Revisiting Prepaint

Do you fabricate painted steel, aluminum or other metals? If so, revisit a process that can improve productivity, reduce processing costs, improve quality, reduce inventory, and reduce environmental emission concerns – all at the same time: coil coating (or prepaint), where large coils of cold-rolled steel, hot dip galvanized, electro galvanized, zinc-steel, aluminum, stainless steel, copper, and brass) are coated in a continuous, highly automated process prior to fabrication.

During prepaint, the metal coil is unwound, the top and bottom sides are cleaned, chemically treated, primed, ovencured, topcoated, oven-cured again, then rewound for shipment. The variety of coatings available is almost unlimited, including polyesters, polyurethanes, epoxies, vinyls, plastisols, acrylics, water-borne emulsions, zinc-rich coatings, fluorocarbons, dry lubricants, and treatment and primer combinations.

Prepainted coils can be printed, striped, or embossed to create special visual effects. What about flexibility? Prepainted coils can be rewound, drawn, formed, bent and blanked. Prepainted metals can be fastened with bolts, screws, rivets, Tog-L Locks, etc., or lockseamed, adhesive bonded, and in some cases, welded.

Conversion to prepainted substrate technology could eliminate your internal spray paint or flow coat finishing operations – probably your biggest production bottlenecks. The precise laydown of the paint provides much better control of film thickness than powder or spray applications. Since minimum paint is used with no waste, paint costs remain low.

Internal finishing probably causes most of your quality problems, too. With coil coating, the metal is painted "in the flat" (before fabrication) for uniform cleaning, pre-treatment, priming and topcoating. Because both sides are prepared, coil coating prevents future problems related to product rusting from the inside out.

Eliminating these bottlenecks in your finishing process can reduce your work-in-process inventory. Being able to eliminate or dismantle your internal paint line frees up valuable plant floor "real estate" for more profitable activities. Also, outsourced coil coating can eliminate your EPA and OSHA environmental compliance problems related to internal finishing.

Internal paint lines tend to be very capital intensive and, if you do your own painting, you must stay abreast of the latest coating equipment, processes, and coatings. Third-party coil coaters eliminate this need by staying up on new ways to apply liquid coatings, or via powder and electron beam. You can get out of the "painting business" and focus on designing and manufacturing your own products.

Is coil coating is right for you? First, consider how and where coil coating can be utilized. It is already used successfully in a number of industries (Figure 1).

Next, consider whether the amount of coating work you need done is economically feasible for outsourced coil coating. If you run small quantities due to a number of different colors, you could arrange coil coaters to do all of the cleaning, treating, and primer application, then apply your own topcoats in your colors of choice. This allows inventory flexibility for the end customer.

Finally consider your design, handling and fastening operations. Will the finished prepaint coat over the complete exterior surface of your products as well as your post-painting does? Design your products such that cut edges are hidden with well-placed bends and trim pieces. Design your handling processes for incoming prepainted rolls so they do not mar or scratch the finished coatings.

For fastening, coil coated metals can be fastened, bonded, and even welded. You can welding if you purchase preprimed coils and then apply your own final finish. New adhesive bonding capabilities happen on a regular basis. Anyone designing a product that will utilize coil coating is remiss if they do not look hard at adhesive possibilities.

For more technical assistance in a decision about conversion to prepaint, the National Coil Coating Association provides assistance through its members, those steel companies, metal service centers, coil coaters, paint companies, metal treatment professionals, and an extended family of support companies that process prepainted metal.

The National Coil Coating Association, 1300 Sumner Avenue, Cleveland, OH 44115, 216-241-7333,Fax: 216-241-0105, ncca@coilcoating.org, www.coilcoating.org.