Calcite-type monodisperse spherical calcium carbonate particles and method for producing the same

Abstract

A simple method for producing calcite-type monodisperse spherical calcium carbonate particles, and calcite-type monodisperse spherical calcium carbonate particles are provided. [Solution] A method for producing calcite-type monodisperse spherical calcium carbonate particles is provided, comprising the steps of: mixing a calcium ion-containing solution containing polycarboxylate amine, a carbonate ion-containing substance, and a pH adjusting agent containing a base to obtain amorphous calcium carbonate particles; and heating the amorphous calcium carbonate particles.

Description

Technical Field

[0001] The present disclosure relates to calcite-type monodisperse spherical calcium carbonate particles and a method for producing the same.

Background Art

[0002] Calcium carbonate is used as an additive for various materials for the purpose of increasing the amount and improving the function. In particular, when it is monodisperse spherical particles, it can be expected to contribute to improving the physical properties of various materials such as the extensibility and touch of cosmetics, and the slipperiness of films.

[0003] As synthesis examples of monodisperse spherical calcium carbonate particles, various examples with a baterlite crystal structure have been proposed. However, baterlite has a metastable crystal structure and, for example, reacts with water and easily deteriorates. Therefore, in terms of stability, it is desirable that the crystal structure is calcite. However, synthesis examples of calcite-type calcium carbonate particles with high monodispersity and close to spherical shape are rare, and even in limited reported examples, there are problems such as the particle size of the product being limited and the need for special equipment for synthesis.

[0004] For example, Patent Document 1 discloses a method for producing calcite-type calcium carbonate particles by adding carbon dioxide gas to a suspension of calcium hydroxide in water.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the production method described in Patent Document 1, complicated operations are required, such as finely adjusting the blowing rate of carbon dioxide gas and the reaction temperature according to the carbonation rate. Furthermore, it is unclear whether the manufacturing method described in Patent Document 1 yields monodisperse spherical calcite-type calcium carbonate particles.

[0007] Therefore, the object of this disclosure is to provide a simple method for producing calcite-type monodisperse spherical calcium carbonate particles, and to provide calcite-type monodisperse spherical calcium carbonate particles. [Means for solving the problem]

[0008] The following [1]-[2] are provided by this disclosure. [1] A step of obtaining amorphous calcium carbonate particles by mixing a calcium ion-containing solution containing polycarboxylate amine, a carbonate ion-containing substance, and a pH adjusting agent containing a base, and The process includes heating the amorphous calcium carbonate particles, A method for producing calcite-type monodisperse spherical calcium carbonate particles, The calcite-type monodisperse spherical calcium carbonate particles are single crystals, A method for producing calcite-type monodisperse spherical calcium carbonate particles having a coefficient of variation of particle size of 15% or less, as represented by the following formula (A). Coefficient of variation = ((Standard deviation of particle size distribution) / (Arithmetic mean particle size)) × 100 ... (A) [2] It is a single crystal, Furthermore, the calcite-type monodisperse spherical calcium carbonate particles have a coefficient of variation of particle size of 15% or less, as represented by the following formula (A). Coefficient of variation = ((Standard deviation of particle size distribution) / (Arithmetic mean particle size)) × 100 ... (A) [Effects of the Invention]

[0009] According to this disclosure, a simple method for producing calcite-type monodisperse spherical calcium carbonate particles and calcite-type monodisperse spherical calcium carbonate particles can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] This is a scanning electron microscope (SEM) image of the calcite-type monodisperse spherical calcium carbonate particles obtained in Example 1. [Figure 2] This is the X-ray diffraction pattern of the calcite-type monodisperse spherical calcium carbonate particles obtained in Example 1. [Figure 3] The images show a transmission electron microscope (TEM) image (left) and an electron diffraction pattern (right) of the calcite-type monodisperse spherical calcium carbonate particles obtained in Example 1. [Modes for carrying out the invention]

[0011] The upper and lower limits of the numerical ranges described herein can be combined in any way. For example, if the numerical ranges "A to B" and "C to D" are described, the numerical ranges "A to D" and "C to B" are also included within the scope of this disclosure. Furthermore, unless otherwise specified, the numerical range "lower limit to upper limit" described herein means that the value is greater than or equal to the lower limit and less than or equal to the upper limit.

[0012] <Method for producing calcite-type monodisperse spherical calcium carbonate particles> The method for producing calcite-type monodisperse spherical calcium carbonate particles according to this disclosure includes the steps of: mixing a calcium ion-containing solution containing a polycarboxylic acid amine, a carbonate ion-containing substance, and a pH adjusting agent containing a base to obtain amorphous calcium carbonate particles; and heating the amorphous calcium carbonate particles.

[0013] The disclosing parties have diligently considered how to resolve the above-mentioned issues. As a result, we have found that the above problem can be solved by a method for producing calcite-type monodisperse spherical calcium carbonate particles, which includes the steps of mixing a calcium ion-containing solution containing polycarboxylate amine, a carbonate ion-containing substance, and a pH adjuster containing a base to obtain amorphous calcium carbonate particles, and heating the amorphous calcium carbonate particles. Based on the above findings, the Disclosing Parties conducted further investigations and completed this disclosure.

