New automotive materials target reduced cost, higher performance.

Apart from air-intake manifolds, there was more news for car interiors than for under the hood at this year's Detroit show.

Cost reduction was an overriding concern among automotive engineers polled at this year's Society of Automotive Engineers (SAE) International Congress & Exposition in Detroit. New materials introduced at the show are designed either to cost less or to cut costs in processing. Examples are fast-cycling grades of nylon 6 and new acetals that are said to provide low friction and high wear resistance at lower cost than PTFE-filled grades. In addition, new PMMA/PP copolymer alloys potentially can reduce the cost of auto plastics recycling by compatibilizing mixtures of resins used in instrument panels so that less disassembly is required to separate them.

Besides cost reduction, the other key theme was materials with higher performance. A new nylon 6 increases weld strength of two-piece molded intake manifolds. New PVC micropellets reportedly permit rotocasting soft-touch interior components with better properties than plastisols or slush molding compounds. Also new are acetals that are laser markable.

Although most of the news was in engineering thermoplastics, there was ample evidence that the auto industry's commitment to thermosets - specifically sheet molding compounds - is strong and getting stronger. There are more than 70 new SMC parts on domestic 1996 cars and trucks, nearly a threefold increase over 1995, according to the SMC Automotive Alliance (SMCAA), Troy, Mich. The SMCAA projects a 20% jump in SMC used by domestic auto makers in '96, from 200 million lb used in 1995 to 240 million lb this year. One outstanding example is Ford Motor Co.'s redesigned AeroMax heavy truck, which carries 450 lb of SMC, reportedly the largest amount for any vehicle. For the 1997 model year, Chrysler's Plymouth Prowler has seven large SMC body panels - front and rear quarter panels, front fenders, and rear valence panel - accounting for 30% of the car's exterior panels. SMC recycling is also growing: More than 20 auto components worldwide contain SMC regrind today, and another 10 are slated for the next few years, say SMCAA sources.

FOCUS ON INTAKE MANIFOLDS

Although injection molded nylon 66 air-intake manifolds made by lost-core and other methods have received much publicity already, the really big swing to nylon intake manifolds on U.S. cars won't come until late '97 and early '98 models, according to Al Winterman, director of BASF Automotive Materials. He says BASF alone has over a dozen projects in development in the U.S. and another 15 in Europe and the Far East. Winterman foresees over 100 million lb of glass-reinforced nylon 66 auto manifolds being used in 2000 worldwide, double his estimate of just a year ago. He expects the U.S. to account for half of the total.

TABLE 1 - PROPERTIES OF NEW TERBLEND S ASA/PC BLENDS

Terblend S Grade

                          KR 2861/1     KR 2864     KR 2865 WU
                          Extrusion,   Extrusion,   Injection
                          Injection    Injection

MFR, g/10 min                3.45         10.35       52.65
Notched Izod Impact,
ft-lb/in. [at] 73 F         11.2          13.1         4.7
[at]-22 F                    2.8           1.5         1.3
HDT, F [at] 66 psi           257           255         181
[at] 264 psi                 223           221         161
UL94 Rating [at] 1.8 mm       HB            HB       V-0(a)

a Non-halogenated.
Source: BASF Corp.

[TABULAR DATA FOR TABLE 2 OMITTED]

Although virtually all the nylon intake manifolds planned for 1997 and '98 cars will be lost-core molded, Winterman says, two-piece welded manifolds will begin making inroads on '99 models because of their lower manufacturing cost. "Welded manifolds are already well on their way in Europe," he says.

In support of that trend, DuPont Automotive introduced a "welding-enhanced" nylon 66 grade for intake manifolds. The new Zytel grade reportedly offers the same thermal and mechanical properties as standard nylon 66, together with a 35% improvement in static burst pressure at the weld joint. Burst strength of the new nylon 66 grade is 160 psi, better than many nylon 6 resins, according to DuPont.

In a related move, DuPont Automotive has invested nearly $500,000 in the past two years on vibration welding equipment to expand its technical-service support for development of welded nylon manifolds.

Meanwhile, AlliedSignal says it has several active auto air-intake programs for its HPN "high-productivity" nylon 6 resin and expects to see a commercial release by the end of the year. HPN reportedly molds 15-50% faster than standard nylon 6 and vibration welds faster too, according to Kevin Byrne, director of sales and marketing. AlliedSignal plans to expand its number of HPN nylon 6 grades to 12 by the end of the year. Also new is a 33% glass-filled nylon that is translucent at 100-mil thickness.

New computer flow-simulation software developed by BASF reportedly predicts the tendency of core shift during injection molding of intake manifolds, reducing undesirable variations in wall thicknesses. BASF says this software addresses a critical potential problem in molding around soft tin-bismuth alloy cores for the lost-core technique. The software predicts cavity-pressure distribution around the core and links the results to a mechanical structural simulation of core displacement caused by uneven pressure distribution in the cavity during the filling stage. One reported advantage of the core shift software is the ease with which the solid model of the core is constructed from the shell model used for flow simulation. Causes of core deformation can be judged and the effects of changing filling behavior can be evaluated by superimposing the core-deformation and melt-flow simulations at different stages.

NEWS IN AUTO INTERIORS

New PVC micropellets were introduced by Teknor Apex Co. as an alternative to drysols and plastisols in rotocasting interior automotive applications. Drysols (easy-flowing PVC powder dryblends) do not slush mold at durometers below 55 Shore A, say Teknor sources, because the compound does not "dry out" and therefore won't distribute well over all areas of the mold. In addition, modifier resins like TP urethane or nitrile rubber cannot readily be added to drysols or plastisols without expensive cryogenic grinding. Even then, compound homogeneity is still suspect, according to Teknor. These drawbacks are overcome by melt mixing the PVC with plasticizers and modifiers, resulting in a homogeneous product that is then converted back to free-flowing micropellets that can be slush molded or roto-molded. The nearly spherical micro-pellets have diameters of 1.25 mm or less, which can be controlled to meet the needs of the part design or manufacturing process.

