JP7694563B2 - Polyimide resin, polyimide varnish and polyimide film - Google Patents

Description

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

Polyimide resins are obtained, for example, from aromatic tetracarboxylic acid anhydrides and aromatic diamines. In general, polyimide resins have excellent heat resistance, chemical resistance, mechanical properties, and electrical characteristics due to molecular rigidity, resonance stabilization, and strong chemical bonds, and are therefore widely used in fields such as molding materials, composite materials, electrical and electronic parts, optical materials, displays, and aerospace.
In the above-mentioned applications, transparency is particularly important, and efforts are being made to improve the transparency of polyimide resins.

Patent Document 1 discloses a polyimide having TAHMBP and the like as a structural unit in order to improve transparency, heat resistance, solvent processability, etc.

International Publication No. 2014/046180

In recent years, applications of polyimide resins have progressed, particularly in displays and the front panels that protect them, and highly elastic polyimide resins are required as replacements for the glass materials that have been used conventionally. However, conventional highly elastic polyimide resins often have problems such as poor transparency.
Recently, polyimide films have also been used in displays and protective plates for smartphones with a foldable structure, so they are required to be flexible while still being highly elastic. They also need properties such as the ability to recover their shape after deformation and the ability to stretch.
Therefore, a polyimide resin having all these properties is desired.
In other words, the problem to be solved by the present invention is to provide a polyimide resin which is capable of forming a film which has both high elasticity and transparency and is also excellent in deformation recovery and elongation while being highly elastic, and a polyimide film which has both high elasticity and transparency and is also excellent in deformation recovery and elongation.

As a result of extensive research, the inventors discovered that a polyimide resin having structural units derived from two specific types of tetracarboxylic dianhydrides can be used to form a film that combines high elasticity with transparency and is highly elastic while also exhibiting excellent deformation recovery and elongation, thus arriving at the present invention.

［２］前記構成単位Ａに対する前記構成単位（Ａ２）の割合が、１０～８０モル％である、前記［１］に記載のポリイミド樹脂。
［３］前記構成単位Ｂが、下記一般式（ｂ１）で表される化合物に由来する構成単位（Ｂ１）を含む、前記［１］又は［２］に記載のポリイミド樹脂。

（式（ｂ１）中、Ｘは単結合又は酸素原子である。）
［４］前記構成単位Ｂが、さらに下記式（ｂ２）で表される化合物に由来する構成単位（Ｂ２）を含む、前記［１］～［３］のいずれか１つに記載のポリイミド樹脂。

［５］前記構成単位Ａに対する前記構成単位（Ａ１）の割合が、２０～９０モル％である、前記［１］～［４］のいずれか１つに記載のポリイミド樹脂。
［６］前記構成単位Ｂに対する前記構成単位（Ｂ１）の割合が、７０モル％以上である、前記［３］～［５］のいずれか１つに記載のポリイミド樹脂。
［７］前記［１］～［６］のいずれか１つに記載のポリイミド樹脂が有機溶剤に溶解してなるポリイミドワニス。
［８］前記［１］～［６］のいずれか１つに記載のポリイミド樹脂を含む、ポリイミドフィルム。 That is, the present invention relates to the following [1] to [8].
[1] A polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine,
A polyimide resin, wherein the structural unit A includes a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from a compound represented by the following formula (a2):

[2] The polyimide resin according to [1] above, wherein the ratio of the structural unit (A2) to the structural unit A is 10 to 80 mol %.
[3] The polyimide resin according to [1] or [2] above, wherein the structural unit B includes a structural unit (B1) derived from a compound represented by the following general formula (b1):

(In formula (b1), X is a single bond or an oxygen atom.)
[4] The polyimide resin according to any one of [1] to [3] above, wherein the structural unit B further contains a structural unit (B2) derived from a compound represented by the following formula (b2):

[5] The polyimide resin according to any one of [1] to [4] above, wherein the ratio of the structural unit (A1) to the structural unit A is 20 to 90 mol %.
[6] The polyimide resin according to any one of [3] to [5] above, wherein the ratio of the structural unit (B1) to the structural unit B is 70 mol % or more.
[7] A polyimide varnish obtained by dissolving the polyimide resin according to any one of [1] to [6] above in an organic solvent.
[8] A polyimide film comprising the polyimide resin according to any one of [1] to [6] above.

