Solvent for active ingredients in insect repellents and insect repellent system using the same

Abstract

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

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 171,316, filed on April 6, 2021, the disclosure of which is incorporated herein by reference.

[0002] The present invention relates generally to spatially dispersed insect repellents, and more particularly to solvent media for promoting the dispersion of insect repellent active ingredients.

Background Art

[0003] Space mosquito repellents, which are airborne chemicals that kill or repel mosquitoes in a proscribed area, are often preferred over rubbing a mosquito repellent on human skin. The most common way to create a concentration of the mosquito repellent in the air is by the use of energy, most often thermal energy. The heat can be generated chemically or electrically. Electric heat can be obtained using electricity from a cord plugged into a socket or from a battery. The amount of heat generated by a battery results in power consumption that affects the battery life. More heat requires more power consumption, resulting in a shortened battery life. For a space repellent to be useful, the battery needs to last long enough to protect the user over the time spent outdoors where mosquitoes are present. Thus, the temperature achieved with a battery - powered device is necessarily lower than that of a corded device plugged into a power source.

[0004] Space repellents are available in various forms. Many, such as mosquito coils and paper mats, are made for single use. Another form, the liquid evaporator, includes a liquid reservoir and a wick from which the liquid is drawn and evaporated at the tip. In this design, the refill period is primarily limited by the volume of liquid contained. Typically, the liquid in the formulation contains the active ingredient and the petroleum distillate used to dissolve that ingredient. One problem with such formulations is that if a child accidentally ingests and inhales part of the liquid, the petroleum distillate can cause chemical pneumonia. Many hydrocarbons and petroleum distillates are considered aspiration hazards. Therefore, there is a need for safer solvents that are compatible with the insect repellent active ingredients and refill container materials. On the other hand, glycol solvents have chemical and physical properties that do not meet the criteria for aspiration hazard.

[0005] Products combining a hydrocarbon solvent containing an insect repellent with a wick to create a mosquito spatial repellent are known in the art. However, the aspiration hazard of such products requires warnings on the label and child-resistant packaging in several jurisdictions. U.S. Patent No. 10,485,228 teaches the use of an aqueous formulation incorporating glycol ether in the formulation as an alternative to hydrocarbon formulations. This formulation requires water, glycol ether, and an active ingredient at a concentration of 0.1% to 3.0% to reliably distribute the formulation. As described in Patent No. 228, such low active ingredient concentrations have a "practical effect in indoor spaces such as living rooms, lounges, and bedrooms...". However, to achieve a greater spatial repellent effect in outdoor settings, higher levels of active ingredient are required to overcome outdoor environmental factors such as wind and generally the lack of spatial enclosure. In aqueous formulations, the ratio of active ingredient to solvent is limited, which can reduce dispersibility and increase volatilization heat input. [Overview of the Initiative]

[0006] As discovered by the inventors, using glycol as the solvent, rather than glycol ether or other related glycol-based solvents, enables a higher percentage of the active ingredient dispersibility, demonstrated to be as high as 27% or more, and resolves certain other problems such as material compatibility presented by glycol ether and aspiration hazards caused by hydrocarbon solvents. Higher ingredient percentages may be close to 40%.

[0007] The insect repellent system comprises a heating element, a storage section, and a wick. The storage section contains a mixture of an active insect repellent component and a glycol solvent. The wick has a proximal end extending into the heating element and a distal end extending into the mixture. In certain embodiments, the active insect repellent component is a pyrethroid insecticide or a combination of pyrethroids (e.g., metofluthrin and prallethrin). In certain aspects of these embodiments, the pyrethroid insecticide may preferably be one of metofluthrin or transfluthrin. In other embodiments, the active insect repellent component is a natural insect repellent such as at least one of lemon eucalyptus oil, lavender, cinnamon oil, thyme oil, Greek catmint oil, soybean oil, citronella, tea oil, geraniol, or neem oil.

[0008] The glycol solvent in various embodiments of the insect repellent system may be one of the following solvents: ethylene glycol, propylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, or tetraethylene glycol. In combination with a pyrethroid insecticide, in certain embodiments, 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 lower boiling point than the second glycol solvent. When the glycol solvent is a mixture of the first and second solvents, one embodiment of the glycol mixture may be a mixture of hexylene glycol and dipropylene glycol. In one aspect of this embodiment, the ratio of hexylene glycol to dipropylene glycol may be about 70% to about 30%. In certain embodiments of the embodiment having a mixture of hexylene glycol solvent and dipropylene glycol solvent, the ratio may be formulated as a hexylene glycol to dipropylene glycol ratio within the range of 65–70 percent hexylene glycol to 35–30 percent dipropylene glycol. Alternatively, the ratio could range from 60–70 percent hexylene glycol to 40–30 percent dipropylene glycol.

