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

Abstract

A poly(amic acid) including a structural unit represented by chemical formula (1); a poly(amic acid) solution comprising an organic solvent and a poly(amic acid) including a structural unit represented by chemical formula (1); a polyimide which is a product of imidization of a poly(amic acid) including a structural unit represented by chemical formula (1); a polyimide film including a product of imidization of a poly(amic acid) including a structural unit represented by chemical formula (1); a layered product comprising a support and a polyimide film including a product of imidization of a poly(amic acid) including a structural unit represented by chemical formula (1); and an electronic device comprising a polyimide film including a product of imidization of a poly(amic acid) including a structural unit represented by chemical formula (1) and an electronic element disposed on the polyimide film.

Description

[Technical Field]

[0001] The present invention relates to polyamic acid, a polyamic acid solution, a polyimide, a polyimide film, a laminate, a method for producing the laminate, and an electronic device. The present invention also relates to 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, using polyimides. [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 coefficient of thermal expansion (CTE) is close 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 applications.

[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), high optical properties (more specifically, transparency, etc.) are now required for the substrate as well.

[0005] In light of this, there is a demand for materials that have heat resistance equivalent to that of existing aromatic polyimides and are excellent in transparency.

[0006] To reduce the coloration of polyimides, there are known techniques for suppressing the formation of CT complexes using aliphatic monomers (Patent Documents 1 and 2), and a technique for increasing transparency using monomers containing fluorine atoms or sulfur atoms (Patent Document 3).

[0007] The polyimides described in Patent Documents 1 and 2 have high transparency and low CTE, but because they have an aliphatic structure, they have a low thermal decomposition temperature, making them difficult to apply to high-temperature processes when forming electronic devices. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-29177 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-41530 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-70139 Summary of the Invention [Problem to be solved by the invention]

[0009] The polyimide described in Patent Document 3 is highly transparent, but because it contains fluorine atoms, the surface free energy decreases, which reduces adhesion to barrier films and electronic elements formed on the polyimide substrate, and the inventors have found that peeling may occur at the interface with the polyimide during high-temperature processes. Furthermore, the inventors have found that the polyimide described in Patent Document 3 may cause poor adhesion between the polyimide and barrier films or electronic elements due to fluorine-based decomposition gases generated during high-temperature processes.

[0010] The present invention was made in view of the above-mentioned circumstances, and aims to provide a polyimide and a polyamic acid precursor thereof that have excellent transparency and high heat resistance and can ensure adhesion to inorganic materials (more specifically, glass substrates, barrier films, etc.) during high-temperature processes. Another aim is to provide a product or component that requires heat resistance and transparency and is manufactured using the polyimide and polyamic acid. In particular, the present invention aims to provide a product or component in which the polyimide film of the present invention is formed on the surface of an inorganic material such as glass, metal, metal oxide, or single-crystal silicon. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that polyimides obtained by imidizing specific polyamic acids having a fluorene skeleton (fluorene structure) have excellent transparency and high heat resistance, and can ensure adhesion to glass substrates and barrier films during high-temperature processes, thereby completing the present invention.

[0012] The polyamic acid according to the present invention contains a structural unit represented by the following chemical formula (1).

[0013] [ka]

[0014] The polyamic acid according to one embodiment of the present invention further contains a structural unit represented by the following general formula (2).

[0015] [ka]

[0016] In the general formula (2), X represents a tetravalent organic group different from the tetracarboxylic dianhydride residue in the chemical formula (1).

[0017] In one embodiment of the polyamic acid according to the present invention, X in the general formula (2) is at least one selected from the group consisting of a tetravalent organic group represented by the following chemical formula (3) and a tetravalent organic group represented by the following chemical formula (4):

[0018] [ka]

[0019] In one embodiment of the polyamic acid according to the present invention, the content of the structural unit represented by the chemical formula (1) is 1 mol % or more based on all structural units.

[0020] In one embodiment of the polyamic acid according to the present invention, the ratio of the total amount of tetracarboxylic dianhydride residues divided by the total amount of diamine residues is 0.900 or more and less than 1.100.

[0021] The polyamic acid solution according to the present invention contains the polyamic acid according to the present invention and an organic solvent.

[0022] The polyimide according to the present invention is an imidized product of the polyamic acid according to the present invention.

[0023] The polyimide according to the present invention preferably has a 1% weight loss temperature of 500° C. or higher, and the polyimide according to the present invention preferably has a glass transition temperature of 400° C. or higher.

[0024] The polyimide film according to the present invention contains the polyimide according to the present invention.

[0025] The polyimide film according to the present invention preferably has a yellowness index of not more than 25. The polyimide film according to the present invention preferably has a haze of less than 1.0%.

[0026] The laminate according to the present invention has a support and the polyimide film according to the present invention.

