WO1998003065A1 - Process for preparing storage-stable pesticide dispersion - Google Patents

Abstract

Aqueous dispersions of microcapsules containing a high loading of pesticide in the form of supercooled melts or supersaturated solutions are stabilised to crystallisation of the pesticide by ensuring that the volume median particle size of the microcapsules is kept below 6νm, and by employing surfactants which do not form micelles under storage conditions, thereby inhibiting transportation of the pesticide through the aqueous phase.

Description

PROCESS FOR PREPARING STORAGE-STABLE PESTICIDE DISPERSION

This invention relates to a process for preparing an aqueous dispersion of polymeric microcapsules containing a supersaturated solution or supercooled melt of water- msoluble materials. In particular, it is concerned w th providing aqueous dispersions of pesticidal material which do not crystallise, so that a product with a high content of active material can be provided which is storage-stable. Storage-stable transportable aqueous dispersions of pesticides are provided which can be applied to crops and the like by conventional spray tecr.niQues .

It is well known to encapsulate highly water- lnsoluole pesticidal material in polymeric microcapsules, in order that the pesticidal material can be applied to crocs ana the l ke. Such microcapsule formulations are commoⁿly provided m the form of spray-dried powders, whicn are rewetted prior to application. For example, US-A-5160530 (Griffin) discloses a process for encapsulating pesticides by melting the active material and combining the melted material with a film-forming polymer, such as a polyvmyl alcohol (PVA) . The materials are then emulsified together and spray-dried. A similar method is disclosed m US-A-4244836 (Hoechst) .

For some applications, however, liquid concentrates, particularly aqueous concentrates, have substantial advantages over dry formulations. Aqueous concentrates are generally easier to formulate for field application, and generate reduced possibility of inhalation by a user. It is known to prepare encapsulated pesticides as wet formulations, i.e. as an aqueous dispersion of microcapsules. However, such aqueous concentrates tend to have a lower loading of active ingredient, and therefore tend to be more costly to store and transport than corresponding dry formulations. For instance, US-A- 4938797 includes an example of a wet formulation of microcapsules in which the suspension has an active ingredient content of 46% by weight.

It is known to prepare pesticide-containing dry microcapsules by carrying out the encapsulation process at an elevated temperature, either employing very low amounts of solvent (so that when the dispersion cools the pesticide is encapsulated in the form of a supersaturated solution) or by encapsulating a melt of the pesticide resulting in microcapsules containing a supercooled melt. We have found however that concentrated aqueous formulations of microcapsules containing supercooled melts or supersaturated solutions are not storage-stable, since, on storage at ambient temperatures, crystallisation of the pesticide occurs. This renders the formulation unusable.

Surprisingly, it has been discovered that storage- stable aqueous dispersions of microcapsules containing a high loading of active product in the form of supercooled melts or supersaturated solutions can be stabilised against crystallisation by providing that the microcapsules have a volume median particle size of not more than 6μm, preferably not more than 5μm, more preferably not more than 2μm. It has further been discovered that crystallisation of the active product from such dispersions can be reduced by avoiding the use of surfactants which form micelles under the conditions of storage (and thereby facilitate transportation of the water-insoluble material through the aqueous phase, resulting in crystallisation) .

WO 95/07614 relates to the use of polymeric stabilisers to alter the chemical potential of emulsion particles n an oil-m-water emulsion, and thereby inhibit Ostwald ripening. The use of such stabilisers in suspension-emulsions is also disclosed, as are a number of aqueous dispersing agents for such dispersions, including a polyvmyl alcohol/polyvinyl acetate copolymer. This reference also discloses certain microcapsule suspensions. There is no disclosure m WO 95/07614 however of the desirability of selecting a non- micellising surfactant, and of the need to avoid surfactants which do form micelles, in order to stabilise par culate dispersions. In fact, the surfactant used to st≤cilise the dispersions of microcapsules disclosed in WO 95/07614 is AT OX 4991™, an ethoxylated alcohol which is a micellismg surfactant.

PCT/US95/15534 discloses the preparation of dry microcapsules by spray-drying aqueous solutions of microcapsules containing PVA surfactants. There is no suggestion in PCT/US95/15534 however that the use of such surfactants (or the use of any non-micellising surfactant) is able to improve the long-term stability of aqueous formulations.

Accordingly, in a first aspect of the invention, there is provided a process for preparing a storage- stable aqueous dispersion of a water-insoluble material, which process comprises emulsifying in water a non- aqueous phase comprising a solution or a melt of the water-insoluble material, so as to form emulsion particles having a volume median particle size of not more than 6μm, and carrying out a polymerisation process to form from the emulsion particles an aqueous dispersion of microcapsules, the said microcapsules having the said water-insoluble material contained therein m the form of a supersaturated solution or a supercooled melt, and stabilising the dispersion with a non-micellising surfactant, wherein the stabilised dispersion is substantially free of micellising surfactant.

The amount and/or nature of the non-micellismg surfactant may be such that the solubility of the water- insoluble material in the aqueous phase is not more than lOOppm preferably not more than 50ppm, more preferably not more than 5ppm.

The term "non-micellising" as used herein is intended to mean a surfactant which does not form micelles (which facilitate transport of tne water- lnsoluble material through the aqueous phase) under the conditions used to store the stabilised dispersion.

The process of the invention generally includes the step of storing the stabilised dispersion, for example after packaging in a closed container.

