JP6994712B2 - Soluble transparent polyimide polymerized in γ-butyrolactone solvent - Google Patents

Description

The present invention relates to a solvent-soluble polyimide having excellent transparency, heat resistance and mechanical properties, and a method for producing the same. The present invention also relates to a polyimide coating film and a film having excellent transparency, heat resistance and mechanical properties.

In recent years, the development of polymer materials has progressed in the field of display devices such as liquid crystal displays and organic EL displays, and the development of polyimide materials having particularly high electrical reliability has been promoted. Conventional display devices are built on rigid glass substrates, but as an alternative to this, the development of lightweight and highly flexible plastic substrates is underway, and they have high transparency and heat resistance in the visible light region. There is a demand for materials, and various proposals have been made for polyimide materials.

In order to enhance the transparency of the polyimide, it is effective to suppress the formation of intramolecular conjugation and charge transfer complex, which are the causes of conventional polyimide coloring. Therefore, a method has been proposed in which a transparent polyimide is obtained by using a monomer having an aliphatic or alicyclic structure or a monomer having a bulky group in the side chain as the raw material tetracarboxylic acid dianhydride or diamine. ..

In addition, the coloring of the polyimide film is also affected by the residual colored matter from the solvent in the manufacturing process, and high-temperature long-term heating with the solvent remaining has strengthened the coloring of the film. There are two methods for producing the polyimide film: a method of producing from a polyimide precursor (polyamic acid) solution and a method of producing from a soluble polyimide solution. In the method from a polyamic acid solution, a polyamic acid is synthesized using an amide solvent which is a good solvent for polyamic acid, and then heated to obtain a polyimide film, and a large excess of anhydrous acetic acid and a chemical imide such as triethylamine. There are methods for obtaining a polyimide film using an agent, but in each case, coloring occurs because the amide-based solvent is removed and the imidization is completed by heating at a high temperature for a long time. Further, in the method of obtaining a polyimide film from a soluble polyimide, an amide solvent such as N-methyl-2-pyrrolidone is used because the highly heat-resistant polyimide obtained from an aromatic monomer has low solubility, and even in the reaction stage. Even at the stage of removing the solvent to form a polyimide film, coloring was unavoidable because it was heated at a high temperature for a long time.

As the transparent polyimide, for example, a polyimide using an aliphatic or alicyclic monomer is disclosed in Patent Document 1. In Patent Document 1, a polyimide obtained by reacting a specific alicyclic tetracarboxylic acid dianhydride with a specific aromatic diamine containing a sulfone group is soluble in an organic solvent and further molded. It is disclosed that the polyimide film obtained with excellent properties is excellent in transparency, heat resistance, toughness and the like. However, as long as the alicyclic tetracarboxylic acid dianhydride is used, it is not easy to dramatically increase the degree of polymerization (molecular weight) of the polyimide, and the alicyclic polyimide using the alicyclic tetracarboxylic acid dianhydride is not easy. In the resin, it has been an extremely difficult task to achieve both transparency and film toughness. Therefore, the strength of the polyimide film was only several tens of MPa.

Further, Patent Document 2 discloses a soluble polyimide composed of a specific alicyclic tetracarboxylic dianhydride and an alicyclic diamine, but the molecular weight distribution is wide and there is a problem in solution stability, and the membrane has a problem. The strength was also several tens of MPa.

Monomers having an aliphatic or alicyclic structure have small intramolecular and intermolecular interactions, so that the solubility of polyimide is high and the transparency of the obtained membrane is high, but the heat resistance is low. Therefore, by using a low molecular weight monomer, the concentration of imide bond in the polyimide is increased and the decrease in heat resistance is suppressed, but the heat resistance is still lower than that of the polyimide obtained from the aromatic monomer, and the strength of the film is also suppressed. Was also low.

Further, Patent Document 3 also shows a transparent polyimide using a monomer having a bulky group. A structure derived from an aromatic fluorine diamine having a unit containing an alicyclic structure and a unit not containing an alicyclic structure in the same molecular chain, and the unit not containing an alicyclic structure having two trifluoromethyl groups. A transparent polyimide film containing the above is disclosed in Patent Document 3. Again, in order to obtain high transparency, it is necessary to increase the ratio of units containing an alicyclic structure, but at the same time, it becomes difficult to increase the degree of polymerization, which leads to a decrease in film strength. Further, the light transmittance of a film having a thickness of 50 μm at a wavelength of 400 nm was 52% (76% in terms of 20 μm), which was not sufficient. In the examples, the polyamic acid consisting of two units is synthesized, chemically imidized, and the solvent is removed by heating to complete the imidization. Since the polyimide having these bulky groups also has increased solvent solubility, it can also be obtained by high-temperature heat polymerization in a polar solvent. However, when the polyimide is prepared by high-temperature heat polymerization, the solvent and the monomer are kept at a high temperature for a long time, so that the polyimide tends to be colored, which leads to a decrease in transparency, and particularly in the case of an amide-based solvent, the coloring becomes intense.

