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PVC-based TPE's seek niche in automotive, wire & cable markets.

PVC-Based TPE's Seek Niche in Automotive, Wire & Cable Markets

Two new lines of vinyl-based thermoplastic elastomers are seeking to establish footholds in automotive and wire and cable cable. These are believed to be the first domestically produced examples of a new class of TPE's based on PVC with some sort of elastomeric modification (see PT, Aug. '88, p. 46). Both appear to be based on non-traditional PVC resins, and neither uses nitrile rubber in the blend, unlike two PVC TPE's being imported from Japan. The Sunprene Co., a Bellevue, Ohio, joint venture of A. Schullman Inc. and Mitsubishi Kasei Vinyl Co. of Japan, just went into production of its product line, called Sunprene. And the Geon Vinyl Div. of BFGoodrich Co., Cleveland, introduced its Flexel material at K'89 (PT, Nov. '89, p. 34). Physical-property data on both materials have just become available (see chart).

 Flexel Sunprene
 1000 Series
Density, g/cc 1.52 1.12-1.35
Tensile Str., psi 2770 1280-4267
Shore Hardness 95A/70D 35-85A
Elongation, % 175 330-550
Brittle, Temp., C -31 Below -50

PVC is the newest entry in the burgeoning TPE field, mounting a cost-competitive competitive challenge to the more established TPE categories, such as styrenic block copolymers and olefinic blends. Flexible PVC traditionally has been excluded from elastomer classification, partly because it is not truly "rubbery," and partly because its flexibility depended on plasticizers, which are subject to migration during long-term exposure to weather and heat aging - two factors especially critical in automotive and wire and cable applications. The materials launched by Sunprene and BFGoodrich are claimed to overcome those inherent limitations.


Apparently, the key to the properties of both new materials is that neither is based on conventional PVC resin. Sunprene says its products are composed of a proprietary PVC resin without any other polymer or elastomer. BFGoodrich officially describes its Flexel as an alloy of low-crystalline co-polymers "based on vinyl technology," though not containing PVC or nitrile rubber. But a top BFGoodrich official told PLASTICS TECHNOLOGY that CPVC - a more heat -distortion resistant, post-chlorinated form of PVC, of which BFG is the only domestic producer -is one of the mystery ingredients. Both BFG and Sunprene spokesmen cite the absence of nitrile rubber in their products as a cost-saving advantage.

Sunprene utilizes Mitsubishi formulating and compounding technology, but gets about 90% of its raw materials from the U.S., with "an important 10%" sourced "offshore." Other industry sources consulted for this article speculate that the special ingredient is a Japanese ultra-high-molecular-weight PVC resin of some type. Sunprene officials say the material's properties result not only from an entirely new class of PVC resin, but also from proprietary compounding methods. Bruce A. Petersen, v.p. of materials management for Schulman, says Sunprene makes use of "different kinds of PVC polymers," combined in a way that creates a proprietary molecular-weight distribution. He said this technology affects the way in which the polymer accepts plasticizer, stabilizer and other additives. Special compounding and process technology reportedly results in the desired viscosity, hardness and surface qualities.

Sunprene vinyl TPE and two flexible PVC's (Vinika and Sunfrost) also to be produced by the joint venture using Mitsubishi technology, have been engineered as extrusion grades dedicated to automotive applications such as body moldings and trim; hoses; window, door and windshield seals; gear-shift boots; weather stripping; glass-run channels; and interior components. Ronald Andres, general manager, said the first goal will be to supply the Japanese North American "transplant" automotive manufacturers, such as Honda and Mazda, and their custom parts vendors. The materials have been designed to compete with cured thermoset rubbers and other TPE's.

In order to meet the quality requirements of the Japanese transplant car producers, Sunprene has developed PVC grades that they say eliminate surface imperfections from the extrusion process, such as gels, pinholes, ripples, waves and "chatter marks." Other key physical properties featured in the three product lines reportedly include enhanced abrasion, cold-impact and chemical resistance, heat aging, and flexing fatigue, compared with EPDM rubber and existing PVC grades.

