Coatings environmental storm era, the development of environmentally friendly coatings is the inevitable choice of enterprises, but environmentally friendly coatings more than a water-based coatings, if enterprises swarm to the development of water-based coatings, it is inevitable that there will be product homogeneity.In addition to water-based coatings, high-solid coatings, solvent-free coatings, and powder coatings are also environmentally friendly coatings, which should become the key development direction of the coatings industry.According to a research report, the value and volume of the powder coatings market in the Asia-Pacific region are expected to reach the highest growth rate from 2017 to 2022. Powder coating technology is rapidly evolving to accommodate a demand-driven market. Driven by the market, it is particularly important to study the application of different powder materials in powder coatings.
Overview of 1. Powder Coatings
Introduction to Powder Coatings
Powder coating began in the 50 s of the last century, is a solid content of 100, and no organic volatile matter (VOC) to produce environmentally friendly coatings, with energy saving, reduce pollution, simple process, easy to achieve industrial automation, excellent coating performance and other characteristics.
Powder coatings are powder coatings composed of polymers, pigments, fillers and additives. Because there is no volatilization of liquid medium, it has good ecological and environmental protection. Powder coating can form a thicker coating at one time, with extremely high production efficiency. Powder coating has excellent mechanical properties and chemical corrosion resistance and excellent coating film performance. The use of powder coating can save energy, resources, the utilization rate can reach 99%, the use is safe and has outstanding economy. Therefore, as a solvent-free coating, powder coating in line with the international popular economy, environmental protection, high efficiency, excellent performance of the "four E" principle.
Overview of Powder Coatings Market
With the increasing demand for electrical appliances and light vehicles, the demand for powder coatings has increased. The growing demand from the end-use industry in developed and emerging countries has also triggered the growth of the powder coatings market. according to the report released by the market research institute Markets and Markets,The global powder coatings market size is expected to reach $134.9 billion billion by 2022, with a compound annual growth rate of 6.75 percent from 2017 to 2022.
Thanks to the joint promotion of many factors, especially the rapid development of urbanization and the joint growth of housing, construction and automobile fields, the growth rate of China's powder coating market is the highest in the world. In 2016, the output of China's powder coating industry reached 2.07 million tons.
Application Analysis of 2. Different Powder Materials in Powder Coatings
The filler in the coating can not only reduce its cost, but also play a great role in improving the performance of the coating product. Such as improving the wear resistance and scratch of the coating, reducing the flow of the coating melt flow, improving the corrosion resistance, improving the moisture resistance, etc.
Powder coatings in the selection of fillers need to consider the density, dispersion, particle size distribution, purity and other factors. Generally speaking, the higher the density, the lower the coverage of the powder coating; the dispersion of large particles is better than the dispersion 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. Powder materials commonly used in powder coatings are calcium carbonate, barium sulfate, talc, mica powder, kaolin, silica, wollastonite and so on.
Application of Calcium Carbonate in Powder Coatings
Calcium carbonate is divided into light calcium carbonate (precipitated calcium carbonate) and heavy calcium carbonate. Regardless of the type of calcium carbonate and the method of production, different particle sizes strongly affect the gloss of the coating. Calcium carbonate is generally not recommended for outdoor use.
Heavy calcium in addition to the increment, mainly used for partial replacement of titanium dioxide and color pigments, instead of light calcium and precipitated barium sulfate, anti-corrosion and partial replacement of anti-rust pigments.
When heavy calcium is used in interior construction paint, it can be used alone or in combination with talc powder. Compared with talcum powder, calcium carbonate can reduce the chalking rate, improve the color retention of light colored paint and increase the resistance to mold. However, due to poor acid resistance, its application in external coatings is hindered.
Compared with heavy calcium, light calcium has a small particle size and a narrow particle size distribution range, high oil absorption and brightness, and light calcium can be used where the maximum matting effect is required.
