Classifications

• • A—HUMAN NECESSITIES
  • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
  • A01N—PRESERVATION OF BODIES OF HUMANS OR ANIMALS OR PLANTS OR PARTS THEREOF; BIOCIDES, e.g. AS DISINFECTANTS, AS PESTICIDES OR AS HERBICIDES; PEST REPELLANTS OR ATTRACTANTS; PLANT GROWTH REGULATORS
  • A01N59/00—Biocides, pest repellants or attractants, or plant growth regulators containing elements or inorganic compounds
• • A—HUMAN NECESSITIES
  • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
  • A01P—BIOCIDAL, PEST REPELLANT, PEST ATTRACTANT OR PLANT GROWTH REGULATORY ACTIVITY OF CHEMICAL COMPOUNDS OR PREPARATIONS
  • A01P1/00—Disinfectants; Antimicrobial compounds or mixtures thereof
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
  • C01B21/068—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with silicon
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
  • C01B21/068—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with silicon
  • C01B21/0682—Preparation by direct nitridation of silicon
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
  • C01B21/068—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with silicon
  • C01B21/0687—After-treatment, e.g. grinding, purification

Definitions

• the present disclosure relates to antimicrobial agents and methods of using compositions containing silicon nitride as antimicrobial agents.
• Silicon nitride is a material with excellent strength, hardness, toughness, heat resistance, corrosion resistance, and thermal shock resistance, and is therefore used in components of various structures. In addition to these properties, silicon nitride is known to have antibacterial properties and biocompatibility (Patent Documents 1 and 2). Patent Document 1 proposes changing the chemical properties of the surface to improve the antibacterial properties of a bioimplant block containing silicon nitride ceramic material. Patent Document 2 proposes filling a bioimplant such as polyether ether ketone (PEEK) with silicon nitride and providing a silicon nitride coating.
• PEEK polyether ether ketone
• the present disclosure provides an antibacterial agent with excellent antibacterial properties. It also provides a method for using a composition containing silicon nitride as an antibacterial agent with excellent antibacterial properties.
• One aspect of the present disclosure provides the following antibacterial agent:
• the antibacterial properties of silicon nitride vary depending on the fluorine content.
• the above antibacterial agent has excellent antibacterial properties because it contains 900 mass ppm or less of fluorine.
• the antibacterial agent [1] above may be any one of the following [2] to [8]. These antibacterial agents have even more excellent antibacterial properties.
• the antibacterial agent according to [1] which is granular and has a BET specific surface area of 0.5 m 2 /g or more.
• [5] The antibacterial agent according to any one of [1] to [4], wherein, after 10 minutes have elapsed since the antibacterial agent is dispersed in water to a concentration of 6.0 w/v%, the content of ammonium ions contained in the liquid phase is 6.0 ⁇ g/mL or less, and the content of ammonia contained in the liquid phase is 0.2 ⁇ g/mL or more.
• [6] The antibacterial agent according to [5], wherein the ratio of the ammonia content to the ammonium ion content is 0.10 or more.
• the antibacterial agent according to any one of [1] to [6] having a fluorine content of 10 ppm by mass or more.
• [8] The antibacterial agent according to any one of [1] to [7], having a chlorine content of 30 ppm by mass or more.
• One aspect of the present disclosure provides the following method:
• the antibacterial properties of silicon nitride vary depending on the fluorine content.
• the above composition contains silicon nitride as the main component and has a fluorine content of 900 mass ppm or less, and therefore has excellent antibacterial properties.
• Such a composition is suitable as an antibacterial agent because of its excellent antibacterial properties.
• an antibacterial agent having excellent antibacterial properties it is possible to provide a method for using a composition containing silicon nitride as an antibacterial agent having excellent antibacterial properties.
• each numerical range indicated with the symbol "to” includes a lower limit and an upper limit.
• a numerical range indicated as "A to B” means A or more and B or less.
• the present disclosure also includes a range in which the upper or lower limit of each numerical range is replaced with the numerical value of any of the examples.
• the antibacterial agent of one embodiment contains silicon nitride as a main component and has a fluorine content of 900 ppm by mass or less.
