JPS6251304B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solvent-free coating composition. In particular, the present invention relates to a coating composition for forming a coating film, which has excellent adhesion, impact resistance, other water resistance, chemical resistance, and mechanical properties. In recent years, solvents contained in paints have become a problem in terms of work environment and work safety, such as air pollution, flammability, and inhalation toxicity.
Furthermore, there is an increasing demand for reducing the amount of water as much as possible from the viewpoint of resource conservation. In order to meet this requirement, when a solvent-free paint is created by combining an epoxy resin and a known acid anhydride, the resulting paint film has poor adhesion and is brittle, making it difficult to put it into practical use. be. On the other hand, there is a growing demand for epoxy resin paints that are non-yellowing and have excellent weather resistance.
It is difficult for amine-based curing agents to meet the first two requirements, and acid anhydride-based curing agents are expected to find a wide range of applications. However, as a result of various studies, the present inventors have found that it is possible to obtain a solvent-free coating composition that satisfies the various required performances as described above, and has completed the present invention. That is, the coating composition of the present invention contains an epoxy resin (), an acid anhydride (), an acid anhydride (-A), and a urethane bond-containing compound (-B) containing a terminal hydroxyl group as essential components. Polycarboxylic acid () and curing accelerator () obtained by reaction
Contains. In the present invention, the objects to be coated include metals, plastics, glass, and molded products thereof. The epoxy resin () used to obtain the coating resin composition of the present invention has the formula (Here Z is hydrogen atom, methyl group, ethyl group)
Epoxy resin (-1) having an average of more than one substituted or unsubstituted glycidyl ether group in the molecule represented by the formula (Here Z is hydrogen atom, methyl group, ethyl group)
Epoxy resin (-2) having an average of more than one substituted or unsubstituted glycidyl ester group in the molecule represented by the formula (Here Z is hydrogen atom, methyl group, ethyl group)
Epoxy resins (-3) having an average of more than one N-substituted or unsubstituted 1,2-epoxypropyl group in the molecule are included. Epoxy resin (-
1) is an epoxy resin obtained by glycidyl etherification of a phenolic hydroxyl group and an epoxy resin obtained by glycidyl etherification of an alcoholic hydroxyl group, and preferred examples of such epoxy resin (-1) include one or polyglycidyl ether (-1-1) of a polyhydric phenol having two or more aromatic nuclei, a polyhydric phenol having one or two or more aromatic nuclei and an alkylene oxide having 2 to 4 carbon atoms; Polyglycidyl ether (-
1-2) or polyglycidyl ether of an aliphatic polyhydroxyl compound that does not contain a nucleus (-1
-3) etc. However, polyglycidyl ether (-1-
1) means, for example, that a polyhydric phenol (A) having at least one aromatic nucleus and an epihalohydrin (b) are mixed in a conventional manner in the presence of a reaction amount of a basic catalyst or basic compound such as sodium hydroxide. An epoxy resin containing polyglycidyl ether as the main reaction product, or a polyhydric phenol (A) having at least one aromatic nucleus, and an epihalohydrin (b) are reacted in a catalytic amount of a basic catalyst such as triethylamine. It is an epoxy resin obtained by reacting a polyhydrin ether obtained by a conventional method in the presence of a basic compound such as sodium hydroxide. Similarly, polyglycidyl ether (-1-2) or polyglycidyl ether (-1-3) is an addition reaction between a polyvalent phenol having at least one aromatic nucleus and an alkylene oxide having 2 to 4 carbon atoms. A polyhydroxyl compound (B) derived from a polyhydroxyl compound (B) or an aliphatic polyhydroxy compound (c) not containing a nucleus is reacted with an epihalohydrin (b) in the presence of an amount of an acidic catalyst such as boron trifluoride by a conventional method. It is an epoxy resin containing as a main reaction product a polyglycidyl ether obtained by reacting a polyhalohydrin ether with a basic compound such as sodium hydroxide. Here, the polyvalent phenol (A) having at least one aromatic nucleus includes a mononuclear polyvalent phenol (A-1) having one aromatic nucleus and a polynuclear polyphenol having two or more aromatic nuclei. phenol (A-