Application of Barium Sulfate in Powder Coatings
Barium sulfate used as paint pigment has two kinds of natural and synthetic, natural products called barite powder, synthetic products called precipitated barium sulfate.
In powder coatings, precipitated barium sulfate can enhance the leveling and gloss retention of powder coatings, and has good compatibility with all pigments. Can make the powder coating in the spraying process to achieve the ideal film thickness, and the powder rate is high.
Barite powder fillers are mainly used for industrial primers and automotive intermediate coatings that require high film strength, high filling force and high chemical inertness, and are also used in topcoats that require higher gloss. In latex paint, due to the high refractive index of barite (1.637), fine barite powder can have the function of translucent white pigment, can replace part of titanium dioxide in the coating.
Application of Mica Powder in Powder Coatings
Mica powder is composed of complex silicate, the particles are scaly, heat resistance, acid and alkali resistance is excellent, has an impact on the melt fluidity of powder coatings, generally used in temperature and insulating powder coatings, can be used as texture powder filler.
Among the many types of mica, the chemical structure of sericite is similar to that of kaolin, which combines 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 the lattice layer of sericite powder, so as to maintain the color for a long time without fading. In addition, sericite powder also has the function of anti-algae and anti-mildew. Therefore, sericite powder is a kind of multifunctional filler with excellent price performance ratio for coatings.
Application of Talcum Powder in Powder Coatings
Talc, also known as hydrous magnesium silicate, is directly crushed by talc ore. The particles are acicular crystals, have a smooth feeling, soft texture and low abrasiveness, have good suspension and dispersion and a certain degree of thixotropy, have a greater impact on the melt fluidity of powder coatings, commonly used in texture powder. At present, it is used in various primers, intermediate coatings, road marking paints, industrial coatings and internal and external architectural coatings.
Talcum powder is inexpensive, but it has disadvantages and is therefore used in limited quantities. First of all, the oil absorption is large. Where low oil absorption is required, it must be matched with filler and barite powder with low oil absorption. Secondly, the wear resistance is not high. Where high wear resistance is required, other fillers should be added to make up for it. Furthermore, talc powder containing other non-metallic minerals is not suitable for external coatings requiring high weather resistance because impurity minerals are easy to react with acid (such as acid rain). In addition, talc powder has matting properties, therefore, it is generally not used in high gloss coatings.
Application of Silica in Powder Coatings
Porous powder quartz is a kind of silica system, the use of safety is recognized, has been widely used in powder coatings, fire retardant coatings, waterproof coatings, anti-corrosion coatings, etc. Cheap porous powder quartz can reduce the cost of powder coatings, while replacing barium sulfate to reduce the content of soluble barium in the product, to meet environmental requirements.
In addition, powder coatings often use fumed silica as a powder coating loose and anti-caking additives. Fumed silica is a kind of multi-functional extender pigment, and it is also an excellent rheology control agent for coatings. In liquid coatings, its rheological control functions include: thickening, thixotropy, anti-flow hanging, and edge coverage; in solid powder coating systems, it enhances the free flow of powder and prevents agglomeration and fluidization.
Application of Kaolin in Powder Coatings
Kaolin can improve thixotropy and precipitation resistance. Calcined clay has no effect on rheological properties, but it can be like untreated clay, with extinction, increased coverage and increased whiteness, which are similar to talcum powder.
Kaolin is generally more absorbent, not suitable for improving the thixotropy of the coating, not suitable for the preparation of hydrophobic coating. The particle size of the kaolin product is between 0.2-1 μm. Large particle size of kaolin water absorption is small; good extinction effect, small particle size of kaolin (1μm below), 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 that of washed kaolin.
Application of Hollow Glass Microspheres in Powder Coatings
Hollow glass microspheres is a small, hollow spherical powder, with light weight, large volume, low thermal conductivity, high compressive strength, insulation, corrosion resistance, non-toxic and dispersion, mobility, stability and other advantages.
