JPH0648732A - Production of dispersion of calcium carbonate fine particle - Google Patents

Abstract

PURPOSE:To obtain precipitated calcium carbonate having fine particle size, causing little secondary agglomeration and having excellent dispersibility on an industrial scale at a low cost. CONSTITUTION:An aqueous suspension of calcium carbonate concentrated beforehand to satisfy the following conditions (a) to (c) is used in the wet-pulverization of precipitated calcium carbonate produced by passing carbon dioxide gas through lime milk. (a). The pH (A) at the end of carbonation reaction satisfies the following formula 8.0<=A<=10.0 (measured at 25 deg.C). (b). The pH (B) of the aqueous suspension measured after stirring and/or leaving standing the aqueous suspension of calcium carbonate obtained by the procedure (a) satisfies the formulas 10.5<=B (measured at 25 deg.C) and B-A>=1.0 at the same time. (c). The solid concentration (C%) of the aqueous suspension of calcium carbonate produced by the procedure (b) is concentrated to a solid concentration (D%) satisfying the following formulas 1.2C<=D and 15<=D<=30 at the same time.

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 precipitated calcium carbonate which is fine, has little secondary aggregation, and has good dispersibility.

[0002]

2. Description of the Related Art At present, the carbon dioxide method is widely adopted as an industrial method for producing precipitated calcium carbonate. This carbon dioxide method is to obtain quicklime (calcium oxide) by firing naturally produced limestone, and to react this quicklime with water to obtain milk of lime (water suspension of calcium hydroxide). This is a method of obtaining calcium carbonate by conducting and reacting carbon dioxide gas generated when firing limestone. The calcium carbonate produced in this way is
Depending on the size of the primary particles, or in order to further improve the physical properties at the time of compounding, the surface of the particles is surface-treated with various inorganic or organic surface-treating agents, such as rubber, plastic, paper, and paints. Is widely used in large quantities. However, the precipitated calcium carbonate produced by the carbon dioxide method originally has a strong cohesive force between particles,
A large number of primary particles aggregate to form large secondary aggregates. Among them, those having a primary particle size of 0.2 μm or less have a particularly strong aggregating force, and even if a large amount of energy is used, the initial primary particle size is reduced. It is impossible to eliminate secondary aggregates while maintaining the above.

When precipitated calcium carbonate containing a large number of such secondary agglomerates is compounded with rubber, plastic, paper, paint, etc., the secondary agglomerated particles behave as if they were large primary particles, resulting in poor dispersion and strength. As a result, physical properties such as deterioration, deterioration in gloss, and insufficient viscosity occur, and various compounding effects originally expected for fine primary particles cannot be obtained. Similarly, even if surface treatment of various inorganic or organic surface treatment agents is performed on the precipitated calcium carbonate containing a large number of such secondary agglomerates, only the secondary agglomerated particle surface is treated and sufficient effect is obtained. Does not come out to the full.

Until now, many methods for dispersing these primary particle aggregates have been reported, but JP-A-59-579.
13, as disclosed in JP-A-60-210521 and the like, generally, precipitated calcium carbonate that has been carbonated is temporarily dehydrated by a filter press or the like to obtain a press cake having a solid content concentration of 60% or more, and then polyacrylic acid. Make a high-concentration water suspension with a dispersant such as sodium, or dry and powder, and then suspend again in water using the above-mentioned dispersant, etc. to obtain a high-concentration water suspension with a solid content concentration of 60% or more. Then, a method of powerfully crushing and destroying with a ball mill, a sand grinder mill or the like is adopted.

However, such a method inevitably consumes a large amount of energy because it is necessary to press up or dry powder as a method for obtaining a highly concentrated water suspension. Not only is it economically disadvantageous because a large amount of energy is indispensable because a dispersion water suspension process must be performed before wet grinding with a Keddy mill, Corless mixer, etc. Excessive crushing and destruction occurs in the crushing container because it is simply mechanically crushed. Thus, the aggregates of calcium carbonate are dispersed and the primary particles are destroyed at the same time. As a result, the surface condition is very unstable, secondary aggregates may be formed again, and the particle size distribution is wide. Only non-uniform calcium carbonate can be obtained.

