PREPARATION OF AQUEOUS SUSPENSION CONCENTRATES CONTAINING A PYRETHRINOID

Abstract: The invention therefore relates to a process of preparation of an aqueous suspension concentrate containing a pyrethroid active ingredient comprising: A) wetting of the pyrethroid active ingredient by a liquid, usually water (Premixing step); B) breaking-up of the aggregates and agglomerates (Grinding step of the Premix obtained in step A) and C) stabilisation of the grinded Premix (Dilution and Thickening step). The invention relates also to the formulations so obtained.

Description: Description PREPARATION OF AQUEOUS SUSPENSION CONCENTRATES CONTAINING A PYRETHRINOID The present invention relates to a process of preparation of aqueous suspension concentrates containing a pyrethroid and the formulations so obtained. The modern use of agrochemicals is highly demanding in terms of biological efficacy and safer use of products. In the field of insecticide formulations the aqueous suspension concentrates referred herein as "SC" or aqueous flowables consist of solid particles of anrganic active ingredient which are homogeneously dispersed in water. These solvent free suspensions are free from toxicity and fiammability concerns associated with the use of oils and organic solvents. The requirement of adequate fineness of the pyrethroid solid particles in suspension to cope with improved stability and biological efficacy demands is increasingly met by using wet milling methods rather those of dry milling which proved to be less efficient. Moreover the pyrethroid SC formulations cover a wide range of pyrethroid active ingredients. The invention therefore relates to a process of preparation of an aqueous suspension concentrate containing a pyrethroid active ingredient comprising: A. Wetting of the pyrethroid active ingredient by a liquid, usually water (Premixing step); B. Breaking-up of the aggregates and agglomerates (Grinding step of the Premix obtained in step A) andStabilisation of the grinded Premix (Dilution and Thickening step). The invention relates to a specific way for producing a pyrethroid SC, the concentration of the active ingredient being 5 to 500 g/l, in particular 7. to 300 g/l. The preferred active ingredient incorporated in said aqueous suspension concentrates is deltamethrin or acrinathrin. For the manufacture of a pyrethroid SC both the process and the recipe of the formulation are intimately linked and indissociable. The final composition is designed so as to keep and to optimize the performance and the quality of the milling (mainly in terms of fineness). According to the invention a pyrethroid SC is prepared by dispersion of the pyrethroid active ingredient into water followed by a wet milling process. A suitable active ingredient (e.g. deltamethrin or acrinathrin) must be insoluble or fairly poorly soluble in water so as to inhibit crystal growth during ageing studies. The active ingredient must not be sensible to hydrolysis. Its melting point should be sufficiently high enough to allow an efficient grinding process and to provide adequate stability at a temperature over 45°C. The invention relates more particularly to a process wherein the pyrethroid is deltamethrin or acrinathrin. One preferred process is a process wherein a high shear mixer or dispersor and a surfactant combination made of an ionic wetting agent and an ionic dispersing agent are used in step A. A. Premixing step: The dispersion of the pyrethroid active ingredient (e.g. deltamethrin or acrinathrin) in water depends on the following parameters: The wetting energy of the external surface of solid particles. The pressure involved in the liquid (e.g. water) penetrating the agglomerates. The penetration rate of the liquid (e.g. water) into the solid agglomerates. That means that the stronger the dispersing agent and wetting agents are adsorbed on the surface of the individual particles, the better they act and fulfill their functions. As a result of this adsorption at the solid/liquid interface, the surface energy is reduced and this facilitates the process of breakdown of solid particles. During the milling process new solid surfaces are created by the mechanical breakdown of the active ingredient. The wetting and dispersing agents must be adsorbed onto the particles as rapidly as these new surfaces are formed. Due to energetical and economical considerations the Premix which has to be milled contains a high loading of active ingredient, between 40 and 90 % w/w, preferably between 50 and 70 % w/w. An efficient dispersion of the solid particles in the liquid phase and an adequate premixing are of extreme importance for the subsequent milling stage. This can be reached by using an