PROCESS OF PRODUCING DIFFRACTION GRATINGS ON THE SURFACES OF ARTICLES

摘要

The invention provides a process of producing an article, such as a foil or a beverage can body, having a surface provided with an optical diffraction grating such that the surface generates visible interference colors when illuminated with diffuse white light. The process comprises producing the article from stock material by one or more steps including a step in which a surface relief pattern forming a diffraction grating is impressed on the surface of the article by a tool having a bearing surface provided with a corresponding surface relief pattern. The pattern on the bearing surface is made up of ridges and/or grooves on or in the bearing surface that are straight parallel lines separated by distances suitable for light diffraction. As the pattern is being impressed, the article is moved relative to the tool in a longitudinal direction of movement and the tool is orientated such that the ridges and/or grooves making up the diffraction pattern are aligned parallel to the direction of movement of the article. Any stretching or deformation of the article produced during the impressing of the diffraction grating takes place in the same direction as the lines of the diffraction pattern, so that the pattern is not destroyed or deformed, but is merely attenuated in the longitudinal direction that does not affect the interference pattern effects (governed by the line spacing). The resulting coloring process produces an attractive article and is capable of being operated at a high rate of throughput.