Cost savings drive R&D on automotive materials.

This year's SAE show in Detroit brought improved economy and performance in plastics for under the hood, fuel systems, electronics, interiors, and exteriors.

Automotive engineers' obsession with cost reduction appeared to be pushing materials developments at the recent annual Society of Automotive Engineers International Congress and Exposition in Detroit. The newest engineering thermoplastic grades pack more performance at the same or lower cost or else promise to reduce cycle times or eliminate processing steps. For auto interiors, new precolored and scratch- or mar-resistant TPEs eliminate the need for painting. Under the hood, new high-flow nylons and fuel-resistant acetals cycle faster. And for exteriors, a new heat-resistant grade of reinforced PET can survive on-line E-coating without distortion, allowing assembly steps to be streamlined.

ACTION UNDER THE HOOD

Much of the excitement at this year's show concerned new materials for electronic parts and fuel-system components. Key challenges are more aggressive new fuel formulations and tough new USCAR standards on temperature and humidity cycling.

Exceptional dimensional stability for on-engine applications is reportedly offered by a new nylon 66 with 30% glass beads from Hoechst Technical Polymers. Heat stabilized NFX-0102 maintains 0.0005-in. tolerances on critical hole sizes, Hoechst says. This low-warp grade is molded into carburetor housings where fuel and air intake geometry is critical. Unlike mineral or chopped-glass reinforcements, glass beads are said to impart nearly isotropic shrinkage (just 0.012 in./in. in the flow direction). The material reportedly also holds dimensions despite prolonged exposure to heat, gasoline, and other chemicals.

A new impact-modified nylon 6 from AlliedSignal contains 25% post-consumer recycled (PCR) materials and 75% post-industrial material. Nypel XB-2461HS BK-102 is expected to be in full production 'at the end of 1997. It's recommended for convoluted tubing used under the hood and for windshield wipers.

Celstran PPG40-03, is a new heat-stabilized PP compound with 40% long glass (0.43 in.) from Hoechst Technical Polymers. It has 5 ft lb/in. notched Izod impact, which is said to be four to five times higher than short-glass-rein-forced PP. It's HDT of 310 F at 264 psi is said to suit it to under-hood uses. Specific gravity of 1.21 is 40% lighter than glass-filled PET and - unlike PET - the PP needs no drying. The compound has 16,000 psi tensile strength, 25,400 psi flexural strength, and 1.1 million psi flex modulus.

LNP has a new family of PEEK compounds that meet requirements for lubricity and heat resistance up to 300 F in transmission and under-hood parts. Three grades include PTFE and carbon fibers. Lubricomp LCL is aimed at transmission components. Lubricomp LTW has better wet-lube performance. Lubricomp LCS is similar to Lubricomp LCL in mechanical properties but costs less.

Improved fuel resistance (minimal swell) is one advantage claimed for new Delrin 511P acetal from DuPont (see PT, Nov. '96, p. 14). Lower shrinkage, faster cycles, and improved mechanical properties are also claimed.

THE HEAT IS ON ELECTRONICS

High-flow Zytel DMX modified nylon 66 was introduced by DuPont Automotive for connectors. Zytel DMX offers three times the flow rate of PBT and twice that of PPE/nylon alloys, DuPont says, making possible thin wall sections for smaller connectors and reduced package size for junction and distributor boxes. Such downsizing will allow engineers to meet goals of 50% weight reduction in wire harnesses, according to DuPont.

Zytel DMX also reportedly outperforms competitive connector materials in USCAR/EWCAP Class III heat aging and hydrolysis testing at 125 C. Mechanical properties of DMX regrind, even after five passes, are said to be higher than those of competing connector materials. DMX is available in 15% and 30% glass-filled versions, and is priced competitively with PPE/nylon.

New hydrolysis-resistant poly-esters for injection molding from GE Plastics reportedly meet class III and class IV USCAR specs for aggressive temperature and humidity cycling. These are lower-viscosity versions of unreinforced hydrolysis-resistant PBTs that were introduced by GE Plastics in 1993 for extrusion of fiber-optic cables. The new unfilled and 30% glass-filled injection grades reportedly have rheology similar to standard polyesters. The company is now applying this hydrolysis-resistant technology to blends of PBT with other polymers.

Eastman Chemical Co. introduced its first commercial liquid-crystal polymer, which boasts very high heat resistance, inherent flame resistance, and very high flow (see table). Thermx LG431 contains 30% glass and comes in black and natural. Eastman says it has excellent dimensional stability, fast molding cycles, low shrinkage, and negligible flashing tendency. It's priced competitively with other LCPs at $6-7/lb.