There is 2). Examples of such mononuclear polyvalent phenols (A-1) include resorcinol, hydroquinone,
Pyrocatechol, phloroglucinol, 1,5
-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, and the like. In addition, as an example of polynuclear polyhydric phenol (A-2), the general formula [wherein Ar is an aromatic divalent hydrocarbon such as a naphthylene group and a phenylene group, with a phenylene group being preferred for the purpose of the present invention. Y′ and Y ₁ may be the same or different and may be an alkyl group such as methyl, n-propyl, n-butyl, n-hexyl, n-octyl, preferably up to 4 carbon atoms. an alkyl group or a halogen atom, that is, a chlorine atom, a bromine atom, an iodine atom, or a fluorine atom, or a methoxy group, a methoxymethyl group, an ethoxy group,
Alkoxy groups are preferably alkoxy groups having up to 4 carbon atoms, such as ethoxyethyl, n-butoxy, amyloxy. When a substituent other than a hydroxyl group is present on either or both of the above-mentioned aromatic divalent hydrocarbon groups, these substituents may be the same or different. m and z are integers having values ranging from 0 (zero) to the maximum value corresponding to the number of hydrogen atoms in the aromatic ring (Ar) that can be substituted with a substituent, and can be the same or different values. R ₁
For example,

[Formula] -O-, -S-, -SO-, -SO ₂ -, -(S) _o - (n is an integer of 2 to 6) or alkylene group such as methylene group, ethylene group, trimethylene group, tetramethylene group , pentamethylene group,
Hexamethylene group, 2-ethylhexamethylene group, octamethylene group, nonamethylene group, decamethylene group or alkylidene group, such as ethylidene group, propylidene group, isopropylidene group, isobutylidene group, amylidene group, isoamylidene group, 1-phenylethylidene group, ω-(halogenated dicyclopentadienyl) alkylidene group or cycloaliphatic group such as 1,4-cyclohexylene group, 1,3-cyclohexylene group, cyclohexylidene group or halogenated alkylene group or halogenated an alkylidene group, a halogenated cycloaliphatic group, an alkoxy- and aryloxy-substituted alkylidene group, an alkoxy- and aryloxy-substituted alkylene group, or an alkoxy- and aryloxy-substituted cycloaliphatic group; For example, methoxymethylene group, ethoxymethylene group, ethoxyethylene group, 2-ethoxytrimethylene group, 3-ethoxypentamethylene group, 1,4-(2-methoxycyclohexane) group, phenoxyethylene group, 2
- phenoxytrimethylene group, 1,3-(2-phenoxycyclohexane) group or alkylene group such as phenylethylene group, 2-phenyltrimethylene group, 1,7-phenylpentamethylene group,
2-phenyldecamethylene group or aromatic group such as phenylene group, naphthylene group or halogenated aromatic group such as 1,4-(2-chlorophenylene) group, 1,4-(2-fluorophenylene) group Alternatively, alkoxy- and aryloxy-substituted aromatic groups such as 1,4-(2-methoxyphenylene) group, 1,4-(2-ethoxyphenylene) group, 1,4-(2-n-propoxyphenylene) group ) group, 1,4-(2-phenoxyphenylene)
or an alkyl-substituted aromatic group such as 1,
4-(2-methylphenylene) group, 1,4-(2-
ethylphenylene) group, 1,4-(2-n-propylphenylene) group, 1,4-(2-n-butylphenylene) group, 1,4-(2-n-dodecylphenylene) group, formula (R is a hydrogen atom, a halogen atom, or a carbon number of 1 to
6 alkyl group), a group represented by the formula formula (wherein R ² is a hydrogen atom or a hydrocarbon group optionally substituted with a hydroxyl group or an epoxy group), or R ₁ is a divalent group such as It can also be a ring fused to one of the Ar groups, as in the case of the compound represented by R ₁
