Silicones
The silicon adhesive on 3M's Post-it® Notes is produced using a platinum catalyst.
Platinum and silicones
Many chemical processes employ platinum catalysts but the most significant in terms of platinum demand is the manufacture of speciality silicones. Addition of a platinum compound to the silicone mixture catalyses the cross-linking or ‘curing’ process which results in the formation of a silicone product with the desired properties.
Silicones are highly durable materials with excellent resistance to chemical corrosion, fire and extremes of temperature. They are also pliable, waterproof and electrically insulating. It is not surprising, therefore, that silicone materials have a large number of uses in everyday life.
Pressure sensitive adhesives
Pressure sensitive adhesives (PSA) are designed to allow the surface on which they are coated to stick to other materials when a small amount of pressure is applied and to peel away cleanly without tearing.
Perhaps the most familiar example of a silicone-based PSA is the adhesive used for Post-it® Notes. The adhesive was invented in 1968 by Dr Spence Silver at 3M and then applied to Post-it® Notes, which were invented by Art Fry in 1973 and launched seven years later in 1980.
Release liners
In contrast to PSAs, silicone-based release liners are used to provide ‘release surfaces’ against aggressive adhesives and other sticky surfaces. They are commonly used for coating the backing paper of sticky labels, allowing the label to be peeled away easily without splitting. Release liners also provide resealability as they allow the sticky surface to be removed and reapplied without loss of adhesion.
Applications include resealable polythene bags and ‘self-wound’ tapes used for construction and roofing as well as medical and hygiene applications. The silicone coating is applied to the non-adhesive surface of the tape allowing it to be unwound in a smooth controlled fashion and resealed if necessary.
Other applications of silicones
Other types of silicones that require platinum process catalysts are water repellent coatings, high consistency rubbers and liquid silicone rubbers. Between them, these products have a vast number of applications which include furniture polishes and cleaning products, aero and automotive engine seals and gaskets, construction sealants, medical devices, high voltage cable covers and personal care products such as lipsticks and shampoos.