Color change devices incorporating areas of contrasting appearance

Abstract

Process for producing color change devices incorporating areas of contrasting appearance, and the devices so produced. The process involves masking limited areas of a layer of a color generating metal (e.g. Ta or Nb, especially commercially sputtered Ta foil), with a mask made of a material which permits anodization of an underlying surface and permits penetration of fluoride as an adhesion-reducing agent at levels employed in the process. The masked metal layer is anodized to form an anodic film on the metal, the anodization being carried out in an electrolyte containing fluoride at a concentration high enough to (a) weaken the adhesion of the anodic film to the underlying metal over the entire area of the film, and (b) to introduce voids in the anodic film in areas not covered by the mask to reduce the density, and thus the refractive index, of the film in these areas compared to areas covered by the mask. Finally the mask is removed. The device has areas of contrasting color which form a visible pattern that disappears on detachment of the anodic film from the metal. The device can be used, for example, as a product identification code which can be made to disappear after use.