Particle and method for producing the same

Abstract

To provide a particle having no coloration when used in products, sufficient storage stability (over time), and high antibacterial performance or antiviral performance, and a method for producing the same.SOLUTION: The particle is a particle of a composite oxide comprising silicon, cerium, and aluminum. The particle has a ratio (R1 / R2) of 1.2 to 1.8 between an average particle diameter (R1) determined by image analysis of electron microscopic photographs and a particle diameter (R2) determined by equivalent sphere conversion from a specific surface area determined by the Sears method. According to a dispersion comprising the particle, a product having suppressed coloration and having at least one of high antibacterial performance and antiviral performance can be obtained.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to composite oxide particles having antibacterial and antiviral properties. The present invention also relates to a method for producing the particles.

Background Art

[0002] Conventionally, various problems have been pointed out in the living environment. In Japan, which has a hot and humid climate, food poisoning caused by bacteria and diseases caused by bacteria and viruses in the living space occur frequently. In our living environment, there are many articles that are touched by individuals as well as an unspecified number of people, such as clothing, tableware, cutting boards, furniture, household appliances, smartphones, display devices having touch panels such as ATMs and ticket vending machines, doorknobs, and straps in trains and buses. The problem is that these surfaces are contaminated with fungi such as Escherichia coli and Staphylococcus aureus, and various viruses, and antibacterial and antiviral properties are required from a hygienic perspective.

[0003] Regarding the imparting of antibacterial and antiviral properties to these articles, it has been conventionally known to apply an antibacterial agent or an antiviral agent to the surface of the article. For example, in the case of an organic antibacterial agent or antiviral agent, the coating itself is relatively easy, but there are problems such as the risk of the film being invaded by a solvent and the persistence of antibacterial performance in terms of the fixability to the film and the abrasion resistance. On the other hand, in the case of an inorganic antibacterial agent or antiviral agent, if these are present in the article, the persistence of antibacterial and antiviral performance can be expected.

[0004] For this reason, as antibacterial materials, silica gel, composite oxides, powders such as titanium oxide, or antibacterial compositions in which antibacterial active metal components such as silver, zinc, and copper having antibacterial properties are supported on colloidal particles are known. Specifically, an antibacterial composition in which silver ions and zinc ions are exchanged in zeolite particles (for example, Patent Document 1), a composite oxide particle of silica alumina or silica alumina zirconia supporting silver or the like (for example, Patent Documents 2 and 3), and an antibacterial titanium oxide powder containing potassium and phosphorus (for example, Patent Document 4) are known.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] In articles containing particles having antibacterial performance, if the particle size is on the order of micrometers, a large amount of the particles must be incorporated in order to obtain the desired antibacterial performance, and there is a risk that the dispersion stability of the coating liquid containing the particles will decrease (for example, Patent Document 1). On the other hand, particles having a size smaller than the micrometer order, such as on the order of nanometers, of particles having antibacterial performance have higher dispersibility and a larger number per unit amount, so that sufficient antibacterial performance is likely to be exhibited even with a small amount of the particles incorporated. However, if silver, which is a metal element exhibiting antibacterial properties, is mixed in the particles as Ag2O, when mixed with tap water containing chlorine or the like, or when mixed with a surfactant, Ag2O may react with other compositions to exhibit coloring, or the particles may aggregate during solvent dispersion because they are non-uniform (for example, Patent Documents 2 and 3). Further, if the site where the antibacterial performance is exhibited is an oxidative decomposition reaction, there is a risk that the dispersion medium and the base material will decompose depending on their types (for example, Patent Document 4). Furthermore, if there are mixed particles with low stability, there is a problem that the stability is low when concentrating the dispersion liquid and it cannot be made into a high concentration, there is a problem that the amount of the dispersion medium brought into the coating liquid increases, and in the production of, for example, a coated base material, there are problems such as a decrease in productivity due to the use of a low-concentration coating liquid and a decrease in the particle dispersibility in the film.

[0007] Therefore, particles that do not cause coloring when used in articles, have sufficient storage stability over time, and have high antibacterial and antiviral performance are required.

Means for Solving the Problems

[0008] In order to solve such problems, the following particles were found.

[0009] These particles are particles of a composite oxide containing silicon, cerium, and aluminum. The ratio (R1 / R2) of the average particle diameter (R1) determined by image analysis of an electron micrograph to the particle diameter (R2) determined by converting to an equivalent sphere from the specific surface area determined by the shear method is 1.2 to 1.8.

[0010] These particles do not cause coloring when used in articles, have sufficient stability over time, and have at least one of high antibacterial performance and antiviral performance. According to a dispersion containing such particles, coloring is suppressed, and an article having at least one of high antibacterial performance and antiviral performance can be obtained. This dispersion can be used as a coating liquid when manufacturing an article, or used as an additive liquid during kneading and molding.

[0011] In order to obtain these particles, the following two manufacturing methods were found.

[0012] As the first method, first, a silicic acid solution and an aqueous cerium solution are mixed to prepare an acidic mixed solution (first step). The mixed solution is added to an alkaline mother liquor containing seed particles to prepare particles containing a composite oxide containing silicon and cerium (second step). To the particles containing the composite oxide prepared in the second step, a silicic acid solution and an acidic aqueous aluminum solution are added to prepare particles of a composite oxide containing silicon, cerium, and aluminum (third step).

[0013] As a second method, first, a silicic acid solution and an acidic aluminum aqueous solution are mixed to prepare an acidic mixed solution (first step). The mixed solution is added to an alkaline mother liquor containing seed particles to prepare particles containing a composite oxide containing silicon and aluminum (second step). To the particles containing the composite oxide prepared in the second step, a silicic acid solution and a cerium aqueous solution are added to prepare particles of a composite oxide containing silicon, cerium, and aluminum (third step).

[0014] The properties of the particles obtained by these production methods conform to the properties of the aforementioned particles.

Advantages of the Invention

[0015] According to the particles of the present invention, a dispersion capable of producing an article having sufficient stability over time and having at least one of high antibacterial performance and antiviral performance can be obtained.

Embodiments for Carrying Out the Invention

[0016] The particles according to the present invention (hereinafter, the particles according to the present invention may be simply referred to as "particles") are particles of a composite oxide containing silicon, cerium, and aluminum. The ratio (R1 / R2) of the average particle diameter (R1) determined by image analysis of an electron micrograph and the particle diameter (R2) determined by equivalent sphere conversion from the specific surface area determined by the shear method is 1.2 to 1.8.

[0017] These particles have at least one of antibacterial and antiviral properties (hereinafter, the property of "at least one of antibacterial and antiviral properties" according to the present invention may be simply referred to as "antibacterial / antiviral property") without supporting silver, copper, zinc, etc. An article using these particles has antibacterial / antiviral property obtained.

[0018] The ratio (R1 / R2) of the average particle diameter (R1) determined by image analysis of an electron micrograph and the particle diameter (R2) determined by equivalent sphere conversion from the specific surface area determined by the shear method is 1.2 to 1.8. When the ratio (R1 / R2) is within this range, the particles are porous and have a high specific surface area.

[0019] Here, if the ratio of the particles (R1 / R2) is less than 1.2, the specific surface area of the particles is low, and there is a risk that sufficient antibacterial and antiviral properties may not be exhibited. Conversely, if it exceeds 1.8, the particles are too fine and form aggregates, and there is a risk that the antibacterial and antiviral effects due to the high dispersibility of the nano-sized particles may not be exhibited. This ratio (R1 / R2) is preferably 1.3 to 1.6, more preferably 1.4 to 1.5.

