Abstract:
Disclosed are substrates suited for dispensing air treatment chemicals upon being heated. Granular particles, preferably sand with a phenolic binder, are adhered together to form a substrate body having a network of pores. A volatile air treatment chemical is disposed in the pores. The particle size and pores are such that the smaller particles of the substrate are grouped at one end, preferably an end adjacent to a projecting nose. This structure tends to wick the volatile air treatment chemical towards the nose, and heating that area can lead to efficient, and rechargeable, dispensing. Methods for using such substrates, and methods for forming such substrates, are disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority based on U.S. Ser. No. 11/348,989, filed Feb. 7, 2006. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
       [0002]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to devices that dispense a volatile air treatment chemical by heating a substrate that is impregnated with, or coated with, the chemical. More particularly it relates to methods for constructing the substrate to create an array of pore size distribution therein, substrates produced thereby, and such substrates further formed with a rechargeable start-up projection. 
         [0004]    Substrates (particularly porous substrates) have previously been used as carriers for air treatment chemicals such as insect control agents (insecticides, insect repellents, insect growth regulators, attractants, synergists, etc.), fragrances and deodorizers. See e.g. U.S. Pat. No. 6,551,560. The disclosure of this patent, and of all other patents referred to herein are incorporated by reference as if fully set forth herein. 
         [0005]    Upon heating of the substrate a volatile air treatment chemical is caused to be dispensed from the substrate. The heating source is typically an electrical heater, but may instead be a flame in some cases. 
         [0006]    A variety of air treating functions can be achieved with such devices. For example, a porous substrate impregnated with volatile insecticide can be used to inhibit mosquito biting in a confined bedroom. Alternatively, a deodorizing or other odor control material can be dispensed to overcome malodors, or to simply provide a desired fragrance. 
         [0007]    One problem with such devices is that the substrate usually rests against or near a heater. The heater heats the substrate, causing the volatized air treatment chemical to be driven off the substrate in a direction away from (essentially perpendicular to) a heater surface. This can create some inefficiencies. For example, the portion of the substrate adjacent the heater can act as an insulator for the portion of the substrate which is releasing the active, making control of the dispensing more difficult. 
         [0008]    Another problem with such devices is that it may take a while after usage begins to adequately treat the air in a defined environment adjacent the device. For example, when someone is about to go to bed they may activate the device in a bedroom. It is undesirable for them to have to wait a long period before feeling secure about insect protection in the room. 
         [0009]    In connection with burnable mosquito coils, U.S. Pat. No. 5,948,425 disclosed in an enlarged outer end of the coil that would initially burn to create a burst of insecticide, before the rate of burning slowed down to a steady state. In connection with a non-burnable substrate, U.S. Pat. No. 6,551,560 disclosed that a central region could be provided having the ability to provide a quick burst of active, followed by the surrounding area releasing active at a slower constant rate. While these patents therefore addressed the need for quickly treating a room at the beginning of operation, they did not address a way to have the same device provide such a burst on multiple days. 
         [0010]    In U.S. Pat. No. 4,286,754 and U.S. patent application publication 2004/0151747 it was discussed that a variety of wicks could be formed from sand (and certain other particulate material) mixed with a binder. The wicks could draw active from a reservoir to an upper portion of the wick, and the upper portion of the wick could be positioned adjacent to (usually through) a heater unit to volatize the active. For example, in U.S. patent application publication 2004/0151747 there is a discussion of forming the wick of silica sand particles bound with a novolac resin. The volatile material was described as optionally being an insecticide dissolved in a hydrocarbon solvent and/or a fragrance. 
         [0011]    However, these wicks were not provided with a means of creating a quick start-up burst, much less a rechargeable start-up burst. Further, they required the use of a reservoir to continuously resupply the wick. 
         [0012]    In unrelated work U.S. patent application publication 2004/0140114 disclosed that tapering pores in a housing can wick liquid away from a battery. 
         [0013]    In any event, there is a need for producing porous substrates which efficiently dispense air treatment chemicals as well as have rechargeable start-up burst characteristics. 
