Analysis of defects in alkyd topcoat and its solutions

The defects of alkyd topcoat in the actual construction and coating process mainly include flow, sagging, wrinkles, orange lines, impurities, slow drying and so on.

1. Flowing, sagging

Because the surface of alkyd paint usually takes 0.5~1.5 hours to dry slightly, and when the surface of the paint film does not reach the level of slightly dry (refers to gently touching the paint film without sticking to the hand), there is still fluidity, which is the main reason why alkyd paint is easy to flow and sag. In order to prevent flow and sagging, first, the spraying viscosity should not be adjusted too thin; Second, the spraying air pressure should not be too large; Third, the distance between the Spray Gun and the surface of the sprayed object should not be too close, and should be controlled within the range of 30~40 cm; Fourth, the movement speed of the Spray Gun should not be too slow when spraying, especially when spraying vertical surfaces or special-shaped surfaces, it should be fast and agile. As long as you grasp these four essentials, you can avoid them.

2. Wrinkles

There are three reasons: one is the excessive thickness of the paint film spraying (testing instrument: coating Thickness Gauge); Second, the sprayed paint film is exposed to sunlight, and the surface shrinks sharply due to heat and forms wrinkles; The third is caused by the improper proportion of the amount of drier in the paint, such as excessive dosage of cobalt and manganese drier, which is easy to wrinkle. Solution: First, the paint film cannot be sprayed too thick at one time; Second, spraying should be carried out indoors as much as possible, such as when spraying outdoors, a clean environment without scorching sun exposure should be selected; Third, when spraying in winter, the amount of cobalt and manganese drier should be strictly controlled.

3. Orange stripes

That is, there is an obvious orange peel on the surface of the paint film, which seriously affects the smoothness and appearance of the paint film, because there are two main types of analysis: one is that the paint is too thick; The second is that the air pressure is too small during spraying, and the atomization is uneven. Therefore, when spraying alkyd topcoat,The spraying viscosity shall not be greater than 40 seconds (No. 4 cup viscometer 25±1 °C), which should be controlled between 25~35 seconds, and the spraying air pressure shall not be less than 0.025MPa (2.5 kg/c㎡). This prevents the appearance of orange streaks.

4. Impurities

There are three reasons for the analysis of impurities: first, the dust and other impurities on the bottom surface are not wiped off and caused by painting; The second is the poor spraying environment, such as spraying in outdoor windy days or indoor spraying on the ground, walls and so on; The third is that the paint contains impurities and is sprayed without filtration. Solution: First, blow the bottom layer first and wipe it repeatedly before spraying paint; Second, when spraying outdoors, you should choose windless weather, and you should pay attention to environmental cleanliness when spraying indoors; The third is the paint that is not beneficial to the open barrel (falling into dust) or unclean paint such as patent leather, which needs to be filtered clean before spraying. impurities can be avoided.

5. Slow drying

Slow drying is mainly caused by too cold weather or too thick paint film at one time, or improper dosage of paint drier. This defect is easier to solve, one is in the winter spraying construction, the paint film is easy to be thin but not thick, the front paint is dry and then sprayed after the back paint; The second is to adjust the type and dosage of drier, such as winter construction, the appropriate addition of cobalt manganese drier can be solved.

The above-mentioned defects mainly refer to the construction drying under normal temperature conditions, if the temperature is too high or the baking time is too long, the alkyd paint is also prone to paint film discoloration, bubbles and other defects, so special attention should be paid to. According to experience, the baking temperature of alkyd paint should not be higher than 100°C, and the time should be 30~40 minutes.