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SAE highlights new automotive plastics materials and technology.

What drives current automotive plastics R&D? Recycling may have a role, but new materials and processing technologies will have more immediate impact.

Among the numerous materials developments and new processing techniques that came to light last month at the Society of Automotive Engineers (SAE) International Congress and Exposition in Detroit, four overall themes stood out.

First, while nearly everyone at the show was talking about a recycling strategy and an "environmental awareness" plan, the hard reality is that recycling of plastic automotive parts remains mainly theoretical. At least that's true on this side of the Atlantic. In Europe, the progress is rapid and substantial. But in North America, too much is still unknown about the technical and economic ramifications of automotive plastics recycling, and both a recycling infrastructure and industry standards have yet to be developed. Equally uncertain are the role and responsibility of processors in the recycling equation. Nonetheless, the SAE conference gave testimony to active R&D on innovative methods of reclaiming plastic car parts.

Second, "next-generation" processing approaches seem to be approaching commercial fruition. In contrast to the vague hints of the past, industry executives now openly discuss these technologies, often in the context of specific future applications. These new concepts include blow molded instrument panels, plastic/metal hybrid structural components and multilayer reflective sheet for lighting applications.

Third, development of injection molded thermoplastic body panels, which has long been a tantalizing possibility, remains stalled with only limited applications. Despite the widely touted benefits of recyclability, lower tooling costs, part design and processing advantages, TP body panels remain a tough sell to car builders. At least one of the Big Three indicates that thermoset technology, often dismissed in recent years as a "mature" area and one vulnerable to recycling difficulties, is seeing a renaissance in body-panel applications at the expense of thermoplastics.

Fourth, there was much less discussion of plastics as "metal replacements" at this year's show. Plastics are firmly entrenched in virtually all areas of automotive design. The current tactic is optimizing or replacing existing plastic applications with new, enhanced plastic materials or processing concepts. Today, a major focus for plastics processing, design and material technology is delivering small, highly engineered precision components for the demanding applications and severe environments of engines, transmission and fuel systems.

BLOW MOLDING BECKONS

This summer, Dow Plastics' Automotive Materials Group will begin a developmental program with a processor (Davidson/Textron Inc. in Portsmouth, N.H.), a moldmaker and one of the Big Three auto builders to assess the manufacturability of a single-shot, blow molded instrument-panel retainer. The part will utilize an advanced grade of Dow's Pulse PC/ABS blend. Dow first revealed its proprietary research in large-part blow molding for instrument panels 18 months ago (see PT, Sept. '91, p. 42). Though Dow declines to comment, General Motors is believed to be the automotive OEM involved in the effort.

The program, if it proves successful, could put such a part on the road in a commercial vehicle by late in this decade. That would represent a major advance for the blow molding process in automotive. Major benefits for such a part include cost savings on tooling and assembly cycles, weight reduction, part consolidation, and the capability to engineer functionality (such as air ducts) into the part.

R.J. Giba, advanced marketing manager for the Automotive Materials Group, says Dow has completed its initial prototyping and is now ready to present the blow molded IP retainer concept as a viable contender for commercial applications. Dimensional stability, part consistency and reproduceability are key requirements that must still be proven out.

The 12-lb part requires an unfilled grade of Pulse with enhanced melt strength to maintain a 70-in. parison drop. It also requires as well as modification to existing large-part blow molding equipment. Another challenge will be design of the complex mold. Unlike Dow's separate, parallel effort for a structural instrument panel, the blow molded IP retainer will not encompass a structural or energy-management system. Giba anticipates the blow molded instrument panel will target niche applications for lower-volume vehicles.

Robert D. Albert, v.p. of Dow's Automotive Materials Group, says the structural version of an engineering thermoplastic instrument panel will debut on a 1994 vehicle platform, with an announcement expected this quarter. This concept, announced by Dow late last year, involves an assembly of structural cross-car beam/duct, structural retainer, and knee bolsters--all injection molded from various Pulse grades. The structural panel eliminates steel supports and incorporates an energy-management system, support for a passenger-side air bag, knee bolsters and air ducts.

