PURPOSE: To improve recording density and running property in a magnetic recording polyester film by a method wherein polyester having a limited specific resistance in a molten state is formed by the electrostatic cooling method into unoriented film and oriented biaxially by the average refractive index and the surface orientation degree within a specific range.
CONSTITUTION: The polyester film to be used has a specific resistance 5×108Ω- cm or less in a molten state and a surface rougness showing an average height of projections on the film surface 0.015μm or less. The polyester film is melted and extruded in the form of the sheet, hardened uniformly by the electrostatic cooling method and formed into unoriented film. The unoriented film is oriented biaxially so that the average refractive index -n and the surface orientation ΔP of the film satisfy Formula 1.
KANEZAKI TAKEO
UCHIUMI SHIGEO
| JPS52136400A | 1977-11-15 | |||
| JPS50136365A | 1975-10-29 | |||
| JPS50139872A | 1975-11-08 | |||
| JPS5075A | 1975-01-06 |