IE54701B1 - Aqueous phenoxy-emulsion - Google Patents

Abstract

Storage-stable, herbicidally- active compositions in the form of a concentrating aqueous emulsion comprising 30 to 75% by weight of one or more herbicidally-active phenoxyalkanecarboxylic acid esters, 0.1 to 5 parts by weight referred to the completed emulsion of one or more oil-soluble emulsifiers which are soluble in the esters and have an HLB value of 9 to 16, and 0.1 to 3 parts by weight referred to the completed emulsion of one or more alkali metal salts of single or multiple unsaturated fatty acid taurides or fatty acid alkyl taurides as watersoluble dispersants, the emulsion having a viscosity of 50 to 3,000 mPa.s., a droplet size of 1 to 5 mu m and a pH value of 6 to 9 and a process for the preparation of such emulsion which comprises forming a solution of the active ester and emulsifier and mixing it with an aqueous solution of the dispersant to form a homogeneous mixture.

Description

This invention relates to a storage-stable, herbicidally-active composition in the form oi a concentrated aqueous emulsion of one or more herbicidaily active phenoxyalkanecarboxylic acid esters, and to a process for the preparation thereof.

Phenoxyalkanecarboxylic acids are amongst the most commonly used herbicides. They are employed in the form of their amine salts and mineral salts, and also as esters, for example the isopropyl, butyl, butylglycol or 2ethylhexyl esters. The advantage of the esters is that they penetrate more rapidly into the plant and accordingly their use is less dependent on the weather. Their solubility in water is low, but they are soluble in oils, such as diesel oil, kerosene, petroleum ether., xylenes, cyclohexanone, isophorone or highly refined hydrocarbons. Usually, the ester is dissolved in one of these solvents, and an emulsifier is added to the solution, giving a concentrated, clear, emulsifiable solution {referred to as an emulsion concentrate or EC), which, for field use, is diluted with water, thereby producing an oil-in-water emulsion.

According to Austrian Patent Specification 307,802 it is also possible to store pesticides by preparing a very viscous formulation of the oii-in-water type, consisting of active ingredient, mineral oil, water and formulation auxiliaries, which, for application, is inverted before use, by means of an additive consisting of solvent and dispersant, giving a mobile water-in-oil dispersion referred to as an inverse emulsion.

Both types of formulation, namely the conventionally used emulsion concentrate and the very viscous dispersion, however, have serious disadvantages, the causes of which rest with the solvent used. AH solvents conventionally used for this purpose are, like most organic solvents, at least detrimental to health, but in particular also flammable. Thus, highly purified,predominantly aliphatic hydrocarbons have a flash point of ¢0° to 80°C., isophorone has a flash point of 93°C., cyclohexanone has a flash point of M°C. and the most commonly used xylenes have a flash point of only about 25°C.

Accordingly, the emulsion concentrates prepared with the aid of these solvents are also flammable, and in the past there have been a number of fires in stores of such concentrates, both on the manufacturer's premises and also on the user's premises.

In contrast to the prior art described above, It has now been found that by using certain auxiliaries it is possible to produce a storage-stable, highly concentrated emulsion of herbicide esters, which Is water-based and is therefore non-flammable and free from solvents detrimental to health. The ability to use an aqueous medium to produce storage-stable emulsions of phenoxy-esters is surprising since the esters are somewhat water-soluble, albeit only slightly, and can therefore undergo hydrolysis.

Accordingly, the present invention provides a storage-stable herbicidally-active composition comprising a concentrated aqueous emulsion of one or more herbicidally active phenoxyalkanecarboxylic acid esters in which the emulsion contains 0,1 to 5 t by weight, referred to the completed emulsion, of one or more oil-soluble emulsifiers which are soluble in the esters, have an HLB value of 9 to 16, and are selected from fatty acid polyethylene glycol esters, polyethylene glycol ethers of fatty alcohols, polyethylene glycol ethers of glycerides, polyethylene glycol ethers of alkylphenols, polyoxyethylene/polyoxypropylene block copolymers and mixtures of the said polyethylene glycol esters, polyethylene glycol ethers or polyethylene giycol/polypropylene glycol block cooolymers with alkylarylsuiphonates; and one or more water-soluble dispersants it ai amount of 0,1 to 3 % by weight, referred to the completed emulsion selected from the group consisting of alkali metal salts of single or multiple unsaturated fatty acid taurides or fatty acid aikyitaurides, in which the amount of herbicidally active ester is 30 to 75 % by weight of the concentrated emulsion, the viscosity of the emulsion is 50 to 3,000 mPa.s, the droplet size is 1 to 5 pm and the pH value is 6 to 9.

