Resin composition, method for producing resin composition, and polyimide film

Abstract

Provided is a resin composition which contains a polyimide precursor that comprises a pyromellitic acid-derived structure, a 3,3',4,4'-biphenyl tetracarboxylic acid-derived structure, and a 2,2'-bis(trifluoromethyl)benzidine-derived structure, and a first solvent. In a 19F-NMR spectrum of the polyimide precursor, when the chemical shift of elemental fluorine of a trifluoroacetic acid group is -76.55 ppm, the peak height (P1) at a chemical shift value of -58.585 ppm, the peak height (P2) at a chemical shift value of -58.550 ppm, and the peak height (P3) at a chemical shift value of -58.515 ppm satisfy the relationship of formula (1).　Formula (1): (P1 + P3) / P2 < 0.65

Description

Resin composition, method for producing the resin composition, and polyimide film

[0001] This invention relates to a resin composition, a method for producing a resin composition, and a polyimide film.

[0002] In recent years, there has been active development of technologies to form functional elements such as display elements on transparent polyimide films, with the aim of making these electronic devices lighter, smaller, thinner, more flexible, and more transparent.

[0003] When forming functional elements such as display elements on the surface of a polyimide film, it is considered ideal to process them using a so-called roll-to-roll process that utilizes the flexibility inherent in polyimide film. However, in industries such as the display industry, process technologies have so far been developed for rigid planar substrates such as wafer-based or glass substrate-based substrates. Therefore, in order to form functional elements on a polyimide film using existing infrastructure, a process is employed in which the polyimide film is bonded to a rigid support made of inorganic material such as a glass plate, ceramic plate, silicon wafer, or metal plate (hereinafter sometimes referred to as an inorganic substrate), the desired element is formed on it, and then it is peeled off from the support.

[0004] In the process of forming a desired functional element on a laminate formed by bonding a polyimide film to an inorganic support, the laminate is often exposed to high temperatures. For example, the formation of functional elements such as polysilicon and oxide semiconductors requires processes in a temperature range of approximately 200°C to 600°C. Furthermore, in the fabrication of hydrogenated amorphous silicon thin films, temperatures of approximately 200°C to 300°C may be applied to the film, and heating to approximately 450°C to 600°C may be necessary to heat and dehydrogenate amorphous silicon to produce low-temperature polysilicon. Therefore, the polyimide film constituting the laminate must have sufficient heat resistance to withstand these conditions. In addition, if there is a large difference in the coefficient of linear thermal expansion (hereinafter sometimes abbreviated as CTE) between the polyimide film and the inorganic material constituting the laminate, warping will occur in the laminate, hindering element formation. Therefore, the difference in CTE between the polyimide film and the inorganic material must be kept as small as possible. Generally, inorganic materials have low CTE, so the polyimide film must also have correspondingly low CTE characteristics.

[0005] Many polyimide resins with high heat resistance and low CTE properties are insoluble and infusible. Therefore, when manufacturing molded articles such as polyimide films made from polyimide resins with high heat resistance and low CTE properties, a manufacturing method that involves a soluble polyimide precursor resin is often used. When manufacturing a polyimide film using this method, for example, it is manufactured by the following process: First, a polyimide precursor resin solution is manufactured, then it is uniformly coated onto a support, and a portion of the solvent is evaporated to manufacture a polyimide precursor film. Next, the polyimide precursor film is peeled from the support, and both ends of the film in the width direction are fixed with pins or clips, and heat treatment is performed while it is transported in a heat treatment furnace, thereby removing the residual solvent and allowing the imidation reaction to proceed to manufacture a polyimide film. Here, when heat treatment is performed while transporting the polyimide precursor film in a heat treatment furnace with both ends fixed with pins or clips, a tensile load acts between the ends of the polyimide precursor film due to the removal of the residual solvent and shrinkage accompanying the progress of the imidation reaction, so the polyimide precursor film needs to have sufficient strength to prevent tearing, etc.

[0006] Patent Document 1 describes a resin composition comprising a polyamic acid, which is a polyimide precursor with a weight-average molecular weight of 110,000 to 250,000, and a solvent, with a solid content of 10 to 25% by mass. The resin composition contains 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (hereinafter sometimes abbreviated as s-BPDA) and pyromellitic acid dianhydride (hereinafter sometimes abbreviated as PMDA) as tetracarboxylic acid dianhydrides, and a fixed amount of 2,2'-bis(trifluoromethyl)benzidine (hereinafter sometimes abbreviated as TFMB) and 3,3'-diaminosulfone or 4,4'-diaminosulfone as diamines, and has a solid content of 10 to 25% by mass. The description states that the resin composition has excellent slit coating properties, and that the polyimide film obtained by curing the resin composition has excellent mechanical and optical properties.

[0007] Patent Document 2 describes a resin composition comprising a polyamic acid containing s-BPDA and PMDA as tetracarboxylic dianhydrides and TFMB as a diamine, and a solvent, wherein the solution viscosity at a solid content concentration of 15% by mass and a temperature of 25°C is approximately 5,800 to 100,000 cP. Although the objective of Patent Document 2 is to obtain a white polyimide film, a transparent polyimide film is described as a comparative example. It is described that when imidizing the resin composition, if the temperature at which the imidization rate reaches 80% or more is relatively high (220°C or higher), the final polyimide film becomes white, but if the temperature at which the imidization rate reaches 80% or more is relatively low at 190°C, the final polyimide film is transparent and has a CTE of 32 to 47 ppm / K.

[0008] Patent Document 3 describes a resin composition containing a polyamic acid and a solvent, with a solid content concentration of 15% by mass, which includes derivatives of s-BPDA and PMDA as tetracarboxylic dianhydrides and a certain amount of a derivative of 2,2'-dimethyl-4,4'-diaminobiphenyl as a diamine. The polyimide film obtained by curing this resin composition is described to have a CTE of 10 ppm / K or less and low warpage.

[0009] Patent Document 4 describes that the haze of the resulting film can be reduced by controlling the amount of residual volatile components in the gel film during the film formation of a polyimide film consisting of s-BPDA and TFMB.

[0010] Japanese Patent Publication No. 2022-167930, Japanese Patent Publication No. 2010-235789, Japanese Patent Publication No. 2019-65266, Japanese Patent Publication No. 2012-51995

[0011] Regarding the resin composition in Patent Document 1, the weight-average molecular weight of the polyimide precursor is low, ranging from 110,000 to 250,000. Therefore, when the polyimide precursor film is peeled from the support and then transported through a heat treatment furnace with both ends fixed by pins or clips, it is likely that it does not have sufficient strength to withstand the removal of residual solvent and the shrinkage associated with the progress of the imidation reaction, resulting in tearing or other damage. Furthermore, although the CTE of the polyimide film in Patent Document 1 is not mentioned, it is likely that it does not achieve low CTE characteristics commensurate with the CTE of inorganic materials, given that it contains a flexible structure within the polyimide structure. Regarding the resin composition in Patent Document 2, the weight-average molecular weight is not specified and is therefore unknown. However, since the solution viscosity is approximately 5,800 to 100,000 cP at a solid content concentration of 15% by mass, the weight-average molecular weight is thought to be low. Therefore, when the polyimide precursor film is peeled from the support and then transported through a heat treatment furnace with both ends fixed by pins or clips, it is thought that it will not have sufficient strength to withstand the removal of residual solvent and the shrinkage associated with the progress of the imidation reaction, resulting in tearing or other damage. Furthermore, the transparent polyimide film described in Patent Document 2 has a high CTE, and it has not yet achieved low CTE characteristics that match those of inorganic materials.

[0012] On the other hand, polyimides can exhibit crystalline properties depending on the combination of diamine and acidic dianhydride used as raw materials. For example, polyimides composed of s-BPDA and TFMB can also exhibit crystalline properties, and when crystalline particles are formed through crystallization, the haze increases due to light scattering depending on the size of the particles. Conventional polyimides were mainly used for molded products and printed circuit boards, so the occurrence of haze was not a major problem. However, when used as a substitute for glass, the occurrence of haze reduces light transmittance, so there is a need for means to suppress haze generation. Patent Document 3 does not describe transparency for the polyimide film, and it is unclear whether this invention can also achieve transparency. The transparent polyimide film described in Patent Document 4 suppresses the generation of haze due to crystallization during imidization, but the haze in the examples is 2 or higher, which is still higher than that of glass, and does not have sufficient transparency.

[0013] As described above, Patent Documents 1 to 4 do not disclose a polyimide film that simultaneously possesses transparency, heat resistance, low CTE characteristics, and mechanical properties at a level suitable for use as a base film for flexible devices such as flexible displays. Furthermore, they do not disclose a resin composition containing a polyimide precursor having the molecular weight necessary to produce a polyimide film without tearing when the polyimide precursor film is peeled from a support and then transported through a heat treatment furnace with both ends fixed by pins or clips, nor do they disclose a method for producing such a resin composition.

[0014] The present invention aims to provide a polyimide film that is excellent in transparency, heat resistance, low CTE properties, and mechanical properties, and in particular has low haze and is extremely transparent, and to provide a resin composition for producing a polyimide film that does not tear, a method for producing the resin composition, and a polyimide film that is excellent in transparency, heat resistance, low CTE properties, and mechanical properties, and in particular has low haze and is extremely transparent.

[0015] As a result of diligent research, the inventors have discovered a polyimide precursor resin composition having a specific solution viscosity, comprising at least a polyimide precursor resin having a specific chemical structure and reduced viscosity, and a solvent, thereby completing the present invention.