The conditions of storage may be any conditions appropriate to the particular dispersion and water- insoluble material, but will generally be ambient conditions . The tendency of a surfactant to form micelles increases with the concentration of the surfactant. The point at which micelles are formed is known as the critical micelle concentration (CMC) . In order to find the CMC for a particular surfactant, the surface tension of tne surfactant is plotted against the log of its concentration. Those surfactants which readily form micelles, such as monomeric anionic and nonionic surfactants, typically show a quite rapid reduction in surface tension with concentration, until a specific concentration for that surfactant (the CMC) at which the reduction in surface tension ceases.

Such a plot is shown in Figure 1, which is a plot of surface tension against log concentration for an ethoxylated alcohol surfactant (shown as "♦") and for a polyvmyl alcohol (shown as "■" ) . It can be seen that the etnoxylated alcohol forms micelles at and above a concentration of 10^"2'⁵ %w/w. By contrast, the curve for the ?VA shows a gradually reducing surface tension with concentration with no clear change in behaviour, indicative that no micelles are formed in this case. A simple plot of surface tension against concentration can therefore be carried out to determine whether the surfactant forms micelles at the concentrations and under the conditions employed in the formulation.

Most surfactants are such that, under essentially all practical conditions of use, they are "micellising" and therefore unsuitable. Examples of such surfactants include nonionic surfactants such as fatty alcohol ethoxylates (alkoxylates ) , such as are employed in WO 95/07614, fatty acid esters (and alkoxylates of fatty acid esters), alkoxylated amines, ethylene oxide- propylene oxide copolymers, fatty acid alkoxylates (PAG esters, specifically PEG esters), tall oil and rosin ester alkoxylates, alkyl phenol alkoxylates, substituted pnenol alkoxylates; anionic surfactants such as dodecyl benzene sulphonic acid and its salts, alkyl sulphates, nonionic alkoyxlates phosphated or sulphated to produce tne corresponding phosphate ester or ether sulphate respectively and cationic surfactants such as cetyl trimethyl ammonium chloride. Other micellismg surfactants can be found in reference works such as "McCutcheons Emulsifiers & Detergents".

Clearly, there is a balance between the emulsifying effect and the tendency to form micelles (both of which ...crease with surfactant concentration) . It will be appreciated that, between preferred surfactants and unsuitable surfactants, there is a group of surfactants hiCT have some stabilising effect but which are not oreferred .

A surfactant may be used which forms micelles under the process conditions, provided that t does not form micelles under the conditions of storage, since it is on storage that crystallisation generally takes place.

As indicated above, the "non-micellising surfactant' is one which is able to stabilise the dispersion such that the dispersed microcapsules remain in suspension on extended storage.

Without wishing to be constrained by theory, it is thought that the surfactants in question inhibit transportation of the water-insoluble material through the aqueous phase, thereby reducing the likelihood of nucleation of the said material and of subsequent crystallisation. By contrast, those surfactants which have a strong ability to form micelles are thought to promote transportation of the water-insoluble material through the aqueous phase, resulting m crystallisation.

In principle any surfactant can be used which has a sufficient emulsifying effect when employed at a concentration below its critical micelle concentration. In practice, suitable surfactants tend to be polymeric surfactants of relatively high molecular weight, for example with a weight average molecular weight of at least 10,000. Lignosulphates with a weight average molecular weight of at least 2,000 are also suitable.

A preferred stabilising surfactant a poly (vinyl pyrrolidone), a co-poly (vinyl alcohol/acetate) PVA, a co- poly (vinyl pyrrolidone/acetate) , a co-poly (vinyl pyrroliαone/acetate/alcohol) , a co-poly (acrylic acid/graft polyethyleneoxide) , a co- poly (aikyl (meth) acrylate) , a lignosulphonate, a co- poly (maleic anhydride/methyl vinyl ether), a co- poly (maleic anhydride/diisobutylene) , a carboxylated PVA, a poly(styrene sulphonate) , a poly (alkyl cellulose) or a poly (carboxyalkyl cellulose). A particularly preferred surfactant is a polyvmyl alcohol (PVA) .

The aqueous dispersions of the present invention may be packaged in a closed container for shipping and transport purposes.

In a preferred embodiment, the stabilising surfactant is added prior to the polymerising step and, more preferaoly, prior to the emulsifying step. Particle size (vmd) may be measured, for example, using a laser diffraction instrument, for example a Malvern Mastersizer™.

As used herein, the term "water-insoluble material' means a material which has a solubility in water of not more than lOOppm, more preferably not more than 50ppm, more preferably still not more than 5ppm.

The polymerisable material is preferably polymerised m an interfacial reaction, and most preferably in an interfacial condensation reaction. In a preferred embodiment, the polymerisable material is a polyisocyanate which is polymerised by means of a condensation reaction with a polyamine.

Alternatively, the polymerisable material may oe a crosslmkable material which is used to coat the emulsion particles by a coacervation method, and thereafter crossimked to form the microcapsules.

Both interfacial and coacervation methods involve the preparation of an oil-in-water emulsion, followed by either a condensation reaction at the oil/water interface to produce a polymeric film, or the production of a coacervate which can then deposit on the oil surface, followed by film forming and hardening, which can take place by a variety of processes. The condensation reaction can for example be a multi-component reaction between, for example:

acid chlorides and polyammes isocyanates and polyamines, isocyanates and polyols, or mixtures of the above.

Coacervates can be formed by any of the processes taught in the art, for example using gelatine/gum arabic.

