METHOD AND APPARATUS FOR MAKING AN OFFSET PLATE

摘要

A plate making method for forming an image on a heat sensitive blank plate by a multichannel method using a plate making machine of outer surface cylinder scanning type. A blank plate (400) is secured to the outer circumferential surface of a hollow cylinder (131). A laser beam (800) is projected from an optical light head (150) onto the surface of the blank plate (400). The laser beam (800) is a beam group consisting of a plurality of infrared laser beams arranged in line. The laser beam (800) is generated based on an image forming signal. Further, the irradiation time of the laser beam (800) is controlled so that the laser irradiation time is short at the center of the line and long at the ends of the line. Application of the laser beam (800) forms an image corresponding to the image forming signal on the heat sensitive layer of the blank plate (400). The control of laser beam irradiation time ensures formation of an image of significantly improved quality thanks to uniform thermal reaction over the entire surface of the heat sensitive blank plate (400).