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How Can Powder Coating Prevent Caking?

Aug 22, 2020

The powder coating has a tendency to agglomerate at a certain temperature, which is mainly caused by the resin and leveling agent in the powder coating being softened by heat. The powder coatings produced by our company are thermosetting powder coatings, that is, the resin as the main film-forming material is an organic polymer with a relatively low molecular weight. These resins have a physical property. At lower temperatures, they appear as hard and brittle glass. When the temperature rises to a certain level, the resin begins to transform into a state with a certain degree of elasticity and adhesion. Temperature, the resin returns to the non-adhesive glass state, the temperature at which the glass state and the viscoelastic state of the resin transition mutually is called the glass transition temperature of the resin. Different resins have different glass transition temperatures. For example, the glass transition temperature of epoxy resin and polyester resin is about 50 degrees Celsius, the glass transition temperature of brightener (701) is about 30 degrees Celsius, and the glass of liquid leveling agent The degree of chemistry is below zero degrees Celsius. The greater the amount of material with low glass transition temperature in the powder coating formulation, the lower the glass transition temperature of the system.

According to experts from China Epoxy Network (China Epoxy Industry Online) www.epoxy-e.cn, the determination of glass transition temperature requires specialized large-scale equipment, and general powder coating manufacturers do not have such expensive equipment. We cannot grasp the glass transition temperature of the powder system in time during the production process. Therefore, during production, the glass transition temperature of the powder system is positioned at about 40 degrees Celsius, and this temperature is set as the safe temperature for powder coating agglomeration. Then in production (and during product storage and transportation), use this as a standard, and relevant personnel should strengthen the random inspection of product agglomeration when the temperature is close to and above this temperature. At present, it has entered the summer production stage. The rising temperature will make it easier for powder coating products to agglomerate. So how to prevent the agglomeration of powder coatings during work? First, we must establish a concept: it is a natural law for powder coatings to agglomerate at a certain temperature. To prevent the powder coating from agglomerating, the powder coating product must be below its glass transition temperature during the whole process of powder coating production, such as grinding, packaging, storage, and transportation. Based on this point of view, there are the following solutions.

In the production of polyester resin, select some alcohols or acids that can increase its glass transition temperature, or reduce the amount of alcohol that can reduce the glass transition temperature of the resin to increase the glass transition temperature of the polyester resin. According to experts from China Epoxy Network (China Epoxy Industry Online) www.epoxy-e.cn, in addition to reducing the use of low glass transition temperature polymers in powder coating formulation design, such as leveling agents and brighteners, Ensure that the glass transition temperature of the powder coating system will not decrease; in terms of production, the broken pieces from the steel belt should be fully cooled before entering the milling process. When milling, the feed speed should be appropriately reduced, and the induced air volume should be increased. The imported air is equipped with air-conditioning to control the temperature of the grinding powder. However, if the crushed flakes cannot be cooled down before milling, the latter means will not play a good role. The method of forced cooling of the crushed flakes can be considered for low-temperature treatment, which is more effective than installing air conditioning; In addition, anti-caking additives can be added, such as nano silica (VK-SP15) or nano aluminum oxide (VK-L20M) powder to prevent adhesion between powder particles. Anti-caking agents are generally ground at the same time as the broken flakes. Powder works best. Nano aluminum oxide (VK-L20M), nano silica (VK-SP15) Application range: thermosetting powder coating: epoxy resin, polyester, acrylic resin.

Examples include epoxy powder coatings, polyester powder coatings, acrylate powder coatings, etc.; thermoplastic powder coatings: thermoplastic powder coatings include polyethylene, polypropylene, polyester, polyvinyl chloride, chlorinated polyether, polyamide, and cellulose , Polyester series. Examples include polyvinyl chloride powder coatings, polyethylene powder coatings, nylon powder coatings, fluororesin powder coatings, latex powder coatings, etc. Nano aluminum oxide (VK-L20M) use characteristics: Nano aluminum oxide (model VK-L20M) is used in powder coatings, which can increase the bulkiness of powder coatings and have a good anti-caking effect. It has good storage properties for powder coatings used in high temperature and high humidity environments. The addition amount is generally 0.2-0.5%. Nano-aluminum oxide can improve the charging performance of the powder, especially when friction charging spraying is used, it can significantly improve the powder loading rate and solve the problem of dead corners, and at the same time, it can improve the gloss of the powder coating. Degree has no effect. Using any single method can not effectively prevent the agglomeration of powder coatings. Excessive use of one method will bring other disadvantages to powder coatings. The use of a variety of methods for scientific cooperation can effectively prevent the agglomeration of powder coatings.