Calcium carbonate and production method for calcium carbonate

Abstract

The purpose of the present invention is to provide a calcium carbonate, and preferably a calcite-type calcium carbonate, that has a novel layered structure. The purpose of the present invention is also to provide a novel method for providing a calcium carbonate, and preferably a calcite-type calcium carbonate, that has a novel layered structure.　The present invention provides a calcium carbonate wherein calcium carbonate that has a cylindrical, acicular, or columnar elongated structure is arranged on the surface of pellets that comprise aggregates of calcium carbonate fine particles. The present invention also provides a production method for calcium carbonate that includes a step for 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, a step for dissolving a surfactant in oil and stirring to obtain a solution B, a step for adding the gelatin / calcite-type calcium carbonate particle mixed slurry A to the solution B and stirring to obtain an emulsion C, a step for adding a cross-linking agent to the emulsion C and stirring to obtain an emulsion D that includes gelatin / calcite-type calcium carbonate composite particles, a step for centrifuging the emulsion D that includes the gelatin / calcite-type calcium carbonate composite particles to obtain the gelatin / calcite-type calcium carbonate composite particles, a step for arranging the gelatin / calcite-type calcium carbonate composite particles on the surface of a substrate to obtain aggregates of the gelatin / calcite-type calcium carbonate composite particles, a step for firing the aggregates of the gelatin / calcite-type calcium carbonate composite particles to obtain pellets that comprise aggregates of calcite-type calcium carbonate fine particles, and a step for placing the pellets that comprise aggregates of calcite-type calcium carbonate fine particles under an atmosphere that includes at least carbon dioxide to obtain a calcium carbonate wherein calcium carbonate that has a cylindrical, acicular, or columnar elongated structure is arranged on the surface of pellets that comprise aggregates of calcium carbonate fine particles.

Description

Calcium carbonate and method for producing calcium carbonate

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

[0002] Calcium carbonate is widely used as a reinforcing filler in rubber, plastics, paper, sealants, paints, inks, etc., a calcium fortifier in foods, feeds, etc., and an alkaline agent in fertilizers, etc. The calcium carbonate used for these purposes is roughly divided into light calcium carbonate, which is obtained by injecting carbon dioxide gas into an aqueous suspension of calcium hydroxide to cause a carbonation reaction, and heavy calcium carbonate, which is obtained by mechanically crushing and classifying high-quality limestone.

[0003] Calcium carbonate is known to have three crystalline phases: calcite, aragonite, and vaterite. Of these, calcite is the most stable crystalline phase, and vaterite, for example, transforms into calcite over time. Calcite-type calcium carbonate is generally a rhombohedral or cubic crystal with a dense structure. In other words, calcium carbonate with a higher structure obtained by conventional crystal growth of calcium carbonate almost always becomes stable calcite crystals with a rhombohedral or cubic shape. Calcium carbonate is inexpensive, easy to prepare, has high whiteness, and is biocompatible and degradable. Therefore, many attempts have been made to produce calcium carbonate in various forms, with the aim of actively utilizing it in fields such as pharmaceuticals and cosmetics.

[0004] Patent Document 1 discloses calcium carbonate characterized by a columnar crystal shape, hollow in the longitudinal direction, with one end of the crystal closed and the other open. The hollow columnar calcium carbonate obtained in Patent Document 1 is a columnar particle characterized by hollow in the longitudinal direction, and is an aragonite crystal with one end closed and the other open. Therefore, it can be converted to a more stable calcite-type calcium carbonate. It is unclear whether the hollow columnar shape is maintained during the crystal form conversion. On the other hand, Non-Patent Document 1 discloses the synthesis of calcite-type calcium carbonate nanotubes by using citric acid as a crystal growth regulator and carbon dioxide bubbles as a template, and flowing calcium chloride aqueous solution and sodium carbonate aqueous solution on both sides of a microporous film and allowing them to react. The method described in Non-Patent Document 1 makes it difficult to completely remove citric acid from the resulting calcite-type calcium carbonate nanotubes, and also makes it 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 is always in demand, but the more complex the structure, the more complex the production method for obtaining it becomes, and no method has been proposed for efficiently obtaining calcium carbonate having a complex structure. There is a demand for producing calcite crystalline calcium carbonate that is more stable and has a more complex structure than has been possible to synthesize so far.

