Polyurethane adhesives play an increasingly important role in assembling automotive interiors, according to Thomas Hohberg, director automotive key accounts of German adhesives company, Jowat Klebstoffe which was exhibiting at a Krauss Maffei Automotive open day in Warren, Michigan on 18 September 2013.
Adhesives simplify assembly of parts such as roof liners and door panels, where they can either replace or supplement mechanical fixings, said Hohberg.
“We can tailor the cure properties of system to match the line speed of the plant or other sub-component production process,” said Hohberg.”Hot melt polyurethane adhesives are used to help assemble instrument panels. (IP), floor panels, headliners. The adhesives can be used with inert substrates such as polyolefins. However, these must be surface, treated, often using corona discharge to produce a surface that is sufficiently reactive for the polyurethane adhesive to bond effectively.”
He added that the versatile chemistry of urethane systems can be modified so that the polyurethanes achieve sufficient green strength at the start of the curing process to enable components to stay physically close together in alignment in a few seconds after application. Full cure and strength builds over a period of hours or days depending on the formulation. This combination of fast green strength and slower full cure often fits well with the
According to Jowat, in a conventional vehicle there can be 15kg of adhesives used to assemble and mount a wide range of parts. These can include dispersion adhesives for laminating operations in interior trim using soft ABS or TPO foils, two-component adhesives, used to laminate interior trim with soft PVC foam foils and ABS or TPO foils on plastics or fibre-board substrates. Finally hot melt PU resins are used to bond foam to foam or textile to textile. The viscosity of the adhesives can range from210mPas to 45 000 mPas.
The firm said that thermoplastic polyurethane adhesives have a number of other benefits, they are 100% solid, and because they are not water-based energy used to evaporate water in other systems can be saved, there is no need to use a spray booth, air extractor and filtration system.
Hot melts can be used successfully with delicate surfaces such as high grain leather. This is because once activated the hot melt is a liquid which allows the laminate to glide into deep-drawn areas without distorting the pattern.
Two component polyurethane adhesives typically give high tack, a long open-time and often have high initial strength, said Jowat. These are often used for laminating interior trim foils made from PVC foam ABS or thermoplastic olefins on plastics or fibreboard substrates.