JP3258290B2 - Method for producing spherical or elliptical spherical vaterite calcium carbonate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing spherical or oval spherical vaterite calcium carbonate having little secondary aggregation and good dispersibility.

[0002]

2. Description of the Related Art At present, a carbon dioxide gas method is widely used as an industrial production method of synthetic calcium carbonate. With the carbon dioxide method, natural limestone is calcined to obtain quicklime (calcium oxide), and the quicklime is reacted with water to obtain lime milk (water suspension of calcium hydroxide).
This is a method of obtaining calcium carbonate by passing carbon dioxide gas generated when calcining limestone through this lime milk and causing it to react.

[0003] Synthetic calcium carbonate produced by the carbon dioxide method is widely used in large quantities as a filler or pigment for rubber, plastic, paper, paint, etc., depending on the size of its primary particles. In addition, in order to further improve the physical properties at the time of compounding, various types of inorganic or organic treating agents depending on the intended use are surface-treated on synthetic calcium carbonate used for these applications, and are generally used. ing.

However, the synthetic calcium carbonate produced by the carbon dioxide method originally has a very strong cohesive force between primary particles, and a large number of primary particles aggregate to form large secondary particles (primary particles). It is said that it is impossible to disperse the slurry of the secondary particles to almost the primary particles even if the stirring is continued for a long time.

[0005] When synthetic calcium carbonate containing a large number of aggregates of such primary particles is used as a filler or pigment for rubber, plastic, paper, paint, etc., the secondary particles behave as if they were primary particles. Therefore, good physical properties such as poor dispersion, decrease in strength, decrease in gloss, deterioration in fluidity, etc. cannot be obtained, and the mixing effect as in the case of mixing primary particles cannot be obtained. Similarly, even if a synthetic calcium carbonate containing such a large number of aggregates is treated with an inorganic or organic surface treating agent, only the surface of the secondary particles is treated, and a sufficient effect is obtained. It doesn't work.

[0006] To date, there have been reported many methods of dispersing these primary particle aggregates.
A method of strongly pulverizing and breaking by a sand grinder mill or the like is employed. However, since such a method is grinding and pulverization using a large amount of energy, the aggregates are dispersed and the primary particles are destroyed at the same time.
As a result, a very unstable surface state, and particles smaller than the desired primary particle diameter, and secondary agglomerated particles with incomplete dispersion are mixed, and the particle size distribution is widened. I do not want to be. Further, in a wet pulverizer such as a sand grinder, fine glass beads are usually used as a pulverizing medium, but the surface of these glass beads is also pulverized and destroyed during the pulverization and destruction step of calcium carbonate. A large number of coarse glass pieces of about 20 μm will be mixed in the calcium carbonate of the present invention. For example, calcium carbonate used as a filler for a thin film having a thickness of about 15 μm is dispersed and prepared using such a wet grinding method. It is not preferable.

[0007] Calcium carbonate includes hexagonal calcite-type crystals, orthorhombic aragonite crystals, and pseudo-hexagonal vaterite-type crystals as polymorphs. Cubic or spindle-shaped calcite-type crystals or acicular or columnar aragonite crystals are mostly used for various applications. In contrast, for vaterite-type calcium carbonate,
Due to its morphological characteristics, it has relatively good dispersibility compared to other two-crystal types and does not contain large coarse aggregates. Therefore, pigments for paper, paint, rubber, and plastics , When used as a filler, improves coatability,
It is expected that effects such as improvement of the filling property can be expected, and eventually, the physical strength, glossiness, whiteness, or printing characteristics of the product will be improved.

From the above viewpoints, various methods for industrially producing vaterite calcium carbonate have been conventionally studied. For example, Japanese Patent Application Laid-Open No. 60-90822 discloses a method in which a carbon dioxide-containing gas is introduced into an aqueous calcium hydroxide suspension containing a magnesium compound, and when a certain degree of carbonation is reached, condensed alkali phosphate or an alkali metal salt thereof. In addition, Japanese Patent Application Laid-Open No. 54-15097 discloses a method of obtaining vaterite calcium carbonate by adding ammonia in advance so that the pH of the slurry at the end of the reaction in the reaction between calcium chloride and calcium bicarbonate becomes ■ 8. A method for obtaining vaterite-type calcium carbonate by performing the reaction is described.

