Finish Strong with PVDF Coatings[October 2015]
The History and Benefits of 70 Percent PVDF Coatings
For 50 years, 70 percent PVDF resin-based coatings have both literally and figuratively stood the test of time. Originally introduced to the market in 1965, 70 percent PVDF coatings have steadily grown to be one of the most sought after and recognized coil and extrusion coatings available. Continuous improvements to the PVDF technology have contributed to the coating’s longevity, and resulted in additional PVDF coatings, formulations and uses.
PVDF is the abbreviation for polyvinylidene difluoride, a fluoropolymer resin. Coatings containing fluoropolymer resins are produced by many manufacturers and branded with a variety of trademarked names. It can be confusing for those outside of the coatings industry to differentiate between the resin manufacturers and the coating manufacturers. Furthermore, although architectural coatings from different manufacturers contain similar PVDF resins, the application and performance of the coating systems can widely vary. This is due to the proprietary formulations of each coating manufacturer. Hylar by Solvay Solexis and Kynar by Arkema Inc. are the two brands of PVDF resins most widely recognized in the U.S., and offer equivalent performance per industry standards for weathering.
The Chemistry of PVDF Coatings
PVDF resin-based coatings are available in two forms: coil and extrusion. Coil-coated, or pre-painted, architectural building products start out as flat sheets and are formed into shapes, such as roof panels, wall panels, gutters and pre-manufactured metal buildings. Substrates may include pre-treated hot-dip galvanized steel, and pre-treated aluminum.
While coil coating is applied to the metal prior to it being shaped into an architectural building product, the aluminum extrusion process creates the metal products first—before a finish is applied. The shape of the die determines the shape of the extrusion. Using aluminum billet and a powerful hydraulic press, extruders can produce almost any shape imaginable. Fenestration products are among the most common examples of extruded aluminum, such as framing for a window, curtainwall, storefront and entrance systems.
To develop these high-quality PVDF coatings, manufacturers create unique formulations that include the use of resins, pigments, solvents and additives:
Resins serve as the binder that forms the paint film and are the principal components that determine the durability of the coating, its appearance and its performance. For coatings other than PVDF, common resin names are epoxy, silicone modified polyester, polyester and urethane.
Pigments are not only used to add color and aesthetic properties, but they also influence the coating’s durability.
Solvents thin the consistency of the mixture so that it can be properly applied. During the curing process, solvents evaporate, while the resin system adheres to the substrate.
Additives are used for processing pigments within the film, for flow and smoothness, regulating the rate of the cure, and enhancing the coating’s hardness, gloss, mar resistance and other performance attributes.
Over the last 50 years, advancements in technology and research have strengthened the chemistry of 70 percent PVDF coatings, leading to being one of the most durable paints on the market. Continuous improvements from manufactures have contributed to the longevity, durability features, and formulation of new PVDF coatings for specific end applications that have distinct requirements, for example low or high gloss. These innovations include delivering enhanced application properties, dependable color consistency, and special formulations such as energy-efficient solar-reflective coatings and color-changing coatings.
Today, in a competitive marketplace, manufacturers of 70 percent PVDF coatings must strive to create a product that withstands the test of time. A few properties that are continuously being tested as they highly affect the durability and application of 70 percent PVDF coatings include:
Chalk and fade resistance. The right combination of resins and pigments are essential to ensuring protection against chalking and fading. No matter how well a coating is made, certain colors are more affected by the outside environment than others, especially bright colors like yellows, oranges and reds. When selecting a color, ultraviolet exposure and intended end-use should be taken into consideration. PVDF coatings have the best UV resistance of any polymer used in coatings today. The carbon-fluorine bond is one of the strongest chemical bonds and gives PVDF resin-based coatings their stubborn resistance to chalking and erosion, as well as harsh airborne industrial and atmospheric pollutants
Film integrity and adhesion quality. Erosion rate, the rate at which a coating degrades, is an extremely crucial component for color and design longevity. The erosion rates of PVDF coatings are relatively small and support a long coating life. The quality of PVDF coating adhesion depends on the superiority of the primer that adheres to the substrate. The primer is meant to create a strong bond with the PVDF topcoat, and resisting the stresses of forming and of weathering.
A Case for 70 Percent PVDF Coating
Recently completed, the JW Marriott Convention Center Hotel in Austin, Texas illustrated the wide range of features and usages of today’s 70 percent PVDF coatings.
The original concept for the building was to integrate natural materials that are found within the Texas landscape. For the façade of the 34-story primary tower, architect HKS | HG sought after a weathered metal appearance, but when the team saw the estimate to use weathered steel, they knew the price was too high—even for a luxury brand like JW Marriott.
Hunt Construction, the contractor on the project, reached out to ProCLAD Inc. and along with HKS, consulted closely to determine if there was an alternative solution that could deliver the appearance of weathered steel at a lower price. Craig Caudill, executive vice president for ProCLAD, suggested using formed Galvalume panels painted in dark, medium and light shades to mimic the appearance of rusted steel. Caudill knew that using a variety of colors of coatings could help create the dimensional variety the architects were looking for. That’s when Valspar was called upon.
The team liked the idea, but wanted to see a sample before committing, and they needed it fast. The company was able to color match the three requested shades, work with Western Extrusion to coat them on steel flat stock, and ship them to ProCLAD in less than two weeks. The architects liked the appearance of the panels, as well as the lower cost of the solution, but still weren’t ready to commit to the colors.
Five new sets of colors in varying shades of brown, along with a few metallic options were created to ensure the best possible result for the team. With the wide variety to choose from, the architects were then able to confidently make their pick and select a color range that was consistent with the original concept.
McElroy Metal supplied 40,000 square-feet of 18-gauge Galvalume steel coil coated with Valspar’s Classic II Fluropon in a custom color combination of Barrel Brown, Fudge and Mustang. The panels, in varying depths and widths, where adhered to the building providing the look of a weathered steel exterior.
Additionally, Win-Con Inc. supplied the curtainwall, carrying glass across the adjacent sides of the hotel. The Win-Con Unitized curtainwall system included 200,000 square-feet of glass with interior mullions and exterior fins covered in the company’s Fluropon Classic II extrusion coating in Bright Silver by Bonnell Aluminum.
The 1.3-million-square-foot hotel was completed under budget in early 2015, and is now both the largest hotel in Austin and the largest JW Marriott in the United States. With the use of 70 percent PVDF coatings, the hotel will maintain its striking appearance due to their strength, durability and color consistency.