Reflective polarizer, fiber, and process for making

Abstract

A fiber comprises a birefringent fibril discontinuous polymeric phase dispersed in a continuous polymeric phase with prescribed matched and mis-matched refractive indices. A diffusely polarizing organic film, optical element, display, and method of making such a film are also disclosed.

1 . A fiber comprising a birefringent fibril discontinuous polymeric phase dispersed in a continuous polymeric phase wherein the refractive indices of the discontinuous and continuous phases in the X and Y directions are substantially matched to each other, the refractive indices of the discontinuous and continuous phases in the X and Y directions are substantially mismatched from the refractive index of the fibril discontinuous polymeric phase in the Z direction, and wherein the extrusion melting temperature of the continuous phase is less than the onset melting range of the discontinuous phase. 
     
     
         2 . The fiber of  claim 1  wherein the cross-sectional shape of the fiber is circular, rectilinear, elliptical, triangular, tri-lobal, or trapezoidal. 
     
     
         3 . The fiber of  claim 1  wherein the cross-sectional shape of the fiber is circular or elliptical. 
     
     
         4 . The fiber of  claim 1  wherein the birefringent fibril discontinuous polymeric phase has a cross-sectional shape that is circular, rectilinear, elliptical, triangular, tri-lobal, or trapezoidal. 
     
     
         5 . The fiber of  claim 1  wherein the birefringent fibril discontinuous polymeric phase has a cross-sectional shape that is circular or elliptical. 
     
     
         6 . The fiber of  claim 1  wherein the birefringent fibril discontinuous polymeric phase comprises a polyester. 
     
     
         7 . The fiber of  claim 6  wherein the polyester comprises polyethylene(terephthalate) , polyethylene(naphthalate) , or any copolymers of either. 
     
     
         8 . The fiber of  claim 6  wherein the polyester comprises polyethylene(naphthalate). 
     
     
         9 . The fiber of  claim 1  wherein the continuous polymeric phase comprises a polyester, an acrylic, or an olefin. 
     
     
         10 . The fiber of  claim 1  wherein the continuous phase comprises polyethylene(terephthalate), poly(methyl-methacrylate), poly(cyclo-olefin), or any copolymers of either. 
     
     
         11 . The fiber of  claim 1  wherein the number of fibrils in the fiber is greater than 50. 
     
     
         12 . The fiber of  claim 1  wherein fibrils each have a cross sectional area of less than 3 square microns. 
     
     
         13 . The fiber of  claim 1  wherein the ratio of discontinuous phase to continuous phase on a weight basis is less than 2 to 1 
     
     
         14 . The fiber of  claim 1  wherein the fiber has been cold drawn at a temperature just above the Tg of the fibril polymer to achieve a high level of birefringence of the discontinuous phase. 
     
     
         15 . The fiber of  claim 14  wherein the fiber temperature is between 2 and 20° C. 
     
     
         16 . The fiber of  claim 14  wherein the fiber has been cold drawn at least 2 to 1. 
     
     
         17 . A process for making a diffusely reflective polarizer film comprising the steps of:
 a) providing fibers that comprise two components distributed as (1) a continuous phase and (2) a discontinuous phase in the form of fibrils, respectively, wherein at least the phase 2 is birefringent;   b) cutting the fibers to a desired length;   c) extrusion melting the cut fibers at a temperature sufficient to melt phase 1 but not melt phase 2;   d) extrusion mixing the melted phase 1 with the unmelted phase 2 at the same time as step c) or after step c) to uniformly disperse the phase 2 fibrils as a mixture within phase 1;   e) subjecting the dispersed mixture to shear forces whereby the fibrils of phase 2 become oriented within the mixture; and   f) forming a composite film from the mixture comprising the oriented phase 2 fibrils.   
     
     
         18 . The process of  claim 17  wherein the discontinuous phase in the form of fibrils has a cross-sectional shape that is circular, rectilinear, elliptical, triangular, tri-lobal, or trapezoidal. 
     
     
         19 . The process of  claim 17  wherein the discontinuous phase in the form of fibrils has a cross-sectional shape that is circular or elliptical. 
     
     
         20 . The process of  claim 17  wherein the discontinuous phase comprises a polyester. 
     
     
         21 . The process of  claim 20  wherein the polyester comprises polyethylene(naphthalate). 
     
     
         22 . The process of  claim 17  wherein the continuous phase 1 comprises a polyester, an acrylic, or an olefin. 
     
     
         23 . The process of  claim 17  wherein the continuous phase 1 comprises poly(1,4-cyclohexylene dimethylene terephthalate) or poly(ethylene-terephthalate/isophthalate) copolymer. 
     
     
         24 . The process of  claim 17  wherein the fibers that comprise two components have greater than 1000 phase 2 fibrils. 
     
     
         25 . The process of  claim 17  wherein the phase 2 fibrils each have a cross sectional area of less than 0.2 square microns. 
     
     
         26 . The process of  claim 17  wherein the refractive indices of the discontinuous and continuous phase in the X and Y directions of the fibers that comprise two components are substantially matched, the refractive indices of the discontinuous and continuous phase in the X and Y directions of the fibers that comprise two components are substantially mismatched from the refractive index of the discontinuous phase of the fibers in the Z direction and wherein the extrusion melting temperature of the continuous phase is less than the onset melting range of the discontinuous phase. 
     
     
         27 . An optical element comprising a film containing a layer including continuous phase and discontinuous phase materials, wherein the discontinuous phase materials are cut fibrils and include a material having a different refractive index in the orthogonal X and Y directions in a plane perpendicular to the direction of light travel. 
     
     
         28 . The optical element of  claim 27  wherein the cut fibrils are cut to a length of less than 5 mm. 
     
     
         29 . The optical element of  claim 27  wherein the cut fibrils are cut to a length of less than 1 mm. 
     
     
         30 . The optical element of  claim 27  wherein the cut fibrils are cut to a length of less than 0.4 mm. 
     
     
         31 . A display comprising the optical element of  claim 27 . 
     
     
         32 . The display of  claim 31  further comprises at least one function selected from the group consisting of image viewing screen, antireflection layer, ambient light suppression, color filter array, light valve, illumination enhancement, light collimation, light directing, light diffusion, stiffening, resistance to thermal expansion, light spreading, a light source, image algorithm, image storage, image buffer, optical brightener, IR reflection and a power source.