According to the present invention, it is possible to provide a polyimide resin that combines high elasticity and transparency and is capable of forming a film that is highly elastic yet also has excellent deformation recovery and elongation, a polyimide varnish that contains the polyimide resin, and a polyimide film that combines high elasticity and transparency and also has excellent deformation recovery and elongation.

FIG. 2 is a conceptual diagram showing a method for measuring the deformation recovery property of a polyimide film.

以下、本発明のポリイミド樹脂について説明する。 [Polyimide resin]
The polyimide resin of the present invention is a polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine,
The structural unit A includes a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from a compound represented by the following formula (a2).

The polyimide resin of the present invention will now be described.

[Structural Unit A]
The structural unit A contained in the polyimide of the present invention is a structural unit derived from a tetracarboxylic dianhydride contained in the polyimide resin.
The structural unit A includes a structural unit (A1) derived from a compound represented by the above formula (a1), and a structural unit (A2) represented by the above formula (a2).

The compound represented by the formula (a1) is 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (TMPBP-TME).
When the structural unit A contains the structural unit (A1), the elastic modulus of the resulting polyimide resin is improved.

The compound represented by the formula (a2) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA).
When the structural unit A contains the structural unit (A2), the transparency can be improved while maintaining the elastic modulus, and the elongation can also be improved.
In this way, by having structural units derived from the two types of tetracarboxylic dianhydrides, high elasticity and transparency are achieved at the same time, and the reason why the resin is also excellent in deformation recovery and elongation is not clear, but it is thought to be due to the rigidity of the ester group and the transparency of the alicyclic compound.

The proportion of the structural unit (A1) relative to the structural unit A is preferably 20 to 90 mol%, more preferably 20 to 80 mol%, even more preferably 30 to 80 mol%, still more preferably 50 to 80 mol%, even more preferably 50 to 70 mol%, and still more preferably 55 to 65 mol%.
The proportion of the structural unit (A2) relative to the structural unit A is preferably 10 to 80 mol%, more preferably 20 to 80 mol%, even more preferably 20 to 70 mol%, still more preferably 20 to 50 mol%, even more preferably 30 to 50 mol%, and still more preferably 35 to 45 mol%.

The total ratio of the structural unit (A1) and the structural unit (A2) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. The upper limit of the total ratio of the structural unit (A1) and the structural unit (A2) is not particularly limited and is 100 mol% or less. The structural unit A may consist of only the structural unit (A1) and the structural unit (A2).

The molar ratio of structural unit (A1) to structural unit (A2) in structural unit A [(A1):(A2)] is, from the viewpoint of improving elastic modulus, elongation, transparency and deformation recovery, preferably 20:80 to 90:10, more preferably 20:80 to 80:20, even more preferably 30:70 to 80:20, still more preferably 50:50 to 80:20, even more preferably 50:50 to 70:30, and even more preferably 55:45 to 65:35.

The polyimide resin of the present invention may contain, in the structural unit A, a structural unit derived from a tetracarboxylic dianhydride other than the compound represented by the above formula (a1) and the compound represented by the above formula (a2), as a structural unit other than the above structural unit (A1) and the structural unit (A2), within a range that does not impair the effects of the present invention.
The tetracarboxylic dianhydride other than the compound represented by the formula (a1) and the compound represented by the formula (a2) is not particularly limited, but examples thereof include aromatic tetracarboxylic dianhydrides such as pyromellitic anhydride, 2,3,5,6-toluenetetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride; alicyclic tetracarboxylic dianhydrides such as 1,2,4,5-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, dicyclohexyltetracarboxylic dianhydride, or positional isomers thereof; and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride and 1,2,3,4-pentanetetracarboxylic dianhydride. These can be used alone or in combination of two or more.

