Silanes as Primers and Adhesion Promoters

Organosilanes are "molecular bridges" that are used as primers and adhesion promoters for coatings or adhesives. The addition of a silane at the interface results in high bond strength and corrosion resistance. The chemical link created by the use of a silane contributes various benefits, such as:

• A strong bond between the inorganic surface and the organic polymer to provide enhanced adhesion in both wet and dry environments;
• a barrier to prevent moisture penetration through the interface;
• improved bulk physical properties of the coating or adhesive through enhanced adhesion between the polymer and the filler particles within the formulation and the efficient transfer of stress from the resin to the filler;
• effective dispersion of fillers and reduction in the apparent viscosity of the system.

Silanes are a group of specialty organo functional compounds that possess dual reactivity. The silanes act chemically with both the metal substrate and the organic base polymer in the coating or adhesive.The silane adhesion promotes and protects the metal substrate by forming covalent bonds across the interface that are both strong and durable.

Silanes can be applied directly to the substrate, similar to conventional primers, or they can be mixed into the coating or adhesive formulation as an additive. Optimum results are generally achieved by using the silane as a substrate primer. When applied directly to the substrate, they are very thin coatings only about one monolayer in thickness. When mixed with the coating, the coupling agent is capable of migrating to the interface and reacting with the substrate surface as the coating or adhesive dries.

Over the last 20 years, the silane adhesion promoter marketplace has evolved to include a plethora of materials of which organosilanes have secured a prominent position. The choice of a particular silane will depend on the specific formulation of the coating or adhesive, on the substrate and on the method of application.

Optimizing the potential properties of silane systems offers a challenge.There are many parameters that can effect the performance of silane. Therefore, it is recommended that the silane supplier be contacted to assist in making a selection.

Silanes are multifunctional in that they can be used to promote crosslinking, and they can be incorporated directly into a polymer chain by various reaction mechanisms. In addition to coatings and adhesives, silanes have multiple commercial uses, such as coupling agents for reinforced plastics, crosslinking agents for polyethylene cables, and dispersants for paints and printing inks.

(source:http://www.ac-chem.net/news/silanes-as-primers-and-adhesion-promoters-b75e.html)