JP5842429B2 - Polyimide precursor and polyimide - Google Patents

Description

  The present invention relates to a polyimide precursor and a polyimide having both high transparency, high heat resistance, and low linear thermal expansion coefficient.

  In recent years, with the advent of the advanced information society, development of optical materials such as liquid crystal alignment films and protective films for color filters in the field of display devices such as optical fibers and optical waveguides in the field of optical communication has been progressing. In the field of equipment, plastic substrates that are lightweight and have excellent flexibility as glass substrate substitutes are being studied, and displays that can be bent and rolled are being actively developed. There is a need for higher performance optical materials that can be used.

  In general, polyimide is essentially yellowish brown due to intramolecular conjugation and the formation of charge transfer complexes. As a solution for this, for example, a method for inhibiting the formation of a charge transfer complex and expressing transparency by introducing fluorine, imparting flexibility to the main chain, or introducing a bulky side chain has been proposed ( Non-patent document 1). In addition, a method for expressing transparency by using a semi-alicyclic or fully alicyclic polyimide resin that does not form a charge transfer complex in principle has been proposed (Patent Documents 1 to 3, Non-Patent Document 2).

  However, when the main solution is to bend the main chain or introduce a bulky side chain, the linear thermal expansion coefficient is very large, and alicyclic polyimide (particularly all alicyclic) is used. When used, there is a problem that heat resistance is reduced as compared with aromatic polyimide. For this reason, in conventional polyimide, it is difficult to achieve both excellent transparency, low thermal expansion coefficient and high heat resistance, and polyimide is used as a transparent substrate for flexible displays, solar cells, and touch panels. Therefore, it has been strongly demanded to satisfy both of these characteristics.

JP 2002-348374 A JP 2005-15629 A JP 2002-161136 A

Polymer, 47, 2337 (2006) High Perform. Polym, 13, S93 (2001)

  An object of the present invention is to provide a polyimide having excellent transparency, low thermal expansion coefficient, and high heat resistance suitable for transparent substrates, solar cells, and touch panels, and a polyimide precursor thereof. is there.

The present invention relates to the following items.
(1) A polyimide precursor having a unit structure represented by the following general formula (1).

〔一般式（１）中、Ｒ_１、Ｒ_２はいずれも独立に、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り、Ａｒは２価の芳香族基であり、Ｘは下記一般式（２）で表される４価の芳香族基である。）

[In General Formula (1), R ₁ and R ₂ are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms, and Ar is a divalent aromatic. X is a tetravalent aromatic group represented by the following general formula (2). )

(2) The Ar in the general formula (1) is a divalent aromatic group represented by the following general formula (3), more preferably 1,4-phenylene or 1,3-phenylene group. Item 2. The polyimide precursor according to Item 1.

〔一般式（３）中、Ｒ_３は水素原子、炭素数１〜６のアルキル基、又はアルコキシ基を表す。〕

[In General Formula (3), R ₃ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group. ]

(3) The above item 1 characterized in that the logarithmic viscosity of the polyimide precursor (temperature: 30 ° C., concentration: 0.5 g / dL, solvent: in N, N-dimethylacetamide solution) is 0.2 dL / g or more. Or the polyimide precursor of 2.

(4) A polyimide precursor solution comprising the polyimide precursor according to any one of Items 1 to 3 and an organic solvent, wherein the concentration of the monomer component comprising tetracarboxylic dianhydride and diamine is the solvent and the monomer component. It is 10 mass% or more with respect to the total amount of the polyimide precursor solution composition characterized by the above-mentioned.

(5) A polyimide having a unit structure represented by the following general formula (4).

〔一般式（４）中、Ｘは前記一般式（２）で表される４価の芳香族基であり、Ａｒは２価の芳香族基である。〕

[In General Formula (4), X is a tetravalent aromatic group represented by General Formula (2), and Ar is a divalent aromatic group. ]

(6) The polyimide as described in (5) above, which is excellent in transparency, having a light transmittance of 400 nm or more when formed into a film of 50% or more.

