LED Plate Exposure Technology Developed for Wide Web Is Making an Impact in Narrow Web

Jason Hammer doesn’t play favorites when it comes to printing processes or label market segments.

Housing flexography, offset and digital under one roof, his aim is to produce the highest-quality labels for all Hammer Packaging customers. With pressure-sensitive, cut and stack, roll fed, in-mold and foam labels, Hammer has the label market covered. Throw in flexible packaging, pouches, shrink sleeve and specialty packs and it’s hard to classify Hammer in any single packaging category.

“Our high-end offset background has instilled a bias for quality throughout our organization,” reflects Hammer. “When we added flexography, we did so with the goal of equaling offset quality. We match printing process to customer needs. We don’t want quality to be one of the criteria.” Installing the initial Esko XPS Crystal 4835 plate exposure unit in North America was one of the key pieces of that plan.

Hammer Packaging implemented XPS Crystal LED Plate Exposure with the goal of equaling offset and digital print quality. Hammer prints with flexography, offset and digital, and serves virtually every segment of the label and packaging market—cut and stack, pressure-sensitive, roll-fed, shrink sleeve, foam and in-mold.

The 35-in. x 48-in. plate exposure unit was a perfect size for Hammer’s existing plate imager. “The side-by-side plate imager/exposure bundle was attractive to us, but we already owned a plate imager that was in near perfect working condition,” reflects Paul Rainville, director of prepress at the Rochester, NY converter. “So, we purchased the LED plate exposure unit, standalone, to work with our existing plate imaging unit.”

In piecing together flexographic plate making technologies, there were two issues of primary importance to Hammer Packaging. One, for sustainability reasons, it wanted to avoid solvent plate processing. Two, it wanted high-quality color reproduction on paper and film. Both had to equal the quality it was already getting in offset and digital.

“Prior to making the move into specialty screening and LED exposure, thermal processed plates took extra efforts for us to meet our high expectations for dot quality,” reveals Rainville. “Now, we are getting consistent dot quality that we need across both paper and film substrates.”

The original 38-in. x 48-in. XPS Crystal LED plate exposure system in North America was installed at Hammer Packaging in Rochester, NY.

German Engineering

Reflecting on the current surge of LED plate exposure units going into narrow web flexographic markets, Esko Director of Business Development Rory Marsoun shares some insights. One reason the technology was developed in large format (50-in. x 80-in.) before small format (35-in. x 48-in.) was related to basic engineering.

“Most industrial equipment is brought to market in smaller sizes, then scaled up to larger sizes, if demand warrants. That’s usually done for marketing reasons,” reflects Marsoun. “From an engineering perspective, you get better equipment if you design for the large size and scale down to smaller sizes. All the uniformity, deflection and structural tolerances for the large size work for the small size, but the reverse is not true—You can’t just take the numbers from the small device, scale them upward and expect the same precision engineering.”

What Is an LED?

LED is an acronym for light-emitting diode. As the name implies, it is a device that emits light. To simplify a complex subject, common lighting can be divided into three categories:

1) Heated filament lighting

2) Gas discharge lighting

3) Solid-state lighting (including LEDs)

For both consumer and industrial applications, the quality, cost and sustainability benefits are moving in favor of solid-state lighting at a rapid pace.

An example of a heated filament light is the incandescent bulb formerly used in typical household lamps. Commonly made in the form of glass bulbs, these devices generate light by passing current through a high-resistance metal, like tungsten. The resistance causes the metal to heat, and at a certain temperature, the heated metal emits radiation in the visible spectrum.

Heated filament lights require a large amount of electricity to produce a small amount of light. The light is also accompanied by a significant amount of heat. Because of inefficiencies, heated filament technology is not common in industrial applications, where high levels of illumination are required.

An example of a gas discharge light is the fluorescent lights which formerly illuminated most stores and office buildings. Commonly made in the form of glass tubes, these devices generate light by passing current through a gas that contains mercury vapor. The excited mercury vapor emits ultraviolet (non-visible) radiation, which in turn causes the phosphor coating on the glass tube to fluoresce (convert invisible radiation to visible radiation).

Gas discharge technology is more efficient than heated filament technology at converting electricity into light. However, it is far less efficient than LED. While less heat-intensive than heated filament technology, fluorescent lights generate significant amounts of heat, which can have negative consequences for many industrial applications. Because they contain mercury, fluorescent lights are classified as hazardous waste and must be disposed of accordingly.

LED technology is based on solid state electronics. These devices generate light by passing current through a semiconductor material. Electrons in the semiconductor re-combine with electron holes to release energy in the form of visible radiation. The actual light emitted from the LED may come directly from the semiconductor material or, in some applications, indirectly through fluorescence, as the light from the semiconductor strikes a phosphor coating on the device cover.

The color of the light is determined by the amount of energy required for the electrons to cross the band gap of the semiconductor, or by the properties of the fluorescent material. A common consumer application uses a blue solid-state emission, combined with a perceived yellow fluorescence, to create a white light.

In comparison to the other categories of lighting, LED is far more efficient at converting electricity into visible light. The common efficiency measure in lighting is lumens per watt.

  • Incandescent lighting produces about 10 lumens of light per watt of electricity
  • Fluorescent lighting typically produces about 60 lumens of light per watt of electricity
  • Modern LED technology has been shown to produce more than 300 lumens of light per watt of electricity

LED’s benefit for industrial uses is related to power efficiency and reliability of solid-state materials. With low heat generation, more uniform illumination, zero warm-up time, longer life (more than 10x compared to fluorescent bank lights), and no hazardous waste, LED technology is in the midst of eclipsing all other illumination technologies for both consumer and industrial applications.

