JPH0575697B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to a novel method for producing calcium carbonate, and more particularly, to an industrially advantageous method for producing columnar calcium carbonate using calcite crystals. ``Prior Art and Problems'' Calcium carbonate has been widely used as a filler in rubber, plastics, paints, paper, inks, sealants, etc. Calcium carbonate as a filler can be roughly divided into heavy calcium carbonate (hereinafter referred to as heavy carbonate) produced by mechanically crushing limestone, and precipitated calcium carbonate (hereinafter referred to as "heavy carbonate") produced by reacting calcium hydroxide with carbon dioxide gas. It is classified as sedimentation coal. Since heavy coal cal is manufactured by mechanical crushing and classification, it generally has a large average particle size, specifically 1.0 μm or more, and has a very wide particle size distribution. For this reason, it is insufficient to meet the strict desired physical properties in various fields, and is often used primarily as an extender. On the other hand, since precipitated coal is synthesized through a chemical reaction, the particle size and shape can be adjusted to some extent, and the particle size distribution also falls within a very narrow range. When precipitated coal is classified based on the type of crystal, there are three types: calcite, aragonite, and vaterite.Currently, most of the coal that has been industrialized is calcite, and only a small portion is aragonite. Vaterite has not been industrialized. On the other hand, when precipitated coal-made cal is classified based on particle shape, calcite crystals tend to be either cubic or spindle-shaped. Aragonite generally tends to be columnar. Currently, in various fields where precipitated coal is used, especially in paper-making fields, columnar-shaped calcium carbonate exhibits extremely superior physical properties compared to conventional cubic or spindle-shaped calcium carbonate. Confirmed. Therefore, columnar calcium carbonate with aragonite crystals is used in only a small part of the paper manufacturing industry. However, since aragonite is difficult to produce unless calcium hydroxide and carbon dioxide are reacted under high pressure and high temperature conditions, industrial production involves many problems such as uniformity of quality and cost. Therefore, it is currently impossible to industrially produce large quantities of uniform columnar aragonite. ``Means for Solving the Problems'' In view of the above circumstances, the present inventors have conducted intensive research to obtain columnar calcium carbonate using calcite crystals, and have found that they can produce columnar calcium carbonate using calcite crystals industrially. It was successfully produced. That is, the first aspect of the present invention is to generate calcium carbonate by reacting carbon dioxide gas and calcium hydroxide, and to collect the whole slurry whose viscosity is 1000 cp or more as measured at 60 rpm using a B-type viscometer. The second aspect of the present invention is a method for producing calcite-type columnar calcium carbonate, which is characterized in that the calcite-type columnar calcium carbonate is ripened by applying a mechanical stirring force that is at least equal to the level of uniformity. Calcite-type columnar carbonate characterized by mixing columnar calcium carbonate slurry with calcium hydroxide slurry at a ratio of 1 mol to 0.5 to 5 mol of columnar calcium carbonate to calcium hydroxide, and introducing carbon dioxide gas into the resulting mixed slurry. Each content covers methods for producing calcium. Conventionally, the methods for producing cubic and spindle-shaped calcium carbonate of calcite crystals include introducing carbon dioxide gas into a calcium hydroxide slurry, or injecting calcium hydroxide into carbon dioxide gas in a spray state. be. For certain uses, the resulting calcium carbonate slurry is aged. The present invention relates to the former method of introducing carbon dioxide gas into calcium hydroxide slurry. In this method, the concentration, temperature, amount of carbon dioxide, etc. of the calcium hydroxide slurry are factors that affect the shape and size of the particles. Needless to say, these are all factors related to the reaction rate. There are no particular restrictions on the concentration of the calcium hydroxide slurry at this time, but for industrial production it is preferably about 40 g to 180 g calcium hydroxide/approximately. There are no particular restrictions on the temperature before the calcium hydroxide slurry is combined, but it is preferably between 10 and 30°C. There are no particular restrictions on the amount of carbon dioxide, but for industrial production, the carbon dioxide concentration must be between 10 and 40.
% of air mixed gas to 50 to 500/carbon dioxide +
Air blended gas/hr/・Calcium hydroxide・
It is efficient to introduce a slurry level. Calcium carbonate obtained by completing carbonation in this manner often has a cubic or rice grain-like primary particle size, but is generally irregular in shape and is a strong secondary aggregate. Immediately after the carbonation is completed, the calcium carbonate slurry produced in this way has a viscosity of at most 200 cp or less when measured at 60 rpm using a B-type viscometer, but the viscosity of the calcium carbonate slurry produced in this way is at most 200 cp or less. Add and mature. Preferably, the temperature of the slurry is between 20℃ and 80℃, and the slurry pH is between 8.5 and 80℃.
11.5, more preferably between 8.5 and 11.0.
