Electrodeposition of paints

Beck, F "Fundamental Aspects of Electrodeposition of Paint", in "Progress in Organic Coatings", 1976,4,1 Elsevier Sequiola S. A., Lasagna. 

The use of electrodeposition to apply paint is a comparatively recent innovation. The history of this development has been detailed by Brewer (2, ). The electrodeposition of paint, or electrocoating as it is commonly labeled, is derived from the old rubber latex technology and has many features in common but it differs in one important respect-- it provides rapid and complete current cutoff. 

A recent development is the use of electrodeposition of paints, which has found wide application in the automobile industry because of the ability to obtain uniform deposition on and in complex geometrical structures. In this, charged particles are caused to move toward the metal surface under the influence of an electric field and to flocculate on meeting the surface. 

Passivation techniques have to compete with other techniques of surface protection, like phosphating, electrodeposition of paint and others. In high-tech systems, especially in micro and nanotechnology [27], passivation has to compete with other microstructuring techniques, like PVD,... 

Liimobilized positive or negative clinrges have been attached to UF membranes. By repelling like-charged species, the tendency to foul is diminished (see section on electrodeposition of paints). 

The electrophoretic priming of motor vehicles was introduced in 1963, some years after the principles of electrodeposition of paint were first established. The process is now widespread indeed, almost all mass-produced, steel car bodies are pretreated in this manner. 

In anaphoretic deposition much less gas is evolved from the anode, but metal ions dissolved from the anode are incorporated into the film, very few of them passing through into the resist bath. It has been recognized in the electrodeposition of paints [3] that anaphoretic coatings are more susceptible to corrosion than cataphoretic coatings, and they result in poorer performance. 

The largest industrial use of ultrafiltration is the recovery of paint from water-soluble coat bases (primers) applied by the wet electrodeposition process (electrocoating) in auto and appliance factories. Many installations of this type are operating around the world. The recovery of proteins in cheese whey (a waste from cheese processing) for dairy applications is the second largest application, where a... 

Recovery of paint from watersoluble coat bases (primers) applied by the wet electrodeposition process (electrocoating) in auto and appliance factories. 

Electrodeposition This method of paint application is basically a dipping process. The paint is water-based and is either an emulsion or a stabilised dispersion. The solids of the paint are usually very low and the viscosity lower than that used in conventional dipping. The workpiece is made one electrode, usually the cathode, in a d.c. circuit and the anode can be either the tank itself or suitably sized electrodes sited to give optimum coating conditions. The current is applied for a few minutes and after withdrawal and draining the article is rinsed with de-ionised water to remove the thin layer of dipped paint. The deposited film is firmly adherent and contains a minimum of water and can be stoved without any flash-off period. This process is used for metal fabrications, notably car bodies. Complete coverage of inaccessible areas can be achieved and the corrosion resistance of the coating is excellent (Fig. 14.1). 

A matter of considerable importance in the selection of an application method is its efficiency. Spray techniques are usually inefficient, since many droplets drift past the target and are lost. Even electrostatic spraying can waste as much as 35% of the paint. There is some loss of paint in most methods, but roller coating, curtain coating and electrodeposition are very efficient. Electrodeposition is also a very useful technique where corrosion resistance is important, since it applies a uniform coating over nearly all surfaces of even the most complex-shaped article. 

After rinsing and dry-off, the primer is applied. In most modern plants this means electrodeposition of the primer (Section 14.1). The most widely used primers are cathodic. The body shell is made the cathode and current flows between it and inert anodes in the electropaint bath. The paint is formulated so that the resin is basic and, when neutralised with an acid such as lactic acid, becomes positively charged. The most widely used resins are epoxy-amine adducts ... 

Applications Electrodeposition of cationic paint resin on automobiles (connected to the cathode) provides a uniform, defect-free coating with high corrosion resistance, but carries with it about 50 percent excess paint that must be washed off. UF is used to maintain the paint concentration in the paint bath while generating a permeate that is used for washing. The spent wash is fed back into the paint path (Zeman et al., Microjiltration and UltrajUtration, Marcel Dekker, New York, 1996). 

PROTECTIVE COATING. A film or thin layer of metal glass of paint applied to a substrate primarily to inhibit corrosion, and secondarily for decorative purposes, Metals such as nickel, chromium, copper, and tin are electrodeposited on the base metal paints may be sprayed or brushed on. Vitreous enamel coatings are also used these require baking. Zinc coating are applied by continuous bath process in which a strip of ferrous metal is passed through molten zinc. 

R.J. Dibert, Symposium on Electrodeposition of Coating, Introduction and principles of electrodeposition of coating, J. Paint Technol., 1966, 43, 421-423 G.E.F. Brewer, Electrodeposition of film-forming macroions, J. Macromol., Sci.-Chem., 1973, A7, 709-713. 

Copper electrodeposition into the pore volume The lock and key mechanisms of paint adherence will also depend upon the specific pore geometry and volume,... 

The uncovered surface of the steel substrate may be lesser in the order of few percentage which acts as an active surface during electrodeposition of the paint in the next step. The phosphate layer thickness and coverage are influenced by the process parameters such as temperature and velocity of the electrolyte, and concentration of the accelerator [24]. 

Even if the polymeric salts are capable of anodic or cathodic electrodeposition, waterborne paints made from them do not have to be applied in this way. The solution or emulsion paints produced can be applied by virtually any technique. There will be an increasing use of this type of paint as legislation, economics and world petroleum shortages encourage the use of decreasing amounts of volatile organic solvents and paints of low flammability. 

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