The microcapsules in accordance with the invention may be prepared by high shear mixing of a solution or a melt containing the water- insoluble material (e.g. pesticide) , preferably a PVA (as an aqueous solution) to enhance microcapsule formation, and one of the materials for forming the microcapsules (e.g. a polymerisable material for instance an isocyanate or a crosslinkable material) . The PVA acts as an emulsifier, and in some systems, no further emulsifier may be required. It is desirable however to add additional emulsifiers, which may be of generally known type in order to produce the desired emulsion of small particle size (provided that the emulsifiers are non-micellising as defined herein) . When the size of the emulsion is as desired, then the other polymeric cross-linker is added (e.g. polyamine), to complete the interfacial polycondensation.

As indicated above, a preferred reactant for the polycondensation is a polyamine, which is usually a water soluble, reactive polyamine, such as diethylene triamine or tetraethylene pentamine. These amines start to react with the isocyanate at the interface as soon as they are added to the emulsion. More complete control can sometimes be achieved by using either a water-soluble amine salt, or an oil-soluble amine salt, dissolved respectively in the aqueous phase or the oil phase at an early stage in the process (for example, before emulsification) . By virtue of the fact that they are salts, they do not immediately react with the isocyanate, but do so promptly when the pH is adjusted to liberate the free amine, whereupon cross -linking occurs.

The high shear mixing can be performed on a batch of the ingredients, or may be conducted continuously (inline) . In the former case, the time of addition or release of the reactive amine is governed by the processing time required to form the emulsion with the correct particle size distribution (which clearly is batch size dependent) , whilst in the latter case, the interfacial reaction can be better controlled, since the amine can be added/released at any desired time simply by choice of injection point in the process stream, thus giving essentially complete control over the urea/urethane ratio.

In a preferred embodiment, an additional non- micellising surfactant is provided in the aqueous dispersion. The dispersion may also preferably comprise an antifreeze agent, for example an ethylene glycol or a propylene glycol.

The water-insoluble material is preferably a pesticidal material. The term "pesticidal material" includes but is not limited to insecticidal, miticidal, herbicidal and fungicidal materials.

Suitable insecticidal materials are:

acrinathnn allethrm alpha-cypermethrin amitraz azinphos -ethyl azinphos-methyl benfuracarb benzoximate beta-cypermethrin be acyfluthrin bifenthrin binapacryl bicallethnn bioallethrin S bioresmethrm bioresmethrm bromophos bromopropylate buprofezm butacarboxim butoxycarbox cambda-cyhalothrin chlordimeform chlorfenvinphos chlorflurazuron chlormephos chlorobenzilate chlorophoxim chloropropylate chlorpyrifos chlorpyrifos- cyanophos cycloprothrm methyl cyfluthrin cyhalothrin cypermethrin cyphenothπn deltamethrin demeton-S -methyl dichlorvos dicofol dinobuton dioxabenzafos dioxacarb disulfoton edifenphos empenthπn endosulfan

EPNethiofencarb esfenvalerate ethoprophos etofenprox etrimphos fenamiphos fenazaquin f emtrothion fenobucarb fenpropathπn fenthiocarb fenthion fenvalerate f lucythrmate flufenoxuron formothion gamma -HCH hexaflumuron hydroprene lsofenphos isoprocarb isoxathion malathion mephospholan methidathion ethoprene methoxychlor mevmphos N-2, 3-dihydro-3- parathion methyl methyl-1, 3- thιazol-2-ylιdene-

2 , -xylιdene permethrin phenothrin phenthoate phosalone phosfolan phosmet piπmiphos -ethyl pirim phos -methyl profenofos promecarb propaphos propargite propetamphos pyrachlofos qumalphos resmethnn tau-fluvalinate tef luthrin tefluthrin temephos terbufos terbufos tetrachlonnphos tetrachlonnohos tetradifon tetramethπn tralomethr tralomethrm tralomethrm triazophos triazophos xylylcarb

Suitable fungicidal materials are.

azaconazole benalaxyl biteranol bupirimate carboxin cyproconazole difenσconazole dimethomorph dmiconazole ditalimfos dodemorph dodine epoxyconazole ethoxyqum etπdiazole fenarimol fenpropid f enpropimorph fluchloral flusilazole lmibenconazole mycloDutanil myclobutanil nuarimol oxycarbox penconazole prochloraz propiconazole pyrifenox tebuconazole tetraconazole tolclofos-methyl tnadimef on tnad menol tπdemorph triflumizole

Su taole herbicidal materials are:

2, 4-D esters 2,4-DB esters acetochlor aclonifen alachlor anilophos benfluralm benfuresate bensulide benzoylprop-ethyl bifenox bro oxynil bromoxyml esters butachlor butamifos butralm butylate carbetamide chlornitrofen chlorpropham cmmethylm clethodim clomazone clopyralid esters CMPP esters cycloate cycloxydim desmedipham dichlorprop esters diclofop- methyldiethatyl dimethachlor dinitramme ethalfluralin ethofumesate fenobucarb fenoxaprop ethyl fluazifop fluazifop-P fluchloralin flufenoxim flumetralin flumetralin fluorodifen fluoroglycofen fluoroxypyr esters ethyl flurecol butyl flurochloralin haloxyfop ethoxyethyl haloxyfop-methyl ioxynil esters isopropalin

MCPA esters mecoprop-P esters metolachlor monalide napropamide nitrofen oxadiazon oxyfluorfen pendimethalin phenisopham phenmedipham picloram esters pretilachlor profluralin propachlor propanil propaquizafop pyridate quizalofop-P triclopyr esters tridiphane tnfluralin

Particularly suitable pesticidal materials are chiorpyrifos and trifluralin.

