Injection Moulding Asia

TPV stacks up in chair design
When US company Humanscale Corporation wanted to design an ergonomic stackable chair, it turned to ExxonMobil Chemical’s TPV.

Because stackable chairs need to be strong, they are often made of steel or from nylon or glass-filled polypropylene (PP) with a surface of vinyl or fabric. Because the materials generally used in the manufacture of stackable chairs allow little or no movement, the person using such a chair becomes stiff and tired very easily.

Humanscale’s objective was to produce an ergonomic chair with a breathable, flexible back for comfort, which included a wide belt attached to the lower back of the chair to support the lumbar region. From a performance perspective, the chair had to pass the Business and Institutional Furniture Manufacturers Association (BIFMA) testing and CAL133 flame retardant tests. The material used for the support belt needed to withstand up to 90 kg weight, be UV resistant, offer good creep resistance and adhere to the structural PP. From an aesthetic viewpoint, the surface of the chair, which required colouring, had to look good.

These requirements were met by Santoprene TPV due to its ability to bond tightly with PP plus ExxonMobil undertook a mould flow analysis to confirm that the TPV would flow well enough to fill the part. Finite element analysis (FEA) tests were done to identify areas of stress concentration.

The lower back support belt, weighing 0.3 kg and measuring 508 mm long by 14 mm) wide by up to 25 mm thick, is manufactured by injection overmoulding Santoprene TPV onto the PP chair back, to create a cohesive bond.  Apart from that the chair is also fully recyclable.