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Exterior use of polyurethane varnish may be problematic due to its susceptibility to deterioration through ultra-violet (UV) light exposure. All clear or translucent varnishes, and indeed all film-polymer coatings (i.e., paint, stain, epoxy, synthetic plastic, etc.) are susceptible to this damage in varying degrees.
UV-328 is a light stabilizer for a variety of plastics and other organic substrates. Its use is recommended for the stabilization of styrene homopolymers and copolymers, acrylic polymers, unsaturated polyesters, polyvinyl chloride, polyolefins, polyurethanes, polyacetals, polyvinyl butyral, elastomers and adhesives. [5]
Charge-transfer complexes of oxygen and polystyrene phenyl groups absorb light to form singlet oxygen, which acts as a radical initiator. [23] Carbonyl impurities in the polymer (c.f. acetophenone) also absorb light in the near ultraviolet range (300 to 400 nm), forming excited ketones able to abstract hydrogen atoms directly from the polymer. [24]
UV-cured powder will melt in 60 to 120 seconds when reaching a temperature 110 °C and 130 °C. Once the melted coating is in this temperature window, it is instantly cured when exposed to UV light. [13] The most common polymers used are polyester, polyurethane, polyester-epoxy (known as hybrid), straight epoxy (fusion bonded epoxy) and acrylics.
Exterior use of polyurethane varnish may be problematic due to its heightened susceptibility to deterioration through ultra-violet light exposure. All clear or translucent varnishes, and indeed all film-polymer coatings (e.g. paint, stain, epoxy, synthetic plastic, etc.) are susceptible to this damage in varying degrees.
A photopolymer or light-activated resin is a polymer that changes its properties when exposed to light, often in the ultraviolet or visible region of the electromagnetic spectrum. [1] These changes are often manifested structurally, for example hardening of the material occurs as a result of cross-linking when exposed to light.
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