REFLECTIVE SHEET LIGHTING

Dow Plastics also is finding initial concept-car applications for its Polymeric Reflective Material (PRM), a technology under development for several years (see PT, Sept. '90, p. 15; Dec. '92, p. 39). Lighting applications employing the reflective-sheet material are incorporated on three concept vehicles from Ford Motor Co.

The technology involves a proprietary extrusion process that produces a sheet containing hundreds of layers of polycarbonate and acrylic, which can create a variety of reflective, "transflective," and pearlescent effects that mimic metal. Especially intriguing is the "transflection" (simultaneous reflection and transmission) effect, whereby the sheet can resemble opaque metal in reflected light, and can also transmit light in various tints when lit from behind. The sheet is made into parts by thermoforming or compression molding.

Gregg Motter, senior associate development scientist, says the PRM sheet is used for the taillamp lenses of the Mustang Mach III, believed to be a prototype for the mid-1994 Mustang model change. Motter says PRM is not yet specified for that platform, but test development work is proceeding at Ford. Two other applications include front and corner lighting bars and lenses for Ford's Nautica concept minivan, and flush headlamps and taillamps for the Synthesis 2010 concept car. In these applications, the PRM lenses are used to provide a metallic-looking accent tone or create a flush, seamless effect with the car body. Additional PRM applications on the Synthesis car include rearview mirror housings and several instrument-panel appointments.

PLASTIC/METAL HYBRIDS

Executives of the Polymer Div. of Miles Inc. say their plastic/metal hybrid structural panel concept is being evaluated by two automotive OEMs, one of which is tooling up for a potential application within the next three years. The concept involves injection molding Miles' impact modified, 30% glass-filled Durethan BRK-130 nylon over a perforated steel sheet, adding both structural stiffening ribs and mounting attachment points (see PT, March '93, p. 82).

Structural applications being evaluated by the OEMs include a lift gate and a cross-car beam. One unnamed OEM already has built prototype tooling and has begun molding test-development parts.

NEW ENGINEERING MATERIALS

Monsanto Co. has quietly commercialized Triax XP40, an unfilled, toughened polycarbonate/polyester/styrenic alloy, which has been under development for several years (see PT, May '92, p. 14). Automotive marketing manager John G. Zessin says the material previously was being evaluated for a blow molded windshield plenum. That program was cancelled last year, and now Monsanto is developing injection molded interior and exterior applications. The material is priced as a premium product for small- to medium-size parts in niche applications.

Triax XP40 reportedly shows processability and impact resistance similar to PC/ABS, with enhanced heat resistance (HDT of 250 F at 264 psi). Monsanto can tailor the melt strength of the alloy for injection molding, blow molding or extrusion.

Monsanto also is developing new toughened nylons for commercial automotive applications in the 1994-95 time frame. Zessin says the new grades incorporate a novel, proprietary elastomeric phase.

DSM Engineering Plastics is introducing two new alloy families that incorporate post-consumer/post-industrial recycled PET. The alloys are designed for interior/exterior automotive trim. Stapron E pairs recycled PET with virgin PC, and Ronfaloy P uses virgin ABS as the alloy partner. Developmental grades are available for test marketing. Mechanical/temperature properties were not available at the SAE show.

NEWS IN POLYOLEFINS

An unusual alloy of several polyethylenes of different molecular weights was unveiled by Hoechst Celanese Corp. Hostalloy 731, the first of a new family, was developed for high-wear applications as an easily processable and lower cost alternative to nylon and acetal. Michael Harvey, market development engineer, says the material is a blend of PEs with molecular weights between 200,000 and 1 million, with "a definite bias to the high-molecular-weight side." It does not, however, contain Hoechst's Hostalen GUR UHMW-PE.

