Since the emergence of powder coatings in the early 1970s, powder coatings have received widespread attention worldwide due to their complete absence of solvents, ability to be fully converted into coatings, high coating efficiency, and good comprehensive performance in protection and decoration, leading to rapid development. Metal profiles are widely used in various aspects of buildings due to their excellent durability, decorative properties, and processing formability. Aluminum profiles account for more than 80% of metal profiles due to their excellent processing performance, light weight, and other characteristics. The application of powder coatings in aluminum profiles has grown rapidly. Currently, the application of powder coatings in aluminum profiles has expanded from Europe to the Americas, Australia, Far East, Middle East, and Africa

At present, there are generally three surface treatment methods for aluminum profiles: anodizing, electrophoretic coating, and powder coating. Each method has its own advantages and occupies a considerable market share. In the coating of aluminum profiles, representative types of powder coatings include epoxy, polyester, acrylic, and silicone resin powder coatings. As applications, such as some aluminum frames, doors and windows, balconies, corridors, partition boards, and other highly corrosion-resistant aluminum profiles, polyester and acrylic powder coatings are mostly used. In addition, due to the excellent adhesion and corrosion resistance of epoxy resin powder coatings, but poor weather resistance, they are generally used indoors or as primers

2. Manufacturing types and properties of powder coatings for aluminum profiles

At present, the powder coating commonly used in aluminum profiles is weather resistant polyester powder coating. Most of the polyester resins used in powder coatings are saturated, and we can usually divide them into two categories based on their end group structure: carboxyl end groups and hydroxyl end groups.

The number average molecular weight of carboxyl terminated polyester is between 2000-8000, and the acid value ranges from 20-100mgKOH/g. Among them, medium to high acid values (45-85) are generally used in epoxy/polyester hybrid powder coatings, while low to medium acid values (20-45) of polyester are treated with isocyanurate diglycidyl ester (TGIC) and hydroxylamide as curing agents to prepare weather resistant pure polyester powder coatings.

The weather resistance of polyester/TGIC powder coatings can be classified into three categories based on the results of Florida sun exposure tests:

1) Standard weather resistant powder coating (can pass the Florida exposure test standard for 1-2 years)

2) Improved weather resistant powder coating (can pass the Florida exposure test standard for 2-3 years)

3) Ultra weather resistant powder coating (can pass the Florida sun exposure test standard for more than 5 years)