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What are nonwovens?
Nonwoven fabrics are engineered fabrics that may be a limited life fabric, disposable-use fabric or a very durable fabric. Nonwoven fabrics provide specific functions such as absorbency, liquid repellency, resilience, stretch, softness, strength, flame resilience, flame retardancy, washability, cushioning, filtering, and bacterial barrier and sterility. These properties are often combined to create fabrics suited for specific jobs, while achieving a good balance between product use-life and cost. In combination with other materials, they provide a spectrum of products with diverse properties and are used alone or as components of apparel, home furnishings, health care, engineering, and industrial and consumer goods.
Nonwovens can be converted by many means and can be a vital part of a filtration system. Pleated cartridges or panels, slit rolls for coolant filters, bags for airs or liquid, pockets, pads, wound elements and more can be used for many applications which range from drinking water to engine oil, from hospital air cleaners to hot gas filtration, from donor blood to jet fuel.
General Production Process of Nonwovens
Nonwovens emerged from the textile, paper, plastic and leather industries and from there a separate, innovative and completely flexible industry has evolved. The production of nonwovens can be described as taking place in three stages, although modern technology allows an overlapping of the stages, and in some cases all three stages can take place at the same time.
The three stages are : Web Formation ▶ Web Bonding ▶ Finishing Treatments
Web Formation
Nonwoven manufacturing starts by arranging fibers in a sheet or web. The fibers can be staple fibers packed in bales or filaments extruded from molten polymer granules. Three basic methods are used to form a web, and nonwovens are usually referred to by one of these methods :
Drylaid process : In what is called a carding machine, a web is formed out of the staple fibers using several rotating rollers fitted with fine wires.
Wetlaid process : The fibers are distributed very finely and evenly in water, and passed over a belt screen, where the water is extracted, and the web thus produced laid onto a belt and then bonded.
Spunbonding process : In this method, the nonwoven is produced in a single continuous process. The raw material is melted, spun through narrow jets to form endless fibers, stretched by hot air flows, and laid into a web.
Web Bonding
Webs, other than spunlaid, have little strength in their unbonded form. The web must therefore be consolidated in some way. This is effectively done through bonding, a vital step in the production of nonwovens.
There are three basic types of bonding :
Chemical (Adhesion) bonding : A bond is established between the fibers of the web using a binding agent. There are many ways of applying the binder. It can be applied uniformly by impregnating, coating or spraying or intermittently, as in print bonding.
Thermal bonding : A web is bonded by passing through a hot rotating cylinder or hot air chamber. This method uses the thermoplastic properties of certain synthetic fibers to form bonds under controlled heating.
Needle Punching : Needles are pushed through the fiber web and pull fibers with them at withdrawal, so that the web bonds and thus obtains the requisite strength.
Finishing Treatments
There is an opportunity to meet the needs of the customer even more precisely by modifying or adding to existing properties. A variety of different chemical substances can be used before or after binding, or various mechanical processes can be applied to the nonwovens after binding. Nonwovens can be made conductive, flame retardant, water repellent, porous, antistatic, breathable, absorbent and so on. They can also, for example, be coated, printed, flocked or dyed and can be combined with other materials to form complex laminates.
Manufacturing Process of Genplus Kafron® Nonwovens
Genplus Kafron® Nonwovens are produced by the needle punch process, and the needle punch process can be used on most types of webs to create bonded media. Barbed needles are punched vertically through the web, hooking tufts of fiber, which become bonded together. During this process, the web travels between two plates while it is pulled by draw rolls.
Special properties of nonwovens can be achieved by adding bonding fibers, antistatic fibers or other special fibers. It is also possible to produce functional compound materials by needling fiber nonwovens to different kinds of base layers such as woven fabrics, foam layers or webs of laid threads. Webs of different characteristics can be needled together to produce a gradation of properties difficult to achieve by other means.
Benefits include strong bonded materials, which with additional binders are particularly suited for heavy weight and high denier fabrics. Applications include engine-intake filtration, industrial dust filtration, HVAC filtration, and air filtration media.
General Production Flow of Genplus Kafron® Nonwovens