Method for producing calcium carbonate particles, calcium carbonate particles, resin filler, method for producing resin filler, and method for fixing carbon dioxide.

Abstract

This invention provides a method for synthesizing calcium carbonate particles using a liquid-gas method, which yields particles with a high aspect ratio. [Solution] A method for producing calcium carbonate particles, comprising: preparing a raw material solution containing water, calcium hydroxide, magnesium ions, and nitrate ions; and introducing a gas containing carbon dioxide into the raw material solution such that the amount of carbon dioxide introduced per 1 L of the raw material solution is 20 mL / min or less. In the raw material solution, the molar ratio of magnesium to calcium (Mg / Ca) is 2 to 4, and the temperature of the raw material solution is maintained at 70°C or higher during the introduction of the gas.

Description

[Technical Field]

[0001] The present invention relates to a method for producing calcium carbonate particles, calcium carbonate particles, a resin filler, a method for producing a resin filler, and a method for fixing carbon dioxide. [Background technology]

[0002] Traditionally, calcium ions (Ca 2+ A method for synthesizing calcium carbonate particles (liquid-gas method) is known, which involves injecting carbon dioxide (CO2) into an aqueous solution containing ) (for example, Patent Documents 1-3). In recent years, from the viewpoint of carbon neutrality, the liquid-gas method for synthesizing calcium carbonate particles has attracted attention as a carbon dioxide fixation technology.

[0003] Calcium carbonate particles are non-toxic, stable, and used in a variety of applications. Examples of calcium carbonate particle applications include viscosity or thixotropy modifiers for inks and paints, whiteness modifiers for paper, and resin fillers mixed into resin materials to improve heat resistance and mechanical strength. It is known that the shape of the resin filler affects the mechanical strength of resin materials; according to the Halpin-Tsai model, a larger aspect ratio (major axis / minor axis) of the resin filler improves the tensile and flexural strength of the resin material. Calcium carbonate is known to exist in three crystalline polymorphs: calcite, aragonite, and vaterite, each with different particle shapes, with aragonite being the most needle-shaped. Patent documents 1-3 disclose methods for producing calcium carbonate particles containing aragonite. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 1057431 [Patent Document 2] Japanese Patent Application Publication No. 5-221633 [Patent Document 3] Japanese Patent Publication No. 2003-63820 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, while the methods for producing calcium carbonate particles disclosed in Patent Documents 1 to 3 yield needle-shaped particles containing aragonite, no whiskers with a high aspect ratio (for example, needle-shaped particles with an average aspect ratio exceeding 20) have been reported. Furthermore, Patent Documents 1 to 3 do not disclose any method for controlling the aspect ratio of calcium carbonate particles.

[0006] Furthermore, Patent Documents 1 and 2 disclose preferred particle size (major axis, minor axis) ranges for the obtained calcium carbonate particles. However, it is not the case that particles with the maximum aspect ratio simply calculated from the disclosed maximum major axis and minimum minor axis will be obtained. This is because, normally, if the major axis of a particle is large, the minor axis will also be large, and if the major axis of a particle is small, the minor axis will also be small.

[0007] Furthermore, from a carbon neutrality perspective, bioplastics have attracted attention in recent years. However, bioplastics generally have lower mechanical strength and heat resistance compared to petroleum-based plastics. Therefore, there has been a need for the development of resin fillers that can efficiently improve the durability of bioplastics.

[0008] The present invention solves the above problems. Specifically, the present invention provides a method for producing calcium carbonate particles using a liquid-gas method (synthesis method) that yields particles with a high aspect ratio. [Means for solving the problem]

[0009] As a result of diligent research to achieve the above objectives, the inventors of this invention have found that the above objectives can be achieved with the following configuration.

[0010] [1] A method for producing calcium carbonate particles, Preparing a raw material liquid containing water, calcium hydroxide, magnesium ions, and nitrate ions, Introducing a gas containing carbon dioxide into the raw material liquid such that the introduction amount of carbon dioxide with respect to 1 L of the raw material liquid is 20 mL / min or less, In the raw material liquid, the molar ratio of magnesium to calcium (Mg / Ca) is 2 to 4, A method for producing calcium carbonate particles, wherein during the introduction of the gas, the temperature of the raw material liquid is 70°C or higher. [2] During the introduction of the gas, the pH of the raw material liquid may be 8 to 10. [3] In the raw material liquid, the molar ratio of nitrate ions to calcium (NO3 - / Ca) may be 4 to 8. [4] The raw material liquid may contain magnesium nitrate as a source of the magnesium ions and / or the nitrate ions. [5] The content of calcium hydroxide in the raw material liquid may be 0.1 mol / L to 0.3 mol / L. [6] The introduction amount of carbon dioxide may be 1 mL / min to 20 mL / min. [7] The gas containing carbon dioxide may contain air. [8] During the introduction of the gas, the temperature of the raw material liquid may be 70°C to 80°C. [9] The calcium carbonate particles may contain aragonite, and the average value of the aspect ratio may be greater than 20.

