JP2000034120A - Heavy calcium carbonate slurry and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous slurry of heavy calcium carbonate having a low content of coarse particles larger than 20 μm and fine particles smaller than 0.2 μm. SOLUTION: In this aqueous slurry of heavy calcium carbonate having 0.5-2 μm average particle diameter of ground calcium carbonate, 73-85 wt.% solid content concentration and <=150 mPas viscosity at 20 deg.C liquid temperature, the BET specific surface area of heavy calcium carbonate contained in the slurry is 6-12 m2/g, the ratio (D50/D10) of particle diameter of 50 wt.% particle diameter of particle size distribution measurement curve to 10 wt.% particle diameter of particle size distribution measurement curve is 1.5-2.5 and the content of heavy calcium carbonate having particle diameters larger than 20 μm is <=40 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to heavy calcium carbonate, particularly to heavy calcium carbonate used in large quantities as a white pigment suitable for coated paper coatings, and to a method for preparing the same.

2. Description of the Related Art Kaolin, heavy calcium carbonate, precipitated calcium carbonate, titanium oxide and the like are widely used as inorganic pigments for coating. These white pigments greatly affect the optical properties of coated paper such as white paper gloss, whiteness, opacity, smoothness, ink acceptability, and printability. Among these white pigments, heavy calcium carbonate has a large particle size and a wide range of particle size distribution as compared with the precipitated calcium carbonate, but is inexpensive and excellent in fluidity, and tends to be frequently used in paper coatings. It is in. When used as a paper coating, the performance of calcium carbonate as a pigment varies greatly depending on the particle size. In the range of 0.2 to 5 μm, opacity, whiteness, gloss, and ink acceptability improve as the particle size decreases. However, when the thickness is less than 0.2 μm, the opacity and whiteness also decrease. In recent years, products having a small particle size have been provided for heavy calcium carbonate. However, simply by mechanical pulverization, the amount of particles having a particle size of 0.2 μm or less increases as the particle size decreases, thereby increasing fluidity. In addition, the required amount of the binder for the coating color increases with an increase in the specific surface area, and there are many problems such as adversely affecting the optical characteristics of the coated paper.

[0002] In general, heavy calcium carbonate is produced by mechanically grinding natural limestone.
The preparation method includes dry pulverization and wet pulverization, and the particle size of the dry pulverized product is adjusted by air classification. In recent years, the development of high-performance classifiers has improved the accuracy of coarse particle removal, but as the particle size decreases, the cohesive force of the particles increases.
It is difficult to separate fine particles of 0.2 μm or less. In the wet pulverization, a method for preparing less coarse particles and fine particles is provided by controlling the raw material particle size and the pulverization conditions, but this method is not sufficient. On the other hand, a vibrating screen is industrially used for removing coarse particles in the slurry, but since the opening of the screen is about 45 μm, mixing of coarse particles is inevitable. Mixing of coarse particles having a particle size larger than 20 μm is a problem in high-speed coating. For example,
As the blade pressure increases with high-speed coating, the moisture in the paint is absorbed by the base paper, resulting in poor fluidity and causing streaks.Also, the pigment particle size distribution of the return color becomes broad and the particle size of the color increases with operating time. This is a factor that changes the paper quality by making the distribution broad.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a heavy calcium carbonate which has a low content of coarse particles larger than 20 .mu.m and a small content of fine particles of 0.2 .mu.m or less. It is intended to provide an aqueous slurry. Another object of the present invention is to provide a method for efficiently preparing such an aqueous slurry of heavy calcium carbonate.

SUMMARY OF THE INVENTION The present invention is an object of the present invention is to provide a highly concentrated heavy calcium carbonate aqueous slurry which is continuously centrifuged under specific conditions to efficiently remove coarse particles (635 mesh on) larger than 20 μm. And / or diluting the separated aqueous slurry and continuously centrifuging it under another condition can efficiently remove fine particles having a particle size of 0.2 μm or less. It was made based on the finding that the issues could be solved efficiently.