A method using a solvent that is difficult to color even when heated at a high temperature for a long time is also disclosed. Patent Document 4 discloses a soluble polyimide having high light transmittance using 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride and other aromatic tetracarboxylic acid dianhydrides. In the examples, a soluble polyimide obtained by polymerizing 2,2'-bis (trifluoromethyl) benzidine (TFMB), which is an aromatic fluorine diamine, with an aromatic tetracarboxylic acid dianhydride is shown. A high molecular weight polyimide is obtained by using cresol as a polymerization solvent. In this case, since the boiling point of the cresol used is high and it is difficult to remove by heating in the film forming process, a film is obtained as a solvent that can be removed by heating by replacing the solvent, which makes the process complicated. The strength of the obtained film was about 110 MPa.

Further, Patent Document 5 also discloses a transparent soluble polyimide using γ-butyrolactone as a polymerization solvent. Here, by using an electron-withdrawing diamine, intramolecular conjugation is suppressed and coloring is further suppressed. However, the polyimide shown here has a low molecular weight because it is synthesized with an excess of acid by shifting the molar ratio in order to maintain solubility, and its use is limited to coating film applications.

Japanese Unexamined Patent Publication No. 2008-297360 Japanese Unexamined Patent Publication No. 2014-114429 Japanese Unexamined Patent Publication No. 2013-82774 Japanese Unexamined Patent Publication No. 2013-1899 Japanese Unexamined Patent Publication No. 2011-140563

The present invention is for solving these problems, and an object thereof is to provide a solvent-soluble polyimide capable of obtaining a polyimide film having high mechanical strength as well as excellent heat resistance and light transmission, and a method for producing the same. There is something in it. Another object of the present invention is to provide a polyimide coating film and a polyimide film having high mechanical strength as well as excellent heat resistance and light transmission.

As a result of studies to solve the above problems, the present inventors react a specific aromatic tetracarboxylic acid dianhydride and a specific aromatic diamine in a γ-butyrolactone solvent in the coexistence of an imidization catalyst. As a result, it has been found that a polyimide having a high molecular weight can be obtained, and that the polyimide film obtained from the polyimide is excellent in transparency, heat resistance, and mechanical strength. The present invention relates to the following items.

1. 1. Including the repeating unit represented by the formula (1), 40% or more of X ₁ in all the repeating units represented by the formula (1) is the polyimide which is the group represented by the formula (2). , A solvent-soluble polyimide having a weight average molecular weight of 40,000 or more and a light transmittance of 80% or more at a wavelength of 400 nm in a film having a thickness of 20 μm.

（式中、Ｘ_１は芳香環を有する４価の基であり、Ｙ_１は芳香環を有する２価の基である。）

(In the formula, X ₁ is a tetravalent group having an aromatic ring, and Y ₁ is a divalent group having an aromatic ring.)

2. 2. The solvent-soluble polyimide according to Item 1 above, wherein 70% or more of Y1 in all the repeating units represented by the formula ( ₁ ) is a group selected from the formulas (3) to (6).

3. 3. Item 2. The solvent-soluble polyimide according to Item 1 or 2, wherein the repeating unit represented by the formula (1) is contained in an amount of 90 mol% or more among all the repeating units.

4. Item 2. The solvent-soluble polyimide according to any one of Items 1 to 3 above, wherein the glass transition temperature is 260 ° C. or higher, the 3% weight loss temperature is 480 ° C. or higher, and the tensile breaking strength of the film is 100 MPa or higher. ..

5. A polyimide coating film or a polyimide film containing the polyimide according to any one of the above items 1 to 4.

6. A substrate for a display, a touch panel, or a solar cell, which comprises the polyimide coating film or the polyimide film according to Item 5.

7. Aromatic tetracarboxylic acid dianhydride containing 2,3,3', 4'-biphenyltetracarboxylic acid dianhydride, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,2 '-Bis (trifluoromethyl) benzidine and aromatic diamines containing at least one diaminobenzoic acid are polycondensed in a γ-butyrolactone solvent in the presence of a tertiary amine compound and a carboxylic acid compound. A method for producing a solvent-soluble polyimide.

8. The amount of 2,3,3', 4'-biphenyltetracarboxylic acid dianhydride is 40 mol% or more of the aromatic tetracarboxylic acid dianhydride, and 4,4'-diaminodiphenyl sulfone, 3,3'. Item 7. The solvent-soluble item according to Item 7, wherein the total amount of -diaminodiphenyl sulfone, diaminobenzoic acid, and 2,2'-bis (trifluoromethyl) benzidine is 70 mol% or more of the aromatic diamine. Method for manufacturing polyimide.

9. The tertiary amine compound is selected from the group consisting of pyridine, picolin, and quinoline, and the carboxylic acid compound is selected from the group consisting of acetic acid, propionic acid, benzoic acid, hydroxybenzoic acid, toluic acid, salicylic acid, and diaminobenzoic acid. Item 4. The method for producing a solvent-soluble polyimide according to Item 7 or 8, wherein the method is characterized by the above.

