Customers today can choose from a vast variety of mattresses. The scope ranges from pocket innerspring mattresses for the widely popular box spring beds, to latex mattresses, and to memory, gel or classic cold foam mattresses. Increasingly complex material structures and patterns promise an ever increasing comfort, for instance due to more anatomically adapted zones and bounce-back elasticity to provide comfort across the entire body. The greater the material diversity, for instance in hybrid mattresses, and the more layers a mattress is composed of, the more challenging are the requirements for the adhesive used for bonding the foam. With a minimal application amount, the adhesive has to provide good adhesion to the different substrates and optimum green strength for the individual manufacturing processes. Another essential requirement for comfort in the lamination of flat and profiled foams is a soft bondline. Modern, powerful adhesives are therefore a prerequisite for modern mattresses with different material combinations and complex structures in batch sizes of one.
Dispersions are widely used in the manufacture of foam mattresses and meet the requirements regarding adhesion and soft bondlines, yet quickly reach their limits in fast manufacturing processes. Due to the low green strength of the water-based adhesives, the mattresses have to be stored for several hours after pressing until the necessary bond strength has built up. To reduce the risk of mould formation, they also have to be completely dry before packaging. Therefore, the mattresses have to be stored for up to 24 hours after assembly until they are ready for transport. At this year’s interzum, Jowat presented several innovative polyurethane hot melt adhesives (PUR HM) from the Jowatherm-Reaktant® series which facilitate optimised production processes in the mattress industry. The high green strength ensures easy handling and provides a substantial increase in efficiency. Foam mattresses can be wrapped and packaged in foil directly after pressing; roll packaging is possible after two to eight hours or immediately, depending on mattress structure and roll packaging machine. Buffer stocks are therefore reduced considerably in size and may even be eliminated. Inefficient dwell times become a thing of the past. The reactive hot melt adhesives provide a solution for shorter and less complex production cycles. The individual mattress layers can be repositioned during assembly if necessary and the tensions in the foam mattress are no longer a challenge.
Coupled with the chemical crosslinking of the adhesive, reactive hot melts provide excellent adhesion to even difficult to bond materials such as latex or gel foams, which may also have different properties depending on the supplier, and are characterised by very good penetration into porous substrates. PUR hot melts are suitable for all materials used in the production of mattresses and have a lower application amount compared to other adhesive types. Due to their high green strength, they can also be used for the manufacture of foam mattresses with innersprings. In addition, PUR hot melt bonds are characterised by high resistance to heat and sterilisation.
Processors will find it easy to change to PUR HM in production. Just like dispersions, these reactive adhesives are applied with an automated roller coater on the full surface of the substrate and only the applicator unit needs to be replaced. Higher transport stability and a longer shelf life compared to water-based adhesives are further benefits provided by the PUR hot melts.
Usually, reactive hot melts are applied on one substrate only. In demanding applications with special mattress structures – for instance high-stress bonding of difficult materials – the adhesive may be applied on both surfaces. The hot melt penetrates in both substrates, creates an anchor, and ensures a superior bond – with a lower total application amount compared to the one-sided application. The result: Permanent bonds for quality mattresses.
The professional article is published in the magazine 'möbelfertigung 4/17' in German language. You can download the original article down below.