By Cynthia A. Gosselin, The ChemQuest Group
Full disclosure: My involvement in the coatings industry centers around the field of prepainted metals. These factory-applied coatings were always fascinating to me because metal coils of all types of substrate pedigrees could be unwound onto a paint line and all the processes needed for painting completed in a matter of minutes. These processes went all the way from cleaning the surface to curing the paint, resulting in pristine coils waiting to be formed into parts for almost every market.
Therefore, for purposes of this article, “factory-applied” is defined as painted before forming, or prepainted. Conversely, “field-applied” refers to painting after forming—regardless of the application method or painting location.
Factory-applied painting was very different from what some call “the traditional” method of applying coatings, which involves forming the parts, putting them together, and then cleaning and painting the end product. This method of painting after parts are formed could be done in an immersion or spray painting section of a facility, outsourced to another company, or painted on location during construction.
Joseph L. Hunter, an early pioneer in the paint and coatings industry, invented the first coil coating apparatus to streamline the very time-consuming chore of painting venetian blind slats in 1930. This coating method was quickly adopted by the venetian blind industry. In the 1950s, coil coating lines were designed to handle large steel and aluminum coils and the industry grew by leaps and bounds.
Since those first rudimentary coil painting lines, technology has advanced significantly to the point where prepainted metal has become a preferred coating method for a wide variety of commercial, industrial, consumer and residential products.
Applications range from automobile parts, appliances, HVAC units, lighting fixtures, metal roofing, interior and exterior wall panel systems, mullions, soffits, gutters, truck trailers, food and beverage containers—in short, anything that can be made from a flat sheet of metal.
In the appliance market today, customers tend to gravitate toward color. The days of the standard white refrigerator, washing machine and dryer are gone. Consumers want durability and beauty in their homes. Appliance manufacturers adopted prepainted metal about 30 years ago. At that time, white was still the “in” trend.
Today, the finish on a refrigerator door or washer/dryer set is a high-value differentiator, and it is not only color where prepainted metal plays a role. Yes, a rainbow of colors does exist for home appliances for those who want bright pops of color to brighten their home.
However, for those who enjoy the look of stainless steel, but don’t want to constantly remove fingerprints, consumers now have the choice of coatings with fingerprint resistance that retains the industrial look. Thin glittery metallics or translucent coatings reminiscent of holograms are also available. Because of the consistency and excellent color match provided by coil-coated metal, some manufacturers even tout custom color matching for the kitchen and laundry room.
Coil lines have grown in size and capacity to accommodate speeds of up to 800 ft/min, with a few lines stating capabilities inching toward 1000 ft/min for some applications. There are anecdotes that some of the accumulator towers used for unwinding and winding at either end of the line at high speeds were so tall that they required air-traffic control clearance! A typical coil coating line schematic is shown in Figure 1.