Patent Publication Number: US-8535756-B2

Title: Method for dispensing random pattern of adhesive filaments

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 12/873,874, filed Sep. 1, 2010 (now U.S. Pat No. 8,399,053), which is a divisional of application Ser. No. 11/610,148, filed Dec. 13, 2006 (now U.S. Pat. No. 7,798,434), the disclosures of which are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to air-assisted nozzles and systems for extruding and moving filaments of viscous liquid in desired patterns and, more particularly, air-assisted dispensing of hot melt adhesive filaments. 
     BACKGROUND 
     Various dispensing systems have been used in the past for applying patterns of viscous liquid material, such as hot melt adhesives, onto a moving substrate. In the production of disposable diapers, incontinence pads and similar articles, for example, hot melt adhesive dispensing systems have been developed for applying a laminating or bonding layer of hot melt thermoplastic adhesive between a nonwoven fibrous layer and a thin polyethylene backsheet. Typically, the hot melt adhesive dispensing system is mounted above a moving polyethylene backsheet layer and applies a uniform pattern of hot melt adhesive material across the upper surface width of the backsheet substrate. Downstream of the dispensing system, a nonwoven layer is laminated to the polyethylene layer through a pressure nip and then further processed into a final usable product. 
     In various known hot melt adhesive dispensing systems, continuous filaments of adhesive are emitted from a multiple adhesive outlet die with multiple process air jets oriented in various configurations adjacent the circumference of each adhesive outlet. The multiple air jets discharge air generally tangentially relative to the orientation of the discharged adhesive filament or fiber as the filament emerges from the die orifice. This process air can generally attenuate each adhesive filament and cause the filaments to move back and forth in overlapping or non-overlapping patterns before being deposited on the upper surface of the moving substrate. 
     Manufacturers of diaper products and others remain interested in small fiber technology for the bonding layer of hot melt adhesive in nonwoven and polyethylene sheet laminates. To this end, hot melt adhesive dispensing systems have incorporated slot nozzle dies with a pair of angled air channels formed on either side of the elongated extrusion slot of the die. As the hot melt adhesive emits from the extrusion slot as a continuous sheet or curtain, pressurized process air is emitted as a pair of curtains from the air channels to impinge upon, attenuate and fiberize the adhesive curtain to form a uniform fibrous web of adhesive on the substrate. Fibrous web adhesive dispensers have incorporated intermittent control of adhesive and air flows to form discrete patterns of fibrous adhesive layers with well defined cut-on and cut-off edges and well defined side edges. 
     Meltblown technology has also been adapted for use in this area to produce a hot melt adhesive bonding layer having fibers of relatively small diameter. Meltblown dies typically include a series of closely spaced adhesive nozzles or orifices that are aligned on a common axis across the die head. A pair of angled air channels or individual air passages and orifices are positioned on both sides of the adhesive nozzles or orifices and align parallel to the common nozzle axis. As hot melt adhesive discharges from the series of aligned nozzles or orifices, pressurized process air is discharged from the air channels or orifices and attenuates the adhesive fibers or filaments before they are applied to the moving substrate. 
     While meltblown technology has been used to produce fibrous adhesive layers on moving substrates, it has various areas in need of improvement. As those skilled in the art will appreciate, meltblown technology typically uses a high volume of high velocity air to draw down and attenuate the emitted adhesive filaments. The high velocity air causes the fibers to oscillate in a plane that is generally aligned with the movement of the substrate, i.e., in the machine direction. To adequately blend adjacent patterns of adhesive to form a uniform layer on the substrate, meltblown dispensers require the nozzles to be closely spaced. Moreover, the volume and velocity of the air must be high enough to sufficiently agitate and blend adjacent fibers. 
     However, the high volume of air used in conventional meltblown dispensers adds to the overall operational cost as well as reduces the ability to control the pattern of emitted fibers. One byproduct of the high velocity air is “fly” in which the fibers get blown away from the desired deposition pattern. The “fly” can be deposited either outside the desired edges of the pattern, or even build up on the dispensing equipment which can cause operational problems that require significant maintenance. Another byproduct of the high velocity air and closely spaced nozzles is “shot” in which adjacent adhesive fibers become entangled and form globules of adhesive on the backsheet substrate. “Shot” is undesirable as it can cause heat distortion of the delicate polyethylene backsheet. 
