Polyimide resin powder, polyimide resin varnish, and polyimide resin film

Abstract

To provide a polyimide resin powder and a polyimide resin varnish which are dissolvable in an organic solvent, enabling production of a polyimide resin film having excellent thermal resistance, adhesiveness, and mechanical properties, and further exhibiting excellent workability under low-temperature conditions.SOLUTION: A polyimide resin powder contains a polyimide synthesized from a diamine compound and a tetracarboxylic dianhydride, where the polyimide is a polyimide resin having (a) a structural unit derived from bisaminophenoxybenzene, (b) a structural unit derived from 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride, and (c) a structural unit derived from 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and includes a polyimide containing the respective structural units in a specific molar ratio.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyimide resin powder and a polyimide resin varnish, and more particularly to a solvent-soluble polyimide resin powder, polyimide resin varnish, and polyimide resin film that provide polyimide resin films with excellent heat resistance and adhesiveness and are suitable for use in semiconductors, sensors, electronic materials, batteries, insulating materials, on-vehicle parts, acoustic parts, and other applications. [Background technology]

[0002] Polyimide resins are polymers with excellent heat resistance and are used in a wide range of fields requiring heat resistance and high reliability, such as aerospace, electrical insulation, and electronics. For example, Kapton (registered trademark) from DuPont, Apical (registered trademark) from Kaneka Corporation, and Upilex (registered trademark) from UBE Corporation are known to be widely used as non-thermoplastic polyimides with excellent heat resistance as film materials. However, such non-thermoplastic polyimides have poor fluidity, which makes them difficult to use in molding processes or as adhesives.

[0003] In recent years, thermoplastic polyimides, such as AURUM (registered trademark) from Mitsui Chemicals, Inc., have been proposed. These materials are heat-resistant yet flowable, and are used in molding applications as moldable materials.

[0004] Conventional thermoplastic polyimides such as these have a problem in that the imide bond generally forms a strong bond, resulting in a high softening temperature and making it difficult to mold at low temperatures. To address this issue, JP 2019-59834 A and other publications propose a polyimide powder that exhibits excellent heat resistance and processability and solvent solubility, and a polyimide film produced using the same.

[0005] On the other hand, as a polyimide that can be molded or bonded at low temperatures, polyimidesiloxanes that have a low softening temperature and can be processed at low temperatures have been proposed in JP-A-11-71457, etc. The use of such polyimidesiloxanes has the advantage of enabling processing at low temperatures of 200°C or less, which was a problem with conventional polyimide materials. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-59834 [Patent Document 2] Japanese Patent Application Publication No. 11-71457 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the polyimide film obtained from the polyimide powder proposed in Patent Document 1 does not necessarily have fluidity, and there is a problem that it is difficult to use as an adhesive after film formation. Furthermore, when polyimide siloxane is used, although processing at low temperatures is possible, the polyimide contains a siloxane structure with poor heat resistance, so decomposition of the polyimide occurs even at temperatures as low as 400°C or less. Patent Document 2 has a problem that the heat resistance of the polyimide is impaired, limiting its use at high temperatures. An object of the present invention is to provide a polyimide resin powder and a polyimide resin varnish that are soluble in organic solvents and that give polyimide resin films that are excellent in heat resistance, adhesiveness, and mechanical properties and also have excellent processability at low temperatures. [Means for solving the problem]

[0008] The present inventors have found that by using a specific diamine compound and two or more specific tetracarboxylic dianhydrides in the synthesis of a polyimide resin, it is possible to obtain a solvent-soluble polyimide resin powder that is easy to handle and that gives a polyimide resin film that is extremely excellent in heat resistance, adhesiveness, and mechanical properties and that exhibits a relatively low softening temperature, and thus have completed the present invention.

[0009] According to the present invention, there are provided the following polyimide resin powder, polyimide resin varnish, and polyimide resin film. [1] A polyimide-based resin powder containing a polyimide synthesized from a diamine compound and a tetracarboxylic dianhydride, wherein the polyimide is (a): a structural unit derived from a diamine compound represented by the following formula 1, and [ka] (b): 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride and (c): A polyimide resin having a structural unit derived from 3,3',4,4'-diphenylethertetracarboxylic dianhydride, the molar amount of the structural units derived from (a) relative to the total molar amount of structural units derived from a diamine compound is 50 mol % or more, A polyimide-based resin powder characterized in that the molar amount of the constituent units derived from (b) is 10 mol% or more, and the molar amount of the constituent units derived from (c) is 30 mol% or more, relative to the total molar amount of the constituent units derived from the tetracarboxylic dianhydride, and the total molar amount of the constituent units derived from (b) and (c) is 50 mol% or more, relative to the total molar amount of the constituent units derived from the tetracarboxylic dianhydride. [2] The polyimide resin powder according to [1], wherein the (a) is a structural unit derived from a diamine compound represented by the following formula 2: [ka] [3] The polyimide resin powder according to [1], which is soluble in an organic solvent at a concentration of 1% by weight or more. [4] The polyimide resin powder according to [1], characterized in that the reduced viscosity is in the range of 0.3 to 3.0 dL / g. [5] The polyimide resin powder according to [1], characterized in that after being formed into a polyimide resin film, the softening temperature measured according to JIS K7196 is in the range of 100 to 200°C. [6] A polyimide resin varnish, characterized in that the polyimide resin powder according to [1] is dissolved in an organic solvent at a concentration of 1 to 50% by weight. [7] The polyimide resin varnish according to [6], wherein the organic solvent is an organic solvent containing, as a main component, an organic solvent that does not contain a nitrogen atom. [8] A polyimide resin film obtained by forming the polyimide resin varnish according to [6]. [9] The polyimide resin film according to [8], characterized in that the softening temperature measured according to JIS K7196 is in the range of 100 to 200°C. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a polyimide resin powder and a polyimide resin varnish which give a polyimide resin film which has excellent heat resistance and mechanical properties, and which also has excellent adhesiveness and a relatively low softening temperature. DETAILED DESCRIPTION OF THE INVENTION

[0011] A polyimide-based resin powder according to a first embodiment of the present invention is a polyimide-based resin powder containing a polyimide synthesized using a diamine compound and a tetracarboxylic dianhydride, in which the polyimide contains, as the diamine compound, structural units derived from bisaminophenoxybenzene, which will be described later, and as tetracarboxylic dianhydrides, structural units derived from 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride (6FDA) and 3,3',4,4'-diphenylethertetracarboxylic dianhydride (ODPA), in specific ratios.

