JP2022190149A - Polyimide, and polyimide precursor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide polyimide having excellent transparency, high mechanical strength and a low linear thermal expansion coefficient simultaneously, which properties are suitable to a transparent substrate for flexible displays, the transparent substance for solar batteries or the transparent substance for touch panels.

SOLUTION: The polyimide is obtained by reacting a diamine derivative (which includes diamine and the derivative thereof) with a tetracarboxylic acid derivative (which includes tetracarboxylic acid and the derivative thereof). The diamine derivative does not have an aromatic ring having 90% or higher light transmittance or has another aromatic ring having 80% or higher light transmittance. The tetracarboxylic acid derivative has 75% or higher light transmittance.

SELECTED DRAWING: None

COPYRIGHT: (C)2023,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a polyimide having high transparency, high mechanical strength, and a low coefficient of linear thermal expansion, and a polyimide precursor thereof.

With the advent of an advanced information society, development of optical materials such as optical fibers and optical waveguides in the field of optical communication, and liquid crystal alignment films and protective films for color filters in the field of display devices is progressing. Furthermore, in the field of display devices, plastic substrates, which are lightweight and excellent in flexibility, are being studied as an alternative to glass substrates, and displays that can be bent or rolled using such plastic substrates are being developed.

Polyimide is a resin obtained from tetracarboxylic dianhydride and diamine, and it has excellent properties such as high dimensional stability and high heat resistance. . However, polyimide is easily colored due to its chemical structure, and it is not easy to suppress coloration of tetracarboxylic dianhydride and diamine as raw materials.

One of raw materials for polyimide is biphenyltetracarboxylic dianhydride. Patent Documents 1 and 2 disclose 3,3',4,4'-biphenyltetracarboxylic dianhydride crystals with reduced coloration and a method for producing the same. However, diamine compounds are generally known to be markedly colored due to oxidation and the influence of trace metals contained as impurities. Even when 4'-biphenyltetracarboxylic dianhydride was used, the light transmittance at 400 nm was 30%, indicating a color.

On the other hand, polyimides using trans-1,4-diaminocyclohexane do not have CT absorption, which is the cause of coloration in aromatic polyimides, and thus are expected to be used in optical materials (Non-Patent Document 1). However, due to coloration assumed to be derived from raw materials, the transmittance at 400 nm when made into a film was less than 80%, and coloration was observed.

In other words, studies on reduction of coloration of polyimide are greatly influenced not only by coloration derived from molecular structure such as CT absorption, but also by coloration of diamine and tetracarboxylic dianhydride as raw materials. Therefore, in order to use polyimide for optical material applications, it is necessary to strictly control the transmittance of diamine and tetracarboxylic dianhydride.

JP-A-2005-314296 JP-A-2006-45198

M. Hasegawa, High Perform. Polym. 13 (2001) S93-S106

An object of the present invention is to provide a polyimide having excellent transparency, high mechanical strength, and a low coefficient of linear thermal expansion suitable for transparent substrates for flexible displays, solar cells, and touch panels, and a polyimide precursor thereof. By strictly controlling the transmittance of , diamine, and tetracarboxylic dianhydride, the transparency of conventional polyimides was greatly improved.

1. A polyimide obtained by reacting a diamine derivative (including diamines and their derivatives, hereinafter the same) with a tetracarboxylic acid derivative (including tetracarboxylic acids and their derivatives, the same hereinafter),
The diamine derivative contains a diamine derivative having no aromatic ring and having a light transmittance of 90% or more, or a diamine derivative having an aromatic ring and having a light transmittance of 80% or more (however, the transmittance of the diamine derivative is , represents the light transmittance at a wavelength of 400 nm and an optical path length of 1 cm for a solution obtained by dissolving in pure water or N,N-dimethylacetamide at a concentration of 10% by mass.),
The tetracarboxylic acid derivative contains a tetracarboxylic acid derivative having a light transmittance of 75% or more (however, the transmittance of the tetracarboxylic acid derivative is 10% by mass when dissolved in a 2N sodium hydroxide solution. represents the transmittance at a wavelength of 400 nm and an optical path length of 1 cm for the solution obtained by
A polyimide characterized by:

2. 2. The polyimide according to item 1, wherein the diamine derivative has a light transmittance of 95% or more at a wavelength of 400 nm and an optical path length of 1 cm, and the tetracarboxylic acid derivative has a light transmittance of 80% or more.

3. 3. The polyimide according to item 1 or 2, wherein at least one of a tetracarboxylic acid derivative and a diamine derivative is an aromatic derivative.

4. 3. The polyimide according to item 1 or 2, wherein the tetracarboxylic acid derivative is an aromatic tetracarboxylic acid derivative and the diamine derivative is an aliphatic diamine derivative.

5. 5. The polyimide according to any one of items 1 to 4, wherein the tetracarboxylic acid derivative is a biphenyltetracarboxylic acid derivative.

6. 5. The polyimide according to any one of items 1 to 4, wherein the diamine derivative is trans-1,4-diaminocyclohexane.