(7) The polyimide according to any one of Items 5 to 6, wherein the film has an average coefficient of linear thermal expansion at 50 ° C to 200 ° C of 50 ppm / K or less.

(8) A polyimide film having a thickness of 1 μm to 200 μm formed of the polyimide according to item 5 above.

(9) The polyimide film according to Item 8, which is used for a display substrate, a touch panel substrate, or a solar cell substrate.

  According to the present invention, it is possible to provide a polyimide having excellent transparency, low thermal expansion coefficient, and high heat resistance suitable for a transparent substrate, a solar cell, and a touch panel, and a polyimide precursor thereof.

  The polyimide precursor of the present invention has a unit structure represented by the general formula (1). Although the logarithmic viscosity of the polyimide precursor of the present invention is not particularly limited, the logarithmic viscosity in a temperature: 30 ° C., concentration: 0.5 g / dL, solvent: N, N-dimethylacetamide solution is preferably 0.2 dL / g or more, preferably Is 0.5 dL / g or more. At 0.2 dL / g or more, the molecular weight of the polyimide precursor is high, so the mechanical strength of the resulting polyimide film is improved. 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. When the logarithmic viscosity is low, the viscosity of the polyimide precursor varnish is low, and the handleability of the film forming process is good.

R ₁ and R _{2 in} the general formula (1) are not particularly limited, but in the case of a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, n In the case of an alkylsilyl group having 3 to 9 carbon atoms such as -butyl group, iso-butyl group, sec-butyl group, etc., trimethylsilyl group, dimethylisopropylsilyl group, tert-butyldimethylsilyl group, triisopropylsilyl group and the like are preferable. In particular, from the viewpoint of economy, in the case of an alkylsilyl group, a trimethylsilyl group is more preferable.

  The polyimide precursor of the present invention is classified into 1) polyamic acid, 2) polyamic acid ester, and 3) polyamic acid silyl ester, and each can be produced by the following three production methods. However, the manufacturing method of the polyimide precursor of this invention is not necessarily limited to the following manufacturing methods.

1) Polyamide acid A diamine is dissolved in an organic solvent, tetracarboxylic dianhydride is gradually added to this solution while stirring, and the polyimide precursor is obtained by stirring for 1 to 72 hours in the range of 0 to 100 ° C. can get.

2) Polyamic acid ester After reacting tetracarboxylic dianhydride with an arbitrary alcohol to obtain a diester dicarboxylic acid, it is reacted with a chlorinating reagent (thionyl chloride, oxalyl chloride, etc.) to obtain a diester dicarboxylic acid chloride. A polyimide precursor is obtained by reacting the diester dicarboxylic acid chloride and diamine. Alternatively, a polyimide precursor can be easily obtained by dehydrating and condensing diester dicarboxylic acid and diamine using a phosphorus condensing agent or a carbodiimide condensing agent. Further, since this polyimide precursor is stable, it can be purified by reprecipitation by adding a solvent such as water or alcohol.

3) Polyamide 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) and dehydrated solvent. The silylated diamine is dissolved therein, while stirring, the tetracarboxylic dianhydride is gradually added, and the polyimide precursor is obtained by stirring in the range of 0 to 100 ° C. for 1 to 72 hours. It is done. Although it does not specifically limit as a silylating agent used here, Since it can be used without refine | purifying silylated diamine, it is suitable by using the silylating agent which does not contain chlorine. Examples of the silylating agent not containing a chlorine atom include 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 low in cost. In addition, amine-based catalysts such as pyridine, piperidine and triethylamine can be used in the silylation reaction of diamine in order to accelerate the reaction. This catalyst can be used as it is as a polymerization catalyst for the polyimide precursor.

