The present invention relates to vertically disposed, rope-like structures that are ignitable from their top to dispense desired volatile materials, including, by way of example only, insect control actives such as insect repellents.
The fact that certain combustible materials can be ignited and will then disperse an active ingredient as they continue to smolder is well known. Incense sticks and mosquito coils are examples of products made from such materials. See e.g. U.S. Pat. Nos. 4,959,925 and 5,657,574. The disclosure of these publications and of all other publications referred to herein are incorporated by reference as if fully set forth herein.
The term "fumigant" herein means a burnable material that releases a volatile ingredient as the material burns, and preferably as it slowly smolders. A "volatile material" or "volatile ingredient," in that context, means any material that can be released by a burning fumigant including, by way of example only, fragrances, disinfectants, and insect control actives. The term "active" refers to a volatile material to be released in order to achieve the desired effect of the fumigant. For a fumigant intended to repel mosquitoes, for example, an insect repellant would be an "active." An "insect control active" is an active that repels, kills, or desirably modifies the behavior of insects. "Insects" herein means actual insects, as well as other small animals commonly controlled in conjunction with insects, such as spiders and the like.
While conventional fumigants in the form of mosquito coils or repellent sticks are fairly inexpensive, they are often used in large quantity (e.g. thirty or so a month may be needed to control mosquitoes on an overnight basis). Further, these coils are most often used in countries having average annual income levels that are very low. In order to make such products more widely available, their cost must be reduced still further. This is particularly important in controlling the spread of malaria and certain other insect-borne diseases.
There have been attempts to reduce the cost of mosquito protection by burning widely available, very inexpensive, smoke-producing materials that are used without any insecticide. However, efforts to control mosquitoes by burning materials of this type, such as by burning cow dung, are not very effective and can have other undesirable characteristics, such as excessive odor.
Academic researchers in India have proposed the use of jute rope that has been impregnated with a mosquito repellant as a fumigant. This approach uses a relatively limp impregnated rope suspended from a hanger, which is lit on its lower end and permitted to smolder overnight. See M. Ansari et al., 31 Indian J. Malariology 57-64 (1994); M. Ansari et al., 29 Indian J. Malariology 203-210 (1992); and V. Sharma et al., 26 Indian J. Malariology 179-185 (1989).
Unfortunately, this technique produces inconsistent results as burning rates can not be precisely controlled and, especially, can be too rapid. Also, there is some fire risk if the characteristics of the rope are not carefully controlled. For example, fire can flash up the rope, contacting structures from which the rope has been hung. Metal mesh fire guards have been shown to attempt to control this risk. Further, a portion of the rope is sometimes wasted near its upper end, as contact with the suspension device snuffs the rope.
Wax candles, having conventional fiber wicks surrounded by wax, are of course also well known. They are sometimes supported in a hollow core of a corkscrew-like wire, positioned on a flat surface. Some such candles have insect repellent (such as citronella) incorporated in the wax. However, such designs require the use of relatively expensive candle wax.
Thus, there is still a need for improved fumigants, particularly those that can dispense insecticide or insect repellent at extremely low cost.