Fast drying water-based 2K PU lacquers? Necowel 720

Fast drying water-based 2K PU lacquers? Necowel 720

Friday, 14 July, 2017

Water-borne, isocyanate- and polyol-based 2K PU systems have for many years proven themselves to be products that offer remarkable performance in terms of being resistant to weather, chemical products and corrosion.

Nevertheless, in less favourable curing conditions, such as high moisture and, in particular, in thicker layers, gas bubbles develop as a result of the CO₂ released in the reaction, and craters and other unwanted faults form on the coating surface.

NECOWEL 700-based paints are more tolerant on these types of applications. Due to the high hydroxyl group content of the polymer and, accordingly, its high crosslink density, the coatings formulated provide excellent results in terms of hardness and chemical resistance. Since it does not contain unsaturated fatty acids it has good yellowing resistance as well as high gloss.

However, if you compare the curing speed of these water-borne systems to traditional solvent-borne systems, the formulator is compelled to increase the hydroxyl group content of the polymer or use additional catalysts in the formulation.

ASK decided to adopt a different approach in order to optimise curing speed in water-borne systems: incorporate reactive blocks in the polymer in order to form a new high molecular weight backbone in the polyol.

This change of chemical structure gave rise to NECOWEL 720.

NECOWEL 720 is a polyol component to formulate high quality and fast drying 2K PU lacquers. The emulsion does not contain APEO and is free of VOC and SVOC

It has a high molecular weight polyester backbone and incorporates blocks which increase the reactivity towards isocyanates. This modification provides:
- Drying time of maximum 3 hours
- Pot-life of more than 6 hours for the mix
- Approximately 25% increase in pendulum hardness after 7 days (between 150 and 180 seconds)

As crosslinkers, HDI- and IPDI-based oligomeric polyisocyanates are recommended. Basically hydrophilic isocyanates specially designed for water-borne systems, as well as common hydrophobic types can be used. Best results have been obtained by a mixture of both. As usual in PU systems, an excess of crosslinker is recommended (e.g. 150 % isocyanate).

In combination with the appropriate hardeners, film thicknesses of more than 100 µm can be achieved without blistering.

For further information about these products, please contact our Technical Sales Advisers.

URL: www.ask-chemicals.com

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