methods for making an oriented film and for forming a thermoplastic polymer alloy film or sheet, extruded oriented film, cellular expanded film, and apparatus for extruding thermoplastic material

摘要

"METHODS FOR MANUFACTURING AN ORIENTED MOVIE AND FORMING A FILM OR THERMOPLASTIC POLYMER ALLOY SHEET, EXTRUSED ORIENTED MOVIE, CELL EXPANDED MOVIE, AND APPLIANCE FOR EXTRUSING THERMOPLASTIC MATERIAL". A mixture of two partially incompatible polymers is extruded to form a film under conditions such that the alloy in the mixture comprises fibrils extending mainly in one direction, the width and thickness of each fibril having a mean lower than 5 µm. , the fibrils being formed of the polymer component having the highest melting point, and the fibrils being surrounded by a matrix of the second polymer having the lowest coefficient of elasticity. Special morphology is achieved by providing grids in a grid chamber upstream of the extrusion die outlet orifice, and by hot sequential stretching to a temperature at which the highest melting polymer is at least partially crystalline, and stretching to in which both polymers are substantially solid. The second cold stretching step is performed under conditions to provide at least 25% elongation at break at 20 ° C. Films are of particular value for forming cross laminates that have high shock resistance. Preferably the fibril forming polymer is polypropylene and the matrix forming polymer is an ethylene polymer, preferably LLDPE.