JP7463964B2 - Polyimide resin, polyimide varnish and polyimide film - Google Patents

Description

The present invention relates to polyimide resins, polyimide varnishes and polyimide films.

Various applications of polyimide resins are being considered in the fields of electric and electronic parts, etc. For example, it is desirable to replace 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 on polyimide films suitable for such plastic substrates is being conducted. Polyimide films for such applications are required to be colorless and transparent.
Furthermore, the polyimide film is required to have a small phase difference due to birefringence and a low retardation.

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

Japanese Patent Application Laid-Open No. 8-134211 International Publication No. 2015/125895

As described above, various characteristics are required for a polyimide film, and it is not easy to satisfy all of these characteristics at the same time.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polyimide resin which is excellent in colorless transparency and is capable of forming a film having low retardation, and a polyimide varnish and a polyimide film which contain the polyimide resin.

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

That is, the present invention relates to the following [1] to [9].
[1]
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 includes at least one structural unit selected from the group consisting of a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2):
A polyimide resin, wherein the structural unit B includes at least one structural unit (B-1) selected from the group consisting of structural units derived from a compound represented by the following general formula (b1-1) and structural units derived from a compound represented by the following general formula (b2-1):

（式中、Ｘ^１～Ｘ^４はそれぞれ独立に、単結合、炭素数１～５のアルキレン基、炭素数２～５のアルキリデン基、－Ｓ－、－ＳＯ－、－ＳＯ_２－、－Ｏ－又は－ＣＯ－を示す。）

(In the formula, X ¹ to X ⁴ each independently represent a single bond, an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, -S-, -SO-, -SO ₂ -, -O- or -CO-.)

[2]
The polyimide resin according to the above-mentioned [1], wherein the ratio of the structural unit (B-1) in the structural unit B is 5 to 100 mol %.
[3]
The polyimide resin according to the above [1] or [2], wherein the structural unit A contains the structural unit (A-1), and the ratio of the structural unit (A-1) in the structural unit A is 45 to 100 mol %.
[4]
The polyimide resin according to any one of the above [1] to [3], wherein the structural unit (B-1) includes at least one structural unit selected from the group consisting of a structural unit derived from a compound represented by the following formula (b1-1-1), a structural unit derived from a compound represented by the following formula (b1-1-2), and a structural unit derived from a compound represented by the following formula (b1-1-3):

[5]
The polyimide resin according to any one of the above [1] to [4], wherein the structural unit B further comprises at least one structural unit selected from the group consisting of a structural unit (B-2) derived from a compound represented by the following formula (b-2), a structural unit (B-3) derived from a compound represented by the following formula (b-3), and a structural unit (B-4) derived from a compound represented by the following formula (b-4):

[6]
The polyimide resin according to the above item [5], wherein the total proportion of the structural units (B-2), (B-3), and (B-4) in the structural unit B is 5 to 95 mol %.
[7]
The polyimide resin according to any one of the above [1] to [6], wherein the structural unit A further contains a structural unit (A-3) derived from a compound represented by the following formula (a-3):

[8]
A polyimide varnish obtained by dissolving the polyimide resin according to any one of the above [1] to [7] in an organic solvent.
[9]
A polyimide film comprising the polyimide resin according to any one of [1] to [7] above.

According to the present invention, it is possible to provide a polyimide resin capable of forming a film having excellent colorless transparency and low retardation, as well as a polyimide varnish and a polyimide film containing the polyimide resin.

[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 includes at least one structural unit selected from the group consisting of a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2):
The structural unit B contains at least one structural unit (B-1) selected from the group consisting of structural units derived from compounds represented by general formula (b1-1) below and structural units derived from compounds represented by general formula (b2-1) below:

（式中、Ｘ^１～Ｘ^４はそれぞれ独立に、単結合、炭素数１～５のアルキレン基、炭素数２～５のアルキリデン基、－Ｓ－、－ＳＯ－、－ＳＯ_２－、－Ｏ－又は－ＣＯ－を示す。）

(In the formula, X ¹ to X ⁴ each independently represent a single bond, an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, -S-, -SO-, -SO ₂ -, -O- or -CO-.)

<Structural Unit A>
The structural unit A is a structural unit derived from a tetracarboxylic dianhydride contained in a polyimide resin, and includes at least one structural unit selected from the group consisting of a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2):

The compound represented by formula (a-1) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride.
When the structural unit A contains the structural unit (A-1), the colorless transparency, heat resistance, and thermal stability of the film are improved.
The compound represented by formula (a-2) is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.
When the structural unit A contains the structural unit (A-2), the transparency of the film is improved, and the solubility of the polyimide in organic solvents is improved.

The structural unit A may contain both the structural unit (A-1) and the structural unit (A-2), but preferably contains either the structural unit (A-1) or the structural unit (A-2), and more preferably contains the structural unit (A-1).

When structural unit A contains structural unit (A-1) and structural unit (A-2), the total ratio of structural units (A-1) and (A-2) in 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 structural units (A-1) and (A-2), that is, it is 100 mol%.

When the structural unit A contains the structural unit (A-1), the ratio of the structural unit (A-1) in the structural unit A is preferably 45 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the ratio is not particularly limited, that is, it is 100 mol%. Similarly, the ratio of the structural unit (A-1) in the structural unit A is preferably 45 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 90 to 100 mol%, and particularly preferably 99 to 100 mol%.
When the structural unit A contains the structural unit (A-2), the ratio of the structural unit (A-2) in the structural unit A is preferably 45 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the ratio is not particularly limited, that is, it is 100 mol%. Similarly, the ratio of the structural unit (A-2) in the structural unit A is preferably 45 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 90 to 100 mol%, and particularly preferably 99 to 100 mol%.