[10] Containing aragonite, Calcium carbonate particles having an average value of the aspect ratio greater than 20.

[11] The average value of the aspect ratio may be greater than 20 and 100 or less.

[12] A filler for resin containing the calcium carbonate particles according to

[10] or

[11] .

[13] A method for producing a filler for resin containing calcium carbonate particles, [1] to [9], which includes producing the calcium carbonate particles by the production method described in any one of

[14] A method for fixing carbon dioxide, preparing a raw material solution containing water, calcium hydroxide, magnesium ions, and nitrate ions; introducing a gas containing the carbon dioxide into the raw material solution such that the introduction amount of carbon dioxide with respect to 1 L of the raw material solution is 20 mL / min or less; in the raw material solution, the molar ratio of magnesium to calcium (Mg / Ca) is 2 to 4; during the introduction of the gas, maintaining the temperature of the raw material solution at 70°C or higher. A method for fixing carbon dioxide. [Advantages of the Invention]

[0011] A method for producing calcium carbonate particles (synthesis method) using a liquid-gas method, which can obtain particles with a high aspect ratio. [Brief Description of the Drawings]

[0012] [Figure 1] A flowchart for explaining the method for producing calcium carbonate particles according to the first embodiment. [Figure 2] An optical microscope photograph of a sample prepared in an example. [Figure 3] A diagram showing the relationship between the introduction amount of carbon dioxide (mL / min) with respect to 1 L of the raw material solution and the average value of the aspect ratio of the obtained sample in an example. [Figure 4] A diagram showing the results (profiles) of X-ray diffraction (XRD) analysis of a sample prepared in an example (Examples 1 to 2 and Comparative Examples 1 to 2). [Figure 5] A diagram showing the results (profiles) of X-ray diffraction (XRD) analysis of a sample prepared in an example (Comparative Examples 3 to 4). [Figure 6] A diagram showing the molar fraction (XA) of aragonite in calcium carbonate in a sample prepared in an example. [Figure 7] A diagram showing the pH change of the raw material solution during sample synthesis in an example (Examples 1 to 2 and Comparative Example 2). [Figure 8]This figure shows the pH change of the raw material solution during sample synthesis in the examples (Example 1 and Comparative Example 3). [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described in detail below. The following descriptions of constituent elements may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits.

[0014] [First Embodiment] As a first embodiment, a method for producing calcium carbonate particles (hereinafter referred to as "this manufacturing method") will be described. As shown in Figure 1, this manufacturing method includes the following steps S1 and S2.

[0015] Step S1: A step of preparing a raw material solution containing water, calcium hydroxide, magnesium ions, and nitrate ions, and Step S2: A step of introducing a gas containing carbon dioxide into the raw material liquid such that the amount of carbon dioxide introduced per 1 L of the raw material liquid is 20 mL / min or less.

[0016] As mentioned above, the synthesis of needle-shaped aragonite particles has been carried out conventionally (for example, Patent Documents 1-3), but no method has been reported for increasing the aspect ratio by preferentially growing the needle-shaped particles in the long axis direction. As a result of diligent research, the inventors of this application have succeeded in producing calcium carbonate particles with a high aspect ratio by introducing carbon dioxide in a specific amount into a raw material liquid having a specific composition. The mechanism is not clear, but it is presumed to be as follows.

[0017] In this manufacturing method, carbon dioxide is slowly introduced into the raw material liquid compared to the conventional liquid-gas method (the amount of carbon dioxide introduced per unit time per liter of raw material liquid is small). In the phase diagram of calcium carbonate crystals, the most stable phase under atmospheric pressure is calcite, while needle-shaped aragonite is a metastable phase. When the carbon dioxide in the raw material liquid becomes supersaturated, calcite is more easily formed, and even if needle-shaped aragonite is formed, the crystals tend to grow in the short axis direction, which normally has low surface energy and is difficult to grow, resulting in a decrease in the aspect ratio. In this manufacturing method, by slowly introducing carbon dioxide into the raw material liquid, it is possible to suppress the formation of calcite while promoting the crystal growth of aragonite in the long axis direction.

