Retroreflective Sheet Structure

Abstract

A retroreflective sheet structure ( 10 ) comprising a transparent layer ( 20 ) having a front light-receiving surface ( 30 ) and a rear retroreflecting surface ( 32 ). Light incident on the front surface ( 30 ) will pass through the layer ( 20 ), impinge on the rear retroreflective surface ( 32 ) and reflect back out through the front surface ( 30 ) in a predetermined direction. An identifying indicia ( 44 ) is chosen and then formed on the retroreflecting surface ( 32 ). This indicia ( 44 ) can be used for identification purposes, even years after an end product incorporating the reflective sheet structure ( 10 ) has been out in the field.

What is claimed is: 
     
         1 . A method of making a transparent layer ( 50 ) that has a front-light receiving surface ( 30 ) and a rear retroreflective surface ( 32 ) that includes a repeating array of retroreflective elements ( 34 ) and identifying indicia ( 44 ) at predetermined positions and/or intervals for retroreflective sheeting ( 48 ), said method comprising the steps of:
 embossing a thermoplastic film ( 60 ) with a tool plate ( 62 ); and   cooling the embossed thermoplastic film ( 60 );   wherein the tool plate ( 62 ) has a topography corresponding to the inverse of reflective elements ( 34 ) and identifying indicia ( 44 ).   
     
     
         2 . The method of  claim 1  wherein the tool plate has a length in the range of about 5 inches to 60 inches. 
     
     
         3 . The method of  claim 1  wherein the tool plate has a width in the range of about 5 inches to 60 inches. 
     
     
         4 . The method of  claim 1  wherein the majority of retroreflective elements ( 34 ) are planar without any outthrusts or depressions. 
     
     
         5 . The method of  claim 1  wherein one face ( 36 ) of at least some of the retroreflective elements ( 34 ) have planar disturbances ( 42 ). 
     
     
         6 . The method of  claim 5  wherein the planar disturbances ( 42 ) correspond to the identifying indicia ( 44 ). 
     
     
         7 . The method of  claim 1  wherein the topography of the tool plate ( 62 ) comprises a series of polyhedron projections ( 64 ). 
     
     
         8 . The method of  claim 7  wherein the polyhedron projections are pyramids each having three faces ( 66 ) arranged at mutually right angles and connected by edges ( 68 ) which join at an apex ( 70 ). 
     
     
         9 . The method of  claim 8  wherein the majority of faces ( 66 ) have flat planar surfaces. 
     
     
         10 . The method of  claim 9  wherein at least some of the remaining faces ( 66 ) have a disturbance formed thereon. 
     
     
         11 . The method of  claim 10  wherein the disturbances ( 72 ) corresponding to the inverse of the intended planar disturbances ( 42 ). 
     
     
         12 . The method of  claim 10  wherein the disturbance ( 72 ) is a depression. 
     
     
         13 . The method of  claim 10  wherein the disturbance ( 72 ) is a projection. 
     
     
         14 . The method of  claim 5  wherein most of the disturbed face ( 36 ) reflective regions remain intact. 
     
     
         15 . The method of  claim 1  wherein the identifying indicia ( 44 ) becomes visually detectable at an inspection distance of about 20 cm or less. 
     
     
         16 . The method of  claim 1  wherein the identifying indicia ( 44 ) will not interfere with or detract from the retroreflective qualities of the structure.