1. Wrinkling
Wrinkles and unevenness appear on the surface of the coating film during the drying process of the coating. Usually, when the surface dries quickly, the surface area is large, resulting in uneven parallel lines and irregular lines. Wrinkles vary in size, and some shrink in irregular patterns. The term wrinkle is used to describe the surface appearance.
Etiology
It is caused by the drying rate of the surface of the dry paint being too fast during the oxidative drying process or when the film is thermally formed in the drying room.
1) The paint film is sprayed too thickly, causing the paint film to not dry on the surface (related instrument: drying time Tester) .
2) Poor dry environment, low temperature, high humidity or excessive air flow on the surface after spraying, or no ventilation.
3) Insufficient drying time between layers.
4) The drying temperature of the coating film is too rapid, and the surface dries too fast.
5) Excessive use of slow drying agent and improper selection of thinner.
6) "Dirty air" in the drying chamber (usually caused by poor ventilation or burning oxides).
7) Some synthetic resin baking varnishes are dried for too long, and then baked after the surface is dry, which is prone to small wrinkles.
8) On the old nitro paint film, after re-spraying with polyurethane topcoat, if it is repaired again, it is easy to wrinkle.
9) Oil-based paint made of tung oil is prone to wrinkling.
prevention
1) Control the amount of tung oil used, use less cobalt and manganese catalysts, and use more lead or zinc catalysts.
2) Avoid spraying too thickly, it is recommended to use thin spray for the first coat.
3) Improve the spraying and drying environment, increase the temperature, and enhance the air flow.
4) Check the pollution degree of the air in the drying room, and make corrections or replace the fuel.
5) The synthetic resin baking paint should be dried after the specified time.
6) Use anti-wrinkle agent, such as alkyd resin paint, which is slightly thicker when sprayed (relevant instrument: coating Thickness Gauge) , and it is easy to wrinkle during drying. Add a small amount (about 5%) of amino resin as an anti-wrinkle agent , One time spraying agent #$$% thickness above drying does not wrinkle.
remedy
1) In the case of light defects, after the paint film is completely dry, effectively polish to remove all wrinkles and respray.
2) When the defect is serious or slow drying due to pollution, it should be removed to the substrate and repainted.
Note: Pea green amino topcoat wrinkling accident: The amino topcoat with medium and high amino resin content is a thermosetting coating. Under normal drying conditions, tumble dry without wrinkling. In the 1970s, the Jiefang brand cab topcoat was replaced with amino topcoat. During the construction, it was found that the finish paint of three cabs was dull, and the paint surface was covered with small wrinkles, and the paint surface of the cabs before and after the production line was normal. It was found out that the cab after spraying the topcoat was parked overnight on the slope at the entrance of the bridge-type drying room, and then passed through the drying room the next day (that is, the surface was dried and then dried to cause wrinkles). 1. The amino topcoat is air-dried at room temperature and can be surface-dry. In order to ensure the quality of the coating, the overnight drying room needs to be emptied.
Two, bite
After the topcoat is applied, the undercoat is bitten off, causing wrinkles, swelling, and blistering, which are called bites. This phenomenon is easy to occur when spraying paints containing strong solvents (such as lacquer).
Etiology
1) Apply the next layer of paint before the coating is completely dry (in a semi-dry state).
2) The coating is not matched, the bottom (such as styrene plastic) and the bottom layer have poor solvent resistance, or the topcoat contains a strong solvent that can swell the bottom layer.
3) Spray too thickly at one time.
prevention
1) After the base coat is dry, apply the top coat.
2) Select a suitable coating system through testing.
3) In the case of supporting coatings that are prone to seizure, the first top coat should be sprayed with a thin layer first, and then sprayed after it dries slightly.
The remedy is the same as for wrinkling defects.
