Water-Bottle Competition Prompts Machinery Advances.

Demand for returnable 3- to 6-gal polycarbonate water bottles is growing 10%/yr in the U.S. and 20%/yr in Europe. But stretch-blown PET is now entering the competition, offering 60% lower resin cost and a precision injection molded neck. PC-bottle advocates say lower PET resin cost is offset by PC bottles' ability to withstand 10 times more return trips. Also, they say PET injection stretch-blow molding requires 200% higher investment in machinery and 300% higher tooling costs. Further, PC bottles retain the advantage of an integral handle, plus ability to withstand high temperatures used for washing returnable bottles.

Meanwhile, three suppliers of extrusion blow molding machinery for PC bottles are upgrading equipment to improve neck quality.

* New reciprocating model: At the upcoming K 2001 show in Dusseldorf, Graham Machinery Group (GMG) in York, Pa., will unveil the model C-30, an upgrade of its B-30 reciprocating-screw system for 1-to 5-gal PC bottles. The C-30 enhances competitiveness of the PC water bottle versus stretch-blow molded PET, says Joseph Spohr, global sales v.p. He says the C-30 yields PC bottles with scar-free necks that have improved precision and surface flatness. The upshot, he says, is a 5-gal (19L) PC bottle with neck quality equal to PET.

Many of the C-30's modifications can be retrofitted to existing B-30s. Anew feature is the flow-through head said to prevent material degradation and to facilitate disassembly and cleaning. Efficiency of the variable-volume pump and accumulator systems is also increased, Spohr says.

* Optimized for water bottles: Uniloy Milacron, Manchester, Mich., introduced the RS13500 P/C, a variant of its basic RS3500 reciprocating-screw machine that's been optimized for molding 3- to 6-gal PC water bottles. The top-fed head reportedly reduces stress and hang-up of the melt, yielding improved clarity. Reject rates and maintenance times are both reduced. Refinements of blow pins and neck-ring cutters are said to produce a fully packed, smooth neck with improved sealing properties. A Siemens 128-point parison programmer ensures more precise wall-thickness control and improved neck quality. Higher clamp force (90 tons) is said to increase parting-line strength. Automatic, integrated take-out and trimming also enhance efficiency.

* Improved accumulator units: According to Peter Andrich, sales v.p. at SIG Plastics Technologies, North Branch, N.J., the company's Blow Pac 2-10 PC (small footprint) and 2-20 PC accumulator-head systems hold bottle-weight variance to [+ or -] 2-3 g vs. [+ or -]10-15 g for reciprocating-screw units. Better control permits lightweighting and resin savings, he adds.

SIG has developed a sliding sleeve that glides over the blow pin, giving the bottle neck a smoother surface comparable to a PET container, Andrich claims. Also new is an "anti-stick die mechanism" to reduce the tendency of PC to stick in the die.