Plant protecting and regulating compositions – Plant growth regulating compositions – Organic active compound containing
Patent
1995-09-13
1997-08-05
Clardy, S. Mark
Plant protecting and regulating compositions
Plant growth regulating compositions
Organic active compound containing
71DIG1, A01N 3318, A01N 2508, A01N 2522
Patent
active
056542585
DESCRIPTION:
BRIEF SUMMARY
This application has been filed under 35 USC 371 as a national stage application of international application PCT/AU94/00137 filed Mar. 17, 1994.
FIELD OF THE INVENTION
This invention relates to storage-stable formulations of trifluralin, in particular solid water-dispersible formulations, and methods for the preparation thereof.
BACKGROUND OF THE INVENTION
Trifluralin (.alpha.,.alpha.,.alpha.-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) is a pre-emergent herbicide with little post-emergent activity. Formulations of the herbicide trifluralin are typically added to spray water at the point of use, and are applied as a fine spray to soil for the purpose of controlling undesirable weeds.
Conventionally, trifluralin formulations for use as aqueous sprays are emulsifiable concentrates. These formulations are liquids which contain a significant quantity of hydrocarbon solvent. Problems may arise from flammability, solvent contamination of the environment, and in the requirement for rigid solvent resistant storage containers which require elaborate disposal strategies.
Solid water-dispersible trifluralin formulations have been proposed, however the main problem associated with the use of solid water-dispersible trifluralin formulations is the problem of long term storage stability. Under prolonged storage, the formulations may be routinely subject to temperatures in the range 0.degree. to 40.degree. C. and may occasionally be subject to temperatures in the ranges -20.degree. to 0.degree. C. and 40.degree. to 55.degree. C. Under such storage conditions, some large (greater than 125 micron) particulate entities may form. These large particulate entities, which may account for less than 3% of the total formulation, fail to redisperse into fine particles (sub 125 micron) in the spray water, and cause blockages in the filters and nozzles of the spraying equipment. In commercial practice, such filters may have a mesh size of as little as 150 microns and it is desirable that a safety margin of at least 25 microns is achieved between the mesh size of the filter and the maximum particle size in the formulation. Filter blockages in the spraying equipment can lead to unacceptable delays in practical usage (such as down-time of major spray rigs), and even to loss in biological efficacy arising from departures from the desired rate of application. It is believed that one cause of the formation of large particulate entities may be coalescence which occurs when the trifluralin melts and freezes.
Currently available tests of long-term storage stability of trifluralin formulations are time consuming and it is frequently difficult to emulate practical storage conditions in laboratory storage tests. There is therefore a dual need. The primary need is to produce trifluralin formulations that do not fail in the field, and the secondary need is to find reliable and simple short-term tests for testing the long-term stability of these formulations.
Australian Patent No. 639678 (corresponding to U.S. application Ser. No. 301458, dated 24 Jan. 1989) discloses that solid trifluralin exists in yellow and orange polymorphic forms. The specification of this patent states that the yellow polymorph of trifluralin has higher herbicidal activity, better water dispersibility and enhanced storage stability compared to the orange polymorph of trifluralin. This specification also describes a method for producing a solid formulation comprising substantially yellow polymorph, the method involving the formation of a molten trifluralin-in-water emulsion in the presence of a water-soluble film-forming polymer such as polyvinyl alcohol-acetate. The emulsion is spray-dried to form dry product, and the yellow polymorph is stabilised by the use of crystallisation initiators such as sodium benzoate, and by the use of crystal stabilisers, such as sodium dioctyl sulfosuccinate. The thermal regime to which the newly manufactured material is subjected is stated to be critical. In particular, it is noted that rapid cooling which results in cold (-5.degree.
REFERENCES:
patent: 4174960 (1979-11-01), Hendriksen
patent: 5073191 (1991-12-01), Misselbrook et al.
patent: 5296450 (1994-03-01), Kimler et al.
IL, A, 84-219 (Ben-Gurion Univ. of Negev.) "Herbicidal Composition Comprising Alachlor or Trifluralin Microcapsules Formed from Reaction Prod. of Toluylene Diisocyanate and Polyfunctional Amine," Oct. 10, 1991 (abstract).
Lichti Gottfried
Park Darren James
Brunelle Jan P.
Clardy S. Mark
Daratech Pty. Ltd.
Dreger Walter H.
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