CN113462278B

CN113462278B - Varnish composition, method for producing polyimide resin, and additive

Info

Publication number: CN113462278B
Application number: CN202110344299.2A
Authority: CN
Inventors: 田所惠典; 菊地浩之; 西条秀树; 盐田大
Original assignee: Tokyo Ohka Kogyo Co Ltd
Current assignee: Tokyo Ohka Kogyo Co Ltd
Priority date: 2020-03-31
Filing date: 2021-03-30
Publication date: 2024-06-07
Anticipated expiration: 2041-03-30
Also published as: JP7437997B2; CN113462278A; JP2021161267A; KR20210122186A

Abstract

The present invention relates to a varnish composition, a method for producing polyimide resin, and an additive. The present invention provides a varnish composition capable of forming a polyimide resin having improved physical properties such as thermal expansion coefficient, elongation at break and tensile strength, a method for producing a polyimide resin using the varnish composition, and an additive suitable for use as a constituent of the varnish composition. A varnish composition for forming a polyimide resin, which contains a polyamide acid (A) and a solvent (S), is blended with a compound represented by the following formula (C1) as an amide compound (C). In the formula (C1), R ^c1 is an n-valent organic group bonded to a carbonyl group via a carbon-carbon bond, R ^c2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 4. R ^c1-(-CO-NH-R^c2)_n (C1).

Description

Varnish composition, method for producing polyimide resin, and additive

Technical Field

The present invention relates to a varnish composition, a method for producing a polyimide resin using the varnish composition, and an additive suitably blended in a varnish composition for forming a polyimide resin.

Background

Polyimide resins have excellent heat resistance, mechanical strength, insulation, low dielectric constant, and other properties. Accordingly, polyimide resins are widely used as insulating materials and protective materials for electric and electronic components such as various elements and electronic substrates such as multilayer wiring boards.

In general, a polyimide resin is formed by heat-treating a polyamic acid obtained by polymerizing a tetracarboxylic dianhydride component and a diamine component in a polar organic solvent. Against such a background, polyimide products for electronic materials are often supplied in the form of a solution of a polyimide precursor such as a polyamic acid. Specifically, in the production of an electric/electronic component, a polyimide precursor solution is supplied to a portion where an insulating material or a protective material is to be formed by a method such as coating or injection, and then the polyimide precursor solution is subjected to a heat treatment to form the insulating material or the protective material.

There have been intensive studies on techniques related to such polyimide resins, and various resin compositions containing polyamide acid and the like have been disclosed (for example, see patent document 1 and the like).

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2018-58918

Disclosure of Invention

Problems to be solved by the invention

However, the polyimide resin disclosed in patent document 1 and the like is required to further improve physical properties such as thermal expansion coefficient, elongation at break and tensile strength.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a varnish composition capable of forming a polyimide resin having improved physical properties such as thermal expansion coefficient, elongation at break and tensile strength, a method for producing a polyimide resin using the varnish composition, and an additive suitable for use as a constituent of the varnish composition.

Means for solving the problems

The present inventors have found that the above problems can be solved by blending an amide compound (C) having a specific structure into a varnish composition for forming a polyimide resin, which contains a polyamic acid (a) and a solvent (S), and have completed the present application. More specifically, the present application provides the following.

The 1 st aspect of the present invention is a varnish composition for forming a polyimide resin, comprising a polyamic acid (A), an amide compound (C), and a solvent (S),

The amide compound (C) is a compound represented by the following formula (C1):

R^c1-(-CO-NH-R^c2)_n···(C1)

(in the formula (C1), R ^c1 is an n-valent organic group bonded to a carbonyl group via a carbon-carbon bond, R ^c2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 4).

A 2 nd aspect of the present invention is a method for producing a polyimide resin, comprising the steps of:

A molding step of molding the varnish composition according to the embodiment 1; and

And an imidization step of imidizing the molded varnish composition by heating it.

The 3 rd aspect of the present invention is an additive for blending into a polyamic acid-containing liquid containing a polyamic acid (A) and a solvent (S) to obtain a varnish composition for forming a polyimide resin,

The additive contains an amide compound (C),

The amide compound (C) is a compound represented by the following formula (C1):

R^c1-(-CO-NH-R^c2)_n···(C1)

(in the formula (C1), R ^c1 is an n-valent organic group bonded to a carbonyl group via a carbon-carbon bond, R ^c2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 4 inclusive.)

When the varnish composition is heated to obtain a polyimide resin, at least one of a decrease in thermal expansion coefficient, an increase in elongation at break, and an increase in tensile strength occurs in the obtained polyimide resin, as compared with the case where the polyimide resin is obtained by heating a polyamic acid-containing liquid.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a varnish composition capable of forming a polyimide resin having improved physical properties such as thermal expansion coefficient, elongation at break and tensile strength, a method for producing a polyimide resin using the varnish composition, and an additive suitable for use as a constituent of the varnish composition can be provided.

Detailed Description

Varnish composition

The varnish composition comprises a polyamic acid (A), an amide compound (C), and a solvent (S). The varnish composition is used to form polyimide resins.

By including the amide compound (C) in the varnish composition, a polyimide resin having improved physical properties such as thermal expansion coefficient, elongation at break, and tensile strength can be formed using the varnish composition. Regarding the amide compound (C), details are set forth later.

The improvement of the thermal expansion coefficient refers to an improvement in the dimensional stability of the polyimide resin due to a decrease in the thermal expansion coefficient. The improvement in the elongation at break means an increase in the elongation at break. The improvement in tensile strength means an increase in tensile strength.

Hereinafter, essential or optional components of the varnish composition will be described.

< Polyamic acid (A) >

The varnish composition comprises a polyamic acid (a). The polyamic acid (a) is a precursor polymer of a polyimide resin formed when the varnish composition is cured. The polyamide acid (a) is not particularly limited as long as it is a resin conventionally used as a precursor polymer in the production of polyimide resins.

The polyamic acid (a) is generally obtained by condensing a monomer component comprising a tetracarboxylic dianhydride and a diamine compound.

The polyamic acid may have a structural unit represented by the following formula (a 1).

(In the formula (a 1), A ¹ is a 4-valent organic group having 6 to 50 carbon atoms, and A ² is a 2-valent organic group.)

Hereinafter, a tetracarboxylic dianhydride, a diamine compound, and a method for producing the polyamic acid (a) used for producing the polyamic acid (a) will be described.

[ Tetracarboxylic dianhydride ]

The tetracarboxylic dianhydride which forms the structural unit represented by the formula (a 1) is represented by the following formula (a 1-1).

The tetracarboxylic dianhydride represented by the formula (a 1-1) reacts with a diamine compound described later to form a polyamic acid (a) having a structural unit represented by the formula (a 1). The tetracarboxylic dianhydride may be used alone or in combination of two or more.

(In the formula (a 1-1), A ¹ is a 4-valent organic group having 6 to 50 carbon atoms.)

In the formula (a 1-1), A ¹ is a 4-valent organic group having 6 to 50 carbon atoms. The organic group is preferably a group containing a carbon atom, more preferably a group containing a carbon atom and 1 or more atoms selected from the group consisting of H, O, S, se, N, B, P and halogen atoms. A ¹ may have one or more substituents in addition to the acid anhydride group represented by 2-CO-O-CO-in the formula (a 1-1).

Preferred examples of the substituent include a fluorine atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms, and a fluoroalkoxy group having 1 to 6 carbon atoms. The compound represented by the formula (a 1-1) may contain a carboxyl group or a carboxylate group in addition to an acid anhydride group.

When the substituent is fluoroalkyl or fluoroalkoxy, perfluoroalkyl or perfluoroalkoxy is preferable.

The above substituents may be similarly described with respect to 1 or more substituents which may be present on an aromatic ring in the aromatic group described later.

In the formula (a 1-1), A ¹ is a 4-valent organic group, the lower limit of the number of carbon atoms is 6, and the upper limit is 50.

The number of carbon atoms constituting a ¹ is more preferably 8 or more, and still more preferably 12 or more. The number of carbon atoms constituting a ¹ is more preferably 40 or less, and still more preferably 30 or less. A ¹ may be an aliphatic group, an aromatic group, or a combination of these structures. A ¹ may contain a halogen atom, an oxygen atom, a nitrogen atom, and a sulfur atom in addition to a carbon atom and a hydrogen atom. In the case where a ¹ contains an oxygen atom, a nitrogen atom, or a sulfur atom, the oxygen atom, the nitrogen atom, or the sulfur atom may be contained in a ¹ in the form of a group selected from the group consisting of a nitrogen-containing heterocyclic group, -CONH-, -NH-, -n=n-, -ch=n-, -COO-, -O-, -CO-, -SO ₂ -, -S-, and-S-, and more preferably in the form of a group selected from the group consisting of-O-, -CO-, -SO ₂ -, -S-, and-S-, and a ¹.

The tetracarboxylic dianhydride may be appropriately selected from among tetracarboxylic dianhydrides conventionally used as raw materials for the synthesis of polyamic acids. The tetracarboxylic dianhydride may be aliphatic tetracarboxylic dianhydride or aromatic tetracarboxylic dianhydride.

Examples of the aliphatic tetracarboxylic dianhydride include 2, 2-bis (3, 4-dicarboxyl) propane dianhydride, bis (3, 4-dicarboxyl) methane dianhydride, and the like. The aliphatic tetracarboxylic dianhydride may contain an alicyclic structure. The alicyclic structure may be polycyclic. Examples of the polycyclic alicyclic structure include bridged alicyclic structures such as bicyclo [2.2.1] heptane. For example, the bridged alicyclic structure may be condensed with another bridged alicyclic structure and/or with another non-bridged alicyclic structure, or the bridged alicyclic structure may be connected with another bridged alicyclic structure and/or with a non-bridged alicyclic structure by screw connection. When the aliphatic tetracarboxylic dianhydride is used, a polyimide resin excellent in transparency tends to be easily obtained by using the varnish composition.

As the aliphatic group constituting a ¹ in the formula (a 1-1), for example, a tetravalent group represented by the following formula (a 2) can be used. When such a group is used, a polyimide resin having excellent transparency tends to be easily obtained.

In view of easy purification of the starting compounds, a in the formula (a 2) is preferably 5 or less, more preferably 3 or less. In addition, a is preferably 1 or more, more preferably 2 or more, from the viewpoint of excellent chemical stability of the raw material compound capable of forming the structural unit represented by the formula (a 1).

A in the formula (a 2) is particularly preferably 2 or 3.

(In the formula (a 2), R ^a11、R^a12 and R ^a13 are each independently 1 kind selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 5 carbon atoms and a fluorine atom, and a is an integer of 0 to 12 inclusive.)

Examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 1, 4-bis (3, 4-dicarboxyphenoxy) benzene dianhydride, 3',4' -oxydiphthalic dianhydride, 3',4,4' -biphenyltetracarboxylic dianhydride, 2, 3',4' -biphenyltetracarboxylic dianhydride, 3',4' -benzophenone tetracarboxylic dianhydride, 3',4' -diphenyl sulfone tetracarboxylic dianhydride, and the like.

The aromatic tetracarboxylic dianhydride may be, for example, compounds represented by the following general formulae (a 1-2) to (a 1-4).

In the above formulae (a 1-2) and (a 1-3), R ^a1、R^a2 and R ^a3 are each any one of an aliphatic group which may be substituted with halogen, an oxygen atom, a sulfur atom, an aromatic group having 1 or more divalent elements interposed therebetween, or a divalent group formed by a combination thereof. R ^a2 and R ^a3 may be the same or different.

That is, R ^a1、R^a2 and R ^a3 may contain a carbon-carbon single bond, a carbon-oxygen-carbon ether bond, or a halogen element (fluorine, chlorine, bromine, or iodine). Examples of the compound represented by the formula (a 1-2) include 2, 2-bis (3, 4-dicarboxyphenoxy) propane dianhydride, 1, 4-bis (3, 4-dicarboxyphenoxy) benzene dianhydride, and the like.

