Through the development of powder coatings and the demand for powder fillers, we will talk about its application and development trend

In the era of environmental protection storm, the development of environment-friendly coatings is the inevitable choice of enterprises, but environmentally friendly coatings are not only water-based coatings, if enterprises swarm to develop water-based coatings, it is inevitable that there will be product homogenization. In addition to water-based coatings, high-solids coatings, solvent-free coatings, and powder coatings are also environmentally friendly coatings, which should become the key development direction of the coatings industry.

The general situation of powder coating

1. Introduction to powder coating

Powder coating began in the 50s of the last century, is a solid content of 100%, and no organic volatile compounds (VOCs) produced by environmentally friendly coatings, with energy saving, pollution reduction, simple process, easy to achieve industrial automation, excellent coating performance and other characteristics.

Powder coatings are powdered 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 in one pass, which has extremely high production efficiency; The mechanical properties and chemical resistance of powder coatings are excellent, and they have excellent coating properties; The use of powder coating can save energy and resources, and the utilization rate can reach 99%, which is safe to use and has outstanding economy; Therefore, as a solvent-free coating, powder coating conforms to the internationally popular "four E" principles of economy, environmental protection, high efficiency and excellent performance.

2. Overview of the powder coating market

With the growing 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 is also triggering the growth of the powder coating market.

Thanks to the joint promotion of a number of factors, especially the rapid development of urbanization and the joint growth of housing, construction and automobiles, the growth rate of China's powder coating market demand ranks first in the world, and the rapid development of powder coating will inevitably drive the growth of powder filler demand.

Analysis of the application of different powder materials in powder coatings

Fillers in coatings can not only reduce their costs, but also play a great role in improving the performance of coating products. For example, improve the wear resistance and scratch resistance of the coating film, reduce the sagging of the coating when it melts and runs, improve the anti-corrosion performance, and improve the moisture resistance.

Factors such as density, dispersion performance, particle size distribution, and purity need to be considered when selecting fillers for powder coatings. In general, the higher the density, the lower the powder coating coverage; The dispersion of large particles is better than that of small particles; The filler is chemically inert and avoids reacting 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 coating 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. Regardless of the type of calcium carbonate and the method used to produce it, different particle sizes strongly affect the gloss of the coating.

In addition to being used for increment, heavy calcium is mainly used to partially replace titanium dioxide and color pigments, replace light calcium and precipitate barium sulfate, anti-corrosion and partially replace anti-rust pigments.

When heavy calcium is used in interior architectural paints, it can be used alone or in combination with talcum powder. Compared to talc, calcium carbonate reduces the rate of chalking, improves color retention and increases mold resistance in light-colored paints. However, due to poor acid resistance, it hinders its application in topical coatings.

Compared with heavy calcium, light calcium has a small particle size and narrow particle size distribution range, high oil absorption and brightness, and light calcium can be used where the maximum matting effect is required.

2. Application of barium sulfate in powder coatings

There are two kinds of barium sulfate used as pigments for paint bodies: natural and synthetic, the natural product weighs spar 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 good compatibility with all pigments. It can achieve the ideal coating thickness in the spraying process and the powder application rate is high.

Barite powder fillers are mainly used in industrial primers and automotive intermediate coatings that require high film strength, high filling force and high chemical inertness, as well as in topcoats that require high gloss. In latex paints, due to the high refractive index of barite (1.637), fine barite powder can have the function of translucent white pigment, which can replace part of titanium dioxide in the coating.

3. Application of mica powder in powder coatings

Mica powder is a complex silicate composition, the particles are flake-like, with excellent heat resistance, acid and alkali resistance, which has an impact on the melt fluidity of powder coatings, and is generally used in temperature-resistant and insulating powder coatings, and can be used as fillers for texture powders.

Among the many mica-like minerals, the chemical structure of sericite is similar to that of kaolin, and it has a variety of characteristics of mica minerals and clay minerals. When applied in coatings, it 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. In addition, sericite powder also has the function of anti-algae and mildew. Therefore, sericite powder is a multifunctional filler with excellent price-performance ratio for coatings.

4. Application of talcum powder in powder coatings

Talc, also known as aqueous magnesium silicate, is made by direct crushing of talc. The particles are needle-like crystals, have a slippery feeling, soft texture and low abrasiveness, have good suspension and dispersion and a certain thixotropy, which has a great impact on the melt fluidity of powder coatings, and are often used in texture powders. At present, it is used in various primers, intermediate coatings, road sign paints, industrial coatings and architectural coatings for interior and exterior use.

Talcum powder is inexpensive, but it has drawbacks and is therefore used in limited quantities. First of all, the oil absorption is larger. In the case of low oil absorption, it must be combined with fillers and barite powder with low oil absorption; Secondly, the wear resistance is not high, and other fillers should be added to make up for the occasion that high wear resistance is required; In addition, talcum powder containing other non-metallic minerals is not suitable for external coatings requiring high weather resistance because impurity minerals are easy to react with acids (such as acid rain); In addition, talc has matting properties, so it is generally not used in high-gloss coatings.

5. Application of silica in powder coatings

Porous powder quartz is a kind of silica system, which is recognized as safe to use, and 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, and at the same time replace barium sulfate to reduce the content of soluble barium in the product, which meets environmental protection requirements.

