Abstract:
An apparatus and method for dispensing one or more liquid beads on a substrate utilizes a liquid dispenser with one or more liquid dispensing outlets and one or more movable electrostatic point sources. Liquid material dispensed from an outlet is attracted to, or otherwise electrostatically influenced by, the electrostatic point source(s) resulting in controlled placement of the liquid material on a substrate passing or positioned between the outlet(s) and the point source(s).

Description:
FIELD OF THE INVENTION 
     The present invention pertains to non-contact dispensing systems for dispensing one or more beads of liquid material onto a substrate, and more particularly to an electrostatic dispensing system for electrostatically dispensing such liquid material. 
     BACKGROUND OF THE INVENTION 
     During electrostatic dispensing operations, a liquid material is electrically biased relative to a target substrate to cause electrostatic attraction between the dispensed liquid material and the substrate for controlled deposition of the liquid material onto the substrate. Prior electrostatic applicators have used charging components directly in the dispensing outlet to create an electrostatic voltage potential between the liquid material being dispensed from the outlet and a grounded substrate. Other applicators, such as disclosed in U.S. patent application Ser. No. 09/429,821 of Borsuk et al., commonly owned by the assignee of the present invention, generate an electrostatic field from beneath a substrate, such as a moving nonwoven web of material. The outlet dispensing the liquid material is grounded to create a voltage potential and thereby cause the dispensed liquid material to be attracted to the substrate and applied in continuous straight lines on the substrate. 
     Notwithstanding the improvements over the prior art provided by Borsuk et al., further improvements in conventional electrostatic applicators are still desirable. For example, conventional electrostatic applicators of the prior art, including the electrostatic dispensing apparatus disclosed by Borsuk et al., are designed to apply a uniform pattern of dispensed liquid materials to a substrate such that the dispensed liquid materials are applied in straight-line beads. In some applications, it is desired to produce oscillating or other patterns of the dispensed liquid material including patterns in which adjacent beads of dispensed liquid material may overlap. This can be especially desirable in adhesive bead or fiber dispensing applications such as in various packaging operations or product manufacturing operations. 
     There is a continuing need for an electrostatic dispensing apparatus capable of controlling the placement of a dispensed liquid material onto a moving substrate to provide various patterns of the dispensed liquid material. 
     SUMMARY OF THE INVENTION 
     The present invention provides an electrostatic dispensing apparatus with the ability to control the placement of one or more beads of liquid, such as a hot melt adhesive, onto a substrate without requiring control or steering of the substrate itself and without requiring controlled movement of the liquid applicator or dispenser. The present invention may be used to control the position of the dispensed liquid bead(s) to form various patterns of the dispensed bead(s) on the substrate. 
     In one embodiment of the present invention, the electrostatic dispensing apparatus includes a liquid dispensing outlet and an electrostatic point source which is spaced from the liquid dispensing outlet. The term “point source,” as used herein, is intended to identify structure capable of generating a localized electrostatic field. The electrostatic point source can be moved relative to the liquid dispensing outlet and can be charged to create a voltage potential between the electrostatic point source and the liquid dispensing outlet. As liquid is dispensed from a liquid dispensing outlet which is grounded, for example, it is attracted to the electrostatic point source. The liquid may be electrostatically influenced and thereby deflected during its travel to a substrate in other ways as well, such as by the introduction of secondary electrostatic fields or metallic elements to influence the primary electrostatic field. 
     The substrate is positioned between the outlet and the point source so that the liquid material dispensed from the outlet will be deposited on the substrate in a precise manner and/or in a specifically desired pattern. Preferably, the substrate moves past a stationary dispensing apparatus. The movement and location of the electrostatic point source may be controlled by any suitable method. For example, position control may be provided by a servo motor coupled to the point source, or by other suitable actuators. 
