Abstract:
A wick assembly is provided for use in a dispensing device that dispenses volatile material from a wick by heat. Two wick sections of differing material are provided in stacked fashion, with a coupler sleeve that can be used to facilitate attachment of the wick structure to a reservoir. One wick section preferably provides control over the rate of dispensing, where the other provides improved thermal resistance and resistance to clogging.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   Not applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   This invention relates to dispensing devices that employ a heat source to promote the release of a volatile material from a wick. More particularly, the invention relates to improved wick assemblies for use with such devices. 
   A variety of devices for dispensing volatizable materials into the atmosphere are known. Such volatizable materials may be air scents (e.g. fragrances), pest control materials (e.g., insecticides), allergen control ingredients, disinfectants, or other chemicals. 
   In one such type of device a lower reservoir is provided into which a wick extends. The wick draws the active chemical up from the reservoir to an area where there is a heat source. The heat source then promotes dispensing of the volatile to the environment. Such devices are plugged into an electrical wall outlet to supply power to an electrical heating coil. Optionally, such devices may also have a fan or other means to further promote evaporation or dispensing. 
   Prior art examples of such devices include U.S. Pat. Nos. 6,361,752, 5,647,053, 5,290,546, 5,222,186, 5,095,647, 5,038,394, and 4,663,315. The disclosure of these patents and all other publications referred to herein, are incorporated herein by reference as if fully set forth. 
   While the foregoing prior art devices have a number of advantages, they also have some deficiencies, particularly with respect to the wicks used with them. For example, when some of these devices are used to dispense certain volatile materials, certain wicks can clog. Other wicks are less susceptible to clogging, but are too brittle to use in certain automated assembly operations. Still other wicks tend to draw liquid too fast, creating a “drool” problem or inefficient use of certain actives. Some other wicks are not sufficiently thermally resistant to use with some types of heating devices. 
   One improvement is described in a U.S. patent application (of our assignee) filed on Jan. 30, 2003 with U.S. Ser. No. 10/354,876. That application disclosed providing an array of granular particles such as sand coated with a polymer binder to form a network of pores in the wick which were less susceptible to clogging. However, this type of wick was not physically strong enough to resist the mechanical stresses encountered in some automated assembly operations. This added some cost to the assembly of such wicks with devices that use them. 
   In unrelated work there have been some disclosures of certain types of multi-part wicks. See e.g. U.S. Pat. Nos. 4,416,616 and 3,262,290 and European Patent Application No. EP 0 897 755 A2. However, these wick constructions have not been suggested as a solution to the above problems, and in any event the means of associating the wick parts are not desirable for the present applications. 
   Thus, there is a need for improved wick assemblies that address the above deficiencies of the prior art. 
   SUMMARY OF THE INVENTION 
   In one aspect, the invention provides a wick assembly for use in a dispensing device that is capable of dispensing volatile material from a reservoir containing that volatile material. The assembly has a first wick section formed from a first material, and a second wick section formed from a second material that includes granules bound together by a binder and that is different from the first material. The second wick section is positioned abutting against or adjacent to the first wick section (e.g. in axially vertically stacked fashion). 
   There is also a coupling sleeve for holding the second wick section against, or adjacent to, the first wick section, and means for mounting the coupling sleeve to the reservoir with the first wick section extending into the reservoir. One such mounting means is providing a radially extending flange adjacent a lower end of the sleeve, and providing a cap ring mountable on the reservoir which can receive the flange in a depressed annular bore. Other such means include any other means of attaching the sleeve to the reservoir (e.g. mechanical means for directly attaching the sleeve to the reservoir such as spring legs; adhesive attachment of the sleeve to the cap ring or reservoir; etc.). 