10. The amount of the tertiary amine compound is 0.01 to 0.5 molar equivalent with respect to 1 molar equivalent of the imide group of the obtained polyimide, and the amount of the carboxylic acid compound is 0. The method for producing a solvent-soluble polyimide according to any one of Items 7 to 9, wherein the equivalent is 01 to 0.4 mol.

According to the present invention, it is possible to provide a solvent-soluble polyimide having excellent transparency, heat resistance, and mechanical properties, and a method for producing the same.

The polyimide of the present invention has high heat resistance, high transparency, and excellent mechanical strength, and can be suitably used for forming a color image display substrate or a flexible substrate for display applications. Further, the polyimide of the present invention can be suitably used for a substrate for a touch panel and a solar cell.

In the present invention, a solution of a solvent-soluble polyimide having a high molecular weight, which suppresses the formation of intramolecular conjugation and charge transfer complex, which are the causes of polyimide coloring, and also reduces the generation of colored substances from monomers and solvents in the manufacturing process. Can be obtained.

The polyimide of the present invention contains a repeating unit represented by the formula (1).

（式中、Ｘ_１は芳香環を有する４価の基であり、Ｙ_１は芳香環を有する２価の基である。）

(In the formula, X ₁ is a tetravalent group having an aromatic ring, and Y ₁ is a divalent group having an aromatic ring.)

In the polyimide of the present invention, among all the repeating units represented by the formula (1), at least a part of X ₁ is a group represented by the formula (2).

Among all the repeating units represented by the formula ( ₁ ), X1 of preferably 40% or more, more preferably 60% or more, still more preferably 80% or more, particularly preferably 100% is represented by the formula (2). Is the basis for being done. Since X ₁ is a group represented by the formula (2), it is possible to obtain a polyimide having excellent solubility, transparency, heat resistance, and mechanical properties. The other structures of X ₁ are not particularly limited. Specific examples thereof include groups introduced by the aromatic tetracarboxylic dianhydride disclosed in the method for producing polyimide of the present invention described later.

Of all the repeating units represented by the formula (1), at least a part of Y ₁ is preferably a group selected from the formulas (3) to (6).

The polyimide of the present invention contains Y1 of preferably 70% or more, more preferably 80% or more, still more preferably 90% or more, and particularly preferably 100% of the repeating units represented by the formula ( ₁ ). It is a group selected from the formulas (3) to (6). Since Y ₁ is a group represented by the formulas (3) to (6), it is possible to obtain a polyimide having excellent solubility, transparency, heat resistance, and mechanical properties. The other structures of Y ₁ are not particularly limited. Specific examples thereof include a group introduced by an aromatic diamine disclosed in the method for producing a polyimide of the present invention described later.

The polyimide of the present invention contains the repeating unit represented by the formula (1) in all the repeating units, preferably 90 mol% or more, more preferably 95 mol% or more, and particularly preferably 100 mol%. By increasing the content ratio of the repeating unit represented by the formula (1) containing a large amount of aromatic groups, the heat resistance and mechanical properties of the polyimide can be improved.

The polyimide of the present invention has a weight average molecular weight of 40,000 or more, preferably 50,000 or more, more preferably 60,000 or more. Having a weight average molecular weight in these ranges can impart excellent heat resistance and mechanical properties to polyimide. The polyimide of the present invention preferably has a weight average molecular weight of 300,000 or less, more preferably 200,000 or less. By having a weight average molecular weight in these ranges, a polyimide having appropriate solubility can be obtained.

The polyimide of the present invention has excellent light transmittance, and the light transmittance at a wavelength of 400 nm in a film having a thickness of 20 μm is 80% or more, and can be 85% or more.

The polyimide of the present invention has high heat resistance. The glass transition temperature (Tg) of the polyimide is preferably 260 ° C. or higher, more preferably 270 ° C. or higher, still more preferably 280 ° C. or higher, and particularly preferably 300 ° C. or higher. The 3% weight loss temperature of the polyimide is preferably 480 ° C. or higher, more preferably 500 ° C. or higher, still more preferably 530 ° C. or higher.

The polyimide of the present invention has high mechanical strength, and the tensile breaking strength of the film is preferably 100 MPa or more, more preferably 110 MPa or more, still more preferably 120 MPa or more.

The polyimide of the present invention comprises an aromatic tetracarboxylic acid dianhydride containing 2,3,3', 4'-biphenyltetracarboxylic acid dianhydride, an aromatic diamine, a tertiary amine compound and a carboxylic acid compound. It is obtained by polycondensing in the presence of a γ-butyrolactone solvent. By adopting such a manufacturing method, it is possible to obtain a polyimide having excellent transparency, heat resistance, and mechanical properties.

