Technology Advances Spurs New Interest In OPP Bottles

A new strategic alliance between two Canadian companies is aimed at capitalizing on renewed interest in oriented polypropylene bottles as a replacement for more costly PET bottles. Container Corporation of Canada (Richmond Hill, ON) and BMPS Inc. (Concord, ON) recently announced an agreement whereby BMPS will act as worldwide distributor for Container Corp.’s line of Enviroclear 2-stage reheat injection stretch blow molding equipment.

Norman Gottlieb, president of Container Corp., says OPP bottles produced on his company’s equipment are made from a special clarified random copolymer grade of polypropylene that took seven years to develop. The Enviroclear machine reheats the preforms imparting bi-axial orientation to the finished bottle.

Gottlieb says there is renewed interest in OPP bottles as new technology has raised the quality, increased throughput and lowered the manufacturing costs. These developments may help acceptance of OPP bottles for mainstream applications, as PP has a number of natural advantages, compared with PET.

Bottle-grade PET has a density of 1.35 g/cc and is currently priced at about 63 cents/lb. Comparatively, the density of clarified PP random copolymer used in oriented bottles is 0.910 g/cc and cost about 56 cents/lb. For a bottle of a given weight and volume, these differences translate into a 40% cost advantage for OPP bottles compared to PET bottles. However, these advantages have been neutralized by slower processing rates for OPP bottles. Output on a high-speed PET bottle line utilizing a two-stage reheat stretch-blow machine can exceed 50,000 bottles/hr. Additionally, OPP has traditionally been seen as having inferior clarity and barrier properties.

Advances in materials, equipment and methods of designing preforms and bottles has narrowed or eliminated the gap in material properties between OPP and PET, say some industry experts.

“The bottles are as clear as PET and cost less on a per gram basis for resin,” claims Gottlieb. “Plus they can be hot filled.”

Gottlieb says the Enviroclear 2-stage ISBM equipment can blow mold bottles at rates of up to 900 bottles per cavity per hour. The machines can be purchased with 2 to 10 cavities. This still puts the rates below those of high output PET lines, but the throughput is acceptable for other types of lower volume and more specialized containers.

In addition to selling its machines through BMPS, Container Corp. of Canada is one of the few companies in North America manufacturing OPP bottles. Gottlieb says the company began making OPP bottles several years ago when he became convinced the bottles offered clear environmental and cost advantages, along with a number of superior properties. Combined with a polypropylene cap, an OPP bottle offers what Gottlieb calls a “unipolymer” package. The company blow molds OPP bottles for flavored water using a common preform; as well it molds OPP bottles for hot-filled foods requiring a moisture barrier. The hot-filled OPP bottles cost about 35% less than heat-resistant PET bottles.