can also be a polyalkoxy group, such as polyethoxy, polypropoxy, polythioethoxy, prbutoxy, polyphenylethoxy, or R ₁ can be, for example, polydimethylsiloxy, polydiphenylsiloxy, polymethyl It can be a group containing a silicon atom, such as a phenylsiloxy group, or R ₁ is separated by an aromatic ring, a tertiary amino group, an ether bond, a carbonyl group, or a sulfur-containing bond, such as a sulfoxide. There are polynuclear dihydric phenols represented by the following two groups, which can be more than one alkylene group or alkylidene group. Particularly preferable polynuclear dihydric phenols have the general formula (In the formula, Y′ and Y ₁ have the same meanings as above,
m and z have values from 0 to 4, and R ₁ is preferably an alkylene or alkylidene group having 1 to 3 carbon atoms or a formula

【formula】

[Formula] or

It is a polynuclear divalent phenol represented by a saturated group represented by the formula: Q is 0 or 1). Examples of such dihydric phenols include 2,2-bis-(4-
hydroxyphenyl)propane, 2,4'-dihydroxydiphenylmethane, bis(2-hydroxyphenyl)methane, bis(4-hydroxyphenyl)methane, bis(4-hydroxy-2,6-dimethyl-3- methoxyphenyl)methane, 1,1
-bis(4-hydroxyphenyl)ethane, 1,
2-bis(4-hydroxyphenyl)ethane,
1,1-bis(4-hydroxy-2-chlorophenyl)ethane, 1,1-bis(3,5-dimethyl-4-hydroxyphenyl)ethane, 1,3-bis(3-methyl-4-hydroxyphenyl)ethane enyl)propane, 2,2-bis3,5-dichloro-4-hydroxyphenyl)propane, 2,2-bis(3-
phenyl-4-hydroxyphenyl)propane,
2,2-bis(3-isopropyl-4-hydroxyphenyl)propane, 2,2-bis(2-isopropyl-4-hydroxyphenyl)propane,
2,2-bis(4-hydroxynaphthyl)propane, 2,2-bis(4-hydroxyphenyl)pentane, 3,3-bis(4-hydroxyphenyl)pentane, 2,2-bis(4-hydroxy phenyl)heptane, bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)cyclohexylmethane, 1,2-bis(4-hydroxyphenyl)-1,2-bis(phenyl)propane, 2 ,2-bis(4-hydroxyphenyl)
-bis(hydroxyphenyl)alkanes such as 1-phenylpropane or 4,4'-dihydroxybiphenyl, 4,4'-dihydroxyoctachlorobiphenyl, 2,2'-dihydroxybiphenyl,
Dihydroxybiphenyl or bis-(4-hydroxyphenyl) sulfone such as 2,4'-dihydroxybiphenyl, 2,4'-dihydroxydiphenyl sulfone, chlor-2,4-dihydroxydiphenyl sulfone, 5-chlor -4,4'dihydroxydiphenylsulfone, 3'-chloro-4,4'-
Di(hydroxyphenyl) sulfone or bis(4-hydroxyphenyl) ether, such as dihydroxydiphenyl sulfone, 4,3'-(or 4,
2'- or 2,2'-dihydroxydiphenyl) ether, 4,4'-dihydroxy-2,6-dimethyldiphenyl ether, bis(4-hydroxy-3
-isobutylphenyl) ether, bis(4-hydroxy-3-isopropylphenyl) ether, bis(4-hydroxy-3-chlorophenyl) ether, bis(4-hydroxy-3-fluorophenyl) ether, bis(4-hydroxy-3-chlorophenyl) ether, -hydroxy-3-bromphenyl) ether, bis(4-hydroxynaphthyl) ether, bis(4-hydroxy-3-chlornaphthyl) ether, bis(2-hydroxy-3-bromphenyl) ether,
-hydroxybiphenyl) ether, 4,4'-dihydroxy-2,6-dimethoxy-diphenyl ether, 4,4'-dihydroxy-2,5-diethoxydiphenyl ether, etc. Also included are 1,1-bis(4-hydroxyphenyl)-2-phenylethane, 1,3,3-trimethyl-1-(4-hydroxyphenyl)-6-hydroxyindan, 2,
4-bis(p-hydroxyphenyl)-4-methylpentane is also suitable. Furthermore, another group of preferred polynuclear dihydric phenols has the general formula: (where R ₃ is a methyl or ethyl group, R ₁ and R ₂ are alkylidene groups having 1 to 9 carbon atoms or other alkylene groups, and p is 0 to 4), for example, 1,4-bis (4-hydroxybenzyl)benzene, 1,4-bis(4-hydroxybenzyl)tetramethylbenzene, 1,4-bis(4-
hydroxybenzyl)tetraethylbenzene,
Examples include 1,4-bis(p-hydroxycumyl)benzene and 1,3-bis(p-hydroxycumyl)benzene. Other polynuclear polyhydric phenols (A-2) include, for example, initial condensates of 1,1,2,2-tetrakis(4-hydroxyphenyl)ethanephenols and carbonyl compounds (e.g. Phenol resin initial condensation product, condensation reaction product of phenol and acrolein, condensation reaction product of phenol and glyoxal, condensation reaction product of phenol and pentanediallyl, condensation reaction product of resorcinol and acetone, xylene-phenol-formalin initial stage Condensation products), condensation products of phenols and polychloromethylated aromatic compounds (eg, condensation products of phenols and bischloromethylxylene), and the like. Therefore, here the polyhydroxyl compound (B)
means the above-mentioned polyhydric phenol (A) having at least one aromatic nucleus and alkylene oxide.