The structural unit A may further contain a structural unit (A-3) derived from a compound represented by the following formula (a-3):

The compound represented by formula (a-3) is norbornane-2-spiro-α-cyclopentanone-α'-spiro-2"-norbornane-5,5",6,6"-tetracarboxylic dianhydride. The colorless transparency of the film is improved by including structural unit (A-3) in structural unit A.

When the structural unit A contains the structural unit (A-3), the amount of the structural unit (A-13) in the structural unit A is preferably no greater than 55 mol %, and more preferably no greater than 30 mol %.
When the structural unit A contains the structural unit (A-3), the structural unit A preferably contains the structural unit (A-1) and the structural unit (A-3), and more preferably consists of the structural unit (A-1) and the structural unit (A-3).

The structural unit A may contain structural units other than the structural units (A-1) to (A-3) as long as the effects of the present invention are not impaired. The tetracarboxylic dianhydride that gives such a structural unit is not particularly limited, but may be pyromellitic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3, Examples of the tetracarboxylic acid dianhydride include aromatic tetracarboxylic acid dianhydrides such as 3'-biphenyltetracarboxylic acid dianhydride; alicyclic tetracarboxylic acid dianhydrides such as 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,2,4,5-cyclopentanetetracarboxylic acid dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, and dicyclohexyltetracarboxylic acid dianhydride; and aliphatic tetracarboxylic acid dianhydrides such as 1,2,3,4-butanetetracarboxylic 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 units other than the structural units (A-1) to (A-3) optionally contained in the structural unit A may be of one type, or of two or more types.
It is preferable that the structural unit A does not contain any structural units other than the structural units (A-1) to (A-3).

<Structural Unit B>
The structural unit B is a structural unit derived from a diamine in a polyimide resin, and includes at least one structural unit (B-1) selected from the group consisting of structural units derived from a compound represented by general formula (b1-1) below, and structural units derived from a compound represented by general formula (b2-1) below:

In formulae (b1-1) and (b2-1), X ¹ to X ⁴ each independently represent a single bond, an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, -S-, -SO-, -SO ₂ -, -O- or -CO-.
When the structural unit B contains the structural unit (B-1), the colorless transparency of the film is improved and the retardation value is reduced. The structural unit (B-1) may be one type or two or more types.

The compound represented by the general formula (b1-1) has a skeleton in which three benzene rings are linked via ^X1 and ^X2 , and ^X1 and ^X2 are bonded to the 1- and 3-positions of the central benzene ring, and the compound represented by the general formula (b2-1) has a skeleton in which three benzene rings are linked via ^X3 and ^X4 , and ^X3 and ^X4 are bonded to the 1- and 2-positions of the central benzene ring. By having such a skeleton structure in the structural unit B in the polyimide resin, it is possible to form a film with excellent low retardation.

In general formulae (b1-1) and (b2-1), X ¹ to X ⁴ each independently represent, from the viewpoint of forming a film having excellent low retardation, preferably an alkylidene group having 3 to 5 carbon atoms, -SO ₂ -, or -O-, more preferably an alkylidene group having 3 to 5 carbon atoms, or -O-, even more preferably an isopropylidene group, or -O-, and still more preferably an isopropylidene group.
^X1 and ^X2 in formula (b1-1) may each have a different group, but are preferably the same group. Similarly, ^X3 and ^X4 in formula (b2-1) may each have a different group, but are preferably the same group.
The amino group in general formulae (b1-1) and (b2-1) is preferably bonded to the para- or meta-position of the benzene ring relative to any one of X ¹ to X ⁴ bonded to the benzene ring to which the respective amino group is bonded.

The structural unit (B-1) preferably contains a structural unit derived from a compound represented by the above general formula (b1-1), and more preferably contains at least one structural unit selected from the group consisting of a structural unit derived from a compound represented by the following formula (b1-1-1), a structural unit derived from a compound represented by the following formula (b1-1-2), and a structural unit derived from a compound represented by the following formula (b1-1-3).

The compound represented by formula (b1-1-1) is 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene,
The compound represented by formula (b1-1-2) is 1,3-bis(4-aminophenoxy)benzene,
The compound represented by formula (b1-1-3) is 1,3-bis(3-aminophenoxy)benzene.

Among the compounds represented by formulas (b1-1-1) to (b1-1-3), at least one compound selected from the group consisting of compounds represented by formula (b1-1-1) and compounds represented by formula (b1-1-2) is preferred, and the compound represented by formula (b1-1-1) is more preferred.

The ratio of the structural unit (B-1) in the structural unit B is preferably 5 mol% or more, more preferably 15 mol% or more, even more preferably 45 mol% or more, and particularly preferably 75 mol% or more. There is no particular upper limit for the ratio of the structural unit (B-1), that is, it is 100 mol%. The structural unit B may be composed only of the structural unit (B-1).
The proportion of the structural unit (B-1) in the structural unit B is preferably from 5 to 100 mol %, more preferably from 15 to 100 mol %, even more preferably from 45 to 100 mol %, and particularly preferably from 75 to 100 mol %.
When the structural unit (B-1) contains a structural unit derived from the compound represented by formula (b1-1-1), the ratio of the structural unit derived from the compound represented by formula (b1-1-1) in the structural unit (B-1) is preferably 50 to 100 mol%, more preferably 75 to 100 mol%, even more preferably 90 to 100 mol%, and particularly preferably 95 to 100 mol%.