  The tetracarboxylic dianhydride and diamine molar ratio [tetracarboxylic dianhydride / diamine] used in the polyimide precursor can be arbitrarily set depending on the required viscosity of the polyimide precursor, preferably 0.90. ˜1.10, more preferably 0.95 to 1.05.

  Moreover, the polyimide precursor of this invention can contain structural units other than the said General formula (1) within the range of the effect of this invention. In this case, the proportion is usually 30 mol% or less, preferably 25 mol% or less, particularly 20 mol% or less. In the structural unit other than the general formula (1), the tetracarboxylic acid component may be replaced, the diamine component may be replaced, or both components may be changed, but preferably the diamine of the general formula (1) It is preferable to introduce structural units in which only the components are replaced. When replacing the diamine component, it is particularly preferable to change to an alicyclic diamine.

  An organic solvent can be used for manufacture of the polyimide precursor solution composition. Specifically, aprotic solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide are preferable, but the raw material monomer and the polyimide precursor to be formed are dissolved. There is no problem, and the structure is not particularly limited. 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, phenol solvents such as m-cresol, p-cresol, 3-chlorophenol, 4-chlorophenol, Acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane, dimethyl sulfoxide and the like are preferably employed. In addition, other common organic solvents such as phenol, 0-cresol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl acetate, ethyl cellosolve, ptyl 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 spirit, Petroleum naphtha solvents can also be used. As a polyimide precursor solution (varnish) finally obtained, the concentration of the tetracarboxylic acid derivative and the diamine monomer is 5% by weight or more, preferably 15 to 50% by weight.

  In the production of the polyimide precursor solution composition, the organic solvent to be used has a purity required by gas chromatography analysis of preferably 99.9% or more, and more preferably 99.95% or more. When the purity of the organic solvent used is low, the light transmittance of the polyimide may be lowered. Further, it is more preferable that the heavy metal component is small and the light transmittance of the solvent (mainly visible light region) is high.

  The polyimide precursor solution composition (varnish) of the present invention is a polyimide precursor solution composition mainly composed of a polyimide precursor and a solvent, and the concentration of the monomer component composed of tetracarboxylic dianhydride and diamine is the above monomer component. And 10% by weight or more based on the total amount of the solvent and more preferably 15% by weight to 50% by weight. When the monomer concentration is 10% by weight or less, it is difficult to control the thickness of the resulting polyimide film. Since the polyimide precursor of the present invention has high solubility, a relatively high concentration polyimide precursor solution composition can be obtained.

  In the polyimide precursor solution composition of the present invention, when the molar ratio between the tetracarboxylic dianhydride of the polyimide precursor and the diamine is excessive diamine, if necessary, the tetraacid derivative of excess diamine in the solution composition or An acid anhydride can be added to obtain a polyimide precursor solution composition. Examples of tetraacid derivatives to be added include 1,2,3,4-butanetetracarboxylic acid, benzene-1,2,4,5-tetracarboxylic acid, biphenyltetracarboxylic acid, and acid anhydrides such as phthalic anhydride, Examples thereof include tetrahydrophthalic anhydride, cis-norbornene-endo-2,3-dicarboxylic anhydride, cyclohexanedicarboxylic anhydride, succinic anhydride, maleic anhydride and the like. By using a tetraacid derivative or an acid anhydride, thermal coloring and thermal deterioration during heating can be further prevented.

  The polyimide precursor solution composition of the present invention comprises a solvent, a chemical imidizing agent (an acid anhydride such as acetic anhydride, an amine compound such as pyridine and isoquinoline), an antioxidant, a filler, a dye, and an inorganic as necessary. Pigments, silane coupling agents, flame retardants, antifoaming agents, leveling agents, rheology control agents (flow aids), release agents and the like can be added.