[0009] However, all of these methods are not only extremely complicated in their production methods as compared with the conventional methods of producing cubic or spindle-shaped calcium carbonate crystals,
The obtained vaterite calcium carbonate has a non-uniform primary particle size and poor dispersibility.

Recently, various methods have been proposed for producing vaterite calcium carbonate by carbonating calcium hydroxide contained in an organic solvent. For example,
Japanese Patent Application Laid-Open No. Sho 61-77622 discloses a method for producing vaterite calcium carbonate by passing carbon dioxide gas through a mixed solution of calcium hydroxide aqueous solution and methanol. A method is described in which carbon dioxide gas is blown into a suspension of calcium hydroxide + water + alcohols to produce amorphous or crystalline calcium carbonate such as vaterite.

[0011] However, in either case,
Although it is possible to obtain vaterite calcium carbonate in a high yield, spherical or elliptical spherical vaterite calcium carbonate in which primary particles are uniform and monodispersed with good dispersion cannot be stably produced. Therefore, veterite-type calcium carbonate prepared by a conventional method is used for industrial applications in which high dispersibility and uniformity of particles are indispensable,
For example, it cannot be used as an anti-blocking agent for polyester films such as films of 5 μm or less, especially polyester films used for 8 mm video tapes used for 8 mm video decks, films for capacitors, etc. There has been a long-awaited demand for calcium carbonate having improved properties such as uniformity.

[0012]

SUMMARY OF THE INVENTION The present invention solves the above problems and can be sufficiently used in fields requiring a high degree of dispersibility and uniformity of particles such as a polyester base film as described above. It is intended to provide a method for producing spherical or elliptical spherical vaterite calcium carbonate.

[0013]

Means for Solving the Problems As a result of diligent research, the present inventors conducted carbon dioxide gas to a methanol suspension containing a specific amount of quicklime and / or slaked lime and a specific amount of water, and during the carbonation reaction. At a specific point in time, the temperature in the reaction system is adjusted to a specific temperature, and the carbonation reaction is performed by specifying the time when the conductivity in the reaction system reaches a specific value from the start of the carbonation reaction, thereby performing a desired carbonation reaction. It has been found that spherical or elliptical spherical vaterite calcium carbonate can be easily and stably produced, and that the resulting spherical or elliptical spherical vaterite calcium carbonate has unique primary particle uniformity and dispersibility. The present invention has been completed based on these new findings.

That is, according to the present invention, the concentration in terms of quicklime is 0.5
To a methanol suspension of quicklime and / or slaked lime of about 12% by weight, water is added in an amount equivalent to 5 to 20 times the molar amount of quicklime (in the case of slaked lime, converted to the same mole of quicklime), and methanol and quicklime and / or Alternatively, after preparing a mixed system of slaked lime and water, carbon dioxide gas is passed through the mixed system, and in the conductivity change curve in the carbonation reaction system, before the conductivity in the carbonation reaction system reaches the maximum point B. Adjust the temperature inside the system to 30 ° C or higher.
From the carbonation reaction start point A, the conductivity in the carbonation reaction system is 100
The method includes producing a monodisperse spherical or elliptical spherical vaterite calcium carbonate, wherein the carbonation reaction is performed by adjusting the time until the point D of μS / cm is reached to less than 120 minutes. Things.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing spherical or elliptical spherical vaterite calcium carbonate of the present invention will be described.
According to the present invention, carbon dioxide gas is passed through a methanol suspension containing a specific amount of quick lime and / or slaked lime and a specific amount of water, and the temperature in the reaction system is adjusted to a specific temperature at a specific time during the carbonation reaction. Then, a spherical or elliptical spherical vaterite calcium carbonate is produced by performing a carbonation reaction by specifying a time at which the conductivity in the reaction system reaches a specific value from the start of the carbonation reaction.

First, quicklime powder and / or slaked lime powder are charged into methanol to prepare a suspension of quicklime and / or slaked lime in methanol. The concentration of quicklime and / or slaked lime is 0.5 to 12% by weight, preferably 1 to 1% by weight of methanol as a concentration of quicklime (in the case of slaked lime, the concentration converted to quicklime of the same mole, hereinafter abbreviated as quicklime).
It may be 8% by weight. When the concentration of quicklime is less than 0.5% by weight, the unit methanol requirement increases, which is not only uneconomical, but also makes it difficult to control the reaction conditions in the subsequent carbonation reaction step. Yield is very poor. When the concentration of quicklime exceeds 12% by weight, the inside of the system is apt to gel in the subsequent carbonation reaction step, and the shape and size of the obtained calcium carbonate particles become non-uniform. Only poor calcium carbonate is obtained.

