There are a variety of factors influencing the yellowing of coatings. First of all, the main film-forming substance of the paint coating is a major influencing factor. When the polymers in the basic components of the main film-forming substances of the coating are degraded and cross-linked under the conditions of photo-oxygen and thermal oxygen, two irreversible chemical reactions will occur. Alkyd resins containing dry oil (high unsaturation), coumaron resins, epoxy resins containing aromatic rings, TDI polyurethanes, phenolic resins, etc., all have a yellowing trend.
Secondly, the substrate also affects the degree of yellowing of the coating. For example, the poor aging resistance of inorganic pigments in the basic components can make coatings prone to yellowing or even blackening. The paint using lead powder formed by the chemical reaction of lead oxide, carbon dioxide and water, that is, lead white as the pigment, and the paint made of the co-precipitate of zinc sulfide and barium sulfate with a molecular ratio of nearly equal molecular ratio and lithopone powder as the pigment are prone to oxidative yellowing.
Thirdly, the external environmental conditions also have a significant influence on the yellowing of the coating. The ultraviolet light wave range of 290 400 nm in sunlight has the greatest damaging effect on the coating, and the strong light energy of this part of the light is the main factor that causes the aging and yellowing of the indoor coating. In addition, specific environmental conditions, such as temperature and humidity variations, can cause the coating to expand and contract, further triggering deformation.
Finally, specific paint properties can also affect the yellowing of coatings. For example, the structural characteristics of thermosetting fluorocarbon powder resin itself make it highly selective to various additives and pigments when designing coating formulations. Under high-temperature baking conditions, the coating will also have abnormal phenomena such as yellowing and water streaks.