TPU Toughness Is Key To Manufacture Of High Performance Ear Seals

Canton, Ohio — While most people might consider headset ear cushions to be a fairly simple design, the performance expectations of today’s high end ear seals can present a real challenge. Evans Industries, Inc., Canton, Ohio, has specialized in ear cushions and seals for many years, and knows that there’s a lot more to it than meets the eye (or the ear). The film converter and fabricator makes what may be the most diverse selection of ear cushions in the world, as many as 60 different types. Some of these, such as a new silicone gel filled ear seal, are so complex they can only be made with a tough, versatile, high performance material such as thermoplastic polyurethane (TPU) from Stevens Urethane, Easthampton, Massachusetts.

“Headsets are used in all kinds of applications, each of which have different technical requirements,” noted John Ebert, director of sales at Evans Industries. “In situations such as commercial and military aviation, an effective ear seal which blocks external noise is essential to ensure clear communication and safety. We’ve found that for demanding applications requiring a long working life, Stevens Urethane gives us the performance edge we need.”

Many ear cushions have short life spans and act simply to reduce noise. Typically made of foam backed expanded vinyl, these cushions need to be economical, functional, disposable, and easy to change. Others, such as those used by commercial and military pilots, are expected to last up to five years, and must endure hot and cold temperature extremes as well as long term exposure to skin oil, an unexpectedly aggressive substance. These cushions generally rely on a TPU cover over a foam pad, to give them the durability and toughness they require.

“Pilots’ headsets take a lot of abuse,” said Ebert. “They get left in the airplane, where they are exposed to extreme temperatures. They have to be strong, impervious to substances such as skin oils, and stay soft and comfortable to wear for hours at a time, year after year. TPU is the only material that will remain flexible and reliable under these conditions. Vinyl covered cushions, for example, become hard and brittle.” Ebert added that because of its performance and reliability, Stevens Urethane is written in to some government specifications for ear seals.

At the highest end of the performance spectrum, Evans Industries manufactures a silicone gel filled ear seal that offers state-of-the-art noise reduction, comfort, and style. Introduced within the last five years, this gel filled ear seal improves on earlier liquid-filled products. It offers superior comfort and fit around eyeglasses, for example, and an exceptional seal around the ear cavity. It also presents a real design and manufacturing challenge.

“Performance and comfort are the key criteria here, and the material which contains the gel has to be absolutely reliable,” said Ebert. “Toughness, strength, and burst resistance are critical. In addition, the gel must be as close as possible to the wearer’s head, so we were looking for a very thin material. Stevens Urethane gave us a consistent material with all the toughness and strength we needed.”

TPU is noted for its high performance and general overall toughness. With tensile strength up to 10,000 psi, and a unique combination of other performance properties such as broad spectrum chemical resistance and low temperature flexibility down to -40°F, TPU is often the material of choice for critical “can’t fail” applications.

Evans begins the manufacture of its gel-filled ear seals with a 10 mil (.01 inch) sheet of transparent or black Stevens Urethane, and vacuum forms it into a female die, during which the sheet thins out to a mere 5 mil (.005 inch). The TPU is filled with a silicone gel which sets at room temperature, then heat sealed to a 15 mil TPU backing to complete the seal.

“At 5 mil, the skin material has to be extremely tough to contain the gel, and not burst under the pressure and abuse ear seals typically encounter,” said Ebert. “TPU is the only option given the strength and durability we needed in this thin skin application. In addition, TPU is impervious to the silicone gel, which can migrate through materials such as vinyl.”

These gel filled ear seals are used for both military and commercial aviation. Their sexy, high tech appearance puts them to use in virtual reality games and other applications where aesthetics and durability are important.

“Stevens Urethane offers a wonderfully consistent product,” said Ebert. “We’ve been working with them for more than 20 years, and no one else in the TPU business can match the quality and consistency of their gauge, color, and finish. Without that support, we’d be hard pressed to make our ear seals to a reliable standard.”

Stevens Urethane is a recognized leader in the design and manufacture of polyurethane film, sheet, and tubing, sold under the Stevens brand name. Stevens Urethane offers a family of urethanes ideal for "can't fail" medical applications. Stevens film and sheet can be manufactured in thicknesses from .001" to .125" and in widths from 5 inches. Tensile strength up to 10,000 psi assures reliability and durability over a long working life, and urethane film and sheet can elongate significantly and still return to its original dimension with no loss of "memory." Stevens Urethane is available in hardnesses from 75 to 95 Shore A, and in a range of standard and custom colors. Various opacities and surface textures are also available.

Stevens Urethane offers a full range of high-performance urethanes for use in a wide variety of "can't fail" applications for the consumer, medical, commercial, and industrial markets. Stevens Urethane is the only company in the world that offers urethane in blown film, extruded sheet, tubing, cord, and profile form.

For additional information, contact: Stevens Urethane, 412 Main Street, Easthampton, MA 01027. Phone: (413) 533-8100, or toll free at 1-877-TPU-FILM (1-877-878-3456). FAX: (413) 552-1195. E-mail: info@stvure.com. Stevens Urethane is a business unit of JPS Elastomerics.