Article having composite lenticular microstructures and method of making

Abstract

Lenticular microstructures and methods of making the same is disclosed. The lenticular microstructures include composite lenticular microstructures having a first light transmissive polymeric layer, a second light transmissive polymeric layer, and an interface therebetween, wherein the first light transmissive polymeric layer has a first index of refraction, the second light transmissive polymeric layer has a second index of refraction, and the first and second indices of refraction have an absolute difference of at least 0.0002.

What is claimed is: 
     
         1 . An article comprising:
 a light transmissive support layer having a generally opposed first and second major surfaces; and   an array of composite microprismatic microstructures disposed on the support layer, each composite microprismatic microstructure comprising a first light transmissive polymeric layer having a first index of refraction and a second light transmissive polymeric layer having a second index of refraction, and an interface therebetween;   wherein the absolute difference between the first refractive index and the second refractive index is at least 0.0002,   
       wherein the light transmissive support layer comprises a printed portion separate from each of the first light transmissive polymeric layer and the second light transmissive polymeric layer. 
     
     
         2 . The article of  claim 1 , wherein each composite microprismatic microstructure comprises up to 95% by volume of the second light transmissive polymeric layer. 
     
     
         3 . The article of  claim 2 , wherein each composite microprismatic microstructure comprises up to 60% by volume of the second light transmissive polymeric layer. 
     
     
         4 . The article of  claim 2 , wherein the first light transmissive polymeric layer comprises the remaining volume of each microprismatic microstructure. 
     
     
         5 . The article of  claim 1 , wherein the absolute difference between the first refractive index and the second refractive index it at least 0.001. 
     
     
         6 . The article of  claim 1 , wherein the first light transmissive polymeric layer and the second light transmissive polymeric layer each comprise a light transmissive polymeric material, and wherein the light transmissive polymeric material in the first light transmissive polymeric layer is a more highly irradiated form of the light transmissive material in the second light transmissive polymeric layer. 
     
     
         7 . The article of  claim 1 , wherein the composite microprismatic microstructures form an optically variable mark. 
     
     
         8 . The article of  claim 7 , wherein the optically variable mark has a varying appearance depending on the viewing angle. 
     
     
         9 . The article of  claim 1 , wherein the interface is a curved surface. 
     
     
         10 . The article of  claim 1 , wherein the interface is visually discernable between first light transmissive polymeric layer and second transmissive polymeric layer. 
     
     
         11 . A method of making a microstructured article, the method comprising:
 providing a molding tool having a microstructured surface including a plurality of microprismatic cavities;   applying an uncured first radiation curable resin to a portion of the microprismatic cavities in a desired pattern, partially filling a portion of the cavities and forming partially filled microprismatic cavities and unfilled microprismatic cavities;   exposing first radiation curable resin to a first irradiation to provide pre-cured partial microprismatic microstructures;   contacting the pre-cured partial microprismatic structures and unfilled microprismatic cavities with a second radiation curable resin, forming a composite;   exposing the composite to a second irradiation to provide composite microprismatic microstructures and monolithic microprismatic microstructures on the surface of the molding tool; and   separating the composite microprismatic microstructures and monolithic microprismatic microstructures from the surface of the molding tool.   
     
     
         12 . The method of  claim 11 , further comprising bringing the second radiation curable resin into contact with a light transmissive support layer prior to the second irradiation.