Hot-melt adhesives (also known as hot glues) are generally 100% solid formulations based on thermoplastic polymers (no water or solvents are involved). Hot melts are sold in a solid state at room temperature and are ‘activated’ upon heating beyond their softening point which is usually between 50 and 160 degrees. Once melted (in a hot melt tank), the adhesive can then be applied onto a substrate in its liquified or molten state. The hot melt wets the substrate, penetrating the surface (and any cavities), and then it solidifies, ensuring cohesion. This setting/cooling process takes very little time. Glues that cool and remain tacky are known as pressure sensitive adhesives (PSA) – these we will cover in depth another time.

When a hot-melt adhesive is being cooled back to room temperature, it rapidly builds up its internal strength. The solidified state of a hot melt is where it has structural integrity and can function as an adhesive. Hot glues can be applied onto a substrate in many ways (when they are in liquid form) such as via a roller or more commonly being jetted or sprayed from a nozzle or gun. There are also many different types of application patterns such as spiral sprays, dots and continuous lines.

Hot-melt adhesives are used in both the commercial and residential sectors across many different industries for countless applications. You can find hot melts in food packaging, woodworking, product assembly, labelling, children’s toys, arts and crafts and so forth. At Beardow Adams, our adhesives bond all kinds of packaging, the spines of books, the layers of fabric in nonwovens, labels on bottles and the edging on furniture – to name just a few applications.

Hot-melt adhesives  need a delicate  balance of formulation components but the main elements of a typical packaging hot melt are polymers (delivers strength and flexibility), resins (provides wetting and adhesion properties) and waxes (controls viscosity and open time/setting speed). With a hot melt pressure sensitive adhesive (HMPSA), there is typically the inclusion of a plasticiser which aids elasticity and controls viscosity.

There are various types of hot melt such as EVA (ethylene vinyl acetate) for general purpose bonding, polyolefin for difficult to bond plastics, and the more modern packaging hot melt - metallocene (mPO) for high strength in smaller quantities, but we will address the various hot melt formulations in a separate article.