[0020] The specific surface area of the particles by the shear method is preferably 150 to 300 m 2 / g. When the specific surface area is in this range, it has a high surface area and is porous, and can exhibit high antibacterial and antiviral properties.

[0021] Here, if the specific surface area of the particles is less than 150 m 2 / g, the surface area is insufficient, and there is a risk that the antibacterial and antiviral effects may not be exhibited. Conversely, if it exceeds 300 m 2 / g, the particles become too small, and there is a risk that the stability decreases and they are likely to aggregate. This specific surface area is more preferably 210 to 280 m 2 / g, even more preferably 210 to 230 m 2 / g.

[0022] As one of its structures, the particles preferably have a layer containing silicon and aluminum on the surface of the composite oxide particles containing silicon and cerium. By having such a layer, a decrease in the specific surface area of the particles is suppressed. This decrease in the specific surface area occurs because the irregularities on the surface of the particles in the dispersion decrease over time. If the specific surface area decreases, the antibacterial and antiviral properties of the particles may also decrease.

[0023] The layer containing silicon and aluminum is preferably a silica-alumina layer. If this layer is silica-alumina, it is preferable because it has a high specific surface area. Also, it can maintain a high zeta potential even at low pH, and it is easy to replace the solvent with an organic solvent.

[0024] As one of its components, the particle preferably has a layer containing silicon and cerium on the surface of the composite oxide particle containing silicon and aluminum. Such particles have high antibacterial and antiviral properties.

[0025] The layer containing silicon and cerium is preferably a silica-ceria layer. If this layer is silica-ceria, it has high antibacterial and antiviral properties and is preferable.

[0026] The content of cerium in the particle is preferably 0.6 to 2.0% by mass with cerium oxide as CeO2. When the content of cerium oxide is in this range, sufficient antibacterial and antiviral properties can be obtained.

[0027] Here, if the content of cerium oxide is less than 0.6% by mass, sufficient antibacterial and antiviral properties may not be obtained. Conversely, even if it exceeds 2.0% by mass, the antibacterial and antiviral properties do not particularly improve. Rather, the particle structure may become brittle, the particle size distribution may become wide, or the particles may aggregate. The content of cerium oxide is more preferably 1.0 to 2.0% by mass, and still more preferably 1.3 to 2.0% by mass.

[0028] The content of aluminum in the particle is preferably 0.5 to 2.0% by mass with aluminum oxide as Al2O3. When the content of aluminum oxide is in this range, the decrease in specific surface area over time can be suppressed, and sufficient antibacterial and antiviral properties can be obtained. Also, since it has a high zeta potential even in the acidic region, the dispersibility of the particles can be kept high.

[0029] Here, if the aluminum oxide content is less than 0.5% by mass, the amount of solid acid may be insufficient and sufficient antibacterial and antiviral properties may not be obtained. Also, there is a risk that the specific surface area decreases over time and the antibacterial and antiviral properties also decrease. Conversely, even if it exceeds 2.0% by mass, the antibacterial and antiviral properties are not particularly improved. Rather, the particle structure may become brittle, the particle size distribution may become wide, or the particles may aggregate. The content of this aluminum oxide is more preferably 1.0 to 2.0% by mass, and even more preferably 1.0 to 1.8% by mass.

[0030] The alkali metal content of the particles is not particularly limited as long as the dispersibility of the particles is high, it has antibacterial and antiviral properties, and the stability over time is high. For example, it is preferably less than 1.5% by mass in terms of the total based on the oxide.

[0031] Here, if it is 1.5% by mass or more, the particles may aggregate and the dispersibility of the particles in the dispersion or in the article may decrease. The alkali metal content is more preferably less than 1.3% by mass, even more preferably less than 1.1% by mass, and particularly preferably less than 1.0% by mass. Incidentally, when the particles contain an alkaline earth metal, the above-mentioned "alkali metal content" shall be read as "the total content of alkali metal and alkaline earth metal". Note that the alkali metals are Li, Na, K, Rb, Cs, Fr, and the alkaline earth metals are Be, Mg, Ca, Sr, Ba, Ra.

[0032] As for the zeta potential of the particles, it is preferable that the absolute value of the zeta potential at pH 2 is 10 to 20 mV. When the zeta potential is in this range, the dispersibility of the particles in the acidic region is high.

[0033] Here, if the absolute value of the zeta potential is less than 10 mV, the particles may become unstable in the acidic region. Conversely, if the absolute value exceeds 20 mV, since the amount of solid acid is too large, for example, when dispersed in an organic solvent or a resin, discoloration or the like may occur. This zeta potential is more preferably 10 to 18 mV, and even more preferably 10 to 15 mV.

[0034] The shape of the particles is not particularly limited. For example, spherical, ellipsoidal (rugby ball) shape, cocoon shape, sugar ball shape, chain shape, dice shape, etc. may be mentioned. Among them, spherical particles are preferable because they have high dispersibility and can be uniformly dispersed in the film. In addition, the surface of the particles preferably has some irregularities rather than being smooth. Having irregularities on the particle surface can increase the surface area of the particles due to the shape effect compared to particles with a smooth surface having the same particle diameter, and higher antibacterial and antiviral properties can be exhibited.

[0035] The average particle diameter of the particles is not particularly limited, but the average particle diameter (R1) determined by image analysis of an electron micrograph is preferably 10 to 25 nm. When the average particle diameter is within this range, the particles can exist stably. Also, the dispersibility is high in the dispersion liquid and articles.

[0036] Here, particles with an average particle diameter of less than 10 nm have low stability over time. Conversely, if it exceeds 25 nm, the dispersibility in the dispersion liquid or articles is low, and thus there is a possibility that the desired antibacterial and antiviral performance cannot be obtained. This average particle diameter is more preferably 10 to 20 nm, and even more preferably 15 to 20 nm.

[0037] The particles may be surface-treated with a known organosilicon compound such as a silane coupling material. The surface-treated particles have high dispersibility in organic solvents and resin materials, and in articles using these particles, aggregation of the particles is suppressed.

[0038] The particles used in the articles should desirably be stably usable in daily life in a living space without discoloring or aggregating when in contact with chlorine-containing water such as tap water. Specifically, when 1.0 g of an aqueous dispersion of the particles adjusted to a solid content concentration of 1.5 mass% is added to 50.0 g of tap water (chlorine concentration Cl of 2 ppm) and allowed to stand for 24 hours, it is preferable that no discoloration or formation of aggregates is observed. Such discoloration and formation of aggregates are due to the aggregation of Ag2O in the particles by chlorine. Since silver is not supported on the particles of the present invention, there is no discoloration or formation of aggregates caused by such silver. The stability of the particles against chlorine-containing water such as tap water means that not only can the active stability against antibacterial and antiviral properties be maintained in daily life, but also suppression of color tone changes of the articles can be achieved.

