by formula (b-1). Compounds that provide the structural unit (B-1) are preferably compounds represented by formula (b-1) (i.e., diamines).
Similarly, examples of compounds that provide the structural unit (B-2) include, but are not limited to, compounds represented by formula (b-2), and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the diamines represented by formula (b-2). Compounds that provide the structural unit (B-2) are preferably compounds represented by formula (b-2) (i.e., diamines).

The diamine component contains the compound that provides the structural unit (B-1) in an amount of preferably 35 to 95 mol %, more preferably 40 to 90 mol %, and even more preferably 45 to 85 mol %.
The diamine component contains the compound that provides the structural unit (B-2) in an amount of preferably 5 to 65 mol %, more preferably 10 to 60 mol %, and even more preferably 15 to 55 mol %.
The diamine component contains, in total, the compound that gives the structural unit (B-1) and the compound that gives the structural unit (B-2), preferably at least 50 mol%, more preferably at least 70 mol%, even more preferably at least 90 mol%, and particularly preferably at least 99 mol%. The upper limit of the total content of the compound that gives the structural unit (B-1) and the compound that gives the structural unit (B-2) is not particularly limited, that is, it is 100 mol%. The diamine component may consist only of the compound that gives the structural unit (B-1) and the compound that gives the structural unit (B-2).

The diamine component may contain a compound other than the compound that provides the structural unit (B-1) and the compound that provides the structural unit (B-2). Examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, as well as derivatives thereof (diisocyanates, etc.).
The compound optionally contained in the diamine component other than the compound providing the structural unit (B-1) and the compound providing the structural unit (B-2) may be one type or two or more types.

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

In addition, in the present invention, in addition to the above-mentioned tetracarboxylic acid component and diamine component, a terminal blocking agent may be used in the production of the polyimide resin. As the terminal blocking agent, monoamines or dicarboxylic acids are preferred. The amount of the terminal blocking agent to be introduced is preferably 0.0001 to 0.1 moles per mole of the tetracarboxylic acid component, and particularly preferably 0.001 to 0.06 moles. As the monoamine terminal blocking agent, 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. Of these, benzylamine and aniline are preferably used. As the dicarboxylic acid terminal blocking agent, dicarboxylic acids are preferred, and a part of them may be ring-closed. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclohexane-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. are recommended. Of these, phthalic acid and phthalic anhydride are preferably used.

The method for reacting the tetracarboxylic acid component and the diamine component is not particularly limited, and any known method can be used.
Specific reaction methods include: (1) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the mixture is stirred at room temperature to 80° C. for 0.5 to 30 hours, and then the temperature is raised to carry out the imidization reaction; (2) a method in which a diamine component and a reaction solvent are charged into a reactor and dissolved, and then a tetracarboxylic acid component is charged, and the mixture is stirred at room temperature to 80° C. for 0.5 to 30 hours as necessary, and then the temperature is raised to carry out the imidization reaction; and (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the temperature is immediately raised to carry out the imidization reaction.

The reaction solvent used in the production of polyimide resins may be any solvent that does not inhibit the imidization reaction and can dissolve the resulting polyimide. Examples include aprotic solvents, phenolic solvents, ether solvents, and carbonate solvents.

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

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

In the imidization reaction, it is preferable to carry out the reaction while removing the water generated during production using a Dean-Stark apparatus or the like. By carrying out such an operation, it is possible to further increase the degree of polymerization and the imidization rate.

In the above imidization reaction, a known imidization catalyst can be used, such as a base catalyst or an acid catalyst.
Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine (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 hydrogencarbonate, and sodium hydrogencarbonate.
Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, oxybenzoic acid, terephthalic acid, benzenesulfonic acid, paratoluenesulfonic acid, naphthalenesulfonic acid, etc. The above imidization catalysts may be used alone or in combination of two or more kinds.
Among the above, from the viewpoint of handleability, it is preferable to use a base catalyst, it is more preferable to use an organic base catalyst, it is even more preferable to use triethylamine, and it is particularly preferable to use a combination of triethylamine and triethylenediamine.

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

<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 has reactivity with a 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 likely 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 crosslink with each other via the crosslinking agent to form a crosslinked polyimide resin. For this reason, the chemical resistance of the film is improved.

The crosslinking 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 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, 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) manufactured by Nippon Shokubai Co., Ltd.

The crosslinking agent is preferably a compound containing an aromatic ring or aromatic heterocycle 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, still more 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 crosslinking agent may be used alone or in combination of two or more kinds.

