JP7633804B2 - Varnish composition, method for producing polyimide resin, and additives - Google Patents

Description

The present invention relates to a varnish composition, a method for producing a polyimide resin using the varnish composition, and an additive that can be blended into the varnish composition.

Polyimide resins have excellent heat resistance, mechanical strength, insulating properties, low dielectric constant, and other properties, and are therefore widely used as insulating and protective materials in electrical and electronic components, such as various elements and electronic substrates, including multilayer wiring boards.

Generally, polyimide resins are formed by heat-treating polyamic acid, which is obtained by polymerizing a tetracarboxylic dianhydride component and a diamine component in a polar organic solvent. Given this background, polyimide products for electronic materials are often supplied as a solution of a polyimide precursor such as polyamic acid. Specifically, when manufacturing electric and electronic parts, a solution of the polyimide precursor is supplied to the area where an insulating material or protective material is to be formed by a method such as coating or injection, and then the polyimide precursor solution is heat-treated to form the insulating material or protective material.

Technology related to such polyimide resins has been actively developed, and various resin compositions containing polyamic acid, etc. have been disclosed (see, for example, Patent Document 1, etc.).

JP 2018-58918 A

However, for polyimide resins, particularly polyimide films, depending on the application, a further reduction in the coefficient of thermal expansion, a further improvement in the elongation at break, or a further improvement in the tensile strength may be desired. However, when a polyimide resin is produced using the resin composition described in Patent Document 1 etc. as a varnish composition, there is a problem in that it is difficult to form a polyimide resin with a sufficiently low coefficient of thermal expansion, a sufficiently high elongation at break, or a sufficiently high tensile strength.

The present invention has been made in consideration of the above problems, and aims to provide a varnish composition capable of forming a polyimide resin having low thermal expansion, excellent elongation at break, or tensile strength, a method for producing a polyimide resin using the varnish composition, and an additive that can be blended into the varnish composition.

The present inventors have found that the above problems can be solved by blending a thermal base generator (B) and an unsaturated carboxylic acid derivative (C) having a specific structure with a varnish composition containing a polyamic acid (A) and a solvent (S), and have thus completed the present invention. More specifically, the present invention provides the following:

The first aspect of the present invention is a method for producing a cellular membrane comprising the steps of:
The composition comprises a polyamic acid (A), a thermal base generator (B) which generates a basic nitrogen-containing heterocyclic compound upon heating, an unsaturated carboxylic acid derivative (C), and a solvent (S),
The unsaturated carboxylic acid derivative (C) is represented by the following formula (C1):
R ^c1 -CR ^c2 =CR ^c3 -CO-R ^c4 ...(C1)
(In formula (C1), R ^c1 is an aromatic group which may have a substituent; R ^c2 and R ^c3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ^c4 is a group represented by -NH-R ^c5 or a group represented by -O-R ^c6 ; R ^c5 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; and R ^c6 is a hydrogen atom or a hydrocarbon group which may have a substituent.)
The present invention relates to a varnish composition for forming a polyimide resin, the varnish composition being a compound represented by the formula:

A second aspect of the present invention is a molding step of molding the varnish composition according to the first aspect;
and an imidization step of heating the molded varnish composition to imidize it.

A third aspect of the present invention is an additive used to obtain a varnish composition for forming a polyimide resin by being blended into a polyamic acid-containing liquid containing a polyamic acid (A), a thermal base generator (B) that generates a basic nitrogen-containing heterocyclic compound upon heating, and a solvent (S), the additive comprising:
The additive comprises an unsaturated carboxylic acid derivative (C),
The unsaturated carboxylic acid derivative (C) is represented by the following formula (C1):
R ^c1 -CR ^c2 =CR ^c3 -CO-R ^c4 ...(C1)
(In formula (C1), R ^c1 is an aromatic group which may have a substituent; R ^c2 and R ^c3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ^c4 is a group represented by -NH-R ^c5 or a group represented by -O-R ^c6 ; R ^c5 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; and R ^c6 is a hydrogen atom or a hydrocarbon group which may have a substituent.)
A compound represented by the formula:
This additive brings about at least one of a decrease in the thermal expansion coefficient, an increase in the breaking elongation, and an increase in the tensile strength of the resulting polyimide resin when the varnish composition is heated to obtain a polyimide resin, compared to when the polyimide resin is obtained by heating a polyamic acid-containing liquid.

The present invention provides a varnish composition capable of forming a polyimide resin having low thermal expansion, excellent elongation at break, or excellent tensile strength, a method for producing a polyimide resin using the varnish composition, and an additive that can be blended into the varnish composition.

<Varnish composition>
The varnish composition contains a polyamic acid (A), a thermal base generator (B) that generates a basic nitrogen-containing heterocyclic compound by heating, an unsaturated carboxylic acid derivative (C), and a solvent (S). The varnish composition is used for forming a polyimide resin.

The unsaturated carboxylic acid derivative (C) is a compound represented by the following formula (C1).
R ^c1 -CR ^c2 =CR ^c3 -CO-R ^c4 ...(C1)
(In formula (C1), R ^c1 is an aromatic group which may have a substituent; R ^c2 and R ^c3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ^c4 is a group represented by -NH-R ^c5 or a group represented by -O-R ^c6 ; R ^c5 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; and R ^c6 is a hydrogen atom or a hydrocarbon group which may have a substituent.)

The varnish composition contains a combination of a thermal base generator (B) that generates a basic nitrogen-containing heterocyclic compound upon heating and an unsaturated carboxylic acid derivative (C), and thus the varnish composition can be used to form a polyimide resin that is excellent in low thermal expansion, elongation at break, or tensile strength.

Below, we explain the essential and optional components of the varnish composition.

<Polyamic Acid (A)>
The varnish composition contains a polyamic acid (A). The polyamic acid (A) is a precursor polymer of a polyimide resin produced when the varnish composition is cured. The polyamic acid (A) is not particularly limited as long as it is a resin that has been conventionally used as a precursor polymer in producing a polyimide resin.

（式（ａ１）中、Ａ^１は炭素原子数６以上５０以下の４価の有機基であり、Ａ^２は２価の有機基である。） The polyamic acid (A) can usually be obtained by condensing a monomer component consisting of a tetracarboxylic dianhydride and a diamine compound.
The polyamic acid may have a structural unit represented by the following formula (a1).

(In formula (a1), ^A1 is a tetravalent organic group having 6 to 50 carbon atoms, and ^A2 is a divalent organic group.)

The following describes the tetracarboxylic dianhydride and diamine compound used in the production of polyamic acid (A), and the method for producing polyamic acid (A).

（式（ａ１－１）中、Ａ^１は炭素原子数６以上５０以下の４価の有機基である。） [Tetracarboxylic acid dianhydride]
The tetracarboxylic dianhydride that produces the structural unit represented by formula (a1) is represented by the following formula (a1-1).
The tetracarboxylic dianhydride represented by formula (a1-1) reacts with a diamine compound described later to give a polyamic acid (A) having a structural unit represented by formula (a1). Such tetracarboxylic dianhydrides may be used alone or in combination of two or more.

In formula (a1-1), A ¹ is a tetravalent organic group having 6 to 50 carbon atoms.

In formula (a1-1), A ¹ is a tetravalent organic group having from 6 to 50 carbon atoms, and may have one or more substituents in addition to the two acid anhydride groups represented by -CO-O-CO- in formula (a1-1).
Preferred examples of the substituent include a fluorine atom, an alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms, a fluorinated alkyl group having from 1 to 6 carbon atoms, and a fluorinated alkoxy group having from 1 to 6 carbon atoms. The compound represented by formula (a1-1) may contain a carboxy group or a carboxylate group in addition to the acid anhydride group.
When the substituent is a fluorinated alkyl group or a fluorinated alkoxy group, it is preferably a perfluoroalkyl group or a perfluoroalkoxy group.
The same applies to the above-mentioned substituents for one or more substituents that the aromatic group described below may have on the aromatic ring.

In formula (a1-1), A ¹ is a tetravalent organic group, the lower limit of the number of carbon atoms thereof being 6 and the upper limit being 50.
The number of carbon atoms constituting A ¹ is more preferably 8 or more, and even more preferably 12 or more. The number of carbon atoms constituting A ¹ is more preferably 40 or less, and even more preferably 30 or less. ^{A 1} may be an aliphatic group, an aromatic group, or a group combining 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. When ^{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 included in A ¹ as a group selected from a nitrogen-containing heterocyclic group, -CONH-, -NH-, -N=N-, -CH=N-, -COO-, -O-, -CO-, -SO-, -SO ₂ -, -S-, and -S-S-, and is more preferably included in A ¹ as a group selected from -O-, -CO-, -SO-, -SO ₂ -, -S-, and -S-S-.

The tetracarboxylic dianhydride can be appropriately selected from tetracarboxylic dianhydrides that have been used as a raw material for synthesizing polyamic acid. The tetracarboxylic dianhydride may be an aliphatic tetracarboxylic dianhydride or an aromatic tetracarboxylic dianhydride.

Examples of the aliphatic tetracarboxylic dianhydride include 2,2-bis(3,4-dicarboxy)propane dianhydride and bis(3,4-dicarboxy)methane dianhydride. The aliphatic tetracarboxylic dianhydride may also 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 a non-bridged alicyclic structure, and the bridged alicyclic structure may be linked to another bridged alicyclic structure and/or a non-bridged alicyclic structure by a spiro bond. When an aliphatic tetracarboxylic dianhydride is used, it is easy to obtain a cured product with excellent transparency using the composition.

（式（ａ２）中、Ｒ^ａ１１、Ｒ^ａ１２、及びＲ^ａ１３は、それぞれ独立に、水素原子、炭素原子数１以上５以下のアルキル基及びフッ素原子からなる群より選択される１種であり、ａは０以上１２以下の整数である。） As the aliphatic group constituting ^A1 in formula (a1-1), for example, a tetravalent group represented by the following formula (a2) can be used. When such a group is used, a polyimide resin having excellent transparency tends to be obtained.
In view of ease of purification of the raw material compound, a in formula (a2) is preferably 5 or less, more preferably 3 or less. In view of excellent chemical stability of the raw material compound that gives the structural unit represented by formula (a1), a is preferably 1 or more, more preferably 2 or more.
In formula (a2), a is particularly preferably 2 or 3.

(In formula (a2), R ^a11 , R ^a12 , and R ^a13 each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, and a fluorine atom, and a represents an integer of 0 to 12.)

Examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 3,3',4,4'-oxybisphthalic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride.

The aromatic tetracarboxylic dianhydride may also be, for example, a compound represented by the following general formulas (a1-2) to (a1-4).