The aqueous dispersion may include an additional pesticidal material to that contained in the microcapsules. This additional pesticidal material may be present in solution, in the form of emulsion particles, as a dispersion of a solid, or contained within microcapsules.

In a second aspect of the invention, there is provided a storage-stable aqueous dispersion of a water- insoluble material, wherein the water-msoluble material is contained within microcapsules having a volume median particle size of not more than 6μm, preferably not more than 5μm, more preferably not more than 2μm, in the form of a supersaturated solution or a supercooled melt, wherein the aqueous dispersion additionally comprises a non-micellismg surfactant to stabilise the dispersion, and wherein the stabilised dispersion is substantially free from micellising surfactant.

Preferred non-micellismg surfactants are described above .

The water- soluble material (preferably a pesticidal material as described above) preferably constitutes at least 50% by weight of the aqueous dispersion, and most preferably at least 70% by weight. When in supersaturated solution (such as in xylene or any other suitable solvent known in the art), the amount of tne said material is preferably at least 70% by weight of solution, most preferably at least 80% by weight of solution .

The aqueous dispersion may include an additional pesticide and/or an additional surfactant as described above .

The aqueous dispersion may be provided in a closed container .

In a third aspect of the invention there is provided the use of a non-micellismg surfactant (as described above) to inhibit crystallisation of a water-msoluble material from an aqueous dispersion containing the sa d material, wherein the water-msoluble material is present the dispersion in the form of microcapsules containing the said material as a supersaturated solution or a supercooled melt. In a further aspect of the invention, there is provided a method for the control or eradication of a pest, which method comprises diluting an aqueous dispersion as described above to a pesticidally-effective concentration, and applying the resultant dispersion to the pest or to a locus in which the pest is to be controlled particularly, without any intervening spray- drying step.

As indicated above, the method of the invention is particularly advantageous for the production of microcapsules having a small particle size, for example having a VMD of 6μm or less, particularly 2μm or less. The chief advantage of such small capsules is that, as the VMD decreases, it is possible to retain the majority of the supercooled/supersaturated active n the liquid form. It is thus possible to produce m a reliable manner liquid core capsules with the minimal use of solvents, which in turn gives environmental advantages, as well as a higher active loading n the final product. Further, such small capsules provide a higher surface area to mass ratio than larger particles, and thus give an enhanced release rate and better knock-down. Yet another benefit of such small capsules is that they can penetrate soil or surface grass thatch better than larger capsules, and so are more efficacious in certain applications where such soil or thatch mobility is needed.

The presence of a liquid core in capsules made with a supercooled molten active has several advantages, of which the most significant from point of view of the present invention is that the core does not crystallise, thus causing rupture of the capsules, which can lead both to premature release, and to formulation instability on storage. A second advantage is that a liquid core will in general release its active more rapidly than will a solid. This, combined with small particle size, gives a significant increase in active release rate. A third advantage of retaining the active in the liquid state is that there is no possibility of producing a biologically less active polymorph during crystallisation - a problem which is addressed in another way in US-A-5160530 (Griffin) .

Any water- insoluble solvent may be employed to dissolve the water-insoluble material in the preparation of the microcapsules if a solvent is deemed desirable. The use of such solvents reduces the tendency of the said material to crystallise. Examples of typical solvents are aromatic solvents, particularly alkyl substituted benzenes such as xylene or propyl benzene fractions, and mixed naphthalene and alkyl naphthalene fractions; mineral oils; kerosene, dialkyl amides of fatty acids, particularly the dimethyl amides of fatty acids such as the dimethyl amide of caprylic acid; chlorinated aliphatic and aromatic hydrocarbons such as 1,1,1- tπchloroethane and chlorobenzene, esters of glycol derivatives, such as the acetate of the n-butyl, ethyl, or methyl ether of diethyleneglycol, the acetate of the methyl ether of dipropyleneglycol, ketones such as isophorone and trimethylcyclohexanone (dihydroisophorone) and the acetate products such as hexyl , or heptylacetate . The preferred organic liquids are xylene, propyl benzene fractions, alkyl acetates, and alkyl naphthalene fractions . Materials may be employed which are normally solid at amoient temperatures, but which are capable of forming eutectic mixtures with the water-insoluble material. The use of such materials will generally reduce the tendency of the water-msoluble material to crystallise.

A further advantage of the encapsulation method in accordance with the invention is that it permits the production of aqueous compositions containing two or more active materials, where the materials are such that direct formulation of the materials (i.e., without encapsulation of one or both of them) would lead to a product which is chemically or physically unstable. In one aspect, the said actives may be separately encapsulated, but in an alternative and preferred embodiment, one or more of the active materials (or some portion of a single active material) may be encapsulated by the method in accordance with the invention, and the oalance not encapsulated, for example, simply dispersed m the aqueous phase. In this way, the un-encapsulated active material is immediately biologically available upon application, whereas the encapsulated material is released more slowly. The amount of each material employed in such different forms will vary dependent upon the particular application but in general terms, each such material may constitute from 0.1 to 99.9% by weight of the total of the encapsulated material.

Compositions of the invention may also include a stabiliser of the kind disclosed WO95/07614.

Other conventional additives may also be incorporated into the formulation such as emulsifiers, dispersants, and film- forming polymers (provided that such additives do not form micelles under storage conditions) .

A number of preferred embodiments of the invention are described in the following Examples.

