JPS6411571B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing aragonitic calcium carbonate. In detail, the BET specific surface area (hereinafter referred to as specific surface area) is 10 m ² /g or more, and the average dimension by electron microscope observation is length (L) = 0.7 to 1.5 μm, respectively.
Width (D) = 0.01 to 0.2 μm, aspect ratio (L/D) =
This invention relates to a method for producing aragonitic calcium carbonate having the shape of 11 or more fine needles. Calcium carbonate has traditionally been widely used as a filler or pigment in rubber, plastics, paper, paints, inks, adhesives, etc., but until now it has been used to reduce the specific surface area of mechanically crushed limestone to 6 m ² /g.
Ultra-fine calcium carbonate consisting of ultra-fine cubic calcite crystals with a specific surface area of 10 m ² /g or more, obtained through a chemical reaction with the coarse-grained heavy calcium carbonate shown below, with a specific surface area of 10 m ² /g or less and a particle size of Precipitated calcium carbonate, called light calcium carbonate, is produced and commercially available, which is composed of somewhat coarse spindle-shaped calcite crystals or columnar aragonite crystals. However, commercially available calcium carbonate has not been incorporated into rubbers and plastics to achieve satisfactory effects in terms of physical properties related to rigidity such as modulus, hardness, and flexural modulus, as well as reinforcing properties such as tensile strength. Among commercially available calcium carbonates, light calcium carbonate in the form of columnar aragonite crystals differs from calcium carbonate in the form of cubic or spindle-shaped calcite crystals;
Although it is possible to obtain a compound with somewhat high rigidity by blending it with plastic, it does not reach a satisfactory level and cannot be said to be sufficient. For this reason, rubber
There has been a strong desire for the appearance of aragonitic calcium carbonate in the form of ultra-fine needles as a calcium carbonate that can be blended into plastics to impart sufficient rigidity. I couldn't get it. Now, methods for producing columnar aragonitic calcium carbonate include a method in which carbon dioxide gas is reacted with an alkaline calcium chloride aqueous solution under specific conditions (Japanese Patent Publication No. 43-22783), and a method in which a calcium hydroxide aqueous suspension is reacted with carbon dioxide gas. A method has been proposed in which the carbonation process is divided into three stages and the temperature and amount of carbon dioxide gas introduced are adjusted at each stage to carry out the carbonation reaction (Japanese Patent Publication No. 51852/1983), but the former produces extremely fine particles. It is not possible to adjust the tightening conditions, and the particle size is coarse (1 to 15 μm).
I've only been able to get what I want. In the latter case, it is difficult to obtain aragonite crystalline calcium carbonate, and even if it is obtained, it can only be obtained with a small specific surface area that does not fall into the extremely fine region. As described above, the technology for producing ultrafine aragonitic acicular calcium carbonate through the reaction of an aqueous calcium hydroxide suspension with carbon dioxide gas has not yet been established. Therefore, the present inventors conducted various studies on the production method of ultrafine needle-shaped aragonitic calcium carbonate, and found that after adding a crystal nucleating agent to an aqueous suspension of calcium hydroxide, carbon dioxide gas was introduced into it. By carrying out the carbonation reaction, it has an aragonitic content of 55% or more, a high specific surface area of 10 m ² /g or more, and the average dimensions as determined by electron microscopy are length (L) = 0.7 to 1.5 μm and width, respectively. It was discovered that calcium carbonate in the form of uniform, ultrafine needle-shaped particles with (D) = 0.01 to 0.2 μm and aspect ratio (L/D) = 11 or more can be easily produced, and the present invention was completed. The BET specific surface area referred to here is the specific surface area measured by low-temperature nitrogen adsorption method, and ultrafine refers to the specific surface area of 10
Particles of m ² /g or more. Aspect ratio (L/
D) is obtained by measuring the ratio of length (L) and width (D) of many needle-like particles from photographs taken by electron microscopy, and averaging them. D) = 11 or more particles. Aragonite is an aragonite crystal determined by X-ray diffraction method.
Contains 55% or more. The ultrafine needle-shaped calcium carbonate of the present invention is
Carbonation reaction conditions including a calcium hydroxide suspension to which a limited crystal nucleating agent has been added, the concentration of the calcium hydroxide suspension, the temperature, the carbon dioxide concentration of the carbon dioxide-containing gas, and the introduction rate of the carbon dioxide-containing gas. This can only be achieved by keeping the value within a specific range. Although the factors leading to the production of the ultrafine needle-shaped aragonitic calcium carbonate of the present invention are not clear,
By combining barium or strontium salts as crystal nucleating agents to an aqueous suspension of calcium hydroxide with limited carbonation reaction conditions,
It is thought that it acts not only on the generation of crystal nuclei but also on the refinement of particles. In the present invention, a crystal nucleating agent is added to a calcium hydroxide aqueous suspension with a concentration of 15 to 40 WT% and a temperature of 32 to 60°C, and then a carbon dioxide-containing gas with a carbon dioxide concentration of 15 V% or more is added at a rate of 12 to 80/min. Kg Ca(OH) ₂ was introduced to carry out the carbonation reaction, and the specific surface area was 10 m ² /g or more, and the average dimension as determined by electron microscopy was length (L) =
A method for producing aragonitic calcium carbonate, which is characterized by producing extremely fine needle-shaped calcium carbonate having a width (D) of 0.7 to 1.5 μm, a width (D) of 0.01 to 0.2 μm, and an aspect ratio (L/D) of 11 or more. This is what we provide. The concentration of the calcium hydroxide aqueous suspension used in the present invention is 15 to 40 wt%, preferably 17 to 35 wt%. When the calcium hydroxide concentration is less than 15wt%, the aspect ratio of the needle-shaped particles becomes smaller,
Or the generation rate of needle-shaped particles decreases,
If it exceeds 40 wt%, the contact with carbon dioxide gas will not be uniform, and the variation in particle size will increase due to local reactions. In addition, the temperature of the calcium hydroxide aqueous suspension must be within the range of 32 to 60℃, and 32℃
