High opacity film and method thereof

A non-symmetrically layered, biaxially oriented polymer film comprising:

• (a) a core thermoplastic polymer matrix material within which is located a strata of voids;
• positioned at least substantially within at least a substantial number of each of said voids, is at least one spherical void-initiating particle which is phase distinct and incompatible with said matrix material, the void space occupied by said particle being substantially less than the volume of said void, with one generally core-sectional dimension of said particle at least approximating a corresponding cross-sectional dimension of said void, said core layer also containing from about 1% to about 8% by weight iron oxide, from about 0.1% to about 1% by weight aluminum, and from about 1.5% to about 3% by weight of TiO.sub.2 ;
• (b) a first void-free skin layer on one surface of the core layer containing up to about 12% by weight of inorganic particulate material;
• (c) a second void-free particulate-free skin layer on the other surface of the core layer;
• and
• wherein the core thickness is about 60 to about 90% of the overall film thickness, skin layer (b) is about 10 to about 30% of the overall film thickness and skin layer (c) is about 1 to about 15% of the overall thickness, said film having an opacity of essentially 100% and light transmission in the 250 nm-450 nm region is essentially zero.