Presintered alumina body for gingival color and method for producing same, method for producing molded alumina body for gingival color, and method for producing alumina particulate material for gingival color

Abstract

The present invention is a presintered alumina body for gingival color, comprising: (A) an α-alumina particulate material having an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red-type colorant. The content of the (B) Mg is 100 to 5000 ppm by mass in terms of metallic magnesium relative to the (A) α-alumina particulate material. When the presintered alumina body for gingival color is fired under atmospheric pressure (1013 hPa) at 1450°C, the resulting sintered body having a thickness of 3.0 mm has an a* value of +4 to +30 and a b* value of -5 to +10 against a black background. When the presintered alumina body for gingival color is fired under atmospheric pressure (1013 hPa) at 1450°C, the resulting sintered body has a flexural strength of 800 MPa or more. The present invention can provide a presintered alumina body for gingival color, from which a sintered body that favorably reproduces gingival color and has high strength can be produced.

Description

Alumina pre-sintered body for gingival coloring and method for manufacturing the same, method for manufacturing alumina molded body for gingival coloring, method for manufacturing alumina granules for gingival coloring

[0001] The present invention relates to a pre-sintered alumina body for gingival coloring, a method for producing the same, a method for producing alumina molded body for gingival coloring, and a method for producing alumina granules for gingival coloring.

[0002] In dental restorations, a variety of materials are used, including metals, ceramics, and resins. Among these, ceramics are a promising alternative to metals and are used in procedures such as crown restorations where aesthetics are important. Zirconia ceramics, in particular, are widely used due to their strength and aesthetic appeal. Dental restorations using zirconia ceramics generally involve cutting a mill blank (workpiece) made of a pre-sintered zirconia ceramic body into a digitally designed shape by a dental technician or dentist, followed by processes such as final sintering and polishing.

[0003] While dental restorations using zirconia ceramics are widely used, there are still issues that need improvement, such as the tendency for strength to decrease when aesthetics (translucency) is enhanced, and the balance of physical properties. Besides zirconia ceramics, lithium disilicate glass ceramics are known as a material with excellent translucency, but their strength is insufficient.

[0004] In recent years, high-purity alumina ceramic materials have been proposed as a technology to solve the above problems. Patent Document 1 discloses an invention relating to a dental oxide ceramic calcined body containing alumina (purity of 99.5% or more) with an average primary particle diameter of 50 to 300 nm, and in which the cumulative distribution of pores has a D10 of 20 nm or more and a D90 of 90 nm or less, and it is described that it has excellent machinability and high light transmittance after sintering. Patent Document 2 discloses an invention relating to a dental oxide ceramic calcined body containing alumina with an average primary particle circularity of 0.81 or more, and a relative density of 43 to 63%, and it is described that it has excellent polishability, and that the polished surface of the calcined body and the surface of the sintered body after sintering have high flatness and excellent aesthetics.

[0005] Patent Document 3 discloses an invention relating to a calcined dental alumina body, comprising high-purity alumina with an average primary particle diameter of 30 to 300 nm, a sintering aid, and a blue-based coloring agent, wherein the sintering aid content is 10 to 5000 ppm. It is stated that this invention suppresses yellowing after sintering, and provides a sintered body with high translucency and linear light transmittance even when sintered under atmospheric pressure, resulting in a highly aesthetic product. Patent Document 4 discloses an invention relating to a dental alumina workpiece, wherein the average crystal grain size differs at a first and second point in a specific interval from one end and the other end of the dental alumina workpiece, and it is stated that the sintered body after sintering has excellent translucency, strength, and linear light transmittance.

