Epoxy-polyamide coatings applications

Fig. 17. Cathodic delamination rates of galvanized steel/epoxy-polyamide coating systems when a 0.1 M CoCl2 dipping pretreatment was applied to the metal substrate prior to the application of the coating 91K (Reprinted with permission from Ref. 91Copyright (1981) American Chemical Society)...

Duvis, T., Papaspyrides, C.D. and Skourlis, T. (1993). Polyamide coating on carbon fibers and potential application in carbon/Kevlar/epoxy hybrid composites. Composites Sci. Technol. 48, 127-133. 

A typical starting formulation for a two-component epoxy-polyamide emulsion is shown in Table 14.3. This formulation can be used as either a coating or an adhesive. In either application, once the mixed emulsion is applied to the substrate, the water must be evaporated. In the case of the adhesive application, this must be completed before nonporous... 

Coating formulations and properties have been detailed in technical bulletins (31). The epoxy-polyamide system is popular because it provides an unusual degree of inherent corrosion resistance. This will be discussed in detail later. The system is unusually tolerant as compared to related systems, such as amine cured, since the ratio of components is not particularly critical. Tolerance is also demonstrated because it may be applied to wet surfaces and to surfaces with tightly bound rust. Indeed, formulations are available that may be applied under water to structures such as submarines and off-shore oil well riggings. Both the corrosion resistance and the tolerance relative to application on poorly prepared wet surfaces are believed to be functions of the surface activity of the polyamide resin. Related also to the surface activity are the unusually strong adhesive properties that the system demonstrates with a broad range of substrates. 

Fatty polyamides are used to cure epoxy resins where a more flexible product is required, particularly in adhesive and coating applications. An advantage of the system is that roughly similar quantities of... 

Polyfunctional amines which are commonly used as curing agents for epoxy resins but which are of a rather different kind to those described above are the so-called fatty polyamides. These polymers, which are described in Section 9.3, are of low molecular weight (2000—5000) and are prepared by treating dimerized and trimerized fatty acids with ethylenediamine or diethylene triamine. Fatty polyamides are used to cure epoxy resins where a more flexible product is required, particularly in adhesive and coating applications. 

Abstract The incorporation of rare earth compounds as corrosion inhibitors in polymeric paint systems is presented. Specifically, uses of cerium salts in an electrolytically deposited coating commonly used in the automotive industry and praseodymium oxide in spray applied epoxy-polyamide primers for aerospace applications are discussed. Special emphasis is placed on the importance of phase of the rare earth material in relation to polymeric matrix as the effectiveness of the corrosion inhibition is strongly link to the starting materials, the formulated paint system and the ambient environment in which the coating operates in practice. 

This specification outhnes a three-coat epoxy-polyamide painting system for the protection of steel surfaces subject to industrial exposure, marine environments, and areas subject to chemical exposure such as acid and alkali. This system, when properly applied and cured, is capable of giving excellent protection to steel surfaces in Environmental Zones 2A (frequently wet by fresh water), 2B (frequently wet by salt water), 3A (chemical, acidic), 3B (chemical, neutral), and 3C (chemical, alkaline) but not in potable water tanks. Although the coating herein specified has exhibited good chemical protection, its resistance against specific chemicals should, in the absence of applicable case histories, be appropriately tested. 

Filiform corrosion occurs with all types of paints acrylic lacquers, epoxy-polyamides, epoxy-amines and polyurethanes, and whatever the classic mode of application, whether with liquid paint or electrostatic powdering. It does not occur under sealed coatings such as electrician s tape. 

For qtplications involving outdoor exposure, a surface treatment such as anodizing or chemical conversion coating is required prior to the application of a primer and a finish (top) coat, such as an epoxy or polyurethane. Some new one-step, self-priming polyurethane top coats are also available as are low volatile-organic compound (VOC) high-performance primers (e.g., epoxy polyamide). 

Elevated temperatures are necessary for cure and the chemical resistance of the laminates is inferior to those from unmodified resins. Because of problems in handling, the polyamides have found only limited use with epoxy resins, mainly for coating and adhesive applications. 

Much attention has been paid to the synthesis of fluorine-containing condensation polymers because of their unique properties (43) and different classes of polymers including polyethers, polyesters, polycarbonates, polyamides, polyurethanes, polyimides, polybenzimidazoles, and epoxy prepolymers containing pendent or backbone-incorporated bis-trifluoromethyl groups have been developed. These polymers exhibit promise as film formers, gas separation membranes, seals, soluble polymers, coatings, adhesives, and in other high temperature applications (103,104). Such polymers show increased solubility, glass-transition temperature, flame resistance, thermal stability, oxidation and environmental stability, decreased color, crystallinity, dielectric constant, and water absorption. 

Ambient-cure systems are often based on lower molecular-weight solid epoxy resins cured with aliphatic polyamines or polyamides. Curing normally occurs at ambient temperatures with a working life (pot life) of 8—24 h, depending on the formulation. Epoxy—polyamine systems are typically used for maintenance coatings in oil refineries, petrochemical plants, and in many marine applications. Such coverings are applied by spray or brush. These are used widely where water immersion is encountered, particularly in marine applications (see COATINGS, MARINE). 

Floors ana walls of structures are obvious areas where epoxy systems may be utilized to prevent deterioration from abrasion and chemical attack. Such systems are now to be found in original specifications. VTall surfaces may be coated viith epoxy systems based on solid resins dissolved in solvents and hardened with polyamines and/or polyamides. Porous surfaces, such as concrete blocks, are first prepared viith fillers to provide a smooth surface for application of coatings. 

The Cg, Cio and C12 dibasic acids, as their butyl, hexyl, 2-ethylhexyl and octyl esters, are used as plasticizers for PVC, as engine lubricants and as intermediates in the production of polyamides, polyesters and polyurethane adhesives, coatings, fibres, inks and resins. The C2i-diacid is used primarily as a surfactant. By condensation with diamines, dimer acids are used extensively to furnish polyamide resins. Their major applications are printing inks, hot-melt adhesives and coatings. Reactive polyamides are used as curing agents for epoxy resins. 

Dimer acids are used mainly as polyamides. Non-reactive polyamides, produced from dimer acids and diamines in stoichiometric amounts, are flexible and tough and have excellent adhesive properties. They are used as shoe adhesives, in printing inks, for surface coatings and in textile applications. Reactive polyamides, with free amine groups which can react further, are used as components of thermosetting epoxy systems in surface coatings. 

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