AIR through bulks up: versatility, uniformity, high loft and a clean production process have manufacturers applauding air through bonded nonwovens.

Used in a variety of disposable and durable end use product segments including hygiene, filtration, bedding, furniture, carpet backings, wipes and fabric softener sheets, air through bonding is definitely considered a "hot technology" in the nonwovens industry. In addition to versatility air through bonded nonwovens feature high tensile strength and loft, bulk, absorbency and thickness, as well as lower weights. Air through bonded nonwovens are processed without chemical binders, offering a much safer production process and working environment for machinery operators and plant employees. Furthermore, manufacturers are able to save energy and achieve lower operating costs, as no binder preparation station is required.

"Air through bonding has been replacing spray latex bonding for the past 10 years," said Frank Maupay, product manager at air through equipment supplier National Drying Machinery Company, Philadelphia, PA.

Whereas spray bonding only sprays the outer layers of the web, air through bonding can bond thicker webs uniformly throughout the core. The use of hot air instead of sprays, resins and solvents in bonding or heating the nonwoven web makes air through bonding more environmentally friendly and hygienic.

Also known as through air bonding, air through technology is a type of thermal bonding. The process involves wrapping a nonwoven web around a drum, up to five feet in diameter, which is considered to be the "heart" of the dryer. Hot air passes through this drum to heat or bond the nonwoven web. Air through dryers can thermal bond or heat set nonwovens formed using a variety of technologies including carding, spunbonding, airlaying, thermal bonding, wetlaying and spunlacing: In the case of a spunlaced or wetlaid nonwoven, air through dryers and ovens can drive off moisture and stiffen the material. Perforated conveyor belts can also create bulkier materials. With such versatility it's no wonder why air through bonded nonwovens have been replacing other nonwoven technologies.

"Air through bonding is the only thermal bonding process that allows the entire product to be exposed to a uniform temperature," explained Chris Caiazzo, sales engineer at Metso, Biddeford, ME. "This segment's steady growth is attributed to the use of air through bonding for medical products, wipes and disposables. Air through bonded materials offer a dryer surface in absorbent products and greater strength per unit weight for heavy weights. Additionally, new fibers, machinery and product enhancements will position this technology well for continued growth."

Bicomponent Benefits

Most air through bonded nonwoven webs consist of either bicomponent or multicomponent fibers. Bicomponent fibers with a high melt temperature polyester core encased in a low melt temperature polypropylene sheath are still one of the most common bicomponent fiber combinations used in air through bonding. This allows a wider temperature range because one fiber is low melt and the other is high and it is generally the least expensive to produce. Additionally, the web is less likely to be subjected to shrinking. Other fibers used include low shrinkage, polypropylene fibers for interimings and disposables and polyethersulfone (PES) or co-PES fibers, featuring lower melting points, which are used in fiberfill webs and filters. Depending on the fiber's melting points, denier and attributes, certain fibers are preferred by manufacturers because they perform better for certain applications. The high melting portion found in some bicomponent fibers allows the nonwoven web to maintain uniformity and integrity while the low melting point easily melts and bonds the fibers together. Single component fibers, while less costly, have a low temperature range and are less sophisticated than multicomponent fibers.

Bicomponent and tricomponent fibers are also preferred over resin bonded polyester fibers. Bicomponent binder fibers used in air through bonded nonwovens is an alternative to fibers with chemical binders, because no additional maintenance and cleaning is needed in production facilities. The bicomponent fiber's core ensures a three-dimensional network throughout the entire web. As a result, manufacturers can make products with bulk that are not over- or under-bonded in certain areas of the web. The benefits of bicomponent fibers tend to outweigh those of a single component fiber. This has more manufacturers paying closer attention to new fiber combinations.

Conserving Costs

Despite the advantages of bicomponent fibers, their higher cost is one of the biggest obstacles facing their proliferation into nonwovens. While multicomponent fibers clearly offer advantages, fluctuating raw material prices have some manufacturers concerned. In response to this, manufacturers are turning toward web consolidation to handle cost challenges.

"The current trend appears to be in consolidating one or more separately formed sheets into a single, multifunctional process," Metso's Mr. Caiazzo explained. "Web consolidation without water removal, when comparing air through bonding to spunlacing, is more energy efficient, requires less floor space and operates at higher production rates. Spunlacing requires a significant amount of energy to generate the high pressure water jets as well as energy required to remove the moisture from the product since it has been bonded. Many air through equipment suppliers are combining monofilaments as layers or using a combination of separate polyethylene and polypropylene spinneret configurations. This multilayering allows the producer to use cheaper, shorter fibers in the inner layer and longer, more expensive fibers in the outer layer."

In addition to combining webs to help conserve costs, manufacturers are relying on new machinery components for air through bonding. For instance, spooling is commonly used in place of winding and slitting to more easily roll lofty air through fabrics.

"Loftier fabrics are more difficult to wind in narrow rolls with high diameters," explained George Levy, sales and marketing manager at air through bonded nonwovens producer Shalag Nonwovens, Upper Galilee, Israel "Relatively short roll lengths are disadvantageous to absorbent product manufacturers. There are solutions available, such as spooling, which increases the cost of the nonwoven but decreases the customer's processing costs."