efficient high shear mixer such as a Silverson mixer, an Ultraturrax mixer or a colloid mill so as to reach a fineness of approximately 200 microns. The ionic wetting agents and ionic dispersing agents are selected from surfactants comprising sodium alkylsulphates, sodium alkyl ether sulfates, alkyl- or alkylphenylsulfonates, sodium lignosulfonate, sodium 2,2'-dinaphtylmethane-6,6'- disulfonate, sodium dibutylnaphtalenesulfonate, sodium oleylmethyltauride, neutralized phosphoric ester or sulfuric ester based on a polyethoxylated polyarylphenol. Of particular use in the invention are sodium laurylsulphate (e.g. Sipon LCS 98®) in combination with a mixture of sodium alkyl ether sulfate and a sodium alkylnaphtalenesulfonate formaldehyde condensate adsorbed on silica (e.g. Dispersant SI®), or the use of the triethanolamine or potassium salt of an acid ester of a polyethoxylated tristyryl phenol (e.g. Soprophor FL® (tre ano\ amine salt) or Soprophor FLK® (potassium salt)). The surfactant combination content is preferably 1 to 30 % w/w, in particular 3 to 20 % w/w. The premixing step requires the use of a suitable antifoam to prevent the formation of undesirable foam. The premix contains preferably 0.05 to 3 % w/w, in particular 0.1 to 2 % w/w of an antifoam based on silicone oils such as a mixture of polydimethylsiloxanes supplied as a compound (e.g. Rhodorsil 416® and/or Rhodorsil 426®). B. Grinding step: Milling is a complex process during which the penetration of a liquid (e.g. water) into channels existing between solid aggregates may provide sufficient excess of air pressure to bring about disintegration. However the energy required for the breakdown of little particles into smaller units is provided by mechanical impaction between beads and particles. The whole milling equipment consists of a horizontal chamber equipped with a central pumping agitator shaft which is electrically rotated (several thousand rolls per minute). Examples of wet milling equipments commercially available are sand mills, ball mills (e.g. Dyno Mill®). In the case of a ball mill the Premix is pumped through the milling chamber containing grinding beads. The grinding efficiency depends on the rotation speed of the shaft, and hence the pumping rate as well as on the the volume of the grinding elements, i.e. beads made of keramic, glass or steel, present in the milling chamber. The volume of beads is preferably ranging from 65 to 95 %, in particular from 75 to 85 %. A small fraction of the applied energy is used during the milling phase while most of the energy is dissipated as heat. The rise of temperature must be limited by intensive cooling of the jacketed grinding container. By using a high-efficiency cooling of the grinding space, milling of high temperature sensitive materials becomes also feasible. The pyrethroid active ingredient must be milled and dispersed until the particle sizes in the suspension are 0.1 to 10 microns (mean diameter). So the invention relates more specifically to a process wherein the pyrethroid active ingredient is milled and dispersed in step B preferably to a fineness below 5 microns so as to to produce a stable and bioactive final product. C. Stabilisation of the grinded premix: The stabilisation of the grinded premix is usually achieved by the use of the above- mentioned ionic surfactants generating repulsive forces which can overcome the ubiquitous and natural Van der Waals attraction between the solid particles. After milling of the Premix and upon storage of the final product, the dispersed particles of the pyrethroid (e.g. deltamethrin or acrinathrin) have an inherent tendency to settle down under gravity to the bottom of the container. This is due to the difference of state (solid/liquid) and density between the dispersed active ingredient content and the aqueous phase. The rate of sedimentation can be modelised using the following Stockes formula: Lowering the speed of inherent destabilisation and thus reducing the particle sedimentation can be achieved by a : Decrease of the particle size distribution. Reduction of the difference of density between the dispersed and continuous phases. Increase of the viscosity of the continuous phase. The inhibition of sedimentation can be achieved by the use of inert solid fine particles in combination with a suitable thickener. It is well known that fine swellable materials such as oxides when incorporated in the aqueous dispersion medium can act against the sedimentation. Oxides such as silica (e.g. Wessalon S®) and alkaline earth metal silicates such as magnesium aluminosilicates (e.g. Vangel B®) can form "chain aggregates". Above a certain volume fraction the "chain aggregates" may form a "three