   In the most preferred form the second wick section is formed from sand particles and a binder (which creates a thermal resistant, clog resistant high flow section around which the heater will be positioned), and the first wick section is formed from a material selected from the group consisting of fibrous materials, wood products, plastic particles, and inorganic particles (which creates a section capable of precise flow control). The second wick section is insertable through a central through bore of a cap ring. Alternatively, the cap ring can be integral with the first wick section. The coupling sleeve has a tapering internal bore, and both the first and second wick sections are essentially cylindrical. 
   In an alternative form the invention provides a wick assembly for use in a dispensing device that is capable of dispensing volatile material from a reservoir containing that volatile material. This wick assembly has a first wick section formed from a plastic material, and a second wick section formed from a composition comprising sand and a binder. The second wick section is positioned abutting against or adjacent to the first wick section, preferably in vertically stacked fashion. 
   In yet another form the invention provides a method for assembling a wick assembly. One obtains wick assembly components comprising a cap ring, a first wick section made of a first material, a second wick section made of a second wick material, and a coupling sleeve. One then inserts the second wick section into the coupling sleeve such that an end of the second wick section terminates inside the coupling sleeve and an opposed end of the second wick section terminates outside the coupling sleeve. One also inserts the first wick section into the cap ring so that an end of the first wick section terminates on one side of the cap ring, and an opposed end of the first wick section terminates on an opposed side of the cap ring. Thereafter, one assembles a sub-combination of the second wick section and coupling sleeve to a sub-combination of the second wick section and cap ring. 
   The wick assemblies of the present invention are preferably used with a ring heater. They may also be used with a fan that facilitates dispensing from the upper portion of the wick. 
   The structures of the present invention have a number of advantages. For one thing, a highly thermally and clog resistant sand based wick section can be used adjacent such heaters. Any concerns about the brittleness of sand based wick sections are addressed by the method of insertion of that wick portion into a tapered coupler, minimizing the stress on the wick due to the insertion. 
   Moreover, any tendency of that wick portion to draw fluid too quickly (and thus lead to drool or inefficient dispensing) is controlled by the first wick segment, which can have carefully sized pores. Further, any tendency of the first wick portion to degrade when exposed to heat is avoided as that portion is positioned away from the heater. 
   Desirably, the same second wick portion can be used with a variety of different first wick portions, depending on the particular chemicals involved and the dispensing needs. Thus, a single sand based wick portion can be made suitable for use with a wide variety of applications, thus reducing production costs by avoiding the need to make multiple different sand wicks. 
   Moreover, the assembly is suitable for using high speed automated assembly equipment. This further reduces the costs. 
   These and still other advantages of the present invention will be apparent from the description which follows and the accompanying drawings. While preferred embodiments will be disclosed in connection therewith, it should be appreciated that still other embodiments are possible within the spirit of the invention. Hence, the claims should be looked to in order to judge the full scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing a prior art device for dispensing volatile materials; 
       FIG. 2  is a vertical cross-sectional view of the device of  FIG. 1  having installed therein a prior art wick and liquid reservoir; 
       FIG. 3  is an exploded perspective view of a device according to the invention; 
       FIG. 4  is a perspective view of the device of  FIG. 3  in assembled form; and 
       FIG. 5  is a cross-sectional view similar to  FIG. 1 , but of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 and 2 , there is shown a prior art dispensing device  20  in which a heat source is used to promote the wicking action and release of a volatile material from a wick immersed in a volatile liquid contained in a reservoir. The dispensing device  20  includes a body  21  having a vapor outlet  24  formed in the center of the top of the body  21 . A ring heater  25  having an opening extending vertically there through is provided inside the body  21  below the vapor outlet  24 . The ring heater  25  is supported by a stay  26 . Provided under the heater  25  is a bottle socket  27  having an opening extending vertically there through. The socket  27  is formed on its inner periphery with a threaded portion  30  adapted for threaded engagement with a threaded portion  29  on the outer periphery of the mouth  28   a  of a volatile liquid bottle  28 . 
