Photopolymer Interaction
Now that the stage has been set for the importance of UV LED technology, how do we, as formulators, deal with this technology? Ink formulators have borne the brunt of being forced to contend with reformulation efforts, new raw materials, functional differences and the like so far. On the plate making side, there are essentially two questions to address: How do current formulations interact with UV LED curing systems? How do we modify or develop new formulations that take advantage of these light sources?
Existing UV LED plate making systems do target the same peak wavelength for curing—365-nm. UV LEDs are inherently near-monochromatic (see Figure 1), i.e. a very narrow wavelength distribution, when compared to fluorescent bulbs (see Figure 2).
As a result, photopolymer formulations that were developed with broad-band bulbs in mind can quite possibly behave differently, and unpredictably, with these new systems despite their wavelength target similarities.
To date, there are many formulations that have become qualified in these systems, so it’s safe to say we, as plate developers, have had a bit of serendipity with respect to the interactions between plates and light sources. There are, however, things that we have learned about along the way that will help guide us on where to go next.
UV LED Future Developments
Future developments aren’t just because we can develop them—there are distinct benefits that are targeted specific to UV LED technology now that these light sources have become more readily available to test on and learn from. These benefits include:
- Productivity: The current class of polymers on the market today has shown distinct differences in its behavior under UV LED conditions. Generically speaking, the inherently flat top dot chemistries cure much faster under UV LED conditions, similar to their behavior under bank light conditions. With the benefits gleaned from the ability to control intensity with said systems, in combination with the uniformity of the intensity, there is the new ability to focus on formulation speed without fear of losing control of the plate consistency.
Future iterations of UV LED products can therefore be developed to best optimize the utilization and efficiency of these systems without harming final quality. When combined with the automation aspect, this has intriguing possibilities for plate making facilities
- Optimized cure/performance: In addition to the monochromatic wavelength structure of UV LED systems, the other main difference in UV LED systems is the overall lamp intensity—It is much higher than typical bank light systems. As a result, the curing mechanism itself can radically change. This has been observed to occur with two main defects on the finished printing plate—inconsistent or unpredictable dot gain, and dot cupping.
While certainly addressable via optimization of process/curing conditions, the goal of new plate developments is to widen the plate making window, allowing for a broader range of optimum conditions that aren’t impacted by slight changes in graphics, relief targets, print applications, etc.
“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.”
Strategic Direction
Within MacDermid’s development and support team, our aim is to fully support UV LED technology, as we truly believe this represents the future of flexo plate making. The reasons for this are articulated in this article. This technology brings out the best in photopolymer formulations. Future plans entail continuing to evolve development programs to further expand the capabilities of flexographic printing.
To summarize, the gateway to UV LED will continue to drive forward because of three main elements:
- Outstanding uniformity of consistency of photopolymer plates derived from UV LED plate making, and the print benefits obtained
- Ability to automate plate making
- Increasing environmental pressures that will ultimately impact mercury-based light sources found in the existing bank light systems on the market today
It is a key plate technology strategy for MacDermid to be prepared for this technological emergence and adoption, rather than waiting for it to happen. By working very closely with the suppliers of UV LED technologies, our platform strategy focused on two areas of strength:
- High-quality formulations that exist today, qualified and proven to work in UV LED systems
- Newer technology platforms that are developed to be tuned to UV LED light sources, providing even greater productivity and wider performance latitude than plate technologies that currently exist
By combining our formulation expertise with outstanding collaborative partnerships, we feel we can help drive this technology not only to full adoption, but to greater and greater capabilities for our industry and customer base. Improved quality, productivity and efficiency will help drive more market share toward flexo and away from competing processes, while continuing to maximize profit.
About the Author: Ryan Vest, global director of innovation at MacDermid Graphics Solutions, has been key in the development of industry-changing technologies, such as LAVA thermal plate processing and LUX flat top dot technologies. He is widely known in the industry for his expertise in liquid photopolymer and corrugated plate technologies.
Ryan earned his bachelor of science in chemistry from Berry College in 1995 and his master of science in chemistry from North Carolina State University in 1998, joining MacDermid that very same year. He and his family live near Milwaukee, WI.