TWI789432B - Polyimide, polyimide varnish and polyimide film - Google Patents

Abstract

This invention provides a polyimide having a constituting unit A that comprises a constituting unit (A-1) derived from a compound represented by the formula (a-1) and a constituting unit (A-2) derived from a compound represented by the formula (a-2), and a constituting unit B that comprises a constituting unit (B-1) derived from a compound represented by the formula (b-1) and a constituting unit (B-2) derived from a compound represented by the formula (b-2). This polyimide can form a polyimide varnish and a polyimide film containing the polyimide, wherein the film has a low linear thermal expansion coefficient while maintaining high transparency and high heat resistance. This invention also provides a polyimide varnish and a polyimide film containing the polyimide.

Description

Polyimide, polyimide varnish and polyimide film

The present invention relates to polyimide, and polyimide varnish and polyimide film containing the polyimide.

In addition to its excellent heat resistance, polyimide also has excellent characteristics such as mechanical properties, chemical resistance, and electrical properties. Therefore, films made of polyimide are widely used in molding materials, composite materials, electrical- In the fields of electronic components and display devices, etc. In the field of display devices, researches on reducing the weight, thickness, and flexibility of display devices by using plastic substrates instead of glass substrates are actively underway. However, for example, when an electronic component made of an inorganic material is formed on a thin film, since the linear thermal expansion coefficient of the inorganic material and the thin film are significantly different, sometimes the thin film formed with the electronic component made of the inorganic material is bent, or even made of the inorganic material. The case where an electronic component made of a material peels off from the film. Therefore, in addition to transparency and heat resistance, polyimide films are also required to have a low coefficient of linear thermal expansion.

Generally speaking, it is known that the polymer chain of polyimide is rigid, and the higher the linearity, the lower the coefficient of linear thermal expansion. Therefore, in order to reduce the linear thermal expansion coefficient of polyimide and improve dimensional stability, various structures of both acid dianhydride and diamine which are raw materials of polyimide have been proposed.

For example, Patent Document 1 discloses 4,4'-(hexafluoroisopropylidene)diphthalic acid as an acid component, and 4,4'-diamino-2,2'-bis(trifluoro Methyl)biphenyl is a polyimide as a diamine component. [Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese National Publication No. 2012-503701

[Problem to be Solved by the Invention]

However, although the polyimide disclosed in Patent Document 1 is excellent in transparency and heat resistance, its coefficient of linear thermal expansion has not reached a satisfactory level, and further improvement is necessary. That is, the problem to be solved by the present invention is to provide a polyimide capable of forming a film having a low linear thermal expansion coefficient while maintaining high transparency and high heat resistance, and a polyimide varnish containing the polyimide and polyimide film. [Means to solve the problem]

As a result of diligent research by the inventors, it was found that polyimide having a specific structural unit can form a film having a low coefficient of linear thermal expansion while maintaining high transparency and high heat resistance. The present invention has been accomplished based on these findings. That is, the present invention relates to the following [1] to [3]. [1] A polyimide having a constituent unit A derived from a tetracarboxylic acid or a derivative thereof and a constituent unit B derived from a diamine; The constitutional unit A contains a constitutional unit (A-1) derived from a compound represented by the following formula (a-1), and a constitutional unit (A-2) derived from a compound represented by the following formula (a-2); 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).

【化2】

【Chemical 1】

【Chemical 2】

In formula (b-1), R each independently represents a hydrogen atom, a fluorine atom, or a methyl group. [2] A polyimide varnish obtained by dissolving the polyimide described in [1] above in an organic solvent. [3] A polyimide film comprising the polyimide of the aforementioned [1]. [Effect of Invention]

According to the present invention, polyimide capable of forming a film having low linear thermal expansion coefficient while maintaining high transparency and high heat resistance, and polyimide varnish and polyimide film containing the polyimide can be provided .

[Polyimide] The polyimide of the present invention is the following polyimide: Having a constituent unit A derived from tetracarboxylic acid or its derivative and a constituent unit B derived from diamine, And the structural unit A contains a structural unit (A-1) derived from a compound represented by the above formula (a-1) and a structural unit (A-2) derived from a compound represented by the above formula (a-2), Structural unit B contains a structural unit (B-1) derived from a compound represented by the above formula (b-1) and a structural unit (B-2) derived from a compound represented by the above formula (b-2). The polyimide of the present invention can be formed with a low line by having specific constitutional unit (A-1), constitutional unit (A-2), constitutional unit (B-1), and constitutional unit (B-2). The coefficient of thermal expansion of the film.

[Constituent Unit A] The structural unit A contained in the polyimide of this invention is a structural unit derived from tetracarboxylic acid or its derivative. Tetracarboxylic acid or its derivative(s) can be used individually or in combination of 2 or more types. As a derivative of tetracarboxylic acid, the acid anhydride or alkyl ester of tetracarboxylic acid is mentioned. For the alkyl ester of tetracarboxylic acid, the carbon number of the alkyl group is preferably 1-3, for example, dimethyl ester, diethyl ester and dipropyl ester of tetracarboxylic acid can be mentioned. Tetracarboxylic acid or derivatives thereof are preferably tetracarboxylic dianhydrides. The structural unit A in this invention contains the structural unit (A-1) derived from the compound represented by following formula (a-1). The compound represented by formula (a-1) is biphenyltetracarboxylic dianhydride. When the structural unit A contains the structural unit (A-1), the heat resistance, mechanical properties (elastic modulus), and organic solvent resistance of the polyimide are improved.

【Chemical 3】

Compounds represented by the formula (a-1) include: 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) represented by the following formula (a-1-1), the following formula (a 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA) represented by -1-2), and 2,2',3,3 represented by the following formula (a-1-3) Among them, '-biphenyltetracarboxylic dianhydride (i-BPDA) is preferably 3,3',4,4'-biphenyltetracarboxylic dianhydride represented by the following formula (a-1-1). The compound represented by formula (a-1) can be used individually or in combination of 2 or more types. s-BPDA is preferable from the viewpoint of organic solvent resistance, and a-BPDA and i-BPDA are preferable from the viewpoint of heat resistance and solution processability.