[0027] The method for producing a laminate 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.

[0028] 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. [Effects of the Invention]

[0029] The polyimide produced using the polyamic acid according to the present invention has excellent transparency and heat resistance and can ensure adhesion to inorganic materials in high-temperature processes, making it suitable as a material for electronic devices that require transparency and heat resistance and are manufactured through high-temperature processes. DETAILED DESCRIPTION OF THE INVENTION

[0030] Preferred embodiments of the present invention will be described in detail below, but the present invention is not limited to these.

[0031] 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 (5) (hereinafter, sometimes referred to as "structural unit (5)").

[0032] [ka]

[0033] In general formula (5), A represents a tetracarboxylic dianhydride residue (a tetravalent organic group derived from a tetracarboxylic dianhydride), and B represents a diamine residue (a divalent organic group derived from a diamine).

[0034] The content of the structural unit (5) 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%.

[0035] The "1% weight loss temperature" is the temperature measured when the weight of the polyimide at a measurement temperature of 150°C is reduced by 1% by weight relative to the reference weight (100% by weight). The 1% weight loss temperature is measured by the same method as in the examples described below or a method equivalent thereto.

[0036] 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."

[0037] The polyamic acid according to this embodiment contains a structural unit represented by the following chemical formula (1) (hereinafter, sometimes referred to as "structural unit (1)").

[0038] [ka]

[0039] The structural unit (1) has a partial structure derived from 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (hereinafter sometimes referred to as "BPAF") and a partial structure derived from 4-aminophenyl-4-aminobenzoate (hereinafter sometimes referred to as "4-BAAB"). That is, the structural unit (1) has a BPAF residue as A in the above-mentioned general formula (5) and a 4-BAAB residue as B in the general formula (5).

[0040] Because 4-BAAB has a rigid structure, it is suitable as a raw material (monomer) for polyimides with a high glass transition temperature (excellent heat resistance). Also, because of its rigid structure, 4-BAAB is suitable as a raw material (monomer) for polyimides with high mechanical strength while suppressing the generation of internal stress. Because BPAF has a bulky fluorene structure, it is suitable as a raw material (monomer) for polyimides with excellent heat resistance and transparency.

[0041] When synthesizing the polyamic acid according to this embodiment, a diamine other than 4-BAAB may be used as a monomer as long as the performance is not impaired. Examples of diamines other than 4-BAAB include 1,4-diaminocyclohexane, p-phenylenediamine, m-phenylenediamine, 4,4'-oxydianiline, 3,4'-oxydianiline, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 4,4'-diaminobenzanilide, N,N'-bis(4-aminophenyl)terephthalamide, 4,4'-diaminodiphenyl sulfone, m-tolidine, o-tolidine, 4,4'-bis(aminophenoxy)biphenyl, 2-(4-aminophenyl)-6-aminobenzoxazole, 3,5-diaminobenzoic acid, 4,4'-diamino-3,3'-dihydroxybiphenyl, 4,4'-methylenebis(cyclohexaneamine), 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and derivatives thereof. These may be used alone or in combination of two or more. From the viewpoints of improving heat resistance, improving mechanical strength, and reducing internal stress, the diamine other than 4-BAAB is preferably at least one selected from the group consisting of p-phenylenediamine and 4,4'-diaminobenzanilide, and more preferably p-phenylenediamine. From the viewpoints of improving transparency, improving heat resistance, improving mechanical strength, and reducing internal stress, the content of 4-BAAB residues relative to all diamine residues constituting the polyamic acid is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and may even be 100 mol%.

[0042] From the viewpoint of improving transparency and reducing internal stress, the polyamic acid according to this embodiment preferably contains, in addition to the structural unit (1), a structural unit represented by the following general formula (2) (hereinafter, sometimes referred to as "structural unit (2)"). When the polyamic acid according to this embodiment contains the structural unit (1) and the structural unit (2), the arrangement of the structural unit (1) and the structural unit (2) in the polyamic acid may be random or block.

[0043] [ka]

[0044] In the general formula (2), X represents a tetravalent organic group different from the tetracarboxylic dianhydride residue in the chemical formula (1). X may be of one type or of two or more types.

[0045] Suitable examples of the acid dianhydride for forming the structural unit (2) (the acid dianhydride that provides X in the general formula (2)) 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 the like. Examples of suitable dianhydrides include phthalic anhydride, 4,4'-oxydiphthalic anhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, 2'-oxodispiro[bicyclo[2.2.1]heptane-2,1''-cycloheptane-3,2''-bicyclo[2.2.1]heptane]-5,5'-6,6'-tetracarboxylic dianhydride, and derivatives thereof, and these may be used alone or in combination.

