Abstract:
An apparatus for producing meltblown webs includes a meltblowing die having a plurality of filament outlets, a collector for receiving filaments of polymeric material expelled from the filament outlets, and a first Coanda effect device positioned adjacent to the path of the filaments adjacent to the last filament outlet at an end of the meltblowing die. Methods of forming meltblown webs using such an apparatus are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/472395, filed Apr. 6, 2011, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to making webs of nonwoven media, and, more particularly, to a method and apparatus for making such webs of nonwoven media. 
         [0003]    In recent years, meltblown media has come into wide commercial use, for uses such as filtration, cleaning wipes, bandages, surgical drapes, battery electrode separation and insulation. 
       SUMMARY 
       [0004]    For many applications, it is desirable that webs of nonwoven media have a uniform basis weight. For example, when a web of nonwoven media has been converted into an air filter, thin spots may provide places where airborne contaminants could bypass the filter. With known melt blowing equipment and methods, it is difficult to maintain uniformity at the edges of the forming media. Thus, for applications requiring a high degree of uniformity, the edges of the media must be trimmed away and discarded as waste. In addition, a meltblowing die of a particular width will provide useful media of a lesser width at the collector. This is especially noticeable when the collector is positioned more than 40 cm from the meltblowing die. For example, a 200 cm wide die may produce usable webs having a width of only 175 cm. 
         [0005]    The need exists for a method and apparatus for forming meltblown webs with better side-to-side uniformity, and/or that can produce webs having a width equal to or greater than the width of the die. 
         [0006]    The present disclosure generally provides a method and apparatus for forming a meltblown web by positioning a Coanda effect device adjacent to the flight path of the fibers emerging from the blowing die on at least one edge of the web. While not wishing to be bound by any theory, it is believed that the Coanda effect provided by the Coanda effect device redirects some of the fibers which would otherwise form an insufficiently thick “ragged edge” on the web formed on the collector. 
         [0007]    In one embodiment, the present disclosure provides a meltblowing apparatus, comprising a meltblowing die having a plurality of filament outlets, a collector for receiving filaments of polymeric material expelled from the filament outlets, and a first Coanda effect device positioned adjacent to the path of the filaments adjacent to the last filament outlet at an end of the meltblowing die. 
         [0008]    In another embodiment, the present disclosure provides a method of forming a meltblown media, comprising providing a meltblowing die having a plurality of filament outlets, positioning a first Coanda effect device adjacent to a first end of the meltblowing die, expelling molten filaments from a meltblowing die, manipulating the flight of the molten filaments with the first Coanda effect device, and collecting the molten filaments to form a web of nonwoven media. 
         [0009]    One advantage of webs formed using the apparatus and method of the present disclosure is that they have more uniform side-to-side basis weights compared to webs made according to conventional techniques. That is, the basis weight of the side edge regions of webs produced using the apparatus and methods described herein are similar to, and consistent with, the basis weight of the central region of the web located between the side edge regions. 
         [0010]    As used herein, forms of the words “comprise”, “have”, and “include” are legally equivalent and open-ended. Therefore, additional non-recited elements, functions, steps or limitations may be present in addition to the recited elements, functions, steps, or limitations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present disclosure, which broader aspects are embodied in the exemplary construction. 
           [0012]      FIG. 1  is a schematic view of a meltblowing apparatus without the inventive features. 
           [0013]      FIG. 2  is a perspective view of one end of a meltblowing die generally as depicted in  FIG. 1 , except that certain inventive features have been added. 
           [0014]      FIG. 3  is a perspective view of a Coanda effect device according to the invention in isolation. 
           [0015]      FIG. 4  is a plan view of the Coanda effect device of  FIG. 3 . 
       
    
    
       [0016]    Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure. 
       DETAILED DESCRIPTION 
       [0017]    Referring now to  FIG. 1  a schematic view of a meltblowing apparatus  20  is illustrated without the inventive features for background and the establishment of nomenclature. A meltblowing apparatus  20  including a meltblowing die  22  is illustrated in a diagrammatic cross-section. The meltblowing die  22  is used to expel a stream  24  of extended polymeric filaments towards a collection belt  26  moving in direction “D,” is illustrated. Although a belt is depicted in connection with this embodiment, those acquainted with the meltblowing art will understand that other collectors, such as a rotating drum, may be used for the purpose of collecting, conveying, and taking off the filaments as media. 
