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October 1, 2006

11 Min Read
TPEs progress in softness, bondability

The recent NPE Show hosted the inaugural Elastomers Pavilion, highlighting the increased importance of this materials family to the processing industry as a whole. Here and elsewhere around the show could be found a wealth of high-performance materials promising better bondability and superior softness.

PolyOne, for example, introduced two new (TPE) product lines: OnFlex-S series styrenic block copolymer (SBC) compounds and OnFlex-V series thermoplastic vulcanizates (TPV). OnFlex-V TPVs offer a unique “rubber-like” performance, low compression set, high operating temperatures (up to 135° C), improved chemical resistance, excellent colorability, and low odor. OnFlex-V Compounds can be used in automotive weather seals and interior trim, building and construction flooring, expansion joints, consumer sports equipment, and household appliances. OnFlex-S Compounds are said to be ideal for use in soft-touch overmolding applications because of their excellent bondability to PC, ABS, nylon, and alloy substrates. In addition, OnFlex-S Compounds provide excellent elastomeric performance over wide temperature spans and broad hardness ranges (10A-90A), as well as colorability.

ExxonMobil Chemical (Akron, OH) has also developed new Santoprene TPE grades which bond successfully to a variety engineered thermoplastics in overmolding applications.

The new grades eliminate the need for adhesives, bonding agents, and physical or mechanical interlocks. Additional benefits include a distinctive soft-touch feel and easy colorability.

“For many years, processors used mechanical interlocks or chemical agents to bond a soft TPE with a rigid ETP substrate in complex parts. This presented numerous problems such as a non-uniform contact surface, bonding failure, and high processing costs,” says Seth Barron, market segment manager. An advantage of the new Santoprene TPE grades is their performance with room-temperature insert substrates and on thinner overmolds. Available in two hardnesses, 60 Shore A and 75 Shore A, Santoprene TPE 291-60B150 and 291-75B150 retain full bond strength in various environments including hot air, oil, and aqueous solutions.

Ultra softness and optical clarity head advances in the new Monprene Ultra Soft Gel SBC series from Teknor Apex (Pawtucket, RI), enabling designers of foot care, personal care, medical, and orthopedic products to add new functionality and consumer appeal. They can be overmolded onto olefinic substrates.

Teknor Apex can formulate them in hardnesses from 30-60 on the Shore 00 scale, values well below those of conventional, non-gel TPEs, which are measured on the Shore A scale. “These altogether haze-free Monprene gels impart a clear, sparkling appearance to grips, cushions, and other padding or ‘soft-touch’ products, while providing a degree of comfort that is unattainable with non-gel TPEs,” says Edwin Tam, senior market manager.

A typical formulation in the new high-clarity series is Monprene MP-1238D, a 50 Shore 00 compound. Typical property values for this grade are: specific gravity, 0.88; tensile strength, 300 psi (2.1 MPa); tensile modulus, 40 psi (0.14 MPa); ultimate elongation, 700%; melt index (condition C), 20 g/10 min. ExxonMobil Chemical, Akron, OH, USA; +1 330-849-5120; www.santoprene.com; PolyOne, Avon Lake, OH, USA; +1 440-930-3154; www.polyone.com; Teknor Apex, Pawtucket, RI, USA; +1 401-725-8000; www.teknorapex.com.

Strong parts, smooth appearance

Promising molders the usual reductions in material usage, part weight, and clamp force required without any surface marring, Trexel (Woburn, MA) announced a collaboration with polyamide supplier Rhodia (Paris) that will make its MuCell microcellular foam technology applicable for highly aesthetic parts like rocker cover panels in cars.

MuCell, which involves the introduction of a supercritical gas, usually nitrogen, during the screw-recovery phase in injection molding (it’s also applied in extrusion), creates a porous part interior, trapping microscopic gas bubbles that measure less than 100 µm.

The bubbles strengthen the part, reducing warpage, while also lessening material usage 8%-10%, lowering cycle times 20%, and dropping the clamp force required by 40% or allowing for another cavity. In the past, the tradeoff has been a swirled surface appearance caused by the gas breaking through the part’s skin in the mold.

Now, two specialized grades of Rhodia’s Technyl Star polyamide 6, 6/6 materials, which the company says have a relative viscosity in their molten state approaching water, have been tailored for MuCell. The higher flow rates create laminar material flow through the mold, coating the cavity walls with a skin that freezes off, preventing any gas from breaking through the surface.