[0006] International Publication No. 2023 / 127559 Brochure International Publication No. 2023 / 127561 Brochure International Publication No. 2023 / 127562 Brochure International Publication No. 2023 / 127564 Brochure

[0007] In dental restoration, it is necessary for the restoration site and its surrounding areas to match in terms of color and tone from an aesthetic standpoint. For example, when fabricating denture frames, materials that can accurately reproduce gingival color are required. As mentioned above, various studies have been conducted on alumina ceramics, and from an aesthetic standpoint, it is known that blue-based coloring agents can be incorporated to suppress yellowing after firing, as described in Patent Document 3. However, Patent Document 3 does not consider any means of reproducing gingival color. Furthermore, while zirconia ceramics have been conventionally used as denture frames, it has been difficult to reproduce the color tone of dentures, i.e., the color tone of gingival color, using zirconia ceramics. In particular, reproducing a dark gingival color requires the incorporation of a large amount of coloring agent, in which case the strength of the zirconia ceramic base material is significantly reduced, making it difficult to withstand practical use.

[0008] Therefore, the present invention aims to provide a pre-sintered alumina body for gingival coloring that can reproduce gingival color well and produce a high-strength sintered body, and a method for manufacturing the same.

[0009] The inventors diligently conducted research to achieve the above objective. As a result, they have developed a gingival color alumina pre-sintered body containing high-purity α-alumina powder with an average primary particle size within a specific range, a specific amount of Mg derived from a sintering aid consisting of a magnesium compound, and a specific red coloring agent, wherein the sintered body after firing a ＊ Value and b ＊ We have found that the above problems can be solved by using a pre-sintered alumina body for gingival coloring with a specific range of values ​​and bending strength, and have completed the present invention. The present invention relates to the following [1] to [6].

[0010] [1] (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, (B) Mg as an element contained in a sintering aid, and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder, and the sintered body of the 3.0 mm thick gingival alumina powder is fired under atmospheric pressure (1013 hPa) at 1450°C, and a black background is used to measure the alumina powder. ＊ The value is +4 to +30, b ＊[2] A pre-sintered alumina body for gingival coloring, wherein the value is -5 to +10, and the sintered body obtained by firing the pre-sintered alumina body for gingival coloring under atmospheric pressure (1013 hPa) and at 1450°C has a bending strength of 800 MPa or more. [2] A method for producing a pre-sintered alumina body for gingival coloring, characterized by pre-sintering a molded alumina body for gingival coloring at 500 to 1000°C, wherein the molded alumina body for gingival coloring contains (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, (B) Mg as an element contained in a sintering aid, and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, and the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder. [3] A method for producing a gingival color alumina molded body, comprising press molding (A) α-alumina powder with an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more, (B) Mg as an element contained in a sintering aid, and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder, and the aggregated particle diameter is 10 to 100 μm, at a pressure of 10 to 400 MPa. [4] A method for producing alumina granules for gingival coloring, comprising spray-drying an alumina dispersion slurry containing (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, (B) Mg as an element contained in a sintering aid, and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder. [5] A method for producing a gingival color alumina pre-sintered body for gingival color according to [1] above, characterized in that (A) α-alumina powder or granules with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, (B) a pre-sintered body containing Mg as an element in a sintering aid, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder or granules, and (C) at least one element selected from Ho, Er, Cr, Mn, Cu, and Eu is supported on the pre-sintered body as a red coloring agent.[6] (A) α-alumina powder granules having an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more, (B) Mg as an element contained in the sintering aid, (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red colorant, wherein the content of (B) Mg is 100 to 5000 ppm in terms of mass as metallic magnesium relative to the (A) α-alumina powder granules; spray-drying the alumina dispersion slurry to obtain alumina granules for gingival color having an aggregated particle diameter of 5 to 100 μm, then press-molding the alumina granules for gingival color at 10 to 400 MPa to obtain an alumina molded body for gingival color, and further pre-sintering the alumina molded body for gingival color at 500 to 1000°C. The method for producing a pre-sintered alumina body for gingival color according to [1] above.

[0011] According to the present invention, there can be provided a pre-sintered alumina body for gingival color that can favorably reproduce gingival color and produce a high-strength sintered body, and a method for producing the same.

