JPH0346404B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to BET specific surface area (hereinafter referred to as specific surface area)
The present invention relates to a method for producing ultrafine calcium carbonate of 60 m ² /g or more. Specifically, it relates to a method for producing extremely fine calcium carbonate with a highly developed chain structure. Calcium carbonate, which has been widely used as a filler for rubber and plastics or as a pigment for paints and inks, includes heavy calcium carbonate obtained by mechanically crushing coal stone and precipitated calcium carbonate obtained from chemical reactions. Precipitated calcium carbonate includes light calcium carbonate with a specific surface area of less than 10 m ² /g and 10 m ² /g.
It is divided into ultrafine calcium carbonate with a size of more than 100 g. Precipitated calcium carbonate is generally produced by a carbonation reaction in which carbon dioxide gas is blown into an aqueous suspension of calcium hydroxide, and the specific surface area is 10 m by adjusting conditions such as concentration, temperature, and amount of carbon dioxide gas blown as appropriate. Light calcium carbonate with large crystal particles of less than ² /g and ultrafine calcium carbonate with small crystal particles with a specific surface area of 10 m ² /g or more are manufactured and commercially available. Among these, ultrafine calcium carbonate with a specific surface area of 10 m ² /g or more is produced in the carbonation process under conditions where a relatively large amount of carbon dioxide gas is blown, but its fineness has so far been approximately 50 to 60 m 2 /g in terms of specific surface area. Very fine calcium carbonate with a specific surface area of up to ² /g is not manufactured or commercially available. Furthermore, even if obtained experimentally, only the so-called aggregate particles of calcium carbonate, in which crystal particles are tightly aggregated in the shape of grape clusters, can be obtained, and these powders can be used as they are in organic polymers such as rubber, plastics, paints, and inks. Even when mixed with molecules and solvents, the dispersibility is very poor, so it has never been commercialized to date. Therefore, in order to improve the dispersibility of ultrafine calcium carbonate, a chain-shaped calcium carbonate with crystal particles similar to Mitarashi dango was studied and investigated. One of these methods is to add zinc salt, which becomes zinc hydroxide through hydrolysis, during the carbonation reaction of an aqueous suspension of calcium hydroxide, when it has denatured into a viscous glue-like emulsion during carbonation ( Special Publication No. 37-519), method of adding water-soluble magnesium salt (Special Publication No. 47-22944)
), a method of adding sulfuric acid or water-soluble sulfates (however, excluding zinc and magnesium) (Japanese Patent Publication No. 50-3995), and a method of adding sulfuric acid to an aqueous suspension of calcium hydroxide to carry out a carbonation reaction (Special Publication No. 50-3995). Kosho 56-
40118) have been proposed. However, these methods are less efficient than conventional methods of simply adjusting the reaction conditions when carbonating an aqueous suspension of calcium hydroxide, that is, the concentration, temperature, and amount of carbon dioxide gas blown into the solution. , the particles have become somewhat finer, and as a result, a small number of particles that have grown in a chain form can be observed, but most of them are large aggregates of calcium carbonate that have secondary condensation in the shape of grape clusters. Even when organic polymers are mixed into a solvent, it is difficult to obtain a completely satisfactory dispersion. Furthermore, a method has been proposed in which the carbonation reaction is started by first blowing carbon dioxide into a calcium hydroxide suspension containing a chelating agent, and then a water-soluble metal salt is added during carbonation (Japanese Patent Publication No. 56-26613). However, even with this method, the crystal particles are made finer, and chain particles are also observed, but rather the chain particles form secondary aggregates in the form of chain bundles, where several to dozens of chain particles are bundled. However, the dispersibility in organic polymers and solvents is still not sufficient. Calcium carbonate is used as a filler for rubbers and plastics, or as a pigment for paints and inks, and it is strongly desired to improve the physical properties of its compounds. Waiting. For this reason, calcium carbonate, used as a filler or pigment in rubber, plastics, paints, inks, etc., has finer particles that do not solidify during the carbonation process, dehydration, or drying process, and are If it can be broken down to primary particles by mechanical grinding, it can be blended into rubber, plastics, etc. to not only improve dispersibility but also to further improve physical properties such as reinforcing properties. The present inventors have developed ultrafine chain particles with a specific surface area of 60 m ² /g or more, and the chain particles do not aggregate into lumps or bundles, and can be crushed with an ordinary crusher and have good dispersibility. As a result of various studies on calcium carbonate, we have found that when carbonating an aqueous suspension of calcium hydroxide, by appropriately selecting the additive chemicals and reaction conditions, it is possible to form ultrafine chain-like structures with a specific surface area of 60 m ² /g or more. The inventors discovered that highly developed calcium carbonate can be easily obtained and completed the present invention. The carbonation rate referred to herein is defined by the following equation, where W is the weight of calcium carbonate in the reaction solution and _W is the weight of calcium hydroxide. Carbonation rate=W/W+W ₁ ×100 BET specific surface area is a low temperature nitrogen adsorption method. The particle shape is determined by electron microscopy observation. In producing calcium carbonate with a specific surface area of 60 m ² /g or more, the present invention involves adding a crystal nucleating agent to an aqueous suspension of calcium hydroxide, and then adding carbon dioxide gas with a concentration of 15 V% or more at a flow rate of 40/min/Kg Ca (OH) ₂ or more, and carbonation reaction is carried out by adding a chain particle formation promoter until the carbonation rate reaches 40%. A manufacturing method is provided. By adding the crystal nucleating agent to the calcium hydroxide aqueous suspension before the carbonation reaction, ultrafine particles with a large specific surface area can be obtained. Even if this crystal nucleating agent is added during the carbonation reaction, a product with a larger specific surface area than that added before the carbonation reaction cannot be obtained. When the chain particle formation promoter is added up to a carbonation rate of 40%, the effect of forming chains is large, and the formed chain particles are less likely to aggregate. When the chain particle formation promoter is added before the crystal nucleation agent, aggregates of chain particles are formed. Furthermore, if it is added after the carbonation rate is 40%, the effect of forming chains will be small, and the dehydrated and dried product will become hard after the carbonation reaction is completed. The crystal nucleating agent used in the present invention is hydrochloric acid, sulfuric acid,