The concentrated aqueous emulsion of the invention optionally may also contain one or more conventional antifreeze agents, conventional anti-foam agents, thickeners or a mixture thereof.

The highly concentrated emulsion according to the invention is prepared by mixing the individual reactants or by mixing 2 solutions. Solution I contains the phenoxyester or phenoxy-esters and an emulsifier soluble in the esters, whilst solution Π contains a dispersant, dissolved in water, and optionally, antifreeze agents, thickeners, anti-foam agents or colorants.

Thus, the invention also provides a process for the preparation of a storage-stable, herbicidally-active composition in the form of a concentrated emulsion of herbicidally active phenoxyalkanecarboxylic acid esters containing 30 to 75 % by weight of active compound having a viscosity of 50 to 3,000 mPa-s, which comprises preparing a solution 1 from one or more phenoxyalkanecarboxylic acid esters and at least one emulsifier which is soluble in the ester and has an HLB value of 9 to 16, in which the amount of emulsifier is 0,15 to 10 parts by weight per 100 parts by weight of the solution I, and mixing solution 1 with an aqueous solution Π, which contains one or more watersoluble dispersants, selected from the group consisting of alkali metal salts of single or multiple unsaturated fatty acid taurides or fatty acid alkyl taurides in the amount of 0.2 to 10 parts by weight of dispersant per 100 parts of aqueous solution Π, and subsequently homogenizing the mixture at a temperature within the range of 15° to 90°C. until the droplet size is 1 to 5 pm, while maintaining the pH of the mixture at a value of from 6 to 9 and then diluting the homogenizate to the desired final volume.

The emulsifiers which are soluble in the phenoxyesters, i.e. fat-soluble emulsifiers, are responsible for the dispersion of the active substance in the continuous phase. Such emulsifiers, having an HLB (hydrophilic-lipophilic balance) value of 9 to 16 are fatty acid polyethylene glycol esters, the polyethylene glycol ethers of fatty alcohols, of monoglycerides or diglycerides and of aikyl-phenols, and polyethylene gly co!/polypropylene glycol block polymers. The emulsifiers may be used individually, as a mixture with one another or as a mixture with ammonium, calcium, magnesium, potassium, sodium or zinc salts of alkyl (Cg-Cj^,-benzenesulphonic acids- Fatty acid polyethylene glycol esters or poJyoxyethyrene/polyoxypropyiene block polymers used together with alkyiarylsulphonates are particularly suitable.

Solution I contains the fat-soiuble emulsifiers in a concentration of 0.15 to 10 per cent by weight, per 100 parts of solution I the range of 2 to 4 parts by weight in solution I being particularly preferred. In the composition of the invention, the emulsifier is present in an amount of 0.1 to 5 % by weight, preferably 1 to 3 9a by weight.

The water-soluble dispersant stabilizes the distribution of the disperse phase, for example through electrostatic charging of the particles or through other forces which cause repulsion, for example steric hindrance.

The dispersants used are the alkali metal salts, especially the sodium salts, of fatty acid taurides or fatty acid alkyl-taurides. Examples of such fatty acids, which are frequently used in the form of mixtures, are straightchain or branched saturated or mono- or poly-unsaturated aliphatic carboxylic acids having about 10 to 20 carbon atoms, such as lauric acid, palmitic acid, stearic acid, myristic acid and especially oleic acid. The alkyl radical in fatty acid alkyl-taurides is a lower alkyl radical with preferably up to U C atoms, especially the methyl radical.

The dispersants can contain inorganic salts, but it is advantageous to keep the salt content low, or avoid any salt content at ail.

Solution II contains the water-soluble dispersant in a concentration of 0.2 to 10 parts by weight, preferably 1 to 3 parts by weight, per 100 parts of solution II. The dispersant concentration in the composition of tbe invention is 0.1 to 3 % by weight, preferably 0.2 to I % by weight.

