The fillers in powder coatings can not only reduce costs, but also play a great role in improving the performance of coating products. Such as improving the wear resistance and scratch resistance of the coating film, reducing the sag of the coating during melting and leveling, improving the corrosion resistance, and improving the moisture resistance.
When selecting fillers for powder coatings, factors such as density, dispersion performance, particle size distribution, purity and other factors need to be considered. Generally speaking, the higher the density, the lower the coverage of the powder coating; the dispersibility of large particles is better than that of small particles; the filler is chemically inert and can avoid reaction with certain components of the powder formulation such as pigments; The color of the filler should be as white as possible. The powder materials commonly used in powder coatings mainly include calcium carbonate, barium sulfate, talc, mica powder, kaolin, silica, wollastonite, etc.
1. Application of calcium carbonate in powder coatings
Calcium carbonate is divided into light calcium carbonate (precipitated calcium carbonate) and heavy calcium carbonate. No matter what kind of calcium carbonate is produced, and what method is used to produce it, different particle sizes strongly affect the gloss of the coating. Calcium carbonate is generally not recommended for outdoor use.
In addition to being used for increments, heavy calcium is mainly used to partially replace titanium dioxide and color pigments, to replace light calcium and precipitated barium sulfate, to prevent corrosion and to partially replace rust preventive pigments.
When heavy calcium is used in interior architectural paint, it can be used alone or in combination with talc. Compared with talcum powder, calcium carbonate can reduce the pulverization rate, improve the color retention of light-colored paints and increase the anti-fungal properties. However, its poor acid resistance hinders its application in exterior coatings.
Compared with heavy calcium, light calcium has a small particle size and a narrow particle size distribution range, high oil absorption and brightness. Light calcium can be used where the greatest matting effect is required.
2. Application of barium sulfate in powder coatings
There are two types of barium sulfate used as extender pigments in paints: natural and synthetic. The natural product is called barite powder, and the synthetic product is called precipitated barium sulfate.
In powder coatings, precipitated barium sulfate can enhance the leveling and gloss retention of powder coatings, and has better compatibility with all pigments. The powder coating can reach the ideal coating film thickness in the spraying process, and the powder coating rate is high.
Barite powder filler is mainly used in industrial primers and automotive intermediate coatings that require high film strength, high filling power and high chemical inertness, and also used in topcoats that require higher gloss. In latex paint, due to the high refractive index of barite (1.637), the fine barite powder can have the function of translucent white pigment and can replace part of the titanium dioxide in the paint.
3. Application of mica powder in powder coating
Mica powder is a complex silicate composition, the particles are scaly, have excellent heat resistance, acid and alkali resistance, and have an impact on the melt fluidity of powder coatings. They are generally used in temperature resistant and insulating powder coatings. They can be used as texture powders. For packing.
Among the many kinds of mica, the chemical structure of sericite is similar to that of kaolin, and it has both the characteristics of mica minerals and clay minerals. Its application in coatings can greatly improve the weather resistance and water permeability of the coating film, enhance the adhesion and strength of the coating film, and improve the appearance of the coating film. At the same time, the dye particles are easy to enter between the lattice layers of sericite powder, so that the color will not fade for a long time. In addition, sericite powder also has the function of anti-algae and mildew resistance. Therefore, sericite powder is a multifunctional filler with excellent price performance ratio for coatings.
4. Application of Talc in Powder Coatings
Talc powder, also known as hydrous magnesium silicate, is directly crushed from talc ore. The particles are needle-like crystals, with a slippery feel, soft texture and low abrasiveness, good suspension and dispersibility, and a certain thixotropy. They have a great influence on the melt fluidity of powder coatings, and are often used in texture powders. It is currently used in various primers, intermediate coatings, road marking paints, industrial coatings and architectural coatings for internal and external use.
Talc is cheap, but it has shortcomings, so the amount is limited. First, the oil absorption is large. In occasions where low oil absorption is required, it must be combined with fillers and barite powder with low oil absorption; secondly, the wear resistance is not high, and other fillers must be added to make up for the occasions where high wear resistance is required; Talc powder containing other non-metallic minerals is not suitable for exterior coatings that require high weather resistance because impurity minerals easily react with acids (such as acid rain); in addition, talc powder has matting properties, so it is generally not used for high-gloss coatings middle.
5. Application of Silica in Powder Coatings
Porous powdered quartz is a kind of silica system, and its safety is recognized. It has been widely used in powder coatings, fireproof coatings, waterproof coatings, and anticorrosive coatings. Inexpensive porous powdered quartz can reduce the cost of powder coatings, and at the same time replace barium sulfate to reduce the content of soluble barium in the product, meeting environmental protection requirements.
In addition, powder coatings often use fumed white carbon black as loosening and anti-caking additives for powder coatings. Fumed silica is a multifunctional extender pigment and a rheology control agent for coatings with excellent performance. In liquid coatings, its rheological control functions include: thickening, thixotropy, anti-sagging, and covering the edges; in solid powder coating systems, it promotes the free flow of powder and prevents agglomeration and fluidization.
6. Application of Kaolin in Powder Coatings
Kaolin can improve thixotropy and precipitation resistance. Calcined clay has no effect on rheological properties, but it can have a matting effect, increase coverage and increase whiteness like untreated clay, which are similar to talc powder.
Kaolin generally has relatively high water absorption and is not suitable for improving the thixotropy of coatings, and is not suitable for preparing water-repellent coating films. The particle size of kaolin products is between 0.2 and 1 μm. Kaolin with large particle size has low water absorption; good matting effect. Kaolin with small particle size (below 1μm) can be used for semi-gloss coatings and internal coatings.
Kaolin can be divided into calcined kaolin and washed kaolin. Generally speaking, the oil absorption, opacity, porosity, hardness and Baidu of calcined kaolin are higher than those of washed kaolin.
7. Application Of Hollow Glass Microspheres In Powder Coatings
Hollow glass beads are a kind of tiny, hollow spherical powder, which has the advantages of light weight, large volume, low thermal conductivity, high compressive strength, insulation, corrosion resistance, non-toxicity, and good dispersion, fluidity, and stability. .
When applied in powder coatings, hollow glass beads can play the following roles:
(1) Heat insulation, insulation and low water absorption rate. The inside of the hollow glass beads is vacuum or rarefied gas, which has a difference in density and thermal conductivity with epoxy resin, so it has the characteristics of heat insulation and is an excellent filler for high temperature resistant powder coatings.
(2) It can improve the physical and mechanical properties of the powder coating. Hollow glass microbead filler can increase the hardness and rigidity of powder coatings. However, the impact resistance decreases, and how much the decrease is related to the surface treatment of the hollow glass beads. If the correct coupling agent is selected for pretreatment, the impact on the impact resistance of the material can be reduced.
(3) Low oil absorption. The oil absorption rate of different types of hollow glass beads per 100g is between 7mg-50mg. This kind of filler material with low oil absorption rate increases the filling volume in a disguised manner during the production process and reduces the overall cost.
8. Application of Wollastonite in Powder Coatings
The main component of wollastonite is calcium silicate, the density is 2.9g/cm3, the refractive index is 1.63, and the oil absorption is 30-50%. It has a needle-like structure and good brightness.
Powder coatings generally use natural wollastonite powder, which is processed by natural wollastonite. Wollastonite can be used as an extender pigment in coatings and replace part of white pigments, which can cover and increase the cost of paint. Because of its good electrical conductivity, it is often used in epoxy insulating powder coatings. Wollastonite has a white needle-like structure, which can improve the bending and tensile properties of powder coatings.
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