Abstract:
Disclosed herein is two-stage mat for dispensing volatile materials. The mat is comprised of two materials varying either in thickness, thermal conductivity and/or porosity (and coated with like volatile material), or coated with volatile materials having different vaporization pressures. In either configuration, the mat provides for both an instant burst of volatile and then a sustained vaporization of volatile. Methods of using such mats are also disclosed.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to dispensing volatile materials such as insecticides, insect repellants, fragrances, and deodorizers. It provides mats designed to be placed on an electric heater to release the volatile material when the mat is heated. 
     It is known in the art to impregnate or coat a solid porous cellulosic mat with a volatile material, and/or to place a volatile material in a metal pan-like mat structure. These mats are then placed on heaters to cause the volatile to vaporize into the ambient air. See generally U.S. Pat. No. 6,031,967 and WO 99/66791. The disclosure of these publications, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein. 
     However, there can be a time lag between the initiation of the heating of the mat and when the concentration of active in the room is at a desired level. For example, when the mat contains an insecticide, it may take a few minutes before the desired level of protection from mosquitoes or other insects is achieved. This is a particular problem where the product is designed to provide a very slow, prolonged release of active (e.g. to provide overnight protection against mosquitoes). 
     To minimize the time lag, one could try increasing the concentration of active on the mat. However, such actives are often costly, and in any event the increased concentration may lead to unnecessarily high levels of insecticide or other active being dispensed into the air after the initial period. 
     Another approach to try to solve this problem would be to modify heaters so that they work at one heat during an initial phase and then work at a reduced heat at all other times. However, this would require extensive cost in revising existing heaters and, in any event, would unnecessarily increase the cost of heaters in the future. 
     U.S. Pat. No. 5,657,574 proposed a mosquito coil having a uniform concentration of insect control agent spread throughout it, but with the coil having an enlarged ignition end. When the coil is first lit an extra burst of insecticide is dispensed because more of the coil is burnt at that time. However, this approach is not suitable for a mat where the entire mat is to be placed on the heater at once. 
     WO 99/66791 provided a slab-type mat system for insertion in an indexed fashion into a heater. Discrete regions of the mat are heated in sequence. The primary purpose of the slab is to provide a mechanism for indexing a new mat section over the heater when the preceding section had been used up. However, the publication also describes that the sequential regions could carry different volatile ingredients or different concentrations of the same volatile ingredient. One example that is given is providing a high concentration section to be used at night and a low concentration section to be used during the day. Unfortunately, this requires the user to sequentially move the slab when the next stage of usage is desired. 
     Complicating matters is the fact that most of the inexpensive heaters used for this purpose take some time to warm up, and many do not have a fully uniform heat presentation across their face. For example, many have a hot region in the center, with progressive cooling outward. In the past, this has caused some insecticides to degrade due to exposure to the too hot central section. 
     Accordingly, a need still exists for an improved volatile dispensing mat. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a mat for dispensing volatile vapors when heated. In one form there is a first mat substrate region having a first volatile material with an active selected from the group consisting of insect control agent, fragrance, deodorizer, and any combination thereof. There is also a second mat substrate region having a second volatile material with an active selected from the group consisting of insect control agent, fragrance, deodorizer, and any combination thereof. The first volatile material of the first mat substrate region releases at an effective rate greater than does the second volatile material of the second mat substrate region, either because of the higher and lower volatility characteristics of the first volatile material versus the second volatile material or because of selected differences between the first and second mat substrate regions. Preferably, the first region is a central region, the second region is an outward region around the central region, and the first volatile material is different from the second volatile material. A volatile material is defined as releasing at a greater or lesser “effective” rate as the intended effect of the active constituting or contained in the volatile material is achieved at a faster or slower rate. 
     The term “mat” is used herein to include any generally flat, thin, extended structure suitable for use with conventional mosquito mat holders, regardless of material, precise outline, texture, and other physical features such as through-holes, incorporated metallic pans, and the like. The typical commercial mosquito mat is usually a generally rectangular card made of a fibrous material, although, as just stated, the term “mat” is not confined to that particular shape or material. The term “insect control” is defined to mean killing, repelling, or otherwise altering the behavior or development of insects. “Insect control agent” is used herein in its broadest sense to include not only insecticides and repellants but also growth regulators and other agents capable of achieving insect control. “Insect” is defined to mean actual insects as well as spiders, millipedes, and other small animals commonly controlled in the same manner or with the same agents as are insects. 
