Abstract: An optical film that includes a reflective polarizer and a stretched polymer film is disclosed. The stretched polymer film is laminated to the reflective polarizer, and the stretched polymer film exhibits a refractive index symmetry point at an angle of incidence in air of at least about 60 degrees in a plane of incidence parallel to a direction of greatest stretch.

Abstract: An optical film that includes a reflective polarizer and a stretched polymer film is disclosed. The stretched polymer film is laminated to the reflective polarizer, and the stretched polymer film exhibits a refractive index symmetry point at an angle of incidence in air of at least about 60 degrees in a plane of incidence parallel to a direction of greatest stretch.

Abstract: A method of stretching films in which all or a portion of the width of the film is cooled during or just after stretching so as to improve the uniformity of the film. The includes stretching a polymeric film in a tenter that grasps the film with a plurality of clips along the opposing edges of the film and propels the clips to thereby stretch the film. The tenter includes driven clips and idler clips, with at least one idler clip between respective pairs of driven clips. The cooling is done so as to improve the uniformity of the clip spacing relative to the spacing obtained at otherwise identical process conditions without such cooling.

Abstract: A simultaneously biaxially stretched polypropylene film having unique properties is disclosed. The properties result from the unique method of making the film and include: a tensile elongation to break in the first stretch direction of at least 110%; a tensile volumetric energy to break in the first stretch direction of at least 18,000 in-lb/in3; and, a variability in film thickness along the first stretch direction, as measured by the standard deviation relative to the average, of less than 10%.

Abstract: A method of biaxially stretching a polymeric film along an overbias stretch profile. The method comprises the steps of: ) imparting a sufficiently high temperature to the film to allow a significant amount of biaxial stretch; and b) biaxial tenter stretching the film to a final first direction stretch parameter and a final second direction stretch parameter, wherein at least 75% 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.

Abstract: A method of biaxially stretching a polymeric film along an overbias stretch profile having the steps of (a) imparting a sufficiently high temperature to the film to allow a significant amount of biaxial stretch; and (b) biaxial tenter stretching the film to a final first direction stretch parameter and a final second direction stretch parameter, wherein at least 75% 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.

Abstract: A method of biaxially stretching a polymeric film according to an overbias or overstretch stretch profile to a final first direction stretch parameter and a final second direction stretch parameter to provide a film having uniform properties. First, a sufficiently high temperature is imparted to the film to allow a significant amount of biaxial stretch. The film is then biaxially tenter stretched to a peak first direction stretch parameter that is at least 1.3 times the final first direction stretch parameter wherein the final first direction stretch parameter is no larger than the final second direction stretch parameter. Finally, the film is retracted in the first direction from the peak first direction stretch parameter to the final first direction stretch parameter to produce a film having uniformity of properties in the first direction.