Solventborne systems

Further, the dislocations in the world oil supply and the resultant discontinuities in petrochemical prices increased the cost of traditional low-solids solventborne systems and the cost of curing higher temperature thermosetting systems as well. The coatings industry responded to these pressures with new technology low-emission coatings. 

A large number of rheological additives for solventborne systems are commercially available. Hydrogenated castor oils, pyrogenic silica, and modified montmoril-lonite clays (organoclays, e.g, bentonite) are preferred. 

Phosphate-containing molybdate pigments are especially suitable for water-thin-nable or latex-based binders, because they improve adhesion to iron substrates. The other molybdate pigments are mainly used in solventborne binder systems. 

Flow Coat Conversion. Solventborne flow coaters are a major source of hydrocarbon emissions. This source became an early target for a replacement system. An alternative to reduce emission was the gas incinerator, but high capital costs and gas consumption precluded its use. 

Wheels are electrocoated engine blocks are coated with heat-resistant, usually waterborne materials. Other parts (e.g., steering equipment and shock absorbers) are painted with two-pack, one-coat epoxy systems that are usually solventborne use of waterborne systems is, however, increasing. 

Field trials have shown that the expected durability of the new waterborne coating systems is equal to that of conventional solventborne paints. As a further advantage, the number of single coats can be reduced from three to two. Standard freight cars are painted with a three-coat alkyd system consisting of an anticorrosive primer, an intermediate coat, and a topcoat, total DFT is ca. 150 pm. Such systems are being replaced by single-coat systems of waterborne acrylic resins and acrylic copolymers to reduce solvent emission. 

Solventborne wood preservatives (about 30% of the market) consist of 10% active ingredients and 90% solvent, usually white spirit or similar petroleum-based hydrocarbons. The active ingredients include preserva-tive/insecticides such as phenols, chlorinated and phosphated organics and copper/zinc naphthenates. Vacuum impregnation is used to apply this type of system. Timber treated by this method is not suitable for direct contact with soil for exterior use, it should be painted to prevent extraction of the active ingredients. It is used where precise control of the dimensions of the timber is important and leaching can be avoided (e.g. in the construction industry for windows, doors, etc.). 

Toxicity concerns surrounding creosote have promoted the newer solventborne and waterborne systems. The use of more controlled, enclosed processes plus emission abatement recovery techniques will restrict emissions from the new solventborne types. There has been little debate, so far, about the relative environmental impacts of the different active biocides and fungicides used in the newer solvent- and water-based systems. 

For the purpose of this chapter, discussion and examples will concentrate on the substrates used for today s high-profile automotive bumper applications (predominantly thermoplastic olefin [TPO]) and the conventional adhesion promoters (solventborne, waterborne) and one-component melamine topcoats (IK/ IK) and two-component isocyanate topcoat systems (2K/2K and 1K/2K). 

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