Making negatives and plates for printing by electroerosion. III. Use of the direct negative and direct plate

Issues related to the practical usage in the pressroom of both the direct negative and direct plate are discussed. Two concerns associated with the usage of the direct negative during platemaking are treated: 1) the effect of light transmission through defects (voids) in the aluminum film, and 2) the effect of light transmission directly through the aluminum. These concerns may be addressed respectively by careful fabrication of the material and careful control of the exposure conditions during platemaking. Two aspects of the usage of the direct plate are considered: 1) the need for a simple prepress 'activation' treatment, and 2) press-life limitations caused by wear of the direct plate on the press. Passing a direct plate through an activator solution immediately prior to mounting it on the press prevented scumming in the image area and blinding in the background (nonimage) area. The life on the press of the direct plate is limited by the wearing away of the aluminum from the background areas, thereby causing scumming. Changes in the structure of the direct plate which could prolong press life were investigated.