Polyimide powder, polyimide varnish and method for producing the same

Abstract

To provide a polyimide powder having excellent handleability which is soluble in organic solvent and gives a polyimide film having excellent heat resistance, transparency, mechanical properties and leveling properties, a varnish using the polyimide powder and methods for producing them.SOLUTION: There is provided a polyimide powder soluble in an organic solvent which contains a polyimide A having a weight average molecular weight Mwa in the range of 30000 g / mol≤Mwa≤100000 g / mol and having a constitutional unit derived from an aromatic diamine compound and a constitutional unit derived from tetracarboxylic dianhydride and a polyimide B having a weight average molecular weight Mwb in the range of 10000 g / mol≤Mwa≤80000 g / mol and having a constitutional unit derived from an aromatic diamine compound and a constitutional unit derived from tetracarboxylic dianhydride, wherein the value of Mwa / Mwb is 1.25 or more and the weight average molecular weight Mwm measured for each polyimide component blend is in the range of 20000 g / mol≤Mwm≤90,000 g / mol.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyimide powder, particularly a polyimide powder that can give a polyimide film having extremely excellent heat resistance, transparency, and leveling properties and is suitable for use in electronic materials and displays; a varnish using the polyimide powder; and methods for producing the varnish and the polyimide powder. [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. In recent years, transparent polyimides that combine heat resistance and transparency have been proposed. For example, Patent Document 1 proposes a soluble polyimide with excellent transparency that is suitable for optical waveguides and is synthesized from a specific monomer containing a fluorine atom. Patent Document 2 proposes a transparent polyimide that is soluble in organic solvents and uses a specific alicyclic diamine. However, Patent Documents 1 and 2 do not disclose polyimide powder, and the polyimide described in Patent Document 2 uses an alicyclic diamine as a raw material, resulting in poor heat resistance and the problem of discoloration upon heating.

[0003] As for polyimide powder, a method has been disclosed in which a poor solvent such as water or methanol is added to a soluble polyimide varnish to precipitate a polyimide resin in bulk form (Patent Document 3).

[0004] Furthermore, Patent Document 4 proposes a powder of an imidized polyamic acid obtained by polymerizing diamines and acid dianhydrides.

[0005] However, the polyimide powders described in Patent Documents 3 and 4 are produced via polyamic acid polymerized using essentially the same molar amounts of diamines and acid anhydrides as raw material monomers. However, such a production method poses the problem that the degree of polymerization of the polyamic acid can vary significantly due to slight weighing errors in the monomers, residual monomers, or variations in the purity of the monomers, resulting in an unstable degree of polymerization of the resulting polyimide powder. To address this issue, methods have been adopted in which the molar ratio of diamines to acid anhydrides is slightly different from 1, but even in such cases, the degree of polymerization still varies due to the influence of the water content in the solvent. Furthermore, even if the polyamic acid solution has the same degree of polymerization, subsequent processes such as imidization, pulverization, and drying can cause problems such as changes in the degree of polymerization due to polymer cleavage.

[0006] Thus, when polyimide powder with a fluctuating degree of polymerization is dissolved in a solvent as it is to be used as a polyimide solution (varnish), there are problems in that the viscosity of the polyimide varnish fluctuates significantly, making it impossible to produce a stable polyimide film and in that the mechanical properties of the resulting polyimide film may be deteriorated.

[0007] From this perspective, Patent Document 5 proposes a polyimide powder that suppresses fluctuations in the degree of polymerization of polyimide by mixing two polyimide powders with different weight-average molecular weights, thereby providing a polyimide varnish with a stable viscosity when dissolved in a solvent. However, the polyimide powder described in Patent Document 5 has a large weight-average molecular weight of 160,000 to 350,000, so the polyimide concentration must be reduced to achieve a viscosity that is easy to handle when used as a polyimide varnish. As a result, although there is no problem when coating a film on a flat substrate, there is a problem in that the surface does not level sufficiently when coating a film on a substrate with unevenness. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 4-235505 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-169579 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-285355 [Patent Document 4] Special Publication No. 2013-523939 [Patent Document 5] Japanese Patent Application Publication No. 2019-59835 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a polyimide powder that is soluble in organic solvents and has excellent handleability, and that can give a polyimide film that is excellent in heat resistance, transparency, mechanical properties, and leveling properties. [Means for solving the problem]

[0010] The present inventors have discovered that by mixing polyimides having different weight-average molecular weights within a specific range, a polyimide powder with good handleability can be obtained, which gives a polyimide film with extremely excellent heat resistance, transparency, mechanical properties, and leveling properties, and has completed the present invention.

[0011] According to the present invention, there are provided the following polyimide powder or polyimide varnish, and methods for producing the same. [1] A polyimide A having a weight average molecular weight Mwa in the range of 30,000 g / mol≦Mwa≦100,000 g / mol and having structural units derived from an aromatic diamine compound and structural units derived from a tetracarboxylic dianhydride; A polyimide powder soluble in an organic solvent, comprising: a polyimide B having a weight average molecular weight Mwb in the range of 10,000 g / mol≦Mwa≦80,000 g / mol, the polyimide B having structural units derived from an aromatic diamine compound and structural units derived from a tetracarboxylic dianhydride; The value of Mwa / Mwb is 1.25 or more, A polyimide powder in which the weight average molecular weight Mwm measured for a blend of polyimide components is in the range of 20,000 g / mol≦Mwm≦90,000 g / mol. [2] The polyimide powder according to [1], wherein Mwa, Mwb, and Mwm are each within the following ranges. 30,000g / mol≦Mwa≦80,000g / mol 10,000g / mol≦Mwb≦50,000g / mol 25,000g / mol≦Mwm≦60,000g / mol [3] The polyimide powder according to [1] or [2], wherein the aromatic diamine compound contains at least one aromatic diamine compound having a fluoro group. [4] The polyimide powder according to any one of [1] to [3], wherein the tetracarboxylic dianhydride contains at least one kind of aromatic tetracarboxylic dianhydride having a fluoro group. [5] The polyimide powder according to any one of [1] to [4], wherein the polyimide is synthesized through polymerization of polyamic acid and chemical imidization reaction. [6] The polyimide powder according to any one of [1] to [5], which is soluble in γ-butyrolactone. [7] The polyimide powder according to [6], characterized in that when dissolved in γ-butyrolactone at a concentration of 20% by mass, the viscosity measured at 30°C using an E-type viscometer is in the range of 500 to 3,000 mPa s. [8] The polyimide powder according to any one of [1] to [7], characterized in that when made into a polyimide film having a thickness of 25 μm, the polyimide film has a total light transmittance of 85% or more and a yellowness index of 3 or less. [9] A polyimide varnish, characterized in that the polyimide powder according to any one of [1] to [8] above is dissolved in an organic solvent.

