SOLVENT FOR INSECT REPELLENT ACTIVE INGREDIENT AND INSECT REPELLENT SYSTEM USING SAME

Abstract

An insect repellent system includes an active insect repellent ingredient and a glycol solvent as part of a thermally activated dispersion using a wick and a heater. The active ingredient may be a pyrethroid insecticide or a natural insect repellent material. The glycol solvent includes at least two hydroxyl groups and may be a mixture of glycol solvents. In one solvent mixture, a combination of hexylene glycol and dipropylene glycol are combined with a pyrethroid insecticide of either metofluthrin or transfluthrin. The insect repellent system may be a portable insect repellent system formed from thermoplastic materials and rely on battery power to generate heat.

Claims

1. An insect repellent system comprising: a heating element; a reservoir containing a mixture of an active insect repellent ingredient and a glycol solvent; and a wick having a proximal end extending into the heating element and a distal end extending into the mixture.

2. The insect repellent system of claim 1 wherein the active insect repellent ingredient is a pyrethroid insecticide and the glycol solvent is a mixture of at least a first glycol solvent and a second glycol solvent wherein the first glycol solvent has a boiling point lower than the second glycol solvent.

3. The insect repellent system of claim 2 wherein the pyrethroid insecticide is one of a metofluthrin active ingredient, a transfluthrin active ingredient, or a prallethrin active ingredient.

4. The insect repellent system of claim 1 wherein the active insect repellent active ingredient is a natural insect repellent comprising at least one of Lemon eucalyptus oil, Lavender, Cinnamon oil, Thyme oil, Greek catmint oil, Soybean oil, Citronella, Tea tree oil, Geraniol, or Neem oil.

5. The insect repellent system of claim 1 wherein the active insect repellent ingredient is metofluthrin and the glycol solvent is one of ethylene glycol, propylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, or tetraethylene glycol solvents.

6. The insect repellent system of claim 1 wherein the active insect repellent ingredient one of metofluthrin or transfluthrin and the glycol solvent is a mixture of hexylene glycol and dipropylene glycol.

7. The insect repellent system of claim 6 wherein the ratio of hexylene glycol to dipropylene glycol is in a range of 65-70 percent hexylene glycol to 35-30 percent dipropylene glycol.

8. The insect repellent system of claim 6 wherein the ratio of hexylene glycol to dipropylene glycol is in a range of 60-70 percent hexylene glycol to 40-30 percent dipropylene glycol.

9. The insect repellent system of claim 6 is configured as a portable insect repellent system powered by a battery and wherein the heating element has a power output in a range of about 3 Watts to about 4 Watts and the battery has a charge capacity of about 2900 mAh to about 3200 mAh.

10. The insect repellent system of claim 1 wherein the housing and the reservoir are formed from thermoplastic materials.

11. The insect repellent system of claim 10 wherein the housing thermoplastic material is an acrylonitrile butadiene styrene (ABS) plastic and a portion of the reservoir is formed from a polycarbonate plastic.

12. The insect repellent system of claim 10 wherein the reservoir includes a sealing element that engages the wick.

13. The insect repellent system of claim 12 wherein the sealing element is a nitrile seal or a nitrile O-ring.

14. The insect repellent system of claim 1 wherein a housing supports the heating element and is formed from an acrylonitrile butadiene styrene (ABS) plastic, a portion of the reservoir is formed from a polycarbonate plastic, the active insect repellent ingredient is one of metofluthrin or transfluthrin, and the glycol solvent is a mixture of hexylene glycol and dipropylene glycol.

15. The insect repellent system of claim 14 wherein the heating element produces a temperature output in a range sufficient for low voltage battery operation, which may range from about 60 degrees Celsius to about 140 degrees Celsius.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a cross sectional view of a dispensing device utilizing an insect repellent solution in accordance with the invention.

[0020] FIG. 2 is an exploded view of the dispensing device of FIG. 1.

[0021] FIG. 3 is an enlarged view of a heating element proximate to a wick position of the dispensing device of FIG. 1.

