1. Bronze back, bright copper color
(1) phenomenon
Partial or entire surface of the coating film exhibits a copper color, that is, it becomes a green and green color or a spot-like discoloration or gloss change phenomenon under sunlight. This defect is specific to certain blue, scarlet, and black pigments. It is also one of the phenomena of poor weather resistance of the coating film.
(2) Reason
① A certain type of specific pigment will show a bright copper color in spraying, which is beyond the control of the construction personnel.
② Failure to follow the prescribed formula for coloring, because some pigments will show serious bright copper color defects when the amount exceeds their upper limit.
③It is caused by the migration of red, blue and other pigments, especially when the particle size of the pigment used is below 0.1 μm.
④ There is oil in the compressed air used for spraying.
⑤ Discoloration caused by sunlight, ultraviolet rays, high temperature, soot and sulfur dioxide gas.
(3) Preventive measures
① Comply with the prescribed formula for paint mixing.
②Choose paints with good weather resistance, and pay attention to the types of pigments used when matching colors.
③ Remove the oil in the compressed air.
(4) Remedy
①Use a neutral liquid polisher and lightly polish with your hands to remove the copper color. Wash and wax frequently to maintain good looks.
② In severe cases, re-spray after wet sanding (preferably after sealing the back with 2K primer).
2. Discoloration and fading
(1) phenomenon
The color of the coating film changes during use, and the phenomenon that its hue, lightness, and chroma obviously deviate from the standard color plate (or primary color plate) is called discoloration. If the color of the coating film becomes lighter (the chroma becomes smaller or the brightness becomes larger), the phenomenon is called fading.
(2) Reason
① It is caused by ultraviolet radiation, humidity, high temperature and corrosive gases (such as sulfur dioxide) in the air. When the vehicle is exposed to the atmosphere with chemical substances for a long time, the resin in the coating film will be eroded and its adsorption effect on the pigment will be weakened.
②Does not follow the prescribed formula for coloring.
③Because of traffic and industrial slag, the surface is stained (yellow).
④ The weather resistance of the paint used is poor or not suitable for outdoor use. Organic pigments migrate through the paint film during the process of film aging, plasticizer precipitation, etc.
⑤ The internal curing agent that is easy to turn yellow is misused in the car repair top coat.
(3) Preventive measures
①Use the correct coloring formula.
②Choose the car repair topcoat and curing agent with excellent weather resistance.
③Clean the vehicle frequently and regularly, and take protective measures (polishing, waxing) on the coating.
(4) Remedy
①First, use crude wax or polishing wax to try grinding and polishing on one part. If the color can be restored, then polish the entire affected part.
② If grinding and polishing are ineffective, use wet grinding to remove the topcoat layer and re-spray.
Note: Crude wax is usually effective when used to remove yellow marks caused by traffic debris.
