Vesiculated silica microspheres
AssigneeE. I. Du Pont de Nemours and Company
InventorLionel Samuel Sandell
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Abstract
Vesiculated silica microspheres having an average diameter from 0.5.mu. to 50.mu., a maximum vesicle diameter less than 50.mu. and a volume of vesicles from 5 to 95% of the total volume of the microspheres, produced by acidifying an oil-in-water-in-oil emulsion prepared by a double emulsion technique. The vesiculated silica microspheres are particularly useful as opacifying agents for coating compositions and as fillers for paper.
Claims12
Vesiculated silica microspheres consisting essentially of from 0 to 90% by weight of pigment, based on the total weight of the microspheres, and from 10 to 100% by weight of silica, based on the total weight of the microspheres, the microspheres, having an average diameter from 0.5.mu. to 50.mu., the average diameter of the vesicles being 0.1.mu. to less than 50.mu. and the volume of the vesicles being from 5 to 95% of the total volume of the microspheres, wherein the vesicles are substantially discrete and spheroidal.
Process for preparing vesiculated silica microspheres by the steps of
- i. forming an oil-in-water emulsion by contacting a siliceous aqueous phase with a first oil phase,
- said siliceous aqueous phase composed of water and at least one silicon compound selected from the group consisting of colloidal silica and alkali metal silicates,
- said first oil phase composed of at least one water-immiscible hydrocarbon selected from the group consisting of liquid and low melting aliphatic and aromatic hydrocarbons,
- distributed in at least one of said phases is at least one oil-in-water emulsifying agent,
- ii. forming an oil-in-water-in-oil emulsion by contacting the oil-in-water emulsion formed in Step (i) with a second oil phase,
- said second oil phase composed of a nonionic water-in-oil emulsifying agent and at least one waterimmiscible hydrocarbon selected from the group consisting of aliphatic, aromatic and chlorinated hydrocarbons,
- iii. adding acid to the oil-in-water-in-oil emulsion formed in Step (ii), said acid being added in an amount from 0.5 to 2.0 times the amount of said acid needed to react stoichiometrically with the total amount of base present in the siliceous aqueous phase of Step (i) to gel the siliceous aqueous phase and form a slurry of vesiculated silica microspheres, and
- iv. separating the vesiculated silica microspheres from the slurry formed in Step (iii).
Dependencies are inferred from the claim text.