Patent Publication Number: US-2013240122-A1

Title: Method of manufacturing a personal hygiene product

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of U.S. Provisional Patent Application Ser. No. 61/610,063, filed on Mar. 13, 2012 (pending), the disclosure of which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This invention relates to dispensing methods for applying foamed hot melt adhesive to various components of a disposable absorbent personal hygiene product during the manufacture of the disposable absorbent personal hygiene product. 
     BACKGROUND 
     Liquid adhesive, such as hot melt adhesive, is applied onto various components during manufacture of a disposable absorbent personal hygiene product such as diapers, adult incontinence products, and feminine hygiene products. Various dispensing systems have been developed for applying hot melt adhesive onto various components of the disposable absorbent personal hygiene product. In one example, these dispensing systems apply a laminating or bonding layer of hot melt adhesive between two flat substrates, such as a nonwoven fibrous layer and a thin polyethylene backsheet. In another example, one or more hot melt adhesive filaments are applied to one or more thin elastic strands and the strand(s) are then adhered to a nonwoven substrate to form an elasticized portion of the disposable absorbent personal hygiene product. Downstream of the dispensing system, the various components (e.g., flat substrate layers and elastic strands) pass through a pressure nip to secure the components together. 
     In these applications, hot melt adhesive filaments must be carefully controlled during dispensing to ensure that the desired adhesive pattern is accurately applied to the thin elastic strands or within well-defined narrow areas on a flat substrate. In known dispensing systems, continuous filaments of liquid adhesive are discharged from a die or nozzle with one or more adhesive outlets. Each adhesive outlet typically has associated process air outlets that discharge air jets at the dispensed filament. The air jets attenuate each liquid adhesive filament and cause the filaments to move generally in a back and forth manner, a spiral manner, or another manner depending upon the position of the air jets. When the filaments are deposited on a moving flat substrate, the filament forms either an overlapping pattern or a non-overlapping pattern. Consequently, the liquid adhesive filament is carefully controlled for accurate positioning and adherence to the moving strand(s) or flat substrate. 
     In order to carefully control the liquid adhesive filament, the process air jets used in these known dispensing systems move at a high velocity that is sufficient to modify the flight of the liquid adhesive filaments in a controlled manner. However, the use of relatively high velocity air can result in excessive “fly” in which the filaments are blown away from the desired dispensed pattern. The “fly” results in adhesive deposition outside of the desired boundary of the pattern. Using relatively high velocity air jets can also lead to “shot” in which adjacent adhesive filaments become entangled and form globules of adhesive on the substrate rather than the desired pattern. Consequently, known dispensing systems require the adhesive to have a sufficiently high viscosity and/or density to enable repeatable and accurate control while minimizing “fly” and “shot.” 
     When evaluating the effectiveness of an adhesive bond between one or more elastic strands and one or more flat substrates, a characteristic that is often measured is creep resistance. “Creep” of an elastic strand is defined as the movement of either end of the elastic strand from an initial location where the end is adhered to a substrate. The level of creep resistance indicates how well the ends of the elastic strand remain adhered in position with respect to a substrate adhered to the elastic strand. Because the elastic strand is adhered to the substrate(s) in a stretched condition, the elastic strand constantly applies force to the substrate and the adhesive in an attempt to return to a relaxed, non-stretched condition. This force enables an elasticized portion of a disposable absorbent personal hygiene product (e.g., leg gathers on a diaper) to remain firmly engaged with the skin surface during use of the product. If an elastic strand in a disposable absorbent personal hygiene product undergoes any significant amount of creep after assembly, at least one end of the elastic strand will effectively de-bond from the substrate and reduce the ability of the elasticized portion to remain firmly engaged with the skin surface. To avoid this undesirable creep, a high quality bond must be formed by the adhesive applied to the elastic strand so that the elastic strand does not de-bond from the substrate. 
     One well understood method of improving the quality of an adhesive bond, and thereby reducing creep, is by applying additional adhesive on the substrate(s) or the elastic strands. However, applying too much adhesive to the elastic strand locks the elastic strand along its length and thereby reduces the effectiveness of the elastic material to apply force to the substrate. In other words, the elastic strand loses the ability to apply sufficient retraction force to the substrate. 
     Moreover, increasing the amount of adhesive used in disposable absorbent personal hygiene product manufacturing significantly increases cost and also reduces the “hand” or softness of the resulting product. Applying too much adhesive material increases the stiffness of the resulting product and may also lead to “burn through,” which occurs when the adhesive material burns or melts through the adhered substrate. Especially in diaper manufacturing, the softness of the assembled product is another important measurement used to evaluate the quality of the disposable absorbent personal hygiene product. Consequently, the amount of adhesive used to adhere elastic strands to substrates should be minimized while also maintaining a high level of creep resistance, a high retraction force, and minimized burn through and stiffness. Adhesive dispensing systems should carefully control the discharged liquid adhesive filament to ensure accurate placement of the adhesive material and a high quality bond with minimized use of adhesive. 
     Also when constructing a disposable absorbent personal hygiene product, two or more substrates may be adhered together by a pattern of adhesive applied to one or both of the substrates. For example, two substrates may be adhered along edge portions of the substrates. As a result, the adhesive filaments discharged towards the substrate(s) must be carefully controlled to ensure accurate positioning along and within the edges of the substrate(s), also referred to as “edge control.” If the adhesive filament undergoes any non-negligible amount of “fly” away from the desired pattern on the substrate(s), then the adhesive is characterized as having poor edge control, which adversely affects the resulting construction of elements in the disposable absorbent personal hygiene product. To this end, adhesive dispensing systems must carefully control the liquid adhesive filament to avoid excessive “fly” and poor edge control in adherence of substrate(s). 