The following materials were used in the Examples:

Trade Name Nature of Material

Atlox 4913 nonionic surfactant Solvesso 200 aromatic solvent Sopropan T-36 anionic copolymer Voranate M-220 isocyanate Voranate M-229 isocyanate PAPI 135 isocyanate Hyv s 30 poly(iso butylene) Hyvis 04 poly(iso butylene)

Goherseran L-3266 anionically modified PVA Morwet EFW anionic surfactant blend Gohsenol GH20 PVA 88% hydrolysed, high MW Gohsenol GL05 PVA 88% hydrolysed, intermediate MW

Gohsenol GL03 PVA 88% hydrolysed, low MW

Example 1 Molten chlorpyrifos at 50°C (615g) was mixed with PAPI 135 (30g) and emulsified into 460g water containing lOg Gohsenol GH20 (an aqueous PVA solution) and lOg Gohsenol GL05 (an aqueous PVA solution) at 50°C. An emulsion of about 2μm vmd was produced. To this was added a solution of diethylenetriamine (lOg), Atlox 4913 (20g) in water (70g) to produce an encapsulated product containing about 600g/l chlorpyrifos. This product showed no significant crystallisation after 2 weeks storage. A comparative example made by emulsification of the same quantity of chlorpyrifos into the same surfactant solution but without encapsulation, crystallised on standing overnight at laboratory temperature .

Example 2: Molten trifluralin at 50°C (615g) was mixed with PAPI 135 (30g) and emulsified into 365g water containing lOg Gohsenol GH20 and lOg Gohsenol GL05 at 50°C. An emulsion of about 3μm vmd was produced. To this was added a solution of diethylenetriamine (lOg), Atlox 4913 (20g) in water (70g) to produce an encapsulated product containing about 600g/l trifluralin. This product showed no significant crystallisation after 2 weeks storage. A comparative example made by emulsification of the same quantity of trifluralin into the same surfactant solution crystallised on standing overnignt at laboratory temperature.

Example 3 : The composition of Example 2 was repeated but emulsified at about 1.5μm and diluted to 500g/l. This product also showed no significant crystallisation after 2 weeks storage.

Example 4 : Molten chlorpyrifos at 50°C (615g) was mixed with PAPI 135 (30g) and emulsified into 440g water containing lOg Gohsenol GH20 and lOg Gohsenol GL05 at 50°C. An emulsion of about 2.5μm vmd was produced. To this was added a solution of diethylenetriamine (lOg), Atlox 4913 (20g) in water (70g) to produce an encapsulated product containing about 600g/l chlorpyrifos with a particle size of about 1.29μm. This product showed no significant crystallisation after 2 weeks storage .

Example 5: Molten chlorpyrifos at 50°C (615g) was mixed with PAPI 135 (30g) and dioctyl phthalate (50g) and emulsified into 380g water containing lOg Gonsenol GH20 and lOg Gohsenol GL05 at 50°C. An emulsion of about 1.4μm vmd was produced. To this was added a solution of diethylenetriamine (lOg), Atlox 4913 (20g) in water (70g) to produce an encapsulated product containing about

600g/l chlorpyrifos with a particle size of about 1.38μm. Th s product showed no significant crystallisation after 2 weeks storage.

Example 6 : Molten chlorpyrifos at 55°C (462g) was mixed witn Voronate M-220 (32g) and emulsified into 400g water containing 40g Poval 203 (PVA 88% hydrolysed supplied by Kuraray) at 50°C. An emulsion of about 1.84μm vmd was produced. To this was added a solution of dietnylenetnamme (8g) in water (98g) to produce an encapsulated product containing about 46% w/w chlorpyrifos. This product showed no significant crystallisation after 2 weeks storage.

Example 7 : Molten chlorpyrifos at 45°C (615g) was mixed with PAPI 135 (lOg) and emulsified into 440g water containing lOg Gohsenol GH20 and lOg Gohsenol GL05 at 45°C. An emulsion of about 1.4μ vmd was produced. To this was added a solution of diethylenetriamine (3.5g), Atlox 4913 (20g) in water (70g) to produce an encapsulated product containing about 600g/l chlorpyrifos with a particle size of about 1.4μm. This product showed no significant crystallisation after 2 weeks storage. Example 8 : Molten chlorpyrifos at 45°C (615g) was mixeα with PAPI 135 (20g) and emulsified into 440g water containing lOg Gohsenol GH20 and lOg Gohsenol GL05 at 45°C. An emulsion of about 1. μm vmd was produced. To this was added a solution of diethylenetriamine (7g) , Atlcx 4913 (20g) m water (79g) to produce an encapsulated product containing about 600g/l chlorpyrifos with a particle size of about 1.4μm. This product showed no significant crystallisation after 2 weeks storage.

Example 9: Molten chlorpyrifos at 45°C (615g) was m xeα with PAPI 135 (lOg) and emulsified into 440g water containing lOg Gohsenol GH20 and lOg Gohsenol GL05 at 45^GC. An emulsion of about 1.4μm vmd was produced. To th s was added a solution of tetraethylenepentamme (3g), Atlox 4913 (20g) water (70g) to produce an encapsulated product containing about 600g/l chlorpyrifos witr a particle size of about 1.4μm. This product showed no significant crystallisation after 2 weeks storage.

