JPS59223225A - Manufacture of calcium carbonate - Google Patents

Abstract

PURPOSE:To manufacture easily needlelike or columnar hyperfine aragonite material calcium carbonate having a large specific surface area by adding a crystal nucleus forming agent to an aqueous suspension of calcium hydroxide having a proper concn. and by introducing gaseous CO2 at a proper temp. to cause a carbonation reaction. CONSTITUTION:A crystal nucleus forming agent is added to an aqueous suspension of calcium hydroxide having 8-40wt%, preferably about 10-35wt% concn. at 15-60 deg.C, and gaseous CO2 is introduced to cause a carbonation reaction. By the reaction, needlelike or columnar hyperfine calcium carbonate contg. >=about 55%, usually >=about 80% aragonite material and having >=10m<2>/g BET specific surface area is obtd. This calcium carbonate consists of uniform particles having about 0.2-1.5mum average length, about 0.01-0.2mum average width and >=about 7 aspect ratio. A halide or an oxygen compound of Ba or Sr is used as said crystal nucleus forming agent, and it is added by about 0.001-0.5mole per 1mole Ca(OH)2.

Description

[Detailed description of the invention] The present invention relates to a method for producing calcium carbonate.

For details, BET specific surface area (hereinafter referred to as specific surface area) 10-
The present invention relates to a method for producing ultrafine acicular aragonitic calcium carbonate having a size of 72 or more.・Calcium carbonate has been widely used as a filler or pigment in rubber, plastics, paper, paints, inks, adhesives, etc. Until now, calcium carbonate has a specific surface area of 6d/9 obtained by mechanically crushing limestone.
- Heavy calcium carbonate with a coarse particle size of less than 10 rr, obtained from a chemical reaction with a specific surface area of 10 rr? Precipitated calcium carbonate called light calcium carbonate, which is composed of spindle-shaped, calcite crystals, or columnar aragonite crystals with a particle size of less than /9 and slightly coarser, is produced and commercially available. However, the calcium carbonate that has been used so far has not been able to provide sufficiently satisfactory effects in terms of physical properties related to rigidity, such as hardness and flexural modulus, when mixed with rubber and plastics. For this reason, there is a strong desire for calcium carbonate in the form of ultrafine acicular aragonite particles to be incorporated into rubbers and plastics as a highly reinforcing calcium carbonate that imparts high rigidity.

Up until now, the method for producing columnar aragonitic calcium carbonate has been to react carbon dioxide gas with an alkaline calcium chloride aqueous solution under specific conditions (*Public Publication No. 45-22783).
, in the carbon dioxide reaction of an aqueous suspension of calcium hydroxide,
A method of dividing the carbonation process into three stages and adjusting the temperature and amount of carbon dioxide introduced at each stage to carry out the carbonation reaction (Japanese Patent Publication No. 55-51
No. 852) has been proposed, but the former cannot control the conditions for producing ultrafine particles and can only produce particles with a coarse grain size. In the latter case, aragonite crystalline calcium carbonate cannot be obtained, but even if it were obtained, it would only have a small specific surface area that does not fall into the extremely fine region. 2 The present inventors have conducted various studies on the production method of ultrafine acicular aragonitic calcium carbonate, and as a result, they added a crystal nucleating agent to an aqueous suspension of calcium hydroxide.
By introducing carbon dioxide gas into this and carrying out a carbonation reaction, calcium carbonate in the form of uniform ultrafine needle-shaped particles having an aragonitic quality of 55 mm or more and a high specific surface area of 10 m''/P or more can be easily produced. This led to the completion of the present invention. The BET specific surface area referred to here is a low-temperature nitrogen adsorption method, and ultrafine means a specific surface area of 10 r.
r? /9- or more particles. Aragonite quality is determined by X-ray diffraction.

The present invention has a concentration of 8 to 40 Wt% + temperature 15 = 6
A crystal nucleating agent is added when carbon dioxide gas is introduced into an aqueous suspension of calcium hydroxide at 0°C to carry out a carbonation reaction.

The present invention provides a method for producing calcium carbonate, which is characterized by producing extremely fine needle-shaped aragonitic calcium carbonate.

