WO2020110947A1 - Polyimide resin, polyimide varnish and polyimide film - Google Patents

Abstract

Provided is a polyimide resin having constituent units A derived from tetracarboxylic dianhydride and constituent units B derived from diamine. The constituent units A include constituent units (A-1) derived from a compound represented by formula (a-1), and constituent units (A-2) derived from a compound represented by formula (a-2). Constituent units B include constituent units (B-1) derived from a compound represented by formula (b-1), and the ratio of constituent units (B-1) in constituent unit B is at least 70 mol%. Also provided are a polyimide varnish and a polyimide film containing said polyimide resin.

Description

Polyimide resin, polyimide varnish and polyimide film

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

Various uses of the polyimide resin are being considered in the fields of electric and electronic parts. For example, it is desired to replace a glass substrate used for an image display device such as a liquid crystal display or an OLED display with a plastic substrate for the purpose of reducing the weight and flexibility of the device. Research is in progress.
In an image display device, when light emitted from a display element is emitted through a plastic substrate, the plastic substrate is required to be colorless and transparent, and when light passes through a retardation film or a polarizing plate ( For example, liquid crystal displays, touch panels, etc.) are required to have high optical isotropy (that is, low Rth) in addition to colorless transparency.

▽Development of various polyimide resins is progressing in order to meet the above required performance. For example, in Patent Document 1, 3,3′-diaminodiphenylsulfone (primary diamine) and 4,4′-diaminodiphenylsulfone are used as polyimide resins that give a polyimide film that is colorless and transparent and has low Rth and excellent toughness. A polyimide resin produced by using a combination with a specific diamine (secondary diamine) as a diamine component is described.

International Publication No. 2016/158825

By the way, for a polyimide film to be suitable as a substrate, not only colorless transparency and optical isotropy but also chemical resistance (solvent resistance, acid resistance and alkali resistance) are important physical properties.
For example, when a varnish for forming the resin layer is applied to the polyimide film to form another resin layer (for example, a color filter or a resist) on the polyimide film, the polyimide film contains a solvent contained in the varnish. Resistance is required. If the solvent resistance of the polyimide film is insufficient, the film may be meaningless as a substrate due to dissolution or swelling of the film.
When a polyimide film is used as a substrate for forming an ITO (Indium Tin Oxide) film, the polyimide film is required to have resistance to the acid used for etching the ITO film. If the acid resistance of the polyimide film is insufficient, the film may turn yellow and impair the colorless transparency.
Further, an alkaline aqueous solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is mainly used for cleaning a support such as a glass plate (a support to which a polyimide varnish is applied) used when manufacturing a polyimide film. .. The cleaning with the alkaline aqueous solution may be performed even in the state where the polyimide film is formed on the support such as a glass plate. Therefore, the polyimide film is also required to have resistance to alkali.
However, in Patent Document 1, chemical resistance is not evaluated.

The present invention has been made in view of such a situation, the object of the present invention is a colorless transparent, optical isotropic, and chemical resistance (solvent resistance, acid resistance and alkali resistance) excellent film It is to provide a polyimide resin capable of forming a film, and a polyimide varnish and a polyimide film containing the polyimide resin.

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

That is, the present invention relates to the following [1] to [4].
[1]
A polyimide resin having a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from a diamine,
A structural unit A is a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) is derived from a compound represented by the following formula (a-2). Including and
The structural unit B contains a structural unit (B-1) derived from a compound represented by the following formula (b-1),
A polyimide resin in which the ratio of the structural unit (B-1) in the structural unit B is 70 mol% or more.

[2]
The ratio of the structural unit (A-1) in the structural unit A is 5 to 95 mol %,
The polyimide resin according to the above [1], wherein the ratio of the structural unit (A-2) in the structural unit A is 5 to 95 mol %.
[3]
A polyimide varnish obtained by dissolving the polyimide resin according to the above [1] or [2] in an organic solvent.
[4]
A polyimide film containing the polyimide resin according to the above [1] or [2].

According to the present invention, it is possible to form a film excellent in colorless transparency, optical isotropy, and chemical resistance (solvent resistance, acid resistance and alkali resistance).

[Polyimide resin]
The polyimide resin of the present invention has a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from a diamine, and the structural unit A is derived from a compound represented by the following formula (a-1). The structural unit (A-1) and the structural unit (A-2) derived from the compound represented by the following formula (a-2) are contained, and the structural unit B is represented by the following formula (b-1). The constitutional unit (B-1) derived from the compound is contained, and the proportion of the constitutional unit (B-1) in the constitutional unit B is 70 mol% or more.

<Structural unit A>
The structural unit A is a structural unit derived from the tetracarboxylic dianhydride occupying in the polyimide resin, and the structural unit (A-1) derived from the compound represented by the following formula (a-1) and the following formula And a structural unit (A-2) derived from the compound represented by (a-2).

The compound represented by the formula (a-1) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride.
The compound represented by the formula (a-2) is 4,4′-oxydiphthalic anhydride.
When the structural unit A contains both the structural unit (A-1) and the structural unit (A-2), the colorless transparency, optical isotropy, and chemical resistance of the film can be improved. The structural unit (A-1) makes a large contribution to the improvement of colorless transparency and optical isotropy, and the structural unit (A-2) makes a large contribution to the improvement of chemical resistance.

The ratio of the structural unit (A-1) in the structural unit A is preferably 5 to 95 mol%, more preferably 15 to 95 mol%, and the film has colorless transparency, optical isotropy, and From the viewpoint of improving the chemical resistance, it is more preferably 20 to 90 mol %, particularly preferably 50 to 90 mol %. On the other hand, particularly from the viewpoint of optical isotropy and acid resistance, it is more preferably 70 to 95 mol %, and particularly preferably 85 to 95 mol %.
The ratio of the structural unit (A-2) in the structural unit A is preferably 5 to 95 mol %, more preferably 5 to 85 mol %, the colorless transparency of the film, optical isotropy, and From the viewpoint of improving the chemical resistance, it is more preferably 10 to 80 mol %, particularly preferably 10 to 50 mol %. On the other hand, from the viewpoint of optical isotropy and acid resistance, the content is more preferably 5 to 30 mol %, particularly preferably 5 to 15 mol %.
The total ratio of the structural units (A-1) and (A-2) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, and further preferably 90 mol% or more. And particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural units (A-1) and (A-2) is not particularly limited, that is, 100 mol%. The structural unit A may consist of the structural unit (A-1) and the structural unit (A-2) only.