[0006] Patent No. 4515780

[0007] Biol. Trace Elem. Res. , 2012, 147: 408-17

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

[0009] An embodiment of the present invention is calcium carbonate in which calcium carbonate particles having elongated cylindrical, needle-like or columnar structures are arranged on the surface of a pellet made of an aggregate of dense calcium carbonate particles.

[0010] In this embodiment, it is preferable that the diameter of the dense calcium carbonate particles is 10 to 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 to 1.0 μm, and the length of the calcium carbonate having an elongated structure is in the range of 0.1 to 30 μm.

[0011] Another aspect of the present invention is a method for producing a gelatin / calcite type calcium carbonate particle mixture, comprising the steps 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; dissolving a surfactant in oil and stirring to obtain a solution B; adding the gelatin / calcite type calcium carbonate particle mixed slurry A to solution B and stirring to obtain an emulsion C; adding a crosslinking agent to the emulsion C and stirring to obtain an emulsion D containing gelatin / calcite type calcium carbonate composite particles; centrifuging the emulsion D containing gelatin / calcite type calcium carbonate composite particles to obtain gelatin / calcite type calcium carbonate composite particles; arranging 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; firing the aggregate of gelatin / calcite type calcium carbonate composite particles to obtain a pellet consisting of an aggregate of calcite type calcium carbonate dense particles; and a step of placing pellets consisting of aggregates of dense particles of calcite-type calcium carbonate in an atmosphere containing at least carbon dioxide to obtain calcium carbonate in which calcium carbonate having elongated cylindrical, needle-like or columnar structures is arranged on the surface of the pellets consisting of aggregates of dense particles of calcium carbonate.

[0012] In this embodiment, 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 to 20:10.

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

[0014] 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 to 10:10.

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

[0016] 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 700°C.

[0017] In this embodiment, it is preferred that the calcium carbonate having a dense structure is in the form of particles having a diameter of 10 to 200 μm, the cross-sectional diameter of the calcium carbonate having an elongated structure is in the range of 0.1 to 1.0 μm, and the length of the calcium carbonate having an elongated structure is in the range of 0.1 to 10 μm.

[0018] The production method of the present invention is a relatively simple process that can produce calcite-type calcium carbonate having a novel structure in high yield. The produced calcite-type calcium carbonate having a novel structure can be used in various fields such as pharmaceuticals, cosmetics, fragrances, toiletries, foods, and beverages by supporting various drugs and the like in the layers of calcium carbonate having an elongated structure.

[0019] 1 is a schematic diagram showing the calcium carbonate of the present invention as viewed from the side. 2 is a schematic diagram showing the calcium carbonate of the present invention as viewed obliquely from above. 3 is a scanning electron microscope photograph (magnification: 10,000 times) of calcium carbonate having a hierarchical structure obtained by the method of Example 1. 4 is a transmission electron microscope photograph (magnification: 150,000 times) of calcium carbonate having a hierarchical structure obtained by the method of Example 1. 5 is an X-ray diffraction pattern, measured by X-ray diffractometry, of calcium carbonate granules having a hierarchical structure obtained by the method of Example 1.

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

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

[0022] Calcium carbonate has the formula CaCO ３ It is a calcium carbonate represented by the formula (I) and is the main component of seashells, eggshells, limestone, chalk, etc. Calcium carbonate is classified into heavy calcium carbonate (natural calcium carbonate) obtained by crushing and classifying limestone, and light calcium carbonate (synthetic calcium carbonate) obtained by chemical reaction, but the calcium carbonate produced in this embodiment is a type of light calcium carbonate. In this specification, when simply referring to calcium carbonate, it refers to light calcium carbonate (synthetic calcium carbonate) unless otherwise specified. Calcium carbonate exists in crystal polymorphs such as calcite crystals (trigonal rhombohedral crystals), aragonite crystals (orthorhombic crystals), and vaterite crystals (hexagonal crystals). The calcium carbonate of this embodiment may be any of the crystals, but calcite type is particularly preferred.

