JP2001139328A - Method for producing spindle-shaped calcium carbonate having excellent dispersibility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily manufacturing bobbin-like calcium hydroxide which has excellent dispersibility and is adequately usable as a paper- making pigment, etc., on an industrial scale. SOLUTION: The bobbin-like calcium carbonate having the excellent dispersibility is manufactured by adding at least one selected from water-soluble monosaccharides and oligosaccharides to a calcium hydroxide slurry before the start of a carbonation reaction or before the carbonation rate thereof attains 30% when the bobbin-like calcium carbonate is produced by introducing carbon dioxide to the calcium hydroxide slurry.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing spindle-shaped calcium carbonate which can be suitably used particularly in applications requiring high dispersibility, such as pigments for papermaking. More specifically, the present invention relates to a method for producing spindle-shaped calcium carbonate having excellent dispersibility by a carbonation reaction of introducing carbon dioxide into a calcium hydroxide slurry.

[0002]

BACKGROUND ART Calcium carbonate used industrially includes heavy calcium carbonate and synthetic (light) calcium carbonate. The former heavy calcium carbonate is a crushed product of limestone produced naturally, and can be produced by a relatively simple process of crushing and classification. On the other hand, since the powder has a wide particle size distribution and an irregular shape peculiar to physical pulverization, it is difficult to produce a powder having excellent functionality provided by a uniform particle diameter and a uniform particle shape.

[0003] On the other hand, the latter synthetic calcium carbonate is produced by introducing carbon dioxide into a calcium hydroxide slurry and chemically precipitating it. During its manufacture,
By appropriately adjusting the conditions such as calcium hydroxide slurry concentration, carbonation temperature, and carbon dioxide introduction rate (carbonation rate), it is possible to control the particle shape and particle diameter within a certain range.

The shape of the synthetic calcium carbonate is a colloid having a particle diameter of 0.02 to 0.08 μm, and a particle diameter of 0.1 to 0.08 μm.
０．２0.2 μm cube, major axis 0.5-5.0 μm, spindle 0.1-1.0 μm minor axis, major axis 1.0-5.0 μm
m, a columnar shape with a minor axis of 0.1 to 0.2 μm, etc. are known,
Utilizing functions and characteristics expressed by each unique particle diameter and particle shape, it is used in a wide range of fields such as plastic, rubber, resin, and papermaking.

Of these, spindle-shaped calcium carbonate is widely used as a filler for papermaking, but has the drawback of agglomeration during production, and therefore has an increasing use in other applications requiring dispersibility. Hindered. In particular,
For pigments for papermaking, high dispersibility of pigment particles is required in terms of quality such as smoothness, gloss and opacity of the paper surface and printability. Therefore, cubic or columnar calcium carbonate having good dispersibility is generally used as a papermaking pigment.

[0006] On the other hand, spindle-shaped calcium carbonate can be synthesized at around normal temperature except for the disadvantage that it is agglomerated at the time of production. Cubic calcium carbonate which requires a step of repeating carbonation at low temperatures, or calcium carbonate at high temperatures As compared with columnar calcium carbonate which requires synthesis in, it can be produced relatively easily, and is excellent in terms of production equipment and production cost. Therefore, in order to provide a spindle-shaped tankal having excellent dispersibility, various studies have been made for a long time, and many proposals have been made.

For example, the proposal proposes that the carbonation reaction
C. or less, and in the initial stage of the carbonation reaction, the amount of carbon dioxide to be introduced is strictly controlled to control the slurry pH lowering rate to be within a certain range so that the carbonation reaction proceeds. A method of adding one or more of a water-soluble saccharide, sulfuric acid and a sulfate while the content is within ~ 75% (Japanese Patent No. 2604202). (Patent No. 273)
0660).