Usually, the storage-stable emulsion of the invention is prepared by preparing an aqueous solution II of a dispersant, which solution optionally contains anti-freeze agents, anti-foam agents or thickeners, and stirring the liquid phenoxy-ester or phenoxy-esters, containing the emulsifier dissolved therein, and constituting solution I, into solution II so as to form a homogeneous mixture. This stirring-in is effected by means of apparatus which genera2 4-1 tes a shearing rate of between 10 and 10 sec in the emulsion. This 2 corresponds, at high viscosity (3,000 mPa.s) to shearing stresses of 3.10 to 3.10 Pa, for which an apparatus such as a Homorex or Uitra-Turrax (Hcmorex and Uitra-Turrax are Trade Marks) or a hanogenizer with a homogenizing nozzle is suitable. At low viscosity (50 mP .s),the stated shearing rates correspond to shearing stresses of 5 to 500 Pa,for which an apparatus such as a vibrator,a low-speed mixer or a centrifugal pump is suitable.Since the viscosity decreases with increasing temperature,it is possible also to use a low-speed apparatus if an elevated temperature,approximately from 50° to 9O°C., is employed. Themixing is intended to produce homogeneous droplet dispersion,with droplet sizes of 1 to 5 pm, preferably of 2 to 3 pm, but in addition to the size of the individual droplets a very narrow size distribution and, at the same time, a low viscosity of the emulsion are of importance.lt is also possible, to put both solutions into a vessel with stirrer and mix subsequently, or to dose both solutions simultane54701 ously via a suitable metering device into the vessel.

The viscosity of the concentrated emulsion is an important factor in its shell life. The higher the viscosity, the better the shelf life. On the other hand, too high a viscosity adversely effects the ease of dilution with water and the spontaneous dispersibility on use. Using the concentrated emulsion prepared according to the invention, it is possible to prepare stable, and at the same time still easily dilutable, formulations having a viscosity within the range of 50 to 3,000 mPa.s. The best results in respect of dilutabiiity and spontaneous dispersibility on the one hand, and stability, on the other hand, are achieved at viscosities of from 500 to 1,500 mPa.s.

Another essential factor in preparing a stable emulsion is the adjustment of the pH value. For each combination of active compound/emulsifier/dispersant there is an optimum pH value at which the emulsion is most stable. This physical stability is best in the alkaline range, but pH values of about 9 should be avoided, since in this range, on prolonged storage and at elevated temperature, partial hydrolysis of the ester may commerce. In an acid medium, pH values of less than 6 are to be avoided, since in this range, on prolonged storage, coalescence may occur, i.e. the emulsion increasingly becomes physically unstable. A pH range of 7 to S is especially preferred.

The composition according to the invention may be prepared with any herbicidaily active phenoxyalkanecarboxylic acid esters, used individually or as mixtures with one another, especially the esters with alcohols of chain length C^-Cg, for example the octyi esters of 2-(4-chioro-2-methylphenoxyI)-propionic acid (CMPP-acid), (2-methyl-4-chlorophenoxy)acetic acid (MCPA-acid) or 2,l*,5-trichlorophenoxyacetic acid(2,l(,5-T-acia),the ethylexyl ester of the 2,k aichlorphenoxy acetic acid (2,U-D-ethylexyl ester),and the butyl ester of the 2,1) aichlorphenoxy acetic acid (2,U-D-hutyl ester).

Since technical-grade phenoxyalkanecarboxylic acid esters, because of their method of preparation, usually have a pH value of about 3 (measured in a % strength aqueous dispersion), the desired pH is obtained by use of a conventional caustic alkali, for example sodium hydroxide Or potassium hydroxide. The pH may be adjusted to the desired value during or after preparation of the emulsion, but it is also possible to use purified neutral esters, which makes subsequent adjustment of the pH value unnecessary.

To ensure adequate low temperature stability, conventional anti-freeze agents, such as ethylene glycol, glycerol, urea, glycol ethers or other alcohols may be added to the emulsions. Furthermore, it is possible to add known inorganic or organic thickeners, (or example xanthan gum, sodium polyacrylate, carboxymethylcellulose, colloidal silica or swelling clay minerals, such as bentonite, in order to adjust the viscosity to a particular value. To reduce foaming, anti-foam agents, such as long-chain alcohols, 2-ethylhexanol or cetyl alcohol, high-polymer glycols and especially silicones may be added.

For field use, the concentrated emulsions prepared according to the invention are diluted with water in exactly the same way as the hitherto customary flammable emulsion concentrates, and may be applied by means of the same spraying apparatus.

The Examples which follow describe the preparation, as well as the chemical and physical stability, of the compositions according to the invention. The technical-grade phenoxyalkanecarboxyiic acid esters used conform to the guideline recommended by the World Health Organization The stability was tested in a storage test, in which a 24-hour temperature cycle between -10°C. and +50°C. was followed. After storage for a period of 4 weeks, the following were measured: 1. Change in pH value 2. Consumption of 0.01 N sodium hydroxide solution, in order to restore the initial pH. 3. Viscosity change (measured on a Brookfield LVT, viscometer, spindle 2, 6 rpm) 4. Change in the turbidity of a 0.01 % strength emulsion, correlated with the change in droplet size (measured by means of a Lange turbidimeter in 100 ml cells).