In the above formula (a 1-4), R ^a4、R^a5 is any one of an aliphatic group which may be substituted with halogen, an aromatic group having 1 or more divalent elements interposed therebetween, halogen, or a monovalent substituent composed of a combination thereof. R ^a4 and R ^a5 may be the same or different. As the compound represented by the formula (a 1-4), difluoro pyromellitic dianhydride, dichloro pyromellitic dianhydride and the like can also be used.

Examples of tetracarboxylic dianhydrides used for obtaining fluorine-containing polyimide having a molecular structure include (trifluoromethyl) pyromellitic dianhydride, bis (heptafluoropropyl) pyromellitic dianhydride, pentafluoroethyl pyromellitic dianhydride, bis {3, 5-bis (trifluoromethyl) phenoxy } pyromellitic dianhydride, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride, 5' -bis (trifluoromethyl) -3,3',4,4' -tetracarboxylic biphenyl dianhydride, 2', 5' -tetra (trifluoromethyl) -3,3', 4' -tetracarboxylic biphenyl dianhydride, 5' -bis (trifluoromethyl) -3,3',4,4' -Tetracarboxydiphenyl ether dianhydride, 5' -bis (trifluoromethyl) -3,3', 4' -tetracarboxylic benzophenone dianhydride, bis { (trifluoromethyl) dicarboxyphenoxy } benzene dianhydride, bis { (trifluoromethyl) dicarboxyphenoxy } (trifluoromethyl) benzene dianhydride, bis (dicarboxyphenoxy) bis (trifluoromethyl) benzene dianhydride, bis (dicarboxyphenoxy) tetrakis (trifluoromethyl) benzene dianhydride, 2-bis {4- (3, 4-dicarboxyphenoxy) phenyl } hexafluoropropane dianhydride, bis { (trifluoromethyl) dicarboxyphenoxy } biphenyl dianhydride, bis { (trifluoromethyl) dicarboxyphenoxy } bis (trifluoromethyl) biphenyl dianhydride, bis { (trifluoromethyl) dicarboxyphenoxy } diphenyl ether dianhydride, bis (dicarboxyphenoxy) bis (trifluoromethyl) biphenyl dianhydride, difluoropyromellitic dianhydride, 1, 4-bis (3, 4-dicarboxyltrifluorophenoxy) tetrafluorobenzene dianhydride, 1, 4-bis (3, 4-dicarboxyltrifluorophenoxy) octafluorobiphenyl dianhydride, and the like.

The tetracarboxylic dianhydride is preferably alicyclic tetracarboxylic dianhydride in view of heat resistance, transparency, and the like of the obtained polyimide resin.

It is to be noted that an acid chloride, an ester, or the like of a tetracarboxylic acid having the same basic skeleton as the above-described compound may also be used.

The tetracarboxylic dianhydride may be used in combination with the dicarboxylic anhydride. When these carboxylic acid anhydrides are used in combination, the properties of the obtained polyimide resin or other polymer containing an imide ring may be further improved. Examples of the dicarboxylic acid anhydride include maleic anhydride, succinic anhydride, itaconic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyl endomethylene tetrahydrophthalic anhydride, chlorobridge anhydride, methyl tetrahydrophthalic anhydride, glutaric anhydride, and cis-4-cyclohexene-1, 2-dicarboxylic anhydride.

[ Diamine Compounds ]

The diamine compound is typically a compound represented by the following formula (a 3-1). The diamine compound may be used alone or in combination of two or more.

H₂N-A²-NH₂···(a3-1)

(In the formula (A3-1), A ² represents a 2-valent organic group.)

In the formula (A3-1), A ² is a 2-valent organic group. The organic group is preferably a group containing carbon atoms, more preferably a group containing 1 or more carbon atoms and 1 or more atoms selected from the group consisting of H, O, S, se, N, B, P and halogen atoms. A ² may have one or more substituents in addition to the 2 amino groups in formula (A3-1).

Preferred examples of the substituent include a fluorine atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms, a fluoroalkoxy group having 1 to 6 carbon atoms, and a hydroxyl group.

In the formula (A3-1), the lower limit of the number of carbon atoms of the organic group as A ² is preferably 2, more preferably 6, and the upper limit is preferably 50, more preferably 30.

A ² may be an aliphatic group, but is preferably an organic group containing 1 or more aromatic rings.

When a ² is an organic group having 1 or more aromatic rings, the organic group may be 1 aromatic group per se, or may be a group in which 2 or more aromatic groups are bonded through a bond of an aliphatic hydrocarbon group and a halogenated aliphatic hydrocarbon group, or a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom. As the bond containing hetero atoms such as an oxygen atom, a sulfur atom and a nitrogen atom contained in A ², examples include-CONH-, -NH-, -N=N-, -CH=N-, -COO-, -O-, -CO-, -SO ₂ -, -S-, and-S-S-, etc., -CO-, -SO ₂ -, and S-, S-S-, etc..

The aromatic ring bonded to the amino group in a ² is preferably a benzene ring. When the ring bonded to an amino group in a ² is a condensed ring containing 2 or more rings, the ring bonded to an amino group in the condensed ring is preferably a benzene ring.

The aromatic ring contained in a ² may be an aromatic heterocycle.

When a ² is an organic group containing an aromatic ring, the organic group is preferably at least one of the groups represented by the following formulas (21) to (24) in view of heat resistance of a polyimide resin formed using the varnish composition.

(In the formulae (21) to (24), R ¹¹¹ represents 1 selected from the group consisting of a hydrogen atom, a fluorine atom, a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, and a haloalkyl group having 1 to 4 carbon atoms.) in the formula (24), Q represents 1 selected from the group consisting of a 9,9' -fluorenylene group and a group represented by the formula ：-C₆H₄-、-CONH-C₆H₄-NHCO-、-NHCO-C₆H₄-CONH-、-O-C₆H₄-CO-C₆H₄-O-、-OCO-C₆H₄-COO-、-OCO-C₆H₄-C₆H₄-COO-、-OCO-、-O-、-S-、-CO-、-CONH-、-SO₂-、-C(CF₃)₂-、-C(CH₃)2-、-CH₂-、-O-C₆H₄-C(CH₃)₂-C₆H₄-O-、-O-C₆H₄-C(CF₃)₂-C₆H₄-O-、-O-C₆H₄-SO₂-C₆H₄-O-、-C(CH₃)₂-C₆H₄-C(CH₃)₂-、-O-C₁₀H₆-O-、-O-C₆H₄-C₆H₄-O-、 and-O-C ₆H₄ -O-.

Examples of Q are-C ₆H₄ -phenylene, preferably m-phenylene, and p-phenylene, more preferably p-phenylene. Further, -C ₁₀H₆ -is a naphthalenediyl group, preferably a naphthalene-1, 2-diyl group, a naphthalene-1, 4-diyl group, a naphthalene-2, 3-diyl group, a naphthalene-2, 6-diyl group, and a naphthalene-2, 7-diyl group, more preferably a naphthalene-1, 4-diyl group, and a naphthalene-2, 6-diyl group. )

R ¹¹¹ in the formulas (21) to (24) is more preferably a hydrogen atom, a hydroxyl group, a fluorine atom, a methyl group, an ethyl group, or a trifluoromethyl group, and particularly preferably a hydrogen atom, a hydroxyl group, or a trifluoromethyl group, from the viewpoint of heat resistance of the polyimide resin to be formed.

As Q in the formula (24), 9' -fluorenylene, -O-C ₆H₄-O-、-C(CF₃)₂-、-O-、-C(CH₃)₂-、-CH₂ -, or-O-C ₆H₄-C(CH₃)₂-C₆H₄ -O-, -CONH-, particularly-O-C ₆H₄-O-、-C(CF₃)₂ -or-O-, is preferable from the viewpoint of heat resistance of the polyimide resin formed.

When an aromatic diamine is used as the diamine compound represented by the formula (a 3-1), for example, the following aromatic diamine can be preferably used.

Namely, as the aromatic diamine, examples thereof include p-phenylenediamine, m-phenylenediamine, 2, 4-diaminotoluene, 4' -diaminobiphenyl, 4' -diamino-2, 2' -bis (trifluoromethyl) biphenyl, 3' -diaminodiphenyl sulfone, 4' -diaminodiphenyl sulfide, and 4,4' -diaminodiphenylmethane, 4' -diaminodiphenyl ether, 3' -diaminodiphenyl ether, 4' -diaminobenzanilide, 3' -diaminobenzanilide, 1, 4-bis (4-aminophenoxy) benzene 4,4' -diaminodiphenylmethane, 4' -diaminodiphenyl ether, 3' -diaminodiphenyl ether 4,4' -diaminobenzanilide, 3' -diaminobenzanilide, 1, 4-bis (4-aminophenoxy) benzene. Among these, p-phenylenediamine, m-phenylenediamine, 2, 4-diaminotoluene, 4 '-diaminodiphenyl ether, and 4,4' -diaminobenzanilide are preferable from the viewpoints of price, availability, and the like.

Further, as a ², a silicon atom-containing group which may have a chain aliphatic group and/or an aromatic ring may be used. As such a group containing a silicon atom, the following group can be typically used.

In addition, from the viewpoint of further improving the mechanical properties of the obtained polyimide resin, a group represented by the following formula (Si-1) may be preferably used as a ².

( In the formula (Si-1), R ¹¹² and R ¹¹³ are each independently a single bond or a methylene group, an alkylene group having 2 to 20 carbon atoms, a cycloalkylene group having 3 to 20 carbon atoms, or an arylene group having 6 to 20 carbon atoms. R ¹¹⁴、R¹¹⁵、R¹¹⁶ and R ¹¹⁷ are each independently an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an amino group having 20 carbon atoms or less, a group represented by-O-R ¹¹⁸ (R ¹¹⁸ is a hydrocarbon group having 1 to 20 carbon atoms), or an organic group having 2 to 20 carbon atoms and containing 1 or more epoxy groups. The organic group containing an epoxy group is preferably a group containing a carbon atom containing an epoxy group, more preferably a group containing a carbon atom and an oxygen atom, and 1 or more atoms selected from the group consisting of H, S, se, N, B, P and halogen atoms. l is an integer of 3 to 50 inclusive. )

The alkylene group having 2 to 20 carbon atoms in R ¹¹² and R ¹¹³ in the formula (Si-1) is preferably an alkylene group having 2 to 10 carbon atoms from the viewpoints of heat resistance and residual stress, and examples thereof include 1, 2-ethylene (dimethylene), 1, 3-propylene, 1, 4-butylene, 1, 5-pentylene and 1, 6-hexylene.

The cycloalkylene group having 3 to 20 carbon atoms in R ¹¹² and R ¹¹³ in the formula (Si-1) is preferably a cycloalkylene group having 3 to 10 carbon atoms from the viewpoints of heat resistance and residual stress, and examples thereof include a cyclobutylene group, a cyclopentylene group, a cyclohexylene group, and a cycloheptylene group.

The arylene group having 6 to 20 carbon atoms in R ¹¹² and R ¹¹³ in the formula (Si-1) is preferably an aromatic group having 6 to 20 carbon atoms from the viewpoints of heat resistance and residual stress, and examples thereof include phenylene and naphthylene.

The alkyl group having 1 to 10 carbon atoms in R ¹¹⁴、R¹¹⁵、R¹¹⁶ and R ¹¹⁷ in the formula (Si-1) is preferable from the viewpoints of heat resistance and residual stress, and specifically, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, and the like are given.

The cycloalkyl group having 3 to 10 carbon atoms in R ¹¹⁴、R¹¹⁵、R¹¹⁶ and R ¹¹⁷ in the formula (Si-1) is preferable from the viewpoints of heat resistance and residual stress, and specifically, cyclopentyl, cyclohexyl, and the like are given.

The aryl group having 6 to 12 carbon atoms in R ¹¹⁴、R¹¹⁵、R¹¹⁶ and R ¹¹⁷ in the formula (Si-1) is preferable from the viewpoints of heat resistance and residual stress, and specifically, phenyl, tolyl, naphthyl, and the like are given.

