FIELD OF THE INVENTION

This invention relates to a controlled release composition that allows an active ingredient to be released in a controlled manner, and in particular to such compositions that are in the form of aqueous dispersions. The invention also relates to methods of preparing controlled release compositions in the form of an aqueous dispersion.

BACKGROUND OF THE INVENTION

Previous aqueous dispersions for the controlled release of active ingredients have included the following types:

a. Dispersions where a chemical reaction occurs after the formation of the dispersion, creating a solid matrix from an originally liquid disperse phase. Examples include the formulation of poly-urea capsules and the formation of a polymer matrix from liquid monomers by polymerisation. Specific examples are disclosed in Australian Patent Application No. 37393/85 and U.S. Patent No. 3,212,967.

b. Dispersions where an organic solvent is removed from the disperse phase after the formation of the dispersion, leaving a solid disperse mass as host of matrix e.g. the formation of polylactide micro-capsules. An example is disclosed in Japanese Patent Application No. 48923/85.

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c. Dispersions in which a solid coating is formed on the outer boundary of the disperse phase by the process of polymer coacervation (i.e. controlled precipitation of polymers at the interface) . An example is disclosed in British

Patent No. 929405.

d. Dispersions in which the solid matrix is molten at elevated temperatures prior to the addition of the active ingredient or ingredients, and in which the molten mass is added with vigorous stirring to an aqueous phase in the presence of surfactants to form a stable emulsion which cools to form a solid dispersion.

This last type of dispersions have been alleged to be useful in the following cases:

(i) Composition for the protection of wood using a dispersion of fungicide and insecticide in an oily matrix (Pojurowski French Patent Publication No. 2,392,787).

(ii) Composition with improved biocidal properties using a dispersion e.g. of pentachlorophenol in paraffin (Mobil Australian Patent Application No. 19222/70). In this instance, it was observed that the dispersions were also useful for imparting water resistant properties to treated surfaces (e.g. wood).

Using these compositions, the delivery of active ingredient at the site of application of the composition occurs at a reduced rate when compared with the performance of standard compositions of the same active substance.

Such standard compositions include the following types:

(i) Emulsifiable concentrates: The active ingredient is dissolved in a solvent which is not miscible with water and which contains surface active materials such that the emulsifiable concentrate self-emulsifies on addition to water to form a liquid dispersion of active/solvent in water.

(ii) Suspension concentrates: The active is suspended in concentrated form as fine solid granules in water. The suspension concentrates can be added to water to form a dilute suspension of the fine solid granules. Alternatively, the active may dissolve in the water upon dilution.

(iϋ) Dry flowables: The active is formulated as a dry granule. When these dry granules are added to water, they disassociate to form much finer granules which are suspended in the water. Alternatively, the active may dissolve in the water upon dilution.

(iv) Aqueous emulsion formulations: The active is a liquid or is dissolved in a liquid which is not miscible with water. This liquid is dispersed in water to form an oil in water emulsion, which can be diluted if desired.

In many cases it is important to decrease the rate of release of active ingredient from the controlled release formulation relative to the rate of release of

active from the standard formulation by a considerable amount before significant product advantages can be obtained. This advantage is usually sought in terms of increased efficacy of the controlled release formulation. See for example, the publication of

Marvin M. Schreiber et al in "Weed Science" Vol 35 No. 3 pages 407-11 (1987) .

The required reduction of release rate in the controlled release product depends on both the nature of the active ingredient and on the performance of the standard formulation of the active material.

SUMMARY OF THE INVENTION

In order to achieve this object, the present invention provides a controlled release formulation comprising an aqueous dispersion of a water insoluble matrix as the disperse phase wherein the matrix contains at least one active ingredient selected from the group consisting of herbicides, insecticides, fungicides and nematocides, characterised in that the matrix is a viscous hydrocarbon.

The term "viscous hydrocarbon" is defined as any naturally occurring crude oil or any residual oil remaining after refining operations which is generally characterised by a viscosity of about 10 2-106 centipoise or greater and otherwise generally, but not necessarily, characterised by an API gravity of about 20 API or less, high metal content, high sulfur content, high asphaltene content and/or high pour point. The term "viscous hydrocarbon" it is to be understood also encompasses the following nomenclature: vacuum residuals, vis—breaker

residuals, catalytic-cracker residuals, catalytic hydrogenated residuals, coker residuals, ROSE (residual oil supercritical extraction) residuals, tars and cut-back tars, bitumen, pitch and any other terms describing residuals of hydrocarbon processing. Viscous hydrocarbons encompass naturally-occurring viscous crude oils (also called heavy crude oils) as well as residual bottom-of-the-barrel products from refineries, such as vacuum resid, other residual fuel oils and asphalt. While low gravity does not necessarily coincide with high density, these characteristics are generally correlated in viscous hydrocarbons.