[0046] From the viewpoints of improving heat resistance, improving mechanical strength, and reducing internal stress, the acid dianhydride that provides X in general formula (2) is preferably one or more selected from the group consisting of PMDA and BPDA, and more preferably BPDA. When PMDA is used as the acid dianhydride, X in general formula (2) is a tetravalent organic group represented by the following chemical formula (3). When BPDA is used as the acid dianhydride, X in general formula (2) is a tetravalent organic group represented by the following chemical formula (4).

[0047] [ka]

[0048] When the polyamic acid according to the present embodiment contains at least one of a PMDA residue and a BPDA residue, from the viewpoints of improving transparency, heat resistance, and mechanical strength, and reducing internal stress, the total content of BPAF residues, PMDA residues, and BPDA residues relative to all acid dianhydride residues constituting the polyamic acid is preferably 60 mol % or more, more preferably 70 mol % or more, and even more preferably 80 mol % or more, and may even be 100 mol %.

[0049] In particular, the BPAF residue has a bulky structure derived from the fluorene structure, which contributes to improved heat resistance, improved transparency, and reduced yellowness. Even a small amount of BPAF residue can suppress polyimide crystallization. Therefore, the content of the structural unit (1) containing the BPAF residue is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and even more preferably 10 mol% or more, based on the total structural units of the polyamic acid according to this embodiment. Furthermore, from the viewpoint of reducing internal stress, the content of the structural unit (1) containing the BPAF residue is preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less, based on the total structural units of the polyamic acid according to this embodiment.

[0050] By setting the content of the structural unit (1) within the above range, it is possible to obtain a polyimide having high transparency, low yellowness index, and high heat resistance while suppressing the generation of internal stress.

[0051] When the polyamic acid according to the present embodiment contains the structural unit (1) and the structural unit (2), from the viewpoints of improving transparency, improving heat resistance, improving mechanical strength, and reducing internal stress, the total content of the structural unit (1) and the structural unit (2) relative to all structural units constituting the polyamic acid is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, and may even be 100 mol %.

[0052] In order to obtain a polyimide that is more excellent in transparency and heat resistance and can more reliably ensure adhesion to inorganic materials in high-temperature processes, the polyamic acid according to the present embodiment preferably satisfies the following condition 1, more preferably satisfies the following condition 2, even more preferably satisfies the following condition 3, and even more preferably satisfies the following condition 4. Condition 1: The polyamic acid contains at least one of a PMDA residue and a BPDA residue, and the total content of the BPAF residue, PMDA residue, and BPDA residue relative to all tetracarboxylic dianhydride residues constituting the polyamic acid is 100 mol %. Condition 2: The above condition 1 is satisfied, and the content of 4-BAAB residues relative to all diamine residues constituting the polyamic acid is 50 mol % or more and 100 mol % or less. Condition 3: The above condition 1 is satisfied, and the content of the structural unit (1) is 1 mol % or more and 30 mol % or less based on the total structural units of the polyamic acid. Condition 4: The above condition 2 is satisfied, and the content of the structural unit (1) is 1 mol % or more and 30 mol % or less based on the total structural units of the polyamic acid.

[0053] From the viewpoint of suppressing a decrease in transparency due to remaining unreacted monomers during polyimide formation, the molar ratio obtained by dividing the total amount of tetracarboxylic dianhydride residues by the total amount of diamine residues is preferably 0.900 or more and less than 1.100, more preferably 0.950 or more and 1.080 or less, and even more preferably 1.000 or more and 1.050 or less. By adjusting the molar ratio within the above range, a polyimide with excellent transparency can be obtained.

[0054] 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. An example of a specific method for synthesizing a polyamic acid is 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.

[0055] 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 ratio of the diamines (or, if multiple diamines are used, the molar ratio of each diamine) and the molar ratio of the tetracarboxylic dianhydrides (or, if multiple tetracarboxylic dianhydrides are used, the molar ratio of each tetracarboxylic dianhydride). The molar ratio of each residue in the polyamic acid corresponds to the molar ratio of each monomer (diamine and tetracarboxylic dianhydride) used in synthesizing the polyamic acid. 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 the diamines and the 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.

[0056] 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 to be 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.

[0057] 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).

[0058] The polyimide according to this embodiment is an imidized product of the polyamic acid according to this embodiment described above. The polyimide according to this embodiment can be obtained by a known method, 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. The imidization is performed by dehydrating and cyclizing the polyamic acid. This dehydrating and cyclizing 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 imidizing by heating, the cyclization reaction from the polyamic acid to the polyimide and the hydrolysis of the polyamic acid proceed simultaneously, which may result in the molecular weight of the polyimide being lower than that of the polyamic acid itself, or coloration due to oxidation of the diamine produced by hydrolysis. Therefore, it is preferable to partially imidize the polyamic acid in the polyamic acid solution before forming the polyimide film described below, from the viewpoint of improving transparency and mechanical properties. In this specification, partially imidized polyamic acids may also be referred to as "polyamic acids."

