Zirconia ceramic manufacturing method

Abstract

The zirconia ceramic according to an embodiment has a crystal structure comprising zirconium, silver, and oxygen ions. The method for producing a zirconia ceramic according to an embodiment includes a sediment formation step (S1) and a firing step (S3). In the sediment formation step (S1), a zirconium compound and a silver compound are mixed in a solution or suspension state and a precipitant is then added to the solution or suspension, thereby obtaining a sediment comprising zirconia derived from the zirconium compound and silver derived from the silver compound. In the firing step (S3), a firing powder obtained by drying the sediment is fired to obtain a zirconia ceramic with which silver ions have combined.

Description

[Technical Field]

[0001] The present invention relates to , a method for producing zirconia ceramic. [Background Art]

[0002] As disclosed in Patent Document 1, zirconia ceramic is used as a material for in vivo implants. In addition, zirconia ceramic is also used in various products such as cutting tools. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. Sho 63-277061 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] An object of the present invention is to provide a novel Naji method for producing zirconia ceramic. [Means for Solving the Problem]

[0005] The zirconia ceramic manufacturing method according to the present invention is A precipitate formation step involves mixing a zirconium compound and a silver compound in the form of a solution or suspension, and then adding a precipitating agent to the solution or suspension to obtain a precipitate containing zirconia derived from the zirconium compound and silver derived from the silver compound. A firing process to obtain a zirconia ceramic in which silver ions are compounded by firing the firing powder obtained by drying the aforementioned precipitate, It holds. The above-mentioned firing process The zirconia ceramic is a substitutional crystal structure containing zirconium ions, silver ions and oxygen ions, wherein a part of zirconium ions in the crystal structure of zirconia are substituted with silver ions, has It's okay to do so. .

[0006] In the zirconia ceramic obtained in the firing process, The silver ions may form a solid solution together with the zirconium ions and the oxygen ions.

[0007] At normal temperature, the substitution type crystal structure may be a mixture of monoclinic crystals and tetragonal crystals, or may consist of tetragonal crystals.

[0008] In the zirconia ceramic obtained in the firing process, The content of the silver ions may be 0.01 mol% or more relative to the zirconium ions.

[0009] The above-mentioned firing process The zirconia ceramic may contain 20% or more of tetragonal crystals. Effects of the Invention

[0014] According to the present invention, a novel Naji method for producing zirconia ceramic is provided. Brief Description of the Drawings

[0015] [Figure 1] A flow chart illustrating the method for producing zirconia ceramic according to an embodiment. [Figure 2] A conceptual diagram showing the structure of the zirconia ceramic according to an embodiment. [Figure 3] A graph showing the relative values of silver content in the zirconia ceramics according to Examples A1-A7. [Figure 4] A graph showing the X-ray diffraction waveform of the zirconia ceramic according to Example C. [Figure 5A] A graph showing the elution amount of silver into PBS from the zirconia ceramics according to Examples A-C and the comparative example. [Figure 5B] A graph showing the elution amount of silver into αMEM from the zirconia ceramics according to Examples A-C and the comparative example. [Figure 6] A graph showing the results of a first antibacterial test on the zirconia ceramics according to Examples A-C and the comparative example. [Figure 7]A graph showing the results of the second antibacterial test of zirconia ceramics according to Examples D-F and the comparative example. [Figure 8] A graph showing the results of the third antibacterial test of zirconia ceramics according to Examples D-F and the comparative example. MODE FOR CARRYING OUT THE INVENTION

[0016] [Embodiment] Referring to Figure 1, a method for producing zirconia ceramic according to an embodiment will be described. First, a zirconium compound (hereinafter referred to as the zirconium compound) and a silver compound (hereinafter referred to as the silver compound) are mixed in the form of a solution or a suspension. Next, a precipitant is added to the solution or suspension to obtain a precipitate (precipitate generation step S1).

[0017] As the zirconium compound, a salt can be used. Specifically, examples of usable zirconium compounds include zirconium chloride, zirconium oxychloride, zirconium oxynitrate, zirconium oxysulfide, zirconium oxyacetate, and zirconium butoxide.

[0018] As the silver compound, a salt can be used. Specifically, examples of usable silver compounds include silver nitrate, silver chloride, silver sulfide, and silver acetate.

[0019] The solvent may be either a non-polar solvent or a polar solvent, as long as it can dissolve or suspend the zirconium compound and silver compound used. Examples of usable solvents include water, alcohols, acetone, phenol, toluene, dimethyl sulfoxide, carboxylic acids, alkanes, carboxylic acid esters, and mixtures thereof. The solvent to be used can be selected according to the properties of the zirconium compound and the silver compound.

