TWI870345B - Polyimide resin, polyimide varnish, and polyimide film - Google Patents

Abstract

A polyimide resin of the present invention is a polyimide resin having structural units A derived from a tetracarboxylic dianhydride and structural units B derived from a diamine, wherein the structural units A include a structural unit (A-1) derived from a compound represented by formula (a-1) and a structural unit (A-2) derived from a compound represented by formula (a-2), and the structural units B include a structural unit (B-1) derived from a compound represented by formula (b-1).

Description

Polyimide resin, polyimide varnish and polyimide film

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

There have been studies on various uses of polyimide resins in the fields of electrical and electronic components. For example, in order to make the device lighter and more flexible, it is expected that the glass substrate used in image display devices such as liquid crystal displays and OLED displays will be replaced with a plastic substrate, and research is being conducted on polyimide films suitable as the plastic substrate. Polyimide films for such uses are required to be colorless and transparent.

Thin-film transistors (TFTs) are used as pixel switching elements in image display devices such as liquid crystal displays and OLED displays. Polycrystalline silicon (polysilicon) with excellent crystallinity has higher electron mobility than amorphous silicon, so the TFT characteristics are greatly improved. One method of forming a polycrystalline silicon film is the excimer laser-annealing (ELA) method. The dehydrogenation treatment of amorphous silicon in this method is a high-temperature treatment. Therefore, in order to form a polycrystalline silicon film on a polyimide film as a plastic substrate, the polyimide film is required to have high heat resistance (i.e., a high glass transition temperature). In addition, in a high temperature state, organic compounds (dissipated gases) emitted from the substrate material itself may have a serious adverse effect on the device. Therefore, polyimide films are also required to have high thermal stability in order to suppress the generation of dissipated gas when the temperature reaches the highest possible level.

Furthermore, when the varnish applied on the glass support or silicon wafer is heated and cured to form a polyimide film, residual stress will be generated in the polyimide film. If the residual stress of the polyimide film is large, the glass support or silicon wafer will warp, so the polyimide film is also required to reduce the residual stress. Patent document 1 discloses a polyimide resin as a polyimide resin for providing a film with low residual stress, which is synthesized using 4,4'-oxydiphthalic dianhydride as a tetracarboxylic acid component, and using α,ω-aminopropyl polydimethylsiloxane with a number average molecular weight of 1000 and 4,4'-diaminodiphenyl ether as diamine components. [Prior art literature] [Patent literature]

[Patent Document 1] Japanese Patent Application Publication No. 2005-232383

[The problem that the invention wants to solve]

As described above, various properties are required of polyimide films, but it is not easy to satisfy these properties at the same time. The present invention is made in view of such a situation. The subject of the present invention is to provide a polyimide resin and a method for producing a film that can form a colorless, transparent, heat-resistant, and thermally stable film with low residual stress, as well as a polyimide varnish and a polyimide film containing the polyimide resin. [Means for Solving the Problem]

The inventors of the present invention have found that a polyimide resin containing a combination of specific structural units can solve the above-mentioned problems and thus complete the invention.

That is, the present invention relates to the following [1] to [9]. [1] A polyimide resin having a structural unit A derived from tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein the structural unit A comprises a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2), and the structural unit B comprises a structural unit (B-1) derived from a compound represented by the following formula (b-1). [Chemical 1]

[2] The polyimide resin described in [1] above, wherein the ratio of the structural unit (A-1) in the structural unit A is 40 to 95 mol%, and the ratio of the structural unit (A-2) in the structural unit A is 5 to 60 mol%. [3] The polyimide resin described in [1] or [2] above, wherein the ratio of the structural unit (B-1) in the structural unit B is 50 mol% or more. [4] The polyimide resin described in any one of [1] to [3] above, wherein the structural unit B further comprises a structural unit derived from 9,9-bis(4-aminophenyl)fluorene. [5] A polyimide resin as described in any one of [1] to [4] above, wherein the ratio of structural unit (A-1) to structural unit (A-2) [(A-1)/(A-2)] (mole/mole) is 25/75 to 95/5. [6] A method for producing a polyimide resin comprises heating a tetracarboxylic acid component comprising a compound represented by the above formula (a-1) and a compound represented by the above formula (a-2) and a diamine component comprising a compound represented by the above formula (b-1) in the presence of a reaction solvent to carry out an imidization reaction. [7] A method for producing a polyimide resin as described in [6] above, wherein the reaction solvent is at least one selected from the group consisting of an amide solvent and a lactone solvent. [8] A polyimide varnish is prepared by dissolving a polyimide resin as described in any one of [1] to [5] above in an organic solvent. [9] A polyimide film contains a polyimide resin as described in any one of [1] to [5] above. [Effects of the Invention]

According to the present invention, a colorless, transparent, heat-resistant, and thermally stable film with low residual stress can be formed.

