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Engineering News 7430
February 19, 1996
18 Min Read
Newton, MA--Not since linear low-density polyethylene (LLDPE) appeared on the scene in 1977 has a development in plastics held as much potential as metallocene single-site catalyst resins.
So reports Richard C. Mastio of Mastio & Co., St. Joseph, MO, a consultant who tracks the plastics industry. Mastio predicts that by the year 2004, consumption of metallocene resins should exceed 3.7 billion pounds. By way of comparison, LLDPE use took 17 years to reach 3.69 billion pounds.
What will make the new resins so popular? Improved strength and toughness, enhanced optics and seal strength, and increased elasticity and cling are only a few of more than 300 features and benefits that metallocene resins have versus LLDPE, LDPE-EVA (ethylene vinyl acetate) copolymers, polypropylene (PP), LDPE, polyvinyl chloride (PVC), and others, Mastio claims. Metallocene displacement of these five resins alone will near 2.9 billion pounds by 2004, Mastio predicts.
The single-site catalyst process is so attractive because the ethylene/olefin group of catalysts has a uniform active center. The result: they can be formulated fast and easily to meet almost any material need.
Leading producers. At present, two companies play the predominant role in producing the single-site catalysts--Dow Chemical and Exxon Chemical. However, several others also hope to make a big impact on the marketplace. Among the other prominent players: Germany's Hoechst AG in collaboration with Exxon, Bayer AG, BASF, Mitsui Sekka (formerly Mitsui Petrochemical Co. Ltd.), Union Carbide, and BP Chemicals.
Dow Chemical, Midland, MI, reports that its octene-ethylene polyolefin elastomers (POEs), made using its award-winning Insite(TM) metallocene catalyst process, can be cross-linked like conventional ethylene propylene rubber (EPR) or ethylene propylene diene rubber (EPDR). The POEs show better heat resistance, heat aging, weatherability, and tensile properties than conventional EPDR, probably because of their octene content.
After 10 days at 347F, for example, POE loses little of its elongation properties, while conventional EPDR has turned brittle. The POE resins, 10 grades in all, are sold under the trade name En-gage. They target flexible underhood automotive applications such as hoses, brake parts, and wire and cable harnesses. POE compounds in thermoplastic olefin (TPO) blends of 30% POE/70% PP also show superior properties for automotive applications like bumper fascia, according to key Dow officials.
Actually, Dow first commercialized a polyolefin plastomer (POP) using the Insite metallocene process under the trade name Affinity. Like POEs, POPs are ethylene-octene copolymers, but have less than 20% octene. Dow now has 14 Affinity grades on the market.
"These materials are unlike anything I have ever seen," says Hernando Correa, president of Proempaques, which uses the POPs in its Bogota, Columbia packaging operation. "By adding Affinity POPs in a blend with other materials, we can enhance the optics of some packaging materials, improve the sealing properties of other structures, and even make some packages tougher--all with the same resin."
DuPont Dow Elastomers, a recently formed joint venture in Wilmington, DE, should greatly expand the introduction of other materials based on Insite technology. "You can expect to see ethylene and styrene copolymers making the scene in the near future," says Chris Pappas, the joint venture's global business vice president in charge of ethylene elastomers. The new entry would expand the metallocene product line for added design benefits, particularly in areas that require more protection against harsh chemicals. The joint venture should become official next month.
Exxon Chemical, Houston, TX, calls its patented metallocene-polyolefin process Exxpol. And, according to Gregory L. McPike, worldwide vice president for the Exxpol venture, "our milestones in this technology are becoming a regular occurrence." The most recent took place last September with "the first successful commercial-scale manufacture of metallocene-catalyzed isotactic propylene polymers." McPike considers the development "the vanguard in a family of new propylene polymers to be introduced by Exxon."
The metallocene propylene polymers are produced under the trade name Achieve. "Polypropylene is already the most versatile polyolefin, and the new family of Exxpol polymers will further penetrate into end-use applications, such as natural and synthetic fibers, cast films, and engineering plastics in molded durable goods," McPike enthuses.
