Novel Multi-Layer Melt Blown Microfiber Webs
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NOVEL MULTI-LAYER MELT BLOWN MICROFIBER WEBS Eugene G. Joseph 3M Company St. Paul, Minnesota, USA.
INTRODUCTION Melt blowing is a melt extrusion process that allows us to start with a material in resin form and obtain a final web product in one step. The fine fibers that are characteristic of this process are in the 0.1 to 15 micron range in diameter. This process was first described in the literature by Wente of the Naval Research Laboratory in 1956 [1] and the purpose of the work was to investigate the feasibility of making ultrafine fibers for evaluation as a filtermedia. Since then melt blowing has been one of the fastest growing technologies in the non-wovens area as evidenced by the numerous articles in the literature and the number of issued patents. For example, an article by McCulloch and Graham [2] illustrated the diverse use of melt blown webs which are also referred to as Blown Micro Fiber(BMF) webs. Further, data published by Smith [3], (see Figure 1), shows how the number of patents dealing with melt blowing has dramatically increased in the last 10 to 15 years. In terms of the technology itself, most of the work published has been related to die designs, understanding air flows and equipment developments [4-7]. Some work has also been published relating Figure 1 - Plot of the number of Meltblown patents granted properties of polypropylene melt between 1970 and 1992 blown webs to process variables [8]. Pioneering work done at 3M Company on co-extruded melt blown webs was presented by Joseph [9] and dealt with the structure - property behaviour of multi-layer blown micro fiber(MMF) webs, i.e. multiple layers within each microfiber. Since then work done on co-extruded melt blowns have been presented and have dealt with process parameters[10] or use of new materials [11]. More recently work has been done on melt blowing of pressure sensitive adhesives(PSA) in single layer and multi-layer forms. One of the attractive features of melt blown PSA’s is that it provides an adhesive that is porous and that can be produced using a “solvent – free” process. Melt blowing of PSA’s in combination with co-extrusion allows for a wide range of materials with novel properties as will be presented later in this paper. In addition, the structure and mechanical properties of novel materials(FILBERS) prepared from these multi-layer webs will also be discussed.
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MATERIALS AND EXPERIMENTAL A wide range of commercially available polymeric materials were melt blown in different combinations to give targeted microfiber crosssections as shown schematically in Figure 2. The number of layers within the microfibers ranged from 2 to 27. In addition to varying the number of layers, for the same polymer pair, the layer sequence was also varied. Some of the non-PSA materials used to Figure 2 - Schematic diagram showing the cross-sections of multiproduce the multi-layer webs include layer microfibers. The layers are made up of alternating layers poly-ethylene(PE), poly-propylene(PP), from two different polymers. Component “A” ca
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