Waterborne paints applications

The coatings industry has developed waterborne paints and coatings that greatly reduce VOC emissions. Some applications include automotive coatings, interior latex paints, and polyurethane coatings (Sherman et al., 1998). 

Case studies illustrate that waterborne paints are indeed feasible for many applications ... 

Possible combinations of red lead with various binder systems are listed in Table 39 [5.114]. Red lead is still used for heavy-duty anticorrosion applications, especially for surfaces bearing residual traces of rust. In waterborne paints, red lead has no advantages over zinc phosphate [5.149]. 

Today, a large and increasing proportion of the automotive OEM metallic basecoats in Europe and North America are already waterborne and refrnish basecoats are also available in waterborne versions. Other paint applications have followed and the significant growth of waterborne systems can easily be seen in the statistics of the paint associations. Also in printing inks, the use of waterborne inks is steadily growing. 

Neutralizing agents are used in waterborne paints to neutralize binders and stabilize the product. Ammonia and various alkylated aminoalcohols are used, depending on the type of binder and method of application. On hardening, the amines mainly evaporate along with the water. 

Waterborne paints provided the technological basis for electrodeposition paints (Section 3.8), in which negatively charged paint particles (anaphoresis, industrial introduction at the beginning of the 1960s), or positively charged paint particles (cataphoresis, industrial introduction at the end of the 1970s) are deposited from aqueous solution onto metallic substrates by application of an electrical field [3.40]. 

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. 

As a result of the particulate nature of the binders only a low gloss and, in some cases, only limited corrosion protection can be obtained. Waterborne paints based on dispersions can be applied by spraying, however they are of only limited use for electrostatic coating and dipping applications due to their rapid drying properties. 

Corrosion-resistant and wear-resistant materials (e.g., stainless steel and in special cases suitable plastics) have to be used for the equipment required to produce and apply waterborne paints. This applies to production vessels, storage and transportation vessels, to the feed system used for application (e.g., closed circuit tanks, pipelines, and pumps) all of which must be able to withstand chemical mechanical stress. The use of corrosion-resistant materials for the spraying equipment is also advantageous. 

For waterborne paint systems (especially emulsions used for decorative purposes) defoamers based on mineral oils are often used. In addition to the mineral oil as carrier, these products contain finely dispersed hydrophobic particles (e.g., silica, metal stearates, polyureas) as defoaming components. A small amount of silicone is sometimes included to intensify the defoaming action. For high-quality waterborne coatings in industrial applications, defoamers are used that contain hydrophobic silicone oils as the principal defoaming component instead of mineral oils. They have a better defoaming effect, but are more expensive. In most cases silicone defoamers do not cause the gloss reduction that is often observed with mineral oil products. 

The neurotoxic effects found in painters and coaters exposed to solvents are the subject of controversy. Some studies describe subjective symptoms such as fatigue, difficulty in concentrating, and short-term memory problems in workers employed in industrial paint and coatings application. These symptoms have not, however, been observed in painters employed in the architectural and exterior-use paints sectors who mainly use waterborne paints [12.11]. 

Uses Defoamer for architectural and waterborne general coatings grind defoamer during production and applic. of waterborne paints Features Effective against microfoam DM-3880-C [Hi-Mar Spec. fhornley]... 

Paint consists of a mixture of pigments which gives body and colour, and a resin or binder which is the actual film-forming component and acts as a glue to hold the pigment together and stick them to the surface. Binders include synthetic resins such as acrylics, polyurethanes, polyesters and epoxies and can be a combination of resins, e.g. epoxy/ acrylic and polyurethane/acrylic. To adjust the curing properties and reduce the viscosity so that the paint can be easily applied, a solvent or carrier is used. These evaporate after application and do not form part of the paint film. In waterborne paints, the carrier is water. With solvent-borne paints, also called oil-based paints, the carrier is a solvent such as acetone, turpentine, naphtha, toluene, xylene and white spirit. 

Papasavva et al. [36] showed diagrams of auto paint lines that indicated abatement on the solvent-borne primer/surfacer ovens, on the heated flashed zone after waterborne basecoat application, and on the solvent-bome clearcoat oven. The abatement equipment included a carbon concentrator, which is likely a device for solvent vapor adsorption on activated carbon. A collection efficiency of 90% was reported. The abatement equipment also included a system for oxidizing the vapors to form water and carbon dioxide. These units were called reactive thermal oxidizers (RTOs) [36], and their destruction efficiency was reported to be 95%. For the various scenarios discussed in Section 6.7.2, the abatement efficiencies were reported to range from 52.3 to 62.5%. Emissions from powder coatings ovens are expected to be so low that abatement is not needed, and calculations with and without powder coating oven abatement gave the same results for VOC emission [36]. 

An overview is presented on the merits of polyurethane dispersions in waterborne paint formulations. In addition to the characteristics listed which they impart to coatings, such binders can offer an even wider range of properties by means of blending or copolymerisation, producing binders which are tailor made for specific applications, it is stated. 

The industrial reaction to this situation is one of compliance, with an increasing use of waterborne paint formulations based on the use of synthetic latices as binders especially in paints for domestic application. Such latices are usually polymeric colloids, of volume fraction from 0.2 to 0.5, dispersed in aqueous surfactant solution, prepared by a process of emulsion polymerization. These dispersions have a slightly turbid appearance, often with a low viscosity of order 1 mPa s. The latices can be readily prepared as near-monodisperse colloids. 

Alkyd paints dominated the architectural coating market for a long period until the appearance of polymer dispersions or the so-called latex paints. Specifically for wall application waterborne paints based on poly(vinyl acetate) homo- and copolymers, styrene-acrylics and pure acrylic latexes almost completely took over the market from the alkyd resins for both interior and exterior application. However, for... 

Forsgren, A. and Palmgren, S., Effect of Application Climate on Physical Properties of Three Waterborne Paints, Report 1997 3E, Swedish Corrosion Institute, Stockholm, 1997. 

Colloidal silica dispersions have also been used in various waterborne paints, coatings and lattices as the silica nanoparticles can affect the properties of the resulting film [24]. However, aqueous colloidal silica dispersions have not reached their full potential in these applications, although a number of properties ofthe resulting films maybe improved. The reasons for this are the colloidal stability of the dispersion and coating formulation as well as the water resistance of dry film coatings containing silica particles. 

Electrostatic painting is the application of electrostatically charged paint particles to an oppositely charged workpiece followed by thermal fusing of the paint particles to form a cohesive paint film. Both waterborne and solvent-borne coatings can be sprayed electrostatically. 

Paints currently used for indoor application are now almost exclusively waterborne. Most of these fall into the following categories AO... 

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