Realistic stone appearance for rotational molding (July 01, 2000)

A uniform stone-like appearance in components of virtually any size is available from Stone Effect linear low-density polyethylene (LLDPE) compounds for rotational molding.

Go Plastics Inc., a rotational molder in Kitchener, Ont., uses the Stone Effect compounds to manufacture its Streetsmart outdoor magazine and newspaper vending racks and its proprietary Urban Images line of park benches, planters and trash receptacles.

The Stone Effect LLDPE compounds are produced by Nu-Past Inc. using pigment systems developed by Teknor Color Co. They are available in sandstone, dark millstone, white marble, green marble, and medium grey hues.

The stone appearance is achieved through precise mixes of different colored linear low-density polyethylene with various mesh screen sizes and controlled amounts of fines.

Rotomolding “appearance” parts presents several challenges, according to Dennis Foy of Teknor Color. “Rotational molding subjects thermoplastics to higher temperatures and much longer heat histories than other processes, requiring pigments and additives like UV stabilizers to be formulated to withstand this stress without degrading part properties. At the same time, static charges inherent in rotomolding must be managed to prevent swirl patterns and other defects in components.”

One unanticipated advantage of designing parts with the Stone Effect products is that polishing of the mold surface is not necessary. “In fact,” says Ed Gollob, CEO of Go Plastics, “the rough surface texture of unfinished tooling actually enhances the stone-like appearance and feel of parts by eliminating smooth sections and minimizing gloss.”

Teknor Color Company 800/554-9885 Circle Reader Service No. 190