Polyamic acid, polyamic acid solution, polyimide, polyimide film, laminate, electronic device, and method for producing polyimide film

Abstract

This poly(amic acid) has a tetravalent organic group represented by general formula (1) as a tetracarboxylic acid dianhydride residue and has one or more residues selected from the group consisting of a p-phenylenediamine residue and a (2-phenyl-4-aminophenyl)-4-aminobenzoate residue as a diamine residue. The content of the tetravalent organic group represented by general formula (1) is 90-100 mol% relative to the total amount of tetracarboxylic acid dianhydride residues. In general formula (1), R1 and R2 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1-12 carbon atoms, an alkenyl group having 2-12 carbon atoms, an alkoxy group having 1-12 carbon atoms, an aryl group having 6-14 carbon atoms, a hydroxyl group, a nitrile group, a nitro group, a carboxyl group, or an amido group.

Description

[Technical Field]

[0001] The present invention relates to polyamic acid, a polyamic acid solution, a polyimide, a polyimide film, a laminate, an electronic device, and a method for producing a polyimide film.The present invention also relates to polyimide-based electronic device materials, thin film transistor (TFT) substrates, flexible display substrates, color filters, printed materials, optical materials, image display devices (more specifically, liquid crystal display devices, organic electroluminescence (EL) devices, electronic paper, etc.), 3D displays, solar cells, touch panels, transparent conductive film substrates, and alternative materials for components currently using glass. [Background technology]

[0002] Rapid advances in electronic devices, such as displays (LCDs, OLEDs, electronic paper, etc.), solar cells, and touch panels, have led to devices becoming thinner, lighter, and more flexible. In these devices, polyimide is being used as the substrate material instead of glass.

[0003] These devices require various electronic elements, such as thin-film transistors and transparent electrodes, to be formed on the substrate, and high-temperature processes are required to form these electronic elements. Polyimide has sufficient heat resistance to be applicable to high-temperature processes, and its linear expansion coefficient is similar to that of glass substrates and electronic elements, making it less susceptible to internal stress and suitable for use as a substrate material for flexible displays and other devices.

[0004] Aromatic polyimides are generally colored yellowish-brown due to intramolecular conjugation and the formation of charge-transfer (CT) complexes, but in top-emission organic electroluminescence (OLED) and other displays, where light is extracted from the opposite side of the substrate, transparency is not required for the substrate, and conventional aromatic polyimides have been used. However, in cases where light emitted from the display element is emitted through the substrate, such as in transparent displays, bottom-emission organic electroluminescence (OLED) and LCD displays, or when sensors or camera modules are placed on the back of the substrate to make smartphones and other devices full-screen (notchless), the substrate is now required to have high optical properties (more specifically, low colorability, etc.).

[0005] Furthermore, when a polyimide substrate is used in an image display device, if the retardation (Rth) in the thickness direction of the polyimide substrate is high, the display performance of the image display device tends to deteriorate.

[0006] In light of this, there is a demand for materials that have a linear expansion coefficient equivalent to that of existing aromatic polyimides, but which have reduced coloration and can achieve a low Rth.

[0007] Polyimides made using monomers with rigid structures are known as plastic materials with a small linear expansion coefficient (low thermal expansion) and high transparency (see, for example, Patent Document 1). Patent Document 2 describes that polyimide films with excellent transparency and heat resistance can be obtained by using diamines with a fluorene structure. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-046054 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-179969 Summary of the Invention [Problem to be solved by the invention]

[0009] However, it is difficult to obtain a polyimide that can reduce Rth and has low colorability and low thermal expansion properties by using only the techniques described in Patent Documents 1 and 2.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a polyimide that can reduce Rth and has low colorability and low thermal expansion, and a polyamic acid as its precursor. Another aim is to provide a product or member that is produced using the polyimide or polyamic acid and that is required to have low Rth, low colorability, and low thermal expansion. [Means for solving the problem]

[0011] The polyamic acid according to the present invention has, as a tetracarboxylic dianhydride residue, a tetravalent organic group represented by the following general formula (1), and, as a diamine residue, one or more selected from the group consisting of p-phenylenediamine residues and (2-phenyl-4-aminophenyl)-4-aminobenzoate residues. The content of the tetravalent organic group represented by the following general formula (1) is 90 mol % or more and 100 mol % or less of all the tetracarboxylic dianhydride residues.

[0012] [ka]

[0013] In the general formula (1), R 1 and R 2 each independently represents a hydrogen atom, a halogen atom, an alkyl group having from 1 to 12 carbon atoms, an alkenyl group having from 2 to 12 carbon atoms, an alkoxy group having from 1 to 12 carbon atoms, an aryl group having from 6 to 14 carbon atoms, a hydroxy group, a nitrile group, a nitro group, a carboxy group, or an amide group.

[0014] In one embodiment of the polyamic acid according to the present invention, in the general formula (1), R 1 and R 2 Each of these represents a hydrogen atom.

[0015] A polyamic acid according to one embodiment of the present invention further has, as a diamine residue, one or more selected from the group consisting of a 4,4'-diaminobenzanilide residue, a 2,2'-bis(trifluoromethyl)benzidine residue, and a 9,9-bis(4-aminophenyl)fluorene residue.

[0016] The polyamic acid solution according to the present invention contains the polyamic acid according to the present invention and an organic solvent.

[0017] The polyimide according to the present invention is an imidized product of the polyamic acid according to the present invention.

[0018] The polyimide according to the present invention preferably has a glass transition temperature of 350° C. or higher.

[0019] The polyimide film according to the present invention contains the polyimide according to the present invention.

[0020] The laminate according to the present invention has a support and the polyimide film according to the present invention.

[0021] An electronic device according to the present invention comprises the polyimide film according to the present invention and an electronic element disposed on the polyimide film.

[0022] The method for producing a polyimide film according to the present invention comprises applying the polyamic acid solution according to the present invention onto a support to form a coating film containing the polyamic acid, and then heating the coating film to imidize the polyamic acid.

[0023] In one embodiment of the method for producing a polyimide film according to the present invention, the maximum temperature when the coating film is heated is 380°C or higher and 500°C or lower.

[0024] In one embodiment of the method for producing a polyimide film according to the present invention, the heating time at the maximum temperature is 5 minutes or more and 60 minutes or less.

[0025] In one embodiment of the method for producing a polyimide film according to the present invention, the polyimide film obtained by heating the coating film is peeled off from the support.

[0026] In one embodiment of the method for producing a polyimide film according to the present invention, the polyimide film is peeled off from the support by laser irradiation. [Effects of the Invention]

[0027] The polyimide produced using the polyamic acid according to the present invention can reduce Rth and is excellent in low colorability and low thermal expansion, and is therefore suitable as a material for electronic devices that require low Rth, low colorability, and low thermal expansion. DETAILED DESCRIPTION OF THE INVENTION

[0028] Preferred embodiments of the present invention will be described in detail below, but the present invention is not limited to these.

[0029] First, the terms used in this specification will be explained. A "structural unit" refers to a repeating unit that constitutes a polymer. A "polyamic acid" is a polymer containing a structural unit represented by the following general formula (2) (hereinafter, sometimes referred to as "structural unit (2)").

[0030] [ka]

[0031] In general formula (2), A 1 represents a tetracarboxylic dianhydride residue (a tetravalent organic group derived from a tetracarboxylic dianhydride), and A 2 represents a diamine residue (a divalent organic group derived from a diamine).

[0032] The content of the structural unit (2) relative to all structural units constituting the polyamic acid is, for example, 50 mol% or more and 100 mol% or less, preferably 60 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, and may be 100 mol%.

[0033] The "1% weight loss temperature" is the measurement temperature at which the weight of polyimide at a measurement temperature of 150°C is reduced by 1% by weight relative to the reference weight (100% by weight).

[0034] Unless otherwise specified, the "linear expansion coefficient" refers to the linear expansion coefficient when the temperature is lowered from 350°C to 100°C (linear expansion coefficient when cooling).

