Method for making a nonwoven web

Abstract

Melt blown or spun bond nonwoven webs are formed by flowing fiber-forming material through a die cavity having a substantially uniform residence time and then through a plurality of orifices to form filaments, using air or other fluid to attenuate the filaments into fibers and collecting the attenuated fibers as a nonwoven web. Each die orifice receives a fiber-forming material stream having a similar thermal history. The physical or chemical properties of the nonwoven web fibers such as their average molecular weight and polydispersity can be made more uniform. Wide nonwoven webs can be formed by arranging a plurality of such die cavities in a side-by-side relationship. Thicker or multilayered nonwoven webs can be formed by arranging a plurality of such die cavities atop one another.

1 . A nonwoven web-forming apparatus comprising a die cavity having a substantially uniform residence time for fiber-forming material flowing through the die cavity, a plurality of filament-forming orifices at the exit from the die cavity, a conduit that can supply a stream of air or other fluid to attenuate the filaments into fibers, and a collector and optional calendaring device on which a layer of the attenuated fibers can form into a nonwoven web.  
     
     
         2 . An apparatus according to  claim 1  wherein the die cavity is configured so that the filaments have the same or substantially the same physical or chemical properties as they exit the die cavity.  
     
     
         3 . An apparatus according to  claim 1  wherein the die cavity is part of a meltblowing die and the attenuating fluid is heated.  
     
     
         4 . An apparatus according to  claim 1  wherein the calculated, simulated or experimentally measured residence time for any portion of a stream of the fiber-forming material flowing through the die cavity is within about ±50% of the average calculated, simulated or experimentally measured residence time for the entire stream.  
     
     
         5 . An apparatus according to  claim 1  wherein the calculated, simulated or experimentally measured residence time for any portion of a stream of the fiber-forming material flowing through the die cavity is within about ±10% of the average calculated, simulated or experimentally measured residence time for the entire stream.  
     
     
         6 . An apparatus according to  claim 1  wherein the residence time in the die cavity is such that the polydispersity of fibers formed by the apparatus differs from the average fiber polydispersity by less than ±5%.  
     
     
         7 . An apparatus according to  claim 6  wherein the basis weight uniformity of a nonwoven web formed by the apparatus is about ±2% or better.  
     
     
         8 . An apparatus according to  claim 1  wherein a plurality of the die cavities are arranged to form a wider or deeper nonwoven web than would be obtained using only a single such die cavity.  
     
     
         9 . An apparatus according to  claim 1  wherein a plurality of the die cavities are arranged in a side-by-side array that can form a uniform or substantially uniform nonwoven web having a width of about one meter or more.  
     
     
         10 . An apparatus according to  claim 1  wherein a plurality of the die cavities having widths less than about 0.33 meters are arranged in a side-by-side array that can form a uniform or substantially uniform nonwoven web having a width of about one meter or more.  
     
     
         11 . An apparatus according to  claim 1  wherein a plurality of the die cavities having widths less than about 0.25 meters are arranged in a side-by-side array that can form a uniform or substantially uniform nonwoven web having a width of about one meter or more.  
     
     
         12 . An apparatus according to  claim 1  wherein a plurality of such die cavities are arranged in a stack.  
     
     
         13 . An apparatus according to  claim 1  wherein the die cavity is part of an annular die having a central axis of symmetry.  
     
     
         14 . An apparatus according to  claim 1  wherein the die cavity can be operated using a flat temperature profile.  
     
     
         15 . An apparatus according to  claim 1  wherein the die cavity has a generally planar die slot and an outlet and the die cavity outlet is angled away from the plane of the die slot.  
     
     
         16 . An apparatus according to  claim 15  wherein the die cavity outlet is angled away from the plane of the die slot at approximately a right angle.  
     
     
         17 . An apparatus according to  claim 1  wherein the die cavity has a manifold having a wall and a die slot having a wall, and the shear rate at the slot wall is substantially the same as the shear rate at the manifold wall.  
     