If it is less than 60°C, irregularly shaped particles will be produced, and if it exceeds 60°C, the particles will grow large and the specific surface area will decrease. The crystal nucleating agents used in the present invention are barium and strontium chlorides, fluorides, hydroxides, oxides, sulfates, nitrates, phosphates, acetates, and oxalates. That is, barium chloride, strontium chloride, barium fluoride, strontium fluoride, barium hydroxide, strontium hydroxide, barium oxide, strontium oxide, barium sulfate, strontium sulfate, barium nitrate, strontium nitrate, barium phosphate, strontium phosphate,
These are barium acetate, strontium acetate, barium oxalate, and strontium oxalate. The amount of the crystal nucleating agent added is 0.001 to 0.5 mol, preferably 0.003 to 0.4 mol, per 1 mol of calcium hydroxide. When the amount added is less than 0.001 mol, the effect of grain refinement disappears, and even when it exceeds 0.5 mol, the effect of grain refinement remains unchanged, and the cost becomes extremely high and uneconomical. The carbon dioxide concentration of the carbon dioxide-containing gas used in the present invention is 15V% or more. Carbon dioxide concentration is 15V%
If it is less than 10 m 2 /g, the carbonation rate will be slow and the particle size of the product will be large, making it impossible to obtain extremely fine calcium carbonate with a specific surface area of 10 m ² /g or more. Carbon dioxide is
Carbon dioxide concentration of purified limestone firing waste gas 15~
A gas containing 40V% carbon dioxide can be used. The amount of carbon dioxide-containing gas introduced in the present invention is
12-80/min/Kg Ca(OH) ₂ . The amount of carbon dioxide gas introduced is 12/min/Kg Ca
If (OH) is less than ₂ , the stirring effect of the reaction system will be poor, and the particle size of the generated particles will become non-uniform due to local reactions, making it impossible to obtain ultrafine calcium carbonate with a specific surface area of 10 m ² /g or more. /min/Kg Ca
If it exceeds (OH) ₂ , gas containing carbon dioxide gas will be released outside the calcium hydroxide suspension before stirring the reaction system, and stirring will not take place and a large amount of carbon dioxide gas will be lost. Therefore, extremely fine calcium carbonate with a specific surface area of 10 m ² /g or more cannot be obtained. The amount of carbon dioxide-containing gas introduced in the present invention is such that it not only performs carbonation but also stirs the reaction system. Regarding the calcium carbonate of the present invention, the specific surface area is 10 m ² /
g or less, and the average dimensions by electron microscope observation are length (L) = 0.7 to 1.5 μm, width (D) = 0.01 to 0.2 μm,
Even if the aspect ratio (L/D) is 11 or more, even if it is outside the range, the reinforcing effect such as rigidity will be poor when blended into rubber, plastic, etc. The calcium carbonate of the present invention is obtained by filtering and dehydrating the suspension after the carbonation reaction, if necessary, to obtain a solid content concentration.
It may be used as a paste with a concentration of 40wt% or more.
Furthermore, this may be dried and pulverized to form a powdered product. Thus, the calcium carbonate according to the present invention can be used as crystal nucleating agents when carbonating an aqueous calcium hydroxide suspension. , acetate, or oxalate (1)
By adding seeds and carbonating under limited carbonation reaction conditions, it is possible to obtain a carbonaceous material containing 55% or more aragonite, mostly 80% or more, a specific surface area of 10 m ² /g or more, and an average particle size of long. Length (L) = 0.7 to 1.5 μm, width
(D)=0.01 to 0.2 μm, and ultrafine needle-shaped particles having a uniform particle size and an aspect ratio of 11 or more can be easily obtained. The calcium carbonate of the present invention can be used in paper, paint, ink,
It can be used in adhesives, etc., but it can also be especially added to rubber, plastics, etc. to provide a reinforcing effect that exhibits high rigidity. That is, it can be blended with rubber to give it high modulus, hardness, and high tensile strength, and it can be blended with plastic to give it high flexural modulus and high isot impact strength. Furthermore, it goes without saying that by subjecting the calcium carbonate obtained by the method of the present invention to a known surface treatment, it can be used as a filler to further improve its physical properties in terms of application. Next, the manufacturing method of the present invention will be specifically explained using examples. Example 1 1000 kg of calcium hydroxide aqueous suspension prepared at a concentration of 17 wt% and a temperature of 55°C was placed in a reaction vessel, and 0.01 Mol/Mol Ca(OH) ₂ of barium chloride was added thereto and mixed. % of carbon dioxide gas was introduced at a flow rate of 30/min/Kg Ca(OH) ₂ to perform a carbonation reaction, resulting in a carbonation reaction of 91% aragonite and a specific surface area of 26%.
m ² /g, ultrafine needle-shaped aragonitic calcium carbonate having a particle shape of 0.8 μm in length, 0.07 μm in width, and aspect ratio of 11 was obtained. The mother liquor of this calcium carbonate suspension was separated using a press dehydrator, then dried and pulverized to give a final product weighing approximately 220 kg. Example 2 1000 kg of calcium hydroxide aqueous suspension prepared at a concentration of 20 wt% and a temperature of 35°C was placed in a reaction vessel, and 0.03 Mol/Mol Ca(OH) ₂ of barium hydroxide was added thereto and mixed. A carbonation reaction was carried out by introducing a gas containing 30V% carbon dioxide gas at a flow rate of 15/min/Kg Ca(OH) ₂ , resulting in a carbonation reaction of 95% aragonite and specific surface area.
28m ² /g, particle shape length 0.7μm, width 0.04μm,
Ultrafine needle-shaped aragonitic calcium carbonate with an aspect ratio of 18 was obtained. The mother liquor of this calcium carbonate suspension was separated using a press dehydrator, then dried and pulverized to a final weight of about 260 kg. Example 3 1000 kg of calcium hydroxide aqueous suspension prepared at a concentration of 30 wt% and a temperature of 40°C was placed in a reaction vessel, and 0.2 Mol/Mol Ca(OH) ₂ of strontium acetate was added thereto and mixed. % of carbon dioxide gas was introduced at a flow rate of 60/min/Kg Ca(OH) ₂ to perform a carbonation reaction, resulting in 99% aragonite, a specific surface area of 15 m ² /g, and a particle shape of 1.3 μm in length and 0.08 in width. μm,
Ultrafine needle-shaped aragonitic calcium carbonate with an aspect ratio of 16 was obtained. The mother liquor of this calcium carbonate suspension was separated using a press dehydrator, then dried and crushed to produce a final product weighing 400 kg. Examples 4 to 9 Ultrafine needle-shaped aragonitic calcium carbonate was obtained in the same manner as in Example 3, except that the barium compounds or strontium compounds shown in Table 1 were added instead of strontium acetate. In addition, the aragonitic quality and specific surface area of the obtained calcium carbonate,
The particle shapes and aspect ratios are shown in Table 1.