It is bonded to the phenol residue through an ether bond obtained by reacting the OH group and the epoxy group in the presence of a catalyst that promotes the reaction.
ROH (where R is an alkylene group derived from alkylene oxide) or (and) -(RO) _o H
(Here, R is an alkylene group derived from alkylene oxide, and one polyoxyalkylene chain may contain a different alkylene group. n is an integer of 2 or more indicating the number of polymerized oxyalkylene groups) It is a compound with In this case, the ratio of the polyhydric phenol (A) to the alkylene oxide is 1:1 (mol: mol) or more, but preferably the polyhydric phenol (A) is
The ratio of alkylene oxide to OH groups is from 1:1 to 10, preferably from 1:1 to 3 (equivalent: equivalent). Examples of the alkylene oxide here include ethylene oxide, propylene oxide, butylene oxide, etc., but those that generate side chains when reacting with the polyhydric phenol (A) to form an ether bond are particularly preferred; Examples include propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, and 1,3-butylene oxide, with propylene oxide being particularly preferred. Among such polyhydroxyl compounds (B), a particularly preferable group has the general formula (In the formula, Y', Y ₁ , m, z and R ₁ are the above (A-
It is the same as that of formula 2-1-1), where R is an alkylene group having 2 to 4 carbon atoms, and n ₁ and n ₂ have values of 1 to 3. Furthermore, another preferred group of such polyhydroxyl compounds has the general formula (In the formula, R ₁ , R ₂ , R ₃ and p are the above (A-2-
It is the same as that of formula 1-2), and R has 2 to 2 carbon atoms.
It is a polyhydroxyl compound represented by four alkylene groups, n ₁ and n ₂ having values of 1 to 3. Other polyhydroxyl compounds containing cores (B)
Examples include alicyclic polyols obtained by hydrogenating the aromatic nucleus of the polyhydroxyl compound (A). Examples of the aliphatic polyhydroxyl compound (C) that does not contain a nucleus include polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, dibutylene glycol, glycerin, and pentaerythritol; Polyhydroxyl compounds such as polyhydric alcohols or other active hydrogen-containing compounds (for example, compounds with groups such as amino groups, carboxyl groups, thiohydroxyl groups, etc.) and alkylene oxides, polyether polyols, etc. Examples include compounds. In addition, the epihalohydrin (b) here is
general formula (Here, Z is a hydrogen atom, a methyl group, an ethyl group,
X' is a halogen atom), and examples of such epihalohydrin (b) include epichlorohydrin, epipromhydrin, 1,2-epoxy-2-methyl-3-chloropropane, 1, 2-epoxy-2-ethyl-3
- Chlorpropane, etc. Examples of acidic catalysts that promote the reaction between the epihalohydrin (b) and the polyhydroxyl compound (B) or polyhydroxyl compound (C) include Lewis catalysts such as boron trifluoride, stannic chloride, zinc chloride, and ferric chloride. acids, derivatives exhibiting these activities (e.g.
