TECHNOLOGY
Electrocoating is growing commercially Many companies are using electrocoating processes to obtain strongly bonded, uniform finishes Electrocoating, a relatively new way to apply paint, is beginning to catch on commercially. Today at least seven firms are using the process on a production basis. Another half dozen have lines that will be in full operation soon. A matter of a year ago just one company, Ford Motor, was finishing products on a large commercial scale with the technique, a method of electrodepositing paint on metal from an aqueous bath of the paint. In fall 1965, General Electric began electrocoating meter parts at its Somersworth, N.H., plant. Last February Tecumseh Products started using the process to coat compressors. This past summer, Medart Locker put a line in operation to coat steel parts for bleacher seats, and International Harvester brought Canada's first electrocoater on stream, a unit to paint disks for agriculture equipment. More recently Federal Pacific Electric Co. started up a unit at its Vidalia, Ga., plant for finishing switch boxes, and Barber-Colman set up a line at Rockford, 111., for painting air distribution parts. A number of products are being electrocoated on a pilot basis, including industrial control equipment, aluminum extrusion, metal office furniture, motor stators, vending machine parts, and steel storage racks. There are now more than 15 lines with a paint capacity of about 125,000 gallons either in use or scheduled to be so soon. Orders have been placed for at least eight new lines with a total capacity of some 150,000 gallons. By the end of 1967, 750,000 to 1 million gallons of paint will be used in electrocoating production, predicts electrocoating equipment supplier Ashdee Corp. Behind this growing use of electrocoating are basically two factors. One is simply advancement in technology, which has overcome many of the early paint and equipment problems. The other factor is heightened interest in water-thinned paint systems, spurred by the passage of Los Angeles County's Rule 66 for controlling organic solvent emission. Advantages. In development for the past decade or so, electrocoating has made far more headway overseas than it has in the U.S. There are more than 50 units now in opera54 C&EN NOV. 21, 1966
BATH. Ford electrocoats with rust-inhibiting primer at its Wixom, Mich., plant to give a thorough, uniform coating on all metal surfaces
tion in Europe. European auto, appliance, and electrical equipment makers, among others, are using the technique. Industrial finishers are attracted to electrocoating for several reasons. It gives a very uniform coating, even over sharp corners and edges. It can be automated. The system offers freedom from runs, sag, and tears typical of conventional dip or flow coat processes. There is little paint waste. Direct labor costs are lower. And it eliminates the fire hazard. Despite technological advances, the technique still has drawbacks. It is limited to one coat since paint is electrically resistant. A second coat could be applied by adding conducting materials to the first coat, but this approach raises cost as well as technical problems. Another disadvantage is that the paints for electrocoating are difficult to formulate and usually don't have properties as good as paints for conventional application methods. For instance, present paints lack the detergent resistance desired by the appliance industry. Typically polycarboxylic acid derivatives of resins, the paints inherently are sensitive to alkali attack. Baking will cross-link the majority of the acid groups,
but will not cross-link all of them. Finally, keeping electrocoating equipment in continuous operation can be complex. Bath temperature, voltage, concentration of bath chemicals and other process variables have to be carefully controlled. Both paint and equipment suppliers are promoting electrocoating. Several paint makers—among them, Celanese Coatings, Du Pont, Glidden, PPG Industries, Mobil Chemical Coatings, and Sherwin-Williams—are now offering water-thinned paints for the process. Others are actively working in this area. Major equipment suppliers include Ashdee Corp., Binks Mfg. Co., DeVilbiss Co., Ransburg Electro-coating Corp., and Udylite Corp. First to use electrocoating on a large scale in the U.S. was Ford. The auto maker began using the technique on a production basis on wheels and Lincoln and Thunderbird bodies in 1963. Today, Ford has installations at Wixom, Mich., for applying base coats to Lincoln and Thunderbird bodies; at Monroe, Mich., for coating wheels; at Cologne, West Germany, for coating Taunus bodies; at Genk, Belgium, for autos and trucks; at Southampton, England, for trucks; and at Halewood, England, for autos.