The desired calcium carbonate can be obtained by using slaked lime having the same molar weight as quick lime instead of quick lime, but the reaction conditions in the carbonation reaction step are much wider than in the case where quick lime is used as a raw material. It is preferable to use quicklime because it is narrow. The preferred activity of quicklime is 80 or more, and is measured by the following method.

Activity: 500 ml of deionized water at 40 ° C. is put into a 1000 cc beaker, and 2 to 3 drops of phenolphthalein are added while stirring with a stirrer. start. After 1 minute, 4N-HCl is continuously added dropwise to keep the solution slightly reddish. 1
Record the amount of 4N-HCl added dropwise every minute,
Continue this work for 0 minutes. The activity is indicated by the cumulative amount (ml) after 10 minutes.

The quicklime and slaked lime used in the present invention are:
In order to adjust the particle size to a certain value, it is preferable to use after dry grinding using a dry grinding machine or wet grinding of a methanol suspension of quicklime and slaked lime using a wet grinding machine.

Next, water is added to the suspension of quicklime and / or slaked lime in methanol in an amount equivalent to 5 to 20 times the molar amount of the quicklime, preferably 5 to 15 times the molar amount of the quicklime,
Prepare a mixed system of (methanol + quicklime or slaked lime) + water. When the amount of water to be added is less than 5 moles, gelation is apt to occur in the subsequent carbonation reaction step, and when it exceeds 20 moles, crystal forms such as calcite and aragonite other than the vaterite calcium carbonate of the present invention are used. Calcium carbonate containing a large amount of calcium carbonate is undesirably obtained.

Next, carbon dioxide gas (or a gas containing carbon dioxide gas) is passed through the mixed system of methanol and quicklime and / or slaked lime and water to carry out a carbonation reaction. The unit supply amount of carbon dioxide gas reaches a point D where the conductivity in the carbonation reaction system is 100 μS / cm from the carbonation reaction start point A in the conductivity change curve in the carbonation reaction system shown in FIG. It is adjusted so that the time until the time is less than 120 minutes, preferably less than 100 minutes. Therefore, for example, when the reaction efficiency of carbon dioxide gas is 100%, carbonation is started at a carbon dioxide gas unit supply amount of 0.224 l / min or more per mol of quick lime in the reaction system, and the pH in the reaction system is 6. The conductivity of the carbon dioxide gas is continued until the value reaches around 5, and the conductivity in the reaction system is 100 μS /
cm (point D in FIG. 1), the vaterite calcium carbonate of the invention is reliably produced. Further, in the above reaction example, even if the conduction of carbon dioxide gas was stopped at a pH of 10.0 in the reaction system, the pH of the reaction system naturally dropped due to the influence of carbon dioxide gas remaining in methanol, and the reaction was stopped. When the electric conductivity in the system reaches 100 μS / cm (point D in FIG. 1), the present invention is applicable if the time from the start of the carbonation reaction until the electric conductivity in the carbonation reaction system reaches point D is less than 120 minutes. Is achieved.

However, in the same manner as in the above reaction example, carbonation was started at a carbon dioxide gas unit supply of 0.224 liter / min or more per mol of quicklime in the reaction system, and the pH in the reaction system was raised to 1
Even if the conduction of the carbon dioxide gas is stopped at 0.5, if the pH rises due to the alkali remaining in the system and the conductivity in the system rises without reaching the point D, the plate-like calcium carbonate becomes Many mixed and irregular calcium carbonates can be obtained, and the dispersibility of these calcium carbonates cannot be said to be good, and the object of the present invention cannot be achieved.