New Thermx EG glass-reinforced PETs were also introduced by Eastman. Priced around $1.50-1.60/lb, the five new grades are said to offer better mechanical properties and process-ability at 25% lower cost than existing Thermx GFR PET compounds. Processing advantages are lower viscosity and full crystallinity at lower mold temperatures (200-220 F), which may permit the use of hot-water molds and result in faster cycles. The new grades are offered with 15%, 20%, 30%, and 45% glass and with 40% glass/mineral combination.

Faster cycles and the ability to use hot-water molds are also attributed to a new generation of glass-reinforced Thermx PCT polyesters from Eastman. They are said to have improved physical and mechanical properties and better processing than earlier Thermx PCT grades. Compatible with surface-mount and infrared-oven soldering temperatures, Thermx CG923 (20% glass), Thermx CG933 (30% glass), and Thermx CG943 (40% glass) reportedly offer higher HDTs, improved ductility, better Izod impact and elongation, lower viscosity, and lower volatility. Priced between $2.60 and $2.80/lb, the new grades are available in white and colors.

THERMX 30% GLASS-FILLED LCP

Specific Gravity                                                1.61
Flow Rate, g/10 min                                              115
Drying Temp., F                                              250-310
Drying Time, hr                                                  4-6
Melt Processing Temp., F                                         640
Mold Temp., F                                                100-200
Deflection Temp. @264 psi, F                                     554
UL94 Flammability @0.03125 in.                                   V-0
Ultimate Tensile Strength, psi                                22,000
Ultimate Elongation, %                                           1.8
Flexural Strength, psi                                        27,850
Izod Impact Str., ft-lb/in.                                      2.0
Dielectric Constant @1 khz                                      2.99
Dissipation Factor @1 khz                                    0.00846

NEW INTERIOR RESINS

The new series of Pulse 2000 PC/ABS resins for energy-management and interior-trim parts was introduced by Dow Automotive. The basic Pulse 2000 resin is for injection molding painted or covered parts. Pulse 2100LG provides low gloss for injection molded parts with molded-in color. A third new grade, Pulse 2200BG, is designed for blow molding painted or covered energy-management system components such as knee bolsters.

Also new is the first application for Dow's Retain PC/ABS, which contains 25% PCR. Introduced about a year ago, Retain PC/ABS is making its commercial debut in the 1997 Buick Park Avenue instrument-panel topper pad and the '97 Buick Regal defroster grille. In both parts, Retain PC/ABS replaced virgin glass-filled SMA and reduced breakage problems, Dow says.

New thermoplastic elastomers that resist scuffing and marring were introduced by Teknor Apex for airbag covers. The new formulations of Telcar TPO and Tekron styrenic-copolymer TPE are said to be suitable for precoloring. The company estimates that the new compounds could save $1/part by eliminating painting.

New scratch-resistant grades of Polyforte polypropylene have been developed by A. Schulman as lower-cost alternatives to painted ABS, PC, ABS/PC, and PPE alloys. The new grades reportedly combine uniform, low gloss with superior uv resistance for unpainted interior applications.

FOR EXTERIOR AND OTHER USES

A new grade of reinforced PET is said to overcome dimensional instability of current glass/mineral-reinforced grades at the 200 C (392 F) oven temperatures used to cure body E-coats. Although current materials have HDTs well above 200 C, they still can show unacceptable shrinkage or warpage at E-coat temperatures due to "cold crystallization," say researchers at Hoechst Technical Polymers. It's new Impet EKX-163 glass/mineral-filled injection grade is said to overcome this problem and can therefore eliminate the off-line painting currently used for most PET exterior parts. Impet EKX-163 has an HDT of 218 C (424 F) at 264 psi and 471 F at 66 psi.

A new polyurethane RIM resin for painted body side trim was introduced by Dow Automotive. Spectrim BST has low coefficient of thermal expansion, high distinctness of image (DOI), superior paint adhesion, and improved chip and gouge resistance, Dow says.

Two new grades of long-glass reinforced thermoplastics from Hoechst contain glass fibers 0.43 in. long and provide exceptional stiffness.

* Celstran PPSG50-01-4, 50% glass in linear PPS, has a notched Izod impact strength of 6 ft-lb/in., four to five times that of short-glass PPS. Flexural modulus is 2.46 million psi, and HDT is 540 F at 264 psi. The material is used in a sensor cap for an anti-lock braking system.