Further, a method of providing a step of subjecting a calcium hydroxide slurry as a raw material to high-energy and high-shear stirring to convert calcium hydroxide into a finely dispersed state (Japanese Patent No. 2857806), A method in which a barium or strontium compound is added under the condition where calcium is generated (Japanese Patent Laid-Open No. 5-238730).
Japanese Patent Application Laid-Open No. 9-309723), a method for strictly adjusting the activity of quicklime as a raw material, a method for preparing a calcium hydroxide slurry, and a method for strictly controlling the viscosity (Japanese Patent Application Laid-Open No. 9-309723). Addition method (JP-A-2-243)
No. 513) has also been proposed as a method for synthesizing spindle calcium carbonate having good dispersibility.

However, any of these methods requires complicated manufacturing operations, requires special manufacturing equipment, or uses expensive additives. No examples have been adopted. In addition, it is also known that the aggregated spindle-shaped calcium carbonate is crushed by a bead mill or the like to produce dispersed spindle-shaped calcium carbonate particles.However, equipment for crushing is required. The primary particles themselves are also destroyed by the process, and fine particles irregular in shape than the spindle-shaped calcium carbonate are mixed in, so that the uniformity of the calcium carbonate particles is reduced and the quality of the product is adversely affected, such as poor fluidity. Lead to.

[0010]

As described above, spindle calcium carbonate is one of the most excellent synthetic calcium carbonates in terms of ease of production and economical efficiency, but forms aggregates. However, there is a disadvantage that the use is limited. If it is possible to improve the disadvantages of this spindle-shaped calcium carbonate and easily produce a spindle-shaped calcium carbonate having excellent dispersibility at an industrial level, high dispersibility is required, including pigments for papermaking. The inventors have thought that the prospects for use in applications can be opened.

In view of such circumstances, the present inventors have conducted intensive studies on a method for producing spindle-shaped calcium carbonate having excellent dispersibility in order to expand the application field of spindle-shaped calcium carbonate. When producing spindle-shaped calcium carbonate by introducing carbon dioxide into a calcium slurry, before the carbonation reaction or before the carbonation rate reaches 30% in the course of the reaction, select from water-soluble monosaccharides and oligosaccharides. It has been found that the problem can be solved by a simple method of adding one or more kinds of compounds, and the present invention has been completed.
That is, an object of the present invention is to provide a method for producing spindle-shaped calcium carbonate having excellent dispersibility, which can be industrially produced efficiently and stably, and which is excellent in economic efficiency. .

[0012]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and the present invention relates to a method for producing spindle-shaped calcium carbonate by introducing carbon dioxide into a calcium hydroxide slurry, comprising the steps of: Excellent dispersibility, characterized by adding at least one selected from water-soluble monosaccharides and oligosaccharides before the start of the conversion reaction or before the carbonation rate reaches 30% in the course of the reaction. A method for producing spindle-shaped calcium carbonate.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments and details of the present invention will be described, but the present invention is not limited thereto, but is specified by the description of the claims. Needless to say. The calcium hydroxide slurry, which is a raw material of the spindle-shaped calcium carbonate of the present invention, is usually obtained by adding water to quicklime containing calcium oxide as a main component, followed by digestion.

The quicklime used as a raw material of the calcium hydroxide slurry used in the present invention is not particularly limited, and may be used in the process of producing naturally occurring limestone or marine waste such as shells, paper and sugar. It is obtained by firing calcium carbonate or a calcium compound which is a calcium carbonate-containing substance or the like discharged as a by-product.

The quick lime digestion performed during the production process of the calcium hydroxide slurry includes a wet digestion method by adding water to quick lime and a dry digestion method by steam, both of which include a ratio of quick lime to water and a digestion temperature. It is known that the properties of the generated calcium hydroxide differ depending on the conditions described above. There is no particular limitation on the calcium hydroxide that can be applied to the present invention.However, in consideration of performing a carbonation reaction in the state of a calcium hydroxide slurry later, quicklime is digested by a wet method and then diluted or concentrated. It is most efficient to prepare a calcium hydroxide slurry having a predetermined concentration.

The concentration of the calcium hydroxide slurry is not particularly limited, but is preferably adjusted within a range of 5 to 20% by weight. The reason is that the slurry concentration is 5
If it is less than 10% by weight, the amount of calcium carbonate obtained in one reaction is small, which is disadvantageous in terms of production efficiency. Also, 2
If the content exceeds 0% by weight, the viscosity of the slurry increases, and sufficient stirring becomes difficult, which may cause a problem in performing a uniform carbonation reaction.