That is, the present invention relates to an aqueous solution of heavy calcium carbonate having an average particle size of 0.5 to 2 μm, a solid content of 73 to 85% by weight, and a viscosity at a liquid temperature of 20 ° C. of 150 mPas or less. A slurry, wherein the heavy calcium carbonate contained in the slurry has a BET specific surface area of 6 to
12 m ² / g, the ratio of the particle size of 50% by weight of the particle size distribution measurement curve to the particle size of 10% by weight of the particle size distribution measurement curve (D ₅₀ /
D ₁₀₎ is 1.5 to 2.5, and particle size to provide a ground calcium carbonate aqueous slurries, wherein the content of 20μm larger heavy calcium carbonate is 40ppm or less. The present invention also provides a heavy calcium carbonate aqueous slurry having an average particle size of 0.5 to 2 μm, a solid content of 74 to 80% by weight, and a viscosity of 300 mPas or less in a centrifuge. Continuously introduced, the centrifugal effect Z represented by the following formula is in the range of 200 to 3000, the heavy liquid and the light liquid, the solid concentration of the aqueous slurry before centrifugation and the light concentration after centrifugation. The liquid is continuously centrifuged so that the difference in solid content concentration is 1% by weight or less, the light liquid is collected, and water is added to the light liquid to obtain a solid concentration of 30 to 70% by weight and a viscosity of 100 mPas. Prepared below, this heavy calcium carbonate aqueous slurry was continuously introduced into a centrifuge, and the centrifugal effect Z
Is in the range of 1,000 to 3,000, and continuously centrifuged into a heavy liquid and a light liquid to recover the heavy liquid.

[0005]

[Formula 1] Z = (N ² π ² r) / (900 g) (where N is the number of revolutions [rpm], r is the radius of gyration [m], and g is the gravitational acceleration [m / sec ² ]. )

BEST MODE FOR CARRYING OUT THE INVENTION The heavy calcium carbonate slurry used as a raw material in the present invention is obtained by adding water and a dispersant to a powder obtained by dry-grinding natural limestone and dispersing the powder in water. . Particularly, the aqueous slurry prepared in this manner is further preferably subjected to wet pulverization using a bead mill or the like.

[0006] In the present invention, natural limestone can be wet-pulverized immediately, but it is better to dry-pulverize the natural limestone before wet pulverization. In dry grinding, the particle size of limestone is reduced to 40
mm or less, preferably the average particle size is about 2 mm to 2 μm. Next, in the present invention, it is preferable to apply an organic dispersant to the surface of the crushed limestone. Although this can be performed by various methods, it is preferable that the dry-ground limestone is wet-ground in the presence of an organic dispersant. Specifically, limestone / aqueous medium (preferably water)
Weight ratio of 30/70 to 85/15, preferably 60
An aqueous medium is added to limestone so as to be in the range of / 40 to 80/20, and a dispersant is added thereto. The amount of the dispersant to be used is not particularly limited, but it is preferable to use 0.1 to 2.0 parts by weight as a solid content per 100 parts by weight of heavy calcium carbonate, and more preferably 0.3 to 1.0 part by weight. And wet-pulverized by a conventional method. Alternatively, an aqueous medium in which a dispersant having an amount in the above range is dissolved in advance is mixed with limestone and wet-pulverized by a conventional method. The wet pulverization may be a batch type or a continuous type, and it is preferable to use a mill using a pulverizing medium such as a sand mill, an attritor, and a ball mill. By the wet pulverization, a powder having an average particle diameter of 2 μm or less, preferably 2 to 0.5 μm, more preferably 1.5 to 0.5 μm is obtained. Also, liquid temperature 2
Preferably, the viscosity at 0 ° C. is adjusted to 300 mPas or less, particularly preferably 50 to 200 mPas.

Here, examples of the dispersant include a water-soluble cationic surfactant (A), a water-soluble anionic surfactant (B), and a water-soluble nonionic surfactant (C). Examples of the water-soluble cationic surfactant (A) used as an organic dispersant include primary, secondary and tertiary amine salt type cationic low molecular weight or high molecular weight surfactants and quaternary ammonium salt type cationic low molecular weight or Polymeric surfactants. Examples of the primary to tertiary amine salt type low molecular surfactants include higher alkylamine salts, higher alkylamine ethylene oxide adducts, higher alkylamine ethylene oxide / propylene oxide adducts, solomin A type amine salts, and sapamin A type. An amine salt, an Arkover A type amine salt, an imidazoline type amine salt and the like can be mentioned. Examples of the quaternary ammonium salt type low molecular surfactant include higher alkyl trimethyl ammonium salts,
Examples thereof include an alkyldimethylbenzylammonium salt, a sapamin-type quaternary ammonium salt, an imidazoline-type quaternary ammonium salt, and an alkylpyridium salt.