     In another embodiment of the present invention, the electrostatic dispensing apparatus includes a plurality of liquid dispensing outlets positioned to dispense a number of liquid beads or fibers onto a substrate which may be moving adjacent to the dispensing apparatus. The device further includes a plurality of electrostatic point sources respectively corresponding to the plurality of liquid dispensing outlets. The electrostatic point sources are aligned to correspond with the liquid dispensing outlets and can be moved to control the position of each of the dispensed liquid beads on the substrate. The electrostatic point sources may be provided on an elongated charging member having multiple extensions to create the individual electrostatic point sources. In a preferred embodiment, the electrostatic point sources are provided on an elongated member having a serrated or scalloped edge to form the individual point sources. The elongated member may be moved relative to the fixed liquid dispensing outlets to control the placement of the dispensed liquid material on the moving substrate. 
     In yet another embodiment of the present invention, the electrostatic point sources are provided on a rotatable charging rod having raised circumferential ridges disposed on an outer surface of the rod and arranged such that the ridges are positioned on the outer surface at an angle to the longitudinal axis of the rod. In this configuration, the charging rod may be rotated to create the effect of a point source at the position closest to the liquid dispensing outlets. In other words, with respect to the fixed liquid dispensing outlets, the ridges on the rotating rod act as oscillating electrostatic point sources. 
     In yet another aspect of the present invention, the electrostatic dispensing apparatus includes two or more rows of multiple liquid dispensing outlets positioned adjacent to one another. The electrostatic dispensing apparatus further includes two or more adjacent rows of multiple electrostatic point sources corresponding to each of the rows of liquid dispensing outlets. The rows of electrostatic point sources may be moved either in unison, in groups, or independently to control the placement of the dispensed liquid material on the substrate or to create patterns of the dispensed liquid material on the moving substrate. As illustrative examples, the rows of electrostatic point sources may be provided as either elongated members having serrated or scalloped edges to create the individual electrostatic point sources, or the point sources may be provided as ridges or projections on a charging rod, and the rod may be rotated as described above. 
     In another aspect of the present invention, a method for dispensing liquid material onto a moving substrate using an electrostatic dispensing apparatus having liquid dispensing outlets and moveable electrostatic point sources includes moving a substrate through a space between the liquid dispensing outlets and the electrostatic point sources. The apparatus dispenses liquid material from the outlets, and the electrostatic point sources generate electrostatic fields which attract the liquid material. The electrostatic point sources move relative to the liquid dispensing outlets to control placement of the liquid material on the moving substrate. During this process, the liquid material is deflected from its normal path out of the outlet by the applied electrostatic force of the point source. 
     These and other advantages, objectives and features of the invention will become more readily apparent to those of ordinary skill upon review of the following detailed description of an illustrative embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE 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 invention. 
     FIG. 1 is a partial perspective view of one embodiment of an electrostatic dispensing apparatus in accordance with the present invention and illustrating deflection of the dispensed liquid material with a single electrostatic point source; 
     FIG. 1A is a perspective view of the electrostatic dispensing apparatus of FIG. 1 illustrating liquid material dispensed to form an oscillating pattern; 
     FIG. 1B is a perspective view of the electrostatic dispensing apparatus of FIG. 1 illustrating liquid material dispensed to form an overlapping pattern; 
     FIG. 2 is an elevation of the electrostatic dispensing apparatus of FIG. 1 illustrating deflection of the dispensed liquid material; 
     FIG. 3 is a schematic illustration of another embodiment of an electrostatic dispensing apparatus in accordance with the present invention and illustrating multiple electrostatic point sources; 
     FIG. 4 is a perspective view of an embodiment of an electrostatic dispensing apparatus of the present invention depicting an alternative form of providing electrostatic point sources; and 
     FIG. 5 is a perspective view of an electrostatic dispensing apparatus in accordance with the present invention depicting multiple rows of dispensing outlets and corresponding electrostatic point sources. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1 there is shown one embodiment of an electrostatic dispensing apparatus  40  incorporating the principles of the present invention. The electrostatic dispensing apparatus  40  includes a single liquid dispenser  42  having a single outlet  44  for dispensing flowable liquid material  46  onto a substrate  48  which is moving relative to the dispenser  42  in a direction represented by arrow  49 . The apparatus  40  further includes a single electrostatic point source  50  which is connected to an electrostatic power source  52  by an electrostatic cable  54 . The electrostatic point source  50  is spaced from the outlet  44  of the liquid dispenser  42  to define a space  56  through which a substrate  48  can pass. The electrostatic point source  50  is capable of generating a localized electric field  58  whereby liquid material  46  dispensed from the liquid dispensing outlet  44  is attracted towards the electrostatic point source  50  and is deposited on a portion of the moving substrate  48  that intersects the electric field  58  between the outlet  44  and the electrostatic point source  50 . 