As the carbon dioxide to be introduced into the calcium hydroxide slurry, it is most economical to use a carbon dioxide-containing gas such as an exhaust gas generated during the production of quick lime or another combustion step, directly or after washing. It is. The concentration of carbon dioxide in the gas at this time is not particularly limited, but if the concentration is low, the efficiency of the carbonation reaction is reduced.
Desirably, it is not less than the capacity%.

As conditions for introducing carbon dioxide into the calcium hydroxide slurry to carry out the carbonation reaction, the temperature of the slurry at the start of the carbonation reaction and the introduction rate of carbon dioxide become important. If these conditions are not properly adjusted, the desired spindle-shaped calcium carbonate may not be produced. The starting temperature of the carbonation reaction is 20 ° C. or more, more preferably 30 ° C.
C. or more is preferable, and the higher the temperature, the better the dispersibility of the spindle calcium carbonate formed.

Therefore, by adjusting the starting temperature of the carbonation reaction, it is possible to control the degree of dispersibility of the manufactured spindle calcium carbonate.
If the initiation temperature of the carbonation reaction is lower than 20 ° C., no effect on the dispersibility is observed even if colloidal calcium carbonate is formed or spindle calcium carbonate is formed. There is no particular upper limit on the starting temperature of the carbonation reaction. In addition, in the carbonation reaction process, the slurry temperature slightly changes due to heat generated by the reaction heat of carbonation or heat release from the reaction vessel to the outside of the reaction system, but the adjustment is particularly performed in the entire process until the carbonation reaction is completed. No need.

The introduction rate of the carbon dioxide-containing gas introduced into the calcium hydroxide slurry is 0.1 to 10 liters / kg of calcium hydroxide in terms of carbon dioxide.
It is preferably set to min. When the introduction rate exceeds 10 liters / min, the starting temperature of the carbonation
When the temperature is 0 ° C or lower, colloidal calcium carbonate is generated, and when the starting temperature is 40 ° C or higher, columnar calcium carbonate is generated.
When the introduction rate is 0.1 liter, columnar calcium carbonate or a mixture of spindle calcium carbonate and columnar calcium carbonate is produced.

The water-soluble monosaccharide or oligosaccharide is added to the calcium hydroxide slurry before the start of the carbonation reaction or before the carbonation rate reaches 30% in the course of the reaction. Even if added after the carbonation rate exceeds 30%, no effect on dispersion is recognized, or the desired spindle-shaped calcium carbonate is not generated. The carbonation rate in the present invention is represented as follows. Carbonation rate (%) = (weight of calcium in generated calcium carbonate / weight of calcium existing in reaction system) × 10
0

The addition amount is preferably 0.001 mol to 10 mol per 1 kg of calcium hydroxide, and if less than this, the effect on dispersing cannot be expected. When the added amount exceeds 10 mol per 1 kg of calcium hydroxide,
When the onset temperature of the carbonation reaction is 40 ° C. or lower, colloidal calcium carbonate is generated. Conversely, when the onset temperature is 40 ° C. or higher, the spindle-shaped calcium carbonate is formed as compared with the case where the addition amount is 10 mol or less. Since there is no change in the dispersibility of the compound, it is desirable that the amount be 10 mol or less from the viewpoints of production efficiency and economy.

It is of course possible to use a combination of two or more monosaccharides or oligosaccharides, as is apparent from the above description. 1 kg of calcium hydroxide
It may be in the range of 0.001 mol to 10 mol per unit.

As the water-soluble monosaccharide to be added, aldohexose represented by glucose and ketohexose represented by fructose can be used. The oligosaccharides are those in which about 2 to 6 monosaccharides are polymerized by a glycooxide bond, non-reducing disaccharides such as saccharose and trehalose, maltose, cellobiose, gentiobiose, melibiose, lactose, turanose, and sophorose. And other reducing disaccharides can be used.