Hostalloy 731 has an HLMI between 8 and 12 g/10 min and injection molding temperature range of 380-450 F. Notched Izod impact tests show no break at ambient temperature. Taber abrasion resistance (1.7 mg loss/1000 cycles) reportedly approaches that of UHMW-PE and exceeds those of nylon and acetal. Specific gravity is 0.95, tensile strength at yield is 5000 psi, ultimate elongation is 100%, and flex modulus is 170,000 psi. Price is $1.50/lb tl. An extrusion grade is planned.

Amoco Chemical Co. introduced seven grades in its new Acctuf PP impact copolymer line. Acctuf 3243, described as a high-impact, general-purpose injection grade, has a melt-flow rate of 5 g/10 min, HDT of 210 F at 66 psi, flex modulus of 205,000 psi, tensile strength at yield of 3700 psi, elongation at break greater than 200%, and notched Izod impact of 11.0 ft-lb/in.

Amoco also is introducing eight grades (four commercial, four developmental) of its new Accpro enhanced nucleated PP. Accpro 9433, an antistatic, injection grade, has a MFR of 12, HDT of 270 F at 66 psi, flex modulus of 350,000 psi, and tensile strength at yield of 6130 psi.

Amoco's sister company, Amoco Performance Products Inc., is extending its Amodel polyphthalamide line with several new grades, some of which already have been specified in high-temperature applications on commercial cars. One developmental grade, currently undergoing trials at Ford and Chrysler for transmission and thrust-washer TABULAR DATA OMITTED parts, is Amodel AS-1630 HS with 30% carbon fibers. James K. Doty, industrial manager, automotive, Amoco Engineering Polymers, says this developmental grade is designed to match the performance of Amoco's Kadel polyketone at half the price.
RECYCLING SMA PARTS
(Physical properties of 15% glass-reinforced SMA)
 70% Wt. Virgin All
Property Units 30% Wt. Recycle Virgin
Tens. Str.(a) psi 8265 8338
Impact Str.(b) ft-lb/sq in. 3.8 3.5
Flex. Mod. kpsi 653 624
HDT |degrees~ F 250 252
a
@ break
b Notched Charpy
Source: RCM GmbH


Two recently introduced Amodel grades, AS-1145 HS (45% glass) and A-1133 HS (33% glass), have already captured several applications. A transmission temperature sensor molded from AS-1145 HS this July will go into production on an unnamed Chrysler car. The material offers high strength, transmission-fluid resistance and service-temperature capability to 300 F.

Amodel A-1133 HS, recently specified on an ultrasonically welded stub tube for Ford, has an HDT of 545 F at 264 psi, continuous-use temperature of 365 F, tensile strength of 32,000 psi, flexural strength of 45,000 psi, flexural modulus of 1.7 million psi, and notched Izod impact strength of 2.4 ft-lb/in.

Although not a new material, it's interesting to note a new use for a high-performance plastic in cars. Headlamp reflectors for the 1993 Lincoln Mark VIII are injection molded of Amoco Performance Products' Radel A polyethersulfone. The extremely low-profile design--2.5 in. high x 18 in. long--required a high-temperature material. Radel PES was selected for its 420 F HDT at 66 psi, high practical toughness (no break unnotched Izod), high flow, and excellent molded finish. The headlamp assembly is made by Osram Sylvania, Inc., Seymour, Ind.

AUTO MAKERS EXPLORE RECYCLING

After 1990's proposed environmental legislation in Germany forced automakers to get serious about recycling, the European automotive community adopted an unofficial policy to describe the climate created by the new laws: "No Recycling Equals No Business." Now, it appears that credo is finding its way into the North American market, as recycling and environmental responsibility seemed to be the buzzwords of this year's conference. Topics ranged from designing for disassembly and reuse to novel methods for recycling thermoplastics and thermosets that could lead to a greater portion of a car's plastic components being put back into the vehicle.

So far, only one North American auto maker is actually putting recycled plastic from its cars back into new vehicles. Working with GE Plastics, Ford is using salvaged bumper material (GE's Xenoy) from seven of its models to mold new taillight housings for its 1993 Taurus. GE calls the recycled grade Xenoy REX.