The concentration of calcium hydroxide used in the present invention is 8~a@v
t ratio, preferably 10 to 35 wt1. If the concentration of icalcium hydroxide is less than 8vrt4, no columnar particles can be obtained, and if it exceeds 40wt4, the contact with carbon dioxide gas will not be uniform, resulting in large variations in particle size based on one local reaction. Also, the temperature of the calcium hydroxide aqueous suspension is 1
It is necessary to carry out the heating within the range of 5 to 60°C; if it is less than 15°C, irregularly shaped particles will be produced, and if it is higher than 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 halides and oxygen compounds.

Compounds such as oxyacid salts and organic acid salts, such as chlorides and fluorides of barium and strontium.

hydroxides, oxides, sulfates, nitrates, phosphates.

Examples include compounds such as acetate and thiolate. The amount of crystal nucleating agent added is 0.0 per mole of calcium hydroxide.
01 to 0.5 mol, preferably 0.005 to 0.4 mol. If the amount added is less than 0.001 mol, the effect of grain refinement is lost, and even if it exceeds 0.5 mol, the effect of grain refinement remains unchanged, but the cost becomes extremely high2, which is uneconomical.

The amount of carbon dioxide introduced in the present invention is 5 to BO4/m4n.
/KfOa(OH)2 is appropriate, and the carbon dioxide concentration is preferably Jf1sv4 or higher.

The calcium carbonate of the present invention may be used as a paste having a solid content of 40 parts or more by dehydrating the suspension after the carbonation reaction, if necessary, and then drying and pulverizing this. It may also be finished into a powdered product.

Thus, the calcium carbonate according to the present invention can be produced by adding a barium compound or a strontium compound as a crystal nucleating agent when carbonating an aqueous suspension of calcium hydroxide to obtain an aragonitic substance of 55 or higher, mostly 80%.
Including the above, specific surface area 1゜-/? The average dimensions of the above nine particle shapes are length L) = 0.2 to 1.5 p, m, width (D) = 0.01 to 0.2 pm, and uniform particle size with an aspect ratio of 7 or more. Ultrafine needle-shaped calcium carbonate could be easily obtained. The aspect ratio referred to here is based on a photograph taken by electron microscopy.

The ratio between the length (L) and the width (D) of a large number of particles is measured and averaged.

The calcium carbonate of the present invention can be used in paper, paint, and ink.

It can be used in adhesives, etc., but it can also be especially blended with rubber, plastics, etc. to provide a reinforcing effect that exhibits high rigidity. That is, when blended with rubber, it provides high modulus, hardness, and high tensile strength, and when blended with plasti 1.1, it provides high flexural modulus and high isotonic strength.

Furthermore, 1. carbonic acid obtained by the method of the present invention. A
It goes without saying that by subjecting silium to a known surface treatment, it can be used as a filler to further improve its physical properties in applications.

Next, the manufacturing method of the present invention will be specifically explained using examples.

Example 1 Concentration 1 ovt, 4. A calcium hydroxide aqueous suspension tooKf adjusted to a temperature of 55°C was placed in a reaction vessel.

To this, barium chloride 0.01 Mol/Mol Ca (
After adding and mixing OH)2, carbon dioxide gas with a concentration
, specific surface area 25 rr? /J9 particle shape is 0.8 in length
An extremely fine needle-shaped aragonitic calcium carbonate having a width of 0.08 μm and an aspect ratio of 10 was obtained. The mother liquor of this calcium carbonate suspension was separated using a press dehydrator, and then dried and pulverized to a final product of approximately 130 Kt.

Example 2 Concentration 20wt4. A 1.000Kf suspension of carlum hydroxide in water prepared at a temperature of 20°C was placed in a reaction vessel, and barium hydroxide 0.03Mol/Mol 0a(OH)2 was added to the reaction vessel.
After adding and mixing, carbon dioxide gas with a concentration xov4 was introduced at a flow rate of 1547/min/boa (OH)2 to perform a carbonation reaction.

Aragonite 92mm, specific surface area 30m'/ψ9, particle shape length 0.6μm, medium 0.03μm, aspect ratio 2
A very fine needle-shaped aragonitic calcium carbonate having a particle size of 0 was obtained. The mother liquor of this calcium carbonate suspension was separated using a press dehydrator, and then dried and pulverized for about 260 cycles.