Further, particularly in JP-A-60-210521, the target calcium carbonate is usually light calcium carbonate, which has a relatively small cohesive force among the precipitated calcium carbonate having an average particle diameter of 1 to 5 μm. However, it is said that it is difficult to obtain desired physical properties unless a large amount of energy is consumed as described above. Furthermore, when a surface treatment agent having a dispersing function such as sodium polyacrylate is used to obtain a high-concentration aqueous suspension, various disadvantages such as limited use applications occur for that, and a preferred method It is hard to say.

Further, in JP-A-59-69425, there is produced a precipitated calcium carbonate having good dispersibility by adding a small amount of strontium salt or barium salt in a carbonation step for adjusting calcium carbonate by a carbon dioxide method. A method has been proposed. According to this method, although the precipitated calcium carbonate having good dispersibility can be adjusted,
In the calcium carbonate obtained by the method, the strontium salt or barium salt added in the carbonation step is mixed, and it is difficult to remove these strontium salt and barium salt by an economically advantageous method. Inconvenience is expected to occur depending on the intended use.

[0008]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention compensates for the drawbacks of the conventional dispersion methods of precipitated calcium carbonate, particularly fine calcium carbonate, and is economically advantageous in carbon dioxide having good dispersibility. A method for producing calcium is provided.

[0009]

As a result of intensive studies to solve the above problems, the present inventors have prepared an aqueous calcium carbonate suspension before grinding so as to satisfy specific conditions when performing wet grinding. However, by reducing the ratio of the alkaline substance, which is considered to be the cause of forming the secondary aggregate, to the solid content of calcium carbonate, and measuring the surface inactivation by removing the alkaline substance from the primary particle surface, It was found that precipitation-precipitated calcium carbonate which is fine and has good dispersibility can be easily obtained without preventing aggregation and addition of a third component which may be an impurity in the calcium carbonate aqueous suspension, and thus completed the present invention. It was

That is, according to the present invention, when wet-grinding precipitated calcium carbonate obtained by passing carbon dioxide gas through lime milk, calcium carbonate water pre-concentrated so as to satisfy the following conditions a, b and c: It is intended to provide a method for producing a calcium carbonate fine particle dispersion characterized by using a suspension. a. The pH (A) at the end of the carbonation reaction satisfies the following formula: Formula 8.0 ≦ A ≦ 10.0 (measured value at 25 ° C.) b. The pH (B) of the aqueous calcium carbonate suspension obtained by stirring and / or allowing the aqueous calcium carbonate suspension obtained in the above step (a) simultaneously satisfies the following equations and 10.5 ≦ B (25 (Measured value in ° C) Formula B-A ≥ 1.0 c. Concentrating the solid content concentration (C%) of the aqueous calcium carbonate suspension obtained in the above b to a solid content concentration (D%) simultaneously satisfying the following formulas and. Formula 1.2 C ≦ D Formula 15 ≦ D ≦ 30

In the present invention, quick lime used for preparing lime milk is not particularly limited, but in the calcining step of limestone, the activity of each quick lime is made as uniform as possible, and an alkaline substance after completion of the carbonation reaction is obtained. In order to make the elution rate from the secondary agglomerates of (1) uniform, the size of the limestone to be fired is preferably 10 mm or less. Moreover, although the activity of quicklime used is not particularly specified,
In order to accelerate the elution rate of the alkaline substance from the secondary aggregate after the completion of the carbonation reaction, it is preferable to use quicklime having an activity of 60 or more. The method for measuring the activity of quicklime in the present invention is as follows. (Method of measuring the activity of quicklime) (i) Deionized water 50 at 40 ° C. in a 1 liter beaker
Add 0 ml and add 2-3 drops of phenolphthalein solution while stirring with a stirrer. (Ii) Into the beaker, 10 g of crushed lime roughly crushed to a diameter of 2 to 5 mm is put all at once, and at the same time, a stopwatch starts counting time. (Iii) After 1 minute, 4N-HCl is continuously added dropwise so as to keep the solution slightly reddish. (Iv) The amount of 4N-HCl added dropwise is recorded every 1 minute, and the total amount of added 4N-HCl (unit: ml) 10 minutes after the addition of quick lime is defined as the activity. Further, regarding the water to be used, in order to speed up the elution rate of the alkaline substance from the secondary aggregate after completion of the carbonation reaction, the chlorine ion concentration in the water which hinders the elution is set to 20%.
It is preferably 0 ppm or less.

