In powder coating coating, there are two main reasons for poor curing of the coating film, one is that the formula design of the powder coating is unreasonable, and the coating performance does not meet the requirements; Second, the performance of the powder coating itself is not a problem, but in the coating process, the coating process control is unreasonable, resulting in the coating film performance failing to meet the technical indicators.

1. Consider from the aspect of powder coating formula design

If the matching of resin and curing agent is unreasonable in formula design, such as the reactivity selection of resin or the selection of the variety and dosage of curing agent is unreasonable, the mass percentage content or volume concentration of the filler is too large, etc., these problems will affect the physical and mechanical properties of the coating film, resulting in poor curing of powder coating in coating.

2. Consider the powder coating process

The reasons why the powder coating process affects the poor curing of the coating film 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, under full load, due to the insufficient total heat supply, sometimes it is not possible to reach the design temperature or the baking temperature required by the powder coating.

Especially in the northern region, the temperature of the workshop in winter is low, if the insulation conditions of the baking oven are poor, the temperature before the coated object enters the baking oven is low, and the coated material has thick walls and large heat capacity, this problem is more likely to occur.

When the oven temperature cannot reach the baking and curing temperature of powder coating, the temperature standard problem can be solved by increasing the heating power; In addition, the curing purpose can also be achieved by extending the baking curing time!

(2) In the baking oven, the baking curing time does not meet 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 coated object reaches the baking temperature, not the time that begins to be calculated after the coated object is placed in the baking oven.

When the thicker the coated material 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.

In ovens of a certain length, the shorter the effective baking time when the speed of the conveyor chain remains constant. If the effective baking time is not enough, the curing of the coating film is incomplete, 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 tester to determine the temperature change of the coated object in the baking oven under full load conditions to determine the reasonable baking and curing temperature and time, so as to ensure the complete curing of the coating film, and also ensure the physical and mechanical properties of the coating film.

(3) The surface treatment of the coated object is not good

If the oil on the surface of the coated object is not cleaned, the oxide scale or rust is not cleaned, or the quality of the phosphating film is not good, and many phosphating liquid residues are stained on the surface, the adhesion between the coating film and the substrate will be affected after powder coating.

At the same time, it will also lead to poor impact resistance of the coating film, which must be solved by improving the surface treatment quality of the coated object.

(4) In terms of film performance inspection, it should be carried out in strict accordance with the test temperature and coating 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 impact strength, flexibility, cupping test and adhesion of the coating film are poor, and it is not easy to pass;

When the coating film thickness is thin and the test temperature is higher than the specified temperature, these physical and mechanical properties are easy to pass. From the perspective of ensuring product quality, try to test the performance indicators of the coating film under more demanding conditions in order to ensure the quality of the coating product without fail.

In addition, it is also necessary to consider that when the baking curing temperature is too high and 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 decrease. Therefore, the baking and curing temperature is too high, and the time is too long is also unfavorable to the physical and mechanical properties of the coating film.

In powder coating spraying, the baking curing temperature and time of powder coating play a decisive role in the curing performance of the coating film. Therefore, it is necessary to reasonably classify the sprayed objects after many tests to determine the number and arrangement of pendants, as well as the corresponding baking temperature and time, in order to ensure the quality of the coating product.