Patent ID: 7883769

Claim:
An article comprising a base layer made of thermoplastic polymer having at least one outer face, said outer face containing over at least one area a plurality of foamed hook shaped microstructures comprised of multiple discrete foam cells, the foamed hook shaped microstructures comprising a semicrystalline thermoplastic polymer, the foamed hook shaped microstructures having at least one dimension which is greater than 10 microns and the discrete foam cells forming the foamed hook shaped microstructures having a mean cell size less than the smallest cross-sectional dimension of the foamed hook shaped microstructures excluding any tips on the foamed hook shaped microstructures and measured at a distance of at least 10 microns from such tips, wherein the smallest cross-sectional dimension of the foamed hook shaped microstructures is a width or thickness dimension and is about 50 microns or more, the foamed hook shaped microstructures have heights of generally 1000 microns or less, the ratio of the mean cell size of the discrete foam cells to the smallest cross-sectional dimension of the foamed hook shaped microstructures is 0.75 or less, the semicrystalline thermoplastic polymer is at least in part a high melt strength polypropylene having a melt strength in the range of 25 to 60 cN at 190° C. and the base layer is oriented in at least one direction.