Solvent for resin synthesis, method for producing resin using solvent, and composition containing solvent and resin

Abstract

To provide a solvent used for synthesizing a polyimide precursor, a polyamideimide precursor, a polyimide resin, a polyamideimide resin, and the like, the solvent being capable of synthesizing a polymer having a high molecular weight in a short time, causing no clouding of a reaction solution during and after reaction, and having high transparency and storage stability; a method for producing these resins using the solvent; and a composition containing these resins.SOLUTION: There is provided a solvent (C) for synthesis of resins, such as a polyimide precursor, a polyamideimide precursor, a polyimide resin, or a polyamideimide resin, the solvent comprising 10 to 99.9999 mass% of an amide-based solvent (A) and 0.0001 to 5 mass% of a reaction accelerator (B). The reaction accelerator (B) is an aliphatic or aromatic tertiary amine compound having one or more tertiary amino groups in each molecule, and the amide-based solvent (A) includes a compound having a specific structure.

Description

[Technical Field]

[0001] The present invention relates to a solvent for synthesizing resins such as polyimide precursors, polyamideimide precursors, polyimide resins, and polyamideimide resins, a method for producing resins using the solvent, and compositions containing these solvents and resins. [Background technology]

[0002] Polyimides (polyimides, polyamideimides, polyesterimides, polyetherimides, etc.) have a strong molecular structure and excellent heat resistance, as well as mechanical and chemical properties not found in other resins. These high-performance plastics are widely used in a variety of applications, including films, coatings, protective films, electrical insulating materials, bearings, heat-resistant paints, insulating shafts, insulating trays, electronic components, and automotive parts. Aromatic polyimides, synthesized from aromatic diamines and aromatic tetracarboxylic dianhydrides, possess a strong molecular structure and strong intermolecular forces, resulting in the highest thermal, mechanical, and chemical properties of any synthetic resin. They are widely recognized as super engineering plastics. Because polyimides are generally infusible and insoluble, they are synthesized by reacting diamines or diisocyanates with dianhydrides in an organic solvent at low temperatures, typically around room temperature, to synthesize the precursor polyamic acid. The resulting precursor solution is then processed into films and other media, followed by dehydration cyclization (imidization) via heating or chemical reaction. Furthermore, when synthesizing polyimides soluble in organic solvents or thermoplastic polyimides, imidization can be carried out by synthesizing a polyimide precursor and then heating it in the same solvent. To obtain high-performance products from various polyimides, it is necessary to stably synthesize a high-molecular-weight precursor solution (varnish), and the resulting precursor solution must have excellent storage stability (solution stability). Therefore, research into precursor synthesis has also been attracting attention.

[0003] Although the type of appropriate solvent (good solvent) varies depending on the chemical structure of the polyimide, organic polar solvents such as amide solvents are generally used to synthesize polyimide precursors. Amide solvents are known to have excellent dissolving power, high boiling points and flash points, and thermal and chemical stability. However, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAC), which are commonly used in the synthesis of polyimide precursors, are liable to cause inflammation when they come into contact with the skin or eyes, and are also suspected of being carcinogenic and teratogenic, raising concerns about their harmfulness to the human body. NMP in particular poses environmental, toxicological, and / or regulatory (REACH) concerns (Patent Documents 1 and 2).

[0004] In order to solve the problems of amide solvents such as NMP and DMF, such as low safety, N-butyl-2-pyrrolidone (NBP) and 3-methoxy-N,N-dimethylpropanamide (KJCMPA (registered trademark)), which are amide solvents with both high safety and high dissolving power, have recently been attracting attention as solvents for synthesizing a group of polyimides, such as polyimide precursors (Patent Documents 3 and 4). However, because these prior art technologies aimed to use NBP or KJCMPA simply as an alternative solvent to NMP, they were only required to exhibit effects such as dissolving power comparable to conventional NMP, and did not solve the various problems associated with conventional NMP, such as difficulty in elongating the molecular weight of polyimide precursors, low solution stability of polyimide precursors (prone to becoming cloudy), susceptibility to whitening during polyimide film formation, and susceptibility to surface unevenness. On the other hand, there have been reports of using KJCMPA or 3-butoxy-N,N-dimethylpropanamide (KJCBPA (registered trademark)) to solve the problems of whitening and surface unevenness during polyimide film formation (Patent Documents 5 to 7), but these solvents require the use of a mixture of a nonpolar organic solvent, alcohol, or water. However, the introduction of large amounts of alcohol or water containing active hydrogen causes side reactions such as hydrolysis of the acid dianhydride and hydrolysis of the resulting precursor polyamic acid, which results in the unavoidable clouding of the polyimide precursor solution and can actually lead to problems such as the inability to achieve a high molecular weight polyimide precursor.

[0005] Although polyurethane is a plastic material, it is soft like rubber and has excellent tensile strength, abrasion resistance, elasticity, and oil resistance. It is used in a wide variety of industrial products, from everyday items such as sports shoe soles and clothing to industrial materials such as soundproofing, heat insulation, and adhesives, as well as automotive materials such as bumpers and headrests. Polyurethanes can be synthesized using a variety of methods depending on their structure and intended use. However, because the urethanization reaction is an exothermic reaction, many thermoplastic polyurethanes are stably synthesized using solution polymerization. To achieve particularly high molecular weights, polar solvents such as DMF are often used, which can uniformly dissolve the resulting polyurethane. However, as mentioned above, safety issues associated with DMF remain a concern.

[0006] As described above, there is no known solvent that can be suitably used for synthesizing polyamic acids such as polyimide precursors and polyamideimide precursors, polyimides, polyamideimides, polyurethanes, etc., which can efficiently and stably synthesize high-molecular-weight polymers, and which can produce synthetic resins that do not become cloudy during or after the reaction, have high transparency and storage stability, and have excellent adhesion to substrates. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-194025 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-023583 [Patent Document 3] Special Publication No. 2017-517582 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-511935 [Patent Document 5] Japanese Patent Application Publication No. 2017-149796 [Patent Document 6] Japanese Patent Application Publication No. 2017-061603 [Patent Document 7] Japanese Patent Application Publication No. 2017-052877 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a solvent that can efficiently and stably synthesize high-molecular-weight polymers, that can provide synthetic resins that do not become cloudy during or after the reaction, that have high transparency and storage stability, and that have excellent adhesion to substrates, and that can be suitably used in the synthesis of polyamic acids such as polyimide precursors and polyamideimide precursors, polyimides, polyamideimides, polyurethanes, etc., and a method for producing the synthetic resins using the solvent. [Means for solving the problem]

[0009] As a result of extensive research to solve the above problems, the present inventors discovered a solvent for resin synthesis (C) containing an amide solvent (A) and a reaction accelerator (B), and arrived at the present invention.

[0010] That is, the present invention is (1) A solvent for resin synthesis (C) containing 10 to 99.9999 mass% of an amide solvent (A) and 0.0001 to 5 mass% of a reaction accelerator (B), wherein the reaction accelerator (B) is an aliphatic or aromatic tertiary amine compound having one or more tertiary amino groups in the molecule, and the amide solvent (A) is an alkoxy-N-substituted propanamide represented by general formula (1); [ka] (In the formula, R1 to R3 each independently represent a linear alkyl group having 1 to 22 carbon atoms, a branched alkyl group having 3 to 22 carbon atoms, an alkyl ether group having 2 to 22 carbon atoms, an alicyclic hydrocarbon having 3 to 22 carbon atoms, or an aromatic hydrocarbon having 6 to 22 carbon atoms; R4 represents a hydrogen atom or a methyl group; R2 and R3 each independently represent a hydrogen atom (except when both are hydrogen atoms), or include those which, together with the nitrogen atom carrying them, form a saturated 5- to 7-membered ring (including one having an oxygen atom).) (2) The solvent for resin synthesis (C) according to (1), wherein the reaction accelerator (B) is an aliphatic or aromatic tertiary amine compound represented by general formula (2), which has one or more tertiary amino groups in the molecule and further has one or more functional groups selected from an ether group, an ester group, and an amide group in the molecule; (In the formula, A, B, and C each independently represent a linear alkyl group having 1 to 22 carbon atoms, a branched alkyl group or alkyl ether group having 3 to 22 carbon atoms, an alkyl ester group, an alkylamide group, an alicyclic hydrocarbon having 3 to 22 carbon atoms, and an aromatic hydrocarbon having 6 to 22 carbon atoms, a substituent having an ether group represented by general formula (3), a substituent having an ester group represented by general formula (4), and a substituent having an amide group represented by general formula (5). (In the formula, R5, R7, and R9 each independently represent a linear alkylene group having 1 to 22 carbon atoms, a branched alkylene group or alkylene ether group having 3 to 22 carbon atoms, an alicyclic hydrocarbon having 3 to 22 carbon atoms, and an aromatic hydrocarbon having 6 to 22 carbon atoms. R6, R8, R 10 and R 11 represents a linear alkyl group having 1 to 22 carbon atoms, a branched alkyl group or alkyl ether group having 3 to 22 carbon atoms, an alkyl ester group, an alkylamide group, an alicyclic hydrocarbon having 3 to 22 carbon atoms, or an aromatic hydrocarbon having 6 to 22 carbon atoms. 10 and R 11 may each independently be a hydrogen atom, and R 10 and R 11 may combine with the nitrogen atom that carries them to form a saturated 5- to 7-membered ring (including one having an oxygen atom). [ka] [ka] [ka] [ka] (3) The solvent for resin synthesis (C) according to (1) or (2) above, further containing one or more solvents selected from the group consisting of aromatic hydrocarbon solvents, urea solvents, lactone solvents, ether solvents, ketone solvents, ester solvents, dimethyl sulfoxide, N-formylmorpholine, and 4-acetylmorpholine; (4) Xylene, toluene, tetramethyl urea, tetraethyl urea, N,N-dimethylpropylene urea, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, α-acetyl-γ-butyrolactone, γ-valerolactone, δ-valerolactone, ethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, the solvent for resin synthesis (C) according to any one of (1) to (3), further containing one or more solvents selected from the group consisting of cyclopentyl methyl ether, 4-methyltetrahydropyran, acetophenone, acetylacetone, butyl acetate, ethyl benzoate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, ethyl acetoacetate, isoamyl acetate, ethyl n-pentylpropionate, 1,3-dioxolane, dimethyl sulfoxide, N-formylmorpholine, and 4-acetylmorpholine; (5) A method for producing a polyimide precursor or a polyamideimide precursor, which comprises mixing an acid dianhydride with a diamine and / or a diisocyanate and polymerizing the mixture using the solvent (C) for resin synthesis according to any one of (1) to (4) above, and a method for producing a polyimide or a polyamideimide, which comprises thermally imidizing the precursor; (6) Any one of a polyimide varnish and a polyamideimide varnish, containing the solvent for resin synthesis (C) described in any one of (1) to (4). (7) A binder resin containing the solvent for resin synthesis (C) according to any one of (1) to (4) above and one or more resin varnishes selected from polyimide varnishes and polyamideimide varnishes; (8) An ink composition containing the solvent for resin synthesis (C) according to any one of (1) to (4) above and one or more resin varnishes selected from polyimide varnishes and polyamideimide varnishes. (9) A photosensitive resin composition containing the solvent for resin synthesis (C) according to any one of (1) to (4) above and at least one resin varnish selected from polyimide varnishes and polyamideimide varnishes. (10) An adhesive resin composition containing the solvent for resin synthesis (C) according to any one of (1) to (4) above and at least one resin varnish selected from polyimide varnishes and polyamideimide varnishes. (11) A resin composition for a lubricating coating film, comprising the solvent (C) for resin synthesis according to any one of (1) to (4) above and one or more resin varnishes selected from polyimide varnishes and polyamideimide varnishes. (12) A heat-resistant coating material containing the solvent for resin synthesis (C) according to any one of (1) to (4) above and one or more resin varnishes selected from polyimide varnishes and polyamideimide varnishes. (13) A method for producing a polyimide film, comprising forming a coating film on a substrate using a coating liquid containing the solvent for resin synthesis (C) according to any one of (1) to (4) above and a polyimide varnish or a polyimide resin solution, and then performing stepwise thermal imidization. (14) A polyimide film obtained by heating a coating film containing the solvent for resin synthesis (C) according to any one of (1) to (4) above and a polyimide varnish or a polyimide resin solution. (15) Polyimide particles obtained by heating a composition containing the solvent for resin synthesis (C) according to any one of (1) to (4) above and a polyimide varnish. This provides: [Effects of the Invention]

[0011] The resin synthesis solvent of the present invention contains an amide solvent (A) and a reaction accelerator (B). By using this synthesis solvent as a reaction solvent for synthesizing polyimide precursors, polyamideimide precursors, etc. from acid dianhydrides and diamines and / or diisocyanates, these reactions proceed at a controllable high rate, while simultaneously producing various high-molecular-weight precursors (polyamic acids). The resulting polyamic acid solutions have excellent transparency, do not become cloudy even after long-term storage, and have good storage stability. From these various polyamic acid solutions, polyimide films, heat-resistant coatings, etc., with high transparency, high smoothness, and excellent mechanical strength can be easily produced. Furthermore, the resin synthesis solvent of the present invention can also be suitably used in the urethane reaction of polyols and diisocyanates. The reaction proceeds at a controllable high rate, while simultaneously producing high-molecular-weight, high-performance polyurethanes. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail. An embodiment of the present invention is a solvent for resin synthesis (C) containing an amide solvent (A) and a reaction accelerator (B). The amide solvent (A) is a compound having one or more amide groups in the molecule, and its content is 10 to 99.9999% by mass relative to the solvent for resin synthesis (C). The amide solvent (A) is preferably a compound having no active hydrogen and / or functional groups reactive with active hydrogen in the molecule, and when its content is 80% by mass or more, it is more preferable that A is in a liquid state in the temperature range of 0°C to 140°C in order to maintain the fluidity of the solvent for resin synthesis (C) at reaction temperatures.

