US Patent 7223809 Polyacetals with improved resistance to bleach

A molding composition exhibiting bleach resistance includes a polyoxymethylene matrix polymer, from about 0.5 to about 10 weight percent of a bleach stabilizer selected from alkali metal or alkaline earth element carbonates or phosphates and mixtures thereof dispersed in the matrix resin. A bleach co-stabilizer is selected from the group consisting of: (a) a poly(alkoxy) stabilizer; (b) a zinc oxide stabilizer; (c) a color stabilizer consisting of a mixture of calcium citrate and calcium propionate, wherein the calcium citrate is the predominant component of the color stabilizer mixture; or (d) mixtures of two or more of (a), (b) and (c). The compositions exhibit a bleach resistance index of at least 2.0.