Webs become fabrics through a mechanical needling process or application of chemical substances, adhesives, or heat. Spun-bonded and melt-blown technology is being combined in some applications where bicomponent or biconstituent webs are needed for barrier and filtration applications. In these combinations, the process is known as spun melt.
Needle Punching or needling consists of passing a dry-laid web over a needle loom as many times as is necessary to produce the desired strength and texture. A needle loom has barbed needles protruding 2 to 3 inches from the base. As the needles stitch up and down through the web, the barbs pull a few fibers through the web, interlocking them mechanically with other fibers. This process is relatively inexpensive.
Blankets, carpeting, and carpet backing are examples of needle-punched products. Fiber denier, fiber type, and product loft vary. Indoor/outdoor needle-punched carpeting made of olefin is used for patios, porches, pools, and putting greens because it is impervious to moisture. Needled carpet backings are used with some tufted carpets.
Needled fabrics can be made of a two-layer web with each layer a different color, often of solution-dyed fibers. By pulling colored fibers from the lower layer to the top surface, geometric designs are possible. Fibers pulled above the surface produce a pile fabric. Needle-punched fabrics are finished by pressing, Steaming, Calendaring, dyeing, and embossing. Other techniques include the use of a closed needle that penetrates the web, opens, grabs some fibers, and draws them back as a yarn like structure that is then chain-stitched through the web. These fabrics are related to the stitch-through fabrics discussed later in this chapter. Needle-punched fabrics also are used for tennis-ball felts, blood filters, papermaking felt, speaker-cover fabrics, synthetic leathers, oil-absorbent pads, some bullet-resistant vests, and insulator padding.
Chemical adhesives are used with dry-laid or wet-laid webs to bond the fibers together. Adhesives include vinyl acetate, vinyl acrylic, and acrylic polymers. Each type has characteristics that make it appropriate for certain applications. The adhesive is applied in a liquid, powder, or foam form and heated and pressed to adhere fibers together in the web.
Heat and pressure are used to bond thermoplastic-fiber webs. Several techniques are used. In area-bond calendaring, the fibers are heated and pressed to form a permeable film-like structure that is stiff, inextensible, and strong. In point-bond calendaring, the heated fiber web passes through a pair of calendar rolls: one is engraved and the other is smooth. The engraved roller presses the web onto the smooth roller and the fibers adhere to each other. Characteristics relate to the size and density of the bond points. Fabrics are usually moderately bulky, elastic, and soft and are used for medical, sanitary, and filtration applications.
Migrate, produced by polymer Group Inc., is a fabric formed directly from fibers using a combination of high-pressure water jets and laser imaging that has two-way stretch and can be made to resemble fabrics such as corduroy, denim, and brocade. End users include dyed and printed wall coverings, upholstery, pillows, comforters, and window treatments. Depending on the fiber content, Migrate may be laundered 50 times with no problem detected.