Processes for manufacturing non-woven fabrics can be grouped into four general categories:
- extrusion-polymer processing related
- hybrid combinations
Textile technologies include garneting, carding, and aerodynamic forming of fibers into selectively oriented webs. Fabrics produced by these systems are referred to as dry laid non-wovens, and they carry terms such as garneted, carded, and air laid fabrics. Textile-based non-woven fabrics, or fiber-network structures, are manufactured with machinery designed to manipulate textile fibers in the dry state. Also included in this category are structures formed with filament bundles or tow, and fabrics composed of staple fibers and stitching threads.
In general, textile-technology based processes provide maximum product versatility, since most textile fibers and bonding systems can be utilized and conventional textile-fiber processing equipment readily can be adapted with minimal capitalization.
Paper-based technologies include dry laid pulp and wetland (modified paper) systems designed to accommodate short synthetic fibers, as well as wood pulp fibers. Fabrics produced by these systems are referred to as dry laid pulp and wet laid non-wovens. Paper-based non-woven fabrics are manufactured with machinery designed to manipulate short fibers suspended in fluid.
Paper-technology based non-woven processes provide the least product versatility and require extensive capitalization, but they yield outstanding uniformity in products at exceptional speeds.
Extrusions include spun bond, melt blown, and porous film systems. Fabrics produced by these systems are referred to individually as spun bonded, melt blown, and textured or apertured film non-wovens, or generically as polymer-laid non-wovens. Extrusion-based non-wovens are manufactured with machinery associated with polymer extrusion. In polymer-laid systems, fiber structures simultaneously are formed and manipulated
Extrusion-technology based processes provide somewhat less versatility in product properties, but they yield fabric structures with exceptional strength-to-weight ratios (spun bonds), high surface-area-to-weight characteristics (melt blown), or high property uniformities per unit weight (textured films) at substantial to modest capitalization levels.
Hybrids include fabric/sheet combining systems, combination systems, and composite systems. Combining systems employs lamination technology or at least one basic non-woven web formation or consolidation technology to join two or more fabric substrates. Combination systems utilize at least one basic non-woven web formation element to enhance at least one fabric substrate. Composite systems integrate two or more basic non-woven web formation technologies to produce web structures. Hybrid processes combine technology advantages for specific applications.
NON-WOVEN WEB FORMING
The web formation phase of non-woven manufacturing processes transforms previously prepared/formed fibers, filaments, (or films), into preferentially arranged layers of lofty and loosely held fiber networks called webs, batts, mats, or sheets. Mechanical and fluid means are employed to achieve the preferred fiber orientation in the web through the use of machinery adapted from the textile, paper, or extrusion industries. Other critical fabric parameters established at web formation are unfinished product weight and manufactured width. In all non-woven manufacturing systems, the fiber material is deposited or laid on a forming or conveying surface, and the physical environment at this phase may be dry, wet, quenched, or molten; hence the terms dry laid, wetland, and fluid polymer laid.
The future trend in web formation is in improved quality, increased speeds, and process monitoring by using electronic information as a feedback mechanism to control the process and quality of the web. Important factors to consider in web formation are economy, versatility, speed, and quality of the web. A cost comparison when dealing in web formation is difficult to compile since each web-forming system is used for specific fibers or products, although an exception is with high loft products where both cards/cross lappers and air-forming systems are used. The current preference is toward air forming. However, this is beneficial when a modest range of product characteristics are desired. The most versatile web-forming system for high loft is carding and cross lapping. The most streamlined system is the use of air formers.