Polyimide resin, varnish, and polyimide film

Abstract

The polyimide resin according to the present invention has a structural unit A derived from a tetracarboxylic acid dianhydride and a structural unit B derived from a diamine. The structural unit B includes a structural unit (B1) derived from a compound represented by formula (b1) and a structural unit (B2) derived from a compound represented by formula (b2). The present invention provides: a polyimide resin that can form a film having a low residual stress, an excellent heat resistance, and a low linear thermal expansion coefficient; a varnish containing a polyamic acid which is a precursor of said polyimide resin; and a polyimide film.

Description

Technical Field

[0001] The present invention relates to a polyimide resin, a varnish, and a polyimide film.

Background Art

[0002] Polyimide resins are being studied 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 flexibilizing the devices, and research on polyimide films suitable as such plastic substrates is underway. Polyimide films for such applications are required to have high transparency, a small retardation due to birefringence, that is, a low retardation, and the like. In addition, when a polyimide film is formed by heat-curing a varnish applied on a glass support or a silicon wafer, residual stress is generated in the polyimide film. If the residual stress in the polyimide film is large, there arises a problem that the glass support or the silicon wafer is warped, and thus reduction of the residual stress is also required for the polyimide film.

[0003] Patent Document 1 discloses a polyimide resin synthesized using α,ω-aminopropylpolydimethylsiloxane and 4,4'-diaminodiphenyl ether as diamine components as a polyimide resin that provides a film with low residual stress. Patent Document 2 discloses a polyimide film formed by imidizing a polyimide resin precursor synthesized using bistrifluoromethylbenzidine and silicon-containing diamines as diamine components as a polyimide film with low residual stress.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] As described above, various properties are required for polyimide films, but it is not easy to satisfy these properties simultaneously. Especially recently, the miniaturization and precision of substrates have advanced, and the integration of electronic circuits has also advanced. Therefore, in order to cope with this, not only the above-mentioned low residual stress but also thermal stability has come to be required. For example, it is required to have heat resistance and a low coefficient of linear thermal expansion. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a polyimide resin capable of forming a film having low residual stress, excellent heat resistance, and a low coefficient of linear thermal expansion, a varnish containing polyamic acid which is a precursor of the polyimide resin, and a polyimide film. [Means for Solving the Problems]

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

[0007] That is, the present invention relates to the following [1] to

[10] . [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 B includes a structural unit (B1) derived from a compound represented by the following formula (b1) and a structural unit (B2) derived from a compound represented by the following formula (b2).

[0008] [Chemical Formula]

[0009] [2] The polyimide resin according to [1] above, wherein the structural unit A contains a structural unit (A1) derived from a compound represented by the following formula (a1).

[0010] [Chemical formula]

[0011] [3] The polyimide resin according to [1] or [2] above, wherein the structural unit B further contains at least one structural unit (B3) selected from the group consisting of a structural unit (B31) derived from a compound represented by the following formula (b31), a structural unit (B32) derived from a compound represented by the following formula (b32), and a structural unit (B33) derived from a compound represented by the following formula (b33).

[0012] [Chemical formula]

[0013] [4] A varnish obtained by dissolving a polyamic acid, which is a precursor of the polyimide resin according to any one of [1] to [3] above, in an organic solvent. [5] The varnish according to [4] above, further containing at least one selected from the group consisting of an imidazole compound and a tertiary amine. [6] The varnish according to [5] above, wherein the imidazole compound is at least one selected from the group consisting of imidazole, 1,2-imidazole, and 1-benzyl-2-methylimidazole. [7] The varnish according to [5] or [6] above, wherein the tertiary amine is triethylenediamine. [8] A polyimide film obtained by applying the varnish according to any one of [4] to [7] above onto a support and heating. [9] A method for producing a polyimide film, comprising applying the varnish according to any one of [4] to [7] above onto a support and heating.

[10] A polyimide film containing the polyimide resin according to any one of [1] to [3].

Advantages of the Invention

[0014] According to the present invention, there can be provided a polyimide resin capable of forming a film having low residual stress, excellent heat resistance, and a low linear thermal expansion coefficient, a varnish containing polyamic acid which is a precursor of the polyimide resin, and a polyimide film.

Modes for Carrying Out the Invention

[0015] [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 B includes a structural unit (B1) derived from a compound represented by the following formula (b1) and a structural unit (B2) derived from a compound represented by the following formula (b2).

[0016]

Chemical Formula

[0017] <Structural Unit A> The structural unit A is a structural unit derived from a tetracarboxylic dianhydride in the polyimide resin. The structural unit A may be any one that can react with the structural unit B to form an imide bond, but the structural unit A preferably includes a structural unit (A1) derived from a compound represented by the following formula (a1).