The structural unit B may contain a structural unit other than the structural unit (B-1). Such a structural unit is not particularly limited, but preferably contains at least one structural unit selected from the group consisting of the structural unit (B-2) derived from a compound represented by the following formula (b-2), the structural unit (B-3) derived from a compound represented by the following formula (b-3), and the structural unit (B-4) derived from a compound represented by the following formula (b-4).

The compound represented by formula (b-2) is 2,2-bis[4-(4-aminophenoxy)phenyl]propane,
The compound represented by formula (b-3) is 4,4'-diaminodiphenyl ether,
The compound represented by formula (b-4) is 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene.
When the structural unit B contains at least one structural unit selected from the group consisting of the structural units (B-2) to (B-4), it may contain two or more of the structural units (B-2) to (B-4), but it is preferable that the structural unit B contains one of the structural units (B-2) to (B-4). In other words, it is preferable that the structural unit B contains the structural unit (B-2), the structural unit (B-3), or the structural unit (B-4).

When structural unit B contains at least one structural unit selected from the group consisting of structural units (B-2) to (B-4), the total proportion of structural units (B-2) to (B-4) in structural unit B is preferably 5 to 95 mol%, more preferably 7 to 85 mol%, even more preferably 10 to 55 mol%, and particularly preferably 12 to 25 mol%.

The structural unit B may contain structural units other than the structural units (B-1) to (B-4). Diamines that provide such structural units are not particularly limited, but include 1,4-phenylenediamine, p-xylylenediamine, 3,5-diaminobenzoic acid, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminodiphenylsulfone, 4,4'-diaminobenzanilide, 3,4'-diaminodiphenylether, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-indene-5- amines, aromatic diamines such as N,N'-bis(4-aminophenyl)terephthalamide, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, and 9,9-bis(4-aminophenyl)fluorene, 1,4-bis(4-aminophenoxy)benzene; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine.
In this specification, 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) to (B-4) optionally contained in the structural unit B may be of one type, or of two or more types.
It is preferable that the structural unit B does not contain any structural units other than the structural units (B-1) to (B-4) described above.

The number average molecular weight of the polyimide resin of the present invention 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 of the present invention may contain a structure other than a polyimide chain (a structure formed by imide bonding between the structural unit A and the structural unit B). Examples of structures other than a polyimide chain that can be contained in the polyimide resin include a structure containing an amide bond.
The polyimide resin of the present invention preferably contains, as a main structure, a polyimide chain (a structure formed by imide bonding between the structural unit A and the structural unit B). Therefore, the ratio of the polyimide chain in the polyimide resin of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 99% by mass or more.

By using the polyimide resin of the present invention, a film which is excellent in colorless transparency and further has low retardation can be formed, and the preferable physical properties of the film are as follows.
The total light transmittance, when made into a film having a thickness of 30 μm, is preferably 85% or more, more preferably 87% or more, even more preferably 88% or more, and still more preferably 89% or more.
The haze, when formed into a film having a thickness of 30 μm, is preferably 2.0% or less, more preferably 1.5% or less, and further preferably 1.0% or less.
The yellow index (YI) when made into a film having a thickness of 30 μm is preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, and still more preferably 2.0 or less.
In the present invention, the thickness retardation (Rth) of the polyimide film is preferably 90 nm or less, more preferably 70 nm or less, even more preferably 50 nm or less, and even more preferably 30 nm or less. In this specification, "low retardation" means that the thickness retardation (Rth) is low, and preferably means that the thickness retardation (Rth) is within the above range.
The above-mentioned physical properties in the present invention can be specifically measured by the methods described in the Examples.

A film that can be formed by using the polyimide resin of the present invention has good heat resistance and mechanical properties, and has the following preferable physical properties.
The glass transition temperature (Tg) is preferably 200° C. or higher, more preferably 230° C. or higher, and even more preferably 250° C. or higher.
The tensile modulus is preferably 2.5 GPa or more, more preferably 3.0 GPa or more, and even more preferably 3.5 GPa or more.
The tensile strength is preferably 70 MPa or more, more preferably 90 MPa or more, and further preferably 100 MPa or more.
The tensile modulus and tensile strength are values measured in accordance with JIS K7127:1999.

[Method of producing polyimide resin]
The polyimide resin of the present invention can be produced by reacting a tetracarboxylic acid component containing at least one selected from the group consisting of compounds which provide the above-mentioned structural unit (A-1) and compounds which provide the above-mentioned structural unit (A-2), with a diamine component which contains a compound which provides the above-mentioned structural unit (B-1).

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. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydride represented by formula (a-1) 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).
Similarly, examples of 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).

The tetracarboxylic acid component preferably contains 50 mol% or more of the compound that gives the structural unit (A-1) and the compound that gives the structural unit (A-2) in total, 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 content of the compound that gives the structural unit (A-1) and the compound that gives the structural unit (A-2), that 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).

When the tetracarboxylic acid component contains a compound that gives the structural unit (A-1) or a compound that gives the structural unit (A-2), the compound that gives the structural unit (A-1) or the compound that gives the structural unit (A-2) is preferably contained in an amount of 45 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. The upper limit of the content of the compound that gives the structural unit (A-1) or the compound that gives the structural unit (A-2) is not limited, that is, it is 100 mol%. The tetracarboxylic acid component may consist only of a compound that gives the structural unit (A-1) or a compound that gives the structural unit (A-2), and it is preferable that the tetracarboxylic acid component consists only of a compound that gives the structural unit (A-1).

The tetracarboxylic acid component may contain a compound that gives the above-mentioned structural unit (A-3) within a range that does not impair the low retardation property.
Compounds that provide the structural unit (A-3) include, but are not limited to, compounds represented by formula (a-3), 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-3) and alkyl esters of the tetracarboxylic acid. Compounds that provide the structural unit (A-3) are preferably compounds represented by formula (a-3) (i.e., dianhydrides).