[0012] The polyimide resin varnish according to the second embodiment of the present invention is a polyimide resin solution in which the polyimide resin powder is dissolved in a solvent at a concentration of 1 to 50% by weight.

[0013] The polyimide resin film according to the third embodiment of the present invention is a resin film obtained by forming the polyimide resin varnish into a film.

[0014] 1.Raw materials 1.1. Diamine compounds In this specification, the term "structural unit derived from" is used synonymously with the corresponding diamine or tetracarboxylic dianhydride, which are raw materials for polyimides. The polyimide contained in the polyimide-based resin powder of the present invention has the above three structural units in a specific ratio. Therefore, the polyimide is produced using bisaminophenoxybenzene, which will be described later as a diamine compound, as an essential raw material, and 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride (6FDA) and 3,3',4,4'-diphenylethertetracarboxylic dianhydride (ODPA) as essential tetracarboxylic dianhydrides, in a specific ratio. The diamine compound used in the production of the polyimide-based resin powder of the present invention is bisaminophenoxybenzene (a) represented by Formula 1. [ka] The bisaminophenoxybenzene represented by formula 1 has multiple isomers that differ in the bonding position of the benzene ring, and specifically, bisaminophenoxybenzenes such as 1,4-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxybenzene), and 1,3-bis(3-aminophenoxy)benzene can be used. From the viewpoints of maintaining the softening temperature of the resulting polyimide resin within an appropriate temperature range, ensuring good adhesion, and obtaining a polyimide resin film that has good heat resistance, mechanical properties, etc., 1,3-bis(3-aminophenoxy)benzene represented by the following formula 2 can be preferably used as the bisaminophenoxybenzene. [ka]

[0015] The molar amount of the bisaminophenoxybenzene represented by formula 1, which is the diamine compound (a), used is 50 mol % or more, preferably 60 mol % or more, and more preferably 70 mol % or more, based on the molar amount of all diamine compounds used in the synthesis of the polyimide resin powder of the present invention. By using the diamine compound (a) in an amount within the above range and combining it with a tetracarboxylic dianhydride described below, it is possible to obtain a solvent-soluble polyimide resin powder that exhibits an appropriate softening temperature and gives a polyimide resin film that is excellent in heat resistance, adhesiveness, and mechanical properties.

[0016] The synthesis of the polyimide resin powder of the present invention can be carried out using only the diamine compound (a) described above, but diamine compounds other than (a) can also be used as long as they account for 50 mol% or less of the total diamine compounds used. Examples of diamine compounds that can be used include 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'- Diaminodiphenylmethane, 2,2-bis(4-aminophenyl)propane, 2,2-bis(3-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2-(3-aminophenyl)-2-(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 4,4'-bis(4-aminophenoxy)biphenyl, 3,3'-bis(4-aminophenoxy)biphenyl, 3,4'-bis(3-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[3-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[3-(4-aminophenoxy)phenyl]sulfide, bis[3-(3-aminophenoxy)phenyl]sulfide, bis[3-(4-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenyl)sulfone, bis[3-(3-aminophenoxy)phenyl]sulfone , bis[4-(3-aminophenyl)sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, bis[3-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(4-aminophenoxy)phenyl]methane, bis[3-(3-aminophenoxy)phenyl]methane, bis[3-(4-aminophenoxy)phenyl]methane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane , 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[3-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[3-(4-aminophenoxy) phenyl)-1,1,1,3,3,3-hexafluoropropane, 1,3-bis[4-(4-amino-6-trifluoromethylphenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-fluoromethylphenoxy)-α,α-dimethylbenzyl]benzene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, etc., and these diamine compounds may be used in combination with the diamine compound (a) described above. In this case, it is preferable to use diaminodiphenyl ethers such as 4,4'-diaminodiphenyl ether and 3,4'-diaminodiphenyl ether as copolymerization components in an amount of about 5 to 30 mol % of the total diamine compounds, since this allows the softening temperature of the resulting polyimide resin film to be controlled and the mechanical strength of the film to be improved.

[0017] 1.2.Tetracarboxylic acid dianhydride The tetracarboxylic dianhydrides used in the production of the polyimide resin powder of the present invention include (b): 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride (6FDA) and (c): 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA) as essential raw materials, and the molar amount of 6FDA, the tetracarboxylic dianhydride (b), used is 10 mol% or more, preferably 15 mol% or more, and the molar amount of ODPA, the tetracarboxylic dianhydride (c), used is 30 mol% or more, preferably 40 mol% or more, based on the total number of moles of tetracarboxylic dianhydrides used. The total molar amount of (b) and (c) used is 50 mol% or more, preferably 60 mol% or more, and more preferably 70 mol% or more. By using the tetracarboxylic dianhydrides (b) and (c) in the above-mentioned molar amounts in combination with the diamine compound, it is possible to obtain a polyimide resin powder that is soluble in organic solvents and that gives a polyimide resin film that is excellent in heat resistance, adhesiveness, and mechanical properties.