[0018] Furthermore, in this manufacturing method, the raw material liquid contains magnesium ions (Mg 2+ The solution contains magnesium (H2CO3, HCO3) and has a molar ratio of magnesium to calcium (Mg / Ca) of 2-4. When the pH of the raw material solution increases, magnesium ions precipitate by forming sparingly soluble magnesium hydroxide (Mg(OH)2), and when the pH of the raw material solution decreases, the precipitated magnesium hydroxide dissolves. This maintains the pH of the raw material solution at a weakly basic to basic level (e.g., pH 8-10). In other words, magnesium ions act as a pH buffer. pH is determined by the form of carbonate ions present in the raw material solution (H2CO3, HCO3). - CO3 2- ) is a dominant factor and affects crystal growth. If the pH is too low, the ratio of H2CO3 increases, making it difficult for the calcium carbonate formation reaction to occur. On the other hand, if the pH is too high, CO3 2- The ratio of becomes too high, and the rate of calcium carbonate formation becomes too fast. As a result, calcite is more easily formed, and even if needle-shaped aragonite is formed, the crystals tend to elongate in the short axis direction as well, reducing the aspect ratio. In this manufacturing method, the pH of the raw material solution is kept weakly basic to basic (for example, pH 8 to 10), so that the HCO3 in the raw material solution is reduced. - and CO3 2-The ratio to can be adjusted to an optimal range for promoting crystal growth in the major axis direction of aragonite. Also, in this production method, slowly introducing carbon dioxide, which is an acidic gas, into the raw material liquid also contributes to keeping the pH of the raw material liquid constant without a sharp decrease. In addition, in the conventional liquid-gas method, magnesium ions may be added to the raw material liquid as a reagent (impurity) that promotes the formation of aragonite. However, there is no report that magnesium ions have an effect of increasing the aspect ratio of aragonite. The inventors of the present application have first discovered that such an effect can be achieved by setting the molar ratio (Mg / Ca) to 2 to 4.

[0019] Furthermore, in this production method, the raw material liquid contains nitrate ions (NO3 - ). Nitrate ions promote the dissolution of calcium hydroxide, which is a calcium supply source, and as a result, increase the aspect ratio of the obtained calcium carbonate particles. When calcium hydroxide dissolves, hydroxide ions are released, but as described above, they react with magnesium ions to form magnesium hydroxide, so the pH of the raw material liquid does not increase sharply.

[0020] In addition, the mechanism described above is speculation and does not limit the scope of the present invention in any way. Hereinafter, each step of this production method will be described.

[0021] <Step S1> In this production method, first, a raw material liquid containing water, calcium hydroxide, magnesium ions, and nitrate ions is prepared.

[0022] Calcium hydroxide (Ca(OH)2) is the calcium source for the calcium carbonate particles, which are the target product. Since calcium hydroxide is inexpensive, it can reduce manufacturing costs. In addition, although carbon dioxide, an acidic gas, is introduced into the raw material liquid in this manufacturing method, using basic calcium hydroxide as the calcium source can suppress a rapid decrease in the pH of the raw material liquid. From the viewpoint of obtaining the effects of this embodiment more effectively, it is preferable that the raw material liquid does not contain any calcium sources other than calcium hydroxide. However, within the range in which the effects of this embodiment can be obtained, the raw material liquid may contain calcium sources other than calcium hydroxide (for example, calcium silicate hydrate (CSH), calcium oxide, limestone, calcined seashell calcium, eggshell, etc.).

[0023] Magnesium ions (Mg 2+ As described above, magnesium ions form magnesium hydroxide (Mg(OH)2) in the raw material solution and act as a pH buffer, maintaining the pH of the raw material solution in the range of weakly basic to basic (for example, pH 8 to 10). Furthermore, magnesium ions are expected to promote aragonite crystal nucleation during the crystal nucleation stage of calcium carbonate. Examples of magnesium ion sources include magnesium salts such as magnesium nitrate, magnesium chloride, magnesium sulfate, and magnesium citrate, among which magnesium nitrate is preferred because it has high solubility in water and also provides nitrate ions. By dissolving magnesium salts in the raw material solution, the raw material solution can contain magnesium ions. One type of compound may be used as the magnesium ion source, or two or more types of compounds may be used.

[0024] Nitrate ion (NO3) - This promotes the dissolution of calcium hydroxide, which is a source of calcium. Examples of nitrate ion sources include nitrates such as magnesium nitrate and sodium nitrate, with magnesium nitrate being preferred as it also provides magnesium ions. By dissolving a nitrate in the raw material solution, the raw material solution can contain nitrate ions. One type of compound may be used as the nitrate ion source, or two or more types of compounds may be used.

[0025] Water is the main component of the solvent (dispersion medium) in the raw material solution. The water is not particularly limited and examples include pure water, ion-exchanged water, RO water, etc. From the viewpoint of obtaining the effects of this embodiment more favorably, it is preferable that the raw material solution does not contain any solvents other than water. However, the raw material solution may contain solvents other than water as long as the effects of this embodiment can be obtained. Examples of solvents other than water include amine-based solvents (e.g., monoethanolamine, diethanolamine, triethanolamine, butylamine, hexylamine, octylamine, etc.).

