Although there are not as many varieties of powder coatings as solvent-based coatings, there are many polymer resins that can be used in powder coatings. In general, they can be divided into two categories: thermosetting and thermoplastic resins.
1. Thermosetting Powder Coatings
They refers to powder coatings that uses thermosetting resin as the film-forming material, adds the curing agent that can cause cross-linking reaction, and finally forms a hard coating with insoluble and non-melting texture after heating. The coating will not soften at higher temperature like thermoplastic coating, but only decompose.
1.1 Epoxy Powder Coating
Because of its excellent adhesion to metal, corrosion resistance, hardness, flexibility and impact strength, epoxy powder coating is the first choice of thermosetting powder coatings. Epoxy powder coating is composed of epoxy resin, curing agent, pigment, filler and assistant. The contribution of these components to the coating performance is mutually constrained. So a suitable formula is the result of the coordinated action of various components.
1.2 Polyester Powder Coating
Polyester powder coating has unique properties compared with other types. Its weather resistance and UV resistance are better than epoxy resin. Since polyester resin has polar groups, its powdering rate is higher than epoxy resin. It is also good for decoration because it’s not easy to yellowing during baking, and has high gloss level, good leveling and rich paint film. It is generally used in refrigerators, washing machines, vacuum cleaners, instrument casings, bicycles, and furniture.
1.3 Acrylate Powder Coating
The biggest advantage of thermosetting acrylic powder coating is that it has excellent weather resistance, color retention, pollution resistance, strong metal adhesion, excellent film appearance, and is suitable for decorative powder coating.
2. Thermoplastic Powder Coatings
Thermoplastic powder coatings came out in 1950. It melts at the spraying temperature and solidifies into a film when cooled. Due to the simple processing and spraying method, thermoplastic powder coatings only need to be heated, melted, leveled, cooled or extracted to solidify into a film without using curing agents.
2.1 Polyvinyl Chloride Powder Coating
It is one of the cheapest polymers produced on an industrial scale. It has excellent solvent resistance, good corrosion resistance to water or acids, impact resistance, and salt spray resistance. It prevents food contamination and has high insulation against electrostatic spraying. It is mainly used for metal panels, steel furniture, chemical equipment, etc.
2.2 Polyethylene Powder Coating
It has excellent anti-corrosion performance, chemical resistance, electrical insulation and UV resistance. The disadvantage is that the mechanical strength is not high, and the adhesion to the substrate is poor. It can be used for chemical tank, impeller, pump, pipe wall, instrument shell, metal plate, refrigerator inner mesh board, auto parts, etc.
2.3 Nylon Powder Coating
Nylon is also known as polyamide, and the melting point of polyamide resin is generally higher. Nylon has the advantages of high mechanical strength, impact resistance, hardness, wear resistance, low coefficient of friction, low dust absorption, etc. It can be used for parts with special requirements.
2.4 Fluorine Resin Powder Coating
There are many types of fluoropolymers that can prepare powder coatings, such as PTFE, PTFCE, and PVDF.
PTFE has high melting point and excellent corrosion resistance, even in aqua regia. It has excellent dielectric properties, very low coefficient of friction and self-lubrication, so it is known as the “King of Plastics”. It is widely used in petroleum, chemical anticorrosive coating, sealing, bearing lubrication material, electronic materials, ship launching guide, non-stick pan coating, etc.
The price of PTFCE is lower than PTFE. Its ability to resist the corrosion of alkali and hydrogen fluoride is better than acid-resistant enamel. And its resistance to the corrosion of hydrochloric acid, dilute sulfuric acid, hydrogen chloride and chlorine is better than stainless steel equipment. It has been widely used in anti-corrosion equipment from chemical plants, pesticide plants, pharmaceutical plants, detergent plants, etc.
The biggest advantage of PVDF powder coating is excellent weather resistance, high degradation resistance in outdoor exposure, and does not absorb dust, thus it is easy to maintain the original gloss of the film.
2.5 Chlorinated Polyether Powder Coating.
Chlorinated polyether has excellent chemical stability, second only to PTFE. The coated film has good corrosion and dissolution resistance to a variety of acids, bases and solvents. Its mechanical and frictional properties are also good. Chlorinated polyether powder coating is mainly used in chemical equipment, pipeline lining, equipment shell, etc. Its disadvantage is that it has poor adhesion with metal. The adhesion with metal can be improved by adding additives.
2.6 Latex Powder Coating
Most of the latex powder are vinyl acetate copolymers. The powder coating produced with latex powder is called latex powder coating. It is the most environmentally friendly coating in wall coatings at present.
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