Coalescing solvents

Mixer-settlers have been the more common type of equipment and, with the development of hydrometallurgy over the past 20 years, designs have improved considerably. To select the appropriate equipment, a clear understanding of the chemical and physical aspects of the process is required. Also the economics must be considered relative to the type of equipment to suit particular conditions of given throughput, solution and solvent type, kinetics and equilibrium, dispersion and coalescence, solvent losses, number of stages, available areas, and corrosion. 

In addition to water, these paints contain biocides, surfactants, pigments, monomers, coalescing solvents, driers, and volatile additives. 3,121 Volatile components contained in these include aldehydes, aliphatic hydrocarbons (straight chain and cyclic), aromatic hydrocarbons, esters, ethers, glycol ethers, glycol ether esters, and halogenated hydrocarbons. Some of these materials are listed in Table 12.4. 

Both examples Illustrate that solvent blends can be used to extract mesophase forming fractions from the A-240. Figure 9 suggests several other solvents may form successful blends. Solvents normally inappropriate should be blended to shift the solubility parameters of the mixture closer to the edge of the enhanced solubility region where the blend can extract a pitch fraction capable of complete coalescence. Solvent blends can also be used to moderate solvent costs without impairing solvent effectiveness. 

The Vinnik group [59b] has recently found that nonionic surfactants act like coalescing solvents in promoting interdiffusion in PBMA latex films. Kim et al. [55] have reported that cetyl and steaiyl alcohol act as plasticizers to promote interdiffusion in PS latex films. 

Smage Store in cool, dry area, away from corrosives Uses Coalescing solvent for coatings, cleaners, cosmetics, agric., electronics, ink, textiles, adhesives wetting agent solubilizer ManMDistrib. Aldrich... 

Uses Resin intermediate coalescing solvent for water-based paints unsat. polyester resin comonomer for surf, coatings plasticizers lubricants printing inks insect repellent ManuUDistrib. Aldrich Eastman Fluka Trade Names TMPD Glycol... 

Butyl Carbitol acetate 2-00 COALESCING SOLVENT Butyl Carbitol acetate 1-00... 

Toxicology LD50 (oral, rat) 4290 mg/kg, (skin, rabbit) 8 g/kg TSCA listed Uses Solvent for paints, cosmetics coalescing solvent for water-based paints Propylene glycol isoceteth-3 acetate CAS 93385-13-8... 

Odor elimination is the additional benefit which has helped to drive the replacement of solvent-based systems. In packaging materials, most odors are related to the solvents used in inks, coatings and adhesives. Also, coalescing solvents from water-based systems caused odors. Elimination of solvent is a priority but solvent replacement may also change the response to the odor because solvents such as toluene and xylene smell like lubricating oils or turpentine whereas isopropanol smells more like a disinfectant. Odors stem not only from solvents but also from products of the thermal and UV degradation of other components and solvents. "... 

RECENT ADVANCES IN COALESCING SOLVENTS FOR WATERBORNE COATINGS... 

Role of a coalescing solvent Most eoatings based on emulsion polymers are used in environments where they will be expeeted to form a coherent film at temperatures as low as 0°C. However, other physical properties besides film forming capability are required from the polymer. These include abrasion resistance, hardness, chemical resistance, impact performance, etc. These can often be impossible to achieve with a polymer of low Tg. The polymers, which most clearly meet these criteria arc acrylics or copolymers of vinyl acetate or styrene. These would, without additions of coalescing species, be brittle, forming incoherent films with little adhesion to the substrate at normal application temperatures. 

Coalescing solvents allow these polymeric systems to form films at ambient or sub-ambient temperatures. The presence of the coalescing solvent has the following effects. 

An emulsion polymer consists of a dispersion of polymeric particles varying in size from 0.05-1 (Xm, dispersed in an aqueous environment. The coalescing solvent may be found in several different locations depending on their nature. They are classified according to their preferred location in the aqueous system. 

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