[0035] An "alkyl group having from 1 to 12 carbon atoms" is linear or branched and unsubstituted. Examples of alkyl groups having from 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, t-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, and n-dodecyl groups.

[0036] The "alkenyl group having from 2 to 12 carbon atoms" is linear or branched and unsubstituted. Examples of the alkenyl group having from 2 to 12 carbon atoms include vinyl, 2-propenyl, 3-butenyl, 2-butenyl, 4-pentenyl, 3-pentenyl, 2-hexenyl, 3-hexenyl, 5-hexenyl, 2-heptenyl, 3-heptenyl, 4-heptenyl, 3-octenyl, 3-nonenyl, 4-decenyl, 3-undecenyl, and 4-dodecenyl.

[0037] An "alkoxy group having from 1 to 12 carbon atoms" is linear or branched and unsubstituted. Examples of alkoxy groups having from 1 to 12 carbon atoms include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, s-butoxy, t-butoxy, n-pentyloxy, isopentyloxy, neopentyloxy, n-hexyloxy, n-heptyloxy, n-octyloxy, n-nonyloxy, n-decyloxy, n-undecyloxy, and n-dodecyloxy.

[0038] An "aryl group having from 6 to 14 carbon atoms" is unsubstituted. Examples of aryl groups having from 6 to 14 carbon atoms include unsubstituted aromatic monocyclic hydrocarbon groups having from 6 to 14 carbon atoms, unsubstituted aromatic fused bicyclic hydrocarbon groups having from 6 to 14 carbon atoms, and unsubstituted aromatic fused tricyclic hydrocarbon groups having from 6 to 14 carbon atoms. More specific examples of aryl groups having from 6 to 14 carbon atoms include phenyl, naphthyl, anthryl, and phenanthryl groups.

[0039] Hereinafter, the compound name may be followed by "system" to refer to the compound and its derivatives collectively. When the compound name is followed by "system" to refer to the name of a polymer, it means that the repeating unit of the polymer is derived from the compound or its derivative. Furthermore, tetracarboxylic dianhydrides may be referred to as "acid dianhydrides."

[0040] The polyamic acid according to this embodiment has, as a tetracarboxylic dianhydride residue, a tetravalent organic group represented by the following general formula (1), and, as a diamine residue, one or more selected from the group consisting of p-phenylenediamine residues and (2-phenyl-4-aminophenyl)-4-aminobenzoate residues. The content of the tetravalent organic group represented by the following general formula (1) is preferably 90 mol % to 100 mol % of all the tetracarboxylic dianhydride residues constituting the polyamic acid according to this embodiment.

[0041] [ka]

[0042] In general formula (1), R 1 and R 2 each independently represents a hydrogen atom, a halogen atom, an alkyl group having from 1 to 12 carbon atoms, an alkenyl group having from 2 to 12 carbon atoms, an alkoxy group having from 1 to 12 carbon atoms, an aryl group having from 6 to 14 carbon atoms, a hydroxy group, a nitrile group, a nitro group, a carboxy group, or an amide group. 1 and R 2 are each independently preferably a hydrogen atom, a methyl group or an ethyl group, and R 1 and R 2 However, it is particularly preferable that both represent a hydrogen atom. Therefore, as the tetravalent organic group represented by general formula (1), a BPAF residue, which is a partial structure derived from 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (hereinafter, sometimes referred to as "BPAF"), is particularly preferable. In other words, the polyamic acid according to this embodiment is 1 It is particularly preferred that R in the general formula (1) has a BPAF residue. 1 and R 2 However, in this explanation, they will all be considered to represent hydrogen atoms.

[0043] BPAF has a bulky fluorene structure, which can suppress the formation of charge-transfer (CT) complexes. Therefore, BPAF is suitable as a raw material (monomer) for polyimides with reduced coloration (low colorability). Furthermore, in polyimides using BPAF as a raw material (monomer), the fluorene ring derived from BPAF is twisted relative to the main chain, making birefringence less likely to occur. Therefore, BPAF is suitable as a raw material (monomer) for polyimides with reduced Rth.

[0044] When synthesizing the polyamic acid according to this embodiment, an acid dianhydride other than BPAF may be used as a monomer as long as the performance is not impaired. Examples of acid dianhydrides other than BPAF include pyromellitic dianhydride (hereinafter sometimes referred to as "PMDA"), 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter sometimes referred to as "BPDA"), p-phenylenebis(trimellitate anhydride), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 4,4'-oxydiphthalic acid dianhydride. Examples of the dicarboxylic acid dianhydride include 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 2'-oxodispiro[bicyclo[2.2.1]heptane-2,1'-cyclopentane-3',2''-bicyclo[2.2.1]heptane]-5,6:5'',6''-tetracarboxylic dianhydride, and derivatives thereof, and these may be used alone or in combination of two or more.

[0045] In order to obtain a polyimide that can further reduce coloration and Rth, the content of BPAF residues is preferably 92 mol % or more, more preferably 95 mol % or more, even more preferably 97 mol % or more, and particularly preferably 100 mol % (having only BPAF residues as acid dianhydride residues) relative to all tetracarboxylic dianhydride residues constituting the polyamic acid.

[0046] When an acid dianhydride other than BPAF is used as a monomer, from the viewpoint of improving heat resistance and mechanical strength, the acid dianhydride other than BPAF is preferably one or more selected from the group consisting of PMDA and BPDA, and more preferably PMDA. In other words, when the polyamic acid according to this embodiment has an acid dianhydride residue other than BPAF residue as the acid dianhydride residue, the acid dianhydride residue other than BPAF residue is preferably one or more selected from the group consisting of PMDA residue and BPDA residue, and more preferably PMDA residue.

[0047] When the polyamic acid according to the present embodiment has one or more residues selected from the group consisting of PMDA residues and BPDA residues, from the viewpoint of improving heat resistance and mechanical strength while reducing coloration, the total content of PMDA residues and BPDA residues relative to all acid dianhydride residues constituting the polyamic acid is preferably 1 mol % or more and 10 mol % or less, and more preferably 3 mol % or more and 7 mol % or less.

[0048] When the polyamic acid according to the present embodiment has one or more residues selected from the group consisting of PMDA residues and BPDA residues, from the viewpoint of improving heat resistance and mechanical strength while reducing coloration and Rth, the total content of BPAF residues, PMDA residues, and BPDA residues relative to all acid dianhydride residues constituting the polyamic acid is preferably 91 mol% or more, more preferably 93 mol% or more, even more preferably 95 mol% or more, even more preferably 97 mol% or more, and may even be 100 mol%.

[0049] The polyamic acid according to this embodiment has, as a diamine residue, one or more selected from the group consisting of a PDA residue, which is a partial structure derived from p-phenylenediamine (hereinafter sometimes referred to as "PDA"), and a PHBAAB residue, which is a partial structure derived from (2-phenyl-4-aminophenyl)-4-aminobenzoate (hereinafter sometimes referred to as "PHBAAB"). That is, the polyamic acid according to this embodiment has, as a diamine residue, one or more selected from the group consisting of A in general formula (2) 2As the functional group, the polyimide has one or more groups selected from the group consisting of PDA residues and PHBAAB residues. Both PDA and PHBAAB have a rigid structure, making them suitable as raw materials (monomers) for low thermal expansion polyimides.