     It will be further appreciated by those skilled in the art that when typical meltblown dies are placed in side-by-side fashion across the width of a moving substrate a less consistent fiber pattern on the substrate results. This occurs since each meltblown die has continuous sheets of air formed on either side and these sheets of air are interrupted between adjacent meltblown dies. 
     Other air-assisted nozzles or dies use capillary style tubes mounted in a nozzle or die body for extruding filaments of thermoplastic material. Air passages are provided adjacent to the tubes, and the ends of the tubes project outwardly relative to the outlets of the air passages. 
     Various forms of laminated plate technology are known for extruding rows of adhesive filaments in an air assisted manner. These include dispensing nozzles or dies constructed with slotted plates for discharging filaments of liquid and process or pattern air for attenuating and moving the discharged filaments in a desired pattern. These nozzles or dies present various issues relating to their performance, design complexity and large numbers of plates needed to complete the assembly. Therefore, improvements remain needed in this area of technology. 
     SUMMARY 
     The present invention, in an illustrative embodiment, provides a nozzle for dispensing a random pattern of liquid adhesive filaments. The nozzle includes first and second air shim plates, an adhesive shim plate and first and second separating shim plates. The first and second air shim plates each have respective pairs of air slots. Each air slot has a process air inlet and a process air outlet and the air slots of each pair converge toward one another such that the process air inlets are farther apart than the process air outlets in each pair. The adhesive shim plate includes a plurality of liquid slots each with a liquid inlet and a liquid outlet. The adhesive shim plate is positioned between and lies parallel to the first and second process air shim plates such that one of the liquid slots extends generally centrally between a pair of the air slots in the first process air shim plate and a pair of the air slots in the second process air shim plate. In this manner, four process air outlets are associated with each of the liquid outlets. The process air slots are adapted to receive pressurized process air and the liquid slots are adapted to receive pressurized liquid adhesive. The pressurized process air discharges from each group of the four process air outlets and forms a zone of turbulence for moving the filament of liquid adhesive discharging from the associated liquid outlet in a random pattern. The nozzle further includes first and second end plates securing together and sandwiching the first and second process air shim plates, the adhesive shim plate and the first and second separating shim plates. The first end plate includes a process air inlet communicating with the pairs of air slots in the first and second process air shim plates and a liquid adhesive inlet communicating with the liquid slots in the adhesive shim plate. 
     Various additional features are incorporated into the illustrative embodiment of the nozzle. For example, the first and second process air shim plates have first and second opposite ends and the pairs of process air slots respectively angle in a progressive manner outwardly from a central portion of each process air shim plate toward the opposite ends of the process air shim plates. This assists with spreading the pattern of adhesive filaments outwardly in opposite directions along the width of the nozzle. The adhesive shim plate also includes opposite ends and at least the liquid slots closest to the opposite ends of the adhesive shim plate respectively angle outwardly toward the opposite ends. This may assist with spreading the adhesive filament pattern in opposite directions. 
     In the illustrative embodiment, the first and second end plates further comprise respective process air passages for directing pressurized process air between the first and second end plates. The first end plate is generally L-shaped and includes a top surface generally orthogonal to planes containing the first and second process air shim plates, the adhesive shim plate and the first and second separating shim plates, and a side surface generally parallel to the planes containing the first and second process air shim plates, the adhesive shim plate and the first and second separating shim plates. The liquid adhesive inlet and the process air inlet are formed in the top surface. 
     The invention further contemplates methods directed generally to the manner in which liquid filaments and process air are discharged to form a random pattern of filaments on a substrate. 
     Various additional features and advantages of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the illustrative embodiment taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an assembled perspective view of a nozzle constructed in accordance with an illustrative embodiment of the invention. 
         FIG. 2  is a disassembled perspective view of the nozzle shown in  FIG. 1 . 
         FIG. 3  is a perspective view the inside of an end plate of the nozzle shown in  FIG. 1 . 