[0012] [Pre-sintered alumina body for gingival color] The pre-sintered alumina body for gingival color of the present invention comprises: (A) α-alumina powder granules having an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more; (B) Mg as an element contained in the sintering aid; (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red colorant; wherein the content of (B) Mg is 100 to 5000 ppm in terms of mass as metallic magnesium relative to the (A) α-alumina powder granules; the pre-sintered alumina body for gingival color, wherein when the pre-sintered alumina body for gingival color is fired under conditions of atmospheric pressure (1013 hPa) and 1450°C to obtain a sintered body with a thickness of 3.0 mm, the a ＊ value is +4 to +30, and the b ＊ value is -5 to +10, and the bending strength of the sintered body obtained by firing the pre-sintered alumina body for gingival color under conditions of atmospheric pressure (1013 hPa) and 1450°C is 800 MPa or more.

[0013] Unless otherwise specified in this specification, the notation "x to y" using numerical values x and y shall mean "x or more and y or less". When a unit is attached only to the numerical value y in such notation, the unit shall also apply to the numerical value x.

[0014] In the present invention, a pre-sintered body means a body in a state before becoming a complete sintered body in the sintering process. In the sintering process, necks formed by partial bonding between constituent particles of the raw material alumina powder particles are formed, and open pores derived from voids between particles (that is, pores open to the outside) are formed in the process of growth of the necks. A pre-sintered body means one that maintains a state in which a large number of these open pores remain without disappearing.

[0015] <(A) α-alumina powder particles> The gingiva-colored alumina pre-sintered body of the present invention (sometimes simply referred to as alumina pre-sintered body) contains α-alumina powder particles. The α-alumina powder particles are an aggregate of α-alumina particles that are primary particles. The average primary particle diameter of the α-alumina powder particles is 30 to 300 nm. If the average primary particle diameter of the α-alumina powder particles is less than 30 nm, the aggregability of the α-alumina powder particles increases, the dispersibility in the dispersion step decreases, and the yield during granule production tends to decrease. If the average primary particle diameter exceeds 300 nm, the strength (such as bending strength) of the obtained alumina sintered body tends to decrease. The average primary particle diameter of the α-alumina powder particles is preferably 50 to 280 nm, more preferably 80 to 270 nm, and still more preferably 150 to 250 nm. The average primary particle diameter is measured using a scanning or transmission electron microscope. Specifically, it is measured as follows. That is, image analysis is performed on n alumina particles that are primary particles, 30 or more randomly selected, preferably 100 or more, from an image captured by an electron microscope with clear contrast and distinguishable particle contours, to obtain the equivalent circle diameter of each alumina particle (the diameter of a circle having the same area as the area of the target particle): X ｉ is determined, and X from the 1st to the nth ｉ sum: ΣX ｉ based on the formula: X = (ΣX ｉ ) / n means the average particle diameter calculated by: X.

[0016] The purity of the α-alumina powder used in this invention is 99.5% or higher. If the purity is less than 99.5%, the strength (flexural strength) of the resulting sintered body tends to decrease. A purity of 99.5% or higher for the α-alumina powder means that the concentration of impurities contained in the α-alumina powder is 0.5% by mass or less. The concentration of impurities can be determined by known measurement methods such as ICP emission spectrometry. The purity of the α-alumina powder is preferably 99.7% or higher, and more preferably 99.9% or higher.

[0017] The content of α-alumina powder in the alumina pre-sintered body for gingival coloring of the present invention is not particularly limited, but is, for example, 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0018] <(B) Mg> The alumina temporary sintered body for gingival coloring of the present invention contains Mg (magnesium). The Mg is an element contained in the sintering aid contained in the alumina temporary sintered body for gingival coloring. That is, the alumina temporary sintered body for gingival coloring of the present invention contains a sintering aid made of a magnesium compound. Examples of magnesium compounds include magnesium oxides, nitrates, acetates, hydroxides, and chlorides, with oxides (magnesium oxide) being preferred. A single magnesium compound may be used, or multiple compounds may be used in combination.

