Here’s the basic fact. Powder coatings for natural wood don’t work — yet. But try it on engineered wood, like MDF and particleboard, the woods of choice for panel processing, the woods of choice for furniture going to the SOHO market (small office, home office) which captures some 35% of the $13 billion business furniture market, and you have a product that:
is environmentally sound — no solvents, only trace amounts of VOCs
- is a one-step finish process
- eliminates need for most sanding using textured finishes
- creates a smooth writing surface or more tactile surfaces
- spray-wraps around virtually any compound curve with a seamless edge
- can be applied after assembly if UV cured
- gives one over-all finish to wood/plastic/ metal used in combination
- is labor and material cost effective
- covers up imperfections in most MDF wood
- maintains abrasion resistance
- is heat resistant to acceptable levels
- erases delamination problems because there is nothing laminated
- and probably has even more pluses that each powder coating manufacturer will eventually introduce to the market. For now, these are claims made by today’s powder coating manufacturers with back-up from end users.
Powder coatings are not new. They have been around since the 1960s in Europe and since the 1970s in the USA for metal products. But getting powder — a more environmentally friendly product with virtually no VOCs that is cost considerate and design flexible — to adhere to wood at temperatures and cure times that are practical has been a work-in-process.
Morton International (since purchased by Rohm-Haas) introduced its powder coatings to the wood industry at IWF98. Lilly experimented with, and was powder coating successfully on wood 20 years ago, “but with limitations,” says Rocky Osborn, Lilly sales director, “not with the application but with the cure. Back then we had traditional curing methods. We were able to reach the temperatures needed to cure the coatings, but the substrate didn’t hold up.”
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| A floor plan view of a typical powder coaing line from Tellkamp. |
It is just now that the technical advances needed to work with heat sensitive wood and retain conductivity is gaining industry attention. Those advances, from Lilly’s perspective, “are from the coupling of infrared heating with convection,” points out Bill Odell, senior research scientist of Industrial Coatings at Lilly. And from Tim Misseldine, Lilly’s new product development specialist, “Since we brought this to market four or five years ago, we are continually refining it so that we can use our process with most brands of MDF.”
Some large end-user companies like Knoll and Herman Miller (both major business furniture manufacturers), and some smaller companies, like Precise MDF Powder Coating Co., Grand Rapids, MI; Valley Design, Fountain, MN; Premier Cabinet Door, Adelanto, CA, and Crest Coating, Inc, Anaheim, CA, (applying powder coatings to kitchen cabinet doors), are moving more successfully into powder coatings for engineered wood products. Meanwhile the rest of the industry is testing the waters or waiting to see what the more aggressive risk takers are finding before jumping on-stream .
Sauder Wood Products, Archbold, OH, and O’Sullivan Industries, Lamar, MO, both RTA producers, have been experimenting with powder coatings. Sauder has market tested products in places like NEOCON, the premiere annual business furniture show in Chicago, where no key RTA manufacturer had tread until two years ago. Sauder continues to test it but has not introduced any product into the market with powder coatings yet. Bush Industries, Jamestown, NY, another key RTA manufacturer, is watching the marketplace very closely.
H.B. Fuller to launch new PC at IWF2000
At IWF2000 this August in Atlanta, H.B. Fuller will be the new “chemical” kid on the block — introducing its ready for market thermoset and UV powder coatings for MDF wood. The company is bringing along 30 years of powder coatings experience in metal. While there now are some 105 manufacturers of powder coating in metal around the world, there are probably only a handful experimenting and introducing powder coatings for wood — including H.B. Fuller, DuPont, Lilly and Morton.
Engineered wood vs. real wood
Applying a dry substance, like powder, to metal is not a problem. Metal is a conductor and the electrostatic application adheres quite easily. But in real wood, “when powder is applied, it rises to the surface, still breathing, still growing. It doesn’t work,” says Steve Couzens, wood technology specialist at H.B. Fuller.
But enter engineered wood, MDF, particleboard that has been pulverized, chopped and refined. In essence, it is now wood that has been “killed” yet reborn into a new-life product that holds its dimensional size, while still maintaining, perhaps, 7-9% moisture content. But it no longer contains sap or those “other juices” so it can work more compatibly with the chemical “intrusions” of powder coatings. “Engineered wood is stablilized, a substrate that is ready to go,” explains Couzens. At high temperatures, real wood will exude moisture, oozing sap and other “juices” thus not making it a candidate for powder coating today. But in MDF, heating the substrate solves one problem. By heating the substrate, moisture is brought to the surface of the MDF, thus giving it a conductivity to attract the charged particles of the powder coating.
Curing Powder Coated Parts
There are various ways to cure the powder coated parts — by gas convection, infrared oven (IR), a combination of the two, or by UV curing.
A typical gas convection cure process works like this:
- The substrate is prepared by routing and sanding the MDF or particleboard
- The substrate goes into a gas-convection oven at temperatures that average 325 degrees for 10-12 minutes for initial attraction — a critical point that “pre-heats” the substrate making it more conductive.
- The part moves into a spray zone for electrostatic powder application, pushed out of the spray gun by air that is electrically charged.
- The powder coated part enters the curing oven .
That is one, very acceptable way to cure heat-sensitive, powder coated MDF wood.
However, DuPont, with its UV-TEC™, and H.B. Fuller, with its Solar Cure™, are now introducing powder coatings using ultra-violet (UV) radiation-curing methods over MDF. It may be the greatest revelation in powder coatings to date, with the ability to reduce the temperature and time required for curing. Metal can take it, but wood loses its structural value when exposed to high temperatures. That has been the prohibitive factor in powder coatings for wood until now.