Examples of the amino group-containing group having 20 or less carbon atoms in R ¹¹⁴、R¹¹⁵、R¹¹⁶ and R ¹¹⁷ in the formula (Si-1) include an amino group, a substituted amino group (for example, a bis (trialkylsilyl) amino group), and the like.

Examples of the group represented by-O-R ¹¹⁸ in R ¹¹⁴、R¹¹⁵、R¹¹⁶ and R ¹¹⁷ in the formula (Si-1) include methoxy, ethoxy, propoxy, isopropoxy, butoxy, phenoxy, tolyloxy, naphthyloxy, propenyloxy (for example, allyloxy), cyclohexyloxy and the like.

Among them, preferred are R ¹¹⁴、R¹¹⁵、R¹¹⁶ and R ¹¹⁷, methyl, ethyl, propyl, and phenyl.

The group represented by the formula (Si-1) can be introduced by reacting a silicon-containing compound having amino groups at both ends with an acid anhydride. Specific examples of such silicon-containing compounds include both terminal amino-modified methylphenyl silicones (for example, X-22-1660B-3 (about number average molecular weight 4,400) and X-22-9409 (about number average molecular weight 1,300) manufactured BY Xin Yue chemical Co.), both terminal amino-modified dimethyl silicones (for example, X-22-161A (about number average molecular weight 1,600) and X-22-161B (about number average molecular weight 3,000) and KF8012 (about number average molecular weight 4,400) manufactured BY Xin Yue chemical Co., BY16-835U (about number average molecular weight 900) manufactured BY Topo Corning, and SILAPLANE FM3311 (about number average molecular weight 1000) manufactured BY JNC Co., ltd.).

[ Method for producing Polyamic acid (A) ]

The polyamide acid (a) having a structural unit represented by the formula (a 1) is typically a polymer obtained by reacting a tetracarboxylic dianhydride represented by the formula (a 1-1) with a diamine compound represented by the formula (a 3-1) in a solvent, and may be a polymer obtained by using 1 or two or more kinds of diamine compounds and/or tetracarboxylic dianhydrides, respectively. For example, the diamine compound may be a polymer obtained by polycondensing a mixture containing two or more kinds of tetracarboxylic dianhydrides. The polyamide acid (a) may be used alone or in combination of two or more.

The amounts of the tetracarboxylic dianhydride and the diamine compound used in the synthesis of the polyamide acid (a) are not particularly limited, but are preferably 0.50 mol or more and 1.50 mol or less, more preferably 0.60 mol or more and 1.30 mol or less, and particularly preferably 0.70 mol or more and 1.20 mol or less, based on 1 mol of the tetracarboxylic dianhydride.

The weight average molecular weight of the obtained polyamic acid (a) may be appropriately set according to the application, and is, for example, 5000 or more, preferably 7500 or more, and more preferably 10000 or more. On the other hand, the weight average molecular weight of the obtained polyamic acid (a) is 100000 or less, preferably 80000 or less, and more preferably 75000 or less.

The weight average molecular weight can be adjusted to the above-mentioned value by adjusting the reaction conditions such as the amount of the tetracarboxylic dianhydride to be mixed with the diamine compound, the solvent, and the reaction temperature.

The reaction of the tetracarboxylic dianhydride with the diamine compound is usually carried out in an organic solvent. The organic solvent used for the reaction of the tetracarboxylic dianhydride and the diamine compound is not particularly limited as long as it is an organic solvent that can dissolve the tetracarboxylic dianhydride and the diamine compound and does not react with the tetracarboxylic dianhydride and the diamine compound. The organic solvent may be used alone or in combination of 2 or more.

Examples of the organic solvent used for the reaction of the tetracarboxylic dianhydride and the diamine compound include N-methyl-2-pyrrolidone, N-dimethylacetamide, N, nitrogen-containing polar solvents such as N-diethylacetamide, N-dimethylformamide, N-diethylformamide, N-methylcaprolactam, and N, N' -tetramethylurea; dimethyl sulfoxide; acetonitrile; ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, and tetrahydrofuran.

Among these organic solvents, N-methyl-2-pyrrolidone, N-dimethylacetamide and N are preferable from the viewpoint of solubility of the polyamide acid (A) to be produced, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methylcaprolactam, N, N, N ', N' -tetramethylurea and the like.

The temperature at which the tetracarboxylic dianhydride reacts with the diamine compound is not particularly limited as long as the reaction proceeds well. Typically, the reaction temperature of the tetracarboxylic dianhydride and the diamine compound is preferably from-5℃to 150℃and more preferably from 0℃to 120℃and particularly preferably from 0℃to 70 ℃. The reaction time of the tetracarboxylic dianhydride and the diamine compound varies depending on the reaction temperature, and is typically preferably 1 hour or more and 50 hours or less, more preferably 2 hours or more and 40 hours or less, and particularly preferably 5 hours or more and 30 hours or less.

By the method described above, a solution containing the polyamic acid (a) can be obtained.

The solution containing the polyamic acid (a) obtained in the above-described manner may be used as it is for the preparation of a varnish composition, or at least a part of the solvent may be removed from the solution of the polyamic acid (a) at a low temperature at which the conversion of the polyamic acid into a polyimide resin does not occur under reduced pressure, and the paste or solid of the polyamic acid thus obtained may be used for the preparation of a varnish composition.

The content of the polyamic acid (a) in the varnish composition can be appropriately determined in consideration of the coatability of the varnish composition, the solubility of the polyamic acid (a) in the solvent (S), and the like. Typically, the content of the polyamic acid (a) in the varnish composition is preferably 5% by mass or more and 45% by mass or less, more preferably 7% by mass or more and 40% by mass or less, and still more preferably 10% by mass or more and 30% by mass or less, relative to the mass of the varnish composition.

< Amide Compound (C) >)

The amide compound (C) is a compound represented by the following formula (C1):

R^c1-(-CO-NH-R^c2)_n···(C1)

By including the amide compound (C) in the varnish composition, a polyimide resin having improved physical properties such as thermal expansion coefficient, elongation at break, and tensile strength can be formed using the varnish composition.

In addition, when the varnish composition contains the amide compound (C), occurrence of cloudiness and gelation with time during storage of the varnish composition is easily suppressed. Therefore, the amide compound (C) is particularly preferably blended in a varnish composition containing the polyamic acid (a) capable of forming a transparent polyimide resin.

In the formula (C1), n is an integer of1 to 4, preferably an integer of1 to 3, more preferably 1 or 2, and even more preferably 1. From the viewpoint of excellent effect of reducing the coefficient of thermal expansion and effect of increasing the tensile strength of the polyimide resin formed using the varnish composition, n is preferably 3 or 4. In view of good solubility stability of the amide compound (C) in the varnish composition, n is preferably 1 or 2, more preferably 1.

In the formula (C1), the number of carbon atoms of R ^c1 is not particularly limited within a range that does not impair the object of the present invention. Typically, R ^c1 has preferably 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and still more preferably 1 to 10 carbon atoms.

Regarding the organic group as R ^c1, a group containing a carbon atom is preferable. The organic group as R ^c1 may contain carbon atoms and hydrogen atoms, and 1 or 2 or more hetero atoms. Examples of the hetero atom include a nitrogen atom, an oxygen atom, a sulfur atom, a selenium atom, a boron atom, a phosphorus atom, and a halogen atom. Examples of the halogen atom include a chlorine atom, a bromine atom, a fluorine atom, and an iodine atom.

When R ^c1 is a monovalent group, preferable specific examples of R ^c1 include saturated aliphatic groups such as alkyl, cycloalkyl, and polycycloalkyl, unsaturated aliphatic groups such as alkenyl, cycloalkenyl, and polycycloalkenyl, aryl (aromatic hydrocarbon group), heteroaryl (aromatic heterocyclic group), arylalkyl, arylalkenyl, heteroarylalkyl, and heteroarylalkenyl.

In addition, R ^c1 preferably contains an aryl group or a heteroaryl group, and more preferably contains an aryl group, in view of easiness in suppressing rapid decomposition, sublimation, volatilization, and the like of the amide compound (C) at the time of producing the polyimide resin, not being limited to the case where R ^c1 is a monovalent group.

The alkyl group and alkenyl group as R ^c1 may be substituted with one or more substituents selected from the group consisting of a halogen atom, a cyano group, a hydroxyl group, an alkoxy group having 1 to 6 carbon atoms, an aliphatic acyl group having 2 to 6 carbon atoms, and an amino group.

The cycloalkyl, polycycloalkyl, cycloalkenyl, and polycycloalkenyl groups, aryl, and heteroaryl groups as R ^c1 may be substituted with one or more substituents selected from the group consisting of a halogen atom, a cyano group, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aliphatic acyl group having 2 to 6 carbon atoms, and an amino group.

The aryl or heteroaryl group contained in the arylalkyl, arylalkenyl, heteroarylalkyl, or heteroarylalkenyl group as R ^c1 may be substituted with one or more substituents selected from the group consisting of a halogen atom, a cyano group, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aliphatic acyl group having 2 to 6 carbon atoms, and an amino group.

In addition, not only the case where R ^c1 is a monovalent group, but also the case where the polyimide resin is transparent, R ^c1 preferably has no amino group or hydroxyl group, because it is easy to form a polyimide resin having high transparency.

Preferred specific examples of the case where R ^c1 is a saturated aliphatic group include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, and n-eicosyl; cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and cyclodecyl; and polycyclic alkyl groups such as adamantyl, norbornyl, isobornyl, tricyclodecyl, and tetracyclododecyl.

Preferred specific examples of the case where R ^c1 is an unsaturated aliphatic group include alkenyl groups such as vinyl, 1-methylvinyl, 1-propenyl, 2-propenyl (allyl), 3-butenyl, 4-pentenyl, 5-hexenyl, 6-heptenyl, 7-octenyl, 8-nonenyl, and 9-decenyl; cycloalkenyl groups such as cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, cyclooctenyl, cyclononenyl, and cyclodecenyl; polycycloalkenyl groups such as adamantenyl, norbornenyl, isobornenyl, tricyclodecenyl, and tetracyclododecenyl.

Preferred specific examples of the case where R ^c1 is an aryl group (aromatic hydrocarbon group) include phenyl, naphthalen-1-yl, naphthalen-2-yl, 1' -biphenyl-4-yl, 1' -biphenyl-3-yl, and 1,1' -biphenyl-2-yl.

As preferable specific examples of the case where R ^c1 is heteroaryl (aromatic heterocyclic group), there may be mentioned pyridyl, furyl, thienyl, imidazolyl, pyrazolyl, oxazolyl, thiazolyl, isoxazolyl, isothiazolyl, benzoxazolyl, benzothiazolyl, benzimidazolyl and the like.

Preferred specific examples of the case where R ^c1 is an arylalkyl group include benzyl, phenethyl, naphthalen-1-ylmethyl, naphthalen-2-ylmethyl, naphthalen-1-ylethyl, naphthalen-2-ylethyl and the like.

Preferred specific examples of the case where R ^c1 is an arylalkenyl group include a 2-phenylvinyl group, a 2- (naphthalen-1-yl) vinyl group, a 2- (naphthalen-2-yl) vinyl group, and the like.

As preferable specific examples of the case where R ^c1 is a heteroarylalkyl group, there may be mentioned 1H-imidazol-2-ylmethyl, 1H-imidazol-2-ylethyl, pyridin-2-ylmethyl, pyridin-3-ylmethyl, pyridin-4-ylmethyl, pyridin-2-ylethyl, pyridin-3-ylethyl, pyridin-4-ylethyl and the like.

As preferable specific examples of the case where R ^c1 is a heteroarylalkenyl group, there may be mentioned 2- (1H-imidazol-2-yl) 2- (pyridin-2-yl) vinyl, 2- (pyridin-3-yl) vinyl, 2- (pyridin-4-yl) vinyl and the like.