【Chemical 4】

The ratio of the constituent unit (A-1) to the constituent unit A is preferably 50 mol% or more, more preferably 55 mol% or more from the viewpoint of heat resistance, mechanical properties (elastic modulus), and organic solvent resistance , preferably more than 60 mol%, more preferably more than 65 mol%, and more preferably more than 70 mol%, and preferably less than 99 mol%, more preferably less than 95 mol%. It is 90 mol% or less, more preferably 85 mol% or less, and especially preferably 80 mol% or less.

Structural unit A contains a structural unit (A-2) derived from a compound represented by the following formula (a-2). 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 to the organic solvent is improved.

【Chemical 5】

The ratio of the constituent unit (A-2) to the constituent unit A is preferably at least 1 mol%, more preferably at least 5 mol%, and most preferably at least 10 mol% from the viewpoint of solubility and high transparency , and more preferably at least 15 mol%, and more preferably at least 20 mol%, and, considering high heat resistance, it is preferably less than 50 mol%, more preferably less than 45 mol%. 40 mol% or less, more preferably 35 mol% or less, and especially preferably 30 mol% or less.

The ratio of the constituent unit (A-1) and the constituent unit (A-2) to the constituent unit A is preferably 50 to 99 mole % for the constituent unit (A-1) and 1 to 99 mole % for the constituent unit (A-2). 50 mol%, more preferably 55-95 mol% for the constituent unit (A-1), 5-45 mol% for the constituent unit (A-2), especially preferably 60% for the constituent unit (A-1) ～90 mol%, the constituent unit (A-2) is 10～40 mol%, and more preferably the constituent unit (A-1) is 65～85 mol%, and the constituent unit (A-2) is 15～40 mol%. 35 mol%, and more preferably 70 to 80 mol% for the constituent unit (A-1), and 20 to 30 mol% for the constituent unit (A-2). The molar ratio [(A-1)/(A-2)] of the constituent unit (A-1) to the constituent unit (A-2) should be 50/50 in consideration of low linear thermal expansion coefficient and high transparency ~99/1, more preferably 55/45~95/5, more preferably 60/40~90/10, more preferably 65/35~85/15, more preferably 70/30~80/20 .

With regard to the polyimide of the present invention, within the scope of not impairing the effect of the present invention, the compound derived from the compound represented by the formula (a-1) and the compound represented by the formula (a-2) may also be contained in the constituent unit A. Structural units of other tetracarboxylic acids or derivatives thereof are preferably contained as structural units other than the aforementioned structural unit (A-1) and structural unit (A-2). The proportion of the total of the constituent unit (A-1) and the constituent unit (A-2) in the constituent unit A is preferably 70 mol% from the viewpoint of low linear thermal expansion coefficient, high transparency, and resistance to organic solvents More than 85 mol%, more preferably 99 mol%, more preferably 100 mol%.

[Constituent unit B] The structural unit B contained in the polyimide of this invention is a structural unit derived from a diamine. The aforementioned structural unit B contains a structural unit (B-1) derived from a compound represented by the following formula (b-1).

【Chemical 6】

In the above formula (b-1), R is each independently selected from the group consisting of a hydrogen atom, a fluorine atom, and a methyl group, and is preferably a hydrogen atom. Compounds represented by the above formula (b-1) include: 9,9-bis(4-aminophenyl) fluorine, 9,9-bis(3-fluoro-4-aminophenyl) fluorine, and 9, 9-bis(3-methyl-4-aminophenyl) fluorine, etc., preferably at least one selected from the group consisting of these 3 compounds, is 9,9-bis(4-aminophenyl Base) fenugreek is better. The polyimide of this invention improves transparency and heat resistance by containing the said structural unit (B-1). In the present invention, the ratio of the constituent unit (B-1) to the constituent unit B is preferably 50 mol% or less, more preferably 40 mol% or less, most preferably 35 mol% in view of the low linear thermal expansion coefficient % or less, more preferably 30 mol % or less, and especially preferably 25 mol % or less, and considering high transparency and high heat resistance, it is preferably 5 mol % or more, more preferably 10 mol % % or more, preferably more than 15 mol%, and more preferably more than 20 mol%.

The structural unit B in this invention contains the structural unit (B-2) derived from the compound represented by following formula (b-2).

【Chemical 7】

The compound represented by the above formula (b-2) is 2,2'-bis(trifluoromethyl)benzidine (alias: 4,4'-diamino-2,2'-bis(trifluoromethyl)bisidine benzene). The polyimide of the present invention can form a film having improved mechanical properties (elastic modulus) and a low coefficient of linear thermal expansion by containing the aforementioned structural unit (B-2). In the present invention, the ratio of the aforementioned constituent unit (B-2) to the constituent unit B is preferably 50 mol% or more in consideration of forming a film having a low linear thermal expansion coefficient while maintaining high transparency and high heat resistance, More preferably more than 60 mole %, especially more than 65 mole %, more preferably more than 70 mole %, more preferably more than 75 mole %, and preferably less than 95 mole %, more preferably It is less than 90 mole%, preferably less than 85 mole%, and more preferably less than 80 mole%.