[0050] The PDA residue is a divalent organic group represented by the following chemical formula (3): The PHBAAB residue is a divalent organic group represented by the following chemical formula (4):

[0051] [ka]

[0052] When synthesizing the polyamic acid according to this embodiment, diamines other than PDA and PHBAAB may be used as monomers as long as the performance is not impaired. Examples of diamines other than PDA and PHBAAB include 4,4'-diaminobenzanilide (hereinafter sometimes referred to as "DABA"), 2,2'-bis(trifluoromethyl)benzidine (hereinafter sometimes referred to as "TFMB"), 9,9-bis(4-aminophenyl)fluorene (hereinafter sometimes referred to as "BAFL"), 4-aminophenyl-4-aminobenzoate, 1,4-diaminocyclohexane, m-phenylenediamine, 4,4'-oxydianiline, 3,4'-oxydianiline, 2,2'-bis(trifluoromethyl)-4,4'- Examples include diaminodiphenyl ether, N,N'-bis(4-aminophenyl)terephthalamide, 4,4'-diaminodiphenyl sulfone, m-tolidine, o-tolidine, 4,4'-bis(4-aminophenoxy)biphenyl, 2-(4-aminophenyl)-6-aminobenzoxazole, 3,5-diaminobenzoic acid, 4,4'-diamino-3,3'-dihydroxybiphenyl, 4,4'-methylenebis(cyclohexanamine), 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and derivatives thereof, and these may be used alone or in combination of two or more.

[0053] In order to further reduce the linear expansion coefficient, the total content of PDA residues and PHBAAB residues is preferably 0.1 mol% or more, and may be 1.0 mol% or more, 10.0 mol% or more, 30.0 mol% or more, 50.0 mol% or more, 70.0 mol% or more, 90.0 mol% or more, 99.0 mol% or more, 99.9 mol% or more, or even 100.0 mol%. The polyamic acid according to this embodiment may have only PDA residues, only PHBAAB residues, only PDA residues and PHBAAB residues, or at least one of PDA residues and PHBAAB residues and diamine residues other than PDA residues and PHBAAB residues.

[0054] When a diamine other than PDA and PHBAAB is used as a monomer, in order to further reduce coloration and Rth while further decreasing the linear expansion coefficient, the diamine other than PDA and PHBAAB is preferably one or more selected from the group consisting of DABA, TFMB, and BAFL. In other words, when the polyamic acid according to this embodiment has diamine residues other than PDA residues and PHBAAB residues as diamine residues, the diamine residues other than PDA residues and PHBAAB residues are preferably one or more selected from the group consisting of DABA residues, TFMB residues, and BAFL residues.

[0055] In order to further reduce the linear expansion coefficient, the polyamic acid according to the present embodiment preferably has a DABA residue as a diamine residue. When the polyamic acid according to the present embodiment has a DABA residue, in order to further reduce the linear expansion coefficient, the content of the DABA residue is preferably 0.1 mol% or more, and may be 1.0 mol% or more, 10.0 mol% or more, 30.0 mol% or more, 50.0 mol% or more, 70.0 mol% or more, 90.0 mol% or more, or 99.0 mol% or more, or may be 99.0 mol% or more but not more than 99.9 mol%.

[0056] To further reduce coloration, the polyamic acid according to this embodiment preferably contains TFMB residues as diamine residues. When the polyamic acid according to this embodiment contains TFMB residues, to further reduce coloration, the content of TFMB residues is preferably 0.1 mol% or more, and may be 1.0 mol% or more, 10.0 mol% or more, 30.0 mol% or more, 50.0 mol% or more, 70.0 mol% or more, 90.0 mol% or more, or 99.0 mol% or more, or may be 99.0 mol% or more but not more than 99.9 mol%.

[0057] In order to further reduce Rth, the polyamic acid according to this embodiment preferably contains a BAFL residue as a diamine residue. When the polyamic acid according to this embodiment contains a BAFL residue, in order to further reduce Rth, the content of the BAFL residue is preferably 0.1 mol% or more, or may be 1.0 mol% or more, 10.0 mol% or more, or 30.0 mol% or more, or may be 30.0 mol% or more and 50.0 mol% or less, based on the total diamine residues constituting the polyamic acid.

[0058] When the polyamic acid according to the present embodiment has one or more residues selected from the group consisting of DABA residues, TFMB residues, and BAFL residues, in order to further reduce the coefficient of linear expansion while further reducing coloration and Rth, the total content of PDA residues, PHBAAB residues, DABA residues, TFMB residues, and BAFL residues relative to all diamine residues constituting the polyamic acid is preferably 90.0 mol% or more, more preferably 93.0 mol% or more, even more preferably 95.0 mol% or more, even more preferably 97.0 mol% or more, and may even be 100.0 mol%.

[0059] To obtain a polyimide that can further reduce the linear expansion coefficient while further reducing coloration and Rth, the polyamic acid according to this embodiment preferably satisfies the following condition 1, more preferably satisfies the following conditions 1 and 2, and even more preferably satisfies the following conditions 1, 2, and 3. To particularly reduce the linear expansion coefficient, it is preferable to satisfy the following conditions 1 and 4. To particularly reduce coloration, it is preferable to satisfy the following conditions 1 and 5. To particularly reduce Rth, it is preferable to satisfy the following conditions 1 and 6. Condition 1: The polyamic acid has only BPAF residues as acid dianhydride residues. Condition 2: The polyamic acid further has, as a diamine residue, one or more selected from the group consisting of a DABA residue, a TFMB residue, and a BAFL residue. Condition 3: The total content of PDA residues, PHBAAB residues, DABA residues, TFMB residues, and BAFL residues relative to all diamine residues constituting the polyamic acid is 100.0 mol %. Condition 4: The polyamic acid has only PDA residues and DABA residues as diamine residues. Condition 5: The polyamic acid has, as diamine residues, only PDA residues and TFMB residues, or only PHBAAB residues and TFMB residues. Condition 6: The polyamic acid has, as diamine residues, only PDA residues and BAFL residues, or only PDA residues and PHBAAB residues.

[0060] In order to prevent a decrease in transparency due to remaining unreacted monomers during polyimide formation, the molar ratio (total amount of tetracarboxylic dianhydride residues divided by the total amount of diamine residues) is preferably 0.900 or more and less than 1.100, and more preferably 0.950 or more and 1.080 or less. By adjusting the molar ratio within the above range, a polyimide with excellent transparency can be obtained.

[0061] The polyamic acid of the present invention can be synthesized by a known, general method, for example, by reacting a diamine with a tetracarboxylic dianhydride in an organic solvent. The monomer components used in the synthesis of the polyamic acid may include components other than the diamine and tetracarboxylic dianhydride. For example, a monofunctional amine or a monofunctional acid anhydride may be used for the purpose of adjusting the molecular weight. A specific example of a method for synthesizing the polyamic acid will be described below. First, a diamine is dissolved or dispersed in a slurry form in an organic solvent in an inert gas atmosphere such as argon or nitrogen to prepare a diamine solution. Then, the tetracarboxylic dianhydride is added to the diamine solution after being dissolved or dispersed in a slurry form in the organic solvent, or in a solid state.

[0062] When synthesizing polyamic acid using diamines and tetracarboxylic dianhydrides, the desired polyamic acid (a polymer of diamines and tetracarboxylic dianhydrides) can be obtained by adjusting the molar amount of diamine (or, if multiple diamines are used, the molar amount of each diamine) and the molar amount of tetracarboxylic dianhydride (or, if multiple tetracarboxylic dianhydrides are used, the molar amount of each tetracarboxylic dianhydride). The molar fraction of each residue in the polyamic acid corresponds, for example, to the molar fraction of each monomer (diamine and tetracarboxylic dianhydride) used in the synthesis of the polyamic acid. Furthermore, blending two polyamic acids can also produce polyamic acids containing multiple tetracarboxylic dianhydride residues and multiple diamine residues. The temperature conditions for the reaction between diamines and tetracarboxylic dianhydrides, i.e., the polyamic acid synthesis reaction, are not particularly limited, but are, for example, in the range of 20°C to 150°C. The reaction time for the polyamic acid synthesis reaction is, for example, in the range of 10 minutes to 30 hours.

