TREATMENT FOR MAKING DURABLE POLARIZING FILM

PURPOSE:To obtain an polarizing film having excellent durability by treating the polarizing film consisting of a film made of PVA or the deriv. thereof on which a polarizing element is adsorbed and which is oriented in a specific temp. range in the stage of treating said polarizing film by a treating agent for making durable said film. CONSTITUTION:The film made of PVA or the deriv. thereof is required to be stretched and oriented at >=55 deg.C or to be heat-treated at >=55 deg.C. The stretched PVA film has an easy tendency to rupture and a low yield at >=80 deg.C and therefore such temp. is undesirable. An aq. soln. contg. formalin, an aq. soln. contg. boric acid, etc. are effective as the treating agent for making durable the film. The polarizing agent having excellent durability is obtd. if the film is treated to be made durable at >=55 deg.C and