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 in which calcium carbonate having a cylindrical, needle-like or columnar elongated structure is arranged at the surface of a pellet composed of an aggregate of calcium carbonate compact particles. Preferably, the diameter of the calcium carbonate compact particles is 10 to 200 μm, and 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 30 μm.SELECTED DRAWING: Figure 1-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, plastics, paper, sealants, paints and inks, etc., a calcium fortifier for foods, feeds, etc., and an alkaline agent in fertilizers, etc. Calcium carbonate used in these applications is roughly classified into light 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 having a rhombohedral or cubic shape. Since calcium carbonate is inexpensive, easy to prepare, has a high whiteness, and is excellent in biocompatibility and degradability, various forms of calcium carbonate have been actively made in the fields of pharmaceuticals and cosmetics, etc.

[0004] Patent Document 1 discloses calcium carbonate characterized in that the crystal has a columnar shape, is hollow in the long-axis direction, the hollow in the long-axis direction is closed at one end of the crystal and open at the other end. The hollow columnar calcium carbonate obtained in Patent Document 1 is columnar particles having the characteristic of being hollow in the long-axis direction, and is an aragonite crystal having a shape in which one end is closed and the other is open, so it can be converted into more stable calcite-type calcium carbonate. Whether the hollow columnar shape is maintained when the crystal form is converted is unknown. On the other hand, Non-Patent Document 1 discloses that citric acid is used in combination with carbon dioxide bubbles as a template as a crystal growth regulator, and an aqueous calcium chloride solution and an aqueous sodium carbonate solution are allowed to flow on both sides of a microporous film and reacted to synthesize calcite-type calcium carbonate nanotubes. The method of Non-Patent Document 1 makes it difficult to completely remove citric acid from the produced calcite-type calcium carbonate nanotubes, and it is also very difficult to control the size and shape of the carbon dioxide bubbles used during synthesis.

[0005] As proposed in Patent Document 1 and Non-Patent Document 1, calcium carbonate having a novel structure has always been desired, but the more complex the structure becomes, the more complex the manufacturing method for obtaining it becomes, and no method for efficiently obtaining calcium carbonate having a complex structure has been proposed. It is desired to manufacture calcite crystal form calcium carbonate having a more stable and more complex structure that could not be synthesized heretofore.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] Accordingly, 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] An aspect of the present invention is calcium carbonate in which calcium carbonate having a cylindrical, needle-like or columnar elongated structure is arranged on the surface of a pellet composed of an aggregate of calcium carbonate dense particles.

[0010] Here, the diameter of the calcium carbonate dense particles is preferably in the range of 10 - 200 μm, the cross-sectional diameter of the calcium carbonate having the elongated structure is in the range of 0.1 - 1.0 μm, and the length of the calcium carbonate having the elongated structure is in the range of 0.1 - 30 μm.

[0011] 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 disposing the gelatin / calcite-type calcium carbonate composite particles on the surface of a substrate to obtain an aggregate of gelatin / calcite-type calcium carbonate composite particles: A step of firing an aggregate of gelatin / calcite calcium carbonate composite particles to obtain a pellet composed of an aggregate of dense calcite calcium carbonate particles; and A step of placing a pellet composed of an aggregate of dense calcite calcium carbonate particles in an atmosphere containing at least carbon dioxide to obtain calcium carbonate in which calcium carbonate having a cylindrical, needle-like or columnar elongated structure is arranged on the surface of the pellet composed of the aggregate of dense calcium carbonate particles A method for producing calcium carbonate, comprising:

[0012] Here, in the gelatin / calcite calcium carbonate particle mixed slurry A, the mass ratio of gelatin to calcite calcium carbonate particles is preferably in the range of 5:10 - 20:10.

[0013] Also, in solution B, the volume ratio of the surfactant to the oil is preferably in the range of 1:100 - 5:100.

[0014] The volume ratio of the gelatin / calcite calcium carbonate particle mixed slurry A to solution B is preferably in the range of 1:10 - 10:10.

