Primers, inhibitive

Non-corrosion-inhibiting primers Corrosion-inhibiting primers Inorganic barrier primers Rubber to metal primers... 

Corrosion-inhibiting primers based on this technology have been in continuous service since they were first utilized with nitrile epoxies in the late 1960s. These inhibitors function by passivating the aluminum. In this process, water permeating the adhesive bondline carries a certain amount of inhibitor to the oxide surface. 

Effect of corrosion inhibiting primer on strength retention after exposure to salt spray [29]... 

Comparison of tensile lap shear strengths solvent-based chromate-inhibited primers versus nonchromate and low VOC primers [42]... 

Non-chromate and low-VOC containing primers are capable of excellent performance. Table 4 shows the results of a comparison of various environmentally acceptable primers with 250°F curing adhesive with the standard BR 127 solvent-based chromate inhibited primer [42]. 

The need to identify replacements for chromate-based technologies has also resulted in the development of alternatives to resin-based corrosion-inhibiting primers. These are primarily inorganic barrier coating techniques, such as sol-gel processes, which may or may not include corrosion inhibitors. These are discussed in a later section. 

A wide variety of paint systems may, however, be used over the pretreatment primers. Applying a coat of inhibitive primer such as zinc chromate after the pretreatment primer is less advantageous than applying an additional coat of finishing paint indeed, unless the inhibitive primer is carefully formulated, it may contribute problems of intercoat adhesion and blistering. 

Brush application is very desirable for inhibitive primers applied directly to steel and for toxic materials. Roller application is not recommended for structural steel surfaces. 

Environment Increase redox potential of solution Addition of anodic inhibitors Passivation of stainless steel by additions of O2, HNO3 or other oxidising species to a reducing acid Additions of chromates, nitrates, benzoates, etc. to neutral solutions in contact with Fe inhibitive primers for metals, e.g. red lead, zinc chromate, zinc phosphate... 

The primary function of a coating is to act as a barrier which isolates the underlying metal from the environment, and in certain circumstances such as an impervious continuous vitreous enamel on steel, this could be regarded as thermodynamic control. However, whereas a thick bituminous coating will act in the same way as n vitreous enamel, paint coatings are normally permeable to oxygen and water and in the case of an inhibitive primer (red lead, zinc chromate) anodic control will be significant, whilst the converse applies to a zinc-rich primer that will provide cathodic control to the substrate. 

Inhibitive Primers. The traditional primers are red lead and linseed oil, alkyd resins and zinc potassium chromate, proprietary epoxy, alkyd, urethane and latex systems with modified phosphate, borate and molybdate pigments. Chromate-based pigments, although in use in aircraft coatings, automotive primers and coil coating primers, are subject to environmental concern on the toxicity of hexavalent chromium which is likely to result in their replacement by innocuous products. 

Corrosion protection by an inhibitive primer may be envisaged as shown in Figure 1.67. Inhibitive metal primers are designed with relatively high pigment volumes to allow sufficient water absorption to dissolve the passivating inhibitor and yet prevent aggressive ions such as chloride which interfere in the passive oxide formation process. 

Volatile organics in the coating film are deemed unacceptable from the environmental point of view and are giving way to water-based inhibitive primers. Some examples of water-based primers are of the acrylic latex type, as well as epoxies and water-borne... 

Surface of steel beneath inhibitive primer is comprised of a passive layer which prevents metal ions from entering electrolyte. 

The vinyl copolymers can be used most efficiently in special applications such as hospital and dental equipment where durability is more important than initial cost. For laboratory equipment, epoxy resins may be preferred because the vinyls are sensitive to some solvents. The vinyl coating systems consisting of corrosion-inhibiting primer and chemical-resistant finish coats are used on new equipment for chemical plants. The metal conditioner based on zinc chromate and polyvinylbutyral are widely used over sandblasted steel as a use for vinyl systems on both industrial and marine equipment. 

Hare, C. H. "Anti-corrosive Barrier and Inhibitive Primers" Unit 27, Federation Series on Coatings Technology, Federation of Societies for Coatings Technology Philadelphia, 1978. 

It is expedient to form single-layer inhibited coatings in a fluidized bed consisting of a homogeneous mixture of the polymer and inhibitor (Fig. 3.23a). The double-layer coatings with inhibited primer layer are commonly formed in a separated layer whose scheme is presented in Fig. 3.23b. A heated article is first dipped in the upper layer enriched with the inhibitor and then into the lower layer with content dominating by the polymer binder. 

A6. Diener, S. L. Development of Improved Electrodeposited Inhibiting Primers, AFML-TR-79-A073, June, 1979 Final Report. 

Hare, C. 1979. Anti-corrosive and Barrier and Inhibitive Primers. Federation of Societies of Coatings... 

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