Znanstveno stručni skup TISKARSTVO 07
15. i 16. Veljače, Stubičke toplice

Mr.sc. Ivana Žiljak

Security graphics with changeable digital print colors in the visible and invisible spectre part
Keywords:security graphics, digital printing, counterfeiting by printing

There are printing inks with changeable tones of color for almost all kinds of printing. The tones depend on the angle of vision, light intensity, light wave length, quantity of used ink, special effects depending on how the ink penetrates into paper, and depending on the combination with screening element form. Printing with changeable color inks is a new and unexplored area in digital printing. Mixing of inks with a changeable UV response is the center of focus for this research. The research aims to determine the way color changes under the influence of different light wave lengths using colorimetric methods. The assertion is that it is possible to determine uniformly the transformation of colors from the invisible into the visible spectral area for an given number of defined colors with the following parameters: lightness, color tone and saturation. There is connection between the response of light from graphics made by digital printing and those to which invisible UV and IR inks have been added. It is possible to prove that a document is counterfeited by exposing it to UV and IR light and finding the UV and IR light specific wave lengths that demarkate inks on the counterfeit product and the authentic one. This subject matter's experimental part is the digital printing techniques and materials because most counterfeits are based on these printing components.

Planning the changeability of color tones

An ink that is considered as a standard one is mixed with UV components and a third non-applied color is made for which it is necessary to determine its transformation area under the influence of UV and IR light. In preliminary research work experimental printing with UV and IR inks was carried out as a basic application of a security document's execution. Furthermore, printing with digital techniques expanded the complexity of experimentally produced securities protection. In a certain sense this made way for a new approach to expanding the topic of preventing counterfeit production.

The light with which we treat the print with prepared inks for this research will be in the range from ultraviolet to the visible and to the specter infrared part. The offered transformation method becomes important when the print's authenticity needs to be proved. The same method will be applied in the visible part of the specter, but by observing color tones and the light intensity changes. In this way the color authenticity will be proved in the visible area, for instance the authentic and forged ball pen signature and to security graphics. Many inks have „their way” in the HSB system if one takes into consideration the difference in the light influencing the print.

The invisible specter part is converted into the visible part in order to carry out the reaction analysis and the color tone changing in respect to the UV and IR light. The importance of this research work is in opening the way for new procedures in proving the graphic product's authenticity. The system of marking products is introduced through a precisely coded tone structure and its behavior under different lighting conditions.

Inks that are invisible in the visible specter part are treated with other sources from the invisible specter with the goal that they will respond in the visible specter part. A dictionary covering this narrow expert area is given for discussion needs. Let us make the following definition: those inks that respond under the influence of UV light, and may be transformed into the visible area will be named as UV inks, and the same will be done with IR color names. Changes take place under the influence of UV and IR light even in respect to inks that are visible in daylight but they change their parameter value depending on the color system we observe them in. Significant changes of such colors are also the subject of this research work. Certain color tones change from dark to light, from one color value to a completely different one depending on saturation values.

Experimental work

A graphic product in the security graphics area is made with several different types of printing. Efforts are made to apply UV inks in all printing techniques and to maximize the security complexity in order to prevent counterfeiting. Digital printing with UV inks is a novelty so that more attention should be paid to this area due to its being unexplored and inaccessible. This new material may be approached with more caution and security and care be taken in respect to the ways of distribution. The ink layer and the covered surface are small because the graphics in question are line graphics. As a consequence the ink costs for specially designed security graphics are also small so that digital techniques may be applied even in cases of big printing runs.

The presence of several printing techniques and different types of inks in respect to the same graphics product requires a specially designed description system, measurements of the light response and formalisms in defining the conditions for quality and characteristics testing, as well as measuring color tone parameters. It is necessary to make design documentation for a produced graphic product with security elements on procedures for determining print, design and material authenticity, as well as methods for revealing possible counterfeits before such a product is distributed, in order to have the possibility of determining exactly which product is authentic and which is counterfeit.

UV inks for digital printing, offset printing and relief printing will be used. These are color tones visible in the specter's visible area, and there will be special inks visible only when exposed to UV light or only under IR light. New digital printing technologies are the center of research and new securities will be made with this method and be offered as a possibility of application in future protective graphics production. Scanning and reflexive light response measurements will be done with the help of the „Preojectina“ analyzing system, with filters in the range from 100 to 400 nm for UV light, and from 770 to 1000 nm for IR light. The counterfeits made with the help of the most recent technology will also be analyzed in a wide UV specter, through the visible area to the IR one. A specially designed database will be organized for all analysis and measurements.


The goal of this research work is to prove that there is connection between the prints made with the CMYK system, the Spot system and by applying UV and IR inks. This is a contribution to better understanding of security printing and on basis of this the designing of a strategy for improving the security of documents produced with the help of graphic techniques. This research work should be a contribution in the determining and better demarkation of technologies in UV and IR color area application in security printing, and thereby a contribution to improving the printing practice of graphic securities realization.

New techniques and materials in digital printing are used in this research work with application in the security area of documentation and securities production. It is an obligation for the graphic experts to work in this unexplored area of counterfeits production because most of them are produced with digital techniques. The paper is a contribution to determining and clearer demarkation of circumstances improving security printing technologies and their application. It is also a contribution to improving printing practice and opening of possibilities in further investigation in the graphic securities area. The transfer of the research results to the security printing area in practice will be part of this work. The method of ink mixing is proposed, the determining and defining of color tones with the goal to create a protected code that may be recognized only through authentication evidenced in the documentation. Planned designing of the database for the sample print parameters is necessary in order to detect the counterfeits precisely through such information.