Urethane oils

Varnishes were widely used in the nineteenth and early twentieth centuries. They have been replaced almost completely by a wide variety of other products, especially alkyds, epoxy esters, and urethane oils. The term varnish has come to be used for transparent coatings, such as trade sales varnishes, even though few of them are varnishes in the original meaning of the word. 

From these, prepolymers are prepared where the diisocyanates may be completely reacted as in the case of the urethane oils which resemble the oil-modified alkyds but have urethane (—NHCOO—) links in place of the ester (—COO—) links of the alkyds, or where one only of the isocyanate groups is combined, leaving the other to participate in crosslinking reactions. Such a reactive prepolymer is the biuret that may be prepared from hexamethylene diisocyanate, has the following structure ... 

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 lacquers, 240 Urethane materials recycling of, 207-208 synthetic methods for, 246-258 Urethane oils, 202, 241 Urethane polymers, 197 Urethanes... 

Macromolecular Materials and Engineering 286, No.9, 28th Sept.2001, p.513-5 SYNTHESIS OE URETHANE OIL VARNISHES EROM WASTE POLY(ETHYLENE TEREPHTHALATE)... 

Waste PETP was depolymerised by glycolysis to give hydroxyl-terminated oligomers(DPET), which were used in the synthesis of urethane oils. The effect of depolymerisation temps., the type of glycol and the amount of catalyst on the yield and composition of the depolymerisation products was studied. The physical properties of the urethane oils were compared with those of a commercially-available product. The reaction of DPET with isocyanates produced random linkage between different molecules with or without terephthaloyl groups. 15 refs. 

Athawale, V.D. M.D. Bhabhe. Chemoenzymatic synthesis and characterization of urethane oils for surface coatings./. Coating Technol. 1998, 70, 43-48. 

Athawale, V.D. K.R. Joshi. The effect of HMMM crosslinker on the coating properties of chemoen-zymatically synthesized aliphatic urethane oil. Paint Coatings Ind. 2004, 20, 108—116. 

Bhabhe, M.D. V.D. Athawale. Chemoenzymatic synthesis of urethane oil based on special functional group oil./. Appl. Polym. Sci. 1998, 69, 1451-1458. 

An excess of isocyanate groups is not permitted, so that the final product, a urethane oil, contains no unreacted -NCO. It is therefore stable to moisture, non-toxic and differs from bodied oil in that it contains urethane linkages and can be much higher in molecular weight. The amount of diisocyanate used and the molecular weight of... 

As with the urethane oils, no unreacted isocyanate groups are permitted in the final alkyd. 

Some authors apply the terms urethane alkyd , urethane oil and uralkyd exclusively to urethane oils as defined here. The urethane alkyds of this book are then called urethane-modified alkyds . 

The urethane linkage is resistant to alkalis and thus urethane oils and alkyds have better alkali resistance than ordinary alkyds. This is usually accompanied by better water resistance. Urethane oils and alkyds possess a property common to all polyurethane finishes good abrasion resistance. It is claimed that they are superior to oils and alkyds for the dispersion of difficult organic pigments and carbon black, but in pigmented form they are prone to chalk and lose gloss earlier than normal alkyds and oleoresinous finishes. 

The main outlets for urethane oils and alkyds are in varnishes for floors, boats and general use in undercoats and in industrial maintenance finishes (where gloss retention is less important than long-lasting film integrity and resistance to water and chemicals). 

Except for urethane oil and alkyd finishes, all polyurethanes require solvents that will not react with isocyanates alcohols and ether-alcohols are obviously out. The water content of the solvents should be negligible. Manufacturers often label their solvents urethane grade , implying low water content. Solvents readily miscible with water, e.g. acetone, should be treated with suspicion, as they can take up water from the atmosphere. Obviously the exact choice of solvent will vary considerably with the finish composition. 

The usual thickeners and flow agents can be used. The usual driers and antioxidants are used in urethane oils and alkyds. Catalysts which speed up the curing reaction (and reduce pot-life) are tertiary amines and metal salts, particularly tin salts. The latter should be checked for toxicity before inclusion in paint. 

Finishes based on urethane oils and alkyds and blocked isocyanates do not present the same hazards. 

Polyurethane 2388 is a urethane oil/alkyd based on safflower oil at 50 % solids in mineral spirits (white spirit) and is made by Cargill Inc., USA. 

Uses Solvent for paints/coatings (NC, cellulose acetate, ethyl cellulose, butyrate, acrylic, urethane), oils, resins, printing inks, photographic film, lacquers, nail polish, cosmetics evaporation retarder, gloss aid in automobile lacquers blush retarder in lacquers varnish removers wood stains textiles leather finishing infood-pkg. adhesives... 

Urethane oil Oil paints for decoration/ maintenance LAWS This may be used with long oil alkyds to improve hardness and chemical resisistance... 

F. S. Guner, A. Gumusel, S. Calica and A.T. Erciyes, Study of film properties of some urethane oils , J Coat Technol, 2002,74,55-9. 

Property Urethane oil Moisture Blocked Two-component Lacquer... 

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