Considering powder coatings, if the matching of resin and curing agent is unreasonable in formula design, for example, the choice of reactivity of resin or the selection of type and dosage of curing agent is unreasonable; the mass percentage content or volume concentration of filler is too large, etc. will affect the physical and mechanical properties of the coating film.
Considering the powder coating process, the reasons that affect the poor curing of the coating are as follows.
(1) The baking temperature of the baking oven fails to reach the baking temperature required by the powder coating. Although the control temperature of the baking oven is easy to reach the design temperature or the baking temperature required by the powder coating when there is no load, but at full load, due to the lack of total heat supply, sometimes it may not be able to reach the design temperature or the required baking temperature of the powder coating. The required baking temperature, especially the winter workshop temperature in the northern region is low, if the insulation conditions of the baking furnace are poor, the temperature of the coated object before entering the baking furnace is low, and the coating material has a thick wall and a large heat capacity, it is easier to This problem occurs. This problem is more likely to occur when the oven temperature does not reach the baking and curing temperature of the powder coating. When the temperature of the baking oven cannot reach the baking and curing temperature of the powder coating, on the one hand, it can be solved by increasing the heating power; on the other hand, it can also be solved by measures such as extending the baking and curing time.
(2) In the baking oven, the baking curing time cannot reach the baking time required by the powder coating. In the baking conditions of powder coatings, the baking time refers to the baking time calculated after the object to be coated reaches the baking temperature, rather than the time calculated after the object to be coated is placed in the baking oven. When the material to be coated is thicker and there are more hanging pieces, the heat capacity of the coated object will be greater, and the time required for the coated object to heat up to the control temperature will be longer. In a certain length of baking oven, when the speed of the conveyor chain is constant, the effective baking time is shorter. If the effective baking time is not enough, the coating film is not fully cured, and the physical and mechanical properties of the coating film cannot meet the requirements. Therefore, in powder coating, it is best to use an oven temperature tracking tester to measure the temperature change of the object to be coated in the baking oven under full load conditions, so as to determine a reasonable baking and curing temperature and time, so as to ensure the coating film. The complete curing of the film can also ensure the physical and mechanical properties of the coating film.
(3) The surface of the coated object is not well treated. The oil stain on the surface of the coated object is not cleaned, the oxide scale or rust is not removed, or the quality of the phosphating film is not good, and many phosphating liquid residues are stained on the surface. In this case, the coating film and the substrate after powder coating The adhesion of the coating is not good, and the impact resistance of the coating film is also not good. This problem is solved by improving the surface treatment quality of the coated object.
(4) In terms of coating film performance inspection, it should be carried out in strict accordance with the conditions of test temperature and coating film thickness specified in the product standard. Generally speaking, the thickness of the coating film is thicker than specified; when the temperature of the test chamber is lower than the specified temperature, the performance of the coating film such as impact strength, flexibility, cupping test and adhesion is poor, and it is not easy to pass; but the coating film is not easy to pass. When the thickness is thin and the test temperature is higher than the specified temperature, these physical and mechanical properties are easily passed. If you want to truly and accurately measure the performance of the coating film, it must be tested under the conditions specified in the standard or close to the conditions. From the point of view of ensuring product quality, it is necessary to test the performance indicators of the coating film under relatively harsh conditions as much as possible, so as to ensure the quality of the coating product without fail.
(5) It should also be considered here that when the baking curing temperature is too high, and the baking time is too long, the color of the coating film will change due to the thermal aging of the coating film, and the physical and mechanical properties such as the flexibility and impact resistance of the coating film will be changed. phenomenon of decline. Therefore, too high baking curing temperature and too long time are also detrimental to the physical and mechanical properties of the coating film.
In powder coating, the baking curing temperature and time of the powder coating play a decisive role in the curing performance of the coating film. Therefore, it is necessary to classify the objects to be sprayed reasonably after many tests to determine the number and arrangement of the pendants, as well as the corresponding baking temperature and time, in order to ensure the quality of the painted products.