Abstract: An optical recording medium protecting film which is a protecting film comprising a single transparent film made of a thermoplastic resin, having a retardation of no greater than 15 nm at a wavelength of 550 nm and a K value of no greater than 40 nm at 550 nm, having a glass transition temperature of 120° C. or higher and a water absorption of no greater than 1 wt %. |R(550)|?15 nm??(1) |K(550)|?40 nm??(2) (the K value being calculated by K=[nz?(nx+ny)/2]×d {where nx, ny and nz are the three-dimensional refractive indexes of the transparent film in the x-axis, y-axis and z-axis directions, respectively, and d is the thickness of the transparent film}). Also, an optical recording medium having a data recording layer and the above-mentioned protecting film on a substrate, wherein light is incident from the protecting film side.

Abstract: In the present invention, a retardation film is produced by adjusting the mixing ratio of at least two kinds of mutually compatible polymers A and B and by forming the resulting mixture into the film. The polymers A and B are copolymers comprising respective two common repeating units and different in copolymerization composition. According to the present invention, the retardation film having the desired wavelength dispersion can industrially and simply be produced. Furthermore, there can be provided the high-quality retardation film capable of controlling the wavelength dispersion of the retardation at a high level.

Abstract: In the present invention, a retardation film is produced by adjusting the mixing ratio of at least two kinds of mutually compatible polymers A and B and by forming the resulting mixture into the film. The polymers A and B are copolymers comprising respective two common repeating units and different in copolymerization composition. According to the present invention, the retardation film having the desired wavelength dispersion can industrially and simply be produced. Furthermore, there can be provided the high-quality retardation film capable of controlling the wavelength dispersion of the retardation at a high level.

Abstract: An optical recording medium protecting film which is a protecting film comprising a single transparent film made of a thermoplastic resin, having a retardation of no greater than 15 nm at a wavelength of 550 nm and a K value of no greater than 40 nm at 550 nm, having a glass transition temperature of 120° C. or higher and a water absorption of no greater than 1 wt %.