JPS61275352A - Soluble polyimide solution - Google Patents

Abstract

PURPOSE:To provide a soluble polyimide soln. which is suitable for use in coating electronic parts and gives a coating film which is homogeneous, has excellent heat resistance, etc. and does not cause loss in tranparency by moisture absorption, by dissolving a soluble polyimide in a lactone-contg. solvent. CONSTITUTION:A soluble polyimide is prepd., e.g., by reacting a tetracarboxylic acid component (e.g. 2, 3, 5-tricarboxy cyclo pentyl acetic dianhydride) with a diamine (e.g. 4,4'-diaminodiphenyl ether) or a diisocyanate (e.g. 2,4-tolylene diisocyanate). The soluble polyimide is dissolved in a solvent contg. a lactone (e.g. gamma-butyrolactone or gamma-valerolactone) and pref. further an amide (e.g. N- methyl-2-pyrrolidone or N,N-dimethylacetamide) to obtain the desired soluble polyimide soln.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a polyimide solution, and more particularly to a solution in which a soluble polyimide is dissolved in a specific organic solvent as a coating material for electronic parts.

Conventionally, polyimide has been used as glabellar insulating films for electronic components such as ICs, transistors, and magnetic heads, insulating films for solar cells, protective films for various elements, α-ray shielding films, and liquid crystal alignment films. Among these, soluble polyimide has superior storage stability when made into a solution compared to polyimide obtained by curing a polyamic acid compound, which is a polyimide precursor, and requires long-term treatment at high temperatures for imidization. It is becoming more and more frequently used for reasons such as the fact that it is unnecessary.

Problems to be Solved by the Invention When forming a thin film of the above-mentioned soluble polyimide, it is usually formed by applying it to a substrate as a solution and then drying it. -Amide solvents such as 2-pyrrolidone and N,N-dimethylacetamide are used, and these solvents are highly hygroscopic, and when a substrate is coated with a hygroscopic solution, the coating film may devitrify. occurs.

Furthermore, even when coating a soluble polyimide solution using an amide solvent using a coating method that uses a spinner, which can form a relatively homogeneous thin film, spots and striations occur in the coating film, making it difficult to obtain a homogeneous coating film. difficult,
There were problems such as increasing the rotation speed of the spinner and requiring a long time for coating.

An object of the present invention is to solve such conventional technical problems and to provide a soluble polyimide solution containing a soluble polyimide and a specific organic solvent and having excellent homogeneity and coatability.

A means for solving the problem, that is, the present invention provides a soluble polyimide solution prepared by dissolving soluble polyimide in a solvent containing lactones.

The soluble polyimide that can be used in the present invention is not particularly limited as long as it can be dissolved in the specific organic solvent system of the present invention. For example, the following tetracarboxylic acid component (A
) and the following diamine (B) or diisocyanate (C)
Examples include polyimides having a polyimide structure obtained by reacting with.

Such tetracarboxylic acid component (A) includes butanetetracarboxylic acid, 1,2.3.4-cyclobutanetetracarboxylic acid, 1.2.3.4-cyclopentanetetracarboxylic acid, 2,3.5-tricarboxylic acid, Carboxycyclopentyl acetic acid, 3.5.6-dolycarpoxynorbornane-2
-acetic acid, 5-(2,5-dioxotetrahydrofuryl)
-3-Methyl-cyclohexenedicarboxylic acid, bicyclo(2,2,2)-octo-7-nin-tetracarboxylic acid, 1.2.3.4-furantetracarboxylic acid, 4,4
'-Bis(3,4-dicarboxyphenoxy)diphenyl sulfide, 4.4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfone, 4.4'-bis(3
,4-dicarboxyphenoxy)diphenylpropane,
3.3'.

4.4'-perfluoroisopropylidene tetracarboxylic acid, 3.3',4.4'-biphenyl ether tetracarboxylic acid, bis(phthalic acid) phenylphosphine oxide, p-phenylene-bis=(triphenylphthalic acid) ), m-phenylene-bis-(triphenylphthalic acid), bis(triphenylphthalic acid)-4,4'
Examples include soluble polyimides using anhydrides of tetracarboxylic acids such as -diphenyl ether and bis(triphenylphthalic acid)-4,4'-diphenylmethane.

