Process for the preparation of spherical microparticles containi

Details Process for the preparation of spherical microparticles containi Process for the preparation of spherical microparticles containi

1997-01-21

1999-06-01

Nutter, Nathan M.

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Biocides; animal or insect repellents or attractants

424419, 424420, 424489, 424490, 424497, 424498, 424501, 424502, 4272133, 42721334, 42721336, 523223, A01N 2528

Patent

active

059086327

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for the preparation of spherical microparticles containing biologically active compounds by addition of the preheated compound to the reaction solution. The invention also relates to the use of said microparticles for the preparation of a composition for controlling plant pests, weeds or animal parasites as well as to aqueous spray mixtures containing the microparticles obtained in the practice of this invention.
The microencapsulation of active ingredients in polymeric materials with different polymers is known and can be carried out by various methods, as described for example in Encyclopedia of Polymer Science, John Wiley Sons, 1968, Vol. 8, pp. 719-736.
Particular demands are made of the release properties of biologically active agrochemicals. The applied microparticles must, on the one hand, be comparably active in field application to e.g. emulsifiable concentrates, and, on the the other, as small an amount as possible shall be released on skin contact, so that a high degree of handling safety is ensured. Amino resins are of ten used as polymeric encapsulating materials for microparticles that contain agrochemical compounds. An overview of the broad field of use of these resins for microencapsulation is given, inter alia, in Acta Polymerica 40, (1989) No. 4, pp. 243-251.
The preparation and properties of microparticles prepared with self-crosslinking amino resins are described in Acta Polymerica 40, (1989) No. 5, pp. 325-331. In the processes referred to therein, the starting materials are solid compounds which are e.g. additionally ground to give a fine dispersion in the aqueous polymer solution and are then encapsulated. The drawback of this process is that the solid materials have to be ground to an average particle size of c. 10-30 .mu.m. Depending on the crystal modification, the time investment and the loss of grinding stock may be considerable. The formation of unwanted and very finely particulate dust constitutes a further problem in this process, especially in lengthy grinding. The grinding process generally results in a broad granular distribution of the grinding stock ranging from very fine dust to fairly large particles. It is also known that the irregular shape of grinding stock particles requires a thick capsule wall for their complete encapsulation, thereby impairing the release properties and often resulting in the formation of unwanted agglomerates.
EP-A-0,379,379 claims a composition and a process for the preparation thereof in which the microparticles are formed by coacervation of at least two water-soluble polymers. The active ingredient is dissolved together with a polymer in an organic solvent, the water-soluble polymers are dissolved in water, and both solutions are combined, with stirring. In a preferred composition, the active ingredient has a melting point below 80.degree. C. and is added in the melt to the aqueous solution at a temperature such that it remains in the molten state. Stable aqueous dispersions of microparticles are obtained. One drawback of this process is that the claimed active ingredients must have low melting points.
EP-A-0,368,576 claims a process for encapsulating chlorpyrifos in a urea-formaldehyde or melamine-formaldehyde resin, wherein in particular the high termite toxicity is also retained in the alkaline range--e.g. when applied to concrete--and the handling safety of these microcapsules is greatly enhanced as compared with e.g. that of an emulsifiable concentrate. Chlorpyrifos (melting point 42-43.degree. C.) is fused and the melt is added to a polymer solution, while the temperature of the reaction medium (polymer solution) may not be below the melting point of chlorpyrifos. The temperature is afterwards raised to 50.degree. C. and the cationic urea-formaldehyde resin is crosslinked under acid conditions. The temperature of the fused chlorpyrifos is always below the temperature of the reaction mixture. In this process too it is only possible to use low-melting active ingredients or melts at low temperatu

REFERENCES:
patent: 5576009 (1996-11-01), Nastke et al.
Derwent Abstract 89-059198.

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