Foamable hot-melt adhesives

Foamable hot-melt adhesives have been commercially available since 1981. Nitrogen or carbon dioxide is introduced into the hot-melt adhesive and results in a 20 - 70% increase in adhesive volume. Foaming increases hot-melt spreading and open time. This method is usually used with polyethylene hot-melt adhesives that are applied to selected metal, plastic, paper, porous, and heat-sensitive substrates. 

Foamable hot-melt adhesives containing polyamides and fluorinated or silicone surfactants are useful on coarse surfaces [10]. 

One of the new developments in hot-melts is the application of foam technology. Several years ago, the Nordson Laboratory (84,85) discovered that the foamed hot-melts are easier to spread than the non-foamed hot-melts. Later, foamability (86) studies were carried out for the following hot-melt adhesives polyethylene, polypropylene, polyamide, ethylene-vinyl acetate copolymer, and polyester. Air, CO2, and nitrogen were used as the blowing... 

A two-step gear pump (Fig. 15) was used to introduce the gas into the hot-melt adhesive. Foamability was later found to vary with the polymers used. Polyethylene is excellent for foaming. Polypropylene, polyester, and 12-polyamide (Nylon 12) are also very good. Styrene-butadiene and ethylene-vinyl acetate are good and dimer acid polyamide is fair. ... 

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