High incidence angle retroreflective sheeting

Abstract

A retroreflective sheeting which comprises a front sheet of an optically transmissive material and a reflective back sheet bonded to the front sheet. The front sheet includes a plurality of parallel channels defining surfaces which reflect light using a total internal reflection and configured to retroreflect high-incidence-angle light rays at least in one plane. The retroreflective sheeting may have a plurality of retroreflective areas with different orientations of the channels and/or different retroreflective properties with respect to light incident onto the retroreflective sheeting at high incidence angles.

What is claimed is: 
     
         1 . A high incidence angle retroreflective article, comprising:
 a flexible sheet-form structure having a thickness between 100 micrometers and 2 millimeters and comprising a front sheet of an optically transmissive material, which has a front surface and a parallel back surface, and a back sheet of an optically transmissive material bonded to the front sheet and having a front surface facing the back surface of the front sheet and a parallel back surface facing away from the front sheet;   a plurality of parallel channels formed in the front sheet and each having a pair of opposing parallel walls extending perpendicular to a plane of the front sheet; and   a mirror coating formed on the back surface of the back sheet,   wherein at least one of the opposing parallel walls is configured to reflect light using a total internal reflection and has a root mean square surface profile roughness parameter of at least 10 nanometers and equal to or less than 60 nanometers at a sampling length between 20 and 100 micrometers.   
     
     
         2 . A high incidence angle retroreflective article as recited in  claim 1 , wherein the thin and flexible sheet-form structure is configured to retroreflect an incident off-axis light ray in a first plane that is perpendicular to the plurality of parallel channels and reflect said light ray without retroreflection in a second plane that is orthogonal to the first plane. 
     
     
         3 . A high incidence angle retroreflective article as recited in  claim 1 , further comprising a prism layer located in front of the front sheet, wherein the prism layer comprises a plurality of asymmetric triangular prisms each having a first sloped face and a second sloped face forming a different dihedral angle with respect to the plane of the front sheet than the first sloped face. 
     
     
         4 . A high incidence angle retroreflective article as recited in  claim 3 , wherein the prism layer is formed in a surface of a flexible sheet substrate which is bonded to the front surface of the front sheet. 
     
     
         5 . A high incidence angle retroreflective article as recited in  claim 3 , wherein the prism layer is formed in the front surface of the front sheet. 
     
     
         6 . A high incidence angle retroreflective article as recited in  claim 3 , wherein the thin and flexible sheet-form structure is configured to be operatively positioned such that the first sloped face is facing an expected light source direction. 
     
     
         7 . A high incidence angle retroreflective article as recited in  claim 1 , further comprising a prism layer positioned in front of the front sheet, wherein the prism layer comprises a plurality of symmetrical triangular prisms each having a first sloped face and a second sloped face forming approximately the same dihedral angle with respect to the plane of the front sheet as the first sloped face. 
     
     
         8 . A high incidence angle retroreflective article as recited in  claim 1 , comprising a plurality of retroreflective areas having different retroreflective properties, wherein the parallel channels within a first one of the plurality of retroreflective areas are disposed in a first orientation and the parallel channels within a second one of the plurality of retroreflective areas are disposed in a second orientation which is different than the first orientation. 
     
     
         9 . A high incidence angle retroreflective article as recited in  claim 1 , wherein the front surface of the front sheet has a light diffusing texture configured to disperse a parallel or near-parallel beam of light within a predetermined range of directions. 
     
     
         10 . A high incidence angle retroreflective article as recited in  claim 1 , wherein the optically transmissive material of the front sheet comprises plasticized polyvinyl chloride. 
     
     
         11 . A high incidence angle retroreflective article as recited in  claim 1 , wherein the parallel channels are configured at a spacing distance L and a depth D which are bounded by a relation 
       
         
           
             
               
                 L 
                 D 
               
               < 
               
                 2 
                 
                   
                     
                       n 
                       2 
                     
                     - 
                     1 
                   
                 
               
             
           
         
       
       in which n is a refractive index of the optically transmissive material of the front sheet. 
     
     
         12 . A high incidence angle retroreflective article as recited in  claim 1 , wherein the parallel channels are spaced from each other by a distance that is 1.5 times greater than a depth of the parallel channels and is at least 6 times an average width of the channels. 
     
     
         13 . A high incidence angle retroreflective article as recited in  claim 1 , wherein a thickness of the front sheet is between 100 micrometers and 1 millimeter. 
     
     
         14 . A high incidence angle retroreflective article having a thin and flexible sheet-form structure and comprising:
 a front sheet of an optically transmissive material;   a back sheet of an opaque material bonded to the front sheet and having a reflective front surface; and   a plurality of retroreflective areas distributed over an area of the flexible sheet-form structure and having different retroreflective properties from one another,   wherein a first one of the plurality of retroreflective areas has a first plurality of channels formed in the front sheet and each defining a first pair of opposing parallel walls configured to reflect light using a total internal reflection, wherein a second one of the plurality of retroreflective areas has a second plurality of channels formed in the front sheet and each defining a second pair of opposing parallel walls configured to reflect light using a total internal reflection, and wherein an orientation of each of the first plurality of channels within the first one of the plurality of retroreflective areas is different than an orientation of each of the second plurality of channels within the second one of the plurality of retroreflective areas.   
     
     
         15 . A high incidence angle retroreflective article as recited in  claim 14 , wherein a surface of at least one of the first pair of opposing parallel walls has a root mean square surface profile roughness parameter of at least 10 nanometers and equal to or less than 60 nanometers at a sampling length between 20 and 100 micrometers, and wherein a thickness of the front sheet is between 100 micrometers and 1 millimeter and a thickness of the back sheet is between 100 micrometers and 2 millimeters. 
     
     
         16 . A high incidence angle retroreflective article as recited in  claim 14 , wherein the parallel channels are configured at a spacing distance L and a depth D which are bounded by a relation 
       
         
           
             
               
                 L 
                 D 
               
               < 
               
                 2 
                 
                   
                     
                       n 
                       2 
                     
                     - 
                     1 
                   
                 
               
             
           
         
       
       in which n is a refractive index of the optically transmissive material. 
     
     
         17 . A high incidence angle retroreflective article as recited in  claim 14 , wherein each of the first and second pairs of opposing parallel walls extend perpendicular to a surface of the front sheet. 
     
     
         18 . A high incidence angle retroreflective article as recited in  claim 14 , further comprising a prism layer formed in a surface of the front sheet, wherein the prism layer comprises a plurality of asymmetric triangular prisms each having a first sloped face and a second sloped face forming a different dihedral angle with respect to a plane of the front sheet than the first sloped face, wherein the thin and flexible sheet-form structure is configured to be operatively positioned such that the first sloped face is facing an expected light source direction. 
     
     
         19 . A high incidence angle retroreflective article as recited in  claim 14 , wherein a third one of the plurality of retroreflective areas comprises a cube-corner or full-cube retroreflective material. 
     
     
         20 . A high incidence angle retroreflective article as recited in  claim 14 , wherein a third one of the plurality of retroreflective areas comprises retroreflective beads.