[0020] In this context, "alcohols" refers to organic molecules that contain one or more hydroxyl groups. Examples of alcohols include monohydric alcohols such as methanol, ethanol, 1-butanol, 1-pentanol, 1-hexanol, 1-octanol, isopropyl alcohol, 2-butanol, 2-pentanol, 2-hexanol, and tert-butanol; dihydric alcohols such as ethylene glycol, diethylene glycol, and propylene glycol; and trihydric alcohols such as glycerin.

[0021] Here, carboxylic acids refer to organic molecules that have one or more carboxyl groups in their molecule. Examples of carboxylic acids include saturated fatty acids such as caproic acid, enanthic acid, lauric acid, capric acid, palmitic acid, and stearic acid, and unsaturated fatty acids such as oleic acid, linoleic acid, arachidonic acid, and sorbic acid.

[0022] The alkanes referred to here are those with the general formula C n H 2n+2 This refers to chain-type saturated hydrocarbons represented by [the formula shown]. Examples of alkanes include pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, and octadecane.

[0023] In this context, a carboxylic acid ester refers to a molecule formed by the polymerization of an organic molecule containing a carboxyl group and an organic molecule containing a hydroxyl group via an ester bond. Examples of carboxylic acid esters include ethyl acetate, methyl salicylate, ethyl formate, methyl butyrate, ethyl propionate, and pentyl valerate.

[0024] The precipitating agent increases the pH of the solution or suspension containing the zirconium compound and the silver compound, thereby promoting the formation of the precipitate. Suitable precipitating agents include those whose aqueous solutions are alkaline, specifically ammonia, sodium hydroxide, ammonium carbonate, arginine, lysine, trisaminomethane, sodium bicarbonate, sodium carbonate, and the like.

[0025] The precipitate is an aggregate of substances containing zirconia derived from a zirconium compound and silver derived from a silver compound. Next, by drying the precipitate, a calcination powder containing silver in zirconia powder is obtained (calcination powder formation step S2). The calcination powder may contain zirconia powder and silver or silver compound powder.

[0026] The calcination powder is preferably a substance consisting of zirconia and silver. The silver content in the calcination powder is preferably 0.01 mol% or more relative to the zirconium ions constituting the zirconia, more preferably 0.01 mol% or more and 10 mol% or less, more preferably 0.5 mol% or more and 10 mol% or less, and even more preferably 1.0 mol% or more and 5 mol% or less.

[0027] In addition, in the above-mentioned calcination powder and precipitate, the silver may be silver ions. In this specification, "calcination powder containing silver ions" means that in the calcination powder, silver atoms exist in a form in which they are ionically bonded to other atoms such as zirconium atoms. That is, silver does not exist in a free ionic form. The same applies to the above-mentioned precipitate. However, in the above-mentioned calcination powder and precipitate, the silver does not necessarily have to be ionically bonded to other atoms, and ionic bonds between silver atoms and other atoms may be formed by the calcination process described later.

[0028] Next, the aforementioned firing powder is fired. Alternatively, the firing powder may be molded and then the resulting molded body may be fired. Zirconia ceramic is obtained by firing (firing step S3). The firing temperature of the firing powder or molded body (hereinafter referred to as the object to be fired) is preferably, for example, 500°C or higher and 700°C or lower. In this specification, "firing temperature" means the maximum temperature reached. In firing step S3, it is preferable to hold the object to be fired at the maximum temperature reached for a period of time of 1 hour or more and 3 hours or less.

[0029] According to the embodiments described above, a novel zirconia ceramic is provided. The form of the zirconia ceramic may be a block, a powder, or a coating. The thickness of the coating is not particularly limited. For example, the thickness of the coating may be 10 nm or more and 10 μm or less. Furthermore, the object constituting the substrate on which the coating is formed is not particularly limited. The coating may be formed on the surface of a plate-like object such as a substrate. The substrate may be made of, for example, ceramic, metal, polymer, etc. The zirconia ceramic powder may be obtained by firing a firing powder without forming it, or by crushing a block-shaped or lump-shaped zirconia ceramic.

[0030] Furthermore, according to this embodiment, a firing powder obtained in the firing powder formation step S2 described above is also provided. As previously stated, the firing powder is used in the manufacture of zirconia ceramics. That is, the firing powder is molded as needed and then subjected to firing.