[10] (Step 1A) A step of synthesizing a polyimide A having a weight average molecular weight Mwa in the range of 30,000 g / mol≦Mwa≦100,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride, and obtaining a solution containing the polyimide A. (Step 2A) A step of powdering a solution containing polyimide A using a poor solvent for polyimide (Step 3A) A step of adding an organic solvent to polyimide A powder to obtain polyimide varnish A (Step 1B) A step of synthesizing a polyimide B having a weight average molecular weight Mwb in the range of 10,000 g / mol≦Mwa≦80,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride, and obtaining a solution containing the polyimide B. (Step 2B) A step of powdering a solution containing polyimide B using a poor solvent for polyimide (Step 3B) A step of adding an organic solvent to the powder of polyimide B to obtain polyimide varnish B (Step 4) Mixing Polyimide Varnish A and Polyimide Varnish B A method for producing a polyimide varnish, comprising:

[11] The manufacturing method according to

[10] , which includes, instead of (Step 4), a step of mixing a solution containing polyimide A and a solution containing polyimide B after (Step 1A) and (Step 1B), and performs (Step 2A), (Step 3A), (Step 2B), and (Step 3B) on the mixture of polyimides A and B.

[12] The manufacturing method according to

[10] , which includes, instead of (Step 4), a step of mixing a powder of polyimide A and a powder of polyimide B after (Step 2A) and (Step 2B), and performs (Step 3A) and (Step 3B) on the mixture of the powders of polyimides A and B. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a polyimide powder that gives a polyimide film having excellent heat resistance, transparency, and mechanical properties, as well as excellent leveling properties. DETAILED DESCRIPTION OF THE INVENTION

[0013] The polyimide powder of the present invention is an organic solvent-soluble polyimide powder comprising: a polyimide A having structural units derived from an aromatic diamine compound and structural units derived from a tetracarboxylic dianhydride, and having a weight-average molecular weight Mwa in the range of 30,000 g / mol≦Mwa≦100,000 g / mol; and a polyimide B having structural units derived from an aromatic diamine compound and structural units derived from a tetracarboxylic dianhydride, and having a weight-average molecular weight Mwb in the range of 10,000 g / mol≦Mwa≦80,000 g / mol; wherein the polyimide powder has an Mwa / Mwb ratio of 1.25 or more and a weight-average molecular weight Mwm measured for a blend of the polyimide components in the range of 20,000 g / mol≦Mwm≦90,000 g / mol.

[0014] 1.Raw materials 1.1. Aromatic diamine compounds An aromatic diamine compound and a tetracarboxylic dianhydride are used as raw materials for producing the polyimide powder of the present invention. Any aromatic diamine compound can be used as the aromatic diamine compound as long as it reacts with the tetracarboxylic dianhydride to give a polyimide that is soluble in a solvent (e.g., N,N-dimethylacetamide (DMAC) or γ-butyrolactone). Specifically, m-phenylenediamine, p-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 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)propane, 2,2-bis(4-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, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 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,Examples of aromatic diamine compounds include 4'-diaminobiphenyl. These aromatic diamine compounds may be used alone or in combination of two or more kinds of aromatic diamine compounds. At least one polyimide to be mixed in the present invention is preferably 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, 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, or 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane. It is preferable to use an aromatic diamine compound having a fluoro group, such as 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, 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, or 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The use of such an aromatic diamine compound having a fluoro group further improves the heat resistance, transparency, mechanical properties, and solvent solubility of the polyimide.

[0015] 1.2.Tetracarboxylic acid dianhydride As the tetracarboxylic acid dianhydride used in the production of the polyimide powder of the present invention, any tetracarboxylic acid dianhydride can be used as long as it gives a polyimide that is soluble in a solvent (for example, N,N-dimethylacetamide (DMAC) or γ-butyrolactone), similarly to the above-mentioned aromatic diamine compound. Specific examples include 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride, pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 1,4-hydroquinonedibenzoate-3, Examples of tetracarboxylic dianhydrides include 3',4,4'-tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenylethertetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride. These tetracarboxylic dianhydrides may be used alone, or two or more types of tetracarboxylic dianhydrides may be used together. From the viewpoint of further improving transparency, heat resistance, mechanical properties, and solvent solubility, it is preferable to use a tetracarboxylic dianhydride having a fluoro group, such as 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride, as at least one of the polyimides to be mixed.

[0016] 2. Polyimide synthesis method The polyimide used in the blend in the present invention is synthesized by the steps of polymerization and imidization of an aromatic diamine compound and a tetracarboxylic dianhydride as raw materials to form a polyamic acid.

[0017] 2.1.Polymerization to polyamic acid The polymerization to form polyamic acid can be carried out by reacting the aromatic diamine compound with a tetracarboxylic dianhydride while dissolving the resulting polyamic acid in a solvent that the polyamic acid is soluble in. Suitable solvents for use in the polymerization to form polyamic acid include N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, and γ-butyrolactone.

[0018] 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.

[0019] 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 that is less colored and has excellent transparency.

[0020] The molar ratio of the aromatic diamine compound to the tetracarboxylic dianhydride used in the polymerization of polyamic acid can be varied within a range of 0.8 to 1.2 (molar ratio of tetracarboxylic dianhydride to aromatic diamine compound) to control the degree of polymerization of the resulting polyamic acid and obtain a polyimide with a desired weight-average molecular weight. To polymerize polyamic acid to give a polyimide with a weight-average molecular weight of 30,000 to less than 100,000 or 10,000 to 80,000, it is important to carefully control the molar ratio of the tetracarboxylic acid to the aromatic diamine compound and the amount of water in the solvent. The molar ratio of the tetracarboxylic acid to the aromatic diamine compound (molar ratio of tetracarboxylic acid to aromatic diamine compound) is preferably 1.02 to 1.2, more preferably 1.03 to 1.15. By using an appropriate excess of tetracarboxylic dianhydride in this way, the degree of polymerization of the resulting polyamic acid can be stabilized within a predetermined range, and units derived from the tetracarboxylic dianhydride can be positioned at the terminals of the polymer, resulting in a polyimide with little coloration and excellent transparency. In this case, if the molar ratio of the tetracarboxylic dianhydride to the aromatic diamine compound is high, the weight-average molecular weight of the resulting polyimide tends to be small, while if the molar ratio is close to 1, the weight-average molecular weight of the resulting polyimide tends to be large.

[0021] The concentration of the resulting polyamic acid solution is preferably adjusted to an appropriate concentration (for example, about 10 to 40% by weight) so that the viscosity of the solution is kept appropriate and handling in the subsequent steps is easy.