The structural unit A may include a structural unit other than the structural units (A-1) and (A-2). The tetracarboxylic acid dianhydride that gives such a constitutional unit is not particularly limited, but pyromellitic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 9,9′ -Bis(3,4-dicarboxyphenyl)fluorene dianhydride, and aromatic tetracarboxylic dianhydrides such as 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (provided that the formula (a-2 A) 1,2,3,4-cyclobutanetetracarboxylic dianhydride and norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5) , 5″, 6,6″-tetracarboxylic dianhydride and the like, alicyclic tetracarboxylic dianhydride (excluding the compound represented by formula (a-1)); And aliphatic tetracarboxylic acid dianhydrides such as 3,4,4-butanetetracarboxylic acid dianhydride.
In this specification, the aromatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing one or more aromatic rings, and the alicyclic tetracarboxylic dianhydride has one alicyclic ring. The above means a tetracarboxylic dianhydride containing no aromatic ring, and the aliphatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring.
The constitutional units arbitrarily contained in the constitutional unit A (that is, constitutional units other than the constitutional units (A-1) and (A-2)) may be one kind or two or more kinds.

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

The compound represented by the formula (b-1) is 3,3′-diaminodiphenyl sulfone.
When the structural unit B contains the structural unit (B-1), the optical isotropy and chemical resistance of the film can be improved. Among them, acid resistance can be improved.

The ratio of the structural unit (B-1) in the structural unit B is 70 mol% or more. The ratio is preferably 75 mol% or more, more preferably 80 mol% or more. The upper limit of the ratio of the structural unit (B-1) may be 90 mol%, 95 mol%, 99 mol% or 100 mol%. The structural unit B may consist of the structural unit (B-1) only.
When the structural unit B contains the structural unit (B-1) in an amount of 70 mol% or more in the structural unit B, the chemical resistance of the film is maintained and the film is uniformly dissolved in an organic solvent used for a polyimide varnish described later. Therefore, the obtained film is considered to be excellent in colorless transparency.

The structural unit B may include a structural unit other than the structural unit (B-1). The diamine which gives such a constitutional unit is not particularly limited, but 1,4-phenylenediamine, p-xylylenediamine, 3,5-diaminobenzoic acid, 1,5-diaminonaphthalene, 2,2′-dimethyl Biphenyl-4,4'-diamine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)hexa Fluoropropane, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-indene-5 Amine, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, N,N'-bis(4-aminophenyl)terephthalamide, 4,4'-bis(4-aminophenoxy)biphenyl 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, 9,9-bis(4-aminophenyl) Aromatic diamines such as fluorene and 4,4′-diamino-2,2′-bistrifluoromethyldiphenyl ether (excluding compounds represented by formula (b-1)); 1,3-bis(aminomethyl) ) Alicyclic diamines such as cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine.
In the present specification, the aromatic diamine means a diamine containing at least one aromatic ring, and the alicyclic diamine means a diamine containing at least one alicyclic ring and containing no aromatic ring, and a fat Group diamine means a diamine containing neither an aromatic ring nor an alicyclic ring.
The constitutional unit arbitrarily contained in the constitutional unit B (that is, the constitutional unit other than the constitutional unit (B-1)) may be one type or two or more types.

Examples of the diamine that gives the structural unit arbitrarily contained in the structural unit B include compounds represented by the following formula (b-2-1), compounds represented by the following formula (b-2-2), and compounds represented by the following formula (b -2-3) and compounds represented by the following formula (b-2-4) are preferable. That is, in the polyimide resin of one embodiment of the present invention, the structural unit B is a structural unit (B-2-1) derived from a compound represented by the following formula (b-2-1), and the following structural formula (b-2) -2), a structural unit (B-2-2) derived from a compound represented by the formula (b-2-3), a structural unit (B-2-3) derived from a compound represented by the following formula (b-2-3), and The compound may further contain a structural unit (B-2) which is at least one selected from the group consisting of structural units (B-2-4) derived from the compound represented by the formula (b-2-4).

(In the formula (b-2-2), each R is independently a hydrogen atom, a fluorine atom or a methyl group.)

The compound represented by the formula (b-2-1) is 4,4′-diamino-2,2′-bistrifluoromethyldiphenyl ether.
When the structural unit B contains the structural unit (B-2-1), the colorless transparency of the film can be improved.

In formula (b-2-2), each R is independently a hydrogen atom, a fluorine atom or a methyl group, and preferably a hydrogen atom. Examples of the compound represented by the formula (b-2-2) include 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(3-fluoro-4-aminophenyl)fluorene, and 9,9. Examples thereof include -bis(3-methyl-4-aminophenyl)fluorene, and 9,9-bis(4-aminophenyl)fluorene is preferable.
When the structural unit B contains the structural unit (B-2-2), the optical isotropy and heat resistance of the film can be improved.

The compound represented by the formula (b-2-3) is 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane.
By including the structural unit (B-2-3) in the structural unit B, the colorless transparency and optical isotropy of the film can be improved.

The compound represented by the formula (b-2-4) is 2,2′-bis(trifluoromethyl)benzidine.
When the structural unit B contains the structural unit (B-2-4), the colorless transparency, chemical resistance, heat resistance and mechanical properties of the film can be improved.

From the viewpoint of improving various performances of the film, the structural unit B is a structural unit (B-2-1) derived from a compound represented by the formula (b-2-1). A structural unit (B-2-2) derived from the compound represented by formula (b-2-2), a structural unit (B-2-2) derived from the compound represented by formula (b-2-3) 3) and at least one selected from the group consisting of structural units (B-2-4) derived from the compound represented by the formula (b-2-4), and in particular, the film is colorless and transparent. From the viewpoint of improving the optical isotropy, the constituent unit B preferably contains a constituent unit (B-2-3) derived from the compound represented by the formula (b-2-3).