[0018] The polyimide resin powder of the present invention can be synthesized using only the tetracarboxylic dianhydrides (b) and (c) described above, but other tetracarboxylic dianhydrides can also be used in combination as long as they account for 50 mol% or less of the total tetracarboxylic dianhydrides used. Examples of tetracarboxylic dianhydrides that can be used other than (b) and (c) include pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 1,4-hydroquinonedibenzoate-3,3',4,4'-tetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0019] 2. Manufacturing method of polyimide resin powder The polyimide resin powder of the present invention can be produced using a diamine compound and a tetracarboxylic dianhydride as essential raw materials through the steps of polymerization to polyamic acid, imidization reaction, powderization, and drying.

[0020] 2.1.Polymerization to polyamic acid The polymerization to form polyamic acid can be carried out by reacting the diamine compound with the tetracarboxylic dianhydride while dissolving the resulting polyamic acid in a solvent that the polyamic acid is soluble in. Examples of the solvent that can be used for the polymerization to form polyamic acid include N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and dimethyl sulfoxide.

[0021] The polymerization reaction to form polyamic acid is preferably carried out in a reaction vessel equipped with a stirrer while stirring. Examples include a method of dissolving a predetermined amount of aromatic diamine compound in the solvent, adding tetracarboxylic dianhydride while stirring, and carrying out a reaction to form polyamic acid, a method of dissolving tetracarboxylic dianhydride in a solvent, adding aromatic diamine compound while stirring, and carrying out a reaction to form polyamic acid, and a method of alternately adding aromatic diamine compound and tetracarboxylic dianhydride and carrying out a reaction to form polyamic acid.

[0022] There are no particular restrictions on the temperature of the polymerization reaction to form polyamic acid, but it is preferably carried out at a temperature of 0 to 70° C., more preferably 10 to 60° C., and even more preferably 20 to 50° C. By carrying out the polymerization reaction within the above range, it is possible to obtain polyamic acid with little coloration.

[0023] Although the diamine compound and tetracarboxylic dianhydride used in the polymerization into polyamic acid are generally used in approximately equimolar amounts, the molar ratio of tetracarboxylic dianhydride to aromatic diamine compound (molar ratio) can be varied within a range of 0.95 to 1.05 to control the degree of polymerization of the resulting polyamic acid and obtain a polyimide-based resin with a desired reduced viscosity. To polymerize a polyamic acid that yields a polyimide-based resin with a reduced viscosity of 0.3 to 3 dL / g, which is the preferred reduced viscosity of the polyimide-based resin powder of the present invention, it is important to carefully control the molar ratio of tetracarboxylic acid to aromatic diamine compound and the water content in the solvent. From this perspective, the molar ratio of tetracarboxylic dianhydride to aromatic diamine compound is preferably in the range of 1.001 to 1.06, and more preferably 1.002 to 1.04. A slight excess of tetracarboxylic dianhydride stabilizes the degree of polymerization of the resulting polyamic acid and allows tetracarboxylic dianhydride-derived units to be located at the polymer terminals, resulting in a polyimide-based resin film that exhibits excellent adhesion to substrates such as metals and polymer films.

[0024] The concentration of the resulting polyamic acid solution is preferably adjusted to an appropriate concentration (for example, about 10 to 30% by weight) so that the viscosity of the solution is kept appropriate and handling in the subsequent steps is easy.

[0025] 2.2.Imidation reaction Next, the polyamic acid in the resulting polyamic acid solution is imidized. Imidization can be performed by thermal imidization, which involves heating the polyamic acid solution, or chemical imidization, which involves using an imidizing agent. Chemical imidization is preferred because it allows for easy control of the degree of polymerization of the resulting polyimide and provides excellent heat resistance, mechanical properties, and other polyimide characteristics. Carboxylic anhydrides such as acetic anhydride, propionic anhydride, succinic anhydride, phthalic anhydride, and benzoic anhydride can be used as the imidizing agent for the chemical imidization reaction. Acetic anhydride is preferred from the standpoints of cost and ease of removal after the reaction. The equivalent weight of the imidizing agent used is equal to or greater than the equivalent weight of the amide bonds in the polyamic acid to be subjected to the chemical imidization reaction, preferably 1.1 to 5 times, and more preferably 1.5 to 4 times, the equivalent weight of the amide bonds. Using a slight excess of the imidizing agent relative to the amide bonds allows for efficient imidization even at relatively low temperatures.

[0026] In addition, in the chemical imidization reaction, aliphatic, aromatic, or heterocyclic tertiary amines such as pyridine, picoline, quinoline, isoquinoline, trimethylamine, triethylamine, etc. can be used as an imidization accelerator. By using such amines, the imidization reaction can be carried out efficiently at a low temperature.

[0027] There are no particular restrictions on the temperature for the chemical imidization reaction, but it is preferably carried out at a temperature of 10° C. or higher but lower than 50° C., and more preferably at a temperature of 15° C. or higher but lower than 45° C. Carrying out the chemical imidization reaction at a temperature of 10° C. or higher but lower than 50° C. suppresses the cleavage of the polyamic acid before imidization, making it easier to control the degree of polymerization of the resulting polyimide-based resin and allowing the production of a polyimide-based resin with little coloration.

[0028] 2.3. Powderization Next, the polyimide resin in the polyimide resin solution obtained by imidization is powdered. While any method can be used to powderize the polyimide resin, the preferred method is to add a poor solvent for the polyimide resin to precipitate the polyimide resin and form a powder. When adding a poor solvent to precipitate and powder the polyimide resin, any poor solvent that can precipitate the polyimide resin can be used as the poor solvent. It is desirable for the poor solvent to be miscible with the solvent in the polyimide resin solution, so specific examples include water, methanol, and ethanol. Furthermore, using methanol as the poor solvent is preferred because it allows for the production of a stable polyimide resin powder with a good yield.

