Waterborne paints solids content

It was also shown that stable latexes of high solid content, and small particle size could be practically obtained by this emulsion polymerization technique. Such microlatexes based on acrylic polymers modified by polyesters are an interesting approach to waterborne coatings leading to high gloss paint films (9). 

One can rationalize a need for small rubber inclusions in some of the newer approaches to waterborne and high solids epoxy coating systems. Water-thinned epoxy coating compositions are described (48) where the two-component system consists of a nitrile rubber modified epoxy resin in the epoxide component and a styrene/ butadiene/methylmethacrylate latex modifier for an emulsion-based polyamide hardener component. Showing improved adhesion, impact and water resistance, the paint has good wetting characteristics and can be formulated to a high solids content at low viscosity. 

The increasing importance of environmental considerations places new requirements on paint resins and has broadened the range of paint systems. Paints are now required that have a low solvent content (medium-solids, high-solids coatings) or are solvent-free (powder coatings), that can be adjusted by dilution with water (waterborne paints), and that are thermoplastic or capable of undergoing cross-linking. All of these properties must be obtained via the polymer structure of the binders. Important parameters are described below. 

Polyester paints with high solids contents (65-75 wt% at application viscosity) can be produced from very low molecular mass resins [2.95]. Low-pollution paints can also be produced from water-soluble polyester resins [2.85]. On account of their good water solubility, HMMM resins are particularly suitable for cross-linking these resins. Organic cosolvents (mostly glycol ethers) must be added to waterborne polyester paints to control their viscosity and applicability (leveling, substrate wetting). 

Characteristic properties of waterborne emulsion paints are relatively high solids contents (50-60 wt%), rapid dilution with water without any viscosity anomaly, and a low content of organic solvents (< 5%). 

Waterborne basecoats with higher solids contents are now available metallic basecoats contain about 18wt% solids and solid (straight) color basecoats 25-40 wt%. The solvent in waterborne paints is not pure water about 15% of organic solvents is still needed as a cosolvent for proper film formation. Metallic basecoats are applied at a DFT of 15 pm, solid color basecoats at a DFT of 20-25 pm. 

Although two-pack epoxy primers and polyurethane intermediate coats have high solids contents, they still contain significant amounts (20-30 wt%) of organic solvents. In polyurethane topcoats, the VOC is even higher. Anticorrosive, waterborne primers based on aqueous dispersions of two-pack epoxy resins and one-pack acrylic resins have been developed to decrease solvent emission. Waterborne, one-pack acrylic topcoats are also used. All of these waterborne paints contain 2 - 5 % organic cosolvents that are required for film formation. 

The main application technique in the decorative area is still by hand (brush). Hence, future trends continue to reflect attention on worker exposure and environmental issues. This is already seen in the move to low aromatic content white spirits and isoparaffin solvents in conventional systems. High solids and waterborne technologies are being developed and both possess certain advantages and disadvantages, mainly relating to appearance and ease of use. Water-based systems bring, in principle, increased potential for water pollution, as consumers continue to rinse their brushes and paint rollers under the tap and transfer the water-soluble components such as amines and biocides to the aqueous environment. The consequence of diffuse water emissions of this type is still under debate. 

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