Urethane-modified alkyds

Urethane-modified alkyds are similar to simple alkyds except that dibasic acid is replaced with a difunctional isocyanate such as toluene diisocyanate or hexamethylene diisocyanate. The process is also similar to simple alkyds. Coatings made with urethane-modified alkyds dry faster and harder than alkyds, yet retain flexibility. These systems have better water-, chemical- and abrasion-resistance than alkyd resins, and cost is also relatively low (Wicks et al., 1998). These are used in clear finishes for wood floors, cabinets, OEM, maintenance, and architectural coatings. The aliphatic-based systems are excellent for exterior use, or where UV exposure is possible, while aromatic-based systems usually have better abrasion-resistance. Chemo-enzymatic synthesis of urethane-based systems produces better control of stereochemistry and can impart unique properties (Athawale Bhabhe, 1998 Athawale Gaonkar, 1999 Athawale Joshi, 2000, 2004 Bhabhe Athawale, 1998). 

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 . 

Alkyds. Alkyd resins (qv) are polyesters formed by the reaction of polybasic acids, unsaturated fatty acids, and polyhydric alcohols (see Alcohols, POLYHYDRic). Modified alkyds are made when epoxy, sUicone, urethane, or vinyl resins take part in this reaction. The resins cross-link by reaction with oxygen in the air, and carboxylate salts of cobalt, chromium, manganese, zinc, or zirconium are included in the formulation to catalyze drying. 

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 ... 

A varnish is a solvent-thinned combination of a drying oil and a hard resin. Also, a varnish is the clear film obtained using a varnish as a coating vehicle. By extension, vehicles used for clear films are called varnishes although the vehicle may be a true varnish, an alkyd resin solution, a urethane-modified oil, or even a lacquer. 

All three products contain vehicles consisting of combinations of oils, resins (an alkyd resin solution or a urethane-modified resin), polymers, and solvents the non-... 

Uses Rheology control agent for variety of air-dry architectural and It-maintenance coating applies., esp. in long/med.-oil alkyds, modified alkyds (acrylics, vinyl toluene, styrene, urethane)... 

Uses Surf, modifier, flow modifier, aniicratering agent for coatings (epoxy, urethane, polyester, alkyds), powd. coalings Features Reduces orange peel, crawling Properties Colorless clear liq. dens. 8.5 Ib/gal vise. 1,000 cps 100% act. 

A urethane alkyd is an alkyd in which some of the dibasic acid is replaced by diisocyanate. The ester links are formed first in the usual way, the diisocyanate is added and the remaining hydroxyls are reacted at 80-95 °C to form the urethane linkages (p. 223). It can be seen that the urethane alkyd shares the features of the urethane oil and the oil-modified alkyd. 

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... 

For the most part, additives control the appHcation or theological properties of a paint. These additives include materials for latex paints such as hydroxyethylceUulose, hydrophobicaHy modified alkah-soluble emulsions, and hydrophobicaHy modified ethylene oxide urethanes. Solvent-based alkyd paints typically use castor oil derivatives and attapulgite and bentonite clays. The volume soHds of a paint is an equally important physical property affecting the apphcation and theological properties. Without adequate volume soHds, the desired appHcation and theological properties may be impossible to achieve, no matter how much or many additives are incorporated into the paint. 

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. 

Although blending with other coating resins provides a variety of ways to improve the performance of alkyds, or of the other resins, chemically combining the desired modifier into the alkyd structure eliminates compatibility problems and gives a more uniform product. Several such chemical modifications of the alkyd resins have gained commercial importance. They include vinylated alkyds, silicone alkyds, urethane alkyds, phenolic alkyds, and polyamide alkyds. 

Inhibitive Primers. The traditional primers are red lead and linseed oil, alkyd resins and zinc potassium chromate, proprietary epoxy, alkyd, urethane and latex systems with modified phosphate, borate and molybdate pigments. Chromate-based pigments, although in use in aircraft coatings, automotive primers and coil coating primers, are subject to environmental concern on the toxicity of hexavalent chromium which is likely to result in their replacement by innocuous products. 

Use Polyester foams, insect repellent, alkyd modifier, plasticizers, urethanes, synthetic lubricants. 

One-Package Urethane Alkyd (Oil-Modified Urethanes) Coatings (ASTM Type 1)... 

Hercules PE. [Hercules] Pentaeryth-ritols used in prod, of alkyd resins, rosin esters, oil-modified urethane resins, drying oils, synthetic lubricants, plasticizers, intumescent paints, plastics, stabilizers for plastics, explosives. 

Uses Pigment for alkyds, oil-based exterior and interior paints and stains, oil-modified urethanes, alkyd melamines, and other systems Colormatch AD-10306 [Plasticolors]... 

Uses Pigment for air-drying alkyds, DIY and archifecfural paints Features Optimum pigmentation low VOC good light- and weather-fastness exc. color reproducibility easy to mix economical compat. with urethane and silicone-modified fatty alkyd paints Holcoprim HC 093 [Holland Colours UK]... 

Uses Surf, modifier, mar resist, aid, antiblocking agent for aq. coatings, wood coatings, varnishes, industrial coatings, acrylic and styrene/acrylic disps., urethane disps., hybrid systems, water-reducible alkyds Features Improved scratch/metal mark resist. uniform matting Properties Micronized disperses easily in aq. coatings without use of added hydrophilic surfactants Lanco 1588 LF [Lubrizol]... 

Uses Surf, modifier for solv.-based coatings, offset, flexographic, and gravure inks, plastics food-contact coatings effective in alkyds, polyesters, acrylics, urethanes, epoxies, NC exc. gloss control for matte or satin gloss finishes... 

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