Abstract:
In an apparatus for the production of a nonwoven web, structure, or article using a nonwovens process in combination with a transfer belt which includes conductive material so as to dissipate static electric charge whilst maintaining a desired air permeability;

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is directed towards the production of nonwovens and concerns associated therewith, in particular, air flow and static electricity.  
       BACKGROUND OF THE INVENTION  
       [0002]     There presently exists apparatus for the production of nonwovens for example, spun-bond webs, structures or articles formed from filaments or fibers typically made from a thermoplastic resin. Such an apparatus is disclosed in U.S. Pat. No. 5,814,349 issued Sep. 29, 1998, the disclosure of which is incorporated herein by reference. These typically include a spinneret for producing a curtain of strands and a process-air blower for blowing process air onto the curtain of strands for cooling the same to form thermoplastic filaments. The thermoplastic filaments are then typically, aerodynamically entrained by the process air for aerodynamic stretching of the themoplastic filaments which are then, after passing through a diffuser, deposited upon a continuously circulating sieve belt for collecting the interentangled filaments and forming a web thereon. The web, structure or article, so formed, is then transferred and subject to further processing.  
         [0003]     Apparatus of the type aforementioned, particularly for high-speed melt-bond web production are currently available from Reifenhauser GmbH Co. Maschinenfabrik, Spicher Strabe D-53839 Troisdort, Germany and sold under the name Reicofil®. The latest generation of such high-speed spun-bond lines is referred to as the Reicofil® 3 type system.  
         [0004]     Another manufacturer of such equipment is Nordson Corporation, 28601 Clemens Road, Westlake, Ohio 44145. Other manufacturers are STP Impianti, Rieter Perfojet, Kobelco, Ason and NWT.  
         [0005]     An airlaid process may also be used to form a non-woven web. The airlaid process begins with a defibration system to open fluff pulp. A conventional fiberizer or other shredding device may also be used to form discrete fibers. Particles of absorbent materials (for example super absorbent powder), abrasives or other materials may then be mixed with the fibers. The mixture is then suspended in an air stream within a forming system and deposited to a moving forming wire, screen or rotating perforated cylinder. The randomly oriented airformed fiber may then be bonded by applying a latex binder and drying, thermally bonding thermoplastic staple fibers in the web, hydrogen or embossed bonding or a combination thereof.  
         [0006]     In addition, the nonwoven web may be optionally compacted before the bonding step noted above. Compaction is typically performed on the forming wire before bonding. During compaction, the absorbents, abrasives or other materials, which are mixed with the fiber, damage the forming wire. A felt may be used on this position during the compaction step to prevent damage to the forming wire. The compressibility of the felt allows the nonwoven web to compact without damaging the felt or the wire.  
         [0007]     There are a number of commercial processes available to produce airlaid nonwoven webs. For example, airlaid processes are available from Dan-Web Corp. having offices in Risskov, Denmark, and from M&amp;J Forming Technologies having offices in Horsens, Denmark.  
         [0008]     The present invention relates to producing nonwovens and the concerns associated therewith, in particular, static electricity.  
         [0009]     In a nonwovens process, there is a large amount of static electricity generated. The present invention relates to addressing this problem. Normally a negative charge builds up on the filaments or fibers as they are being processed. Successive layers of fibers, since they are the same polarity, tend to repel each other. Charged fibers tend to cling to the press rolls. They also tend to be repelled from the forming fabric, since it will develop a charge thereon during the processing of the charged fibers. This charge tends to accumulate.  
         [0010]     In European Patent Application No. EP 0 950 744 A1 it proposes using press rolls having a dielectric surface which is charged with a polarity that will repel the fibers. The forming fabric is also made from a dielectric material and charged such that it is opposite to that of the fibers, thereby attracting the fibers thereto.  
         [0011]     The present invention concerns dissipating static electric charge whilst maintaining air permeability of a transfer belt. Heretofore, U.S. Pat. No. 4,428,736 proposed dissipating the static charge that is built up by a dryer fabric, thereby preventing adhesion of the paper to the fabric when it is transferred from one fabric to another.  
         [0012]     U.S. Pat. No. 4,541,895 is a PM fabric made up of a plurality of impervious non-woven sheets joined together in a laminated arrangement. Each of the layers serves a particular purpose such as resistance to static charge. In addition, yarns could be incorporated between the laminates to add anti-static properties.  
         [0013]     U.S. Pat. No. 6,001,749 provides a patterned conductive textile by applying a finish to selective parts of a fabric which inhibits the formation of a conductive polymer coating in those areas.  
         [0014]     U.S. Pat. No. 6,153,124 is an electrically conductive knitted fabric made of 2-30 percent by weight of a conductor yarn. The conductor yarn is made of 5-30 percent by weight of galvanized iron fiber and 70-95 percent by weight of a polyester fiber. The conductivity is proportional to the concentration of the yarn.  
