Patent Publication Number: US-2007102841-A1

Title: Applicators and methods for dispensing a liquid material

Description:
FIELD OF THE INVENTION  
      The present invention generally relates to liquid material dispensing and, more particularly, to applicators with gas jets that impinge a dispensed liquid material filament and methods of dispensing liquid material filaments with gas jet impingement.  
     BACKGROUND OF THE INVENTION  
      Dispensers discharge fluid or liquid materials, such as hot melt adhesives, in the form of a thin continuous filament to form a desired pattern onto a moving substrate. Common substrates include, but are not limited to, flat sheets or webs of paper or cardboard of the type commonly used in packaging, or a variety of products in other manufacturing operations. In these familiar dispensing operations, the patterns formed on the substrate may be characterized as either overlapping or non-overlapping. Overlapping patterns include any pattern where the filament crosses over itself in a controlled or predictable pattern, such as spiral patterns, swirl patterns, and overlapping waving or back-and-forth patterns. Non-overlapping patterns include any pattern in which the filament does not cross over itself, such as sinusoidal patterns, non-overlapping waving or back-and-forth patterns, and omega-shaped patterns.  
      The width of the pattern placed on the substrate can be widened to many times the width of the filament itself. Such overlapping and non-overlapping patterns are especially useful for accurately covering a wide area on a substrate with liquid material dispensed as single filaments or as multiple side-by-side filaments from nozzle passages having small diameters, such as on the order of 0.010 inch to 0.060 inch. This is especially useful at the edges of a substrate and on very narrow substrates, for example, on strands of elastic material used in the leg bands of diapers.  
      Dispensers capable of dispensing liquid material filaments to form overlapping and non-overlapping patterns on a substrate are distinct from other types of dispensers that discharge continuous filaments that form a chaotic and random pattern on a substrate. Generally, such random pattern dispensers are used in spunbonding manufacturing operations to dispense filaments that form a nonwoven web. The gas impinging these filaments lacks the ability to selectively create overlapping or non-overlapping patterns.  
      Impinging a continuous solid filament of liquid material with plural gas jets to provide a controlled pattern of liquid material on the substrate has many advantages, some of which are explained above. Generally, multiple dispensing applications would benefit from dispensed patterns having an amplitude (i.e., pattern width on the substrate) and/or frequency that exceed the amplitudes and frequencies currently available when using dispensing continuous filaments. In addition, multiple dispensing applications would benefit from the ability to effectively increase the width covered by the discharged filament on the moving substrate without changing the mass of liquid material per unit length of the filament.  
      For these and other reasons, it would be desirable to provide improved applicators and methods for creating an overlapping or non-overlapping filament pattern on a substrate.  
     SUMMARY OF INVENTION  
      In accordance with an embodiment of the invention, an applicator comprises a dispenser body including a liquid material passage communicating with a liquid material outlet and a plurality of first gas outlets positioned near the liquid material outlet. The liquid material passage is configured to discharge a stream of a liquid material from the liquid material outlet as a hollow filament. Each of the first gas outlets configured to emit a corresponding one of a plurality of streams of a first gas that impinges the hollow filament after discharge from the liquid material outlet to cause movement of the filament.  
      In another embodiment of the present invention, an applicator comprises a dispenser body includes a liquid material passage with a liquid material outlet configured to discharge a stream of a liquid material and a plurality of gas outlets positioned about the liquid material outlet. The liquid material outlet is shaped to produce a plurality of filament lobes as the stream of the liquid material is discharged. Each of the gas outlets emits a corresponding one of a plurality of gas streams that impinges the lobes of the filament after discharge from the liquid material outlet to cause movement of the filament.  
      In another aspect of the present invention, a method of forming a hollow filament of a liquid material comprises extruding a stream of the liquid material and introducing a gas into an open core of the stream as the stream is being extruded to form the hollow filament. The forming method further includes impinging the hollow filament with a plurality of gas jets to cause movement of the hollow filament.  
      In another aspect of the present invention, a method of forming a continuous filament of a liquid material comprises extruding a stream of the liquid material with continuous filament having a plurality of lobes. The method further includes impinging the lobes of the filament with a plurality of gas jets to cause movement of the filament  
      These and other advantages of the present invention shall become more apparent from the accompanying drawings and description thereof. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.  
       FIG. 1  is a perspective view of a liquid material dispenser constructed in accordance with an embodiment of the invention.  
       FIG. 2A  is a top view of the liquid material dispenser of  FIG. 1 .  
       FIG. 2B  is a bottom view of the liquid material dispenser of  FIG. 1  with the nozzle removed.  
       FIG. 3  is an exploded cross-sectional view taken generally along line  3 - 3  of  FIG. 2A .  
       FIG. 3A  is a detailed view of a portion of  FIG. 3 .  
       FIG. 4  is an exploded cross-sectional view taken generally along line  4 - 4  of  FIG. 2A .  
       FIG. 5  is a bottom view of the liquid material dispenser of  FIG. 1 .  
       FIG. 6  is a cross-sectional view similar to  FIG. 3A  in which the nozzle is mounted to the dispenser body.  
