JPH01119512A - Platy basic calcium carbonate and its production - Google Patents

Abstract

PURPOSE:To obtain the title platy basic calcium carbonate having excellent dispersibility by specifying the relative gaseous carbon dioxide blowing velocity to the primary falling point in correspondence to the respective combinations of the activity indexes of quick lime and the maximum screened particle size values of the milk of the slaked lime as the slaked material, and carbonating the slaked lime milk. CONSTITUTION:The quick lime having 200-400 activity index is added with water, and slaked to prepare the milk of slaked lime having 44-250mum maximum screened particle size. The maximum relative gaseous carbon dioxide blowing velocity to the primary falling point is controlled to 23-3ml/min.g-Ca(OH)2 in correspondence to the respective combinations of the activity indexes and the maximum screened particle size values, and the slaked lime milk is carbonated. By this method, the highly dispersible platy basic calcium carbonate having <=1.5 degree of dispersion, 0.2-2mum mean diameter of the platy part, 0.05-0.25mum mean thickness, and 4-20 ratio of the mean diameter to the man thickness is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polygonal plate-like basic calcium carbonate having extremely good dispersibility and a method for producing the same. More specifically, the present invention is useful as a pigment or filler in the production of paper, rubber, plastics, paints, etc., with quality properties such as excellent whiteness, gloss, smoothness and ink absorption, and good workability. The present invention relates to a polygonal plate-like basic calcium carbonate having extremely good dispersibility, and an industrial method for producing the same.

[Conventional technology]

In Japan, precipitated calcium carbonate is commercially available in various shapes such as cubes, spindles, columns, needles, and chains. They are used in fields such as paper manufacturing, rubber, plastics, and paint industries, but calcium carbonate is more frequently used in place of plate-shaped kaolin and talc, which are widely used in these fields. For this purpose, there is a strong desire for something that has a plate-like shape. However, the current situation is that it has not yet been established industrially from both quality and cost perspectives.

In order to meet the above requirements, the following publications were developed:
2-113718, XCaCO3・YCa (
It has been proposed to produce a plate-shaped basic calcium carbonate or its complex represented by the composition formula OH)2 ・ZH20,
Attempts are being made to industrialize it.

However, basic calcium carbonate and its complexes produced by these proposed methods can only be obtained as agglomerated products with poor dispersibility, do not have sufficient properties such as gloss and ink absorption, and have poor workability. As a result, the development of effective uses has not progressed, and industrialization is currently at an early stage.

[Problem that the invention seeks to solve]

Thus, as in the prior art, electrical conductivity, pH
However, if the carbonation reaction is carried out by controlling the blowing speed of carbon dioxide gas at a certain carbonation rate or the like, the resulting products will contain a large amount of aggregates with poor dispersibility, resulting in insufficient performance and quality. It was not possible to obtain this product.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to overcome the above-mentioned drawbacks of the prior art and to provide polygonal plate-shaped basic calcium carbonate having extremely good dispersibility. That is, when used as a coating pigment in the paper industry, for example, the present invention has excellent quality characteristics such as whiteness, gloss, ink receptivity, and smoothness, comparable to that of Sachin White, let alone kaolin clay, and is easy to work with. The object of the present invention is to provide a plate-shaped basic calcium carbonate which has no problems in terms of properties and does not cause defects such as streaks and uneven coating.

[Means for solving problems]

In order to achieve the above object, the present inventors have conducted extensive research into solving the above problems, especially in attempting to industrialize the method described in Japanese Patent Publication No. 62-32130. The mechanism is that as the reaction progresses, unevenness occurs during the crystallization process, and the crystal nucleation reaction and crystal growth reaction occur simultaneously and intermingled. It has been found that a good product can be manufactured. In other words, we focused on the activity of quicklime, which is not controlled by conventional methods, and the particle size of slaked lime particles in slaked lime milk obtained by slaking the quicklime, and investigated various combinations of both activity and particle size. It has been found that the above object of the present invention can be achieved by carbonating slaked lime milk while correspondingly controlling the maximum value of the relative carbon dioxide gas blowing speed within a certain range.

That is, according to the present invention, plate-like basic calcium carbonate with good dispersibility is provided, and this plate-like basic calcium carbonate has a dispersion degree of 1.5 or less and an average of the plate-like portions. Diameter is 0.2~2.0μm, average thickness is 0.05~
0.25 μm, average diameter/average thickness ratio (aspect ratio)
The plate-like basic calcium carbonate according to the present invention, which is characterized in that is 4 to 20, has the composition formula
CaCO3・YCa(OH)2・ZH20 (however, X=
2, Y = 0.5 to 1.0, and Z =
0.7 to 1.5 Te), and the average diameter of the plate-like crystal grains (Da
y) 0.5 D a v ~ 2, OD a v
It is preferable that particles having a diameter of 100% account for 80% or more, particularly 90% or more of the total.