General Motors is using the technique experimentally at its Buick-Oldsmobile-Pontiac plant in Kansas City, Kan. Both Chrysler and American Motors say they are evaluating electrocoating. Electrical parts. One of the first large-scale commercial electrocoating installations to go into operation outside the auto industry was at GE's Somersworth, N.H., plant. GE is using the technique to paint parts for watt-hour meters and instrument transformers made by its meter department. Two lines are now in use. One is for applying a gray, modified acrylic paint on meter sockets, and the other is for applying black oleoresinous paint on meter parts. Parts move through the gray coat system at 8 feet per minute, the black coat at 2 feet per minute. After rinsing, coated parts are baked at 350° to 400° F. The finished parts, says GE, have a more uniform coating than possible by spray application and have improved corrosion resistance. For the past eight months Tecumseh Products has been electrocoating compressors used in refrigerators, air conditioners, and the like at its Marion, Ohio, plant. Like GE, Tecumseh is also using a one-coat system. International Harvester's new unit at Hamilton, O n t , replaces a flow coater. The installation applies a black finish to harrow disks. The paint is a modified alkyd and the equipment will handle 480 disks, each 2 feet in diameter, per hour. After coating and a cold spray rinse, the disks go a 400° F. bake oven for 15 minutes. The finished disks have a very even coating of paint, even on the edges, which protects them from corrosion during shipping and storage. Started up in September, Federal Pacific Electric's line at Vidalia, Ga., applies a single-coat acrylic finish to 3000 switchboxes per day. The company has been operating a pilot line at its Newark, N.J., headquarters.
Savings in labor and material cost at Vidalia amount to at least 50% over conventional spray application, points out R. B. Goody, manager of special products engineering. This winter a line will be installed in a new plant now under construction at Vidalia. It will have five times the capacity of the existing line. Barber-Colman's electrocoating line for finishing air distribution parts such as grilles and returns has been running since last month. It replaces a flow coat and spray operation. The paint is a modified acrylic, and currently a beige finish is being applied. Now at full production, the installation is electrocoating about 4400 parts per day in two shifts. Since August, Art Metal, a major manufacturer of metal office furniture, has been operating an electrocoating system on a pilot-plant basis at its Jamestown, N.Y., plant. Several firms are studying electrocoating of aluminum extrusion for building products. For instance, V. E. Anderson Mfg. Co. has installed a line at its Rome, Ga., plant and is currently coating 10,000 square feet of extrusion per day on a pilot basis. Paint is a white, semigloss modified acrylic. Anderson plans to be commercial with the process in January. Royce Aluminum Co. has installed a line at Taunton, Mass., and plans to have it operating next month. Seeburg Corp., Chicago, is experimenting with a line to coat vending machine parts with a high-gloss beige finish. Globe Industries has a line at Dayton, Ohio, and is attempting to finish motor stators. Unarco Industries, Chicago, is installing an electrocoating line at Springfield, Tenn., for finishing steel storage racks and other material handling products. Whirlpool Corp. is putting in a system at Clyde, Ohio, for finishing appliance gear housings. And a line is going in at GE's Salem, Va., plant for coating industrial control equipment.
ALKYD COATINGS. International Harvester's new electrocoating unit at Hamilton, O n t , finishes harrow disks with black, modified alkyd paint to ensure corrosion resistance for outdoor exposure
Electrocoating is similar to electroplating Electrocoating is similar to depositing metals by electroplating. The part to be coated is connected as an electrode in a cell and the electrolyte is an aqueous solution or suspension. In metal plating the part is usually the cathode and the electrolyte is an inorganic salt. In electrocoating, the part usually functions as the anode, the electrolyte is a water-thinned paint in alkaline solution, and the tank holding the paint is the cathode. An electrocoating installation generally consists of a metal preparation system, an electrodeposition tank, a rinse stage, and a bake oven. Water-thinned paints used in the process are usually based on amine-solubilized polycarboxylic acid derivatives of alkyd, acrylic, epoxy, or polyester resins. Finishes now available include red oxide, black, gray, beige, clear, white, green, blue, brown, yellow, and tan. The amine, often diethylamine, reacts with the resin's carboxyl groups to form a water-soluble salt. As current is applied between the two electrodes, negatively charged resin and pigment particles are attracted to the anode (the part to be coated). The result is deposition of the anionic resin on the object as insoluble polycarboxylic acids: (RCOO)n +
nH + - *
(RCOOH)n
The positively charged amine ions are attracted to the cathode to balance the reaction electrically. Work is now under way to develop a cationic paint which will deposit at a cathode. The process continues depositing paint at the anode until a continuous, even film covers the entire surface. Thickness of the film depends on the voltage—deposition stops when the coating creates enough electrical resistance to cut off current flow and on-time in the bath. Film thickness ranges from 0.3 to 1.8 mils. Voltage requirements vary from 50 to 250 volts; current requirements range from 2 to 5 amp. per square foot of area coated per minute. The part leaves the tank with an almost dry coating of paint. This results from an electroendosmotic effect—the film becomes semipermeable as it is deposited and any volatile solvent (mostly water) is driven from the anode through the film and into the bath by endosmotic force. The coated part is then spray rinsed. Finally, it is baked to cross-link the carboxyl groups.
NOV. 21, 1966 C&EN 55
