Patent ID: 8124666

Claim:
An energy ray-curable ink composition comprising a coloring material; a polyfunctional monomer having three or more ethylenical double bonds in one molecule and a polymerizable monomer having one or two ethylenical double bonds in one molecule as polymerizable compounds, said polymerizable compounds consisting of (meth)acrylate monomers; an α-aminoalkylphenone-based compound and a thioxanthone-based compound as photopolymerization initiators; and a hindered amine-based compound having a 2,2,6,6-tetramethylpiperidinyl group as an antigelling agent, wherein said energy ray-curable ink composition contains the polyfunctional monomer in an amount of 10 to 65% by mass, the polymerizable monomer having one or two ethylenical double bonds in one molecule in an amount of 10 to 70% by mass, the α-aminoalkylphenone-based compound in an amount of 2 to 20% by mass, the thioxanthone-based compound in an amount of 0.1 to 10% by mass and the hindered amine-based compound in an amount of 0.01 to 2% by mass, based on the entire amount of the ink composition, and wherein said energy ray-curable ink composition contains the α-aminoalkylphenone-based compound in an amount of 40 to 99% by mass and the thioxanthone-based compound in an amount of 1 to 60% by mass, based on the entire amount of the photopolymerization initiator; wherein the thioxanthone-based compound is selected from the group consisting of thioxanthone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, and 1-chloro-4-propoxythioxanthone.