Process for producing abrasion-resistant cast article

Claim 1

An improvement in a process for producing a synthetic resin cast article having an abrasion-resistant polymer surface layer integrated with the polymer body, which process includes the steps of: a. spreading onto all or part of the inner surface of a mold member a liquid polymerizable material selected from (i) a compound having a total of at least two acryloxy (CH 2 =CH.CO.O--) and/or methacryloxy (CH 2 =C(CH 3 ).CO.O--) groups in the molecule, and having a molecular weight of at least 150, (ii) a mixture comprising at least 30% by weight of said compound and at most 70% by weight of at least one other copolymerizable monoethylenically unsaturated compound, and (iii) a partially polymerized product of said compound or said mixture, b. polymerizing the polymerizable material to an extent such that the polymerized material is not swollen with or dissolved in a monomer to be formed into the polymer body, thereby forming an abrasion-resistant polymer layer on the inner surface of the mold member, c. charging a mixture of the monomer for the polymer body and a polymerization initiator into the mold and then, polymerizing the monomer, and d. after completion of polymerization, releasing the cast article from the mold, wherein the improvement comprises carrying out the polymerization step (b) of said polymerizable material in two steps; in the first step the polymerizable material is polymerized, while covered with a closely adhering covering body having little or no affinity therewith, to a gel content that is within the range of 40% to 95% and at which the covering body is easily separated from the polymerizable material without simultaneous separation of the polymerizable material from the inner surface of said mold member, and in the succeeding second step polymerization is continued in the absence of the covering body with exposure to air until the gel content increases by 0.5% to 60% and reaches at least 90% and to an extent such that the polymerized material is not swollen with or dissolved in the monomer to be formed into the polymer body, the polymerization in the second step being completed prior to step (c), and wherein said first and second steps are carried out in the presence of a photosensitizer capable of activating the polymerizable material with light of a predominant wave length of from 3,000 to 4,000 A.