Patent ID: 8896802

Claim:
A method for producing a light transmissive substrate having a flat portion and recesses on at least one side of the substrate, comprising: making a light transmissive substrate having a flat portion and recesses on at least one side of the substrate; and forming a layer containing at least a slip agent on the side of the substrate with the recesses, the making of a light transmissive substrate comprising: casting a polymer solution containing at least a thermoplastic resin and a solvent on a support to form a web, stripping the web from the support and drying the web, the polymer solution containing two or more solvents at least one of which has a dielectric constant of 35 or higher, and with phase separation between the thermoplastic resin and the at least one solvent having a dielectric constant of 35 or higher in the solution during film formation or while the solvents evaporate after the film formation.