[0019] The amount of Mg (magnesium element) in the alumina pre-sintered body for gingival coloring is 100 to 5000 ppm by mass as metallic magnesium relative to the α-alumina powder. If the amount of Mg is less than 100 ppm or more than 5000 ppm, the strength of the resulting alumina sintered body tends to decrease. The amount of Mg is preferably 300 to 3000 ppm, and more preferably 500 to 2500 ppm, by mass as metallic magnesium relative to the α-alumina powder. The amount of Mg is adjusted by the amount of magnesium compound added as a sintering aid when manufacturing the alumina pre-sintered body for gingival coloring.

[0020] <(C) Red-based coloring agent> The alumina temporary sintered body for gingival coloring of the present invention contains a specific red-based coloring agent. By incorporating the specific red-based coloring agent, as described in a below ＊ Value and b ＊ By adjusting the values ​​to a predetermined range, it becomes easier to reproduce the gingival color well. Furthermore, the gingival color alumina temporary sintered body of the present invention, by containing a specific red coloring agent, has improved strength such as bending strength of the resulting sintered body. By incorporating the red coloring agent, the strength of the resulting alumina sintered body is improved compared to when it is not incorporated. ＊ This is a coloring agent that increases the value. The red coloring agent in this invention is at least one element selected from the group consisting of Ho (holmium), Er (erbium), Cr (chromium), Mn (manganese), Cu (copper), and Eu (europium). By using such a specific red coloring agent, the a of the sintered body described later can be ＊ Value and b ＊ This makes it easier to adjust the values ​​to a specific range and reproduce gingival color. The red coloring agent is preferably at least one element selected from the group consisting of Cr and Mn. By selecting such a red coloring agent, the strength of the resulting alumina sintered body can be further increased.

[0021] The content of red coloring agent (in oxide equivalent) in the alumina pre-sintered body for gingival coloring is not particularly limited, but is preferably 10 to 3000 ppm, more preferably 50 to 2000 ppm, and even more preferably 100 to 1000 ppm, on a mass basis relative to the α-alumina powder granules. The content of the red coloring agent is expressed in oxide equivalent. Note that when calculating the oxide equivalent content of Ho, Er, Cr, Mn, Cu, and Eu, the oxides are as follows: ２ O ３ Er ２ O ３ , Cr ２ O ３ Mn ３ O ４ CuO, Eu ２ O ３ That is the case.

[0022] The content of the red coloring agent can be adjusted by the amount of raw materials for the red coloring agent used as raw materials when producing the alumina sintered body. The raw materials for the red coloring agent are the elemental sources of the red coloring agent (Ho, Er, Cr, Mn, Cu, Eu). The content of the red coloring agent can also be measured by ICP emission spectroscopy or other methods using the alumina sintered body as an analytical sample.

[0023] Examples of red coloring agents used as raw materials when producing alumina sintered bodies include holmium compounds containing Ho, erbium compounds containing Er, chromium compounds containing Cr, manganese compounds containing Mn, copper compounds containing Cu, or europium compounds containing Eu. Examples of the above compounds include salts and complexes containing the aforementioned elements. Examples of raw materials for red colorants include holmium compounds such as holmium chloride, holmium nitrate, holmium sulfate, holmium oxalate, and holmium acetate; erbium compounds such as erbium chloride, erbium nitrate, erbium fluoride, and erbium acetate; chromium compounds such as chromium chloride, chromium nitrate, chromium fluoride, chromium sulfate, and chromium acetate; manganese compounds such as manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate; copper compounds such as copper chloride, copper fluoride, copper bromide, copper sulfate, copper nitrate, copper oxalate, and copper acetate; and europium compounds such as europium chloride, europium nitrate, europium fluoride, and europium acetate.

[0024] The alumina pre-sintered body of the present invention may contain other components besides the above-mentioned components (A) to (C) to the extent that it does not impair its performance.