[0023] Here, in the embodiments, dense particles refer to particles having a dense structure with almost no pores on the surface of calcium carbonate. Dense particles are higher-order structures, such as dense secondary structures of calcium carbonate, formed by aggregation of primary particles of calcium carbonate. The dense calcium carbonate particles are preferably composed of calcite-type calcium carbonate. Furthermore, the term "aggregate of dense calcium carbonate particles" refers to a state in which multiple dense calcium carbonate particles are aggregated to form a single mass. While the term "pellet" generally refers to a synthetic resin in a granular shape like a grain of rice, in this specification it refers to a state in which multiple dense calcium carbonate particles are aggregated to a certain size. By controlling the number of dense calcium carbonate particles to be aggregated, the size of the pellets can also be controlled, and pellets of various sizes, such as 1 mm or more, 10 mm or more, or 100 mm or more, can be obtained as desired.

[0024] On the other hand, calcium carbonate having a cylindrical, needle-like, or columnar elongated structure is preferably composed of calcite-type calcium carbonate. These elongated calcium carbonates are aggregated and arranged on the surface of pellets composed of aggregates of dense calcium carbonate particles, forming layers. Calcium carbonate having a cylindrical, needle-like, or columnar elongated structure is also a higher-order structure, such as a secondary structure of calcium carbonate, formed by the aggregation of primary calcium carbonate particles. Calcium carbonate having a cylindrical elongated structure is calcium carbonate having a so-called tube-like shape (having a cavity inside). Calcium carbonate having a needle-like elongated structure is calcium carbonate having a tapered tube-like shape. Furthermore, calcium carbonate having a columnar elongated structure is calcium carbonate having a solid columnar shape, rather than a hollow tube-like structure. The term "elongated structure" generally refers to a structure with an aspect ratio, such as a cylinder, needle, or column, but also includes a structure with an aspect ratio of 1 (i.e., the length of the long and short parts is equal).

[0025] The calcium carbonate of one embodiment has a hierarchical structure composed of pellets (first layer) consisting of aggregates of dense calcium carbonate particles and a layer (second layer) in which calcium carbonate having an elongated structure such as a cylindrical, needle-like, or columnar shape is arranged. The hierarchical structure generally refers to a structure in which layers are stacked in order from lower to upper. In other words, the calcium carbonate of one embodiment is calcium carbonate having a novel hierarchical structure, in which layers of calcium carbonate having different shapes and structures are stacked in order.

[0026] Here, the dense calcium carbonate particles are preferably particles having a diameter of 10-200 μm. As described above, the dense calcium carbonate particles are preferably formed by the aggregation of primary particles of calcite-type calcium carbonate, and have a dense, high-order structure, but are preferably particles with a high-order structure. The diameter of the dense particles 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 0.2-0.8 μm, and more preferably 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 0.2-8 μm, and more preferably 0.3-7 μm, but there is no limit to the length, and it may be possible to increase it to, for example, 30 μm in some cases.

[0027] The calcium carbonate of the embodiment has a unique shape in which multiple calcium carbonate particles having elongated cylindrical, needle-like, or columnar structures extend from the surface of a pellet composed of an aggregate of calcium carbonate particles having a dense structure. The calcium carbonate particles having elongated cylindrical, needle-like, or columnar structures are aligned to form an array. FIG. 1-A is a schematic diagram showing the calcium carbonate of the embodiment as viewed from the side. In FIG. 1-A, 1 denotes the array of calcium carbonate particles having elongated structures, and 2 denotes the pellet formed by the aggregation of calcium carbonate particles having a dense structure. In FIG. 1-A, the calcium carbonate particles having elongated structures 1 are depicted as being columnar, but this is not limited thereto and may be cylindrical or columnar. In FIG. 1-A, all of the calcium carbonate particles having elongated structures 1 are depicted as having the same length, but this is not limited thereto and the calcium carbonate particles having elongated structures 1 may have different lengths. FIG. 1-B is a schematic diagram showing the calcium carbonate of the embodiment as viewed obliquely from above. In FIG. 1-B, 1 denotes an array of calcium carbonate having an elongated structure, and 2 denotes a pellet formed by the aggregation of calcium carbonate particles having a dense structure. In FIG. 1-B, the pellet 2 formed by the calcium carbonate particles having a dense structure is depicted as being circular, but this is not limited thereto. The pellet can have any desired shape. The calcium carbonate of the embodiment can carry various drugs in an orderly manner in 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, fragrances, food, and daily necessities.

