JP2000169142A - Production of calcium carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cubic calcite crystal calcium carbonate having a large particle size by ageing acicular aragonite crystal calcium carbonate. SOLUTION: The acicular aragonite crystal calcium carbonate used has preferably 1 to 200 μm major diameter, 0.1 to 10 μm minor diameter, >=3 aspect ratio and >=3 m2/g and <=30 m2/g BET specific surface area. In order to accelerate ageing, a small amt. of calcite crystal calcium carbonate particles is preferably added to the water slurry of the acicular aragonite crystal calcium carbonate. The amt. of the calcite crystal calcium carbonate preliminarily added is preferably 0.1 to 20 wt.% of the acicular aragonite calcium carbonate particles, and the particle size of the calcite crystal is preferably 0.02 to 10 μn. Thereby, a cubic calcite crystal calcium carbonate having a large particle size, preferably >=1 μm, can be easily obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing calcium carbonate, and more particularly to a method for producing cubic calcite crystalline calcium carbonate having a large particle diameter from acicular aragonite crystalline calcium carbonate.

[0002]

2. Description of the Related Art Conventionally, calcium carbonate has been widely used as a filler or a functional material in various industrial materials, for example, rubber, plastics, papermaking, paints, sealants, foods, and the like. By the way, the shape, particle size, etc. of calcium carbonate have a great influence on the quality of products in which calcium carbonate is used. Therefore, it is very important how to accurately control the shape, particle size, and the like of calcium carbonate.

[0003] In general, synthetic calcium carbonate for industrial use is produced by introducing carbon dioxide gas into a slurry of calcium hydroxide to generate calcium carbonate. By changing the compounding conditions, the primary calcium carbonate formed is changed. The particle size and shape can be controlled to some extent. As another method for controlling the particle diameter and shape, there is a method of aging calcium carbonate particles formed by such a compound.
In general, the purpose of aging calcium carbonate particles is often to improve the dispersibility of primary particles and increase the particle diameter. However, in the conventional aging method, when used industrially, the degree of freedom in controlling the particle size and shape is not so large. For example, in the aging method that is generally performed, the primary particle size is 0.01 to 0. It is only possible to control particles of about 0.1 μm to a size of about 0.1 to 0.3 μm.

Japanese Patent Application Laid-Open No. Hei 5-319816 discloses that particles having a particle size of about 0.01 to 0.8 μm
A method of controlling the size to about μm is described,
As the particle diameter is increased, the production efficiency becomes extremely poor, and practical use is difficult. In particular, it is very difficult to ripen particles of about 0.01 to 0.1 μm to have a size of 1 μm or more, both in terms of cost and in terms of technology.

Cubic calcium carbonate having a particle diameter of 1 μm or more and having uniform particles and excellent dispersibility is useful for a wide variety of uses such as an antiblocking agent for plastic films and a light diffusing agent for various plastics. However, producing such calcium carbonate is not easy both technically and costly. As a conventional production method, a method of reacting a soluble inorganic substance called a solution method is common, and for example, a method of reacting NaCO ₃ and CaCl ₂ . However, this manufacturing method also has many technical problems, such as accuracy of particle diameter control and uniformity of particle diameter.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention solves these problems by increasing the precision of particle size control and increasing the size of cubic calcite crystal calcium carbonate having a large particle size. It is intended to provide a low-cost manufacturing method.

[0007]

According to the present invention, there is provided a calcium carbonate comprising the steps of: aging a needle-shaped aragonite crystalline calcium carbonate to obtain a cubic calcite crystalline calcium carbonate. The manufacturing method is described as a content.

[0008] In a preferred embodiment, the major axis of the needle-shaped aragonite crystalline calcium carbonate is 1 µm or more, the minor axis is 0.1 µm or more, and the aspect ratio (major axis / minor axis) is 3 or more.
That is all (claim 5). As a preferred embodiment, aging is performed by adding calcite crystal calcium carbonate (claim 2). In a preferred embodiment, the calcite crystal calcium carbonate has a particle size of 0.02 to 10 μm.
m (claim 3). In a preferred embodiment, the addition amount of calcite crystal calcium carbonate is 0.1 to 20% by weight of the needle-like aragonite crystal calcium carbonate (Claim 4).