7. 7. The polyimide according to any one of items 1 to 6, wherein a film having a thickness of 10 μm has a light transmittance of 80% or more at 400 nm.

8. 8. The polyimide according to any one of items 1 to 7, which is used as an optical material.

9. Wavelength for a solution obtained by dissolving a polyimide precursor containing 50 mol% or more of a diamine derivative having no aromatic ring in a polar solvent at a concentration of 10% by mass with respect to the total molar amount of the diamine derivative used. A polyimide precursor having a light transmittance of 90% or more at 400 nm and an optical path length of 1 cm.

10. Wavelength 400 nm for a solution obtained by dissolving a polyimide precursor containing 50 mol% or more of a diamine derivative having an aromatic ring in a polar solvent at a concentration of 10% by mass with respect to the total molar amount of the diamine derivative used. , a polyimide precursor having a light transmittance of 50% or more at an optical path length of 1 cm.

11. 11. The polyimide precursor according to any one of items 9 and 10 above, which has a logarithmic viscosity of 0.2 dL/g or more in a 0.5 g/dL N,N-dimethylacetamide solution at 30°C.

12. 12. The polyimide precursor according to item 9 or 11, characterized by containing a unit structural formula of the following general formula (1).

〔一般式（１）中、Ｘは４価の有機基であり、Ｒ_１は水素原子又は炭素数１～４のアルキル基であり、Ｒ_２、Ｒ_３は水素原子、炭素数１～６のアルキル基又は炭素数３～９のアルキルシリル基である。〕

[In general formula (1), X is a tetravalent organic group, R ₁ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ₂ and R ₃ are hydrogen atoms, and It is an alkyl group or an alkylsilyl group having 3 to 9 carbon atoms. ]

13. 13. A polyimide precursor solution composition, wherein the polyimide precursor according to any one of items 9 to 12 is uniformly dissolved in a solvent.

14. 13. A polyimide obtained by imidizing the polyimide precursor according to any one of 9 to 12 above.

By the present invention, it is possible to provide a polyimide and its polyimide precursor having both excellent transparency, high mechanical strength, and a low coefficient of linear thermal expansion suitable for flexible displays, solar cells, and transparent substrates for touch panels.

The polyimide of the present invention is a polyimide obtained by reacting a diamine derivative (including diamines and their derivatives, hereinafter the same) with a tetracarboxylic acid derivative (including tetracarboxylic acids and their derivatives, the same hereinafter), The diamine derivative has a light transmittance of 90% or more, preferably 95% or more and does not have an aromatic ring (including diamines and their derivatives as described above), or a light transmittance of 70%. Above, preferably 80% or more containing diamine derivatives (including diamines and their derivatives as described above) having an aromatic ring (however, the light transmittance is pure water or N,N-dimethylacetamide light transmittance at a wavelength of 400 nm and an optical path length of 1 cm for a solution obtained by dissolving at a concentration of 10% by mass in
The tetracarboxylic acid derivative contains a tetracarboxylic acid derivative having a light transmittance of 80% or higher, preferably 85% or higher, more preferably 90% or higher (as described above, including tetracarboxylic acids and derivatives thereof). (However, the light transmittance is the transmittance at a wavelength of 400 nm and an optical path length of 1 cm for a solution obtained by dissolving the compound in a 2N sodium hydroxide solution at a concentration of 10% by mass). When the light transmittance of the diamine derivative and the tetracarboxylic acid derivative is within the above range, the coloring of the obtained polyimide is reduced, which is favorable. In addition, preferably 80% or more, more preferably 90% or more, still more preferably 95% or more, and most preferably 100% of the diamine component (one or more) constituting the diamine derivative has the above light transmittance. meet. Preferably 80% or more, more preferably 90% or more, still more preferably 95% or more, and most preferably 100% of the tetracarboxylic acid component (one or more) constituting the tetracarboxylic acid derivative is the above light Meet transmittance.

Although the polyimide of the present invention is not particularly limited, at least one of the tetracarboxylic acid derivative and the diamine derivative is preferably an aromatic derivative because of its high heat resistance. Furthermore, it is more preferable that the tetracarboxylic acid derivative is an aromatic tetracarboxylic acid derivative and the diamine derivative is an aliphatic diamine derivative, since transparency can be improved and a low coefficient of linear thermal expansion can be achieved.