[0026] The molar ratio of magnesium to calcium (Mg / Ca) in the raw material solution is 2 to 4. Maintaining this molar ratio (Mg / Ca) makes it easier to keep the pH of the raw material solution weakly basic to basic (e.g., pH 8 to 10), promoting the growth of aragonite along its long axis and resulting in high-aspect-ratio calcium carbonate particles. Here, the number of moles of calcium in the raw material solution (Ca) refers to the total number of moles of dissolved calcium ions and calcium present in undissolved calcium salts (calcium hydroxide, calcium carbonate, etc.). Similarly, the number of moles of magnesium (Mg) refers to the total number of moles of dissolved magnesium ions and magnesium present in undissolved magnesium salts (magnesium hydroxide, etc.). The molar ratio (Mg / Ca) can be adjusted by the amount (number of moles) of calcium source (calcium hydroxide) and magnesium ion source (e.g., magnesium nitrate, etc.) used during the preparation of the raw material solution.

[0027] The molar ratio of nitrate ions to calcium in the raw material solution (NO3 - The molar ratio (NO3) is preferably 4-8. - By keeping the number of moles of calcium (Ca) in the raw material solution within this range, the dissolution of calcium hydroxide, which is the calcium source, is promoted, and as a result, the resulting calcium carbonate particles tend to have a higher aspect ratio. Here, the number of moles of calcium (Ca) in the raw material solution is as described above. Also, the number of moles of nitrate ions (NO3) -) is equivalent to the number of moles of NO3 contained in the nitrate ion supply source used in the raw material solution. Molar ratio (NO3 - The amount of calcium ( / Ca) can be adjusted by the amount (in moles) of calcium source (calcium hydroxide) and nitrate ion source (e.g., magnesium nitrate) used during the preparation of the raw material solution.

[0028] The calcium hydroxide content in the raw material solution is not particularly limited, but from the viewpoint of achieving better effects in this embodiment, for example, 0.01 mol / L to 1.0 mol / L or 0.1 mol / L to 0.3 mol / L is preferred. Furthermore, the magnesium ion source content in the raw material solution is not particularly limited as long as the molar ratio (Mg / Ca) in the raw material solution is within the above predetermined range (for example, 2 to 4), and for example, the magnesium (Mg) content in the raw material solution may be adjusted to 0.02 mol / L to 4.0 mol / L or 0.2 mol / L to 1.2 mol / L. Furthermore, the nitrate ion source content in the raw material solution is not particularly limited, and for example, the molar ratio (NO3 - It is preferable that the concentration of nitrate ions ( / Ca) be adjusted to be within the above predetermined range (for example, 4 to 8). The content of the nitrate ion source in the raw material solution may be adjusted, for example, so that the nitrate ion concentration in the raw material solution is 0.04 mol / L to 8.0 mol / L, or 0.4 mol / L to 2.4 mol / L.

[0029] The raw material solution may consist only of calcium hydroxide, a magnesium ion source, a nitrate ion source, and water, or it may contain other components as long as the effects of this embodiment are obtained. Examples of other components include the amine-based solvents mentioned above. The method for preparing the raw material solution is not particularly limited, and it can be obtained, for example, by mixing calcium hydroxide, a magnesium ion source, a nitrate ion source, water, and other components as needed, using conventionally known methods.

[0030] <Process S2> Next, a gas containing carbon dioxide is introduced into the raw material liquid so that the amount of carbon dioxide introduced per liter of raw material liquid is 20 mL / min or less. In the raw material liquid, calcium ions react with carbon dioxide, and the target product, calcium carbonate, precipitates.

[0031] The gas introduced into the raw material liquid (hereinafter referred to as "introduced gas") is not particularly limited as long as it contains carbon dioxide. The introduced gas may be carbon dioxide itself (CO2: 100 vol%), air (CO2: approximately 0.03 vol%), or a mixture of carbon dioxide and another gas. Examples of other gases include air, nitrogen, nitrogen oxides (NOx), hydrocarbons, etc. The concentration of carbon dioxide in the introduced gas is not particularly limited and may be, for example, 0.03 vol% to 100 vol%.

[0032] In this manufacturing method, compared to the conventional liquid-gas method, the introduced gas is introduced slowly into the raw material liquid. Specifically, the amount of carbon dioxide contained in the introduced gas introduced per liter of raw material liquid is 20 mL / min or less, preferably 15 mL / min or less, or 10 mL / min or less. By slowly introducing carbon dioxide into the raw material liquid, abrupt changes in the pH of the raw material liquid can be prevented, and the ion balance in the raw material liquid can be maintained optimally. The lower limit of the amount of introduced gas introduced is not particularly limited, but from the viewpoint of shortening the synthesis time of calcium carbonate particles, for example, it should be 1 mL / min or more, or 5 mL / min or more. In this manufacturing method, the introduced gas is introduced into a heated raw material liquid (for example, 70°C or higher), but the amount of carbon dioxide introduced (mL / min) specified in this specification is the value at room temperature and atmospheric pressure (20°C, 1 atm = approximately 101 kPa).

