In powder coating, there are two reasons for poor film curing. One is that the formula design of powder coating is unreasonable, and the film performance can not meet the requirements; the other is that the performance of powder coating itself is not bad, but in powder coating, the coating process control is unreasonable, resulting in the film performance failing to reach the technical indicators.
Considering from the powder coating, if the matching of resin and curing agent is not reasonable in formula design, such as the selection of reaction activity of resin or the variety and dosage of curing agent are not reasonable;
The physical and mechanical properties of the film will be affected by the mass percentage or volume concentration of filler.
Considering from the powder coating process, the reasons for the poor curing of the coating are as follows.
1. The baking temperature of baking oven fails to reach the baking temperature required by powder coating.
Although the control temperature of the oven can easily reach the design temperature or the baking temperature required by the powder coating under no load, under the condition of full load, due to the lack of total heat supply, sometimes it can not reach the design temperature or the baking temperature required by powder coating.
Especially in the northern area, the temperature of the workshop is lower in winter. If the heat preservation condition of the oven is poor, the temperature of the coating material before entering the oven is low, and the coating material has thick wall and large heat capacity, this problem is more likely to occur.
When the oven temperature can not reach the curing temperature of powder coating, this problem is more likely to occur.
When the oven temperature can not reach the curing temperature of 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 curing time and other measures.
2. In the baking oven, the curing time can 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 coating reaches the baking temperature, rather than the time when the coating materials are put into the baking furnace.
The thicker the coating material is and the more pieces are hung, the greater the heat capacity of the coated material is, and the longer it takes for the coated material to rise to the control temperature.
In a certain length of baking oven, when the speed of conveyor chain is constant, the effective baking time is shorter. If the effective baking time is not enough, the film curing is not complete, the physical and mechanical properties of the film can not meet the requirements.
Therefore, in powder coating, it is better to use furnace temperature tracking instrument to measure the temperature change of the coating material in the baking furnace under full load condition, so as to determine the reasonable 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 coating is not good.
On the surface of the coating, the oil is not cleaned, the scale or rust is not removed, or the quality of the phosphating film is not good, and many residues of phosphating solution are smeared on the surface.
In this case, the adhesion to the coating film is not good at the same time. This problem is solved by improving the surface treatment quality of the coating.
4. In terms of film performance inspection, it should be carried out in strict accordance with the test temperature and film thickness specified in the product standard.
Generally speaking, the film thickness is thicker than the specified; when the laboratory temperature 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;
However, when the film 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 truly and accurately determine the performance of the film, it must be tested according to the conditions specified in the standard or similar conditions.
From the point of view of ensuring product quality, the coating performance index should be inspected under relatively harsh conditions as far as possible, so as to ensure the quality of coating products.
5. In this case, too high curing temperature should be considered
When the baking time is too long, the color of the film changes due to the thermal aging of the film, and the physical and mechanical properties of the film such as flexibility and impact strength decrease. Therefore, the curing temperature is too high and the curing time is too long.
In powder spraying, curing temperature and time of powder coating play a decisive role in curing performance of coating. Therefore, it is necessary to carry out several tests and reasonably classify the sprayed objects to determine the number and arrangement of hanging pieces, as well as the corresponding baking temperature and time, so as to ensure the quality of coating products.
