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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-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.
UV coatings have been applied to mechanical tubing, safety/water suppression pipe and OCTG/line pipe for many years. UV coatings advantages in this application can be summarized as faster, smaller, and cleaner with no thermal ovens required. The coating and curing (almost instantly) at speeds ranging from 100 feet per minute to over 800 feet ...
Light stabilizer are used to inhibit polymer photo-oxidation, which is the combined result of the action of light and oxygen. Like autoxidation this is a free radical process, hence the antioxidants described above are effective inhibiting agents, however additional classes of additives are also beneficial, such as UV absorbers, quenchers of ...
This is of particular interest in the area of polyurethane coatings, where light stability is a critical factor and is the main reason that aliphatic isocyanates are used in making polyurethane coatings. When PU foam, which is made using aromatic isocyanates, is exposed to visible light, it discolors, turning from off-white to yellow to reddish ...
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]
Photo-oxidative degradation occurs when plastic degrades from exposure to ultraviolet (UV) or visible light; the most damaging wavelengths depend on the composition of the polymer. [14] In general, plastic will be affected by light, and it is best practice to keep plastic away from light sources as much as possible, especially during longterm ...