AU5963894A - Agrichemical tablet formulations containing active material encapsulated in water-soluble polymers - Google Patents

Description

TITLE AGRICHEMICAL TABLET FORMULATIONS CONTAINING ACTIVE MATERIAL ENCAPSULATED IN WATER-SOLUBLE POLYMERS The Dresent invention is a non-effervescent formulation in tablet form that comprises a pesticide encapsulated in a polymer all of which is dispersed in a water-disintegratable matrix.

BACKGROUND OF THE INVENTION WO90/00007 discloses effervescent pesticidal tablets comprising an acid and a base which react upon exposure to water to produce the effervescent reaction. However, there is no disclosure therein of the non-effervescent tablets of the present invention in which the pesticide is microencapsulated.

SUMMARY OF THE INVENTION The present invention are formulations in tablet form which: a) are non-effervescent; b) are unaffected by high humidity storage; c) begin disintegration immediately in 15-35°C water and completely disintegrate in less than five minutes, preferably in less than one minute; said formulations comprising:

1) about 0.1% to 89%, based on the total weight of the composition, of a pesticide encapsulated in;

2) about 1% to 50%, based on the weight of the pesticide, of a water- soluble polymer coating, and the coated pesticide particles are dispersed in;

3) about 10% to 99.899%, based on the total weight of the composition, of a water-disintegratable compressible matrix, each being used to total 100%.

By "tablet" is meant any solid compaction form (e.g., tablet, pellet, briquette, etc.) made from the composition described herein.

One advantage of the present invention over conventional pesticidal formulations is dermal safety. Ihe potentially toxic pesticide is completely encased in a polymer coating thereby reducing the risk of harmful dermal exposure during manufacture an.I handling of the formulation. This formulation is useful where there is involved the spraying of aqueous solutions or dispersions of a pesticide and is especially useful when the pesticide is an insecticide. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel tablet composition comprising an agricultural pesticide encapsulated in a water-soluble polymer and dispersed in a tablet or briquette matrix which disintegrates rapidly in water.

The prior art contains many examples of biologically active materials, most notably drugs, encapsulated in water-insoluble or slow-dissolving polymeric barrier designed for slow release of the active component in mammalian systems. In most agricultural spray applications, the pesticide is formulated for rapid dispersion in water and immediate availability for spraying. While there are some advantages for controlled release formulations, use of the required water-resistant barrier may not only reduce water dispersibility, but also may diminish the initial bioefficacy of the active material. Methomyl, an insecticide that is potentially toxic to man, has been formulated as a wettable powder (e.g., Lannate® 90WP, Du Pont Co.) which disperses rapidly in water and has the desirable effect of almost instantaneous knock-down of insects. This fast action is diminished by any formulation that retards methomyl release, such as encapsulation in a water- resistant polymeric barrier. One approach to safen powdered toxic agrichemical products, such as

Lannate® WP, is to package them in water-soluble bags. The user adds the bags to water in preparation for spraying, and if the bag remains unopened before addition, the user is protected from dermal contact with the chemical. However, as a result of physical abuse of the package through rough handling or deliberate opening, there is a possibility of exposure to the dangerous compound with such use forms.

The solid tablet compositions of the present invention reduce the risk of exposure to the pesticide compared to water-soluble bags. The tablets can be handled without gloves and if the product is broken, the encapsulated active is still shielded from the user by the water-soluble polymer. In a sense, each pesticidal particle or aggregate is individually enclosed in a polymer that protects the active ingredient and shields the handler.

This product protection is especially important when application is performed using backpack sprayers as is done in lesser-developed regions where protective equipment such as gloves and face masks are not readily available. The tablet of the invention when added to water initially floats followed by rapid disintegration in the water.

