Polyimide resin, polyimide varnish, and polyimide film

Abstract

The present invention provides a polyimide resin, a polyimide varnish, and a polyimide film, the polyimide resin having constituent units A derived from tetracarboxylic dianhydrides and constituent units B derived from diamines, and being such that: the constituent units A include constituent units (A-1) derived from a compound represented by formula (a-1), and constituent units (A-2) derived from a compound represented by formula (a-2); and the constituent units B include constituent units (B-1) derived from a compound represented by formula (b-1), and constituent units (B-2) derived from a compound represented by formula (b-2), the polyimide resin making it possible to form a film that has exceptional optical isotropy and furthermore has exceptional release properties and chemical resistance.

Description

Technical Field

[0001] The present invention relates to polyimide resins, polyimide varnishes, and polyimide films.

Background Art

[0002] Polyimide resins are being considered for various uses in fields such as electric and electronic components. For example, it is desired to replace the glass substrates used in image display devices such as liquid crystal displays and OLED displays with plastic substrates for the purpose of reducing the weight and flexibility of the devices, and research on polyimide films suitable as the plastic substrates is underway. Various optical properties are required for films used in image display device applications. For example, when light emitted from a display element is emitted through a plastic substrate, the plastic substrate is required to have colorless transparency. On the other hand, when used in applications where light passes through a retardation film or a polarizing plate, for example, in liquid crystal displays, touch panels, etc., it is particularly required to have high optical isotropy (that is, low Rth).

[0003] In order to satisfy the above-described performance, polyimide resins having various compositions have been developed. For example, Patent Document 1 discloses a polyimide film containing a polyamide having good solubility in a solvent and excellent processability, being colorless and transparent, and having excellent toughness, and having a structure including a combination of 3,3'-diaminodiphenyl sulfone and other specific diamines as a diamine component.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, particularly for applications such as displays, polyimide films with excellent optical isotropy are required. Furthermore, polyimide films with high chemical resistance are also required. For example, when applying a varnish for forming such a resin layer to a polyimide film in order to form another resin layer (for example, a color filter, a resist) on the polyimide film, the polyimide film is required to have resistance to the solvent contained in the varnish. If the solvent resistance of the polyimide film is insufficient, there is a risk that the film will dissolve or swell and lose its meaning as a substrate. However, as described above, in order to ensure optical properties, the polyimide film must be in the form of a solution during production, and it has been difficult to achieve both of these properties. Also, when using a polyimide film as a substrate, in the process of forming an electronic circuit on the film, the film is adhered to a support such as a glass plate. Therefore, properties that allow the polyimide film to be easily peeled off from the support after circuit formation are also required. Thus, there has been a demand for a polyimide resin capable of obtaining a polyimide film that maintains the optical properties of the resulting polyimide film, particularly optical isotropy, and is excellent in peelability and chemical resistance. Therefore, an object of the present invention is to provide a polyimide resin, a polyimide varnish, and a polyimide film that can form a film having excellent optical isotropy and further excellent peelability and chemical resistance.

Means for Solving the Problems

[0006] The inventors of the present invention have found that a polyimide resin containing a combination of structural units derived from specific two tetracarboxylic dianhydrides and structural units derived from specific two diamines can solve the above problems, and have completed the invention.

[0007] That is, the present invention relates to the following <1> to <5>. <1> A polyimide resin having a structural unit A derived from a 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) and a structural unit (B-2) derived from a compound represented by the following formula (b-2).

[0008]

Chemical formula

[0009] <2> The polyimide resin according to <1> above, wherein the ratio of the structural unit (A-1) in the structural unit A is 20 to 80 mol%, and the ratio of the structural unit (A-2) in the structural unit A is 20 to 80 mol%. <3> The polyimide resin according to <1> or <2> above, wherein the ratio of the structural unit (B-1) in the structural unit B is 5 to 80 mol%, and the ratio of the structural unit (B-2) in the structural unit B is 20 to 95 mol%. <4> A polyimide varnish obtained by dissolving the polyimide resin according to any one of <1> to <3> above in an organic solvent. <5> A polyimide film containing the polyimide resin according to any one of <1> to <3> above.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a polyimide resin, a polyimide varnish, and a polyimide film that can form a film having excellent optical isotropy and further excellent peelability and chemical resistance.

Modes for Carrying Out the Invention

[0011] [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, 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) and a structural unit (B-2) derived from a compound represented by the following formula (b-2).

[0012]

Chemical formula

[0013] Although the reason why the polyimide resin of the present invention is excellent in peelability and chemical resistance while maintaining optical isotropy is not clear, it is considered that the polyimide resin of the present invention has a sulfonyl structure in addition to an ether structure and also has an alicyclic structure, so it is excellent in optical isotropy and further excellent in peelability and chemical resistance.

[0014] <Structural unit A> The structural unit A is a structural unit derived from a tetracarboxylic dianhydride in the polyimide resin. 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).