When the structural unit B includes the structural unit (B-1) and the structural unit (B-2), the ratio of the structural unit (B-1) in the structural unit B is preferably 70 to 95 mol %, and It is preferably 75 to 95 mol %, more preferably 75 to 90 mol %, and the ratio of the structural unit (B-2) in the structural unit B is preferably 5 to 30 mol %, and more preferably It is 5 to 25 mol %, and more preferably 10 to 25 mol %.
The total ratio of the structural unit (B-1) and the structural unit (B-2) in the structural unit B is preferably 75 mol% or more, more preferably 80 mol% or more, further preferably 90 mol%. % Or more, particularly preferably 99 mol% or more. The upper limit of the total ratio of the structural unit (B-1) and the structural unit (B-2) is not particularly limited, that is, 100 mol%. The structural unit B may consist of only the structural unit (B-1) and the structural unit (B-2).

The structural unit (B-2) may be only the structural unit (B-2-1) or only the structural unit (B-2-2), and the structural unit (B-2-3) Or only the structural unit (B-2-4).
Further, the structural unit (B-2) may be a combination of two or more structural units selected from the group consisting of the structural units (B-2-1) to (B-2-4).

The number average molecular weight of the polyimide resin of the present invention is preferably 5,000 to 200,000 from the viewpoint of mechanical strength of the obtained polyimide film. The number average molecular weight of the polyimide resin can be determined, for example, from a standard polymethylmethacrylate (PMMA) conversion value measured by gel filtration chromatography.

The polyimide resin of the present invention may include a structure other than a polyimide chain (a structure in which the structural unit A and the structural unit B are imide-bonded). Examples of the structure other than the polyimide chain that may be contained in the polyimide resin include a structure containing an amide bond.
The polyimide resin of the present invention preferably contains a polyimide chain (a structure in which the structural unit A and the structural unit B are imide-bonded) as a main structure. 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, further preferably 90% by mass or more, particularly preferably 99% by mass. % Or more.

By using the polyimide resin of the present invention, a film excellent in colorless transparency, optical isotropy and chemical resistance can be formed, and suitable physical property values of the film are as follows.
The total light transmittance is preferably 88% or more, more preferably 88.5% or more, still more preferably 89% or more when a film having a thickness of 10 μm is formed.
The yellow index (YI) of the film having a thickness of 10 μm is preferably 4.0 or less, more preferably 2.5 or less, and further preferably 2.0 or less.
b ^* is preferably 2.0 or less, more preferably 1.2 or less, still more preferably 1.0 or less when a film having a thickness of 10 μm is formed.
The absolute value of the thickness retardation (Rth) is preferably 70 nm or less, more preferably 60 nm or less, still more preferably 50 nm or less when a film having a thickness of 10 μm is formed.
The mixed acid ΔYI is preferably 1.5 or less, more preferably 1.3 or less, and still more preferably 1.0 or less when a film having a thickness of 10 μm is formed.
The mixed acid Δb ^* is preferably 0.8 or less, more preferably 0.6 or less, still more preferably 0.5 or less when a film having a thickness of 10 μm is formed.
The mixed acid ΔYI and mixed acid Δb ^* mean the difference in YI and the difference in b ^* before and after the immersion of the polyimide film in a mixture of phosphoric acid, nitric acid and acetic acid, respectively. It can be measured by the method described in the examples. It means that the smaller ΔYI and Δb ^* are, the more excellent the acid resistance is. By using the polyimide resin of the present invention, a film having excellent chemical resistance can be formed and excellent resistance to acid is also exhibited. In particular, a mixed solution of mixed acids (for example, 50 to 97% by mass of phosphoric acid, 1 to 20% by mass of nitric acid, 1 to 10% by mass of acetic acid, and 1 to 20% by mass of water, preferably 63 to 87% of phosphoric acid). %, nitric acid 5 to 15% by mass, acetic acid 3 to 7% by mass, and water 5 to 15% by mass).

The film that can be formed using the polyimide resin of the present invention has good mechanical properties and heat resistance, and has the following suitable physical property values.
The tensile strength is preferably 60 MPa or more, more preferably 70 MPa or more, and further preferably 80 MPa or more.
The tensile elastic modulus is preferably 2.0 GPa or more, more preferably 2.5 GPa or more, and further preferably 3.0 GPa or more.
The glass transition temperature (Tg) is preferably 230°C or higher, more preferably 250°C or higher, and further preferably 270°C or higher.
The above-mentioned physical property values in the present invention can be specifically measured by the methods described in Examples.

[Method for producing polyimide resin]
The polyimide resin of the present invention comprises a tetracarboxylic acid component containing a compound giving the above structural unit (A-1) and a compound giving the above structural unit (A-2), and the above structural unit (B-1). It can be produced by reacting with a diamine component containing 70 mol% or more of the compound to be given.

Examples of the compound that provides the structural unit (A-1) include compounds represented by the formula (a-1), but the compound is not limited thereto, and a derivative thereof may be used as long as the same structural unit is provided. Examples of the derivative include a tetracarboxylic acid corresponding to the tetracarboxylic acid dianhydride represented by the formula (a-1) (that is, 1,2,4,5-cyclohexanetetracarboxylic acid) and an alkyl of the tetracarboxylic acid. Esters can be mentioned. As the compound providing the structural unit (A-1), a compound represented by the formula (a-1) (ie, dianhydride) is preferable.
Similarly, examples of the compound that provides the structural unit (A-2) include compounds represented by the formula (a-2), but the compound is not limited thereto, and a derivative thereof may be used as long as the same structural unit is provided. .. Examples of the derivative include a tetracarboxylic acid corresponding to the tetracarboxylic dianhydride represented by the formula (a-2) and an alkyl ester of the tetracarboxylic acid. As the compound providing the structural unit (A-2), the compound represented by the formula (a-2) (ie, dianhydride) is preferable.

