Introduction to UV LEDs for the wood market During the production of kitchen furniture, wood floors or cladding, varnishing is a crucial step of the process that offers a better protection along with an aesthetic appeal to the wood.
The many standards applying to varnishes mainly concern their resistance to breaking, stain and scratches. In order to meet every demand of the market, several varnish formulations have been created as well as different curing methods: thermal, infrared, mercury lamps, etc…
The curing process using UV LEDs illumination is one of the fastest there is and will soon replace current solutions such as mercury lamps. The photo-initiators present in the formulation are activated upon UV light insulation and instantly harden the varnish layer. Only a few seconds of exposure is needed for the varnish to be fully cured and have the required characteristics of brightness, resistance to thermal shocks, solidity…
UWAVE and the Technological Institute FCBA (Forest Cellulose, Construction-wood and Furniture) The FCBA is a technological institute whose mission is to promote technical progress, participate in improving the performance and quality assurance of industries.
Aware of the growing popularity of UV LED technology in the wood industry, the FCBA wanted to create a project involving different players in the field (paint manufacturers, manufacturers of UV LED equipment and end users). The objective was to determine the technical viability of such a solution, to draw conclusions on the formulation and its results after the varnish has been applied.
In order to verify the curing quality on varnishes, FCBA has carried out numerous standardized tests including anti-scratch, breakage and stain resistance tests.
Energy saving, Money saving
Strong varnishes, more resistant against scratches
Increased production speed
The results are excellent on two points. First of all, some varnishes have shown a very high scratch resistance up to 3 times higher than current varnishes. Secondly, the production speed can be doubled, depending on the application, without loss of varnish resistance.
Each element of the process continues to advance, meeting the needs of an evolving industry.
With so many stories of digital press launches and installations dominating the label industry news feed, to some, flexography has become an afterthought. However, despite the inroads digital printing has made in recent years – and they are indeed significant – the majority of PS labels and packaging printed around the world are done so via flexography. In fact, it’s really not even close.
There are several reasons why the tried and true flexo print method has been the backbone of the label industry for decades. As the name of the process suggests, flexo is flexible. Its versatility plays a pivotal role in its adoption and success. Flexo attributes that set it apart from competing technologies such as offset, litho, gravure and digital, include high press speeds, low equipment and maintenance costs, low cost of consumables, suitability for medium to long runs and ease of integration with other printing processes.
Furthermore, flexo’s flexibility allows the process to continue to evolve, with suppliers responsible for every element in the process working in lockstep to keep moving forward into the future.
Flint Group Narrow Web has recently announced developments in the up-and-coming UV LED flexo and shrink sleeve sectors, as well as addressing the extended gamut trend.
“We knew from interviews with clients specializing in the short-run shrink sleeve market, that they want a UV dual-curable ink with better adhesion and increased curing speed to boost productivity and reduce yield losses,” states Kelly Kolliopoulos, global marketing director for Flint Group Narrow Web. “Our experience in LED and conventional mercury curable ink system technology, combined with our understanding of the shrink market, enabled our R&D team to develop this best-in-class system.” She concludes, “EkoCure XS combines the latest ink chemistry, including novel binders, that provide perfect cure and sufficient flexibility of the cured ink, allowing the adhesion to remain fool-proof – especially after post shrink processing is completed. The full range of Pantone shades and opaque white are available.”
Dowa Electronics Materials has successfully developed a deep ultraviolet LED chip, which it says feature the world’s highest output power of 90mW, with a peak wavelength of 310 nm, and dimensions of 1 mm × 1 mm.
Deep ultraviolet lights with a wavelength of 310 nm are used for curing and skin therapy. Replacing conventional mercury and excimer lamps with these LEDs enables equipment to be smaller and mercury-free. With the advantages of long life time and power saving, this product is expected to find new applications.
Combining a high-quality AlN template with unique crystal growth technology, Dowa has been prepared for a mass production for deep ultraviolet LED chips, which boast the world’s highest output power in the disinfection wavelength of 280 nm.
