JP2015209488A - Varnish, laminate, and manufacturing method of laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide varnish that is useful when forming a polyimide film excellent in transparency and mechanical characteristics and having a low thermal expansion coefficient, and to provide a laminate obtained using the varnish, and a manufacturing method of the laminate.SOLUTION: Varnish contains a polyimide having a repeating unit having a specific rigid structure, and a specific solvent. A laminate is obtained using the varnish. A manufacturing method manufactures the laminate.

Description

  The present invention relates to a varnish useful for forming a polyimide film having excellent transparency and mechanical properties and a low coefficient of thermal expansion, a laminate obtained using the varnish, and a method for producing the laminate.

In recent years, liquid crystal displays and organic EL displays have been required to be thin, light, and flexible.
For this reason, it has been proposed to use an extremely thin glass film as a transparent substrate used for such applications.
For example, Patent Document 1 describes a specific glass roll obtained by winding a glass film having a film thickness of 200 μm or less into a roll. Patent Document 1 also describes that the glass film is used as a display substrate.

In addition, polyimide is known as a resin excellent in heat resistance and transparency.
For example, Patent Document 2 describes a polyimide having a specific alicyclic structure, high glass transition temperature, excellent transparency, and low water absorption.

Japanese Unexamined Patent Publication No. 2011-042508 JP 2007-284414 A

When using the glass film of patent document 1 as a base material, it is thought that it becomes difficult to break a glass film by providing a resin layer on the glass film surface and making it a laminated film.
However, when the polyimide described in Patent Document 2 is used as the material for the resin layer, the thermal expansion coefficient of the resin layer is likely to be larger than that of the glass film, and when the thermal load is applied to the laminated film, The resin layer may be warped or peeled off from the glass film.
In addition, by introducing a rigid structure in which the π bond is expanded in the polyimide chain, the thermal expansion coefficient of the polyimide can be lowered. In this case, the polyimide film is yellowish or the solubility of the polyimide is increased. There was a problem that it was not possible to prepare an appropriate concentration of varnish.

  The present invention has been made in view of the above-described prior art, and is a varnish useful for forming a polyimide film having excellent transparency and mechanical properties and a low coefficient of thermal expansion, and a laminate obtained by using this varnish. And it aims at providing the manufacturing method of this laminated body.

  In order to solve the above-mentioned problems, the present inventor diligently studied about polyimide and a polyimide film obtained using the polyimide. As a result, using a varnish containing a polyimide having a repeating unit having a specific rigid structure, a polyimide film formed by a specific method is found to have excellent transparency and mechanical properties, and a low coefficient of thermal expansion, The present invention has been completed.

Thus, according to the present invention, the following [1] to [2] varnish, [3] to [4] laminate, and [5] to [10] laminate production methods are provided.
[1] A varnish containing a polyimide and a solvent, wherein the polyimide has in its molecule a repeating unit represented by the following formula (1), or a repeating unit represented by the following formula (1) and the following formula (2 ), The total amount of the repeating unit represented by the following formula (1) and the repeating unit represented by the following formula (2) is 80 to 100 mol% in all repeating units, and the formula The molar ratio of the repeating unit represented by (1) and the repeating unit represented by formula (2) [repeating unit represented by formula (1): repeating unit represented by formula (2)] is from 20:80 to A varnish, which is a polymer of 100: 0, and the solvent is an aprotic polar solvent having a boiling point of 170 ° C. or lower.

[Wherein, R ¹ and R ² each independently represent a halogen atom, a hydroxyl group, a linear or branched alkyl group having 1 to 6 carbon atoms, a linear or branched alkoxyl group having 1 to 6 carbon atoms, Or represents a trifluoromethyl group. A ¹ represents the following formula (3a) or (3b)

(In the formula, * represents a bond.)
Represents a group represented by a and b each independently represents an integer of 0 to 4; When a and b are each 2 or more, a plurality of R ^{1 s} and R ^{2 s} may be the same or different. ]

(In the formula, R ^{3 to} R ⁶ are each independently a halogen atom, a hydroxyl group, a linear or branched alkyl group having 1 to 6 carbon atoms, a linear or branched alkoxyl group having 1 to 6 carbon atoms, Or A ¹ represents a group represented by the formula (3a) or (3b), and cf each independently represents an integer of 0 to 4. c, d, e, When f is 2 or more, a plurality of R ^{3 s} , R ^{4 s} , R ^{5 s,} and R ^{6 s} may be the same or different.
[2] The varnish according to [1], wherein when the polyimide is formed into a film having a thickness of 10 μm, the light transmittance of light having a wavelength of 400 nm of the film becomes 85% or more.
[3] A laminate having a base material and a polyimide film formed on the base material, wherein the polyimide film is formed using the varnish according to claim 1 or 2, and has a thermal expansion coefficient. A laminate characterized by being a film of 30 ppm / ° C. or less.
[4] The laminate according to [3], wherein the substrate is a glass substrate.
[5] A method for producing a laminate,
A step of applying the varnish described in [1] or [2] on a substrate and prebaking the obtained coating film (AI)
After the step (AI), the coating film is immersed in a poor solvent for the polyimide contained in the varnish (A-II)
After step (A-II), the coating film is dried by heating to form a polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less (A-III)
The manufacturing method of the laminated body characterized by having.
[6] The method for producing a laminate according to [5], wherein the amount of residual solvent in the coating film after step (AI) is 5 to 45% by weight.
[7] The poor solvent is a solvent selected from the group consisting of water, an alcohol solvent having 1 to 4 carbon atoms, a ketone solvent having 2 to 4 carbon atoms, and an acetate ester solvent having 3 to 4 carbon atoms. [5] or [6] The manufacturing method of the layered product according to [6].
[8] The substrate is a long glass film having a film thickness of 100 μm or less, and the steps (A-1) to (A-III) are continuously performed while the glass film is conveyed in a certain direction. The manufacturing method of the laminated body in any one of [5]-[7] characterized by performing.
[9] A method for producing a laminate,
A step of applying the varnish described in [1] or [2] on a substrate so that the film thickness after drying is 5 μm or less (BI)
Step (B-II) of forming a polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less by heating and drying the coating film obtained in step (BI) at 100 to 200 ° C.
The manufacturing method of the laminated body characterized by having.
[10] The substrate is a long glass film having a thickness of 100 μm or less, and the steps (B-1) to (B-II) are continuously performed while the glass film is conveyed in a certain direction. It is performed, The manufacturing method of the laminated body as described in [9] characterized by the above-mentioned.

  According to the present invention, a varnish useful for forming a polyimide film having excellent transparency and mechanical properties and a low coefficient of thermal expansion, a laminate obtained using the varnish, and a method for producing the laminate are provided. Is done.

  Hereinafter, the present invention will be described in detail by dividing it into 1) varnish, 2) a laminate, and 3) a method for producing a laminate.

