Injection Moulding Asia

Brilliant colours for automotive parts
Manufacturers of automotive thin skin interior components like instrument panels, airbag covers and interior trim with moulded-in colour are now offered vinyl microbeads from Teknor Apex.

After years of producing beads with a micro particle-size distribution for non-automotive markets, Teknor Apex has acquired the rights to market the beads internationally to the automotive industry through an agreement with Bayer MaterialScience.

Tek-Spheres microbeads are produced by melt compounding PVC resin with colour, plasticiser and other additives, producing a homogeneous material that melts rapidly in contact with a heated mould. The product is said to have tactile properties while being simpler to process and less energy-intensive than powder blends and plastisols.

Of the various hollow-mold processes available for thin-skin applications on automotive components such as instrument panels and headrests, one of the most commonly used is slush moulding, in which a partially open mould rotates on a single axis. Another method, rotational moulding, uses a closed mould in a two-axis system. To meet the requirements of these processes, Teknor Apex supplies Tek-Spheres products at different size levels and in Shore A durometers as low as 55.

The direct product of the melt compounding method used for making Tek-Spheres is actually minibeads, with diameters from 0.5 to 1.5 mm, smaller than the 3.2 mm pellet compound used in injection moulding and extrusion and more suitable for slush moulding. In a subsequent step, Teknor Apex produces smaller beads that are more suitable for rotomoulding and for slush moulding applications involving deep draw areas, severe undercuts or fine detailing.

The alternative method for producing the beads are plastisols that are a liquid formulation of PVC resin in a carrier consisting primarily of plasticiser. Plastisols vary in viscosity in accordance with ambient temperature and other mixing conditions, may contain entrapped air that causes pinholes or voids in finished products, may undergo separation of components during storage, can require up to three times longer for colour changeovers and entail use of volatile organic solvents for cleanup after spills, says Teknor Apex.

Another type of conventional vinyl material used in slush moulding is that of powder blends, highly plasticised mixtures of PVC and other additives, which place a limit on low-durometer formulation requiring more plasticiser and preventing the material from acting as a free-flowing powder.