• the antibacterial agent may be, for example, granular, a powder composed of an aggregate of multiple particles, or a solid such as a film.
• a powder containing 90% or more by mass of silicon nitride is referred to as a "silicon nitride powder.”
• silicon nitride powder may be the antibacterial agent.
• the "main component” refers to the component that is contained in the largest amount when multiple components are contained. Components other than the "main component" are referred to as "secondary components.”
• the antibacterial agent may consist of only the main component, or may contain the main component and secondary components.
• the silicon nitride content in the antibacterial agent may be 90% by mass or more, 95% by mass or more, 98% by mass or more, 99% by mass or more, 99.5% by mass or more, or 99.7% by mass or more.
• minor components contained in the antibacterial agent include fluorine, chlorine, oxygen, iron, aluminum, and calcium. These may form compounds.
• the fluorine content in the antibacterial agent may be 700 ppm by mass or less, 500 ppm by mass or less, 300 ppm by mass or less, 250 ppm by mass or less, 100 ppm by mass or less, or 60 ppm by mass or less.
• One of the reasons for this is that when the fluorine content is low and hydrolysis occurs in contact with moisture, the ratio of ammonia (NH 3 ) to ammonium ions (NH 4 + ) increases.
• the fluorine content in the antibacterial agent varies depending on the raw material composition and the presence or absence of surface treatment when the antibacterial agent is manufactured.
• the fluorine content can be reduced by thoroughly washing the antibacterial agent with a washing liquid such as water.
• the fluorine content in the antibacterial agent may be 10 ppm by mass or more, 20 ppm by mass or more, or 30 ppm by mass or more. This makes it possible to reduce the manufacturing cost of the antibacterial agent.
• An example of the fluorine content in the antibacterial agent may be 10 to 900 ppm by mass.
• the chlorine content in the antibacterial agent may be 30 ppm by mass or more, 50 ppm by mass or more, 100 ppm by mass or more, 300 ppm by mass or more, 400 ppm by mass or more, or 500 ppm by mass or more.
• a higher chlorine content tends to improve antibacterial performance, especially against gram-negative bacteria.
• the chlorine content in the antibacterial agent varies depending on the raw material composition used in producing the antibacterial agent and whether or not the particles are surface-treated. For example, the higher the chlorine content of the raw materials used in synthesizing silicon nitride, the higher the chlorine content in the antibacterial agent tends to be.
• the chlorine content in the antibacterial agent may be 1000 ppm by mass or less, 800 ppm by mass or less, or 700 ppm by mass or less. This makes it possible to suppress corrosion caused by chlorine.
• An example of the chlorine content in the antibacterial agent may be 30 to 1000 ppm by mass.
• the oxygen content in the antibacterial agent may be 2.0 mass% or less, 1.5 mass% or less, or 1.0 mass% or less.
• the oxygen may be contained, for example, as silicon dioxide (SiO 2 ). The lower the oxygen content of the antibacterial agent, the more improved the antibacterial performance tends to be.
• the oxygen content in the antibacterial agent varies depending on the raw material composition and the firing atmosphere when the antibacterial agent is manufactured. For example, if the oxygen concentration in the firing atmosphere when synthesizing silicon nitride by the direct nitridation method is lowered, the oxygen content in the antibacterial agent tends to be lower.
• the oxygen content in the antibacterial agent may be 0.2 mass% or more, 0.4 mass% or more, or 0.5 mass% or more. This makes it possible to use raw materials and gases with low purity, thereby reducing the manufacturing cost of the antibacterial agent.
• An example of the oxygen content in the antibacterial agent may be 0.2 to 2.0 mass%.
• the total content of aluminum, iron, and calcium in the antibacterial agent may be 2000 ppm by mass or less, or 1800 ppm by mass or less. By reducing these total contents, the content of silicon nitride increases, and antibacterial performance tends to improve.
• the total content of aluminum, iron, and calcium in the antibacterial agent may be 10 ppm by mass or more, 50 ppm by mass or more, 500 ppm by mass or more, or 1000 ppm by mass or more. This makes it possible to use raw materials with low purity, and the production cost of the antibacterial agent can be reduced.
