Presstek Direct Imaging Press Technology
High Quality and Environmentally Friendly Digital Offset Printing
Direct Imaging / DI® printing is the process of sending a digital file directly to a digital offset press. This process eliminates the production steps associated with film-based or other offline platemaking. Presstek DI presses allow printers to be more competitive in a market that continually demands faster turnaround time and shorter press runs at lower costs—without sacrificing quality. DI is an enabling process brought about by the interaction of three core Presstek technologies—laser imaging, thermal digital media, and a unique press design.
ProFire Excel Imaging
ProFire Excel, Presstek’s latest generation laser imaging technology, delivers exceptional image quality while dramatically reducing the possibility of moiré patterns in standard screen rulings. Fine details, color fidelity, minimum screen values, and large solids are produced with results that meet the most demanding offset printing needs.
ProFire Excel easily supports screen rulings up to 300 lpi and FM (stochastic) screening.
ProFire Excel combines all of the imaging components—infrared laser diodes, laser drivers, data electronics, and motion control— into one compact system. The foundation of ProFire Excel is a single image data board that controls the laser diodes. Each diode contains four uniquely addressable, 16-micron beams for high reliability, unmatched accuracy, and high-resolution imaging.
Presstek’s DI plates are environmentally friendly waterless plates that provide more consistent color, larger color gamut, better color saturation, lower dot gain and more detail. Without the use of fountain solutions there are fewer variables and printing is cleaner—both operationally and on the sheet; plus there is no ink/water balance to manage.
Presstek DI presses set the standard for digital offset printing by combining the high quality and versatility of offset with the automation and speed of digital printing. Presstek’s ProFire Digital Media is a key component of this superior performance and productivity. The combination of Presstek’s ProFire Digital Media and ProFire Excel imaging technology provides an optimized plate/laser system that yields the highest quality offset printing.
ProFire Digital Media is designed to work as a system with the laser imaging, ink-profiling, and plate loading features of Presstek DI presses. In conjunction with ProFire Excel imaging, ProFire Digital Media allows for a 16-micron imaging spot and supports up to 300-line screen and stochastic (FM) screening— with the push of a button.
The advanced imaging features of ProFire Digital Media result in superior rendering of details using any screen ruling—from highlight areas to shadows. Minimum screen values and subtle tonal transitions reproduce accurately and consistently. ProFire Digital Media reduces waste, saves time, and meets the most demanding quality requirements on runs up to 20,000 impressions.
Presstek DI plates are manufactured with an ink-accepting polyester base layer, a middle layer of titanium oxide, and a top layer of silicone. During imaging, the heat from lasers removes the top two layers of the plate, exposing the ink receptive polyester layer. Areas that remain covered with the top layer of silicone will repel the ink.
Unique Press Design
Presstek DI presses use Presstek’s Zero Transfer Printing (ZTP) process. With ZTP all four colors are laid down onto the sheet without any sheet transfer between colors. ZTP provides:
- First sheet register
- Precise registration, sheet-to-sheet, job-to-job
- Sellable color within 20 sheets
- Excellent ink coverage and reduced waste
A satellite V-shaped 5-cylinder system consists of two sets of double-diameter blanket cylinders and plate cylinders which rotate around a triple diameter impression cylinder. Each sheet is tightly held by the impression cylinder grippers and rotated twice without being transferred for precise four-color printing. The large diameter of the impression cylinder reduces paper curling as well as damage to the substrate. Click here to see it work .
- Presstek DI presses use waterless offset inks, for faster drying and better solid ink coverage. The ink train has four form rollers; three chilled rollers cool ink, eliminating toning.
- Ink keys are preset during ripping, based on color profiles and exposure area for each color in a specific job, meaning less intervention is required on the part of the press operator to generate the highest possible printing quality. Auto start-up pre-inks plates before sheets move through the press. The landscape format 52DI has 16 ink keys and the portrait format 34DI has 11.
- ProFire Digital Media inside each double plate cylinder is automatically dispensed; plates are then tensioned. The press declutches, freeing plate cylinders to spin at 300 rpm during imaging.
- Presstek’s ProFire Excel imaging unit precisely images all four cylinders at 2540 dpi in 4.5 minutes.
- ProFire Digital Media spools contain enough material for 28 (Presstek 34DI) or 44 (Presstek 52DI) full size printing jobs; used plates are automatically transferred to a take-up area.
- Once imaging has been completed, a two-step automatic plate cleaning is initiated. A vacuum then removes any remaining debris from the plate.
- DI presses feature double-plate cylinders, with matching double blanket cylinders beneath. The bearer design assures consistent impression pressure. A V-shaped configuration radiates from a common impression cylinder.
- The triple-sized common impression cylinder holds three sheets tightly, eliminating potential for misregistration because there is no gripper change. A sheet picks up four colors in two revolutions
- A register board/push guide precisely shuttles stock to ensure accurate infeed. Proven feed systems accommodate a wide range of standard stocks, or even plastics, envelopes, and other specialty stocks, in calipers from .0024"–0.02" (0.06–0.5 mm).
- An infrared dryer expedites curing of waterless inks. An autoclean cycle prepares ink rollers, blanket, and plate cylinders for the next image. Total changeover takes about 10 minutes
How does Zero Transfer Printing work?