PPG experts discuss choosing the right coil coating system for every application, comparing the pros and cons of SMP and PVDF coatings
Silicone-Modified Polyester (SMP) and Polyvinylidene Fluoride (PVDF) coatings are two widely used coil-applied coating systems in the metalbuilding products industry.
Because these polymers are engineered to withstand extreme weather conditions, each provides a formidable barrier against UV exposure, humidity, salt spray and chemicals that can degrade the coating system. While both are excellent choices for preserving the structural integrity and aesthetics of metal building products, there are important distinctions between them due to their specific chemical compositions.
This paper will explore the differences between 70% PVDF and SMP coatings in terms of their chemistry, expected long-term performance, cost considerations, UV durability and colour stability. The paper will also provide an update on newer generations of SMP formulations that are closing the performance gap with PVDF fluoropolymers, as well as market forces that are driving demand and use of SMPs on a wider range of applications.
All coil coatings, including SMPs and PVDFs, are comprised of four primary components: resins, pigments, solvents and additives.
Resins are the building blocks of any coating system. They act as binders to hold pigment particles together and help the paint adhere to the metal. Resins are also responsible for the performance properties of a coating, such as colour and gloss retention; resistance to moisture, UV rays and chemicals; and mechanical properties like flexibility, impact resistance and hardness.
Common coil resin types include silicone-modified polyester, polyester, acrylic, epoxy and polyvinylidene fluoride. While the resin is a component of the coating, they are commonly referred to by their resin type, hence the classification of SMP and PVDF paint systems.
Pigments are insoluble solid particles produced from natural occurring minerals or by man-made chemical processes that give coatings their colour and, in some instances, solar reflectivity. There are two main classes of pigments – inorganic and organic. The chemical structure of each pigment determines their colour space, strength and stability.
The role of pigments is not limited to aesthetics. Each type varies widely in terms of quality, corrosion resistance and UV durability —factors that impact the overall performance of the coating. Some important attributes of pigments include their colour, hiding power, solar reflectance, tinting strength and special effect capabilities.
In terms of resilience, inorganic pigments are the most chemically stable and fade resistant, offering robust defense against light, chemicals, weather and heat. Consequently, they are the default choice for coatings systems used for exterior buildings and warranted to meet the most demanding performance expectations.
These synthetic or naturally occurring colourants do not contain carbon-based molecules and are made from minerals, metal oxides, metal salts or, in some cases, metal oxides fused under high temperatures. The latter are referred to as “ceramic” pigments and are valued for their stable nature.
Organic pigments are typically produced from carbon-based molecules. Though they offer a wide colour selection, these pigments are less resilient to UV degradation and change colour over time. Compared to inorganic pigments, organic pigments are less commonly used in exterior applications and only in specific colour spaces with limited warranties.
The colour space determines the choice of pigments, but the majority of premium PVDF and SMP products engineered for commercial building products use inorganic pigments with very limited or no organic pigments.
Unlike pigments and resins that determine the long-term protection and retention of colour and gloss, solvents have minimal impact on actual coating performance, but they do play a critical role in an essential function — application.
Solvents dissolve the resins and other additives to a desired consistency and disperse pigments throughout the paint for uniform colour, easier application and a smooth, even finish.
During the curing process, these solvents evaporate, leaving the resins and pigments behind to form a high- quality paint film. When specifically formulated, both SMP and PVDF coatings can be applied by a coil coating process or spray applications.
Additives are used to prevent defects in the coatings, like bubbling or uneven levelling, or to impart specialised properties, such as UV protection or colour stability.
When it comes to film integrity, colour stability and UV durability, a coating is only as good as the sum of its parts. Both strong resins and high-quality pigments are needed for robust performance.
Premium resins blended with weak pigments have a greater potential to chalk and fade, but strong resins coupled with strong pigments in a balanced formula will deliver long-lasting performance.
PVDF resins
PVDF is a semi-crystalline, highly inert and stable thermoplastic fluoropolymer. PVDF resin-based coatings are one of the most widely used ultradurable coating systems on the market today and set the benchmark for performance in the metal coating industry. Coatings companies have used this technology for over five decades, proving their superior longevity.
PVDF polymers consist of alternating carbon-hydrogen and carbon-fluorine groups. The carbon-fluorine bonds are one of the strongest in the chemical world, providing PVDF with exceptional chemical and photochemical resistance to UV radiation, moisture and atmospheric pollutants. What drives this gold-standard level of protection is a formulation that is comprised of 70% polyvinylidene fluoride polymer and30% proprietary acrylic resins. This balance offers optimal adhesion, weatherability and UV durability properties.
SMP resins
SMP coating systems are created by combining a durable polyester resin backbone with silicone-based polymers to achieve longer-lasting gloss and colour retention than what would be achieved by the polyester resin alone. SMP molecules are based on carbon- hydrogen, carbon-oxygen, carbon- silicone and silicon-oxygen bonds. While these chemical bonds are strong, they are generally less robust than those found in fluoropolymers, making them more vulnerable than PVDFs to long-term UV exposure that can degrade the coating. While these varying chemical structures explain their performance differences, newer, higher-quality SMPs are closing the performancegap with PVDFs.
Caption: SMP coatings used in a residential scenario
Cost and market applications:
From both a performance and cost perspective, fluoropolymers are a premium coating system. For applications that demand the highest durability, 70% PVDF coatings are regarded as the top choice due to their strong resistance to UV exposure, humidity and pollution. They are the preferred system for use on metal roofing, curtain walls, wall panels and monumental applications like skyscrapers, stadiums and high-end commercial buildings.