Epoxy-Zinc-Rich Primers

Organic (epoxy) zinc-rich primers are used in place or to repair imperfections of the inorganic zinc-rich primer. Their advantages over inorganic zincs include improved adhesion to the epoxy primer coating and better tolerance to poor surface cleaning. 

Most pigments can be used in any type of binder therefore, paints cannot be identified by pigment type alone. For example, micaceous iron oxide pigment is traditionally in an oil-based binder but is being increasingly used in epoxies, etc. In the paint coating film, the pigment content may vary from 15 to 60 per cent. In the special case of zinc rich primers, it is over 90 per cent. 

Suitable paints for use underwater include vinyl resin systems, coal tar paints over inorganic zinc-rich primers, and some coal-tar epoxy primers have also proved themselves Special paints are available for application under water, e.g. epoxy modifications with polyamides. 

Organic zinc-rich primers are based on epoxy/polyamides, high-molecular-weight linear epoxies, moisture-cured urethanes, high-styrene resins, chlorinated rubbers and epoxy esters. In this type of primer zinc is covered with a monomolecular layer of the binder which facilitates the adhesion of the film to the substrate. 

Anti-corrosion coating based on epoxy rein and zinc-rich primer ... 

As indicated in Table 10.18, a zinc-rich primer is often recommended. It can be an organic zinc-epoxy or an inorganic zinc-ethyl-silicate primer. Zinc-rich primers are also used as so-called shop primers, or prefabrication primers, for temporary protection of semi-manufactured steel goods. After fabrication, e.g. of welded steel structures, the shop primer surface must be cleaned (degreased), and possible shop primer defects and weld joints have to be blast cleaned and coated with a primer before the whole structure is painted. Iron oxide is also used as a pigment in some shop primers. These must not be overpainted with a zinc-rich paint. 

C3 Interiors with high relative humidity, some air pollution. Exteriors in urban and industrial Sa2 /2 Zinc-rich primer. Finishing coats vinyl, chlorinated rubber or epoxy 3-4 175-240... 

Chem. Descrip. Polyamidoamine (70%) in xylene Uses Crosslinking agent for epoxy resins in soiv.-based primers and coatings for min. and metallic substrates, anticorrosion primers, zinc-rich primers, coatings for lock gates, concrete, and underground conduits (in combination with tar)... 

Uses Epoxy curing agent for two-pkg. air-dry coatings, e.g., industrial maintenance primers, midcoats, and topcoats, anticorrosive marine primers, zinc-rich primers, methanol-resist, tank coatings, concrete floor coatings... 

Uses Epoxy for high-performance, two-package systems tor coatings (structural steel primers, concrete sealers and surfaces, tank linings, topcoats for zinc rich primers)... 

Uses Thixotrope for high polarity and oxygenated solv. systems such as nail lacquers, paints/coatings (nitrocellulose lacquers, sol n. vinyls, epoxies, acrylics, wash primers, inorg. zinc-rich primers, chlorinated mb-ber, unsat. polyesters)... 

Two types of paint systems were used for experiments. First system used was zinc phosphate primer (50 % Zn as compound) with micaceous iron oxide (MIO) as intermediate coat followed by polyurethane (PU) as top coat denoted as ZP. Other system used was zinc rich primer (80 % Zn as dust) with MIO as intermediate coat and PU as top coat denoted as ZR. This system is costlier with respect to ZP and considered for laboratory evaluations purpose only. ZP is designed with respect to places where test panels are deployed for exposure based on manufacturers catalogues and standards [4]. These systems possess good resistance from water permeability, weathering, abrasion and good adhesion to maintain a proper barrier to the environment. The drying mechanism of the systems is the reaction between epoxy resin and polyamide. The details of each paint system used comprising primer, intermediate and top coats with the respective layer of film thickness are shown in Table 2.2. 

Combinations of zinc dust (particle diameter 12-20 xm) and extrafine zinc dust (particle diameter 3-6 p,m) yield optimal corrosion resistance. Small amounts of aluminum paste or powder, added to obtain a more silvery appearance, will however decrease corrosion resistance—as found in comparative weathering tests by Van Eijnsbergen (personal communication). Generally, nonsaponifiable binders, such as vinyl copolymers, chlorinated mbber, methacrylic resins, and epoxy resins, are used. For welding zinc-rich primers, epoxy-polyamide binders are widely used. They allow a wider range of sealers and top coatings. 

One good example is a primer containing zinc. As zinc is anodic to steel, zinc corrodes in preference to steel and protects the steel from corrosion. Experience has shown that a zinc-rich primer can double the life of a chlorinated rubber or an epoxy top coat. 

The acrylic topcoat is normally applied over an epoxy primer or rm inorganic/organic zinc rich primer, which maximises the anti-corrosion characteristics of the complete system. 

Micrograph of a cross section of a typical coating system for heavy duty corrosion protection (e.g. C5M climate [2]), consisting of a zinc-rich primer, micaceous iron oxide (MIO) containing epoxy-based mid coat and MIO containing polyurethane-based top coat... 

Figure 19.60 illustrates a steel surface which should have been blast cleaned to a high standard before being coated at works with a zinc-rich epoxy primer and on site with two-pack intermediate and finishing coats. After exposure for 18 months in a marine environment, flaking millscale from beneath the paint was observed, and a survey showed that the paint... 

Prime coating is either a two-pack, zinc-rich epoxy primer with a DFT of ca. 30-40 pm, or a chromate-free, two-pack epoxy primer. Topcoats based on PVC copolymerisates, chlorinated rubber, silicone-reinforced epoxy esters, or alkyds were used for many years. Now, the standard European topcoat is based on acrylic resins with terminal epoxy groups that are cross-linked with amine adducts or aminoamide resins. 

Epoxy primers, zinc-rich, cured with polyamines or polyamides... 

Coil coatings are normally applied by roller coating machines, but are sometimes sprayed. The topside of the metal band is normally painted with a primer (DFT ca. 5 pm) and a topcoat (DFT 20-22 pm). Zinc-rich coil coatings are applied with a DFT of 5-20 pm, plastisol films have a DFT of 80-400 pm. The reverse side of the coils is coated with backing coats based on binders, such as alkyd, polyester, and epoxy resins (DFT 8-10 pm). 

Chem. Descrip. Barium metaborate monohydrate-based Uses Corrosion inhibitor, pigment for use in trade saies primers, indus-triai coatings, heavy-duty maintenance coatings, aq. systems (emuisions, water-reducibie aikyds), and soiv.-based systems (aikyds, urethanes, epoxies) stabiiizer for cerfain mefais and metai saits, esp. zinc in zinc-rich coatings... 

Chem. Desaip. Epoxy ester in xylene and fatty acids Uses Epoxy for high-quality zinc-rich and anticorrosive paints, air-diying and stoving primers and topcoats Features Fast drying and exc. water resist. 

The two-component epoxy topcoat, 2-C EP, without and with zinc-rich epoxy primer (56 + 5 p,m) was applied on the panels in the same way ... 

Zinc-rich epoxy primer = Zn-EP and epoxy topcoat 2-C EP(152 + 15 p,m)... 

FIGURE 1.24 Bode plots of coated steel panels for different times of immersion in 5% NaCl solution, (a) 2-C epoxy topcoat without primer and (b) zinc-rich epoxy primer and 2-C epoxy topcoat. (Reprinted from Wessling, B. and Posdorfer, J., Electrochim. Acta., 44, 2139, 1999. With permission. Copyright 1999 Elsevier Science)... 

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