[0015] It is preferable to add a crosslinking agent to the emulsion C such that the mass ratio of gelatin to the crosslinking agent is in the range of 1:1 - 1:20.

[0016] Furthermore, it is preferable to fire the gelatin / calcite calcium carbonate composite particles at a temperature of 570°C or higher and lower than 700°C.

[0017] 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 preferably 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

[0018] The manufacturing method of the present invention can produce calcite-type calcium carbonate with a novel structure in a relatively simple process with a high yield. The produced calcite-type calcium carbonate with a novel structure can be used in various fields such as pharmaceuticals, cosmetics, perfumes, foods, and beverages by loading various drugs and the like on the part of the calcium carbonate layer having an elongated structure.

Brief Description of the Drawings

[0019]

Figure 1-A

Figure 1-B

Figure 2-A

Figure 2-B

Figure 3

Modes for Carrying Out the Invention

[0020] The embodiments of the present invention will be described in more detail, but the present invention is not limited only to the following embodiments.

[0021] One embodiment of the present invention is calcium carbonate in which calcium carbonate having a cylindrical, needle-like or columnar elongated structure is arranged on the surface of a pellet composed of an aggregate of calcium carbonate dense particles.

[0022] 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 kind of light calcium carbonate. When simply referred to as calcium carbonate in this specification, it means 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). The calcium carbonate of the embodiment may be any crystal, but is preferably of the calcite type.

[0023] Here, in the embodiment, dense particles refer to particles that have almost no pores on the surface of calcium carbonate and have a dense structure. Dense particles are higher-order structures such as a dense secondary structure of calcium carbonate formed by the aggregation of primary particles of calcium carbonate. The calcium carbonate dense particles are preferably composed of calcite-type calcium carbonate. In addition, an aggregate of calcium carbonate dense particles refers to a state in which a plurality of calcium carbonate dense particles gather to form a lump of an object. A pellet generally refers to a synthetic resin in the form of grains like rice grains, but in this specification, it refers to a state in which a plurality of calcium carbonate dense particles are aggregated to a certain size. By controlling the number of calcium carbonate dense particles to be aggregated, the size of the pellet can also be controlled. For example, pellets of various sizes such as 1 mm or more, 10 mm or more, 100 mm or more, etc. can be obtained as desired.

[0024] On the one hand, calcium carbonate having an elongated structure in the form of a cylinder, needle, or column is preferably composed of calcite-type calcium carbonate. Calcium carbonate having these elongated structures aggregates and arranges on the surface of pellets composed of an aggregate of dense particles of calcium carbonate to form a layer. Calcium carbonate having an elongated structure in the form of a cylinder, needle, or column is also a higher-order structure such as a secondary structure of calcium carbonate formed by the 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 (with a cavity inside). Calcium carbonate having a needle-shaped elongated structure is calcium carbonate having a shape like a tube with a tapered structure. Furthermore, 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 with an aspect ratio such as a cylinder, needle, or column, but includes a structure with an aspect ratio of 1 (i.e., the lengths of the long part and the short part are equal).

[0025] Calcium carbonate of one embodiment has a hierarchical structure composed of a pellet (first layer) composed of an aggregate of dense particles of calcium carbonate and a layer (second layer) in which calcium carbonate having an elongated structure in the form of a cylinder, needle, or column is arranged. The hierarchical structure generally refers to a structure in which the whole is constructed by stacking layers in order from the lower layer to the upper layer. That is, calcium carbonate of one embodiment is calcium carbonate having a novel hierarchical structure, and it can be said that layers of calcium carbonate having different shapes and structures are stacked in order.

[0026] Here, the calcium carbonate dense particles are preferably particles with a diameter of 10 - 200 μm. As described above, the calcium carbonate dense particles are preferably a higher-order structure having a dense structure formed by aggregation of primary particles of calcite-type calcium carbonate, and are preferably particles of a higher-order structure. The diameter of the dense particles is 10 - 200 μm, preferably 20 - 150 μm, more preferably 30 - 100 μm. Further, 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 to make it as long as 30 μm or the like in some cases.

