A cured product obtained from a composition comprising: a copolymer (i) including structural units represented by the general formulae, and below, and an amino resin (ii) (in the formulae, and, the letters a, b and c indicate the proportions of the respective structural units relative to the total number of the structural units denoted by a, b and c taken as 100 (a + b + c = 100), A 1 denotes a single bond, a C 1-10 divalent hydrocarbon group, a group represented by the formula below, or a group represented by the formula below, A 2 denotes a single bond, a C 1-10 divalent hydrocarbon group, a group represented by the formula below, or a group represented by the formula below, A 3 denotes a single bond, a C 1-10 divalent hydrocarbon group, a group represented by the formula below, or a group represented by the formula below, R 1, R 2 and R 3 are each independently a hydrogen atom or a methyl group, R 4 at each occurrence is a hydrogen atom, a methyl group, an ethyl group, a propyl group or a butyl group, and R 4 s may be the same as or different from each other, R 10 denotes a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a methoxy group, an ethoxy group, a propoxy group or a butoxy group, M denotes a hydrogen atom, an alkali metal ion, an alkaline earth metal ion having 1/2 atomic valence, an ammonium ion or an amine ion, and in the formulae,,,, and, n and n2 are each independently an integer of 1 to 10, n1 is an integer of 0 to 10, m is an integer of 1 to 6, m1 is an integer of 0 to 6, 1 is an integer of 0 to 4, R 5 and R 6 are each independently a hydrogen atom or a methyl group, * means that the indicated end is bonded to SO 3 M, ** means that the indicated end is bonded to the epoxy group, and *** means that the indicated end is bonded to the Si atom) a copolymer (i) including structural units represented by the general formulae, and below, and an amino resin (ii) (in the formulae, and, the letters a, b and c indicate the proportions of the respective structural units relative to the total number of the structural units denoted by a, b and c taken as 100 (a + b + c = 100), A 1 denotes a single bond, a C 1-10 divalent hydrocarbon group, a group represented by the formula below, or a group represented by the formula below, A 2 denotes a single bond, a C 1-10 divalent hydrocarbon group, a group represented by the formula below, or a group represented by the formula below, A 3 denotes a single bond, a C 1-10 divalent hydrocarbon group, a group represented by the formula below, or a group represented by the formula below, R 1, R 2 and R 3 are each independently a hydrogen atom or a methyl group, R 4 at each occurrence is a hydrogen atom, a methyl group, an ethyl group, a propyl group or a butyl group, and R 4 s may be the same as or different from each other, R 10 denotes a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a methoxy group, an ethoxy group, a propoxy group or a butoxy group, M denotes a hydrogen atom, an alkali metal ion, an alkaline earth metal ion having 1/2 atomic valence, an ammonium ion or an amine ion, and in the formulae,,,, and, n and n2 are each independently an integer of 1 to 10, n1 is an integer of 0 to 10, m is an integer of 1 to 6, m1 is an integer of 0 to 6, 1 is an integer of 0 to 4, R 5 and R 6 are each independently a hydrogen atom or a methyl group, * means that the indicated end is bonded to SO 3 M, ** means that the indicated end is bonded to the epoxy group, and *** means that the indicated end is bonded to the Si atom) (in the formulae, and, the letters a, b and c indicate the proportions of the respective structural units relative to the total number of the structural units denoted by a, b and c taken as 100 (a + b + c = 100), A 1 denotes a single bond, a C 1-10 divalent hydrocarbon group, a group represented by the formula below, or a group represented by the formula below, A 2 denotes a single bond, a C 1-10 divalent hydrocarbon group, a group represented by the formula below, or a group represented by the formula below, A 3 denotes a single bond, a C 1-10 divalent hydrocarbon group, a group represented by the formula below, or a group represented by the formula below, R 1, R 2 and R 3 are each independently a hydrogen atom or a methyl group, R 4 at each occurrence is a hydrogen atom, a methyl group, an ethyl group, a propyl group or a butyl group, and R 4 s may be the same as or different from each other, R 10 denotes a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a methoxy group, an ethoxy group, a propoxy group or a butoxy group, M denotes a hydrogen atom, an alkali metal ion, an alkaline earth metal ion having 1/2 atomic valence, an ammonium ion or an amine ion, and in the formulae,,,, and, n and n2 are each independently an integer of 1 to 10, n1 is an integer of 0 to 10, m is an integer of 1 to 6, m1 is an integer of 0 to 6, 1 is an integer of 0 to 4, R 5 and R 6 are each independently a hydrogen atom or a methyl group, * means that the indicated end is bonded to SO 3 M, ** means that the indicated end is bonded to the epoxy group, and *** means that the indicated end is bonded to the Si atom)