Method for producing calcium carbonate and calcium carbonate

Abstract

To provide: calcium carbonate having a novel hierarchical structure, preferably calcite type calcium carbonate; and a novel method for producing the calcium carbonate.SOLUTION: The present invention provides calcium carbonate having a hierarchical structure, which comprises calcium carbonate having a cylindrical, needle-like or columnar elongated structure at the surface of calcium carbonate having a compact structure. The calcium carbonate having the compact structure is preferably a particle having a diameter of 10 to 200 μm, the calcium carbonate having the elongated structure has a cross-sectional diameter in a range of 0.1 to 1.0 μm and a length in a range of 0.1 to 10 μm. Also, the calcium carbonate having the compact structure is preferably a hollow particle having an outer diameter of 10 to 200 μm, the calcium carbonate having the elongated structure has a cross-sectional diameter in a range of 0.1 to 1.0 μm and a length in a range of 0.1 to 10 μm.SELECTED DRAWING: Figure 2-A

Description

Technical Field

[0001] The present invention relates to calcium carbonate and a method for producing calcium carbonate.

Background Art

[0002] Calcium carbonate is widely used as a reinforcing filler for rubber, plastic, paper, sealant, paint / ink, etc., a calcium fortifier for food, feed, etc., and an alkali agent in fertilizers. Calcium carbonate used in these applications is roughly classified into precipitated calcium carbonate obtained by blowing carbon dioxide gas into an aqueous suspension of calcium hydroxide to carry out a carbonation reaction, and heavy calcium carbonate obtained by mechanically pulverizing and classifying high-quality limestone.

[0003] It is known that calcium carbonate has three types of crystal phases: calcite, aragonite, and vaterite. Among these, calcite is the most stable crystal phase. For example, vaterite gradually transforms into calcite over time. Calcite-type calcium carbonate generally has rhombohedral or cubic crystals and has a dense structure. That is, calcium carbonate with a higher-order structure crystallized by a conventional method mostly forms stable calcite crystals with a rhombohedral or cubic shape. Since calcium carbonate is inexpensive, easy to prepare, has a high whiteness, and is excellent in biocompatibility and degradability, attempts have been made to create various forms of calcium carbonate for active use in fields such as pharmaceuticals and cosmetics.

[0004] The production method disclosed in Patent Document 1 is a method in which carbon dioxide is blown into lime milk to generate aragonite, a dispersant is added to the dehydrated water-containing cake and then slurried again, wet pulverized, mixed with another lime milk, a soluble phosphate compound is added thereto, and carbon dioxide is introduced again. By having aragonite crystal form calcium carbonate present in the raw material water slurry, the calcium carbonate obtained by the carbonation reaction of calcium hydroxide is made into the aragonite crystal form.

[0005] On the other hand, in the production method disclosed in Patent Document 2, carbon dioxide is introduced into milk of lime to synthesize calcium carbonate. The introduction of carbon dioxide is temporarily stopped when the carbonation rate is in the range of 10 to 90%. Then, fresh milk of lime is added to this suspension to proceed with carbonation. After repeating the process of stopping the introduction of carbon dioxide at least once when the carbonation rate reaches 10 to 90% again, fresh milk of lime is added again, and the carbonation reaction is completed while maintaining the temperature of the suspension at 40°C or higher, thereby obtaining calcium carbonate aggregates in which aragonite-based calcium carbonate having a needle-like or columnar shape is aggregated.

[0006] Calcium carbonate produced by the methods of Patent Documents 1 and 2 is in the aragonite crystal form, so it has low stability and easily transfers to the calcite crystal form. Therefore, it has been desired to produce calcite crystal form calcium carbonate that is more stable and has a more complex structure that could not be synthesized until now.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, an object of the present invention is to provide calcium carbonate having a novel hierarchical structure, preferably calcite-type calcium carbonate. Furthermore, an object of the present invention is to provide a novel method for providing calcium carbonate having a novel hierarchical structure, preferably calcite-type calcium carbonate.

Means for Solving the Problems

[0009] Aspects of the present invention are calcium carbonates having a hierarchical structure, with calcium carbonate having an elongated structure, such as cylindrical, needle-shaped, or columnar, on the surface of calcium carbonate having a dense structure.

[0010] Here, it is preferable that the calcium carbonate having a dense structure is particles with a diameter of 10 - 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, and the length of the calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm.

[0011] Also, it is preferable that the calcium carbonate having a dense structure is hollow particles with an outer diameter of 10 - 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, and the length of the calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm.