Further, the conductivity in the carbonation reaction system is reduced to a point D from the start of the carbonation reaction due to the shortage of the unit supply amount of the carbon dioxide gas or the reduction of the reaction efficiency of the carbon dioxide gas due to the insufficient stirring power of the reactor. If the time to reach the point exceeds 120 minutes, for example, if the time to reach the point D is 200 minutes, plate-like calcium carbonate will be obtained,
It goes without saying that the object of the present invention is not achieved. The temperature of the mixed system at the start of the carbonation reaction is preferably 20 ° C. in order to prevent gelation during the carbonation reaction step.
As described above, it is more preferable to set the temperature to 30 ° C. or higher. However, in the conductivity change curve in the carbonation reaction system shown in FIG. 1, before the conductivity in the carbonation reaction system reaches the maximum point B, As long as the temperature in the system is adjusted to 30 ° C. or higher, preferably 40 ° C. or higher, the object of the present invention is achieved irrespective of the temperature of the mixing system at the start of the carbonation reaction. Before the conductivity in the carbonation reaction system reaches the maximum point B, the temperature in the system is 3
When the temperature is lower than 0 ° C., after the conductivity in the carbonation reaction system reaches the maximum point B, the viscosity of the carbonation reaction system rapidly rises and gels easily, and the carbonation reaction tends to be unable to be continued. Further, when the viscosity of the carbonation reaction system rises sharply, even if the carbonation reaction can be continued by vigorous stirring or the like, the carbonation reaction in the system becomes a heterogeneous reaction. Are not uniform and vaterite calcium carbonate having good dispersibility cannot be obtained.

The spherical or elliptical spherical vaterite calcium carbonate obtained as described above has almost the same average particle diameter as measured by an electron microscope and the average particle diameter measured by a particle size distribution analyzer as shown below. Not only that, the particle size distribution is extremely sharp, and the particles are monodispersed without agglomeration in the dispersion medium.

According to the present invention, the following (A), (A),
It is possible to obtain spherical or oval spherical vaterite calcium carbonate satisfying all of the requirements of (c), (d), (e) and (f). (A) 0.1 μm ≦ DS ≦ 2.0 μm (A) DP3 / DS ≦ 1.25 (C) 1.0 ≦ DP2 / DP4 ≦ 1.4 (D) 1.0 ≦ DP1 / DP5 ≦ 2.5 (E) (DP2-DP4) /DP3≦0.35 (f) S ≧ 40, where DS is an average particle diameter (μm) examined by a scanning electron microscope (SEM), and primary particles are spheres having the same volume. DP1: Centrifugal sedimentation type particle size distribution analyzer (SA manufactured by Shimadzu Corporation)
-CP3), the particle size (μ) at a cumulative weight of 10% calculated from the larger particle size side.
m) DP2: In the particle size distribution measured using the above measuring device, the particle size (μm) at 25% of the cumulative weight calculated from the larger particle diameter side DP3: In the particle size distribution measured using the above measuring device, Particle size at 50% cumulative weight calculated from particle size side (μm) DP4: Particle size at 75% cumulative weight calculated from large particle size side (μm) DP5: In the particle size distribution measured using the above measuring device, the particle size (μm) at a cumulative weight of 90% calculated from the larger particle size side. S: The particle size relative to the area of the circle circumscribed in the projected view of the vaterite particles. Projected area ratio S = (projected cross-sectional area of particle / area of circle circumscribing particle) ×
100

The measurement of the particle size by the centrifugal sedimentation type particle size distribution analyzer in the present invention is measured and calculated in the following manner. Measurement model: SA-CP3 manufactured by Shimadzu Corporation Measurement method: Solvent: sodium ionized polyacrylate 0.004 in ion exchanged water
Preliminary dispersion: 100 seconds of ultrasonic dispersion Measured temperature: 25.0 ° C. ± 2.5 ° C. Measurement method: The following calculation example is used.

[0027]

[Table 1]

The DP calculated from the above particle size distribution measurement results
1, 2, 3, 4, and 5 are as follows: DP1 = 2.00 + (11.0-10.0) x (3.00-2.00) ÷ (11.
0 -6.0) = 2.20 DP2 = 0.80 + (28.0-25.0) x (1.00-0.80) ÷ (28.0
-18.0) = 0.86 DP3 = 0.50 + (58.0-50.0) x (0.60-0.50) ÷ (58.
0−42.0) = 0.55 DP4 = 0.30 + (82.0−75.0) × (0.40−0.30) ÷ (82.
0−72.0) = 0.37 DP5 = 0.15 + (94.0−90.0) × (0.20−0.15) ÷ (94.
0-89.0) = 0.19 The DS of the present invention was measured using a scanning electron microscope manufactured by Hitachi, Ltd. at a magnification of 20,000.