When the tetracarboxylic acid component contains a compound that gives the structural unit (A-3), it preferably contains 55 mol % or less, more preferably 30 mol % or less, of the compound that gives the structural unit (A-3). When the tetracarboxylic acid component contains a compound that gives the structural unit (A-3), it is preferable that the tetracarboxylic acid component consists only of the compound that gives the structural unit (A-1) and the compound that gives the structural unit (A-3).

The tetracarboxylic acid component may contain a compound other than the compound that provides the structural unit (A-1), the compound that provides the structural unit (A-2), and the compound that provides the structural unit (A-3). Examples of such 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 that gives the structural units (A-1) to (A-3) that is 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 compounds represented by general formula (b1-1) and compounds represented by general formula (b2-1), but are not limited thereto, and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compounds represented by general formula (b1-1) and diisocyanates corresponding to the diamines represented by general formula (b2-1). As a compound that provides the structural unit (B-1), at least one compound (i.e., a diamine) selected from the group consisting of compounds represented by general formula (b1-1) and compounds represented by general formula (b2-1) is preferred.

The compound that provides the structural unit (B-1) preferably includes a compound represented by general formula (b1-1), more preferably includes at least one compound selected from the group consisting of compounds represented by formula (b1-1-1), compounds represented by formula (b1-1-2), and compounds represented by formula (b1-1-3), even more preferably includes at least one compound selected from the group consisting of compounds represented by formula (b1-1-1) and compounds represented by formula (b1-1-2), and particularly preferably includes a compound represented by formula (b1-1-1).

The diamine component contains the compound that gives the structural unit (B-1) in an amount of preferably 5 mol % or more, more preferably 15 mol % or more, even more preferably 45 mol % or more, and particularly preferably 75 mol % or more. There is no particular upper limit to the content of the compound that gives the structural unit (B-1), that is, it is 100 mol %. The diamine component may consist of only the compound that gives the structural unit (B-1).
When the compound that provides the structural unit (B-1) contains a compound represented by formula (b1-1-1), the ratio of the compound represented by formula (b1-1-1) in the compound that provides the structural unit (B-1) is preferably 50 to 100 mol %, more preferably 75 to 100 mol %, even more preferably 90 to 100 mol %, and particularly preferably 95 to 100 mol %.

The diamine component may contain at least one compound selected from the group consisting of compounds that provide the above-mentioned structural unit (B-2), compounds that provide the above-mentioned structural unit (B-3), and compounds that provide the above-mentioned structural unit (B-4), within a range that does not impair the physical properties of colorless transparency and low retardation.
Compounds that give the structural units (B-2) to (B-4) include compounds represented by formulas (b-2) to (b-4), respectively, but are not limited thereto and may be derivatives thereof as long as they give the same structural units. Examples of such derivatives include diisocyanates corresponding to the diamines represented by formulas (b-2) to (b-4). Compounds that give the structural units (B-2) to (B-4) are preferably compounds represented by formulas (b-2) to (b-4), respectively (i.e., diamines).

When the diamine component contains a compound that provides at least one structural unit selected from the group consisting of structural units (B-2) to (B-4), it may contain compounds that provide two or more structural units among the structural units (B-2) to (B-4), but it is preferable that the diamine component contains a compound that provides one structural unit among the structural units (B-2) to (B-4). In other words, it is preferable that the structural unit B contains a compound that provides the structural unit (B-2), a compound that provides the structural unit (B-3), or a compound that provides the structural unit (B-4).

When the diamine component contains a compound that provides at least one structural unit selected from the group consisting of structural units (B-2) to (B-4), the diamine component contains the compound in an amount of preferably 5 to 95 mol %, more preferably 7 to 85 mol %, even more preferably 10 to 55 mol %, and particularly preferably 12 to 25 mol %.

The diamine component may contain compounds other than the compounds that provide the structural units (B-1) to (B-4). Examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, as well as derivatives thereof (diisocyanates, etc.).
The compound other than the compound that gives the structural units (B-1) to (B-4) that is optionally contained in the diamine component may be one type, or two or more types.

In the present invention, the ratio of the amounts 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, 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, N-methylcaprolactam, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone-based solvents such as γ-butyrolactone 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, methyl ethyl ketone, 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, 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 one or more selected from triethylamine and triethylenediamine, and it is particularly preferable to use triethylamine or 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.

[Polyimide varnish]
The polyimide varnish of the present invention is obtained by dissolving the polyimide resin of the present invention in an organic solvent. That is, the polyimide varnish of the present invention contains the polyimide resin of the present invention and an organic solvent, and 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 of the present invention may be a polyimide solution itself in which a polyimide resin obtained by polymerization is dissolved in a reaction solvent, or may be a polyimide solution to which a dilution solvent is further added.
The polyimide varnish of the present invention may be prepared by dissolving the polyimide resin of the present invention in a low-boiling point solvent having a boiling point of 130° C. or less. By using the low-boiling point solvent as the organic solvent, the heating temperature during the production of the polyimide film described below can be lowered. Examples of the low-boiling point solvent include carbon tetrachloride, dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran, and acetone, and among these, dichloromethane is preferred.