[0016] In other words, the present invention has the following configuration. Item 1. A resin composition comprising a polyimide precursor having an acid-based component structure and an amine-based component structure and a first solvent, wherein the acid-based component structure comprises a pyromellitic acid-derived structure and a 3,3',4,4'-biphenyltetracarboxylic acid-derived structure, and the amine-based component structure comprises a 2,2'-bis(trifluoromethyl)benzidine-derived structure, the molar ratio of the pyromellitic acid-derived structure to the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure is 50:50 to 90:10, and the polyimide precursor １９In the F-NMR spectrum, when the chemical shift of the fluorine element of trifluoroacetic acid is set to -76.55 ppm, the peak height at a chemical shift value of -58.585 ppm (P1), the peak height at a chemical shift value of -58.550 ppm (P2), and the peak height at a chemical shift value of -58.515 ppm (P3) satisfy the following relationship (P1 + P3) / P2 < 0.65 ... Equation (1) The resin composition wherein the reduced viscosity of the polyimide precursor in an N,N-dimethylacetamide solution at a temperature of 25.0°C and a concentration of 0.2 g / dL is 3.0 dL / g or more, and the solution viscosity of the resin composition measured at 20°C using an E-type viscometer is 150 Pa·s or more and 300 Pa·s or less. Item 2. A method for producing the resin composition according to Item 1, comprising a step of polymerizing a polyimide precursor by carrying out the following steps I to V in this order. Step I: Replace the inside of the polymerization reaction vessel with an inert gas. Step II: Introduce a second solvent into the polymerization reactor. Step III: Introduce an acidic component and an amine component into the polymerization reactor in an amount such that their concentration is greater than 20% by mass, assuming that they completely react to form a polyimide precursor, and dissolve the acidic component and the amine component while heating and stirring at a temperature of 35°C or higher. Step IV: After confirming the dissolution of the acidic component and the amine component, stop heating and continue stirring. Step V: Add a third solvent four hours or more after the start of step IV. Item 3. A method for producing the resin composition according to item 2, characterized in that the temperature of the polymerization solution is controlled so as not to exceed 55°C in at least the polymerization steps from step III onward. Item 4. A polyimide film obtained from the resin composition according to item 1. Item 5. The polyimide film according to item 4, characterized in that the yellowness value YI (calculated for a film thickness of 15 μm) is 20 or less, the haze is 1.0% or less, the total light transmittance is 85% or more, the 1% weight loss temperature is 450°C or higher, the average coefficient of linear expansion between 50°C and 200°C is -5 to +20 ppm / °C, and the tensile elongation is 10% or more.

[0017] The effects of the present invention are to provide a polyimide film that is excellent in transparency, heat resistance, low CTE properties, and mechanical properties, and in particular has low haze and is extremely transparent, and to provide a resin composition for producing a polyimide film that does not tear, a method for producing the resin composition, and a polyimide film that is excellent in transparency, heat resistance, low CTE properties, and mechanical properties, and in particular has low haze and is extremely transparent.

[0018] The present invention will be described in detail below, but these are only some aspects of the present invention, and the present invention is not limited to these. Unless otherwise specified, "ppm" means "mass ppm".

[0019] <Resin Composition> The resin composition of the present invention is a resin composition comprising a polyimide precursor having an acid-based component-derived structure and an amine-based component-derived structure and a solvent, wherein the acid-based component-derived structure includes a pyromellitic acid derivative-derived structure (hereinafter sometimes abbreviated as pyromellitic acid-derived structure) and a 3,3',4,4'-biphenyltetracarboxylic acid derivative-derived structure (hereinafter sometimes abbreviated as 3,3',4,4'-biphenyltetracarboxylic acid-derived structure), and the amine-based component-derived structure includes a 2,2'-bis(trifluoromethyl)benzidine derivative-derived structure (hereinafter sometimes abbreviated as 2,2'-bis(trifluoromethyl)benzidine-derived structure), the molar ratio of the pyromellitic acid-derived structure to the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure is 50:50 to 90:10, and the polyimide precursor １９In the F-NMR spectrum, when the chemical shift of trifluoroacetic acid is set to -76.55 ppm, the peak height at a chemical shift of -58.585 ppm (height P1), the peak height at a chemical shift of -58.550 ppm (peak P2), and the peak height at a chemical shift of -58.515 ppm (peak P3) satisfy the following relationship: (P1 + P3) / P2 < 0.65 ... Equation (1) The resin composition is characterized in that the reduced viscosity of the polyimide precursor in an N,N-dimethylacetamide solution at a temperature of 25.0°C and a concentration of 0.2 g / dL is 2.0 dL / g or more, and the solution viscosity of the resin composition measured at 20°C using an E-type viscometer is 150 Pa·s or more and less than 300 Pa·s.

[0020] The total ratio of pyromellitic acid-derived structures and 3,3',4,4'-biphenyltetracarboxylic acid-derived structures to acid-based component-derived structures is not particularly limited, but is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 98 mol% or more, particularly preferably 99 mol% or more, and may be 99.5 mol% or more or 100 mol%. Examples of structures included in the acid-based component-derived structures that are neither pyromellitic acid-derived nor 3,3',4,4'-biphenyltetracarboxylic acid-derived structures include structures derived from tetracarboxylic acids and dicarboxylic acids other than the two tetracarboxylic acids mentioned above, as well as their derivatives.

[0021] The pyromellitic acid-derived structure has a rigid backbone and linear structure, which contributes to the high heat resistance and low CTE properties of the resulting polyimide film. However, the pyromellitic acid-derived structure alone results in insufficient strength and poor film-forming properties of the polyimide film. In contrast, the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure has a moderately rigid backbone and linear structure while ensuring a certain degree of polyimide molecular chain mobility. Therefore, it contributes to the development of high strength and toughness without significantly impairing the high heat resistance and low CTE properties of the polyimide film. Furthermore, the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure has a twisted structure, which contributes to the suppression of intramolecular charge transfer complex formation in polyimide, and thus contributes to the high transparency of the resulting polyimide film.

[0022] The ratio (molar ratio) of the pyromellitic acid-derived structure to the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure is preferably 50:50 to 90:10. By setting the molar ratio of the pyromellitic acid-derived structure to the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure within the above range, the strength of the polyimide precursor film, as well as the transparency, heat resistance, low CTE properties, and mechanical properties of the final polyimide film, are better balanced. The preferred ratio (molar ratio) of the pyromellitic acid-derived structure to the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure may vary depending on the desired application, the type of polyimide precursor, the solid content of the resin composition, the type of solvent the resin composition may contain, etc., but is preferably 55:45 to 85:15, 60:40 to 80:20, 60:40 to 75:25, or 60:40 to 70:30.

[0023] The ratio of the 2,2'-bis(trifluoromethyl)benzidine-derived structure to the amine-derived structure is not particularly limited, but is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 98 mol% or more, particularly preferably 99 mol% or more, and may be 99.5 mol% or more or 100 mol%. Examples of structures included in the amine-derived structure that are not derived from 2,2'-bis(trifluoromethyl)benzidine include structures derived from diamines other than the diamines listed above.

[0024] The 2,2'-bis(trifluoromethyl)benzidine-derived structure has a rigid skeleton and linear structure, which contributes to the high heat resistance and low CTE properties of the final polyimide film. Furthermore, the 2,2'-bis(trifluoromethyl)benzidine-derived structure has a side chain with highly electron-withdrawing and bulky trifluoromethyl groups, as well as a twisted structure, which contributes to the suppression of intramolecular and intermolecular charge transfer complex formation in polyimides, and thus contributes to the high transparency of the final polyimide film.

[0025] The polyimide precursor of the present invention is １９In the F-NMR spectrum, when the chemical shift of trifluoroacetic acid is set to -76.55 ppm, the peak height at a chemical shift of -58.585 ppm (P1), the peak height at a chemical shift of -58.550 ppm (P2), and the peak height at a chemical shift of -58.515 ppm (P3) satisfy the following relationship (1): (P1 + P3) / P2 < 0.65 ... (1) (P1 + P3) / P2 is an index related to the ratio of the chain consisting of the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure and the 2,2'-bis(trifluoromethyl)benzidine-derived structure to the entire polymer chain consisting of the pyromellitic acid-derived structure, the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure, and the 2,2'-bis(trifluoromethyl)benzidine-derived structure. A high (P1 + P3) / P2 ratio indicates a high ratio of chains consisting of structures derived from 3,3',4,4'-biphenyltetracarboxylic acid and structures derived from 2,2'-bis(trifluoromethyl)benzidine. (P1 + P3) / P2 is preferably greater than 0 and less than 0.65, more preferably 0.10 to 0.63, even more preferably 0.20 to 0.60, and may also be 0.30 to 0.60.

[0026] For the polyimide precursor in the present invention １９When performing F-NMR measurements, a peak originating from the element F of the trifluoromethyl group in the 2,2'-bis(trifluoromethyl)benzidine-derived structure is detected when the chemical shift of trifluoroacetic acid is set to -76.55 ppm. When the acidic component structures bonded to both sides of the 2,2'-bis(trifluoromethyl)benzidine-derived structure are both 3,3',4,4'-biphenyltetracarboxylic acid-derived structures, three peaks are detected with peaks at -58.585 ppm, -58.550 ppm, and -58.515 ppm. On the other hand, when the acidic component structures bonded to both sides of the 2,2'-bis(trifluoromethyl)benzidine-derived structure are both pyromellitic acid-derived structures, a peak is detected at -58.550 ppm, but no peaks are detected at -58.585 ppm and -58.515 ppm. Furthermore, when one of the acidic component-derived structures bonded to either side of the 2,2'-bis(trifluoromethyl)benzidine-derived structure is a 3,3',4,4'-biphenyltetracarboxylic acid-derived structure and the other is a pyromellitic acid-derived structure, a peak is detected at -58.550 ppm, but no peaks are detected at -58.585 ppm and -58.515 ppm.

[0027] Therefore, the peak height of P1 + P3, the molecular term in formula (1), increases with the amount of chemical structures in which both acidic component structures bonded to the 2,2'-bis(trifluoromethyl)benzidine-derived structure are 3,3',4,4'-biphenyltetracarboxylic acid-derived structures. On the other hand, the amount of chemical structures in which both acidic component structures bonded to the 2,2'-bis(trifluoromethyl)benzidine-derived structure are pyromellitic acid-derived structures, or where one adjacent structure is 3,3',4,4'-biphenyltetracarboxylic acid-derived and the other adjacent structure is pyromellitic acid-derived, does not affect the peak height of P1 + P3, the molecular term in formula (1). Furthermore, the denominator term P2 in formula (1) increases in proportion to the amount of chemical structures in which both acid component structures bonded to the 2,2'-bis(trifluoromethyl)benzidine-derived structure are 3,3',4,4'-biphenyltetracarboxylic acid-derived structures, as well as the amount of chemical structures in which both acid component structures bonded to the 2,2'-bis(trifluoromethyl)benzidine-derived structure are pyromellitic acid-derived structures, and chemical structures in which one adjacent structure is 3,3',4,4'-biphenyltetracarboxylic acid-derived and the other adjacent structure is pyromellitic acid-derived structures.

[0028] Furthermore, the reason why three peaks are detected when the acidic component structures bonded to both sides of the 2,2'-bis(trifluoromethyl)benzidine-derived structure are both 3,3',4,4'-biphenyltetracarboxylic acid-derived structures is unclear. However, it is speculated that this is based on three patterns in which the two carboxyl groups in the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure bonded to the 2,2'-bis(trifluoromethyl)benzidine-derived structure are located: at the 3,3' position, at the 4,4' position, and at the 3,4' position.