[0018]

Chemical Formula

[0019] The compound represented by formula (a1) is norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride. By including a structural unit A derived from a compound represented by formula (a1), the film of the present invention can improve heat resistance and optical isotropy while having low residual stress and a low linear thermal expansion coefficient.

[0020] From the viewpoint of improving heat resistance and optical isotropy, the ratio of the structural unit (A1) in the structural unit A is preferably 45 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of the ratio is not particularly limited, that is, it is 100 mol%.

[0021] The structural unit A may contain a structural unit other than the structural unit (A1) as long as the effects of the present invention are not impaired. The tetracarboxylic dianhydride that provides such a structural unit is not particularly limited, but aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride; alicyclic tetracarboxylic dianhydrides such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and dicyclohexyltetracarboxylic dianhydride; and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride can be mentioned. Among these, from the viewpoints of improving heat resistance, optical isotropy, and transparency, 1,2,3,4-cyclobutanetetracarboxylic dianhydride and 1,2,4,5-cyclohexanetetracarboxylic dianhydride are preferable. The structural units other than the structural unit (A1) optionally contained in the structural unit A may be one kind or two or more kinds. The structural unit A preferably does not contain structural units other than the structural unit (A1).

[0022] 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.

[0023] <Structural unit B> The structural unit B is a structural unit derived from a diamine in the polyimide resin, and includes a structural unit (B1) derived from a compound represented by the following formula (b1) and a structural unit (B2) derived from a compound represented by the following general formula (b2). By the structural unit B containing both the structural unit (B1) and the structural unit (B2), it is considered to have low residual stress, excellent heat resistance, low linear thermal expansion coefficient, and excellent thermal physical properties.

[0024]

Chemical formula

[0025] The compound represented by the formula (b1) is 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA). By containing the structural unit (B1) derived from the compound represented by the formula (b1), in addition to the effects of the present invention, elongation, strength, and transparency can be imparted. The compound represented by the formula (b2) is 4,4'-diaminobenzanilide (DABA). By including the structural unit (B2) derived from the compound represented by the formula (b2), the residual stress can be reduced.

[0026] The ratio of the structural unit (B1) in the structural unit B is preferably 5 to 60 mol%, more preferably 10 to 40 mol%, and still more preferably 10 to 30 mol%. The ratio of the structural unit (B2) in the structural unit B is preferably 40 to 95 mol%, more preferably 60 to 90 mol%, and still more preferably 70 to 90 mol%. The total ratio of the structural units (B1) and (B2) in the 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 value of the total ratio of the structural units (B1) and (B2) is not particularly limited, that is, it is 100 mol%. The structural unit B may consist only of the structural unit (B1) and the structural unit (B2). The molar ratio [(B1) / (B2)] of the structural unit (B1) to the structural unit (B2) in the structural unit B is preferably 5 / 95 to 60 / 40, more preferably 5 / 95 to 50 / 50, still more preferably 5 / 95 to 40 / 60, and even more preferably 10 / 90 to 30 / 70. On the other hand, from the viewpoint of mechanical properties such as elongation and toughness, it is preferably 5 / 95 to 60 / 40, more preferably 10 / 90 to 60 / 40, still more preferably 30 / 70 to 60 / 40, and even more preferably 40 / 60 to 60 / 40.

[0027] The structural unit B may contain structural units other than the structural units (B1) and (B2). In addition to the structural units (B1) and (B2), the structural unit B preferably contains at least one structural unit (B3) selected from the group consisting of the structural unit (B31) derived from the compound represented by the following formula (b31), the structural unit (B32) derived from the compound represented by the following formula (b32), and the structural unit (B33) derived from the compound represented by the following formula (b33).

[0028] [Chemical formula]

[0029] The compound represented by formula (b31) is 4,4'-diaminodiphenyl ether (ODA), the compound represented by formula (b32) is 9,9-bis(4-aminophenyl)fluorene, and the compound represented by formula (b33) is 2,2'-bis(trifluoromethyl)benzidine. The structural unit (B3) may be only the structural unit (B31), only the structural unit (B32), only the structural unit (B33), or any combination thereof.

[0030] When the structural unit B contains the structural unit (B1), the structural unit (B2), and the structural unit (B3), the total ratio of the structural unit (B1) and the structural unit (B2) in the structural unit B is preferably 50 mol% or more, more preferably 60 mol% or more, still more preferably 70 mol% or more, and the ratio of the structural unit (B3) 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 unit (B1), the structural unit (B2), and the structural unit (B3) 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 unit (B1), the structural unit (B2), and the structural unit (B3) is not particularly limited, that is, it is 100 mol%. The structural unit B may consist only of the structural unit (B1), the structural unit (B2), and the structural unit (B3).

