Web-fed offset printing press capable of image conversion without web

Abstract

An offset perfecting press is disclosed which has a pair of blanket cylinders on opposite sides of a web traveling along a predefined path. Bearing different images to be printed, two plate cylinders are disposed in circumferentially spaced apart positions on each blanket cylinder. Each plate cylinder is independently movable between an image transfer position, where the plate cylinder is held to the blanket cylinder in order to print an image thereon for subsequent transfer to the web, and an image nontransfer position where the plate cylinder is spaced from the blanket cylinder. Only one plate cylinder is held in the image transfer position on each side of the web. For a change from one image to another, the plate cylinders that have been printing the opposite sides of the web are retracted to the image nontransfer positions, and the other plate cylinders, rotating in phase with the blanket cylinders, are moved to the image transfer positions. There is no need for stopping the web or the blanket cylinders. An electronic control system is provided for automatic image conversion. A multiple-unit, multiple-tower, multiple-web rotary press is also disclosed which comprises a multiplicity of printing units, including one or more constructed as in the foregoing, which are arranged in multiple towers for concurrently printing multiple webs under automatic control.