In addition to 2,3,3', 4'-biphenyltetracarboxylic dianhydride, other aromatic tetracarboxylic dianhydrides may be mixed and polymerized as long as the solvent solubility is not impaired. Other aromatic tetracarboxylic acid dianhydrides include pyromellitic acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 3,3', 4,4'-diphenyl ether tetra. Carboxydic dianhydride, 3,3', 4,4'-diphenylsulfonetetracarboxylic acid dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic acid dianhydride, 2,2-bis (3) , 4-Dicarboxyphenyl) Hexafluoropropane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, etc. Illustrated, these can be used alone or in combination of two or more. Among these, 3,3', 4,4'-diphenyl ether tetracarboxylic dianhydride and 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride are polyimide soluble and transparent. It is particularly preferable because it keeps the sex. Further, an alicyclic tetracarboxylic dianhydride such as bicyclo [2.2.2] octo-7-ene 2,3,5,6 tetracarboxylic dianhydride may be further mixed and polymerized.

Preferred aromatic diamines are 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,2'-bis (trifluoromethyl) benzidine, and diaminobenzoic acid. Diaminobenzoic acid includes all structural isomers, but 3,5-diaminobenzoic acid is preferred.

Other aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,5-diaminotoluene, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3, 4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) ) Benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis (4- (3-aminophenoxy) phenyl) sulfone, bis (4- (4-aminophenoxy) phenyl) sulfone, 2,2-bis Fragrances of (4- (4-aminophenoxy) phenyl) propane, 2,2-bis (4- (4-aminophenoxy) phenyl) hexafluoropropane, 2,2-bis (4-aminophenyl) hexafluoropropane, etc. Group diamines are exemplified, and these can be used alone or in combination of two or more as appropriate. Further, an alicyclic diamine such as diaminopolysiloxane or norbornanediamine or an aliphatic diamine may be further mixed and polymerized.

In the production of the polyimide of the present invention, a solvent containing γ-butyrolactone (γ-butyrolactone solvent) is used. By using γ-butyrolactone as a solvent, highly transparent polyimide can be obtained. The content of γ-butyrolactone in the solvent is preferably 50% by weight or more, more preferably 70% by weight or more, and may be 100% by weight. Other solvents can be used in combination as long as the transparency is not impaired. Examples of other organic solvents include amide solvents such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide and 1,3-dimethylimidazolidone, and ethers such as diglime, triglime and dioxane. Examples thereof include a system solvent, a ketone such as cyclohexanone, cyclopentanone, methyl benzoate, and ethyl benzoate, and an ester solvent. The content of these solvents other than γ-butyrolactone is preferably 30% by weight or less of the total solvent, and more preferably 10% by weight or less of the total solvent in order to maintain transparency and solubility.

Further, in the reaction, a non-polar solvent compatible with γ-butyrolactone may be mixed and used for the purpose of efficiently taking out the water generated by the imidization reaction to the outside of the system, and the non-polar solvent may be used. Examples include aromatic hydrocarbons such as toluene and xylene. The amount used may be usually in the range of 1 to 20% by weight, preferably 2 to 15% by weight of the total solvent.

The tertiary amine compound is not particularly limited, but is preferably pyridine, picoline, or quinoline. The suitable amount of the tertiary amine compound to be used is 0.01 to 0.5 molar equivalent, more preferably 0.02 to 0.3 molar equivalent, relative to 1 molar equivalent of the imide group of the obtained polyimide. When the amount of the tertiary amine compound is small, the degree of polymerization of the obtained polyimide is low, and when the amount is large, the coloring of the polyimide film becomes stronger than the effect of increasing the degree of polymerization.

The carboxylic acid compound is not particularly limited, but is preferably acetic acid, propionic acid, benzoic acid, hydroxybenzoic acid, toluic acid, salicylic acid, and diaminobenzoic acid. The carboxylic acid compound is an aromatic diamine having a carboxyl group, and may be a raw material for polyimide. For example, diaminobenzoic acid is a monomer constituting a repeating unit of polyimide, but it is also one of carboxylic acid compounds. When diaminobenzoic acid is used as a raw material for polyimide, another carboxylic acid compound is further added. It doesn't have to be. When the carboxylic acid compound is not the aromatic diamine forming the polyimide, the suitable amount of the carboxylic acid compound to be used is 0.01 to 0.4 mol equivalent with respect to 1 molar equivalent of the imide group of the obtained polyimide. More preferably, it is 0.02 to 0.3 molar equivalent. If the amount of the carboxylic acid compound is small, the degree of polymerization of the obtained polyimide is low, and if the amount is large, the effect of increasing the degree of polymerization is low.

In order to improve the polymerizable property and transparency of the obtained polyimide, the molar ratio of the tertiary amine compound to the carboxylic acid compound is 0.2 to 5 with respect to the tertiary amine compound 1. It is preferably 0.4 to 3, and more preferably 0.4 to 3.

In the present invention, by using a catalytic amount of a tertiary amine compound and a carboxylic acid compound, the γ-butyrolactone solvent can be used without using an amide solvent such as N-methyl-2-pyrrolidone, which is preferred as a polyimide polymerization solution. Can produce a solvent-soluble polyimide having a high degree of polymerization.