In the above formulae (a1-2) and (a1-3), R ^a1 , R ^a2 and R ^a3 each represent an aliphatic group optionally substituted with halogen, an oxygen atom, a sulfur atom, an aromatic group connected via one or more divalent elements, or a divalent group constituted 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 each contain a carbon-carbon single bond, a carbon-oxygen-carbon ether bond or a halogen element (fluorine, chlorine, bromine, iodine). Examples of the compound represented by formula (a1-2) include 2,2-bis(3,4-dicarboxyphenoxy)propane dianhydride and 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride.

In the above formula (a1-4), R ^a4 and R ^a5 are either an aliphatic group which may be substituted with halogen, an aromatic group via one or more divalent elements, or a halogen, or a monovalent substituent constituted by a combination thereof. R ^a4 and R ^a5 may be the same or different. As the compound represented by formula (a1-4), difluoropyromellitic dianhydride, dichloropyromellitic dianhydride, etc. can also be used.

Examples of tetracarboxylic acid dianhydrides for obtaining fluorine-containing polyimides containing fluorine in the molecular structure include (trifluoromethyl)pyromellitic dianhydride, di(trifluoromethyl)pyromellitic dianhydride, di(heptafluoropropyl)pyromellitic dianhydride, pentafluoroethylpyromellitic dianhydride, bis{3,5-di(trifluoromethyl)phenoxy}pyromellitic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 5,5'-bis(trifluoromethyl)pyromellitic dianhydride, and 2,2',5,5'-tetrakis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxydiphenyl ether dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybenzophenone dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}benzene dianhydride, bis{(trifluoromethyl )dicarboxyphenoxy}(trifluoromethyl)benzene dianhydride, bis(dicarboxyphenoxy)(trifluoromethyl)benzene dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)benzene dianhydride, bis(dicarboxyphenoxy)tetrakis(trifluoromethyl)benzene dianhydride, 2,2-bis{4-(3,4-dicarboxyphenoxy)phenyl}hexafluoropropane dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}biphenyl dianhydride, bis{(trif Examples of such compounds include 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-dicarboxytrifluorophenoxy)tetrafluorobenzene dianhydride, and 1,4-bis(3,4-dicarboxytrifluorophenoxy)octafluorobiphenyl dianhydride.

As the tetracarboxylic dianhydride, it is preferable to use an alicyclic tetracarboxylic dianhydride in consideration of the heat resistance and transparency of the resulting polyimide resin.
Acid chlorides and esters of tetracarboxylic acids having the same basic skeleton as these can also be used.

The tetracarboxylic dianhydride may be used in combination with a dicarboxylic anhydride. The combined use of these carboxylic anhydrides may result in even better properties for the resulting imide ring-containing polymer, such as a polyimide resin. Examples of dicarboxylic anhydrides include maleic anhydride, succinic anhydride, itaconic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyl-end-methylene-tetrahydrophthalic anhydride, chlorendic anhydride, methyltetrahydrophthalic anhydride, glutaric anhydride, and cis-4-cyclohexene-1,2-dicarboxylic anhydride.

[Diamine Compound]
The diamine compound may typically be a compound represented by the following formula (a3-1): The diamine compound may be used alone or in combination of two or more kinds.
_H2NA2 - ^NH2 _... (a3-1)
(In formula (a3-1), ^A2 represents a divalent organic group.)

In formula (a3-1), ^A2 is a divalent organic group which may have one or more substituents in addition to the two amino groups in formula (a3-1).
Preferred examples of the substituent are a fluorine atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a fluorinated alkyl group having 1 to 6 carbon atoms, a fluorinated alkoxy group having 1 to 6 carbon atoms, or a hydroxyl group.
When the substituent is a fluorinated alkyl group or a fluorinated alkoxy group, it is preferably a perfluoroalkyl group or a perfluoroalkoxy group.

In formula (a3-1), the lower limit of the number of carbon atoms in the organic group for ^A2 is preferably 2, more preferably 6, and the upper limit is preferably 50, more preferably 30.
^A2 may be an aliphatic group, but is preferably an organic group containing one or more aromatic rings.

When ^A2 is an organic group containing one or more aromatic rings, the organic group may be one aromatic group itself, or may be a group in which two or more aromatic groups are bonded via an aliphatic hydrocarbon group, a halogenated aliphatic hydrocarbon group, or a bond containing a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom. Examples of the bond containing a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom contained in ^A2 include -CONH-, -NH-, -N=N-, -CH=N-, -COO-, -O-, -CO-, -SO-, -SO ₂ -, -S-, and -S-S-, and -O-, -CO-, -SO-, -SO ₂ -, -S-, and -S-S- are preferred.

The aromatic ring bonded to the amino group in ^A2 is preferably a benzene ring. When the ring bonded to the amino group in ^A2 is a condensed ring containing two or more rings, the ring bonded to the amino group in the condensed ring is preferably a benzene ring.
The aromatic ring contained in ^A2 may be an aromatic heterocycle.

（式（２１）～（２４）中、Ｒ^１１１は、水素原子、フッ素原子、水酸基、炭素原子数１以上４以下のアルキル基、及び炭素原子数１以上４以下のハロゲン化アルキル基よりなる群から選択される１種を示す。式（２４）中、Ｑは、９，９’－フルオレニリデン基、又は、式：－Ｃ_６Ｈ_４－、－ＣＯＮＨ－Ｃ_６Ｈ_４－ＮＨＣＯ－、－ＮＨＣＯ－Ｃ_６Ｈ_４－ＣＯＮＨ－、－Ｏ－Ｃ_６Ｈ_４－ＣＯ－Ｃ_６Ｈ_４－Ｏ－、－ＯＣＯ－Ｃ_６Ｈ_４－ＣＯＯ－、－ＯＣＯ－Ｃ_６Ｈ_４－Ｃ_６Ｈ_４－ＣＯＯ－、－ＯＣＯ－、－Ｏ－、－Ｓ－、－ＣＯ－、－ＣＯＮＨ－、－ＳＯ_２－、－Ｃ（ＣＦ_３）_２－、－Ｃ（ＣＨ_３）_２－、－ＣＨ_２－、－Ｏ－Ｃ_６Ｈ_４－Ｃ（ＣＨ_３）_２－Ｃ_６Ｈ_４－Ｏ－、－Ｏ－Ｃ_６Ｈ_４－Ｃ（ＣＦ_３）_２－Ｃ_６Ｈ_４－Ｏ－、－Ｏ－Ｃ_６Ｈ_４－ＳＯ_２－Ｃ_６Ｈ_４－Ｏ－、－Ｃ（ＣＨ_３）_２－Ｃ_６Ｈ_４－Ｃ（ＣＨ_３）_２－、－Ｏ－Ｃ_１０Ｈ_６－Ｏ－、－Ｏ－Ｃ_６Ｈ_４－Ｃ_６Ｈ_４－Ｏ－、及び－Ｏ－Ｃ_６Ｈ_４－Ｏ－で表される基よりなる群から選択される１種を示す。
Ｑの例示における、－Ｃ_６Ｈ_４－はフェニレン基であり、ｍ－フェニレン基、及びｐ－フェニレン基が好ましく、ｐ－フェニレン基がより好ましい。また、－Ｃ_１０Ｈ_６－は、ナフタレンジイル基であり、ナフタレン－１，２－ジイル基、ナフタレン－１，４－ジイル基、ナフタレン－２，３－ジイル基、ナフタレン－２，６－ジイル基、及びナフタレン－２，７－ジイル基が好ましく、ナフタレン－１，４－ジイル基、及びナフタレン－２，６－ジイル基がより好ましい。） When ^A2 is an organic group containing an aromatic ring, from the viewpoint of the heat resistance of a cured product formed using the resin composition, the organic group is preferably at least one of the groups represented by the following formulas (21) to (24).

In formulae (21) to (24), R ¹¹¹ represents one selected from the group consisting of a hydrogen atom, a fluorine atom, a hydroxyl group, an alkyl group having from 1 to 4 carbon atoms, and a halogenated alkyl group having from 1 to 4 carbon atoms. In formula (24), Q represents a 9,9'-fluorenylidene group, or a group represented by the formula: -C ₆ H ₄ -, -CONH-C ₆ H ₄ -NHCO-, _-NHCO -C ₆ H ₄ -CONH-, -O-C _{6 H 4} -CO-C ₆ H ₄ -O-, -OCO-C ₆ H ₄ -COO-, -OCO-C ₆ H ₄ -C 6 H 4 -COO-, -OCO-, -O-, -S-, -CO-, -CONH-, -SO ₂ -, -C(CF ₃ ) ₂ This represents one type selected from the group consisting of groups represented by -, -C(CH ₃ ) ₂ -, -CH ₂ -, -O-C ₆ H ₄ -C(CH ₃ ) ₂ -C ₆ H ₄ -O-, -O-C ₆ H _{4 -C} (CF ₃ ) _{2 -C 6} H ₄ -O-, _-O -C ₆ H ₄ -SO ₂ -C ₆ H ₄ -O-, -C(CH ₃ ) ₂ -C ₆ H ₄ -C(CH ₃ ) 2 -, -O-C ₁₀ H ₆ -O-, -O-C ₆ H 4 -C 6 H ₄ -O-, and -O-C ₆ H ₄ -O-.
In the examples of Q, -C ₆ H ₄ - is a phenylene group, preferably an m-phenylene group or a p-phenylene group, more preferably a p-phenylene group. Also, -C ₁₀ H ₆ - 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, or a naphthalene-2,7-diyl group, more preferably a naphthalene-1,4-diyl group or a naphthalene-2,6-diyl group.

In terms of the heat resistance of the polyimide resin to be formed, R ¹¹¹ in 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.

In terms of the heat resistance of the polyimide resin formed, Q in formula (24) is preferably a 9,9'-fluorenylidene group, -O-C ₆ H ₄ -O-, -C(CF ₃ ) ₂ -, -O-, -C(CH ₃ ) ₂ -, -CH ₂ -, -O-C ₆ H ₄ -C(CH ₃ ) ₂ -C ₆ H ₄ -O- or -CONH-, with -O-C ₆ H ₄ -O-, -C(CF ₃ ) ₂ - or -O- being particularly preferred.

When an aromatic diamine is used as the diamine compound represented by formula (a3-1), for example, the aromatic diamines shown below can be suitably used.
That is, examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminobenzanilide, 3,3'-diaminobenzanilide, 1,4-bis(4-aminophenoxy)benzene, 1, Examples of the bis(4-aminophenoxy)phenyl include 3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, and 4,4'-[1,4-phenylenebis(1-methylethane-1,1-diyl)]dianiline. Among these, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 4,4'-diaminodiphenyl ether, and 4,4'-diaminobenzanilide are preferred in view of cost, availability, and the like.