In the present invention, the dispersion obtained by monodispersing the obtained vaterite calcium carbonate is subjected to solid-liquid separation by a method such as concentration and dehydration, and methanol obtained by the solid-liquid separation is used again for the synthesis of calcium carbonate. Can be.
Further, to further increase the stability of the monodispersed particles in the dispersion of vaterite calcium carbonate obtained according to the present invention, by adding a carboxylic acid or an alkali salt thereof to the obtained dispersion. Thus, it becomes possible to obtain a dispersion of vaterite calcium carbonate having a long-term stable dispersibility. It is also easy to replace methanol in the dispersion with another organic solvent.For example, monodisperse spherical or elliptical spherical ethylene carbonate slurry of vaterite calcium carbonate is applied to polyester fibers, polyester films, etc. Exhibits anti-blocking properties. Furthermore, if the vaterite calcium carbonate obtained according to the present invention is dried after adding a fatty acid, a resin acid or an alkali salt thereof to the monodispersed dispersion, a vaterite calcium carbonate powder having good dispersibility is prepared, Calcium carbonate having good optical properties, mechanical properties, good fluidity and filling properties as pigments for coatings, inks, fillers for rubber and plastics, and papermaking for known applications, such as fillers for paints and inks, is prepared. .

[0030]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. The measurement of conductivity and the measurement of pH were performed by the following methods. Measurement of conductivity: Toa Denpa Kogyo CM-40S conductivity meter was used. However, the value when the reference temperature is 25 ° C. Measurement of pH: Yokogawa's personal pH meter PH81-
11-J was used.

Preparation Example: Preparation of Dispersions of Methanol Suspension Used in Examples and Comparative Examples Granular quicklime (reagent grade) and slaked lime (reagent grade) having an activity of 82 were crushed with a dry pulverizer (Coloplex, Alpine Company). Lime), the obtained quicklime powder is put into methanol, coarse particles are removed using a 200-mesh sieve, and then a quicklime methanol suspension having a solid content concentration of 20% as quicklime and A methanol suspension of slaked lime was prepared. The methanol suspension is wet-milled (Dynomill P
(ILOT type, manufactured by WAB Co., Ltd.) to prepare a suspension of quicklime and a suspension of slaked lime in methanol.

Example 1 Methanol was additionally added to the methanol dispersion of quick lime obtained in the above preparation example to give a quick lime concentration of 3.0% by weight.
Then, water was added in an amount equivalent to 11 times mol of quicklime to prepare a mixed system of methanol, quicklime and water. The mixed system containing 200 g of quicklime was heated to 42 ° C.
Then, carbon dioxide gas was passed through the mixed system at a flow rate of 0.082 mol / min per mol of quick lime under stirring to initiate a carbonation reaction. Five minutes after the start of the carbonation reaction, the conductivity in the system reached a maximum point (point corresponding to point B in FIG. 1), and the temperature in the system at the maximum point was adjusted to 45 ° C. Thereafter, the carbonation reaction was continued, and the carbonation reaction was started 1
After 9 minutes, when the conductivity in the system reached 100 μS / cm (point corresponding to point D in FIG. 1), the supply of carbon dioxide gas was stopped, and the carbonation reaction was stopped. The pH in the system at point D was 7.0. FIG. 2 shows the measurement results of the conductivity and the pH in the system during the carbonation reaction of Example 1. Table 2 shows the conditions of the carbonation reaction in Example 1. Further, the calcium carbonate prepared according to Example 1 showed 1
A calcium carbonate having a 00% vaterite structure,
Table 4 shows the physical properties of the vaterite calcium carbonate, and FIG. 3 shows a photograph taken with a scanning electron microscope. From the results shown in Table 4 and FIG. 3, it can be seen that the calcium carbonate prepared according to Example 1 was a highly dispersed vaterite calcium carbonate having almost no secondary aggregation.

Examples 2 and 3 Calcium carbonate was prepared in the same manner as in Example 1 except that the specific values of the production method of Example 1 shown in Table 2 were changed to the specific values shown in the same table. Was synthesized. As a result of X-ray diffraction, calcium carbonate prepared according to Examples 2 and 3
The calcium carbonate has a 0% vaterite structure. Table 4 shows the physical properties of the vaterite calcium carbonate. From the results in Table 4, it can be seen that the calcium carbonate prepared in Examples 2 and 3 is a vaterite calcium carbonate having little secondary aggregation and good dispersibility.

