UV-resistant coatings

Support spacing must be much closer than for carbon steel. As temperature increases, the allowable stress for many plastic pipes decreases very rapidly, and heat from sunlight or adjacent hot uninsiuated equipment has a marked effect. Many plastics deteriorate with exposure to ultraviolet light if not provided with a UV-resistant coating or other surface barrier. Successful economical underground use of plastic pipe does not necessarily indicate similar economies outdoors aboveground. 

Monomeric vinylic metal n complexes undergo polymerisation reactions to form polymers that have limited applications because of their poor thermo-mechanical properties but they absorb UV without degrading in the process. Such polymers can be used as a UV-resistant coating and act as catalysts in other monomer reactions. Metallocene methylene polymers are high temperature resistant materials and have uses as ablative materials for space capsule heat shields. These materials use Fe and Ru in their metal polymers. 

Because of the molecular size and remarkable reactivity of water-borne fluoroalkylsilane systems, the penetration depth in concrete and other porous building materials is very low. This desirable effect results in the high efficiency of this special product. Substrates of relatively low porosity such as concrete need about 150-200 g/m of Protectosil Antigraffiti to impart permanent anti-graffiti properties. Approximately 20-50 g/m are necessary for an excellent water and oil-repellent, chemical- and UV-resistant coating (about 200 g/m of the aforementioned product). 

Chemical additives are usually used for light-stabilization of plastic materials, while UV resistant coatings (e.g. clear polyurethane coatings) are applied for wood products protection, since photo-degradation processes cause increased water sensitivity and further their biodegradation under outdoor exposure conditions [32]. In most cases, it is preferable to use materials with greater resistance to UV radiation in order to prevent the increased damage of these materials under outdoor exposure to solar radiation. 

The thermal and UV resistance will depend on the stabiliser systems used. The hardness of the coating will depend on the amount and type of plasticiser used. Correct selection of the plasticiser can permit the use of the plastisols at high or low temperatures, provide fire resistance or oil resistance. Plastisols can be produced in a range of gloss levels from 80 units down to 10 gloss units. 

Etherification to produce cyanoethyolated, benzylated or allylated wood surfaces does not result in an improvement in UV resistance, but the latter two treatments have been found to improve the performance of clear coatings on the modified substrate (Kiguchi, 1990b). Kalnins (1984) methylated wood by pre-treating with concentrated aqueous... 

Figure 48. Ultraviolet absorbance spectrum of IBM s experimental mid UV resist. The resist was coated on quartz and the spectrum was recorded before and after exposure. This figure should be compared to Figure 24 with respect to the extent of bleaching at 313 and 334 nm.

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