Monoxially-oriented and annealed films with high cross machine toughness and related process
View Patent ↗A monoaxially-oriented polymeric film material formed from an impact copolymer and having increased toughness relative to films that are monoaxially-oriented at conventional temperatures. A process for imparting high cross machine toughness to polymer films comprises forming a film; subjecting the film to monoaxial orientation, drawing the film; tempering the film, and annealing the film.
1. A process for imparting high cross machine toughness to polymer film tape yarns, comprising:
forming a film from an impact copolymer:
subjecting said film to monoaxial orientation involving drawing at stages where said film is sequentially directed over a series of rollers as the film is sequentially subjected to a stage of preheating, then a stage of drawing and then a stage of tempering;
wherein said stage of tempering said film is conducted at temperatures of from between about 20 to about 45 percent lower than the temperature at which said film is subjected to during the stage of drawing;
annealing said film, wherein said film has an average cross machine toughness value of at least 3,000 lbs/in 2 after the annealing step; and
slitting said film subsequent to said annealing.
2. The process of claim 1 , further comprising an olefin-based polymer blended with said impact copolymer.
3. The process of claim 2 , wherein said blend comprises
a) from greater than 0 to about 70 parts by weight of said olefin-based polymer; and
b) at least about 30 parts by weight of said impact copolymer,
wherein the total of a) and b) is 100 parts by weight.
4. The process of claim 2 , wherein said olefin-based polymer is polypropylene and said impact copolymer comprises a continuous phase of polypropylene with a dispersed phase of polypropylene/ethylene rubber.
5. The process of claim 2 , wherein said olefin-based polymer has a melt flow index of from about 0.6 to about 5 and said impact copolymer has a melt flow index of from about 0.6 to about 3.5.
6. The process of claim 1 , wherein said film has an average cross machine toughness value of between about 3000 lbs/in 2 to 16,000 lbs/in 2 after the annealing step.