engleski

THE OFFSET PRINTING PLATE CHARACTERISTICS RELATED TO DEVELOPING PROCESS

Offset printing is one of the most common printing techniques used today. It is characterized by two features, the printing ink is not transferred directly from the printing plate to the printing substrate and the selective ink adsorption in the printing process is achieved by opposite physical-chemical properties of printing and nonprinting areas. The majority of the printing plates are built from aluminium foil, which is chemically and electrochemically processed in order to form rough and porous aluminium-oxide film and coated by a photoactive coating. In the plate-making process the plate is exposed to a certain electromagnetic irradiation and then developed to remove parts of the photoactive coating. The developing solutions are in often highly alkaline solution and could dissolve aluminium oxide layer. The aim of this paper is to determine the influence of the developer temperature on the printing plate characteristics. For that purpose, printing plate samples were made by varying developer temperature. Contact angle was measured to evaluate developer’s temperature influence on the nonprinting areas, and coverage values were measured for evaluation of the image elements transfer on the printing plate. The results have shown that the developer’s temperature influences both, the printing and nonprinting areas. The contact angle on the nonprinting areas has polynomial dependence on the developer temperature while increase of the developer temperature causes coverage values to decrease. This research has proved that changing developer temperature in the plate-making process influences printing and nonprinting areas which makes it a significant parameter to watch and optimize for every plate-making process to ensure best possible results in reproduction.

lithography; printing plate; developing process

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