[0009] In certain embodiments of the insect repellent system, the device is configured as a battery-powered portable insect repellent system. The heating element may have a power output in the range of about 3 watts to about 4 watts, and the battery may have a charging capacity of about 2900 mAh to about 3200 mAh. In certain other embodiments, the heating element generates a temperature output in a range sufficient for low-voltage battery operation, which may be in the range of about 60 degrees Celsius to about 140 degrees Celsius.

[0010] In any embodiment of the insect repellent system described herein, the housing and the storage section may be formed from a thermoplastic material. In one embodiment, the thermoplastic material of the housing is acrylonitrile butadiene styrene (ABS) plastic, and a portion of the storage section is formed from polycarbonate plastic. The storage section may further include sealing elements such as a nitrile rubber seal that engages a core, which may be configured as an O-ring.

[0011] The present invention relates to a solvent that dissolves insect repellents, enabling the dispersion of insect repellent active ingredients, such as pyrethroids including d-allethrin, prallethrin, transfluthrin, and metofluthrin, natural oils and other natural components, saltidine, and para-menthane-3,8-diol, and reducing temperature requirements. In one embodiment, a glycol-based solvent was found to be compatible with insect repellent active ingredients such as metofluthrin and to volatilize the spatial insect repellent formulation within a sufficient thermal range for low-voltage battery operation, which may be in the range of 60 to 140°C. In one embodiment, the low-voltage battery is a lithium-ion battery, but any battery energy storage unit may be used without departing from the scope of the present invention. In one configuration, the lithium-ion battery may be in the range of about 2900 mAh to about 3200 mAh, but larger or smaller battery sizes, or multiple batteries, may be used. In this configuration, the battery may have a charging capacity based on a power source of about 5 volts DC and about 1000 mA. The heater, which is attached to the battery and configured to vaporize a mixture of the active ingredient and glycol, can consume power in the range of 3-4 watts. Such a battery can provide up to 6 hours of use before needing to be recharged, which is a suitable timeframe for one mosquito-repellent treatment per night.

[0012] These insect repellent products can protect humans and their pets from a variety of biting insects, including mosquitoes from the Culicidae family, black flies from the Simulidae family, sandflies from the Psychodidae family, midges from the Ceratopogonidae family, and other problematic flying or crawling arthropods.

[0013] While metofluthrin alone may be volatile at room temperature, the action of the delivery system affects the concentration of the substance that can be effectively delivered. Therefore, a specific formulation is a product of the surface area of ​​the delivery device and the temperature of the substance. If a sufficiently large surface area can be provided, enough metofluthrin can be delivered into the air to repel and, in some cases, kill mosquitoes. However, such a surface area requirement results in an unwieldy and impractical delivery system. For smaller substrates, some form of energy input is required to deliver an effective amount of the active ingredient to repel insects such as mosquitoes. The energy input can be in the form of forced airflow, heat, or a combination of both. To provide a suitable package size that is inconspicuous but effective, the distribution device features a wick preferably in the size range of about 2 mm to about 8 mm in diameter, more preferably about 5 mm in size. Such a wick slowly draws the liquid formulation to its tip, where the wick is heated, releasing the active ingredient into the air in the form of vapor and small particles, a state referred to as volatilization. The exposed surface area of ​​the wick located in close proximity to the heater and the capillary action (porosity) of the wick material contribute to the rate of volatilization of the substance into the surroundings. In one embodiment, the wick is sized to provide metofluthrin or other repellent in an amount that is sufficient to minimize or eliminate insects, particularly mosquitoes, within an area of ​​about 15 to 25 feet in diameter and within a specific range of about 20 feet in diameter, at an active ingredient level of up to 27%. Such a combination of metofluthrin and a glycol solvent can volatilize to create an insect-free (or insect-reduced) space with the aforementioned lithium-ion battery life of about 6 hours.