     The electrostatic dispensing apparatus  40  further includes an actuator  59  coupled to the point source  50  for imparting motion to the electrostatic point source  50 . The actuator  59  may be any device capable of moving the electrostatic point source  50 , such as a linear servo motor. In general, various known actuators may be used to move the point source  50  in a linear direction transverse to the direction  49  of the moving substrate  48  and represented by arrow  51 . However, more complex motion of the actuator may be desired, as more fully explained below, and the invention is not limited to actuators for imparting purely linear motion to the point source. 
     Because the dispensed liquid material  46  is attracted to the electrostatic point source  50 , movement of the electrostatic point source  50 , causes a displacement of the dispensed liquid material  46  relative to the substrate  48 . This displacement of the dispensed liquid material  46  is illustrated in FIG. 2, where point source  50  is moved to a new position represented by  50 ′ (shown in dashed lines) and the dispensed liquid material  46  correspondingly moves to a position represented by  46 ′ (shown in dashed lines). In this manner, substantially precise placement of the liquid material  46  on the substrate  48  can be achieved by controlling the position of the electrostatic point source  50  relative to the fixed liquid dispensing outlet  44 . 
     In one test conducted to determine the amount of liquid material displacement possible, displacements of ±7 mm and ±4 mm were measured at voltages of 60 kV and 29 kV, respectively, when the electrostatic point source was incrementally displaced ±20 mm from nominal position. The test was conducted using a Nordson H200 module with a single tooth ES tip and a 0.020-inch shim, a Nordson EPS9 ES power supply, and a Nordson Series 6000 Melter, all available from Nordson Corporation, Westlake, Ohio. The distance from the tip to the substrate was set at 2.034 inches and the distance from the substrate to the point source was set at 0.219 inch. Bostik Findley HX2712-02 adhesive, available from Bostik Findley, Wauwatosa, Wis., was dispensed at a rate of 2.4 g/min to 0.0015-inch thick clear polypropylene substrate moving at a line speed of 250 ft/min and the temperature of all zones was set at 275° F. 
     The moveable electrostatic point source  50  of the present invention is useful for controlling the placement of the dispensed liquid material  46  on the substrate  48 , as illustrated in FIG.  1 . In certain applications it may be desirable to create patterns of dispensed liquid material on a substrate  48 . For example, an oscillating or overlapping pattern of dispensed liquid material  46  may be desired when the material is an adhesive, to achieve improved bonding of the substrate  48  with another material. The movable electrostatic point source  50  can be used to create such patterns through appropriate control of the actuator  59 . FIG. 1A illustrates the dispensing of adhesive material  46   a  onto a moving substrate  48   a  in an oscillating pattern which may be achieved by utilizing the actuator  59   a  to reciprocate the point source  50   a  in a direction  51   a  transverse to the direction  49   a  of the substrate  48   a.  FIG. 1B illustrates an overlapping adhesive pattern which may be achieved by utilizing an actuator  59   b  capable of imparting an orbital motion  51   b  to the point source  50   b  in a plane substantially parallel to the substrate  48   b.  These examples illustrate just a few of the many patterns that are possible by controlling the motion of the point source  50  with the actuator  59  and the invention is not limited to the patterns disclosed. 