[0031] The zirconia ceramic according to this embodiment has a crystalline structure (hereinafter referred to as "zirconia crystal"). The zirconia crystal is preferably a mixture of monoclinic and tetragonal crystals, or composed of tetragonal crystals, at room temperature. However, the zirconia crystal may also contain cubic crystals. In this specification, "room temperature" refers to a temperature between 5°C and 35°C.

[0032] The zirconia ceramic according to this embodiment contains silver composites. Specifically, the silver is contained in the zirconia crystal in the form of silver ions. In other words, the zirconia crystal consists of zirconium ions, silver ions, and oxygen ions. Here, "consisting of zirconium ions, silver ions, and oxygen ions" means that in the zirconia crystal, each of the zirconium atom, silver atom, and oxygen atom exists in a form where they are ionically bonded with other atoms. The atoms do not exist as free ions. Note that the silver ions may also form a solid solution together with the zirconium ions and oxygen ions that constitute the zirconia ceramic.

[0033] Furthermore, in the zirconia ceramic according to this embodiment, silver can function as a stabilizing element. As a stabilizing element, silver exists in the tetragonal structure in a solid solution form within the tetragonal crystal. Here, "stabilizing element" refers to an element that acts as a stabilizer, extending the temperature range in which the tetragonal or cubic crystal, which is originally a high-temperature phase, can stably exist, to a temperature range that includes room temperature. In particular, extending the temperature range in which the tetragonal crystal can exist to a temperature range that includes room temperature is called "stabilization." By stabilizing the tetragonal crystal with the stabilizing element, the phase transition from tetragonal to monoclinic is suppressed. Therefore, the occurrence of cracks caused by volume expansion associated with the phase transition is suppressed.

[0034] In this embodiment, the zirconia ceramic preferably has 20% or more tetragonal crystals when the crystal phase is measured at room temperature by X-ray diffraction. This allows the zirconia ceramic to exhibit excellent toughness.

[0035] One reason why silver can act as a stabilizing element is that its ionic radius (1.0-1.15 Å) is similar to that of yttrium (0.90 Å), a typical stabilizing element. The ionic radius of a stabilizing element incorporated into a crystal is an important factor in preventing the transformation of its crystal structure.

[0036] Yttrium can function as a stabilizing element even when its addition amount to zirconium ions is 0.01 mol% or less (excluding 0 mol%). Therefore, similar to silver, it is considered that yttrium can function as a stabilizing element even when its addition amount to zirconium ions is 0.01 mol% or less (excluding 0 mol%).

[0037] In this embodiment, the silver ion content in the zirconia ceramic is preferably 0.01 mol% or more relative to the zirconium ions, more preferably 0.01 mol% or more and 10 mol% or less, more preferably 0.5 mol% or more and 10 mol% or less, and even more preferably 1.0 mol% or more and 5 mol% or less. In the firing process S3 described above, if a firing temperature is adopted such that the amount of silver evaporation is negligible, the silver ion content relative to the zirconium ions in the zirconia ceramic is equal to the silver content relative to the zirconium ions in the firing powder described above.

[0038] However, the zirconia ceramic according to this embodiment may further contain, as a stabilizing agent, oxides other than silver compounds, such as calcium oxide, magnesium oxide, yttrium oxide, sodium oxide, lanthanum oxide, praseodymium oxide, neodymium oxide, ytterbium oxide, and gadolinium oxide.

[0039] The zirconia ceramic according to this embodiment can be used as a component of an in vivo implant. In this specification, the concept of an in vivo implant includes not only oral implants such as dental crowns (e.g., crowns, bridges) and implant fixtures (artificial tooth roots) embedded in the jawbone, but also those used in parts of the body other than the oral cavity, such as artificial joints and artificial bone.

[0040] Figure 2 is a conceptual diagram showing the structure of the zirconia ceramic according to this embodiment. Silver atoms are coordinated to at least a portion of the surface of the zirconia ceramic according to this embodiment. Since silver exhibits antibacterial properties, bacteria are less likely to grow on the surface of the zirconia ceramic according to this embodiment.

[0041] In other words, silver not only acts as a stabilizing element that stabilizes the tetragonal crystal structure, but also provides an antibacterial effect to the surface of the zirconia ceramic. Therefore, when the zirconia ceramic according to this embodiment is used, for example, as an oral implant, the growth of bacteria in the oral cavity is suppressed. Thus, a preventive effect against oral inflammation, aspiration pneumonia, and the like can be expected.

[0042] Furthermore, even if cracks develop in the zirconia ceramic during use, silver atoms will be exposed on the cracked surface. In this way, a surface with coordinated silver atoms is always exposed, so even if cracks occur, that area is unlikely to become a focal point for infection.