. Supernatant liquid, in % 6. Coalescence (formation of an oily phase) 7. Re-emuisifiability.

The results of the measurements relating to the Examples have been summarized in a table. The results of the measurement show that in none of the Examples in question was the change in 1., 2., 3., 4. and 5. more than 10 % after a storage time of 4 weeks with a 24-hour temperature cycle between -10°C. and +50°C- No coalescence occurred and any non-coalesced sediment which might be present was completely re-emulsifiable.

Example 1 Solution I: 640 g of 2,4,5-T-amyI ester, technical grade g of fatty acid polyethylene giycol ester Solution II: 5 g of Na oleyl-methyl-tauride (95 % strength) 25 g of ethylene glycol, technical grade 1.3 g of xanthan gum 443 g of distilled water.

Solution II was taken and Solution I was stirred into it by means of a Homorex mixer.

After completion of addition) stirring was continued for 10 minutes at the highest speed, the pH value was then adjusted to 7.25 with half-normal NaOH solution, and the mixture was again stirred briefly.

Example 2: Solution f: 350 g of MCPA-ethylhexyl ester, technical grade 10 g of fatty acid polyethylene glycol ester Solution II: 2.5 g of the sodium salt of palm kernel fatty acid methyl-tauride (30% strength aqueous solution containing 7% of NaC!) 10 g of ethylene glycol 126 g of distilled water The method employed was as described in Example I. The pH value was Adjusted to 7.55. Example 3: Solution I: 350 g of 2,4-D-ethylhexyl ester 10 g of fatty acid polyethylene glycol ester Solution II: 2.5 g of the sodium salt of a fatty acid methyl 25 tauride (30% strength aqueous solution containing 7% of NaCl, fatty acid = paimitic/stearic acid) 10 g of ethylene glycol 151 g of distilled water.

The method employed was as described in Example I. The pH value was adjusted to 7.6.

Solution It . 350 10 2.5 Solution It: Example 4; g of MCPA-ethylhexyl ester, technical grade g of fatty acid polyethylene glycol ester g of the sodium salt of a fatty acid tauride 4 7 0 1 (containing inorganic and organic salts, fatty acid = Jauric/myristic acid) g of ethylene glycol 125 g of distilled water The method employed was as described in Example 1. The pH value was adjusted to 7.5.

Example 5: Solution I: 350 g of CMPP-butylglycoI ester 10 g of fatty acid polyethylene glycol ester Solution Π: 2.5 g of Na oleyl methyl tauride (25% strength aqueous solution) 1*5 g of distilled water The method employed was as described in Example 1. The pH value was adjusted to 7.5. Example 6: Solution I; 350 g of 2,4,5-T-amyi ester 10 g of a mixture of nonyiphenyl-polyethylene oxide, polyoxyethylene/polyoxypropylene block polymer (molecular weight 1,800 to 9,000) and alkylarylsulfonate Solution Π: 10 g of Na oleyl methyl tauride (25% strength aqueous solution) 10 g of ethylene glycol 150 g of distilled water 1 g of antifoam agent (silicone emulsion) The method employed was as described in Example 1. The pH value was adjusted to 8.0. Example 7: Solution I: 350 g of 2,4-D-butyI ester 10 g of polyoxyethylene triglyceride and alkylarylsulfonate Solution Π: 10 g of Na oleyl methyl tauride (25% strength aqueous solution) 10 g of ethylene glycol 165 g of distilled water ΙΟ The method employed was as described in Example 1. The pH value was adjusted to 7.0. Solution I: 1,200 30 Solution Π: 9 Example 8: g of 2,4,5-T-ethylhexyI ester, technical grade g of fatty acid polyglycol ester g of Na oleyl methyl tauride (25% strength 105 aqueous solution) g of ethylene glycol 6 1,830 2 1.68 g of xanthan gum g of distilled water g of antifoam (silicone emulsion) g of NaOH In a preliminary experiment, it was established that 0.56 g/Iitre of NaOH are required to neutralize the formulation, after which the calculated amount of NaOH (1.68 g) was added to Solution II. Thereupon, Solutions I and II were fed by means of metering pumps to an apparatus which essentially consisted of a centrifugal pump with bypass for product recycling and pressure-maintaining valve at the exit. The optimum droplet distribution was obtained at a metering pump:centrifugai pump feed ratio of 1 : 15 to 1 : 25.

