The optical performance of silica in varnish is mainly due to its unique physical and chemical properties. The following is a detailed analysis of the optical performance of silica in varnish:

1. Basic properties of silica

Silica is a general term for white powdered X-ray amorphous silicic acid and silicate products, with high purity, high inertness, and UV resistance. Its composition can be expressed as SiO2·nH2O, where nH2O exists in the form of surface hydroxyl groups, which can be soluble in caustic alkali and hydrofluoric acid, but insoluble in water, solvents and most acids. In addition, silica also has good high temperature resistance, non-flammability, tastelessness, odorlessness and electrical insulation.

2. Application of silica in varnish

Varnish is a transparent or light yellow coating, the main components of which are resin and solvent. After being applied to the surface of an object and drying, it can form a smooth film and show the original texture of the surface. Adding silica to varnish can significantly improve its optical properties.

3. Effect of silica on the optical properties of varnish

Matting effect:

Since the refractive index of amorphous silica is 1.46, which is similar to the refractive index of most resins used in the coating industry, when silica is evenly distributed in the varnish film, it can form a micro-rough surface. When the incident light reaches the uneven surface of the paint film, diffuse reflection, that is, scattering, occurs, resulting in a low-gloss matte and matte appearance.

The average particle size of silica and its particle size distribution play an important role in reducing the gloss of the coating. Generally speaking, the larger the average particle size, the greater the surface roughness of the paint film, and the better the matting performance. However, too coarse particles will affect the appearance and feel, and too fine particles will increase the viscosity of the paint. Therefore, choosing the right silica particle size is crucial to achieving the ideal matting effect.

Optical transparency:

Although silica particles will increase the micro-roughness of the coating film, due to its high purity and refractive index similar to that of resins, the addition of silica to the varnish does not significantly reduce the optical transparency of the coating film. On the contrary, it can achieve a matting effect while maintaining the transparency of the coating film.

Scratch resistance and anti-settling effect:

Silica matting agent treated with organic coating (such as polymer wax) is not only easy to disperse in varnish, but also improves the scratch resistance of the coating.

At the same time, silica can also prevent the hard precipitation of the coating during storage. Adding an appropriate amount of fumed silica matting agent to high-grade matting paint is enough to prevent sedimentation and promote suspension.

4. Conclusion

In summary, silica shows good optical performance in varnish. It can not only achieve the matting effect, but also improve the scratch resistance and anti-settling effect of the coating while maintaining the transparency of the coating. Therefore, silica has a wide range of application prospects as a matting agent in varnish.