• An example of the total content of aluminum, iron, and calcium in the antibacterial agent may be 10 to 2000 ppm by mass.
• the contents of fluorine, chlorine, oxygen, aluminum, iron and calcium in the antibacterial agent can be measured by the method described in the Examples.
• the antibacterial agent may contain other subcomponents than those mentioned above.
• the alpha-phase ratio of silicon nitride (phase ratio of ⁇ -Si 3 N 4 to the whole Si 3 N 4 ) may be 80% or more, 85% or more, 88% or more, or 90% or more. Increasing the alpha-phase ratio tends to improve antibacterial performance against gram-negative bacteria.
• the alpha-phase ratio of silicon nitride may be 99% or less, 97% or less, or 96% or less. This can reduce the manufacturing cost of the antibacterial agent.
• An example of the alpha-phase ratio of silicon nitride may be 80 to 99%.
• the alpha-phase ratio of silicon nitride can be adjusted, for example, by changing the firing conditions (e.g., firing temperature and firing time) when synthesizing silicon nitride by firing.
• the BET specific surface area of the antibacterial agent may be 0.5 m 2 /g or more, 1.0 m 2 /g or more, 2.0 m 2 /g or more, 5.0 m 2 /g or more, or 7.0 m 2 /g or more.
• the BET specific surface area can be adjusted by changing the firing conditions (e.g., firing temperature and firing time) when synthesizing silicon nitride and the size of the raw material powder.
• the BET specific surface area of the antibacterial agent may be 20 m 2 /g or less, 15 m 2 /g or less, or 10 m 2 /g or less. This can improve the handleability of the antibacterial agent.
• An example of the BET specific surface area is 0.5 to 20 m 2 /g.
• the BET specific surface area can be measured by the method described in the Examples.
• the average particle size (D50, median size) may be 20 ⁇ m or less, 10 ⁇ m or less, 3 ⁇ m or less, or 1 ⁇ m or less.
• the average particle size may be 0.2 ⁇ m or more, 0.3 ⁇ m or more, or 0.5 ⁇ m or more.
• An example of the average particle size is 0.2 to 20 ⁇ m.
• the particle size distribution is measured in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - laser diffraction and scattering method".
• the particle size distribution (cumulative distribution) shown with the horizontal axis being the particle size [ ⁇ m] on a logarithmic scale and the vertical axis being the frequency [volume %]
• D50 average particle size
• the particle size (D10) when the cumulative value from the small particle size reaches 10% of the total may be 0.1 to 5 ⁇ m, or 0.1 to 0.5 ⁇ m.
• the particle size (D90) when the cumulative value from the small particle size reaches 90% of the total may be 0.8 to 5.0 ⁇ m, or 1.0 to 3.0 ⁇ m.
• D10, D50, and D90 can be adjusted by changing the firing conditions (e.g., firing temperature and firing time) when synthesizing silicon nitride by firing, or the crushing conditions after firing.
• the amount of fluorine eluted from the antibacterial agent into the liquid phase may be 250 ppm by mass or less, 200 ppm by mass or less, 100 ppm by mass or less, 70 ppm by mass or less, 30 ppm by mass or less, or 10 ppm by mass or less.
• One of the reasons for this is thought to be that as the amount of fluorine elution decreases, the ratio of ammonia to ammonium ions in the liquid phase tends to increase.
• the amount of fluorine elution varies depending on the fluorine content near the surface of the antibacterial agent.
• the amount of fluorine elution can be reduced by thoroughly washing the antibacterial agent with a washing liquid such as water.
• the amount of fluorine elution may be 1 mass ppm or more, 3 mass ppm or more, or 5 mass ppm or more. This can reduce the manufacturing cost of the antibacterial agent.
• An example of the amount of fluorine elution is 1 to 250 mass ppm.
• the amount of fluorine eluted from the antibacterial agent into the liquid phase (aqueous phase) may be in the above-mentioned range.
• the amount of chlorine eluted from the antibacterial agent into the liquid phase may be 10 ppm by mass or more, 20 ppm by mass or more, or 40 ppm by mass or more.
