Epoxy resin-based coating composition

1. An epoxy resin coating composition which comprises, at least, epoxy resin, a thiol-type curing agent and a curing assistant, being composed of a mixture of two liquids of liquid (A) containing epoxy resin, a thiol-type curing agent and an aprotic volatile solvent and liquid (B) containing a curing assistant, which liquids are mixed just before using, wherein the thiol-type curing agent contains a branched compound containing a thiol group (P), which compound is an ester of polyhydric alcohol with secondary thiol group- or tertiary thiol group-containing carboxylic acid represented by formula (1)

HOCO(CH 2 ) n CR 1 R 2 SH  (1)

wherein R 1 represents a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms, R 2 represents a linear or branched alkyl group having 1 to 10 carbon atoms, and n represents an integer of 1 to 4,

wherein the epoxy resin coating composition does not contain a protic solvent, wherein the content of the thiol-type curing agent is 35 to 82 parts by mass based on 100 parts by mass of epoxy resin, and the content of the curing assistant is 0.1 to 20 parts by mass based on 100 parts by mass of the epoxy resin coating composition.

2. The epoxy resin coating composition according to claim 1 , wherein the branched compound containing a thiol group (P) is an ester of polyhydric alcohol with secondary thiol group- or tertiary thiol group-containing carboxylic acid represented by formula (2)

HOCOCH 2 CR 1 R 2 SH  (2)

wherein R 1 and R 2 have the same meanings as in claim 1 .

3. The epoxy resin coating composition according to claim 2 , wherein the branched compound containing a thiol group (P) is an ester of polyhydric alcohol with secondary thiol group- or tertiary thiol group-containing carboxylic acid represented by formula (3)

HOCOCH 2 CH(CH 3 )SH  (3)

4. The epoxy resin coating composition according to claim 1 , wherein the polyhydric alcohol is a polyhydric alcohol having 2 to 30 carbon atoms and having a valence of 2 to 6.

5. The epoxy resin coating composition according to claim 4 , wherein the polyhydric alcohol is at least one member selected from a group consisting of ethylene glycol, 1,2-propylenediol, 1,3-propanediol, 1,4-butanediol, trimethylolpropane, pentaerythritol, 2,2-bis(2,3-dihydroxypropyloxyphenyl)propane, glycerin, trimethylolethane, tris(2-hydroxyethyl)isocyanurate and dipenthaerythritol.

6. The epoxy resin coating composition according to claim 1 , wherein the branched compound containing a thiol group (P) is at least one compound selected from a group consisting of ethylene glycol bis(3-mercaptobutyrate), 1,2-propylene glycol bis(3-mercaptobutylate), 1,3-propylene glycol bis(3-mercaptobutylate), 1,4-butanediol bis(3-mercaptobutylate), 2,2-bis(3-(3-mercaptobutyryloxy)-2-hydroxypropyloxyphenyl)propane, glycerin tris(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptobutyrate), trimethylolpropane bis(3-mercaptobutyrate), trimethylolethane bis(3-mercaptobutyrate), pentaerythritol bis(3-mercaptobutyrate), trimethylolethane tris(3-mercaptobutyrate), pentaerythritol tris(3-mercaptobutyrate), tris(3-mercaptobutyryloxyethyl)isocyanurate, a compound wherein two 3-mercaptobutanoic acid have undergone addition to tris(2-hydroxyethyl)isocyanurate, pentaerythritol tetrakis(3-mercaptobutyrate), dipentaerythritol pentakis(3-mercaptobutyrate), dipentaerythritol hexakis(3-mercaptobutyrate), bisphenol A ethoxylate bis(3-mercaptobutyrate), 4,4′-(9-fluorenylidene)bis(2-phenoxyethanol)bis(3-mercaptobutyrate), pentaerythritol tris(3-mercaptovalerate), ethyleneglycol bis(3-mercaptovalerate), trimethylolpropane tris(3-mercaptovalerate), trimethylolpropane bis(3-mercaptovalerate), pentaerythritol bis(3-mercaptovalerate), pentaerythritol tris(3-mercaptovalerate), pentaerythritol tetrakis(3-mercaptovalerate), ethyleneglycol bis(3-mercaptoisovalerate), pentaerythritol bis(3-mercaptoisovalerate), trimethylpropane tris(3-mercaptoisovalerate), trimethylpropane bis(3-mercaptoisovalerate), pentaerythritol tris(3-mercaptoisovalerate) and pentaerythritol tetrakis(3-mercaptoisovalerate).

7. The epoxy resin coating composition according to claim 1 , wherein the solvent of the liquid (A) comprises one or more solvents selected from the group consisting of aliphatic hydrocarbon, aromatic hydrocarbon, ethers, esters other than the said thiol-type curing agent or curing assistant, ketones and N,N-dialkylamides; and the solvent does not contain any functional group of an alcoholic hydroxyl group, a phenolic hydroxyl group, a carboxyl group or an amino group.

8. The epoxy resin coating composition according to claim 1 , wherein the liquid (B) contains at least one amine-type curing agent selected from a group consisting of polyamine, modified polyamine and polyamide amine.

9. The epoxy resin coating composition according to claim 1 , wherein the epoxy resin is a glycidyl ether compound of polyol.

10. The epoxy resin coating composition according to claim 1 , wherein the curing assistant is tertiary amine.