Patent Publication Number: US-2006011733-A1

Title: Wick to reduce liquid flooding and control release rate

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the benefit of, and incorporates by reference, U.S. Provisional Patent Application No. 60/583,787, filed Jun. 30, 2004. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to wicks used for transporting liquids. Specifically, this invention relates to a wick-based delivery system for transporting liquids, such as fragrances or insecticides, from a reservoir to the ambient environment. Preferably, the liquids are transported to the surface of an orifice plate which atomizes the liquid and ejects the atomized droplets into the ambient air.  
      2. Description of the Related Art  
      Devices that dispense vapors into the ambient air are well-known in the art and useful in many applications. Generally, the purpose of these devices is to deodorize or disinfect the ambient air, or to distribute toxins into the air to kill or repel unwanted pests.  
      A common method of dispersing vapors into the air utilizes a wick to deliver a vaporizable liquid from a reservoir to an exposed surface. The wick transports the liquid from the reservoir to the surface of the wick using capillary action. When the liquid reaches the surface of the wick, after migrating through porous material of the wick, it vaporizes and disperses into the air.  
      More recently, liquid atomizing devices have been used to disperse fragrances, insecticides, or the like into the ambient air. An example of such an atomizing device is shown in U.S. Pat. No. 6,450,419. Often in atomization devices, a wick is used to convey liquid from a reservoir to an orifice plate. Vibration of the orifice plate atomizes the liquid and ejects the minute droplets into the ambient air.  
      However, when an atomizer device using fluid delivered by a wick is not activated, the capillary action of the wick may still be active and lead to migration of the liquid to parts of the atomizer. In such cases, an excess supply of liquid can flood the orifice plate and degrade the efficacy of the atomizer, when operated. To reduce such flooding, it is preferable to reduce the rate of fluid transfer through the wick to the orifice plate. Conventional methods of reducing the liquid flow rate through the wick, such as decreasing the porosity or changing the size of the wick, have drawbacks due to the preferred size and compressibility of the wicks for proper operation of an atomizer device. Accordingly, there is a need for a wick that can limit and control the flow rate of liquid from a reservoir to an orifice plate in an atomizer device, while still supplying a sufficient amount of liquid to the orifice plate for preferred atomization and meeting the preferred size and compressibility of the wick.  
     SUMMARY OF THE INVENTION  
      Our invention addresses the problems mentioned above by improving the delivery of liquid through a wick. More preferably, our invention is an improved wick for delivery of liquids from a reservoir (preferably, to an orifice plate in an atomizer device). More specifically, our invention reduces the flow rate through the wick to reduce flooding, while maintaining a flow rate suitable for atomization, as well as the preferred size and rigidity of the wick.  
      The wick comprises a porous portion having capillary passages for drawing the liquid from a lower end to an upper end and a substantially non-porous portion that draws little or no liquid. The combination of a porous portion with a substantially non-porous portion allows for preferred control of the reduction of the flow rate of the liquid through the wick.  
      Most preferably, the non-porous portion is completely non-porous; however, as a practical matter, a portion of wick with no porosity may be difficult to achieve, given manufacturing limitations. The term non-porous will refer to wicks having a porosity of less than about five percent by volume. A more preferred wick will have a Anon-porous@ portion having a porosity of less than about four percent by volume. Even more preferably, the wick will have a non-porous portion having a porosity of less than about three percent by volume. Even more preferably, the wick will have a non-porous portion having a porosity of less than about two percent by volume. More preferably, the wick will have a non-porous portion having a porosity of less than about one percent by volume. Most preferably, the will wick will have a non-porous portion that has a porosity of substantially zero percent by volume. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows an elevational cross-section of an atomizer device embodying our invention.  
       FIG. 2  shows a top view of a wick according to the preferred embodiment.  
       FIG. 3  shows a cross-sectional view of the wick from  FIG. 2 .  
