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Bayer MaterialScience: Environment-friendly two-component coating now more productive Novel waterborne dispersions for accelerated drying and curing

Published on 2009-04-03. Author : SpecialChem

LEVERKUSEN -- That environmental compatibility and economic advantages go hand in hand is being demonstrated by Bayer MaterialScience AG at this year's European Coatings Show (ECS) in Nuremberg, Germany, where the company is displayed a series of novel waterborne polyacrylate dispersions (PAC) from the Bayhydrol® A product line. These are combined with tailored, hydrophilized polyisocyanate crosslinkers from the Bayhydur® range for the formulation of waterborne, two-component coatings systems that set new standards in terms of ecology and economy.

"Our hydroxyfunctional polyacrylate dispersions developed specially for waterborne, twocomponent polyurethane systems offer excellent properties for durable, chemicalresistant topcoats," says Dr. Christoph Irle, a Bayer MaterialScience expert for twocomponent, waterborne coating systems. They facilitate the emulsification of the polyisocyanates in the aqueous phase and make it possible to achieve performance comparable to that of a solventborne standard. After crosslinking, the polyacrylate chains bound in the polyurethane network make an important contribution to the chemical resistance of the coating film.

Due to the production process, such secondary PAC dispersions used to contain as much as eight percent cosolvent. Ecological compatibility has now been enhanced even further by significantly reducing the solvent content. At the same time, the Bayer experts have developed two different solutions to accelerate the drying or curing of the coating films, and thus to increase the production efficiency of the coating process. "This is one area Bayer MaterialScience at the European Coatings Show 2009 Environment-friendly two-component coating now more productive Novel waterborne dispersions for accelerated drying and curing where many waterborne, two-component clearcoat systems formulated with secondary PAC dispersions have traditionally lagged behind solventborne coatings. We are therefore doubly proud of these most recent successes," adds Irle.

In the case of Bayhydrol® A 2651, a special manufacturing process was used to obtain a PAC dispersion that dries quickly and yields coating films whose appearance, e.g. in terms of gloss, corresponds to that of solventborne films. Cosolvent content was reduced to just 3.4 percent.

The PAC dispersion Bayhydrol® A 2646 achieves the desired high final properties such as scratch and water resistance after only brief drying times. The key to success lies in this case with a novel, patented technology by means of which the polyisocyanate-polyol reaction is activated internally. The crosslinking reaction then runs significantly faster with no meaningful change in viscosity or pot life.

Benefiting most from this internal activation are, for example, floor coverings that should cure as quickly as possible at room temperature. The undesired shortening of the pot life prohibits the use of catalysts. Internal activation raises the reactivity of light-stable, waterborne, two-component polyurethane systems to the level of waterborne, twocomponent epoxy systems.

Similar advantages emerge with related binder grades even at elevated temperatures, such as those encountered in industrial coating or automotive refinishing applications. Corresponding, internally-activated formulations cure completely in less than 20 minutes at approximately 60 °C. To achieve the same hardness, a standard waterborne coating system would require an entire additional day at room temperature; a solventborne, highsolids coating even longer.

About Bayer MaterialScience:

With 2008 sales of EUR 9.7 billion, Bayer MaterialScience is among the world's largest polymer companies. Business activities are focused on the manufacture of high-tech polymer materials and the development of innovative solutions for products used in many areas of daily life. The main segments served are the automotive, electrical and electronics, construction and the sports and leisure industries. At the end of 2008, Bayer MaterialScience had 30 production sites and employed approximately 15,100 people around the globe. Bayer MaterialScience is a Bayer Group company.

Source: Bayer MaterialScience

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