The challenges of substrate wetting and flow are especially problematic for formulators of water-based coatings.1-4 Creating a closed, defect-free aqueous coating film is difficult not only on common low-energy substrates like plastics, but also when wetting a high-energy substrate such as metal, since it may not always be clean or free of surface contaminants. Wetting on wood can be critical because wood needs proper penetration into pores and grains, and often contains natural oils.
Substrate wetting additives – special surfactants that modify interfacial tensions – are commonly used to overcome such problems. Generally, they reduce the surface tension of a coating to a homogeneously low level, enabling the coating to wet the substrate successfully. Very strong surface tension reduction is required to achieve satisfactory wetting over oily and greasy contaminants. However, the same substrate wetting additives that dramatically reduce surface tension often cause a significant degree of foam and air entrapment. Through an innovative development in additive technology, a siloxane based multifunctional approach can now achieve surface tension reduction while providing a defoaming effect.