In 1962, the American Society for testing and materials gave the first written definition of nonwovens. The association defined nonwovens as "textiles made of combed webs or fiber webs bonded by adhesives". At present, the Nonwovens Industry Association Inda, Nonwovens are defined as "sheet or web structures bonded together by winding fibers or filaments (and perforated films)", mechanical, thermal or chemical. These substrates are flat perforated plates directly made of separated fibers or molten plastics or plastic films. They are not made by weaving or weaving and do not need to convert fibers into yarns (Inda).
The technical definition expresses the basic basis of nonwovens, but due to the diversity of production technology, it is not enough to describe nonwovens in general. Like woven or knitted fabrics, each process has unique characteristics. The resulting fabrics have little in common except that they are classified as nonwovens. Nonwoven components, such as:; Fiber selection, web formation, bonding and finishing techniques can be changed to manipulate fabric properties or reverse engineer fabrics according to functional requirements. Because nonwovens have many realizable characteristics, they have penetrated into a wide range of markets, including medical treatment, clothing, automobile, filtration, construction, geotextile and protective materials.
There are several nonwovens processes that can be used to make these materials.
Air assisted Nonwovens
Compared with other nonwoven technologies, airraid has the unique ability to lay short fibers, whether 100 percent pulp fibers or a mixture of pulp and chopped synthetic fibers, to form a uniform and continuous web. The super absorbent powder or fiber can also be mixed to form a super absorbent net.
The air auxiliary network can be bonded in several ways. In latex bonding (lbal), a liquid adhesive is applied to both sides of the mesh and then dried and cured to achieve the required dry and wet strength. Typical applications include desktop products, wet and dry wipes, industrial wipes and household products. Thermal bonding air assist (tbal) includes bonding fibers, usually two-component fibers. In the formation of fiber web, the fiber web is heated to activate the molten components of synthetic fibers to bond the fiber web. It is usually used for water absorbent cores, in which there can also be a super absorbent resin owder, which is locked in the mesh structure by synthetic fibers.
Multiple bonding (mbal) is a bonding process combining latex and thermal bonding. Usually, the interior of the product is thermally bonded, and there is a layer of slight adhesive on the surface to eliminate dust and fluff. Usually used for absorbent cores, household products, dry and wet wipes, these materials can also contain sap.
In hydrogen bonding (Xbal), the so-called hydrogen bond is formed by combining pressure, humidity and temperature, thus eliminating the need for other bonding methods. Usually used for absorbent core.
Air bonding (thermal bonding)
Air bonding is a kind of thermal bonding, which relates to the application of hot air to the surface of nonwovens. During the all air bonding process, the heated air flows through the vent above the nonwoven material. Unlike the hot oven, the hot oven pushes air through the material. The process of penetrating the air uses negative pressure to attract air through an open conveyor belt. When the nonwovens are sucked into the oven, the conveyor belt holds the nonwovens. By sucking air into the material, heat can be transferred quickly and evenly, so as to minimize the deformation of nonwovens.
The adhesives used in the through air bonding process include crystalline adhesive fibers and powders, which melt and form molten droplets on the entire cross-section of the nonwovens. When the material cools, these droplet points will bond. Nonwovens produced by air method have the characteristics of softness and large volume.
flame spray
Melt blown nonwovens extrude molten polymer fibers through rotating mesh or mold (up to 40 holes per inch) to form slender fibers, which are stretched and cooled by hot air when they fall from the mold. The final net is collected into rolls and then transformed into finished products. Microfibers (usually polypropylene) are different from other extrudates, especially spunbonded, because they have lower inherent strength, but much smaller size and key properties. Melt blown nonwovens can use very fine fibers, which are usually used in respirators, masks and filter media. Typically, melt blown nets are added to spunbonded nets to form SM or SMS nets, which are used in disposable diapers and women's care industries.