Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Reexamination Certificate
1998-03-24
2001-09-25
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
C423S165000
Reexamination Certificate
active
06294143
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a process and a product produced using the process. The product is discrete particles of calcium carbonate having an average particle size, a specific surface area and high purity. The method for preparing the discrete calcium carbonate particles of the present invention requires carbonating an aqueous calcium hydroxide slurry in the presence of carbohydrates, while varying the selected starting carbonation temperature, and/or the concentration of the carbohydrates.
The calcium carbonate particles produced according to the method of the present invention are particularly useful as fillers in paper, as pigment for coated paper, as pigments for paints, as impact modifiers in polymers, and because of such high purity, may find specific application in the food, nutrition, cosmetic and pharmaceutical industries.
BACKGROUND OF THE INVENTION
Precipitated calcium carbonate (PCC) pigments have found increasing application as fillers and as coating pigments in the manufacture of paper and paper board. This utility arises by virtue of PCC's excellent optical and physical properties when used for papermaking.
PCC is traditionally prepared by carbonating an aqueous calcium hydroxide slurry with a carbon dioxide gas to obtain calcium carbonate particles. The traditional process for the production of PCC is quite adequate for particles that do not require discreteness. However, there are problems with the traditional method for producing PCC where discreteness of the final particle is required.
When attempting to precipitate discrete PCC particles by using the traditional process that would naturally form clustered or agglomerated morphologies, it is very difficult to control process parameters so as to consistently produce discrete particles of calcium carbonate. Consequently, particles made according to the traditional process result in average particle size particles and specific surface area that are not very predictable with regard to control. The present invention resolves the problems of the prior art.
It is therefore an object of the present invention to provide a method for producing discrete calcium carbonate particles. Another object of the present invention is to provide a method for producing discrete calcium carbonate particles having a predictable average particle size and having a specific surface area. While another object of the present invention is to provide a reliable method for the preparation of discrete calcium carbonate particles. While a further object of the present invention is to produce discrete calcium carbonate particles having high calcium carbonate purity. While still a further object of the present invention is to produce discrete calcium carbonate products from lime sources of varying quality.
These and other objectives of the present invention will become more apparent as further provided in the related art and detailed description which follows.
RELATED ART
U.S. Pat. No. 5,332,564 discloses a process for producing rhombic or barrel shaped PCC comprising slaking quicklime in an aqueous sugar solution to form a slaked lime slurry, carbonating the slaked lime slurry with carbon dioxide containing gas until rhombic shape calcium carbonate is precipitated.
U.S. Pat. No. 4,237,147 discloses a dry carbonate beverage concentrate and a process for preparing the same which comprises admixing with water a) amorphous calcium carbonate and b) an anhydrous nontoxic acid.
U.S. Pat. No. 4,018,877 discloses an improved process for producing a calcium carbonate by introducing a complexing agent into the calcium carbonate slurry either during or after the primary nucleation stage. The complex agent is selected from a group which includes sucrose or glucose.
U.S. Pat. No. 3,443,890 discloses a process for producing PCC by carbonating an aqueous calcium hydroxide slurry in the presence of saccharides and a second active component selected from the group consisting of active silicon dioxide compounds.
U.S. Pat. No. 2,467,082 discloses a process for producing chalk by carbonating an aqueous calcium hydroxide slurry in the presence of sugar beet residue extract.
U.S. Pat. No. 2,188,633 discloses the use of saccharides and polyvinyl alcohol as an additive to an aqueous calcium hydroxide slurry prior to carbonation to form a calcium carbonate product.
J.P. 9-156,923 discloses a process at 250° C. using a polymeric saccharide and a calcium carbonate seeded aqueous calcium hydroxide slurry to produce a calcium carbonate particle of 25 m
2
/g.
J.P. 9-271,313 discloses a method for using inexpensive low grade furnace gas (CO
2
) to make a spindle shaped Precipitated Calcium Carbonate at 50° C. to 65° C. The method depends on the mesh size of the lime to control particle size and no additives are used.
After viewing the related art, there continues to be a need for a novel method for producing discrete calcium carbonate.
SUMMARY OF INVENTION
The present invention provides a product and a process for producing discrete calcium carbonate particles. The method requires the preparation of an aqueous calcium hydroxide slurry, adjusting the slurry to a selected starting carbonating temperature, adding carbohydrates to the slurry and carbonating the aqueous calcium hydroxide slurry with carbon dioxide gas to produce discrete calcium carbonate particles.
The present invention also provides discrete calcium carbonate particles, as opposed to traditionally formed clustered particles, are more economical to produce, since they may require less additives, less processing, and result in a predictable, discrete, calcium carbonate particle of ninety-eight percent purity.
REFERENCES:
patent: 2188663 (1940-01-01), McClure et al.
patent: 2467082 (1949-04-01), Fleck
patent: 3443890 (1969-05-01), Sisson et al.
patent: 4018877 (1977-04-01), Woode
patent: 4237147 (1980-12-01), Merten et al.
patent: 5227025 (1993-07-01), Kunesh et al.
patent: 5332564 (1994-07-01), Chapnerkar et al.
patent: 5741471 (1998-04-01), Deutsch et al.
Deutsch Donald Richard
Wise Kenneth James
Griffin Steven P.
Hendrickson Stuart L.
Minerals Technologies Inc.
Morris Terry B.
Powell Marvin J.
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