Melt-blowing process

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). 

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... 

The melt blowing process has the inherent ability to convert almost any material into microfibrous webs provided the material is fibrous form-able and the viscosity is sufficiently low at the die tip to permit... 

The melt blowing process responds to process variables more readily than most of the other nonwoven processes to produce a wide variety of end products. The actual process parameters that determine final web properties involve the selection of polymer or resin, conditions in the extruder or melt tank, geometry and condition at the die tip and fiber distribution and separation at laydown. Modem melt-blown lines are designed with highly automated machine and process control equipment, which allow for quick selection of particular parameters and easy machine adjustments. 

The melt blowing process by itself, or by integration with other nonwoven or film and paper processes, has tremendous flexibility to produce new and specialty products and to improve existing products, provided that new product conceptualizers and equipment manufacturers effectively interact to meet existing and new market needs. 

However, modern melt spinning distribution system technology has clearly demonstrated the capability to produce fibers with smaller size and better consistency than either of the two aforementioned techniques. Multicomponent fiber sizes as low as -0.04 pm (-40 nm) have now been demonstrated commercially at attractive production rates [22]. In addition, micro-sized (1-10 pm) and nano-sized (<1 pm) multicomponent fibers can be produced with improved production rates, economics and physical properties over the other systems, and with an even broader choice of polymers [22]. Multicomponent fiber production can be used to create fibers in staple or continuous filament form using the spunbond and melt blowing processes. 

Hot compressed air leaves the spinning head close to the melt drops and elongates them to long filaments up to breaking (e.g., the Exxon Melt Blow Process see the next section). 

The most commonly accepted and current definition for the melt blowing process is A one-step process in which high-velocity fluid, normally air, blows molten thermoplastic resin from an extmder die tip onto a conveyor, or take-up screen, or substrate to form a fine fibered self-bonded web. This very broad definition covers the extremely versatile melt blowing process (Fig. 8.41) that has the following characteristics ... 

Figure 8.41 Schematic diagram of horizontal and vertical melt blowing processes. ...

The key to the melt blowing process is the spin head. The basic principle is the extrusion of low viscosity polymer melt through a single row of very fine holes placed close together in the order of 1000-4000 holes per m. lliese... 

Melt blowing is used commercially as a one-step process for converting polymer resin directly into a nonwoven mat of superfine fibers. In the melt blowing process, high velocity hot air streams impact upon a stream of molten polymer as the polymer issues from a fine capillary. The result of this impact is that the polymer is rapidly (in about 50 ps) attenuated into fiber as fine as 1 pm in diameter. 

Figure 13.6. Schematic of the melt blowing process. For simplicity, only a single nozzle is shown. In actual production, multiple nozzles are used simultaneously.

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