When R ^c1 is a divalent group, preferable specific examples of R ^c1 include divalent saturated aliphatic groups such as alkanediyl, cycloalkanediyl, and polycycloalkanediyl having 2 or more carbon atoms, divalent unsaturated aliphatic groups such as alkenediyl, cycloalkenediyl, and polycycloalkenediyl, arylene, heteroarylene, groups obtained by removing 1 hydrogen atom from each of an alkyl group and an aryl group in an alkylaromatic hydrocarbon, groups obtained by removing 1 hydrogen atom from each of an alkenyl group and an aryl group in an alkylaromatic hydrocarbon, groups obtained by removing 1 hydrogen atom from each of an alkyl group and a heteroaryl group in an alkylaromatic hydrocarbon, groups obtained by removing 1 hydrogen atom from each of an alkenyl group and a heteroaryl group in an alkenylheteroaromatic hydrocarbon, groups obtained by removing 1 hydrogen atom from each of 2 alkyl groups in a dialkylheteroaromatic hydrocarbon, and groups obtained by removing 1 hydrogen atom from each of 2 alkyl groups in a dialkylheteroaromatic hydrocarbon.

When R ^c1 is a trivalent group, preferable specific examples of R ^c1 include an alkanetriyl group, a group represented by N- (-R ^c3-)₃, an arylhydrocarbon triyl group, and a heteroaromatic hydrocarbon triyl group R ^c3 is an alkylene group having 1 to 4 carbon atoms, and R ^c3 is preferably ethane-1, 2-diyl or propane-1, 3-diyl.

When R ^c1 is a tetravalent group, preferred specific examples of R ^c1 include an alkanetetrayl group, a group represented by-R ^c4-)₂-N-(-R^c5-)-N-(-R^c4-)₂, an aromatic hydrocarbon tetrayl group, and a heteroaromatic tetrayl group, R ^c4 and R ^c5 are each independently an alkylene group having 1 to 4 carbon atoms, and R ^c4 and R ^c5 are preferably an ethane-1, 2-diyl group and a propane-1, 3-diyl group.

In the formula (C1), R ^c2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms of R ^c2 include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl and n-hexyl. Among these alkyl groups, methyl and ethyl groups are preferable, and ethyl groups are more preferable.

Preferable examples of the amide compound (C) when R ^c1 is a monovalent saturated aliphatic hydrocarbon group include acetamide (acetamide), propionamide, butyramide (butyramide), isobutyramide, valeramide (n-valeramide), isovaleramide, pivaloamide, 2-methylbutanoamide, n-caproamide, 2-methylpentanamide, 3-methylpentanamide, 4-methylpentanamide, 2-dimethylbutyramide, n-heptanamide, n-octanamide, n-nonanamide, n-decanoamide, n-dodecanamide, n-tridecanoamide, n-tetradecanoimide, n-pentadecanoamide, n-hexadecanoimide, n-heptadecanoamide, n-octadecanoamide, n-nonadecanoamide, n-eicosamide, cyclopropanecarboxamide, cyclopentane carboxamide, cyclopropanecarboxamide, cycloheptanecarboxamide, and cyclooctanecarboxamide. Also preferred are amide compounds (C) which are substituted with a C1-C6 alkyl group on the nitrogen atom in the amide group of these compounds, and more preferred are amide compounds (C) which are substituted with a methyl group on the nitrogen atom in the amide group of these compounds.

Preferable examples of the amide compound (C) in which R ^c1 is an alkyl group substituted with a halogen atom, cyano group, hydroxyl group, acetyl group or methoxy group include chloroacetamide, dichloroacetamide, trichloroacetamide, bromoacetamide, dibromoacetamide, tribromoacetamide, fluoroacetamide, difluoroacetamide, trifluoroacetamide, cyanoacetamide, acetoacetamide, 3-chloropropionamide, 3-bromopropionamide, 3-methoxypropionamide, pentafluoropropionamide, heptafluorobutyramide and lactamide. Also preferred are amide compounds (C) which are substituted with a C1-C6 alkyl group on the nitrogen atom in the amide group of these compounds, and more preferred are amide compounds (C) which are substituted with a methyl group on the nitrogen atom in the amide group of these compounds.

Preferable examples of the amide compound (C) when R ^c1 is a monovalent unsaturated aliphatic hydrocarbon group include unsaturated aliphatic carboxylic acids such as acrylamide, methacrylamide, butenamide, and oleamide. Also preferred are amide compounds (C) which are substituted with a C1-C6 alkyl group on the nitrogen atom in the amide group of these compounds, and more preferred are amide compounds (C) which are substituted with a methyl group on the nitrogen atom in the amide group of these compounds.

Preferable examples of the amide compound (C) when R ^c1 is an aryl group include benzamide, 4-methylbenzamide, 3-methylbenzamide, 2-methylbenzamide, 4-methoxybenzamide, 3-methoxybenzamide, 2-methoxybenzamide, 4-chlorobenzamide, 3-chlorobenzamide, 2-chlorobenzamide, 4-bromobenzamide, 3-bromobenzamide, 2-bromobenzamide, 4-fluorobenzamide, 3-fluorobenzamide, 2-fluorobenzamide, 4-hydroxybenzoamide, 3-hydroxybenzoamide, 2-hydroxybenzoamide, 4-aminobenzamide, 3-aminobenzamide, 2-aminobenzamide, naphthalene-2-carboxamide, naphthalene-1-carboxamide, and 1,1' -biphenyl-4-carboxamide. Also preferred are amide compounds (C) which are substituted with a C1-C6 alkyl group on the nitrogen atom in the amide group of these compounds, and more preferred are amide compounds (C) which are substituted with a methyl group on the nitrogen atom in the amide group of these compounds.

As preferable examples of the amide compound (C) when R ^c1 is arylalkyl, phenyl acetamide, 4-methylphenyl acetamide, 3-methylphenyl acetamide, 2, 5-dimethylphenyl acetamide, 2,4, 6-trimethylphenyl acetamide, 4-tert-butylphenyl acetamide, 4-hydroxyphenylacetamide, 3-hydroxyphenylacetamide, 2-hydroxyphenylacetamide, 4-methoxyphenylacetamide, 3-methoxyphenylacetamide, 2-methoxyphenylacetamide, 4-chlorophenyl acetamide, 3-chlorophenyl acetamide, 2-chlorophenyl acetamide, 4-bromophenyl acetamide, 3-bromophenyl acetamide, 2-bromophenyl acetamide, 4-fluorophenyl acetamide, 3-fluorophenyl acetamide, 2-fluorophenyl acetamide, 4-trifluoromethylphenyl acetamide, 3-trifluoromethylphenyl acetamide, 4-hydroxymethylphenyl acetamide, 3-methoxyphenylacetamide, 4-aminophenylacetamide, 2-phenylpropionamide, 2-phenylisobutyramide, naphthalene-1-yl acetamide, naphthalene-2-yl acetamide, 1' -biphenyl-4-yl acetamide, and the like can be cited. Also preferred are amide compounds (C) which are substituted with a C1-C6 alkyl group on the nitrogen atom in the amide group of these compounds, and more preferred are amide compounds (C) which are substituted with a methyl group on the nitrogen atom in the amide group of these compounds.

Preferable examples of the amide compound (C) when R ^c1 is arylalkenyl include cinnamamide, 4-methylcinnamamide, 3-methylcinnamamide, 2, 5-dimethylcinnamamide, 2,4, 6-trimethylcinnamamide, 4-t-butylcinnamamide, 4-hydroxycinnamamide, 3-hydroxycinnamamide, 2-hydroxycinnamamide, 4-methoxycinnamamide, 3-methoxycinnamamide, 2-methoxyphenyl acetamide, 4-chlorocinnamamide, 3-chlorophenyl acetamide, 2-chlorocinnamamide, 4-bromophenylacetamide, 3-bromocinnamamide, 2-bromocinnamamide, 4-fluorocinnamamide, 3-fluorocinnamamide, 2-fluorocinnamamide, 4-trifluoromethinnamamide, 3-trifluoromethinnamamide, 4-hydroxymethylcinnamamide, 3-methoxycinnamamide, and 4-aminocinnamamide. Also preferred are amide compounds (C) which are substituted with a C1-C6 alkyl group on the nitrogen atom in the amide group of these compounds, and more preferred are amide compounds (C) which are substituted with a methyl group on the nitrogen atom in the amide group of these compounds.

Preferable examples of the amide compound (C) when R ^c1 is a 2-valent organic group include malonamide, succinamide (succinamide), adipoamide, sebacamide, dodecanedioic acid diamide, dichloropropionamide, dibromomalonamide, terephthalic acid diamide, isophthalic acid diamide, phthalic acid diamide, naphthalene-2, 6-dicarboxylic acid diamide, naphthalene-2, 7-dicarboxylic acid diamide, naphthalene-1, 4-dicarboxylic acid diamide, biphenyl-4, 4' -dicarboxylic acid diamide, 1, 4-phenylene diacetic acid diamide, 1, 3-phenylene diacetic acid diamide, and 1, 2-phenylene diacetic acid diamide. Also preferred as the amide compound (C) is a substituent in which 1 or 2 of nitrogen atoms in an amide group of these compounds are substituted with a C1-C6 alkyl group, and more preferred is a substituent in which 1 or 2 of nitrogen atoms in an amide group of these compounds are substituted with a methyl group.

Preferable examples of the amide compound (C) when R ^c1 is a 3-valent organic group include 1,2, 3-tricarballylic acid triamide, 1,2, 3-propanetriamide, 3' -nitrilotris (propionamide), benzene-1, 2, 3-tricarballylic acid triamide, benzene-1, 2, 4-tricarballylic acid triamide, benzene-1, 3, 4-tricarballylic acid triamide, and benzene-1, 3, 5-tricarballylic acid triamide. Also preferred are amide compounds (C) which are substituted with 1 to 3 nitrogen atoms in the amide group of these compounds by a C1-C6 alkyl group, and more preferred are amide compounds (C) which are substituted with 1 to 3 nitrogen atoms in the amide group of these compounds by a methyl group.

Preferable examples of the amide compound (C) when R ^c1 is a 4-valent organic group include ethylenediamine tetraacetic acid tetra-amide and naphthalene-1, 4,5, 8-tetracarboxylic acid tetra-amide. Also preferred are amide compounds (C) which are substituted with a C1-C6 alkyl group for 1 to 4 of the nitrogen atoms in the amide groups of these compounds, and more preferred are amide compounds (C) which are substituted with a methyl group for 1 to 4 of the nitrogen atoms in the amide groups of these compounds.

Among the amide compounds (C) described above, acetamide, N-methylacetamide, N-ethylacetamide, benzamide, N-methylbenzamide, N-ethylbenzamide, phenylacetamide, N-methylphenyl acetamide, N-ethylphenylacetamide, cinnamamide, N-methylcinnamamide, N-ethylcinnamamide, malonamide, N, N ' -dimethylpropionamide, N ' -diethylmalonamide, 3' -nitrilotris (propionamide), 3',3 "-nitrilotris (N-methylpropionamides), and 3,3',3" -nitrilotris (N-ethylpropionamides).

The amount of the amide compound (C) used in the varnish composition is not particularly limited within a range that does not impair the object of the present invention. The amount of the amide compound (C) used is preferably 1 part by mass or more and 40 parts by mass or less, more preferably 3 parts by mass or more and 30 parts by mass or less, still more preferably 5 parts by mass or more and 25 parts by mass or less, relative to the total solid content of the varnish composition, in terms of preventing excessive sublimation and volatilization of the amide compound (C) at the time of producing the polyimide resin and easily obtaining a desired effect of improving the physical properties of the polyimide resin.

In addition, in the case where the varnish composition contains the thermal alkaline agent (B), the mass ratio of the thermal alkaline agent (B) to the amide compound (C) ((B): (C)) is, for example, 100: 30-100: 500, more preferably 100: 100-100: 300. the thermal alkaline generator (B) is preferably a compound represented by the following formula (B1), formula (B2), or formula (B4), and more preferably a compound represented by the following formula (B4).

< Solvent (S) >

The varnish composition contains a solvent (S). The varnish composition may be a paste containing a solid or a solution, and is preferably a solution. The solvent (S) may be used alone or in combination of 2 or more.

