Finishing coatings based on aliphatic and cycloaliphatic epoxy resins, cured and polymerized with organosilanes

Abstract

Conventional epoxy coatings are widely known, achieving high commercial acceptance for protecting various substrates (steel, concrete, etc.). Nevertheless, they generally do not have good resistance to UV from sunlight when exposed for prolonged periods to weather since aromatic structures cause loss of gloss and color retention.Taking into account the excellent physicochemical properties of conventional epoxy coatings and their above mentioned poor UV resistance, it becomes necessary to develop coatings based on epoxy resins with appropriate color and gloss retention. This is possible achieve it by modifying the glycidic epoxy resins (prepared from bisphenol A and epichlorohydrin) with acrylic resins and also by using melamine resins co-etherified with epoxy groups and epoxidized polyester resins. It is worth mentioning that the cited developments display better weather resistance than those based on conventional epoxy resins but lower than the polyester- or acrylic-polyurethane coatings, which are usually used as finishing in systems for industrial protection.The aliphatic and cycloaliphatic epoxy resins are based on alcohols (usually diols and, in some cases, polyols) epoxy-functionalized with epichlorohydrin, generating in this way di- and poly-functional glycidyl ethers. These resins allow formulate coatings with greater color and gloss retention than those based on conventional epoxy resins.Moreover, protective systems with hybrid finishing coatings comprised of aliphatic and cycloaliphatic epoxy resins and organosilanes are being also studied to improve performance against sunlight. For this purpose, amino functional silanes as curing agents,and reactive silanes for copolymerizing the epoxies through hydrolysable groups, are being used; coating films based on the above-mentioned film-forming materials have similar or greater UV resistance than the polyester- or acrylic-polyurethane coatings.