[0039] Also, the particles should desirably be stably usable without discoloring or aggregating with respect to surfactants. Specifically, 15 g of a strongly acidic cation exchange resin (SK 1B manufactured by Mitsubishi Chemical Corporation) was gradually added to 150 g of an aqueous dispersion of the particles adjusted to a solid content concentration of 1.5 mass%, stirred for 20 minutes, and then separated from the resin. To 100 g of this ion-exchanged aqueous dispersion, 1.0 g of a mixture of 1.0 g of Lipgard 210-80MSPG (manufactured by Lion Specialty Chemicals Co., Ltd.) and 99 g of pure water was added, and after stirring for 1 hour, it is preferable that no discoloration or formation of aggregates is observed. Such discoloration and formation of aggregates are due to the aggregation of the particles themselves or Ag2O in the particles. Since silver is not supported on the particles of the present invention, there is no formation of discoloration and aggregates caused by such silver. The stability of the particles against surfactants means that not only can the active stability against antibacterial and antiviral properties be maintained in daily life, but also suppression of color tone changes of the articles can be achieved.

[0040] It is preferable that the change rate (decrease rate) of the specific surface area of the particles after heating the aqueous dispersion of the particles adjusted to pH 9.5 and a solid content concentration of 10% by mass at 70°C for 6 days is 10% or less with respect to the specific surface area of the particles before heating. This evaluates the change over time of the particles in the aqueous dispersion with respect to the specific surface area. In the dispersion, the irregularities on the particle surface decrease. As described above, if the particle surface has irregularities, compared with particles having a smooth surface with the same particle diameter, the shape effect can increase the specific surface area of the particles, and higher antibacterial and antiviral properties can be exhibited. In other words, a decrease in the irregularities on the particle surface means a decrease in antibacterial and antiviral properties. That is, the stability of the specific surface area of the particles over time is related to the stability of the activity over time of the antibacterial and antiviral properties of the particle dispersion. Note that the conditions for evaluating this decrease rate of the specific surface area are for accelerating and evaluating the change over time of the particles.

[0041] The antibacterial test of the particles is carried out in accordance with JIS Z 2801. It is preferable that this antibacterial activity value is 2.0 or more. If it is 2.0 or more, it can be judged to have antibacterial properties. This antibacterial activity value is more preferably 4.0 or more.

[0042] The antiviral test of the particles is carried out in accordance with ISO21702. It is preferable that this antiviral activity value is 2.0 or more. If it is 2.0 or more, it can be judged to have antiviral properties. This antibacterial activity value is more preferably 3.0 or more.

[0043] As the material used for the article, conventionally known materials can be used. For example, resins such as glass, plastic, polycarbonate, acrylic resin, urethane resin, polyethylene terephthalate (PET), triacetyl cellulose (TAC), polyimide, polymethyl methacrylate resin (PMMA), and cycloolefin polymer (COP) are preferable.

[0044] [Manufacturing method of particles] One of the methods for manufacturing particles according to the present invention includes a first step of mixing a silicic acid solution and an aqueous cerium solution to prepare an acidic mixed solution, a second step of adding the mixed solution prepared in the first step to an alkaline mother liquor containing seed particles to prepare particles containing a composite oxide containing silicon and cerium, and a third step of adding a silicic acid solution and an acidic aluminum aqueous solution to the particles containing the composite oxide prepared in the second step to prepare particles of a composite oxide containing silicon, cerium, and aluminum.

[0045] The silicic acid solution used in the first step is a silicic acid solution obtained by ion-exchanging an alkali silicate. Examples of this alkali silicate include sodium silicate, potassium silicate, and the like. Among them, sodium silicate is preferable in terms of being industrially easily available.

[0046] The silicic acid solution used here has previously reduced the alkali amount such as sodium by ion exchange. Therefore, it is relatively easy to control particle growth. In addition, the washing load for reducing the contents of alkali metals and alkaline earth metals in the particles can be reduced.

[0047] Examples of the aqueous cerium solution used in the first step include aqueous solutions of cerium(IV) diammonium nitrate, cerium(IV) sulfate tetraammonium, cerium(III) chloride, and the like. Among them, cerium(IV) diammonium nitrate is preferable in terms of antibacterial and antiviral properties. These silicic acid solution and aqueous cerium solution are acidic solutions. The "acidic mixed solution" obtained by mixing them is a homogeneous solution without precipitation of composite oxide particles such as silica-ceria particles.

[0048] The "acidic mixed solution" used in the next second step is preferably one from which nitrate ions (NO3 - ) or sulfate ions (SO4 2- ) and the like have been removed for stable particle growth.

[0049] In the production of "particles containing a composite oxide containing silicon and cerium" in the second step, it is preferable to maintain the pH of the reaction solution at an alkaline level from the start to the end of the addition. For this reason, when adding the acidic mixed solution prepared in the first step, it is preferable to adopt a method of previously adjusting the pH of the mother liquor to a high level or a method of simultaneously adding an alkaline solution such as an aqueous sodium hydroxide solution or aqueous ammonia. Further, a method (seed method) of previously preparing seed particles such as fine silica or silica ceria in the mother liquor is adopted. The "particles containing a composite oxide containing silicon and cerium" produced in this second step serve as nucleating particles when adding the "silicate solution and acidic aluminum aqueous solution" in the third step.

[0050] The conditions for adding the "silicate solution and acidic aluminum aqueous solution" in the third step are not particularly limited as long as they satisfy the properties of the desired particles, but it is preferable to maintain the pH of the reaction solution at an alkaline level from the start to the end of the addition.

[0051] The silicate solution to be used may be the same as that used in the first step or may be different.

[0052] Examples of the acidic aluminum aqueous solution to be used include aqueous solutions of aluminum sulfate, aluminum nitrate, aluminum chloride, etc. Among them, an aqueous aluminum sulfate solution is preferably used because of its low corrosivity and reduced load on wastewater treatment.

[0053] When expressing silica as SiO2 and alumina (aluminum oxide) as Al2O3, the "silicate solution and acidic aluminum aqueous solution" to be added preferably has a molar ratio (SiO2 / Al2O3) of 30 to 120. When the molar ratio (SiO2 / Al2O3) is within this range, the specific surface area is high and the antibacterial and antiviral properties are also high.

[0054] Here, when the molar ratio (SiO2 / Al2O3) is less than 30, the proportion of Al2O3 forming the particles increases, so the structure of the particles becomes brittle. As a result, for example, there is a risk that the particle size distribution will become wider, or that the particles will dissolve in the acidic region and the particle structure will no longer be maintainable.

[0055] Conversely, when the molar ratio exceeds 120, the proportion of Al2O3 in the particles decreases, so the dispersibility of the particles in the acidic region decreases and there is a risk of aggregation. In addition, since the amount of solid acid in the particles decreases, there is a risk that sufficient antibacterial and antiviral properties cannot be obtained. This molar ratio (SiO2 / Al2O3) is more preferably 40 to 85, and even more preferably 50 to 85.

[0056] The difference between the average particle diameter of the particles produced in the third step and the average particle diameter of the particles produced in the second step is preferably 2 to 10 nm. This difference corresponds to "twice the thickness" of the silica-alumina layer formed in the third step. By providing a silica-alumina layer of such thickness, a suitable specific surface area and zeta potential can be obtained, and high antibacterial and antiviral properties and stability over time can be achieved. This difference is more preferably 4 to 10 nm, and even more preferably 4 to 6 nm.

