DIGITAL PLATES -- Covering the Spectrum

BY MARK SMITH

Adopting a computer-to-plate (CTP) workflow is as much about buying into a technology and process as it is purchasing products. Visible laser systems can lay claim to having created the product segment. However, it really took the introduction of thermal technology for CTP to gain mainstream acceptance, at least in the North American market.

Now violet systems are causing a stir and generating a bit of controversy. More on that later.

While product offerings continue to grow, key decisions made by CTP buyers early on still can dictate their subsequent product options. Typically this process begins with the selection of a chosen imaging technology and inexorably leads to a plate. It can work the other way, though, especially in the case of processless plates. If a buyer is sold on this technology, then at least for now thermal imaging is the only option.

Developments in plate sensitivity and platesetter capabilities tend to be so interdependent that if they don't move in lock step, leading-edge products will be of little practical use. Picking which platesetter and plate to buy can almost end up being a single decision. This is particularly true in the violet laser segment due to differences in the energy requirements of silver vs. polymer plates and the output energy of first-, second- and third-generation diodes.

Turning Bluer
First-generation violet laser diodes have a maximum power output of 5mW. The high sensitivity of a silver-based reactive coating is required for plates to respond at that low of a threshold. The downsides to silver-halide plates—controlling processing and disposing of chemicals—are seen as potential barriers to adoption of the process.

These concerns are being answered by the new violet-sensitive polymer plates just coming to market, but they require at least a 30mW violet laser source. Such diodes only recently have become available, so platesetters that image at that power naturally are still a new development. A number of product introductions in this category are expected at PRINT 01. (Since platesetters will be the focus of an article in an upcoming issue of Printing Impressions, they won't be discussed in any depth here.)

In the usual game of high-tech one-upmanship, diode manufacturers now have started announcing 100mW units. As impressive as a 10-fold increase may seem, these diodes likely will have their greatest impact on the speed of platesetters, not the range of materials they can image. The energy output would have to be increased by several orders of magnitude to image conventional ("analog") plates, for example. One exception may be high-speed UV (ultraviolet) plates, since 100mW violet laser diodes may be sufficient to image these plates, if they can support the slightly higher imaging frequency.

High-speed UV systems have been somewhat of a special case to date. Platesetter manufacturer basysPrint and plate supplier Citiplate more or less teamed up to pioneer the concept of CTcP (computer-to-conventional plate) using this technology. In this system, a digital UV exposure unit is used to image high-performance UV plates.

The relationship between the two companies was fundamentally changed by Citiplate's announcement that it planned to market its own UV platesetter line, reportedly due out later this year. In response, basysPrint has been playing up the fact that its UV-Setters can image a range of alternative plates.

Turning back to true violet systems, their main advantage is the relatively lower cost of the laser diodes, which proponents say should translate into cheaper platesetters. The imaging unit only represents a fraction of a platesetter's cost, however, which is why violet imaging is often touted for the smaller format (four-up or less) market. The smaller the platesetter and the fewer automation features added, the greater the percentage of cost attributable to the imaging unit—thereby maximizing violet's advantage.

Manufacturers of competing technologies counter this argument by stressing the importance of considering the total cost of ownership—platesetter, plates, processing, maintenance, etc. They also point out that other attributes of a technology should be factored in, as well, including run length and resolution.

The number of variables makes it difficult to back up any blanket statement about the cost advantages of one technology over another. Exceptions to the rule usually can be found, and other considerations can outweigh costs. In addition, competition tends to put pressure on pricing, so any cost advantage may be short lived.

Limited Availability
Regardless of the imaging technology, one concern that continues to dog the adoption of CTP is the availability of plates. Actually, there are two parts to this issue—intentional and unintentional supply restrictions.

In the digital plate arena, manufacturers have tended to preview, or even formally introduce, new products long before they go into commercial production. A number of plates were shown at DRUPA 2000 that have yet to be fully commercialized, and some still haven't even been given formal product names.