Exxon had announced last summer that it was working with Hoechst AG, Frankfurt, Germany, on catalyst development. "Now, we have proven that our catalyst process has made world-scale production of metallocene propylene polymers a commercial reality," McPike adds.
In December, Exxon added five grades of its Exact(R) plastomers to its FDA-compliant metallocene specialty portfolio. The FDA had allowed Exxon to increase the allowed hexene comonomer content from 10 wt % to 20 wt % in film applications intended for direct food contact. Next: lower density and lower melting-point packaging film resins.
Moreover, Exxon added to its stable of metallocene-catalyzed materials last September with what it claims is the world's first metallocene-produced, low-density polyethylene (mLLDPE) resins, following numerous customer trials. The Exceed(TM) film "has the ability to withstand an increased puncture force of about 50%," says McPike. "Its ultimate tensile strength is as much as 40% greater than those found in conventional products."
In the works. Meanwhile, Union Carbide, Danbury, CT, unveiled its development of proprietary, single-site metallocene catalyst systems customized for its gas-phase Unipol polyethylene process. The company said it will introduce a new family of the LLDPE resins based on this technology, with commercial-scale trial runs just beginning. Also on tap: higher-performing products to compete with LDPE in extrusion coating, shrink and clarity film, and wire and cable markets.
"The system used in the commercial trials is one of several under development at Union Carbide using advanced catalyst process technology that simplifies and streamlines single-site catalyst chemistry," adds Union Carbide CEO William H. Joyce.
BASF AG disclosed at the K'95 show in Germany last fall that it has begun commercial-scale polyethylene production using its metallocene catalyst process. The copolymers of ethylene and olefins are marketed by BASF under the trade name Luflexen.
The metallocene catalysts are especially well-suited for use in BASF's high-pressure Novolen gas-phase tubular reactor processes, since they can be metered in homogeneously as a solution. In this way, an access route has been provided to obtain copolymers with very low densities.
Films constitute one of the first applications for the Luflexen grades.They also will be used to replace ethylene-vinyl acetate copolymers (with more than 20% vinyl acetate), to injection mold distortion-free parts, to create medical containers such as catheters or ampoules, and to produce cable sheathing and hoses.
Other players discussed their work on metallocene-based polymers at the Metallocenes '95 conference:
Italy's Himont Srl's development of an atactic PP.
Netherlands-based Shell BV's creation of a tough PP copolymer.
Japan's Mitsui Sekka's production of an LLDPE (ethylene with hexene-1 comonomer).
With all of these prominent players in the field, it's only a matter of time before a plethora of metallocene polymers enter the market. Such competition should bring down the price of these versatile resins (they currently are selling for $1 to $1.50 per lb). This will give design engineers a smorgasbord of new materials for their design activities. And, says Dow Chemical's Ed Gambrell, vice president for the Insite process, "they can have the material of their choice in a matter of days."
WHAT THIS MEANS TO YOU
You could be using metallocene-based resins for your next design project.
Metallocene materials can be formulated quickly to meet most product design needs.
Areas where metallocene materials might meet your needs: wire and cable, automotive, and medical applications.
--Gary Chamberlain, Senior Editor
Rapid tool design corrects tolerance problem
Indianapolis--Imagine discovering that a critical tool is making parts out of tolerance--after full-scale production has begun. That's what happened to engineers at medical-device manufacturer Boehringer Mannheim.
Boehringer's Accu-Chek(R) Advantage(TM) system is a popular self-administered home-monitoring device for diabetics. Boehringer's manufacturing team produces disposable test strips for the device that provide very accurate blood-sugar readings. To deliver such accuracy, Boehringer designed an instrument called a ROM Key to accompany each box of strips. The ROM Key acts as an identification tag for the specific test strips and uses a single microprocessor to automatically calibrate the monitor's meter to the strips.