The pH value was 7.8. Solution I: 429.5 226.6 1.2 Solution Π: 25 Example 9: g of MCPA-ethyihexyl ester, technical grade g of 2,4,5-T-ethylhexyI ester, technical grade g of fatty alcohol polyglycol ether g of Na oleyl methyl rauride (25% strength aqueous solution) 25 g of ethylene glycol 0.6 g of xanthan gum 321 g of distilled water Solution Π was taken, Solution I was stirred into it by means of a Homorex mixer, and the pH of the mixture was adjusted to S.30 with halfnormal NaOH solution. For further homogenization, the emulsion was forced through a homogenizing head under a pressure of 90 bar. 4 7 0 1 — Ο <Ν © 9s 00 Ο 9s υ ο ο + « «ο <0 •σ > *ί « μ α, ο C υ Ε I 1 ♦ > b χ £ βίο *υ w « *5 «β ο α. U Ρ «η C > 2 « -S * > " χ c α a ε C X ω Ο W « 5 ° Ν - S <Μ ν\ »*\ ™ — — (Ν Ο©ν\©©νΝθ©«Γ\ <Ν©0\«ηβ0Γ\*\Ο·Λ Κ X Ό* Κ sfi Ν Μί Κ Ν So*>S^ooSS — — —· fN F* 00 fx βθ s0 rx eO 9s

Claims (12)

1. A storage-stable herbidically-active composition comprising a concentrated aqueous emulsion of one or more herbicidaily active phenoxyalkanecarboxylic acid esters in which the emulsion contains 0.1 to 5 S by weight, referred to the completed emulsion, of one or more oil-soluble emulsifiers which are soluble in the esters, have an HLB value of 9 to 16, and are selected from fatty acid polyethylene glycol esters, polyethylene glycol ethers of fatty alcohols, polyethylene glycol ethers of glycerides, polyethylene glycol ethers of alkylphenols, poiyoxyethylene/polyoxypropylene block copolymers and mixtures of the said polyethylene glycol esters, polyethylene glycol ethers or polyethylene glyeoi/polypropylene glycol block copolymers with alkylarylsulphqnates; and one or more water-soluble dispersants inaa amount of 0.1 to 3 % by weight, referred to the completed emulsion selected from the group consisting of alkali metal salts of single or multiple unsaturated fatty acid taurides or fatty acid alkyltaurides, in which the amount of herbicidaily active ester is 30 to 75 % by weight of the concentrated emulsion, the viscosity of the emulsion is 50 to 3,000 mPa.s, the droplet size is I to 5 ym and the pH value is 6 to 9.

2. A composition according to claim I, which additionally contains one or mote conventional anti-freeze agents, conventional anti-foam agents, thickeners or a mixture thereof.

3. A composition according to claim 1 or 2, in which the ester soluble emulsifiers are one or more fatty acid polyethylene glycol esters.

4. A composition according to claims I to 3, in which the watersoluble dispersant is Sodium-oleyl-methyitauride.

5. A composition according to claims I to 4, in which the herbicidallyactive phenoxyalkanecarboxylic acid esters are the octyl esters.

6. A composition according to claims I to 5, in which the amount of emulsifier is 1 to 3 % by weight.

7. A composition according to claims 1 to 6, in which the amount of dispersant is 0.2 to 1 % by weight.

8. A composition according to claims 1 to 7, in which the viscosity is 500 to 1,500 mPa.s.

9. A composition according to claims 1 to 8 in which the pH-value is 7 to 8. 5 4 7 01

10. A process {or the preparation of a storage-stable herbicidally-active composition in the form of concentrated emulsion of herbicidally active phenoxyalkanecarboxylic acid esters containing 30 to 75% by weight of active compound having a viscosity of 50 to 3,000 mPa.s., which comprises preparing 5 a solution I from one or more phenoxyalkanecarboxylic acid esters and at least one emulsifier which is soluble in the ester and has an HLB value of 9 to 16, in which the amount of emulsifier is 0.15 to 10 parts by weight per 100 parts by weight of the solution I, and mixing solution f with an aqueous solution II, which contains one or more water-soluble dispersants, selected from the group 10 consisting of alkali metal salts of single or multiple unsaturated fatty acid taurides or fatty acd alkyl taurides in the amount of 0.2 to 10 parts by weight of dispersant per 100 parts of aqueous solution II, and subsequently homogenizing the mixture at a temperature within the range of 15° to 90°C. until the droplet size is I to 5 pm, while maintaining the pH of the mixture at a value 15 of from 6 to 9 and then diluting the homogenizate to the desired final volume.

11. A storage-stable herbicidaily-active composition according to claim f, and substantially as hereinbefore described with reference to the Examples.

12. A process for the preparation of a storage-stable herbicidally-active composition according to claim 10, and substantially as hereinbefore described 20 with reference to the Examples.