[0063] The organic solvent used in the synthesis of polyamic acid is preferably a solvent capable of dissolving the tetracarboxylic dianhydride and diamine used, and more preferably a solvent capable of dissolving the polyamic acid produced. Examples of organic solvents used in the synthesis of polyamic acid include urea-based solvents such as tetramethylurea and N,N-dimethylethylurea; sulfoxide-based solvents such as dimethyl sulfoxide; sulfone-based solvents such as diphenyl sulfone and tetramethyl sulfone; amide-based solvents such as N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), and hexamethylphosphoric triamide; ester-based solvents such as γ-butyrolactone; alkyl halide solvents such as chloroform and methylene chloride; aromatic hydrocarbon solvents such as benzene and toluene; phenol-based solvents such as phenol and cresol; ketone-based solvents such as cyclopentanone; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, and p-cresol methyl ether. These solvents are typically used alone, but two or more may be used in combination as needed. In order to enhance the solubility and reactivity of polyamic acid, the organic solvent used in the synthesis reaction of polyamic acid is preferably one or more solvents selected from the group consisting of amide solvents, ketone solvents, ester solvents, and ether solvents, and more preferably an amide solvent (more specifically, DMF, DMAC, NMP, etc.). The synthesis reaction of polyamic acid is preferably carried out under an inert gas atmosphere such as argon or nitrogen.

[0064] The weight-average molecular weight of the polyamic acid according to the present invention varies depending on its intended use, but is preferably in the range of 10,000 to 1,000,000, more preferably 20,000 to 500,000, and even more preferably 30,000 to 200,000. A weight-average molecular weight of 10,000 or more facilitates the formation of coating films or polyimide films from the polyamic acid or polyimides obtained using the polyamic acid. On the other hand, a weight-average molecular weight of 1,000,000 or less exhibits sufficient solubility in solvents, allowing the formation of coating films or polyimide films with smooth surfaces and uniform thicknesses using a polyamic acid solution, as described below. The weight-average molecular weight used here refers to a polyethylene oxide equivalent value measured using gel permeation chromatography (GPC).

[0065] The polyamic acid solution according to this embodiment contains the polyamic acid according to this embodiment and an organic solvent. Examples of the organic solvent contained in the polyamic acid solution include those listed above as examples of organic solvents that can be used in the polyamic acid synthesis reaction. Preferred are one or more solvents selected from the group consisting of amide solvents, ketone solvents, ester solvents, and ether solvents, with amide solvents (more specifically, DMF, DMAC, NMP, etc.) being more preferred. When polyamic acid is obtained by the above-described method, the reaction solution (post-reaction solution) itself may serve as the polyamic acid solution according to this embodiment. Alternatively, the polyamic acid solution according to this embodiment may be prepared by dissolving the solid polyamic acid obtained by removing the solvent from the reaction solution in an organic solvent. The content of polyamic acid in the polyamic acid solution according to this embodiment is not particularly limited, but is, for example, 1% by weight to 80% by weight based on the total weight of the polyamic acid solution.

[0066] The polyimide according to this embodiment is an imidized product of the polyamic acid according to this embodiment. The polyimide according to this embodiment can be obtained by known methods, and its manufacturing method is not particularly limited. An example of a method for obtaining the polyimide according to this embodiment by imidizing the polyamic acid is described below. Imidization is performed by dehydration ring-closing the polyamic acid. This dehydration ring-closing can be performed by an azeotropic method using an azeotropic solvent, a thermal method, or a chemical method. Furthermore, the imidization ratio of the polyamic acid to the polyimide can be any ratio between 1% and 100%. In other words, a partially imidized polyamic acid may be synthesized. In particular, when imidization is performed by heating, the ring-closing reaction from the polyamic acid to the polyimide and the hydrolysis of the polyamic acid proceed simultaneously, which may result in a polyimide with a lower molecular weight than the polyamic acid itself. Therefore, from the perspective of improving mechanical properties, it is preferable to partially imidize the polyamic acid in the polyamic acid solution before forming the polyimide film described below. In this specification, partially imidized polyamic acid may also be referred to as "polyamic acid."

[0067] The dehydration ring closure of the polyamic acid can be carried out by heating the polyamic acid. The method for heating the polyamic acid is not particularly limited. For example, the polyamic acid solution according to the present embodiment described above can be applied to a support such as a glass substrate, a metal plate, or a PET (polyethylene terephthalate) film, followed by heat treatment of the polyamic acid at a temperature ranging from 40°C to 500°C. This method can produce a laminate according to the present embodiment, which includes a support and a polyimide film (specifically, a polyimide film containing an imidized product of the polyamic acid according to the present embodiment) disposed on the support. Alternatively, the dehydration ring closure of the polyamic acid can be carried out by placing the polyamic acid solution directly in a container that has been subjected to a release treatment, such as coating with a fluorine-based resin, and then heating and drying the polyamic acid solution under reduced pressure. Polyimides can be obtained by dehydration ring closure of the polyamic acid using these methods. The heating time for each of the above treatments varies depending on the treatment amount and heating temperature of the polyamic acid solution undergoing dehydration ring closure, but is generally preferably in the range of 1 minute to 300 minutes, more preferably 5 minutes to 60 minutes, from the time the treatment temperature reaches the maximum temperature. To shorten the heating time or to enhance properties, an imidizing agent and / or a dehydration catalyst may be added to the polyamic acid solution, and the polyamic acid solution to which the imidizing agent and / or dehydration catalyst has been added may be heated by the above method for imidization.

[0068] The imidizing agent is not particularly limited, but a tertiary amine can be used. The tertiary amine is preferably a heterocyclic tertiary amine. Specific preferred examples of the heterocyclic tertiary amine include pyridine, picoline, quinoline, isoquinoline, and 1,2-dimethylimidazole. Specific preferred examples of the dehydration catalyst include acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride.

[0069] The amount of imidizing agent added is preferably 0.5 to 5.0 molar equivalents, more preferably 0.7 to 2.5 molar equivalents, and even more preferably 0.8 to 2.0 molar equivalents, relative to the amide groups of the polyamic acid. The amount of dehydration catalyst added is preferably 0.5 to 10.0 molar equivalents, more preferably 0.7 to 5.0 molar equivalents, and even more preferably 0.8 to 3.0 molar equivalents, relative to the amide groups of the polyamic acid. In this specification, "amide groups of polyamic acid" refers to amide groups formed by the polymerization reaction of diamines and tetracarboxylic dianhydrides. The imidizing agent and / or dehydration catalyst may be added directly to the polyamic acid solution without dissolving them in an organic solvent, or they may be added dissolved in an organic solvent. If the imidizing agent and / or dehydration catalyst are added directly without dissolving them in an organic solvent, the reaction may proceed too quickly before the imidizing agent and / or dehydration catalyst can diffuse, resulting in the formation of a gel. Therefore, it is preferable to add a solution obtained by dissolving the imidizing agent and / or dehydration catalyst in an organic solvent to the polyamic acid solution.

[0070] The polyimide film according to this embodiment (specifically, the polyimide film containing the imidized polyamic acid according to this embodiment) is colorless, transparent, and has a low yellowness index and a glass transition temperature (heat resistance) that can withstand the TFT fabrication process, making it suitable as a transparent substrate material for flexible displays. The content of polyimide in the polyimide film according to this embodiment (specifically, the imidized polyamic acid according to this embodiment) is, for example, 70% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, and may even be 100% by weight, based on the total weight of the polyimide film. Examples of components other than polyimide in the polyimide film include additives (more specifically, nanosilica particles, etc.) described below.

[0071] The electronic device according to this embodiment includes the polyimide film according to this embodiment and electronic elements disposed directly or indirectly on the polyimide film. When manufacturing the electronic device according to this embodiment for use in a flexible display, a polyimide film is first formed on an inorganic substrate such as glass as a support. Electronic elements such as TFTs are then disposed (formed) on the polyimide film to form the electronic device on the support. The TFT formation process is generally carried out over a wide temperature range of 150°C to 650°C. However, to actually achieve the desired performance, the oxide semiconductor layer or a-Si layer is formed at 300°C or higher, and in some cases, the a-Si or other layer may be further crystallized using a laser or the like.