[0029] If the polyimide precursor of the present invention does not satisfy formula (1), the randomness of the chain state of the polyimide precursor becomes low (i.e., the blocking property becomes high). When the randomness of the chain state of the polyimide precursor becomes low, the proportion of chain states in which 3,3',4,4'-biphenyltetracarboxylic acid-derived structures are bonded to both sides of a 2,2'-bis(trifluoromethyl)benzidine-derived structure increases. However, the imide obtained from chains in which 3,3',4,4'-biphenyltetracarboxylic acid-derived structures are bonded to both sides of a 2,2'-bis(trifluoromethyl)benzidine-derived structure tends to grow locally, and as a result of growing to a size that affects light scattering, the haze becomes significantly high, and it is thought that a polyimide film with excellent transparency cannot be obtained.

[0030] The weight-average molecular weight of the polyimide precursor in the present invention is not particularly limited, but is preferably 260,000 to 1,000,000, more preferably 280,000 to 900,000, even more preferably 300,000 to 800,000, and particularly preferably 320,000 to 700,000. Having a molecular weight within this range ensures sufficient strength to withstand tensile loads caused by evaporation of residual solvent during heat treatment and shrinkage associated with the progression of the imidation reaction during film formation. Furthermore, it allows for adjustment to a solution viscosity with excellent coating properties. The preferred weight-average molecular weight may vary depending on the desired application, the type of polyimide precursor, the solid content of the resin composition, the type of solvent the resin composition may contain, and so on.

[0031] The reduced viscosity of the polyimide precursor in the present invention is not particularly limited, but is preferably 3.0 dL / g or more and 6.0 dL / g or less, more preferably 3.25 to 4.75, and even more preferably 3.5 to 4.5. Having a reduced viscosity within this range allows the polyimide precursor film to have sufficient strength to withstand the tensile loads caused by the evaporation of residual solvent during heat treatment and shrinkage associated with the progress of the imidation reaction, thus enabling the production of a high-quality polyimide film. Furthermore, the solution viscosity can be adjusted to provide excellent coating properties.

[0032] In the present invention, the molecular weight distribution Mw / Mn, which is the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn of the polyimide precursor, is not particularly limited, but is preferably 1.0 to 5.0, more preferably 1.5 to 4.5, and even more preferably 2.0 to 4.0. By setting the molecular weight distribution within the above range, the heat resistance of the final polyimide film can be further improved.

[0033] The type of first solvent contained in the resin composition of the present invention is not particularly limited, but examples include N,N-dimethylformamide, N,N-dimethylacetamide (hereinafter sometimes abbreviated as DMAc), N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as NMP), N-methyl-ε-caprolactam, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, 3-methyl-2-oxazolidone, hexamethylphosphoramide, γ-butyrolactone (hereinafter sometimes abbreviated as GBL), and these may be used alone or in combination of two or more. In addition, poor solvents such as toluene and xylene may be used in combination with these solvents to the extent that the resin solids do not precipitate.

[0034] In the present invention, the concentration of the polyimide precursor in the resin composition is preferably 5 to 20% by mass. By setting the concentration of the polyimide precursor within an appropriate range, it becomes easier to achieve an appropriate thickness for the polyimide precursor film or the final polyimide film, making it easier to obtain a polyimide film that is less prone to tearing during film formation and has sufficient mechanical strength. Furthermore, suppressing tearing during the film formation process increases manufacturing efficiency and lowers manufacturing costs. In addition, the solution viscosity of the resin composition becomes within an appropriate range, making it easier to perform uniform coating. The preferred concentration of the polyimide precursor may vary depending on the desired application, the type of polyimide precursor, the weight-average molecular weight, the type of solvent contained in the resin composition, etc., but is preferably 7 to 19% by mass, more preferably 9 to 18% by mass, and even more preferably 11 to 17% by mass or less.

[0035] The resin composition in the present invention may contain an imidation accelerator. The type of imidation accelerator is not particularly limited, and two or more compounds may be used in combination. Examples of suitable imidation accelerators include basic catalysts such as pyridine compounds, azole compounds, and tertiary amine compounds, and acidic catalysts such as benzoic acid. Examples of the pyridine compounds include isoquinoline, 1-methylisoquinoline, 4-dimethylaminopyridine, 2,2'-bipyridyl, nicotinic acid, pyridine, 4-phenylpyridine, 4-hydroxypyridine, and 2-methylpyridine. Examples of the azole compounds include 1-methylimidazole, N-tert-butoxycarbonylimidazole (N-Boc-imidazole), 2-methylimidazole, 2-phenylimidazole, benzimidazole, 2-ethyl-4-methylimidazole, 4-ethyl-2-methylimidazole, 4-methyl-2-phenylimidazole, 2-undecylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1H-imidazole, 1,2-dimethylimidazole, triazole, and benzotriazole. Examples of tertiary amine compounds include 1,8-diazabicyclo[5.4.0]-7-undecene, 1,5-diazabicyclo[4.3.0]nonene-5, and 1,4-diazabicyclo[2.2.2]octane. Examples of acidic catalysts include tetrazole, p-hydroxybenzoic acid, o-hydroxybenzoic acid, p-hydroxyphenylacetic acid, 2,4-dihydroxybenzoic acid, 4-hydroxyphenylpropionic acid, p-phenolsulfonic acid, p-aminophenol, m-aminobenzoic acid, and p-aminobenzoic acid.

[0036] The content of the imidation accelerator is not particularly limited, but is preferably 0.2 to 4.0 moles per mole of the repeating structure of the polyimide precursor, more preferably 0.5 to 3.5 moles, even more preferably 0.8 to 3.0 moles, still more preferably 1.0 to 2.5 moles, and particularly preferably 1.1 to 2.0 moles. By setting the content of the imidation accelerator within the above range, the storage stability of the resin composition can be appropriately maintained, while the mechanical strength of the film can be maintained at a higher level during film formation, especially during heat treatment, and the flatness of the film can be maintained at a higher level. Furthermore, the mechanical strength of the final polyimide film can be further improved, and the flatness can be maintained at a higher level.

[0037] The resin composition in the present invention may contain inorganic fillers, surfactants, and other functional additives, as long as they do not impair the properties of the polyimide film. The amount of functional additives is not particularly limited, but it is preferably 10% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, relative to the polyimide precursor in the resin composition.

[0038] The solution viscosity of the resin composition in the present invention, when measured at 20°C using an E-type viscometer, is 100 Pa·s or more and 300 Pa·s or less. By setting the solution viscosity within the above range, the occurrence of uneven coating thickness and coating streaks can be suppressed during the coating process when forming a polyimide precursor film from the resin composition, resulting in a more uniform coating film. The preferred range of solution viscosity may vary depending on the desired application, the type of polyimide precursor, the solid content of the resin composition, the type of solvent the resin composition may contain, etc., but for example, it may be 110 to 280 Pa·s, 120 to 260 Pa·s, or 130 to 240 Pa·s.

[0039] <Method for Producing Resin Composition> The method for producing a resin composition according to the present invention is not particularly limited, but it is preferable that the step of polymerizing a polyimide precursor comprises the following Steps I to V performed in this order in the step of polymerizing the polyimide precursor in the resin composition. Step I: replacing the inside of the polymerization reaction vessel with an inert gas Step II: introducing a second solvent into the polymerization reactor Step III: introducing an acid-based component and an amine-based component into the polymerization reactor in an amount such that the concentration thereof would be more than 20% by mass when it is assumed that both components completely react to form a polyimide precursor, and dissolving the raw materials while heating and stirring at a temperature of 35°C or higher Step IV: stopping heating after confirming dissolution of the raw materials, and continuing stirring Step V: adding a third solvent after 4 hours or more have elapsed since the completion of Step IV

[0040] <Step I> The inert gas used in Step I is not particularly limited, and for example, nitrogen gas, helium gas, neon gas, rare gases such as argon gas, and the like are preferable. Replacing the inside of the polymerization reaction vessel with an inert gas reduces the amounts of moisture and oxygen in the polymerization reaction vessel, which leads to suppression of deactivation of the acid-based component and the amine-based component in the subsequent polymerization step, and as a result, the degree of polymerization is likely to increase.

[0041] <Step II> The type of the second solvent in Step II is not particularly limited, and examples thereof include N,N-dimethylformamide, N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), N-methyl-ε-caprolactam, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, 3-methyl-2-oxazolidinone, hexamethylphosphoramide, γ-butyrolactone (GBL), and the like. These may be used alone or in combination of two or more thereof. In addition, along with these solvents, a poor solvent such as toluene or xylene may be used in combination in an amount such that resin solids do not precipitate in the subsequent polymerization step.

[0042] The water content of the solvent in the step II is not particularly limited, but from the viewpoint of increasing the molecular weight of the polyimide precursor, a lower water content is preferred. For example, it is preferably 200 ppm by mass or less, more preferably 150 ppm by mass or less, still more preferably 100 ppm by mass or less, and may be 50 ppm by mass or less. Setting the water content of the solvent within the above range can suppress the deactivation of the acid-based component in the subsequent polymerization step, and as a result, the degree of polymerization of the polyimide precursor tends to increase.

[0043] <Step III> The pyromellitic acid derivative in the acid-based component is not particularly limited, but pyromellitic acid, or acid chlorides, esterified products and acid anhydrides thereof are preferred; acid anhydrides are more preferred, and pyromellitic dianhydride (PMDA) is even more preferred.

[0044] The 3,3',4,4'-biphenyltetracarboxylic acid derivative in the acid-based component is not particularly limited, but 3,3',4,4'-biphenyltetracarboxylic acid, or acid chlorides, esterified products and acid anhydrides thereof are preferred; acid anhydrides are more preferred, and 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) is even more preferred.

[0045] The 2,2'-bis(trifluoromethyl)benzidine derivative in the amine-based component is not particularly limited, but 2,2'-bis(trifluoromethyl)benzidine, or silylated products and amidated products thereof are preferred, and 2,2'-bis(trifluoromethyl)benzidine (TFMB) is more preferred.

[0046] The polyimide precursor may contain acidic components other than pyromellitic acid derivatives and 3,3',4,4'-biphenyltetracarboxylic acid derivatives. Examples of such acidic components include aromatic tetracarboxylic acid derivatives, aliphatic tetracarboxylic acid derivatives, and alicyclic tetracarboxylic acid derivatives. Among these, aromatic tetracarboxylic acid derivatives and alicyclic tetracarboxylic acid derivatives are preferred, aromatic tetracarboxylic acid derivatives are more preferred from the viewpoint of heat resistance, and alicyclic tetracarboxylic acid derivatives are more preferred from the viewpoint of transparency. These may be used individually or in combination of two or more types.