       BRIEF SUMMARY OF THE INVENTION 
       [0014]    In one aspect the invention provides a method for dispensing a volatile material from a substrate. One obtains a porous substrate having a projecting nose, the substrate being impregnated with a volatile air treatment chemical, heats the substrate such that heat is applied to at least an end of the nose to cause a first burst of volatile air treatment chemical to be dispensed from the substrate, allows the nose of the substrate to cool and permitting additional volatile air treatment chemical to be drawn from the substrate to the nose, and re-heats the substrate such that heat is applied to at least an end of the nose to cause a second burst of volatile air treatment chemical to be dispensed from the substrate. The porous substrate comprises sand and a binder. 
         [0015]    In preferred forms of this method the substrate has a first end defined by the nose and a second opposed end, and an average size of the sand in the nose is less than an average size of the sand adjacent the second end, and the porous substrate further comprises a fragrance. 
         [0016]    In another aspect the invention provides a substrate that can actively dispense a volatile air treatment chemical upon being heated. The substrate is formed from granular sand particles adhered together to form a body having a network of pores, and volatile air treatment chemical is disposed in the pores. 
         [0017]    The substrate has a first end and a second opposed end, and an average size of the granular particles adjacent the first end is sufficiently less than an average size of the granular particles adjacent the second end such that the first end tends to wick air treatment chemical towards the first end as air treatment chemical is dispensed from pores of first end. As a result the substrate is capable of delivering a first burst of the volatile air treatment chemical from the first end when the substrate is heated adjacent the first end, and if thereafter the substrate is allowed to cool it is capable of delivering a second burst of the volatile air treatment chemical from the first end when the substrate is thereafter heated for a second time adjacent the first end. The second burst has at least in part volatile air treatment chemical that has been wicked towards the first end from elsewhere in the substrate, and the granular particles comprise sand and a binder such as a phenolic resin. 
         [0018]    In yet another aspect the invention provides a method for forming a substrate that can actively dispense a volatile air treatment chemical upon being heated. One places sand particles in a mold, shakes the mold to cause smaller sand particles to move downward relative to larger sand particles in the mold, and thereafter forms the substrate in the mold. As a result, the average particle size of the substrate at the bottom of the substrate in the mold will be less than the average particle size of the substrate at the top of the substrate in the mold. 
         [0019]    The sand can be impregnated after the shaking step and before the forming step. Alternatively, it can be impregnated by exposing the already-formed substrate to the impregnation fluid. 
         [0020]    It should be appreciated that the substrates of the present invention are inexpensive to produce, use heat extremely efficiently, and are capable of multiple initiation bursts. The foregoing and other advantages of the present invention will be apparent from the following description. In the description that follows reference is made to the accompanying drawings which form a part thereof, and in which there is shown by way of illustration, and not limitation, expected preferred embodiments of the invention. Such embodiments do not necessarily represent the full scope of the invention, and reference should therefore be made to the claims herein for interpreting the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a lower frontal perspective view of an air treatment device suitable to use a preferred substrate of the present invention; 
           [0022]      FIG. 2  is a frontal perspective view of a preferred substrate of the present invention; 
           [0023]      FIG. 3  is a sectional view of the  FIG. 1  structure taken along line  3 - 3  of  FIG. 1 , albeit with an indicator unit  26  removed; 
           [0024]      FIG. 4  is a sectional view of a mold used to prepare the substrate of  FIG. 2 ; 
           [0025]      FIG. 5  is a view similar to  FIG. 4 , but with the mold shown partially filled; 
           [0026]      FIG. 6  is a view similar to  FIG. 5 , but with the mold shown filled, after it has been shaken, and after a cover/lid has been placed over the mold cavity; 
           [0027]      FIG. 7  is a view similar to  FIG. 6 , but with heat being applied to the mold; 
           [0028]      FIG. 8  is a view of the substrate formed in the  FIG. 7  mold, after it has been removed from the mold; and 
           [0029]      FIG. 9  is a detailed view of the region designated  9 - 9  in  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Referring first to  FIG. 1 , air treatment device  10  has a housing  12  with electrical prongs  14  at a rear end  16  and a removable cartridge unit  18  at an opposing forward end  20 . 
         [0031]    The cartridge unit  18  preferably has a substrate  22  mounted to project through its rearward end and a separately installable indicator unit  26  mounted to project out from its forward end. There is a substantially circular cavity  38  (see  FIG. 3 ) in the rearward center of the unit  18  which tapers rearwardly to hold the substrate  22 . 
