The Sound Of Silence

By Ellen Wuagneux, Associate Editor | April 2, 2008

acoustic nonwovens keep down the noise

Shhhh. Hear that? Probably not, thanks to the use of nonwovens as sound absorbing substrates in your car as well as your home and office. Typical end use applications range from automotive, appliances and marine to office partitions and aviation. Designed to control noise, acoustic nonwovens are supplied in widths from about 20 to 80 inches and in varying thicknesses of 1/8 of an inch to six inches.

    As noise control assumes greater priority, acoustical nonwoven materials are making their way into an increasing number of end use markets across North America. “Consumers spend more time in their automobiles and in their homes,” noted David Schlaefer, business manager, 3M Acoustic Solutions. “In both locations, the need for quiet is being driven by the need for improved communication and comfort.” According to an analysis from Frost & Sullivan, revents in this market reached $443 million in 2005 and will reach $580 million by 2012.

    In terms of market trends, the good news for nonwovens is that they offer advantages such as superior performance, lower weights and comparatively inexpensive pricing, all of which appeal to original equipment manufacturers (OEMs) and Tier One suppliers. While shoddy is the most inexpensive of acoustic materials, fiberglass offers superior thermal resistance and acoustic insulation in certain niche applications. With foam prices on the rise, many Tier One suppliers are actively considering the use of alternatives such as nonwovens. Going forward, the impact of these trends will no doubt grow as raw material prices and recyclablility continue to be of paramount importance.

    On the other hand, despite such positive trends, increasing raw material prices as well as OEM price pressures are two major hurdles in the North American market. Nonwovens suppliers are feeling a serious profitability squeeze as crude oil prices soar and OEMs apply additional pressure to reduce costs.

Silence Is Golden

Nowhere is price pressure from OEMs and Tier Ones stronger than in the automotive market, which represents the largest end use sector for acoustic nonwovens. Here nonwovens are used in hood liners, inner and outer dash materials, tunnel insulation, firewalls, underbody shields, headliners and more. Even in the face of such pressures, market growth continues, according to Detlev Käppel, technical nonwovens division director for eswegee Vliesstoff GmbH. “The market has been growing in recent years because OEMs have upgraded cars with acoustic parts to provide more comfort to customers.” He added that an increasing number of smaller cars are now equipped with acoustic parts such as hoodliners.

    In response to these market demands, Hof has developed a new generation of spunlaced nonwovens under the Zetajet brand. “We just started to supply the first commercial platforms for BMW, VW, Audi, Mercedes, GM, Chrysler and others,” commented Mr. Kappel. “Zetajet nonwovens will not substitute our existing product groups but will help us gain even more marketshare.” He defined the major advantages of the new Zetajet product group as excellent moldability and coverage with low fiber weight and cost competitiveness.

    Belgium-based Libeltex is another company debuting an automotive-related innovation in acoustics. The company’s new Quiet Web 500 M is a hydrophobic, acoustical barrier that consists of a thermally bonded polyester nonwoven including a high percentage of microfibers (<1 dtex). Quiet Web is easily moldable and weldable and is also totally recyclable, odor-free and does not support bacterial growth. The materials vary in weight from 80 to 500 gpsm and can be supplied either in rolls or as diecut parts.

    Another European player in the automotive market is Sandler, which sells PET-based carded nonwoven products that meet strict requirements for emissions, fogging, odor, temperature stability, flame resistance and recyclability. Sandler’s lightweight, acoustically effective sawasorb absorber nonwovens are used as interior (hidden) and exterior (visible) vehicle components. For visible applications, anthracite colored versions are available. The company also offers sawasorb exterior nonwovens featuring fluid and dust repellent characteristics with quick drying behavior. These materials are suitable for applications such as wheel house liners in vehicles or as insulation substrates in the construction sector. Self-supporting, lightweight and temperature-stable molding parts made of sawaform offer high mechanical stability, acoustical efficiency and excellent molding.

    As Sandler sees it, the market for automotive components is as challenging as ever for the nonwovens producer. “Not only does the market demand low weights, excellent technical data, low emission rates and recyclability,” observed Ulrich Horn­feck, sales director, “the various end uses often require a combination of different properties such as water-repellency, trim rigidity and sound absorption in one medium that must be adjustable to specific customer needs.”

    He added that the company’s answer is sawasorb exterior, which is water and oil-repellent, made from 100% PET and acoustically efficient. “The fibrous structure and the excellent surface bonding allow perfect molded or cut trims without adding a film or support layer. Due to its precise reproducibility, sawasorb and sawa­form are appropriate materials for a simulative product development.”

    Dr. Hornfeck went on to say that new versions and products are no longer identified by long-lasting trials but are simulated on the computer according to the required absorber profile prior to carrying out initial machine trials. “Through this computer-aided development, Sandler is capable of realizing the ideal absorber very fast and cost-efficiently,” he said.

    Involved exclusively in the European market, J.H. Ziegler GmbH is active in the automotive area but also supplies acoustic nonwovens for loud speaker boxes and for construction applications. The company produces drylaid microfiber nonwovens as well and regular drylaid nonwovens, which are available in white and black. “The products can be laminated if required for improved acoustical properties,” explained Peter Hartwig, managing director. “Furthermore, hydrophobic/oleophobic impregnated products can be offered. Upon request the materials are cut (punched) to specification.”

