Anticorrosive coatings primers

Uses Binder for anticorrosion coatings, primers, topcoats, single-layer coatings... 

Maybe, the most important real application of ion-exchange pigments is their use in coil coating primers, mostly in combination with other anticorrosive pigments. 

Zinc chromate is used in the following applications in pigments in paints, varnishes and oil colors, as an anticorrosive in primer coatings, as metal conditioners prior to priming, and as a catalyst. 

It is convenient to introduce Cl into the primer or adhesive layer of the tape from which the anticorrosion coating is formed or into the PU insulation. In the latter case the PU mass is foamed by a gas saturated with Cl. 

Although two-pack epoxy primers and polyurethane intermediate coats have high solids contents, they still contain significant amounts (20-30 wt%) of organic solvents. In polyurethane topcoats, the VOC is even higher. Anticorrosive, waterborne primers based on aqueous dispersions of two-pack epoxy resins and one-pack acrylic resins have been developed to decrease solvent emission. Waterborne, one-pack acrylic topcoats are also used. All of these waterborne paints contain 2 - 5 % organic cosolvents that are required for film formation. 

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... 

Long oil alkyd resins have been the workhorse as binders for architectural and do-it-yourself paints, anticorrosive coatings (linseed oil based), metal primers and intermediate coats. They are mainly based on such oils as soybean oil, linseed oil, dehydrated castor oil and safflower oil. 

Matamala G, Smeltzer W, Droguett G (1994) Use of tannin anticorrosive reaction primer to improve traditional coating systems. Corrosion 4 270-275 Matis KA, Zouboulis AI, Grioriadou AA, Lazaridis NK, Ekateriniadou LV... 

Primers. The primer is a universal component of all anticorrosive coatings and is considered to be one of the most important element of a protective system. A good primer generally provides the ability to stifle or retard the spread of corrosion discontinuities such as pinholes, holidays, or breaks in the film. To perform satisfactorily they must themselves adhere well to the base metal or any surface conversion coating that might be present. They should also contain an adequate concentration of a leachable inhibitor, where this is considered an important feature of the protection system, and this is usually a chromate pigment. The primary functions of a primer are... 

The film thickness of ED coatings is essentially self-limiting. As film thickness increases, electrical resistance increases. Deposition rate decreases correspondingly until the film thickness is reached at which deposition stops. Because the entire surface of the metal object acts as an electrode, ED coatings are used to provide complete, void-free coverage. This is particularly important in the application of anticorrosion coatings. The corrosion protective primers used on automobiles are in most cases applied by electrodeposition. This system is also used to prime and topcoat many appliances. 

A primer On metal, the purposes of a primer are to enhance corrosion protection and to give excellent adhesion. The primer will contain anticorrosive pigments, such as strontium chromate or zinc phosphate, which will slowly release ions that can repair damage or faults in the underlying conversion coating. 

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... 

The protection of metal surfaces by anticorrosion agents " - is also applied to heat exchangers, in the hydrogen fluoride cleaning of surfaces, with printing inks, with primers for coatings, etc. A typical derivative having corrosion inhibitor and surfactant properties is represented by 583, employed on steel surfaces. ... 

This pigment is said to be bifunctional. It combines corrosion protection and light scattering in a single pigment [5.95]. It is recommended for application in water-and solvent-borne primers as well as in cathodic electrodeposition coatings and coil coatings [5.95]. The typical properties of this anticorrosive are summarized in Table 5.12. 

This section does not cover the topic of coatings and finishes. These finishes are usually highly formulated and are applied as multiple-pass coatings which include special primers and intermediate layers. They may include pigments, additives, other resins, and more than one fluoropolymer. The main applications of fluoropolymer finishes are in cookware and industrial anticorrosion and high-temperature uses. A separate volume, Fluorinated Coatings and Finishes, a Plastics Design Library (PDL) volume in the Fluorine Handbook Series published by William Andrew, Inc., covers the topic. 

Such coating systems must ensure optimal bonding to the metallic substrate and be compatible with a variety of top coats. Anticorrosive primers of this kind are currently undergoing large-scale industrial tests a product for the home handyman for repairing metal parts affected by rust is also in the test phase. 

I.L. Rozenfeld and F.I. Rubinstein. Anticorrosion Primers and Inhibited Pa,int Coatings. Moscow, Khimiya, 1980. 

A complete coating system, recommended for highly demanding situations, consists of several layers - the primer, the intermediate coats and the topcoat. The primer is an essential component for corrosion protection, because it is responsible for the adhesion of the coating to the substrate and also it provides most of the anticorrosive properties, through the use of inhibitors. Its requirements are a good adhesion to the substrate and to the intermediate coat, flexibility and cohesion and good chemical resistance. 

Heavy-duty coating systems generally comprise two primer coats and two topcoats, modern system sometimes consist of one primer coat and two topcoats. The total dry film thickness (DFT) of such anticorrosive paint systems is 150 - 200 pm, each layer has a minimum DFT of 40-50 pm. Due to their excellent adhesion, the first and second primers prevent corrosion of the metal surface. The pigments and extenders allow the primers to react with ions (CD and SO4") that diffuse into the film from the atmosphere. The pigmented organic film also forms a barrier against humidity that may otherwise initiate a corrosive process. 

Car paints are cured with heat in special oven lines. Electrodeposition coatings (used as anticorrosive primers) contain only small amounts of volatile organic compounds (VOC), whereas intermediate and topcoats release considerable amounts of VOCs. Intermediate coats based on waterborne resins have been developed to decrease VOC emission and are already being used in some automotive plants. Basecoats, as part of base-clear topcoat systems, contain very high amounts of volatile organic solvents. Waterborne basecoats were developed more recently to lower this source of solvent emission. Some car manufacturers are operating pilot lines with the aim of introducing waterborne basecoats into their production processes. Many car producers in the United States and Europe have already switched their topcoat lines over to waterborne basecoats [11.3]. 

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