Urethane alkyds application

Urethane alkyds and urethane oils are oil and alkyd resin-modified polyurethanes dissolved in a volatile solvent. Upon application and solvent evaporation, the coating is crosslinked and cured via oxidation by atmospheric oxygen. 

Urethane alkyds Epoxy resins are also chemically combined with drying oils as part of the molecule that further reacts with isocyanates to produce urethane alkyds. Upon application as a liquid coating, the resin-oil combination converts by oxidation to a solid. 

In varnish manufacture, (he drying oil. i.c.. linseed oil. lung oil. or mixtures of the two. and the resin are cooked together to high temperatures to yield a homogeneous solution for the proper viscosity. The varnish is then thinned with hydrocarbon solvents lo application viscosity. Varnishes were widely used in the nineteenth and early twentieth centuries. They have been replace almost completely by a wide variety uf other products, especially alkyds. epoxy esters, and urethane oils. 

Among these resin fortified oil based paints are included the alkyds, epoxy esters, oil modified urethanes, etc. These paints may be formulated as airdrying or baking types, and with suitable pigments be formulated to be resistant to a variety of moisture and chemical fume environments, as well as application over wood, metal, and masonry substrates. These paints have the following advantages ... 

Urethane oils are generally similar to alkyd resins of comparable type and oil length but are quicker drying. They give films with superior mar and abrasion resistance and resistance to solvents and chemicals. On the other hand, films from uretliane oils discolour more rapidly than those from alkyd resins. Urethane oils find application in wood varnishes and quick-drying enamels. 

It should be noted that while these modifications will improve certain properties, they may also cause a compromise with other properties. For example, rosin modification causes brittleness, poor color retention and water sensitivity of the film. In vinylated alkyds, due to reduced residual unsaturation after grafting, the cross-link density is lower compared to the unmodified alkyd, and hence solvent resistance is reduced. Such resins also have an increased tendency for yellowing. Certain modifications, such as by urethane, silicone or acrylic components, increases the cost of the resin, rendering them only suitable for specific applications that justify their higher cost. 

Traditionally acrylic/melamine and alkyd/melamine systems have been used for high quaUty original finishes on automobiles. Two component acryUc urethane used in some OEM applications offer ... 

Curing of oil-modified alkyds with polyisocyanates results in faster drying, better chemical resistance and abrasion resistance. Hydroxylated polyesters crosslinked with both aromatic and aliphatic polyisocyanates are finding extensive applications in high-quality maintenance finishes. These two-component finishes cure at ambient temperature. Aliphatic urethane types are used on aircraft, rail and other transportation equipment where excellent gloss retention and... 

PET in fibers and bottles and polycarbonates in compact discs represent large-volume markets. As with most polymer families, there is a wide diversity of applications, many of which involve combinations with other materials. Aliphatic polyesters have been used as lubricants and vinyl plasticizers. Hydrolytic stability is a factor to be considered in many applications. As a rule, aryl acids and branched-chain diols resist hydrolysis. Fibers and films of terephthalic acid esters and polycarbonates are not particularly sensitive to moisture. Alkyd resins are so highly cross-linked in the final coating that water is not a major problem, although alkaline solutions of soaps and detergents can cause film failure. It is in the urethane foams that hydrolytic stability... 

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