[0029] When precipitating and powdering a polyimide resin using a poor solvent, the amount of poor solvent used must be sufficient to precipitate and powder the polyimide resin. This amount is determined taking into consideration the structure of the polyimide resin, the solvent used in the polyimide resin solution, and the concentration of the polyimide resin solution. Typically, the amount of poor solvent used is at least 0.5 times the weight of the polyimide resin solution, preferably at least 0.8 times the weight of the polyimide resin solution, and more preferably at least 1 time the weight of the polyimide resin solution. Using a poor solvent at least 0.5 times the weight of the polyimide resin solution allows for the production of a stable polyimide resin powder in high yield. Furthermore, the amount of poor solvent used is typically at most 10 times the weight of the polyimide resin solution, preferably at most 7 times the weight of the polyimide resin solution, more preferably at most 5 times the weight of the polyimide resin solution, and even more preferably at most 4 times the weight of the polyimide resin solution.

[0030] When the polyimide resin is powdered by adding a poor solvent to the polyimide resin solution as described above, it is preferable to add the poor solvent dropwise while stirring the polyimide resin solution. To facilitate diffusion of the poor solvent, it is desirable to adjust the concentration of the polyimide resin solution in advance to preferably about 5 to 30 wt %, more preferably about 10 to 20 wt %.

[0031] In the present invention, there is no particular limitation on the temperature for powdering the polyimide resin. However, when precipitation and powdering are carried out by adding a poor solvent, the temperature is preferably 50°C or less, and more preferably 40°C or less, from the viewpoint of suppressing evaporation of the poor solvent and carrying out efficient precipitation.

[0032] 2.4.Drying Next, the obtained polyimide resin powder is dried to remove the solvent, imidizing agent, imidization accelerator, poor solvent, etc. In order to efficiently perform drying, it is preferable to perform drying after previously filtering the polyimide resin powder using a filtering device and further washing it as necessary to remove most of the solvent, imidizing agent, and imidization accelerator from the polyimide resin.

[0033] The polyimide resin powder can be dried at any temperature as long as it can remove residues such as the solvent, imidization agent, imidization accelerator, and poor solvent. However, if a poor solvent containing a hydroxyl group, such as methanol or ethanol, is used as the poor solvent, drying at a temperature above 100°C can result in the carboxylic acid or carboxylic anhydride groups in the polyimide reacting with the poor solvent to form ester bonds, potentially resulting in problems such as reduced heat resistance, coloration, and even a decrease in molecular weight. Therefore, the drying process is preferably carried out in two or more stages: at a temperature below 100°C and at a temperature between 100 and 350°C, or by increasing the temperature from a temperature below 100°C to a temperature between 100 and 350°C. The polyimide resin powder can be dried at normal pressure or under reduced pressure.

[0034] 3. Polyimide resin powder The polyimide-based resin powder according to the first embodiment of the present invention is a polyimide-based resin powder obtained by the above-described method, and containing units derived from (a) bisaminophenoxybenzene, which is a diamine compound essential for synthesis, and (b) 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride (6FDA) and (c) 3,3',4,4'-diphenylethertetracarboxylic dianhydride (ODPA), which are tetracarboxylic dianhydrides similarly essential for synthesis.

[0035] The polyimide resin powder of the present invention has a reduced viscosity of 0.3 to 3.0 dL / g, preferably 0.4 to 2.5 dL / g, and more preferably 0.5 to 2.0 dL / g. Controlling the reduced viscosity within the range of 0.3 to 3.0 dL / g makes it easier to control the viscosity when the polyimide resin powder is dissolved in a solvent to form a varnish, and improves the mechanical properties and heat resistance of the polyimide resin film that is finally obtained.

[0036] The heat resistance of the polyimide resin powder of the present invention can be indicated by the 5% weight loss temperature (Td5), which can be measured using a thermogravimetric differential thermal analyzer (TG-DTA) as the temperature at which the weight of the polyimide resin powder decreases by 5%.

[0037] The polyimide resin powder of the present invention is characterized by having heat resistance, mechanical properties, and solvent solubility, as well as adhesiveness to various substrates, and from that viewpoint, when made into a polyimide resin film obtained by the method described below, the softening temperature measured according to JIS K7196 is preferably 100 to 200° C., more preferably 100 to 175° C., and even more preferably 100 to 150° C. By giving the softening temperature of 100 to 200° C. when made into a polyimide resin film, it is possible to obtain a polyimide resin that has excellent adhesiveness while maintaining heat resistance and mechanical properties.

[0038] 4. Polyimide resin varnish The polyimide resin varnish according to the second embodiment of the present invention can be obtained by dissolving the polyimide resin powder according to the first embodiment in any solvent in which the polyimide resin is soluble, at a concentration of 1 to 50% by weight.

[0039] The solvent used in the polyimide resin varnish of the present invention can be any solvent that can dissolve the polyimide resin powder of the present invention, and examples include N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, 2-butanone, cyclopentanone, and γ-butyrolactone. Among these solvents, a solvent primarily composed of a non-nitrogen-containing organic solvent such as 2-butanone, cyclopentanone, or γ-butyrolactone is preferred for producing a polyimide resin varnish, as it allows for efficient drying of the solvent when the polyimide resin varnish is cast and dried to form a polyimide resin film. Here, a solvent primarily composed of a non-nitrogen-containing organic solvent refers to a solvent containing 80% by weight or more of a non-nitrogen-containing organic solvent that does not contain nitrogen atoms, such as 2-butanone, cyclopentanone, or γ-butyrolactone.

[0040] The viscosity of the polyimide resin varnish of the present invention can be appropriately determined depending on the method of use of the polyimide resin varnish, the thickness of the polyimide resin film to be formed, etc., but is usually 10 to 1,000,000 mPa·s, preferably 100 to 500,000 mPa·s, and more preferably 200 to 200,000 mPa·s. By adjusting the viscosity of the polyimide resin varnish to 10 to 1,000,000 mPa·s, a polyimide resin film with few defects can be easily formed.