[0022] 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 weight-average molecular weight of the resulting polyimide and provides polyimide properties such as good heat resistance, mechanical properties, and transparency. 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 bond 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 bond. Using a slight excess of the imidizing agent relative to the amide bond allows for efficient imidization even at relatively low temperatures.

[0023] Furthermore, 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 low temperatures, and as a result, coloration during the imidization reaction can be suppressed, and a more transparent polyimide can be obtained.

[0024] 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 cleavage of the polyamic acid before imidization, makes it easier to control the weight-average molecular weight, and suppresses coloration of the polyimide, allowing the production of a polyimide with excellent transparency.

[0025] 3. Polyimide powder production 3.1.Powderization The polyimide in the polyimide solution obtained by imidization can be powdered by any method, including adding a poor solvent for the polyimide to the polyimide solution to precipitate the polyimide and form a powder, or by adding the polyimide solution to a poor solvent for the polyimide to precipitate the polyimide. However, adding a poor solvent for the polyimide to the polyimide solution to precipitate the polyimide and form a powder is simpler and preferred. When adding a poor solvent to precipitate and powder the polyimide, any poor solvent that can precipitate the polyimide can be used. It is desirable for the poor solvent to be miscible with the solvent in the polyimide solution, specifically, water, methanol, ethanol, 1-propanol, 2-propanol, etc. Furthermore, using lower alcohol poor solvents such as methanol, ethanol, 1-propanol, and 2-propanol, or mixtures thereof, as the poor solvent, is preferred because it allows for the efficient production of stable polyimide powder.

[0026] When precipitating and powdering polyimide using a poor solvent, the amount of poor solvent used must be sufficient to precipitate and powder the polyimide. This amount is determined taking into consideration the polyimide structure, the solvent used in the polyimide solution, and the concentration of the polyimide solution. Typically, the amount of poor solvent used is at least 0.5 times the weight of the polyimide solution, preferably at least 0.8 times the weight of the polyimide solution, and more preferably at least 1 time the weight of the polyimide solution. Using a poor solvent at least 0.5 times the weight of the polyimide solution allows for the production of a stable polyimide powder in high yield. Furthermore, the amount of poor solvent used is typically at most 10 times the weight of the polyimide solution, preferably at most 7 times the weight of the polyimide solution, more preferably at most 5 times the weight of the polyimide solution, and even more preferably at most 4 times the weight of the polyimide solution.

[0027] When the polyimide is powdered by adding a poor solvent to the polyimide solution as described above, it is preferable to add the poor solvent dropwise while stirring the polyimide solution. To facilitate diffusion of the poor solvent, it is desirable to adjust the concentration of the polyimide solution to about 10 to 40 wt % in advance. The polyimide powder obtained by the present invention preferably has an average particle size of 0.02 to 0.8 mm, but this can be controlled by the rate at which the poor solvent is added to the polyimide solution.

[0028] In the present invention, there is no particular limitation on the temperature for powdering the polyimide. 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.

[0029] In the present invention, two or more polyimides having different weight-average molecular weights are mixed by the method described below. The polyimides may be powdered before being mixed, or they may be mixed in the form of a polyimide solution first and then powdered.

[0030] 3.2.Drying Next, the obtained polyimide 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 powder using a filtration device and further washing it as necessary to remove most of the solvent, imidizing agent, and imidization accelerator from the polyimide.

[0031] The polyimide powder can be dried at any temperature as long as it can remove residues of the polyimide solvent, imidization agent, imidization accelerator, poor solvent, etc. However, if a poor solvent containing hydroxyl groups, such as methanol, ethanol, or propanol, is used as the poor solvent, drying at a temperature of 100°C or higher 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 powder can be dried at either atmospheric pressure or reduced pressure.

[0032] 3.3.Mixing In the present invention, two or more polyimides having different weight-average molecular weights are mixed, and the mixing method may involve powdering each polyimide in advance by the above-mentioned method and then mixing the powdered polyimides, or mixing each polyimide in the form of a polyimide solution before powdering and then mixing the polyimides.Furthermore, it is also possible to dissolve another polyimide powder in a polyimide solution before powdering and then mix the polyimide solution.

[0033] The polyimide powders can be mixed by any method capable of uniformly mixing two or more polyimide powders, such as a method using a rotary mixer, a method using a horizontal agitation mixer, a method using a vertical agitation mixer, etc. When mixing in a solution state, such as when mixing polyimide solutions together or when dissolving polyimide powder in a polyimide solution and mixing, mixing can be performed using any mixing device, such as an agitation mixer, a planetary mixer, or a kneading roll.

[0034] When polyimide powders are mixed together as they are, the resulting polyimide powder becomes the polyimide powder of the present invention. When polyimide powders are mixed in the form of a polyimide solution, the polyimide powder of the present invention can be obtained by undergoing the above-mentioned powdering and drying steps.

[0035] Polyimide A and polyimide B can be used in any mixing ratio as long as the weight average molecular weight (Mwm) after mixing falls within the range of 20,000 to 90,000. Polyimide A and polyimide B can be mixed in a ratio of 5 / 95 to 95 / 5, based on the mass of the powder, and are preferably mixed in a ratio of 10 / 90 to 90 / 10.

[0036] 4. Polyimide powder The polyimide powder of the present invention is a polyimide having structural units derived from two or more aromatic diamine compounds with different weight-average molecular weights and structural units derived from a tetracarboxylic dianhydride. The polyimide powder includes polyimide A having a weight-average molecular weight (Mwa) of 30,000 to 100,000 and polyimide B having a weight-average molecular weight (Mwb) of 10,000 to 80,000. The polyimide powder is ultimately in the form of a powder and is soluble in an organic solvent. Among the polyimides to be blended, polyimide A has a weight-average molecular weight (Mwa) of 30,000 to 100,000, preferably 30,000 to 80,000. Furthermore, among the polyimides to be blended, polyimide B has a weight-average molecular weight (Mwb) of 10,000 to 80,000, preferably 10,000 to 50,000, with a relationship of Mwa / Mwb ≥ 1.25. By setting the weight average molecular weight (Mwa) of polyimide A to 30,000 to 100,000, the weight average molecular weight (Mwb) of polyimide B to 10,000 to 80,000, and the ratio Mwa / Mwb ≧1.25, and setting the weight average molecular weight (Mwm) of the polyimide powder finally obtained by mixing to 20,000 or more and 90,000 or less, preferably 25,000 or more and 60,000 or less, it is possible to obtain a polyimide powder that is easy to handle, has excellent mechanical properties, transparency, and leveling, and has a stable weight average molecular weight.

