How to prevent caking of powder coating
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Powder coatings tend to agglomerate at a certain temperature, which is mainly caused by the softening of resin, leveling agent and other materials in powder coatings when heated. 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 low molecular weight. These resins have a physical property. At a lower temperature, they show a hard and brittle glass state. When the temperature rises to a certain extent, the resin starts to change into a state with certain elasticity and adhesion. Below this temperature, the resin returns to a non adhesive glass state. The temperature at which the glass state and viscoelastic state of the resin change 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 ℃, the glass transition temperature of brightener (701) is about 30 ℃, and the glass transition temperature of liquid leveling agent is below zero ℃. The higher the amount of material with low glass transition temperature in powder coating formula, the lower the glass transition temperature of the system. To measure the glass transition temperature, a special large instrument is required. General powder coating manufacturers do not have such expensive instruments and equipment. We cannot grasp the glass transition temperature of the powder system in time during the production process. Therefore, the glass transition temperature of the powder system is set at about 40 ℃ during production, which is the safe temperature for the caking of powder coating. Then in the production (as well as product storage and transportation), the relevant personnel shall strengthen the sampling inspection of product agglomeration when the temperature is close to or higher than this temperature. At present, it has entered the production stage in summer, and the rising temperature will be more likely to cause the caking problem of powder coating products. So how to prevent caking of powder coating in work?
First of all, we should establish a concept that it is a natural law for powder coatings to agglomerate at a certain temperature. To prevent caking of powder coating, the powder coating product must be below its glass transition temperature during the whole process of powder grinding, packaging, storage and transportation of powder coating production.
According to this view, there are the following solutions:
1) In the production of polyester resin, select some alcohols or acids that can increase the glass transition temperature, or reduce the amount of alcohols that can reduce the glass transition temperature of the resin to increase the glass transition temperature of polyester resin.
2) In the formulation design of powder coatings, reduce the use of polymers with low glass transition temperature, such as leveling agents and brighteners, to ensure that the glass transition temperature of the powder coating system will not decrease.
3) In terms of production, the broken pieces on and off the steel belt shall be fully cooled before entering the grinding process. During grinding, the feeding speed shall be appropriately reduced, the induced air volume shall be increased, and the inlet air shall be equipped with air conditioner to control the grinding temperature. However, if the crushed flakes cannot be cooled down before grinding, the latter means will not play a good role. It is more effective to consider the method of forced cooling of crushed flakes for low temperature treatment than to install air conditioner.
In addition, anti caking additives, such as nano silica (VK-SP15) or nano aluminum oxide (VK-L20M) powder, can be added to prevent adhesion between powder particles. Generally, anti caking agents and broken sheets can be grinded at the same time with the best effect.
Application scope of nano aluminum oxide (VK-L20M) and nano silicon dioxide (VK-SP15):
1. Thermosetting powder coating: epoxy resin system, polyester system, acrylic resin system. For example, epoxy powder coating, polyester powder coating, acrylate powder coating, etc.
2. Thermoplastic powder coating: thermoplastic powder coating includes polyethylene, polypropylene, polyester, polyvinyl chloride, chlorinated polyether, polyamide series, cellulose series and polyester series. E.g. PVC powder coating, polyethylene powder coating, nylon powder coating, fluororesin powder coating, latex powder coating, etc
Use characteristics of nano aluminum oxide (VK-L20M):
Nanometer aluminum oxide (model VK-L20M) used in powder coatings can improve the puffiness of powder coatings and have good anti caking effect. For powder coating used in high temperature and high humidity environment, it has good storage property. The addition amount is generally 0.2-0.5%. Nanometer aluminum oxide can improve the electrification performance of the powder, especially when using friction electric spraying, which can significantly improve the powder loading rate and solve the problem of dead angle, while having no effect on the glossiness of the powder coating.
Any single method can not effectively prevent the caking of powder coatings, and excessive use of one method will bring other disadvantages to powder coatings. The use of a variety of scientific methods can effectively prevent the caking of powder coatings