Patent ID: 7815972

Claim:
A method of producing a polarizing film, comprising the steps of: allowing a hydrophilic polymer film to swell wherein the polymer film is conveyed by means of a guide roll so as to be impregnated in an aqueous solvent in a swelling bath, wherein the aqueous solvent is water, and wherein a temperature of the swelling bath is in a range of from 15 to 50° C.; dyeing the polymer film using a dichroic substance; and stretching the polymer film, wherein the hydrophilic polymer film is a polyvinyl alcohol-based film containing (i) polyvinyl alcohol having an average degree of polymerization in the range of from 1,000 to 4,000 and a saponification degree in the range of from 98 to 100 mol %, and (ii) glycerine in an amount of from 5 to 15% by mass as an additive, wherein in the swelling step, at least a first guide roll and a second guide roll are arranged in the swelling bath, and when the polymer film is impregnated in and allowed to travel in the aqueous solvent, the polymer film is brought into contact with the first guide roll within a time up to when swelling of the polymer film occurs abruptly and further is brought into contact with the second guide roll after the swelling of the polymer film has occurred abruptly, wherein a required length of time (a) between the time when the polymer film is brought into contact with the aqueous solvent and the time when the polymer film is brought into contact with the first guide roll is 2 to 11 seconds, wherein a required length of time (b) between the time when the polymer film is brought into contact with the first guide roll and the time when the polymer film is brought into contact with the second guide roll is 13 to 120 seconds, and wherein an arbitrary point on the film is impregnated in the swelling bath for a total length of time of from 63 to 130 seconds, and wherein a length of time between the time when the polymer film is brought into contact with the aqueous solvent and a time when swelling of the polymer film occurs abruptly is 15 to 25 seconds.