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

（式（Ｓｉ－１）中、Ｒ^１１２及びＲ^１１３は、それぞれ独立に、単結合又はメチレン基、炭素原子数２以上２０以下のアルキレン基、炭素原子数３以上２０以下のシクロアルキレン基、又は炭素原子数６以上２０以下のアリーレン基等であり、Ｒ^１１４、Ｒ^１１５、Ｒ^１１６、及びＲ^１１７は、それぞれ独立に、炭素原子数１以上２０以下のアルキル基、炭素原子数３以上２０以下のシクロアルキル基、炭素原子数６以上２０以下のアリール基、炭素原子数２０以下のアミノ基を含む基、－Ｏ－Ｒ^１１８で表される基（Ｒ^１１８は炭素原子数１以上２０以下の炭化水素基）、炭素原子数２以上２０以下の１以上のエポキシ基を含む有機基であり、ｌは、３以上５０以下の整数である。） From the viewpoint of further improving the mechanical properties of the resulting polyimide resin, a group represented by the following formula (Si-1) can also be preferably used as ^A2 .

(In formula (Si-1), R ¹¹² and R ¹¹³ are each independently a single bond or a methylene group, an alkylene group having from 2 to 20 carbon atoms, a cycloalkylene group having from 3 to 20 carbon atoms, or an arylene group having from 6 to 20 carbon atoms, etc.; R ¹¹⁴ , R ¹¹⁵ , R ¹¹⁶ , and R ¹¹⁷ are each independently an alkyl group having from 1 to 20 carbon atoms, a cycloalkyl group having from 3 to 20 carbon atoms, an aryl group having from 6 to 20 carbon atoms, a group containing an amino group having from 20 to 20 carbon atoms, a group represented by -O-R ¹¹⁸ (R ¹¹⁸ is a hydrocarbon group having from 1 to 20 carbon atoms), or an organic group containing one or more epoxy groups having from 2 to 20 carbon atoms, and l is an integer of from 3 to 50.)

In R ¹¹² and R ¹¹³ in formula (Si-1), the alkylene group having 2 to 20 carbon atoms is preferably an alkylene group having 2 to 10 carbon atoms from the viewpoint of heat resistance and residual stress, and examples of such groups include a dimethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, and a hexamethylene group.

As the cycloalkylene group having 3 to 20 carbon atoms for R ¹¹² and R ¹¹³ in formula (Si-1), from the viewpoints of heat resistance and residual stress, a cycloalkylene group having 3 to 10 carbon atoms is preferable, and examples thereof include a cyclobutylene group, a cyclopentylene group, a cyclohexylene group, and a cycloheptylene group.
In the formula (Si-1), the arylene group having 6 to 20 carbon atoms in R ¹¹² and R ¹¹³ is preferably an aromatic group having 6 to 20 carbon atoms in terms of heat resistance and residual stress, and examples of such groups include a phenylene group and a naphthylene group.

As the alkyl group having 1 to 20 carbon atoms for R ¹¹⁴ , R ¹¹⁵ , R ¹¹⁶ , and R ¹¹⁷ in formula (Si-1), an alkyl group having 1 to 10 carbon atoms is preferable from the viewpoint of heat resistance and residual stress, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, and a hexyl group.
As the cycloalkyl group having 3 to 20 carbon atoms for R ¹¹⁴ , R ¹¹⁵ , R ¹¹⁶ , and R ¹¹⁷ in formula (Si-1), a cycloalkyl group having 3 to 10 carbon atoms is preferable from the viewpoint of heat resistance and residual stress, and specific examples thereof include a cyclopentyl group, a cyclohexyl group, etc.
In the formula (Si-1), the aryl group having 6 to 20 carbon atoms for R ¹¹⁴ , R ¹¹⁵ , R ¹¹⁶ , and R ¹¹⁷ is preferably an aryl group having 6 to 12 carbon atoms from the viewpoints of heat resistance and residual stress, and specific examples thereof include a phenyl group, a tolyl group, and a naphthyl group.
Examples of the amino group-containing group having 20 or less carbon atoms for R ¹¹⁴ , R ¹¹⁵ , R ¹¹⁶ and R ¹¹⁷ in formula (Si-1) include an amino group and a substituted amino group (for example, a bis(trialkylsilyl)amino group).
Examples of the group represented by —O—R ¹¹⁸ in R ¹¹⁴ , R ¹¹⁵ , R ¹¹⁶ , and R ¹¹⁷ in formula (Si-1) include a methoxy group, an ethoxy group, a propoxy group, an isopropyloxy group, a butoxy group, a phenoxy group, a tolyloxy group, a naphthyloxy group, a propenyloxy group (for example, an allyloxy group), and a cyclohexyloxy group.
Of these, R ¹¹⁴ , R ¹¹⁵ , R ¹¹⁶ and R ¹¹⁷ are preferably a methyl group, an ethyl group, a propyl group or a phenyl group.

The group represented by formula (Si-1) can be derived by reacting a silicon-containing compound having amino groups at both ends with an acid anhydride. Specific examples of such silicon-containing compounds include methylphenyl silicone modified with amino groups at both ends (e.g., X-22-1660B-3 (number average molecular weight of about 4,400) and X-22-9409 (number average molecular weight of about 1,300) manufactured by Shin-Etsu Chemical Co., Ltd.), dimethyl silicone modified with amino groups at both ends (e.g., X-22-161A (number average molecular weight of about 1,600), X-22-161B (number average molecular weight of about 3,000) and KF8012 (number average molecular weight of about 4,400) manufactured by Shin-Etsu Chemical Co., Ltd.; BY16-835U (number average molecular weight of about 900) manufactured by Dow Corning Toray; and Silaplane FM3311 (number average molecular weight of about 1000) manufactured by JNC Corporation).

[Method for producing polyamic acid (A)]
The polyamic acid (A) having a structural unit represented by formula (a1) is typically a polymer obtained by reacting a tetracarboxylic dianhydride represented by the above formula (a1-1) with a diamine compound represented by the above formula (a3-1) in a solvent, and may be a polymer obtained by using one or more types of diamine compound and/or tetracarboxylic dianhydride. For example, it may be a polymer obtained by polycondensation of a diamine compound and a mixture containing two or more types of tetracarboxylic dianhydrides. The polyamic acid (A) may be used alone or in a mixture of two or more types.

The amounts of the tetracarboxylic dianhydride and the diamine compound used in synthesizing the polyamic acid (A) are not particularly limited, but the amount of the diamine compound used is 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, per 1 mol of the tetracarboxylic dianhydride.
The weight average molecular weight of the resulting polyamic acid (A) may be appropriately set depending on the application, and is, for example, not less than 5000, preferably not less than 7500, and more preferably not less than 10000. On the other hand, the weight average molecular weight of the resulting polyamic acid (A) is, for example, not more than 100000, preferably not more than 80000, and more preferably not more than 75000.
The weight average molecular weight can be adjusted to the above-mentioned value by adjusting the amounts of the tetracarboxylic dianhydride and the diamine compound mixed together, and reaction conditions such as the solvent and reaction temperature.

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

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

Among these organic solvents, nitrogen-containing polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea are preferred in terms of the solubility of the resulting polyamic acid (A).

The temperature at which the tetracarboxylic dianhydride and the diamine compound are reacted is not particularly limited as long as the reaction proceeds smoothly. Typically, the reaction temperature between the tetracarboxylic dianhydride and the diamine compound is preferably from -5°C to 150°C, more preferably from 0°C to 120°C, and particularly preferably from 0°C to 70°C. The time for reacting the tetracarboxylic dianhydride and the diamine compound varies depending on the reaction temperature, but typically, it is preferably from 1 hour to 50 hours, more preferably from 2 hours to 40 hours, and particularly preferably from 5 hours to 30 hours.

By the method described above, a solution containing the polyamic acid (A) is obtained.
The solution containing the polyamic acid (A) obtained as described above can be used as it is for preparing the varnish composition, or a paste or solid of polyamic acid obtained by removing at least a part of the solvent from the solution of polyamic acid (A) under reduced pressure at a low temperature at which conversion of the polyamic acid to a polyimide resin does not occur can be used for preparing the varnish composition.

The content of polyamic acid (A) in the varnish composition is appropriately determined taking into consideration the coatability of the varnish composition, the solubility of polyamic acid (A) in the solvent (S), etc. Typically, the content of 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 even more preferably 10% by mass or more and 30% by mass or less, based on the mass of the varnish composition.

<Solvent (S)>
The varnish composition contains a solvent (S). The varnish composition may be a paste containing a solid or a solution, but is preferably a solution. The solvent (S) may be used alone or in combination of two or more kinds.
The type of the solvent (S) is not particularly limited as long as it 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 dienes 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 monoacetates 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-methyl-3-methoxybutyl acetate, 3-ethyl-3-methoxybutyl acetate, 2-ethoxybutyl acetate, 4-ethoxybutyl acetate, monoether monoacetates of diols such as dibutyl acetate, 4-propoxybutyl acetate, 2-methoxypentyl acetate, 3-methoxypentyl acetate, 4-methoxypentyl acetate, 2-methyl-3-methoxypentyl acetate, 3-methyl-3-methoxypentyl acetate, 3-methyl-4-methoxypentyl acetate, and 4-methyl-4-methoxypentyl acetate; acetone, methyl ethyl ketone, diethyl ketone, methyl perisobutyl ketone, ethyl isobutyl ketone, and cyclohexane. Ketones such as dihydrohexanone; methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl 2-hydroxypropionate, ethyl 2-hydroxypropionate, 2-hydroxy-2-methyl, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethyl 3-ethoxypropionate, ethyl 3-propoxypropionate, propyl 3-methoxypropionate, isopropyl 3-methoxypropionate, ethyl ethoxyacetate, ethyl oxyacetate esters such as 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, propyl pyruvate, butyl pyruvate, methyl acetoacetate, ethyl acetoacetate, benzyl acetate, ethyl benzoate, diethyl oxalate, diethyl maleate, and γ-butyrolactone; ethers such as diethyl ether, dipropyl ether, dibutyl ether, dihexyl ether, benzyl methyl ether, benzyl ethyl ether, and tetrahydrofuran; aromatics 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; glycerin; and the like.
In addition, the solvent used in the reaction between the above-mentioned tetracarboxylic dianhydride and the diamine compound can also be suitably used as the solvent (S).

（式（Ｓ１）中、Ｒ^Ｓ１及びＲ^Ｓ２は、それぞれ独立に炭素原子数１以上３以下のアルキル基であり、Ｒ^Ｓ３は、水素原子、又は下記式（Ｓ１－１）若しくは下記式（Ｓ１－２）：

で表される基であり、Ｒ^Ｓ４は、水素原子又は水酸基であり、Ｒ^Ｓ５及びＲ^Ｓ６は、それぞれ独立に、水素原子、炭素原子数１以上３以下のアルキル基であり、Ｒ^Ｓ７及びＲ^Ｓ８は、それぞれ独立に水素原子、又は炭素原子数１以上３以下のアルキル基であり、Ｒ^Ｓ３が式（Ｓ１－１）で表される基である場合、Ｒ^Ｓ２及びＲ^Ｓ３は、互いに結合して環を形成してもよい。） The solvent (S) may contain a nitrogen-containing compound represented by the following formula (S1).

