Epoxy/epoxies primer

As discus.sed earlier, puny filling is generally not advisable unless the surface is poor, uneven or has pin holes. If is advisable to use primer surfacer, which provides a thicker coal and helps to fill such surfaces. The epoxy primer is thicker and may do this job in most cases. 

Epoxy based primer systems remain the best suited for the corrosion protection of magnesium. Cathodic epoxy electrophoretic paints , chromate inhibited epoxy-polyamide primers and high temperature stoving epoxy sealers are used to provide protection up to 180°C. For higher temperature applications up to 300°C, epoxy silicone or polyimide based systems can be used. 

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. 

Assuming maximum corrosion resistance is required, then an anticorrosive primer will be needed, with best protection coming from a crosslinked epoxy stoving primer. Most other properties are dominated by the finish, which will be based on a high molecular weight-polymer, either linear or (more usually) crosslinked. The precise selection of the polymer depends on the balance of properties required, but will be constrained by the type and rate of curing necessary. 

Generally, systems developed in the USA favour a combination of polyethylene with either butyl-rubber or hot-applied mastic adhesives, the latter consisting of a blend of rubber, asphalt and high molecular weight resins. In European and Far East coating plants, epoxy type primers and hard ethylene copolymer adhesives have been successfully employed. 

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... 

A484 Baseplate epoxy primer BSPL EPOXY c 20 ... 

Materials. The adhesives and primers used in this study were model and commercial materials that were cured according to conditions appropriate for the specific adhesive chemistry. Adhesives A and B were conventional epoxy/Versamid and epoxy/dlcyandiamlde adhesives, respectively. Adhesives C and D were commercial urethane and epoxy/polyamlde adhesives, respectively. Adhesive E was a conventional two-part epoxy/amldoamlne adhesive. Adhesive F was a vinyl plastlsol adhesive. The adhesive primers used in this study were a urethane crosslinked epoxy electrocoat primer and spray primers based on tall oil modified epoxy ester, and polyesterpolyol/isocyan-ate chemistry. Dicyandlamlde was obtained from Aldrich Chemical Company. Epon 828 was obtained from Shell Chemical Company. 

Wedge test results suggest that the curing process (e.g., percent crosslinking) of the epoxy-polyamide primer system is not affected by the addition of organosilanes, but may be affected by NTMP. The results of substrate surface characterization, adsorption behavior of applied films, and evaluation of candidate inhibitors by chemical, mechanical, and electrochemical test methods are presented. Mechanisms to explain the observed behavior of the various phosphonate and silane polymer systems are discussed. 

Wedge Test. The adhesive bond durabilities of the Inhibitor-treated 7075-T6 surfaces were evaluated by wedge tests (ASTM D-3762) on bonded specimens using the FM 123-2 epoxy adhesive to simulate the epoxy primer. The specimens were placed In a humidity chamber at 65°C and 95% relative humidity and removed at specified time Intervals to record the crack tip locations after each examination, they were returned to the humidity chamber. 

Primer Epoxy vs. Nitrile-Modified Epoxy. The compatibility of the epoxy-polyamide primer with the nitrile-modified epoxy adhesive facsimile and the aluminum oxide surface was also evaluated by the wedge test, since earlier tests using the primer as the adhesive had failed immediately. As shown in Fig. 8, the addition of the primer directly to the prepared... 

The corrosion resistance and polymer-bonding compatibilities of the lonizable organophosphonates and the neutral organo-silanes are directly related to their inherent chemical properties. Specifically, NTMP inhibits the hydration of AI2O2 and maintains or Improves bond durability with a nitrile-modified epoxy adhesive which is cured at an elevated temperature. The mercaptopropyl silane, in addition to these properties, is compatible with a room temperature-cured epoxy-polyamide primer and also exhibits resistance to localized environmental corrosion. These results, in conjunction with the adsorbed Inhibitor films and the metal substrate surfaces, are subsequently discussed. 

Adsorbed NTMP exhibits a pH-dependent surface coverage on anodized aluminum, which Includes a region characterized by a multilayer of hydrogen-bonded phosphonate molecules. These thick layers are weak and fall to provide good bond durability in a humid environment. NTMP monolayers are protective against hydration and are compatible with a nitrile-modified epoxy adhesive, but not with an epoxy-polyamide primer topcoat. 

In contrast, hydrolyzed silane compounds, presumably adsorbed as oligomeric films, confer corrosion resistance in both hydrating and Cl environments. These inhibitors can also couple with applied epoxy primer or adhesive formulations to further protect the metal against corrosion by strengthening the metal-epoxide bond. The organosilanes do not appear to affect the curing process, e.g., % crosslinking, of the polymeric epoxy systems. 

Anticorrosive pigment Air- drying alkyd primers Alkyd- melamine primers 2-Compo- nent epoxy primers 2-Compo-nent acrylic isocyanate primers Chlor- inated rubber primer Aqueous polymer dispersions Poly(vinyl- butyral) primers Electro- deposition coatings Mirror coatings References... 

Epoxy-based primers are commonly used in the aerospace and automotive industries. These primers have good chemical resistance and provide corrosion resistance to aluminum and other common metals. Primer base resins, curing agents, and additives are much like adhesive or sealant formulations except for the addition of solvents or low-viscosity resins to provide a high degree of flow. 

The usual approach to good bonding practice is to prepare the aluminum surface as thoroughly as possible, then wet it with the adhesive as soon afterward as practical. In any event, aluminum parts should ordinarily be bonded within 48 h after surface preparation. However, in certain applications this may not be practical, and primers are used to protect the surface between the time of treatment and the time of bonding. Primers are also applied as a low-viscosity solution which wets a metal surface more effectively than more viscous, higher-solids-content adhesives. Corrosion-resistant epoxy primers are often used to protect the etched surface during assembly operations. Primers for epoxy adhesive systems are described in Chap. 10. 

Micaceous iron oxide epoxy primer High-build epoxy lining... 

Cohen, S.M. Electrochemical impedance spectroscopy evaluation of various aluminum pretreatments painted with epoxy primer. J. Coatings Techn. 1996, 68 (859), 73. 

The coating is two-component and needs mixing on-site prior to application. It can be applied either using conventional airless spray equipment or by brush or roller. A final thickness of 1 mm to 2 mm can be obtained with two coats. Pretreatment of the substrate with an epoxy primer ensures good adhesion. Defects in the concrete or brickwork are sealed with an elastomeric sealant which is resistant to the fluid being stored in the tank. 

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