[0033] During the introduction of the gas, the temperature of the raw material liquid should be 70°C or higher. Exposure to a high-temperature environment promotes aragonite crystal nucleation during the calcium carbonate crystal nucleation stage. While there is no particular upper limit to the temperature of the raw material liquid, since the main component of the solvent is water, it should be, for example, 100°C or lower, or 80°C or lower.

[0034] The pH of the raw material solution is preferably 8 to 10. As described above, maintaining the pH of the raw material solution to be weakly basic to basic promotes the crystal growth of aragonite along its long axis, resulting in a higher aspect ratio. In this manufacturing method, the pH of the raw material solution can be adjusted to 8 to 10 by introducing carbon dioxide in a specific amount into the raw material solution having the specific composition described above, thus eliminating the need to add a pH adjusting agent to the raw material solution separately. It is preferable that the pH of the raw material solution be kept at 8 to 10 at all times during this process (for example, during the introduction of the gas). Furthermore, it is preferable that the pH of the raw material solution be kept at 8 to 10 from the start of carbon dioxide introduction until all the calcium in the raw material solution precipitates as calcium carbonate. In this specification, the pH of the raw material solution refers to the pH of the raw material solution at room temperature (for example, 20°C). The pH during the introduction of the gas is measured after sequentially sampling the solution from the raw material solution (70°C or higher) and allowing the temperature of the sampled solution to drop to room temperature.

[0035] During the introduction of the introduced gas, the raw material liquid may be stirred by conventionally known methods. Furthermore, the introduction time (duration of introduction) of the introduced gas is not particularly limited and may be adjusted as appropriate based on the composition of the raw material liquid, the amount of carbon dioxide introduced, etc. The introduction (duration) time of the introduced gas may be, for example, 6 minutes to 24 hours.

[0036] After step S1, before the introduction of the introduced gas, magnesium ions and hydroxide ions react to precipitate magnesium hydroxide (e.g., brucite) in the raw material liquid. In the initial stages of this process, calcium carbonate (precipitate) and magnesium hydroxide (precipitate) coexist, but as the introduction time of the introduced gas (reaction time) increases, the amount of calcium carbonate (aragonite) produced increases, while the amount of magnesium hydroxide decreases and eventually disappears (dissolves). The calcium carbonate crystals and magnesium hydroxide crystals in the product can be confirmed by, for example, X-ray diffraction (XRD) analysis, as described in the examples below. For example, the end point of the introduction time of the introduced gas (reaction time) may be set at the point when the presence of magnesium hydroxide crystals in the product can no longer be confirmed. This results in calcium carbonate particles with fewer impurities (by-products, magnesium hydroxide). Furthermore, when used in applications where the influence of impurities is minimal, the introduction of the introduced gas may be stopped at the stage when magnesium hydroxide crystals are present in the product.

[0037] <Other> After step S2, the calcium carbonate particles precipitated in the raw material solution may be separated from the raw material solution by a conventionally known method, and washing and drying may be performed as necessary.

[0038] The method for producing calcium carbonate particles described above yields needle-shaped particles (whiskers) with a high aspect ratio. The calcium carbonate particles obtained by this method can be suitably used, for example, as a filler for resins. Therefore, the method described above can be applied to the production of resin fillers. Details of the calcium carbonate particles obtained by this method will be described in the following second embodiment. Furthermore, the method for producing calcium carbonate particles described above, since it uses carbon dioxide (carbon dioxide gas), can be applied to methods for fixing carbon dioxide.

[0039] [Second Embodiment] As a second embodiment, calcium carbonate particles (whiskers) having a high aspect ratio (major axis / minor axis) will be described. The method for producing the calcium carbonate particles of this embodiment is not particularly limited, but they can be efficiently produced by the method of the first embodiment described above.

[0040] The calcium carbonate particles in this embodiment are needle-shaped particles (whiskers), and the average value of the aspect ratio (major axis / minor axis) is greater than 20, and may be 30 or more. The upper limit of the average value of the aspect ratio is not particularly limited, but for example, it is 100 or less. Furthermore, as long as the aspect ratio is within the above range, the average particle diameter of the calcium carbonate particles is not particularly limited, but for example, the average particle diameter of the major axis of the needle-shaped particles may be 5 μm to 200 μm, or 10 μm to 100 μm, and the average particle diameter of the minor axis may be 0.1 μm to 10 μm, or 0.5 μm to 5 μm.