[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, wherein the structural unit A includes a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2), and the structural unit B includes a structural unit (B-1) derived from a compound represented by the following formula (b-1). [Chemical 2]

>Structural unit A> Structural unit A is a structural unit derived from tetracarboxylic dianhydride in the polyimide resin, and includes a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2). [Chemistry 3]

The compound represented by formula (a-1) is 9,9'-bis(3,4-dicarboxyphenyl)fluorene anhydride. The structural unit A includes the structural unit (A-1), which improves the colorless transparency, heat resistance, and thermal stability of the film.

The compound represented by formula (a-2) is biphenyltetracarboxylic acid dianhydride (BPDA), and specific examples thereof include: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA) represented by the following formula (a-2s), 2,3,3',4'-biphenyltetracarboxylic acid dianhydride (a-BPDA) represented by the following formula (a-2a), and 2,2',3,3'-biphenyltetracarboxylic acid dianhydride (i-BPDA) represented by the following formula (a-2i). [Chemistry 4]

By including the structural unit (A-2), the structural unit A improves the heat resistance and thermal stability of the film and reduces the residual stress.

The ratio of the structural unit (A-1) in the structural unit A is preferably 25 to 95 mol%, more preferably 30 to 90 mol%, more preferably 35 to 85 mol%, more preferably 40 to 80 mol%, and particularly preferably 50 to 80 mol%. The ratio of the structural unit (A-2) in the structural unit A is preferably 5 to 75 mol%, more preferably 10 to 70 mol%, more preferably 15 to 65 mol%, more preferably 20 to 60 mol%, and particularly preferably 20 to 50 mol%. Furthermore, the ratio of structural unit (A-1) to structural unit (A-2) [(A-1)/(A-2)] (mole/mole) is preferably 25/75 to 95/5, preferably 30/70 to 90/10, more preferably 35/65 to 85/15, more preferably 40/60 to 80/20, and particularly preferably 50/80 to 50/20. The total ratio of structural units (A-1) and (A-2) in structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total ratio of structural units (A-1) and (A-2) is not particularly limited, that is, 100 mol%. The structural unit A may also be composed of only the structural unit (A-1) and the structural unit (A-2).

The structural unit A may also include structural units other than the structural units (A-1) and (A-2). There are no particular limitations on the tetracarboxylic dianhydrides that provide such structural units, and examples thereof include aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (but excluding the compound represented by the formula (a-1) and the compound represented by the formula (a-2)); alicyclic tetracarboxylic dianhydrides such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride; and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride. In addition, 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 ring, and aliphatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring. The structural units other than the structural units (A-1) and (A-2) optionally contained in the structural unit A may be one type or two or more types.

>Structural unit B> Structural unit B is a structural unit derived from diamine in the polyimide resin, including a structural unit (B-1) derived from a compound represented by the following formula (b-1). [Chemistry 5]

The compound represented by formula (b-1) is 2,2'-bis(trifluoromethyl)benzidine. The structural unit B includes the structural unit (B-1), which improves the colorless transparency, heat resistance, and thermal stability of the film and reduces the residual stress.

The ratio of the structural unit (B-1) in the structural unit B is preferably 50 mol% or more, more preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the ratio of the structural unit (B-1) is not particularly limited, that is, 100 mol%. The structural unit B may also be composed only of the structural unit (B-1).

The structural unit B may also include structural units other than the structural unit (B-1). There are no particular limitations on the diamines that provide such structural units, and examples thereof include: 1,4-phenylenediamine, p-phenylenediamine, 3,5-diaminobenzoic acid, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminodiphenylsulfone, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-indene-5-amine, α,α'-bis(4-aminophenyl)-1,4-diisopropyl Aromatic diamines such as benzene, N,N'-bis(4-aminophenyl)phthalamide, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, and 9,9-bis(4-aminophenyl)fluorene (but excluding compounds represented by formula (b-1)); alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine, among which aromatic diamines are preferred, and 9,9-bis(4-aminophenyl)fluorene is more preferred. In addition, 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 and no aromatic ring, and aliphatic diamine means a diamine containing neither an aromatic ring nor an alicyclic ring. The structural unit other than the structural unit (B-1) optionally contained in the structural unit B may be one or more.

Considering the mechanical strength of the obtained polyimide film, the number average molecular weight of the polyimide resin of the present invention is preferably 5,000 to 300,000, more preferably 5,000 to 100,000. In addition, the number average molecular weight of the polyimide resin can be obtained, for example, by using a standard polymethyl methacrylate (PMMA) conversion value measured by gel filtration chromatography.

