Paints high solvent

The term reactive diluents denotes low molecular mass reactants that act as solvents with an extremely low volatility and participate in the cross-linking reaction. Reactive diluents have become especially important in one-pack systems because they can partially or wholly replace the solvent in high-solvent paints. Reactive diluents participate in the cross-linking reaction because their functional groups are identical or similar to those of the principal binder. They are completely incorporated into the polymer network during curing. Good compatibility with the principal... 

The need for waste air treatment can generally be avoided by replacing conventional, high-solvent paints by low-solvent coatings. In some cases smaller waste air treatment plants may be necessary for specific demarcated areas where, for example, a solventborne layer is applied. 

The paint industry has always been seen as rather conservative. Despite the continuous experimentation with new formulations, only a few reach the market (Kemp, 1993). The main problem is associated with the lack of demand for cleaner products (Interviews, 1999). While the development of fast drying (high solvent) paints was pulled by the automobile industry, the development of low solvents paints has mainly been the result of regulatory pressures (and, sometimes, the sheer threat of regulations) rather then the product itself. Indeed, the architectural market has been quite hard to penetrate, given the well established preferences of do-it-yourself users. Gloss, durability and ease of application have always driven this market segment. Low solvent paints (such as waterbased paints) have not always matched up with these requirements. 

High, solvent vapors Light Piston flow, vettical from above Paint booth... 

Another important qninone is anthanthrone, especially its dibromo derivative (2.73), Cl Pigment Red 168. This latter pigment is scarlet in colonr and shows excellent resistance to solvents and is one of the most light fast and weather fast pigments known. It is nsed in high-grade paints. 

High-Solids Paints. Hitherto, for paints for spraying purposes, the mixed solids contents have been of the order of 5% to 15% by volume. However, with more modern spray equipment and other improvements in plant, the use of paint with solids contents in the range 30% to 40% is possible—which means in turn a diminished need for organic solvents. 

The solvency of hydrocarbon solvents used in paint and lacquer formulations is empirically described by their kauri butanol numbers, i.e. the volume in milHliters at 25 °C of the solvent required to produce a defined degree of turbidity when added to 20 g of a standard solution of kauri resin in 1-butanol [120]. Standard values are KB = 105 for toluene and KB = 40 for -heptane/toluene (75 25 cL/L). A high KB number corresponds to high solvent power. An approximately linear relationship exists between Hildebrand s 8 values and KB numbers for hydrocarbons with KB >35 8 = Q.Q6-KB+U.9 [99, 177]. 

Paints may contain all typical coatings components, although the use of organic solvents is being reduced to rely more heavily on water or high-solids paints. 

Emulsion paints are characterized by the fact that the binder (polymer) is in a water-dispersed form, whereas in a solvent paint it is in solution form. In emulsion systems the external water phase controls the viscosity, and the molecular weight of the polymer in the internal phase does not affect it, so polymers of high molecular weight are readily utilized in these systems. This is an advantage of emulsion paints. 

The development of low-solvent (high-solids) paints requires resins with a very low viscosity. The principal viscosity-determining parameters for such binders are the molecular mass and molecular mass distribution [2.45]-[2.47], [2.50]-[2.53]. Oligomers with a molecular mass of ca. 1000 3000 are required for high-solids paints [2.48], [2.54]. An acrylate binder with a molecular mass of 100000 can be processed to form a paint with 12.5% solids content at the application viscosity a molecular mass of ca. 6000 results in a paint with 50% solids content [2.46]. A narrow molecular mass distribution is beneficial in achieving low viscosity [2.45],... 

Solvent emission from paints can be reduced without lowering the molecular mass by using nonaqueous dispersions (NAD) (see Section 3.6). Acrylates have been described as binders for NADs, but apart from a low viscosity they offer few advantages over conventional coatings [2.50] and moreover must compete with high-solids paints and powder coatings [2.56]. 

Solvent-Free and Low-Solvent (High-Solids) Paints... 

Low-solvent paints are commonly referred to as high-solids paints and are defined as systems with a solids content exceeding 85 wt %. In practice, however, paints with a solids content of 60-80 wt% are also termed high-solids paints, particularly if the corresponding conventional (high-solvent) system normally contains <50wt% nonvolatile components [3.28]. 

Given the possibilities for postcombustion of the solvent in industrial coating, the trend towards high-solids paints is, however, not so pronounced in this class of binders as it is, for example, in the case of maintenance paints and architectural coatings. High-quality paints with a solids content > 70 wt% are not widely available. Powder coatings are preferred as an alternative in the industrial sector. 

Epoxy paints (see also Section 2.10) are usually applied as two-pack systems. Curing with amines is preferred in high-solids systems. Epoxy resins may also be used as coreactants or reactive diluents in low-solvent paints based on acrylic, polyester, or alkyd resins. 

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