[0008] Examples of the primary to tertiary amine salt type polymer surfactants include polyethyleneimine, polyalkylene polyamine salts, polyamine / dicyandiamide condensed salts, and polydiallylamine salts, and quaternary ammonium salt type polymer surfactants. Examples of the surfactant include polystyrene methylaminotrimethylammonium salt, polydiallyldimethylammonium salt, trimethylaminoethyl (meth) acrylate ammonium salt, and polyN-alkylpyridine salt. Among these cationic surfactants, an amine salt-type polymer surfactant or a quaternary ammonium salt-type polymer surfactant is preferable in order to obtain a high-concentration slurry during wet pulverization. Examples include salts of diallylamine alone or copolymers with vinyl compounds and polydiallyldimethylammonium salts. As such a polymer dispersant, a water-soluble cationic copolymer dispersant described in JP-A-7-300568 is preferable. JP-A-7-300
The description of the water-soluble cationic copolymer dispersant in JP 568 is included in the description of the present specification.
These molecular weights are not particularly limited, but are preferably 10
00 to 150,000, more preferably 5,000 to
80,000.

As the water-soluble surfactant (B) used as an organic dispersant, a low-molecular or high-molecular surfactant having a carboxylate, a sulfate, a sulfonate or a phosphate as a functional group is exemplified. Can be Examples of the low-molecular carboxylate include higher fatty acid salts such as sodium laurate, sodium stearate and sodium oleate, higher alcohol polyethylene oxide ether acetate, perfluoroalkyl carboxylate, and the like. Are, for example, polyacrylic acid salts, carboxylic acid monomers such as salts of polyacrylic acid-maleic acid copolymers alone or copolymers comprising at least two or more salts thereof, vinyl compounds and carboxylic acid monomers And a carboxymethylcellulose and a copolymer thereof with a body or a salt thereof. Examples of the low molecular sulfate ester salt include higher alcohol polyethylene oxide sulfate salt, sulfated oil, sulfated fatty acid ester, sulfated fatty acid, sulfated olefin, and alkylphenol polyethylene oxide sulfate salt.

The low molecular sulfonic acid salt includes, for example, alkylbenzene sulfonic acid salt, α-olefin sulfonic acid salt, alkane polysulfonic acid salt, perfluoroalkyl sulfonic acid salt, Igephone T type and aerosol type, etc. Examples of the salt include a formalin condensate of a naphthalene sulfonate, a polystyrene sulfonate, a polyvinyl sulfonate, a polyaryl sulfonate, and a salt of a copolymer of acrylamide and acrylamidopropanesulfonic acid. Examples of the copolymerizable polymer surfactant include a copolymer composed of a carboxylic acid monomer and a sulfonic acid monomer or a salt thereof. Examples of the low molecular phosphate ester salt include a higher alcohol monophosphate ester salt, a higher alcohol polyethylene oxide phosphate ester salt and an alkylphenol polyethylene oxide phosphate ester salt.

Among these anionic surfactants, in order to obtain a high-concentration slurry at the time of wet pulverization, a polymer type surfactant is preferred, and particularly preferred are polyacrylic acid or a salt thereof, and polyacrylic acid. A carboxylic acid monomer such as a maleic acid copolymer or a salt thereof, or a copolymer of at least two or more of them or a salt thereof. These molecular weights are not particularly limited, but are preferably 1,000 to 100,000, and more preferably 5,000 to 50,000. Examples of the water-soluble surfactant (C) used as the organic dispersant include polyethylene glycol type and polyhydric alcohol type nonionic surfactants. As polyethylene glycol type, for example, higher alcohol ethylene oxide adduct,
Examples thereof include alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts, polyhydric alcohol fatty acid ester ethylene oxide adducts, fatty acid amide ethylene oxide adducts, polypropylene glycol ethylene oxide adducts, and polyether modified silicones.