     By contrast, in other adhesive dispensing fields such as adhesive dispensing on packaging (e.g., boxes), the total amount of adhesive used in an application has been minimized by injecting nitrogen or another gas into the liquid hot melt adhesive to form a foamed adhesive. The gas is injected into liquid adhesive by a foaming mixer that conventionally is a large piece of equipment requiring significant manufacturing space. The foamed adhesive is then deposited in a pattern onto relatively large bonding areas of the packaging. As a result of the large bonding areas used in the packaging fields, highly precise and accurate control of the adhesive is not an important design consideration. More particularly, the foamed adhesive is sprayed, in most circumstances, with a wide pattern that is unassisted by air rather than being discharged as a filament moved by process air. In addition, forming strong bonds between the large bonding areas is not an important design consideration in the packaging field. To this end, even when process air is used with foamed adhesive in these applications, relatively low velocity process air streams may be used to control the flight of foamed adhesive filaments in the packaging field. Thus, any problems of “fly” and “shot” in the packaging field caused by using a low density foamed adhesive are minimized because of the low velocity of the process air. 
     However, these low velocity process air streams do not adequately control the adhesive filaments when dispensing adhesive onto an elastic strand or onto a nonwoven substrate used in a disposable absorbent personal hygiene product. Furthermore, it was believed that using high velocity process air streams with a lower density adhesive such as foamed adhesive would cause significant “fly” and “shot,” which leads to low creep resistance and/or poor edge control in the disposable absorbent personal hygiene products field. In addition, the large size of conventional foaming mixers prevented manufacturers from positioning the foaming mixers in close proximity to the adhesive applicators, which is desired in nonwoven applications. As a result, foamed adhesive has not been used in the manufacture of disposable absorbent personal hygiene products. 
     There is a need, therefore, for a method of dispensing adhesive in the manufacture of a disposable absorbent personal hygiene product that provides improved characteristics, including creep resistance, force retraction, and softness in the resulting product. 
     SUMMARY 
     In one embodiment of the invention, a method of manufacturing a disposable absorbent personal hygiene product includes mixing a pressurized gas and hot melt adhesive to form a foamed adhesive. A filament of the foamed adhesive is discharged toward a stretched elastic strand. The filament of foamed adhesive is impacted with high velocity process air to move the filament. The filament of foamed adhesive is deposited onto the stretched elastic strand such that the foamed adhesive expands in volume on the stretched elastic strand. The method also includes securing the stretched elastic strand to a first flat substrate portion with the foamed adhesive. 
     In one aspect, the process air is a plurality of air jets directed to impart a spiral motion on the filament. Due to the adhesive filament moving in a spiral motion and the elastic strand moving faster than the filament, the filament contacts the stretched elastic strand at first and second contact points and begins to wrap around the stretched elastic strand and stretch between the first and second contact points. In this regard, the stretched elastic strand accelerates the filament of foamed adhesive such that the filament forms localized masses of adhesive at the first and second contact points separated by a thin fiber section that breaks as the adhesive engages the stretched elastic strand. When the thin fiber section breaks, the halves or sections on either side of the break snap back towards the respective first and second contact points and wrap around the stretched elastic strand at those contact points to form the localized masses of adhesive, which are configured to become discrete bond points when securing the stretched elastic strand to the first flat substrate portion. The discrete bond points are separated by sections of stretched elastic strand with no adhesive or minimal adhesive material such that the stretched elastic strand is not rigidly bonded to the first flat substrate portion between the discrete bond points, thereby maximizing the elasticity of the stretched elastic strand in those sections. 
     The foamed adhesive begins expanding in volume during flight and prior to deposit on the stretched elastic strand. Moreover, the method includes expanding the foamed adhesive in volume by at least 14% total during flight and after deposit on the stretched elastic strand. In another aspect, the process air includes multiple air jets directed in a manner that imparts a substantially back-and-forth motion or any kind of desired motion on the filament. The amount of pressurized gas mixed with a predetermined volume of hot melt adhesive may be increased to increase the amount of foaming that the foamed adhesive will undergo following discharge. This increased foaming leads to increased creep resistance of the stretched elastic strand following securing to the first flat substrate portion. More particularly, the mixing of the pressurized gas and the hot melt adhesive may include sufficient quantities of pressurized gas to result in at least 26% total expansion in volume of the foamed adhesive deposited onto the stretched elastic strand, and preferably enough to result in at least 34% total expansion in volume of the foamed adhesive. This expansion provides a desirable creep resistance, such as less than 10% creep, for industry-standard add on weights. 
     The method may also include securing a second flat substrate portion to the stretched elastic strand and to the first flat substrate portion with the foamed adhesive. The first and second flat substrate portions may be provided as separate substrates in some embodiments, and may alternatively be provided as separate portions of a single flat substrate (e.g., folded over itself) in other embodiments. In embodiments where the disposable absorbent personal hygiene product includes a plurality of stretched elastic strands, the method includes discharging a plurality of filaments of foamed adhesive and impacting those filaments with process air before deposit onto the plurality of stretched elastic strands. 
     In another embodiment of the invention, a method of manufacturing a disposable absorbent personal hygiene product includes mixing a pressurized gas and hot melt adhesive to form a foamed adhesive. A filament of the foamed adhesive is discharged toward a first flat nonwoven substrate. The filament of foamed adhesive is impacted with high velocity process air to move the filament. For example, the process air is a plurality of air jets directed asymmetrically towards one another to produce a randomized pattern of adhesive on the nonwoven substrate. Alternatively, the process air is a plurality of air jets that produces a spiral pattern of adhesive on the nonwoven substrate. The filament of foamed adhesive is deposited onto the first flat nonwoven substrate such that the foamed adhesive expands in volume on the first flat nonwoven substrate. The method also includes securing the first flat nonwoven substrate to a second flat nonwoven substrate with the foamed adhesive. 
     Various additional features and advantages of the invention will become more apparent to those of ordinary skill in the art upon review of the following detailed description of the illustrative embodiments taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a disposable absorbent personal hygiene product during assembly of various components. 
         FIG. 2  is a perspective view of foamed adhesive being applied to an elastic strand. 
