Plastic and nonmetallic article shaping or treating: processes – Encapsulating normally liquid material – Liquid encapsulation utilizing an emulsion or dispersion to...
Patent
1982-03-24
1984-08-07
Lovering, Richard D.
Plastic and nonmetallic article shaping or treating: processes
Encapsulating normally liquid material
Liquid encapsulation utilizing an emulsion or dispersion to...
71DIG1, 424 19, 424 22, 42721332, 427344, B01J 1302, A01N 2528, A61K 926
Patent
active
044643179
ABSTRACT:
A method for forming discrete capsules that contain an active agent, such as a pesticide, involves first forming a suspension of the active agent suspended in a solution of an alkali metal silicate such as sodium silicate or a suspension of the active agent suspended in a liquid coacervate resulting from the addition of a coacervation agent such as acetone to the alkali metal silicate solution. The suspension, preferably in the form of droplets formed by ejecting the suspension through an orifice (e.g. a needle), is then contacted with an aqueous solution of a salt such as calcium chloride which reacts with the alkali metal silicate to form an insoluble silicate (e.g., calcium silicate) coating for the active agent while hardening the dispersed active agent in a silicate core matrix. Thus, capsules of the active agent are produced with an insoluble silicate coating. The capsules are maintained in the aqueous salt solution for a sufficient period of time to permit a high degree of conversion of soluble silicate to insoluble silicate. The capsules are then isolated and dried thereby providing structurally intact capsules which act as a free-flow powder. The capsules provide controlled release of the active agent over a prolonged period of time. Methods for preparing such capsules within a three hour period have been devices thereby improving substantially the economics of encapsulating active agents with inorganic coatings. Such brief preparation times are achieved through the use of soluble silicates rich in SiO.sub.2 and by increasing the temperature of the aqueous solution of the salt such as calcium chloride to effectively expedite the capsule curing process.
REFERENCES:
patent: 2243296 (1941-05-01), Sweetland
patent: 3301701 (1967-01-01), Baker et al.
patent: 3785798 (1974-01-01), Horai et al.
patent: 3790497 (1974-02-01), Sato et al.
patent: 3854981 (1974-12-01), Schon et al.
Linek Francis W.
Thies Curt
Lovering Richard D.
The Washington University
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