[0047] Examples of aromatic tetracarboxylic acid derivatives include 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid, 4,4'-oxydiphthalic acid, 3,4'-oxydiphthalic acid, bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylic acid)1,4-phenylene, bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-yl)benzene-1,4-dicarboxylate, and 4,4'-[4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(benzene-1,4-diyloxy)]dibenzate n-1,2-dicarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 4,4'-[(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(1,4-xylene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(4-isopropyl [4,4'-(3-oxo-1,3-dihydro-2-benzofuran-1,1-diyl)bis(naphthalene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxatiol-1,1-dioxide-3,3-diyl)bis(benzene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-benzophenonetetracarboxylic acid, 4,4'-[(3H-2,1-benzoxatiol- 1,1-dioxide-3,3-diyl)bis(toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(1,4-xylene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(4-isopropyl-toluene-2,5-diyloxy)]dibenzene-1,2-dicarboxylic acid, 4,4'-[4,4'-(3H-2,Examples include tetracarboxylic acids such as 1-benzoxathiol-1,1-dioxide-3,3-diyl)bis(naphthalene-1,4-diyloxy)]dibenzene-1,2-dicarboxylic acid, 3,3',4,4'-diphenylsulfonetetracarboxylic acid, 2,3,3',4'-biphenyltetracarboxylic acid, 2,2',3,3'-biphenyltetracarboxylic acid, 2,2'-diphenoxy-4,4',5,5'-biphenyltetracarboxylic acid, 4,4'-[spiro(xanthene-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)]diphthalic acid, and 4,4'-[spiro(xanthene-9,9'-fluorene)-3,6-diylbis(oxycarbonyl)]diphthalic acid, as well as their acid chlorides, esters, and acid anhydrides. Furthermore, examples include double-decker type silsesquioxane derivatives containing an acid anhydride group, represented by the structure of the following chemical formula (1).

[0048]

[0049] Examples of alicyclic tetracarboxylic acid derivatives include 1,2,3,4-cyclobutanetetracarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, 1,2,3,4-cyclohexanetetracarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, 3,3',4,4'-bicyclohexyltetracarboxylic acid, bicyclo[2,2,1]heptane-2,3,5,6-tetracarboxylic acid, bicyclo[2,2,2]octane-2,3,5,6-tetracarboxylic acid, and bicyclo[2,2,2]octo-7-ene-2,3,5,6-tetracarboxylic acid. Rubonic acid, tetrahydroanthracene-2,3,6,7-tetracarboxylic acid, tetradecahydro-1,4:5,8:9,10-trimethanoanthracene-2,3,6,7-tetracarboxylic acid, decahydronaphthalene-2,3,6,7-tetracarboxylic acid, decahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid, decahydro-1,4-ethano-5,8-methanonaphthalene-2,3,6,7-tetracarboxylic acid, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane ¾-5,5'',6,6''-tetracarboxylic acid (also known as "norbornane-2-spiro-2'-cyclopentanone-5'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid"), methylnorbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-(methylnorbornane)-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclohexanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid (also known as "norbornane-2-s Pyrro-2'-cyclohexanone-6'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid), methylnorbornane-2-spiro-α-cyclohexanone-α'-spiro-2''-(methylnorbornane)-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclopropanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclobutanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cycloheptanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclooctanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclononanone-α'-spiro-2''-norbornane-5,5'',6 ,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclodecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cycloundecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclododecanone-α'-spiro-2''-norbornane-5,5'' Examples include 6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclotridecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclotetradecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-cyclopentadecanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, norbornane-2-spiro-α-(methylcyclopentanone)-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid, and acid chlorides, esters, and acid anhydrides thereof.

[0050] The content of acidic components other than pyromellitic acid derivatives and 3,3',4,4'-biphenyltetracarboxylic acid derivatives is not particularly limited, but when the total amount of all acidic components is taken as 100 mol%, the content of acidic components other than pyromellitic acid derivatives and 3,3',4,4'-biphenyltetracarboxylic acid derivatives is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, even more preferably 2 mol% or less, particularly preferably 1 mol% or less, and may be 0.5 mol% or less or 0 mol%.

[0051] The acidic component may further include dicarboxylic acids. Examples of dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 4,4'-oxydibenzenecarboxylic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, glutaric acid, adipic acid, heptanediic acid, octanedioic acid, azelaic acid, sebacic acid, undecadioic acid, dodecanediic acid, 2-methylsuccinic acid, and maleic acid; and acid chlorides, esters, and anhydrides of these.

[0052] The content of dicarboxylic acids is not particularly specified, but it is preferable that the content of dicarboxylic acids be 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, even more preferably 5 mol% or less, and particularly preferably 1 mol% or less, and may be 0.5 mol% or less or 0 mol%.

[0053] The polyimide precursor may contain diamines other than 2,2'-bis(trifluoromethyl)benzidine derivatives as amine components. Examples of such amine components include aromatic diamine derivatives, aliphatic diamine derivatives, and alicyclic diamine derivatives. Among these, aromatic diamine derivatives are preferred from the viewpoint of heat resistance, and alicyclic diamine derivatives are preferred from the viewpoint of transparency. Diamines other than 2,2'-bis(trifluoromethyl)benzidine derivatives may be used alone or in combination of two or more types.

[0054] Examples of aromatic diamine derivatives include 2,2'-dimethyl-4,4'-diaminobiphenyl, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 4-amino-N-(4-aminophenyl)benzamide, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 2,2'-trifluoromethyl- 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diamino Benzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, bis[4-(4-aminophenoxy)phenyl]methane, 1,1-bis[4-(4-aminophenoxy)phenyl]ethane, 1,2-bis[4-(4-aminophenoxy)phenyl]ethane, 1,1-bis[4-(4-aminophenoxy)phenyl]propane, 1,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,1-bis[4-(4-aminophenoxy)phenyl]butane, 1,3-bis[4-(4-aminophenoxy)phenyl]butane, 1,4-bis[4-(4-aminophenoxy)phenyl]butane, 2,2-bis[4-(4-aminophenoxy)phenyl]butane, 2,3-bis[4-(4-aminophenoxy)phenyl]butane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3-methylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane [nophenoxy)-3-methylphenyl]propane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis( 4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfoxide, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4- Bis[4-(3-aminophenoxy)benzoyl]benzene, 4,4'-bis[(3-aminophenoxy)benzoyl]benzene, 1,1-bis[4-(3-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)phenyl]propane, 3,4'-diaminodiphenyl sulfide, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, bis[4-(3-aminophenoxy)phenyl]methane, 1,1-bis[4-(3-aminophenoxy)phenyl]ethane, 1,2-bis[4-(3-aminophenoxy)phenyl]ethane, bis[4-(3-aminophenoxy)phenyl]sulfoxide, 4,4'-bis[3-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[3-(3-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenylsulfone, bis[4-{4-(4-aminophenoxy)pheno [Xy}phenyl]sulfone, 1,4-bis[4-(4-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-trifluoromethylphenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-fluorophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-methylphenoxy)-α,α-dimethylbenzyl]benzene , 1,3-bis[4-(4-amino-6-cyanophenoxy)-α,α-dimethylbenzyl]benzene, 3,3'-diamino-4,4'-diphenoxybenzophenone, 4,4'-diamino-5,5'-diphenoxybenzophenone, 3,4'-diamino-4,5'-diphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4-phenoxybenzophenone, 3,4'-diamino-5'-phenoxybenzophenone, 3,3'-diamino-4, 4'-Dibiphenoxybenzophenone, 4,4'-Diamino-5,5'-Dibiphenoxybenzophenone, 3,4'-Diamino-4,5'-Dibiphenoxybenzophenone, 3,3'-Diamino-4-Biphenoxybenzophenone, 4,4'-Diamino-5-Biphenoxybenzophenone, 3,4'-Diamino-4-Biphenoxybenzophenone, 3,4'-Diamino-5'-Biphenoxybenzophenone, 1,3-Bis(3-amino-4-phenoxybenzoyl)benzene, 1,4-Bis(3-amino-4-phenoxybenzoyl)benzene, 1,3-bis(4-amino-5-phenoxybenzoyl)benzene, 1,4-bis(4-amino-5-phenoxybenzoyl)benzene, 1,3-bis(3-amino-4-biphenoxybenzoyl)benzene, 1,4-bis(3-amino-4-biphenoxybenzoyl)benzene, 1,3-bis(4-amino-5-biphenoxybenzoyl)benzene, 1,4-bis(4-amino-5-biphenoxybenzoyl)benzene, 2,6-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzonitrile, 4,4'-[9H-fluorene-9,9-diyl]bisaniline (also known as "9,9-bis(4-aminophenyl)fluorene"), spiro(xanthene-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)]bisaniline, 4,4'-[spiro(xanthene-9,9'-fluorene)-2,6-diylbis(oxycarbonyl)] Examples include bisaniline (xycarbonyl), 4,4'-[spiro(xanthene-9,9'-fluorene)-3,6-diylbis(oxycarbonyl)]bisaniline, 9,10-bis(4-aminophenyl)adenine, 2,4-bis(4-aminophenyl)cyclobutane-1,3-dicarboxylate dimethyl, aromatic diamines having a benzoxazole structure, amino group-containing double-decker type silsesquioxane derivatives represented by the structure of the following chemical formula (2), and aromatic diamines in which some or all of the hydrogen atoms on the aromatic ring of the above aromatic diamine are substituted with halogen atoms, C1-C3 alkyl or alkoxyl groups, cyano groups, or C1-C3 halogenated alkyl or alkoxyl groups in which some or all of the hydrogen atoms of the alkyl or alkoxyl group are substituted with halogen atoms, and their silylates, amidates, etc. Furthermore, there are no particular limitations on the aromatic diamines having the benzoxazole structure, and for example, 5-amino-2-(p-aminophenyl)benzoxazole, 6-amino-2-(p-aminophenyl)benzoxazole, 5-amino-2-(m-aminophenyl)benzoxazole, 6-amino-2-(m-aminophenyl)benzoxazole, 2,2'-p-phenylenebis(5-aminobenzoxazole), 2,2'-p-phenylenebis(6-aminobenzoxazole), 1-(5-aminobenzoxazolo)-4-(6-aminobenzoxazolo)benzene, 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, 2,6-(3,4'-diaminodi Examples include phenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,6-(3,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, 2,6-(3,3'-diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, and 2,6-(3,3'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole. These may be used individually or in combination of two or more types.

[0055]

[0056] Examples of alicyclic diamine derivatives include alicyclic diamines such as 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-propylcyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-butylcyclohexane, 1,4-diamino-2-tert-butylcyclohexane, and 4,4'-methylenebis(2,6-dimethylcyclohexylamine), as well as their silylated and amidated derivatives. These may be used individually or in combination of two or more.

