Since the advent of powder coatings in the early 1970s, these coatings have gained worldwide attention due to their advantages such as complete solvent-free nature, the ability to fully form a coating, high coating efficiency, and excellent comprehensive performance in protection and decoration. As a result, they have experienced rapid development. Metal profiles, with their excellent durability, decorative properties, and processing and forming capabilities, are widely used in various aspects of buildings. Aluminum profiles, due to their excellent processing performance and light weight, account for over 80% of the metal profiles. The application of powder coatings in aluminum profiles has seen a rapid increase. 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, the surface treatment methods for aluminum profiles mainly include anodizing, electrophoretic coating, and powder spraying. Each method has its own advantages and occupies a considerable market share. In the coating process of aluminum profiles, the representative powder coating types include epoxy type, polyester type, acrylic type, and silicone resin powder coatings, etc. For application, such as some aluminum frames, doors and windows, balconies, corridors, partition boards and other high-corrosion-resistant aluminum profiles, most of them adopt polyester and acrylic powder coatings. 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 primer coatings. 

2. Types and Properties of Aluminum Profile Powder Coatings 

Currently, the most commonly used powder coating for aluminum profiles is the weather-resistant polyester powder coating. The polyester resins used in powder coatings are mostly saturated types. Generally, we classify them into two major categories based on the structure of their terminal groups: terminal carboxyl groups and terminal hydroxyl groups. 

The number average molecular weight of the carboxyl-containing polyester ranges from 2000 to 8000, and the acid value is from 20 to 100 mgKOH/g. Among them, medium and high acid values (45-85) are generally used in epoxy/polyester mixed type powder coatings, while low to medium acid values (20-45) of the polyester are prepared with triisocyanurate glycidyl ester (TGIC) and hydroxyamide as curing agents to produce pure polyester powder coatings with excellent weather resistance. 

The weather resistance performance of polyester/TGIC powder coatings, classified according to the Florida natural exposure test results, can divide this system's powder coatings into three categories: 

1) Standard type weather-resistant powder coating (can withstand exposure to Florida's harsh conditions for 1-2 years as per the standard test) 

2) Improved weather-resistant powder coating (can withstand exposure to Florida's harsh conditions for 2-3 years as per the standard test)