In this specification, aromatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing one or more aromatic rings, alicyclic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing one or more alicyclic rings and no aromatic rings, and aliphatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring.

[Structural Unit B]
The structural unit B contained in the polyimide of the present invention is a structural unit derived from a diamine.
There are no limitations on the diamine-derived structural unit contained in the structural unit B, but preferred structural units will be described below.

（式（ｂ１）中、Ｘは単結合又は酸素原子である。） The structural unit B contained in the polyimide of the present invention preferably contains a structural unit (B1) derived from a compound represented by the following general formula (b1): By containing the structural unit (B1), the elastic modulus, elongation, transparency, and deformation recovery property are improved.

(In formula (b1), X is a single bond or an oxygen atom.)

The structural unit (B1) preferably contains at least one structural unit selected from the group consisting of a structural unit (B11) derived from a compound represented by the following formula (b11) and a structural unit (B12) derived from a compound represented by the following formula (b12), and from the viewpoints of transparency, elastic modulus, and colorlessness, it is more preferable that the structural unit (B11) derived from a compound represented by the following formula (b11) is contained. Also, from the viewpoint of elongation, it is more preferable that the structural unit (B12) derived from a compound represented by the following formula (b12) is contained.
The structural unit (B1) may include only one of the structural unit (B11) or the structural unit (B12), or may include both.

The compound represented by formula (b11) is 2,2'-bis(trifluoromethyl)benzidine (TFMB).

The compound represented by formula (b12) is 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA).

The ratio of the structural unit (B1) to the structural unit B is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 70 mol% or more, and even more preferably 85 mol% or more. The upper limit of the ratio of the structural unit (B1) is not particularly limited and is 100 mol% or less.

The structural unit B may contain a structural unit (B2) derived from a compound represented by the following formula (b2), and from the viewpoint of improving the elastic modulus, it preferably contains a structural unit (B2) derived from a compound represented by the following formula (b2):

The ratio of the structural unit (B2) to the structural unit B is preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less, from the viewpoints of transparency and deformation recovery. It may be 15 mol% or less. In addition, the lower limit of the ratio of the structural unit (B2) is not particularly limited and is 0 mol% or more, but from the viewpoint of improving the elastic modulus, it is preferably 5 mol% or more.

When the structural unit B contains the structural unit (B1) and the structural unit (B2), the total ratio of the structural unit (B1) and the structural unit (B2) in the structural unit B is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. The upper limit of the total ratio of the structural units (B1) and (B2) is not particularly limited and is 100 mol% or less. The structural unit B may be composed of only the structural unit (B1) and the structural unit (B2).

The polyimide resin of the present invention may contain, in the structural unit B, a structural unit derived from a diamine other than the compound represented by the general formula (b1) above and the compound represented by the formula (b2) above, as a structural unit other than the structural unit (B1) and the structural unit (B2) above, as long as the effects of the present invention are not impaired.
Diamines other than the compound represented by the general formula (b1) and the compound represented by the formula (b2) are not particularly limited, and examples thereof include 1,4-phenylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenylmethane, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro- Examples of the diamines include aromatic diamines such as 1,3,3-trimethyl-1H-indene-5-amine, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, N,N'-bis(4-aminophenyl)terephthalamide, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, and 1,4-bis(4-aminophenoxy)benzene; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; aliphatic diamines such as ethylenediamine and hexamethylenediamine; and modified silicone diamines. These can be used alone or in combination of two or more.

In this specification, aromatic diamine means a diamine containing one or more aromatic rings, alicyclic diamine means a diamine containing one or more alicyclic rings but no aromatic rings, and aliphatic diamine means a diamine containing neither an aromatic ring nor an alicyclic ring.

