Agrochemical formulation

Abstract

The present invention relates to the provision of stable agrochemical suspension concentrate compositions, together with methods of preparing and using the same.

Description

[0001] AGROCHEMICAL FORMULATION

[0002] The present invention relates to the provision of stable herbicidal suspension concentrate compositions, together with methods of preparing and using the same.

[0003] The control of undesired vegetation is extremely important in order to achieve high crop efficiency. Herbicides have a phytotoxic effect on unwanted plants and so are used in the plant protection industry for controlling weeds or inhibiting their growth. Herbicides can be non-selective, which means that they can destroy all growth. Other types of herbicides are selective herbicides, which kill specific target plants while leaving the desired / economically important plants relatively unharmed. However, these selective herbicides may not be effective against specific types of weeds which may also be present in the crop to be protected. In some cases it may be desirable to combine different agrochemicals to provide a single formulation taking advantage of the additive properties of each separate agrochemical.

[0004] Mesotrione is a systemic pre- and post-emergence herbicide for the selective contact and residual control of broadleaf weeds. Mesotrione possesses a broad spectrum of activity on a number of commercially important weeds. In order to achieve broad efficacy against a variety of weeds, mesotrione is often sold as a mixture with other agrochemically active ingredients.

[0005] One such family of ingredients is the triazine herbicides. The triazine herbicides are a well-known class of herbicides which include, for example, atrazine, metribuzin, cyanazine, prometon, hexazinone and simazine.

[0006] The combination of mesotrione and one or more triazines is well known for the effective control of triazine-tolerant weeds. Mixtures of mesotrione and atrazine are known to have a synergistic effect in killing certain weeds and this is disclosed in US patent 5 698 493. US Patent No. 7071147 provides a process of controlling triazine-tolerant weeds by the application of a combination of mesotrione and a triazine herbicide (atrazine) to the locus of said weeds. US Patent Publication No. 2011263425 provides method for controlling or modifying the growth of large crabgrass or white clover, comprising applying to the locus of the large crabgrass or white clover, a herbicidally effective amount of a composition comprising a mixture of mesotrione and atrazine.

[0007] Agriculturally active ingredients are often provided in the form of concentrates suitable for dilution with water. Many forms of agricultural concentrate are known and these consist of the active ingredient, a carrier and can include various other components. Waterbased concentrates are obtained by dissolving, emulsifying and / or suspending agriculturally active technical materials in water.

[0008] Mesotrione compositions as liquid formulations are well known in the art. When mesotrione is dissolved, it exhibits a tendency to slow, long-term chemical degradation. This is especially true in aqueous systems. The aqueous solubility of mesotrione increases with increasing pH. It is, therefore, highly soluble at high pH and sparingly soluble at low pH. Mesotrione is therefore often formulated at low pH where its solubility is greatly reduced and its chemical stability significantly increased.

[0009] When the agrochemical active ingredients are insoluble or only partly soluble in water, it is convenient to formulate these in the form of an aqueous suspension concentrate (SC). Suspension concentrates contain finely milled solid particles which remain suspended in solution. In the case of agrochemical suspension concentrate compositions, the solid particles are particles of pesticide active ingredient.

[0010] It is therefore ideal to formulate pesticides such as mesotrione, as suspension concentrates under conditions of low pH.

[0011] Due to the relatively complex supply chain for crop protection products, formulations are often stored for long periods. They may also be subjected, during storage and shipping, to extreme temperature variations, high-shear and repetitive vibration patterns. Such supply chain conditions can increase the likelihood of formulation failure due to, for example, water mediated degradation, flocculation, crystal growth, sedimentation or phase separation. It is important, on long term storage of suspension concentrates, that the solid particles remain suspended. If severe separation or sedimentation is observed, it is often difficult to re-disperse the particles. These types of formulation failure are one of the biggest challenges in the agrochemical industry.

[0012] In order to mitigate against these problems, co-formulants such as dispersants or thickeners are often added to suspension concentrates. However, if the pH of the suspension concentrate composition is acidic, the dispersant or thickener choice may be further limited due to poor performance of these co-formulants at pH levels less than 5. Although traditional xanthan gum functions quite well initially in acidic conditions, over the typical shelf life of such a composition, the composition will lose viscosity.

