Method of coloring water-absorbable plastics and colored water-absorbable plastics

摘要

A method of coloring a water-absorbable plastic partially or totally in a single color or multiple colors in such a manner that no migration or separation of the coloring agents used can take place. A copolymer of a coupler monomer and a water-absorbable plastic monomer, a polymer of a coupler polymer and a water-absorbable plastic monomer or a polymer of a coupler monomer and a water-absorbable plastic polymer is formed into an intermediate product shaped in the form of any desired final product. The intermediate product is immersed in an aqueous solution of a developer consisting of a diazonium double salt and allowed to swell, whereby the diazo-component of the developer penetrates into the plastic. The swollen product is then immersed in an aqueous acid or alkaline solution having an optimum pH value for coupling reaction to allow formation of an azoic dye on the plastic as a result of the coupling reaction. A partially colored plastic is produced by application of ultraviolet rays to a portion or portions of the plastic on which no coloring is required, whereby the diazo-component on those portions is decomposed to leave those portions uncolored. Multiple coloring is effected by repeating the partial coloring process by changing diazonium double salts.