For the wavelength of 310 nm, combining this technology and the fine-structured sapphire substrate developed by Oji Holdings Corporation, Dowa proceeded to improve luminous efficiency, enabling a 20 percent higher output power compared to current products, resulting in an output power of 90 mW, the highest in the world for the wavelength of 310 nm.
Is there a business opportunity for the commercial printing segment in industrial printing applications? The most reliable answer at this point is a definite maybe. But, a market that’s been described by many pundits as “ready to pop for a long time” is definitely worth exploring.
When printing stops being printing for its own sake, it’s time to recognize it for what it actually is: industrial printing.
Another way to delineate industrial printing is by application. Broadly speaking, points out Josh Hope, senior manager of 3D Printing & Engineering Projects, Mimaki USA, industrial printing is putting ink onto “anything that isn’t paper,” but often in small batches that don’t scale up to true “industrial” quantities. He advises printers to look at the printable objects they are outsourcing for clues to the kinds of industrial printing they might be able to do in-house.
At Fujifilm Dimatix, says Timothy Rosario, senior project manager, Fujifilm Inkjet Technology, “we define ‘industrial printing’ by the various substrates we are printing on, including sandpaper, waterproof seam tape, cement board, drywall, house wrap and insulation.” This gives a sense of the role industrial printing can play in non-traditional markets such as homebuilding, where Fujifilm Dimatix has introduced an LED-UV solution, the StarFire SG1024 industrial inkjet printing system, for printing construction materials.
Flatbed UV inkjet printers that can accommodate solid objects, as well as flat substrates, work best. Hope says that Mimaki’s UJF Mark II (MkII) Series LED-UV tabletop printers are tailor-made for late-stage customization of phone cases, USB drives, skateboards and other items produced in small batches. With its 4˝ inkjet head height, the Ricoh Pro T7210 UV flatbed — the device that printed cinder blocks at the SGIA Expo — has been used to image bar stool seats and guitars, according to Dollard.
Unlike in traditional production, the printing isn’t the dominant technique, but one of a number of steps in a complex sequence of events. In industrial printing, “print adds value within a bigger process,” says Tom Molamphy, business development manager of the Industrial Inkjet Ink Div. at Agfa Graphics.
Molamphy points out that while there are industrial applications for Agfa devices such as the Jeti Tauro hybrid LED-UV inkjet printer, wide-format equipment generally isn’t geared for the high-speed, single-pass performance that industrial printing on an industrial scale requires. As a supplier of industrial inks, Agfa is working with printhead manufacturers and system developers to push wide-format inkjet further in this direction.
UV LED curing makes its mark in the labels and packaging space.
From converters to their customers, environmentally friendly practices are profoundly affecting the labels and packaging space. One such way that the industry can save – both from sustainable and cost perspectives – involves ultraviolet (UV) light emitting diode (LED) curing.
UV curing technologies have been designed to instantly cure specially formulated inks, coatings and adhesives through polymerization. UV curing can include medium-pressure mercury arc and microwave-powered lamps, as well as LEDs.
According to Phoseon Technology, both arc and microwave curing technologies rely on the vaporization of mercury within a sealed quartz tube containing an inert gas mixture. Mercury emits ultraviolet light when vaporized, while electrodeless lamps utilize microwaves to vaporize the mercury.
Electrode lamps harness a high-voltage arc struck between two electrodes to achieve the same result. When the mercury is vaporized into an extremely high-temperature plasma gas, it emits a spectral output across UVA, UVB, UVC and UVV bands that can be manipulated by introducing metallic additives to the inside of the lamps. When the ink, adhesive or coating formulations are exposed to ultraviolet energy, they are crosslinked into a photopolymer.
UV LEDs, however, are solid-state semiconductors. Compared to conventional lamp technology, LEDs contain no moving parts or mercury plasma gas. In addition, they often operate at temperatures nearly 1/10th of those dealing with conventional lamps.
Martin Kugler, corporate communications for GEW, states that the electricity consumption of a typical mercury arc system is 2,005,000 kWh over a 10-year period. The equivalent UV LED system would consume 950,000 kWh, a reduction of over 50%. In the US, at approximately 12¢/kWh, this equals a savings of $126,000. This is based on an 18″ 8-lamp system with chiller, 60% uptime, two shifts per day and six days a week.
