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Graffiti-resistant and environmentally compatible

Bayer MaterialScience AG : 22 April, 2005  (Company News)
The gloss and resistance properties of two-component waterborne polyurethane coatings depend to a considerable extent on how finely and homogeneously the hardener can be dispersed in the aqueous phase.
The latest Bayhydur® generation from Bayer MaterialScience AG contains an ionic sulfonate group (chemically linked to the isocyanate molecule) which improves the dispersibility of the polyisocyanate. The result is excellent. Coatings formulated with the new products are in no way inferior to solvent-based systems, for example in terms of their hardness and drying rate. They are also more resistant to chemicals than waterborne coatings based on conventional hydrophilically modified polyisocyanates.

The three new products differ in the proportion of sulfonate groups they contain. “The hydrophilic modification of Bayhydur® XP 2487/1 is minimal. Its dispersibility is just as good as that of standard products but the resultant coatings have much better properties,” says Dr. Martin Melchiors, a coatings expert with Bayer MaterialScience. It means that graffiti can be removed from substrates coated with this system even more easily than from solvent-based two-component polyurethane systems. Other advantages are the high resistance of the finish to acids and gasoline, the improved adhesion on certain plastics, and the system’s rapid drying. Its properties make the hardener ideal for coatings for rail vehicles, cars, industrial goods and high-quality furniture.

Coatings based on Bayhydur® XP 2570 also dry quickly. Because the hydrophilic modification is stronger than that of Bayhydur® XP 2487/1, it is very easy to stir in by hand. This makes it suitable above all for vehicle repair finishes and other applications in which complex mixing equipment and industrial processes cannot be used. Its excellent dispersibility results in particularly brilliant coatings.

The third new product, Bayhydur® XP 2547, contains only a very small proportion of hydrophilic sulfonate groups, but still has good dispersibility because of its extremely low viscosity. One important application for this hardener is floor coatings. It can be used to formulate systems that have good chemical resistance and do not emit any volatile organic compounds (VOC).

“With the aminosulfonic acid-modified polyisocyanates, we can offer our customers products that enable them to comply easily with the stricter VOC guidelines,” says. Dr. Raul Pires, a specialist for polyurethane coatings at Bayer MaterialScience. He is particularly pleased with the fact that the new hardener generation is covered by patent and quite unique in the world of surface coatings.
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