Considering from the powder coating, if the matching between the resin and the curing agent is unreasonable in the formulation design, for example, the reactivity selection of the resin or the selection of the type and amount of the curing agent is unreasonable; the mass percentage or the volume concentration of the filler is too large, etc. Will affect the physical and mechanical properties of the film.
Considering the powder coating process, the reasons for the poor curing of the coating film are as follows.
(1) The curing temperature of the baking oven failed to reach the curing temperature required for the powder coating. Although the control temperature of the baking oven is easy to reach the design temperature or the curing temperature required for the powder coating when no load is applied, at full load, sometimes the design temperature or the powder coating solution may not be reached due to insufficient total heat supply. The required curing temperature, especially in the winter workshop, is relatively low. If the holding condition of the curing oven is poor, the temperature of the coated object before entering the baking oven is low, and the wall thickness of the coated material is large and the heat capacity is large, which is more likely to occur this kind of problem. This problem is more likely to occur when the temperature of the baking oven does not reach the curing temperature of the powder coating. When the baking oven temperature does not reach the baking temperature of the powder coating, on the one hand, it is solved by increasing the heating power; on the other hand, it can also be solved by extending the baking curing time,etc.
(2) In the baking oven, the baking curing time does not reach the baking time required for the powder coating. In the baking condition of the powder coating, the baking time refers to the baking time calculated after the coating reaches the baking temperature, and does not refer to the time when the coating is started after being placed in the baking oven. When the material to be coated is thicker, the more pieces are hung, the greater the heat capacity of the object to be coated, and the longer the time required for the object to be heated to control the temperature. In a certain length of baking oven, the effective baking time is shorter when the speed of the conveyor chain is constant. If the effective baking time is not enough, the curing of the coating film is not complete, and the physical and mechanical properties of the coating film are not satisfactory. Therefore, in powder coating, it is better to use a furnace temperature tracking tester to measure the temperature change of the coated object in the baking furnace under full load conditions to determine a reasonable baking curing temperature and time, so as to ensure the coating film. Complete curing, while also ensuring the physical and mechanical properties of the film.
(3) The surface of the object to be coated is not well treated. The oil stain on the surface of the object to be coated is not cleaned, the scale or rust is not cleaned, or the quality of the phosphate film is not good, and many phosphating solution residues are stained on the surface. In this case, the film and the substrate are coated after the powder coating. The adhesion 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 film performance test, it should be carried out in strict accordance with the test temperature and film thickness specified in the product standard. Generally, the thickness of the coating film is thicker than specified; when the temperature of the laboratory is lower than the specified temperature, the impact resistance, flexibility, cupping test and adhesion of the coating film are poor, and it is not easy to pass; These physical and mechanical properties are easily passed when the thickness is thin and the test temperature is higher than the specified temperature. If you want to accurately measure the performance of the film, it must be tested according to the conditions specified in the standard or close to the conditions. From the perspective of ensuring product quality, it is necessary to test the performance index of the coating film under more severe conditions, in order to ensure the quality of the coated product without failure.
(5) Here also need to consider the baking curing temperature be too high, when the baking time is too long, the color of the coating film changes due to the heat aging of the coating film, and the physical and mechanical properties such as flexibility and impact strength of the coating film are also obtained the phenomenon of decline. Therefore, the baking curing temperature too high and the long time is also unfavorable for 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 conduct a number of tests to properly classify the objects to be sprayed to determine the number and arrangement of the pendants, and the corresponding curing temperature and time to ensure the quality of the coated products.