Examples of the polyhydric alcohol type include fatty acid esters of glycerol, fatty acid esters of pentaerythritol, fatty acid esters of sorbitol and sorbitan, fatty acid esters of sucrose, alkyl ethers of polyhydric alcohols, polyglycerin fatty acid esters and ethylene oxide thereof. Adducts and fatty acid amides of alkanolamines; and methylcellulose (MC), hydroxyethylcellulose (HE
C), polyvinyl alcohol (PVA), polyalkylene oxide vinyl ether compound, polyhydroxylalkyl (meth) acrylate, and the like. Among these nonionic surfactants, in order to obtain a high-concentration slurry at the time of wet pulverization, a polymer type surfactant is preferred, and particularly preferred are partially saponified popal and polyhydroxyalkyl ( Meta)
Acrylate and the like. Among the above various dispersants, a polyacrylic acid-based dispersant (for example, F-130 manufactured by San Nopco) is particularly preferred.

In the present invention, in the above method, the concentration of the aqueous calcium carbonate slurry is adjusted to a predetermined concentration, and then the aqueous calcium carbonate aqueous slurry of the present invention is prepared by the following method using a centrifuge. . Method 1 The average particle size obtained by wet grinding according to the above method is 0.5 to 2 μm.
m, the solid content concentration is 74 to 80% by weight (preferably 75 to 80% by weight).
77% by weight) and the viscosity at a liquid temperature of 20 ° C. is 30.
0 mPas or less (more preferably 200 mPas or less, especially 50 mPas or less)
１５０150 mPas) of heavy calcium carbonate aqueous slurry was introduced into a centrifuge, and the centrifugal effect Z represented by the following formula was in the range of 200 to 3000 (preferably 500 to 1500), and the heavy liquid and the light liquid were mixed. Continuously, the difference between the solid content of the aqueous slurry before centrifugation and the solid content of the light liquid after centrifugation is 1% by weight or less (preferably 0.2 to 0.5% by weight). Centrifuging to remove heavy liquid containing coarse particles and collecting light liquid;
9% by weight (preferably 74 to 76% by weight) having a content of heavy calcium carbonate having a particle size of more than 20 μm is 4%.
A method for preparing an aqueous slurry of heavy calcium carbonate having a concentration of 0 ppm or less (preferably 20 ppm or less).

[Formula 2] Z = (N ² π ² r) / (900 g) (where N is the number of revolutions [rpm], r is the radius of gyration [m], and g is the gravitational acceleration [m / sec ² ]. )

Method 2 The average particle size obtained by wet pulverization according to the above method is 0.5 to 2 μm.
m, the solid concentration is 30 to 70% by weight (preferably 40 to 70% by weight).
60% by weight) and the viscosity at a liquid temperature of 20 ° C. is 10%.
0 mPas or less (preferably 50 mPas or less, especially 10 to 40
mPas) of heavy calcium carbonate aqueous slurry is introduced into a centrifuge, and the centrifugal effect is continuously centrifuged into a heavy liquid and a light liquid within a range of 1000 to 3000 (preferably 1500 to 3000). , Remove light liquid containing fine particles,
Collecting the heavy liquid, the solid content concentration is 73 to
85% by weight (preferably 75-80% by weight)
A method for preparing an aqueous slurry of heavy calcium carbonate having a BET specific surface area of 6 to 12 m ² / g.

Method 3 The average particle diameter obtained by wet pulverization according to the above method is 0.5 to 2 μm.
m, the solid content concentration is 74 to 80% by weight (preferably 75 to 80% by weight).
77% by weight) and the viscosity at a liquid temperature of 20 ° C. is 30.
0 mPas or less (more preferably 200 mPas or less, especially 50 mPas or less)
１５０150 mPas) of a heavy calcium carbonate aqueous slurry was introduced into a centrifuge, and the centrifugal effect Z was 200 to 3000.
Within a range of (preferably 500 to 1500), the difference between the solid concentration of the aqueous slurry before centrifugation and the solid concentration of the light liquid after centrifugation is 1% by weight or less between the heavy liquid and the light liquid. To remove the heavy liquid containing coarse particles, collect the light liquid, and then dilute the obtained light liquid with water to reduce its solid content to 30 to 70% by weight (preferably Is 40
６０60% by weight) and a viscosity of 100 mPas or less (preferably 5 mPas).
0 mPas or less, especially 10 to 40 mPas), and this heavy calcium carbonate aqueous slurry is introduced into a centrifuge,
The centrifugal effect Z is 1000 to 3000 (preferably 1500
3,000), a heavy liquid and a light liquid are continuously centrifuged, a light liquid containing fine particles is removed, and the heavy liquid is recovered. weight%
(Preferably 75 to 80% by weight), and a method for preparing an aqueous slurry of heavy calcium carbonate having a BET specific surface area of 6 to 12 m ² / g.

