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A method of making a composite pigment of precipitated calcium carbonate (PCC) and a silicon compound, in which the resulting composite pigment is endowed with an excellent combination of optical and mechanical properties. Among other things, a PCC/silicate composite pigment made according to this i

A method of making a composite pigment of precipitated calcium carbonate (PCC) and a silicon compound, in which the resulting composite pigment is endowed with an excellent combination of optical and mechanical properties. Among other things, a PCC/silicate composite pigment made according to this invention imparts increased bulk, light scattering power, porosity and printing properties to paper. The composite pigment material made according to this invention also is very competitive from the standpoint of its production cost. The method for making the composite pigment includes the step of introducing a soluble silicate compound into an aqueous medium containing a precipitate of calcium carbonate formed by carbonation of lime milk, and at a time when the calcium carbonate precipitation reaction has progressed to near completion. Then, an insoluble silicon compound is precipitated upon the precipitated calcium carbonate by carbonation of the reaction mixture in a manner in which the maximum temperature variation of the reaction mixture is kept less than 20° C. The soluble silicate compound is added when the precipitation of the calcium carbonate has reached approximately 90% to less than 100% of completion. Further, the temperature of the reaction mixture during deposition of the silicon compound upon the precipitated calcium carbonate is at least 50° C. or greater, and more preferably is kept between approximately 60 to 100° C.

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A method of making a composite pigment of precipitated calcium carbonate (PCC) and a silicon compound, in which the resulting composite pigment is endowed with an excellent combination of optical and mechanical properties. Among other things, a PCC/silicate composite pigment made according to this i

A method of making a composite pigment of precipitated calcium carbonate (PCC) and a silicon compound, in which the resulting composite pigment is endowed with an excellent combination of optical and mechanical properties. Among other things, a PCC/silicate composite pigment made according to this invention imparts increased bulk, light scattering power, porosity and printing properties to paper. The composite pigment material made according to this invention also is very competitive from the standpoint of its production cost. The method for making the composite pigment includes the step of introducing a soluble silicate compound into an aqueous medium containing a precipitate of calcium carbonate formed by carbonation of lime milk, and at a time when the calcium carbonate precipitation reaction has progressed to near completion. Then, an insoluble silicon compound is precipitated upon the precipitated calcium carbonate by carbonation of the reaction mixture in a manner in which the maximum temperature variation of the reaction mixture is kept less than 20° C. The soluble silicate compound is added when the precipitation of the calcium carbonate has reached approximately 90% to less than 100% of completion. Further, the temperature of the reaction mixture during deposition of the silicon compound upon the precipitated calcium carbonate is at least 50° C. or greater, and more preferably is kept between approximately 60 to 100° C. claim 6 wherein a distinct vessel is connected to a purifier for recovering the rain therein. 8. The dehydrator of claim 5 wherein the heating means is a condensation chamber defined by a plurality of disks, each disk defining an inside space, each disk having a partition positioned within the inside space, each partition constituting a baffle, each inside space being in fluid communication one with the other such that the vapor passes in turn through the inside spaces, the disks mounted on a common tube, the inside space being in fluid communication with the compressor via the tube. 9. The dehydrator of claim 8 wherein the plurality of discs are stacked vertically one above the other creating an upper most inside space and the tube has an exit in the upper most inside space such that the vapor exiting the tube travels downward through the stack. 10. The dehydrator of claim 9 wherein the stacked discs create a bottom most inside space, and the bottom most disk defines an exit from the bottom most inside space. 11. The dehydrator of claim 5 further including a heat exchanger in fluid communication with the heating means. 12. The dehydrator of claim 11 wherein the heat exchanger is positioned within the evaporation chamber and the heat exchange includes a trough for holding a fluid and a coil, at least a portion of the coil disposed in the trough, the coil in fluid communication with the heating means. 13. The dehydrator of claim 12 further including a burner in fluid communication with the coil such that the vapor exits the coil into the burner. 14. The dehydrator of claim 12 wherein the coil is in fluid communication with the trough. 15. The dehydrator of claim 1 wherein the purifying solution in the step of passing the vapor through a neutral rain consists essentially of water. 16. The dehydrator of claim 7 wherein the at least one purifying solution that is neutral consists essentially of water.