In Europe, though, the situation is progressing more rapidly (see PT, May '92, p. 101). One of the more innovative recycling processes discussed at SAE was developed by the German engineering firm RCM GmbH in conjunction with resin supplier Arco Chemical and auto maker Adam Opel AG. It allows post-consumer recycling of complex parts produced with a styrene maleic anhydride (SMA) copolymer core, such as foam-sheet-laminate headliners and instrument-panel supports.

In the process, being done at a pilot plant in Germany, the SMA is dissolved from the laminates in a solvent. Then a precipitation agent causes the SMA to come out of the solution so it can be recovered. The solvent and precipitation agent--selected because of their lack of chlorinated or aromatic hydrocarbons--are reused in the process. About 30% by weight of the recyclate is compounded with virgin SMA to make a 15% glass-reinforced material with physical properties within 10% of those of all-virgin material. Adam Opel recently test molded that compound into instrument panels, air ducts and headliners, saying the initial results were promising.

While energy cost to recycle the panels and headliners in this manner is higher than it would be if a mechanical process were used, all the parties involved say the quality of the recyclate justifies the increased cost. On the downside, RCM GmbH says the instrument panels and headliners have a limited life and can probably be recycled only a few times, since repeated reprocessing shortens the polymer chain, eventually rendering the material unusable.

Instrument panels are also the focus of developmental work being done at two of the Big Three auto makers. Ford Motor Co. is looking at a mechanical rather than chemical approach to separating components from IPs, while General Motors is channeling its efforts toward redesigning IPs to allow the whole assembly to be recycled together.

At Ford, scrap and rejected instrument-panel parts are run through a nitrogen-cooled granulator and the granulate is separated into its various material types. The SMA particles being heavier than the other components in the instrument panel fall to the bottom of the cyclone separator and are easily separated from the lighter vinyls and foams. As much as 70% of the available SMA is recovered, Ford says, and, even though it may contain small traces (less than 2%) of vinyl and foam, it can be blended with virgin SMA and fiberglass to make molded substrates that exceed the company's material specifications.

GM has taken a different approach to making recyclable IPs, proposing that the multi-part components be made entirely from polyolefins. In GM's design, glass-reinforced PP would be used for the upper portion (retainer) of the IPs, reducing cycle times 15% to about 60 sec. GM says using a mica filler adds dimensional stability to the retainers. Uncrosslinked polyolefin foams would form the interior of the IPs with a rubber-modified PP or TPO being used for the skins. The PP foams being examined have adequate densities, GM says, but they do not stand up well to repeated impact because their cell walls are prone to collapse. TPO skins can be made as thin as 9-18 mils, and GM says the skins will not cause windshield fogging (unlike vinyl), provide lot-to-lot consistency, and result in better weatherability, chemical resistance, uv stability, and mechanical properties than conventional PVC skins. The whole instrument panel in the GM experiment is held together by either thermoforming the skin and foam over a hard PP retainer treated with an adhesion promoter; or by placing the skin and foam in an injection mold and molding the retainer behind the skin and foam laminate. GM says the process cannot yet be used for making a highly stylized instrument panel, because the TPO skin material is too stiff to allow for conforming or styling lines. Also, GM says the polyolefins tend to reflect glare and must be painted to obtain a lower gloss.

SPREADING THE 'R' WORD

Closely related to GM's concept are two all-olefin component designs from Exxon Chemical--an all-olefin instrument panel and a bumper/fascia assembly made solely from polypropylene. Exxon's version of the all-olefin IP is identical to GM's in that it uses PP structural components, polyolefin foams, and a TPO skin. An Exxon spokesman says the system will be used in at least one 1996 model.

The company's design for an all-PP bumper/fascia system is a three-part assembly: a bumper compression molded of Taffen glass-reinforced sheet, a PP foam core, and a PP-based fascia. Weighing in at less than 15 lb, the system is about half as heavy as many other bumper/fascia assemblies, Exxon says. Manufacturing costs are estimated to be as much as 50% lower.