         FIG. 4  is a cross sectional view taken along line  4 - 4  of  FIG. 1 . 
         FIG. 5  is a cross sectional view taken along line  5 - 5  of  FIG. 1 . 
         FIG. 6  is a bottom view of the nozzle shown in  FIG. 1 . 
         FIG. 7  is a cross sectional view generally taken along lines  7 - 7  of  FIGS. 1 and 4 . 
         FIG. 8  is an elevational view of a random filament pattern produced with a nozzle constructed in accordance with the principles discussed herein. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
     Referring first to  FIGS. 1 and 2 , a nozzle  10  in accordance with one illustrative embodiment is shown and generally includes first and second process air shim plates  12 ,  14 , an adhesive shim plate  16 , first and second separating shim plates  18 ,  20 , and first and second end plates  22 ,  24 . The entire assembly is held together as shown in  FIG. 1  by, for example, a pair of threaded fasteners  26 ,  28  that extend through holes  30 ,  32  in the first end plate  22  and into threaded holes  34 ,  36  in the second end plate  24 . As further shown in  FIG. 2 , respective holes  40  in the air shim plates  12 ,  14 , separating shim plates  18 ,  20  and adhesive shim plate  16  allow passage of the threaded fasteners  26 ,  28  as well. The second end plate  24  includes a projection  42  serving as a locating member that extends through respective upper slots  44  in the air shim plates  12 ,  14 , separating shim plates  18 ,  20 , and adhesive shim plate  16 . The projection or locating member  42  is then received in a blind bore  50  ( FIG. 3 ) in the first end plate  22 . 
     The first end plate  22  is a generally L-shaped member and includes a top surface  60  generally orthogonal to planes that contain the first and second process air shim plates  12 ,  14 , the adhesive shim plate  16  and the first and second separating shim plates  18 ,  20 . A side surface  62  generally parallel to the planes containing these same shim plates receives the threaded fasteners  26 ,  28 . The top surface  60  includes an adhesive inlet  70  and a pair of process air inlets  72 ,  74 . The first end plate  22  also includes oppositely extending projections  80 ,  82  that may be used for securing the nozzle  10  to a dispensing valve or module (not shown) as further shown and described in U.S. Pat. No. 6,676,038, the disclosure of which is hereby incorporated by reference herein. 
     Referring to  FIGS. 2-5 , the first end plate  22  includes a process air inlet passage  90  ( FIG. 4 ) communicating with the inlet  72  and a liquid adhesive inlet passage  92  ( FIG. 5 ) communicating with the liquid inlet  70 . A seal member  93  located in a groove  94  may be used to seal liquid inlet  70 . As also shown in  FIG. 4 , the process air inlet passage  90  communicates with first and second air distribution passages  100 ,  102  that respectively communicate with opposite sides of the shim plate assembly  12 ,  14 ,  16 ,  18 ,  20 . It will be appreciated that a second identical distribution passage system (not shown) in the first end plate  22  communicates with the second air inlet  74  ( FIG. 2 ) to provide additional pressurized air to opposite sides of shim plate assembly  12 ,  14 ,  16 ,  18 ,  20 . The upper distribution passage  100  passes through the shim plate assembly  12 ,  14 ,  16 ,  18 ,  20  through aligned holes  110  and through a vertical recess  112  ( FIGS. 2 and 4 ) and, finally, into a horizontally extending slot  116  in the second end plate  24 . Another series of aligned holes  120  and another vertical recess  122  are provided to receive process air from the other air inlet  74  through the previously mentioned identical distribution passage system. In this regard, distribution passages  124 ,  126  shown in  FIG. 3  communicate with air inlet  74 . Passage  124  aligns with holes  120  and slot  122  shown in  FIG. 2 , while passage  126  communicates with recess  132  as shown in  FIG. 3 . The horizontally extending slot  116  communicates with one side of the shim plate assembly, as discussed further below. The other distribution passage  102  communicates with a lower horizontal recess  132  contained in the first end plate ( FIGS. 3 and 4 ). This horizontal recess  132  communicates with the right side of the shim plate assembly (as viewed in  FIG. 4 ) for supplying process air to the first process air shim plate  12 . As shown in  FIG. 5 , the liquid inlet passage  92  communicates with a liquid distribution passage  140  and an upper horizontal slot  142  ( FIG. 3 ) in the first end plate  22 . This upper horizontal slot  142  communicates with the adhesive shim plate  16  as further described below. 