The ratio of the constituent units (B-1) and (B-2) to the constituent unit B is preferably 5 to 50 mol% for the constituent unit (B-1) and 50 to 95 mole% for the constituent unit (B-2). Mole%, more preferably 10-40 mole% for the constituent unit (B-1), 60-90 mole% for the constituent unit (B-2), especially preferably 15-35 mole% for the constituent unit (B-1) Mole%, constituent unit (B-2) is 65-85 mole%, and more preferably constituent unit (B-1) is 15-30 mole%, constituent unit (B-2) is 70-85 mole% Mole%, and more preferably, the constituent unit (B-1) is 20-25 mole%, and the constituent unit (B-2) is 75-80 mole%. The molar ratio [(B-1)/(B-2)] of the constituent unit (B-1) to the constituent unit (B-2) is considered to maintain high transparency and high heat resistance while having a low linear thermal expansion coefficient From the point of view of the thin film, it is preferably 50/50～5/95, more preferably 40/60～10/90, especially 35/65～15/85, and more preferably 30/70～15/85. 25/75～20/80 is especially good.

In the polyimide of the present invention, diamines derived from compounds other than the compounds represented by the formulas (b-1) to (b-2) may be contained in the constituent unit B within the range not impairing the effects of the present invention. Constituent units, but should not be included. The proportion of the total of the constituent unit (B-1) and the constituent unit (B-2) in the constituent unit B is preferably from the viewpoint of forming a film with a low linear thermal expansion coefficient while maintaining high transparency and high heat resistance. It is more than 70 mol%, more preferably 85 mol%, more preferably 99 mol%, and more preferably 100 mol%.

[Manufacturing method of polyimide] The polyimide of the present invention is obtained by reacting a tetracarboxylic acid component providing the structural unit A with a diamine component providing the structural unit B.

As a tetracarboxylic acid component, tetracarboxylic acid or its derivative(s) are mentioned. The tetracarboxylic acid component can be used individually or in combination of 2 or more types. As a derivative of tetracarboxylic acid, the acid anhydride or alkyl ester of this tetracarboxylic acid is mentioned. For the alkyl ester of tetracarboxylic acid, the carbon number of the alkyl group is preferably 1-3, for example, dimethyl ester, diethyl ester and dipropyl ester of tetracarboxylic acid can be mentioned. The tetracarboxylic acid component used in the present invention contains biphenyl tetracarboxylic acid or its derivatives, and 4,4'-(hexafluoroisopropylidene) diphthalic acid or its derivatives. Among them, it is preferable to contain biphenyltetracarboxylic dianhydride [the above formula (a-1)] and 4,4'-(hexafluoroisopropylidene) diphthalic anhydride [the above formula (a-2)], Contains 3,3',4,4'-biphenyltetracarboxylic dianhydride [above formula (a-1-1)] and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride better.

The amount of biphenyltetracarboxylic acid or its derivatives should be 50-99 mole % relative to all tetracarboxylic acid components, more preferably 55-95 mole %, especially preferably 60-90 mole %, and More preferably, it is 65-85 mole %, and still more preferably, it is 70-80 mole %. The amount of 4,4'-(hexafluoroisopropylidene)diphthalic acid or its derivatives is preferably 1-50 mole%, more preferably 5-45 mole% relative to the total tetracarboxylic acid components %, preferably 10-40 mol%, more preferably 15-35 mol%, and especially preferably 20-30 mol%. The total amount of biphenyl tetracarboxylic acid, 4,4'-(hexafluoroisopropylidene) diphthalic acid, and their derivatives used is preferably 70-100 moles relative to the total tetracarboxylic acid components %, more preferably 85-100 mol%, especially preferably 99-100 mol%, and more preferably 100 mol%.

Furthermore, the tetracarboxylic acid component used in the present invention may contain tetracarboxylic acid other than biphenyl tetracarboxylic acid and 4,4'-(hexafluoroisopropylidene) diphthalic acid, or derivatives thereof. Acid component. The tetracarboxylic acid component includes at least one selected from the group consisting of an aromatic ring-containing tetracarboxylic acid or a derivative thereof, and an alicyclic hydrocarbon structure-containing tetracarboxylic acid or a derivative thereof. These tetracarboxylic acid components can be used individually or in combination of 2 or more types.

Tetracarboxylic acids containing aromatic rings or their derivatives include: pyromellitic acid, 3,3',4,4'-diphenyl tetracarboxylic acid, 3,3',4,4'-benzophenone Tetracarboxylic acid, 4,4'-oxydiphthalic acid, 2,2',3,3'-benzophenone tetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl) Propane, 2,2-bis(2,3-dicarboxyphenyl)propane, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane, 1,1-bis(2,3-bis Carboxyphenyl)ethane, 1,2-bis(2,3-dicarboxyphenyl)ethane, 1,1-bis(3,4-dicarboxyphenyl)ethane, 1,2-bis(3 ,4-dicarboxyphenyl)ethane, bis(2,3-dicarboxyphenyl)methane, bis(3,4-dicarboxyphenyl)methane, 4,4'-(p-phenylenedioxy ) diphthalic acid, 4,4'-(m-phenylenedioxy) diphthalic acid, 2,3,6,7-naphthalene tetracarboxylic acid, 1,4,5,8-naphthalene tetracarboxylic acid Carboxylic acids and their derivatives.

Tetracarboxylic acids containing alicyclic hydrocarbon structures or their derivatives include: 1,2,3,4-cyclobutane tetracarboxylic acid, 1,2,4,5-cyclopentane tetracarboxylic acid, 1,2 ,4,5-cyclohexanetetracarboxylic acid, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid, dicyclohexyltetracarboxylic acid, cyclopentanone bispiri norcamphene Alkanetetracarboxylic acids or their positional isomers, and their derivatives. Tetracarboxylic acids or derivatives thereof that do not contain any of an alicyclic hydrocarbon structure and an aromatic ring, examples include 1,2,3,4-butane tetracarboxylic acid, 1,2,3,4-pentane Tetracarboxylic acids, etc. or their derivatives.

The amount of tetracarboxylic acid components other than biphenyltetracarboxylic acid or its derivatives and 4,4'-(hexafluoroisopropylidene) diphthalic acid or its derivatives, relative to the total tetracarboxylic acid components It is preferably less than 30 mol%, more preferably less than 15 mol%, especially preferably less than 1 mol%, and more preferably 0 mol%.