[Table] Example 10 A carbonation reaction was carried out in the same manner as in Example 3 except that the carbon dioxide concentration of the carbon dioxide-containing gas was changed to ^50V %. Aragonitic calcium carbonate in the form of extremely fine needles having a length of 1.2 μm, a width of 0.07 μm, and an aspect ratio of 17 was obtained. Comparative Example 1 A carbonation reaction was carried out in the same manner as in Example 1 except that the concentration of the aqueous calcium hydroxide suspension was 5 wt%, and the results of analysis of the product are shown in Table 3. Comparative Example 2 A carbonation reaction was carried out in the same manner as in Example 2 except that the temperature of the calcium hydroxide aqueous suspension was 10°C.
The results of product analysis are shown in Table 3. Comparative Example 3 A carbonation reaction was carried out in the same manner as in Example 2 except that the temperature of the calcium hydroxide aqueous suspension was 70°C.
The results of product analysis are shown in Table 3. Comparative Example 4 A carbonation reaction was carried out in the same manner as in Example 1 except that no crystal nucleating agent was added to the calcium hydroxide aqueous suspension, and the results of analysis of the product are shown in Table 3. Comparative Examples 5-6 Using the additives shown in Table 2 instead of barium chloride
A carbonation reaction was carried out in the same manner as in Example 2 except that 0.05Mol/Mol Ca(OH) ₂ was added, and the results of analysis of the product are shown in Table 2.