Examples include mineral acids such as nitric acid, lower carboxylic acids such as formic acid, acetic acid, and propionic acid and/or their ammonium salts, polyhydric alcohols such as sorbitol and pentaerythritol, and sucrose. Chain particle formation promoters used in the present invention include hydroxycarboxylic acids such as citric acid and malic acid, polyhydroxycarboxylic acids such as gluconic acid and tartaric acid, aminocarboxylic acids such as ethylenediaminetetraacetic acid and nitrilotriacetic acid, sodium tripolyphosphate, Chelating agents such as polyphosphates such as sodium hexametaphosphate and polymeric polycarboxylic acids such as isobutylene-maleic acid copolymers, styrene-maleic acid copolymers, acrylic acid-maleic acid copolymers, and polyacrylic acid. Examples include anionic polymer compounds that are alkali metal salts and ammonium salts. The amount of the crystal nucleating agent used in the present invention is 0.5 to 15 parts by weight per 100 parts by weight of calcium hydroxide.
Preferably it is 1 to 12 parts by weight. When the amount added is less than 0.5 part by weight, the specific surface area of the particles produced becomes small. If the amount added exceeds 15 parts by weight, irregularly shaped particles will be generated. The amount of chain particle formation promoter used in the present invention is 0.05 to 8 parts by weight per 100 parts by weight of calcium hydroxide.
Parts by weight, preferably 0.1 to 7 parts by weight. If the amount added is less than 0.05 part by weight, fewer particles will form a chain. If the amount added exceeds 8 parts by weight, aggregates of chain particles will be formed and the specific surface area will decrease. The carbon dioxide concentration used in the present invention needs to be 15V% or more. If the carbon dioxide concentration is less than 15V%, coarse particles will be generated. The amount of carbon dioxide gas used in the present invention is 40/
min/Kg Ca(OH) ₂ or more, preferably 50-150
/min/Kg Ca(OH) ₂ . When the carbon dioxide gas flow rate is less than 40/min/Kg Ca(OH) ₂ , a condensate of chain particles is formed. The concentration of the calcium hydroxide aqueous suspension used in the present invention is 2 to 8 Wt.%, preferably 3 to 7 Wt.%. If the concentration is less than 2 Wt.% or more than 8 Wt.%, the formation of the generated particles will be non-uniform and the specific surface area will also become small. The temperature of the calcium hydroxide aqueous suspension used in the present invention is 0 to 25°C, preferably 3 to 25°C. When the temperature exceeds 25°C, coarse particles begin to form. After the carbonation reaction, the calcium carbonate of the present invention
Press dehydration was carried out, and this was dried and ground to obtain a powdered product. In this way, the calcium carbonate of the present invention can be made into a polar material with a specific surface area of 60 m ² /g or more depending on the order and timing of addition of the selected additive chemicals added to the calcium hydroxide aqueous suspension and the severe conditions during carbonation. For the first time, we have obtained a product in which the ultrafine chain particles are dispersed in a single form without agglomeration. Further, the calcium carbonate of the present invention was a bulky powder that was smooth to the touch with the tip of a finger. The calcium carbonate of the present invention is easily dispersed when compounded as a filler in rubber or plastic, and the compound provides high tensile strength and high stiffness. When kneaded as an extender pigment in paints, it provides good early dispersion, making the paint film smooth and giving it high gloss. It goes without saying that by further subjecting the calcium carbonate obtained by the method of the present invention to a known surface treatment, it can be used as a filler or pigment to further improve its physical properties such as dispersibility and reinforcing properties. 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 6 Wt.% and a temperature of 15°C was placed in a reaction vessel, and 50 kg of a sulfuric acid aqueous solution adjusted to a concentration of 10 Wt.% was added and mixed. Carbon dioxide flow rate 80
/min/Kg Ca(OH) ₂ injection, carbonation rate 15
Carbonate up to %. Next, 3.6 kg of an aqueous sodium citrate solution prepared to a concentration of 10 Wt.% was added to carry out a carbonation reaction, yielding extremely fine calcium carbonate with a highly developed chain structure. The mother liquor of this calcium carbonate suspension was separated using a press dehydrator, then dried and pulverized to produce a final product weighing approximately 80 kg. The results of testing the obtained preform of the present invention are shown in Table 1, and an electron micrograph of chain calcium carbonate is shown in FIG.
Note that Table 1 also shows the results for the products obtained in Examples 2 to 4. Example 2 1000 kg of an aqueous calcium hydroxide suspension prepared at a concentration of 4 Wt.% and a temperature of 20°C was placed in a reaction vessel, and 28 kg of acetic acid aqueous solution prepared at a concentration of 10 Wt.% was added and mixed, and then the suspension was adjusted to a concentration of 35 V%. The flow rate of carbon dioxide gas is 50
/min/Kg Ca(OH) ₂ injection, carbonation rate 25
Carbonate up to %. Next, an anionic polymer compound (trade name: Isoban,
A carbonation reaction was carried out by adding 20 kg of an aqueous solution (sodium salt of isobutylene-maleic anhydride copolymer, manufactured by Kuraray Co., Ltd.) to obtain extremely fine calcium with a highly developed chain structure. 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 53 kg. Example 3 1000 kg of calcium hydroxide aqueous suspension prepared at a concentration of 7 Wt.% and a temperature of 18°C was placed in a reaction vessel, and 10.5 kg of a sorbitol aqueous solution prepared at a concentration of 10 Wt.% was added to the reaction vessel.
is added and mixed, and then carbonated by blowing carbon dioxide gas with a concentration of 35V% at a flow rate of 100/min/Kg Ca(OH) ₂ to a carbonation rate of 7%. Next, 7 kg of disodium ethylenediaminetetratetraacetate adjusted to a concentration of 5 Wt.% was added to carry out a carbonation reaction. A highly developed chain of extremely fine calcium carbonate 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 94 kg. Example 4 1000 kg of calcium hydroxide aqueous suspension adjusted to a concentration of 5 Wt.% and a temperature of 12°C was placed in a reaction vessel, and 25 kg of a sucrose aqueous solution adjusted to a concentration of 10 Wt.% was added and mixed. % carbon dioxide flow rate
120/min/Kg Ca(OH) ₂ injection, carbonation rate
Carbonate up to 18%. Next, 25 kg of sodium tripolyphosphate aqueous solution adjusted to a concentration of 10 Wt.% was added to carry out a carbonation reaction. A highly developed chain of extremely fine calcium carbonate 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 67 kg.