The diamine component used in the present invention contains a compound represented by the above formula (b-1) and 2,2'-bis(trifluoromethyl)benzidine [the above formula (b-2)]. In addition, the diamine component providing the structural unit B is not limited to diamine, and its derivative (diisocyanate, etc.) may be used as long as it can form the same structural unit, but diamine is preferable. The amount of the compound represented by the above formula (b-1) is preferably 5-50 mol%, more preferably 10-40 mol%, and most preferably 10-35 mol%, relative to the total diamine components. More preferably, it is 15-30 mole %, more preferably, it is 15-25 mole %, and even more preferably, it is 20-25 mole %. The amount of 2,2'-bis(trifluoromethyl)benzidine used is preferably 50-95 mol%, more preferably 60-90 mol%, and especially preferably 65-90 mol%, relative to the total diamine components. %, more preferably 70-85 mol%, and especially preferably 75-85 mol%, and more preferably 75-80 mol%. The total amount of the compound represented by the above formula (b-1) and 2,2'-bis(trifluoromethyl)benzidine used is preferably 70 to 100 mol%, more preferably 85% with respect to the total diamine components. ~100 mole %, preferably 99-100 mole %, more preferably 100 mole %.

Furthermore, the diamine component used in the present invention may contain a compound represented by the above formula (b-1) and a diamine component other than 2,2'-bis(trifluoromethyl)benzidine. As this diamine component, at least 1 sort(s) chosen from the group which consists of an aromatic diamine and an aliphatic diamine is mentioned. These diamine components can be used individually or in combination of 2 or more types. In addition, "aromatic diamine" refers to a diamine in which an amine group is directly bonded to an aromatic ring, and a part of its structure may contain an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and other substituents (for example, Halogen atom, sulfonyl group, carbonyl group, oxygen atom, etc.). "Aliphatic diamine" refers to a diamine in which an amine group is directly bonded to an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, and a part of its structure may also contain an aromatic hydrocarbon group, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and other substituents (For example, a halogen atom, a sulfonyl group, a carbonyl group, an oxygen atom, etc.).

Examples of aromatic diamines include: p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, benzidine, o-toluidine, m-phenylenediamine Toluidine, hexafluorobenzidine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3, 3'-dichloro-4,4'-diaminobiphenyl, 3,3'-difluoro-4,4'-diaminobiphenyl, 2,6-diaminonaphthalene, 1,5-di Aminonaphthalene, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl Benzene, 3,4'-diaminodiphenylphenone, 4,4'-diaminobenzophenone, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 2,2-bis[4-(2-methyl-4-aminophenoxy)phenyl]propane, 2,2-bis[4-(2,6-dimethyl-4-aminophenoxy) base)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2-methyl-4-aminophenyl Oxy)phenyl]hexafluoropropane, 2,2-bis[4-(2,6-dimethyl-4-aminophenoxy)phenyl]hexafluoropropane, 4,4'-bis(4 -aminophenoxy)biphenyl, 4,4'-bis(2-methyl-4-aminophenoxy)biphenyl, 4,4'-bis(2,6-dimethyl-4- Aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]pyridine, bis[4-( 2-methyl-4-aminophenoxy)phenyl]pyridine, bis[4-(2,6-dimethyl-4-aminophenoxy)phenyl]pyridine, bis[4-(4 -aminophenoxy)phenyl]ether, bis[4-(2-methyl-4-aminophenoxy)phenyl]ether, bis[4-(2,6-dimethyl-4- Aminophenoxy)phenyl]ether, 1,4-bis(4-aminophenoxy)benzene, 1,4-bis(2-methyl-4-aminophenoxy)benzene, 1, 4-bis(2,6-dimethyl-4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(2-methyl-4 -aminophenoxy)benzene, 1,3-bis(2,6-dimethyl-4-aminophenoxy)benzene, 1,4-bis(4-amino-α,α-dimethyl benzyl)benzene;

2,2-bis(4-aminophenyl)propane, 2,2-bis(2-methyl-4-aminophenyl)propane, 2,2-bis(3-methyl-4-amino Phenyl)propane, 2,2-bis(3-ethyl-4-aminophenyl)propane, 2,2-bis(3,5-dimethyl-4-aminophenyl)propane, 2, 2-bis(2,6-dimethyl-4-aminophenyl)propane, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis(2-methyl-4 -aminophenyl)hexafluoropropane, 2,2-bis(2,6-dimethyl-4-aminophenyl)hexafluoropropane, α,α'-bis(4-aminophenyl)- 1,4-Diisopropylbenzene, α,α'-bis(2-methyl-4-aminophenyl)-1,4-diisopropylbenzene, α,α'-bis(2,6-di Methyl-4-aminophenyl)-1,4-diisopropylbenzene, α,α'-bis(3-aminophenyl)-1,4-diisopropylbenzene, α,α'-bis (4-aminophenyl)-1,3-diisopropylbenzene, α,α'-bis(2-methyl-4-aminophenyl)-1,3-diisopropylbenzene, α,α '-Bis(2,6-dimethyl-4-aminophenyl)-1,3-diisopropylbenzene, α,α'-bis(3-aminophenyl)-1,3-diiso Propylbenzene, 9,9-bis(2-methyl-4-aminophenyl) fluorene, 9,9-bis(2,6-dimethyl-4-aminophenyl) fluorene, 5-amino -1,3,3-trimethyl-1-(4-aminophenyl)-dihydroindene, 1,1-bis(4-aminophenyl)cyclopentane, 1,1-bis(2 -Methyl-4-aminophenyl)cyclopentane, 1,1-bis(2,6-dimethyl-4-aminophenyl)cyclopentane, 1,1-bis(4-amino Phenyl)cyclohexane, 1,1-bis(2-methyl-4-aminophenyl)cyclohexane, 1,1-bis(2,6-dimethyl-4-aminophenyl) Cyclohexane, 1,1-bis(4-aminophenyl)4-methyl-cyclohexane, 1,1-bis(4-aminophenyl)norbornane, 1,1-bis(2 -Methyl-4-aminophenyl)norbornane, 1,1-bis(2,6-dimethyl-4-aminophenyl)norbornane, 1,1-bis(4-amino Phenyl)adamantane, 1,1-bis(2-methyl-4-aminophenyl)adamantane, 1,1-bis(2,6-dimethyl-4-aminophenyl)adamantane wait. These can be used individually or in combination of 2 or more types.