According to the present invention, the plate-like basic calcium carbonate of the present invention has an activity of quicklime of 200 to 400, and a maximum sieved particle size of slaked lime milk, which is a slaked product thereof, of 44 μm to 250 μm.
m, the maximum value of the relative carbon dioxide gas blowing rate up to the primary drop point is 23 ml/sin-g-Ca corresponding to each combination of these activities and maximum sieve particle size.
(OH) 2~3o+1/min-g-Ca (OH)
2 can be produced by carbonating slaked lime milk.

[For production]

Representative examples of basic calcium carbonate obtained by the method of the present invention and conventional methods were examined using a scanning electron microscope (SEM).
) Photo and light transmission type particle size analyzer (Shimadzu 5A-CP3
) are shown in Table 1 below.

As seen in the SEM photograph (Fig. 1), the plate-shaped basic calcium carbonate obtained by the method of the present invention exhibits a polygonal shape ranging from a square to a hexagon, and the particle size of the plate-shaped portion is good. It is observed that the particles are uniform and are extremely well dispersed even into individual particles. On the other hand, in the case of the conventional method, it is observed that about several dozen individual particles aggregate to form a large aggregate (FIG. 2).

Here, the quality of dispersibility is determined by the degree of dispersion, that is, the 50% average diameter (Ds.) μm measured by a light transmission type particle size analyzer (SA-CF2).
/ average diameter μm measured by a scanning electron microscope (SEM), as shown in Table 1 above, in the case of the method of the present invention, the degree of dispersion = 0.3210.3 = 1.07,
It can be seen that the value is almost the theoretical value, that is, a value close to 1, but on the other hand, in the case of the conventional method, the degree of dispersion is extremely high at 3.7410.4=9.35. Generally, when measuring with a light transmission type particle size analyzer, ultrasonic dispersion is performed, so if it is an aggregate due to mere physical bonding, it should be relatively easy to disperse into individual particles, but conventional methods In case,. -3.74 μm, which is extremely large compared to the average diameter of the plate-shaped portion observed by SEM, which is 0.4 μm, and it can be seen that it is an aggregate due to strong chemical bonding force. However, in the case of the method of the present invention, D. = 0.32 μm, which shows an extremely good dispersion state.

On the other hand, such agglomerated products have the disadvantage that they are clearly inferior in gloss, smoothness, ink receptivity, etc. when, for example, a paper coating test is performed, when compared with a good dispersion product. There is. In addition, such aggregated products are difficult to be easily dispersed by ultrasonic dispersion treatment. Therefore, we temporarily crushed the agglomerated product in a vibrating mill for about 30 minutes, observed it by SEM, and
Looking at the particle size in A-CF2, the aggregates are fragmented, lose their plate-like shape, and turn into granules (Figures 13 and 14). When a paper coating test was conducted using this product, it was confirmed that white paper gloss, printing gloss, smoothness, etc. were reduced (Table 4).

On the other hand, according to the present invention, average particle diameters of 0.3 μm and 0.7 μm
A comparative coating test was conducted using plate-like basic calcium carbonate with Sachin White, commercially available light calcium carbonate, etc. (Example 8). It is several orders of magnitude superior in properties, ink receptivity, and smoothness, and shows values that are comparable to those of Satin White, which shows high quality results. Furthermore, it was found that compared to Satin White, it gave significantly superior results not only in strength but also in terms of workability such as pigment viscosity, streaks, and uneven coating (Tables 4 and 5).

Furthermore, the plate-shaped basic calcium carbonate according to the present invention surprisingly shows a comparison between three-way blending of simple pigments, that is, a blending of the product of the present invention and kaolin clay, and a blending of commercially available light calcium carbonate and kaolin clay. , while maintaining the characteristics of each single pigment, and also exhibiting a synergistic effect,
It was found that excellent results were obtained in terms of glossiness, overturning conventional wisdom (Table 6).

When the aqueous slurry of plate-like basic calcium carbonate according to the present invention is heated and aged (50°C x 3 days), it shows excellent results in white paper gloss and printing gloss in paper coating tests,
The measured values increased by about 2% (Table 7).

