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Move over rubber! Today's TPEs have more to give.

Softer, stiffer, clearer, more paintable, easier flowing, and more heat-resistant - the latest generations of thermoplastic elastomers won't take a back seat to cured rubber.

Though no longer the new kid in town, thermoplastic elastomers (TPEs) remain one of the fastest-growing plastic material categories - in terms of total poundage and proliferation of new grades. TPEs' number-one claim to fame is still their cost-saving processability advantages over thermoset rubber: faster cycles, lower scrap rates, and reprocessability. What's new is that TPEs today come much closer to matching conventional rubbers in soft touch and feel, compression set, long-term mechanical strength, and resistance to heat, chemicals, and weathering. Ten or 15 years ago, TPEs were the upstarts - trying to muscle aside thermoset rubbers in established applications. Nowadays, TPEs are more likely to be specified for an application from the beginning.

Of the four primary TPE categories, the olefinics, styrenics, and TP urethanes are the most active focus of technical and market development. There's much less new in the "engineering" or specialty types.

Except for the latter category, consumption of TPEs in North America is expected to grow at least 10% annually over the next five years, according to various industry sources. Conservative estimates hold that current market volume will double by the year 2000.

This bullish outlook is reflected in capacity expansions by several suppliers. Advanced Elastomer Systems (AES), DSM Thermoplastic Elastomers, and D&S Plastics International are all expanding capacity this year and next.

Olefinics

To the two main classes of olefinic TPEs - thermoplastic olefins (TPOs) and thermoplastic vulcanizates (TPVs) - a third category was added in the past year. Unlike the first two, which generally consist of rubber in a PP matrix, new low-density ethylene copolymers produced by metallocene catalyst technology are inherently elastomeric (see PT, March '94, p. 17). There are two commercial families - Dow's Engage polyolefin elastomers (POEs) and Exxon's Exact plastomers. These products are finding uses in shoe soles, scrub brushes, tablecloths, and elastic films. They are also serving as the "rubber" component in new generations of TPOs.

TPVs PROLIFERATE

TPVs (which have a crosslinked rubber phase) constitute the high end of the olefinic performance spectrum. Partial or full crosslinking of the EPDM or EPR rubber phase through "dynamic vulcanization" during compounding results in long-term resistance to temperatures of 275 F and above, enhanced resistance to chemicals and fluids, improved ozone resistance, and mechanical properties that equal or surpass those of thermoset rubbers. Growing applications for TPVs are drawing more suppliers into the market.

The longest-established family of TPVs is Advanced Elastomer Systems' Santoprene. The most exciting developments in Santoprene today are taking place overseas, where two automotive programs will soon produce results of interest to North American processors. One program is the Santoprene "150 C Plus" project, which seeks to raise the material's continuous-use temperature range to above 300 F. The current limit is 275 F.

This program has been under way for more than three years and involves a European car builder. AES aims to replace copolyester elastomers in blow molded under-hood air ducts with an all-new Santoprene composition that utilizes resin alloys other than PP.

The second Santoprene development program involves both a new processing innovation and a novel material grade for water-based foam extrusion. Mark A. Wright, director of sales for AES's North American Automotive Div., says the new process is being used by Mitsubishi in Japan to produce a hood seal for a recreational vehicle. It replaces EPDM rubber, providing a 16% weight savings. The new patented process involves water foaming of the specially modified Santoprene grade, combined with a coextrusion technique that produces a continuous extrusion with both hard and soft segments. Hard segments are used for attachment points, while the soft foam seals and insulates.

Similar Santoprene hood-seal development is progressing in North America at an undisclosed car company, which has slated commercial applications for a 1997 or 1998 vehicle.

This year, AES reintroduced its Vyram line of partially crosslinked EPDM/PP as a lower-cost complement to Santoprene for lower-performance applications. The new Vyram 9000 series replaces the discontinued 6000 line. The latter consisted of PP and natural rubber. Composition of the new series is proprietary.