The equivalent ratio of tetracarboxylic dianhydride to diamine in the polymerization reaction is a factor that determines the molecular weight of the obtained polyimide. The equivalent ratio of tetracarboxylic dianhydride: diamine is preferably in the range of 100: 102 to 100: 96, more preferably 100: 101 to 100: 98. If either the tetracarboxylic dianhydride or the diamine is too much, the molecular weight will be low and the strength of the obtained film will be low. In particular, when the amount of diamine is too large, the amount of diamine increases at the end of the polyimide, which causes coloring. Further, excess diamine causes depolymerization of the polyimide, which may reduce the solubility of the polyimide, which is not preferable.

The polymerization reaction may be carried out by a known method. The charged weight ratio of the γ-butyrolactone solvent and all the monomers is not particularly limited, but the concentration of the polyimide in the obtained polyimide solution is preferably 10% by weight to 40% by weight, preferably 15% by weight to 40% by weight. It is more preferably 35% by weight. If the concentration is low, the polymerization reaction is lowered, and if it is too high, the viscosity of the obtained polyimide solution becomes high, which hinders a uniform reaction, which is not preferable. The polymerization reaction may be carried out, for example, by dissolving tetracarboxylic acid dianhydride and diamine in a γ-butyrolactone solvent under an inert gas stream such as nitrogen, and carrying out the reaction temperature at a reaction temperature of 120 ° C. to 220 ° C., preferably 150 to 200 ° C. can. Since the reaction of tetracarboxylic dianhydride and diamine does not proceed to imidization at room temperature and may become amid acid and precipitate in γ-butyrolactone, it is preferable to raise the reaction temperature from the beginning. The reaction time is usually 0.5 to 24 hours, but is appropriately determined depending on the progress of the reaction.

The polyimide solution thus obtained may be used as it is, or it may be added to a poor solvent to precipitate it in a solid state and then dissolved in another solvent for use.

Further, the solvent-soluble polyimide of the present invention and the polyimide solution in which the polyimide solution is dissolved may be used, for example, as an organic silane, a pigment, a filler such as conductive carbon black and metal particles, an abrasive, a dielectric, and the like. Known additives such as lubricants can be added as long as the effects of the present invention are not impaired. Further, other polymers can be added as long as the effects of the present invention are not impaired. In particular, since the soluble polyimide of the present invention absorbs less light in the visible light region, a clear colored polyimide solution can be obtained by dispersing the coloring pigment in the polyimide solution.

The polyimide of the present invention can be molded to obtain a polyimide coating film or a polyimide film. The polyimide coating film can be produced by applying a polyimide solution on a substrate and drying it to remove a solvent. For example, a polyimide solution is applied onto a substrate such as glass or a silicon wafer by a known method such as a spin coating method, a spray coating method, or a dipping method, and the solvent is dried and removed to form a transparent polyimide film on the substrate. Can be formed. The polyimide film can be produced by extruding a polyimide solution from a slit-shaped nozzle, applying it on a base material with an applicator or the like, drying it to remove a solvent, and then peeling it off from the base material.

Since the polyimide solution obtained in the present invention can be a polyimide film having high transparency and high heat resistance, it is used for applications such as display materials and protective films for solar cells, which require both transparency and electrical reliability. Are suitable. Further, the polyimide film obtained from the polyimide solution has excellent strength and is extremely preferable as a colorless and transparent substrate material.

Hereinafter, the present invention will be specifically described with reference to Examples. However, the present invention is not limited to these examples.

The polyimide solutions and polyimide films obtained in Examples and Comparative Examples were evaluated as follows.

(1) Weight average molecular weight (polystyrene equivalent Mw)
-Equipment: High Performance Liquid Chromatograph (TOSOH HLC-8320GPC, manufactured by Tosoh Corporation)
-Column: Filled product TSK-GEL α-M, 2 bottles-Development solution; NMP with a small amount of potassium bromide and phosphoric acid added. The detector is RI.
-Measurement conditions: Flow rate 0.8 ml / min, column temperature 40 ° C (pressure approx. 3.8 MPa)
-Calibration curve: According to 14 standard polystyrene molecular weights.
-Sample: 0.3 g was taken from the NMP solution of polyimide and uniformly mixed with 10 g of the NMP developing solution to prepare a measurement sample.

(2) Thermal analysis <Preparation of test film>
The polyimide solution is applied onto a glass plate using a spacer with a thickness of 300 μm, allowed to stand and dry on a hot plate at 80 ° C. for 20 minutes, and the polyimide film having no adhesiveness is peeled off from the glass plate and fixed to a metal frame. Then, it was dried at 250 ° C. for 30 minutes.
<3% weight loss temperature>
The obtained polyimide film was subjected to DTG measurement under the condition of a temperature rise rate of 10 ° C./min under a nitrogen stream with a TG-DTA apparatus manufactured by McScience, and a 3% weight loss temperature was determined.
<Glass transition temperature>
The obtained polyimide film was measured for expansion change under the conditions of a nitrogen stream, a temperature rise rate of 10 ° C./min, and a load of 5 g using a TMA-60 device manufactured by Shimadzu Corporation, and an inflection point was determined.