A dried product obtained by, for example, spray drying from the aqueous slurry of the plate-like basic calcium carbonate of the present invention is easily redispersed in water using a daysilver or the like. In this way, a slurry with a concentration of 60% by weight is made, and this is used for SE
When observed with M, it was found that the particles were mostly in the same dispersed state as before. When a paper coating test was conducted using this product, there was almost no difference in quality compared to when the product before treatment was used (Table 8).

The composition formula of the plate-like basic calcium carbonate according to the present invention is determined from the results of thermogravimetric analysis (70 curve) and gas analysis shown in Figures 5 and 11.
- In the X-ray diffraction diagrams shown by ZH20 and shown in Figures 6 and 12, only the peak of basic calcium carbonate is found, and the peaks of calcite and slaked lime are almost absent. From the results of thermogravimetric analysis, the compositional formula of basic calcium carbonate of the present invention is, when X = 2, Y = 0.5 to 1.0,
It is recognized that it is polygonal plate-like basic calcium carbonate with Z = 0.7 to 1.5.

The plate-shaped basic calcium carbonate with good dispersibility of the present invention can be produced, for example, as follows.

In the method of the present invention, the maximum value of the relative carbon dioxide gas blowing speed up to the blowdown point is adjusted in accordance with various combinations of the activity of quicklime and the maximum sieve particle size of milk of slaked lime, which is its slaked product. It carbonates slaked lime milk within a predetermined range. First, the present inventors used the coarse particle titration method (4N-HCI, 1 to 4
．． The particles were classified according to the 5-minute value (76 mm particle size, 50 g method).

Next, the slaked lime milk obtained by slaking the quicklime is sieved according to the classification. Water is added to the slaked lime milk obtained by sieving to adjust the slaked lime concentration according to the classification. Adjust the temperature of slaked lime milk when starting the carbonation reaction according to the classification.

Next, carbon dioxide gas is introduced into the slaked lime milk to perform a carbonation reaction.The relative carbon dioxide gas blowing rate is expressed by the following formula, and carbonation is performed according to the classification.

Relative carbon dioxide gas blowing speed = carbon dioxide gas introduction! (Gas introduction amount ×
002% by volume, standard a): ml/1 lin/amount of Ca (OH)2 in slaked lime milk: g The electrical conductivity during the carbonation reaction was continuously measured, and the electrical conductivity at the -blowing point was measured. 7 or more, and the end point of the reaction is when the electrical conductivity in the secondary drop is in the range of 4 to 5.

If the above is summarized and the manufacturing conditions are shown as a list, for example, it will be as shown in Table 2 below.

The following table shows the remaining days. 2 According to the inventor's study, when the activity of quicklime is in the range of 200 to 400, the relative carbon dioxide gas blowing speed is:
23-3 ml/win-g-Ca(OH)2.

Desirable conditions for producing plate-like basic calcium carbonate with good dispersion are when the activity of quicklime is high (for example, 35
0), the relative carbon dioxide gas blowing speed is large (for example, 10
~19 ml/IIIin-g), and when the activity is low (for example, 250), the relative carbon dioxide gas blowing speed must be reduced (for example, 5 to 11 ml/min.g).

For quicklime with the same activity (e.g. 350), the coarser the maximum sieve particle size of the milk of slaked lime (e.g. 250 μm), the lower the relative carbon dioxide gas blowing speed (e.g. 10IIIl/m
in-g), the finer it is (e.g. 44 μm), the higher the relative carbon dioxide gas blowing speed can be (e.g. 19 ml/sin-g).
). For the maximum sieve particle size of the same slaked lime milk (for example, 74
μm) The higher the activity of quicklime (e.g. 350), the higher the relative carbon dioxide gas blowing speed (e.g. 18 l/llin).
-g), the lower the activity of quicklime (e.g. 250), the smaller the relative carbon dioxide gas blowing speed needs to be (e.g. 10
ml/m+in-g).

If the relative carbon dioxide gas blowing speed exceeds this limit range, it will be difficult to obtain basic calcium carbonate, and even if it is obtained, it will not be possible to obtain one with good dispersibility; The productivity is low at a carbon dioxide gas blowing speed, which is not practical.

Products produced under the above production conditions using slaked lime obtained by dry slaking lime of the same activity level (e.g. 350) are irregular in shape, have many aggregates, and have an irregular crystal shape. In addition to the shape, there were various types of particles such as granular and thread-like.

The higher the activity level (for example, 350), the lower the upper limit of the concentration of Ca (OH)2, which is subsequently carbonated in the sieve fraction (for example, 12% by weight or less, preferably 10% by weight or less). Conversely, the lower the activity level (for example, 250), the higher the upper limit concentration (for example, 15% or less, preferably 13% or less)
. On the other hand, the lower I@ concentration is preferably 5% by weight or more, preferably 8% by weight or more, and if it is less than this, the productivity decreases, which is not preferable.

