Embossed Metallic Flakes Process And Product

Abstract

A process for preparing embossed fine particulate thin metal flakes having high levels of brightness and color intensity. The process comprises forming a release coat on a flexible polymeric carrier film, embossing the release coat with a diffraction grating pattern that is monoruled at an angle above 45°, vacuum metalizing the embossed release surface with a highly reflective metal such as aluminum, and solubilizing the metalized release coat in a solvent for removing the metal from the carrier to form embossed metal flakes that replicate the embossment pattern. The flakes are recovered from the solution containing the solvent and release coat polymer while avoiding high shear, particle sizing or other application of energy that would excessively break up the flakes, so that the D50 particle size of the flakes is maintained at or above 75 microns. The flakes have application to coatings and printing inks that produce extremely high brightness characterized as an optically apparent glitter or sparkle effect in combination with high color intensity or chromaticity.

1 . A process for making embossed fine particulate thin metallic flakes having brightness and color intensity, comprising providing a release surface on a carrier, embossing the release surface with a diffraction grating pattern having an angular ruling pattern greater than 45°, metalizing the embossed release surface with a thin reflective metal film, removing the metal film from the release surface to form a solvent dispersion of embossed metal flakes that have replicated the diffraction grating pattern, and controlling the particle size of the flakes contained in the dispersion to maintain the embossed flakes contained therein at a D50 particle size at or above 75 microns. 
     
     
         2 . The process according to  claim 1  in which the metal layer is applied to a polymeric release coat which is coated on the carrier and then embossed with the diffraction grating pattern. 
     
     
         3 . The process of forming a first coating containing the embossed metal flakes of  claim 1  dispersed in a polymeric binder, in which the first coating has a substantially higher chromaticity reading and a substantially higher color intensity reading at 75° and 110° angular measurements when measured on a multi-angle spectrophotometer, when compared with a second coating containing a dispersion of D50, 50 micron size embossed flakes made by a similar process and contained in the same polymeric binder. 
     
     
         4 . The process of  claim 1  comprising forming a coating containing a polymeric binder containing the embossed metal flakes of  claim 1 . 
     
     
         5 . The process according to  claim 1  in which the embossed metal flakes have a diffraction grating pattern of less than about 14,000 grooves per centimeter, a flake thickness from about 50 nm to about 100 nm, and a groove depth of less than about 140 nm. 
     
     
         6 . The process according to  claim 1  in which the embossed metal flakes have a particle size range of (a) or (b):
 (a) from 75 to 200 microns, or 
 (b) from 75 to 150 microns. 
 
     
     
         7 . The process according to  claim 1  in which the embossed metallic flakes have a thickness range of (a) or (b):
 (a) from about 5 nm to about 100 nm, or 
 (b) from about 50 nm to about 100 nm; or alternatively, an optical density from about 1.0 to about 3.5. 
 
     
     
         8 . The process according to  claim 1  in which the embossed metallic flakes contained in the solvent dispersion are subjected to no applied energy that would reduce particle size greater than low speed mixing, or would reduce particle size more than 20 microns. 
     
     
         9 - 20 . (canceled) 
     
     
         21 . The process of  claim 1 , wherein controlling the particle size of the embossed metal flakes contained in the dispersion to maintain the embossed flakes contained therein at a D50 particle size at or above 75 microns comprises,
 allowing the embossed metal flakes to settle to a bottom of a vessel,   removing a resin-rich liquid layer from a top of said vessel, and   collecting the embossed metal flakes.   
     
     
         22 . The process of  claim 1 , wherein after removing the metal film from the release surface, said process is free of centrifuging of the solvent dispersion, sonolater treatment of the solvent dispersion, and high shear mixing of the solvent dispersion. 
     
     
         23 . The process of  claim 1 , wherein the embossed metal flakes have a diffraction grating pattern of from about 5,000 to less than about 14,000 grooves per cm. 
     
     
         24 . The process of  claim 1 , wherein the embossed metal flakes have a groove depth to flake thickness ratio of greater than 1.0. 
     
     
         25 . The process of  claim 1 , wherein said angular ruling pattern is 60°. 
     
     
         26 . The process of  claim 1 , wherein said embossed metal flakes have an optical density of 3.0 or more and a D50 average flake size greater than 200 microns. 
     
     
         27 . The process of  claim 1 , wherein said embossed metal flakes have a groove depth from about 125 nm to about 140 nm.