Disassembly for recycling is unnecessary--instead, the entire assembly is granulated intact, and the regrind can be used at levels around 10% in under-the-hood polyolefin parts. These parts, Exxon says, meet GM specifications for parts containing 20% glass.

Also talking about a fresh approach to thermoplastic recycling was DuPont Automotive, which says it has developed a chemical process for recycling reinforced and painted nylon parts back into pure monomer ingredients that can be repolymerized into virgin nylon. Because patents have been applied for this process but not yet granted, DuPont is reluctant to provide any details on its workings, saying only that it can handle molded parts or fibers of either nylon 6 or 66, allowing the recycled material to be fed directly back into the virgin feedstock stream. Apparently, the company is committed to this process. In October of last year, DuPont opened a 500,000 lb/yr nylon recycling plant in Glasgow, Del.

Recycling presentations were not limited to thermoplastics, RIM, RRIM and SRIM, as well as SMC, were also explored. Dow Plastics discussed two on-going projects, one showing how to incorporate as much as 25% recycled material from a mixed plastics stream into fresh SRIM systems for non-appearance parts; and the second using up to 10% of pulverized, PVC-covered, low-density RRIM scrap as filler in a new part.

In the SRIM project, the recycled granulate--which could include painted fascia, vinyl-clad instrument panels, or even bumper beams--is sandwiched between the fiberglass mat reinforcements in a new SRIM part, helping to hold the glass in place during RIM injection and increasing the flexural modulus of the SRIM part. Because of this, the process is being targeted for use in instrument-panel topper pads, rear parcel shelves and load floors.

Dow's second research project, besides showing that recycled RRIM scrap can be put back into new parts, points out some other benefits of RRIM over SRIM for production of covered interior door panels. Because no glass mat is required, conventional RIM processing technology can be employed, allowing one-step molding of entire door panels, Dow says. Vinyl skins are placed in the mold and after a filler/regrind mix is added to the B side of the RIM system, the material is shot into the mold. In order to keep viscosities from getting too high, Dow recommends keeping the total filler/regrind content in the system to less than 25%, with no more than 10% being RRIM regrind. Panels molded with regrind levels up to 6% show little or no change in flexural modulus, impact resistance, or dimensional stability. Tensile and elongation properties also remain about the same, Dow says.

Meanwhile, a glycolysis process developed by the German-based Polyurethanes Div. of Miles Inc. can regenerate liquid RIM components from solid RIM waste. The new chemical technology starts with grinding painted and unpainted, filled and unfilled parts together into 0.12-0.40 in. particles. The granulate is then mixed with a preheated glycol and the entire mixture is heated to 410 F. The result is a clear, stable, single-phase polyol solution with low reactivity and low viscosity. The process is very consistent, Miles says. The polyol mixtures produced by the new process reportedly can be used in the same RRIM applications as the original material. Miles has combined as much as 60% by weight of these recycled polyols with its Bayflex 110-80 urethane system in laboratory trials, with only a slightly negative effect on processing and physical properties. However, the low reactivity of a system using 100% recycled polyol requires a great deal of catalysis and Miles warns that the proper choice of isocyanate in these cases is critical to achieve good demolding characteristics.

At Ford, Green Light for SMC, Red for TP Body Panels

Ford Motor Co. will introduce several car and light-truck platforms during the next four years that make expanded use of thermoset sheet-molding compound (SMC) for vertical and horizontal body panels. The wider use of SMC reflects the continued incompatibility of thermoplastic body panels with Ford's existing assembly operations and counters the widespread notion that thermoplastics' inherent material properties automatically surpass those of thermosets for body-panel applications.

Ford will also increase its utilization of aluminum body panels on cars and trucks in the near term. Both SMC and aluminum were picked over steel panels for their lower weight and tooling costs. Ford currently employs SMC hoods on its Lincoln Mark VIII, Aerostar and Econoline vans, and uses aluminum hoods for its Lincoln Town Car, Crown Victoria and Grand Marquis. At least four car and light-truck platforms for 1995-96 may already have been specified and received final engineering approval for the SMC and aluminum body panels.