Generally the following characteristics are considered typical of the types of crude oils and residual oils which are useful for the present invention.

1. Low API gravity, generally at or below 20 API. This is the most frequently used criterion, both because it is easily measured and because 20 API crude roughly corresponds to the lower limit recoverable with conventional production techniques.

2 6 2. Viscosities in the range of about 10 to 10 centipoise (cp) or even higher in some cases.

3. High metal contents. For example, heavy crudes often have nickel and vanadium contents as high as 500 PPm-

4. High sulfur content, e.g., 3 weight percent or more.

High asphaltene content.

High pour point.

The viscous hydrocarbons can be generally defined as having a paraffin content of about 50% by weight or less and an aromatic content of about 15% by weight or greater with viscosities of about 100 centipoise or greater at 65 . The viscous residuals generally are characterised by a paraffin content in the range from about 4% to about 40% by weight, an aromatic content in the range from about 15% to about 70% by weight and an asphaltene content from about 5% to about 80% by weight.

These materials may also occur naturally as deposits in the earth. So far as we are aware, these materials have not previously been proposed as a matrix for active ingredients in aqueous dispersions and in particular have not been proposed where the active ingredients is a dinitroaniline herbicide or trifluralin, and we have found them to be surprisingly effective in achieving the slow release of active ingredient applied to soil. In addition, these materials exhibit low viscosity at temperatures below 140oC, so that many active ingredients can be incorporated in the matrix without themselves undergoing degradation by heat, and direct emulsification of the matrix in water may occur.

Preferred active ingredients are the dinitroaniline herbicides, most preferably trifluralin.

Mixtures of more than one active ingredient may be useful for certain uses. Preferably the active ingredient is soluble or compatible with the matrix material at ambient temperatures. We have found that if the matrix and active are insoluble the certain active ingredient, may be dumped into the aqueous phase rendering the compositions less useful.

Stabilising amounts of surfactants are present in compositions of our invention. The surfactants may be anionic, cationic or non-ionic. Mixtures of surfactants such as non-ionic and anionic and non-ionic and cationic may be particularly useful. Preferred surfactants are Vinsol, oleyl alcohol ethoxylates, methyl glucoside sequistearate ethoxylates, alpha oleum sulfonate, glycerol mono-stearate, stearyl dimethyl benzyl ammonium chloride, octadecylmine ethoxylate. Typically the particle size of the disperse phase is less than 50 microns diameter and more usually less than 25 microns diameter.

The formulation may also comprise a solvent for the active ingredient. Aromatic solvents are preferred, e.g. xylene or Solvesso 150. Solvents may aid the emulsification process and also modify the release characteristics of the active.

The present invention also provides a method of preparing the controlled release formulations above defined, comprising; melting a viscous hydrocarbon, then dispersing or dissolving the active ingredient in the molten hydrocarbon and then dispersing the hydrocarbon in water.

The present invention further provides a method of treating soil to retard the growth of vegetation thereon, comprising applying to the soil a controlled release formulation as above defined, wherein the active ingredient is a herbicide.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are graphs illustrating the results of the trials described inthe following examples, which illustrate the invention.

Figs la and lb relate to Example 1 ;

Figs 2a and 2b relate to Example 2; and Figs 3a and 3b relate to Example 3.

Example 1

Materials

The viscous hydrocarbon used as the matrix in this example was bitumen of type C170, PD tar free. This bitumen is defined in the Australia Standard AS 2341 ,

entitled "Properties of Residual Bitumens for Pavements" " .

The trifluralin was technical material supplied by Nufarm Pty Ltd, Pipe Road, Laverton, Victoria, Australia.

One of the surfactants used to form and stabilise the bitu enous dispersion was oleic acid, and the other was Vinsol. Vinsol was sourced from Hercules Pty Ltd through their Australia distributors A C Hatrick Pty Ltd. This material consists of residues from an extraction process using pine tree stumps. It contains high molecular weight phenolic material as well as other neutral material, and is a standard component of many anionic bitumen emulsions in Victoria, Australia.