[0014] The inventors have found that the use of glycol as a solvent for metofluthrin is compatible with the heating element described above to provide an effective amount of metofluthrin to create a 20-foot mosquito-repellent zone. The inventors have also found that certain glycol solvents are more effective solubilizers for insect repellent active ingredients. While not bound by theory, the effectiveness of certain glycol solvents may be based in part on chemical polarity and lower molecular weight. Glycol formulations suitable for dissolving active ingredients can rise up the wick and evaporate when heated at the tip of the wick. These glycol formulations combine these multiple properties to act in the product. For example, for the purpose of dissolving typical active ingredients such as pyrethroid insecticides (which can also function as insect repellents), the glycol formulations tested may provide a molecular weight and chemical polarity or other chemical / physical properties sufficient to dissolve the substance and allow volatilization within the target heat output limit. The typical active ingredient concentration required to provide sufficient mosquito repellency outdoors can vary from 4% metofluthrin to 27% transfluthrin in different embodiments.

[0015] The properties of the core limit the viscosity of the glycol, which allows the glycol to move through the core's pores at a rate sufficient to release the active ingredient at a rate adequate to repel mosquitoes. Therefore, the properties of the core and the solvent mutually influence each other. Typical cores used in testing these formulations were composite structures containing components such as polyethylene terephthalate or acrylic compounds, or ceramic structures. The core porosity was in the range of 40-70%, and the density was 0.40-0.80 mg / mm³. 3 It may be within this range. The tested glycol exhibits a vapor pressure high enough to evaporate at the tip of the wick, which is subjected to the relatively low battery heat generated by the device, or a boiling point low enough to evaporate. In certain embodiments, the glycol combination may provide the properties necessary to yield the desired active ingredient release rate. In one embodiment, a 70:30 combination of hexylene glycol and dipropylene glycol yields 0.45-0.55 mg / mm³ 3It is effective in releasing the active ingredient at an effective rate through the core of the density.

[0016] A further constraint on solvent selection is the interaction between the solvent and the bottle and heater components. For example, glycol ethers have been found to be incompatible with acrylonitrile butadiene styrene, polycarbonate, and nitrile materials, which are typically used in these products. Certain glycols exhibited incompatibility with the composite core, narrowing the list of acceptable solvents, although this can be mitigated by combining them with non-reactive glycols.

[0017] Therefore, glycol solvents provide the dissolving power to incorporate insect repellent components at a higher level, particularly to improve the effectiveness of the product and enable effective use of the product for mosquito repellent outdoors without creating aspiration hazards. Several factors in selecting a glycol solvent or solvent combination, including dissolving power, appropriate release rate through the wick, device temperature requirements, and compatibility with the refill structure and device components, interact with each other. A specific glycol, or a glycol combination such as a 70:30 combination of hexylene glycol and dipropylene glycol, must satisfy each of these test categories.

[0018] Various aspects of the present invention will become apparent to those skilled in the art by reading the following detailed description of preferred embodiments in reference to the accompanying drawings. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a cross-sectional view of a dispensing device using an insect repellent solution according to the present invention. [Figure 2] Figure 2 is an exploded view of the distribution device shown in Figure 1. [Figure 3] Figure 3 is an enlarged view of the heating element located near the core position of the distribution device in Figure 1. [Figure 4]Figure 4 is a table of test data showing the physical and chemical properties of the glycol solvents tested. The test data shows the compatibility of the dispensing device with the glycol solvents listed. [Figure 5] Figure 5 is a table of test data showing the physical and chemical properties of the glycol-related solvents and glycol ether solvents tested. [Figure 6] Figure 6 is a table of test data showing the solubility of the selected pyrethroid active ingredients in glycol solvents. [Figure 7] Figure 7 is a table of test data showing the solubility of the selected pyrethroid active ingredients in glycol-related solvents. [Figure 8] Figure 8 is a table of test data showing the compatibility and evaporation rate of a dispensing device using glycol solvents. [Figure 9] Figure 9 is a table of test data showing the compatibility and evaporation rate of a dispensing device using glycol-related solvents. [Figure 10] Figure 10 is a graph of the boiling point versus the average evaporation rate of glycol solvents.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] As referred to and described herein, the term "glycol" means an organic compound having two hydroxyl (-OH) groups bonded to different carbon atoms in the molecular chain, including glycerol which contains three hydroxyl groups. Further, as referred to and described herein, the term "glycol-related" compounds are organic compounds that may have a chemical structure similar to glycols, where in this case, one or more of the hydroxyl groups are converted or modified by one of an ether group (an oxygen atom connected to two alkyl or aryl groups), an ester group (where the hydroxyl group is modified to an oxygen-alkyl group), or an acetyl group (e.g., glycol ether, glycol ester, or glycol acetate).

