Data storage disk

Claim 1

A storage disk for information that is to be read optically comprising a transparent data storage medium which is an at least ternary acrylic copolymer exhibiting low water absorption and consisting essentially of (A) 20 to 85 percent of methyl methacrylate; (B) at least 10 percent of a monomer of the formula ##STR5## wherein R' is hydrogen or methyl, R" is hydrogen or alkyl having from 1 to 7 carbon atoms, Ar is phenyl or phenyl substituted with alkyl having from 1 to 7 carbon atoms, n is an integer from 1 to 6, and m is 0 or 1, but n and m are not both 1; (C) at least 10 percent of a monomer of the formula ##STR6## wherein R'" is linear or branched hydrocarbon having from 2 to 20 carbon atoms, or alicyclic hydrocarbon having up to 12 carbon atoms and at least 5 ring carbon atoms; (D) 0 to 40 percent or styrene or alphamethyl styrene; (E) 0 to 9.9 percent of 4-methylstyrene; (F) 0 to 10 percent of a copolymerizable monomer, different from (A)-(E) whose solubility in water is less than 50 g per liter at 25° C. and which is an alpha-olefin, a halogenated olefin, an ester of an unsaturated dicarboxylic acid, or a vinyl ester of a C 3 -C 8 carboxylic acid; and (G) 0 to 10 percent of acrylonitrile, methylacrylonitrile, or a crosslinking monomer having in its molecule more than one group capable of free radical polymerization, all said percentages being by weight of said copolymer.