[0028] A second embodiment of the present invention comprises the following steps: 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; 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 solution B and stirring to obtain an emulsion C; a step of adding a crosslinking agent to the 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 arranging 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 consisting of an aggregate of calcite-type calcium carbonate dense particles; and a step of placing pellets consisting of aggregates of dense particles of calcite-type calcium carbonate in an atmosphere containing at least carbon dioxide to obtain calcium carbonate in which calcium carbonate having elongated cylindrical, needle-like or columnar structures is arranged on the surface of the pellets consisting of aggregates of dense particles of calcium carbonate.

[0029] The second embodiment is a method for producing the 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, heating and stirring, and obtaining a gelatin / calcite-type calcium carbonate particle mixed slurry A. The calcium carbonate used as a raw material in this step is 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. The gelatin used in this step is a protein obtained by extracting collagen fibers contained in animal bones and skin with hot water. Gelatin may be derived from any of bovine, porcine, and fish. When calcite-type calcium carbonate particles, gelatin, and water are mixed and stirred at 50-60°C, preferably 50-55°C, an aqueous slurry in which gelatin and calcite-type calcium carbonate particles are dispersed is obtained. In this case, gelatin and calcite-type calcium carbonate are mixed so that the mass ratio of gelatin to calcite-type calcium carbonate particles in the gelatin / calcite-type calcium carbonate particle mixed slurry A 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. It is also preferable to use water in an amount 3 to 6 times, preferably 3 to 4.5 times, the total mass of gelatin and calcite-type calcium carbonate.

[0030] The manufacturing method of the second embodiment includes, apart from the step of obtaining the gelatin / calcite-type calcium carbonate particle mixed slurry A, a step of dissolving a surfactant in oil and stirring to obtain a solution B. The surfactant used in this step may be any surfactant that dissolves in the oil described below, and can be selected from, for example, anionic surfactants such as monoalkyl sulfates, alkyl polyoxyethylene sulfates, alkyl benzene sulfonates, and monoalkyl phosphates; cationic surfactants such as alkyl trimethyl ammonium salts, dialkyl dimethyl ammonium salts, and alkyl benzyl dimethyl ammonium salts; amphoteric surfactants such as alkyl carboxybetaine; and nonionic surfactants such as polyoxyethylene alkyl ethers, fatty acid sorbitan esters, alkyl polyglycosides, fatty acid diethanolamides, and alkyl monoglyceryl ethers. In particular, water-soluble nonionic surfactants such as polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monopalmitate, and polyoxyethylene sorbitan monolaurate, known as Tween or polysorbates, and sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate, and sorbitan monolaurate, known as SPAN, are preferred. Furthermore, oils that are liquid at room temperature, such as paraffinic base oils, naphthenic base oils, vegetable or animal edible oils, and industrial oils and fats, can be used as oils to dissolve the surfactants. Paraffinic base oils or edible oils are particularly preferred. The volume ratio of surfactant to oil can be in the range of 1:100-5:100, preferably 1:100-2:100.

[0031] After obtaining the gelatin / calcite-type calcium carbonate particle mixed slurry A and solution B, a step of mixing and stirring the gelatin / calcite-type calcium carbonate particle mixed slurry A with solution B is carried out to obtain an emulsion C. The gelatin / calcite-type calcium carbonate particle mixed slurry A is added to solution B and mixed so that 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, preferably in the range of 1:10 to 2:10. When mixing the two, the gelatin / calcite-type calcium carbonate particle mixed slurry A may be added to solution B all at once, or solution B may be added dropwise while stirring solution B. Alternatively, solution B may be added all at once to the gelatin / calcite-type calcium carbonate particle mixed slurry A, or solution B may be added dropwise while stirring the gelatin / calcite-type calcium carbonate particle mixed slurry A. The mixture of the two can be stirred using an existing stirring device such as a magnetic stirrer, a stirrer equipped with various stirring blades, or an ultrasonic stirrer. The stirring speed is, for example, 300-1500 rpm, preferably 700-1200 rpm. In this manner, emulsion C is obtained. Emulsion C is a liquid in which aggregates of gelatin and calcite-type calcium carbonate particles are emulsified (dispersed) in oil. By appropriately changing the stirring speed in this step, the aggregation morphology of the gelatin and calcite-type calcium carbonate particles can be changed. In general, slowing the stirring speed tends to result in a structure in which gelatin (hydrophilic portion) and calcite-type calcium carbonate (hydrophobic portion) are randomly aggregated around large aggregates of gelatin (hydrophilic portion), and the diameter of the aggregates tends to be relatively large. Furthermore, if the stirring speed is increased, the gelatin (hydrophilic portion) and the calcite-type calcium carbonate (hydrophobic portion) tend to form a structure in which they are randomly aggregated, and the diameter of the aggregates tends to become relatively small.

