Metallization prime coats

Use Component of structural-metal priming coat paints, rust-inhibitor in paints, lubricants, vinyl plastics, and rubber products. 

Cathodic Protection Systems. Metal anodes using either platinum [7440-06 ] metal or precious metal oxide coatings on titanium, niobium [7440-03-17, or tantalum [7440-25-7] substrates are extensively used for impressed current cathodic protection systems. A prime appHcation is the use of platinum-coated titanium anodes for protection of the hulls of marine vessels. The controUed feature of these systems has created an attractive alternative... 

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. 

The priming coat provides the bond between the metal and subsequent coats. It gives electrochemical control of corrosion. Adhesion is dependent largely on the nature of the binder and the cleanliness of the metal surface. 

Good adhesion to the metal. The coating must have an excellent bond to steel. Priming systems are frequently used to assist adhesion. 

The metal oxide supports can be oxidized to produce either a catalytic coating or an anchor for added catalytic components. The use of a ceramic prime coating is not particularly suitable because of spalling. 

Typically at least two slurries are used. The first of these is called the face coat or prime coat slurry. It is made up of very fine ceramic flour usually 200 mesh or finer. This slurry is the first slurry the wax patterns are dipped into and the very fine texture is required to faithfully replicate the fine details of the pattern. It is also the surface that the molten metal comes in contact with, when it is poured into the mold. Because of this, it is very important that the ceramic selected for this first or prime layer be inert chemically to the molten metal being poured. If not, the molten metal will react with the ceramic and lose its desirable metallic character. 

The prime coat of refractory on the wax is usually only about 0.010-0.025 in. thick and is not strong enough by itself to support the load of the molten metal being poured. It is dried and then additional layers of slurry are added, stuccoed, and dried. Usually no more than two prime coats of very fine refractory are used. The rest of the shell is made up of back-up coats. 

Silicone adhesives, one-pack, setting under the influence of atmospheric moisture. Uses glass, metals, ceramics, plastics some substrates need a priming coat. 

The new technique gained industrial significance when the Ford Motor Co. [1] elaborated a method for prime-coating metal automobile bodies. Following several years research to produce inexpensive, safe, water-soluble electrodepositable (ED) paints, the first production facility opened in 1963. The superior coating performance, uniformity on complex surfaces, freedom from pinholes, efficient use of paint solids, reduced solvent emission and reduced overall costs led to rapid worldwide market penetration in the automobile and other sheet-metal... 

Corrosion Inhibitors. A water-soluble corrosion inhibitor reduces galvanic action by making the metal passive or by providing an insulating film on the anode, the cathode, or both. A very small amount of chromate, polyphosphate, or silicate added to water creates a water-soluble inhibitor. A slightly soluble inhibitor incorporated into the prime coat of paint may also have a considerable protective influence. Inhibitive pigments in paint primers are successful inhibitors except when they dissolve sufficiently to leave holes in the paint film. Most paint primers contain a partially soluble inhibitive pigment such as zinc chromate, which reacts with the steel... 

A cmcial development for zinc phosphate coatings came in 1943 when it was found that more uniform and finer crystals would develop if the surface was first treated with a titanium-containing solution of disodium phosphate (6). This method of crystal modification is a prime reason for the excellent paint (qv) adhesion seen on painted metal articles. 

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