Metal surfaces coating technologies and their environmental footprint: Anodization, PVDF Liquid Paint or Powder Coatings. ―
Since it is a major contributing factor into the overall environmental footprint of a project, the choice of ecological technologies of surface treatment and coating of metal architectural components becomes one of the most important considerations in architectural specifications.
Currently, there are three major metal coating technologies: Anodization, PVDF liquid paints and ecological powder coatings. Which are the pros and cons of each method?
Anodization, that can only be applied on aluminum, is the oldest method of surface treatment; it is an electrochemical process that causes structural changes in the metal surface layer. The surface is artificially hardened and becomes a thin crust with greater resistance to corrosion. The metal component is bathed in a battery pack of chemical reagent tanks, where potential difference causes the electrochemical alteration of the surface, creating an anti-corrosion layer. Using suitable chemical solutions in the anodization tanks, different surface color hues are obtained. Anodization maintains the natural color of the metal and increases life expectancy in an intensely corrosive environment. Architects often prefer anodization, because of the perception of a “natural” appearance. However, since anodization is not an environmentally friendly process, in fact it opposes the nature of materials. Besides the limited colors available through anodization, its main drawbacks are the need for increased process precision to achieve optimal results, visible color variations batch-to-batch, the lack of possibility to restore damages during transportation or installation of the metal components, notwithstanding the huge environmental impact.
Liquid paint applications are not only limited to aluminum but are also suitable for steel. The method is popular in the US and Middle East markets, and it involves the application of multiple PVDF layers. Those materials are produced by mixing polyvinylfluoride and acrylic resins. Liquid paints are elastic and they are very resistant to UV solar radiation. However, their application comes with a huge environmental toll: It involves multiple layers of paint and the preparation of metal with chromium compounds. Their resistance to mechanical stresses is limited. Besides the increased energy consumption for painting, their solvents emit volatile organic compounds (VOCs) and this is the main reason for their decline in popularity.
Electrostatic powder coating is a process of covering the metal surface with a solid color, in order to withstand corrosion and to acquire the desired color tonality, gloss and texture. Powder coatings are applied on aluminum or steel, opening possibilities for combining architectural components from both materials in the same project. Powder coating becomes increasingly popular due to its significant advantages, compared to the other two coating methods:
First, powder coatings provide excellent anti-corrosion protection. Interpon D powder coatings are applied in one layer only and withstand the most challenging aluminium salt spray tests without the need of primers, as is necessary in the case of liquid paints. With the place-specific proper chemical preparation of the metal surface (pre-anodization, seaside chrome-free etc) and the application of superdurable Interpon D2525 powder coatings, long anti-corrosion protection is guaranteed.
As opposed to anodization, powder coatings provide a vast array of color tonalities, gloss, textures and special effects: Interpon D architectural powder coatings are distributed in a great variety of colors. To facilitate architectural specifiers, powder coatings are available in accordance with current color codifications (RAL Classic, NCS S, British Standards). Moreover, Interpon D architectural powder coatings create color trends, with or without metallic effects; those are developed by the company in collaboration with the trend consultants of the AkzoNobel Aesthetic Center. Powder coatings cover the entire range from full gloss to dead matt. Finishes may be smooth or finely textured, Sable, Silky etc. Any combination of tonality, gloss and texture is feasible!
Powder coatings have superior weather resistance: Interpon D2525 superdurable and D3020 hyperdurable powder coatings successfully pass the challenging Florida test of natural weathering (respectively, 5 and 10 years), come with all international qualifications and meet the most demanding international standards (Qualicoat, GSB, AAMA etc). They are the first superdurable powder coatings to appear in the market and, after 30 years, their performance exceeds initial expectations! They are accompanied by Project Guarantees, specially issued for the location and the class of project, provided by the certified Interpon Approved Applicators; those cover the preservation of tonality, gloss and other features, up to 30 years.
Most important, powder coatings have been developed to be easily, effectively and ecologically applied. Powder coatings are solvent-free, they are only applied in one layer and the excess material is recycled and reused, with almost zero waste. In the case of damage, powder-coated surfaces can be easily repaired on site or during transportations. They do not emit VOCs, like liquid paints. Interpon D powder coatings do not contain toxic components and their polymerization does not produce toxic waste. They come with an EPD environmental product declaration.
In Greece, where sunlight is intense and most environments are coastal, with high salinity and strong UV reflectance, architectural specifiers understand that powder coatings are the most suitable method for painting and protecting metal surfaces. As the construction technology evolves, in the near future we are ready to see many original powder coating applications, specially developed for place-specific demands and conditions.