Are Thermally Processed Plates Susceptible to “Melt Lines”?
As mentioned, thermal processing has come a long way. Some newer processors are able to remove unexposed polymer more evenly, while older equipment has sometimes been criticized for producing plates with “melt lines,” or visible ridges in the plate floor immediately after large solids. In some cases, these ridges were so pronounced that they themselves printed, resulting in dirty shadows on one side of large solid images.
Some plate materials have a tendency to take on the pattern of the nonwoven developer material on the plate surface—this results in a textured surface. Again, there have been situations where this surface texture was severe enough to print on certain substrates. Furthermore, minor variations in processing conditions (main exposures or thermal processing settings) could increase or decrease the severity of this texture, resulting in a lack of consistency in plate surface characteristic. Some printers have become wary of thermal plates, simply due to this slightly unpredictable print characteristic.
Finally, because of the amount of heat and pressure used to thermally process plates, it is important to understand how this affects the dimensional stability of finished examples. As graphics become more and more intricate and challenging, it is critical presses hold tighter and tighter register between all colors. Any discrepancy in plate width or length will interfere with this registration, and should be thoroughly considered when making a decision on a thermal processing system.
Are “Flat Top Plates” Available?
To also reiterate: Plate technologies are always advancing. The newest technology—those with inherently flat top dots—has caught on in the industry as a means of simplifying the plate making process.
The transition to thermal plate making, or upgrading your current thermal processing system, provides a good opportunity to also consider upgrading to this new flat top plate technology, providing the material is available from the vendor you choose for your new thermal processing system.
Does a Thermal Plate Processor Create Condensate?
Thermal plate processing requires a significant amount of heat to melt photopolymer. A potential byproduct of this heating/melting process is vaporized monomers, which can be harmful if inhaled, and can cause damage to objects that come into contact with these vapors after they have condensed; this may include the inside of the processor, the floor underneath the processor, or the area around the exhaust outlet outside of the building. Making sure your new thermal processor properly handles these kinds of vapors will be beneficial; it will prevent you from encountering unforeseen costs in terms of repairs down the road. Of course, reducing or eliminating these kinds of vapors is also good for the environment.
What Else Can the Vendor Provide?
For printers looking to bring plate making in-house, another obvious consideration is the whole equipment package. A thermal processor alone is not enough to make plates—you’ll also need an imager (“laser”) and, ideally, a combination exposure unit capable of handling back, face, post and detack exposures
Most folks today are familiar with the concept of “bundling,” or purchasing/leasing multiple products for a reduced price. With that concept in mind, finding a vendor who can provide most (or all) of the equipment and consumables (plates and developer rolls) needed to start a plate making operation will likely yield some significant savings, in addition to the benefit of having a single contact for ongoing sales and support.
These eight questions are a great starting point for a good conversation with your potential vendors, and will likely lead to additional topics of discussion. In the broadest sense, the key things to consider when researching thermal processing systems are upfront costs (equipment), cost of consumables, cost of operation, productivity (in terms of size capacity and processing time), ease of operation, plate quality and environmental friendliness.
Of course, it is up to you, the consumer, to determine which of these questions and concerns is most relevant to you. There are certainly other questions worth asking, based on your own unique requirements. The most important thing is to make sure you are asking as many questions as possible, in order to make the most informed decision possible!
About the Author: Andy Knapp is the senior technical advisor for Flint Group Flexographic Products. He has been involved in the flexo industry for several years, with experience in prepress, plate making and educational environments, and holds two degrees in graphic arts and flexography from Central Piedmont Community College in Charlotte, NC.