These can be used alone or in combination.

Further, as the general diamine (B) or isocyanate (C) to be reacted with the tetracarboxylic acid component (A), compounds represented by the general formula: H2N-R-NH, or the general formula: 0CN-R-NGO (R represents an organic group such as a divalent aromatic group, aliphatic group, alicyclic group, or organosiloxane group).

Preferred R in the general formula is, for example, Y.

(In the formula, X3, X2, X, and X4 may be the same or different, -Hl-CH3 or OCH3, Yo is -
CHt-1CzHa-1-〇-1-5-1-C-1-CONH-, and n represents 0 or 1. ) aromatic group represented by -(CH,)n- (where n is 2 to 20
indicates an integer. ), represents a divalent aliphatic group, alicyclic group, or aromatic group having 2 to 20 carbon atoms, and R# is Cn H2a+ 1 (In the formula, n represents an integer of 1 to 20.) represents a monovalent aliphatic, alicyclic, or aromatic hydrocarbon group, and m is an integer of 1 to 100. ] Examples include organosiloxane groups represented by the following.

Specific examples of the diamine (B) include 1, para-phenylene diamine, meta-phenylene diamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, benzidine, 4°4'-diaminodiphenyl sulfide, 4 .4'-diaminodiphenyl sulfone, 4
．． 4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,4'-diaminobenzanilide, 3
．． 4'-diaminodiphenyl ether, 3゜3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone, metaxylylene diamine, 1,3-propanediamine, tetramethylene diamine, pentamethylene diamine, Hexamethylene diamine, heptamethylene diamine, octamethylene diamine, nonamethylene diamine, 4,4'-dimethylhebutamethylene diamine, 1,4-diaminocyclohexane, isophorone diamine, tetrahydrodicyclopentadienyl diamine, hexahydro-4, 7-methanoindanilene symethylenediamine, tricyclo(6,2,
Examples include diaminoorganosiloxanes represented by 1,0''.7]-landecylenedimethyldiamine and the like.

These diamines can be used alone or in combination of two or more.

Further, specific examples of the diisocyanate (C) include:
2.4-tolylene diisocyanate, 2゜6-tolylene diisocyanate, p-phenylene diisocyanate,
m-phenylene diisocyanate, 4.4'-diphenylmethane diisocyanate, 4.4'-diphenyl ether diisocyanate, 4.4'-diphenylsulfone diisocyanate, 4,4'-diphenylsulfide diisocyanate, 1,5-naphthalene diisocyanate, 2.6- naphthalene diisocyanate, tolidine isocyanate), 4,4'-biphenyl diisocyanate,
Aromatic diisocyanates such as p-xylylene diisocyanate and m-xylylene diisocyanate, isophorone diisocyanate, 1.3-bis(isocyanatomethyl)cyclohexane, 1.4-bis(isocyanatomethyl)cyclohexane, 4.4'-dicyclohexylmethane diisocyanate , 4,4'-dicyclohexyl ether diisocyanate, and aliphatic diisocyanates such as butane diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, lysine diisocyanate, and trimethylhexamethylene diisocyanate.

These diisocyanates can be used alone or in combination.

Examples of other soluble polyimides include polyimides having a polyimide structure obtained by reacting the following tetracarboxylic acid component (D) with the following diamine (E).

In addition to the tetracarboxylic acid component (A), such tetracarboxylic acid component (D) includes pyromellitic acid, 3.3
', 4.4'-benzophenonetetracarboxylic acid, 3.
3',4.4'-biphenylsulfonetetracarboxylic acid, 1.4.5.8-naphthalenetetracarboxylic acid, 2.
3.6.7-naphthalenetetracarboxylic acid, 3.3',
4.4'-biphenyl ether tetracarboxylic acid, 31
Examples include anhydrides of tetracarboxylic acids such as 3'+4,4'-dimethyldiphenylsilanetetracarboxylic acid and 3.3',4.4'-tetraphenylsilanetetracarboxylic acid.