[0041] In addition to the polyimide resin and solvent, additives such as fillers, inorganic fibers, nanofibers, pigments, dyes, dispersants, viscosity stabilizers, and antifoaming agents can also be added to the polyimide resin varnish of the present invention for the purpose of facilitating the formation of a polyimide resin film obtained using this varnish and improving the performance of the polyimide resin film. By adding appropriate amounts of these additives, a polyimide resin film can be obtained that is free of defects and has excellent heat resistance and mechanical properties.

[0042] 5. Polyimide resin film The polyimide resin varnish of the present invention is cast onto any supporting substrate, and then the solvent in the polyimide resin varnish is dried to obtain a polyimide resin film according to the third embodiment of the present invention. The thickness of the polyimide resin film of the present invention is arbitrary, but from the viewpoints of ease of coating and the mechanical strength of the resulting polyimide resin film, it is preferably in the range of 0.5 to 200 μm, more preferably in the range of 1 to 100 μm, and even more preferably in the range of 2 to 50 μm.

[0043] The polyimide resin film of the present invention is designed in consideration of good adhesion to other substrates and processability, and from these viewpoints, the softening temperature measured according to JIS K7196 is preferably in the range of 100 to 200°C, more preferably in the range of 100 to 175°C, and even more preferably in the range of 100 to 150°C. [Example]

[0044] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0045] <Method for measuring reduced viscosity of polyimide resin powder> A polyimide resin solution was prepared by dissolving polyimide resin powder in N,N-dimethylacetamide (DMAC) to a concentration of 0.5 g / dL. Using an Ubbelohde viscometer, the outflow time (T) of the polyimide resin solution and the outflow time (T0) of the DMAC solvent alone were measured at 30°C, and the reduced viscosity was calculated using the following formula: Reduced viscosity (dL / g)=(T-T0) / T0 / 0.5

[0046] <Method for measuring the 5% weight loss temperature of polyimide resin powder> Measurement was performed using a thermogravimetric differential thermal analyzer (Shimadzu Corporation, DTG-60). 10 mg of polyimide resin powder was placed in a platinum measurement pan to serve as a measurement sample. The polyimide resin powder placed in the measurement pan was heated at a rate of 10°C / min in a nitrogen gas flow, and the temperature at which the weight of the polyimide resin powder had decreased by 5% was defined as the 5% weight loss temperature.

[0047] <Method for measuring tensile strength and elongation of polyimide resin film> Polyimide resin powder was dissolved in cyclopentanone (CP) in the amount specified in the following Examples and Comparative Examples. Next, using an applicator, a polyimide resin film was formed on a smooth, 3-mm-thick glass plate to a thickness of 50 μm after drying, taking care to avoid the inclusion of foreign matter, bubbles, or other defects in the polyimide resin film. The film was then held at 130°C for 60 minutes in a hot air oven, then heated from 130°C to 260°C at a rate of 5°C / min, and further held at 260°C for 10 minutes to dry. The film was then peeled off from the glass plate to prepare a polyimide resin film sample for measurement.

[0048] The resulting polyimide film was then cut using a feather blade to prepare 10 test pieces measuring 10 mm x 150 mm. Ten test pieces were subjected to a tensile test using a tensile testing machine (Shimadzu Corporation, Autograph AGS-H, Load Cell 500N) with a chuck distance of 50 mm and a pulling speed of 50 mm / min. The tensile strength and elongation at break were measured, and the average values ​​of 10 tests were calculated as the tensile strength and elongation, respectively.

[0049] <Method for measuring the softening temperature of polyimide resin film> Using a polyimide resin film produced by the same method as that for measuring the tensile strength and elongation of the polyimide resin film, a thermomechanical analyzer (TMA-60 manufactured by Shimadzu Corporation) was used, and the temperature was raised at a rate of 5°C / min in a nitrogen gas flow while applying a pressure of 0.5 N using a 0.5 mm diameter indenter, according to the method specified in JIS K 7196. The softening temperature was calculated from the displacement of the resin layer at this time, based on the calculation method specified in JIS K 7196. When two or more stages of displacement were observed in the resin layer, the lower temperature was taken as the softening temperature.

[0050] <Method for measuring adhesion> The polyimide resin varnishes prepared in each Example and Comparative Example were applied to a 30 μm-thick stainless steel foil to a thickness of 25 μm. The coating was then heat-treated for 4 minutes at temperatures of 90°C, 110°C, 130°C, 160°C, 190°C, and 250°C, followed by a further heat treatment in air at 400°C for 10 minutes to produce a stainless steel-polyimide resin film laminate. Next, a photosensitive dry film resist was laminated onto the stainless steel foil, exposed to light through a mask, and the metal foil was etched using an aqueous ferric chloride solution. After etching, the dry film resist was peeled off, washed with water, and dried, resulting in multiple 1 mm x 150 mm etched patterns. The polyimide surface of the etched laminate was then fixed to a 1 mm-thick stainless steel plate using double-sided tape. The etched metal foil was peeled off at a 90° angle from the polyimide using a tensile tester (Shimadzu Corporation, Autograph AGS-H), and the adhesion strength was measured as the peel strength.

[0051] The abbreviations used in the examples and comparative examples are as follows: APB: 1,3-bis(3-aminophenoxy)benzene DAPE: 4,4'-diaminodiphenyl ether TFMB: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl 6FDA: 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride ODPA: 3,3',4,4'-diphenyl ether tetracarboxylic acid dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride DMAC: N,N-dimethylacetamide

[0052] Example 1 A 2-L glass separable flask equipped with a stirrer and agitator blade was charged with 376 g of DMAC and 58.468 g (0.2000 mol) of the diamine compound APB, and the mixture was stirred to dissolve the diamine compound in the DMAC. Next, under a nitrogen stream, 37.599 g (0.1212 mol) of the tetracarboxylic dianhydride ODPA and 35.895 g (0.0808 mol) of 6FDA were added over approximately 10 minutes while stirring the contents of the separable flask. The polymerization reaction was continued for 6 hours while adjusting the temperature to a range of 20 to 40 °C, resulting in a viscous polyamic acid solution. The molar ratio of the tetracarboxylic dianhydride to the diamine compound used was 1.01, and the concentration of the polyamic acid solution was 26 wt%.