1) Varnish The varnish of the present invention is a varnish containing a polyimide and a solvent, and the polyimide is a repeating unit represented by the above (1) or a repeating unit represented by the above formula (1) in the molecule. And the total amount of the repeating unit represented by the formula (1) and the repeating unit represented by the formula (2) is 80 to 100 mol% in all repeating units. And the molar ratio of the repeating unit represented by formula (1) to the repeating unit represented by formula (2) [repeating unit represented by formula (1): repeating unit represented by formula (2)] is , 20:80 to 100: 0, and the solvent is an aprotic polar solvent having a boiling point of 170 ° C. or lower.

[Polyimide]
The polyimide used in the present invention has a repeating unit represented by the formula (1) in the molecule (hereinafter sometimes referred to as “repeating unit (1)”), or the repeating unit (1) and the formula (1). 2) (hereinafter also referred to as “repeating unit (2)”), and the total amount of the repeating unit (1) and the repeating unit (2) is 80 to 80% of all the repeating units. The molar ratio of the repeating unit (1) to the repeating unit (2) [repeating unit (1): repeating unit (2)] is 20:80 to 100: 0 at 100 mol%.

In the repeating unit (1), R ¹ and R ² are each independently a halogen atom, a hydroxyl group, a linear or branched alkyl group having 1 to 6 carbon atoms, or a linear or branched structure having 1 to 6 carbon atoms. An alkoxyl group or a trifluoromethyl group is represented.

Examples of the halogen atom for R ¹ and R ² include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
R ^1, the number of carbon atoms of the linear or branched alkyl group having 1 to 6 carbon atoms ^{R 2} is 1-3 are preferable. Examples of the linear or branched alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, isopropyl group, isobutyl group, Examples thereof include s-butyl group and t-butyl group.
R ^1, the number of carbon atoms of the linear or branched alkoxyl group having 1 to 6 carbon atoms ^{R 2} is 1-3 are preferable. Examples of the linear or branched alkoxyl group having 1 to 6 carbon atoms include methoxy group, ethoxy group, n-propoxy group, n-butoxy group, n-pentyloxy group, n-hexyloxy group, isopropoxy group, isobutoxy group. Group, t-butoxy group and the like.

a and b each independently represents an integer of 0 to 4; When a and b are integers of 2 to 4, the plurality of R ¹ may be the same or different from each other, and the plurality of R ² may be the same or different from each other. It may be.
A ¹ represents a group represented by the formula (3a) or (3b).

The repeating unit (1) has a structure obtained by reacting a tetracarboxylic dianhydride represented by the following formula (4a) or (4b) with a diamine represented by the following formula (5).
The part derived from tetracarboxylic dianhydride [compound represented by the following formula (4a) or (4b)] has an alicyclic structure.

  For this reason, the polyimide used for this invention is excellent in transparency. Moreover, the polyimide which has this alicyclic structure is excellent in the solubility with respect to an organic solvent. Therefore, by using this polyimide, the varnish of the present invention having a sufficient resin concentration can be obtained efficiently.

  Moreover, the part derived from diamine [compound shown by following formula (5)] has a rigid structure where a pi bond spreads.

  For this reason, the polyimide film | membrane with a low thermal expansion coefficient can be efficiently formed by using the polyimide used for this invention.

In the repeating unit (2), R ^{3 to} R ⁶ are each independently a halogen atom, a hydroxyl group, a linear or branched alkyl group having 1 to 6 carbon atoms, or a linear or branched structure having 1 to 6 carbon atoms. An alkoxyl group or a trifluoromethyl group is represented.
Specific examples of these groups include the same groups as those exemplified as R ¹ and R ² .
cf represents the integer of 0-4 each independently. When c is an integer of 2 to 4, a plurality of R ³ may be the same as or different from each other. The same applies to R ^{4 to} R ⁶ when e to f are integers of 2 to 4.
A ¹ represents a group represented by the formula (3a) or (3b).

The repeating unit (2) has a structure obtained by reacting the tetracarboxylic dianhydride represented by the formula (4a) or (4b) with the diamine represented by the following formula (6).
The part derived from tetracarboxylic dianhydride [the compound represented by the above formula (4a) or (4b)] is the same as the tetracarboxylic dianhydride of the repeating unit (1). Therefore, the polyimide used in the present invention is excellent in transparency and solubility in organic solvents.

  Moreover, the part derived from diamine [the compound shown by following formula (6)] has a fluorene ring.

  The polyimide having this fluorene ring structure is excellent in solubility in an organic solvent. Therefore, by using this polyimide, the varnish of the present invention having a sufficient resin concentration can be obtained efficiently.

The total amount of the repeating unit (1) and the repeating unit (2) in the polyimide is 80 to 100 mol%, preferably 90 to 100 mol%, more preferably 95 to 100 mol% in all repeating units. .
When the total of the repeating unit (1) and the repeating unit (2) is within the above range, a polyimide useful as a raw material for a polyimide film having excellent transparency and mechanical properties and a low coefficient of thermal expansion can be obtained.

The molar ratio of the repeating unit (1) to the repeating unit (2) [repeating unit (1): repeating unit (2)] of the polyimide used is 20:80 to 100: 0, preferably 30:70. ~ 70: 30.
If the ratio of the repeating unit (1) is too small, it becomes difficult to form a polyimide film having a low coefficient of thermal expansion. Moreover, since the solubility with respect to an organic solvent increases by having a repeating unit (2) moderately, when preparing a varnish, the organic solvent to be used can be selected from many types of organic solvents.

  The polyimide to be used may have an arbitrary repeating unit other than the repeating units (1) and (2). Examples of such a repeating unit include tetracarboxylic dianhydrides other than the tetracarboxylic dianhydrides represented by the formulas (4a) and (4b) described later (hereinafter, “other tetracarboxylic dianhydrides”). And repeating units formed using diamines other than the diamines represented by the formulas (5) and (6) (hereinafter sometimes referred to as “other diamines”).

  The method for synthesizing the polyimide used in the present invention is not particularly limited. For example, the tetracarboxylic dianhydride represented by the above formula (4a) or (4b), the diamine represented by the above formula (5), the diamine represented by the above formula (6), and other used as necessary. The target polyimide can be synthesized by performing a reaction using tetracarboxylic dianhydride or other diamine as a raw material.

  Examples of the other tetracarboxylic dianhydrides include 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, pyromellitic acid anhydride, 1,2,3,4-benzenetetracarboxylic acid anhydride. 1,4,5,8-naphthalenetetracarboxylic anhydride, 2,3,6,7-naphthalenetetracarboxylic anhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2 , 3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 2,3,3 ′, 4′-benzophenonetetracarboxylic dianhydride Anhydride, 3,3 ′, 4,4′-diphenyl ether tetracarboxylic dianhydride, 2,3,3 ′, 4′-diphenyl ether tetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenyl Sul Tetracarboxylic dianhydride, 2,3,3 ′, 4′-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis (3,3 ′, 4,4′-tetracarboxyphenyl) tetrafluoropropane Dianhydride, 2,2′-bis (3,4-dicarboxyphenoxyphenyl) sulfone dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2-bis ( 3,4-dicarboxyphenyl) propane dianhydride, cyclobutane-1,2,3,4-tetracarboxylic dianhydride and the like.

