In 1963, the first unfilled hot melt based on EVA (ethylene vinyl acetate) entered the market and the combination of edgebanding machine and hot melt adhesive marked the beginning of cost-effective furniture mass production. A technology that is still firmly established.
As the quality of furniture rose, so did the requirements regarding the performance of the adhesives. From polyester to polyamide and later polyolefin – a clear trend emerged towards a completely different adhesives technology in edgebanding applications: PUR hot melts. The first reactive PUR (polyurethane) hot melt adhesives for edgebanding were launched in 1987 and were a real quantum leap forward. The chemical crosslinking inside the adhesive coupled with the chemical binding to the bonding partners facilitates a significantly increased resistance of the bond against heat (over 120 °C) as well as water and steam.
Handling the then new adhesives presented a learning curve for processors, engineering companies and also adhesives manufacturers. However, the times when processing was a matter of concern are long past thanks to special melting units, non-stick machine surfaces and continuous product optimisations.
Apart from applications in the furniture industry, the popularity of PUR hot melt adhesives has also been increasing rapidly in the crafts and trade sector as well. Due to entry-level edgebanders suitable for PUR and the availability of PUR hot melt adhesives in granulate form, it has never been easier for small consumers to use this technology. The patented granulation process of Jowat SE for manufacturing PUR hot melt granules opens up the “World of PUR” to everyone.
What is PUR?
Like all hot melt adhesives, reactive PUR hot melt adhesives are also supplied in solid state. However, they are delivered in special moisture-proof packaging, which is opened only right before the adhesive is melted in the glue pot or in an external melter. Application is generally by roller onto the carrier substrate. The cooling of the adhesive after it has been applied onto the substrate leads to a purely physical build-up of strength which results in the initial strength of the bond. This is followed by a chemical crosslinking in which the adhesive reacts with water molecules (from material moisture or humidity). Due to that crosslinking process, reactive hot melt adhesives meet higher requirements regarding strength and resistance to water and heat. In addition, the reactive groups in PUR hot melt adhesives facilitate a permanent chemical binding of the adhesive with suitable reaction partners on the substrate surface, thus improving adhesion and making it possible to bond even difficult materials, for instance aluminium edgebands.
PUR hot melt adhesives with hazard-free labelling
For several years, there has been an alternative technology of PUR hot melt adhesives on the market. Conventional PUR hot melt adhesives generally contain an excess of free monomeric isocyanate (mostly 4-4‘-diphenylmethane diisocyanate – also referred to as MDI) in the order of 2 %. Since 2002, products containing 0.1 % or more of free monomeric isocyanate must be labelled with the GHS hazard pictogram 8 (health hazard) and the related safety information (H and P statements). Adhesives with a free monomeric isocyanate content of less than 0.1 % are not subject to hazard labelling and therefore play a major role in facilitating a safe workplace.
Hot melt adhesives and edgebanders – an ongoing success story since the 1960s.
The article is published in the magazine BM 09/19 in German language. You can download the original article down below.