Rhodia anticipates business in any large parts where aesthetics are a key, with one large potential market being automotive rocker covers in the U.S. Six- to eight-cylinder engines common in the U.S. market have precluded plastic rocker cover panels at times, since the larger parts require long hold times and sizable amounts of back pressure to pack parts and reduce warpage. In addition to a lengthy cycle, this can introduce stress, leading to failures in the field or during installation. During NPE, Rhodia and Trexel representatives said the process already had one U.S.-based customer, which they couldn’t identify, with deals pending in Europe and Asia. Rhodia Polyamide Corp., www.rhodia.com; Trexel Inc., www.trexel.com

Basell TPOs enable and integrated airbag designs

Basell is supplying its high-performance Hostacom advanced thermoplastic (TPO) resins to several major North American OEMs for use in the production of their latest generation automotive instrument panels.

Three Hostacom grades—TKC717N, TYC727N and TRC787N—have been selected as the substrate materials for several new instrument panel designs now being launched.

Basell’s Hostacom resins are said to provide economical processing, reduced mass, uniformity in gloss and color stability, as well a unique balance of stiffness, impact resistance, and aesthetics to meet the demanding operational requirements of today’s instrument panel designs. Hostacom resins are used in designs involving seamless and discrete air bags, molded-in color instrument panels, and painted and skin/foam technologies. Flexural modulus requirements range between 1600 and 2200 MPa, with 15 MPH multiaxial impact performance ductility from 0° to -30°C. Overall temperature performance must be achieved from -30°C to 85°C. The Hostacom grades cover the performance range and also have melt flow properties from 12 to 29 g/10 min. Basell, Hoofddorp, The Netherlands, +1 410 996 1366; www.basell.com

Propylene elastomer lowers PP heat-seal temperature

Mitsui Chemicals continues to make inroads with its metallocene-based Tafmer XM series of propylene-based elastomers in packaging applications. For instance, when used as blends with polypropylene (PP) for the heat-sealing layer of PP films—in particular OPP films—the new series will allow heat sealing at a temperature 20°C lower when compared to the existing propylene-based Tafmer XR grades to significantly raise the efficiency of the food packaging process. Furthermore, the excellent antiblocking properties of Tafmer XM prevent film from blocking, or sticking together, during storage and transportation. Another advantage of the XM Series is less effect on the haze properties of PP film.

Mitsui Chemicals has also inked an agreement with Dow Chemical to further the development of catalyst systems for the production of olefin block copolymers (OBC) having flexibility and rubber elasticity over a wide range of temperatures. Dow had previously made a major announcement at NPE 2006 regarding its plans to sell OBC as Infuse (August 2006 MPW). Mitsui Chemicals, + 81-3-6253-3457, www.mitsui-chem.co.jp

TPU extends belt life

Noveon has unveiled its latest Estane thermoplastic polyurethane (TPU) for conveyor drive belts. Accelerated testing of grade X-1222 using a special belt test rig developed by Noveon to better replicate real usage conditions indicates up to three times the life expectancy (or time-to-break failure) compared to competing TPU-based belts. Durability improvements are attributed to superior creep resistance, which give rise to low abrasions and low belt slippage in the final application. Traditional static testing methods have proven ineffective in determining belt life expectancy. “Static rubbing is meaningless for testing belts because slip is an important parameter,” notes Lou Brandewiede, senior applications development scientist at Noveon.

Noveon has also introduced new Estane grades with improved chemical resistance, particularly against fuels such as biodiesel. The new grades are X-1181 (85A), X-1130 (90A), and HS85DN (85D). The latter is a water-clear new class of polymer with very low permeability to hydrocarbons. “HS85DN TPU provides the stiffness needed to act as a barrier to fuels,” says Ralf Hüther, marketing manager for Noveon TPUs. “It’s a great alternative to replace more expensive polymers.”

The third new offering from Noveon is two low durometer (softer) breathable Estane grades suited for use in protective garments, personal care products, strapping, and medical applications. Test results show volume swell of less than 5% in water compared to 20%–30% in other breathable grades. Tensile set is less than 8%. Noveon, Cleveland, OH, USA; +1 888-234-2436; www.estane.com

This TPU takes the heat

BASF’s Elastollan C85A15 HPM thermoplastic polyurethane (TPU) meets ISO 6722 Temperature Classification Type “D” (150°C, 3000 hours) and is available in 50–70 Shore A hardnesses, making it suitable for deployment in auto interiors, as well as underhood applications and antilock braking system cables. The grade does not employ plasticizer. BASF, Ludwigshafen, Germany, +49 621 600; www.basf.com


Namib beetle, lotus come together in film

Polymers by nature exhibit hydrophobic or hydrophilic properties, attracting and repelling water, usually exclusively, but now a group of researchers at the Massachusetts Institute of Technology’s Materials Science and Engineering Dept. have created a material that can combine these characteristics.