Example 4 After the carbonation reaction was started in the same manner as in Example 1, the supply of carbon dioxide gas was stopped 13 minutes after the start of the carbonation reaction, when the pH in the system reached 10.0. The stirring in the system was continued even after the supply of carbon dioxide was stopped, and the conductivity in the system reached 100 μS / cm 20 minutes after the start of the carbonation reaction. The pH in the system at point D was 9.7. FIG. 4 shows the results of measuring the conductivity and the pH of the system during the carbonation reaction of Example 4. Table 2 shows the conditions of the carbonation reaction in Example 4. Further, as a result of X-ray diffraction, the calcium carbonate prepared in Example 4 was a calcium carbonate having a 100% vaterite structure. Table 4 shows the physical properties of the vaterite calcium carbonate, and FIG. Shown in Table 4 and FIG.
From the results, it can be seen that the calcium carbonate prepared in Example 4 is a vaterite calcium carbonate having little secondary aggregation and good dispersibility.

Example 5 The methanol suspension dispersion of quicklime used in Example 1 was changed to the methanol suspension dispersion of slaked lime obtained in the above preparation example. Calcium carbonate was synthesized in the same procedure as in Example 1, except that the specific value of the production method 1 was changed to the specific value shown in the same table. As a result of X-ray diffraction, the calcium carbonate prepared in Example 5 was a calcium carbonate having a 100% vaterite structure. Table 4 shows the physical properties of the vaterite calcium carbonate. From the results in Table 4, it can be seen that the calcium carbonate prepared according to Example 5 is a vaterite calcium carbonate having little secondary aggregation and good dispersibility.

Comparative Example 1 Table 3 shows the specific values of the production method of Example 1 shown in Table 2.
The carbonation reaction was carried out in the same procedure as in Example 1 except that the special values shown in (1) were used. However, during the carbonation reaction, the inside of the system was remarkably thickened and the inside of the system became a sherbet-like state, making it difficult to continue the carbonation reaction. Therefore, the carbonation reaction was stopped.

Comparative Examples 2 to 5 Specific values of the production method of Example 1 shown in Table 2 are shown in Table 3.
Calcium carbonate was synthesized in the same procedure as in Example 1 except that the characteristic values were changed to the following. Table 5 shows the physical properties of calcium carbonate prepared in Comparative Examples 2 to 5. FIG. 6 shows the measurement results of conductivity and pH in the system during the carbonation reaction of Comparative Example 5. From Table 5, it can be seen that the vaterite calcium carbonate prepared in Comparative Examples 2 and 4 is calcium carbonate having extremely poor dispersibility. Comparative Example 3
It can be seen that the calcium carbonate prepared by the method described above contains a large number of calcite calcium carbonate and calcium aragonite carbonate, and the particle size distribution is broad and poor. Further, the calcium carbonate prepared in Comparative Example 5 was confirmed by a scanning electron micrograph to be a calcium carbonate having a plate shape.

Comparative Example 6 Lime milk prepared by adding water to quick lime was mixed with a specific gravity of 1.07.
0, the temperature was adjusted to 10 ° C., and furnace gas having a carbon dioxide gas concentration of 25% by weight was supplied at a conduction rate of 20 m ³ / min into 7.2 m ^{3 of the} lime milk to carry out a carbonation reaction. The reaction was completed. The temperature of the aqueous calcium carbonate suspension after the completion of the carbonation reaction was adjusted to 50 ° C., and the mixture was stirred for 24 hours. The calcium carbonate thus prepared was calcite-type calcium carbonate and had a primary particle diameter of 0.2 μm in a scanning electron micrograph. The aqueous suspension of calcium carbonate was dehydrated according to a conventional method, and sodium polyacrylate was added to the obtained dehydrated cake in an amount of 1.5% by weight based on the solid content of calcium carbonate. An aqueous slurry of 35% by weight of calcium carbonate was obtained. The water slurry was repeated at a flow rate of 60 cc / min.
0 times, wet pulverizer (Dyno mill Pilot type, WAB
Company, media filling rate 80%, media 0.6-0.9
mm, rotation speed 1500 rpm) and wet pulverization was performed to disperse the aggregates. Table 5 shows the physical properties of calcium carbonate prepared in Comparative Example 6, and FIG. 7 shows a photograph taken with a scanning electron microscope. From the results in Table 5 and FIG. 7, the calcium carbonate prepared in Comparative Example 6 was prepared by repeatedly performing strong wet pulverization.
It can be seen that the particle size distribution is broad and the particle shape is non-uniform.

