Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-03-29
2003-10-28
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C504S116100, C504S156000, C504S172000, C504S360000, C504S361000, C504S362000
Reexamination Certificate
active
06638994
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an aqueous suspension of particles, said particles comprising an organic active ingredient. A controlled release of the ingredient occurs. The invention is especially suitable for the controlled release of organic agrochemical active ingredients useful in crop sciences, such as pesticides.
Controlled release of an active organic ingredient is of interest in many fields. Depending on the ingredient to be released and its use, different issues may be addressed. Some uses require the ingredient to be released slowly at low concentration. Some uses require the ingredient to be released slowly, or quickly, at high concentrations.
Using a liquid carrier for releasing an active ingredient is of great interest in many fields. The ingredient to be released may be easily spread onto a surface, for example by spraying, injected into a body to be treated, or added into a formulation. For example, spreading emulsions of an organic ingredient in water is known. Spreading or injecting a suspension of particles comprising an active ingredient is also known. The size of an emulsion or of particles may be of great importance to control the exchange of an active ingredient with the object it is supposed to interact with. Usually, the higher the surface area to volume is, the more efficient the carrier is. Controlling the size may also avoid a spreading device such as a nozzle to clog on spraying.
Therefore, both controlling the size of a carrier of an active ingredient and controlling the concentration of the active ingredient may be of great importance, for technical, environmental, or economical reasons.
Especially in crop sciences, slow release of pesticide systems offer several advantages. Firstly, controlled release systems are more economical, as fewer applications to the crop are needed. Secondly, these systems offer safety to the environment by preventing pesticide overuse and subsequent runoff or soil leaching into waterways. Thirdly, they also reduce phytotoxicity to crops where large doses of conventional formulations can be phytotoxic. Controlled release systems also reduce the risk of toxicity to the people applying the pesticide in the fields.
Traditionally, one-phase controlled release pesticidal compositions are prepared, and involve co-melting a pesticide with a suitable polymer, followed by grinding to a desired size. This method suffers many disadvantages, including the requirement of the pesticide to be milled and combined with wetting and dispersing agents to produce a suspension concentrate. Often these formulations are not homogenous and the particle sizes are large, in the order of 10 &mgr;m.
Another technique to produce pesticidal particles is microencapsulation. One method of microencapsulation is via interfacial polymerization. U.K patent GB 2,027,346 describes the encapsulation of insecticides (methomyl and oxamyl) via microencapsulation. Particles of 30-130 &mgr;m are obtained.
Another form of microencapsulation utilizes phase separation where an organic solution of polymer is an encapsulating medium (for encapsulating a hydrophobic active material). Upon addition to a non-solvent the active material is encapsulated by the polymer. U.S. Pat. Nos. 4,282,209 and 4,722,838 describe such a precipitation of an insecticide (methomyl and oxamyl) embedded in a preformed polymer. The latter patent is an improvement on the former, requiring only mild agitation of the organic solvent and water during precipitation. However, 2 parts of the polymer (poly(methyl methacrylate)) to one part of the active are required to form particles of 50 &mgr;m in diameter, and a surfactant is also needed to disperse the particles in the aqueous phase.
U.S. Pat. No. 4,435,383 describes a dispersion of particles obtained by dispersing in water a solid composition comprising a cross-linked polymer and an active ingredient. The size of the particles is greater than 5 &mgr;m.
Nanoparticles of polymers are known. U.S. Pat. No. 5,145,684 describes nanoparticulate compositions consisting of a poorly soluble therapeutic or diagnostic agent with a non-crosslinked surface stabilizer adsorbed on the surface. It is recognized that not all surface stabilizers will produce a stable, non-agglomerated nanoparticulate composition for all agents. Thus, there is a need to identify new surface stabilizers that have superior properties over the known surface stabilizers.
Boehm et al., J. Microencapsulation, 17, 195 (2000) teach pesticidal active ingredients have been formulated by nanoprecipitation with a poly(&egr;-caprolactone) polymer and a surfactant. Nanoparticles of 200-300 nm were formed using at least 1:1 surfactant to active ingredient. Liu et al., Journal of Applied Polymer Science, 79, 458 (2001) describe incorporating the fungicides tebuconazole and chlorothalonil into nanoparticles of 100-250 nm in diameter, using a copolymer polyvinylpyridine-co-styrene and polyvinylpyridine (PVPy). It was found that the delivery of the biocides to wood via a polymer matrix showed improved efficacy compared to being introduced via a solution or liquid-liquid emulsion. However, a high ratio of polymer to active is required (at least 1:1) and surfactants such as Tween 80 are also necessary for stabilization of the nanoparticles.
U.S. Pat. No. 5,766,635 describes nanoparticles comprising a pharmaceutical active ingredient, and a polylactic copolymer. However, the ratio between the active ingredient and the copolymer is low (20% by weight). Such a low amount is not suitable in agrochemical formulations.
U.S. Pat. No. 5,510,118 describes a process for preparing therapeutic compositions containing nanoparticles. The process comprises using various surface modifiers and carrying out an expensive microfluidizing step. Obtained nanoparticles have a size of less than 400 nm, and consist of a solid therapeutic compound having the surface modifier absorbed on their surface.
U.S. Pat. No. 6,074,441 describes a process for producing ultrafine organic crystallization products, for example naphthalene, comprising an expensive atomizing step. The process comprises the use of a high amount of a surfactant (5 g for 0.75 g of a naphthalene chloroform solution).
U.S. Pat. No. 5,118,528 describes a process for making nanoparticles comprising the steps of combining (1) a first liquid phase comprising a film-forming compound, a biologically active substance and a surfactant, in a solvent, and (2) a non-solvent of the film-forming compound, to form a nanoparticles precipitate. The film-forming compound is a polymer such as polylactic acid, cellulose derivatives, or Arabic gum. The active substance is a pharmaceutical substance, or a fatty substance. Obtained nanoparticles comprise the film-forming compound, the active substance, and the surfactant. However, the ratio between the surfactant together with the film forming compound and the active substance is very high.
U.S. Pat. No. 5,683,723 describes a process for making polymeric nanoparticles by mixing a solution of a polymer and a non-solvent of said polymer. A surfactant is also used. The polymer is a polyoxyethylene-polylactic block copolymer. Said copolymer has a therapeutic effect, and no further organic ingredient is added.
Published International application WO 97/13503 describes the synthesis of drug nanoparticles by spray drying. According to this process a dispersion of nanoparticles of a drug in a polymeric matrix is obtained, and not an aqueous suspension of nanoparticles.
Published International application WO 97/18787 describes powder formulations comprising a water insoluble active and a copolymer dispersant, comprising &agr;-&bgr;-unsaturated oxyacids, and further dispersion in an aqueous medium. The powder is obtained with powder-formation means, and comprises large particles.
Published International applications WO 00/60942 and WO 01/93679 describe powder formulations comprising an agrochemical and a styrene(meth)acrylic copolymer. The particle size of the powder is of 5 to 50 &mgr;m.
BRIEF SUMMARY OF THE INVENTION
The in
Coret Joel
Crooks Regan
Joanicot Mathieu
Prud'Homme Robert K.
Cain Edward J.
Lee Katarzyna W.
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