[0027] The calcium carbonate of the embodiment has a special shape in which a plurality of calcium carbonates having a cylindrical, needle-like or columnar elongated structure extend from the surface of a pellet composed of an aggregate of calcium carbonate particles having a dense structure. The calcium carbonates having a cylindrical, needle-like or columnar elongated structure are aligned to form an array. FIG. 1-A is a diagram schematically showing how the calcium carbonate of the embodiment looks when viewed from the side. In FIG. 1-A, 1 is a portion of an array of calcium carbonates having an elongated structure, and 2 is a portion where calcium carbonate particles having a dense structure are aggregated to form a pellet. In FIG. 1-A, the calcium carbonate 1 having an elongated structure is depicted as being columnar, but it is not limited thereto and may be cylindrical or columnar. Also, in FIG. 1-A, all the lengths of the calcium carbonates 1 having an elongated structure are depicted as being the same, but it is not limited thereto, and the calcium carbonates 1 having an elongated structure may each have a different length. FIG. 1-B is a diagram schematically showing how the calcium carbonate of the embodiment looks when viewed obliquely from above. In FIG. 1-B, 1 is a portion of an array of calcium carbonates having an elongated structure, and 2 is a portion where calcium carbonate particles having a dense structure are aggregated to form a pellet. In FIG. 1-B, the pellet 2 formed by the calcium carbonate particles having a dense structure is depicted as being circular, but it is not limited thereto. The pellet can be made into any desired shape. The calcium carbonate of the embodiment can regularly carry various drugs on the portion of the array of calcium carbonates having an elongated structure. The calcium carbonate of the embodiment can be used in a wide range of fields such as pharmaceuticals, cosmetics, perfumes, foods, and daily sundries.

[0028] 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: Step of adding a crosslinking agent to emulsion C, stirring to obtain emulsion D containing gelatin / calcite-type calcium carbonate composite particles: Step of centrifuging emulsion D containing gelatin / calcite-type calcium carbonate composite particles to obtain gelatin / calcite-type calcium carbonate composite particles: Step of disposing gelatin / calcite-type calcium carbonate composite particles on the surface of a substrate to obtain an aggregate of gelatin / calcite-type calcium carbonate composite particles: Step of firing the aggregate of gelatin / calcite-type calcium carbonate composite particles to obtain pellets composed of an aggregate of calcite-type calcium carbonate dense particles; and Step of placing the pellets composed of an aggregate of calcite-type calcium carbonate dense particles in an atmosphere containing at least carbon dioxide to obtain calcium carbonate in which calcium carbonate having a cylindrical, needle-shaped or columnar elongated structure is arranged on the surface of the pellets composed of an aggregate of calcium carbonate dense particles A method for producing calcium carbonate, comprising the above steps.

[0029] The second embodiment is a method for producing calcium carbonate of the 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 - 20:10, more preferably 10:10 - 20:10. If 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. If 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 3 - 6 times, preferably 3 - 4.5 times the total mass of gelatin and calcite-type calcium carbonate.

[0030] 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-mentioned gelatin / calcite-type calcium carbonate particle mixed slurry A. The surfactant used in this step may be any surfactant that can be dissolved in the oil described later. 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 name of Tween, and sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate, sorbitan monolaurate, known under the name of Span. As the oil for dissolving the surfactant, oils that are liquid at room temperature, such as paraffinic base oils, naphthenic base oils, vegetable or animal edible oils, and industrial fats and oils, can be used. In particular, it is preferable to use paraffinic base oils or edible oils. 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.

[0031] 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 and the two 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 dropped 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 dropped 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 is likely to be formed in which gelatin (hydrophilic part) and calcite calcium carbonate (hydrophobic part) randomly aggregate around a large aggregate of gelatin (hydrophilic part), 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 be formed, and the diameter of the aggregate is likely to be relatively small.

