Chemistry of Polyurethane Finishes
From contributor D:
In many countries and cultures lacquer is a generic term for a coating. I have not used either of these finishes, but am about to begin samples with ICA (brand) 2k poly. A 2k refers to it being a two component coating, which means it requires a catalyst be added. I would expect it to be a very durable hard finish and in the case of the ICA brand, it can be built up to 8-12 mils, which is something you can not do with a conversion varnish, my usual choice for kitchens and baths. Also polyurethanes tend to yellow, although ICA has a catalyst available that is supposed to reduce that tendency.
An acrylic poly I would tend to refer to as a piggybacked coating of which the acrylic would reduce the tendency of the poly to yellow but would never be as hard as a 2k.
From contributor S:
Polyurethane normally refers to the use of an isocyanate cross-linker to provide a urethane bond between other components. The other components can be fatty acids (urethane oil), epoxy, acrylic, or any other resin that can offer an -OH group to react with (including H-OH, good old H2O).
The level of yellowing depends upon the isocyanate used. Aromatic (having a benzene ring) ones are cheaper but yellow; aliphatics (no ring) are more expensive but give non-yellowing films.
Aliphatic isocyanates are used to cross-link thermo-setting acrylic resins to form 2K paints for top-end automotive work.
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