[0032] Next, a crosslinking agent is added to the emulsion C, followed by stirring to obtain an emulsion D containing gelatin / calcite-type calcium carbonate composite particles. Any compound can be used as the crosslinking agent as long as it can crosslink the gelatin contained in the gelatin / calcite-type calcium carbonate particles emulsified and dispersed in the emulsion D. Examples of crosslinking agents include 3-ethylcarbodiimide hydrochloride (1-(3-dimethylaminopropyl-3-ethylcarbodiimide hydrochloride, etc.), 3-ethylcarbodiimide sulfate (1-(3-dimethylaminopropyl-3-ethylcarbodiimide sulfate, etc.), 3-ethylcarbodiimide nitrate (1-(3-dimethylaminopropyl-3-ethylcarbodiimide nitrate, etc.), transglutaminase, olefin-maleic anhydride copolymer, ammonia reaction products with ethylenically unsaturated anhydride-maleic anhydride copolymer, polyamide epoxy resin, Glutaraldehyde or genipin can be used. In this case, the crosslinking agent can be added to emulsion C so that the mass ratio of gelatin to crosslinking agent is in the range of 1:1 to 1:20, preferably 1:1 to 1:10. When the crosslinking agent is added to 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. In other words, emulsion D is a liquid in which gelatin / calcite-type calcium carbonate composite particles are emulsified and dispersed in oil.

[0033] Next, emulsion D containing the gelatin / calcite-type calcium carbonate composite particles is centrifuged to obtain gelatin / calcite-type calcium carbonate composite particles. The obtained gelatin / calcite-type calcium carbonate composite particles are granular solids formed by the combination of crosslinked gelatin and calcite-type calcium carbonate. For example, they may be composite particles in which gelatin is used as a template and calcite-type calcium carbonate surrounds it. Alternatively, they may be composite particles having a sea-island structure, in which islands of crosslinked gelatin are contained within a sea structure of calcite-type calcium carbonate. Furthermore, gelatin / calcite-type calcium carbonate composite particles may have a structure in which specifically crosslinked gelatin aggregates in the center, and the crosslinked gelatin and calcite-type calcium carbonate form a sea-island structure around it. The gelatin / calcite-type calcium carbonate composite particles obtained by centrifugation can be washed with a cleaning solvent such as water or alcohol and appropriately dried. The particle size of the gelatin / calcite type calcium carbonate particles depends on the stirring speed and the amount of crosslinking agent in the step of obtaining emulsion C, and is usually in the range of 1 to 500 μm, preferably 5 to 200 μm.

[0034] Next, a step is carried out in which the gelatin / calcite-type calcium carbonate composite particles are disposed on the surface of a substrate to obtain an aggregate of gelatin / calcite-type calcium carbonate composite particles. The gelatin / calcite-type calcium carbonate composite particles are disposed on the surface of a glass, plastic, or metal substrate, such as a petri dish, well, or mold, to produce an aggregate of gelatin / calcite-type calcium carbonate composite particles. After this step, the aggregate of gelatin / calcite-type calcium carbonate composite particles can be compressed using a press or the like to give the aggregate of gelatin / calcite-type calcium carbonate composite particles a certain degree of dimensional consistency.