[0057] The content of amine components other than the 2,2'-bis(trifluoromethyl)benzidine derivative is not particularly limited, but when the total amount of all amine components is taken as 100 mol%, the content of diamines other than the 2,2'-bis(trifluoromethyl)benzidine derivative is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, even more preferably 2 mol% or less, particularly preferably 1 mol% or less, and may be 0.5 mol% or less or even 0 mol%.

[0058] In step III, the amounts of acidic and amine components introduced are preferably such that, assuming they react completely to form a polyimide precursor, their concentration is greater than 20% by mass. More preferably, it is greater than 23% by mass, and even more preferably greater than 26% by mass. In a typical example of the present invention, s-BPDA is used as the acidic component and TFMB as the amine component. However, since s-BPDA and TFMB, especially TFMB, have low reactivity, polymerization takes a long time. As a result, the total amount of polymerization inhibitors (such as water and oxygen) entering from outside the system during the polymerization process increases, and as a result, the degree of polymerization tends to be difficult to increase. Therefore, by focusing on the initial concentrations of the acidic and amine components and adjusting the amounts of acidic and amine components introduced in step III to the above concentration range, it was found that the polymerization reaction rate increased and the polymerization time could be shortened. Shortening the polymerization time also leads to a reduction in the total amount of polymerization inhibitors entering from outside the system, and it was possible to increase the achievable degree of polymerization. As a result, a polyimide precursor was obtained in which the reducing viscosity in an N,N-dimethylacetamide solution at a temperature of 25.0°C and a concentration of 0.2 g / dL was 3.0 dL / g or higher. Although there is no particular upper limit to the amount of acidic and amine components introduced in step III, it is preferable that the concentration of the polyimide precursor in step III is 40% by mass or less, as the solubility of the acidic and amine components deteriorates as the concentration of the polyimide precursor increases, and furthermore, the viscosity of the polymerization solution increases, making stirring for polymerization homogenization difficult.

[0059] In step III, the method for introducing the acidic and amine components is not particularly limited. Examples include introducing the acidic and amine components together, introducing the amine component first and then the acidic component, or introducing the acidic component first and then the amine component. However, the preferred method for obtaining a polyimide precursor that satisfies formula (1) is to introduce the acidic and amine components together. In a typical example of the present invention, PMDA and s-BPDA are used as the acidic components, and TFMB is used as the amine component. Since these are all powdered solids, they may stick together during or after introduction. This sticking delays the dissolution of the raw materials, prolonging the polymerization process. Furthermore, the degree of sticking varies each time, leading to lot-to-lot differences in the polymerization progress, which is undesirable in terms of productivity. Furthermore, since the dissolution rate of s-BPDA is extremely slow compared to PMDA and TFMB, when PMDA, TFMB, and s-BPDA coexist in the system, the reaction between PMDA and TFMB proceeds first, and TFMB, which is the reaction partner of s-BPDA, is consumed without s-BPDA contributing to the reaction. As a result, the dissolution rate of s-BPDA slows down even further, and the degree of polymerization does not increase. Therefore, it is preferable to prevent PMDA, s-BPDA, and TFMB from becoming fixed, and to dissolve s-BPDA as quickly as possible. One way to achieve this is to heat the reaction system when introducing PMDA, s-BPDA, and TFMB, or immediately after introducing them. However, if heating is performed in a state where moisture can easily penetrate the system, the acid anhydride moieties of PMDA and s-BPDA will open, making it difficult for both to contribute to the polymerization reaction, and as a result, the degree of polymerization will not increase easily. Therefore, to avoid this, it is preferable to heat the system after ensuring that moisture does not easily penetrate it. The preferred temperature during heating is not particularly limited, but 35°C or higher is preferred, 40°C or higher is more preferred, and 45°C or higher is even more preferred. The upper limit of the temperature is also not particularly limited, but 55°C or lower is preferred. As a method of ensuring that moisture does not easily penetrate the system, the ring opening of the raw materials before polymerization can be prevented by weighing the raw materials and solvent in an environment where the absolute humidity is controlled to 1% or less.

[0060] In step III, if the amine system contains two or more components, including the 2,2'-bis(trifluoromethyl)benzidine derivative, the method for introducing the amine components is not particularly limited. Examples include introducing all amine components, including the 2,2'-bis(trifluoromethyl)benzidine derivative, at once, or introducing the 2,2'-bis(trifluoromethyl)benzidine derivative first and then introducing all amine components other than the 2,2'-bis(trifluoromethyl)benzidine derivative at once. The time from introducing the 2,2'-bis(trifluoromethyl)benzidine derivative to introducing all amine components other than the 2,2'-bis(trifluoromethyl)benzidine derivative at once varies depending on the acidic and amine components used, their ratio, solvent, etc., but is typically preferably within 30 minutes, more preferably within 15 minutes, even more preferably within 10 minutes, and still more preferably within 5 minutes.

[0061] The method for introducing the pyromellitic acid derivative and the 3,3',4,4'-biphenyltetracarboxylic acid derivative, which are acidic components, in step III is not particularly limited, but examples include a method of introducing the pyromellitic acid derivative and the 3,3',4,4'-biphenyltetracarboxylic acid derivative at the same time, a method of introducing the 3,3',4,4'-biphenyltetracarboxylic acid derivative first and then introducing the pyromellitic acid derivative, and a method of introducing the pyromellitic acid derivative first and then introducing the 3,3',4,4'-biphenyltetracarboxylic acid derivative. The time from introducing the 3,3',4,4'-biphenyltetracarboxylic acid derivative first to introducing the pyromellitic acid derivative, or from introducing the pyromellitic acid derivative first to introducing the 3,3',4,4'-biphenyltetracarboxylic acid derivative, varies depending on the acidic components used, their ratio, solvent, etc., but is typically 30 minutes or more, more preferably 15 minutes or less, even more preferably 10 minutes or less, even more preferably 5 minutes or less, and particularly preferably 1 minute or less.

[0062] <Step IV> In Step IV, it is preferable to stop heating and stir after confirming that the raw materials have dissolved. The temperature during stirring is not particularly limited, but it is preferably 55°C or lower, more preferably 50°C or lower, and even more preferably 45°C or lower. If the temperature is raised unnecessarily high, the depolymerization of the polyimide precursor will proceed, making it difficult to increase the degree of polymerization, and thus making it difficult to obtain a polyimide precursor with a reduced viscosity of 3.0 dL / g or higher.

[0063] <Step V> Step V is preferably carried out at least four hours after Step IV, more preferably at least five hours after Step IV, and even more preferably at least six hours after Step V. In a typical example of the present invention, s-BPDA is used as the acidic component and TFMB as the amine component. However, since s-BPDA and TFMB, especially TFMB, have low reactivity, polymerization takes a long time. As a result, the total amount of polymerization inhibitors (such as water and oxygen) entering from outside the system during the polymerization process increases, and as a result, the degree of polymerization tends to be difficult to increase. Therefore, by focusing on the initial concentrations of the acidic and amine components and adjusting the amounts of the acidic and amine components introduced in Step III to reach the aforementioned concentration range, it was found that the polymerization reaction rate increased and the polymerization time could be shortened. Shortening the polymerization time also leads to a reduction in the total amount of polymerization inhibitors entering from outside the system, and it was possible to increase the achievable degree of polymerization. Furthermore, by performing step IV at least four hours after step III, it became even easier to obtain a polyimide precursor having a reduced viscosity of 3.0 dL / g or more in an N,N-dimethylacetamide solution at a temperature of 25.0°C and a concentration of 0.2 g / dL.

[0064] The amount of the third solvent added in step V is not particularly limited, but it is preferable to add an amount such that the concentration of the polyimide precursor in the resin composition becomes 5 to 20% by mass. The solvent can be added in multiple steps.

[0065] The type of third solvent in step V is not particularly limited, but examples include N,N-dimethylformamide, N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), N-methyl-ε-caprolactam, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, 3-methyl-2-oxazolidone, hexamethylphosphoramide, γ-butyrolactone (GBL), etc. These may be used alone or in combination of two or more. In addition, a poor solvent such as toluene or xylene may be used in combination with these solvents to the extent that the resin solids do not precipitate. Furthermore, the type of second solvent used in step II and the type of third solvent used in step V may be the same or different.

[0066] The water content of the solvent in step V is not particularly limited, but from the viewpoint of increasing the molecular weight of the polyimide precursor, a lower amount is preferable. For example, it is preferably 200 ppm by mass or less, more preferably 150 ppm by mass or less, even more preferably 100 ppm by mass or less, and still more preferably 50 ppm by mass or less. If water is present, the acidic components are deactivated by hydrolysis, making it difficult to increase the degree of polymerization. However, by keeping the water content of the solvent within the above range, the amount of deactivation of tetracarboxylic dianhydride can be suppressed, and as a result, the degree of polymerization of the polyimide precursor can be increased, making it easier to obtain a polyimide precursor with a weight-average molecular weight of 260,000 to 1,000,000. Similarly, for the same reason, the water content of the raw materials other than the solvent is preferably 3,000 ppm by mass or less, and more preferably 1,000 ppm by mass or less.

[0067] The water content of the second solvent in step II and the third solvent in step V is thought to be affected by the grade of the solvent used, the solvent container, the storage conditions, and the time elapsed between opening and use. It is also thought to be affected by factors such as the replacement of the reaction vessel with an inert gas before polymerization and the presence or absence of inert gas flow during polymerization. Therefore, when polymerizing polyimide precursors, it is recommended to use high-purity raw materials, solvents with low water content, and measures to prevent water from the external environment from entering the system before and during the reaction.

[0068] The molar ratio (acid / amine ratio) of the acidic component to the amine component when polymerizing the polyimide precursor in the resin composition of the present invention is not particularly limited, but is preferably 0.990 to 1.010, more preferably 0.992 to 1.008, even more preferably 0.994 to 1.006, and still more preferably 0.996 to 1.004. Setting the acid / amine ratio within the above range makes it easier to increase the degree of polymerization of the polyimide precursor.

[0069] The temperature at which the polyimide precursor contained in the resin composition of the present invention is polymerized is not particularly limited, but heating may be used as necessary when dissolving the acidic or amine-based component in the solvent. However, if the temperature is raised unnecessarily, the depolymerization of the polyimide precursor will proceed, making it difficult to increase the molecular weight to the specified molecular weight. The temperature at which the acidic or amine-based component is dissolved is preferably 30 to 55°C, more preferably 35 to 50°C, and even more preferably 40 to 45°C.