[0057] The second method for manufacturing the particles according to the present invention includes a first step of mixing a silicic acid solution and an acidic aluminum aqueous solution to prepare an acidic mixed solution, and adding the mixed solution prepared in the first step to an alkaline mother solution containing seed particles to produce particles containing a composite oxide containing silicon and aluminum. A second step, and a third step of adding a silicic acid solution and a cerium aqueous solution to the particles containing the composite oxide produced in the second step to produce particles of a composite oxide containing silicon, cerium, and aluminum.

[0058] The silicic acid solution used in the first step is a silicic acid solution obtained by ion-exchanging an alkali silicate. Examples of this alkali silicate include sodium silicate, potassium silicate, etc. Among them, sodium silicate is preferable in terms of being easily available industrially.

[0059] The silicic acid solution used herein has its alkali content such as sodium reduced in advance by ion exchange. Therefore, it is relatively easy to control particle growth. In addition, the washing load for reducing the contents of alkali metals and alkaline earth metals in the particles can be reduced.

[0060] Examples of the acidic aluminum aqueous solution used in the first step include aqueous solutions of aluminum sulfate, aluminum nitrate, aluminum chloride, etc. Among them, an aluminum sulfate aqueous solution is preferably used because of its low corrosivity and reduced load on wastewater treatment.

[0061] For the "acidic mixture" used in the next second step, in order to achieve stable particle growth, it is preferable to use one from which sulfate ions (SO4 2- ) and nitrate ions (NO3 - ) etc. have been removed.

[0062] In the production of "particles containing a composite oxide containing silicon and aluminum" in the second step, it is preferable to maintain the pH of the reaction solution at an alkaline level from the start to the end of the addition. For this reason, when adding the acidic mixture prepared in the first step, it is preferable to adopt a method of adjusting the pH of the mother liquor to a high level in advance, or a method of simultaneously adding an alkaline solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution. In addition, a method (seed method) of preparing seed particles such as fine silica or silica alumina in the mother liquor in advance is adopted. The "particles containing a composite oxide containing silicon and aluminum" produced in this second step serve as nuclei when adding the "silicic acid solution and an aqueous cerium solution" in the third step.

[0063] The conditions for adding the "silicic acid solution and an aqueous cerium solution" in the third step are not particularly limited as long as they satisfy the properties of the desired particles, but it is preferable to maintain the pH of the reaction solution at an alkaline level from the start to the end of the addition.

[0064] The silicic acid solution to be used may be the same as that used in the first step or may be a different one.

[0065] Examples of the cerium aqueous solution to be used include aqueous solutions of cerium(IV) diammonium nitrate, cerium(IV) sulfate tetraammonium, cerium(III) chloride, etc. Among them, cerium(IV) diammonium nitrate is preferable in terms of antibacterial and antiviral properties. These silicic acid solution and cerium aqueous solution are acidic solutions. The "acidic mixed solution" obtained by mixing them is a homogeneous solution without precipitation of composite oxide particles such as silica-ceria particles.

[0066] When expressing silica as SiO2 and ceria (cerium oxide) as CeO2, the "silicic acid solution and cerium aqueous solution" to be added preferably have a molar ratio (SiO2 / CeO2) of 40 to 140. When the molar ratio (SiO2 / CeO2) is within this range, the specific surface area is high and the antibacterial and antiviral properties are also high.

[0067] Here, when the molar ratio (SiO2 / CeO2) is less than 40, the antibacterial and antiviral properties are not particularly enhanced. On the contrary, the particle structure may become brittle, the particle size distribution may become wide, or the particles may aggregate. Conversely, when the molar ratio exceeds 140, sufficient antibacterial and antiviral properties may not be obtained. This molar ratio (SiO2 / CeO2) is more preferably 50 to 110, and even more preferably 70 to 95.

[0068] The difference between the average particle diameter of the particles produced in the third step and the average particle diameter of the particles produced in the second step is preferably 2 to 10 nm. By providing such a silica-ceria layer with such a thickness, a suitable specific surface area, a high zeta potential, as well as high antibacterial and antiviral properties and stability over time can be achieved. This difference is more preferably 4 to 10 nm, and even more preferably 4 to 6 nm.

[0069] In each production method, the particles may be surface-treated with a known organosilicon compound such as a silane coupling material. When this treatment is performed, it is preferably carried out after the third step.

[0070] In each production method, the finally obtained particles preferably have a total content of alkali metals and alkaline earth metals in the particles of less than 1.0% by mass on an oxide basis. For this reason, it is preferable to wash using an ion exchange resin or an ultrafiltration membrane after at least one of the first step, the second step, and the third step.

[0071] The finally obtained particles may be used as an aqueous dispersion, may be replaced with an organic dispersion medium, or may be further dried and used as a powder.

[0072] Hereinafter, examples of the present invention will be described.

[0073] [Example 1] [Preparation of acidic mixed solution (first step)] Sodium silicate No. 3 (manufactured by AGC SI TECH Co., Ltd.) was diluted to 5% by mass with ion-exchanged water and cooled to a liquid temperature of 10°C. This was passed through a column filled with 1700 ml of a strongly acidic cation exchange resin (SK 1B manufactured by Mitsubishi Chemical Corporation) at a space velocity of 9 L / Hr to obtain 9500 g of a silicic acid solution having a SiO2 equivalent concentration of 4.5% by mass. To 1592 g of this silicic acid solution, 870 g of an aqueous solution of cerium diammonium nitrate (CeO2 equivalent concentration 0.26% by mass, NO3 concentration 0.55% by mass) was added to prepare a mixed solution.

[0074] [Preparation of particles containing a composite oxide containing silicon and cerium (second step)] 285 g of ion-exchanged water and 17.9 g of sodium silicate No. 3 were placed in a 5 L stainless steel separable flask set on a mantle heater, mixed and stirred. After adding 8.1 g of a silicic acid solution having a SiO2 equivalent concentration of 4.5% by mass thereto, the temperature was raised, and the liquid temperature was maintained at 61°C for 30 minutes to prepare an alkaline mother liquor containing seed particles of silica.

[0075] Next, while maintaining the liquid temperature at 61°C, 2462 g of the mixed solution prepared in the first step and 2000 g of a 0.2 mass% aqueous sodium hydroxide solution were simultaneously added to the mother liquor over 20 hours. After the addition was completed, the liquid temperature was maintained at 61°C for 30 minutes and then cooled to obtain 4773 g of a dispersion of silica-ceria particles. Next, this dispersion was concentrated to 785 g using an ultrafiltration membrane (SIP-1013 manufactured by Asahi Kasei Corporation), and while maintaining the liquid level at this time, 3000 g of ion-exchanged water was continuously added for washing. The solid content concentration at this time was 10 mass%.

[0076] <Preparation of Composite Oxide Particles Containing Silicon, Cerium, and Aluminum (Third Step)> 1102 g of an aqueous aluminum sulfate solution (Al2O3 conversion concentration 0.038 mass%, SO4 concentration 0.11 mass%) was added to 303 g of a silicic acid solution with a SiO2 conversion concentration of 4.5 mass% prepared in the same manner as in the first step to prepare a mixed solution.

[0077] 1191 g of ion-exchanged water and 2.9 g of sodium silicate No. 3 were placed in a 5 L stainless steel separable flask set on a mantle heater, mixed and stirred. 202.6 g of the dispersion of silica-ceria particles obtained in the second step was added thereto, mixed and stirred. Then, the temperature was raised and the liquid temperature was maintained at 95°C for 30 minutes to prepare an alkaline mother liquor.

