Solventborne paints

In solventborne paints, small amounts of the organic solvents may remain in the resultant film after cross-linking. Solvent retention can reduce internal tension, linear shrinkage behavior, and the glass transition temperature [3.14]. 

The high polarity of water is responsible not only for differences between the application behavior of waterborne paints and solvent-containing paints. It also means that the organic polymers used as binders for waterborne paints must have a different structure from those used in solventborne paints. 

The wet point in waterborne paints is analogous to the oil number in solventborne paints. It represents the number of milliliters of water (containing 2% wetting agent) that are required to convert 100 g of extender to a compact mass. 

Fillers are applied with electrostatic spraying devices (fast-rotating bells) to give dry film thicknesses of about 40 pm. Waterborne fillers with polyester-melamine binders (primer surfacers) have been developed to reduce the volatile organic content. They yield a film thickness of 30 pm after a prereaction time of 10 min at lOO C and a reaction time of 20 min at 165 °C. The properties of the films are similar to those formed by solventborne paints. More recently, waterborne fillers based on blocked isocyanates have been developed. Field trials have shown that their mechan-ieal resistance is very good. 

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 paints are based on synthetic resins (e.g., acrylate styrene copolymers) which are soluble in aliphatic and/or aromatic hydrocarbons. The properties of these coatings are chiefly determined by the nature and proportion of the monomers. 

Environmental Protection. On account of the high paint transfer efficiency and low solvent content, environmental pollution in electrodeposition coating is much lower than with spray coating. The solvent contents of electrodeposition paints relative to the solids content are 5-10% in comparison with solventborne spray paints with a solvent content of 50-100%. The most important sources of emission are the electrodeposition tank, the rinsing zone, the stoving oven, and the drain of the ultrafiltrate [3.125]. Developments in new electrodeposition paints aim to reduce the organic volatile solvent content, to have fewer condensation products in the stoving ovens, and to have lead-free formulations [3.126]. 

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. 

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. 

However, the poor adhesion of the surface does not allow a further painting stage. The surface of Parylene coatings can be modified by a special plasma coating. In this way, an interlayer is placed to provide good adhesion to the substrate as well as to a subsequent primer. After this procedure, the hydrophobic Parylene polymer again becomes paintable with both solventborne and waterborne spray primers." ... 

Decorative paints, so called because they form a decorative coating inside and outside buildings, represent over 50% of coatings consumption in both the USA and Europe. This market can be further divided into trade and retail sectors. The former supplies the professional painter while the latter serves the retail outlets. One of the most noticeable developments in the retail sector in recent years has been the increase in paint sales from the large DIY stores at the expense of the smaller suppliers. Both retail and trade sectors can be further divided into waterborne emulsion paints , for walls, ceilings, etc., and solventborne gloss, primer, varnish, etc. 

This market has not been characterised by complex technology hence many paint producers exist. There are, however, several major companies who share approximately 40% of the decorative market. Resins for paint manufacture, both waterborne and solventborne, are produced by independent manufacturers who sell them to the paint producers, many of whom possess no (or limited) resin production facilities. The European decorative paint market is 2.7 million tonnes per annum (Mtpa), split 65% trade and 35% retail, while the US market is slightly smaller, at 2.5 Mtpa. 

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.). 

The procedures specified by the US EPA for testing paint products for compliance with VOC limits are described in Federal Reference Method 24, which employs several ASTM test standards. VOC values for waterborne or solventborne coatings are calculated by the following formula ... 

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