Use of silicas

In the broad field of obtainable silicas for matting there are two groups which differ in terms of their production process. One is the hydro-thermal process, which produces silicas with a relatively soft morphology. By using the silica-gel process products can be obtained which have a harder morphology. Both processes are capable of producing standard silica and after treated products. After treatment means that the silica surface can be partially modified with organic (waxes) or inorganic materials. Compared to silica-gel matting agents, modified silica possess a different particle size, particle size distribution, in the pore volume. Hydrothermal matting agents are different in particle size and distribution. We can also find untreated and treated materials. Currently there is only one product popular for specific application, which is produced according to pyrogenic process, and shows a very high matting efficiency, especially in water-based systems.

Silicas have a relatively high efficiency in terms of matting power, and with higher concentration an increase in viscosity is possible. During storage they have a tendency to build up sediment, this is particularly the case with untreated silicas. To avoid this tendency combinations of silicas and wax or pyrogenic silicas are used. It is possible to adjust the matting degree under angle of 45? 60?and 85°. The coatings containing silica matting agents are recoatable. All of them are ‘stir-in’ products.

Synthetic Aluminum silicates are applied in emulsion paints primarily as a high quality extender to partly replace the Titandioxyd. However, they may also be used to impart an evenly balanced matting effect into the dried emulsion paint. In long oil Alkyd systems they work as a matting agent, but must be dispersed with pigment and fillers. Matting silicas are used in all-coating systems, though not in powder coatings.