Examples of aliphatic diamines include ethylenediamine, hexamethylenediamine, polyethylene glycol bis(3-aminopropyl) ether, polypropylene glycol bis(3-aminopropyl) ether , 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, m-xylylenediamine, p-xylylenediamine, 1,4-bis (2-amino-isopropyl)benzene, 1,3-bis(2-amino-isopropyl)benzene, isophoronediamine, norbornanediamine, siloxanediamine, 4, 4'-Diaminodicyclohexylmethane, 3,3'-Dimethyl-4,4'-diaminodicyclohexylmethane, 3,3'-Diethyl-4,4'-diamino Dicyclohexylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodicyclohexylmethane, 2,3-bis(aminomethyl)-bicyclo[2.2.1] Heptane, 2,5-bis(aminomethyl)-bicyclo[2.2.1]heptane, 2,6-bis(aminomethyl)-bicyclo[2.2.1]heptane, 2,2-bis (4,4'-diaminocyclohexyl)propane, 2,2-bis(4,4'-diaminomethylcyclohexyl)propane, etc.

The amount of the compound represented by the above formula (b-1) and diamine components other than 2,2'-bis(trifluoromethyl)benzidine used is preferably 30 mol% or less, more preferably It is less than 15 mol%, preferably less than 1 mol%, and more preferably 0 mol%.

When producing the polyimide of the present invention, the addition ratio of the tetracarboxylic acid component to the diamine component is preferably 0.9 to 1.1 mol of the diamine component relative to 1 mol of the tetracarboxylic acid component.

In addition to the above-mentioned tetracarboxylic acid component and the above-mentioned diamine component, an end-capping agent can also be used when producing the polyimide of the present invention. The blocking agent is preferably monoamine or dicarboxylic acid. The amount of the end-capping agent introduced is preferably 0.0001-0.1 mole, more preferably 0.001-0.06 mole, relative to 1 mole of the tetracarboxylic acid component. In terms of monoamine blocking agents, for example, recommended: methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline, etc. Among these, benzylamine and aniline are preferably used. The dicarboxylic acid-type end-capping agent is preferably a dicarboxylic acid, and a part of it may form a closed ring. For example recommended: phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenone dicarboxylic acid, 3,4-benzophenone dicarboxylic acid Carboxylic acid, cyclohexane-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. Among these, phthalic acid and phthalic anhydride can be preferably used.

The method of making the said tetracarboxylic-acid component and diamine component react is not specifically limited, A well-known method can be used. In terms of specific reaction methods, it can be enumerated: (1) Add tetracarboxylic acid component, diamine component, and reaction solvent into the reactor, stir at room temperature to 80° C. for 0.5 to 30 hours, and then heat up and carry out A method of imidization reaction; (2) After adding the diamine component and the reaction solvent into the reactor and dissolving it, adding the tetracarboxylic acid component, stirring at room temperature to 80°C for 0.5 to 30 hours if necessary, and then , the method of raising the temperature and carrying out the imidization reaction; (3) adding the tetracarboxylic acid component, the diamine component, and the reaction solvent into the reactor, immediately raising the temperature and carrying out the imidization reaction method, etc.

The reaction solvent used in the production of polyimide may be any one that can dissolve the produced polyimide without hindering the imidization reaction. For example, an aprotic solvent, a phenol type solvent, an ether type solvent, a carbonate type solvent, etc. are mentioned.

Specific examples of aprotic solvents include: N,N-dimethylisobutylamide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl- Amide-based solvents such as 2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone, tetramethylurea, etc.; lactone-based solvents such as γ-butyrolactone, γ-valerolactone, etc. Phosphorus-containing amide solvents such as hexamethylphosphoramide and hexamethylphosphine triamide; sulfur-containing solvents such as dimethylsulfide, dimethylsulfoxide, and cyclobutylene; acetone, cyclohexanone, Ketone solvents such as methylcyclohexanone; amine solvents such as picoline and pyridine; ester solvents such as acetic acid (2-methoxy-1-methylethyl ester), etc.

Specific examples of phenolic solvents include: phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6 -Xylenol, 3,4-Xylenol, 3,5-Xylenol, etc. 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, 1,4-dioxane, etc. Moreover, specific examples of carbonate-based solvents include diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and the like. Among the above-mentioned reaction solvents, an aprotic solvent is preferred, and an amide-based solvent or a lactone-based solvent is more preferable. Moreover, the said reaction solvent can be used individually or in mixture of 2 or more types.

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

In the above imidization reaction, known imidization catalysts can be used. As an imidization catalyst, an alkali catalyst or an acid catalyst is mentioned. Alkaline catalysts include: pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethyl Amine, tripropylamine, tributylamine, imidazole, N,N-dimethylaniline, N,N-diethylaniline and other organic base catalysts; potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, bicarbonate Potassium, sodium bicarbonate and other inorganic alkali catalysts. Moreover, examples of the acid catalyst include: crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, hydroxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid , naphthalenesulfonic acid, etc. These imidization catalysts can be used individually or in combination of 2 or more types. Among the above, from the viewpoint of operability, an alkali catalyst is preferable, an organic alkali catalyst is more preferable, and triethylamine is especially preferable.