  Examples of the other diamines include 4,4′-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'- Diaminobenzophenone, 4,4′-diaminobenzophenone, 3,4′-diaminobenzophenone, 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane, 2,2-di (3 -Aminophenyl Propane, 2,2-di (4-aminophenyl) propane, 2- (3-aminophenyl) -2- (4-aminophenyl) propane, 2,2-di (3-aminophenyl) -1,1, 1,3,3,3-hexafluoropropane, 2,2-di (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2- (3-aminophenyl) -2 -(4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 1,1-di (3-aminophenyl) -1-phenylethane, 1,1-di (4-amino) Phenyl) -1-phenylethane, 1- (3-aminophenyl) -1- (4-aminophenyl) -1-phenylethane, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis ( 4-aminophenoxy) benzene, 1, -Bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminobenzoyl) benzene, 1,3-bis (4-aminobenzoyl) benzene, , 4-bis (3-aminobenzoyl) benzene, 1,4-bis (4-aminobenzoyl) benzene, 1,3-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,3-bis ( 4-amino-α, α-dimethylbenzyl) benzene, 1,4-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,4-bis (4-amino-α, α-dimethylbenzyl) benzene 1,3-bis (3-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,3-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,4 Bis (3-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,4-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 2,6-bis (3-aminophenoxy) benzo Nitrile, 2,6-bis (3-aminophenoxy) pyridine, 4,4′-bis (3-aminophenoxy) biphenyl, 4,4′-bis (4-aminophenoxy) biphenyl, bis [4- (3- Aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [ -(3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4 -(4-aminophenoxy) phenyl] propane, 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [ 4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (4-aminophenoxy) benzene Zoyl] benzene, 1,3-bis [4- (3-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] Benzene, 1,4-bis [4- (3-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,4-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene, 4,4′-bis [4- (4-aminophenoxy) benzoyl] diphenyl ether, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenylsulfone, 4,4′-bis [4- (4-aminophenoxy) phenoxy] diphenylsulfone, 3, 3'-diamino-4,4'-diphenoxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4 -Biphenoxybenzophenone, 5-amino-2- (p-aminophenyl) benzoxazole, 2,2'-di (p-aminophenyl) -6,6'-bisbenzoxazole, 2- (4-aminophenyl) -6-aminobenzoxazole, N- (4-aminophenyl) -4-aminobenzamide, N, N'-bis (4-aminophenyl) terephthalamide, 4-aminophenyl-4-aminobenzoate, 2,2 ' -Dimethylbiphenyl-4,4'-diamine etc. are mentioned.

  As a method for synthesizing the polyimide used in the present invention, after reacting tetracarboxylic dianhydride and diamine (hereinafter, these compounds may be collectively referred to as “monomer”) to obtain a polyimide precursor, Examples include a method of imidizing the obtained polyimide precursor to synthesize polyimide (method 1), a method of directly synthesizing polyimide from tetracarboxylic dianhydride and diamine (method 2), and the like.

In Method 1 (method of imidizing a polyimide precursor), the method for synthesizing the polyimide precursor is not particularly limited, and a known method can be adopted.
For example, first, a diamine represented by the above formula (5) and a diamine represented by the above formula (6) and other diamines used as needed are dissolved in a solvent to obtain a solution, and this is then stirred. To the solution, gradually add the tetracarboxylic dianhydride represented by the above formula (4a) or (4b) and other tetracarboxylic dianhydrides used as necessary, which are substantially equivalent to the diamine used. The solution of a polyimide precursor can be obtained by adding to and making it react by continuing stirring.
The monomer concentration at this time is not particularly limited, but is usually 5 to 50% by weight, preferably 10 to 40% by weight.

  The solvent used when synthesizing the polyimide precursor is not particularly limited as long as it sufficiently dissolves the monomer and the polyimide precursor. For example, amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, hexamethylphosphate triamide; sulfolane, dimethyl sulfoxide, dimethyl sulfone, tetramethylene Sulfur-containing solvents such as sulfone and dimethyltetramethylenesulfone; phenolic solvents such as cresol, phenol and xylenol; diglyme-based solvents such as diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme) and tetraglyme; γ-butyrolactone, Lactone solvents such as γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone; isophorone, cyclohexanone, 3,3,5-trimethylcyclo Examples include ketone solvents such as hexanone; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; other solvents such as pyridine, ethylene glycol, dioxane, and tetramethylurea. These solvents can be used alone or in combination of two or more.

Although reaction temperature is not specifically limited, Usually, it is -10-80 degreeC, Preferably it is 0-40 degreeC.
Although reaction time is not specifically limited, Usually, it is 0.5 to 150 hours, Preferably it is 3 to 24 hours.

The obtained polyimide precursor solution can be subjected to the next imidation reaction as it is or after adjusting the concentration without isolating the polyimide precursor. Alternatively, the polyimide precursor can be isolated by dropping the polyimide precursor solution into a large amount of poor solvent such as water or methanol to precipitate the polyimide precursor, which is filtered, washed and dried. .
In the present specification, the poor solvent refers to a solvent having poor solubility in the target product (in the above case, a polyimide precursor). For example, a solvent in which the concentration of the saturated solution of the target product at 25 ° C. is 1% by weight or less is mentioned, and a solvent that is 0.5% by weight or less is preferable.

  Examples of the poor solvent include water; alcohol solvents having 1 to 4 carbon atoms such as methanol, ethanol, n-propanol, and isopropanol; ketone solvents having 2 to 4 carbon atoms such as acetone; and 3 to 4 carbon atoms such as ethyl acetate. And the like, and the like. These solvents can be used alone or in combination of two or more.

  The method for imidizing the polyimide precursor is not particularly limited, and for example, a known chemical imidization method or thermal imidization method can be employed. Especially, since it is not necessary to heat too much and the molecular weight fall of a polyimide can be suppressed, a chemical imidation method is used more suitably.

The chemical imidization method can be performed, for example, by dropping an organic acid anhydride and an organic base into this solution while stirring the solution of the polyimide precursor.
Examples of the solvent for the polyimide precursor solution include the same solvents as those shown as the solvent for the synthesis of the polyimide precursor.
Examples of the organic acid anhydride include acetic anhydride, propionic anhydride, maleic anhydride, and phthalic anhydride. Among these, acetic anhydride is preferably used from the viewpoint of easy removal after the reaction and cost.
Although the usage-amount of an organic acid anhydride is not specifically limited, 1-10 equivalent of the theoretical dehydration amount of a polyimide precursor is preferable, and 2-5 equivalent is more preferable.

