In a recent article I wrote for whattheythink.com, I predicted that violet CtP was now the future of CtP. I wrote this on the basis of the new Fujifilm High Definition violet plate was now at least comparable in terms of imaging quality as any thermal CtP plate. I would now like to follow up on that theme, but instead look at the subject from the technology of imaging, rather than looking at the printing plate. On the subject of printing plates, it has taken time for the formulations of visible light photopolymer plate coatings to catch up with those for thermal plates. Now this has happened the question of which technology to use in future for imaging requires a serious look at ongoing developments in light or power sources for plate imaging.

Thermal plates are imaged by infrared power sources that generate heat. The majority of thermal CtP engines use infrared diodes operating at 830 nm. Violet diode CtP uses laser diodes operating between 400 - 415 nm. How the diodes are used in the two processes is very different. Thermal CtP using heat requires a substantial amount more power to image a plate than violet CtP. Because of this, in order to run at acceptable times for plate imaging, thermal CtP engines require multiple imaging beams. Kodak (Creo) uses 240 imaging beams, and Agfa and Dainippon Screen use up to 512 imaging beams. In most cases violet CtP uses only a single imaging beam. For thermal CtP, to generate the multiple beams either requires a large number of individual diodes, or one very powerful diode bar with multiple emitters, focused onto a switching or optical system that generates the multiple beams. In such cases, for example the Kodak “Square Spot” head, the diode requires liquid cooling, and is prone to failure after a period of time. I have heard the following are expected failure rates. It is likely that 3% need replacement after 2,500 hours of operation, 25% after 5,000 hours, and 65% after 7,500 hours, and almost all within 10,000 hours. The latest “Square Spot” head with a 100-watt diode has a high selling price. This explains why the service contracts on all thermal CtP systems are so much higher than violet CtP systems.

What I want to look at is where things will go in future. The only way I understand to increase the performance of thermal CtP is by ever more powerful diodes. The latest 3 rd generation “Square Spot” head has 100 watts, whereas the 2 nd generation had 40 watts, and I believe the 1 st generation had less than 20 watts. I believe the diodes used in the latest Agfa and Dainippon Screen heads are similar in power. With more power comes the need for more cooling and more sophisticated electronics, and with that more cost. Diodes operating at 830 nm are unique to the imaging of printing plates, so there are no benefits from mass-market diode developments to bring down the costs.