New technology for formulating fast-drying water-borne 2K polyurethane coatings

New technology for formulating fast-drying water-borne 2K polyurethane coatings

Monday, 15 January, 2018

Water-borne two-component polyurethane coatings with an isocyanate and polyol formulation offer excellent weather, chemical and corrosion resistance properties as well as optimal anti-graffiti performance.

In unfavourable curing conditions, for instance, high humidity and high dry film thicknesses, CO₂ bubbles form in the reaction which are released causing the appearance of craters and other defects on the coating surface.

Comindex is offering a solution to this. Paints that are based on/formulated with NECOWEL 700 are more tolerant in these applications. On account of the high content of hydroxyl groups in the polymer and, as a result, the high crosslink density, the coatings formulated show excellent properties in terms of mechanical and chemical resistance. Since they are free from unsaturated fatty acids, yellowing is prevented and the surface achieves a remarkable gloss.

When comparing the curing speed of these water-borne systems to traditional solvent-based systems, the formulator is compelled to increase the polymer’s content of hydroxyl groups or use additional catalysers in the formulation that may have unwanted side effects.

Comindex’s principal – ASK – decided to implement a different strategy to optimise curing speed in water-borne systems; namely, by adding reagent blocks in the polymer to form a new high molecular weight backbone in the polyol.

The outcome of this change in chemical structure is NECOWEL 720.

Necowel 720 is a polyol for formulating high quality, fast-drying, two-component PU lacquers. The upshot is a VOC- and SVOC-free emulsion that doesn’t contain APEO.

With a high molecular weight polyester backbone, it incorporates blocks that enhance reactivity towards isocyanates. Moreover:

- Drying time is reduced to 3 hours
- Maintains a pot-life of more than 6 hours
- Increases pendulum hardness by 25% after seven days (from 150 to 180 seconds)

For the crosslinking agents, 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, although the best results have been obtained by a mixture of both.

As is common in PU systems, an excess of crosslinking agent is recommended (e.g. 150% isocyanate).

By following these steps, 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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