The tetracarboxylic acid derivative (including tetracarboxylic acids and derivatives thereof) used in the polyimide of the present invention is not particularly limited, and any tetracarboxylic acids and derivatives thereof employed in ordinary polyimides may be used. .
The aromatic tetracarboxylic dianhydrides include 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride, 2,3 ',3,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3' ,4,4′-diphenylsulfonetetracarboxylic dianhydride, m-terphenyl-3,3′,4,4′-tetracarboxylic dianhydride, 4,4′-(2,2-hexafluoroiso Propylene)diphthalic dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)propanes, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7- naphthalenetetracarboxylic dianhydride, (1,1′:3′,1″-terphenyl)-3,3″,4,4″-tetracarboxylic dianhydride, 4,4′-(dimethylsiladiyl ) diphthalic dianhydride, 4,4′-(1,4-phenylenebis(oxy))diphthalic dianhydride, etc.
Examples of alicyclic tetracarboxylic dianhydrides include bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2 ] Octane-2,3,5,6-tetracarboxylic dianhydride, 5-(dioxotetrahydrofuryl-3-methyl)-3-cyclohexene-1,2-dicarboxylic anhydride, 4-(2,5 -dioxotetrahydrofuran-3-yl)-tetralin-1,2-dicarboxylic anhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic dianhydride, bicyclo-3,3′,4,4′- tetracarboxylic dianhydride, 3c-carboxymethylcyclopentane-1r,2c,4c-tricarboxylic acid 1,4,2,3-dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride and the like. In particular, since polyimide has excellent mechanical properties and heat resistance, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride, 2, 3',3,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 4,4'-(2,2-hexafluoroisopropylene) diphthalic dianhydride, 4,4'-( Dimethylsiladiyl)diphthalic dianhydride is preferred. 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride, 2,3′,3,4′-biphenyltetracarboxylic acid Dianhydrides are particularly preferred due to the low coefficient of linear thermal expansion of polyimides.

The tetracarboxylic acid derivative used in the present invention is preferably purified for the purpose of reducing coloration. The purification method is not particularly limited and known methods can be used, but the following methods are suitable.
(1) A solvent and a tetracarboxylic acid derivative powder are mixed in a heterogeneous state in which at least a part of the tetracarboxylic acid derivative powder is not dissolved, and then the undissolved tetracarboxylic acid derivative powder is separated and recovered from the mixed liquid. purification method,
(2) a purification method of recrystallization with a solution containing an acid anhydride;
(3) Purification method of sublimation under heating and reduced pressure Further, these methods can be repeated multiple times or a combination thereof can be used for purification.

The diamine derivative (including diamines and derivatives thereof) used in the polyimide of the present invention is not particularly limited, and any diamines or derivatives thereof that are used in ordinary polyimides may be used. The following diamines are suitable for improving transparency.
For example, diamines having no aromatic ring include linear and branched aliphatic diamines such as diaminobutane, diaminopentane, diaminohexane, diaminoheptane, diaminooctane, diaminononane, diaminodecane, diaminoundecane, and diaminododecane; 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 3-methyl-1,4-diaminocyclohexane, 3-methyl-, 3-aminomethyl-, 5,5-dimethylcyclohexylamine , 1,3-bisaminomethylcyclohexane, bis(4,4′-aminocyclohexyl)methane, bis(3,3′-methyl-4,4′-aminocyclohexyl)methane, bis(aminomethyl)norbornane, bis( diamines having an alicyclic structure such as aminomethyl)-tricyclo[5,2,1,0]decane, isophoronediamine, 1,3-diaminoadamantane;
Diamines having an aromatic ring include 3,5-diaminobenzotrifluoride, 2-(trifluoromethyl)-1,4-phenylenediamine, 5-(trifluoromethyl)-1,3-phenylenediamine, 1,3 -diamino-2,4,5,6-tetrafluorobenzene, 2,2-bis[4-(4-aminophenoxy)phenyl]-hexafluoropropane, 2,2-bis(3-aminophenyl)1,1 , 1,3,3,3-hexafluoropropane, 2,2′-bis-(4-aminophenyl)-hexafluoropropane, 4,4-bis(trifluoromethoxy)benzidine, 3,3′-diamino- 5,5′-trifluoromethylbiphenyl, 3,3′-diamino-6,6′-trifluoromethylbiphenyl, 3,3′-bis(trifluoromethyl)benzidine; 2,2-bis[4-(4 -aminophenoxy)phenyl] hexafluoropropane, 4,4'-trifluoromethyl-2,2'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3 -dichloro-4,4'-diaminobiphenyl, 2,2',5,5'-dichloro-4,4'-diaminobiphenyl, 4,4'-methylene-bis(2-chloroaniline) and other halogen groups an aromatic diamine having
4,4'-diaminobenzophenone, 3,3'-diaminobenzophenone, 4-aminophenyl-4-aminobenzoate, terephthalic acid bis(4-aminophenyl) ester, biphenyl-4,4'-dicarboxylic acid bis(4- aminophenyl)1,4-bis(4-aminobenzoyloxy)benzene, 1,3-bis(4-aminobenzoyloxy)benzene, 4,4'-diaminobenzanilide, N,N-bis(4-amino aromatic diamines having a carbonyl group such as phenyl)terephthalamide, N,N'-p-phenylenebis(p-aminobenzamide), N,N'-m-phenylenebis(p-aminobenzamide);
3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diamino-4,4'-dihydroxydiphenylsulfone, O-tolysine sulfone, bis[4 aromatic diamines having a sulfonyl group such as -(4-aminophenoxy)phenyl]sulfone and bis[4-(3-aminophenoxy)phenyl]sulfone;
Using 1,4-diaminocyclohexane, bis(4,4'-aminocyclohexyl)methane, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminodiphenylsulfone Polyimide is more preferable because of its excellent transparency and heat resistance, and trans-1,4-diaminocyclohexane is particularly preferable because of its low linear thermal expansion coefficient.