[0015]

Chemical formula

[0016] The compound represented by the formula (a-1) is 4,4'-oxydiphthalic anhydride. By including the structural unit (A-1) in the structural unit A, the chemical resistance, optical isotropy, and transparency can be improved. The compound represented by the formula (a-2) is 1,2,4,5-cyclohexanetetracarboxylic dianhydride. By including the structural unit (A-2) in the structural unit A, it is possible to enhance the solubility of the resulting polyimide resin in varnish while improving chemical resistance and optical isotropy.

[0017] The ratio of the structural unit (A-1) in the structural unit A is preferably 20 to 80 mol%, more preferably 30 to 70 mol%, and still more preferably 40 to 60 mol%. The ratio of the structural unit (A-2) in the structural unit A is preferably 20 to 80 mol%, more preferably 30 to 70 mol%, and still more preferably 40 to 60 mol%. The total ratio of the structural units (A-1) and (A-2) in the structural unit A is preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more. The upper limit of the total ratio of the structural units (A-1) and (A-2) is not particularly limited, that is, it is 100 mol%. The structural unit A may consist only of the structural unit (A-1) and the structural unit (A-2). In the polyimide resin of the present invention, by including the structural unit A containing both the structural units (A-1) and (A-2), not only is it excellent in all of optical isotropy, peelability, and chemical resistance as described above, but also the solubility of the polymer generated during the imidization reaction in the solvent when producing the polyimide resin is high, and a transparent varnish and film can be obtained. The molar ratio [(A-1) / (A-2)] of the structural unit (A-1) and the structural unit (A-2) in the structural unit A is preferably 20 / 80 to 80 / 20, more preferably 30 / 70 to 70 / 30, and still more preferably 40 / 60 to 60 / 40 from the viewpoint of improving optical isotropy and chemical resistance.

[0018] The structural unit A may contain structural units other than the structural units (A-1) and (A-2). The tetracarboxylic dianhydrides that provide such structural units are not particularly limited, but include aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (however, excluding the compound represented by formula (a-1)); alicyclic tetracarboxylic dianhydrides such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride and norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride (however, excluding the compound represented by formula (a-2)); and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride. In the present specification, the aromatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing one or more aromatic rings, the alicyclic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing one or more alicyclic rings and no aromatic rings, and the aliphatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring. The structural units optionally contained in the structural unit A may be one kind or two or more kinds.

[0019] <Structural unit B> The structural unit B is a structural unit derived from a diamine in the polyimide resin, and includes a structural unit (B-1) derived from a compound represented by the following formula (b-1) and a structural unit (B-2) derived from a compound represented by the following formula (b-2).

[0020]

Chemical formula

[0021] The compound represented by formula (b-1) is 4,4'-diaminodiphenyl sulfone. By including structural unit B containing structural unit (B-1), the toughness and peelability of the film can be improved, and furthermore, the heat resistance can also be made good.

[0022] The compound represented by formula (b-2) is bis(aminomethyl)cyclohexane, and specific examples thereof include 1,3-bis(aminomethyl)cyclohexane represented by the following formula (b-2a) and 1,4-bis(aminomethyl)cyclohexane represented by the following formula (b-2b).

[0023] [Chemical formula] The cis:trans ratio of the compound represented by formula (b-2) is preferably 0:100 to 80:20, more preferably 0.1:99.9 to 70:30, still more preferably 0.5:99.5 to 60:40, and even more preferably 1:99 to 20:80, from the viewpoints of organic solvent resistance and heat resistance. By including structural unit B containing structural unit (B-2), the colorless transparency and optical isotropy of the film can be improved.

[0024] The ratio of structural unit (B-1) in structural unit B is preferably 5 to 80 mol%, more preferably 10 to 70 mol%, still more preferably 30 to 70 mol%, even more preferably 45 to 70 mol%, and even more preferably 45 to 60 mol%. The ratio of structural unit (B-2) in structural unit B is preferably 20 to 95 mol%, more preferably 30 to 90 mol%, still more preferably 30 to 70 mol%, even more preferably 30 to 55 mol%, and even more preferably 40 to 55 mol%. The total ratio of structural units (B-1) and (B-2) in structural unit B is preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more. The upper limit of the total ratio of structural units (B-1) and (B-2) is not particularly limited, that is, it is 100 mol%. Structural unit B may consist only of structural unit (B-1) and structural unit (B-2). In the polyimide resin of the present invention, since structural unit B contains both structural unit (B-1) and (B-2), not only is it excellent in all of optical isotropy, peelability, and chemical resistance as described above, but also the solubility of the polymer generated by the progress of the imidization reaction in the solvent during the production of the polyimide resin is high, and a transparent varnish and film can be obtained. The molar ratio [(B-1) / (B-2)] of structural unit (B-1) and structural unit (B-2) in structural unit B is preferably 5 / 95 to 80 / 20, more preferably 10 / 90 to 70 / 30, from the viewpoint of improving optical isotropy and chemical resistance, still more preferably 30 / 70 to 70 / 30 from the viewpoint of heat resistance, and even more preferably 45 / 55 to 70 / 30, and even more preferably 45 / 55 to 60 / 40 from the viewpoint of toughness.

[0025] Structural unit B may contain structural units other than structural units (B-1) and (B-2). In addition to structural units (B-1) and (B-2), structural unit B preferably contains a structural unit (B-3) derived from a compound represented by the following formula (b-3) from the viewpoints of heat resistance and colorless transparency.

