Elastomers expand design options 11216

DN Staff

February 3, 1997

21 Min Read
Elastomers expand design options

What do sunglasses, winter sports gear, home appliances, cars,a gas furnace system, and a versatile Army vehicle have in common? All make prominent use of elastomeric materials, many of which are new to the market and will add increased flexibility to an even wider range of products.

Here's a closer look at how these materials expanded the design opportunities for a number of engineers, improved the product under design, and cut production costs. In many cases, the solutions enabled the engineers to design the product in record time, and, as a result, beat the competition to market.

Sunglasses prove eye openers

Setting a fashion trend can mean the difference between big profits and just average rewards. That scenario faced Bausch & Lomb, Rochester, NY, when it came to the design of the company's latest Ray-Ban(R) sunglasses.

Already one of the most popular choices of today's trend-conscious consumers, Bausch & Lomb designers wanted to keep that distinction going when they introduced their latest Ray-Ban model--Orbs(R). One strategic decision helped them meet that goal: use of "new" materials that were, up to that point, fairly uncommon in the manufacture of high-quality fashion sunglasses.

The Ray-Ban Orbs sunglasses incorporate high-tech, lightweight metal for the frames, time-proven lens technology--and thermoplastics elastomers (TPEs) for the nosepads and earpieces. The TPEs replaced an acetate, the hard plastic most commonly used in this application. Bausch & Lomb's major reason for switching from acetate to a super-soft TPE material was to provide a product that would offer the highest level of comfort to ensure the most perfect fit possible.

For this project, Bausch & Lomb decided to look outside the sunglass industry to find a material that would stand out against the competition. "Our goal was to differentiate the Ray-Ban Orbs from other sunglasses on the market," says Jon Gieselman, marketing manager for the Ray-Ban products. "At the same time, we wanted to produce a cutting-edge fashion product that blended technical design with a highly emotional and psychological concept."

In response to that decision, Bausch & Lomb sought the assistance of the Thermoplastic Elastomers Div. of GLS Corp., Cary, IL. The firm specializes in developing soft, custom-formulated TPE compounds designed for injection-molded and extruded goods. The advantages offered by TPE, notes Gieselman, include: improved softness, ease of processability, and a special "tactile" feel.

GLS features the Dynaflex(R) series of TPEs based on Kraton(R) G polymers, from Shell Chemical, Houston, TX. The compounds are easily colorable and processable, and can be recycled without suffering a significant loss of physic-al properties.

Formidable task. Bausch & Lomb engineers had the seemingly insurmountable task of developing this program, from concept to the final product, in three months. In addition, the project was virtually "unbudgeted"--handed to the engineers as a challenge to see if they could make it work.

"The normal development period for a project of this magnitude is six months," notes Doug Caswell, lead engineer. "We had to go from paper to product in half that time. It was clear we needed the assistance of a company that would step in and become involved right away. GLS more than met our requirements."

Bausch & Lomb's engineering team sought TPE materials that would offer several wide-ranging properties: extreme softness, a "grippy" feel, colorability, and low toxicity. If found, they felt, the materials would give the new design the ultimate in comfort, style, and product performance that active, sports-minded consumers demand.

Because of the sport-specific applications of Orbs, they are regarded as a medical device. Therefore, the properties required of the TPEs prompted the GLS design team to recommend two different grades. It suggested a Dynaflex compound for the nosepads, and a Kraton material for the earpieces. The unfilled, translucent Dynaflex grade has a 44 Shore A hardness, which offers high resilience, good puncture resealing, and a high coefficient of friction. The soft, "grippy" texture of this material met Bausch & Lomb's requirements for a comfortable, adhering nosepad.

The Kraton TPE, also an unfilled, translucent material, has a 57 Shore A hardness, offering a more rigid feel, as required for the earpieces. It also resists heat distortion, sweat, and moisture associated with sports activity, while providing a comfortable and "snug" fit.

The injection molding for this project is done by All Mold, Inc., Rochester, NY, who also builds the molds. Other Ray-Ban Orbs components include: nickel-silver alloy frames made from Monel steel and Bausch & Lomb's G/15TM constant-density glass lenses, which were specifically developed for World War II U.S. Army Corps aviators. More important, this latest addition to the Ray-Ban line should maintain Bausch & Lomb's leadership in the high-end sunglass market.