In a preferred embodiment, the BET specific surface area of the needle-shaped aragonite crystalline calcium carbonate is 3 m ² / g or more. In a preferred embodiment, the BET specific surface area of the needle-like aragonite crystalline calcium carbonate is 5.0 m ² / g or more (claim 7). In a preferred embodiment, the specific surface area of the cubic calcite crystal calcium carbonate obtained by aging the needle-shaped aragonite crystal calcium carbonate is 30.
m ² / g or less (claim 8). In a preferred embodiment, the specific surface area of the cubic calcite crystalline calcium carbonate obtained by aging the needle-like aragonite crystalline calcium carbonate is 20 m ² / g or less (claim 9).

In the present invention, the cubic shape means a substantially cubic shape, and also includes a shape having oblique or rounded corners. The particle diameter refers to an average particle diameter determined from an electron micrograph, and the BET specific surface area refers to a value measured by a nitrogen adsorption method.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Calcium carbonate has three types of crystal forms, aragonite crystals, calcite crystals, and vaterite crystals. Generally, aragonite crystals are needle-shaped,
Calcite crystals have a cubic shape, and vaterite crystals have a spherical shape. As a crystal form, calcite crystals are the most stable, and aragonite crystals and calcite crystals are easily transformed into calcite crystals by heating or the like. However, aragonite crystals do not migrate to calcite crystals simply by standing at room temperature or the like.

The present invention is a method for obtaining cubic calcite crystalline calcium carbonate having a large particle diameter by aging acicular aragonite crystalline calcium carbonate. The aragonite crystalline calcium carbonate to be aged may be either synthetic or naturally occurring. When it is a synthetic product, its production method is described in, for example, JP-A-63-260815 and JP-A-1-261225.
And JP-A-4-321515. The size of the needle shape can be arbitrarily changed by the manufacturing methods described in these. The size of the aragonite crystalline calcium carbonate produced by the above method or the like is, for example, as small as about 0.01 to 0.1 μm in short diameter, about 0.1 to 1 μm in long diameter, and about 3 or more in aspect ratio, and large. Thickness: 1 to 15 μm in short diameter, 1 in long diameter
It is about 0 to 250 μm and has an aspect ratio of about 3 or more.
Of course, these intermediate particle diameters can also be easily formed by appropriately setting the production conditions. The size of the particle diameter can be adjusted by the amount of calcium hydroxide added to the basic aragonite crystal calcium carbonate as described in, for example, JP-A-4-321515.

The needle-shaped aragonite crystalline calcium carbonate used in the present invention preferably has a major axis of 1 to 200.
μm, the minor axis is 0.1 to 10 μm, more preferably the major axis is 5 to 50 μm, and the minor axis is 0.1 to 2 μm, and the aspect ratio is preferably 3 or more, more preferably 5 to 50 μm.
It is. The BET specific surface area is preferably at least 3 m ² / g, more preferably at least 5 m ² / g, and the upper limit is not particularly limited, but is about 30 m ² / g from the viewpoint of cost and productivity.

The aragonite crystalline calcium carbonate having a needle shape is matured to produce cubic calcite crystalline calcium carbonate. The ripening method may be performed according to the method of ripening calcite crystals, heating,
Conditions such as pH control, stirring and the like are appropriately set, and they are performed alone or in combination of two or more. The aging of the aragonite crystalline calcium carbonate is carried out in a water slurry, and the temperature of the water slurry is preferably higher. The temperature is preferably 50 ° C. or higher, more preferably 70 ° C. or higher, but is preferably 90 ° C. or lower in terms of cost and operation. The pH of the slurry is
Preferably 8.5 to 11.5, more preferably 9.5 to
11.0. It is desirable that the stirring power is strong,
Appropriate conditions may be set in consideration of the cost. Specifically, the peripheral speed varies depending on the shape of the stirring blade,
m / sec or more is preferable, and 2.0 to 100 m / sec is more preferable. The combination of heating, pH, and stirring is appropriately determined in each of the above ranges. The aging time is appropriately determined according to the aging conditions.

The reason why the acicular aragonite crystalline calcium carbonate is transformed into a cubic calcite crystalline calcium carbonate by ripening is not always clear, but the energy is higher because the cubic shape has a smaller surface area than the acicular shape. This is probably because the target is more stable.
In addition, needle-shaped aragonite crystal calcium carbonate,
It is considered that the aragonite crystal is transformed into calcite crystal by being once collapsed and recrystallized, since it is transformed into cubic calcite crystal calcium carbonate smaller than its major axis. Therefore, the aragonite crystal progresses at once when the transition to the calcite crystal starts. This is presumably because the aragonite crystal that had been formed firmly initially was deposited on the calcite crystal at an accelerated rate when the calcite crystal began to form, and grew.

