Paper 1: Hot Melt Adhesives and Machinery Design Requirements for Their Application

Simple and sometimes rather crude melt adhesives have been used in a limited number of industries for centuries, but in the last five years new adhesives based on synthetic polymers, resins, and waxes have become of growing importance in the packaging and similar industries. The increasing usage has been brought about by the need for higher rates of output, simplification of packaging machinery, and a movement towards more sophisticated packaging which often requires the bonding together of two impermeable surfaces. The increasing availability of new synthetic materials, often at reduced cost, has enabled the adhesives technologist to formulate a wide range of versatile melt adhesives which fulfils these needs.

An outline of the constitution of melt adhesives is presented. Melt adhesives are thermoplastic solids which are brought to a working viscosity by heating, and bond by cooling alone without the loss of volatiles. The significance of this, in their ability to bond both porous and non-porous materials at great speed, is considered.

To build successful applicators the thermal properties of melt adhesives require careful design of heating and temperature control. Principles of heating and control are discussed and materials of construction indicated. The types of applicator that can be used are reviewed. The effect on machinery design of the fast setting potential of hot melt adhesives is also discussed.