Although the types of powder coatings are not as diverse as solvent based coatings, there are many polymer resins that can be used as powder coatings.
It can be divided into two categories: thermosetting and thermoplastic.
1. Thermosetting powder coating refers to a curing agent that uses thermosetting resin as a film-forming substance and undergoes heating cross-linking reaction to form an insoluble and non melting hard coating. No matter how high the temperature is, the coating will not soften like thermoplastic coatings and can only decompose. Due to the low degree of polymerization and molecular weight of prepolymers used in thermosetting powder coatings, the coatings have better leveling and decorative properties. Moreover, after curing, low molecular weight prepolymers can form a network of cross-linked macromolecules, thus the coating has good anti-corrosion and mechanical properties. Therefore, the development of thermosetting powder coatings is particularly rapid.
1.1 Epoxy powder coating. Due to its excellent adhesion to metals, corrosion resistance, hardness, flexibility, and impact strength, it was the first variety used for thermosetting powder coatings. The formula of epoxy powder coating consists of epoxy resin, curing agent, pigment, filler, and other additives. The contributions of these components to the performance of formed powder coatings are mutually constrained and influenced. A suitable formula is actually the result of the coordination of various components.
1.2 Polyester powder coating. Compared with other types of powder coatings, polyester powder coatings have unique properties. It has better weather resistance and UV resistance than epoxy resin [2]. In addition, due to the polar functional groups of polyester resin, the pulverization rate is higher than that of epoxy resin. During the baking process, it is not prone to yellowing, has high glossiness, good leveling, full paint film, and light color. Very decorative. Generally used in fields such as refrigerators, washing machines, vacuum cleaners, instrument casings, bicycles, furniture, etc.
1.3 Acrylic powder coating. There are two types of acrylic resin powder coatings: thermoplastic and thermosetting. The biggest advantage of thermosetting acrylic resin powder coating is its excellent weather resistance, color retention, pollution resistance, strong metal adhesion, and excellent paint film appearance. Suitable for decorative powder coatings.
2. Thermoplastic powder coating. Thermoplastic powder coatings began to appear in 1950. They melt at the spraying temperature and solidify into a thin film when cooled. Due to the simple processing and spraying methods, powder coatings only require heating, melting, leveling, cooling, or extraction to solidify into a film, without the need for complex curing equipment. The raw materials used are mostly common polymers in the market, which can meet performance requirements under most conditions. But there are also disadvantages such as high melting point, low coloring degree, and poor adhesion to metal surfaces. However, commonly used thermoplastic powder coatings still exhibit some unique properties. Among them, polyolefin powder coatings have excellent solvent resistance; Polyvinylidene fluoride coating has outstanding weather resistance; Polyamide has excellent wear resistance; Chloroethylene has a good cost-effectiveness; Thermoplastic polyester powder coating has the advantages of beautiful appearance and high artistic quality. These characteristics make thermoplastic powder coatings occupy a large proportion of the coating market.
2.1 Polyvinyl chloride powder is one of the cheapest polymers produced on a large scale in industry. It has excellent solvent resistance, good water resistance, acid corrosion resistance, impact resistance, salt spray resistance, can prevent food contamination, and has high insulation strength for electrostatic spraying. Mainly used for painting metal mesh panels, steel furniture, chemical equipment, etc.
2.2 Polyethylene powder coating has excellent corrosion resistance, chemical resistance, electrical insulation, and UV radiation resistance. The disadvantage is that the mechanical strength is not high and the adhesion to the substrate is poor. Can be used for chemical tanks, impellers, pumps, inner walls of pipelines, instrument casings, sheet metal, refrigerator screens, automotive parts, etc.
2.3 Nylon powder coating. Nylon is also known as polyamide. Due to the tendency of the nitrogen atom of the chlorine group on the molecular chain to form hydrogen bonds with the hydrogen atom on adjacent segments, the melting point of polyamide resin is generally high. Nylon has high mechanical strength, impact resistance, high hardness, wear resistance, low friction coefficient, and low dust absorption, and can be used for parts with special requirements. Such as water pump impellers, textile machinery parts, diesel engine starting piston parts, motor sailboat propeller impellers, car wheels, motorcycle brackets, agricultural machinery, construction and sports equipment, etc. In addition, nylon powder coating is non-toxic, odorless, and not susceptible to mold corrosion. Due to its salt water resistance and inertness to mold and bacteria, it does not promote bacterial growth. Suitable for spraying food industry parts, drinking water pipelines, and food packaging.
2.4 Fluororesin powder coating. There are many types of fluorinated polymers that can be used to prepare powder coatings, such as polytetrafluoroethylene (PTFE), polytetrafluoroethylene (PTFCE), polyvinylidene fluoride (PVDF), etc. The melting point of polytetrafluoroethylene is as high as 327 ℃, and it can be used for a long time in the range of -250 to 250 ℃. In addition, it has excellent corrosion resistance, does not corrode even in aqua regia, excellent dielectric properties, extremely low friction coefficient and self-lubricating properties, and is therefore known as the "king of plastics". Widely used in petroleum and chemical anti-corrosion coatings, seals, bearing lubrication materials, electronic and electrical materials, ship launching guides, and non stick coatings. Polytrifluorochloroethylene is cheaper than polytetrafluoroethylene and can be processed at lower temperatures. The coating can be used for a long time below 130 ℃. Its resistance to alkali and hydrogen fluoride corrosion is superior to acid resistant enamel, hydrochloric acid, dilute sulfuric acid, hydrogen chloride, and chlorine gas corrosion. Superior to stainless steel equipment. It has been widely used in anti-corrosion equipment such as chemical plants, pesticide plants, pharmaceutical plants, detergent plants, etc. Vacuuming can easily maintain the original luster. 5. Chlorinated polyether powder coating. Chlorinated polyether has excellent chemical stability. The coating has good corrosion resistance and solubility to various acids, alkalis, and solvents. The chemical stability is second only to polytetrafluoroethylene, and the mechanical and frictional properties are also very good. Chlorinated polyether powder coating is mainly used for chemical equipment, pipeline lining, instrument equipment shell, etc. Its disadvantage is poor adhesion to metals. Adding additives can improve adhesion to metals.
2.5 Latex powder coating
Latex powder is prepared by spray drying lotion, most of which are vinyl acetate copolymers. Coatings produced with latex powder are called latex powder coatings. Adding water and stirring on site is the most environmentally friendly coating in wall paint.