  The polyimide of the present invention is obtained by ring-closing imidization of the polyimide precursor of the present invention, and has a unit structure represented by the general formula (4). The imidization method is not particularly limited, and conventionally known thermal imidization and chemical imidization methods can be suitably applied. Examples of the form of polyimide obtained include films, polyimide laminates, powders, beads, molded articles, foams, and varnishes.

Next, a method for producing a polyimide film and a polyimide / substrate laminate, and a polyimide film that can suitably use the polyimide precursor of the present invention will be described. In addition, the use of a polyimide precursor is not limited to the following uses.
First, a polyimide precursor solution (composition) is cast on a substrate made of ceramic (glass, silicon, alumina), metal (copper, aluminum, stainless steel), heat-resistant plastic film (polyimide), etc. Drying is performed at 20 to 180 ° C., preferably 20 to 150 ° C. using hot air or infrared rays in an inert gas or air. Next, a film made of a polyimide precursor having a self-supporting property with most of the obtained solvent removed is left laminated with the substrate, or the film made of the polyimide precursor is peeled off from the substrate, for example, at the end of the film In a vacuum, in an inert gas such as nitrogen, or in the air, using hot air or infrared rays, and heating at 200 to 500 ° C., more preferably 250 to 450 ° C., polyimide film, polyimide film / A board | substrate laminated body can be manufactured. In order to prevent oxidative degradation of the resulting polyimide, it is desirable to perform imidization in a vacuum or in an inert gas. However, if the imidization temperature is not too high, imidation may be performed in air.

  The imidation reaction may be carried out by immersing the polyimide precursor in a solution containing a dehydrating cyclization reagent such as acetic anhydride in the presence of a tertiary amine such as pyridine or triethylamine instead of the heat treatment as described above. Is possible. In addition, these dehydration cyclization reagents are charged and stirred in advance in a polyimide precursor solution (composition), which is cast and dried on the substrate to obtain a partially imidized polyimide precursor. A polyimide can be obtained by further heat-treating it as described above.

  The polyimide of the present invention is not limited because it varies depending on the application, but the light transmittance at 400 nm when the film is 10 μm thick is 50% or more, preferably 60% or more.

  The polyimide of the present invention is not limited because it varies depending on the application, but the average coefficient of thermal expansion at 50 ° C. to 200 ° C. when the film is 10 μm thick is 50 ppm / K or less, preferably 30 ppm / K. .

  Although the polyimide of this invention is not specifically limited, From the characteristic which has the outstanding transparency and a low thermal expansion coefficient, the transparent base material for displays which uses this polyimide as the main base material, the transparent base material for touch panels, the base material for solar cells Can be suitably obtained.

  The polyimide film of the present invention is not limited because it varies depending on the application, but the thickness of the film is preferably about 1 μm to 200 μm, more preferably about 1 μm to 100 μm.

  Furthermore, regarding the polyimide laminate used with the polyimide precursor of the present invention, as described above, the polyimide precursor solution composition is applied to a ceramic substrate, a metal substrate, and a heat-resistant plastic substrate, and in vacuum, nitrogen or air Then, following the process of heating to 200 to 500 ° C. to imidize and producing a polyimide / substrate laminate, a ceramic thin film or a metal thin film is formed on the polyimide surface of the laminate without peeling the polyimide from the substrate. The step of producing a thin film / polyimide / substrate laminate, and then the step of peeling the polyimide from the substrate can be suitably performed. In this way, since subsequent processing such as sputter deposition can be performed directly in the polyimide / substrate laminate state without peeling the polyimide from the substrate, the transportability and dimensional stability are improved. Are better. Especially when used as an alternative glass substrate for displays, touch panels, and solar cells, a polyimide substrate is formed on the glass, which is suitable because the existing transport equipment for glass substrate processes can be used as it is. .

  Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples. In addition, this invention is not limited to a following example.

