Computer-to-Screen systems have boosted prepress productivity in many segments of the industry. Discover the benefits it can have for your shop.

Mark Coudray (2005-12-05)
I recently attended the Print 05 exhibition in Chicago and gave a presentation about the state of the screen-printing industry. As I walked the show and contemplated the exhibitors' offerings, it became obvious to me that digital technology, which has influenced the way some screen printers do business, has also had an effect on traditional sheet-fed offset printers.

In that market, which includes equipment from manufacturers such as Heidelberg, Kormori, MAN Roland, and others, printers have realized numerous benefits from computer-to-plate systems. Bringing digital prepress in house has helped them stay competitive as other printing technologies make inroads.
In fact, it's abundantly clear that many segments of the graphics-printing industry have made wholesale changes in the prepress workflow in order to strip unproductive waste and cost from their processes.

Computer-to screen (CTS) technology is one solution that screen printers use to maximize efficiency in prepress. The current state of CTS equipment was the focus of my column in the July 2005 issue of Screen Printing (page 22). In that column, I concluded that inkjet-based CTS, whether the consumable is ink or wax, is viable for operations that use as few as 25 screens per day. This month, I would like to go into some of the economies you can realize by implementing
CTS technology.

How CTS benefits prepress

Increases in digital-imaging speeds and reductions in investment costs should be enough reason for traditional screen printers to develop serious cost-reduction plans and implement productivity enhancements in order to minimize the inevitable confrontation with digital printing. The biggest bang for the buck comes at the front end of the process. Anything you can do to reduce overall steps, handling, and process time in prepress will be magnified and multiplied down stream. In addition, you have the opportunity to insert other productivity-enhancing capabilities into the prepress segment.

A traditional, film-based workflow can have 14 or more steps from the creation of the artwork until the screen is ready to print. Table 1 offers a typical comparison of a CTS workflow to a traditional workflow. In this comparison, there are 17 steps in the traditional workflow and seven steps in the CTS workflow. All steps are not equal, and each step introduces variables into the final outcome. Each step must further have its own quality-control point. In the film workflow, there are huge problems with exposure and processing of film.
  
Consider the flaws of three of the most common methods of generating film. Inkjet-printed film can suffer from density and laydown issues. Thermal printing can lead to problems with density, bloom, and streaking issues. Conventional photo-based film is known for producing challenges with density and developing. All can hinder registration and create fit problems if the films are capstan or roll driven.

Mounting film to the screen poses another set of variables. Is the film in the exact position (accurate register) if pin registration is even in use? If the film is not taped perfectly flat to the screen, then buckling, twist, and distortion become problems. Any time you handle or move film, you risk damaging it by crimping, scratching, or transferring dirt and debris from tape or exposure glass.
Improper application of vacuum when creating stencils creates one more layer of quality problems. Besides adding 30 seconds or more to the exposure of each screen, the problems range from poor registration to destructive moiré. Image undercutting is common if the vacuum is incomplete or localized. A weak vacuum combined with low film density is a recipe for highlight-halftone disaster. If you're even able to capture the dot, you will likely generate moiré in the tone.

CTS works without a vacuum. In fact, the systems create perfect contact between the image and the emulsion surface—just one of the major advantages. The intimate contact is key to achieve higher print resolution. When comparing a film-based output system that supports 600-dpi output to a CTS system of similar value, CTS will win every time.

Screen exposure with CTS can be up to 40% faster because glass isn't part of the equipment. Plate glass absorbs up to 40% of the emitted UV light from the exposure source. Combine this with dirt, tape, scratches, and other defects in the glass, and the variables are further magnified.

A common solution screen printers use in film-based screenmaking is to increase exposure to burn through all of the surface flaws, but doing so causes pinholes. Even if a pinhole does not immediately develop, it will on press, further delaying production. CTS screens, on the other hand, are virtually free of these defects. Nothing stands between the exposure arc and the mesh to hold the light back.

Dismounting and archiving film increases the damage factor to the image. Even if the film is handled carefully, the danger of losing or improperly filing a color exists—a very large problem in screen departments that make 25 or more screens per day. Think of all the time you've spent looking for an errant positive. You certainly weren't on press while you were hunting.

When it comes to washout, the improved image-to-emulsion contact produced with CTS makes the process faster. Dots are cleaner, and detail is sharper. With film, it's not unusual at all to spend considerable time washing out fine details that have partially closed in due to low film-image density or poor vacuum contact.

The final step involves final re-touching of pinholes and blocking out the film-based screen. Drying the blockout and taping follow. Meanwhile, a CTS-generated screen can be taped and immediately taken to press. Avoiding the process of retouching can save up to 15 minutes per screen. The actual amount of time you save is based on how large your screens and files are.
RIPing the image for a CTS is comparable with RIPing it for a film imagesetter, and imaging of the positive and screen are also similar processes. But with a CTS system, time is saved in processing and retouching the film; punching, transporting, handling, and positioning the film; loading the vacuum frame; pulling the vacuum; exposing the screen; unloading the frame; developing the exposed frame; dealing with pinholing; and blocking out the screen.

Other advantages of CTS

In addition to the direct time reductions within the workflow the come from using CTS technology, the need for labor also is decreased. For a medium-sized print shop that produces 50 screens per day, it is not unreasonable to see a 50% reduction in support personnel in the screenmaking area. There are simply fewer steps to spend time on, and the overall timeline is compressed. Simply put, more screens in less time.

One of the biggest advantages of using CTS comes with the implementation of a pin-registration system. Accuracy of pin-registered screens improves when you eliminate so many handling steps. Consequently, accuracy of registration on press also improves, and set-up times decrease. All of these time savings lead to more hours available to print. Think of this as more opportunities to increase revenue.

With more printing hours available in the same time period, the net effect on the bottom line is far from insignificant. You'll find that it's not uncommon for your net profit on sales to double, triple, or even quadruple as a result of the combined parallel savings and increased productivity that only a simplified workflow can deliver.

While all of these time savings are impressive, the real value comes with increased reliability on press. Every printer knows the "sweet spot." This is the point in the production run where everything is going great. The press is humming along, and the quality is excellent. But as soon as you stop to make an adjustment, fix a pinhole, or tweak registration, that wonderful stability is lost. Screens produced through the use of CTS technology are more reliable because they do not break down as frequently as screens made in a film-based workflow. The real value is faster printing with less interruption and higher, more consistent, quality.

Let me pose one final argument in favor of adopting CTS—that is, simply, control. When the first laser imagesetters hit the market, they were priced in the $125,000 range, with RIP, and another $8000-25,000 for a film processor. This was for 16 x 22-in. output. How could a printer possibly justify this investment when comparing the cost to analog camera output? The answer was in control and increased speed.

Of all the investments I have made over the years, the drum imagesetter has consistently been one of the best performers because of the incredible control it generated for us downstream on press and in production. CTS is now in exactly the same position imagesetters were 15 years ago. We know history repeats itself, and this is one instance where the economics are a mirror of what they were during a past example of another analog-to-digital conversion.
©2005 Mark Coudray. Republication of this material in whole or in part, electronically or in print, without the permission of the author is forbidden.

http://www.screenweb.com/index.php/channel/1/id/2641