Most conventional plastic parts have low wear and solvent resistance and are easily scratched, fogged, and damaged on the surface, so plastic parts need to be decorated and protected on the surface. Plastic materials with poor light aging performance can also be protected by light-stabilized UV coatings to prevent or delay the aging of plastic substrates.
Wetting ability of coatings on plastic substrates
The wetting process is the result of the interaction between the substrate and the liquid coating. In order to achieve the purpose of substrate wetting, in addition to trying to increase the surface tension of the substrate, reducing the surface tension of the coating is also one of the main methods. UV coatings mainly contain diluent monomers, resins, etc., and wetting surface additives can be added to promote wetting, but the use of wetting additives may also cause side effects such as blistering, craters, and difficulty in re-coating.
Commonly used diluents such as HDDA, TMPTA, TPGDA and 3EOTMPTA generally have high surface tension and are not conducive to wetting, but the new diluent obtained after compounding can solve this problem.
In addition, the effect of temperature on the surface tension of the liquid can sometimes be utilized. By increasing the temperature, the surface tension of the coating decreases slightly, which is beneficial to wetting.
The role of wetting additives
Modified siloxane is a commonly used wetting agent. It can cover the entire coating surface with a very small amount, greatly reducing the surface tension and fully wetting the substrate. The siloxane chain segment has a very low surface energy, is incompatible with organic coatings and floats on the surface of the coating, but the organic segment of its modified molecule is compatible with organic coatings, similar to the relationship between the stems, leaves and roots of trees.
The resin in the light-curing coating has a very limited ability to penetrate and swell the plastic substrate due to its large molecular weight and viscosity, so it is more suitable to use monomers to complete.
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