[0013] The object of this invention is to overcome the chemical and physical challenges created by formulating aqueous suspension concentrate compositions under acidic conditions. This is a very complex challenge as the formulation must still be efficacious, as well as chemically and physically stable during storage, substantially maintaining their viscosity or have reduced viscosity loss over an extended period of time.

[0014] The present invention relates to the provision of stable herbicidal suspension concentrate compositions, together with methods of preparing and using the same.

[0015] It has surprisingly been found that the technical problems mentioned above are resolved by the present invention. There is therefore provided an agrochemical suspension concentrate composition comprising: (a) mesotrione; (b) at least one triazine herbicide; (c) a thickener comprising an acid stabilised xanthan gum, wherein the average acetyl content is from less than 1.5% by weight of the xanthan gum; (d) a dispersant comprising: (i) an acrylic graft co-polymer, and / or (ii) a modified styrene-maleic anhydride co-polymer; and (e) water.

[0016] Suspension concentrate compositions are formulations having insoluble, solid active ingredients suspended in water optionally with the aid of dispersing and thickening agents for application onto plant surfaces.

[0017] Preferably, the mesotrione is present in an amount from 0.1 to 25%, from 0.5 to 15%, preferably from 0.75 to 12%, more preferably from 1 to 10%, even more preferably from 1 to 5%, by weight of the composition.

[0018] The terms ‘agrochemical’ and ‘active ingredient’ are used interchangeably herein.

[0019] Preferably, the composition contains at least one agrochemically acceptable triazine herbicide.

[0020] Examples of triazine herbicides include atrazine, metribuzin, cyanazine, prometon, hexazinone and simazine.

[0021] Preferably, the triazine herbicide is present from 1 to 95%, more preferably from 2 to 80%, even more preferably from 5 to 75%, yet further preferably from 8 to 65%, and most preferably from 10 to 60%, by weight of the composition.

[0022] Preferably, the triazine herbicide is atrazine.

[0023] The term "thickener" as used herein means any agrochemically acceptable thickening agent or thickener that enables an increase in the viscosity of a liquid, without substantially changing the properties of the liquid. Thickeners can be organic or inorganic in nature. Preferably, the thickener is organic in nature. Preferably, the thickener is a polysaccharide or a polysaccharide derivative. However, according to the present invention the thickener must comprise, and indeed may even consist of, an acid stabilised xanthan gum as described infra.

[0024] The structure of xanthan gum is well known in the prior art, it is composed of pentasaccharide alternating repeat units, comprising D-glucose, D-mannose, and D- glucuronic acid, in the molar ratio of about 2:2:1. Structurally, the main chain of xanthan gum is composed of cellobiose duplicate units, which are stable against the changes of pH, temperature, and shear stress. Pyruvate acid is linked in an unknown distribution to about half of terminal D-mannose in positions 4 and 6. The D-mannose monosaccharide linked to the backbone of the polymer has an acetyl group at oxygen-6 position.

[0025] The term “traditional xanthan gum”, includes native xanthan gum. Native xanthan gums are heteropolysaccharides produced, for example, when strains of Xanthomonas campestris are cultured in a suitable medium as described inter alia US 3020206, US 30020207 and US 3391060. The bacteria fermentation process results in a sticky protective coat that has a consistency that makes it suitable for binding or thickening.

[0026] The term ’’acid stabilised xanthan gum” includes treated and / or modified xanthan gum, deacetylated xanthan gum, non-acetylated xanthan gum, low acetylated xanthan gum, low acetylated xanthan gum cross-linked with polyvalent cations, as well as xanthan gum / glyoxal complexes. Low acetylated xanthan gum includes xanthan gums which have been deacetylated (such as by chemical means). Acid stabilised xanthan gums may also include any combination of the preceding examples. The term “acid stabilised xanthan gum” and “low acetylated xanthan gum” are used interchangeably herein.

[0027] Details of acid stabilised xanthan gums can be found in US patent 6139895.

[0028] Traditional xanthan gum typically contains approximately 5% acetate by weight of xanthan gum. Preferably the acid stabilised xanthan gum has an acetate content of less than 1.5%, less than 1.35%, preferably less than 1.25%, more preferably less than 1.1 %, even more preferably less than 1.0%, by weight of the xanthan gum.

