Melt blowing apparatus with parallel flow filament attenuating slot

Abstract

A melt blowing die for extruding filaments of a polymer by a suitable configured air supply system to provide critical influencing and control over the molecular orientation, crystallinity and crystal orientation in high speed fiber spin line applications. Control of the both the magnitude and location of the applied shearing force is provided, through the design characteristics of the air supply system and, in particular, the attenuation of the filament through an attenuation slot; in one form in conjunction with the introduction of the air flow to the filament in a parallel flow caused by a Coanda bend in a second form in conjunction with a properly designed internal channel.

1 . A melt blowing die apparatus, for extruding a plurality of polymer filaments for the manufacture of non-woven thermally insulating polymer mats, comprising: 
 a) a die having a downwardly facing die face, defining a plurality of polymer filament extruding nozzles having axes directed to extrude the filaments vertically downwardly;    b) a slot defined by vertical opposed parallel side walls evenly spaced on opposite sides of the axes, through which the filaments, extruded by the die through the nozzles, pass; and    c) a pair of air supply channels located adjacent the downwardly facing die face, one on either side of the axes, each for the supply of a hot air stream vertically downwardly to and through the slot on opposite sides of said axes in contact with the filaments to attenuate the filaments passing vertically downwardly through the slot thereby to produce attenuated filaments to form the mats subsequent to downward exit from the slot.    
     
     
         2 . The apparatus of  claim 1 , wherein the nozzles are disposed in an evenly spaced straight line array and the slot is common to all nozzles in the array.  
     
     
         3 . The apparatus of  claim 1 , wherein the air supply channels are identical in mirror image and each bounded, at least adjacent the nozzles, by the die face and a nozzle bar defining the slot.  
     
     
         4 . The apparatus of  claim 3 , wherein the air supply channels each decrease in cross-section to accelerate the air stream flowing therethrough to a desired velocity for supply to and through said slot.  
     
     
         5 . The apparatus of  claim 4 , wherein the channels each have a relatively large radius bend remote from said slot providing a relatively high acceleration of the air stream and a relatively small radius bend, adjacent said slot to orient the air stream to flow substantially vertically into and through the slot, providing relatively small acceleration of the air stream.  
     
     
         6 . The apparatus of  claim 5 , wherein the relatively small radius bend is a Coanda bend.  
     
     
         7 . The apparatus of  claim 3 , wherein each channel has a Coanda bend therein to direct the hot air stream passing therethrough vertically into the slot.  
     
     
         8 . The apparatus of  claim 7 , wherein each channel has a duct for the introduction of ambient air, to the hot air stream adjacent the downwardly facing die face at the entrance to the Coanda bend for entrainment with the upper boundary of the hot air stream to ensure continuous contact of the hot air stream with a curved surface defined by the nozzle bar and smoothly joining said side walls to provide said hot air stream in said slot.  
     
     
         9 . The apparatus of  claim 1 , wherein the slot has a transverse width of about 0.15 inch to about 0.30 inch and a height of about 1.0 inch to about 2.5 inches; the air streams in the slot have a velocity of about Mach no. 0.5 to about 0.75.  
     
     
         10 . The apparatus of  claim 1 , wherein the channels and slot are configured to provide laminar flow of the air streams in the slot at the desired the velocity.  
     
     
         11 . A method of melt blowing polymer filaments, for the manufacture of non-woven thermally insulating polymer mats, comprising the steps of: 
 a) extruding a plurality of polymer filaments downwardly;    b) passing the filaments centrally through a slot, having vertical parallel slot defining side walls, common to all the filaments;    c) providing heated air streams on opposite sides of the filaments, to flow vertically with the filaments through the slot to attenuate the filaments while in the slot to produce attenuated filaments for the formation of the mats subsequent to exit from the slot.    
     
     
         12 . The method of  claim 11  comprising directing the heated air streams to flow vertically through the slot by the use of Coanda bend.  
     
     
         13 . The method of  claim 11  comprising providing a laminar flow of the air streams through the slot.  
     
     
         14 . The method of  claim 11  comprising providing an air flow through the slot which becomes turbulent upon exit from said slot to impart large lateral accelerations to the filaments subsequent to the exit from the slot to facilitate the required fiber entanglement.  
     
     
         15 . The method of  claim 11 , wherein the height of the slot as defined by said side walls provides for the attenuation of the filaments by the air streams in the slot by at least 50:1.  
     
     
         16 . The method of  claim 11  comprising providing the air streams as they contact the filaments at about 500° F. to about 700° F. and heating the slot side walls to a temperature of about 400° F. to about 700° F.