The tetracarboxylic acid component preferably contains the compound giving the structural unit (A-1) in an amount of 5 to 95 mol %, more preferably 15 to 95 mol %, and has colorless transparency of the film, optical isotropy, and From the viewpoint of improving the chemical resistance, the content is more preferably 20 to 90 mol %, particularly preferably 50 to 90 mol %. On the other hand, particularly from the viewpoint of optical isotropy and acid resistance, the content is more preferably 70 to 95 mol %, and particularly preferably 85 to 95 mol %.
The tetracarboxylic acid component preferably contains 5 to 95 mol% of the compound giving the structural unit (A-2), more preferably 5 to 85 mol%, and the film has colorless transparency, optical isotropy, and From the viewpoint of improving the chemical resistance, the content is more preferably 10 to 80 mol %, particularly preferably 10 to 50 mol %. On the other hand, from the viewpoints of optical isotropy and acid resistance, the content is more preferably 5 to 30 mol %, particularly preferably 5 to 15 mol %.
The tetracarboxylic acid component contains a compound giving the structural unit (A-1) and a compound giving the structural unit (A-2) in a total amount of preferably 50 mol% or more, more preferably 70 mol% or more, and further preferably Is 90 mol% or more, particularly preferably 99 mol% or more. The upper limit of the total content ratio of the compound providing the structural unit (A-1) and the compound providing the structural unit (A-2) is not particularly limited, that is, 100 mol%. The tetracarboxylic acid component may consist of only the compound which gives the structural unit (A-1) and the compound which gives the structural unit (A-2).

The tetracarboxylic acid component may include a compound other than the compound which gives the structural unit (A-1) and the compound which gives the structural unit (A-2), and the compound is the aromatic tetracarboxylic dianhydride described above. Alicyclic tetracarboxylic dianhydride, aliphatic tetracarboxylic dianhydride, and derivatives thereof (tetracarboxylic acid, alkyl ester of tetracarboxylic acid, etc.).
The compound optionally contained in the tetracarboxylic acid component (that is, the compound other than the compound giving the structural unit (A-1) and the compound giving the structural unit (A-2)) may be one type or two or more types. It may be.

Examples of the compound that provides the structural unit (B-1) include compounds represented by the formula (b-1), but the compound is not limited thereto, and a derivative thereof may be used as long as the same structural unit is provided. Examples of the derivative include diisocyanates corresponding to the diamine represented by the formula (b-1). As the compound providing the structural unit (B-1), a compound represented by the formula (b-1) (that is, diamine) is preferable.

The diamine component contains 70 mol% or more of the compound giving the structural unit (B-1). The diamine component preferably contains 75 mol% or more, more preferably 80 mol% or more, of the compound providing the structural unit (B-1). The upper limit of the content ratio of the compound providing the structural unit (B-1) may be 90 mol%, 95 mol%, 99 mol% or 100 mol%. The diamine component may consist of only the compound which gives the structural unit (B-1).

The diamine component may include a compound other than the compound that provides the structural unit (B-1), and examples of the compound include the above-mentioned aromatic diamine, alicyclic diamine, and aliphatic diamine, and their derivatives (diisocyanate, etc.). Is mentioned.
The compound optionally contained in the diamine component (that is, the compound other than the compound providing the structural unit (B-1)) may be one type or two or more types.

As the compound optionally contained in the diamine component, a compound giving the structural unit (B-2) (that is, a compound giving the structural unit (B-2-1), a compound giving the structural unit (B-2-2), At least one selected from the group consisting of a compound giving the structural unit (B-2-3) and a compound giving the structural unit (B-2-4) is preferable, and among them, the structural unit (B-2-3) Are more preferred.
Examples of the compound providing the structural unit (B-2) include a compound represented by the formula (b-2-1), a compound represented by the formula (b-2-2), and a compound represented by the formula (b-2-3). Examples thereof include the compound represented by the formula (b-2-4) and the compound represented by the formula (b-2-4), and the derivative may be used as long as the same constitutional unit can be formed. Examples of the derivative include diisocyanates corresponding to the diamines represented by the formulas (b-2-1) to (b-2-4). As the compound providing the structural unit (B-2), compounds represented by formula (b-2-1) to formula (b-2-4) (that is, diamine) are preferable.

When the diamine component contains a compound which gives the structural unit (B-1) and a compound which gives the structural unit (B-2), the diamine component preferably contains 70 to 95 mol% of the compound which gives the structural unit (B-1). Included, more preferably 75 to 95 mol%, still more preferably 75 to 90 mol%, preferably 5 to 30 mol%, more preferably 5 to 25 mol% of the compound providing the structural unit (B-2). And more preferably 10 to 25 mol %.
The total amount of the diamine component containing the compound giving the structural unit (B-1) and the compound giving the structural unit (B-2) is preferably 75 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more. It is contained in an amount of not less than mol %, particularly preferably not less than 99 mol %. The upper limit of the total content ratio of the compound providing the structural unit (B-1) and the compound providing the structural unit (B-2) is not particularly limited, that is, 100 mol%. The diamine component may consist of only the compound which gives the structural unit (B-1) and the compound which gives the structural unit (B-2).

The compound giving the structural unit (B-2) may be only the compound giving the structural unit (B-2-1), or may be only the compound giving the structural unit (B-2-2), Only the compound providing the structural unit (B-2-3) may be used, or only the compound providing the structural unit (B-2-4) may be used.
The compound that provides the structural unit (B-2) is a combination of two or more compounds selected from the group consisting of compounds that provide the structural units (B-2-1) to (B-2-4). Good.

In the present invention, the charge ratio of the tetracarboxylic acid component and the diamine component used for producing the polyimide resin is preferably 0.9 to 1.1 mol of the diamine component with respect to 1 mol of the tetracarboxylic acid component.

In the present invention, in addition to the above-mentioned tetracarboxylic acid component and diamine component, an endcapping agent may be used in the production of the polyimide resin. As the terminal blocking agent, monoamines or dicarboxylic acids are preferable. The amount of the terminal blocking agent introduced is preferably 0.0001 to 0.1 mol, and particularly preferably 0.001 to 0.06 mol, per 1 mol of the tetracarboxylic acid component. Examples of monoamine endcapping agents include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3- Ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline and the like are recommended. Of these, benzylamine and aniline can be preferably used. As the dicarboxylic acid end capping agent, dicarboxylic acids are preferable, and a part thereof may be ring-closed. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenone dicarboxylic acid, 3,4-benzophenone dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1 , 2-dicarboxylic acid and the like are recommended. Of these, phthalic acid and phthalic anhydride can be preferably used.

