Spun-bonding process

The term spun-bonding process appears to have several definitions. Perhaps the most general one, and the one used here, is defined as the method wherein the production of fibers and fabrics or webs is combined. The usual spun-bonding process consists of laying down a 

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The typical spun-bonding process includes a spinneret with a means of conveying the continuous filaments out into the form of a web, or else several spinnerets arranged in a row whose length may approximate the width of the web to be produced. In either case, the process of melting and fiber formation is identical to that used in conventional melt spinning. 

According to DIN 61205, felt is a two- or three-dimensional fabric made of mechanically stabilized fiber webs. A needled nonwoven without adhesive binder needs a bulk density of <0.15 g/cml If the bulk density is higher, it is regarded as a felt. As soon as an adhesive binder is added, the product is always a nonwoven. In addition, nonwovens are all products manufactured with the spun-bonding process or those that became popularly known as spin-laced (water jet-bonded). See Fig. 6.2 for the area weight of typical nonwovens. 

Apart from the aerodynamic and mechanical spun-bonding processes, electrostatic processes are also gaining importance. In this process, the filaments are developed between two charged electrodes that are at opposite poles, for example, between a spinning nozzle and a sieve belt. 

This process resembles the spun-bond process with the major difference in the quenching of the filaments by hot air at high speed. This leads to very thin fibers (1-5 pm diameter) and hence to thin nonwoven structures. Crucial for these parameters are both air velocity and temperature as well as melt viscosity. 

One of the important aspects of the development of P-plastomers was the expectation that these materials were amenable to plastics processing such as fiber and film formation and yet would yield soft elastic fabrication. This combination was hitherto unknown [24]. The formation of nonwoven fabrics including spun-bond and melt-blown nonwoven fabrics as well as their laminated forms has been documented. Similarly, cast film operation to form elastic monolithic films or composite structures which are not only amenable to these processes, but also to a variety of postfabrication processes have been described. 

Polymer scientists and engineers have developed a wide variety of processes by which to convert polypropylene into useable articles. These processes include fiber-spinning, production of melt blown and spun bond non-woven fabrics, film production, blow molding, and injection molding. The following sections describe these processes and the resulting properties of the product as a function of the process. 

Nonwovens The textile and paper industries are based on the two oldest (wet and dry) processes. Manufacturers of nonwovens for plastics draw on both. With the wet, there are basically two types namely the Fourdrinier and cylinder machine types that have been modified. In addition, two basic types exist for the process formation of the web and application of the bonding agent or system where mechanical carding of fibers is used. The particular equipment and method of operation to be used, with their many modifications, is influenced by desired requirements such as mechanical properties, softness, surface condition, tenacity, etc. There are certain t) es of so-called nonwoven fabric that are directly formed from short or chopped fiber as well as continuous filaments. They are produced by loosely compressing together fibers, yarns, rovings, etc. with or without a scrim cloth carrier assembled by mechanical, chemical, thermal, or solvent methods. Products of this type include melted and spun-bonded fabrics. 

Nonwoven spun-bonded They are distinguished from other nonwoven fabrics by a one-step operation that provides a complete chemical to fabric route. The process integrates the spinning, lay-down, consolidation, and bonding of continuous filaments to form fabrics. Its largest growth area is disposable diaper cover stock. 

Polymer extrusion-based processes Some of the most significant contributions to the nonwoven industry came from the development of the direct polymer-to-fabric converting processes. These processes include spun-bonding, melting-blowing, and porous film. Nonwovens made by these processes are known as spunbond (SB) nonwovens, melting blown (MB) nonwovens, and apertured-fllm nonwovens. 

Based on conventional wisdom, such a starch composition would exhibit decreased melt processability and would not be suitable for melt extensional processes. However, the results reveal that the starch composition shows a significant increase in extensional viscosity when even a small amoimt of high pol5mer is added. Consequently, the starch composition is expected to have an enhanced melt extensibility and is suitable for melt extensional processes, such as blow molding, spun bonding, blown film molding, or foam molding (1). 

Spun bonded media production processes exploit the thermosetting properties of polymers, to form fibres that can be bonded by combinations of heat, pressure and chemical activation. Melt spinning, using conventional synthetic fibre technology, was the earliest method used for producing spun bonded filter media and continues to be of major importance, but finer fibres are produced by melt blowing and flash spinning processes. 

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