The diamine derivative used in the present invention is preferably purified for the purpose of reducing coloration. The purification method is not particularly limited and known methods can be used, but the following methods are suitable.
(1) Purification method by sublimation (2) Purification method by treatment with adsorbent (3) Purification method by recrystallization Further, these methods can be repeated or combined for purification.

A diamine derivative can also be suitably used as a diamine derivative by reacting the aforementioned diamine with a silylating agent (such as an amide-based silylating agent) for the purpose of imparting reactivity and solubility to the product.

The polyimide precursor of the present invention is a polyimide precursor containing 50 mol% or more of a diamine derivative having no aromatic ring, with respect to the total molar amount of the diamine derivative used, in a polar solvent at a concentration of 10% by mass is 90% or more, preferably 95% or more, at a wavelength of 400 nm and an optical path length of 1 cm with respect to a solution obtained by dissolving in On the other hand, in the case of a polyimide precursor containing 50 mol% or more of a diamine derivative having an aromatic ring with respect to the total molar amount of the diamine derivative used, it was obtained by dissolving in a polar solvent to a concentration of 10% by mass. The light transmittance of the solution at a wavelength of 400 nm and an optical path length of 1 cm is 50% or more, preferably 55% or more. The polar solvent used for measurement here is not particularly limited as long as it can dissolve the polyimide precursor, but N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl - Amide solvents such as 2-pyrrolidone, cyclic ester solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, α-methyl-γ-butyrolactone, ethylene carbonate, propylene carbonate, etc. carbonate solvents, glycol solvents such as triethylene glycol, m-cresol, p-cresol, 3-chlorophenol, phenol solvents such as 4-chlorophenol, acetophenone, 1,3-dimethyl-2-imidazolidinone, Sulfolane, dimethylsulfoxide and the like are preferably employed. In addition, other common organic solvents, namely phenol, O-cresol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, Tetrahydrofuran, dimethoxyethane, diethoxyethane, dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methyl ethyl ketone, acetone, butanol, ethanol, and the like can also be used. A combination of a plurality of these solvents can also be used.

Although the polyimide precursor of the present invention is not particularly limited, it can be easily produced by the following production method.
1) Polyamic acid Diamine is dissolved in an organic solvent, and tetracarboxylic dianhydride is gradually added while stirring to this solution, and stirred at 0 to 100 ° C. for 1 to 72 hours to obtain a polyimide precursor. is obtained.

2) Polyamic acid silyl ester A diamine and a silylating agent are reacted in advance to obtain a silylated diamine (if necessary, the silylated diamine is purified by distillation or the like.), A silylated diamine is dissolved in the solution, and while stirring, tetracarboxylic dianhydride is gradually added and stirred at 0 to 100 ° C. for 1 to 72 hours to obtain a polyimide precursor. . As the silylating agent used here, it is preferable to use a chlorine-free silylating agent because it is not necessary to purify the silylated diamine. The chlorine atom-free silylating agent includes N,O-bis(trimethylsilyl)trifluoroacetamide, N,O-bis(trimethylsilyl)acetamide and hexamethyldisilazane. N,O-bis(trimethylsilyl)acetamide and hexamethyldisilazane are preferred because they do not contain fluorine atoms and are inexpensive. In addition, an amine-based catalyst such as pyridine, piperidine, or triethylamine can be used for the silylation reaction of diamine in order to promote the reaction. This catalyst can be used as it is as a polymerization catalyst for the polyimide precursor.

3) Polyamic Acid Ester A tetracarboxylic dianhydride is reacted with any alcohol to obtain a diester dicarboxylic acid, which is then reacted with a chlorinating reagent (thionyl chloride, oxalyl chloride, etc.) to obtain a diester dicarboxylic acid chloride. A polyimide precursor is obtained by reacting this diester dicarboxylic acid chloride with a diamine. A polyimide precursor can also be easily obtained by subjecting a diester dicarboxylic acid and a diamine to dehydration condensation using a phosphorus-based condensing agent, a carbodiimide condensing agent, or the like. Further, since this polyimide precursor is stable, it can be purified by reprecipitation by adding a solvent such as water or alcohol.

Moreover, since all of the above production methods can be suitably carried out in an organic solvent, as a result, the polyimide precursor solution composition of the present invention can be easily obtained.

In any of these production methods, the molar ratio of the tetracarboxylic acid component and the diamine component can be arbitrarily set depending on the required viscosity of the polyimide precursor, preferably 0.90 to 1.10, more preferably 0.95 to 1.05.