There is also no particular limitation on the method for conducting carbon dioxide gas to lime milk to obtain precipitated calcium carbonate, for example, a method for conducting carbon dioxide gas in lime milk, a method for conducting carbon dioxide gas in sprayed lime milk, etc. According to. Regarding the carbonation reaction conditions, if the method is to obtain the desired fine calcium carbonate, the conditions such as lime milk concentration, lime milk temperature, carbon dioxide gas concentration, and carbon dioxide gas conduction amount are arbitrarily selected to start the carbonation reaction. The pH (A) at the end of the carbonation reaction is 8.0
It must be above 10.0 and below. If the pH at the end of the carbonation reaction is less than 8.0, the surface of the secondary agglomerate particles will be tightly covered with calcium carbonate to prevent the elution of alkaline substances, while the pH at the end of the carbonation reaction will be 10.0. If it exceeds, the concentration of the residual alkaline substance surrounding the secondary agglomerate is high and the elution of the alkaline substance is hindered. Then, the obtained aqueous suspension of fine calcium carbonate is stirred and / or allowed to stand to have a pH (B) of the aqueous suspension of 10.5 or more and pH values before and after stirring and / or standing. The difference B-A is adjusted to 1.0 or more. PH of 1 after stirring and / or standing
If it is less than 0.5, or if the difference in pH value B A before and after stirring and / or standing is less than 1.0, the elution of the alkaline substance is insufficient, and therefore the following operations are performed. However, calcium carbonate with good dispersibility cannot be obtained.

By concentrating the calcium carbonate aqueous suspension thus obtained, the solid content concentration is adjusted to 1.2 times or more and 15% or more and 30% or less compared to before concentration, and then wet pulverization. Should be done. If the ratio of the solid content concentration before and after the concentration is less than 1.2 times, the reduction ratio of the alkaline substance, which is considered to be the cause of forming the secondary aggregate, to the calcium carbonate solid content is insufficient, and the solid content concentration after the concentration is increased. 15%
If it is less than the above range, the pulverization efficiency is low, which is disadvantageous. If the solid content concentration after concentration exceeds 30%, the viscosity increases due to dispersion of fine particles, and the subsequent operation becomes difficult. Also, the pH of the calcium carbonate aqueous suspension during wet grinding
Does not need to be specified, but 10.0 or more and 11.0
The following is the most efficient. When the pH of the aqueous suspension is adjusted to the above range, by adding a calcium carbonate aqueous suspension having pH adjustment obtained by conducting and / or leaving the carbon dioxide gas before stirring and / or standing. You can do it.

The concentrating device to be used does not require a large-scale device such as a filter press, and a suction filter such as an oliver filter or a pressure filter such as a rotary filter may be used. Alternatively, a concentration method by spontaneous precipitation may be adopted.
The wet pulverization referred to here is generally a dyno mill in which a pulverizing chamber is filled with media such as glass beads and alumina beads, and a disc or a rotor is rotated to pulverize a suspension of an object to be pulverized supplied to the pulverizing chamber. It is to grind using a device called a sand grinder mill. After wet pulverization, it can be used at the same pH as it is, but if there is a harmful effect due to alkali etc. during use, such as PVC paste sol, silicone one-component sealing agent, etc. It is preferable that the pH of the calcium carbonate aqueous suspension is set to 7.5 or less by the conduction of carbon dioxide gas. The fine precipitated calcium carbonate used for these usually refers to precipitated calcium carbonate having a primary particle size of 1.0 μm or less, but the fine and secondary agglomerates produced by the present invention have very few and good dispersibility. In the case of precipitated calcium carbonate, it is particularly effective to use those having a primary particle size of 0.2 μm or less, and more preferably 0.07 μm or less, which have a strong cohesive property, as compared with other methods. . After performing wet pulverization, if necessary, after performing surface treatment with a commonly used inorganic or organic surface treatment agent, or without treatment, supply to subsequent steps such as dehydration and drying It is possible.