[0025] <a ＊ value, b ＊ Value > The alumina sintered body of the present invention, with a thickness of 3.0 mm, was fired under atmospheric pressure (1013 hPa) and 1450°C (2-hour anchoring), and the value of the alumina sintered body under a black background. ＊ The value is between +4 and +30, b ＊ The value is between -5 and +10. The alumina sintered body is such a ＊ Value and b ＊ Being a value makes it easier to reproduce gum color. (a)＊ The value is preferably +5 to +28, and more preferably +6 to +24. (See b above) ＊ The value is preferably -2 to +10, and more preferably +1 to +9. a of the alumina sintered body ＊ Value and b ＊ The value can be adjusted by the type and amount of red coloring agent used. ＊ Value and b ＊ The value represents chromaticity in the CIELab color system and is an index of hue and saturation. ＊ Value and b ＊ The value is measured using a spectrophotometer. Also, a ＊ Value and b ＊ The values ​​are measured against a black background. A black background is defined as a surface with a lightness of 1 or less according to the Munsell color system and a spectral reflectance of 10% or less at wavelengths of 380 to 780 nm.

[0026] <Bending Strength> The bending strength of the sintered body (alumina sintered body) obtained by firing the alumina pre-sintered body of the present invention under atmospheric pressure (1013 hPa) and 1450°C (2-hour anchoring) is 800 MPa or more. If the bending strength is less than 800 MPa, defects such as breakage are likely to occur when applied to applications requiring strength. The bending strength of the above alumina sintered body is preferably 850 MPa or more, and more preferably 900 MPa or more. The upper limit of the bending strength of the above alumina sintered body is not particularly limited, but the bending strength is, for example, 1500 MPa or less. The bending strength is biaxial bending strength and can be measured by the method described in the examples.

[0027] The alumina temporary sintered body for gingival coloring described above can be obtained by the method for manufacturing the alumina temporary sintered body for gingival coloring described later.

[0028] [Method for Manufacturing a Pre-Sintered Alumina Body for Gum Coloring] The present invention provides the following method for manufacturing a pre-sintered alumina body for gum coloring. Specifically, the present invention provides a method for manufacturing a pre-sintered alumina body for gum coloring, characterized by pre-sintering a molded alumina body for gum coloring at 500 to 1000°C, which comprises: (A) α-alumina powder with an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder.

[0029] In the method for producing a pre-sintered alumina body for gingival coloring, it is preferable to manufacture the alumina molded body for gingival coloring using alumina granules for gingival coloring as a raw material.

[0030] <Alumina Granules for Gingival Coloring> The alumina granules for gingival coloring in the present invention are obtained by spray-drying an alumina dispersion slurry containing (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, (B) Mg as an element contained in a sintering aid, and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder.

[0031] The alumina dispersion slurry is prepared by dispersing the above-mentioned α-alumina powder and granules, a magnesium compound used as a sintering aid, and raw materials for a red coloring agent in a solvent. The dispersion process can be carried out using a mixing device such as a bead mill. Additives may be added to the alumina dispersion slurry as needed. The solvent (dispersion medium) contained in the alumina dispersion slurry may include water, and may also include organic solvents such as ethanol, isopropyl alcohol, and dimethylformamide. The amount of solvent (dispersion medium) used is usually 25 to 300 parts by mass per 100 parts by mass of α-alumina powder and granules. The slurry concentration of the alumina dispersion slurry is usually 25 to 80% by mass. Additives that may be added to the alumina dispersion slurry as needed include dispersants, plasticizers, binders, defoamers, and release agents.

[0032] The alumina dispersion slurry prepared as described above contains (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher, (B) Mg as an element contained in the sintering aid, and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder. Details of components (A) to (C) contained in the alumina dispersion slurry, and the respective contents of (B) Mg and (C) red coloring agent relative to component (A) in the alumina dispersion slurry are the same as those described in the "Alumina Pre-sintered Body for Gingival Color" above.

[0033] As described above, the alumina dispersion slurry is spray-dried to obtain alumina granules for gingival coloring. The spray-drying method can be employed in which the alumina dispersion slurry is sprayed in fine droplets using a high-speed airflow and dried, or in which the alumina dispersion slurry is dropped onto a disc-shaped rotating body rotating at a rotational speed of 1,000 to 50,000 rpm and dried by being ejected in a mist by centrifugal force.