[0078] Next, while maintaining the liquid temperature at 95°C, 1405 g of a mixed solution of a silicic acid solution and an aluminum sulfate aqueous solution prepared as described above and 1340 g of a 0.1 mass% sodium hydroxide aqueous solution were simultaneously added to this mother liquor over 12 hours. After the addition was completed, the liquid temperature was maintained at 95°C for 30 minutes. Then, it was cooled to obtain 4142 g of a dispersion of composite oxide particles containing silicon, cerium, and aluminum. Next, this dispersion was concentrated to 700 g using an ultrafiltration membrane (SIP-1013 manufactured by Asahi Kasei Corporation), and while maintaining the liquid level at this time, 3000 g of ion-exchanged water was continuously added for washing. The solid content concentration at this time was 5 mass%. This was concentrated to a solid content concentration of 10 mass% using a rotary evaporator to obtain a dispersion of composite oxide particles containing silicon, cerium, and aluminum.

[0079] The particles and their dispersions were measured by the following methods.

[0080] The characteristics in each manufacturing process of the particles are shown in Table 1. Also, the properties of the particles and the dispersions are shown in Table 2 (the same applies to the following examples and comparative examples).

[0081] (1) Average particle diameter (R1) The average particle diameter (R1) is determined by image analysis from a scanning electron micrograph of the target particles. Specifically, it was determined by the following method.

[0082] First, a drop of the target particles with ultrapure water added to adjust the solid content concentration to 0.01 mass% was placed on a sample stage, and then dried to prepare an observation target sample. Next, the observation target sample was photographed at a magnification of 300,000 times using a scanning electron microscope (Scanning Electron Microscope S-5500 manufactured by Hitachi, Ltd.). In the photographed photo projection diagram, the maximum diameter of each particle was taken as the major axis, and its length was measured, and the value was taken as the major axis diameter (D L ). Also, a point that bisects the major axis on the major axis was determined, and two points where a straight line orthogonal to it intersects the outer edge of the particle were obtained, and the distance between the two points was measured and taken as the minor axis diameter (D S ). And the major axis diameter (D L ) and the minor axis diameter (D S) The average value with [it] was determined and taken as the particle diameter of the particles. In this measurement, the photographic projection diagram was evenly divided into six sections, 10 particles were randomly extracted from each section, a total of 60 particle diameters were measured, the number average value thereof was calculated, and the obtained value was taken as the average particle diameter of the composite oxide particles. Also, at this time, the particle shape was observed together.

[0083] (2) Specific surface area and average particle diameter (R2) by the shear method A sample (dispersion of particles) corresponding to 1.5 g as SiO2 was collected in a beaker, transferred to a constant temperature reaction tank maintained at 25 °C, pure water was added to make the liquid volume 90 ml. Next, after adding a 0.1 mol / L hydrochloric acid aqueous solution so that the pH became 3.6, 30 g of sodium chloride was added, diluted to 150 ml with pure water, and stirred for 10 minutes. Next, a pH electrode was set, and while stirring, a 0.1 mol / L sodium hydroxide solution was added dropwise to adjust the pH to 4.0. This dispersion adjusted to pH 4.0 was titrated with a 0.1 mol / L sodium hydroxide solution, and the titration amount and pH value in the range of pH 8.7 to 9.3 were recorded at four or more points. Taking the titration amount of the 0.1 mol / L sodium hydroxide solution as X and the pH value at that time as Y, a calibration curve was made. Note that the consumption volume V (ml) of the 0.1 mol / L sodium hydroxide solution required from pH 4.0 to 9.0 per 1.5 g of SiO2 was determined from formula (1), and the specific surface area SA (m 2 / g) was determined from formula (2). Also, for the average particle diameter R2 (nm), it was determined from formula (3).

[0084] V = (A × f × 100 × 1.5) / (W × C) ··· (1) (Here, A is the consumption volume (ml) of the 0.1 mol / L sodium hydroxide solution required from pH 4.0 to 9.0 per 1.5 g of SiO2, f is the titer of the 0.1 mol / L sodium hydroxide solution, C is the SiO2-converted concentration (mass%) of the sample (dispersion of particles), and W represents the sample collection amount (equivalent to 1.5 g as SiO2)) SA = 29.0V - 28 ··· (2) R2 = 6000 / (ρ × SA) ··· (3) (Here, ρ is the density of the particles (g / cm 3represents this. In this case, 2.2 is used).

[0085] Incidentally, the "difference between the average particle diameter of the particles produced in the third step and the average particle diameter of the particles produced in the second step" was calculated in the same manner as the aforementioned average particle diameter (R2). That is, for the particles produced in the second and third steps, the average particle diameter was determined from the specific surface area by the Shear's method, and the difference was calculated.

[0086] (3) Dispersion solid content concentration It was determined by subjecting the particle dispersion to ignition loss at 1000 °C and weighing.

[0087] (4) Metal element concentration The content rate of each element was measured by the following method. First, a sample equivalent to about 0.2 g as a solid content was collected in a platinum dish. To this, 3 ml of phosphoric acid, 5 ml of nitric acid, and 10 ml of hydrofluoric acid were added, and it was heated on a sand bath. After this dried up, a small amount of water and 50 ml of nitric acid were added and dissolved, and it was transferred to a 100 ml volumetric flask and water was added to make 100 ml. Using this solution, the alkali metal content was measured using an atomic absorption spectrophotometer (Z-2310 manufactured by Hitachi, Ltd.) and converted to oxides. Next, from the solution adjusted to 100 ml in the same manner, for Ce and Al, using the aliquot solution, it was measured using an ICP plasma emission spectrometer (SPS5520 manufactured by SII Co., Ltd.) and converted to oxides.

[0088] (5) Concentration of SiO2 To 10 g of the particle dispersion, 2 ml of a 50% sulfuric acid aqueous solution was added, and it was evaporated to dryness on a platinum dish. The obtained solid was calcined at 1000 °C for 1 hour, cooled, and weighed. Next, the weighed solid was dissolved in a small amount of 50% sulfuric acid aqueous solution. Further, 20 ml of hydrofluoric acid was added, then it was evaporated to dryness on a platinum dish, calcined at 1000 °C for 15 minutes, cooled, and weighed. The silica content was determined from these mass differences.

