Photopolymerizable composition containing a certain xanthene or thioxanthene dyestuff

A photopolymerizable composition comprising a polymerizable compound and a photopolymerization initiator, wherein the photopolymerization initiator comprises:

• (a) a xanthene or thioxanthene dyestuff having the formula ##STR4## wherein A represents an oxygen atom or a sulfur atom, X represents a hydrogen atom or a halogen atom, Y represents a carbon atom or a nitrogen atom, provided that when Y represents a carbon atom the bond with the adjacent carbon atom which is shown by the dotted line is a double bond, and when Y represents a nitrogen atom the bond with the adjacent carbon atom is a single bond, Z represents an oxygen atom wherein the bond with the adjacent carbon atom is a double bond, a lower alkoxy group or a lower alkanoyloxy group, R.sup.1 represents a lower alkyl group, a hydroxy lower alkyl group, a lower alkoxy lower alkyl group, a di- lower alkylamino lower alkyl group or an aryl group, R.sup.2 represents a hydrogen atom, a lower alkoxy group or a di- lower alkylamino group, or Z and R.sup.1 together represent the formula ##STR5## (b) a photosensitizer selected from the group consisting of N-phenylglycine, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, and a mixture of p-dimethylaminobenzoic acid isopentyl ester and 2,4-diisopropylthioxanthone, and
• (c) a peroxide.