[0031] The structural unit B may contain structural units other than the structural units (B1) to (B3). The diamine that provides such a structural unit is not particularly limited, but examples include 1,4-phenylenediamine, p-xylylenediamine, 3,5-diaminobenzoic acid, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenylmethane, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl ether, 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, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 1,4-bis(4-aminophenoxy)benzene and other aromatic diamines; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine. In the present specification, the aromatic diamine means a diamine containing 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 units (B1) and (B2) optionally contained in the structural unit B may be one kind or two or more kinds.

[0032] The polyimide resin of the present invention may contain a structure other than the polyimide chain (a structure in which the structural unit A and the structural unit B are imide-bonded). Examples of the structure other than the polyimide chain that can be contained in the polyimide resin include a structure containing an amide bond. The polyimide resin of the present invention preferably contains a polyimide chain (a structure in which structural unit A and structural unit B are imide-bonded) as a main structure. Therefore, the ratio of the polyimide chain in the polyimide resin of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, particularly preferably 99% by mass or more, and may be 100% by mass.

[0033] By using the polyimide resin of the present invention, a film having low residual stress, excellent heat resistance, and a low linear thermal expansion coefficient can be formed, and the suitable physical property values of the film are as follows. The total light transmittance is preferably 85% or more, more preferably 87% or more, still more preferably 89% or more when the film has a thickness of 10 μm. The yellow index (YI) is preferably 10 or less, more preferably 9 or less, still more preferably 8 or less when the film has a thickness of 10 μm. The residual stress is preferably 30 MPa or less, more preferably 25 MPa or less, still more preferably 20 MPa or less, and even more preferably 15 MPa or less. The glass transition temperature (Tg) is preferably 370 °C or higher, more preferably 380 °C or higher, still more preferably 390 °C or higher, and even more preferably 400 °C or higher. 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 polyamic acid and polyimide resin] The polyimide resin of the present invention can be produced by reacting a tetracarboxylic acid component containing a compound that provides the above structural unit A with a diamine component containing a compound that provides the above structural unit (B1) and a compound that provides the above structural unit (B2). The polyimide resin of the present invention is preferably produced by a method of imidizing (dehydrative ring-closure) a polyamic acid which is a precursor of the polyimide resin. Specifically, it is preferable to apply or mold the polyamic acid contained in the varnish described later on a support, then remove the organic solvent by heating, and imidize (dehydrative ring-closure) by heating to obtain a polyimide resin. The production of a polyimide film which is a film-shaped polyimide resin will be described later. Note that the polyamic acid is a product of the polyaddition reaction of the above-described tetracarboxylic acid component and the above-described diamine component.

[0035] Among the compounds that give the structural unit A, preferable compounds include, but are not limited to, the compound represented by the formula (a1) which is a compound that gives the above-described structural unit (A1), and derivatives thereof may also be used as long as they give the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic dianhydride represented by the formula (a1) and alkyl esters of the tetracarboxylic acids. As the compound that gives the structural unit (A1), the compound represented by the formula (a1) (i.e., dianhydride) is preferable.

[0036] The tetracarboxylic acid component may contain compounds other than the compound that gives the structural unit (A1). Examples of such compounds include the above-described aromatic tetracarboxylic dianhydrides, alicyclic tetracarboxylic dianhydrides, and aliphatic tetracarboxylic dianhydrides, and derivatives thereof (tetracarboxylic acids, alkyl esters of tetracarboxylic acids, etc.). The compounds other than the compound that gives the structural unit (A1) optionally contained in the tetracarboxylic acid component may be one kind or two or more kinds.

[0037] Examples of the compound that gives the structural unit (B1) include, but are not limited to, the compound represented by the general formula (b1), and derivatives thereof may also be used as long as they give the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compound represented by the general formula (b1). As the compound that gives the structural unit (B1), the compound represented by the general formula (b1) (i.e., diamine) is preferable. Similarly, examples of the compound that provides the structural unit (B2) include, but are not limited to, the compound represented by the general formula (b2), 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 general formula (b2). As the compound that provides the structural unit (B2), the compound represented by the general formula (b2) (i.e., diamine) is preferred.

[0038] The diamine component preferably contains 5 to 60 mol%, more preferably 10 to 40 mol%, and still more preferably 20 to 30 mol% of the compound that provides the structural unit (B1). Similarly, the diamine component preferably contains 40 to 95 mol%, more preferably 60 to 90 mol%, and still more preferably 70 to 80 mol% of the compound that provides the structural unit (B2).