[0013] The amide solvent (A) is not particularly limited, but is preferably one that is low in risk and harmfulness to human health, the ecology, and the environment, and more preferably a highly safe compound that has no effect on human health, the ecology, and the environment. Examples of such compounds include N-alkyl (carbon number 4 or more)-2-pyrrolidones (N-butyl-2-pyrrolidone, N-hexyl-2-pyrrolidone, etc.), N-alkyl (carbon number 1 or more) alkane (carbon number 2 or more) amides (N-ethylhexanamide, N-butylbutanamide, etc.), N,N-dialkyl (carbon number 1 or more) alkane (carbon number 2 or more) amides (N,N-dimethylbutanamide, N,N-diethylbutanamide, N,N-dimethyloctanamide, etc.), alkoxy (carbon number 1 or more)-N-alkyl((carbon number 1 or more) alkane (carbon number 2 or more) amides (ethoxy-N-methylpropanamide, hexyloxy-N-ethylbutanamide, etc.), alkoxy (carbon number 1 or more)-N,N-dialkyl((carbon number 1 or more) alkane (carbon number 2 or more) amides (methoxy-N,N-dimethylpropanamide, ethoxy-N,N-di Examples of the amide solvent (A) include methylbutanamide, lauroxy-N,N-dimethylpropanamide, phenyloxy-N,N-methylethylpropanamide, etc.), alkanoyl (carbon number 2 or more) morpholines (propanoylmorpholine, butanoylmorpholine, hexanoylmorpholine, octanoylmorpholine, etc.), alkoxy (carbon number 1 or more) alkanoyl (carbon number 2 or more) morpholines (methoxyethanoylmorpholine, 4-(3-methoxypropynoyl)morpholine, etc.), and N,N-dialkyl (carbon number 2 or more) acetamides (N,N-diethylacetamide, N,N-dipropylacetamide, N,N-diisopropylacetamide, N,N-dibutylacetamide, N,N-diisobutylacetamide, N,N-dihexylacetamide, etc.). These amide solvents (A) may be used alone or in combination of two or more.

[0014] The amide solvent (A) is preferably an alkoxy-N-substituted propanamide or an alkoxy-N,N-disubstituted propanamide represented by the following general formula (1): (wherein R1 to R3 each independently represent a linear alkyl group having 1 to 22 carbon atoms, a branched alkyl group having 3 to 22 carbon atoms, an alkyl ether group having 2 to 22 carbon atoms, an alicyclic hydrocarbon having 3 to 22 carbon atoms, or an aromatic hydrocarbon having 6 to 22 carbon atoms; and R4 represents a hydrogen atom or a methyl group. R2 and R3 each independently represent a hydrogen atom (except when both are hydrogen atoms), or a saturated 5- to 7-membered ring (including one containing an oxygen atom) formed together with the nitrogen atom carrying them.) This is because alkoxy-N-substituted propanamides and alkoxy-N,N-disubstituted propanamides are industrially produced, have both an ether group and an amide group in the molecule, and exhibit excellent solubility in various synthetic resins and their raw materials. [ka]

[0015] The alkoxy-N-substituted propanamide and alkoxy-N,N-disubstituted propanamide are compounds formed by any combination of functional groups represented by R1, R2, and R3, and examples thereof include methoxy-N-methylpropanamide (when R1 and R2 are methyl groups, and R3 is a hydrogen atom), methoxy-N,N-dimethylpropanamide (when R1, R2, and R3 are all methyl groups), 3-methoxy-N,N-diethylpropanamide (when R1 is a methyl group, and R2 and R3 are ethyl groups), butoxy-N,N-dimethylpropanamide (when R1 is a butyl group, and R2 and R3 are methyl groups), lauroxy-N,N-dimethylpropanamide (when R1 is a lauryl group, and R2 and R3 are methyl groups), stearoxy-N-ethylpropanamide (when R1 is a stearyl group, R2 is a hydrogen atom, and R3 is an ethyl group), and phenyloxy-N,N-methylethylpropanamide (when R1 is a phenyl group). R1 is a methyl group, R2 is a hydrogen atom, and R3 is an ethyl group), ethoxy-N-phenylpropanamide (when R1 is an ethyl group, R2 is a hydrogen atom, and R3 is a phenyl group), methoxy-N-cyclohexylpropanamide (when R1 is a methyl group, R2 is a cyclohexyl group, and R3 is a hydrogen atom), isooctyloxy-N-ethoxyethylpropanamide (when R1 is an isooctyl group, R2 is a hydrogen atom, and R3 is an ethoxyethyl group), cyclohexyl Examples include xyloxy-N,N-methyloleylpropanamide (when R1 is a cyclohexyl group, R2 is a methyl group, and R3 is an oleyl group), 3-isopropoxy-N,N-dimethylpropanamide (when R1 is an isopropyl group, and R2 and R3 are methyl groups), and 4-(3-methoxypropynoyl)morpholine (when R1 is a methyl group, and R2 and R3, together with the nitrogen atom carrying them, form a saturated 6-membered ring containing an oxygen atom). These compounds may be used alone or in combination of two or more.

[0016] The alkoxy-N-substituted propanamide and the alkoxy-N,N-disubstituted propanamide are represented by the general formula (6) (wherein R 12 is a linear alkyl group having 1 to 18 carbon atoms or a branched alkyl group having 3 to 18 carbon atoms, R 13 and R 14each independently represents a hydrogen atom, or a linear alkyl group having 1 to 6 carbon atoms or a branched alkyl group having 3 to 6 carbon atoms (except when both are hydrogen atoms), R 15 represents a hydrogen atom or a methyl group. Compounds represented by the formula (I) are preferred because inexpensive industrial raw materials are readily available and they can be industrially produced in high yield due to their structure with low steric hindrance. Furthermore, methoxy-N,N-dimethylpropanamide and butoxy-N,N-dimethylpropanamide are particularly preferred because they are highly safe for workers and the environment and are commonly handled as industrial products. [ka]

[0017] The reaction accelerator (B) in the present invention is a compound having one or more tertiary amino groups in its molecule. The substituents on the amino groups in the reaction accelerator (B) are not particularly limited and may be aliphatic or aromatic, linear or cyclic, and may or may not have an unsaturated group. Furthermore, if the reaction accelerator (B) does not have a hydrogen atom bonded to a heteroatom in its molecule, B does not undergo side reactions with acid dianhydrides or isocyanate compounds, which are raw materials for synthetic resins, and a high molecular weight synthetic resin can be obtained in a short period of time. When carrying out a resin synthesis reaction using a resin synthesis solvent (C), it is preferable to select a reaction accelerator (B) whose boiling point is higher than the reaction temperature, as this prevents volatilization during the reaction and efficiently promotes the reaction. Examples of the reaction accelerator (B) include tertiary aliphatic amines such as trialkyl (having one or more carbon atoms, which may be the same or different) amines, dialkyl (having one or more carbon atoms, which may be the same or different) cyclohexylamines, and tricyclohexylamines; tertiary aromatic amines such as dialkyl (having one or more carbon atoms, which may be the same or different) anilines, dialkyl (having one or more carbon atoms, which may be the same or different) 2,4,6-trimethylanilines, N-methyldiphenylamine, and triphenylamine; and tertiary aliphatic amines having an aromatic substituent such as N,N-dimethylbenzylamine and N-methyldibenzylamine. These reaction accelerators (B) may be used alone or in combination of two or more.

[0018] It is more preferable that the reaction accelerator (B) further contains one or more functional groups selected from an ether group, an ester group, and an amide group in the molecule. The presence of these functional groups tends to improve the reaction-accelerating effect of the reaction accelerator (B) (increasing the reaction rate and / or increasing the molecular weight of the resulting polymer). The mechanism behind these effects is unclear, but the inventors speculate that this is due to the increased polarity of the reaction accelerator (B) caused by the coexistence of an ether group, an ester group, or an amide group.

[0019] The reaction accelerator (B) having an ether group in the molecule (hereinafter referred to as "reaction accelerator (b1)" or simply "b1") is not particularly limited, and may have one or more ether groups in any of the substituents of the tertiary amino group. Furthermore, these ether groups may be formed in a chain structure or a cyclic structure. Examples of the reaction accelerator (b1) include (methoxyethyl)diethylamine, N,N-dimethyldimethoxymethaneamine, (ethoxyethyl)dibutylamine, (methoxyhexyl)ethylhexylamine, (methoxyethyl)diphenylamine, di(methoxyethyl)cyclohexylamine, and tri(butoxymethyl)amine. These reaction accelerators (b1) may be used alone or in combination of two or more.

[0020] The reaction accelerator (B) having an ester group in the molecule (hereinafter also referred to as "reaction accelerator (b2)" or simply "b2") is not particularly limited, and may have one or more ester groups in any of the substituents of the tertiary amino group. These ester groups may be formed in either a chain structure or a cyclic structure. Examples of the reaction accelerator (b2) include methyl 3-methoxypropionate, methyl dimethylaminopropionate, butyl dimethylaminopropionate, methyl dibutylaminopropionate, butyl dibutylaminopropionate, ethyl diethylaminobutyrate, butyl ethylhexylaminoacetate, isopropyl morpholinopropionate, and ethyl methylbenzylaminolaurate. These reaction accelerators (b2) may be used singly or in combination.

[0021] The reaction accelerator (B) having an amide group in the molecule (hereinafter referred to as "reaction accelerator (b3)" or simply "b3") is not particularly limited except for the amide solvent (A), and may have one or more amide groups in any of the substituents of the tertiary amino group. These amide groups may be formed in either a chain structure or a cyclic structure. Examples of the reaction accelerator (b3) include dimethylamino-N,N-dimethylpropionic acid amide, dimethyl-N,N-dibutylaminopropionic acid amide, dibutylamino-N,N-dimethylpropionic acid amide, dibutylamino-N,N-dibutylpropionic acid amide, diethylamino-N,N-dimethylbutyric acid amide, ethylhexylamino-N,N-diethylacetic acid amide, morpholinopropionic acid morpholide, methylbenzylamino-N,N-dimethyllauric acid amide, and N,N-dimethylpropionamide. These reaction accelerators (b3) may be used singly or in combination.

[0022] The reaction accelerator (b1) having an ether group in the molecule, the reaction accelerator (b2) having an ester group in the molecule, and the reaction accelerator (b3) having an amide group in the molecule may be used singly or in combination of two or more selected from the group consisting of these.