Therefore, in order to advance ripening more quickly, it is desirable to add a small amount of calcite crystal calcium carbonate particles to a needle-like water slurry of aragonite crystal calcium carbonate in advance. This is probably because the calcite crystal calcium carbonate particles act as seed crystals, so that the aragonite crystal calcium carbonate particles disintegrate more rapidly.

The amount of the calcite crystal calcium carbonate particles to be added in advance is preferably 0.1 to 20% by weight of the needle-like aragonite crystal calcium carbonate particles.
It is more preferably about 1.0 to 15% by weight. The calcite crystal calcium carbonate particles to be added in advance are not particularly limited, but it is preferable that the particles are dispersed as much as possible. When the original calcite crystal calcium carbonate particles are more dispersed, more dispersed particles of calcite crystal calcium carbonate particles generated by the aging of the present invention are also generated. The original calcite crystal particles preferably have a particle size of about 0.02 to 10 μm, more preferably about 0.05 to 0.5 μm. Calcite crystal calcium carbonate having a particle size of less than 0.02 μm has strong cohesiveness of primary particles, and a particle size of 10 μm or more has a small surface area and reduces the efficiency of deposit.

On the other hand, in order to promote ripening, water slurry
-Various inorganic and organic additives may be added during
No. In order to promote ripening,
Seed additives may be added in advance. for example
If the aging accelerator is CaCl _Two, NaOH, etc.
Can be

The most important feature of the present invention is that large particles, preferably cubic calcite crystal calcium particles having a size of 1 μm or more, which cannot be produced conventionally, can be easily produced. If the particles are about 0.4 μm or less, the conventional method of aging only calcite crystal particles can cope with the problem, but the particles of 1 μm or more are very inefficient by the conventional aging method.

Particles of calcite crystal calcium carbonate generated by a gas-liquid reaction method in which carbon dioxide is simply introduced into calcium hydroxide are cubic particles having primary particles of about 0.02 to 0.04 μm or about 1 to about 0.04 μm. Spindle-shaped particles of ~ 2 µm. Only one of these can be performed in one carbonation reaction. Growing the former particles into cubic particles having a particle diameter of, for example, 0.5 μm by a conventional aging method requires a considerably long time and a large amount of energy such as heating and stirring.
Also, the latter particles hardly undergo aging in the conventional method, and remain in a strongly aggregated spindle state. Therefore, none of the above methods is industrially satisfactory.

As another method, calcite crystal calcium carbonate is reduced to a particle size of about 0.01 μm, and then calcium hydroxide is added (the addition amount is appropriately changed depending on the target particle size). There is a method to increase the particle size by depositing calcium carbonate of calcite crystal newly on the surface of the original particle size by carbonation,
The manufacturing process becomes complicated and the equipment cost increases.
When the thickness is about 0.8 μm, there is a problem that deposit is not sufficiently performed.

According to the present invention, a cubic calcite crystal calcium carbonate having a large particle size, which has not been obtained conventionally, can be obtained in proportion to the major axis of the aragonite crystalline calcium carbonate having a needle shape used as an aging raw material. For example, aragonite crystalline calcium carbonate having a major axis of about 5 μm and a minor axis of about 0.15 μm can provide cubic calcite crystalline calcium carbonate having a particle diameter of about 0.2 μm.
A cubic calcite crystal calcium carbonate of about 1 to 3 μm can be obtained from aragonite crystal calcium carbonate of about 1 μm and a minor axis of about 1 μm.

The calcite crystalline calcium carbonate having a large particle diameter produced by the method of the present invention is extremely useful in the fields of an anti-blocking agent for various films and a light diffusing agent for plastics. Then, depending on these applications, secondary processing may be performed to further bring out the intended function. For example, in order to further improve the dispersibility, the obtained particles are subjected to wet pulverization using a pulverizing medium in a state of various slurries such as water and a solvent, passed through fine voids at high speed, and dispersed by ultrasonic waves. And the like.

Further, depending on the matrix to be used, various organic and inorganic substances can be used for surface treatment in order to improve compatibility with the matrix. Representative organic substances include fatty acids, resin acids, acrylic acid, methacrylic acid, oxalic acid, citric acid, and the like, and inorganic substances include tartaric acid, phosphoric acid, condensed phosphoric acid, and fluoric acid. Also included are coupling agents such as these polymers, alkali metal salts, esters, silane, and titanium. These may be used alone or in combination of two or more as necessary. After the obtained calcite crystal calcium carbonate is dried, it may be used not only as a powder but also as a suspension of water, various solvents and the like.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but these do not limit the present invention in any way.