In formula (S1), R ^S1 and R ^S2 each independently represent an alkyl group having 1 to 3 carbon atoms, and R ^S3 represents 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 or 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 formula (S1-1), R ^S2 and R ^S3 may be bonded to each other to form a ring.

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

Among the nitrogen-containing compounds represented by formula (S1), specific examples in which R ^S3 is a group represented by formula (S1-1) and R ^S2 and R ^S3 are bonded to each other to form a ring include N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

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

Among the above examples of the nitrogen-containing compound represented by formula (S1), particularly preferred compounds include N,N-dimethylformamide, N,N-dimethylacetamide, N,N,2-trimethylpropionamide, and N,N,N',N'-tetramethylurea. Among these, N,N,2-trimethylpropionamide and N,N,N',N'-tetramethylurea are preferred. The boiling point of N,N,2-trimethylpropionamide under atmospheric pressure is 175°C, and the boiling point of N,N,N',N'-tetramethylurea under atmospheric pressure is 177°C. Thus, N,N,2-trimethylpropionamide and N,N,N',N'-tetramethylurea have relatively low boiling points among the organic solvents (S-I).
For this reason, when a varnish composition containing a solvent (S) including at least one selected from N,N,2-trimethylpropionamide and N,N,N',N'-tetramethylurea is used, the solvent (S) is unlikely to remain in the polyimide resin produced by heating during formation of the polyimide resin, and deterioration of the mechanical properties of the resulting polyimide resin is unlikely to occur.

Furthermore, N,N,2-trimethylpropionamide and N,N,N',N'-tetramethylurea are also useful in that they are low-hazard substances, as they are not designated as SVHCs (Substances of Very High Concern), substances of concern due to their harmful effects, under the REACH regulations of the EU (European Union).

The content of the solvent (S) in the varnish composition is not particularly limited as long as it does not impede 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 to 99.9% by mass, preferably 5% by mass to 70% by mass, and more preferably 10% by mass to 60% by mass.

<Thermal Base Generator (B)>
The varnish composition contains a thermal base generator (B) that generates a basic nitrogen-containing heterocyclic compound upon heating, for the purposes of smoothly promoting the production of a polyamide resin from the polyamic acid (A) by baking and of obtaining the above-mentioned effects by the combined use of the varnish composition with the unsaturated carboxylic acid derivative (C).

The basic nitrogen-containing heterocyclic compound generated by the thermal base generator (B) may be an aliphatic cyclic compound or an aromatic compound. When the basic nitrogen-containing heterocyclic compound is a compound in which two or more monocyclic rings are condensed, the two or more monocyclic rings may consist of only aliphatic rings, may consist of only aromatic rings, or may consist of a combination of aliphatic and aromatic rings.

Examples of the basic nitrogen-containing heterocyclic compound generated by the thermal base generator (B) include nitrogen-containing 5-membered ring compounds such as pyrrolidine, pyrazolidine, imidazolidine, triazolidine, tetrazolidine, pyrroline, pyrazoline, imidazoline, triazoline, tetrizoline, pyrrole, pyrazole, imidazole, triazole, and tetrazole; nitrogen-containing 6-membered ring compounds such as piperidine, piperazine, triazinane, pyridine, pyridazine, pyrimidine, and pyrazine; compounds in which these compounds are substituted with one or more substituents; and compounds in which these compounds are condensed with cyclopentane, cyclohexane, benzene, or the like.
When the basic nitrogen-containing heterocyclic compound has a substituent on the nitrogen-containing heterocycle, examples of the substituent include the same groups as R ¹ , R ² , and R ³ in formula (B1) described later.

（式（Ｂ１）中、Ｒ^１、Ｒ^２、及びＲ^３は、それぞれ独立に水素原子、ハロゲン原子、水酸基、シリル基、シラノール基、ニトロ基、ニトロソ基、スルホナト基、ホスフィノ基、ホスフィニル基、ホスホナト基、又は有機基である。）
で表されるイミダゾール化合物が好ましい。 In view of the good effect of promoting the formation of a polyimide resin from a polyamic acid (A), the basic nitrogen-containing heterocyclic compound generated by the thermal base generator (B) component is preferably a compound represented by the following formula (B1):

In formula (B1), R ¹ , R ² , and R ³ 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 sulfonato group, a phosphino group, a phosphinyl group, a phosphonato group, or an organic group.
Preferred is an imidazole compound represented by the following formula:

Examples of the organic group in R ¹ , R ² , 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 or a substituent other than a hydrocarbon group, such as a heteroatom, in the organic group. The organic group may be linear, branched, or cyclic. The organic group is usually monovalent, but may be a divalent or higher organic group when forming a cyclic structure.

^R1 and ^R2 may be bonded to form a cyclic structure, or may further include a bond of a heteroatom. Examples of the cyclic structure include a heterocycloalkyl group and a heteroaryl group, and may be a condensed ring.

The bonds contained in the organic groups of R ¹ , R ² , 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, or a silicon atom. Specific examples of bonds containing a heteroatom 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, and an azo bond.

As the bond containing a hetero atom which the organic groups of R ¹ , R ² , and R ³ may have, from the viewpoint of the 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 preferred.

When the organic groups of R ¹ , R ² , and R ³ are substituents other than a hydrocarbon group, R ¹ , R ² , and R ³ are not particularly limited as long as the effect of the present invention is not impaired. As described above, specific examples of ^{R 1} , R ² , and R ³ are halogen atoms, hydroxyl groups, silyl groups, silanol groups, nitro groups, nitroso groups, sulfonato groups, phosphino groups, phosphinyl groups, and phosphonato groups. The hydrogen atoms contained in the above-mentioned substituents may be substituted with a hydrocarbon group. In addition, the hydrocarbon group contained in the above-mentioned substituents may be any of linear, branched, and cyclic.

R ¹ , R ² , 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 base generator (B) is not particularly limited as long as it is a compound that can generate a basic nitrogen-containing heterocyclic compound by heating. For compounds (thermal base generators) that generate amines by the action of heat, which have been conventionally blended into various compositions, a compound to be used as the thermal base generator (B) can be obtained by replacing the skeleton derived from the amine generated upon heating with a skeleton derived from the desired basic nitrogen-containing heterocyclic compound.

（式（Ｂ２）中、Ｒ^１、Ｒ^２、及びＲ^３は、式（Ｂ１）におけるこれらと同様であり、Ｒ^ｂ１及びＲ^ｂ２は、それぞれ独立に水素原子、ハロゲン原子、水酸基、シリル基、シラノール基、ニトロ基、ニトロソ基、スルフィノ基、スルホ基、スルホナト基、ホスフィノ基、ホスフィニル基、ホスホノ基、ホスホナト基、又は有機基を示し、Ｒ^ｂ３、Ｒ^ｂ４、Ｒ^ｂ５、Ｒ^ｂ６、及びＲ^ｂ７は、それぞれ独立に水素原子、ハロゲン原子、水酸基、シリル基、シラノール基、ニトロ基、ニトロソ基、スルフィノ基、スルホ基、スルホナト基、ホスフィノ基、ホスフィニル基、ホスホノ基、ホスホナト基、アミノ基、アンモニオ基、又は有機基を示し、Ｒ^ｂ３、Ｒ^ｂ４、Ｒ^ｂ５、Ｒ^ｂ６、及びＲ^ｂ７は、それらの２つ以上が結合して環状構造を形成していてもよく、ヘテロ原子の結合を含んでいてもよい。）
で表される化合物が挙げられる。 A suitable thermal base generator (B) is represented by the following formula (B2):

(In formula (B2), R ¹ , R ² , and R ³ are the same as those in formula (B1), 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 sulfino group, a sulfo group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphono group, a phosphonato 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 silyl group, a silanol group, a nitro group, a nitroso group, a sulfino group, a sulfo group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphono group, a phosphonato group, an amino group, an ammonio group, or an organic group, R ^b3 , R ^b4 , R ^b5 , R ^b6 , and R Two or more of ^b7 may be bonded to form a cyclic structure, and may contain a bond to a heteroatom.
Examples of the compound include compounds represented by the following formula:

In formula (B2), R ¹ , R ² and R ³ are the same as those explained in formula (B1).

In 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 sulfino group, a sulfo group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphono group, a phosphonato group, or an organic group.

Examples of the organic group in R ^b1 and R ^b2 include the groups exemplified for R ¹ , R ² , and R ^3. This organic group may contain a heteroatom in the same manner as in the case of R ¹ , R ² , and R ^3. In addition, this organic group may be linear, branched, or cyclic.

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

In formula (B2), 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 sulfide group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfino group, a sulfo group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphono group, a phosphonato group, an amino group, an ammonio group, or an organic group.

Examples of the organic group in R ^b3 , R ^b4 , R ^b5 , R ^b6 , and R ^b7 include the groups exemplified for R ¹ , R ² , and R ^3. As in the case of R ¹ , R ² , and R ³ , this organic group may contain a bond or a substituent other than the hydrocarbon group, such as a heteroatom, in the organic group. In addition, this organic group may be linear, branched, or cyclic.

Two or more of R ^b3 , R ^b4 , R ^b5 , R ^b6 , and R ^b7 may be bonded to form a cyclic structure. Each of R ^b3 , R ^b4 , R ^b5 , R ^b6 , and R ^b7 may contain a bond containing a heteroatom. Examples of the cyclic structure include a heterocycloalkyl group and a heteroaryl group, and may be a condensed ring. For example, two or more of R ^b3 , R ^b4 , R ^b5 , R ^b6 , and R ^b7 may be bonded to form a condensed ring such as naphthalene, anthracene, phenanthrene, or indene by sharing the atom of the benzene ring to which R ^b3 , R ^b4 , R ^b5 , R ^b6 , and R ^b7 are bonded. When a condensed ring is formed, it is preferable in that the absorption wavelength becomes longer.

Among the above, R ^b3 , R ^b4 , R ^b5 , R ^b6 , and R ^b7 are each preferably independently 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 and a cyano group, an alkyl group having 1 to 10 carbon atoms and a hydroxyl group, an alkoxy group having 1 to 10 carbon atoms, an amide 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 having 6 to 20 carbon atoms and substituted with an electron donating group and/or an electron withdrawing group, a benzyl group substituted with an electron donating group and/or an electron withdrawing group, a cyano group, and a nitro group.