[0023] The resin synthesis solvent (C) of this embodiment contains an amide solvent (A), and the content of A is 10 to 99.9999 mass% based on the total resin synthesis solvent (C). The content of A is preferably 20 to 99.99 mass%, more preferably 30 to 99.8 mass%. It is preferable for the resin synthesis solvent (C) to contain 10 mass% or more of A, as this provides sufficient dissolving power for various resin synthesis raw materials and the resulting synthetic resin. Furthermore, when A is contained at 99.9999 mass% or less, it is possible to contain 0.0001 mass% or more of the reaction accelerator (B), which is an essential component of the resin synthesis solvent (C), and the reaction-accelerating effect of B can be confirmed, which is preferable.

[0024] In this embodiment, the resin synthesis solvent (C) contains a reaction accelerator (B) in addition to the amide solvent (A). The content of B is 0.0001 to 5% by mass relative to the total resin synthesis solvent (C). A content of B of 0.0001% by mass or more in the resin synthesis solvent (C) is preferred because it can accelerate the resin synthesis reaction. On the other hand, a content of the reaction accelerator (B) exceeding 5% by mass relative to the total synthesis solvent (C) is undesirable because it may make it difficult to control the reaction rate. Because the reaction accelerator (B) contains a tertiary amino group, it easily forms a neutralized salt with the carboxylic acid groups generated during resin synthesis. By protecting the carboxylic acid groups of the polyimide precursor and polyamic acid, which are polyamideimide precursors, as neutralized salts, the transparency and storage stability of these precursor solutions are improved. This neutralized salt evaporates during thermal imidization of the precursor, and the deprotected carboxylic acid groups undergo an imidization reaction to produce high-molecular-weight polyimide resins and polyamideimide resins. From these viewpoints, the content of the reaction accelerator (B) is preferably 0.001 to 2 mass % and more preferably 0.01 to 1 mass % based on the total amount of the solvent for resin synthesis (C).

[0025] The content of the reaction accelerators (b1), (b2), and (b3) contained in the reaction accelerator (B) is 0.0001 to 5 mass% for each of b1, b2, and b3 relative to the total amount of the solvent for resin synthesis (C), since b1, b2, and b3 can be used alone. However, when two or more of b1, b2, and b3 are used in combination, the total content does not exceed 5 mass% relative to the total amount of the solvent for resin synthesis (C).

[0026] The reaction accelerator (B) is preferably a reaction accelerator (b3) having an amide group in its molecule. Having one or more amino groups and one or more amide groups improves the polarity of the entire molecule, and the amide groups enhance the reaction-accelerating effect of the amino groups. Alternatively, the interaction between the amide groups and the amino groups in the b3 molecule may result in the reaction-accelerating effect of the amide groups in addition to the amino groups. Depending on the reaction conditions, such as the raw materials and products used in the resin synthesis, the ratio of the raw materials, the reaction temperature, and the reaction time, as well as the desired molecular weight of the resulting synthetic resin, b3 can be mixed with a reaction accelerator (b2) having an ester group in its molecule, b3 can be mixed with a reaction accelerator (b1) having an ether group in its molecule, or b3 can be mixed with b2 and b1.

[0027] In one embodiment of the resin synthesis solvent (C), the amide solvent (A) can be used in combination with other solvents. Examples of other solvents include aromatic hydrocarbon solvents such as xylene, solvent naphtha, toluene, ethylbenzene, and tetralin; urea solvents having a urea group such as 1,3-dimethylurea, 1,3-diethylurea, 1,3-diphenylurea, 1,3-dicyclohexylurea, tetramethylurea, tetraethylurea, 2-imidazolidinone, propyleneurea, 1,3-dimethyl-2-imidazolidinone, and N,N-dimethylpropyleneurea; lactone solvents such as β-propiolactone, γ-butyrolactone, α-acetyl-γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone; dibutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and ethylene glycol. Examples of the solvent include ether solvents such as dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 1,4-dioxane, 2-methyltetrahydrofuran, cyclopentyl methyl ether, 4-methyltetrahydropyran, acetophenone, acetylacetone, butyl acetate, ethyl benzoate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, ethyl acetoacetate, isoamyl acetate, n-pentyl acetate, and ethyl propionate, as well as general-purpose solvents such as ketone solvents, ester solvents, 1,3-dioxolane, dimethyl sulfoxide, nitrobenzene, N-formylmorpholine, and 4-acetylmorpholine. These solvents may be used alone or in combination of two or more as other solvents.

[0028] The content of the other solvent is 89.9999% by mass or less, preferably 5 to 50% by mass, and more preferably 10 to 30% by mass, based on the total amount of the solvent for resin synthesis (C). When the content of the other solvent is 89.9999% by mass or less, the solvent for resin synthesis (C) can contain 10% by mass or more of the amide solvent (A), which is an essential component of the solvent for resin synthesis (C), and 0.0001% by mass or more of the reaction accelerator (B), which is preferable because it is possible to confirm the high dissolving power of A for various raw materials for resin synthesis and the resulting synthetic resin, and the reaction accelerator effect of B.

[0029] In one embodiment, the boiling points of the amide solvent (A) and other solvents are preferably 80°C to 400°C at atmospheric pressure. Furthermore, the boiling points of these solvents are more preferably 100°C to 350°C, and particularly preferably 180°C to 280°C at atmospheric pressure. If the boiling point of the solvent is less than 80°C, the concentration of the reaction solution will change due to evaporation of the solvent when the reaction is carried out at a temperature of 80°C or higher in the synthetic resin production process, making it difficult to reproduce the molecular weight and solution viscosity of the resulting resin precursor or synthetic resin. On the other hand, if the boiling point of the solvent is greater than 400°C, the solvent may not completely evaporate during the production process in which a polyamic acid solution is formed into a film on a substrate such as a metal and then imidized stepwise at a temperature of 100°C to 500°C. This can result in the solvent not completely evaporating, leaving a large amount of solvent in the resulting product, such as a polyimide film, or carbonizing in the product, resulting in problems such as reduced transparency, strength, elongation, heat resistance, and chemical resistance of the product.

[0030] In one embodiment of the resin synthesis solvent (C), an amide-based solvent (A) and an ionic liquid can be used in combination. Furthermore, the resin synthesis solvent (C) can be a combination of the amide-based solvent (A), other solvents, and an ionic liquid. In the present invention, the ionic liquid is a salt composed of an anion and a cation, and is in a liquid state at temperatures ranging from 0°C to 150°C. Ionic liquids are highly polar and have excellent dissolving power for poorly soluble synthetic resins. Therefore, by incorporating an ionic liquid, a polyamic acid solution or the like with improved transparency and stability can be obtained. Furthermore, ionic liquids are non-volatile, flame-retardant, highly thermally and chemically stable, and have high ionic conductivity and excellent electrochemical properties. Therefore, they do not adversely affect the high-temperature imidization reaction of polyamic acid. Furthermore, the inclusion of a trace amount of ionic liquid in a product such as a polyimide film can impart flexibility to the product, allow the imidization reaction to proceed at temperatures above the glass transition temperature, and further improve heat resistance.

[0031] Ionic liquids can be classified based on the cation of their basic skeleton, including imidazolium salts, pyrrolidinium salts, pyridinium salts, piperidinium salts, ammonium salts, and phosphonium salts. Furthermore, various ionic liquids can be selected by changing the anion species of these salts or by changing the substituents, such as alkyl groups, on the cations and anions. Among these, imidazolium salts, pyrrolidinium salts, pyridinium salts, piperidinium salts, and ammonium salts are preferred because they contain nitrogen atoms and exhibit basicity. This is thought to be because many of the amide-based solvents contained in the resin synthesis solvent (C) are neutral to weakly basic, and basic ionic liquids are compatible with amide-based solvents. Furthermore, imidazolium salts and ammonium salts are more preferred because high-purity industrial products are readily available. These ionic liquids may be used alone or in combination.

[0032] The content of the ionic liquid is 20% by mass or less, preferably 0.001 to 10% by mass, and more preferably 0.01 to 5% by mass, based on the total mass of the resin synthesis solvent (C). If the content of the ionic liquid exceeds 20% by mass, a large amount of the ionic liquid will remain in the final product, such as a polyimide film obtained by directly heating the polyamic acid solution. Even if the polyamic acid solution is first precipitated and then imidized, a small amount of the ionic liquid will remain in the final product, which may adversely affect product quality. On the other hand, a content of 0.001% by mass or more of the ionic liquid is preferred because it can provide flexibility, elongation, and electrochemical properties to final products, such as polyimide films.

[0033] The resin synthesis solvent (C) of this embodiment may further contain a stabilizer (D). The stabilizer (D) in this specification refers to a compound having an active hydrogen atom in its molecule, specifically, water, alcohol, amine, etc. Because the stabilizer (D) has an active hydrogen atom in its molecule, it reacts with acid dianhydrides and diisocyanates, which are raw materials for synthetic resins, and protects the reactive groups of these compounds. This allows for slowing the reaction rate of the resin synthesis as needed and preventing the reaction solution from becoming cloudy or producing insoluble matter (gelation). This allows for more precise control of the resin synthesis reaction rate, the molecular weight of the resin, and the stability of the resin solution. In particular, in multi-stage reactions in which the reaction is carried out while varying reaction conditions such as temperature, the combined use of the reaction accelerator (B) and stabilizer (D) allows the reaction to proceed smoothly over a wide temperature range, resulting in the production of high-molecular-weight resins and resin solutions with high transparency and storage stability.

[0034] From the viewpoint of ease of deprotection, the stabilizer (D) is preferably water, an alcohol having a boiling point of less than 140°C, or an amine having a boiling point of less than 140°C (excluding (B)). From the viewpoint of ease of removal from the reaction solution by distillation, the stabilizer (D) is more preferably water, an alcohol having a boiling point of 120°C or less, or an amine having a boiling point of 120°C or less (excluding (B)), and is particularly preferably an alcohol having a boiling point of 100°C or less, or an amine having a boiling point of 100°C or less (excluding (B)). The stabilizer (D) may be used alone or in combination of two or more types.

[0035] The alcohol used as the stabilizer (D) is not particularly limited as long as it has a hydroxyl group in the molecule. Examples of alcohols that can be used include monofunctional alcohols having only one hydroxyl group in the molecule, bifunctional alcohols having two hydroxyl groups in the molecule, and polyfunctional alcohols having three or more hydroxyl groups in the molecule. Among these, monofunctional alcohols are preferred because both the protection reaction and the deprotection reaction proceed relatively easily. Examples of monofunctional alcohols include monofunctional alcohols having one primary or secondary hydroxyl group in the molecule, such as methyl alcohol, ethyl alcohol, isopropanol, t-butyl alcohol, 9-decen-1-ol, 1-octacosanol, diethylene glycol monomethyl ether, propylene glycol-1-monomethyl ether, 4-dimethylamino-1-butanol, cyclohexanol, and benzyl alcohol. Among these, methyl alcohol, ethyl alcohol, n-propanol, isopropanol, n-butyl alcohol, and t-butyl alcohol are more preferred because their boiling points at normal pressure are 120°C or less, allowing deprotection at low temperatures. These alcohols may be used alone or in combination of two or more.

[0036] The amine used as the stabilizer (D) is not particularly limited as long as it is a primary amine or secondary amine having an amino group in the molecule, excluding the reactivity accelerator (B). Among these, secondary amines are preferred because both the protection reaction and the deprotection reaction proceed relatively easily. Examples of secondary amines include dimethylamine, ethylmethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, diisobutylamine, dicyclohexylamine, diallylamine, piperidine, pyrrolidine, morpholine, N-methylbenzylamine, and dibenzylamine. Among these, dimethylamine, ethylmethylamine, diethylamine, dipropylamine, diisopropylamine, diallylamine, piperidine, and pyrrolidine are more preferred because their boiling points are 120°C or lower at normal pressure, allowing for deprotection at low temperatures. These amines may be used alone or in combination.

[0037] The stabilizer (D) may be any one selected from the group consisting of water, the various alcohols described above, and the various amines described above, and may be used alone or in combination of two or more.