dimensional gel network" in the aqueous phase containing the dispersed oxides particles. The presence of this specific structure in the continuous aqueous phase delays the settling of the organic particles of the pyrethroid active ingredient. The content of swelling agents is preferably 0.5 to 10 % w/w, in particular 1.5 to 4% w/w. The use of a thickener such as a swellable anionic heteropolysaccharide such as xanthan gum (e.g. Rhodopol 23 ® or r e/zan ® ) is also necessary to obtain a significant long term storage stability and to prevent sedimentation of solid particles. The positive effect or phenomena produced by using this thickener is called "gravitational stabilisation by continuous phase structuration". Xanthan gum which is produced by fermentation of carbohydrates by means of Xanthomonas microorganisms forms a network of entangled rod molecules in water which acts against settling down. The content of swellable polysaccharides is preferably 0 to 5 % w/w, in particular 0.2 to 3.5 % w/w. The aqueous solution of the thickener is prepared in a separate vessel by using a high speed agitator to provide a good dispersion and an efficient swelling of the thickener and is added to the Premix obtained in step B. The pyrethroid SC additionally comprises a preservative to protect the solution of the thickener against bacterial development so as to prevent a complete destruction of the suspending network. Examples of efficient preservatives are formaldehyde and alkyl parahydroxybenzoate (e.g. propyl parahydroxybenzoate such as Preserval P ® ). The content of preservative in the pyrethroid SC is preferably 0.15 to 3 % w/w, in particular 0.1 to 1.5 % w/w. As a water-based formulation the pyrethroid SC must be protected against low temperatures (frost). The pyrethroid SC optionally contains an antifreeze selected from glycols (e.g. monopropylene glycol and ethylene glycol), triols (e.g. glycerol), urea or an inorganic salt (e.g. calcium chloride), in particular monopropylene glycol. The content of the antifreeze is preferably 0 to 18 % w/w, in particular 0 to 16 % w/w. The further dilution of the pyrethroid SC in water prior to application in the field leads to a spray mixture free from inclusive and surface foams. The air bubbles which can affect the application of the spray mixture on the crop can be eliminated by using a non ionic oil-in-water emulsion of polydimethyisiloxanes (e.g. Rhodorsil 426R ® ). The content of the antifoam is preferably 0 to 1 % w/w, in particular 0 to 0,5 % w/w. Further additives or auxiliaries such as an active ingredient stabiliser (e.g. acetic acid, citric acid) and a colouring agent may be added to the pyrethroid SC according to the invention. The content of stabiliser is preferably 0 to 1 % w/w. The content of colouring agent is preferably 0 to 2 % w/w. At the end of the production process the following physico-chemical properties of the pyrethroid SC are determined: The blooming or spontaneity of the formulation when diluted with water which has to be excellent. The suspensibility to check the homogeneity of the treatment which has to be superior to 85 %. The fineness of the particles in order to make sure that there is no crystal growth or flocculation. The rheological behaviour to control the physico-chemical stability. So the viscosity values of the pyrethroid SC according to the invention are 150 - 500 mPas at 30 rpm (Brookfield measurement). The invention also relates to a method of controlling harmful insects, which comprises applying an effective amount of the above-mentioned pyrethroid SC in the form of an aqueous dilution to these harmful insects or to the plants, soils, surfaces, and the like infested with them, and to the use of the pyrethroid SC in crop protection or environmental health. The compositions according to the invention are simply applied by diluting the suspension concentrates with the desired amount of water, stirring the mixture briefly and applying to the plants, soils, surfaces and the like. The present invention using the process described above is illustrated by the following examples. Example 1 Using the process described above a SC formulation containing 7,5 g/l deltamethrin active ingredient is obtained. Example 2 Using the process described above a SC formulation containing 25 g/l deltamethrin active ingredient is obtained. Example 3 Using the process described above a SC formulation containing 50 g/l deltamethrin active ingredient is obtained. Example 4 Using the process described above a SC formulation containing 200 g/l deltamethrin active ingredient is obtained. Example 5 Using the process described above a SC formulation containing 50 g/l acrinathrin active ingredient is obtained.