The polyimide resin of the present invention may also contain structures other than the polyimide chain (structure formed by imide bonding of structural unit A and structural unit B). As structures other than the polyimide chain that can be contained in the polyimide resin, for example, structures containing amide bonds can be listed. The polyimide resin of the present invention preferably contains the polyimide chain (structure formed by imide bonding of structural unit A and structural unit B) as the main structure. Therefore, the ratio of the polyimide chain in the polyimide resin of the present invention is preferably 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and particularly preferably 99% by mass or more.

By using the polyimide resin of the present invention, a film having colorless transparency, excellent heat resistance, and thermal stability, and low residual stress can be formed, and the ideal physical property values of the film are as follows. When a film having a thickness of 10 μm is made, the total light transmittance is preferably 85% or more, preferably 87% or more, and even more preferably 88% or more. When a film having a thickness of 10 μm is made, the yellowness index (YI) is preferably 5.0 or less, preferably 4.0 or less, and even more preferably 3.5 or less. The glass transition temperature (Tg) is preferably 370°C or more, preferably 380°C or more, and even more preferably 400°C or more. The weight loss rate at 450°C is preferably 1.00% or less, preferably 0.80% or less, and even more preferably 0.50% or less. The weight loss rate at 480°C is preferably 3.00% or less, preferably 2.50% or less, and even more preferably 2.00% or less. The residual stress is preferably 40.0MPa or less, preferably 35.0MPa or less, and even more preferably 30.0MPa or less.

The film formed by using the polyimide resin of the present invention also has good mechanical properties and has the following ideal physical property values. The tensile elastic modulus is preferably 2.5 GPa or more, preferably 3.0 GPa or more, and even more preferably 3.5 GPa or more. The tensile strength is preferably 70 MPa or more, preferably 90 MPa or more, and even more preferably 100 MPa or more. In addition, the above physical property values in the present invention can be specifically measured using the method described in the embodiment.

[Production method of polyimide resin] The polyimide resin of the present invention can be produced by reacting a tetracarboxylic acid component containing a compound providing the above structural unit (A-1) and a compound providing the above structural unit (A-2) with a diamine component containing a compound providing the above structural unit (B-1). More specifically, the production method of the polyimide resin of the present invention is to carry out an imidization reaction by heating a tetracarboxylic acid component containing a compound providing structural unit A and a diamine component containing a compound providing structural unit (B-1) in the presence of a reaction solvent. That is, an imidization reaction is carried out by heating a tetracarboxylic acid component containing a compound represented by formula (a-1) and a compound represented by formula (a-2) and a diamine component containing a compound represented by formula (b-1) in the presence of a reaction solvent.

As for the compound providing the structural unit (A-1), the compound represented by formula (a-1) can be listed, but it is not limited to this. Within the scope of providing the same structural unit, it can also be a derivative thereof. As for the derivative, the tetracarboxylic acid corresponding to the tetracarboxylic dianhydride represented by formula (a-1) and the alkyl ester of the tetracarboxylic acid can be listed. As for the compound providing the structural unit (A-1), it is preferably a compound represented by formula (a-1) (that is, a dianhydride). Similarly, as for the compound providing the structural unit (A-2), the compound represented by formula (a-2) can be listed, but it is not limited to this. Within the scope of providing the same structural unit, it can also be a derivative thereof. As for the derivative, the tetracarboxylic acid corresponding to the tetracarboxylic dianhydride represented by formula (a-2) and the alkyl ester of the tetracarboxylic acid can be listed. The compound providing the structural unit (A-2) is preferably a compound represented by the formula (a-2) (that is, a dianhydride).

The tetracarboxylic acid component preferably contains 25 to 95 mol% of the compound providing the structural unit (A-1), preferably 30 to 90 mol%, more preferably 35 to 85 mol%, more preferably 40 to 80 mol%, and particularly preferably 50 to 80 mol%. The tetracarboxylic acid component preferably contains 5 to 75 mol% of the compound providing the structural unit (A-2), preferably 10 to 70 mol%, more preferably 15 to 65 mol%, more preferably 20 to 60 mol%, and particularly preferably 20 to 50 mol%. The tetracarboxylic acid component preferably contains a total of 50 mol% or more of the compound providing the structural unit (A-1) and the compound providing the structural unit (A-2), preferably 70 mol% or more, more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the total content 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 also be composed only of the compound providing the structural unit (A-1) and the compound providing the structural unit (A-2).

The tetracarboxylic acid component may also contain compounds other than the compound providing the structural unit (A-1) and the compound providing the structural unit (A-2). Examples of such compounds include the above-mentioned aromatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride, and aliphatic tetracarboxylic dianhydride, and their derivatives (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.). The compounds other than the compound providing the structural unit (A-1) and the compound providing the structural unit (A-2) optionally contained in the tetracarboxylic acid component may be one or more.