[0043] Furthermore, silver atoms exist within the zirconia ceramic structure in a form chemically bonded to other atoms. Specifically, silver atoms are chemically bonded to oxygen atoms in a form where they are substituted for zirconium atoms. For this reason, silver atoms are less likely to leach from the surface of the zirconia ceramic. In other words, the antibacterial effect described above is exerted not by silver ions leached from the tissue, but by silver atoms present on the surface of the tissue.

[0044] As described above, the zirconia ceramic according to this embodiment is less prone to discoloration and exhibits stable aesthetics over a long period of time because silver ions are less likely to leach from the surface. Furthermore, because silver ions are less likely to leach from the surface of the zirconia ceramic according to this embodiment, even when silver functions as a stabilizing element, it is less likely to discolor the living tissue when used as an in-vivo implant.

[0045] [Examples] The following describes one example of a method for manufacturing zirconia ceramics having a crystalline structure composed of zirconium ions, silver ions, and oxygen ions.

[0046] First, I will describe the first experiment conducted to investigate the preferred range of firing temperatures.

[0047] Zirconium oxychloride octahydrate (ZrCl2O·8H2O) was dissolved in distilled water to obtain a 2 mol / L zirconium oxychloride solution. Silver nitrate (AgNO3) was also dissolved in distilled water to obtain a 200 mmol / L silver nitrate solution. These zirconium oxychloride and silver nitrate solutions were then thoroughly mixed with pure water to obtain a mixed solution.

[0048] As described above, zirconium oxychloride octahydrate and silver nitrate were mixed in solution. Here, zirconium oxychloride octahydrate is an example of a zirconium compound shown in Figure 1. Silver nitrate is an example of a silver compound shown in Figure 1.

[0049] Next, a 28% aqueous ammonia solution was added to the above mixed solution to precipitate a precipitate. The amount of ammonium ions added was 50 mol% or more relative to the zirconium ions dissolved in the above mixed solution. Here, the ammonia in the aqueous ammonia solution is an example of a precipitating agent shown in Figure 1.

[0050] Then, the mixed solution to which the ammonia aqueous solution was added was stirred for more than one hour to uniformly diffuse the precipitate. After that, the obtained precipitate was thoroughly dried, and the dried material was pulverized to obtain a powder for calcination.

[0051] The resulting calcination powder contains 1 mol% silver relative to 100 mol% zirconium. That is, the mixing ratio of the zirconium oxychloride solution and the silver nitrate solution was adjusted during the preparation of the mixed solution so that the silver content in the calcination powder was 1 mol% relative to zirconium.

[0052] Next, the obtained firing powder was fired in an electric furnace under an atmospheric environment to obtain zirconia ceramics. Following the above procedure, zirconia ceramics according to Examples A1-A7 were obtained, differing only in the firing temperature conditions of the firing powder.

[0053] Figure 3 shows the firing temperature for each example in parentheses. Specifically, the zirconia ceramics for Examples A1, A2, A3, A4, A5, A6, and A7 were fired using firing powders at 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, and 1000°C, respectively.

[0054] In this experiment, "calcining the calcining powder at T°C" specifically refers to the process of heating the calcining powder from room temperature to T°C at a heating rate of 8°C / min, then holding it at T°C for 2 hours, and then cooling it from T°C to room temperature at a cooling rate of 5°C / min.

[0055] Figure 3 shows the silver content in the zirconia ceramics for each example as bar graphs. The height of each bar graph represents the relative value of the silver content. The silver content was measured by X-ray fluorescence (XRF) analysis. In each example, the number of silver content measurements (n) was set to three. The 95% confidence interval is also shown at the top of each bar graph.

[0056] As shown in Figure 3, the higher the firing temperature of the firing powder, the more significantly the silver content in the resulting zirconia ceramic tended to decrease. This is thought to be due to the evaporation of silver during heating. In other words, the lower the firing temperature, the more silver tends to remain.

[0057] According to the results of this experiment, the firing temperature of the firing powder is preferably less than 1000°C, more preferably 800°C or lower, even more preferably 700°C or lower, and still more preferably 600°C or lower. Furthermore, the firing temperature of the firing powder is preferably 400°C or higher, and more preferably 500°C or higher.

[0058] The above describes the first experiment, in which the silver content in the calcination powder was kept the same across all examples, while the calcination temperature varied. Next, we will describe the second experiment, in which the silver content in the calcination powder was varied across all examples, while the calcination temperature was kept the same.