[0026]

Chemical formula

[0027] When the structural unit B contains the structural units (B-1), (B-2) and (B-3), the total ratio of the structural units (B-1) and (B-2) in the structural unit B is preferably 50 mol% or more, more preferably 60 mol% or more, still more preferably 70 mol% or more, and the ratio of the structural unit (B-3) in the structural unit B is preferably 1 to 50 mol%, more preferably 5 to 40 mol%, still more preferably 10 to 30 mol%. The total ratio of the structural units (B-1), (B-2) and (B-3) in the structural unit B is preferably 80 mol% or more, more preferably 90 mol% or more, particularly preferably 99 mol% or more. The upper limit value of the total ratio of the structural units (B-1), (B-2) and (B-3) is not particularly limited, that is, it is 100 mol%. The structural unit B may consist only of the structural units (B-1), (B-2) and (B-3).

[0028] The structural unit B may contain structural units other than the structural units (B-1), (B-2), and (B-3). The diamine that provides such a structural unit is not particularly limited, but examples include 1,4-phenylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-indene-5-amine, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, N,N'-bis(4-aminophenyl)terephthalamide, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, and aromatic diamines such as 9,9-bis(4-aminophenyl)fluorene (excluding the compound represented by formula (b-1) and the compound represented by formula (b-3)); alicyclic diamines (excluding the compound represented by formula (b-2)); and aliphatic diamines such as ethylenediamine and hexamethylenediamine. In the present specification, the aromatic diamine means a diamine containing one or more aromatic rings, the alicyclic diamine means a diamine containing one or more alicyclic rings and no aromatic rings, and the aliphatic diamine means a diamine containing neither an aromatic ring nor an alicyclic ring. The structural units other than the structural unit (B-1) and the structural unit (B-2) optionally contained in the structural unit B may be one kind or two or more kinds.

[0029] <Properties of the polyimide resin> From the viewpoint of the mechanical strength of the obtained polyimide film, the number average molecular weight of the polyimide resin is preferably 5,000 to 300,000. The number average molecular weight of the polyimide resin can be determined, for example, from the standard polymethyl methacrylate (PMMA) conversion value by gel filtration chromatography measurement.

[0030] The polyimide resin may contain a structure other than the polyimide chain (a structure in which structural unit A and structural unit B are imide-bonded). Examples of the structure other than the polyimide chain that can be contained in the polyimide resin include a structure containing an amide bond and the like. The polyimide resin preferably contains a polyimide chain (a structure in which structural unit A and structural unit B are imide-bonded) as the main structure. Therefore, the ratio of the polyimide chain in the polyimide resin is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, particularly preferably 99% by mass or more, and may be 100% by mass.

[0031] The polyimide resin composition of the present invention containing the above polyimide resin can form a film excellent in optical isotropy, peelability, and chemical resistance, and the suitable physical property values of the film are as follows.

[0032] The total light transmittance is preferably 88% or more, more preferably 88.5% or more, still more preferably 89% or more when the film has a thickness of 10 μm. The yellow index (YI) is preferably 4.5 or less, more preferably 3.0 or less, still more preferably 2.0 or less, and even more preferably 1.5 or less when the film has a thickness of 10 μm. The absolute value of the thickness retardation (Rth) is preferably 70 nm or less, more preferably 50 nm or less, still more preferably 40 nm or less, and even more preferably 30 nm when the film has a thickness of 10 μm.

[0033] In addition, the film that can be formed using the above polyimide resin also has good mechanical properties and heat resistance, and has the following suitable physical property values. The tensile strength is preferably 70 MPa or more, more preferably 90 MPa or more, still more preferably 100 MPa or more. The tensile modulus of elasticity is preferably 1.5 GPa or more, more preferably 2.0 GPa or more, and still more preferably 2.5 GPa or more. The tensile elongation at break is preferably 5% or more, more preferably 6% or more, and still more preferably 7% or more. The glass transition temperature (Tg) is preferably 200 °C or more, more preferably 230 °C or more, and still more preferably 250 °C or more. In addition, the above physical property values in the present invention can be specifically measured by the methods described in the examples.

[0034] <Method for producing polyimide resin> In the present invention, the polyimide resin can be produced by reacting a tetracarboxylic acid component containing a compound that provides the above structural unit (A-1) and a compound that provides the above structural unit (A-2) with a diamine component containing a compound that provides the above structural unit (B-1) and a compound that provides the above structural unit (B-2).

[0035] Examples of the compound that provides the structural unit (A-1) include, but are not limited to, the compound represented by the formula (a-1), and derivatives thereof may be used as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydrides represented by the formula (a-1) (i.e., 4,4'-oxydiphthalic acid), and alkyl esters of such tetracarboxylic acids. Among them, the tetracarboxylic dianhydride represented by the formula (a-1) is preferred. Similarly, examples of the compound that provides the structural unit (A-2) include, but are not limited to, the compound represented by the formula (a-2), and derivatives thereof may be used as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydrides represented by the formula (a-2) (i.e., 1,2,4,5-cyclohexanetetracarboxylic acid), and alkyl esters of such tetracarboxylic acids. Among them, the tetracarboxylic dianhydride represented by the formula (a-2) is preferred.