Among other TPV producers, DSM Thermoplastic Elastomers unveiled two new grades in its Sarlink 4000 line at the annual SAE show in Detroit (PT, April '95, p. 69). Sarlink 4139D (39 Shore D) and 4149D (49 D) are designed for auto under-hood blow molded parts.

Recent additions to DuPont's Alcryn line of chlorinated TPVs include lower-cost extrusion grades and unfilled translucent grades.

A new TPV that's said to show better paint adhesion than others is Novalast 8000AB from Nova Polymers. It's available in a broad hardness range from 50A upwards. Aimed at air-bag covers and other automotive parts, it can be injection and blow molded and extruded.

Among the newer suppliers of TPVs is Himont Advanced Materials (now Montell Polyolefins), which brought out HiFax XL two years ago (PT, April '93, p. 105). Late last year, Teknor Apex launched the Uniprene 7000 Series of TPV injection molding and extrusion grades (PT, Jan. '95, p. 12). The initial Uniprene offering includes five grades with hardnesses of 55-87 Shore A and 40-50 Shore D.

M.A. Hanna Thermoplastic Elastomers (formerly North Coast Compounders) plans to commercialize two lines of TPVs by July 1996. Michael Merk, v.p., says the HTE 3000 Series will differ from Santoprene types because it contains a proprietary rubber other than EPDM.

ACTIVE DEVELOPMENT IN TPOs

There has been plenty of news in TPOs, including new firms entering the field, new products from established factors, and a new marketing and technical alliance of two producers. Auto fascias and trim remain key applications. Current R&D is aimed at increasing flow and higher so as to permit molding thinner gauges. Improved paint adhesion to reduce finishing costs is another area of continuing development. TPOs are also appearing more and more inside the vehicle, as air-bag covers have emerged as a major new application.

A new joint marketing accord between Novacor Chemicals and RheTech Inc. will allow each firm to offer Novacor's in-reactor TPOs and RheTech's compounded grades. The two firms are test marketing TPOs for injection molded auto exterior and interior parts. These include developmental Novacor in-reactor TPOs (PD8215HS and PD7715HS), whose high flow (15-20 g/10 min) can shorten molding cycles and reduce clamp-tonnage requirements. RheTech is compounding the new Novacor materials with glass, mineral fillers, EPR, and functionalized polyolefins to yield combinations of high flow with higher stiffness (flex modulus up to 250,000 psi). Superior low-temperature impact strength, improved paint adhesion, and low CLTE are also claimed.

D&S Plastics has two new families of TPOs. Last year, D&S commercialized the new Sequel 1700 series (80,000 to 300,000 psi flex moduli), which has CLTEs about 50% lower than those of typical TPOs (PT, June '94, p. 15).

The firm's new Sequel 1400 Series is for injection molding bumper fascias and interior trim. Research manager Satchit Srinivasan says Sequel 1400 is undergoing trials at automotive customers and will be commercially introduced by year's end. This family is designed to address automotive demands for thinner-walled parts (under 3 mm) that retain structural properties and low-temperature toughness (PT, Dec. '94, p. 15). Srinivasan cites recent molding trials that produced bumper fascias 2.2-2.5 mm thick (the industry standard is 3.2-3.7 mm).

Along with standard grades, Srinivasan says D&S will customize Sequel compounds to meet specific tooling and end-use requirements. He describes the 1400 Series as being "substantially olefinic," but declines to identify other resin components. The series will have a Rockwell R hardness range of 60-75, flex moduli of 100,000 to 220,000, and a melt-flow range of 15-30 g/10 min.

Working along similar lines is Washington Penn Plastic Co. It is developing higher-flow (15-20 MFR), higher-modulus (200,000-psi) TPOs for thin-walled fascias.