The method for reacting the above-mentioned tetracarboxylic acid component and diamine component is not particularly limited, and a known method can be used.
As a specific reaction method, (1) a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged in a reactor, stirred at room temperature (about 20° C.) to 80° C. for 0.5 to 30 hours, and then heated. A method of performing an imidization reaction by heating, (2) charging a diamine component and a reaction solvent into a reactor and dissolving them, and then charging a tetracarboxylic acid component, if necessary, at room temperature (about 20°C) to 80°C A method of stirring for 0.5 to 30 hours and then raising the temperature to perform an imidization reaction, (3) charging a tetracarboxylic acid component, a diamine component, and a reaction solvent into a reactor and immediately raising the temperature to perform the imidization reaction. And the like.

The reaction solvent used for producing the polyimide resin may be any solvent that does not inhibit the imidization reaction and that can dissolve the generated polyimide. For example, an aprotic solvent, a phenol solvent, an ether solvent, a carbonate solvent, etc. are mentioned.

Specific examples of the aprotic solvent include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone and tetramethylurea. Amide solvents, γ-butyrolactone, γ-valerolactone, and other lactone solvents, hexamethylphosphoric amide, hexamethylphosphinetriamide, and other phosphorus-containing amide solvents, dimethyl sulfone, dimethyl sulfoxide, sulfolane, and other sulfur-containing solvents Examples thereof include system solvents, ketone solvents such as acetone, cyclohexanone and methylcyclohexanone, amine solvents such as picoline and pyridine, ester solvents such as acetic acid (2-methoxy-1-methylethyl).

Specific examples of the phenolic solvent include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4. -Xylenol, 3,5-xylenol and the like can be mentioned.
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 and the like can be mentioned.
In addition, specific examples of the carbonate-based solvent include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate and the like.
Among the above reaction solvents, amide solvents or lactone solvents are preferable. Moreover, you may use the said reaction solvent individually or in mixture of 2 or more types.

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

In the above imidization reaction, a known imidization catalyst can be used. Examples of the imidization catalyst include a base catalyst and an acid catalyst.
As the base catalyst, pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, tripropylamine, tributylamine, triethylenediamine, imidazole, N,N Examples include organic base catalysts such as dimethylaniline and N,N-diethylaniline, and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogen carbonate, and sodium hydrogen carbonate.
As the acid catalyst, 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. Is mentioned. The above imidization catalysts may be used alone or in combination of two or more.
Among the above, from the viewpoint of handleability, it is preferable to use a base catalyst, more preferable to use an organic base catalyst, further preferable to use triethylamine, and particularly preferable to use triethylamine and triethylenediamine in combination.

The temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C., from the viewpoint of reaction rate and suppression of gelation and the like. 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 can dissolve the polyimide resin, but it is preferable to use the compounds described above as the reaction solvent used in the production of the polyimide resin, 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 a polymerization method is dissolved in a reaction solvent, or may be one obtained by further adding a diluting solvent to the polyimide solution.

Since the polyimide resin of the present invention has solvent solubility, it can be a highly concentrated varnish stable at room temperature. The polyimide varnish of the present invention preferably contains the polyimide resin of the present invention in an amount of 5 to 40% by mass, more preferably 10 to 30% by mass. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, more preferably 2 to 100 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 is an inorganic filler, an adhesion promoter, a release agent, a flame retardant, an ultraviolet stabilizer, a surfactant, a leveling agent, a defoaming agent, and a fluorescent enhancer within a range that does not impair the required properties of the polyimide film. It may contain various additives such as a whitening agent, a crosslinking agent, a polymerization initiator, and a photosensitizer.
The method for producing the polyimide varnish of the present invention is not particularly limited, and a known method can be applied.

[Polyimide film]
The polyimide film of the present invention contains the polyimide resin of the present invention. Therefore, the polyimide film of the present invention is excellent in colorless transparency, optical isotropy, and chemical resistance (solvent resistance, acid resistance and alkali resistance). Suitable 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 a known method can be used. For example, the polyimide varnish of the present invention, a glass plate, a metal plate, after coating on a smooth support such as plastic, or molded into a film, an organic solvent such as a reaction solvent or a diluting solvent contained in the varnish. Examples include a method of removing by heating.

Examples of the coating method include known coating methods such as spin coating, slit coating, and blade coating. Among them, the slit coat is preferable from the viewpoint of controlling intermolecular orientation and improving chemical resistance and workability.
As a method of removing the organic solvent contained in the varnish by heating, after evaporating the organic solvent at a temperature of 150° C. or less to be tack-free, a temperature equal to or higher than the boiling point of the used organic solvent (not particularly limited, preferably It is preferable to dry at 200 to 500°C. Further, it is preferable to dry under an air atmosphere or a nitrogen atmosphere. The pressure of the dry atmosphere may be any of reduced pressure, normal pressure and increased pressure.
The method of peeling the polyimide film formed on the support from the support is not particularly limited, but a laser lift-off method or a method of using a sacrificial layer for peeling (a release agent is applied to the surface of the support in advance. Method).

Further, the polyimide film of the present invention can also be produced using a polyamic acid varnish obtained by dissolving polyamic acid in an organic solvent.
The polyamic acid contained in the polyamic acid varnish includes a compound that gives the above-mentioned structural unit (A-1) and a compound that gives the above-mentioned structural unit (A-2), which are precursors of the polyimide resin of the present invention. It is a product of a polyaddition reaction between a tetracarboxylic acid component and a diamine component containing 70 mol% or more of the compound which gives the structural unit (B-1). By imidizing (dehydrating and ring-closing) this polyamic acid, the final product of the polyimide resin of the present invention can be obtained.
As the organic solvent contained in the polyamic acid varnish, the organic solvent contained in the polyimide varnish of the present invention can be used.
In the present invention, the polyamic acid varnish may be a polyamic acid solution itself obtained by polyaddition reaction of a tetracarboxylic acid component and a diamine component in a reaction solvent, or further diluted with respect to the polyamic acid solution. It may be a solvent added.