[0059] Zirconium oxychloride octahydrate (ZrCl2O·8H2O) was dissolved in distilled water to obtain a 2 mol / L zirconium oxychloride solution. Silver nitrate (AgNO3) was also dissolved in distilled water to obtain a 200 mmol / L silver nitrate solution. These solutions were then added dropwise to a beaker using a pipette in predetermined amounts to pure water, and thoroughly mixed using a stirrer.

[0060] As described above, zirconium oxychloride octahydrate and silver nitrate were mixed in solution form to prepare a mixed solution. Zirconium oxychloride octahydrate is an example of a zirconium compound shown in Figure 1. Silver nitrate is an example of a silver compound shown in Figure 1.

[0061] Furthermore, in order to obtain zirconia ceramics according to Example AF, each with different silver ion content, mixed solutions according to Example AF were prepared with different mixing ratios of zirconium oxychloride solution, silver nitrate solution, and pure water. In addition, in order to obtain a zirconia ceramic according to the Comparative Example that does not contain silver ions, a mixed solution of zirconium oxychloride solution and pure water was prepared as the mixed solution according to the Comparative Example.

[0062] Next, a 28% aqueous ammonia solution was added to each of the mixed solutions of Example AF and the Comparative Example to precipitate a precipitate in each solution. The amount of ammonium ions added was 50 mol% or more relative to the zirconium ions dissolved in each mixed solution. Here, the ammonia in the aqueous ammonia solution is an example of the precipitating agent shown in Figure 1. Table 1 below specifically shows the composition of each solution of Example AF and the Comparative Example.

[0063] [Table 1]

[0064] Subsequently, the solutions according to Example AF and the Comparative Example were stirred for at least one hour to uniformly distribute the precipitate in the solution. Then, the obtained precipitate was thoroughly dried in a constant temperature bath at 80°C for at least 12 hours, and the dried material was pulverized to obtain the calcination powders according to Example AF and the Comparative Example.

[0065] Next, each of the firing powders according to Example AF and the Comparative Example was formed into a block shape, and the resulting molded bodies were fired in an electric furnace under an atmospheric environment to obtain zirconia ceramics according to Example AF and the Comparative Example.

[0066] In both Example A and Comparative Example, the firing temperature of the firing powder was set to 600°C. Specifically, firing was performed by raising the temperature of the molded body from room temperature to 600°C at a heating rate of 8°C / min, then holding it at 600°C for 2 hours, and then cooling it to room temperature at a cooling rate of 5°C / min. In other words, the experimental conditions for Example A shown in Table 1 are the same as the experimental conditions for Example A3 described above, shown in Figure 3.

[0067] In Table 1, “Ag / Zr” refers to the silver ion content relative to zirconium ions in each of the zirconia ceramics related to Example AF and the Comparative Example. When the firing temperature is 600°C, the amount of silver evaporation during firing is negligibly small, so the silver ion content relative to zirconium ions in the zirconia ceramic can be considered equal to the silver content relative to zirconium ions in the firing powder.

[0068] By adjusting the mixing ratio of the zirconium oxychloride solution, silver nitrate solution, and pure water as described above, the zirconia ceramics in Examples A, B, C, D, E, and F were adjusted to contain 1 mol%, 3 mol%, 5 mol%, 0.01 mol%, 0.1 mol%, and 0.5 mol%, respectively, relative to the zirconium ions, as shown in Table 1. The zirconia ceramic in the comparative example does not contain silver ions.

[0069] Figure 4 shows the X-ray diffraction waveform of the zirconia ceramic according to Example C at room temperature. A peak appears at 2θ = 30.2° indicating the presence of the (111) plane of tetragonal zirconia. This confirms that tetragonal zirconia, which is originally a high-temperature phase, exists stably even at room temperature. In other words, it was confirmed that silver indeed played a role as a stabilizing element.

[0070] Regarding the zirconia ceramic in Example C, the amount of tetragonal material in the zirconia ceramic was determined in the following manner.

[0071] First, the amount of monoclinic crystals in the zirconia ceramic was determined using the following formula. This formula is adapted from the formula described in ISO-13356, section 4.4.3.

[0072] Amount of monoclinic crystals [%] = 100 × {M(-111) + M(111)} / {M(-111) + T(111) + M(111)}

[0073] In the above equations, M represents a monoclinic crystal and T represents a tetragonal crystal. The values ​​in parentheses indicate the plane indices. Specifically, M(-111) represents the diffraction intensity of the (-111) plane of monoclinic zirconia (2θ=28.2°). M(111) represents the diffraction intensity of the (111) plane of monoclinic zirconia (2θ=31.3°). T(111) represents the diffraction intensity of the (111) plane of tetragonal zirconia (2θ=30.2°).