As described above, by preparing the calcium carbonate aqueous suspension before the wet grinding according to the present invention,
It is not necessary to consume a large amount of energy to obtain a high-concentration water suspension prior to wet milling, and even in wet milling at a low solid content concentration, which is economically disadvantageous in the prior art, a short time, for example, 20%. Dwell times of less than a minute, but also low shear, eg disk or rotor peripheral speeds of 15
Even if it is less than m / sec, it can be sufficiently dispersed in one crushing treatment, and further, there is no re-aggregation due to activation of the particle surface, which occurs in the prior art, and the primary particles are not destroyed, and the particle size is A fine particle dispersion having a uniform distribution and good dispersibility can be obtained. In addition, the calcium carbonate prepared according to the present invention has extremely good dispersibility as compared with the conventional calcium carbonate powder even when dehydrated and dried into powder,
Even after being surface-treated with various surface-treating agents, it can be used in various industrial applications such as rubber, plastics, paper and paints, and exhibits good physical properties.

[0016]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 A limestone of 1 to 5 mm was used for firing in an electric furnace to obtain an activity of 80.
100 g of lime milk having a specific gravity of 1.055 and a temperature of 8 ° C. was prepared by hydrating the quick lime of 1. with water having a chlorine ion concentration of 30 ppm. A furnace gas having a carbon dioxide concentration of 27% by weight (hereinafter abbreviated as carbon dioxide gas) is passed through the lime milk at a flow rate of 20000 liters / hour to carry out a carbonation reaction, and the pH at 25 ° C. is 8.4 and the solid content concentration is 12 An aqueous suspension of calcium carbonate in weight% was obtained. As a result of observing with an electron microscope, this calcium carbonate has a primary particle diameter of 0.
It was calcium carbonate of 05 μm. Then 5 at 25 ℃
Stir for 25 hours at 25 ° C.
When the pH reached 10.7, the mixture was left to stand still, and after 5 hours, the supernatant was removed to obtain a calcium carbonate aqueous suspension concentrated to a solid content concentration of 20% by weight. The pH of this product at 25 ° C. was 10.9. The concentrated calcium carbonate aqueous suspension was subjected to a disk peripheral speed of 12 using a dyno mill pilot type wet mill (manufactured by WAB).
Wet pulverization was performed under the pulverization conditions of m / sec, apparent loading of media (glass beads of 0.8 mm diameter) of 80%, and residence time of 10 minutes. Table 1 shows the results of particle size distribution measurement of calcium carbonate in the water suspension obtained in this example by a centrifugal sedimentation type particle size distribution analyzer SA-CP3 (manufactured by Shimadzu Corporation). From the measurement result of the particle size distribution, it is confirmed that the calcium carbonate in the water suspension obtained in this example has extremely good dispersibility.

Example 2 By the same method as in Example 1, specific gravity 1.070, temperature 1
100 liter of 5 ° C. lime milk was prepared. Carbon dioxide gas with a carbon dioxide gas concentration of 21% by weight was passed through the lime milk at a flow rate of 10,000 liters / hour to carry out a carbonation reaction, and a water suspension of calcium carbonate with a pH of 9.8 at 25 ° C. and a solid content concentration of 15% by weight. A suspension was obtained. As a result of observing with an electron microscope, this calcium carbonate was calcium carbonate having a primary particle diameter of 0.15 μm. Then, the mixture was allowed to stand still at 30 ° C for 24 hours, and when the pH of the calcium carbonate aqueous suspension at 25 ° C reached 11.3, 25% by weight was measured using an oliver filter.
An aqueous suspension of calcium carbonate concentrated to the above was obtained. The pH of this product at 25 ° C. was 11.5. The concentrated calcium carbonate aqueous suspension was wet-milled in the same manner as in Example 1. Table 1 shows the results of particle size distribution measurement of calcium carbonate in the water suspension obtained in this example by a centrifugal sedimentation type particle size distribution analyzer SA-CP3 (manufactured by Shimadzu Corporation). From the measurement result of the particle size distribution, it is confirmed that the calcium carbonate in the water suspension obtained in this example has extremely good dispersibility.