[0014] Next, the details of the method for producing calcite-type monodisperse spherical calcium carbonate particles of the present disclosure will be described.

[0015] 〔Mixing step〕 The method for producing calcite-type monodisperse spherical calcium carbonate particles according to the present disclosure includes a step of mixing a calcium ion-containing solution containing a polycarboxylic acid amine, a carbonate ion-containing substance, and a pH adjuster containing a base to obtain amorphous calcium carbonate particles. The reason for obtaining amorphous calcium carbonate particles with high monodispersity by the above mixing step is not clear, but it is presumed to be due to reasons such as the following.

[0016] In order to obtain monodisperse particles in the crystal growth reaction from a solution, Method 1: By devising a mixing method such as using a microreactor, creating a uniform high supersaturation state in an instant, and causing nucleation on a short time scale; Method 2: Designing a system in which the reaction rate of crystal growth (heterogeneous nucleation) is smaller than the reaction rate of homogeneous nucleation; Method 3: Utilizing Ostwald ripening to control the particle size by selecting a solvent with a suitable solubility and taking advantage of the dissolution and reprecipitation after particle precipitation due to the difference in solubility depending on the particle size, etc. can be mentioned. In the calcium ion-containing solution containing a polycarboxylic acid amine used in the production method according to the present disclosure, it is considered that the polycarboxylic acid amine or its carboxylate ion coordinates with the calcium ion and forms a complex. For this to react with carbonate ions to produce calcium carbonate, it is necessary for a part of the polycarboxylic acid amine or its carboxylate ion coordinated with the calcium ion to desorb. That is, it is considered that both the reaction rates of homogeneous nucleation and crystal growth (heterogeneous nucleation) are smaller compared to the case where no polycarboxylic acid amine is present. It is presumed that monodisperse particles were obtained either because the reaction rate of homogeneous nucleation is low, allowing for the creation of a uniform, highly supersaturated state simply by mixing without any special techniques (corresponding to Method 1 described above), or because the reaction rate of crystal growth (heterogeneous nucleation) is kept sufficiently low (corresponding to Method 2 described above). Furthermore, in a calcium ion-containing solution containing polycarboxylate amine, the polycarboxylate amine or its carboxylate ions coordinate with the calcium ions to form a complex. Therefore, the polycarboxylate amine is easily incorporated into the particles, and it is presumed that amorphous calcium carbonate particles can be obtained using the manufacturing method according to this disclosure. The amorphous calcium carbonate particles obtained using the manufacturing method according to this disclosure are in a state where the polycarboxylate amine is complexed with the calcium carbonate particles; that is, the polycarboxylate amine is incorporated not only on the surface of the calcium carbonate particles but also inside the calcium carbonate particles and is embodied in the particles.

[0017] Furthermore, in the step of mixing the calcium ion-containing solution containing the polycarboxylate amine of this disclosure, a carbonate ion-containing substance, and a pH adjusting agent containing a base, there are no particular restrictions on the order in which the components are mixed. For example, a mixture of a pH adjusting agent containing a base and a carbonate ion-containing substance may be prepared in advance by mixing them together, and then a calcium ion-containing solution containing polycarboxylate amine may be mixed with the mixture of the carbonate ion-containing substance and the pH adjusting agent (hereinafter also referred to as mixing step 1). Alternatively, a calcium ion-containing solution containing polycarboxylate amine may be mixed separately with a carbonate ion-containing substance and a pH adjusting agent containing a base (hereinafter also referred to as mixing step 2). In other words, the step of obtaining amorphous calcium carbonate particles according to the present disclosure may include the step of mixing a carbonate ion-containing substance with a pH adjusting agent containing a base to prepare a mixture of the carbonate ion-containing substance and the pH adjusting agent containing a base.

[0018] (A calcium ion-containing solution containing polycarboxylate amine) A calcium ion-containing solution containing polycarboxylate amine comprises a calcium ion source, polycarboxylate amine, and a solvent that dissolves both. Examples of calcium ion sources include calcium chloride (CaCl2), calcium nitrate (Ca(NO3)2), calcium acetate (Ca(CH3COO)2), and calcium hydroxide (Ca(OH)2), with calcium chloride (CaCl2) being the preferred choice. A single calcium ion source may be used, or two or more may be mixed together. Polycarboxylate amines are compounds having an amine skeleton (-N<) and two or more carboxyl groups. For example, a polycarboxylate amine represented by the following formula (1) can be used.

[0019] [ka]

[0020] In formula (1), A represents a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, an aryl group having 6 to 10 carbon atoms, a hydroxyl group, or a carboxyl group, and L 1 ~L 3 Each of these independently represents a single bond or an alkylene group having 1 to 3 carbon atoms.

[0021] The alkyl group having 1 to 15 carbon atoms may be linear, branched, or cyclic. Examples include methyl, ethyl, t-butyl, and cyclohexyl groups, and may also have substituents such as hydroxyl and carboxyl groups. Among these, linear alkyl groups having 1 to 3 carbon atoms are preferred, and methyl groups are more preferred. The aryl group having 6 to 10 carbon atoms includes phenyl groups, naphthyl groups, etc., and may further have substituents such as hydroxyl groups, carboxyl groups, sulfonic acid groups, and amino groups. Among these, the phenyl group is preferred. The alkylene group having 1 to 3 carbon atoms may be linear or branched, and examples include methylene groups and ethylene groups, and may further have substituents such as hydroxyl groups and carboxyl groups. Among these, linear alkylene groups are preferred, and methylene groups and ethylene groups are more preferred.