[0036] The tetracarboxylic acid component preferably contains a compound providing the structural unit (A-1) in an amount of 20 to 80 mol%, more preferably 30 to 70 mol%, and still more preferably 40 to 60 mol%. The tetracarboxylic acid component preferably contains a compound providing the structural unit (A-2) in an amount of 20 to 80 mol%, more preferably 30 to 70 mol%, and still more preferably 40 to 60 mol%. The tetracarboxylic acid component preferably contains a total of a compound providing the structural unit (A-1) and a compound providing the structural unit (A-2) in an amount of 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 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, it is 100 mol%. The tetracarboxylic acid component may consist only of a compound providing the structural unit (A-1) and a compound providing the structural unit (A-2). The molar ratio [(A-1) / (A-2)] of the compound providing the structural unit (A-1) to the compound providing the structural unit (A-2) in the tetracarboxylic acid component is preferably 20 / 80 to 80 / 20, more preferably 30 / 70 to 70 / 30, and still more preferably 40 / 60 to 60 / 40.

[0037] The tetracarboxylic acid component may contain a compound other than the compound providing the structural unit (A-1) and the compound providing the structural unit (A-2). Examples of such optional compounds include the above-mentioned aromatic tetracarboxylic dianhydrides, alicyclic tetracarboxylic dianhydrides, and aliphatic tetracarboxylic dianhydrides, as well as their derivatives (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.). The compound 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 kind or two or more kinds.

[0038] Examples of the compound that provides the structural unit (B-1) include, but are not limited to, the compound represented by the formula (b-1), and derivatives thereof may also be used as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compound represented by the formula (b-1). As the compound that provides the structural unit (B-1), the compound represented by the formula (b-1) (i.e., diamine) is preferred. Similarly, examples of the compound that provides the structural unit (B-2) include, but are not limited to, the compound represented by the formula (b-2), and derivatives thereof may also be used as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compound represented by the formula (b-2). As the compound that provides the structural unit (B-2), the compound represented by the formula (b-2) (i.e., diamine) is preferred.

[0039] The diamine component preferably contains 5 to 80 mol%, more preferably 10 to 70 mol%, still more preferably 30 to 70 mol%, even more preferably 45 to 70 mol%, and even more preferably 45 to 60 mol% of the compound that provides the structural unit (B-1). The diamine component preferably contains 20 to 95 mol%, more preferably 30 to 90 mol%, still more preferably 30 to 70 mol%, even more preferably 30 to 55 mol%, and even more preferably 40 to 55 mol% of the compound that provides the structural unit (B-2). The diamine component preferably contains 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more in total of the compound that provides the structural unit (B-1) and the compound that provides the structural unit (B-2). The upper limit of the total content of the compound that provides the structural unit (B-1) and the compound that provides the structural unit (B-2) is not particularly limited, that is, it is 100 mol%. The diamine component may consist only of the compound that provides the structural unit (B-1) and the compound that provides the structural unit (B-2). The molar ratio [(B-1) / (B-2)] of the compound providing the structural unit (B-1) and the compound providing the structural unit (B-2) in the diamine component is preferably 5 / 95 to 80 / 20, more preferably 10 / 90 to 70 / 30, even more preferably 30 / 70 to 70 / 30 from the viewpoint of improving optical isotropy and chemical resistance, and even more preferably 45 / 55 to 70 / 30, even more preferably 45 / 55 to 60 / 40 from the viewpoint of toughness.

[0040] The diamine component may contain a compound other than the compound providing the structural unit (B-1) and the compound providing the structural unit (B-2).

[0041] In addition to the compound providing the structural unit (B-1) and the compound providing the structural unit (B-2), the diamine component may further contain a compound providing the structural unit (B-3). Examples of the compound providing the structural unit (B-3) include, but are not limited to, the compound represented by the formula (b-3), and derivatives thereof may also be used as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compound represented by the formula (b-3). The compound providing the structural unit (B-3) is preferably the compound represented by the formula (b-3) (i.e., diamine).

[0042] The diamine component preferably contains 1 to 50 mol%, more preferably 5 to 40 mol%, even more preferably 10 to 30 mol% of the compound providing the structural unit (B-3). When the diamine component contains a compound that provides the structural unit (B-3), the diamine component preferably contains, in total, 80 mol% or more, more preferably 90 mol% or more, and still more preferably 99 mol% or more of the compound that provides the structural unit (B-1), the compound that provides the structural unit (B-2), and the compound that provides the structural unit (B-3). The upper limit of the total content of the compound that provides the structural unit (B-1), the compound that provides the structural unit (B-2), and the compound that provides the structural unit (B-3) is not particularly limited, i.e., it is 100 mol%. The diamine component may consist only of the compound that provides the structural unit (B-1), the compound that provides the structural unit (B-2), and the compound that provides the structural unit (B-3).