[0012] Another aspect of the present invention is the following steps: A step of mixing calcite-type calcium carbonate particles, gelatin, and water, heating and stirring to obtain a gelatin / calcite-type calcium carbonate particle mixed slurry A: A step of dissolving a surfactant in oil and stirring to obtain a solution B: A step of adding the gelatin / calcite-type calcium carbonate particle mixed slurry A to the solution B and stirring to obtain an emulsion emulsion C: A step of adding a crosslinking agent to the emulsion emulsion C and stirring to obtain an emulsion D containing gelatin / calcite-type calcium carbonate composite particles: A step of centrifuging the emulsion D containing gelatin / calcite-type calcium carbonate composite particles to obtain gelatin / calcite-type calcium carbonate composite particles: A step of firing the gelatin / calcite-type calcium carbonate composite particles to obtain calcite-type calcium carbonate dense particles; and A step of placing the calcite-type calcium carbonate dense particles in an atmosphere containing at least carbon dioxide to obtain calcium carbonate having a hierarchical structure, with calcium carbonate having an elongated structure, such as cylindrical, needle-shaped, or columnar, on the surface of the calcium carbonate dense particles A method for producing calcium carbonate having a hierarchical structure, which includes

[0013] Here, in the gelatin / calcite-type calcium carbonate particle mixed slurry A, the mass ratio of gelatin to calcite-type calcium carbonate particles is preferably in the range of 5:10 - 25:10.

[0014] Also, in the solution B, the volume ratio of the surfactant to the oil is preferably in the range of 1:100 to 5:100.

[0015] The volume ratio of the gelatin / calcite-type calcium carbonate particle mixed slurry A to the solution B is preferably in the range of 1:10 - 10:10.

[0016] It is preferable to add a crosslinking agent to the emulsion C so that the mass ratio of gelatin to the crosslinking agent is in the range of 1:1 - 1:25.

[0017] Furthermore, it is preferable to bake the gelatin / calcite-type calcium carbonate composite particles at a temperature of 570°C or higher and lower than 650°C.

[0018] In this embodiment, the calcium carbonate having a dense structure is particles with a diameter of 10 - 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, and the length of the calcium carbonate having an elongated structure is preferably in the range of 0.1 - 10 μm.

[0019] Also, in this embodiment, the calcium carbonate having a dense structure is hollow particles with an outer diameter of 10 - 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, and the length of the calcium carbonate having an elongated structure is preferably in the range of 0.1 - 10 μm.

Advantages of the Invention

[0020] The manufacturing method of the present invention can produce calcite-type calcium carbonate granules with a relatively simple process and a high yield. By loading various drugs and the like into the pores of the produced calcite-type calcium carbonate, it can be used in drug delivery systems, cosmetic additives, food additives, health foods, catalyst carriers, and the like.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2-A

Figure 2-B

Figure 3

Figure 4-A

Figure 4-B

Figure 5

Modes for Carrying Out the Invention

[0022] The embodiments of the present invention will be described in more detail, but the present invention is not limited only to the following embodiments.

[0023] One embodiment of the present invention is calcium carbonate having a hierarchical structure, which has calcium carbonate having an elongated structure in a cylindrical, needle-like or columnar shape on the surface of calcium carbonate having a dense structure.

[0024] Calcium carbonate is a carbonate of calcium represented by the compositional formula CaCO3 and is the main component of shells, chicken eggshells, limestone, chalk, etc. Calcium carbonate is classified into heavy calcium carbonate (natural calcium carbonate) obtained by pulverizing and classifying limestone and light calcium carbonate (synthetic calcium carbonate) obtained by chemical reaction. However, the calcium carbonate produced in this embodiment is a type of light calcium carbonate. When simply referred to as calcium carbonate in this specification, it refers to light calcium carbonate (synthetic calcium carbonate) unless otherwise specified. Calcium carbonate has crystal polymorphs such as calcite crystals (trigonal rhombohedral crystals), aragonite crystals (orthorhombic crystals), and vaterite crystals (hexagonal crystals). However, the calcium carbonate particles of the embodiment may be any crystal, but are particularly preferably of the calcite type.

[0025] Here, in the embodiment, a hierarchical structure generally refers to a structure in which layers are stacked in order from the lower layer to the upper layer to form the whole. Calcium carbonate having a hierarchical structure means that layers of calcium carbonate having different shapes and structures are stacked in order. In the embodiment, in particular, it preferably has at least two layers, namely, a layer of calcium carbonate having a dense structure and a layer composed of an aggregate of calcium carbonate having an elongated structure such as a cylindrical, needle-like or columnar shape. Calcium carbonate having a dense structure refers to calcium carbonate having a dense structure with almost no pores on the surface of the calcium carbonate. Calcium carbonate having a dense structure is preferably composed of calcite-type calcium carbonate. Calcium carbonate having a dense structure is a higher-order structure such as a dense secondary structure of calcium carbonate formed by aggregation of primary particles of calcium carbonate. On the other hand, calcium carbonate having an elongated structure such as a cylindrical, needle-like or columnar shape is preferably composed of calcite-type calcium carbonate, has these shapes, and an aggregate of calcium carbonate having an elongated structure forms a layer. Calcium carbonate having an elongated structure such as a cylindrical, needle-like or columnar shape is also a higher-order structure such as a secondary structure of calcium carbonate formed by aggregation of primary particles of calcium carbonate. Calcium carbonate having a cylindrical elongated structure is calcium carbonate having a shape like a so-called tube (having a cavity inside). Calcium carbonate having a needle-like elongated structure is calcium carbonate having a shape like a tube having a tapered structure (taper). Further, calcium carbonate having a columnar elongated structure is calcium carbonate having a shape of a column with a filled interior, rather than a structure with a cavity like a tube. The elongated structure generally means a structure having an aspect ratio such as a cylinder, a needle, or a column, but also includes a structure having an aspect ratio of 1 (that is, the lengths of the long part and the short part are equal).

