engleski

Contribution to the printing ink - printing plate – run lenght interactions

The most common printing technique today is lithography. The difference between printing and nonprinting areas on a printing plate is accomplished by opposite physical and chemical properties of those areas. The printing areas are made of photoactive layer that attracts oil and chemical substances with oil solvent – printing inks. The nonprinting areas are made of aluminium-oxide which attracts water based substances – the fountain solution. The amount and stability of printing ink and fountain solution adsorption on these areas have direct influence on the quality level of the final product. It is well known that different printing inks have different chemical composition and that their interaction with the printing areas and wearing of the printing plates is different. It is important to predict these interactions and more over, to predict the stability of the printing process. The aim of this paper was to observe the changes of the coverage of image areas for four main printing colours (cyan, magenta, yellow and black) on the prints in leniency with run length. From this data it will be possible to define the changes of the printing areas on the printing plate. For detail observation of lower (0- 20%) and higher coverage areas they were defined with more control fields. The results obtained in this research confirmed the presumption. Different printing inks have various behaviours during the printing process and different role in wearing of printing plate. Black has smaller influence on wearing of photoactive layer because coverage values of black are nearly the same through the whole printing run. The highest decrease of coverage values was detected by yellow. Generally, all printing inks cause certain decrease of coverage values. These results have been indicating that hard substances in printing inks and friction between printing plate and ink rollers reduce the areas on printing plate covered with photoactive layers. The decreased coverage values have to be taken into consideration before the printing process starts. This information is necessary for the adjustment of all components included in printing process on time for obtaining the prints with adequate quality level.

lithography; coverage value; printing plate; wear of materials; printing ink

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