After several months of successful production, an internal quality check revealed that although the critical dimensions of individual ROM Keys being made were within acceptable tolerances set for production, the dimensioning did not allow for the stacking up of tolerances. Therefore, when the dimensions were at minimum or maximum tolerance, the ROM Keys being produced wouldn't function in monitors already sold.
The ROM Key's intricate ribbed design must align perfectly in the back of the monitor to make the necessary contacts with the monitor's internal electrodes, explains Boehringer Senior Supplier Quality Engineer Paul Belase. "It's critical that these ribs be managed statistically, by design, by process capability, so that when they're aligned into the monitor, they fit." Small pieces of plastic sheared off during production were compounding the problem. "We were basically shut down," recalls Belase.
The fastest quote from tool makers for getting a new tool was 22 weeks, which would have spelled disaster in the highly competitive market. Instead, Boehringer teamed with Compression Engineering, Indianapolis, to design a new tool more quickly.
A full-scale 16-cavity tool would require precious time to create, so Compression engineers chose to create a 4-cavity tool. "Because of the tight time-frame, we chose to go straight from CAD to tooling," explains Todd Ray, Compression's director of technology. "We built the components and did our analysis, tolerance and assembly checking with Pro/ENGINEER from Parametric Technology. Because of the small size and accuracy we needed for the product, it would have been very difficult to rapid-prototype."
Going directly from the CAD files, engineers used a CNC machine to create the tool from P20 steel. "Molding began within two weeks, and the tool has produced over one million parts within tolerance to date," says Ray. Adds Belase: "We had ROM Keys ready to ship in two weeks, and that got us out of trouble."
Technology turns old rubber into tires
Santa Ana, CA--Urethane Technologies, Inc. (UTI) has found an innovative way to recycle discarded tires. And, it results in raw material cost savings in the production of some polyurethane parts--bike tires in particular.
Funded by the California Integrated Waste Management Board, the project shows that "finely ground rubber can be used successfully as a cost-effective filler in polyurethane bicycle tires, industrial wheels, shoe outsoles, and other products," says Urethane Technologies' John D. McNeill.
Champion Recycling, Inc., Apple Valley, CA, subcontracted the technical development and testing procedure for the project to UTI. UTI holds patents on the novel process to treat ground rubber so that it can be used as the filler in molding polyurethane products. The company also holds patents on a centrifugal molding process used to make non-pneumatic polyurethane bicycle tires. "The recycling technology has the potential to open sizable new markets for polyurethane systems," McNeill predicts.
Earlier attempts to use ground rubber as a filler in high-performance polyurethane systems had limited success, "because of problems in getting the rubber to bond well with the polymer," McNeill explains. The poor bonds, due to the atmospheric moisture in the ground rubber, "were considered a major barrier to further development," he adds.
The ground-rubber treatment process developed by UTI takes a surface modification approach. The post-treated rubber, called Stermic(TM), produces greatly enhanced adhesion of the rubber particles to the polymer. Also, a new non-ozone-depleting blowing agent helped yield optimum performance for wear-resistant applications.
Initially, researchers had planned to use water-blown technology instead of chlorofluorocarbon (CFC) and hydrogenated CFC (HCFC) blowing agents. However, "water-blown test plaques did not produce a skin and did not exhibit sufficient abrasion resistance to meet severe and diverse road conditions," McNeill says.
Using the Ariser technology, test polyurethane bicycle tires were molded having a tread pattern similar to pneumatic tires made by Korea's Cheng Shin in a 27- by 1.25-inch size and inflated to 65 psi. Both the pneumatic rubber and non-pneumatic polyurethane/Stermic tires were tested on a treadmill under severe and accelerated conditions. The pneumatic tires were destroyed within 60 minutes, while each polyurethane/Stermic tire withstood more than 3 hours of rotation and oscillation before the test was terminated.
Beyond the environmental benefit of diverting scrap tires from landfills, the Stermic approach offers a significant price advantage for the molded products, McNeill says: 20 to 25% in material costs alone. "Also, improved physical characteristics are possible for some applications," he notes.
