Color change devices incorporating thin anodic films

Abstract

A laminated color change device which exhibits an irreversible color change upon delamination. The device comprises two layers capable of generating a color by a light interference and absorption phenomenon that requires direct and intimate contact between the two layers. One of the layers is a color-generating metal, such as a valve metal (e.g. tantalum), and the other is an overlying light-transmitting film thin enough to cause light interference effects. The film is produced by coating the color generating metal with aluminum or an aluminum alloy and then anodizing (preferably porous anodizing) the aluminum to consumption in the presence of an adhesion-reducing agent, e.g. fluoride, that reduces the strength of attachment between the layers so that the laminate can be uniformly and reliably separated at the interface between the adjacent two layers. An overlying layer of transparent or translucent material is normally adhered to the laminate to facilitate the separation of the layers. When the thin film is detached from the color-generating metal, the generated color is lost, thus providing a color change that is in effect irreversible. The device can be incorporated into a variety of closable articles or products to provide evidence of opening or tampering, or can be used for other purposes.