Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Biocides; animal or insect repellents or attractants
Reexamination Certificate
1999-11-10
2002-05-14
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
C424S409000, C424S417000, C427S213310
Reexamination Certificate
active
06387385
ABSTRACT:
The present invention relates to improved formulations of solid chemical agents. In particular, the invention relates to encapsulated or capsule suspension (CS) formulations of particles of solid chemical agent compositions, such as pesticides, and more particularly it pertains to the coating of solid particles with polymer film(s) in an aqueous environment.
It is known that solid materials can be microencapsulated by solvent evaporation, solvent extraction, coacervation, in-situ polymerization, and spray-drying. However, these microencapsulation processes tend to involve either the use of organic solvents which are often toxic or hazardous to either the environment or the personnel involved, or the processes are complicated and difficult to apply on a commercial scale. As a result, there are but a few methods by which solid insoluble chemical agents can be safely and efficiently microencapsulated.
The present invention provides encapsulating techniques that are water-based and hence economical and environmentally friendly. By avoiding organic solvents, the costs and dangers of recycling such materials are avoided. The method can be conducted in relatively simple equipment using relatively simple process steps.
A surprising observation is that encapsulation can be conducted with an encapsulating agent that can be transformed into an insoluble form and which, in the insoluble form, can coat the solid material. Further, the process of encapsulation can unexpectedly be conducted in an aqueous suspension without agglomerating the particles of solid material.
SUMMARY OF THE INVENTION
The present invention relates to encapsulated or capsule suspension (CS) formulations of chemical agents that are coated with a first encapsulating agent and then optionally double-coated with a second encapsulating agent. The particles of the encapsulated formulation preferably have a particle size from about 1 &mgr;m to about 100 &mgr;m; more preferably from about 1 &mgr;m to about 30 &mgr;m. The compositions of the present invention are of the type commonly referred to by skilled artesians as microencapsulated.
The present invention also relates to methods for preparing the formulations of chemical agents. The method of the invention involves encapsulation of chemical agents according to the following steps: (a) providing a dispersion or suspension, in an aqueous solvent, of particles of a chemical agent (such as a bioactive agent), a water-soluble or water dispersible first encapsulating agent, which also has wetting agent characteristics, and optionally an antifoam agent; (b) converting the first encapsulating agent to an encapsulating polymer that coagulates or precipitates from the aqueous solvent on and around the particles of the chemical agent, thereby forming encapsulated particles of the chemical agent.
In preferred embodiments, the encapsulated particles remain in suspension. The process can involve a step (c) of reacting the precipitated encapsulating polymer with a first curing agent. Certain embodiments involve the further steps of (d) optionally agitating the dispersion while adding to it, either neat or in an aqueous solution or dispersion, a second encapsulating agent and; (e) optionally curing the second encapsulating agent by raising the temperature. In one embodiment, all of the above steps are carried out with the particles suspended in the aqueous solvent.
The process has two particularly preferred embodiments. Where the first encapsulating agent is a polymer, the converting step (b) comprises changing the pH of the aqueous solvent to precipitate the polymer. Where the first encapsulating agent comprises dispersible oligomers or dispersible polymers, the converting step (b) comprises forming the precipitated polymer from the first encapsulating agent.
In one particular embodiment where pH change is used in the converting step, the first encapsulating agent is a polymer having pendant functional groups derived from carboxylic acid anhydride functional groups, for example, an ammonium salt of a carboxamic acid. In this embodiment, derivatives of copolymers of styrene and maleic anhydride are particularly useful.
In another particular embodiment where converting involves forming the precipitated polymer, the first encapsulating agent is a water-dispersible polyisocyanate or a polymerizable oligomer of a suitable resin such as the oligomers that result from partial condensation of formaldehyde with, for example, phenol, urea, or melamine.
The encapsulated particles are, optionally, further treated with heat alone or heat in combination with a curing agent, of which calcium lignosulphate is but one example. In some embodiments, the encapsulated particles are subjected to a second encapsulation procedure in which the encapsulating agent is the same as or different from the encapsulating agent used in the first encapsulation. When two encapsulation procedures are carried out, the conversion in the second procedure is advantageously effected by forming the encapsulating polymer from the encapsulating agent.
DEFINITIONS
Aqueous solvent: is water or a mixture of water and an organic solvent that is freely miscible with water. Ethanol is but one example of an organic solvent that can be mixed with water to form an aqueous solvent. Preferably, water comprises at least about 50% v/v, more preferably about 95% v/v, of the aqueous solvent.
Average particle size shall mean that at least about 50% of the particles shall have a diameter within ±5% of the diameter cited, where diameter is measured by light scattering using an instrument, such as a Laser Scattering Particle Size Distribution Analyser, Horiba Instrument Corp., Irvine, Calif.
Bioactive agent: is a substance such as a chemical that can act on a cell, virus, organ or organism, including but not limited to drugs (i.e. pharmaceuticals) and pesticides, to create a change in the functioning of the cell, virus, organ or organism. In one embodiment of the invention, the method of the invention is applied to bioactive agents that are organic molecules having molecular weight of about 500 or less or to polymeric species such as proteins, nucleic acids, and the like. A “pesticide” is a molecule or combination of molecules that repels, retards, or kills pests, such as, but not limited to, deleterious or annoying insects, weeds, worms, fungi, bacteria, and the like, and can be used for crop protection, edifice protection, turf protection, or protection of a person; pesticide as used herein also refers to growth regulators, either used to encourage growth of a desired plant species or retard growth of an undesired pest.
Chemical agent: is an organic or inorganic compound, such as a compound to be used as a reactant in a synthetic or preparative process, as a reagent in an analytical method, a dye, a bioactive agent, and the like.
Encapsulating effective amount: is an amount of encapsulating agent which, used in a method of the present invention, is sufficient to form a coating on or admixture with at least 90% of the particles of chemical agent, where the coating or admixture is a functional amount.
Encapsulating agent: is a monomeric, oligomeric, or polymeric substance soluble or dispersible in an aqueous solvent under at least one set of conditions and which can be converted to an insoluble form by appropriate changes in process conditions or chemical form. Upon such conversion, an encapsulating agent forms a coating on or intimate solid admixture with particles dispersed or suspended in the aqueous solvent in which the encapsulating agent is dissolved.
Functional amount: is an amount of an encapsulant which, for example, slows release of the encapsulated agent, reduces the toxicity of the agent to mammals, stabilizes the form of the agent, inhibits crystallization of the agent, reduces the volatility of the agent, or produces any other benefit of coating a chemical agent with a polymer or admixing the chemical agent with the polymer.
Microparticles: are particles of chemical agent having average diameter from about 1 &mgr;m to about 100
FMC Corporation
FMC Corporation
Levy Neil S.
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