The type of the solvent (S) is not particularly limited within a range that does not impair the object of the present invention, and examples thereof include: glycol monoethers such as water, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, and diethylene glycol monophenyl ether; glycol diethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dipropyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dipropyl ether; glycol monoacetate such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monophenyl ether acetate, diethylene glycol monomethyl ether acetate, and diethylene glycol monoethyl ether acetate; diethylene glycol monopropyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monophenyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, 2-methoxybutyl acetate, 3-methoxybutyl acetate, 4-methoxybutyl acetate, 2-methyl-3-methoxybutyl acetate, 3-ethyl-3-methoxybutyl acetate, 2-ethoxybutyl acetate, 4-propoxybutyl acetate, 2-methoxypentyl acetate, 3-methoxypentyl acetate, 4-methoxypentyl acetate, Monoether monoacetate of glycols such as 2-methyl-3-methoxypentanoate, 3-methyl-4-methoxypentanoate, and 4-methyl-4-methoxypentanoate; ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, ethyl isobutyl ketone, and cyclohexanone; methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl 2-hydroxypropionate, ethyl 2-hydroxypropionate, methyl 2-hydroxy-2-methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, ethyl 3-propoxypropionate, propyl 3-methoxypropionate, isopropyl 3-methoxypropionate, ethyl ethoxyacetate, ethyl oxoacetate, methyl 2-hydroxy-3-methylbutanoate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isoamyl acetate, methyl carbonate, ethyl carbonate, propyl carbonate, butyl carbonate, methyl pyruvate, ethyl pyruvate, Esters such as propyl pyruvate, butyl pyruvate, methyl acetoacetate, ethyl acetoacetate, benzyl acetate, ethyl benzoate, diethyl oxalate, diethyl maleate, and gamma-butyrolactone; ethers such as diethyl ether, dipropyl ether, dibutyl ether, dihexyl ether, benzyl methyl ether, benzyl ethyl ether, and tetrahydrofuran; aromatic compounds such as benzene, toluene, xylene, ethylbenzene, cresol, and chlorobenzene; aliphatic alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, n-hexanol, and cyclohexanol; glycols such as polyethylene glycol, ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol; glycerol; etc.

In addition, a solvent used in the reaction of the tetracarboxylic dianhydride and the diamine compound described above may also be preferably used as the solvent (S).

The solvent (S) may contain a nitrogen-containing compound represented by the following formula (S1).

(In the formula (S1), R ^S1 and R ^S2 are each independently an alkyl group having 1 to 3 carbon atoms, and R ^S3 is a hydrogen atom or a group represented by the following formula (S1-1) or the following formula (S1-2):

R ^S4 is a hydrogen atom or a hydroxyl group, R ^S5 and R ^S6 are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, R ^S7 and R ^S8 are each independently a hydrogen atom, or an alkyl group having 1 to 3 carbon atoms, and when R ^S3 is a group represented by the formula (S1-1), R ^S2 and R ^S3 may be bonded to each other to form a ring. )

Specific examples of the nitrogen-containing compound represented by the formula (S1) include N, N-dimethylformamide, N-dimethylacetamide, N, 2-trimethylpropionamide, N-ethyl-N, 2-dimethylpropionamide, N-diethyl-2-methylpropionamide, N, 2-trimethyl-2-hydroxypropionamide, N-ethyl-N, 2-dimethyl-2-hydroxypropionamide, and N, N-diethyl-2-hydroxy-2-methylpropionamide when R ^S3 is a hydrogen atom or a group represented by the formula (S1-1).

Specific examples of the nitrogen-containing compound represented by the formula (S1) include N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, when R ^S3 is a group represented by the formula (S1-1) and R ^S2 and R ^S3 are bonded to each other to form a ring.

Specific examples of the nitrogen-containing compound represented by the formula (S1) include N, N, N ', N' -tetramethylurea, N, N, N ', N' -tetraethylurea, and the like when R ^S3 is a group represented by the formula (S1-2).

Among the above examples of the nitrogen-containing compound represented by the formula (S1), N, N-dimethylformamide, N, N-dimethylacetamide, N, N, 2-trimethylpropionamide, and N, N, N ', N' -tetramethylurea are particularly preferable. Of these, N, N, 2-trimethylpropionamide, and N, N, N ', N' -tetramethylurea are preferred. The boiling point of N, N, 2-trimethylpropionamide was 175℃at atmospheric pressure and the boiling point of N, N, N ', N' -tetramethylurea was 177℃at atmospheric pressure. Thus, N, N, 2-trimethylpropionamide, and N, N, N ', N' -tetramethylurea have low boiling points in organic solvents (S-I).

Therefore, when a varnish composition containing a solvent (S) containing at least one selected from the group consisting of N, 2-trimethylpropionamide and N, N' -tetramethylurea is used, the solvent (S) is less likely to remain in the polyimide resin produced by heating when forming the polyimide resin, and the mechanical properties of the polyimide resin obtained are less likely to be degraded.

N, 2-trimethylpropionamide and N, N' -tetramethylurea are substances having low toxicity, and are not specified as substances SVHC (Substance of Very High Concern, highly interesting substances) having a fear of toxicity in the REACH regulations of EU (european union), and are also useful in this respect.

The content of the solvent (S) in the varnish composition is not particularly limited within a range that does not impair the object of the present invention. The content of the solvent (S) in the varnish composition is appropriately adjusted according to the solid content in the varnish composition. The solid content in the varnish composition is, for example, in the range of 5% by mass or more and 99.9% by mass or less, preferably 5% by mass or more and 70% by mass or less, and more preferably 10% by mass or more and 60% by mass or less.

< Thermoalciferous agent (B) >)

For the purpose of enabling a polyamide resin to be well formed from the polyamide acid (a) by firing, the varnish composition preferably contains a thermal alkali generator (B) that generates a basic nitrogen-containing heterocyclic compound by heating.

The basic nitrogen-containing heterocyclic compound produced by the thermal alkaline generator (B) may be an aliphatic cyclic compound or an aromatic compound. When the basic nitrogen-containing heterocyclic compound is a compound in which 2 or more single rings are condensed, the 2 or more single rings may contain only aliphatic rings, only aromatic rings, or a combination of aliphatic rings and aromatic rings.

Examples of the basic nitrogen-containing heterocyclic compound produced by the thermal alkaline generator (B) include: nitrogen-containing 5-membered ring compounds such as pyrrolidine, pyrazolidine, imidazolidine, triazolidine, tetrazolidine, pyrroline, pyrazoline, imidazoline, triazoline, tetrahydrozoline, pyrrole, pyrazole, imidazole, triazole, and tetrazole; nitrogen-containing 6-membered rings such as piperidine, piperazine, triazinane, pyridine, pyridazine, pyrimidine, pyrazine and the like; compounds in which these compounds are substituted with one or more substituents; these compounds are fused with cyclopentane, cyclohexane, benzene, etc.

When the basic nitrogen-containing heterocyclic compound has a substituent on the nitrogen-containing heterocyclic ring, the substituent includes the same groups as R ¹、R² and R ³ in the formula (B1) described below.

The basic nitrogen-containing heterocyclic compound produced as the component (B) of the thermoalcifer is preferably an imidazole compound represented by the following formula (B1) in terms of promoting good effect of producing a polyimide resin from the polyamic acid (a), and the like:

(in the formula (B1), R ¹、R² and R ³ are each independently a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a thioether group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfonate group (sulfonatogroup), a phosphine group, a phosphino group, a phosphonate group (phosphonato group), or an organic group).

The organic group in R ¹、R² and R ³ is preferably a group containing carbon atoms, more preferably a group containing 1 or more carbon atoms and 1 or more atoms selected from the group consisting of H, O, S, se, N, B, P, si and halogen atoms. Examples of the organic group in R ¹、R² and R ³ include an alkyl group, an alkenyl group, a cycloalkyl group, a cycloalkenyl group, an aryl group, and an aralkyl group. The organic group may contain a bond other than a hydrocarbon group, such as a heteroatom, or a substituent. The organic group may be any of linear, branched, and cyclic. The organic group is usually monovalent, but may be divalent or more in the case of forming a cyclic structure or the like.

R ¹ and R ² may be bonded to each other to form a cyclic structure, or may further contain a bond of a heteroatom. Examples of the cyclic structure include heterocycloalkyl groups and heteroaryl groups, and may be condensed rings.

The bonds contained in the organic groups of R ¹、R² and R ³ are not particularly limited as long as the effects of the present invention are not impaired. The organic group may contain a bond containing a heteroatom such as an oxygen atom, a nitrogen atom, a silicon atom, or the like. Specific examples of the heteroatom-containing bond include an ether bond, a carbonyl bond, a thiocarbonyl bond, an ester bond, an amide bond, a urethane bond, an imino bond (-n=c (-R) -, -C (=nr) -: R represents a hydrogen atom or an organic group), a carbonate bond, a sulfonyl bond, an azo bond, and the like.

The organic group of R ¹、R² and R ³ may have a hetero atom-containing bond, and from the viewpoint of heat resistance of the imidazole compound, an ether bond, a carbonyl bond, a thiocarbonyl bond, an ester bond, an amide bond, a urethane bond, an imino bond (-n=c (-R) -, -C (=nr) -: R represents a hydrogen atom or a monovalent organic group), a carbonate bond, or a sulfonyl bond is preferable.

When the organic groups of R ¹、R² and R ³ are substituents other than hydrocarbon groups, R ¹、R² and R ³ are not particularly limited as long as the effects of the present invention are not impaired. Specific examples of R ¹、R² and R ³ are as described above, a halogen atom, a hydroxyl group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfonate group, a phosphine group, a phosphino group, and a phosphonate group. The hydrogen atom contained in the above substituent may be substituted with a hydrocarbon group. The hydrocarbon group contained in the substituent may be any of linear, branched, and cyclic.

R ¹、R² and R ³ are preferably a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an aryl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or a halogen atom, and more preferably a hydrogen atom.

The thermal alkaline generator (B) is not particularly limited as long as it is a compound capable of generating a basic nitrogen-containing heterocyclic compound by heating. The compound (thermolyzing agent) which has been conventionally blended in various compositions and generates an amine by the action of heat can be used as the thermolyzing agent (B) by substituting the skeleton derived from the amine generated upon heating with the skeleton derived from the desired basic nitrogen-containing heterocyclic compound.

Examples of suitable thermal alkaline agents (B) include compounds represented by the following formula (B2):

(in the formula (B2), R ¹、R² and R ³ are each independently a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a thioether group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphino group, a phosphinoyl group, a phosphonate group, or an organic group, and R ^b3、R^b4、R^b5、R^b6 and R ^b7 are each independently a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a thioether group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphino group, a phosphonate group, an amino group, an ammonium group, or an organic group, and two or more of them may be bonded to form a cyclic structure or a bond that may contain a heteroatom, as in the formula (B2).

In the formula (B2), R ¹、R² and R ³ are the same as R ¹、R² and R ³ described for the formula (B1).

In the formula (B2), R ^b1 and R ^b2 each independently represent a hydrogen atom, a halogen atom, a hydroxyl group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphinyl group, a phosphonyl group, a phosphonate group, or an organic group.

Examples of the organic groups in R ^b1 and R ^b2 include those exemplified for R ¹、R² and R ³. The organic group may contain a heteroatom as in the case of R ¹、R² and R ³. The organic group may be any of linear, branched, and cyclic.

Among the above, R ^b1 and R ^b2 are each independently preferably a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 4 to 13 carbon atoms, a cycloalkenyl group having 4 to 13 carbon atoms, an aryloxyalkyl group having 7 to 16 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an alkyl group having 2 to 11 carbon atoms having a cyano group, an alkyl group having 1 to 10 carbon atoms having a hydroxyl group, an alkoxy group having 1 to 10 carbon atoms, an amido group having 2 to 11 carbon atoms, an acyl group having 1 to 10 carbon atoms, an ester group having 2 to 11 carbon atoms (-COOR, -OCOR: R represents a hydrocarbon group), an aryl group having 6 to 20 carbon atoms substituted with an electron donating group and/or an electron withdrawing group, or a benzyl group. More preferably, R ^b1 and R ^b2 are both hydrogen atoms, or R ^b1 is methyl and R ^b2 is hydrogen atom.