The diamine component (E) to be reacted with the tetracarboxylic acid component (D) includes bis(4-aminophenyl)fluorene, diaminotetraphenylthiophene, 4.4'
-phthalido-3,3'-diaminodiphenyl ether,
4.4'-phthalido-3,3'-diaminodiphenylmethane, 4,4'-phthalido-3,3'diaminobenzophenone, 4.4'-acetamido-3,3'-diaminodiphenyl ether, 4.4' -acetamide-3゜3
'-Diaminodiphenylmethane, 4.4'-acetamido-3,3'-diaminobenzophenone, 4-sulfonamido-12,3-phenylenediamine, 4.6-bis(aminophenyl)-1,3-phenylenediamine, 5
-amino-1(4'-aminophenyl)-1,3,3-
Examples include 1-limethylindane, 6-amino-1(4'-aminophenyl)-1,3,3-)limethylindane, and the like.

These tetracarboxylic acid components (D) or diamines (E
) can be used alone or in combination of two or more.

The most preferred example of the soluble polyimide used in the present invention is a polyimide having a repeating structural unit represented by the following general formula (I).

(In the formula, R is the same as above) Intrinsic viscosity Cηt of soluble polyimide used in the present invention
nh =fn'7rat/c, c=0.5g/d!
, 30°C in dimethylformamide) is preferably 0
．． 05d! /g or more, particularly preferably 0.05 to 5 a
/g, and particularly preferred is a soluble polyimide having preferably 50% by weight or more, particularly preferably 75% by weight or more of repeating units represented by the above general formula.

When these soluble polyimides of the present invention are produced, for example, via a polyamic acid obtained from a reaction between a tetracarboxylic dianhydride and a diamine, an imidization reaction is performed by heating and dehydrating the polyamic acid, or It can be produced by performing a generally known chemical imidization reaction, such as in the presence of an acid anhydride.

In addition, when producing soluble polyimide by reacting tetracarboxylic dianhydride and diisocyanate, triethylamine, pyridine, picoline, quinoline, isoquinoline, triethylenediamine, 1,8-diazabicyclo(5,,4,0)- It can be produced by carrying out a heating reaction using a basic compound such as 7-undecene as a catalyst.

The soluble polyimide preferably used in the present invention having a repeating structural unit represented by the general formula (I) is, for example, a polyamic acid obtained from 2.3.5-tricarboxycyclopentyl acetic dianhydride and a diamine. 2,3.5-1-lycarboxycyclopentyl acetic dianhydride and diisocyanate are dissolved in an organic solvent and imidized in the presence of an organic carboxylic anhydride (Japanese Patent Application Laid-Open No. 199720/1983). React inside (
JP-A No. 60-1218).

Here, 2.3.5-1-ricarboxycyclobentyl acetic acid (hereinafter referred to as rTCAJ) can be obtained by, for example, ozonolysis of dicyclopentadiene and oxidation with hydrogen peroxide [UK Patent No. 872355, J ,Org,Chem
28.2537 (1963)) or a method of oxidizing hydroxydicyclopentadiene obtained by hydrating dicyclopentadiene with nitric acid (West German Patent No. 1078120)
This TC can be manufactured by
By dehydrating A, 2.3.5-tricarboxycyclopentyl acetic acid dianhydride (hereinafter referred to as rTCA-AHJ) can be produced.

The organic solvent that can be used in the reaction system in the production of polyimide is not particularly limited as long as it can dissolve the polyamic acid and soluble polyimide.
For example, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N.

N-dimethylformamide, dimethyl sulfoxide, T
-Aprotic polar solvents such as butyrolactone, tetramethylurea, hexamethylphosphorotriamide, m-
Examples include phenolic solvents such as cresol, xylenol, phenol, and halogenated phenol.

Among soluble polyimides, halogenated hydrocarbons, ether solvents, and the like can also be used for systems with particularly excellent solubility.

The soluble polyimide solution of the present invention is obtained by dissolving such soluble polyimide in a solvent containing lactones.

Here, the lactones include T-butyrolactone, γ
- Valerolactone, γ-caprolactone/δ-valerolactone, δ-chloro-γ-valerolactone, δ-caprolactone, α, α-dimethylbutyrolactone, γ, γ-
Examples include dimethylbutyrolactone, and preferred lactones are those having 3 to 6 carbon atoms.

