Spherical zinc oxide particles

Abstract

To provide a zinc oxide particle having low adhesiveness and cohesiveness, and also showing excellent dispersibility and fluidity.SOLUTION: A spherical zinc oxide particle has a median diameter (D50) of 1-300 μm, and a BET specific surface area of 50-300 m2 / g.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to spherical zinc oxide particles, and more particularly to spherical zinc oxide particles having a high specific surface area. [Background technology]

[0002] Zinc oxide particles possess characteristics such as UV shielding (UV absorption), near-infrared reflection, and photocatalytic effects, making them useful for a variety of applications including cosmetics, photocatalytic materials, UV-blocking materials, antibacterial materials, antifungal materials, and heat-dissipating materials. In particular, spherical zinc oxide particles are even more useful in the above applications because their dispersibility, fluidity, and packing properties are improved, as well as their handling performance.

[0003] Patent Document 1 discloses a method for producing ultrafine zinc oxide particles from metallic zinc vapor, wherein the obtained ultrafine zinc oxide particles have a specific surface area of ​​10 to 200 m². 2 The tapping density is 4-40 mL / g. Patent Document 2 discloses a method for producing hydroxide and / or oxide fine particles by electrodialysis, with zinc oxide fine particles being an example of the obtained fine particles. The average primary particle diameter of these fine particles is 0.2 to 15 nm, and the specific surface area when the fine particles are zinc oxide is 22 to 180 m². 2 It is approximately / g [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2000 / 046152 [Patent Document 2] International Publication No. 2008 / 044544 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The ultrafine zinc oxide particles actually obtained in Patent Document 1 have a specific surface area of ​​14-34 m². 2 With a particle size of 31-76 nm and an average particle size of 0.47-0.55 μm, the material exhibited high adhesion and aggregation properties, indicating room for improvement in dispersibility and fluidity.

[0006] Similarly, the zinc oxide nanoparticles obtained in Patent Document 2 also have a specific surface area of ​​22 to 180 m². 2 Due to its high adhesion and aggregation properties ( / g) and primary particle size of 0.2-15 nm, there was room for improvement in terms of dispersibility and fluidity.

[0007] This invention has been made in view of the above circumstances, and aims to provide spherical zinc oxide particles that exhibit low adhesion and aggregation properties, as well as good dispersibility and fluidity. [Means for solving the problem]

[0008] The inventors have discovered spherical zinc oxide particles that satisfy a specific range of specific surface area and median diameter (D50), exhibiting low adhesion and aggregation properties, as well as good dispersibility and fluidity, and have completed the present invention.

[0009] In other words, the present invention consists of either (1) or (2) below. (1) The median diameter (D50) is 1 to 300 μm, and BET specific surface area 50-300m 2 Spherical zinc oxide particles, weighing / g. (2) Total pore volume calculated by the BJH method is 0.10 to 1.50 cm³ 3 Spherical zinc oxide particles as described in (1) above, which are / g. [Effects of the Invention]

[0010] The spherical zinc oxide particles according to the present invention have a high specific surface area and are spherical with a median diameter (D50) within a specific range. Therefore, they are expected to have better dispersibility and fluidity than submicron-sized zinc oxide particles, and are also expected to have oil absorption properties, moisture absorption properties, photocatalytic activity, antibacterial properties, and antifungal properties, taking advantage of their high specific surface area.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 summarizes SEM images of spherical zinc oxide particles obtained in Examples 1 to 3 and Comparative Example 1.

Modes for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In this specification, "~" indicating a numerical range is used to mean that the numerical values described before and after it are included as the lower limit value and the upper limit value.

[0013] <Spherical zinc oxide particles> The spherical zinc oxide particles according to the present invention have a BET specific surface area of 50 to 300 m 2 / g and are spherical with a median diameter (D50) of 1 to 300 μm. That the zinc oxide particles are spherical means a shape that is generally rounded, and is not limited to being a perfect sphere. For example, it includes shapes in which a perfect sphere is slightly flattened or distorted, and an elliptical shape. In addition, the spherical zinc oxide particles according to the present invention are preferably closer to a perfect sphere in applications where sphericity is required, such as in cosmetic applications. For any plurality of particles, the ratio (a / b) of the long diameter a to the short diameter b is obtained, and the closer the arithmetic mean value (aspect ratio) is to 1, the closer it is to a perfect sphere. In cases where higher sphericity is required, the aspect ratio is preferably 1.15 or less, more preferably 1.10 or less, and even more preferably close to 1.00. The long diameter a and the short diameter b in the aspect ratio correspond to the long side and the short side, respectively, when a rectangle circumscribing the particle is drawn.