[0074] When the diffraction intensities described above were determined using the X-ray diffraction waveforms, the results were M(-111) = 6293, M(111) = 4859, and T(111) = 16988. Therefore, from the above equation, the amount of monoclinic crystals in the zirconia ceramic is 39.6%.

[0075] Furthermore, given the firing temperature, it can be said that cubic crystals were not formed, so zirconia ceramic is considered to be a polycrystalline material consisting of monoclinic and tetragonal crystals. Therefore, the amount of tetragonal crystals in zirconia ceramic is 100 - 39.6 = 60.4%.

[0076] Next, I will explain the leaching test conducted to confirm that silver is less likely to leach from zirconia ceramics.

[0077] The zirconia ceramics from each of Examples AC and Comparative Example were pulverized to obtain powder. Then, 0.1 g of the zirconia ceramic powder from each of Examples AC and Comparative Example was added to 10 mL of PBS (Phosphate-buffered saline) and αMEM (alpha Modified Eagle Minimum Essential Medium), respectively, and shaken at a repetition rate of 60 rpm at a temperature of 37°C in a sealed container. After 1 and 3 days, the culture medium solution in the sealed container was sampled, filtered through a syringe filter with a mesh size of 220 nm, and then diluted 20-fold with a 2% nitric acid solution. The concentration of silver contained in the solution was measured. An ICP emission spectrometer was used for the measurement.

[0078] Figure 5A shows the measurement results of the silver elution concentration in PBS. Graph D1p shows the silver elution concentration from zirconia ceramic powder to PBS for the comparative example after 1 day. Graph A1p shows the silver elution concentration from the zirconia ceramic powder in Example A into PBS after 1 day. Graph B1p shows the silver elution concentration from the zirconia ceramic powder in Example B into PBS after 1 day. Graph C1p shows the silver elution concentration from the zirconia ceramic powder in Example C into PBS after 1 day.

[0079] Graph D3p shows the silver elution concentration from the zirconia ceramic powder in the comparative example into PBS after 3 days. Graph A3p shows the silver elution concentration from the zirconia ceramic powder in Example A into PBS after 3 days. Graph B3p shows the silver elution concentration from the zirconia ceramic powder in Example B into PBS after 3 days. Graph C3p shows the silver elution concentration from the zirconia ceramic powder in Example C into PBS after 3 days.

[0080] Figure 5B shows the measurement results of the silver elution concentration against αMEM. Graph D1a shows the silver elution concentration from zirconia ceramic powder to αMEM in the comparative example after 1 day. Graph A1a shows the silver elution concentration from the zirconia ceramic powder in Example A into αMEM after 1 day. Graph B1a shows the silver elution concentration from the zirconia ceramic powder in Example B into αMEM after 1 day. Graph C1a shows the silver elution concentration from the zirconia ceramic powder in Example C to αMEM after 1 day.

[0081] Graph D3a shows the silver elution concentration from zirconia ceramic powder to αMEM in the comparative example after 3 days. Graph A3a shows the silver elution concentration from the zirconia ceramic powder in Example A into αMEM after 3 days. Graph B3a shows the silver elution concentration from the zirconia ceramic powder in Example B into αMEM after 3 days. Graph C3a shows the silver elution concentration from the zirconia ceramic powder in Example C to αMEM after 3 days.

[0082] As shown in Figure 5B, the maximum elution concentration of silver into αMEM was 1.2 ppm, as shown in Graph C1a. Furthermore, as shown in Figure 5A, the elution concentration of silver into PBS was 0.4 ppm or less in both Examples A and C. From the above, it was confirmed that the zirconia ceramic according to Example A is less prone to silver elution during use, even when used as an in-vivo implant, for example.

[0083] Next, we will explain the antibacterial test conducted to confirm the antibacterial properties of zirconia ceramics.

[0084] First, I will explain the first antimicrobial test, which examined the antimicrobial activity against Streptococcus mutans (type culture strain: NBRC number 13955T), a representative caries-causing bacterium.

[0085] The above-mentioned Streptcoccus mutans was purchased from the NITE Biotechnology Center. This was then seeded onto broth medium (Pearl Core Infusion: manufactured by Eiken Chemical Industry Co., Ltd.) and cultured overnight in a constant-temperature shaking incubator at 37°C in an atmospheric environment to prepare a bacterial suspension.

