Electrocoatings

The Fe, Co, and Ni deposits are extremely fine grained at high current density and pH. Electroless nickel, cobalt, and nickel—cobalt alloy plating from fluoroborate-containing baths yields a deposit of superior corrosion resistance, low stress, and excellent hardenabiUty (114). Lead is plated alone or ia combination with tin, iadium, and antimony (115). Sound iasulators are made as lead—plastic laminates by electrolyticaHy coating Pb from a fluoroborate bath to 0.5 mm on a copper-coated nylon or polypropylene film (116) (see Insulation, acoustic). Steel plates can be simultaneously electrocoated with lead and poly(tetrafluoroethylene) (117). Solder is plated ia solutioas containing Pb(Bp4)2 and Sn(Bp4)2 thus the lustrous solder-plated object is coated with a Pb—Sn alloy (118). 

PVDF-based microporous filters are in use at wineries, dairies, and electrocoating plants, as well as in water purification, biochemistry, and medical devices. Recently developed nanoselective filtration using PVDF membranes is 10 times more effective than conventional ultrafiltration (UF) for removing vimses from protein products of human or animal cell fermentations (218). PVDF protein-sequencing membranes are suitable for electroblotting procedures in protein research, or for analyzing the phosphoamino content in proteins under acidic and basic conditions or in solvents (219). 

Flux is maximized when the upstream concentration is minimized. For any specific task, therefore, the most efficient (minimum membrane area) configuration is an open-loop system where retentate is returned to the feed tank (Fig. 8). When the objective is concentration (eg, enzyme), a batch system is employed. If the object is to produce a constant stream of uniform-quahty permeate, the system may be operated continuously (eg, electrocoating). 

G. E. E. Brewer, paper presented at Electrocoat 72, Electrocoating Committee and the National Paint and Coatings Association, Chicago, lU., Oct. 2-4,1972. 

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. 

A generalised model of electrical equivalent circuit for painted surfaces has been considered in many of the recent publications. Googan ( 2) used it to study vinyl coatings free of defects and coatings containing defects. Electrocoatings were also evaluated. Muslanl et al (27) in their investigation of mild steel... 

In technical processes, several high-temperature molten salts are employed for electrocoating, and the morphology of the deposit is strongly influenced by the composition of the baths. Some attempts have been made to deposit Nb and Ta from ionic liquids [21, 22]. In [21] the authors focused on the electrodeposition of AlNb alloys from room-temperature ionic liquids containing both AICI3 and chlorides of Nb. 

Other types of equipment that can yield even higher efficiency values are roller and flow coating machines (90 to 98%) and electrocoating systems (90 to 99%). Roller and flow coating machines, however, are limited in their applicability based on the shape of the parts. Electrocoating systems require a shift from solvent-based to waterbased paint. 

The effect of emulsifier structure on the electrodeposition of cationic latexes has been investigated. The electrocoating performance of these systems can be correlated with the reducibility of the emulsifier. 

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. 

The modem process of electrodeposition can thus be described as a combination of three basic elements (a) Electrophoresis - migration of charged polymer particles to metal surface (b) Deposition - colloidal de-stabilization of particles at the metal-bath interface and (c) Insulation - formation of an adherent, non-conductive layer of resin on the metal surface. The last named element is responsible for the high throwing power which can be achieved with the electrocoating process. 

Commercial electrocoating formulations are made up with low molecular weight resins containing ionizable groups. Typically, they are converted to aqueous dispersions by first dissolving the resin in a water-miscible coupling solvent, then adding the appropriate... 

Both anodic and cathodic electrocoating systems are in use. The anodic systems contain carboxylated polymers where the acid groups are neutralized with amines or KOH. The cathodic systems contain amino-functional resins where the amine groups are neutralized with an acid. 

The H and OH" ions are supplied by the simultaneous electrolysis of water during electrodeposition. Electrode reactions involving the resins are of little significance. However, oxidation of the metal substrate does play a role in anodic electrocoating. 

Since particle charge in these latexes is not pH dependent, the mechanism outlined above for the conventional electrocoating systems cannot apply. It was clear from the start that the difference in the behavior of sulfonium and quaternary ammonium stabilized latexes is related to the greater reactivity of the sulfonium ion. Though stable in dilute aqueous solutions, sulfonium ions might be expected to undergo rapid decomposition under the conditions obtained at the cathode surface while current is flowing. However, the specific reactions involved were not known. 

ACK94] VAN ACKER K., DE BUYSER L., CELIS IP., VAN HOUTTE P., Characterization of thin nickel electrocoatings by the low incident beam angle diffraction method , J. Appl. Cryst, vol. 27, p. 56-66, 1994. 

Figure 7. Decrease of slope b for h.e.r. at Ni-Mo electrocoated cathodes with temperature (O) upper c.d. region, and (x) lower c.d. region (from Ref. 46).

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