[0037] In addition to the polyimide A and polyimide B, the polyimide powder of the present invention may contain one or more other polyimides having a weight-average molecular weight between Mwb and Mwa. Furthermore, the polyimide powder may contain polyimides having a weight-average molecular weight of 100,000 or more or 10,000 or less, as long as the amount does not impair the effects of the present invention and the weight-average molecular weight (Mwm) of the polyimide powder finally obtained by mixing falls within the range of 20,000 to 90,000. The weight-average molecular weights of the polyimides to be mixed are preferably selected so that polyimide A has the highest weight-average molecular weight among the components and polyimide B has the lowest weight-average molecular weight among the components.

[0038] It is preferable that at least one of polyimide A and polyimide B has a structural unit derived from an aromatic diamine compound having at least one type of fluoro group or a tetracarboxylic dianhydride having at least one type of fluoro group, from the viewpoint of further improving the heat resistance, transparency, mechanical properties, and solubility in solvents of the polyimide.

[0039] A polyimide varnish can be obtained by dissolving the polyimide powder of the present invention in an organic solvent in which the polyimide is soluble. As mentioned above, polyimide A and polyimide B can be mixed at any stage. Therefore, polyimide A and polyimide B powders may be mixed separately and then made into a varnish, or a solution containing polyimide A and a solution containing polyimide B may be mixed before being powdered and then powdered to make a varnish, or polyimide A and polyimide B powders may be made into varnishes separately and then mixed. The organic solvent used to make the varnish can be used in an amount such that the concentration of polyimide A, polyimide B, or a mixture thereof is 1 to 30 wt % relative to the organic solvent.

[0040] Therefore, the method for producing a polyimide powder and the method for producing a polyimide varnish of the present invention can be summarized as a method including the following steps. (Step 1A) A step of synthesizing polyimide A having a weight average molecular weight Mwa in the range of 30,000 g / mol≦Mwa≦100,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride, and obtaining a solution containing polyimide A. (Step 2A) A step of powdering a solution containing polyimide A using a poor solvent for polyimide (Step 3A) A step of adding an organic solvent to polyimide A powder to obtain polyimide varnish A (Step 1B) A step of synthesizing a polyimide B having a weight average molecular weight Mwb in the range of 10,000 g / mol≦Mwa≦80,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride, and obtaining a solution containing the polyimide B. (Step 2B) A step of powdering a solution containing polyimide B using a poor solvent for polyimide (Step 3B) A step of adding an organic solvent to the powder of polyimide B to obtain polyimide varnish B (Step 4) Mixing Polyimide Varnish A and Polyimide Varnish B Here, the above (Step 4) can be performed not only on polyimide varnish, but also on two different forms of the solutions before powdering, the powders, or the solution-powder-varnish. For example, instead of (Step 4), a step of mixing a solution containing polyimide A and a solution containing polyimide B can be performed after (Step 1A) and (Step 1B), and (Step 2A), (Step 3A), (Step 2B), and (Step 3B) can be performed on a mixture of polyimides A and B. Alternatively, instead of (Step 4), a step of mixing a powder of polyimide A and a powder of polyimide B can be performed after (Step 2A) and (Step 2B), and (Step 3A) and (Step 3B) can be performed on a mixture of powders of polyimides A and B.

[0041] 5. Polyimide Properties (Part 1: Powder Properties) The weight-average molecular weight (Mwm) of the polyimide powder after mixing in the present invention is 20,000 to 90,000, preferably 25,000 to 60,000. If the weight-average molecular weight Mwm is less than 20,000, the mechanical properties of the final polyimide film may be impaired and the polyimide may absorb more moisture. If the weight-average molecular weight Mwm exceeds 90,000, the viscosity of the polyimide solution at a predetermined concentration may become too high, making handling difficult and resulting in poor filling properties when the polyimide solution is coated on a substrate having uneven surfaces. If the concentration is reduced to solve this problem, the thickness of the resulting polyimide film may become small, resulting in poor leveling properties when the polyimide solution is coated on a substrate having uneven surfaces.

[0042] Furthermore, in the present invention, by mixing a polyimide A having a high weight-average molecular weight with a polyimide B having a low weight-average molecular weight, it becomes easier to control the weight-average molecular weight of the polyimide for each production run, which has been a problem in conventional polyimide synthesis, and there are also advantages in that the mechanical properties of the resulting polyimide film tend to be better than those of a polyimide film obtained from a polyimide powder that is not mixed.

[0043] The average particle size of the polyimide powder is preferably 0.02 to 0.8 mm, more preferably 0.03 to 0.6 mm. When the average particle size is in the range of 0.02 to 0.8 mm, residual volatile components such as the solvent, poor solvent, and imidizing agent in the polyimide powder are efficiently removed, making it easier to obtain a polyimide with extremely little coloration and excellent transparency.

[0044] The average particle size of the polyimide powder of the present invention can be measured by a laser diffraction / scattering particle size distribution measuring device.

[0045] The polyimide powder of the present invention has excellent solubility in solvents, and can be made into a polyimide powder soluble in solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, acetone, 2-butanone, and ethyl acetate. Furthermore, because the polyimide powder has a stable weight-average molecular weight in the relatively low molecular weight range of 20,000 to 90,000, when dissolved in, for example, γ-butyrolactone, it can be made into a varnish with a low viscosity of 500 to 3,000 mPa s, even at a relatively high concentration of 20%, which makes it easier to obtain a thick polyimide film and improves leveling when coated on a substrate with uneven surfaces.

[0046] 6. Polyimide Properties (Part 2: Film Properties) The transparency of the polyimide in the polyimide powder of the present invention can be determined by measuring the total light transmittance and yellowness index using a spectrophotometer. The polyimide film obtained by dissolving the polyimide powder in N,N-dimethylacetamide (DMAC) or γ-butyrolactone (GBL) to prepare a polyimide varnish and then applying it to a transparent substrate such as quartz glass to a thickness of 25 μm after drying can be determined. The total light transmittance of the polyimide film obtained from the polyimide powder of the present invention is preferably 85% or more, more preferably 90% or more. The yellowness index is preferably -3 to 3, more preferably -2 to 2, and even more preferably -1.5 to 1.5. If the total light transmittance is below the above lower limit or the yellowness index is outside the above range, it may be difficult to obtain a film with excellent transparency suitable for applications such as displays and photosensitive resists. The imidization ratio of the polyimide constituting the polyimide powder of the present invention is preferably 90% or more, more preferably 95% or more. The imidization rate can be determined by Fourier transform infrared spectroscopy (FT-IR method) of the polyimide film obtained by the above method.