[0086] On the other hand, a broth medium was prepared to which powder obtained by crushing the zirconia ceramics related to each of Examples A and C (hereinafter referred to as zirconia ceramic powder) was added. Zirconia ceramic powder was added at a rate of 100 mg per 1 mL of broth medium. Immediately after addition, the above bacterial suspension was inoculated into this broth medium in an L-shaped tube to a viable cell count of 10⁶ / mL, and the inoculated medium was cultured in an incubator set to 37°C for 24 hours with shaking at 60 rpm. After culturing, the broth medium was diluted with PBS, and 200 μL of the diluted solution was spread onto an agar plate using a cone-large rod.

[0087] Hereinafter, the agar medium coated with the broth medium containing the zirconia ceramic powder according to Example A will be referred to as "the medium according to Example A." Similarly, the agar medium coated with the broth medium containing the zirconia ceramic powder according to Example B will be referred to as "the medium according to Example B." Furthermore, the agar medium coated with the broth medium containing the zirconia ceramic powder according to Example C will be referred to as "the medium according to Example C."

[0088] Furthermore, an agar medium coated with the broth medium to which the zirconia ceramic powder related to the comparative example was added (hereinafter referred to as the medium related to the comparative example in this first antimicrobial test) was prepared. For comparison, an agar medium coated with the broth medium to which the zirconia ceramic powder was not added (hereinafter referred to as the unadded medium in this first antimicrobial test) was also prepared.

[0089] Then, at 1 day and 2 days after the experiment, the number density of colonies in each of the culture media according to Example A, Example B, Example C, Comparative Example, and the unadded culture medium was measured.

[0090] Figure 6 shows the results of the measurement of colony number density. The culture media used in Example A, Example B, and Example C all exhibited significantly superior antibacterial activity compared to the culture media used in the comparative example.

[0091] As previously mentioned with reference to the elution test results shown in Figures 5A and 5B, silver does not easily elute from zirconia ceramics. Nevertheless, the culture media for Example A, Example B, and Example C all showed sufficient antibacterial activity. This supports the idea that, as shown in Figure 2, silver is coordinated to the surface of the zirconia ceramic, and that the antibacterial activity is exerted by the silver on that surface.

[0092] Furthermore, when the antibacterial activity value of the zirconia ceramic according to Example A was measured in accordance with the provisions of JIS Z 2801, it was found to be 2.0. From this, it was found that sufficient antibacterial activity can be obtained even with a silver addition amount of 1 mol% to the zirconia. However, as shown in Figure 6, it was observed that the higher the silver content in the zirconia ceramic, the better the antibacterial activity tends to be. From the viewpoint of antibacterial activity, it is considered preferable to have a higher silver content.

[0093] Next, we will describe the second antimicrobial test, which examined the antimicrobial activity against Staphylococcus aureus (NBRC100910T), a representative Gram-positive bacterium specified in ISO 22196:2011.

[0094] The above-mentioned Staphylococcus aureus was purchased from NBRC (NITE Biological Resource Center). A bacterial suspension was prepared by culturing the purchased Staphylococcus aureus in the same manner as in the first antimicrobial test.

[0095] On the other hand, the zirconia ceramic powders corresponding to each of Examples DF were sterilized with 70% ethanol, washed with PBS, and then added to broth medium. The zirconia ceramic powder was added at a rate of 100 mg per 1 mL of broth medium. Immediately after addition, 0.1 mL of the above bacterial suspension was inoculated into 4.9 mL of this broth medium, and the inoculated mixture was cultured for 24 hours with shaking in an incubator (BioShaker BR-13LP, TAITEC) set to 37°C to obtain a suspension. The obtained suspension was then diluted and pipetted onto agar medium and cultured overnight at 37°C.

[0096] Hereinafter, in this second antimicrobial test, the agar plates on which the suspensions containing zirconia ceramic powder according to Examples D, E, and F were pipetted will be referred to as "the medium according to Example D," "the medium according to Example E," and "the medium according to Example F," respectively. For comparison, an agar plate coated with the suspension without zirconia ceramic powder (hereinafter referred to as "the unadded medium" in this second antimicrobial test) was also prepared.

[0097] Figure 7 shows the results of measuring the number density of colonies in the culture medium for Example DF and in the unadded culture medium. It was confirmed that the number density of colonies in the culture medium for Example DF was significantly lower than that in the unadded culture medium. In other words, the antibacterial activity of the zirconia ceramic powder in each of Examples DF against the above-mentioned Staphylococcus aureus was confirmed.

[0098] Next, we will explain the third antimicrobial test, which examined the antimicrobial activity against Escherichia coli (NBRC102203T), a representative Gram-negative bacterium, as specified in ISO 22196:2011.