Technology tips scale for bathroom scrubber

Advanced Elastomer Systems, L.P., Akron, OH, recently introduced "the industry's first fully vulcanized, non-hygroscopic TPE." Based on a proprietary technology, the new product line broadens the spectrum of AES' Santoprene(R) thermoplastic rubber offering. It also should boost sales for Black and Decker (B&D) Household Products, Shelton, CT, one of the material's first customers.

The new line of thermoplastic vulcanizates (TPVs)--the Santoprene 8000 Rubber Series--offers such value-added characteristics as non-hygroscopicity (requires no drying) and ease of coloring. "Although other technologies can yield a non-hygroscopic partially cured TPE, our new technology allows for a fully cured TPE," reports Jay Griffith, worldwide product director for AES. "This, in turn, permits our product to better withstand the rigorous demands of engineered applications."

In addition, the new technology made possible the improved colorability of Santoprene 8000. "In some cases as much as 80% less colorant is required to achieve bright, maximum color and cost savings, while maintaining performance properties," Griffith explains. Both injection-molding and extrusion grades have a Shore A hardness that ranges from 35 to 90.

The low halogen content of the material makes it well suited for applications that must resist corrosion. Add in the full-cure, improved-colorability features of Santoprene 8000, and B&D was sold on the material. Currently, 12 injection-molding and extrusion grades are on the market.

The material debuts in B&D's cordless ScumBusterTM, a motorized scourer/scrubber that tackles one of the most dreaded of all tasks--cleaning the bathroom. The appliance operates on rechargeable batteries. Working with liquid cleansers, the portable, hand-held scrubber eliminates the "rub-a-dub-dub" drudgery of cleaning porcelain and tile with pushbutton power.

The appliance gets the electrical energy it needs from rechargeable battery technology developed and used by B&D's Power Tools division. The unit drives three attachable tools: a 41/4-inch scouring pad for lifting grime and gook from tub and tile, a 2-inch cylindrical detail brush for getting at dirt nestled around fixtures and corners, and a short-bristled 41/2-inch circular brush to scrub sediment deposits from grout lines.

B&D had a special problem when it came to designing the motorized cleaning tool--what material to use that would stand up to bathroom chemicals, moisture, and tough use, yet be competitive in price, have a certain soft feel, a consistent color, and interact compatibly with a polypropylene substructure. It found all those ingredients, and more, in the new Santoprene 8000 TPV.

After an extensive search for the right material without success, B&D turned to AES for assistance. AES recommended Santoprene 8000 TPV. "Technical support from AES was excellent from the time we would start a process to making sure we had the right material based on trial runs," says Patrick Gutelius, B&D project engineer.

Key ScumBuster motorized scrubber TPV components include an internal O-ring and the skin for the appliance's housing and battery cap. The skin is applied 2-mm-thick in a one-step injection overmolding process. "We also found that the material gave us the ability to mold in thick and thin cross sections without telltale sink marks," Gutelius notes. He also explains that the final product has a "desirable luster," no noticeable parting line, and withstood tough drop tests.

Face-to-face supplier support proved critical to the project because of the 10-month design cycle placed on the design team. The product had to be on the market in time to capture this year's Christmas sales. Not only did the team meet the deadline, but sales of the appliance, which retails for under $60, have taken off.

Boards 'snow' the competition

Snowboards have come a long way since they first appeared on the mountains of winter resorts in the 1980s. In fact, in 1998, snowboarding will join the events to be included in the Winter Olympics.

Among the characteristics of this sport that haven't changed, however, are the tremendous demands placed on the snowboards. In addition to the harsh weather conditions in which snowboards are used, they are frequently subjected to torque and stress inflicted while skimming along icy slopes or striking a glancing blow off trees.

One manufacturer, Universal Bindings, Benicia, CA, says it has found the answer to these performance demands in two engineering resins supplied by Dow Plastics, Midland, MI--IsoplastTM engineering thermoplastic polyurethane (TPU) and PellethaneTM thermoplastic polyure-thane elastomer (TPE).

Manufacturers confirm that the snowboard market relies heavily--and equally--on the design and performance demands placed upon them by consumers. "In some ways, snowboards are part of an image-driven industry," explains Rich Harley, Universal Bindings' purchasing manager, whose firm makes the bindings used by Avalanche Snowboards.

