Method of producing amorphous silica of controlled oil absorption

Claim 1

A method of producing a synthetic amorphous silica useful as a polishing agent in a dentifrice comprising a solid phase comprising from 10 to 50% by weight of the dentifrice, of said synthetic amorphous silica and a liquid phase comprising water and a polyhydric alcohol humectant selected from the group consisting of sorbitol, glycerin and mixtures thereof; wherein fluoride is present in the dentifrice composition and the dentifrice has an RDA of less than 500 when the silica has 100% of the particles below 44 microns, an oil absorption greater than 60 cc/100 g and a BET surface area between 40 and 420 sq. m/g; as a flatting pigment in a paint coating composition wherein said flatting pigment has a 60 degree gloss of less than 8 when the silica has 100% of the particles below 10 microns and having an average particle size of from 2 to 5 microns, an oil absorption greater than 60 cc/100 g and a BET surface area between 40 and 420 sq. m/g; and as an adsorbent for polyol purification when the silica has at least 70% of the silica larger than 44 microns, an oil absorption of from 60 to 140 cc/100 g and a BET surface area greater than 60 sq. m/g when the synthetic silica contains up to 5% by weight of a metal cation adduct selected from the group consisting of aluminum, magnesium, zinc and calcium, said method comprising the steps of: (a) subjecting an aqueous dispersion including finely divided silica and a sodium hydroxide to hydrothermal treatment at a temperature in the range of from about 138 to 210 degrees Celsius and for a period of time of from about 2.5 to 4.5 hours and sufficient to react the silica and said sodium hydroxide to form a reaction mixture of partly polymerized sodium silicate, said aqueous dispersion having a silica to sodium oxide weight ratio of at least 1.8:1; (b) spray-drying said reaction mixture at a temperature of at least 204 degrees Celsius to form minute hollow spheres of sodium polysilicate having a bulk density of from 0.128 to 0.416 g/cc; (c) reacting the polysilicate with a 5 to 15% sulfuric acid solution to form a synthetic amorphous silica; and (d) filtering, washing and drying the synthetic amorphous silica.

Claim 2

A method of producing a synthetic amorphous silica useful as a polishing agent in a dentifrice comprising a solid phase comprising from 10 to 50% by weight of the dentifrice, of said synthetic amorphous silica and a liquid phase comprising water and a polyhydric alcohol humectant selected from the group consisting of sorbitol, glycerin and mixtures thereof; wherein fluoride is present in the dentifrice composition and the dentifrice has an RDA of less than 500 when the silica has 100% of the particles below 44 microns, an oil absorption greater than 60 cc/100 g and a BET surface area between 40 and 420 sq. m/g; as a flatting pigment in a paint coating composition wherein said flatting pigment has a 60 degree gloss of less than 8 when the silica has 100% of the particles below 10 microns and having an average particle size of from 2 to 5 microns, an oil absorption greater than 60 cc/100 g and a BET surface area between 40 and 420 sq. m/g; and as an adsorbent for polyol purification when the silica has at least 70% of the silica larger than 44 microns, an oil absorption of from 60 to 140 cc/100 g and a BET surface area greater than 60 sq. m/g when the synthetic silica contains up to 5% by weight of a metal cation adduct selected from the group consisting of aluminum, magnesium, zinc and calcium, said method comprising the steps of: (a) subjecting an aqueous dispersion including finely divided silica and a sodium hydroxide to hydrothermal treatment at a temperature in the range of from about 138 to 210 degrees Celsius and for a period of time of from about 2.5 to 4.5 hours and sufficient to react the silica and said sodium hydroxide to form a reaction mixture of partly polymerized sodium silicate, said aqueous dispersion having a silica to sodium oxide weight ratio of at least 1.8:1; (b) spray-drying said reaction mixture at a temperature of at least 204 degrees Celsius to form minute hollow spheres of sodium polysilicate having a bulk density of from 0.128 to 0.416 g/cc; (c) reacting the polysilicate with a 5 to 15% sulfuric acid solution to form a synthetic amorphous silica; and (d) filtering, washing and drying the synthetic amorphous silica.