WATERBORNE EPOXY ACRYLICS

Epoxy resins have been made water reducible by the use of acid functional acrylic resins. They find widespread application as internal lacquers for DWI beer and beverage cans (see Chapter 7- Waterborne Applications). They are often made in solution in butyl glycol and butanol and are then neutralised and dispersed into water under agitation. A full discussion of this technology and all of its variants is given in the Epoxy volume of this series of books. A brief outline of some of the chemistry will be given here. 

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Waterborne Epoxy Acrylics by Andrew Hoggan BSc and David Pane BSc... 

Chemical modification of the epoxy resin includes either attaching hydrophilic groups to the epoxy resin or attaching the epoxy resin to hydrophilic polymers. This is most often done by grafting. For example, one of the largest volume uses for waterborne epoxy is the coating of metal cans. In this application the epoxy resin is rendered water-dispersible by the grafting of the epoxy resins to acrylic polymer. 

Surfactants act as wetting agents by lowering the surface tension of the waterborne epoxy. Silanes can be used to increase adhesion to certain substrates and fillers, as shown in Table 14.4, formulation C. Water-compatible thickeners and protective colloids such as polyvinyl alcohol, substituted cellulosics and sugars, and some acrylics improve application properties and offset viscosity decrease seen with water dilution. 

Pigmented, two-pack, waterborne epoxy resin coatings (garages) or one-pack waterborne acrylic resin emulsion paints are used for areas that receive less wear (e.g., cellars). Wooden parquet floors are coated with one- or two-pack polyurethane varnishes that can be applied by spraying or brushing. Acrylate-based waterborne parquet varnishes are also used because they are environmentally friendly. 

The cellulose based materials that are used as nano-reinforcements are cellulose nanocrystals (i.e. whiskers and nanospheres), nanofibrillated cellulose, regenerated cellulose nanoparticles and electrospun nanofibers. A wide range of polymer matrices have been used to form cellulose nanocomposites. Synthetic polymers such as polypropylene, poly(vinyl chloride) (PVC) [102], waterborne epoxy [103], waterborne polyurethane [104], polyurethane [105], poly-(styrene-co-butyl acrylate) [106], poly(oxyethylene) [107], polysiloxanes [108], polysulfonates [109], cellulose acetate butyrate [110,111], poly(caprolactone) [112], poly(viny 1 alcohol) [113] and poly (vinyl acetate) [114]. Different biopolymers such as starch-based... 

Chem. Descrip. Proprietary polysiloxane-based defoamer in wh. spirit Uses Defoamer for nonaq. high-solids and waterborne epoxy coatings, alkyds, acrylics, PU, polyester, disp. adhesives, polymerization Regulatory DOT regulated SARA 311/312 reportable Properties Yel. clear liq. aromatic odor negligible sol. in water sp.gr. 0.80 dens. 6.7 Ib/gal vise. 15 cps flash pt. (PMCC) 55 C VOC 74.2% (EPA method 24) 100% act., 20.6% solids Use Level 0.2-1.0% on total wt. 

Chem. Descrip. Mixf. of special polyols, emulsifiers, and polysiloxane Uses Air release agenf and defoamer for general purpose high-solids and industrial coatings (all ds, epoxies, acrylics, waterborne architectural), printing inks, adhesives, latex applies. 

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. 

The use of polymeric blend composites for corrosion protection of AA 2024-T3 has been reported, including composites formed by incorporating water-soluble conducting polymers (either polymethox-yaniline sulfonic acid or poly(4-(3-pyrrole) )butane sulfonate) into various binders (a cross-linked polyvinyl alcohol, a waterborne epoxy, a modified water-dispersible polyester, and a UV-curable urethane acrylate binder) [149]. The preparation of epoxy and polyaniline composite coatings has been described, using either nanodispersed EB particles [91] or EB that was first dissolved in selected amine hardeners before adding the epoxy resin [98]. Even with very low EB loadings, these workers reported enhanced corrosion protection for steel. 

S. Zafar, F. Zafar, U. Riaz and S. Ahmad, Synthesis, characterization, and anticorrosive coating properties of waterborne interpenetrating polymer network based on epoxy-acrylic-oleic acid with bntylated melamine formaldehyde , / Appl Polym Sci, 2009,113, 827-38. 

Polymer complexes of PANI and a polymeric dopant such as poly(acrylic acid) or poly (methylvinlyether-flif-maleic acid) have been synthesized using what the authors describe as a template-guided synthetic method to form aqueous solutions or dispersions of the complex [230]. An advantage of these polymer complexes is that they remain conductive at pH value up to 9, making them potentially useful in marine environments. The PANI complexes were used as additives (l%-5%) in a commercial waterborne epoxy, which was then applied to various A1 alloys (AA 2024-T3, AA 7075-T6, and AA 6061). The coatings were found effective in inhibiting corrosion of the A1 alloys in air-saturated seawater. 

In the 1970s, the development of two breakthrough waterborne coating technologies based on epoxy resins helped establish the dominant position of epoxies in these markets PPG s cathodic electrodeposition automotive primer and ICI-Glidden s epoxy acrylic interior can coatings. 

Waterborne coatings. These are based on two-component epoxy-polyamine/polyamidoamine or epoxy-acrylic latex hybrids. One limitation of the water-borne systems is their poor cure in high humidity conditions. They have made some penetration in industrial maintenance coatings and are expected to grow more significantly in the future. 

The dispersion of fibers in polymer latex to prepare composite has been reported for poly(6-hydroxyoctanoate) (PHO) [101, 102], polyvinylchloride (PVC) [103], waterborne epoxy [104] and polyvinyl acetate (PVAc) [94]. Most of the works focus on the use of non-polar, non-water-sensitive polymers, while keeping an aqueous media for the processing of the films to preserve the dispersion of the nanoparticles. In their pioneering work, Favier et al [94] adopted the technique of solvent casting using a synthetic latex obtained by the copolymerization between styrene (35 wt%) and butyl-acrylate (65 wt%) (poly(S-co-BuA)). Nanowhiskers were dispersed in the latex and evaporated. The nanocomposite films were obtained by water evaporation and particle coalescence at room temperature, that is at a temperature higher than Tg of poly(S-co-BuA), around 0 C. 

The following is a typical example of an " epoxy-acrylic graft co-polymer used in waterborne epoxy can coating lacquers. 

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acrylic (52). The acrylic—vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aliphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, solid epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

The flammability problem was resolved by converting to waterborne flow coat primers. The first waterborne appliance flow coat primer was installed on a dryer drum line in 1972 (9 ). The primer was a water-soluble epoxy-modified acrylic that had excellent hardness, abrasion resistance, and chemical resistance. 

A second generation of phenolic dispersions, patented by J. S. Fry (33). involved the post dispersion of phenolic resins in a mixture of water and water-miscible solvents. To conform with air pollution regulations, the solvent was held to 20 volume %, or less, of the volatiles. A heat-reactive phenolic resin dispersion (34) and a phenolic-epoxy codispersion have become commercially available based on the above technology. Supplied at 40-45% solids, these products, which have a small particle size (0.75-1.0 ym), are better film formers than the earlier dispersions. Used alone or in blends with other waterborne materials, corrosion-resistant baking coatings may be formulated for coil coating primers, dip primers, spray primer-surfacers, and chemically resistant one-coat systems. Products of this type are also tackifiers for acrylic latexes, and such systems have been employed as contact, heat seal, and laminating adhesives for diverse substrates. 

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