Читать книгу Additives for Water-borne Coatings - Wernfried Heilen - Страница 74

It is possible to defoam water-borne systems using only hydrophobic particles, but it is more common to use them in combination with other defoamer actives. Commonly used hydrophobic particles are surface-modified silica, aluminium oxide, urea, waxes (e. g. magnesium stearate) or polymer particles (e.g. polyamides, polypropylene). Particles with an irregular amorphous surface are usually more effective than spherical or smooth particles [1] [3] [4]. The hydrophobicity of the particle needs to be such that the particle orientates preferentially on the interface of the defoamer oil to the water phase. If the particle is too compatible with the oil, it will be completely wetted by the oil. If it is too hydrophilic it will migrate into the water phase. In both cases the efficiency of the defoamer will fall. In practice partially hydrophobic particles have proved particularly effective [4].