In waterborne coatings, the polyol and the isocyanate have to be emulsified in water, resulting in a three phase system of water, dispersed polymer and dispersed isocyanate. When hydrophobic crosslinkers are used, high shear and/or additional co-solvents are required to improve the miscibility. Insufficient miscibility between the resin and tbe hydrophobic crosslinker can lead to inferior film properties and poor film appearance. The alternative is to use hydrophilic polyisocyanates. This ensures improved miscibility and therefore improved film homogeneity, resulting in optimised coating properties such as gloss and resistances, but is not always favourable from an economic point of view.
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