Polyvinyl fluoride (PVF) is a highly stable and durable polymer that is used in several demanding applications requiring the highest level of chemical, weathering, and hydrolytic stability.  Originally commercialized by DuPont under the trade name Tedlar®, PVF has been used for over 60 years in a variety of applications that require the highest level of surface protection in the harshest environments.  Tedlar® PVF can be formulated into both a film and a coating. One of the most important applications for PVF film is in building and construction, where it provides durable aesthetics and barrier properties when laminated onto the surface of materials that are used for both building exteriors and interiors (Figure 1).  The film enables users to ensure the surface aesthetics remain in like-new condition for decades, despite heavy exposure to UV light, rain, wind, humidity, graffiti, chemicals, cleaners and disinfectants, bird droppings, pollution, and a wide variety of other environmental stressors.  The secret of the best-in-class durability is the polyvinyl fluoride resin, which is a fluorinated polymer with a single repeating fluorine unit in the backbone.  This single carbon-fluorine bond strengthens the chemical bonds throughout the polymer, making it extremely stable and resistant to attack from a variety of chemical and energy stressors.  The polymer resin does not absorb UV light, is unreactive with acids and bases, and does not dissolve in any known solvents at room temperature.  It is a durable matrix which holds pigments in a stable configuration, imparting a durable color and appearance that changes very little over time.  It is also naturally flexible, withstanding a variety of hot and cold forming operations and other mechanical stresses without cracking or breaking to expose the substrate beneath.

Coatings made from PVF bring the same benefits of the film in a more versatile format that can be custom tailored to specific architectural design needs. Just like in the film, the durable PVF polymer is the matrix that holds pigments and other special ingredients that enable a wide range of color and gloss aesthetics as well as various customized functions like metallic appearance or surface texture. PVF coatings are particularly suitable for coil or extrusion coating since the metal surfaces are suitable for the relatively high temperatures needed to fully coalesce the PVF into a dense, durable film layer.

PVF coatings are unique in that they simultaneously provide superior chemical resistance, flexibility, hydrolytic, and UV stability, which cannot be achieved by any of the current coil and extrusion coating resin (for example, PVDF, SMP, FEVE, PE, or PU).  The fluorinated backbone (Figure 2) provides similar weathering and UV stability to premium PVDF coatings, but the difference in the dielectric properties and the nature of the crystallinity mean that it is more resistant to acids, bases, and solvents than any other coating material, and the pure polymer can elongate easily making it more flexible without cracking or breaking.

Chemical resistance testing can be used to demonstrate the extreme durability of PVF coating and its superior protective capability for the substrate. Immersing the PVF coated panels in strong acids, bases, oxidants and disinfectants is used to accelerate the degradation seen in real harsh-environment scenarios, such exposure to acid rain, chemical plant or hospital interiors. The longevity data (Table 1) shows that PVF coated panels offer substantially more resistance to chemicals compared with the existing premium PVDF coated panel (Figure 3).

Table 1 Longevity of PVF and PVDF coating in various harsh chemicals

The simple nature of the semicrystalline molecular structure makes PVF coatings flexible even when 100% pure.  No additives or plasticizers are needed to make PVF formable.  The PVF coating can be bent after application, even to a very harsh “0T” radius of curvature, without damaging or cracking the finish (Figure 4).  This is important to enable the coating to still maintain its barrier properties and extreme chemical and environmental resistance on formed panels.  PVDF, however, typically must be blended with acrylic or other additives to achieve desired flexibility, diluting the fluoropolymer resin often at the cost of reducing its environmental performance.

Discussing coating technology also necessitates a review of regulatory matters that impact this market. Many state, national and international bodies have and are continuing to introduce legislation for per and polyfluoroalkyl substances (PFAS). Because of the large number of chemical substances which are potentially in scope of any new legislation, it is important to understand how PFAS are being regulated. Polyvinyl fluoride contains only one fluorine molecule attached to the carbon backbone of the polymer and does not contain any fully fluorinated methyl or methylene carbon atoms. As such, polyvinyl fluoride does not meet the chemical structure definition of a PFAS as published by several U.S. states, OECD, the European Chemical Agency (ECHA), and the EPA. Additionally, no PFAS are used in the manufacture of PVF. In fact, polyvinyl fluoride has been specifically identified by ECHA in the PFAS Restriction Proposal and Graham Sustainability Institute at the University of Michigan as a viable alternative to other PFAS polymers for use in a variety of industries, including the paint and coating market.