       FIG. 4  shows a top view of a wick according to another possible embodiment of the present invention.  
       FIG. 5  shows a top view of a wick according to another possible embodiment of the present invention.  
       FIG. 6  shows a top view of a wick according to another possible embodiment of the present invention.  
       FIG. 7  shows a cross-sectional, side view of another possible embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The preferred use of the wick described in this invention is for transporting liquid from a reservoir to an orifice plate in an atomization device. As shown in  FIG. 1 , an atomization device  20  according to our invention typically comprises an atomizer assembly  34 , which includes an orifice plate  37 , and a replaceble reservoir assembly  30 . The reservoir assembly  30  includes a reservoir  31  containing fluid and a wick  56 .  
      The piezoelectrically actuated atomization device  20  according to a preferred embodiment of our invention comprises a housing  22  formed as a hollow plastic shell and closed by a flat bottom wall  24 . A horizontal platform  25  extends across the interior of the housing  22 . A battery  26  is supported by means of support prongs  25   a  which extend down from the underside of the platform  25  inside the housing  22 . In addition, a printed circuit board  28  is supported on support elements  25   b  which extend upwardly from the platform  25 . A liquid reservoir assembly  30  is replaceably mounted to the underside of a dome-like formation  25   c  on the platform  25 .  
      The liquid reservoir assembly  30  comprises a liquid container  31  for holding a liquid to be atomized, a plug  33 , which closes the top of the container, and the wick  56 , which extends from within the liquid container  31  through the plug  33 , to a location above the liquid container  31 . The plug  33  is constructed to allow removal and replacement of the complete liquid reservoir assembly  30  from the underside of the dome-like formation  25   c  on the platform  25 . Preferably, the plug  33  and the platform are formed with a bayonet attachment (not shown) for this purpose. When the replaceable liquid reservoir assembly  30  is mounted on the platform  25 , the wick  56  extends up through a center opening in the dome-like formation  25   c . The wick  56 , which is described in greater detail hereinafter, operates by capillary action to deliver liquid from within the liquid container  31  to a location just above the dome-like formation  25   c  on the platform  25 .  
      An atomizer assembly  34  is supported on the platform  25  in cantilever fashion by means of a resilient, elongated wire-like support  27 . The wire-like support  27  is attached at the ends, which protrude upward from the platform  25 . The wire-like support  27  is shaped such that it resiliently supports the lower surface of the orifice plate  37  and a spring housing  39 , while a spring  43  resiliently presses on the upper surface of the orifice plate  37 . (Rather than press on the orifice plate  37  itself, the spring  43  may alternatively or additionally press on a member, such as an actuator element  35 , discussed below, which is connected to the orifice plate  37 .) Together, the support  27  and the spring  43  hold the orifice plate  37  in place in a manner that allows the orifice plate  37  to move up and down against the resilient bias of the wire-like support  27 .  
      The atomizer assembly comprises an annularly shaped piezoelectric actuator element  35  and the circular orifice plate  37 , which extends across and is soldered or otherwise affixed to the actuator element  35 . When alternating voltages are applied to the opposite upper and lower sides of the actuator element  35  these voltages produce electrical fields across the actuator element  35  and cause it to expand and contract in radial directions. This expansion and contraction is communicated to the orifice plate  37  causing it to flex so that a center region thereof vibrates up and down. The center region of the orifice plate  37  is domed slightly upward to provide stiffness and to enhance atomization. The center region is also formed with a plurality of minute orifices which extend through the orifice plate  37  from the lower or under surface of the orifice plate  37  to its upper surface. A flange is provided around the center region of the dome.  
      In operation, the battery  26  supplies electrical power to circuits on the printed circuit board  28  and these circuits convert this power to high frequency alternating voltages. A suitable circuit for producing these voltages is shown and described in U.S. Pat. No. 6,296,196. As described in that patent, the device may be operated during successive on and off times. The relative durations of these on and off times can be adjusted by an external switch actuator  40  on the outside of the housing  22  and coupled to a switch element  42  on the printed circuit board  28 .  