         [0032]    The indicator unit  26  is removable from the cartridge unit  18 . The indicator unit  26  preferably houses a separate indicator chemical, which may indicate to a user the amount of air treatment chemical remaining in the substrate  22 . A removable indicator unit  26  allows the indicator unit  26  and/or the substrate  22  to be separately replaced. However, the indicator chemical may be directly housed in a well of the cartridge unit  18 . 
         [0033]    The device  10  is most preferably plugged into an electric socket on a vertical wall. Hence, the directional terms in this patent are used with that type of installation in mind. However, appropriate electric sockets on horizontal or other surfaces may also be used to provide power. Thus, the terms such as “front”, “rear”, “upper”, “lower”, and “side” should be interpreted in an analogous manner when the devices are used for that type of installation. 
         [0034]    The prongs  14  shown in the figures are merely for purposes of example. Cylindrical prongs of this type are suitable for linking to electric power in some countries. However, in other countries blade prongs, or mixtures of blades, cylinders and other shaped prong elements will be used to supply the linkage to the available power (as is well recognized in the art). 
         [0035]    The housing  12  has a series of elongated vents  30  on the upper and lower sides of the housing  12 . The vents  30  allow in air from the environment and permit it to pass along with the air treatment chemical dispensed from the substrate  22  through the vents  30  on the upward side of the housing  12 . Nose  25  of the substrate  22  is preferably positioned closely adjacent the heating element  56  with room around the nose  25  for air to pass completely around its periphery. 
         [0036]    As is evident from  FIGS. 2 and 3 , the preferred cartridge unit  18  has a substrate  22  having a forward frustum shaped section  23  and a rearward projecting nose  25 . The particular shape of the substrate  22  is not critical insofar as the broadest aspects of the invention are concerned. However, the projecting nose  25  has certain advantages for quick start-up in some preferred embodiments. 
         [0037]    The substrate  22  is preferably impregnated with a volatile air treatment chemical capable of being dispensed from the substrate  22  when the substrate  22  is heated. However, as an alternative to being completely impregnated with the air treatment chemical, the substrate  22  may instead be only partially impregnated. The extent of dispensing of the air treatment chemical can be indicated by a visible cue whose appearance results from the dispensing of an indicator chemical  28  associated with the indicator unit  26 . 
         [0038]    Referring specifically to  FIG. 2 , the substrate  22  has a first end  62  and a second end  60  opposed to the first end, and the average size of the granular particles adjacent the first end  62  is less than the average size of the granular particles adjacent the second end  60 . The substrate  22  thus is preferably configured such that the first end  62  tends to wick air treatment chemical towards itself as air treatment chemical is dispensed from the second end  60 . 
         [0039]    The housing  12  of the overall device  10  preferably encloses a heating element  56  such that the heating element  56  is positioned proximal to a rearward end of the cartridge unit  18 . The heating element  56  is preferably activated by inserting the electrical prongs  14  into an outlet (not shown). 
         [0040]    Heat from the heating element  56  may also be permitted to pass against other surfaces of the cartridge unit  18  through a series of openings. Note however a separator panel  48  (as shown in  FIG. 3 ) which provides some insulation to the indicator unit  26 . 
         [0041]    The substrate  22  is preferably positioned in front of the heating element  56  with the nose  25  of the substrate  22  (containing the highest density and smallest pore size) closest to the heating element  56 . 
         [0042]    In use, heat is applied to at least an end and side walls of the nose of the substrate. This causes a first burst of the volatile air treatment chemical to be dispensed from the substrate. 
         [0043]    Upon dispensing the first burst of air treatment chemical and typically after a continuing period of use, the nose of the substrate is preferably allowed to cool, thus permitting additional volatile air treatment chemical to be drawn from the substrate to the nose  25 . Then, the substrate is re-heated such that heat is applied to at least a rearward end and side walls of the nose, causing a second burst of volatile air treatment chemical to be dispensed from the substrate. 
         [0044]    Referring next to  FIGS. 4-9 , a method for forming the substrate  22  of the present invention is schematically depicted. A mold  64  of the substrate  22 , having a projecting nose  70 , is filled with the substrate material, preferably a sand/resin mix. The mold  64  is then covered with a lid  66  and shaken. By shaking the mold  64 , the sand particles  68  having a smaller size are shifted downward, towards the nose  70  of the mold  64 . In this manner, a substrate  22  having smaller particle size at the bottom end and larger particle size at the top end of the substrate  22  is formed. 
