초록 ▼

The invention concerns precipitated calcium carbonate products containing polynuclear regular agglomerates having a number of calcium carbonate particles (aggregates) attached to each other and having a particle size of about 40 to 200 nm. According to the invention, these products are prepared by a

The invention concerns precipitated calcium carbonate products containing polynuclear regular agglomerates having a number of calcium carbonate particles (aggregates) attached to each other and having a particle size of about 40 to 200 nm. According to the invention, these products are prepared by adjusting the Z potential of the calcium carbonate suspension to -1 . . . -20 mV by adjusting the pH of the suspension to 6.5 . . . 9.5. The pH of the calcium carbonate slurry obtained by causticizing is adjusted to a desired value in a box filter, where after the suspension is stirred by a heavy-duty mixer such that it is subjected to differences of about 50 to 200 m/s in peripheral speed. The products according to the invention have good opacity and are very well suited for coating paper.

대표청구항 ▼

1. Precipitated calcium carbonate agglomerates containing a number of spherical calcium carbonate particles which are attached to each other and have a particle size of approximately 40 to 200 nm, wherein the particles are spherical with a deviation of less than about 10%. 2. The agglomerates accord

1. Precipitated calcium carbonate agglomerates containing a number of spherical calcium carbonate particles which are attached to each other and have a particle size of approximately 40 to 200 nm, wherein the particles are spherical with a deviation of less than about 10%. 2. The agglomerates according to claim 1, wherein the agglomerates have a size of approximately 0.1 to 10 μm and the calcium carbonate particles have a size of approximately 40 to 120 nm. 3. The agglomerates according to claim 1, wherein the agglomerates have a plurality of internal reflecting surfaces. 4. A method for preparing calcium carbonate, which comprises: reacting a calcium oxide containing starting material with carbonate ions by adjusting a Z potential to -1 to -20 mV in a suspension by lowering a pH to 8.4±0.5; and recovering calcium carbonate in the form of agglomerates whose size is approximately 0.1 to 10 μm and which contain calcium carbonate particles having a size of approximately 40 to 200 nm, and the calcium carbonate particles are spherical with a deviation of less than about 10%. 5. The method according to claim 4, wherein the agglomerates have a plurality of internal reflecting surfaces. 6. The method according to claim 4, wherein dispersion auxiliaries are added to the suspension whereafter the pH value of the suspension is adjusted such that the crystals have a Z potential of -1 to -20 mV. 7. The method according to claim 6, wherein in that as the dispersion auxiliaries, polyelectrolyte is used. 8. The method according to claim 4, wherein precipitated calcium carbonate particles are prepared being in the form of polynuclear, essentially spherical agglomerates having a size of about 400 to 750 nm. 9. The method according to claim 4, wherein to adjust the pH of the suspension, inorganic or organic acids are used. 10. The method according to claim 9, wherein carbonic acid or phosphoric acid is used to adjust the pH. 11. The method according to claim 4, wherein lowering the pH of the suspension is performed by introducing carbon dioxide gas into the suspension during filtering. 12. The method according to claim 4, wherein the calcium carbonate is formed according to the following reaction: CaO+H2O+Na2CO3→CaCO3+2NaOH. 13. The method according to claim 4, wherein the calcium carbonate is formed according to the following reaction: CaO+H2O+CO2→CaCO3+H2O.