Claims: Claims: 1 ) A process of preparation of a suspension concentrate (SC) of a pyrethroid comprising: A. Wetting of the pyrethroid active ingredient by a liquid (Premixing); B. Breaking-up of aggregates and agglomerates (Grinding of Premix) and C. Stabilisation of the grinded Premix (Dilution and Thickening). 2) A process of preparation according to claim 1 wherein the pyrethroid SC comprises 5 to 500 g/l of pyrethroid active ingredient. 3) A process of preparation according to claims 1 and 2 wherein the pyrethroid is deltamethrin or acrinathrin. 4) A process of preparation according any of the claims 1 to 3 wherein a high shear mixer or dispersor and an ionic surfactant combination as the wetting and dispersing agents are used in step A. 5) A process of preparation according any of the claims 1 to 4 wherein the ionic surfactant combination is sodium laurylsulphate in combination with a mixture of sodium alkyl ether sulfate and a sodium alkylnaphtalenesulfonate formaldehyde condensate adsorbed on silica, or the use of the triethanolamine or potassium salt of an acid ester of a polyethoxylated polyarylphenol. 6) A process according to any of the claims 1 to 5 wherein the SC formulation comprises 1 to 30 % w/w of the ionic surfactant combination defined in claim 4. 7) A process according to any of the claims 1 to 6 wherein the SC formulation comprises 3 to 15 % w/w of the ionic surfactant combination defined in claim 4. 8) A process according to any of the claims 1 to 7 wherein in step B the pyrethroid active ingredient is milled and dispersed to a fineness below 5 microns. 9) A process according to any of the claims 1 to 8 wherein in step C swelling agents and an anionic heteropolysaccharide thickener are used to act against sedimentation. 10) A process according to any of the claims 1 to 9 wherein the pyrethroid SC formulation comprises 0.5 to 10 % w/w of oxides and alkaline earth metal silicates as swelling agents. 11 ) A process according to any of the claims 1 to 10 wherein the pyrethroid SC formulation comprises 0 to 5 % w/w of xanthan gum as the anionic heteropolysaccharide. 12) A process according to any of the claims 1 to 11 wherein the pyrethroid SC formulation comprises several or each of the additives selected from preservatives, antifreezes, antifoams, active ingredient stabilisers and colouring agents. 13) A process according to any of the claims 1 to 12 wherein the pyrethroid SC formulation additionally comprises 0.15 to 0.3 % w/w of preservative, 0 to 18 % w/w of glycol or triol antifreeze, 0 to 1.0 % w/w of antifoam, 0 to 1 % w/w of active ingredient stabilisers and 0 to 2 % of colouring agents 14) Pyrethroid SC formulations prepared by the process of any of the claims 1 to 5) A method of controlling harmful insects, which comprises applying an effective amount of a pyrethroid SC formulation as claimed in claim 14 in the form of an aqueous dilution to these harmful insects or to the plants, soils and surfaces infested with them.

Inventors: BOURGOGNE MICHEL, FRANSON CLAUDE, HENRIET MICHEL, LAMBERT BERNARD, TARANTA CLAUDE, BOURGOGNE, MICHEL, FRANSON, CLAUDE, HENRIET, MICHEL, LAMBERT, BERNARD, TARANTA, CLAUDE
Applicants: AVENTIS CROPSCIENCE GMBH, BOURGOGNE MICHEL, FRANSON CLAUDE, HENRIET MICHEL, LAMBERT BERNARD, TARANTA CLAUDE, BOURGOGNE, MICHEL, FRANSON, CLAUDE, HENRIET, MICHEL, LAMBERT, BERNARD, TARANTA, CLAUDE
Application year: 2000
Main classification: A01N25
IPC codes: A01N25, A01N53