[0059] 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 synthesis reaction of polyamic acid. 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 a 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.

[0060] The dehydration ring closure of 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 has a support and a polyimide film (specifically, a polyimide film containing an imidized polyamic acid according to the present embodiment) disposed on the support. Alternatively, the dehydration ring closure of polyamic acid can be carried out by directly placing the polyamic acid solution in a container that has been subjected to a release treatment, such as coating with a fluorine-based resin, and heating and drying the polyamic acid solution under reduced pressure. Polyimide can be obtained by dehydration ring closure of polyamic acid using these methods. The heating time for each of the above treatments varies depending on the amount of polyamic acid solution to be dehydrated and the heating temperature, but is generally preferably in the range of 1 minute to 300 minutes after the treatment temperature reaches its maximum temperature. Furthermore, in order to shorten the heating time or to develop the desired 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-mentioned method to effect imidization.

[0061] 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.

[0062] 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 more preferable to add a solution obtained by dissolving the imidizing agent and / or dehydration catalyst in an organic solvent to the polyamic acid solution.

[0063] 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.

[0064] The electronic device according to this embodiment includes the polyimide film according to this embodiment and electronic elements disposed 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, but to actually achieve the desired performance, the oxide semiconductor layer and a-Si layer are formed at 300°C or higher, and in some cases, the a-Si layer may be further crystallized using a laser or the like.

[0065] If the thermal decomposition temperature of the polyimide film is low, outgassing may occur during the formation of electronic devices. This may result in sublimate deposits inside the oven, contaminating the furnace and potentially peeling off 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. The upper limit of the 1% weight loss temperature of the polyimide is preferably 520°C, although the higher the upper limit, the better. The 1% weight loss temperature can be adjusted, for example, by changing the content of residues with rigid structures (more specifically, 4-BAAB residues, BPDA residues, etc.). More specifically, before TFT formation, an inorganic film such as a silicon oxide film (SiOx film) or a silicon nitride film (SiNx film) is formed on the polyimide film as a barrier film. If the polyimide has low heat resistance, volatile components such as polyimide decomposition gases may cause peeling between the polyimide and the inorganic film during high-temperature processes after lamination of the inorganic film. Therefore, it is desirable that the 1% weight loss temperature of the polyimide is 500°C or higher, and that the weight loss rate when the polyimide is isothermally maintained at a temperature in the range of 400°C to 450°C is less than 1%.

[0066] Furthermore, the inventors of the present invention have found a clear difference in adhesion between a polyimide film containing fluorine atoms and a polyimide film not containing fluorine atoms. This is thought to be due to the significantly lower surface free energy of the polyimide film containing fluorine atoms. Therefore, in order to prevent peeling of the polyimide film from the inorganic film in a high-temperature process, it is preferable that the polyimide contain a small amount of fluorine atoms, and it is more preferable that the polyimide be derived from a monomer not containing fluorine atoms.

[0067] 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 elements. 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. Furthermore, because the thermal expansion coefficient of a glass substrate is generally lower 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 or electronic element 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 30 MPa or lower, more preferably 25 MPa or lower, and even more preferably 20 MPa or lower.

[0068] 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, a method is often adopted in which an electronic device (specifically, an electronic device in which electronic elements are formed on a polyimide film) is formed on a support as described above, and then the polyimide film is peeled off from the support. In addition, alkali-free glass is suitably used as the material for the support. An example of a method for producing a laminate of a polyimide film and a support will be described in detail below.

[0069] First, a polyamic acid solution according to this embodiment is applied to a support to form a coating film-containing laminate comprising 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 is heated, for example, at a maximum temperature of 200°C to 500°C. The heating time (heating time at the maximum temperature) is, for example, 1 minute to 300 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 250°C to 450°C. A maximum temperature of 250°C or higher allows for sufficient imidization, while a maximum temperature of 450°C or lower can suppress thermal degradation and discoloration of the polyimide. Furthermore, any temperature may be maintained for any time before reaching the maximum temperature. The imidization reaction can be carried out under air, reduced pressure, or an inert gas such as nitrogen. However, to achieve higher transparency, it is preferable to carry out the reaction under reduced pressure or an inert gas such as nitrogen. Furthermore, 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 of the support and the polyimide film (imidized polyamic acid). Furthermore, to shorten the heating time and enhance properties, an imidizing agent or a dehydration catalyst may be added to the polyamic acid solution, and the solution may be heated and imidized by the above-mentioned method.

[0070] 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 peeling the polyimide film by infiltrating a silicon oxide etchant between the substrate and the silicon oxide film can also be employed. Another method of separating the polyimide film by irradiation with laser light can also be employed.

