Coatings hindered amine light stabilizers

The exterior durabiHty of relatively stable coatings can be enhanced by use of additives. Ultraviolet absorbers reduce the absorption of uv by the resins and hence decrease the rate of photodegradation. Eurther improvements can be gained by also adding free-radical trap antioxidants (qv) such as hindered phenols and especially hindered amine light stabilizers (HALS). A discussion of various types of additives is available (113). 

A number of antioxidants were examined for solubility in the monomer, effect upon the photoinitiator, UV stability, effect upon physical properties of the cured coating and their effectiveness as stabilizers. The addition of hydrogen donors, HD-2 or HD-3, or a hindered amine light stabilizer, HALS-1, improves the stability of a cured epoxy acrylate system with a minimal change in the physical properties of the resin. DSC and oxygen absorption measurements show that the secondary hindered amine, HALS-1, imparts the best stability to the resin. 

The light stabilizer category, hindered amine light stabilizers (HALS) are very effective stabilizers for urethane coatings. These compounds, developed primarily by Ciba-Geigy, do not act as UV absorbers but act by Inhibiting the degradation of the binder that is already in an excited state. 

Ciassification Hindered amine light stabilizer Uses UV absorber, light stabilizer for coatings, liq. pigment disps. 

Other materials may include pigments and fillers, surfactants, mold release/lubricants, and flame retardants. Coatings will have additional components, including UV stabilizers and hindered amine light stabilizers. 

The number of studies in this area is limited, but a few have shown exposure of coatings to atmospheric contaminants to be detrimental. Sampers [35] reports that, in a study of polyolefin samples exposed both in Florida and on the Mediterranean coast of France, a dramatic difference was seen in polymer lifetime. Samples exposed on the Mediterranean had only half the life of those in Florida. The two stations had broadly similar weathering parameters the differences should have led to longer lifetimes in France. Sampers concluded that constituents in the rain or wind had chemically interacted with the hindered amine light stabilizers in the polymers exposed in France, causing these samples to be especially vulnerable to UV degradation. 

Typically hindered amine light stabilizers are used up to 3 % by mass of coating, depending on other formulation parameters such as type of binder and pigments. A combination of UV absorbers and hindered amine light stabilizers are often used in demanding applications due to their synergistic effect. 

Schaller C, Rogez D, Braig A. Hindered amine light stabilizers in pigmented coatings. J Coating Technol Res 2009 6(l) 81-8. 

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