By FEDERICO FASAN

Hot-melt ethyl-vinyl acetate (HMEVA) is the most popular thermos-plastic adhesive used in edge banding machines. There is now a marked shift to hot-melt polyurethane (HMPUR) for better glue line, higher heat resistance and, most importantly, a waterproof joint.

But the switchover needs a steep learning curve. Additionally, special equipment will be required to ensure smooth operations. On the other hand, hot-melt polyolefins (HMPO) are ignored, mostly due to lack of awareness.

HMPO is also a thermos-plastic adhesive which offers very high heat and moisture resistance, but without the need for special equipment.

The technical datasheet of each product gives information on multiple characteristics. Pay close attention to the ring and ball (softening) temperature, operating temperature, and recommended feed speeds. The connection between the three critical performance criteria is explained below:

• Ring and ball (R&B) temperature: This is the “softening point”. It’s the temperature where the glue stops being solid and starts to flow. The connection: high R&B equals high heat resistance. If a shutter is installed above the hob, a low R&B glue will soften, and the edge might peel off earlier.
• Open time/ machine speed: Open time is the “working window” you have before the glue sets and viscosity increases. Your ‘glue open time’ must match your machine feed speed. Ideally the temperature between glue roller and first pressure roller must be 15-20 °C higher than the R&B temperature. Lower temperature will lead to higher viscosity and hence the bonding will not happen.
• Mismatch risk: If your machine is slow but you use a ‘short open time’ glue, the glue will set before the pressure roller hits it. If your machine is very fast (30 metres per minute and above) and you use a ‘long open time’ glue, then the glue will still be wet by the time it passes the pressure rollers.

The showdown

HMEVA is the standard workhorse. It is best for general-purpose furniture, standard dry areas. It has moderate heat resistance (~75°C to 85°C). While HMEVAs are easy to use, cost-effective and come in multiple variants, they have lower heat and moisture resistance.

HMPOs, on the other hand, are a high-performance upgrade. They are best for kitchens, bathrooms and high-heat environments. Their superior heat resistance (~100°C to 130°C) gives HMPOs excellent thermal stability (no burning in the pot), thinner invisible glue line and higher yield (less glue needed).

Moving to HMPOs is the easiest way to upgrade your quality without buying a new machine. It offers near-PUR performance with the ease of EVA.

– The writer is Sales Director at Italy’s Unicol Srl, manufacturer of eco-friendly industrial adhesives, including those for wooden furniture.