Many encapsulation processes can be used. For reasons of economy, simplicity and environmental safety, a solventless process is preferred. The preferred process involves the use of water-soluble polymers for encapsulation which can be applied to the active as a melt. Examples of said polymers are polyethylene glycol (PEG), polypropylene glycol (PPG), block copolymers of PEG and PPG, and derivatives thereof. The polymer selected must be of sufficient molecular weight to be a solid at room temperature. One possible process involves spraying the molten polymer on the active, and subjecting the sprayed active to a cooler environment to activate solidification into small solid microdroplets. The preferred process involves aggregation and simultaneous coating of the active with molten water-soluble polymer by simple mixing, followed by granulation. The granulation can take place on a rotating pan as taught in WO90/12643, or by extrusion which involves forcing the heat-softened mixture through orifices such as a screen. Sufficient polymer is used in all the processes to ensure complete coverage of the pesticide. Non-porous, non- absorbent pesticides, such as those of the consistency of sand, can be used with the lower limit amount of polymer for complete converage. In contrast, porous or absorbent pesticide particles require more polymer for complete coverage. One skilled in the art will recognize the amount of polymer needed based on the physical properties of the pesticide.

The pesticide can be a finely-divided technical-grade material or, preferably, a material that has been formulated for rapid dispersion upon dilution with water such as a water-dispersible granule premix or a commercial water-dispersible powder.

Contemplated active ingredients include those selected from the following classes, including mixtures thereof: herbicides, fungicides, bactericides, insecticides, nematocides, acaricides, and growth regulants. Examples of suitable pesticides include: insecticides such as monocrotophos, carbofuran, tetrachlorvinphos, malathion, parathion-methyl, methomyl, chlσrdimeform, diazinon, deltamethrin, oxamyl, fenvalerate, esfenvalerate, permethrin, profenofos, sulprofos, triflumuron, diflubenzuron, methoprene, buprofezin, thiodicarb, acephate, azinphosmethyl, chlorpyrifos, dimethoate, fipronil, flufenprox, onophos, isofenphos, methidathion, methamidophos, phosmet, phosphamidon, phosalone, pirimicarb, phorate, terbufos, trichlorfon, methoxychlor, bifenthrin, biphenate, cyfluthrin, fenpropathrin, fluvalinate, flucythrinate, tralomethrin, metaldehyde and rotenone; fungicides such as carbendazim, thiuram, dodine, maneb, chloroneb, benomyl, cymoxanil, fenpropidine, fenpropimorph, triadimefon, captan, thiophanate- methyl, thiabendazole, phosethyl-Al, chlorothalonil, dichloran, metalaxyl, captafol, iprodione, oxadixyl, vinclozolin, kasugamycin, myclobutanil, tebuconazole, difenoconazole, diniconazole, fluquinconazole, ipconazole, metconazole, penconazole, propiconazole, uniconzole, flutriafol, prochloraz, pyrifenox, fenarimol, triadimenol, diclobutrazol, copper oxychloride, furalaxyl, folpet, flusilazol, blasticidin S, diclomezine, edifenphos, isoprothiolane, iprobenfos, mepronil, neo-asozin, pencycuron, probenazole, pyroquilon, tricyclazole, validamycin, and fhitolanil; nematocides such as aldoxycarb, fenamiphos and fosthietan; bactericides such as oxytetracyline, streptomycin and tribasic copper sulfate; acaricides such as binapacryl, oxythioquinox, chlorobenzilate, dicofol, dienochlor, cyhexatin, hexythiazox, amitraz, propargite, tebufenpyrad and fenbutatin oxide; and biological agents such as Bacillus thuringiensis and baculovirus.

Preferred pesticides are methomyl, bensulfuron methyl and N-[[(4,6- dimethoxy-2-pyrimidinyl)amino]carbonyl]-l-methyl-4-(2-methyl-2H-tetrazol-5- yl)- lH-pyrazole-5-sulfonamide.

Although any water-dispersible or water-soluble tablet matrix can be used, the preferred compressed matrix disintegrates or dissolves rapidly in water and is non-effervescent. Generally, effervescent tablets are sensitive to liigh humidity, leading to premature gas evolution and, consequently, the rate of disintegration slows and complete disintegration takes an unpractically long time.

Certain matrixes of finely divided silica, swelling agents and clays can be compressed to solid forms (e.g., a tablet) that meet the dispersion and safening requirements. Such mixtures are well known in the art. Anyone skilled in the art can formulate a variety of mixtures to accomplish the ready disintegration requirement. The preferred tablet size is 0.5 to 100 g. However, smaller or larger tablet sizes may be used if desired. The tablets are strong enough to remain intact during normal shipping and handling. The tablet density may be less than or greater than one. Tablets which float in water (i.e., have a density less than one) are preferred. A preferred tablet composition forms an aqueous suspension after disintegration in water which passes through a 60 mesh screen. Said aqueous suspension can be readily sprayed without clogging the spray nozzle.

Other adjuvants can be included to accelerate wetting, breakup and storage stability, such as surfactants, dispersants and bactericides. EXAMPLE 1

Lannate® 90WP (90% a.i. methomyl wettable powder, Du Pont Co.) in an amount of 5.0 g and Carbowax® 8000 (polyethylene glycol of average molecular weight 8000, Union Carbide Co.) in an amount of 1.0 g were mixed with 0.1 mg of FD&C Blue Dye No. 1 (Hilton Davis Co.) as an indicator. The mixture was heated to about 70°C to melt the polymer and promote intimate mixing, and die mixture was then forced through a 25 mesh screen to obtain granules.

A portion of the granules obtained (1.8 g) were mixed with a powdered matrix material consisting of 0.5 g Wessalon® 50S (a precipitated silica filler/carrier, Degussa Corp.), 0.5 g Polyplasdone® XL-10 (crosslinked polyvinyl pyrrolidone dispersant, GAF Corp.), and 0.6 g Celite® 209 (diatomaceous clay, John Manville Corp.) and 0.01 g Aerosol® OTB (sodium alkylsulfosuccinate surfactant, American Cyanamid Corp.). This mixture was pressed at 2500 psi to form a 28 mm diameter tablet containing 40% methomyl.

The tablet was added to 500 mL of water and began to disintegrate almost immediately. The tablet fragments floated and continued to disintegrate over a 60 second period to form a sprayable solution. The dye released only after considerable disintegration took place indicating that the methomyl was protected inside the PEG barrier. Also, the dye did not release during manual handling for about 20 seconds. The dispersed particles could be washed through a 60 mesh screen.

Various other formulations within the scope of the invention can be prepared by the procedure indicated in the above example.

Claims (10)

What is claimed is:

1. Formulations in tablet form which comprise: a) 0.1 % to 89%, based on the total weight of the composition, of a pesticide encapsulated in; b) 1 % to 50%, based on the weight of the pesticide, of a water-soluble polymer coating, said coated pesticide particles dispersed in; c) 10% to 99.899%, based on the total weight of the composition, of a water-disintegratable compressible matrix.

2. The formulation of Claim 1 wherein the polymer coating is polyethylene glycol.

3. The formulation of Claim 1 wherein the polymer coating is a block polymer of polyethylene glycol and polypropylene glycol.

4. The formulation of Claim 1 wherein the matrix comprises starch, cellulose, silica and sodium stearate.

5. The formulation of Claim 1 wherein the pesticide is methomyl.

6. The formulation of Claim 1 wherein the pesticide is bensulfuron methyl.

7. A method for controlling the growth of undesired vegetation which comprises adding die formulation of Claim 1 to water and applying to the locus to be protected an effective amount of the dispersed formulation in water.

8. A method for controlling the growth of undesired vegetation which comprises adding die formulation of Claim 2 to water and applying to the locus to be protected an effective amount of the dispersed formulation in water.

9. A method for controlling the growth of undesired vegetation which comprises adding die formulation of Claim 3 to water and applying to the locus to be protected an effective amount of the dispersed formulation in water.

10. A method for controlling the growth of undesired vegetation which comprises adding die formulation of Claim 6 to water and applying to the locus to be protected an effective amount of the dispersed formulation in water.