In each of the following examples, the evaluation was performed by the following method.
[Logarithmic viscosity]
A polyimide precursor solution of 0.5 g / dL N, N-dimethylacetamide was measured at 30 ° C. using an Ubbelohde viscometer.
[Light transmittance]
The light transmittance at 400 nm of a polyimide film having a film thickness of about 10 μm was measured using MCPD-300 manufactured by Otsuka Electronics.
[Elastic modulus]
A polyimide film having a film thickness of about 10 μm was punched into a IEC450 standard dumbbell shape as a test piece, and the initial elastic modulus and elongation at break were measured at 30 mm between chucks and a tensile speed of 2 mm / min using a TENILON manufactured by ORIENTEC. .
[Coefficient of thermal expansion (CTE)]
A polyimide film having a thickness of about 10 μm is cut into a strip having a width of 4 mm to form a test piece, and the temperature is raised to 300 ° C. using a TMA-50 manufactured by Shimadzu Corporation with a length between chucks of 15 mm, a load of 2 g, and a heating rate of 20 ° C./min did. From the obtained TMA curve, the average coefficient of thermal expansion from 50 ° C. to 200 ° C. was determined.
[5% weight loss temperature]
A polyimide film having a thickness of about 10 μm was used as a test piece, and a simultaneous differential thermothermal gravimetric measurement device (TG / DTA6300) manufactured by SII NanoTechnology was used. The temperature was raised to. From the obtained weight curve, a 5% weight loss temperature was determined.

[Example 1] Production of polyimide precursor (polyamic acid) 1.484 g (0.01 mol) of 1,4-bis (4-aminobenzoyloxy) benzene (BABB) in a reaction vessel, dehydrated using molecular sieve N , N-dimethylformamide (DMF) 37.31 g was added and dissolved under a nitrogen stream at room temperature (25 ° C.). To this solution, 3.102 g (0.01 mol) of 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride (ODPA) was gradually added and stirred at room temperature (about 25 ° C.) for 12 hours. A uniform and viscous polyimide precursor solution (varnish) was obtained.

The obtained polyimide precursor varnish was applied to a glass substrate, and directly imidized on the substrate at 100 ° C. for 15 minutes, 200 ° C. for 60 minutes, 300 ° C. for 10 minutes to obtain a colorless and transparent polyimide / glass laminate. It was. Further, the polyimide / glass laminate was immersed in water and then peeled to obtain a film having a thickness of about 10 μm, and the characteristics of the film were measured.
The results are shown in Table 1.

[Example 2] Production of polyimide precursor (polyamic acid silyl ester) 1.742 g (0.005 mol) of 1,4-bis (4-aminobenzoyloxy) benzene (BABB) in a reaction vessel and dehydration using molecular sieve 18.65 g of N, N-dimethylacetamide (DMAc) having a purity of 99.99% was added and dissolved under a nitrogen stream at room temperature (25 ° C.). To the solution, 2.70 g (0.0105 mol) of N, O-bis (trimethylsilyl) trifluoroacetamide (BSTFA) and 0.79 g (0.01 mol) of pyridine were added and stirred for 2 hours for silylation. . Further, 1.551 g (0.005 mol) of 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride (ODPA) was gradually added to this solution and stirred at room temperature (about 25 ° C.) for 12 hours. Thus, a uniform and viscous polyimide precursor solution (varnish) was obtained.

The obtained polyimide precursor varnish was applied to a glass substrate, and directly imidized on the substrate at 100 ° C. for 15 minutes, 200 ° C. for 60 minutes, 300 ° C. for 10 minutes to obtain a colorless and transparent polyimide / glass laminate. It was. Further, the polyimide / glass laminate was immersed in water and then peeled to obtain a film having a thickness of about 10 μm, and the characteristics of the film were measured.
The results are shown in Table 1.

