An article to understand the application characteristics of fumed silica in coatings!

Fumed silica, also known as fumed silica, is a white fluffy high-purity nano-inorganic non-metallic oxide, widely used in silicone elastomers, coatings, adhesives, inks, paper, food, cosmetics, chemical machinery polishing and other fields.

In the field of coatings, fumed silica has the functions of thickening, thixotropy, anti-precipitation, matting, etc., and can improve the process applicability of coatings in production, storage, application and curing of paint films, and is an important functional filler.

1. Used as a rheological additive
The surface of fumed silica has a large number of hydroxyl groups, these hydroxyl groups will form hydrogen bonds between their aggregates, and when fully dispersed in the coating, they will form a silica network structure.

On the one hand, during the construction process, since the solvent at the edge of the coating volatilizes quickly, it is easy for the coating to move to the edge. The silica network can effectively prevent the movement of the coating to form edges, and can also prevent the coating from sagging during the curing process, making the coating uniform.

On the other hand, fumed silica can form hydrogen bonds to increase the medium and low shear viscosity of the system, play a thickening role, and produce thixotropy. For this reason, fumed silica is widely used in oily systems.

In addition, fumed silica has a large specific surface area, high surface energy, and is very easy to agglomerate. It must be properly dispersed during the application process to achieve the best results. In the coating production process, the surface treatment of fumed silica, the method of addition, and the choice of dispersing equipment will all affect the dispersion state of fumed silica in the coating. In general, it is best to first disperse the fumed silica into a pre-slurry, and then add the powder to disperse completely.

2. Used as anti-settling agent
Fumed silica has small particle size, large specific surface area and silanol groups on the surface. These silanol groups can interact with adjacent fumed silica particles to form hydrogen bonds.

Hydrogen bonding causes it to form a thixotropic structure. This network structure makes the particles in the system less prone to agglomeration and phase separation. At the same time, the increase of the viscosity of the system is also beneficial to prevent the movement of each component in the system.

As an ideal anti-settling agent, fumed silica is very effective in preventing pigment precipitation in coating systems. Especially for the color paste system, the appropriate addition amount will greatly improve the stability of the color paste, so as to improve the applicability of the color paste and reduce the influence of the color paste on the coating system.

In addition, the anti-settling effect of fumed silica is very beneficial to the storage of coatings, especially some pigments, such as metal powder and flakes, are very easy to precipitate and cannot be completely suspended. The use of fumed silica can ensure that they are dispersed without precipitation.

3. Used as auxiliary dispersant
In the powder coating system, due to the small particle size and high surface energy of fumed silica, it can be adsorbed on the surface of the coating powder and form a surface layer on the surface of the powder to improve the dispersion and spraying performance of the coating, so it can be used as a A dispersant is used.

To improve the adhesion of co-dispersants to powder particles, hydrophobic silicas are more recommended because they maximize the adsorption of powder particles in the small micron size range. At the same time, because it is a hydrophobic product, it can reduce the adsorption of moisture when covering the powder particles, which can prevent the coating from caking.