     The first and preferably central region can be made of a metallic or other substrate which transmits heat faster than a surrounding substrate, preferably made of cellulose. This will cause different vaporization rates, even where the volatiles are the same. 
     One can alternatively (or in addition) retard or increase the rate of release by the selection of suitable solvents, binders, actives, and active concentrations. We prefer to use a highly volatile active for the first region, such as transfluthrin or prallethrin, esbiothrin, d-allethrin, S-bioallethrin and dichlorvos, as well as to select a metallic, thin, and nonporous substrate for the first region which will release the volatile very quickly. Particularly preferred is where the active in the volatile material of the second region is transfluthrin and the active in the volatile material of the first region is d-allethrin. 
     In especially preferred forms, the first and second regions are comprised of materials differing with respect to a material property selected from the group consisting of thickness, thermal conductivity, porosity, and combinations thereof. In such a case, the second region would preferably be in the form of a slab having a bore therethrough, and the first region would preferably be defined by a metal foil cup positioned in the bore. Preferably the bore and cup would be centrally located in the slab, “centrally” located being construed to mean generally centrally located or at least so located that slab material completely surrounds the bore. 
     Alternatively, the second region can be a ceramic slab having a recess in an upper side, and the first region can be defined by a ceramic glaze lining the recess. 
     In yet another variant, the second region can be a frame of cellulosic material and the first region can be a metallic tray having a recessed center extending preferably at least to the bottom surface of the frame or even further, whereupon it actually supports the frame. 
     In yet another form, the invention provides a mat for dispensing volatile vapors when heated. Again, there are first and second mat substrate regions, each having a volatile material with an active selected from the group consisting of insect control agent, fragrance, deodorizer, and a combination thereof. Regardless of their juxtaposition relative to each other (e.g. side by side; central and surrounding donut), the first and second regions are comprised of materials differing with respect to a material property selected from the group consisting of thickness, thermal conductivity, porosity, and combinations thereof. 
     In still another form, the invention provides a method for dispensing volatile vapors. One positions a mat on an electric heater. The mat has a first and a second mat substrate region having first and second volatile materials, respectively, the volatile materials each including an active selected from the group consisting of insect control agent, fragrance, deodorizer, and combinations thereof. One then simultaneously heats both the first and second mat substrate regions such that the active in the first volatile material is vaporized from the first region at a greater effective rate than the active in the second volatile material from the second region. 
     When used as an insect control device, the device of the invention allows the user to achieve desired protection very quickly, without sacrificing long-term protection. When dispensing a deodorizer or fragrance, the invention has the advantage of covering over existing malodors very quickly (e.g. in a bathroom), without sacrificing the ability to provide fragrance over the long term. 
     Importantly and surprisingly, the present invention is capable of turning a disadvantage of inexpensive heaters (non-uniform heating across the heating face) into an advantage. This is achieved by centrally placing the fast release section. 
     These and still other advantages of the invention will appear from the following description. In the description reference is made to the accompanying drawings in which there is shown by way of illustration preferred embodiments of the invention. However, 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 of a two-stage mat of the present invention being used with an electric heater; 
     FIG. 2A is a top view of a first embodiment of the two-stage mat of the present invention; 
     FIG. 2B is a cross-sectional view taken along line  2 — 2  of FIG. 2A; 
     FIG. 3 is a vertical cross-sectional view of a second embodiment of the present invention; 
     FIG. 4 is a vertical cross-sectional view of a third embodiment of the present invention; 
     FIG. 5A is a top view of a fourth embodiment of the present invention; 
     FIG. 5B is a cross-sectional view taken along line  5 — 5  of FIG. 5A; 
     FIG. 6 is a vertical cross-section view of a fifth embodiment of the present invention; 
     FIG. 7A is a top view of a sixth embodiment of the present invention; and 