While chemical resistance and flexibility are the main advantages of a PVF coating, there is no compromise on weather and UV resistance.  Just like PVDF and other fluoropolymer resins, the high electronegativity of the carbon-fluorine bond stabilizes the polymer chain and enables it to withstand the photon energy imparted upon it by sunlight.   While PVF is transparent to UV light in the solar spectrum, pigments and additives can be incorporated in the PVF coating to safely reflect or absorb and dissipate UV energy and protect the underlying materials from the UV damage.

Coatings made from PVF are formulated and applied in a similar way to PVDF coatings.  PVF resin is the key ingredient in coating formulation, which takes about 25% of the coating mixture by weight. Various pigments typically make up 15% of the coating formulation by weight and are used to add color and visual features to PVF coating.  Proper selection of the pigments and additives is critical for the coating durability, including adhesion to the substrate and the color and gloss retention.  Organic pigments make PVF coating have more vibrant color compared to inorganic pigments, but they may not be stable as inorganic pigments under UV exposure. Inorganic pigments typically provide the highest level of stability.  Solvents are typically around 55% in formulation by weight and serve as the vehicle to transport the coating solids to substrate, enabling it to form a thin, uniform, and level wet film on the substrate.  The choice of solvent is critical for PVF coating because PVF resin is insoluble in any known solvent at room temperature and can only coalesce to form a uniform coating in certain solvents. Propylene carbonate is the most used solvent for PVF coatings.  Additives are used in a small amount for uniform dispersion, regulating flow and smoothness, and enhancing the coating’s adhesion, color, gloss, and other performance features.

PVF coatings can be applied to metal surfaces by coil coating or spray coating.  In coil coatings, the liquid dispersion is applied to a flat sheet of metal from a coil using a roll application process and is cured and dried at a peak metal temperature of around 250 °C (480 °F).  In spray coating, the liquid dispersion is sprayed on a three-dimensional part and cured at around the same metal temperature.   In both methods, the coating process generally includes cleaning and chemical pretreatment of the metal surface, applying primer to impart adhesion and additional corrosion resistance, and finally applying PVF topcoat.

The finished PVF coatings are currently being used in many different projects and applications worldwide.  A few examples include the very prestigious new site for the World Laureate Forum in Lin’gang, Shanghai. Scientists from around the world who have won Nobel Peace or Wolf Prizes are invited to an annual conference in this building. Tedlar® PVF coating was used on the aluminum in the cornice and entrance of the building. PVF coating was chosen due to the site’s proximity to the sea, ensuring resistance to corrosion due to sea salt spray. The dirt-shedding and UV-resistant properties of the PVF coating also mean that the building will not fade over decades in the sun, and will look clean and new over its lifetime.

Another highly visible PVF coating project was the renovation of the Shanghai Stadium. This is the third largest stadium in China and has hosted many significant events including football and soccer during the 2008 Summer Olympics. The stadium was originally built in 1997 but was transformed in 2021 prior to hosting the FIFA World Cup. Tedlar® PVF coating was chosen to protect the new aluminum siding and cladding due to its durability and cleanability. The aluminum honeycomb panels are highly resistant to UV damage, and the paint’s dirt-shedding properties ensure a clean, fresh for years to come.

A third project in Zhongshan City involved aluminum curtain walls protected by PVF paint and installed on a large office building downtown. This structure will not only withstand outdoor elements and resist fading, can be easily cleaned of graffiti and quickly shed dirt, smog build-up, or other damaging effects of cities.

PVF coatings have been used in commercial and public spaces like these examples, but also in corrosive industrial facilities. These coatings typically carry long warranties, ranging up to 50 years. This coating technology is tried and tested in the long history of PVF film and enables the same trusted PVF performance with color and application flexibility for the user. PVF coatings are in-stock and available, offering a truly innovative solution to the coil coating industry.