Patent ID: 7149031

Claim:
A polarizing filter comprising: a polarized film; a first protective film adhered to one surface of said polarized film; and a second protective film adhered to another surface of said polarized film, said second protective film being different from said first protective film in at least one of thickness, physical properties and materials; wherein when Ml is a coefficient of expansion by water absorption of said first protective film in a direction of a light absorption axis of said polarizing filter and M 2 is a coefficient of expansion by water absorption of said second protective film in the direction of the light absorption axis of said polarizing filter, then the coefficients of expansion M 1 , M 2 satisfying a formula; 0.65· M 1< M 2<1.55· M 1; and wherein said first or second protective film is cut to a strip specimen having 120 mm length in the direction of the light absorption axis of said polarizing filter, said strip specimen is set under a temperature of 23° C. and relative humidity of 65% for two hours, two holes having diameter of 6mm are thereafter formed to have a distance about 100 mm in the direction of the light absorption axis, the distance is measured to obtain an initial distance L 1 , said strip specimen is dipped in a water for 30 minutes, said distance between said two holes is measured to obtain a water absorption distance L 2 , and said coefficients of expansion M 1 and M 2 are calculated from a formula; M 1 and M 2={( L 2− L 1)/ L 1}×100.