Patent ID: 8128746

Claim:
An ink composition comprising (i) a polymerization initiator, (ii) a (meth)acrylate which includes a (meth)acryloyl group and an additional double bond having, at an α position, a carbon atom having an sp 3 hybrid orbital, (iii) an N-vinyllactam as another polymerizable compound other than the (meth)acrylate having a double bond with a carbon atom having an sp 3 hybrid orbital at an α position, and (iv) a colorant, wherein the (meth)acrylate is represented by following formula (I): wherein R 1 to R 4 each independently represents a hydrogen atom or an alkyl group, all of R 1 to R 4 are not hydrogen atoms, and at least one alkyl group represented by R 1 to R 4 is bonded to an acrylate group represented by formula (II), or a methacrylate group represented by formula (III), directly or via a bivalent linking group: wherein in the formula (II) or (III), * represents a binding site for the alkyl group represented by any one of R 1 to R 4 , or for a linkage bound to the alkyl group, wherein in the formula (I), two or more alkyl groups represented by R 1 to R 4 are not bonded to form a ring structure, the alkyl group represented by R 1 , R 2 , R 3 , or R 4 has two or more carbon atoms, and the other three of R 1 to R 4 are selected from the group consisting of a hydrogen atom and a methyl group, and wherein the bivalent linking group in formula (I) is an alkylene group, or an alkylene group wherein a methylene group in the alkylene group is replaced with a divalent group selected from —O—, —S—, or —NR 5 — wherein R 5 represents an alkyl group, and wherein the content of the colorant is from 1 to 10% by mass with respect to the total content of the ink composition.