[Characteristics of polyimide resin]
From the viewpoint of the mechanical strength of the resulting polyimide film, the number average molecular weight of the polyimide resin of the present invention is preferably 5,000 to 100,000. The number average molecular weight of the polyimide resin can be measured by gel filtration chromatography or the like.

The polyimide resin of the present invention may further contain various additives, such as antioxidants, light stabilizers, surfactants, flame retardants, plasticizers, and polymer compounds other than the polyimide resin, as long as the effects of the present invention are not impaired.
Examples of the polymer compound include polyimides other than the polyimide resin of the present invention, polycarbonates, polystyrenes, polyamides, polyamideimides, polyesters such as polyethylene terephthalate, polyethersulfones, polycarboxylic acids, polyacetals, polyphenylene ethers, polysulfones, polybutylenes, polypropylenes, polyacrylamides, and polyvinyl chlorides.

[Method for producing polyimide resin]
The polyimide resin of the present invention can be produced by reacting a tetracarboxylic acid component containing a compound which provides the structural unit (A1) and a compound which provides the structural unit (A2) with a diamine component.

Compounds that provide the structural unit (A1) include, but are not limited to, compounds represented by formula (a1), and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydride represented by formula (a1) and alkyl esters of the tetracarboxylic acid. Compounds that provide the structural unit (A1) are preferably compounds represented by formula (a1) (i.e., dianhydrides).
Similarly, examples of compounds that provide the structural unit (A2) include, but are not limited to, compounds represented by formula (a2), and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydride represented by formula (a2) and alkyl esters of the tetracarboxylic acid. Compounds that provide the structural unit (A-2) are preferably compounds represented by formula (a2) (i.e., dianhydrides).

The tetracarboxylic acid component contains a compound that provides the structural unit (A1) in an amount of preferably 20 to 90 mol %, more preferably 20 to 80 mol %, even more preferably 30 to 80 mol %, still more preferably 50 to 80 mol %, even more preferably 50 to 70 mol %, and even more preferably 55 to 65 mol %.
The tetracarboxylic acid component contains a compound that provides the structural unit (A2) in an amount of preferably 10 to 80 mol %, more preferably 20 to 80 mol %, even more preferably 20 to 70 mol %, still more preferably 20 to 50 mol %, even more preferably 30 to 50 mol %, and even more preferably 35 to 45 mol %.

The total content ratio of the compound that gives the structural unit (A1) and the compound that gives the structural unit (A2) is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more, in the total tetracarboxylic acid component. The upper limit of the total content ratio of the compound that gives the structural unit (A1) and the compound that gives the structural unit (A2) is not particularly limited and is 100 mol% or less. The tetracarboxylic acid component may consist only of the compound that gives the structural unit (A1) and the compound that gives the structural unit (A2).

The molar ratio of the compound that provides structural unit (A1) to the compound that provides structural unit (A2) in the tetracarboxylic acid component [(A1):(A2)] is, from the viewpoint of improving the elastic modulus and transparency, preferably 20:80 to 90:10, more preferably 20:80 to 80:20, even more preferably 30:70 to 80:20, still more preferably 50:50 to 80:20, even more preferably 50:50 to 70:30, and even more preferably 55:45 to 65:35.

The tetracarboxylic acid component may contain a compound other than the compound that provides the structural unit (A1) and the compound that provides the structural unit (A2). Examples of such compounds include the above-mentioned aromatic tetracarboxylic acid dianhydrides, alicyclic tetracarboxylic acid dianhydrides, and aliphatic tetracarboxylic acid dianhydrides, as well as derivatives thereof (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.).
The compound optionally contained in the tetracarboxylic acid component (that is, the compound other than the compound that provides the structural unit (A1) and the structural unit (A2)) may be one type, or two or more types.

The diamine component is not limited, but preferably contains a compound that provides the above-mentioned structural unit (B1).
Compounds that provide the structural unit (B1) include compounds represented by formula (b1), but are not limited thereto, and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the diamines represented by formula (b1). Compounds that provide the structural unit (B1) are preferably compounds represented by formula (b1) (i.e., diamines).

