Hot-melt and water based adhesives are the most commonly used adhesives in the mattress industry. For this reason, we would like to point out some of their advantages and disadvantages.
Depending on handling and drying times when manufacturing final products and also depending on the type of machinery, it will be better to use an industrial hot-melt adhesive or a water based adhesive.
The most common industrial adhesives within the hotmelt are those derived from synthetic rubber (PSA) and amorphous polyolefin (APAO), while the most used among water based adhesives are polychloroprene and polyurethane derivatives.
Hotmelt adhesives offer the advantage of finishing the manufacturing process very quickly, being able to pack almost immediately (process known as Pack&Go or Roll&Pack). This prevents the odour and humidity problems generated by water based adhesives inside packed mattresses when they are packed too fast. This is because hotmelt adhesive is 100% solid and it shows an open time (time when adhesive sticks while cooling) from about 10 seconds to a maximum of about 4 minutes, depending on the raw materials used and substrates to be bonded.
Hotmelt adhesives are quite stable to external conditions and agents, before and after their application. However, temperatures above 50 ºC should be avoided because they could soften.
For industrial processes in which production time is very important, hotmelt adhesives are more suitable because they allow to adjust manufacturing processes, handling time and finalisation of the product.
For pocket springs manufacture, there is not better industrial adhesive than hotmelt, being used for automatic and very efficient production lines.
For assembling box springs, hotmelt adhesives are the best choice since water based adhesives show much longer handling and drying time. In addition, the control of water drying is very limited and it is subject to machinery investments and extra expenses for energy consumption.
The use of hotmelt adhesives is essential in production lines where gluing both fabric covers to the foam core is done in just few minutes and the manufacture and packaging process ends right away.
For rubber based adhesives (PSA), if any of the areas of the mattress is not stuck initially and there is a part of the adhesive on the top side and the rest on the bottom side, this can generate a Velcro-like noise when touching both parts, especially noticeable in the silence of the night. However, this effect does not occur with APAO hotmelt adhesives, neither with water based adhesives.
Water based adhesives
Water based adhesives offer greater resistance to high temperatures. This is important when shipping or stocking goods, for instance into containers, where high temperatures can be reached during long transports and in summer.
Although water based adhesives are expensive and normally a higher quantity than hotmelt adhesives is needed, water based adhesives have a lower energy cost, since they are applied cold. Installations to apply water based adhesives are usually simpler than those for applying hotmelt adhesives.
Water based adhesives are especially suitable for roller machines, where the adhesive is applied over the entire surface without wasting a single drop of adhesive. When gluing different foam sheets to manufacture foam cores, water based adhesives offers the advantage of gluing the entire surface at lower cost than hotmelt adhesives. With roller machines, it is possible to impregnate the whole surface of the core foam with water based adhesive in a quick and easy way, with little electricity consumption.
A higher quantity of water based adhesive is applied on mattress surface than hotmelt adhesives (Between 50 to 100 g/m2). If we compare prices of water based and hotmelt adhesives and we take into account that water based adhesives contains 50-60% of solids and rest is water and that a higher amount is applied, the application of hotmelt adhesives is less expensive than water based adhesives.
Water based adhesives require between 12 to 24 hours to remove 100% of the contained water in the adhesive and get completely dry. During that time the mattress must remain unpacked, thus it slows down the manufacture process. In addition, certain spaces at factories are occupied, which could be used for production, instead of as stock spaces. This is unfeasible for highly productive and efficient manufacturing processes.
Water based adhesives, before being applied on mattresses, are unstable to manipulation, transport, external agents and high or low temperatures between 5ºC and 30 ºC), If the dispersion is destabilized, the adhesive coagulates and it irreversibly spoils.