Nonwoven fabrics begin with either synthetic or natural fibers in a staple fiber form or as continuous filaments. Staple fibers are short, chopped fibers that can be blended with other fiber types. Both staple and continuous filament fibers can be made with varying diameters. Fibers can be made from a single synthetic polymer, but they can also be combined to form a bi-component sheath-core or bi-constituent side-by-side fiber. Even though round is the most common fibrous shape, fibers can be extruded in different cross-section shapes depending on desired functionality.
All nonwoven fabrics start out in the same form: loosely connected masses of fibers. To convert this loose mass into a reliable end-product, the fibers are put through one of four web forming processes.The initial stages of the spunbond process are similar to the principles of a spaghetti press or meat grinder where a lump of dough or meat is pressed through a grate. The resulting resin is then melted and fed through a spinneret to create string-like filaments. These strings are drawn down through an attenuation process to alter the denier diameter and jetted onto a moving conveyor belt to form the web. There are various methods of attenuation and jetting which dictate the type of spunlaid fabric manufactured.
Meltblown is another type of spunlaid with extremely fine denier fibers.In this process, fibers are arranged so they lay parallel, then cylinders with wire roll over the fibers creating a webbed structure. Carded nonwovens tend to be stronger in the direction that the machine’s teeth roll, but can be reinforced to increase the strength or absorbency of the fabric by layering.Unlike carding, which relies on strict structure, air laying is a bit more erratic. Specially engineered machines shoot short fibers in a jet-like air stream that collides with a moving screen. The impacts caused by the moving screen meshes the short fibers into webbed formation.This process takes staple fibers and puts them in aqueous slurry. The slurry is then laid down on a mesh table and dried, leaving a loose mechanically-bonded web. The most common wetlaid process is paper manufacturing.
Typically the web that is created through one of the forming processes above is held together by weak mechanical bonds. There are several bonding technologies available to strengthen the fabric.Typically synthetic fibers are thermoplastic, which means they soften and re-melt when heat is applied, providing an opportunity for adjacent fibers to bond together. The main types of thermal bonds are:By applying heat and consistent pressure in the form of a flat calender across the web, flat bonding creates a smooth surface where fibers are bonded to each other.Also known as pattern bond, point bonding is the process of applying a heated roll with a pattern embossed in the roll. Fibers are bonded together only at the points of the roll.This bonding process uses fine high-pressure jets of water sprayed down on top of the fabric. The pressure from the jet causes fibers to become mechanically entwined through the depth of the fabric.
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