[0022] The number of carboxyl groups in a polycarboxylate amine is not particularly limited as long as it is two or more, but it is preferably 2 to 5, more preferably 2 to 3, and even more preferably 2. In other words, the polycarboxylate amine is even more preferably a dicarboxylate amine. Only one type of polycarboxylate amine may be used, or two or more types may be used in mixture form.

[0023] Examples of polycarboxylate amines represented by formula (1) include hydroxyethyliminodiacetic acid (sometimes abbreviated as HIDA), methyliminodiacetic acid (sometimes abbreviated as Me-IDA), benzyliminodiacetic acid (sometimes abbreviated as Benzyl-IDA), and iminodiacetic acid (sometimes abbreviated as IDA). These polycarboxylate amines have the following structures.

[0024] [ka]

[0025] During the mixing process, the particle size of the resulting amorphous calcium carbonate can be adjusted by changing the type of polycarboxylic acid amine. For example, when using hydroxyethyliminodiacetic acid as the polycarboxylic acid amine, it is easier to produce amorphous calcium carbonate with a larger particle size when methyliminodiacetic acid is used.

[0026] The solvent can be a source of calcium ions and a solvent that dissolves polycarboxylic acid amines. Water is usually used, but it may also contain water-soluble organic solvents such as alcohols, tetrahydrofuran, and oxazine.

[0027] The calcium ion source and polycarboxylate amine content in the calcium ion-containing solution are not particularly limited; the calcium ion-containing solution can be prepared by dissolving an equal molar equivalent of calcium ions and polycarboxylate amine in a solvent. For example, a solution with a calcium ion concentration of 50-100 mmol / L or a calcium content of 0.2-0.4% by mass can be prepared by adding an equal molar equivalent of calcium ions and polycarboxylate amine. Note that the mass percentage concentration of polycarboxylic acid in the solution varies depending on the molecular weight of the polycarboxylic acid amine.

[0028] (Substances containing carbonate ions) A carbonate ion-containing substance is a substance that contains carbonate ions, and its form may be gas, liquid, or solid. The carbonate ion-containing substance used in mixing step 1 is pre-mixed with a pH adjusting agent containing a base, and is used as a "mixture of carbonate ion-containing substance and pH adjusting agent containing a base" that also contains a pH adjusting agent containing a base in addition to carbonate ions. The carbonate ion-containing substance used in mixing step 2 does not contain a pH adjusting agent containing a base. Hereinafter, in this specification, when the term "carbonate ion-containing substance" is used, it refers to a carbonate ion-containing substance that does not contain a pH adjusting agent containing a base. A mixture of a carbonate ion-containing substance and a pH adjusting agent containing a base, such as the carbonate ion-containing substance used in mixing step 1, may be described as "base and carbonate ion-containing substance."

[0029] Examples of carbonate ion-containing substances (carbonate ion-containing substances that do not contain pH adjusting agents containing bases) include carbon dioxide (CO2 gas); a solution of carbon dioxide (CO2 gas) dissolved in a solvent; and a solution of a carbonate ion source such as sodium bicarbonate or sodium carbonate dissolved in a solvent. For example, when carbon dioxide is used as the carbonate ion-containing substance, the step of mixing the calcium ion-containing solution containing polycarboxylate amine with the carbonate ion-containing substance can be carried out by blowing carbon dioxide into the calcium ion-containing solution containing polycarboxylate amine. Among the carbonate ion-containing substances mentioned above, aqueous solutions of metal carbonates are preferred, and aqueous solutions of sodium carbonate are more preferred. Furthermore, any solvent capable of dissolving the carbonate ion source can be used without particular restrictions, but water is usually used. Furthermore, the carbonate ion-containing substance may be used alone or in a mixture of two or more types.

[0030] (pH adjuster) In mixing step 1, the carbonate ion-containing substance further contains a pH adjusting agent containing a base. When using carbon dioxide as the carbonate ion-containing substance, a solution can be prepared by dissolving carbon dioxide in a solvent such as water, and then adding a pH adjuster containing a base. Alternatively, carbon dioxide can be dissolved in a solution prepared by dissolving a pH adjuster containing a base in a solvent such as water. The bases included in the pH adjuster can be ammonia, methylamine, trimethylamine, tetramethylamine hydroxide, etc., and can be used individually or in combination of two or more. The amount of pH adjusting agent containing a base added is adjusted according to the concentration and type of base contained in the pH adjusting agent, so that the pH after mixing the calcium-containing solution containing polycarboxylate amine with the carbonate ion-containing substance containing the pH adjusting agent reaches a value at which composite particles of calcium carbonate and dicarboxylate amine precipitate. The particle size of the resulting amorphous calcium carbonate can be adjusted by changing the type of base and using an appropriate amount of pH adjuster. For example, when using ammonia as the base, it is easier to produce larger amorphous calcium carbonate particles when using trimethylamine.