MIT’s Michael Rubner says the coating at a basic level is comprised of, in order, positively and negatively charged polymers, glass nanoparticles, and small, perflourinated molecules that are assembled onto a surface.

According to Rubner, the process has already been scaled up to a commercial level, which was made easier by the fact that the entire coating is created from water solutions. Building off of the work of prior researchers, who had successfully created materials that parallel a lotus leaf, with water forming droplets and rolling off for self-cleaning surfaces, as well as research by Oxford’s Andrew Parker into the Namib desert beetle’s ability to derive water from fog. MIT’s team developed a method to pattern materials that parallel the lotus-leaf surface and the beetle.

According to Rubner, patents for the material have been submitted, and negotiations are underway for possible commercial partners. Applications include water-harvesting surfaces for areas where water is scarce or polluted, open-air microfluidics, and drug-delivery systems.

Just as the desert beetle draws moisture from the air in arid regions of the world, the material’s superhydrophillic areas could cause moisture to condense on the surface until the droplet burst. The water could then be guided to collection channels by the superhydrophobic portions of the film. Massachusetts Institute of Technology’s Materials Science and Engineering Dept., Cambridge, MA, USA; +1 617-253-1000; "A HREF="http://dmse.mit.edu">http://dmse.mit.edu.


PEEK-based composites

Polyetheretherketone (PEEK) is now being used as the polymer matrix for thermoplastic composite pre-pregs, suspending carbon, glass, or aramid continuous fibers for a composite material that can replace metals and thermosets in aerospace, offshore, medical, and industrial applications.

The material comes in viscosities ranging from standard, to medium, to very low. The standard and medium grades are applicable for highly filled composites with the low-viscosity grade allowing greater wetting of the fibers.

PEEK is able to withstand continuous operating temperatures of up to 260°C (500°F) in low-stress applications, and 120°C (248°F) in aerospace structural applications. The material also offers thermal stability, low coefficient of expansion, abrasion resistance, low smoke and toxic gas emission, and excellent stiffness and density in addition to good hydrolysis, corrosion, chemical, and radiation resistance.

The material’s manufacturer has partnered with composite producers to create dry and multiaxial fabrics; braid, two, and unidirectional tape; unidirectional sheet, and consolidated fabric.

The composites produced from PEEK are made in a solvent-free environment and can be stored at ambient temperatures. The material can be processed via compression molding, roll forming, thermoforming, pultrusion, filament winding, autoclave and vacuum bag molding, diaphragm forming, and bladder inflation molding. Victrex USA Inc., Greenville, SC, USA; www.victrex.com

LFRT/COC blend cuts warpage

Celstran long-fiber-reinforced thermoplastics (LFRT) have been blended with Topas cyclic olefin copolymer (COC) to reportedly reduce warpage in large structural parts by as much as 80%-90%. The manufacturer offers an example of an automotive molder that improved the dimensional stability of a structural component made of polypropylene (PP)-based Celstran from 4 mm to less than .5 mm.

The material’s producer says use of the material to reduce warpage can speed time to market by obviating tool corrections, and permit for the use of more PP in parts, which could in turn facilitate more recycling.

The mixture has already been applied in a cup holder, and the manufacturer says the blend could see application in sunroof elements, door modules, and interior and exterior body panels.

In addition to reduced warpage, Celstran offers high impact strength and low creep in a wide range of temperatures and ambient conditions. Ticona Technical Partners, Florence, KY, USA; www.ticona.com. Topas Advanced Polymers Inc., Florence, KY, USA; +1 895-746-6447; www.topas.com


Stock shapes help improve sensitivity of marine devices

As world oil consumption continues to accelerate, offshore exploration and ocean surveying have become increasingly essential for production companies to keep pace with demand. Ertacetal stock shapes (rods, plates, and tubes made of acetal copolymer) for machining are helping seismic acquisition company Sercel Europe to construct oil filler blocks for seismic streamers. The stock shapes are deliverable in complex geometries with high chemical resistance and low specific weight. The result is a strong, flexible streamer able to map the seabed more quickly and with greater sensitivity. Quadrant Engineering Plastic Products, Tielt, Belgium; +32 51 423598; www.quadrantplastics.com

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