In the formula (B2), R ^b3、R^b4、R^b5、R^b6, R ^b7 each independently represent a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a thioether group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphino group, a phosphono group, a phosphonate group, an amino group, an ammonium group, or an organic group.

Examples of the organic group in R ^b3、R^b4、R^b5、R^b6 and R ^b7 include groups exemplified by R ¹、R² and R ³. The organic group may contain a bond or a substituent other than a hydrocarbon group, such as a heteroatom, as in the case of R ¹、R² and R ³. The organic group may be any of linear, branched, and cyclic.

Regarding R ^b3、R^b4、R^b5、R^b6 and R ^b7, two or more of them may be bonded to form a cyclic structure. Each of R ^b3、R^b4、R^b5、R^b6, and R ^b7 may comprise a bond containing a heteroatom. Examples of the cyclic structure include heterocycloalkyl groups and heteroaryl groups, and may be condensed rings. For example, two or more of R ^b3、R^b4、R^b5、R^b6 and R ^b7 may be bonded to each other, and the atoms of the benzene ring to which R ^b3、R^b4、R^b5、R^b6 and R ^b7 are bonded may be used together to form a condensed ring such as naphthalene, anthracene, phenanthrene, indene, or the like. When a condensed ring is formed, the absorption wavelength is preferably a long wavelength.

Among the above, R ^b3、R^b4、R^b5、R^b6 and R ^b7 are each independently preferably a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 4 to 13 carbon atoms, a cycloalkenyl group having 4 to 13 carbon atoms, an aryloxyalkyl group having 7 to 16 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, an alkyl group having 2 to 11 carbon atoms having a cyano group, an alkyl group having 1 to 10 carbon atoms having a hydroxyl group, an alkoxy group having 1 to 10 carbon atoms, an amido group having 2 to 11 carbon atoms, an acyl group having 1 to 10 carbon atoms, an ester group having 2 to 11 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aryl group substituted with an electron donating group and/or electron withdrawing group, a benzyl group substituted with an electron donating group and/or electron withdrawing group, a cyano group, or a nitro group.

Among the compounds represented by the above formula (B2), the compounds represented by the following formula (B3) are preferable:

R ¹、R² and R ³ in the formula (B3) have the same meaning as those in the formulae (B1) and (B2), R ^b1～R^b6 has the same meaning as those in the formula (B2), R ^b8 represents a hydrogen atom or an organic group, R ^b3 and R ^b4 do not become hydroxyl groups, and two or more of them may be bonded to form a cyclic structure or may contain a bond of a heteroatom with respect to R ^b3、R^b4、R^b5 and R ^b6.

The compound represented by the formula (B3) has a substituent-O-R ^b8, and therefore has excellent solubility in the solvent (S).

In the formula (B3), R ^b8 is a hydrogen atom or an organic group. When R ^b8 is an organic group, examples of the organic group include R ¹、R² and R ³. In the case of the organic group, a heteroatom may be contained in the organic group. The organic group may be any of linear, branched, and cyclic. R ^b8 is preferably a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, more preferably a methyl group.

Of the compounds represented by the formula (B1), specific examples of compounds particularly suitable as the thermal alkaline generator (B) are shown below.

The imidazole compound represented by the following formula (B4) is also suitable as the thermoalcifer (B).

(In the formula (B4), R ¹、R² and R ³ are the same as R ¹、R² and R ³ in the formula (B1), R ^b9 is a hydrogen atom or a monovalent organic group, R ^b10 is an aromatic group which may have a substituent, and R ^b9 may be bonded to another R ^b9 or R ^b10 to form a cyclic structure.)

In the formula (B4), R ^b9 is a hydrogen atom or a monovalent organic group. The monovalent organic group is not particularly limited, and may be, for example, an alkyl group which may have a substituent, an aromatic group which may have a substituent, or the like. When R ^b9 is an alkyl group, the alkyl group may have an ester bond in the chain, or the like.

The alkyl group may be the same as R ^b11 in the formula (B4 a) described below, for example. The carbon number of the alkyl group is preferably 1 to 40, more preferably 1 to 30, particularly preferably 1 to 20, and most preferably 1 to 10.

The substituent that the alkyl group may have may be the same as the substituent that the alkylene group of R ^b11 in the formula (B4 a) described later may have, for example.

As the aromatic group which may have a substituent, an aryl group is preferable, and a phenyl group is more preferable, similarly to R ^b10 in the formula (B4 a) described later. The aromatic group which may have a substituent(s) for R ^b9 may be the same as or different from R ^b10.

In the formula (B4), preferably, one R ^b9 is a hydrogen atom, more preferably, one R ^b9 is a hydrogen atom, and the other R ^b9 is an alkyl group which may have a substituent or an aromatic group which may have a substituent.

In formula (B4), R ^b9 may be bonded to another R ^b9 or R ^b10 to form a cyclic structure. For example, when at least one R ^b9 is an alkyl group which may have a substituent, R ^b9 may be bonded to another R ^b9 or R ^b10 to form a cyclic structure.

The imidazole compound represented by the formula (B4) may be a compound represented by the following formula (B4 a).

(In the formula (B4 a), R ¹、R² and R ³ are the same as R ¹、R² and R ³ in the formula (B1), R ^b11 is a hydrogen atom or an alkyl group, R ^b10 is an aromatic group which may have a substituent, R ^b12 is an alkylene group which may have a substituent, and R ^b12 may be bonded to R ^b10 to form a cyclic structure.)

In the formula (B4 a), R ^b11 is a hydrogen atom or an alkyl group. When R ^b11 is an alkyl group, the alkyl group may be a straight-chain alkyl group or a branched-chain alkyl group. The number of carbon atoms of the alkyl group is not particularly limited, but is preferably 1 to 20, more preferably 1 to 10, and still more preferably 1 to 5.

Specific examples of the preferable alkyl group as R ^b11 include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethyl-n-hexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, and n-eicosyl.

In the formula (B4 a), R ^b10 is an aromatic group which may have a substituent. The aromatic group which may have a substituent may be an aromatic hydrocarbon group which may have a substituent, or may be an aromatic heterocyclic group which may have a substituent.

The type of the aromatic hydrocarbon group is not particularly limited within a range that does not impair the object of the present invention. The aromatic hydrocarbon group may be a monocyclic aromatic group, a group in which 2 or more aromatic hydrocarbon groups are condensed, or a group in which 2 or more aromatic hydrocarbon groups are bonded by a single bond. As the aromatic hydrocarbon group, preferred is a phenyl group, a naphthyl group, a biphenyl group, an anthryl group, a phenanthryl group.

The type of the aromatic heterocyclic group is not particularly limited within a range that does not impair the object of the present invention. The aromatic heterocyclic group may be a monocyclic group or a polycyclic group. As the aromatic heterocyclic group, pyridyl, furyl, thienyl, imidazolyl, pyrazolyl, oxazolyl, thiazolyl, isoxazolyl, isothiazolyl, benzoxazolyl, benzothiazolyl, and benzimidazolyl are preferable.

Examples of the substituent that the phenyl group, polycyclic aromatic hydrocarbon group, or aromatic heterocyclic group may have include a halogen atom, a hydroxyl group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphino group, a phosphono group, a phosphonate group, an amino group, an ammonium group, and an organic group. When the phenyl group, the polycyclic aromatic hydrocarbon group, or the aromatic heterocyclic group has a plurality of substituents, the plurality of substituents may be the same or different.

When the substituent of the aromatic group is an organic group, examples of the organic group include an alkyl group, an alkenyl group, a cycloalkyl group, a cycloalkenyl group, an aryl group, and an aralkyl group. The organic group may contain a bond other than a hydrocarbon group, such as a heteroatom, and a substituent. The organic group may be any of a linear, branched, and cyclic structure, and a combination of these structures. The organic group is usually monovalent, and may be divalent or more when a cyclic structure is formed or the like.

When the aromatic group has a substituent on an adjacent carbon atom, 2 substituents bonded to the adjacent carbon atom may be bonded to form a cyclic structure. Examples of the cyclic structure include an aliphatic hydrocarbon ring and an aliphatic ring containing a heteroatom.

When the substituent of the aromatic group is an organic group, the bond contained in the organic group is not particularly limited as long as the effect of the present invention is not impaired, and the organic group may contain a bond containing a heteroatom such as an oxygen atom, a nitrogen atom, or a silicon atom. Specific examples of the heteroatom-containing bond include an ether bond, a carbonyl bond, a thiocarbonyl bond, an ester bond, an amide bond, a urethane bond, an imino bond (-n=c (-R) -, -C (=nr) -: R represents a hydrogen atom or an organic group), a carbonate bond, a sulfonyl bond, an azo bond, and the like.

The heteroatom-containing bond that the organic group may have is preferably an ether bond, a carbonyl bond, a thiocarbonyl bond, an ester bond, an amide bond, an amino bond (-NR-: R represents a hydrogen atom or a monovalent organic group), a urethane bond, an imino bond (-N=C (-R) -, -C (=NR) -: R represents a hydrogen atom or a monovalent organic group), a carbonate bond, or a sulfonyl bond from the viewpoint of heat resistance of the imidazole compound represented by the formula (B4) or the formula (B4 a).

When the organic group is a substituent other than a hydrocarbon group, the type of substituent other than a hydrocarbon group is not particularly limited within a range that does not impair the object of the present invention. Specific examples of the substituent other than the hydrocarbon group include a halogen atom, a hydroxyl group, a mercapto group, a thioether group, a cyano group, an isocyano group, a cyanate group, an isocyanate group, a thiocyanate group, an isothiocyanate group, a silyl group, a silanol group, an alkoxy group, an alkoxycarbonyl group, an amino group, a monoalkylamino group, a dialkylamino group, a monoarylamino group, a diarylamino group, a carbamoyl group, a thiocarbamoyl group, a nitro group, a nitroso group, a carboxylate group, an acyl group, an acyloxy group, a sulfinyl group, a sulfonate group, a phosphine group, a phosphino group, a phosphonate group, an alkyl ether group, an alkenyl ether group, an aryl ether group, and the like. The hydrogen atom contained in the above substituent may be substituted with a hydrocarbon group. The hydrocarbon group contained in the substituent may be any of linear, branched, and cyclic.

The substituent of the phenyl group, polycyclic aromatic hydrocarbon group, or aromatic heterocyclic group is preferably an alkyl group having 1 to 12 carbon atoms, an aryl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryloxy group having 1 to 12 carbon atoms, an arylamino group having 1 to 12 carbon atoms, or a halogen atom.

R ^b10 is preferably a phenyl group, a furyl group or a thienyl group each of which may have a substituent, from the viewpoint that the imidazole compound represented by the formula (B4) or the formula (B4 a) can be synthesized easily and at low cost and the solubility of the imidazole compound in water or an organic solvent is good.

In the formula (B4 a), R ^b12 is an alkylene group which may have a substituent. The substituent that the alkylene group may have is not particularly limited within a range that does not impair the object of the present invention. Specific examples of the substituent that the alkylene group may have include a hydroxyl group, an alkoxy group, an amino group, a cyano group, and a halogen atom. The alkylene group may be a linear alkylene group or a branched alkylene group, and is preferably a linear alkylene group. The number of carbon atoms of the alkylene group is not particularly limited, but is preferably 1 to 20, more preferably 1 to 10, particularly preferably 1 to 5. The number of carbon atoms of the alkylene group does not include the carbon atoms of the substituent bonded to the alkylene group.

The alkoxy group as a substituent bonded to the alkylene group may be a linear alkoxy group or a branched alkoxy group. The number of carbon atoms of the substituent alkoxy group is not particularly limited, but is preferably 1 to 10, more preferably 1 to 6, particularly preferably 1 to 3.

The amino group as a substituent bonded to the alkylene group may be a monoalkylamino group or a dialkylamino group. The alkyl group contained in the monoalkylamino group or dialkylamino group may be a linear alkyl group or a branched alkyl group. The number of carbon atoms of the alkyl group contained in the monoalkylamino group or the dialkylamino group is not particularly limited, but is preferably 1 to 10, more preferably 1 to 6, particularly preferably 1 to 3.