[0047] The leveling property and mechanical strength (bending resistance) of the polyimide film can be evaluated, for example, by checking the irregularities after the coating film is dried on the circuit, or by checking for cracks when bent. [Example]

[0048] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0049] (Method for measuring weight-average molecular weight of polyimide) A 1 mg / mL solution of polyimide in tetrahydrofuran was prepared and analyzed using a size exclusion chromatograph (Tosoh Corporation, HLC-8320GPC) under the following conditions: eluent: tetrahydrofuran (stabilizer-free), column: TSKgel SuperHM-M (two columns in series), detector: differential refractometer, measurement temperature: 40 °C, flow rate: 0.6 mL / min, injection volume: 40 μL. Molecular weights were calculated using the relative molecular weight values ​​converted to standard materials (standard materials: 12 standard polystyrenes (molecular weights 504 to 1,090,000), calibration curve: cubic approximation curve).

[0050] (Method for measuring the average particle size of polyimide powder) The measurement was carried out using a laser diffraction / scattering particle size distribution analyzer (LA-950V2 manufactured by Horiba Ltd.) and ethanol as the dispersion medium.

[0051] (Method for measuring total light transmittance and yellowness index of polyimide) (1) How to prepare polyimide film samples for measurement Polyimide powder was dissolved in γ-butyrolactone in the amounts specified in the following Examples and Comparative Examples. Using an applicator, a film was formed on a smooth, 3 mm-thick quartz glass plate to a thickness of 25 μm after drying. The film was then heated in a hot air oven at 130°C for 60 minutes, then heated from 130°C to 260°C at a rate of 5°C / min, and further dried at 260°C for 10 minutes to prepare a polyimide film sample for measurement.

[0052] (2) Measurement of total light transmittance Using a spectrophotometer (CM-5 manufactured by Konica Minolta, Inc.), the total light transmittance of the 25 μm thick polyimide film formed on the quartz glass was determined in accordance with ASTM E 1164 under the conditions of light source C and a field of view of 2°.

[0053] (3) Yellowness index (YI) measurement Using a spectrophotometer (CM-5 manufactured by Konica Minolta, Inc.), the yellowness index (YI) of the 25 μm-thick polyimide film formed on the quartz glass was determined by scanning in the wavelength range of 360 to 740 nm under the conditions of light source C and a field of view of 2° in accordance with ASTM D 1925.

[0054] (Method for measuring viscosity of polyimide solution) The viscosity of the polyimide solutions (polyimide varnishes) prepared in the following examples and comparative examples was measured at 30° C. using an E-type viscometer (TVE-25H, manufactured by Toki Sangyo Co., Ltd.).

[0055] (Evaluation of polyimide leveling properties) A CCL for circuit boards was prepared, which consisted of a 25-μm-thick polyimide film on which a 18-μm-thick copper layer was formed as a conductor. The conductor copper was linearly formed into circuits on the circuit board with a circuit width of 20 μm and a circuit spacing of 20 μm. Next, a polyimide varnish prepared by dissolving the polyimide powder described in each Example and Comparative Example in GBL was applied at a rate of 0.1 g / cm. 2 The solution was applied to a circuit board on which a circuit had been formed so that the amount was 100% by weight, and the solution was dried at 130° C. for 30 minutes and then at 260° C. for 10 minutes. Thereafter, the cross section of the circuit board coated with the polyimide prepared in each Example and Comparative Example was observed, and the height T1 (μm) of the conductor portion of the circuit board consisting of the polyimide film substrate, conductor circuit, and coated polyimide layer, and the height T2 (μm) of the non-conductor portion of the circuit board consisting of the polyimide film substrate and coated polyimide were measured, and the difference (T1 - T2) was used as an index of leveling ability for evaluation.

[0056] (Evaluation of bending resistance of polyimide) Using a sample prepared for the leveling evaluation described above, in which a polyimide layer was formed on a circuit with a circuit width of 20 μm and a circuit spacing of 20 μm, the occurrence of cracks when the sample was bent 180° along the circuit was examined.

[0057] The abbreviations used in this example are as follows: TFMB: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl BAPP-F: 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane 6FDA: 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride BPDA: 3,4,3',4'-biphenyltetracarboxylic dianhydride DMAC: N,N-dimethylacetamide GBL: gamma-butyrolactone

[0058] (Synthesis Example 1) A 2-L separable glass flask equipped with a stirrer and agitator blade was charged with 443 g of DMAC (containing 100 ppm of water; the same applies to DMAC used in all other examples and comparative examples) and 64.047 g (0.2000 mol) of TFMB, an aromatic diamine compound with a fluoro group, and stirred to dissolve the TFMB in the DMAC. Next, 91.513 g (0.2060 mol) of 6FDA, a tetracarboxylic dianhydride, was added over approximately 10 minutes under a nitrogen stream while stirring the contents of the separable flask. The polymerization reaction was carried out with continued stirring for 6 hours while maintaining the temperature within the 20-40°C range, yielding a viscous polyamic acid solution. The molar ratio of tetracarboxylic dianhydride to aromatic diamine compound used was 1.03, and the concentration of the polyamic acid solution was 26 wt%.

[0059] To the obtained polyamic acid solution, 15.82 g of pyridine (hereinafter sometimes referred to as "Py") as an imidization accelerator was added, and the polyamic acid solution was kept at a temperature of 30 to 40°C while being stirred. 163.34 g (1.60 mol) of acetic anhydride (hereinafter sometimes referred to as "AN") as an imidization agent was slowly added dropwise over about 10 minutes, and then the liquid temperature was further kept at 30 to 40°C while being stirred for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.

[0060] Next, 500 g of the obtained polyimide solution containing the imidization agent and the imidization accelerator was transferred to a 3 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. 750 g of methanol was added dropwise thereto at a rate of 10 g / min to precipitate the polyimide.

[0061] Next, the contents of the separable flask were filtered using a suction filtration device, and then washed and filtered with 500 g of methanol.

[0062] The filtered polyimide powder was then dried in a dryer equipped with a local exhaust 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 weight-average molecular weight of polyimide powder (i) was measured to be 79,000.

[0063] (Synthesis Example 2) Polyimide powder (ii) was obtained in the same manner as in Example 1, except that the amount of DMAC used was changed from 443 g to 445 g and the amount of 6FDA was changed from 91.513 g (0.2060 mol) to 92.402 g (0.2080 mol) in Synthesis Example 1. The molar ratio of tetracarboxylic dianhydride / aromatic diamine compound used was 1.04, and the weight-average molecular weight of the obtained polyimide powder (ii) was 61,000.

[0064] (Synthesis Example 3) Polyimide powder (iii) was obtained in the same manner as in Example 1, except that the amount of DMAC used was changed from 443 g to 448 g and the amount of 6FDA was changed from 91.513 g (0.2060 mol) to 93.290 g (0.2100 mol) in Synthesis Example 1. The molar ratio of tetracarboxylic dianhydride / aromatic diamine compound used was 1.05, and the weight-average molecular weight of the obtained polyimide powder (iii) was 49,000.