[0031] The concentration of the carbonate ion source in a carbonate ion-containing substance is not particularly limited; a solution containing the same molar equivalent of the carbonate ion source as the calcium ion source in a calcium ion-containing solution can be prepared. When a carbonate ion-containing substance contains a pH adjusting agent containing a base, in other words, when preparing a "base and carbonate ion-containing substance," add a pH adjusting agent containing 2 to 8 molar equivalents of base to the carbonate ion source. For example, for 100 g of a carbonate ion-containing solution with a concentration of 50 mmol / L to 100 mmol / L, add 3 to 6 mL of 25% by mass aqueous ammonia. Furthermore, the higher the concentration of calcium ion source and carbonate ion source in the calcium ion-containing solution, the easier it is to produce small-particle amorphous calcium carbonate particles.

[0032] In mixing step 2 according to this disclosure, in addition to mixing the calcium ion-containing solution with the carbonate ion-containing substance, a pH adjusting agent containing a base is further mixed. At this time, the carbonate ion-containing substance does not contain the pH adjusting agent containing a base. Furthermore, as methods for adding a pH adjuster containing a base to a calcium ion-containing solution, the method of combining the pH adjuster containing a base with a carbonate ion-containing substance and then adding it to the calcium ion-containing solution is called "combined addition," while the method of adding the pH adjuster containing a base separately to the calcium ion-containing solution without combining them is called "separate addition." In other words, the method of adding the pH adjuster containing a base in mixing step 1 is "combined addition," and the method of adding the pH adjuster containing a base in mixing step 2 is "separate addition."

[0033] An example of the mixing process related to this disclosure when carbon dioxide is used as the carbonate ion-containing substance is described below, both for blending and separate addition. In the case of compounding (mixing step 1), as described above, either add the pH adjuster to a solution in which carbon dioxide is dissolved in a solvent such as water, or dissolve carbon dioxide in a solution in which the pH adjuster is dissolved in a solvent such as water. Then, mix the solution containing dissolved carbon dioxide and pH adjuster with the calcium ion-containing solution containing polycarboxylate amine.

[0034] In the case of separate addition (mixing step 2), the pH adjuster should be added to the calcium ion-containing solution containing polycarboxylate amine, and then carbon dioxide gas should be blown in. Furthermore, adding a pH adjuster to the carbonate ion-containing substance by compounding shortens the production time for amorphous calcium carbonate particles; therefore, compounding is preferable from the viewpoint of production efficiency. On the other hand, if added separately, for example, by gradually adding a pH adjuster containing a base after mixing the calcium ion-containing solution and the carbonate ion-containing substance, the pH in the system can be slowly increased, which can improve the uniformity of the system and is expected to yield particles with higher monodispersity.

[0035] When using amines such as ammonia, methylamine, trimethylamine, or tetramethylamine hydroxide as a separate pH adjuster, a pH adjuster containing 2 to 8 molar equivalents of base relative to the carbonate ion source used in mixing step 2 can be used. The specific amount used will vary depending on the type and concentration of the amine used. In addition, when using a separate adder, metal hydroxides such as sodium hydroxide or potassium hydroxide can also be used as pH adjusters, and a pH adjuster containing 1 to 3 molar equivalents of base relative to the carbonate ion source used in mixing step 2 can be used.

[0036] The mixing of each component in mixing step 1 and mixing step 2 can be carried out under atmospheric pressure (0.1 MPa) and room temperature (25°C). The mixing of each component can be carried out for 1 to 5 minutes using a stirring device as needed. In the case of adding a calcium ion-containing solution and then mixing a pH adjusting agent containing a base, it is preferable to add the pH adjusting agent to the reaction system over 40 to 50 minutes, depending on the concentration of the base in the pH adjusting agent, from the viewpoint of maintaining uniformity within the system. After stirring for a predetermined time, the mixture is filtered through filter paper or similar material, washed with alcohol, and the solid matter on the filter paper is dried to obtain amorphous calcium carbonate particles.

[0037] [Amorphous calcium carbonate particles] The amorphous calcium carbonate particles of this disclosure are amorphous calcium carbonate particles produced by the mixing step described above, and are a composite of polycarboxylic acid amine and calcium carbonate particles. Furthermore, the amorphous nature of calcium carbonate particles can be confirmed, for example, by X-ray diffraction (XRD) or by electron diffraction patterns obtained using a transmission electron microscope (TEM).

[0038] [Heating process] The method for producing calcite-type monodisperse spherical calcium carbonate particles according to the present disclosure further includes a heating step. By heating the amorphous calcium carbonate particles obtained in the mixing step, the amorphous calcium carbonate particles crystallize, and calcite-type monodisperse spherical calcium carbonate particles can be obtained. Furthermore, the calcite-type monodisperse spherical calcium carbonate particles obtained by the production method of the present disclosure maintain their amorphous calcium carbonate particle shape almost entirely without the particles sintering together.

[0039] The heating temperature for obtaining calcite-type monodisperse spherical calcium carbonate particles is not particularly limited as long as it is a temperature at which amorphous calcium carbonate can undergo a phase transition to calcite-type monodisperse spherical calcium carbonate. However, from the viewpoint of facilitating the phase transition, a temperature of 300°C or higher is generally preferred. Furthermore, there is no particular upper limit as long as it is a temperature at which calcium carbonate does not thermally decompose. However, from the viewpoint of preventing sintering of particles, it is preferably less than 600°C, more preferably 500°C or lower, even more preferably 400°C or lower, and even more preferably 350°C or lower.

