Powder Developments for Heat-Sensitive Substrates

Posted on Wednesday, April 6, 2016

By: Paul Mills

What is influencing the course of powder coatings on unconventional substrates? From low-temperature UV powder coating to ultra-low bake powders to plasma treating for surface preparation, this article talks about what’s happening in this segment of the industry.

At the end of the 1990s, a handful of office furniture manufacturers began powder coating medium density fiberboard (MDF) using low-temperature powder coatings. Powder allowed furniture designers to seamlessly finish sharp edges and routed surfaces in a way that could not be accomplished with traditional high-pressure laminates.

Then, in 1998, the first ultra violet (UV) powder coating line was installed, driving process temperatures and oven dwell times even lower. What followed was a flurry of activity among UV and low-temperature powder coating formulators and equipment builders with both technologies vying for acceptance and technical supremacy. Nearly 20 years later, the penetration of powder into these new markets can hardly be called spectacular, and, to some extent, the UV vs. thermoset competition continues.

This article is not a cheerleader piece for powder coating on wood or plastic, but neither is it a tale of doom and gloom. Rather, we examine some important developments that are influencing the course of powder coatings on unconventional substrates. This activity ranges from how some suppliers are doing business to new resin technology and the appearance of some heavyweight end users who have weighed in on the side of powder coatings. Taken together, this is good news for those who are eager to see powder fulfil some of its expectations after these many years.

Going Vertical

Mike Knoblauch knows as much about the ins and outs of powder coating wood as anyone. His line at Decorative Veneer installed in Plainwell, Mich., in 2001, was one of the first lines for MDF in North America and the first UV powder coating line for wood anywhere. But just months after the line began making parts, 9/11 and a crashing dot-com economy decimated demand for office furniture, freezing the capital development plans of many end-users and suppliers to convert to powder. “This put us in a tough spot,” Knoblauch reflects. “Our [UV] powder suppliers went away.”

Knoblauch recalls he was left with only one formulator that continued to manufacture UV powder for him, and that even their commitment to the technology was marginal. With his investment at risk, and not getting the support he needed, Knoblauch took matters into his own hands. “We truly believed in the technology and wanted to grow our business, so we realized we would have to formulate powder for ourselves,” reports Knoblauch. The powder line was relocated to Cleveland, and a UV powder coating business, DVUV, was spun off as an independent company in 2005. Then, in late 2006, Knoblauch founded Keyland Polymer, Ltd., the first powder formulator completely dedicated to formulating and manufacturing UV-curable powder coatings. Today, Keyland’s operation is located next to DVUV’s Cleveland headquarters.

“Having a close relationship between a powder formulator and a powder applicator has a lot of advantages for everyone,” observes Bob VanAmburgh, the lead R&D chemist at Keyland Polymer. “You can become a better end user when you know how the powder works and talk directly to the chemists making it about the process. And you can certainly be a better formulator when you learn first-hand how the powder is being stored, applied, cured, and tested on a wide range of substrates and parts,” says VanAmburgh. According to Knoblauch, having a responsive UV powder formulator has made all the difference and is the main reason that DVUV’s sales nearly doubled in the first year after Keyland began operations.

Although Keyland is the exclusive powder supplier of powder coatings to DVUV since 2007, Keyland also provides powder to other applicators. Keyland Polymer is a strong believer in the benefits of UV curing for powder coatings, pointing out that UV-cured powder coating provides the important benefit of low substrate thermal exposure. “Heating wood can cause gasses from within the material to escape and can form surface defects in the coating. UV-cured powder coatings minimize the substrate’s thermal exposure to provide a high quality finish,” Knoblauch says.

How Low Can You Go?

Although UV powder—which relies mostly on light rather than heat to cure—has long been recognized by applicators like DVUV for its low-temperature process, recent developments in “ultra-low bake” thermal powder coatings are claiming to push temperatures to new lows.

“With new thermal powder chemistry, you’re not heating up the core of the wood and getting that pop we were getting back in the late 1990s and early 2000s with the Lamineer type powders—or even the UV powders,” says Tony Varda, vice president of sales for IGP North America, the U.S. startup for a division of IGP Pulvertechnik AG of Switzerland. “Compared to what UV powder guys are currently promoting, none of them are anywhere as low bake as our ultra-low cure thermoset, particularly when it comes to preheating. Our process currently is working at 1 minute or less and at temperatures around 248- 257°F (120-125°C). One of our North American customers uses almost no preheat at all. “For curing, we don’t want to exceed 5 minutes, particularly with MDF.”