[Table] The hardness of dry lumps before pulverization is determined from hard to hard.
It was rated as ``slightly hard'' and ``soft.'' From the results shown in Table 1 and FIG. 1, it is clear that the product of the present invention is extremely fine calcium carbonate with a highly developed chain structure. Comparative Examples 1 to 5 Sulfuric acid and sodium citrate were added to the calcium hydroxide aqueous suspension at the same time (Comparative Example 1), sulfuric acid was not added (Comparative Example 2), and sodium citrate was not added (Comparative Example 3). ), the same as Example 1 except that sodium citrate was added instead of sulfuric acid, sulfuric acid was added instead of sodium citrate (Comparative Example 4), or sulfuric acid and sodium citrate were not added at all (Comparative Example 5). Table 2 shows the results of testing the product of Comparative Example obtained by carrying out a carbonation reaction, and FIG. 2 shows an electron micrograph of the chain bundled calcium carbonate of Comparative Example 4. Table 2 also shows the results for the products obtained in Comparative Examples 6 to 12. Comparative Examples 6 to 8 Add 3 kg of a sulfuric acid aqueous solution with a concentration of 10 Wt.% (Comparative Example 6), add 0.2 kg of a sodium citrate aqueous solution with a concentration of 10 Wt.% (Comparative Example 7), or add a sodium citrate solution with a carbonation rate of 50 % (comparative example 8), in the same manner as in Example 1,
A carbonation reaction was carried out. Comparative Examples 9 to 12 Either the concentration of the calcium hydroxide aqueous suspension is 10 Wt.% (Comparative Example 9), the temperature of the calcium hydroxide aqueous suspension is 30°C (Comparative Example 10), or the carbon dioxide gas Carbonation was carried out in the same manner as in Example 3, except that the concentration was 10V% (Comparative Example 11) or the carbon dioxide gas blowing rate was 30/min/Kg Ca(OH) ₂ (Comparative Example 12). The reaction was carried out.