The above centrifugation operation can be performed by passing the solution through the centrifuge once or a plurality of times. The centrifuge used in the present invention may be one generally used for solid-liquid separation or classification, and examples thereof include a decanter type and a basket type centrifuge. Among them, a decanter type centrifuge is preferable, and this centrifuge is used for wastewater treatment, kaolin classification, etc., and is used for separation and dehydration of large particles from fine particles having a specific gravity difference of about 2 to 5 μm or more. Although it is used, it is not suitable for separating ultrafine particles, and its allowable supply concentration is said to be 0.5 to 50% by weight. When a heavy calcium carbonate slurry with good dispersibility provided for coating is treated with a centrifuge, a hard cake is formed in the centrifuge and it is said that it is difficult to discharge the slurry. Has not been done. In the present invention, by supplying the heavy calcium carbonate slurry at a high concentration, the sedimentation speed in the centrifuge is controlled, and discharge in a dilatant slurry state without making a hard cake is enabled. The particle size distribution can be arbitrarily controlled by arbitrarily adjusting the centrifugal effect, the concentration of the supply liquid, and the amount of the supply liquid.

[0017]

According to the present invention, there is provided an aqueous slurry of heavy calcium carbonate having a low content of coarse particles of more than 20 μm and a low content of fine particles of 0.2 μm or less.
Further, according to the present invention, there is provided a method capable of efficiently preparing a heavy calcium carbonate aqueous slurry having such properties. The heavy calcium carbonate aqueous slurry obtained by the present invention is suitably used for paper coating, but its use is not limited to paper coating, and it is dried as it is or by a conventional method, and a paint, an abrasive, a building material, And it can be used as a filler for plastics and rubbers. Next, the present invention will be described with reference to examples.

[0018]

Example 1 Water was added to heavy calcium carbonate having an average particle diameter of 8 μm (a dry-pulverized product of Japanese cement limestone raw material), and anionic dispersant (polyacrylic acid-based dispersant, 100 parts by weight of heavy calcium carbonate) was added. 0.8 parts by weight of San Nopco Co., Ltd .: F-130) was added, and the mixture was wet pulverized using a table-type medium stirring mill at a filling rate of glass beads having a diameter of 1.2 mm of 170% at a peripheral speed of 10 m / sec. A heavy calcium carbonate aqueous slurry was prepared by pass-through classification (average particle diameter 1.1).
08 μm, particle size 20 μm or more and 100 ppm, particle size 0.2 μm
0.8% or less, solid content concentration: 7.55% by weight, viscosity at 20 ° C .: 130 mPas). This aqueous slurry was centrifuged in a decanter type (rotational radius 0.077 m, effective volume 1.
8 liters) at 0.367m ³ / h and 1500G
(Centrifugal effect Z1500), coarse particles settled on the inner wall of the centrifuge. The sedimented coarse particles were transported to the outside by a screw and discharged. At this time, the concentration of the discharged slurry (heavy liquid) containing coarse particles was 83.2.
8 wt%, and the average particle size of the heavy calcium carbonate contained therein was 1.399 μm.

On the other hand, the concentration of the aqueous slurry (light liquid) discharged from the centrifugal separator was 79.35% by weight, and the average particle diameter of the heavy calcium carbonate contained therein was 1.084 μm.
m, the content of coarse particles larger than 20 μm is 0.8 ppm
Met. In addition, an appropriate amount of water was showered on the aqueous slurry recovery side from the centrifugal separator to adjust the solid content concentration of the aqueous slurry and to prevent solidification. The properties of the aqueous calcium carbonate aqueous slurry thus obtained are summarized in Table 1.

