CoatingsPro Magazine - January 2022
Acrylic Polysiloxanes: Art on a Water Tank
William Seawell 2021-12-28 22:08:46
Acrylic polyurethanes, fluoro urethanes, and perhaps even cross-linked epoxy siloxanes are among the most common chemistries we encounter in the realm of industrial finishes. What do all these technologies have in common? They are all multi-component products that require some degree of expertise to apply them, and they typically carry with them a very large VOC (volatile organic compound) and HAPS (hazardous air pollutant) burden.
However, there are alternatives: water-borne urethanes and water-borne acrylics. These may be considered the “darlings” of the commercial and residential industries because they have significantly reduced VOCs, generally lower HAPs, and are single-component products. They are known for being easy to apply — but at the expense of dry film performance.
Lesser-known acrylic polysiloxanes offer a single-component finish, which splits the difference between the constructability enjoyed by water-borne acrylics and the performance many have come to rely on from the cross-linked members of the performance finish family.
How Does It Work?
One can think of single-component acrylic polysiloxanes as curing in a manner similar to that of “normal” acrylic emulsions. The curing mechanism involves little-to-no formation of covalent bonds, but it relies on the evaporation of water and solvents so that the resin particles suspended in liquid emulsion (in this case, acrylic functionalized siloxane globules) can physically knit together and form a continuous polymer membrane.
The key difference here is in the dry film properties of the siloxanes. Siloxanes are defined by the chemistry of the silicon-oxygen covalent bond. This bond is known by chemists for being particularly robust (aka having a very negative binding energy), and, incidentally, it is also the reason for the extreme chemical stability of many of the fillers used in many polymer and coating products (think silica and sand).
Organic coatings weather due to degradation of the carbon-carbon, carbon-hydrogen, carbon-oxygen, and carbon-nitrogen bonds contained within their cured films, but the siloxane bond is not subject to these same degradation mechanisms since they’re not organic, resulting in a robust weathering finish. The resultant films can achieve extremely high gloss levels with great color and gloss retention due to their highly ordered and silicone resin-rich surfaces. This same property lends itself to a soiling-resistant low surface tension film as well.
Acrylic polysiloxanes can accomplish this with low VOCs and HAPs footprints while also being completely isocyante-free and having relatively quick drying times for single-component finishes.
Acrylic Siloxane Artwork
In this project, the single component nature of acrylic siloxanes enabled the top coating to be able to be placed into an aerosol can in several colors for the artwork. This level of graphic complexity would not have been achievable with a two-component finish, and nothing in the way of weather-ability or performance was sacrificed to achieve that using an acrylic siloxane.
Conclusion
Water tanks can be painted with almost any resin type, but for specific scenarios, it pays to stop and consider which coatings would be ideal for the situation. Top coats are often treated as interchangeable in our industry, but the choice of top coat, in this case an acrylic siloxane, allowed the artist to do his best work. The Continental Gin Company water tank in Deep Ellum became more than a rehabilitated water tank; it is now a work of art that will stand out for decades to come.
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