[0071] Lifting at the interface between a polyimide film and a support (e.g., a glass substrate) can cause the polyimide film to peel off during the formation of electronic devices or can reduce yields when the polyimide film is peeled off after the formation of electronic devices. The term "lifting" refers to poor adhesion between a polyimide film and other material layers (e.g., a glass substrate, a barrier film, etc.) due to secondary components (more specifically, elimination components, etc.) generated during imidization or residual solvent. Specific examples of "lifting" include a state in which the polyimide film lifts off the glass substrate, a state in which a portion of the polyimide film is destroyed, causing interlayer delamination between the polyimide film and other material layers, and a state in which a barrier film lifts off the polyimide film. For example, polyimides formed from BPDA and 4-BAAB have highly oriented molecular chains that are densely packed, which makes it difficult for secondary components generated during imidization to escape, making lifting more likely. The inventors' research has revealed that lifting can be prevented by introducing a bulky structure into the molecular chain or at the end. Furthermore, the inventors' investigations have revealed that the combined use of BPAF, which has a bulky structure with a low degree of rotational freedom, and 4-BAAB can achieve both good gas release properties and a high Tg. The polyamic acid according to this embodiment has structural units (1) containing BPAF residues and 4-BAAB residues, which can suppress the occurrence of lifting. Therefore, the polyamic acid according to this embodiment can ensure adhesion to inorganic materials during high-temperature processes.

[0072] The transparency of a polyimide film can be evaluated by its total light transmittance (TT) according to JIS K7361-1:1997 and its 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 haze of the polyimide film is preferably 1.5% or less, more preferably 1.2% or less, even more preferably less than 1.0%, and may even be 0%. In applications requiring high transparency, the polyimide film is required to have high transmittance across the entire wavelength range, but polyimide films tend to absorb light at short wavelengths, often resulting in a yellow coloration of the film itself. When a polyimide film is used in an application requiring high transparency, the yellowness index (YI) of the polyimide film is preferably 25 or less, more preferably 20 or less, even more preferably 15 or less, and may even be 0. The YI can be measured according to JIS K7373-2006. A polyimide film having transparency imparted thereto is suitable for transparent substrates used as a glass substitute, etc., and for substrates having a sensor or camera module provided on the back surface.

[0073] Furthermore, there are two types of light extraction methods for flexible displays: a top-emission method in which light is extracted from the TFT element side, and a bottom-emission method in which light is extracted from the back side of the TFT element. The top-emission method is characterized by its ease of increasing the aperture ratio because light is not blocked by the TFT element, 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 element and the pixel electrode. Since the TFT element is transparent, the aperture ratio can also be improved in the bottom-emission method, so 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.

[0074] 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 more preferable. Here, adhesion refers to adhesion strength. In a fabrication process in which electronic elements or the like are formed on a polyimide film on a 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 viewpoint of improving productivity. Specifically, the peel strength is preferably 0.05 N / cm or more, and more preferably 0.1 N / cm or more.

[0075] 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.

[0076] 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.

[0077] In order 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 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] The content of imidazoles is preferably 0.005 mol to 0.1 mol, more preferably 0.01 mol to 0.08 mol, and even more preferably 0.015 mol to 0.050 mol per mol of amide group in the polyamic acid. By incorporating 0.005 mol or more of imidazoles, the film strength and transparency of the polyimide can be improved, while by incorporating 0.1 mol or less of imidazoles, the Tg and heat resistance of the polyamic acid can be improved while maintaining its storage stability. Regarding the improvement in transparency, polymerization solvents such as NMP are known to form complexes with the carboxyl groups of the polyamic acid through hydrogen bonding. Therefore, if the imidization rate is slow, NMP or the like may remain in the polyimide film and oxidize or decompose, potentially causing discoloration. When imidazoles are added, they coordinate with the carboxyl groups of the polyamic acid and promote imidization, making it difficult for NMP and other substances to remain in the polyimide film. At the same time, decomposition of the polyamic acid during the thermal imidization process is suppressed, which is thought to improve transparency.

[0083] 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).

[0084] The polyamic acid solution according to the present embodiment may contain a silane coupling agent to achieve appropriate adhesion to the support. Although known silane coupling agents may be used without particular limitation, compounds containing an amino group are particularly preferred in terms of reactivity with polyamic acid.

[0085] 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.

[0086] 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.

[0087] The polyimide film according to the present embodiment is heat-resistant, has low thermal expansion, and is transparent. Furthermore, it generates little internal stress when laminated with a glass substrate, ensuring good adhesion to inorganic materials during high-temperature processes. Therefore, it is preferable for use in fields and products where these properties are valuable. 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. In these applications, the thickness of the polyimide film is, for example, 1 μm to 200 μm, preferably 5 μm to 100 μm. The thickness of the polyimide film can be measured using a laser hologram.

