The newspaper industry has recently been considering computer-to-plate as a way to improve quality, reduce time and eliminate platemaking expenses. Even more recently, though, a new technology has emerged with the potential to leapfrog computer-to-plate---digital presses.
Among several vendors in this area are AM MultiGraphics, Indigo America Inc. and Man Roland Inc. As with any embryonic technology, there is no standard approach.
AM MultiGraphics' Xeikon DCP digital web press uses an electrophotographic process similar that found in color copiers. Dry toner "ink" consisting of 7.5 micron particles is electrostatically transferred to a charged drum to form a latent image, which is then transferred to the paper web. Since the image is recreated after each print cycle, changeover to a new image is instantaneous.
Unlike a copier, which uses a reflected laser beam to image the drum, Xiekon uses a fixed array of light-emitting diodes at a density of 600 per inch. The combination of this array and the very fine toner particles allows the press to achieve a screen resolution of about 170 lines per inch.
AM MultiGraphics says the Xeikon's LED array can create up to 64 gray levels for each dot, while lasers produce only black and white. The Xeikon uses eight print stations to print the four process colors. The manufacturer says this permits excellent registration and reliability at a throughput of 4,200 pages per hour.
Indigo manufactures two types of digital presses---the sheet fed E-PRINT 1000, and the web fed, packaging-oriented Omnius. While both use an offset process, they differ considerably from traditional offset presses.
A laser generates a latent image on an image cylinder. This image is inked with Indigo's liquid "ElectroInk," transferred to a blanket and then to paper. Unlike traditional presses, 100 percent of the ElectroInk is transferred during each impression, allowing a different image to be printed on the blanket after each revolution. Because the blanket cleans up perfectly, Indigo presses use only one blanket and impression cylinder for all four-color impressions, passing the paper across the blanket four times to create process color. As with the Xeikon, the image is recreated during each pass, allowing instant image changes while running. Indigo states that the ElectroInk process allows 800 to 2,000 dots-per-inch printing on a 144-200 lpi screen.
Man Roland's DICOWEB is a hybrid of direct-to-press and traditional offset technologies. In this approach, a thermal transfer mechanism images a water-accepting metal sleeve, which then functions as a traditional offset plate. An automatic cloth-and-solvent system completely cleans the sleeve, which is then re-imaged without removal. Like a standard offset press, the DICOWEB produces one original image and many impressions. Unlike a plate however, the sleeve is not changed unless it is physically damaged. The DICOWEB cylinder and ink-train configurations are similar to those of traditional offset presses.
Steve Ostrofsky is president of Publishing Productivity Systems, Denver. E-mail, stevevelo@aol.com; phone (303) 733-5268.
Related items:
©1997 Newspaper Association of America. All rights reserved.