Long-documented problems of dimensional stability (coefficient of thermal expansion), and insufficient stiffness for horizontal panels have undermined the ambitious projections for body panels made by resin producers during the last 10 years (see PT, Sept. '89, p. 84).

Except for vertical panels on Saturn models and limited applications for fenders on Chrysler and GM cars, injection molded thermoplastic body panels continue to see scant use on commercial automotive platforms.

"It would be a fair statement that injection molded engineering thermoplastics are not high on our list of body-panel materials," says Richard Kollar of Ford body & chassis engineering. Kollar directs the final engineering/design releases for plastic body panels and leads programs that direct and control body-panel material selection.

Ford is arguably the most conservative of the Big Three auto builders with regard to usage of injection molded thermoplastic body panels. In recent years, Ford delayed several times, then eventually cancelled, a program for thermoplastic fenders on its Taurus SHO model. Thermoplastic contenders for the Taurus program included DuPont's Bexloy K-550 PET/glass compound, which currently is being successfully used in fenders for Chrysler's three LH cab-forward models.

According to Kollar, dimensional stability was the primary reason for Ford's preference of SMC over injection molded thermoplastics. Ford's quality philosophy insists any alternative body panel material must be equivalent to steel in all assembly requirements, which includes fit, finish and exposure to E-coat temperatures (400 F). In Ford's assembly operation, plastic panels are bolted onto chassis and structural members alongside steel panels, so there is no tolerance for thermal expansion at E-coat temperatures. Fear of contaminating colors prohibits off-line painting of plastic panels, in Ford's view. Also, the trend at Ford engineering is toward ever-tighter body panel margins, which conflicts with the wider spacing between panels to "forgive" thermal expansion of thermoplastics, such as in the margins engineered into body-panel design for GM's Saturn vehicles.

Kollar says, "We would have to build a 'greenfield' |assembly~ plant in order for us to consider thermoplastics as they exist today for use on body panels. It's safe to say SMC has the inside track in the near term for programmed vehicles with plastic body panels." He says Ford will utilize SMC for vertical and horizontal panels, molded by a processor list that includes Rockwell International, Troy, Mich.; GenCorp Automotive, Akron, Ohio; and Budd Co., Madison Heights, Mich.

Kollar indicates that Ford is actively involved in recycling programs for all car parts, including SMC, and apparently finds no inherent economic/technical advantage for thermoplastics in the recycling area. Ford's choice of SMC also challenges the gospel of thermoplastic superiority to thermoset with regard to surface quality and painting. Kollar says a new, proprietary in-mold coating process, now being used on the Mark VIII hood, greatly reduces traditional SMC problems stemming from surface porosity and "paint pops." From the perspective of Ford's assembly operations--of which in-house painting remains an important component--SMC "Class-A" surface quality for painted body panels is equivalent to thermoplastics and steel.

TP FENDERS HURT BY SUCCESS?

Turning from Ford to operations at another Big Three auto maker, it appears that thermoplastic body panels, even where successful, can suffer from too much of a good thing. Last month, Chrysler launched an internal task force to study a possible switch to steel from injection molded thermoplastic for the fenders of its three "cab forward" LH models. A final decision was expected as early as April 1.

The study comes just as Chrysler is preparing to expand production of the LH platform, owing to unexpectedly large sales. Another platform, the luxury New Yorker, also is scheduled to incorporate the cab-forward design.

Chrysler uses Bexloy K-550 glass-filled PET from DuPont Automotive. While the material has performed successfully in the fender application, it is believed that the Chrysler task force deliberations focus mainly on projected tooling costs of thermoplastic vs. steel. Thermoplastic could actually become a casualty of the LH platform's successful launch, as growing sales volumes may favor the economics of tooling for steel stamping over thermoplastic injection molding.
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Title Annotation:Society of Automotive Engineers
Author:Monks, Richard
Publication:Plastics Technology
Date:Apr 1, 1993
Words:4302
Previous Article:Building higher value into injection molds.
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