Paint, electrocoated

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... 

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 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. 

Electrocoating paints are usually sold as approximately 40 wt % dispersions of paint nonvolatiles in the presence of 10 wt % volatile organic cosolvents and 50 wt % water. The paint solid concentration in the coating tank is selected to give the best performance and varies for individual installations from 5 to 20 wt %. 

Metallic objects are first cleaned to remove impurities and materials associated with metal forming, welding, temporary rust protection, etc. In many instances phosphate and/or chromate treatments are applied. Overall, any electrically conductive surface preparation will impart benefits to electropainted articles similar to the benefits imparted to spray painted or dip-coated articles. The workpieces go from pretreatment to the electrocoating tank either water wet or dried. 

The fill of an electrocoating dip tank is actually an inventory of diluted paint. Concentrated paint is added to the tank to replace the paint that is removed from the tank on the surfaces of painted merchandise. The time interval in which the paint additions to the tank equal the original fill is called the turnover period. Electrocoating tanks are reported to have turnover periods ranging from several days to several months. Since both freshly added paint and older paint are coated onto the surfaces of merchandise, sizable quantities of paint reside in the tank for long periods, as predictable from the law of averages. 

Furthermore, as in all dip processes, the paint is subject to a long residence period in the tanks requiring high resistance against saponification, oxidation, bacteria, etc. Experience tells that electrocoating baths should have a pumping stability exceeding four turnover periods. 

Brewer, G. E. F. Hamilton, R. D. "Paint for Electrocoating" ASTM Gardner-Sward Paint Testing Manual, 13th ed, ASTM Philadelphia, 1972 pp. 486-89. 

Rinsing of ware provides an economy as electrocoating solids can be returned to the tank, providing high utilization of paint. The pH must also be carefully controlled to avoid kick out of the resin. Cooling must also be provided to control bath temperature. 

Luhydran . [BASF AG] Water-dilutable binders for electrocoating finishes, baking finishes, wood and plastic coatings, anticcNTOsion paints, printing inks, overprint varnishes. 

The use of electrocoat or e-coat paints and primers is another technology that found extensive use in the 1980s. Electrocoated paint is applied on the part to be coated in a paint bath, and electrical current is applied. This method enables painting of the most intricate parts. The electrocoated automobiles were more corrosion resistant. The surface rust was approximately three times higher, and the number of perforations were also higher in vehicles that were treated in the standard conventional manner. Some of these differences may be because of zinc coating on the steel and phosphatizing. However, electroplated paint systems had a noticeable effect on corrosion resistance. 

Anticorrosive Primers. Anticorrosive primers are applied in dip tanks so that they reach all parts of the car body dipping is a fast method of application. The standard method for application of primers is electrodeposition. Anodic electrodeposition paints were used when the electrocoating technique was first applied, but cathodic electrodeposition is now predominant because it provides better corrosion protection. 

The binders for cathodic electrodeposition are epoxy resin combinations dispersed in water (see Section 3.8). Advantages of anticorrosive electrocoatings include excellent corrosion resistance at a dry film thickness of ca. 20-30 pm. Electrocoats are stoved at 165 -185 °C to obtain films with the desired properties. The paint industry is now developing electrocoats that can be cured at lower temperatures (140 150 "C). Electrocoating produces a homogeneous film that covers the entire car body surface, including recesses and cavities. 

Wheels are electrocoated engine blocks are coated with heat-resistant, usually waterborne materials. Other parts (e.g., steering equipment and shock absorbers) are painted with two-pack, one-coat epoxy systems that are usually solventborne use of waterborne systems is, however, increasing. 

The major process in anodic electrocoating will be the evolution of O, leading to an increase in pH and cons iuent deposition of the paint in its acid form, j.e. ... 

---