[0034] The resulting alumina granules for gingival coloring are composed of multiple aggregated particles, each aggregated by the aggregation of multiple primary α-alumina particles. Any α-alumina particle constituting an aggregated particle is in contact with any other α-alumina particle constituting the same aggregated particle. The formation of aggregated particles can be confirmed, for example, by scanning electron microscopy. The aggregated particle diameter of the alumina granules for gingival coloring is preferably 5 to 100 μm, more preferably 10 to 100 μm, and even more preferably 10 to 80 μm. When the aggregated particle diameter of the alumina granules for gingival coloring is within this range, molding defects in the molded product can be suppressed. The aggregated particle diameter can be adjusted to a desired range by adjusting manufacturing conditions, such as the amount of dispersion medium used in the spray drying method. The aggregated particle diameter refers to the average aggregated particle diameter (median diameter in volume statistics) measured by laser diffraction-scattering.

[0035] The alumina granules for gingival coloring contain (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher, (B) Mg as an element contained in the sintering aid, and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm in mass as metallic magnesium relative to the (A) α-alumina powder, and the aggregated particle size is 5 to 100 μm. Details of components (A) to (C) contained in the alumina granules for gingival coloring, and the respective contents of (B) Mg and (C) red coloring agent relative to component (A) in the alumina granules for gingival coloring, are the same as those described in the "Alumina Pre-sintered Body for Gingival Coloring" above.

[0036] <Alumina Molded Body for Gingival Color> The alumina molded body for gingival color in the present invention is preferably manufactured by molding alumina granules for gingival color. Examples of molding methods include press molding, extrusion molding, injection molding, and casting, with press molding being preferred. Examples of press molding include uniaxial press molding and CIP (Cold Isostatic Pressing). Press molding may be carried out in multiple stages, and CIP (Cold Isostatic Pressing) molding may be performed after uniaxial press molding.

[0037] The press pressure used during press forming is, for example, 10 to 400 MPa, preferably 100 to 300 MPa.

[0038] The shape of the alumina molded body for gingival coloring can be determined appropriately depending on the purpose, but typically disc-shaped (disk type) or rectangular or roughly rectangular (block type) shapes are common.

[0039] The alumina molded body for gingival coloring contains (A) α-alumina powder or granules with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher, (B) Mg as an element contained in the sintering aid, and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder or granules. Details of components (A) to (C) contained in the alumina molded body for gingival coloring, and the respective contents of (B) Mg and (C) red coloring agent relative to component (A) in the alumina molded body for gingival coloring, are the same as those described in the "Alumina Pre-sintered Body for Gingival Coloring" above.

[0040] <Pre-sintering> A pre-sintered alumina body for gingival coloring is obtained by pre-sintering the alumina molded body for gingival coloring obtained as described above. The temperature during pre-sintering is generally lower than the temperature during main sintering, for example, 500 to 1000°C, preferably 550 to 900°C. During pre-sintering, heating causes a diffusion (adhesion, fusion) phenomenon of molecules and atoms on the surface of the alumina particles, resulting in a state where the constituent alumina particles are partially joined together (a state where a so-called neck is formed), and the strength of the pre-sintered body can be improved to a strength that is easy to handle and process. The pre-sintered alumina body for gingival coloring obtained by pre-sintering is a microporous pre-sintered body having pores that open outwards. Before pre-sintering, degreasing treatment may be performed as needed. Here, degreasing treatment means a treatment to remove adsorbed water, dispersants, plasticizers, binders, defoamers, release agents, etc. contained in the alumina molded body for gingival coloring by volatilization or decomposition.

[0041] Conventional methods known as degreasing and / or pre-sintering can be used without particular limitation, and may be carried out continuously or in multiple stages. Furthermore, it is preferable to carry out the process in an oxygen-containing air atmosphere in order to efficiently remove organic matter. Degreasing and / or pre-sintering can be carried out, for example, by heating in an electric furnace.