[0072] If the thermal decomposition temperature of the polyimide film is low, outgassing occurs during the formation of electronic devices. This sublimate deposits inside the oven, potentially contaminating the furnace and potentially causing delamination of inorganic films (such as the barrier film described below) and electronic devices formed on the polyimide film. Therefore, the 1% weight loss temperature of the polyimide is preferably 500°C or higher. More specifically, before TFT formation, an inorganic barrier film, such as a silicon oxide (SiOx) film or a silicon nitride (SiNx) film, is formed on the polyimide film. If the polyimide has low heat resistance, delamination between the polyimide and the inorganic film may occur due to volatile components, such as polyimide decomposition gases, during high-temperature processes after lamination of the inorganic film. Therefore, it is desirable for the polyimide to have a 1% weight loss temperature of 500°C or higher and a weight loss rate of less than 1% when the polyimide is isothermally maintained at a temperature between 400°C and 450°C.

[0073] Furthermore, if the glass transition temperature (Tg) of the polyimide is significantly lower than the process temperature, misalignment or other issues may occur during the formation of electronic devices. Therefore, the Tg of the polyimide is preferably 300°C or higher, more preferably 350°C or higher, and even more preferably 400°C or higher. The upper limit of the Tg of the polyimide is preferably as high as possible, for example, 450°C. The Tg of the polyimide can be adjusted, for example, by changing the content of residues having a rigid structure (more specifically, PDA residues, PHBAAB residues, etc.). Furthermore, since the linear expansion coefficient of a glass substrate is generally smaller than that of a resin, internal stress occurs between the glass substrate and the polyimide film. If the internal stress of a laminate formed by a glass substrate used as a support and a polyimide film is high, the laminate containing the polyimide film will expand during the high-temperature TFT formation process and then shrink when cooled to room temperature, resulting in problems such as warping or breakage of the glass substrate and peeling of the polyimide film from the glass substrate. Therefore, the internal stress generated in the laminate formed by the polyimide film and the glass substrate is preferably 50 MPa or less.

[0074] In order to suppress the generation of the internal stress, the linear expansion coefficient of the polyimide film is preferably 100 ppm / K or less, more preferably 90 ppm / K or less, and even more preferably 80 ppm / K or less. The linear expansion coefficient of the polyimide film may be −10 ppm / K to 80 ppm / K, 0 ppm / K to 80 ppm / K, 10 ppm / K to 80 ppm / K, 20 ppm / K to 80 ppm / K, 30 ppm / K to 80 ppm / K, 40 ppm / K to 80 ppm / K, or 50 ppm / K to 80 ppm / K.

[0075] In order to suppress deterioration of display performance when applied to an image display device, the thickness direction retardation (Rth) of the polyimide film for light with a wavelength of 550 nm, converted into a value for a polyimide film with a thickness of 10 μm, is preferably 200 nm or less, more preferably 100 nm or less, even more preferably 90 nm or less, even more preferably 80 nm or less, and particularly preferably 70 nm or less.

[0076] The transparency of a polyimide film can be evaluated by the total light transmittance (TT) according to JIS K7361-1:1997, the transmittance of light at a wavelength of 450 nm (hereinafter sometimes simply referred to as "light transmittance"), and the haze according to JIS K7136-2000. When a polyimide film is used in an application requiring high transparency, the total light transmittance of the polyimide film is preferably 75% or more, more preferably 80% or more. When a polyimide film is used in an application requiring high transparency, the light transmittance of the polyimide film is preferably 75% or more, more preferably 78% or more. When a polyimide film is used in an application requiring high transparency, the haze of the polyimide film is preferably 1.5% or less, more preferably 1.2% or less, and even more preferably less than 1.0%. When a polyimide film is used in an application requiring high transparency, the polyimide film is required to have high transmittance across the entire wavelength range. However, polyimide films tend to absorb light at short wavelengths, and the film itself often becomes yellow. In order to use a polyimide film in applications requiring high transparency, the yellowness index (YI) of the polyimide film is preferably 25 or less, more preferably 20 or less, even more preferably 14 or less, and particularly preferably 12 or less. YI can be measured in accordance with JIS K7373-2006. A polyimide film having such transparency is suitable for transparent substrates used as a glass replacement, etc., or for substrates having a sensor or camera module provided on the back surface.

[0077] Furthermore, there are two types of light extraction methods for flexible displays: a top-emission method in which light is extracted from the front side of the TFT, and a bottom-emission method in which light is extracted from the back side of the TFT. The top-emission method is characterized by its ease of increasing the aperture ratio because light is not blocked by the TFT, resulting in high-definition image quality. The bottom-emission method is characterized by its ease of manufacturing, as it simplifies the alignment of the TFT and pixel electrode. Since the aperture ratio can be improved even in the bottom-emission method if the TFT is transparent, the bottom-emission method, which is easy to manufacture, tends to be adopted for large displays. The polyimide film according to this embodiment has a low YI and excellent heat resistance, making it applicable to both of the above light extraction methods.

[0078] In the manufacturing process of electronic devices, electronic elements such as thin-film transistors and transparent electrodes are provided on a substrate. The process of forming electronic elements on a polyimide substrate can be divided into a batch process and a roll-to-roll process. In the roll-to-roll process, electronic elements are sequentially provided on a polyimide substrate (polyimide film) while the long polyimide substrate is transported. In the batch process, a laminate is formed by providing a polyimide substrate (polyimide film) on, for example, a glass support, and then electronic elements are provided on the polyimide film of the laminate, and the support is then peeled off from the polyimide film. The polyimide according to this embodiment can be applied to either process. The batch process is advantageous in terms of cost because it can utilize existing equipment for glass supports.

[0079] The polyimide according to this embodiment can be suitably used as a material for display substrates such as TFT substrates and touch panel substrates. When using polyimide for the above applications, as described above, an electronic device (specifically, an electronic device in which electronic elements are formed on a polyimide film) is formed on a support, and then the polyimide film is peeled off from the support. In addition, alkali-free glass is suitably used as the support material. Hereinafter, an example of a method for producing a polyimide film according to this embodiment and an example of a method for producing a laminate according to this embodiment (a laminate of a polyimide film and a support) will be described in detail.

[0080] First, a polyamic acid solution according to this embodiment is applied to a support to form a coating film-containing laminate consisting of a coating film containing polyamic acid and the support. Next, the coating film-containing laminate is heated, for example, at a temperature of 40°C to 200°C. The heating time is, for example, 3 minutes to 120 minutes. A multi-stage heating process may be performed, for example, by heating the coating film-containing laminate at 50°C for 30 minutes and then at 100°C for 30 minutes. Next, to promote imidization of the polyamic acid in the coating film, the coating film-containing laminate (polyamic acid film-containing laminate) is heated, for example, at a maximum temperature of 250°C to 500°C. The heating time (heating time at the maximum temperature) is, for example, 1 minute to 300 minutes, preferably 5 minutes to 60 minutes. It is preferable to gradually increase the temperature from a low temperature to the maximum temperature. The heating rate is preferably 2°C / min to 10°C / min, more preferably 4°C / min to 10°C / min. The maximum temperature is preferably in the range of 380°C or higher and 500°C or lower. A maximum temperature of 380°C or higher allows for sufficient imidization, while a maximum temperature of 500°C or lower can suppress thermal degradation of the polyimide. The reaction may be maintained at any temperature for any length of time before reaching the maximum temperature. The imidization reaction can be carried out in air, under reduced pressure, or in an inert gas such as nitrogen. To achieve higher transparency, however, it is preferable to carry out the reaction under reduced pressure or in an inert gas such as nitrogen. Known heating devices, such as hot air ovens, infrared ovens, vacuum ovens, inert ovens, and hot plates, can be used. Through these steps, the polyamic acid in the coating film is imidized, resulting in a laminate (laminate according to the present embodiment) of the support and the polyimide film (polyimide film containing the imidized polyamic acid according to the present embodiment). The polyimide film formed on the support can be peeled from the support, for example, by the method described below, to obtain the polyimide film according to the present embodiment (polyimide film containing the imidized polyamic acid according to the present embodiment). Electronic elements may be provided on the polyimide film peeled from the support. In order to shorten the heating time and to develop the desired properties, an imidizing agent or a dehydration catalyst may be added to the polyamic acid solution, and the solution may be heated by the above-mentioned method to effect imidization.