Example 2 First, an aqueous slurry of heavy calcium carbonate was prepared in the same manner as in Example 1 (average particle size: 1.341 μm,
Particle size 20 μm or more and 455 ppm, particle size 0.2 μm or less 0.6
9%, solids concentration 76.22% by weight, viscosity at 20 ° C. 120 mPas). This aqueous slurry was fed at 0.825 m ³ / h to the same centrifuge as used in Example 1 and
Example 1 A centrifugal force of 0 G was applied (centrifugal effect Z1500).
The coarse particles and the aqueous slurry were recovered in the same manner as described above. The concentration of the slurry (heavy liquid) containing coarse particles was 86.0% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 2.01%.
It was 8 μm. On the other hand, the concentration of the aqueous slurry (light liquid) discharged from the centrifuge was 79.89% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 1.328.
μm, the content of coarse particles larger than 20 μm is 6 ppm
Met.

Example 3 First, a heavy calcium carbonate aqueous slurry was prepared in the same manner as in Example 1 (average particle size: 1.284 μm,
Particle size 20 μm or more and 375 ppm, particle size 0.2 μm or less 0.8
2%, solids concentration 73.93% by weight, viscosity at 20 ° C. 70 mPas). This aqueous slurry was fed at 0.590 m ³ / h to the same centrifuge as used in Example 1 and 600 G
(Centrifugal effect Z600), and coarse particles and an aqueous slurry were recovered in the same manner as in Example 1. The concentration of the slurry (heavy liquid) containing coarse particles was 85.63% by weight, and the average particle diameter of the heavy calcium carbonate contained therein was 2.079 μm.
m. On the other hand, the concentration of the aqueous slurry (light liquid) discharged from the centrifugal separator was 73.53% by weight, and the average particle size of heavy calcium carbonate contained therein was 1.284 μm.
m, the content of coarse particles larger than 20 μm is 12 ppm
Met.

Example 4 First, a heavy calcium carbonate aqueous slurry was prepared in the same manner as in Example 1 (average particle size: 1.104 μm,
Particle size 20 μm or more and 105 ppm, particle size 0.2 μm or less 1.0
2%, solid content concentration 76.95% by weight, viscosity at 20 ° C. 150 mPas). The aqueous slurry was fed at 0.684 m ³ / h to the same centrifuge as used in Example 1 and
Example 1 A centrifugal force of 0 G was applied (centrifugal effect Z2100).
The coarse particles and the aqueous slurry were recovered in the same manner as described above. The concentration of the slurry (heavy liquid) containing coarse particles was 84.23% by weight,
The average particle size of heavy calcium carbonate contained in it is 1.3
It was 92 μm.

On the other hand, the concentration of the aqueous slurry (light liquid) discharged from the centrifugal separator was 74.91% by weight, and the average particle size of the heavy calcium carbonate contained therein was 1.096 μm.
m, the content of coarse particles larger than 20 μm was 3 ppm. The aqueous slurry thus obtained was diluted with water to adjust the solid content concentration to 56% by weight, supplied to a centrifuge of the same type as used in the previous step at 0.162 m ³ / h, and supplied with 1700 G Centrifugal force (centrifugal effect Z170)
0), a heavy liquid and a light liquid were separated in the same manner as in Example 1.
The concentration of the light liquid was 36.28% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 0.354 μm. On the other hand, the concentration of heavy liquid discharged from the centrifuge was 78.
The content of fine particles having an average particle size of 1.174 μm and 0.2 μm of heavy calcium carbonate contained therein was 0%.

Example 5 First, a heavy calcium carbonate aqueous slurry was prepared in the same manner as in Example 1 (average particle size: 1.100 μm,
Particle size 20 μm or more and 95 ppm, particle size 0.2 μm or less 0.91
%, Solids concentration 58.0% by weight, viscosity at 20 ° C. 30
mPas). This aqueous slurry was supplied to the same centrifugal separator used in Example 1 at 0.252 m ³ / h, and centrifugal force of 1400 G was applied (centrifugal effect Z1400). The slurry was collected. The concentration of the slurry containing coarse particles was 80.35% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 1.342 μm. On the other hand, the concentration of the aqueous slurry discharged from the centrifugal separator was 57.0% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 0.762 μm, and the content of coarse particles larger than 20 μm was 0%. .1 ppm. The aqueous slurry thus obtained was fed to a centrifuge of the same type as used in the previous step at 0.162 m ³ / h,
A centrifugal force of 00 G was applied (centrifugal effect Z2100), and the heavy liquid and the light liquid were separated in the same manner as in Example 1. The concentration of the light liquid was 40.26% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 0.365 μm.