       FIG. 7  is a bottom view similar to  FIG. 5  of a liquid material dispenser constructed in accordance with an alternative embodiment of the invention.  
       FIG. 7A  is a diagrammatic side view of the hollow filament dispensed from the liquid material dispenser of  FIG. 7 .  
       FIG. 8  is a bottom view similar to  FIG. 7  of a liquid material dispenser constructed in accordance with an alternative embodiment of the invention.  
       FIG. 8A  is a diagrammatic side view of the hollow filament dispensed from the liquid material dispenser of  FIG. 8 .  
       FIG. 9  is a bottom view similar to  FIG. 7  of a liquid material dispenser constructed in accordance with an alternative embodiment of the invention.  
       FIG. 9A  is a diagrammatic side view of the hollow filament dispensed from the liquid material dispenser of  FIG. 9 .  
       FIG. 10  is a bottom view similar to  FIG. 7  of a liquid material dispenser constructed in accordance with an alternative embodiment of the invention.  
       FIG. 10A  is a diagrammatic end view of the hollow filament dispensed from the liquid material dispenser of  FIG. 10 .  
       FIG. 11  is a bottom view similar to  FIG. 7  of a liquid material dispenser constructed in accordance with an alternative embodiment of the invention.  
       FIG. 11A  is a diagrammatic end view of the hollow filament dispensed from the liquid material dispenser of  FIG. 11 .  
       FIG. 12  is a perspective view of a liquid material dispenser constructed in accordance with an alternative embodiment of the invention.  
       FIG. 13  is a bottom view of the liquid material dispenser of  FIG. 12 .  
       FIG. 14  is a detailed view of a portion of  FIG. 13 .  
       FIG. 15  is a perspective view of a liquid material dispenser constructed in accordance with an alternative embodiment of the invention.  
       FIG. 16  is a graphical representation of the oscillation frequency as a function of fiber hollowness.  
       FIG. 17  is a schematic representation of a pattern traced by a hollow filament after landing on a substrate.  
       FIG. 18  is a graphical representation of the oscillation frequency for a prior art filament and a plus-shaped filament of the invention as a function of swirl gas pressure.  
       FIG. 19  is a graphical representation of the oscillation width for the filaments of  FIG. 18  as a function of swirl gas pressure.  
       FIG. 20  is a graphical representation of the oscillation frequency for a prior art filament and for various filaments of the invention as a function of swirl gas pressure. 
    
    
     DETAILED DESCRIPTION  
      With reference to  FIGS. 1, 2A  and  3 , an applicator or liquid material dispenser  10  generally includes a dispenser body  12  and a nozzle  14  removably secured by a threaded engagement with a lower portion  12   a  of the dispenser body  12 . The lower portion  12   a  has a smaller diameter than an upper portion  12   b , which is barrel shaped. Extending axially along the length of the dispenser body  12  is a plurality of liquid supply passageways  16 ,  18 ,  20 ,  22  each in fluid communication proximate to the nozzle  14  with an annular liquid material passage  24  ( FIG. 3A ). The liquid supply passageways  16 ,  18 ,  20 ,  22  are inclined axially so as to converge in a direction toward the annular liquid material passage  24  and intersect at one end with the liquid material passage  24 .  
      An opposite end of each of the liquid supply passageways  16 ,  18 ,  20 ,  22  communicates with a liquid supply  21  ( FIG. 3 ) for receiving amounts or a flow of a liquid material, including but not limited to molten hot melt adhesives and other molten synthetic polymers. Liquid supply  21  may include a pneumatically-actuated or electrically-operated valve mechanism (not shown) to regulate the flow of liquid material to dispenser  10 . Provided on the upper portion  12   b  of the dispenser body  12  is a mounting flange  25  adapted to interface the dispenser  10  with the liquid supply  21  and to mount the dispenser  10  at a position suitable for dispensing a continuous hollow filament  29  of liquid material onto a substrate  33  ( FIG. 6 ) to produce a desired overlapping or non-overlapping pattern on the substrate  33 . Typically, the substrate  33  is moved relative to liquid material dispenser  10  so that the hollow filament  29  deposits on a moving substrate  33 .  
      Among the nozzles  14  suitable for use in the invention are the family of Controlled Fiberization (CF®) applicator nozzles commercially available from Nordson Corporation (Westlake, Ohio). Such CF® applicator nozzles may have, for example, either six (6) gas openings or twelve (12) gas openings, the latter of which are referred to as high-frequency nozzles. The nozzle  14  may consist of a mounting section and a separate disk carrying the gas openings. Similar applicator nozzles are disclosed in U.S. Pat. Nos. Re 33,481, 4,969,602, 5,065,943, 5,194,115 and 5,169,071, the disclosures of which are hereby incorporated by reference herein in their entirety. In an alternative embodiment, the present invention contemplates that the nozzle  14  may be an integral, one-piece construction with the dispenser body  12  and, hence, non-removable.  