The bindings are the plastic parts that connect the rider to the snowboard, they must be sufficiently flexible above the ankle to allow some movement in the rider's leg, yet rigid enough at the base to permit the rider to influence the snowboard's direction. And they must be strong enough to endure the rigorous pounding and frigid temperatures experienced during use. In response to these needs, Rick Stephens of General Polymers, a nationwide distributor of Dow resins, recommended the use of the Isoplast TPU and Pellethane TPE for the bindings' rotor discs and ankle and toe straps.

"We wanted to replace aluminum because it didn't offer the strength and rigidity needed for the discs, and because of its higher cost," explains Chris Sanders, co-owner of Avalanche Snowboards and Universal Bindings. "We specified glass-filled Isoplast resins for the application because they have excellent abrasion and impact resistance, particularly at low temperatures."

The Isoplast 101-LGF40 resins are 40% long-glass, fiber-filled materials. Because of their lower melt viscosity, the resins flow easily. According to the injection molder on the project, the replacement of the anodized aluminum with the TPU reduced overall costs by at least 50%, while dramatically accelerating the rate of production.

Universal Bindings also sought a reliable raw material for the large ankle and toe straps used to hold the rider's boot in the bindings. "Experienced snowboard riders sometimes grab the board with their hand and twist it while they're flying through the air, which puts an excessive amount of stress on those straps," notes Sanders. "Yet, once a rider lands, those straps need to hold securely and feel snug."

Recognizing those requirements, General Polymers recommended Pellethane TPEs for the two components. "Pellethane provides strength at low temperatures, and the fatigue resistance, controlled flexibility, and high molding productivity needed for this application," says LuAnn Peters, a senior account specialist for Dow Plastics. "The elastomer also demonstrates exceptional resistance to tears and scratches, and allows for shorter cycle times and set up than competitive thermoplastic materials."

Such strength and durability will undoubtedly be key requirements of the snowboards used in the 1998 Winter Olympic Games. Sanders feels confident the Avalance Snowboards will be part of that competition.

Gloves give skiers a warmer grip

It's a beautiful, crisp, cold day, perfect for skiing. From the top of a snowy mountain, the slope stretches invitingly below. The only problem? Cold hands and stiff fingers, numb from the long ride up the chair lift. However, a new type of glove designed specifically for skiers can make cold hands a thing of the past.

These premium ski gloves, based on a design originally used by astronauts, feature a thermoplastic polyurethane (TPU) "liquid heat transfer" bladder filled with an oil-based fluid. This hand-shaped bladder absorbs heat generated by an iron oxide heat pack, and spreads the warmth evenly over the entire hand for several hours at a time.

Sealtech, Inc., Athens, TN, fabricates the bladder. It's made from Stevens Urethane supplied by JPS Elastomerics Corp., Holyoke, MA. The material's Shore A hardness ranges from 75 to 95. Through a special conversion process, Sealtech combines sheets of the urethane, pressure-sensitive adhesives, and an oil-based solution to produce the filled bladder, which is then inserted into the ski gloves during the manufacturing process.

The glove design includes a built-in pocket for an iron oxide heat pack, commonly known as a "hand warmer," which can be found in almost every ski shop. When the heat pack is activated and inserted into the glove's pocket, the wearer simply clenches his or her fist or moves the hand. This distributes the fluid in the bladder over the heat pack, which warms it up, and disperses the warmth across the entire hand.

Designed to last. Although it seems a simple design, several critical factors had to be addressed when it came to the selection of the bladder material. "This is a high-quality glove, and it had to be designed to last," says Jim Clare, Sealtech's national sales manager. "Durability and flex fatigue resistance are essential, since the wearer must close the hand frequently to keep the oil moving over the heat source. Polyurethane was the only material durable enough to withstand this flexing during the long life space of the glove."

Sealtech also found it could use a thinner gauge of urethane when compared to other materials, such as PVC. This proved important for streamlining the glove design, and making it easy to wear.

For the glove, Sealtech uses a polyester grade of Stevens Urethane, which offers oil resistance. The 8-mil sheets provide a combination of performance and fit. By contrast, a vinyl material would have to be a bulky 20- to 25-mil thick to achieve the same performance, Clare claims.