The polyimide resin composition of the present invention preferably contains a polyimide resin and a crosslinking agent in such a ratio that the molar ratio of the oxazolyl groups in the crosslinking agent to the carboxyl groups in the polyimide resin (oxazolyl groups/carboxyl groups) is in the range of 1/8 to 1/0.5, more preferably 1/6 to 1/1, and even more preferably 1/4 to 1/2.
The above molar ratio means the molar ratio between the oxazolyl group contained in the crosslinking agent and the carboxyl group contained in the compound that provides the structural unit (B-1) used in the production of the polyimide resin, and is calculated based on the amount of the crosslinking agent added and the amount of the compound that provides the structural unit (B-1) added.

[Polyimide varnish]
A preferred embodiment of the polyimide resin composition of the present invention is a polyimide resin composition (hereinafter, also referred to as a "polyimide varnish") which further contains an organic solvent in addition to the above-mentioned polyimide resin and the above-mentioned crosslinking agent, and in which the polyimide resin is dissolved in the organic solvent.
The organic solvent is not particularly limited as long as it dissolves the polyimide resin. However, it is preferable to use the above-mentioned compounds as reaction solvents used in the production of the polyimide resin, either alone or in combination of two or more kinds.
The polyimide varnish may be prepared by adding a crosslinking agent to a solution in which a polyimide resin obtained by polymerization is dissolved in a reaction solvent, or by adding a dilution solvent and a crosslinking agent to the solution.

The polyimide varnish preferably contains 5 to 40% by mass of polyimide resin, more preferably 7 to 30% by mass, and even more preferably 8 to 20% by mass. 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 measured at 25°C using an E-type viscometer.

In addition, the polyimide varnish of the present invention may contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, UV stabilizers, surfactants, leveling agents, defoamers, fluorescent brightening agents, crosslinking agents, polymerization initiators, and photosensitizers, as long as the additives do not impair the required properties of the polyimide film.
The method for producing the polyimide varnish of the present invention is not particularly limited, and any known method can be applied.

[Polyimide film]
The polyimide film of the present invention is obtained by crosslinking the above-mentioned polyimide resin contained in the polyimide resin composition of the present invention with the above-mentioned crosslinking agent. That is, the polyimide film of the present invention contains a crosslinked polyimide resin which is a crosslinked product of polyimide resins via a crosslinking agent. Therefore, the polyimide film of the present invention is excellent in heat resistance, colorless transparency, and chemical resistance, and further has low residual stress. The preferable physical properties of the polyimide film of the present invention are as described above.

There are no particular limitations on the method for producing the polyimide film of the present invention, so long as it includes a step of crosslinking at a temperature at which the crosslinking reaction between the polyimide resin and the crosslinking agent proceeds (preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 150°C or higher). For example, the above-mentioned polyimide varnish can be applied to a smooth support such as a glass plate, a metal plate, or a plastic, or formed into a film, and then heated. This heat treatment can remove organic solvents such as reaction solvents and dilution solvents contained in the polyimide varnish while proceeding with the crosslinking reaction between the polyimide resin in the polyimide varnish and the crosslinking agent. If necessary, a release agent may be applied in advance to the surface of the support.

The following method is preferred for the heat treatment. That is, it is preferable to first evaporate the organic solvent at a temperature of 120°C or less, and then further dry at a temperature equal to or higher than the boiling point of the organic solvent to produce a polyimide film. It is also preferable to dry under a nitrogen atmosphere. The pressure of the drying atmosphere may be reduced pressure, normal pressure, or pressurized pressure. By drying at two temperatures, a film with a smooth surface and no defects can be obtained. The drying temperature in the second stage is not particularly limited, but is preferably 200 to 450°C, more preferably 300 to 430°C, and particularly preferably 350 to 400°C. Drying within this temperature range improves the transparency and yellowness of the film, and further improves solvent resistance.

The polyimide film of the present invention can also be produced by using a polyamic acid varnish prepared by dissolving a polyamic acid and a crosslinking agent in an organic solvent.
The polyamic acid contained in the polyamic acid varnish is a precursor of the polyimide resin of the present invention, and is a product of a polyaddition reaction between a tetracarboxylic acid component containing a compound that gives the above-mentioned structural unit (A-1) and a diamine component containing a compound that gives the above-mentioned structural unit (B-1) and a compound that gives the above-mentioned structural unit (B-2). The polyamic acid is imidized (dehydration ring closure) to obtain a polyimide resin.
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 which gives the above-mentioned structural unit (A-1) to a polyaddition reaction in a reaction solvent with a diamine component containing a compound which gives the above-mentioned structural unit (B-1) and a compound which gives the above-mentioned structural unit (B-2), or may be a polyamic acid solution to which a dilution solvent has been further added.

