Foams are quite common in everyday life: they are used in everything from upholstery and mattresses to insulation materials. They are based on a wide range of plastics as raw materials. However, not every adhesive is suitable for every material. Given the wide range of variants, it can therefore be useful to always test how the adhesive behaves on small material samples beforehand.
In principle, almost all plastics are suitable for foaming, e.g. polyurethane (PUR rigid/soft foam), polypropylene, EPP (expanded polyurethane), expanded polystyrene (EPS), expanded polypropylene (EPE). The properties can be determined by the selection of the raw materials. Thus, strongly cross-linked hard foams are produced when short-chain polyols are used, whereas soft to elastic foams are produced with long-chain polyols.
In physical foaming, the material is expanded by means of a physical process.
In chemical foaming, a blowing agent (e.g. pentane or CO2) is added to the plastic granulate, which splits off as a volatile component when heat is added. The result: the melt foams.
Most foams are produced by means of foam extrusion: the heated plastic expands to 20 to 50 times its volume as it flows out of a perforated nozzle. Rotating knives then shorten the resulting foam strands into foam particles of a few millimetres in size.
The moulding process is used to process closed-cell foam beads made of (EPE, EPP, EPS) into moulded foam parts, such as toolboxes or transport packaging. Such materials have enormous lightweight construction potential combined with good thermal insulation properties because they consist of more than 90 percent air.
Using a special particle foam technology, the chemical giant BASF recently succeeded in producing the world's first expanded thermoplastic polyurethane (E-TPU) under the name Infinergy. The new, closed-cell particle foam is marketed, among other things, as cushioning in newly developed running shoes.
The different types of foam can be bonded with numerous adhesives.
The well-known rigid foams such as polystyrene, also known as Styrofoam, can be bonded well with dispersion adhesives, for example, and form a bond that can hardly be separated. However, solvent-based adhesives (e.g. all-purpose adhesives) dissolve the material. Open-pored foam made of polyurethane, also called ""foam rubber"", on the other hand, can be glued quite well with commercially available all-purpose adhesives.
However, some types can hardly be glued at all: Polyethylene foam, which is used to make sleeping mats, for example, cannot be glued at all with adhesives. It may be better to weld the material instead. To do this, heat the surfaces to be glued with a hot air gun until they begin to melt, and then press them firmly together until they adhere.
Problems can also arise when gluing foam, for example, as foam is very elastic and therefore quickly detaches from the substrate if the wrong gluing technique is used.
Which adhesive is best suited depends on the type of foam and the substrate to which it is to be bonded. Find below an overview of potential solutions to bond foam.
Spray adhesives show themselves to be true all-rounders. The aerosols are particularly suitable for bonding foams to large surfaces and for hard substrates such as wood, concrete, GRP and metals. Advantage: It can be applied quickly and easily with the spray can at the touch of a button.
Dispersion adhesives, such as the 3M™ Fastbond™ 49, the 3M™ Fastbond™ 30NF and the 3M™ Fast Tack Water Based Adhesive 1000NF, have similar properties and areas of application as solvent adhesives. However, such adhesives are dispersed in water. They are applied to one or both surfaces.
Hot-melt adhesives are suitable for temperature-insensitive foam products such as EPP or polyethylene foam, whereas the low melt technology can be used for temperature sensitive substrates such as EPS. Common hot melt adhesives, such as 3M's low-melt and hot-melt technologies, have good wetting properties in molten form and develop good strength in foams and many other materials.
Thin bonding enables the attachment of different foam substrates or composites using a strong but very thin tape or adhesive transfer tape to keep the overall profile as thin as possible. Double coated or adhesive transfer tapes provide shear strength, conformability and high initial adhesion. Thin bonding lets your design shine without bulky fasteners by using a virtually invisible industrial-strength bond.
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