Microencapsulated solid pesticides

Details Microencapsulated solid pesticides Microencapsulated solid pesticides

2001-10-15

2004-06-08

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

C424S405000, C424S408000, C424S417000, C427S213340, C428S407000, C514S229200, C514S361000

Reexamination Certificate

active

06746684

ABSTRACT:

The present invention relates to a technique for forming a microcapsule of a pesticide, and more particularly to a microcapsule containing a solid pesticide as a core material, which microcapsule is excellent in release-controllability of the pesticidal component, safety, workability, etc.; a composition containing said microcapsule; a method for producing said microcapsule; and a method for application of said microcapsule.
With the aim of controlling the elution of pesticidal component to thereby enhance the durability of pesticidal efficacy and to improve the water-resistance, weather resistance and safety of the pesticide, a variety of microencapsulated pesticides have so far been proposed.
According to such known micro-encapsulation techniques, some of the microcapsules contain a liquid pesticide as a core material. Regarding such liquid core type microcapsules, a technique for forming pesticide droplets by a method of emulsification and coating the droplets with a wall material having a desired thickness has already been developed and practically used without difficulty. On the other hand, regarding solid pesticides including powdery and granular ones, there has so far been provided no microcapsule of satisfactory characteristics because it is quite difficult to make the particle size and shape of such solid pesticides even and to smoothen and uniform the surface thereof. Nevertheless, many of the practically used pesticides are solid materials, and especially in recent years a variety of solid pesticides exhibiting a markedly high efficacy at a very low dose are being manufactured and marketed.
Under these circumstances, Japanese Patent Publication JP-B-2-29642 and Japanese Patent Kokai JP-A-59-6813 have disclosed microcapsules of hydrophobic pesticides using, as the film material, a resin prepared by polycondensation of an amino resin prepolymer with a water-soluble cationic urea resin in the presence of an anionic surfactant, for example. These micro-encapsulated pesticides according to the prior art, however, allow the component contained therein to be eluted out of the capsule in such a short period of time as about 10-20 days. Especially in cases where a powerful solid pesticides such as those mentioned above are contained therein, such rapid release can cause a strong chemical injury, and the released component can cause an significant damage and loss to a cultured crop if such a type of microcapsule is applied to sensitive infant plants just after seeding. Further, for manufacturing a microcapsule of desired type according to the above mentioned prior art microcapsules, it has been necessary to use a hydrophobic solvent exercising an undesirable influence upon the workers, which can be disadvantageous from the viewpoint of safety and cost of manufacture.
In WO 91/04661 an invention is disclosed concerning a microcapsule prepared by adding a liquid-miscible urea, thiourea, melamine-formaldehyde prepolymer or a combination thereof to a suspension of a solid pesticide having a high leachability and curing the mixture. Although this microcapsule was devised for the purpose of weed control, suppression of the leaching of pesticidal component into the areas other than the intended area, namely improving the residence protery in soil and preventing the chemical injury, in the practice this capsule type is insufficient in release-controllability, especially in the relatively early stage after application.
Pesticides according to present invention include fungicides (including plant activators improving the resistance), insecticides, herbicides, plant growth regulators, and the like. These agents, however, are different from one another in the time at which the efficacy of agent is to be exhibited. For instance, in the cultivation of rice plant, an improved harvest can be realized by applying a relatively mild fungicide capable of preventing the injuries caused by viruses and microorganisms to the seedling boxes in which seeding, germination and rooting of the plants are practiced, and then applying an insecticide to repulse the attack of pests in the greening period when spindly growth of stems and leaves occur, if necessary, and then again applying an insecticide and a fungicide just before transplantation to the main paddy field, and after the transplantation by using a herbicide in combination therewith. Especially on big farms cultivating large areas of land, it is desirable to complete the application of pesticides efficiently, i.e. with the smallest frequency of application to the smallest area and preferably with a single application process at the time of seeding and irrigation in the seedling box or in the greening period or just after transplantation, instead of applying the necessary pesticide every time when it is required, because thereby some of the work for cultivation and raising can be saved. If this can be realized, it will lessen the labor necessary for applying pesticides to the large main paddy field after the transplantation, which is quite advantageous.
Even if a powerful solid pesticide is applied in the early stage of plant growth, the occurrence of chemical injury in the infant period of plant can be prevented so far as the solid pesticide is encapsulated in a microcapsule capable of sufficiently controlling the release of component thereof. By such means, the useless loss of active ingredient before the time at which its efficacy is desired can be prevented. Further, the use of such microcapsules will have the beneficial effect of preventing the decomposition of a combination of diverse pesticidally active ingredients in cases where a plurality of pesticidal active ingredients have to be applied in combination at the same time. In the practice often such combinations decompose caused by interaction of the pesticides. The use of microcapsules for at least one component of such combination can prevent the decomposition where otherwise the different pesticides cannot be used in one single conventional formulation and must then be applied separately.
In view of the above, the object of the present invention consists in providing a microcapsule containing a solid pesticide which has a desirable ability to control the leaching of the active component thereof and can realize an improved workability with a suppressed occurrence of chemical injury.
In order to achieve the above-mentioned objective, the present invention provides a microcapsule with the desirable characteristic properties, even when the core material is a solid pesticide. The microcapsules according to the invention may be obtained by subjecting a prescribed melamine-formaldehyde resin type prepolymer showing a sparingly water-soluble property to a polycondensation reaction in the presence of a dispersant which is a condensation product of naphthalenesulfonic acid and/or alkylnaphthalenesulfonic acid and formaldehyde or a salt thereof.
Accordingly, the first aspect of the present invention is a microcapsule characterized by coating a solid pesticide as a core material with a wall material which is a resin formed by subjecting a sparingly water-soluble melamine-formaldehyde resin type prepolymer to a polycondensation reaction in the presence of a dispersant which is a condensation product of a naphthalenesulfonic acid and/or alkylnaphthalenesulfonic acid and formaldehyde or a salt thereof, provided that the solubility of water in said sparingly water-soluble melamine-formaldehyde resin type prepolymer is 2000 g or less at +25° C. per 100 g of solid component of said prepolymer.
Said dispersant is preferably sodium naphthalenesulfonate-formaldehyde condensation product having a weight-average molecular weight of 500 to 8000 (the second aspect of the present invention). By using such a dispersant, both the solid pesticide constituting the core material and the microcapsule formed by polycondensation of the prepolymer can be mono-dispersed in a desirable state in the reaction mixture without agglomeration of the sparingly water-soluble melamine-formaldehyde resin type prepolymer.
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