Surface-reacted precipitated calcium carbonate, process to make same, and uses thereof

Abstract

The present invention relates to a process for the preparation of a surface-reacted precipitated calcium carbonate (PCC) pigment having an insoluble, at least partially crystalline calcium salt on its surface. In the process of the present invention, a PCC containing pigment is contacted with H 3 O + ions and a solubilized anion in an aqueous medium in the presence of excess solubilized calcium ions to form the surface-reacted PCC having an insoluble, at least partially crystalline calcium salt of the anion formed on its surface.

1 . A surface-reacted precipitated calcium carbonate (PCC) pigment prepared by the process comprising the following steps:
 a) providing at least one precipitated calcium carbonate (PCC)-comprising pigment;   b) providing H3O+ ions;   c) providing at least one anion being capable of forming water-insoluble calcium salts, said anion being solubilized in an aqueous medium;   d) contacting said PCC-comprising pigment with said H3O +  ions and with said solubilized anions in an aqueous medium to form a slurry of surface-reacted PCC-comprising pigment, wherein said surface-reacted PCC comprises an insoluble, at least partially crystalline calcium salt of said anion formed on the surface of at least part of the PCC provided in step a);   
       characterised in that an excess of solubilized calcium ions is provided during step d). 
     
     
         2 . The surface-reacted PCC pigment according to  claim 1 , which is prepared by the process comprising the following steps:
 a) providing at least one precipitated calcium carbonate (PCC)-comprising pigment; and   b) contacting the PCC-comprising pigment in an aqueous medium with at least one anion that is solubilized in an aqueous medium and forms water-insoluble calcium salts in the presence of excess solubilized calcium ions that are present in the aqueous medium, wherein the anion is in the form of a soluble neutral or acid salt, or is in the form of an acid, wherein the anion is a phosphate-comprising anion, PO 4   3− , HPO 4   2− , an oxalate anion (C 2 O 4   2− ), a carbonate-comprising anion in the form of CO 3   2− , a phosphonate anion, a succinate anion or a fluoride anion, wherein the anion is added in a quantity corresponding to between 5 and 50% by weight, based on the weight of said PCC provided in step a), and wherein the PCC-comprising pigment in the aqueous medium, the at least one anion, and excess solubilized calcium ions are mixed so as to develop a laminar flow;   to form a slurry of surface-reacted PCC comprising an insoluble, at least partially crystalline calcium salt of said anion formed on the surface of at least part of the PCC provided in step a), wherein the excess solubilized calcium ions are provided by the addition to the aqueous medium of:
 (i) H 3 O +  ions by addition of an acid or an acid salt that provides all or part of excess solubilized calcium ions in the aqueous medium, wherein the acid or acid salt is a sulphur-comprising acid, sulphuric acid, hydrochloric acid, perchloric acid, formic acid, lactic acid, acetic acid, or nitric acid, or an acid salt thereof, or a soluble calcium acid salt thereof, and/or 
 (ii) a soluble neutral calcium salt that provides all or part of excess solubilized calcium ions in the aqueous medium. 
   
     
     
         3 . The surface-reacted PCC pigment according to  claim 2 , wherein the H 3 O +  ions provide all or part of said excess solubilized calcium ions by dissolution of the PCC to liberate calcium ions. 
     
     
         4 . The surface-reacted PCC pigment according to  claim 2 , wherein the acid or acid salt that provides all or part of the excess solubilized calcium ions is sulphuric acid, hydrochloric acid, acetic acid, or nitric acid, or an acid salt thereof, or a soluble calcium acid salt thereof. 
     
     
         5 . The surface-reacted PCC pigment according to  claim 2 , wherein the anion of step b) is a phosphate-comprising anion, PO 4   3− , or HPO 4   2− . 
     
     
         6 . The surface-reacted PCC pigment according to  claim 2 , wherein the anion of step b) is a carbonate-comprising anion that is generated in situ via the introduction of gaseous CO 2  to the slurry. 
     
     
         7 . The surface-reacted PCC pigment according to  claim 2 , wherein the anion in step b) is added in a quantity corresponding to between 15 and 30% by weight, based on the weight of said PCC provided in step a). 
     