[0040] The heating time is not particularly limited as long as it is the time required to obtain calcite-type monodisperse spherical calcium carbonate particles. However, from the viewpoint of ensuring the completion of the phase transition, for example, 10 minutes or more is preferred, 30 minutes or more is more preferred, 1 hour or more is even more preferred, and 3 hours or more is even more preferred. Furthermore, there is no particular upper limit to the heating time, but from the viewpoint of preventing sintering between particles, 24 hours or less is preferred, 15 hours or less is more preferred, 10 hours or less is even more preferred, and 5 hours or less is even more preferred.

[0041] Furthermore, the atmosphere used for heating is not particularly limited as long as it is an atmosphere from which calcite-type monodisperse spherical calcium carbonate particles can be obtained, but examples include an air atmosphere, an inert gas atmosphere (e.g., a nitrogen atmosphere, an argon atmosphere), and a vacuum atmosphere. Similarly, there are no particular restrictions on the heating method, but examples include using a firing furnace or a hot plate.

[0042] [Calcite-type monodisperse spherical calcium carbonate particles] The calcite-type monodisperse spherical calcium carbonate particles obtained by the manufacturing method of this disclosure have a single crystal structure of calcite, are spherical, and have a coefficient of variation of particle size of 15% or less, represented by the following formula (A). Coefficient of variation = ((Standard deviation of particle size distribution) / (Arithmetic mean particle size)) × 100 ... (A)

[0043] In this disclosure, "monodisperse" means that the coefficient of variation of the aforementioned particles is 15% or less.

[0044] Furthermore, the coefficient of variation of particle size is preferably 14.5% or less, more preferably 14.0% or less, and even more preferably 13.5% or less.

[0045] Furthermore, in this disclosure, "spherical" means that the average value of the circularity of 100 particles randomly selected from SEM images obtained by scanning electron microscopy (SEM) observation is 0.80 or higher. The circularity is calculated as A / B, where A is the area calculated by assuming each particle image is a two-dimensional planar figure projected onto the SEM image, and B is the area of ​​a perfect circle relative to the perimeter PM.

[0046] Here, "calcite type" refers to the hexagonal crystal structure among the possible crystal structures of calcium carbonate. In X-ray diffraction (XRD) analysis using a copper tube, the diffraction lines of calcite appear, for example, around 2θ = 23.1°, 29.4°, 31.4°, 36.0°, and 39.4°.

[0047] Furthermore, because the calcium carbonate particles are single crystals, it is expected that the particle strength will be improved compared to polycrystalline materials which have weaker grain boundaries. For example, when using calcium carbonate particles as an additive in a base material such as resin or rubber, it is expected that mechanical strength will be more easily improved compared to when using polycrystalline materials.

[0048] Furthermore, the fact that the calcium carbonate particles are single crystals can be confirmed, for example, by observing the electron diffraction pattern obtained using a transmission electron microscope (TEM).

[0049] Furthermore, by calculating the ratio of the crystallite size calculated from the Scherrer formula to the arithmetic mean particle size measured by dynamic light scattering (DLS) [(crystallite size) / (arithmetic mean particle size)], it is possible to determine whether the calcium carbonate particles are single crystals. For example, calcium carbonate particles are defined as single crystals if the value of [(crystallite size) / (arithmetic mean particle size)] is 0.18 or greater. The crystallite size described above is calculated specifically by the method described in the examples.

[0050] The reason why the coefficient of variation of particle size of the calcite-type monodisperse spherical calcium carbonate obtained by the manufacturing method of this disclosure is small is not clear, but it is presumed that, for the same reasons as described in paragraph 0016 of this disclosure, the amorphous calcium carbonate particles of this disclosure are uniform particles with a small coefficient of variation of particle size, and the calcite-type monodisperse spherical calcium carbonate particles obtained by heating them also maintain almost the monodispersity and shape of the amorphous calcium carbonate particles, and similarly become uniform particles with a small coefficient of variation of particle size.

[0051] Furthermore, the arithmetic mean particle size of the calcite-type monodisperse spherical calcium carbonate obtained by the manufacturing method of this disclosure can be controlled, for example, within the range of 50 to 600 nm. Furthermore, the arithmetic mean particle size may be 60-550 nm or 65-500 nm. As mentioned above, calcite-type monodisperse spherical calcium carbonate has a variety of potential applications, but the required particle size varies depending on the application. For example, when added to cosmetics to improve slipperiness, a particle size of 500 nm or larger is preferred; when added to paper to enhance smoothness or as an antiblocking agent to resins, a particle size of around 200-300 nm is preferred; and when added to rubber for reinforcement, a particle size of around 50 nm is sometimes preferred.

[0052] The arithmetic mean particle size and coefficient of variation of the calcite-type monodisperse spherical calcium carbonate in this disclosure are values ​​measured by dynamic light scattering (DLS).