“Improvements in conventional reflector geometry have increased intensity at the web by capturing more UV energy and directing it in a true elliptical focus at the web, increasing curing power by 35%, thus reducing energy consumption,” notes Mark Hahn, VP of sales and marketing at AAA Press International. “UV LED curing technology has seen dramatic improvements in output power going from 16W/CM2 to over 30W/CM2, as well as significant improvements in optics design, allowing complete curing at higher line speeds.”
According to AMS Spectral UV – A Baldwin Technology Company, a mercury arc bulb can last 2,000 hours while the chips in an LED UV module can last 20,000 hours or more. This eliminates the need to frequently replace them as part of production maintenance.
“Over the first 20,000 hours of life, a typical LED system will lose about 15-20% of its UV output,” says Kugler. “After 20,000 hours, the LEDs will continue to work but output will degrade more quickly and the probability of LED failure increases. When a single LED fails, the user will not notice, as surrounding LEDs automatically increase in power to accommodate the loss. However, eventually, enough LEDs in a single area will fail and curing results will suffer.”
Stefanie DeBetta Langler, sales and customer service manager at Southern Lamps, explains that life expectancy and cost play a large role in a customer’s decision-making process regarding UV systems. “A typical LED system can cost $102,000 and the replacement lamp is $49,200. LED lamps are predicted to last 10 times as long as an arc lamp, but for 200 times the cost,” she says. “In comparison, a typical arc UV system will cost $28,500 and a lamp will be $258. The system is almost 1/4 of the cost and the lamps are 1/190th of the cost.”
The company says it is 100% focused on LED technology and providing rugged, high-performance products.
When it comes to label and packaging solutions, Phoseon Technology has the (LED) cure. Phoseon’s UV LED (light emitting diodes) curing products are currently being utilized in the printing, coating and adhesive industries, and the technologies are available to clients in custom configurations.
According to Phoseon, the company is 100% focused on LED technology–providing rugged, high-performance products for application specific solutions. Phoseon’s patented Semiconductor Light Matrix (SLM) technology encapsulates LEDs, arrays, optics and thermal management to ensure curing performance. Each of these four components is a strictly engineered system that provides maximum UV energy and superior performance while also increasing long-term robustness for demanding applications.
While arc and microwave curing technologies rely on the vaporization of mercury within a sealed quartz tube containing an inert gas mixture, LEDs are solid-state semiconductors. They contain no moving parts or mercury plasma gas and operate at temperatures that are often less than 1/10 the operating temperatures of conventional lamps. When connected to a DC power source, an electric current flows through the semiconductors, dropping electrons into a state of lower energy as they travel from the negative to the positive side of each discrete LED. The energy differential is released from the device in the form of a relatively monochromatic spectral distribution.
Commercially, UV LED technology has significant market adoption with longer UVA wavelengths (365, 385, 395 and 405 nm), and development work in shorter UVB and UVC bands continues, says Phoseon.
Phoseon describes UV LED curing sources as “high-tech electronics,” so the technology has blossomed with that of smartphones, laptops, tablets and televisions. During the technological boom, which has occurred between 2010 and 2017, UV LED sources have become more powerful, more efficient, more reliable and less expensive.
“UV LED curing technology has arrived,” the company says. “It is no longer an emerging technology but an enabling technology− one that is bringing a host of advanced capabilities to screen printing, flexographic and digital printing. These advances and new capabilities are helping industrial, graphics and specialty printing operations be more productive, versatile and energy efficient.”
Options abound in today’s ever-changing label industry.
A recent study conducted by label industry market research firm LPC, Inc., determined that new digital press installations in North America are growing at 11.9% per year. The firm estimates the rate of new conventional press installations are contracting at an annual 8-9% clip. Taking into account these forcasted rates, LPC believes that in the year 2020, one in four new label presses sold in the US and Canada will be conventional, and three out of four will be digital. Times sure have changed.
A fact that has emerged since the proliferation of digital printing, is that digital technology adoption is not one size-fits-all. What is a great fit for one label company may vastly differ from others. Specialization, location, finishing needs and markets served all play key roles in digital press adoption decisions.