（式（Ｂ３）中、Ｒ^１、Ｒ^２、及びＲ^３は、式（Ｂ１）及び（Ｂ２）と同義である。Ｒ^ｂ１～Ｒ^ｂ６は式（Ｂ２）と同義である。Ｒ^ｂ８は、水素原子又は有機基を示す。Ｒ^ｂ３及びＲ^ｂ４が水酸基となることはない。Ｒ^ｂ３、Ｒ^ｂ４、Ｒ^ｂ５、及びＲ^ｂ６は、それらの２つ以上が結合して環状構造を形成していてもよく、ヘテロ原子の結合を含んでいてもよい。）
で表される化合物が好ましい。 Among the compounds represented by the above formula (B2), those represented by the following formula (B3):

(In formula (B3), R ¹ , R ² , and R ³ are the same as those in formulae (B1) and (B2). R ^b1 to R ^b6 are the same as those in formula (B2). R ^b8 represents a hydrogen atom or an organic group. R ^b3 and R ^b4 are not hydroxyl groups. Two or more of R ^b3 , R ^b4 , R ^b5 , and R ^b6 may be bonded to form a cyclic structure, or may contain a bond to a hetero atom.)
Preferred is a compound represented by the following formula:

The compound represented by formula (B3) has excellent solubility in the solvent (S) because it has the substituent --O--R ^b8 .

In 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 the groups exemplified for R ¹ , R ² , and R ^3. This organic group may contain a heteroatom in the organic group. In addition, this organic group may be linear, branched, or cyclic. R ^b8 is preferably a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and more preferably a methyl group.

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

（式（Ｂ４）中、Ｒ^１、Ｒ^２、及びＲ^３は、式（Ｂ１）におけるこれらと同様であり、Ｒ^ｂ９は、水素原子又は１価の有機基を表し、Ｒ^ｂ１０は置換基を有してもよい芳香族基を表し、Ｒ^ｂ９は他方のＲ^ｂ９又はＲ^ｂ１０と結合して環状構造を形成してもよい。） In addition, an imidazole compound represented by the following formula (B4) is also suitable as the thermal base generator (B).

(In formula (B4), R ¹ , R ² , and R ³ are the same as those in formula (B1), R ^b9 represents a hydrogen atom or a monovalent organic group, R ^b10 represents an aromatic group which may have a substituent, and R ^b9 may bond with the other R ^b9 or R ^b10 to form a cyclic structure.)

In 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, etc. When R ^b9 is an alkyl group, the alkyl group may have an ester bond or the like in the chain.

The alkyl group may be, for example, the same as R ^b11 in formula (B4a) described later. The number of carbon atoms in 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 which the alkyl group may have may be the same as the substituent which the alkyl group represented by R ^b11 in formula (B4a) described later may have.

The aromatic group which may have a substituent is the same as R ^b10 in formula (B4a) described later, and is preferably an aryl group, more preferably a phenyl group. The aromatic group which may have a substituent as R ^b9 may be the same as or different from R ^b10 .
In formula (B4), it is preferable that one R ^b9 is a hydrogen atom, and it is more preferable that 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 the other 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 the other R ^b9 or R ^b10 to form a cyclic structure.

The imidazole compound represented by formula (B4) may be a compound represented by the following formula (B4a):

（式（Ｂ４ａ）中、Ｒ^１、Ｒ^２、及びＲ^３は式（Ｂ１）におけるこれらと同様であり、Ｒ^ｂ１１は水素原子又はアルキル基であり、Ｒ^ｂ１０は置換基を有してもよい芳香族基であり、Ｒ^ｂ１２は置換基を有してもよいアルキレン基であり、Ｒ^ｂ１２はＲ^ｂ１０と結合して環状構造を形成してもよい。）

(In formula (B4a), R ¹ , R ² , and R ³ are the same as those in 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 bond with R ^b10 to form a cyclic structure.)

In formula (B4a), R ^b11 is a hydrogen atom or an alkyl group. When R ^b11 is an alkyl group, the alkyl group may be a linear alkyl group or a branched 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 even more preferably 1 to 5.

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

In formula (B4a), R ^b10 represents 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 an aromatic heterocyclic group which may have a substituent.

The type of aromatic hydrocarbon group is not particularly limited as long as it does not impede the object of the present invention. The aromatic hydrocarbon group may be a monocyclic aromatic group, a group formed by condensing two or more aromatic hydrocarbon groups, or a group formed by bonding two or more aromatic hydrocarbon groups with a single bond. As the aromatic hydrocarbon group, a phenyl group, a naphthyl group, a biphenylyl group, an anthryl group, or a phenanthrenyl group is preferable.

The type of aromatic heterocyclic group is not particularly limited as long as it does not impair the object of the present invention. The aromatic heterocyclic group may be a monocyclic group or a polycyclic group. Preferred aromatic heterocyclic groups are pyridyl, furyl, thienyl, imidazolyl, pyrazolyl, oxazolyl, thiazolyl, isoxazolyl, isothiazolyl, benzoxazolyl, benzothiazolyl, and benzimidazolyl.

Examples of the substituents that the phenyl group, polycyclic aromatic hydrocarbon group, or aromatic heterocyclic group may have include halogen atoms, hydroxyl groups, silyl groups, silanol groups, nitro groups, nitroso groups, sulfino groups, sulfo groups, sulfonato groups, phosphino groups, phosphinyl groups, phosphono groups, phosphonato groups, amino groups, ammonio groups, and organic groups. When the phenyl group, polycyclic aromatic hydrocarbon group, or aromatic heterocyclic group has multiple substituents, the multiple 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 or a substituent other than the hydrocarbon group, such as a heteroatom, in the organic group. The organic group may be linear, branched, cyclic, or a combination of these structures. The organic group is usually monovalent, but may be a divalent or higher organic group when it forms a cyclic structure, etc.

When an aromatic group has substituents on adjacent carbon atoms, the two substituents bonded to the adjacent carbon atoms may be bonded to form a cyclic structure. Examples of cyclic structures 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 bonds containing a heteroatom 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, and an azo bond.

From the viewpoint of the heat resistance of the imidazole compound represented by formula (B4) or formula (B4a), the bond containing a heteroatom 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.

When the organic group is a substituent other than a hydrocarbon group, the type of the substituent other than the hydrocarbon group is not particularly limited as long as it does not impair the purpose of the present invention. Specific examples of the substituent other than the hydrocarbon group include halogen atoms, hydroxyl groups, mercapto groups, sulfide groups, cyano groups, isocyano groups, cyanato groups, isocyanato groups, thiocyanato groups, isothiocyanato groups, silyl groups, silanol groups, alkoxy groups, alkoxycarbonyl groups, amino groups, monoalkylamino groups, dialkylaluminum groups, monoarylamino groups, diarylamino groups, carbamoyl groups, thiocarbamoyl groups, nitro groups, nitroso groups, carboxylate groups, acyl groups, acyloxy groups, sulfino groups, sulfonato groups, phosphino groups, phosphinyl groups, phosphonato groups, alkyl ether groups, alkenyl ether groups, and aryl ether groups. The hydrogen atoms contained in the above substituents may be substituted with a hydrocarbon group. The hydrocarbon groups contained in the above substituents may be linear, branched, or cyclic.

As the substituents of the phenyl group, the polycyclic aromatic hydrocarbon group, or the aromatic heterocyclic group, preferred are 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, and a halogen atom.

As R ^b10 , a phenyl group, a furyl group, or a thienyl group, each of which may have a substituent, is preferable, because the imidazole compound represented by Formula (B4) or Formula (B4a) can be synthesized inexpensively and easily, and the imidazole compound has good solubility in water or an organic solvent.

In formula (B4a), R ^b12 is an alkylene group which may have a substituent. The substituent which the alkylene group may have is not particularly limited as long as it does not impair the object of the present invention. Specific examples of the substituent which 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 straight chain alkylene group or a branched chain alkylene group, and a straight chain alkylene group is preferable. The number of carbon atoms of the alkylene group is not particularly limited, and is preferably 1 to 20, more preferably 1 to 10, and 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 straight-chain alkoxy group or a branched-chain alkoxy group. The number of carbon atoms of the alkoxy group as a substituent is not particularly limited, and is preferably 1 to 10, more preferably 1 to 6, and 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 the dialkylamino group may be a straight-chain alkyl group or a branched-chain alkyl group. The number of carbon atoms in the alkyl group contained in the monoalkylamino group or the dialkylamino group is not particularly limited, and is preferably 1 to 10, more preferably 1 to 6, and particularly preferably 1 to 3.

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

Among the imidazole compounds represented by the above formula (B4), the compound represented by the following formula (B4-1a) is preferred because it is inexpensive and can be easily synthesized.

（式（Ｂ４－１ａ）中、Ｒ^１、Ｒ^２、及び^Ｒ３は、式（Ｂ１）におけるこれらと同様であり、Ｒ^ｂ９は、式（Ｂ４）と同様であり、Ｒ^ｂ１３、Ｒ^ｂ１４、Ｒ^ｂ１５、Ｒ^ｂ１６、及びＲ^ｂ１７は、それぞれ独立に、水素原子、ハロゲン原子、水酸基、シリル基、シラノール基、ニトロ基、ニトロソ基、スルフィノ基、スルホ基、スルホナト基、ホスフィノ基、ホスフィニル基、ホスホノ基、ホスホナト基、アミノ基、アンモニオ基、又は有機基である。Ｒ^ｂ１３、Ｒ^ｂ１４、Ｒ^ｂ１５、Ｒ^ｂ１６、及びＲ^ｂ１７のうち少なくとも２つが結合して環状構造を形成してもよい。Ｒ^ｂ９はＲ^ｂ１５と結合して環状構造を形成してもよい。）
なお、式（Ｂ４－１ａ）において、Ｒ^ｂ１３、Ｒ^ｂ１４、Ｒ^ｂ１５、Ｒ^ｂ１６、及びＲ^ｂ１７は、全て水素原子であってもよい。また、式（Ｂ４－１）で表される化合物の溶媒（Ｓ）への溶解性の点で、Ｒ^ｂ１３、Ｒ^ｂ１４、Ｒ^ｂ１５、Ｒ^ｂ１６、及びＲ^ｂ１７のうちの少なくとも１つが水素原子以外の基であるのが好ましい。

(In formula (B4-1a), R ¹ , R ² , and ^R3 are the same as those in formula (B1), R ^b9 is the same as 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 sulfino group, a sulfo group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphono group, a phosphonato group, an amino group, an ammonio 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 may be bonded to R ^b15 to form a cyclic structure.)
In formula (B4-1a), R ^b13 , R ^b14 , R ^b15 , R ^b16 and R ^b17 may all be hydrogen atoms. In terms of the solubility of the compound represented by 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 formula (B4-1) described later. In formula (B4-1a), 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 (B4a) or formula (B4-1a), the compound represented by the following formula (B4-1) is preferred, from the viewpoints that it can be synthesized inexpensively and easily and has excellent solubility in water or organic solvents, and the compound represented by formula (B4-1) in which R ^b12 is a methylene group is more preferred.