         [0015]     None of the prior art however provides for an antistatic transfer belt for use in the production of nonwovens having a woven or spiral formed base to which a conductive batt, foam or other material is added whilst maintaining a desired air permeability.  
       SUMMARY OF THE INVENTION  
       [0016]     It is therefore a principal object of the invention to provide a transfer belt for the production of non-woven webs, structures or articles, which dissipates static electric charge.  
         [0017]     It is a further object of the invention that an adequate air permeability of the antistatic transfer belt is maintained.  
         [0018]     These and other objects and advantages are achieved by the present invention. In this regard the invention is directed towards generally a transfer belt for use in the production of non-woven webs, structure or articles. So as to address the static electricity problem, the transfer belt may include a conductive material which allows the dissipation of the static electric charge on the web whilst maintaining the desired permeability of the belt. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Thus by the present invention, its objects and advantages will be realized, the description of which should be taken in conjunction with the drawings wherein:  
         [0020]      FIG. 1  is a schematic representation of an apparatus wherein a non-woven web, structure or article is transferred; and  
         [0021]      FIG. 2  is an enlarged sectional view of the transfer belt of the present invention taken along the machine direction of the belt. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     Turning now more particularly to the figures where like elements will be similarly numbered,  FIG. 1  shows schematically a part of an apparatus  10  for producing a non-woven web  12  by a process other than weaving, for example, by airlaid, drylaid, or spunlace processes. During the transfer of the web  12  before handling from a first position  14  to a second position  16 , a large amount of static electric charge is built up on the web  12  and the transfer belt  18 , which is undesirable. Related to this concern is the need for the transfer belt  18  to be permeable to air drawn through a vacuum system  19  that assists with the transfer of the web  12 .  
         [0023]     Advantageously, the present invention is a transfer belt for use in a nonwovens process which dissipates the static electric charge, whilst maintaining the desired air permeability. In this regard, shown in  FIG. 2  is a cross section of the antistatic transfer belt  18  used in the present invention. The transfer belt  18  comprises a base substrate or structure  20  made from a woven or spiral polymer material (which itself can be conductive) or of other construction suitable for the purpose covered with an electrically conductive batt, foam or other material  22  able to maintain air permeability in the range of approximately 20 to 200 CFM, or higher when the belt is coated, while having a low resistivity in the range of 10 0  ohm/square to 10 8  ohm/square.  
         [0024]     The base substrate may be any one of the structures used as bases for paper machine clothing, such as, for example, a woven or a spiral-link fabric. The base substrate may also be assembled from a strip of one of woven materials spirally wound in a plurality of turns, each turn being joined to those adjacent thereto by a continuous seam which is disclosed in commonly assigned U.S. Pat. No. 5,360,656 to Rexfelt et al., the teachings of which are incorporated herein by reference. Further, the base substrate may be woven endless, or flat woven and subsequently rendered into endless form with a woven seam.  
         [0025]     The base substrate may also be a laminated structure comprising two or more base substrates, each of which may be one of the structures described above. Where the base substrate is laminated, one of the component base substrates may be an on-machine-seamable fabric, so that the belt may be seamed into endless form during installation on a paper machine.  
         [0026]     The base substrate may be woven, or otherwise assembled, from yarns of any of the varieties used in the manufacture of paper machine clothing and industrial process fabrics. That is to say, the base substrate may include monofilament, plied monofilament, multifilament, plied multifilament or yarns spun from staple-fibers of any of the synthetic polymeric resins used by those skilled in the art.  
         [0027]     In the example shown in  FIG. 2 , the substrate  20  imparts dimensional stability and compressibility to the belt  18 ; the conductive batt, foam or other material  22  dissipates the static electricity from the web  12  to the ground through the belt  18 . Note that the substrate  20  may be joined to the batt, foam or other material  22  by needling, thermal bonding, stitching, chemical process, or other means suitable for the purpose.  
         [0028]     In addition, the conductive material  22  may be coating on base substrate or structure  20 . The coated conductive material  22  may be applied to the base substrate or structure  20  by spraying, extruding, or being a layer of thermofusible material.  
         [0029]     As a further advantage, the web-facing surface of the batt, foam or other material  22  is smooth in order to avoid plugging and marking problems associated with certain nonwovens production utilizing a large amount of what is commonly referred to as Super Absorbent Powder or SAP. For example, the surface of a coated conductive material  22  may be made to obtain the desired surface topography or smoothness by compacting or sanding.  
         [0030]     Accordingly, the antistatic transfer belt  18  of the present invention is a multi-layer structure which may contain one or more bases  20  and one or more layers of batt, foam or other material  22 , a portion of which is conductive. Such a transfer belt  18  reduces static electric charge during nonwovens production whilst providing a desired air permeability in the web production process.  
         [0031]     Although a preferred embodiment has been disclosed and described in detail herein, its scope should not be limited thereby; rather its scope should be determined by that of the appended claims.