Examples of the organic base include heterocyclic compounds such as pyridine and picoline; tertiary amines such as triethylamine and N, N-dimethylaniline;
Although the usage-amount of an organic base is not specifically limited, 0.1-2 equivalent is preferable with respect to an organic acid anhydride, and 0.2-1.5 equivalent is more preferable.

  In the chemical imidization method, the reaction temperature is not particularly limited, but is usually 0 to 130 ° C, preferably 20 to 110 ° C. Although reaction time is not specifically limited, Usually, it is 0.5 to 48 hours, Preferably it is 1 to 24 hours.

  The thermal imidization method can be performed, for example, by heating a solution of the polyimide precursor to a temperature at which a dehydration ring-closing reaction occurs. When heating, either a method of raising the temperature up to the maximum temperature in one step or a method of raising the temperature in multiple steps may be used.

Examples of the solvent for the polyimide precursor solution include the same solvents as those shown as the solvent for the synthesis of the polyimide precursor.
In the thermal imidization method, the reaction temperature is not particularly limited, but is usually 130 to 450 ° C, preferably 300 to 400 ° C. Although reaction time is not specifically limited, Usually, it is 0.1 to 24 hours, Preferably it is 0.5 to 5 hours.
The reaction can be carried out in vacuum, in an inert gas such as nitrogen or argon, or in the air. In the reaction system, an organic base such as γ-picoline or water as a by-product is azeotroped. To distill off, toluene, xylene or the like may be added.

Moreover, the isolated polyimide precursor can also be heat-imidized by heating as it is.
Although reaction temperature is not specifically limited, Usually, it is 200-400 degreeC, Preferably it is 250-300 degreeC.
Although reaction time is not specifically limited, Usually, it is 0.5 to 48 hours, Preferably it is 1 to 24 hours.
The reaction can be performed in a vacuum, in an inert gas such as nitrogen or argon, or in the air. However, since the coloring can be prevented, the reaction is preferably performed in a vacuum or an inert gas.

  When a polyimide is synthesized by Method 2 (a method of directly synthesizing polyimide from tetracarboxylic dianhydride and diamine), for example, by changing reaction conditions of a method for synthesizing a polyimide precursor in Method 1, tetracarboxylic acid is obtained. Polyimide can be synthesized directly from dianhydride and diamine.

Examples of the solvent used for the reaction include the same solvents as those shown for the synthesis of the polyimide precursor. Of these, amide solvents and phenol solvents are preferable.
Although reaction temperature is not specifically limited, Usually, 130-250 degreeC, Preferably it is 150-200 degreeC.
Although reaction time is not specifically limited, Usually, it is 0.5 to 48 hours, Preferably it is 1 to 24 hours.
To the reaction system, toluene, xylene or the like may be added in order to azeotropically distill off an organic base such as γ-picoline or water as a by-product as a catalyst.

The reaction can be performed by the above-described method 1 or method 2, and the resulting polyimide solution can be dropped into a large amount of poor solvent to precipitate the polyimide. Furthermore, the polyimide can be isolated by filtering, washing, drying, etc. the deposited polyimide.
As a poor solvent, the thing similar to what was shown as a poor solvent of a polyimide precursor is mentioned.

The weight average molecular weight of the polyimide used in the present invention is usually 5,000 to 1,000,000, preferably 10,000 to 500,000.
The molecular weight distribution of the polyimide is usually 1.3 to 3, preferably 1.5 to 2.5.
By using a polyimide having a weight average molecular weight or molecular weight distribution within the above range, it becomes easy to form a polyimide film having excellent transparency and mechanical properties and a low coefficient of thermal expansion.
In addition, a weight average molecular weight and molecular weight distribution are the polystyrene conversion values obtained by the gel permeation chromatography method which uses cyclopentanone as a solvent.

  The polyimide used in the present invention is excellent in transparency. The polyimide to be used preferably has a light transmittance of 85% or more, more preferably 90% or more, when formed into a film having a thickness of 10 μm.

  The polyimide used in the present invention has high solubility in organic solvents. When the polyimide to be used is dissolved in cyclopentanone at 25 ° C. to prepare a saturated solution, the concentration of the saturated solution is preferably 5% by weight or more, more preferably 10% by weight or more. There is no particular upper limit for the concentration of the saturated solution, but it is usually 50% by weight or less.

〔solvent〕
The solvent used in the present invention is an aprotic polar solvent having a boiling point of 170 ° C. or lower.
When the boiling point of the solvent is 170 ° C. or lower, the solvent can be efficiently removed when forming the polyimide film. The boiling point of the solvent is preferably 150 ° C. or lower.
A polyimide can fully be dissolved because a solvent is an aprotic polar solvent.

Examples of the solvent to be used include amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, hexamethylphosphate triamide; sulfolane, dimethyl sulfoxide, Sulfur-containing solvents such as dimethylsulfone, tetramethylenesulfone, dimethyltetramethylenesulfone; lactone solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone; diethylketone, methylisobutyl And ketone solvents such as ketone, cyclopentanone, isophorone, cyclohexanone, and 3,3,5-trimethylcyclohexanone. These solvents can be used alone or in combination of two or more.
Among these, a ketone solvent is preferable and cyclopentanone is more preferable because it can be efficiently removed when forming a polyimide film.

〔varnish〕
The polyimide concentration (resin concentration) in the varnish of the present invention can be appropriately determined according to the coating method of the varnish and the target polyimide film thickness. The resin concentration is preferably 5 to 30% by weight, more preferably 5 to 20% by weight.

  The varnish may contain an additive as long as the effects of the present invention are not impaired. Examples of the additive include an oxidation stabilizer, a filler, an adhesion promoter, a silane coupling agent, a photosensitizer, a photopolymerization initiator, a sensitizer, a terminal blocking agent, and a crosslinking agent.

  The method for preparing the varnish is not particularly limited. For example, what adjusted the density | concentration of the reaction liquid immediately after synthesize | combining a polyimide can be used as a varnish. Moreover, a varnish can be prepared by dissolving the once isolated polyimide in a suitable solvent.

By using the varnish of the present invention, a polyimide film having excellent transparency and mechanical properties and a low coefficient of thermal expansion can be efficiently formed.
Therefore, the varnish of the present invention is preferably used as a protective film forming agent for brittle materials such as glass.

2) Laminate The laminate of the present invention is a laminate having a substrate and a polyimide film formed on the substrate, and the polyimide film is formed using the varnish of the present invention. It is a film having an expansion coefficient of 30 ppm / ° C. or less.

〔Base material〕
The base material constituting the laminate of the present invention is not particularly limited as long as it can support a polyimide film and is stable under heating conditions when forming the polyimide film.
Examples of the base material include inorganic base materials such as glass base materials, ceramic base materials, and semiconductor base materials, metal base materials such as stainless steel base materials, aluminum base materials, and copper base materials, and resin film base materials.