For example, McNeill says that compared to rubber bicycle tires, the polyurethane/Stermic tires offer superior tear and abrasion resistance, better impact resistance, greater sound absorption, and a reduction in heat buildup.
Adhesives breathe life into oxygen concentrator
San Diego--When engineers at SeQual Technologies, Inc. developed an improved air-separation system for in-home oxygen concentrators, they weren't quite sure how they were going to build it.
Their patented design, which generates supplemental oxygen from room air for respiratory patients, offers several advantages over conventional systems. By eliminating about 250 parts, the Advanced Technology Fractionator (ATF(R)) makes oxygen concentrators less expensive to maintain, more reliable and durable, and more energy-efficient, says SeQual Marketing Vice President Edward Radtke. A rotary distribution valve driven at low speed by a small motor further simplifies the unit.
At first, engineers couldn't find a practical manufacturing method for the new system. "We normally would have dip-brazed the assembled aluminum components to make the entire structure leak-free," explains Engineering Vice President Theodore Hill. "But this turned out to be expensive. It also required temperatures so high that we would've had to send the parts to be brazed."
Instead, engineers used ESP 308(TM) one-component epoxy adhesive from the Permabond International division of National Starch and Chemical Co., Bridgewater, NJ. The heat-cure adhesive provides high-strength bonds that seal joints and hold the unit together, says Hill. "Its strong structural properties withstand the product's operating pressures, and its high viscosity prevents drips that can detract from the finished appearance."
The fractionator consists of about 40 parts. Key components are aluminum die castings and 12 aluminum sieve tubes. Epoxy adhesive bonds and seals the structure's 37 joints, and doubles as gasketing to seal the manifold passages.
Other applications for the new technology include breathing systems for small unpressurized aircraft, and industrial waste-water treatment.
Custom controllers cut costs
Mountain View, CA--Often, engineers find themselves in need of a motion controller with special capabilities, one that's unusually small or capable of interfacing with a particular microprocessor. Unable to meet the need with a standard, off-the-shelf product, they divert engineering resources to the task of designing a controller in-house.
To address this trend, Galil Motion Control has formally launched a customization program for volume OEMs. It enables companies to contract Galil to develop a custom controller in fewer than 12 weeks for less than $100 an axis, the company says. "We sit down with the company and listen to their needs," says Jacob Tal, Galil's president. "We then design from scratch a new controller that meets these needs, and we deliver it in three months."
The idea sprouted from Galil's realization that the company had amassed over the years a powerful inventory of more than 300 customized firmware and dozens of customized hardware solutions. But until now, delivering this engineering capability wasn't formalized--and few outside the company knew of it. "We found customers who had designed their own system because they thought they didn't have a choice," says Tal.
He cites as a typical customization example a controller Galil built for SAIC (San Diego, CA). Part of a space satellite, the controller needed to endure severe vibration and thermal conditions. SAIC also required an interface for an absolute encoder, and needed the hardware in 12 weeks. "This was a perfect match," says Tal. "They came to us knowing what they needed, but not how to get there."
Charges start at $5,000 for a custom board, whereas a custom firmware design for an existing Galil controller begins at $500 and takes two weeks or less to complete.
Laptop displays grow CAD-sized
Las Vegas--It's tough to do CAD on an 8-inch screen.
So even as notebook PCs have gotten more and more powerful, small displays have caused some engineers to balk at doing serious design work on the machines. However, Zenith Data Systems says a new generation of active-matrix color displays offers almost as much screen area as a typical 14-inch desktop monitor.
The 12.1-inch Z-NOTE GT color display, developed by NEC Electronics, offers 800- x 600-SVGA resolution, 262,000 colors, and 38% more screen area than a conventional 10.4-inch laptop. Computers with the display should be on the market early this year.
"These units will be running AutoCAD-type environments," predicts Susan Krusee at Zenith. A prototype system shown at the fall Comdex show included a 90-MHz Pentium processor, 1.3G hard drive, quad-speed CD-ROM drive, internal MPEG video card, and two PCMCIA slots. Estimated retail price: $5,700.