[0053] [One aspect of the disclosure provided] One aspect of this disclosure provides the following [1] to [6]. [1] A step of obtaining amorphous calcium carbonate particles by mixing a calcium ion-containing solution containing polycarboxylate amine, a carbonate ion-containing substance, and a pH adjusting agent containing a base, and The process includes heating the amorphous calcium carbonate particles, A method for producing calcite-type monodisperse spherical calcium carbonate particles, The calcite-type monodisperse spherical calcium carbonate particles are single crystals, A method for producing calcite-type monodisperse spherical calcium carbonate particles having a coefficient of variation of particle size of 15% or less, as represented by the following formula (A). Coefficient of variation = ((Standard deviation of particle size distribution) / (Arithmetic mean particle size)) × 100 ... (A) [2] A method for producing calcite-type monodisperse spherical calcium carbonate particles according to [1], wherein the step of obtaining the amorphous calcium carbonate particles includes the step of mixing the pH adjusting agent containing the base with the carbonate ion-containing substance to prepare a mixture of the carbonate ion-containing substance and the pH adjusting agent containing the base. [3] A method for producing calcite-type monodisperse spherical calcium carbonate particles according to [1] or [2], wherein the temperature of the heating step is 300°C or higher. [4] A method for producing calcite-type monodisperse spherical calcium carbonate particles according to any one of [1] to [3], wherein the polycarboxylic acid amine is a dicarboxylic acid amine. [5] It is a single crystal, Furthermore, the calcite-type monodisperse spherical calcium carbonate particles have a coefficient of variation of particle size of 15% or less, as represented by the following formula (A). Coefficient of variation = ((Standard deviation of particle size distribution) / (Arithmetic mean particle size)) × 100 ... (A) [6] Calcite-type monodisperse spherical calcium carbonate particles as described in [5], wherein the arithmetic mean particle size is 50-600 nm. [Examples]

[0054] The technology of this disclosure will now be specifically described by examples, but the technology of this disclosure is not limited in any way by these examples.

[0055] [Example 1] Calcium chloride aqueous solution (50 mmol / L) (Ca 2+ To the source, 1 molar equivalent of hydroxyethyliminodiacetic acid (HIDA) (organic molecule) was dissolved in calcium ions to prepare solution A (solution A1). The same concentration and volume of sodium carbonate aqueous solution (CO3) as the prepared calcium chloride aqueous solution. 2- To the source, 8.0 molar equivalents of ammonia (NH3) (base) were added relative to the carbonate ions to prepare solution B (solution B1). Solution A (Solution A1) was added to Solution B (Solution B1), stirred at room temperature for 5 minutes, filtered, and the product on the filter paper was washed with ethanol and then dried. The powder was collected after washing and heated at 300°C for 3 hours in an air atmosphere.

[0056] [Examples 2-4] In the preparation of Solution A (Solution A1) in Example 1, methyliminodiacetic acid (Me-IDA), benzyliminodiacetic acid (Benzyl-IDA), or iminodiacetic acid (IDA) were used as organic molecules instead of hydroxyethyliminodiacetic acid (HIDA), as shown in Table 1. Otherwise, Solution A was prepared in the same manner as in Example 1. Solution A in Example 2 is designated as Solution A2, Solution A in Example 3 as Solution A3, and Solution A in Example 4 as Solution A4. In Example 1, the procedure was the same as before, except that Solution A (Solution A2, Solution A3, or Solution A4) was used instead of Solution A (Solution A1). Solution A was added to Solution B, stirred at room temperature for 1 to 5 minutes, filtered, and the product on the filter paper was washed with ethanol and then dried. The powder was collected after washing and heated at 300°C for 3 hours in an air atmosphere.

[0057] [Examples 5-7] In preparing Solution B (Solution B1) in Example 1, trimethylamine (NMe3), methylamine (MeNH2), or tetramethylamine hydroxide (NMe4(OH)) were used as the base in the pH adjusting agent instead of ammonia (NH3), as shown in Table 1. The amount of each pH adjusting agent added was determined so that the pH of the mixed solution after mixing Solution A and Solution B was the same as in Example 1. Solution B was prepared in the same manner as in Example 1. Solution B in Example 5 is designated as Solution B2, Solution B in Example 6 as Solution B3, and Solution B in Example 7 as Solution B4. In Example 1, the procedure was the same as before, except that Solution B (Solution B2, Solution B3, or Solution B4) was used instead of Solution B (Solution B1). Solution A was added to Solution B, stirred at room temperature for 5 minutes, filtered, and the product on the filter paper was washed with ethanol and then dried. The powder was collected after washing and heated at 300°C for 3 hours in an air atmosphere.

[0058] [Examples 8-9] In preparing Solution A (Solution A1) and Solution B (Solution B1) in Example 1, the concentrations of calcium chloride and sodium carbonate were set to 75 mmol / L or 100 mmol / L, as shown in Table 1, except that Solution A and Solution B were prepared in the same manner as in Example 1. Note that Solution A and Solution B in Example 8 are designated as Solution A5 and Solution B5, and Solution A and Solution B in Example 9 are designated as Solution A6 and Solution B6. In Example 1, the same procedure was followed except that Solution A (Solution A1) was replaced with Solution A (Solution A5 or A6), and Solution B (Solution B1) was replaced with Solution B (Solution B5 or B6). Solution A was added to Solution B, stirred at room temperature for 5 minutes, filtered, and the product on the filter paper was washed with ethanol and then dried. The powder was collected after washing and heated at 300°C for 3 hours in an air atmosphere.

