Mica’s Characteristics
Mica’s characteristics are explained as follows:
Moisture resistance
Added sericite powder can significantly increase the water resistance of paints and coatings with high waterproofing requirements.
Experimental results
Iron red containing no added sericite was soaked starting after 30 hours. When 5% sericite powder was added, no change had occurred after 200 hours. Some processes use a 0.5:1 mixture of zinc oxide and sericite powder; 8% of this mixture added to paints reduces settling, and can take the place of some barium sulfate and talc powder. This filler can significantly increase anti-corrosion properties without changing abrasion resistance, and can prevent settling. The use of sericite powder is recommended in heavy anti-corrosion coatings. A 1:0.25:1.25 mixture of zinc phosphate (aluminum phosphate), zinc oxide, and sericite powder yields the best results. Sericite powder used in ordinary paints and coatings can prevent settling. While some manufacturers use large quantities of organic bentonite to improve the settling properties of their paints, excessive organic bentonite can severely degrade the tightness of paint surface and reduce water resistance. On the other hand, too little bentonite will do nothing to prevent settling. The use of sericite instead of organic bentonite can prevent settling while also enhancing water resistance. Sericite is easy to use, and can be added directly. Unlike organic bentonite, there is no need to use a pre-gelling agent, so sericite can simplify manufacturing processes.
Anti-covering applications
Many types of aluminum powder paints, including oil tank paints and ordinary floating aluminum powder paint used for protection and anti-covering, can only be used for approximately one year before the surface dulls and begins to craze. The addition of 5%-8% sericite powder can prevent most discoloration for three years (color may darken slightly).
Improving paint durability
Artificial aging-resistance tests were performed using building paint with the same formulation and the same pigment binder ratio but with or without added sericite powder. The paint without sericite powder began to discolor after 250 hours. The paint containing 5% sericite powder began to discolor after 1,000 hours, but did not release powder.
Note: The foregoing experiment using paint with the same formulation and the same pigment binder ratio clearly showed that building paint with added sericite powder can dramatically boost the paint’s durability indicators. Sericite powder possesses extremely strong matting and protective ability, and can reflect close to 90% of UV radiation. Sericite powder’s ability to protect against UV radiation is chiefly connected with two factors: Improved mechanical strength and water resistance: The addition of ultrafine sericite powder made using the wet method to paint improves the surface luster and mechanical properties. In particular, addition of sericite increases water resistance by a factor of three or more. This is mainly due to the high aspect ratio of the laminar sericite crystals. Sericite particles retain a laminar structure regardless of the fineness of the powder. The effect of inorganic minerals on the film strength and covering ability of paint is connected with the physical shape of the mineral particles. Effectiveness generally decreases in the following order: laminar > fibrous > columnar > particulate. Furthermore, sericite powder contains active hydroxyl groups that readily tight form molecular bonds with latex and solvents. The parallel, overlapping arrangement of the sericite particles forms a tight-knit multilayer network inside the paint film, which dramatically increases the paint’s impermeability and mechanical strength. Anti-flex performance, anti-expansion, elongation: The addition of mica powder to the engineering plastic PVC almost doubles deformation temperature, but has no significance effect on mechanical properties, and slightly increases impact strength. And because PVC is costly, but mica powder costs much less than PVC, the addition of mica powder to PVC also offers economic benefits.
Although the addition of 20% mica powder to nylon 66 slightly degrades mechanical properties, it significantly improves product appearance and enhances banding resistance. Mica powder can significantly improve the insulating ability of rubber mats. It can boost the expansion resistance, elongation rate, and perpendicular tear strength of plastic films to above normal standards. Plastic greenhouse film containing mica can withstand a temperature 1-3°C higher than ordinary film.
Conduction: Antistatic coatings are usually made by adding conducting matter such as carbon or metal powder to some kind of polymer. Antistatic coatings containing carbon are excellent conductors and are widely used in many applications, including petroleum and chemicals. On the other hand such coatings provide poor adhesion and oil-wetting properties, and are available only in unattractive colors. Antistatic coatings containing metal powder are costly, heavy, and prone to surface oxidation of the metal particles. A new solution consists of a composite material containing mica powder and with one or several surface layers of corrosion-resistant conducting material with stable chemical properties. This material can offer good conduction, and is a permanent conductor. Chemical properties are stable, corrosion resistance is excellent, and colors can be freely adjusted. Light colors can be readily achieved. Mica can be mixed with other pigments to obtain antistatic coatings with different colors. Density is low, and mica and pigments are readily dispersed in the polymer material. This type of paint is convenient to use, and can be used for in the manufacture of electronics, communications, computer CPUs, pharmaceuticals, chemicals, and precision instruments.
Learn more about Mica’s comparison with other conducting materials.