As for the compound providing the structural unit (B-1), the compound represented by formula (b-1) can be cited, but it is not limited thereto, and can also be a derivative thereof within the scope of providing the same structural unit. As for the derivative, diisocyanate corresponding to the diamine represented by formula (b-1) can be cited. As for the compound providing the structural unit (B-1), it is preferably a compound represented by formula (b-1) (that is, a diamine).

The diamine component preferably contains 50 mol% or more of the compound providing the structural unit (B-1), more preferably 70 mol% or more, more preferably 80 mol% or more, more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the content of the compound providing the structural unit (B-1) is not particularly limited, that is, 100 mol%. The diamine component may also be composed only of the compound providing the structural unit (B-1).

The diamine component may also contain compounds other than the compound providing the structural unit (B-1), and examples of such compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, and their derivatives (diisocyanates, etc.). The number of compounds other than the compound providing the structural unit (B-1) optionally contained in the diamine component may be one or more.

In the present invention, the feed ratio of the tetracarboxylic acid component to the diamine component used in the production of the polyimide resin is preferably 0.9 to 1.1 mol of the diamine component per 1 mol of the tetracarboxylic acid component.

Furthermore, in the present invention, in addition to the aforementioned tetracarboxylic acid component and diamine component, a capping agent may also be used in the production of the polyimide resin. As for the capping agent, it is preferably a monoamine or a dicarboxylic acid. As for the feed amount of the capping agent to be introduced, it is preferably 0.0001 to 0.1 mol, and 0.001 to 0.06 mol is particularly preferred relative to 1 mol of the tetracarboxylic acid component. As for the monoamine capping agent, for example, methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline, etc. are recommended. Among them, benzylamine and aniline can be appropriately used. As for the dicarboxylic acid capping agent, it is preferably a dicarboxylic acid, and a part of it can also be ring-closed. Recommended examples include phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenone dicarboxylic acid, 3,4-benzophenone dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, and 4-cyclohexene-1,2-dicarboxylic acid. Among these, phthalic acid and phthalic anhydride can be suitably used.

The method for reacting the tetracarboxylic acid component and the diamine component is not particularly limited, and a 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 fed into a reactor, stirred at room temperature to 80°C for 0.5 to 30 hours, and then the temperature is raised to carry out an imidization reaction; (2) a method in which a diamine component and a reaction solvent are fed into a reactor and dissolved, a tetracarboxylic acid component is fed, and stirred at room temperature to 80°C for 0.5 to 30 hours as needed, and then the temperature is raised to carry out an imidization reaction; (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are fed into a reactor, and the temperature is immediately raised to carry out an imidization reaction, etc.

The reaction solvent used in the production of polyimide resin can be any solvent that does not hinder the imidization reaction and can dissolve the generated polyimide. Examples include aprotic solvents, phenolic solvents, etheric solvents, carbonate solvents, and the like.

Specific examples of aprotic solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactone, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone solvents such as γ-butyrolactone and γ-valerolactone; phosphorus-containing amide solvents such as hexamethylphosphatamide and hexamethylphosphotriamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and cyclobutane sulfone; ketone solvents such as acetone, cyclohexanone, and methylcyclohexanone; amine solvents such as picolinyl and pyridine; ester solvents such as acetic acid (2-methoxy-1-methylethyl ester), and the like.

Specific examples of phenolic solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, etc. Specific examples of etheric solvents include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, 1,4-dioxane, etc. Specific examples of carbonate-based solvents include diethyl carbonate, ethyl methyl carbonate, ethyl carbonate, propyl carbonate, etc. Among the above reaction solvents, amide solvents and/or lactone solvents are preferred, and lactone solvents are more preferred. In addition, the above reaction solvents may be used alone or in combination of two or more. When two or more solvents are used in combination, it is particularly preferred to use an amide solvent and a lactone solvent in combination.

The imidization reaction is preferably carried out using a Dean-Stark apparatus or the like, while removing water generated during the production. By carrying out such an operation, the degree of polymerization and the imidization rate can be further increased.

In the above-mentioned imidization reaction, a known imidization catalyst can be used. As for the imidization catalyst, alkali catalysts or acid catalysts can be listed. As for the alkali catalyst, organic alkali catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-dipicoline, 2,6-dipicoline, trimethylamine, triethylamine, tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, N,N-diethylaniline, etc.; inorganic alkali catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, etc. can be listed. In addition, as for the acid catalyst, there can be listed: crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, hydroxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, etc. The above-mentioned imidization catalyst can be used alone or in combination of two or more. Among the above, considering the viewpoint of operability, it is preferable to use an alkaline catalyst, and it is more preferable to use an organic alkaline catalyst, and it is more preferable to use triethylamine, and it is particularly preferable to use a combination of triethylamine and triethylenediamine.