Since the polyimide resin of the present invention has solvent solubility, it can be made into a highly concentrated varnish that is stable at room temperature. The polyimide varnish of the present invention preferably contains 5 to 40 mass %, more preferably 10 to 30 mass %, of the polyimide resin of the present invention. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, more preferably 5 to 150 Pa·s. The viscosity of the polyimide varnish is a value measured at 25°C using an E-type viscometer.
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 contains the polyimide resin of the present invention. Therefore, the polyimide film of the present invention is excellent in colorless transparency and low retardation. The preferable physical properties 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, and known methods can be used. For example, the polyimide varnish of the present invention is applied to a smooth support such as a glass plate, a metal plate, or a plastic plate, or formed into a film, and then the organic solvents contained in the varnish, such as a reaction solvent or a dilution solvent, are removed by heating. If necessary, a release agent may be applied to the surface of the support in advance.
The following method is preferred as a method for removing the organic solvent contained in the varnish by heating. That is, it is preferred to evaporate the organic solvent at a temperature of 120° C. or less to form a self-supporting film, and then peel the self-supporting film from the support, fix the ends of the self-supporting film, and dry at a temperature equal to or higher than the boiling point of the organic solvent used to produce a polyimide film. It is also preferred to dry under a nitrogen atmosphere. The pressure of the drying atmosphere may be reduced pressure, normal pressure, or pressurized. The heating temperature when drying the self-supporting film to produce a polyimide film is not particularly limited, but is preferably 200 to 400° C.
When the organic solvent contained in the polyimide varnish of the present invention is a low-boiling point solvent having a boiling point of 130° C. or less, the heating temperature of the self-supporting film is preferably 100 to 180° C. Furthermore, it is preferable to subject the polyimide film obtained by removing the low-boiling point solvent to an annealing treatment in which the polyimide film is further heated at a temperature equal to or higher than the glass transition temperature.

The polyimide film of the present invention can also be produced by using a polyamic acid varnish prepared by dissolving a polyamic acid 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 at least one selected from the group consisting of a compound that gives the above-mentioned structural unit (A-1) and a compound that gives the above-mentioned structural unit (A-2), and a diamine component containing a compound that gives the above-mentioned structural unit (B-1). The polyamic acid is imidized (dehydration ring closure) to obtain the final product, the polyimide resin of the present invention.
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 at least one selected from the group consisting of compounds which provide the above-mentioned structural unit (A-1) and compounds which provide the above-mentioned structural unit (A-2) to a polyaddition reaction in a reaction solvent with a diamine component containing a compound which provides the above-mentioned structural unit (B-1), or may be a polyamic acid solution to which a dilution solvent has been further added.

The method for producing a polyimide film using the polyamic acid varnish is not particularly limited, 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 plate, or formed into a film, and the organic solvent contained in the varnish, such as a reaction solvent or a dilution solvent, is removed by heating to obtain a polyamic acid film, and the polyamic acid in the polyamic acid film is imidized by heating, 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 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 280° 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), and haze The total light transmittance, YI, and haze were measured using a color and turbidity simultaneous measuring instrument "COH400" manufactured by Nippon Denshoku Industries Co., Ltd. The total light transmittance and YI were measured in accordance with JIS K7361-1:1997, and the haze was measured in accordance with JIS K7136:2000. (4) Thickness retardation (Rth)
The thickness retardation (Rth) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The thickness retardation value was measured at a measurement wavelength of 550 nm. Rth is expressed by the following formula, where the maximum in-plane refractive index of the polyimide film is nx, the minimum is ny, the refractive index in the thickness direction is nz, and the thickness of the film is d.
Rth = [{(nx + ny) / 2} - nz] x d

The tetracarboxylic acid components and diamine components used in the examples and comparative examples, as well as their abbreviations, are as follows:
<Tetracarboxylic acid component>
HPMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (a-1))
CpODA: norbornane-2-spiro-α-cyclopentanone-α'-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (manufactured by JXTG Energy Corporation; compound represented by formula (a-3))
<Diamine component>
BisAM: 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene (manufactured by Mitsui Fine Chemicals, Inc., a compound represented by formula (b1-1-1))
TPER: 1,3-bis(4-aminophenoxy)benzene (manufactured by Wakayama Seika Kogyo Co., Ltd., a compound represented by formula (b1-1-2))
APBN: 1,3-bis(3-aminophenoxy)benzene (manufactured by Mitsui Chemicals, Inc., a compound represented by formula (b1-1-3))
TPEQ: 1,4-bis(4-aminophenoxy)benzene (manufactured by Wakayama Seika Kogyo Co., Ltd.)
3,5-DABA: 3,5-diaminobenzoic acid (manufactured by Nippon Junryo Pharmaceutical Co., Ltd.)
BAPA: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (manufactured by Wakayama Seika Kogyo Co., Ltd.)
ODA: 4,4'-diaminodiphenyl ether (manufactured by Wakayama Seika Kogyo Co., Ltd., a compound represented by formula (b-3))
BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (manufactured by Wakayama Seika Kogyo Co., Ltd., a compound represented by formula (b-2))
3,4'-DPE: 3,4'-diaminodiphenyl ether (manufactured by Wakayama Seika Kogyo Co., Ltd.)
BisAP: 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene (manufactured by Mitsui Fine Chemicals, Inc., a compound represented by formula (b-4))

Details of the solvents and catalysts used in the examples and comparative examples are as follows.
γ-Butyrolactone (Mitsubishi Chemical Corporation)
N,N-Dimethylacetamide (Mitsubishi Gas Chemical Company, Inc.)
Triethylenediamine (Tokyo Chemical Industry Co., Ltd.)
Triethylamine (Kanto Chemical Co., Ltd.)