Example 10: Molten chlorpyrifos (615g) at 50°C was mixed with PAPI 135 (20g) and Solvesso 200 (200g) and emulsified into 390g water containing 20g Atlox 4991 at 50^CC. An emulsion of about 1.5μm vmd was produced. To this was added a solution of diethylenetriamine (7g), Atlox 4913 (20g) in water (130g) to produce an encapsulated product containing about 45% w/w cnlorpyrifos with a particle size of about 1.5μm. This product showed no significant crystallisation after 2 weeks storage. A comparative example made by emu_s fication of the same quantity of chlorpyrifos an Solvesso 200 into the same surfactant solution but witnout encapsulation crystallised on storage at laooratory temperature. Example 11: Molten chlorpyrifos at 45°C (615g) was mixed with PAPI 135 (30g) and emulsified nto 430g water containing 20g of a 10,000 mol wt 88% hydrolysed polyvinyl alcohol (PVA) and 20g Atlox 4913 at 45°C. An emulsion of about 1.65μm vmd was produced. To this was added a solution of diethylenetriamine (lOg) in water (70g) to produce an encapsulated product containing about 600g/l chlorpyrifos with a particle size of about 1.63μm. This product showed no significant crystallisation after 4 weeks storage.

Example 12: Molten trifluralin at 50°C (462g) was mixed witn PAPI 135 (7.4g) and emulsified into 430g water containing 60g polystyrene sulphonate (Sodium salt) at 50°C. An emulsion of about 6μm vmd was produced. To t s was added a solution of diethylenetriamine (2.5g) in water (iOOg) to produce an encapsulated product containing about 45% w/w trifluralin. This product snoweo no significant crystallisation after 2 weeks storage. A comparative example made by emulsification of the same quantity of trifluralin into the same surfactant solution crystallised on standing overnight at laboratory temperature .

Example 13: Molten trifluralin at 50°C (515g) was mixed with PAPI 135 (8.2g) and emulsified into 380g water containing 67g polystyrene sulphonate (Sodium salt) at 50°C. An emulsion of about 4μm vmd was produced. To this was added a solution of diethylenetriamine (2.7g) m water (IOOg) to produce an encapsulated product containing about 45% w/w trifluralin. This product showed no significant crystallisation after 2 weeks storage. A comparative example made by emulsification of tne same quantity of trifluralin into the same surfactant solution crystallised on standing overnight at laboratory temperature .

Example 14 : Molten chlorpyrifos at 50°C (615g) was mixed with PAPI 135 (lOg) and emulsified into 450g water containing 80g polystyrene sulphonate (Sodium salt) at 50°C. An emulsion of about 4.2μm vmd was produced. To this was added a solution of diethylenetriamine (2.7g) in water (IOOg) to produce an encapsulated product containing about 50%w/w chloripyrifos. This product showed no significant crystallisation after 2 weeks storage .

Example 15. Molten chloripyrifos at 50°C (615g) was mixed witn PAPI 135 (lOg) and emulsified into 450g water containing 125g PVP K-30 at 50°C. An emulsion of about 1 49u vmd was produced. To this was added a solution of diethylenetriamine (2.7g) in water (IOOg) to produce an encapsulated product containing about 50%w/w chlorpyrifos This product showed no significant crystallisation after 2 weeks storage.

Example 16. Molten chlorpyrifos at 50°C (615g) was mixed with PAPI 135 (lOg) and Hyvis 30 (30g) and emulsified into 450g water containing IOOg Sopropon T-36 at 50°C. An emulsion of about 1.2μm vmd was produced. To this was added a solution of diethylenetriamine (2.5g) water (IOOg) to produce an encapsulated product containing about 50%w/w chlorpyrifos. Th s product showed no significant crystallisation after 2 weeks storage.

Example 17 Molten chlorpyrifos at 50°C was mixed with Voronate M-220 (20g) and emulsified into 550g water containing IOOg Sopropon T-36 at 50°C. An emulsion of about 1.8μm vmd was produced. To this was added a solution of diethylenetriamine (5g) in water (IOOg) to produce an encapsulated product containing about 47%w/w chlorpyrifos. This product showed no significant crystallisation after 2 weeks storage.

Example 18. Molten chlorpyrifos at 50°C (615g) was mixed with Voronate M-220 (30g) and emulsified into 400g water containing 40g Gohsenol GL03 at 50°C. An emulsion of about 1.84μm was produced. To this was added a solution of diethylenetriamine (lOg) in water (120g) to produce an encapsulated product containing about 51.5%w/w chlorpyrifos. This product showed no significant crystallisation after 2 weeks storage.

Example 19 Molten chlorpyrifos at 50°C (615g) was mixed with Voronate M-220 (lOg) and emulsified into 300g water containing 20g Gohsenol GL03 and Morwet EFW (5g) and 50°C An emulsion of about 1.7μm vmd was produced. To this was added a solution of diethylenetriamine (3g) in water (250g) to produce an encapsulated product containing about 51%w/w chlorpyrifos. This product showed no significant crystallisation after 2 weeks storage.

Example 20 Chlorpyrifos-methyl (42g) was dissolved in methyl oleate (20g) at 35°C and then added to 3g Voronate M-229. This oil phase was emulsified into 40g of water containing 4g Gohsenol GL03 at about 35°C to produce an emulsion of about 2.4μm vmd. To this was added lg diethylenetriamine in lOg water to produce an encapsulated product containing about 35% chlorpyrifos- methyl (about 53% encapsulated oil) . Example 21 Chlorpyrifos- ethyl was dissolved in Solvesso 200 (20g) at 35°C and then added to 3g Voronate M-229. This oil phase was emulsified into 40g of water containing 4g Gohsenol G 03 at about 35°C to produce an emulsion of about 1.9μm. To this was added lg diethylenetriamine in lOg water to produce an encapsulated product containing about 35% chlorpyrifos- methyl (about 53% encapsulated oil) .

