Elastomers expand design options

By: 
February 03, 1997

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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