The organic solvent used in the production method is preferably an aprotic solvent such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, or dimethylsulfoxide. There is no particular limitation on the structure, as long as the monomer and the resulting polyimide precursor are dissolved, they can be used without any problem. Amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, α-methyl-γ - Cyclic ester solvents such as butyrolactone, carbonate solvents such as ethylene carbonate and propylene carbonate, glycol solvents such as triethylene glycol, phenolic solvents such as m-cresol, p-cresol, 3-chlorophenol and 4-chlorophenol, Acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane, dimethylsulfoxide and the like are preferably employed. In addition, other common organic solvents, namely phenol, O-cresol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, Tetrahydrofuran, dimethoxyethane, diethoxyethane, dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methyl ethyl ketone, acetone, butanol, ethanol, xylene, toluene, chlorobenzene, terpene, mineral spirits, Petroleum naphtha-based solvents and the like can also be used.

The logarithmic viscosity of the polyimide precursor of the present invention is not particularly limited, but temperature: 30 ° C., concentration: 0.5 g / dL, solvent: logarithmic viscosity in N,N-dimethylacetamide solution is 0.2 dL / g or more, preferably is 0.5 dL/g or more. When it is 0.2 dL/g or more, the mechanical strength of the obtained polyimide film is improved because the molecular weight of the polyimide precursor is high. The logarithmic viscosity of the polyimide precursor of the present invention is not particularly limited, but is preferably 2.5 dL/g or less, more preferably 2.0 dL/g or less, and particularly preferably 1.5 dL/g or less. When the logarithmic viscosity is low, the viscosity of the polyimide precursor varnish is low, so that the handleability in the polyimide film manufacturing process is improved.

Although the polyimide precursor of the present invention is not particularly limited, it preferably contains a unit structural formula of the following general formula (1).

〔一般式（１）中、Ｘは４価の有機基であり、Ｒ_１は水素原子又は炭素数１～４のアルキル基であり、Ｒ_２、Ｒ_３は水素原子、炭素数１～６のアルキル基又は炭素数３～９のアルキルシリル基である。〕
得られるポリイミドの耐熱性が高いことから、Ｘは下記一般式（２）の４価の有機基であることがより好ましく、４価のビフェニル異性体であることが特に好ましい。

[In general formula (1), X is a tetravalent organic group, R ₁ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ₂ and R ₃ are hydrogen atoms, and It is an alkyl group or an alkylsilyl group having 3 to 9 carbon atoms. ]
X is more preferably a tetravalent organic group represented by the following general formula (2), particularly preferably a tetravalent biphenyl isomer, since the resulting polyimide has high heat resistance.

The polyimide of the present invention can be produced by subjecting a polyimide precursor to a dehydration ring closure reaction (imidization reaction). The imidization method is not particularly limited, and known thermal imidization and chemical imidization methods can be applied. Forms of the obtained polyimide include films, polyimide laminates, coating films, powders, beads, moldings, foams, varnishes, and the like.

Although not limited thereto, the polyimide of the present invention has a light transmittance at 400 nm of 80% or more, preferably 85% or more, more preferably 90% or more when formed into a film having a thickness of 10 μm, and has excellent transparency. have

In addition, the polyimide of the present invention, although not limited thereto, has an average coefficient of linear thermal expansion of 50 ppm/K or less, preferably 30 ppm/K or less, more preferably 20 ppm/K or less at 50 ° C. to 200 ° C. when made into a film. .

The film made of the polyimide of the present invention preferably has a thickness of about 1 μm to 200 μm, more preferably about 1 μm to 100 μm, depending on the application.

Although the polyimide of the present invention is not particularly limited, it is suitable as an optical material due to its excellent transparency and toughness. For example, it can be suitably used as a transparent substrate for displays, a transparent substrate for touch panels, and a transparent substrate for solar cells.

An example of a method for producing a polyimide film/substrate laminate or a polyimide film using the polyimide precursor of the present invention will be described below. However, it is not limited to the following methods.
For example, the polyimide precursor solution composition of the present invention is cast on substrates such as ceramics (glass, silicon, alumina), metals (copper, aluminum, stainless steel), heat-resistant plastic films (polyimide), and the like, in a vacuum, nitrogen, etc. or in the air, using hot air or infrared rays, in a temperature range of 20 to 180°C, preferably 20 to 150°C.
Next, the obtained polyimide precursor film is placed on the substrate, or the polyimide precursor film is peeled off from the substrate, and in a state where the edge of the film is fixed, in vacuum, in an inert gas such as nitrogen, or A polyimide film/substrate laminate or a polyimide film can be produced by thermal imidization in air at a temperature of about 200 to 500° C., more preferably about 250 to 450° C. using hot air or infrared rays. In order to prevent the obtained polyimide film from being oxidized and degraded, it is desirable to perform the imidization by heating in a vacuum or in an inert gas. As long as the heat imidization temperature is not too high, it may be carried out in air. The thickness of the polyimide film (polyimide film layer in the case of a polyimide film/substrate laminate) is preferably 1 to 250 μm, more preferably 1 to 150 μm, for transportability in subsequent steps.

