UV-A Curable Polyurethane Dispersions in Wood Coatings

By Robert A. Wade, Michael J. Dvorchak, Christoph Irle

Radiation curable coatings have been used in the wood coatings industry for several years. Major benefits of radiation cure are the high curing speed and high crosslink density. High performance coatings with extremely low VOC/VHAPS, excellent abrasion, as well as chemical resistance, are obtained. When complex substrates must be coated there is always the concern of uncured surfaces in shadow areas.

Typically, more expensive UV equipment that optimizes a homogeneous radiation exposure is necessary, which requires higher capital investment. This has been seen for years as the largest hurdle for the industrial coater. A new waterborne coatings system based on UV-PUDs can be cured with low energy UV-A lights, without sacrifice of performance properties for wood coatings applications.

These types of lamps are significantly cheaper in their investment costs as well as in their maintenance. In this article, coatings performances are discussed with special respect to low intensity UV-A lamps, UV-curing PUDs, and the effect of adding self-crosslinking dispersions. The effects of adding water-dispersible polyisocyanates and carbodiimide crosslinkers to such coatings are also be presented.