(1) phenomenon
The surface of the coating film is affected by the invasion of foreign substances or its own precipitates, resulting in stains that are not the same color as most of the surface or adhesion of foreign matter such as dust. The gas and falling matter (there is a rough feeling when the mold is touched, but there is nothing to see) from the industrial area is acidic or alkaline, and it invades the coating film to cause color spots, which is called industrial falling dust, as shown in Figure 9_26.
(2) Reason
① It is invaded and polluted by dirt in the air (such as dust, cement ash, tar, soot, acidic substances, insects and bird droppings, etc.). There are many substances (such as road asphalt, lubricating oil, hydraulic oil, antifreeze, battery water, and synthetic or natural rubber, etc.) that adhere to the coating film and cause surface stains (Staining), and many media are water-soluble and can invade inside the paint film.
② During use, foreign matter (such as sweating) is precipitated from the coating film or softened and sticky back due to heat.
③ The paint used has poor acid and alkali resistance or poor mildew resistance.
④The area where there is a lot of "acid rain".
(3) Prevention
① Choose a paint with good stain resistance and acid and alkali resistance, and use a paint that does not stick back, soften, or precipitate foreign matter when heated.
②Park the vehicle away from pollution sources. During long-term storage and transportation, paint or stick a temporary protective film on the paint surface.
③The dirt adhering to the paint surface should be properly wiped with water or gasoline as soon as possible.
(4) Remedy
①Slightly polluted, when the falling objects or dirt have not penetrated into the surface, they can be removed by grinding and polishing.
②Serious pollution can be removed by chemical cleaning. Use 10% oxalic acid solution (54g oxalic acid plus 0.5L water) for cleaning.
Note: Oxalic acid is toxic, avoid contact with skin and eyes, and wear protective goggles and PvlC gloves during operation. In case of contact, rinse with clean water immediately, and clothes must be washed effectively before wearing again.
③If the coating surface has been damaged by dirt intrusion, it needs to be polished to remove the damaged coating and re-spray.
