What is the best solution for powder coatings to prevent caking
Powder coatings will be caking under certain temperature. This is because of the constituent in the coatings, such as resin, leveling agents or other materials that are softened by heating up. The powder coatings we produced are all thermosetting powder coatings. The main film-forming component is resin, which is organic polymer with lower polymer. These resins have a type of physical performance, that is, under the lower temperature environment, it appears as hard as glass, but once level up the temperature to a certain degree, the resins will turn flexible with adhesion. If the temperature is lower than this degree, it will turn back to the glass-like state without adhesion. The changing of the temperature of this phenomenon is called glass transition temperature of resin. Different resin has different glass transition temperature, 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 transition temperature of liquid leveling agent is minus degree Celsius. The more amount of materials with low glass transition temperature, the lower the glass transition temperature it is in the formulation of the powder coatings.
First we have to set up an idea: powder coating caking is the laws of nature under the certain temperature. To prevent powder coating caking, it must be stored in the lower glass transition temperature environment while producing, packing, storing, transmitting.
Below are the solutions according to this idea:
1）1. During the production of polyester resin, select some alcohol or acid that is able to level up the glass transition temperature, or reduce the alcohol amount that would lower down the glass transition temperature, to raise the glass transition temperature of polyester resin.
2）Reduce the amount of glass transition temperature compounds in powder coating formulation design, for example, leveling agent and brightening agent, this is to make sure that the glass transition temperature won’t lower down in powder coating system.
3）For production aspect, the broken pieces coming off the steel belt should be fully frozen then to the grinding process. While grinding, the speed should be properly lowered in the right time, boost the induced air volume, and install air-conditioning for imported wind to control the temperature of grinding. However, if the pieces couldn’t be frozen before grinding, the process after won’t be any good. In the circumstances, the broken pieces could be frozen in a compulsory way to lower down the temperature. This is a more effective way than installing air-conditioning.
Secondly, anti-caking additives can be added, such as silica (VK-SP15) or nano aluminum oxide (VK-L20M) micropowder, to prevent the adhesion between powder particles. Generally, if anti-caking agent grinds together with broken pieces all at once will meet the best effect.
The application range of silica (VK-SP15) and nano aluminum oxide (VK-L20M):
Thermosetting powder coatings: epoxy resin, polyester, acrylic resin. For example, epoxy powder coatings, polyester powder coatings, acrylic powder coatings, etc.
Thermoplastic powder coatings: Polyethylene, polypropylene, polyester, polyvinyl chloride, chlorinated polyether, polyamide, cellulose, polyester. For example, polyvinyl chloride powder coatings, polyethylene powder coatings, nylon powder coatings, fluorine resin powder coatings, latex powder coatings, etc.
The application features of nano aluminum oxide (VK-L20M):
Nano aluminum oxide (VK-L20M) is applied to powder coatings to enhance the bulkiness of powder coatings with good anti-caking effect. Good storage for the powder coatings under high temperature or humidity. Regularly the additional level is between 0.2%-0.5%. Nano aluminum oxide can boost the electrified performance of powder coatings, especially while using friction electrified spraying, it could obviously boost the powder rate and solve the problems of the edges, meanwhile, there is no effects on the glossiness of powder coatings.
Using either one method is not going to prevent caking of powder coating effectively. If over using one method will bring other disadvantages of powder coatings. Using multiple methods and collaborating them in a scientific way can effectively prevent caking of powder coatings.