Multicolor interference coating

Abstract

Several techniques may be used for forming a colored interference filter coating on a substrate such as polyester film. The interference filter has two metal reflective films, at least one of which is semi-transparent. A layer of transparent acrylate polymer dielectric between the metal layers completes the interference filter, which may be sandwiched between protective layers. The dielectric is formed by evaporating an acrylate monomer having a molecular weight in the range of from 150 to 600. Preferably the acrylate monomer has a molecular weight to acrylate group ratio in the range of from 150 to 400. The acrylate condenses on the substrate and is polymerized in situ for forming a monolithic film with a sufficient thickness to produce an interference color. In several embodiments different areas of the film have different thicknesses for producing different interference colors. The thickness of the dielectric can be controlled by the amount of monomer condensed, by either controlling the temperature of the condensation surface or controlling the amount of monomer evaporated adjacent a predetermined area of the substrate. Thickness may also be controlled by condensing a uniform layer of monomer and polymerizing the monomer to different degrees for varying the shrinkage of the film and hence the thickness of the film and color.

What is claimed is:  
     
         1 . A method for forming an interference color coating on a substrate comprising the steps of: 
 evaporating an acrylate monomer having a molecular weight to acrylate group ratio in the range of from 150 to 400;    condensing the acrylate monomer on a substrate as a monomer film;    polymerizing the acrylate for forming a polymer film having a thickness sufficient for producing an interference color; and    providing at least partially reflective coatings on both faces of the polymer film.    
     
     
         2 . A method as recited in    claim 1    wherein one of the reflective coatings comprises metal sufficiently thick to be substantially completely reflective.  
     
     
         3 . A method as recited in    claim 2    wherein the metal coating is between the substrate and the acrylate.  
     
     
         4 . A method as recited in    claim 1    wherein both reflective coatings are semi-reflective.  
     
     
         5 . A method as recited in    claim 1    further comprising a release layer between one of the reflective coatings and the substrate for removing the film and coatings from the substrate.  
     
     
         6 . A method as recited in    claim 1    further comprising a protective layer over at least one of the reflective coatings.  
     
     
         7 . A method for forming an interference coating on a substrate comprising the steps of: 
 evaporating a first acrylate monomer;    condensing the first acrylate monomer on a substrate as a monomer film less than one micron thick;    polymerizing the acrylate for forming a first polymer film having a first index of refraction;    evaporating a second acrylate monomer;    condensing the second acrylate monomer on the first film as a monomer film less than one micron thick;    polymerizing the acrylate for forming a second polymer film having a second index of refraction, wherein the second index of refraction is different from the first index of refraction.    
     
     
         8 . A method as recited in    claim 7    further comprising the steps of: 
 evaporating a third acrylate monomer;  
 condensing the third acrylate monomer on the second film as a monomer film less than one micron thick;  
 polymerizing the acrylate for forming a third polymer film having the first index of refraction;  
 evaporating a fourth acrylate monomer;  
 condensing the fourth acrylate monomer on the third film as a monomer film less than one micron thick;  
 polymerizing the acrylate for forming a fourth polymer film having the second index of refraction;  
 evaporating a fifth acrylate monomer;  
 condensing the fifth acrylate monomer on the fourth film as a monomer film less than one micron thick;  
 polymerizing the acrylate for forming a fifth polymer film having the first index of refraction;  
 evaporating a sixth acrylate monomer;  
 condensing the sixth acrylate monomer on the fifth film as a monomer film less than one micron thick; and  
 polymerizing the acrylate for forming a sixth polymer film having the second index of refraction.  
 
     
     
         9 . A method as recited in    claim 7    wherein each polymer film has a molecular weight to acrylate group ratio in the range of from 150 to 400.  
     