[0042] <Other Manufacturing Methods> As described above, the method for manufacturing the alumina temporary sintered body for gingival coloring of the present invention has been explained, but other methods may also be employed. For example, a method may be adopted in which the temporary sintered body is manufactured without using (C) a red coloring agent, and then (C) a red coloring agent is incorporated into the temporary sintered body. That is, the alumina temporary sintered body for gingival coloring of the present invention may be manufactured by supporting (A) α-alumina powder granules with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, and (B) a sintering aid containing Mg, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder granules (hereinafter sometimes referred to as an uncolored temporary sintered body) with (C) a red coloring agent, at least one element selected from Ho, Er, Cr, Mn, Cu, and Eu on it.

[0043] An uncolored pre-sintered body can be manufactured in the same manner as described in the method for manufacturing a pre-sintered alumina body for gingival coloring, except that (C) a red coloring agent is not used. Specifically, an uncolored alumina dispersion slurry for gingival coloring containing α-alumina powder and a magnesium compound as a sintering aid is spray-dried to obtain uncolored alumina granules for gingival coloring, which are then molded to obtain a molded alumina body for gingival coloring. The molded alumina body for gingival coloring is then pre-sintered to obtain a pre-sintered alumina body for gingival coloring (uncolored pre-sintered body). Methods for incorporating (C) a red coloring agent into the uncolored pre-sintered body include immersing the uncolored pre-sintered body in a liquid in which the red coloring agent raw material described above is dissolved or dispersed, or dropping or coating the liquid in which the red coloring agent raw material described above is dissolved or dispersed onto the uncolored pre-sintered body. As a result, the red coloring agent raw material penetrates into the pores of the uncolored pre-sintered body, and the coloring agent is supported on the inside and surface of the pre-sintered body. The solvent (coloring agent solvent) constituting the liquid in which the red coloring agent raw materials are dissolved or dispersed is water and / or an organic solvent, preferably water, an alcohol-based organic solvent such as ethanol or isopropyl alcohol, or a glycol-based organic solvent such as ethylene glycol or propylene glycol. One type of solvent (coloring agent solvent) may be used alone, or two or more types may be used in combination. The concentration of each coloring agent raw material in the liquid in which the red coloring agent raw materials are dissolved or dispersed is not particularly limited, and can be adjusted as appropriate so that the concentration of each coloring agent in the gingival color alumina sintered body of the present invention produced is the desired concentration, but it is preferable that the total amount of coloring agent raw materials be about 0.001 to 10% by mass relative to the solvent.

[0044] Furthermore, although a method using granular gingival coloring alumina for manufacturing a pre-sintered body has been described, it is also possible to manufacture it without using the aforementioned granular material. For example, a mixture of α-alumina powder, a magnesium compound which is a sintering aid, and a raw material for a red coloring agent may be molded to obtain a molded body of gingival coloring alumina, and the molded body may be pre-sintered.

[0045] [Use of Gingival-Colored Alumina Pre-Sintered Body] The gingival-colored pre-sintered body of the present invention is used for the purpose of dental restoration and may be machined into an appropriate shape as needed. Machining can be performed using a CAD / CAM system. A CAD / CAM system refers to a system that uses computer-aided design to design desired three-dimensional shape data (CAD) and performs computer-aided manufacturing (CAM). By sintering (final sintering) the gingival-colored alumina pre-sintered body, a gingival-colored alumina sintered body that can reproduce gingival color well can be obtained. The gingival-colored pre-sintered body to be sintered may or may not have been machined as described above. Generally, the gingival-colored alumina pre-sintered body is machined before sintering. The temperature during sintering is, for example, 1200 to 1700°C, preferably 1300 to 1600°C. The pressure during final sintering can be, for example, atmospheric pressure in the range of 960 to 1060 hPa. The sintering time depends on the sintering temperature, but is usually about 5 minutes to 6 hours, preferably about 10 minutes to 4 hours. The gingival-colored alumina sintered body obtained as described above reproduces gingival color well and has high strength, making it suitable for use as a frame for complete dentures or partial dentures.

