Formulation and testing of waterborne coatings based on 2K PVDF-acrylic hybrid dispersions

 
Poly(vinylidene fluoride)-acrylic hybrid dispersions with OH functionality can be combined with water-reducible polyisocyanates to give highly weatherable, hydrophobic 2-k polyurethane coatings. By reducing the acrylic resin Tg, we have recently developed new versions with a minimum film formation temperature (MFFT) < 0 °C, allowing for formulation in field-applied topcoats with extremely low VOCs (< 25 g/liter), as well as in highly flexible and weatherable OEM coatings for substrates such as wood and architectural fabrics. In this paper we will compare the performance of higher- and lower-MFFT hybrid dispersions, when formulated as 2-k topcoats. Of particular focus is the performance of primer-topcoat systems on metal in cyclic corrosion tests, including ISO 20340 for steel substrates, which alternates between salt fog, UVA exposure, and freeze-thaw cycling.