[0038] When a stabilizer (D) is used, its mechanism of action is presumed to vary depending on the type of stabilizer (D) and the types of raw materials used in the resin synthesis reaction. For example, in the synthesis of a polyimide precursor and a polyimide resin from a dianhydride and a diamine, the dianhydride and the diamine undergo a ring-opening polyaddition reaction in a solvent to produce a polyamic acid (containing carboxylic acid groups and amide groups) as a polyimide precursor. Then, heating the reaction induces intramolecular cyclodehydration of the polyamic acid (the formation of imide groups by dehydration of carboxylic acid groups and amide groups), resulting in the production of a polyimide. The presence of water in this reaction system hydrolyzes one carboxylic acid anhydride group in the dianhydride to generate two carboxylic acid groups, increasing the number of functional groups reactive with amino groups. This disrupts the stoichiometry of the diamine and dianhydride, preventing the degree of polymerization of the polyamic acid and ultimately preventing the production of a high-molecular-weight polyimide resin. Therefore, adding water as a stabilizer is not recommended. On the other hand, if an alcohol or amine is present in the reaction system, one carboxylic acid anhydride group reacts with the alcohol to produce one carboxylic acid group and one carboxylic acid ester group, or one carboxylic acid anhydride group reacts with the amine to produce one carboxylic acid group and one carboxylic acid amide group, without changing the number of functional groups reactive with the amino group, resulting in a high degree of polymerization and a polyamic acid partially substituted with an amic acid ester group or a polyamic acid partially substituted with an amic acid amide group. Polyamic acid esters and polyamic acid amides have higher solution stability than the corresponding polyamic acids, so adding an alcohol or amine as a stabilizer to the resin synthesis solvent can produce a highly transparent and stable polyimide precursor solution. Furthermore, polyamic acid esters and polyamic acid amides undergo imidization upon heating, accompanied by elimination of the alcohol or amine, ultimately yielding a high-molecular-weight polyimide resin. For this reason, when synthesizing polyimide precursors and polyimide resins from acid dianhydrides and diamines, it is preferable to add an alcohol or amine as a stabilizer to the solvent.

[0039] Furthermore, when synthesizing polyamideimide precursors and polyamideimide resins from acid dianhydrides and diisocyanates using stabilizer (D), adding a small amount of water to the reaction system hydrolyzes the acid anhydride groups to form carboxylic acid groups, which then react with the isocyanate groups of the diisocyanates to form amide groups. This prevents a decrease in the degree of polymerization of the polyamide acid (the polyamideimide precursor) and instead improves the reaction rate and molecular weight (degree of polymerization). Furthermore, the presence of alcohols or amines in the reaction system produces effects similar to those of the polyimide precursor reaction system. Furthermore, the alcohols and amines also have a protective effect on the isocyanate groups, allowing for protection and deprotection as needed to produce polyimide precursor solutions and high-molecular-weight polyamideimide resins with higher transparency and stability. Therefore, when synthesizing polyamideimide precursors and polyamideimide resins from acid dianhydrides and diisocyanates, it is preferable to add water, alcohols, or amines as stabilizers to the solvent.

[0040] The content of stabilizer (D) can be varied as appropriate depending on the type of resin synthesis reaction and the type of reaction accelerator (B) or stabilizer (D) used, but is preferably 10 to 500% by mass relative to the total amount of B. Within this range, the reaction rates within a predetermined temperature range can be easily controlled for the synthesis of precursors such as polyamideimide precursors and polyimide precursors, as well as for the synthesis of polyurethane. The content of D relative to B is more preferably 20 to 300% by mass, and particularly preferably 50 to 200% by mass.

[0041] The solvent for resin synthesis (C) of this embodiment can be suitably used for synthesizing polyimide precursors, polyamideimide precursors, polyesterimide precursors, polyetherimide precursors, polyimide resins, polyamideimide resins, polyesterimide resins, polyetherimide resins, polyimide copolymer resins composed of any two or more selected from the above-mentioned various resin precursors, polyamide resins, polyurethane resins, polyester resins, polyacrylic resins, and fluororesins.

[0042] Acid dianhydrides used as raw materials for polyimide resins, polyamideimide resins, polyesterimide resins, polyetherimide resins, and precursors thereof include, for example, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)ethane dianhydride, aliphatic tetracarboxylic acid dianhydrides such as 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4'-oxydiphthalic dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 9,9-bis(4-(3,4-dicarboxyphenoxy)phenyl)fluorene dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 2,3,5,6-pyridinetetracarboxylic acid dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, and butanetetracarboxylic acid dianhydride; and aliphatic tetracarboxylic acid dianhydrides containing a cyclic aliphatic group such as 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride. These acid dianhydrides may be used alone or in combination of two or more.

[0043] Diamine compounds used as raw materials for polyimide resins, polyamideimide resins, polyesterimide resins, polyetherimide resins, and precursors thereof include, for example, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 1,4-bis(4-aminophenoxy)benzene, benzidine, m-phenylenediamine, p-phenylenediamine, 1,5-naphthalenediamine, 2,6-naphthalenediamine, bis(4-aminophenoxy)biphenyl, bis(4-(4-aminophenoxy)phenyl)ether, 1,4-bis(4-aminophenoxy)benzene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-diethyl-4,4'-diaminobiphenyl, Examples of suitable diamine compounds include 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-diethyl-4,4'-diaminobiphenyl, 2,2',3,3'-tetramethyl-4,4'-diaminobiphenyl, 3,3',4,4'-tetramethyl-4,4'-diaminobiphenyl, 2,2'-di(trifluoromethyl)-4,4'-diaminobiphenyl, 9,9-bis(4-aminophenyl)fluorene, 2,2'-bis(trifluoromethyl)-5,5'-dihydroxybenzidine, 3,5-diaminobenzoic acid, 3,4-diaminobenzoic acid, 2,5-diaminobenzoic acid, aromatic diamines such as compounds in which at least a portion of the hydrogen atoms in these aromatic rings are substituted with alkyl groups or halogen atoms, and aliphatic diamines containing alicyclic groups such as cyclohexyldiamine and methylenebiscyclohexylamine. These diamine compounds may be used alone or in combination of two or more.

[0044] Examples of diisocyanates used as raw materials for polyamide-imide resins and their precursors, and for polyurethane resins include aliphatic diisocyanates, aromatic diisocyanates, and araliphatic diisocyanates. These diisocyanate compounds may be used alone or in combination of two or more.

[0045] Examples of aliphatic diisocyanates include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), octamethylene diisocyanate, nonamethylene diisocyanate, 2,2'-dimethylpentane diisocyanate, 2,2,4-trimethylhexane diisocyanate, decamethylene diisocyanate, butene diisocyanate, 1,3-butadiene-1,4-diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 1,6,11-undecamethylene triisocyanate, 1,3,6-hexamethylene triisocyanate, 1, Examples of the diisocyanate include aliphatic diisocyanates such as 8-diisocyanate-4-isocyanatomethyloctane, 2,5,7-trimethyl-1,8-diisocyanate-5-isocyanatomethyloctane, bis(isocyanatoethyl)carbonate, bis(isocyanatoethyl)ether, 1,4-butylene glycol dipropyl ether-ω,ω'-diisocyanate, lysine isocyanatomethyl ester, lysine triisocyanate, 2-isocyanatoethyl-2,6-diisocyanate hexanoate, 2-isocyanatopropyl-2,6-diisocyanate hexanoate, bis(4-isocyanato-n-butylidene)pentaerythritol, and 2,6-diisocyanate methyl caproate.

[0046] Furthermore, examples of the alicyclic diisocyanate having a cyclic structure among the aliphatic diisocyanates include isophorone diisocyanate (IPDI), 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane or a mixture thereof (bis(isocyanatomethyl)cyclohexane (H6XDI)), 4,4'-, 2,4'-, or 2,2'-dicyclohexylmethane diisocyanate or a mixture thereof (H12MDI), 1,3- or 1,4-cyclohexane diisocyanate or a mixture thereof, 1,3- or 1,4-bis(isocyanatoethyl)cyclohexane, methylcyclohexane diisocyanate, 2,2'-dimethyldicyclohexylmethane diisocyanate, dimer acid diisocyanate, 2,5- or 2,6-diisocyanatomethylbicyclo[2,2,1]-heptane (NBDI), 2-isocyanatomethyl -2-(3-isocyanatopropyl)-5-isocyanatomethylbicyclo-[2,2,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-isocyanatomethylbicyclo-[2,2,1]-heptane, 2-isocyanatomethyl-3-(3-isocyanatopropyl)-5-(2-isocyanatoethyl)-bicyclo-[2,2,1]-heptane, 2-isocyanatomethyl-3-(3-isocyanatopropyl)-5-(2-isocyanatoethyl)-bicyclo-[2,2,1]-heptane alicyclic diisocyanates such as 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo-[2,2,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-5-(2-isocyanatoethyl)-bicyclo-[2,2,1]-heptane, and 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo-[2,2,1]-heptane.

[0047] Examples of aromatic diisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and isomer mixtures of these tolylene diisocyanates (TDI), 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, and any isomer mixtures of these diphenylmethane diisocyanates (MDI), toluidine diisocyanate (TODI), paraphenylene diisocyanate, and naphthalene diisocyanate (NDI).

[0048] Examples of the araliphatic diisocyanate include araliphatic diisocyanates such as 1,3- or 1,4-xylylene diisocyanate or a mixture thereof (XDI), and 1,3- or 1,4-tetramethylxylylene diisocyanate or a mixture thereof (TMXDI).

[0049] Specific examples of polyols used as raw materials for polyurethane resins include polyether polyols, polyester polyols, polycarbonate polyols, polyurethane polyols, epoxy polyols, vegetable oil polyols, polyolefin polyols, acrylic polyols, silicone polyols, fluorine polyols, and vinyl monomer-modified polyols. These polyols may be used alone or in combination of two or more.

[0050] The solvent (C) for resin synthesis of this embodiment has excellent solubility for polyimide resins, polyamideimide resins, polyesterimide resins, polyetherimide resins and their precursors, as well as polyurethane resins, polyamide resins, polyacrylic resins, fluororesins, etc., and can therefore be suitably used as a solvent for producing and dissolving various resins. Furthermore, by using the solvent (C) for resin synthesis of this embodiment, the synthesis reaction of the various resins can be completed in a short time, the reaction proceeds easily even at low temperatures, and can be easily controlled even at high temperatures, and resins having a high molecular weight, high transparency, and good heat resistance and mechanical properties can be obtained.

[0051] When various resins are synthesized using the resin synthesis solvent (C), the reaction can be carried out under known reaction conditions. That is, the reaction apparatus, raw materials and raw material charge ratios, raw material charge method, reaction temperature, reaction time, purification method, etc. are the same as conventional ones. Furthermore, when synthesizing polyimide precursors, polyamideimide precursors (hereinafter collectively referred to as polyamic acids), and polyurethanes, the reaction can be completed at lower reaction temperatures than conventional ones. On the other hand, the dehydration imidization reaction of various precursors can be carried out at higher temperatures than conventional ones, and resin products such as polyimides and polyamideimides having higher heat resistance and chemical resistance can be obtained.

[0052] In one embodiment, in the reaction for synthesizing a polyimide precursor from an acid dianhydride and a diamine using a resin synthesis solvent (C), the reaction temperature is −20° C. to 80° C., preferably 0° C. to 70° C., and more preferably 10° C. to 60° C. In the reaction for synthesizing a polyamideimide precursor from an acid dianhydride and a diisocyanate, the reaction temperature is 40° C. to 140° C., preferably 60° C. to 130° C., and more preferably 80° C. to 120° C. When the reaction temperature is equal to or higher than the respective lower limit temperatures, the synthesis of these precursors proceeds at a sufficient rate and can be completed in a short time, resulting in good productivity. Furthermore, when the reaction temperature is equal to or lower than the respective upper limit temperatures, the progress of the intramolecular imidization reaction of the produced polyamic acid is suppressed, resulting in good transparency of the polyamic acid solution, no clouding over time, and no precipitation of gel-like insoluble matter, resulting in good storage stability. The reaction time for these reactions varies depending on the reaction temperature, but is typically in the range of 1 hour to 24 hours.