  Examples of the glass substrate include those made of glass materials such as soda lime glass, soda potash glass, soda aluminum silicate glass, alumino borosilicate glass, aluminoborosilicate glass, low expansion glass, quartz glass and the like.

  Examples of the ceramic substrate include those made of a ceramic material such as alumina, zirconia, mullite, cordierite, steatite, magnesium titanate, calcium titanate, strontium titanate, aluminum nitride, silicon carbide, and silicon nitride.

  As a semiconductor substrate, elemental semiconductor materials such as silicon (Si), germanium (Ge), selenium (Se), tin (Sn), tellurium (Te), SiC, GaN, GaP, GaAs, GaSb, AlP, AlAs , AlSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, AlGaAs, GaInAs, AlInAs, AlGaInAs, and the like.

  Although the thickness of a base material is not specifically limited, Usually, it is 600 micrometers or less, Preferably it is 200 micrometers or less, More preferably, it is 10-100 micrometers, Most preferably, it is 20-60 micrometers.

  In the present invention, it is preferable to use a single layer substrate having a thermal expansion coefficient of +1 to +21 ppm / ° C. or a composite substrate formed by laminating two or more single layer substrates as the substrate. By using such a base material, the difference from the coefficient of thermal expansion of the polyimide film formed thereon is reduced, so that the warpage of the laminate is reduced.

  These base materials may be used as they are, or may be subjected to a surface treatment in order to enhance adhesion with the polyimide film or to form a polyimide film having a lower coefficient of thermal expansion. As the surface treatment, a conventionally known general method can be used. Specific examples include silane coupling agent treatment, aluminum alcoholate treatment, aluminum chelate treatment, titanate coupling agent treatment, and the like. . Especially, since a surface treatment can be performed efficiently, a silane coupling agent treatment is preferable, and an aminosilane-based coupling agent treatment such as aminopropyltriethoxysilane is more preferable.

[Polyimide film]
The polyimide film constituting the laminate of the present invention is a film having a coefficient of thermal expansion of 30 ppm / ° C. or less formed using the varnish of the present invention.
A polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less can be formed by the method described later.

  Although the thickness of a polyimide film is not specifically limited, Usually, 1-500 micrometers, Preferably it is 1-100 micrometers, More preferably, it is 1-50 micrometers.

  The polyimide film is excellent in transparency. The light transmittance of light having a wavelength of 400 nm of the polyimide film is preferably 85% or more, and more preferably 90% or more.

  The polyimide film is excellent in mechanical properties. When a tensile test was performed at a rate of 100 mm / min using a polyimide film having a thickness of 10 μm and a width of 10 mm, the breaking strength is preferably 60 MPa or more, more preferably 80 MPa or more, and the upper limit is not particularly limited, but 200 MPa Degree. The elongation at break is preferably 5% or more, more preferably 10% or more, and the upper limit is not particularly limited, but is about 50%.

  The mechanical properties of the polyimide film can be measured by separating the polyimide film from the substrate by the method described in the examples to obtain a measurement sample, and using this.

[Laminate]
The laminated body of this invention has the said base material and a polyimide film.
Since the polyimide film also functions as a protective film, the strength of the laminate is high even when a brittle material such as glass is used as the base material.
Moreover, since the said polyimide film has a low coefficient of thermal expansion, even if it applies a heat load, a laminated body will warp or a polyimide film will hardly peel from a base material.
Moreover, since the said polyimide film is excellent in transparency, when a transparent base material is used as a base material, a laminated body is excellent in transparency.

  Since it has these characteristics, the laminated body of this invention is used suitably as display substrates, such as a thin organic EL display, a flexible liquid crystal display, and a touch panel, sealing sheet material, etc.

3) Manufacturing method of laminated body The manufacturing method of the laminated body of this invention is the manufacturing method (A) or (B) of the following laminated bodies.
A method for producing a laminate comprising: applying a varnish of the present invention on a substrate; and pre-baking the obtained coating film (AI), after step (AI), the coating film is a poor solvent Steps (A-II) and (A-II) for immersing the coating film, followed by heating and drying the coating film to form a polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or lower (A-III). A method for producing a laminate (A), comprising:
It is a manufacturing method of a laminated body, Comprising: It obtained by the step (BI) and the step (BI) which apply | coat the varnish of this invention so that the film thickness after drying might be 5 micrometers or less on a base material. A method for producing a laminate (B-II), which comprises a step (B-II) of forming a polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less by heating and drying the coating film at 100 to 200 ° C. ).
Each of these production methods (A) and (B) is characterized by forming a polyimide film while efficiently removing the solvent in the coating film formed by applying the varnish of the present invention.

[Production method (A)]
The production method (A) includes the steps (AI) to (A-III).
Step (AI) is a step of applying the varnish of the present invention on a substrate and prebaking the obtained coating film.
Examples of the substrate and varnish are the same as those described above.
The method for applying the varnish is not particularly limited, and a conventionally known method can be used. Examples of the coating method include spin coating, dip coating, roll coating, curtain coating, die coating, and slit coating.

The method for pre-baking the coating film is not particularly limited, and for example, it can be pre-baked using a hot plate, a heating furnace or the like.
The heating temperature is usually 30 to 100 ° C., preferably 40 to 80 ° C., and the heating time is usually 1 to 60 minutes, preferably 1 to 50 minutes, more preferably 1 to 40 minutes.

The pre-bake in step (AI) is to dry the coating film to the extent that a certain amount of solvent remains. By subjecting such a coating film to the immersion treatment in step (A-II), a polyimide film having a low thermal expansion coefficient can be finally formed.
The amount of residual solvent in the coating film after step (AI) is preferably 5 to 45% by weight, more preferably 10 to 40% by weight. When the residual solvent amount is within the above range, the solvent can be efficiently removed in the immersion treatment of step (A-II), and a polyimide film having a low coefficient of thermal expansion can be formed.

Step (A-II) is a step of immersing the coating film in a poor solvent after step (AI).
The poor solvent is not particularly limited as long as it is difficult to dissolve polyimide. Especially, since the solvent derived from a varnish which remains in a coating film can be removed efficiently, the solvent in the used varnish [hereinafter referred to as “solvent (A)”. And a solvent that is uniformly mixed with the same volume of the solvent (A) at 25 ° C. is more preferable.
In step (A-III), a solvent having a relatively low boiling point is preferable as the poor solvent because it can be efficiently removed by drying. The boiling point of the poor solvent is preferably 120 ° C. or lower, more preferably 110 ° C. or lower. The lower limit of the boiling point of the poor solvent is not particularly limited as long as the immersion treatment can be performed near room temperature.

