Automotive plastics: recycle-content resins head the news at SAE show.
If Detroit wants to recycle, resin suppliers are ready with the goods. There were more recycle-content engineering resins introduced than any other type of material at this year's annual Society of Automotive Engineers (SAE) Congress in Detroit. Even thermosets saw some interesting recycle developments - most notably in urethane RIM.
Other new materials introductions reflected a trend toward more uv-stable acetals and the growing popularity of thermoplastic elastomers. Also new was a medium-impact ABS developed specifically to use the same color concentrate as general-purpose ABS. Another interesting development is a "thermoformable" epoxy laminate that eliminates the manufacturing constraints of traditional thermoset composites.
RECYCLED RESINS ABOUND
Automotive OEMs continue to demand resin grades that contain some percentage of post-consumer or post-industrial recycled plastic, both thermoplastic and thermoset. Ford Motor Co., for example, says it is aiming for 25% post-consumer reclaim (PCR) content in its plastics parts. At the same time, however, automotive OEMs insist that recycle-content grades must not carry any price premium and their performance must be equivalent to comparable virgin-polymer grades used previously for similar applications.
Retain ABS 7490 from Dow Chemical Co. is a new grade that contains an average of 25% PCR. It's designed for paintable exterior parts. Retain 7490 has tensile strength at yield of 6830 psi, elongation at break of 12%, flexural modulus of 363,200 psi, notched Izod impact of 3.4 ft-lb/in., HDT of 174 F at 264 psi, and Vicat softening [TABULAR DATA OMITTED] point of 230 F. Dow also has a new glass-filled PC/ABS (Retain 8209) with 25% PCR for instrument-panel retainers.
Another new material for IP substrates (already used on several Ford and Mazda vehicles) is Dylark 378 P20A from Arco Chemical. This product consists of Dylark SMA blended with 20% glass and up to 10% recycled acrylic resin. The material was developed jointly with Ford in order to consume acrylic scrap from Ford's taillight and IP lens production. An Arco spokesman said the reclaimed acrylic actually imparts added toughness, compared with virgin SMA grades. Arco says this is the first in a planned line of Dylark products containing up to 25% recycle.
Virgaloy VG101, a new material from MRC Polymers, is composed of recycled polycarbonate and acrylic scrap (from bottles, light lenses, and outdoor signs) with a minimum 25% post-consumer content. MRC sources say Virgaloy costs less than comparable virgin resins and will find applications in automotive, business-equipment, electronic, and lawn-and-garden parts. VG101 offers a specific gravity of 1.19, melt-flow rate of 12 g/10 min, notched Izod impact of 8 ft-lb/in., tensile strength at yield of 9000 psi, elongation at break of 50%, flexural strength of 13,400 psi, flexural modulus of 345,000 psi, and HDT of 200 F at 264 psi.
Three grades of 100%-PCR PET were introduced as DuPont's new Rynite PCR line. The grades differ in their filler/reinforcement type and loading to correspond to various automotive applications, such as exterior trim, structural housings and frames, and headlamp attachment components.
Rynite PCR230 BK505 contains 35% glass and mica content; PRC140 BK504 has 45% glass fiber; and PRC130 BK503 has 30% glass fiber. The company says the three grades offer superior melt flow for multicavity injection molding.
THERMOSET RECYCLING PROGRESSES
There was also news in thermoset recycling at the show. The Chevrolet Corvette is now using a urethane RIM rear fascia containing 10% in-plant RIM scrap. The fascia is molded by Polyrim Greenlane, Markham, Ont., part of Magna International's Decoma Exterior Systems Div. Polyrim grinds and pulverizes sprues, runners, and reject parts (filled or unfilled, painted or unpainted) to less than 250-micron size, then dries the regrind and introduces it into the polyol stream at up to 10% level. This is known as the Dow three-stream process for RIM recycling. Polyrim used the Dow process to produce the first Class-A recycle-content RIM part in North America - fascias for Chrysler minivans (PT, Nov. '94, p. 80).
In addition, Dow has performed studies showing that up to 15% of reground polyester SMC can be used as a lower-cost substitute for milled glass in PUR low-density RRIM for interior and exterior parts. Adding in 5% LDRRIM process scrap can bring the recycled content up to 20%. Dow hopes to push that level to 25%.