In addition to flex fatigue, temperature considerations had to be addressed. The ski slope's naturally cold environment means that many people are on the slopes for a long time before they turn to a heat source. Wind chill is an added factor. Therefore, the gloves must endure very low, even sub-freezing temperatures, and withstand repeated cold and hot cycles. Because urethane is free of plasticizers, which can cause brittleness and cracking in cold conditions, its performance is unaffected by temperature extremes found on ski slopes.

Camry becomes a millimeter better

Design News readers voted the 1996 Toyota Camry the "best engineered" car. They may have an added incentive to so again this year.

The 1997 Camry's rear fascia, the first thin wallstock polyurethane RIM bumper in commercial production in the U.S., walked off with the materials award at the 26th annual Society of Plastic Engineers Automotive Division awards. Made using a new Bayflex(R) elastomeric RIM system with a proprietary filler (Bayer Corp., Pittsburgh), the bumper has a nominal thickness of only 2.7 mm. This compares with 3.8 mm for standard RIM bumpers and 4.5 mm for the previous model's bumper.

Here's how the Bayflex thin wallstock system compares with a typical fascia RIM system. A typical system has a flex modulus, MPa, of 340, while the Bayflex system's flex modulus is 1,030. A typical system provides an elongation of 110%, the Bayflex system 140%. And using a -30C dart impact, J, test, the typical system had a rating of 4.1 compared to the Bayflex system's 17.

Not only did the RIM system produce a fascia with an excellent surface, the component easily passed the 5-mph on-car impact test. In addition, the Bayer-developed crosslinker/internal mold release package gave the part added stiffness, while the proprietary material's chemistry improved flowability for the component's thin cross sections. Finally, the material's toughness and quick cure enabled Toyota to improve part productivity.

Elastomers stretch airbag cover designs

In another automotive application, the Plastics Div. of Teknor Apex Co., Pawtucket, RI, has under development several families of elastomeric compounds for use in producing airbag covers. The new Telcar(R) TPOs and Tekron(R) TPEs will eliminate secondary painting and coating operations.

Traditionally, airbag covers have required costly secondary finishing steps to improve aesthetics--painting for color and the addition of a clear coat for protection. Not only will the new materials eliminate these steps, but they will feature a flex modulus from 18,000 to 45,000 psi. Equally important, the materials will come in custom precolored compounds.

The pre-product announcement follows increasing requests from automakers to Teknor Apex for such materials since they concentrate on more efficient and cost- effective ways to make airbags. "We're on the forefront of a growing trend," says Charles Gates, the company's automotive industry manager. "Our compounds have caught the attention of many of the key car manufacturers, and they're excited about the cost savings we can deliver."

Gates adds that Teknor Apex already has some products developed and being tested on a restrictive level for molding deployment and for scuff and mar resistance. The customers are Tier 1 suppliers to the automotive industry in both Europe and the U.S. Once Teknor Apex gets past the styling guides with these customers, which should occur shortly according to Gates, the material could appear on a 1998-model vehicle.

Vent system improves gas-furnace safety

Leakage of deadly carbon monoxide can prove a serious problem in homes with mid-efficiency gas furnaces that use plastic pipes to vent flue gases. In Canada's Ontario province, where more than 11,000 of these side-wall venting systems exist, the government issued a public alert to this safety hazard, and insisted that all leak-prone systems be corrected. As a result, thousands of homeowners in the "golden horseshoe" had to replace or retrofit their gas heating systems to eliminate this hazard and comply with new safety standards.

The problem, according to heating experts, resides with the plastic vent pipes used to carry hot combustion gases from the furnace to the side-wall exhaust port. Chemicals contained in the gases (primarily hydrochloric and sulfuric acids) have attacked the adhesive-sealed joint, creating cracks and separations that allow carbon monoxide gas to leak into the home. Since the deadly gas is colorless and odorless, this leakage is difficult to detect and presents a serious hazard.

Ontario's Ministry of Consumer and Commercial Relations (MCCR) gave homeowners three options for dealing with the problem: replace the entire furnace installation; install a vacuum system and power vent to exhaust the gas; or install a leak-free vent piping system. Heating experts agreed that the quickest and most cost-effective way to eliminate the hazard was to rebuild the vent pipe system with materials that can handle the damaging chemicals. Such a system has been tested and certified by UL of Canada and is available there and in the U.S.

