Floor Coating Manufacturers Are Seeing the UV Light
By Brent Ehrlich
UV-cured coatings have been used in factories for years because they cure instantly under exposure to ultraviolet light and have very low levels of VOCs and hazardous airborne pollutants (HAPs). Their use increases the manufacturing efficiency of products such as wood flooring while protecting workers and the environment from harmful emissions. Once considered too unwieldy and expensive to be practical for onsite applications, UV-cured coating technology is now being specialized for wood, concrete, and other hard-surface flooring by companies such as UVolve/DSM and Flash UV.
How UV curing works
UV-cured floor coatings use a photoinitiator that, when exposed to a specific wavelength of light, acts as a curing agent. The UV light is focused directly on the floor by a machine that looks a bit like a lawnmower, and upon exposure, the photoinitiators instantly crosslink individual urethane monomers together to form the polyurethane floor coating. In contrast, conventional high-traffic polyurethanes or epoxies contain two parts that, when mixed together, undergo a chemical reaction to crosslink the product; once mixed, these coatings have to be used within a short time and can take days to fully cure.
Typical floor coatings contain several potentially toxic ingredients, including isocyanates, hazardous airborne pollutants, glycol ethers found in polyurethanes, and bisphenol-A found in epoxy coatings. Even the most environmentally responsible waterborne polyurethanes have VOC levels of 180 grams per liter or more. These floor coatings continue to emit VOCs until they are fully cured, which is 7–9 days for the best waterborne products and more than 14 days for more toxic, oil-modified products. While regular coatings have to be thrown out after some time, UV coatings have no such “pot life,” which reduces waste.
UV-cured wood coatings from Flash UV
Flash UV is a UV-cured polyurethane that avoids the most environmentally problematic chemicals typically found in polyurethane floor coatings. According to founder Ken Tran, “The advantage of Flash UV is extremely low VOC levels—below 10 grams per liter—and we have completely removed toxic chemicals and isocyanates from the curing process.” Yet, he claims, “The viscosity is the same as with water-based products, so you don’t have to change how you apply it, except for the curing.” For new floors, Tran applies two coats over a traditional sealant, but for a recoat, only one coat is usually necessary. After the UV lamp cures the coating, the floor is ready for use immediately. As with any polyurethane coating application, floors containing oil finishes still need to be sanded.
Tabor flooring abrasion tests have shown the durability of Flash UV to be two to three times higher than that of standard polyurethanes, yet it is also remains flexible: Tran claims he has coated a playing card and bent it into a circle without cracking the coating. This combination of durability and flexibility is necessary for wood floors, which move with changing temperatures and humidity. Tran expects the Flash to continue to improve since he can build specific performance attributes into it, such as adding ceramics to improve durability, whereas improving traditional polyurethanes is more difficult because of their complex solvent chemistry.
Hard-surface coatings from UVolve
UVolve coatings, like Flash UV, also contain photoinitiators, but instead of urethanes they use clear acrylic resins formulated for use on concrete and other hard surfaces. UVolve uses UV coatings from the Dutch company DSM Functional Materials, which coats 80%–90% of the fiber optic cables in the world and has been making floor coatings for about five years, according to Melissa Hayes, marketing manager at the company. “Our products are primarily used as a coating over polished or stained concrete and a sealer over terrazzo and VCT [vinyl composite tile],” said Hayes.
Both terrazzo and VCT protective coatings typically have to be stripped, waxed, and buffed regularly using solvents and other chemicals. UVolve, on the other hand, can be cleaned with simple detergents, and the next time the floor needs treatment, no stripping is required. For concrete, a different UVolve formula is used to protect decorative or stained concrete without the long cure times required by epoxies. UVolve is a thin coating, so it is not intended to replace all epoxy coatings, which can be applied in a thicker layer, but it is durable enough that maintenance can be significantly reduced, claimed Hayes.
Fast application times are one of the main benefits for both UVolve and Flash UV. These coatings are often used when a floor cannot be out of commission for extended periods, and this is where costs are carefully weighed. “Photoinitiators are used in other markets and are expensive,” said Hayes, and since a laborer has to run the UV light over the flooring, both materials and labor tend to cost more than with traditional coatings—but for hospitals whose floors cannot be out of commission or retail spaces that lose money when closed, the time savings are usually worth it. And, according to Tran, Flash UV costs only 10%–15% more than conventional coatings, so clients think it is well worth the upfront cost.
UV-cured coatings have the potential to change the floor coating industry, but challenges remain. UV-curing machines are expensive, so these coatings are unlikely to replace inexpensive polyurethanes, epoxies, and VCT coatings where cure and application times are not important. Although machines block most of the UV light from getting out into the room, appropriate clothing and eye protection have to be worn by properly trained workers, and occupants have to be kept out of the area.
A hands-down environmental winner, onsite UV curing isn’t yet common, but expect to see it catch on and be integrated into other coatings in the near future.
For more information:
DSM Functional Materials/Floor Coatings Group