[0065] (Synthesis Example 4) Polyimide powder (iv) was obtained in the same manner as in Example 1, except that the amount of DMAC used was changed from 443 g to 461 g and the amount of 6FDA was changed from 91.513 g (0.2060 mol) to 97.733 g (0.2200 mol) in Synthesis Example 1. The molar ratio of tetracarboxylic dianhydride / aromatic diamine compound used was 1.10, and the weight-average molecular weight of the obtained polyimide powder (iv) was 31,000.

[0066] (Synthesis Example 5) Polyimide powder (v) was obtained in the same manner as in Example 1, except that the amount of DMAC used was changed from 443 g to 468 g and the amount of 6FDA was changed from 91.513 g (0.2060 mol) to 100.398 g (0.2260 mol) in Synthesis Example 1. The molar ratio of tetracarboxylic dianhydride / aromatic diamine compound used was 1.13, and the weight-average molecular weight of the obtained polyimide powder (v) was 18,000.

[0067] (Synthesis Example 6) Polyimide powder (vi) was obtained in the same manner as in Example 1, except that the amount of DMAC used was changed from 443 g to 439 g, and 83.961 g (0.1890 mol) of 6FDA and 6.179 g (0.0210 mol) of BPDA were used as the tetracarboxylic dianhydride instead of 91.513 g (0.2060 mol) of 6FDA. The molar ratio of tetracarboxylic dianhydride / aromatic diamine compound used was 1.05, and the weight-average molecular weight of the resulting polyimide powder (vi) was 47,500.

[0068] (Synthesis Example 7) Polyimide powder (vii) was obtained in the same manner as in Example 1, except that the amount of DMAC used was changed from 443 g to 470 g, and 51.238 g (0.1600 mol) of TFMB and 20.738 g (0.0400 mol) of BAPP-F were used instead of 64.047 g (0.2000 mol) of TFMB in Synthesis Example 1. The molar ratio of tetracarboxylic dianhydride / aromatic diamine compound used was 1.05, and the weight-average molecular weight of the resulting polyimide powder (vii) was 48,300.

[0069] (Synthesis Example 8) A 2-L glass separable flask equipped with a stirrer and agitator blade was charged with 460 g of DMAC and 64.047 g (0.2000 mol) of TFMB, and the mixture was stirred to dissolve the TFMB in the DMAC. Next, 89.292 g (0.2010 mol) of (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 within the range of 20–40°C, yielding a viscous polyamic acid solution. The molar ratio of tetracarboxylic dianhydride to aromatic diamine compound used was 1.005, and the concentration of the polyamic acid solution was 25 wt%.

[0070] Next, 409 g of DMAC was added to the obtained polyamic acid solution to dilute it so that the concentration of polyamic acid became 15% by weight, and then 15.82 g of pyridine was added as an imidization accelerator, and the polyamic acid solution was kept at a temperature of 30 to 40°C while being stirred. 163.34 g (1.60 mol) of acetic anhydride was slowly added dropwise as an imidization agent over a period of about 10 minutes, and then the liquid temperature was further kept at 30 to 40°C while being stirred for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.

[0071] 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.

[0072] Next, the contents of the separable flask were filtered using a suction filter, and then washed and filtered with 1000 g of methanol.

[0073] 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 (viii). The weight-average molecular weight of the polyimide powder (viii) was measured to be 210,000.

[0074] [Table 1]

[0075] Example 1 The polyimide powder (i) having a weight-average molecular weight of 79,000 obtained in Synthesis Example 1 and the polyimide powder (iv) having a weight-average molecular weight of 31,000 obtained in Synthesis Example 4 were thoroughly mixed using a rotary mixer at a mass ratio of polyimide powder (i):polyimide powder (iv) = 10:90 to obtain the target polyimide powder. The weight-average molecular weight of the obtained polyimide powder was 35,800.

[0076] Next, 5 g of the resulting mixed polyimide powder was dissolved in 20 g of GBL, yielding a uniform polyimide solution with a concentration of 20% by mass and a viscosity of 820 mPa·s. This polyimide solution was then applied to quartz glass using the method described above, resulting in a polyimide film with a total light transmittance of 99% and a yellow index (YI) of 0.7. Furthermore, after applying this polyimide solution to a circuit and drying, the difference in unevenness (T1-T2) on the polyimide surface was a small 2 μm, confirming good leveling properties. Furthermore, no cracks were observed in the polyimide film during a bending test.

[0077] Example 2 The polyimide powder (ii) having a weight-average molecular weight of 61,000 obtained in Synthesis Example 2 and the polyimide powder (iv) having a weight-average molecular weight of 31,000 obtained in Synthesis Example 4 were thoroughly mixed using a rotary mixer at a mass ratio of polyimide powder (ii):polyimide powder (iv) = 20:80 to obtain the target polyimide powder. The weight-average molecular weight of the resulting polyimide powder was 37,000.

[0078] A polyimide solution was prepared in the same manner as in Example 1, in which polyimide was dissolved in GBL at a concentration of 20% by mass. A homogeneous polyimide solution was obtained, with a viscosity of 880 mPa·s. Furthermore, a 25 μm-thick polyimide film sample prepared on quartz glass in the same manner as in Example 1 had a total light transmittance of 99% and a yellowness index of 0.7. Furthermore, after applying this polyimide solution to a circuit and drying, the difference in unevenness (T1-T2) on the polyimide surface was a small 3 μm, confirming good leveling properties. Furthermore, no cracks were observed in the polyimide film during a bending test.

[0079] Example 3 The polyimide powder (iii) having a weight-average molecular weight of 49,000 obtained in Synthesis Example 3 and the polyimide powder (v) having a weight-average molecular weight of 18,000 obtained in Synthesis Example 5 were thoroughly mixed using a rotary mixer at a mass ratio of polyimide powder (iii):polyimide powder (v) = 30:70 to obtain the target polyimide powder. The weight-average molecular weight of the obtained polyimide powder was 27,300.

[0080] A polyimide solution was prepared by dissolving polyimide in GBL at a concentration of 20% by mass in the same manner as in Example 1. A homogeneous polyimide solution was obtained with a viscosity of 500 mPa·s. Furthermore, a 25 μm-thick polyimide film sample prepared on quartz glass in the same manner as in Example 1 had a total light transmittance of 98% and a yellowness index of 0.7. After applying this polyimide solution to a circuit and drying, the unevenness difference (T1-T2) of the polyimide surface was a small 2 μm, confirming good leveling properties. Furthermore, no cracks were observed in the polyimide film during a bending test.