[0053] In one embodiment, the reaction temperature for synthesizing polyurethane from polyol and diisocyanate using the resin synthesis solvent (C) is typically 20°C to 150°C, preferably 30°C to 120°C, and more preferably 40°C to 110°C. The presence of the reaction accelerator (B) allows the urethane reaction to proceed even at temperatures as low as 20°C, resulting in the production of high-molecular-weight polyurethane. Furthermore, the presence of an alcohol or amine stabilizer protects the isocyanate group of the diisocyanate, suppressing self-polymerization of the diisocyanate (e.g., urethionation or isocyanuration) due to heating and side reactions between the diisocyanate and the amide solvent at high temperatures, resulting in the production of a high-molecular-weight polyurethane solution that does not gel. The resulting polyurethane solution has low viscosity and is suitable for use as a binder resin in coatings, inks, adhesives, and other applications.

[0054] Polyurethane dispersions (PUDs) are produced by adding a polyurethane resin solution containing the synthesis solvent (C) produced in one embodiment to water to disperse the polyurethane resin in water. PUDs are widely used in environmentally friendly, low-VOC water-based paints, adhesives, ink binders, coating agents, and the like. Because the organic solvent contained in PUDs must be water-soluble and highly safe, the resin synthesis solvent (C) is considered to be ideal as a solvent for synthesizing polyurethane resins for PUDs. PUDs containing the resin synthesis solvent (C) have excellent storage stability because the isocyanate groups are protected by the stabilizer (D). Even when stored for long periods of time, they can be stored over a wide temperature range of -20 to 80°C without experiencing phase separation of the dispersion or the generation of insoluble matter (gelation). Furthermore, because the amide groups of the amide solvent (A) in the resin synthesis solvent (C) have good adhesion to a variety of substrates, from rubber and plastic to metal, the PUDs are suitable for use in steel sheet treatment agents for various steel sheets, such as hot-dip galvanized steel sheets, electrogalvanized steel sheets, hot-rolled steel sheets, and cold-rolled steel sheets, as rubber coating agents, and as coating agents and primers for films and substrates made of polyethylene terephthalate, polycarbonate, polyacrylic, polyvinyl chloride, polyamide, etc. The polyurethane resin produced by the present invention can be made to have a high molecular weight, and the viscosity of the PUDs prepared therefrom can be adjusted as desired depending on the purpose. They are applicable to various printing methods, such as inkjet printing, screen printing, flexographic printing, and gravure printing, and can be used as a printing ink binder for textiles (printing), films, sheets, etc.

[0055] The polyimide precursor solution (also referred to as a polyamic acid solution or resin varnish) produced using the resin synthesis solvent (C) of this embodiment exhibits good stability during long-term storage (transportation and storage) and use (production of polyimide molded bodies). The polyimide precursor solution obtained using the resin synthesis solvent (C) can be used as a binder resin in polyimide molded bodies, coating solutions for polyamideimide molded bodies, inks, insulating protective films, conductive inks, photosensitive resins, heat-resistant paints, and the like. Furthermore, the coating solution for polyimide molded bodies can be used, for example, to form a coating film of a desired thickness on a metal or glass substrate by a conventional film-forming method (spin coating, dip coating, solvent casting, slot die coating, spray coating, roll coating, etc.), followed by stepwise thermal imidization to produce molded articles such as polyimide films, polyimide sheets, polyamideimide heat-resistant coating films, lubricating coating films, adhesive films for metal bonding, and liquid crystal alignment films.

[0056] A polyimide film can be produced using the solvent for resin synthesis (C) of this embodiment. The production method is not particularly limited, but examples include a method in which a polyimide varnish (polyimide precursor solution, partially imidized polyimide precursor solution) or a polyimide resin solution (soluble polyimide resin solution) synthesized using the solvent for resin synthesis (C) is used to form a coating on a metal or glass substrate, and then the coating is imidized by stepwise heat treatment at temperatures of 100°C to 500°C in a high-temperature convection oven or the like. The heat treatment is carried out in an inert gas atmosphere such as nitrogen at 100°C to 300°C for 10 to 60 minutes, 300°C to 400°C for 30 to 60 minutes, and 400°C to 500°C for 5 to 30 minutes, preferably at 100°C to 150°C for 10 to 30 minutes, 220°C to 250°C for 10 to 30 minutes, 350°C for 30 minutes, and 450°C for 10 minutes. A polyimide film heat-treated at such a temperature for such a time can have the solvent removed stepwise and completely, and has high transparency and high heat resistance.

[0057] Polyimide particles can be produced using the resin synthesis solvent (C) of this embodiment. The production method is not particularly limited, but examples include a method in which a polyimide varnish (polyimide precursor solution, partially imidized polyimide precursor solution) synthesized using the resin synthesis solvent (C) is heated stepwise at temperatures of 50°C to 300°C while stirring to disperse and precipitate the imidized and insolubilized polyimide particles, and a method in which a polyimide varnish synthesized using the resin synthesis solvent (C) is added to a high-boiling nonpolar solvent (poor solvent) and heated stepwise at temperatures of 50°C to 300°C while stirring or irradiating with ultrasound to disperse and precipitate the imidized and insolubilized polyimide particles. Examples of high-boiling nonpolar solvents include xylene, acetophenone, ethyl benzoate, benzyl benzoate, and tetralin. Here, stepwise heating at 50°C to 300°C means heating at 50°C to 200°C for 30 to 120 minutes, and then at 200°C to 300°C for 10 to 60 minutes, and preferably heating at 70°C for 60 minutes, then at 120°C for 60 minutes, and finally at 240°C for 30 minutes.The polyimide particles produced by these methods are preferably obtained as powder by centrifugation or vacuum drying, and then further heat-treated at 350°C for 120 minutes.

[0058] The polyimide particles obtained by the production method of the present invention have properties similar to polyimide resins, such as high heat resistance, solvent resistance (chemical resistance), and excellent electrical insulation, and are therefore widely used in high-tech industries such as the electrical and electronics technical fields and the aerospace and space technical fields. For example, they are expected to be applied to electrical and electronic materials such as powder toner additives for image formation, coating materials for electrical insulating parts, molding fillers, and spacers for liquid crystal displays, as well as composite materials such as additives for heat-resistant paints and lubricants.

[0059] By using the resin synthesis solvent (C) of the present invention, high-quality polyimide varnish, polyamideimide varnish, polyesterimide varnish, polyetherimide varnish, polyurethane resin varnish, polyamide resin varnish, polyacrylic resin varnish, and fluororesin varnish can be obtained. Furthermore, by appropriately heat-treating and molding these varnishes, high-quality polyimide-based, polyamideimide-based, polyesterimide-based, polyetherimide-based, polyurethane-based, polyamide-based, polyacrylic-based, and fluororesin resins, films, particles, and the like can be obtained. Molded articles such as these resins, films, and particles can be suitably used as polyimide films and polyimide sheets such as flexible electronic substrate films, copper-clad laminate films, laminate films, electrical insulating films, porous films for fuel cells, and separation films; insulating coatings, heat-resistant coatings, IC packages, adhesive films, liquid crystal alignment films, resist films, planarizing films, microlens array films, electric wire coating films, and polyimide coatings such as optical fiber coating films; drive belts; and belts for electrophotographic image forming apparatuses (e.g., intermediate transfer belts, transfer belts, fixing belts, and conveyor belts). [Example]

[0060] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following, "parts", "%", and " / " are all by mass unless otherwise specified.

[0061] The materials used in the examples and comparative examples are as follows. (A) Amide solvents A-1: N-butyl-2-pyrrolidone A-2: 3-Methoxy-N,N-dimethylpropanamide (manufactured by KJ Chemicals, registered trademark "KJCMPA") A-3: 3-butoxy-N,N-dimethylpropanamide (manufactured by KJ Chemicals, registered trademark "KJCBPA") A-4: 3-Lauroxy-N,N-dimethylpropanamide A-5: 3-Methoxy-N,N-diethylpropanamide A-6: 3-ethoxy-N-phenylpropanamide A-7: 3-Methoxy-N-cyclohexylpropanamide A-8: N,N-diethylbutanamide A-9: N-propanoylmorpholine A-10: 4-(3-methoxypropionyl)morpholine A-11: N,N-diisopropylacetamide A-12: 3-Isopropoxy-N,N-dimethylpropanamide (B) Reaction accelerator B-1: Tributylamine B-2: Triethylenediamine b1-1: (Methoxyethyl)diphenylamine b1-2: N,N-dimethyldimethoxymethanamine b2-1: methyl dimethylaminopropionate b2-2: butyl dibutylaminopropionate b2-3: 3-Methoxypropionic acid methyl ester b3-1: Dibutylamino-N,N-dimethylpropionic acid amide b3-2: Morpholinopropionic acid morpholide b3-3: Dimethylamino-N,N-dimethylpropionic acid amide b3-4: N,N-dimethylpropionamide (D) Stabilizer D-1: Water D-2: Methanol D-3: Isopropyl alcohol D-4: Diethylamine D-5: Pyrrolidine (E) Ionic liquid E-1: Tetrabutylammonium trifluoromethanesulfonate E-2: 1-methyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide (F) Other solvents F-1: 1,3-dimethyl-2-imidazolidinone F-2: Dimethyl sulfoxide F-3: γ-valerolactone F-4: γ-butyrolactone F-5: N-formylmorpholine F-6: 4-acetylmorpholine F-7: Dipropylene glycol dimethyl ether F-8: 4-methyltetrahydropyran F-9: Cyclopentyl methyl ether F-10: Xylene

[0062] Example 1 (Synthesis and Evaluation of Polyimide Precursor Solution) A 1000 mL four-neck flask equipped with a stirrer, thermometer, dropping funnel, and nitrogen gas inlet tube was charged with 350 g of solvent C-1 (shown in Table 1) and 25.0 g (125 mmol) of 4,4'-diaminodiphenyl ether (ODA) as a diamine compound. The mixture was stirred at room temperature for 30 minutes while passing nitrogen gas through it to obtain a colorless, clear solution. The solution was then heated to 80 °C, and 37.8 g (128 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was slowly added as an acid dianhydride while maintaining the temperature at 80 °C. After stirring at 80 °C for an additional hour, the mixture was cooled to room temperature, and 5 g of solvent C-1 was added to obtain a colorless, clear, viscous polyimide precursor solution (varnish). The transparency and coloration of the resulting varnish were visually observed, and viscosity measurements and analysis of the number-average molecular weight of the polyimide precursor were carried out by the methods described below. The results are shown in Table 1. The resulting varnish was stored at 40°C for 30 days, and then its viscosity was measured. The rate of change in viscosity over time was calculated using the formula below. The viscosity after storage and the rate of change in viscosity over time are shown in Table 1. Viscosity change rate over time (%) = (viscosity after 30 days - initial viscosity) / initial viscosity x 100%

[0063] (viscosity measurement) The viscosity of the varnish was measured at 25° C. using a cone-plate viscometer (RE550 type viscometer manufactured by Toki Sangyo Co., Ltd.) in accordance with JIS K5600-2-3.

[0064] (number average molecular weight) A Hitachi L6000 high-performance liquid chromatograph and a Hitachi ATT-8 data analyzer were used, with two Gelpack GL-S300MDT-5 columns and a mobile phase of 0.06 M phosphoric acid and 0.06 M lithium bromide dissolved in a 1 / 1 (L / L) mixture of DMF and THF. Measurements were performed at a sample concentration of 0.2% and a flow rate of 1.0 ml / min, and the number-average molecular weight was calculated using a calibration curve using polystyrene standard samples.

[0065] Preparation and evaluation of polyimide films The resulting polyimide precursor solution (varnish) was applied to a glass substrate and heated in a hot air dryer under a nitrogen stream at 120°C for 10 minutes, 250°C for 10 minutes, and 350°C for 30 minutes. The polyimide film and glass substrate laminate was immersed in water for 10 minutes, and the polyimide film was peeled off from the glass substrate and dried in a hot air dryer at 80°C for 10 minutes, yielding a colorless, transparent polyimide film with a thickness of approximately 10 μm. The appearance, optical transparency, strength, elongation, and linear thermal expansion coefficient of the resulting polyimide film were evaluated using the methods described below, and the results are shown in Table 1.

