New blow molding resins: a peek at the future.
From higher clarity and barrier properties to increased chemical and heat resistance, a new crop of blow molding materials will offer enhanced properties for applications from packaging to automotive bumpers and fuel tanks. Before long, you'll be seeing blow molding grades of metallocene-enhanced polyolefins, brand-new engineering resins, reactor alloys, foams, and long-fiber-reinforced compounds. The last two are already commercial, though activity has been limited so far. Detailed information on most of these new materials is scarce, so this report provides a quick peek ahead at what's coming and why you'll want to stay on top of these new developments as they emerge.
LONG FIBERS ADD STRENGTH
Long glass-fiber reinforcements at levels up to 15% recently have been shown to offer several performance advantages in blow molded parts. The benefits of using glass fibers 0.4-0.5 in. long include higher flexural modulus, impact resistance, and tensile and flexural strengths; reduced warpage; improved melt strength; and increased creep resistance. The end result is the ability to blow mold thinner walls, says Robert V. Hoy, application development specialist at Ticona (formerly Hoechst Technical Polymers). Ticona, which supplies Celstran long-glass-reinforced HDPE and PP compounds, is one of two firms exploring this technology. The other is LNP Engineering Plastics, which supplies Verton long-fiber PP for blow molding.
Potential applications include pallets, panels, and children's playsets, as well as automotive parts. Celstran has found commercial use in HDPE panels with 10% long glass for a hospital utility cart. Ticona is also working with a manufacturer of children's playsets. Meanwhile, Verton product manager Dick Sabo says PP's good chemical resistance plus the higher HDT and impact strength conferred by long glass fibers make the material suitable for under-the-hood and passenger-compartment applications.
Up to 10% long-glass loading is often processable on standard blow molding equipment with minor modifications, says Hoy. Among them, the extruder should not impart intensive mixing in order to prevent fiber degradation. Also, because long-glass-reinforced HDPE does not stretch as easily as neat HDPE, Ticona recommends limiting the blow ratio - e.g., 2.5:1 for 10% glass content. Ticona is developing new lower-MFR, higher-melt-strength resins for its Celstran compounds that are more compatible with the typical blow molding grade HDPE.
FOAM LIGHTENS PALLETS
Another new technology, one that has seen limited commercialization in Europe, is blow molding foam technology (BFT), jointly developed by Borealis A/S of Denmark, Krupp Kautex of Germany, and OBG Design, a Norwegian mold builder. Benefits of the foamed parts reportedly include weight savings, increased stiffness, noise reduction, thermal insulation, and improved compressive and flexural strengths. The BFT process is being used by BFT Plastics, Ltd. of Northern Ireland, to make HDPE foam-core pallets, (see PT, Aug. '97, p. 106). Other potential applications for BFT include collapsible food containers, automotive air ducts, and double-wall partitions and panels.
The BFT process was developed for polyolefins. Borealis, which developed the resins and chemical foaming agent, is negotiating with a U.S. partner to supply foamable materials here.
This continuous-extrusion blow molding process can produce walls of varying thickness with a skin/foam or skin/foam/skin structure. The foam's closed-cell structure and cell size can be influenced by the amount of blowing-agent concentrate and the processing parameters. The one-step process typically uses two extruders: one for the skin(s) and the other for the foam layer. A two- or three-layer coextrusion head forms a multi-layer parison that is molded into a finished product. Foaming takes place at the extrusion die, and blowing is done at a relatively low pressure to prevent the foam from collapsing, according to Krupp.
REACTOR ALLOY FOR BUMPERS
Originally developed by Montell Polyolefins for injection molding, the Hivalloy line of PP/PS grafted alloys show some promise for blow molded car bumper beams, according to business development director Ken Dargis (PT, Feb. '97, p. 25). He explains that Hivalloy has a somewhat wider processing window than PC/PBT - the only other material that has been used in such an application - in terms of melt strength and temperature range. Also, Hivalloy's specific gravity of about 0.93 is about 25% lower than that of PC/PBT. Even though PC/PBT is about twice as stiff as Hivalloy, Dargis says, a Hivalloy bumper beam can be molded slightly thicker to provide equal stiffness while maintaining a 5-10% lighter part.
Montell has tested two developmental Hivalloy grades that are designed for low-temperature performance: GXPA058 and slightly stiffer GXPA068. Preliminary tests have shown fairly good parison strength and consistent wall thickness throughout the part. As Hivalloy products are refined for bumper applications, Dargis foresees achieving improved stiffness and low-temperature impact in a lighter part. He hopes to see Hivalloy specified on at least one automotive platform by 2000.
POLYKETONE FOR FUEL TANKS
First commercialized a year ago for injection molding applications, Carilon aliphatic polyketone from Shell Chemical also presents blow molding possibilities in automotive applications (PT, Feb. '97, p. 50; Sept. '97, p. 20). Shell's R&D emphasis is on use of Carilon as a barrier layer in coextrusion blow molded fuel tanks. (Carilon also has potential in the general industrial market, as a barrier layer in containers for pesticides and other hazardous or corrosive chemicals, says automotive market manager Paul Sykes.) Sykes expects to have a well-defined Carilon blow molding process for application development within the next nine to 12 months. Shell is working with suppliers of tie-layer resins to develop a material for bonding Carilon to HDPE. Sykes believes that a commercially available tie-layer product is six to 12 months away.