When a stirring force is applied to the slurry to make it uniform, the viscosity of the slurry gradually increases.
This is because the aggregate particles are dispersed and a hydration layer is formed on the surface of each dispersed particle, and as a result, the viscosity of the slurry increases because the free water required for flow decreases. The slurry, which has a viscosity of 1,000 cp or more, is further stirred with a stirring force sufficient to make the entire system uniform. Thus, the short axis is 0.02 to 2 μm, and the long axis is
Calcium carbonate having a columnar shape with a diameter of 0.1 to 20 μm and an aspect ratio of 4 or more can be obtained.
Conventionally, mechanical stirring force has been applied to calcium carbonate slurry that has undergone carbonation in order to disperse aggregated particles, arrange each particle into cubic uniform particles, and increase the size of the particles. . However, the above purpose can be achieved simply by adjusting the viscosity of the slurry to about 1000 cp to 2000 cp. On the other hand, the feature of the present invention is that the slurry is 1000 cp or more, preferably 1000 cp ~
After raising the temperature to about 2000 cp, a mechanical stirring force is further applied to make the entire system uniform, thereby producing coal in a columnar shape. The following are the reasons why the operation of continuously stirring a slurry whose viscosity has reached 1000 cp or more has not been performed in the past. In order to stir a slurry with a viscosity of 1000 cp or more to a uniform degree, various measures are required in terms of equipment, and a considerable amount of stirring energy is required, resulting in high running costs. Applying a weak stirring force to a slurry of 1000 cp or more has been done in conventional equipment, but if the stirring force is weak, the physical properties will not improve in proportion to the stirring force, so no further investigation was attempted. Therefore, it was unimaginable that column-shaped particles would be produced on the extension line of strong stirring. Under such conventional circumstances, the present inventors went against the common sense of those skilled in the art and unexpectedly applied a strong stirring force to a highly viscous slurry to make the entire system uniform. This is a successful development of columnar coal scum that has high added value as an industrial raw material. In the present invention, the calcium carbonate slurry may be aged with stirring without adding any other additives, but it is preferably aged in the presence of a magnesium salt and/or a chlorine compound. Examples of the magnesium salt used in the present invention include magnesium chloride, magnesium carbonate, magnesium sulfate, magnesium hydroxide, magnesium oxide, magnesium iodide, and magnesium bromide, and these may be used alone or in a mixture of two or more. It will be done. Examples of the chlorine compound used in the present invention include sodium chloride, zinc chloride, aluminum chloride, potassium chloride, etc., and these may be used alone or in combination of two or more. The above magnesium salt and/or chlorine compound may be added to the calcium hydroxide slurry before starting carbonation, or may be added to the calcium carbonate slurry after carbonation. Furthermore, calcium hydroxide slurry is produced by adding water to CaO,
It may be added to the water at this time, ie, the digestion water. There is no particular restriction on the amount added, but it is usually 0.01 to 20% by weight, preferably 1 to 5% by weight (based on the calcium carbonate produced). On the other hand, the short axis, long axis, and aspect ratio can be changed freely to some extent by setting the conditions during carbonation reaction and aging. In order to further increase production efficiency and make the columnar calcium carbonate thus produced more uniform in particle size, it is also possible to add the following steps. Specifically, by mixing columnar calcium carbonate slurry with calcium hydroxide slurry at a ratio of calcium carbonate/calcium hydroxide = 1 mol/0.1 to 0.5 mol, and introducing carbon dioxide gas into this mixed slurry, a uniform calcium hydroxide slurry is produced. Columnar calcium carbonate of site crystals can be generated. The concentration, temperature, and amount of carbon dioxide gas of the mixed slurry at this time may be the same as those for the one-stage carbonation reaction described above. Also, instead of the milk of lime added at this time, a slurry that has been carbonated to some extent may be added. Specifically, for example, if it takes one hour to completely convert a certain amount of calcium hydroxide slurry into calcium carbonate slurry, this refers to slurry in which CO ₂ gas is only introduced for 10 or 20 minutes. shall be. However, the amount of gas is always constant. Furthermore, a batch method or a continuous method may be used. The calcium carbonate obtained as above is
When analyzed using lines, all of them are calcite crystals. When comparing calcite crystals and aragonite crystals, aragonite crystals are extremely unstable and have the property of always trying to migrate like calcite crystals. Particularly when exposed to heat and moisture, it is relatively easily converted to calcite. Therefore, making columns of calcite has much greater significance in terms of quality stability than columns of aragonite.