Next, as for the temperature of slaked lime milk at the time of starting the reaction, the higher the activity of quicklime (e.g. 350), the lower the upper limit (e.g. 13°C or less, preferably 10"C or less). This upper limit temperature (e.g. 13°C or less) ) or above, basic calcium carbonate with good dispersibility cannot be obtained.

On the other hand, the lower limit temperature is 5° C. or higher (preferably 8° C. or higher); lower temperature is not preferred because the reaction rate is slow and the productivity is low.

In any case, the temperature at the -down point must be kept below 18°C. If the temperature is 18° C. or higher, plate-like basic calcium carbonate with good dispersibility cannot be obtained. Cooling may be performed if necessary.

The carbon dioxide gas introduced may be a single gas or a mixed gas such as air. It is also possible to use exhaust furnace gas (C02 concentration of about 30%) during limestone firing.

If you want to obtain the required optimum particle size according to each application such as paper making, rubber use, plastic use, etc., the activity of the quicklime used and the sieve content of the slaked lime milk that has slaked the quicklime should be determined according to the maximum particle size. By adjusting the starting temperature and Ca(OH)2 concentration of the slaked lime milk and controlling the relative carbon dioxide gas blowing rate, the desired particle size can be obtained. Also,
The particle size distribution can also be adjusted arbitrarily, and this point is also one of the features of the present invention.

Next, the degree of carbonation during the reaction process is desirably adjusted by controlling the relative carbon dioxide gas blowing rate while measuring the electrical conductivity, and keeping it within the above-mentioned limit range. If the blowing speed is suppressed initially (that is, until the primary drop point is reached), it is possible to increase the blowing speed later.

When the electrical conductivity at the primary drop point falls below 7, it becomes very difficult to form basic calcium carbonate.

Furthermore, it is important that the end point of the reaction is the midpoint of the quadratic descent, that is, the electrical conductivity is in the range of 4 to 5, in practice 4.5. The descent speed is very fast, so it is important to be careful at the final point. If it is 5 or more, unreacted slaked lime remains, which is not preferable.

On the other hand, if it is less than 4, calcite will start to form and this will be mixed into the product, which is not preferable.

In addition to the above, equipment factors that influence the reaction include the dimensions of the reaction layer, the shape and rotational speed of the stirring blade, the carbon dioxide gas blowing means, etc., and it is important to appropriately select these factors.

〔Effect of the invention〕

The plate-like basic calcium carbonate according to the present invention has extremely good dispersibility, the particle size can be arbitrarily adjusted, and the particle size distribution is also extremely small, and the purity is also extremely high. It is of high quality.

When used as a coating agent for paper manufacturing, the plate-like basic calcium carbonate of the present invention is superior to conventional kaolin clay and commercially available light calcium carbonate in terms of whiteness, gloss, ink receptivity, smoothness, etc. The effect is much higher than that of Satin White, and the effect is comparable to that of Satin White, and it can be expected to have far superior effects in terms of workability and economy. In addition to being used as a coating for paper manufacturing, it can also be effectively used as a filler for rubber and plastics and as a pigment for paints.

〔Example〕

Next, the plate-shaped basic calcium carbonate of the present invention and the method for producing the same will be further explained with reference to Examples.

Example 1: The present invention (activity 350) 2.4 kg of industrial quicklime with an activity of 350 was put into 17.6 kg of water at 40°C, and while stirring,
Do a minute of decontamination. Thereafter, the mixture was sieved using a classifier to take out the slaked lime milk that passed 74 μm, and water was added thereto to obtain 20 kg of slaked lime milk with a slaked lime concentration of 10% by weight. This was placed in a reaction container (inner diameter 345 x height 360 mm, inner volume 401 mm), and while stirring (paddle-shaped impeller, diameter 100 mm, 500 r
pm) After cooling to 10℃, add 100% carbon dioxide gas to 25℃.
Introduce at a rate of 1/min. The relative carbon dioxide gas blowing rate at this time was 12.5ml/win-g-Ca (OH)
It is 2.

Continue cooling for at least 15 minutes from the start of the reaction to 15°C.
After maintaining the liquid temperature below, the electrical conductivity is 4.5mS/Cm.
The injection of carbon dioxide gas was stopped.

The reaction conditions and results are shown in Table 3 below.