[0022] FIG. 4 is a table of test data showing physical and chemical properties of glycol solvents tested. test data showing compatibility of a dispensing device with listed glycol solvents.

[0023] FIG. 5 is a table of test data showing physical and chemical properties of glycol-related and glycol ether solvents tested.

[0024] FIG. 6 is a table of test data showing the solubility of select Pyrethroid active ingredients in glycol solvents.

[0025] FIG. 7 is a table of test data showing the solubility of select Pyrethroid active ingredients in glycol-related solvents.

[0026] FIG. 8 is a table of test data showing compatibility and vaporization rates of the dispensing device with glycol solvents.

[0027] FIG. 9 is a table of test data showing compatibility and vaporization rates of the dispensing device with glycol-related solvents.

[0028] FIG. 10 is a graph of glycol solvent boiling point vs. average vaporization rates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] As referred to and described herein, the term glycol refers to organic compounds with two hydroxyl (OH) groups attached to different carbon atoms of a molecular chain, including glycerol that contains 3 hydroxyl groups. Furthermore, as referred to and described herein, the term glycol-related compounds are organic compounds that may have a similar chemical structure to glycols where one or more of the hydroxyl groups have been transformed or modified (e.g. glycol ether, glycol ester, or glycol acetate) with one of an ether group (an oxygen atom connected to two alkyl or aryl groups), an ester group (a hydroxyl group modified to become an oxygen-alkyl group), or acetyl group.

[0030] Referring now to the drawings, there is illustrated in FIGS. 1-3 an insect repeller, shown generally at 10. The repeller 10 is presented as an example of an insect repellent dispenser utilizing a repellent formulation in accordance with the invention and may be configured in other forms. The repeller 10 includes a base 12 that locates and supports a repellent reservoir 14 and a power source 16, configured as a rechargeable battery, capable of powering a heating element 18. In one embodiment, the heating element may be a cylindrical heating element having a power output of about 3-4 Watts. The heating element 18 may be supported within a cover 20, though the heating element may also be supported on the base 12 or as part of a separate housing structure (not shown). The cover 20 may provide electrical contact between the battery 16 and the heating element 18. In one embodiment, the base and cover may be formed from a thermoplastic such as Acrylonitrile Butadiene Styrene (ABS) plastic.

[0031] The repellent reservoir 14 includes a fluid containment vessel portion or bottle 22. In one embodiment, the bottle 22 is formed from a thermoplastic such as polycarbonate. The reservoir 14 includes a top portion 24 that supports a wick 26 and a sealing structure 28, configured in one embodiment as a nitrile O-ring. The chemical compatibility of the various structural component materials with the repellent formulation, and fluid uptake compatibility of the formulation with the wick structure are influential in developing a commercially viable and efficacious insect repeller device. The wick 26 may be configured as a fibrous, capillary structure formed from natural or artificial fibers or formed from composite or ceramic materials including sintered materials. Typical wicks used in testing the various formula embodiments were of composite construction, including ingredients such as polyethylene terephthalate, acrylic compounds, or ceramics. In one embodiment, the porosity of the wick may be in a range of 40 to 70% and density from 0.40 to 0.80 mg/mm.sup.3. In another embodiment, the wick porosity may be in a range of 50-60% and have a density of 0.55-0.65 mg/mm.sup.3. The influence of wick characteristics is balanced with the viscosity of the glycol, solubility of active ingredient in the selected glycol solvent, and the concentration of active ingredient. These factors are balanced with the level of heat output to provide a formulation that enables it to travel through the pores in the wick and vaporize at a rate to create a concentration of active ingredient sufficient to repel mosquitoes.

[0032] As shown in FIG. 1, the exposed area of the wick 26 is positioned proximate to and generally within the heater 18. As heat is applied to a wick end 26a proximate to the heater, the formula contained in that area is volatized and the active ingredient emitted into the surrounding area. As the material leaves the wick, a pressure differential created by exiting material permits the capillary action to draw more fluid up towards the wick proximate end. The amount of heat radiant energy available to volatize the formula is an influential factor, particularly in the context of a portable insect repeller device. In order to create a commercially-viable, portable repeller device, unit size, battery charge life, and heater output are designed in consideration of the formulation properties. Because of demonstrated effectiveness and regulatory acceptance, synthetic pyrethroids such as, for example, metofluthrin and transfluthrin are good candidates for the repellent portion of the formula. Alternatively, other synthetic or natural repellent materials may be used. For example, natural repellent materials such as Lemon eucalyptus oil, Lavender, Cinnamon oil, Thyme oil, Greek catmint oil, Soybean oil, Citronella, Tea tree oil, Geraniol, or Neem oil may be used.

