US Patent 7632430 Process for producing polarizing film

The invention provides a continuous method for producing polarizing films that includes a step of monoaxially stretching a polyvinyl alcohol film having a width of at least 2 m in an aqueous boric acid solution, wherein the polyvinyl alcohol film is stretched on the condition that it satisfies the following formulae (1) and (2):A≧5 (m)  (1)A/B≧0.5 (min) (2)wherein A indicates the stretching distance (m); and B indicates the stretched film speed (m/min). The method gives wide polarizing films of wide and good polarization performance, and the polarizing films thus produced are useful as the material for polarizers that may be in large-size liquid-crystal displays.