With outgassing, warpage and brittleness a possibility at 375 degree temperatures, UV curing now reduces that temperature to where MDF never sees temperatures any higher than 220-240 degrees, “which is well within the heat-resistant threshold of the MDF,” says Michael E. Stuhldreher, market development manager for DuPont.
UV powder melts and flows on the part at about 220-240 degrees in an infrared or convection heat oven and then is cured under a UV lamp within seconds. “The lower melt/flow/curing temperatures associated with UV powder decrease the coater’s energy consumption, shorten the production line and therefore require less plant floor space. This allows for heat-sensitive substrates, such as MDF, to be powdered coated, he points out.
The RadTech Report—
Uniform Edges
Peter Gottschling, Zbyszek Stachyra and Maria Strid, DuPont Chemists, wrote a comprehensive report on powder coatings, including wood applications, which was published in the July/August 1999 issue of the Radtech Report, an association paper. In that report, they pointed out that UV-cured powder coating technology “is at a point where a thin stripe of powder can be uniformly applied to the edge of MDF… and can be applied uniformly at high film thicknesses without drips or sags like liquid coatings.”
Powder coatings also will apply uniformly over complex curves and edges. It’s not just for flat panel applications anymore. And UV-cured powder coatings can be formulated to give a very hard edge. As has already been pointed out, these writers agree the UV-cured powder coatings have the ability to “coat fully assembled parts that include both wood and metal components and plastic, providing a matched, uniform appearance on the entire assembly.”
Stilexo, a UK company located in Wales (producers of a wide range of furniture products for the European television industry), has the first production line in Europe to use UV-cured powder coatings on MDF wood products — in development partnership with DuPont.
Stilexo test marketed customer needs and concluded powder coatings on UV-cured MDF was the route to future product requirements based on customer comments that stressed “old or current techniques for laminating, wet coating, etc. would not satisfy the company’s requirements for future new products.
“We are finding our new products are showing better ‘design’ through having more flexibility when it comes to component form and color,” says Bengt Ake Nilsson, managing director of Stilexo. “Quality and cost are more competitive than when using traditional finishing methods and… our products are now more environmentally friendly.”
Manufacturers like DuPont, Lilly and H.B. Fuller agree that powder coatings for wood are an attractive, durable, easy to apply, solvent-free alternative to liquid coatings with only trace amounts of volatile organic compounds (VOCs).
“Powder coaters can switch colors with minimal downtime,” says Stuhldreher. “When they are done spraying one color, they roll that spray booth back, roll the clean booth up, and are ready to switch colors quickly. When not in use, the other booth can be easily cleaned with a squeegee and air hose. The ease of color changing gives the coater more flexibility and reduces the time and costs associated with batch set-ups.”
Waste and cost are advantages. Overspray is recaptured and recycled with a 95% to 98% recapture rate, depending on what company you are talking to. The overspray is mixed with new powder and resent through the system so there is virtually no waste involved.
Big Potential in Office Furniture
With a $13 billion office (business) furniture market in the U.S. alone (including the ever-growing home office), “the use of powder coatings offers tremendous labor savings over traditional methods,” offers Osborn.
In office manufacturing there is a mating of metal components, plastic components and MDF. With powder coatings, the manufacturer is able to get exact appearance among the different materials. And powder coating MDF saves labor in sanding, priming, sealers and top coating. It addresses environmental issues. Liquid finishes involve some level of VOC emissions.
Powder Coating Systems—the Equipment
Fortunately, powder coatings for wood can use — virtually— the same equipment as that provided for powder coating metal. The procedure appears relatively simple. Nordson Corp., Duluth, GA, ITW-Gema, Indianapolis, IN, and Tellkamp Systems, Santa Fe Springs, CA, are three companies actively working with powder coatings producers and manufacturing systems for powder coatings.
In general, substrates are loaded onto an overhead conveyor, travel through an oven where the substrate is pre-heated to accept the powder coating, the powder is applied electrostatically with spray guns in a spray booth, and the part moves on to a post-cure oven for final cure, then to a cooling tunnel or area to reduce the heat in the product.
Overspray, suspended in the air, passes through a separation process and is retrieved for re-use.
The final product, according to one systems producer — Tellkamp Systems, Inc. (see illustration of typical system) — is similar to vinyl or high density laminates. They can be re-coated to change color or repair defects.
ITW-Gema, points out that systems can run the gamut “from a one-gun operation with a batch booth, to a highly complex multi-gun, totally automated configuration with guns, booths, and other peripherals to meet the occasion. Each gun has a control unit that regulates the voltage and the rate of deliverance,” says Jeff Hale at ITW-Gema. When selecting a system, consider these points:
- Efficiency of the charge
- Consistency of the powder flow
- Accuracy with which both can be adjusted to provide the right level of performance
- Ability of settings to be repeated systematically each time they are used.
Powder booths also are similar but use different types of recovery equipment, Hale adds. They are either cartridge filters or a cyclone separator. To select the appropriate booth system, consider these points:
- The production batch size
- Number of different types or colors of powder being used
- Frequency with which they are changed
- Finish quality of the desired coating.
"If you expect to change powders frequently, then a fast color change time will be hot on the list of necessary features. If, however, you do long runs using the same powder throughout, then highly efficient reclaim system will be more critical,” advises Hale. “If the parts are all the same, automatic guns may be cost-effective, but if they are intricate structures that are too difficult to coat, manual operators may make more sense.
You can see most of the companies mentioned in this article up close and personal at the August 24-27 International Woodworking Machinery & Furniture Supply Fair — U.S.A.® (IWF2000), Georgia World Congress Center, Atlanta, GA USA.
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