On the other hand, the concentration of the heavy liquid discharged from the centrifugal separator is 78.29% by weight, and the average particle diameter of the heavy calcium carbonate contained therein is 0.879 μm, which is smaller than 0.2 μm. The content was 0.67%. Example 6 First, a heavy calcium carbonate aqueous slurry was prepared in the same manner as in Example 1 (average particle size: 1.100 μm,
Particle size 20 μm or more and 95 ppm, particle size 0.2 μm or less 0.91
%, Solids concentration 60.3% by weight, viscosity at 20 ° C. 45
mPas). This aqueous slurry was supplied to the same centrifugal separator used in Example 1 at 0.162 m ³ / h, and centrifugal force of 1700 G was applied (centrifugal effect Z1700). The liquid was collected. The concentration of the light liquid was 49.12% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 0.512 μm. On the other hand, the concentration of the heavy liquid discharged from the centrifuge was 77.58% by weight, and the average particle size of the heavy calcium carbonate contained therein was 1.249 μm.
m, the content of fine particles smaller than 0.2 μm was 0%. The characteristics described in Examples 1 to 6 and the characteristics of the obtained slurries and commercial products A and B were measured by the following methods.

After adjusting the temperature of the viscosity aqueous slurry to 20 ° C., Tokyo Keiki Co., Ltd .: B-type viscometer, spindle # 2, rotor rotation speed 60
Measured at rpm. The absolute dry weight at a solid concentration of 105 ± 5 ° C. was determined, and the solid concentration was calculated. BET specific surface area measuring method BET specific surface area measuring device: manufactured by Yuasa Ionics Co., Ltd .: measured with a monosoap type. Particle size distribution Laser diffraction particle size distribution analyzer: Nikkiso Co., Ltd .: Microt
It was measured with rac X-100. 5 of the obtained particle size distribution measurement curve
A particle size of 0 wt% as the average particle diameter was determined 10% by weight ratio of the particle diameter of 50 wt% of the particle size and particle size distribution measurement curve of Matatsubu size distribution measurement curve as D ₅₀ / D _10. Note that this ratio approaches 1 as the width of the particle size distribution becomes narrower. Table 1 shows the characteristics of the slurries obtained in Examples 1 to 3, and Table 2 shows the characteristics of the slurries obtained in Examples 4 to 6 and the commercial products A and B.

[0027]

[Table 1] Table-1  Example Average particle size Solids concentration Solid before and after treatment Larger than 20 μm No. (μm) (%) Difference in concentration (%) Particle amount (ppm) 1 1.084 75.39 0.20 0.8 2 1.328 75.89 0.33 63 1.284 73.53 0.40 12

[0028]

[Table 2] Table-2 BET ratio D ₅₀ / D ₁₀ Average particle Solid content Viscosity Hunter Surface area Diameter (μm) Concentration (mPas) Whiteness (m ² / g) (%) (%) Commercial product A 10.8 2.63 1.156 75.2 130 95.2 Commercial product B 14.9 2.65 0.807 75.2 250 94.8 Example 4 6.7 2.14 1.174 78.42 103.0 96.2 Example 5 8.6 2.08 0.879 78.29 148.5 96.2 Example 6 6.9 2.02 1.249 77.58 77.5 95.7

The heavy particles of the present invention whose particle size distribution is controlled in Table 2
Calcium carbonate slurry is D₅₀/ D _TenAnd BET specific surface area
However, it is clear that the fine particles are
Call For example, commercial product B is provided for the purpose of improving gloss.
However, the specific surface area is higher than that of the commercially available product A which is generally used.
The required amount of binder etc. increases greatly and the optical properties of coated paper
Adversely affect However, in Example 5 of the present invention product,
Despite the smaller average particle size compared to A, BET
Coated paper with small specific surface area and low binder requirement
Can have a favorable effect on the optical characteristics of the device. Also,
Although the whiteness of commercial products decreases with the atomization,
Brightness of fine product is less than 0.2μm,
Has improved.

[Brief description of the drawings]

FIG. 1 shows a particle size distribution curve of a commercial product A.

FIG. 2 shows a particle size distribution curve of a commercial product B.

FIG. 3 shows a particle size distribution curve of the aqueous solution of heavy calcium carbonate obtained in Example 4.