Additionally, calcite has a specific gravity of 2.7, and aragonite has a specific gravity of 2.85. When used in the paper industry,
The purpose of use is determined not by weight but by volume and shape. Therefore, a small specific gravity brings about a great advantage in reducing the weight of paper. "Function/Effect" White paper for printing is coated with coating pigments to improve the optical properties, smoothness, ink receptivity, etc. of the paper. Clay has traditionally been used as a pigment in this field, but clay has problems with ink set, paper whiteness, and ink receptivity, so in order to compensate for these physical properties, clay with a primary particle size of about 0.1 to 1.0 μm is used. Cubic sedimentation charcoal has been used. However, these precipitated charcoals cause the white gloss of coated paper,
The four points of printing gloss, ink receptivity, and high-speed shear surface viscosity of the paint cannot be satisfied at the same time. For example, particles with relatively small primary particle diameters of about 0.1 to 0.2 μm have white paper gloss and good ink receptivity, but have low printing gloss and high high-speed shear viscosity. However, particles with a primary particle size of about 0.4 to 0.7 μm have high printing gloss, low high-speed shear viscosity, low white paper gloss, and poor ink receptivity. Regarding high-speed shear viscosity, in order to apply the paint at high speed, the viscosity of the paint must be low. The calcite columnar calcium carbonate of the present invention satisfies all of the above-mentioned four physical properties. Next, the characteristics when used as an internal filler for paper manufacturing will be described. As a filler for thin paper, spindle-shaped precipitated carbonaceous carbon having a diameter of about 0.5 to 3 μm has conventionally been used to improve opacity. In these fields, titanium dioxide has been used in combination to improve opacity and whiteness. When the columnar calcium carbonate of the calcite crystals of the present invention is used as a filler in tissue paper, it has superior opacity and whiteness compared to conventional spindle-shaped calcium carbonate, so expensive titanium dioxide can be saved. When used as a pigment in coated paper, it exhibits the above-mentioned excellent physical properties probably because the calcium carbonate particles are aligned in a certain direction on the coated surface due to the columnar shape. Conventional cubes appear to be arranged in random order. These were confirmed by viewing the coated surface using an electron microscope. On the other hand, when it is used as a filler in thin paper, it is thought that the pillars allow it to intertwine well with the pulp fibers and disperse it. "Examples" The present invention will be described below with reference to Examples and Comparative Examples, but the present invention is not limited by these in any way. Example 1 Concentration: 140g calcium hydroxide/10000g of air mixed gas with a carbon dioxide concentration of 30% added to a water slurry of calcium hydroxide adjusted to a temperature of 20°C.
A blown calcium carbonate slurry was produced at a rate of /hr. The calcium carbonate slurry thus generated is maintained at a temperature of 40°C or higher, and the pH of the slurry is
The mixture was kept at a temperature of 10.0 to 11.0 and left for 15 hours with stirring until the entire system was homogeneous. The viscosity of the slurry thus produced was 2500 cp as measured on a Type B viscosity system at 60 rpm. This slurry was further aged for 48 hours while applying sufficient stirring power to make the entire system uniform. Example 2 Compounding and aging were carried out under the same conditions as in Example 1 except that the concentration of the calcium hydroxide slurry was 70 g calcium hydroxide/. The viscosity of the charcoal thriller produced in this way was measured at 60 rpm using a B-type viscosity system.
It was 1200 cp. This slurry was aged for 48 hours in the same manner as in Example 1 while further stirring force was applied. Comparative Example 1 Compounding and aging were carried out in the same manner as in Example 1, except that the viscosity of the charcoal slurry obtained after aging for 15 hours was 500 cp as measured with a B-type viscometer at 60 rpm. This slurry was further aged in the same manner as in Example 1. Example 3 For 10% of the charcoal slurry (1890g as charcoal) produced in Example 1, 20% of the calcium hydroxide water slurry with a concentration of 140g calcium hydroxide was added.
In addition, carbon dioxide gas was introduced while mixing to terminate carbonation. Table 1 shows the shapes of the coals produced in the above Examples and Comparative Examples.

[Table] *Evaluation method The state of formation of columnar particles was determined from micrographs. Evaluation was made on a five-point scale, with the photograph in FIG. 1 (Example 3) being rated "5" and the photograph in FIG. 2 (Comparative Example 1) being "0". Next, the calcium carbonate obtained in these Examples and Comparative Examples was tested as a pigment for coated paper. The results are shown in Table 2. Coating test method: Apply paint prepared under the following formulation conditions to coated base paper.