     A test conducted to determine dynamic response characteristics of dispensed liquid adhesive to an oscillating point source indicated that the adhesive effectively tracked the motion of the point source up to frequencies of at least 7.3 Hz. The test also indicated that line speed had a negligible effect on effective adhesive placement, but that adhesive flow did affect displacement, resulting in decreased displacement with increased adhesive flow rates. The test was conducted using a Nordson H200 module with a single tooth ES tip and a 0.020-inch shim, a Nordson EPS9 ES power supply, and a Nordson Series 6000 Melter, all available from Nordson Corporation, Westlake, Ohio. The distance from the tip to the substrate was set at 2.034 inches and the distance from the substrate to the point source was set at 0.219 inch. Bostik Findley HX2712-02 adhesive, available from Bostik Findley, Wauwatosa, Wis., was dispensed at a rates of 5.0 g/min and 9.5 g/min to 0.0015-inch thick clear polypropylene substrate moving at a line speeds of 100, 250, and 500 ft/min. Voltages ranging from 29 kV to 75 kV were tested and the temperature of all zones was set at 275° F. 
     It is further contemplated that the dispensed liquid material may be displaced without physically moving the point source, but by influencing the localized electrostatic field to effectively shift the field. This may be accomplished by the introduction of a metallic element or secondary electrostatic field generators in the vicinity of the localized electrostatic field to cause the dispensed liquid material to be deflected to a desired location on the substrate. 
     Referring to FIG. 3, another embodiment of an electrostatic dispensing apparatus  60  incorporating the principles of the present invention includes a liquid dispenser  62  having multiple liquid dispensing outlets  64 . In this embodiment, the electrostatic dispensing apparatus  60  includes an electrostatic charging bar  66  having multiple point sources  68 , with each point source  68  corresponding to a liquid dispensing outlet  64  of the dispenser  62 . The electrostatic charging bar  66  is connected to a power source  70  via an electrostatic cable  72 . The multiple point sources  68  on the electrostatic charging bar  66  are created by serrated or scalloped edges of the electrostatic charging bar  66 , which define individual electrostatic point sources  68 . The electrostatic charging bar  66  is spaced from the liquid dispensing outlets  64  to define a space  74  through which a substrate  76 , moving in a direction normal to the plane of the figure, may pass between the electrostatic charging bar  66  and the liquid dispensing outlets  64 . The electrostatic charging bar  66  is capable of generating a series of localized electric fields  78  about the individual point sources  68  whereby liquid material  80  dispensed from the outlets  64  is attracted to the corresponding electrostatic point sources  68  through the localized electrostatic fields  78 . The electrostatic charging bar  66  is coupled to an actuator  82  which may be a linear servo motor or other actuator, whereby translational motion  77  may be imparted to the electrostatic charging bar  66  relative to the fixed liquid dispensing outlets  64 . In this manner, liquid  80  dispensed from the outlets  64  may be deposited on the moving substrate  76  in a substantially precise manner by controlling the position of the electrostatic charging bar  66  relative to the fixed liquid outlets  64 . 
     The electrostatic dispensing apparatus  60  may also be used to create patterns of multiple lines of dispensed liquid material  80 , such as oscillating or overlapping patterns, by moving the electrostatic charging bar  66  in reciprocating or orbital motions as described above for the single point source apparatus  40 . Alternatively, charging bar  66  could be split up into independently movable point sources or groups of point sources, as desired. 
     FIG. 4 shows another embodiment of an electrostatic dispensing apparatus  90  incorporating principles of the present invention for creating oscillating patterns of dispensed liquid material on a moving substrate. The apparatus  90  includes a liquid dispenser  92  having multiple liquid dispensing outlets  94  and an electrostatic charging bar in the form of an elongated rod  96 . The rod  96  is cylindrical and has raised circumferential ridges  98  disposed on an outer surface  100  of the rod  96  and is connected to an electrostatic power source  102  by an electrostatic cable  104 . The raised circumferential ridges  98  define the electrostatic point sources and are arranged along the rod  96  to correspond to the liquid dispensing outlets  94 . 