Air-bag covers are a major new application for TPOs. Multi-Flex 1047AH (45 D) is a new TPO for this application from Multibase, Inc. It's based on an in-reactor alloy and offers a broadened use range of 40 F to +212 F.

The most recent entrant in TPOs is HiTech Polymers, which recently introduced the HTP 1000, 1100, and 1200 series (PT, Feb. '95, p. 70).

Last year, Quantum Chemical commercialized the first of a growing line of Flexathene in-reactor TPOs for automotive, film, wire and cable, blow molding, and compounding (PT, April '94, p. 72). They can contain 20-50% EPR. Two newer automotive grades (Flexathene TPP 1008 and 1010) are formulated for superior paint adhesion. The grades reportedly performed much better than compounded TPOs in both Ford and General Motors paint-adhesion tests. Quantum's automotive TPOs are sold by A. Schulman under the Polytrope name.

In addition, Schulman launched its own Schulaflex line of TPOs last year. They are in the 85 Shore A hardness range and are designed to compete with flexible PVC.

Styrenics

Users of styrenic block copolymers (SBCs) have coped with last May's explosion and fire at Shell Chemical Co.'s plant in Belpre, Ohio. The accident derailed much of the plant's 325-million-1b/yr production of Kraton SBC. Within weeks, the rest of the plant was again making most Kraton grades used in plastics - except footwear resins, which Shell has discontinued permanently.

Shell plans to restore full production of Kraton by the first quarter of 1996. According to one SBC user, manufacture of Kraton G SEBS rubber wasn't significantly damaged by the explosion. "Shell's done a good job in keeping up to speed with its Kraton G," this source notes.

Kraton D SBS production was severely disrupted, but the three other SBC polymer makers - Dexco Polymers, EniChem Elastomers, and Fina Oil & Chemical - filled the gap.

The partial supply disruption has not halted the flow of new products, especially from compounders. Ultra-soft grades, clear versions, and products designed for overmolding of other resins are areas of recent development.

CAN'T GET MUCH SOFTER

GLS Corp. is developing new "super-soft" TPEs made of Kraton, PP, and a proprietary elastomer. GLS recently released Dynaflex G-6703, which at 3 Shore A durometer is said to be the softest commercially available TPE for injection molding (PT, April '95, p. 86).

GLS also has a new Dynaflex G-2700 series of very soft, translucent, Kraton-based TPEs (PT, Aug. '94, p. 54). Two medical grades - transparent Dynaflex G-2707 (32 A) and translucent G-2711 (44 A) - can be gamma sterilized (PT, Nov. '94, p. 49).

Other new products include four grades from 35 to 70 Shore A in the general-purpose Dynaflex G-7700 series (PT, April '95, p. 87). And GLS is developing Kraton-based TPEs alloyed with Dow's Engage POE. Two developmental translucent grades, XU4 (43A) and XU-6 (58A), will compete with PVC in tool grips.

Very soft SEBS grades are new from J-Von. Hercuprene 600742A (7-9 A) is for industrial pads, seals, and gaskets. At NPE '94, J-Von introduced Hercuprene S2954 (47 A) for overmolding or coinjection with ABS, PP, or PS. The company recently came out with Hercuprene 3959 (40 A), an "ultra-clear" SEBS for medical and sports equipment.

Teknor Apex introduced two new grades in its Tekron 4000 Series at this year's SAkE show (PT, April '95, p. 71). Tekron 4000-60 and 4000-30 are based on Kraton G and formulated to replace EPDM in automotive gaskets.

Several new Multibase automotive SEBS compounds are now in testing at various domestic and foreign car makers. Muti-Flex A8502, A9002, A9305, and A9402 injection molding grades are rated at 85 A to 94 A hardness. They show a broadened use-temperature window from -40 to +220 F. Air-bag cow ers are an intended use.

Multibase also recently introduced these SEBS compounds:

* RP6568C (45 A) is designed for air-bag covers and dual-shot molding of large parts. It can be overmolded onto TPOs and is a candidate for PVC replacement in instrument-panel covers.

