Causes and preventive measures of non drying or poor drying of coatings
Time：2020/09/17 Visits：848
Related statements
False drying, insufficient baking, slow drying and low hardness
Related instructions
The film drying (after self drying or baking) can not be completely dry and solid within the specified time, the film feels moist when touching by hand, and the overall hardness of the film is low, which can not reach the specified hardness or the phenomenon that the surface is dry but the interior is not dry. In severe cases, the phenomenon of back sticking appeared after long time exposure to sunlight.
Related reasons
1. The temperature of self drying or drying does not meet the requirements. Generally speaking, the drying rate of two-component coatings will be greatly reduced below 10 ℃, and the drying process of coatings will be extremely slow or even stop. The time of chemical crosslinking is doubled when the temperature is reduced by 10 ℃.
2. The curing barn reaches the set temperature after heating up, but the heating will stop without holding for a period of time.
3. One time continuous spraying is too thick, resulting in abnormal accumulation of solvent in the film. Especially in the use of common coatings for continuous spraying, according to the requirements can spray 2 to 3 times, but in order to pursue a better appearance or leave margin for polishing, spray 4 or 5 times, so that although the film is thick, but the drying performance of the coating is greatly reduced, it is difficult to meet the drying requirements within the specified time.
4. There is no curing thinner. In the use of curing agent and diluent and other accessories, we must adhere to the principle of matching, can not casually use different brands of accessories to replace each other. Even products of the same brand should be used according to the manufacturer's regulations.
5. The poor ventilation or high humidity in the self drying place cause the solvent contained in the coating can not volatilize normally, and the drying speed of the coating is greatly reduced.
6. Poor cleaning of the coated surface, leaving wax, oil, water and other substances affecting the drying. In the small area repair, there are many drying problems caused by this.
7. Too much high boiling solvent is added into the coating. In order to improve the phenomenon of "whitening" in the flat or rainy days, excessive "cyclohexanone" and other high boiling solvents are added. These solvents volatilize very slowly and remain in the film for a long time, affecting the drying.
8. Insufficient or excessive amount of curing agent. Curing agent is not dispensable in two-component coatings, it is in accordance with a certain proportion of cross-linking reaction with the resin in the coating to form a film. If the curing agent is insufficient or redundant, it will cause poor drying. It must be added according to the requirements of the coating regulations.
9. The diluent contains excessive water, alcohol and acid. This situation is more common in the use of cheap alternative thinner occasions. In particular, various nitro diluents are used instead of 2K diluents. Such thinners not only contain more impurities such as water and alcohol, but also may contain substances that react with curing agent, resulting in abnormal drying of coatings.
10. Improper polishing. Especially before the coating is completely dry, that is, before the solvent in the coating is completely volatilized, polishing will not only cause the surface loss of the paint film, but also cause the abnormal drying of the coating due to the solvent erosion in the wax.
11. Some incorrect spraying process results in incomplete or false drying of coatings. For example, in the painting of plain paint, if 2K plain paint is used for priming, but no curing agent is added, and then varnish is sprayed on it, the result of this operation is that the paint film will not dry.
12. Mistakes in color matching. The typical phenomenon is that the paint film is soft due to insufficient resin, which is mainly caused by insufficient resin supplement in the process of fine adjustment or wrong resin calculation when adding formula. This situation is rare, in addition to the performance of soft film, usually accompanied by low gloss, easy to scratch off, debris easy to powdering. If the resin is used wrongly in color matching, for example, 2K resin is used in two times plain color paint, it will not dry for a long time.
preventive measure
Some of the above reasons for the abnormal drying of paint film are human factors, which can be effectively avoided as long as the construction is carried out according to the correct operating procedures. There are some restrictive factors that need to be solved after the working conditions are improved. However, the following basic operation requirements must be observed:
1. Coatings and accessories must be used together.
2. According to different seasons, choose different drying speed accessories.
3. The standard container is required to be used for coating proportioning, and it is added according to the scale.
4. Keep good ventilation circulation in paint baking room or painting place.
5. Do not use cheap and inferior diluents.
6. The mixing work of coating after adding curing agent and diluent should not be ignored.
7. Master the correct coating performance requirements and do not force too thick coating.
8. Polish after the specified polishing time.
9. For the repair shop with conditions, the infrared drying mode can be used to solve the problem of coating drying completely by using the principle of infrared drying heating from inside to outside.
resolvent
1. In case of serious non drying, wire drawing sticking, forgetting to add curing agent, or wrong resin addition, remove the topcoat to the bottom surface, and then spray it again. When removing such problem topcoat, it can be wiped off with thinner problem topcoat, and then re sprayed after cleaning with degreaser.
2. For less serious cases, that is to say, when the coating dries slowly, it can be heated for 60 ℃ for 45 minutes.
3. In most cases, the defective bottom surface can be sealed with insulating primer and then repainted with topcoat.
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