Taking the reaction rate and gelation inhibition into consideration, the temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C. The reaction time is preferably 0.5 to 10 hours after the distillation of the generated water begins.

[Polyimide varnish] The polyimide varnish of the present invention is prepared 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. It is preferable to use the above-mentioned compound used as a reaction solvent for the production of the polyimide resin alone, or to use two or more of them in combination. The polyimide varnish of the present invention may be a polyimide solution itself obtained by dissolving a polyimide resin obtained by a polymerization method in a reaction solvent, or may be a polyimide solution obtained by further adding a diluting solvent.

The polyimide resin of the present invention is solvent-soluble, so it can be made into a high-concentration varnish that is stable at room temperature. The polyimide varnish of the present invention preferably contains 5 to 40% by mass of the polyimide resin of the present invention, preferably 5 to 30% by mass, and more preferably 10 to 30% by mass. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, preferably 1 to 150 Pa·s, and more preferably 5 to 150 Pa·s. The viscosity of the polyimide varnish is a value measured at 25°C using an E-type viscometer. Furthermore, the polyimide varnish of the present invention may also contain various additives such as inorganic fillers, adhesion promoters, stripping agents, flame retardants, ultraviolet stabilizers, surfactants, leveling agents, defoaming agents, fluorescent whitening agents, crosslinking agents, polymerization initiators, and photosensitizers within the range that the properties required of the polyimide film are not impaired. The method for preparing the polyimide varnish of the present invention is not particularly limited, and a known method can be used.

[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 has excellent colorless transparency, heat resistance, and thermal stability, and has low residual stress. The ideal physical property values of the polyimide film of the present invention are as described above. The method for manufacturing 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 is coated on a smooth support such as a glass plate, a metal plate, or a plastic, or after forming it into a film, the organic solvent such as a reaction solvent and a dilution solvent contained in the varnish is removed by heating. The surface of the aforementioned support may also be coated with a release agent in advance as needed. As for the method of removing the organic solvent contained in the varnish by heating, the following method is preferable. That is, after the organic solvent is evaporated at a temperature below 120°C to form a self-supporting film, the self-supporting film is peeled off from the support, and the ends of the self-supporting film are fixed, and then dried at a temperature above the boiling point of the organic solvent used to produce a polyimide film. In addition, it is preferable to dry in a nitrogen environment. The pressure of the drying environment can be any of reduced pressure, normal pressure, and increased pressure. There is no particular limitation on the heating temperature when the self-supporting film is dried to produce a polyimide film, and it is preferably 200 to 500°C, and more preferably 200 to 400°C.

In addition, the polyimide film of the present invention can also be produced using a polyimide varnish in which polyimide is dissolved in an organic solvent. The polyimide contained in the aforementioned polyimide varnish is a precursor of the polyimide resin of the present invention, and is a product of an addition polymerization reaction of a tetracarboxylic acid component containing a compound providing the aforementioned structural unit (A-1) and a compound providing the aforementioned structural unit (A-2) and a diamine component containing a compound providing the aforementioned structural unit (B-1). By subjecting the polyimide to imidization (dehydration and ring closure), the final product, i.e., the polyimide resin of the present invention, can be obtained. As for the organic solvent contained in the aforementioned polyamide varnish, the organic solvent contained in the polyimide varnish of the present invention can be used. In the present invention, the polyamide varnish may be a polyamide solution itself obtained by subjecting a tetracarboxylic acid component including a compound providing the aforementioned structural unit (A-1) and a compound providing the aforementioned structural unit (A-2) and a diamine component including a compound providing the aforementioned structural unit (B-1) to addition polymerization in a reaction solvent, or may be obtained by further adding a diluting solvent to the polyamide solution.

The method of using polyamide varnish to make polyimide film is not particularly limited, and a known method can be used. For example, the polyamide varnish can be applied on a smooth support such as a glass plate, a metal plate, or a plastic, or formed into a film, and the polyamide film can be obtained by removing the organic solvents such as the reaction solvent and the dilution solvent contained in the varnish by heating, and then the polyamide in the polyamide film is imidized by heating to make the polyimide film. The heating temperature when drying the polyamide varnish to obtain the polyamide film is preferably 50 to 120°C. The heating temperature for imidizing polyamine by heating is preferably 200 to 500°C, more preferably 200 to 480°C, more preferably 200 to 450°C, and even more preferably 200 to 400°C. In addition, the imidization method is not limited to thermal imidization, and chemical imidization can also be used.

