Epoxy resins waterborne coatings

Uses Emulsifier for epoxy resins, waterborne industrial coatings Properties Dens. 9.1 Ib/ l vise. 12,000 cps HLB 18 nonionic 65% act., 65% solids, 35% water Use Level 3-5% solids on epoxy resin Hydropalal 88 [Cognis/Coatings Inks Cognis KGaA/Coatings]... 

Waterborne Coatings. In the switch from solvent-home to waterborne systems, epoxies are successfully bridging the gap largely by adaptation of conventional resins. Waterborne coatings accoimted for almost 25% of epoxy coating consumption in 2001. 

Waterborne Costing s. These coatings utilize either Hquid or soHd epoxy resins that have been modified to allow their use with water. They are usually in the form of emulsions, suspensions, dispersions, or water-dilutable resins that can be heat- or RT-cured. They are appHed by convenient methods such as roUer-coating, dipping, spray, or electro deposition. 

Significant advances in waterborne coatings have been made by PPG Industries utilizing epoxies as co-resins. These coatings are used in cathodic electrodeposited systems, widely accepted for automobile primers. Many patents have been issued for this important technology (50,51). 

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acryHc (52). The acryhc-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 aHphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, soHd 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. 

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. 

Bauer, R. S., Formulating Weatherable Epoxy Resin for Maximum Performance, Waterborne and Higher Solids Coating Symposium, New Orleans, 1982. 

Both processes are applicable to waterborne epoxy adhesives and coatings, although the emulsification process is generally used with adhesives. Preparation of epoxy resin emulsions is covered in Chap. 4. 

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. 

COOH HOOC xAr COOH branched, low molecular mass, carboxy-functional 1000- 5000 triglycidylisocya-nurate, epoxy resins, melamine resins powder coatings, waterborne paints... 

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. 

For many years, paints used to coat cans contained considerable amounts of volatile organic solvents. Waterborne can coatings were developed to reduce solvent emissions and are used worldwide. Binders used in waterborne can coatings are modified epoxy resins (see Section 2.10). Acidic acrylate chains are grafted onto an epoxy molecule. After partially neutralizing with amines, the resins can be dispersed in water. 

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. 

H. Matsuki, R. Nishida, and M. Murata. Storage-stable one-liquid waterborne epoxy resin dispersions for coatings with good thamal curability and resistance to corrosion and impact. JP Patent 2 003 253 004, assigned to Kansai Paint Co., Ltd., Japan, September 10,2003. 

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. 

In recent years, water-dispersed epoxy resins also have gained importance in a variety of applications. Water-soluble epoxy resins are prepared by the esterification of epoxy resin with drying oils/ fatty acids of drying oil, followed by the formation of either half esters of dicarboxylic epoxy esters, or maleinised epoxy esters through reaction with polybasic acid anhydrides. They become water soluble on neutralisation with dimethyl etha-nolamine (Fig. 7.4). The cationic polymerisation of emulsified epoxy resins by 1 % perchloric acid has also been reported. The polyols obtained were cross-linked with MF resin to produce waterborne coatings, which are free from co-solvent and show excellent solvent resistance at low bake temperatures. ... 

The results were positive and promising. Bagherzadeh et al. [81] found that the anticorrosion performance of a two-component water-based epoxy resin coating system was improved by adding only 0.02 wt% nano-PANI. Ahmad et al. [82] investigated the corrosion protection behavior of waterborne resorcinol formaldehyde (RF)-cured composite coatings of poly(l-naphthylamine) (PNA)/poly(vinyl alcohol) (PVA) on mild steel, and even superior corrosion protective performance was observed in different corrosive media when compared with the reported solvent-based conductive polymer coatings. 

Designed for epoxy resin systems, Anquamine 401 and Ancamide 2424 (by Air Products) are a modified aliphatic curing agent at 70% solids in water for waterborne two-component epoxy coatings and a modified polyamide curing agent for liquid epoxy resins in two-component structural adhesives. 

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