Varnishes oleoresinous

Plastics. Vehicles in offset inks for plastics (polyethylene, polystyrene, vinyl) are based on hard drying oleoresinous varnishes which sometimes are diluted with hydrocarbon solvents. Letterset inks for polystyrene employ vehicles of somewhat more polar nature. Polyester or other synthetic resins (acryhc) dissolved in glycol ethers and/or esters are used in some of the older inks. Uv inks are widely used for decoration of these preformed plastic containers. 

Substituted heat-reactive resins are most widely used in contact-adhesive appHcations and, to a lesser extent, in coatings (77,78) -butylphenol, cresol, and nonylphenol are most frequendy used. The alkyl group increases compatibiHty with oleoresinous varnishes and alkyds. In combination with these resins, phenoHcs reduce water sensitivity. Common appHcations include baked-on and electrical insulation varnishes, and as modifiers for baking alkyds, rosin, and ester gum systems. Substituted heat-reactive resins are not used for air-dry coatings because of theh soft, tacky nature in the uncured state substituted nonheat-reactive phenoHcs are the modifying resin of choice in this case. 

Substituted nonheat-reactive resins do not form a film and are not reactive by themselves, but are exceUent modifier resins for oleoresinous varnishes and alkyds. Thein high glass-transition temperature and molecular weight provide initial hardness and reduce tack oxygen-initiated cross-linking reactions take place with the unsaturated oils. 

Oleoresinous varnishes Air drying and/or stoving Condensation and/or oxidative polymerisation Aliphatic and/or aromatic hydrocarbons Fair Bad Fair/good Poor Fair/good Pale-coloured finishes that yellow on exposure... 

As noted, coating systems were advanced from oil-only vehicles to oleoresinous varnishes for improved performances. These are basically oils that have been... 

Phenolic resins are well known for their contribution in improving hardness, gloss, and water and chemical resistance in oleoresinous varnishes. Those based on p-alkyl-substituted phenols and with heat-reactive methylol groups have also been incorporated into alkyd resins. The reaction has not been well smdied. Presumably, the methylol group would react with the unsaturation functionality on the fatty acid chain to form the chroman stmcture, similar to what is believed to have occurred in the varnish. Etherification between the methylol group and free hydroxyl of the alkyd resin, catalyzed by the residual acidity in the resin, would be another possible reaction. 

Use Adhesives, gloss oils, paper label coatings, oleoresinous varnishes, solder flux, spirit varnishes, waxed paper and hot melt compounds, synthetic resins. 

The main use for phenolic resins is in oleoresinous varnishes. Apart from the chemical-resistant finishes produced with epoxy resins (Chapter 14), other outlets include modification of alkyds to improve resistance to water and alkali, combination with U/F resins (Chapter 13) to provide metal coatings and combination with polyvinyl formal or butyral resins to produce wire enamels. 

Alkyds, like oleoresinous varnishes, have an oil length and this is expressed as a percentage the number of grams of oil used to make 100 grams of resin. Below 45 per cent oil is a short oil alkyd, 45-60... 

Benguela copal n. Fairly hard natural copal obtained from West Africa. Sometimes known as Lisbon copal and, like other similar copals from this part of West Africa, gives satisfactory oleoresinous varnishes after running. 

Gold size n. Oleoresinous varnish which dries rapidly to a tacky condition, but which hardens slowly. It is used chiefly as an adhesive for fixing gold leaf to a surface. 

Oil length n. Ratio of oil to resin in a medium. For an oleoresinous varnish, the oil length may be expressed in terms of parts by weight of oil to one part by weight of resin or, in American practice, in terms of USA gallons of oil per 100 lb of resin. Thus, a 25 gal varnish would mean, in American usage, a varnish composed of 25 USA... 

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