Esko’s XPS Crystal LED flexographic plate exposure technology was announced at drupa 2016 and brought to market in the 50-in. x 80-in. format that summer. “The primary focus was wide web flexible packaging and the timing and technology were a perfect fit,” recalls Marsoun.

Two years later, the 35-in. x 48-in. unit was introduced with a focus on labels and other narrow web applications. “It was about this time that customers were telling us that LED plate exposure benefits were not only about consistency, but also about quality,” notes Marsoun.

The difference between XPS Crystal plate exposure and “conventional” plate exposure is the light source. Conventional flexographic plate exposure units use high UV output fluorescent bank lights; XPS Crystal plate exposure devices use light emitting diodes (LEDs) [see sidebar]. Fluorescent bank lights have a large amount of variation, require warm-up time, generate heat—which adds to variation—and are classified as a hazardous waste for disposal purposes. LEDs have extremely high consistency, no warm-up time, generate very little heat and can be disposed of as normal waste. Additionally, LEDs last at least 10 times longer than fluorescent bank lights and have numerous sustainability benefits.

US Entry

Esko’s original LED plate exposure system to be installed in the US was a 50-in. x 80-in. system at SGS in Minneapolis, MN in the fall of 2016. This system included a plate imager combined with an LED plate exposure unit.

The large format fit perfectly with SGS’ objective of offering a higher quality, more consistent plate to wide web flexible packaging converters. SGS Plateroom Manager Chuck Schoen reveals: “We’ve been running non-stop since installation more than three years ago. I can tell you that it produces the most consistent plates that I have seen in 32 years of working and managing flexographic platerooms.”

Scott Thompson, VP of technical sales and innovation, adds, “LED plate exposure technology has demonstrated the ability to produce flexographic print quality we couldn’t have imagined just a few short years ago.” SGS liked the LED plate exposure technology so much that it added a second unit in its Mississauga, Ontario facility. “The greatest benefit of all may be the ability to make the exact same plate in two locations,” states Ken Derstroff, director of operations for SGS Mississauga. “For a company like SGS, to satisfy brands and converters around the world, inter-device consistency is critical.”

Automation a Priority

In 2018, Simon Dumais, prepress manager of Imprimerie Ste-Julie in Sainte-Julie Quebec, Canada, began a major search to improve flexographic print quality. “We serve traditional markets such as labels, shrink sleeve and pouches, as well as high-quality niche markets, such as liquors, linerless and cosmetics,” he reveals. “Continuous quality improvement is an integral part of my job.” Having recently replaced a film lamination flexographic plate system with a LAMS system, Dumais had already created, used and analyzed a variety of test charts to show specific aspects of flexographic print quality.

“Testing the LED plate technology was simple,” he recalls. “I sent the test charts to Esko, it made plates and we printed the plates on our press. You could see the difference and measure the difference.” Bringing in a new CDI posed an interesting choice for Imprimerie Ste-Julie. “We could go with the tried-and-true CDI Spark or the new CDI Crystal,” says Dumais. “We went with the CDI Crystal because it has the growth path toward automation.

“Automation may be an even higher priority than print quality,” he continues. “It’s at the heart of every decision we make.” The plate making architecture currently installed at Ste-Julie uses the automatic plate loading to load and unload plates on the CDI, and uses a human to slide the plate from the CDI table to the adjoining XPS table. “We’re happy with the level of automation we have today,” says Dumais. “I like the idea that we can add the automated plate mover when we desire.”

Closely related to automation is productivity. Combining the throughput of the plate imager and LED plate exposure units with thermal plate processing, a complete set of plates can be produced and press ready in less than 45 minutes.

“We did time studies of our former masked-based system, compared to our new system and found that throughput is more than 50 percent higher,” reveals Dumais. “We not only get a plate out faster with less human touch points, we also produce more plates per shift.” As a supplier of both flexographic and digital technologies, Imprimerie Ste-Julie’s policy is to remain impartial. But when asked if flexographic print quality was as good as digital print quality, Dumais had a very simple response: “It’s better!”

Print Quality Hub

“Business growth was the factor that drove us to upgrade our plateroom,” remarks Thomas Dahbura, Hub Labels president. “Our current Hagerstown, MD location has grown to 110,000 sq. ft. with more than 20 presses.” More presses means a demand for more plates. “We began the investigation to update our plateroom in 2019,” he recalls. “We had three parameters we set out to optimize: sustainability, productivity and quality.”

Sustainability was the simplest. For plate exposure, it meant LED over bank. For plate processing, it meant thermal processing over solvent. “Bank lights are classified as a hazardous waste. The process of replacing and disposing of the fluorescent tubes is non-value adding activity with both safety and environmental implications,” says Dahbura. “LED lights last at least 10 times longer, are replaced on a very infrequent basis, and are not classified as a hazardous waste.”

Crystal Screening, combined with XPS Crystal LED Plate Exposure, enable Hammer to vastly improve dot quality when printing with UV inks on specialty films.

Plate processing may yield an even larger environmental benefit. Compared to solvent plate processing, DuPont’s FAST thermal plate processing system boasts 63 percent less non-renewable energy consumption, 53 percent less greenhouse gas emissions, and 99.7 percent less Volatile Organic Compound (VOC) emissions. “In terms of sustainability, there’s just no comparison between an LED/thermal workflow and a bank light/solvent workflow.”