[0081] Example 4 The polyimide powder (iii) having a weight-average molecular weight of 49,000 obtained in Synthesis Example 3 and the polyimide powder (v) having a weight-average molecular weight of 31,000 obtained in Synthesis Example 5 were thoroughly mixed using a rotary mixer at a mass ratio of polyimide powder (iii):polyimide powder (v) = 50:50 to obtain the target polyimide powder. The weight-average molecular weight of the resulting polyimide powder was 40,000.

[0082] A polyimide solution was prepared by dissolving polyimide in GBL at a concentration of 20% by mass in the same manner as in Example 1. A homogeneous polyimide solution was obtained with a viscosity of 1,050 mPa·s. Furthermore, a 25 μm-thick polyimide film sample prepared on quartz glass in the same manner as in Example 1 had a total light transmittance of 99% and a yellowness index of 0.7. After applying this polyimide solution to a circuit and drying, the unevenness difference (T1-T2) of the polyimide surface was a small 3 μm, confirming good leveling properties. Furthermore, no cracks were observed in the polyimide film during a bending test.

[0083] Example 5 Polyimide powder (ii) having a weight-average molecular weight of 61,000 obtained in Synthesis Example 2, polyimide powder (iv) having a weight-average molecular weight of 31,000 obtained in Synthesis Example 4, and polyimide powder (iii) having a weight-average molecular weight of 49,000 obtained in Synthesis Example 3 were thoroughly mixed using a rotary mixer in a mass ratio of polyimide powder (ii):polyimide powder (iv):polyimide powder (iii) = 20:70:10 to obtain the desired polyimide powder. The weight-average molecular weight of the resulting polyimide powder was 38,800.

[0084] A polyimide solution was prepared in the same manner as in Example 1, in which polyimide was dissolved in GBL at a concentration of 20% by mass. A homogeneous polyimide solution was obtained, with a viscosity of 980 mPa·s. Furthermore, a 25 μm-thick polyimide film sample prepared on quartz glass in the same manner as in Example 1 had a total light transmittance of 99% and a yellowness index of 0.7. After applying this polyimide solution to a circuit and drying, the unevenness difference (T1-T2) on the polyimide surface was a small 2 μm, confirming good leveling properties. Furthermore, no cracks were observed in the polyimide film during a bending test.

[0085] Example 6 The polyimide powder (vi) having a weight-average molecular weight of 47,500 obtained in Synthesis Example 6 and the polyimide powder (iv) having a weight-average molecular weight of 31,000 obtained in Synthesis Example 4 were thoroughly mixed using a rotary mixer at a mass ratio of polyimide powder (vi):polyimide powder (iv) = 50:50 to obtain the target polyimide powder. The weight-average molecular weight of the resulting polyimide powder was 39,300.

[0086] A polyimide solution was prepared by dissolving polyimide in GBL at a concentration of 20% by mass in the same manner as in Example 1. A homogeneous polyimide solution was obtained with a viscosity of 1,010 mPa·s. Furthermore, a 25 μm-thick polyimide film sample was prepared on quartz glass in the same manner as in Example 1, and the total light transmittance was 99% and the yellowness index was 0.7. After applying this polyimide solution to a circuit and drying, the unevenness difference (T1-T2) of the polyimide surface was a small 2 μm, confirming good leveling properties. Furthermore, no cracks were observed in the polyimide film during a bending test.

[0087] Example 7 The polyimide powder (vii) having a weight-average molecular weight of 48,300 obtained in Synthesis Example 7 and the polyimide powder (iv) having a weight-average molecular weight of 31,000 obtained in Synthesis Example 4 were thoroughly mixed using a rotary mixer at a mass ratio of polyimide powder (vii):polyimide powder (iv) = 50:50 to obtain the target polyimide powder. The weight-average molecular weight of the resulting polyimide powder was 39,700.

[0088] A polyimide solution was prepared in the same manner as in Example 1, in which polyimide was dissolved in GBL at a concentration of 20% by mass. A homogeneous polyimide solution was obtained, with a viscosity of 1,040 mPa·s. Furthermore, a 25 μm-thick polyimide film sample prepared on quartz glass in the same manner as in Example 1 had a total light transmittance of 99% and a yellowness index of 0.7. After applying this polyimide solution to a circuit and drying, the unevenness difference (T1-T2) on the polyimide surface was a small 3 μm, confirming good leveling properties. Furthermore, no cracks were observed in the polyimide film during a bending test.

[0089] Example 8 The polyimide powder (i) having a weight-average molecular weight of 79,000 obtained in Synthesis Example 1 and the polyimide powder (iii) having a weight-average molecular weight of 49,000 obtained in Synthesis Example 3 were thoroughly mixed using a rotary mixer at a mass ratio of polyimide powder (i):polyimide powder (iii) = 10:90 to obtain the target polyimide powder. The weight-average molecular weight of the obtained polyimide powder was 52,000.

[0090] A polyimide solution was prepared by dissolving polyimide in GBL at a concentration of 20% by mass in the same manner as in Example 1. A homogeneous polyimide solution was obtained with a viscosity of 2,140 mPa·s. Furthermore, a 25 μm-thick polyimide film sample was prepared on quartz glass in the same manner as in Example 1, and the total light transmittance was 99% and the yellowness index was 0.7. After applying this polyimide solution to a circuit and drying, the unevenness difference (T1-T2) of the polyimide surface was a small 3 μm, confirming good leveling properties. Furthermore, no cracks were observed in the polyimide film during a bending test.

[0091] Example 9 The polyimide solutions prepared in Synthesis Example 3 and Synthesis Example 4 before powderization were collected and mixed in a 3-L separable flask equipped with a stirring blade so that the mass ratio of the dissolved polyimides was 20:80 (polyimide in Synthesis Example 3:polyimide in Synthesis Example 4) and the total mass of the polyimide solutions was 500 g. Next, 750 mL of methanol was added dropwise at a rate of 10 mL / min to precipitate the polyimide. The mixture was then filtered and dried in the same manner as in Example 1 to obtain a polyimide powder. The weight-average molecular weight of the resulting polyimide powder was 34,600.

[0092] A polyimide solution was prepared by dissolving polyimide in GBL at a concentration of 20% by mass in the same manner as in Example 1. A homogeneous polyimide solution was obtained with a viscosity of 770 mPa·s. Furthermore, a 25 μm-thick polyimide film sample was prepared on quartz glass in the same manner as in Example 1, and the total light transmittance was 99% and the yellowness index was 0.7. After applying this polyimide solution to a circuit and drying, the unevenness difference (T1-T2) of the polyimide surface was a small 2 μm, confirming good leveling properties. Furthermore, no cracks were observed in the polyimide film during a bending test.

