The general surface modification process varies according to the surface modification method, equipment and powder preparation method. At present, the surface modification process used in industry mainly includes three categories: dry process, wet process and composite process.
1, dry process
This is one of the most widely used surface modification technology for nonmetallic mineral powders. At present, for non-metallic mineral fillers and pigments, such as heavy calcium carbonate and light calcium carbonate, kaolin and calcined kaolin, talc, wollastonite, silicon powder, glass beads, aluminum hydroxide and light magnesium oxide, clay, ceramic pigments, etc., most of the dry surface modification process is used. The reasons are simple process, flexible operation, low investment and good applicability of modifier.
(1) intermittent dry process
The characteristics are that it can flexibly adjust the time of surface modification (i.e. residence time) in a large range, but the particle surface modifier is difficult to coat evenly, the unit product consumption is more, the production efficiency is low, the labor intensity is high, there is dust pollution, it is difficult to adapt to large-scale industrial production, and is generally used in small-scale production.
(2) Continuous modification process
It is characterized by good dispersion of powder and surface modifier, uniform coating of particle surface, less consumption of modifier per unit product, low labor intensity and high production efficiency, which is suitable for large-scale industrial production. Continuous dry surface modification process is often put after the dry powder preparation process, mass continuous production of a variety of non-metallic mineral active powder, especially for plastics, rubber, adhesives and other polymer matrix composite materials of inorganic fillers and pigments.
2. Wet surface organic modification process
Compared with the dry process, it has the characteristics of better dispersion of surface modifier and uniform surface coating, but it needs subsequent dehydration (filtration and drying). Is generally used in water soluble or hydrolyzable organic surface modification agent, as well as the front for the wet powder legal system (including the wet ultra-fine grinding and chemical milling machine) technology and then segment the need to dry and occasions, such as light calcium carbonate (especially nanometer calcium carbonate), wet fine grinding of heavy calcium carbonate, ultra-fine aluminum hydroxide and magnesium hydroxide, the surface modification of ultrafine silicon dioxide and so on, This is because the slurry generated after the chemical reaction should be filtered and dried even without wet surface modification. Surface modification before filtration and drying can also make the material dry without forming hard agglomeration and improve its dispersibility.
Inorganic precipitation coating modification is also a wet modification process. It includes pulping, hydrolysis, precipitation reaction and subsequent washing, dehydration, calcination or roasting and other processes or processes.