New stretch-blow molding resin: polymethylpentene.

New Stretch-Blow Molding Resin: Polymethylpentene

Phillips 66 Co., Bartlesville, Okla., has developed a new grade of polymethylpentene capable of stretch-blow molding with nearly the clarity of glass. Previous extrusion blown PMP was translucent at best, and the resin was thought to achieve clarity only with injection molding.

PMP is a crystalline polyolefin, the lowest-density (0.835 g/cc) clear resin on the market, and the most chemical resistant. It's retortable, with Vicat heat-distortion temperature of 347-370 F, and nearly impervious to water and oil. PMP polymers have also complied with FDA food-contact requirements for years. But they were only commercially made by one company, Mitsui Petrochemical Industries Ltd. of Japan, under the brand name TPX, and were relatively expensive at $2.25-$2.30/lb. So PMP was considered a high-priced specialty for uses like corn-popper lids and sterilizable hospital supplies.

But now with Phillips' new technology for stretch-blow molding clear bottles, and its less expensive resin manufacturing process, the company thinks PMP can enter new food bottle markets. The stretch-blow success also appears to have caught Phillips by surprise, shaking up its commercial plans for the resin. (Phillips has also come out with an engineering grade of glass-filled PMP which it has high hopes for in appliance, automotive and aerospace applications.)

Phillips has been supplying test quantities of its Crystalor PMP for a year, from a pilot plant that is now producing around 500,000 lb/yr, to be expanded to over 1 million lb/yr in 1991. Material has been sampled for injection molling, extrusion and coating applications. Phillips says its six unfilled resins--1-decene copolymers made by a slurry process--are in compliance with FDA food-contact rules.

Phillips is telling customers it will build a 50-million-lb/yr PMP plant for 1992 start-up. But if bottle applications pan out, particularly what a Phillips source describes as "an entirely new barrier technology" now in testing (believed to be a three-layer coextrusion), 50 million lb of PMP two years from now may not be enough. So Phillips has "begun a dialog" to buy an existing chemical plant that could produce PMP as early as late 1991.

STRETCH-BLOW SUCCESS

According to Phillips, no one ever achieved clarity in blow molding PMP before. A source at Mitsui Plastics Inc., White Plains, N.Y., says it has had a customer extrusion blowing a TPX bottle for eight years. But Seiji Oshima, manager of specialty polymers at Mitsui Petrochemicals (USA), N.Y.C., says the result is "translucent, not clear like PET or glass." Blow-molded TPX also doesn't meet FDA food-contact requirements, because it's made with an alphaolefin monomer that doesn't comply, Mitsui says.

Phillips' research found that PMP was not amenable to normal injection blow molding. Success was achieved with stretch-blowing on a Nissei ASB 250-T, commonly used to blow PET soda bottles. Only a $300 modification to the reheating rod was required: substituting a 2-in. heating element, designed to provide more uniform heat distribution, for more even bottle wall thickness, and to prevent the PMP from scorching. PMP stretch-blowing research is continuing at Nissei ASB Co. in College Park, Ga., on a modified two-cavity Nissei machine (photo), which will be delivered to Bartlesville in July. For now, Phillips says it will make the modification on a customer's machine only under a secrecy agreement.

In many ways, PMP doesn't process like other polyolefins, Phillips researchers say. For one thing, stretch-blowing worked with Crystalor CBN-020, the 20 melt-flow copolymer, the highest-flow grade, where a fractional melt flow rate might have been expected.

The successful stretch-blow process involves proprietary additives and "slightly longer" temperatue preconditioning than usual. Tests have produced a variety of 6-12 oz bottles with the contact clarity of PET or glass. Unlike PET there is no darkening or thickening of the resin at neck fold or bottom of the bottle. Cycle time on the Nissei machine is around 25 sec.

Testing is now focusing on different mold shapes for a prospective monolayer customer. Baby bottles, for example, are a monolayer food possibility where PMP could compete favorably with polycarbonate because PMP is less expensive, doesn't craze or yellow with repeated sterilizing, and gives easier mold release, says Daretia Schuler, in charge of package marketing. "That's a 10 million-lb/yr market," she adds. PMP costs around 5^/cu. in., versus 7^/cu in. for PC.

Without a successful barrier technology, Phillips' vision of high-volume retorted food jars is "pie in the sky," admits Charles Capshew, head of Crystalor market development. Capshew hopes for preliminary results, above all a patent application, on the barrier work this summer.

FILLED AND UNFILLED RESINS

Phillips is sampling three homopolymers (HBM-005, HBN-010 and HBN-020) and three copolymers (CBN-005, CBN-010 and CBN-020); numbers indicate MFR. All six resins sell for $1.75/lb delivered; the 30% glass-filled homopolymer, HBG-30 sells for $2/lb.

Melting point of the homopolymer resins is slightly higher (464 F) than copolymers (455 F); Vicat temperatures are 365-370 F for homopolymers and 347 F for copolymers. Flex modulus runs 268,000-278,000 psi for the homopolymers and 180,000 psi for copolymers.

The glass-filled product has been tested for radiator intakes and other automotive applications. Based on a 20-MFR homopolyme, HBG-30 has a specific gravity of 1.05, roughly the density of unfilled nylon, and 25% lighter than comparable glass-filled nylon, Phillips says. Its tensile strength is 9700 psi, flex modulus is 860,000 psi, notched Izod impact strength is 1.6 ft-lb/in., unnotched Izod is 4.2 ft-lb/in., and HDT is 440 F at 66 psi, 370 F at 264 psi.

PMP's dielectric strength of 1096 v/mil (unfilled) is significantly higher than that of PET (800 v/mil), Capshew said. Its nonconductivity and light weight have piqued government interest for submarine wire coating, for instance.

Phillips expects initial sales to be evenly divided among film, coating, housewares, nonbarrier bottles, appliance and automotive uses, where on a ^/cu in. basis, PMP can compete against PC, PBT, PET and nylon. By the year 2000, Phillips expects sales to be roughly half in neat resins, including blow molded containers, half in glass-filled and other "engineering" compounds. A flame-retardant engineering grade will be introduced later this year for testing.

Phillips filed suit against Mitsui last August over Mitsui's U.S. sales, which Phillips estimates at 3-5 million lb/yr, and Mitsui says are 2.2 million lb. Phillips claims exclusive U.S. and Canadian PMP patents until 1999. Mitsui, which bought its TPX business from Britain's ICI PLC in 1973, has said it will match Phillips prices when Phillips reaches the market. (CIRCLE 13)