Use of Clear Toner in Electrophotography for Security Applications

Abstract

Most electrophotographic printers consist of four development modules to generate images based on CYMK process colors. Often a printer hardware design can accommodate more than the standard four development modules. In such cases, extra modules can be used to provide additional features to the resulting image. When colors other than CYMK are used in such fifth or higher electrophotographic modules of a color printer, various enhanced improvements that are possible in the printed image include: spot or corporate colors, extended color gamut colors, and pentachrome or even hexachrome color processes.If a clear toner is used in one of these additional modules, a wide variety of image enrichments can be integrated into the final image. The most common application for the clear toners is to provide a protective barrier to physical abrasion to the image as well as to impart uniform image gloss.Because of increased emphasis on incorporating security features in a color print, clear toner can also be utilized to provide both overt and covert security features within the image. There are several types of security features that can be enabled with the use of these special clear toners. Clear toner can be judiciously placed in or around the image to provide either a positive or a negative watermark to the image. Another security feature that can be enabled with clear toner is raised letter printing to provide a tactile appearance similar to thermography. Not only are these features difficult to copy, but they also provide an easy detection capability. By proper selection of suitable toner additives, clear toner can also be used for alternate features such as traceless security printing and UV fluorescent detection. This work will summarize the novel image features that can be implemented in an electrophotographic system by using a special clear toner in addition to the four process colors.