Bonding Rubber to Metal

There is a stronger case for using polyurethane adhesives to bond rubber to metal than metal to metal. It is reported that an observation made during investigation of the isocyanates as vulcanizing agents. leads to their examination in bonding rubber to metal. When the new technique became known in 1945 it was considered to be an important advance, but time has since shown it to be only limited industrial value. There are today a number of adhesive capable of bonding rubber to metal satisfactory, for example, some epoxy resins and some of the two-polymer adhesives. But there is one important difference; the polyisocyanates are capable of satisfactorily bonding unvulcanized rubber, whereas the other adhesives are not. Polyisocyanates can therefore to be used to bond rubber to metal, as can also be done in the brass plating method during the process of vulcanisation. The reactivity of the rubber composition usually makes the addition of a crosslinking agent unecessary.

The most satisfactory results are obtained with aluminum and magnesium alloys and with steel, the preferred isocyanate being triphenylmethane triisocyanate. The rubber to metal bond strength has been claimed to be of the same order as that obtained by the brass plating method. The compatibility of the isocyanates with certain rubber has enabled involved polyurethane adhesives to be formulated by the incorporation of a proportion of rubber.