UV Curable Wood Finishing

Many U.S. cabinet shops and furniture manufacturers are now using ultraviolet (UV) curing systems. Ultraviolet (UV) curing is a photochemical reaction—photopolymerization—when specialized coatings are exposed to UV light they cure, instead of relying heat and time to evaporate carriers like in solvent-based coatings.

Flat stock, such as cabinet doors, is an ideal application for UV coatings. All sides of flat panels are easily reached by UV light sources. As the technology advances, UV coatings are seeing greater use for more intricate or detailed furniture.

Quality advantages of UV coatings include:

• Increased hardness and durability
• Increased solvent resistance

Production advantages of UV coatings include:

• Quick curing. Curing can happen in less than five seconds.
• Shorter finishing lines, creating more floor space
• Increased line speeds
• Products can be immediately handled and packaged
• High solids, resulting in little or no volatile organic compounds (VOCs)

Coatings
Four different polymers—urethane, epoxy and polyester acrylates, and unsaturated polyesters—are used in UV wood-coatings to create a coating's physical properties through their different chemical reactions. Other components include additives, pigments and fillers, which are designed for flow, leveling, curing and color characteristics.

Application Equipment
UV coatings can be applied by airless or conventional spray guns, with about 50 to 75 percent transfer efficiency. Spray systems are used for three-dimensional pieces (case goods). Roller and curtain coater systems are best suited for flat-panel production, nearing 100 percent transfer efficiency.

The Sherwin-Williams Company estimates that a new UV-coating line costs from $50,000 at the very low end to $1 million, depending on the sophistication of the system.

If you are interested in learning more about how this technology can enhance your operation, MnTAP can arrange for you to:

• See a demonstration of the technology in place at another shop.
• Have vendors test coat samples of your parts.
• Test UV coating on samples of your products at a job shop.
• Have UV coating equipment tested in your shop.

Contact Paul Pagel, MnTAP’s coating specialist, at 612.624.4638 or e-mail Paul. From greater Minnesota, call 800.247.0015 and ask for Paul.

Resources
RadTech International North America This nonprofit association supports the advancement of ultraviolet and electron beam (UV & EB) technology. Its Web page on UV curing for wood finishers includes numerous articles and case studies. See the case study on Artistic Finishes Inc., Roseville, MN, on waterborne and UV-cured coatings.

UV Curing for Wood Applications This RadTech Report article (May/June 1999) describes the main chemical classes used in UV wood-coatings, and has an at-a-glance table showing how they compare. Another table shows a physical property comparison of UV cured epoxy acrylate and two non-UV waterborne coatings.