     
         18 . An apparatus according to  claim 1  wherein the die cavity has an outlet edge and a centerline, and further has manifold arms and a die slot that meet within curves defined by the equation:  
       
         
           
             
               
                 y 
                 ⁡ 
                 
                   ( 
                   x 
                   ) 
                 
               
               = 
               
                 
                   ( 
                   
                     1 
                     ± 
                     0.5 
                   
                   ) 
                 
                 ⁢ 
                 2 
                 ⁢ 
                 
                   
                     W 
                     ⁡ 
                     
                       ( 
                       
                         
                           
                             b 
                             - 
                             x 
                           
                           W 
                         
                         - 
                         1 
                       
                       ) 
                     
                   
                   
                     1 
                     / 
                     2 
                   
                 
               
             
           
         
       
       where x and y are coordinates in an x-y coordinate space in which the x-axis corresponds to the outlet edge and the y-axis corresponds to the centerline, b is the die cavity half-width and W is the manifold arm width.  
     
     
         19 . An apparatus according to  claim 18  wherein the manifold arms and die slot meet within curves defined by the equation  
       
         
           
             
               
                 y 
                 ⁡ 
                 
                   ( 
                   x 
                   ) 
                 
               
               = 
               
                 
                   ( 
                   
                     1 
                     ± 
                     0.1 
                   
                   ) 
                 
                 ⁢ 
                 2 
                 ⁢ 
                 
                   
                     
                       W 
                       ⁡ 
                       
                         ( 
                         
                           
                             
                               b 
                               - 
                               x 
                             
                             W 
                           
                           - 
                           1 
                         
                         ) 
                       
                     
                     
                       1 
                       / 
                       2 
                     
                   
                   . 
                 
               
             
           
         
       
     
     
         20 . A nonwoven web having a width of at least about 0.5 meters and comprising at least one layer of melt blown or spun bond fibers having substantially uniform polydispersity.  
     
     
         21 . A web according to  claim 20  wherein the polydispersity of the fibers differs from the average fiber polydispersity by less than ±3%.  
     
     
         22 . A web according to  claim 20  wherein the layer of fibers has a basis weight uniformity of about ±2% or better.  
     
     
         23 . A web according to  claim 20  wherein the layer of fibers has a basis weight uniformity of about ±1% or better.  
     
     
         24 . A web according to  claim 20  having a width greater than about 1 meter.  
     
     
         25 . A web according to  claim 20  wherein the fibers comprise melt blown microfibers averaging less than about 10 micrometers in diameter.  
     
     
         26 . A web according to  claim 20  wherein the fibers comprise melt blown ultrafine fibers averaging less than about 5 micrometers in diameter.  
     
     
         27 . A web according to  claim 20  wherein the fibers comprise polyethylene, polypropylene, polybutylene, polystyrene, polyethylene terephthalate, polybutylene terephthalate, linear polyamides such as nylon 6 or nylon 11, polyurethane, poly (4-methyl pentene-1), or a mixture or combination thereof.  
     
     
         28 . A web according to  claim 20  wherein the fibers comprise polypropylene or at least one layer or blend thereof  
     
     
         29 . A nonwoven web comprising at least one layer of melt blown ultrafine fibers having an average fiber diameter less than about 5 micrometers and substantially uniform polydispersity.  
     
     
         30 . A web according to  claim 29  wherein the polydispersity of the fibers differs from the average fiber polydispersity by less than ±3%.  
     
     
         31 . A web according to  claim 29  wherein the layer of fibers has a basis weight uniformity of about ±2% or better.  
     
     
         32 . A web according to  claim 29  wherein the layer of fibers has a basis weight uniformity of about ±1% or better.  
     
     
         33 . A web according to  claim 29  having a width greater than about 0.5 meter.  
     
     
         34 . A web according to  claim 29  having a width greater than about 1 meter.  
     
     
         35 . A web according to  claim 29  wherein the fibers comprise polyethylene, polypropylene, polybutylene, polystyrene, polyethylene terephthalate, polybutylene terephthalate, linear polyamides such as nylon 6 or nylon 11, polyurethane, poly (4-methyl pentene-1), or a mixture or combination thereof.  
     
     
         36 . A web according to  claim 29  wherein the fibers comprise polypropylene or at least one layer or blend thereof.