[0089] (6) Zeta potential First, pure water was added to adjust the solid content concentration of the aqueous dispersion of the particles to 0.5% by mass. This was adjusted to each pH of 11, 10, 9, 8, 7, 6, 5, 4, 3, and 2. Note that on the acidic side, the pH was adjusted using a 0.25 - 0.5% by mass hydrochloric acid aqueous solution, and on the alkaline side, the pH was adjusted using a 0.25 - 0.5% by mass sodium hydroxide aqueous solution. The zeta potential at each adjusted pH was measured using a Zetasizer nanoZS manufactured by Malvern

[0090] (7) Stability test against tap water 1.0 g of the aqueous dispersion of the particles adjusted to a solid content concentration of 1.5% by mass was added to 50.0 g of tap water (chlorine concentration 2 ppm as Cl) and left to stand for 24 hours. The color change state and the presence or absence of precipitate formation were observed according to the following evaluation criteria No color change and no precipitate: ◎ Color changed but no precipitate: 〇 No color change but there is a precipitate: △ Color changed and a precipitate was also formed: ×

[0091] (8) Stability test against surfactants 15 g of a strongly acidic cation exchange resin (SK 1B manufactured by Mitsubishi Chemical Corporation) was gradually added to 150 g of the aqueous dispersion of the particles adjusted to a solid content concentration of 1.5% by mass, and after stirring for 20 minutes, it was separated from the resin. 1.0 g of a mixture obtained by adding 99 g of pure water to 1.0 g of Lipoguard 210 - 80MSPG (manufactured by Lion Specialty Chemicals Co., Ltd.) was added to 100 g of this ion-exchanged aqueous dispersion and stirred for 1 hour. The color change state and the presence or absence of precipitate formation were observed according to the following evaluation criteria No color change and no precipitate: ◎ Color changed but no precipitate: 〇 No color change but there is a precipitate: △ Color changed and a precipitate was also formed: ×

[0092] (9) Aging test of particles An aqueous dispersion of particles with a solids concentration of 10% by mass adjusted to pH 9.5 with an aqueous sodium hydroxide solution was prepared. 100 g of this dispersion was collected in a plastic container and the container was sealed. Next, this was heated to a water temperature of 70 °C and immersed in a constant temperature bath maintained at this temperature for 6 days. This was measured in the same manner as the specific surface area by the aforementioned shear method. Regarding this specific surface area, the rate of change (rate of decrease in specific surface area) with respect to the specific surface area before heating was determined from the following formula (4).

[0093] Rate of change (%) = ((Specific surface area before heating - Specific surface area after heating) / Specific surface area before heating) × 100 ··· (4)

[0094] 〈Preparation of coating liquid for film formation〉 A dispersion of particles equivalent to 8 g as solids was concentrated to 267 g using an ultrafiltration membrane (Vivaflo Mw10000 manufactured by Sartorius Co., Ltd.). Next, while continuously adding 1600 g of methanol, the filtrate was discharged to replace the dispersion medium with methanol. The solids concentration of this methanol replacement product was 3.7% by mass and the water content was 0.3% by mass. 90 g of this methanol replacement product was placed in a plastic container, 21 g of methanol was added, and the solids concentration was adjusted to 3% by mass. Next, while stirring this, 0.33 g of a silane coupling agent (KBM503 manufactured by Shin-Etsu Chemical Co., Ltd.) was added and further stirred for 30 minutes. Next, the container was sealed and stirred in a constant temperature bath at 50 °C for 15 hours to produce particles surface-treated with a silane coupling agent. 80 g of the dispersion of these surface-treated particles was placed in an eggplant-shaped flask, 150 g of methyl isobutyl ketone (MIBK) was added, and it was attached to a rotary evaporator. While reducing the pressure, it was solvent-exchanged with MIBK in a hot water bath at 80 °C to produce a MIBK dispersion of the particles. The solids concentration at this time was 2.0% by mass and the water content was 0.2% by mass.

[0095] Next, to the anti-reflection film-forming paint (sometimes referred to as Anti-Reflection paint or AR paint) ELCOM-P-5062 (solids concentration 3.0% by mass) manufactured by Nichi-etsu Catalytic Chemical Co., Ltd., 5% by mass equivalent of the above-mentioned MIBK dispersion with a solids concentration of 2.0% by mass was added in terms of the solids ratio of the particles to prepare a coating liquid for film formation.

[0096] <Production of Substrate with Coating> The hard coat paint (ELCOM HP-1004 manufactured by Nippon Shokubai Catalysts & Chemicals, Ltd.) was applied to a TAC film (FT-PB80UL-M manufactured by Panac Co., Ltd., thickness 80 μm, refractive index 1.51) by the bar coater method (#18), and dried at 80°C for 120 seconds. Then, ultraviolet rays of 300 mJ / cm 2 were irradiated and cured to produce a hard coat film. The film thickness of this hard coat film was 8 μm.

[0097] Next, the coating liquid for film formation using the particles of the present invention was applied by the bar coater method (#4), and dried at 80°C for 120 seconds. Then, ultraviolet rays of 400 mJ / cm 2 were irradiated and cured in an N2 atmosphere to produce a substrate with a coating.

[0098] The substrate with a coating was measured for the following items. The results are shown in Table 2 (the same applies to the following Examples and Comparative Examples).

[0099] (10) Antibacterial Test The antibacterial test was carried out according to JIS Z 2801, and the antibacterial activity value was determined by the following formula (5).

[0100] Q B =U Bt -A Bt ····(5) (However, Q B is the antibacterial activity value, U Bt is the average value of the logarithm of the viable cell count per 1 cm 2 of the unprocessed test piece after 24 hours, A Bt is the average value of the logarithm of the viable cell count per 1 cm 2 of the antibacterial processed test piece after 24 hours.)

[0101] It was determined that there was an antibacterial effect when this antibacterial activity value was 2.0 or more.

[0102] As test bacteria, Staphylococcus aureus (Staphylococcus aureus NBRC 12732) and Escherichia coli (Escherichia coli NBRC3972) were used, and 1 / 500 normal broth medium (3 g of meat extract + 10 g of peptone and 5.0 g of sodium chloride per 1000 ml of medium) was used as nutrition.

[0103] For the measurement, 0.4 ml of the bacterial solution was dropped onto each of the coated substrate cut into a 5 cm square and the unprocessed film, and then covered with a 4 cm square PE film. The test pieces were cultured at 35°C ± 1°C and a relative humidity of 90% or more for 24 hours. After washing and collecting the test bacteria on the test pieces with 10 ml of SCDLP medium, the viable cell count of the washing solution was measured by the plate mixing culture method at 1 cm 2 per viable cell count.

[0104] (11) Antiviral test The antiviral test was conducted according to ISO 21702, and the antiviral activity value was determined by the following formula (6).

[0105] Q V =U Vt -A Vt ····(6) (However, Q V is the antiviral activity value, U Vt is the average value of the logarithm of the virus infectivity titer per 1 cm 2 of the unprocessed test piece after 24 hours, A Vt is the average value of the logarithm of the virus infectivity titer per 1 cm 2 of the antiviral processed test piece after 24 hours.)

[0106] When this antiviral activity value is 2.0 or more, it was judged that there is an antiviral effect.

[0107] For the measurement, 1 - 5×10 70.4 ml of a virus suspension (Influenza A virus (H3N2) ATCC VR-1679) prepared at pfu / ml was dropped and covered with a 4 cm square PE film. The test piece was cultured at 25°C ± 1°C and a relative humidity of 90% or more for 24 hours. After washing and collecting the test bacteria on the test piece with 10 ml of SCDLP medium, a 10-fold dilution series of the washing solution was prepared, and the virus infectivity titer per 1 cm 2 was measured by the plaque measurement method.

[0108] [Example 2] In the mixed solution used in the third step, 123.9 g of silicic acid solution, 450.9 g of aluminum sulfate aqueous solution are used, 1660 g of ion-exchanged water, 1.7 g of sodium silicate No. 3, and 288.4 g of a dispersion of silica-ceria particles are used for the alkaline mother liquor prepared in a separable flask. Also, a dispersion of composite oxide particles containing silicon, cerium, and aluminum, 3864.9 g, was obtained in the same manner as in Example 1, except that 574.8 g of the above mixed solution and 1340 g of a 0.04 mass% sodium hydroxide aqueous solution were added to this mother liquor. Thereafter, in the same manner as in Example 1, a dispersion of composite oxide particles containing silicon, cerium, and aluminum with a solid content concentration of 10 mass% was obtained.