* A8299 (82 A) and A7727 (77 A) are designed for under-hood noise abatement. They can be injection molded into parts weighing up to 15 lb.

* A7606UV is designed to be extruded over EPDM to provide a uv-stabilized color coating on automotive trim. Another uv-stabilized grade, A6221UV, is a black, scurf-resistant product that's being used as headlight gaskets on Chrysler's Neon.

* In the non-automotive area, Multi-Flex A7318 is an injection molding grade designed as a lower-cost ($1.25-1.30/lb) replacement for cured rubber or urethane caster wheels. It can be molded over PP hubs and is colorable and abrasion resistant.

Consolidated Polymer Technologies recently expanded its C-Flex SEBS elastomer line with a new range of grades (5 to 75 Shore A) for industrial applications. C-Flex products previously were focused on medical uses.

Earlier this year, M .A. Hanna introduced its HTE 1100 Series of SBS elastomers based on Dexco SBCs. Hanna is also test marketing developmental compounds based on SEBS and SEPS elastomers from Kuraray of Japan.

HiTech Polymers is developing new formulations of both its styrenic and olefinic TPEs that will greatly enhance their resistance to aromatic and ketone solvents. The goal is to achieve non-swelling characteristics similar to neoprene rubber. Commercial products are about six months away.

Fina reports development of two new oil-extended SBS grades in Europe, which may become available here in the next six months. Aimed at footwear and compounding, the new grades are said to be more receptive to oil absorption than previous materials.

TP Urethanes

Officials at Bayer Corp. note that key R&D trends in TPUs are toward sorer grades (less than 80 Shore A), wider usage in blow molding, and improvements in chemical resistance, flame retardancy, and uv stability. Automotive, medical, and wire and cable applications are major targets.

Aliphatic TPUs are the focus of Bayer's product developments. Bayer says the aliphatic chemistry offers significant advantages in weatherability and uv resistance compared with aromatic TPUs. Four developmental aliphatic grades now being scaled up for commercial applications are Texin DP7-3005, 3006, 3007, and 3013. Their respective hardness levels are 88 Shore A, 50 Shore D, 55 D, and 85 A.

In addition, Bayer is launching two new aromatic grades: Desmopan KU2-8651 (75 Shore A) and KU2-8655 (80 Shore A). The materials reportedly offer good low-temperature flexibility and toughness (down to -50 F), as well as good chemical and abrasion resistance.

Michael Marasch, senior marketing manager for the Estane Div. of BFGoodrich, cites several examples of continuing improvement in TPU performance. New Estane 58238 and 58661 are said to offer 50-100% better deformation recovery or resistance to "induced set" than previous Estane compounds or other TPU offerings.

BFG also has two new grades aimed at the growing market for high-moisture-vapor-transmission (HMVT) films in medical applications such as wound dressings and surgical drapes and garments. Estane 58237 and 58245 are formulated to allow moisture to diffuse readily through the film.

BFG recently came out with new antistatic TPUs (Estane 58241 and 58242), which are alloyed with the company's Stat-Rite inherently conductive elastomer. Stat-Rite itself is described as a high-molecular-weight polyether copolymer based on urethane chemistry.

NON-HALOGEN FR GRADES

At NPE '94, BFG unveiled its second generation of non-halogen flame-retardant TPUs for wire and cable (PT, Aug. '94, p. 54). These products have a UL 94V-0 rating and oxygen index of 53 - reportedly the highest of any non-halogen TPU. Two grades are Estane 58243 and 58244, intended as cost-effective alternatives to fluoropolymer wire/cable compounds.

Another new TPU with a non-halogen flame-retardant package is BASF's Elastollan 1185A-10FHF. It's a polyether type for wire and cable. It has a UL94 V-0 rating at 1/32 in., oxygen index of 25, and Shore A hardness of 85. Now in market-development trials in Europe, the new grade will be available in North America by year's end.