[0033] Through significant research and testing, as evidenced in the tables of FIGS. 2-9, the inventors have found that certain glycol solvents are compatible with insect repellent active ingredients, such as metofluthrin, to volatilize a spatial insect repellent formula within a heat range sufficient for low voltage battery operation and be compatible with various materials of the device 10. In one embodiment, a target temperature range of 60? C. -140? ? C. provides sufficient volatilization of metofluthrin. In one embodiment, the low voltage battery is a lithium ion battery, though any battery energy storage unit may be used and remain within the scope of the invention. In one configuration, the lithium ion battery may be sized in a range of about 2900 mAh to about 3200 mAh though larger or smaller battery sizes or multiple batteries may be used. In this configuration, the battery may have a charge capacity based on an electrical input source of about 5 volts DC and about 1000 mA. A heater associated with the battery and configured to volatize the active ingredient and glycol mix may draw in a range of 3-4 Watts of power. Such a battery may deliver a usage time, before requiring recharging, of up to 6 hours, which is an appropriate time frame for an evening of mosquito protection.

[0034] In the development of active ingredient and solvent formulations, glycols, like glycol-related solvents, have physical and chemical characteristics that would not be considered an aspiration hazard. Evaluations of a range of glycol and modified glycol solvents also involved consideration of a variety of materials in contact with these solvents. A glycol ether, dipropylene glycol propyl ether, was found to be incompatible with certain device materials, such as ABS plastics. Another tested solvent was a variation on glycerol, isopropylidene glycerol, which was also incompatible with ABS plastic. As shown in the tables of FIGS. 8 and 9, unmodified glycols were considered to be preferred solvent candidates related to device compatibility. In addition to considerations of the device, solubility of the active ingredients is a significant consideration on several levels. Some of the glycol solvents, such as ethylene glycol and propylene glycol, were not good solvents for some of the insect repellents, particularly prallethrin as shown in FIG. 6. Considerations of not only the solvent material but the concentration levels of particular active ingredients ae necessary to create an efficacious formula compatible with heated repeller devices. Some repellents, such as transfluthrin, were found to require higher concentration percentages in the formula, as much as 27%, to be effective outdoors. Incorporating active ingredients at such high levels creates additional solubility challenges which further reduces suitable active ingredient candidates.

[0035] Once candidate materials are identified, considerations of whether release rates relative to the selected glycols would be sufficient to deliver good spatial mosquito repellency. In certain test conditions glycerol and tetraethylene glycol have limited release rate capacity relative to metofluthrin and transfluthrin, though may be considered for other pyrethroids. In a preferred embodiment, a formulation of hexylene glycol and dipropylene glycol in combination with metofluthrin provides desired release rates and spatial efficacy for insect repellency outdoors. In this embodiment, the combination of the two glycol solvents to obtain a target release rate ameliorated the observed individual conditions where hexylene glycol by itself volatized too fast and dipropylene glycol was too slow. In one embodiment, an approximate 70:30 solvent ratio of two solvents is provided. In another aspect, the solvent ratio may be a ratio range such as 60-70:40-30, or 65-70:35-30, wherein the sum of specific glycol amounts totals to 100. In a preferred embodiment, summarized below, an approximate ratio of a 66 weight percent Hexylene glycol and 28% weight percent Dipropylene glycol mixed with a 5.5% weight percent of metofluthrin provided desired repellency results.

TABLE-US-00001 Ingredient Weight percent Metofluthrin (96.65%) 5.69 (5.5%) Hexylene glycol 66.02 Dipropylene glycol 28.29

[0036] The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.