Abstract Anhydrous dicalcium phosphate having an assay of at least 90 percent by weight and composed of particles, a major proportion of which have a particle size of from about 0.1 to 1.0 microns and a specific surface area of at least 10 square meters per gram is prepared by adding well dispersed, substantially dry calcium oxide or calcium hydroxide to phosphoric acid having a concentration of from about 40% to 80% H3PO4 by weight and maintaining the temperature of the reaction medium sufficiently high to provide dicalcium phosphate substantially free from water of crystallization. Dentifrice compositions containing this product provide effective polishing action without undue abrasion. Such compositions are prepared by direct blending of conventional dentifrice ingredients with an aqueous paste containing 45 percent to 65 percent by weight anhydrous dicalcium phosphate.
The paste of claim 1 wherein the amount of water admixed is from about 35 to 45 percent by weight.
Claim 2
Dependent Claim
227 words
In a dentifrice composition comprising a polishing agent in combination with conventional dentifrice ingredients the improvement wherein a major proportion of said polishing agent is anhydrous dicalcium phosphate having an assay of at least 90 percent based on dry weight, at least about 90 percent by weight of said anhydrous dicalcium phosphate being composed of particles having a particle size of from about 0.1 to about 1.0 microns and a specific surface area of at least 10 square meters per gram and a dentin abrasion value of about 50 to about 150, said anhydrous dicalcium phosphate being the product of a process comprising the steps of: (a) adding, in well dispersed form a calcium base selected from the group consisting of calcium oxide, calcium hydroxide, and mixtures thereof, said calcium base containing less than 15 percent by weight free water, to phosphoric acid having an initial concentration of from about 40 to 80 percent by weight H3PO4, (b) agitating the calcium base and the acid to provide a substantially homogeneous reaction medium during the addition of the calcium base to the acid, (c) maintaining the temperature of the reaction medium sufficiently high to provide dicalcium phosphate substantially free from water of crystallization and (d) continuing the addition of said calcium base to the acid until the pH of the reaction medium is from about 5 to 8.5.