When the above-mentioned catalyst is used, the temperature of the imidization reaction is preferably 120-250°C, more preferably 160-190°C, and most preferably 180-190°C in consideration of the reaction rate and inhibition of gelation. ℃. Also, the reaction time is preferably 0.5 to 10 hours after the start of distillation of produced water. In addition, when no catalyst is used, the temperature of the imidization reaction is preferably 200-350°C. In the reaction of the diamine component and the tetracarboxylic acid component, a polyimide solution containing at least polyimide and a reaction solvent can be obtained after the imidization reaction is completed.

[Polyimide] The weight average molecular weight of the polyimide of the present invention is preferably from 500 to 1,000,000, more preferably from 5,000 to 100,000, in consideration of the mechanical strength of the obtained polyimide film. In addition, the weight average molecular weight of polyimide can be measured by gel filtration chromatography etc. Examples of measurement of the weight average molecular weight include a method of measuring the absolute molecular weight with a light scattering detector using N,N-dimethylformamide as a developing solvent.

The polyimide of the present invention may further contain various additives within the range not impairing the effect of the present invention. Examples of additives include antioxidants, photostabilizers, surfactants, flame retardants, plasticizers, inorganic fillers, polymer compounds other than the aforementioned polyimides, and the like. Examples of polymer compounds include: polyimides other than the polyimides of the present invention, polycarbonate, polystyrene, polyamide, polyamideimide, polyethylene terephthalate Alcohol esters and other polyesters, polyether sulfide, polycarboxylic acid, polyacetal, polyphenylene ether, polysulfide, polybutene, polypropylene, polyacrylamide, polyvinyl chloride, etc.

[Polyimide varnish] The polyimide varnish of the present invention is obtained by dissolving the polyimide of the present invention in an organic solvent. That is, the polyimide varnish of the present invention contains the polyimide of the present invention and an organic solvent, and the polyimide is dissolved in the organic solvent. The organic solvent is not particularly limited as long as it can dissolve polyimide, and it is preferable to use the above-mentioned compounds as reaction solvents used in the production of polyimide alone or in combination of two or more. The polyimide of the present invention has solvent solubility, so it can be made into a high-concentration varnish that is stable at room temperature.

The aforementioned polyimide varnish may also be a polyimide solution itself obtained by dissolving polyimide obtained by a polymerization method in a reaction solvent. In addition, it may be obtained by mixing at least one selected from the solvents exemplified above as a solvent for dissolving the polyimide with the polyimide solution. The solid content concentration of the polyimide varnish of the present invention can be appropriately selected in consideration of the workability of the polyimide film described later, etc., and can also be determined by using the reaction solvent used in the production of the polyimide of the present invention. Volatilize and condense, or add an organic solvent as a diluting solvent to adjust the solid content concentration and viscosity of the polyimide varnish of the present invention. The organic solvent is not particularly limited as long as it can dissolve polyimide. The solid content concentration of the polyimide varnish of the present invention is preferably 5 to 45% by mass, more preferably 5 to 35% by mass, and most preferably 5 to 25% by mass. The viscosity of the polyimide varnish of the present invention is preferably 0.1-200 Pa･s, more preferably 0.5-180 Pa･s, and most preferably 1-150 Pa･s. The viscosity of the polyimide varnish is a value measured at 25° C. using an E-type viscometer.

[Polyimide film] The polyimide film of the present invention is characterized by containing the polyimide of the present invention, maintaining high transparency and high heat resistance, and having a low linear thermal expansion coefficient. The polyimide film of the present invention is preferably composed of the polyimide of the present invention. The method for producing the polyimide film of the present invention is not particularly limited, and known methods can be used. For example, the following methods can be mentioned: coating the polyimide varnish containing the polyimide of the present invention, or the polyimide varnish containing the polyimide of the present invention and the above-mentioned various additives, on a glass plate or a metal plate. , plastic, or other smooth supports, or after forming into a film, remove the solvent components such as reaction solvents and dilution solvents contained in the varnish. By adjusting the solid content concentration and viscosity of the polyimide varnish in the above manner, the thickness of the polyimide film of the present invention can be easily controlled.

A release agent may also be coated on the surface of the aforementioned support as needed. The following method is suitable for the method of applying the polyimide varnish to the support and then heating it to evaporate the solvent component. That is, after the solvent is evaporated at a temperature below 120° C. to form a self-supporting film, the self-supporting film is peeled off from the support, and the end of the self-supporting film is fixed. Drying is performed at a temperature above the boiling point of the components and below 350°C to produce a polyimide film. In addition, drying is preferably carried out under a nitrogen atmosphere. The pressure of the dry environment may be any of reduced pressure, normal pressure, and increased pressure.

The thickness of the polyimide film of the present invention can be appropriately selected according to the application, but it is preferably in the range of 1-250 μm, more preferably 5-100 μm, especially 7-90 μm, and more preferably 10-80 μm. With a thickness of 1 to 250 μm, it can be practically used as a self-supporting film.

In the present invention, the polyimide film can be formed with a total light transmittance of preferably 80% or more, more preferably 85% or more, especially 88% or more, and more preferably 89% or more when the thickness is 10 μm. In the present invention, a polyimide film having a yellowness index (YI value) of preferably 6.0 or less, more preferably 5.0 or less, and especially preferably 4.5 or less can be formed. In the present invention, a polyimide film having a haze of preferably 1.0 or less, more preferably 0.8 or less, and especially preferably 0.5 or less can be formed. In the present invention, it is possible to form a polyimide film having a glass transition temperature of preferably above 250°C, more preferably above 300°C, and especially preferably above 350°C.

