Two Components Adhesives
Two component adhesives are 100% solids systems that obtain their storage stability by separating the reactive components. They are supplied as “resin” and “hardener” in separate containers. It is important to maintain the prescribed ratio of the resin and hardener in order to obtain the desired cure and physical properties of the adhesive. The two components are only mixed together to form the adhesive a short time before application with cure occurring at room temperature. Since the reaction typically begins immediately upon mixing the two components, the viscosity of the mixed adhesive increases with time until the adhesive can no longer be applied to the substrate. When cured, two component adhesives are typically tough and rigid with good temperature and chemical resistance. Two component adhesives can be mixed and applied by hand for small applications. However, this requires considerable care to insure proper ratio of the components and sufficient mixing to insure proper cure and performance. There is usually considerable waste involved in hand mixing as well. Four major types of two component adhesives include:
- Acrylics + Benzoate peroxide
- Silicone Adhesives
These more traditional adhesives are formulated from solvents containing polychloroprene, polyurethane, acrylic, and natural and synthetic rubbers (elastomers). Solvent based adhesives contain significant levels of volatile organic compounds (VOCs). These adhesives are applied by brush, roller, and spray or as beads or ribbons either manually or automatically. Solvent based adhesives are available with a variety of drying and bonding times to match the application method and assembly process. These adhesives are typically intermediate in final bond strength and heat resistance providing good bond line flexibility. Because they contain organic solvent, they are less sensitive than other types of adhesives to contaminate on the surfaces to be bonded.