[0014] By being spherical with a median diameter (D50) of 1 μm or more, good dispersibility and fluidity can be expected. The median diameter (D50) is preferably 3 μm or more, and more preferably 5 μm or more. On the one hand, when the median diameter (D50) is 300 μm or less, it can exert its effects without hindering the performance of the material when used as a cosmetic, photocatalyst material, ultraviolet protection material, antibacterial material, antifungal material, heat dissipation material, etc. The median diameter (D50) is preferably 100 μm or less, and more preferably 20 μm or less. The median diameter (D50) refers to the particle diameter corresponding to 50% of the cumulative percentage based on volume, obtained by determining the particle size distribution using a nanoparticle size distribution measuring device.

[0015] When the BET specific surface area of the spherical zinc oxide particles according to the present invention is 50 m 2 / g or more, the number of active sites, adsorption capacity, etc. increase, and good oil absorption characteristics, moisture absorption characteristics, photocatalytic activity, antibacterial properties, antifungal properties, etc. can be expected. The BET specific surface area is preferably 100 m 2 / g or more, and more preferably 150 m 2 / g or more. Also, from the viewpoint of exhibiting oil absorption properties, the higher the BET specific surface area, the more preferable. On the other hand, as the BET specific surface area increases, the density of the spherical zinc oxide particles decreases, and the particles are more likely to fly, resulting in a decrease in handleability. Therefore, when considering handleability, the BET specific surface area is preferably 300 m 2 / g or less, more preferably 280 m 2 / g or less, and even more preferably 250 m 2 / g or less.

[0016] The total pore volume of the spherical zinc oxide particles according to the present invention can be calculated by the BJH method from the results of nitrogen adsorption / desorption measurement by the BET method. The total pore volume of the spherical zinc oxide particles according to the present invention, calculated by the BJH method, is 0.10 cm 3 / g or more is preferable from the viewpoint of increasing the adsorption capacity, and 0.15 cm 3 / g or more is more preferable. Also, from the viewpoint of increasing the adsorption capacity, the larger the total pore volume, the more preferable. On the other hand, as the total pore volume increases, the density of the spherical zinc oxide particles decreases, and the particles are more likely to fly, resulting in a decrease in handleability. Therefore, when considering handleability, the total pore volume is preferably 1.50 cm 3 / g or less, preferably 1.30 cm3 Less than / g is preferable.

[0017] The spherical zinc oxide particles according to the present invention preferably have a crystallite size within a certain width range. Specifically, it is preferable that the full width at half maximum of the zinc oxide (101) plane peak in the X-ray diffraction pattern obtained by X-ray diffraction measurement is 0.6 to 3.5°. A full width at half maximum (FWHM) of 0.6° or higher prevents the crystallite size constituting the particles from becoming too large, thereby achieving a high specific surface area. Furthermore, a FWHM of 3.5° or lower prevents the crystallites from becoming too small, allowing for a high specific surface area while maintaining the properties of zinc oxide. A FWHM of 1.0° or higher is more preferable, and 3.0° or lower is even more preferable.

[0018] The above full width at half maximum can be determined by performing an X-ray diffraction measurement under the following conditions. (X-ray diffraction measurement conditions) Radiation source: CuKα, Measurement range (2θ): 10~80°, Step width: 0.02°, Scan speed: 2° / min, Tube voltage: 40kV, Tube current: 30mA, Cathode: Cu, Receiving slit: 0.3mm, Divergence slit: 1°, Scattering slit: 1° The XRD pattern obtained under the above measurement conditions is subjected to background processing and smoothing, and the width between the two ends at half the intensity value of the zinc oxide (101) plane peak intensity is defined as the width at half maximum.

[0019] <Method for producing spherical zinc oxide particles> The method for producing spherical zinc oxide particles according to the present invention is not particularly limited, but they can be produced, for example, by the following steps (A) to (C). Step (A): An aqueous solution containing a zinc compound and at least one of ammonium ions and a compound that generates ammonium ions is heated to obtain a precipitate of basic zinc carbonate. Step (B): The obtained basic zinc carbonate is calcined to obtain zinc oxide particles. Step (C): After step (A) or step (B) above, the basic zinc carbonate or zinc oxide particles are crushed and spray-dried.

[0020] The above process may be carried out in the order of process (A), process (B), process (C), or in the order of process (A), process (C), process (B). When the process is carried out in the order of steps (A), (B), and (C), spherical zinc oxide particles are obtained in step (C) by crushing and spray-drying the zinc oxide particles obtained in step (B). On the other hand, when the process is carried out in the order of process (A), process (C), and process (B), in process (C), spherical basic zinc carbonate particles are obtained by crushing and spray-drying the basic zinc carbonate obtained in process (A), and spherical zinc oxide particles are obtained by calcining these particles in process (B).