[0029] A reduction in acetate content results in xanthan gum that is stable in the presence of acid, in contrast traditional xanthan gum does not remain stable in the presence of acid.

[0030] Acid stability can be confirmed by performing a viscosity retention test. A solution of the xanthan gum is prepared at less than 0.5% by weight in an aqueous solution containing about 4% by weight of citric acid or at a pH of 3 or less. If the viscosity is retained after a period of 3 to 7 days, the xanthan gum is considered to be acid stabilised.

[0031] The determination of acetyl content is well known in the art. The total acetyl content, as acetate, in the xanthan gum may be determined by HPLC, for example, Cheetham, N.W.H. and Punruckvong, A., Carbohydrate polymers, volume 5 issue 6 (1985) p399- 406.

[0032] Preferably the acid stabilised xanthan gum is present from 0.01 to 10%, more preferably from 0.02 to 8%, even more preferably from 0.03 to 7%, yet further preferably from 0.05 to 5%, and most preferably from 0.05 to 2%, by weight of the composition.

[0033] Acid stabilised xanthan gum is provided by the following manufactures under a number of tradenames; Kelzan™ AP-AS (ex. CP Kelco), Xanthan gum FFST™ (ex. Jungbunzlaur) or Xanthan gum FED™ (ex. Jungbunzlaur).

[0034] The term "dispersant" as used herein means any agrochemically acceptable dispersing agent or dispersant system that enables the dispersal of other substances or particles, in a medium such as water, to form a colloidal solution. Dispersants can be inorganic or organic in nature. Preferably, the dispersant is an organic polymer. More preferably the polymeric dispersant is an organic co-polymer. Graft co-polymers are branched co-polymers, where the components of the side chain are chemically and structurally different than those of the main chain. The term "graft co-polymers" in relation to dispersants, is used herein to refer to those polymers the structure of which, similar to that of a comb, have a backbone polymer chain to which are appended polymer chains different from the backbone which can be the same or of different natures and lengths.

[0035] The agrochemical compositions according to the present invention comprise one or more dispersants comprising a graft co-polymer.

[0036] A graft co-polymer is a material that has polymer chains of one chemical composition branching out from a polymer backbone with a different chemical composition. The preferred graft co-polymer for use in the present invention has a polymer backbone and polyether groups appended to the polymer backbone.

[0037] Graft co-polymers that can be used in accordance with this invention include but are not limited to graft co-polymers having a backbone polymer of at least one of acrylic acid, methacrylic acid, acrylate, methacrylate or methyl methacrylate, which have chains of another polymer, by way of non-limiting example, a polyether such as polyethylene oxide, extending from the polymer backbone. In this example the two-dimensional representation will draw the PEG branches perpendicular to the polymer backbone (usually linear) and resemble the teeth of a comb. Graft co-polymers of this type are occasionally referred to as "comb-graft polymers".

[0038] In one embodiment, the polymer is an acrylic graft co-polymer. In a preferred embodiment, the acrylic graft co-polymer is an amphipathic co-polymer.

[0039] In one preferred embodiment of the invention, the graft co-polymer has a backbone chain of a polymer such as (meth)acrylic polymer or co-polymer to which are appended polyoxyalkylated lateral groups such as polyethylene oxide groups.

[0040] Suitable graft co-polymer dispersants include, but are not limited to, non-ionic polyacrylate graft co-polymers, such as Dispersogen PSL 100 from Clariant, modified polyacrylic acids such as Sokolan CP N40 from BASF, acrylic co-polymers, such as Atlox 4913 and Zephyrm PD3315 from Croda and Tersperse 2500 from Indorama, acrylic polymers such as Emulson AG TRN 14105, Emulson AG TP1 and Emulson AG RHS from Lamberti and / or other graft co-polymers such as Ethacryl P (a 35-45 percent comb-graft co-polymer solution from Lyondell Chemical Co.) and / or AGNIQUE CP-72L.

[0041] Tersperse 2500 is a comb-graft co-polymer solution (approx. 35 weight percent polymer) commercially available from Indorama.

[0042] Atlox 4913 is a emulsion of a comb-graft co-polymer comprising 36.6% methyl methacrylate, 1.9% methacrylic acid, both grafted with methoxypoly(ethylene glycol) 750 methacrylate (61.5%), and is commercially available from Croda. Altox 4913 has a CAS number of 119724-54-8.