The method for producing a polyimide film using a polyamic acid varnish is not particularly limited as long as it includes a step of crosslinking at a temperature at which the crosslinking reaction between the polyimide resin and the crosslinking agent proceeds (preferably 80° C. or higher, more preferably 100° C. or higher, and even more preferably 150° C. or higher), and a known method can be used. For example, the polyamic acid varnish is applied to a smooth support such as a glass plate, a metal plate, or a plastic, or formed into a film, and organic solvents such as reaction solvents and dilution solvents 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 further the polyimide resin is reacted with a crosslinking agent to crosslink, thereby producing a polyimide film.
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.
The imidization method is not limited to thermal imidization, and chemical imidization can also be applied.

The thickness of the polyimide film of the present invention can be appropriately selected depending on the application, etc., but is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, and even more preferably 10 to 80 μm. When the thickness is 1 to 250 μm, practical use as a free-standing film becomes possible.
The thickness of the polyimide film can be easily controlled by adjusting the solids concentration and viscosity of the polyimide varnish.

The polyimide film of the present invention is suitable for use as a film for various components such as color filters, flexible displays, semiconductor parts, and optical components. The polyimide film of the present invention is particularly suitable for use as a substrate for image display devices such as liquid crystal displays and OLED displays.

The present invention will be described in detail below with reference to examples, although the present invention is not limited to these examples in any way.
The solids concentration of the varnishes and the physical properties of the films obtained in the examples and comparative examples were measured by the methods described below.

(1) Solid Content Concentration The solid content concentration of the varnish was measured by heating a sample at 320° C. for 120 min in a small electric furnace “MMF-1” manufactured by AS ONE Corporation, and calculating from the mass difference 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 and turbidity simultaneous measuring instrument "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 Corp., the specimen was heated to a temperature sufficient to remove the residual stress under the conditions of a sample size of 2 mm x 20 mm, a load of 0.1 N, and a heating rate of 10°C/min in tensile mode, and then cooled to room temperature. The test piece elongation was then measured under the same conditions as in the treatment for removing the residual stress, and the point at which an inflection point in the elongation was observed was determined as the glass transition temperature.

(5) Residual Stress Polyimide varnish or polyamic acid varnish was applied using a spin coater onto a 4-inch silicon wafer with a thickness of 525 μm ± 25 μm, the "warpage" of which had been measured in advance using a residual stress measuring device "FLX-2320" manufactured by KLA-Tencor Corporation, and the wafer was pre-baked. After that, a heat curing treatment was performed at 350 to 400°C for 30 minutes in a nitrogen atmosphere using a hot air dryer, and a silicon wafer with a polyimide film having a thickness of 8 to 15 μm after curing was produced. The warpage of this 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 chuck distance 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 the polyimide film formed on a glass plate at room temperature, and the film surface was checked for any changes. Propylene glycol monomethyl ether acetate (PGMEA) was used as the solvent.
The evaluation criteria for solvent resistance were as follows.
A: No change was observed on the film surface.
Δ: Slight cracks occurred on the film surface.
×: The film surface was cracked or 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 were as follows:
◯: The film did not dissolve and maintained its shape.
×: The film was dissolved and could not maintain its shape.

(9) Cleaning Ability N-methyl-2-pyrrolidone and polyimide varnish were mixed and checked for uniform mixing at room temperature. The evaluation criteria for cleaning ability were as follows:
◯: The polyimide varnish and the NMP mixed solution were mixed uniformly.
×: The polyimide varnish and the NMP mixed solution were not mixed uniformly, and a precipitate was formed.

The tetracarboxylic acid components and diamine components used in the examples and comparative examples, as well as their abbreviations, are as follows:

<Tetracarboxylic acid component>
CpODA: norbornane-2-spiro-α-cyclopentanone-α'-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (manufactured by JX Nippon Oil & Energy Corporation; 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 Kogyo Co., Ltd.; compound represented by formula (b-1))
3,5-DABA: 3,5-diaminobenzoic acid (manufactured by Nippon 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 Co., Ltd.)

＜Other＞
GBL: γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation)
TEA: Triethylamine (Kanto Chemical Co., Ltd.)

Example 1
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 placed in a 1 L five-neck round-bottom flask equipped with a stainless steel half-moon shaped stirring blade, a nitrogen inlet tube, a Dean-Stark equipped with a cooling tube, a thermometer, and a glass end cap, and the mixture was stirred at a system temperature of 70° C. under a nitrogen atmosphere at a rotation speed of 150 rpm to obtain a solution.
To this solution, 38.438 g (0.100 mol) of CpODA and 20.130 g of GBL were added all at once, and then 0.506 g of TEA and 0.056 g of triethylenediamine (Tokyo Chemical Industry Co., Ltd.) were added as imidization catalysts, and the mixture was heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 190° C. and refluxed for 2 hours while adjusting the rotation speed according to the increase in viscosity.
Thereafter, 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 the mixture was further stirred for about 1 hour to be homogenized. Next, 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 the mixture was stirred for 30 minutes to be homogenized, thereby obtaining a polyimide varnish.
Next, the obtained polyimide varnish was applied by spin coating onto a glass plate and a silicon wafer, and then held on a hot plate at 80°C for 20 minutes. Thereafter, the solution was heated in a hot air dryer at 400°C for 30 minutes under a nitrogen atmosphere to evaporate the solvent, thereby obtaining a film having a thickness of 10 µm.