      With reference to  FIGS. 1, 2B  and  4 , a central gas supply passageway  26  extends axially along the length of dispenser body  12  at a location generally between the liquid supply passages  16 ,  18 ,  20 ,  22 . The gas supply passageway  26  receives a flow of a gas, such as nitrogen or process air, from a gas supply  15  ( FIG. 1 ) communicating with gas supply passageway  26  by way of a port  17  ( FIG. 4 ) extending radially through dispenser body  12 . The gas supply  15  may be any gas supply capable of precision flow metering useful for controlling the hollow area in the core of the hollow filament  29  formed by the dispenser  10 . Precision mass flow controllers suitable for use in metering the flow of gas from gas supply  15  to gas supply passageway  26  are commercially available, for example, from Emerson Process Management—Brooks Instrument of Hatfield, Pa. The gas supply  15  may also be provided with a backpressure regulator, such as those used in the FoamMix® family of applicators commercially available from Nordson Corporation (Westlake, Ohio), the assignee of the present invention.  
      A gas passage  28  communicating with the gas supply passageway  26 , which constitutes the smallest diameter portion of passageway  26 , is positioned inside the annular liquid material passage  24 . The liquid material passage  24  and the gas passage  28  may be arranged coaxially along a common central axis or the gas passage  28  may be non-concentric. A tubular dividing wall or partition  34  separates the gas passage  28  from the annular liquid material passage  24  and thereby defines the gas passage  28 . The liquid material stream discharged from annular liquid material passage  24  combines with the gas stream discharged from gas passage  28  to define the hollow filament  29 . The gas stream occupies a central region or core  62  ( FIG. 6 ) of the stream of liquid material discharged from liquid material passage  24  and, thereby, cooperates with the annular shape of the liquid material passage  24  to create the continuous hollow filament  29 . The enclosed gas in the core  62  keeps the surrounding liquid material from collapsing inward and coalescing into a solid filament.  
      With reference to  FIGS. 2B, 3 ,  3 A and  4 , an annular trough  30  defined in the lower portion  12   a  of dispenser body  12  receives a flow of gas, such as nitrogen or process air, from a gas supply passageway  32  ( FIG. 4 ) extending axially through the dispenser body  12 . This may be the same gas supplied to central gas supply passageway  26  or a different gas. The gas supplied to gas supply passageway  32  originates from a gas supply  11  ( FIG. 1 ) coupled by a supply port  13  ( FIG. 4 ) for communication with gas supply passageway  32 . The concentric arrangement of gas passage  28  and annular liquid material passage  24  causes the gas emitted by an outlet  27  of gas passage  28  to be injected into the core of the annular stream of liquid material emitted from annular liquid material passage  24 . In cross-section profile viewed from a perspective parallel to the filament length, the resulting hollow filament  29  has a hollow, axially-extending core surrounded by a tubular shell of semi-solid or partially-solidified liquid material. Preferably, the hollow core is a continuous open void extending axially along the length of the continuous hollow filament  29 .  
      The diameter of the hollow filament  29  is preferably larger than the diameter of a solid filament of equivalent mass per unit length and, in addition, the surface area per unit mass of the hollow filament  29  is greater than the surface area per unit mass of a solid filament of equivalent mass per unit length. The area of the unfilled core to the area of the surrounding tubular liquid material in cross-section is a function of, among other things, the type of liquid material constituting the filament  29  and the characteristics of the gas type and gas stream emitted from gas passage  28 .  
      With reference to  FIGS. 2B, 3 ,  3 A,  4 ,  5 , and  6 , the nozzle  14  is removably mounted with the dispenser body  12 . When a mounting surface  36  of the nozzle  14  is seated against a mounting surface  38  of dispenser body  12 , a frustoconical discharge tip  40  of the dispenser body  12  projects into a correspondingly dimensioned frustoconical clearance opening  42  centrally defined in the nozzle  14 . Discharge tip  40  and clearance opening  42  have substantially identical included angles. Recessed in the mounting surface  36  of nozzle  14  is an annular groove  44  that communicates with a plurality of separate gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  defined within nozzle  14 . The annular groove  44  encircles the frustoconical clearance opening  42 .  
      Located on discharge tip  40  is an annular liquid material outlet  23  ( FIG. 5 ) of the liquid material passage  24  from which liquid material is discharged. The liquid material outlet  23  is defined at the intersection between liquid material passage  24  and an exposed surface  41  of discharge tip  40 . The plane of the liquid material outlet  23  may be substantially co-planar with respective gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  of gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56 .  
      The present invention contemplates that the dispenser  10  may have other gas passage configurations for emitting gas streams  31  effective to move the hollow filament  29  in the controlled pattern that ultimately produces the desired pattern of liquid material on the substrate  33 . Although dispenser  10  is illustrated as having six gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  and corresponding gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57 , respectively, the invention is not so limited.  
      Gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  in nozzle  14  receive gas from the gas supply passage  32  of the dispenser body  12 . This gas is diffused and slowed down in the annular trough  30  so that none of the gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  directly receives the gas. Consequently, the gas flow is more uniform and balanced for all gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56 , as arrayed about the annular liquid material passages  24  from which the hollow filament  29  is discharged. The annular liquid material passage  24  is centrally located in the frustoconical tip  40  and the free surface of the partition  34  projects from the nozzle  14  and below a plane containing the gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57 .  