When applied in powder coatings, hollow glass microspheres can play the following roles:
(1) heat insulation, insulation, low water absorption. The inside of the hollow glass beads is vacuum or thin gas, and there is a density and thermal conductivity difference with epoxy resin, so it has the characteristics of heat insulation, is an excellent filler for high temperature resistant powder coatings.
(2) can improve the physical and mechanical properties of powder coating. The hollow glass bead filler can increase the hardness and stiffness of the powder coating. However, the impact resistance decreases, and the decrease is related to the surface treatment of 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) the oil absorption rate is low. The oil absorption rate of different types of hollow glass microspheres per 100g is between 7mg and 50mg. The filling material with low oil absorption rate increases the filling amount in disguise and reduces the comprehensive cost in the production process.
Application of Wollastonite in Powder Coatings
Wollastonite is mainly composed of calcium silicate, with a density of 2.9g/cm3, a refractive index of 1.63, an oil absorption of 30-50%, a needle-like structure, and a good brightness.
Powder coatings generally use natural wollastonite powder, made of natural wollastonite processing. Wollastonite in the paint can be used as a body pigment and instead of part of the white pigment, cover, incremental role, reduce the cost of paint. Because of its good conductivity, it is often used in epoxy insulating powder coatings. Wollastonite is a white needle-like structure, which can improve the bending and tensile properties of powder coatings.
Development Trend of Powder Fillers for 3. Powder Coatings
Surface treatment of powder filler
Powder coating fillers are polar, and the polarity of powder coating resin is very small, which will cause poor compatibility between the two, which will have a negative impact on powder coating processing and coating performance. Therefore, it is usually necessary to carry out physical methods (surface coating and surface adsorption) or chemical methods (surface substitution, hydrolysis, polymerization and grafting, etc.) to treat the powder filler, so that the particle diameter of the aggregate is significantly reduced or the fluidity of the system is improved, and the processing performance, apparent quality (such as gloss, color and brilliance, etc.) and mechanical strength of the coating are improved.
powder filler micronization
When the ratio of powder coating resin to filler is constant, the smaller the particle size of the filler, the better the surface performance and mechanical properties of the coating film. If the particle size of the filler is reduced to a level similar to the particle size of titanium dioxide (0.2~0.5 μm), the agglomerated titanium produced in the formula can be isolated to form more effective dispersion centers and improve the hiding power of titanium dioxide. This is the space separation principle of micronized filler. Likewise, the amount of pigment can be reduced by micronizing the filler.
Nano-technology of powder filler
The most commonly used nanomaterials are nano-silica, nano-titanium dioxide and nano-calcium carbonate. According to reports, nano-titanium dioxide has transparency, can improve the mechanical properties and ultraviolet absorption of coatings, applied to automotive varnish, can make the powder coating weather resistance has been significantly improved. Because nanomaterials are very small particles, the surface activity is quite high, it is easy to agglomerate and flocculate, so the surface treatment of nanofillers, the selection of adding methods and dispersion equipment, the amount of nanomaterials in powder coatings and how to disperse into the base resin Among them, it is the key to the application of nanomaterials in powder coatings. When designing the powder coating formulation, different fillers can be selected according to the product performance requirements to achieve the best results.
powder coating filler functionalization
The development direction of functional powder coatings is to improve the physical, chemical and mechanical properties of some aspects of powder coatings, or to give powder coatings new functions. For example, kaolin and wollastonite powder are used to produce electrical insulating powder coatings, which can reduce the cost of powder coatings and improve electrical insulation. Aluminum hydroxide and magnesium hydroxide have flame retardant effect, can be made into flame retardant powder coating, can also control rheology, improve adhesion, control gloss, improve hiding power, etc.. Therefore, the filler for powder coatings should turn from simple cost reduction to other functional research, and develop more new fillers with excellent performance and low price to meet the needs of the continuous development of powder coatings.