[0053] The obtained polyamic acid solution was diluted with 372 g of DMAC to a concentration of 15 wt %, and then 7.91 g of pyridine was added as an imidization accelerator. The polyamic acid solution was stirred while maintaining the temperature in the range of 30 to 40°C, and 81.67 g (0.80 mol) of acetic anhydride (AN) was slowly added dropwise as an imidization agent over a period of about 10 minutes. The liquid temperature was then maintained at 30 to 40°C and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.

[0054] Next, 1000 g of the obtained polyimide solution containing the imidization agent and the imidization accelerator was transferred to a 5 L separable flask equipped with a stirrer and a stirring blade, and the temperature was kept at 15 to 25°C while stirring at a speed of 120 rpm. 1500 g of methanol was added dropwise thereto at a rate of 10 g / min to precipitate the polyimide.

[0055] Next, the contents of the separable flask were filtered using a suction filter, and then washed and filtered using 3000 g of methanol.

[0056] 50 g of the filtered polyimide powder was then dried in a dryer equipped with a local exhaust ventilation system at 50°C for 24 hours and then further dried at 260°C for 2 hours to remove the remaining volatile components, yielding polyimide powder (i). The reduced viscosity of polyimide powder (i) was measured to be 1.12 dL / g, and the 5% weight loss temperature was an excellent 543°C.

[0057] Next, 10 g of polyimide powder (i) was dissolved in 40 g of cyclopentanone (CP) to prepare 50 g of polyimide varnish with a concentration of 20 wt %. The viscosity of the polyimide varnish was 12,000 mPa·s.

[0058] The obtained polyimide varnish was applied to a 3 mm thick glass plate by the method described above and dried to form a 50 μm thick polyimide film, and the tensile strength, elongation, and softening temperature were measured, finding values ​​of 140 MPa, 60%, and 120° C. The polyimide varnish was also applied to a 30 μm thick stainless steel foil (SUS304 foil manufactured by Proterial Metal Co., Ltd.) to form a 25 μm thick polyimide film, and the peel strength of the stainless steel foil was measured by the method described above, showing an excellent adhesive strength of 1.2 kN / m.

[0059] Example 2 The amounts of DMAC used for dilution before the polyamic acid polymerization and imidization reactions were 351 g and 348 g, respectively. As diamine compounds, 43.851 g (0.1500 mol) of APB and 10.012 g (0.0500 mol) of DAPE were used instead of 58.468 g (0.2000 mol) of APB. As tetracarboxylic dianhydrides, 46.998 g (0.1515 mol) of ODPA and 22.434 g (0.0505 mol) of 6FDA were used instead of 37.599 g (0.1212 mol) of ODPA and 35.895 g (0.0808 mol) of 6FDA. The procedure was carried out in the same manner as in Example 1, except that polyimide powder (ii) was obtained. The reduced viscosity of the resulting polyimide powder was 1.04 dL / g, and the 5% weight loss temperature was 546 °C. Next, a 20% polyimide varnish was prepared using cyclopentanone as the solvent, as in Example 1. The viscosity of the obtained polyimide varnish was 11,000 mPa·s. Furthermore, when a polyimide film 50 μm thick was prepared in the same manner as in Example 1, it had a tensile strength of 150 MPa, an elongation of 55%, and a softening temperature of 129°C. Similarly to Example 1, the polyimide varnish was applied to a 30 μm thick stainless steel foil to form a 25 μm thick polyimide film, creating a stainless steel-polyimide two-layer material. The adhesive strength of the stainless steel foil was then examined in the same manner as in Example 1. It was confirmed that the adhesion was strong, at 1.0 kN / m.

[0060] Example 3 The amounts of DMAC used for dilution before the polyamic acid polymerization and imidization reactions were 361 g and 358 g, respectively. As diamine compounds, 46.774 g (0.1600 mol) of APB and 8.0096 g (0.0400 mol) of DAPE were used instead of 58.468 g (0.2000 mol) of APB. As tetracarboxylic dianhydrides, 40.732 g (0.1313 mol) of ODPA and 31.408 g (0.0707 mol) of 6FDA were used instead of 37.599 g (0.1212 mol) of ODPA and 35.895 g (0.0808 mol) of 6FDA. The procedure was carried out in the same manner as in Example 1, except that polyimide powder (iii) was obtained. The reduced viscosity of the resulting polyimide powder was 0.92 dL / g, and the 5% weight loss temperature was 545 °C. Next, a 20% polyimide varnish was prepared using cyclopentanone as the solvent, as in Example 1. The viscosity of the resulting polyimide varnish was 9,000 mPa·s. Furthermore, a 50 μm-thick polyimide film was prepared in the same manner as in Example 1, and found to have a tensile strength of 160 MPa, an elongation of 60%, and a softening temperature of 135°C. Similarly to Example 1, the polyimide varnish was applied to a 30 μm-thick stainless steel foil to form a 25 μm-thick polyimide film, creating a stainless steel-polyimide two-layer material. The adhesion strength of the stainless steel foil was then measured in the same manner as in Example 1, and strong adhesion of 1.1 kN / m was confirmed.

