engleski

INFLUENCE OF SODIUM METASILICATE SOLUTION’S CHARACTERISTICS ON THE DEVELOPING OF THE OFFSET PRINTING PLATE

Lithographic printing is characterized by the fact that the selective ink adsorption in the printing process is achieved by opposite physical-chemical properties of printing and nonprinting areas on the printing plate. The majority of the printing plates used in the offset printing are built from aluminium foil, which is chemically and electrochemically processed in order to form rough and porous aluminium-oxide film and in the end coated by a photoactive coating. The rough aluminium-oxide film will form nonprinting areas, and the photoactive coating forms printing areas. In the plate making process the plate is exposed to an electromagnetic radiation with certain wavelength and subsequently developed to remove parts of the photoactive coating and open the aluminium-oxide layer. The developing solutions are often highly alkaline and could as well dissolve the aluminium oxide layer, thus deteriorating its wetting characteristics. The aim of this paper is to determine influence of the developer saturation and developing time on the characteristics of a printing plate. For that purpose, printing plate samples were made by varying the investigated parameters. To evaluate the influence of considered parameters, contact angle measurements and determination of roughness parameters were performed. Results of the investigation showed that both, developer saturation and the developing time influence surface properties of the made printing plate. It could be concluded that for the investigated range of process parameters increase of the developer saturation and of the developing time increases the wetting characteristics of printing plate. In addition, future research is needed to investigate range of the developer saturation in which the noticed behaviour is occurring i.e. which developer saturation results in unacceptable printing plate’s surface properties.

printing plate; wetting; developing process; sodium metasilicate

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