   The bottle  28  is provided with a wick  31  that is insertable into the ring heater  25  concentrically therewith when the bottle  28  is threaded at its mouth  28   a  into the socket  27 . The wick  31  is immersed in the liquid  34  in the bottle  28  and upwardly transports the liquid  34  contained in the bottle  28  by capillary action. The wick  31  in this prior art design was formed from a fired porous ceramic or a sintered plastic material. 
   Electrical plug blades  32  are fixed to the body  21  on its rear side. The plug blades  32  are connected to the ring heater  25  in the usual manner using electrical connections. The ring heater  25  is energized by inserting the plug blades  32  into an electrical outlet and activating switch  35 , whereby the ring heater  25  produces heat to heat the upper section of the wick  31 . The heat may promote upward transport of the liquid  34  in the wick  31 . The liquid chemical  34  in the wick  31  is vaporized by the heat from the ring heater  25 . For other designs of this general type see e.g. U.S. Pat. No. 5,290,546. 
   Turning now to  FIGS. 3 ,  4  and  5 , there is shown a device constructed in accordance with the present invention. There is a wick assembly  40  and a reservoir  44  suitable for use in a heated volatile dispensing device analogous to that shown in  FIGS. 1 and 2 . Where the parts are numbered the same, the parts numbered in  FIGS. 3-5  are essentially identical to the parts of  FIGS. 1 and 2 . The reservoir  44  includes a mouth  45  having an inner surface  49  and an outer surface  47  with threads  48 . A rim  46  of the mouth  45  defines an opening for the reservoir  44 . The reservoir  44  can be formed from a thermoplastic material such as polyethylene, polypropylene or polyethylene terephthalate, albeit a glass reservoir is often preferred to provide a consumer with an easy view of how much liquid is left in the reservoir. 
   The wick assembly  40  includes a lower wick section  50 , a cap ring  60 , an upper wick section  70  and a coupling sleeve  80 . The lower wick section  50 , the cap ring  60 , the upper wick section  70  and the coupling sleeve  80  are assembled together as described below. 
   The lower wick section  50  may be formed in any number of shapes. In the example embodiment shown the wick section  50  is in the shape of an elongated cylinder. The wick section  50  may be formed from fibrous materials, wood products, thermoplastic particles and inorganic particles. Non-limiting examples of fibrous materials include bonded polyester fibers, cellulose, carbon fibers or the like. Non-limiting examples of wood products include compressed sawdust or wood flour. Non-limiting examples of thermoplastic particles include particles that may be sintered into a porous body. 
   However, preferred materials for the wick section  50  are polyolefins such as polyethylene and polypropylene, and thermoplastic polyesters. A particularly preferred plastic is an ultra-high molecular weight high density polyethylene from Porex Technologies. Such plastics can be lightly packed into a mold, and the packed mold can then be heated to a temperature which is sufficient to allow the thermoplastic particles to bond together, but not sufficient to liquefy the thermoplastic to such an extent that it can flow. This results in a solid wick that is porous and therefore wicks liquid. 
   Alternatively, wick section  50  could be formed of inorganic particles such as kaolin, clay, talc, perlite, bentonite, alumina, alumina silica, titania or the like. The inorganic powder particles can be lightly packed into a mold, and the packed mold can then be heated to a temperature which is sufficient to allow the powdered particles to bond together at contact points. This results in a solid wick that is porous and therefore wicks liquid. 
   The upper wick section  70  may be formed in any number of shapes, and in the example embodiment shown is in the shape of an elongated cylinder. The most preferred upper wick section  70  comprises sand particles adhered together by a binder to form a network of pores and passages. In one example method for making the upper wick section  70 , individual sand particles can be coated with a thin coating of the binder. The coated sand particles are then placed in a mold and compacted under elevated temperature conditions. The binder coated on the particles flows to form a thin coating on the individual particles, with the coatings fused together at their points of contact. The binder only partially fills the interstices between the particles, whereby an interconnected network of pores and passages is formed. 