     Again referring to  FIG. 2 , the adhesive shim plate  16  includes a plurality of liquid slots  150  each with a liquid inlet  152  and a liquid outlet  154 . The adhesive shim plate  16  is positioned between and lies parallel to the first and second process air shim plates  12 ,  14  such that one of the liquid slots  150  extends generally centrally between a first pair of air slots  160 ,  162  in the first process air shim plate  12  and also generally centrally between a second pair of the air slots  164 ,  166  in the second process air shim plate  14 . As best viewed in  FIG. 7 , each first pair of air slots  160 ,  162  is directly aligned with a corresponding second pair of air slots  164 ,  166  (not shown in  FIG. 7 ), although the pairs of air slots  160 ,  162  and  164 ,  166  are separated by adhesive shim plate  16  and separating shim plates  18 ,  20 . Thus, as shown in  FIG. 6 , four process air outlets  160   a ,  162   a ,  164   a ,  166   a  are associated with each of the liquid outlets  154 . As further shown in  FIGS. 2 and 7 , air slots  160 ,  162  converge toward each other and air slots  164 ,  166  converge toward each other such that the process air inlets  160   b ,  162   b  and  164   b ,  166   b  are farther apart than the corresponding process air outlets  160   a ,  162   a  and  164   a ,  166   a  in each pair. However, none of the air slots  160 ,  162 ,  164 ,  166  converge toward their associated liquid slot  150  since the respective pairs of slots  160 ,  162  and  164 ,  166  are each contained in parallel planes different from the plane containing he liquid slots  150 . From a review of  FIG. 7 , it will be appreciated that for each of the liquid slots  150 , one pair of converging process air slots  160 ,  162  is shown and another pair is hidden behind the first pair but is directly aligned therewith in the second process air shim plate  14 . 
     In the manner previously described, pressurized process air is directed downwardly through the respective pairs of slots  160 ,  162  and  164 ,  166  in both process air shim plates  12 ,  14 . In this regard, the horizontal slot  132  communicates pressurized air to the inlets  160   b ,  162   b  of slots  160 ,  162  in the first process air shim plate  12 . The horizontal slot  116  communicates pressurized air to the inlets  164   b ,  166   b  of the slots  164 ,  166  in the second process air shim plate  14 . Liquid hot melt adhesive is directed into the liquid inlet passage  70  to the distribution passage  140  and the upper horizontal slot  142  in the first end plate  22 . The upper horizontal slot  142  in the first end plate  22  communicates with respective aligned holes  170 ,  172  in the first process air shim plate  12  and the first separating shim plate  18  and, finally, into the upper inlets  152  of the liquid slots  150 . The second process air shim plate  14  also includes such holes  170  to allow full interchangeability between the first and second process air shim plates  12 ,  14 . In the construction shown in  FIG. 2 , the holes  170  in the second process air shim plate  14  remain unused. The separating shim plates  18 ,  20  are utilized to seal off the respective air slots  160 ,  162  and  164 ,  166  from the liquid slots  150 . 
     Nozzle  10  has a design such that it may be flipped or rotated 180° from left to right when mounting to a valve module (not shown). Furthermore, the respective liquid slots  150  and air slots  160 ,  162 ,  164 ,  166  may be formed along any desired width or width portion(s) of the respective air shim plates  12 ,  14  and adhesive shim plate  16  depending on the needs of the application. The air shim plates may always have the full distribution of air slots  160 ,  162 ,  164 ,  166  as shown for nozzle  10  since providing additional air streams typically will not adversely affect the discharged filaments. 
