Brightness enhancing film with embedded diffuser

Abstract

Brightness enhancing films with embedded diffusers are described. More specifically, films including a birefringent substrate, a prismatic layer carried by the substrate having linear prisms, and an embedded structured surface disposed between the substrate and the prismatic layer are disclosed. The embedded structured surface may include closely-packed structures. Processes for producing embedded structured surfaces having particular topographies are also disclosed.

What is claimed is: 
     
         1 . An optical film, comprising:
 a birefringent substrate;   a prismatic layer carried by the substrate, the prismatic layer having a major surface comprising a plurality of side by side linear prisms extending along a same prism direction; and   an embedded structured surface disposed between the substrate and the prismatic layer comprising larger first structures and smaller second structures, the first and second structures both being limited in size along two orthogonal in-plane directions;   wherein the first structures are non-uniformly arranged on the embedded structured surface;   wherein the second structures are closely packed and non-uniformly dispersed between the first structures; and   wherein an average size of the first structures is greater than 15 microns and an average size of the second structures is less than 15 microns.   
     
     
         2 . The optical film of  claim 1 , wherein the embedded structured surface is characterized by a bimodal distribution of equivalent circular diameter (ECD) of structures of the embedded structured surface, the bimodal distribution having a first and second peak, the larger first structures corresponding to the first peak and the smaller second structures corresponding to the second peak. 
     
     
         3 . The optical film of  claim 1 , wherein the average size of the first structures is in a range from 20 to 30 microns. 
     
     
         4 . The optical film of  claim 1 , wherein the average size of the second structures is in a range from 4 to 10 microns. 
     
     
         5 . The optical film of  claim 1 , wherein the embedded structured surface has a topography characterizable by a first and second Fourier power spectrum associated with respective first and second orthogonal in-plane directions, and wherein:
 the first Fourier power spectrum includes one or more first frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a first baseline, each first frequency peak having a first peak ratio of less than 0.8, the first peak ratio being equal to an area between the first frequency peak and the first baseline divided by an area beneath the first frequency peak; and   the second Fourier power spectrum includes one or more second frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a second baseline, each second frequency peak having a second peak ratio of less than 0.8, the second peak ratio being equal to an area between the second frequency peak and the second baseline divided by an area beneath the second frequency peak.   
     
     
         6 . The optical film of  claim 5 , wherein the first and second peak ratios are each less than 0.5. 
     
     
         7 . An optical film, comprising:
 a birefringent substrate;   a prismatic layer carried by the substrate, the prismatic layer having a major surface comprising a plurality of side by side linear prisms extending along a same prism direction; and   an embedded structured surface disposed between the substrate and the prismatic layer, wherein the embedded structured surface is made by microreplication from a tool structured surface, the tool structured surface being made by forming a first layer of a metal by electrodepositing the metal using a first electroplating process resulting in a major surface of the first layer having a first average roughness, and forming a second layer of the metal on the major surface of the first layer by electrodepositing the metal on the first layer using a second electroplating process resulting in a major surface of the second layer having a second average roughness smaller than the first average roughness, the major surface of the second layer corresponding to the tool structured surface.   
     
     
         8 . The optical film of  claim 7 , wherein the embedded structured surface comprises larger first structures and smaller second structures, the first and second structures both being limited in size along two orthogonal in-plane directions;
 wherein the first structures are non-uniformly arranged on the embedded structured surface;   wherein the second structures are closely packed and non-uniformly dispersed between the first structures; and   wherein an average size of the first structures is greater than 15 microns and an average size of the second structures is less than 15 microns.   
     
     
         9 . The optical film of  claim 8 , wherein the embedded structured surface is characterized by a bimodal distribution of equivalent circular diameter (ECD) of structures of the embedded structured surface, the bimodal distribution having a first and second peak, the larger first structures corresponding to the first peak and the smaller second structures corresponding to the second peak. 
     
     
         10 . The optical film of  claim 7 , wherein the embedded structured surface has a topography characterizable by a first and second Fourier power spectrum associated with respective first and second orthogonal in-plane directions, and wherein:
 the first Fourier power spectrum includes one or more first frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a first baseline, each first frequency peak having a first peak ratio of less than 0.8, the first peak ratio being equal to an area between the first frequency peak and the first baseline divided by an area beneath the first frequency peak; and   the second Fourier power spectrum includes one or more second frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a second baseline, each second frequency peak having a second peak ratio of less than 0.8, the second peak ratio being equal to an area between the second frequency peak and the second baseline divided by an area beneath the second frequency peak.   
     
     
         11 . The optical film of  claim 10 , wherein the first and second peak ratios are each less than 0.5. 
     
     
         12 . An optical film, comprising:
 a birefringent substrate;   a prismatic layer carried by the substrate, the prismatic layer having a major surface comprising a plurality of side by side linear prisms extending along a same prism direction; and   an embedded structured surface disposed between the substrate and the prismatic layer comprising larger first structures and smaller second structures, the first and second structures both being limited in size along two orthogonal in-plane directions;   wherein the first structures are non-uniformly arranged on the embedded structured surface;   wherein the second structures are closely packed and non-uniformly dispersed between the first structures; and   wherein the embedded structured surface is characterized by a bimodal distribution of equivalent circular diameter (ECD) of structures of the embedded structured surface, the bimodal distribution having a first and second peak, the larger first structures corresponding to the first peak and the smaller second structures corresponding to the second peak.   
     
     
         13 . The optical film of  claim 12 , wherein the embedded structured surface has a topography characterizable by a first and second Fourier power spectrum associated with respective first and second orthogonal in-plane directions, and wherein:
 the first Fourier power spectrum includes one or more first frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a first baseline, each first frequency peak having a first peak ratio of less than 0.8, the first peak ratio being equal to an area between the first frequency peak and the first baseline divided by an area beneath the first frequency peak; and   the second Fourier power spectrum includes one or more second frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a second baseline, each second frequency peak having a second peak ratio of less than 0.8, the second peak ratio being equal to an area between the second frequency peak and the second baseline divided by an area beneath the second frequency peak.   
     
     
         14 . The optical film of  claim 13 , wherein the first and second peak ratios are each less than 0.5. 
     
     
         15 . The optical film of  claim 12 , wherein an average size of the first structures is in a range from 20 to 30 microns, and an average size of the second structures is in a range from 4 to 10 microns.