[Example 3] Production of polyimide precursor (polyamic acid silyl ester) In a reaction vessel, 2,787 g (0.008 mol) of 1,4-bis (4-aminobenzoyloxy) benzene (BABB), Bis (4-aminobenzoyloxy) benzene (13p-BABB) 0.697 g (0.002 mol), 37,30 g of N, N-dimethylacetamide (DMAc) dehydrated using molecular sieves were added, and room temperature (25 ° C.) was added. And dissolved under a nitrogen stream. To the solution, 4.27 g (0.021 mol) of N, O-bis (trimethylsilyl) acetamide (BSA) and 1.58 g (0.02 mol) of pyridine were added and stirred for 2 hours for silylation. Further, 3.103 g (0.01 mol) of 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride (ODPA) was gradually added to this solution and stirred at room temperature (about 25 ° C.) for 12 hours. Thus, a uniform and viscous polyimide precursor solution (varnish) was obtained.

The obtained polyimide precursor varnish was applied to a glass substrate, and directly imidized on the substrate at 100 ° C. for 15 minutes, 200 ° C. for 60 minutes, 300 ° C. for 10 minutes to obtain a colorless and transparent polyimide / glass laminate. It was. Further, the polyimide / glass laminate was immersed in water and then peeled to obtain a film having a thickness of about 10 μm, and the characteristics of the film were measured.
The results are shown in Table 1.

[Example 4] Production of polyimide precursor (polyamic acid) In a reaction vessel, 2,787 g (0.008 mol) of 1,4-bis (4-aminobenzoyloxy) benzene (BABB) and trans-1,4- 0.228 g (0.002 mol) of diaminocyclohexane (t-DACH) and 34.57 g of N, N-dimethylformamide (DMF) dehydrated using a molecular sieve were added, and the mixture was dissolved at room temperature (25 ° C.) under a nitrogen stream. . To this solution, 3.102 g (0.01 mol) of 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride (ODPA) was gradually added and stirred at room temperature (about 25 ° C.) for 12 hours. A uniform and viscous polyimide precursor solution (varnish) was obtained.

The obtained polyimide precursor varnish was applied to a glass substrate, and directly imidized on the substrate at 100 ° C. for 15 minutes, 200 ° C. for 60 minutes, 300 ° C. for 10 minutes to obtain a colorless and transparent polyimide / glass laminate. It was. Further, the polyimide / glass laminate was immersed in water and then peeled to obtain a film having a thickness of about 10 μm, and the characteristics of the film were measured.
The results are shown in Table 1.

[Example 5] Production of polyimide precursor (polyamic acid silyl ester) 1.742 g (0.005 mol) of 1,4-bis (4-aminobenzoyloxy) benzene (BABB) in a reaction vessel and dehydration using molecular sieve 22.44 g of N, N-dimethylacetamide (DMAc) was added and dissolved under a nitrogen stream at room temperature (25 ° C.). To the solution, 2.70 g (0.0105 mol) of N, O-bis (trimethylsilyl) trifluoroacetamide (BSTFA) and 0.79 g (0.01 mol) of pyridine were added and stirred for 2 hours for silylation. . Further, 2.223 g (0.005 mol) of 4,4 ′-(2,2-hexafluoroisopropylidene) diphthalic dianhydride (6FDA) was gradually added to this solution, and the solution was added at room temperature (about 25 ° C.) at 12 ° C. The mixture was stirred for a time to obtain a uniform and viscous polyimide precursor solution (varnish).

The obtained polyimide precursor varnish was applied to a glass substrate, and directly imidized on the substrate at 100 ° C. for 15 minutes, 200 ° C. for 60 minutes, 300 ° C. for 10 minutes to obtain a colorless and transparent polyimide / glass laminate. It was. Further, the polyimide / glass laminate was immersed in water and then peeled to obtain a film having a thickness of about 10 μm, and the characteristics of the film were measured.
The results are shown in Table 1.

