Acid-stabilized calcium carbonate, process for its production and method for its use in the manufacture of acidic paper
AssigneePfizer Inc.
InventorJune D. Passaretti
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Abstract
A form of calcium carbonate, acid-stabilized by the addition to finely divided calcium carbonate of one of a calcium- chelating agent and a conjugate base, such as sodium hexametaphosphate, followed by the addition of a weak acid, such as phosphoric acid, is disclosed. A process for producing this material, and a method for its use in the making of neutral to acidic paper in order to improve the optical properties of the paper are also disclosed.
Claims32
An acid-stabilized finely divided calcium carbonate comprising a mixture of at least about 0.1 weight percent of a compound selected from the group consisting of a calcium-chelating agent and a conjugate base, together with at least about 0.1 weight percent of weak acid, with the balance to give 100 weight percent being finely divided calcium carbonate, such that the calcium carbonate is coated by and is in equilibrum with the calcium-chelating agent or conjugate base and the weak acid.
A process for producing an acid-stabilized finely divided calcium carbonate comprising the steps of:
- a) forming a mixture by adding to finely divided calcium carbonate, at least about 0.1 weight percent, based on the dry weight of calcium carbonate, of a compound selected from the group consisting of a calcium-chelating agent and a conjugate base;
- b) adding at least about 0.1 weight percent of a weak acid, based on the dry weight of calcium carbonate, to the mixture to reduce the pH of the resulting final mixture to from about 5 to about 7;
- and
- c) agitating the final mixture to ensure uniform mixing.
Dependencies are inferred from the claim text.