When the reaction product was observed with a scanning electron microscope (SEM), it had a plate-like shape with an average particle size of 0.3 μm and a thickness of 0.08 μm (FIG. 1). There are no agglomerated parts, and the individual particles are well dispersed.

On the other hand, the average particle diameter (50% value: D5°) determined with a light transmission particle size analyzer (manufactured by Shimadzu, 5A-CF2) was 0.32 μm.
(Figure 3), which is the value 0.3 obtained from SEM.
Toyo (they match. The degree of dispersion at this time is 0.3210
．． 3-1.07. This also shows that according to the present invention, plate-like basic calcium carbonate with almost no agglomerated portions and an extremely well dispersed state can be obtained.

It can be seen that the crystal grain size is also in the range of 0.2 to 0.8 μm, and the width is also small. On the other hand, the thickness is 0.08, so the aspect ratio is 4. Furthermore, from the results of thermogravimetric analysis (TO curve) (Fig. 5) and X-ray diffraction (Fig. 6) of this product, almost no peaks of calcite or slaked lime were observed, and 2CaCOs.0. 63Ca
It was confirmed that it was basic calcium carbonate having the composition formula of (OH)2.0.86H20.

Comparative Example 1-1: Agglomerated product Same as Example 1, slaked and without sieving.
20 kg of slaked lime milk with a slaked lime concentration of 11% by weight was prepared.

After cooling the slaked lime milk to 10°C, 100% carbon dioxide gas was blown into it at a rate of 201/lll1n (relative carbon dioxide gas blowing rate -9.1 ml/min-g-Ca (OH) 2) to carbonate it and conduct electricity. degree is 4.5 ms/cn+
The reaction stopped when The reaction conditions and results are shown in Table 3. When observing the reaction product with SEM (Fig. 2), primary particles of 0.3 to 0.7 μm (average 0.4 μm)
were aggregated to form secondary coarse agglomerated particles with a size of approximately 3.0 to 4.0 pm.

Figure 4 shows the results for 5A-CF2. When the degree of dispersion is calculated, it shows an extremely large value of 3.7410.4 to 9.35. Relative carbon dioxide gas blowing speed is 10 m1/Ilin-g
Although it was within the conditions specified in the present invention, the slaked lime milk was not sieved, resulting in an agglomerated product.

Comparative Example 1-2: Granular calcium carbonate was slaked in the same manner as in Example 1, and the slaked lime milk was sieved at 74 μm to obtain 20 kg of slaked lime milk with a slaked lime concentration of 10% by weight.
g was prepared. After cooling this slaked lime milk to 10°C, 100% carbon dioxide gas was added at 37 ffi/win (relative carbon dioxide gas blowing rate = 18.5a+l/sin-g-Ca(OH)
2). About 10 minutes after starting the reaction, the electrical conductivity decreased to 2 as/cm, and at the same time the viscosity of the reaction solution increased and gelled. When carbon dioxide gas was continued to be blown into the solution, the electrical conductivity increased again and the viscosity returned to its original state. If the blowing of carbon dioxide gas continues, the electrical conductivity decreases again, but the electrical conductivity is 4.5 ms/c.
The reaction was stopped when m. The reaction conditions and results are shown in Table 3.

When the reaction product was observed with a SEM, it was found to be calcite-type calcium carbonate in the form of fine particles of 0.1 μm or less.

Even if slaked lime milk was sieved, plate-like basic calcium carbonate could not be obtained when carbonation was carried out at a relative carbon dioxide gas blowing rate equal to or higher than the limit of the present invention.

Example 2: Present invention (activity 250) 260g of industrial quicklime with an activity of 250 is put into 1760g of water at 40°C, and slaked for 15 minutes while stirring. Thereafter, it was sieved using a classifier, and the slaked lime milk that had passed through 44 μm was taken out, and water was added to this to obtain 2 kg of slaked lime milk with a slaked lime concentration of 10% by weight. Place this in a reaction container (inner diameter 15
0 x height 220 mm, internal volume 41) and stirred (paddle-shaped impeller, diameter 60 mm, 700 rpm) at 10°C.
After cooling to 0.341/1l of 100% 4 degree carbon dioxide gas
Introduce at a rate of Iin.

The relative carbon dioxide gas blowing speed at this time was 1.7 ml/min.
-g-Ca (OH)2. Electrical conductivity 4.5
The blowing of carbon dioxide gas was stopped at ms/cva.

The reaction conditions and results are shown in Table 3.

When the reaction product was observed with SEM, the average diameter was 0.8μ.
m, and had a plate-like shape with a thickness of 0.15 μm (7th
figure). There were almost no agglomerated parts, indicating a good dispersion state.