Example 5 Concentration 31. 1.0OOKF of calcium hydroxide aqueous suspension prepared at a temperature of 40°C was placed in a reaction vessel, and stoytium acetate 0.2 Mol/Mol 0a(OH)2 was added to the reaction vessel.
After mixing, carbon dioxide gas with a concentration of 30V% was introduced at a flow rate of 60 l/min/Kfoa (OH)2 to perform a carbonation reaction, resulting in aragonitic material of 99% and specific surface area of 15%.
tr? IP, particle shape is 1.3 μm in length and 0.08 μm in width.
A very fine needle-shaped aragonitic calcium carbonate having an aspect ratio of 16 was obtained. This large suspension of Calcilla carbonate is separated from the mother liquor using a press dehydrator, and then dried.

It was crushed to a finish of approximately 400Kf.

Comparative Example 1 A carbonation reaction was carried out in the same manner as in Example 1 except that the concentration of the calcium hydroxide aqueous suspension was 5wt4.

Analysis of the product revealed that it was spindle-shaped calcitic calcium carbonate.

Comparative Example 2 A carbonation reaction was carried out in the same manner as in Example 2, except that the temperature of the aqueous calcium hydroxide suspension was 10°C.

As a result of analyzing the product, it was found to be calcitic calcium carbonate with a mixture of cubic particles and spindle-shaped particles.Comparative Example 3 Example 2 except that the temperature of the calcium hydroxide aqueous suspension was 70°C. Carry out the carbonation reaction in the same manner as above.

As a result of analyzing the product, the specific surface area was 3rr? /f- acicular aragonitic calcium carbonate.

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. Analysis of the product revealed that it was calcium carbonate of five aragonite types. Ta.

Application Example When applied as a filler for rubber 100 parts by weight of the invention of Example 1, EPDM (Product name 1 Nippon Gosei EP
21/EP57C=70/30) 100 parts by weight], 5 parts by weight of zinc white, 1 part by weight of stearic acid, 1 part by weight of accelerator 0, 1.5 parts by weight of TT'Th! HiBZ0.5 ii
1.5 parts by weight of sulfur, process oil (product name 9,
Table 1 shows the results of kneading 10 parts by weight of Idemitsu PW380) and measuring the vulcanized rubber material. Table 1 shows commercially available calcium carbonate as Comparative Product A (surface-treated colloidal calcium carbonate; 100% calcite, cubic shape.

Specific surface area 16rr? /P) and comparative product B (light calcium carbonate; calcitic 1004, spindle-shaped, specific surface area 5 m'/P, aspect ratio 6) in place of the present invention. The results are also shown.

Table 1 As is clear from the results in Table 1, the products of the present invention have higher modulus and higher hardness than the comparative products.

・Moreover, it exhibits high tensile strength and has a large reinforcing effect.

Application example 3 When applied as a filler for plastics 50 parts by weight of the invention of Example 1 and polypropylene resin (trade name: Sumitomo Noprene AW564, manufactured by Sumitomo Chemical) 1
After rolling 00 parts by weight at 200° C. for 10 minutes, the sample was taken out in the form of a sheet. Next, it was pelletized using a pelletizer, and a test piece was prepared using an injection molding machine (injection temperature 230"C). The results of measuring each physical property are shown in Table 2. Table 2 shows the comparison of commercially available calcium carbonate. The results obtained when the amount A and the comparative amount B mentioned above were used in place of the product of the present invention are also shown.

The physical properties listed in Table 2 above are measured using the following flexural modulus i ASTM D-790 A1
Zod impact strength: As is clear from the results in Table 2, the ASTM D-256 wood invention product has a higher flexural modulus and higher Izot impact strength than the comparative product, and has a strong reinforcing effect.

[Brief explanation of drawings]

FIG. 1 shows an electron micrograph of calcium carbonate obtained by the method of the present invention. Figure 1 (and above) Procedural amendment C method) % formula % 1. Indication of the case 1982 Patent application No. 94598 Z Title of the invention Method for producing calcium carbonate 5 Relationship with the amended party Patent applicant address 4-78 Motohama-cho, Amagasaki-shi Delete the entire text and figures in the column "Brief explanation of drawings" on the page. c or more)

Claims (2)

[Claims] (1) Concentration 8-40vrt4. Temperature 15-60°C
A crystal nucleating agent is added when carbonation reaction is carried out by introducing 1 ton of liquefied calcium hydroxide in water and carbon dioxide gas. A method for producing calcium carbonate, which comprises producing ultrafine acicular aragonitic calcium carbonate having a BET specific surface area of 10 m''72 or more. (2) The method for producing calcium carbonate according to claim 1, wherein the crystal nucleating agent is a barium compound or a strontium compound.