[0066] (Appearance of polyimide film) The obtained polyimide film was visually observed to check for the occurrence of defects such as bubbling and cracking, and was evaluated according to the following criteria. ⊚: Light yellow, transparent, no bubbles or cracks. ◯: Light yellow to yellow, transparent, with slight bubbles or cracks. △: Yellow or translucent with several bubbles or cracks. ×: Yellow to brown or opaque with many bubbles or cracks.

[0067] (transparency) The obtained polyimide film was left standing overnight under conditions of a temperature of 23°C and a relative humidity of 50%, and then its light transmittance was measured. The measurement was carried out using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-2000) in accordance with JIS K7105. The higher the light transmittance, the better the transparency of the polyimide film.

[0068] (Tensile strength and tensile elongation) The resulting polyimide film was cut into test pieces 100 mm long and 10 mm wide, and left to stand for 24 hours at a temperature of 23°C and a relative humidity of 50%. Then, a tensile test was performed using a tensile tester (ORIENTEC Corporation, Tensilon RTA-100) with a check gap of 50 mm, a tensile speed of 50 mm / min, and n=5. The higher the tensile strength, the stronger the polyimide film. Furthermore, the higher the tensile elongation, the higher the elongation of the polyimide film.

[0069] (coefficient of linear thermal expansion) The resulting polyimide film was cut into test pieces measuring 20 mm in length and 2 mm in width and left overnight at 23°C and 50% relative humidity. Measurements were then performed using a thermomechanical analyzer (SII NanoTechnology, EXSTAR6000) under a nitrogen stream. The temperature was increased from room temperature to 220°C at a rate of 5°C / min, then decreased from 220°C to room temperature, and then increased again at a rate of 5°C / min to measure the average linear expansion coefficient from 50°C to 200°C. The lower the average linear expansion coefficient, the better the heat resistance and dimensional stability.

[0070] Examples 2 to 12 and Comparative Examples 1 to 6 In Examples 2 to 12, polyimide precursor solutions (varnishes) with a solids concentration of 15% by mass were synthesized and polyimide films were produced in the same manner as in Example 1, except that the diamine components, acid dianhydride components, solvents (C-2 to C-12), and other components listed in Tables 1 and 2 were used. The resulting varnishes and films were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2. In Comparative Examples 1 to 6, polyimide precursor solutions (varnishes) were synthesized and polyimide films were produced in the same manner as in Example 1, using the diamine components, acid dianhydride components, solvents, and other components listed in Table 3. The resulting varnishes and films were evaluated in the same manner as in Example 1, and the results are shown in Table 3.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] As can be seen from the results of the Examples and Comparative Examples shown in Tables 1 to 3, the resin synthesis solvent (C) according to an embodiment of the present invention, which contains an amide solvent (A) and a reaction accelerator (B), can rapidly and stably promote the reaction between a diamine compound and an acid dianhydride, thereby producing a highly transparent, colorless, and low-viscosity polyimide precursor solution (varnish). Furthermore, the viscosity of the resulting varnish changes very little over time, making it suitable for long-term storage and transportation. Furthermore, polyimide films obtained using these varnishes exhibit high transparency, high light transmittance, and low coloration, as well as excellent strength, elongation, heat resistance, and dimensional stability. The effects of the present invention are due to the synergistic effect of the excellent dissolving power of the amide solvent (A), a component of the resin synthesis solvent (C), and the reaction acceleration provided by the reaction accelerator (B). These effects cannot be achieved by using the amide solvent (A) alone or by combining the reaction accelerator (B) with other solvents.

[0075] Example 13 (Synthesis of polyamideimide precursor solution) A 3 L four-neck flask equipped with a stirrer, condenser, thermometer, and nitrogen gas inlet tube was charged with 117.6 g (0.6 mol) of trimellitic dianhydride (TMA), 128.8 g (0.4 mol) of 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 250.2 g (1.0 mol) of 4,4'-diphenylmethane diisocyanate (MDI), and 500 g of solvent C-13 (listed in Table 4). The mixture was heated to 120 °C with stirring and reacted at 120 °C for 6 hours. After completion of the reaction, the reaction solution was cooled to 80 °C and diluted with solvent C-13 (660 g) to a solids concentration of 30 wt%. A colorless, transparent polyamideimide precursor solution (varnish) was obtained. The viscosity of the resulting precursor solution and the number-average molecular weight of the precursor were measured using the same method as described above, and the results are shown in Table 4.

[0076] Examples 14 to 24 and Comparative Examples 7 to 12 In Examples 14 to 24, polyamideimide precursor solutions were synthesized in the same manner as in Example 13, except that the acid dianhydride components, diisocyanate components, solvents (C-14 to C-24), and other components listed in Tables 4 and 5 were used. In Comparative Examples 7 to 12, polyamideimide precursor solutions were synthesized in the same manner as in Example 13, using the acid dianhydride components, diisocyanate components, solvents, and other components listed in Table 6. The viscosity of the obtained precursor solutions and the number average molecular weight of the precursor were measured by the same methods as above, and the results are shown in Tables 4 to 6.

[0077] Coating preparation and evaluation The obtained polyamideimide precursor solution (varnish) was applied as a test coating to a 1.0 mm thick aluminum substrate or copper foil to a dry film thickness of approximately 5 μm, pre-dried at 80° C. for 20 minutes, and baked at 400° C. for 10 minutes to obtain a coating film. The obtained coating film was used to evaluate adhesion, bending resistance, acid resistance, alkali resistance, and steam resistance, and the results are shown in Tables 4 to 6.

[0078] (adhesion) According to JIS-K5600, 100 1 mm squares were made on the coating film, and a peel test was carried out using adhesive tape. The number of remaining squares was counted and the adhesion was evaluated according to the following criteria. ◎: No peeling after 100 pieces 〇: 95 to 99 pieces, no peeling △: 70 to 94 pieces, no peeling ×: 0 to 69 pieces, no peeling

[0079] (bending resistance) When the coating film (with aluminum plate) was bent with the coated surface facing outward, the aluminum plate used for coating was sandwiched between the bent portions, and the bending resistance was evaluated according to the following criteria based on the number of plates sandwiched when a crack appeared in the bent portion. ◎: 0 sheets 〇: 1 to 2 sheets △: 3 to 5 sheets ×: 6 or more

[0080] (acid resistance) A test piece with the non-coated surface of the coating (with aluminum plate) protected with adhesive tape was immersed in a 5% sulfuric acid solution and left to stand at room temperature for one week. The condition of the coating was then visually observed and the acid resistance was evaluated according to the following criteria. ○: No change △: Blisters are visible ×: Coating peeled off

[0081] (alkali resistance) A test piece with the non-coated surface of the coating (with aluminum plate) protected with adhesive tape was immersed in a 5% sodium hydroxide solution and left to stand at room temperature for one week. The condition of the coating was then visually observed and the alkali resistance was evaluated according to the following criteria. ○: No change △: Blisters are visible ×: Coating peeled off

[0082] (Steam resistance) The coating film (with aluminum plate) was brought into contact with steam at 120°C and pressurized to 2 atm in an autoclave for 100 hours, after which the adhesion was evaluated in the same manner as above, with higher adhesion indicating higher steam resistance.

[0083] [Table 4]

[0084] [Table 5]

[0085] [Table 6]

[0086] As can be seen from the results of the Examples and Comparative Examples shown in Tables 4 to 6, the resin synthesis solvent (C) according to an embodiment of the present invention contains an amide solvent (A) and a reaction accelerator (B), which allows the reaction of a diisocyanate compound with an acid dianhydride to proceed stably and at a high reaction rate, enabling the production of a highly transparent, colorless, and low-viscosity polyamideimide precursor solution (varnish). Furthermore, the viscosity of the resulting varnish changes very little over time, making it suitable for long-term storage and transportation. Furthermore, by applying these varnishes to metal substrates and baking them at high temperatures of 300°C to 550°C, high-performance coating films with excellent adhesion, bending resistance, acid resistance, alkali resistance, and steam resistance can be obtained. The effects of the present invention are due to the synergistic effect of the excellent dissolving power of the amide solvent (A), a component of the resin synthesis solvent (C), and the reaction acceleration provided by the reaction accelerator (B). These effects cannot be achieved by using the amide solvent (A) alone or by combining the reaction accelerator (B) with other solvents. The coating film thus obtained has heat resistance above the baking temperature, and therefore the various polyamideimide precursor solutions (varnishes) obtained by the present invention can be suitably used as heat-resistant coating materials.

[0087] Example 25 (Synthesis of polyurethane resin solution) A 2 L four-neck flask equipped with a stirrer, condenser, and thermometer was charged with 150.0 g (0.05 mol) of polypropylene glycol (PPG), 100.0 g (0.05 mol) of polyester polyol (PEs), 62.6 g (0.25 mol) of 4,4'-diphenylmethane diisocyanate (MDI), and 800 g of solvent C-25 (listed in Table 7). The mixture was heated to 70 °C with stirring and reacted at 70 °C for 2 hours to obtain a prepolymer. Next, 9.3 g (0.15 mol) of ethylene glycol (EG) was added, and the mixture was reacted at 60 °C for 3 hours. The reaction solution was cooled to room temperature and diluted with solvent C-25 (490 g) to a solids concentration (polyurethane resin) of 25.0 wt% to obtain a colorless, transparent polyurethane resin solution. The viscosity of the resulting resin solution and the number-average molecular weight of the resin were measured using the same method as described above and are shown in Table 7.

[0088] Examples 26 to 36 and Comparative Examples 13 to 18 The polyurethane resins of Examples 26 to 36 and Comparative Examples 13 to 18 were synthesized in the same manner as in Example 25, except that the conditions were changed as shown in Tables 7 to 9. The viscosity of each of the resulting resin solutions and the number average molecular weight of the resin were measured in the same manner as above, and the results are shown in Tables 7 to 9.

[0089] Using the obtained polyurethane resin solution, a coating film was produced by the following method. The tensile strength (breaking strength) and tensile elongation (breaking elongation) of the coating film were measured by the same tensile test as above, and the results are shown in Tables 7 to 9.

[0090] (Breathability test and water pressure resistance test) The resulting polyurethane resin solution was applied to a water-repellent treated nylon taffeta using a roll-on knife coater to a dry thickness of 40 μm, and then coagulated in water for 2 minutes. The fabric was then immersed in 50°C warm water for 3 minutes to wash, and then dried at 150°C for 1 minute to obtain a moisture-permeable waterproof fabric with a polyurethane resin film. The resulting moisture-permeable waterproof fabric was measured for moisture permeability according to JIS L-1099 (A-1 method) and for water pressure resistance according to JIS L-1092. The measurement results are shown in Tables 7 to 9.

[0091] [Table 7]

[0092] [Table 8]

[0093] [Table 9]

[0094] As can be seen from the results shown in Tables 7 to 9, the resin synthesis solvent (C) according to an embodiment of the present invention, which contains an amide solvent (A) and a reaction accelerator (B), can stably promote the reaction between polyol and diisocyanate, and the resulting polyurethane resin has a high molecular weight, allowing for the production of a highly transparent, colorless polyurethane resin solution. Furthermore, the viscosity of the resulting polyurethane resin solution changes very little over time, making it suitable for long-term storage and transportation. Furthermore, by applying these polyurethane resin solutions to release paper or plastic sheets, coatings with high strength and elongation can be obtained, and by applying them to nylon taffeta, waterproof products such as breathable, waterproof fabrics that combine breathability and water resistance can be produced. The effects of the present invention are due to the synergistic effect of the excellent dissolving power of the amide solvent (A), a component of the resin synthesis solvent (C), and the reaction acceleration provided by the reaction accelerator (B). These effects cannot be achieved by using the amide solvent (A) alone or by combining the reaction accelerator (B) with other solvents. Furthermore, since the polyurethane resin obtained by the present invention has excellent water resistance, various polyurethane dispersions (PUDs) can be produced by dispersing it in water.