[0035] Next, a step is performed in which the aggregate of gelatin / calcite-type calcium carbonate composite particles is fired to obtain pellets consisting of aggregates of dense calcite-type calcium carbonate particles. If the aggregate of gelatin / calcite-type calcium carbonate composite particles obtained in the previous step has low fluidity and a certain degree of definite shape, the aggregate of gelatin / calcite-type calcium carbonate composite particles is removed from the substrate and fired. If the aggregate of gelatin / calcite-type calcium carbonate composite particles has a certain degree of fluidity and no definite shape, the substrate can be fired as is. The aggregate of gelatin / calcite-type calcium carbonate composite particles is fired in air, carbon dioxide, or an inert gas atmosphere such as nitrogen or argon at a temperature of 570°C or higher and lower than 650°C, preferably 580°C or higher and lower than 600°C. When firing is performed in the atmosphere, the temperature can be 570°C or higher and lower than 650°C; when firing is performed in carbon dioxide, the temperature can be 580°C or higher and lower than 630°C; and when firing is performed in an inert gas, the temperature can be 590°C or higher and lower than 650°C. The aggregate of gelatin / calcite-type calcium carbonate composite particles can be fired using an existing ceramic firing furnace. When the aggregate of gelatin / calcite-type calcium carbonate composite particles is fired, the gelatin portion is first incinerated (burned), leaving only the calcite-type calcium carbonate portion. That is, among the gelatin / calcite-type calcium carbonate particles, only the island-structured portion (gelatin) is removed by firing (burning), leaving only the sea-structured portion (calcite-type calcium carbonate), resulting in particles (granules) with a generally dense structure with occasional pores. Further firing within the above temperature range closes the pores present in the granules, and at least a portion of the calcite-type calcium carbonate (particularly the calcium carbonate on the surface of the granules) is converted to calcium oxide. Thus, pellets consisting of aggregates of dense calcite-type calcium carbonate particles, some of which have been converted to calcium oxide, are obtained. In this specification, the term "dense calcite-type calcium carbonate particles" also includes particles in which some of the calcite-type calcium carbonate has been converted to calcium oxide.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, and is usually in the range of 1-500 μm, preferably 5-200 μm, or the particle diameter may be slightly smaller due to 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 pellets composed of the aggregates of calcite-type dense calcium carbonate particles are placed in an atmosphere containing at least carbon dioxide to obtain calcium carbonate, in which calcium carbonate particles with elongated structures such as cylindrical, needle-like, or columnar structures are arranged on the surface of the pellets composed of aggregates of calcium carbonate dense particles. The surface of the pellets composed of aggregates of calcite-type dense calcium carbonate particles obtained by firing in the previous step becomes unstable, resulting in the formation of numerous cracks and pores. If the pellets are left at room temperature in this state, two changes may occur on the surface of the dense calcium carbonate particles. First, the particle surface absorbs moisture from 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 pores react with carbonate ions or carbon dioxide to form calcium carbonate. The calcium carbonate formed by the reaction of the released calcium ions with carbonate ions or carbon dioxide is calcite-type. The reaction between the released calcium ions and carbonate ions or carbon dioxide occurs simultaneously throughout the surface of the pellets consisting of aggregates of calcite-type calcium carbonate dense particles, and calcium carbonate crystal growth also begins simultaneously throughout the surface of the pellets consisting of aggregates of calcite-type calcium carbonate dense particles. The other change is that trace amounts of calcium oxide present on the surface of the pellets consisting of aggregates of calcite-type calcium carbonate dense particles obtained by firing in the previous step, due to decomposition, react with carbon dioxide in an atmosphere containing at least carbon dioxide to form calcium carbonate. The calcium carbonate formed by the reaction of calcium oxide with carbon dioxide is calcite-type. The reaction between calcium oxide and carbon dioxide occurs simultaneously throughout the surface of the pellets consisting of aggregates of calcite-type calcium carbonate dense particles, and calcium carbonate crystal growth also begins simultaneously throughout the surface of the pellets consisting of aggregates of calcite-type calcium carbonate dense particles. As a result, the calcite-type calcium carbonate grows to have an elongated structure, such as a cylindrical, needle-like, or columnar shape.In this process, if pellets consisting of aggregates of dense calcite-type calcium carbonate particles are placed in an atmosphere with a controlled carbon dioxide concentration, the growth of calcite-type calcium carbonate with an elongated, cylindrical, needle-like, or columnar structure can be controlled. If the carbon dioxide concentration in the atmosphere in which pellets consisting of aggregates of dense calcite-type calcium carbonate particles are placed is similar to that of the atmosphere (at least 0.03%), calcite-type calcium carbonate with an elongated, cylindrical, needle-like, or columnar structure will grow. Furthermore, the temperature of the atmosphere containing at least carbon dioxide in which pellets consisting of aggregates of dense calcite-type calcium carbonate particles are placed should be in the range of from near room temperature (20°C or higher) to 80°C, preferably 20-40°C. In this way, calcium carbonate with a hierarchical structure can be obtained, having at least a layer consisting of aggregates of dense calcite-type calcium carbonate particles and a layer in which elongated, cylindrical, needle-like, or columnar calcite-type calcium carbonate structures are arranged.

