TABLE OF CONTENTS These adhesives are important as structural adhesives especially in metal bonding. They comprise a thermosetting and a thermoplastic polymer, including certain elastomers. Although each component has adhesive properties by itself, on the whole the conjoint system forms a stronger and more versatile adhesive. The two-polymer systems have been particularly successful as film and tape adhesives.
The physical properties of each component polymer are modified by the addition of the other, possibly increasing heat resistance of one component, while reducing that of the other. Similarly, the toughness of one may be increased by sacrificing the flexibility of the other. Therefore, it is possible to formulate a variety of adhesives with a wide range of characteristics by simply varying the ratio of one polymer to the other.
In most widely used two-polymer adhesives, the thermosetting component is phenolic. Phenolic resins are generally compatible, although not easily miscible, with a number of thermoplastic polymers. Particularly good compatibility is demonstrated between conventional alcohol-soluble phenolic resins and polyvinyl esters and acetals. Epoxies are important in two polymer adhesive systems. The most important thermoplastic components are the polyvinyl acetals (polyvinyl formal and butyral) and synthetic rubber, particularly nitrile rubber. Soluble nylons are also an important class.[5]
Five of the most important two-polymer adhesives used in films and tapes include vinyl-phenolics, epoxy-phenolics, nitrile-phenolics, nylon-epoxies, and elastomer-epoxies. Neoprene-phenolics are available in organic solutions and in supported and unsupported films. These adhesives are used to bond a variety of substrates. Curing takes place...