[0081] The polyimide film can be peeled from the resulting laminate of the support and the polyimide film by known methods. For example, the film may be peeled by hand, or by using a mechanical device such as a drive roll or a robot. Furthermore, a method of providing a peeling layer between the support and the polyimide film, or a method of forming a silicon oxide film on a substrate having a large number of grooves, forming a polyimide film using the silicon oxide film as an underlayer, and then infiltrating a silicon oxide etching solution between the substrate and the silicon oxide film to peel the polyimide film can also be employed. Another method of peeling the polyimide film from the support by irradiation with laser light can also be employed.

[0082] Furthermore, in a batch-type device fabrication process in which a polyamic acid solution is applied to a support such as a glass substrate, heated to imidize, and then electronic elements or the like are formed, followed by peeling off the polyimide film, excellent adhesion between the support and the polyimide film is preferred. Here, adhesion refers to adhesion strength. In this fabrication process in which electronic elements or the like are formed on the polyimide film on the support, and then the polyimide film on which the electronic elements or the like are formed is peeled off from the support, excellent adhesion between the polyimide film and the support allows for more accurate formation or mounting of electronic elements or the like. In a manufacturing process in which electronic elements or the like are arranged on a support via a polyimide film, the higher the peel strength between the support and the polyimide film, the better from the perspective of improving productivity. Specifically, the peel strength is preferably 0.05 N / cm or more, and more preferably 0.1 N / cm or more.

[0083] In the manufacturing process described above, when peeling a polyimide film from a laminate of a support and a polyimide film, the polyimide film is often peeled from the support by laser irradiation. In this case, since the polyimide film needs to absorb the laser light, the cutoff wavelength of the polyimide film is required to be longer than the wavelength of the laser light used for peeling. Since a XeCl excimer laser with a wavelength of 308 nm is often used for laser peeling, the cutoff wavelength of the polyimide film is preferably 312 nm or longer, and more preferably 330 nm or longer. On the other hand, since a longer cutoff wavelength tends to cause the polyimide film to turn yellow, the cutoff wavelength of the polyimide film is preferably 390 nm or shorter. From the viewpoint of achieving both transparency (low yellowness) and ease of laser peeling, the cutoff wavelength of the polyimide film is preferably 320 nm or longer to 390 nm or shorter, and more preferably 330 nm or longer to 380 nm or shorter. In this specification, the cutoff wavelength means a wavelength at which the transmittance is 0.1% or less as measured by an ultraviolet-visible spectrophotometer.

[0084] The polyamic acid and polyimide according to this embodiment may be used as they are in coating or molding processes for producing products or components, or may be used as materials for further coating or other treatments on molded articles formed into films. For use in coating or molding processes, the polyamic acid or polyimide may be dissolved or dispersed in an organic solvent as needed, and further blended with a photocurable component, a thermosetting component, a non-polymerizable binder resin, and other components as needed to prepare a polyamic acid composition or a polyimide resin composition.

[0085] To impart processing properties and various functionalities to the polyamic acid and polyimide according to this embodiment, various organic or inorganic low-molecular-weight compounds or high-molecular-weight compounds may be blended into the polyamic acid solution as additives. Examples of additives that can be used include dyes, surfactants, leveling agents, plasticizers, silicones, fine particles, and sensitizers. Examples of fine particles include organic fine particles made of polystyrene, polytetrafluoroethylene, and the like, and inorganic fine particles made of colloidal silica, carbon, layered silicates, and the like, which may have a porous or hollow structure. Furthermore, the function and form of the fine particles are not particularly limited, and they may be, for example, pigments, fillers, or fibrous particles.

[0086] To improve the heat resistance while maintaining the transparency of the polyimide film, nanosilica particles may be used as the additive to composite the polyamic acid with the nanosilica particles. From the viewpoint of maintaining the transparency of the polyimide film, the average primary particle diameter of the nanosilica particles is preferably 200 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, and may even be 30 nm or less. On the other hand, from the viewpoint of ensuring dispersibility in the polyamic acid, the average primary particle diameter of the nanosilica particles is preferably 5 nm or more, more preferably 10 nm or more. Methods for composite the polyamic acid with the nanosilica particles can be known, such as a method using an organosilica sol in which nanosilica particles are dispersed in an organic solvent. As a method for composite the polyamic acid with the nanosilica particles using an organosilica sol, the polyamic acid may be synthesized and then mixed with the synthesized polyamic acid and the organosilica sol. However, to more highly disperse the nanosilica particles in the polyamic acid, it is preferable to synthesize the polyamic acid in the organosilica sol.

[0087] Furthermore, to enhance the interaction with polyamic acid, the nanosilica particles can be surface-treated with a surface treatment agent. Known surface treatment agents, such as silane coupling agents, can be used. Silane coupling agents include alkoxysilane compounds having functional groups such as amino groups or glycidyl groups, and these can be selected appropriately. To further enhance the interaction with polyamic acid, amino group-containing alkoxysilanes are preferred. Examples of amino group-containing alkoxysilanes include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-phenylaminopropyltrimethoxysilane, 2-aminophenyltrimethoxysilane, and 3-aminophenyltrimethoxysilane. However, from the viewpoint of raw material stability, 3-aminopropyltriethoxysilane is preferred. A surface treatment method for nanosilica particles includes stirring a mixture of a dispersion (organosilica sol) and a silane coupling agent at an ambient temperature of 20°C to 80°C. The stirring time is, for example, 1 hour to 10 hours. A catalyst or the like may be added to accelerate the reaction.

[0088] A nanosilica particle-containing polyamic acid composition, which is a composite of polyamic acid and nanosilica particles, preferably contains 1 to 30 parts by weight, and more preferably 1 to 20 parts by weight, of nanosilica particles per 100 parts by weight of polyamic acid. When the content of nanosilica particles is 1 part by weight or more, the heat resistance of the nanosilica particle-containing polyimide can be improved and internal stress can be sufficiently reduced, while when the content of nanosilica particles is 30 parts by weight or less, adverse effects on the mechanical properties and transparency of the nanosilica particle-containing polyimide can be suppressed.

[0089] Imidazoles may also be added to the polyamic acid of this embodiment as additives for imparting the aforementioned functionality. In this specification, imidazoles refer to compounds having a 1,3-diazole ring (1,3-diazole ring structure). The imidazoles added to the polyamic acid of this embodiment are not particularly limited, but examples include 1H-imidazole, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole. Of these, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole are preferred, and 1,2-dimethylimidazole and 1-benzyl-2-methylimidazole are more preferred.

[0090] The content of the imidazoles is preferably 0.005 mol or more and 0.1 mol or less, more preferably 0.01 mol or more and 0.08 mol or less, and even more preferably 0.015 mol or more and 0.050 mol or less, per mol of amide group in the polyamic acid. By including 0.005 mol or more of the imidazoles, the film strength and transparency of the polyimide can be improved, and by including the imidazoles in an amount of 0.1 mol or less, the storage stability of the polyamic acid can be maintained while the Tg and heat resistance can be improved.

[0091] The method for mixing the polyamic acid and the imidazoles is not particularly limited. From the viewpoint of ease of molecular weight control of the polyamic acid, it is preferable to add the imidazoles to the polyamic acid after polymerization. In this case, the imidazoles may be added directly to the polyamic acid, or the imidazoles may be dissolved in a solvent in advance and this solution may be added to the polyamic acid; the addition method is not particularly limited. The polyamic acid solution according to this embodiment (a solution containing polyamic acid and imidazoles) may be prepared by adding the imidazoles to a solution containing the polyamic acid after polymerization (a solution after reaction).

