New system of powder coating and coating technology

New System of Powder Coatings and Coating Technology
Abstract: Powder coatings as a solvent-free coating with its high efficiency, excellent coating performance, ecological environmental protection, economical excellent quality has become the new talent in the paint industry has been rapid development and widely used. This paper introduces the new technology system and future development trend of powder coating and coating. Powder coating and coating technology is a new technology and process developed in the middle of the 20th century, with no organic solvent, no pollution, low pollution, simple process, energy saving, high coating efficiency, good comprehensive performance of protection and decoration, can be filmed at once, it is a new type of "green coating
China
. Since the beginning of the 21st century, more attention has been paid to the protection of the environment, the restrictions on the emission of volatile organic compounds (VOCs) into the atmosphere have become more and more stringent, and the problems of how to save and use limited resources have become more and more concerned, resulting in more attention to powder coating and coating technology in the coating and coating community.
1 Development process
In 1950, the successful application of polyethylene powder flame spraying experiments began, and in 1952, Geitmel of Germany invented the thermoplastic powder process for fluidized bed coatings to ensure the uniformity of the coating, thus making powder coatings of practical application value. Shortly thereafter, PVC and nylon thermoplastic powder coatings were introduced in the United States. In the 1960s, Shell developed the first thermoo-solid powder coating, epoxy powder coating, while Samais of France first introduced powder electrostatization spraying equipment and industrialized production in 1966. In the 1970s, powder coatings developed rapidly. Countries have not only developed polyester epoxy hybrid, polyester, polyurethane and other types of thermoo-solid powder coatings, but also polypropylene, PVC, polyamide, ethylene-acetylene, polyphenyl ether, fluorine resin and other thermoplastic powder coatings. For more than half a century, with the improvement and development of manufacturing process and coating technology, this industrial technology has been developed to the present day in the field of home appliances, construction, automotive, pipeline and anti-corrosion and other fields. The global powder coatings market had sales of approximately $7.77 billion in 2013 and is expected to reach $12.53 billion in 2020, with an average annual growth rate of 7.1%.
2 New Technology System for Powder Coatings
2.1 UV-cured powder coatings
UV-cured powder coatings are thermo-cured powder coatings that generate freelance or active cations through UV light excitation for cross-linking polymerization and curing. Its advantages include: 1) low temperature curing; 2) a single application can obtain the ideal coating thickness, and the appearance of the coating film can be comparable with the appearance of solvent plastic coating film, performance is better than solvent-based coating film performance; It can be coated with thermally sensitive substrates such as plastics, wood, paper and electronic components. Ultraviolet curing powder coating has been industrialized in developed countries in Europe and the United States, successfully applied to medium density fiberboard. However, the coating is expensive and hassles in coating complex and large-scale work parts.
2.2 Composite
Composite Powder Coatings technology uses incompatible principles to form a two-sided composite coating of powder coatings (epoxy/acrylic) with two resin components through one coating and one heating. One side of its contact with air is an acrylic resin system with excellent weather resistance, and the substrate metal is connected with an excellent corrosion-resistant epoxy resin system, the composite system can not only reduce the process, but also give the coating film dual performance, is a new powder coating that not only adapts to environmental protection requirements, but also saves energy.
2.3 Low-temperature cured epoxy powder coating coating coating technology
encumbase technology refers to the process at the molecular level by the formation of the main crystal compound of the encumbase compound and the wrapped yellow body to form the encumbase compound. The encumbase compound is not a simple mixture, but has a specific crystalline structure, which is very different from the original compound in terms of thermal stability, melting point, chemical reactivity, solubility, etc. There are two types of encumerate compounds:
1) single-molecule encumerate; Figure 2 shows.
TEP (1,1,2,2-four (4-hydroxyl benzene) ethane is a practical main crystal compound, its encased jaundial compounds have good stability, water solubility, evaporation speed, skin irritation, etc. are reduced to one to one thousandth. Compounds that are normally decomposed within a few days can achieve several years of stability after being wrapped in TEP, and thermal stability is greatly improved, with melting and boiling points rising by 10 to 100 degrees C.
low-temperature cured epoxy powder coating manufactured by enculation technology has excellent performance, coating suitability and storage stability, so it has good application prospects in pipes, pipe fittings, auto parts, steel furniture and so on.
2.4 crystalline polyester resin
crystalline polyester resin compared to the traditional non-stereotyped thermo-solid polyester has the following advantages: 1) Under similar molecular weight conditions, crystalline polyester than amorphous polyester melting viscosity is low, with a better melt flow leveling. The resulting film orange peel is slight, the coating is flat, smooth and shiny higher; 2) the reaction between crystalline polyester and closed isocyanate crosslinker is faster, the curing temperature is greatly reduced, and the resulting coating has excellent physical properties, and 3) crystalline polyester coating has excellent anti-adhesion at room temperature. There are two types of crystalline polyester: liquid crystal polyester and semi-crystalline polyester. Liquid crystal polyester has the advantages of high molecular orientation, good resysurance, strong impact resistance, low melt viscosity and low density. The narrow melting point and low melting viscosity of semicrystalline polyester facilitate the flow of the powder coating prior to the start of the curing reaction, thus contributing to a smooth coating. The acid value of polyester, relative molecular mass and glassing temperature can be regulated by the selection of monomers, catalysts and reaction conditions used.
3 New system for powder coating
new technology for powder coating includes electromagnetic brush coating technology, NIR (near-infrared) radiation curing powder coating technology and powder coating induction heating curing technology.