[0061] Example 4 Polyimide powder (iv) was obtained by the same procedure as in Example 1, except that the amounts of DMAC used for the dilution before the polyamic acid polymerization and imidization reactions were 367 g and 364 g, respectively, and 37.599 g (0.1212 mol) of ODPA, 26.921 g (0.0606 mol) of 6FDA, and 5.943 g (0.0202 mol) of BPDA were used instead of 37.599 g (0.1212 mol) of ODPA and 35.895 g (0.0808 mol) of 6FDA. The reduced viscosity of the resulting polyimide powder was 1.05 dL / g, and the 5% weight loss temperature was 550 °C. Next, a 20% polyimide varnish was prepared using cyclopentanone as the solvent, as in Example 1. The viscosity of the resulting polyimide varnish was 10,000 mPa·s. Furthermore, when a 50 μm thick polyimide film was prepared in the same manner as in Example 1, it had a tensile strength of 170 MPa, an elongation of 50%, and a softening temperature of 145° C. As in Example 1, polyimide varnish was applied to a 30 μm thick stainless steel foil to form a 25 μm thick polyimide film, creating a stainless steel-polyimide two-layer material.The adhesion strength of the stainless steel foil was then examined in the same manner as in Example 1, and it was confirmed to be 0.9 kN / m, indicating strong adhesion.

[0062] Example 5 The same procedure as in Example 1 was repeated, except that the amounts of DMAC used for dilution before the polyamic acid polymerization and imidization reactions were 355 g and 352 g, respectively; 43.851 g (0.1500 mol) of APB and 10.012 g (0.0500 mol) of DAPE were used instead of 58.468 g (0.2000 mol) of APB as diamine compounds; and 47.929 g (0.1545 mol) of ODPA and 22.878 g (0.0515 mol) of 6FDA were used instead of 37.599 g (0.1212 mol) of ODPA and 35.895 g (0.0808 mol) of 6FDA as tetracarboxylic dianhydrides, respectively. Polyimide powder (v) was obtained. The mole ratio of tetracarboxylic dianhydride to diamine compound was 1.03. The reduced viscosity of the resulting polyimide powder was 0.45 dL / g, and the 5% weight loss temperature was 525 °C. Next, a 20% polyimide varnish was prepared using cyclopentanone as the solvent, as in Example 1. The viscosity of the resulting polyimide varnish was 1,500 mPa·s. A 50 μm-thick polyimide film was then prepared as in Example 1, and the results showed a tensile strength of 130 MPa, an elongation of 40%, and a softening temperature of 120°C. Similarly to Example 1, the polyimide varnish was applied to a 30 μm-thick stainless steel foil to form a 25 μm-thick polyimide film, creating a stainless steel-polyimide two-layer material. The adhesion strength of the stainless steel foil was then measured as in Example 1, and strong adhesion of 1.2 kN / m was confirmed.

[0063] (Comparative Example 1) A 2-L glass separable flask equipped with a stirrer and agitator blade was charged with 438 g of DMAC and 64.048 g (0.2000 mol) of the diamine compound TFMB. The diamine compound was dissolved in the DMAC. Next, 89.736 g (0.2020 mol) of tetracarboxylic dianhydride 6FDA was added over approximately 10 minutes under a nitrogen stream while stirring the contents of the separable flask. The polymerization reaction was continued for 6 hours while adjusting the temperature to a range of 20-40°C, yielding a viscous polyamic acid solution. The molar ratio of tetracarboxylic dianhydride to diamine compound used was 1.01, and the concentration of the polyamic acid solution was 26 wt%.

[0064] The obtained polyamic acid solution was diluted with 434 g of DMAC to a concentration of 15 wt %, and then 7.91 g of pyridine was added as an imidization accelerator. The polyamic acid solution was stirred while maintaining the temperature in the range of 30 to 40°C, and 81.67 g (0.80 mol) of acetic anhydride was slowly added dropwise as an imidization agent over a period of about 10 minutes. The liquid temperature was then maintained at 30 to 40°C, and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.

[0065] Next, 1000 g of the obtained polyimide solution containing the imidization agent and the imidization accelerator was transferred to a 5 L separable flask equipped with a stirrer and a stirring blade, and the temperature was kept at 15 to 25°C while stirring at a speed of 120 rpm. 1500 g of methanol was added dropwise thereto at a rate of 10 g / min to precipitate the polyimide.

[0066] Next, the contents of the separable flask were filtered using a suction filter, and then washed and filtered using 3000 g of methanol.

[0067] Thereafter, 50 g of the filtered polyimide powder was dried in a dryer equipped with a local exhaust device at 50°C for 24 hours and then further dried at 260°C for 2 hours to remove the remaining volatile components, yielding polyimide powder (vi). The reduced viscosity of polyimide powder (vi) measured was 2.50 dL / g, and the 5% weight loss temperature was 530°C.

[0068] Next, 10 g of polyimide powder (vi) was dissolved in 40 g of cyclopentanone to prepare 50 g of polyimide varnish with a concentration of 20 wt %. The viscosity of the polyimide varnish was 60,000 mPa·s.

[0069] The obtained polyimide varnish was applied to a 3 mm thick glass plate using the method described above and dried to create a 50 μm thick polyimide film.The tensile strength, elongation, and softening temperature were measured, and the results were 170 MPa, 50%, and 360°C, respectively.The softening temperature was significantly high, confirming poor processability at low temperatures.In addition, the polyimide varnish was applied to a 30 μm thick stainless steel foil (SUS304 foil manufactured by Proterial Metal Co., Ltd.) to form a 25 μm thick polyimide film.The peel strength of the stainless steel foil was measured using the method described above, and only a low adhesive strength of 0.2 kN / m was obtained.

[0070] (Comparative Example 2) A 2-L separable glass flask equipped with a stirrer and stirring blade was charged with 424 g of DMAC, 28.034 g (0.1400 mol) of DAPE, and 51.600 g (0.0600 mol) of diaminosiloxane (KF-8010, manufactured by Shin-Etsu Chemical Co., Ltd., amino equivalent weight 430), a diamine compound having a siloxane structure. The diamine compound was dissolved in the DMAC. Next, 46.998 g (0.1515 mol) of tetracarboxylic dianhydride ODPA and 22.434 g (0.0505 mol) of 6FDA were added over approximately 10 minutes under a nitrogen stream while stirring the contents of the separable flask. The polymerization reaction was continued for 6 hours while adjusting the temperature to a range of 20 to 40 °C, yielding a polyamic acid solution. The molar ratio of tetracarboxylic dianhydride to diamine compound used was 1.01, and the concentration of the polyamic acid solution was 26 wt%.