     
         10 . A method for forming a multi-color coating on a substrate comprising the steps of: 
 evaporating at least one acrylate monomer having an average molecular weight in the range of from 150 to 600;    condensing the acrylate monomer on a substrate as a monomer film;    polymerizing the acrylate for forming a polymer film having a thickness sufficient for producing an interference color; and    providing at least partially reflective coatings on both faces of the polymer film; and characterized by    forming a predetermined area of the film with a different thickness than the thickness of an adjacent area of the film for producing different interference colors from the respective areas.    
     
     
         11 . A method as recited in    claim 10    comprising the step of controlling the temperature of the substrate to be different in the predetermined area than the temperature of the substrate in the adjacent area during the condensing step.  
     
     
         12 . A method as recited in    claim 11    comprising printing a thermal pattern on the surface of the substrate immediately before the condensing step.  
     
     
         13 . A method as recited in    claim 11    wherein the controlling step comprises condensing the acrylate monomer on a front face of a thin film substrate while a back face of the substrate is in contact with a temperature controlled surface, and maintaining thermal contact between the temperature controlled surface and the predetermined area different from thermal contact between the surface and the adjacent area.  
     
     
         14 . A method as recited in    claim 10    wherein the polymerizing step comprises polymerizing the acrylate in the predetermined area to a different degree than polymerization of the acrylate in the adjacent area.  
     
     
         15 . A method as recited in    claim 14    wherein the polymerizing step comprises exposing the film to radiation and includes irradiating the predetermined area of the film to a different total exposure of radiation from the total exposure of the adjacent area of the film.  
     
     
         16 . A method as recited in    claim 15    wherein the exposing step comprises shielding a portion of the film from irradiation.  
     
     
         17 . A method as recited in    claim 14    wherein the polymerizing step comprises irradiating the film with an electron beam and includes irradiating the predetermined area of the film to a total exposure of electron energy different from the total exposure of electron energy of the adjacent area of the film.  
     
     
         18 . A method as recited in    claim 17    wherein the irradiating step comprises steering the electron beam for irradiating different portions of the film to different total exposures.  
     
     
         19 . A method as recited in    claim 10    wherein the predetermined area comprises a first plurality of stripes and the adjacent area comprises a second plurality of stripes interleaved between the first stripes.  
     
     
         20 . A method as recited in    claim 10    wherein the forming step comprises selectively shrinking the thickness of the predetermined area of the film to a different degree from shrinkage of thickness of the adjacent area of the film.  
     
     
         21 . An interference color filter comprising: 
 a first at least partially reflective layer;    a crosslinked transparent acrylate layer having a molecular weight to acrylate group ratio in the range of from 150 to 400, the acrylate layer having a thickness sufficient for producing an interference color; and    a second at least partially reflective layer on the opposite face of the acrylate layer from the first reflective layer.    
     
     
         22 . An interference color filter as recited in    claim 21    herein one of the reflective layers comprises a substantially completely reflective metal.  
     
     
         23 . An interference color filter as recited in    claim 21    further comprising a protective layer of crosslinked acrylate covering at least one of the reflective layers.  
     
     
         24 . An interference color filter as recited in    claim 21    further comprising a plastic film substrate and wherein one of the reflective coatings is between the substrate and the acrylate layer.  
     
     
         25 . An interference color filter as recited in    claim 21    wherein both reflective coatings are semi-reflective.  
     
     
         26 . A multiple color interference filter comprising: 
 a substrate; and    a monolithic acrylate polymer film deposited on the substrate with a sufficient thickness for producing interference color, a predetermined area of the acrylate film having a first thickness and a second area of the acrylate film adjacent to the predetermined area having a second thickness different from the thickness of the predetermined area.    
     
     
         27 . A multiple color interference filter comprising: 
 a substrate; and    a monolithic acrylate polymer film deposited on the substrate with a sufficient thickness for producing interference color, a predetermined area of the acrylate film having a first degree of polymerization and a second area of the acrylate film adjacent to the predetermined area having a second degree of polymerization different from the polymerization of the predetermined area.