In addition, it is preferable to use a solvent consisting of amides in the soluble polyimide solution of the present invention, and examples of the amides include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and tetrapropylene. Examples include methylurea, hexamethylphosphortriamide, formamide, N-methylformamide, acetamide, N-methylacetamide, N-methylpropionamide, 2- and lolidone, and the like.

When amide is used in combination, the composition of lactones in the solvent is 5 to 95 parts by weight, preferably 10 to 90 parts by weight, and the composition of amide is 5 to 95 parts by weight, preferably 10 parts by weight.
~90 parts by weight.

If the composition of lactones is less than 5 parts by weight, it will not be possible to prevent devitrification of the coating film when the solvent absorbs water, while if it exceeds 95 parts by weight, it will be difficult to maintain the surface uniformity of the coating state during coating film formation with a spinner. It becomes difficult.

The soluble polyimide solution of the present invention usually has a soluble polyimide concentration of 0.1 to 30% by weight, preferably 0.1 to 20% by weight.
The concentration is adjusted to % by weight.

In addition to the above-mentioned specific solvent, the soluble polyimide solution of the present invention also contains other general organic solvents such as alcohols,
Phenols, ketones, esters, ethers, halogenated hydrocarbons, hydrocarbons such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, propylene glycol, 1.4-7
'Tandiol, triethylene glycol, ethylene glycol monomethyl ether, phenol, m-cresol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, butyl acetate, diethyl oxalate, diethyl malonate, diethyl ether, ethylene glycol methyl ether,
Ethylene glycol ethyl ether, ethylene glycol n-propyl ether, ethylene glycol is
o-, propyl ether, ethylene glycol n-7
'Tyle ethyl, ethylene glycol dimethyl ether, ethylene glycol ethyl ether acetate, diethylene glycol dimethyl ether, tetrahydrofuran, dichloromethane, 1,2-dichloroethane, 1,4
- Dichlorobutane, trichloroethane, chlorobenzene, O-dichlorobenzene, hexane, heptane, octane, benzene, toluene, xylene, etc. may also be mixed with the solvent in which the specific soluble polyimide is dissolved to an extent that the soluble polyimide will not be precipitated. I can do it.

The soluble polyimide solution of the present invention prepared in this way is applied to a substrate by a roll coater method, a spinner method, a printing method, etc., and then, for example, at 80 to 250°C, 5 to 18
A coating film of soluble polyimide can be formed by drying for 0 minutes.

Examples Hereinafter, the present invention will be explained in more detail with reference to Examples.
The invention is not limited to these examples.

Reference example 1 Diaminodiphenyl ether (DDE) 20.48g
(0,102 mol) was dissolved in 247.5 g of N,N-dimethylformamide (DMF), and then 2.3.5-tricarboxycyclopentyl acetic dianhydride (TCA-A
23.15 g (0.103 mol) of H) was added as a powder and reacted at 25° C. with stirring. After 24 hours, a small amount of this reaction solution was sampled and the polyamic acid content was 0.
5g/100mj! DM·F was added to the solution to give a concentration of 10%, and the intrinsic viscosity (30° C.) was measured.

The obtained polyamic acid has an η□□ of 0.9! b/g.

Next, 30 g of a solution obtained by adding DMF to the reaction solution to reduce the polyamic acid concentration to 6.1% by weight was transferred to a 100 ml flask, and 1.32 g of acetic anhydride and 1.02 g of pyridine were sequentially added to this solution and mixed. After stirring, 1
The reaction was carried out at 35°C for 2 hours.

Next, the reaction product was poured into a large amount of methanol to coagulate and collect the soluble polyimide, which was then dried at 80'C overnight.

Viscosity η of the obtained soluble polyimide in DMF at 30°C
(nh was 0.79 d!/g.

This soluble polyimide was dissolved in DMF again, cast on a glass plate, dried, and then the film was peeled off to measure the infrared absorption spectrum.
Absorption based on C=O stretching vibration of imide was observed at 90 cm-'.

This shows that soluble polyimide can be obtained by heating and reacting a polyamic acid solution in the presence of acetic anhydride and pyridine.