[0070] The heating time when polymerizing the polyimide precursor contained in the resin composition of the present invention is not particularly limited, but heating may be performed as necessary when dissolving the acidic or amine-based components in the solvent. However, if the temperature is kept high for a long time, the depolymerization of the polyimide precursor will progress, making it difficult to increase the molecular weight to the specified molecular weight. Therefore, it is desirable to limit the heating to the stage of dissolving the raw materials in the initial stages of polymerization. The optimal time for dissolving the acidic or amine-based components may vary depending on the heating temperature, but it is preferably 20 to 180 minutes, more preferably 30 to 120 minutes, and even more preferably 40 to 90 minutes.

[0071] The polymerization time for polymerizing the polyimide precursor contained in the resin composition of the present invention is preferably in the range of 6 to 72 hours. More preferably, the polymerization time is set within this range of 8 to 48 hours. By setting the polymerization time within this range, sufficient time can be provided for polymerization to proceed, and polymerization can be carried out with minimal influence from the inflow of water, oxygen, etc. into the system, thereby obtaining a high molecular weight polyimide precursor. Furthermore, from the viewpoint of productivity, a polymerization time of 72 hours or less is preferable.

[0072] The polymerization of the polyimide precursor contained in the resin composition of the present invention is preferably carried out under an inert gas atmosphere. The inert gas is not particularly limited, but examples include nitrogen gas, helium gas, neon gas, argon gas, and other noble gases.

[0073] <Polyimide Film> A polyimide film can be obtained from the resin composition of the present invention. The method for producing the polyimide film is not particularly limited, but preferred embodiments are as described below. Furthermore, the physical properties of the polyimide film are not particularly limited, but preferred embodiments are as follows.

[0074] The thickness of the polyimide film in the present invention is not particularly limited, but is preferably in the range of 1 to 50 μm, and more preferably in the range of 5 to 20 μm.

[0075] In the present invention, the yellowness value YI of the polyimide film, calculated based on a film thickness of 15 μm, is preferably 20.0 or less, more preferably 15.0 or less, and even more preferably 10.0 or less. When YI is 20.0 or less, it can be suitably used in flexible devices and flexible displays where transparency is required. The lower limit of YI is not particularly limited.

[0076] The haze of the polyimide film in the present invention is preferably 2.0% or less, more preferably 1.7% or less, and even more preferably 1.5% or less. When the haze is 2.0% or less, it can be suitably used as a component of flexible devices where transparency is required, particularly as a component of flexible displays. The lower limit of the haze is not particularly limited.

[0077] The total light transmittance of the polyimide film in the present invention is preferably 85% or higher, more preferably 86% or higher, even more preferably 87% or higher, and still more preferably 88% or higher. When the total light transmittance is 85% or higher, it can be suitably used as a component of a flexible device where transparency is required, particularly as a component of a flexible display. There is no particular upper limit to the total light transmittance.

[0078] The average coefficient of linear expansion (CTE) of the polyimide film in the present invention between 50°C and 200°C is preferably -5 to +20 ppm / °C, more preferably -4 to +15 ppm / °C, and even more preferably -3 to +10 ppm / °C. When the CTE is within the above range, in the process of forming a desired functional element on the laminate side surface of a laminate formed by bonding an inorganic support and a polyimide film, large warping does not occur, there is no hindrance to element formation, and the processability is excellent.

[0079] The tensile strength of the polyimide film in the present invention is preferably 150 MPa or more, more preferably 200 MPa or more, even more preferably 250 MPa or more, and still more preferably 300 MPa or more. If the tensile strength is 150 MPa or more, it becomes less likely to break during processing of functional elements, etc., and the handling properties are improved. There is no particular upper limit to the tensile strength, but it is preferably 1000 MPa or less, more preferably 900 MPa or less, and even more preferably 800 MPa or less.

[0080] The tensile modulus of the polyimide film in the present invention is preferably 2 GPa or higher, more preferably 4 GPa or higher, and even more preferably 6 GPa or higher. If the tensile modulus is 2 GPa or higher, it becomes less susceptible to tensile deformation during processing of functional elements, etc., resulting in superior handling. The upper limit of the tensile modulus is not particularly limited, but it is preferably 20 GPa or lower, more preferably 18 GPa or lower, and even more preferably 16 GPa or lower.

[0081] The tensile elongation at break of the polyimide film in the present invention is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. If the tensile elongation at break is 10% or more, appropriate flexibility can be ensured in processing processes for functional elements, etc., resulting in better handling. The upper limit of the tensile elongation at break is not particularly limited, but it is preferably 200% or less, more preferably 180% or less, and even more preferably 160% or less.

[0082] The glass transition temperature of the polyimide film in the present invention is preferably 350°C or higher, more preferably 360°C or higher, even more preferably 370°C or higher, still more preferably 380°C or higher, and particularly preferably 390°C or higher. A glass transition temperature of 350°C or higher allows the film to be applied to processes requiring high-temperature processing, such as the formation of functional elements.

[0083] <Method for producing polyimide film> The method for producing polyimide film, which is a cured product of the resin composition in the present invention, is not particularly limited, but preferably includes a step α in which a resin composition containing a polyimide precursor is coated onto a support and a portion of the solvent is dried to produce a polyimide precursor film, and a step β in which the polyimide precursor film is peeled from the support and subjected to a dehydration ring-closing reaction while removing the solvent by heat treatment with the edges fixed.

[0084] The support used in step α is not particularly limited, but examples include resin film substrates, stainless steel belt substrates, and glass substrates. As the resin film substrate, it is preferable to use a resin film substrate that does not swell or dissolve in the solvent contained in the resin solution, such as polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, polyolefin (PO) film, and cycloolefin (COP) film. Furthermore, it is preferable to use a support that is easily peelable in order to peel the resin film containing the solvent from the support.

[0085] In step α, the method for coating the support with the resin composition is not particularly limited, but examples include die coating, comma coating, blade coating, roll coating, knife coating, and bar coating, and two of these methods may be combined. Comma coating, die coating, or a combination thereof are preferred from the viewpoint of productivity.

[0086] In step α, the method for drying a portion of the solvent of the resin composition on the support is not particularly limited, but examples include forced air drying, hot air drying, infrared heating drying, and heat transfer drying from the support, and two or more of these methods may be combined. The solvent content of the polyimide precursor film obtained by drying a portion of the solvent is preferably 3 to 50% by mass, more preferably 5 to 40% by mass, and even more preferably 7 to 30% by mass. If the solvent content is above the upper limit, the elastic force of the polyimide precursor film becomes too weak, making it difficult to peel from the support, and if it is below the lower limit, the adhesion between the polyimide precursor film and the support becomes too strong, making peeling failures more likely when peeling from the support. However, by setting the solvent content within the above range, peeling from the support becomes easier.

[0087] In step β, the method for peeling the polyimide precursor film from the support is not particularly limited, but examples include mechanically peeling it from the edge during transport, making an incision in the laminate, attaching adhesive tape to one side of the incision, and then peeling it from the tape portion, or vacuum adsorption of one side of the incision in the resin film and then peeling it from that portion.

[0088] In step β described above, the method for fixing the ends of the polyimide precursor film is not particularly limited, but when heat treatment is performed during transport, a tenter-type transport device is generally used. When using a tenter-type transport device, it is preferable to grip both ends of the polyimide precursor film by piercing them with multiple pins of a pin tenter-type transport device. When using a clip tenter-type transport device, it is preferable to grip both ends of the polyimide precursor film by clamping them with multiple clips of a clip tenter-type transport device. It is preferable to fix the polyimide precursor film only at the aforementioned ends. It is also preferable to adjust the pin spacing or clip spacing in the film width direction during transport so that unnecessary slack does not occur in the polyimide precursor film.

[0089] The heating method in step β is not particularly limited, but examples include blowing air, blowing hot air, irradiation with infrared and / or far-infrared rays, and heat transfer from a support, and two or more of these methods may be combined. The maximum heating temperature is not particularly limited, but is preferably 300 to 450°C, more preferably 310 to 400°C, and even more preferably 320 to 380°C. By setting the maximum heating temperature within this range, high mechanical strength and low CTE can be achieved without degrading the YI of the resulting polyimide film. The method of raising the temperature to reach the maximum temperature is not particularly limited, but the temperature may be raised in one step at a predetermined heating rate, or it may be raised in steps to reach the maximum temperature. Furthermore, the heating rate in this case is preferably 300°C / min or less, more preferably 100°C / min or less, even more preferably 40°C / min or less, still more preferably 30°C / min or less, especially more preferably 20°C / min or less, and particularly preferably 10°C / min or less.

[0090] <Applications of Polyimide Film> The polyimide film obtained from the polyimide precursor according to this embodiment can be used, for example, as a semiconductor insulating film, a TFT-LCD insulating film, an electrode protective film, etc. Furthermore, it can be suitably used in the manufacture of flexible devices, particularly as a TFT substrate, a color filter substrate, or a touch panel substrate. Here, examples of flexible devices to which the polyimide film according to this embodiment can be applied include TFT devices for flexible displays, flexible solar cells, flexible touch panels, flexible lighting, flexible batteries, flexible printed circuit boards, flexible color filters, and surface cover lenses for smartphones.

[0091] The present invention will be described in detail below with reference to examples, but is not limited to the following examples. Unless otherwise specified, the measured values ​​in the examples and comparative examples were measured by the following methods.

[0092] <Reduced Viscosity of Polyimide Precursor> A sample solution was prepared by mixing a predetermined amount of resin composition with N,N-dimethylacetamide so that the concentration of the polyimide precursor was 0.2 g / dL. The viscosity was then measured in a constant temperature water bath at 25 ± 1°C using an Ubbelohde-type viscosity tube.

[0093] <Solution Viscosity (η) of Resin Compositions> The viscosity of the resin composition to be measured was measured at 20°C using a temperature-controlled E-type viscometer (RE85U manufactured by Toki Sangyo Co., Ltd.) and a cone rotor with a rotational speed and cone rotor capable of measuring the viscosity of the resin composition. Measurable rotational speeds include, for example, 0.5, 1, 2.5, 5, 10, 20, 50, and 100 rpm. Specific examples of measurable cone rotors include, for example, 1°34' (angle of cone rotor) × R24 (diameter of cone rotor), 1°34' × R12, 0.8° × R24, 0.8° × R12, 3° × R24, 3° × R12, 3° × R17.65, 3° × R14, 3° × R12, and 3° × R9.7.

