Meltblown! Spunbond! What other types of non-woven fabrics do you know?
The first written definition of nonwovens came from the American Society for Testing and Materials in 1962, which defined nonwovens as “textiles made of cotton or fiber webs bonded together by adhesives.” Currently, the nonwovens industry association INDA defines nonwovens as “sheet-like or net-like structures in which fibers or filaments (and perforated films) are intertwined by mechanical, thermal or chemical means. These substrates are flat, Perforated sheets made directly from individual fibers or from molten plastic or plastic films, they are not made by weaving or weaving and do not require the conversion of fibers into yarns.
The technical definition expresses the basic basis of the nonwovens process, but a general description of nonwovens is insufficient due to the diversity of production technologies. Just like woven or knitted fabrics, each process has its own unique characteristics. Aside from being classified as a nonwoven, the resulting fabric doesn’t have much in common. Nonwoven components, for example; fiber selection, mesh formation, bonding and finishing techniques can be varied to manipulate fabric properties or reverse engineer fabrics according to functional requirements. Due to its achievable properties, the nonwoven category penetrates a wide range of markets including medical, apparel, automotive, filtration, construction, geotextiles and protection.
There are several nonwovens that can be used to make these materials.
Air Mesh Nonwovens
Compared to other nonwoven technologies, airlaid has the unique ability to lay down short fibers, either 100% pulp fibers or a mixture of pulp and short fibers, to form a uniform and continuous web. Superabsorbent powders or fibers can also be mixed to form a superabsorbent web.
Airflow paving can be bonded in a number of ways. In latex bonding (LBAL), a liquid adhesive is applied to both sides of the web, which is then dried and cured to achieve the desired wet and dry strength. Typical applications are desktop products, dry wipes, industrial wipes and household products. Thermal Bonding Air Distribution (TBAL) consists of bonding fibers, usually bicomponent fibers, to form a web and heat to activate the fusion component of the synthetic fibers to bond the web. It is commonly used in absorbent cores, where superabsorbent powders may also be present and locked in a mesh structure by synthetic fibers.
Multiple Bonding (MBAL) is a bonding process that combines latex and thermal bonding. Usually the inside of the product is thermally bonded and the surface is coated with a lightweight adhesive to remove dust and lint. Commonly used in absorbent cores, household items, dry wipes, these materials may also contain SAP.
In hydrogen bonding (XBAL), bonding is achieved by a combination of pressure, humidity and temperature, resulting in so-called hydrogen bonding, without the need for other bonding methods. Typically used for absorbent cores.
Hot air non-woven fabric
Air bonding is a type of thermal bonding that involves the application of heated air to the surface of a nonwoven fabric. During air bonding, heated air flows through a hole in the plenum above the nonwoven. Unlike a hot oven that pushes air through the material, the ventilation process uses negative pressure to draw air through an open conveyor belt that carries the nonwoven as it is pulled through the oven. By letting air pass through the material, heat can be transferred quickly and evenly, minimizing deformation of the nonwoven. The binders used in the air bonding process include crystalline binder fibers and powders that melt on the cross-section of the nonwoven to form droplets. These droplets combine as the material cools. The non-woven fabric prepared by the air-permeable method is soft and fluffy.
Meltblown non-woven fabric
Meltblown nonwovens are made by extruding molten polymer fibers through a spinning mesh or die with 40 holes per inch to form elongated fibers that are pulled by hot air as they come off the die stretch and cool. The resulting fiberboard is collected into rolls, which are then converted into finished products. Very fine fibers (usually polypropylene fibers) differ from other extrudates, especially spunbond fibers, in that they have lower inherent strength but are much smaller in size, providing key properties. Meltblown nonwovens can benefit from very fine fibers and are commonly used in masks and filter media. Typically melted and added to spinning binders to form SM or SMS webs for use in the disposable diaper and feminine care industries.
Hydrospun or bonded nonwovens are produced in a continuous process. The fibers are spun into fibers, which are then dispersed directly into a web through baffles or airflow guidance. This technology makes conveyor belts faster and cheaper. Several variants of this concept are available. Polypropylene spins faster and cooler than PET, mainly due to the different melting point. Polypropylene spunbond is a widely selected material in hygiene products such as baby diapers and feminine hygiene products, as well as medical apparel. Polyester-based spunbond materials are commonly used in durable nonwoven applications such as roofing and construction, automotive and geotextiles.
The spunbond method has been combined with meltblown nonwovens, making them a layered product called SMS (spun melt melt spinning). Meltblown nonwovens have very fine fiber diameters, but are not strong fabrics. SMS fabric is completely made of PP, waterproof, excellent and disposable. Meltblown is often used as a filter medium to capture very fine particles. The spine is glued with resin or heat.
Wetlaid non-woven fabric
In the wet process, short fibers up to 12 mm long are usually mixed with viscose or wood pulp and suspended in water using large tanks. The aqueous fiber or slurry dispersion is then pumped in and continuously deposited on the resulting wire. Water is siphoned, filtered and recovered. In addition to synthetic fibers, glass fibers, ceramic fibers and carbon fibers can also be processed.
The difference between wet-laid non-woven fabric and wet-laid paper is that the fiber content of wet-laid non-woven fabric is more than 30%, which is composed of fibers with an aspect ratio greater than 300, and its density is less than 0.40 g/cm3. Wipes are commonly used in applications such as tea bags, coffee filters, and dispersible wipes.
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