Wood flooring coatings provide substrate protection and maintain aesthetics for a number of years. Resins used to manufacture these coatings must be resistant to yellowing and have high scratch and abrasion resistance. Use of high-quality resins, paired with additives and fillers to enhance the scratch and abrasion resistance, allows formulation of coatings with long service life. The typical warranty of commercial flooring finish is 20–25 years.

UCB Chemicals offers a variety of urethane acrylates for formulation of high-performance coatings for flooring applications. Typical resin properties, summarized in Table 1, illustrate products that have been used to formulate wood flooring finishes with properties comparable to commercial floor finishes.

Application Area: Wood Flooring Formulation

Wood flooring finishes are built in multiple layers, one or more of which consists of a wood filler/sealer with good sandability. UCB offers Ebecryl 809, a low viscosity, resilient polyester acrylate, for this application. Starting point formulations for sealer and top coats are indicated in Table 2. The viscosity of the sealer is 3,000 cP at 25ºC. Viscosity of the top coat ranges from 600 cP for the coating based on RX 03975 to 4,000 for that using Ebecryl 4866.

Application method: Draw down bar # 5. Approximate coating thickness is 0.35 mil.

UV Curing and Process Finishing on Wood

Two Fusion H lamps were operated at 300 watt/inch with line speeds of 90 feet/min. The dose is approximately 300 mJ/cm2. The Process entails the following:

• Sanding of wood panel

• Application of filler/sealer

• UV curing

• Sanding

• Application of filler/sealer

• UV curing

• Sanding

• Application of top coat

• UV curing, one pass

• Application of top coat

• UV curing, three passes

Coating Properties Taber Scratch Resistance

The Taber scratch resistance has been determined with a Taber shear scratch tester using a conical diamond tool. The scratch resistance is given as the weight required to break through the film. The test simulates scratching by sharp objects.

The figure shows the results obtained for the topcoats based on the oligomers indicated in Table 1, as well as results obtained from two commercial flooring samples. As can be seen from the figure, the coatings based on urethane acrylates have equal or higher Taber scratch resistance than the Bruce hardwood sample. Eb 264 and Eb 284 give comparable hardness to the Pergo laminate sample.

The Pergo laminate is finished with melamine resin filled with aluminum oxide to impart high scratch and abrasion resistance. The Bruce hardwood flooring is coated with a urethane finish, Bruce Dura-Luster. Both finishes carry a warranty of 25 years.

Steel Wool Scratch Resistance

Fine steel wool, #000, wrapped around the head of a 2-lb ball peen hammer is used to determine the number of double rubs the coating resists before visible marks appear on the surface.

The results observed with the urethane acrylate based coatings and the commercial flooring samples can be summarized as follows.

RX 03975 and the Pergo Laminate sample resist more than 200 double rubs.
• Eb 264, Eb 284, Eb 4866 and the Bruce Hardwood sample resist fewer than 5 double rubs.

Taber Abrasion Resistance

The resistance to abrasion is measured with CS-17 abrasive wheels using 500 gm on each wheel. All the coatings, as well as the commercial floor samples, indicated resistance over 1,000 cycles without breaking through to the substrate. A visual inspection of coating wear and remaining film integrity indicates the following relative order for abrasion resistance.

Pergo Laminate >> urethane acrylate coatings > Bruce Dura-Luster finish

The higher performance of Pergo laminate flooring was expected due to the presence of aluminum oxide to enhance scratch and abrasion resistance.

Conclusion

Ebecryl 264, 284, 4866 and RX 03975 are suitable resins for use in formulating high-performance coatings for wood flooring applications. Formulations based on these oligomers show scratch and abrasion resistance, with values equal to or higher than those obtained from commercial urethane finishes. Abrasion resistance of unfilled coatings is significantly lower than for Pergo laminate flooring, which is based on melamine resin filled with aluminum oxide.

For more information on aliphatic urethanes, contact UCB Chemicals Corp., 2000 Lake Park Drive, Smyrna, GA 30080; phone 770/434.6188; fax 770/434.8314; visit www.ucbgroup.com.