         FIG. 3  is a perspective view of foamed adhesive being applied to a plurality of elastic strands. 
         FIG. 4  is a schematic diagram view of one embodiment of an adhesive dispensing system used to perform the method of the invention. 
         FIG. 5  is a cross-sectional side view of an exemplary foaming mixer used in the adhesive dispensing system of  FIG. 4 . 
         FIG. 6  is a perspective view of an exemplary adhesive applicator used in the adhesive dispensing system of  FIG. 4  to produce a pattern of foamed adhesive on elastic strands as shown in  FIG. 3 . 
         FIG. 7  is an enlarged perspective view of the adhesive applicator of  FIG. 6 . 
         FIG. 8  is a rear view of the adhesive applicator of  FIG. 6 , showing internal flow paths for adhesive and process air. 
         FIG. 9  is a graphical representation showing test results for creep resistance and add-on weight for various levels of foaming the adhesive when using the adhesive dispensing system of  FIG. 4 . 
         FIG. 10  is a top view of foamed adhesive being applied to a flat substrate. 
         FIG. 11  is a first cross-sectional side view taken along line  11 - 11  in  FIG. 13  of another exemplary adhesive applicator used in the adhesive dispensing system of  FIG. 4  to produce a pattern of foamed adhesive on a substrate as shown in  FIG. 10 . 
         FIG. 12  is a second cross-sectional side view taken along line  12 - 12  in  FIG. 13  of the adhesive applicator of  FIG. 11 . 
         FIG. 13  is a bottom view of the adhesive applicator of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
       FIG. 1  illustrates one embodiment of a disposable absorbent personal hygiene product  10  manufactured using an illustrative method of the invention. The illustrated disposable absorbent personal hygiene product  10  is a disposable diaper  10  including first and second ends  12 ,  14  configured to wrap around the waist of the user and a narrowed central portion  16  configured to extend between the legs of the user. The diaper  10  includes a flat nonwoven substrate portion  18  (hereinafter first substrate  18  or flat nonwoven substrate  18 ), leg gathers  20  formed along each longitudinal side  22 ,  24  of the diaper  10  between the first and second ends  12 ,  14 , and a second flat substrate portion  26  (hereinafter second flat substrate  26 ) secured to the nonwoven substrate  18  to enclose the leg gathers  20 . The leg gathers  20  are formed by one or more elastic strands  28  that are secured to the nonwoven substrate  18  in a stretched condition so as to provide the diaper  10  with elasticity around the legs of the user. As shown, the second flat substrate  26  is a separate substrate from the flat nonwoven substrate  18  in the illustrated embodiment. However, it will be understood that the second flat substrate  26  alternatively could be a folded-over portion (not shown) of the flat nonwoven substrate  18  in other embodiments. The nonwoven substrate  18 , leg gathers  20 , and second substrate  26  are secured to each other with hot melt adhesive  30 . 
     To achieve various benefits in the manufacture and use of the diaper  10 , the hot melt adhesive  30  is injected with a pressurized gas such as nitrogen to form a foamed adhesive  30 , which is then dispensed on the nonwoven substrate  18  or onto a stretched elastic strand  28 . Exemplary deposits of foamed adhesive  30  are shown in  FIG. 2  on an elastic strand  28 , in  FIG. 3  on a plurality of elastic strands  28 , and in  FIG. 10  on a nonwoven substrate  18 . A schematic of an adhesive dispensing system  50  configured to produce these exemplary deposits of foamed adhesive  30  is provided in  FIG. 4  and described in further detail below. 
     With reference to  FIG. 2 , a filament of the foamed adhesive  30  exits a nozzle outlet  32  in a pressurized state such that the filament of foamed adhesive  30  generally resembles a bead of liquid adhesive immediately after discharge. However, the foamed adhesive  30  begins expanding in volume immediately upon discharge from the nozzle outlet  32  as shown in  FIG. 2 . The filament of foamed adhesive  30  is impacted by air jets to cause the filament of foamed adhesive  30  to move with a generally spiral motion and wrap around the elastic strand  28 , which is moving in the direction of arrow  34 . As shown in  FIG. 2 , the foamed adhesive  30  is accelerated and stretched out when applied to the faster moving elastic strand  28 , which causes the foamed adhesive  30  to form a plurality of localized areas of increased masses  35  of adhesive coupled by thinner filament sections  36  of adhesive. In the preferred operation, these thinner filament sections  36  will break between adjacent masses  35 , leaving no adhesive between the localized adhesive masses  35 . These localized adhesive masses  35  become discrete bond points during bonding of the elastic strand  28  to the substrate  18 , which advantageously provides desirable force retraction and creep resistance qualities. 
     The expansion in volume of the foamed adhesive  30  occurs both before and after deposit of the filament of foamed adhesive  30  on the elastic strand  28 . The volume of the filament of foamed adhesive  30  increases by up to 100% total (for example), after discharge from the nozzle outlet  32  as a result of the expansion of nitrogen within the hot melt adhesive  30 . In this regard, the filament of foamed adhesive  30  is up to 50% less dense than a liquid bead of adhesive having a similar volume. It will be understood that the filament of foamed adhesive  30  could be deposited onto a plurality of parallel stretched elastic strands  28  (i.e., at least two elastic strands  28 ) in other embodiments of the invention, and the claims of this application are thus not limited to deposit of a single filament of foamed adhesive  30  onto a single elastic strand  28 . It will also be understood that depositing the foamed adhesive  30  onto the elastic strand  28  may result in the foamed adhesive  30  being in substantially complete contact the with elastic strand  28  as shown in  FIG. 2 , but this wrap or deposit onto the elastic strand  28  may also result in the foamed adhesive  30  only coming into partial contact with the elastic strand  28  with another portion of the foamed adhesive  30  drooping away from the elastic strand  28  in other embodiments. 