Example 1
A 0.3 L 5-neck glass round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark apparatus equipped with a cooling tube, a thermometer, and a glass end cap was used as the reaction apparatus. In the round-bottom flask, 25.920 g (0.075 mol) of BisAM, 35.0 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation), and 0.048 g of triethylenediamine and 3.80 g of triethylamine were placed, and the mixture was heated to 70° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. To this solution, 16.830 g (0.075 mol) of HPMDA and 17.1 g of γ-butyrolactone were added in one lump, and then the mixture was heated with a mantle heater, and the temperature in the reaction system was raised to 200° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 200° C. for 5.5 hours. After adding 67.71 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a homogeneous polyimide varnish having a solid content concentration of 25% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 30 μm. The evaluation results of this polyimide film are shown in Table 1.

Example 2
Using the same reaction apparatus as in Example 1, 24.899 g (0.085 mol) of APBN, 40.0 g of γ-butyrolactone, and 4.30 g of triethylamine as a catalyst were placed in a round-bottom flask, and the temperature was raised to 70 ° C. while stirring at 150 rpm under a nitrogen atmosphere to obtain a solution. To this solution, 19.074 g (0.085 mol) of HPMDA and 13.7 g of γ-butyrolactone were added in one lump, and then the reaction system temperature was raised to 190 ° C. over about 20 minutes by heating with a mantle heater. The components distilled off were collected, and the reaction system temperature was maintained at 190 ° C. for 3.3 hours. After adding 41.6 g of N,N-dimethylacetamide, the mixture was stirred at about 100 ° C. for about 1 hour to obtain a uniform polyimide varnish with a solid content concentration of 30% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 47 μm. The evaluation results of this polyimide film are shown in Table 1.

Example 3
Using the same reaction apparatus as in Example 1, 24.337 g (0.083 mol) of TPER, 45.1 g of γ-butyrolactone, and 2.11 g of triethylamine as a catalyst were placed in a round-bottom flask, and the mixture was heated to 70 ° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. To this solution, 18.701 g (0.083 mol) of HPMDA and 19.4 g of N,N-dimethylacetamide were added in one lump, and then the mixture was heated with a mantle heater to raise the temperature in the reaction system 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. for 2.7 hours. After adding 64.5 g of N,N-dimethylacetamide, the mixture was stirred at about 100 ° C. for about 1 hour to obtain a uniform polyimide varnish with a solid content concentration of 24 mass%.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 31 μm. The evaluation results of this polyimide film are shown in Table 1.

<Comparative Example 1>
Using the same reaction apparatus as in Example 1, 23.370 g (0.080 mol) of TPEQ, 40.4 g of γ-butyrolactone, and 0.41 g of triethylamine as a catalyst were placed in a round-bottom flask, and the temperature was raised to 80 ° C. while stirring at 150 rpm under a nitrogen atmosphere to obtain a solution. To this solution, 17.934 g (0.080 mol) of HPMDA and 10.1 g of γ-butyrolactone were added in one lump, and then the reaction system temperature was raised to 200 ° C. over about 20 minutes by heating with a mantle heater. The components distilled off were collected, and the reaction system temperature was maintained at 200 ° C. for 2.5 hours. After adding 103.3 g of N,N-dimethylacetamide, the mixture was stirred at about 100 ° C. for about 1 hour to obtain a uniform polyimide varnish with a solid content concentration of 20 mass%.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 18 μm. The evaluation results of this polyimide film are shown in Table 1.

<Comparative Example 2>
Using the same reaction apparatus as in Example 1, 28.559 g (0.188 mol) of 3,5-DABA, 132.1 g of γ-butyrolactone, and 0.95 g of triethylamine as a catalyst were placed in a round-bottom flask, and the mixture was heated to 70° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. 42.132 g (0.188 mol) of HPMDA and 33.03 g of γ-butyrolactone were added to the solution in a lump, and then the mixture was heated with a mantle heater to raise the temperature in the reaction system 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. for 5.0 hours. After adding 90.86 g of γ-butyrolactone, the mixture was stirred at about 100° C. for about 1 hour to obtain a uniform polyimide varnish with a solid content concentration of 20% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C for 20 minutes in an air atmosphere to remove the solvent, yielding a film with a thickness of 29 μm. The evaluation results of this polyimide film are shown in Table 1.

<Comparative Example 3>
Using the same reaction apparatus as in Example 1, 42.278 g (0.115 mol) of BAPA, 81.8 g of γ-butyrolactone, and 0.58 g of triethylamine as a catalyst were placed in a round-bottom flask, and the mixture was heated to 70 ° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. 25.877 g (0.115 mol) of HPMDA and 20.4 g of γ-butyrolactone were added to the solution in one lump, and then the mixture was heated with a mantle heater to raise the temperature in the reaction system 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. for 5.0 hours. After adding 153.8 g of γ-butyrolactone, the mixture was stirred at about 100 ° C. for about 1 hour to obtain a uniform polyimide varnish with a solid content concentration of 20% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 26 μm. The evaluation results of this polyimide film are shown in Table 1.

<Comparative Example 4>
Using the same reaction apparatus as in Example 1, 20.024 g (0.100 mol) of ODA, 45.0 g of γ-butyrolactone, and 1.52 g of triethylamine as a catalyst were placed in a round-bottom flask, and the mixture was heated to 70° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. 22.417 g (0.100 mol) of HPMDA and 18.7 g of γ-butyrolactone were added to the solution in a lump, and the mixture was heated with a mantle heater to raise the temperature in the reaction system to 200° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 200° C. for 4.0 hours. 91.7 g of N,N-dimethylacetamide was added, and the mixture was stirred at about 100° C. for about 1 hour to obtain a uniform polyimide varnish with a solid content concentration of 20% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 40 μm. The evaluation results of this polyimide film are shown in Table 1.