• the greater the amount of chlorine eluted the greater the tendency for antibacterial performance, especially against gram-negative bacteria, to be improved.
• the amount of chlorine eluted varies depending on the chlorine content near the surface of the antibacterial agent.
• the amount of chlorine eluted near the surface of the antibacterial agent varies depending on the raw material composition when the antibacterial agent is manufactured. For example, the amount of chlorine eluted tends to increase as the chlorine content in the raw material increases.
• the amount of chlorine eluted may be 200 mass ppm or less, 100 mass ppm or less, or 80 mass ppm or less. This makes it possible to suppress corrosion caused by chlorine.
• An example of the amount of chlorine eluted is 10 to 200 mass ppm.
• An example of the amount of fluorine eluted may be 1 to 250 mass ppm.
• the amount of chlorine eluted from the antibacterial agent into the liquid phase (aqueous phase) may be within the above-mentioned range.
• the amount of elution is synonymous with the content in the liquid phase. Therefore, the amount of elution into the liquid phase can be determined by measuring the content in the liquid phase. The amount of elution is measured under conditions of atmospheric pressure and a temperature of 20°C, and can be measured by the method described in the Examples. In this disclosure, the unit "w/v %" is synonymous with "g/100 mL.”
• the pH of the liquid phase (aqueous phase) after 10 minutes from dispersing the antibacterial agent in water to a concentration of 6.0 w/v% is 7.0 or more, 7.5 or more, 8.0 or more, or 8.5 or more. This increases the ratio of ammonia (NH 3 ) to ammonium ions (NH 4 + ) in the liquid phase, thereby improving the antibacterial performance.
• the pH of the liquid phase may be 10 or less or 9.5 or less.
• the pH of the liquid phase can be adjusted by changing the composition of the surface of the antibacterial agent. For example, the pH tends to be lowered by treating the antibacterial agent with hydrofluoric acid, and the pH tends to be higher by washing the antibacterial agent with water or the like thereafter.
• An example of the pH of the liquid phase may be 7.0 to 10.0.
• the pH of the liquid phase (aqueous phase) may be in the above-mentioned range even after 10 minutes from dispersing the antibacterial agent in water to a concentration of 3.6 w/v%.
• the content of ammonium ions contained in the liquid phase may be 6.0 ⁇ g/mL or less, 5.0 ⁇ g/mL or less, or 4.0 ⁇ g/mL or less.
• the content of ammonium ions may be 0.5 ⁇ g/mL or more, or 1.0 ⁇ g/mL or more.
• An example of the range of the content of ammonium ions contained in the liquid phase may be 0.5 to 6.0 ⁇ g/mL.
• the ammonia content in the liquid phase may be 0.2 ⁇ g/mL or more, 0.3 ⁇ g/mL or more, or 0.4 ⁇ g/mL or more. Such antibacterial agents tend to have even better antibacterial properties.
• the ammonia content may be 2.0 ⁇ g/mL or less, or 1.0 ⁇ g/mL or less.
• An example of the range of the ammonia content in the liquid phase is 0.2 to 1.0 ⁇ g/mL.
• the ammonia content in the liquid phase may be in the above range.
• the ratio of the ammonia content to the ammonium ion content in the liquid phase may be 0.10 or more, 0.12 or more, or 0.14 or more. Such an antibacterial agent has better antibacterial properties.
• the ratio ( NH3 / NH4 + ) may be 1.0 or less, or 0.5 or less.
• the contents of ammonia and ammonium ions in the liquid phase, and the pH are measured under atmospheric pressure and a temperature of 20°C by the method described in the Examples.
• the zeta potential of the liquid phase after 10 minutes from dispersing the antibacterial agent in water to a concentration of 6.0 w/v% may be -10 mV or less, -20 mV or less, -30 mV or less, or -40 mV or less.
• Such an antibacterial agent combines excellent antibacterial properties with excellent biocompatibility.
• the zeta potential of the liquid phase may be in the above range even after 10 minutes from dispersing the antibacterial agent in water to a concentration of 3.6 w/v%.
