As photopolymer plate formulators, manufacturers and suppliers, we often get inquires on emerging technologies and their impacts on flexographic printing plate development. Sustainability, printed electronics and 3D printing are among buzzwords we hear often. Still, UV LED outshines them in sheer volume of interest.
Notably, the most common application of UV LED in flexographic printing today falls within the on-press or print application area, yet its use for curing flexographic plates has been around longer than one may think. From the plate development and supply side of the fence, here is a look at the history of this technology, how we see it playing out and where we stand in this growing field.
A Historical Recap of UV LED
Major developments in UV LED curing for plates list out in the following milestones:
- Use of UV LEDs has been most successfully applied via technology that combined plate ablation systems with UV LED curing technology—the plate could be ablated and cured on the same unit. While the combination brought about an advancement in equipment consolidation, along with solid print performance that was sustained over a period of years, a separate back exposure step was required and the additional curing step resulted in a productivity bottleneck
- An additional application surfaced within the last few years, in which UV LED light sources were used in concert with standard fluorescent bulbs to produce a flat top dot printing plate, without the need for tying up the imager. The UV LED’s main function, in this case, was to outrun oxygen during the curing step, allowing for the formation of a flat dot surface, while the fluorescent bulbs completed the bulk curing process in the printing plate. While it certainly did isolate the curing step back to a separate exposure frame and away from the imager, a modified exposure unit was required, along with the need for multiple curing steps; thus, the productivity and expense of such a unit may not have been ideal for certain segments of the market
- The most recent addition to UV LED curing is a full LED-based, standalone exposure system. Several of these have been publicized within the past two to three years. A modern example of these system allows for simultaneous, UV LED-based curing on the back and front side of the printing plate, in a manner that is consistent in its application—pass to pass, and plate to plate. This technology has also allowed for the introduction of a platform approach to plate making automation, in which all steps—ablation to exposure—are aligned within a single production system
UV LED Advantages
Why are we even interested in UV LED curing to begin with? The answer, relative to flexographic plate making, is short and simple: Consistency!
Photopolymers are not moody, nor highly intelligent, autonomous creatures. They:
- Are a mixture of chemicals designed with a class of behaviors and performance characteristics in mind, targeting a finished print application
- Require many other technologies to be successful—exposure, washout, on-press components, etc.
- Do not like discrepancy. Any difference in these components can lead to a difference in the application of said photopolymer materials, and this includes plate exposure technology
- Also do not like variance. The more widely variable the exposure technology, the more variation one can expect from the photopolymer plate
UV LED’s distinct advantage comes from its unparalleled uniformity of light intensity across the width of the exposure device, which translates into more uniformity of the finished printing plate itself. More uniformity means more consistency. More consistency lends itself to more repeatable and predictable finished results. This, simply put, was sorely needed within our industry.
Supplying consistent and predictable amounts of UV energy to the plate and applying it in a consistent manner is critical, as is the ability to cure each plate the same way, meaning no differences relative to temperature, energy or even the time between the front side and back side exposures. This leads to greater and greater consistency. With consistency comes standardization and predictability.
UV LEDs are extremely powerful for their size, but it’s the size itself that brings the most flexibility into the plate making arena. UV LEDs are most aptly integrated into smaller arrays that can be applied as a “light bar” for plate making in which the bar itself, or the plate, moves under the irradiation source. This allows for a streamlined design, albeit one that is still highly, highly complex in its application, despite the simplicity of the appearance.
This streamlined approach has enabled several integrations of UV LED designs to date. One such integration is the connection of ablation to exposure, wherein the plate is automatically transferred from one unit to the other. Additionally, several examples of exposure to processor integrations have been implemented—limited to solvent processing—and currently can be found within the industry.
The ultimate consolidation is the full combination: ablation to exposure to processing. Of additional interest is how well thermal or water-wash systems can integrate into this technology in the future.
While automation is certainly a future consideration when evaluating UV LED technology, other concerns relate to productivity and the environment. For productivity purposes, inherently flat top formulations, pioneered by MacDermid Graphics Solutions, have integrated into the market within the past few years. These formulations have opened new possibilities by increasing plate making speed and efficiency. Therefore, our “new normal” has changed. Speed is here! UV LED can help enhance control during plate making.
Additionally, a long-term consideration of UV LEDs, when compared to existing fluorescent systems, is the environmental aspect and the elimination of mercury-based components. There will come a time in which mercury-based light sources may well be highly regulated, or even banned in the future. We as an industry must prepare for that eventuality.