Summary

CTP, Computer-to-Plate, has become established as a production process at newspaper plants primarily in Eu-rope. It is estimated that in Europe approximately 30-40% of all newspaper plates are produced by the CTP process. In other regions also, the number of imagers is increasing. However, the seemingly perfect optical process of laser-imaged plates is poor in allowing sufficient conclusions to be drawn concerning the actual plate quality. In many cases, defective plates are not recognised before being found unsuitable for printing on the press. For this reason, it would be desirable to have available a quality assurance system for the CTP process that would permit immediate confirmation and guaranteed print run stability of the CTP plate as well as the desired dot gain. As many process parameters as possible should be recorded by the CTP production system for the purposes of analysis and correction in a closed loop process. Ideally, such a closed loop control system would permit automatic optimal plate quality. A first step towards automatic quality control would be for the system concerned to draw attention to a faulty plate. In a further step, it would be desirable for the system to provide details relating to the location or cause of the problem. The process of identifying the cause has already been developed and partially tested in practice. A detailed test under production conditions is scheduled to follow. An automatic control could be conceivable only as a third and final step. The Ifra Working Group on CTP Closed Loop Measurement was formed from users and manufacturers who are involved in a CTP production line. The Ifra Special Report "Automated process control in CTP production" documents the results of this Ifra Working Group. The object of the work was the start of a study to show possible measuring and control solutions for improving the quality of CTP production. The Working Group concentrated on photopolymer plates that are imaged in the visible light range. The decision to do so was based on the fact that photopolymer plates have a large market share among European newspaper CTP installations and quality control is more extensive there than, for example, in the silver-based plates market. The manufacturers participating in the project had already demonstrated the feasibility of such a process control concept to an interested trade public at the Ifra Expo 2000 in Amsterdam. In August 2001, a prototype control system (see Figs. 10 and 11) was integrated for a limited period for test purposes into one of the two CTP production lines installed at the Darmstädter Echo. The integra-tion of a final version of the prototype is planned for September 2001. After the Ifra feasibility study is completed, the project will be independently pursued further by the two participating manufacturing companies with a view to developing a prototype for the final objective of obtaining a practice-oriented product solution that is suitable for serial production. GmbH, Königstein, D