     The rod  96  is spaced from the liquid dispensing outlets  94  to define a space  106  through which a moving substrate  108  may pass. The raised circumferential ridges  98  create localized electrostatic fields  110  which attract the liquid material  112  dispensed from corresponding liquid dispensing outlets  94  to be deposited on the moving substrate  108  as it passes between the outlets  94  and the rod  96 . An actuator  114  coupled to the rod  96  moves the rod  96  whereby the dispensed liquid material  112  may be deposited onto the moving substrate  108  to create a desired pattern of dispensed material  112 . For example, the actuator  114  may reciprocate the rod  96  in a linear direction  115  transverse to the direction  117  of the substrate  108  to create oscillating patterns of adhesive on the moving substrate, as depicted in FIG.  4 . Alternatively, the actuator may move the rod in an orbital motion to create overlapping patterns of adhesive (not shown) on the substrate  108 , as was described above with respect to FIG.  1 B and single dispenser  42   b.    
     In a preferred embodiment, the raised circumferential ridges  98  are arranged on the rod  96  at an angle to the longitudinal axis of the rod  96  and the actuator  114  is a rotary actuator adapted to rotate the rod  96 . In this arrangement the raised circumferential ridges  98  on the rotating rod  96  act as oscillating point sources relative to the fixed liquid dispensing outlets  94 . As depicted in FIG. 4, as the substrate  108  passes between the dispenser  92  and the rotating rod  96 , dispensed liquid material  112  is deposited on the substrate  108  in an oscillating pattern. 
     Referring to FIG. 5, another embodiment of an electrostatic dispensing apparatus  120  incorporating principles of the present invention is shown. The electrostatic dispensing apparatus  120  includes two rows of liquid dispensing outlets  122 ,  124  aligned adjacent one another on a dispenser  126  and further includes two electrostatic charging bars  128 ,  130  positioned adjacent one another. In the embodiment depicted, the charging bars  128 ,  130  are in the form of elongated rods with raised circumferential ridges  132 ,  134  disposed on the rods at angles to the longitudinal axes of the rods to form the point sources and localized electrostatic fields  133 ,  135 , as described above. The charging bars  128 ,  130  are positioned such that the raised circumferential ridges  132 ,  134  on the charging bars  128 ,  130  correspond generally in number and spacing with the liquid dispensing outlets  122 ,  124  on the dispenser  126 . The electrostatic charging bars  128 ,  130  are connected to an electrostatic power source  136  via electrostatic cables  138 ,  140  and are coupled to actuators  142 ,  144  for imparting rotation to the electrostatic charging bars  128 ,  130  about their longitudinal axes. The electrostatic charging bars  128 ,  130  may be rotated either in unison or independently to control the placement of liquid material  146 ,  147  flowing from the corresponding liquid dispensing outlets  122 ,  124 . 
     As depicted in FIG. 5, each of the rotating charging bars  128 ,  130  acts as a series oscillating point sources relative to the corresponding fixed liquid dispensing outlets  122 ,  124  to cause the dispensed liquid material  146 ,  147  to be deposited on the substrate  148  in an oscillating pattern, as was described above for FIG.  4  and the single row of liquid dispensing outlets  94 . In the embodiment depicted in FIG. 5, the spacing of the charging bars  128 ,  130  and liquid dispensing outlets  122 ,  124  is configured to cause the successive beads of dispensed liquid material  146 ,  147  to overlap such that an interlaced sinusoidal pattern is created. When the dispensed liquid material  146 ,  147  is an adhesive, such a pattern may be desirable to provide for improved bonding of the substrate  148  to a mating surface. 
     While the present invention has been illustrated by the description of various 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. 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 Applicants&#39; general inventive concept.