NEC Engineers designing the larger display needed to increase the panel's glass display area while keeping the same overall size. This meant reducing the border area, according to Omid Milani at NEC. They worked to pack such things as inverter circuitry, which controls voltage to the display, into a smaller space--in part by special ASIC designs and also by using smaller packaging in general.
Two years ago, a typical notebook-PC screen measured 8 inches, and producers' main concern was to improve yields so they could drive down costs. "We know much more about that now," Milani says. "Now the issue is to look at the rest of the panel so we can squeeze in more glass."
Instrument panel blends softness, recyclability
Munich, Germany--Blend the flexible properties of an elastomer with the harder properties of a thermoplastic and what do you get? An instrument panel for the Opel Vectra that has the soft look and feel consumers want; and the recyclability, low cost, and reduced fogging that automakers demand.
The new dashboard, made from polyolefin, is said to be the first example of its kind in large-scale production. Supplier Alkor GmbH Kunststoffe can produce cover films that retain the embossed grain intact after the deep-drawing process. The new compound, formulated from Surlyn(R) ionomer resins, plays a major role in the film's good processability, according to Richard L. Bell, development specialist at DuPont Automotive. The halogen-free materials are based on a new elastomeric thermoplastic-thermoplastic polyolefin (ETP-TPO) technology from DuPont.
Previous TPO films suffered from the crystalline nature of polyolefins in a narrow processing window when compared with other standard PVC/ABS films. If that window closed too soon or too late, a large number of rejects would result, Bell explains. "Using our patented process," he adds, "the technique facilitates straightforward deep-drawing on conventional heat-form machines, with no need for costly modifications. Processing is carried out according to size and contour, with the films competitively priced with standard PVC/ABS films."
In weathering tests conducted by various car manufacturers in tropical and desert climates, the TPO dashboard proved to be remarkably resistant to aging compared with the conventional PVC-based decorative films, Bell reports. Also, there was no evidence of embrittlement or dimensional changes, which could lead to beveled edges and surface cracks.
The light weight of the TPO film is an added bonus. Because of the lower density, the Vectra dashboard weighs 20% less in terms of decorative foil than comparable ABS/PVC foil often used in this automotive application.
DC-9 aircraft subjected to ultrasound
Albuquerque, NM--DC-9 aircraft safety inspections can be done more thoroughly and about 15 times faster with ultrasound, according to government researchers. The technique, developed by a team headed by Sandia National Laboratories, uses sound waves projected through the aircraft's skin. The waves reflect back in distinctive patterns, revealing whether corrosion is occurring inside the plane.
Sandia's Airworthiness Assurance Nondestructive Inspection Validation Center (AANC) predicts the use of ultrasound could save about $9,000 per aircraft. In addition, reducing maintenance down time of each DC-9 amounts to savings of about $20,000 per day. "We look to replace visual techniques with non-destructive testing (NDT) methods," says Jeff Register, non-destructive testing manager, Northwest Airlines. "The result is a substantial reduction in project work hours and down time."
The technique came about after Northwest Airlines became interested in a more economical way to inspect DC-9 wing boxes for corrosion. The visual method Northwest used previously called for an inspector to get inside the wing, which also serves as a fuel tank on the DC-9. The process of removing access panels, emptying fuel from the tanks, inspecting for corrosion, and then reassembling the aircraft meant than one inspection required about 800 work hours. Repair or replacement required additional time.
The inspections are important for the first 700 DC-9s manufactured by McDonnell Douglas between 1968 and 1970 because they contain T-caps that are susceptible to corrosion. About 20% of these have had their T-caps replaced, leaving 560 that require additional monitoring.
The wingbox and T-cap redistribute the weight of the wing to the aircraft body or fuselage. The T-cap is an approximately 12-foot-long metal structure located in the wingbox and spanning the width of the wing. Because the T-cap is located in a low spot of the wing, any water in the fuel tends to settle out there, which can lead to corrosion.
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