[0032] Next, a crosslinking agent is added to the emulsion C and stirred to obtain an emulsion D containing gelatin / calcite-type calcium carbonate composite particles. Any compound that can crosslink the gelatin contained in the gelatin / calcite-type 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 - 1:20, preferably in the range of 1:1 - 1:10. When the crosslinking agent is added to the emulsion C and stirred, the gelatin in the gelatin / calcite-type calcium carbonate particles is crosslinked to form gelatin / calcite-type calcium carbonate composite particles. That is, the emulsion D is a liquid in which the gelatin / calcite-type calcium carbonate composite particles are emulsified and dispersed in oil.

[0033] 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 surrounded by calcite calcium carbonate around it. Alternatively, they can be composite particles forming a sea-island structure that includes an island structure of cross-linked gelatin in a sea structure of calcite calcium carbonate. Furthermore, there may be a case 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 around it form a sea-island structure. 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 diameter 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.

[0034] Subsequently, a step of disposing the gelatin / calcite calcium carbonate composite particles on the surface of a substrate to obtain an aggregate of the gelatin / calcite calcium carbonate composite particles is performed. The gelatin / calcite calcium carbonate composite particles are disposed on the surface of a substrate made of glass, plastic, or metal, such as a petri dish, a well, a mold, etc., to produce an aggregate of the gelatin / calcite calcium carbonate composite particles. After this step, the aggregate of the gelatin / calcite calcium carbonate composite particles can be compacted using a press or the like to give the aggregate of the gelatin / calcite calcium carbonate composite particles a certain degree of shape retention.

[0035] Next, a step of firing an aggregate of gelatin / calcite-type calcium carbonate composite particles to obtain a pellet composed of an aggregate of dense calcite-type calcium carbonate particles is performed. When the aggregate of gelatin / calcite-type calcium carbonate composite particles obtained in the previous step has low fluidity and a certain degree of shape retention, the aggregate of gelatin / calcite-type calcium carbonate composite particles is removed from the substrate and fired. When the aggregate of gelatin / calcite-type calcium carbonate composite particles has a certain degree of fluidity and no shape retention, firing can be performed while the substrate remains. The firing of the aggregate of 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 set to 570 °C or higher and less than 650 °C. When firing is carried out under carbon dioxide, the temperature is set to 580 °C or higher and less than 630 °C. When firing is carried out under an inert gas, the temperature can be set to 590 °C or higher and less than 650 °C. The firing of the aggregate of gelatin / calcite-type calcium carbonate composite particles can be carried out using an existing ceramics firing furnace. When the aggregate of gelatin / calcite-type calcium carbonate composite particles is fired, first, the gelatin portion is incinerated (burned), and only the calcite-type calcium carbonate portion remains. That is, among the gelatin / calcite-type calcium carbonate particles, only the island-structured portion (gelatin) is removed by firing (burning), and only the sea-structured portion (calcite-type calcium carbonate) remains, that is, particles (granules) having 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 at least a part of the calcite-type calcium carbonate (especially the calcium carbonate on the surface portion of the granules) changes to calcium oxide. Thus, a pellet composed of an aggregate of dense calcite-type calcium carbonate particles, a part of which has become calcium oxide, is obtained. In this specification, when referring to dense calcite-type calcium carbonate particles, it is assumed to include particles in which a part of the calcite-type calcium carbonate has changed to calcium oxide in this way.The diameter of the calcite-type calcium carbonate dense particles is almost the same as that 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 diameter becomes slightly smaller due to the pores of the gelatin / calcite-type calcium carbonate particles obtained in the previous step being blocked. The resulting calcite-type calcium carbonate dense particles are almost spherical.

