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Potential Seen for Protective Coatings
Based on Silicone-Epoxy Hybrid Resins

Tuesday, April 20, 2010

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Last week’s American Coatings Show and Conference certainly can’t be faulted for lack of new territories explored and brought into sharper view.

The conference surveyed a range of emerging technologies, including biobased and novel materials, radiation curing, waterbornes, nanomaterials, and smart coatings.

This informative and wide-ranging scope extended to protective-coatings technologies as well, in the form of two program sessions. This news bureau last week reported on protective-coatings presentations on advances in coatings based on fluoropolymer resins, and a new thick-film moisture-cure urethane technology (see The first session, Protective Coatings I, was presented by SSPC.

At the Protective Coatings II session, the topics addressed included the development of silicone-epoxy resins that offer intriguing possibilities for applications in high-performance anticorrosion industrial and marine coatings, including materials for oil platforms, bridges, storage tanks, steel structures, concrete walls and floors, and ship decks.

This silicone-epoxy technology was discussed by Christopher Howard, Evonik Goldschmidt Corp., in a paper titled “Novel High-Solids Systems Based on Silicone-Epoxy Resins.” His co-authors are Evonik’s Markus Hallack and Wernfried Heilen.

In short, Howard said silicone-epoxy coatings offer the potential for high-performance coatings with widespread application potential, thanks to the combination of an epoxy component that offers the advantages of mechanical toughness and adhesion, and a silicone component that provides the coating with hardness and UV-stability properties. The silicone-epoxy resin combination offers a high degree of weathering and chemical resistance in two-component coatings that are isocyanate free and low in VOCs at less than 100 grams per liter, the authors say.

Silicone-epoxy hybrid resins

Howard reviewed the development of a silicone-epoxy hybrid polymer, which he said represents a new class of resins for protective coatings. He noted that most protective coatings are based on organic resin systems, while silicone resins are of an inorganic nature, and are highly resistant to degradation by thermal and UV-induced oxidation.

The silicone inorganic resins discussed in the paper are polysiloxanes characterized by thermal stability, UV and weathering resistance, color stability, and water resistance. The polysiloxane was combined with an aliphatic epoxy resin in a condensation reaction. The result is a two-component, ambient-cure, thermoset composition with low viscosity that allows for formulation of high-solids, low-VOC coatings, the authors say.

Testing of the coatings

The resulting coatings are said to offer the economics of a two-coat protective system with a high-performance profile. In a review of testing, the paper compares a two-coat system composed of a zinc-rich primer and silicone-epoxy hybrid coating with a three-coat system composed of zinc-rich primer, epoxy intermediate coat, and polyurethane topcoat. The testing included coatings based on a “first-generation” version of the silicone-epoxy resin, and coatings based on a more recently developed “second-generation” version that is reported to exhibit greater cured-film flexibility as a result of modification of the polysiloxane component of the resin.

In first comparing performance test results of the two silicone-epoxy coatings, the authors say the first-generation version exhibits greater film hardness and a shorter cure time, while the newer, second-generation version possesses stronger adhesion, a longer pot life, and higher initial gloss.

Turning to a comparison of the two silicone-epoxy coatings systems (with zinc-rich primer) and three-coat zinc-rich primer/epoxy/polyurethane system, the authors say the silicone-epoxy systems exhibited superior chemical resistance with most acids, bases, and solvents. The silicone-epoxy coatings also compared favorably in accelerated testing involving salt-spray, humidity, and QUV methods.

The paper also reports on gloss and color retention of the silicone-epoxy coatings systems in South Florida exposures of 60 months, although this testing does not include comparisons with other protective-coatings chemistries. The results indicate that the second-generation silicone-epoxy coating initially exhibits and also retains a significantly higher gloss level, while both versions show strong color retention in the harsh conditions of the test location.

Two are better than one?

The authors say the novel hybrid resin technology results in coatings that exhibit stronger performance than coatings based on organic or inorganic resins alone. Coatings based on the hybrid resin technology are reported to be high-solids and low-VOC, isocyanate free, and tolerant of humidity due to the type of curing mechanism.

Also noted in the paper is the potential for application in antigraffiti coatings, due to the high crosslink density of the cured coating film and the inherent release properties, or “slipperiness,” of the siloxane resin. This characteristic requires attention to the recommended “recoat window,” but also presents the potential for antigraffiti-coatings applications for steel structures, bridges, rail cars, and other industrial and industrial maintenance settings.

Also starring in Protective Coatings II…

Other papers presented at the Protective Coatings II session were:

“Improving Waterborne Anticorrosion Coatings via New Binder Concepts,” Oihana Elizalde, BASF;

Epoxy Silane Oligomer for Protective Coatings,” Christopher Byrne, Momentive Performance Materials;

“Novel Mg-Rich Primers Based on Organically Modified Silica Nanoparticles,” Bret Chisholm, North Dakota State University;

“Polymer Capsules Loaded with Corrosion Inhibitors for Corrosion Protection,” Ji Hoon Park, Pohang University of Science and Technology /Graduate Institute of Ferrous Technology (Korea); and

“Developing High-Build Aliphatic Moisture-Cure Coatings,” Ahren Olson, Bayer MaterialScience.

Joe Maty is a PaintSquare News editor


Tagged categories: American Coatings Association (ACA); Marine Coatings; Protective coatings

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