Coatings, protective inhibitive primers

It is applied using a fluidised bed process, generally in two coats. A precompounded blend of p.v.d.f., corrosion-inhibitive pigments and adhesive components is applied first, followed by a top coat of pure p.v.d.f. The primer coat protects the metal and the top coat protects the primer coat from attack by the chemicals. 

After Pre-treatment of metals prior to bonding, it may be several weeks before the adhesive is applied. Most pre-treated surfaces are stable for considerably less than 24 h, so protection by priming is needed. However, the effectiveness of primers, particularly of the corrosion inhibiting primers, can be very sensitive to coating thickness a change in thickness from 2-5 ftm to above 8-10 p.m can halve the peel performance of some adhesives. 

If only small isolated areas of the structure show corrosion while the majority of the structure appears sound, it can prompt the maintenance engineer to schedule a spot blast or power tool white metal cleaning of the rusty spots, a spot prime with an inhibitive primer, and a new refresher coat of the topcoat of the system. Again, the economy comes in avoiding a total breakdown of the protective coating system, which would require total removal and replacement of the entire system. That is the most costly of all maintenance programs. 

For primers with self-healing and corrosion inhibitive properties, it is desirable to have one component to inhibit corrosion of the underlying metal and a second component to repair the polymer coating. These individual components can be multifunctional or multistep. For the protection of metals, many paint systems consist of an inhibitive primer and a topcoat. In case the coating is mechanically damaged or local delaminations are present, the repair function is usually achieved via release of the inhibitors from the inhibitive primer, whereby the corrosion performance of the underlying metal surface benefits from autonomous surface recovery processes by the precipitation of stable inhibitor compounds at cathodic and/or anodic sites. 

With the exception of coupling agent technology, primers for structural adhesive bonding have received little theoretical treatment in the literature beyond a discussion of mechanisms of corrosion inhibition by primer additives and limited discussion about statistical techniques for primer formulation. Perhaps because of the much more widespread use and greater economic importance of corrosion-protective coatings, the design and function of primers for these systems have... 

Application of protective paints consists of surface preparation of steel, priming coat and finishing coats. Wherever possible, steel should be blast-cleaned before painting. Primers thoroughly wet the metal to promote adhesion of finishing paints and carry inhibitive pigments. For example, red lead oxide will minimize the spread of rust on metal surfaces. The total thickness of fmishing coats must be at least 0.125 mm for adequate protection and life. Four coats of paint usually are necessary to achieve this. 

Uses Corrosion inhibiting pigmentfor metal protective coatings and primers, high gloss industrial enamels pigment for traffic marking paints Manuf/Distrib. Am. Disps. D.N. Lukens Nichem... 

Toxicology Toxic material TLV (as Pb) 0.15 mg/m of air Uses Corrosive inhibitive pigment for metal protective coatings, primers, and finishes industrial enamels requiring a high gloss heat stabilizer for PVC... 

Corrosion inhibitors in paints protect metallic surfaces from oxidation. Coating primers are used when there is continuous exposure to corrosive elements, e.g., in marine applications. Examples are coal-tar derivatives, epoxy resins and coal-tar modified epoxies. Primers that inhibit corrosion by anodic or cathodic polarization contain inorganic metallic pigments such as chromates or leads or both. Composite pigments containing calcium oxide, zinc, silica, and oxides of phosphorus and boron can also be used (Mathias 1984). Nowadays, powder paints such as polyester and epoxy powder paints can also be used for corrosion inhibition (Rose and Vance 1997). 

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