UV-STABLE ACETALS PROLIFERATE
Spurred by demand from the Big Three auto builders, all three major U.S. acetal suppliers - DuPont, Hoechst Celanese, and BASF - have recently come out with a new generation of uv-stable acetals. These products address primarily interior applications such as switches and knobs, window handles, and speaker grilles.
Several elements figure into this trend. First, the auto makers want all interior plastic components to be more resistant to sunlight and heat as part of an overall goal of achieving 10-year vehicle life. Weatherability requirements have also become more severe as larger, aerodynamic windshield designs have increased the sunlight exposure of vehicle interiors.
Another trend in acetal is toward molded-in color and fewer painted parts. In the past, the paint would have served as protection against uv light. Acetal producers have had to reformulate their grades and develop new additive packages in order to attain the required uv resistance. This has meant utilizing new pigments and colorants that contain no heavy metals. (U.S. car manufacturers will not accept plastic parts that contain cadmium pigments beginning in the 1998 model year.)
Richard Bell, development manager for DuPont Automotive, says acetals traditionally have experienced some difficulty in achieving a broad range of colors - especially reds - without cadmium-based pigments, due to the resin's reactivity with organic colorants. He says the newer acetal formulations overcome this problem.
Kenneth D. Baraw, manager of applications development for BASF Corp., notes that in the past, nylon or PBT had been used for these interior parts, but auto builders recently have shown a preference for acetal because of its superior surface properties. However, prior to the advent of enhanced uv-stabilization packages, acetal had been considered prone to color shifts and color-matching problems due to sensitivity to compounding and processing. The auto builders are now seeking tighter tolerances on color matching for interior parts, Baraw says.
The newest entry in uv-stable acetals is DuPont's Delrin 527 homopolymer. After exposure to 600 kJ/[m.sup.2] of xenon-arc accelerated testing, it reportedly retains 80% or more of its initial elongation, compared with 30-40% for Delrin 507, an earlier uv-stabilized acetal. In the same test, Delrin 527 shows a color change of about 2 "Delta E" units, vs. 7 units for Delrin 507. And accelerated air-oven aging for 40 days at 266 F shows twice the stability of an earlier-generation uv-stabilized grade. DuPont says the new product has three times the short-term thermal stability of previous uv-stabilized grades, providing molders with greater processing latitude and perhaps the possibility of using higher regrind levels. It also has a notched Izod impact strength of 0.93 ft-lb/in.
Late last year, BASF launched Ultraform N2320-U017 acetal copolymer for auto interior parts (see PT, Jan. '95, p. 55). The company says its new stabilization package provides superior weathering properties without the loss of impact that can occur with other uv stabilizers and carbon black. Notched Izod value is 1.30 ft-lb/in., equivalent to the natural version of this resin. Xenon-arc accelerated testing according to SAE J1885 reportedly shows this material can withstand uv exposures up to 750 kJ/[m.sup.2] with Delta E values well below 3.
And in mid-1993, Hoechst Celanese introduced Celcon UV90Z cadmium-free, precolored acetals that were said to provide 50% improvement in uv stability over cadmium-pigmented Celcon grades. Selected colors were exposed to 1240.8 kJ/[m.sup.2] in a xenon-arc chamber under SAE test method J1885. The average color difference was less than 1 CIELab unit, vs. up to 17 units for competitive acetals. Automotive specs typically allow no more than 3 CIELab units of color change. Notched Izod impact value is 2.6 ft-lb/in.
NEWS IN TP ELASTOMERS
Thermoplastic elastomers lately have been a focus of active development. Two suppliers showed off new products at SAE.
A pair of higher-durometer grades have been added to the Sarlink 4000 Series of PP/EPDM thermoplastic vulcanizates (TPVs) from DSM Thermoplastic Elastomers. This is DSM's newest line of TPEs, which competes directly with Santoprene TPVs from Advanced Elastomer Systems (AES), St. Louis. New Sarlink 4139D (39 Shore D) and 4149D (49 Shore D) are suitable for blow molded air ducts and flexible "boots," injection molded cable grommets, and extruded cable and hose covers. The Sarlink 4000 series now ranges from 65 Shore A to 49 D. DSM is also test marketing a softer 55 A material for weather seals and gasketing.