BASF is also broadening its Elastollan offerings in sorer grades with two recent introductions: C60A-10WN (60 Shore A) and C70A-10WN (70 A). These polyester TPUs are stabilized to improve hydrolysis resistance. Technical-service manager Armando Sardanopoli notes that while polyether TPUs are inherently more hydrolysis-resistant, polyesters cost less. BASF's goal was to develop a new stabilizer technology to boost the hydrolytic stability of polyester TPUs while maintaining their price advantage.

Softer grades, breathable films with enhanced HMVT, and lower-cost products are also in the pipeline at Dow. Product manager Mark Remmert says several new Pellethane TPUs these needs will be introduced in coming months. For example, the current Pellethane grades are 70 Shore A, but products in the 60 A range are coming.

Remmert also says Dow has identified substantial market areas - especially in recreational products - in which "over-engineered" TPUs could be replaced with lower-cost TPU grades.

Dow is exploring blends and alloys as routes to cost savings.

TRYING OUT NEW CHEMISTRY

Morton International is extending its existing line of Morthane aliphatic, polycaprolactone, and aromatic TPUs with several developmental grades now undergoing customer trials. The company is trying out new monomers and polymerization techniques to modify the resin's molecular backbone.

Vikram Kapasi, director of R&D, cites developmental grades for low compression set (L425.125D), fuel resistance (LA25.85), stretch recovery (L425.155J), improved flow (L425.83), and enhanced HMVT (L428177, LA28179, and L428133). The company recently introduced PB363-200, an extrudable HMVT grade for medical, recreational, and industrial fabrics.

A. Schulman has a new line of weight-saving TPUs that are highly glass-and mineral-filled but still low in specific gravity (1.15). These "Line 3" compounds are aimed at auto rocker and side moldings, which typically have densities of 1.3-1.4. Other features include low CLTE and flex modulus from 80,000 to 300,000 psi. Injection grades are now available; an extrusion version is coming.

In the medical sector, Thermedics has developed a new Carbothane TPU/PC for long-term implants. It has passed the USP Class 6 implant test of more than 30 days. It comes in hardnesses from 75 A to 72 D and in injection and extrusion grades, as well as a solution grade for dip coating.

J-Von introduced S2954 TPU alloys at NPE last year. Available in hardnesses of 47-49 and 60 A, they are designed for over-molding ABS, PC, and ABS/PC in computer housings.

A new line of TPUs is being scaled up by M.A. Hanna for commercial roll-out early next year. The HTE 2000 Series will include polyesters (2100 grades) and polyethers (2200 grades).

Engineering TPEs

The higher-priced engineering or specialty grades of TPEs are the slowest growing sector and have seen the fewest technical developments of late. The dominant member of this TPE category is the copolyester elastomers, such as DuPont's Hytrel, GE Plastics' Lomod, and DSM's Arnitel.

Only DSM Engineering Plastics has recent product developments to report: Its new Arnitel U polyester/esters target automotive under-hood cables and tubing. They offer high continuous-use temperatures (up to 338 F), as well as abrasion resistance, uv stability, and colorfastness (PT, Oct. '94, p. 11).

In addition, DuPont notes that its Hytrel is going after breathable film applications. Breathable films are also a market for polyamide TPEs, the second major factor in the engineering/specialty category. Elf Atochem North America is introducing Pebax MV3000 for breathable films. Pebax is a nylon 12/polyether block copolymer. MV3000 is a 40 Shore D medical grade with a density of 1.02 and a MVFR reading of 3300 g/[m.sup.2]/24 hr).
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Title Annotation:thermoplastic elastomers
Author:Gabriele, Michael C.
Publication:Plastics Technology
Article Type:Cover Story
Date:Jun 1, 1995
Words:3211
Previous Article:New-generation LLDPE film resins.
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