METHODS OF STRETCHING FILMS AND SUCH FILMS

摘要

A method of biaxially stretching a polymeric film along an overbias stretch profile. The method comprises the steps of: a) imparting a sufficiently high temperature to the film to allow a significant amount of biaxial stretch; an d b) biaxial tenter stretching the film to a final first direction stretch parameter and a final second direction stretch parameter, wherein at least 7 5 % of the final first direction stretch parameter is attained before no more than 50 % of the final second direction stretch parameter is attained, and wherein the final first direction stretch parameter is no greater than the final second direction stretch parameter. An alternative method comprises a method of biaxially stretching a polymeric film along an overbias stretch profile. The method comprising the steps of: a) imparting a sufficiently hig h temperature to the film to allow a significant amount of biaxial stretch; an d b) biaxial tenter stretching the film according to a stretch profile to a final first direction stretch parameter and a final second direction stretch parameter, wherein the final first direction stretch parameter is no greater than the final second direction stretch parameter. In such a method: i) a straight line between the point defining zero stretch parameter and the poin t defining the final first and second direction stretch parameters represents a proportional stretch profile and defines a proportional stretch area; and ii ) the curve representing the stretch profile between the point defining zero stretch parameter and the point defining the final first and second directio n stretch parameters defines an area at least 1.4 times the proportional stret ch area.