[0059] [Example 10] Solution A (Solution A1) was prepared in the same manner as in Example 1, and the same concentration and volume of sodium carbonate aqueous solution was added to Solution A1. To this mixed solution, 1.2 molar equivalents of sodium hydroxide aqueous solution were added relative to the carbonate ions. Specifically, 900 μL of 10 mol / L sodium hydroxide aqueous solution was added at a rate of 50 μL / min. After the addition of the sodium hydroxide aqueous solution was complete, the mixture was stirred for several minutes, filtered, and the product on the filter paper was washed with ethanol and then dried. The powder was collected after washing and heated at 300°C for 3 hours in an air atmosphere.

[0060] [Comparative Example 1] In the preparation of solution B (solution B1) in Example 1, ammonia (NH3) was not used, except that the same procedure as in Example 1 was followed. Solution B in Comparative Example 1 is designated as solution B101. In Example 1, the procedure was the same as before, except that solution B (solution B101) was used instead of solution B (solution B1). Solution A was added to solution B and stirred at room temperature for 5 minutes.

[0061] <Rating> The products prepared in Examples 1 to 10 were evaluated for their crystal structure, arithmetic mean grain size and grain size distribution, and whether they were single crystals, using scanning electron microscopy (SEM), dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction. The specific evaluation methods and measurement conditions are described below. The evaluation results are shown in Table 1. In Comparative Example 1, no particles precipitated, therefore the above evaluation was not performed. Table 1 also shows the components of Solution A and Solution B, as well as the reaction time. Table 1 shows "Ca 2+ "Concentration" column and "CO3" 2- In the "Concentration" column, "mM" means "mmol / L".

[0062] 1. Analysis by X-ray diffraction (XRD) X-ray diffraction patterns were measured using an X-ray diffractometer ("AERIS," manufactured by Spectris). Measurements were taken under the following conditions: CuKα radiation (40kV, 7.5mA), scanning axis 2θ / θ, scan range 3-70 degrees, scan step 0.01 degrees, and scan speed 0.27 degrees / min. Furthermore, under the following conditions, the crystallite size D [nm] was calculated from the Scherrer equation represented by the following formula (B) for the diffraction line of the (10⁴) plane in the X-ray diffraction pattern. D=(K·λ) / (β·cosθ)···(B) In equation (B), K is the Scherrer constant, λ is the wavelength of the X-ray (CuKα line) [nm], β is the diffraction line broadening (fiber width at half maximum) [radians], and θ is the Bragg angle [radians]. For the calculation, K=0.9 and λ=0.15148 [nm] were used.

[0063] 2. Scanning electron microscope (SEM) observation Scanning electron microscopy observations were performed using a scanning electron microscope (JCM-6000, manufactured by JEOL Ltd.) (acceleration voltage 15kV). As a pretreatment, gold deposition was performed on the sample for 2 minutes using a sputtering apparatus (Smart Coater, manufactured by JEOL Ltd.).

[0064] 3. Analysis using Dynamic Light Scattering (DLS) method Using a dynamic light scattering instrument ("ELSZneo," manufactured by Otsuka Electronics Co., Ltd.), particle size distribution measurements were performed, and the arithmetic mean particle size and coefficient of variation of particle size were calculated. A predetermined amount of sample particles was dispersed in ethanol and used as the analytical sample.

[0065] 4. Analysis by transmission electron microscopy (TEM) and electron diffraction. Using a transmission electron microscope ("H-9500," manufactured by Hitachi High-Tech Corporation), we obtained transmission electron microscope observations (acceleration voltage 200kV) and electron diffraction patterns. The electron diffraction pattern was measured using area 1, shown in the TEM image on the left side of Figure 3.

[0066] [Table 1]

[0067] Furthermore, the results of analyzing the product of Example 1 using a scanning electron microscope (SEM) ("JCM-6000", manufactured by JEOL Ltd.), an X-ray diffraction (XRD) spectrometer ("AERIS", manufactured by Spectris Corporation), and a transmission electron microscope (TEM) ("H-9500", manufactured by Hitachi High-Tech Corporation) are shown in Figures 1 to 3. In Figure 1, the notation "2μm" to the right of the white line at the bottom indicates that the length of the white line corresponds to 2μm. In Figure 2, the vertical axis represents "Intensity / cps" and the horizontal axis represents "2θ(° / CuKα)". In Figure 3, the notation "100nm" to the right of the white line at the bottom indicates that the length of the white line corresponds to 100nm.