[0088] 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]

[0089] Examples of the present invention will be described below, but the scope of the present invention is not limited to the following examples.

[0090] <Methods for measuring and evaluating physical properties> First, methods for measuring and evaluating the physical properties of polyimide will be described.

[0091] [Yellowness (YI)] The polyimide films obtained in the examples and comparative examples described below were measured for transmittance of light with a wavelength of 200 nm or more and 800 nm or less 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.

[0092] [Hayes] The haze of the polyimide films obtained in the examples and comparative examples described below was measured using an integrating sphere haze meter ("HM-150N" manufactured by Murakami Color Research Laboratory) according to the method described in JIS K7136-2000.

[0093] Internal Stress Each polyamic acid solution prepared in the following Examples and Comparative Examples was spin-coated onto 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. The substrate was then heated in air at 120°C for 30 minutes, followed by heating in a nitrogen atmosphere at 430°C for 30 minutes 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 at 25°C in a nitrogen atmosphere using a thin film stress analyzer (KLA-Tencor FLX-2320-S). The internal stress generated between the glass substrate and the polyimide film was calculated using the Stoney equation based on the warpage of the glass substrate before the polyimide film formation and the warpage of the laminate.

[0094] [Glass transition temperature (Tg)] A 3 mm wide, 10 mm long sample was prepared from the polyimide films obtained in the Examples and Comparative Examples described below to obtain samples for Tg measurement. Using a thermal analyzer (Hitachi High-Tech Science Corporation, "TMA / SS7100"), a load of 98.0 mN was applied to the obtained samples, and the temperature was raised from 20°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).

[0095] [1% weight loss temperature (TD1)] Polyimide films (samples) obtained in the examples and comparative examples described below were heated 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).

[0096] [Whether or not there is a gap between the glass substrate and the polyimide film] Each polyamic acid solution prepared in the Examples and Comparative Examples described below was applied to a Corning glass substrate (material: alkali-free glass, thickness: 0.7 mm, size: 100 mm × 100 mm) using a spin coater, heated in air at 120°C for 30 minutes, and then heated in a nitrogen atmosphere at 430°C for 30 minutes to obtain a laminate comprising a 10 μm-thick polyimide film on the glass substrate. The obtained laminate was visually inspected for any floating between the glass substrate and the polyimide film.

[0097] [Whether or not there is a gap between the SiOx film and the polyimide film] Each polyamic acid solution prepared in the Examples and Comparative Examples described below was applied to a Corning glass substrate (material: alkali-free glass, thickness: 0.7 mm, size: 100 mm x 100 mm) using a spin coater, and the substrate was heated in air at 120°C for 30 minutes, followed by heating in a nitrogen atmosphere at 430°C for 30 minutes to form a 10 μm thick polyimide film on the glass substrate. Next, a SiOx film (thickness: 1 μm) was laminated on the resulting polyimide film by plasma CVD, and the resulting laminate was heated in a nitrogen atmosphere at 430°C for 60 minutes. The laminate after heating was then visually inspected for any floating between the SiOx film and the polyimide film.

[0098] <Preparation of polyimide film> The methods for producing polyimide films (laminates) 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 synthesis was carried out 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 4-BAAB: 4-aminophenyl-4-aminobenzoate PDA: p-phenylenediamine TFMB: 2,2'-bis(trifluoromethyl)benzidine DMI: 1,2-dimethylimidazole

[0099] [Example 3] A 300 mL glass separable flask equipped with a stainless steel stirrer and a nitrogen inlet tube was charged with 39.6 g of NMP as the polymerization organic solvent. Next, while stirring the contents of the flask, 3.030 g of 4-BAAB was added to the flask and dissolved. Next, 0.183 g of BPAF was added to the flask, followed by 3.788 g of BPDA. The contents of the flask were stirred for 24 hours at 25°C to obtain a polyamic acid solution. The resulting polyamic acid solution was applied to a glass substrate (manufactured by Corning Incorporated, material: alkali-free glass, thickness: 0.7 mm, size: 100 mm x 100 mm) using a spin coater and heated in air at 120°C for 30 minutes, followed by heating in a nitrogen atmosphere at 430°C for 30 minutes to obtain a laminate comprising a 10 μm-thick polyimide film on the glass substrate.

