1. Defects in the second primer
According to the type of surfacer commonly used in automobile painting, it can be divided into three types: self-drying surfacer defects, drying surfacer defects and quick-drying surfacer defects.
1. Defects of self-drying surfacer
During the construction, there are mainly three kinds of defects: not covering the bottom, slow drying and wrinkling of the bottom.
(1) No bottom cover
That is, the hiding power of the paint is poor, and it cannot completely cover the bottom layer (related equipment: hiding power paper) after spraying, so that the paint film exposes the primer (prime paint). There are mainly two reasons for the analysis: one is that the paint is not stirred evenly before spraying, the pigment or filler (body pigment ) is deposited at the bottom, and the upper paint has less pigment, resulting in poor hiding power after spraying and the bottom is exposed; the other is The paint is adjusted too thin and sprayed too thinly. Fortunately, this kind of defect is firstly to be effectively stirred evenly before spraying, and secondly, it can be avoided by using wet-on-wet continuous spraying when spraying.
(2) slow drying
The paint contains too much resin and is caused by excessive spraying, or the temperature is too low when spraying and the weather is too cold . Solution: For slow drying after spraying due to excessive resin content, the construction method of thin spraying and two coats can be used to dry the paint film in time; for slow drying caused by low temperature and cold weather, appropriate amount of cobalt, manganese and lead mixed liquid can be added to catalyze Desiccant to facilitate drying .
(3) Bite bottom wrinkle
One is that the paint film is too thick and not fully dried, and wrinkling occurs when the top coat or intermediate paint is sprayed; the other is that the performance of the top coat or intermediate paint is different from that of the primer. If the base paint or polyurethane paint is used, it is easy to cause wrinkling at the bottom. Solution: one is to spray the topcoat after the paint is effectively dry; the other is to spray a thin layer of nitro paint or polyurethane paint first, and wait until the paint film after spraying is dry on the surface and there is no wrinkle at the bottom , and then evenly spray one, you can prevent
end.
2. Defects of drying secondary primer
During the construction and baking process, there are mainly two defects: bubbling and air bubbles.
(1) bubbling
It mainly occurs in the putty parts, and the reasons are as follows: First, the bottom putty is too thick and not fully dried, and the water vapor in the putty (referring to water-quality putty) evaporates rapidly during baking to lift up the paint film, resulting in bubbling; second, the texture of the bottom putty Loose and air-permeable , if there are pores such as welding seams under the putty layer, the moisture in the gaps will evaporate through the putty and lift up the paint film during drying, causing bubbling. The solution to this kind of bubbling: one is to wait for the bottom putty to dry effectively before applying the paint; the other is to fill the pores such as weld seams with heat-resistant sealant before scraping the putty, and then scrape the putty and apply the primer paint.
(2) Bubbles
The main reason is that the temperature of the paint is too high or the baking time is too long to produce rice-shaped, bean-shaped, and finger- shaped air bubbles. The solution is to strictly control the baking temperature and time according to the drying performance of the paint, which can be avoided .
3. Defects of quick-drying secondary primer
Quick-drying surfacer such as nitro, perchlorethylene surfacer, etc., the main defects in the construction process are poor filling and leveling . The reason analysis is mostly because the quick-drying surfacer has low solid content and high solvent content, and the paint film is too thin after drying (related instruments: paint Film Thickness Gauge), resulting in The simple solution is to use the quick-drying performance of the paint to spray several coats continuously until the defects such as sand marks are filled and smoothed, which can prevent them.
2. Defects in intermediate paint
It mainly refers to the defects caused by the amino paint and the polyurethane paint. The defects caused by the amino-based paint are basically similar to those caused by the drying surfacer, so the defect analysis and solution can refer to the drying surfacer. while polyurethane primer
The defects produced by the paint are mainly pinholes and bubbles. The reason analysis is mostly caused by improper use of solvents or excessive spraying.
Solution: First, when spraying, special matching thinners should be selected according to different seasons; second, the paint film should not be too thick when spraying. As long as these two essentials are mastered, defects can be prevented.