In the present invention, a polyimide film having a coefficient of linear thermal expansion preferably below 40 ppm/°C, more preferably below 35 ppm/°C, and especially preferably below 30 ppm/°C can be formed. In the present invention, it is possible to form a polyimide film having a tensile elastic modulus (measurement temperature: 23° C., humidity: 50% RH) of preferably 3.0 GPa or higher, more preferably 3.5 GPa or higher. The total light transmittance, YI value, haze, glass transition temperature, linear thermal expansion coefficient, and tensile elastic modulus of the polyimide film can be specifically measured by the method described in the examples.

The polyimide film containing the polyimide of the present invention has excellent transparency and heat resistance, and has a low coefficient of linear thermal expansion so that the dimensional change due to heat is small, and can be ideally used as a color filter and a flexible display , Semiconductor parts, optical components and other various components of the film. Since the polyimide film of the present invention has high dimensional stability, it can be used in high-temperature steps in the manufacturing steps of image display devices. Therefore, at least a part of image display devices such as liquid crystal displays and organic EL displays can utilize the polyimide film of the present invention. [Example]

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples. The physical properties of the polyimide varnishes, polyimide precursor varnishes, and polyimide films obtained in the following examples and comparative examples were measured by the methods shown below.

(1) Solid content concentration: The determination of the solid content concentration of polyimide varnish or polyimide precursor varnish is to use a small electric furnace MMF-1 manufactured by AS ONE (stock) company to heat the sample at 320 ° C × 120 min, and from before and after heating Calculate the mass difference of the sample. (2) Film thickness: The thickness of the polyimide film was measured using a micrometer manufactured by Mitutoyo Co., Ltd.

(3) Tensile modulus of elasticity The measurement system is based on JIS K7127, using the tensile testing machine "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd. to measure the conditions of temperature 23°C, humidity 50%RH, distance between chucks 50mm, and tensile speed 50mm/min. A tensile test was performed to obtain a tensile modulus of elasticity. (4) Glass transition temperature (Tg) Using a differential scanning calorimeter device "DSC 6200" manufactured by Hitachi High-Tech Science Co., Ltd., DSC measurement was performed at a heating rate of 10° C./min to obtain the glass transition temperature.

(5) Total light transmittance, yellow index (YI), haze The color-turbidity simultaneous measuring device "COH400" manufactured by Nippon Denshoku Kogyo Co., Ltd. was used. The measurement of total light transmittance and YI is based on JIS K7361-1:1997, and the measurement of haze is based on JIS K7136:2000. (6) Coefficient of thermal expansion (CTE) Using a thermomechanical analyzer (TMA/SS 6100) manufactured by Hitachi High-Tech Science Co., Ltd., TMA was performed under the conditions of tensile mode, sample size 2mm×20mm, load 0.1N, and heating rate 10°C/min Measure and obtain the CTE at 100-250°C. The closer the CTE value is to 0, the better the dimensional stability.

<Example 1> Put 2,2'-bis(trifluoromethyl ) benzidine (manufactured by Wakayama Seika Kogyo Co., Ltd.) 29.462 g (0.092 mol), 9,9-bis(4-aminophenyl) fennel (manufactured by Tagoka Chemical Industry Co., Ltd.) 8.014 g (0.023 mole), N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) 111.263 g, and stirred at a rotation speed of 200 rpm at an internal temperature of 70° C. under a nitrogen atmosphere to obtain a solution. 27.066 g (0.092 moles) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Co., Ltd.), 4,4'-(hexafluoroiso Propyl)diphthalic anhydride (manufactured by Daikin Industries Co., Ltd.) 10.218g (0.023 mol) and N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) 27.816g, then, put As an imidization catalyst, 0.582 g of triethylamine (manufactured by Kanto Chemical Co., Ltd.) was heated with a heating mantle, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The distilled components were collected, and the rotation speed was adjusted according to the increase in viscosity, while the temperature in the reaction system was kept at 190° C. and refluxed for 1 hour and 30 minutes. After that, 512.54 g of N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) was added, and the temperature in the reaction system was cooled to 120° C., and stirred for about 3 hours to make it homogenized, and the solid content concentration was obtained. 10% by mass of a polyimide-containing solution (polyimide varnish). Then, the obtained polyimide varnish was coated on a glass plate, kept at 80° C. for 30 minutes using a heating plate, and then heated at 300° C. for 30 minutes in a hot air drier under nitrogen purge to evaporate the solvent to obtain Film with a thickness of 10 μm. The results are shown in Table 1.

<Example 2> Put 2,2'-bis(trifluoromethyl ) benzidine (manufactured by Wakayama Seika Kogyo Co., Ltd.) 19.685 g (0.061 mol), 9,9-bis(4-aminophenyl) fennel (manufactured by Tagoka Chemical Industry Co., Ltd.) 5.343 g (0.015 mole), N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) 75.897 g, and stirred at 200 rpm at an internal temperature of 70° C. under a nitrogen atmosphere to obtain a solution. To this solution, 15.789 g (0.054 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Co., Ltd.), 4,4'-(hexafluoroiso Propyl) diphthalic anhydride (manufactured by Daikin Industries Co., Ltd.) 10.218 g (0.023 moles) and N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) 18.974 g, and then, put As an imidization catalyst, 0.388 g of triethylamine (manufactured by Kanto Chemical Co., Ltd.) was heated with a heating mantle, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The distilled components were collected, and the rotation speed was adjusted according to the viscosity increase, while the temperature in the reaction system was kept at 190° C. and refluxed for 3 hours and 10 minutes. After that, 349.97 g of N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) was added, and the temperature in the reaction system was cooled to 120° C., and stirred for about 3 hours to make it homogenized, and the solid content concentration was obtained. 10% by mass of polyimide varnish. Then, the obtained polyimide varnish was coated on a glass plate, kept at 80° C. for 30 minutes with a heating plate, and then heated at 300° C. for 30 minutes in a hot air drier under nitrogen purge to evaporate the solvent to obtain Film with a thickness of 10 μm. The results are shown in Table 1.

