Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Biocides; animal or insect repellents or attractants
Reexamination Certificate
1999-02-19
2003-01-14
Levy, Neil S. (Department: 1616)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Biocides; animal or insect repellents or attractants
C424S417000, C424S418000, C424S419000, C424S420000, C424S490000, C424S498000, C514S919000
Reexamination Certificate
active
06506397
ABSTRACT:
This invention relates to pest controlling and more particularly to a sustained-release, long-term pest-control microcapsule which is environmentally friendly and non-toxic.
Use of microcapsules containing various active pest-control agents is well known. Several patents disclose such microcapsules, e.g., U.S. Pat. Nos. 3,429,827, 3,577,515, 4,280,833, 4,285,720, 4,417,916, 4,900,551, and 4,936,901. Interfacial polycondensation is often used as the technique to form microcapsules loaded with active pest-control agents, although techniques including complex coacervation and in situ polymerization can also be used. These and other microencapsulation techniques for preparing microcapsules have been described in various review articles.
Microencapsulation
, Thies, C., Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed., Vol. 16, John Wiley, NY, 1995, pp 628-652.
Microcapsule Processing and Technology
, Kondo, A., (edited and revised by J. Wade van Valkenburg), Marcell Dekker, NY, 1979.
Mikrokapseln
, Sliwka, W., Ullmmanns Encyklopadie der technischen chemie, Vol. 16, Verlag Chemie, Weinhein, 1978, pp 675-682.
It is an important object of the invention to provide improved methods and means for pest controlling.
The invention features a sustained-release, long-term pest-control microcapsule which prolongs its potency adaptive to the temperature of the surrounding medium and which is environmentally friendly and nontoxic.
One aspect of this invention relates to a pest-control microcapsule which releases an active pest-control agent at a sustained rate, thereby prolonging the potency of the microcapsule. In general, a microcapsule includes a capsule core and a capsule shell. Historically, it has not been recognized that both the shell and core can provide resistant paths to the mass transfer of active pest-control agent contained in the capsule core. The pest-control microcapsule of the present invention utilizes this new concept, thereby reducing the rate of release of active ingredient distributed to the surrounding medium, thereby extending the length of performance of the capsules in the field, and reducing the cost of pest control as well as the potential for environmental pollution. Furthermore, candidate diluents natural and/or are biodegradable materials compatible with the environment.
The diluent is distributed in the core in such a manner that the active pest-control agent is effectively bound by the diluent and diffuses through the resistant paths formed by the diluent to reach the capsule shell through which it then diffuses. The diluent may form a solid-like, matrix-like or mesh-like structure inside the core and entrap the active ingredient inside such matrix and mesh. The diluent may also simply form a homogeneous solution with the active ingredient (AI) in which the AI and diluent interact (i.e., AI-diluent interaction), thereby slowing release of the AI from the capsule. Accordingly, a formulator can obtain desirable permeability or release rate of the active ingredient by manipulating several factors, such as the amount or percentage of the diluent contained in the capsule core, distribution pattern of the diluent in the core, method of entrapping the active ingredient in the diluent, and other physical properties of the diluent.
The capsule shell separates the core volume material from the surrounding medium, and is arranged to provide additional resistant paths to diffusion of the active ingredient from the capsules. Thus, permeability or release rate of the active ingredient can be manipulated by controlling several features of the shell such as pore size, length, density, tortuosity, pattern of pore distribution, and other physical properties of the material composing the shell.
A pest-control microcapsule can be composed in such a way that the permeability or release rate of the active ingredient depends upon the physical and/or chemical properties and melting point of the diluent and the temperature of the surrounding medium. Lipids such as oils, waxes, fats cholesterol are used as diluents and incorporated into the capsule core through microencapsulation. Most candidate lipids have at least one ester linkage. In general, these lipids have melting points of 80° C.-90° C., but some lipids may be liquids at room temperature. Melting of lipid solids may occur over a wide range of temperature, especially when the diluent consists of a mixture of various lipids with different melting points or when those lipids are solids at or just below room temperature (e.g., 20°-30° C.). When the temperature of the surrounding medium rises near or above the melting point of the lipid, i.e., usually during the season and/or the time of the day with high insect activity or mating, the lipid diluent begins to soften or melt, and the active ingredient previously entrapped by the solid diluent is able-to diffuse from the capsule at a higher rate. However, when the temperature falls below the melting point of the lipid and enough to suppress insect activities, the lipid diluent hardens or solidifies and effectively reduces the release of the active pest-control agent by re-entrapping the agent in the hardening or solidifying lipid.
In general, the lipid has a relatively high boiling point, e.g., higher than 200° C. at atmospheric pressure and, therefore, hardly evaporates. Accordingly, the potency of the pest-control microcapsule can be effectively prolonged adaptive to the temperature of the surrounding medium. It is appreciated that lipids capable of prolonging functionality of the capsules may melt below room temperature. In this case, the lipid-active ingredient interactions alone in the liquid state prolong release of the active ingredient from the capsules. That is, the pest-control microcapsule includes, in its core, a lipid diluent that is capable of dissolving the active pest-control agent in liquid state to form a homogeneous solution at room temperature (20°-30° C.) By mixing such diluent with the active ingredient, a formulator can effectively entrap the active ingredient within the lipid diluent. When using lipid diluents that are solids at the room temperature, the formulator can customize the melting point of the diluent by manipulating the molecular size and chemical structure of the lipid. For example, the melting point of the lipid including oils, waxes, and fats can vary over a wide range of temperature by manipulating the number of ester linkages as well as the number and characteristics of the short-, medium-, and long-chained fatty acids attached to those ester linkages.
Lipids with aforementioned properties can be obtained from a variety of sources, including minerals, plants, and animals, and may be manufactured by chemical synthesis. Such lipids may be used in their natural form or may be treated by mechanical or chemical processes including filtration, purification, distillation, hydrogenation, and selective crystallization. Examples of those lipids include mineral oil, plant oil, animal oil, animal fat, butterfat oil, butter fat, lard, natural wax, beeswax, insect wax, candellila wax, carnauba, hydrogenated tallow or various plant oils, paraffin wax, and the like. Yet other examples of such lipids include monoglyceride, diglyceride, and triglyceride such as tristearin, tripalmitin, and trilaurin, with or without a free fatty acid.
The sustained-release, pest-control microcapsule of the present invention can be composed of biodegradable and nontoxic compounds. The pest-control microcapsule can include in its core a biopesticide (such as pheromones, pyrethroids, insect growth regulators, and insect attractants or repellents) and an inactive, biodegradable and non-toxic lipid diluent (such as oils, waxes, and fats with ester linkages or cholesterol). However, conventional toxic pest-control agents can also be used along with the inactive, biodegradable, and nontoxic lipid diluent.
The pest-control microcapsule of the present invention can have a density lighter than or comparable to that of water. Generally, lipid diluents are lighter than water and,
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