[0036] Next, a pellet composed of an aggregate of the obtained calcite-type calcium carbonate dense particles is placed in an atmosphere containing at least carbon dioxide, and a step of obtaining calcium carbonate in which calcium carbonate having an elongated structure, such as cylindrical, needle-shaped or columnar, is arranged on the surface of the pellet composed of the aggregate of the calcite-type calcium carbonate dense particles is performed. The surface of the pellet composed of the aggregate 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 pellet in this state is left at room temperature, two changes may occur on the surface of the calcite-type calcium carbonate dense particles. First, one is a change in which the surface of the particles absorbs moisture in the air 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 pellet composed of the aggregate of the calcite-type calcium carbonate dense particles, and the growth of calcium carbonate crystals also starts simultaneously everywhere on the surface of the pellet composed of the aggregate of the calcite-type calcium carbonate dense particles. Another is a change in which trace amounts of calcium oxide existing on the surface of pellets composed of an aggregate of calcite-type calcium carbonate dense particles obtained by firing in the previous step react with carbon dioxide in an atmosphere containing at least carbon dioxide to become calcium carbonate. 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 pellets composed of an aggregate of calcite-type calcium carbonate dense particles, and the growth of calcium carbonate crystals also starts simultaneously everywhere on the surface of the pellets composed of an aggregate of 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 pellets composed of an aggregate of calcite-type calcium carbonate dense particles are placed in an atmosphere with 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 pellets composed of an aggregate of 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 pellets composed of an aggregate of calcite-type calcium carbonate dense particles is preferably in the range of around room temperature (20°C or higher) to 80°C, preferably 20 - 40°C. In this way, calcium carbonate having a hierarchical structure can be obtained, which has at least a layer composed of an aggregate of calcite-type calcium carbonate dense particles and a layer in which calcite-type calcium carbonate with an elongated structure such as a cylindrical, needle-like, or columnar shape is arranged.

[0037] Here, among the calcium carbonates having such 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 the aggregation of primary particles of calcite-type calcium carbonate, and preferably, it is a particle of a higher-order structure. The diameter of this particle is 10 - 200 μm, preferably 20 - 150 μm, more preferably 30 - 100 μm. Further, among the 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 can be lengthened to 30 μm or the like in some cases.

[0038] The production method of the second embodiment can obtain calcite-type calcium carbonate having a special hierarchical structure with a high yield by a relatively simple process. The calcium carbonate having a unique hierarchical structure obtained by the second embodiment has a plurality of calcium carbonates having a cylindrical, needle-like or columnar elongated structure extending from the surface of an aggregate of calcium carbonate particles having a dense structure. The calcium carbonates having a cylindrical, needle-like or columnar elongated structure are aligned to form an array. Various drugs can be regularly supported on the part of the array of calcium carbonate having an elongated structure. The calcium carbonate of the embodiment can be used in a wide range of fields such as pharmaceuticals, cosmetics, perfumes, foods, and daily sundries.

Examples

[0039] The embodiments of the present invention will be specifically described below. The present invention is not limited to the following examples.

[0040] <Production of Calcite-Type Calcium Carbonate Having a Hierarchical Structure> [Example 1] Gelatin (manufactured by Fuji Film Wako Pure Chemical Corporation) and calcite calcium carbonate with a particle size of 80 nm (manufactured by 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 calcium carbonate particle mixed slurry (gelatin / calcite calcium carbonate particle mixed slurry A).

[0041] On the other hand, a surfactant (Span 80, manufactured by Fuji Film Wako Pure Chemical Corporation) and liquid paraffin (manufactured by 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 calcium carbonate particle mixed slurry A was added to solution B so that the volume ratio of the gelatin / calcite calcium carbonate particle mixed slurry A to solution B was 1:10, and it was stirred at a stirring speed of 1200 rpm at room temperature to obtain an emulsion emulsion (emulsion emulsion C).