The thickness of the polyimide film of the present invention can be appropriately selected according to the application, etc., preferably 1 to 250 μm, more preferably 5 to 100 μm, more preferably 8 to 80 μm, and even more preferably 10 to 80 μm. When the thickness is 1 to 250 μm, it can be used as a self-supporting film in practical applications. The thickness of the polyimide film can be easily controlled by adjusting the solid component concentration and viscosity of the polyimide varnish.

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

The present invention is specifically described below using examples. However, the present invention is not limited to these examples. The solid content concentration of the varnish obtained in the examples and comparative examples and the various physical properties of the film are measured using the method shown below.

(1) Solid content concentration The solid content concentration of the varnish was measured by heating the sample at 320℃×120min using a small electric furnace "MMF-1" manufactured by AS ONE Co., Ltd. and calculating the mass difference of the sample before and after heating. (2) Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation. (3) Total light transmittance, yellowness index (YI) (evaluation of colorless transparency) The total light transmittance and YI were measured in accordance with JIS K7361-1:1997 using the color-turbidity simultaneous tester "COH400" manufactured by Nippon Denshoku Industries Co., Ltd. The closer the total light transmittance is to 100%, the smaller the YI value is, and the better the colorless transparency is. (4) Glass transition temperature (Tg) (Evaluation of heat resistance) Using the thermomechanical analyzer "TMA/SS6100" manufactured by Hitachi High-Tech Science Co., Ltd., the residual stress was removed by heating to a temperature sufficient to remove the residual stress under the conditions of sample size 2mm×20mm, load 0.1N, and heating rate 10℃/min in the tensile mode, and then cooling to room temperature. Thereafter, the elongation of the test piece was measured under the same conditions as the treatment used to remove the residual stress, and the glass transition temperature was obtained when the inflection point of the elongation was observed. The larger the Tg value, the better the heat resistance. (5) Weight loss rate at 450℃ and 480℃ (evaluation of thermal stability) The differential thermal thermogravimetric simultaneous measurement device "TG/DTA6200" manufactured by Hitachi High-Tech Science Co., Ltd. was used. The sample was heated from 40℃ to a predetermined temperature (450℃ or 480℃) at a heating rate of 10℃/min and kept at that temperature for 1 hour. The weight loss rate at 450℃ was calculated as the ratio of the weight loss at 450℃ to the weight before the temperature was kept for 1 hour, and the weight loss rate at 480℃ was calculated as the ratio of the weight loss at 480℃ to the weight before the temperature was kept for 1 hour. The larger the value of each weight loss temperature, the better the thermal stability. (6) Residual stress The residual stress measuring device "FLX-2320" manufactured by KLA-Tencor was used. Polyimide varnish or polyamide varnish was applied to a 4-inch silicon wafer with a thickness of 525μm±25μm and a pre-measured "warp" using a spin coater and pre-baked. Thereafter, a hot air dryer was used to heat and cure the wafer at 400°C for 1 hour in a nitrogen environment to obtain a silicon wafer with a polyimide film having a thickness of 8 to 20μm after curing. The warp of the wafer was measured using the aforementioned residual stress measuring device to evaluate the residual stress generated between the silicon wafer and the polyimide film. The smaller the residual stress value, the better. (7) Tensile modulus and tensile strength Tensile modulus and tensile strength were measured in accordance with JIS K7127 using a tensile testing machine "STROGRAPH VG-1E" manufactured by Toyo Seiki Co., Ltd.

The tetracarboxylic acid components and diamine components used in the examples and comparative examples and their abbreviations are as follows. >Tetracarboxylic acid component> BPAF: 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride (manufactured by JFE Chemical Co., Ltd.; compound represented by formula (a-1)) BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Co., Ltd.; compound represented by formula (a-2)) HPMDA: 1,2,4,5-cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Co., Ltd.) >Diamine component> TFMB: 2,2'-bis(trifluoromethyl)benzidine (manufactured by Wakayama Seika Co., Ltd.; compound represented by formula (b-1)) BAFL: 9,9-bis(4-aminophenyl)fluorene (manufactured by TAOKAKA CHEMICAL CO., LTD.)

