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 - 10 . (canceled) 
   
   
       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 27 , 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.