[0041] In this embodiment, the average particle size and the average aspect ratio of calcium carbonate particles can be calculated, for example, by the method used in the example described later.

[0042] The calcium carbonate particles of this embodiment contain aragonite, which tends to exhibit a needle-like shape. As shown in the examples described later, the mole fraction of aragonite in the calcium carbonate particles (XRD) was determined by X-ray diffraction (XRD) analysis. A ) can be calculated (Kontoyannis and Vagenas, 2000, Analyst, 125, 251-255; the contents of this document are incorporated herein by reference). In the calcium carbonate particles of this embodiment, aragonite is the main component, and the mole fraction of aragonite (X A ) may be, for example, 0.90 or higher, or 0.99 or higher. From the viewpoint of further increasing the aspect ratio, the calcium carbonate particles may consist only of aragonite (i.e., X A (=1.00).

[0043] <Application> The calcium carbonate particles of this embodiment can be used in a variety of applications, such as viscosity modifiers or thixotropic modifiers for inks and paints, whiteness modifiers for paper, and resin fillers mixed into resin materials to improve heat resistance and mechanical strength.

[0044] The calcium carbonate particles (whiskers) of this embodiment, having a high aspect ratio (for example, an average aspect ratio greater than 20), are particularly suitable as fillers for resins and can efficiently improve the mechanical strength, heat resistance, and other properties of the resin.

[0045] The resins to which the resin filler (calcium carbonate particles) of this embodiment can be used are not particularly limited, and include conventionally known resins such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyamide (PA), polyvinyl chloride, and natural rubber. In particular, the resin filler of this embodiment is suitable for use in bioplastics, which generally have lower mechanical strength and heat resistance compared to petroleum-based plastics. The resin filler of this embodiment, which has a high aspect ratio, can effectively improve the mechanical strength and heat resistance of bioplastics. By combining bioplastics made from biomass and the resin filler of this embodiment, which is manufactured using carbon dioxide gas, more carbon-neutral resin products can be obtained. [Examples]

[0046] The present invention will be further described using examples and comparative examples, but the scope of the present invention is not limited in any way by the examples and comparative examples.

[0047] [Example 1] The starting solution was prepared by adding these reagents to 4 L of water to achieve a magnesium nitrate concentration of 0.375 mol / L and a calcium hydroxide concentration of 0.125 mol / L. In the starting solution, the molar ratio of magnesium to calcium (Mg / Ca) = 3 and the molar ratio of nitrate ions to calcium (NO3) -The formula ( / Ca) = 6. The temperature of the raw material solution was raised to 75°C and maintained there. Next, air containing 30 vol% carbon dioxide was used as the introduction gas, and the raw material solution was stirred while introducing the introduction gas so that the amount of carbon dioxide introduced per liter of raw material solution was 7.5 mL / min. After 9 hours, temperature control and stirring were stopped, and the raw material solution was allowed to stand until its temperature reached room temperature. After removing the supernatant of the raw material solution, pure water was added and stirred for 1 hour to wash the product. Then, the product (solid) was extracted by suction filtration, and this was dried in a 90°C oven for several hours to obtain the sample.

[0048] [Example 2] A sample was obtained in the same manner as in Example 1, except that the amount of gas introduced into the raw material liquid was adjusted so that the amount of carbon dioxide introduced per 1 L of raw material liquid was 11.3 mL / min.

[0049] [Comparative Example 1] A sample was obtained in the same manner as in Example 1, except that the amount of raw material liquid was changed from 4 L to 2 L, and the amount of introduced gas introduced into the raw material liquid was adjusted so that the amount of carbon dioxide introduced per 1 L of raw material liquid was 30.0 mL / min.

[0050] [Comparative Example 2] A sample was obtained using the same method as in Example 1, except that the amount of raw material liquid was changed from 4 L to 2 L, the amount of introduced gas introduced into the raw material liquid was adjusted so that the amount of carbon dioxide introduced per 1 L of raw material liquid was 50.0 mL / min, and the reaction time was changed from 9 hours to 7 hours.

[0051] [Comparative Example 3] A sample was obtained in the same manner as in Example 1, except that the amount of raw material solution was changed from 4 L to 2 L, and the concentration of magnesium nitrate was changed to 0.125 mol / L. In the raw material solution, the molar ratio of magnesium to calcium (Mg / Ca) = 1, and the molar ratio of nitrate ions to calcium (NO3) - ( / Ca) = 2.

[0052] [Comparative Example 4] A sample was obtained in the same manner as in Example 1, except that magnesium chloride was used instead of magnesium nitrate. In the raw material solution, the molar ratio of magnesium to calcium (Mg / Ca) = 3. Also, since it does not contain nitrate ions, the molar ratio of nitrate ions to calcium (NO) 3- / Ca) = 0 (zero).

