Amine also HALS

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). 

The Good-rite 3125 was also combined with the Chimassorb 944LD and Cyanox STDP to evaluate possible synergistic effects between combinations of a hindered phenol stabilizer with first a thioester and then a hindered amine light stabilizer (HALS). 

Set B Based on the results of set A discussed below, a third set. Set B, was prepared (Table IV). Cyasorb 531 (a benzophenone UV light absorber) was found to be the most effective stabilizer in Set A. It was therefore rerun at an even lower add-on in Set B, and since it was the only UV light absorber included in Set A, a second type of UV absorber, Tinuvin 327 (a benzotriazole) was included in Set B. Two new non-polymeric hindered amine light stabilizers (HALS) Tinuvin 770 and Tinuvin 765 were also evaluated in Set B with the hope that they might be more effective than the polymeric HALS (Chimassorb 944LD) included in Set A which was quite detrimental to the heat stability. Combinations of these four additives were also applied in Set B. The three new compounds evaluated have been reported to be effective light stabilizers for polyester and polyamide fibers (Capocci, G., Ciba Geigy Corporation, Ardsley, NY, personal communication, 1986). 

Light stabilisers also prevent photodegradation. UV absorbers such as hydroxybenzophenone or hydroxyphenyl triazole types, operate by absorbing and dissipating UV radiation prior to potential degradation of the polymer. No permanent chemical change occurs, so activity is retained. Hindered amine light stabilisers (HALS) are also used but their activity is not particularly well understood (80). 

Other additives include materials such as hindered amine light stabilizers (HALS) and UV light absorbers (UVAs) to protect the colorants from destruction due to the environment, as well as items such as defoamers and wetting or levehng agents to help improve lay down and flow out on the media. Some of these additives such as the stabilizers and the HALS and UVAs must be added in small amounts as they can also impede curing. 

Interaction Between the HALS Compound and the Antioxidant Present in the Polymer System. Thermal oxidation of the films containing different amounts of IRGANOX and TINUVIN 770 as a function of TINUVIN 770 concentration is shown in Figure 4. As expected, the induction period of the oxygen absorption increases with the antioxidant content, but also with the increase of the TINUVIN 770 concentration. That means that the hindered amine can operate during the radical process of the thermal oxidation as a radical scavenger. 

The exact mechanisms for the conversion of hindered amine to nitroxide are not known in these coatings. According to the treatment above, the initial rate of formation of nitroxide should be proportional to [Y00 ]. From the scheme of equation 5, the overall rate of photooxidation should also be proportional to [Y00 ]. Even though there appears to be a qualitative correlation between the initial nitroxide formation rate and the rate of degradation, the initial formation rate is hardly proportional to either K or Ke. Apparently nitroxide formation from HALS- is more complex than indicated by the simple scheme above. Compared to the excellent correlation found between photodegradation rates and photoinitiation rates in these coatings, no single parameter in the... 

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