     
         8 . The surface-reacted PCC pigment according to  claim 2 , wherein the excess solubilized calcium ions are provided by addition of sulphuric acid, hydrochloric acid or acetic acid. 
     
     
         9 . The surface-reacted PCC pigment according to  claim 2 , wherein the excess solubilized calcium ions are provided by addition of a soluble neutral calcium salt selected from the group consisting of CaCl 2  and Ca(NO 3 ) 2 . 
     
     
         10 . The surface-reacted PCC pigment according to  claim 2 , wherein H 3 O +  ions are provided by addition of hydrochloric acid, and the anion of step b) is a phosphate-comprising anion provided by addition of H 3 PO 4 . 
     
     
         11 . The surface-reacted PCC pigment according to  claim 2 , wherein H 3 O +  ions are provided by addition of acetic acid, and the anion of step b) is a phosphate-comprising anion provided by addition of H 3 PO 4 . 
     
     
         12 . The surface-reacted PCC pigment according to  claim 2 , wherein the H 3 O +  ions are provided by addition of sulphuric acid, and the anion of step b) is a phosphate-comprising anion provided by addition of H 3 PO 4 . 
     
     
         13 . The surface-reacted PCC pigment according to  claim 2 , wherein the solubilized calcium ions are provided by addition of CaCl 2 , and the anion of step b) is a phosphate-comprising anion provided by addition of H 3 PO 4 . 
     
     
         14 . The surface-reacted PCC pigment according to  claim 2 , wherein the solubilized calcium ions are provided by addition of Ca(NO 3 ) 2 , and the anion of step b) is a phosphate-comprising anion provided by addition of H 3 PO4. 
     
     
         15 . The surface-reacted PCC pigment according to  claim 2 , wherein H 3 O +  ions are provided by addition of hydrochloric acid, and the anion of step b) is a phosphate-comprising anion provided by addition of Na 3 PO 4  or Na 4 HPO 4 . 
     
     
         16 . The surface-reacted PCC pigment according to  claim 2 , wherein H3O +  ions are provided by addition of hydrochloric acid, the anion of step b) is a phosphate-comprising anion provided by addition of H 3 PO 4 , and step b) takes place in the presence of NaCl. 
     
     
         17 . The surface-reacted PCC pigment according to  claim 2 , wherein H3O +  ions are provided by addition of hydrochloric acid, the anion of step b) is a phosphate-comprising anion provided by addition of H 3 PO 4 , and step b) takes place in the presence of KNO 3 . 
     
     
         18 . The surface-reacted PCC pigment according to  claim 2 , wherein the surface-reacted PCC so obtained in step b) has a calcium anion salt:calcium carbonate mass ratio of 20:80 to 60:40 as determined by thermogravimetric analysis. 
     
     
         19 . The surface-reacted PCC pigment according to  claim 2 , which is in the form of a slurry. 
     
     
         20 . The surface-reacted PCC pigment according to  claim 2 , which is dried to obtain a dry surface-reacted PCC product. 
     
     
         21 . The surface-reacted PCC pigment according to  claim 20 , wherein the dry surface-reacted PCC product is treated with one or more fatty acids. 
     
     
         22 . The surface-reacted PCC pigment according to  claim 2 , wherein the salt of the anion extends from the surface of at least part of the surface-reacted PCC pigment. 
     
     
         23 . The surface-reacted PCC pigment according to  claim 2 , wherein the salt of the anion comprises one or more of octacalcium phosphate (OCP), hydroxyapatite (HAP) and tricalcium phosphate (TCP). 
     
     
         24 . The surface-reacted PCC pigment according to  claim 2 , having a BET specific surface area that is at least three times greater than the BET specific surface area of the PCC in the PCC-comprising pigment provided in step a). 
     
     
         25 . The surface-reacted PCC pigment according to  claim 2 , having a BET specific surface area of from 20 to 120 m 2 /g. 
     
     
         26 . The surface-reacted PCC pigment according to  claim 2 , a pore volume of 1 to 2.2 cm 3 /g. 
     
     
         27 . Paper, tissue paper, plastic, paint or water treatment comprising the surface-reacted PCC pigment according to  claim 2  in the form of a slurry or a dried surface-reacted PCC.