[0043] Compounds other than the compound that provides the structural unit (B-1) and the compound that provides the structural unit (B-2) optionally contained in the diamine component are not limited to the compound that provides the structural unit (B-3). Such optional compounds include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, as well as their derivatives (such as diisocyanates). Compounds other than the compound that provides the structural unit (B-1) and the compound that provides the structural unit (B-2) optionally contained in the diamine component may be one kind or two or more kinds.

[0044] In the present invention, the charging amount ratio of the tetracarboxylic acid component to the diamine component used in the production of the polyimide resin is preferably such that the diamine component is 0.9 to 1.1 mol with respect to 1 mol of the tetracarboxylic acid component.

[0045] In addition, in the present invention, a terminal blocking agent may be used in the production of the polyimide resin in addition to the aforementioned tetracarboxylic acid component and diamine component. Monamines or dicarboxylic acids are preferred as the terminal blocking agent. The charged amount of the terminal blocking agent to be introduced is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, per 1 mol of the tetracarboxylic acid component. Examples of the monoamine terminal blocking agent include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline, etc., and benzylamine and aniline are preferred. As the dicarboxylic acid terminal blocking agent, dicarboxylic acids are preferred, and a part of them may be ring-closed. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclohexane-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. are mentioned, and phthalic acid and phthalic anhydride are preferred.

[0046] There is no particular limitation on the method for reacting the aforementioned tetracarboxylic acid component and diamine component, and known methods can be used. Specific reaction methods include: (1) charging the tetracarboxylic acid component, diamine component, and reaction solvent into a reactor, stirring at 0 to 80°C for 0.5 to 30 hours, and then raising the temperature to carry out the imidization reaction; (2) charging the diamine component and reaction solvent into a reactor and dissolving them, then charging the tetracarboxylic acid component, and stirring at room temperature (0 to 80°C) for 0.5 to 30 hours as necessary, and then raising the temperature to carry out the imidization reaction; (3) charging the tetracarboxylic acid component, diamine component, and reaction solvent into a reactor and immediately raising the temperature to carry out the imidization reaction, etc.

[0047] The reaction solvent used in the production of the polyimide resin may be any one that does not inhibit the imidization reaction and can dissolve the resulting polyimide. For example, aprotic solvents, phenolic solvents, ether solvents, carbonate solvents, etc. can be mentioned.

[0048] Specific examples of aprotic solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), N-methylcaprolactam, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone solvents such as γ-butyrolactone (GBL) and γ-valerolactone; phosphorus-containing amide solvents such as hexamethylphosphoric triamide and hexamethylphosphine triamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and sulfolane; ketone solvents such as acetone, cyclohexanone, and methylcyclohexanone; amine solvents such as picoline and pyridine; ester solvents such as (2-methoxy-1-methylethyl) acetate, etc.

[0049] Specific examples of phenolic solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, etc. Specific examples of ether solvents include 1,2-dimethoxyethane, bis(2-methoxyethyl) ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl] ether, tetrahydrofuran, 1,4-dioxane, etc. In addition, specific examples of carbonate solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, etc. Among the above reaction solvents, aprotic solvents are preferred, and amide solvents and lactone solvents are more preferred. Also, the above reaction solvents may be used alone or in a mixture of two or more.

[0050] 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 performing such an operation, the degree of polymerization and the imidization rate can be further increased.

[0051] In the above imidization reaction, a known imidization catalyst can be used. Examples of the imidization catalyst include 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 (TEA), tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, N,N-diethylaniline, and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogen carbonate, and sodium hydrogen carbonate. Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methyl benzoic acid, oxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, and the like. The above imidization catalysts may be used alone or in combination of two or more. Among the above, from the viewpoint of handleability, it is preferable to use a base catalyst, more preferably an organic base catalyst, and even more preferably triethylamine.

[0052] From the viewpoints of reaction rate and suppression of gelation and the like, 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 start of distillation of the generated water.

[0053] Since the polyimide resin of the present invention contains the structural unit A including the structural units (A-1) and (A-2) and the structural unit B including the structural units (B-1) and (B-2), the solubility of the polymer generated as the imidization reaction proceeds in the solvent is high, and a transparent varnish can be obtained.

[0054] [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 and the organic solvent of the present invention, and the polyimide resin is dissolved in the organic solvent. The organic solvent may be any one in which the polyimide resin can be dissolved, and is not particularly limited. However, it is preferable to use the above-described compounds alone or in admixture of two or more as the reaction solvent used in the production of the polyimide resin. The polyimide varnish of the present invention may be the polyimide solution itself in which the polyimide resin obtained by the polymerization method is dissolved in the reaction solvent, or may be a solution obtained by further adding and diluting a solvent to the polyimide solution.

[0055] Since the polyimide resin of the present invention has solvent solubility, a high-concentration varnish stable at room temperature can be obtained. The polyimide varnish of the present invention preferably contains 5 to 40% by mass, more preferably 10 to 30% by mass of the polyimide resin of the present invention. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, more preferably 1 to 100 Pa·s. The viscosity of the polyimide varnish is a value measured at 25°C using an E-type viscometer. Further, the polyimide varnish of the present invention may contain various additives such as an inorganic filler, an adhesion promoter, a release agent, a flame retardant, an ultraviolet stabilizer, a surfactant, a leveling agent, an antifoaming agent, a fluorescent brightening agent, a crosslinking agent, a polymerization initiator, and a photosensitive agent, as long as the required properties of the polyimide film are not impaired. The method for producing the polyimide varnish of the present invention is not particularly limited, and a known method can be applied.