Method of formulation of Dispersion

The aqueous phase of the dispersion was prepared by dissolving Vinsol (1 part by weight) and oleic acid (1 parts by weight) at pH 12 (adjusted with sodium hydroxide) and taking the temperature to 45 C.

The non-aqueous phase was prepared by adding bitumen at 100°C (57.5 parts by weight) to trifluralin (2.5 parts by weight), mixing well and taking the temperature to 120 C.

The non-aqueous phase was added to the aqueous phase in the presence of high shear provided by an Ultra-Tumax type T45 agitator, made by Janke and Kunkel.

The particle size of the dispersion varied in the range 1—30 microns, and the final formulation comprised 2.5% active material on total weight.

The formulation was called TF16.

BIOASSAY PROTOCOL

The bioassay protocol for the determination of efficacy of the trifluralin formulations was as follows.

Soil (acidic yellow duplex, as typical of Wonwondah, Victoria, Australia) was air dried and brought to 10% water by weight. The soil was placed into containers of dimension 85mm x 140mm x 50mm (depth) and the containers were arrayed outdoors for spraying. The containers of soil were sprayed at rates of formulation equivalent to 0, 0.1, 0.2, 0.5, 1 and 1.5 litres/hectare of trifluralin emulsifiable concentrate. The standard emulsifiable concentrate formulation contained 40% trifluralin active. A spray volume of 230 litres/hectare of water was used, and the dilute formulation were sprayed through Spraying System nozzles of type 11003 using 200 kilopascals of air pressure. Ambient temperature was 30 + 3 C.

The sprayed containers were treated in a variety of ways:

soil was immediately mixed thoroughly after spraying to effect instant and complete incorporation of active, and returned to the container.

b. sprayed soil was left for 2 hours, then mixed as above .

c. sprayed soil was left for 24 hours, then mixed as above.

The treated soil portions were bioassayed for trifluralin according to the following protocol.

Soil portions were sown at 24 hours after spraying with 20 seeds of annual ryegrass (lollium rigidum) to a depth of 1cm. The samples were kept at 18-22 C in a glass house for 10 days, and were watered twice daily. The result was obtained by calculating the percentage emergence from each container of soil.

The results are tabulated and are graphed using points which represent the mean value of six duplicates. The graphs are presented as % emergence vs log. _Q (dose + 1 ) • The numerical value for the dose is in units of litres per hectare equivalent of trifluralin emulsifiable concentrate.

In general, efficacy results for controlled release formulations are compared with efficacy results for the emulsifiable concentrate standard formulation sprayed at the same time .

Results of Example 1

The results are tabulated in Table 1 and graphed in

Figures 1 (a) and 1 (b).

Figure 1 ( a ) shows the behaviour of the standard formulation ( emulsi f iable concentrate or EC ) .

Figure 1 (b) shows the behaviour of the controlled release (CR) formulation TF16.

Table 1

% Emergence Vs Rate EC and TF16 Delay (0, 2, 24 hours)

DELAY RATE LOG E.C. TF16

(HRS) (1/hal (Rate+1 ) (%) (%)

0 0.00 0.00 62.0 62.0

0 0.10 0.04 66.0 7.5

0 0.20 0.08 25.0 4.0

0 0.50 0.18 5.0 4.0

0 1.00 0.30 1.0 1.0

0 1.50 0.40 1.0 0.0

2 0.00 0.00 61.0 61.0

2 0.10 0.04 57.0 53.0

2 0.20 0.08 68.0 54.0

2 0.50 0.18 41.0 15.0

2 1.00 0.30 18.0 0.0

2 1.50 0.40 5.0 6.0

24 0.00 0.00 70.0 70.0

24 0.10 0.04 66.0 68.0

24 0.20 0.08 60.0 68.0

24 0.50 0.18 60.0 29.0

24 1.00 0.30 34.0 4.0

24 1.50 0.40 21.0 6.0

It is apparent that at equivalent incorporation delay

(0, 2 or 24 hours) the controlled release formulation is signi icantly more efficacious than is the standard formulation, i.e., weed emergence is suppressed to a greater extent at a given rate of application of active material.

Example 2

In this example, the formulation TF16 of the previous example was compared with the standard EC formulation using incorporation delays of 0, 0.25 and 2 hours instead of the previous delays of 0, 2 and 24 hours.

The experiment was carried out on a different day than was Example 1 , but the bioassay protocol was the same in other features.

Results of Example 2

The results are tabulated in Table 2 and graphed in Figures 2 (a) and 2 (b).