Reference example 2 TCA-AH22.4g and 4.4' under nitrogen atmosphere
-25.0 g of diphenylmethane diisocyanate was dissolved in 200 ml of metacresol. Next, 4 g of triethylamine was added as a catalyst, the temperature was raised to 180 to 190°C, and the mixture was reacted for 7 hours. By mixing this reaction solution with a large amount of acetone to coagulate and precipitate polyimide, and drying it,
8 g of polyimide powder was obtained.

The intrinsic viscosity (vtnh) of the obtained soluble polyimide is
It was 0.99 dl/g. This soluble polyimide was dissolved in DMF again, cast on a glass plate, dried, the film was peeled off, and the infrared absorption spectrum was measured.
1710cm-', 1780cm-' and 1370c
Absorption based on C=0 stretching vibration of imide was observed at m-'.

Reference example 3 TCA-AH/3°3' as the tetracarboxylic acid component
, 4.4'-benzophenonetetracarboxylic acid = 75/
25 (molar ratio), the reaction was carried out in the same manner as in Reference Example 1, and the intrinsic viscosity (ηinh) was 0.76 dl/
g of soluble polyimide was obtained.

Reference Example 4 The reaction was carried out in the same manner as in Reference Example 1, except that the diamine component was 4,4'-diaminodiphenyl ether/(3-aminopropyl)tetramethyldisiloxane-90/10 (molar ratio), and the intrinsic viscosity ( ηink') is 0.6
8d! /g of soluble polyimide was obtained.

Example 1 A 5% by weight polyimide solution of the soluble polyimide obtained in Reference Example 1 was prepared using a mixed solvent consisting of γ-butyrolactone/N,N-dimethylacetamide=80/20 (weight ratio).

The resulting solution was filtered through a membrane filter with a pore size of 0.22 μm to remove insoluble matter.

Spread this solution onto a glass substrate using a spinner for 2,000
When the coating was applied under the conditions of 60 seconds at Orpm, it was possible to uniformly coat the substrate without flickering.

After coating, it was dried in a clean oven at 150°C for 1 hour. The polyimide coating film after drying was uniform with no interference fringes, spots, or striations.

Comparative Example 1 Spin coating and drying were performed in the same manner as in Example 1, using N,N-dimethylacetamide instead of the mixed solvent system used in Example 1.

The resulting coating film had many devitrified spots and was non-uniform.

Example 2 T-butyrolactone was used instead of the mixed solvent system used in Example 1, and spin coating (conditions were 3.00 rpm, 3 minutes) and drying were performed in the same manner as in Example 1. The resulting coating film was transparent and uniform without striations.

Example 3 The composition of the mixed solvent used in Example 1 was changed to T-butyrolactone/N,N-dimethylacetamide = 20/80 (weight ratio), and the concentration of polyimide was further changed to 0.5% by weight. Spin coating and drying were performed in the same manner as in 1. The resulting coating film is transparent and has no interference fringes, spots, or
It was uniform with no striae.

Comparative Example 2 Spin coating and drying were performed in the same manner as in Example 1, using N,N-dimethylacetamide instead of the mixed solvent system used in Example 3. The resulting coating film was transparent, unlike Comparative Example 1, but spots were observed around the glass substrate, and it could not be said to be a uniform coating film.

Example 4 γ-butyrolactone was used instead of the mixed solvent system used in Example 3, and spin coating was performed in the same manner as in Example 1 (however, the conditions were 3.00 Orpm).

3 minutes), and was dried. The obtained coating film is transparent,
It was also uniform with no striations.

Example 5 Water was added to the polyimide solution used in Example 3 so that the polyimide concentration was 0.5% by weight.

Using this solution, spin coating and drying were performed in the same manner as in Example 1. The resulting coating film was transparent and uniform with no interference fringes, spots, or striations.

Example 6 Spin coating and drying were carried out in the same manner as in Example 1, except that the composition of the mixed solvent used in Example 1 was changed to γ-butyrolactone/N,N-dimethylformamide=60/40 (weight ratio). The resulting coating film is transparent and has no interference fringes or
It was uniform with no spots or striations.