[0071] The obtained polyamic acid solution was diluted with 420 g of DMAC to a concentration of 15 wt %, and then 7.91 g of pyridine was added as an imidization accelerator. The polyamic acid solution was stirred while maintaining the temperature in the range of 30 to 40°C, and 81.67 g (0.80 mol) of acetic anhydride was slowly added dropwise as an imidization agent over a period of about 10 minutes. The liquid temperature was then maintained at 30 to 40°C, and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.

[0072] Next, 1000 g of the resulting polyimide solution containing the imidization agent and imidization accelerator was transferred to a 5 L separable flask equipped with a stirrer and a stirring blade, and the solution was kept at a temperature of 15 to 25°C while stirring at a speed of 120 rpm. 1500 g of methanol was added dropwise to the flask at a rate of 10 g / min, and the precipitation of a polyimide having a siloxane skeleton in the form of a block was confirmed.

[0073] Next, the contents of the separable flask were filtered using a suction filter, and then washed and filtered with 1000 g of methanol.

[0074] 50 g of the filtered block polyimide was then dried in a dryer equipped with a local exhaust ventilation system at 50°C for 24 hours and then further dried at 260°C for 2 hours to remove the remaining volatile components, yielding solid polyimide (vii). The reduced viscosity of polyimide (vii) measured was 0.35 dL / g, and the 5% weight loss temperature was 380°C.

[0075] Next, 10 g of polyimide (vii) was dissolved in 40 g of cyclopentanone to prepare 50 g of polyimide varnish with a concentration of 20 wt %. The viscosity of the polyimide varnish was 2,000 mPa·s.

[0076] The obtained polyimide varnish was applied to a 3 mm thick glass plate by the method described above and dried to form a 50 μm thick polyimide film, and the tensile strength, elongation, and softening temperature were measured, yielding values ​​of 50 MPa, 120%, and 110° C. Although this polyimide has a low softening temperature and excellent processability at low temperatures, its 5% weight loss temperature was as low as 380° C., limiting its use at high temperatures, and it was difficult to say that it had excellent heat resistance.

[0077] (Comparative Example 3) A 2-L glass separable flask equipped with a stirrer and agitator blade was charged with 312 g of DMAC and 40.048 g (0.2000 mol) of the diamine compound DAPE, and the mixture was stirred to dissolve the diamine compound in the DMAC. Next, under a nitrogen stream, 46.998 g (0.1515 mol) of the tetracarboxylic dianhydride ODPA and 22.434 g (0.0505 mol) of 6FDA were added over approximately 10 minutes while stirring the contents of the separable flask. The polymerization reaction was carried out for 6 hours while maintaining the temperature within the range of 20 to 40 °C, resulting in a viscous polyamic acid solution. The molar ratio of the tetracarboxylic dianhydride to the diamine compound used was 1.01, and the concentration of the polyamic acid solution was 26 wt%.

[0078] The resulting polyamic acid solution was diluted with 309 g of DMAC to a polyamic acid concentration of 15 wt%, and then 7.91 g of pyridine was added as an imidization accelerator. The polyamic acid solution was stirred and kept at a temperature of 30-40°C. 81.67 g (0.80 mol) of acetic anhydride was slowly added dropwise over approximately 10 minutes as an imidization agent. The solution temperature was then maintained at 30-40°C to carry out the chemical imidization reaction. However, the polyimide obtained by this synthesis had poor solubility and solidified, resulting in an unsatisfactory polyimide solution. The results are summarized in Table 1 below.

[0079] [Table 1]

Claims

1. A polyimide-based resin powder containing a polyimide synthesized from a diamine compound and a tetracarboxylic dianhydride, the polyimide comprising: (a): a structural unit derived from a diamine compound represented by the following formula 1, and 【Chemical 1】 (b): 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride and (c): a polyimide resin having a structural unit derived from 3,3',4,4'-diphenylethertetracarboxylic dianhydride; the molar amount of the structural units derived from (a) relative to the total molar amount of structural units derived from a diamine compound is 50 mol % or more; A polyimide-based resin powder characterized in that the molar amount of the structural units derived from (b) is 10 mol% or more, and the molar amount of the structural units derived from (c) is 30 mol% or more, relative to the total molar amount of structural units derived from tetracarboxylic dianhydride, and the total molar amount of the structural units derived from (b) and (c) is 50 mol% or more, relative to the total molar amount of structural units derived from tetracarboxylic dianhydride.

2. 2. The polyimide resin powder according to claim 1, wherein the (a) is a structural unit derived from a diamine compound represented by the following formula 2: 【Chemistry 2】

3. 2. The polyimide resin powder according to claim 1, which is soluble in an organic solvent at a concentration of 1% by weight or more.

4. 2. The polyimide resin powder according to claim 1, wherein the reduced viscosity is in the range of 0.3 to 3.0 dL / g.

5. 2. The polyimide resin powder according to claim 1, wherein the softening temperature of the polyimide resin powder measured according to JIS K7196 after being formed into a polyimide resin film is in the range of 100 to 200°C.

6. A polyimide resin varnish, comprising the polyimide resin according to claim 1 dissolved in an organic solvent at a concentration of 1 to 50% by weight.

7. 7. The polyimide resin varnish according to claim 6, wherein the solvent is a solvent containing a non-nitrogen-containing organic solvent as a main component.

8. A polyimide resin film obtained by coating the polyimide resin varnish according to claim 6.

9. 9. The polyimide resin film according to claim 8, wherein the softening temperature measured in accordance with JIS K7196 is in the range of 100 to 200°C.

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