[0056] [Polyimide film] The polyimide film of the present invention contains the polyimide resin of the present invention. Therefore, the polyimide film of the present invention is excellent in optical isotropy, peelability, and chemical resistance. The suitable physical property values of the polyimide film of the present invention are as described above. The method for producing the polyimide film of the present invention is not particularly limited, and known methods can be used. For example, the polyimide varnish of the present invention can be applied onto a smooth support such as a glass plate, a metal plate, or plastic, or formed into a film shape, and then an organic solvent such as a reaction solvent or a diluting solvent contained in the varnish is removed by heating.

[0057] Examples of the coating method include known coating methods such as spin coating, slit coating, and blade coating. Among them, slit coating is preferable from the viewpoint of controlling intermolecular orientation and improving chemical resistance and workability. As a method for removing the organic solvent contained in the varnish by heating, it is preferable to evaporate the organic solvent at a temperature of 150°C or lower to make it tack-free, and then dry it at a temperature equal to or higher than the boiling point of the used organic solvent (not particularly limited, but preferably 200 to 500°C). Also, it is preferable to dry in an air atmosphere or a nitrogen atmosphere. The pressure of the drying atmosphere may be any of reduced pressure, normal pressure, and increased pressure. The method for peeling the polyimide film formed on the support from the support is not particularly limited, and a laser lift-off method or the like can be used.

[0058] Further, the polyimide film of the present invention can also be produced using a polyamic acid varnish obtained by dissolving a polyamic acid in an organic solvent. The polyamic acid contained in the polyamic acid varnish is a precursor of the polyimide resin of the present invention, and is a product of a polyaddition reaction between a tetracarboxylic acid component containing a compound that gives the above structural unit (A-1) and a compound that gives the above structural unit (A-2), and a diamine component containing a compound that gives the above structural unit (B-1) and a compound that gives the structural unit (B-2). By imidizing (dehydration ring-closing) this polyamic acid, the polyimide resin of the present invention, which is the final product, can be obtained. As the organic solvent contained in the polyamic acid varnish, the organic solvent contained in the polyimide varnish of the present invention can be used. In the present invention, the polyamic acid varnish may be the polyamic acid solution itself obtained by subjecting a tetracarboxylic acid component and a diamine component to a polyaddition reaction in a reaction solvent, or may be a solution obtained by further adding and diluting a solvent to the polyamic acid solution.

[0059] There is no particular limitation on the method for producing a polyimide film using the polyamic acid varnish, and known methods can be used. For example, the polyamic acid varnish is applied onto a smooth support such as a glass plate, a metal plate, or plastic, or formed into a film shape, and an organic solvent such as a reaction solvent or a diluting solvent contained in the varnish is removed by heating to obtain a polyamic acid film, and the polyamic acid in the polyamic acid film is imidized by heating to produce a polyimide film. The heating temperature when drying the polyamic acid varnish to obtain a polyamic acid film is preferably 50 to 120°C. The heating temperature when imidizing the polyamic acid by heating is preferably 200 to 400°C. Note that the imidization method is not limited to thermal imidization, and chemical imidization can also be applied.

[0060] The thickness of the polyimide film of the present invention can be appropriately selected according to the use and the like, but is preferably in the range of 1 to 250 μm, more preferably 5 to 100 μm, still more preferably 8 to 80 μm, and even more preferably 10 to 80 μm. When the thickness is 1 to 250 μm, practical use as a self-supporting film becomes possible. The thickness of the polyimide film can be easily controlled by adjusting the solid content concentration and viscosity of the polyimide varnish.

Examples

[0061] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited by these examples.

[0062] <Film Physical Properties and Evaluation> Each physical property of the films obtained in the examples and comparative examples was measured by the following methods.

[0063] (1) Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

[0064] (2) Tensile strength, tensile modulus, and elongation at break The tensile strength, tensile modulus, and elongation at break were measured in accordance with JIS K7127:1999 using a tensile testing machine "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd. The distance between chucks was 50 mm, the test piece size was 10 mm × 70 mm, and the test speed was 20 mm / min.

[0065] (3) Glass transition temperature (Tg) Using a thermomechanical analyzer "TMA / SS6100" manufactured by Hitachi High-Tech Science Corporation, in tensile mode, with a sample size of 2 mm × 20 mm, a load of 0.1 N, and a heating rate of 10 °C / min, the temperature was raised to a temperature sufficient to remove the residual stress, and the residual stress was removed, and then cooled to room temperature. Thereafter, the measurement of the test piece elongation was performed under the same conditions as the treatment for removing the residual stress, and the point of inflection of the elongation was determined as the glass transition temperature.

[0066] (4) Total light transmittance and yellowness index (YI) The total light transmittance and YI were measured in accordance with JIS K7136 using a color and haze simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.

[0067] (5) Haze The measurement was performed in accordance with JIS K7361-1 using a color and haze simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd.

