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Pros and Cons of Pre-, Post- and No-bake Plates
Here's a riddle for you: It's not cake batter, it's not cookie dough, but you still have to bake it to get the most enjoyment out of it. What is it? To some the answer will be obvious: it's a printing plate.
Even if you didn't guess the answer to the riddle, you may still find yourself deriving enjoyment—or at least increased print runs and other benefits—from baking digital plates. Depending upon the plate and the print job it's intended for, you stand to gain significant production advantages by using a plate that requires baking either before or after imaging. You can also derive benefits from plates that require baking for longer print runs. If you'd rather leave the baking to bakers, you can find some plates on the market today that do not require baking at all.
But choosing to use baking in your plate production process is not without its downsides. The upside of cake and cookies is the enjoyment of eating them—the downside is the calorie intake. The upside of baking is composed of the production benefits—the downside can be additional costs and time. The overall benefit you derive overall lies in how you put the "recipe" together.
When you heat a plate before you expose it, you open up avenues to several benefits, including the use of inexpensive radiant heat, not expensive laser light, to prepare the plate for imaging. You still have to image the plate, but pre-heating means the plate is warmer that it would ordinarily be when it enters the imaging stage. Thus, less laser energy is required during the imaging process.
With thermal plates, pre-heating creates a negative-working plate, which can then be used with either other thermal plates or conventional, negative film.
Jeffrey Zaloom, director of R&D for PDI, says that pre-baking is required when using some thermal plates. "Pre-baking thermal CTP surface plates is necessary to fully expose the image. Portions of the plate exposed to the platesetter form a strong acid in the coating matrix. Heating catalyzes the reaction between the acid and polymer to either cause crosslinking or de-protection of the polymer system to create an image."
Likewise, post-baking (heating the plate after it has been imaged, but before it goes on-press) offers several advantages depending upon the type of plate that is heated. It can also convey advantages to printers that want to make sure the plates will stand up under demanding press conditions.
David Bartram, worldwide marketing manager for Kodak Polychrome Graphics, explains how post-baking helps American printers. "Thermal plates in the United States must be post-baked more often than not. Generally, this is because press chemistry in this country has evolved to be compatible with conventional, negative plates." Post-baking gives thermal plates the edge they need and creates a very durable plate.
Post-baking is also sometimes used to extend the run length of a thermal plate beyond its normal run length of several hundred thousand impressions. With post-baking, those run lengths can be extended into the millions. Agfa, for example, already offers Thermostar, a thermal plate with run lengths of several hundred thousand without baking, and into the millions with post-baking. Anocoil's new 830 T-Plate is the same: no pre-heat with typical run lengths into the hundreds of thousands and much longer print runs after post-baking.
According to Jim Crawford, PS Plate product manager for Fuji Photo Film USA, the need for the commercial sheetfed market to avoid ovens and baking is the reason Fujifilm introduced the Brillia LH-PI thermal plate. It requires no pre-bake and no post-bake for run lengths that reach hundreds of thousands, which actually exceeds the needs of most commercial printers.
"The adoption rate for this product is so high because many printers never had ovens in their production environment, and didn't want to start baking just because of thermal plates," says Crawford.
The downside of baking, whether you do it before or after the plate is imaged, is that you have to spend the time and the money on this additional step in the process. You will also have to spend the money to acquire the baking ovens and money to house and run them. And, as with any process, you run the risk of losing additional time and money if the steps aren't done correctly.
Some plate manufacturers that sell plates which can be pre- or post-baked have decided to help eliminate some of the downside of heating plates by creating new equipment. In late 1999, Kodak Polychrome Graphics, for example, announced the All in One compact thermal plate processor with an integrated, pre-heating oven.
The company now offers two other products, in addition to the All in One, which are also designed to reduce the energy and floor space requirements needed for heating plates. The Quick Bake unit is a new product that can be attached to the back of a plate processor. The CTP1 is a smaller plate processor that's less that 10-feet long and comes with a built-in heating unit.
Zaloom is convinced that having to bake plates at all is a considerable downside. In fact, he says, "Ovens are for baking pizzas, not printing plates." He cites several problems with baking in general. Difficulties can prevent printers from doing the pre-baking step properly, thus leading to problems with the development of the plate, such as image loss. Fogging or banding from under-exposure can also occur, he says.
And sending different-size plates through the same oven can cause development and image problems. "Larger plates with more mass will require higher temperatures to get to the proper pre-heat (or post-bake) temperatures compared to the smaller plates that have less mass," Zaloom adds. Post-baking must be consistent, as well, otherwise problems with plate cracking can occur.
Two problems with post-baking that printers need to be aware of stem from a lack of understanding how to undertake the post-bake process. If the oven is too hot, it can weaken the aluminum, Zaloom explains. "Some recommended temperatures for post-baking are close to the annealing temperature of aluminum—the temperature at which aluminum begins to change its physical characteristics." A too-hot oven can warp the plate, leading to problems when the plate is mounted and the plate usually cracks.
The other problem arises when plates are under-baked, and the plate has reduced durability and run length compared to what would be possible if the plate had been baked properly. "Harsh chemicals (very alkaline washes) and ultra-violet and electron beam inks, known for their chemically aggressive tendencies, can weaken the plate's polymer and lead to early replacement." Rough papers, older presses and very long print runs can also affect under-baked plates adversely.
There are plates that require no baking whatsoever and there are thermal plates that don't require pre-baking. The PDI bi-metal plates for thermal platesetters also do not require baking. The Prisma 830 Thermal Plate is a bake-free plate with run lengths into the millions.
With all this talk about baking and when and how you should do it, you might come to the conclusion that you shouldn't consider any plate that requires baking to get the most out of it. According to Leigh Kimmelman, product manager, output products, for CreoScitex, that's not necessarily the best decision to make.
"Traditionally, post-baking is done to extend run length," he says. In addition, post-baking is sometimes used to help plates stand up to aggressive chemicals used in the wet market. However, to bake or not to bake is not the only factor to consider when choosing plates. "It's really a preference; plates are often tied into proofing or other factors. [Baking] ovens are often given as a part of the deal. It's more a salesmanship and relationship [with suppliers] issue. They all work on-press."
Whatever your personal preference is—to bake or not to bake—it's a sure bet that plate vendors will continue to move toward plate products that require less baking or no baking at all. However, it could be some time before the need for post-baking is completely eliminated. Bartram comments on the need to post-bake to get these much longer run lengths: "It won't go away soon. It's necessary to satisfy the million-run-length needs."
Despite what Bartram says about post-baking for extending run length into the millions, plate vendors are also working on developing, or improving, current offerings—plates that have run lengths into the millions without the need for baking. The major vendors are either offering products that already fit this category or are working furiously to add them to their product offerings.
That's because the plate vendors, especially those that make thermal plates, realize that baking is not the ideal way to condition a plate. Concerns about the downside may keep printers from using plates that require baking; it all boils down to the common-sense idea that the less you have to do to the plate the better. Plate vendors understand this and will continue to experiment with technology that eliminates or reduces the need to apply heat to a plate anywhere except inside the platesetter itself.
In the Meantime
While plate vendors continue working in their R&D labs toward an image-and-go plate that can stand up to print runs in the millions, printers need to understand the upside and downside of applying heat to plates as part of the plate development process. Heating the plate before imaging or afterwards can help the plate, but the heating process must be done carefully and consistently to avoid potential problems.
In addition, there are some no-bake alternatives available to printers today, if baking hasn't worked for you or you'd rather not invest time, energy and money into plates for this reason. There are fewer plate choices in the no-bake category, but there are some—which is always better than none at all.
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