Hydroxyphenyl-triazine UV absorber
Hydroxyphenyl-triazines are the high-performance class of UV absorbers, chosen where a coating has to protect itself and what lies beneath it for many years.
HPTs are a class of UV absorbers, not a single compound, so there is no single CAS number. Each molecule has a 1,3,5-triazine ring carrying one or more 2-hydroxyphenyl groups, with different side chains that tune solubility, compatibility and volatility. They are supplied as liquids, solids or waterborne dispersions by additive manufacturers.
HPTs are used in automotive and industrial clearcoats, wood coatings, plastics coatings and other durable finishes to stop UV light from degrading the binder and, in clearcoats, the basecoat, primer or substrate underneath. They are usually paired with hindered amine light stabilizers (HALS).
Hazards depend on the specific product and its carrier solvent or dispersion. Many grades have low acute toxicity, but some are classified as hazardous to aquatic life. Follow the SDS for the product used.
A UV absorber stops UV light before it reaches the binder and the layers below. HALS do not absorb UV; they trap the free radicals that UV creates. Used together, they protect both the bulk and the surface of the film.
HPTs are generally more photostable and less volatile, so they last longer in demanding uses such as automotive clearcoats and high-bake systems. Benzotriazoles remain widely used where those demands are lower.
It depends on film thickness and required protection. Thinner films need a higher concentration to absorb the same amount of UV. Supplier guidance is usually given as a percentage of binder solids.