On the other hand, the average particle diameter (D s.) determined by 5A-CF2 is 0.
．． 88 μm (Figure 9), which has an SEM value of 0.
It is in good agreement with 8 μm. Dispersity is 0.8810.8
=1.1. This also shows that the plate-like basic calcium carbonate according to the present invention has almost no agglomerated parts and is in an extremely good dispersion state. Crystal grain size is also 0
．． It can be seen that the width is in the range of 5 to 1.5 μm, and the width is also small. On the other hand, the thickness is 0.15 μm, and the aspect ratio is 0.8810.15',6.

Furthermore, from the TG curve (Fig. 11), gas analysis, and x1 diffraction pattern (Fig. 12) of this product, no peaks of calcite or slaked lime were found, and 2CaC03.0.72Ca
It was confirmed that it was basic calcium carbonate having the composition formula of (OH)2.0.96H20.

Comparative Example 2-1: Agglomerated product Same as Example 2 (2 kg 5 li of slaked lime milk with a slaked lime concentration of 13% by weight was produced without slaking and sieving.

After cooling this slaked lime milk to 15°C, 100% carbon dioxide gas was added at 0.341/m1n (relative carbon dioxide gas blowing rate -
1.3 ml/min-g-Ca (OH) 2 ) and carbonated, the electrical conductivity was 4.5 ms/cm.
The blowing was stopped. The reaction conditions and results are shown in Table 3.

When the reaction product was observed by SEM, it was found that primary particles of about 1.3 μm were strongly aggregated to form secondary coarse particles of about 4 to 5 μm in size (FIG. 8). Next, the results of measurement using 5A-CF2 are shown (FIG. 10).

When calculating the degree of dispersion, 4.4 / 1.3 = 3.4
It can be seen that this shows a very high value. In this example, as in Comparative Example 1-1, even if the relative carbon dioxide gas blowing rate was within the conditions specified in the present invention, the slaked lime milk was not sieved, resulting in agglomerated products. ing.

Comparative Example 2-2 - Granular calcium carbonate was slaked in the same manner as in Example 2, and the slaked lime milk was sieved at 44 μm to prepare 2 kg of slaked lime milk with a slaked lime concentration of 10% by weight. After cooling this slaked lime milk to 10°C, 100% concentration of carbon dioxide gas was added at 2.511/win (relative carbon dioxide gas blowing rate = 12.5 ml/min-g-Ca(OH)2
) and carbonation was carried out while cooling, the electrical conductivity decreased to 5 ms/co+ about 10 minutes after the start of the reaction, and then rose again immediately. When the carbon dioxide gas was continued to be blown, the electrical conductivity started to decrease again after about 20 minutes and stopped at 4.5 ms/cm.

The reaction conditions and results are shown in Table 3. SEM of reaction products
When observed, it was found to be calcite-type calcium carbonate in the form of fine particles of 0.1 μm or less. Even if slaked lime milk was sieved as in Comparative Example 1-2, plate-like basic calcium carbonate was not obtained when carbonation was carried out at a relative carbon dioxide gas blowing rate equal to or higher than the limit of the present invention.

Example 3: (High activity - sieved particle size - relative carbon dioxide gas blowing rate) Industrial quicklime 2 with the same activity of 350 as used in Example 1
40g was put into 1740g of water at 40°C and slaked for 15 minutes with stirring. The sifted milk of slaked lime was subjected to a carbonation reaction by varying the particle size and carbon dioxide gas blowing rate. The reaction was stopped at an electrical conductivity of 4.5 ms/cm. The reaction conditions and results are shown in Table 3.

In the case of highly active quicklime, it can be seen that there is a maximum value of the relative carbon dioxide gas blowing rate depending on the particle size of the sifted lime milk, and carbonation needs to be carried out below this value.

Example 4: (Low activity - sieve particle size - relative carbon dioxide gas blowing rate) Industrial quicklime 2 with the same activity of 250 as used in Example 2
60g was put into 1740g of water at 40°C and slaked for 15 minutes with stirring. The sifted milk of slaked lime was subjected to a carbonation reaction by varying the particle size and carbon dioxide gas blowing rate. The reaction was stopped at a conductivity of 4.5 ms/cm.

The reaction conditions and results are shown in Table 3.

In the case of low-activity quicklime, it can be seen that there is a maximum value of the relative carbon dioxide gas blowing rate depending on the particle size of the sieved lime milk, and it is necessary to carry out carbonation below this value.