[0100] [Example 4] A 300 mL glass separable flask equipped with a stainless steel stirrer and a nitrogen inlet tube was charged with 39.6 g of NMP as the polymerization organic solvent. Next, while stirring the contents of the flask, 3.030 g of 4-BAAB was added to the flask and dissolved. Next, 0.183 g of BPAF was added to the flask, followed by 3.788 g of BPDA. The contents of the flask were stirred for 24 hours under an atmosphere at 25°C. Next, 1 part by weight of DMI was added to the flask per 100 parts by weight of polyamic acid in the flask to obtain a polyamic acid solution. The resulting polyamic acid solution was applied to a glass substrate (manufactured by Corning Incorporated, material: alkali-free glass, thickness: 0.7 mm, size: 100 mm x 100 mm) using a spin coater and heated in air at 120°C for 30 minutes, followed by heating in a nitrogen atmosphere at 430°C for 30 minutes to obtain a laminate comprising a 10 μm-thick polyimide film on the glass substrate.

[0101] [Examples 1, 5, 7, 9 and 11] Laminates having a 10 μm-thick polyimide film on a glass substrate were obtained in the same manner as in Example 3, except that the charging ratio of BPAF and BPDA was changed to the ratio shown in Table 1. In all of Examples 1, 5, 7, 9, and 11, the total amount of acid dianhydride was the same as in Example 3.

[0102] [Examples 2, 6, 8, 10 and 12] Laminates having a 10 μm-thick polyimide film on a glass substrate were obtained in the same manner as in Example 4, except that the charging ratio of BPAF and BPDA was changed to the ratio shown in Table 1. In all of Examples 2, 6, 8, 10, and 12, the total amount of acid dianhydride was the same as in Example 4.

[0103] [Examples 13 and 15] Laminates having a 10 μm-thick polyimide film on a glass substrate were obtained in the same manner as in Example 3, except that the charging ratio of BPAF and BPDA was changed to the ratio shown in Table 1, and that 4-BAAB and PDA were used as diamines for synthesizing polyamic acid in the ratio shown in Table 1. In both Examples 13 and 15, the total amount of dianhydrides and the total amount of diamines were the same as in Example 3.

[0104] [Examples 14 and 16] Laminates having a 10 μm-thick polyimide film on a glass substrate were obtained in the same manner as in Example 4, except that the charging ratio of BPAF and BPDA was changed to the ratio shown in Table 1, and that 4-BAAB and PDA were used as diamines for synthesizing polyamic acid in the ratios shown in Table 1. In both Examples 14 and 16, the total amount of dianhydrides and the total amount of diamines were the same as in Example 4.

[0105] [Example 17] A laminate having a 10 μm-thick polyimide film on a glass substrate was obtained in the same manner as in Example 4, except that PMDA was used instead of BPDA and that BPAF and PMDA were used in the charging ratio shown in Table 1. The total amount of acid dianhydrides used in Example 17 was the same as that used in Example 4.

[0106] [Comparative Example 1] A 300 mL glass separable flask equipped with a stainless steel stirrer and a nitrogen inlet tube was charged with 39.6 g of NMP as the polymerization organic solvent. Next, while stirring the contents of the flask, 3.058 g of 4-BAAB was added to the flask and dissolved. Next, 3.942 g of BPDA was added to the contents of the flask, and the contents of the flask were stirred for 24 hours under an atmosphere at 25°C to obtain a polyamic acid solution. The resulting polyamic acid solution was applied to a glass substrate (manufactured by Corning Incorporated, material: alkali-free glass, thickness: 0.7 mm, size: 100 mm x 100 mm) using a spin coater, heated in air at 120°C for 30 minutes, and then heated in a nitrogen atmosphere at 430°C for 30 minutes to obtain a laminate comprising a 10 μm-thick polyimide film on the glass substrate.

[0107] Comparative Example 2 A 300 mL glass separable flask equipped with a stainless steel stirrer and a nitrogen inlet tube was charged with 39.6 g of NMP as the polymerization organic solvent. Next, while stirring the contents of the flask, 3.058 g of 4-BAAB was added to the flask and dissolved. Next, 3.942 g of BPDA was added to the flask, and the contents were stirred for 24 hours under an atmosphere at 25°C. Next, 1 part by weight of DMI was added to the flask per 100 parts by weight of the polyamic acid in the flask to obtain a polyamic acid solution. The resulting polyamic acid solution was applied to a glass substrate (manufactured by Corning Incorporated, material: alkali-free glass, thickness: 0.7 mm, size: 100 mm x 100 mm) using a spin coater, heated in air at 120°C for 30 minutes, and then heated in a nitrogen atmosphere at 430°C for 30 minutes to obtain a laminate comprising a 10 μm-thick polyimide film on the glass substrate.

[0108] Comparative Example 3 Except for using PDA instead of 4-BAAB, a laminate having a 10 μm-thick polyimide film on a glass substrate was obtained in the same manner as in Comparative Example 1. The molar amount of PDA used in Comparative Example 3 was the same as that of 4-BAAB used in Comparative Example 1.