All three Sunprene product lines are priced in the $1 to $1.35/lb. range. All three come in a range of unfilled and mineral-filled versions. Sunprene TPE has no gels, a gloss range between 5 and 90, and compression set as low as 38%.

Vinika, a "classic flexible PVC composition," according to Andres, also reportedly has no gels, Shore hardness range of 40-55 Shore A, specific gravity between 1.15 and 1.50, elongation of 250-500%, gloss rating between 5 and 90, and brittleness temperatures below -50 C. Sunfrost, a low-gloss, matte-finish flexible PVC, has the same hardness and density range as Vinika, with a gloss rating of zero to 50 and elongation up to 450%. (CIRCLE 25)


Besides the Sunprene joint venture, Schulman has licensed a separate PVC powder slush-molding compound technology from Mitsubishi Kasei, known as PMC. It's a combination of materials, compounding and mold design for slush-molding of soft skins for auto dashboards and other interior parts, according to Bruce Petersen. He says PMC will compete with the existing approach of thermoforming nitrile rubber sheets. The proprietary PMC formulation is sourced about 85% from U.S. suppliers, with the balance coming from offshore. The mold design and process technology for PMC come from "another Japanese company," which he declined to name.

According to Petersen, PMC technology greatly reduces the scrap levels (up to 35%) and stress points over curves that are inherent in the draped thermoformed sheet process, while providing a superior surface finish. He said parts made from the PMC technology will be supplying domestic OEM's and Japanese transplants during the next 14 months for the 1992 model year. (Testifying to the growing interest in slush molding in the U.S., Vista Chemical Co., Houston, recently was licensed by Sumitomo Chemical of Japan to make another powder slush-molding compound - see PT, June '88, p. 29). (CIRCLE 26)


BFGoodrich's new Flexel material is aimed initially at building plenum cable jacketing, where flame resistance and low smoke are essential. That presumably explains the use of CPVC, which is even more combustion resistant than PVC, owing to its higher chlorine level. Also, BFG has proprietary CPVC compouding technology for critical low-smoke-and-flame applications. It does not depend on high filler loadings for these properties.

Flexel 1000 has an oxygen index of 48 and NBS smoke-density ratings of 28 to 34 in flaming and nonflaming modes. The product reportedly has passed UL 910 listing requirements for plenum cable, and also passed UL 1581 90 C operating-temperature requirements for Classes 12 and 43 insulation and jackets. Grades for 105 C approval are being developed. Flexel 1000 also has passed the ASTM D746 impact brittleness test at -23 F, as well as the UL 83 mandrel-wrap flexibility test at -67 F.

Right now, BFG has a single Flexel 1000 grade, but senior marketing manager Peter Lloyd anticipates that by midyear there will be new entries in the 1000 series, plus a Flexel 2000 series, which will have a different balance of properties and further enhanced combustion resistance, though perhaps at the sacrifice of some low-temperature flexibility. Potential applications could include voice/video/data cable jackets, signal/control cable insulation, and optical fiber cable jackets. In the latter case, it would benefit from having no plasticizer to migrate. Future grades for applications other than wire and cable may include glass or mineral reinforcement, and perhaps even nitrile rubber, Lloyd says.

Flexel 1000 is said to have low-smoke and low-flammability properties "broadly comparable" with fluoropolymers, yet with processing characteristics similar to standard PVC. Processor feedback during Flexel's development was crucial in determining the material's behavior and physical properties, Lloyd said. For extrusion, Flexel has a basic processing range of 320-375 F, utilizing PVC screws and dies. It's priced at $3.50-4.50/lb. Though intended mainly for extrusion, Flexel 1000, can also be calendered and injection molded. (CIRCLE 27)

PHOTO : Low smoke and flame resistance are among the key properties of BFG's new Flexel 1000 TPE, which targets applications in plenum cable jacketing.
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Title Annotation:thermoplastic elastomers
Publication:Plastics Technology
Date:Feb 1, 1990
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