One intriguing possibility is to take advantage of Carilon's excellent fuel resistance to reduce the number of layers in an automotive fuel tank from six to four. A potential structure is Carilon/tie/regrind/HDPE. Over the longer term, it may even be possible to reduce the number of layers further by eliminating the need for separate regrind and HDPE layers, says Sykes.
No blow molding grades currently exist for Questra syndiotactic polystyrene (SPS), commercially introduced this year by Dow Plastics (PT, June '97, p. 52). But this new crystalline engineering thermoplastic does have potential for blow molded under-the-hood auto parts, according to Fred Daniell, Questra's global automotive market-development manager. Questra is based on a styrene monomer that is polymerized with a metallocene catalyst to produce a polymer with a high melting temperature (518 F) and good resistance to moisture and chemicals (except gasoline).
LCP AS COEX BARRIER LAYER
Blow molding liquid-crystal polymers is being pioneered by Superex Polymer, Inc. (see PT, June '96, p. 11). The company is in the early stages of developing a multi-layer LCP/HDPE fuel tank. Because of the excellent chemical resistance of LCP, it can come into direct contact with gasoline, opening up the possibility of three-layer fuel tanks.
Superex has other LCP blow molding projects that are closer to commercialization. In packaging, the firm has developed special machinery and techniques (now available for licensing) for blow molding PET bottles with an inside skin of oriented LCP, an outside layer of unoriented PET, and a proprietary tie layer. The coextrusion blow molding process orients the LCP layer by the counter-rotating action of cylinders in the die. Suprex says that an LCP layer comprising just 5% of the wall thickness will increase the oxygen barrier by more than 20% compared with a pure PET container.
The next phase of development is a multi-layer PET/LCP container with an oriented PET layer. The bottle would be comparable to a PET stretch-blow molded bottle with a multi-layer construction, says Superex president Rick Lusignea. Although the high price of LCP remains an obstacle, Lusignea expects the price to fall with higher usage. If that happens, LCP's improved barrier performance can make LCP competitive with EVOH, he says.
NEW PACKAGING POLYESTER?
Launched earlier this year by Shell Chemical, the Corterra family of polytrimethylene terephthalate (PTT) polyesters was originally developed for fibers and injection molding (PT, July '97, p. 20). Shell is now in the very early stages of investigating the resin's potential for blow molded rigid packaging, according to Phil Dalton, Corterra's manager of business development. Possibilities include tailoring the polymer for enhanced barrier to moisture, C[O.sub.2], and oxygen. Dalton cautions not to expect a commercial offering in the near term.
The new Topas family of metallocene-catalyzed cyclic olefin copolymers (COCs) that was introduced to the market by Ticona earlier this year (PT, June '97, p. 58), reportedly has been test run successfully in a number of small injection blow molded containers. Topas COCs offer a good potential for glass replacement in pharmaceutical packaging, according to Dr. Donal McNally, head of Topas marketing in the Americas. Although bottle applications are still developmental, one container is very close to commercialization, he says.
Key properties of COC include high clarity and high moisture barrier. Metallocene catalysis provides precise control of molecular weight and low levels of catalyst and residual monomer, says McNally. Ticona has blow molded three out of the five basic grades of Topas, which differ mostly in their glass-transition temperatures and flow rates. The company has also done some developmental work on impact-modified and glass-reinforced grades.
METALLOCENES FOR PACKAGING
Although metallocene polyolefins offer desirable properties for rigid packaging - low extractables, controlled but variable molecular weights, and high clarity - most development efforts with these resins are currently focused on extruded film. Only two of the four U.S. firms currently making metallocene polyolefins would comment on blow molding for this article.
Kurt Swogger, global R&D director for polyethylene and Insite products at Dow Plastics, says that metallocene-type HDPE resins do have potential benefits in blow molding. Downgauged packaging is one example where Dow's Insite technology could be advantageous, says Swogger. He says blow molding grades may be sampled as early as 1999. Although commercialization may start outside the U.S., there is also potential in the U.S. market for such a packaging resin, he says.
Two recent metallocene-PP developments from Fina Oil and Chemical Co. have some potential for blow molded packaging. Neither material contains low-molecular-weight atactic fractions, making them suitable for pharmaceutical and food applications. One is Fina's syndiotactic PP (sPP), which reportedly offers better clarity and lower moisture-transmission rates than random copolymers. Because of its low melt strength, syndiotactic PP would be limited to injection blow molding, according to Joe Schardl, manager of market development. Although the present cost of sPP is around five times that of conventional homopolymer, Schardl expects a gradual reduction in price over the next couple of years. He says Fina has a few development projects with blow molding customers, and expects one to go commercial within the next six months.
Fina's metallocene isotactic PP, introduced for sampling last year, also has some potential in blow molding, although Fina has not developed it yet. Possible applications include small bottles, where the material would bring incremental improvements in toughness and clarity over conventional polypropylene but would probably cost 20-30% more, Schardl says.
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|Author:||De Gaspari, John|
|Article Type:||Cover Story|
|Date:||Dec 1, 1997|
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