Example 2
A polyimide varnish with a solid content concentration of 10 mass % was obtained by the same method 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).
Using the obtained polyimide varnish, a film having a thickness of 9 μm was produced in the same manner as in Example 1, except that the drying temperature in the second stage was changed to the conditions shown in Table 1.

Example 3
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 placed in a 1 L five-neck round-bottom flask equipped with a stainless steel half-moon shaped stirring blade, a nitrogen inlet tube, a Dean-Stark equipped with a cooling tube, a thermometer, and a glass end cap, and the mixture was stirred at a system temperature of 70° C. under a nitrogen atmosphere at a rotation speed of 150 rpm to obtain a solution.
To this solution, 30.750 g (0.08 mol) of CpODA, 5.884 g (0.02 mol) of s-BPDA, and 39.178 g of GBL were added all at once, and then 0.506 g of TEA as an imidization catalyst and 0.056 g of triethylenediamine (Tokyo Chemical Industry Co., Ltd.) were added, and the mixture was heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 190° C. and refluxed for 2 hours while adjusting the rotation speed according to the increase in viscosity.
Thereafter, GBL was added so that the solid content concentration became 10% by mass, and the temperature in the reaction system was cooled to 120° C., and then the mixture was further stirred for about 1 hour to be homogenized. Then, 0.173 g of 1,3-PBO (0.25 mol % relative to 1 mol % of 3,5-DABA) was added, and the mixture was stirred for 30 minutes to be homogenized, thereby obtaining a polyimide varnish having a solid content concentration of 10% by mass.
Next, the obtained polyimide varnish was applied by spin coating onto a glass plate and a silicon wafer, and then held on a hot plate at 80°C for 30 minutes. Thereafter, the solution was heated in a hot air dryer at 350°C for 20 minutes under a nitrogen atmosphere to evaporate the solvent, thereby obtaining a film having a thickness of 10 µm.

Example 4
A polyimide varnish was prepared 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), to obtain a polyimide varnish having a solid content concentration of 10 mass %.
The obtained polyimide varnish was used to prepare a film in the same manner as in Example 3, to obtain a film having a thickness of 10 μm.

Example 5
A polyimide varnish with a solid content concentration of 10 mass % was obtained by the same method 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).
The obtained polyimide varnish was used to prepare a film in the same manner as in Example 3, to obtain a film having a thickness of 9 μm.

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

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

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

The obtained films were evaluated as described above. The results are shown in Table 1.

As shown in Table 1, the polyimide films of Examples 1 to 5 had excellent heat resistance and colorless transparency, low residual stress, excellent chemical resistance, and good washability. On the other hand, the polyimide film of the comparative example had poor solvent resistance.

Claims (10)

A polyimide resin composition comprising a polyimide resin and a crosslinking agent having at least two oxazolyl groups,
The polyimide resin is a polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, the structural unit A including a structural unit (A-1) derived from a compound represented by the following formula (a-1), the structural unit B including 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 %,
A polyimide resin composition , wherein 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. However, 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. Note that, m1+m2+m3+m4 is 1 or more, and when p is 2, each of the two Xs and the two m2 to m4 is independently selected.) 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):
The polyimide resin composition according to claim 1 or 2, in which the ratio of structural unit (A-1) in structural unit A is 40 mol % or more. The polyimide resin composition according to any one of claims 1 to 3 , wherein the structural unit A further contains a structural unit (A-2) derived from a compound represented by the following formula (a-2):
5. The polyimide resin composition according to claim 1 , wherein the structural unit A further comprises a structural unit (A-3) derived from a silicone modified with an acid anhydride at both ends. 6. The polyimide resin composition according to claim 1, wherein the crosslinking agent is a compound containing an aromatic ring or an aromatic heterocycle to which at least two oxazolyl groups are bonded. 7. The polyimide resin composition according to claim 1 , wherein the crosslinking agent is a compound containing a benzene ring to which at least two oxazolyl 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. A polyimide varnish obtained by dissolving the polyimide resin composition according to any one of claims 1 to 8 in an organic solvent. A polyimide film obtained by crosslinking the polyimide resin in the polyimide resin composition according to any one of claims 1 to 8 with the crosslinking agent.