The method for producing a polyimide film using a polyamic acid varnish is not particularly limited, and a known method can be used. For example, a polyamic acid varnish is applied on a smooth support such as a glass plate, a metal plate, or a plastic, or formed into a film, and an organic solvent such as a reaction solvent or a diluting solvent contained in the varnish is removed by heating. Then, a polyamic acid film is obtained, and the polyamic acid in the polyamic acid film is imidized by heating to produce a polyimide film.
The heating temperature for drying the polyamic acid varnish to obtain a polyamic acid film is preferably 50 to 120°C. The heating temperature for imidizing the polyamic acid 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 further preferably 10 to 80 μm. A thickness of 1 to 250 μm enables practical use as a self-supporting film.
The thickness of the polyimide film can be easily controlled by adjusting the solid content concentration and viscosity of the polyimide varnish.

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

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples.

In Examples and Comparative Examples, each physical property was measured by the methods described below.
(1) Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.
(2) Tensile Strength and Tensile Elastic Modulus Tensile strength and tensile elastic modulus were measured using a tensile tester “STROGRAPH VG-1E” manufactured by Toyo Seiki Co., Ltd. according to JIS K7127:1999. The distance between chucks was 50 mm, the size of the test piece was 10 mm×70 mm, and the test speed was 20 mm/min.
(3) Glass transition temperature (Tg)
Residual stress is removed using a thermo-mechanical analyzer "TMA/SS6100" manufactured by Hitachi High-Tech Science Co., Ltd. in the tensile mode under the conditions of sample size 2 mm x 20 mm, load 0.1 N, and heating rate 10 °C/min The temperature was raised to a temperature sufficient to remove residual stress, and then cooled to room temperature. Then, the elongation of the test piece was measured under the same conditions as the treatment for removing the residual stress, and the point where the inflection point of the elongation was observed was determined as the glass transition temperature.
(4) Total light transmittance, yellow index (YI), b ^*
The total light transmittance, YI and b ^* were measured according to JIS K7105:1981 using a color/turbidity simultaneous measuring device “COH400” manufactured by Nippon Denshoku Industries Co., Ltd.
(5) Thickness phase difference (Rth)
The thickness retardation (Rth) was measured using an ellipsometer “M-220” manufactured by JASCO Corporation. The value of the thickness retardation at a measurement wavelength of 590 nm was measured. Note that Rth is represented by the following formula when the maximum in-plane refractive index of the polyimide film is nx, the minimum is ny, the thickness direction refractive index is nz, and the film thickness is d. It is something.
Rth=[{(nx+ny)/2}-nz]×d
(6) Solvent resistance A solvent was dropped at room temperature on a polyimide film formed on a glass plate, and it was confirmed whether the film surface was changed. In addition, propylene glycol monomethyl ether acetate (PGMEA) was used as a solvent.
The evaluation criteria for solvent resistance were as follows.
A: There was no change on the film surface.
B: The surface of the film was slightly cracked.
C: The film surface was cracked or the film surface was dissolved.
(7) Acid resistance (mixed acid ΔYI and mixed acid Δb ^* )
Of a mixed acid (H ₃ PO ₄ (70 mass %)+HNO ₃ (10 mass %)+CH ₃ COOH (5 mass %)+H ₂ O (15 mass %) obtained by heating a polyimide film formed on a glass plate to 40° C. It was immersed in a mixed solution) for 4 minutes and then washed with water. After washing with water, the water was wiped off, the mixture was heated on a hot plate at 240° C. for 50 minutes, and dried. YI and b ^* were measured before and after the test, and the change (ΔYI and Δb ^* ) was determined. The YI measurement and the b ^* measurement here were carried out in a state in which a polyimide film was formed on a glass plate (a glass plate+a polyimide film).
(8) Alkali resistance A polyimide film formed on a glass plate was immersed in an aqueous potassium hydroxide solution having a concentration of 3% by mass for 5 minutes at room temperature and then washed with water. After washing with water, it was confirmed that the film surface did not change.
The evaluation criteria of alkali resistance were as follows.
A: There was no change on the film surface.
B: The surface of the film was slightly cracked.
C: The film surface was cracked or the film surface was dissolved.

The tetracarboxylic acid component and diamine component used in the examples and comparative examples, and their abbreviations are as follows.
<Tetracarboxylic acid component>
HPMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Co., Inc.; compound represented by formula (a-1))
ODPA: 4,4′-oxydiphthalic anhydride (manac KK; compound represented by formula (a-2))
<Diamine component>
3,3′-DDS: 3,3′-diaminodiphenyl sulfone (manufactured by Seika Ltd.; compound represented by formula (b-1))
6FODA: 4,4′-diamino-2,2′-bistrifluoromethyldiphenyl ether (manufactured by ChinaTech Chemical (Tianjin) Co., Ltd.; compound represented by formula (b-2-1))
BAFL: 9,9-bis(4-aminophenyl)fluorene (manufactured by Taoka Chemical Co., Ltd.; compound represented by formula (b-2-2))
HFBAPP: 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane (manufactured by Seika Ltd.; compound represented by formula (b-2-3))
TFMB: 2,2'-bis(trifluoromethyl)benzidine (manufactured by Seika Ltd.; compound represented by formula (b-2-4))

<Example 1>
32.841 g of 3,3'-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.132 mol) and γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) (63.328 g) were added, and the solution was obtained by stirring at a system internal temperature of 70° C. and a nitrogen atmosphere at a rotation speed of 200 rpm.
To this solution, 23.720 g (0.106 mol) of HPMDA, 8.206 g (0.026 mol) of ODPA, and 15.832 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. Then, 0.669 g of triethylamine (manufactured by Kanto Kagaku Co., Ltd.) was added as an imidization catalyst and heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was maintained at 190° C. and refluxed for about 5 hours while adjusting the number of rotations according to the increase in viscosity.
Then, 160.841 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 1.

