April 26, 2009

Anodized Flat Printing Plates

Anodizing is used in the printing industry to increase the life of that aluminum printing plates. The increase life is due to the high mechanical resistance of the anodic oxide film and also to its high adsorptive capacity for the greasy transfer ink. This later property ensures a film fixing of the image of the plate. In the same way, the colloidal water adsorbing film, obtained. In the etching of the plates, is also firmly held. It appears that when printing from anodized plates, less moisture is required, which helps to reduce dimensional changes in the paper. The oxide films used on printing plates must be hard, wear resistant, and should have a good adsorptive capacity. In making plates for printing maps, the aluminum is anodized with alternating current in a 1-2 per cent sulfuric solution with current density 5 amps/ft2, solution temperature not above 30oC, anodizing time 30 minutes and distance between electrodes 150-200 mm.

The process comprises chemical or electrolytic degreasing in an alkaline solution, washing in running water; smudge removal in 50 per cent nitric acid solution, washing in running water; anodizing; washing in running water, drying in a drying oven at 40-50 oC; application of the light sensitive layer and its substance processing. The anodized printing plates are etches with a solution of phophoric acid to which starch is added to act as a colloid. The PH of the etching solution is about 1.

The use of alternating current simplifies the necessary equipment since no D.C. generators or rectifiers are required but the mechanical strength of films obtained by using direct current is better. One set of conditions which has been recommended for the anodizing of printing plates is as follows; solution 150 g/l sulfuric acid, anodic current density, 5-8 amps per sq.ft, temperature of solution, 15-23oC; anodizing time, 15-20 minutes. Films obtained by this treatment have a thickness of 0.0025 min to 0.005 mm and double the life of the printing plate.

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