Practical use of lens structures in ID-documents

摘要

Polymer ID-documents mostly are made of plastic foils which are laminated to one massive card by applying heat and pressure. During this lamination process, some structures can be transferred from the metal laminating plate to the card surface. These structures can be shaped in the form of a lens. Both are possible, positive as well as negative lens structures, for example in the form of lines or (micro) text. Also lens arrays of cylinder lenses can be made. The lens structures can be combined with the security design which is printed on the document, resulting in optically variable effects of moire patterns. Also these lens structures can be combined with laser engraving during the personalization of the document. In this way it is even possible to personalize the document with a stereo photo, the so called stereogram. The tactility of the structures on the ID-document, combined with the optical effects, makes these structures a very strong first line security feature. This kind of security features are completely integrated into the card body and combined with the personalization, which make them hard to manipulate by counterfeiters. Because of the fact that the human eye can handle images with a lot of noise, the optical quality of the lenses as well as the focal point seems to be less important for the most applications. Some applications need a rather high optical quality.