Also, non-reducing trisaccharides such as gentianose, raffinose and meletitose, maltotriose, cellotriose, cellotriose, manninotriose,
Oligosaccharides obtained by polymerizing four or more reducing trisaccharides such as panose and monosaccharides can also be used. Further, isomerized sugars, starch sugars and the like which are industrially used as a mixture of the above-mentioned monosaccharides, oligosaccharides and the like can also be used. The form of addition to the calcium hydroxide slurry may be in the form of a solution dissolved in a solvent such as water, or may be in the form of a solid.

The termination of the carbonation reaction in the present invention can be determined by the pH of the slurry being reduced to near neutrality. That is, during the carbonation reaction, unreacted calcium hydroxide is present, so that the slurry pH is 11
The pH of the slurry is about neutral when the reaction is completed and the calcium hydroxide is consumed.

The spindle-shaped calcium carbonate obtained by the above method has a major axis of 0.5 to 5 μm and a minor axis of 0.1 to 1.0 μm.
It has a spindle shape of μm. The spindle-shaped calcium carbonate obtained by the known production method has poor dispersibility, and almost all particles form strong aggregates of 5 to 10 μm,
The production method of the present invention has remarkably excellent dispersibility, and exhibits excellent performance in papermaking pigments and other uses that require high dispersibility.

The above-mentioned Japanese Patent No. 2604202 proposes, as described above, to produce a spindle-shaped calcium carbonate by adding a water-soluble saccharide in the same manner as in the present invention. Compared with the invention proposed there (hereinafter referred to as invention No. 02), the manufacturing process is simple and has remarkable advantages, and the advantages are specifically shown as follows.

1) In the initial stage of the carbonation reaction, particularly in the stage until the carbonation ratio reaches 5%,
There is no need to strictly control the amount of carbon dioxide introduced to suppress and control the slurry pH lowering rate to a certain range as in the invention. 2) In the present invention, it is sufficient to basically add the monosaccharide or oligosaccharide before the start of the carbonation reaction.
There is no need to strictly adjust the timing of addition as in the second invention. 3) The carbonation reaction is an exothermic reaction, and the temperature of the reaction solution rises when left naturally. However, in the present invention, the reaction solution may be left standing after the start of the carbonation reaction. It is not necessary to control the temperature of the reaction solution by cooling or the like in order to keep the temperature below a certain value.

[0030]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples of the present invention. However, the present invention is not limited to these examples and the like, and is understood by the description in the claims. Needless to say,

Example 1 2.0 kg of industrial quicklime was added to 7
It was poured into 15 kg of tap water heated to 0 ° C., stirred for 1 hour and digested. Subsequently, digestion residue was removed with a 100 mesh sieve, and tap water was added to prepare 20 kg of a 12.0% by weight calcium hydroxide slurry. After adjusting the calcium hydroxide slurry temperature to 60 ° C.,
A carbonation reaction was carried out by introducing a mixed gas of carbon dioxide and air at a rate of 16.0 liter / min per kg of calcium hydroxide by volume.

At this time, when the carbonation rate reaches 5%, the reagent glucose 0.50 mol (1 kg of calcium hydroxide)
0.21 mol / mol) and continuously introduce a mixed gas to continue the carbonation reaction.
When the number reached 7, the carbonation reaction was terminated. According to observation of the obtained product with a scanning electron microscope (SEM), primary particles are spindle-shaped calcium carbonate having a major axis of 1.5 μm and a minor axis of 0.3 μm, of which about 50% is monodisperse particles. there were.

Example 2 20 kg of a 12.3% by weight calcium hydroxide slurry prepared in the same manner as in Example 1
Was adjusted to 80 ° C., and after adding 1.50 mol of reagent glucose (0.63 mol / kg of calcium hydroxide), a mixed gas of carbon dioxide and air having a concentration of 25% by volume was added to 17.0 liter / kg of calcium hydroxide. / M
The carbonation reaction was carried out until the slurry pH reached 7. According to observation with a scanning electron microscope (SEM), the obtained product had a primary particle having a major axis of 2.0 μm.
m, a spindle-shaped calcium carbonate having a minor axis of 0.4 μm, of which about 80% was monodisperse particles.