(3) Mechanical strength A polyimide film prepared for thermal analysis is cut into strips with a width of 5 mm, and the tensile breaking strength is determined at a tensile speed of 5 mm / min using a tensile tester (3342 type manufactured by INSTRON) with a chuck spacing of 2 cm. It was measured.

(4) 400 nm light transmittance The polyimide film produced for thermal analysis was measured for absorbance at a wavelength of 400 nm with a spectrophotometer (AS ONE ASV11D), and the light transmittance converted to a thickness of 20 μm was determined.

[Example 1]
A glass 500 ml separable three-necked flask equipped with a stainless steel Ikari-type stirrer was fitted with a beaded cooling tube equipped with a moisture separation trap. The flask was placed in a silicone oil bath, heated and stirred while passing nitrogen gas. 2,3,3', 4'-biphenyltetracarboxylic acid dianhydride (hereinafter referred to as a-BPDA) 29.42 g (100 mmol) and 3,3'-diaminodiphenyl sulfone (hereinafter referred to as m-DADS) 12. 42 g (50 mmol) and 2,2'-bis (trifluoromethyl) benzidine (hereinafter referred to as TFMB) 16.01 g (50 mmol) were placed in a flask, and 140.0 g of γ-butyrolactone and 1.58 g of pyridine (hereinafter referred to as TFMB) were added. 20 mmol) and 1.20 g (20 mmol) of acetic acid were added, and the mixture was immersed in a silicone oil bath at 160 ° C. and heated and stirred. After the monomer was dissolved, 10 g of toluene was added, and the mixture was heated and stirred for 6 hours while passing through nitrogen and removing toluene and water distilling at a silicone oil bath temperature of 180 ° C. A pale yellow transparent viscous liquid was obtained, and the weight average molecular weight was measured to be Mw67,500. This polyimide solution was applied onto a glass plate, dried, and heat-treated in an oven (air atmosphere) at 250 ° C. for 30 minutes to obtain a colorless and transparent film. The 400 nm transmittance of this film at a thickness of 20 μm was 85%, the glass transition temperature was 312 ° C., the thermal decomposition temperature (3% weight loss) was 532 ° C., and the breaking strength of the film was 120 MPa.

[Example 2]
Flasks of a-BPDA 27.07 g (92 mmol), 4,4'-diaminodiphenyl sulfone (hereinafter referred to as p-DADS) 11.42 g (46 mmol), and TFMB 14.73 g (46 mmol) as in Example 1. 149.7 g of γ-butyrolactone, 1.42 g (18 mmol) of pyridine, and 1.62 g (27 mmol) of acetic acid were added thereto, and the mixture was immersed in a silicone oil bath at 160 ° C. and heated and stirred. After the monomer was dissolved, 10 g of toluene was added, and the mixture was heated and stirred for 6 hours while passing through nitrogen and removing toluene and water distilling at a silicone oil bath temperature of 180 ° C. A pale yellow transparent viscous liquid having a weight average molecular weight of Mw64,000 was obtained. This polyimide solution was applied onto a glass plate, dried, and heat-treated in an oven (air atmosphere) at 250 ° C. for 30 minutes to obtain a colorless and transparent film. The 400 nm transmittance of this film at a thickness of 20 μm was 80%, the glass transition temperature was 360 ° C., the thermal decomposition temperature (3% weight loss) was 553 ° C., and the breaking strength of the film was 116 MPa.

[Example 3]
Similar to Example 1, a-BPDA 30.01 g (102 mmol), m-DADS 21.11 g (85 mmol), and 3,5-diaminobenzoic acid (hereinafter referred to as DABz) 2.59 g (17 mmol) are placed in a flask. The mixture was charged, 150 g of γ-butyrolactone and 1.58 g (20 mmol) of pyridine were added, and the mixture was immersed in a silicone oil bath at 160 ° C. and heated and stirred. After dissolving the monomer, 8 g of toluene was added, and the mixture was heated and stirred for 6 hours while passing through nitrogen and removing toluene and water distilling at a silicone oil bath temperature of 180 ° C. A pale yellow transparent highly viscous liquid having a weight average molecular weight of Mw128,000 was obtained. This polyimide solution was applied onto a glass plate, dried, and heat-treated in an oven (air atmosphere) at 250 ° C. for 30 minutes to obtain a colorless and transparent film. The 400 nm transmittance of this film at a thickness of 20 μm was 83%, the glass transition temperature was 294 ° C, the thermal decomposition temperature (3% weight loss) was 482 ° C, and the breaking strength of the film was 130 MPa.

