Technical definitions express the fundamental basis of nonwoven processes, but due to the wide variety of production techniques, a general description of nonwoven fabrics is not sufficient. As with woven or knitted fabrics, each process has unique characteristics. The resulting fabrics have little in common other than being classified as nonwovens. Non-woven components such as; Techniques for fiber selection, web formation, bonding and finishing can be modified to manipulate fabric properties or reverse engineer the fabrics according to functional requirements. Due to its assortment of achievable characteristics, nonwoven fabrics enter a wide range of markets including medical, apparel, automotive, filtration, construction, geotextiles and protection.
There are several types of nonwoven processes by which these materials are made.
Compared to other nonwoven technologies, airlaid has the unique ability to deposit short fibers, either 100% pulp fibers or mixtures of pulp and short cut synthetic fibers, to form a web. homogeneous and continuous. It is also possible to mix superabsorbent powders or fibers, thus creating very absorbent webs.
The airlaid sheet can be linked in several ways. In Latex Bonding (LBAL), a liquid binder is applied to both sides of the tape, which is then dried and cured to achieve the necessary wet and dry strength. Typical applications are table products, wet and dry wipes, industrial wipes and household products. Aerial thermal bonding (TBAL) includes binder fibers, typically bicomponent fibers, in the formation of the web, and the web is heated to activate the molten components of the synthetic fibers to bind the web. Typically used for absorbent cores, where a superabsorbent powder may also be present and blocked in the web structure by the synthetic fibers.
Multiple Bonding (MBAL) is a bonding process where latex and thermal bonding are combined, usually when the internal part of the product is heat sealed and the surfaces have a light layer of binder to remove dust and lint. Typically used for absorbent cores, household products, wet and dry wipes, these materials may also contain SAP.
In hydrogen bonding (XBAL), bonding is achieved by a combination of pressure, humidity and temperature to create what are called hydrogen bonds, thus eliminating the need for other bonding methods. Typically used for absorbent cores.
Air bonding is a type of thermal bonding that involves the application of heated air to the surface of the nonwoven fabric. During the through-air bonding process, heated air flows through holes in a plenum above the non-woven material. Unlike hot ovens, which push air through the material, the air-through process uses negative suction pressure to pull air through an open conveyor apron holding the nonwoven as it is sucked. through the oven. Pulling air through the material allows for rapid and even heat transfer to minimize distortion of the non-woven material.
Binding agents used in the air bonding process include crystalline binder fibers and powders, which melt to form molten droplets throughout the cross section of the nonwoven. When the material is cooled, bonding occurs at these droplet points. Nonwovens created by the air-pass process have the characteristics of being soft and bulky.
Blown molten nonwovens are produced by extruding molten polymer fibers through a spinning net or die comprising up to 40 holes per inch to form long, thin fibers which are stretched and cooled by passing hot air. on the fibers as they fall from the spinneret. The resulting web is collected in rolls and then converted into finished products. Extremely fine fibers (usually polypropylene) differ from other extrusions, especially bonded spinning, in that they have low inherent strength but a much smaller size providing key properties. Meltblown nonwovens can benefit from extremely fine fibers and are often used in respirators, face masks and filter media. Often, meltblown is added to the spun bond to form SM or SMS tapes, which are used in the disposable diaper and feminine care industries.
Spunlace (also known as hydroentanglement) is a bonding process for wet or dry fibrous webs made by carding, airlaying or wet-laying, the resulting bonded fabric being a nonwoven. This process uses fine jets of high pressure water which penetrate the belt, strike the conveyor belt (or “thread” as in the papermaking conveyor) and rebound, causing the fibers to become entangled.
Spunlace nonwoven fabrics used short staple fibers, the most popular being viscose and polyester staple fibers, but polypropylene and cotton are also used. The main applications of spunlace include wipes, fabric face masks, and medical products.
Spunlaid, also called spunbond, nonwovens are made in one continuous process. The fibers are spun and then dispersed directly in a web by deflectors or can be directed with air flows. This technique leads to faster belt speeds and lower costs. Several variations of this concept are available. Polypropylene spunbonds work faster and at lower temperatures than PET spunbonds, mainly due to the difference in melting points. Polypropylene-based spunbond is widely the material of choice in hygiene products such as baby diapers and feminine hygiene products as well as in medical clothing. Polyester-based nonwoven materials are typically used in durable nonwoven applications such as roofing and construction, automobiles, and geotextiles.
The spunbond was combined with meltblown nonwovens, shaping them into a layered product called SMS (spun-melt-spun). Melt blown nonwovens have extremely fine fiber diameters but are not strong fabrics. SMS fabrics, made entirely from PP, are water repellent and thin enough to serve as disposable fabrics. Melt-blown is often used as a filter medium, capable of capturing very fine particles. Spunlaid is resin or thermally bonded.
In the wet process, staple fibers with a maximum length of 12 mm, very often mixed with viscose or wood pulp, are suspended in water, using large tanks. Then, the dispersion of water fibers or water pulp is pumped and continuously deposited on a forming wire. The water is sucked, filtered and recycled. Besides synthetic fibers, glass ceramic and carbon fibers can be processed.
To distinguish wetlaid nonwovens from wetlaid papers more than 30% by mass of its fibrous content consists of fibers with a length to diameter ratio greater than 300, its density is less than 0.40 g / cm3. Wetlaid is commonly used in applications such as tea bags and coffee filters and dispersible wipes.