3.1 Electromagnetic Brush Coating Technology (EMB)
Electromagnetic Brush Coating Technology (EMB) is a new technology for analog copying or laser printing, especially for applying powder coatings to flat substrates at high speed. The device consists of a magnetic brush and a magnetic drum that can be attached to the coating. Powder coating can be seen as the magnetic powder of the copier, flat-shaped coating can be seen as paper to be copied. When static electricity is turned on, the magnetic field coats it with powder coating as the coating passes through. The technology can be applied to metal, wood, paper substrate and cardboard coating and other fields.
3.2 NIR (near-infrared) curing technology
NIR curing is the intense vibration of coating molecules by near-infrared high radiation energy, which makes the coating heat-cured in a short period of time. The advantages are: powder coatings that do not require special preparation, work parts with slightly more complex shapes, short curing times, and a wide range of applications that affect substrate heat. NIR cured powder coatings can be applied to thermally sensitive products such as wood, medium density fiberboards, plastics, paper, electronics, etc., and can also be used in large steel structures such as bridges, high-rise buildings, ships, tanks and industrial plants based on the mobile and short curing time characteristics of radiation light sources. Near-infrared light energy conversion efficiency of up to 60%, is 15% of the thermal air conversion rate of 4 times, can save about 50% of electricity, is an energy-saving products;
3.3 induction heating curing technology
powder coating induction heating curing technology is achieved by exposing the substrate to a variable electromagnetic field. The special advantage of induction heating for powder curing is that when heated in this form, the work piece is heated only on the surface, which greatly saves the energy required for the curing coating for bulky and thick-walled work parts. At the same time, the induction heating process is very flexible, the workware can be heated at any time during coating construction. The coating quality is excellent due to the consistent temperature of the paint area.
4 Powder coating and coating trends
In order to make powder coatings better popularized and applied, the diversification of powder coating varieties, low temperature rapid curing, thin coating, coating equipment improvement, powder coating manufacturing new process development is still the future development trend of powder coatings.
4.1 Functional powder coatings
With the further development of powder coating technology, the demand for functional powder coatings will be greatly increased, including ultraviolet curing powder coatings, antibacterial anti-mold powder coatings, electrical insulation powder coatings, high temperature powder coatings, anti-graffiti powder coatings, fine art powder coatings, thermal transfer powder coatings, electrophoretic powder coatings, water dispersion powder coatings and other new varieties.
4.2 Optimized resin varieties
In powder coating formulations, the most critical factors in determining the performance of powder coatings and coatings are film-forming resins and curing agents, where resin research and development is the most important way to increase powder varieties. Therefore, the variety of resins used in powder coatings is changing from year to year. In recent years, resin manufacturers have developed a series of UV powder coating resin products, storage stability of dry mixed anti-light polyester powder coating polyester resin, ultra-weather-resistant powder coating polyester resin, epoxy-polyester powder resin, polyester powder with pyride polyester resin, polyurethane powder coating with hydroxyl resin, but these resin varieties still have shortcomings, still need to be improved.
4.3 New curing agents
the development of new curing agents for powder coatings has been mixed. For example, hydroxyacetylamide has the advantages of lower curing temperature, good storage stability and non-toxicity compared with traditional curing agents, but there is a problem that can't be thick coated and thick coated film is prone to coarse pores; No closed polyurethane powder coating curing agent diosterone in the baking process without a closed agent release, with environmentally friendly characteristics, the current weather-resistant polyurethane powder in the United States and Japan accounted for a considerable proportion of the use, but because of the high price of this powder coating, China's current promotion and application there are still many problems, so the development of a reasonable price of environmentally friendly curing agent is one of the future direction of powder coating development.
4.4 Thin-film powder coating
powder coating early development advantages are thick coating, a coating can reach the thickness of solvent-based coating several coatings, saving coating time, high production efficiency. However, the thickness of some products does not require too thick, thick coating belongs to the quality of excess, waste of resources. General powder coating thickness to reach 60 to 80 m is relatively easy, and to achieve 30 to 40 m thin coating is more difficult, the need for powder coating particle size distribution, cover force, dry powder fluidity, electrostitive efficiency and other aspects of improvement, in order to achieve the purpose of thin coating, so the thin layering of powder coating is the focus of research in recent years.
4.5 Ultra-weather-resistant ultra-durable powder coatings
With the development of industrial technology, large-scale long-term, durability engineering projects and ultra-high-rise buildings more and more, the decorative and anti-corrosion properties of powder coatings are becoming more and more demanding, while the service life is also increasingly demanding, so the demand for ultra-weather and ultra-durable powder coatings is increasing. In terms of ultra-weather-resistant powder coatings, the development of polyester, polyurethane, acrylic powder coatings with a service life of 5-10 years or more based on general weather-resistant powder coatings, especially fluorine powder coatings with a service life of 10-20 years or more, meet the coating requirements of ultra-high-rise buildings and steel structures, and develop powder coatings such as ultra-durable epoxy, polyphenyl sulfur ether and other powder coatings is the future direction of development.
addition, improving powder coating manufacturing equipment, powder coating manufacturing process and rapid color matching of powder coatings are also important directions for the future.
4.6 Trends in Powder Coating
The quality of powder coating products depends not only on the quality of the powder coating, but also on the powder coating process. At present, the main coating method is to use electrostitive powder coating method, how to improve the electrostitive efficiency of electrostitive powder gun, maintain the uniformity and stability of spray gun supply, improve the accuracy of powder supply, the rapid color change of the coating system and change powder coating resin varieties are the key issues to be solved.