engleski

Chemical Processes in Printing Technology

One of the most commonly used printing technique today is lithography. The printing plate, which is composed of printing (accept printing ink) and nonprinting (must not accept printing ink) areas is highly important factor for all printing processes. Selective ink adsorption on printing plates is usually achieved by geometrical difference between printing and nonprinting areas, but in lithography it is achieved by their different physical-chemical properties. Printing areas are oleophilic (hydrophobic) while nonprinting areas are hydrophilic (oleophobic). In the first step of the printing process, on the printing plate comes fountain solution (water and additives) which is adsorbed only by the nonprinting areas. Printing ink is applied in the second step and it is adsorbed only by the nonprinting areas (not covered with fountain solution). The printing plates are mainly built of aluminium strips that are mechanically, chemically and electrochemically processed in order to make thin and porous film of aluminium oxide (nonprinting areas) and then coated with photoactive layer (printing areas). The plate making process is by aluminium printing plates composed of exposure and developing which remove photoactive layer from nonprinting areas. The aim of this paper is to present the plate making processes and plate parameters’ measuring methods, for example contact angle measurement, determination of the roughness parameters and electrochemical impedance spectroscopy (EIS). In addition, as printing plate-fountain solution interaction is influential for the printing quality, one should define fountain solution’s optimal chemical composition, for what measurements of pH value, electrical

Graphic technology; printing plate; physical-chemical processes; offset printing

Sekcijsko predavanje