[0068] According to the X-ray diffraction pattern in Figure 2, the product of Example 1 was found to have diffraction lines at 2θ = 23.1°, 29.4°, 31.4°, 36.0°, and 39.4°, which are attributed to calcite. Therefore, the product of Example 1 was determined to be calcite. In Example 1, the average circularity of 100 randomly selected particles from the SEM image including Figure 1 was 0.80 or higher, so it was determined that the particle shape was spherical. Furthermore, results from particle size distribution measurements using dynamic light scattering (DLS) confirmed that the coefficient of variation particle size of the product in Example 1 was 15% or less, indicating that the particle size variation of the product in Example 1 was small. Furthermore, the electron diffraction pattern obtained by transmission electron microscopy (TEM) in Figure 3 confirmed that the product of Example 1 exhibited a pattern of regularly arranged diffraction spots, leading to the conclusion that the product of Example 1 was a single crystal. Generally, in electron diffraction, when the sample being measured is a single crystal, a diffraction pattern with regularly arranged diffraction spots is shown; when the sample is polycrystalline, a ring-shaped diffraction pattern is shown; and when the sample is amorphous, no clear spots or rings are shown, but rather a blurry halo is observed. Furthermore, the ratio of the crystallite size calculated from the Scherrer formula to the arithmetic mean grain size measured by dynamic light scattering (DLS) [(crystallite size) / (arithmetic mean grain size)] was 0.18 or greater, which also led to the conclusion that the product of Example 1 was a single crystal. From the above, it can be said that the product produced in Example 1 is single-crystal calcite-type monodisperse spherical calcium carbonate particles. Similarly, the products prepared in Examples 2-10 were determined to be single-crystal calcite-type monodisperse spherical calcium carbonate particles.

[0069] On the other hand, in Comparative Example 1, since no base was added, amorphous calcium carbonate particles could not be produced in the first place.

[0070] As can be seen from the comparison of Examples 1 to 4 in Table 1, by changing the type of organic molecule, calcite-type monodisperse spherical calcium carbonate particles with different particle sizes can be produced. Among Examples 1 to 4, the calcite-type monodisperse spherical calcium carbonate particles produced in Example 1, using hydroxyethyliminodiacetic acid (HIDA) as the organic molecule, were the largest.

[0071] Furthermore, as can be seen from the comparison of Examples 1, 5, 6, and 7 in Table 1, by changing the type of base in the pH adjuster of Solution B and adding an appropriate amount, calcite-type monodisperse spherical calcium carbonate particles of different particle sizes can be produced. Among Examples 1, 5, 6, and 7, the calcite-type monodisperse spherical calcium carbonate particles produced in Example 5, which used trimethylamine (NMe3) as the base, were the largest.

[0072] As can be seen from the comparison of Examples 1, 8, and 9 in Table 1, calcite-type monodisperse spherical calcium carbonate particles of different particle sizes can be produced by adjusting the calcium ion concentration and carbonate ion concentration of solution A and solution B. Among Examples 1, 8, and 9, the calcite-type monodisperse spherical calcium carbonate particles in Example 1, with calcium ion and carbonate ion concentrations of 50 mM, were the largest.

[0073] As can be seen from the comparison of Examples 1-9 and Example 10 in Table 1, Examples 1-9, in which the pH adjuster is added and mixed with the carbonate ion-containing substance, can produce calcite-type monodisperse spherical calcium carbonate particles in a shorter time than Example 10, in which the pH adjuster is added separately. [Industrial applicability]

[0074] According to this disclosure, calcite-type monodisperse spherical calcium carbonate particles can be easily manufactured. These calcite-type monodisperse spherical calcium carbonate particles are expected to be used in the cosmetics field by being added to foundations and the like to improve smoothness and texture, in the papermaking field by being used to enhance smoothness, or as an antiblocking agent when added to resins that are raw materials for films, and as an additive to rubber to improve mechanical strength.

Claims

1. A step of obtaining amorphous calcium carbonate particles by mixing a calcium ion-containing solution containing polycarboxylate amine, a carbonate ion-containing substance, and a pH adjusting agent containing a base, and A method for producing calcite-type monodisperse spherical calcium carbonate particles, comprising the step of heating the amorphous calcium carbonate particles, The calcite-type monodisperse spherical calcium carbonate particles are single crystals, A method for producing calcite-type monodisperse spherical calcium carbonate particles having a coefficient of variation of particle size of 15% or less, as represented by the following formula (A). Coefficient of variation = ((Standard deviation of particle size distribution) / (Arithmetic mean particle size)) × 100 ... (A)

2. A method for producing calcite-type monodisperse spherical calcium carbonate particles according to claim 1, wherein the step of obtaining the amorphous calcium carbonate particles includes a step of mixing the pH adjusting agent containing the base with the carbonate ion-containing substance to prepare a mixture of the carbonate ion-containing substance and the pH adjusting agent containing the base.

3. A method for producing calcite-type monodisperse spherical calcium carbonate particles according to claim 1 or 2, wherein the temperature of the heating step is 300°C or higher.

4. A method for producing calcite-type monodisperse spherical calcium carbonate particles according to any one of claims 1 to 3, wherein the polycarboxylic acid amine is a dicarboxylic acid amine.

5. It is a single crystal, Furthermore, the calcite-type monodisperse spherical calcium carbonate particles have a coefficient of variation of particle size of 15% or less, as represented by the following formula (A). Coefficient of variation = ((Standard deviation of particle size distribution) / (Arithmetic mean particle size)) × 100 ... (A)

6. Calcite-type monodisperse spherical calcium carbonate particles according to claim 5, wherein the arithmetic mean particle size is 50 to 600 nm.

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