[0053] [evaluation] Optical microscope observation and calculation of the average aspect ratio were performed on the samples obtained in Examples 1-2 and Comparative Examples 1-4. Furthermore, during sample synthesis (during the introduction of the gas), solutions were successively collected from the raw material liquid, and X-ray diffraction (XRD) analysis of the products in the collected solutions and pH measurement of the collected solutions were performed. The results are described below.

[0054] [Table 1]

[0055] (1) Observation with an optical microscope and calculation of the aspect ratio Morphological observations were performed on the samples obtained in Examples 1-2 and Comparative Examples 1-4. Microscopic images of the samples from Examples 1-2 and Comparative Example 2 are shown in Figure 2. The average aspect ratio of each sample was calculated using the method described below. The results are shown in Table 1. Furthermore, Figure 3 shows the relationship between the amount of carbon dioxide introduced per 1 L of raw material liquid (mL / min) during the preparation of each sample and the average aspect ratio.

[0056] <Method for calculating the average aspect ratio> Using particle analysis software (e.g., Mac-View, manufactured by Mountec Co., Ltd.) to analyze microscope images, the actual length of each particle was calculated based on the length of the scale bar displayed on the screen. The thickness (minor axis) at the center of each whisker-like particle was measured using the particle analysis software, followed by the measurement of its maximum length (major axis). The aspect ratio of a single particle was calculated from this major axis / minor axis ratio. This process was performed on approximately 100 randomly selected whisker-like particles, and the average value was calculated.

[0057] As shown in Figure 2, whisker-like particles were obtained in Examples 1 and 2, and the average aspect ratio exceeded 20. As shown in Figure 3, the average aspect ratio tended to increase as the amount of carbon dioxide introduced per liter of raw material liquid (mL / min) decreased, and in Example 1, where the introduction amount was 10 mL / min or less, the average aspect ratio was 30 or higher.

[0058] On the other hand, in Comparative Examples 1 and 2, where the amount of carbon dioxide introduced per 1 L of raw material liquid (mL / min) was higher than in Examples 1 and 2, in Comparative Example 3, where the molar ratio (Mg / Ca) was lower, and in Comparative Example 4, which did not contain nitrate ions, needle-shaped particles were obtained. However, their short diameter was larger compared to Examples 1 and 2 (for example, Figure 2), and as a result, the average aspect ratio was smaller (20 or less).

[0059] (2) X-ray diffraction (XRD) analysis Figure 4 shows the XRD profiles of the samples obtained in Examples 1-2 and Comparative Examples 1-2, and Figure 5 shows the XRD profiles of the samples obtained in Comparative Examples 3-4. In Figures 4 and 5, "A" represents the peaks attributed to aragonite (calcium carbonate), "C" to calcite (calcium carbonate), and "B" to brucite (magnesium hydroxide). Furthermore, quantification by XRD peak analysis (see Kontoyannis and Vagenas, 2000, Analyst, 125, 251-255) revealed the mole fraction of aragonite in calcium carbonate contained in each sample (X A The result was calculated. The results are shown in Figure 6 and Table 1.

[0060] In Examples 1 and 2, peak A originating from aragonite was observed, while no peaks originating from calcite or vaterite were seen, indicating the molar fraction of aragonite in calcium carbonate (X A The ratio was 1.00. In other words, all the calcium carbonate contained in the samples of Examples 1 and 2 was aragonite.

[0061] On the other hand, in Comparative Examples 1 and 2, where the amount of carbon dioxide introduced per 1 L of raw material solution (mL / min) was higher than in Examples 1 and 2, in Comparative Example 3, where the molar ratio (Mg / Ca) was lower, and in Comparative Example 4, which did not contain nitrate ions, peak C derived from calcite was observed along with peak A derived from aragonite. As shown in Figure 6 and Table 1, the molar fraction of aragonite in calcium carbonate (X) in the samples of Comparative Examples 1, 2 and 4 was observed. A ) was relatively high at 0.99, but the mole fraction of aragonite in calcium carbonate (X) in the sample of Comparative Example 3 was A The value was low at 0.29. In Comparative Example 3, peak C, derived from calcite, was observed from the beginning of the synthesis reaction, and then peak A, derived from aragonite, was observed 5 hours after the start of the synthesis.

[0062] Furthermore, in the initial stages of synthesis for each sample, peak A or C derived from calcium carbonate, along with peak B derived from the by-product brucite (magnesium hydroxide), were observed in the XRD profile. However, as the synthesis reaction progressed, peak B became smaller. The sample obtained in Example 1 (reaction time: 9 hours) shows peak B, which originates from brucite. Extrapolating from the peak intensity of peak B, it is inferred that if the reaction time (time during which the introduced gas is introduced) exceeds 12 hours, peak B disappears (i.e., the brucite in the sample dissolves). In the sample obtained in Example 2 (reaction time: 9 hours), peak B, which was observed in the initial stages of synthesis, had disappeared and was not observed. It is presumed that the by-product (brucite) disappeared in a shorter reaction time in Example 2 because a larger amount of carbon dioxide was introduced than in Example 1.