In addition, fumed silica is often used as a loose and anti-caking additive for powder coatings. Fumed silica is a multifunctional pigment and a rheology control agent for coatings with excellent performance. In liquid coatings, its rheological control functions include: thickening, thixotropy, anti-sagging, covering edges; In solid powder coating systems, the free flow of powders is enhanced, and caking and fluidization are prevented.

6. Application of kaolin in powder coatings

Kaolin can improve thixotropy and sedimentation resistance. Calcined clay has no effect on rheological properties, but can have the same matting effect, increased coverage and increased whiteness as untreated clay, which is similar to talc.

Kaolin generally has high water absorption, which is not suitable for improving the thixotropy of coatings and is not suitable for the preparation of hydrophobic coating films. The particle size of kaolin products is between 0.2 and 1 μm. Kaolin with large particle size has low water absorption; Kaolin (less than 1 μm) with good matting effect and small particle size 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, and hardness of calcined kaolin are higher than those of washed kaolin.

7. Application of hollow glass beads in powder coatings

Hollow glass beads are a tiny, hollow spherical powder, which has the advantages of light weight, large volume, low thermal conductivity, high compressive strength, insulation, corrosion resistance, non-toxicity, dispersion, fluidity and stability.

When used in powder coatings, hollow glass beads can do the following:

(1) Low heat insulation, insulation, and water absorption. The inside of the hollow glass beads is a vacuum or thin gas, and there is a difference in density and thermal conductivity between the epoxy resin and the 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 powder coating. Hollow glass bead fillers increase the hardness and stiffness of powder coatings. However, the impact resistance decreases, and the decline is related to the surface treatment of insulating glass beads. Pretreatment with the right coupling agent can reduce the impact impact of the material.

(3) Low oil absorption. The oil absorption rate of different types of hollow glass beads per 100g is between 7mg~50mg, and this low oil absorption rate filler material increases the filling amount in disguise during the production process and reduces the comprehensive cost.

8. Application of wollastonite in powder coatings

The main component of wollastonite is calcium silicate, with a density of 2.9g/cm3, a refractive index of 1.63, and an oil absorption of 30~50%, which has a needle-like structure and good brightness.

Powder coatings are generally made of natural wollastonite powder, which is processed from natural wollastonite. Wollastonite can be used as a physical pigment and replace some white pigments in coatings, playing a role in covering and incrementing, and reducing the cost of paint. Because of its good electrical conductivity, it is often used in epoxy insulation powder coatings. Wollastonite has a white needle-like structure that improves the flexural and tensile properties of powder coatings.

The development trend of powder fillers for powder coatings

1. Surface treatment of powder filler

Powder coating fillers are polar, while powder coating resins are extremely polar, 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 treat the powder filler by physical methods (surface coating and surface adsorption) or chemical methods (surface substitution, hydrolysis, polymerization and grafting, etc.), so that the particle diameter of the aggregate can be significantly reduced or the fluidity of the system can be improved, and the processing performance, apparent quality (such as gloss, color brightness, etc.) and mechanical strength of the coating can be improved.

2. Powder filler is fine

When the ratio of powder coating resin to filler is constant, theoretically, the smaller the particle size of the filler, the better the surface properties 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 (0.2~0.5μm), the polycarbonated titanium produced in the formula can be isolated, more effective dispersion centers can be formed, and the hiding power of titanium dioxide can be improved, which is the spatial separation principle of the fine filler. Similarly, micro-refinement fillers can also reduce the amount of pigment used.

3. Nanotechnology of powder filler

The most commonly used nanomaterials are nano-silica, nano-titanium dioxide, and nano-calcium carbonate. It is reported that nano titanium dioxide has transparency, can improve the mechanical properties and ultraviolet absorption of coatings, and can be used in automotive overlay varnishes, which can significantly improve the weather resistance of powder coatings. Because nanomaterials are very fine particles, the surface activity is quite high, and it is easy to agglomerate and flocculate, so the surface treatment of nano fillers, the selection of adding methods and dispersion equipment, the amount of nanomaterials added in powder coatings, and how to disperse into the base resin are the key to the application of nanomaterials in powder coatings. In the design of powder coating formulation, different fillers can be selected according to the product performance requirements to achieve the best results.

4. Functionalization of powder coating filler

The development direction of functionalized powder coating is to improve the physical, chemical and mechanical properties of some aspects of powder coating, or to give powder coating a new function. For example, kaolin and wollastonite powder powder are used in the production of electrically insulating powder coatings, which can not only reduce the cost of powder coatings, but also improve electrical insulation. Aluminum hydroxide and magnesium hydroxide have flame retardant effects, which can be made into flame retardant powder coatings, and can also control rheology, improve adhesion, control gloss, improve hiding power, etc. Therefore, the fillers for powder coating should shift 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.

Powder coating is an energy-saving, resource-saving, low-pollution environmentally friendly coating. Due to the increasing demand for energy in countries around the world, reducing energy consumption and protecting the environment have become the main development directions. Therefore, the development of powder coatings that can be cured at low temperatures, have high weather resistance, are highly decorative and can be applied thinly will be the main development direction in the future. Driven by the demand for powder coatings, the demand for powder fillers such as calcium carbonate, quartz, mica powder, talc, and kaolin will inevitably increase. And the requirements for the fineness, functionalization, and surface modification of powder fillers are getting higher and higher.