The new grades are designed to retain mechanical properties under heat aging conditions (92% retention of tensile strength after 168 hr at 302 F) while providing superior oil resistance and good compression set and flex fatigue. The 4139D grade has a tensile strength of 2596 psi and an ultimate elongation of 570%.
Two soft TP elastomer grades with reportedly superior compression set were introduced by Tekron Apex Co. Two new grades in its Tekron 4000 Series of styrenic block copolymer (SBC) TPEs (based on Shell's Kraton G) are designed to replace EPDM in gaskets for General Motors cars.
Tekron 4000-60 and 4000-30 (60 and 30 Shore A, respectively) have a specific gravity of 1.18. Tensile strength of 4000-60 is 1280 psi; that of 4000-30 is 840 psi. Elongation of 4000-60 is 725% and flex modulus is 4700 psi, vs. 830% elongation and 400 psi modulus for grade 4000-30.
'CO-COLORABLE' ABS DEBUTS
Dow aims to cut costs and reduce inventories for molders of low-gloss automotive interior trim with a new grade of medium-heat ABS that can utilize the same color concentrates as Dow's g-p ABS. New Magnum 344CC accepts concentrates developed for Magnum 342EZ ABS without changing the 25:1 letdown ratio. In developing this product, Dow found that use of n-phenyl maleimide as a comonomer for added heat resistance makes the resin more co-colorable than does alphamethyl styrene.
BLOW MOLDABLE NYLONS
Nylon can be a lower-cost blow molding material than PP, despite nylon's higher cost and specific gravity. AlliedSignal Plastics makes that case in an SAE paper concerning applications such as resonators and other underhood air-induction components that must resist temperature spikes up to 300 F. Because of its higher HDT, nylon 6 can be blow molded much thinner for such parts than PP and can provide equivalent performance, as well as lighter weight and lower cost, AlliedSignal claims.
Two more materials have joined the company's series of blow moldable modified nylon 6 compounds that are said to offer a wide processing window, excellent parison strength (up to 15-lb parisons have been molded), and good melt extensibility for complex shapes. Capron 8274G HS is a nylon 6 with 30% glass, and Dimension D9300 is an unfilled nylon 6/PPO alloy. AlliedSignal is also developing glass-filled Dimension blow molding grades.
A new SMA grade from Arco Chemical is dubbed "universal Dylark" because it offers an optimal combination of the properties of all currently commercial grades. Besides simplifying customer purchasing and inventories, new Dylark 480 offers improved toughness and lower specific gravity. The latter property reportedly makes it possible to create parts with the stiffness of higher-glass-content grades at up to 3% lower weight.
Dylark 480 comes with 12%, 16%, and 20% glass and offers specific gravities of 1.15 to 1.20, tensile strengths of 9250 to 12,050 psi, flexural moduli of 608,000 to 815,000 psi, HDTs of 239-244 F at 264 psi, and notched Izod values of 1.6 to 1.9 ft.-lb/in.
A new reinforced epoxy laminate supplied in cured board form can be reshaped at temperatures less than 392 F with the application of only vacuum pressure. Hexcel Corp. originally developed this novel material for athletic footwear but envisions possible industrial applications such as small leaf springs, lever arms, high-strength covers, and selective reinforcement of larger molded components. Sports equipment is another potential market.
The laminate is composed of a highly modified epoxy and woven or nonwoven glass fabric. The resin's glass-transition temperature is around 212 F. Net-shape blanks are precut from the board (water jets are applicable for high-volume uses) and then formed in net-shape tools. Formed parts reportedly exhibit no springback and no shrinkage. For high-performance applications, Hexcel recommends annealing for 30 rain at 194 F to relieve the forming stresses.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||Society of Automotive Engineers Congress|
|Author:||Gabriele, Michael C.|
|Date:||Apr 1, 1995|
|Previous Article:||How to injection mold metallocene polyolefins.|
|Next Article:||Which twin-screw compounder is for you?|