Examples of the poor solvent include water; alcohol solvents having 1 to 4 carbon atoms such as methanol, ethanol, n-propanol, and isopropanol; ketone solvents having 2 to 4 carbon atoms such as acetone; and 3 to 4 carbon atoms such as ethyl acetate. And the like, and the like. These solvents can be used alone or in combination of two or more.
Among these, as a poor solvent, the 2 or more types of mixed solvent chosen from water, acetone, and methanol is preferable, and the mixed solvent of water and acetone is more preferable. In the mixed solvent of water and acetone, the mixing ratio (weight ratio of water: acetone) is usually 1:99 to 99: 1, preferably 5:95 to 95: 5.

The temperature at which the coating film is immersed in the poor solvent is usually 10 to 40 ° C, preferably 15 to 35 ° C. Since the immersion temperature is within this range, evaporation of the poor solvent can be suppressed, so that the operation can be performed safely. Moreover, when using 2 or more types of poor solvents, since the change of a mixing ratio can be suppressed by using the said temperature conditions, the solvent A can be removed from a coating film with high reproducibility.
The time for immersing the coating film in the poor solvent is usually 1 to 60 minutes, preferably 1 to 45 minutes, more preferably 1 to 30 minutes. When the immersion time is within this range, the solvent A can be efficiently removed from the coating film.

  In step (A-II), at least the coating film may be immersed in a poor solvent. Therefore, the coating film may be immersed in the poor solvent together with the base material, or the coating film may be immersed in the poor solvent in a state where a part of the base material is not in contact with the poor solvent.

Step (A-III) is a step in which after the step (A-II), the coating film is heated and dried to form a polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less.
The heating temperature is usually 130 to 250 ° C, preferably 150 to 240 ° C, more preferably 170 to 230 ° C. The heating time is not particularly limited, but is usually 1 to 120 minutes, preferably 1 to 90 minutes, and more preferably 1 to 60 minutes.
A polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less can be efficiently formed by sufficiently drying the coating film that has been subjected to the treatments of steps (A-I) and (A-II). The thermal expansion coefficient of the polyimide film is preferably 20 ppm / ° C. or less, and more preferably 1 to 20 ppm / ° C.

  The production method (A) is suitably used when a relatively thick polyimide film is formed. The thickness of the polyimide film formed by the production method (A) is usually 5 to 500 μm, preferably 5 to 100 μm, more preferably 5 to 50 μm.

[Production method (B)]
The production method (B) includes the steps (B-I) to (B-II).
Step (B-I) is a step of applying the varnish of the present invention on the substrate so that the film thickness after drying is 5 μm or less.
Step (BI) can be carried out in the same manner as the coating method of step (AI) except that the film thickness of the coating film is reduced.

Step (B-II) is a step of forming a polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less by heating and drying the coating film obtained in Step (BI) at 100 to 200 ° C. .
The heating temperature in step (B-1) is 100 to 200 ° C, preferably 150 to 200 ° C. The heating time is not particularly limited, but is usually 1 to 120 minutes, preferably 1 to 90 minutes, and more preferably 1 to 60 minutes.

The manufacturing method (B) is used when forming a thin polyimide film. The thickness of the polyimide film formed by the production method (B) is 5 μm or less, preferably 1 to 5 μm.
As described above, when the varnish of the present invention is used to form a thin polyimide film, the solvent can be efficiently removed without performing immersion treatment, and the polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less. Can be formed efficiently.

In the production methods (A) and (B), a long laminate can be produced by performing a roll-to-roll method using a long glass film as a substrate.
For example, a long glass film having a film thickness of 100 μm or less is used as the base material, and while transporting it in a certain direction, steps (A-1) to (A-III) or steps (B-1) to By performing (B-II) continuously, a long laminate can be produced efficiently.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples. In the following Examples and Comparative Examples, “parts” and “%” are based on weight unless otherwise specified.

The materials used in the examples are as follows.
Base material (1): A surface treatment was performed on a white glass substrate manufactured by Dow Corning using a silane coupling agent (manufactured by Chisso, trade name: Sila Ace S330).

[Production Example 1]
4,4′-diaminobenzanilide (DABA) 3.41 g (0.015 mol), 9,9′-bis (4-aminophenyl) fluorene (BAFL) 5.23 g (0.015 mol), N, N -Dimethylacetamide (DMAc) 107.60g was mixed and the whole volume was stirred at 25 degreeC for 20 minutes. The resulting solution was then ice-cooled, and 18.259 g (0.03) of bis (octahydro-1,3-dioxo-5-isobenzofurancarboxylic acid) 4,4′-sulfonyldianilide (PSHT) was added to this solution. Mol) was added and stirred for 2 hours under ice cooling and then for 20 hours at 25 ° C. to obtain a polyimide precursor varnish.
To the obtained polyimide precursor varnish, 12.25 g (0.12 mol) of acetic anhydride and 11.87 g (0.15 mol) of pyridine were added, and the whole volume was 1 hour at 25 ° C., 1 hour at 80 ° C., 110 ° C. The mixture was stirred for 4 hours to conduct a chemical imidization reaction. At this time, the reaction solution did not gel. After completion of the reaction, the reaction solution is diluted with DMAc so that the resin concentration becomes 7%, and the obtained diluted solution is dropped into 8 L of methanol to precipitate a polyimide, which is recovered by filtration. .
The polyimide obtained was washed twice with methanol and then vacuum-dried at 130 ° C. for 6 hours (yield: 25.12 g, yield: 97.1%).

[Production Example 2]
In Production Example 1, instead of PSHT, 14.05 g (0.03 mol) of bis (octahydro-1,3-dioxo-5-isobenzofurancarboxylic acid) 1,4-phenylenediamide (PPHT) was used, and DMAc A polyimide was obtained in the same manner as in Production Example 1 except that the amount of was changed to 90.74 g (yield: 20.78 g, yield: 96.2%).

[Production Example 3]
In Production Example 1, polyimide was used in the same manner as in Production Example 1 except that the amount of DABA used was changed to 4.77 g (0.021 mol) and the amount of BAFL used was changed to 3.14 g (0.009 mol). Obtained (yield: 22.91 g, yield: 91%).

[Production Example 4]
In Production Example 1, only 6.82 g (0.03 mol) of DABA was used as the diamine, and polyimide was obtained in the same manner as in Production Example 1 except that the amount of DMAc used was changed to 100.31 g ( Yield: 22.44 g, Yield: 93.5%).

[Production Example 5]
In Production Example 1, only BAFL 10.45 g (0.03 mol) was used as the diamine, and polyimide was obtained in the same manner as Production Example 1 except that the amount of DMAc used was changed to 114.85 g ( (Yield: 25.78 g, yield: 93.3%).

[Example 1]
The polyimide obtained in Production Example 1 was dissolved in cyclopentanone (CPN) to obtain a varnish 1 having a resin concentration of 20% and a viscosity of 15.3 poise.