      When the atomizer assembly  34  is supported by the support member  27 , the flange of the orifice plate  37  is positioned in contact with the upper end of the wick  56 . The atomizer assembly  34  is thereby supported above the liquid reservoir assembly  30  such that the upper end of the wick  56  touches the underside of the orifice plate  37 . Thus, the wick  56  delivers liquid from within the liquid reservoir  31  by capillary action to the underside of the orifice plate  37 , which upon vibration, causes the liquid to pass through its orifices and be ejected from its opposite side (i.e., the upper surface) in the form of very small droplets.  
      It will be appreciated from the foregoing that the horizontal platform  25  serves as a common structural support for both the liquid reservoir assembly  30  and the atomizer assembly  34 . Thus, the horizontal platform maintains the liquid reservoir assembly  30 , and particularly, the upper end of the wick  56 , in alignment with the orifice plate  37  of the atomizer assembly  34 . Moreover, because the atomizer assembly  34  and the orifice plate  37  are resiliently mounted, the upper end of the wick  56  preferably presses against the under surface of the orifice plate  37  and/or the actuator element  35  irrespective of dimensional variations which may occur due to manufacturing tolerances when one liquid reservoir is replaced by another. This is because if the wick  56  of the replacement liquid reservoir assembly  30  is higher or lower than the wick  56  of the original liquid reservoir assembly  30 , the action of the spring  43  will allow the orifice plate  37  to move up and down according to the location of the wick  56  in the replacement reservoir assembly  30 , so that the wick  56  will properly press against the underside of the orifice plate  37  and/or the actuator element  35 . It will be appreciated that the wick  56  preferably is formed of a solid, dimensionally stable material so that it will not become deformed when pressed against the underside of the resiliently supported orifice plate  37 .  
      The preferred wick in the present invention consists of a porous section and a substantially non-porous section. The porous section transports the liquid from the reservoir to the orifice plate through capillary action and the substantially non-porous section impedes the flow of liquid through a portion of the wick. The size of the substantially non-porous section of the wick may be varied as necessary to reduce the flow rate of liquid enough to reduce flooding, but preferably not so much that the desired amount of liquid does not reach the orifice plate. The addition of the substantially non-porous section of the wick facilitates control of the flow rate through the wick while still maintaining a wick of the necessary size for operation of the atomizer device. Of course, a wick according to our invention may be used in other devices, other than atomization devices, to achieve preferred flow rates.  
      As shown in  FIG. 2 , the substantially non-porous portion  201  of the preferred wick  200  is a cylindrical section and the porous portion/section  202  of wick  200  is a cylindrical ring-shaped section surrounding, and substantially concentric with, the non-porous portion  201 .  FIG. 3  shows a cross-sectional view of the wick from  FIG. 2  in which non-porous portion  201  is surrounded on its longitudinal sides by the porous portion  202  and extends throughout the entire length of the wick  200 , exposing the ends of the substantially non-porous portion  201  at both ends of the wick  200 .  
      In one embodiment, a preferred cylinder comprising the substantially non-porous portion  201  of wick  200  has a length of about 0.5 to about 5 cm and a diameter of about 0.1 to about 2 cm. A preferred cylindrical ring-shaped section comprising the porous portion  202  has a length of about 0.5 to about 5 cm and a diameter of about 0.2 to about 2.2 cm. A wick of this size is suitable for a preferred atomization device. However, the present invention is by no means limited by this size of wick and different wick sizes, both smaller and larger, are envisioned.  
