Epoxy zinc coatings

Figure 10. SIMS positive secondary ion images of the interfacial substrate surface of zinc phosphated steel after adhesion failure of epoxy-ester coating in cathodic polarization testing. Images obtained at the intact coating edge of the delaminated zone. Image diameter 400 fm. Image a mass 55 Fe+ image b mass 54 Zn+ image c mass 31 P+.

It has been shown clearly, that in gaps, which are mostly the starting point of a far reaching corrosion, the polyaniline-containing coating act as a noble metal. In contrast to a well established zinc powder primer with an epoxy top coating, a structure of polyaniline-primer and epoxy top coat, had perfectly fulfilled the demands of the tests (see Figure 11.59). 

Araldte GY 281 Araldte GY 9580 epoxy, zinc-rich coatings... 

FTIR spectroscopy was used for the analysis of ultrathin organic films on metals. FTIR in the reflection mode (IRRAS) was used to study the interaction of ultrathin films of dicyandiamide (hardener of most one-pack epoxy resins) with various substrates, model ones such as gold or zinc and industrial ones such as steel and zinc-coated steels. Pure zinc surfaces and, to a lesser extent, zinc-coated steels are shown to react with dicyandiamide after heating at 180 C, as evidenced by the frequency shift of the absorption band characteristic for nitrile groups. Some mechanically tested specimens are then analysed, after failure, by FTIR microspectrometry. The spectra obtained, corresponding to the fracture initiation zone which is about 100 micrometers in diameter, indicate the presence of an ultrathin layer of modified polymer still covering the substrate. 28 refs. 

The most significant marine use of resins is actually in the form of paint corrosion protection systems for hulls. These include polyurethane and epoxide systems, the latter giving good alkali and solvent resistance in addition to providing superior adhesion to most substrates. Such systems take the form of zinc-rich epoxy and epoxy coal-tar combination hull paints. Epoxy powder coatings are also commonly used for the protection of steel pipelines, both on land and offshore. 

ZP Primer coat Epoxy zinc phosphate 1 X 75 250 Laboratory and... 

Based on the primers, two sets of coated panels ZP and ZR were taken for the experiments. Spray gnn was nsed to apply the coatings in a standard paint booth maintaining humidity and temperature. ZP system was coated with epoxy zinc... 

The benefits of a duplex coating are achieved only if there is good, long-lasting adhesion of the paint to the zinc coating. The NMP (A(-methyl-pyrrolidone) test has been described by Van Ooij et al. (1982). The test panels are immersed in the heated solution at 60 C (Fig. 1.16) and the time before the paint lifts is measured. Figure 1.17 shows the use of this test to demonstrate how silanes increase adhesion of an automotive epoxy-polyurethane primer to galvanized steel. 

Built in 1959, the dike at Delfzijl was painted green (epoxy coating) to match the grass. The wall protects the town against flooding by the sea. An inspection made in 1991 showed the zinc coating to be still 80-120 xm thick. No rust had appeared after 32 years. 

Zinc-coated steel is increasingly used in situations that otherwise would be too aggressive to steel. Five-year trials in the agricultural industry, particularly in animal waste environments, showed (Kim, 1991) the superior corrosion resistance of galvanizing after fabrication, compared to epoxy-coated steel. 

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. 

Epoxy-based adhesion primer/ seaier 57 38 1 h 8 h Two components for atmospheric and underwater systems, exceiient adhesion to and seaiing of aged zinc coatings, resists temperatures up to 175°C in dry exposure... 

Epoxy high buiid/finish coat 55 75-150 3 h 10 h Two components, topcoat on primed steei and concrete for atmospheric conditions, seais inorganic zinc 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. 

System 3. A premium factory-applied exterior coating system combines the longterm corrosion protection of the inorganic zinc primer with a polyamide epoxy intermediate coat and an acrylic urethane topcoat. The ultimate in welded tank exterior systems. System 3 provides off shore protection and extended color and oss retention. This coating system is further enhanced by factory baking at 200 F (93°C). 

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