A polymerizable composition for an optical material of the present invention includes polyisocyanate (a) including aliphatic polyisocyanate (a1) and a modified aliphatic polyisocyanate (a2), an episulfide (b), and a polythiol (c).

A process for producing an episulfide compound for an optical material of the present invention includes a step of chlorinating glycerin to obtain dichloropropanol; a step of epoxidizing the dichloropropanol to obtain epichlorohydrin; a step of reacting the epichlorohydrin with a sulfating agent to obtain a bis(chlorohydrin) (di)sulfide compound thought a thiol compound; a step of epoxidizing the bis(chlorohydrin) (di)sulfide compound under basic conditions to obtain an epoxy compound; and a step of reacting the epoxy compound with a sulfating agent to obtain an episulfide compound represented by following General Formula (1):

##STR00001## wherein, in the formula, n represents 0 or 1.

A layered phase difference film including, in the following order: a resin layer A1 formed of a resin A1 having a positive intrinsic birefringence; a resin layer B formed of a resin B having a negative intrinsic birefringence; and a resin layer A2 formed of a resin A2 having a positive intrinsic birefringence, wherein the resin layer A1 and the resin layer B are in direct contact with each other, the resin layer B and the resin layer A2 are in direct contact with each other, the resin layer A1 and the resin layer A2 are negative C-plates, the resin layer B is a positive B-plate, and the layered phase difference film has an Nz coefficient within a range of 0 to 1.

Disclosed are a polyvinyl alcohol film and a preparation method therefor. The saturated water absorption of the amorphous structure in the polyvinyl alcohol film is x, the water absorption increased due to destruction of the crystal surface defect structure in the polyvinyl alcohol film is y, and x/(x+y) is 0.82 to 0.93. The polyvinyl alcohol film has a softening point of 65 C. to 75 C., and a degree of swelling of 180% to 220%.