         [0018]    According to conventional practice, the meltblowing die  22  is provided with cavities  28  and  30  for directing two streams of heated gas against the stream  24  of polymeric filaments just after the stream  24  has been extruded from a line of extrusion orifices  32 . The heated gas jets emerging from cavities  28  and  30  extend and thin the filaments emerging from the extrusion orifices  32  so that the filaments have the proper size and dispersion to form the desired media  34  upon the collector  26 . 
         [0019]    The meltblowing apparatus  20  further includes a pair of ducts  40  and  42 , one upstream and one downstream of the stream  24  compared to the direction “D”. Secondary flow is expelled from ducts  40  and  42  against the filament stream  24  so the filaments, when they impinge upon the collection belt  26 , have the properties desired in the media  34 . The foregoing description generally corresponds to the disclosure of coassigned U.S. Pat. No. 6,861,025 to Breister et al, and is adequate for the production of meltblown media at low and moderate speeds of collector  26 . As discussed in copending and coassigned U.S. Application Publication 20060265169, additional manifolds  44  and  46  may be provided for the purpose of disrupting standing vortices. 
         [0020]    Referring now to  FIG. 2 , a perspective view of one end of the meltblowing die  22  including certain inventive features is illustrated. Specifically, a first Coanda effect device  50  is positioned adjacent to the path of the filaments emerging from the last orifice  32   a  at an end of the meltblowing die  22 . The Coanda effect device  50  generally comprises a convex surface arranged along the direction of the filament flow path. In the illustrated embodiment, the convex surface flares outwardly away from the array of orifices  32  in the direction away from the meltblowing die  22 . Arranged in this manner, the convex surface serves to alter, or can be used to adjust or control, the flow path of the filaments in the region adjacent to the Coanda effect device  50 , thereby producing a web of media having a more consistent and uniform basis weight across its entire width. 
         [0021]    A shield  52  is positioned between the lateral end of the array of orifices  32  and the first Coanda effect device  50 . The shield  52  is positioned to direct and regulate the entrainment of ambient air from the side of the die  22  towards the leading edge  54  of the first Coanda effect device  50 . It will be recognized that a second Coanda effect device and a second shield may optionally be provided at the other end of the array of orifices  32 . 
         [0022]    Referring now to  FIGS. 3 and 4 , there is shown a perspective view and a plan view, respectively, of a Coanda effect device  50  shown in isolation. The Coanda effect device  50  has a leading edge  54  and a trailing edge  56 . The exact parameters of an advantageous Coanda effect device will vary depending on the material being extruded from the orifices  32  and other process parameters. However, some general observations for achieving desirable results have been made. 
         [0023]    According to one aspect, the Coanda effect device may be characterized in terms of a first radius of curvature “R 1 ” adjacent to the leading edge  54 , a second radius of curvature “R 2 ” adjacent to the trailing edge  56 , and/or an angle of attack α. The angle of attack α can be defined generally as the angle between the surface of the Coanda effect device and a line generally parallel to the streamlines of material  24  emerging from the orifices  32 . 
         [0024]    For most applications, the first R 1  and second R 2  radii of curvature and the angle of attack α should be selected so as to minimize vortex shedding at the trailing edge  56 . In specific embodiments, the angle of attack α may be less than about 45 degrees, less than about 35 degrees, or less than 25 degrees. Negative angles of attack are less commonly indicated, but not considered to be outside the scope of the invention. In specific embodiments, the first radius of curvature R 1  may be at least about 4 cm, at least about 6 cm or at least about 7.5, and no greater than about 24 cm, no greater than about 20 cm, or no greater than about 18 cm. In another embodiment, the second radius of curvature R 2  may be at least about 14 cm, at least about 16 cm, or at least about 18 cm. It is to be noted that the approximation of the Coanda effect device into two radii of curvatures R 1  and R 2  is guidance as to operable embodiments. Cross sectional shapes corresponding to diverse geometries including, for example, spline curves, facets, or combinations of the two, are considered to be within the scope of the invention. 
         [0025]    For simplicity of manufacture, it may be desirable for the Coanda effect device to have a uniform cross section, but this is not considered essential. Also, in embodiments where two Coanda effect devices are provided, it may be desirable that the first and second Coanda effect devices be similar or even identical, but this is not considered essential. The Coanda effect devices may optionally include mechanical expedients such as cams, levers, bolts or the like so that minor adjustments to the radii of curvature and/or angle of attack can be made to the Coanda effect device during, for example, the production of meltblown media. 
         [0026]    Other modifications and variations to the present disclosure may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present disclosure, which is more particularly set forth in the appended claims. It is understood that aspects of the various embodiments may be interchanged in whole or part or combined with other aspects of the various embodiments. All cited references, patents, or patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.