[0092] Furthermore, the polyamic acid solution according to this embodiment may contain a silane coupling agent in order to achieve appropriate adhesion to the support. The silane coupling agent may be added to the monomer solution before the polymerization reaction, to the solution during the polymerization reaction, or to the polyamic acid solution after the polymerization reaction. Any known silane coupling agent may be used without any particular limitation, but compounds containing an amino group are particularly preferred in terms of reactivity with polyamic acid.

[0093] The blending ratio of the silane coupling agent to 100 parts by weight of polyamic acid is preferably 0.01 to 0.50 parts by weight, more preferably 0.01 to 0.10 parts by weight, and even more preferably 0.01 to 0.05 parts by weight. By making the blending ratio of the silane coupling agent 0.01 parts by weight or more, the peeling suppression effect on the support is sufficiently exhibited, and by making the blending ratio of the silane coupling agent 0.50 parts by weight or less, the decrease in molecular weight of the polyamic acid is suppressed, and therefore embrittlement of the polyimide film can be suppressed.

[0094] On the surface of the polyimide film according to this embodiment, various inorganic thin films such as metal oxide thin films, transparent electrodes, etc. The method for forming these inorganic thin films is not particularly limited, and examples thereof include CVD, sputtering, vacuum deposition, ion plating, and other PVD methods.

[0095] The polyimide film according to the present embodiment is heat-resistant, has low thermal expansion, and is transparent, and also exhibits low internal stress when laminated with a glass substrate. Therefore, it is preferably used in fields and products where these properties are beneficial. For example, the polyimide film according to the present embodiment is preferably used in image display devices such as liquid crystal displays, organic electroluminescence (EL) displays, and electronic paper, as well as printed materials, color filters, flexible displays, optical films, 3D displays, touch panels, transparent conductive film substrates, solar cells, and more preferably as a replacement material for glass currently used in these applications. In these applications, the thickness of the polyimide film is, for example, from 1 μm to 200 μm, and preferably from 5 μm to 100 μm. The thickness of the polyimide film can be measured using a laser hologram.

[0096] Furthermore, the polyamic acid solution according to this embodiment can be suitably used in a batch-type device fabrication process in which the polyamic acid solution is applied to a support, heated to imidize the solution, electronic elements, etc. are formed, and the polyimide film is then peeled off. Therefore, this embodiment also includes a method for fabricating an electronic device, which includes the steps of applying the polyamic acid solution to a support, heating to imidize the solution, and forming electronic elements, etc. on the polyimide film formed on the support. Furthermore, this method for fabricating an electronic device may further include the step of peeling off the polyimide film on which the electronic elements, etc. are formed, from the support. [Example]

[0097] Examples of the present invention will be described below, but the scope of the present invention is not limited to the following examples.

[0098] <Methods for measuring physical properties> First, the method for measuring the physical properties of polyimide (polyimide film) will be described.

[0099] [Light transmittance] The transmittance of light with a wavelength of 450 nm was measured for each of the polyimide films obtained in the examples and comparative examples described below using an ultraviolet-visible-near-infrared spectrophotometer ("V-650" manufactured by JASCO Corporation).

[0100] [Yellowness (YI)] For each polyimide film obtained in the Examples and Comparative Examples described below, the transmittance of light with a wavelength of 200 nm or more and 800 nm or less was measured using an ultraviolet-visible-near-infrared spectrophotometer ("V-650" manufactured by JASCO Corporation), and the yellowness index (YI) of the polyimide film was calculated using the formula described in JIS K7373-2006. When the YI was 14 or less, the film was evaluated as having "excellent low colorability." On the other hand, when the YI was greater than 14, the film was evaluated as having "not excellent low colorability."

[0101] [Hayes] For each polyimide film obtained in the examples and comparative examples described below, the haze was measured using an integrating sphere haze meter ("COH 300A" manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method described in JIS K7136-2000.

[0102] Internal Stress A polyimide film was formed on a Corning glass substrate (material: alkali-free glass, thickness: 0.7 mm, size: 100 mm x 100 mm) whose warpage had been measured in advance, using the same method as in the Examples and Comparative Examples described below, to obtain a laminate with a 10 μm-thick polyimide film on the glass substrate. To eliminate the influence of water absorption by the polyimide film, the laminate was dried at 120°C for 10 minutes, and then the warpage of the laminate was measured in a nitrogen atmosphere at 25°C using a thin film stress measurement device (KLA-Tencor Corporation, "FLX-2320-S"). The internal stress generated between the glass substrate and the polyimide film was calculated using the Stoney equation from the warpage of the glass substrate before polyimide film formation and the warpage of the laminate.

[0103] [Retardation] For each polyimide film obtained in the examples and comparative examples described below, the retardation in the thickness direction (Rth) for light with a wavelength of 550 nm was measured using a phase difference meter ("OPTIPRO" manufactured by Shintech Co., Ltd.). Then, the thickness D (unit: μm) of the measurement sample (polyimide film) was converted into a value (Rth) for a polyimide film with a thickness of 10 μm based on the following formula:10 ) was calculated. 10 When Rth is 80 nm or less, it is evaluated as "retardation is reduced." 10 When the retardation was more than 80 nm, it was evaluated as "the retardation could not be reduced." Rth 10 =Rth×10 / D

[0104] Coefficient of Linear Expansion (CTE) Each polyimide film obtained in the examples and comparative examples described below was sampled to a size of 3 mm wide and 10 mm long and used as a sample for CTE measurement. Using a thermal analyzer (Hitachi High-Tech Science Corporation, "TMA / SS7100"), the sample was heated from 10°C to 400°C at a heating rate of 10°C / min under a load of 29.4 mN, and then cooled at a rate of 40°C / min. The CTE was then calculated from the strain during cooling from 350°C to 100°C. A CTE of 80 ppm / K or less was evaluated as having "excellent low thermal expansion." On the other hand, a CTE of more than 80 ppm / K was evaluated as having "poor low thermal expansion."

[0105] [Glass transition temperature (Tg)] Each polyimide film obtained in the Examples and Comparative Examples described below was sampled to a size of 3 mm wide and 10 mm long and used as a sample for Tg measurement. Using a thermal analyzer (Hitachi High-Tech Science Corporation, "TMA / SS7100"), a load of 98.0 mN was applied to the sample, and the temperature was raised from 10°C to 450°C at a rate of 10°C / min. The temperature and strain (elongation) were plotted to obtain a TMA curve. The inflection point temperature of the obtained TMA curve (the temperature corresponding to the peak in the differential curve of the TMA curve) was determined as the glass transition temperature (Tg).

[0106] [1% weight loss temperature (TD1)] Each polyimide film obtained in the examples and comparative examples described below (specifically, a polyimide film sampled so as to have a weight of 10 mg) was used as a measurement sample, and the temperature was raised from 25°C to 650°C at a rate of 20°C / min in a nitrogen atmosphere using a simultaneous differential thermal and thermogravimetric analyzer ("TG / DTA7200" manufactured by Hitachi High-Tech Science Corporation). The measurement temperature at which the sample weight at a measurement temperature of 150°C was reduced by 1% by weight relative to this reference weight was defined as the 1% weight loss temperature (TD1).

[0107] <Preparation of polyimide film> The methods for preparing polyimide films in Examples and Comparative Examples are described below. In the following, compounds and reagents are abbreviated as follows: In both Examples and Comparative Examples, polyamic acid solutions were prepared under a nitrogen atmosphere. NMP: N-methyl-2-pyrrolidone BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PMDA: Pyromellitic dianhydride PDA: p-phenylenediamine PHBAAB: (2-phenyl-4-aminophenyl)-4-aminobenzoate TFMB: 2,2'-bis(trifluoromethyl)benzidine DABA: 4,4'-diaminobenzanilide BAFL: 9,9-bis(4-aminophenyl)fluorene

[0108] [Example 1] First, a polyamic acid solution was prepared according to the following procedure. 400.0 g of NMP, the organic solvent for polymerization, was placed in a 1 L glass separable flask equipped with a stainless steel stirrer and a nitrogen inlet tube. Next, 19.1 g of PDA was added to the flask while stirring the contents of the flask and dissolved. Next, 80.9 g of BPAF was added to the flask while stirring the contents of the flask, and the contents of the flask were stirred for 24 hours in an atmosphere at 25°C. Finally, NMP was added to the contents of the flask so that the concentration of polyamic acid in the flask after stirring was 10.0 wt % to obtain a polyamic acid solution.

