Which Side Is Stochastic?

The latest generation of polyester-based digital plates is suitable for most printed products—even fine halftones, screen tints and heavy coverage.

As the front cover's apples-and-oranges comparison shows, Mitsubishi Imaging's Silver DigiPlates are capable of 175-line screen resolution. Poly plates can hold stochastically screened dots, too, also demonstrated on the cover. The stochastic fruit was imaged on a separate set of plates and printed in the first of two passes through the press on the 78,000-run job. Know which are conventional? (The answer is at www.graphicartsmonthly.com.)

Polyester has become a viable alternative for process-color printing on two- and four-up presses. Mitsubishi Imaging claims that today's poly prints as well as metal plates. More than half of all CTP installations are non-metal, according to a 2005 State Street study, including an installed base of 20,000 analog and digital DPX platesetters reported by Esko-Graphics, before ECRM acquired the product line last year.

Poly can run on a range of presses, including the 4-color, two-up 20´´ Hamada B452 used to print this month's covers at PPI Graphics, a $4.4-million printer in Canton, OH. The press's auto mounting precisely tensions plates for on-press registration, alleviating concerns about stretch and other mechanical issues. The two- and four-up DPX 2 and DPX 4 platesetters, distributed by Mitsubishi Imaging, feature in-drum punching to ensure accurate register—even on plates made at different times.

With the high price of aluminum and other raw materials, poly plates give small- to medium-sized printers a cost-effective way to realize the benefits of computer-to-plate (CTP) workflow. Automated metal CTP systems cost at least 30% more, says Mitsubishi Imaging.

Particularly for commercial print shops with shorter run lengths, under 25,000 impressions, the poly option offers unattended operation, a smaller footprint and faster throughput. PPI Graphics reports saving some 47% on plate costs alone. Polyester also carries green, eco-friendly aspects—including lower image energy requirements—important to environmentally sensitive printers like PPI.

The half-size B452's auto loading can hang each plate in about 50 seconds. The Hamada dealer packaged the DPX plates with PPI's press when it was purchased in late 2001. Last October, the printer upgraded to a new four-up platesetter “because we wanted to convert the entire pressroom [four presses] to poly plates, and the DPX 4 makes plates big enough for our 20×26´´ [press],” says president Kevin Smith, who employs 20 people at his 25,000-sq.ft. operation.

For this project, PPI used Mitsubishi Imaging's SDP Smart Tools digital workflow software in prepress. Paper is M-real's 80-lb. Galerie Art Gloss Cover.

“There has been no downside to running all poly,” says Smith, who adds that the firm no longer keeps plates for reuse. “Even if run length exceeds the plate life [rated at 25,000 impressions], it's cost-effective to just make another set—our Hamada gets up to color again quickly.”