Example 5: (Influence of carbon dioxide concentration) 2 kg of slaked lime milk prepared by sifting the slaked lime milk prepared in Example 4 through a 44 μm sieve was cooled to 10°C, and carbon dioxide gas (100
% concentration) was set to 1/min, nitrogen gas was mixed therein, and the carbonation reaction was carried out by changing the carbon dioxide concentration. Table 3 shows the reaction conditions and results, which were stopped at a conductivity of 4.5 a+s/c+w.

It can be seen that the particle size of the produced plate-like basic calcium carbonate tends to increase as the concentration of carbon dioxide gas decreases.

Example 6: (Effect of temperature at the start of the reaction) The slaked lime milk prepared in Example 5 was cooled, and the temperature of the slaked lime milk at the start of the reaction was changed to perform the carbonation reaction. Shown in Table 3.

It can be seen that the particle size of the produced plate-like basic calcium carbonate tends to increase as the temperature of the slaked lime milk increases at the start of the reaction.

Example 7: - Temperature limit at the first drop point After cooling the slaked lime milk prepared in Example 6 and adjusting it to 16°C, the carbonation reaction was started, and the temperature of the slaked lime milk at the first drop point of electrical conductivity was The carbonation reaction was carried out by changing the

The reaction conditions and results are shown in Table 3.

It can be seen that when the temperature at the second drop point exceeds 18° C., plate-like basic calcium carbonate with good dispersibility can no longer be obtained.

Example 8: Coating test Platy basic calcium carbonate having an arbitrary particle size was prepared by changing the activity of quicklime and the concentration of carbon dioxide gas on the scale of the reaction vessel 401. The reaction conditions and results are shown in Table 3. Two types of aqueous slurries of plate-shaped basic calcium carbonate with average particle diameters of 0.3 μm and 0.7 μm and good dispersibility were obtained. The resulting slurry was dehydrated to form a wet cake, which was then redispersed in water to form a slurry having a concentration of 60% by weight.

Next, a coating test was conducted using this product.

Below, these will be referred to as 03 items and 07 items.

The following was used as a control sample.

(1) Mechanically crushed plate-like basic calcium carbonate product with aggregates of Comparative Example 1-1.2-1 (2) Satin White: Commercial product (3) Light calcium carbonate: Commercial product (4) Present invention (5) Kaolin clay: Commercially available product (6) Spray-dried product of the present invention (Example 1) (carbonated The resulting slurry was spray-dried, and the dried product was redispersed in water to obtain a 60% slurry.) The coating test was conducted under the following conditions.

(1) Coated base paper: Approximately 80gr10f high-quality paper (2)
Coating method: Wire bar Hand-painted Wire bar used: 1lkL12 Coating amount ζ20gr/rrr (3) Color formulation 1) Type and blending ratio of color pigments (as solid content) The following blended products (blending ratio: Tables 4 to 8) 100 Part Kaolin Cresatin White Heavy Calcium Light Calcium Carbonate Product of the invention and crushed product 2) Binder latex (SBR type) 10 parts Starch (oxidized starch type) 5 parts 3) Lubricant (stearic acid type) 1.0 parts 4 ) Dispersant (polycarboxylic acid type) 0.6
Part 5) Coating liquid Solids concentration #60% (4) Super calender processing conditions Linear pressure 100 kg/cm Temperature 55・C Number of passes 3 times Calender speed 8 m/ll1in (5) Measurement method Brightness Hunter whiteness meter "MR" -2” White paper gloss Gloss meter “GM-260” Print gloss
Gloss meter "G?l-260"K&N whiteness low degree drop whiteness meter "MR-2" 2 minute value.

Ink used: Phthalocyanine blue printing RI printing tester Ink used: TVI2, Red Number of revolutions: 3 Orpm RI Dry Pick TVI 8 Red6
0rpm+, 5-level rating.

B viscosity BL type, 60 rpm The results of the coating test are as follows.

CI) Comparison with commercial products (Table 4): Blending ratio: 15 parts of sample/85 parts of kaolin clay (1)
In comparing products 03 and 07 of the present invention, whiteness,
Product 03 is superior in both print gloss. On the other hand, RIDry Pi
The 07 product is superior in ck strength.

(2) Even when plate-shaped basic calcium carbonate containing aggregates is mechanically crushed, good dispersibility cannot be obtained, and both white paper gloss and printing gloss are inferior to the products of the present invention.

(3) Comparing Sachin White and the product of the present invention,
The results are much the same, and the results are no better. The product of the present invention is far superior in workability.

(4) When comparing commercially available light calcium carbonate with the product of the present invention, the product of the present invention is clearly superior in both white paper gloss and print gloss.