[Example 2]
The polyimide obtained in Production Example 1 was dissolved in CPN to obtain varnish 2 having a resin concentration of 10% and a viscosity of 3.6 poise.

Example 3
The polyimide obtained in Production Example 2 was dissolved in CPN to obtain varnish 3 having a resin concentration of 20% and a viscosity of 12.8 poise.

Example 4
The polyimide obtained in Production Example 2 was dissolved in CPN to obtain varnish 4 having a resin concentration of 10% and a viscosity of 3.0 poise.

Example 5
The polyimide obtained in Production Example 3 was dissolved in CPN to obtain varnish 5 having a resin concentration of 17% and a viscosity of 23 poise.

Example 6
The polyimide obtained in Production Example 4 was dissolved in DMAc to obtain varnish 6 having a resin concentration of 20% and a viscosity of 18.9 poise.

[Comparative Example 1]
4,4′-diaminobenzanilide (DABA) 3.41 g (0.015 mol), 9,9′-bis (4-aminophenyl) fluorene (BAFL) 5.23 g (0.015 mol), N, N -Dimethylacetamide (DMAc) 107.60g was mixed and the whole volume was stirred at 25 degreeC for 20 minutes. Subsequently, the obtained solution was ice-cooled, and 18.26 g (0.03) of bis (octahydro-1,3-dioxo-5-isobenzofurancarboxylic acid) 4,4′-sulfonyldianilide (PSHT) was added to this solution. The mixture was stirred for 2 hours under ice cooling and then for 20 hours at 25 ° C. to obtain a polyimide precursor varnish (varnish 7).

[Comparative Example 2]
The polyimide obtained in Production Example 5 was dissolved in CPN to obtain varnish 8 having a resin concentration of 20% and a viscosity of 13.2 poise.
The monomer ratio, solvent, resin concentration, and viscosity of the polymers contained in the varnishes obtained in Examples 1 to 6 and Comparative Examples 1 and 2 are summarized in Table 1.

Example 7
The varnish 1 obtained in Example 1 was coated on the base material (1) using a doctor blade so that the film thickness after drying was about 20 μm. Subsequently, the base material (1) on which the coating film was formed was placed on a hot plate and prebaked at 80 ° C. for 6 minutes. The amount of residual solvent in the coating film after pre-baking was 8.7%.
The substrate with film (1) after pre-baking was immersed in an acetone: water (7: 3) mixed solvent for 8 minutes, and then the surface was dried by blowing nitrogen gas. Further, the substrate with film (1 ) Was placed in an oven and heated and dried at 80 ° C. for 10 minutes and then at 150 ° C. for 15 minutes under a nitrogen stream to obtain a laminate 1 composed of the substrate (1) and the polyimide film.
The amount of residual solvent after pre-baking was determined by performing a GC analysis using a solution obtained by dissolving a sample separately prepared under the same conditions [substrate with coating (1)] in NMP.

Example 8
In Example 7, the laminated body 2 was obtained by the same method as Example 7 except having used the varnish 3 instead of the varnish 1.

Example 9
In Example 7, using varnish 5 instead of varnish 1, the same method as in Example 7 except that coating was performed on the substrate (1) so that the film thickness after drying was about 10 μm. A laminate 3 was obtained.

Example 10
In Example 7, the varnish 6 was used instead of the varnish 1, and the pre-baking conditions were changed to 6 minutes at 60 ° C. and then 3 minutes at 90 ° C. Body 4 was obtained.

Example 11
Varnish 2 was coated on the substrate (1) by a dip method so that the film thickness after drying was about 2 μm. Subsequently, the base material (1) on which the coating film was formed was suspended at 25 ° C. for 6 minutes to make the film thickness uniform.
Subsequently, this base material with a coating film (1) was put in an inert oven, and was heated and dried at 150 ° C. for 15 minutes under a nitrogen stream to obtain a laminate 5 composed of the base material (1) and a polyimide film.

[Comparative Example 3]
In Example 7, a laminate 6 was obtained in the same manner as in Example 7 except that the immersion treatment was not performed.

[Comparative Example 4]
In Example 7, it replaced with the varnish 1 and except having used the varnish 7, the varnish was applied by the method similar to Example 7, and the prebaking process and the immersion process were performed.
When the immersion treatment was performed, the coating film became turbid. Subsequently, the base material with a coating film (1) was put in an inert oven, and heated under nitrogen flow at 50 ° C. for 30 minutes, 150 ° C. for 30 minutes, and 250 ° C. for 60 minutes to perform thermal imidization treatment. The substrate was immersed in warm water to attempt to recover the polyimide film, but the polyimide film was very brittle and could not be peeled off. Further, the polyimide film was turbid.

[Comparative Example 5]
In Example 7, it replaced with the varnish 1 and obtained the laminated body 8 by the method similar to Example 7 except having used the varnish 8. FIG.

After cutting into the polyimide film of the laminated bodies 1-8 obtained in Examples 7-11 and Comparative Examples 3-5 with a cutter knife, it was immersed in warm water 50 degreeC for 24 hours, and the polyimide film was peeled. The obtained polyimide film was vacuum-dried at 130 ° C. for 3 hours.
The following measurements were performed on the polyimide film. The results are shown in Table 2.

[Film thickness measurement]
The film thickness of the polyimide film before peeling was measured using a stylus type shape measuring device (DEKTAK150).

(Measurement of thermal expansion coefficient)
Using a thermomechanical analyzer (product name: TMASS7100, manufactured by SII), under a nitrogen atmosphere, temperature range: room temperature to 300 ° C., heating rate: 5 ° C./min, thermal expansion coefficient of polyimide film under conditions of 2 cycles (Ppm / ° C.) was measured, and the measured value of the second cycle was adopted.

[Membrane breaking strength, breaking elongation]
Using a precision universal testing machine (manufactured by Shimadzu Corporation, product name: Autograph AG), a tensile test was conducted at a rate of 100 mm / min using a polyimide film having a thickness of 10 μm and a width of 10 mm, and the breaking strength (MPa). The elongation at break (%) was measured.

(Measurement of light transmittance)
In the above polyimide film forming method, a varnish was applied on a glass substrate so that the film thickness was 10 μm, and a laminate was obtained. The light transmittance at wavelengths of 400 nm and 600 nm of each laminate was measured using an ultraviolet-visible-near infrared spectrophotometer (manufactured by JASCO Corporation, product name: V-570). In addition, about Example 11, it measured using said laminated body 5 (thickness is 2 micrometers).

