New Process for Painting Venetian Blinds Triggers Rise of Important Finishing Technology

California industrialist and inventor Joseph L. Hunter without question was blessed with great vision, and his keen eye for the next big thing in metals and machines helped trigger the meteoric ascent of the Venetian blind as a mega-selling window-treatment product.

The rise of the seemingly unremarkable Venetian blind - and Hunter's newfangled method of painting it - also opened the way to a finishing-industry revolution and a significant new market segment for coatings manufacturers.

Before Hunter came along, the painting of thin strips of metal that were attached in an accordion-like apparatus known as the Venetian blind was a time-consuming chore. Hunter changed all that, and in the process helped create a new industrial phenomenon known as coil coating.

Today, approximately 70 years after Hunter devised the first coil system to paint blinds, the coil-coating process is used to apply a durable finish to a host of metallic products, from cans to auto parts, to sheet metal for farm-storage buildings, household appliances and airplane hangars, to the facades of towering skyscrapers.

Still, "coil" didn't exactly spring forward at warp speed from its humble 1930s origins at Hunter's Riverside, CA, machine shop to become a multibillion-dollar global industry. It wasn't until after World War II that the process really caught on with industrial finishers.

Coil coating is the high-speed application of industrial coatings to continuous coils of aluminum or steel. The pre-finished metal is then shipped to manufacturers who convert it to finished products.

In the continuous and highly automated coating process, a coil of metal up to 72 inches wide and traveling as fast as 700 feet per minute unwinds, and both the top and bottom sides are cleaned, chemically treated, primed, oven-cured, top-coated, oven-cured again, and recoiled for shipment.

Hunter's ‘Revolution No. 2'

Joseph L. Hunter was best known in the Southern California city of Riverside as a legendary "machine maker" who helped revolutionize aluminum manufacturing. Historical accounts documenting the evolution of Hunter's company and its successors describe his continuous casting machine for production of aluminum slats as "Hunter Revolution No. 1."

But before his shop cooked up the aluminum-casting process, Hunter had secured his first major patent with a continuous coating process for metal strips. The process, called "Revolution No. 2" in Hunter company lore, played a pivotal role in the emergence of Hunter Engineering as a groundbreaking innovator in the Venetian-blind industry.

A historical review of the Hunter company's early years relates that "To ensure preeminence in this (coating) process, Al Upson, one of the country's foremost paint chemists, was spirited away from Sherwin-Williams" to head the Hunter paint lab. Upson stayed with Hunter Douglas and its successor companies into the 1980s, retiring from Alumax Mill Products after helping perfect wide-sheet coating lines, the Hunter company's historical review says.

The production and continuous-coating processes for steel Venetian blinds developed by Hunter in the 1930s quickly gained favor among most of the manufacturers of blinds. World War II put Hunter's Venetian-blind business on hold, but the company returned to the market in 1945 and by 1950 had come out with the big-selling "Flexalum" brand of aluminum Venetian blind.

Still, coil coating remained a minor player in the industrial-coating arena until the 1950s, when companies such as Chicago-based Litho-Strip, Roll-Coater of Indianapolis and Pre Finish Metals of Elk Grove Village, IL, built major coil-coating lines.

A successor company of Hunter Engineering participated in this expansion by designing and building paint lines for coil operators. The company, now part of FATA S.p.a., of Torino, Italy, has built coil-coating facilities all over the world.

Coil coating offered an attractive alternative to other methods, such as spray, by providing nearly 100% application efficiency - virtually zero loss of coating - a high rate of speed and an enviable environmental profile thanks to a contained operational setting and advanced solvent-emissions abatement systems.

Coil lines grew in size and capacity, and can stretch a city-block long, with an "accumulator" tower at each end of the line to wind and unwind the coil strips. Some of these towers are so high they must get air-traffic clearance.

Formulation Advances Boost Performance

Important coatings formulators for the emerging coil market included Hanna Chemical Coatings, later acquired by Reliance Universal and then by Akzo. Other key players were Pennwalt, American Marietta (later part of Mobil Chemical) and Lilly. Whittaker Corp., DuPont, Dexter, Glidden, and DeSoto also participated in the segment. Today, the global coil-coatings market is dominated by BASF, Akzo Nobel, PPG, and Beckers, while The Valspar Corp. also holds a significant position in North America.

Frank Graziano, a retired coil-industry veteran who held key technical positions at different times for coil-coatings applicators and coatings suppliers, recalled that manufacturers of steel farm-storage buildings helped greatly in creating a significant early market for coil coating. While at The Dexter Corp, Graziano helped formulate the first silicone polyester, a revolutionary technical advance that boosted long-term durability on exterior metal substrates.

Graziano, who retired several years ago from Pre Finish Metals, said coatings technology evolved from early solution vinyls, alkyds and epoxies to polyesters for general uses, silicone polyesters for weatherable applications, and on to highly durable fluorocarbons for the most demanding settings and maximum color strength. Modification with other materials, such as melamine formaldehyde resins and isocyanates, also is employed to address specific performance needs or cost considerations. Organosol and plastisol coil coatings offer excellent properties where post-finish metal fabrication is of prime importance.

Coil-coated powders have been developed and are seen as offering the potential for enhanced abrasion resistance, flexibility and appearance properties. But powder has failed to make a major impact in the coil segment, reportedly due to shortcomings in process speed and film-thickness control.

Coil-coating companies that have figured prominently in the industry's growth include Pre Finish Metals, which traces its beginnings to 1951 as All Weather Steel Products. The company has pioneered a number of coil technologies, including coil electrogalvanizing coating for automotive applications.

Other major coil operators are Roll Coater, based in Indianapolis, and Precoat Metals, headquartered in St. Louis. Precoat is reported to rank at the top of the coil-coating industry, with 10 coating lines at various U.S. sites and a total annual finishing capacity of more than 1 million tons of metal. The company says that equals approximately 1.2 billion linear feet of steel, or enough to circle the globe more than nine times.