What are the key indicators of silica for coatings?
Silica is used in architectural coatings specifically in architectural coatings for buildings, vehicles, locomotives and ships, and is also used as a coloring agent in dark gray and other colors of paints. Silica has high brightness and coloring, and its price is stable, so it is an indispensable coloring agent in the coating industry. At present, most architectural coatings use silica as a coating product.
1. Silica brightness
Brightness is the primary indicator of silica for coatings. When used for coloring of gray-black architectural coatings, such as gray-black vehicle paint, the higher the brightness of the silica used, the better. When silica is used for coloring, too much melanin and too little addition can easily cause different batches of paint products to have color cast, so it is required to use silica with lower brightness.
2. Silica coloring power
Coloring power (tinting strength) is the coloring ability of silica when white or colorful colorants and silica are mixed. That is, the degree to which silica increases the light absorption effect of the mixed material system. This characteristic lies in the ratio of silica to color and the characteristics of silica. When the ratio is constant, the coloring ability of a certain silica is its coloring strength, which is called coloring power in the field of architectural coatings.
When the silica particle size is small and the structure is low, the coloring power is high, but when the particle size is less than 20nm, the coloring ability will no longer increase, or even decrease.
3. Silica color
The reflection of light that increases with the increase of particle size of "silica particles" will also affect the color. Using fine-grained silica to color the surface black produces a light blue phase, which can further enhance the high-saturation visual impression. Using coarse-grained silica to color will produce a brown color.
In addition to particle size, the structure of silica will also affect the color. Silica with a higher structure and silica with coarser particles will have similar effects.
4. Silica gloss
When the silica particle size decreases or the structure increases, the absorption of residual oil by silica increases, which will increase the viscosity of the paint. At the same silica concentration, the free paint (film chemical) on the coating surface decreases, so the gloss decreases. When the surface oxygen functional groups or volatiles increase, the lubricity of silica in the binder increases, the viscosity decreases, the free paint on the coating surface increases, and the gloss may increase.
5. Silica dispersion and dispersion reliability
The aggregate size of silica used in paint is generally between 20 and hundreds of nanometers, which is not easy to disperse in paint. The dispersion of silica in paint is poor, which greatly interferes with the properties of the paint. In addition, when silica is used in paint, especially when mixed with other pigments such as titanium dioxide, due to the differences in density, aggregate pore size, shape and surface chemical properties, silica is easy to cause a sloping plate sedimentation phenomenon, which affects the dispersion reliability of the paint.