[0039] The total content ratio of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2) is preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more in the total diamine component. The upper limit value of the total content ratio of the compound that provides the structural unit (B-1) and the compound that provides the structural unit (B2) is not particularly limited, i.e., it is 100 mol%. The diamine component may consist only of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2). The molar ratio [(B1) / (B2)] of the compound that provides the structural unit (B1) and the compound that provides the structural unit (B2) in the diamine component is preferably 5 / 95 to 60 / 40, more preferably 5 / 95 to 50 / 50, still more preferably 5 / 95 to 40 / 60, and even more preferably 10 / 90 to 30 / 70. On the other hand, from the viewpoint of mechanical properties such as elongation and toughness, it is preferably 5 / 95 to 60 / 40, more preferably 10 / 90 to 60 / 40, still more preferably 30 / 70 to 60 / 40, and even more preferably 40 / 60 to 60 / 40.

[0040] The diamine component may contain, in addition to the compound providing the structural unit (B1) and the compound providing the structural unit (B2), a compound providing the structural unit (B3). Examples of the compound providing the structural unit (B3) include, but are not limited to, the compound represented by the general formula (b31), the compound represented by the general formula (b32), and the compound represented by the general formula (b33), and derivatives thereof may be used as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compound represented by the general formula (b31), the compound represented by the general formula (b32), and the compound represented by the general formula (b33). As the compound providing the structural unit (B3), the compound represented by the general formula (b31), the compound represented by the general formula (b32), and the compound represented by the general formula (b33) (i.e., diamine) are preferred. When the diamine component contains a compound providing the structural unit (B3), the compound providing the structural unit (B3) is preferably contained in an amount of 1 to 50 mol%, more preferably 5 to 40 mol%, and still more preferably 10 to 30 mol%. The total content ratio of the compound providing the structural unit (B1), the compound providing the structural unit (B2), and the compound providing the structural unit (B3) is preferably 80 mol% or more, more preferably 90 mol% or more, and still more preferably 99 mol% or more in the total diamine component. The upper limit value of the total content ratio of the compound providing the structural unit (B1), the compound providing the structural unit (B2), and the compound providing the structural unit (B3) is not particularly limited, that is, it is 100 mol%. The diamine component may consist only of the compound providing the structural unit (B1), the compound providing the structural unit (B2), and the compound providing the structural unit (B3).

[0041] The diamine component may contain a compound other than the compound providing the structural unit (B1), the compound providing the structural unit (B2), and the compound providing the structural unit (B3). Examples of such a compound include the above-mentioned aromatic diamines, alicyclic diamines, and aliphatic diamines, and their derivatives (such as diisocyanates). Compounds that provide the structural unit (B1) optionally contained in the diamine component and compounds other than the compound that provides the structural unit (B2) may be one kind or two or more kinds.

[0042] In the present invention, the charge 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 moles of the diamine component per 1 mole of the tetracarboxylic acid component.

[0043] Further, in the present invention, in the production of the polyimide resin, in addition to the above-mentioned tetracarboxylic acid component and diamine component, a terminal blocking agent may be used. Monamines or dicarboxylic acids are preferred as the terminal blocking agent. The charged amount of the introduced terminal blocking agent is preferably 0.0001 to 0.1 mole, particularly preferably 0.001 to 0.06 mole, per 1 mole 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. Among these, benzylamine and aniline can be preferably used. Dicarboxylic acids are preferred as the dicarboxylic acid terminal blocking agent, 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, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. are recommended. Among these, phthalic acid and phthalic anhydride can be preferably used.

[0044] There is no particular limitation on the method for reacting the above-mentioned tetracarboxylic acid component and diamine component to obtain the polyamic acid, and a known method can be used. As a specific reaction method, a method can be exemplified in which the tetracarboxylic acid component, the diamine component, and a solvent are charged into a reactor and stirred at 0 to 120°C, preferably 5 to 80°C, for 1 to 72 hours. When reacting at 80°C or lower, since the molecular weight of the resulting polyamic acid does not vary depending on the temperature history during polymerization and the progress of thermal imidization can also be suppressed, the polyamic acid can be stably produced.

[0045] The solvent used for producing the polyamic acid may be any solvent that can dissolve the resulting polyamic acid. For example, aprotic solvents, phenolic solvents, ether solvents, carbonate solvents, etc. can be mentioned.

[0046] Specific examples of aprotic solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone, tetramethylurea, etc., lactone solvents such as γ-butyrolactone, γ-valerolactone, etc., phosphorus-containing amide solvents such as hexamethylphosphoric triamide, hexamethylphosphine triamide, etc., sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, sulfolane, etc., ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, methylcyclohexanone, etc., ester solvents such as (2-methoxy-1-methylethyl) acetate, etc.