Example 3 1.5 kg of industrial quicklime was added to 70
It was poured into 10 kg of tap water heated to 0 ° C., stirred for 30 minutes and digested. Subsequently, after removing digestion residue with a 100-mesh aperture sieve, tap water was added and 8.5% by weight.
20 kg of a calcium hydroxide slurry was prepared. After adjusting the calcium hydroxide slurry temperature to 30 ° C., 0.15 mol of reagent saccharose (1 kg of calcium hydroxide)
0.09 mol / kg), and a mixed gas of 25% by volume of carbon dioxide and air was introduced at a rate of 13.8 liters / min per kg of calcium hydroxide until the pH of the slurry reached 7. The reaction was terminated. According to observation of the obtained product by SEM, the primary particles were spindle-shaped calcium carbonate having a major axis of 1.0 μm and a minor axis of 0.2 μm, of which about 40% were monodisperse particles.

[Embodiment 4] The same operation as in Embodiment 3 is performed to obtain 8.7.
After preparing 20 kg of a weight-% calcium hydroxide slurry and adjusting the temperature to 35 ° C., carbonation was carried out under the same conditions as in Example 1. At that time, when the carbonation ratio reached 20%, 1.22 mol of reagent saccharose (calcium hydroxide 1k)
(0.70 mol / g), and a mixed gas was continuously introduced. When the pH of the slurry reached 7, the carbonation reaction was terminated. According to observation with a SEM, the obtained product has a primary particle having a major axis of 1.5 μm and a minor axis of 0.1 μm.
It was a spindle-shaped calcium carbonate of 3 μm, of which about 50% was monodisperse particles.

[Embodiment 5] The operation is performed in the same manner as in Embodiment 3 to 8.8.
After preparing 20 kg of a weight% calcium hydroxide slurry and adjusting the temperature to 40 ° C., carbonation was carried out under the same conditions as in Example 1. At that time, when the carbonation rate reached 10%, the reagent saccharose 0.36 mol (calcium hydroxide 1k)
(0.20 mol per g), and a mixed gas was continuously introduced. When the pH of the slurry reached 7, the carbonation reaction was terminated. According to observation with a SEM, the obtained product has a primary particle having a major axis of 2.0 μm and a minor axis of 0.1 μm.
4 μm spindle-shaped calcium carbonate, of which about 50% was monodisperse particles.

[Embodiment 6] 8.7 is performed in the same manner as in Embodiment 3.
Prepare 20 kg of calcium hydroxide slurry by weight%,
0.88 mol of reagent saccharose (calcium hydroxide 1
(0.52 mol / kg), the slurry temperature was adjusted to 90 ° C., and then carbonation was carried out under the same conditions as in Example 1. According to observation by SEM, the obtained product was spindle-shaped calcium carbonate having a primary particle size of 2.0 μm in major axis and 0.4 μm in minor axis, of which about 90% were monodisperse particles.

Example 7 1.0 kg of industrial quicklime was added to 70
It was poured into 10 kg of tap water heated to 0 ° C., stirred for 30 minutes and digested. Subsequently, tap water was added to remove digestion residue with a 100 mesh sieve, and 20 kg of a 6.4% by weight calcium hydroxide slurry was prepared. Next, after adjusting the temperature of the calcium hydroxide slurry to 50 ° C.,
A carbonation reaction was performed by introducing a mixed gas of volume% of carbon dioxide and air at a rate of 10.0 liter / min per kg of calcium hydroxide.

At that time, when the carbonation rate reached 5%,
Isomerized sugar (glucose 30% by weight, fructose 45
%, Moisture 25%) in a total amount of glucose and fructose of 1.30 mol (1 per 1 kg of calcium hydroxide).
02 mol) was added, and a mixed gas was continuously introduced to continue the carbonation reaction. When the slurry pH reached 7, the carbonation reaction was terminated. The resulting product is
According to observation by SEM, the primary particles had a major axis of 1.0 μm.
m, a spindle-shaped calcium carbonate having a minor axis of 0.2 μm, of which about 60% was monodisperse particles.