Example 1 Synthesis of aragonite crystals having an average particle size of 30 μm in major axis and 1.2 μm in minor axis 30 kg of water was added to 3 kg of calcium carbonate to obtain a calcium carbonate water slurry. This slurry was stirred for 150 hours while maintaining the temperature at 70 ° C. (360 rpm,
(Circuit speed: 3.8 m / sec). At this time, the pH of the slurry was maintained at 10.5. When the calcium carbonate in the slurry was confirmed by an electron micrograph, it was found to be well dispersed cubic particles having an average particle diameter of about 2 μm.

Example 2 The aragonite crystalline calcium carbonate of Example 1 was used with a major axis of 15 mm.
All were the same as Example 1 except that the diameter was changed to μm and the minor axis was changed to 0.9 μm. When the obtained calcium carbonate was confirmed by an electron micrograph, it was found to be well dispersed cubic particles having an average particle diameter of about 1 μm.

Example 3 The aragonite crystalline calcium carbonate of Example 1 was used with a major axis of 7 μm.
m, and the same as Example 1 except that the minor axis was changed to 0.2 μm. When the obtained calcium carbonate was confirmed with an electron microscope, it was found to be well-dispersed cubic particles having an average particle diameter of about 0.5 μm.

Example 4 In the slurry aged in Example 1, 0.2 kg of cubic calcite crystal calcium carbonate having an average particle diameter of 0.1 μm was previously added (6 kg to the needle-like aragonite crystal calcium carbonate in the slurry). (0.7% by weight) and the aging time was 30 hours, except that all were the same as in Example 1. When the obtained calcium carbonate was confirmed by an electron micrograph, the particles were almost the same as those in Example 1.

Comparative Example 1 Example 1 was the same as Example 1 except that the aragonite crystalline calcium carbonate was changed to cubic calcite crystalline calcium carbonate having an average particle size of 0.03 μm. When the obtained calcium carbonate was confirmed by an electron micrograph, it was calcite crystal calcium carbonate having an average particle diameter of 0.15 μm.

Comparative Example 2 In Example 1, aragonite crystalline calcium carbonate was added with a major axis of 2 μm.
m, a spindle-shaped calcite crystal having a minor axis of 0.8 μm. When the obtained calcium carbonate was confirmed by an electron micrograph, the spindle shape was slightly broken, but as a whole, it was in a state close to the original spindle shape.

Table 1 shows the aging conditions and the shapes before and after aging in the above Examples and Comparative Examples, and Table 2 shows the crystal morphology and BET specific surface area before and after aging.

[0033]

[Table 1]

[0034]

[Table 2]

As is clear from the results of Tables 1 and 2, the aragonite crystalline calcium carbonate having a needle shape is aged to easily produce a cubic calcite crystalline calcium carbonate having a desired particle size. be able to.

[0036]

As described above, according to the present invention, calcite crystal calcium carbonate having a large particle size can be easily produced, and is useful as an antiblocking agent for various films, a light diffusing agent for plastics, and the like. It is. In particular, calcite crystal calcium carbonate having a large particle diameter of 1 μm or more, which has been conventionally difficult to produce, can be easily produced, and its usefulness is extremely large.

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Claims (9)

[Claims] 1. A method for producing calcium carbonate, characterized by obtaining cubic calcite crystalline calcium carbonate by aging needle-like aragonite crystalline calcium carbonate. 2. The production method according to claim 1, wherein aging is performed by adding calcite crystal calcium carbonate. 3. The method according to claim 2, wherein the calcite crystal calcium carbonate has a particle size of 0.02 to 10 μm. 4. The addition amount of calcite crystal calcium carbonate is 0.1% of needle-like aragonite crystal calcium carbonate.
The production method according to claim 2 or 3, wherein the content is 20 to 20% by weight. 5. The needle-shaped aragonite crystalline calcium carbonate having a major axis of 1 μm or more, a minor axis of 0.1 μm or more, and an aspect ratio (major axis / minor axis) of 3 or more. The production method described in 1. 6. The aragonite crystalline calcium carbonate having a needle shape having a BET specific surface area of 3 m ² / g or more.
6. The production method according to any one of 5. 7. The method according to claim 6, wherein the BET specific surface area of the needle-shaped aragonite crystalline calcium carbonate is 5.0 m ² / g or more. 8. The cubic calcite crystal calcium carbonate obtained by aging the needle-like aragonite crystalline calcium carbonate has a specific surface area of 30 m ² / g or less. Manufacturing method. 9. The method according to claim 8, wherein the specific surface area of the cubic calcite crystal calcium carbonate obtained by aging the needle-shaped aragonite crystal calcium carbonate is 20 m ² / g or less.