[0047] 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. Specific examples of carbonate solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, etc. Among the above reaction solvents, amide solvents or lactone solvents are preferred, amide solvents are more preferred, and N-methyl-2-pyrrolidone is even more preferred. The above reaction solvents may be used alone or in combination of two or more.

[0048] By the above method, a polyamic acid solution containing polyamic acid dissolved in a solvent is obtained. The concentration of the polyamic acid in the obtained polyamic acid solution is usually 1 to 50% by mass in the polyamic acid solution, preferably 3 to 35% by mass, and more preferably in the range of 10 to 30% by mass.

[0049] From the viewpoint of the mechanical strength of the obtained polyimide film, the number average molecular weight of the polyamic acid is preferably 5,000 to 300,000. The number average molecular weight of the polyamic acid can be determined, for example, from the standard polymethyl methacrylate (PMMA) conversion value by gel filtration chromatography measurement.

[0050] [Varnish] The varnish of the present invention is obtained by dissolving polyamic acid, which is a precursor of the polyimide resin of the present invention, in an organic solvent. That is, the varnish of the present invention contains polyamic acid, which is a precursor of the polyimide resin of the present invention, and an organic solvent, and the polyamic acid is dissolved in the organic solvent. The organic solvent may be any solvent in which polyamic acid can be dissolved and is not particularly limited. However, it is preferable to use the above-described compounds alone or in combination of two or more as the solvent used for the production of polyamic acid. The varnish of the present invention may be the above-described polyamic acid solution itself, or may be a solution obtained by further adding a diluting solvent to the polyamic acid solution.

[0051] From the viewpoint of efficiently promoting imidization, the varnish of the present invention preferably further contains an imidization catalyst and can contain a dehydration catalyst. The imidization catalyst is preferably a liquid at room temperature (25°C), and the boiling point of the imidization catalyst is preferably 120°C or higher, more preferably 170°C or higher, still more preferably 200°C or higher, and even more preferably 250°C or higher. There is no limit to the upper limit of the boiling point, but it is usually about 400°C.

[0052] Preferred imidization catalysts include imidazole compounds and tertiary amines. That is, the varnish of the present invention preferably contains at least one selected from the group consisting of imidazole compounds and tertiary amines, and more preferably contains an imidazole compound.

[0053] The imidazole compound is preferably at least one selected from the group consisting of imidazole, 1,2-imidazole, and 1-benzyl-2-methylimidazole, more preferably at least one selected from the group consisting of imidazole and 1,2-imidazole, and from the viewpoint of improving colorless transparency, 1,2-imidazole is even more preferred. The tertiary amine is preferably triethylenediamine (1,4-diazabicyclo[2.2.2]octane). By using the imidazole compound and tertiary amine shown here, perhaps because the molecular weight of the polyimide increases, the tensile strength and elongation can be improved. In addition, the linear thermal expansion coefficient and residual stress can be further reduced, and the colorless transparency when the polyimide is made into a film is also improved. The above imidization catalyst may be used alone or in combination of two or more.

[0054] The content of the imidization catalyst is preferably 100 ppm or more, more preferably 1000 ppm or more, still more preferably 5000 ppm or more, based on the polyamic acid contained in the varnish. Also, 50000 ppm or less is preferred.

[0055] Examples of the dehydration catalyst include acid anhydrides such as acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride; carbodiimide compounds such as dicyclohexylcarbodiimide, etc. These may be used alone or in combination of two or more.

[0056] Since the polyamic acid contained in the varnish of the present invention has solvent solubility, a high-concentration varnish stable at room temperature can be obtained. The varnish of the present invention preferably contains 3 to 40% by mass of polyamic acid, more preferably 5 to 30% by mass. The viscosity of the varnish is preferably 0.1 to 100 Pa·s, more preferably 0.1 to 20 Pa·s. The viscosity of the varnish is a value measured at 25°C using an E-type viscometer. Further, the varnish of the present invention may contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, ultraviolet stabilizers, surfactants, leveling agents, defoaming agents, fluorescent brighteners, crosslinking agents, polymerization initiators, and photosensitizers within a range that does not impair the required properties of the polyimide film. The method for producing the varnish of the present invention is not particularly limited, and known methods can be applied.

[0057] [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 low residual stress, excellent heat resistance, and a low linear thermal expansion coefficient. The suitable physical property values of the polyimide film of the present invention are as described above. The polyimide film of the present invention is preferably produced using a varnish obtained by dissolving the aforementioned polyamic acid in an organic solvent.

[0058] The method for manufacturing a polyimide film using the varnish of the present invention is not particularly limited, and known methods can be used. For example, after applying the varnish of the present invention on a smooth support such as a glass plate, a metal plate, or plastic, or forming it into a film shape, organic solvents such as reaction solvents and diluting solvents contained in the varnish are removed by heating to obtain a polyamic acid film. The polyamic acid in the polyamic acid film is imidized (dehydration ring closure) by heating, and then peeled off from the support to manufacture a polyimide film.