Whether it’s EP or inkjet, a desktop printer for a few thousand dollars, or a hybrid production class press with a 7-figure pricetag, there have never been more options for both first-time digital technology adopters or longtime users with multiple machines. Some products target brand owners, suggesting they’d benefit from producing labels themselves. Some are entry-level priced for the small to medium sized label company. Others are even designed with speed in mind to compete with flexo operations.
There are many, many vendors now, with some offering several different machines. While the information that follows is not all-inclusive, it’s L&NW’s attempt to share the capabilities, benefits and specifications of digital and hybrid label printers and presses on the market today. Suppliers appear in alphabetical order.
By John Cafferkey, Marketing Manager, Cambridge Nanotherm
Over the past 30 years or so, UVA curing has revolutionised the way manufacturers have made products. UV’s ability to change a liquid to a solid has paved the way to widespread ink curing, adhesive bonding and coatings used in a large number of applications, like general consumer electronics, automotive, telecoms, graphic arts and more.
For decades UVA curing used high-intensity discharge (HID) UVA lamps. Only recently has the industry seen LED alternatives come to the fore. Compared to HID lamps, LED form factors are smaller and less fragile, while operationally they use less power, run cooler, and power cycle instantly when needed. These characteristics are improving the efficiency of the UV curing industry while opening up new curing techniques through hand-held devices — something that would not have been possible with HID lamps.
While LEDs run cooler than HIDs, they are still relatively inefficient. LEDs only convert around 40% of the power that goes into them as light, converting the remaining 60% as heat. This heat is a huge problem because if it can’t escape quickly enough, it can cause the quality of the UVA light to deteriorate or, worse, cause the LED to fail and/or shorten its lifecycle. And as designers today seek to pack more, and more powerful, UVA LEDs closer together on modules, this heat problem is only set to worsen.
Why heat is a problem for LEDs
LEDs cannot convect or radiate enough of the heat away from the source through the ambient air surrounding them because the surface area is too small and the temperature too low for this process to take place. The only way LEDs can shed excess heat is by conduction out of the back of the die, through the materials in the PCB, to a heatsink and the surrounding environment.
Therefore, the substrate material that the PCB uses needs to a high level of thermal efficiency. With UVA applications, the module substrate tends to be either a thermally effective metal-clad PCB (MCPCB) or electronics-grade ceramics like aluminium nitride (AlN). In higher-power density applications, epoxy-based MCPCBs do not have the requisite thermal performance (<100W/mK vs 170W/mK for AlN), making AlN the substrate of choice where heat is a significant issue.
However, AlN isn’t perfect. First, the material itself is expensive. Secondly its characteristics can pose problems for manufacturers — AlN is inherently brittle, making it difficult to manufacturer into circuits. That brittleness restricts the tile size to just 4×4-inches (occasionally 7×5-inch). Any larger and the brittleness begins to wreck the yield rate. Even with 4×4-inch tiles, a yield loss of 20% is not uncommon.
The other issue with brittleness is when mounting the finished module onto its heatsink. Ideally, the circuit should be attached as firmly as possible to reduce any air gaps between the circuit and the heatsink. But screwing a brittle AlN module to a heatsink is likely to fracture it if too much pressure is applied.
Now, however, there exists an alternative material that offers a comparative thermal performance to AlN without the issues around manufacturing. That alternative is nanoceramics.
Nanoceramics — a better choice than AlN
LED thermal management innovator Cambridge Nanotherm has devised a way to produce nanoceramics specifically for the UV curing industry. The secret is in the process. Using a patented electro-chemical oxidation (ECO) process, Cambridge Nanotherm converts the surface of an aluminium board into thin layer of alumina (Al2O3) just tens of microns thick. This alumina layer performs the dielectric function, insulating the circuits from the aluminium below, while conducting excess heat through the back of the LED quickly. And while alumina is far less thermally conductive than AlN the sheer thinness of the layer more than cancels that issue out, removing heat efficiently.
