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New polymers and processes for plastics in automotive.

The auto industry is suffering from a weight problem. As designers continue searching for methods to chop a few pounds from each car so their vehicles comply with rising fuel-efficiency standards, some effort is being put into developing ways to mold thinner, yet still strong body panels. This was the subject of considerable discussion at February's 1992 SAE World Congress and Exposition in Detroit. Among the more newsworthy presentations was a new form of stampable glass-reinforced thermoplastic sheet that can take on-line E-coating and achieve a Class A finish with the aid of an in-mold coating. Another novelty was a developmental SRIM formulation that achieves a Class A surface. There was also talk of an entirely new thermoplastic for body panels. Besides exterior panels, there was also news in plastics for interior and exterior trim, under the hood, blow molded gas tanks and seating foams.

HORIZONTAL TP BODY PANELS

What was billed as the first thermoplastic system for Class A horizontal body panels was introduced in developmental form by Du Pont Automotive Products, Troy, Mich. Du Pont has come up with a novel stampable glass-reinforced PET sheet, known as Du Pont XTC. Unlike other reinforced TP sheet products on the market, this one is supplied in roll form, rather than consolidated slabs. The slit-to-width roll stock is made by a wet-laying, papermaking type of process (with resin in a fiber form), which results in a porous scrim of random 1-in. fibers, weighing a little more than 1 lb/sq meter. A photomicrograph of the sheet reveals that in drying, the resin fibers are fused, leaving an irregular coating on the glass fibers (which flows and becomes more uniform during press consolidation). Two grades, with 25% and 40% glass, are now being studied.

About 14 layers of XTC sheet can be stacked to mold a panel of 100-mil final thickness. The porous nature of the sheet makes heating very easy, without predrying, Du Pont says. In an oven, forced hot air at 525-570 F can be blown through the sheet stack, simultaneously drying the thin layer of polymer on the glass and heating it to its melting point in 30-45 sec. A proprietary additive package reportedly minimizes change in molecular weight.

Like SMC, XTC parts are molded in a high-speed compression press with shear-edge tools. Du Pont achieves a Class A finish by injecting an adhering thermoset in-mold coating (IMC) into the closed mold during the cycle. Du Pont says various commercial IMCs for SMC have been used successfully. Button-to-button cycle times of 60-75 sec are claimed. Coated parts reportedly show little or no warpage on cooling in fixtures.

Du Pont says Class A finish has been demonstrated in actual assembly-plant paint trials. Because of the high heat-distortion temperature of the sheet (495 F at 264 psi), it can withstand on-line electrocoat painting (e.g., 390 F for 30 min) along with steel panels, according to Du Pont. Unlike SMC, it does not require sanding or other post-finishing. Instrumented surface analysis reveals a finish exceeding SMC standards, the company says. Conventional adhesives bond XTC sheet with even higher strength than is attained with SMC.

Martin D. Drigotas, senior development programs manager, says XTC sheet matches the mechanical and thermal-expansion properties of SMC, while offering 15% weight savings, and is expected to be cost-competitive with SMC on a total-system basis. Du Pont also notes that XTC is readily recyclable-- either by granulating scrap for injection molding, or by depolymerizing the PET back to precursor chemicals (via methanolysis) and then repolymerizing it to "virgin" PET. (CIRCLE 9)

NEW BODY-PANEL POLYMER IN R&D

What's said to be an entirely new thermoplastic for injection molded exterior body panels is now being developed by Dow Plastics, Midland, Mich. Still several years away from potential commercial development, according to Robert D. Albert, v.p. of Dow's Automotive Materials Group, the unnamed new copolymer has an HDT of 400 F, giving it on-line paintability with steel panels. Early research indicates the new polymer offers lower moisture absorption and better dimensional stability than existing body-panel resins, while attaining a TABULAR DATA OMITTED Class-A surface finish and DOI comparable to steel.