After coating to a weight of 14 g/m ² , a coated paper was prepared by supercalendering under the following conditions. Super calender processing conditions: Linear pressure 70Kg/cm, 50Kg/cm, 0Kg/cm Temperature 60℃ Number of paper passes 3 times Calendar speed 8m/min Paint composition: Demple (MS4600) 7 parts by weight SBR latex (JSR 0692) 13 Water 40 Sample calcium carbonate
60 (Solid concentration adjusted to 55wt%) Clay and calcium carbonate are actually used together, but in this case, calcium carbonate alone was used to understand the effects of calcium carbonate more accurately. Coating physical properties measurement conditions: Weigh the weight of coated paper with a coating weight of 10 x 10 (cm) on a chemical balance, subtract the weight of the base paper, and measure the average value of 10 test pieces.Paper whiteness JIS-P -8123 Average value of the measured values of 10 test pieces White paper gloss JIS-P-8142 Average value of the measured values of 10 test pieces Print gloss JIS-P-8142 Average of the measured values of 10 test pieces Peripheral speed: 1 m/sec, 1 rotation, ink supply amount: 0.4 ml (Ink used: Toyo Ink
TKU70G ink sip) RI.Dry.Pick peripheral speed 3m/sec, 15 rotations, ink supply amount 0.35ml (ink used: Dainippon Ink
Tactical grade TV = 14 Black) Evaluation using 5 point system,
Average value of the measured values of 10 test pieces RI.Ink.Set Circumferential speed 1 m/sec, 1 rotation, ink supply amount 0.3 ml (Ink used: Toyo Ink
TKU 70G Beniguchi) Visually evaluate and set completion sec
Displayed in ink receptivity Circumferential speed 3 m/sec, 1 rotation color development, dampening water 2.5
ml, refill ink supply amount 0.6ml (Ink used: Toyo Ink TKU 70G Beniguchi) Printing whiteness is measured, expressed as whiteness reduction rate, average value of the measured values of 10 test pieces K&N concentration K&N Ink 2min value

[Table] Next, in order to determine the high-speed shear viscosity of the paint, the sample of Example 1 and the sample of Comparative Example 1 were measured using a Hercules viscometer, and the results are shown in FIGS. 3 and 4. In addition, the sample of Example 1 and the aragonite purity of 85 ~
X-ray charts of 90% calcium carbonate are shown in Figures 5 and 6, respectively. It was confirmed that all the materials in Example 1 were calcite.

[Brief explanation of the drawing]

1 and 2 are electron micrographs showing the particle structure of calcium carbonate obtained in Example 3 and Comparative Example 1, respectively. 3 and 4 are graphs showing the results of measuring the sample of Example 1 and the sample of Comparative Example 1 using a Hercules viscometer, respectively. FIGS. 5 and 6 are X-ray charts of Example 1, aragonite purity 85-90% calcium carbonate, respectively.

Claims (1)

[Claims] 1. When carbon dioxide gas and calcium hydroxide undergo a gas-liquid reaction to produce calcium carbonate, the viscosity of the obtained calcium carbonate slurry is determined by a B-type viscometer.
A method for producing calcite-type columnar calcium carbonate, which is characterized in that a slurry of 1000 cp or more as measured at 60 rpm is further aged by applying a stirring force that is at least enough to make the entire slurry uniform. 2. The manufacturing method according to claim 1, wherein the stirring time is 10 hours or more. 3. The manufacturing method according to claim 1, wherein the calcium carbonate slurry is adjusted to a temperature in the range of 20°C to 80°C and aged. 4. The production method according to claim 1, wherein the pH of the calcium carbonate slurry is adjusted to a range of 8.5 to 11.5 and ripened. 5. The production method according to claim 1, wherein the calcite-type columnar calcium carbonate has an aspect ratio of 4 or more. 6 The short axis of calcite-type columnar calcium carbonate is
The manufacturing method according to claim 1, wherein the length is 0.02 to 2 μm and the major axis is 0.1 to 20 μm. 7 When carbon dioxide gas and calcium hydroxide undergo a gas-liquid reaction to produce calcium carbonate, the viscosity of the resulting calcium carbonate slurry is determined by a B-type viscometer.
A slurry of 1000 cp or more measured at 60 rpm is further aged by applying a stirring force that is at least sufficient to make the entire slurry uniform, and then a calcium hydroxide slurry is added to the columnar calcium carbonate slurry to form a columnar calcium carbonate vs. calcium hydroxide slurry. is 0.1 to 1 mol
A method for producing calcite-type columnar calcium carbonate, which comprises mixing at a ratio of 5 mol and introducing carbon dioxide gas into the resulting mixed slurry. 8. The manufacturing method according to claim 7, wherein the stirring time is 10 hours or more. 9. The manufacturing method according to claim 7, wherein the calcium carbonate slurry is aged at a temperature in the range of 20°C to 80°C. 10 Adjust the pH of calcium carbonate slurry to 8.5 to 11.5
The manufacturing method according to claim 7, wherein the production method is adjusted to a range of and ripened. 11. The production method according to claim 7, wherein the calcite-type columnar calcium carbonate has an aspect ratio of 4 or more. 12 The short axis of calcite-type columnar calcium carbonate is
The manufacturing method according to claim 7, wherein the length is 0.02 to 2 μm and the major axis is 0.1 to 20 μm.