The diamine component preferably contains 30 mol% or more of the compound that gives the structural unit (B1), more preferably 40 mol% or more, even more preferably 50 mol%, even more preferably 70 mol% or more, and even more preferably 85 mol% or more. The upper limit of the proportion of the compound that gives the structural unit (B1) is not particularly limited, and is 100 mol% or less.

The diamine component may contain a compound that provides the structural unit (B2), and from the standpoint of improving the elastic modulus, it preferably contains a compound that provides the structural unit (B2).
Compounds that provide the structural unit (B2) include, but are not limited to, compounds represented by formula (b2), and may be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the diamines represented by formula (b2). Compounds that provide the structural unit (B2) are preferably compounds represented by formula (b2) (i.e., diamines).

The total content ratio of the compound that gives the structural unit (B1) and the compound that gives the structural unit (B2) is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more, in the total diamine component. The upper limit of the total content ratio of the compound that gives the structural unit (B1) and the compound that gives the structural unit (B2) is not particularly limited and is 100 mol% or less. The diamine component may consist only of the compound that gives the structural unit (B1) and the compound that gives the structural unit (B2).

The diamine component may contain a compound other than the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2). Examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, modified silicone diamines, and derivatives thereof (diisocyanates, etc.).
The compound optionally contained in the diamine component (that is, compounds other than the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2)) may be one type, or two or more types.

When producing the polyimide resin of the present invention, the ratio of the tetracarboxylic acid component to the diamine component is preferably 0.9 to 1.1 moles of the diamine component per mole of the tetracarboxylic acid component.

When producing the polyimide resin of the present invention, a terminal blocking agent may be used in addition to the tetracarboxylic acid component and the diamine component. As the terminal blocking agent, monoamines or dicarboxylic acids are preferred. The amount of the terminal blocking agent to be introduced is preferably 0.0001 to 0.1 moles, more preferably 0.001 to 0.06 moles, per mole of the tetracarboxylic acid component. Preferred monoamine terminal blocking agents include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, and 4-methylaniline. Of these, benzylamine and aniline are more preferred. As the dicarboxylic acid terminal blocking agent, dicarboxylic acids are preferred, and a part of them may be ring-closed. Preferred dicarboxylic acids include phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclohexane-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. Of these, phthalic acid and phthalic anhydride are more preferred.

The method for reacting the tetracarboxylic acid component and the diamine component is not particularly limited, and any known method can be used.
Specific reaction methods include: (1) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the mixture is stirred at 10 to 110° C. for 0.5 to 30 hours, and then the temperature is raised to carry out the imidization reaction; (2) a method in which a diamine component and a reaction solvent are charged into a reactor and dissolved, and then the tetracarboxylic acid component is charged, and the mixture is stirred at 10 to 110° C. for 0.5 to 30 hours as necessary, and then the temperature is raised to carry out the imidization reaction; and (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, and the temperature is immediately raised to carry out the imidization reaction.

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

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

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

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

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

When the above catalyst is used, the temperature of the imidization reaction is, from the viewpoint of the reaction rate and suppression of gelation, preferably 120 to 250° C., more preferably 160 to 190° C., and even more preferably 180 to 190° C. The reaction time is preferably 0.5 to 10 hours after the start of distillation of the generated water.
When no catalyst is used, the temperature for the imidization reaction is preferably 200 to 350°C.

[Polyimide varnish]
The polyimide varnish of the present invention is obtained by dissolving the polyimide resin of the present invention in an organic solvent. That is, the polyimide varnish of the present invention contains the polyimide resin of the present invention and an organic solvent, and the polyimide resin is dissolved in the organic solvent.
The organic solvent is not particularly limited as long as it dissolves the polyimide resin. However, it is preferable to use the above-mentioned compounds as reaction solvents used in the production of the polyimide resin, either alone or in combination of two or more kinds.
The polyimide varnish of the present invention preferably contains the polyimide resin of the present invention in an amount of 5 to 60% by mass, more preferably 5 to 45% by mass, and has a viscosity of preferably 0.1 to 200 Pa·s, more preferably 0.5 to 150 Pa·s.