Technological and mechanical advancements are boosting the presence of air through bonded nonwovens in end use applications. Air through bonded nonwovens are rapidly replacing lower-end cotton, shoddy and polyurethane foam materials and other materials that were previously used to obtain bulk in applications such as furniture, bedding and padding and in hygiene applications, such as diapers and sanitary napkins.

"Acquisition/distribution layers made with air through bonded nonwovens are considered by hygiene product manufacturers to be exceptionally efficient in attaining improved penetration and in preventing rewetting," said Mr. Levy. "The demand for air through bonded nonwovens is rising and will continue to do so, relative to the need for thinner and higher quality absorbent products."

What's On Tap For Air Through?

Not only are these markets broadening air through bonding's role, they are also opening new markets for nonwovens.

"We have been seeing a lot of odd requests for air through machines that can produce materials for the insides of speakers and underneath door frames--areas where you never would suspect air through bonded material could be used," National Drying's Mr. Maupay explained. "It is now also more common for regional companies to purchase air through bonding machinery, instead of the larger roll goods manufacturers. Lately, there has been a big move toward the actual vendors and end product manufacturers who are directly purchasing air through bonding lines to make the product themselves."

One of the reasons this trend is gaining speed, according to Mr. Maupay, is many companies are looking to horizontally integrate their products. When manufacturers horizontally integrate, they will introduce new products that are similar to or complement their product lines, in order to incorporate a wider variety for end use applications.

Most manufacturers are reporting that new applications for air through bonded nonwovens are appearing literally every day, leading machinery manufacturers to incorporate higher speeds and working widths onto their machinery lines to increase capacity and stretch air through bonded nonwovens into previously untapped markets.

Fleissner GmbH & Co., Egelsbach, Germany, a supplier of thermal bonding lines, perforated drums and calibrating units for interlinings, filters, padding material and nonwoven wall coverings, has kept its focus on machinery advancements to increase high temperature uniformity profile advancements into its machines.

"Automatic material transfers through the line, integrating cooling drums at the end of the air through units and integrating calibration units to adjust the web's thickness and density on either cooled or heated rolls are some advancements on the machinery side of the business," explained Alfred Watzl, vice president of Fleissner. "The benefits are then seen in the final products. Geotextiles, for example, can reach a higher tensile strength when they are thermal bonded. Costs are saved because the same results are achieved with air through bonding as with other processes, but with lower fiber weights."

The variety of new machinery components for air through bonding equipment, such as calibration units, allows manufacturers more flexibility in what characteristics the end roll good product can obtain. A large part of this flexibility revolves around temperature control, which is vital for manufacturers in order to uniformly bond materials consisting of different fibers.

"Most of the major air through advancements have been on supply air temperature control," said Mr. Caiazzo. "Metso can regulate the supply air cross machine temperature profile within 5[degrees]F. As a result, our customers can uniformly bond higher loft products and control the temperature through and across the web."

Also focusing on temperature control in air bonding is Cavitec AG, Muenchwilen, Switzerland. The company's forced through air bonding system (FTA) saves energy, offers a higher output and allows a uniform heat transfer throughout the web. This system is used to manufacture carded or airlaid thermal bonded products, man made and natural fibers, cellulose pulp for acoustic and heat insulation, geotextiles, acquisition/distribution layers for the hygiene market and cleaning wipes. In addition to the fibers and web forming methods used in air through bonding, the interaction of temperature and air distribution and fiber control have a significant influence on quality, efficiency and flexibility.

"The FTA system runs at higher speeds and has a better heat transfer from air to the fiber," explained Christian Haas, sales director at Cavitec AG. "Using this system allows a shorter heating up and drying period for the material."

As manufacturers push the envelope with different material combinations, fiber configurations, higher speeds and machinery advancements air through bonding is constantly evolving. As a result of this, air through bonding manufacturers are incorporating pilot lines and spending more time in the research and development process.

Mr. Caiazzo has seen an increased focus on researching temperature control and improvements in producing a porous web to allow for even airflow distribution throughout the web.

"Product permeability is a critical issue in the air through process. If we cannot force air through the product, then we cannot bond the entire sheet," explained Mr. Caiazzo. "Temperature sensitivity is another big issue for air through bonding. Therefore, prior to committing its customers to a full-size production machine, Metso will conduct trials on its pilot line to determine how new fibers will react to our process."

Mr. Maupay agreed that the use of pilot lines is a key component to the air through bonding research process. "There is such a diversity of applications right now. It really requires a lab to test all the different products and fibers," Mr. Maupay said.

As air through bonded nonwovens continue to establish themselves in larger end use markets as well as in newer specialty markets in the nonwovens industry, the need for air through bonded material will increase.

"Thermal bonded nonwovens using air through technology for hygiene applications, sanitary products and makeup removal pads have definite benefits over binder bonded products," Fleissner's Mr. Watzl opined. "With the development of new fibers, this technology will continue to keep its marketshare."