(n) Comparison with commercially available products (Table 5) Blending ratio: 30 parts of sample / 30 parts of calcium bicarbonate / 40 parts of kaolin clay (1) Comparing commercially available light calcium carbonate and the product of the present invention, white paper gloss The product of the present invention shows superior results in both print gloss and printing gloss.

(I[[) Mixing synergistic effect of color combination (Table 6) Kaolin, the product of the present invention (product 03), and commercially available light calcium carbonate were used alone (100 parts) and in combination (blending ratio: 20 parts of sample), respectively. /80 parts of kaolin).

(11) In the case of the combination of the product of the present invention and kaolin, both the white paper gloss and the printing gloss were superior to each other, and good results were obtained in which a synergistic effect was expected.

(2) On the other hand, in the case of a combination of commercially available light calcium carbonate and kaolin, in contrast to the above, the value was intermediate between the values of each single component.

(IV) Heating effect (50°C x 3 days, Table 7) (1)
Both white paper gloss and print gloss were clearly improved by heating.

(V) Dry product test (spray-dried product, Table 8) (1) In the comparative coating test of the slurry and the powder obtained by spray-drying it, it can be said that there is almost no difference between the two.

(2) In a comparative test with commercially available light calcium carbonate in dry powder form, it was found that the product of the present invention was several orders of magnitude superior in terms of both white paper gloss and print gloss.

Margin below Table 5 Table 6 Table 7 Table 8

[Brief explanation of the drawing]

Figures 1 and 2 are Example 1 and Comparative Example 1-1, respectively.
This is a scanning electron micrograph showing the crystal particle structure of basic calcium carbonate obtained in . Figures 3 and 4 are Example 1 and Comparative Example 1-1, respectively.
2 is a graph showing the measurement results of the crystal grain size of basic calcium carbonate obtained using a light transmission type particle size measuring device. FIG. 5 is a graph showing the relationship between temperature and change in fIi amount in thermogravimetric analysis of Example 1. FIG. 6 is an X-ray diffraction diagram of the product obtained in Example 1. Figures 7 and 8 are Example 2 and Comparative Example 2-1, respectively.
This is a scanning electron micrograph showing the crystal particle structure of basic calcium carbonate obtained in . Figures 9 and 10 are Example 2 and Comparative Example 2-
1 is a graph showing the measurement results of the crystal grain size of basic calcium carbonate obtained in Example 1 using a light transmission type particle size analyzer. FIG. 11 and FIG. 12 are diagrams showing the results of thermogravimetric analysis and X-ray diffraction for Example 2, respectively. FIGS. 13 and 14 are scanning electron micrographs of crushed aggregates and the results of light transmission particle size measurement.

Claims (1)

[Claims] 1. The degree of dispersion is 1.5 or less, and the average diameter of the plate-shaped portion is 0.2 to 2.0 μm, and the average thickness is 0.05 to 0.25.
Plate-shaped basic calcium carbonate with good dispersibility, characterized in that the ratio of average diameter/average thickness is 4 to 20. 2. Composition formula XCaCO_3・YCa(OH)_2・ZH
The plate-like basic calcium carbonate according to claim 1, which is represented by _2O. However, if X=2, Y=0
．． 5 to 1.0, and Z=0.7 to 1.5. 3. 0.5Dav for the average diameter (Dav) of the plate-shaped part
The plate-shaped basic calcium carbonate according to claim 1, wherein particles having a diameter of ~2.0Dav account for 80% or more of the total. 4. The degree of dispersion is 1.5 or less, and the average diameter of the plate-shaped portion is 0.2 to 2.0 μm, and the average thickness is 0.05 to 0.25.
In producing plate-like basic calcium carbonate with good dispersibility, having an average diameter/average thickness ratio of 4 to 20 μm,
When the activity of quicklime is 200 to 400 and the maximum sieve particle size of slaked lime milk, which is its slaked product, is 44 μm to 250 μm, the primary The maximum relative carbon dioxide gas blowing rate up to the drop point was set at 23 ml/min・g-Ca (OH
) A method for producing plate-like basic calcium carbonate, comprising carbonating slaked lime milk in a range of 2 to 3 ml/min.g-Ca(OH)_2. 5. The activity of quicklime is 250 to 380, and the maximum particle size of the slaked lime, which is its slaked product, is 44 μm to 250 μm.
, the maximum relative carbon dioxide gas blowing speed up to the primary drop point is 21 ml/mi for each combination.
n・ga(OH)_2-5ml/min・g-Ca(
OH)_2.