[0021] Next, referring to the drawings, Figures 1 to 3 show an insect repellent device, collectively designated 10. The repellent device 10 is presented as an example of an insect repellent dispensing device using a repellent formulation according to the present invention, and may be configured in other forms. The repellent device 10 includes a base 12 that houses and supports a repellent storage unit 14 and a power supply 16, which is configured as a rechargeable battery and can supply power to a heating element 18. In one embodiment, the heating element may be a cylindrical heating element having a power output of about 3 to 4 watts. The heating element 18 may be supported within a cover 20, but the heating element may be supported on the base 12 or may be part of a separate housing structure (not shown). The cover 20 can 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 plastic such as acrylonitrile butadiene styrene (ABS) plastic.

[0022] The repellent storage section 14 includes a fluid storage container portion or a bottle 22. In one embodiment, the bottle 22 is formed from a thermoplastic such as polycarbonate. The storage section 14 includes an upper portion 24 that supports a core 26 and a sealing structure 28, which in one embodiment is configured as a nitrile O-ring. The chemical compatibility of various structural component materials with the repellent formulation, and the fluid intake compatibility of the formulation with the core structure, influence the development of a commercially viable and effective insect repellent device. The core 26 may be configured as a fibrous capillary structure formed from natural or artificial fibers, or from a composite or ceramic material containing sintered materials. Typical cores used in testing various formulation embodiments were composite cores containing components such as polyethylene terephthalate, acrylic compounds, or ceramics. In one embodiment, the porosity of the core is in the range of 40-70%, and the density is 0.40-0.80 mg / mm³. 3 It may be within the range of . In another embodiment, the porosity of the core may be in the range of 50-60%, and 0.55-0.65 mg / mm 3It may have a density of . The influence of the core properties is balanced with the viscosity of the glycol, the solubility of the active ingredient in the selected glycol solvent, and the concentration of the active ingredient. These factors are balanced with the level of thermal output to obtain a formulation that can evaporate at a rate sufficient to move through the pores of the core and create an active ingredient concentration sufficient to repel mosquitoes.

[0023] As shown in Figure 1, the exposed region of the wick 26 is located in close proximity to the heater 18, and is generally situated within it. As heat is applied to the wick end 26a adjacent to the heater, the formulation contained in that region is volatilized, and the active ingredient is released into the surrounding region. As the substance is released from the wick, the pressure difference created by the released substance allows capillary action to draw further fluid towards the adjacent end of the wick. The amount of thermal radiation energy available to volatilize the formulation is an influential factor, particularly in the context of portable insect repellent devices. To create a commercially viable portable repellent device, the unit size, battery charge life, and heater output are designed taking into account the formulation characteristics. For reasons of demonstrated efficacy and regulatory acceptance, synthetic pyrethroids such as metofluthrin and transfluthrin are good candidates for the repellent portion of the formulation. As an alternative, other synthetic or natural repellents may be used. For example, natural repellents such as lemon eucalyptus oil, lavender, cinnamon oil, thyme oil, Greek catmint oil, soybean oil, citronella, tea plant oil, geraniol, or neem oil may be used.

[0024] Through extensive research and testing, as supported by the tables in Figures 2 to 9, the inventors have found that certain glycol solvents are compatible with insect repellent active ingredients such as metofluthrin, volatilize spatial insect repellent formulations within a sufficient thermal range during low-voltage battery operation, and are compatible with various materials of device 10. In one embodiment, a target temperature range of 60°C to 140°C provides sufficient volatilization of metofluthrin. In one embodiment, the low-voltage battery is a lithium-ion battery, but any battery energy storage unit may be used without departing from the scope of the invention. In one configuration, the lithium-ion battery may be in the size range of about 2900mAh to about 3200mAh, but larger or smaller battery sizes, or multiple batteries, may be used. In this configuration, the battery may have a charging capacity based on a power source of about 5 volts DC and about 1000mA. The heater, which is attached to the battery and configured to vaporize a mixture of the active ingredient and glycol, can consume power in the range of 3-4 watts. Such a battery can provide up to 6 hours of use before needing to be recharged, which is a suitable timeframe for one mosquito-repellent treatment per night.

