Air drying systems

A water-reducible coating or resin is one that is diluted with water before use. Water-reducible alkyds give comparable drying performance to solvent-bome alkyds. However, they are not widely used because film properties tend to be poorer than those of solvent-bome alkyds, especially in air-dry systems (26). This is pardy because of alcoholysis of the alkyd by primary alcohols such as 1-butanol [71-36-3] C H qO, a common solvent in water-reducible alkyds (27,28) secondary alcohols such as 2-butanol [78-92-2] C qH O, minimize this problem (27). In any case, the slow loss of amine or ammonia leads to short-term high sensitivity to water. Even in the fully dry films, the presence of unreacted carboxyHc acid groups leads to films having comparatively poor water resistance limiting their usehilness. 

In the paint industry, transparent types are used only to a limited extent. In air drying systems, P.O.34 equals step 6-7 on the Blue Scale in full shades, while opaque colorations with TiOz (1 5) only reach step 3 for lightfastness. In baking enamels, the pigment is not fast to overpainting. 

In the print field the pigment is almost exclusively used in air drying systems. P.R.4 is very likely to bloom in stoving enamels. At only 120°C, the concentration limit for blooming is as low as 2.5%, and at 140°C the limit is at 5%, which makes it necessary to carry out test experiments. Application is consequently restricted to baking enamels targeted for low temperature purposes. In epoxy resins, the pigment turns brown, as does P.O.5, and is therefore unsuitable for use in these media. 

The paint industry has little demand for P.R.2. The pigment finds some use in household paints, especially in air drying systems. 

Apart from air drying systems, P.R.14 is also used in baking enamels however, it blooms beyond certain concentration limits. In an alkyd-melamine resin system, for instance, the pigment shows resistance to blooming up to 160°C, independent of the concentration the concentration limit at 180°C is 0.2%, and at 200°C it is 1%. Blooming is accompanied by considerable bleeding. 

P.R.14 is very lightfast its full shade lightfastness in air drying systems equals step 6-7 on the Blue Scale in baking enamels, it reaches step 7-8. In white reductions (1 7 Ti02), the lightfastness of the same systems equals step 5-6 and 6-7, respectively. 

The paint industry employs P.R.22 in air drying systems, in emulsion paints, and occasionally in industrial finishes although there is some danger of blooming, and the appropriate limit has to be observed. Again, P.R.22 is much less lightfast in these media than P.R.l 12. Areas of application include paper mass and surface coloration, colored pencils, artists colors, and other purposes. 

In oven dyring and air drying systems, for instance, P.R.48 4 equals step 7 on the Blue Scale, while its weatherfastness after one year of exposure matches step 4-5 on the Gray Scale. Its shade darkens upon weathering. In such deep shades the pigment satisfies more stringent requirements and may even be used in applications such as automobile refinishes. 

P.R.88 is also found in other systems throughout the paint industry, such as in various types of air drying systems and powder coatings. 

Briefly, air is introduced by a large compressor to a cooling system, where it is cooled down to 3-5°C and most of the moisture is condensed. From there, the air is passed through a dehumidifier, such as silica gel, where the last traces of moisture are retained. Figure 22 shows Ballestra s air drying system. 

The baking systems have excellent resistance to alcohols, aromatics, hydrocarbons, aliphatics, and ketones. Special formulations with both the air dry or low force cure type materials can be produced to provide resistance to the same solvents as the high bake systems. Many of the air dry systems will be resistant to splash and fumes of the solvents mentioned. 

The air dry systems demonstrate excellent resistance to various concentrations of alkalies but are generally limited to a maximum temperature of 150°F (66°C). 

Plastisols are not "air dry systems, i.e.y they require fusion temperatures of at least 250°F for the copolymers and 300°F for the homopolymers. Plastisols enable us to obtain very low durometer hardness, thick fused sections, and excellent chemical resistance. High durometer hardness values are difficult to obtain. 

Flash dryers utilizing superheated steam as the drying medium often have unique quality and energy advantages over air drying systems. More recently, flash dryers consisting of inert media... 

Mechanical incorporation of air into the paste or the use of chemical "blowing agents" into the formulations allows foam products to be produced. Plastisols are not "air-dry" systems that is, they require fusion temperatures of at least 250 °F for the copolymers and 300 °F for the homopolymers. 

Chem. Descrip. Silicone-contg. defoamer in diisobutyl ketone soiv. Uses Defoamer for solv.-born coatings, air-drying systems, industrial and decorative finishes, and airless spray coatings Properties Colorless clear Iiq. dens. 0.80-0.82 g/cm (20 C) flash pt. 47 C ref. index 1.410-1.420 Use Level 0.5-1.0% (on total formulation)... 

Uses Corrosion inhibitor, adhesion promoter for paints or coatings onto metal substrates, for use in baking and air-drying systems with alkyds, polyesters, acrylics, urethanes metal pretreatment Properties Yellowish liq. very strong odor partly sol. in water sp.gr. 1.08 dens. 9.03 Ib/gal vise. 17,000 cps b.p. 137 C flash pt. (PMCC) 38 C 66% NV... 

Uses Lt. stabilizer, gloss retention aid for plastics and clear or pigmented coatings incl. automotive urethanes, industrial maintenance, UV-cured coatings, solv.-free polyesters, air-drying systems, baking enamels, inks Features Decreases crack formation... 

Chem. Descrip. Modified silicone polyether Uses Substrate wetting agent for waterborne coatings and inks on difficult substrates, aq. primers, fillers, top coats, oven- and air-drying systems, two-component PU FeaMes High efficiency low dynamic surf. tens. 

Arylzene 7173 Aryjzene 7175 adhesion promoter, air-dry systems Lubrizol 2061 Lubrizol 2062 adhesion promoter, alkyd air-dry coatings CK-2400 CK-2500 adhesion promoter, alkyd coatings SK... 

---