Editor’s Note: Given their nature, FLEXO Magazine’s non-commercialism policy was relaxed for all Technical Innovation Award-winning articles. The articles utilize and expand upon information submitted and considered in their receipt of the award.
After receiving a 2017 FTA Technical Innovation Award for our UV LED Low Migration EkoCure ANCORA Ink technology, Flint Group has noticed an increased interest from a wide range of market segments, and especially flexible packaging printers. But UV LED technology first started in the narrow web label industry as a joint development project aimed at finding a way to lower the total applied cost to print pressure sensitive labels. Flint Group personnel discovered during an improvement audit discussion at a customer in California that the cost of electricity and power needed to run UV presses was such a significant factor that it had a major impact on the total applied cost. As a way to investigate means of reducing this, a low powered variant (12-w/cm2) was tested, with far better results than expected.
In order to gather the benefits of this technology successfully, a cooperation between ink, lamp and press manufacturer was started and at Labelexpo Americas 2012, the world’s first UV LED Flexo press was shown. The project’s partners were Flint Group Narrow Web, Phoseon and Mark Andy. The technology shown was regarded by show attendees as “very interesting,” and when the results from the pioneering beta sites were revealed, the industry change was put in motion.
UV LED Technology: How Does It Work?
The key differences between UV LED and traditional mercury UV are reflective of the light source differences between mercury and LED as is depicted in Figure 1. Mercury vapor light output is depicted, starting with short-wave/UVC light on the left, all the way to infrared output on the right. The LED light output is the narrow wavelength with peak output in the 395-nm. range, represented by the bell curve in the middle of the chart.
You can also see the light intensity of the LED output is much higher than mercury vapor light, which helps inks cure better and faster, adding to reactivity of the process. Additionally, the UVA light is a deeper penetrating light source that helps to cure thicker, more opaque/densely colored ink films.
Improved Productivity & Bottom Line
After five years of commercial usage, there are now many converters that have invested in UV LED technology and report this to be a very sound business proposition with a clear advantage in lowering the total applied cost versus alternative technologies.
A four-year report card from customers for LED inks and printing processes claims the main benefits to be:
- Up to 80 percent reduction in power consumption
- Greatly improved productivity (resulting in up to a 15 percent higher throughput)
- Zero lamp failures and up to a 75 percent reduction in maintenance time
- A total—100 percent—reduction in ozone, eliminating the need for air exhaustion
- Great improvement in cure reliability/assuredness
- Ultimately, many converters reported very short payback time, which makes the investment in UV LED a very solid business case
While converters in North America were very fast in adopting UV LED technology, their European equivalents have been more hesitant—solely because of the market demand for low migration ink technology. Driven by many food producers, there has been a direct request for food packaging compliant inks—also for pressure sensitive label applications for many years. It was clear from the start that unless a true low migration solution was developed, UV LED would not have a major impact, in spite of the economic benefits it provided.
A Rewarding Discovery
UV LED low migration inks proved to be very technically challenging to develop, primarily because the main ingredients used in a UV ink were not really available. A UV LED ink formula is pretty much built on similar structure or components as its mercury UV curing counterpart.
An ink consists of a mixture of:
| Component | Function |
| Pigment |
Color shade, strength and light fastness |
| Oligomer binder |
Adhesion properties, pigment wetting and press performance |
| Monomer diluent | Viscosity, cure rate and adhesion |
| Photoinitiator | Reactive ingredient to start polymerization, cure properties and odor |
| Additives | Stabilizers and flow agents |
When creating a robust UV LED system, the formulation of the ink/coating is, in many respects, even more critical to success in creating a good cure rate than the light source selection. Cure rate is a function of amount of UV energy and how well matched that UV energy is to the spectral response of the photo initiator used in the formulation. But it doesn’t stop there; the photo initiator is just one small component of the material, which also contains oligomers (pigments) and monomers. In fact, the photo initiator makes up only a small percentage of the UV system (typically 0.5 percent to 10 percent). The photoinitiator plays the pivotal role in determining the cure rate, but oligomer and monomer selection are also important factors.
In order to formulate an ink that meets all migration requirements and both performs on press and in print, proved to be a real technical challenge. It took more than two-and-one-half years of intense R&D to create the necessary ingredients and optimize them to an ink series that performed on press and met stringent end user demands for migration properties.
With food and beverage brand owners wary of using UV inks in general, we have noticed a slight change in mindset when they hear and understand the benefits of UV LED. They have realized UV LED is something totally different. The new technology has documented low migration properties achieved at very high print speeds (in excess of 500 fpm) meeting specific migration levels below 10 ppb, 50 ppb or SML. All components are compliant to Swiss Ordinance and FDA regulations, and migration tests are verified via third-party accredited test labs using the food simulants of 95 percent Ethanol, Tenax and Acetic Acid at 40 degrees Celsius for 10 days.
Creating Better Business Proposition for Converters
There is an additional benefit with UV LED, and that is the ensured cure aspect over the lifetime of LED lamps, illustrated in Figure 2. Consistency and assuredness of cure at the highest level provides peace of mind to converters and their customers. This is the perfect solution for food compliant production that satisfies even most stringent end user demands.
One of the leading LED lamp suppliers claims to have tests showing that, in order to maintain the same level of cure stability, a mercury lamp would need to be changed every 200 hours, or 125 times in 25,000 hours.
We believe UV LED flexo, combined with low migration ink, is a revolution for the packaging industry, as it will address a growing “mismatch” in the industry.
We know there is a huge demand for shorter runs as the ongoing trend for more SKUs in retail/supermarkets puts pressure on packaging suppliers. “Traditional” wide web flexible packaging is being challenged, both in terms of simple economics—it’s not cost effective to produce short runs on wide web presses.
- Makeready and setup expenses are high
- Response times on new designs are shrinking
- Brand owners demand quicker time-to-market, more fast-moving “packaging” campaigns to sell more and introduce new brands quicker, etc.
With modern flexo technology, we know of converters who compete with 24-hour lead time—from artwork to finished print. That is changing the competitive landscape with traditional gravure able to change designs in six to eight weeks!
So, with a technology that is proven through in-depth migration tests, we know we are compliant with the most stringent demands by food producers and major brand owners—we see no limitation.
We see UV LED as the future—it addresses printer economics, brand owner concerns for food packaging safety and the industry’s drive for more sustainable solutions that use less energy and create less waste.
Flint Group is continuing to develop this technology further, optimizing every part that is possible. With our research and development centers being equipped with state-of-the-art UV LED combination printing presses, we can evaluate real life applications, and test and test again to refine the parameters required to reach an award-winning print quality at the lowest total applied cost possible.
About the Author: Niklas Olsson started his career with Flint Group in 1984 as a fresh chemist. His first assignment was to develop water-based flexo inks for printing self-adhesive labels. Ever since, he has been “attached” to this market segment and has enjoyed several positions within the company.
He is presently working as global brand manager for the Narrow Web division within Flint Group, where he is responsible for co-supplier networking, end user marketing, marketing communications and global branding strategies within Narrow Web Inks.
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