Patent ID: 7166648

Claim:
A photoinitiator consisting essentially of a compound having a molecular weight of 1000 or less, and having a chemical structure represented by formula (1), wherein R 3 and R 4 independently denote an alkyl group having a carbon number of 1 to 8, and R 1 and R 2 independently denote 1) an electron attracting group, 2) an alkyl group having a carbon number of 1 to 8, or 3) an alkyl group having a carbon number of 1 to 8, which has an electron attracting group at the β,γ, or δ position with respect to both of the carbonyl groups, wherein the alkyl group 2) is methyl or ethyl group when each of the two substituents is the alkyl group 2), and the weight percentage of the C 3 O 2 chemical structure elements represented by the following formula (2), in the compound, is within the range of 17% to 54% of the total mass of the compound.