[Polyimide film]
The polyimide film of the present invention contains the above-mentioned polyimide resin.
That is, the polyimide resin has a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, in which the structural unit A contains a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from a compound represented by the following formula (a2).
By containing such a polyimide resin, the polyimide film of the present invention achieves both high elasticity and transparency, and is also excellent in deformation recovery.

There is no particular limitation on the method for producing the polyimide film of the present invention, and any known method can be used. For example, a solution containing the polyimide resin of the present invention, or a solution containing the polyimide resin of the present invention and the various additives described above, is applied to a smooth support such as a glass plate, a metal plate, or a plastic, or formed into a film, and then the solvent components such as organic solvents contained in the solution are removed.

The solution containing the polyimide resin may be a polyimide resin solution obtained by polymerization. It may also be a solution in which at least one compound selected from the compounds exemplified above is mixed with the polyimide resin solution as a solvent in which the polyimide resin dissolves. By adjusting the solids concentration and viscosity of the solution containing the polyimide resin as described above, the thickness of the polyimide film of the present invention can be easily controlled.

A release agent may be applied to the surface of the support as necessary. The following method is preferable as a method for applying a solution containing the polyimide resin or the polyimide resin composition to the support and then heating to evaporate the solvent component. That is, it is preferable to evaporate the solvent at a temperature of 120°C or less to form a self-supporting film, peel the self-supporting film from the support, fix the ends of the self-supporting film, and dry at a temperature of the boiling point of the solvent component used and 350°C or less to produce a polyimide film. It is also preferable to dry under a nitrogen atmosphere. The pressure of the drying atmosphere may be reduced pressure, normal pressure, or pressurized.

The thickness of the polyimide film of the present invention can be appropriately selected depending on the application, etc., but is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, and even more preferably 10 to 80 μm. When the thickness is 1 to 250 μm, practical use as a free-standing film becomes possible.
In the present invention, the polyimide film can have a total light transmittance at a thickness of 50 μm of preferably 85% or more, more preferably 88% or more, and even more preferably 89% or more.
In the present invention, the polyimide film can have a yellow index (YI value) of preferably 8.0 or less, more preferably 7.5 or less, even more preferably 6.0 or less, and still more preferably 4.0 or less.
The total light transmittance and YI value of the polyimide film can be specifically measured by the method described in the Examples.

Polyimide films containing the polyimide resin of the present invention are suitable for use as films for various components such as color filters, flexible displays, semiconductor components, and optical components.

The present invention will be specifically explained below with reference to examples. However, the present invention is not limited to these examples in any way.

The physical properties of the polyimide films obtained in the following Examples and Comparative Examples were measured by the methods described below.
(1) Film Thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.
(2) Tensile modulus (evaluation of elasticity) and tensile strength: Measurements were performed in accordance with JIS K7127 using a tensile tester "Strograph VG1E" manufactured by Toyo Seiki Co., Ltd.
(3) Tensile elongation at break (evaluation of elongation)
The tensile elongation at break was measured by a tensile test (measurement of elongation) in accordance with JIS K 7127. Test pieces having a width of 10 mm and a thickness of 10 to 70 μm were used.
(4) Total Light Transmittance (Evaluation of Transparency), YI Value The measurement was carried out in accordance with ASTM E313-05 using a color and turbidity simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.
(5) Deformation recovery property As shown in Fig. 1(a), a polyimide film 1 cut to 10 mm width x 100 mm length was fixed with a jig at R = 3 mm and left to stand at 65 ° C and 90% relative humidity for 24 hours. After that, the jig was removed at 23 ° C and 50% relative humidity, and the film was left to stand for 2 hours, and the deformation recovery property was evaluated by measuring the angle θ shown in Fig. 1(b) of the return of the film. Note that the smaller the measured angle, the better the deformation recovery property, and the smaller the value, the more preferable.