[0021] (Process (A)) The zinc compound in step (A) may contain any zinc salt. Examples of zinc salts include inorganic salts such as zinc nitrate, zinc acetate, zinc sulfate, zinc chloride, zinc formate, zinc oxalate, and zinc citrate, as well as organic salts. The compound may contain one or more of these zinc salts. Specifically, examples include zinc nitrate hexahydrate, zinc acetate dihydrate, zinc acetate (anhydrous), zinc sulfate heptahydrate, and zinc chloride.

[0022] Examples of aqueous solutions containing ammonium ions in step (A) include aqueous ammonia. Examples of compounds that generate ammonium ions include urea, hexamethylenetetramine, and ethylenediamine. Among these, urea is preferred.

[0023] Preferably, the aqueous solution in step (A) further contains an organic acid. By including an organic acid, the specific surface area of ​​the resulting spherical zinc oxide particles can be increased. This is presumed to be because the addition of the organic acid causes the spherical zinc oxide particles to crystallize appropriately, i.e., without excess or deficiency.

[0024] Examples of organic acids include carboxylic acids. The mixture may contain one or more organic acids. Examples of carboxylic acids include citric acid, maleic acid, malic acid, succinic acid, and tartaric acid. Among these, at least one acid selected from the group consisting of citric acid, maleic acid, and malic acid is more preferred because it has a significant effect in increasing the specific surface area.

[0025] In step (A), a precipitate of basic zinc carbonate is obtained by heating an aqueous solution containing the above-mentioned zinc compound, at least one of ammonium ions and a compound that generates ammonium ions, and preferably an organic acid.

[0026] The resulting basic zinc carbonate precipitate can be identified by X-ray diffraction. The precipitate can be isolated by filtration, centrifugation, etc., and, if necessary, washed and dried before proceeding to step (B) or step (C).

[0027] (Process (B)) By calcining the basic zinc carbonate obtained in step (A), or the spherical basic zinc carbonate particles obtained by subjecting the basic zinc carbonate obtained in step (A) to step (C) described later, zinc oxide particles or spherical zinc oxide particles can be obtained. The firing temperature is preferably 150 to 400°C. A firing temperature of 150°C or higher prevents undecomposed basic zinc carbonate from remaining in the resulting particles, while a firing temperature of 400°C or lower allows for a higher specific surface area of ​​the final spherical zinc oxide particles. The firing time is not particularly limited, but 1 to 5 hours is preferred.

[0028] (Process (C)) The zinc oxide particles obtained by step (B), which is performed following step (A), or the basic zinc carbonate obtained by step (A), can be made spherical by crushing and spray-drying them. The pulverization process breaks down the zinc oxide particles or basic zinc carbonate particles, facilitating subsequent spheroidization by spray drying.

[0029] The grinding method is not particularly limited; either dry grinding or wet grinding is acceptable, but wet grinding is preferred because it is more effective at breaking down particles. Specifically, examples include dry bead mills, wet bead mills, ball mills, jet mills, and wet jet mills, but wet bead mills and wet jet mills are preferred. The dispersant used in wet grinding is not particularly limited, but examples include ammonium polyacrylate and ammonium polycarboxylate.

[0030] In spray drying, pulverized zinc oxide particles or basic zinc carbonate particles are sprayed into a gas as a mixture (slurry) with a liquid, and then rapidly dried to form spherical particles. By changing the conditions of the liquid delivery rate and atomizer rotation speed during spray drying, the median diameter (D50) and sphericity of the resulting spherical particles can be adjusted.

[0031] Spherical particles can be obtained by spraying a slurry into fine droplets and drying the material with high-temperature hot air. A drying temperature of 160°C or higher is preferable from the viewpoint of promoting droplet drying. There is no particular upper limit to the drying temperature as long as the crystal growth of the obtained particles is not promoted, and the upper limit should be the temperature limit of the equipment used for drying. [Examples]

[0032] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples.

[0033] <Example 1> (A-1) Zinc nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd., special grade), urea (manufactured by Wako Pure Chemical Industries, Ltd., special grade), and 0.1% by weight aqueous ammonia (manufactured by Wako Pure Chemical Industries, Ltd., special grade) were added to distilled water according to the composition shown in Table 1. The mixture was then heated at 95°C for 2 hours while stirring with a hot stirrer. The resulting white precipitate was filtered, washed, and dried in an oven at 110°C for 2 hours. The white precipitate was confirmed to be basic zinc carbonate particles (Zn5(CO3)2(OH)6) by X-ray diffraction measurement. (B-1) Subsequently, zinc oxide particles were obtained by calcining the obtained basic zinc carbonate particles at 250°C for 2 hours. (C-1) The obtained zinc oxide particles were then ground using a bead mill, and the resulting slurry was spray-dried to obtain spherical zinc oxide particles. The grinding conditions using the bead mill and the spray drying conditions are shown in Tables 2 and 3. Furthermore, the fact that the obtained spherical particles were zinc oxide particles was confirmed by X-ray diffraction measurement.