    Back in the U.S., Minneapolis, MN-based 3M has been busy rolling out Thinsulate products for a variety of transportation and appliance applications. In acknowledgement of these efforts, last year Frost & Sullivan selected 3M Acoustic Solutions, makers of Thinsulate Acoustic Insulation, as the recipient of the North American Acoustic Nonwovens Growth Strategy Leadership of the Year award for its innovative products and business strategies, which fuelled higher than average growth rates in North American acoustic nonwovens markets. 

    3M Acoustic Solutions launched its first acoustic insulation material in the mid-1990s for use in the automotive market. Today’s version of Thinsulate insulations being used in cars is several generations beyond the introductory materials. A polypropylene/polyester blended meltblown product, Thin­sulate acoustic insulations are composed of very fine fibers, a key factor that is responsible for their excellent sound absorption capability. The materials are extremely lightweight yet strong, hydrophobic, flexible and easy to install.

Quiet Down

When it comes to developing new technologies, companies are upping the ante and doing everything they can to keep both noise and costs down. Elmarco, headquartered in Liberec, Czech Republic, has shaken things up recently by incorporating nanotechnology in its production of sound absorption materials. Nominated for an INDEX award by INDEX08 sponsor EDANA, the company’s new Nanospider AcousticWeb product is composed of a PES carded web coated with nanofibers (polyvinylalcohol). Crosslapping technology then transforms the web into the required number of layers. A result of years of joint R&D efforts by Elmarco and the Technical University of Liberec, the newly patented material has unique sound absorption characteristics and is about three times lighter than traditional materials. It is able to absorb sounds across a range of frequencies, especially low frequency sounds below 1000 Hz.

    Partnering with Elmarco to bring this technology to the forefront of carded nonwovens is machinery specialist Oerlikon Neumag, which has entered into an agreement to combine Elmarco’s nano­fiber know-how and Oerlikon Neu­mag’s nonwovens technologies. The companies plan to offer complete technological solutions for nanofiber applications such as Nanospider Acous­ticWeb sound absorbent materials as well as filtration uses.

    Stefan Schlichter, head of Oerlikon Neumag’s carding division, sees potential in the company’s future cooperation with Elmarco for ultra lightweight nonwoven applications. “Together with Elmarco,” he said, “we will explore the potential of new nanotechnology in the nonwovens world market. We have made strong progress, adapted a modified carding process to the Nanospider and will show the first practical results at INDEX.”

    Nanospider AcousticWeb is being billed as the first sound absorption material that benefits from nanotechnology. It is versatile in its use—from aviation to building and construction—and can be produced in different thicknesses and formats according to the client’s specification and the final application. Other advantages include good heat insulation coefficient, very low area weight and easy manipulation and shaping.

    Elmarco’s product manager Denisa Stranska explained how the process works. “Sound waves landing on the acoustic resonating membrane make the membrane oscillate. Fibrous underlay material ensures the sufficient suppression of the resonant membrane so that most of the sound energy accumulated in the resonator is transferred into heat energy. The technology for producing this type of material consists of several steps—opening and blending, carding, Nanospider, crosslapping and oven,” she said.

    “The combination of carded webs with nanofiber layers offers advantages in combining high surface with low weight (initiated from the nano layers),” commented Mr. Schlichter. “Softer open structures of the carded web enable combined and ‘add-up effects’ of both layers. In sound absorption, this means different sound absorption characteristics and in filtering, it translates to different filter efficiencies by ‘catching’ different particle sizes.”

Will The Future Be Super Silent?

While the future of the acoustic market remains to be seen, one thing is certain: suppliers will need to continue intensive R&D activities and investments in state-of-the-art production technologies. “New products must be developed in an application-oriented way in close cooperation with OEMs, system suppliers and renowned R&D institutions,” stated Dr. Hornfeck of Sandler. “The only chance for established European and German companies to remain competitive is to provide innovative, high quality and reliable products and excellent customer service—flexibility in every way.”  

    Despite recent strides toward growth, acoustic nonwovens are still a relatively small piece of the overall nonwovens picture, especially when compared to larger segments like hygiene and household uses. Mr. Hartwig of Ziegler was one supplier predicting that acoustic nonwovens will remain a specialty market. “It is one of these niche markets and will remain just that, as volumes are small compared to hygiene, geotextiles and other applications.”

    Even if it is from a small base, future growth is expected to come as acoustic end uses expand into new areas and strive toward super silent efficiency levels, increased integration and lower weights. “Sound absorption products not only head for automotive end uses,” said Mr. Schlichter of Oerlikon Neumag. “There are a lot other applications in household products, the building industry and special applications that are still in the market introduction phase. They may not be up for public discussion yet, but they’re very close to market introduction.”

    3M’s Mr. Schlaefer also expects some interesting product twists to come down the pike. “Overall, the market is trending toward ‘solutions' that involve more than just a material. This could incorporate several materials as a composite or be uniquely provided to the customer in other ways.” He also predicted that green products will gain momentum in the future, ranging from complete recyclability and total recycled content to a clean material that does not emit volatile organic compounds.”