Electrophoretic deposition of paint

Relatively recently electrochemistry has turned its attention to colloidal solutions of organic polymers. A new line of processes of industrial importance has thereby been opened up, that of electrophoretic deposition of paints and plastic coatings, which provide improved adherence and has technological advantages over classical spraying processes[4]. 

When the substrate is conducting, electrophoretic deposition of paint may be carried out. Indeed, in the case of steel automobile bodies, almost all factory-based primer coating is performed by electrophoretic painting. 

The electrocoat process for primer coating involves the electrophoretic deposition of charged colloidal resinous particles in aqueous dispersion onto a conductive substrate such as an automobile body. The process is universally favored because once the paint particles are deposited, they insulate the body from further deposition at that point. The impressed electric field thereby causes the migration of paint particles to uncoated areas. The result is an extremely uniform, coherent and defect free coating-even on sharp edges and in recessed areas inaccessible to other methods. 

The electrophoretic deposition of organic paints onto steel is coniidered in Chapter 8. A much smallerbiochemical species from natural sources including body fluids (such as blood plasma or muscle tissue extract). 

Insulation of the probe was insured by electrophoretic deposition of an anodic paint. The natural tendency of this kind of paint to retract upon curing resulted in the spontaneous exposure of the tip extremity, which formed an approximately hemispherical microelectrode characterized by a tip radius in the submicron range. In that sense, this hand-made probe was the first AFM-SECM probe integrating an actual (sub)-microelectrode. Again no electrochemical current images were recorded but contact mode AEM images allowed the electrochemically induced etch pits to be visualized (see Figure 21.4). 

Electrophoretic deposition is an important process for the undercoating and painting of metallic products, especially automobiles. It is obviously necessary for the processor to know and control the electrical properties of the pigments being used in order to optimize the process and produce the best finished surface possible. 

Cathodic electrophoretic paint is the preferred polymeric material used to insulate the carbon fibers as the negative potentials required for deposition avoid any possibility of further oxidative dissolution of the carbon fiber. The usual approach for electrophoretic deposition is to suspend the article being coated in an appropriate suspension of polymer particles and polarising the iton versus a secondary electrode. 

The leading role for the protection against corrosion of metal sheets utilized for structures (i.e. car bodies, panels for electric household appliances) is now played by paint formulations based on synthetic polymers, which are generally apfdied to the substrate by electrophoretic deposition. 

Although the principle of electrophoresis has been known since 1809, from the work of Reuss, it has remained confined to a very few areas of application in medical, analytical and other technological fields. The process of electrophoretically depositing paints and lacquers could only be applied industrially when new ionizable paints and resins were developed that could be diluted with water and deposited from an aqueous medium under the influence of an electric current, similarly to the electrodeposition of metals (although the electrodeposition of organic material is much more complex). It was not possible to electrodeposit conventional organic-based paints, since these did not form ions, and known water-soluble paints that could be applied by conventional immersion or spraying techniques were too expensive. 

Electrocoating The deposition of larger-than-ion electrically charged particles (paint, glass, etc.) from an electrolyte under an applied voltage. The deposition is usually on the cathode (cathodic electrocoating) but can be on the anode (anodic electrocoating) side of the electrolytic cell. Also called Electrophoretic deposition. 

Cathodic electrodeposition tends to be more costly and involve complex resin chemistry but its increasing adoption since the mid 1970s reflects the ability to offer major advantages in corrosion protection at a justifiable premium. Indeed, the majority of electropriming is performed currently by cathodic deposition. The main advantages of electrophoretic painting may be summarized. 

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