SRIM VIES FOR BODY PANELS

Among the more interesting concepts talked about was a developmental program at Miles Inc., Pittsburgh, to use structural RIM (SRIM) for exterior body panels. According to Miles, a Class A surface comparable to SMC is possible at a 30% weight savings. Miles demonstrated this with a Pontiac Fiero hood tool, STR/C 400 polyurethane system, continuous-strand glass mat, and a fine glass-fiber surfacing veil, together with an externally applied wax mold release. In a 600-ton Cannon clamp, cure time was about 90 sec. Miles calculated its SRIM process was about 7% more costly than molding the part from SMC. The hoods, Miles says, had DOI, Ashland Index, D-Sight, and Orange Peel surface analysis results equal to or better than SMC parts. (CIRCLE 10)

Dow Plastics explained a means of downgauging particulate-reinforced RIM (RRIM) components in order to lower fascia costs while actually improving the quality of the parts. Dow says wall thicknesses can be reduced from the current 4-4.5 mm down to 3.2 mm by replacing the 12% milled glass filler frequently used in RIM fascia with an equal amount of mica filler in a polyurethane/urea or high-performance polyurea matrix resin. This, the company claims, results in parts with a 23% weight reduction but with the necessary impact resistance and improved painted surface quality and dimensional stability. (CIRCLE 11)

The RRIM process is also getting some consideration for interior applications. Both Dow and ICI Polyurethanes of West Deptford, N.J., discussed efforts in this direction. Dow's work, aimed at vinyl-covered door panels, instrument panels, spare-tire covers and seat backs, suggests that certain polyurethane systems with internal mold release and low-cost fillers like wollastonite can reduce cycle times by about a third and material costs by 7-10%. Compared with thermoplastics and pressed wood used for these same applications, as much as a 40% weight savings can be realized by using these systems, Dow claims. The resulting components, Dow says, have mechanical properties just about equal to glass-mat reinforced thermoplastic sheet substrates. RIM is also attractive, Dow says, because it can be used to mold the urethane directly onto the vinyl and cloth surfaces and fasteners or attachments can be molded in place, making parts ready for assembly upon removal from the mold.

Dow has developed two methods to make these lighter weight panels. The first, called low-density mat molding, involves injection and foaming over a reinforcing mat. The second method, low-density RRIM, incorporates a short-fiber reinforcement in the liquid resin. Both approaches use carbon dioxide generated from water reacting with isocyanate as the blowing agent. (CIRCLE 12)

ICI, too, has developed low-density polyurethane resins for SRIM interior trim. ICI's systems are designed for use with glass mat and also are aimed at weight reduction. ICI says the RIM-line GMR-8700 system can provide as much as 50% weight savings over other materials. (CIRCLE 13)

Another new development in body-panel thermosets was a one-component, low-profile polyester said to be the first RTM resin that can withstand a bake cycle of 1 hr at 400 F without gel coating and provide a Class A finish. Arotran Q-6530, introduced by Ashland Chemical Co., Columbus, Ohio, can be on-line painted along with steel and SMC panels. (CIRCLE 33)

PVC FOR TRIM

Developmental flexible vinyl blow molding compounds and reinforced flexible PVCs aimed at replacing a variety of thermoplastics currently used in automotive parts were introduced by BFGoodrich Co., Cleveland. Glass-reinforced flexible PVC will challenge painted, glass-reinforced TPUs, TPOs and TPEs in body side molding and cladding trim packages, BFG says. These compounds offer the advantage of adhering easily to other vinyls using in-mold film transfer or overmolding. According to preliminary data, the reinforced PVCs reportedly offer excellent flow properties, good heat-sag resistance at 250 F, CLTEs less than 2.5 x |10.sup.-5~ in./in./|degrees~F, flex moduli between 14,000 and 354,000 psi, and notched Izod impact strengths from 6 to 10 ft-lb/in. (CIRCLE 14)

The blow molding compounds, which the company hopes to commercialize in the second half of this year, are designed for interior trim. They offer very low gloss and Shore A hardnesses of 65 to 85. Market manager Ken Moore, Sr. says blow molding offers more efficient material utilization than vinyl slush molding, which produces heavy walls and a lot of scrap. Vacuum forming produces somewhat less scrap, but sacrifices esthetic detailing. And injection molding has design limitations and high tooling costs relative to blow molding. According to Moore, future PVC developments from BFG will enable blow molding of large parts to withstand long-term exposure to temperatures up to 250 F. BFG has molded parts from parisons up to 5 ft long. (CIRCLE 15)