     With reference to  FIG. 3 , the foamed adhesive  30  may be deposited onto a plurality of parallel elastic strands  28  moving along the direction indicated by arrow  34 . Similar to the deposit of foamed adhesive  30  onto a single elastic strand  28  as described above, each filament of foamed adhesive  30  is discharged from a corresponding nozzle outlet  32  and begins expanding in volume immediately upon discharge. Once again, each filament of foamed adhesive  30  is accelerated upon deposit onto the respective elastic strand  28  such that the foamed adhesive  30  stretches out to form a plurality of localized areas of increased masses  35  of adhesive separated by broken-apart filament sections. These adhesive masses  35  advantageously form discrete bond points for each elastic strand  28  when adhered to the substrate  18 . It will be understood that a single filament of foamed adhesive  30  may be moved with a swirl motion across multiple elastic strands  28  to form these discrete bond points in other embodiments consistent with this invention. In addition to reducing the total volume of adhesive  30  being applied to the elastic strand  28 , the foamed adhesive  30  unexpectedly exhibits improved creep resistance compared to liquid adhesive as evidenced in test results discussed with reference to  FIG. 9  below. Accordingly, the dispensing system and methods of the current application significantly reduce adhesive add on and manufacturing costs while improving and/or maintaining the bond quality necessary in the disposable absorbent personal hygiene product field. 
     As briefly discussed above,  FIG. 4  shows an exemplary embodiment of an adhesive dispensing system  50  used to dispense one or more filaments of foamed adhesive  30 . The adhesive dispensing system  50  may include components such as the Signature® spray nozzles and SureWrap® nozzles commercially available from Nordson Corporation of Westlake, Ohio, but it will be understood that any type of spray nozzle may be used without departing from the scope of the invention. The adhesive dispensing system  50  includes a foaming mixer  52  connected to an adhesive supply  54  and a pressurized gas supply  56 . The foaming mixer  52  is operable to mix or inject pressurized gas into hot melt adhesive. The foaming mixer  52  is coupled to a metering pump  58  and an adhesive dispenser or applicator  60 . The metering pump  58  supplies a metered amount of foamed adhesive  30  to the applicator  60  while recycling the remaining foamed adhesive  30  back to the foaming mixer  52 . Thus, the foamed adhesive  30  in the metering pump  58  remains pressurized and continuously replenished by the foaming mixer  52 . The applicator  60  discharges the foamed adhesive  30  and process air to produce a desired deposit of foamed adhesive  30  onto either a nonwoven substrate  18  or an elastic strand  28  as described above with reference to  FIGS. 2 and 3 . 
     In one embodiment, the foaming mixer  52  is a mixer as described in U.S. Pat. No. 7,703,705 to Ganzer, the entire disclosure of which is hereby incorporated by reference herein. This exemplary embodiment of a foaming mixer  52  is also shown in  FIG. 5 . The foaming mixer  52  includes a mixing body  102  with a side wall  104 , a tubular mixing chamber  106  bound by the side wall  104 , and a mixer element  108  located inside the mixing chamber  106 . The mixer  52  is heated by heaters (not shown), such as cartridge-style resistance heating elements, embedded in the side wall  104 . The heaters are controlled using feedback from a conventional temperature sensor (not shown), such as a resistance temperature detector, a thermistor or a thermocouple. The heaters ensure that the adhesive material in the mixer  52  is maintained within an acceptable temperature range for dispensing by the applicator  60 . 
     In one example, the foaming mixer  52  receives Bostik  2861  hot melt adhesive and nitrogen supplied at about 50 psi. The foaming mixer  52  is maintained at about 315 degrees Fahrenheit and operates at about 600 rpm such that the foamed adhesive  30  exits the foaming mixer  52  at a pressure of about 900 psi. With these settings, the foaming mixer  52  is operative to discharge about 20-45 milligrams per meter of elastic strand  28  when the adhesive dispensing system  50  applies adhesive to an elastic strand  28 . 
     The foaming mixer  52  includes an adhesive inlet port  110  leading into the mixing chamber  106 . The adhesive supply  54  is coupled in fluid communication with the adhesive inlet port  110  by an elbow fitting  112  mounted in the adhesive inlet port  110  by, for example, a threaded engagement and a supply hose (not shown) connected to the elbow fitting  112 . A flow control element such as a spring-loaded check valve  114  is located in the adhesive inlet port  110  between the mixing chamber  106  and the adhesive supply  54 . The check valve  114 , which has a conventional construction, prevents gas-filled adhesive material from infiltrating into the elbow fitting  112  and being transported upstream to the adhesive supply  54 . 
     The foaming mixer  52  also includes a gas inlet port (not shown) leading into the mixing chamber  106 . The gas supply  56  is coupled in fluid communication with the gas inlet port. The gas inlet port may be disposed adjacent to the adhesive inlet port  110  in the mixing body  102 . The foaming mixer  52  also includes a measurement port  116  extending into the mixing chamber  106  opposite the adhesive inlet port  110 . The measurement port  116  receives an elbow connector  118  configured to receive a pressure gage (not shown) for measuring the pressure within the mixing chamber  106 . The foaming mixer  52  includes a pair of outlet ports  122  extending into the mixing chamber  106 . One of the outlet ports  122  is inactive in  FIG. 5  and closed with a plug  124 , while the other outlet port  122  receives an elbow fitting  126  leading to the metering pump  58  and the applicator  60 . Consequently, adhesive material enters the foaming mixer  52  at the adhesive inlet port  110  as shown by arrow  128  and leaves the foaming mixer  52  at the outlet port  122  as shown by arrow  130 . 