After the ECO process, Cambridge Nanotherm sputters the copper circuit layer directly to the nanoceramic dielectric via thin-film processing, further improving the thermal efficiency of the stack. Nanotherm DMS (a direct replacement for AlN for UV modules) has a composite thermal performance of 152W/mK, slightly lower then high-grade AlN but more than enough to cope with all but the most demanding UVA applications.
In terms of manufacturability, nanoceramics can be treated in the same way as a standard MCPCB. Because it’s less brittle, there’s less loss of yield, and the product can be screw-mounted to a heatsink without breaking. In short, nanoceramics offer the best of both worlds — the thermal performance of AlN and the robust characteristics of an aluminium MCPCB.
LED technology is having a profound impact on the UVA industry, and has seen costs drop and efficiencies increase. However, heat remains a central issue with LEDs, and a challenge that needs addressing if the curing industry is to see further cost and efficiency benefits.
The global digital printing market for packaging is anticipated to expand at a steady rate, reaching yearly growth close to 11% for 2017-2021, according to research firm Technavio (London).
We’re seeing it used for applications that are largely if not essentially wholly devoted to printing onto flexible material substrates such as labels and rigid to semi-rigid surfaces including for corrugated cases and also paperboard folding cartons.
There’s also been a unique method of direct digital print onto rigid containers, the Direct Print Powered by KHS digital printing process, specifically for PET bottles. I’ve covered the no-label process as an editor on sister publication Packaging Digest as a breakthrough, efficient and source-reducing technology for bottling operations. It’s important to point out that labels, particularly shrink film labels, may be problematic for recycling in addition to the source reduction gains of their elimination.
It turns out there’s an angle of interest for PlasticsToday readers, too: the recyclability of these digitally-printed bottles, which was first certified by the European PET Bottle Platform (EPBP) in 2013, has now been reconfirmed as having no negative impact on rPET, making it officially approved for bottle-to-bottle PET recycling.
“The washing water must not be contaminated during the recycling process,” explains Martin Schach, head of the Printing Technology Department at KHS GmbH (Dortmund, Germany). “The ink must also not deposit itself on the crushed PET bottles.”
KHS developed a digital printing process with low-migration, LED UV-curing inks for the food-safe decoration of PET bottles where the print reliably flakes off during the recycling process.
Current laboratory tests for the Belgium market, where recycled PET bottles were examined for chemical residues in random checks, confirm the safeness of the process in which printed PET bottles from customer Martens Brouwerij brewery had been fed into the recycling chain. In 2015 the Belgium brewery was the first beverage producer to launch PET bottles with Direct Print Powered by KHS to market and make use of the technology, which has subsequently been further developed for the customer. These further developments include a higher print quality and new forms of decoration, resulting in a level of flexibility that enables individualized print on separate bottles such as the use of different motifs.
High demand for coated filaments across a wide and growing spectrum of applications ranging from cell phones to fabrics, is causing manufacturers to increasingly turn to Phoseon Technology’s revolutionary UV LED curing because of the advantages it offers compared with traditional UV or arc light curing methods.
There are many types of coated filaments, ranging from copper wire covered with a thin layer of insulation used in everyday appliances, to coated threads used in specialized clothing materials that improve athletic performance, personal comfort and protection from the elements.
Until recently, manufacturers cured the coating on filaments using UV or arc lights. Now an increasing number of manufacturers utilize Phoseon Technology’s UV LED curing for filament coating because it produces faster and more consistent results than traditional curing methods.
“UV LED curing uses a fine-tuned light source that enables better process control, resulting in a superior and more consistent overall product,” said Ed Kiyoi, technical marketing engineer at Phoseon Technology. “That process control leads to higher yields and reduces scrap for manufacturers.”
Rapid curing and improved process consistency are important benefits, but UV LED curing also can reduce operation costs and energy usage up to 70 percent. In addition, because UV LED curing does not contain mercury, which is used in arc lights, it is safer for the environment and workplace.
Furthermore, UV LED curing enables manufacturers to produce filament coatings that are not possible with conventional methods. For example, because UV LED curing creates less heat than traditional arc or microwave lamps, it allows manufacturers to coat fine thread with specialized chemicals to produce “smart textiles” for applications such as protective clothing.