Online discussion forums have become a particular rich source of information about ongoing technology developments, but these reports from the bleeding edge often don't reflect the product options open to mainstream users. To help clarify matters, here's an update on the status of some digital plates that are getting talked about, but have yet to be commercialized:

• Agfa categorizes its Mistral processless plate as being in "controlled sales," with no announced timetable for full commercialization.
• Citiplate recently has said it will formally announce two new plate lines later in 2001. The Aqua Violet plate will be a silverless, photopolymer product that can be imaged with a 30mW laser diode. Aqua Thermal plates reportedly will be offered in negative- and positive-working versions with 830nm sensitivity.
• Fujifilm's thermal processless and violet plates reportedly are still undergoing evaluation in its R&D facility.
• Kodak Polychrome Graphics' Thermal No-process and Thermal Waterless plates are both still in beta testing.
• Mitsubishi Chemical (Western Lithotech) was expecting to begin placements of it DiamondPlate LV-1 violet-sensitive, photopolymer plate by the time this article is in print.
• Mitsubishi Paper reportedly plans to introduce its SDP Alpha Violet silver-halide plate at PRINT 01, with commercial shipments beginning in the fourth quarter.

Verify the Source
New plates usually go through a period of limited sales because initial production is done as a pilot project. Ramping up to full production of any new technology presents technological and marketing challenges, which can result in supply disruptions. A manufacturer may simply underestimate demand, or it may hit an unforeseen glitch that has no reflection on the soundness of the underlying technology.

Digital plate shortages are beginning to have the feel of an urban myth or FOAF (friend of a friend) report as they crop up from time to time. Everyone seems to have heard about someone else running into plate shortages, but CTP users typically report encountering no significant supply disruptions in their operations. Such information is notorious for being out of date.

That's not to say that all digital plates will always be readily available. Having a supply clause written into the contract can provide some protection, although a printer must be able to fairly accurately predict its plate needs. Another common tactic used by early adopters is to keep extra plate inventory on hand. This adds to the cost of using the process, but is small potatoes compared to losing a customer because the work doesn't get out.

A couple other points are worth considering to help clarify the great digital plate debate. The industry seems to be standardizing on the term "processless" to designate the class of plates that do not require a traditional processing step. What this typically means is that no chemicals are required to prep exposed plates before they are put on press.

However, some form of physical preparation step still is required. This may simply involve wiping or washing the plates with water prior to installation on the press. Or, plates may be "processed" on-press by the action of the ink, water and blanket during makeready.

Thermal ablative imaging is the most common technology used in processless plates, but Agfa currently also offers a phase-change product and other options are being explored in labs around the world. By definition, the ablative process involves removing material from the surface of the plate through the application of energy by the laser. As a result, a platesetter must be fitted with a vacuum/evacuation system to capture loosened particles, if it is to be used for imaging ablative plates.

Whether or not this system can be added as a retrofit depends on the manufacturer and model. In addition to the capital cost of the extra unit, vacuum systems have a filter that must be changed regularly.

Hot and Hotter
The term thermal has become a generic reference, but it actually encompasses imaging systems with two different sensitivities—830nm and 1,064nm. The majority of thermal plates are sensitive to 830nm, but some are dual range. One implication of the different sensitivities is an external—versus internal—drum design in the platesetter.

Photopolymer is another term that tends to be used imprecisely as the designation for a special category of plates. Non-ablative thermal plates typically also use a cross-linking polymer coating, just one that has a different spectral sensitivity. Aside from processing requirements, what sets polymer plates apart is the ability to post-bake them for increased durability. This enables the plates to produce longer runs and better withstand applications such as using UV inks.

Opinions vary widely on the significance of a plate's imaging resolution. A potential wrinkle in the debate is the apparent re-emergence of stochastic/FM screening and other related technologies, which require high-resolution imaging. CTP is considered to be an enabling technology for specialty screening, but it remains to be seen if that will be enough of a boost to get potential users to buy into the process this time around.

A final thought worth keeping in mind is that the CTP technology war is far from over, despite thermal's early advances. The general consensus puts the percentage of shops having adopted the process still in the single digits. There's still plenty of potential business to support a number of players.

Fortunately, or unfortunately, that leaves printers free to weigh all the alternatives and determine which solution is best for their individual operations.