Heat-curable urethane resin composition

A solder resist obtained by curing a heat-curable resin composition comprising (A) a polyurethane having two or more carboxyl groups in one molecule and (B) a heat-curable component which is an epoxy resin,

• wherein the polyurethane (A) is obtained by reaction using a polyol (d) having a carboxyl group in addition to a polymer polyol (b) and a polyisocyanate (c), further by a terminal sealing reaction by means of a monocarboxylic acid compound (a) having both a functional group reactive with an isocyanate group to cause an addition reaction or a condensation reaction and a carboxyl group in its molecule;
• or by a terminal sealing reaction by means of a monohydroxy compound selected from an aliphatic alcohol or a monohydroxymono(meth)acrylate compound, without containing residues of isocyanate group derived from the polyisocyanate (c),
• wherein the polymer polyol (b) is a polycarbonate diol that is not a polyester-based polyol, wherein the polycarbonate diol contains as structural units, repeating units derived from a linear aliphatic diol and an alicyclic diol, the number average molecular weight of the polycarbonate diol is from 400 to 2,000 and the copolymerization ratio between the linear aliphatic diol and the alicyclic diol is from 3:7 to 7:3 in mass ratio,
• wherein the polyisocyanate (c) is one or more diisocyanates selected from the group consisting of 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethylene diisocyanate, (o, m, or p)-xylene diisocyanate, hydrogenated (o, m, or p)-xylene diisocyanate, methylenebis(cyclohexylisocyanate), trimethylhexamethylene diisocyanate, cyclohexane-1,3-dimethylene diisocyanate, cyclohexane-1,4-dimethylene diisocyanate and 1,5-naphthalene diisocyanate, and
• wherein the polyol (d) having a carboxyl group is a dihydroxy aliphatic carboxylic acid.