     FIG. 7B is a vertical cross-sectional view taken along line  7 — 7  of FIG.  7 A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, two-stage mat  10  is shown placed upon a horizontal burner face  12  of an electric heater  14 . The term “burner face” refers to the heated surface (typically solid but alternatively a mesh or other structure) of an electric heater on which it is intended that a user place a mosquito mat for heating. The heater  14  can be an electrical-resistance heater such as the heater sold by in Italy and other countries as the RAID® heater by S.C. Johnson &amp; Son, Inc. However, other heaters could also be used without limitation on the horizontal, vertical, or other orientation of their heating surfaces. 
     A first preferred embodiment of the mat is shown in FIGS. 2A and 2B. Although other embodiments of the mat are shown, all generally include two non-integral substrate sections. Each is impregnated or coated with the same or different volatile materials. The substrates preferably have distinctly different volatile release parameters, such as thickness, thermal conductivity, and/or porosity. The volatile materials or formulations may also have distinctly different vaporization rates. 
     The first embodiment of the mat  10  includes a slab-like body  16  having a generally cylindrical bore  18  therethrough. The bore  18  is lined with a cup-shaped insert  20  that is preferably adhered to the body  16  by an adhesive at the inner diameter of the bore  18 . 
     The body  16  and the insert  20 , respectively, are impregnated and coated with volatile materials or formulations. When placed over the heater  12 , the volatile is released from the mat  10  (when the mat  10  is heated). Advantageously, the bore  18  is essentially in the center of the body  16 , which takes advantage of the often higher temperatures in the center of the burner surface typically associated with low cost heaters. 
     The body  16  is preferably a pulp or other cellulose-based material formed into a slab of approximately 3.5 cm×1.75 cm.×0.25 cm. The insert  20  is preferably a metallic foil approximately 0.5 mm thick, such as an aluminum alloy foil. The insert  20  is adhered to the inner diameter of the bore  18  by a polymeric adhesive, such as adhesive “711” (commercially available from Manufacturer Resources, Inc. of New Berlin, Wis.). 
     Preferably, body  16  is impregnated with a second volatile material  22  having a slower releasing active ingredient and the inside surface of the insert  20  is coated with a chemically distinct first volatile material  24  having a faster releasing active ingredient. As an insect control device, preferably second volatile material  22  is 100 mg of a liquid solution having a chemical composition of 40% d-allethrin (an insecticide active ingredient), 40% piperonyl butoxide (PBO, synergist/release agent), and 20% Isopar M (solvent). First volatile material  24  is preferably 50 mg of a liquid solution having a chemical composition of 4% transfluthrin (insecticide active ingredient) and 96% Isopar E (solvent). Transfluthrin vaporizes more quickly than does the d-allethrin because it has a higher vaporization pressure. 
     Note also that insert  20  has a significantly decreased thickness and porosity (and increased thermal conductivity) relative to the body  16 . Moreover, the insert  20  is coated with a faster releasing volatile material  24  than that with which the body  16  is impregnated. In this preferred construction using the above selected materials, when the mat  10  is heated, the mat  10  provides for an instant burst of the first volatile material  24  at startup of the heater  16 . It also provides uniform and efficient sustained release of second volatile material  22  for prolonged protection lasting at least 6 to 8 hours and as much as a day or more. 
     It should be noted that other materials could be selected that would provide two-stage vaporization. For example, the body  16  could be made of other solid porous substrates, such as sintered glass, a polymeric block, plastic beads, natural or synthetic fabrics, and other absorbent and adsorbent materials. The insert  20  could be any other suitable metallic foil (or even other substrates), and the adhesive used to join the insert  20  to the body  16  can be any other acrylic, urethane, or other adhesive resistant to high temperatures. 
     Alternatively, the volatile materials  22  and  24  could be any other suitable known insecticides, repellants, growth regulators, or other insect control agent. For example, the volatile materials  22  and  24  could include organic phosphorus insecticides, lipidamide insecticides, natural repellants such as citronella oil, natural pyrethrum and pyrethrum extract, and synthetic pyrethroids. Suitable synthetic pyrethroids include allethrin as d-allethrin, allethrin, benfluthrin, bifenthrin, S-bioallethrin, esbiothrin, esbiol, bioresmethrin, cycloprothrin, cyfluthrin, beta-cyfluthrin, cyhalothrin, deltamethrin, empenthrin, esfenvalerate, fenpropathrin, fenvalerate, flucythrinate, tau-fluvalinate, kadethrin, permethrin, phenothrin, prallethrin, resmethrin, tefluthrin, tetramethrin or tralomethrin. Other volatile insecticides as described in U.S. Pat. No. 4,439,415 can also be used. 
     Volatile insect growth control agents such as methoprene and hydroprone may also be used. Alternatively or in addition, fragrances and deodorizers may be used, such as imonene, eucalyptus, and citronella. 
     We tested the FIG. 2A mat as follows. Groupings of four test mats (with specified ages) were prepared, one being a standard single-stage pulp body mat and the other three being the FIG. 2A two-stage mat of the present invention and constructed as described above. One of the three had active only in the center, one had active only in the peripheral substrate, and one had active in both. 
     The test conditions and volatile materials used for each mat are as follows. 
     
