How to bond silicone rubber?
Silicone rubber, such a challenging material to bond!
Silicone rubber is a commonly used material in the industry. Thanks to its exceptional properties, such as its resistance to UV or chemical aggressions, as well as its stability over a wide range of temperatures, it is a preferred material used for numerous sealing applications in various industrial sectors. It has become common to see O-rings, preformed seals, or even silicone cords in diverse fields such as agri-food, automotive, or household appliances.
However, silicone elastomer also possesses another property: a very low surface energy, making it not only hydrophobic but also very difficult to bond! It is regularly listed in the “blacklist” of products known to be impossible to bond, such as polyethylene, polypropylene, or PTFE. This characteristic presents challenges when assembling silicone components in applications where bonding is necessary.
Fortunately, our partner Permabond has developed solutions to overcome this challenge. Specific surface preparation techniques can be used to enhance silicone adhesion. Moreover, the use of adhesives specially formulated for silicone rubber allows for the creation of strong and durable bonds.
Example 1: Bonding Silicone Elastomer to Itself
A typical case involves bonding two pieces of silicone rubber cord together, end to end, for example, for custom seal fabrication or O-ring repair. For straightforward rubber cases, Permabond offers a range of standard cyanoacrylate (“super glue”) adhesives to achieve bonding in seconds.
However, concerning difficult-to-bond rubbers, especially silicone elastomers, standard cyanoacrylates do not work. Our partner Permabond has developed a now industry-proven solution: simply apply a few drops of PERMABOND POP primer to the bonding area and use the “special difficult rubbers” cyanoacrylate adhesive PERMABOND 105. The bonding is immediate, resulting in a strong and durable bond.
In the video below, Permabond provides instructions for the optimal use of the POP primer before applying cyanoacrylate 105. You will observe how the use of primer enhances adhesive bonding to silicone rubber. Once the POP primer is applied, it needs to dry completely.
Polyolefin surfaces can be bonded up to 2 hours after treatment.
PTFE surfaces must be bonded immediately.
In the video below, our partner Permabond provides instructions on properly applying cyanoacrylate adhesive on different substrates: Metal and particularly the rubber which is of particular interest in this article. Follow the instructions step by step for effective bonding.
Example 2: Fixing a Silicone Seal in a Groove
Another typical case involves bonding a seal in place (for example, in assembling a production machine for the agri-food or pharmaceutical industry) to prevent it from shifting.
It is sometimes said that only silicone can bond to another silicone: that’s why we can offer you with the brand Dowsil DOWSIL™ 732 white for this application.
It is an acetic silicone sealant, one-component, which is also approved for food applications (FDA, NSF-51, and NSF-61 approvals).
DOWSIL™ 732 is available in the following shades: colorless, black, and white.
It adheres particularly well to stainless steel and silicone rubber, making it a product commonly used in the agri-food industry.