Comparative Example 3 Spin coating and drying were performed in the same manner as in Example 1, using N,N-dimethylformamide instead of the mixed solvent system used in Example 6. The resulting coating film was opaque.

Example 7 Spin coating and drying were carried out in the same manner as in Example 1, except that the composition of the mixed solvent used in Example 1 was changed to γ-butyrolactone/N-methyl-2-pyrrolidone=40/60 (weight ratio). The resulting coating film was transparent and uniform.

Example 8 Water was added to the polyimide solution used in Example 7 to make the concentration of the solution 0.5% by weight, and spin coating and drying were performed in the same manner as in Example 7.

The resulting coating film was transparent and uniform without devitrification.

Example 9 A 3% by weight polyimide solution of the soluble polyimide obtained in Reference Example 2 was prepared using a mixed solvent consisting of γ-butyrolactone/N,N-dimethylacetamide=50150 (weight ratio).

The resulting solution was filtered through a membrane filter with a pore size of 0.22 μm to remove insoluble matter.

Spread this solution onto a glass substrate using a spinner at 2.00%
When the coating was applied under the conditions of 60 seconds at Orpm, the coating was uniformly applied to the substrate without flickering.

After coating, it was dried in a clean oven at 150°C for 1 hour. The polyimide coating film after drying was uniform with no interference fringes, spots, or striations.

Comparative Example 4 Spin coating and drying were performed in the same manner as in Example 9, using N,N-dimethylacetamide instead of the mixed solvent system used in Example 9.

The resulting coating film was non-uniform with many opaque spots appearing.

Example 10 The polyimide obtained in Reference Example 3 was treated with T-butyrolactone/
N,N-dimethylacetamide = 40/60 (weight ratio)
A 1% by weight polyimide solution was prepared using a mixed solvent consisting of:

The resulting solution was filtered through a membrane filter with a pore size of 0.22 μm to remove insoluble matter.

Spread this solution onto a glass substrate using a spinner at 2.00%
When the coating was applied under the conditions of 60 seconds at Orpm, the coating was uniformly applied to the substrate without flickering.

After coating, it was dried in a clean oven at 150°C for 1 hour. The polyimide coating film after drying was uniform with no interference fringes, spots, or striations.

Comparative example 5 N instead of the mixed solvent system used in Example 10.

Spin coating and drying were performed in the same manner as in Example 1O using N-dimethylacetamide.

The resulting coating film had opaque spots and was unsatisfactory.

Example 11 Polyimide cage γ-butyrolactone obtained in Reference Example 4/
N,N-dimethylacetamide = 40/60 (weight ratio)
A 3% by weight polyimide solution was prepared using a mixed solvent consisting of:

The resulting solution was filtered through a membrane filter with a pore size of 0.22 μm to remove insoluble matter.

Spread this solution onto a glass substrate using a spinner for 2,000
When the coating was applied under the conditions of 60 seconds at Orpm, the coating was uniformly applied to the substrate without flickering.

After coating, it was dried in a clean oven at 150'C for 1 hour. After drying, the polyimide coating has interference fringes, spots,
It was uniform with no striations.

Comparative example 6 N instead of the mixed solvent system used in Example 11.

Spin coating and drying were performed in the same manner as in Example 10 using N-dimethylformamide.

The resulting coating film was non-uniform with opaque spots appearing.

Effects of the Invention According to the present invention, a solution consisting of a soluble polyimide and a specific organic solvent does not devitrify the coating film even when it absorbs moisture, and the coating surface obtained by spin coating has no spots or striations and is uniform. A coating film can be formed.

Therefore, the soluble polyimide solution of the present invention has excellent heat resistance, mechanical properties, electrical properties, chemical resistance, etc., and is used in the electronic industry, for example, as interlayer insulating films for ICs, transistors, magnetic heads, etc., insulating films for solar cells, etc. It can also be suitably used as a protective film for various elements, an α-ray shielding film, and a liquid crystal alignment film, such as organic polymer materials such as polyester,
It exhibits particularly excellent performance as a coating material for glass silicon wafers and xTo4 bright electrodes.

Claims (1)

[Claims] (1) A soluble polyimide solution obtained by dissolving soluble polyimide in a solvent containing lactones.