＜Comparative example 1＞ Put 9,9-bis(4-aminobenzene Base) 24.392g (0.070 mole) of fennel (manufactured by Tianoka Chemical Industry Co., Ltd.), 66.786g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.), and at a temperature of 70°C in the system under a nitrogen atmosphere, The solution was obtained by stirring at a rotation speed of 200 rpm. To this solution, 31.097 g (0.070 moles) of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (manufactured by Daikin Industries, Ltd.) and γ-butyrolactone (Mitsubishi Chemical (Co., Ltd.) 16.697g, then, drop into 0.212g of triethylamine (Kanto Chemical Co., Ltd.) as the imidization catalyst, utilize the heating mantle to heat, and last about 20 minutes to make the reaction system The temperature rose to 190°C. The distilled components were collected, and the rotation speed was adjusted according to the viscosity increase, while the temperature in the reaction system was kept at 190° C. and refluxed for 1 hour. After that, 394.709 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added, and after cooling the temperature in the reaction system to 120° C., it was further stirred for about 3 hours to make it homogeneous, and to obtain a solid content concentration of 10% by mass. Polyimide varnish. Then, the obtained polyimide varnish was coated on a glass plate, kept at 80° C. for 20 minutes with a heating plate, and then heated at 400° C. for 30 minutes in a hot air drier under nitrogen purge to evaporate the solvent to obtain Film with a thickness of 10 μm. The results are shown in Table 1.

＜Comparative example 2＞ Put 9,9-bis(4-aminobenzene 34.845 g (0.100 mol) of N,N-dimethylacetamide (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and 120.202 g of N,N-dimethylacetamide (manufactured by Tianoka Chemical Industry Co., Ltd.), and the temperature in the system was 50 °C under a nitrogen atmosphere, stirring at a rotation speed of 200 rpm to obtain a solution. 29.420 g (0.100 moles) of 3,3', 4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Co., Ltd.) and N,N-dimethylacetamide ( Mitsubishi Gas Chemical Co., Ltd.) 30.050 g, after confirming the dissolution, return to room temperature and continue stirring for 5 hours while adjusting the rotational speed according to the increase in viscosity. Then, 92.91 g of N,N-dimethylacetamide (manufactured by Mitsubishi Gas Chemical Co., Ltd.) was added, stirred for about 1 hour to make it homogenized, and a polyimide precursor with a solid content concentration of 20% by mass was obtained ( polyamide acid) solution (polyimide precursor varnish). Then, the obtained polyimide precursor varnish was coated on a glass plate, kept at 80° C. for 20 minutes using a heating plate, and then heated at 400° C. for 30 minutes in a hot air dryer under nitrogen purge to evaporate the solvent , to obtain a polyimide film with a thickness of 10 μm. The results are shown in Table 1.

【Table 1】

The abbreviations in the table are as follows. s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride [compound represented by formula (a-1-1)] 6FDA: 4,4'-(hexafluoroisopropylidene) diphthalic anhydride [compound represented by formula (a-2)] BAFL: 9,9-bis(4-aminophenyl) fluorine [compound represented by formula (b-1) (R: hydrogen atom)] TFMB: 2,2'-bis(trifluoromethyl)benzidine [compound represented by formula (b-2)]

It can be seen from Table 1 that the polyimide films of Examples 1 and 2 not only have high transparency and high heat resistance, but also have a low coefficient of linear thermal expansion. Therefore, all these properties are good and balanced. On the other hand, the polyimide films of comparative examples 1 and 2, although the heat resistance is excellent, the coefficient of linear thermal expansion is high, and the transparency of the polyimide films of comparative example 2 is also poor, so with respect to these polyimide films In other words, it has not been possible to obtain a film having a low coefficient of linear thermal expansion in addition to high transparency and high heat resistance.

Claims (8)

A kind of polyimide, has the constitutional unit A that comes from tetracarboxylic acid or derivative thereof, and the constitutional unit B that comes from diamine; Constituent unit A contains the constitutional unit (A- 1), and the structural unit (A-2) derived from the compound represented by the following formula (a-2); the structural unit B contains the structural unit (B-1) derived from the compound represented by the following formula (b-1), and The constituent unit (B-2) of the compound represented by the following formula (b-2); relative to the constituent unit A, the ratio of the constituent unit (A-1) is 55 mol% or more, and the ratio of the constituent unit (A-2) 45 mol% or less; relative to the constituent unit B, the proportion of the constituent unit (B-1) is less than 40 mole%, and the proportion of the constituent unit (B-2) is 60 mole% or more;

In formula (b-1), R each independently represents a hydrogen atom, a fluorine atom, or a methyl group. Such as the polyimide of claim 1, wherein the total ratio of the constituent unit (A-1) and the constituent unit (A-2) in the constituent unit A is 70 mol% or more. For example, the polyimide of claim 1 or 2 of the scope of the patent application, wherein the total proportion of the constituent unit (B-1) and the constituent unit (B-2) in the constituent unit B is 70 mol% or more. Such as the polyimide of claim 1 or 2, wherein, relative to the constituent unit B, the proportion of the constituent unit (B-1) is 5 mol% or more. Such as the polyimide of claim 1 or 2 of the patent scope, wherein, relative to the constituent unit A, the ratio of the constituent unit (A-1) is 60~90 mole%, and the ratio of the constituent unit (A-2) is 10~40 mole%. For example, the polyimide of claim 1 or 2 of the patent scope, wherein, relative to the constituent unit B, the ratio of the constituent unit (B-1) is 15-30 mole%, and the ratio of the constituent unit (B-2) is 70~85 mole%. A polyimide varnish is formed by dissolving the polyimide according to any one of items 1 to 6 in the scope of the patent application in an organic solvent. A polyimide film, containing the polyimide according to any one of items 1 to 6 in the scope of the patent application.