     The mixer element  108  includes a central shaft  132  extending longitudinally through the mixing chamber  106 , a cylindrical body  134  rigidly coupled for rotation with the central shaft  132 , and fins  136  that project outwardly from the cylindrical body  134  toward the confronting inner surface  138  of the side wall  104  of the mixing chamber  106 . The central shaft  132  includes a first end  140  located adjacent to the outlet ports  122  and a second end  142  located adjacent to the adhesive inlet port  110 . The first end  140  of the central shaft  132  is supported for rotation relative to the side wall  104  by a bushing or bearing  144  in the mixing chamber  106 . A thrust bearing  146  fitted in the bushing  144  provides a thrust load support for central shaft  132 . The bushing  144  and the thrust bearing  146  are assembled together and secured to the mixing body  102  with conventional threaded fasteners. 
     The second end  142  of the central shaft  132  projects through another bushing  148  situated in the mixing chamber  106  adjacent the adhesive inlet port  110 . Another thrust bearing  150  provides a thrust load support for the second end  142  of the central shaft  132 . The second end  142  of the central shaft  132  is coupled by a coupling element  152  with a drive shaft  154  of a motor  156 . The coupling element  152  and the thrust bearing  150  adjacent the coupling element  152  are formed from a material having a low thermal conductivity so that heat transfer is reduced from the mixing body  102  to the motor  156 . The motor  156  is also isolated thermally from the mixing body  102  by a standoff  158  separating the motor  156  from the mixing body  102 . The standoff  158  includes slots  160  that promote cooling. The motor  156  drives the powered rotation of the drive shaft  154  and the central shaft  132  for moving the fins  136  relative to the side wall  104  of the mixing chamber  106 . 
     The adhesive material is bounded inside the mixing chamber  106  in a region between the bushings  144 ,  148 . The bushings  144 ,  148  include various sealing members that assist in confining the fluid material inside the mixing chamber  106 . A cowling  164  and a cap  166  are secured by conventional fasteners to the mixing body  102  and protectively cover the mixing body  102  opposite the motor  156 . 
     The fins  136  on the mixer element  108  are distributed in rows along the length of the cylindrical body  134  (and the length of the central shaft  132 ). The tip of each fin  136  has a close clearance with the side wall  104 . The adhesive material and the pressurized gas delivered into the mixing chamber  106  are forced through gaps between adjacent fins  136 , as the fins  136  rotate, for mixing, stirring and agitating the gas and adhesive material into the foamed adhesive  30 . Rotation of the fins  136  relative to the stationary side wall  104  therefore operates to repeatedly divide the gas and adhesive into small streams and then recombine the streams to create a substantially homogeneous blend or mixture of gas and adhesive with the pressurized gas entrained in solution. 
     The fins  136 , which are fashioned from an initially continuous helical thread extending along the length of the cylindrical body  134 , define a helical arrangement likewise winding along the length of the cylindrical body  134 . As the central shaft  132  of the mixer element  108  is continuously rotated by operation of motor  156 , the helical arrangement of the fins  136  tends to force the adhesive material toward the adhesive inlet port  110 , which counters the forward flow of the gas/adhesive mixture toward the outlet ports  122 . The foaming mixer  52  is therefore operable to supply foamed adhesive  30  to the metering pump  58  and the applicator  60 . Additionally, the foaming mixer  52  is smaller in size than many conventional foaming mixers, which enables the foaming mixer  52  to be positioned in close proximity to the metering pump  58  and the applicator  60 . 
     The metering pump  58  may be the pump used with the VersaBlue® melters commercially available from Nordson Corporation of Westlake, Ohio. The metering pump  58  operates at a rotational speed similar to the rotational speeds used during metering of liquid adhesive because the pressurized foamed adhesive  30  in the metering pump  58  is in substantially a liquid state. For example, the foamed adhesive  30  may circulate between the foaming mixer  52  and the metering pump  58  at about 900 psi to maintain the substantially liquid state until discharge from the applicator  60 . The metering pump  58  then delivers a metered supply of the foamed adhesive  30  into one of the applicators  60  described below. It will be understood that different types of pumps may be used in other embodiments. 
     In one embodiment, the applicator  60  is a spiral dispensing module  202  as described in U.S. Pat. No. 7,578,882 to Harris et al., the entire disclosure of which is hereby incorporated by reference herein. This embodiment of a dispensing module  202  is also shown in  FIGS. 6-8 . 
     With reference to  FIGS. 6 and 7 , the dispensing module  202  includes a module body  204  including a central body portion  206  and a lower body portion  208 . The module  202  also includes a clamping or quick disconnect mechanism  210  for connecting a nozzle  212  to the lower body portion  208 . As well understood, the central body portion  206  may include a valve stem  206   a  that engages with a valve seat  208   a  formed in the lower body portion  208  to control flow of hot melt adhesive into a passage  208   b  leading to the nozzle  212  (the valve stem and valve seat may also be located in other locations within the dispensing module  202  in other embodiments). The quick disconnect mechanism  210  is further described in U.S. Pat. No. 6,619,566 to Gressett, Jr. et al., the entire disclosure of which is hereby incorporated by reference herein. The nozzle  212  receives pressurized foamed adhesive  30  and pressurized process air from respective supply passages ( 208   b , not shown) located in the lower body portion  208 . 
     Referring now to  FIGS. 7 and 8 , the exemplary nozzle  212  is shown in more detail. The nozzle  212  includes angled cam surfaces  214 ,  216 , as more fully described in U.S. Pat. No. 6,619,566, to facilitate coupling the nozzle  212  with the dispensing module  202 . The nozzle  212  includes a first side  218  configured to mount to the lower portion  208  of the dispensing module  202 . The first side  218  includes an adhesive supply port  220  and at least one process air supply port  222  which mate to the corresponding adhesive and air supply passages in the dispensing module  202 . The nozzle  212  defines a generally wedge-shaped cross-section including second and third sides  226 ,  228 . A plurality of frustoconically-shaped protrusions  230  extend from the second side  226  of the nozzle  212 , each including an adhesive discharge outlet  232  disposed on a distal end of the protrusion  230 . The adhesive discharge outlets  232  are in fluid communication with adhesive discharge passages  234 , which in turn are in communication with the adhesive supply port  220 . At least a portion of the adhesive discharge passages  234  are oriented to form an acute angle with a plane parallel to the first side  218 , and thus form an angle with a direction corresponding to of movement of the strand  28 , generally indicated by arrow  34 . The adhesive discharge passages  234  of the exemplary embodiment are inclined at approximately 20° to the first side  218 , whereby the foamed adhesive  30  is dispensed from the adhesive discharge outlets  232  to the elastic strands  28  generally in the direction of strand movement. 
