Storage and dilution of stable aqueous dispersions

Details Storage and dilution of stable aqueous dispersions Storage and dilution of stable aqueous dispersions

1996-08-02

2000-06-13

Clardy, S. Mark

Plant protecting and regulating compositions

Plant growth regulating compositions

424405, 516 53, A01N 2504, B01F 308

Patent

active

060749865

DESCRIPTION:

BRIEF SUMMARY
This application has been filed under 35 USC 371 on the national stage of international application PCT/US 94/10416, filed Sep. 14, 1994.
This invention relates generally to the preparation of queous dispersions, which term is used herein to include both dispersions of solid particles, and in particular, aqueous emulsions, which are stable on storage and dilution, and in particular to the preparation of emulsions containing pesticides, for example herbicides, insecticides, or fungicides which are stable on storage and dilution.
The continuing emphasis on environmental pollution caused by the use of organic solvents makes it increasingly desirable to prepare various formulations as emulsion preparations, rather than as solutions in organic solvents. There are very many examples of this, for example in the preparation of adhesives and the like. A particularly important area is in the field of pesticidal compositions, for example herbicidal, insecticidal, or fungicidal compositions, in which large quantities of solvent typically need to be employed in order to present the active materials at the desired rate of application, to the intended locus.
Although many pesticidal materials are readily emulsifiable, problems arise in the preparation of concentrates of dispersed pesticides (particularly emulsions) which are both storage stable, and stable on dilution prior to application.
Emulsion formulations can be caused to become unstable for a variety of reasons. The most important of these may be summarized as follows: ultimately to immiscible bulk liquids; migrates through the continuous phase between particles of the dispersed phase, thus allowing a change in overall particle size distribution.
This invention is concerned with diminishing or preventing Ostwald ripening as a cause of emulsion instability.
Ostwald ripening can occur whenever a component of the disperse phase is capable of being transported through the continuous phase from one particle to another. The usual mechanism for such transport is by dissolution of the transportable material in the continuous phase, which can occur even if the solubility of the material is low. Other transport mechanisms are however possible. For example, even materials having a very low water solubility indeed, which might not be expected to display Ostwald ripening, can do so, when certain surfactants are used in the preparation and stabilization of the emulsion. This is believed to be due to transport of the water insoluble materials through the aqueous phase by dissolution in surfactant micelles.
The direction of migration of the non-aqueous phase tends to be from smaller particles to larger particles, because of the respective chemical potential of the non-aqueous materials in the emulsion particles. Thus, the overall effect of the migration of materials between the emulsion particles is to tend to cause the particle size distribution to shift towards larger particle sizes, which is very disadvantageous in many cases.
Various attempts have been made to control Ostwald ripening of emulsions. For example, U.S. Pat. No. 4,348,385 (Mobay Chemical) is concerned with the control of Ostwald ripening of a dispersion of a solid pesticide material in an organic solvent. The proposed solution to the problem of Ostwald ripening of the solid pesticide dispersion is the addition of a solid ionic dispersant.
W092/09197 (KVK Agro) is concerned with the preparation of a herbicidal composition containing a solid herbicide dispersed in a liquid. The product is stabilised on dilution by the addition of a water-soluble polymer to the herbicide concentrate. The concentrate is not an oil-in-water emulsion, and the water-soluble polymer stabiliser acts as a dilution aid, on addition of the concentrate to water.
W089/03175 (Dow Chemical) is concerned with the production of water diluable pesticide compositions, which are stabilised by the addition of a polymer latex. The polymer latex comprises solid particles insoluble in the solvents employed.
W093/15605 (Schering Agrochemicals) discloses p

REFERENCES:
patent: 5371105 (1994-12-01), Damo
S. S. Davis and A. Smith, "The Influence of the Disperse Phase on the Stability of Oil-in-Water Emulsions", Theory and Practice of Emulsion Technology, Academic Press, London, 1974.
S. Wang and F. J. Schork, Journal of Applied Polymer Science, 54, 2157-2164 (1994).

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