Paint coatings continued processes

The standard of cleanliness which must be achieved has been stated to be that which will allow the subsequent process to be carried out satisfactorily . As an example, the degree of cleanliness required to satisfactorily zinc plate from an acid solution is somewhat higher than that required prior to zinc plate from a high-cyanide alkali zinc solution. This should never be taken as a licence to skimp on surface preparation. However, the arguments over surface-tolerant paint coatings abound and will probably continue. It is to a very large extent true that problems of early failure in metal finishing are traceable to incorrect or insufficient surface preparation. 

Coil coating is an advanced technique for applying organic coatings as a liquid or film to sheet metal in a continuous process. This process is also referred to as pre-coated, pre-painted or pre-finished. The technology is based on the simple fact that it is easier to coat a flat surface, than paint individual irregular shapes after they have been formed. 

The latices that result from the emulsion polymerization find immediate application as adhesives, paints, coatings, or in the processing of leather. For this, control over the distribution of the latex particles is desired. If emulsifier and water are added at the beginning of the polymerization and monomer and initiator are added continually during the course of the polymerization, then only those latex particles initially formed will continue to grow. The latex particles are relatively small and show a narrow distribution of size. If, on the other hand, just one part of the initial sample is polymerized and the rest is added as an emulsion during polymerization, then new latex particles will be produced. Since the particles formed first are very large and those formed last remain relatively small, the distribution of sizes becomes very wide. 

Coil-coated steel can be supplied in coils or blanks of practically any size. In coil coating, multiple coats of paint are applied wet to one or both surfaces of the steel and cured to develop the required thickness. This all happens in one continuous process. The average thickness of paint is 0.001-0.0015 in. per side. 

Coat n. Paint, varnish or lacxjuer applied to a surface in a single application (one layer) to form a properly distributed film when dry. A coating system sexually consists of a number of coats separately apphed in a predetermined order at suitable intervals to allow for drying or curing. It is possible with certain types of material to build up coating systems of adequate thickness and opacity by a more or less continuous process of application, e.g., wet-on-wet spraying. In this case, no part o the system can be defined as a separate coat in the above sense. 

The mechanical coatings are primarily barrel processed on to parts up to about 150 mm long or 400 g mass. Adhesive bonding (with a conductive adhesive to maintain the electrochemical protection by zinc) is particularly suitable for wrapping pipes. Vapour deposition has some use in products but the newest development is application on continuous strip for car-body manufacture—the surface is smooth so that the subsequently painted surface has no unevenness. 

Curtain coating With this process, paint falls in a continuous curtain from a closely machined gap in a header tank on to the flat article passing below on a horizontal conveyor the excess paint is collected in the main tank and then passed up to the header tank. It is an ideal method of applying thicker coatings (60/im and above) to sheet metalwork. 

Even small traces of certain corrosion stimulants, notably soluble chlorides and sulphates, can maintain a continuing corrosion process under a paint film because the salts accelerate the initial dissolution of ferrous iron (and other metal ions) but are not immobilised in the hydrated oxide corrosion products. Filiform corrosion is the most spectacular example of this phenomenon, but progressive spread, preceded by blistering, is also observed from scratches or other breaks in a coating, for example during salt spray tests. 

The modern motor car is made from steel, zinc or zinc alloy-coated steel and some plastic parts, all of which require painting. The main component is the body shell, made from the above metals, and this is coated in a continuous production process. A full finishing system with all four coatings is usually applied for maximum protection and a high quality appearance. 

This task represents a continuation of efforts to maximize the hydrophobicity of acrylic, epoxy, and other polymeric systems for resistance to water penetration and environmental degradation, and to minimize the dielectric constant and improve the processability for adhesives and coatings, without compromising the necessary structural characteristics for materials used for, e.g., structural elements, liners, paints, and microelectronic devices. 

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