[0059] When drying the polyamic acid varnish to obtain a polyamic acid film, the heating temperature is preferably 50 to 150°C. When imidizing the polyamic acid by heating, the heating temperature is preferably 350 to 450°C, more preferably 380 to 420°C. The heating time is usually 1 minute to 6 hours, preferably 5 minutes to 2 hours, more preferably 15 minutes to 1 hour. By setting such temperature and time, the physical properties of the obtained polyimide film become good. Examples of the heating atmosphere include air gas, nitrogen gas, oxygen gas, hydrogen gas, nitrogen / hydrogen mixed gas, etc. In order to suppress the coloring of the obtained polyimide resin, nitrogen gas with an oxygen concentration of 100 ppm or less and nitrogen / hydrogen mixed gas containing 0.5% or less of hydrogen concentration are preferred. 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, and still more preferably 7 to 50 μm. When the thickness is within the above range, 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 varnish.

Examples

[0061] The present invention will be specifically described below with reference to examples. However, the present invention is not limited by these examples in any way.

[0062] <Film Physical Properties and Evaluation> Each physical property of the films obtained in the examples and comparative examples was measured by the methods shown below. (1) Film Thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation. (2) Total Light Transmittance, Yellowness Index (YI) The total light transmittance and YI were measured in accordance with JIS K7105:1981 using a color and haze simultaneous measuring instrument "COH400" manufactured by Nippon Denshoku Industries Co., Ltd. (3) Haze The measurement was carried out in accordance with JIS K7361-1 using a color and haze simultaneous measuring instrument "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd. (4) 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 3 mm × 20 mm, a load of 0.1 N, under a nitrogen gas flow (flow rate 200 mL / min), and a heating rate of 10 °C / min, the temperature was raised to a temperature sufficient to remove the residual stress to remove the residual stress, and then cooled to room temperature. Thereafter, the measurement of the specimen elongation was carried out under the same conditions as the treatment for removing the residual stress, and the inflection point of the elongation was determined as the glass transition temperature. (5) Coefficient of Thermal Expansion (CTE) Using a thermomechanical analyzer "TMA / SS6100" manufactured by Hitachi High-Tech Science Corporation, TMA measurement was carried out in tensile mode under the conditions of a sample size of 2 mm × 20 mm, a load of 0.1 N, and a heating rate of 10 °C / min, and the CTE from 100 to 350 °C was determined. (6) 1% Weight Loss Temperature (Td1%) The differential thermal and thermogravimetric simultaneous measurement device "TG / DTA6200" manufactured by Hitachi High-Tech Science Corporation was used. The sample was heated from 40 to 550 °C at a heating rate of 10 °C / min, and the temperature at which the weight decreased by 1% compared to the weight at 300 °C was defined as the 1% weight loss temperature. The higher the weight loss temperature, the better. (7) Elastic modulus and strength The elastic modulus and strength are the tensile elastic modulus and tensile strength conforming to JIS K7127, and were measured using the tensile tester "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd. (8) Elongation The elongation was carried out by a tensile test (measurement of elongation rate) conforming to JIS K 7127. Test pieces with a width of 10 mm and a thickness of 10 to 60 μm were used. (9) Residual stress Using the residual stress measurement device "FLX-2320" manufactured by KLA-Tencor, the "warpage amount" was measured in advance. On a 4-inch silicon wafer with a thickness of 525 μm ± 25 μm, polyamic acid varnish was applied using a spin coater and pre-baked. Then, using a hot air dryer, a heat curing treatment was performed at 350 °C for 30 minutes (heating rate: 5 °C / min) in a nitrogen atmosphere to produce a silicon wafer with a polyimide film having a film thickness of 6 to 20 μm after curing. The warpage amount of this wafer was measured using the aforementioned residual stress measurement device, and the residual stress generated between the silicon wafer and the polyimide film was evaluated.

