engleski

Characterization of the silver halide printing plate's surface properties

Lithography is a highly complex process, based on different physical-chemical properties of image and nonimage areas. Image areas are hydrophobic and oleophilic which enables them to adsorb printing ink, while nonimage areas are hydrophilic to adsorb fountain solution. It is essential to obtain and keep wanted surface characteristics throughout whole printing process to achieve desired quality level of imprints. Majority of the offset printing plates used are made of an aluminium foil which is mechanically, chemically and electrochemically processed to make a thin porous aluminium-oxide film which forms nonprinting areas. The foil is then covered with a photoactive layer which enables image transfer on the printing plate and builds image areas. There are many photoactive layers used, among others is silver halide layer. The usage of the silver halide technology in the graphic reproduction is not a novelty. The filmmaking phase is based on the usage of the silver halide as the photoactive ingredient. This paper presents results of the surface characterization of Computer to Plate (CtP) silver halide printing plates used in newspaper printing. The investigation was divided in two parts ; first part was to determine influence of the processing solution’s saturation due to the number of plates made and second to determine changes in surface characteristics by the exploitation process. Results of the investigation showed that increasing number of processed printing plates causes decrease of its electrical conductivity causing change in wetting properties of nonprinting areas. Printing process is causing wear of the printing plate but depending on the printing machine construction and position of the plate in it wear of the printing plate is changing.

Lithography; silver halide printing plate; contact angle; surface roughness; material wear

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