Home » Crosslinking With Amino-Functional Siloxane Resin Improves Flexibility of Bis-Phenol A Epoxy Paints
Combining the rapid cure and excellent barrier properties of epoxy resins with the thermal and UV stability of silicon-based materials, formulators created high-performance coatings with excellent resistance to corrosion and chemical attack, as well as thermal and UV degradation, as early as 1959.1 These innovations relied on a broad spectrum of silicone-based technologies (SBT). Monomeric alkoxy silanes, silicone resins and fluids of various molecular weights and chain lengths, along with a myriad of functional groups, provide a plethora of options for tailoring the organic epoxy resin system. These options are robust enough to meet specific performance requirements for such far-ranging applications as electronic conformal coatings and automotive finishes.
Epoxy resin compositions have been employed for a variety of uses, such as laminating, coating, adhesion, encapsulating, molding, etc. In some uses, the polymeric materials are exposed to high temperatures that reduce the film integrity. A blend of an epoxy resin, a curing agent for epoxy resins, an organo-functional alkoxy silane and a catalyst for effecting condensation polymerization of a silane compound was found to provide high heat resistance and excellent mechanical strength.2 Similarly, complete or partial hydrolysis of alkyl/phenyl alkoxy silanes to form silanol or alkoxy-functional siloxane resins and the subsequent reaction with epoxy resins have been shown to produce copolymers with improved water and moisture resistance.3,4 The formulator must balance the desired property improvements with the cold-blend compatibility between the epoxy resin and the siloxane. Bis-phenol A epoxies have limited acceptance of silicones. Aliphatic epoxies are more tolerant of silicones, whereas cycloaliphatic epoxy systems are very compatible with silicones. Traditional modification of epoxy resins with SBT resins relies on cold blend mixtures with the potential reaction between silanol (SiOH) or alkoxy (SiOR) with available hydroxyl groups on the epoxies. This reaction, however, is not chemically favored. The Si-bonded reactive groups are more likely to homopolymerize rather than react with the epoxy. Any co-reaction is minimal and results in the formation of Si-O-C bonds. While these Si-O-C bonds are somewhat sterically hindered within the final resin matrix, they are ultimately hydrolyzable - creating a potentially weak link in the resin matrix. However, this copolymer form of silicone-epoxy bonds is widely utilized in the industry.
October highlights distributors, and includes an interview with the National Association of Chemical Distributors, as well as company profiles of many specialty chemical distributors serving the coatings industry. The issue also includes articles on new ambient-curing resins, the impact of silanes on the solution stability of latex, an overview of colorant technologies worldwide, and much more.