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While the range of powder coatings is not as extensive as that of solvent-borne coatings, a considerable number of polymer resins can serve as their film-forming substances. These are broadly classified into two main categories: thermosetting and thermoplastic.

1. Thermosetting Powder Coatings: The High-Performance Mainstream

Thermosetting powder coatings use thermosetting resins as the film-forming material. When heated with a cross-linking agent (hardener), they form a hard, infusible coating. This coating will not soften upon re-exposure to heat like thermoplastics do; instead, it will decompose. The resins used are low-molecular-weight prepolymers with a low degree of polymerization, which grants excellent flow properties, resulting in a smooth, high-quality finish with strong decorative appeal. Once cured, these prepolymers form a cross-linked network, endowing the coating with superior mechanical properties and corrosion resistance. Consequently, thermosetting powder coatings have seen particularly rapid development.

1.1. Epoxy Powder Coatings: Pioneers in Adhesion and Corrosion Resistance

As one of the first thermosetting types to be applied, epoxy powder coatings are renowned for their exceptional adhesion to metal, corrosion resistance, hardness, flexibility, and impact strength. Their formulation is a careful balance of epoxy resin, hardener, pigments, fillers, and additives, where each component influences the final coating properties.

1.2. Polyester Powder Coatings: Exemplary Weatherability and Decorative Finish

Polyester powder coatings offer unique advantages. Their weather resistance and UV stability are significantly better than those of epoxy resins. Furthermore, the polar groups in the polyester resin provide high chargeability during application, leading to excellent transfer efficiency. They also exhibit minimal yellowing during curing, high gloss, good flow, a full finish, and light color, making them ideal for decorative applications. They are widely used on refrigerators, washing machines, instrument housings, furniture, etc.

1.3. Acrylic Powder Coatings: Superior Appearance and Durability

Acrylic powder coatings come in both thermoplastic and thermosetting forms. The thermosetting type is most notable for its excellent weather resistance, color retention, stain resistance, strong adhesion to metal, and outstanding appearance, making it a premium choice for decorative applications.

2. Thermoplastic Powder Coatings: Specialists for Specific Applications

Thermoplastic powder coatings emerged in the 1950s. They melt when heated during application and solidify upon cooling to form a film. This simple process requires no complex curing equipment. They are based on commonly available polymers and often meet performance requirements for many applications. However, they have drawbacks, including high melting temperatures, relatively poor adhesion to metal, and limited coloring potential. Despite this, common thermoplastic powders exhibit distinct, valuable properties, securing their share in the coatings market.

2.1. Polyvinyl Chloride (PVC) Coatings: The Cost-Effective Choice

PVC is one of the most inexpensive polymers produced on anindustrial scale. PVC coatings offer excellent solvent resistance, good resistance to water and acids, high impact strength, salt spray resistance, prevention of food contamination, and high dielectric strength. They are mainly used for coating metal mesh, steel furniture, and chemical equipment.

2.2. Polyethylene (PE) Coatings: Corrosion Protection Specialists

Polyethylene coatings provide excellent chemical resistance, corrosion protection, electrical insulation, and UV resistance. Their disadvantages include relatively low mechanical strength and poor adhesion to substrates. Typical applications include chemical tanks, pump impellers, pipe linings, and automotive parts.

2.3. Nylon (Polyamide) Coatings: Experts in Wear Resistance and Food-Safe Applications

The amino groups in the nylon molecular chain form hydrogen bonds, leading to generally high melting points. Nylon coatings offer high mechanical strength, impact resistance, hardness, excellent abrasion resistance, a low friction coefficient, and low dust pick-up. They are also inert to mold and bacteria, and are non-toxic and odorless, making them suitable for food industry components, drinking water pipes, and marine applications due to their resistance to salt water.

2.4. Fluororesin Coatings: Peak Performance for Extreme Environments

Several fluoropolymers can be used, including Polytetrafluoroethylene (PTFE), Polychlorotrifluoroethylene (PCTFE), and Polyvinylidene Fluoride (PVDF).

PTFE: Known as the “Plastic King,” it has a very high melting point (327°C), can be used continuously from -250 to 250°C, and offers exceptional chemical resistance (even to aqua regia), excellent dielectric properties, and a very low friction coefficient. It is used in chemical anti-corrosion coatings, non-stick pans, and bearings.

PCTFE: Less expensive and processable at lower temperatures than PTFE, with a maximum service temperature of 130°C. Its resistance to alkalis and hydrofluoric acid surpasses that of acid-resistant enamel, and its resistance to hydrochloric acid, dilute sulfuric acid, and chlorine is better than stainless steel. It is widely used in chemical plants.

PVDF: The key advantage is exceptional weatherability and resistance to degradation when exposed outdoors, along with low dirt pickup, helping to maintain gloss.

2.5. Chlorinated Polyether Coatings: Chemically Stable Specialty Material

Chlorinated polyether exhibits outstanding chemical stability, with resistance to a wide range of acids, alkalis, and solvents, second only to PTFE. It also has good mechanical and frictional properties. Its main application is for lining chemical equipment and pipes. A drawback is poor adhesion to metal, which can be improved with additives.

2.6. Latex Powder Coatings: The Eco-Friendly Choice for Walls

Latex powder is produced by spray-drying emulsions, often vinyl acetate copolymers. Coatings made from these powders are mixed with water on-site, representing one of the most environmentally friendly options for wall coatings.