Hollow microspheres with organosilicon-silicate walls
AssigneePQ Corporation
InventorsBruce W. Sands, Robert J. Nehring, Jr.
Life of this patent
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Abstract
Hollow microspheres of reduced surface energy and reactivity and of improved packing and sphericity are prepared by simultaneously forming said microspheres and reacting them with an organosilicon compound. The microspheres are prepared by spray drying a solution of alkali metal silicate and a "polysalt." The organosilicon is present as the microspheres are formed, penetrates and reacts to form a shell consisting of a silicate, polysalt and the organosilicon compound. The resulting product is more discrete, more free-flowing, has better packaging characteristics, improved packing factor and improved filler properties when compared to prior-art microspheres.
Claims22
Hollow microspheres of 5 to 300 microns diameter with shells containing alkali metal silicate, a polysalt, an organosilicon compound multiply bonded within said silicate shell, said microspheres being characterized in that:
- (a) the ratio of polysalt solids to silicate solids is between 0.02:1 and 3.0:1, said polysalt being an inorganic salt of an alkali metal and/or ammonium cations wherein the anion to cation ratio is reduced when the salt is dissolved and becomes hydrolyzed and said alkali metal silicates having 1.5 to 4.0 moles of SiO.sub.2 per mole of M.sub.2 O wherein M is sodium or potassium;
- (b) the organosilicon constitutes 0.01 to 4.0% by weight of the microspheres, said organosilicon being the thermally and hydrolytically stable portion of an initial organosilicon compound having at least one thermally stable and non-hydrolyzable organic group and two or three reactive groups;
- (c) the ratio of true density to bulk density being between 1.2 and 1.9, the true density being 0.05 to 0.90 g/cm.sup.3 and the bulk density being 0.05 to 0.24 g/cm.sup.3 ;
- (d) the porosity (%P) of 5 to 10% as calculated by the formula ##EQU2## wherein ED is the effective density which has a value of 0.05 to 0.90 g/cm.sup.3 and TD is the true density as recited in section (c) and 2.45 is the density of the wall in g/cm.sup.3.
The process of preparing hollow microspheres of 5 to 300 microns diameter with shells containing alkali metal silicate and a polysalt, and an organosilicon compound multiply bonded within said silicate shell, comprising the steps of:
- (a) forming a homogeneous solution of 0.02 to 3.0 parts by weight of a polysalt for each part by weight of an alkali metal silicate, said "polysalt" being an inorganic salt of an alkali metal and/or ammonium cations wherein the anion to cation ratio is reduced when the salt is dissolved and becomes hydrolyzed, said alkali metal silicates having 1.5 to 4.0 moles of SiO.sub.2 per mole of M.sub.2 O, wherein M is sodium or potassium;
- (b) injecting said homogeneous polysalt-silicate solution into a spray dryer with an inlet temperature of about 150.degree. to 500.degree. C. and an outlet temperature of about 100.degree. to 400.degree. C., and simultaneously injecting into said spray dryer a liquid containing an organosilicon compound through a separate injection device in close proximity to the injection point for the homogeneous polysalt-silicate solution, said organosilicon compound having at least one thermally stable and non-hydrolyzable organic group and two or three reactive groups;
- and
- (c) recovering the product from the spray dryer.
Dependencies are inferred from the claim text.