      While a cylindrical substantially non-porous section extending completely through the wick and surrounded by a cylindrical ring-shaped porous section may be used, any one of a number of other shapes may be used for both the porous section of wick or the non-porous section of wick. For example, as shown in  FIG. 4 , a wick  400  could comprise a substantially non-porous rectangular section  401  inside a cylindrical porous portion  402 . Furthermore, as shown in  FIG. 5 , the substantially non-porous portion  501  of wick  500  need not be contained within the porous portion  502 . Instead, sections  501  and  502  are adjacent to each other. Also, as shown in  FIG. 6 , multiple substantially non-porous portions  601  may be dispersed in a porous portions  602  to form wick  600 , or vice-versa.  
      In addition, as shown in  FIG. 7 , the substantially non-porous portion  701  of wick  700 , within the porous portion of wick  702 , need not extend throughout the entire length of the wick so long as the substantially non-porous portion can reduce the flow rate in the manner desired, based on design preferences.  
      When such alternative designs are used, the preferred dimensions of the porous and substantially non-porous sections may be analyzed as the preferred percentages of cross-sectional areas for the respective portions. Specifically, preferred embodiments may be defined based on their respective cross-sectional areas of the wick (rather than their respective diameters), with the cross-section being taken in a plane substantially perpendicular to the length of the wick (i.e., direction of liquid migration). When the respective cross-sectional areas vary along the length of the wick, the measurement can be the average cross-sectional area.  
      In a preferred embodiment, the substantially non-porous section accounts for between about 20 to about 50% of the cross-sectional area (or average cross sectional area), and the porous section accounts for between about 80 to about 50%.  
      In one embodiment, the material for construction of the wick for both the porous and substantially non-porous section of the wick is preferably high density polyethylene. High density polyethylene was chosen because it can be easily manufactured to produce a wick with two sections meeting the size requirements for a wick in an atomizer device. Furthermore, high density polyethylene can produce a solid, dimensionally stable wick with the chosen porosities to vary the flow rate through the wick in the desired manner. While high density polyethylene is preferred, numerous other suitable materials may be used, including polypropylene, for example.  
      The preferred method of manufacturing a wick used in this embodiment, is a sintering process. A sintering process is preferred because of the ease of producing the desired characteristics of the wick in a cost effective manner. This process involves sintering inorganic or organic beads of, for example, a ceramic, PE, PP, HDPE, or the like. Preferably, the process involves a first step of sintering the core (typically, the nonporous section). Once the core is formed, the other section (e.g., porous section) is then sintered around the core. While a sintering process may be preferred, other manufacturing techniques, such as inserting a fully-formed substantially non-porous portion of wick into a fully-formed porous portion, may be used.  
      To control the flow rate of liquid through the wick to supply adequate liquid to the orifice plate and reduce flooding, the porous portion of wick has a preferred porosity of approximately sixty percent by volume and, ideally, the substantially non-porous portion of the wick has no porosity. However, as a practical matter, a section of wick with no porosity may be difficult to manufacture. Accordingly, the porosity of the inner portion of the wick is preferably less than about five percent by volume. A porosity of less than about five percent by volume produces a substantially non-porous section of wick and can provide the desired limitation of flow rate needed to reduce flooding of the orifice plate. While a porosity of approximately sixty percent by volume for the porous portion of wick and a porosity of less than about five percent by volume for the substantially non-porous portion of wick are preferred, these values may vary and other embodiments may contain different porosities.  
      While specific embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Many different arrangements and configurations are envisioned in this invention and can be used to achieve the desired results. The scope of the invention should be accorded the broadest interpretation so as to encompass all such modifications, equivalent structures, and functions.  
     INDUSTRIAL APPLICABILITY  
      The present invention provides a wick with a controlled flow rate. We envision that this wick preferably can be used, for example, to transport liquid from a reservoir to an orifice plate in an atomization device for dispersing vapor into the ambient air while reducing flooding of the orifice plate. Since the wick reduces flooding of the orifice plate, this invention facilitates the continuous operation of an atomizer device that dispenses fragrances, insecticides, and any other vaporizable materials into the ambient air to freshen or deodorize the air or exterminate or repel unwanted pests.