<Comparative Example 5>
Using the same reaction apparatus as in Example 1, 43.745 g (0.107 mol) of BAPP, 81.4 g of γ-butyrolactone, and 0.54 g of triethylamine as a catalyst were placed in a round-bottom flask, and the temperature was raised to 70 ° C. while stirring at 150 rpm under a nitrogen atmosphere to obtain a solution. 23.887 g (0.107 mol) of HPMDA and 20.3 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added to this solution all at once, and then the solution was heated with a mantle heater to raise the temperature in the reaction system 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. for 4.0 hours. After adding 154.2 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation), the mixture was stirred at about 100 ° C. for about 1 hour to obtain a uniform polyimide varnish with a solid content concentration of 20% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C for 20 minutes in an air atmosphere to remove the solvent, yielding a film with a thickness of 33 μm. The evaluation results of this polyimide film are shown in Table 1.

<Comparative Example 6>
Using the same reaction apparatus as in Example 1, 20.024 g (0.100 mol) of 3,4'-DPE, 45.0 g of γ-butyrolactone, and 0.065 g of triethylenediamine and 1.52 g of triethylamine as catalysts were added in a round-bottom flask, and the temperature was raised to 70 ° C. while stirring at 150 rpm under a nitrogen atmosphere to obtain a solution. 22.417 g (0.100 mol) of HPMDA and 18.7 g of γ-butyrolactone were added to this solution in one lump, and then the solution was heated with a mantle heater to raise the temperature in the reaction system to 200 ° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 200 ° C. for 4.0 hours. After adding 91.7 g of N,N-dimethylacetamide, the mixture was stirred at about 100 ° C. for about 1 hour to obtain a uniform polyimide varnish with a solid content concentration of 20% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C for 20 minutes in an air atmosphere to remove the solvent, yielding a film with a thickness of 25 μm. The evaluation results of this polyimide film are shown in Table 1.

Example 4
Using the same reaction apparatus as in Example 1, 14.417 g (0.072 mol) of ODA, 6.201 g (0.018 mol) of BisAM, 40.0 g of γ-butyrolactone, and 0.050 g of triethylenediamine and 4.55 g of triethylamine as catalysts were placed in a round-bottom flask, and the mixture was heated to 70° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. 20.175 g (0.090 mol) of HPMDA and 10.0 g of γ-butyrolactone were added to the solution in a lump, and the mixture was heated with a mantle heater to raise the temperature in the reaction system to 200° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 200° C. for 0.7 hours. After adding 38.0 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a homogeneous polyimide varnish having a solid content concentration of 30% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 42 μm. The evaluation results of this polyimide film are shown in Table 1.

Example 5
Using the same reaction apparatus as in Example 1, 10.012 g (0.050 mol) of ODA, 17.225 g (0.050 mol) of BisAM, 48.7 g of γ-butyrolactone, and 0.056 g of triethylenediamine and 5.06 g of triethylamine as catalysts were placed in a round-bottom flask, and the mixture was heated to 70° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. 22.417 g (0.10 mol) of HPMDA and 12.2 g of γ-butyrolactone were added to the solution in a lump, and the mixture was heated with a mantle heater to raise the temperature in the reaction system to 200° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 200° C. for 0.6 hours. After adding 77.8 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a homogeneous polyimide varnish having a solid content concentration of 25% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 34 μm. The evaluation results of this polyimide film are shown in Table 1.

Example 6
As a reaction apparatus, a 3.0 L apparatus similar to that in Example 1 was used, and 23.228 g (0.116 mol) of ODA, 159.848 g (0.464 mol) of BisAM, 307.0 g of γ-butyrolactone, and 0.325 g of triethylenediamine and 29.345 g of triethylamine as catalysts were placed in a round-bottom flask, and the mixture was heated to 70° C. while stirring at 150 rpm under a nitrogen atmosphere to obtain a solution. 130.019 g (0.580 mol) of HPMDA and 76.8 g of γ-butyrolactone were added to this solution in one lump, and then the mixture was heated with a mantle heater, and the temperature in the reaction system was raised to 200° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 200° C. for 2.0 hours. After adding 300.0 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a homogeneous polyimide varnish having a solid content concentration of 30% by mass.

The resulting polyimide varnish was then applied to a PET substrate and the temperature was gradually increased, with the maximum temperature being held at 140°C for approximately 2 minutes to volatilize the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 32 μm. The evaluation results of this polyimide film are shown in Table 1.

Example 7
Using the same reaction apparatus as in Example 1, 27.259 g (0.066 mol) of BAPP, 5.719 g (0.017 mol) of BisAM, 50.6 g of γ-butyrolactone, and 0.047 g of triethylenediamine and 4.20 g of triethylamine as catalysts were placed in a round-bottom flask, and the mixture was heated to 70° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. To this solution, 18.606 g (0.083 mol) of HPMDA and 12.6 g of γ-butyrolactone were added in one lump, and then the mixture was heated with a mantle heater, and the temperature in the reaction system was raised to 200° C. over about 20 minutes. The components distilled off were collected, and the temperature in the reaction system was maintained at 200° C. for 0.5 hours. After adding 83.0 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a homogeneous polyimide varnish having a solid content concentration of 25% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 47 μm. The evaluation results of this polyimide film are shown in Table 1.