[0026] Here, calcium carbonate having a dense structure is preferably particles with a diameter of 10 - 200 μm. As described above, calcium carbonate having a dense structure is preferably a higher-order structure having a dense structure formed by aggregation of primary particles of calcite-type calcium carbonate, and is preferably particles of a higher-order structure. The diameter of the particles is 10 - 200 μm, preferably 20 - 150 μm, more preferably 30 - 100 μm. Further, the cross-sectional diameter of calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, preferably in the range of 0.2 - 0.8 μm, more preferably in the range of 0.3 - 0.6 μm. The length of calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm, preferably in the range of 0.2 - 8 μm, more preferably in the range of 0.3 - 7 μm, but there is no limit to the length, and for example, it can be extended to 30 μm or the like in some cases.

[0027] Furthermore, as another form in the embodiment, calcium carbonate having a dense structure may be hollow particles with a diameter of 10 - 200 μm. As described above, calcium carbonate having a dense structure is preferably a higher-order structure having a dense structure formed by aggregation of primary particles of calcite-type calcium carbonate, and is preferably hollow particles of a higher-order structure. In this case, the calcium carbonate having a hierarchical structure in the embodiment comprises at least three layers: a cavity part inside the hollow particles, a layer of calcium carbonate having a dense structure, and a layer composed of an aggregate of calcium carbonate having an elongated structure in a cylindrical, needle-like or columnar shape. Here, the diameter of the hollow particles is 10 - 200 μm, preferably 20 - 150 μm, more preferably 30 - 100 μm. Further, the cross-sectional diameter of calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, preferably in the range of 0.2 - 0.8 μm, more preferably in the range of 0.3 - 0.6 μm. The length of calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm, preferably in the range of 0.2 - 8 μm, more preferably in the range of 0.3 - 7 μm, but there is no limit to the length, and for example, it can be extended to 30 μm or the like in some cases.

[0028] Calcium carbonate having at least a two-layer hierarchical structure according to an embodiment has a special shape such as "sea urchin" or "hedgehog" because a plurality of calcium carbonates having a cylindrical, needle-like or columnar elongated structure radially extend from the surface of the calcium carbonate particles having a dense structure at the center. FIG. 1 is a diagram schematically showing an example of calcium carbonate having a hierarchical structure according to the embodiment. In FIG. 1, 1 is calcium carbonate having a dense structure, and 2 is calcium carbonate having a cylindrical, needle-like or columnar (in FIG. 1, it is assumed to be needle-like for convenience) elongated structure. Although not depicted in FIG. 1, the calcium carbonate having a dense structure of 1 may be hollow. Since the calcium carbonate having a hierarchical structure according to the embodiment can carry a drug in a portion of a layer of calcium carbonate having a cylindrical, needle-like or columnar elongated structure or in a portion of hollow particles having a dense structure at the center, it can be used in a wide range of fields such as pharmaceuticals, cosmetics, perfumes, foods, and daily sundries.

[0029] The second embodiment of the present invention is the following steps: A step of mixing calcite-type calcium carbonate particles, gelatin, and water, heating and stirring to obtain a gelatin / calcite-type calcium carbonate particle mixed slurry A: A step of dissolving a surfactant in oil and stirring to obtain a solution B: A step of adding the gelatin / calcite-type calcium carbonate particle mixed slurry A to the solution B and stirring to obtain an emulsion emulsion C: A step of adding a crosslinking agent to the emulsion emulsion C and stirring to obtain an emulsion D containing gelatin / calcite-type calcium carbonate composite particles: A step of centrifuging the emulsion D containing gelatin / calcite-type calcium carbonate composite particles to obtain gelatin / calcite-type calcium carbonate composite particles: A step of firing the gelatin / calcite-type calcium carbonate composite particles to obtain calcite-type calcium carbonate dense particles: and Placing calcite-type calcium carbonate dense particles in an atmosphere containing at least carbon dioxide to obtain calcium carbonate having a hierarchical structure, where the surface of the calcium carbonate dense particles has calcium carbonate having an elongated structure in the shape of a cylinder, needle, or column It is a method for producing calcium carbonate having a hierarchical structure, including