In the imidization reaction of the polyimide precursor, instead of heat imidization by heat treatment as described above, the polyimide precursor is treated with a dehydration cyclization reagent such as acetic anhydride in the presence of a tertiary amine such as pyridine or triethylamine. It is also possible to carry out by chemical treatment such as immersion in a solution. In addition, these dehydration cyclization reagents are added in advance to a polyimide precursor solution composition and stirred, and the mixture is cast on a substrate and dried to prepare a partially imidized polyimide precursor. It is also possible to obtain a polyimide film/substrate laminate or a polyimide film by further heat-treating this as described above.

A flexible conductive substrate can be obtained by forming a conductive layer on one or both sides of the thus obtained polyimide film/substrate laminate or polyimide film.

A flexible conductive substrate can be obtained, for example, by the following method. That is, as a first method, a conductive material (metal or metal oxide) is applied to the surface of the polyimide film by sputtering deposition, printing, etc., without peeling the polyimide film from the base material. , conductive organic matter, conductive carbon, etc.) to form a conductive layer/polyimide film/substrate conductive laminate. Thereafter, if necessary, by peeling the electrically conductive layer/polyimide film laminate from the substrate, a transparent and flexible conductive substrate comprising the electrically conductive layer/polyimide film laminate can be obtained.
As a second method, the polyimide film is peeled off from the substrate of the polyimide film/substrate laminate to obtain a polyimide film, and a conductive substance (metal or metal oxide, conductive organic substance, A conductive layer of conductive carbon, etc.) can be formed in the same manner as in the first method to obtain a transparent and flexible conductive substrate comprising a conductive layer/polyimide film laminate.
In the first and second methods, if necessary, before forming the conductive layer on the surface of the polyimide film, a gas barrier layer such as water vapor, oxygen, etc., and a light adjustment layer are formed by sputtering deposition, gel-sol method, etc. You may form inorganic layers, such as.
A circuit is preferably formed on the conductive layer by a method such as a photolithography method, various printing methods, an inkjet method, or the like.

The substrate of the present invention has a circuit of a conductive layer on the surface of a polyimide film composed of the polyimide of the present invention via a gas barrier layer or an inorganic layer, if necessary. This substrate is flexible, excellent in transparency, bendability and heat resistance, and further has an extremely low coefficient of linear thermal expansion and solvent resistance, so that fine circuits can be easily formed. Therefore, this substrate can be suitably used as a substrate for displays, touch panels, or solar cells.
That is, a transistor (inorganic transistor, organic transistor) is further formed on this substrate by vapor deposition, various printing methods, or an ink jet method to manufacture a flexible thin film transistor, and a liquid crystal element for a display device, an EL element, a photoelectric It is preferably used as an element.

The present invention will be further described below with reference to examples and comparative examples. In addition, the present invention is not limited to the following examples.

Raw materials used in the following examples are as follows.
Trans-1,4-diaminocyclohexane: manufactured by ZHEJIANG TAIZHOU QINGQUAN MEDICAL & CHEMICAL Co., Ltd. Purity 99.1% (GC analysis)
1,4-bis (4-aminobenzoyloxy) benzene (BABB): BABB manufactured by Mikuni Pharmaceutical Industry Co., Ltd.
3,3′,4,4′-Biphenyltetracarboxylic dianhydride (s-BPDA): Purity 99.9% manufactured by Ube Industries, Ltd. (3,3′,4,4′-biphenyltetracarboxylic acid after ring opening Purity determined by HPLC analysis of carboxylic acid), acid anhydride conversion rate 99.8%, Na, K, Ca, Al, Cu, Si: each <0.1 ppm, Fe: 0.1 ppm, Cl: <1 ppm
2,3,3′,4′-Biphenyltetracarboxylic dianhydride (a-BPDA): Purity 99.6% manufactured by Ube Industries, Ltd. (2,3,3′,4′-biphenyltetracarboxylic acid after ring opening Purity determined by HPLC analysis of carboxylic acid), acid anhydride conversion rate 99.5%, Na, K, Al, Cu, Si: each <0.1 ppm, Ca, Fe: each 0.1 ppm, Cl: <1 ppm
2,2',3,3'-biphenyltetracarboxylic dianhydride (i-BPDA): manufactured by CHANGZHOU WEIJIA CHEMICAL Co., Ltd. Purity 99.9% (2,2',3,3'-biphenyl after ring opening Purity determined by HPLC analysis of tetracarboxylic acid), acid anhydride conversion rate 99%
4,4'-(2,2-hexafluoroisopropylene) diphthalic dianhydride (6FDA): Purity 99% manufactured by Daikin Industries, Ltd.
4,4′-(Dimethylsiladiyl)diphthalic dianhydride, (DPSDA): Purity 99.8% manufactured by Toray Fine Chemicals Co., Ltd. (3,3′,4,4′-biphenyltetracarboxylic acid after ring opening Purity determined by HPLC analysis), acid anhydride conversion rate 99%
Each solvent: Wako Pure Chemical Co., Ltd. special grade, first class equivalent, or those purified 2N sodium hydroxide aqueous solution: Tokyo Kasei Co., Ltd. sodium hydroxide aqueous solution Adsorbent: Nippon Norit Co., Ltd. Activated carbon Norit SX Plus BET Specific surface area 1100 m ² /g determined by the method

Evaluation was performed in each of the following examples by the following methods.