[Examples 6 to 8] Production of polyimide precursor (polyamic acid) As an acid component, 2,3,3 ', 4'-biphenyltetracarboxylic dianhydride (a-BPDA), 2,2,3', 3'-biphenyltetracarboxylic dianhydride (i-BPDA), 4,4 '-(dimethylsiladiyl) diphthalic dianhydride (DPSDA) as solvent, dehydrated N, N-dimethylacetamide (using molecular sieve) A polyimide precursor solution (varnish) was obtained in the same manner as in Example 1 except that DMAc) was used.

  The obtained polyimide precursor solution was applied to a glass substrate, and the substrate was kept under nitrogen atmosphere (oxygen concentration of 200 ppm or less) as it was at 120 ° C. for 1 hour, 150 ° C. for 30 minutes, 200 ° C. for 30 minutes, and then at 350 ° C. Heat treatment was performed for 3 minutes to thermally imidize, and a colorless transparent copolymer polyimide / glass laminate was obtained. Next, the obtained copolymerized polyimide / glass laminate was immersed in water and then peeled to obtain a copolymerized polyimide film having a thickness of about 10 μm. The results of measuring the properties of this film are shown in Table 1.

[Comparative Example 1]
1.4-bis (4-aminobenzoyloxy) benzene (BABB) 3.484 g (0.01 mol) and 36.38 g of N, N-dimethylformamide (DMF) dehydrated using a molecular sieve were added to the reaction vessel, It melt | dissolved under room temperature (25 degreeC) and nitrogen stream. To this solution, 2.942 g (0.01 mol) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) was gradually added and stirred at room temperature (about 25 ° C.) for 12 hours. Thus, a uniform and viscous polyimide precursor solution (varnish) was obtained.

The obtained polyimide precursor varnish was applied to a glass substrate, and directly imidized on the substrate at 100 ° C. for 15 minutes, 200 ° C. for 60 minutes, 300 ° C. for 10 minutes to obtain a yellow transparent polyimide / glass laminate. It was. Further, the polyimide / glass laminate was immersed in water and then peeled to obtain a film having a thickness of about 10 μm, and the characteristics of the film were measured.
The results are shown in Table 1.

  As can be seen from the results shown in Table 1, the polyimide obtained from the polyimide precursor of the present invention has both excellent light transmittance and low linear thermal expansion coefficient, compared with the conventional polyimide shown in the comparative example. This is a significant improvement.

  The polyimide obtained according to the present invention has excellent light transmittance and a low coefficient of linear thermal expansion. Therefore, in particular, glass substrate substitute substrates for displays such as liquid crystal displays, EL displays and electronic paper, touch panel substrates, solar It can be suitably used as a battery substrate.

Claims (7)

A polyimide precursor having a unit structure represented by the following general formula (1).

[In General Formula (1), R ₁ and R ₂ are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms, and Ar is represented by the following general formula ( 3) is a divalent aromatic group represented by 3), and X is a tetravalent aromatic group represented by the following general formula (2). )

[In General Formula (3), R ₃ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group. ] Logarithmic viscosity of the polyimide precursor (temperature: 30 ° C., concentration: 0.5 g / dL, solvent: N, N-in-dimethylacetamide solution) according to claim 1, characterized in that 0.2 dL / g or more Polyimide precursor. A polyimide having a unit structure represented by the following general formula (4).

[In General Formula (4), X is a tetravalent aromatic group represented by General Formula (2), and Ar is a divalent aromatic group represented by General Formula (3) . ] 4. The polyimide according to claim 3 , wherein the film has a transparency of 400 nm when the film has a thickness of 10 μm and has a light transmittance of 50% or more. 5. Polyimide according to any one of claims 3-4 in which the average linear thermal expansion coefficient at 50 ° C. to 200 DEG ° C. when formed into a film having a thickness of 10μm is equal to or less than 50 ppm / K. A polyimide film having a thickness of 1 μm to 200 μm formed of the polyimide according to claim 3 . The polyimide film according to claim 6 , which is used for a display substrate, a touch panel substrate, or a solar cell substrate.