In the powder coating powder curing bad reasons
Considering from powder coating, if the matching of resin and curing agent in the formulation design is not reasonable, such as the choice of reactivity of resin or the species and dosage of curing agent is not reasonable; the mass percentage content of filler or volume concentration is too large, etc. These problems will affect the physical and mechanical properties of the coating film.
Considering from the powder coating process, the reasons that affect the poor curing of the coating film are as follows.
(1) The baking temperature of the oven fails to reach the required baking temperature of 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 under full load, due to the lack of total heat supply, sometimes it may not reach the design temperature or the baking temperature required by the powder coating, especially in northern areas where the workshop temperature is low in winter, if the insulation condition of the baking oven is poor, the temperature of the coated material before entering the baking oven is low, and the coated material is thick and has a large heat capacity. When the wall is thick and the heat capacity is large, it is more likely to have this problem. When the temperature of the baking oven does not reach the curing temperature of powder coating baking, it is more likely to have this problem. When the oven temperature does not reach the powder coating baking and curing temperature, on the one hand, by increasing the heating power to solve; on the other hand, can also be solved by extending the baking and curing time and other measures.
(2) In the baking oven, the baking and curing time cannot reach the baking time required for powder coatings. In the powder coating baking conditions, the baking time refers to the baking time calculated after the coated material reaches the baking temperature, not the time calculated after the coated material is put into the baking oven. When the coated material is thicker and more pieces are hung, then the heat capacity of the coated material is bigger and the time needed for the coated material to warm up to the control temperature is longer. In a certain length of baking oven, when the speed of the conveyor chain is constant, the effective baking time will be shorter. If the effective baking time is not enough, the coating film will not be cured completely and the physical and mechanical properties of the coating film will not reach the requirements. Therefore, in powder coating, it is best to use the oven temperature tracking meter to determine the temperature change of the coated material in the baking oven under the full load condition to determine the reasonable baking and curing temperature and time, so as to ensure the complete curing of the coating film, and also to ensure the physical and mechanical properties of the coating film.
(3) The surface of the coated material is not well treated. In the coated surface oil is not clean, oxidation or rust is not clean, or phosphate film quality is not good, in the surface stains many phosphate residues, etc., in this case, powder coating after the adhesion of the coating film and the substrate is not good, while leading to the impact resistance of the coating film is also bad. This problem is solved by improving the quality of surface treatment of the coated material.
(4) In the inspection of coating film performance, the test temperature and coating film thickness should be carried out in strict accordance with the product standard. Generally speaking, the film thickness is thicker than specified; when the test room temperature is lower than the specified temperature, the film's impact strength, flexibility, cup burst test and adhesion and other properties are poor and not easy to pass; but the film thickness is thin, the test temperature is higher than the specified temperature, these physical and mechanical properties are easy to pass. If you want to really accurate determination of coating film performance, you must test under the conditions specified in the standard or close to the conditions to be better. From the point of view of ensuring product quality, try to test the coating film performance indicators under more severe conditions in order to ensure the quality of the coating product without fail.
(5) Here we should also take into account the baking curing temperature is too high, baking time is too long, due to the thermal aging of the coating film so that the color of the coating film changes, while the film flexibility, impact strength and other physical and mechanical properties of the phenomenon of decline. Therefore, the baking curing temperature is too high, too long for the same physical and mechanical properties of the coating film is also unfavorable.
In powder coating, powder coating baking curing temperature and time on the curing performance of the coating film plays a decisive role. Therefore, it is necessary to go through several tests and reasonably classify the object to be sprayed in order to determine the number and arrangement of the pegs and the corresponding baking temperature and time in order to ensure the quality of the coating products.
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