[0094] <Analysis of the chain state of polyimide precursors> After dissolving 20 mg of varnish with a solid content concentration of 14.5% by mass in 0.7 mL of dimethyl sulfoxide-d6 / trifluoroacetic acid (95 / 5 vol ratio) to prepare the measurement solution, 19Measurements were performed using F-NMR under the following conditions: Instrument: BRUKER AVANCE NEO 500 Resonance frequency: 470.5 MHz Flip angle of detection pulse: 30° Data acquisition time: 1 sec Delay time: 2 sec Proton decoupling: Yes Number of integrations: 64 Measurement temperature: 30°C When the chemical shift of trifluoroacetic acid was set to -76.55 ppm by F-NMR measurement, the chemical shift values ​​of the peak height (P2) were -58.549, -58.549, and -58.551 ppm for n=3, so the chemical shift value of the peak height (P2) was set to -58.550 ppm. The peak heights at chemical shift values ​​of -58.585 ppm (P1), -58.550 ppm (P2), and -58.515 ppm (P3) were defined. The values ​​of (P1) and (P3) were calculated when the height of (P2) was set to 15. The calculated values ​​were obtained by using (P1) + (P3) as the numerator and (P2) as the denominator.

[0095] <Polyimide Film Thickness> The thickness of the polyimide film was measured using a film thickness measuring instrument HKT-1216 (manufactured by Mahr). A 50 mm square piece of film was cut from the center of the film in the width direction, and the film thickness at the center was measured. Samples were taken from three different locations along the length of the film roll, and the average of the three measurements obtained by taking one measurement for each sample was taken as the film thickness.

[0096] <Total Light Transmittance (TT) of Polyimide Film> The total light transmittance (TT) of the film was measured using a HAZEMETER (NDH5000, manufactured by Nippon Denshoku Co., Ltd.). A D65 lamp was used as the light source. A 50 mm square section of film was cut from the center of the film's width direction, and the total light transmittance was measured. Samples were taken from three different locations along the length of the film roll, and the average of the three measurements obtained by taking one measurement for each sample was taken as the total light transmittance (TT) of the film.

[0097] <Haze of Polyimide Film> The haze of the film was measured using a HAZEMETER (NDH5000, manufactured by Nippon Denshoku Co., Ltd.). A D65 lamp was used as the light source. The sampling, measurement, and handling of the measurement results were the same as for the total light transmittance measurement samples described above.

[0098] <Yellowness Index of Polyimide Film (YI) Equivalent to 15 μm Film Thickness> Using a colorimeter (ZE6000, manufactured by Nippon Denshoku Co., Ltd.) and a C2 light source, the tristimulus values ​​XYZ of the film were measured in accordance with ASTM D1925, and the yellowness index (YI) equivalent to a film thickness of 15 μm was calculated using the following formula (where t is the thickness of the polyimide film, unit: μm). The sampling, measurement, and handling of measurement values ​​of the measurement samples were the same as for the total light transmittance measurement samples described above. YI = {100 × (1.28X - 1.06Z) / Y} × 15 / t

[0099] <1% Weight Loss Temperature of Polyimide Film> The measurement was performed using a TGA apparatus (TGA-50, Shimadzu Corporation). A sample of approximately 10 mg was cut from the center of the width direction, placed on an aluminum pan, and measured under a nitrogen atmosphere at a heating rate of 10°C / min. The weight at which the film reached 150°C was used as the baseline, and the temperature at which the weight decreased by 1% was defined as the 1% weight loss temperature.

[0100] <Linear Expansion Coefficient (CTE) of Polyimide Film> Test specimens were cut from polyimide film into strips measuring 15 mm x 4 mm, with the flow direction (MD direction) or width direction (TD direction) as the longitudinal direction. Measurements were performed using a TMA (TMA4000S, BRUKER AXIS). The sample was set in the apparatus with a chuck distance of 10 mm and a load of 5 gf. Under an argon atmosphere, the temperature was raised to 250°C at a heating rate of 20°C / min, and then cooled to 30°C at a rate of 5°C / min. The difference in chuck length / temperature difference was measured at 15°C intervals, such as 200°C to 185°C and 185°C to 170°C, and this measurement was performed up to 50°C. The average of 10 measurements from 200°C to 50°C was calculated and taken as the CTE for that measurement. Each polyimide film sample was measured twice, once in the MD direction and once in the TD direction, and the average value was taken as the CTE of that polyimide film.

[0101] <Tensile Elongation at Break of Polyimide Film> Test specimens were made by cutting polyimide film into strips of 100 mm x 10 mm, with the flow direction (MD direction) or width direction (TD direction) as the longitudinal direction. Six test specimens were cut from the center of the roll film in the width direction, with three points each in the MD direction and TD direction as the longitudinal direction. Tensile elongation at break (unit: %) was measured using a tensile testing machine (Shimadzu Corporation, Autograph®, model name AG-5000A) under the conditions of a temperature of 25°C, a tensile speed of 50 mm / min, and a chuck distance of 40 mm. The average of the six measured values ​​was taken as the tensile elongation at break of the film.

[0102] <Examples of Production of Polyimide Precursor Resin Compositions> <Example 1> After replacing the inside of a reaction vessel equipped with a nitrogen inlet tube, thermometer, and stirring blade with nitrogen, DMAc (691 parts by mass) with a moisture content of 80 ppm was introduced into the reactor under a nitrogen stream. Subsequently, 2,2'-bis(trifluoromethyl)benzidine (TFMB) (144.09 parts by mass), 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) (52.74 parts by mass), and pyromellitic dianhydride (PMDA) (58.65 parts by mass) were sequentially introduced and stirred for 45 minutes in an oil bath with the temperature control function set to 50°C. Upon inspection of the inside, the raw materials were found to be completely dissolved. After that, the reaction vessel was removed from the oil bath and stirred for 6 hours in a 20°C environment. Subsequently, DMAc (816 parts by mass) with a moisture content of 80 ppm was introduced and stirred for 24 hours to obtain resin composition A1. The physical properties of resin composition A1 were as shown in Table 1.

[0103] The degassed resin composition A1 was coated onto the non-slip surface of polyethylene terephthalate film A4100 (manufactured by Toyobo Co., Ltd.) using a comma coater to a thickness such that the final polyimide film thickness would be 15 μm. Next, a heat treatment was performed in a dry atmosphere at 96°C for 10 minutes to obtain a self-supporting film (polyimide precursor film) made of polyimide precursor. The polyimide precursor film was peeled from the support and passed through a pin tenter having a pin sheet with pins arranged on it. The film ends were gripped by inserting them into the pins, and the film was transported while adjusting the spacing between the pin sheets to prevent unnecessary sagging. Heat treatments were then performed in a dry atmosphere at 145°C for 3 minutes, 230°C for 3 minutes, 365°C for 3 minutes, and 355°C for 3 minutes to allow the imidation reaction to proceed. After that, it was cooled to room temperature in 2 minutes, and the parts with poor flatness at both ends of the film were cut off with a slitter to obtain a 10 m polyimide film roll A2 with a width of 680 mm. Furthermore, the film properties of polyimide film roll A2 were as shown in Table 1.

[0104] <Example 2> Resin composition B1 and polyimide film roll B2 were obtained in the same manner as in Example 1, except that the temperature control setting was 45°C and the stirring in the oil bath was 90 minutes. The physical properties and processability of resin composition B1 and the film properties of polyimide film roll B2 are as shown in Table 1.

[0105] <Example 3> After replacing the inside of a reaction vessel equipped with a nitrogen inlet tube, thermometer, and stirring blade with nitrogen, DMAc (682 parts by mass) with a moisture content of 80 ppm was introduced into the reactor under a nitrogen stream. Subsequently, 2,2'-bis(trifluoromethyl)benzidine (144.09 parts by mass), 3,3',4,4'-biphenyltetracarboxylic dianhydride (39.56 parts by mass), and pyromellitic dianhydride (68.43 parts by mass) were sequentially introduced and stirred for 45 minutes in an oil bath with the temperature control function set to 50°C. Upon inspection of the inside, the raw materials were found to be completely dissolved. After that, the reaction vessel was removed from the oil bath and stirred for 6 hours in an environment of 20°C. Subsequently, DMAc (804.8 parts by mass) with a moisture content of 80 ppm was introduced and stirred for 24 hours to obtain resin composition C1.

[0106] A polyimide film roll C2 was obtained using the same method as in Example 1, except that resin composition A1 was replaced with C1. The physical properties and processability of resin composition C1 and the film properties of polyimide film roll C2 are as shown in Table 1.

[0107] <Example 4> After replacing the inside of a reaction vessel equipped with a nitrogen inlet tube, thermometer, and stirring blade with nitrogen, DMAc (448.2 parts by mass) with a moisture content of 80 ppm was introduced into the reactor under a nitrogen stream. Subsequently, 2,2'-bis(trifluoromethyl)benzidine (96.06 parts by mass), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (17.58 parts by mass), and pyromellitic dianhydride (52.14 parts by mass) were sequentially introduced and stirred for 45 minutes in an oil bath with the temperature control function set to 50°C. Upon inspection of the inside, the raw materials were found to be completely dissolved. After that, the reaction vessel was removed from the oil bath and stirred for 6 hours in an environment of 20°C. Subsequently, DMAc (529.3 parts by mass) with a moisture content of 80 ppm was introduced and stirred for 24 hours to obtain resin composition D1.

[0108] A polyimide film roll D2 was obtained using the same method as in Example 1, except that resin composition A1 was replaced with D1. The physical properties and processability of resin composition D1 and the film properties of polyimide film roll D2 are as shown in Table 1.

[0109] <Comparative Example 1> After replacing the inside of a reaction vessel equipped with a nitrogen inlet tube, thermometer, stirring blade, and temperature control function with nitrogen, and setting the temperature control function to 20°C under a nitrogen flow, DMAc (691 parts by mass) with a moisture content of 80 ppm was introduced into the reactor, followed by 2,2'-bis(trifluoromethyl)benzidine (144.09 parts by mass). After 2 minutes, 3,3',4,4'-biphenyltetracarboxylic dianhydride (52.74 parts by mass) was introduced and stirred for 120 minutes. Subsequently, pyromellitic dianhydride (58.65 parts by mass) was introduced and stirred for 4 hours, followed by DMAc (816 parts by mass) with a moisture content of 80 ppm, and stirred for 24 hours to obtain resin composition E1.

[0110] Polyimide film E2 was prepared in the same manner as in Example 1, except that resin composition E1 was used instead of resin composition A1. The physical properties and processability of resin composition E1 and the film properties of polyimide film roll E2 are as shown in Table 1. The film was cloudy, and a transparent polyimide film roll could not be obtained.