[Table] Comparative Example 7 A carbonation reaction was carried out in the same manner as in Example 3 except that the concentration of the aqueous calcium hydroxide suspension was 45 wt%, and the results of analysis of the product are shown in Table 3. Comparative Example 8 A carbonation reaction was carried out in the same manner as in Example 1, except that the carbon dioxide concentration of the carbon dioxide-containing gas introduced into the calcium hydroxide aqueous suspension was 8%, and the results of analyzing the product were It is shown in Table 3. Comparative Examples 9-10 The amount of carbon dioxide-containing gas introduced into the calcium hydroxide aqueous suspension was 7/min/Kg Ca(OH) ₂
(Comparative Example 9) and 85/min/Kg Ca(OH) ₂
(Comparative Example 10) Same as Example 2 except that
The results of the carbonation reaction and product analysis are shown in the third column.
Shown in the table.

[Table] Application example 1 When applied as a filler for rubber 100 parts by weight of the invention of Example 1, 100 parts by weight of EPDM (trade name: Nippon Gosei EP21/EP579=70/30), 5 parts by weight of zinc white, stearin 1 part by weight of acid, 1 part by weight of accelerator CZ, 1.5 parts by weight of TT and 0.5 parts by weight of BZ, 1.5 parts by weight of sulfur, process oil (trade name;
Table 4 shows the results of kneading 10 parts by weight of Idemitsu PW380) and measuring the physical properties of the vulcanized rubber. Table 4 shows commercially available calcium carbonate as comparative product A (surface-treated colloidal calcium carbonate; 100% calcite, cubic shape,
The results of using the product instead of the present invention as specific surface area 16 m ² /g) and comparative product B (soft calcium carbonate; 100% calcite, spindle-shaped, specific surface area 5 m ² /g, aspect ratio 6) are also included. show.

[Table] As is clear from the results in Table 4, the product of the present invention has higher modulus and hardness, as well as tensile strength and greater reinforcing effect than the comparative product. Application example 2 When applied as a filler for plastics 50 parts by weight of the invention of Example 1 and 100 parts by weight of polypropylene resin (trade name: Sumitomo Noblen AW564, manufactured by Sumitomo Chemical) were roll-kneaded at 200°C for 10 minutes, and then formed into a sheet. Take it out. Next, it was made into pellets using a pelletizer, and a test piece was made using an injection molding machine (injection temperature 230°C).The results of measuring each physical property were
Shown in the table. Table 5 also shows the results when commercially available calcium carbonate was used as Comparative Product A and Comparative Product B in place of the product of the present invention.

[Table] The physical properties shown in Table 5 above were measured using the following methods: flexural modulus; ASTM D-790; Izot impact strength; ASTM D-256; Compared to other products, it has a high bending modulus and high Izot impact strength, and has a large reinforcing effect.

Claims (1)

[Claims] 1. After adding a crystal nucleating agent to an aqueous suspension of calcium hydroxide at a concentration of 15 to 40 wt% and a temperature of 32 to 60°C,
12 Carbon dioxide containing gas with a carbon dioxide concentration of 15V% or more
~80/min/Kg Ca(OH) ₂ is introduced to perform the carbonation reaction, and the BET specific surface area is 10 m ² /g or more, and the average dimension by electron microscopy is length (L) =
A method for producing aragonitic calcium carbonate, which is characterized by producing ultrafine needle-shaped calcium carbonate having a width (D) of 0.7 to 1.5 μm, a width (D) of 0.01 to 0.2 μm, and an aspect ratio (L/D) of 11 or more. 2. Aragonite according to claim 1, wherein the crystal nucleating agent is a chloride, fluoride, hydroxide, oxide, sulfate, nitrate, phosphate, acetate, or oxalate of barium and strontium. A method for producing quality calcium carbonate.