Melt-Blowing

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. 

The steps beyond filament extrusion are diverse and are usually proprietary. The yarns are pulled from the spinneret, perhaps by air jets, given an electric charge, and are then laid down on a moving screen. Alternatively, the yarns may be pulled away by rolls and drawn between a set of rolls before they are fed to the air jets. In the former case, the yarns are usually only partially oriented, even though they are stretched at very high speeds. After they are formed, the fabrics are thermally bonded by calendering, or needle-punched, or chemically bonded. For information in the patent literature, the reader should see Gillies [181]. 

The melt-blowing process was developed on a small scale at the U.S. Naval Research Laboratories subsequently, larger-scale development was carried out by Exxon and the Beloit Corporation. The process produces nonwoven fibrous webs from any thermoplastic resin but has been used most extensively with polypropylene, which appears to be particularly 

Temperature— The temperature, at which centrifugal spinning is carried out also plays an important role in controlling the fiber stractnre. Typically, with increase in temperature, the fluid viscosity decreases. This favors the reduction of fiber diameter, but also may lead to the formation of beads. 

Melt blowing was developed in the 1950s at the Naval Research Laboratory in Washington, D.C., and it currently is one of the leading fiber and non-woven manufacturing processes. Fibers produced by melt blowing typically have diameters greater than 1 fim. However, by the careful control of operation conditions, it is possible to produce nanofibers from certain materials. 

The structure of melt-blown fibers can be controlled by varying flow rates of polymer melt and air, temperatures of polymer melt and air, nozzle geometry, and intrinsic properties of polymer melt. For example, higher air flow rate can 

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Glass Melt blowing and spinning High strength Low modulus Low temperature Low cost Insulation Reinforced plastics... 

Melt Blowing. The melt blowing process uses very high melt flow polymers, sometimes in excess of 400 dg/min, and extrusion and tempeiatuies above 300°C to pioduce very fine fibeis (<5 pm dia). 

In principle, the gas-assisted injection molding process is similar to co-injection molding. Here, the second or core component is nitrogen, which is injected through a needle into the polymer melt, blowing the melt out of the way and depositing it against the mold surfaces. 

Union Carbide Extruder delivers melt + blowing gas into a pressurized accumulator, from which a short shot is injected into a low-pressure mold. 

Among the described types of materials are those modified by Cl melt blowing. Polymer melt-blown materials are produced by a special kind of extrusion when the fibers in a viscous-flow state are squeezed through a spinneret, dispersed by a gaseous flow and then deposited on a substrate [77]. Such polymer materials can be processed jointly with liquid Cl, or the fibers can be modified by inhibiting aerosols in the course of dispersion and deposition. 

Since the air carrying molten polymer particles from the melt generator to the substrate is a poor heat insulator, the transported particles cool down quickly. Figure 3.28 illustrates the catastrophic heat energy loss by PE melt particles sprayed in atmosphere by a melt-blowing device [52]. 

The extrusion method or melt blowing consists of spra3ung of fibers squeezed from the extruder spinneret by a jet of compressed gas and their deposition on the article surface. The layout chart of the process is presented in Fig. 3.32. 

L.S. Pinchuk, V.A. Goldade, A.V. Makarevich, V.N. Kestelman. Melt Blowing. Equipment, Technology, and Polymer Fibrous Materials. Berlin Heidelberg New York, Springer-Verlag, 2002. 

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. 

The diameter of natural and synthetic fibres usually ranges from 7 to 20 xm. Microfibres and bicomponent split fibres allow a range of 3-7 pm and finer. Tightly woven textiles made of fine microfibres are watertight, but are permeable to water vapour. Melt-blow and flash spinning fibres have a 1 pm diameter. With electro-spinning, a diameter of 100 nanometres or lower can be produced. These fine fibres are very suitable for the filtering of small particles. 

The Chemical Abstract Service has defined these materials under the CAS number 142844-00-6 as Refractories, fibers, aluminosilicates. Amorphous man-made fibers produced from melting, blowing or spinning of calcinated kaolin clay or a combination of alumina (AI2O3) and silica (SiOa). Oxides such as zirconia, ferric oxide, magnesium oxide, calcium oxide and alkalines may also be added. 

In the present paper a kinetic theory of crystal nucleation is considered for the polymers subjected to time-dependent deformation rates, with transient effects of the chain relaxation. The considerations provide a theory useful in modelling fast polymer processing with stress-induced crystallization, like high-speed melt spinning, melt blowing, electro-spinning, etc. 

General purpose fibers are prepared by two different spinning methods, centrifugal spinning and melt blowing, both of which are high-productivity processes. A more detailed discus.sion of these processes will be found in Lavin (2001b). 

Production Processes. Because of the very refractory nature of these materials, the standard production processes of melt blowing and spinning are not practical. In these processes, the precursor material is melted, usually in an arc furnace, drawn through spinnerets and spun in a high-pressure air stream. Instead, the fibers (smd whiskers) are produced by sol-gel or by chemical-vapor deposition (CVD). 

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