Air-drying paints

Both the barium lake P.R.49 1 and the calcium lake P.R.49 2 resemble Lake Red C pigments (P.R.53 1) in terms of fastness to organic solvents, to alkali and acid, and to fastness in application. However, P.R.49 grades are much less heat stable, which narrows their applicability in plastics. Areas of application, especially in the USA, include elastomers, to a lesser extent also inexpensive industrial paints, air drying and nitro paints. Their main market, however, is in printing inks. 

Uses Rheology control agenL pigment antisettling agent, thixotrope, gel-lant, antisagging agent for trade sales and industrial finishes, stains, aerosol paints, air-dry and force-dry alkyds, architectural paints, appli-ance/metal furniture topcoats Features Post-additive no shear required Properties Straw-colored clear liq. sp.qr. 1.05 dens. 8.76 Ib/qal 71% NV in water... 

Uses Wetting and dispersing agent for water-thinnable paints, air-dry and stoving alkyds, emulsion paints... 

Zinc arc spraying is an inexpensive process in terms of equipment and raw materials. Only 55—110 g/m is required for a standard 0.05—0.10 mm Zn thickness. It is more labor intensive, however. Grit blasting is a slow process, at a rate of 4.5 m /h. AppHcation of an adhesive paint layer is much quicker, 24 m /h, although the painted part must be baked or allowed to air dry. Arc sprayed 2inc is appHed at a rate of 9—36 m /h to maintain the plastic temperature below 65°C. The actual price of the product depends on part complexity, number of parts, and part size. A typical price in 1994 was in the range of 10—32/m. ... 

PhenoHcs that are not heat-reactive may be incorporated into both air-dried and baked oleoresinous coatings. AppHcations vary widely and include clear and pigmented exterior varnishes, aluminum-maintenance paints, 2inc-rich primers, can coatings, insulation varnishes, and concrete paints. As modifiers in a great variety of appHcations, they enhance the performance of oleoresinous and alkyd coatings. 

Llthol Reds. Lithol Red or Pigment Red 49 1/7103-38-4] is one of the most important of the precipitated salt pigments. They comprise a family of sodium (PR 49), barium (PR 49 1), calcium (PR 49 2), and strontium (PR 49 3) salts of dia2oti2ed Tobias acid or 2-naphthylamine-l-sulfonic acid coupled with 2-naphthol. The most popular are the barium and calcium salts, the former being yellower in shade. These reds are used where brightness, bleed resistance, and low cost ate of primary importance. They are neither resistant to heat nor chemicals, and are used primarily in printing inks and some inexpensive air-dried industrial paints where good durabiUty is not requited. 

Silicone resins with high phenyl contents may be used with medium or short oil alkyds as blends in air-dried or baked coatings to improve heat or weather resistance the alkyd component contributes to adhesion and flexibiUty. AppHcations include insulation varnishes, heat-resistant paints, and marine coatings. 

The differences in composition between water-borne and solvent-bome air-drying paints necessitate change in driers and drier combinations. Since traditional driers are dissolved in mineral spirits, xylene, or other aUphatic/aromatic solvents, they are not readily dispersed in an aqueous system. If traditional driers are used, they must be dissolved in the vehicle before neutralization, which may result in a severe viscosity increase and processing problems. 

Air-drying epoxy paints are not required to be stoved due lo chemical reaction at about I20°C, which may affect its hardness. To speed up the curing, it may be stoved at a maximum temperature of, say, 60-80°C as noted in column 2. 

Air-drying paints are easily available as noted above but they may not suit a regular production line as ... 

Air-drying alkyds (similar to the resins in conventional gloss paints) ... 

A paint rarely consists solely of pigment dispersed in a solution of a binder. For one reason or another, small quantities of ancillary materials called additives are included. The oldest and still the most important are the driers which are used in all air-drying and many stoving paints containing drying oils. They are organic salts of certain metals, notably cobalt, calcium, barium, zirconium and manganese, with lead very much in decline. 

All members of this pigment family share good lightfastness, combined with poor solvent and migration resistance. These properties define and limit their application. Monoazo yellow pigments are used extensively in air-dried alkyd resin and in emulsion paints, and certain inks used in flexo and screen printing. Other applications are in letterpress and offset inks, as well as in office articles. 

Fig. 54 Influence of the pigment concentration on the rheological behavior. P.Y.73 in air drying alkyd resin paint.

This compound has entered pigment history as Hansa Yellow G . The commercial varieties are products with comparatively coarse particle sizes and specific surface areas of approximately 8 to 30 m2/g. P.Y.l provides good hiding power, it is used primarily in air drying paints as well as in packaging and textile printing. 

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