     The second side  226  of the nozzle  212  further includes a plurality of air discharge outlets  236  proximate each of the adhesive discharge outlets  232  and in fluid communication with air discharge passages  238 ,  240 , which are in communication with the air supply port  222  on the first side  218  of the nozzle  212 . In the exemplary nozzle  212 , four air discharge outlets  236  are disposed in a generally square pattern around each adhesive discharge outlet  232  at the base of the frustoconical protrusion  230 . The air discharge passages  238 ,  240  of the exemplary nozzle  212  are angled with respect to the corresponding adhesive discharge passage  234  so that high velocity process air jets indicated by arrows  242  are directed to be tangential to a discharged filament of foamed adhesive  30  from the adhesive discharge outlet  232 . Each air discharge outlet  236  is positioned at the same radial distance from a common center defined at the location of the corresponding adhesive discharge outlet  232 . Consequently the process air jets tangentially swirl about the discharged filament of foamed adhesive  30  at generally the same location downstream of the adhesive discharge outlet  236  and the air discharge outlets  236 . Variation of the filament movement pattern is possible by adjusting the offset spacing and orientation of the air discharge passages  238 ,  240  relative to the adhesive discharge passage  234 , as will be apparent to those skilled in the art. In one alternative, the process air includes at least two air jets directed in a manner that imparts a substantially back-and-forth motion on the filament. 
     The nozzle  212  further includes notches  250  formed into an end of the nozzle  212  opposite the first side  218  and proximate the adhesive discharge outlet  232  to direct the elastic strands  28  past the air and adhesive discharge outlets  232 ,  236  disposed on the second side  226  of the nozzle  212 . As shown more clearly in  FIG. 8 , the notches  250  extend between the second and third sides  226 ,  228  of the nozzle  212 . The notches  250  guide each elastic strand  28  to be located below the corresponding adhesive discharge outlet  232 . In an exemplary embodiment, the second and third sides  226 ,  228  are configured to form acute angles with the first side  218 . In one exemplary embodiment, the second side  226  forms an angle of approximately 60°-80° with the first side  218 . In another aspect of the invention, the third side  228  forms an angle no greater than approximately 70° with the first side  218 . Advantageously, the angle of the third side  228  facilitates the passage of knots formed in the elastic strand  28  without causing breakage of the elastic strand  28 . 
     In operation, an elastic strand  28  is received into each notch  250  and moves in a direction indicated by the arrow  34 . As the elastic strands  28  pass beneath the adhesive discharge outlets  232 , a filament of foamed adhesive  30  is dispensed from each adhesive discharge outlet  232 , generally toward the corresponding elastic strand  28  so as to be deposited at least partially on the elastic strand  28 . More specifically, the filament of foamed adhesive  30  may be deposited in complete contact with the elastic strand  28 , or may be in partial contact with other portions of the foamed adhesive  30  drooping from the elastic strand  28 . Pressurized process air is discharged from the air discharge outlets  236  and directed generally tangentially toward the filaments of foamed adhesive  30 , as depicted by arrows  242 . The pressurized process air causes the filaments of foamed adhesive  30  to move in a spiral motion as the filaments are deposited on the elastic strands  28 . As described in greater detail above, the elastic strands  28  accelerate the filaments  30  and cause the filaments  30  to stretch and form discrete masses  35  of adhesive that form discrete bond points when the elastic strands  28  are adhered to a substrate  18 . The filaments of foamed adhesive  30  expands in volume on the elastic strands  28  as shown in  FIGS. 6 and 7 . The elastic strands  28  are then ready to be secured to another substrate in the disposable absorbent personal hygiene product  10 , such as to form the leg gathers  20  of a diaper  10 . 
     As described above, the foamed adhesive  30  is highly pressurized and maintained in nearly liquid form until discharge from the applicator  60 . Thus, the foamed adhesive  30  is not completely expanded in volume when process air impacts or tangentially contacts or otherwise moves the discharged filaments of foamed adhesive  30  in flight. As a result, the density of the foamed adhesive  30  remains high enough to avoid fly or shot caused by the high pressure of the process air. Moreover, even though the foamed adhesive  30  begins expanding prior to deposit on an elastic strand, the foamed adhesive  30  retains enough integrity in flight to avoid bouncing off the elastic strand. The filaments of foamed adhesive  30  are still adequately and precisely controllable so as to be deposited in desired patterns on the elastic strand(s)  28 , similar to filaments of liquid hot melt adhesive. 
     When using the foamed adhesive  30  to bond one or more elastic strands  28  to a nonwoven substrate  18 , the bond quality exhibited by the foamed adhesive  30  is substantially similar to the bond quality formed by liquid adhesive. For example, using the same volume of foamed adhesive  30  and liquid adhesive results in substantially similar levels of creep resistance. Furthermore, the foamed adhesive  30  continues to form discrete bond points along the elastic strand  28  during bonding, which provides high force retraction qualities. Considering that the foamed adhesive  30  includes about half of the normal amount of hot melt adhesive material as a liquid adhesive, the resulting softness or hand of the diaper  10  is improved compared to conventional designs. The expansion of the foamed adhesive  30  effectively forms a web-like structure of hot melt adhesive and gas that effectively adheres to the elastic strand  28  upon deposit on the elastic strand  28 . 
