Analysis of the causes of poor curing of powder spraying

In powder coating, there are two reasons why the coating is not cured well. One is that the formula design of the powder coating is unreasonable, and the coating performance does not meet the requirements; the other is that the performance of the powder coating itself is fine, but in powder coating, the coating process control is unreasonable, resulting in the coating performance failing to meet the technical indicators. From the perspective of powder coating, if the matching of resin and curing agent in the formula design is unreasonable, such as the selection of the reaction activity of the resin or the selection of the type and amount of the curing agent; the mass percentage of the filler or the volume concentration is too large, these problems will affect the physical and mechanical properties of the coating. From the perspective of the powder coating process, there are several reasons that affect the poor curing of the coating.

1. The baking temperature of the baking furnace fails to reach the baking temperature required by the powder coating.

Although the control temperature of the baking furnace is easy to reach the design temperature or the baking temperature required by the powder coating when it is not loaded, under full load, due to insufficient total heat supply, it may not always reach the design temperature or the baking temperature required by the powder coating.

This problem is more likely to occur when the temperature of the baking furnace does not reach the baking curing temperature of the powder coating. When the temperature of the baking furnace does not 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 extending the baking and curing time.

2. In the baking furnace, the baking and curing time does not reach the baking time required by the powder coating.

In the baking conditions of powder coating, the baking time refers to the baking time calculated after the coated object reaches the baking temperature, not the time calculated after the coated object is placed in the baking furnace.

The thicker the material of the coated object and the more parts are hung, the greater the heat capacity of the coated object, and the longer it takes for the coated object to heat up to the control temperature. If the effective baking time is not enough, the coating film is not completely cured, and the physical and mechanical properties of the coating film cannot meet the requirements. Therefore, in powder coating, it is best to use a furnace temperature tracking meter to measure the temperature change of the coated object in the baking furnace under full load conditions to determine a reasonable baking and curing temperature and time, so as to ensure the complete curing of the coating film and the physical and mechanical properties of the coating film.

3. The surface treatment of the coated object is not good.

The oil stains on the surface of the coated object are not cleaned, the scale or rust is not removed, or the quality of the phosphating film is not good, and there are many phosphating liquid residues on the surface. In this case, the adhesion between the coating and the substrate is not good after powder coating, and the impact resistance of the coating is also poor. This problem is solved by improving the surface treatment quality of the coated object.

4. In terms of coating performance inspection, it should be carried out strictly in accordance with the test temperature and coating thickness conditions specified in the product standard. When the coating thickness is thin and the test temperature is higher than the specified temperature, these physical and mechanical properties are easy to pass. If you want to accurately measure the coating performance, it is better to test it under the conditions specified in the standard or close to the conditions.

5. Here we should also consider that the baking and curing temperature is too high. When the baking time is too long, the color of the coating changes due to the thermal aging of the coating, and the physical and mechanical properties of the coating, such as flexibility and impact resistance, decrease. Therefore, too high a baking and curing temperature and too long a time are also unfavorable to the physical and mechanical properties of the coating.

In powder spraying, the baking curing temperature and time of powder coating play a decisive role in the curing performance of the coating. Therefore, it is necessary to conduct multiple tests and reasonably classify the objects to be sprayed to determine the number and arrangement of the hanging parts, as well as the corresponding baking temperature and time, in order to ensure the quality of the coating products.