FIG. 4 shows a particle size distribution curve of the aqueous calcium carbonate aqueous slurry obtained in Example 5.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yumiko Takase 2-8-6 Nishi-Shimbashi, Minato-ku, Tokyo Sumitomo Realty & Development Hibiya Building 12th Floor F-Tech Co., Ltd. F-term (reference) 4G076 AA16 AC04 BC08 BF10 CA15 CA26 CA28 CA40 DA15 4J037 AA10 DD05 DD07 DD24 EE28 EE29 EE43 FF04

Claims (4)

[Claims] An average particle size of the heavy calcium carbonate is 0.5 to 0.5.
An aqueous slurry of heavy calcium carbonate having a solid content of 73 to 85% by weight, a viscosity at a liquid temperature of 20 ° C. of 150 mPas or less, and a BET specific surface area of heavy calcium carbonate contained in the slurry of 6 to 12 m. ² / g, 50% by weight of particle size distribution measurement curve and particle size distribution measurement curve 1
0 wt% of the ratio of the particle diameter (D ₅₀ / D ₁₀₎ is 1.5 to 2.5, and the particle size is characterized by a content of 20μm larger heavy calcium carbonate is 40ppm or less Heavy calcium carbonate aqueous slurry. 2. The heavy calcium carbonate has an average particle size of 0.5 to 0.5.
A heavy calcium carbonate aqueous slurry having a concentration of 2 μm and a solid content of 74 to 80% by weight and a viscosity at a liquid temperature of 20 ° C. of 300 mPas or less is continuously introduced into a centrifuge, and is represented by the following formula. When the centrifugal effect Z is in the range of 200 to 3000, the difference between the solid content of the aqueous slurry before centrifugation and the solid content of the light liquid after centrifugation is 1% by weight or less between the heavy liquid and the light liquid. And a light liquid is collected, wherein the content of heavy calcium carbonate having a solid content of 73 to 79% by weight and a particle size of more than 20 μm is 40 ppm or less. Preparation method of heavy calcium carbonate aqueous slurry. Z = (N ² π ² r) / (900 g) (where N is the number of revolutions [rpm], r is the radius of gyration [m], and g is the gravitational acceleration [m / sec ² ].) 3. The heavy calcium carbonate has an average particle size of 0.5 to 0.5.
An aqueous slurry of heavy calcium carbonate having a solid concentration of 2 μm, a solid concentration of 30 to 70% by weight, and a viscosity at a liquid temperature of 20 ° C. of 100 mPas or less is continuously introduced into a centrifugal separator.
Is in the range of 1000 to 3000, and continuously centrifuged into a heavy liquid and a light liquid, and the heavy liquid is collected. The solid content concentration is 73 to 85% by weight and the BET specific surface area is A method for preparing a heavy calcium carbonate aqueous slurry of 6 to 12 m ² / g. Z = (N ² π ² r) / (900 g) (where N is the number of revolutions [rpm], r is the radius of gyration [m], and g is the gravitational acceleration [m / sec ² ].) 4. The heavy calcium carbonate having an average particle size of 0.5 to 0.5.
A heavy calcium carbonate aqueous slurry having a concentration of 2 μm and a solid content of 74 to 80% by weight and a viscosity at a liquid temperature of 20 ° C. of 300 mPas or less is continuously introduced into a centrifuge, and is represented by the following formula. When the centrifugal effect Z is in the range of 200 to 3000, the difference between the solid content of the aqueous slurry before centrifugation and the solid content of the light liquid after centrifugation is 1% by weight or less between the heavy liquid and the light liquid. The light liquid is recovered by adding water to the light liquid to adjust the solid concentration to 30 to 70% by weight and the viscosity at a liquid temperature of 20 ° C. to 100 mPas or less. The calcium aqueous slurry is continuously introduced into the centrifuge, and the centrifugal effect Z is 1000 to 3000.
2. The method for preparing an aqueous slurry of heavy calcium carbonate according to claim 1, wherein the heavy liquid and the light liquid are continuously centrifuged within the range described above, and the heavy liquid is recovered. Z = (N ² π ² r) / (900 g) (where N is the number of revolutions [rpm], r is the radius of gyration [m], and g is the gravitational acceleration [m / sec ² ].)