[0109] [Example 3] In the mixed solution used in the third step, 459.3 g of silicic acid solution, 1671.4 g of aluminum sulfate aqueous solution are used, 781.8 g of ion-exchanged water, 3.9 g of sodium silicate No. 3, and 127.6 g of a dispersion of silica-ceria particles are used for the alkaline mother liquor prepared in a separable flask. Also, a dispersion of composite oxide particles containing silicon, cerium, and aluminum, 4383.3 g, was obtained in the same manner as in Example 1, except that 2130 g of the above mixed solution and 1340 g of a 0.15 mass% sodium hydroxide aqueous solution were added to this mother liquor. Thereafter, in the same manner as in Example 1, a dispersion of composite oxide particles containing silicon, cerium, and aluminum with a solid content concentration of 10 mass% was obtained.

[0110] [Example 4] [Preparation of Acidic Mixed Solution (First Step)] Sodium silicate No. 3 (manufactured by AGC SI TECH Co., Ltd.) was diluted to 5% by mass with ion-exchanged water and cooled to a liquid temperature of 10°C. This was passed through a column filled with 1700 ml of strongly acidic cation exchange resin (SK 1B manufactured by Mitsubishi Chemical Corporation) at a space velocity of 9 L / Hr to obtain 9500 g of a silicic acid solution with a SiO2 equivalent concentration of 4.5% by mass. To 1592 g of this silicic acid solution, 5793.5 g of an aqueous aluminum sulfate solution (Al2O3 equivalent concentration: 0.038% by mass, SO4 concentration: 0.11% by mass) was added to prepare a mixed solution.

[0111] <Production of Particles Containing a Composite Oxide Containing Silicon and Aluminum (Second Step)> 285.3 g of ion-exchanged water and 17.9 g of sodium silicate No. 3 were placed in a 10 L stainless steel separable flask set on a mantle heater, mixed, and stirred. After adding 8.1 g of a silicic acid solution with a SiO2 equivalent concentration of 4.5% by mass thereto, the temperature was raised and the liquid temperature was maintained at 61°C for 30 minutes to prepare an alkaline mother liquor containing seed particles of silica.

[0112] Next, while maintaining the liquid temperature at 61°C, 7385.6 g of the mixed solution prepared in the first step and 2000 g of a 0.35% by mass aqueous sodium hydroxide solution were simultaneously added to the mother liquor over 20 hours. After completion of the addition, the liquid temperature was maintained at 61°C for 30 minutes and then cooled to obtain 9385.6 g of a dispersion of silica-alumina particles. Next, this dispersion was concentrated to 785 g using an ultrafiltration membrane (SIP-1013 manufactured by Asahi Kasei Corporation), and while maintaining the liquid level at this time, 3000 g of ion-exchanged water was continuously added for washing. The solid content concentration at this time was 10%.

[0113] <Production of Composite Oxide Particles Containing Silicon, Aluminum, and Cerium (Third Step)> To 303 g of a silicic acid solution with a SiO2 equivalent concentration of 4.5% by mass prepared in the same manner as in the first step, 1102.7 g of an aqueous cerium diammonium nitrate solution (CeO2 equivalent concentration: 0.038% by mass, NO3 concentration: 0.06% by mass) was added to prepare a mixed solution.

[0114] 1191.3 g of ion-exchanged water and 2.9 g of sodium silicate No. 3 were placed in a 5-L separable flask made of stainless steel set on a mantle heater, and mixed and stirred. To this, 202.6 g of the dispersion of silica alumina particles obtained in the second step was added and mixed and stirred. Then, the temperature was raised and the liquid temperature was maintained at 95°C for 30 minutes to prepare an alkaline mother liquor.

[0115] Next, while maintaining the liquid temperature at 95°C, 468.3 g of the mixed solution of the silicic acid solution and the ammonium cerium nitrate aqueous solution prepared as described above and 1340 g of a 0.06 mass% sodium hydroxide aqueous solution were simultaneously added to this mother liquor over 12 hours. After the addition was completed, the liquid temperature was maintained at 95°C for 30 minutes. Then, it was cooled to obtain 3205 g of a dispersion of composite oxide particles containing silicon, aluminum, and cerium. Next, this dispersion was concentrated to 700 g using an ultrafiltration membrane (SIP-1013 manufactured by Asahi Kasei Corporation), and while maintaining the liquid level at this time, 3000 g of ion-exchanged water was continuously added for washing. The solid content concentration at this time was 5 mass%. This was concentrated to a solid content concentration of 10 mass% using a rotary evaporator to obtain a dispersion of composite oxide particles containing silicon, aluminum, and cerium.

[0116] [Example 5] 830 g of an aqueous mixed solution of aluminum sulfate (concentration in terms of Al2O3: 0.13 mass%, SO4 concentration: 0.36 mass%) and cerium chloride (concentration in terms of CeO2: 0.13 mass%, Cl concentration: 0.08 mass%) was added to 1520 g of the silicic acid solution prepared in the same manner as in the first step of Example 1 to prepare a mixed solution.

[0117] [Preparation of Composite Oxide Particles Containing Silicon, Cerium, and Aluminum] 289 g of ion-exchanged water and 12.3 g of sodium silicate No. 3 were placed in a 5-L separable flask made of stainless steel set on a mantle heater, and mixed and stirred. After adding 50.6 g of a silicic acid solution having a SiO2 conversion concentration of 4.5 mass% thereto, the temperature was raised and the liquid temperature was maintained at 79°C for 30 minutes to prepare an alkaline mother liquor containing seed particles of silica.

[0118] Next, while maintaining the liquid temperature at 79°C, 2350 g of the mixed liquid prepared in the first step and 2000 g of a 0.19% by weight aqueous sodium hydroxide solution were simultaneously added to the mother liquid over 20 hours. After the addition was completed, the liquid temperature was maintained at 79°C for 30 minutes and then cooled to obtain 4702 g of a dispersion of composite oxide particles containing silicon, cerium, and aluminum. This dispersion was then concentrated to 757 g using an ultrafiltration membrane (SIP-1013, manufactured by Asahi Kasei Corporation). While maintaining the liquid level at this time, 3000 g of ion-exchanged water was continuously added for washing, yielding a dispersion of composite oxide particles containing silicon, cerium, and aluminum. The solids concentration at this time was 10% by weight.

[0119] [Example 6] In the first step of preparing the acidic mixed solution, 1621.5 g of silicic acid solution and 840.5 g of diammonium cerium nitrate aqueous solution (CeO2 equivalent concentration 0.106 mass%, NO3 concentration 0.23 mass%) were used to prepare 2462 g of mixed solution. The same procedure as in Example 1 was repeated to obtain a dispersion of composite oxide particles containing silicon, cerium, and aluminum with a solid content concentration of 10 mass%.

[0120] [Comparative Example 1] Preparation of the acidic mixture (first step) A mixed solution was prepared by adding 830 g of an aqueous solution of diammonium cerium nitrate (CeO2 equivalent concentration 0.26 mass%, NO3 concentration 0.55 mass%) to 1,520 g of a silicic acid solution with an SiO2 equivalent concentration of 4.5 mass%, which was prepared in the same manner as in the first step of Example 1.