Varda cautions that the UV process may introduce heat in unintended ways. “Some UV users think that UV is already a low bake process because it’s UV, but if you put your hand in front of a microwave or arc lamp UV light, you quickly realize how much heat is produced in UV curing.”

“The ultra-low bake temperatures open the doors to new substrates [other than] MDF,” says Varda. “We are successfully powder coating natural hardwoods [such as] beach, walnut and cherry.” IGP is also finding success with low thermal cure powders on complex parts that cannot easily be cured with line-of-sight UV. “Take hardwood chairs, for example,” he says. “Although many people have tried, nobody has really found a very good way to UV cure a chair. There’s just too many shadow areas to do it cost-effectively. A low bake one-coat powder is a great way to powder coat a hardwood chair, especially when the customer wants to do a solid colored texture. Hands-down it becomes a no-brainer to use a low-cure thermal powder.”

Bern Fitzgerald, founder of Integra Doors, an IGP customer in South Carolina, agrees. “The process of powder coating wood is going to change the industry significantly. Every customer that we have shown the powder coated product to has jumped on board with enthusiasm. Homeowners are clamoring for powder coated doors because they realize that this is a durable, hygienic and attractive product.”

Varda also sees low-bake powder being used for metal surfaces as well. “We work with a customer who manufactures polyurethane and polyisocyanurate foam insulating panels like those used for garage and exterior doors. The low process temperature allows us to powder coat the metal exterior structure without raising the core temperature to a point where the foam reacts or where we could melt adhesives used in manufacturing the panels.”

The IKEA Effect

An important milestone in the development of powder on wood might be the vote of confidence from one of the largest furniture producers in the world—IKEA. The company owns and operates 381 stores in 47 countries, with annual sales of $23.1 billion and consumes approximately 1 percent of commercial wood products. It is one of the largest users of wood in the retail sector. However, IKEA is also known for its commitment to design and for promoting environmental responsibility across its supply chain. So the company’s intention to convert to using 80 percent powder coatings in its product finishes by 2018 is a victory for powder coatings—particularly for powder on MDF. “One of the early adopters of the ultra-low bake process is IKEA,” says Varda. “They are really pushing the needle on this in Europe where one of IKEA’s key suppliers, Ekoltech in Slovakia, is using the low bake IGP powder in really large volumes. Dušan Pisár, production manager at Ekoltech, has reported, “in the past powder coating was not suitable for volume production from either a technical or a cost perspective. The new technology eliminates problems such as edge coating, outgassing and high costs, so we opted to invest in two completely new powder coating lines with the latest conveyor and oven systems.” This is a move that Pisár has described as “a very good decision.” In describing its powder coated MDF products such as its Ramsätra product line, IKEA reports that powder coated fiberboard makes the surface durable and scratch resistant.

The decision to transition to more powder coating has promoted other MDF furniture manufacturers to follow suit and has had ripples through the supply chain. For example, Jotun Powder Coatings in Norway, a longtime IKEA partner and the world’s third largest powder producer, has also launched a new line of MDF coatings that meet the demanding IKEA specifications. According to Olaf Conreur, Jotun’s global marketing manager, “MDF powder offers exceptional smoothness, semi-matte appearance and superior scratch resistance while reducing the carbon footprint.” The IKEA shadow is even prompting leading wood suppliers like Egger, headquartered in Tyrol, Austria, to offer specially developed MDF boards with reduced formaldehyde content suitable for powder coating and complying with IKEA IOS MAT standards.

Plasma Preps Plastics

“It’s one thing to get powder onto the part; it’s another thing to get it to adhere,” says VanAmburgh, about his company’s often-thwarted attempts to coat plastics. While the physical and chemical mechanisms that provide adhesion are complex and difficult to disentangle, most powder formulators agree that powder has difficulty adhering to many common plastic substrates. “That’s because of the low surface energy of these materials,” says Andy Stecher, president of Plasmatreat North America. “The surface of many plastics is relatively inert compared to metals,” says Stecher. “And when the plastic surface is also soiled, the bond between powder and plastic to be even weaker, causing the powder to delaminate.”

Varda agrees. “Poor adhesion of powder to plastics has been a major impediment to growth in that area for us,” he says.

Some relief appears to be coming in the form of plasma treatment that makes plastic surfaces more powder friendly. “Plasma works on the principle of applying energy to matter to cause it to change state. In fact, plasma has been dubbed the fourth state of matter,” explains Stecher.