Evaluation of diamine powder and tetracarboxylic anhydride powder
[Light transmittance]
Predetermined amounts of diamine powder and tetracarboxylic anhydride powder were dissolved in a measurement solvent to obtain a 10% by mass solution. Using MCPD-300 manufactured by Otsuka Electronics Co., Ltd., a standard cell with an optical path length of 1 cm, the light transmittance of the diamine powder and the tetracarboxylic anhydride powder at 400 nm was measured using a blank solvent as the measurement solvent.

Evaluation of polyimide precursors
[Logarithmic Viscosity]
A 0.5 g/dL polyimide precursor N,N-dimethylacetamide solution was measured at 30° C. using an Ubbelohde viscometer.
[Light transmittance]
The polyimide precursor was diluted with N,N-dimethylacetamide so as to obtain a 10 mass % polyimide precursor solution. Using Otsuka Electronics MCPD-300, a standard cell with an optical path length of 1 cm, and using N,N-dimethylacetamide as a blank, the light transmittance of a 10% by weight polyimide precursor solution at 400 nm was measured.

Evaluation of polyimide
[Light transmittance]
Using MCPD-300 manufactured by Otsuka Electronics Co., Ltd., the light transmittance at 400 nm of a polyimide film having a thickness of about 10 μm was measured.
[Elastic modulus, elongation at break]
The polyimide film was punched into a dumbbell shape of IEC450 standard to obtain a test piece, and the initial elastic modulus and breaking elongation were measured using TENSILON manufactured by ORIENTEC at a chuck distance of 30 mm and a tensile speed of 2 mm/min.
[Coefficient of thermal expansion (CTE)]
The polyimide film was cut into strips with a width of 4 mm to form a test piece, and a TMA-50 manufactured by Shimadzu Corporation was used to raise the temperature to 300° C. with a chuck distance of 15 mm, a load of 2 g, and a heating rate of 20° C./min. From the obtained TMA curve, the average thermal expansion coefficient from 50°C to 200°C was determined.

[Reference Example 1] Purification of t-DACH powder A glass sublimator was charged with 10.0 g of unpurified trans-1,4-diaminocyclohexane, and the pressure was reduced to 1 Torr or less. The temperature of the bottom surface of the wall in contact with trans-1,4-diaminocyclohexane was heated to 50°C, and a sublimate was obtained on the top surface of the opposite wall which was temperature-controlled at 5°C. Yield was 8.2 g. Table 1 shows the light transmittance of the trans-1,4-diaminocyclohexane powder obtained by this method.

[Reference Example 2] Purification of BABB powder 20.0 g of BABB and 140 g of N,N-dimethylacetamide were placed in a glass vessel and heated to 60°C to dissolve. 0.20 g of adsorbent (Norit SX Plus) was added to the solution and stirred for 2 hours. The adsorbent was removed by filtration, pure water was added, the mixture was cooled to 5°C, and the precipitate was collected. Further, 10.0 g of the resulting precipitate was placed in a glass sublimation apparatus, and the pressure was reduced to 1 Torr or less. The temperature of the lower surface of the wall in contact with BABB was heated to 300 to 350°C, and a sublimate was obtained on the upper surface of the opposite wall which was temperature-controlled at 25°C. Yield was 8.5 g. Table 1 shows the results of the light transmittance of BABB obtained by this method.

[Reference Example 3] Purification of s-BPDA powder 10.0 g of unpurified s-BPDA and 10.0 g of N-methyl-2-pyrrolidone as a solvent were placed in a glass vessel and thoroughly stirred at 25°C for 3 hours. . The solution was filtered, and the obtained solid was vacuum-dried at 100° C. for 2 hours to obtain s-BPDA powder with reduced coloration. Table 1 shows the results of light transmittance.

[Reference Example 4] Purification of a-BPDA powder 10.0 g of unpurified a-BPDA and 10.0 g of acetone as a solvent were placed in a glass vessel and thoroughly stirred at 25°C for 3 hours. The solution was filtered, and the obtained solid was vacuum-dried at 100° C. for 2 hours to obtain 9.4 g of a-BPDA with reduced coloration. Table 1 shows the results of light transmittance.

[Reference Example 5] Purification of i-BPDA powder 10.0 g of unpurified i-BPDA and 10.0 g of N-methyl-2-pyrrolidone as a solvent were placed in a glass container and thoroughly stirred at 25°C for 3 hours. . The solution was filtered, and the obtained solid was vacuum-dried at 100° C. for 2 hours to obtain i-BPDA with reduced coloring. Table 1 shows the results of light transmittance.

[Example 1]
1.40 g (0.0122 mol) of trans-1,4-diaminocyclohexane (t-DACH) purified in the same manner as in Reference Example 1 was placed in a reaction vessel, and dehydrated N,N- Dissolved in 28.4 g of dimethylacetamide. This solution was heated to 50° C. and 3.50 g (0.0119 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) purified in the same manner as in Reference Example 3. and 0.09 g (0.0003 mol) of a-BPDA purified in the same manner as in Reference Example 4 were gradually added. After stirring at 50° C. for 6 hours, a uniform and viscous polyimide precursor solution was obtained.