[0030] A second embodiment is a method for producing calcium carbonate having a hierarchical structure of a first embodiment. The production method of the second embodiment includes a step of mixing calcite-type calcium carbonate particles, gelatin, and water, and heating and stirring to obtain a gelatin / calcite-type calcium carbonate particle mixed slurry A. The calcium carbonate used as a raw material in this step is of the calcite type, and its primary particle size is 10 - 300 nm, preferably 30 - 150 nm, more preferably 50 - 120 nm, and most preferably 80 - 100 nm. Also, the gelatin used in this step is a protein obtained by extracting collagen fibers contained in animal bones and skins with hot water. Gelatin can be used regardless of whether it is derived from cows, pigs, or fish. When calcite-type calcium carbonate particles, gelatin, and water are mixed and stirred at 50 - 60°C, preferably 50 - 55°C, a water slurry in which gelatin and calcite-type calcium carbonate particles are dispersed is obtained. At this time, in the gelatin / calcite-type calcium carbonate particle mixed slurry A, gelatin and calcite-type calcium carbonate are mixed so that the mass ratio of gelatin to calcite-type calcium carbonate particles is in the range of 5:10 - 30:10, more preferably 10:10 - 20:10. When the mass of gelatin relative to the mass of calcite-type calcium carbonate particles is reduced, the calcite-type calcium carbonate granules finally obtained in this embodiment tend to have a dense structure rather than a hollow structure. When the mass of gelatin relative to the mass of calcite-type calcium carbonate particles is increased, the calcite-type calcium carbonate granules finally obtained in this embodiment tend to have a hollow structure. Also, it is preferable to use water in an amount of 2.5 - 6 times, preferably 3 - 4.5 times, the total mass of gelatin and calcite-type calcium carbonate.

[0031] The manufacturing method of the second embodiment includes a step of dissolving a surfactant in oil and stirring to obtain solution B, separately from the step of obtaining the above gelatin / calcite calcium carbonate particle mixed slurry A. Any surfactant that can be dissolved in the oil described below may be used. For example, anionic surfactants such as monoalkyl sulfates, alkyl polyoxyethylene sulfates, alkylbenzene sulfonates, and monoalkyl phosphates; cationic surfactants such as alkyltrimethylammonium salts, dialkyldimethylammonium salts, and alkylbenzyldimethylammonium salts; amphoteric surfactants such as alkyl carboxybetaines; and nonionic surfactants such as polyoxyethylene alkyl ethers, fatty acid sorbitan esters, alkyl polyglycosides, fatty acid diethanolamides, and alkyl monoglyceryl ethers can be selected. In particular, it is preferable to use water-soluble nonionic surfactants such as polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monolaurate, known under the names of Tween and polysorbate, and sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate, sorbitan monolaurate, etc., known under the name of Span. As the oil for dissolving the surfactant, an oil that is liquid at normal temperature, such as paraffinic base oil, naphthenic base oil, vegetable or animal edible oil, and industrial fats and oils, can be used. In particular, it is preferable to use paraffinic base oil or edible oil. The volume ratio of the surfactant to the oil can be in the range of 1:100 - 5:100, preferably in the range of 1:100 - 2:100.

[0032] After obtaining the gelatin / calcite calcium carbonate particle mixed slurry A and the solution B, a step of mixing the gelatin / calcite calcium carbonate particle mixed slurry A and the solution B, stirring them, and obtaining an emulsion emulsion C is performed. The volume ratio of the gelatin / calcite calcium carbonate particle mixed slurry A to the solution B is in the range of 1:10 - 10:10, preferably in the range of 1:10 - 2:10. The gelatin / calcite calcium carbonate particle mixed slurry A is added to the solution B so that they are mixed. When mixing the two, the gelatin / calcite calcium carbonate particle mixed slurry A may be added to the solution B at once, or it can also be added dropwise while stirring the solution B. Also, the solution B may be added to the gelatin / calcite calcium carbonate particle mixed slurry A at once, or the solution B can be added dropwise while stirring the gelatin / calcite calcium carbonate particle mixed slurry A. Stirring of the mixture of the two can be carried out using existing stirring devices such as a magnetic stirrer, a stirrer equipped with various stirring blades, an ultrasonic stirrer, etc. The stirring speed is preferably, for example, 300 - 1500 rpm, preferably 700 - 1200 rpm. In this way, the emulsion emulsion C is obtained. The emulsion emulsion C is a liquid in a state where grains in which gelatin and calcite calcium carbonate particles are aggregated are emulsified (dispersed) in oil. By appropriately changing the stirring speed in this step, the aggregation form of gelatin and calcite calcium carbonate particles can be changed. Generally, if the stirring speed is slowed down, a structure in which gelatin (hydrophilic part) and calcite calcium carbonate (hydrophobic part) randomly aggregate around a large aggregate of gelatin (hydrophilic part) is likely to form, and the diameter of the aggregate is likely to be relatively large. Also, if the stirring speed is increased, a structure in which gelatin (hydrophilic part) and calcite calcium carbonate (hydrophobic part) randomly aggregate is likely to form, and the diameter of the aggregate is likely to be relatively small.

[0033] Next, a crosslinking agent is added to the emulsion C and stirred to obtain an emulsion D containing gelatin / calcite calcium carbonate composite particles. Any compound that can crosslink the gelatin contained in the gelatin / calcite calcium carbonate particles emulsified and dispersed in the emulsion D can be used as the crosslinking agent. As the crosslinking agent, for example, 3-ethylcarbodiimide hydrochloride (such as 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride), 3-ethylcarbodiimide sulfate (such as 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide sulfate), 3-ethylcarbodiimide nitrate (such as 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide nitrate), transglutaminase, an olefin-maleic anhydride copolymer, an ammonia reaction product with an ethylenically unsaturated anhydride-maleic anhydride copolymer, a polyamide epoxy resin, glutaraldehyde, or genipin can be used. At this time, the crosslinking agent can be added to the emulsion C so that the mass ratio of gelatin to the crosslinking agent is in the range of 1:1 to 1:25, preferably in the range of 1:1 to 1:10. When the crosslinking agent is added to the emulsion C and stirred, the gelatin in the gelatin / calcite calcium carbonate particles is crosslinked to form gelatin / calcite calcium carbonate composite particles. That is, the emulsion D is a liquid in which the gelatin / calcite calcium carbonate composite particles are emulsified and dispersed in oil.