      The gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  are arranged adjacent to the annular liquid material passage  24  with a ring-shaped configuration effective to discharge gas to impinge the hollow filament  29 . The impinging gas causes the hollow filament  29  to move in a controlled pattern and to produce the desired pattern of liquid material on the substrate  33 . Typically, the gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  are arranged about the annular liquid material passage  24  at a constant radius measured relative to a central axis  58  and with equal angular spacings. In one embodiment of the present invention, the gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  of the gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  are disposed with a radially symmetric hexagonal arrangement about the annular liquid material passage  24  and, hence, are offset radially from annular liquid material passage  24 . Diagonally opposite pairs of gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  are disposed in planes that are at least nearly parallel to each other and equidistant from annular liquid material passage  24 . The gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  may be offset the same distance from a central axis of the gas passage  28 , which is coaxial with liquid material passage  24 .  
      A respective centerline  60  of each of the gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  is each inclined relative to the centrally-located annular liquid material passage  24  such that the corresponding gas jets or streams  31  emitted from gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57 , respectively, are aligned at a shallow acute angle relative to the direction of motion of the discharged hollow filament  29 . The acute angle is approximately tangential to the motion direction. The gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  are also directed in a generally tangential manner relative to the annular liquid material passage  24  and are all angled in either a clockwise direction or a counterclockwise direction about the annular liquid material passage  24  so that the gas streams  31  cooperate to transfer momentum to the hollow filament  29  for defining the pattern. The angular alignment of the gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  relative to the liquid material passage  24  is apparent in  FIGS. 5 and 6 . The tangential angle of the gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  is referenced relative to the central axis  58  about which the liquid and gas passages  24 ,  28  are coaxially aligned and is defined as the acute angle, α, between the centerline  60  of each of the gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  and the central axis  58 .  
      The hollow filament  29  dispensed from dispenser  10  has a tubular sidewall of liquid material that, in certain embodiments of the invention, may be a molten hot melt adhesive or a molten polymer. The molten liquid material is heated to a temperature sufficient for supplying a stream of the molten liquid material to dispenser body  12  and emitted from annular liquid material passage  24  with a core occupied by gas. The gas-filled core of hollow filament  29  is preferably not collapsed by the impinging gas from gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57 .  
      In one specific embodiment of the invention, the clearance opening  42  is angled at 26° relative to the axial centerline of the nozzle  14  to form a wider entrance diameter to a narrower exit diameter of about 0.011″. The gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  are each oriented at a tangential angle of about 31° so the emitted gas jets from the gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  generally tangentially intersect the outer surface of the hollow filament  29  discharged from liquid material passage  24 . Each of the individual gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  is 0.018″ in diameter, as are the gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57 , and the gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  are arranged with equal angular spacings on a 0.118″ diameter circle centered on the frustoconical clearance opening  42 .  
      The present invention contemplates that the dispenser  10  may have other configurations of cooperating liquid material passage(s) and/or gas passage(s) effective for producing continuous hollow filament  29  and other arrangements of gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  and gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  for steering the hollow filament  29  to define the controlled pattern in a space  43 .  
      The gas streams  31  discharged from the gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  impinge or impact the airborne hollow filament  29  discharged from the annular liquid material passage  24  to provide a controlled pattern in space  43  separating the liquid material outlet  23  from substrate  33 . Ultimately, the controlled pattern of motion in space  43  produces an overlapping or non-overlapping desired pattern of liquid material on the substrate  33 . Depending on the specific application, the temperature of the gas streams  31  may be about 9° C. to 15° C. above the application temperature of the liquid material and is supplied at a gas pressure of about 2 psi to about 30 psi.  
      Because the filament  29  is hollow and has an enhanced diameter relative to a solid filament, the ratio of the filament surface area to filament mass per unit length is increased as compared with a solid filament that would have a lesser diameter for an equivalent mass of liquid material per unit length. As a result, impinging the hollow filament  29  with the gas streams  31  from the gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57 , while the hollow filament  29  travels in the space  43 , has a greater effect upon the controlled overlapping or non-overlapping pattern traced by the hollow filament  29  in space  43  and also upon impact with the substrate  33 . This enhanced effect may increase the amplitude of filament motion, increase the frequency of filament motion, or both, as compared with the amplitude and frequency of conventional patterns produced by impacting a solid filament of equivalent mass per unit length with equivalent gas streams  31 . Typically, the amplitude of motion for the controlled pattern can be increased by decreasing the frequency and vice-versa, as these parameters are inversely related or complementary. In comparison with solid filaments, the hollow filament  29  provides a thicker fiber at lower add-on, which provides an improved bond strength at an equivalent add-on, and has a higher stretch ratio because the gas streams  31  are more effective in stretching the hollow filament  29  having a greater effective surface area.  
      The amplitude and/or frequency of the controlled pattern traced by hollow filament  29  in space  43  and the pattern traced on the substrate  33  may increase with increasing hollowness when other dispensing parameters are held constant. In one embodiment of the present invention, the controlled pattern has a frequency that is approximately uniform as a function of time or periodic.  