Example 22 Chlorpyrifos-methyl (42g) was dissolved in Solvesso 200 (20g) and Hyvis 30 (3g) at 35°C and then added to 3g Voronate M-229. This oil phase was emulsified into 40g of water containing 4g Gohsenol GL03 at about 35°C to produce an emulsion of about 2.25μm vmd. To this was added lg diethylenetriamine in lOg water to produce an encapsulated product containing about 34% chlorpyrifos-methyl (about 55% encapsulated oil).

Example 23 Chlorpyrifos-methyl (42g) was dissolved in

Solvesso 200 (20g) at 35°C and then added to lg Voronate M-229. This oil phase was emulsified into 40g of water containing 4g Gohsenol GL03 at about 35°C to produce an emulsion of about 2.98μm vmd. To this was added 0.33g diethylenetriamine in lOg water to produce an encapsulated product containing about 35% chlorpyrifos- methyl (about 53% encapsulated oil) .

Example 24 Chlorpyrifos-methyl (42g) was dissolved in Solvesso 200 (20g) at 35°C and then added to lg Voronate M-229. This oil phase was emulsified into 40g of water containing 8g Gohsenol GL03 at about 35°C to produce an emulsion of about 0.69μm vmd. To this was added 0.33g diethylenetriamine in lOg water to produce an encapsulated product containing about 35% chlorpyrifos- methyl (about 55% encapsulated oil) .

Example 25 Chlorpyrifos-methyl (42g) was dissolved in Solvesso 200 (20g) at 35°C and then added to lg Voronate M-229. This oil phase was emulsified into 40g of water containing 6g Gohsenol GL03 at about 35°C to produce an emulsion of about 1.38μm vmd. To this was added 0.33g diethylenetriamine in lOg water to produce an encapsulated product containing about 35% chlorpyrifos- methyl (about 55% encapsulated oil) .

Samples from examples 20-25 all stored for 2 weeks at - 5°C showed no crystallisation whereas emulsions prepared from the same oil and aqueous phases showed crystallisation typical of supersaturated oil phases.

Example 26 Chlorpyrifos (300g) and Lindane (120g) were dissolved in Trimethylcyclohexanone and Solvesso 100. 67g cf this oil phase was mixed with PAPI 135 (20g) .

This was emulsified into 300g water containing Anonaid HF (lOg) and Atlox 4991 (20g) to produce an emulsion of about 0.62μm vmd. To this was added 7g diethylenetriamine and 30g Atlox 4913 in 150g water to produce a product containing 300g/l chlorpyrifos and 120g/l Lindane. This product was stored at -5°C for 1 week and then tested by dilution into cold water (5°C) and being passed through a 45μm sieve. No crystals were observed. A parallel study with an emulsion prepared by the same route resulted in gross crystallisation of both chlorpyrifos and Lindane in the same time period.

Example 27 Molten chlorpyrifos (480g) was mixed with Voronate M-220 (25g) , Solvesso 200 (107g) and Hyvis 04 (25g) and emulsified into 400g water containing 50g Gohsenol GL03. An emulsion of about 1.64μm vmd was produced. To this was added a solution of diethylenetriamine (18g) and propylene glycol (40g) m water (IOOg total) to produce an encapsulated product containing about 480g/l chlorpyrifos. This product showed no significant crystallisation after 2 weeks storage .

Example 28 Molten chlorpyrifos (480g) was mixed with Voronate M-220 (25g) , Solvesso 200 (107g) and Hyvis 04 (25g) and emulsified into 400g water containing 45g Gohsenol GL03 and 30g Gohseran L-3266. An emulsion of about 0 82μm vmd was produced. To this was added a solution of diethylenetriamine (18g) and propylene glycol (40g) water (IOOg total) to produce an encapsulated product containing about 480g/l chlorpyrifos. This product showed no significant crystallisation after 2 eeKs storage .

Example 29 Trifluralin (55.9g) and ethalfluralin (11.3g) as a eutetic mixture were melted at 40°C and 7.5g of methylene diisocyanate was added thereto. This oil phase was added to water (60g) containing sodium polyacrylate (1.5g) at 40°C with high shear. An emulsion was produced of approximately Sμm vmd. To this was added diethylenetriamine (5g) in water (8.5g). The mixture was stirred at 40°C for thirty minutes. The capsules produced were storage stable.

Claims

1. A process for preparing a storage-stable aqueous dispersion of a water-msoluble material, which process comprises emulsifying in water a non-aqueous phase comprising a solution or a melt of the water- msoluble material, so as to form emulsion particles having a volume median particle size of not more than 6μm, and carrying out a polymerisation process to form from the emulsion particles an aqueous dispersion of microcapsules, the said microcapsules having the said water-insoluble material contained therein in the form of a supersaturated solution or a supercooled melt, and stabilising the dispersion with a non-micellising surfactant, wherein the stabilised dispersion is substantially free of m cel. sing surfactant.

2. A process as claimed in Claim 1, including the step of storing the stabilised dispersion.

3. A process as claimed in Claim 1 or Claim 2, including the step of packaging the said aqueous dispersion in a closed container.

4. A process as claimed in any one of the preceding claims, wherein the said volume median particle size

5. A process as claimed in Claim 4, wherein the said volume median particle size is not more than 2μm. O 98/030

29

6. A process as claimed m any one of the preceding claims, wherein the surfactant is added prior to the said polymerisation process.

