Smart Offset
The latest generation of Direct Imaging presses combines the simplicity and speed of digital print with all the advantages of offset.
If you have detected a resurgence of interest in Direct Imaging (DI) offset presses, you’re not alone. New generation presses, using technology first shown at drupa 2004, are reinventing the offset printing process and expanding market opportunities for print.
Earlier DI presses carried a number of the same features as today’s models—waterless offset, on-press plate imaging, chemistry- free thermal plates. But that’s where the similarities end. Enhancements to the enabling technologies—including improved RIP speeds and color management, refined laser imaging and plates, and presses with fully automated changeover cycles—have increased the advantages inherent in a DI press.
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The latest wave of DI presses is driven by three integrated, newly optimized technologies: Presstek’s ProFire Excel Imaging, its compatible ProFire Digital Media, and an enhanced waterless offset press design. Now “smart offset” DI presses truly combine the superior quality and versatility of ink-on-paper production with the ease and automation of digital print. This simplified four-color offset printing process makes these presses ideal for graphic arts businesses seeking the ability to cost-effectively produce small-format high quality short run color.
The complete Presstek DI solution is bundled into a compact simple-to-operate, one-source package. Increased throughput and reduced labor makes it possible to profitably produce same-day runs, even at quantities as low as a few hundred, at very attractive prices. These Presstek-enabled DI presses are growing in popularity as print buyers discover the benefits of extremely short-run high-quality print. New adopters of DI printing include small commercial print shops and quick printers, who require a streamlined four-color workflow to become more competitive. Also adding DI technologies are prepress shops, which require a “smart offset” press that offers a short learning curve, but can intelligently use color data to produce the highest quality. Even larger commercial web and newspaper plants are adding DI presses, augmenting their capabilities so they can compete in the growing short-run color market.
The new generation of DI presses images all four highresolution plates in perfect register in 4.5 minutes. Ink keys are automatically set to match the digital color data supplied by the original source file, significantly reducing press makeready times. The innovative Presstek ProFire Excel imaging module and chemistry- free ProFire Digital Media deliver up to 300-line conventional screening, as well as stochastic and hybrid screens—mixing conventional and FM dots. Patented features offer a host of operational advantages over conventional offset and toner-based machines.
Another attractive feature of the DI press is its small footprint, just 10´7" long by 8´8" wide. This consumes over 30% less floor space than a conventional four-color press, an important consideration in smaller shops and high-cost major metropolitan locations.
Today’s highly automated DI presses easily deliver sheets up to 18.11°—13.39" at top speeds of 7,000 per hour. The Presstek DI speedy changeover—just 10 minutes between runs—allows more jobs to be printed per shift. A 500-run four-color job is completed in less than 20 minutes—half the time of off-line CTP, one-third the time of a film-to-press workflow. Time saved eliminating register adjustment, plate mounting and removal is a key factor in DI press efficiency.
It is in consistent front-to-back register and infeed capabilities,
that Presstek DI presses especially excel over toner-based systems. Sheets are held
tightly without gripper changes as all four colors are applied, eliminating potential
misregister. A wide range of substrates can be used, including plastics, envelopes,
Tyvec and other specialty materials, in calipers from .0024" to .012" , with sheet
size ranges from 3.54 x 3.95" to 18.11 x 13.39".
Since plates are imaged directly on press, a DI press begins operation by processing an electronic job file. Up to 50 incoming print files can be queued for processing. The RIP converts PDF or PostScript files to an industry standard CMYK 1-bit TIF format, driving the dual ProFire Excel imagers (one per plate cylinder) to expose the ProFire Digital Media at 2,540 dpi-rendering up to a 300-line screen with a 16-micron spot.
Presstek Image Plus software optimizes exposure of the thermal, chemistry-free plates to ensure even tints and to minimize moiré. This feature-the integrated conveyance of job color data simultaneously to the integrated imager and press systemexplains why DI presses hold particular appeal for two groups: color trade shops, who know color well and have high expectations; and smaller shops, who need to make quality four-color runs predictable and simple.
Even before the job file begins imaging, a programmed makeready cycle begins. Autocleaners prepare inkers, plate, and blanket cylinders. Next, Presstek ProFire Digital Media is dispensed from spools inside each of the pairs of double-sized plate drums. (Two plates are mounted across each cylinder.) Rolls contain enough digital plate media for 28 full-sized jobs.
As imaging commences the plate cylinders rotate at 300 rpm. ProFire Excel images the chemistry-free digital media, exposing an ink-receptive polyester layer. Any remaining debris left from the imaging process is removed during the automated plate cleaning cycle.
As this 4.5-minute sequence nears completion, the press presets the 11 ink keys at each of four fountains, calculating density based on color data embedded in the job file and the coverage area on the plate.
Then the plate cylinders re-engage the gears and revolve three times as the 15-roller train inks them up. Final saleable pages can be produced very quickly with a total elapsed time between jobs of less than 10 minutes.
