Although the varieties of powder coatings are not as diverse as the varieties of solvent-based coatings, there are also many types of polymer resins that can be used as powder coatings. Powder coatings can be divided into two types: thermosetting and thermoplastic.
1. Thermosetting powder coating refers to the use of thermosetting resin as a film-forming substance, adding a curing agent capable of crosslinking reaction to form an insoluble and infusible hard coating after heating. No matter how high the heating temperature is, the coating will not soften like a thermoplastic coating, but can only decompose. Because the resin used in thermosetting powder coatings is a prepolymer with a low degree of polymerization and a low molecular weight, the coating has better leveling properties and strong decoration. Moreover, after the low molecular weight prepolymer is cured, It can form network cross-linked macromolecules, so the coating has better corrosion resistance and mechanical properties. Therefore, the development of thermosetting powder coatings is particularly rapid.
1.1 Epoxy powder coating.
Due to its excellent adhesion to metal, corrosion resistance, hardness, flexibility and impact strength, it is the first variety used in thermosetting powder coatings. The formulation of epoxy powder coating is composed of epoxy resin (Epoxy Resin), curing agent (curing agent), pigment (pigment), filler (filler) and other assistants (assistant). The contribution of these several components to the performance of the formed powder coating is mutually restricted and affects each other. An appropriate formula is actually the result of 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. In addition, because the polyester resin has polar groups, the powdering rate is higher than that of epoxy resin, it is not easy to yellow during the baking process, has high gloss, good leveling, full paint film, light color and other characteristics, so it has the characteristics of Very decorative. Generally used in refrigerators, washing machines, vacuum cleaners, instrument housings, bicycles, furniture and other fields.
1.3 Acrylic powder paint.
Acrylic resin powder coatings have two types: thermoplastic and thermosetting. The biggest advantage of thermosetting acrylic resin powder coating is that it has excellent weather resistance, color retention, pollution resistance, strong metal adhesion, and excellent film appearance. It is suitable for decorative powder coatings.
2. Thermoplastic powder coating. Thermoplastic powder coatings began to appear in 1950. They melted at the spraying temperature and solidified into a film when cooled. Due to the simple processing and spraying methods, the powder coating only needs to be heated, melted, leveled, cooled or extracted to solidify to form a film, and does not require complex curing devices. Most of the raw materials used are common polymers on the market, which can meet the performance requirements under most conditions. But there are also some shortcomings, such as high melting temperature, low coloring level, poor adhesion to the metal surface, etc. Nevertheless, the commonly used thermoplastic powder coatings still show some unique properties. Among them, polyolefin powder coatings have excellent solvent resistance; polyvinylidene fluoride coatings have outstanding weather resistance; polyamides have excellent wear resistance; Vinyl chloride has a good price/performance ratio; thermoplastic polyester powder coatings have the advantages of beautiful appearance and high artistic quality. These characteristics make thermoplastic powder coatings occupy a large proportion of the coatings market.
2.1 Polyvinyl chloride powder is one of the cheapest polymers produced on a large scale industrially.
It has excellent solvent resistance, good corrosion resistance to water and acid, impact resistance, salt spray resistance, can prevent food pollution and has high insulation strength for electrostatic spraying. Mainly used for coating metal mesh panels, steel furniture, chemical equipment, etc.
2.2 The polyethylene powder coating has excellent corrosion resistance.
Chemical resistance and excellent electrical insulation and resistance to ultraviolet radiation. The disadvantage is that the mechanical strength is not high, and the adhesion to the substrate is poor. It can be used in chemical tanks, impellers, pumps, pipeline inner walls, instrument shells, sheet metal, refrigerator inner screens, auto parts, etc.
2.3 Nylon powder coating.
Nylon is also known as polyamide. Because the N atom of the chlorine group on the molecular chain easily forms hydrogen bonds with the hydrogen atoms on the adjacent segment, the melting point of polyamide resin is generally higher. Nylon has the advantages of high mechanical strength, impact resistance, hardness, wear resistance, low friction coefficient, low dust absorption, etc., and can be used for parts with special requirements. Such as water pump impellers, textile machinery parts, starting piston parts of diesel engines, motor sailing propeller impellers, automobile wheels, motorcycle brackets, agricultural machinery, construction and sports equipment, etc. In addition, nylon powder coating is non-toxic, odorless, not corroded by mold, and will not promote the growth of bacteria due to its salt water resistance and inertness to mold and bacteria. Suitable for spraying food industry parts, drinking water pipes and food packaging, etc.
4 Fluorine resin powder coating.
There are many types of fluoropolymers that can be used to prepare powder coatings, such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PTFCE), polyvinylidene fluoride (PVDF), etc. The melting point of PTFE is as high as 327℃, and it can be used for a long time in the range of -250～250℃. In addition, it has excellent corrosion resistance and does not corrode even in aqua regia, excellent dielectric properties, extremely low friction coefficient and Self-lubricating, so it is known as the "Plastic King". It is widely used in petroleum, chemical anti-corrosion coatings, seals, bearing lubricating materials, electronic and electrical materials, ship launching rails and non-stick coatings, etc. The price of polychlorotrifluoroethylene is cheaper than PTFE, and the processing temperature can be lowered. The coating can be used for a long time under 130℃. Its alkali resistance and hydrogen fluoride corrosion resistance are better than acid resistance enamel, hydrochloric acid, dilute sulfuric acid, hydrogen chloride and chlorine corrosion. Better than stainless steel equipment. It has been widely used in anti-corrosion equipment in chemical plants, pesticide plants, pharmaceutical plants, detergent plants, etc. The biggest advantage of polyvinylidene fluoride powder coating is excellent weather resistance, high degradation resistance when exposed to outdoor exposure, and does not absorb dust, and it is easy to maintain the original gloss. 5 Chlorinated polyether powder coating. Chlorinated polyether has excellent chemical stability. The coating film has good corrosion resistance and anti-dissolution properties against a variety of acids, alkalis and solvents. The chemical stability is second only to PTFE, and the mechanical and friction properties are also very good. Chlorinated polyether powder coatings are mainly used in chemical equipment, pipeline linings, instrument equipment shells, etc. The disadvantage is poor adhesion to metal. Adding additives can improve the adhesion to metal.
5. Latex powder coating
Latex powder is prepared by spray drying the emulsion, and currently most of it is vinyl acetate copolymer. The paint produced with latex powder is called latex powder paint. It is the most environmentally friendly paint among wall paints at present by adding clean water and mixing for construction.