[0034] Subsequently, a step of centrifuging emulsion D containing gelatin / calcite calcium carbonate composite particles to obtain gelatin / calcite calcium carbonate composite particles is performed. The obtained gelatin / calcite calcium carbonate composite particles are granular solids formed by the composite of cross-linked gelatin and calcite calcium carbonate. For example, they can be composite particles with gelatin as a template and calcite calcium carbonate surrounding it. Alternatively, they can be composite particles forming a sea-island structure, including an island structure of cross-linked gelatin in a sea structure of calcite calcium carbonate. Furthermore, there may be cases where cross-linked gelatin specifically aggregated in the central part of the gelatin / calcite calcium carbonate composite particles forms a structure in which cross-linked gelatin and calcite calcium carbonate form a sea-island structure around it. The gelatin / calcite calcium carbonate composite particles obtained by centrifugation can be washed with a washing solvent such as water or alcohol and dried as appropriate. The particle size of the gelatin / calcite calcium carbonate particles depends on the stirring speed in the step of obtaining emulsion C and the amount of the cross-linking agent, and usually those in the range of 1 - 500 μm, preferably in the range of 5 - 200 μm can be obtained.

[0035] The step of firing the thus obtained gelatin / calcite-type calcium carbonate composite particles to obtain calcite-type calcium carbonate dense particles is carried out. The firing of the gelatin / calcite-type calcium carbonate composite particles is carried out at a temperature of 570 °C or higher and less than 650 °C, preferably 580 °C or higher and less than 600 °C, in air or under carbon dioxide, or in an inert gas atmosphere such as nitrogen or argon. When firing is carried out in air, the temperature is 570 °C or higher and less than 650 °C, when firing is carried out under carbon dioxide, the temperature is 580 °C or higher and less than 630 °C, and when firing is carried out under an inert gas, the temperature can be 590 °C or higher and less than 650 °C. The firing of the gelatin / calcite-type calcium carbonate composite particles can be carried out using an existing ceramics firing furnace. When the gelatin / calcite-type calcium carbonate composite particles are fired, first, the gelatin part is incinerated (burned), and only the calcite-type calcium carbonate part remains. That is, among the gelatin / calcite-type calcium carbonate particles, only the part with the island structure (gelatin) is removed by firing (burning), and only the part with the sea structure (calcite-type calcium carbonate) remains, that is, particles (granules) with a generally dense structure with pores here and there are formed. When firing is continued at a temperature within the above range, the pores present in the granules are blocked, and a part of the calcite-type calcium carbonate (especially the calcium carbonate on the surface part of the granules) is changed to calcium oxide. Thus, calcite-type calcium carbonate dense particles in which a part has become calcium oxide are obtained. In this specification, when referring to calcite-type calcium carbonate dense particles, it is assumed that particles in which a part of the calcite-type calcium carbonate has been changed to calcium oxide are also included. The diameter of the calcite-type calcium carbonate dense particles is almost the same as the particle diameter of the gelatin / calcite-type calcium carbonate particles obtained in the previous step, usually in the range of 1 - 500 μm, preferably in the range of 5 - 200 μm, or the particle diameter becomes slightly smaller due to the blocking of the pores of the gelatin / calcite-type calcium carbonate particles obtained in the previous step. The obtained calcite-type calcium carbonate dense particles are almost spherical.