[Example 1]
A 300 mL five-neck round-bottom flask equipped with a stainless steel half-moon shaped stirring blade, a nitrogen inlet tube, a Dean-Stark apparatus equipped with a cooling tube, a thermometer, and a glass end cap was charged with 18.76 g (0.059 mol) of 2,2'-bis(trifluoromethyl)benzidine (manufactured by Wakayama Seika Kogyo Co., Ltd., a compound represented by formula (b11), hereinafter referred to as TFMB) as a diamine component, 85.8 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation, hereinafter referred to as GBL) as an organic solvent, and 0.296 g of triethylamine (manufactured by Kanto Chemical Co., Ltd., hereinafter referred to as TEA) as an imidization catalyst, and the mixture was stirred at a system temperature of 70°C under a nitrogen atmosphere at a rotation speed of 150 rpm to obtain a solution. To this, 5.25 g (0.023 mol) of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Company, Inc., compound represented by formula (a2), hereinafter HPMDA) and 21.75 g (0.035 mol) of 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl=bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (manufactured by Honshu Chemical Industry Co., Ltd., compound represented by formula (a1), hereinafter TMPBP-TME) and 21.3 g of GBL were added all at once, and the mixture was heated with a mantle heater to raise the temperature in the reaction system to 190°C over about 20 minutes. The components distilled off were collected, and the reaction system was refluxed for 2 hours while maintaining the temperature at 190°C, while adjusting the rotation speed according to the increase in viscosity, to obtain a polyimide solution. Thereafter, when the temperature in the reaction system was cooled to 120°C, N,N-dimethylacetamide (manufactured by Mitsubishi Gas Chemical Company, Inc.) was added to a predetermined solid content concentration, and the mixture was further stirred for about 3 hours to be homogenized, thereby obtaining a polyimide varnish (A) having a solid content concentration of 15.0 mass%.

Next, polyimide varnish (A) was applied onto a glass substrate and held at 60°C for 20 minutes, 80°C for 20 minutes, and 100°C for 30 minutes to volatilize the solvent, yielding a self-supporting, transparent, primary dried film, which was then fixed onto a stainless steel frame and dried at 220°C in an air atmosphere for 20 minutes to remove the solvent, yielding a polyimide film. The measurement and evaluation results of the physical properties are shown in Table 1.

[Example 2]
A polyimide varnish (B) having a solid content concentration of 15.0 mass% was obtained by the same method as in Example 1, except that the amount of TFMB was changed to 17.27 g (0.054 mol), 0.91 g (0.0060 mol) of 3,5-diaminobenzoic acid (manufactured by Nippon Junryo Chemical Co., Ltd., a compound represented by formula (b2), hereinafter referred to as 3,5-DABA) was added, the amount of HPMDA was changed to 5.37 g (0.024 mol), and the amount of TMPBP-TME was changed to 22.23 g (0.036 mol). Using the obtained polyimide varnish (B), a polyimide film was obtained by the same method as in Example 1. The measurement results and evaluation results of physical properties are shown in Table 1.

[Example 3]
A polyimide varnish (C) having a solid content concentration of 15.0 mass% was obtained by the same method as in Example 1, except that the amount of TFMB was changed to 19.56 g (0.061 mol), the amount of 3,5-DABA was changed to 1.03 g (0.0068 mol), the amount of HPMDA was changed to 9.13 g (0.041 mol), and the amount of TMPBP-TME was changed to 16.79 g (0.027 mol). Using the obtained polyimide varnish (C), a film was obtained by the same method as in Example 1. The measurement results and evaluation results of physical properties are shown in Table 1.