[0109] The resulting polyamic acid solution was then applied to a glass substrate (Corning Incorporated "Eagle XG," material: alkali-free glass, thickness: 0.7 mm, size: 150 mm × 150 mm) using a spin coater and heated in air at 80°C for 30 minutes to obtain a laminate (polyamic acid film-containing laminate) in which a film containing polyamic acid was formed on the glass substrate. The polyamic acid film-containing laminate was then heated in a nitrogen atmosphere under the following heating conditions to imidize the polyamic acid, thereby obtaining a laminate comprising a 10 μm-thick polyimide film on the glass substrate. The heating conditions for imidization were as follows: first, the ambient temperature was increased from 20°C to 350°C at a heating rate of 5°C / min and maintained at 350°C for 30 minutes; then, the ambient temperature was increased to 420°C at a heating rate of 5°C / min and maintained at 420°C for 30 minutes; and the polyimide film was peeled off from the glass substrate of the resulting laminate to obtain the polyimide film of Example 1.

[0110] [Examples 2 to 35 and Comparative Examples 1 to 7] The polyimide films of Examples 2 to 35 and Comparative Examples 1 to 7 were obtained by the same method as in Example 1, except that the types and ratios (feed ratios) of acid dianhydrides and the types and ratios (feed ratios) of diamines were as shown in Tables 1 and 2. In each of Examples 2 to 35 and Comparative Examples 1 to 7, the total amount of acid dianhydrides and the total amount of diamines were the same as in Example 1.

[0111] Tables 1 and 2 show the types and ratios of dianhydrides and the types and ratios of diamines for Examples 1 to 35 and Comparative Examples 1 to 7. In all of Examples 1 to 35 and Comparative Examples 1 to 7, the molar fraction of each polyamic acid residue in the prepared polyamic acid solution matched the molar fraction of each monomer (diamine and tetracarboxylic dianhydride) used in the synthesis of the polyamic acid. In Examples 2 to 14 and 16 to 33, two types of diamines (component 1 and component 2) were used. In Examples 34, 35, and Comparative Examples 4 to 7, two types of dianhydrides (component 1 and component 2) were used. In all of Examples 2 to 14, 16 to 35, and Comparative Examples 4 to 7, component 1 and component 2 were simultaneously added to a flask. In Tables 1 and 2, the numerical values ​​for the ratios of dianhydrides represent the content (unit: mol%) of each dianhydride relative to the total amount of dianhydrides used. In Tables 1 and 2, the numerical values ​​of the diamine ratios are the content (unit: mol %) of each diamine relative to the total amount of diamines used.

[0112] [Table 1]

[0113] [Table 2]

[0114] <Measurement results> The measurement results of each physical property for each of Examples 1 to 35 and Comparative Examples 1 to 7 are shown in Tables 3 and 4. In Tables 3 and 4, "-" means that no measurement was performed. In Tables 3 and 4, "light transmittance" refers to the transmittance of light with a wavelength of 450 nm.

[0115] [Table 3]

[0116] [Table 4]

[0117] The polyamic acids synthesized in Examples 1 to 35 had BPAF residues as acid dianhydride residues. The polyamic acids synthesized in Examples 1 to 35 had one or more diamine residues selected from the group consisting of PDA residues and PHBAAB residues. In the polyamic acids synthesized in Examples 1 to 35, the content of BPAF residues was 90 mol % or more and 100 mol % or less of the total acid dianhydride residues.

[0118] In Examples 1 to 35, the YI was 14 or less. Therefore, the polyimide films of Examples 1 to 35 were excellent in low coloration. 10 was 80 nm or less. Therefore, the polyimide films of Examples 1 to 35 had reduced retardation. In Examples 1 to 35, the CTE was 80 ppm / K or less. Therefore, the polyimide films of Examples 1 to 35 were excellent in low thermal expansion.

[0119] The polyamic acids synthesized in Comparative Examples 1 to 3 did not contain one or more diamine residues selected from the group consisting of PDA residues and PHBAAB residues. The polyamic acids synthesized in Comparative Examples 2 and 3 did not contain BPAF residues as acid dianhydride residues. The polyamic acids synthesized in Comparative Examples 4 to 7 had a BPAF residue content of less than 90 mol% based on the total acid dianhydride residues.

[0120] In Comparative Example 1, the CTE exceeded 80 ppm / K. Therefore, the polyimide film of Comparative Example 1 did not have excellent low thermal expansion properties. In Comparative Example 2, Rth 10 was greater than 80 nm. Therefore, the polyimide film of Comparative Example 2 was unable to reduce retardation. In Comparative Examples 2 to 7, the YI was greater than 14. Therefore, the polyimide films of Comparative Examples 2 to 7 were not excellent in low coloration properties.

[0121] The above results demonstrate that the polyimide obtained from the polyamic acid according to the present invention can reduce Rth and is excellent in low colorability and low thermal expansion.

Claims

1. The tetracarboxylic acid dianhydride residue has a tetravalent organic group represented by the following general formula (1), and the diamine residues have a p-phenylenediamine residue and a 4,4'-diaminobenzanilide residue: the content of the tetravalent organic group represented by the following general formula (1) is 90 mol % or more and 100 mol % or less based on all tetracarboxylic dianhydride residues, The polyamic acid has a content of 4,4'-diaminobenzanilide residues of 1.0 mol % or more based on the total diamine residues. 【Chemical 1】 (In the general formula (1), R １ and R ２ each independently represents a hydrogen atom, a halogen atom, an alkyl group having from 1 to 12 carbon atoms, an alkenyl group having from 2 to 12 carbon atoms, an alkoxy group having from 1 to 12 carbon atoms, an aryl group having from 6 to 14 carbon atoms, a hydroxy group, a nitrile group, a nitro group, a carboxy group, or an amide group.

2. In the general formula (1), R １ and R ２ and each represent a hydrogen atom.

3. 3. The polyamic acid according to claim 1, further comprising, as a diamine residue, at least one selected from the group consisting of a 2,2'-bis(trifluoromethyl)benzidine residue and a 9,9-bis(4-aminophenyl)fluorene residue.

4. A polyamic acid solution containing the polyamic acid according to any one of claims 1 to 3 and an organic solvent.

5. A polyimide which is an imidized product of the polyamic acid according to any one of claims 1 to 3.

6. 6. The polyimide according to claim 5, which has a glass transition temperature of 350°C or higher.

7. A polyimide film comprising the polyimide according to claim 5 or 6.

8. A laminate comprising a support and the polyimide film according to claim 7.

9. An electronic device comprising the polyimide film according to claim 7 and an electronic element disposed on the polyimide film.

10. A method for producing a polyimide film, comprising: applying the polyamic acid solution according to claim 4 onto a support to form a coating film containing the polyamic acid; and heating the coating film to imidize the polyamic acid.

11. The method for producing a polyimide film according to claim 10, wherein the maximum temperature when the coating film is heated is 380°C or higher and 500°C or lower.

12. The method for producing a polyimide film according to claim 11, wherein the heating time at the highest temperature is 5 minutes or more and 60 minutes or less.

13. The method for producing a polyimide film according to any one of claims 10 to 12, wherein the polyimide film obtained by heating the coating film is peeled off from the support.

14. The method for producing a polyimide film according to claim 13, wherein the polyimide film is peeled off from the support by laser irradiation.

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