>Example 1> 32.024g (0.100 mol) of TFMB and 89.499g of N-methylpyrrolidone (Mitsubishi Chemical Co., Ltd.) were placed in a 1L 5-necked round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark apparatus equipped with a cooling tube, a thermometer, and a glass end cap, and stirred at an internal temperature of 70°C, a nitrogen environment, and a rotation speed of 150 rpm to obtain a solution. After adding 36.674g (0.080 mol) of BPAF, 5.884g (0.020 mol) of BPDA, and 22.375g of N-methylpyrrolidone (Mitsubishi Chemical Co., Ltd.) to the solution at once, 0.506g of triethylamine (Kanto Chemical Co., Ltd.) as an imidization catalyst was added, and the temperature in the reaction system was raised to 190°C in about 20 minutes by heating with a mantle heater. The distilled components were collected, and the rotation speed was adjusted according to the increase in viscosity, while the temperature in the reaction system was kept at 190°C for 3 hours of reflux. After that, 526.935 g of γ-butyrolactone (Mitsubishi Chemical Co., Ltd.) was added, the temperature in the reaction system was cooled to 120°C, and then further stirred for about 3 hours to make it uniform, and a polyimide varnish with a solid content concentration of 10.0 mass% was obtained. Then, the obtained polyimide varnish was applied to a glass plate and a silicon wafer, and kept at 80°C for 20 minutes with a heating plate, and then heated at 400°C for 30 minutes in a hot air dryer in a nitrogen environment to evaporate the solvent, and a film with a thickness of 8 μm was obtained. The results are shown in Table 1.

>Example 2> The amount of BPAF was changed from 36.674 g (0.080 mol) to 27.506 g (0.060 mol), and the amount of BPDA was changed from 5.884 g (0.020 mol) to 11.769 g (0.040 mol). In addition, a polyimide varnish was prepared in the same manner as in Example 1 to obtain a polyimide varnish having a solid content concentration of 10.0 mass %. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1 to obtain a film having a thickness of 9 μm. The results are shown in Table 1.

>Example 3> The amount of BPAF was changed from 36.674 g (0.080 mol) to 18.337 g (0.040 mol), the amount of BPDA was changed from 5.884 g (0.020 mol) to 17.653 g (0.060 mol), and the dilution solvent after 3 hours of reaction was changed from γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) to N-methylpyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.). In addition, a polyimide varnish was prepared in the same manner as in Example 1 to obtain a polyimide varnish having a solid content concentration of 10.0 mass%. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1 to obtain a film having a thickness of 10 μm. The results are shown in Table 1.

>Example 4> The amount of BPAF was changed from 36.674g (0.080 mol) to 22.921g (0.050 mol), the amount of BPDA was changed from 5.884g (0.020 mol) to 14.711g (0.050 mol), the amount of TFMB was changed from 32.024g (0.100 mol) to 16.012g (0.050 mol), 17.423g (0.050 mol) of BAFL was added, and the synthesis solvent was changed from N-methylpyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) to γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.). In addition, a polyimide varnish was prepared by the same method as in Example 1, and a polyimide varnish with a solid content concentration of 10.0 mass% was obtained. The obtained polyimide varnish was used to prepare a film in the same manner as in Example 1, and a film with a thickness of 9.5 μm was obtained. The results are shown in Table 1.

>Example 5> The amount of BPAF was changed from 36.674g (0.080 mol) to 22.921g (0.050 mol), the amount of BPDA was changed from 5.884g (0.020 mol) to 14.711g (0.050 mol), the amount of TFMB was changed from 32.024g (0.100 mol) to 25.619g (0.080 mol), 6.969g (0.020 mol) of BAFL was added, and the synthesis solvent was changed from N-methylpyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) to γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.). In addition, a polyimide varnish was prepared by the same method as in Example 1, and a polyimide varnish with a solid content concentration of 10.0 mass% was obtained. The obtained polyimide varnish was used to prepare a film in the same manner as in Example 1, and a film with a thickness of 9 μm was obtained. The results are shown in Table 1.

>Comparative Example 1> The amount of BPAF was changed from 36.674 g (0.080 mol) to 45.843 g (0.100 mol), and BPDA was not added. In addition, a polyimide varnish was prepared in the same manner as in Example 1, and a polyimide varnish having a solid content concentration of 10.0 mass % was obtained. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1, and a film having a thickness of 9 μm was obtained. The results are shown in Table 1.

>Comparative Example 2> 36.674g (0.080 mol) of BPAF and 5.884g (0.020 mol) of BPDA were replaced with 22.417g (0.100 mol) of HPMDA, and the synthesis solvent was changed from N-methylpyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) to γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.). In addition, a polyimide varnish was prepared in the same manner as in Example 1 to obtain a polyimide varnish having a solid content concentration of 10.0 mass %. Using the obtained polyimide varnish, a film was prepared in the same manner as in Example 1 to obtain a film having a thickness of 9μm. The results are shown in Table 1.

>Comparative Example 3> The amount of BPAF was changed from 36.674 g (0.080 mol) to 22.922 g (0.050 mol), 11.209 g (0.050 mol) of HPMDA was added, BPDA was not added, the synthesis solvent was changed from N-methylpyrrolidone (manufactured by Mitsubishi Chemical Co., Ltd.) to γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.), and in addition, a polyimide varnish was prepared by the same method as in Example 1 to obtain a polyimide varnish having a solid content concentration of 10.0 mass %. Using the obtained polyimide varnish, a film was prepared by the same method as in Example 1 to obtain a film having a thickness of 15 μm. The results are shown in Table 1.

