JPH0451488B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a novel vaterite-type calcium carbonate having the characteristics of being hollow and spherical, and a method for stabilizing the same. [Prior Art] Calcium carbonate has three crystal polymorphisms: calcite, which is a rhombohedral crystal, aragonite, which is rod-shaped, and vaterite, which is spherical. It has long been well known that by spheroidizing powder, various physical properties of the powder can be improved, such as improved filling and dispersibility, and reduced abrasion. In this field, spherical vaterite-type calcium carbonate has attracted attention, and various production methods have been proposed. Japanese Patent Publication No. 43-25148 and Japanese Patent Publication No. 48-35159 disclose a method for synthesizing spherical vaterite-type calcium carbonate by blowing carbon dioxide into an aqueous solution of calcium salt. Further, JP-A-55-95617 discloses a method for producing spherical vaterite-type calcium carbonate in an aqueous solution reaction between a calcium salt and a carbonate under control of the reaction concentration and reaction temperature. Tokukai Akira
No. 61-168524 discloses a method for producing spherical calcium carbonate by blowing carbon dioxide into calcium hydroxide containing dissolved polyphosphate. However, with these methods, although it is possible to produce spherical vaterite-type calcium carbonate, it is not possible to form it into a hollow structure, which is a feature of the present invention. The interfacial reaction method (Nakahara, Tazawa, Miya: Journal of the Chemical Society of Japan, 5 , 732
(1976)), but it has the drawback of being too complicated as an industrial production method because it requires a centrifugal separation operation. As mentioned above, at present, an industrial method for producing hollow, spherical vaterite-type calcium carbonate has not yet been established. On the other hand, spherical vaterite-type calcium carbonate does not change its crystal shape at room temperature and pressure unless water is present. However, in the presence of water, it easily loses its spherical shape and transforms into the stable rhombohedral calcite phase. For this reason, various methods for stabilizing spherical vaterite-type calcium carbonate have been proposed. JP-A-55-95617 discloses a method of stabilizing the surface of spherical vaterite-type calcium carbonate by treating it with higher fatty acids, but the problem is that the treatment with higher fatty acids greatly deteriorates the dispersibility in water. occurs. Furthermore, JP-A No. 57-92520 discloses a method of adding divalent metal ions other than calcium when producing spherical vaterite-type calcium carbonate through an aqueous reaction between calcium salt and carbonate. The effect is insufficient. Furthermore, JP-A-57-92521 discloses a method of heat-treating spherical vaterite-type calcium carbonate at a temperature of 400 to 800°C to transform it into spherical lateral calcite. There are problems such as problems and increased heat treatment costs. As mentioned above, an economically viable industrial stabilization method for spherical vaterite-type calcium carbonate has not yet been established. [Problems to be Solved by the Invention] As described above, an industrial method for producing hollow and spherical vaterite-type calcium carbonate and a method for stabilizing the same have not yet been established. The present invention is made of vaterite-type calcium carbonate, which is spherical, has excellent filling properties and dispersibility, has low abrasion properties, and has a low specific gravity because the inside of the particle is hollow, and is chemically stable. The aim is to provide an industrial manufacturing method. [Means and effects for solving the problem] As a result of intensive research into the method for producing hollow and spherical calcium carbonate, the present inventors have found that calcium chloride or nitric acid is contained in specific alcohols that have no or low solubility in water. A method in which calcium is dissolved and an aqueous carbonate solution is dropped into the solution and mixed to create a water-in-oil emulsion in which the continuous phase is alcohol and the dispersed phase is water, and calcium carbonate is generated at the interface between alcohol and water. It was discovered that medium and spherical calcium carbonate can be easily produced by this method. The alcohol used in the present invention includes:
Alcohols that can dissolve calcium chloride or calcium nitrate but have no solubility in water or are limited to small alcohols, specifically butanol (1-butanol, 2-butanol, isobutanol), pentanol (1-pentanol) ,2
-Pentanol, 3-pentanol, 2-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-1-butanol, 3-methyl-
2-butanol) is used. As the carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate, etc. can be used. Put alcohol in which calcium chloride or calcium nitrate is dissolved into a reaction vessel equipped with a stirrer,
Add the carbonate aqueous solution dropwise while stirring. The volume ratio of alcohol and carbonic acid aqueous solution can be set to any desired volume ratio within a range where alcohol can maintain a continuous phase. The molar ratio of carbonate ions in water/calcium ions in alcohol is preferably 0.1 to 10. The optimum molar ratio is 1. Although an emulsifier is not necessarily necessary in this reaction for producing hollow and spherical vaterite type calcium carbonate, an emulsifier having an HLB of 6 to 15 can be used. The particle size of the calcium carbonate of the present invention can be controlled by changing the alcohol/water volume ratio, the degree of stirring, and the type and amount of the emulsifier added. Furthermore, the degree of hollowness can be controlled by changing the concentration of calcium ions in alcohol and the concentration of carbonate ions in water, and also by changing the volume ratio of alcohol/water, the degree of stirring, and the type and amount of emulsifier added. It can be controlled. Next, the hollow and spherical calcium carbonate obtained in claim 1 is of the vaterite type, and can be used in areas where there is no moisture. However, in the presence of moisture, the calcium carbonate transforms to a rhombohedral calcite type, and the hollow, spherical shape characteristic of the calcium carbonate of the present invention is lost, which limits its uses. As a result of intensive studies on stabilizing hollow and spherical vaterite-type calcium carbonate, the present inventors found that by treating the surface of the calcium carbonate with a specific acid to make the surface inactive, it was possible to stabilize the calcium carbonate in water. Also hollow/
It was discovered that the spherical shape could be maintained. Specifically, phosphorus oxoacids such as orthophosphoric acid, pyrophosphoric acid, hypophosphorous acid, phosphorous acid, pyrophosphorous acid, hypophosphoric acid, polyphosphoric acid, metaphosphoric acid, and ultraphosphoric acid can be used. Stabilization is achieved by dropping an aqueous phosphorus oxoacid solution into an aqueous suspension of hollow/spherical vaterite-type calcium carbonate and mixing. The amount of the phosphorus oxoacid added is preferably 0.1% by weight or more based on the absolute dry weight of the hollow/spherical vaterite type calcium carbonate. 0.1
When the amount is less than % by weight, the stabilizing effect is small. It is thought that the surface layer of the hollow/spherical vaterite-type calcium carbonate reacts with the phosphorus oxo acid and changes into a poorly soluble or insoluble phosphorus oxo acid calcium salt, thereby stabilizing it. [Example] Hereinafter, the present invention will be explained in more detail with reference to Examples. However, the present invention is not limited in any way by the contents shown in the examples. Example 1 In Examples 1-1 to 1-7, 700 ml of pentanol or butanol in which a predetermined amount of calcium chloride was dissolved was placed in a homogenizer, and while stirring with the homogenizer, 300 ml of water in which a predetermined amount of sodium carbonate was dissolved was added. The solution was added dropwise, and stirring was continued for 5 minutes after the completion of the addition. The molar ratio of calcium ions/carbonate ions was set to 1. The produced calcium carbonate was separated, washed with anhydrous methanol, air-dried, and its shape and crystal type were investigated. The shape was observed using a scanning electron microscope, and the crystal form was examined using an X-ray diffraction device. Example 1-8 was carried out in the same manner as Example 1-1 except that the calcium salt dissolved in 1-pentanol was changed to calcium nitrate. Examples 1-9, 10, and 11 were carried out in the same manner as in Example 1-1, except that the carbonate to be dissolved in water was changed to potassium carbonate, ammonium carbonate, or sodium hydrogen carbonate. As a result of electron microscope observation and X-ray diffraction analysis,
As shown in Table 1, spherical vaterite type calcium carbonate was produced in all of Examples 1-1 to 1-11.

