Ultraviolet-curable composition for optical disk, and optical disk

An ultraviolet-curable composition for forming a light transmission layer in an optical disk in which at least both a light reflection layer and the light transmission layer are laminated on a substrate, and in which a data is read using a laser beam striking from a light transmission layer side,

• the ultraviolet-curable composition comprising:
• an epoxy(meth)acrylate;
• a (meth)acrylate having two radical polymerizable unsaturated bonds;
• and a free-radical photopolymerization initiator, wherein
• the (meth)acrylate having two radical polymerizable unsaturated bonds comprises a (meth)acrylate represented by formula (1):
• [in the formula (1),
• R1 represents a hydrogen atom or a methyl group,
• R2 represents a single bond, an alkylene oxide, or a group represented by formula (2):
• (wherein X1 represents an alkylene group having 2 to 12 carbon atoms with or without a branched chain, and m represents an integer of 1 to 5),
• R3 and R4 represents an alkylene group having 2 to 12 carbon atoms with or without a branched chain, and
• R5 represents a single bond, an alkylene oxide group, or a group represented by formula (3):
• (wherein X2 represents an alkylene group having 2 to 12 carbon atoms with or without a branched chain and n represents an integer of 1 to 5)],
• the (meth)acrylate represented by the formula (1) accounts for 10 to 40% by mass of the ultraviolet-curable compounds in the ultraviolet-curable composition, and
• the free-radical photopolymerization initiator accounts for 1 to 4% by mass of the ultraviolet-curable composition.