Autodeposition of Organic Coatings
Publication Date: July 1999
Links Last Checked: July 2004
Autodeposition is a unique, waterborne organic coating process which uses chemical reactions to achieve deposition of a high quality finish on an assortment of substrates. The autodeposition process is simple in comparison to other processes used for applying corrosion-resistant coatings. Following conventional cleaning and rinsing stages, metal parts are immersed in a coating chemical bath where the deposition of pigment and resin particles takes place. The growth in thickness of the film is time dependent. There is an initially rapid deposition rate followed by a decrease in growth limited by the diffusion of ions on the metal surface and then "self-sealing" of the coating. A protective barrier film is formed wherever the coating bath makes contact with the metal workpiece.
The autodeposition coating process reduces the complexity and capital required by competing technologies. It requires no electric current, because self-limiting organic coatings are developed through a chemical reaction with the metal surface. Because the process coats anywhere it wets, it generates exceptionally uniform protective coatings even on difficult to coat parts. These parts are coated at a fraction of the conventional energy costs of competing technologies.
Autodeposited coatings can be uniquely applied on the same production line for parts with many different end-use market applications. No conversion coating is required; the only pretreatment necessary is cleaning. With no Volatile Organic Compounds (VOCs), no toxic heavy metals, and low-temperature curing, air emision are minimized and the work environment is improved.
Below are advantages and limitations of using the autodeposition process. This report also provides a Quick Reference table that helps an applicator identify the performance achievements of this coating process and a case study of how this process saved money, achieved environmental compliance and improved product quality.
|Case Study - Steelcase Replaces Zinc Plating Lines
"We have a system now that is less labor-and-energy-intensive, that has, in one line, more than doubled our previous capacity from four lines, and that has almost entirely eliminated waste treatment costs. Most importantly, we have a process that gives us the ability to satisfy customer requirements while being sensitive to the environment."
Steelcase Inc. replaced four zinc plating lines with a new Autophoretic/Autodeposition line at its Desk Division in Grand Rapids, Michigan.
Steelcase has a corporate policy that encourages environmental initiatives. According to their plant manager, Steelcase is "committed to getting any problematic chemicals out of the workplace and out of the environment. No carcinogens, no toxins, lower VOC's."
The autodeposition process utilizes a chemical reaction with the steel part to achieve deposition. The immersion bath consists primarily of a mildly acidic latex emulsion polymer in combination with deionized water and certain patented ingredients. The coating thickness is controlled by time and temperature, and ultimately is self-limiting, based on the release of iron ions from the steel surface.
Steelcase evaluated several coating alternatives to their zinc plating process lines. Among the coating systems evaluated were: new plating lines, high solids, electrocoating, epoxy coating, and simply outsourcing the work. The manufacturing department had known about autodeposition since 1985 and knew "it had too many benefits to pass up."
The various coating processes were tested for hardness, abrasion resistance and corrosion resistance, as well as finish consistency. Autophoretic coatings passed their standard of 144 hours salt spray exposure and had an excellent, uniform quality finish.
Steelcase also did some additional testing outside of the performance parameters. They evaluated environmental impacts and associated waste treatment costs, as well as customer acceptance. Customer reaction to the uniform finish was very good, especially if it meant less of an impact to the environment.
Payback in Two Years
- "Process of Most Resistance", Products Finishing Vol. 56, No. 10 July 1992. pp. 47-51. Authored by Beverly A. Graves.
- "Autodeposition of Organic Coatings", Metal Finishing: Organic Finishing Guidebook and Directory Issue for '94 Elsevier Science, Inc. 1994. pp.136-140. Authored by Tom Jones.
- "Autodeposition - the Environmental Advantage", Technical Paper FC91-371 Society of Manufacturing Engineers. September 1991. pp. 47-51. Authored by Tom Jones.
- "Autodeposition - Tough Coatings and no VOCs", Finishing Line. 1990. Authored by Tom Jones.
- "Official Conference/Expo Directory: 1994 Appliance Manufacturer Conference and Exposition", Appliance Manufacturer Vol. 42, No. 9 September 1994. pp. A1 - A16.
- "Custom Coater Installs Autodeposition Line", Industrial Finishing. March 1988. Authored by Joe Schrantz.
- "Autodeposition Protects Brake Components", Industrial Finishing. July 1986. Authored by James R. Wagg.
- "Materials, Finishing and Coating", Tool and Manufacturing Engineers Handbook Vol. 3, 4th edition 1985. Authored by Charles Wick and Raymond F. Veilleux.