Adhesives Magazine

Ask Dr. Dave

September 1, 2010

Question: We are looking for a pressure-sensitive adhesive to bond to a 50-durometer silicone rubber. What do you recommend?

Answer: The highest performing adhesives for this application are silicone-based pressure-sensitive adhesives (PSAs). They can usually be bonded to a smooth silicone surface with no surface preparation and have very high and low temperature resistance.

However, these types of adhesive can be expensive and are almost exclusively solvent-based, although at least one 100%-solids version has been introduced recently. Some high-performance and lower cost acrylic PSAs can also be used on silicone rubber, although extensive surface preparation is required to ensure good adhesion.

Question: What is the difference between a liquid gasket maker and a cut gasket? I have a lot of different gaskets and it is difficult to justify buying many different types of pre-formed gaskets.

Answer: Most modern industrial and automotive gaskets are pre-formed by molding them from rubber. However, liquid gaskets have been available for many years and are often called “form-in-place” gaskets. The most common types are RTV silicones and anaerobics. In general, the flexible silicones are used where some flange movement is expected in an assembly, and anaerobics are used for very rigid assemblies.

Pre-formed and liquid gaskets create seals in different ways; a pre-formed gasket relies on compression to make a seal, whereas a liquid gasket is applied between flanges just before assembly, completely fills the space between flanges, and does not require compression. Liquid form-in-place gaskets have been used successfully by agricultural or off-the-road manufacturers, where the volume of engines produced cannot justify the cost of special-cut gaskets. I would recommend that you look at the two types of liquid gaskets.