1. Field of the Invention
The present invention relates to an improved system for making printing plates for newspaper printing by a computerized direct laser drawing technique.
2. Description of the Prior Art
The recent progress of computer information and image processing technologies has found its way into such fields as newspaper printing, too, bringing about development of a system for making printing plates for newspaper printing by the so-called computer to plate (CTP) technique. In this method, image signals from the computer activate a laser scanning head to draw desired images directly on a printing plate.
Examples of this type of plate making system were developed by the inventors of the present invention and are disclosed in the Japanese patent applications published unexamined under Nos. 9-66595 and 9-334320. Those plate-making systems are formed from a plate feeder (plate feeding section), an exposure unit (electrostatic charge/drawing section), a plate discharging mechanism (plate discharging section) and development unit (heating, developing, rinsing, rubber coating, and drying), a bending mechanism (bender), and a printing plate storing device (stacker). These elements are arranged in the order specified and can make printing plates in different sizes ranging from one page of newspapers to several pages.
Large-size printing plates made by such plate-making systems save much time required to replace plates on the rotary press. That in turn raises the rate of operation, thereby printing more pages of the newspaper.
Meanwhile, newspaper report articles have been getting more and more locally diversified in content in recent years, and advertisements have also been diversified, with newspapers now being printed in many different forms and editions. That has resulted in increased printing of local editions, newspapers having local newspaper sections, that is, zoning newspapers, newspapers with pages suited for specially chosen readers (tailored newspapers), and newspapers with pages suited for specially chosen advertisers (targeted newspapers).
In printing such newspapers, it often happens that articles (that is, the contents) of a specific page in the newspaper has to be replaced. In conventional newspaper printing, a printing plate wound around the plate cylinder of the rotary press had four or two pages. For replacement, where a four-page plate was used, a whole plate having four pages had to be replaced with a new plate having four pages. If two plates, each for two pages, are mounted on the rotary press, one plate of the two had to be replaced with a new one.
To further illustrate, if the printing face B1 of a two-page printing plate P on the rotary press as shown in FIG. 9 is to be switched to printing face A1 or A3, or if the printing face B2 of a two page printing plate P is replaced with a printing face A1 or A3, four printing plates P as shown in FIG. 10 are prepared for any of those changes, so that the printing plate P mounted on the rotary press can be replaced by one of the four plates P shown in FIG. 10.
In the conventional plate-making systems, however, the maximum number of printing plates that can be produced by one operation of plate production is two two-page printing plates R To make the four printing plates P as shown in FIG. 10, the plate-making process has to be repeated twice, requiring a long time for producing replacement printing plates R Where a plurality of rotary presses are in operation, the number of printing plates P to be replaced will inevitably increase. That means that many new replacements have to be prepared. Thus the time and cost required for making replacement printing plates P have become a still more significant problem.