The main reason for powder coating caking
Considering the external factors here, the ambient temperature is higher than 30 degrees; the composition analysis of the powder coating shows that the resin glass transition temperature is lower than 60°C, the leveling agent and brightener are excessive in the formula, and the powder coating contains more ultrafine powder. From these aspects, some commonly used anti-caking methods of powder coatings are introduced below.
Selection of raw materials
Adjust the resin curing agent and the ratio of pigments and fillers, and select a base material with a higher glass transition temperature of the resin and curing agent composition. The choice of polyester resin is very important. For example, terephthalic acid in the monomer has better anti-agglomeration and weather resistance than phthalic acid. In actual use, agglomeration of polyester resin is often found. The proportion of filler in the agglomeration formula is large, and the possibility of powder agglomeration becomes less.
In the formulation design process, additives that affect the glass transition temperature and storage stability should be added as little as possible, such as leveling agents, wax matting agents and accelerators.
Adding an anti-caking agent can improve the porosity of the powder coating, reduce the angle of repose of the powder coating, and make the powder difficult to agglomerate. After adding, adjusting the affinity and cohesion between the film-forming substances in the powder coating can improve the anti-caking temperature, storage stability and dry powder fluidity of the powder coating. In addition, when electrostatic powder spraying, the powder coating is not easy to block the spray gun.
Externally add fumed silica, alumina and other additives with large specific surface area and strong hygroscopicity to make powder coating particles form a barrier, reduce the chance of powder coating particles collision and agglomeration, reduce mutual attraction and friction between powder coating particles, and prevent particles The mutual contact between the powder coatings is not easy to agglomerate.
Production process control
The extruded sheet should be cooled to room temperature and sealed, and 10% of the space should be reserved; the crushing environment should be controlled within 30 degrees of room temperature, humidity below 70%, and cooling and dehumidification are required to go up; under the premise of not affecting the coating, the powder The particle size can be coarsened, and there are many ultra-fine powders in the powder. In a high temperature and high humidity environment, powder agglomeration is prone to occur during spraying.
Requirements for transportation and storage
During storage and transportation, the powder coating will become wet by absorbing moisture in the air, or agglomerate due to pressure and rising ambient temperature. Therefore, the temperature of transportation or storage in the warehouse should not exceed 40°C. Of course, do not squeeze it. Too much weight.