[0121] <Preparation of particles containing a composite oxide containing silicon and cerium (second step)> A 5 L stainless steel separable flask was placed on a mantle heater and mixed with stirring, and 289 g of ion-exchanged water and 12.3 g of No. 3 sodium silicate were added. 50.6 g of silicic acid solution with an SiO2 equivalent concentration of 4.5 mass % was added, and the temperature was then raised and maintained at 79°C for 30 minutes to prepare an alkaline mother liquor containing silica seed particles.

[0122] Next, while maintaining the liquid temperature at 79°C, 2350 g of the mixed solution prepared in the first step and 2000 g of a 0.19 mass% sodium hydroxide aqueous solution were simultaneously added to the mother liquor over 20 hours. After the addition was completed, the liquid temperature was maintained at 79°C for 30 minutes and then cooled to obtain 4702 g of a dispersion of silica-ceria particles. Next, this dispersion was concentrated to 757 g using an ultrafiltration membrane (SIP-1013 manufactured by Asahi Kasei Corporation). While maintaining the liquid level at this time, 3000 g of ion-exchanged water was continuously added for washing to obtain a dispersion of composite oxide particles containing silicon and cerium. The solid content concentration at this time was 10 mass%.

[0123] [Comparative Example 2] In the third step, 1661.4 g of an aluminum sulfate aqueous solution (Al2O3 conversion concentration 0.013 mass%, SO4 concentration 0.036 mass%) was added to 468.6 g of a silicic acid solution with a SiO2 conversion concentration of 4.5 mass% prepared in the same manner as in the first step of Example 1 to prepare a mixed solution.

[0124] 781.8 g of ion-exchanged water and 3.9 g of sodium silicate No. 3 were placed in a 5 L separable flask made of stainless steel set on a mantle heater, mixed and stirred. 127.6 g of the dispersion of silica-ceria particles prepared in the same manner as in the second step of Example 1 was added thereto, and the mixture was stirred. Then, the temperature was raised and the liquid temperature was maintained at 95°C for 30 minutes to prepare an alkaline mother liquor.

[0125] Next, while maintaining the liquid temperature at 95°C, 2130 g of a mixed solution of a silicic acid solution and an aluminum sulfate aqueous solution prepared as described above and 1340 g of a 0.05 mass% sodium hydroxide aqueous solution were simultaneously added to this mother liquor over 12 hours. After the addition was completed, the liquid temperature was maintained at 95°C for 30 minutes. Then, it was cooled to obtain 4383.4 g of a dispersion of composite oxide particles containing silicon, cerium, and aluminum. Next, this dispersion was concentrated to 700 g using an ultrafiltration membrane (SIP-1013 manufactured by Asahi Kasei Corporation), and while maintaining the liquid level at this time, 3000 g of ion-exchanged water was continuously added for washing. The solid content concentration at this time was 5 mass%. This was concentrated to a solid content concentration of 10 mass% using a rotary evaporator to obtain a dispersion of composite oxide particles containing silicon, cerium, and aluminum.

[0126] [Comparative Example 3] In the third step, 1681 g of an aluminum sulfate aqueous solution (Al2O3 conversion concentration 0.064 mass%, SO4 concentration 0.18 mass%) was added to 449.8 g of a silicic acid solution with a SiO2 conversion concentration of 4.5 mass% prepared in the same manner as in the first step of Example 1 to prepare a mixed solution.

[0127] 781.8 g of ion-exchanged water and 3.9 g of sodium silicate No. 3 were placed in a 5 L stainless steel separable flask set on a mantle heater, mixed and stirred. To this, 127.6 g of a dispersion of silica-ceria particles prepared in the same manner as in the second step of Example 1 was added and mixed and stirred. Then, the temperature was raised, and the liquid temperature was maintained at 95°C for 30 minutes to prepare an alkaline mother liquor.

[0128] Next, while maintaining the liquid temperature at 95°C, 2130 g of a mixed solution of a silicic acid solution and an aluminum sulfate aqueous solution prepared as described above and 1340 g of a 0.05 mass% sodium hydroxide aqueous solution were simultaneously added to this mother liquor over 12 hours. After the addition was completed, the liquid temperature was maintained at 95°C for 30 minutes. Then, it was cooled to obtain 4383.4 g of a dispersion of composite oxide particles containing silicon, cerium, and aluminum. Next, this dispersion was concentrated to 700 g using an ultrafiltration membrane (SIP-1013 manufactured by Asahi Kasei Corporation), and while maintaining the liquid level at this time, 3000 g of ion-exchanged water was continuously added for washing. The solid content concentration at this time was 5 mass%. This was concentrated to a solid content concentration of 10 mass% using a rotary evaporator to obtain a dispersion of composite oxide particles containing silicon, cerium, and aluminum.

[0129]

Table 1

[0130]

Table 2

Claims

1. Particles containing silicon, cerium, and aluminum, The average particle diameter (R １ ), obtained by image analysis of the electron micrograph, and the particle diameter (R ２ ), obtained by equivalent sphere conversion from the specific surface area determined by the shear method, and the ratio (R １ / R ２ ) is 1.2 to 1.

8.

2. The particles according to claim 1, wherein the particles have a layer containing silicon and aluminum on the surface of composite oxide particles containing silicon and cerium.

3. The particles according to claim 1, wherein the particles have a layer containing silicon and cerium on the surface of composite oxide particles containing silicon and aluminum.

4. Among the above particles, cerium oxide is contained in an amount of 0.6 to 2.0% by mass as CeO ２ , and aluminum oxide is contained in an amount of 0.5 to 2.0% by mass as Al ２ O ３ . The particle according to claim 1.

5. The average particle diameter (R １ ) of the particles according to claim 1, wherein the average particle diameter (R １ ) is 10 to 25 nm.

6. The particles according to claim 1, wherein the water dispersion of the particles is adjusted to pH 9.5 and a solid content concentration of 10% by mass, and the reduction rate of the specific surface area of the particles after heating at 70°C for 6 days is 10% or less with respect to the specific surface area of the particles before heating.

7. A first step of mixing a silicic acid solution and an aqueous cerium solution to prepare an acidic mixed solution, A second step of adding the mixed solution to an alkaline mother liquor containing seed particles to prepare particles containing a composite oxide containing silicon and cerium, A method for producing particles, comprising a third step of adding a silicic acid solution and an acidic aqueous aluminum solution to the particles containing the composite oxide to prepare particles containing a composite oxide containing silicon, cerium, and aluminum.

8. The method for producing particles according to claim 7, wherein the difference between the average particle diameter of the particles produced in the third step and the average particle diameter of the particles produced in the second step is 2 to 10 nm.

9. A first step of mixing a silicic acid solution and an acidic aqueous aluminum solution to prepare an acidic mixed solution, A second step of adding the mixed solution to an alkaline mother liquor containing seed particles to prepare particles containing a composite oxide containing silicon and aluminum, A method for producing particles, comprising a third step of adding a silicic acid solution and an aqueous cerium solution to the particles containing the composite oxide to prepare particles containing a composite oxide containing silicon, cerium, and aluminum.

10. The method for producing particles according to claim 9, wherein the difference between the average particle diameter of the particles produced in the third step and the average particle diameter of the particles produced in the second step is 2 to 10 nm.

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