A hot melt adhesive is an adhesive that melts at higher temperatures of approx. 100 ° C and is often processed at temperatures of 120 ° C-200 ° C. Due to the large difference to the ambient temperature, hot melt adhesives can quickly cool down to their solid state. This makes it possible for many industrial applications to glue products in a time frame of approx. 1 second and to transport them over the production line.
In principle, anything that can melt and stick can be called hotmelt.
IT ALL BEGAN WITH EVA HOTMELT
An EVA hotmelt owes its name to the main raw material in the hotmelt, although it is normally used, but for 35% of the formulation. The remaining ingredients are additives such as resin to increase the stickiness and a wax to increase the binding speed and to reduce the viscosity.
ADVANTAGES OF EVA MELT ADHESIVES
A hot melt EVA adhesive has had great success in the food packaging and shoe manufacturing industries. Machines could be made more compact and the production environment took up less space. In addition, EVA hotmelts are free from volatile solvents, so that EVA hotmelt also offered enormous advantages in terms of the environment and working conditions.
DISADVANTAGES OF EVA MELT ADHESIVES
EVA hot melt adhesives are usually processed at approx. 160 ° C, the adhesive systems work under high pressure. A certain amount of caution is required when processing hot melt adhesives. You can also read more about working safely with hot melt adhesives in our blog: “How to change an adhesive”.
EVA hot melt adhesives tend to "creep"; under high structural stress, the adhesive bond can be too plastic and move too much with the forces exerted on it. This can also occur at temperatures above 50 ° C. An EVA hotmelt adhesive can also lose its strength at low temperatures, below 0 ° C, as the adhesive film becomes hard and brittle.
BENEFITS OF POLYOLEFIN MELT ADHESIVES
Polyolefin hot melt adhesives seem to be a perfect successor to EVA hot melt adhesives, the heat resistance can be increased enormously with these hot melt adhesives, as well as the frost resistance. In addition, many polyolefin hot melt adhesives are more thermally stable than EVA hot melt adhesives, which can contribute to less adhesive burn and a more reliable production process.
PUR MELT ADHESIVES
The PUR polymer was used in order to be able to really constructively bond with large production quantities in automated production environments. PUR was already known from cold wood compounds for the construction and furniture industry. By adapting PUR adhesives to warmer application temperatures, the advantages of faster processing with a hot melt adhesive built into PUR adhesives have been realized.
PUR hot melt adhesives are reactive, which makes them a very special group of hot melt adhesives, as most hot melt adhesives are thermoplastic. The reactivity also leads to additional health risks and to more thoughtful handling in general, such as the care of the adhesive equipment in which PUR hot melt adhesive is incorporated.
PSA MELT ADHESIVES
PSA hot melt adhesives have also been around for a long time. This group uses water-based and solvent-based adhesives in the self-adhesive sector. Not only because of the quick processability and better environmental conditions, but also because hotmelt adhesives can be applied with a thicker layer on materials such as adhesive tape and labels. Because of the thicker layer of adhesive, it is easy to make stronger self-adhesive materials that offer higher bond strength, also known as rolling ball tack and loop tack. Use in self-adhesive applications can lead to new products, such as duct tape, but production lines that apply self-adhesive labels can also produce faster due to the increased instantaneous adhesion.
HOT MELT ADHESIVE FORMULATIONS
Hot melt adhesives can be formulated almost endlessly to develop the best adhesive for a particular application. Adhesion area, open time, sticking time can be set according to priorities