[0043] In another preferred embodiment of the invention, the graft co-polymer comprises a monomer of a beta unsaturated acid or anhydride, or an agrochemically acceptable salt thereof, and a second monomer comprising an olefinic compound containing one or more polymerizable double bonds.

[0044] Preferably the first monomer comprises a beta-unsaturated oxyacid or anhydride selected from the group consisting of fumaric acid and anhydride, and the esters, amides and imides derived from them, maleic acid esters, amides and imides, itaconic acid and anhydride and the corresponding esters amides and imides derived from them, acrylic and methacrylic acids and the corresponding esters and amides derived from them, vinyl phosphonic acid and the corresponding esters and amides derived from it, and ethylene sulphonic acid and the esters and amides derived from it.

[0045] Preferably the first monomer comprises maleic acid anhydride or agrochemically acceptable salt or derivative.

[0046] Preferably, the first monomer is further reacted, at one of the acid groups, with an amine of a polyoxyalkylate groups producing a carboxyamide polyalkoxylate. The polyoxyalkylate groups comprise of polyethylene glycol or polypropylene glycol groups, or a mixture thereof.

[0047] Preferably the second monomer comprises an olefinic compound containing one or more polymerizable double bonds selected from the group consisting of styrene and its alkyl and halo derivatives, vinyl esters, internal olefins, exocyclic and endocyclic olefins, allylic alcohols and their corresponding ester derivatives, allylic ethers and allylic halo compounds, allylic aryl compounds, vinyl amides, vinyl chloride and vinylidene chloride.

[0048] Preferably the second monomer comprises styrene or an alkyl styrene.

[0049] A modified styrene-maleic anhydride dispersant combines the advantages of aromatic dispersants and comb polymer dispersants into a single comb polymer with aromatic groups on the backbone. The aromatic groups can interact more effectively than other comb polymer backbones with aromatic-containing active ingredients, such as mesotrione.

[0050] When the first monomer is maleic acid anhydride or agrochemically acceptable salt or derivative, and the second monomer is styrene or an alkyl styrene, the resulting copolymer is referred to as a modified styrene-maleic anhydride co-polymer.

[0051] The agrochemical compositions according to the present invention comprise a copolymer dispersant comprised of modified styrene-maleic anhydride graft co-polymer. Preferably the modified styrene-maleic anhydride dispersant has styrene to maleic anhydride molar ratio of at least 4.0:1.0 and a monofunctional polyalkylene glycol comprised of an alkyl or aromatic group.

[0052] Suitable graft co-polymer dispersants include, but are not limited to, Tersperse 2612 (Indorama).

[0053] Preferably, the dispersant comprises a modified styrene-maleic anhydride copolymer.

[0054] Preferably, the dispersant comprises an acrylic graft co-polymer and a modified styrene-maleic anhydride co-polymer.

[0055] Preferably the total dispersant is present from less than 25%, more preferably from less than 20%, even more preferably from less than 15%, yet furthermore preferably from less than 12%, and most preferably from less than 10%, by weight of the composition.

[0056] The composition may further comprise additional thickeners such as, for example, polyvinylpyrrolidones, alkylated polyvinylpyrrolidones such as C4 alkylated polyvinylpyrrolidone, lignosulphonates, condensates of naphthalene sulphonates and magnesium aluminium silicates.

[0057] In one embodiment the composition will comprise one additional thickener, in a further embodiment the composition will comprise two additional thickeners.

[0058] The composition comprises water.

[0059] Preferably, water is present from less than 75%, more preferably from less than 60%, even more preferably from less than 55% and most preferably less than 50%, of the composition.

[0060] Compositions of the invention preferably have a pH of 5 or less. Aqueous formulations can be acidified using an agrochemically acceptable acid. Agriculturally acceptable acids include acetic acid, citric acid, formic acid, phosphoric acid, malic acid, succinic acid, sulphuric acid, hydrochloric acid. Preferably the acid is citric acid. Preferably the pH is from of less than 5, from 0.25 to 5, preferably from 0.5 to 5, more preferably from 1 to 4, even more preferably from 1.5 to 4, most preferably from 2 to 3.