Example 3 A carbonation reaction was carried out in the same manner as in Example 1 except that quicklime, which had an activity of 50 and was obtained by firing limestone of 12 to 15 mm in an electric furnace, was used. pH is 9.0
Thus, an aqueous suspension of calcium carbonate having a solid content concentration of 12% by weight was obtained. As a result of observing with an electron microscope, this calcium carbonate was calcium carbonate having a primary particle diameter of 0.04 μm. Then, the mixture was stirred at 35 ° C for 12 hours, and when the pH of the calcium carbonate aqueous suspension at 25 ° C reached 10.5,
An aqueous calcium carbonate suspension concentrated to 21% by weight was obtained using an Oliver filter. The pH of this product at 25 ° C. was 10.5. The concentrated calcium carbonate aqueous suspension was subjected to a disk peripheral speed of 15 m / sec, a media (0.8 mm diameter glass beads) filling amount of an apparent 80%, and a residence time of 15 using a wet mill Dinomill pilot type (manufactured by WAB). It was wet-milled under a pulverizing condition of minutes. Table 1 shows the results of particle size distribution measurement of calcium carbonate in the water suspension obtained in this example by a centrifugal sedimentation type particle size distribution analyzer SA-CP3 (manufactured by Shimadzu Corporation). From the measurement result of the particle size distribution, it is confirmed that the calcium carbonate in the water suspension obtained in this example has extremely good dispersibility.

Example 4 The aqueous calcium carbonate suspension obtained by the carbonation reaction described in Example 1 was stirred at 25 ° C. for 12 hours, and the pH of the aqueous calcium carbonate suspension at 25 ° C. was adjusted to 11.8. Once reached, an aqueous calcium carbonate suspension concentrated to 18% by weight using an Oliver filter was obtained. 25 ℃ of this thing
The pH at 12 was 12.1 By supplying carbon dioxide gas to the calcium carbonate aqueous suspension again, a concentrated calcium carbonate aqueous suspension having a pH of 10.3 at 25 ° C. was obtained. The concentrated calcium carbonate aqueous suspension was subjected to a disk peripheral velocity of 12 m / sec, a media (0.8 mm diameter glass beads) filling amount of an apparent 80%, and a residence time of 5 using a wet mill Dinomill pilot type (manufactured by WAB). It was wet-milled under a pulverizing condition of minutes. Table 1 shows the results of particle size distribution measurement of calcium carbonate in the water suspension obtained in this example by a centrifugal sedimentation type particle size distribution analyzer SA-CP3 (manufactured by Shimadzu Corporation). From the measurement result of the particle size distribution, it is confirmed that the calcium carbonate in the water suspension obtained in this example has extremely good dispersibility.

Comparative Example 1 A calcium carbonate aqueous suspension having a primary particle diameter of 0.05 μm and a solid content concentration of 12% by weight was prepared in the same manner as in Example 1 except that the pH at the end of the carbonation reaction was 7.2. A liquid was obtained.
This product had a pH of 8. at 25 ° C. after standing for 5 days.
Although it was 3, a 20 wt% calcium carbonate aqueous suspension was obtained by removing the supernatant. The concentrated calcium carbonate aqueous suspension was wet-milled in the same manner as in Example 1. Table 2 shows the results of particle size distribution measurement of calcium carbonate in the water suspension obtained in this comparative example using a centrifugal sedimentation type particle size distribution analyzer SA-CP3 (manufactured by Shimadzu Corporation). From the measurement result of the particle size distribution, it is confirmed that the calcium carbonate in the water suspension obtained in this Comparative Example has poor dispersibility as compared with Example 1.