A boron trifluoride-ether complex compound) or a mixture thereof can be used. In addition, basic catalysts that similarly promote the reaction between epihalohydrin (b) and polyhydric phenol (A) include alkali metal hydroxides (e.g., sodium hydroxide), alkali metal alcoholates (e.g., sodium ethylate), Tertiary amine compounds (e.g. triethylamine, triethanolamine), quaternary ammonium compounds (e.g. tetramethylammonium bromide) or mixtures thereof can be used, thus producing glycidyl ether simultaneously during such reaction. Examples of basic compounds that can be used to generate glycidyl ether by ring-closing the halohydrin ether produced as a result of the reaction through a dehydrohalogenation reaction include alkali metal hydroxides (e.g., sodium hydroxide), aluminic acid, Alkali metal salts (eg, sodium aluminate) and the like are conveniently used. Of course, these catalysts and basic compounds can be used as they are or as solutions in appropriate inorganic and/or organic solvents. In addition, epoxy resins (-
2) includes aliphatic polycarboxylic acids or aromatic polycarboxylic acids (e.g. phthalic acid, isophthalic acid,
Terephthalic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, endomethylenetetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid, maleic acid, phthalic acid, itaconic acid, succinic acid, glutaric acid , adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dimeric fatty acids, trimethic acid, trimesic acid, pyromellitic acid, cyclopentanetetracarboxylic acid, in addition to these halogen-substituted compounds, these polyhydric carboxylic acids and There are also polyglycidyl esters (including terminal carboxyl polyester oligomers obtained from polyhydric alcohols), such as glycidyl methacrylate synthesized from epihalohydrin (b) represented by the above general formula (2) and methacrylic acid. It also includes epoxy resins such as those obtained by polymerizing. Examples of epoxy resins (-3) having more than one N-substituted or unsubstituted 1,2-epoxypropyl group in the molecule include aromatic amines (e.g. aniline or alkyl substituents on the nucleus). aniline) and the epihalohydrin (b) represented by the above general formula (2), an initial condensate of an aromatic amine and an aldehyde (e.g. aniline-formaldehyde initial condensate, aniline-phenol-formaldehyde initial condensate) (b) and epihalohydrin (b). Other epoxy resins include epoxidized oils (e.g., epoxidized linseed oil, epoxidized soybean oil, epoxidized safflower oil, epoxidized tung oil,
epoxidized eno oil, epoxidized dehydrated castor oil, epoxidized oiticica oil, epoxidized tall oil, etc.), epoxidized fatty acids, epoxidized cyclic olefin compounds [e.g. vinyl cyclohexene dioxide, 1-(1-methyl-1,2-epoxy ethyl)-3,4-epoxy-4-methylcyclohexane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6 -Methylcyclohexanecarboxylate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, dicyclopentene dioxide, dipentene dioxide, tetrahydroindene dioxide, or these rings are replaced by the general formula (A
_-2-1 ), AralditeCY-175 (product name of Ciba Corporation), etc.), epoxidized conjugated diene polymers (e.g., epoxidized polybutadiene, epoxidized epoxidized styrene-butadiene copolymer, epoxidized acrylonitrile-styrene copolymer), epoxidized polymers containing unsaturated bonds (e.g. epoxidized polypropylene, epoxidized polyisobutene), polyglycidyl ether of polysiloxane In addition, examples of epoxy resins containing a heterocycle include epoxy resins in which an epoxy group is bonded to an oxazolidinone ring via a carbon atom, diglycidyl etherified furan, diglycidyl etherified dioxane, and diglycidyl spirobi(m-dioxane). Examples include etherified compounds, polyepoxy compounds obtained from imidazolines substituted with a polyunsaturated alkenyl group at the 2-position, triglycidyl isocyanurate, and the like. In addition, conventionally known epoxy resins such as the various epoxy resins described in "Manufacture and Application of Epoxy Resins" (edited by Hiroshi Kakiuchi) may be used. The acid anhydrides () used in the present invention include phthalic anhydride, tetrahydrophthalic anhydride, pyromellitic anhydride, dodecylsuccinic anhydride, maleic anhydride, chlorenditic anhydride, hexahydrophthalic anhydride, and methyl Examples include acid anhydrides such as tetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride. The polycarboxylic acid () of the present invention is an acid anhydride (
It is obtained by reacting -A) with a urethane bond-containing compound (-B) having a terminal hydroxyl group. The acid anhydride (-A) used at this time is the same as the acid anhydride (-), and the urethane bond-containing compound (-B) is the polyhydroxyl compound (-
B-1) is an organic polyisocyanate (-B-
2) can be obtained by reacting. At this time, the polyisocyanate (-B-
The isocyanate groups in 2) are used in an equivalent or less proportion, preferably 0.7 to 0.2. Polyhydroxyl compounds (-B-1) include polyether polyols (addition of alkylene oxide to various active hydrogen-containing compounds,
Various materials such as polytetramethylene glycol, polyester polyol, polyhydric alcohol, hydroxyl group-containing glycerides (castor oil, etc.), and polylactone diol can be used. Furthermore, organic polyisocyanate (-B-2)
As such, various aromatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates, etc. can be used. Polycarboxylic acid () can be obtained by reacting the above reaction components in a conventional manner, but if excess acid anhydride (i.e. ()
It is also possible to obtain a curing agent mixture by reacting the urethane bond-containing compound (-B) with the total amount of (-A) and (-A), and this method is simpler. As curing accelerators () in the composition of the present invention, dicyandiamide, imidazoles, tertiary amines, tris(dimethylaminomethyl)phenols, triethanolamine, hydrazide, urea,
alkali metal or alkaline earth metal hydroxides,
Octylate, naphthenate, etc. can be used. In the composition of the present invention, an epoxy resin ();
The blending ratio of acid anhydride () and polycarboxylic acid () is ()/() in a weight ratio of 95/5 to 30/70.