      Given a targeted frequency and amplitude for a controlled pattern, moving a hollow filament  29  with multiple gas jets will reduce gas consumption in comparison with a solid filament of equivalent mass per unit length. Specifically, the gas velocity of the gas streams  31  discharged from the respective gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  of gas passages  46 ,  48 ,  50 ,  52 ,  54 ,  56  may be reduced, which reduces the mass flow requirement for the gas supply to the corresponding gas jets. This will also reduce any turbulence introduced by the gas streams  31  because of the reduction in gas velocity, which may result in improved control of filament amplitude reflected in edge control on the substrate  33  and less contamination due to reductions in the number of airborne particles induced by the reduced velocity gas jets.  
      The present invention that it may be advantageous to impinge a hollow filament  29  of the same diameter as a solid filament (i.e., with less mass per length) with the gas streams  31 . Specifically, such hollow filaments  29  vibrate more rapidly than comparable solid filaments of the same diameter because of the inherent resonant frequency of hollow versus solid filaments.  
      With reference to  FIGS. 7 and 7 A in which like reference numerals refer to like features in  FIG. 5  and in accordance with an alternative embodiment of the invention, the liquid material dispenser  10  may be modified such that a hollow filament  63  ( FIG. 7A ), which is similar or identical to hollow filament  29  ( FIG. 6 ), is produced without the assistance of active gas injection into the filament core. Instead, the hollow core is formed passively by gas entrained from the ambient environment surrounding the liquid material dispenser  10 . The dispenser body  12  includes a plurality of, for example, four liquid material passages  64 ,  66 ,  68 ,  70  each having a corresponding one of a plurality of outlets  65 ,  67 ,  69 ,  71  emerging on surface  41  of discharge tip  40  from which liquid material is discharged. The liquid material outlets  65 ,  67 ,  69 ,  71  are arranged symmetrically in a ring or arc about a solid center with a discontinuity  61  between each of the adjacent pairs of outlets  65 ,  67 ,  69 ,  71 .  
      During operation of liquid material dispenser  10 , a discrete stream of liquid material is transferred through the liquid material passages  64 ,  66 ,  68 ,  70  and dispensed from the corresponding liquid material outlets  65 ,  67 ,  69 ,  71 , respectively. Adjacent liquid material streams are separated by gaps  72  that define open breaches so that gas from the ambient environment surrounding the liquid material dispenser  10  can enter and be entrained into the center of the separate outlet streams. Each of the gaps  72  coincides with one of the discontinuities  61 . Downstream from the liquid material dispenser  10 , the individual streams of liquid material coalesce or combine to form single hollow filament  63 . When the separate outlet streams combine, the entrained gas results in a hollow filament core of filament  63 .  
      The set of liquid material outlets  65 ,  67 ,  69 ,  71  has an open planar geometrical shape surrounding a solid center and discontinuities  61  in the open planar geometrical shape such that ambient gas flows from the environment through each discontinuity  61  and into the core of the liquid material stream. The shape of the set of liquid material outlets  65 ,  67 ,  69 ,  71  is not closed because the nearest end points of adjacent pairs of outlets  65 ,  67 ,  69 ,  71  define boundaries.  
      With reference to  FIGS. 8 and 8 A in which like reference numerals refer to like features in  FIGS. 7 and 7 A and in accordance with an alternative embodiment of the invention, the liquid material dispenser  10  may be modified to include an arc-shaped or C-shaped liquid material passage  74 . The liquid material passage  74  includes an arc-shaped or C-shaped outlet  75  formed by the intersection of passage  74  with surface  41 . A discontinuity  76  is defined in discharge outlet  75  between the confronting ends of the C-shape.  
      The filament  78  ( FIG. 8A ) discharged from liquid material passage  74  will initially have a C-shape reflecting the geometry of the outlet  75 . Gas from the environment surrounding the liquid material dispenser  10  is suctioned through an opening or breach  80  in the filament sidewall coinciding initially at surface  41  with the location of the discontinuity  76  and is incorporated into the center of the liquid material outlet stream. As the filament streams away from the liquid material passage  74 , the breach  80  in the filament sidewall will heal and close. The entrained gas is reflected structurally as a hollow gas-filled core of filament  78 . The gas discharged from gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  does not significantly impact the gas entrainment.  
      The liquid material outlet  75  has an open planar geometrical shape surrounding a solid center. The discontinuity  76  in the open planar geometrical shape permits ambient gas to flow from the environment and into the core of the liquid material stream. The shape of the liquid material outlet  75  is not closed because the end points are its boundaries.  
      With reference to  FIGS. 9 and 9 A in which like reference numerals refer to like features in  FIGS. 7 and 7 A and in accordance with an alternative embodiment of the invention, the liquid material dispenser  10  may be modified to include a triangular-shaped liquid material passage  82  that includes a triangular shaped outlet  84  at the intersection of passage  82  with surface  41 . The liquid material outlet  84  includes a discontinuity  86  near one corner and through which gas may be entrained to produce the core of a hollow filament  88  ( FIG. 9A ) similar or identical to hollow filament  29  ( FIG. 6 ).  