Comparative Example 2 The calcium carbonate aqueous suspension (12% by weight) having a pH of 10.7 at 25 ° C. obtained in Example 1 was used as it was without concentration, and wet grinding was carried out in the same manner as in Example 1. . Table 2 shows the results of particle size distribution measurement of calcium carbonate in the water suspension obtained in this comparative example using a centrifugal sedimentation type particle size distribution analyzer SA-CP3 (manufactured by Shimadzu Corporation). From the measurement result of the particle size distribution, it is confirmed that the calcium carbonate in the water suspension obtained in this Comparative Example has poor dispersibility as compared with Example 1.

Comparative Example 3 A calcium carbonate aqueous suspension obtained by the same carbonation reaction as in Example 2 was stirred at 25 ° C. for 3 hours, and the pH of the aqueous calcium carbonate suspension at 25 ° C. was 10.5. When the temperature reached, a calcium carbonate aqueous suspension concentrated to 25% by weight was obtained using an Oliver filter. 25 ℃ of this thing
The pH at was 0.7. The concentrated calcium carbonate aqueous suspension was wet-milled in the same manner as in Example 1. Table 2 shows the results of particle size distribution measurement of calcium carbonate in the water suspension obtained in this comparative example using a centrifugal sedimentation type particle size distribution analyzer SA-CP3 (manufactured by Shimadzu Corporation). From the measurement result of the particle size distribution, it is confirmed that the calcium carbonate in the water suspension obtained in this Comparative Example has poor dispersibility as compared with Example 2.

Comparative Example 4 A calcium carbonate aqueous suspension having a pH of 11.3 at 25 ° C. and a solid concentration of 15% obtained in Example 2 was used as a 55% by weight press cake using a filter press. did. This product does not have fluidity as it is, and it is difficult to pulverize it in a wet manner. Sodium polyacrylate (1.2 wt%) is added to the calcium carbonate solid content, and the mixture is stirred for 3 hours with a dissolver type disperser. After maintaining the fluidity by carrying out, it was wet pulverized in the same manner as in Examples 1 and 2. The pH of this product at 25 ° C before grinding is 1
It was 0.5. Centrifugal sedimentation type particle size distribution analyzer SA-CP3 of calcium carbonate in water suspension obtained in this comparative example
Table 2 shows the results of particle size distribution measurement (manufactured by Shimadzu Corporation). From the measurement result of the particle size distribution, it is confirmed that the calcium carbonate in the water suspension obtained in this Comparative Example has poor dispersibility as compared with Example 2.

In Tables 1 and 2, A to E represent the following numerical values. A: pH value at 25 ° C. at the end of carbonation reaction B: pH value at 25 ° C. after stirring and / or leaving the obtained calcium carbonate aqueous suspension C: Calcium carbonate obtained by carbonation reaction Solid content concentration (% by weight) of water suspension D: Solid content concentration (% by weight) of calcium carbonate aqueous suspension after concentration E: 25 ° C. of concentrated calcium carbonate aqueous suspension to be wet-milled PH values in Tables D25, D50, and D75 in Tables 1 and 2 indicate the particle sizes of 25% by weight, 50% by weight, and 75% by weight calculated from the coarse particle side of the particle size distribution measurement results.

[0025]

[Table 1]

[0026]

[Table 2]

Application Example 1 Carbon dioxide gas is further conducted to the calcium carbonate aqueous suspensions obtained in Examples 1 and 4 and Comparative Examples 1 and 2, and the calcium carbonate aqueous suspension obtained in Example 1. By 2
A fatty acid soda was surface-treated at 4.0% by weight with respect to the one having a pH of 7.0 at 5 ° C. (Example 1 → abbreviated as pH 7), dehydrated by a filter press, and dried and powdered to form calcium carbonate. A powder was obtained. Using these 5 kinds of powders, a vinyl chloride paste sol was prepared with the following composition, and its viscosity and storage stability were investigated. The results are shown in Table 3. From the results of Table 3, the powder prepared using the calcium carbonate aqueous suspension of Example as the raw material has higher viscosity and thixotropic property (T) than the calcium carbonate powder of Comparative Example.
It shows that the dispersibility is extremely good. Further, in Example 1 → pH 7, the storage stability is extremely good because the alkaline substances are almost completely removed. (Compounding) Vinyl chloride paste resin (Nippon Zeon 121, manufactured by Nippon Zeon Co., Ltd.) 100 parts by weight DOP 100 parts by weight Polyamide (Henkel DSX140E, manufactured by Henkel Hakusui Co., Ltd.) 10 parts by weight Solvent (ester and hydrocarbon) 5 parts by weight Calcium carbonate sample 70 parts by weight

