Coupling agents are compounds containing groups with different polarities at both ends of the molecule. The two end groups can be combined with the adhesive molecules and the adherend respectively to play a “bridging” role to improve the bonding strength. There is also a non-polar part, which was originally used in the fiberglass industry and has also been widely used in the adhesive industry in recent years.
Adding 1% to 10% coupling agent to the adhesive can improve the bonding strength, improve water resistance, moisture resistance, heat resistance, etc., and expand the application range of the adhesive.
Classification and Application
The coupling agents currently used in the adhesive industry mainly include: organic carboxylic acids, polyisocyanates, titanates, silicone coupling agents, etc. Although various types of coupling agents have different structures, their mechanisms of action are similar. Now take the most commonly used silicone coupling agent as an example to illustrate the mechanism of action of tackifiers.
Organic silicone coupling agents are low molecular compounds with inactive reactive groups at both ends. Not only does it have strong mobility, but the different groups at both ends of the molecule can connect two different substances (such as organic matter and inorganic matter) through chemical reactions.
The use of adhesives to bond metal, ceramics, glass and other materials is a combination of organic matter (adhesive) and inorganic matter. The function of a tackifier is that the active groups at one end of the molecule, such as alkoxy groups, halogens, etc., combine with the surface of the adhered inorganic substance, while the active groups at the other end of the molecule, such as amino groups, bind to the adhesive molecules such as epoxy resin. The combination of epoxy groups, etc. plays a so-called “bridging role” between the adhesive and the adherend, thus increasing the bonding force between them. At the same time, because the tackifier molecules are small and have strong mobility, they will also promote the adhesive molecules to better diffuse and penetrate into the surface of the adherend. For example, when aminomethyltriethoxysilane is added to epoxy resin glue. It not only increases the intermolecular force of the epoxy resin itself and improves the cohesive strength of the adhesive, but also plays a certain “bridging” role between the epoxy resin and the adherend, such as glass.