     As further shown in  FIG. 7 , twelve respective groupings of 1) pairs of air slots  160 ,  162 , 2) pairs of air slots  164 ,  166  ( FIGS. 2 ) and 3) individual liquid slots  150  are shown in the illustrative embodiment. The right hand side of  FIG. 7  illustrates respective centerlines  180  centered between the respective pairs of converging air slots  160 ,  162 . These air slot centerlines and, therefore, the respective pairs of air slots  160 ,  162  gradually angle toward an outer end of the process air shim plate  12 . Thus, for example, the angles of the respective centerlines  180  may gradually become smaller relative to horizontal with β 1  being the largest angle at 90° and β 6  being the smallest angle at 87.5°. In this illustrative embodiment, the angles may, for example, be as follows:
     β 1 =90°   β 2 =89.5°   β 3 =89°   β 4 =88.5°   β 5 =88°   β 6 =87.5°   

     Of course, other angles may be chosen instead, depending on application needs. The second process air shim plate  14  may be configured in an identical manner. 
     On the left hand side of  FIG. 7 , additional centerlines  200  are shown through the respective centers of the liquid slots  150 . In this embodiment, angle a may be 90°, while angle α 1  may be less than 90°, such as 88.3°. In this manner, the outermost or endmost liquid slot  150  is angled outwardly toward the outer edge of the shim plate  16 . The outermost liquid slot  150  on the opposite edge of the assembly may also include this feature. Likewise, the respective six pairs of process air slots  160 ,  162  on the left hand side of  FIG. 7  may also be gradually fanned (as pairs) outward or to the left just as the six pairs on the right hand side of  FIG. 7  are “fanned” or angled to the right. It will be understood that any “fanning” or angling of air or liquid slots on the left side of the nozzle  10  will be to the left while any “fanning” or angling of air or liquid slots on the right side of the nozzle  10  will be to the right. Adhesive filaments discharging from the liquid slots  150  will fan outwardly generally from the center point of the nozzle  10 , i.e., to the left and to the right as viewed in  FIG. 7 , such that the overall pattern width of randomized adhesive filaments will be greater than the width between the two outermost or endmost liquid slot outlets  152  and, desirably, may have a width at least as great as the width of the nozzle  10  itself. It will further be appreciated that any number of the liquid slots  150  may each be gradually fanned or angled outwardly relative to a center point of the nozzle, as shown in  FIG. 7 , rather than only the outermost liquid slots  150  having this configuration. 
     As one additional modification, more than one adhesive shim plate  16  may be used in adjacent, side-by-side stacked format. In this format, adhesive slots in one adhesive shim plate would communicate, respectively, with adhesive slots in an adjacent adhesive shim plate. This would allow, for example, the adhesive slots in each adhesive shim plate to form only a portion of the overall adhesive outlet. If, for example, one or more of the adhesive slots of each adhesive shim plate that communicate with each other is formed with a different shape, a desired overall cross sectional shape for the resulting adhesive filament may be obtained. In this manner, a variety of different adhesive filament shapes may be obtained in different nozzles or along the width of the same nozzle. Cross sectional shapes of the adhesive filaments may, for example, take the form of “plus” signs or “C”-shapes or other geometric configurations. 
     The discharged stream of pressurized air exiting from each process air outlet  160   a  converges and impacts against a process air stream exiting from each associated outlet  162   a  of the pair  160   a ,  160   b.  In a similar manner, respective process air streams exiting outlets  164   a  impact against the streams exiting from process air outlets  166   a.  This forms a zone of air turbulence directly below each liquid outlet  154  of the nozzle and causes the continuous adhesive filaments  180  exiting the associated liquid outlets  154  to move side-to-side or back and forth in random directions forming an erratic, non-uniform or random pattern as, for example, shown in  FIG. 8 . In this regard,  FIG. 8  illustrates a substrate  182  onto which the random pattern of multiple, continuous filaments  180  has been deposited after discharge from one or more nozzles constructed in accordance with nozzle  10  as generally described herein. 
     While the present invention has been illustrated by a description of various illustrative embodiments and while these embodiments have been described in some detail, it is not the intention of the Applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The various features of the invention may be used alone or in any combination depending on the needs and preferences of the user. This has been a description of the present invention, along with the preferred methods of practicing the present invention as currently known.