[0028]

[Table 3]

Application Example 2 The calcium carbonate aqueous suspensions obtained in Example 2 and Comparative Examples 3 and 4 were surface-treated with 3.0% by weight of fatty acid soda, dehydrated by a filter press, and dried and powdered. To obtain powders of calcium carbonate. Using these three types of powder, make an acrylic resin paint with the following formulation,
The gloss and dispersibility (dispersion time until the dispersed particle size according to JIS K5400 becomes 10 μm or less) were examined. The results are shown in Table 4. From the results of Table 4, the powder prepared using the aqueous calcium carbonate suspension of the example as a raw material
Compared with the calcium carbonate powder of the comparative example, it shows high gloss and dispersibility, and is confirmed to be extremely good. (Compounding) Acrylic resin 48.1 parts by weight Titanium white 20.9 parts by weight Calcium carbonate sample 10.2 parts by weight Thinner 20.8 parts by weight

[0030]

[Table 4]

[0030]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a precipitated calcium carbonate which is fine, has little secondary aggregation, and has good dispersibility is industrially advantageously provided.

Claims (8)

[Claims] 1. When wet pulverizing precipitated calcium carbonate obtained by passing carbon dioxide gas through lime milk, the following a.
A method for producing a calcium carbonate fine particle dispersion, which comprises using a calcium carbonate aqueous suspension which is pre-concentrated so as to satisfy the conditions b and c: a. The pH (A) at the end of the carbonation reaction satisfies the following formula: Formula 8.0 ≦ A ≦ 10.0 (measured value at 25 ° C.) b. The pH (B) of the aqueous calcium carbonate suspension obtained by stirring and / or allowing the aqueous calcium carbonate suspension obtained in the above step (a) simultaneously satisfies the following equations and 10.5 ≦ B (25 (Measured value in ° C) Formula B-A ≥ 1.0 c. Concentrating the solid content concentration (C%) of the aqueous calcium carbonate suspension obtained in the above b to a solid content concentration (D%) simultaneously satisfying the following formulas and. Formula 1.2 C ≦ D Formula 15 ≦ D ≦ 30 2. The method for producing a calcium carbonate fine particle dispersion according to claim 1, wherein the size of the limestone charged into the firing furnace when producing quicklime which is a raw material of lime milk is 10 mm or less. 3. The quicklime used has an activity of 60 ml (4N).
-HCl) or more, and the method for producing a calcium carbonate fine particle dispersion according to claim 1. 4. The method for producing a calcium carbonate fine particle dispersion according to claim 1, wherein the concentration of chlorine ions in water used for hydrating quicklime to obtain lime milk is 200 ppm or less. 5. The method for producing a calcium carbonate fine particle dispersion according to claim 1, wherein the primary particle diameter of the precipitated calcium carbonate prepared by wet pulverization is 0.2 μm or less. 6. The pH of the calcium carbonate aqueous suspension after concentration
A method for producing a calcium carbonate fine particle dispersion according to claim 1, wherein (E) is prepared in the range of the following formula: Formula 10.0 ≦ E ≦ 11.0 (measured value at 25 ° C.) 7. The pH of the calcium carbonate aqueous suspension after concentration
7. (E) is prepared by conducting carbon dioxide gas before wet grinding and / or adding the calcium carbonate aqueous suspension obtained under the condition b of claim 1 to produce a calcium carbonate fine particle dispersion. Method. 8. A calcium carbonate aqueous suspension after wet grinding
The method for producing a calcium carbonate fine particle dispersion according to claim 1, wherein the pH is adjusted to 7.5 (measured value at 25 ° C.) or less by passing carbon dioxide gas.