[0025] In the development of formulations of active ingredients and solvents, glycols, such as glycol-related solvents, possess physical and chemical properties that do not pose aspiration hazards. The evaluation of various glycols and modified glycol solvents included consideration of the various substances that come into contact with these solvents. Dipropylene glycol propyl ether, a glycol ether, was found to be incompatible with certain device materials, such as ABS plastics. Another solvent tested, isopropylideneglycerol, a modification of glycerol, also showed incompatibility with ABS plastics. As shown in the tables in Figures 8 and 9, unmodified glycols were considered preferred solvent candidates in relation to device compatibility. In addition to device considerations, the solubility of the active ingredient is also an important consideration at several levels. Some glycol solvents, such as ethylene glycol and propylene glycol, were not good solvents for certain insect repellents, particularly for prallethrin, as shown in Figure 6. Consideration of the concentration level of the specific active ingredient, as well as the solvent substance, is necessary to create effective formulations compatible with heated repellent devices. Some repellents, such as transfluthrin, have been found to require higher concentrations of up to 27% in their formulations to be effective outdoors. Incorporating active ingredients at such high levels presents further solubility challenges, which further reduces the number of suitable active ingredient candidates.

[0026] Once candidate substances are identified, consideration is given to whether the release rate for the selected glycol is sufficient to provide good spatial mosquito repellent. Under certain test conditions, glycerol and tetraethylene glycol had limited release rate capabilities for metofluthrin and transfluthrin, but can be considered for other pyrethroids. In a preferred embodiment, formulations combining hexylene glycol and dipropylene glycol with metofluthrin provide the desired release rate and spatial effect for outdoor insect repellent. In this embodiment, the combination of the two glycol solvents to obtain the target release rate improved the observed individual conditions that hexylene glycol alone volatilized too quickly and dipropylene glycol volatilized too slowly. In one embodiment, a solvent ratio of approximately 70:30 of the two solvents is provided. In another embodiment, the solvent ratio may be in the range of 60-70:40-30 or 65-70:35-30, with a total specific glycol amount of 100. In a preferred embodiment outlined below, the desired repellency was obtained by mixing approximately 66 weight percent hexylene glycol and 28 weight percent dipropylene glycol with 5.5 weight percent metofluthrin.

[0027] [Table 1]

[0028] The principles and modes of operation of the present invention have been described and demonstrated in preferred embodiments. However, it should be understood that the present invention may be put into practice in a manner different from what has been specifically described and demonstrated, without departing from its spirit or scope.

Claims

1. heating element, A storage section containing a mixture of an effective insect repellent component and a glycol solvent, and A core having a proximal end extending into the heating element and a distal end extending into the mixture, Equipped with, The effective insect repellent component is one of metofluthrin or transfluthrin. The glycol solvent is a mixture of hexylene glycol and dipropylene glycol. Insect repellent system.

2. The insect repellent system according to claim 1, wherein the ratio of hexylene glycol to dipropylene glycol is within the range of 65 to 70 percent hexylene glycol to 35 to 30 percent dipropylene glycol.

3. The insect repellent system according to claim 1, wherein the ratio of hexylene glycol to dipropylene glycol is within the range of 60 to 70 percent hexylene glycol to 40 to 30 percent dipropylene glycol.

4. The insect repellent system according to claim 1, configured as a battery-powered portable insect repellent system, wherein the heating element has a power output in the range of 3 watts to 4 watts, and the battery has a charging capacity of 2900 mAh to 3200 mAh.

5. The insect repellent system according to claim 1, wherein the housing and the storage section are formed from a thermoplastic material.

6. The insect repellent system according to claim 5, wherein the thermoplastic material of the housing is acrylonitrile butadiene styrene (ABS) plastic, and a portion of the storage section is formed from polycarbonate plastic.

7. The insect repellent system according to claim 5, wherein the storage section includes a sealing element for engaging the core.

8. The insect repellent system according to claim 7, wherein the sealing element is a nitrile seal or a nitrile O-ring.

9. The insect repellent system according to claim 1, wherein the housing supports the heating element and is formed from acrylonitrile butadiene styrene (ABS) plastic, and a portion of the storage section is formed from polycarbonate plastic.

10. The insect repellent system according to claim 9, wherein the heating element generates a sufficient range of temperature output when operated by a low-voltage battery, which may be in the range of 60 degrees Celsius to 140 degrees Celsius.

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