[0095] Examples 37 to 46 (lubricating paint) and Comparative Examples 19 to 24 The various varnishes (polyimide precursor solutions, polyimideamide precursor solutions) obtained in Examples 1 to 24 and Comparative Examples 1 to 12 were mixed with the solid lubricants and additives shown in Tables 10 and 11, and diluted with the solvent used in each varnish to a solids concentration of 15% by mass to prepare lubricating coatings. The prepared lubricating coatings were used to evaluate coating properties and paintability using the methods described below, and the results are shown in Table 10. Furthermore, lubricating coating films were produced from the lubricating coatings using the methods described below, and their wear resistance and adhesion were evaluated, and the results are shown in Tables 10 and 11. In the tables, "MoS2" represents molybdenum disulfide (manufactured by Sumitomo Lubricant Co., Ltd., Molypowder PS, density 4.8 g / cm). 3 ), "PTFE" is polytetrafluoroethylene (Central Glass Co., Ltd., Ceflalube), and "graphite" is flake graphite W-5 (Ito Graphite Industries Co., Ltd., density 2.2 g / cm 3), "epoxy resin" refers to a novolac type epoxy resin (Epicoat 152, manufactured by Yuka Shell Co., Ltd.).

[0096] (paint quality) The prepared lubricating coating materials were visually inspected for the dispersion state of the solid lubricant and the presence or absence of aggregation of the resin varnish (polyimide varnish, polyamideimide varnish), and were evaluated according to the following criteria. ⊚: No aggregates were observed in the lubricating paint during the mixing process or after preparation, the resin varnish was dissolved, and the paint was homogeneous (practical level). ○: The solid lubricant was not uniformly dispersed during the mixing process, but the final lubricating paint was free of agglomerates, the varnish resin was dissolved, and it was homogeneous (practical level). ×: The varnish resin in the lubricating paint during the mixing process or after preparation aggregates, causing gelation.

[0097] (paintability) The prepared lubricating paint was used to spray paint a 10 μm thick film onto the surface of a SUS316 disk (diameter 100 mm, thickness 5 mm). The condition of the painted surface was visually inspected and evaluated according to the following criteria. ◯: The coated surface is uniform and good (practical level). ×: The painted surface is uneven, with undulations and irregularities.

[0098] (Sliding characteristics (wear resistance)) The prepared lubricating coating was spray-coated onto the surface of a SUS316 disk (100 mm diameter, 5 mm thickness) preheated to 90°C to a coating thickness of 10 μm. The disk was then dried at 100°C for 10 minutes, 200°C for 10 minutes, and further heated at 400°C for 1 hour to obtain a coating test piece. A reciprocating sliding wear test was performed using a steel ball (SUJ2) as the mating material. The sliding test conditions were 15 mm / s and 100 cycles. After the sliding test, the wear depth of the coating was measured and evaluated according to the following criteria. ⊚: The wear depth of the most worn part is 3 μm or less (practical level). ◯: The wear depth of the most worn part is more than 3 μm and 5 μm or less (practical level). △: The wear depth of the most worn part is more than 5 μm and 7 μm or less (practical level). ×: The wear depth of the most worn part is 7 μm or more.

[0099] (adhesion) The prepared lubricating coating was spray-coated onto the surface of a SUS316 plate (50 mm diameter x 50 mm, 5 mm thick) under fixed coating conditions to achieve a coating thickness of 10 μm. The coated surface was dried at 100°C for 10 minutes, then at 200°C for 10 minutes, and then heated at 400°C for 1 hour to form a coating. According to JIS-K5600, 100 1 mm squares were created on the coating, and a peel test was performed using adhesive tape. The number of remaining squares was counted, and adhesion was evaluated according to the following criteria. ◎: No peeling after 100 pieces 〇: 95 to 99 pieces, no peeling △: 70 to 94 pieces, no peeling ×: 0 to 69 pieces, no peeling

[0100] [Table 10]

[0101] [Table 11]

[0102] Examples 47 to 52 (adhesive) and Comparative Examples 25 to 28 Using a tabletop coater (Coater TC-1, manufactured by Mitsui Electric Seiki Co., Ltd.), the various varnishes (polyimide precursor solutions, polyimideamide precursor solutions) obtained in Examples 1-24 and Comparative Examples 1-12 were applied to one side of a polyimide film (DuPont, Kapton ENS, length x width x thickness = 200 mm x 300 mm x 25 μm) with a bar coater (RDS #15) to a dry thickness of 35 μm. The film was then dried at 100 °C for 10 minutes and then at 200 °C for 10 minutes to produce a coverlay film with a 35 μm adhesive layer. The resulting coverlay film (adhesive layer side) was placed on copper foil from which the anticorrosive metal layer on the surface had been removed (polyimide film / adhesive layer / copper foil), pressed at 400 °C, 1 MPa, and for 1 minute, and then heated in an oven at 400 °C for 24 hours to obtain a three-layer laminate consisting of polyimide film / adhesive layer / copper foil.

[0103] A polyimide copper-clad laminate (Nippon Steel Chemical Co., Ltd., Espanex MC18-25-00FRM) was circuit-processed to prepare a printed circuit board with a circuit of wiring width / wiring spacing (L / S) = 1 mm / 1 mm. The above coverlay film (adhesive layer side) was placed on the circuit side of the printed circuit board (polyimide film / adhesive layer / printed circuit board / adhesive layer / polyimide film), pressed at a temperature of 400°C, a pressure of 1 MPa, and for 1 minute, and then heated in an oven at a temperature of 400°C for 24 hours to obtain a wiring board with a coverlay film (a five-layer laminate of polyimide film / adhesive layer / printed circuit board / adhesive layer / polyimide film).

[0104] The adhesive strength of the obtained laminate was measured by the following method and evaluated according to the following criteria, and the results are shown in Table 12. In addition, the solder heat resistance (dry and humidity resistance) of the obtained wiring board was evaluated by the following method, and the results are shown in Table 12.

[0105] (Adhesive strength) The laminate was cut into a test piece 10 mm wide and 100 mm long, and the polyimide film and copper foil were peeled off in a 180° direction at a rate of 50 mm / min using a tensile tester (Strograph-M1, manufactured by Toyo Seiki Co., Ltd.). The peel strength was taken as the adhesive strength and evaluated according to the following criteria. ◎:0.35kN / m or more ○: 0.2kN / m or more and less than 0.35kN / m ×: Less than 0.2 kN / m

[0106] (Solder heat resistance (dry)) The obtained wiring board was left in a thermo-hygrostat chamber at a temperature of 105°C and a relative humidity of 50% for 1 hour, and then immersed in a heated solder bath for 10 seconds. The adhesion state was observed to check for defects such as foaming, swelling, and peeling, and evaluated according to the following criteria. ○: No defects such as foaming, swelling, or peeling occurred even at a solder bath temperature of 300°C. ×: Defects such as foaming, swelling, and peeling occurred when the solder bath temperature was less than 300°C.

[0107] (Solder heat resistance (moisture resistance)) The obtained wiring board was left in a constant temperature and humidity chamber at a temperature of 85°C and a relative humidity of 85% for 24 hours, and then immersed in a heated solder bath for 10 seconds. The adhesion state was observed to check for defects such as foaming, swelling, and peeling. ○: No defects such as foaming, swelling, or peeling occurred even at a solder bath temperature of 280°C. ×: Defects such as foaming, swelling, and peeling occurred when the solder bath temperature was less than 280°C.

[0108] [Table 12]

[0109] Examples 53 to 58 (photosensitive resin) and Comparative Examples 29 to 32 Each varnish (polyimide precursor solution) obtained in Examples 1-12 and Comparative Examples 1-6 was weighed out to a solids content of 10 g, and 1.6 g of 1,2-naphthoquinone diazide-5-sulfonic acid ester of α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene (TS150-A, manufactured by Toyo Gosei Co., Ltd.) as a quinone diazide compound and 0.42 g of WPAG-567 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a photoacid generator were added to obtain a photosensitive polyimide precursor composition. The obtained photosensitive polyimide precursor composition was applied to a 6-inch silicon wafer so that the film thickness after prebaking would be 14-16 μm, and the wafer was prebaked at 120°C for 2 minutes using a hot plate (Mark-7 coater and developer, manufactured by Tokyo Electron Limited) to obtain a photosensitive resin film. Next, the patterned reticle was placed in an exposure machine (GCA i-line stepper DSW-8000), and the resulting photosensitive resin film was exposed to i-line (365 nm) from a mercury lamp at an intensity of 365 nm for varying exposure times. Using a Tokyo Electron Mark-7 developing device, the exposed film was sprayed with a 2.38% aqueous solution of tetramethylammonium hydroxide for 10 seconds at 50 rpm. The film was then left to stand for 40 seconds at 0 rpm, sprayed again for 10 seconds, left to stand for 40 seconds, rinsed with water at 400 rpm, and dried for 10 seconds at 3000 rpm to obtain a developed photosensitive resin film. The developed photosensitive resin film was subjected to heat treatment in an inert oven INH-21CD manufactured by Koyo Thermo Systems Co., Ltd. under a nitrogen stream (oxygen concentration 20 ppm or less) at 140°C for 30 minutes, then heated to 350°C over 1 hour, and then at 350°C for 1 hour to produce a cured film.

[0110] The storage stability, sensitivity and resolution in pattern processing, shrinkage of film thickness before and after heat treatment, and adhesive properties of the cured film of the obtained photosensitive polyimide precursor composition were evaluated by the following methods. The results are shown in Table 13.

[0111] (Storage stability) The photosensitive polyimide precursor composition was prepared and then immediately patterned. The absolute value of the difference between the optimal exposure time and the optimal exposure time for a composition that had been left at 23°C for 2 weeks and then patterned was calculated, and the results were evaluated according to the following criteria. ◎: The absolute value of the difference is 100 msec or less ○: The absolute value of the difference is over 100 msec and 200 msec or less ×: The absolute value of the difference is over 200 msec

[0112] (sensitivity) After exposure and development, the exposure time (optimum exposure time) required to form a 50 μm line and space pattern (1L / 1S) with a width of 1:1 was determined and evaluated according to the following criteria. The shorter the optimal exposure time, the higher the sensitivity. ◎: Optimal exposure time is 700 msec or less ○: Optimal exposure time is over 700 msec and 800 msec or less ×: Optimal exposure time is over 800 msec

[0113] (resolution) After exposure and development, the minimum pattern size at the optimum exposure time was measured and evaluated according to the following criteria: the smaller the minimum pattern size, the higher the resolution. ◎: The minimum pattern dimension is 5 μm or less ○: The minimum pattern dimension is more than 5 μm and 10 μm or less ×: The minimum pattern dimension is more than 10 μm

[0114] (shrinkage rate) Using a Lambda Ace STM-602 manufactured by Dainippon Screen Mfg. Co., Ltd., the film thickness of the photosensitive resin film after development (refractive index 1.629) and the film thickness of the cured film (refractive index 1.773) were measured, and the shrinkage rate of the film thickness was calculated according to the following formula and evaluated according to the following criteria. Shrinkage rate (%) = (film thickness after development - film thickness after curing) ÷ film thickness after development × 100 ◎: Shrinkage rate is 25% or less ○: Shrinkage rate is over 25% and 30% or less ×: Shrinkage rate exceeds 30%

[0115] (Adhesive properties) The photosensitive polyimide precursor composition was applied to a silicon substrate so that the film thickness after prebaking was 10 μm, and the substrate was prebaked at 120°C for 2 minutes using a hot plate (Tokyo Electron Mark-7 Coater / Developer). The substrate was then heat-treated in an air atmosphere at 170°C for 30 minutes and then at 350°C for 1 hour to obtain a polyimide film. The polyimide film was subjected to a pressure cooker test (PCT) at 120°C and 2 atmospheres under saturated conditions for 400 hours. One hundred 2 mm squares were then cut into the cross-cuts, and a peel test was performed using adhesive tape. The number of peeled squares was counted, and the adhesion properties were evaluated according to the following criteria. ○: Number of peeled pieces is less than 30 ×: 30 or more peeled pieces

[0116] [Table 13]

[0117] Examples 59 to 64 (ink compositions) and Comparative Examples 33 to 36 The various varnishes (polyimide precursor solutions, polyimideamide precursor solutions) obtained in Examples 1 to 24 and Comparative Examples 1 to 12 were used as ink compositions as they were, and the warpage, solvent resistance, plating resistance, flame retardancy, and printability after printing (application and drying) were evaluated by the following methods. The results are shown in Table 14.

