Optical bodies including strippable boundary layers

Abstract

The present disclosure is directed to optical bodies including a first optical film, a second optical film and one or more strippable boundary layers disposed between the first and second optical films. Each major surface of a strippable boundary layer may be disposed adjacent to an optical film or another strippable boundary layer. At least one of the first and second optical films may include a reflective polarizer. The present disclosure is also directed to methods of processing such optical bodies.

1 . An optical body comprising a first optical film, a second optical film and one or more strippable boundary layers disposed between the first and second optical films such that each major surface of a strippable boundary layer is disposed adjacent to an optical film or another strippable boundary layer, wherein at least one of the first and second optical films comprises a reflective polarizer.  
     
     
         2 . The optical body of  claim 1 , wherein the reflective polarizer is a diffuse reflective polarizer comprising a disperse polymeric phase and a continuous polymeric phase.  
     
     
         3 . The optical body of  claim 2 , wherein the reflective polarizer has a thickness of no more than 1 mil.  
     
     
         4 . The optical body of  claim 2 , wherein at least one of the disperse or continuous phase has an in-plane birefringence of at least 0.1.  
     
     
         5 . The optical body of  claim 1 , further comprising a third optical film and at least one additional strippable boundary layer disposed between the third optical film and the second optical film.  
     
     
         6 . The optical body of  claim 1 , wherein the reflective polarizer is a multilayer reflective polarizer comprising a plurality of first and second optical layers.  
     
     
         7 . The optical body of  claim 6 , wherein the reflective polarizer has no more than optical layers.  
     
     
         8 . The optical body of  claim 6 , wherein at least one of the first and second optical layers has an in-plane birefringence of at least 0.1.  
     
     
         9 . The optical body of  claim 1 , wherein a strippable boundary layer comprises at least one of: a fluropolymer, a polypropylene, a modified polypropylene, an aliphatic polyolefin, a polyethylene, a polyethylene copolymer, polymethylpentene, a cyclic olefin copolymer, a syndiotactic polymer, an atactic vinyl aromatic polymer, a polysyrene, and a copolymer of styrene.  
     
     
         10 . The optical body of  claim 1 , further comprising at least one outer skin layer.  
     
     
         11 . A method for processing an optical body, comprising: 
 providing an optical body comprising a first optical film, a second optical film and at least one strippable boundary layer disposed between the first and second optical films;    conveying the optical body into a stretching region;    stretching the optical body to increase a transverse dimension of the optical body while conveying the opposing edges of the optical body along generally diverging paths in a machine direction, wherein the generally diverging paths are configured and arranged to provide a machine direction draw ratio (MDDR), a normal direction draw ratio (NDDR) and a transverse direction draw ratio (TDDR) that approach the following relationship:        MDDR=NDDR =( TDDR ) −1/2      during the stretching.    
     
     
         12 . The method of  claim 11 , wherein the diverging paths are substantially parabolic.  
     
     
         13 . The method of  claim 11 , wherein the diverging paths are linear approximations of substantially parabolic paths.  
     
     
         14 . The method of  claim 11 , wherein the diverging paths are coplanar.  
     
     
         15 . The method of  claim 11 , wherein in the stretched optical body at least one of the first and second optical films comprises a reflective polarizer.  
     
     
         16 . The method of  claim 11 , wherein stretching the film comprises stretching the optical body to a draw ratio in excess of four.  
     
     
         17 . The method of  claim 11 , wherein the step of stretching comprises moving the opposing edge portions along diverging paths that are substantially symmetrical about a center axis of the optical body.  
     
     
         18 . The method of  claim 11 , further comprising providing the optical body to the stretcher in a continuous manner from a roll of film.  
     
     
         19 . The method of  claim 11 , further comprising coextruding the optical body in-line with stretching.  
     
     
         20 . The method of  claim 20 , wherein coextruding the optical body comprises multiplication and the at least one boundary layer is added prior to multiplication.  
     
     
         21 . The method of  claim 11 , wherein the stretched film comprises at least one material with indices of refraction in a length direction corresponding to the machine direction and a thickness direction that are substantially the same but substantially different from an index of refraction in a width direction.  
     
     
         22 . The method of  claim 11 , wherein the minimum value of the extent of uniaxial character, U, is at least 0.7, wherein U is defined as  
           U= (1 /MDDR− 1)/( TDDR   1/2 −1).  
     
     
         23 . A method of processing an optical body, the method comprising: 
 providing an optical body comprising a first optical film, a second optical film and at least one strippable boundary layer disposed between the first and second optical films;    conveying the optical body within a stretcher along a machine direction while holding opposing edge portions of the optical body; and    stretching the optical body to a draw ratio in excess of four within the stretcher by moving the opposing edge portions along diverging non-linear paths, wherein, during the stretching, the minimum value of the extent of uniaxial character, U, is at least 0.7 over a final portion of the stretching after achieving a TDDR of 2.5 and U is less than 1 at the end of the stretching, wherein U is defined as        U= (1 /MDDR− 1)/( TDDR   1/2 −1)    wherein MDDR is the machine direction draw ratio and TDDR is the transverse direction draw ratio as measured between the diverging paths.    
     
     
         24 . The method of  claim 24 , wherein the minimum value of the extent of uniaxial character is at least 0.8.  
     
     
         25 . The method of  claim 24 , wherein the extent of uniaxial character, U, is at least 0.8 over a final portion of the stretching after achieving a TDDR of 2.0.  
     
     
         26 . The method of  claim 24 , wherein at least one of the first and second optical films comprises a multilayer film having a plurality of alternating layers of different polymeric composition.  
     
     
         27 . A method of processing an optical body, the method comprising: 
 providing an optical body comprising a first optical film, a second optical film and at least one strippable boundary layer disposed between the first and second optical films;    conveying the optical body within a stretcher along a machine direction while holding opposing edge portions of the optical body; and    stretching the optical body within the stretcher by moving the opposing edge portions along diverging non-linear paths, wherein, during the stretching of the optical body, the speed of the film along the machine direction decreases by a factor of approximately λ 1/2  where λ is the transverse direction draw ratio.    
     
     
         28 . The method of  claim 28 , wherein at least one of the first and second optical film comprises a multilayer film having a plurality of alternating layers of different polymeric composition.