[Embodiment 8] 6.5 in the same operation as in Embodiment 7.
20 kg by weight of a calcium hydroxide slurry was prepared. The temperature of the calcium hydroxide slurry was adjusted to 95 ° C., and 0.55 mol of reagent glucose and 0.20 mol of reagent maltose (0.58 mol per kg of calcium hydroxide in a total amount of glucose and maltose) were added. Of mixed gas of carbon dioxide and air at 10.0 liters / m 2 per kg of calcium hydroxide
The carbonation reaction was carried out until the slurry pH reached 7. According to observation by SEM, the obtained product was a spindle-shaped calcium carbonate having primary particles of 1.5 μm and a minor axis of 0.3 μm, of which about 90% were monodisperse particles.

[Embodiment 9] The same operation as in Embodiment 7 is performed to obtain 6.6.
20 kg by weight of a calcium hydroxide slurry was prepared. The temperature of the calcium hydroxide slurry was adjusted to 70 ° C., and 0.85 mol of reagent saccharose and 0.10 mol of reagent raffinose (0.72 mol per kg of calcium hydroxide in a total amount of saccharose and raffinose) were added. Was introduced at a rate of 10.0 liters / min per kg of calcium hydroxide, and a carbonation reaction was carried out until the pH of the slurry reached 7. According to observation by SEM, the obtained product had primary particles of 1.5 μm and a minor axis of 0.3 μm.
m of spindle-shaped calcium carbonate, of which about 80% were monodisperse particles.

[Comparative Example 1] 1.5 kg of industrial quicklime was added to 70
It was poured into 10 kg of tap water heated to 0 ° C., stirred for 30 minutes and digested. Subsequently, digestion residue was removed with a 100-mesh aperture sieve, and tap water was added to the mixture to obtain 8.6% by weight.
20 kg of a calcium hydroxide slurry was prepared. After adjusting the calcium hydroxide slurry temperature to 30 ° C., a mixed gas of carbon dioxide and air having a concentration of 25% by volume was introduced at a rate of 14.0 liters / min per kg of calcium hydroxide until the slurry pH reached 7. Then, the carbonation reaction was terminated. According to observation by SEM, the obtained product had a primary particle of spindle-shaped calcium carbonate having a major axis of 1.5 μm and a minor axis of 0.3 μm, but formed a strong aggregate of 5 to 10 μm. .

[Comparative Example 2] 8.9 by the same operation as Comparative Example 1.
20 kg by weight of a calcium hydroxide slurry was prepared. After adjusting the slurry temperature to 70 ° C., a carbonation reaction was performed under the same conditions as in Comparative Example 1. At that time, the carbonation rate was 6
When it reaches 0%, reagent saccharose 0.36 mol
(0.20 mol per 1 kg of calcium hydroxide) was added, and a mixed gas was continuously introduced to continue the carbonation reaction. When the slurry pH reached 7, the carbonation reaction was terminated. The obtained product was columnar calcium carbonate having primary particles of 2.0 μm in major axis and 0.1 μm in minor axis.

[Comparative Example 3] 8.8 was operated in the same manner as in Comparative Example 1.
Prepare 20 kg of calcium hydroxide slurry by weight%,
After adjusting the slurry temperature to 15 ° C., 1.00 mol of reagent saccharose (0.5 mol / kg of calcium hydroxide) was added.
7 mol), and a carbonation reaction was carried out under the same conditions as in Comparative Example 1. The obtained product was colloidal calcium carbonate having primary particles of 0.06 μm as observed by SEM.

[Comparative Example 4] 8.8 was operated in the same manner as in Comparative Example 1.
Prepare 20 kg of calcium hydroxide slurry by weight%,
After adjusting the slurry temperature to 30 ° C., a carbonation reaction was performed under the same conditions as in Comparative Example 1. At that time, the carbonation rate is 5%
At the time of reaching 0.0005 mol of reagent saccharose
(0.0003 mol per kg of calcium hydroxide)
Was added, and a mixed gas was continuously introduced. When the pH of the slurry reached 7, the carbonation reaction was terminated. The product obtained, according to SEM observation,
Although the spindle-shaped calcium carbonate had a primary particle diameter of 1.5 μm in major axis and 0.3 μm in minor axis, it formed strong aggregates of 5 to 10 μm, and almost no monodispersed particles were recognized.