[0109] Comparative Example 4 Except for using TFMB instead of 4-BAAB, a laminate comprising a 10 μm-thick polyimide film on a glass substrate was obtained by the same method as in Comparative Example 2. The molar amount of TFMB used in Comparative Example 4 was the same as that of 4-BAAB used in Comparative Example 2.

[0110] Comparative Example 5 A laminate comprising a 10 μm-thick polyimide film on a glass substrate was obtained by the same method as in Example 4, except that TFMB was used instead of 4-BAAB and the charging ratio of BPAF to BPDA was changed to the ratio shown in Table 1. The molar amount of TFMB used in Comparative Example 5 was the same as the molar amount of 4-BAAB used in Example 4. The total molar amount of the acid dianhydrides used in Comparative Example 5 was the same as the total molar amount of the acid dianhydrides used in Example 4.

[0111] Table 1 shows the materials used and their proportions for each of Examples 1 to 17 and Comparative Examples 1 to 5, and Table 2 shows the physical properties and evaluations. In Table 1, "-" indicates that the corresponding component was not used. In Table 1, the values ​​in the "Acid Dianhydride" column indicate the content (unit: mol%) of each acid dianhydride relative to the total amount of acid dianhydrides used. In Table 1, the values ​​in the "Diamine" column indicate the content (unit: mol%) of each diamine relative to the total amount of diamines used. In addition, the values ​​in the "Additive" column indicate the amount of additive added (unit: parts by weight) relative to 100 parts by weight of polyamic acid in the flask content.

[0112] [Table 1]

[0113] [Table 2]

[0114] As described above, in this example, in which polyamic acid having the structural unit (1) was used, all of the following conditions (1) to (4) were satisfied. (1) TD1 exceeds 500°C. (2) YI is 25 or less. (3) The internal stress is 30 MPa or less. (4) Tg is greater than 400°C.

[0115] In Comparative Examples 1 and 2, Tg and TD1 were high, but the haze was high, and separation occurred between the glass substrate and the polyimide film. In Comparative Example 3, Tg and TD1 were high, but the YI was high, and separation occurred between the glass substrate and the polyimide film. In Examples 1 to 17, Tg and TD1 were high, and the YI and haze were low. Furthermore, in Examples 1 to 17, there was no separation between the glass substrate and the polyimide film, and there was no separation between the SiOx film and the polyimide film.

[0116] In Comparative Examples 4 and 5, which contained fluorine atoms, the YI was low, but lifting occurred between the SiOx film and the polyimide film.

[0117] The above results demonstrate that the polyimide obtained from the polyamic acid according to the present invention has excellent transparency and heat resistance, and can ensure adhesion to inorganic materials during high-temperature processes.

Claims

1. It contains a structural unit represented by the following chemical formula (1) and a structural unit represented by the following general formula (2), A polyamic acid having only 4-aminophenyl-4-aminobenzoate residues as diamine residues, or having 4-aminophenyl-4-aminobenzoate residues and p-phenylenediamine residues as diamine residues. 【Chemical 1】 【Chemistry 2】 (In the general formula (2), X represents a tetravalent organic group different from the tetracarboxylic dianhydride residue in the chemical formula (1).)

2. 2. The polyamic acid according to claim 1, wherein X in the general formula (2) is at least one selected from the group consisting of a tetravalent organic group represented by the following chemical formula (3) and a tetravalent organic group represented by the following chemical formula (4): 【Chemistry 3】

3. 3. The polyamic acid according to claim 1, wherein the content of the structural unit represented by the chemical formula (1) is 1 mol % or more based on all structural units.

4. The polyamic acid according to any one of claims 1 to 3, wherein a substance amount ratio obtained by dividing the total substance amount of tetracarboxylic dianhydride residues by the total substance amount of diamine residues is 0.900 or more and less than 1.

100.

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

6. A polyimide which is an imidized product of the polyamic acid according to any one of claims 1 to 4.

7. 7. The polyimide according to claim 6, which has a 1% weight loss temperature of 500°C or higher.

8. 8. The polyimide according to claim 6, which has a glass transition temperature of 400°C or higher.

9. A polyimide film comprising the polyimide according to any one of claims 6 to 8.

10. 10. The polyimide film according to claim 9, having a yellowness index of 25 or less.

11. 11. The polyimide film according to claim 9 or 10, having a haze of less than 1.0%.

12. A laminate comprising a support and the polyimide film according to any one of claims 9 to 11.

13. A method for producing a laminate having a support and a polyimide film, comprising the steps of: A method for producing a laminate, comprising applying the polyamic acid solution according to claim 5 onto a support to form a coating film containing the polyamic acid, and heating the coating film to imidize the polyamic acid.

14. An electronic device comprising the polyimide film according to any one of claims 9 to 11 and an electronic element disposed on the polyimide film.

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