Fake drying, insufficient baking, slow drying, low hardness

Instructions

The paint film fails to completely dry and solidify within the specified time after drying (self drying or baking), and there is a feeling of moisture regain when touching the paint film. The overall hardness of the paint film is low, and it has not reached the specified hardness or there is a phenomenon of surface drying but not drying. Severe cases may experience rebound after prolonged exposure to sunlight.

Related reasons

1. The temperature for self drying or drying does not meet the requirements. Generally speaking, the drying speed of two-component coatings will be greatly reduced below 10 degrees Celsius, and the drying process of the coating will be extremely slow or even stopped. For every 10 degrees Celsius decrease in temperature, the chemical cross-linking time doubles.

2. The oven has reached the set temperature after heating up, but it has not been kept warm for a period of time before the heating stops.

3. Excessive thickness during a continuous spraying process resulted in abnormal accumulation of solvents within the coating. Especially when using ordinary coatings for continuous spraying, 2-3 coats can be sprayed according to regulations. However, in order to pursue a better appearance or leave room for polishing, 4 or 5 coats are sprayed. Although the paint film is thicker, the drying performance of the coating is greatly reduced, making it difficult to meet the drying requirements within the specified time.  

4. The curing agent and diluent are not used together. When using curing agents, diluents, and other auxiliary materials, the principle of matching must be adhered to, and different brands of auxiliary materials cannot be used interchangeably. Even products of the same brand should be used according to the manufacturer's regulations.  

5. Poor ventilation or high humidity in self drying areas can cause solvents in the coating to not evaporate properly, resulting in a significant decrease in the drying speed of the coating.

6. Poor cleaning of the coated bottom surface, leaving substances such as wax, oil, and moisture that affect drying. In small-scale repairs, many drying issues are caused by this.

7. Excessive high boiling point solvents were added to the coating. In order to improve leveling or prevent the phenomenon of "whitening" on rainy days, excessive high boiling point solvents such as "cyclohexanone" were added. These solvents evaporate very slowly and remain in the coating for a long time, affecting drying.

8. Insufficient or excessive amount of curing agent. Curing agents are not optional in two-component coatings. They undergo cross-linking reactions with the resin in the coating in a certain proportion to form a paint film. Insufficient or excessive curing agent can cause poor drying. It must be added according to the requirements of the coating regulations.

9. Diluents contain excessive amounts of water, alcohol, and acid. This situation is more common in situations where cheap substitute thinners are used. Especially when using various nitro diluents instead of 2K diluent. Such thinners not only contain a large amount of impurities such as water and alcohol, but may also contain substances that react with the curing agent, causing abnormal drying of the coating.  

10. Improper polishing. Especially before the coating is completely dry, that is, before the solvent in the coating is completely evaporated, starting polishing can not only cause the surface of the paint film to lose its luster, but also cause abnormal drying of the coating due to the corrosive effect of the solvent in the wax solution.

11. Some incorrect spraying processes result in incomplete drying or false drying of coatings. For example, in the secondary coating method of plain paint, if 2K plain paint is used as the base without adding curing agent, and then clear paint is sprayed on top, the result of this operation is that the paint film is not dry.

12. Errors occurred during the color matching process. A typical phenomenon is the softening of the paint film caused by insufficient resin, which is often due to insufficient resin replenishment during the fine-tuning process or incorrect resin calculation during formula addition. This situation is not common. In addition to appearing as a soft paint film, it is usually accompanied by low gloss, easy scratching and peeling, and fragments that are prone to powdering. If resin is used incorrectly in color matching, such as using 2K resin in a second coat of solid paint, there may also be a phenomenon of not drying for a long time.

Preventive measure

Some of the reasons for abnormal drying of paint films mentioned above are human factors. As long as the correct operating procedures are followed during construction, it can be effectively avoided. Some are limiting factors that need to be addressed after improving working conditions. But the following basic operational requirements must be followed:

1. Coatings and auxiliary materials must be used together.

2. Select auxiliary materials with different drying speeds according to different seasons.

3. Standard containers are required to be used for coating proportioning, and additives should be added according to the scale scale.

4. Maintain good ventilation and circulation in the paint booth or spraying area.

5. Do not use cheap and inferior diluents.

6. The stirring work of coatings after adding curing agents and diluents cannot be ignored.

7. Master the correct requirements for coating performance and do not force excessive coating.

8. Polish after the specified polishing time.

9. Conditional repair shops can use infrared drying mode, which utilizes the principle of heating from the inside out of infrared drying to completely solve the problem of coating drying.

Solution

1. If it is seriously not dry, or if there is wire drawing and sticking, or if the curing agent is forgotten to be added, or if the resin is added incorrectly, remove the topcoat to the bottom, redo the bottom, and spray. When removing such problematic topcoats, they can be wiped off with thinner problematic topcoats, then cleaned with degreaser and re sprayed.

2. In less severe cases, where the coating is only drying slowly, it can be further heated to 60 degrees Celsius in the oven for 45 minutes to continue drying.  

3. In most cases, the problematic bottom surface can be sealed with isolation primer and then repainted with topcoat.