[0118] (warp) Each varnish was applied to a copper foil measuring 50 mm x 50 mm x 13 μm in length x width x thickness, so that the dried film thickness would be 10 μm. The coating was then dried in an oven at 400°C for 30 minutes to obtain a laminate in which a polyimide resin layer or a polyamideimide resin layer was laminated on the copper foil (substrate). The average amount of warping at the four corners of the laminate was calculated and evaluated according to the following criteria. ◎: Average warpage is 1mm or less ○: Average warpage is over 1mm and 2mm or less ×: The average amount of warpage is over 2 mm

[0119] (Solvent resistance test) Each of the laminates (substrate: copper foil) obtained in the above (warpage) test was immersed in the solvent shown in Table 14 at room temperature for 5 minutes, and the condition of the surface (resin layer) was visually observed and evaluated according to the following criteria. ◎: No change ○: Roughness or dissolution is observed on some parts of the surface ×:Dissolution

[0120] (Plating resistance) Each of the laminates (substrate: copper foil) obtained in the above (warpage) test was subjected to electroless gold plating treatment in the following steps to obtain test specimens. Specifically, the laminates were immersed in the baths for each step in sequence and then dried. The surface condition of the obtained test specimens was visually observed and evaluated according to the following criteria. (Electroless gold plating process) Degreasing treatment (acid degreasing = acid treatment), water rinsing, soft etching, water rinsing, desmear treatment, Palladium chloride catalysis, nickel (nickel nitrate) plating, Gold (potassium cyanide gold) plating, water washing, drying (Evaluation criteria) ◎: No change ○: Damage near the edge ×: Plating adheres to the surface in granular form

[0121] (Flame retardant) Each varnish was applied to a polyimide film (Toray DuPont, Kapton 100H, 25 μm thick) to a dry thickness of 10 μm. The film was then dried in an oven at 400°C for 30 minutes to obtain a laminate (substrate: polyimide film) in which a polyimide resin layer or a polyamideimide resin layer was laminated on a polyimide film (substrate). The flame retardancy of the resulting laminate was evaluated according to the UL94 Vertical Flame Test (VTM) for film materials, using the following flammability classification. ◎:V-0 ○:V-1 ×:V-2

[0122] (Printability) Various varnishes were printed onto polyimide film (Toray DuPont Co., Ltd., Kapton 100H, 25 μm thick) using a 100 μm thick stainless steel metal mask to form line-and-space patterns with 500 μm line widths and 500 μm spacings. Specifically, a metal mask was placed on the polyimide film and pressed tightly against it. The various varnishes were then applied, and the openings in the metal mask were filled with the liquid using a fluororesin spatula. The excess liquid was then removed, and the metal mask was slowly removed. After printing, the film was immediately placed in a thermo-hygrostat at approximately 100% humidity and 50°C for 8 minutes, and then heated in an oven at 400°C for 30 minutes to obtain a laminate (substrate: polyimide film) consisting of a 15-20 μm thick polyimide resin or polyamideimide resin layer laminated on a polyimide film (substrate). The printability of the resulting laminate was evaluated according to the following criteria. ◎: No bleeding or fading in the pattern. ○: The pattern is recognizable, but there is slight blurring or fading. ×: There is bleeding or fading to the extent that the pattern cannot be confirmed.

[0123] [Table 14]

[0124] As can be seen from the results of the Examples and Comparative Examples shown in Tables 10 to 14, the polyimide precursors and polyamideimide precursors synthesized using the resin synthesis solvent (C) containing the amide solvent (A) and the reaction accelerator (B) according to an embodiment of the present invention have high molecular weights, while the precursor solutions (resin varnishes) obtained are low in viscosity, highly transparent, and highly stable. Such resin varnishes can be suitably used as various binder resins, lubricating coatings (lubricating paints), adhesives, photosensitive resins, and ink compositions. [Industrial Applicability]

[0125] As described above, the resin synthesis solvent (C) according to an embodiment of the present invention contains an amide solvent (A) and a reaction accelerator (B) and is suitable for use in synthesizing polyimides, polyamideimides, polyesterimides, polyimide copolymers composed of precursors thereof and / or two or more precursors selected from these, and polyurethane resins. Resin varnishes, such as polyimide varnish, polyamideimide varnish, and polyurethane resin varnish, produced using the resin synthesis solvent according to an embodiment of the present invention are suitable for use as binder resins in a variety of applications. Furthermore, polyimide films obtained by molding and processing exhibit excellent physical properties and are suitable for use as surface protection films and interlayer insulating films for semiconductor devices, insulating layers and spacer layers for organic electroluminescence (EL) devices, planarizing films for thin-film transistor substrates, insulating films for organic transistors, flexible printed circuit boards, flexible device substrates, substrates for liquid crystal displays, organic electroluminescence (EL) displays, electronic paper substrates, thin-film solar cell substrates, and other light-receiving device substrates, as well as binders for electrodes in lithium-ion secondary batteries and adhesives for semiconductors. Furthermore, the polyimide precursor produced using the solvent for resin synthesis according to an embodiment of the present invention has excellent solubility in soluble polyimides, and is therefore suitable for use in producing a liquid crystal aligning agent.

Claims

1. A polyimide precursor, a polyamideimide precursor, a polyimide resin, and a solvent (C) for synthesizing a polyamideimide resin, comprising 10 to 99.9999 mass% of an amide solvent (A) and 0.0001 to 5 mass% of a reaction accelerator (B), the amide solvent (A) is one or more compounds selected from the group consisting of N-alkyl(C4-C6)-2-pyrrolidone, N-alkyl(C1-C4)alkane(C2-C6)amide, N,N-dialkyl(C1-C2)alkane(C2-C8)amide, alkoxy(C1-C6)-N-alkyl(C1-C2)alkane(C2-C4)amide, alkoxy(C1-C12) or phenyloxy-N,N-dialkyl(C1-C2)alkane(C2-C4)amide, alkanoyl(C2-C8)morpholine, alkoxy(C1)alkanoyl(C2-C3)morpholine, and N,N-dialkyl(C2-C6)acetamide; The reaction accelerator (B) is a solvent for resin synthesis (C), which is an aliphatic or aromatic tertiary amine compound having one or more tertiary amino groups in the molecule.

2. The solvent (C) for resin synthesis according to claim 1, wherein the reaction accelerator (B) is an aliphatic or aromatic tertiary amine compound represented by general formula (2), which has one or more tertiary amino groups in the molecule and further has one or more functional groups selected from an ether group, an ester group, and an amide group in the molecule. 【Chemical 1】 (In the formula, A, B, and C each independently represent a linear alkyl group having 1 to 22 carbon atoms, a branched alkyl group or alkyl ether group having 3 to 22 carbon atoms, an alkyl ester group, an alkylamide group, an alicyclic hydrocarbon having 3 to 22 carbon atoms, and an aromatic hydrocarbon having 6 to 22 carbon atoms, a substituent having an ether group represented by general formula (3), a substituent having an ester group represented by general formula (4), a substituent having an amide group represented by general formula (5) (R ５ , R ７ and R ９ R respectively represent a linear alkylene group having 1 to 22 carbon atoms, a branched alkylene group or alkylene ether group having 3 to 22 carbon atoms, an alicyclic hydrocarbon having 3 to 22 carbon atoms, and an aromatic hydrocarbon having 6 to 22 carbon atoms. ６ , R ８ , R １０ and R １１ represents a linear alkyl group having 1 to 22 carbon atoms, a branched alkyl group or alkyl ether group having 3 to 22 carbon atoms, an alkyl ester group, an alkylamide group, an alicyclic hydrocarbon having 3 to 22 carbon atoms, or an aromatic hydrocarbon having 6 to 22 carbon atoms. １０ and R １１ may each independently be a hydrogen atom, and R １０ and R １１ may combine with the nitrogen atom carrying them to form a saturated 5- to 7-membered ring (including one containing an oxygen atom). 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】

3. The solvent for resin synthesis (C) according to claim 1 or 2, further comprising one or more solvents selected from the group consisting of aromatic hydrocarbon solvents, urea solvents, lactone solvents, ether solvents, ketone solvents, ester solvents, 1,3-dioxolane, dimethyl sulfoxide, nitrobenzene, N-formylmorpholine, and 4-acetylmorpholine.

4. Toluene, xylene, ethylbenzene, solvent naphtha, tetralin, 1,3-dimethylurea, 1,3-diethylurea, 1,3-diphenylurea, 1,3-dicyclohexylurea, tetramethylurea, tetraethylurea, propyleneurea, N,N-dimethylpropyleneurea, 2-imidazolidinone, 1,3-dimethyl-2-imidazolidinone, β-propiolactone, γ-butyrolactone, α-acetyl-γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, dibutyl ether, cyclopentyl methyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether 4. The solvent for resin synthesis (C) according to claim 1, further comprising one or more solvents selected from the group consisting of ethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, dipropylene glycol dimethyl ether, 1,4-dioxane, 2-methyltetrahydrofuran, 4-methyltetrahydropyran, acetophenone, acetylacetone, butyl acetate, ethyl benzoate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, ethyl acetoacetate, isoamyl acetate, n-pentyl acetate, and ethyl propionate.

5. The solvent for resin synthesis (C) according to any one of claims 1 to 4, further comprising a stabilizer (D) and / or an ionic liquid.

6. A method for producing a polyimide precursor or a polyamideimide precursor, which comprises using the solvent for resin synthesis (C) according to any one of claims 1 to 5, mixing an acid dianhydride with a diamine and / or a diisocyanate, and polymerizing the mixture; and a method for producing a polyimide or a polyamideimide, which comprises heating and imidizing these precursors.

7. 6. A resin varnish selected from polyimide varnish and polyamideimide varnish, comprising the solvent for resin synthesis (C) according to claim 1.

8. A binder resin comprising the solvent for resin synthesis (C) according to any one of claims 1 to 5 and one or more resin varnishes selected from polyimide varnishes and polyamideimide varnishes.

9. An ink composition comprising the solvent for resin synthesis (C) according to any one of claims 1 to 5 and at least one resin varnish selected from polyimide varnishes and polyamideimide varnishes.

10. A photosensitive resin composition comprising the solvent for resin synthesis (C) according to any one of claims 1 to 5 and one or more resin varnishes selected from polyimide varnishes and polyamideimide varnishes.

11. An adhesive resin composition comprising the solvent for resin synthesis (C) according to any one of claims 1 to 5 and at least one resin varnish selected from polyimide varnishes and polyamideimide varnishes.

12. A resin composition for a lubricating coating film, comprising the solvent for resin synthesis (C) according to any one of claims 1 to 5 and one or more resin varnishes selected from polyimide varnishes and polyamideimide varnishes.

13. A heat-resistant coating material comprising the solvent for resin synthesis (C) according to any one of claims 1 to 5 and one or more resin varnishes selected from polyimide varnishes and polyamideimide varnishes.

14. A liquid crystal alignment treatment agent comprising the solvent for resin synthesis (C) according to any one of claims 1 to 5 and at least one resin varnish selected from polyimide varnishes and polyamideimide varnishes.

15. A method for producing a polyimide film, comprising forming a coating film on a substrate using a coating liquid containing the solvent for resin synthesis (C) according to any one of claims 1 to 5 and a polyimide varnish or a polyimide resin solution, and then performing stepwise thermal imidization.

16. A polyimide film obtained by heating a coating film containing the solvent for resin synthesis (C) according to any one of claims 1 to 5 and a polyimide varnish or a polyimide resin solution.

17. Polyimide particles obtained by heating a composition containing the solvent for resin synthesis (C) according to any one of claims 1 to 5 and a polyimide varnish.

18. A metal laminate comprising a metal substrate and a coating film formed from the resin varnish according to claim 7 or the binder resin according to claim 8.

19. A metal laminate comprising the polyimide film according to claim 16 or the polyimide particles according to claim 17 and a metal substrate.

20. A wiring board comprising the metal laminate according to claim 18 or 19.

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