Specific examples of suitable alkylene groups for R ^b12 include methylene, ethane-1, 2-diyl, n-propane-1, 3-diyl, n-propane-2, 2-diyl, n-butane-1, 4-diyl, n-pentane-1, 5-diyl, n-hexane-1, 6-diyl, n-heptane-1, 7-diyl, n-octane-1, 8-diyl, n-nonane-1, 9-diyl, n-decane-1, 10-diyl, n-undecane-1, 11-diyl, n-dodecane-1, 12-diyl, n-tridecane-1, 13-diyl, n-tetradecane-1, 14-diyl, n-pentadecane-1, 15-diyl, n-hexadecane-1, 16-diyl, n-heptadecane-1, 17-diyl, n-octadecane-1, 18-diyl, n-nonadecane-1, 19-diyl, and n-eicosane-1, 20-diyl.

Among the imidazole compounds represented by the above formula (B4), the compounds represented by the following formula (B4-1 a) are preferable in view of being capable of being synthesized at low cost and easily.

( In the formula (B4-1 a), R ¹、R² and R ³ are the same as R ¹、R² and R ³ in the formula (B1), R ^b9 is the same as the formula (B4), and R ^b13、R^b14、R^b15、R^b16 and R ^b17 are each independently a hydrogen atom, a halogen atom, a hydroxyl group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphino group, a phosphonyl group, a phosphonate group, an amino group, an ammonium group, or an organic group. At least two of R ^b13、R^b14、R^b15、R^b16 and R ^b17 may be bonded to form a cyclic structure. R ^b9 can bond with R ^b15 to form a cyclic structure. )

In the formula (B4-1 a), R ^b13、R^b14、R^b15、R^b16 and R ^b17 may all be hydrogen atoms. In addition, from the viewpoint of solubility of the compound represented by the formula (B4-1) in the solvent (S), it is preferable that at least one of R ^b13、R^b14、R^b15、R^b16 and R ^b17 is a group other than a hydrogen atom.

R ^b13、R^b14、R^b15、R^b16 and R ^b17 are the same as those in the formula (B4-1) described below. In the formula (B4-1 a), R ^b9 may be bonded to R ^b15 to form a cyclic structure. For example, when R ^b9 is an alkyl group which may have a substituent, R ^b9 may be bonded to R ^b15 to form a cyclic structure.

Among the imidazole compounds represented by the above formula (B4 a) or (B4-1 a), the compounds represented by the following formula (B4-1) are preferable, and the compounds represented by the formula (B4-1) and R ^b12 are more preferable, because they can be synthesized at low cost and easily and have excellent solubility in water and organic solvents.

( In the formula (B4-1), R ¹、R² and R ³ are the same as R ¹、R² and R ³ in the formula (B1), R ^b11 and R ^b12 are the same as R ^b11 and R ^b12 in the formula (B4 a), and R ^b13、R^b14、R^b15、R^b16 and R ^b17 are each independently a hydrogen atom, a halogen atom, a hydroxyl group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphino group, a phosphono group, a phosphonate group, an amino group, an ammonium group, or an organic group. At least two of R ^b13、R^b14、R^b15、R^b16 and R ^b17 may be bonded to form a cyclic structure. R ^b12 can bond with R ^b15 to form a cyclic structure. )

In the formula (B4-1), R ^b13、R^b14、R^b15、R^b16 and R ^b17 may all be hydrogen atoms. In addition, from the viewpoint of solubility of the compound represented by the formula (B4-1) in the solvent (S), it is preferable that at least one of R ^b13、R^b14、R^b15、R^b16 and R ^b17 is a group other than a hydrogen atom.

When R ^b13、R^b14、R^b15、R^b16 and R ^b17 are organic groups, the organic groups are the same as those of R ^b10 in the formula (B4 a) as a substituent. From the viewpoint of solubility of the imidazole compound in the solvent (S), R ^b13、R^b14、R^b15 and R ^b16 are preferably hydrogen atoms.

Among them, at least one of R ^b13、R^b14、R^b15、R^b16 and R ^b17 is preferably a substituent described below, and particularly preferably R ^b17 is a substituent described below. When R ^b17 is a substituent described below, R ^b13、R^b14、R^b15 and R ^b16 are preferably hydrogen atoms.

-O-R^b18

(R ^b18 is a hydrogen atom or an organic group.)

When R ^b18 is an organic group, the organic group is the same as the organic group having R ^b10 in the formula (B4 a) as a substituent. R ^b18 is preferably an alkyl group, more preferably an alkyl group having 1 to 8 carbon atoms, particularly preferably an alkyl group having 1 to 3 carbon atoms, and most preferably a methyl group.

Among the compounds represented by the above formula (B4-1), the compounds represented by the following formula (B4-1-1) are preferable.

( In the formula (B4-1-1), R ¹、R² and R ³ are the same as R ¹、R² and R ³ in the formula (B1), R ^b11 is the same as the formula (B4 a), and R ^b19、R^b20、R^b21、R^b22 and R ^b23 are each independently a hydrogen atom, a hydroxyl group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphino group, a phosphono group, a phosphonate group, an amino group, an ammonium group, or an organic group. Wherein at least one of R ^b19、R^b20、R^b21、R^b22 and R ^b23 is a group other than a hydrogen atom. )

Of the compounds represented by the formula (B4-1-1), at least one of R ^b19、R^b20、R^b21、R^b22 and R ^b23 is preferably a group represented by-O-R ^b18 as described above, and particularly preferably R ^b23 is a group represented by-O-R ^b18. When R ^b23 is a group represented by-O-R ^b18, R ^b19、R^b20、R^b21 and R ^b22 are preferably hydrogen atoms.

Preferred specific examples of the imidazole compound represented by the formula (B4) or (B4 a) include the following compounds.

The content of the thermal alkaline agent (B) in the varnish composition is preferably 5 mass% or more and 50 mass% or less, more preferably 10 mass% or more and 40 mass% or less, relative to the mass of the varnish composition. By using the thermal alkaline agent (B) in an amount within this range, the formation of the polyamide resin from the polyamide acid (a) can be effectively promoted without excessive volatilization or sublimation of the thermal decomposition product of the thermal alkaline agent (B).

< Other ingredients >

The varnish composition may contain various additives as required. Examples of the additives include colorants, dispersants, sensitizers, adhesion promoters, antioxidants, ultraviolet absorbers, anti-coagulants, antifoaming agents, surfactants, and the like. In addition, the varnish composition may contain various filler materials or reinforcing materials as needed.

The amount of each additive used is not particularly limited within a range that does not impair the object of the present invention. The amount of the solid content in the varnish composition may be appropriately adjusted, for example, in the range of 0.001 mass% to 60 mass%, preferably 0.05 mass% to 5 mass%.

The amount of the filler or reinforcing material to be used is not particularly limited within a range that does not impair the object of the present invention. Typically, the amount of the filler or reinforcing material to be used is preferably 1% by mass or more and 300% by mass or less, more preferably 5% by mass or more and 200% by mass or less, and still more preferably 10% by mass or more and 100% by mass or less, relative to the mass of the polyamic acid (a).

As described above, when the varnish composition is used, a polyimide resin having improved physical properties such as thermal expansion coefficient, elongation at break and tensile strength can be obtained.

Method for producing polyimide resin

The polyimide resin can be produced by a method comprising the steps of:

a molding step of molding the varnish composition described above; and

When the varnish composition is molded, the shape of the molded varnish composition is not particularly limited. The method for molding the varnish composition is not particularly limited. For example, there may be mentioned: a method of injecting a varnish composition into a mold of a desired shape; a method of filling a varnish composition into a mold using a squeegee or the like; a method of coating a varnish composition on a substrate; etc.

Among these methods, a method of applying the varnish composition to a substrate is preferable in that the polyimide resin film is in great demand and the solvent (S) is easily removed from the varnish composition at the time of producing the polyimide resin.

After the varnish composition is applied, the resultant film is dried under heating and/or vacuum or reduced pressure to form a dried film.

The temperature at which the varnish composition or the varnish composition after the drying step is heated is not particularly limited as long as the temperature is a temperature at which a polyimide resin having desired properties can be obtained. The temperature for heating the polyamic acid is preferably 120℃or more and 430℃or less, more preferably 150℃or more and 420℃or less. By heating the varnish composition at a temperature in this range, the solvent (S) can be removed and the polyimide resin can be produced while suppressing thermal degradation and thermal decomposition of the polyimide resin produced.

In addition, from the viewpoint of easy formation of a polyimide resin having a high glass transition temperature and tensile strength, a low thermal expansion coefficient, and little coloration, it is also preferable to heat the polyamic acid stepwise at a temperature of 70 ℃ or higher and 120 ℃ or lower for about 10 minutes to 2 hours, and further at a temperature of 150 ℃ or higher and 420 ℃ or lower for about 10 minutes to 2 hours, to produce the polyimide resin.

According to the above-described method for producing a polyimide resin, a polyimide resin having improved physical properties such as thermal expansion coefficient, elongation at break and tensile strength can be produced.

Additive

The additive is used for blending into a polyamic acid-containing liquid containing a polyamic acid (a) and a solvent (S) to obtain a varnish composition for forming a polyimide resin. The additive contains an amide compound (C). As for the additives, the polyamic acid (a), the solvent (S), and the amide compound (C) are as described above for the varnish composition. In addition, optional components as set forth above for the varnish composition for forming a polyimide resin may be appropriately blended into the polyamic acid-containing liquid described above or the varnish composition to which the additive is added.

When the varnish composition containing the above additive is heated to obtain a polyimide resin, at least one of a decrease in coefficient of thermal expansion, an increase in elongation at break, and an increase in tensile strength can be caused in the obtained polyimide resin, as compared with the case where the polyimide resin is obtained by heating a polyamic acid-containing liquid. Preferably, by using the additive, all of a decrease in thermal expansion coefficient, an increase in elongation at break, and an increase in tensile strength occur.

The form of the additive is not particularly limited. The additive may be in a solid state or in a liquid state. When the additive is in a solid state, the amide compound (C) may be mixed with at least one component selected from the group consisting of a colorant, a dispersant, a sensitizer, an adhesion promoter, an antioxidant, an ultraviolet absorber, an anticoagulant, an antifoaming agent, a surfactant, and the like, and processed into a form such as granules. In the case where the additive is a liquid, the amide compound (C) is preferably dispersed or dissolved in the above-mentioned solvent (S). At least one component selected from the group consisting of a colorant, a dispersant, a sensitizer, an adhesion promoter, an antioxidant, an ultraviolet absorber, an anticoagulant, an antifoaming agent, a surfactant, and the like may be blended with the amide compound (C) in the liquid additive.

The amount of the additive to be used is not particularly limited as long as the desired effect due to the use of the additive can be obtained. The amount of the additive to be used is preferably 1 part by mass or more and 40 parts by mass or less, more preferably 3 parts by mass or more and 30 parts by mass or less, still more preferably 5 parts by mass or more and 25 parts by mass or less, based on 100 parts by mass of the polyamic acid (a) contained in the polyamic acid-containing liquid.

In addition, the amide compound (C) as an additive may be combined with the thermal alkaline agent (B), and the mass ratio ((B): C)) of the thermal alkaline agent (B) to the amide compound (C) is, for example, 100: 30-100: 500, more preferably 100: 100-100: 300. the thermal alkaline generator (B) is preferably a compound represented by the following formula (B1), formula (B2), or formula (B4), and more preferably a compound represented by the following formula (B4).

Examples

Hereinafter, the present invention will be described in detail with reference to examples, but the scope of the present invention is not limited to these examples.

[ Preparation example 1]

First, a three-necked flask having a capacity of 30mL was heated by a hot air gun, and dried sufficiently. Then, the atmosphere in the three-necked flask was replaced with nitrogen to obtain a nitrogen atmosphere in the three-necked flask. To the three-necked flask, 0.2045g (0.90 mmol: DABAN, manufactured by Nippon pure pharmaceutical Co., ltd.) of 4,4' -diaminobenzanilide was added, and then N, N, N ', N ' -Tetramethylurea (TMU) was added. The contents of the three-necked flask were stirred to obtain a slurry in which an aromatic Diamine (DABAN) was dispersed in TMU.