PLATABLE PC/ABS ALLOY

A new PC/ABS alloy contains additives to enhance chrome-plating adhesion. TAPP 2100-Triax 2953 was developed by Monsanto Chemical Co., St. Louis, in cooperation with Siegel-Robert Inc., a molder and plater of automotive parts in Farmington Hills, Mich. The alloy offers a continuous-use temperature of 230 F. Priced at about $2.40/lb tl, it has been approved by GM and Ford. (CIRCLE 16)

Another new material from Monsanto is Vydyne R525 nylon 66, a 25% glass-filled grade which replaces a 33%-glass grade known as Vydyne R538H The new grade features a newly optimized glass fiber, providing better flow characteristics and surface appearance than the higher-glass material, with comparable rigidity and dimensional stability. R525 has a continuous-use temperature in excess of 300 F, making it suitable for under-hood components. (CIRCLE 17)

MELT-PROCESSABLE PBI

The Houston-based PBI Performance Parts Group of Hoechst Celanese Corp. this year will begin injection molding high-performance automotive parts, such as piston rings, valve guides, bearings, connectors, and brake components, from four grades of a new melt-processable Celazole T-Series polybenzimidazole (PBI) blend. At present, the company is currently selling molded parts, produced with proprietary technology, rather than raw material. But the company eventually may sell the resin and/or license the technology to other processors, once they are demonstrated to be commercially viable for automotive parts.

In pure form, PBI is a non-melting resin that is processed by sintering. To make it melt-processable, the PBI is blended in a polyetherketone matrix through a proprietary extrusion process, according to Lorenzo DiSano, technical marketing and development manager. The company will compound four grades of the Celazole PBI T-Series: unfilled, 30% glass or carbon fiber, and graphite-lubricated.

Properties of the unfilled grade include a tensile strength of 16,000 psi, elongation of 2.8%, a flexural strength of 24,500 psi, flex modulus of 815,000 psi, compressive strength of 30,000 psi, specific gravity of 1.3, and HDT above 600 F. (CIRCLE 18)

GAS-TANK TECHNOLOGY

Solvay Automotive Inc., Troy, Mich., which reportedly produces about 60% of all HDPE automotive fuel tanks in North America, is seeking to license its Solvay Optimized Fluorination Process. President Norman W. Johnston says the company's process rivals the permeation resistance of coextrusion with EVOH.

The technology involves the in-situ introduction of fluorine gas during the blow molding process. Tests reportedly show that the technology yields hydrocarbon permeation rates of 0.1 to 0.4 gm per day. (CIRCLE 19)

ADHESIVE-FREE SEATING

For the past few years, foam-in-place technology has been on the cutting edge of automobile seat making. SAE '92 offered a first-time look at a new process--Trim Retention Bonding. Introduced by Woodbridge Foam Corp. of Mississauga, Ontario, the process uses an MDI-based foam poured into a mold cavity to bond a foam-pad base and a fabric seat cover.

The TDI-based foam pad is placed in the bottom of the mold while a vacuum holds the seat cover in the top of the mold. After a robot pours a measured dosage of MDI-based foam formulation into the hollow cavity between the seat pad and cover, the foam is allowed to rise and as much gas as possible is removed. The mold is then closed and after about 2 min, the liquid MDI has adhered to both the TDI pad and the fabric cover, resulting in a completed, adhesive-free seat. (Urethane chemicals for the process come from Dow.) There is about a 2% scrap rate. The company has reportedly received its first production order to manufacture front and rear seats for 40,000 vehicles. (CIRCLE 20)

Also aimed at seat producers is a new PHD polyol--Multranol 9184--from the Polymers Div. of Miles, Inc. The new polyol reportedly provides increased load-building capacity in high-resilience (HR) urethane foams, allowing seat makers to achieve higher hardness values with little or no increase in polyol level nor any loss in physical and processing properties. (CIRCLE 21)
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Title Annotation:automobile industry
Author:Monks, Richard
Publication:Plastics Technology
Date:Apr 1, 1992
Words:2130
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