[0099] The above-mentioned E. coli was purchased from NBRC (NITE Biological Resource Center). A bacterial suspension was prepared by culturing the purchased E. coli in the same manner as in the first antimicrobial test.

[0100] On the other hand, suspensions containing zirconia ceramic powder for each of Examples D and F were obtained in the same manner as in the second antimicrobial test, except for the bacterial suspension used. The obtained suspensions were diluted, pipetted onto agar plates, and incubated overnight at 37°C.

[0101] Hereinafter, in this third antimicrobial test, the agar plates in which the suspensions containing the zirconia ceramic powder according to Examples D, E, and F were pipetted will be referred to as "the medium according to Example D," "the medium according to Example E," and "the medium according to Example F," respectively. In addition, an agar plate was prepared in which the bacterial suspension in which the zirconia ceramic according to the comparative example was added instead of the zirconia ceramic powder according to Examples D, E, and F was pipetted (hereinafter referred to as "the medium according to the comparative example" in this third antimicrobial test).

[0102] Figure 8 shows the measurement results of the colony number density in the culture medium for Example DF and the culture medium for the Comparative Example. It was confirmed that the colony number density in the culture medium for Example DF was significantly lower than that in the culture medium for the Comparative Example. In other words, the antibacterial activity of the zirconia ceramic powder in each of Examples DF against the above-mentioned E. coli was confirmed.

[0103] The embodiments and examples have been described above. The present invention is not limited thereto, and the following modifications are also possible.

[0104] In the above examples, zirconia ceramics containing tetragonal crystals as zirconia crystals were illustrated, but zirconia ceramics do not necessarily have to contain tetragonal crystals. For example, zirconia ceramics may consist of monoclinic crystals as zirconia crystals. In that case, silver ions do not play a role as a stabilizer, but antibacterial activity is obtained because silver ions are contained in the zirconia crystals.

[0105] Furthermore, in the above embodiment, a firing powder used in the manufacture of zirconia ceramics was exemplified as containing zirconia powder and silver powder, but a silver compound powder may be used instead of silver powder or in combination with silver powder.

[0106] The present invention is subject to various modifications without departing from its broad spirit and scope. The above embodiments and examples are for illustrative purposes only and do not limit the scope of the present invention. The scope of the present invention is indicated by the claims, not by the embodiments and examples. Various modifications made within the scope of the claims and the equivalent scope of the invention are considered to be within the scope of the present invention.

[0107] This application is based on Japanese Patent Application No. 2022-165432, filed in Japan on 14 October 2022. The entire specification, claims, and drawings of Japanese Patent Application No. 2022-165432 are incorporated herein by reference. [Industrial applicability]

[0108] The zirconia ceramic according to the present invention is particularly suitable for applications requiring antibacterial properties, specifically for use in in-vivo implants. However, the applications of the zirconia ceramic according to the present invention are not limited to in-vivo implants. The zirconia ceramic according to the present invention can also be used as a material for various products such as knives, jewelry (e.g., rings, earrings), and as a radiosensitizer.

Claims

1. A precipitate formation step involves mixing a zirconium compound and a silver compound in the form of a solution or suspension, and then adding a precipitating agent to the solution or suspension to obtain a precipitate containing zirconia derived from the zirconium compound and silver derived from the silver compound. A firing process to obtain a zirconia ceramic in which silver ions are compounded by firing the firing powder obtained by drying the aforementioned precipitate, A method for manufacturing zirconia ceramics, comprising the characteristics of a zirconia ceramic.

2. The zirconia ceramic obtained in the firing step is A substitutional crystal structure containing zirconium ions, silver ions, and oxygen ions, wherein some of the zirconium ions in the crystal structure of zirconia are replaced by silver ions. A method for manufacturing zirconia ceramics according to claim 1, comprising the features described above.

3. In the zirconia ceramic obtained in the firing step, The silver ions together with the zirconium ions and oxygen ions form a solid solution. The method for manufacturing zirconia ceramics according to claim 2.

4. At room temperature, the substitutional crystal structure is a mixture of monoclinic and tetragonal crystals, or consists of tetragonal crystals. The method for manufacturing zirconia ceramics according to claim 2.

5. In the zirconia ceramic obtained in the firing step, The content of the silver ions is 0.01 mol% or more relative to the zirconium ions. The method for manufacturing zirconia ceramics according to claim 2.

6. The zirconia ceramic obtained in the firing step is Contains 20% or more tetragonal crystals. The method for manufacturing zirconia ceramics according to claim 4.

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