Table 2 shows the following.
The polyimide films of laminates 1 to 4 obtained in Examples 7 to 10 are excellent in transparency and mechanical properties and have a low coefficient of thermal expansion.
Moreover, in Example 11, although the immersion process was not performed, since the polyimide film thickness is thin, the polyimide film of the laminated body 5 is also excellent in transparency and has a low coefficient of thermal expansion.
On the other hand, in Comparative Example 3, since the immersion treatment was not performed, the polyimide film of the laminate 6 has a high coefficient of thermal expansion.
In Comparative Example 4, a coating film was formed using a varnish of a polyimide precursor and later imidized, and the formed polyimide film was brittle and cloudy.
Further, in Comparative Example 5, since a polyimide varnish not containing a DABA-derived repeating unit was used, the polyimide film of the laminate 8 has a high coefficient of thermal expansion.

Example 12
A thin glass plate (Nippon Electric Glass Co., Ltd., width 30 mm × length 100 mm) having a thickness of 50 μm was washed with a degreasing detergent and pure water and then dried at 130 ° C. for 10 minutes. The thin glass plate was exposed to the vapor of a silane coupling agent (manufactured by Chisso Corporation, trade name: Sila Ace S330) for 30 minutes in a state of being suspended in a closed container. Next, the substrate was left in an oven at 150 ° C. for 5 minutes to activate the silane coupling agent to obtain a substrate (2).

Varnish 2 was coated on the substrate (2) by a dip method. Next, the base material (2) on which the coating film was formed was suspended at 25 ° C. for 3 minutes to make the film thickness uniform.
Subsequently, this base material with a coating film (2) was put into an inert oven, heated at 60 ° C. for 10 minutes in a nitrogen stream and pre-baked, and then mixed with an acetone: water mixed solvent (acetone: water = 40: 60). Soaked for 3 minutes.
Next, the substrate with a coating film (2) is put again in an inert oven, and dried under a nitrogen stream at 80 ° C. for 10 minutes and then at 150 ° C. for 10 minutes to carry out a drying treatment. A laminate 9 having the following was obtained. The film thickness of the transparent polyimide film was 3 μm.

  A bending test was performed in which one end of the laminated body 9 was fixed by hand and the laminated body 9 was bent until another end was raised by 50 mm, and then the operation of returning to the original position was repeated 30 cycles. When the appearance of the laminate 9 after the test was observed, no cracks, breaks, etc. were observed.

  The laminated body 9 was placed on a hot plate and heated at 150 ° C. for 5 minutes, and then the test of transferring to a metal plate at 25 ° C. and rapidly cooling was repeated 20 cycles, and a heating / cooling test was performed. When the appearance of the laminate 9 after the test was observed, no cracks, breaks, etc. were observed.

Example 13
In Example 12, a laminated body 10 was obtained in the same manner as in Example 12 except that the varnish 4 was used instead of the varnish 2.
When the above-described bending test and heating / cooling test were performed on the laminate 10, no cracks, breakage, etc. were observed.

[Comparative Example 6]
Varnish 8 was diluted with CPN, and the resin concentration was adjusted to 10% to obtain varnish 8 ′.
In Example 12, a laminate 11 was obtained in the same manner as in Example 12 except that the varnish 8 ′ was used instead of the varnish 2.
When the laminate 11 was subjected to the bending test and the heating / cooling test, cracks occurred in the heating / cooling test.

Claims (10)

A varnish containing a polyimide and a solvent,
The polyimide has in its molecule a repeating unit represented by the following formula (1), or a repeating unit represented by the following formula (1) (1) and a repeating unit represented by the following formula (2):
The total amount of the repeating unit represented by the following formula (1) and the repeating unit represented by the following formula (2) is 80 to 100 mol% in all repeating units, and
The molar ratio of the repeating unit represented by the formula (1) and the repeating unit represented by the formula (2) [the repeating unit represented by the formula (1): the repeating unit represented by the formula (2)] is 20:80. A polymer that is ~ 100: 0,
A varnish, wherein the solvent is an aprotic polar solvent having a boiling point of 170 ° C. or lower.

[Wherein, R ¹ and R ² each independently represent a halogen atom, a hydroxyl group, a linear or branched alkyl group having 1 to 6 carbon atoms, a linear or branched alkoxyl group having 1 to 6 carbon atoms, Or represents a trifluoromethyl group. A ¹ represents the following formula (3a) or (3b)

(In the formula, * represents a bond.)
Represents a group represented by a and b each independently represents an integer of 0 to 4; When a and b are each 2 or more, a plurality of R ^{1 s} and R ^{2 s} may be the same or different. ]

(In the formula, R ^{3 to} R ⁶ are each independently a halogen atom, a hydroxyl group, a linear or branched alkyl group having 1 to 6 carbon atoms, a linear or branched alkoxyl group having 1 to 6 carbon atoms, Or A ¹ represents a group represented by the formula (3a) or (3b), and cf each independently represents an integer of 0 to 4. c, d, e, When f is 2 or more, a plurality of R ^{3 s} , R ^{4 s} , R ^{5 s,} and R ^{6 s} may be the same or different.   The varnish according to claim 1, wherein when the polyimide is formed into a film having a thickness of 10 μm, the light transmittance of light having a wavelength of 400 nm of the film becomes 85% or more. A laminate having a substrate and a polyimide film formed on the substrate,
A laminate, wherein the polyimide film is a film having a coefficient of thermal expansion of 30 ppm / ° C. or less, formed using the varnish according to claim 1.   The laminate according to claim 3, wherein the substrate is a glass substrate. A method for producing a laminate,
A step of applying the varnish according to claim 1 or 2 on a substrate and prebaking the obtained coating film (AI)
After the step (AI), the coating film is immersed in a poor solvent for polyimide contained in the varnish (A-II)
After step (A-II), the coating film is dried by heating to form a polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less (A-III)
The manufacturing method of the laminated body characterized by having.   The manufacturing method of the laminated body of Claim 5 whose residual solvent amount in a coating film after a step (AI) is 5-45 weight%.   The poor solvent is a solvent selected from the group consisting of water, an alcohol solvent having 1 to 4 carbon atoms, a ketone solvent having 2 to 4 carbon atoms, and an acetate solvent having 3 to 4 carbon atoms. The manufacturing method of the laminated body of 5 or 6.   The substrate is a long glass film having a film thickness of 100 μm or less, and the steps (A-1) to (A-III) are continuously performed while the glass film is conveyed in a certain direction. The manufacturing method of the laminated body in any one of Claim 5-7 characterized by the above-mentioned. A method for producing a laminate,
A step of applying the varnish according to claim 1 or 2 on a substrate so that a film thickness after drying is 5 μm or less (BI)
Step (B-II) of forming a polyimide film having a coefficient of thermal expansion of 30 ppm / ° C. or less by heating and drying the coating film obtained in step (BI) at 100 to 200 ° C.
The manufacturing method of the laminated body characterized by having.   The base material is a long glass film having a thickness of 100 μm or less, and the steps (B-1) to (B-II) are continuously performed while the glass film is conveyed in a certain direction. The manufacturing method of the laminated body of Claim 9 characterized by the above-mentioned.