<Example 2>
In a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap, 31.073 g of 3,3′-DDS ( 0.125 mol) and 63.077 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added, and the solution was obtained by stirring at a system internal temperature of 70° C. and a nitrogen atmosphere at a rotation speed of 200 rpm.
To this solution, 14.027 g (0.063 mol) of HPMDA, 19.410 g (0.063 mol) of ODPA, and 15.769 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. Then, 0.633 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) was added as an imidization catalyst and heated by a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was maintained at 190° C. and refluxed for about 5 hours while adjusting the number of rotations according to the increase in viscosity.
After that, 161.154 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogenize. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 1.

<Example 3>
29.486 g of 3,3'-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.119 mol) and γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) (62.851 g) were added, and the solution was obtained by stirring at a system internal temperature of 70° C. and a nitrogen atmosphere at a rotation speed of 200 rpm.
To this solution, 5.324 g (0.024 mol) of HPMDA, 29.470 g (0.095 mol) of ODPA, and 15.713 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. Then, 0.601 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) was added as an imidization catalyst and heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was maintained at 190° C. and refluxed for about 5 hours while adjusting the number of rotations according to the increase in viscosity.
Thereafter, 161.436 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., followed by stirring for about 1 hour to homogenize the mixture. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 1.

<Comparative Example 1>
In a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a Dean Stark equipped with a nitrogen introducing tube, a cooling tube, a thermometer, and a glass end cap, 34.192 g of 3,3′-DDS ( 0.137 mol) and γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added in an amount of 63.495 g, and the solution was obtained by stirring at a system internal temperature of 70° C. and a nitrogen atmosphere at a rotation speed of 200 rpm.
To this solution, 30.746 g (0.0137 mol) of HPMDA and 15.874 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added all at once, and triethylamine (manufactured by Kanto Chemical Co., Ltd.) was used as an imidization catalyst. 0.693 g was added, the mixture was heated with a mantle heater, the temperature in the reaction system was kept at 190° C. over about 20 minutes, and the mixture was refluxed for about 5 hours.
Then, 160.631 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 1.

<Comparative example 2>
28.588 g of 3,3'-DDS was placed in a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.115 mol) and 62.704 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were charged, and the solution was obtained by stirring at a system internal temperature of 70° C. and a nitrogen atmosphere at a rotation speed of 200 rpm.
To this solution, 35.541 g (0.115 mol) of ODPA and 15.676 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once, and triethylamine (manufactured by Kanto Chemical Co., Ltd.) was used as an imidization catalyst. ) Was charged and heated by a mantle heater, and the temperature in the reaction system was raised to 190° C. in about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was maintained at 190° C. and refluxed for about 5 hours while adjusting the number of rotations according to the increase in viscosity.
Thereafter, 161.620 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogenize. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 1.

<Comparative example 3>
36.092 g (0.103 mol) of BAFL was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 63.309 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added, and the solution was obtained by stirring at a system internal temperature of 70° C. and a nitrogen atmosphere at a rotation speed of 200 rpm.
To this solution, 11.598 g (0.052 mol) of HPMDA, 16.35 g (0.052 mol) of ODPA, and 15.577 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. Then, 0.523 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) was added as an imidization catalyst and heated by a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was maintained at 190° C. and refluxed for about 5 hours while adjusting the number of rotations according to the increase in viscosity.
Then, 162.113 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and then stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 1.

<Example 4>
25.353 g of 3,3′-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.102 mol), 6FODA (8.547 g (0.025 mol)), and γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) (63.142 g) were added, the system temperature was 70°C, and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 22.797 g (0.102 mol) of HPMDA, 7.880 g (0.025 mol) of ODPA, and 15.785 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.643 g of triethylamine (manufactured by Kanto Kagaku Co., Ltd.) was added as an imidization catalyst and heated by a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Then, 161.073 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration became 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogenize. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Example 5>
In a 300 mL five-necked round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap, 24.04 g of 3,3'-DDS ( 0.096 mol), 6.106 g (0.024 mol) of 6FODA, and 62.910 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were charged, and the system temperature was 70° C., under a nitrogen atmosphere, and the rotation speed was 200 rpm. A solution was obtained by stirring.
To this solution, 13.512 g (0.060 mol) of HPMDA, 18.681 g (0.060 mol) of ODPA, and 15.728 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.609 g of triethylamine (manufactured by Kanto Kagaku Co., Ltd.) was charged as an imidization catalyst and heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Thereafter, 161.362 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Example 6>
25.822 g of 3,3′-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.103 mol), 6.706 g (0.026 mol) of 6FODA, and 63.225 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were charged, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 26.121 g (0.116 mol) of HPMDA, 4.013 g (0.013 mol) of ODPA, and 15.806 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.654 g of triethylamine (manufactured by Kanto Kagaku Co., Ltd.) was charged as an imidization catalyst and heated by a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Then, 160.969 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Example 7>
25.218 g of 3,3′-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.101 mol), 8.821 g (0.025 mol) of BAFL, and 63.118 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were charged, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 22.676 g (0.101 mol) of HPMDA, 7.838 g (0.025 mol) of ODPA, and 15.780 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.639 g of triethylamine (manufactured by Kanto Kagaku Co., Ltd.) was charged as an imidization catalyst and heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Then, 161.102 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Example 8>
23.921 g of 3,3'-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.096 mol), 8.367 g (0.024 mol) of BAFL, and 62.889 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were charged, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 13.444 g (0.060 mol) of HPMDA, 18.587 g (0.060 mol) of ODPA, and 15.722 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.606 g of triethylamine (manufactured by Kanto Kagaku Co., Ltd.) was added as an imidization catalyst and heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Thereafter, 161.389 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogenize. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Example 9>
23.530 g of 3,3'-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.094 mol), 12.247 g (0.024 mol) of HFBAPP, and 62.820 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 21.158 g (0.094 mol) of HPMDA, 7.313 g (0.024 mol) of ODPA, and 15.705 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.596 g of triethylamine (manufactured by Kanto Kagaku Co., Ltd.) was charged as an imidization catalyst and heated by a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Then, 161.475 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Example 10>
22.397 g of 3,3'-DDS was placed in a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.090 mol), 11.657 g (0.022 mol) of HFBAPP, and 62.620 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were charged, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 12.587 g (0.056 mol) of HPMDA, 17.402 g (0.056 mol) of ODPA, and 15.655 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.568 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) was added as an imidization catalyst and heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Then, 161.725 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogenize. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Example 11>
23.933 g of 3,3'-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.096 mol), 12.457 g (0.024 mol) of HFBAPP, and 62.891 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 24.211 g (0.108 mol) of HPMDA, 3.719 g (0.012 mol) of ODPA, and 15.723 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.607 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) was added as an imidization catalyst and heated by a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Thereafter, 161.386 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration became 20% by mass, and the temperature in the reaction system was cooled to 100° C., and then stirred for about 1 hour to be uniform. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Example 12>
26.000 g of 3,3'-DDS was placed in a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.104 mol), 8.351 g (0.026 mol) of TFMB, and 63.256 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 26.302 g (0.117 mol) of HPMDA, 4.041 g (0.013 mol) of ODPA, and 15.814 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.659 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) was added as an imidization catalyst and heated by a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Thereafter, 160.930 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and then stirred for about 1 hour to homogenize. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Comparative example 4>
15.356 g of 3,3'-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.062 mol), 21.485 g (0.062 mol) of BAFL, and 63.004 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 27.594 g (0.123 mol) of HPMDA and 15.751 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added all at once, and triethylamine (manufactured by Kanto Chemical Co., Ltd.) was used as an imidization catalyst. 0.623 g was added and the mixture was heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. in about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
After that, 162.246 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Comparative Example 5>
13.053 g of 3,3'-DDS was added to a 300 mL 5-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.052 mol), 18.263 g (0.052 mol) of BAFL, and 62.353 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 32.455 g (0.105 mol) of ODPA and 15.588 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once, and triethylamine (manufactured by Kanto Chemical Co., Ltd.) was used as an imidization catalyst. ) Was charged and heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. in about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Thereafter, 162.059 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, the temperature in the reaction system was cooled to 100° C., and the mixture was further stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