[0034] [Table 1]

[0035] [Table 2]

[0036] [Table 3]

[0037] <Example 2> (A-2) Zinc nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd., special grade), urea (manufactured by Wako Pure Chemical Industries, Ltd., special grade), and 0.1% by weight aqueous ammonia (manufactured by Wako Pure Chemical Industries, Ltd., special grade) were added to distilled water according to the composition shown in Table 1. The mixture was then heated at 95°C for 2 hours while stirring with a hot stirrer. The resulting white precipitate was filtered, washed, and dried in an oven at 110°C for 2 hours. The white precipitate obtained was basic zinc carbonate particles (Zn5(CO3)2(OH)6). (C-2) The obtained basic zinc carbonate particles were then pulverized in a bead mill, and the resulting slurry was spray-dried to obtain spherical basic zinc carbonate particles. The pulverization conditions in the bead mill and the spray drying conditions are shown in Tables 2 and 3. (B-2) Subsequently, spherical zinc oxide particles were obtained by calcining the obtained spherical basic zinc carbonate particles at 250°C for 2 hours.

[0038] <Example 3> (A-3) Zinc nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd., special grade), urea (manufactured by Wako Pure Chemical Industries, Ltd., special grade), 0.1% by weight aqueous ammonia (manufactured by Wako Pure Chemical Industries, Ltd., special grade), and citric acid monohydrate (manufactured by Wako Pure Chemical Industries, Ltd., food additive) were added to distilled water according to the composition shown in Table 1. The mixture was then heated at 95°C for 2 hours while stirring with a hot stirrer. The resulting white precipitate was filtered, washed, and dried in an oven at 110°C for 2 hours. The white precipitate obtained was basic zinc carbonate particles (Zn5(CO3)2(OH)6). (C-3) The obtained basic zinc carbonate particles were then pulverized in a bead mill, and the resulting slurry was spray-dried to obtain spherical basic zinc carbonate particles. The pulverization conditions in the bead mill and the spray drying conditions are shown in Tables 2 and 3. (B-3) Subsequently, spherical zinc oxide particles were obtained by calcining the obtained spherical basic zinc carbonate particles at 250°C for 2 hours.

[0039] <Comparative Example 1> (C-4) Spherical zinc oxide particles were obtained by grinding zinc oxide powder (manufactured by Kojun Chemical Laboratory Co., Ltd., 4N) in a bead mill and spray-drying the resulting slurry. The grinding conditions in the bead mill and the spray drying conditions are shown in Tables 2 and 3.

[0040] <External observation> The obtained spherical zinc oxide particles were observed for their appearance using SEM (JSM-5500LV, manufactured by JEOL Ltd.). The SEM images of the zinc oxide particles obtained in Examples 1 to 3 and Comparative Example 1 are collectively shown in Fig. 1, and it was confirmed that all of the zinc oxide particles are spherical. Further, the median diameter (D50) of the obtained spherical zinc oxide particles was calculated for the particle diameter corresponding to 50% of the cumulative percentage based on volume using a nanoparticle size distribution measuring device (SALD-7100, manufactured by Shimadzu Corporation). The results are shown in Table 4.

[0041] <BET specific surface area, total pore volume> The BET specific surface area of the spherical zinc oxide particles was measured using a specific surface area meter (BELSORP-miniII, manufactured by MicrotracBEL Corp.), and the total pore volume was calculated by the BJH method. The results are shown in Table 4.

[0042] <Half-value width of the zinc oxide (101) plane peak> The half-value width of the zinc oxide (101) plane peak of the spherical zinc oxide particles was measured using an X-ray diffractometer (XRD-⑥000, manufactured by Shimadzu Corporation), and the half-value width was calculated. The results are shown in Table 4.

[0043]

Table 4

[0044] From the above results, it was confirmed that spherical zinc oxide particles with a high specific surface area and a median diameter (D50) within a specific range were obtained.

Industrial Applicability

[0045] The spherical zinc oxide particles according to the present invention have a high specific surface area and are spherical with a median diameter (D50) of 1 μm or more. Therefore, better dispersibility and fluidity can be expected compared to zinc oxide fine particles of submicron or less, and oil absorption characteristics, moisture absorption characteristics, photocatalytic activity, antibacterial properties, antifungal properties, etc. that utilize the high specific surface area can be expected, and its technical significance is extremely great.

Claims

1. The median diameter (D50) is 5 to 100 μm, and BET specific surface area is 100-300 m² ２ Spherical zinc oxide particles weighing / g.

2. The total pore volume calculated by the BJH method is 0.10 to 1.50 cm³. ３ Spherical zinc oxide particles according to claim 1, wherein the particle size is / g.

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