[Table] Reference example 1 100 parts by weight of the invention of Example 1, 100 parts by weight of SBR1502, 5 parts by weight of zinc white, 1 part by weight of stearic acid,
Accelerator DM 1.2 parts by weight, TT 0.2 parts by weight and sulfuric acid 2 parts
Table 3 shows the results of kneading parts by weight and measuring the physical properties of the vulcanized rubber. Table 4 shows the calcium carbonate of Comparative Examples 3 and 4, commercially available calcium carbonate, comparative commercial product A (surface-treated calcium carbonate, cubic shape, specific surface area 50 m ² /g), comparative commercial product (soft calcium carbonate, spindle). The results are also shown in terms of surface area and specific surface area of 5 m ² /g) when used in place of the present invention.

[Table] Dispersibility evaluation: The cross section of the vulcanized rubber was judged by the naked eye based on the number of lumps. The evaluation was ``◎'', ``○'', ``△'', ``x'', and ``XX'' from the best fraction. As is clear from the results in Table 3, the product of the present invention has very good dispersibility, high modulus, high tensile strength, and high hardness compared to the comparative example calcium carbonate and the comparative commercially available calcium carbonate. It has a great reinforcing effect.

[Brief explanation of drawings]

Figure 1 shows the extremely fine particle structure of calcium carbonate well developed in the form of chains obtained in Example 1 using the method of the present invention, and Figure 2 shows the particle structure of the calcium carbonate in the form of chain bundles obtained in Comparative Example 4. These are electron micrographs showing each.

Claims (1)

[Claims] 1. In producing calcium carbonate with a BET specific surface area of 60 m ² /g or more, a crystal nucleating agent is added to an aqueous suspension of calcium hydroxide, and then carbon dioxide gas with a concentration of 15 V% or more is added at a flow rate of 40 m 2 /g. /min/Kg Ca(OH) ₂ or more is blown into the carbonation reaction by adding a chain particle formation promoter until the carbonation rate reaches 40%. A method for producing calcium carbonate. 2. Claim 1 in which the crystal nucleating agent is a mineral acid, a lower carboxylic acid and/or an ammonium salt of these acids, a polyhydric alcohol, and a sucrose.
The method for producing calcium carbonate described in Section 1. 3. The method for producing calcium carbonate according to claim 1, wherein the chain particle formation promoter is a chelating agent or an anionic polymer compound.