| 摘要 |
PROBLEM TO BE SOLVED: To prevent the change of potential in spike shape from occurring on an electrified printing plate when a notch reaching the periphery part of the printing plate is formed on a surface plane for plotting. SOLUTION: In the case of forming the notch 154 reaching the periphery part of the printing plate 12 at the end in the moving direction of the plotting surface plane 22, a numerical aperture Q being the ratio of the total sum Ws of the width dimension Wd of the notch to the width dimension WD of the plotting surface plane is set to be <=75% when the notch is formed at one spot or dispersed to plural spots in a width direction orthogonal to the moving direction of the plotting surface plane. Thus, the potential at the end in the moving direction of the printing plate is prevented from rising in the spike shape when exposure is performed by moving the plotting surface plane relatively to an electrifier while controlling the current of a high voltage power source for discharge, and all the surface of the printing plate is electrified so that its potential may be uniform.
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