Coating processes – Particles – flakes – or granules coated or encapsulated – Solid encapsulation process utilizing an emulsion or...
Patent
1998-05-07
1999-12-07
Nutter, Nathan M.
Coating processes
Particles, flakes, or granules coated or encapsulated
Solid encapsulation process utilizing an emulsion or...
42721331, 427214, 4284022, 42840221, 264 41, 264 433, B01J 1310
Patent
active
059979461
DESCRIPTION:
BRIEF SUMMARY
This invention relates to solid compositions and in particular to solid, water-dispersible compositions containing microencapsulated materials and to a process for their manufacture.
Microencapsulation is a technique used in a variety of industries including for example the agrochemical industry. The technique of microencapsulation generally involves the formation of a dispersion or emulsion of a relatively water-immiscible liquid in an aqueous medium to form an oil phase. The oil phase contains the material to be encapsulated, for example a liquid, water-immiscible agrochemical, as well as one or more monomers which forms a polymeric microcapsule wall surrounding the oil phase droplet when polymerisation is initiated, for example by heating. A large number of variants of the microencapsulation process are known. Thus, for example, the liquid, water-immiscible pesticide which forms the material to be encapsulated may be a low-melting solid agrochemical which is emulsified as a melt or the liquid, water-immiscible agrochemical may be a solution of a solid agrochemical in an appropriate water-immiscible solvent. As used herein the term "microencapsulated material" means any material housed within a polymeric microcapsule shell. As noted above, the microencapsulated material is generally a relatively water-immiscible material and is formed as a suspension of the microcapsules in an aqueous phase.
Microencapsulated materials have a number of advantages as compared with a simple oil-in-water emulsion. In the agrochemical industry for example, microencapsulated suspension formulations are used to reduce toxicity and operator exposure as compared with simple emulsion concentrate formulations. Microencapsulated suspension formulations are also used to provide controlled release of the agrochemical, the rate of release being determined for example by the thickness of the wall of the microcapsule and by the nature of the polymeric wall material.
As noted above, microencapsulated formulations are manufactured and used in the form of an aqueous suspension. In agrochemical use for example, the suspension is generally diluted prior to use. There is however increasing interest in the agrochemical industry in the use of solid rather than liquid formulations, since such formulations have advantages in terms of reduced transport costs, greater ease of handling and greater customer acceptability. Container contamination may also be greatly reduced by the use of a day, solid formulation and container disposal may thus be simplified. We have found however that conventional methods for the conversion of liquid formulations into solid compositions, for example conventional granulation techniques, fail with microencapsulated suspensions because the processing involved tends to rupture the microcapsule wall and release the microencapsulated material. There is thus a need for a solid formulation of a microencapsulated material in which the microcapsules remain largely intact and which permits the regeneration of a suspension of microencapsulated material when the solid formulation is dissolved in water.
We have now found that such a product may be formed by means of the casting of a film-forming aqueous medium containing the microencapsulated material.
The casting of film-forming polymers, for example "tape casting" to form polymer sheets is used in a number of industries and the techniques involved will be known to those skilled in the art.
In WO 93123999 there is disclosed a packaging for storing and releasing incompatible crop protection materials in which a chemical is "encapsulated" in a water-soluble polymer film. However, the crop protection chemical, which may be in the form of a high-melting solid, a liquid, a wax, a granule or a powder, is merely added to a solution of the polymer in water and dried to form a suspension in the polymer film. Whilst the solid film containing the crop protection chemical does provide some handling advantages, once re-dissolved in water the crop protection chemical is regenerated in the form
REFERENCES:
patent: 5250344 (1993-10-01), Williamson et al.
patent: 5271961 (1993-12-01), Mathiowitz et al.
patent: 5296266 (1994-03-01), Kunugi et al.
Bell Gordon Alastair
Landham Rowena Roshanthi
LeCroy David P.
Nutter Nathan M.
Zeneca Limited
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