<Comparative example 6>
14.109 g of 3,3'-DDS was added to a 300 mL five-neck round bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen introduction tube, a Dean Stark equipped with a cooling tube, a thermometer, and a glass end cap. 0.057 mol), 19.740 g (0.057 mol) of BAFL, and 62.651 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were charged, and the system temperature was 70° C. and the rotation speed was 200 rpm under a nitrogen atmosphere. A solution was obtained by stirring.
To this solution, 12.687 g (0.057 mol) of HPMDA, 17.540 g (0.057 mol) of ODPA, and 15.663 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. After that, 0.572 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) was added as an imidization catalyst and heated by a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the temperature in the reaction system was kept at 190° C. and refluxed for 5 hours while adjusting the number of rotations according to the increase in viscosity.
Thereafter, 161.686 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content concentration was 20% by mass, and the temperature in the reaction system was cooled to 100° C., and further stirred for about 1 hour to homogeneity. To obtain a polyimide varnish.
Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, kept at 80°C for 20 minutes on a hot plate, and then heated at 260°C for 30 minutes in a hot air dryer in an air atmosphere to evaporate the solvent. To obtain a film. The results are shown in Table 2.

The film of Comparative Example 1 was significantly deteriorated when immersed in a mixed acid in the acid resistance test, so that the YI and b ^* after immersion could not be measured. Therefore, ΔYI and Δb ^* of Comparative Example 1 were not obtained.

As shown in Table 1, the polyimide films of Examples 1 to 3 were produced by using HPMDA and ODPA in combination as the tetracarboxylic acid component and 3,3′-DDS as the diamine component. As a result, it was excellent in colorless transparency, optical isotropy, and chemical resistance (solvent resistance, acid resistance and alkali resistance).
On the other hand, the polyimide film of Comparative Example 1 was manufactured using only HPMDA as the tetracarboxylic acid component. As a result, the acid resistance was poor.
The polyimide film of Comparative Example 2 was manufactured using only ODPA as the tetracarboxylic acid component. As a result, the colorless transparency and the optical isotropy were poor.
The polyimide film of Comparative Example 3 was manufactured using BAFL only without using 3,3′-DDS as a diamine component. As a result, the acid resistance was poor.

Further, as shown in Table 2, the polyimide films of Examples 4 to 12 used not only 3,3′-DDS as the diamine component but also a second diamine (6FODA, BAFL, HFBAPP, or TFMB) other than that. Manufactured. However, 3,3′-DDS and secondary diamine were used in combination so that the ratio of 3,3′-DDS was 70 mol% or more. As a result, it was excellent in colorless transparency, optical isotropy, and chemical resistance (solvent resistance, acid resistance and alkali resistance).
On the other hand, the polyimide film of Comparative Example 4 was produced by using 3,3′-DDS as the diamine component in combination with the other second diamine (BAFL), and the ratio of the 3,3′-DDS used was 70. It was less than mol %. Further, only HPMDA was used as the tetracarboxylic acid component. As a result, the acid resistance was poor.
The polyimide film of Comparative Example 5 was produced by using 3,3′-DDS as the diamine component and the other secondary diamine (BAFL) in combination, and the ratio of the 3,3′-DDS used was 70 mol %. Was less than. Furthermore, only ODPA was used as the tetracarboxylic acid component. As a result, the colorless transparency (total light transmittance), optical isotropy, and acid resistance were poor.
The polyimide film of Comparative Example 6 was produced by using 3,3'-DDS as the diamine component and the other secondary diamine (BAFL) in combination, and the ratio of the 3,3'-DDS used was 70 mol%. Was less than. As a result, the optical isotropy and acid resistance were poor.

Claims (4)

1. A polyimide resin having a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from a diamine,
   A structural unit A is a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) is derived from a compound represented by the following formula (a-2). Including and
   The structural unit B contains a structural unit (B-1) derived from a compound represented by the following formula (b-1),
   A polyimide resin in which the ratio of the structural unit (B-1) in the structural unit B is 70 mol% or more.
   

   
2. The ratio of the structural unit (A-1) in the structural unit A is 5 to 95 mol %,
   The polyimide resin according to claim 1, wherein the ratio of the structural unit (A-2) in the structural unit A is 5 to 95 mol%.
3. A polyimide varnish obtained by dissolving the polyimide resin according to claim 1 or 2 in an organic solvent.
4. A polyimide film containing the polyimide resin according to claim 1 or 2.