The manufacturers of pocket spring core mattresses traditionally opt for gluing with hot-melt adhesives.
In order to be able to follow the body movements during sleep, the system of steel springs can move independently of one another. The spring pockets are bonded to each other by means of a sideways bead application (2-3 beads next to each other).
A compromise is made in the selection of the adhesive: The hot-melt should be flexible in the solidified state in order to follow the movements, but also hard enough in itself so that the bond does not come off.
When selecting these properties, the Shore hardness of the adhesive is crucial – not too high, otherwise the hot-melt adhesive will be too brittle – but not too soft either.
Hot-melt adhesives are solvent-free. High-quality hot-melt adhesives do not contain any chemical double bonds that can react or cross-link. Without double bonds, the adhesives are UV light-stable and do not change colour when exposed to light. When gluing the spring core cover (fleece and foams), a visually perfect result is important so that the adhesive does not shimmer through with very light foams.
The average body temperature of a person is 37 °C. With the adhesives used, attention is paid to sufficient heat resistance. Fibrous and non-fibrous are used for the fabric cover of the pockets. In order to achieve a sufficient bond, the adhesive must be able to flow into the tissue of the fabric, as this creates mechanical anchoring. Hot-melt adhesives with a long open time and fast setting are ideal.
Another good combination of properties consists of high initial tack and rapid cohesion build-up. The mattresses can be lifted, transported and packed immediately after bonding. In this way the production process is efficient without waiting time.