The resulting polyimide precursor solution was applied to a glass substrate and thermally imidized in a nitrogen atmosphere by heating to 120°C for 1 hour, 150°C for 30 minutes, 200°C for 30 minutes, and 350°C for 5 minutes. to obtain a colorless and transparent polyimide/glass laminate. Then, the obtained copolymer polyimide/glass laminate was immersed in water and then peeled off to obtain a polyimide film having a thickness of 10 μm. Table 2 shows the results of measuring the properties of this film.

[Examples 2 to 6]
A polyimide precursor solution and a polyimide film were obtained in the same manner as in Example 1, except that the diamine component and acid component listed in Table 2 were used. Table 2 shows the results of measuring the characteristics.

[Comparative Examples 1 to 3]
A polyimide precursor solution and a polyimide film were obtained in the same manner as in Example 1, except that the diamine component and acid component listed in Table 2 were used. Table 2 shows the results of measuring the characteristics.

As can be seen from the results shown in Table 2, the polyimide of the present invention has a light transmittance of 80% or more at 400 nm, and is suitable as a polyimide for optical materials.

By the present invention, it is possible to provide a polyimide and its polyimide precursor having both excellent transparency, high mechanical strength, and a low coefficient of linear thermal expansion suitable for flexible displays, solar cells, and transparent substrates for touch panels.

Claims (14)

A polyimide obtained by reacting a diamine derivative (including diamines and their derivatives, hereinafter the same) with a tetracarboxylic acid derivative (including tetracarboxylic acids and their derivatives, the same hereinafter),
The diamine derivative contains a diamine derivative having no aromatic ring and having a light transmittance of 90% or more, or a diamine derivative having an aromatic ring and having a light transmittance of 80% or more (however, the transmittance of the diamine derivative is , represents the light transmittance at a wavelength of 400 nm and an optical path length of 1 cm for a solution obtained by dissolving in pure water or N,N-dimethylacetamide at a concentration of 10% by mass.),
The tetracarboxylic acid derivative contains a tetracarboxylic acid derivative having a light transmittance of 75% or more (however, the transmittance of the tetracarboxylic acid derivative is 10% by mass when dissolved in a 2N sodium hydroxide solution. represents the transmittance at a wavelength of 400 nm and an optical path length of 1 cm for the solution obtained by
A polyimide characterized by: The diamine derivative has a light transmittance of 95% or more at a wavelength of 400 nm and an optical path length of 1 cm, and the tetracarboxylic acid derivative has a light transmittance of 80% or more at a wavelength of 400 nm and an optical path length of 1 cm. Polyimide as described. 3. The polyimide according to claim 1, wherein at least one of the tetracarboxylic acid derivative and the diamine derivative is an aromatic derivative. 3. The polyimide according to claim 1, wherein the tetracarboxylic acid derivative is an aromatic tetracarboxylic acid derivative and the diamine derivative is an aliphatic diamine derivative. 5. The polyimide according to any one of claims 1 to 4, wherein the tetracarboxylic acid derivative is a biphenyltetracarboxylic acid derivative. 5. The polyimide according to any one of claims 1 to 4, wherein the diamine derivative is trans-1,4-diaminocyclohexane. 7. The polyimide according to any one of claims 1 to 6, wherein a film having a thickness of 10 μm has a light transmittance of 80% or more at 400 nm. 8. The polyimide according to any one of claims 1 to 7, which is used as an optical material. Wavelength for a solution obtained by dissolving a polyimide precursor containing 50 mol% or more of a diamine derivative having no aromatic ring in a polar solvent at a concentration of 10% by mass with respect to the total molar amount of the diamine derivative used. A polyimide precursor having a light transmittance of 90% or more at 400 nm and an optical path length of 1 cm. Wavelength 400 nm for a solution obtained by dissolving a polyimide precursor containing 50 mol% or more of a diamine derivative having an aromatic ring in a polar solvent at a concentration of 10% by mass with respect to the total molar amount of the diamine derivative used. , a polyimide precursor having a light transmittance of 50% or more at an optical path length of 1 cm. 11. The polyimide precursor according to claim 9, wherein the logarithmic viscosity in a 0.5 g/dL N,N-dimethylacetamide solution at 30° C. is 0.2 dL/g or more. 12. The polyimide precursor according to claim 9 or 11, comprising a unit structural formula of the following general formula (1).

[In general formula (1), X is a tetravalent organic group, R ₁ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ₂ and R ₃ are hydrogen atoms, and It is an alkyl group or an alkylsilyl group having 3 to 9 carbon atoms. ] A polyimide precursor solution composition, wherein the polyimide precursor according to any one of claims 9 to 12 is uniformly dissolved in a solvent. A polyimide obtained by imidating the polyimide precursor according to any one of claims 9 to 12.