     In another related example, foaming of the foamed adhesive  30 , to a larger extent, provides improved creep resistance for the same amount of add on adhesive weight. With reference to  FIG. 9 , test results are shown that prove the amount of creep resistance has been increased by the application of more foaming to the adhesive in operation. In this regard,  FIG. 9  includes a graph  280  representing average creep in percent measured against add on adhesive weight in milligrams per meter of elastic strand  28 . The creep measurements were taken after an extended aging period of 28 hours following bonding of the elastic strand  28  to a nonwoven substrate  18 , and various data points (not shown) were plotted on the graph  280  for different levels of foaming (0% or liquid adhesive, 14%, 26%, and 34%) within the foamed adhesive  30 . By “% foaming,” the percentages shown in this Figure mean the percent of total volume expansion undergone by the foamed adhesive during and after deposit onto the elastic strand  28 . Although the industry standard add on range is about 35-50 milligrams per meter, test results were provided both inside and outside this standard range so that trend lines  290   a ,  290   b ,  290   c ,  290   d  could be generated to illustrate the improvements for different levels of foaming the foamed adhesive  30 . 
     As shown in the graph  280 , the addition of more foaming to the foamed adhesive  30  significantly improved the resulting creep resistance over the extended sample aging period of 28 hours. To this end, the first trend line  290   a  for liquid adhesive (0% foam) shows a relatively high creep of about 25% for the industry standard add on range, while the second trend line  290   b  for 14% foaming drops the creep exhibited down toward 15% in the industry standard add on range. The third trend line  290   c  for 26% foaming further reduces the amount of creep exhibited in the test results, and the fourth trend line  290   d  for 34% foaming achieves an ideal amount of creep (e.g., less than 10%) within the industry standard add on range. Therefore, providing enough pressurized gas in the foamed adhesive  30  to result in at least 26% foaming or total volume expansion, or even more preferably, at least 34% foaming, provides a desirable level of creep resistance for most applications in the industry-standard add on range for adhesive weight per length of strand. It will be understood that the specific percentages of foaming and levels of creep resistance achieved may vary based on material differences for some adhesives in other embodiments. However, for all materials tested, increasing the amount of foaming that occurs by increasing the amount of pressurized gas entrained within the liquid hot melt adhesive will result in improved creep resistance for the same amount of add on weight. Thus, foaming the foamed adhesive  30  provides unexpected benefits in improving creep resistance while maintaining a high bond quality. 
     Furthermore, the expansion of the foamed adhesive  30  results in more rapid cooling of the outermost or external layers of adhesive material, and thus reduces the likelihood of the foamed adhesive  30  burning through a second substrate  26 . More specifically, the foamed adhesive remains warm enough to form a reliable adhesive bond between elements of the diaper  10  while cooling enough to avoid burn-through on temperature sensitive substrates. Additionally, testing has revealed the unexpected benefit that the use of foamed adhesive  30  reduces the pinch pressure that a pressure nip or pressure roller needs to apply to produce the high quality bond between the elastic strands  28  and the substrate  18 . Thus, less forceful pressure nips may be utilized with the adhesive dispensing system  50  of this invention. 
     Turning to another embodiment shown in  FIG. 10 , a plurality of filaments of foamed adhesive  30  exit corresponding nozzle outlets (not shown) in a pressurized state so that the filaments of foamed adhesive  30  resemble beads of liquid adhesive upon initial discharge from the nozzle outlets. Process air in the form of multiple air jets is also discharged and moves the filaments of foamed adhesive  30  in a desired manner before deposit on the nonwoven substrate  18 . The substrate is moving in the direction of arrow  34 . The process air is operative to cause any desired motion of the filaments, including but not limited to, randomized motion or spiral motion. In this embodiment, the process air imparts a randomized motion of each filament of foamed adhesive  30  as evidenced by the random pattern of adhesive on the nonwoven substrate  18 . As shown in  FIG. 10 , the foamed adhesive  30  forms a number of localized areas of increased or overlapping adhesive masses  35  along the length of the substrate  18 . These localized adhesive masses  35  become discrete bond points during bonding of an elastic strand  28  to the substrate  18 , which advantageously provides adequate force retraction and creep resistance qualities of the resulting bond. Similar to the elastic strand embodiment shown in  FIGS. 2 and 3 , the foamed adhesive  30  begins expanding in volume immediately after discharge from the nozzle outlet and increases in volume by at least 14% total during flight and after deposit on the nonwoven substrate  18 . Furthermore, the foamed adhesive  30  produces adequate full coverage of the substrate  18  with less add on and a thinner overall adhesive coating. 
     In another embodiment, the applicator  60  includes a dispensing nozzle  302  as described in U.S. Patent Publication No. 2010/0327074 to Bondeson et al., the entire disclosure of which is hereby incorporated by reference herein. This exemplary embodiment of a dispensing nozzle  302  is also shown in  FIGS. 11-13 . 
     With reference to  FIGS. 11 and 12 , the nozzle  302  includes first and second process air shim plates  304 ,  306 , an adhesive shim plate  308 , first and second separating shim plates  310 ,  312 , and first and second end plates  314 ,  316 . The entire assembly of plates  304 ,  306 ,  308 ,  310 ,  312 ,  314 ,  316  is held together by a pair of threaded fasteners  317  that extend through corresponding apertures in the first end plate  314  (as well as the shim plates  304 ,  306 ,  308 ,  310 ,  312 ) and into threaded holes in the second end plate  316 . The shim plates  304 ,  306 ,  308 ,  310 ,  312  are arranged in order from the first end plate  314  to the second end plate  316  as follows: the first process air shim plate  304  (adjacent the first end plate  314 ), the first separating shim plate  310 , the adhesive shim plate  308 , the second separating shim plate  312 , and the second process air shim plate  306  (adjacent the second end plate  316 ). The second end plate  316  also includes a projection  318  serving as a locating member that extends through respective upper slots  320  in the air shim plates  304 ,  306 , the separating shim plates  310 ,  312 , and the adhesive shim plate  308 . The projection  318  is then received in a blind bore  322  in the first end plate  314 . 