（式（Ｂ４－１）中、Ｒ^１、Ｒ^２、及び^Ｒ３は式（Ｂ１）におけるこれらと同様であり、Ｒ^ｂ１１、及びＲ^ｂ１２は、式（Ｂ４ａ）におけるこれらと同様であり、Ｒ^ｂ１３、Ｒ^ｂ１４、Ｒ^ｂ１５、Ｒ^ｂ１６、及びＲ^ｂ１７は、それぞれ独立に、水素原子、ハロゲン原子、水酸基、シリル基、シラノール基、ニトロ基、ニトロソ基、スルフィノ基、スルホ基、スルホナト基、ホスフィノ基、ホスフィニル基、ホスホノ基、ホスホナト基、アミノ基、アンモニオ基、又は有機基である。Ｒ^ｂ１３、Ｒ^ｂ１４、Ｒ^ｂ１５、Ｒ^ｂ１６、及びＲ^ｂ１７のうち少なくとも２つが結合して環状構造を形成してもよい。Ｒ^ｂ１２はＲ^ｂ１５と結合して環状構造を形成してもよい。）
なお、式（Ｂ４－１）において、Ｒ^ｂ１３、Ｒ^ｂ１４、Ｒ^ｂ１５、Ｒ^ｂ１６、及びＲ^ｂ１７は、全て水素原子であってもよい。また、式（Ｂ４－１）で表される化合物の溶媒（Ｓ）への溶解性の点で、Ｒ^ｂ１３、Ｒ^ｂ１４、Ｒ^ｂ１５、Ｒ^ｂ１６、及びＲ^ｂ１７のうちの少なくとも１つが水素原子以外の基であるのが好ましい。

(In formula (B4-1), R ¹ , R ² , and ^R3 are the same as those in formula (B1), R ^b11 and R ^b12 are the same as those in formula (B4a), 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 sulfino group, a sulfo group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphono group, a phosphonato group, an amino group, an ammonio 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 may be bonded to R ^b15 to form a cyclic structure.)
In formula (B4-1), R ^b13 , R ^b14 , R ^b15 , R ^b16 and R ^b17 may all be hydrogen atoms. In terms of the solubility of the compound represented by 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 the organic groups that R ^b10 in formula (B4a) has as a substituent. ^{R b13} , R ^b14 , R ^b15 , and R ^b16 are preferably hydrogen atoms in terms of the solubility of the imidazole compound in the solvent (S).

Among these, at least one of R ^b13 , R ^b14 , R ^b15 , R ^b16 and R ^b17 is preferably the following substituent, and R ^b17 is particularly preferably the following substituent. When R ^b17 is the following substituent, R ^b13 , R ^b14 , R ^b15 and R ^b16 are preferably a hydrogen atom.
-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 that R ^b10 in formula (B4a) has 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.

（式（Ｂ４－１－１）において、Ｒ^１、Ｒ^２、及び^Ｒ３は式（Ｂ１）におけるこれらと同様であり、Ｒ^ｂ１１は、式（Ｂ４ａ）と同様であり、Ｒ^ｂ１９、Ｒ^ｂ２０、Ｒ^ｂ２１、Ｒ^ｂ２２、及びＲ^ｂ２３は、それぞれ独立に、水素原子、水酸基、シリル基、シラノール基、ニトロ基、ニトロソ基、スルフィノ基、スルホ基、スルホナト基、ホスフィノ基、ホスフィニル基、ホスホノ基、ホスホナト基、アミノ基、アンモニオ基、又は有機基である。ただし、Ｒ^ｂ１９、Ｒ^ｂ２０、Ｒ^ｂ２１、Ｒ^ｂ２２、及びＲ^ｂ２３のうち少なくとも１つは水素原子以外の基である。） Among the compounds represented by the above formula (B4-1), the compound represented by the following formula (B4-1-1) is preferred.

(In formula (B4-1-1), R ¹ , R ² , and ^R3 are the same as those in formula (B1), R ^b11 is the same as formula (B4a), 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 sulfino group, a sulfo group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphono group, a phosphonato group, an amino group, an ammonio group, or an organic group, with the proviso that at least one of R ^b19 , R ^b20 , R ^b21 , R ^b22 , and R ^b23 is a group other than a hydrogen atom.)

Among the compounds represented by formula (B4-1-1), it is preferable that at least one of R ^b19 , R ^b20 , R ^b21 , R ^b22 , and R ^b23 is the group represented by the above-mentioned -O-R ^b18 , and it is particularly preferable that R ^b23 is a group represented by -O-R ^b18 . When R ^b23 is a group represented by -O-R ^b18 , it is preferable that R ^b19 , R ^b20 , R ^b21 , and R ^b22 are hydrogen atoms.

Preferable specific examples of the imidazole compound represented by formula (B4) or formula (B4a) include the following compounds.

The content of the thermal base generator (B) in the varnish composition is preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 2 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of the total solid content. By using an amount of the thermal base generator (B) within this range, it is possible to effectively promote the production of polyamide resin from the polyamic acid (A) without excessive volatilization or sublimation of the thermal decomposition product of the thermal base generator (B).

<Unsaturated Carboxylic Acid Compound (C)>
The varnish composition contains an unsaturated carboxylic acid derivative (C) for the purpose of obtaining the above-mentioned effects by using it in combination with the thermal base generator (B).

The unsaturated carboxylic acid derivative (C) is a compound represented by the following formula (C1).
R ^c1 -CR ^c2 =CR ^c3 -CO-R ^c4 ...(C1)
(In formula (C1), R ^c1 is an aromatic group which may have a substituent; R ^c2 and R ^c3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ^c4 is a group represented by -NH-R ^c5 or a group represented by -O-R ^c6 ; R ^c5 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; and R ^c6 is a hydrogen atom or a hydrocarbon group which may have a substituent.)

R ^c1 in formula (C1) is an aromatic group which may have a substituent. The aromatic group which may have a substituent is the same as the aromatic group which may have a substituent as R ^b10 in formula (B4) described above.
The aromatic group which may have a substituent as R ^c1 is preferably a phenyl group which may have a substituent, or a naphthyl group which may have a substituent, and more preferably a phenyl group which may have a substituent.
When the aromatic group has a substituent, the number of the substituent is not particularly limited. When the aromatic group has a substituent, the number of the substituent is preferably 1 or more and 5 or less, more preferably 1 or 2, and even more preferably 1.
When R ^c1 is a phenyl group having one substituent, the position of the substituent on the phenyl group is preferably position 4. When ^{R c1} is a phenyl group having one substituent, the substituent is preferably an alkyl group, an alkoxy group, a halogen atom, a hydroxyl group, or an amino group. When a non-colored polyimide resin is formed using the varnish composition, the substituent on the phenyl group is preferably an alkyl group, an alkoxy group, or a halogen atom.

R ^c2 and R ^c3 in formula (C1) are each independently a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms. Examples of the alkyl group having from 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.
R ^c2 and R ^c3 are preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom. It is particularly preferable that ^{R c2} and R ^c3 are both hydrogen atoms.

In formula (C1), R ^c4 is a group represented by -NH-R ^c5 or a group represented by -O-R ^c6 . R ^c5 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. R ^c6 is a hydrogen atom or a hydrocarbon group which may have a substituent.
Examples of the alkyl group represented by R ^c5 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, and an n-hexyl group.
Examples of the hydrocarbon group represented by R ^c6 include an alkyl group having from 1 to 20 carbon atoms, an alkenyl group having from 1 to 20 carbon atoms, a cycloalkyl group having from 3 to 20 carbon atoms, a cycloalkenyl group having from 3 to 20 carbon atoms, an aryl group having from 6 to 20 carbon atoms, and an aralkyl group having from 7 to 20 carbon atoms.
Among the hydrocarbon groups represented by R ^c6 , preferred are alkyl groups having from 1 to 20 carbon atoms and aralkyl groups having from 7 to 20 carbon atoms, more preferred are alkyl groups having from 1 to 12 carbon atoms and aralkyl groups having from 7 to 12 carbon atoms, further preferred are alkyl groups having from 1 to 6 carbon atoms, a benzyl group and a phenethyl group, and particularly preferred are a methyl group and a benzyl group. Specific preferred examples of the alkyl groups having from 1 to 6 carbon atoms represented by R ^c6 are the same as the preferred examples of the alkyl groups represented by R ^c5 .
From the viewpoint of facilitating the formation of a polyimide resin with little coloration and excellent tensile strength, it is preferable that R ^c4 is a group represented by —O—R ^c6 , and R ^c6 is a benzyl group which may have a substituent.

Specific examples of preferred compounds represented by the following formula (C1) as the unsaturated carboxylic acid derivative (C) include cinnamic acid, 4-methoxycinnamic acid, 3-methoxycinnamic acid, 2-methoxycinnamic acid, 4-methylcinnamic acid, 3-methylcinnamic acid, 2-methylcinnamic acid, 4-chlorocinnamic acid, 3-chlorocinnamic acid, 2-chlorocinnamic acid, 4-bromocinnamic acid, 3-bromocinnamic acid, 2-bromocinnamic acid, methyl cinnamate, methyl 4-methoxycinnamate, methyl 3-methoxycinnamate, methyl 2-methoxycinnamate, methyl 4-methylcinnamate, methyl 3-methylcinnamate, methyl 2-methylcinnamate, methyl 4-chlorocinnamate, methyl 3- Methyl chlorocinnamate, methyl 2-chlorocinnamate, methyl 4-bromocinnamate, methyl 3-bromocinnamate, methyl 2-bromocinnamate, ethyl cinnamate, ethyl 4-methoxycinnamate, ethyl 3-methoxycinnamate, ethyl 2-methoxycinnamate, ethyl 4-methylcinnamate, ethyl 3-methylcinnamate, ethyl 2-methylcinnamate, ethyl 4-chlorocinnamate, ethyl 3-chlorocinnamate, ethyl 2-chlorocinnamate, ethyl 4-bromocinnamate, ethyl 3-bromocinnamate, ethyl 2-bromocinnamate, benzyl cinnamate, benzyl 4-methoxycinnamate, benzyl 3-methoxycinnamate, 2-methoxycinnamic acid Benzyl, 4-methyl benzyl cinnamate, 3-methyl benzyl cinnamate, 2-methyl benzyl cinnamate, 4-chloro benzyl cinnamate, 3-chloro benzyl cinnamate, 2-chloro benzyl cinnamate, 4-bromo benzyl cinnamate, 3-bromo benzyl cinnamate, 2-bromo benzyl cinnamate, cinnamic acid amide, 4-methoxy cinnamic acid amide, 3-methoxy cinnamic acid amide, 2-methoxy cinnamic acid amide, 4-methyl cinnamic acid amide, 3-methyl cinnamic acid amide, 2-methyl cinnamic acid amide, 4-chloro cinnamic acid amide, 3-chloro cinnamic acid amide, 2-chloro cinnamic acid amide, 4-bromo cinnamic acid amide, 3-bromo Examples of cinnamic acid amide include cinnamic acid amide, 2-bromo cinnamic acid amide, N-methyl cinnamic acid amide, N-methyl 4-methoxy cinnamic acid amide, N-methyl-3-methoxy cinnamic acid amide, N-methyl-2-methoxy cinnamic acid amide, N-methyl-4-methyl cinnamic acid amide, N-methyl-3-methyl cinnamic acid amide, N-methyl-2-methyl cinnamic acid amide, N-methyl-4-chloro cinnamic acid amide, N-methyl-3-chloro cinnamic acid amide, N-methyl-2-chloro cinnamic acid amide, N-methyl-4-bromo cinnamic acid amide, N-methyl-3-bromo cinnamic acid amide, and N-methyl-2-bromo cinnamic acid amide.

Among these, cinnamic acid, 4-methoxycinnamic acid, 3-methoxycinnamic acid, 4-methylcinnamic acid, 3-methylcinnamic acid, 4-chlorocinnamic acid, 3-chlorocinnamic acid, 4-bromocinnamic acid, 3-bromocinnamic acid, methyl cinnamate, methyl 4-methoxycinnamate, methyl 3-methoxycinnamate, methyl 4-methylcinnamate, methyl 3-methylcinnamate, methyl 4-chlorocinnamate, methyl 3-chlorocinnamate, methyl 4-bromocinnamate, methyl 3-bromocinnamate, benzyl cinnamate, 4-methoxycinnamic acid Benzyl, benzyl 3-methoxycinnamate, benzyl 4-methylcinnamate, benzyl 3-methylcinnamate, benzyl 4-chlorocinnamate, benzyl 3-chlorocinnamate, benzyl 4-bromocinnamate, benzyl 3-bromocinnamate, cinnamic acid amide, 4-methoxycinnamic acid amide, 3-methoxycinnamic acid amide, 4-methylcinnamic acid amide, 3-methylcinnamic acid amide, 4-chlorocinnamic acid amide, 3-chlorocinnamic acid amide, 4-bromocinnamic acid amide, and 3-bromocinnamic acid amide are preferred.
Among these, cinnamic acid, 4-methoxycinnamic acid, 4-methylcinnamic acid, 4-chlorocinnamic acid, 4-bromocinnamic acid, methyl cinnamate, methyl 4-methoxycinnamate, methyl 4-methylcinnamate, methyl 4-chlorocinnamate, methyl 4-bromocinnamate, benzyl cinnamate, benzyl 4-methoxycinnamate, benzyl 4-methylcinnamate, benzyl 4-chlorocinnamate, benzyl 4-bromocinnamate, cinnamic acid amide, 4-methoxycinnamic acid amide, 4-methylcinnamic acid amide, 4-chlorocinnamic acid amide, and 4-bromocinnamic acid amide are preferred.

The content of the unsaturated carboxylic acid derivative (C) in the varnish composition is preferably 1 part by mass or more and 40 parts by mass or less, and more preferably 2 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the total solid content. By using the unsaturated carboxylic acid derivative (C) in an amount within such a range, it is easy to obtain good effects in terms of improving the low thermal expansion, breaking elongation, tensile strength, etc., of the polyimide resin formed using the varnish composition.
The mass ratio ((C):(B)) of the contents of the unsaturated carboxylic acid derivative (C) and the thermal base generator (B) is, for example, 99:1 to 1:99. In terms of the stability of the varnish composition and the low thermal expansion, breaking elongation, tensile strength, and the like of the formed polyimide resin, the mass ratio is preferably 99:1 to 50:50, more preferably 95:5 to 60:40, and even more preferably 90:10 to 70:30.

<Other ingredients>
The varnish composition may contain various additives as required. Examples of the additives include colorants, dispersants, sensitizers, adhesion promoters, antioxidants, UV absorbers, anti-aggregation agents, defoamers, surfactants, etc. In addition, the varnish composition may contain various fillers or reinforcing materials as required.
The amount of each additive used is not particularly limited as long as it does not impair the object of the present invention. It may be appropriately adjusted within a range of, for example, 0.001% by mass to 60% by mass, preferably 0.05% by mass to 5% by mass, based on the mass of the solid content of the varnish composition.
The amount of the filler or reinforcing material used is not particularly limited as long as it does not impair the object of the present invention. The amount of the filler or reinforcing material used is typically preferably 1 mass% or more and 300 mass% or less, more preferably 5 mass% or more and 200 mass% or less, and even more preferably 10 mass% or more and 100 mass% or less, based on the mass of the polyamic acid (A).

As described above, the varnish composition described above can form a polyimide resin that has low thermal expansion, excellent elongation at break, and excellent tensile strength.

<Production method of polyimide resin>
a molding step of molding the varnish composition described above;
and an imidization step of heating the molded varnish composition to imidize it, thereby producing a polyimide resin.

When molding the varnish composition, the shape of the molded varnish composition is not particularly limited. The method of molding the varnish composition is not particularly limited. For example, the method of injecting the varnish composition into a mold of a desired shape, the method of filling the varnish composition into a mold using a squeegee or the like, the method of applying the varnish composition onto a substrate, etc. can be mentioned.
Among these methods, the method of applying a varnish composition onto a substrate is preferred because of the high demand for polyimide resin films and the ease with which the solvent (S) can be removed from the varnish composition during the production of the polyimide resin.
After the varnish composition is applied, the applied film is dried by heating and/or placing in a vacuum or reduced pressure environment to form a dry 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 it is a temperature at which a polyimide resin with desired properties can be obtained. The temperature at which the polyamic acid is heated is preferably 120° C. or higher and 430° C. or lower, more preferably 150° C. or higher and 420° C. or lower. By heating the varnish composition at a temperature in this range, the solvent (S) can be removed while suppressing thermal deterioration or thermal decomposition of the polyimide resin produced, and the polyimide resin can be produced.
In addition, since it is easy to form 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 generate a polyimide resin by heating the polyamic acid at a temperature of 70° C. or higher and 120° C. or lower for about 10 minutes to 2 hours, and then at a temperature of 150° C. or higher and 420° C. or lower for about 10 minutes to 2 hours, while gradually increasing the temperature.

The method for producing polyimide resin described above makes it possible to produce polyimide resin with low thermal expansion, excellent elongation at break, and excellent tensile strength.

Additives
The additive is used to obtain a varnish composition for forming a polyimide resin by blending it with a polyamic acid-containing liquid containing a polyamic acid (A), a thermal base generator (B) that generates a basic nitrogen-containing heterocyclic compound upon heating, and a solvent (S).
The additive contains an unsaturated carboxylic acid derivative (C). The unsaturated carboxylic acid derivative (C) is represented by the following formula (C1):
R ^c1 -CR ^c2 =CR ^c3 -CO-R ^c4 ...(C1)
(In formula (C1), R ^c1 is an aromatic group which may have a substituent; R ^c2 and R ^c3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ^c4 is a group represented by -NH-R ^c5 or a group represented by -O-R ^c6 ; R ^c5 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; and R ^c6 is a hydrogen atom or a hydrocarbon group which may have a substituent.)
It is a compound represented by the formula:

In formula (C1), R ^c1 to R ^c4 and preferred specific examples of the compound represented by formula (C1) are as described above.

The content of polyamic acid (A) in the varnish composition is appropriately determined taking into consideration the coatability of the varnish composition, the solubility of polyamic acid (A) in the solvent (S), etc. Typically, the content of 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 even more preferably 10% by mass or more and 30% by mass or less, based on the mass of the varnish composition.

The content of the solvent (S) in the varnish composition is not particularly limited as long as it does not impede 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 to 99.9% by mass, preferably 5% by mass to 70% by mass, and more preferably 10% by mass to 60% by mass.

The content of the thermal base generator (B) in the varnish composition is preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 2 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of the total solid content. By using an amount of the thermal base generator (B) within this range, it is possible to effectively promote the production of polyamide resin from the polyamic acid (A) without excessive volatilization or sublimation of the thermal decomposition product of the thermal base generator (B).

The content of the unsaturated carboxylic acid derivative (C) in the varnish composition is preferably 1 part by mass or more and 40 parts by mass or less, and more preferably 2 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the total solid content. By using an amount of the unsaturated carboxylic acid derivative (C) within this range, it is easy to obtain good effects in terms of improving the low thermal expansion, breaking elongation, tensile strength, etc., of the polyimide resin formed using the varnish composition.

When the above varnish composition is heated to obtain a polyimide resin, the resulting polyimide resin has at least one of a lower coefficient of thermal expansion, a lower elongation at break, and an improved tensile strength compared to when a polyimide resin is obtained by heating a polyamic acid-containing liquid.

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

Preparation Example 1
First, a three-neck flask with a capacity of 30 mL was heated with a heat gun and thoroughly dried. Next, the atmosphere in the three-neck flask was replaced with nitrogen, and the three-neck flask was made into a nitrogen atmosphere. 0.2045 g of 4,4'-diaminobenzanilide (0.90 mmol: manufactured by Nippon Junryo Pharmaceutical Co., Ltd.: DABAN) was added to the three-neck flask, and then N,N,N',N'-tetramethylurea (TMU) was added. The contents of the three-neck flask were stirred to obtain a slurry liquid in which aromatic diamine (DABAN) was dispersed in TMU.
Next, 0.3459 g (0.90 mmol) of a tetracarboxylic dianhydride of the following formula was added to the three-neck flask, and the contents of the flask were stirred for 12 hours at room temperature (25° C.) under a nitrogen atmosphere to obtain a reaction solution. In this way, a polyamic acid solution containing polyamic acid A-1 at a solid content concentration of 18 mass % was obtained. The obtained polyamic acid A-1 gives a transparent polyimide resin.

Preparation Example 2
A polyamic acid solution containing polyamic acid A-2 at a solid content concentration of 18% by mass was obtained in the same manner as in Preparation Example 1, except that the diamine component was changed to 9,9-bis(4-aminophenyl)fluorene. The obtained polyamic acid A-2 gives a transparent polyimide resin.

Preparation Example 3
A polyamic acid solution containing polyamic acid A-3 at a solid content concentration of 20 mass % was obtained in the same manner as in Preparation 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 obtained polyamic acid A-3 gives an opaque polyimide resin.