   The sand particles may comprise silica sand particles, chromite sand particles, zircon sand particles, and mixtures thereof. Silica sand particles are typically preferred because an upper wick section  70  formed using silica sand particles has superior fluid transport properties. Spherical particles are the preferred particles because of the greater uniformity in porosity achieved and because rounded particles can be closely packed together. 
   A number of different binders can be used to adhere the sand particles together. Thermoset polymeric materials, i.e., materials that become relatively infusible upon heating, are preferred for the binder because these cross-linking polymeric materials will not flow when the formed upper wick section  70  is heated in a dispensing device. If the binder were to flow excessively upon heating, clogging of the network of pores and passages could result. However, as used herein, the term “thermoset polymeric material” is not limited to traditional thermosetting materials but also encompasses cross linked thermoplastic materials that chemically react to become relatively infusible upon heating. 
   The most preferred binder material is a novolac resin. Other non-limiting examples of thermoset binder materials include urethane resins and highly cross linked thermoplastics such as cross linked polyethylene. Furthermore, most polymeric materials can be used to bind the sand particles together, so long as the polymeric material is non-reactive and non-absorptive with respect to the volatile material to be dispensed and the polymeric material can resist the temperatures to which the upper wick section  70  will be exposed in the dispensing device. 
   Because sand particles individually coated with the binder are flowable until adhered into a upper wick section  70 , they may be introduced into molds of various sizes and shapes and heated to form virtually any shape structure for the upper wick section  70 . Advantageously, the sand particles may be purchased pre-coated. For example, resin coated sand particles are available from Technisand Division of Fairmount Minerals, Wedron, Ill., USA. One type of commercially available resin coated sand comprises a phenol formaldehyde novolac resin (1-6% by total weight) and a hexamethylenetetramine curing agent (&lt;2% by total weight) coated on an aggregate including iron oxides (&lt;15% by total weight), aluminum silicate (&lt;15% by total weight) and silica sand (i.e., quartz). Another type of commercially available resin coated sand comprises a phenol formaldehyde novolac resin and a hexamethylenetetramine curing agent coated on chromite sand. Yet another type of commercially available resin coated sand comprises a phenol formaldehyde novolac resin and a hexamethylenetetramine curing agent coated on zircon sand. 
   A method of forming the upper wick section  70  from a novolac resin coated silica sand will now be described. The novolac resin coated silica sand is low pressure injected into a heated mold at 300° F.-700° F. to form the upper wick section  70 . The mold heat completes the irreversible cross-linking of the novolac resin. Preferably, the network of pores and passages formed occupies at least 25 to 30% by volume percent of the upper wick section  70 , and most preferably, the network of pores and passages formed occupies at least 40% by volume percent of the upper wick section  70 . Preferably, the average pore size is in the range of 20 to 200 microns, and most preferably, the average pore size is in the range of 4 to 100 microns. In one form, the upper wick section  70  may have different densities at different regions of the substrate. 
   Still referring to  FIGS. 3-5 , the lower wick section  50  is positioned in the mouth  45  of the reservoir  44  through a central path of the cap ring  60 . The cap ring  60  has a lower tubular collar section  61 , a middle collar  62  with an outer surface  66 , and an upper collar  63  with a lower surface  67 , which help define the path. The lower wick section  50  may be held in place in the cap ring  60  by way of an interference fit with inner surfaces of the lower tubular collar  61 , the middle collar  62  and the upper collar  63 . Alternatively, the lower wick section may be integral with the cap ring  60 . Preferably, the cap ring  60  is formed from a thermoset or thermoplastic polymeric material such as a polyolefin, a polyester or a polyamide, albeit separate formation is preferred to avoid the cap ring  60  being made of a porous material (thereby avoiding lateral capillary action). 
