Because of government restrictions on Volatile Organic Chemical (VOC) emissions, it is imperative that alternatives to traditional solvent-based coatings be considered. Of those alternatives, water-based finishing and new technologies in UV coatings seem to have caught the attention of the wood products industry.
Water-based finishes have been touted as the industry’s solution to the tightening grip of the EPA. However, reaction to the new finishes has been lukewarm up until now. That is beginning to change, according to industry representatives.
“Over the years, we’ve seen steady growth in the acceptance of waterborne coatings,” says Chuck Susnis, market manager, Chemical Coatings Forest Products, The Sherwin-Williams Company. “The industry segment that has embraced waterborne finishes the most has been the millwork segment. The majority of coatings being used today by this segment of the wood finishing industry are waterborne, so that currently, most windows, doors and wood siding are now coated with waterborne finishes. This is because waterborne products provide the performance and appearance necessary for this market segment, while enabling finishers to meet regulatory requirements.”
Certain segments of the industry have remained cautious about using waterborne finishes. “In the furniture industry, acceptance of waterborne coatings has been slower, in part due to difficulties encountered by the industry in controlling the drying environment for optimum curing of the coatings,” Susnis says. “New dehumidification equipment that makes it possible to improve conditions in a finishing line’s drying area will make it easier for furniture manufacturers to use waterborne coatings.”
“Depending on what particular industry you ask, you will get answers from high to low acceptance,” adds Steve Bosley, sales manager, Delle Vedove. “As regulations get tougher, the easiest, cheapest way for a company to comply is to switch to water-based coatings. They can then use their same ovens, just running the line more slowly due to the longer dry times. The water-based primers have made significant advancements for both interior as well as exterior components. Generally, most people associate water-based coatings with grain-raising and sanding difficulty. Higher solids with new resins and new abrasives have helped to minimize both of these issues.”
Water-based coatings |
ADVANTAGES
• Necessary performance and appearance, with ability to meet regulatory requirements
• Existing ovens may be used
with longer drying times
• Water-based stain suited for
application under UV clear coats
DISADVANTAGES
• Possible drying environment problems
• Associated grain-raising and sanding difficulties
• Scratch resistance and clarity not as good
• Not typically recyclable
• Difficult to clean off of equipment
• Not always EPA compliant |
| |
UV coatings |
ADVANTAGES
• Greatly reduce VOCs
• More durable finish
• Instant cure
• Small floor spare requirement
• Less energy consumption
• Transfer efficiency
• Can be spray-applied (vacuum technology)
• Easy equipment maintenance
DISADVANTAGES
• Investment in new equipment |
Water-based stains are particularly suited for application under UV clear coats, according to Bob Kostelnik, product manager – finishing, Stiles Machinery. “They have good drying properties, and since they open the grain more than solvent stains, they improve coatings adhesion when using UV. Water-based primers are very fast drying and are easily re-coated in the field by painting contractors.
“Water-based coatings have not been accepted as clear coats (sealers and topcoats) in the furniture and cabinet industries. They typically do not have the scratch resistance or the clarity of the film as offered by conventional solvent-borne coatings.”
Problems/Misconceptions with Waterborne Finishes
Part of the industry’s reluctance to switch to water-based coatings is the amount of change in process needed. “A common misconception regarding waterborne finishes is that they just can be substituted for solvent-based lacquers.” Susnis says. “Waterborne coatings can provide the appearance and performance equivalent of solvent-based lacquers, or sometimes even better, but they must be handled differently. When implementing waterborne coating systems, there are trade-offs. You may need to make changes in your sanding procedures or in your curing process to achieve the quality desired, but by making these changes you can lower your VOCs.”
Just because a company makes the adjustment to water-based finishes does not mean it is EPA compliant. “A common misconception is that water-based coatings are free of VOC and other substances that concern regulatory agencies,” says Kostelnik. “We have seen some water-based coatings that contain high VOC levels and virtually all water-based coatings contain some level of VOC. Also, it is always necessary to obtain permits when using water-based coatings.
For those not convinced there are alternatives
Other environmentally friendly finishing solutions available exist for the manufacturer who remains unsold on waterborne coatings. “As an alternative to using waterborne systems, we are seeing the use of hybrid systems comprising a solvent-based sealer and a waterborne topcoat,” says Susnis. “The solvent-based sealer minimizes grain-raising while the waterborne topcoat lowers VOCs.”
UV coatings have become a popular solution as well. “UV coatings eliminate (or greatly reduce) the VOCs, and give numerous additional advantages,” says Bosley. “Some of these include: more durable finish, instant cure, small floor space required, less energy consumption, and cheaper per linear foot (in some applications).”
Transfer efficiency is possibly the greatest advantage in the use of ultraviolet coatings. “UV coatings have a chemical called a photo-initiator which, when in contact with a certain wave length and intensity of UV light emitted from a UV oven, instantly cross-links and cures the coatings. By using a vacuum coater to apply 100 percent solid UV coatings to mouldings, 100 percent transfer efficiency is achieved,” explains Bosley.
The advance of spray coat technology, production space savings and increased production volume has paved the way for UV acceptance. “It used to be that UV coatings had to be applied by roller coaters, but UV has become a popular alternative for lowering VOCs because more people are now spray-applying these coatings,” Susnis says. “One reason for this is the increasing popularity of the vacuum coating process, particularly for moulding and picture frames. It is very economical to apply UV coatings in this way. These finishing lines require about one-quarter of the space of a regular finishing line. The coatings are spray-applied with vacuum technology.
“The advantages to UV applications are quite dramatic.” says Kostelnik. “They are the easiest coatings to recycle. They offer the fastest curing times. They are the most scratch and chemical resistant film. They are not post-cure thermoplastic so “block stacking” of parts is not an issue as it is with water-based and conventional films. UV coatings are immediately converted from a liquid to a solid when subject to ultraviolet radiation. This conversion is complete without the use of catalysts or lengthy drying time.”
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