• Powdered antibacterial agents can be prepared by, for example, surface treating silicon nitride powder obtained by known methods such as direct nitridation, imide pyrolysis, and combustion synthesis, and washing with water as necessary. However, there are no particular limitations on the manufacturing method.
• the prepared silicon nitride powder can be dispersed in resin or attached to fibers as an antibacterial agent to produce antibacterial products in various forms.
• the antibacterial agent of this embodiment has excellent antibacterial properties against both gram-positive and gram-negative bacteria.
• the antibacterial agent can also be called an antibacterial composition.
• the form of the antibacterial agent is not particularly limited, and may be, for example, a powder, bulk, thin film, or coating.
• the powdered antibacterial agent may be dispersed in a matrix such as a film or filter.
• the antibacterial agent has excellent antibacterial properties and is also biocompatible. For this reason, it may be coated onto a biological implant, for example.
• a composition containing silicon nitride as a main component and having a fluorine content of 900 mass ppm or less is used as an antibacterial agent.
• the composition contains silicon nitride as a main component.
• the contents of the main component and the subcomponents are as described in the embodiment of the antibacterial agent.
• the description of the embodiment of the antibacterial agent also applies to the method of use of this embodiment. That is, the composition may contain the same components as the above-mentioned antibacterial agent and may have the same shape and properties as the above-mentioned antibacterial agent.
• the form of the composition is not particularly limited, and may be, for example, powder, bulk, thin film, or coating.
• the powdered composition may be dispersed in a matrix such as a film or filter.
• the composition used in the method of this embodiment has excellent antibacterial properties and can be suitably used as an antibacterial agent.
• the silicon nitride powder obtained by wet milling was post-treated by immersing it in hydrofluoric acid (concentration: 10% by mass) at 60°C for 2 hours. The silicon nitride powder was then removed from the hydrofluoric acid, washed with water, and dried under a nitrogen atmosphere. In this way, the silicon nitride powder (antibacterial agent) of Example 1 was obtained.
• the BET specific surface area of the silicon nitride powder was measured by the BET single point method using nitrogen gas in accordance with JIS Z 8830:2013 "Method for measuring specific surface area of powder (solid) by gas adsorption.” The results are shown in the "SSA" column of Table 1.
• ⁇ Particle size distribution> The particle size distribution of the silicon nitride powder was measured by a laser diffraction/scattering method. The measurement was performed in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - laser diffraction/scattering method". In the particle size distribution (cumulative distribution) shown with the horizontal axis as the particle size [ ⁇ m] on a logarithmic scale and the vertical axis as the frequency [volume %], the particle sizes at which the cumulative value from the small particle size reached 10%, 50%, and 90% of the total were determined as D10, D50, and D90, respectively. The results are shown in Table 1.
• the fluorine, chlorine, ammonia (NH 3 ) and ammonium ion (NH 4 + ) in the filtrate were each quantified using an ion chromatograph (Thermo Fisher Scientific, instrument name: ICS-2100).
• the pH of the filtrate was measured using a pH meter (Mettler Toledo, instrument name: FP20-Std-Kit).
• the zeta potential of the filtrate was measured using a zeta potential meter (Otsuka Electronics, instrument name: ELSZneo).
• the contents of fluorine, chlorine, ammonia (NH 3 ) and ammonium ion (NH 4 + ), pH and zeta potential of the filtrate are shown in Table 1.
• the ratio of the ammonia content to the ammonium ion content (NH 3 /NH 4 + ) is also shown in Table 1.
• Bacteria (Staphylococcus aureus) were pre-cultured in BHI liquid medium to prepare a bacterial suspension ( 1x105-1x106 CFU/mL). 0.15g of silicon nitride powder and 1mL of distilled water were added to a microtube to obtain a 15w/v% dispersion. After sterilization with ultraviolet light, 1mL of the bacterial suspension was added to the microtube. After mixing for 5 minutes at room temperature (about 20°C) with a tube rotator, the supernatant was collected and the bacterial survival rate was measured by WST-8 assay (absorbance 450nm).
• the survival rate was measured in the same manner when Staphylococcus epidermidis or Escherichia coli was used as the bacteria. The results are shown in Table 1. In Table 1, the results of the survival rate when silicon nitride powder was not used are shown in the "ref.” column.
