Factors Affecting Weather Resistance of Powder Coatings
1. Selection of powder coating formulation system and resin
There are many classification methods of powder coatings. The common varieties in the market are pure polyester type, pure epoxy type and epoxy polyester type. The output of these three types of powder coatings accounts for more than 80% of the entire industry. Generally, indoor powder coatings do not have weather resistance. Due to the influence of the molecular structure of functional groups and the compactness of the coating film, they cannot resist the strong solar radiation in nature. "Indoor powder"; in many practical applications, pure polyester and polyurethane powder coatings show excellent performance in weathering resistance. This type of powder coating is often used in open places, especially in harsh environments Among them, it is customarily called "outdoor powder". The output of pure epoxy powder coating is the least among the three. The main defects are long curing time and slow reaction speed, which are affected by the ether bond in epoxy resin. It plays an important role in the field of heavy anti-corrosion and chemical corrosion resistance. effect. The reason why powder coatings exhibit different properties is that the number, number, variety and relative molecular weight of functional groups in the resin play an important role that needs no repeating.
2. Powder coating construction process
Powder coatings are mainly composed of resins, curing agents, additives, pigments and fillers, and are produced through processes such as melt extrusion, tableting, crushing, and screening. Customers protect the workpieces by pretreatment, spraying, and baking into films Decorative substrate. Different types of powder coatings have different baking times and temperatures, which depend on the activation energy of the curing agent. The powder coating can protect the substrate only after forming a dense coating film. When the curing temperature and time are not reached or the heat energy absorbed by the powder coating exceeds its heat resistance, the coating can also coat the surface of the substrate to play a decorative role. , but this type of coating film does not have weather resistance.
3. Selection of powder coating pigments
The weather resistance test of powder coatings is usually measured by color difference and gloss retention. The gloss retention of the coating film depends entirely on the resin used in powder coatings, while the color difference is related to the pigments and resins in the powder coating formulation. Pigments used in powder coatings must first meet the requirements of the powder coating baking process, followed by the light resistance of the pigment itself, and thirdly, the performance of the pigment itself must also meet the requirements of the powder coating application field.
