AEROSIL® fumed silica as anti-settling agent
The use of AEROSIL® fumed silica as an anti-settling agent for pigments and fillers in paints and coatings is the oldest application in this industry. The desired anti-settling effect is generally accompanied by an increase in viscosity and the associated yield value. Standard amounts used range between 0.4 and 0.8 percent of hydrophobic AEROSIL® grades, especially AEROSIL® R 972, related to the total formulation.
The selection of the hydrophobic AEROSIL® fumed silica with the best suspension effect is dependent on the usual factors, such as the binder system, the concentration level, other additives and especially on the particular type of pigment and filler.
water-soluble filler (PUR dispersion/melamine resin):
right: 0,8 % AEROSIL® R 972
Hydrophobic AEROSIL® fumed silica is not only a virtually indispensable component in zinc dust paints, but it has also been proven successful in anti-corrosive paints containing alkaline-earth metal chromates, hydrogen phosphates, lead silicates and alkaline-earth metal borates. Electrically conductive coatings containing copper, nickel, silver or steel powders are also notable.
In the case of zinc dust primers up to 1.5 percent of AEROSIL® fumed silica, usually AEROSIL® R 972, needs to be added to achieve good suspension behavior and to ensure that any sediment can be easily redispersed. This obviously high amount is due to the high specific gravity of zinc, approximately 7 g/cm3.
When using lamellar metal particles, the use of AEROSIL® R 805 should be considered. This product normally has a good anti-settling efficiency and will maintain the necessary lamellar orientation of the metal particles.
Furthermore the stabilization of non treated flatting agents can be easily achieved by using AEROSIL® products. In this case the recommendation is to use 10 to 15 percent of AEROSIL® R 972, calculated to the amount of flatting agent.