[0036] Next, the obtained calcite-type calcium carbonate dense particles are placed in an atmosphere containing at least carbon dioxide, and a step of obtaining calcium carbonate having a hierarchical structure, which has calcium carbonate having an elongated structure such as a cylinder, a needle, or a column, on the surface of the calcium carbonate dense particles is performed. The surface of the calcite-type calcium carbonate dense particles obtained by firing in the previous step becomes unstable, and many cracks and pore structures are generated. When the calcite-type calcium carbonate dense particles in this state are left at room temperature, two changes may occur on the surface of the calcium carbonate dense particles. First, one is a change in which the surface of the calcium carbonate dense particles absorbs moisture in the atmosphere and releases calcium ions and carbonate ions. In an atmosphere containing at least carbon dioxide, the calcium ions released into the cracks and pore structures react with carbonate ions or carbon dioxide to change into calcium carbonate. The calcium carbonate formed by the reaction of the released calcium ions with carbonate ions or carbon dioxide is of the calcite type. The reaction of the released calcium ions with carbonate ions or carbon dioxide occurs simultaneously everywhere on the surface of the calcite-type calcium carbonate dense particles, and the growth of calcium carbonate crystals also starts simultaneously everywhere on the surface of the calcite-type calcium carbonate dense particles. Another is a change in which a small amount of calcium oxide existing on the surface of an aggregate of calcite-type calcium carbonate dense particles obtained by firing in the previous step reacts with carbon dioxide in an atmosphere containing at least carbon dioxide to become calcium carbonate by decomposition. The calcium carbonate formed by the reaction of calcium oxide and carbon dioxide is of the calcite type. The reaction of calcium oxide and carbon dioxide occurs simultaneously everywhere on the surface of the calcite-type calcium carbonate dense particles, and the growth of calcium carbonate crystals also starts simultaneously everywhere on the surface of the calcite-type calcium carbonate dense particles. For this reason, calcite-type calcium carbonate grows to have an elongated structure such as a cylindrical, needle-like or columnar shape. In this step, if the calcite-type calcium carbonate dense particles are placed in an atmosphere with a controlled carbon dioxide concentration, the growth of calcite-type calcium carbonate with an elongated structure such as a cylindrical, needle-like or columnar shape can be controlled. If the carbon dioxide concentration of the atmosphere in which the calcite-type calcium carbonate dense particles are placed is about that of the atmosphere (at least 0.03%), calcite-type calcium carbonate with an elongated structure such as a cylindrical, needle-like or columnar shape grows. Also, the temperature of the atmosphere containing at least carbon dioxide for placing the calcite-type calcium carbonate dense particles is preferably in the range of around room temperature (about 20 °C) to 80 °C, preferably 20 - 40 °C. In this way, calcium carbonate having a hierarchical structure having at least a layer of calcite-type calcium carbonate dense particles and a layer of calcite-type calcium carbonate having an elongated structure such as a cylindrical, needle-like or columnar shape can be obtained.

[0037] Here, among calcium carbonates having a hierarchical structure, the calcium carbonate having a dense structure is preferably particles with a diameter of 10 - 200 μm. The calcium carbonate having a dense structure is preferably a higher-order structure having a dense structure formed by aggregation of primary particles of calcite-type calcium carbonate, and preferably, it is particles of a higher-order structure. The diameter of these particles is 10 - 200 μm, preferably 20 - 150 μm, more preferably 30 - 100 μm. Further, among calcium carbonates having a hierarchical structure, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, preferably in the range of 0.2 - 0.8 μm, more preferably in the range of 0.3 - 0.6 μm. The length of the calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm, preferably in the range of 0.2 - 8 μm, more preferably in the range of 0.3 - 7 μm, but there is no limit to the length, and for example, it is also possible in some cases to make it as long as 30 μm or the like.

[0038] Furthermore, as another form in the second embodiment, among calcium carbonates having a hierarchical structure, the calcium carbonate having a dense structure may be hollow particles with a diameter of 10 - 200 μm. The calcium carbonate having a dense structure is preferably a higher-order structure having a dense structure formed by aggregation of primary particles of calcite-type calcium carbonate, and preferably, it is a hollow particle of a higher-order structure. In this case, the calcium carbonate having a hierarchical structure produced in the second embodiment includes at least three layers: a cavity portion inside the hollow particle, a layer of calcium carbonate having a dense structure, and a layer composed of an aggregate of calcium carbonate having an elongated structure such as a cylindrical, needle-shaped, or columnar shape. Here, the diameter of the hollow particle is 10 - 200 μm, preferably 20 - 150 μm, and more preferably 30 - 100 μm. Furthermore, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, preferably in the range of 0.2 - 0.8 μm, and more preferably in the range of 0.3 - 0.6 μm. Among the calcium carbonates having a hierarchical structure, the length of the calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm, preferably in the range of 0.2 - 8 μm, and more preferably in the range of 0.3 - 7 μm, but there is no limit to the length, and it can be made long up to, for example, 30 μm or the like in some cases.

[0039] The production method of the second embodiment can obtain calcite-type calcium carbonate having a hierarchical structure with a high yield by a relatively simple process. The calcium carbonate having at least a two-layer hierarchical structure obtained by the second embodiment has a special shape such as "murasaki uni" or "iga guri" because a plurality of calcium carbonates having an elongated structure such as a cylindrical, needle-shaped, or columnar shape radially extend from the surface of the particles of calcium carbonate having a dense structure in the central part. For example, since a drug can be supported on a part of the layer of calcium carbonate having an elongated structure such as a cylindrical, needle-shaped, or columnar shape, or on a part of the hollow particle having a dense structure in the central part, it can be used in a wide range of fields such as pharmaceuticals, cosmetics, perfumes, foods, and daily sundries.

Examples

[0040] The embodiments of the present invention will be specifically described below. The present invention is not limited to the following examples.

[0041] <Production of Calcite-Type Calcium Carbonate Having a Hierarchical Structure> [Example 1] Gelatin (Fuji Film Wako Pure Chemical Corporation) and calcite-type calcium carbonate with a particle diameter of 80 nm (Shiraishi Central Research Institute Co., Ltd.) were dispersed in water so that the mass ratio was 1:1. It was heated to a temperature of 50 - 60 °C and stirred using a stirrer to obtain a gelatin / calcite-type calcium carbonate particle mixed slurry (gelatin / calcite-type calcium carbonate particle mixed slurry A).

