Intaglio printing is one of the basic methods for protection of the strict accounting documents, in particular banknotes, all over the world. The peculiarity of this printing method is the possibility to form the strokes with different ink layer thickness (up to 320 microns) on the prints. It provides identification of the authenticity of the strict accounting documents by the public, including visually impaired people. But there is the paucity of theoretical and practical developments regarding the intaglio printing. The dissertation is devoted to the establishment of regularities of the influence of the intaglio printing technological factors on the prints quality.
The following new scientific results were obtained in the dissertation. The generalized hierarchical model of intaglio prints quality forming, based on a detailed analysis of professional literature and scientific sources, was developed for the first time. It consists of the group of quality indicators and the main technological factors that influence prints quality. This model, in conjunction with the developed set of models of prints quality dependence on technological factors, allows to determine the conditions of the qualitative technological process of intaglio printing;
The phenomenological model of intaglio ink transferring was developed and a mathematical description of physical processes, occurring during intaglio ink transferring, was made for the first time . Thus, the basic technological parameters that influence the prints quality were determined. This model allows to determine the function of the dependence of the transferred ink amount on the technological printing parameters.
The conceptual model of intaglio ink relief formation was improved. In particular, the influence of inertia and heat exchange processes on intaglio ink layer formation was modeled. The modelling in combination with the experimentally established dependencies of the ink layer properties on the parameters of the printing plate (profile type, width, depth of the engraved elements, width of the non-image portions) and the printing process (printing pressure and printing speed) can be used for the purposefully influence on the prints quality.
These models explained the cause of asymmetry of the cross-sectional shape of strokes obtained by the intaglio printing.
The model of intaglio ink penetration and its distribution during intaglio printing was further developed. It allowed to investigate how the pressure that acts throughout the printing contact can influence the ink penetration depth.
The results of modeling are confirmed by experimental research which was carried out with using of the developed method of determination of the generalized quality index of intaglio printing. The method allowed to increase the objectivity of quality evaluating and detect the regularities of the influence of the technological process parameters on the intaglio prints quality parameters.
The methodology is based on surface profilometric and microscopic analyses as well as on organoleptic and visual analyses of prints.
The group of quality indices, which were subject to investigation, consist of thickness of ink layer, the width of the printed strokes, the size of vertical ink penetration, the value of lateral ink penetration, the values of the left and right edge angles of printed strokes and coefficient of loss ink layer thickness, the rate of ink injection, the rate of ink outflow, percentage of tactile discrimination of samples, visual rate of samples.
It was found that the most effective factors that influence the quality of the ink relief forming are the geometric parameters of the plate as well as the technological print parameters, such as print pressure and print speed.
Based on the experimental study results, it was recommended to use a printing plate with the engraved elements of a rectangular profile or trapezoidal profile with an angle of 75 degrees and the element width to depth ratio of more than 1.3 times. It was also recommended to use reduced printing speed and high pressure in printing nip.
The correlation analysis of the dependence of the generalized quality index on technological factors was made. As a result, the ranking of the factors on the weight of their influence was carried out. Due to the weight of influence, technological factors were ranked as follows: engraved elements width - engraved elements profile - engraved elements depth - pressure in the printing contact - printing speed - width of the non-image portions.
These conclusions became the basis for the recommendations given to the Banknote Printing and Minting Works of National Ukrainian Bank. The recommendations were aimed at ensuring the quality of the intaglio printing which is produced by the plates made by direct laser engraving.
