From the perspective of pure polyester powder coating process, the following are some reasons that affect the poor curing of the coating film:
Powder Coating
The baking temperature of the oven fails to reach the required baking temperature for the powder coating.
This problem is more likely to occur, especially in northern regions where workshop temperatures are low in winter. If the oven insulation is poor, the temperature of the material being coated is low before entering the oven, and the material has thick walls and a large heat capacity.
This problem is more likely to occur when the oven temperature does not reach the powder coating's baking and curing temperature.
When the oven temperature does not reach the powder coating's baking and curing temperature, this can be addressed by increasing the heating power or extending the baking and curing time.
The baking and curing time in the oven does not reach the required baking time for the powder coating.
In powder coating baking conditions, the baking time refers to the baking time calculated after the material being coated reaches the baking temperature, not the time calculated from the moment the material is placed in the oven.
The thicker the coating material and the more components it supports, the greater its heat capacity, and the longer it takes to heat up to the controlled temperature.
In a baking oven of a given length, with a constant conveyor chain speed, the effective baking time is shorter. If the effective baking time is insufficient, the coating will not cure completely, and its physical and mechanical properties will not meet requirements.
Therefore, in powder coating, a furnace temperature tracking instrument is used to measure the temperature change of the coated material in the baking oven under full load conditions to determine a reasonable baking and curing temperature and time. This ensures complete curing of the coating and guarantees its physical and mechanical properties.
Poor surface preparation of the coated material:
If oil stains, oxide scale, or rust are not thoroughly cleaned from the surface of the coated material, or if the phosphating film is of poor quality and contains residual phosphating solution, etc.,
In such cases, the adhesion between the powder-coated film and the substrate will be poor, resulting in poor impact resistance. This problem can be solved by improving the surface preparation quality of the coated material.
In coating performance testing, the test should be conducted strictly according to the test temperature and coating thickness specified in the product standard.
Generally, when the coating thickness is thicker than specified and the test temperature is lower than specified, the coating's impact strength, flexibility, cupping test, and adhesion properties will be poor and difficult to pass.
However, when the coating thickness is thinner and the test temperature is higher than specified, these physical and mechanical properties are easier to pass. To accurately determine coating performance, it is best to conduct the test under conditions specified in the standard or close to these conditions.
From the perspective of ensuring product quality, testing coating performance indicators under relatively stringent conditions is crucial to guaranteeing the quality of the coated product.
Excessive Baking and Curing Temperature
When baking time is too long, the coating's color changes due to thermal aging, and its flexibility, impact strength, and other physical and mechanical properties decrease. Therefore, excessively high baking and curing temperatures and excessively long times are also detrimental to the physical and mechanical properties of the coating.
In powder coating, the baking and curing temperature and time of the powder coating play a decisive role in the coating's curing performance. Powder coating manufacturers - Therefore, it is essential to conduct multiple trials and properly classify the objects to be coated to determine the quantity and arrangement of hangers, as well as the corresponding baking temperature and time, in order to ensure the quality of the coated products.