      The filament  88  discharged from liquid material passage  82  will initially have a triangular shape reflecting the geometry of the outlet  84 . Gas from the environment surrounding the liquid material dispenser  10  is suctioned through an opening or breach  90  in the filament sidewall and into the center of the liquid material outlet stream. The gas discharged from gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  does not significantly impact the gas entrainment. As the filament  88  streams away from the liquid material passage  82 , the breach  90  in the filament sidewall will heal and close to complete the gas trapping.  
      The liquid material outlet  84  has an open planar geometrical shape surrounding a solid center. The discontinuity  86  in the open planar geometrical shape permits ambient gas to flow from the environment and into the core of the liquid material stream. The shape of the liquid material outlet  84  is not closed because the end points of outlet  84  are its boundaries.  
      The use of open figure outlet geometries, as shown in  FIGS. 7-9 , results in the formation of hollow filaments without the use of active gas injection into the filament core, as described with regard to  FIGS. 1-6 . This simplifies the construction of a liquid material dispenser because the geometry of the liquid material outlet provides gas entrainment for forming a hollow filament core.  
      With reference to  FIGS. 10 and 10 A in which like features refer to like reference numerals in  FIG. 5  and in accordance with an alternative embodiment of the invention, the liquid material dispenser  10  may be modified to include a liquid material passage  92  that has a liquid material outlet  94  defined at the intersection between surface  41  and passage  92 . The liquid material outlet  94  includes a plurality of, for example, four arms generally having a plus-shape or cross-shape. In cross section, a continuous filament  96  ( FIG. 10A ) discharged from the discharge passage  92  will have a solid cross section and a plus or cross shape reflecting the geometry of the outlet  94 . The filament  96  includes four arms or lobes  96   a - d  projecting from a central solid core  97  defined at the intersection of the lobes  96   a - d  and evenly distributed about the circumference of the solid core  97 . The lobes  96   a - d  extend along the length of the filament  96  and each of the lobes  96   a - d  coincides with one arm of outlet  94 . The gas from gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57  will impinge the lobes  96   a - d  of the filament  96 . The impinging gas will provide an impulse to the filament  96  by momentum transfer and cause movement that ultimately results in an overlapping or non-overlapping pattern on substrate  33  ( FIG. 6 ). After the filament  96  is impinged by the gas from gas outlets  47 ,  49 ,  51 ,  53 ,  55 ,  57 , the lobes  96   a - d  of filament  96  may coalesce to form a more cylindrical shape that deposits on the moving substrate  33 .  
      The number and/or shape of arms in outlet  94  may be modified to provide a different filament cross-sectional profile. For example and as shown in  FIG. 11 , a liquid material passage  98  may include a liquid material outlet  100  shaped to discharge a continuous trilobal filament  102  ( FIG. 11A ) having three arms or lobes  102   a - c , each similar to arms  96   a - d , that intersect at a core  101 .  
      One advantage of the invention is to effectively increase the surface area of the discharged hollow filaments while retaining the same mass of liquid material per unit length, which conserves the amount of liquid material while permitting a larger width to be covered on the moving substrate. To that end, the surface area of the dispensed filament is increased by making the discharged filament hollow along its length. Hollow filaments have a greater outer diameter and surface area in comparison with a solid filament of comparable mass per unit length. When impinged by gas jets, the increase in the filament surface area may result in greater oscillation frequency and/or greater oscillation amplitude due to the increased momentum transfer from the gas jets to the filament, as compared with a solid core filament.  
      Alternatively, the filament may be shaped to include multiple lobes, as opposed to a smoothly curved outer surface. Shaped filaments have plural intersecting arms or lobes (e.g., plus-shaped), which may have a greater surface area, that are impinged by the gas jets to provide surfaces for momentum transfer. When impinged by gas jets, the change in filament shape may result in greater oscillation frequency and/or greater oscillation amplitude due to the increased momentum transfer from the gas jets to the filament, as compared with a solid core filament having a smoothly curved (e.g., cylindrical) cross-sectional profile without lobes or arms. Overlapping or non-overlapping patterns may be ultimately dispensed onto the substrate.  
      With reference to  FIGS. 12-14  in which like reference numerals refer to like features in  FIGS. 1-11  and in accordance with an alternative embodiment of the invention, a liquid material dispenser  110  includes a plurality of arc-shaped or C-shaped liquid material passages  112 ,  114 ,  116  that are arranged in a line across a dispenser body  119 . Each of the liquid material passages  112 ,  114 ,  116  is similar or identical to liquid material passage  74  ( FIGS. 8 and 8 A). Each of the liquid material passages  112 ,  114 ,  116  includes an arc-shaped or C-shaped outlet  113 ,  115 ,  117  formed by the intersection of the corresponding one of the liquid material passages  112 ,  114 ,  116  with a surface of a frustoconical discharge tip  118 ,  120 ,  122 , respectively.  