[0068] (6) Thickness retardation (Rth) (evaluation of optical isotropy) The thickness retardation (Rth) was measured using an ellipsometer "M-220" manufactured by JASCO Corporation. The value of the thickness retardation was measured at a measurement wavelength of 590 nm. Note that Rth is expressed by the following formula when the maximum value among the in-plane refractive indices of the polyimide film is nx, the minimum value is ny, the refractive index in the thickness direction is nz, and the film thickness is d. Rth = [{(nx + ny) / 2} - nz] × d

[0069] (7) Peelability The peelability was evaluated by making a cut with a cutter knife into an 8 cm square on the polyimide film formed on a glass plate and peeling the film from the glass plate with tweezers. Those that can be peeled without immersing the film and the glass plate in water have good peelability, and those that cannot be peeled without immersing the film and the glass plate in water have poor peelability. In Table 1, when the peelability was good, it was designated as "A", and when the peelability was poor, it was designated as "C". In the evaluations of (1) to (6) above, when using a film immersed in water, the film was dried at 90°C for 1 hour before measurement and evaluation.

[0070] (8) Solvent resistance The polyimide film formed on a glass plate was immersed in a solvent at room temperature, and it was confirmed whether there was any change on the film surface. Note that propylene glycol monomethyl ether acetate (PGMEA) was used as the solvent. The evaluation criteria for solvent resistance were as follows. A: There was no change on the film surface. B: Slight cracks appeared on the film surface. C: Cracks appeared on the film surface or the film surface was dissolved.

[0071] <Abbreviations of components, etc.> The tetracarboxylic acid components and diamine components used in the examples and comparative examples, and their abbreviations are as follows.

[0072] (Tetracarboxylic acid component) ODPA: 4,4'-Oxydiphthalic anhydride (manufactured by Manac Co., Ltd.; compound represented by formula (a-1)) HPMDA: 1,2,4,5-Cyclohexanetetracarboxylic dianhydride (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (a-2)) 6FDA: 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride

[0073] (Diamine component) 4,4'-DDS: 4,4'-Diaminodiphenyl sulfone (manufactured by Seika Co., Ltd.; compound represented by formula (b-1)) 1,3-BAC: 1,3-Bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (b-2a)) 1,4-BACT: 1,4-Bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc.; compound represented by formula (b-2b); trans ratio 85%) 6FODA: 4,4'-Diamino-2,2'-bis(trifluoromethyl)diphenyl ether (manufactured by ChinaTech Chemical (Tianjin) Co., Ltd.; compound represented by formula (b-3)) 3,3'-DDS: 3,3'-Diaminodiphenyl sulfone (manufactured by Seika Co., Ltd.)

[0074] <Manufacture of polyimide resin, varnish and polyimide film> Example 1 Into a 300 mL five-neck round-bottom flask equipped with a stainless-steel semi-circular stirring blade, a nitrogen inlet tube, a Dean-Stark apparatus with a cooling tube, a thermometer, and a glass end cap, 12.415 g (0.050 mol) of 4,4'-DDS, 7.113 g (0.050 mol) of 1,4-BACT, and 55.496 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added. The mixture was stirred at a system temperature of 70 °C under a nitrogen atmosphere at a rotation speed of 200 rpm to obtain a solution. To this solution, 15.511 g (0.050 mol) of ODPA, 11.209 g (0.050 mol) of HPMDA, and 13.874 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added all at once. Then, 0.506 g of triethylamine (manufactured by Kanto Chemical Co., Inc.) was introduced as an imidization catalyst, and the mixture was heated with a mantle heater. The temperature inside the reaction system was raised to 190 °C over about 20 minutes. The components to be distilled off were collected, and while adjusting the rotation speed according to the increase in viscosity, the temperature inside the reaction system was maintained at 190 °C and refluxed for about 5 hours. Thereafter, 101.200 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) was added so that the solid content concentration became 20% by mass. After cooling the temperature inside the reaction system to 100 °C, it was further stirred for about 1 hour for homogenization to obtain a polyimide varnish. Subsequently, the obtained polyimide varnish was applied onto a glass plate by spin coating, held at 80 °C for 20 minutes on a hot plate, and then heated at 260 °C for 30 minutes in a hot air dryer under an air atmosphere to evaporate the solvent and obtain a film.

[0075] Example 2 A polyimide varnish with a solid content concentration of 20% by mass was obtained in the same manner as in Example 1, except that the amount of 1,4-BACT was changed from 7.113 g (0.050 mol) to 11.380 g (0.080 mol), and the amount of 4,4'-DDS was changed from 12.415 g (0.050 mol) to 4.966 g (0.020 mol). Using the obtained polyimide varnish, a film was obtained in the same manner as in Example 1.

[0076] Example 3 A polyimide varnish with a solid content concentration of 20% by mass was obtained in the same manner as in Example 1, except that the amount of 1,4-BACT was changed from 7.113 g (0.050 mol) to 8.535 g (0.060 mol), and the amount of 4,4'-DDS was changed from 12.415 g (0.050 mol) to 9.932 g (0.040 mol). Using the obtained polyimide varnish, a film was obtained in the same manner as in Example 1.