[0093] (Comparative Example 1) An attempt was made to prepare a polyimide solution in GBL at a concentration of 20% by mass using only the polyimide powder (viii) with a weight-average molecular weight of 210,000 prepared in Synthesis Example 8, as in Example 1. The resulting polyimide solution had an extremely high viscosity of 830,000 mPa·s, making it difficult to handle. Furthermore, when this polyimide solution was applied to a circuit and dried, and the cross section was observed, unfilled voids were found at the base of the circuit. Therefore, the solution was further diluted with GBL to obtain a 10% by mass polyimide solution. The viscosity of the 10% by mass polyimide solution was 5,400 mPa·s. The 10% by mass polyimide solution was applied to a quartz glass plate using an applicator and dried under the same drying conditions as in Example 1. The resulting 25 μm-thick polyimide film on the quartz glass plate exhibited a good total light transmittance of 99% and a yellowness index of 0.7. However, after this polyimide solution was applied to a circuit and dried, the unevenness difference (T1-T2) on the polyimide surface was as large as 12 μm, confirming that the leveling properties were poor.

[0094] (Comparative Example 2) A polyimide solution was prepared in the same manner as in Example 1, using only the polyimide powder (v) prepared in Synthesis Example 5, in which polyimide was dissolved in GBL at a concentration of 20 mass %, and a uniform polyimide solution with a viscosity of 400 mPa s was obtained. A polyimide film sample with a thickness of 25 μm prepared on quartz glass in the same manner as in Example 1 had a good total light transmittance of 95% and a yellowness index of 0.9. However, when the sample was applied to a circuit and dried, cracks occurred in the formed polyimide film, confirming poor bending resistance.

[0095] [Table 2] [Industrial Applicability]

[0096] By using the polyimide powder or polyimide varnish according to the present invention, it is possible to produce a polyimide film having excellent heat resistance, transparency, mechanical properties, and leveling properties, particularly a polyimide film suitable for use in displays and electronic materials, and the polyimide film is of extremely high industrial value.

Claims

1. a polyimide A having a weight average molecular weight Mwa in the range of 30,000 g / mol≦Mwa≦100,000 g / mol, the polyimide A having structural units derived from an aromatic diamine compound and structural units derived from a tetracarboxylic dianhydride; A polyimide powder soluble in an organic solvent, comprising: a polyimide B having a weight average molecular weight Mwb in the range of 10,000 g / mol≦Mwb≦80,000 g / mol, the polyimide B having structural units derived from an aromatic diamine compound and structural units derived from a tetracarboxylic dianhydride; The aromatic diamine compound is 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, 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]- at least one selected from the group consisting of 2,2-bis[3-(4-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, 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl; the tetracarboxylic dianhydride includes at least one aromatic tetracarboxylic dianhydride having a fluoro group, The value of Mwa / Mwb is 1.25 or more, A polyimide powder, wherein the weight average molecular weight Mwm measured for a blend of polyimide components is in the range of 20,000 g / mol≦Mwm≦90,000 g / mol.

2. 2. The polyimide powder according to claim 1, wherein Mwa, Mwb, and Mwm are each in the following ranges: 30,000g / mol≦Mwa≦80,000g / mol 10,000g / mol≦Mwb≦50,000g / mol 25,000g / mol≦Mwm≦60,000g / mol

3. A polyimide powder as described in claim 1 or 2, characterized in that polyimide A and polyimide B are mixed in a ratio of 5 / 95 to 95 / 5 based on the mass of the powder.

4. 4. The polyimide powder according to claim 1, wherein the polyimide is synthesized through polymerization of polyamic acid and chemical imidization reaction.

5. The polyimide powder according to any one of claims 1 to 4, which is soluble in γ-butyrolactone.

6. The polyimide powder according to claim 5, characterized in that when dissolved in γ-butyrolactone at a concentration of 20% by mass, the polyimide powder has a viscosity in the range of 500 to 3,000 mPa s as measured at 30°C with an E-type viscometer.

7. 7. The polyimide powder according to claim 1, which, when made into a polyimide film having a thickness of 25 μm, gives a polyimide film having a total light transmittance of 85% or more and a yellowness index of 3 or less.

8. A polyimide varnish comprising the polyimide powder according to any one of claims 1 to 7 dissolved in an organic solvent.

9. (Step 1A) A step of synthesizing a polyimide A having a weight average molecular weight Mwa in the range of 30,000 g / mol≦Mwa≦100,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride, and obtaining a solution containing the polyimide A. (Step 2A) A step of powdering a solution containing polyimide A using a poor solvent for polyimide. (Step 3A) A step of adding an organic solvent to polyimide A powder to obtain polyimide varnish A (Step 1B) A step of synthesizing a polyimide B having a weight average molecular weight Mwb in the range of 10,000 g / mol≦Mwb≦80,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride, and obtaining a solution containing the polyimide B. (Step 2B) A step of powdering a solution containing polyimide B using a poor solvent for polyimide. (Step 3B) A step of adding an organic solvent to the powder of polyimide B to obtain polyimide varnish B (Step 4) Step of mixing polyimide varnish A and polyimide varnish B The method for producing the polyimide varnish according to claim 8, comprising:

10. (Step 1A) synthesizing polyimide A having a weight average molecular weight Mwa in the range of 30,000 g / mol≦Mwa≦100,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride, and obtaining a solution containing polyimide A; (Step 1B) synthesizing a polyimide B having a weight average molecular weight Mwb in the range of 10,000 g / mol≦Mwb≦80,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride to obtain a solution containing the polyimide B; mixing the solution containing the polyimide A and the solution containing the polyimide B; A step of powdering a mixed solution of polyimide A and polyimide B using a poor solvent for polyimide; A process in which polyimide varnish is obtained by adding an organic solvent to the powder made from a mixed solution of polyimide A and polyimide B. The method for producing the polyimide varnish according to claim 8, comprising:

11. (Step 1A) A step of synthesizing polyimide A having a weight average molecular weight Mwa in the range of 30,000 g / mol≦Mwa≦100,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride, and obtaining a solution containing polyimide A. (Step 2A) A step of powdering a solution containing polyimide A using a poor solvent for polyimide. (Step 1B) A step of synthesizing a polyimide B having a weight average molecular weight Mwb in the range of 10,000 g / mol≦Mwb≦80,000 g / mol from an aromatic diamine compound and a tetracarboxylic dianhydride, and obtaining a solution containing the polyimide B. (Step 2B) powdering a solution containing polyimide B using a poor solvent for polyimide; a step of mixing the polyimide A powder and the polyimide B powder obtained in the step 2A and the step 2B, respectively; and A process in which an organic solvent is added to the powder mixture of polyimide A and polyimide B to obtain polyimide varnish. The method for producing the polyimide varnish according to claim 8, comprising:

Images