Comparative Example 5 The same operation as in Comparative Example 1 was performed for 8.7.
Prepare 20 kg of calcium hydroxide slurry by weight%,
After adjusting the slurry temperature to 35 ° C, 40 mol of reagent saccharose (23 mol / kg of calcium hydroxide)
l) The aqueous solution was added, and carbonation was carried out under the same conditions as in Comparative Example 1. The obtained product was colloidal calcium carbonate having a primary particle diameter of 0.06 μm according to observation by SEM.

For the above Examples and Comparative Examples, the conditions for producing calcium carbonate and the results of SEM observation of the obtained products are shown in Table 1 so as to be listed. That is, Table 1 shows the carbonation initiation temperature, the substance name of the added monosaccharide or oligosaccharide, the time of addition, the form of the generated calcium carbonate, and the ratio of the dispersed particles in the product.

[0048]

[Table 1]

[0049]

According to the present invention, there is provided a method for producing spindle-shaped calcium carbonate, wherein water-soluble monosaccharides and oligosaccharides are selected before the start of the carbonation reaction or before the carbonation rate reaches 30% in the course of the reaction. Is a simple method of adding one or more of the above, and the additive is a safe and easily available monosaccharide or oligosaccharide, and the resulting spindle-shaped calcium carbonate is dispersible. It has an outstanding effect of being excellent.

The spindle calcium carbonate excellent in dispersibility obtained by the production method of the present invention exhibits excellent effects in applications requiring high dispersibility, such as pigments for papermaking. In addition, even in comparison with the invention of Japanese Patent No. 2604202 which proposes to produce a spindle-shaped calcium carbonate by adding a water-soluble saccharide similarly to the present invention, the method is simple and excellent effects can be obtained. To play.

Specific advantages of the present invention are as follows. 1) In the initial stage of the carbonation reaction, particularly in the stage until the carbonation ratio reaches 5%, the amount of carbon dioxide introduced is strictly adjusted as in the invention of No. 02 to control the slurry pH lowering rate to a certain range. No need to do. 2) Basically, it is sufficient to add the monosaccharides and oligosaccharides before the start of the carbonation reaction, and it is not necessary to strictly adjust the addition times as in the invention of No. 02 3) The carbonation reaction is an exothermic reaction, and the temperature of the reaction solution rises when left naturally. However, after the carbonation reaction starts, there is no need to control the temperature of the reaction solution as in the invention of No. 02.

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Claims (6)

[Claims] 1. A method for producing spindle-shaped calcium carbonate by introducing carbon dioxide into a calcium hydroxide slurry, wherein a water-soluble calcium carbonate is obtained before the carbonation reaction starts or before the carbonation rate reaches 30% in the course of the reaction. A method for producing spindle-shaped calcium carbonate having excellent dispersibility, characterized by adding one or more selected from monosaccharides and oligosaccharides. 2. The amount of the water-soluble monosaccharide or oligosaccharide added is from 0.001 mol to 10 mol / kg of calcium hydroxide.
2. The method for producing spindle-shaped calcium carbonate according to claim 1, wherein the amount is mol. 3. The method for producing spindle-shaped calcium carbonate according to claim 1, wherein the water-soluble monosaccharide is glucose. 4. The water-soluble oligosaccharides are selected from disaccharides and trisaccharides.
2. The method for producing spindle-shaped calcium carbonate according to item 1. 5. The method for producing spindle-shaped calcium carbonate according to claim 1, wherein the water-soluble oligosaccharide is saccharose. 6. The spindle-shaped calcium carbonate according to claim 1, wherein the carbonation reaction is started at a temperature of 20 ° C. or higher, and the temperature of the reaction solution is not controlled after the start of the reaction. Production method.