Natural rubber-based pressure coating

Unlike all the other classes described above these adhesives do not typically undergo hardening after they have been applied to the substrate surfaces and the joint formed. They are generally in the form of an already polymerized adhesive which is coated onto one or both sides of a backing material such as cellulose, polyester, foamed polyurethane, poly(vinyl chloride), aluminium or lead. The adhesive is usually permanently tacky and based upon natural rubber, styrene-butadiene rubber (random and, more recently, block copolymers), polyisobutylene or an acrylic polymer, but as usual is a complex formulation containing many additives. The adhesive is formulated so that it flows sufficiently, when hand pressure is applied to the joint for a short period of time, to wet the substrate adequately in order to attain a certain, albeit minimal, level of joint strength. Thus, the term pressure-sensitive is often applied to this class of adhesives. 

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