engleski

Contribution to the corrosion of aluminium-oxide during developing process of the printing plates

Printing plates in offset printing are almost exclusively made of aluminium foils on which two types of surface properties must be enhanced to enable printing process. As in the printing process the surface of the printing plate is in contact with two rollers, first with the fountain solution roller and then with the inking roller, the two surfaces must have opposite surface properties. The printing areas must repel fountain solution but must attract printing ink. The nonprinting areas must repel printing ink, but to enable this they attract fountain solution in a thin but adequate layer. To enable good adhesion of the fountain solution, the aluminium foils is mechanically, chemically and electrochemically processed to make needed surface roughness and to build thin layer of the aluminium-oxide which has hydrophilic properties. Printing areas are built of photo active layer which is needed to enable transfer of the image onto the printing plate [1]. The plate making process is consisted of two main processes, imaging and developing. In the imaging step, photoactive layer is irradiated by a compatible light source to cause change in the solubility in a certain solution – the developer. In the developing step, the imaged plate is immersed in the developer until soluble parts of the photoactive layer are dissolved. As most common developers used today are highly alkaline, the developing process could diminish adhesion properties of the aluminium-oxide layer [2]. Aim of this paper is to determine corrosion of the aluminium-oxide film when immersed into the developer. The developer will be prepared by dissolving crystals of sodium metasilicate in distilled water in concentration of 0.2 mol dm-3. The determination of the developer’s influence on the aluminium-oxide corrosion will be evaluated by conducting potentiostatic and potentiodynamic measurements. In addition, to determine corrosion influence on the printing properties, a laboratory printing will be performed to determine functionality of the nonprinting areas. The results showed that aluminium-oxide is probably dissolving in the developing solution after photoactive layer is removed from its surface. This dissolving is influencing printing properties (as pourer wetting with the fountain solution), but with proper optimization of the developing process one could expect good printing results.

offset printing plates, corrosion, sodium metasilicate, potentiostatic measurements

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