Developed by Alternate Energy Resources, Markham, Ontario, the new, safer system consists of durable steel piping coated with chemical-resistant porcelain enamel. To assemble a furnace exhaust vent, lengths of this special pipe are joined with mechanical clamping devices and sealing gaskets made from Viton fluoroelastomer from DuPont Dow Elastomers, Wilmington, DE.

A sponge gasket of Viton installed on the male end of each pipe provides a gas-tight connection between pipes. This U-shaped gasket is adhered to the pipe with special caulking grade of Viton to assure permanent attachment and provide a secondary sealing barrier.

During field assembly, the gasketed end of a pipe is inserted into the flange of the mating section. As the two pipes are pushed together, the sponge is compressed within the joint, forming a resilient, gas-tight seal. A special turnbuckle tightens the joint and prevents the pipes from separating after installation.

The combination of flexible caulk and resilient sponge of Viton produces durable, gas-tight seals that resist acid, are heat stable, and can withstand contraction and expansion of the jointed pipes.

Thermal management keeps Humvee humming

When engineers at AM General Corp., Livonia, MI, were asked to modify the Humvee, the Army's high-mobility multi-purpose transport vehicle, into a commercial product for urban use, they knew the task would not be as simple as changing the color of the paint. In designing a product that civilians would find as appealing for its comfort as it was for its rugged image, the engineers had to re-engineer some systems, including rerouting cable harnesses and ventilation lines to accommodate the added demands.

Some areas would be impossible to redesign, making alternative thermal-management solutions necessary. One such "hot-zone" was the vehicle's air conditioning system. Here, the exhaust system passes within inches of the fire wall, rendering the A/C system virtually ineffective, and creating a potential system failure.

The engineers experimented with a variety of thermal-management concepts before finally choosing RF-120, a special composite product from the High Performance Elastomers Div. of Rogers Corp., East Woodstock, CT. RF-120's layers of durable, reflective scrim and high-temperature silicone foam add only 0.2 inch to the overall design of the firewall, yet the combination of radiant shielding and insulation effectively allows the system to perform at designed levels.

The product is part of the Bisco line of elastomeric, silicone-based materials from Rogers. Designed to meet critical demands in various industries, these products minimize weight and volume, while maximizing thermal management and acoustic performance. They are often co-designed in direct cooperation with engineers, according to Bisco's David Marsh.

Rogers bought the former Bisco Products silicone foam material business of Dow Corning Corp., and incorporated Bisco's silicone foams with Rogers' Poron(R) urethane foams. Together, the product lines offer design engineers an array and depth of options for gasketing, shielding, and cushioning, says Rogers' Dave Belden.

Only on the Web

Global elastomer demand expected to exceed 9 million metric tons by 2000

According to a new study, World Commodity Elastomers published by The Freedonia Group Inc. of Cleveland, OH, global demand for elastomers is forecast to increase 3.6% a year to 9.2 million metric tons by the year 2000.

The major tire elastomers -- solid styrene-butadiene, polybutadiene and butyl -- will benefit from growth in motor vehicle production and expansion in tire replacement. Solid styrene-butadiene will remain by far the leading type of synthetic rubber, although polybutadiene which has more diverse end users, will post stronger gains.

Demand for elastomers in industrial rubber products such as hoses, belts and mechanical goods will remain flat due to intense intermaterial competition.

Dyneon has new bulk container system for fluorel fluoroelastomer customers

Dyneon now offers a bulk container system for large-volume users of fluorel fluoroelastomers. The palletized containers are collapsible and returnable which saves space and reduces waste disposal and material handling costs. Each high-density polyethylene container holds up to 1,320 pounds of material. The containers are made of structural foam molded from up to 40% post-consumer high-density polyethylene and have a foot print of approximately 4 feet square with a height of 25 inches. Dyneon is a joint venture company between 3M and Hoechst AG Hostaflon GmbH.

New thermoplastic rubber
has low gas permeability

Advanced Elastomer Systems L.P. now has a thermoplastic elastomer (TPE) grade for application where low gas permeability is critical. The TPE also have good fluid resistance, heat aging properties, and can be processed on thermoplastic equipment. These Trefsin(TM) rubbers are available in hardnesses of 65, 75 and 85 Shore A in black or natural pellets.

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