[0061] In general pesticides present in agrochemical suspension concentrate formulations are milled to specific sized particles during the formulation process. Particle sizes can be defined by techniques such as Laser diffraction particle sizing, which is known in the art. The d50 value, measured in microns, defines the mean or average particle size of solid particles in a suspension.

[0062] Preferably particles in the suspension concentrate compositions of the invention have a d50 value of less than 100 microns, more preferably from 0.1 to 50 microns, even more preferably from 0.1 to 25 microns, yet further preferably from 0.1 to 12 microns, and most preferably from 0.1 to 8 microns.

[0063] The compositions may further comprise one or more surfactants.

[0064] Preferably, the surfactant is present between 0.1 to 20% by weight of the composition, more preferably from 0.15 to 15%, more preferably from 0.25 to 10%, even more preferably from 0.5 to 7.5% and most preferably from 1 to 5% by weight of the composition.

[0065] The term "surfactant" as used herein means any agrochemically acceptable surfactant or surfactant system that decreases the surface tension or interfacial tension of between two liquids, a liquid and a gas or a liquid and a solid. Preferably, the surfactant is a polyoxyalkylene alkyl ether. Preferably the polyoxyalkylene alkyl ether is an alcohol ethoxylate. Preferably the alcohol ethoxylate has an alkyl chain length from 4 to 26, more preferably from 6 to 24, even more preferably from 8 to 20 and most preferably from 10 to 16.

[0066] The compositions may further comprise one or more flowability agents. The term "flowability agent" as used herein means any agrochemically acceptable flowability agent or flowability system that increases the mobility of liquids and solid particles when they interact in solution. Examples of flowability agents include silicon dioxide. Preferably the flowability agent is present from less than 10% by weight of the composition, more preferably less than 7.5%, even more preferably from less than 7.5%, yet further preferably from less than 5% and most preferably from less than 4% by weight of the composition. Preferably, the flowability agent is a silicon dioxide or a fumed silica, or a mixture thereof.

[0067] The composition may additionally comprise further formulation additives such as, for example, antioxidants, antifoaming agents, inorganic filler, buffer, coating agents, safeners and the like as well as any mixtures thereof. The skilled man will be familiar with the use of these as they are routine in the field of agrochemical formulation.

[0068] A second aspect of the present invention provides for a method of controlling weeds, comprising applying the composition as described herein to the locus of said plants.

[0069] In a third aspect of the invention, there is provided a method of preparing a suspension concentrate composition according to any of the claims comprising of:

[0070] (a) Combining the mesotrione and a triazine herbicide;

[0071] (b) Combining the dispersant(s), and water;

[0072] (c) Mixing the products of step (a) and step (b);

[0073] (d) Milling the particulate composition resulting from step (c), such that the desired particle size in achieved, and checking the resulting particle size;

[0074] (e) Combining and mixing the acid stabilised xanthan gum, and water; (f) Mixing the products of step (c) and step (e) and adjusting the pH to from 2.2 to 2.8; and

[0075] (g) Filtering the product of step (f). Optionally, one or more surfactants may be incorporated in step (b) of the above method.

[0076] Unless otherwise stated, the weights and concentrations are expressed herein in percentage by weight of the composition.

[0077] The invention is illustrated by the following non-limiting examples.

[0078] EXAMPLES

[0079] Mesotrione and atrazine suspension concentrate formulations were prepared in combination with a range of the co-formulants listed in Table 1. Table t

[0080] Pre-selection of acid stabilised xanthan gums

[0081] The four xanthan gum materials were tested for stability under acidic conditions. Solutions of xanthan gum in water were tested under acidic conditions. Citric acid was used to adjust the pH of the aqueous solution to 2.2. Samples of xanthan gum were prepared at 0.09% in acidic solution. For each sample, a control was also prepared wherein the pH was not adjusted. Samples were stored for 7 days at a temperature of 40 degrees Celsius.

[0082] The samples were scored after storage from 1 to 4. A score of 4 indicated no sedimentation and no separation was observed, whilst a score 1 indicated failure of the solution with flocculation and aggregation observed. The test results can be found in Table 2.

[0083] Table 2

[0084] The results show that non-acid stabilised xanthan gums do not pass the acid stability check under all conditions. According to the current invention the xanthan gum used must be stable and effective under acidic conditions. The three acid stabilised xanthan gums were used in the following experiments.