【table】

[Table] Example 2 In Examples 2-1 to 2-9, various phosphorus oxoacids were added dropwise to the aqueous suspension of spherical vaterite-type calcium carbonate produced in Example 1-1 to stabilize calcium carbonate. I processed it. After treatment, the calcium carbonate was separated and placed in hot water at 80°C. Samples were taken at predetermined intervals to examine the transition rate from vaterite type to calcite type by X-ray diffraction, and the remaining vaterite type calcium carbonate was determined. The rate was calculated. The vaterite residual rate was calculated using the following formula. f (c) = I ₁₀₄ (c) / I ₁₁₀ (v) + I ₁₁₄ (v) + I ₁₀₄ (c) f (v) = I - f (c) Vaterite residual rate (%) = 100 × f (v) For example, I ₁₀₄ (c) is the X-ray peak intensity at the 104 plane of calcite, and I ₁₁₀ (v) is the 110 peak intensity of vaterite.
This is the X-ray peak intensity at the surface. Figure 1 shows the crystal structure of hollow and spherical vaterite type calcium carbonate obtained in Example 2-1.
This is a 5000x electron micrograph, and Figure 2 is Example 2.
Shows the crystal structure of the hollow and spherical vaterite type calcium carbonate obtained in -1, which was crushed by ultrasonic waves.
This is a 10,000x electron micrograph, in which the central particle is partially destroyed and the voids inside can be observed. Examples 2-10 and 11 were carried out in the same manner as in Example 2-1 except that the amount of phosphorus oxoacid added was changed. As shown in the results in Table 2, it can be seen that spherical vaterite type calcium carbonate is stabilized by treatment with various phosphorus oxoacids. Note that Example 1
The spherical vaterite type calcium carbonate obtained in Examples -2 to 1-11 could also be stabilized by the same treatment.

【table】

[Table] *% of solid weight of spherical vaterite calcium carbonate.
Example 3 700 ml of 1-pentanol containing a predetermined amount of dissolved calcium chloride was placed in a homogenizer, and while stirring, 300 ml of water containing a predetermined amount of sodium carbonate was dissolved.
ml was added dropwise, and after the addition was completed, stirring was continued for 5 minutes.
The molar ratio of calcium ions/carbonate ions was set to 1. In Examples 3-1 to 3-4, spherical vaterite-type calcium carbonate was prepared by changing the dissolved amounts of calcium chloride and sodium carbonate. After filtering the prepared calcium carbonate and slurrying it with water again,
Stabilization treatment was performed by adding orthophosphoric acid. After the treatment, it was dried and the bulk specific gravity of this spherical calcium carbonate was measured. To measure bulk specific gravity, follow the true specific gravity measurement method described in the Viscosity Handbook (Gihodo) (p495)
I followed. In Comparative Example 2, the true specific gravity of commercially available calcite-type heavy calcium carbonate (trade name: Escalon #800, manufactured by Sankyo Seifun Co., Ltd.) was measured. Comparative Example 3 uses an aqueous solution reaction (Japanese Patent Application Laid-open No. 57-92520)
The true specific gravity of the spherical vaterite-type calcium carbonate obtained was measured. As shown in Table 3, it can be seen that the bulk specific gravity of spherical vaterite type calcium carbonate obtained in the present invention is smaller than the true specific gravity of the comparative example and has a hollow structure.

[Table] * Percentage of spherical vaterite calcium carbonate based on solid weight.

〔Effect of the invention〕

The present invention relates to a novel method for producing and stabilizing calcium carbonate, which is of the spherical vaterite type and has a characteristic of having a low specific gravity due to its hollow structure, and has extremely high industrial value.

[Brief explanation of the drawing]

Figure 1 shows the crystal structure of hollow and spherical vaterite type calcium carbonate obtained in Example 2-1.
This is a 5000x electron micrograph, and Figure 2 is Example 2.
Shows the crystal structure of the hollow and spherical vaterite type calcium carbonate obtained in -1, which was crushed by ultrasonic waves.
This is a 10,000x electron micrograph.

Claims (1)

[Claims] 1. An emulsion in which calcium chloride or calcium nitrate is dissolved in an alcohol that is insoluble or sparingly soluble in water, and an aqueous carbonate solution is dropped into the solution and mixed, so that the continuous phase is alcohol and the dispersed phase is water. A method for producing hollow, spherical vaterite-type calcium carbonate, which is characterized by producing calcium carbonate at the interface between alcohol and water. 2. The method for producing hollow, spherical vaterite-type calcium carbonate according to claim 1, wherein the alcohol is butanol or pentanol. 3. A method for stabilizing vaterite-type calcium carbonate crystals, which comprises adding a phosphorus oxoacid to the aqueous suspension of the hollow and spherical vaterite-type calcium carbonate according to claims 1 and 2.