[0042] On the other hand, a surfactant (Span 80, Fuji Film Wako Pure Chemical Corporation) and liquid paraffin (Fuji Film Wako Pure Chemical Corporation) were mixed so that the volume ratio was 1:100 and stirred to obtain a solution (solution B). Next, the gelatin / calcite-type calcium carbonate particle mixed slurry A was added to solution B so that the volume ratio of the gelatin / calcite-type calcium carbonate particle mixed slurry A to solution B was 1:10, and stirred at a stirring speed of 1200 rpm at room temperature to obtain an emulsion (emulsion C).

[0043] A cross-linking agent was added to emulsion C so that the mass ratio of gelatin to the cross-linking agent carbodiimide hydrochloride (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, Fuji Film Wako Pure Chemical Corporation) was 1:2. When this was stirred, an emulsion containing gelatin / calcite-type calcium carbonate particles (emulsion D) was obtained. Emulsion D was separated using a centrifuge, and the obtained solid part was washed 5 times with acetone and dried at room temperature in the air to obtain gelatin / calcite-type calcium carbonate composite particles. When the gelatin / calcite-type calcium carbonate composite particles were calcined at 570 °C in the air using a firing furnace, dense particles of calcite-type calcium carbonate were obtained.

[0044] Next, the obtained calcite-type calcium carbonate dense particles were left at room temperature in the atmosphere for 3 days. Calcium carbonate having a hierarchical structure in which a large number of calcium carbonates with an elongated structure were formed on the surface of the calcite-type calcium carbonate dense particles was obtained. The diameter of the elongated structure was about 0.3 μm, and the shape was needle-like.

[0045] Figure 2-A is a scanning electron micrograph (magnification: 5000 times) of calcium carbonate having a hierarchical structure obtained by the method of Example 1. In the observation field of view, particles of calcium carbonate in which a large number of needle-like elongated structures were formed were seen. Figure 2-B is a scanning electron micrograph with a magnification of 20,000 times, which is an enlarged view of the elongated structure portion on the surface of calcium carbonate. An elongated structure portion with some cracks was observed. From this photograph, it was found that there was a cavity in the center of the elongated structure. Regarding the hierarchical structure obtained in Example 1, when crystal structure analysis was performed by X-ray diffraction method, it was also confirmed that calcium carbonate was calcite crystal (Figure 3).

[0046] [Example 2] Gelatin (Fuji Film Wako Pure Chemical Industries, Ltd.) and calcite-type calcium carbonate with a particle diameter of 80 nm (Shiraishi Central Research Institute Co., Ltd.) were dispersed in water so that the mass ratio was 2:1. It was heated to a temperature of 50-60 °C and stirred using a stirrer to obtain a gelatin / calcite-type calcium carbonate particle mixed slurry (gelatin / calcite-type calcium carbonate particle mixed slurry A).

[0047] On the other hand, a surfactant (Span 80, Fuji Film Wako Pure Chemical Industries, Ltd.) and liquid paraffin (Fuji Film Wako Pure Chemical Industries, Ltd.) were mixed so that the volume ratio was 1:100 and stirred to obtain a solution (solution B). Solution B was placed in an ice bath and cooled to 0 °C. Next, the gelatin / calcite-type calcium carbonate particle mixed slurry A was added to solution B so that the volume ratio of the gelatin / calcite-type calcium carbonate particle mixed slurry A to solution B was 1:10, and stirred at 0 °C (in an ice bath) at a stirring speed of 1000 rpm to obtain an emulsion emulsion (emulsion emulsion C).

[0048] To emulsion C, a cross-linking agent was added such that the mass ratio of gelatin to carbodiimide hydrochloride (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, manufactured by FUJIFILM Wako Pure Chemical Corporation), which is a cross-linking agent, was 1:1. When this was stirred, an emulsion (emulsion D) containing gelatin / calcite calcium carbonate particles was obtained. Emulsion D was separated using a centrifuge, and the obtained solid portion was washed 5 times with acetone and dried at room temperature under the atmosphere to obtain gelatin / calcite calcium carbonate composite particles. When the gelatin / calcite calcium carbonate composite particles were calcined at 570 °C in the atmosphere using a firing furnace, dense particles of calcite calcium carbonate with a cavity in the center were obtained.

[0049] Next, the obtained dense calcite calcium carbonate particles were left at room temperature under the atmosphere for 3 days. Calcium carbonate having a hierarchical structure in which a large number of calcium carbonates having an elongated structure were formed on the surface of the dense calcite calcium carbonate particles was obtained. The diameter of the elongated structure was about 0.1 to 0.3 μm, and the shape was needle-like.

[0050] Figure 4-A is a scanning electron micrograph (magnification: 500 times) of calcium carbonate (hollow body) having a hierarchical structure obtained by the method of Example 2. In the observation field of view, hollow particles of calcium carbonate in which a large number of needle-like elongated structures were formed were seen. Figure 4-B is a scanning electron micrograph with a magnification of 1,000 times, which is an enlarged view of the calcium carbonate hollow body having a hierarchical structure. When crystal structure analysis by X-ray diffraction method was performed on the calcium carbonate having a hierarchical structure obtained in Example 2, it was also confirmed that the calcium carbonate was calcite crystal (Figure 5).