[Example 4]
A polyimide varnish (D) having a solid content concentration of 15.0 mass% was obtained by the same method as in Example 1, except that the amount of TFMB was changed to 22.56 g (0.070 mol), 1.19 g (0.0078 mol) of 3,5-DABA was added, the amount of HPMDA was changed to 14.04 g (0.063 mol), and the amount of TMPBP-TME was changed to 9.68 g (0.016 mol). Using the obtained polyimide varnish (D), a film was obtained by the same method as in Example 1. The measurement results and evaluation results of physical properties are shown in Table 1.

[Example 5]
A polyimide varnish (E) having a solid content concentration of 15.0 mass% was obtained in the same manner as in Example 1, except that TFMB was changed to 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (manufactured by ChinaTech Chemical (Taijin) Co., Ltd., a compound represented by formula (b12), hereinafter referred to as 6FODA) at 19.44 g (0.058 mol), the amount of HPMDA was changed to 5.18 g (0.023 mol), and the amount of TMPBP-TME was changed to 21.46 g (0.035 mol). Using the obtained polyimide varnish (E), a film was obtained in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[Example 6]
A polyimide varnish (F) having a solid content concentration of 15.0 mass% was obtained by the same method as in Example 1, except that TFMB was changed to 17.79 g (0.053 mol) of 6FODA, 0.90 g (0.0059 mol) of 3,5-DABA was added, the amount of HPMDA was changed to 5.27 g (0.024 mol), and the amount of TMPBP-TME was changed to 21.82 g (0.035 mol). Using the obtained polyimide varnish (F), a film was obtained by the same method as in Example 1. The measurement results and evaluation results of physical properties are shown in Table 1.

[Comparative Example 1]
A polyimide varnish (G) having a solid content concentration of 15.0 mass% was obtained in the same manner as in Example 1, except that the amount of TFMB was 15.96 g (0.050 mol), HPMDA was not used, and the amount of TMPBP-TME was changed to 30.83 g (0.050 mol). Using the obtained polyimide varnish (G), a film was obtained in the same manner as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

[Comparative Example 2]
A polyimide varnish was prepared in the same manner as in Example 1, except that the amount of TFMB was changed to 37.75 g (0.12 mol), TMPBP-TME was not used, and the amount of HPMDA was changed to 26.43 g (0.12 mol), to obtain a polyimide varnish (H) having a solid content concentration of 20 mass %. A film was obtained in the same manner as in Example 1 using the obtained polyimide varnish (H).

[Comparative Example 3]
A polyimide varnish (I) having a solid content concentration of 20 mass% was obtained by the same method as in Example 1, except that TFMB was replaced with 38.44 g (0.11 mol) of 6FODA, TMPBP-TME was not used, and the amount of HPMDA was changed to 25.63 g (0.11 mol). Using the obtained polyimide varnish (I), a film was obtained by the same method as in Example 1. The measurement results and evaluation results of the physical properties are shown in Table 1.

From Table 1, it can be seen that the polyimide films of Examples 1 to 6 combine transparency and elastic modulus, and also have excellent deformation recovery and elongation.

Claims (6)

A polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine,
The structural unit A includes a structural unit (A1) derived from a compound represented by the following formula (a1) and a structural unit (A2) derived from a compound represented by the following formula (a2):
the ratio of the structural unit (A1) to the structural unit A is 20 to 65 mol %,
A polyimide resin , wherein the ratio of the structural unit (A2) to the structural unit A is 35 to 80 mol % .
2. The polyimide resin according to claim 1 , wherein the structural unit B comprises a structural unit (B1) derived from a compound represented by the following general formula (b1):

(In formula (b1), X is a single bond or an oxygen atom.) The polyimide resin according to claim 1 or 2 , wherein the structural unit B further comprises a structural unit (B2) derived from a compound represented by the following formula (b2):
3. The polyimide resin according to claim 2 , wherein a ratio of the structural unit (B1) to the structural unit B is 70 mol % or more. A polyimide varnish obtained by dissolving the polyimide resin according to any one of claims 1 to 4 in an organic solvent. A polyimide film comprising the polyimide resin according to any one of claims 1 to 4 .

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