| abstract |
A combination of two partially incompatible polymers is extruded to form a film under conditions such that the alloy in the combination comprises fibrils that extend primarily in one direction, the width and thickness of each fibril has an average of less than 5 µm, Fibrils are formed of the polymer component that has the highest melting point, and the fibrils are surrounded by a matrix of the second polymer, which has a lower elasticity coefficient. The special morphology is obtained by providing grids (301, 302) in a grid chamber upstream of the exit hole of the extrusion die and by sequential hot drawing at a temperature at which the polymer with the highest melting point is therefore less partially crystalline, and cold drawn, in which both polymers are substantially solid. The second cold drawing stage is carried out under conditions to provide an elongation at break at 20 degree C of at least 25%. The films are particularly useful for forming transverse laminates that have high resistance to shock. Preferably, the polymer that forms fibrils is polypropylene and the polymer that forms the matrix is an ethylene polymer, preferably LLDPE. |