The first necessary condition for the aging or photochemical reaction of the color-coated board is that the surface components of the color-coated board can absorb radiant energy; secondly, when the radiant energy absorbed by the molecules is greater than the molecular bond energy, the color-coated board coating can degrade. The shorter the wavelength of light, the higher the energy it contains.
According to the above theory, the aging of the color-coated board in the atmospheric environment is that the coating molecules absorb the energy in the ultraviolet wavelength band higher than their molecular bond energy in the sunlight, resulting in the degradation of the coating molecules. With the aging of the coating film, the body of the base material gradually loses, and the surface of the coating gradually becomes rough and loses its gloss. This loss of binder ultimately leaves relatively stable pigment particles that remain on the surface of the coating film as an unbonded powder, a process known as chalking.
In summary, polyester color-coated boards with different coating thicknesses have great differences in aging resistance. The aging resistance of thin-coated color-coated boards is poor, and the aging resistance of normal thickness coatings is relatively good.