[0085] Preparation of the suspension concentrate compositions

[0086] The suspension concentrate compositions according to the invention were prepared by the following general procedure. The mesotrione and atrazine active ingredients were weighed and combined. The dispersants, propylene glycol, anti-foam agent, some citric acid, some biocide and some of the water, were weighed and combined in a separate container to form a co-formulant pre-mixture. The active ingredients and the co-formulant mixture were combined mixed and then milled. A check was made of the appearance and particle size. A pre-gel was prepared comprising of the acid stabilised xanthan gum, some BIT biocide and some water. The pre-gel was added to the active ingredients and the co- formulant mixture and then pH adjusted to the required level with anhydrous citric acid. All weights, unless specified, are percentage weight for weight of the composition.

[0087] EXAMPLE 1

[0088] The aim of the experiment was to investigate the effect of the current invention on the sedimentation, re-dispersibility and phase separation of SC formulations. Five suspension concentrate formulations 1-1 to 1-5, according to the invention, were prepared by combining some of the ingredients indicated in Table 1. All compositions apart from one were prepared according to the invention. Formulation 1-3 was made without the acid stabilised xanthan gum. The compositions are shown in Table 3. Table 3

[0089] Tables 4, 5 and 6 show the rating scales for sedimentation, redispersibility and phase separation. For each parameter a score of 2 was very good and a score of 0 was unacceptable.

[0090] Table 4 Table 5

[0091] Table 6 All formulations prepared according to the invention showed good performance when sedimentation volume, re-dispersability and separation were evaluated. The results form the experiments can be seen in Table 7.

[0092] Table 7

[0093] EXAMPLE 2

[0094] The aim of this experiment was to investigate whether the source of the acid stabilised xanthan gum affected the stability of the compositions prepared according to the invention. Three formulations were prepared with three different sources of acid stabilised xanthan gum.

[0095] Table 8

[0096]

[0097] All formulations prepared according to the invention showed good performance when sedimentation volume, re-dispersability an separation were evaluated. The results form the experiments can be seen in Table 9.

[0098] Table 9

Claims

CLAIMS1. An agrochemical suspension concentrate composition comprising:(a) mesotrione;(b) at least one triazine herbicide;(c) a thickener comprising an acid stabilised xanthan gum, wherein the average acetyl content of the xanthan gum is from less than 1.5% by weight of the xanthan gum;(d) a dispersant comprising:(i) an acrylic graft co-polymer, and / or(ii) a modified styrene-maleic anhydride co-polymer; and(e) water.

2. A composition according any of the preceding claims, wherein the concentration of mesotrione is from 0.1 to 25% by weight of the composition.

3. A composition according any of the preceding claims, wherein the concentration of the triazine herbicide is from 1 to 95% by weight of the composition.

4. A composition according to any of the preceding claims, wherein the triazine herbicide is atrazine.

5. A composition according to any of the preceding claims wherein the concentration of the acid stabilised xanthan gum is from 0.01 to 10% by weight of the composition.

6. A composition according to any of the preceding claims, wherein the acid stabilised xanthan gum has an average acetyl content of less than 1.5% by weight of the xanthan gum.

7. A composition according any of the preceding claims wherein the dispersant is present at less than 10% by weight of the composition.

8. A composition according to any of the preceding claims, further comprising a surfactant, wherein the surfactant is present between 0.1 to 10% of the composition.

9. A composition according to claim 8, wherein the surfactant is an alcohol ethoxylate.

10. A composition according any of the preceding claims, having a pH from 0.1 to 5.

11. A composition according any of the preceding claims, wherein mesotrione and the triazine pesticide particles comprise a d50 particle size from 0.1 to 8 microns.

12. A method of preparing a composition according to any of the preceding claims in the order of the following steps; (a) combining the mesotrione and triazine herbicides;(b) combining the dispersants and solvent;(c) mixing the products of step (a) and step (b); and(d) milling composition resulting from step (c);13. A method according to claim 12, further comprising one or more surfactants in step (b).

14. A method according to claim 12 and 13, further comprising of adjusting the pH of the composition in step (d) and combining it with one or more thickeners.

15. Use of a composition according to claims 1 to 11 for the treatment of weeds.

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