       
         
               
               
               
             
           
               
                   
               
               
                 Mat# 
                 Mat Type 
                 Volatile Composition 
               
               
                   
               
             
             
               
                 1 
                 standard 
                 PF-40%; PBO-40%; IM-20% 
               
               
                 2 
                 outside only 
                 PF-40%; PBO-40%; IM-20% 
               
               
                 3 
                 center only 
                 T-4%; IE-96% 
               
               
                 4 
                 2-stage 
                 body: PF-40%; PBO-40%; IM-20% 
               
               
                   
                   
                 insert: T-4%; IE-96% 
               
               
                   
               
               
                 PF = d-allethrin (insecticide)  
               
               
                 PBO = piperonyl butoxide (insecticidal synergist)  
               
               
                 IM = Isopar M (solvent)  
               
               
                 T = transfluthrin (insecticide)  
               
               
                 IE = Isopar E (solvent)  
               
             
          
         
       
     
     The study was conducted in a 0.42 cubic meter glass chamber using ten free-flying female  culex quinquefasciatus  (mosquitoes). The mats, heaters and mosquitoes were all introduced into the chamber at the same time. 
     Mean knockdown percentage data was collected for each thirty second time interval. Knockdown data was also collected in thirty second intervals until 100% knockdown was achieved, or until the expiration of twenty minutes. 
     The study showed that knockdown began much earlier using the two-stage mat (MAT 3 ) of the present invention than the standard single-stage mat (MAT 1 ). The same was true for the time necessary to achieve 100% knockdown. 
     FIGS. 3-7 illustrate alternate embodiments of the present invention, wherein similar components are referred to with similar reference numbers, albeit with an A, B, C, D or E suffix. Unless indicated otherwise, the alternate embodiments preferably use the same materials and volatile materials mentioned above with respect to the first embodiment. Moreover, the alternate embodiments are used in the same manner as the first embodiment, providing for multiple rate vaporization of the volatile materials when sufficiently heated by a heater. 
     Referring now to FIG. 3, mat  10 A includes a cellulosic body  16 A having a through bore  18 A at its center. A metallic foil layer  30 A is adhered to the bottom side of the entire body  16 A to distribute heat more evenly along the bottom side of the body  16 A. A thin pulp insert  20 A, preferable made of a filter paper, is adhered to a top side of the foil layer  30 A within the through bore  18 A so that it does not contact the pulp body  16 A directly. The pulp body  16 A is impregnated with a slow release volatile material  22 A and the insert  20 A is impregnated with a fast release volatile  24 A. The separation minimizes leaching of the respective volatiles into each other&#39;s region during storage. 