[0063] (3) Change in pH Figure 7 shows the relationship between synthesis time (time during introduction of the introduced gas) and the pH of the raw material solution in Examples 1 and 2 and Comparative Example 2. In Examples 1 and 2, the pH of the raw material solution was 8 to 10 during sample synthesis (during introduction of the introduced gas). In Example 1, the pH of the raw material solution remained almost constant at approximately 9 during the 9-hour reaction, and in Example 2, the pH remained almost constant at approximately 9 until 7 hours of synthesis, after which it decreased slightly. On the other hand, in Comparative Example 2, where a large amount of carbon dioxide was introduced per liter of raw material liquid, the pH of the raw material liquid was approximately 9 until 1.5 hours of synthesis, but then it decreased significantly, and the pH after 7 hours was 6.2.

[0064] Figure 8 shows the relationship between synthesis time (time during which the introduced gas is introduced) and the pH of the raw material solution in Comparative Example 3, where the molar ratio (Mg / Ca) is small (Mg / Ca = 1). For comparison, the results for Example 1 are also shown in Figure 8. In Comparative Example 3, the pH of the reaction solution was high at about 10 at the start of synthesis, and then gradually decreased to about pH 9 after 5 hours of synthesis and to less than pH 8 after 8 hours of synthesis. [Industrial applicability]

[0065] The calcium carbonate particles of this embodiment described above can be used, for example, as a viscosity modifier or thixotropic modifier for inks, paints, etc., a whiteness modifier for paper, or a resin filler mixed into resin materials to improve heat resistance or mechanical strength.

Claims

1. A method for producing calcium carbonate particles, To prepare a raw material solution containing water, calcium hydroxide, magnesium ions, and nitrate ions, This includes introducing a gas containing carbon dioxide into the raw material liquid such that the amount of carbon dioxide introduced per liter of the raw material liquid is 20 mL / min or less, In the aforementioned raw material liquid, the molar ratio of magnesium to calcium (Mg / Ca) is 2 to 4. A method for producing calcium carbonate particles, wherein the temperature of the raw material liquid is maintained at 70°C or higher during the introduction of the gas.

2. The method for producing calcium carbonate particles according to claim 1, wherein the pH of the raw material liquid is 8 to 10 during the introduction of the gas.

3. In the aforementioned raw material liquid, the molar ratio of nitrate ions to calcium (NO ３ － A method for producing calcium carbonate particles according to claim 1 or 2, wherein the value of / Ca) is 4 to 8.

4. A method for producing calcium carbonate particles according to any one of claims 1 to 3, wherein the raw material liquid contains magnesium nitrate as a source of magnesium ions and / or nitrate ions.

5. A method for producing calcium carbonate particles according to any one of claims 1 to 4, wherein the content of calcium hydroxide in the raw material liquid is 0.1 mol / L to 0.3 mol / L.

6. A method for producing calcium carbonate particles according to any one of claims 1 to 5, wherein the amount of carbon dioxide introduced is 1 mL / min to 20 mL / min.

7. A method for producing calcium carbonate particles according to any one of claims 1 to 6, wherein the gas containing carbon dioxide contains air.

8. A method for producing calcium carbonate particles according to any one of claims 1 to 7, wherein the temperature of the raw material liquid is set to 70°C to 80°C during the introduction of the gas.

9. The calcium carbonate particles are Contains aragonite, A method for producing calcium carbonate particles according to any one of claims 1 to 8, wherein the average aspect ratio is greater than 20.

10. Contains aragonite, Calcium carbonate particles with an average aspect ratio greater than 20.

11. The calcium carbonate particles according to claim 10, wherein the average value of the aspect ratio is greater than 20 and less than or equal to 100.

12. A resin filler comprising calcium carbonate particles according to claim 10 or 11.

13. A method for producing a resin filler containing calcium carbonate particles, A method for producing a resin filler, comprising producing the calcium carbonate particles by the manufacturing method described in any one of claims 1 to 9.

14. A method for fixing carbon dioxide, To prepare a raw material solution containing water, calcium hydroxide, magnesium ions, and nitrate ions, This includes introducing a gas containing carbon dioxide into the raw material liquid such that the amount of carbon dioxide introduced per liter of the raw material liquid is 20 mL / min or less, In the aforementioned raw material liquid, the molar ratio of magnesium to calcium (Mg / Ca) is 2 to 4. A method for fixing carbon dioxide, wherein the temperature of the raw material liquid is maintained at 70°C or higher during the introduction of the gas.

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