7. A process as claimed in any one of the preceding claims, wherein the surfactant is added prior to the said emulsification step.

8. A process as claimed in any one of the preceding claims, wherein the surfactant is a polymeric surfactant with a weight average molecular weight of at least 10,000.

9. A process as claimed any one of the preceding claims, wherein the surfactant is a poly(vιnyl pyrrolidone), a co-poly (vinyl alcohol/acetate) PVA, a co-poly (vinyl pyrrolidone/acetate ) , a co- oo y (vinyl pyrrolidone/acetate/alcohol) , a co- poly (acrylic acid/graft polyethyleneoxide) , a co- poly (alkyl (meth) acrylate) , a lignosulphonate, a co- poly (maleic anhydride/methyl vinyl ether), a co- poly (maleic anhydride/diisobutylene), a carboxylated PVA, a poly(styrene sulphonate), a poly(alkyl cellulose) or a poly (carboxyalkyl cellulose).

10. A process as claimed in any one of Claims 1 to 7, wherein the surfactant is a lignosulphonate with a weight average molecular weight of at least 2,000.

11. process as claimed m any one of the preceding claims, wherein the microcapsules are formed by polymerising a polymerisable material in an interfacial reaction or by coating the emulsion particles with a crossl kable material by a coacervation method, and thereafter crosslinkmg the said crosslmkable material.

12. A process as claimed in Claim 11, wherein the interfacial reaction is a condensation reaction.

13. A process as claimed in any one of the preceding claims, wherein the water-insoluble material is a pesticidal material.

14. A process as claimed in Claim 13 wherein the aqueous dispersion includes an additional pesticidal material .

15. A process as claimed in Claim 14, wherein the said additional pesticidal material is present in solution, in the form of emulsion particles, as a dispersion of a solid, or is contained within microcapsules .

16. A process as claimed n any one of the preceding claims, wherein the aqueous dispersion includes an additional non-micellising surfactant.

17. A process as claimed in any one of the preceding claims, wherein the aqueous dispersion includes an antifreeze agent.

18. A storage-stable aqueous dispersion of a water- insoluble material, wherein the water-msoluble material is contained within microcapsules having a volume median particle size of not more than 6μm in the form of a supersaturated solution or a supercooled melt, wherein the aqueous dispersion additionally comprises a non-micellising surfactant to stabilise the dispersion, and wherein the stabilised dispersion is substantially free from micellising surfactant.

19. An aqueous dispersion as claimed m Claim 18, which is packaged in a closed container.

20. An aqueous dispersion as claimed in Claim 18 or Claim 19, wherein the surfactant is a polymeric surfactant with a weight average molecular weight of at least 10,000.

21. An aqueous dispersion as claimed in any one of Claims 18 to 20, wherein the surfactant is a poly(vιnyl pyrrolidone), a co-poly (vinyl alcohol/acetate) PVA, a co-poly (vinyl pyrrolidone/acetate) , a co-poly (vinyl pyrrolidone/acetate/alcohol) , a co-poly (acrylic acid/graft polyethyleneoxide) , a co- poly (alkyl (meth) acrylate) , a lignosulphonate, a co- poly (maleic anhydride/methyl vinyl ether), a co- poly (maleic anhydride/diisobutylene), a carboxylated PVA, a poly(styrene sulphonate), a polyfalkyl cellulose) or a poly (carboxyalkyl cellulose).

22. An aqueous dispersion as claimed in any one of Claims 18 or 19, wherein the surfactant is a lignosulphonate with a weight average molecular weight of at least 2,000.

23. An aqueous dispersion as claimed in any one of Claims 18 to 22, which includes an additional non- micellismg surfactant.

24. An aqueous dispersion as claimed in any one of Claims 18 to 23, wherein the water-insoluble material is a pesticidal material.

25. An aqueous dispersion as claimed in Claim 24, additionally comprising an additional pesticidal material dispersed in the aqueous phase.

26. The use of a non-micellismg surfactant to inhibit crystallisation of a water-insoluble material from an aqueous dispersion containing that material, wherein the water-msoluble material is present in the dispersion in the form of microcapsules containing the said material as a supersaturated solution or a supercooled melt.

27. The use as claimed in Claim 26, wherein the surfactant is a poly (vinyl pyrrolidone), a co- poly (vinyl alcohol/acetate) PVA, a co-poly (vinyl pyrrolidone/acetate) , a co-poly (vinyl pyrrolidone/acetate/alcohol) , a co-poly (acrylic acid/graft polyethyleneoxide) , a co- poly (alkyl (meth) acrylate) , a lignosulphonate, a co- poly (maleic anhydride/methyl vinyl ether), a co- poly (maleic anhydride/diisobutylene), a carboxylated PVA, a poly(styrene sulphonate), a poly (alkyl cellulose) or a poly (carboxyalkyl cellulose).

28. A method for the control or eradication of a pest, which method comprises diluting an aqueous dispersion as claimed in Claim 24 or Claim 25 to a pesticidally-effective concentration, and applying the resultant dispersion to the pest or to a locus m which the pest is to be controlled.

29. A method of treating a pest using an aqueous dispersion of a pesticidal material as claimed in Claim 24 or Claim 25 which is packaged in a closed container, comprising removing the said dispersion from the container, diluting the said dispersion to a pesticidally-effective concentration, and applying the resultant dispersion to the pest.