         [0045]    Examples of a suitable substrate  22  include but are not limited to porous sand with a binder such as novolac resin, urethane resins or highly cross linked thermoplastics such as cross linked polyethylene. Particularly preferred sand substrates can be made in a fashion analogous to the sand wicks described in U.S. patent application publication 2005/0284952. Alternative substrates include other particulates such as metal, cellulose and ceramic particulates. 
         [0046]    The air treatment chemical is preferably an insecticide, fragrance and/or disinfectant. In some cases more than one air treatment chemical may be used alone or in combination in the substrate  22 . 
         [0047]    When the air treatment chemical is an insecticide and/or insect repellent, 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, metofluthrin or transfluthrin. Other volatile insecticides, such as those described in U.S. Pat. No. 4,439,415, can also be employed. 
         [0048]    In particularly preferred versions the volatile insecticide is selected from the group consisting of transfluthrin, metofluthrin, vapothrin, permethrin, prallethrin, tefluthrin and esbiothrin. Transfluthrin is the most preferred insecticide. 
         [0049]    Possible solvents for carrying these air treatment chemicals include, but are not limited to, ISOPAR™C, ISOPAR™E, ISOPAR™L, heptane, methanol, acetone, ethanol, isopropyl alcohol, dodecene and tetraydrofuran. ISOPAR™C, ISOPAR™E and ISOPAR™L are hydrocarbon solvents of varying chain length and are available from Exxon Chemical Company. 
         [0050]    Typically, volatile insect control agents will be carried in an organic solvent such as a hydrocarbon. One particularly desirable impregnation formulation for mosquito control is 50 wt. percent transfluthrin dissolved in ISOPAR C hydrocarbon. Alternatively, and often preferably, transfluthrin can first be warmed to liquefy it and then applied neat to a warmed substrate. 
         [0051]    A wide variety of volatile fragrances may be used which may optionally also have insect control attributes. Alternatively, some fragrances may be selected that provide a deodorizing function (e.g. certain terpenes). For example, 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 
         [0052]    When an volatile air treatment chemical is a disinfectant, preferred disinfectants include, but are not limited to, glycols, trimethylene and dipropylene. Organic acids compatible with the use of the substrate  22  and environment may also be used. 
         [0053]    Regarding the amount of particles  68 , either sand or otherwise, the mold  64  should be filled to capacity, thereby creating a substrate  22 . The sand or other particulate should be shaken thoroughly in the mold (e.g. for ten or more seconds), although the exact time and degree of force required will depend on the type of particles  68  and the needs of the user. 
         [0054]    The lid  66  can be present during the shaking. However, it is preferred that it be removed with the top of the sand smoothed, by dragging a blade across it, prior to starting the heating. 
         [0055]    As one example, we formed a substrate of the  FIG. 2  shape where the front wall had a diameter of 1.6 cm and the rear nose had a rear view maximum diameter of 0.5 cm. To do this, we placed 1.85 g of silica sand along with 0.07 g of novolac resin uniformly mixed therein, in a suitable shaped mold. We then shook the mold for 15 seconds, smoothed the top of the sand mix, and heated the mold for 10 minutes at 300.degree.C. We allowed the mold to cool and added 300 mg of transfluthrin by gently positioning it on the top surface of the sand. We removed the formed substrate, positioned it in a device like that of  FIG. 3 , and tested the operation of the device with an insect challenge. 
         [0056]    The mold  64  used to form the substrate  22  of the present invention may be made from any suitable material, including but not limited to plastic, metal or wood molds. Hence, the mold itself is not critical. 
         [0057]    While the preferred embodiment of the present invention has been described above, it should be appreciated that the invention could be used in a variety of other embodiments. For example, instead of adding the neat active or the impregnation fluid after the formation of the substrate, one could dose the active on the substrate in the mold prior to the formation of the substrate. One could also dip a formed substrate into a fluid bath containing 50% transfluthrin and 50% ISOPAR C. 
         [0058]    Thus, the principles of the present invention can be applied in a wide variety of other ways apart from those specifically noted herein. Still other modifications may be made without departing from the spirit and scope of the invention. Thus, the claims (rather than just the preferred embodiment) should be reviewed in order to understand the full scope of the invention. 
       INDUSTRIAL APPLICABILITY 
       [0059]    The present invention provides improved substrates for use with air treatment devices, along with improved methods to make such substrates.