and preferably 80/20 to 60/40. Also, ()/(()+()) is an equivalent ratio of 100/120~
It is about 100/70, preferably 100/100 to 100/90. In addition, the blending ratio of the curing accelerator () is 0.5 to 3, preferably 1 to 100% by weight of the resin component ().
It is 1.5. In addition, other additives such as reactive diluents such as monoepoxides, non-reactive diluents, dyes, pigments, fillers, and thixotropic agents may be appropriately blended. The thus obtained coating composition of the present invention has excellent adhesion, impact resistance, other water resistance, chemical resistance, and mechanical properties, and is extremely useful as a solvent-free coating. EXAMPLES The present invention will be explained in more detail below with reference to Examples. Note that parts in the examples are based on weight. Production Example 1 100 parts of polyester polyol (average molecular weight = 1200) obtained by dehydration reaction of 1,4-butanediol and adipic acid and 7 parts of hexamethylene diisocyanate were stirred at 120°C for 4 hours in a nitrogen stream. Urethane prepolymer containing terminal hydroxyl groups
Obtained 107 copies. 107 parts of this urethane prepolymer was added to 500 parts of hexahydrophthalic anhydride, and the mixture was stirred and reacted at 100°C for 4 hours. Obtained urethane-modified acid anhydride (1)
The acid value was 590 and the viscosity was W (Gardner-Holdt method). Further, this urethane-modified acid anhydride (1) contained 20% by weight of polycarboxylic acid. Production example 2 Polypropylene glycol (average molecular weight =
300), 60 parts of glycerin-based triol (average molecular weight = 750), and 70 parts of hydrogenated MDI (methylene bisphenyl diisocyanate) in a nitrogen stream.
The reaction was carried out at 130°C for 5 hours to obtain a prepolymer containing terminal hydroxyl groups. Add 760 parts of methyltetrahydrophthalic anhydride to 230 parts of the prepolymer and heat at 105°C.
The mixture was stirred and reacted for 5 hours. The obtained urethane-modified acid anhydride (2) had an acid value of 540 and a viscosity of X (Gardner-Hold method). Further, this urethane-modified acid anhydride (2) contained 30% by weight of polycarboxylic acid. Production Example 3 100 parts of polyester polyol (average molecular weight = 1300) obtained by the dehydration reaction of 1,4-butanediol and isophthalic acid, 50 parts of castor oil, and 19 parts of xylylene diisocyanate were heated at 120°C in a nitrogen stream.
The mixture was stirred for 5 hours to obtain 169 parts of a urethane prepolymer containing terminal hydroxyl groups. Adding 169 parts of this urethane prepolymer to 254 parts of methylnadic anhydride,
The reaction was stirred at 110°C for 6 hours. The obtained urethane-modified acid anhydride (3) had an acid value of 420 and a viscosity of Z ₄ (Gardner-Hold method). In addition, this urethane-modified acid anhydride (3) contains 45% by weight of polycarboxylic acid.
It was included. Examples 1 to 3, Comparative Examples 1 to 3 Epoxy resin compositions having the formulation shown in Table 1 were prepared. This composition was applied to mild steel sheet JIS G-3141.
The film performance was measured by baking at 150°C for 3 hours. The results are shown in Table 1.

【table】

【table】

Claims (1)

[Claims] 1 Epoxy resin () as an essential component,
Acid anhydride (), acid anhydride (-A) and urethane bond-containing compound containing terminal hydroxyl group (-B)
A coating composition containing a polycarboxylic acid () obtained by reacting with a curing accelerator ().