Example 8
Using the same reaction apparatus as in Example 1, 16.421 g (0.040 mol) of BAPP, 13.780 g (0.040 mol) of BisAM, 40.0 g of γ-butyrolactone, and 0.044 g of triethylenediamine and 4.05 g of triethylamine as catalysts were placed in a round-bottom flask, and the mixture was heated to 70 ° C. while stirring at 150 rpm under a nitrogen atmosphere to obtain a solution. To this solution, 17.934 g (0.080 mol) of HPMDA and 18.8 g of γ-butyrolactone were added in one lump, and then 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. for 2.2 hours. After adding 122.2 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a homogeneous polyimide varnish having a solid content concentration of 20% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 30 μm. The evaluation results of this polyimide film are shown in Table 1.

<Example 9>
Using the same reaction apparatus as in Example 1, 6.568 g (0.016 mol) of BAPP, 22.048 g (0.064 mol) of BisAM, 30.0 g of γ-butyrolactone, and 0.044 g of triethylenediamine and 4.05 g of triethylamine as catalysts were placed in a round-bottom flask, and the mixture was heated to 70° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. To this solution, 17.934 g (0.080 mol) of HPMDA and 16.6 g of γ-butyrolactone were added in one lump, and then the mixture was heated with a mantle heater to raise the temperature in the reaction system 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. for 1.4 hours. After adding 84.4 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a homogeneous polyimide varnish having a solid content concentration of 25% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 35 μm. The evaluation results of this polyimide film are shown in Table 1.

Example 10
Using the same reaction apparatus as in Example 1, 27.560 g (0.080 mol) of BisAM, 30.8 g of γ-butyrolactone, and 0.022 g of triethylenediamine and 2.02 g of triethylamine as catalysts were placed in a round-bottom flask, and the mixture was heated to 70° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. 8.967 g (0.040 mol) of HPMDA, 15.375 g (0.040 mol) of CpODA, and 32.9 g of γ-butyrolactone were added to the solution in a lump, and the mixture was heated with a mantle heater to raise the temperature in the reaction system 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. for 2.0 hours. After adding 88.0 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a homogeneous polyimide varnish having a solid content concentration of 25% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C for 20 minutes in an air atmosphere to remove the solvent, yielding a film with a thickness of 38 μm. The evaluation results of this polyimide film are shown in Table 1.

Example 11
Using the same reaction apparatus as in Example 1, 13.780 g (0.040 mol) of BisAP, 13.780 g (0.040 mol) of BisAM, 40.0 g of γ-butyrolactone, and 0.044 g of triethylenediamine and 4.05 g of triethylamine as catalysts were placed in a round-bottom flask, and the mixture was heated to 70° C. under a nitrogen atmosphere while stirring at 150 rpm to obtain a solution. 17.934 g (0.080 mol) of HPMDA and 15.6 g of γ-butyrolactone were added to this solution in one lump, and then the mixture was heated with a mantle heater to raise the temperature in the reaction system 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. for 3.5 hours. After adding 114.8 g of N,N-dimethylacetamide, the mixture was stirred at about 100° C. for about 1 hour to obtain a homogeneous polyimide varnish having a solid content concentration of 20% by mass.

The resulting polyimide varnish was then applied to a PET substrate and held at 100°C for 20 minutes to evaporate the solvent, yielding a colorless, transparent, self-supporting primary dried film. The film was then fixed to a stainless steel frame and dried at 210°C in an air atmosphere for 20 minutes to remove the solvent, yielding a film with a thickness of 35 μm. The evaluation results of this polyimide film are shown in Table 1.

As shown in Table 1, the polyimide films of Examples 1 to 11 produced using a specific tetracarboxylic acid component and a specific diamine component were excellent in colorless transparency and had low retardation.
On the other hand, the polyimide films of Comparative Examples 1 to 6, which did not use a diamine that provides the structural unit (B-1) as the diamine component, had a large retardation value (Rth) compared to the polyimide films of Examples 1 to 3.
The polyimide films of Examples 4 to 6, which used BisAM and ODA in combination as the diamine acid components, had significantly reduced retardation values (Rth) compared to the polyimide film of Comparative Example 4, which was produced using only ODA.
The polyimide films of Examples 7 to 9, which used BisAM and BAPP in combination as the diamine acid components, had significantly reduced retardation values (Rth) compared to the polyimide film of Comparative Example 5, which was produced using only BAPP.

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.

Claims (6)

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 includes a structural unit (A-1) derived from a compound represented by the following formula (a-1):
The structural unit B includes a structural unit (B-1) derived from a compound represented by the following general formula (b1-1-1):
At least one of the structural unit A and the structural unit B contains two or more types of structural units,
When the structural unit A contains two or more types of structural units, the structural unit A further contains a structural unit (A-3) derived from a compound represented by the following formula (a-3) as a structural unit other than the structural unit (A-1):
A polyimide resin in which, when the structural unit B contains two or more types of structural units, the structural unit B further contains, as a structural unit other than the structural unit (B-1), 5 to 55 mol % of at least one structural unit selected from the group consisting of a structural unit (B-2) derived from a compound represented by the following formula (b-2), a structural unit (B-3) derived from a compound represented by the following formula (b-3), and a structural unit (B-4) derived from a compound represented by the following formula (b-4):

The polyimide resin according to claim 1, in which the ratio of structural unit (B-1) in structural unit B is 5 to 100 mol %. The polyimide resin according to claim 1 or 2, wherein the structural unit A contains the structural unit (A-1) and the ratio of the structural unit (A-1) in the structural unit A is 45 to 100 mol %. The polyimide resin according to any one of claims 1 to 3 , wherein the total proportion of the structural units (B-2), (B-3), and (B-4) in the structural unit B is 5 to 55 mol %. A polyimide varnish obtained by dissolving the polyimide resin according to any one of claims 1 to 4 in an organic solvent. A polyimide film comprising the polyimide resin according to any one of claims 1 to 4.