Figure 2 (a) shows the behaviour of the standard formulation (EC) and Figure 2 (b) shows the controlled release controlled release formulation TF16.

Table 2 o Emergence Vs Rate

EC and TF16i: Delay (0, 0 .25, 2 hours)

DELAY RATE LOG E.C. TF16

(HRS) ( 1 /h ) (Rate+1 ) (%) (%)

0 0.00 0.00 51.0 51.0

0 0.025 0.01 55.0 67.0

0 0.05 0.02 64.0 63.0

0 0.10 0.04 71.0 24.0

0 0.20 0.08 27.0 5.0

0 0.50 0.18 6.0 2.0

0 1.00 0.30 0.0 0.0

0.25 0.00 0.00 51.0 51.0

0.25 0.025 0.01 70.0 75.0

0.25 0.05 0.02 56.0 66.0

0.25 0.10 0.04 54.0 50.0

0.25 0.20 0.08 39.0 24.0

0.25 0.50 0.18 4.0 0.0

0.25 1.00 0.30 0.0 2.0

2 0.00 0.00 51.0 51.0

2 0.025 0.01 77.0 64.0

2 0.05 0.02 68.0 60.0

2 0.10 0.04 62.0 52.0

2 0.20 0.08 47.0 25.0

2 0.50 0.18 35.0 4.0

2 1.00 0.30 12.0 5.0

It is apparent that at equivalent incorporation delay (0, 0.25, or 2 hours) the controlled release formulation is more efficacious than is the standard formulation.

Example 3

Materials

Bitumen and trifluralin were identical to the samples used in Example 1, as was the surfactant Vinsol.

Para-xylene (AR grade) was used as the organic solvent.

The auxiliary surfactants were Ameroxyl OE2 and Ameroxyl OE10, and were sourced from Amerchol via the Australian distributors Bronson & Jacobs Pty Ltd. Ameroxyl OE2 was an oleyl alcohol ethoxylate with an 5 average of two oxyethylene units per molecule, and Ameroxyl OE10 was similar but with an average of ten oxyethylene units per molecule.

Method of Formulation of the Dispersion

10

The aqueous phase of the dispersion was prepared by dissolving Vinsol (0.6 parts by weight) and Ameroxyl OE10 (0.6 parts by weight) in water (67.4 parts by weight) at pH 12 (adjusted with sodium hydroxide), and taking the temperature to 85 C.

The non-aqueous phase of the dispersion was prepared by adding para-xylene (4.4 parts by weight) and Ameroxyl OE2 (0.4 parts by weight) to bitumen (17.7

20 parts by weight) at 80 C, and pouring this mixture onto trifluralin (8.9 parts by weight), with mixing. The combined mixture was taken to 120 C.

The aqueous dispersion was made by high shear „,. agitation as in Example 1.

The particle size of the dispersion varied in the range 1-20 microns, and the final formulation comprised 8.9% active material on total weight.

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The formulation was called TF95

Results of Example 3

- The bioassay protocol was as in Example

The results are tabulated in Table 3 and graphed in Figures 3 (a) and 3 (b).

Figure 3 (a) shows the behaviour of the standard formulation (EC) . Figure 3 (b) shows the behaviour of the controlled release formulation TF95.

Table 3 o Emergence Vs Rate

EC and TF95 I: Delay ⁽ 0, 2 and 24 hours)

DELAY RATE LOG E.C. TF16

(HRS) (1/ha) (Rate+1 ) (%) (%)

0 0.00 0.00 63.0 63.0

0 0.05 0.02 65.0 60.0

0 0.10 0.04 55.00 25.0

0 0.20 0.08 22.0 2.0

0 0.50 0.18 1.0 2.0

0 1.00 0.30 1.0 0.0

2 0.00 0.00 47.0 47.0

2 0.05 0.02 61.0 54.0

2 0.10 0.04 50.0 48.0

2 0.20 0.08 44.0 3.0

2 0.50 0.18 13.0 2.0

2 1.00 0.30 1.0 0.0

24 0.00 0.00 58.0 58.0

24 0.05 0.02 58.0 68.0

24 0.10 0.04 60.0 55.0

24 0.20 0.08 61.0 11.0

24 0.50 0.18 14.0 11.0

24 1.00 0.30 7.0 0.0

It is apparent that at equivalent incorporation delay (0, 2 or 24 hours) the controlled release formulation TF95 is significantly more efficacious than is the standard formulation.