• Example 2 After replacing the air in the vertical reaction tank with nitrogen gas, liquid ammonia and toluene were introduced. In the vertical reaction tank, liquid ammonia and toluene were separated into an upper layer and a lower layer, respectively. A toluene solution containing silicon tetrachloride at a concentration of 20 to 35 mass % and the remainder being toluene was slowly supplied to the stirred lower layer through a conduit attached to the vertical reaction tank. When the toluene solution was supplied, a white reaction product (silicon diimide) was precipitated near the interface between the upper and lower layers. After the reaction was completed, the reaction liquid in the vertical reaction tank was transferred to a filtration tank and the product was filtered out.
• silicon tetrachloride at a concentration of 20 to 35 mass % and the remainder being toluene was slowly supplied to the stirred lower layer through a conduit attached to the vertical reaction tank.
• a white reaction product (silicon diimide) was precipitated near the interface between the upper
• Example 2 The product was washed with liquid ammonia to purify the silicon diimide.
• This silicon diimide was heated to about 1500 ° C. in a nitrogen atmosphere and decomposed to obtain silicon nitride powder. This was used as the silicon nitride powder (antibacterial agent) of Example 2.
• the silicon nitride powder was evaluated using the same procedure as in Example 1. The evaluation results were as shown in Table 1.
• Comparative Example 1 A commercially available silicon nitride powder (manufactured by Höganäs, product name: HPforPV) was used as the silicon nitride powder (antibacterial agent) of Comparative Example 1. The silicon nitride powder was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.
• the filled powder was ignited by the heat generated by the self-combustion of Ti when Ti was nitrided by igniting Ti pellets with a diameter of 20 mm placed on top of the powder with a ribbon-shaped carbon heater for several seconds.
• the products generated by combustion were considerably aggregated due to the high temperature during combustion synthesis.
• the particles contained in the products also grew.
• Approximately 100 g of the products were wet-milled in methanol for 72 hours using silicon nitride balls and a polyethylene container to obtain a slurry. After filtering and separating the slurry, the obtained solids were vacuum-dried at 100°C to obtain silicon nitride powder. This was used as the silicon nitride powder (antibacterial agent) of Example 3.
• the silicon nitride powder was evaluated using the same procedures as in Example 1. The evaluation results are shown in Table 1.
• Example 4 The silicon nitride powder of Example 3 was pulverized using a planetary ball mill (manufactured by Retsch, device name: PM100). The pulverization time was 60 minutes. The pulverized product was used as silicon nitride powder (antibacterial agent) of Example 4. The evaluation results were as shown in Table 1.
• Comparative Example 2 A commercially available silicon nitride powder (manufactured by Höganäs, product name: M11) was used as the silicon nitride powder (antibacterial agent) of Comparative Example 2. The silicon nitride powder was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.
• Example 5 0.6 g of the silicon nitride powder of Comparative Example 2 was mixed with 10 g of distilled water and stirred for 30 minutes at atmospheric pressure and room temperature (about 20°C). After stirring, the dispersion was filtered using a membrane filter with a mesh size of 0.45 ⁇ m. The silicon nitride powder (antibacterial agent) of Example 5 was thus obtained after washing once with distilled water. The silicon nitride powder was evaluated using the same procedure as in Example 1. The evaluation results were as shown in Table 2.
• Example 6 The washing with distilled water performed in Example 5 was repeated twice to obtain a silicon nitride powder (antibacterial agent) of Example 6.
• the silicon nitride powder was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.
• Example 7 The washing with distilled water performed in Example 5 was repeated three times to obtain a silicon nitride powder (antibacterial agent) of Example 7. The silicon nitride powder was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.
• Example 8 The washing with distilled water performed in Example 5 was repeated four times to obtain a silicon nitride powder (antibacterial agent) of Example 8. The silicon nitride powder was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.
• an antibacterial agent having excellent antibacterial properties it is possible to provide an antibacterial agent having excellent antibacterial properties. It is also possible to provide a method for using a composition containing silicon nitride as an antibacterial agent having excellent antibacterial properties.

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