[0039]

[Table 2]

Quick lime equivalent concentration: quick lime equivalent concentration in methanol suspension dispersion before carbonation reaction (% by weight) Water addition amount: added to 1 mol of quick lime in methanol suspension dispersion before carbonation reaction Amount of added water (mol) Temperature 1: In-system temperature at the start of carbonation reaction (° C) Rate 1: Carbon dioxide gas supplied to 1 mol of quicklime in methanol suspension dispersion before carbonation reaction Temperature (mol / min) Temperature 2: Temperature in the system at the maximum point B of conductivity in the system (° C.) Gelation: Presence of thickening / gelation during carbonation reaction pH1: Carbon dioxide supply PH in the system at the time of shutdown Time 1: Elapsed time (minute) from the start of the carbonation reaction to the stoppage of the carbon dioxide gas supply halfway Time 3: The conductivity in the system is 1 after the start of the first carbonation reaction
Elapsed time (minutes) until reaching point D at which 00 μS / cm is reached.

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

As described above, according to the present invention, spherical or elliptical spherical vaterite calcium carbonate having little secondary aggregation and excellent dispersibility is provided.

[Brief description of the drawings]

FIG. 1 is a conductivity change curve in a carbonation reaction system.

FIG. 2 shows the results of conductivity measurement and pH measurement in the carbonation reaction system of Example 1.

FIG. 3 is an electron micrograph showing the particle structure of vaterite calcium carbonate obtained in Example 1.

FIG. 4 shows the results of conductivity measurement and pH measurement in the carbonation reaction system of Example 4.

FIG. 5 is an electron micrograph showing the particle structure of vaterite calcium carbonate obtained in Example 4.

6 shows the results of conductivity measurement and pH measurement in the carbonation reaction system of Comparative Example 5. FIG.

FIG. 7 is an electron micrograph showing the particle structure of calcium carbonate obtained in Comparative Example 6.

[Explanation of symbols]

 A carbonation reaction start point B conductivity maximum point in carbonation reaction system C conductivity drop start point in carbonation reaction system D point where conductivity in carbonation reaction system is 100 μS / cm

Continuation of the front page (56) References JP-A-61-77622 (JP, A) JP-A-63-103824 (JP, A) JP-A-1-301511 (JP, A) JP-A-64-72916 (JP) (A) JP-A-2-243514 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01F 11/18 C09C 1/02 D21H 17/67

Claims (5)

(57) [Claims] 1. In a methanol suspension of quicklime and / or slaked lime having a quicklime-converted concentration of 0.5 to 12% by weight, 5 to 20 times mol of quicklime (in the case of slaked lime, it is converted to the same mole of quicklime). After adding a considerable amount of water to prepare a mixed system of methanol and quicklime and / or slaked lime and water, carbon dioxide gas is passed through the mixed system, and the carbonation reaction curve in the carbonation reaction system shows Before the conductivity in the system reaches the maximum point, adjust the temperature in the system to 30 ° C. or more, and time from the start point of the carbonation reaction to the point where the conductivity in the carbonation reaction system reaches 100 μS / cm. Wherein the carbonation reaction is carried out by adjusting the temperature to less than 120 minutes, thereby producing a monodisperse spherical or elliptical spherical vaterite calcium carbonate. 2. The method according to claim 1, wherein the concentration of quicklime in the methanol suspension is 1 to 8% by weight. 3. The amount of water added to quicklime is 5 to 5.
2. The production method according to claim 1, wherein the amount is 15-fold molar equivalent. 4. The method according to claim 1, wherein the temperature in the system adjusted before the conductivity reaches the maximum point is 40 ° C. or higher. 5. The time from the start of the carbonation reaction to the point at which the conductivity in the carbonation reaction system reaches 100 μS / cm,
The method according to claim 1, wherein the time is less than 100 minutes.