>Comparative Example 4> 32.024 g (0.100 mol) of TFMB and 196.627 g of N-methylpyrrolidone (Mitsubishi Chemical Co., Ltd.) were placed in a 1L 5-necked round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark device equipped with a cooling tube, a thermometer, and a glass end cap, and stirred at an internal temperature of 50°C, a nitrogen environment, and a rotation speed of 150 rpm to obtain a solution. 294.22 g (0.100 mol) of BPDA and 49.157 g of N-methylpyrrolidone (Mitsubishi Chemical Co., Ltd.) were placed in the solution at once, and stirred for 7 hours at 50°C using a heating pack. Then, 307.230 g of N-methylpyrrolidone (Mitsubishi Chemical Co., Ltd.) was added and further stirred for about 3 hours to make it uniform, and a polyamide varnish with a solid content concentration of 10 mass% was obtained. Then, the obtained polyamide varnish was applied on a glass plate and a silicon wafer, and kept at 80°C for 20 minutes with a heating plate, and then heated at 400°C for 30 minutes in a hot air dryer under a nitrogen environment to evaporate the solvent, and then thermal imidized to obtain a film with a thickness of 12μm. The results are shown in Table 1.

[Table 1]

As shown in Table 1, the polyimide films of Examples 1 to 5 prepared using a specific tetracarboxylic acid component and a specific diamine component have excellent colorless transparency, heat resistance, and thermal stability, and have low residual stress. On the other hand, the polyimide film of Comparative Example 1 prepared using only BPAF without combining BPAF and BPDA as tetracarboxylic acid components has a larger residual stress when compared with the polyimide films of Examples 1 to 5. The polyimide film of Comparative Example 4 prepared using only BPDA without combining BPAF and BPDA as tetracarboxylic acid components has a larger YI, so the colorless transparency is poor, and the Tg is low, so the heat resistance is poor. The polyimide film of Comparative Example 2, which was prepared using only HPMDA as the tetracarboxylic acid component, was compared with the polyimide films of Examples 1 to 5. Its Tg was low, so its heat resistance was poor, and its weight loss rate at 450°C and 480°C was large, so its thermal stability was poor, and its residual stress was large. The polyimide film of Comparative Example 3, which was prepared using BPAF and HPMDA as the tetracarboxylic acid components, was compared with the polyimide films of Examples 1 to 5. Its weight loss rate at 450°C and 480°C was large, so its thermal stability was poor, and its residual stress was large.

Claims (9)

A polyimide resin comprises a structural unit A derived from tetracarboxylic dianhydride as a tetracarboxylic acid component and a structural unit B derived from a diamine, wherein the structural unit A comprises a structural unit (A-1) derived from a compound represented by the following formula (a-1) and a structural unit (A-2) derived from a compound represented by the following formula (a-2), and the structural unit B comprises a structural unit (B-1) derived from a compound represented by the following formula (b-1). The feed ratio of the tetracarboxylic acid component to the diamine component used in the production of the polyimide resin is 1 to 1.1 mol of the diamine component relative to 1 mol of the tetracarboxylic acid component.

For example, the polyimide resin of item 1 of the patent application scope, wherein the ratio of the structural unit (A-1) in the structural unit A is 25 to 95 mol%, and the ratio of the structural unit (A-2) in the structural unit A is 5 to 75 mol%. For example, in the polyimide resin of item 1 or 2 of the patent application, the ratio of the structural unit (B-1) in the structural unit B is 50 mol% or more. For example, in the polyimide resin of claim 1 or 2, the structural unit B further comprises a structural unit derived from 9,9-bis(4-aminophenyl)fluorene. For example, in the polyimide resin of item 1 or 2 of the patent application, the ratio of the structural unit (A-1) to the structural unit (A-2) [(A-1)/(A-2)] (mole/mole) is 25/75~95/5. A method for producing a polyimide resin comprises heating a tetracarboxylic acid component comprising a compound represented by the following formula (a-1) and a compound represented by the following formula (a-2) and a diamine component comprising a compound represented by the following formula (b-1) in the presence of a reaction solvent to carry out an imidization reaction; the feeding amount ratio of the tetracarboxylic acid component to the diamine component is 1 to 1.1 mol of the diamine component relative to 1 mol of the tetracarboxylic acid component;

For example, in the method for producing polyimide resin of item 6 of the patent application, the reaction solvent is at least one selected from the group consisting of amide solvents and lactone solvents. A polyimide varnish is prepared by dissolving a polyimide resin as described in any one of items 1 to 5 of the patent application scope in an organic solvent. A polyimide film containing a polyimide resin as described in any one of items 1 to 5 of the patent application scope.