Abstract: There are disclosed opaque, biaxially oriented polymeric film structures each comprising a thermoplastic polymer matrix material, e.g., polypropylene, within which is located a stratum of voids, and positioned within each of at least a substantial number of the voids is at least one spherical void-initiating solid particle (i.e., a cavitating agent) of cross-linked polystyrene (CLPS) which is phase-distinct and incompatable with the matrix material, the volume of the particle being substantially less than the volume of the void, with one generally cross-sectional dimension of the particle at least approximating a corresponding cross-sectional dimension of the void.Also disclosed is a method of preparing the foregoing film structure by extruding into a film a combination of the matrix material and CLPS particles dispersed therein, and biaxially orienting the film either simultaneously or sequentially.

Abstract: There are disclosed opaque, biaxially oriented polymeric film structures each comprising a thermoplastic polymer matrix material, e.g., polypropylene, within which is located a stratum of voids, and positioned within each of at least a substantial number of the voids is at least one spherical void-initiating solid particle (i.e., a cavitating agent) of cross-linked polystyrene (CLPS) which is phase-distinct and incompatible with the matrix material, the volume of the particle being substantially less than the volume of the void, with one generally cross-sectional dimension of the particle at least approximating a corresponding cross-sectional dimension of the void.Also disclosed is a method of preparing the foregoing film structure by extruding into a film a combination of the matrix material and CLPS particles dispersed therein, and biaxially orienting the film either simultaneously or sequentially.