      With reference to  FIG. 14 , liquid material passage  112  includes a discontinuity  124  defined in liquid material outlet  113  between the confronting ends of the C-shape. A plurality of, for example, four gas outlets  126 ,  128 ,  130 ,  132  surround the discharge outlet  113  and are each defined by the intersection of a corresponding one of a plurality of gas passages  136 ,  138 ,  140 ,  142  with an inclined surface  134  that is inclined in a direction toward the discharge tip  118 . The liquid material outlet  113  is defined in a generally flat surface  144  at the end of discharge tip  118 . Surface  144  is separated from surface  134  so that the liquid material outlet  113  is non-planar with the gas outlets  126 ,  128 ,  130 ,  132 .  
      The gas outlets  126 ,  128 ,  130 ,  132  direct gas streams generally toward the discharged stream of liquid material and cooperate to transfer momentum to the hollow filament  18  ( FIG. 8A ) discharged from discharge outlet  113 . The gas streams discharged from the gas outlets  126 ,  128 ,  130 ,  132  operate to move and attenuate the discharged stream of the liquid material that defines the hollow filament. The orientation of the gas streams is determined by the inclination angle of the corresponding one of the gas passages  136 ,  138 ,  140 ,  142  relative to the discharge outlet  113 .  
      The other liquid material outlets  115 ,  117  are each surrounded by a set of gas outlets similar to gas outlets  126 ,  128 ,  130 ,  132 . Consequently, the liquid material dispenser  110  is adapted to dispense a plurality of hollow filaments ( FIG. 8A ) such that each individual filament contacts the substrate  33  ( FIG. 6 ) with a pattern. A person having ordinary skill in the art will understand the liquid material passages  112 ,  114 ,  116  and the liquid material outlets  115 ,  117 ,  119  thereof may be configured to have any of the configurations described herein.  
      With reference to  FIG. 15  in which like reference numerals refer to like features in  FIGS. 1-14  and in accordance with another alternative embodiment of the invention, a liquid material dispenser  150  includes a plurality of substantially identical arc-shaped or C-shaped liquid material passages  152  that are arranged in a line across a dispenser body  154 . Each of the liquid material passages  154  is similar or identical to liquid material passage  74  ( FIGS. 8 and 8 A) and liquid material passages  112 ,  114 ,  116  ( FIGS. 12-14 ). Each of the liquid material passages  154  includes an arc-shaped or C-shaped outlet, similar or identical to outlet  113  ( FIG. 14 ) and including a discontinuity, similar or identical to discontinuity  124  ( FIG. 14 ).  
      With reference to  FIG. 14 , the line of liquid material passages  154  is flanked on opposite sides by a pair of slots  156 ,  158  extending along the length of the dispenser body  154 . Slot  156  includes a plurality of gas outlets  160  that are arranged in pairs. A person having ordinary skill in the art will appreciate that other arrangements of gas outlets  160  may be used to generate gas streams that impinge the filament discharged from each of the liquid material passages  154 . The impinging gas streams from each pair of gas outlets  160 , which are directed generally toward the discharged stream of liquid material, cooperate with a similar pair of gas outlets (not shown but similar to gas outlets  160 ) in slot  158  to transfer momentum to the hollow filament  18  ( FIG. 8A ) discharged from the outlet of one of the liquid material passages  154 . The gas streams discharged from the gas outlets  160  operate to move and attenuate the discharged stream of the liquid material that defines the hollow filament. A person having ordinary skill in the art will understand that the liquid material passages  154  and the outlets of the liquid material passages  154  may be configured to have any of the configurations described herein.  
      For purposes of this description, words such as “vertical”, “horizontal”, “bottom”, “right”, “left” and the like are applied in conjunction with the drawings for purposes of clarity and for purposes of defining a frame of reference. As is well known, dispensers for liquid materials, like hot melt adhesives, may be oriented in substantially any orientation, so these directional words should not be used to imply any particular absolute directions for a dispenser consistent with the invention.  
      Further details and embodiments of the invention will be described in the following examples and comparative examples.  
     EXAMPLE 1  
      Hollow filaments of an adhesive were oscillated by a process consistent with the embodiment of the invention described with regard to  FIGS. 1-6 . The frequency of the oscillating hollow filament after striking the substrate was measured as a function of fiber hollowness. Fiber hollowness was determined from the flow rate of gas injected into the filament center.  
      Hollow filaments were formed using an annular liquid material outlet surrounding a coaxial gas discharge outlet and then steered by gas streams by an apparatus similar to dispenser  10  ( FIG. 1 ) to define an oscillating pattern. The filaments were formed from a ZEROPACK® hot melt adhesive commercially available from HB Fuller (St. Paul, Minn.) and using thirteen (13) standard liters per minute (SLM) of non-heated gas discharged for oscillating the filament. The adhesive was discharged at fifty-four (54) grams per minute at a temperature of 150° C. (head &amp; hose) through an annular ring outlet of a dispensing die and a flow of nitrogen was injected through a central hole into the center of the dispensed adhesive to form the hollow fibers. A modified standard Controlled Fiberization (CF®) applicator nozzle, commercially available from Nordson Corporation, was mated with the dispensing die in which the cone was removed to allow it to fit on the die and to define a clearance opening for the discharge tip. The diameter of the gas passage was 0.022″ and the radial dimension of the annular liquid material passage was 0.040″ with an inner diameter of 0.050″ and an outer diameter of 0.090″. The axial dimension of the annular liquid material passage was 0.140″.  
