The defects caused by perchlorethylene topcoat mainly include whitening, backlighting, pinholes, and air bubbles.
1. Whitening
The reason for the whitening of the paint film is mainly caused by the relatively high relative temperature of the spraying construction environment (excessive moisture). For example, the paint film after spraying in rainy days is easy to absorb moisture and whiten, which seriously affects the quality. Solution: First, choose a dry and clean environment for spraying construction; Second, when spraying on rainy days, add 15~20% F-2 perchlorethylene paint moisture-proof agent according to the amount of thinner to prevent whitening; Third, For the whitened paint film, first smooth it with fine water sandpaper, wipe it off and dry the water effectively, then choose a dry and clean environment and then spray 1-2 coats of the color finish evenly (testing instrument: drying time Tester), Or add an appropriate amount of moisture-proof agent when thinning, stir well and spray 1-2 times evenly.
2. Backlight
Backlighting is also called light absorption. It means that the gloss of the perchlorethylene topcoat is good at that time, but the gloss of the paint film is poor or even dull after drying. The reasons are as follows: First, the sand marks on the surface of the bottom paint film are deep, and the paint after spraying is fully leveled and infiltrated into the sand marks, resulting in poor gloss (testing instrument: gloss meter); second, the top coat is sprayed too thin, However, the putty on the surface of the primer has a strong permeability to the topcoat (that is, the tiny sand holes on the surface of the putty penetrate into the topcoat), causing the topcoat to shine. In addition, when the vinyl chloride topcoat is sprayed, the surrounding moisture is too high and it is easy to cause light reflection. Backlighting solutions can be used in the following ways:
(1) The base layer before spraying the vinyl chloride topcoat should be water-grinded with No. 360-400 water sandpaper. For the body (shell) of large and medium-sized buses, it should be water-grinded vertically from top to bottom. After water grinding, the sand marks should be straight and smooth. Evenly, so that it is not easy to produce backlight after spraying the topcoat.
(2) The perchlorethylene topcoat should not be sprayed too thinly, but at least two coats should be sprayed to make the paint film have a certain thickness, so as to avoid backlighting.
(3) For parts such as the greasy layer with strong absorption, 1-2 coats of perchlorethylene topcoat should be sprayed locally first, and 20-30 minutes after the paint film is half-dried), and then 2-3 coats should be evenly sprayed on the whole vehicle, It can prevent backlighting.
(4) For the backlight caused by high humidity in the spraying environment, an appropriate amount of moisture-proof agent can be added to solve it.
3. Pinhole
Pinholes are mainly caused by improper use of solvents or too thick one-time spraying. Because perchlorethylene paint is also a volatile paint, more thinner needs to be added when thinning. If the type of solvent is improper, or the coating film is too thick, the solvent will evaporate rapidly and penetrate the paint film to form pinholes. Therefore, when encountering pinhole defects, it should be smoothed after the paint film is dry, and if necessary, scrape a full layer of putty to fully fill the pinholes, and then adjust the thinner to spray evenly, which can prevent it.
4. Bubbles
There are two reasons for bubbles: one is that the solvent used in the paint volatilizes too fast to form bubbles; the other is that there is moisture in the bottom layer (such as the moisture after water grinding is not fully dried, etc.), resulting in bubbles or blisters after spraying. Therefore, attention should be paid to solvent selection and construction operation.