Then, 0.3459g (0.90 mmol) of tetracarboxylic dianhydride of the following formula was added to the three-necked flask, and the flask contents were stirred at room temperature (25 ℃) for 12 hours under a nitrogen atmosphere to obtain a reaction solution. Thus, a polyamic acid solution containing polyamic acid A-1 at a solid concentration of 18% by mass was obtained. The obtained polyamic acid A-1 can form a transparent polyimide resin.

[ Preparation example 2]

A polyamic acid solution containing polyamic acid a-2 at a solid concentration of 18 mass% was obtained in the same manner as in production example 1, except that the diamine component was changed to 4,4' -diaminodiphenyl ether, the tetracarboxylic dianhydride component was changed to pyromellitic dianhydride, and the solvent was changed to N-methyl-2-pyrrolidone (NMP). The resulting polyamic acid A-2 can form an opaque polyimide resin.

Examples 1 to 9

The varnish compositions of examples 1 to 9 were obtained by mixing 80 parts by mass of a polyamic acid solution containing a polyamic acid (a) of the type shown in table 1, 10 parts by mass of a thermal alkaline agent (B) as a compound having the following structure, and 10 parts by mass of an amide compound (C) of the type shown in table 1, and then diluting the mixture to a solid concentration of 15% by mass with a solvent (S) of the type shown in table 1.

Comparative example 1

After mixing a polyamic acid solution containing 80 parts by mass of polyamic acid a-1 and 20 parts by mass of the thermal alkaline generator (B) used in the example, the mixture was diluted to a solid content concentration of 15% by mass with a solvent (S) of the kind shown in table 1, to obtain a varnish composition of comparative example 1.

Comparative example 2

After mixing a polyamic acid solution containing 90 parts by mass of polyamic acid a-1 and 10 parts by mass of the thermal alkaline generator (B) used in the example, the mixture was diluted to a solid content concentration of 15% by mass with a solvent (S) of the kind shown in table 1, to obtain a varnish composition of comparative example 2.

[ Comparative example 3]

The polyamic acid solution containing polyamic acid a-1 was diluted to a solid concentration of 15% by mass with a solvent (S) of the type described in table 1, to obtain a varnish composition of comparative example 3.

[ Comparative example 4]

After mixing a polyamic acid solution containing 80 parts by mass of polyamic acid a-2 with 20 parts by mass of the thermal alkaline generator (B) used in the example, the mixture was diluted to a solid content concentration of 15% by mass with a solvent (S) of the kind shown in table 1, to obtain a varnish composition of comparative example 4.

The varnish compositions of the examples and comparative examples obtained in the above manner were used to evaluate the storage stability of the varnish compositions according to the following method. Further, a polyimide resin was formed using the varnish composition after the storage stability evaluation, and the polyimide resin thus formed was evaluated for haze, yellowness Index (YI), light transmittance, coefficient of Thermal Expansion (CTE), elongation at break, and tensile strength according to the following methods. In the varnish composition of comparative example 1, the polyimide resin was not evaluated because it was thickened during storage and could not be formed into a film.

< Storage stability >

The varnish compositions of the examples and comparative examples prepared in the above manner were stored at 23℃for 10 days, and the varnish compositions after storage were observed. The varnish after storage was judged to be good when neither cloudiness nor gelation occurred, and was judged to be x when at least one of cloudiness and gelation occurred.

The varnish compositions of examples 1 to 6, comparative example 2 and comparative example 3 were used to form polyimide resin films in the following manner.

< Polyimide resin film Forming method >

The varnish composition after storage obtained in the above manner was spin-coated on a glass substrate (length 100mm, width 100mm, thickness 1.3 mm) so that the thickness of the coating film after heat curing became 13. Mu.m, to form a coating film. Subsequently, the glass substrate having the coating film was vacuum-dried at a temperature of 50℃and a pressure of 13Pa, and the solvent in the coating film was removed.

After the solvent was removed, the glass substrate having the coating film was put into an inert oven through which nitrogen flowed at a flow rate of 3L/min. The coated film was cured in an inert oven under nitrogen atmosphere at a temperature of 80 ℃ for 0.5 hour, and then further heated at a temperature of 400 ℃ for 0.5 hour (final heating temperature), to obtain a polyimide coated glass coated with a film formed of polyimide (polyimide film).

The polyimide coated glass obtained was immersed in hot water at 90℃to peel the polyimide film from the glass substrate, thereby obtaining a polyimide film (film having a length of 100mm, a width of 100mm, and a thickness of 13 μm).

< Haze, yellowness Index (YI), light (all light) transmittance >

The haze, yellowness Index (YI) and total light transmittance (light transmittance) values (unit:%) of the polyimide films of the examples and comparative examples were determined as follows: a measurement was carried out in accordance with JIS K7361-1 (published 1997) using a trade name "Hazemeter NDH-5000" manufactured by Nippon electric color Co., ltd.

Coefficient of Thermal Expansion (CTE) >

The polyimide films of each of examples and comparative examples were formed to have a length: 20mm, width: a measurement film having a size of 5 mm.

Next, the obtained measurement film was heated from 30 to 200 ℃ at a heating rate of 10 ℃/min under a nitrogen atmosphere using a thermal mechanical analyzer (trade name "TMA-60" manufactured by shimadzu corporation) as a measurement device, then cooled to 30 ℃ temporarily, and the temperature was again heated from 30 to 500 ℃ at a heating rate of 10 ℃/min, and the change in length of the sample at this time was measured at 100 to 350 ℃ to determine the average value of the change in length per 1 ℃ in 100 to 350 ℃. The stretching mode was set to 49mN.

< Elongation at break and tensile Strength >

For the polyimide films of each example and comparative example, trade name "Super Dumbbell cutter (model: SDMK-1000-D, a22 standard compliant with JIS K7139 (release 2009)") manufactured by Dumbbell co., ltd was attached to an SD type lever type sample cutter (Dumbbell co., cutter (model SDL-200) manufactured by Ltd) so that the polyimide film had a full length: 75mm, tab (tab) section spacing: 57mm, length of parallel portion: radius of 30mm, shoulder: 30mm, width of end: width of 10mm, central parallel portion: 5mm, thickness: a test piece having a dumbbell shape (a test piece conforming to JIS K7139 type A22 (a test piece of a scaled-down size) except for having a thickness of 13 μm) was prepared as a measurement sample by cutting in a 13 μm manner.

Next, using a Tensilon universal tester (model "UCT-10T" manufactured by A & D Company), the measurement samples were arranged so that the width between the clamps was 57mm and the width of the clamping portion was 10mm (the total width of the end portions), and then the tensile test was performed under conditions of a full load scale of 0.05kN and a test speed of 1 to 300 mm/min, to obtain values of tensile strength and elongation at break.

The test described above was a test in accordance with JIS K7162 (published 1994).

The value (%) of the elongation at break was calculated by taking the length of the parallel portion of the test piece (=length of the parallel portion: 30 mm) as L0, and the length of the parallel portion of the test piece until breaking (length of the parallel portion of the test piece at breaking: 30mm+α) as L, and calculated by the following equation:

[ elongation at break (%) ] = { (L-L0)/L0 } ×100.

In table 1 below, the types of the amide compounds (C) are as follows.

C-1: cinnamamide

C-2: benzamide compound

C-3: phenyl acetamide

C-4: butenamide

C-5: n-methylacetamide

C-6:1,2, 3-propane trimethamide

In the examples and comparative examples, when the varnish compositions containing the same polyamide acid (a) were compared, it was found that the polyimide resin formed using the varnish composition had a lower thermal expansion coefficient and increased elongation at break and tensile strength when the amide compound (C) was contained.

Further, as is clear from the comparative example, when the varnish composition does not contain the amide compound (C), cloudiness and gelation may occur when the varnish composition is stored at room temperature.

On the other hand, the varnish composition of the example containing the amide compound (C) was stable even when stored at room temperature for a certain period of time.

From the evaluation results of the varnish compositions of examples 1 to 6, comparative example 2 and comparative example 3 containing the polyamide acid a-1 capable of forming a transparent polyimide resin, it was found that the varnish compositions of examples 1 to 6 containing the amide compound (C) can form a highly transparent polyimide resin having no blurring, less coloration and high light transmittance.

Claims

1. A varnish composition for forming a polyimide resin, which comprises a polyamic acid (A), an amide compound (C), and a solvent (S),

The amide compound (C) is a compound represented by the following formula (C1):

R^c1-(-CO-NH-R^c2)_n···(C1)

In the formula (C1), R ^c1 is an n-valent organic group bonded to a carbonyl group via a carbon-carbon bond, R ^c2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, n is an integer of 1 to 4, and when n is 1, R ^c1 is an unsubstituted group selected from the group consisting of an alkyl group, a cycloalkyl group, a polycycloalkyl group, an alkenyl group, a cycloalkenyl group, a polycycloalkenyl group, an aryl group, a heteroaryl group, an arylalkyl group, an arylalkenyl group, a heteroarylalkyl group, and a heteroarylalkenyl group.

2. The varnish composition according to claim 1, wherein the amide compound (C) comprises a compound in which R ^c1 is benzyl and n is 1.

3. The varnish composition according to claim 1, wherein the amide compound (C) comprises a compound in which n is 3 or 4.

4. A varnish composition according to any one of claims 1 to 3 comprising a thermal alkaline generator (B) which generates a basic nitrogen-containing heterocyclic compound by heating.

5. The varnish composition according to claim 4, wherein the basic nitrogen-containing heterocyclic compound is a compound represented by the following formula (B1):

In the formula (B1), R ¹、R² and R ³ are each independently a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a thioether group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfonate group, a phosphine group, a phosphino group, a phosphonate group, or an organic group.

6. The varnish composition according to claim 5, wherein the thermal alkaline agent (B) is at least 1 selected from the group consisting of a compound represented by the following formula (B2) and a compound represented by the following formula (B4),

In the formula (B2), R ¹、R², and R ³ are the same as R ¹、R² and R ³ in the formula (B1), R ^b1 and R ^b2 each independently represent a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a thioether group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphino group, a phosphono group, a phosphonate group, or an organic group, R ^b3、R^b4、R^b5、R^b6, and R ^b7 each independently represent a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a thioether group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfinyl group, a sulfo group, a sulfonate group, a phosphino group, a phosphonate group, an amino group, an ammonium group, or an organic group,

In the formula (B4), R ¹、R² and R ³ are the same as R ¹、R² and R ³ in the formula (B1), R ^b9 represents a hydrogen atom or a monovalent organic group, and R ^b10 represents an aromatic group having a substituent.

7. The varnish composition according to claim 1 to 3, wherein the content of the amide compound (C) is 1 to 40 parts by mass based on 100 parts by mass of the entire solid content.

8. A method for producing a polyimide resin, comprising the steps of:

A molding step of molding the varnish composition according to any one of claims 1 to 7; and

9. An additive for blending into a polyamic acid-containing liquid containing a polyamic acid (A) and a solvent (S) to obtain a varnish composition for forming a polyimide resin,

The additive comprises an amide compound (C),

The amide compound (C) is a compound represented by the following formula (C1):

R^c1-(-CO-NH-R^c2)_n···(C1)

In the formula (C1), R ^c1 is an n-valent organic group bonded to a carbonyl group via a carbon-carbon bond, R ^c2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, n is an integer of 1 to 4, and when n is 1, R ^c1 is an unsubstituted group selected from the group consisting of an alkyl group, a cycloalkyl group, a polycycloalkyl group, an alkenyl group, a cycloalkenyl group, a polycycloalkenyl group, an aryl group, a heteroaryl group, an arylalkyl group, an arylalkenyl group, a heteroarylalkyl group, and a heteroarylalkenyl group,

When the varnish composition is heated to obtain a polyimide resin, at least one of a decrease in thermal expansion coefficient, an increase in elongation at break, and an increase in tensile strength is caused in the obtained polyimide resin, as compared with the case where the polyamic acid-containing liquid is heated to obtain a polyimide resin.