[0077] Example 4 The amount of 4,4'-DDS was changed from 12.415 g (0.050 mol) to 4.966 g (0.020 mol), and 6FODA was added in an amount of 10.087 g (0.030 mol). Otherwise, in the same manner as in Example 1, a polyimide varnish with a solid content concentration of 20% by mass was obtained. Using the obtained polyimide varnish, a film was obtained in the same manner as in Example 1.

[0078] Example 5 1,4-BACT 7.113 g (0.050 mol) was changed to 1,3-BAC 7.113 g (0.050 mol). Otherwise, in the same manner as in Example 1, a polyimide varnish with a solid content concentration of 20% by mass was obtained. Using the obtained polyimide varnish, a film was obtained in the same manner as in Example 1.

[0079] Comparative Example 1 ODPA 15.511 g (0.050 mol) and HPMDA 11.209 g (0.050 mol) were changed to 6FDA 44.424 (0.100 mol). Otherwise, in the same manner as in Example 1, a polyimide varnish with a solid content concentration of 20% by mass was obtained. Using the obtained polyimide varnish, a film was obtained in the same manner as in Example 1.

[0080] Comparative Example 2 HPMDA 11.209 g (0.050 mol) was changed to 6FDA 22.212 g (0.050 mol). Otherwise, in the same manner as in Example 1, a polyimide varnish with a solid content concentration of 20% by mass was obtained. Using the obtained polyimide varnish, a film was obtained in the same manner as in Example 1.

[0081] Comparative Example 3 4,4'-DDS 12.415 g (0.050 mol) was changed to 3,3'-DDS 12.415 g (0.050 mol). Otherwise, in the same manner as in Example 1, a polyimide varnish with a solid content concentration of 20% by mass was obtained. Using the obtained polyimide varnish, a film was obtained in the same manner as in Example 1.

[0082] Comparative Example 4 The imidization reaction was carried out in the same manner as in Example 1, except that HPMDA was not used and the amount of ODPA was changed from 15.511 g (0.050 mol) to 31.021 g (0.100 mol). However, after the addition of triethylamine, the reaction solution became turbid during the process of raising the temperature of the reaction system to 190 °C, and no varnish was obtained.

[0083] Comparative Example 5 The imidization reaction was carried out in the same manner as in Example 1, except that 1,4-BACT was not used and the amount of 4,4'-DDS was changed from 12.415 g (0.050 mol) to 24.830 g (0.100 mol), and HPMDA was not used and the amount of ODPA was changed from 15.511 g (0.050 mol) to 31.021 g (0.100 mol). However, after the addition of triethylamine, the reaction solution became turbid during the process of raising the temperature of the reaction system to 190 °C, and no varnish was obtained.

[0084] Comparative Example 6 The imidization reaction was carried out in the same manner as in Example 1, except that 1,4-BACT was not used and the amount of 4,4'-DDS was changed from 12.415 g (0.050 mol) to 24.830 g (0.100 mol), and ODPA was not used and the amount of HPMDA was changed from 11.209 g (0.050 mol) to 22.417 g (0.100 mol). However, after the addition of triethylamine, the reaction solution became turbid during the process of raising the temperature of the reaction system to 190 °C, and no varnish was obtained.

[0085] The above physical property measurements and evaluations were performed on the polyimide films obtained in the examples and comparative examples. The results are shown in Table 1.

[0086] [Table 1]

[0087] As shown in Table 1, it can be seen that the polyimide films of the examples have good optical isotropy and are further excellent in peelability and chemical resistance.

Industrial Applicability

[0088] The polyimide film containing the polyimide resin of the present invention has good optical isotropy, and is further excellent in peelability and chemical resistance, and is suitably used as a film for various members such as color filters, flexible displays, semiconductor components, and optical members. The polyimide film containing the polyimide resin of the present invention is particularly suitably used as a substrate for image display devices such as liquid crystal displays and OLED displays.

Claims

1. A polyimide resin having a structural unit A derived from a 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), the structural unit B includes a structural unit (B-1) derived from a compound represented by the following formula (b-1) and a structural unit (B-2) derived from a compound represented by the following formula (b-2), the molar ratio [(A-1) / (A-2)] of the structural unit (A-1) to the structural unit (A-2) in the structural unit A is 20 / 80 to 80 / 20, and the molar ratio [(B-1) / (B-2)] of the structural unit (B-1) to the structural unit (B-2) in the structural unit B is 5 / 95 to 80 / 20. 【Chemical 1】

2. The polyimide resin according to claim 1, wherein the ratio of the structural unit (A-1) in the structural unit A is 20 to 80 mol%, and the ratio of the structural unit (A-2) in the structural unit A is 20 to 80 mol%.

3. The polyimide resin according to claim 1 or 2, wherein the ratio of the structural unit (B-1) in the structural unit B is 5 to 80 mol%, and the ratio of the structural unit (B-2) in the structural unit B is 20 to 95 mol%.

4. A polyimide varnish obtained by dissolving the polyimide resin according to any one of claims 1 to 3 in an organic solvent.

5. A polyimide film containing the polyimide resin according to any one of claims 1 to 3.

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