[0063] The tetracarboxylic acid components and diamine components used in the examples and comparative examples, as well as their abbreviations, etc. are as follows. <Tetracarboxylic acid component> CpODA: Norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride (manufactured by JX Energy Corporation; compound represented by formula (a1)) <Diamine component> 6FODA: 2,2'-Bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (manufactured by ChinaTech (Tianjin) Chemical Co., Ltd., compound represented by formula (b1)) DABA: 4,4'-Diaminobenzanilide (compound represented by formula (b2))

[0064] In the examples and comparative examples, the abbreviations of solvents and the like are as follows. NMP: N-Methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Corporation)

[0065] Example 1 Into a 500 mL five-necked round-bottom flask equipped with a stainless-steel semi-circular stirring blade, a nitrogen inlet tube, a Dean-Stark with a cooling tube, a thermometer, and a glass end cap, 17.405 g (0.075 mol) of DABA, 8.406 g (0.025 mol) of 6FODA, and 94.921 g of NMP were charged. The mixture was stirred at a rotation speed of 200 rpm under a nitrogen atmosphere at a system temperature of 70 °C to obtain a solution. To this solution, 38.438 g (0.100 mol) of CpODA and 23.730 g of NMP were charged all at once, heated to 100 °C with a mantle heater, and held for 30 minutes. After confirming dissolution, it was cooled to 25 °C and stirred at 25 °C for 7 hours. Thereafter, 243.388 g of NMP was added and homogenized to obtain a polyamic acid varnish with a solid content concentration of 15% by mass. Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes under a nitrogen atmosphere (heating rate: 5 °C / min) to evaporate the solvent and further thermally imidize to obtain a polyimide film. The results are shown in Table 1.

[0066] Example 2 A polyamic acid varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 1, except that the amount of DABA was changed from 17.405 g (0.075 mol) to 14.773 g (0.065 mol) and the amount of 6FODA was changed from 8.406 g (0.025 mol) to 11.768 g (0.035 mol). Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes under a nitrogen atmosphere (heating rate: 5 °C / min) to evaporate the solvent and further cause thermal imidization to obtain a polyimide film. The results are shown in Table 1.

[0067] Example 3 A polyamic acid varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 1, except that the amount of DABA was changed from 17.405 g (0.075 mol) to 11.364 g (0.050 mol), and the amount of 6FODA was changed from 8.406 g (0.025 mol) to 16.812 g (0.050 mol). Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 420 °C for 30 minutes under a nitrogen atmosphere (heating rate: 5 °C / min) to evaporate the solvent and further cause thermal imidization to obtain a polyimide film. The results are shown in Table 1.

[0068] Comparative Example 1 A polyamic acid varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 1, except that the amount of DABA was changed from 17.405 g (0.075 mol) to 22.727 g (0.100 mol), and 6FODA was not used. Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 420 °C for 30 minutes under a nitrogen atmosphere (heating rate: 5 °C / min) to evaporate the solvent and further cause thermal imidization to obtain a polyimide film. The obtained film was brittle, and it was difficult to maintain the film shape when peeled from the glass. Therefore, the glass transition temperature (Tg), coefficient of linear thermal expansion (CTE), elastic modulus, strength, elongation, and residual stress could not be measured. The results are shown in Table 1.

[0069] Comparative Example 2 The amount of 6FODA was changed from 8.406 g (0.025 mol) to 33.624 g (0.100 mol), and a polyamic acid varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 1 except that DABA was not used. Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes (heating rate: 5 °C / min) under a nitrogen atmosphere to evaporate the solvent and further perform thermal imidization to obtain a polyimide film. The results are shown in Table 1.

[0070]

Table 1

[0071] Example 4 Into a 500 mL five-necked round-bottom flask equipped with a stainless-steel semi-circular stirring blade, a nitrogen inlet tube, a Dean-Stark with a cooling tube, a thermometer, and a glass end cap, 18.182 g (0.080 mol) of DABA, 6.725 g (0.020 mol) of 6FODA, and 94.112 g of NMP were charged, and the mixture was stirred at a rotation speed of 200 rpm at a system temperature of 70 °C under a nitrogen atmosphere to obtain a solution. To this solution, 38.438 g (0.100 mol) of CpODA and 23.528 g of NMP were charged all at once, the temperature was raised to 100 °C with a mantle heater and held for 30 minutes. After confirming dissolution, it was cooled to 25 °C and stirred at 25 °C for 7 hours. Thereafter, 241.312 g of NMP was added for homogenization, and then 0.633 g (0.00930 mol: 1% by mass based on the total amount of polyamic acid (tetracarboxylic acid component and diamine component)) of imidazole was added to obtain a polyamic acid varnish with a solid content concentration of 15% by mass. Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes (heating rate: 5 °C / min) under a nitrogen atmosphere to evaporate the solvent and further perform thermal imidization to obtain a polyimide film. The results are shown in Table 2.

[0072] Example 5 A polyamic acid varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 4, except that the amount of DABA was changed from 18.182 g (0.080 mol) to 15.909 g (0.070 mol), and the amount of 6FODA was changed from 6.725 g (0.020 mol) to 10.087 g (0.030 mol). Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 420 °C for 30 minutes (heating rate: 5 °C / min) under a nitrogen atmosphere to evaporate the solvent and further perform thermal imidization to obtain a polyimide film. The results are shown in Table 2.

