Erzsébet Novotny, Ildikó Endrédy

Abstract
Surface refining procedures have an increasing significance in satisfying quality and other special demands (uniqueness, appearance) made on printing house products. Besides the effects intended to be achieved (gloss, mechanical protection) surface refining technologies occasionally can go together with other changes of the optical appearance of the prints.

Within surface refining procedures our tests focused on the effect of varnishing on print appearance. The purpose was to determine the extent and direction of colour changes occurring when paper based cards are produced using different print carrier and varnish combinations.

We examined the change of metric chroma as a function of sample lightness, the change of lightness as a function of the chroma of the samples, hue differences as a function of hue angles of the samples. We established that the Sericol type varnish on matt paper samples showed the biggest, and Wessco type varnish on glossy paper samples the smallest change. Based on our test results we propose some improvement of technological processes.

Keywords: Card printing, UV-varnishing, Gloss measurement, Abrasion test, Colour measurement
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Ivana Žiljak, Klaudio Pap, Jana Žiljak Vujić

Abstract
The development of printing graphics with two images of which one is observed under IR light and the other in daylight is becoming a reality in graphic product protection (Žiljak V., Pap K., Žiljak I., 2008). If we look back into history, up till now there have been two methods for producing double images: on basis of the lenticular method or with the help of holography. Both of the methods require a carrier with specific characteristics in respect to micro lens use or a highly embossed master on special material. In comparison with the mentioned methods infrared graphics are not limited with dimension characteristics. Infrared design is a method independent of material, and all kinds of paper may be used, even silk and textile. In the same way that holograms require specific conditions such as (monochromatic) light sources, infrared design recognizes two images in two different wavelength areas. For instance, any video camera today has the possibility of using the IR area along with the daylight area owing to CCD technology development. This is why the INFRAREDESIGN method can be checked easily, introduced into production and set as the simplest printing method in the graphic securities area.

Keywords: Security, Infrared, Steganography, Printing
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Slavtcho Bonev

Abstract
Security printing based on DataGrid and EpiCode is a novel, very effi cient anti-counterfeiting technique based on the individuality of prints. DataGrid is a high-density halftone data storage which forms a unique signature – the so called EpiCode - when it is printed. The EpiCode is caused by the physical interaction between printing medium (ink) and substrate (paper) and is used as a fi ngerprint for authentication. In sheet-fed offset printing the signature of the printing plate is a novel feature for anti-counterfeit applications. In the presented printing tests, the infl uence of the substrate on the EpiCode and the long-term stability of the offset printing process regarding the plate signature are determined using biometrical analysis. Equal error rates (EER) better than 10-40 are achieved in the case of four paper grades commonly used for labels and packaging. Further, the printing plate signature has proven a stabile feature for a cluster of printed DataGrids and is therefore called ClusterCode. Authentication based on ClusterCode achieved equal error rates (EER) better than 10-10. In addition, a recognition system using a reduced database is proposed.

Keywords: Security printing, Paper substrate, Long-term stability, Print quality control, Biometrical system
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