   When the lower wick section  50  is held in place in the cap ring  60 , an annular depression  64  forms between the lower wick section  50  and the upper collar  63  and middle collar  63  of the cap ring  60 . The lower wick section  50  and the cap ring  60  are assembled to the reservoir  44  by an interference fit between the outer surface  66  of the middle collar  62  and the inner surface  49  of the mouth  45  of the reservoir  44 . The lower surface  67  of the upper collar  63  also rests on the rim  46  of the mouth  45  of the reservoir  44  as shown in  FIGS. 4 and 5 . When the lower wick section  50  and the cap ring  60  are assembled to the reservoir  44 , the lower end  54  of the lower wick section  50  is immersed in liquid  34  in the reservoir  44 , and the upper end  56  of the lower wick section  50  extends above the upper collar  63 . 
   The lower end  72  of the upper wick section  70  is held in abutting or adjacent relationship to the upper end  56  of the lower wick section  50  by way of the coupling sleeve  80 . The coupling sleeve  80  includes an annular base  82  and a tubular section  83  that extends upward from the annular base  82 . The tubular section  83  of the coupling sleeve  80  has an inner diameter that decreases from a bottom end  86  of the tubular section  83  of the coupling sleeve  80  to a top end  88  of the tubular section  83  of the coupling sleeve  80 . Thus, the inner surface  84  of the tubular section  83  tapers inward from the bottom end  86  of the coupling sleeve  80  to the top end  88  of the coupling sleeve  80 . Preferably, the coupling sleeve  80  is formed from a thermoset or thermoplastic polymeric material such as a polyolefin, a polyester or a polyamide. 
   The upper wick section  70  is inserted up into the annular base  82  of the coupling sleeve  80  and moved toward the top end  88  of the coupling sleeve  80 . The outer surface  76  of the upper wick section  70  then forms an interference fit with the inner surface  84  of the tubular section  83  of the coupling sleeve  80 . However, the points of contact are limited due to the tapering, thereby reducing the stress on the sand wick caused by the insertion. When the upper wick section  70  and the coupling sleeve are assembled, the upper end  74  of the upper wick section  70  extends beyond the top end  88  of the coupling sleeve  80  as shown in  FIG. 4 , and an opposite end of the upper wick section  70  terminates inside the coupler. This creates a first subassembly. 
   Separately, the lower wick section  50  can be positioned in the cap ring  60  such that opposed ends  54  and  56  extend beyond the ring on opposite sides thereof. This is a second subassembly. 
   The annular base  82  of the coupling sleeve  80  is then press fit in the annular depression  64  between the lower wick section  50  and the upper collar  63  and middle collar  62  of the cap ring  60  such that the lower end  72  of the upper wick section  70  is held in abutting or adjacent relationship to the upper end  56  of the lower wick section  50 . It should be appreciated that while this method of assembly is preferred for the use of automated equipment, the wick  40  and the reservoir  44  may be assembled in suitable alternative sequences. 
   The above structure may be installed in/on the volatile dispensing device  20 A as shown in  FIG. 5 . Specifically, the threads  48  on the outer surface  47  of the mouth  45  of the reservoir  44  may be engaged with the threaded portion  30  on the inner surface of the bottle socket  27  of the volatile dispensing device  20 A by rotating the reservoir  44 . When the wick  40  and reservoir  44  are installed in the volatile dispensing device  20 A, the upper wick section  70  is positioned in the opening in the ring heater  25  of the volatile dispensing device  20 A, the coupling sleeve  80  is positioned below the ring heater  25 , and the upper end  56  of the lower wick section  50  is positioned below the ring heater  25 . 
   In operation of the volatile dispensing device  20 A, the lower wick section  50  is immersed in the liquid  34  in the reservoir  44  and therefore upwardly transports the liquid  34  contained in the reservoir  44  by capillary action. The liquid  34  reaches the upper end  56  of the lower wick section and enters the lower end  72  of the upper wick section  70 . Preferably, the upper end  56  of the lower wick section  50  and the lower end  72  of the upper wick section  70  abut each other to facilitate liquid transfer between the upper end  56  of the lower wick section  50  and the lower end  72  of the upper wick section  70 . However, the upper end  56  of the lower wick section  50  and the lower end  72  of the upper wick section  70  may be spaced apart in adjacent relationship as long as liquid transfer between the upper end  56  of the lower wick section  50  and the lower end  72  of the upper wick section  70  is possible. 