To understand how plasma works, consider a block of ice: water in a crystalline, solid state. Adding heat to ice turns it into a liquid state. Applying more heat creates a third, gaseous state called steam. Finally, if even more energy is applied to a gas, the molecules can be torn apart creating a highly reactive mixture of particles. Typically a gas such as oxygen is used in plasma treatment. Tearing apart oxygen produces ions, radicals, electrons, and photons of UV energy. These highly reactive species react with the plastic’s surface, breaking less reactive hydrocarbon bonds, and replacing them with more reactive hydroxyl and carbonyl groups. This modified plastic surface is much higher in surface energy and creates stronger electrostatic bonds between the powder coating and the plastic surface. This results inbetter adhesion without changing the chemistry of the powder or the underlying plastic itself.

“We have had great success plasma treating parts that were otherwise too difficult to powder coat,” says Stecher. “Most of the plastics that did not provide adhesion passed ASTM crosshatch tests easily after quick, safe, plasma treatment. While not all plastics perform equally, we find that adjusting the gas used to produce the plasma, the intensity and dwell time of the plasma jet can all influence the extent of adhesion.”

Enter Wood-Plastic Composites

While powder coaters have been nibbling at the fringes of wood and plastics finishing for more than a decade, a new material that has attracted recent consumer interest appears to be a promising prospect for powder. Wood-plastic composites (WPCs) are made of wood fiber/wood flour and thermoplastics, including HDPE, LDPE, PVC, PP, ABS, PS, and PLA, etc. In essence, WPCs combine the attributes of wood, plastics and plastic composites.

First introduced into the decking market in the early 1990s, WPCs are still relative newcomers to the building products market. The most widespread use of WPCs insofar has been in outdoor decking, but WPCs are also used for outdoor railings, fencing, park benches, window and door frames, and various trim and molding components. Manufacturers claim that WPCs are more environmentally friendly and require less maintenance than natural lumber. WPCs are manufactured by mixing ground wood particles and thermoplastic resins. This mixture is usually extruded into the desired shape often with simulated wood grain. The properties of WPC can be adjusted by adding colorants, UV stabilizers, coupling agents, foaming agents, and lubricants to help manufacturing and to customize the properties of the final product. WPCs are extruded into both solid and hollow profiles. Because WPCs are commonly used outdoors, powder formulations need to be weatherable, withstanding large swings in temperature and humidity, as well as rain, snow and prolonged UV exposure.

What does powder have to offer WPC manufacturers? “First, we can offer a wider range of colors and special effects,” says Kevin Biller, president of the Powder Coating Research Group, which has had success powder coating WPCs in the laboratory. “The current method of finishing limits WPCs to fairly limited selection of colors. That makes it impractical to offer custom colors,” says Biller. “Color is expensive to do as an in-mold process since it requires a good deal of pigment throughout the entire part. Or, they may use a co-extrusion process like cap-stock. With powder coating, colors can be customized, changed quickly, and changing color is fast and relatively inexpensive,” says Biller.

Super durable architectural powder coatings that can pass stringent AAMA specifications have already shown that powders can be formulated to achieve the demanding specifications for outdoor building products. However, powder coatings can also add other value to the WPC. “A coating can provide properties that are difficult or expensive to build into the composite,” says Biller. “For example, one of the problems with WPCs is preventing bacterial growth. An antimicrobial coating can help hinder some of these problems. Also, the use of heat-reflective pigments can protect the underlying substance from UV degradation, leading to deteriorating in strength, fading, and warping due to heat build.”

The idea of powder coating on WPC decking may not be as great a leap as it seems. Powder is already earning its stripes in the outdoor decking market.

Don Garrison, president of Nexan Building Products of Cullman, Ala., says, “The rich wood grain finish offers our customers the beauty and appeal of natural wood in a truly maintenance-free surface.” Nexan applies a powder coated finish to aluminum decking products, claiming that its “strong, durable powder coat surface finish is UV stable for color retention, and completely eliminates the need to scrape, stain, seal or paint again, ever. ” Nexan’s high-density polyester powder coating meets or exceeds AAMA 2604 specifications and 5 years of with minor color change or fade, as well as 3,000 hours of salt fog testing and humidity tests. “The textured powder finish also provides a non-skid surface that stays cooler than most composite decks and is three times thicker than baked-on enamel finishes,” says Garrison.

At the Finish Line

Although the trajectory of powder coatings on heat-sensitive substrates might be viewed as the tortoise rather than the hare over the past 15 years, the technology has managed to amble on. Today, with major players like IKEA committing to the technology, and advances in chemistry that overcome prior technical hurdles, powder on wood, plastic and new materials like WPCs may yet fulfill powder’s promise and make it to the finish line.

Paul Mills is a marketing and business development consultant to industry chemistry and equipment suppliers. He has been a writer for the powder coating industry since 1994 and is a regular contributor to Powder Coated Tough. He can be reached at 440-570-5228 or via email at pmillsoh@aol.com.