[0037] Among calcium carbonates having such a hierarchical structure, calcium carbonate having a dense structure is preferably particles having a diameter of 10-200 μm. The calcium carbonate having a dense structure is preferably a high-order structure formed by the aggregation of primary particles of calcite-type calcium carbonate, and is preferably a particle having a high-order structure. The diameter of these particles is 10-200 μm, preferably 20-150 μm, and more preferably 30-100 μm. Furthermore, among calcium carbonates having a hierarchical structure, calcium carbonate having an elongated structure has a cross-sectional diameter in the range of 0.1-1.0 μm, preferably 0.2-0.8 μm, and more preferably 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 0.2-8 μm, and more preferably 0.3-7 μm, but there is no limit to the length, and it may be possible to increase the length to, for example, 30 μm, in some cases.

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

[0039] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following examples.

[0040] <Production of calcite-type calcium carbonate having a hierarchical structure> [Example 1] Gelatin (FUJIFILM Wako Pure Chemical Industries, Ltd.) and calcite-type calcium carbonate with a particle size of 80 nm (Shiraishi Central Research Institute Co., Ltd.) were dispersed in water at a mass ratio of 1:1. The mixture 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).

[0041] On the other hand, a surfactant (Span 80, Fujifilm Wako Pure Chemical Industries, Ltd.) and liquid paraffin (Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed at a volume ratio of 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 the mixture was stirred at room temperature at a stirring speed of 1200 rpm to obtain an emulsion (Emulsion C).

[0042] To emulsion C, carbodiimide hydrochloride (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, Fujifilm Wako Pure Chemical Industries, Ltd.) was added so that the mass ratio of gelatin to the crosslinking agent was 1:1. Stirring the mixture yielded an emulsion (emulsion D) containing gelatin / calcite-type calcium carbonate particles. Emulsion D was separated using a centrifuge, and the resulting solid portion was washed five times with acetone and dried at room temperature in the air to obtain gelatin / calcite-type calcium carbonate composite particles. The resulting gelatin / calcite-type calcium carbonate composite particles were then placed in a metal molding mold to obtain an aggregate of gelatin / calcite-type calcium carbonate composite particles. The aggregate of gelatin / calcite-type calcium carbonate composite particles was solidified using a vise heat press. The aggregate of gelatin / calcite-type calcium carbonate composite particles was fired in the molding mold at 570°C in a firing furnace under atmospheric pressure, yielding pellets consisting of aggregates of dense calcite-type calcium carbonate particles.

[0043] Pellets consisting of aggregates of dense particles of calcite-type calcium carbonate were left to stand in the air at room temperature for two days. Calcium carbonate with a hierarchical structure was obtained, in which numerous elongated calcium carbonate particles were arranged on the surface of the pellets consisting of aggregates of dense particles of calcite-type calcium carbonate. The diameter of the elongated structures was approximately 10 to 30 μm, and they were needle-like in shape.

[0044] Figure 2-A is a scanning electron microscope photograph (magnification: 10,000x) of the surface portion of calcium carbonate having a hierarchical structure obtained by the method of Example 1. Numerous calcium carbonate particles with elongated needle-like structures were observed within the observation field. Figure 2-B is a transmission electron microscope photograph at a magnification of 150,000x, which shows an enlarged view of the elongated structures on the surface of calcium carbonate. Crystal structure analysis of the calcium carbonate having a hierarchical structure obtained in Example 1 by X-ray diffraction confirmed that the calcium carbonate was a 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 through a relatively simple process. The calcite-type calcium carbonate having a unique hierarchical structure produced can support various drugs and the like in an orderly manner on the array portions of the calcium carbonate having an elongated structure. The calcite-type calcium carbonate of the present invention is expected to be used in drug delivery systems, cosmetic additives, food additives, health foods, catalyst supports, 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 an aggregate of calcium carbonate dense particles. A method for producing calcium carbonate comprising the steps.

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 method for producing 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 method for producing 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 method for producing 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 method for producing 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 method for producing 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 method for producing 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 method for producing 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 method for producing 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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