[0073] Example 6 A polyamic acid varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 4, except that the amount of DABA was changed from 18.182 g (0.080 mol) to 13.636 g (0.060 mol), and the amount of 6FODA was changed from 6.725 g (0.020 mol) to 13.450 g (0.040 mol). Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes (heating rate: 5 °C / min) under a nitrogen atmosphere to evaporate the solvent and further perform thermal imidization to obtain a polyimide film. The results are shown in Table 2.

[0074] Example 7 A polyamic acid varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 5, except that 0.633 g (0.00930 mol: 1% by mass based on the total amount of the polyamic acid (tetracarboxylic acid component and diamine component)) of imidazole was changed to 0.633 g (0.00659 mol: 1% by mass based on the total amount of the polyamic acid (tetracarboxylic acid component and diamine component)) of 1,2 - imidazole. Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes (heating rate: 5 °C / min) under a nitrogen atmosphere to evaporate the solvent and further cause thermal imidization to obtain a polyimide film. The results are shown in Table 2.

[0075] Example 8 A polyamic acid varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 6, except that 0.655 g (0.00962 mol: 1% by mass based on the total amount of the tetracarboxylic acid component and the diamine component of the polyamic acid) of imidazole was changed to 0.655 g (0.00682 mol: 1% by mass based on the total amount of the tetracarboxylic acid component and the diamine component of the polyamic acid) of 1,2-imidazole. Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes (heating rate: 5 °C / min) under a nitrogen atmosphere to evaporate the solvent and further cause thermal imidization to obtain a polyimide film. The results are shown in Table 2.

[0076] Example 9 A polyamic acid varnish with a solid content concentration of 15% by mass was obtained in the same manner as in Example 6, except that 0.655 g (0.00962 mol: 1% by mass based on the total amount of the tetracarboxylic acid component and the diamine component of the polyamic acid) of imidazole was changed to 0.655 g (0.00380 mol: 1% by mass based on the total amount of the tetracarboxylic acid component and the diamine component of the polyamic acid) of 1-benzyl-2-methylimidazole. Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes (heating rate: 5 °C / min) under a nitrogen atmosphere to evaporate the solvent and further cause thermal imidization to obtain a polyimide film. The results are shown in Table 2.

[0077] Example 10 The amount of DABA was changed from 13.636 g (0.060 mol) to 11.364 g (0.050 mol), and the amount of 6FODA was changed from 13.450 g (0.040 mol) to 16.812 g (0.050 mol). Otherwise, in the same manner as in Example 9, a polyamic acid varnish with a solid content concentration of 15% by mass was obtained. Subsequently, the obtained polyamic acid varnish was applied onto a glass plate by spin coating, held on a hot plate at 80 °C for 20 minutes, and then heated in a hot air dryer at 400 °C for 30 minutes (heating rate 5 °C / min) under a nitrogen atmosphere to evaporate the solvent and further thermally imidize to obtain a polyimide film. The results are shown in Table 2.

[0078]

Table 2

[0079] As shown in Tables 1 and 2, it can be seen that the polyimide films of the examples have a high glass transition temperature, excellent heat resistance, low residual stress, and low linear thermal expansion coefficient.

Industrial Applicability

[0080] The polyimide film of the present invention is suitably used as a film for various members such as color filters, flexible displays, semiconductor components, and optical members. The polyimide film 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 (A1) derived from a compound represented by the following formula (a1), and the structural unit B includes a structural unit (B1) derived from a compound represented by the following formula (b1) and a structural unit (B2) derived from a compound represented by the following formula (b2). 【Chemical 1】

2. The polyimide resin according to claim 1, wherein the structural unit B further includes at least one structural unit (B3) selected from the group consisting of a structural unit (B31) derived from a compound represented by the following formula (b31), a structural unit (B32) derived from a compound represented by the following formula (b32), and a structural unit (B33) derived from a compound represented by the following formula (b33). [Chemical 2]

3. A varnish obtained by dissolving a polyamic acid, which is a precursor of the polyimide resin according to claim 1 or 2, in an organic solvent.

4. The varnish according to claim 3, further comprising at least one selected from the group consisting of an imidazole compound and a tertiary amine.

5. The varnish according to claim 4, wherein the imidazole compound is at least one selected from the group consisting of imidazole, 1,2-imidazole, and 1-benzyl-2-methylimidazole.

6. The varnish according to claim 4 or 5, wherein the tertiary amine is triethylenediamine.

7. A polyimide film obtained by applying the varnish according to any one of claims 3 to 6 onto a support and heating it.

8. A method for producing a polyimide film, comprising applying the varnish according to any one of claims 3 to 6 onto a support and heating it.

9. A polyimide film comprising the polyimide resin according to claim 1 or 2.

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