Method for making PEN/PMMA multilayer optical films

Abstract

Methods and apparatuses are provided for the manufacture of coextruded polymeric multilayer optical films. The multilayer optical films have an ordered arrangement of layers of two or more materials having particular layer thicknesses and a prescribed layer thickness gradient throughout the multilayer optical stack. The methods and apparatuses described allow improved control over individual layer thicknesses, layer thickness gradients, indices of refraction, interlayer adhesion, and surface characteristics of the optical films. The methods and apparatuses described are useful for making interference polarizers, mirrors, and colored films that are optically effective over diverse portions of the ultraviolet, visible, and infrared spectra.

1 - 8 . (canceled)  
     
     
         9 . A method for making a multilayer optical film comprising alternating layers of a first and second polymer, the first polymer comprising homopolymer polyethylene naphthalate (PEN) and the second polymer comprising polymethyl methacrylate (PMMA), wherein the first and second polymers are coextruded at a melt temperature of about 275° C. without substantial degradation of the PMMA.  
     
     
         10 . The method of  claim 9 , wherein the first and second polymers are coextruded at a melt temperature in the range of 270-275° C.  
     
     
         11 . The method of  claim 9 , wherein an extrudate comprising the coextruded first and second polymers is quenched to form a cast multilayer film, the method further including stretching the cast multilayer film to develop birefringence in at least one of the alternating layers.  
     
     
         12 . The method of  claim 11 , wherein the cast multilayer film is stretched substantially uniaxially.  
     
     
         13 . The method of  claim 11 , wherein the cast multilayer film is stretched substantially biaxially.  
     
     
         14 . A method of making a multilayer optical film, comprising: 
 (a) providing at least a first and a second stream of resin, wherein the first stream of resin comprises homopolymer polyethylene naphthalate (PEN) and the second stream of resin comprises polymethyl methacrylate (PMMA),    (b) dividing the first and second streams into a plurality of layers such that the layers of the first stream are interleaved with the layers of the second stream to yield a composite stream; and    (c) coextruding the composite stream at a melt temperature of about 275° C. through a die to form a multilayer web wherein each layer is generally parallel to the major surface of adjacent layers.    
     
     
         15 . The method of  claim 14 , wherein the first and second polymers are coextruded at a melt temperature in the range of 270-275° C.  
     
     
         16 . The method of  claim 14 , further comprising: 
 (d) quenching the multilayer web to form a cast multilayer film.    
     
     
         17 . The method of  claim 16 , wherein the quenching step comprises casting the multilayer web onto a casting roll.  
     
     
         18 . The method of  claim 14 , further comprising after step (b): 
 (d) passing the composite stream into a multiplier where the composite stream is divided into a plurality of substreams, the multiplier expanding at least one of the substreams in a direction transverse to its direction of flow; and    (e) recombining the substreams to increase the number of layers in the composite stream.    
     
     
         19 . The method of  claim 16 , further comprising: 
 (e) stretching the cast multilayer film to develop birefringence in at least one of the layers.    
     
     
         20 . The method of  claim 19 , wherein the cast multilayer film is stretched longitudinally.  
     
     
         21 . The method of  claim 19 , wherein the cast multilayer film is stretched transversely.  
     
     
         22 . The method of  claim 20 , wherein the cast multilayer film is stretched transversely.  
     
     
         23 . The method of  claim 19 , wherein the cast multilayer film is simultaneously stretched biaxially.