   The upper wick section  70  then upwardly transports by capillary action the liquid  34  received from the lower wick section  50 . The ring heater  25  produces heat to heat the upper wick section  70 . The liquid  34  in the upper wick section  70  is vaporized by the heat from the ring heater  25  and enters the surrounding air. 
   The liquid to be dispensed is inserted in the reservoir  44  prior to mounting the wick assembly on the reservoir. Where the liquid is an insect control ingredient, the active can be selected from the group consisting of insecticides, insect repellents, and insect growth control ingredients. Examples include organic phosphorous insecticides, lipidamide insecticides, natural repellents as citronella oil, natural pyrethrins and pyrethrum extract, and synthetic pyrethroids are preferred. Suitable synthetic pyrethroids are acrinathrin, allethrin as D-allethrin, Pynamin®, benfluthrin, bifenthrin, bioallethrin as Pynamin Forte®, S-bioallethrin, esbiothrin, esbiol, bisoresmethrin, cycloprothrin, cyfluthrin, beta-cyfluthrin, cyhalothrin, lambda-cyhalothrin, cypermethrin, alpha-cypermethrin, beta-cypermethrin, cyphenothrin, deltamethrin, empenthrin, esfenvalerate, fenpropathrin, fenvalerate, flucythrinate, taufluvalinate, kadethrin, permethrin, phenothrin, prallethrin as Etoc®, resmethrin, tefluthrin, tetramethrin, tralomethrin, or transfluthrin. 
   When the present invention is used for the purpose of delivering fragrance, various natural and artificial perfumes may be used. Non-limiting examples of these perfumes include animal-based and plant-based natural perfumes, and artificial perfumes such as alcohols, phenols, aldehydes, ketones, terpenes, and esters. 
   The choice of volatile material or mixtures of volatile materials may depend on the temperatures provided by the dispensing device. For instance, the heated volatile dispensing device  20 A of  FIG. 5  may typically produce a wick surface temperature of about 100° C. when used with insecticides. Therefore, the volatile material or mixture of volatile materials is selected to provide an efficient release of the volatile materials from the upper wick section  70 . 
   One particular formulation of active can be prepared by mixing the following ingredients in Table 1. A heater temperature of about 140° F. is preferred for volatilizing that formulation. 
   
     
       
             
             
             
             
           
             
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               Weight 
                 
                 
                 
             
             
               Percent of 
               Common name or 
                 
               Function in the 
             
             
               Formulation 
               commercial name 
               Chemical name 
               formulation 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               2.5% 
               Pyrethrum Extract, 50% 
               pyrethrins 
               insecticide 
             
             
               1.2% 
               ETOC 
               prallethrin 
               insecticide 
             
             
               2.0% 
               BHT 
               butylated hy- 
               antioxidant 
             
             
                 
                 
               droxy toluene 
             
             
               1.0% 
               Takasago 35787 
               fragrance mix- 
               aroma 
             
             
                 
                 
               ture 
             
             
               93.3% 
               Isopar-V 
               isoparaffinic 
               solvent 
             
             
                 
                 
               hydrocarbon 
             
             
                 
             
           
        
       
     
   
   Although the present invention has been described in considerable detail with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. For example, the sleeve could be coupled directly to the reservoir with a lower wick of multiple diameters positioned against the upper wick. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein. 
   INDUSTRIAL APPLICABILITY 
   The invention relates to dispensing devices for delivering volatile materials from improved wick structures.