PROCESS FOR PRODUCING WATER-PROOF POLARIZING FILM

摘要

Heretofore, polarizing films each utilizing an organic dye having a sulfonate group in which a sulfonate ion and a univalent cation are bound to each other is known. However, the polarizing films have poor water resistance because the organic dye is dissolved in water. For solving the problem, a process in which the univalent cation in the sulfonate group is replaced by a water-insoluble polyvalent cation to produce a water-proof polarizing film that is insoluble or slightly soluble in water is known. The water-proof polarizing films produced by the aforementioned conventional process, however, have such disadvantages that the dichroism is low and fine cracking occurs on the surface. Disclosed is a water-proof polarizing film which has high dichroism and undergoes no cracking. The water-proof polarizing film is produced by bringing a polarizing film produced from a mixture of an organic dye and a polyvinyl alcohol polymer into contact with a water-resistance-imparting treatment solution containing (i) at least one of an organic amine cation and a polyvalent metal cation and (ii) a tetrahydroxyborate anion to impart water resistance to the polarizing film.