| 摘要 |
There is described a simultaneously oriented polyolefinic (e.g. polypropylen e) film comprising particles in at least one layer thereof, said particles incompatible with said layer to cause the initiation of voids therein when t he cast polyolefin is stretched simultaneously in both the MD and TD, and where the particles comprise: (i) particles having a mean aspect ratio x/y of at least 2 (e.g. long and thin) and a mean size of the longest particle dimensi on greater than about 3 microns (preferably about 6 microns); and/or (ii) particles having a mean aspect ratio of about 1 (e.g. spherical or boulder- like), with a narrow size distribution, a mean particle size of from about 3 to about 10 microns, (preferably about 6 microns), and which are substantial ly free of particles above about 12 microns in size and optionally also substantially free of particles below about 3 microns in size. Preferred BOP P films are further characterised in that ratio of at least one of the followi ng properties measured in the MD with respect to TD is: (a) tensile strength of above 0.5; (b) elongation at break of below 2.0; (c) Young's modulus of at least 0.7; and/or (d) shrinkage of at least 0.45,. the TD shrinkage being other than zero. |