[0042] To the emulsion emulsion C, a crosslinking agent was added so that the mass ratio of gelatin to the crosslinking agent carbodiimide hydrochloride (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, manufactured by Fuji Film Wako Pure Chemical Corporation) was 1:1. When this was stirred, an emulsion (emulsion D) containing gelatin / calcite calcium carbonate particles was obtained. The 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 calcium carbonate composite particles. Next, the obtained gelatin / calcite calcium carbonate composite particles were put into a molding mold (made of metal) to obtain an aggregate of gelatin / calcite calcium carbonate composite particles. The aggregate of gelatin / calcite calcium carbonate composite particles was hardened using a universal power press. When the aggregate of gelatin / calcite calcium carbonate composite particles was fired in a firing furnace at 570°C in the air while still in the molding mold, pellets composed of an aggregate of dense particles of calcite calcium carbonate were obtained.

[0043] Pellets composed of an aggregate of calcite-type calcium carbonate dense particles were left standing in the air at room temperature for 2 days. Calcium carbonate having a hierarchical structure was obtained, which was formed such that a large number of calcium carbonates having an elongated structure were arranged on the surface of the pellets composed of the aggregate of calcite-type calcium carbonate dense particles. The diameter of the elongated structure was about 10 to 30 μm, and the shape was acicular.

[0044] Figure 2-A is a scanning electron micrograph (magnification: 10,000 times) of the surface portion of calcium carbonate having a hierarchical structure obtained by the method of Example 1. A large number of acicular calcium carbonates having an elongated structure were observed in the observation field of view. Figure 2-B is a transmission electron micrograph at a magnification of 150,000 times, which is an enlarged view of the elongated structure portion on the surface of calcium carbonate. When the crystal structure analysis of the calcium carbonate having a hierarchical structure obtained in Example 1 was performed by X-ray diffraction method, it was also confirmed that the calcium carbonate was calcite crystal (Figure 3).

[0045] 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 special hierarchical structure can be produced by a relatively simple process. The produced calcite-type calcium carbonate having a unique hierarchical structure can regularly support various drugs and the like in the array portion of the calcium carbonate having the elongated structure. It can be expected to use the calcite-type calcium carbonate of the present invention for drug delivery systems, cosmetic additives, food additives, health foods, catalyst carriers and the like.

Claims

1. Calcium carbonate in which calcium carbonate having a cylindrical, needle-like or columnar elongated structure is arranged on the surface of a pellet composed of an aggregate of calcium carbonate dense particles.

2. The calcium carbonate according to claim 1, wherein the diameter of the calcium carbonate dense particles is 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 - 30 μm.

3. 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 cross-linking 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 disposing the gelatin / calcite-type calcium carbonate composite particles on the surface of a substrate to obtain an aggregate of gelatin / calcite-type calcium carbonate composite particles: A step of firing the aggregate of gelatin / calcite-type calcium carbonate composite particles to obtain a pellet composed of an aggregate of calcite-type calcium carbonate dense particles; and A step of placing the pellet composed of an aggregate of calcite-type calcium carbonate dense particles in an atmosphere containing at least carbon dioxide to obtain calcium carbonate in which calcium carbonate having a cylindrical, needle-like or columnar elongated structure is arranged on the surface of the pellet composed of the aggregate of calcium carbonate dense particles A method for producing calcium carbonate, comprising:

4. The method for producing calcium carbonate according to claim 3, 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 - 20:

10.

5. The method for producing calcium carbonate according to claim 4, wherein in the solution B, the volume ratio of the surfactant to the oil is in the range of 1:100 - 5:

100.

6. The manufacturing method of calcium carbonate according to claim 4, wherein the volume ratio of the gelatin / calcite-type calcium carbonate particle mixed slurry A to the solution B is in the range of 1:10 - 10:

10.

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

10.

8. The manufacturing method of calcium carbonate according to claim 4, 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 - 1:

20.

9. The manufacturing method of calcium carbonate 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 - 1:

20.

10. The manufacturing method of calcium carbonate 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 - 1:

20.

11. The manufacturing method of calcium carbonate 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 - 1:

20.

12. The manufacturing method of calcium carbonate according to any one of claims 3 to 11, wherein the gelatin / calcite-type calcium carbonate composite particles are calcined at a temperature of 570 °C or higher and lower than 700 °C.

13. The manufacturing method of calcium carbonate according to claim 12, 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.

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