       FIG. 16  graphically shows the measured results in which it is apparent that the frequency of oscillation of the controlled pattern traced by the hollow filament after discharge increases with increasing fiber hollowness. Increases in the hollowness were provided by concomitant increases in the flow rate of nitrogen to the fiber center, while holding all other variables constant. The period, p, is determined from by counting the number of discrete swirls per second in the dispensed pattern formed after the hollow filament  29  lands on the substrate  33 , as indicated in  FIG. 17  and as illustrated for purposes of description with an overlapping pattern. The frequency is then determined from the period. Each oscillation cycle is measured between repeating features in the pattern traced on the substrate. The width, w, of the pattern traced by the oscillating hollow filament on the substrate may also be measured.  
      The gas-filled core of the hollow filament was observed to be retained after discharge despite the momentum transferred to the hollow filament from the impinging gas streams. The hollow filament, which was impinged by the gas streams immediately after discharge and before the molten hot melt adhesive constituting the annular sidewall of the hollow filament had experienced significant cooling or solidification, was not collapsed by the gas impingement.  
     EXAMPLE 2 AND COMPARATIVE EXAMPLE 1  
      Multi-lobed, plus-shaped filaments of an adhesive were oscillated by a process consistent with the embodiment of the invention described with regard to  FIG. 10 . The dispensed adhesive had a viscosity of 4,500 centipoise (cps). For the frequency measurement, the filament was impinged by gas jets from four gas passages arranged about the adhesive outlet. For the width measurement, the filament was impinged by gas jets from eight gas passages arranged about the adhesive outlet. The filament was dispensed at a throughput of about 33 grams per minute from a height of about 30 mm above the recipient substrate and with the substrate moving at about 5 feet per minute. The swirl gas pressure was varied to acquire the data shown in  FIGS. 14 and 15 .  
      With reference to  FIGS. 18 and 19 , the frequency and width of the pattern of the oscillating filament, which has an appearance similar to that of filament  96  shown in  FIG. 10A  after discharge from the dispenser, after striking the substrate was measured as a function of swirl gas pressure and compared with the pattern traced by a comparable solid filament having a circular cross-sectional profile. As is apparent from  FIG. 18 , a frequency curve  200  for the plus-shaped filament exhibits a greater oscillation frequency at all swirl gas pressures than a frequency curve  202  representing the oscillation frequency for the comparable solid, circular filament. Similarly, a width curve  204  for the plus-shaped filament exhibits a greater width for swirl gas pressures greater than about 1 psi than a width curve  206  representing the oscillation width for the comparable solid, circular filament. The oscillation frequency for the plus-shaped filament impinged by eight gas jets was similar to that of the solid, circular filament.  
      The filament lobes were observed to be retained when impinged by the gas streams after discharge despite the transferred momentum from the impinging gas streams. The lobes, which were impinged by the gas streams immediately after discharge and before the molten hot melt adhesive in the lobes had experienced significant cooling or solidification, were not significantly deformed by the gas impingement.  
     EXAMPLE 3 AND COMPARATIVE EXAMPLE 2  
      Hollow filaments of an adhesive were oscillated by a process consistent with the embodiment of the invention described with regard to  FIGS. 7-9 . The dispensed adhesive had a viscosity of 4,500 centipoise (cps) and the filament was impinged by process gas from four gas passages arranged about the adhesive outlet.  
      With reference to  FIG. 20 , the frequency of the pattern of the oscillating hollow filament, after striking the substrate was measured as a function of swirl gas pressure and compared with the frequency of a pattern traced by a comparable solid filament having a circular cross-sectional profile. As is apparent from  FIG. 20 , a frequency curve  208  for a hollow filament formed using the liquid/gas outlet arrangement of  FIG. 8  and a frequency curve  210  for a hollow filament formed using the liquid/gas outlet arrangement of  FIG. 9  each exhibits a greater oscillation frequency at all swirl gas pressures than a frequency curve  212  representing the oscillation frequency for the comparable solid, circular filament. In addition, a hollow filament formed using the liquid/gas outlet arrangement of  FIG. 7  had an oscillation frequency similar to frequency curve  212  at the measured swirl gas velocities.  
      The gas-filled core of the hollow filament was observed to form passively by gas entrained from the ambient environment and be retained despite the momentum transferred to the hollow filament from the impinging gas streams. The hollow filament, which was impinged by the gas streams immediately after discharge and before the molten hot melt adhesive constituting the annular sidewall of the hollow filament had experienced significant cooling or solidification, formed while influenced by the gas impingement and, after forming, was not collapsed by the gas impingement.  
      While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in considerable detail in order to describe the best mode of practicing the invention, it is not the intention of applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the spirit and scope of the invention will readily appear to those skilled in the art. The invention itself should only be defined by the appended claims, wherein we claim: