This section includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the present invention, or that any publication specifically or implicitly referenced is prior art.
Insecticides, particularly pyrethroids such as bifenthrin, lambda cyhalothrin, cypermethrin, fenvalerate, permethrin, alpha-cypermethrin, and similar compounds, which are moderately toxic in the technical form, have a high skin irritant property and in some cases may provoke an adverse skin reaction such as burning, tingling, numbness or prickling sensation, also generally known as paraesthesia. These skin irritant properties are most pronounced in the areas of an operator's face, hand, and neck during application of these insecticides. For delivering such agriculturally active materials to a target, encapsulation or microencapsulation is one of the safest modes. Encapsulation, or more specifically microencapsulation, is increasingly being used to target specific insects, as it also provides a safer handling of toxic fungicides and insecticides. A microcapsule is a 10-3 m to 10-9 m diameter particle, composed of an inner core material and an outer shell.

Microencapsulation of a number of different agriculturally active materials and pesticides has been known for many years by using various processes or techniques for solving other problems such as volatility, UV degradation of the actives, reducing aquatic toxicity, pollution in air, water, soil, and also protecting untargeted insects and the like.

The use of microcapsules for the slow or controlled release of liquid or solid active ingredient is well known in the art. Typically, for slow or controlled release, the walls of the microcapsules are porous in nature releasing the entrapped material to the surrounding medium at a slow or controlled rate by diffusion through the pores of the wall. The controlled-release techniques have improved the efficiency of herbicides, insecticides, bactericides and fertilizers. Non-agricultural uses of slow-release or controlled release microcapsules include encapsulated dyes, pigments, inks, flavoring agents, fragrances etc.

Typically, microcapsules may be formed by physical methods such as spray coating, spray drying, pan coating, rotary disk atomization and the like; and chemical methods such as phase separation, interfacial polymerization, simple and complex coacervation method and the like. For example, U.S. Pat. No. 4,280,833 discloses a process for microencapsulating water-immiscible materials, such as herbicides, and, specifically, trifluralin. The microencapsulation process involves an aqueous phase containing an emulsifier and an organic phase. The organic phase consists of a water-immiscible material, such as trifluralin, and polymethylene polyphenyl isocyanate. The organic phase is added to the aqueous phase with agitation to form a dispersion of small droplets of the organic phase within the aqueous phase. Thereafter, a polyfunctional amine is added to the dispersion. The polyfunctional amine reacts with the isocyanate to form a capsular polyurea shell about the herbicide droplet. This type of microencapsulation process is termed interfacial polycondensation. Other patents which involve microencapsulation by polycondensation processes include U.S. Pat. Nos. 4,360,376; 4,417,916; 4,563,212; 3,429,827; 3,577,515; 3,959,464 and 4,640,709. The amines having at least difunctional character chiefly used in these methods to either form a polyurethane, polyurea, polyamide, polysulfonamide, polyester or polycarbonate.

Most important required properties for aqueous microcapsule suspension liquid include that it is stable without causing sedimentation or separation of the microcapsules during storage and preservation, that even if some sedimentation of microcapsules is caused, the microcapsule suspension liquid or aqueous diluted suspension liquid thereof is capable of easy re-dispersion by a light degree of shaking. However, according to our study, it has been found that a microcapsule suspension liquid known in the art especially of bifenthrin causes high sedimentation or viscosity increase with time and results in a state, such as aggregation or caking, which makes difficult the use thereof by re-dispersion, after long-term of storage. Therefore, there is a need to develop capsule suspension form of pesticides especially of bifenthrin that substantially overcome the deficiencies associated with the known arts.

SUMMARY OF THE INVENTION
The present invention relates to a bifenthrin microcapsule suspension liquid which is stable against sedimentation of microcapsules during storage and preservation and a process for preparing such a microcapsule suspension liquid.

In accordance with one of the embodiment of the present invention, the present invention relates to a bifenthrin formulation encapsulated within a shell of polyurea.

In accordance with one of the embodiment of the present invention, the present invention relates to a bifenthrin formulation encapsulated within a shell of polyurea wherein bifenthrin is present in an amount of 1-35 % by weight of the formulation.

In accordance with one of the preferred embodiment of the present invention, the present invention relates to a bifenthrin formulation encapsulated within a shell of polyurea wherein bifenthrin is present in an amount of 5-12 % by weight of the formulation.

In accordance with one of the most preferred embodiment of the present invention, the present invention relates to a bifenthrin formulation encapsulated within a shell of polyurea wherein bifenthrin is present in an amount of 8.8 % by weight of the formulation.

In accordance with another embodiment of the present invention, the encapsulated bifenthrin further comprising surfactants, defoamer, rheology modifier, and solvents.

In accordance with one of the embodiment of the present invention, the surfactants are selected from ethoxylated polyalkylarylphenol phosphate ester, alkylphenol ethoxylate, linear alcohol ethoxylate, lignosulfonates such as Reax 88M, polymeric surfactants based on acrylate sulfonic acid.

In accordance with one of the preferred embodiment of the present invention, the surfactants are selected from ethoxylated polyalkylarylphenol phosphate ester and alkylphenol ethoxylate.

In accordance with one of the preferred embodiment of the present invention, the defoamer is silicone defoamer.

In accordance with one of the preferred embodiment of the present invention, the silicone defoamer is polydimethyl siloxane emulsion.

In accordance with one of the preferred embodiment of the present invention, the solvents are selected from C-IX and water.

In accordance with one of the preferred embodiment of the present invention, the polyurea shell is formed by a process comprising the steps of:
(i) Preparing an aqueous phase solution by mixing ethoxylated polyalkylaryl phenol phosphate ester in presence of KOH and blend of alkyl phenol ethoxylate in water in presence of silicone defoamer;
(ii) Preparing an organic solution by dissolving bifenthrin and polymethylene polyphenyl isocyanate (PMPPI) in CIX aromatic solvent;
(iii) Dispersing the organic phase solution as prepared in step (ii) in the aqueous phase solution as prepared in step (i) in a high speed 2500 rpm homogeniser having cutter dispersible blades;
(iv) adding polyvinyl alcohol, water, xanthum gum to a suspension as obtained in step (iii) to form homogenised capsule suspension.
DESCRIPTION OF THE INVENTION
The following is a description of embodiments of the present invention. The embodiments are in such details as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention.
Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including”, but not limited to.”
As used in the description herein and throughout the claims that follow, the meaning of “a”, “an” and “the” includes plural reference unless the context clearly dictates otherwise.
In some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment.
The present invention utilizes two substantially immiscible liquids, one termed an aqueous phase and the other termed an organic phase, and which comprises establishing a physical dispersion of the organic phase containing the organic isocyanate monomer for formation of polyurea capsule skin or enclosure in the aqueous phase.

The present invention particularly discloses a method of microencapsulation of bifenthrin based on in situ interfacial condensation polymerization which consists of dispersing an organic pesticide phase containing isocyanate monomer into an aqueous phase at a high cutting agitator speed around 2500 rpm. The wall forming reaction is initiated by heating the mixture to an elevated temperature around 50-70ºC at which point the isocyanate monomers are hydrolyzed at the interface to form amines, which in turn react with unhydrolyzed isocyanate monomers to form the polyurea microcapsule wall. The addition of no other reactant is required once the dispersion establishing droplets of the organic phase within a continuous phase, i.e., aqueous phase, has been established. Thereafter, and preferably with moderate agitation of the dispersion, the formation of the polyurea capsule skin or enclosure around the dispersed organic droplets is brought about by heating the continuous liquid phase or by introducing an agent capable of increasing the rate of isocyanate hydrolysis, optionally in addition adjusting the pH of the dispersion, thereby effecting the desired condensation reaction at the interface between the organic droplets and the continuous phase. The product from the process of this invention is particularly suitable for direct agricultural pesticidal applications. The initial dispersion of the organic phase in the aqueous phase may be assisted with an appropriate emulsifying or dispersing agent. The size and uniformity of capsules are readily affected by any convenient method used to disperse one liquid into another. Further, compatible additional agents can be added, such as thickners, biocides, surfactants.

In this fashion, fully satisfactory, discrete bifenthrin capsules are formed having a skin consisting of the polyurea. It is found that microencapsulated bifenthrin obtained by the present invention has many beneficial properties such as stability, increased efficacy, capability of causing reduced side effects.

Experiments conducted with polyurea wall forming monomers in the presence of surfactants such as lignosulfonates, linear alkyl ethoxylates either alone or in combination with other alkyl aryl ethoxylates or cross linked polymers could not provide suspension which remains stable over a prolonged time.

The following examples of formulations according to the invention are presented to illustrate, but not to restrict, this invention:

FORMULATION EXAMPLE
A capsule suspension formulation of bifenthrin was prepared having the following composition:
Component Content (%w/w)
Bifenthrin a.i. 8.8
Ethoxylated polyalkylarylphenol phosphate ester 2.4
Blend of alkylphenol ethoxylate 1.8
Silicone defoamer 1.5
Polyvinyl alcohol 2.0
C-IX 10.0
Polymethylene polyphenyl isocyanate 1.2
KOH 0.12
Xanthum gum (2% aqueous solution) 4.5
Water Q.S.
Total 100
Step wise manufacturing process of Bifenthrin 8.8% CS composition:
(i) An aqueous phase is prepared by mixing dispersing agent ethoxylated polyalkylaryl phenol phosphate ester (2.4 parts by weight) in presence of KOH (0.12 parts by weight) and wetting agent blend of alkyl phenol ethoxylate (1.8 parts by weight) in water in presence of silicone defoamer (1.5 parts by weight).
(ii) A solution is prepared by dissolving Bifenthrin (8.8 parts by weight) and polymethylene polyphenyl isocyanate (PMPPI) (1.2 parts by weight) in CIX aromatic solvent (10 parts by weight) to form a solution. The solution is then dispersed into aqueous phase at a high speed around 2500 rpm in a homogeniser having cutter dispersible blades at a temperature 50-70ºC over a period of 2 hrs.
(iii) The obtained suspension is cooled at ambient temperature and added with polyvinyl alcohol (2 parts by weight), water, xanthum gum (4.5 parts by weight) and balance quantity of water to form homogenised capsule suspension to set viscosity near 210 cp at 25-30ºC.
Surprisingly, it is observed that addition of surfactants, phosphate ester of ethoxylated polyalkylarylphenol and alkylphenol ethoxylate in combination effectively showing a long-term storage stability. On the other hand, other surfactants failed in stability in short to long run. The following table shows the effect of different surfactants in stabilizing the encapsulated bifenthrin when used in encapsulated bifenthrin:

S.No.
Type of surfactants Sedimentation
6 months 12 months 18 months 24 months

1 Linear alcohol ethoxylate 2 ml 5 ml 7 ml 8 ml

2 Ethoxylated polyalkylarylphenol phosphate ester + alkylphenol ethoxylate Nil Nil Nil 1 ml
3 Lignosulfonate Reax PSM 1 ml 3 ml 6 ml 8 ml

Further, it is also found that capsule suspension form of bifenthrin as obtained in the present invention did not cause phytotoxicity in any form (injury to leaf tips and leaf surface, wilting of plants, vein clearing, necrosis, epinasty and hyponasty) even up to 1200 ml/ha dose.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto.

We Claim:

1) A bifenthrin formulation encapsulated within a shell of polyurea.

2) The bifenthrin formulation as claimed in claim 1, comprising bifenthrin in an amount of 1-35 % by weight of the formulation.

3) The bifenthrin formulation as claimed in claim 2, comprising bifenthrin in an amount of 8.8% by weight of the formulation.

4) The bifenthrin formulation as claimed in claim 1, further comprising surfactants, defoamer, solvents and rheology modifier.

5) The bifenthrin formulation as claimed in claim 4, wherein the surfactants are selected from ethoxylated polyalkylarylphenol phosphate ester and alkylphenol ethoxylate.

6) The bifenthrin formulation as claimed in claim 4, wherein the defoamer is silicone defoamer.

7) The bifenthrin formulation as claimed in claim 6, wherein the silicone defoamer is polydimethyl siloxane emulsion.

8) The bifenthrin formulation as claimed in claim 4, wherein the solvents are selected from C-IX and water.

9) The bifenthrin formulation as claimed in claim 4, wherein the rheology modifier is xanthum gum.

10) The bifenthrin formulation as claimed in any of the preceding claim, wherein the polyurea shell is formed by a process comprising the steps of:
(i) Preparing an aqueous phase solution by mixing ethoxylated polyalkylaryl phenol phosphate ester in presence of KOH and blend of alkyl phenol ethoxylate in water;
(ii) Preparing an organic solution by dissolving bifenthrin and polymethylene polyphenyl isocyanate (PMPPI) in CIX aromatic solvent along with silicon defoamer;
(iii) Dispersing the organic phase solution as prepared in step (ii) in the aqueous phase solution as prepared in step (i) in a high speed 2500 rpm homogeniser having cutter dispersible blades at a temperature 50-70ºC over a period of 2 hrs;
(iv) adding polyvinyl alcohol, water, xanthum gum to a suspension as obtained in step (iii) to form homogenised capsule suspension.