1.What are the symptoms and causes of discoloration and fading?
Symptoms: A change in coating color, typically manifesting as a lighter (fading), darker, yellower, or loss of vibrant color. Different pigments have varying weather resistance, with bright colors like red and blue fading more easily.
Cause: Primarily due to UV radiation, which decomposes the chromophores in the pigment and resin. High temperatures, acid rain, and chemical pollutants can also accelerate discoloration.
2.What are the symptoms and causes of chalking?
Symptoms: A loose, powdery substance appears on the coating surface, leaving noticeable marks when wiped with hands or a cloth. In severe cases, the powder may drift away with the wind, exposing the underlying coating or substrate.
Cause: Ultraviolet rays, oxygen, moisture, and other factors cause the resin component on the coating surface to degrade, embrittle, and break into powder, dislodging the pigment particles. This is a key sign that coating degradation has reached a more advanced stage.
3.What are the symptoms and causes of loss of light?
Symptoms: The coating's surface gloss decreases significantly, shifting from high-gloss or semi-gloss to matte or semi-matte, resulting in a dull, matte finish.
Cause: The coating surface becomes rough and uneven due to UV exposure, temperature fluctuations, and air pollutants, increasing light scattering and reducing specular reflection. Chalking can also cause gloss loss.
4.What are the symptoms and causes of cracking?
Symptoms:
Fine lines/microcracks: Very fine, network-like cracks appear on the coating surface (similar to a dry riverbed).
Crocodile patterns/wide cracks: Cracks deepen and widen, forming a pattern resembling crocodile skin or tortoise shell.
Linear cracks: Distinct, straight cracks appear along bending lines or areas of concentrated stress.
Cause: The coating loses its flexibility and elasticity due to aging. It is unable to adapt to deformation caused by thermal expansion and contraction, wind pressure and vibration, processing stress, or substrate deformation, leading to cracking. Resin degradation is the primary cause.
5.What are the symptoms and causes of flaking/shedding?
Symptoms: Partial or large-scale separation, lifting, or detachment of the coating from the substrate or underlying coating, exposing the underlying layer (primer, chemical conversion film, plating, or substrate).
Cause: This is a further development of cracking or severe loss of coating adhesion due to aging (resin degradation, interfacial corrosion, hydrolysis caused by water vapor penetration, etc.). Moisture and oxygen infiltrate through cracks or defects, accumulating at the coating-substrate interface and accelerating delamination.