[Example 4]
14.42 g (49 mmol) of a-BPDA, 15.20 g (49 mmol) of 3,3', 4,4'-diphenyl ether tetracarboxylic acid dianhydride (hereinafter referred to as ODPA) and 24.33 g of m-DADS (hereinafter referred to as ODPA) in a flask. 98 mmol) was added, 151.3 g of γ-butyrolactone, 1.58 g (20 mmol) of pyridine, and 1.20 g (20 mmol) of acetic acid were added, and the mixture was immersed in a silicone oil bath at 160 ° C. and heated and stirred. After dissolving the monomer, 12 g of toluene was added, and the mixture was heated and stirred for 6 hours while passing through nitrogen and removing toluene and water distilling at a silicone oil bath temperature of 180 ° C. A pale yellow transparent viscous liquid was obtained, and the weight average molecular weight was measured to be Mw78,000. This polyimide solution was applied onto a glass plate, dried, and heat-treated in an oven (air atmosphere) at 250 ° C. for 30 minutes to obtain a colorless and transparent film. The 400 nm transmittance of this film at a thickness of 20 μm was 82%, the glass transition temperature was 275 ° C, the thermal decomposition temperature (3% weight loss) was 531 ° C, and the breaking strength of the film was 145 MPa.

[Example 5]
14.71 g (50 mmol) of a-BPDA, 15.51 g (50 mmol) of ODPA, 20.73 g (83.5 mmol) of m-DADS, and 2.51 g (16.5 mmol) of DABz were put into a flask, and γ- 149.8 g of butyrolactone and 1.58 g (20 mmol) of pyridine were added, and the mixture was immersed in a silicone oil bath at 160 ° C. and heated and stirred. After the monomer was dissolved, 10 g of toluene was added, and the mixture was heated and stirred for 6 hours while passing through nitrogen and removing toluene and water distilling at a silicone oil bath temperature of 180 ° C. A pale yellow transparent highly viscous liquid having a weight average molecular weight of Mw123,000 was obtained. This polyimide solution was applied onto a glass plate, dried, and heat-treated in an oven (air atmosphere) at 250 ° C. for 30 minutes to obtain a colorless and transparent film. The 400 nm transmittance of this film at a thickness of 20 μm was 84%, the glass transition temperature was 284 ° C, the thermal decomposition temperature (3% weight loss) was 487 ° C, and the breaking strength of the film was 147 MPa.

[Example 6]
Take 18.24 g (62 mmol) of a-BPDA and 9.93 g (31 mmol) of TFMB in a flask, and add 80 g of γ-butyrolactone, 1.50 g (19 mmol) of pyridine and 2.62 g (19 mmol) of hydroxybenzoic acid. In addition, the mixture was immersed in a silicone oil bath at 160 ° C., 10 g of toluene was further added, and the mixture was heated and stirred while passing nitrogen. After 30 minutes, 9.62 g (31 mmol) of ODPA and 15.39 g (62 mmol) of p-DADS were added together with 70 g of γ-butyrolactone, and 6 hours while removing toluene and water distilled at a silicone oil bath temperature of 180 ° C. through nitrogen. It was heated and stirred. A pale yellow transparent viscous liquid having a weight average molecular weight of Mw59,000 was obtained. This polyimide solution was applied onto a glass plate, dried, and heat-treated in an oven (air atmosphere) at 250 ° C. for 30 minutes to obtain a colorless and transparent film. The 400 nm transmittance of this film at a thickness of 20 μm was 81%, the glass transition temperature was 348 ° C, the thermal decomposition temperature (3% weight loss) was 540 ° C, and the breaking strength of the film was 118 MPa.

[Example 7]
11.77 g (40 mmol) of a-BPDA, 12.41 g (40 mmol) of ODPA and 19.86 g (80 mmol) of p-DADS are placed in a flask, 164.6 g of γ-butyrolactone and 1.26 g (16 mmol) of pyridine. ) And 2.21 g (16 mmol) of hydroxybenzoic acid were added, and the mixture was immersed in a silicone oil bath at 160 ° C. and heated and stirred. After dissolving the monomer, 12 g of toluene was added, and the mixture was heated and stirred for 6 hours while passing through nitrogen and removing toluene and water distilling at a silicone oil bath temperature of 180 ° C. A pale yellow transparent viscous liquid was obtained, and the weight average molecular weight was measured to be Mw54,000. This polyimide solution was applied onto a glass plate, dried, and heat-treated in an oven (air atmosphere) at 250 ° C. for 30 minutes to obtain a colorless and transparent film. The 400 nm transmittance of this film at a thickness of 20 μm was 86%, the glass transition temperature was 352 ° C, the thermal decomposition temperature (3% weight loss) was 533 ° C, and the breaking strength of the film was 127 MPa.

[Examples 8 to 12]
Table 1 shows the measurement results of the molecular weight and transmittance of the polyimide obtained by polymerizing in the same manner as in Example 4 except that the types and amounts of the tertiary amine compound and the carboxylic acid compound were changed.