Hoechst Celanese's Advanced Materials Group introduced two new grades of Vandar PBT polyester alloy that are said to offer improved paintability with primerless, solvent-based, and waterborne paint systems. Vandar 9118 (35 Shore D hardness) is designed for injection molded "soft touch" single-piece airbag doors. Vandar 9114 (57 Shore D) is suitable for parts such as airbag doors that require the look and feel of a harder surface. Both grades are aimed at new "invisible" airbag-door designs that utilize a molded-in crease on the back side, so that the airbag can tear through the seam when it inflates. The resins are said to exhibit splinter-less tear-off along split lines over a temperature range of -40 F to 180 F, as well as low energy consumption during tear-off, high strength in hinge regions, and excellent dimensional stability.

Auto interior parts such as instrument panels are one intended application of three new Terblend S ASA/PC blends from BASF Corp. (see Table 1). They're also aimed at truck mirror housings, electrical distribution boxes, lawn mower decks, and housings for motors and portable computers. ASA/PC is more weatherable than ABS/PC and also has greater resistance to heat aging, BASF reports.

Interior applications are one target for Montell's new Hivalloy propylene-based engineering alloys. These novel resins are based on unique polymerization technology in which an amorphous monomer such as styrene is diffused into a porous PP particle and reacts, producing a graft-copolymer alloy. When subjected to extrusion compounding, melt mixing of the two phases pro duces an extremely fine, uniform dispersion, Montell reports. One of the newest versions is the Hivalloy W series of PP/PMMA alloys, which are said to offer better stiffness than the initial Hivalloy G PP/PS grades, as well as good low-temperature impact, colorability, and weatherability. Hivalloy W is expected to become commercial in May or June. Another new series, Hivalloy T (PP/SMA copolymer), is expected to reach the market around August or September. It has higher HDT and is being evaluated for under-hood applications such as timing-belt covers.

EASIER RECYCLING

One potential application of Montell's Hivalloy W, in particular, is to enhance recyclability of auto-interior components. Montell reported at the SAE conference on experiments with ground-up blends of Hivalloy W and typical instrument-panel skin consisting of a tri-laminate of expanded PVC skin, PUR back coating, and vinyl-acrylic topcoat. The extrusion blended and remolded mixtures reportedly showed good surface appearance and reasonable mechanical properties. Montell speculates that the acrylic portion of the alloy compatibilizes the PVC in the blend. According to Ken Dargis, director of business development for Hivalloy, these results suggest that if Hivalloy W were used as the rigid IP substrate, then the entire IP could be ground and remolded without stripping and separating incompatible materials. Reducing the amount of disassembly would presumably improve the economics of recycling.

Dargis noted that another concept for a readily recyclable IP would use its Hivalloy G as the rigid substrate, together with PP foam cushioning and a flexible skin of a propylene copolymer made by Montell's Catalloy process.

Equipment developments will also aid automotive plastics recycling. Two new plastics-identification systems focus on portability. The P/ID 22 from Bruker Instruments is a smaller, more portable, and lower-cost ($35,000) version of the P/ID 28 instrument introduced last year. It also reportedly has improved accuracy and an increased library of recognizable plastics. The P/ID 22 uses mid-infrared sensing to identify plastics within 5 sec and is operated by a notebook computer.

Also new is the hand-held Tribopen device, developed by the University of South Hampton in England and manufactured under license by Fluid Film Devices Ltd., also in the U.K. It uses an electrostatic sensing head to help sort mixtures of certain plastics (e.g., PP and polycarbonate) based on tribo-electric properties (electrically induced static charge).

RELATED ARTICLE: Plastic/Metal Cross-Car Beam Advances "Outsert" Molding Method

A plastic-on-metal "outsert" injection molding technique championed by Bayer Corp. moved closer to commercialization with the development last year of a plastic/metal hybrid cross-car beam for instrument-panel support. The part was a joint project of Bayer, General Motors, and GM's Inland Fisher Guide Div. (now Dephi Automotive). Although it was originally intended for a 1997 vehicle, Bayer now expects it to appear in 1998.

The beam consists of a simple stamped "U" profile of sheet steel 0.8 m thick, onto which 30% glass-filled nylon 6 is injection molded to provide stiffening ribs and an airbag pocket. This combination of two relatively simple operations achieved a 40% weight reduction with seven fewer parts and 10% lower cost compared with an all-metal beam, Delphi reports.

A key feature of the part is the stamped and extruded holes in the sheet metal, through which the plastic flows to create a "button" that serves to provide mechanical bonding and transfer of load between plastic and metal. The X-shaped nylon ribs have a nominal wall thickness of 0.118 in. and a 2 [degrees] draft to facilitate ejection. Special locator pins were designed into the tooling to ensure proper alignment of the large steel insert. Extra cooling was provided to the extended airbag pocket. The two outer lips of the open U-profile are encapsulated with about 0.158 in. of plastic around the entire insert, providing added stiffness as well as a convenient flow channel for filling the large mold.

The tool was optimized in two mold trials using a 2000-ton press. Metal inserts were hand-loaded, although this can be automated. As the mold closed, the thin sheet metal warmed up almost instantly to the mold temperature. As a result, the average cycle time was 60 sec, essentially the same as for a standard molded part of similar size.