[0111] <Comparative Example 2> After replacing the inside of the reaction vessel, which was equipped with a nitrogen inlet tube, a thermometer, and a stirring blade, with nitrogen, DMAc (691 parts by mass) with a moisture content of 80 ppm was introduced into the reactor under a nitrogen stream, and 2,2'-bis(trifluoromethyl)benzidine (144.09 parts by mass) was introduced. After 2 minutes, 3,3',4,4'-biphenyltetracarboxylic dianhydride (52.74 parts by mass) was introduced and the mixture was stirred for 30 minutes in an oil bath with the temperature control function set to 50°C. Then the reaction vessel was removed from the oil bath and pyromellitic dianhydride (58.65 parts by mass) was introduced under a 20°C environment and the mixture was stirred for 5.5 hours. Subsequently, DMAc (816 parts by mass) with a moisture content of 80 ppm was introduced and stirred for 24 hours to obtain resin composition F1.

[0112] Polyimide film F2 was prepared in the same manner as in Example 1, except that resin composition F1 was used instead of resin composition A1. The physical properties and processability of resin composition F1 and the film properties of polyimide film roll F2 are as shown in Table 1. The film was cloudy, and a transparent polyimide film roll could not be obtained.

[0113] <Comparative Example 3> After replacing the inside of a reaction vessel equipped with a nitrogen inlet tube, thermometer, stirring blade, and temperature control function with nitrogen, and setting the temperature control function to 20°C under a nitrogen flow, DMAc (691 parts by mass) with a moisture content of 80 ppm was introduced into the reactor, followed by 2,2'-bis(trifluoromethyl)benzidine (144.09 parts by mass). After 2 minutes, 3,3',4,4'-biphenyltetracarboxylic dianhydride (52.74 parts by mass) and pyromellitic dianhydride (19.55 parts by mass) were sequentially introduced and stirred for 30 minutes. Subsequently, pyromellitic dianhydride (39.10 parts by mass) was introduced and stirred for 5.5 hours, and then DMAc (816 parts by mass) with a moisture content of 80 ppm was introduced and stirred for 24 hours to obtain resin composition G1.

[0114] Polyimide film G2 was prepared in the same manner as in Example 1, except that resin composition A1 was replaced with G1. The physical properties and processability of resin composition G1 and the film properties of polyimide film roll G2 are as shown in Table 1. The film was cloudy, and a transparent polyimide film roll could not be obtained.

[0115] <Comparative Example 4> After replacing the inside of a reaction vessel equipped with a nitrogen inlet tube, thermometer, and stirring blade with nitrogen, DMAc (691 parts by mass) with a moisture content of 80 ppm was introduced into the reactor under a nitrogen stream. Subsequently, 2,2'-bis(trifluoromethyl)benzidine (144.09 parts by mass), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (52.74 parts by mass), and pyromellitic acid dianhydride (58.65 parts by mass) were sequentially introduced over 2 minutes, but the powder adhered to the bottom of the vessel. The mixture was stirred and mixed for 6 hours at 20°C. Subsequently, DMAc (816 parts by mass) with a moisture content of 80 ppm was introduced and stirred for 24 hours to confirm that the adhered powder had dissolved, and resin composition H1 was obtained. The physical properties of resin composition H1 were as shown in Table 1.

[0116] Polyimide film H2 was prepared in the same manner as in Example 1, except that resin composition H1 was used instead of resin composition A1. The physical properties of resin composition H1 and the film properties of polyimide film roll H2 are as shown in Table 1. The film was cloudy, and a transparent polyimide film roll could not be obtained.

[0117] <Comparative Example 5> Resin composition I1 was obtained in the same manner as in Example 1, except that the temperature setting for the temperature control was set to 55°C and the stirring in the oil bath was performed for 90 minutes.

[0118] An attempt was made to produce polyimide film I2 using the same method as in Example 1, except that resin composition I1 was used instead of resin composition A1. The physical properties of resin composition I1 were as shown in Table 1. However, the film broke, and it was not possible to obtain a polyimide film roll.

[0119] <Comparative Example 6> Resin composition J1 was obtained in the same manner as in Example 1, except that the temperature setting of the temperature control was set to 60°C and the stirring in the oil bath was performed for 45 minutes.

[0120] An attempt was made to create polyimide film J2 using the same method as in Example 1, except that resin composition J1 was used instead of resin composition A1. The physical properties of resin composition J1 were as shown in Table 1. However, the film broke, and a transparent polyimide film roll could not be obtained.

[0121]

[0122] In Examples 1 and 2, heating accelerated the reaction between 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2'-bis(trifluoromethyl)benzidine, resulting in rapid dissolution and amide oxidation of 3,3',4,4'-biphenyltetracarboxylic dianhydride. １９ When F-NMR was examined, the peak height originating from the bonding chain between 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 2,2'-bis(trifluoromethyl)benzidine, which is less reactive than pyromellitic dianhydride, was suppressed and low. When films were fabricated using the resin compositions of Examples 1 and 2, polyimide films with excellent transparency were produced. From these results, it is inferred that the polymerization of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride proceeded in parallel with that of pyromellitic dianhydride.

[0123] In Example 3, the proportion of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was reduced compared to Example 1, and it dissolved and polymerization proceeded rapidly by amide oxidation. １９ When F-NMR was examined, the peak height originating from the bonding chain between 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 2,2'-bis(trifluoromethyl)benzidine was low and suppressed. From this result, it is inferred that the polymerization of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride proceeded in parallel with that of pyromellitic acid dianhydride without delay. In Example 4, the blending ratio of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was reduced compared to Example 1, and it dissolved and polymerization proceeded rapidly by amide oxidation. １９Examination by 19F-NMR showed that the peak height derived from the bonded chain of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2'-bis(trifluoromethyl)benzidine was suppressed to a low level. From this result, it is inferred that the polymerization of 3,3',4,4'-biphenyltetracarboxylic dianhydride proceeded in parallel with pyromellitic dianhydride without delay.

[0124] In Comparative Examples 1 to 3, the charging time difference between the two types of acid components is intentionally increased. Comparative Example 4 does not intentionally set a charging time difference between the two types of acid components, but polymerization was carried out at room temperature. The resin composition １９ Examination by 19F-NMR showed that the peak height derived from the bonded chain of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2'-bis(trifluoromethyl)benzidine was higher than that of the resin composition of the examples. When a film was formed using the resin composition, the film became cloudy, and a transparent polyimide film roll could not be obtained. In Comparative Examples 1 to 3, it is inferred that a large amount of block polymer of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2'-bis(trifluoromethyl)benzidine was formed because only 3,3',4,4'-biphenyltetracarboxylic dianhydride reacted with 2,2'-bis(trifluoromethyl)benzidine. It is inferred that crystallization derived from the block polymer of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2'-bis(trifluoromethyl)benzidine occurred during the heat treatment, forming a density difference in the film, and as a result, haze was significantly deteriorated.

[0125] In Comparative Example 4, the starting material was fixed to the bottom of the reaction vessel. This is presumed to be 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, which is poorly soluble in the solvent. Since the fixed starting material reacts gradually from the surface, it is presumed that the reaction between 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 2,2'-bis(trifluoromethyl)benzidine anhydride was delayed compared to the reaction between other acidic components and 2,2'-bis(trifluoromethyl)benzidine. After the reaction between other acidic components and 2,2'-bis(trifluoromethyl)benzidine proceeded, only the reaction between 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 2,2'-bis(trifluoromethyl)benzidine anhydride proceeded, resulting in the formation of a large amount of block polymer of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 2,2'-bis(trifluoromethyl)benzidine. Comparative Examples 5 and 6 attempted to shorten the raw material dissolution time by polymerizing at high temperatures, but the viscosity remained low and stagnant, resulting in dopes with insufficient polymerization. When film formation was attempted, the films fractured, and film formation was not possible. From these results, it is presumed that the reaction between the acid anhydride and water was activated at high temperatures, which significantly affected the deactivation of the raw materials.

[0126] As described above, the polyimide film roll obtained by solution deposition of the polyimide precursor discovered in this invention exhibits excellent heat resistance, low opacity, and high permeability. Therefore, it can be used as a transparent substrate material in manufacturing processes at temperatures above 300°C. It is suitable for use in flexible devices, particularly flexible displays.

Claims

1. A resin composition comprising a polyimide precursor having an acid-based component structure and an amine-based component structure, and a first solvent, wherein the acid-based component structure comprises a pyromellitic acid-derived structure and a 3,3',4,4'-biphenyltetracarboxylic acid-derived structure, and the amine-based component structure comprises a 2,2'-bis(trifluoromethyl)benzidine-derived structure, the molar ratio of the pyromellitic acid-derived structure to the 3,3',4,4'-biphenyltetracarboxylic acid-derived structure is 50:50 to 90:10, and the polyimide precursor １９ In the F-NMR spectrum, when the chemical shift of the fluorine element of trifluoroacetic acid is set to -76.55 ppm, the peak height at a chemical shift value of -58.585 ppm (P1), the peak height at a chemical shift value of -58.550 ppm (P2), and the peak height at a chemical shift value of -58.515 ppm (P3) satisfy the following relationship: (P1 + P3) / P2 < 0.65 ... Equation (1) The resin composition wherein the reduced viscosity of the polyimide precursor in an N,N-dimethylacetamide solution at a temperature of 25.0°C and a concentration of 0.2 g / dL is 3.0 dL / g or more, and the solution viscosity of the resin composition measured at 20°C using an E-type viscometer is 150 Pa·s or more and 300 Pa·s or less.

2. A method for producing a resin composition according to claim 1, comprising a step of polymerizing a polyimide precursor by carrying out the following steps I to V in this order. Step I: Replace the inside of the polymerization reaction vessel with an inert gas. Step II: Introduce a second solvent into the polymerization reactor. Step III: Introduce an acidic component and an amine component into the polymerization reactor in an amount that would result in a concentration greater than 20% by mass if it were assumed that both components completely react to form a polyimide precursor, and dissolve the acidic component and the amine component while heating and stirring at a temperature of 35°C or higher. Step IV: After confirming the dissolution of the acidic component and the amine component, stop heating and continue stirring. Step V: Add a third solvent more than 4 hours after the start of step IV.

3. A method for producing a resin composition according to claim 2, characterized in that the polymerization is carried out by controlling the temperature of the polymerization solution so as not to exceed 55°C in at least the polymerization steps from step III onward.

4. A polyimide film obtained from the resin composition described in claim 1.

5. The polyimide film according to claim 4, characterized in that the yellowness value YI (calculated on a film thickness of 15 μm) is 20 or less, the haze is 1.0% or less, the total light transmittance is 85% or more, the 1% weight loss temperature is 450°C or higher, the average coefficient of linear expansion between 50°C and 200°C is -5 to +20 ppm / °C, and the tensile elongation is 10% or more.

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