* Celstran ACG40-01-4, 40% glass in acetal copolymer, has 7.9 ft-lb/in. notched Izod - seven times that of conventional glass-coupled acetal. Flex modulus is 1.65 million psi. It's aimed at window-lift gears, windshield-wiper pivot housings, and other mechanical parts.

RELATED ARTICLE: New Gasketing Technique Cuts Costs

What is described as an improved foam-in-place gasketing technique for automotive rear lighting assemblies is said to save costs, reduce material consumption, and eliminate tedious manual operations. Norton Performance Plastics developed the technique to utilize its Dynafoam gasketing material, a single-component, rubber-modified thermosetting polyester compound that is applied in place and cures quickly at ambient humidity.

Used in Europe since 1992, the new technique is said to cut gasket installation costs by 55% on average. Dynafoam is claimed to have several processing advantages. It holds its shape right out of the nozzle, even when applied to an incline or upside down. It adheres well to many substrates, requires no adhesive, and generates minimal waste. It has heat resistance to 285 F and also resists chemicals, solvents, weather, ozone, and exhaust fumes, Norton says. Several U.S. rear-light applications are now in the late stages of development.

Norton's patented "transfer molding" process is said to have advantages in applying foam-in-place gaskets to difficult 3-D surfaces. It will hold it's shape in very large profiles. Many light assemblies require the gasket to be applied to severely inclined surfaces (greater than 50 [degrees]). Conventional foam-in-place materials are too runny to stay put on an inclined part or to be transfer molded, says Norton. Light manufacturers have been forced to use hand-placed, die-cut gaskets instead.

Norton's material and process offer a solution to this problem. In the first step, Dynafoam is dispensed into a groove of a specially treated, water-cooled mold. The mold filled with Dynafoam is then pressed onto the part to be gasketed. Five seconds later, the mold is removed, leaving the gasket adhering to the part. Depending on the size and shape of the gasket, total processing time runs 7 to 20 sec. Dynafoam reacts quickly with ambient moisture, causing the outer skin of the gasket to cure. Full curing will occur as the gasket continues to absorb ambient moisture, or the gasketed parts can be run through a humidity cabinet for 12 to 20 min.

Compared with conventional foam-in-place methods, Dynafoam gasket transfer molding reportedly offers several advantages. The gasket can be molded easily to flat, round, or triangular cross sections - which can even change throughout the gasket. Height of the gasket can exceed its width. (In other foam-in-place methods, the height of the gasket is typically half the width.) Molding also provides superior consistency in gasket size and surface finish, Norton says. The Dynafoam process is claimed to create an effective water seal around the part using 30% less material.

Norton claims that several European manufacturers have used the Dynafoam gasketing technique to achieve savings of $1-2 per car and reduce material volumes sevenfold. Automated turnkey work cells, including foam dispenser, molds, and parts-handling equipment, ranges from $250,000 to $450,000, depending on the complexity of automation.

RELATED ARTICLE: SMC Hogs the Road

Although most of the attention at SAE was focused on thermoplastics, the number of SMC components on 1997 cars and trucks continues to climb. There are 106 new components (out of 438 total) on 29 North American cars and trucks in 1997, according to the SMC Automotive Alliance, Troy, Mich. Although body panels represent 85% of the SMC applications, there were also 38 new structural SMC components in 1997.

Notable SMC parts this year include a Jeep Wrangler roof with the first pigmented SMC that eliminates the need for painting the roof's interior. All of the major exterior panels on GM's first electric car are made from low-density SMC, which has a specific gravity of 1.3 versus 1.9 for conventional SMC. Kenworth's T-2000 class-8 truck has 1000 lb of SMC, representing the single largest use of SMC. It also has what's said to be the largest SMC automotive part in its sleeper-cab roof (see PT, March '97, p. 36).

In the interest of lowering SMC processing costs, one resin supplier, Ashland Chemical, is working on lowering the cure temperature of its SMC Lite low-density/low-pressure formulation to 150 F. That will allow its use with lower-cost epoxy tooling, according to David Hearn, sales and technical service manager of Ashland Chemical's automotive molding resins. Epoxy, kirksite, or cast-aluminum tools are also said to be usable with new low-pres-sure/low-temperature SMC from Cambridge Industries, Madison Heights, Mich. It can be molded at as little as 100 psi and 180 F.