Radiation-curing, water-based polyurethane systems for wood finishes are both economical and environmentally friendly. They cure very quickly under UV light, which means that the finished wood can be stacked immediately it leaves the production line. Apart from that, the systems contain little or no solvent apart from water, so they emit only minimal quantities of volatile organic compounds (VOC).
Bayer MaterialScience AG has recently introduced a number of new polyurethane systems of this kind to the market, the latest being Bayhydrol® UV XP 2420. "We now have a tailor-made polyurethane system for outdoor applications," says Dr. Christoph Irle, the expert for polyurethane wood finishes at Bayer MaterialScience. He sees window frames and shutters, doors and all kinds of exterior wood paneling as potential applications. The finishes may be either transparent or pigmented and are highly flexible, even at low temperatures. They also have very good chemical and mechanical resistance properties. Above all, however, they are noted for their outstanding weather stability. Their chemical backbone is formed by special aliphatic polyurethanes that remain virtually unaffected by sunlight.
Bayhydrol® UV XP 2420 is very easy to apply. It dries on wood within a few minutes. After this, it takes only a few seconds under UV radiation for the finish to cure. "This makes for maximum productivity, which is a major advantage over other solvent-based and waterborne outdoor wood finishes," says Irle. But it is not only the wood-processing industry and its customers that will benefit from this economical, environmentally friendly, weatherproof system. It also adheres very well indeed on metals and plastics.
UV-curing polyurethane dispersions of this kind are experiencing high growth rates on the world market, mainly because there is no need for the user to mix the polyol and polyisocyanate before application, making life that much easier. At the same time, the coating system is able to meet particularly high quality requirements, thanks mainly to the subsequent crosslinking of the polyurethane molecules under UV radiation.
In addition to the new product for outdoor applications, Bayer MaterialScience also has its proven product line centering on Bayhydrol® UV VP LS 2282. This universal grade is suitable above all for clear and colored primers and topcoats. Other products include Bayhydrol® UV VP LS 2348 and Bayhydrol® UV VP LS 2280. The former is noted for its outstanding adhesion on 'critical' wood types and its ability to accentuate the wood grain, which more or less predestines it for use on furniture and parquet flooring. The other product was developed specifically for pigmented formulations and also adheres very well to metal. Last but not least, there is Bayhydrol® UV VP 2317 which is characterized by its excellent wet film transparency, which means that it is also clear during application, and can be re-emulsified without problem. The latter property is an advantage above all for recycling the overspray, which can be collected easily with water or coating material and returned to the coating cycle.