[0051] The present invention can provide calcium carbonate having a novel and unique hierarchical structure. Using the production method of the present invention, calcite-type calcium carbonate having a hierarchical structure can be produced by a relatively simple process. The produced calcite-type calcium carbonate having a hierarchical structure can carry various drugs and the like on the layers of calcium carbonate having an elongated structure. By the production method of the present invention, it is also possible to produce calcite-type calcium carbonate having at least a three-layer structure with a cavity in the center. It is expected that the obtained calcite-type calcium carbonate having a three-layer structure can be used for drug delivery systems, cosmetic additives, food additives, health foods, catalyst carriers, and the like.

Claims

1. Calcium carbonate having a hierarchical structure, wherein the surface of the calcium carbonate having a dense structure has calcium carbonate having a cylindrical, needle-shaped or columnar elongated structure.

2. The calcium carbonate having a hierarchical structure according to claim 1, wherein the calcium carbonate having a dense structure is particles with a diameter of 10 - 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, and the length of the calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm.

3. The calcium carbonate having a hierarchical structure according to claim 1, wherein the calcium carbonate having a dense structure is hollow particles with an outer diameter of 10 - 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, and the length of the calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm.

4. The following steps: A step of mixing calcite-type calcium carbonate particles, gelatin, and water, heating and stirring to obtain a gelatin / calcite-type calcium carbonate particle mixed slurry A: A step of dissolving a surfactant in oil and stirring to obtain a solution B: A step of adding the gelatin / calcite-type calcium carbonate particle mixed slurry A to the solution B and stirring to obtain an emulsion emulsion C: A step of adding a crosslinking agent to the emulsion emulsion C and stirring to obtain an emulsion D containing gelatin / calcite-type calcium carbonate composite particles: A step of centrifuging the emulsion D containing gelatin / calcite-type calcium carbonate composite particles to obtain gelatin / calcite-type calcium carbonate composite particles: A step of firing the gelatin / calcite-type calcium carbonate composite particles to obtain calcite-type calcium carbonate dense particles: and A step of placing the calcite-type calcium carbonate dense particles in an atmosphere containing at least carbon dioxide to obtain calcium carbonate having a hierarchical structure, wherein the surface of the calcium carbonate dense particles has calcium carbonate having a cylindrical, needle-shaped or columnar elongated structure A method for producing calcium carbonate having a hierarchical structure, comprising the above steps.

5. The method for producing calcium carbonate having a hierarchical structure according to claim 4, wherein in the gelatin / calcite-type calcium carbonate particle mixed slurry A, the mass ratio of gelatin to calcite-type calcium carbonate particles is in the range of 5:10 - 25:

10.

6. The method for producing calcium carbonate having a hierarchical structure according to claim 5, wherein in solution B, the volume ratio of the surfactant to the oil is in the range of 1:100 to 5:

100.

7. The method for producing calcium carbonate having a hierarchical structure according to claim 5, wherein the volume ratio of the gelatin / calcite-type calcium carbonate particle mixed slurry A to solution B is in the range of 1:10 to 10:

10.

8. The method for producing calcium carbonate having a hierarchical structure according to claim 6, wherein the volume ratio of the gelatin / calcite-type calcium carbonate particle mixed slurry A to solution B is in the range of 1:10 to 10:

10.

9. The method for producing calcium carbonate having a hierarchical structure according to claim 5, wherein a crosslinking agent is added to the emulsion emulsion C such that the mass ratio of gelatin to the crosslinking agent is in the range of 1:1 to 1:

25.

10. The method for producing calcium carbonate having a hierarchical structure according to claim 6, wherein a crosslinking agent is added to the emulsion emulsion C such that the mass ratio of gelatin to the crosslinking agent is in the range of 1:1 to 1:

25.

11. The method for producing calcium carbonate having a hierarchical structure according to claim 7, wherein a crosslinking agent is added to the emulsion emulsion C such that the mass ratio of gelatin to the crosslinking agent is in the range of 1:1 to 1:

25.

12. The method for producing calcium carbonate having a hierarchical structure according to claim 8, wherein a crosslinking agent is added to the emulsion emulsion C such that the mass ratio of gelatin to the crosslinking agent is in the range of 1:1 to 1:

25.

13. The method for producing calcium carbonate having a hierarchical structure according to any one of claims 4 to 12, wherein the gelatin / calcite-type calcium carbonate composite particles are calcined at a temperature of 570 °C or higher and less than 650 °C.

14. The method for producing calcium carbonate having a hierarchical structure according to claim 13, wherein the calcium carbonate having a dense structure is particles with a diameter of 10 - 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, and the length of the calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm.

15. The method for producing calcium carbonate having a hierarchical structure according to claim 13, wherein the calcium carbonate having a dense structure is hollow particles with an outer diameter of 10 - 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 - 1.0 μm, and the length of the calcium carbonate having an elongated structure is in the range of 0.1 - 10 μm.

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