     The first end plate  314  is a generally L-shaped member and includes a top surface  326  generally orthogonal to planes that contain the first and second process air shim plates  304 ,  306 , the adhesive shim plate  308  and the first and second separating shim plates  310 ,  312 . A side surface  328  generally parallel to the planes containing these same shim plates  304 ,  306 ,  308 ,  310 ,  312  receives the threaded fasteners. The top surface  326  includes an adhesive inlet  330  and a process air inlet  332 . The first end plate  314  also includes oppositely extending projections  334 ,  336  at the top surface  326  that may be used for securing the nozzle  302  to a dispensing valve or module  337   a  as well understood. The dispensing module  337   a  includes a valve stem  337   b  that may engage with a valve seat  337   c  to control flow of hot melt adhesive into the adhesive inlet  330  of the nozzle  302 . 
     With reference to  FIG. 11 , the first end plate  314  includes a process air inlet passage  338  communicating with the process air inlet  332 . The process air inlet passage  338  communicates with first and second air distribution passages  340 ,  342  that respectively communicate with opposite sides of the shim plate assembly  304 ,  306 ,  308 ,  310 ,  312 . The first air distribution passage  340  passes through the shim plate assembly  304 ,  306 ,  308 ,  310 ,  312  at aligned holes  344 , then through a vertical recess  346  in the second end plate  316 , and finally into a horizontally extending slot  348  in the second end plate  316 . Process air from the first air distribution passage  340  enters corresponding pairs of air slots  350 ,  352  ( FIG. 13 ) in the second process air shim plate  306 . The second air distribution passage  342  extends into a horizontally extending recess  354  in the first end plate  314 . Process air from the second air distribution passage  342  enters corresponding pairs of air slots  356 ,  358  ( FIG. 13 ) in the first process air shim plate  304 . The arrangement of the air slots  350 ,  352 ,  356 ,  358  is described in further detail with reference to  FIG. 13  below. 
     With reference to  FIG. 12 , the first end plate  314  includes an adhesive inlet passage  362  communicating with the adhesive inlet  330 . A seal member  364  located in a groove  366  may be used to seal the adhesive inlet  330  at the top surface  326 . The adhesive inlet passage  362  communicates with an adhesive distribution passage  368  and an upper horizontal slot  370  in the first end plate  314 . This upper horizontal slot  370  communicates with the adhesive shim plate  308  via respective aligned apertures  372 ,  374  in the first process air shim plate  304  and the first separating shim plate  310 . The adhesive shim plate  308  includes a plurality of adhesive slots  376  each having an adhesive inlet  378  and an adhesive outlet  380 . It will be understood that the second process air shim plate  306  also includes an adhesive aperture  372  to allow full interchangeability between the first and second process air shim plates  304 ,  306 . However, the adhesive aperture  372  in the second process air shim plate  306  is blocked from use by the second separating shim plate  312  in the embodiment shown in  FIG. 12 . The separating shim plates  310 ,  312  are utilized to seal off the respective air slots  350 ,  352 ,  356 ,  358  from the adhesive slots  376 . 
     Each of the adhesive slots  376  is located generally in the center of a corresponding set of air slots  350 ,  352 ,  356 ,  358  in the first and second process air shim plates  304 ,  306 . Thus, as shown in  FIG. 13 , each pair of air slots  350 ,  352  in the second process air shim plate  306  is directly aligned with a corresponding pair of air slots  356 ,  358  in the first process air shim plate  304 , so as to surround a corresponding adhesive outlet  380  in the adhesive shim plate  308 . Although not clearly shown in  FIG. 13 , the air slots  350 ,  352  converge toward each other along their length and the air slots  356 ,  358  converge toward each other along their length such that the process air ejected from each pair of air slots  350 ,  352 ,  356 ,  358  is configured to intersect. However, none of the air slots  350 ,  352 ,  356 ,  358  converge toward their associated adhesive outlet  380  because the respective pairs of slots  350 ,  352 ,  356 ,  358  are each contained in parallel planes different from the plane containing the adhesive slot  376 . 
     In operation, pressurized high velocity process air is delivered into the nozzle  302  at the process air inlet  332  and then is discharged from the corresponding air slots  350 ,  352 ,  356 ,  358  in the first and second process air shim plates  304 ,  306 . The pressurized foamed adhesive  30  is delivered into the nozzle  302  at the adhesive inlet  330  and then is discharged from the corresponding adhesive slots  376  at the adhesive outlets  380 . It will be understood that any number of adhesive slots  376  and adhesive outlets  380  may be provided along the length of the nozzle  302  depending on the substrate to be coated with adhesive  30 . 
     The discharged stream of pressurized air exiting from each air slot  350  converges and impacts against a process air stream exiting from each associated air slot  352 . In a similar manner, respective process air streams exiting air slots  356  impact against the streams exiting from air slots  358 . These asymmetric impacts cause the filaments of foamed adhesive  30  exiting the associated adhesive outlets  380  to move side-to-side or back and forth in random directions. As a result, the filaments of foamed adhesive  30  form an erratic, non-uniform or random pattern as, for example, shown in  FIG. 10 . However, this pattern of adhesive  30  exhibits good edge control on the substrate  18  because excessive “fly” or “shot” is avoided during the dispensing process. As previously described with reference to  FIG. 10 , the nozzle  302  is therefore operable to deposit a random pattern of filaments of foamed adhesive  30 , the foamed adhesive  30  increasing in volume on the nonwoven substrate  18 . Additionally, testing has revealed the unexpected benefit that the foamed adhesive  30  permeates more readily into the relatively porous nonwoven material of the substrate  18  than a corresponding liquid bead of adhesive. As a result, less total adhesive add on is required to form an adequate bond with the nonwoven substrate  18 . In sum, the foamed adhesive  30  produces high quality bonds with good edge control and substantially less adhesive add on than what is present when using liquid adhesive. 
     While the present invention has been illustrated by the description of specific embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept. What is claimed is: