Cool melt: is it worth switching?

Why use high-temperature melt adhesives when low-temperature adhesives are also an option? So-called cool melts are hot-melt adhesives that are processed at lower temperatures. For many applications, especially in the packaging industry, they can replace conventional hot melts, saving on energy. This article explores the possibilities that cool melts offer the industry.

Cool melts are hot melts that are applied at lower temperatures

What exactly are cool melts? Low-temperature adhesives, as cool melts are also called, are hot-melt adhesives that become liquid at temperatures as low as 90°C and are applied at 100 to 150°C. This means that they do not need to be heated as high as conventional hot melts, which are applied at temperatures of 180 to 200°C. This offers a lot of advantages:

• Adhesive application with cool melts requires less energy than with conventional hot-melt adhesives, making production cheaper and more sustainable.
• Cool melts require less time to heat up as they are applied between 95 and 150°C. This helps to make the production more efficient.
• Cool melts have short setting times, which allows for higher machine speeds. This contributes to increased productivity at the packaging plant.
• The low temperatures reduce the risk of burns for line staff. Work safety benefits from this.
• Low processing temperatures mean less wear on the adhesive application system, enabling maintenance costs to be minimised. That, too, is efficient.
• Hot-melt adhesives that are not heated to such high temperatures coke less quickly. This means less cleaning and less downtime.

Are cool melts green?

Low-temperature adhesives are made from the same raw materials as high-temperature adhesives; namely, different thermoplastic polymers. Therefore, they should not be confused with organically based adhesives, which are partly produced from renewable raw materials. Nevertheless, cool melts contribute to increased sustainability in production, as they not only consume less energy when being applied, but also enable higher machine speeds and help to increase the productivity of packaging lines.

How much energy can be saved with cool melts?

Robatech tests its adhesive application systems with different adhesives — including cool melts — from different manufacturers. When comparing the energy consumption of low-temperature adhesives and conventional hot melts, it found that on average up to 8.5% less energy is required for every 10°C drop in temperature. This means that around 40% of energy can be saved by reducing the application temperature from, for example, 170 to 120°C with a cool melt, or even more in some cases.

“By switching to the new low-temperature adhesive, we were able to reduce power consumption by almost 50% while maintaining the same performance and functionality of the adhesive application. An interesting win-win situation for us,” said Daniel Brack, Coordinator Production and Logistics at Oel-Brack AG, Switzerland.

What kind of adhesive melter for cool melts?

Cool melts are offered by different manufacturers in granular form. Apart from their lower application temperatures, they are processed in the same way as conventional hot-melt adhesives. Robatech adhesive application systems have no temperature restrictions, meaning they can also be used to process cool melts. The temperature is set according to the adhesive data sheet — for the melter about 10°C below the application temperature, the hose plus 5°C, and the application head at the desired application temperature. Of course, new adhesives must be tested before making the switch and the adhesive application system must be cleaned thoroughly before every adhesive change.

What are cool melts suitable for?

The bad news first: cool melts are not equally suitable for all substrates. Since the adhesive is heated to a lower temperature, it does not penetrate as deeply into the substrate. This makes it more difficult to achieve adhesion on smooth surfaces. But here’s the good news: for many substrates, especially in end-of-line packaging, there are proven cool melts that have the same adhesion as conventional hot-melt adhesives.

This is also important to consider: low-temperature adhesives are not only applied at lower temperatures, but they also soften again at lower temperatures. The softening point refers to the temperature at which the adhesive passes from the solid to the liquid state. This also applies, of course, to adhesives that have already been processed. Products glued with cool melt should therefore not be exposed to temperatures higher than the softening point temperature, which needs to be taken into account when storing or transporting the products.

Why cool melt?

Depending on the application and the product to be glued, cool melts are a reasonable alternative to conventional hot melts. They can help to save energy and, in doing so, contribute to sustainable production. Making the switch should be considered, especially in the packaging industry. Adhesive manufacturers can advise on adhesive options. and Robatech is happy to test new adhesives for its customers — after all, nothing should be rushed.