4. By Thermal Bonding

This process generally involves making of a web having synthetic fibers such as polyethylene, polypropylene, polybutene, ethylene copolymers, propylene copolymers and butene copolymers. The webs are made to be homogeneous and then joined by interfiber bonding to form a coherent web structure which is able to withstand necking. Necking refers to making a material constricted in at least one direction by means of processes like drawing/gathering. Interfiber bonding may be produced by entanglement between individual melt-blown fibers. The fiber entangling is inherent in the melt-blown process but may be generated or increased by processes such as, for example, hydraulic entangling or needle punching. These webs are then passed through a set of nip rollers to impart desired necking or simply stretching. The material is then heat treated for it to memorize the new, necked dimensions. This is done by passing the material over heated steam cans. The material is then cooled in its necked condition. This completes formation of the reversibly necked material. The reversibly necked material can extend to at least its original, pre-necked dimensions upon application of a stretching force in a direction generally parallel to the direction of necking and then recover to within at least about 50 percent of its reversibly necked dimensions upon release of the stretching force. The heat treatment should raise the neckable material to a temperature range for a specified time period where it is believed that additional polymer crystallization occurs while the material is in the necked condition. Certain types of fibers are formed by methods like melt-blowing and spun-bonding which cool the fibers very quickly; it is believed that the polymers forming the fibers are not fully crystallized. That is, the polymers harden before the crystallization is complete. It is also apparent that additional crystallization can be effected by increasing the temperature of the material to a temperature below the material's melting point. When this additional crystallization occurs while the material is in the necked condition, it is believed that memory of the necked condition is imparted to the material. Different combinations of fibers can be used in such webs and SMS combinations are also popular ⁷⁾. These fabrics find applications in disposable sanitary protection products, medical products, protective work-wear or personal use items ¹⁾.

Conclusion

Elastic nonwoven composites have wide applications in various fields ranging from diapers to garment linings. Depending on the type of final product required, and the types of raw materials used, elastic composites can be made by using one of the several bonding techniques. It is important to choose appropriate technique so that the final product lies within the desired specifications.

References:

1. De-Sheng, Te-Hsin, E. I. Du Pont de Nemours and Company (2005) Process For Preparing an Elastic Nonwoven Web, WO/2005/056900.
2. Morman, T., Kimberley-Clark Corporation (1987) Composite Nonwoven Elastic Web, U.S. Pat. 4,657,802.
3. Wideman, H.A., Poly Wide, Inc. (1974) Disposable Laminate Product and Methods of Making It, U.S. Pat. 3,842,832.
4. Romanek, G.A., Phillips Petroleum Company (1984) Textured Nonwoven Textile Fabric Laminate and Process of Making Said, U.S. Pat. 4,446,189.
5. Likhyani, K., E. I. Du Pont de Nemours and Company (1984) Spunlaced Facric Containing Elastic Fibers, U.S. Pat. 4,426,420.
6. Quantrille; Thomas, E., Fiberweb North America, Inc. (1994) Composite Elastic Nonwoven Fabric, U.S. Pat. 5,334,446.
7. Morman, T., Kimberley-Clark Corporation (1988) Reversibly Necked Material, U.S. Pat. 4,965,122.

About the Author:

The author is Graduate Research Assistant at North Carolina State University.