[Comparative Examples 1 to 5]
Table 1 shows the measurement results of the molecular weight and transmittance of the obtained polyimide obtained by polymerizing in the same manner as in Example 4 without using the tertiary amine compound and / or the carboxylic acid compound.

[Comparative Example 6]
Table 1 shows the measurement results of the molecular weight and transmittance of the obtained polyimide obtained by polymerization in the same manner as in Comparative Example 2 using N-methyl-2-pyrrolidone (NMP) without using γ-butyrolactone as the polymerization solvent. .. The molecular weight of the obtained polyimide was lower than that of Example 4, the transmittance was lower than that of Example 4 and Comparative Example 2, and the transparency was poor.

[Comparative Example 7]
Similar to Example 1, ODPA 11.17 g (36 mmol) and m-DADS 17.88 g (72 mmol), 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA) 10.59 g ( 36 mmol) was placed in a flask, 111.2 g of γ-butyrolactone, 1.14 g (14 mmol) of pyridine, and 0.86 g (14 mmol) of acetic acid were added, and the mixture was immersed in a silicone oil bath at 160 ° C. and heated and stirred. After the monomer was dissolved, 10 g of toluene was added, and the mixture was heated and stirred for 6 hours while passing through nitrogen and removing toluene and water distilling at a silicone oil bath temperature of 180 ° C. A yellow transparent highly viscous liquid was obtained, and the weight average molecular weight was measured to be Mw62,500. This polyimide solution was applied onto a glass plate, dried, and heat-treated in an oven (air atmosphere) at 250 ° C. for 30 minutes to obtain a colorless and transparent film. The 400 nm transmittance of this film at a thickness of 20 μm was 58%, the glass transition temperature was 272 ° C, the thermal decomposition temperature (3% weight loss) was 497 ° C, and the breaking strength of the film was 152 MPa. Further, when the polyimide solution was sealed and stored at room temperature, the fluidity was lost the next day, and the dissolution stability was poor.

Claims (9)

Including the repeating unit represented by the formula (1), 40% or more of X ₁ is the group represented by the formula (2) among all the repeating units represented by the formula (1), and 70%. The above Y ₁ is a polyimide which is a group selected from the formulas (3) to (6) , has a weight average molecular weight of 40,000 or more, and transmits light at a wavelength of 400 nm in a film having a thickness of 20 μm. The rate is 80% or more ,
A solvent-soluble polyimide obtained by polycondensing a raw material tetracarboxylic acid dianhydride and a diamine compound in the presence of a tertiary amine compound and a carboxylic acid compound in a γ-butyrolactone solvent .

(In the formula, X ₁ is a tetravalent group having an aromatic ring, and Y ₁ is a divalent group having an aromatic ring.)

The solvent-soluble polyimide according to claim 1 , which contains 90 mol% or more of the repeating units represented by the formula (1) among all the repeating units. The solvent-soluble polyimide according to claim 1 or 2 , wherein the glass transition temperature is 260 ° C. or higher, the 3% weight loss temperature is 480 ° C. or higher, and the tensile breaking strength of the film is 100 MPa or higher. A polyimide coating film or a polyimide film containing the polyimide according to any one of claims 1 to 3 . A substrate for a display, a touch panel, or a solar cell, which comprises the polyimide coating film or the polyimide film according to claim 4 . Aromatic tetracarboxylic acid dianhydride containing 2,3,3', 4'-biphenyltetracarboxylic acid dianhydride, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,2 '-Bis (trifluoromethyl) benzidine and aromatic diamines containing at least one diaminobenzoic acid are polycondensed in a γ-butyrolactone solvent in the presence of a tertiary amine compound and a carboxylic acid compound. A method for producing a solvent-soluble polyimide. The amount of 2,3,3', 4'-biphenyltetracarboxylic acid dianhydride is 40 mol% or more of the aromatic tetracarboxylic acid dianhydride, and 4,4'-diaminodiphenyl sulfone, 3,3'. The solvent-soluble according to claim 6 , wherein the total amount of -diaminodiphenyl sulfone, diaminobenzoic acid, and 2,2'-bis (trifluoromethyl) benzidine is 70 mol% or more of the aromatic diamine. Method for manufacturing polyimide. The tertiary amine compound is selected from the group consisting of pyridine, picolin, and quinoline, and the carboxylic acid compound is selected from the group consisting of acetic acid, propionic acid, benzoic acid, hydroxybenzoic acid, toluic acid, salicylic acid, and diaminobenzoic acid. The method for producing a solvent-soluble polyimide according to claim 6 or 7 , wherein the solvent-soluble polyimide is produced. The amount of the tertiary amine compound is 0.01 to 0.5 molar equivalent with respect to 1 molar equivalent of the imide group of the obtained polyimide, and the amount of the carboxylic acid compound is 0. The method for producing a solvent-soluble polyimide according to any one of claims 6 to 8 , wherein the amount is 01 to 0.4 molar equivalent.