     In the embodiment shown in FIG. 4, the mat  10 B includes a pulp body  16 B having a central through bore  18 B in which is disposed a plug insert  20 B of the same material and thickness. Preferably, the plug insert  20 B is the material removed from the body  16 B when the through bore  18 B is created. This mat  10 B also includes a metallic foil layer  30 B adhered to the bottom side of the body  16 B and the plug insert  20 B. Like before, the body  16 B is impregnated with a slow release volatile material  22 B and the plug insert  20 B is impregnated with a fast release volatile material  22 B. In this embodiment, the plug insert  20 B should be treated with the volatile material  24 B and allowed to dry prior to assembly so that the volatile material  24 B does not bleed into the body  16 . Similarly, the volatile material  22 B should be impregnated into the body  16 B and allowed to dry before the plug is inserted. 
     Referring now to FIGS. 5A and 5B, the mat  10 C includes a pulp body  16 C roughly half the length of the prior embodiments. The body  16 C is adhered at its bottom side to a full-length metallic foil layer  30 C to which is also adhered a thin pulp material strip  20 C, preferably made of filter paper less porous than the pulp of the body  16 C. The strip  20 C is adhered to the foil layer  30 C so as not to contact the body  16 C. The body  16 C is impregnated with a slow release volatile material  22 C and the strip  20 C is impregnated with a fast release volatile material  24 C. As in mat  10 A (see FIG.  3 ), the decreased thickness and less porosity of the strip  20 C further aids in rapid vaporization of the fast release volatile material  24 C. 
     Referring now to FIG. 6, the mat  10 D includes a slab-like body  16 D made of a ceramic material such as terra cotta or earthenware. The body  16 D includes a central, dished recess  18 D that is lined by a suitable ceramic glaze, such as silica-based low fire clear glaze. The ceramic glaze liner  20 D is preferably less porous than the ceramic of the body  16 D. This feature, and the decreased thickness under the glaze, allows more rapid vaporization of a fast release volatile material  24 D coating the liner  20 D. As before, the body  16 D is impregnated with a slow release volatile material  22 D. 
     Referring now to FIGS. 7A and 7B, rather than having a slab-like body, mat  10 E has a pulp frame  16 E which rests upon a raised perimeter rim  32  of a metallic foil tray  20 E having a recessed center. The frame  16 E is impregnated with a slow release volatile material  22 E and the tray  20 E is coated with a fast release volatile material  24 E. 
     It should be appreciated that the mats of the present invention could be formed in still other embodiments. These are also intended to be within the scope of the present invention. For example, a single volatile material could be used and still provide for two-stage vaporization, provided that there are two or more substrates having different volatile release properties, such as thickness, thermal conductivity and porosity. 
     Moreover, the two-stage mat of the present invention could also be a disinfectant/fragrancer/deodorizer, using any of a wide variety of active ingredients for such purposes, including glycols, trimethylene and dipropylene known in the art. Further, even with the same active and substrates, a FIG. 4 like structure could work if solvents, binders, and the like were adjusted to suitably control release rates. Accordingly, the claims should be referenced in order to determine the full scope of the invention. 
     INDUSTRIAL APPLICABILITY 
     The invention provides mats for the controlled release of insect control agents, fragrances, disinfectants, and similar useful, volatile materials, where a burst of a volatile material occurs when the product is first used, followed by a prolonged release of the same or another volatile.