[Examples 1 to 16]
In Examples 1 to 16, the following C-1 to C-7 were used as the unsaturated carboxylic acid derivative (C).
C-1: Cinnamic acid C-2: 4-methoxycinnamic acid C-3: 3-methoxycinnamic acid C-4: 4-chlorocinnamic acid C-5: Cinnamic acid amide C-6: Methyl cinnamate C-7: Benzyl cinnamate

The polyamic acid solutions obtained in Preparation Examples 1 to 3 containing the polyamic acid (A) of the type and amount shown in Table 1, the thermal base generator (B) which is a compound having the structure shown below in the amount shown in Table 1, and the unsaturated carboxylic acid derivative (C) of the type and amount shown in Table 1 were mixed together, and the mixture was diluted with the type of solvent (S) shown in Table 1 so that the solids concentration was 15 mass %, thereby obtaining the varnish compositions of Examples 1 to 16.

[Comparative Examples 1 to 4 and Comparative Example 6]
The polyamic acid solutions obtained in Preparation Examples 1 to 3 containing the polyamic acid (A) of the type and amount shown in Table 1 were mixed with the thermal base generator (B) used in the Examples in the amount shown in Table 1, and the mixture was then diluted with the type of solvent (S) shown in Table 1 so that the solids concentration was 15 mass %, thereby obtaining the varnish compositions of Comparative Examples 1 to 4 and Comparative Example 6.

Comparative Example 5
A polyamic acid solution containing 100 parts by mass of polyamic acid A-1 was mixed with 20 parts by mass of the thermal base generator (B) used in the examples, and the mixture was then diluted with the type of solvent (S) shown in Table 1 so that the solid content concentration became 15% by mass, thereby obtaining a varnish composition of Comparative Example 5.

Using the varnish compositions of each of the Examples and Comparative Examples obtained as described above, polyimide resin films were formed according to the following method, and the yellowness index (YI), light transmittance, coefficient of thermal expansion (CTE), elongation at break, and tensile strength of the formed polyimide resin films were evaluated.

<Method of forming polyimide resin film>
The varnish composition obtained as described above was spin-coated onto a glass substrate (length: 100 mm, width: 100 mm, thickness: 1.3 mm) so that the thickness of the coating film after heat curing was 13 μm to form a coating film. The glass substrate with the coating film was then vacuum-dried at a temperature of 50° C. and a pressure of 13 Pa to remove the solvent in the coating film.
After removing the solvent, the glass substrate with the coating film was placed in an inert oven in which nitrogen was flowing at a flow rate of 3 L/min. In the inert oven, the glass substrate was left to stand under a nitrogen atmosphere at a temperature of 80° C. for 0.5 hours, then at a temperature of 100° C. for 0.5 hours, and further heated at a temperature of 400° C. (final heating temperature) for 0.5 hours to harden the coating film, thereby obtaining a polyimide-coated glass coated with a thin film (polyimide film) made of polyimide.
The obtained polyimide-coated glass was immersed in hot water at 90° C. to peel the polyimide film from the glass substrate, thereby obtaining a polyimide film (a film having dimensions of 100 mm length, 100 mm width, and 13 μm thickness).

<Yellowness (YI), light ray (total ray) transmittance>
The total light transmittance (light transmittance) value (unit: %) and yellowness index (YI) of the polyimide films of each of the Examples and Comparative Examples were determined by measurements in accordance with JIS K7361-1 (issued in 1997) using a measuring device manufactured by Nippon Denshoku Industries Co., Ltd. under the trade name "Haze Meter NDH-5000."
For Examples 15 and 16, and Comparative Example 6, the yellowness index (YI) and light (total light) transmittance were not measured because the polyimide films formed were not transparent.

<Coefficient of thermal expansion (CTE)>
A measurement film having a length of 20 mm and a width of 5 mm was formed from the polyimide film of each of the Examples and Comparative Examples.
Next, using a thermomechanical analyzer (manufactured by Shimadzu Corporation under the trade name "TMA-60") as the measuring device, the obtained film for measurement was heated from 30°C to 200°C at a heating rate of 10°C/min in a nitrogen atmosphere, then cooled to 30°C, and again heated from 30°C to 500°C at a heating rate of 10°C/min, and the change in length of the sample from 100°C to 350°C was measured, and the average value of the change in length per 1°C from 100°C to 350°C was calculated. The tensile mode was 49 mN.

<Breaking elongation and tensile strength>
For each of the polyimide films in the Examples and Comparative Examples, a "Super Dumbbell Cutter (type: SDMK-1000-D, conforming to the A22 standard of JIS K7139 (issued in 2009))" manufactured by Dumbbell Co., Ltd. was attached to an SD-type lever-type sample cutter (a cutter (model SDL-200) manufactured by Dumbbell Co., Ltd.)) was used to cut the polyimide film into a total length of 75 mm, a distance between tabs of 57 mm, a length of a parallel portion of 30 mm, a radius of a shoulder of 30 mm, a width of an end portion of 10 mm, a width of a parallel portion at the center of 5 mm, and a thickness of 13 μm. Dumbbell-shaped test pieces (test pieces conforming to the standard of JIS K7139 Type A22 (reduced-scale test piece) except for the thickness of 13 μm) were prepared as measurement samples.
Next, using a Tensilon type universal testing machine (model number "UCT-10T" manufactured by A & D Co., Ltd.), the measurement sample was arranged so that the width between the gripping tools was 57 mm and the width of the gripping part was 10 mm (total width of the end), and then a tensile test was performed in which the measurement sample was pulled under conditions of a full-scale load of 0.05 kN and a test speed of 1 to 300 mm/min, to determine the tensile strength and breaking elongation values.
The above test is a test conforming to JIS K7162 (issued in 1994).
The breaking elongation value (%) was calculated by the following formula, where L0 is the length of the parallel part of the test piece (=length of the parallel part: 30 mm) and L is the length of the parallel part of the test piece until it breaks (length of the parallel part of the test piece at break: 30 mm + α):
[Breaking elongation (%)] = {(L - L0) / L0} x 100
was calculated and found.

In addition, the varnish compositions of each Example and Comparative Example were left to stand at 23°C for 5 days to carry out a storage stability test. Specifically, the varnish compositions after 5 days of storage were evaluated by visual observation, and the haze of the polyimide film produced by the above method using the varnish composition after 5 days of storage was evaluated. COH7700 manufactured by Nippon Denshoku Industries Co., Ltd. was used to measure the haze. For Example 15, Example 16, and Comparative Example 6, the haze was not measured because the polyimide film formed was not transparent.
The evaluation criteria based on visual observation of the varnish composition are as follows.
○: No change in appearance from the start of storage.
Δ: Slight cloudiness or gelation was observed.
×: Significant cloudiness or gelation is observed.

Comparisons of Examples 1 to 7 with Comparative Examples 1 and 3, comparisons of Examples 8 to 14 with Comparative Examples 2 and 4, and comparisons of Examples 15 and 16 with Comparative Example 6 show that by blending a thermal base generator (B) and an unsaturated carboxylic acid derivative (C) having a predetermined structure with a varnish composition containing a polyamic acid (A) and a solvent (S), a polyimide resin having a low coefficient of thermal expansion (CTE) and excellent tensile elongation and tensile strength can be formed.
On the other hand, according to Comparative Examples 1 to 6, it is found that even if nothing is added or only the thermal base generator (B) is added to a varnish composition containing a polyamic acid (A) and a solvent (S), a polyimide resin having a low coefficient of thermal expansion (CTE) and excellent tensile elongation and tensile strength cannot be formed.
In addition, the varnish composition containing the polyamic acid (A), the thermal base generator (B), the unsaturated carboxylic acid derivative (C) having a specific structure, and the solvent (S) also has excellent storage stability.

Claims (6)

The composition comprises a polyamic acid (A), a thermal base generator (B) which generates a basic nitrogen-containing heterocyclic compound upon heating, an unsaturated carboxylic acid derivative (C), and a solvent (S),
The unsaturated carboxylic acid derivative (C) is represented by the following formula (C1):
R ^c1 -CR ^c2 =CR ^c3 -CO-R ^c4 ...(C1)
(In formula (C1), R ^c1 is an aromatic group which may have a substituent, R ^c2 and R ^c3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ^c4 is a group represented by -O -R ^c6 , and R ^c6 is a benzyl group which may have a substituent .)
A varnish composition for forming a polyimide resin, which is a compound represented by the formula: The basic nitrogen-containing heterocyclic compound is represented by the following formula (B1):

In formula (B1), R ¹ , R ² , and R ³ each independently represent a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a sulfide group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphonato group, or an organic group.
The varnish composition according to claim 1 , wherein the compound is represented by the formula: The thermal base generator (B) is represented by the following formula (B2):

(In formula (B2), R ¹ , R ² , and R ³ are the same as those in formula (B1), R ^b1 and R ^b2 each independently represent a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a sulfide group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfino group, a sulfo group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphono group, a phosphonato 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 sulfide group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfino group, a sulfo group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphono group, a phosphonato group, an amino group, an ammonio group, or an organic group, and R ^b3 and R Two or more of ^{R b4} , R ^b5 , R ^b6 , and R ^b7 may be bonded to form a cyclic structure, and may contain a bond to a heteroatom.
and a compound represented by the following formula (B4):

(In formula (B4), R ¹ , R ² , and R ³ are the same as those in formula (B1), R ^b9 represents a hydrogen atom or a monovalent organic group, R ^b10 represents an aromatic group which may have a substituent, and R ^b9 may be bonded to the other R ^b9 or R ^b10 to form a cyclic structure.)
The varnish composition according to claim 2 , wherein the compound is one or more selected from the group consisting of compounds represented by the formula: The varnish composition according to any one of claims 1 to 3 , wherein the content of the unsaturated carboxylic acid derivative (C) is 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the total solid content. A molding step of molding the varnish composition according to any one of claims 1 to 4 ;
and an imidization step of heating the molded varnish composition to imidize it. An additive used to obtain a varnish composition for forming a polyimide resin by being blended with a polyamic acid-containing liquid containing a polyamic acid (A), a thermal base generator (B) which generates a basic nitrogen-containing heterocyclic compound upon heating, and a solvent (S),
the additive comprises an unsaturated carboxylic acid derivative (C),
The unsaturated carboxylic acid derivative (C) is represented by the following formula (C1):
R ^c1 -CR ^c2 =CR ^c3 -CO-R ^c4 ...(C1)
(In formula (C1), R ^c1 is an aromatic group which may have a substituent, R ^c2 and R ^c3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ^c4 is a group represented by -O -R ^c6 , and R ^c6 is a benzyl group which may have a substituent .)
A compound represented by the formula:
An additive which, when the varnish composition is heated to obtain a polyimide resin, causes at least one of a decrease in thermal expansion coefficient, a decrease in elongation at break, and an increase in tensile strength of the resulting polyimide resin compared to a polyimide resin obtained by heating the polyamic acid-containing liquid.