[0046] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these examples.

[0047] [Measurement Method] The sintered bodies prepared by firing the pre-sintered bodies made in each example and comparative example at atmospheric pressure (1013 hPa) and 1450°C for 2 hours were measured as follows.

[0048] <a ＊ , b ＊ > The sintered bodies (3.0 mm thick) obtained by firing the pre-sintered bodies prepared in each example and comparative example as described above were subjected to a spectrophotometer equipped with a standard light C light source (Tokyo Denshoku Co., Ltd.: TC-1800MKII) to measure the color tone of the reflected light under black background conditions, and CIEL was used. ＊ a ＊ b ＊ chromaticity a, expressed in a color system. ＊ , b ＊ They obtained the following, respectively.

[0049] <Color Tone> The sintered bodies (3.0 mm thick) obtained by firing the temporary sintered bodies prepared in each example and comparative example as described above were visually evaluated to determine whether they corresponded to pink or light pink when compared to hardened bodies (3 mm thick) of GC Corporation's "Acron" (product name) No. 3 (pink) and No. 2 (light pink), which are common denture base resins. If the color was confirmed to be pink or light pink by visual inspection, it was judged that the gingival color was well reproduced. On the other hand, if the color tone was anything other than these, it was judged as "not applicable" and that the gingival color was not reproduced.

[0050] <Bending Strength> The pre-sintered bodies prepared in each example and comparative example were fired as described above to obtain test specimens consisting of disc-shaped sintered bodies with a diameter of approximately 16.9 mm and a thickness of approximately 1.2 mm. The test specimens were set in an Autograph (manufactured by Shimadzu Corporation), and the biaxial bending fracture strength was measured with an indenter radius of 0.7 mm, a support circle radius of 5 mm, and a crosshead speed of 1 mm / min. The bending strength was calculated using the following formula. Five test specimens were evaluated, and the average value was taken as the bending strength. Formula: σ = (-0.2387F)(X - Y) / (t ２ ) X=(1+ν)ln(r ２ / r ３ ) ２ +{(1-ν) / 2}(r ２ / r ３ ) ２ Y=(1+ν){1+ln(r １ / r ３ ) ２} + (1 - ν) (r １ / r ３ ) ２ The symbols above represent, respectively: σ: biaxial bending strength (MPa), F: load at fracture of the specimen (N), t: specimen thickness (mm), ν: Poisson's ratio (0.24 for alumina), r １ : Support circle radius (5 mm in this test), r ２ : Indenter radius (0.7 mm in this test), r ３ : Represents the radius of the test specimen (mm).

[0051] The raw materials used in the examples and comparative examples are as follows:

[0052] <(A) α-Alumina powder> - α-Alumina powder: NXA100 (manufactured by Sumitomo Chemical Co., Ltd.) Average primary particle size 150 nm, purity 99.99% - α-Alumina powder: NXA150 (manufactured by Sumitomo Chemical Co., Ltd.) Average primary particle size 200 nm, purity 99.99%・α-Alumina powder: AKP-20 (manufactured by Sumitomo Chemical) Average primary particle size 420 nm, purity 99.99%

[0053] <(B) Mg> Magnesium oxide powder: 500A (manufactured by Ube Materials Co., Ltd.)

[0054] <(C) Red Colorants> The following compounds were used as raw materials for the red colorants: Manganese(IV) chloride tetrahydrate as the Mn source Chromium(III) chloride hexahydrate as the Cr source Holmium(III) acetate monohydrate as the Ho source Erbium chloride hexahydrate as the Erbium chloride hexahydrate as the Cu source Copper(II) nitrate trihydrate as the Cu source Europium(III) chloride hexahydrate as the Eu source

[0055] <Colorants not included in component (C)> As an Ag source: Silver(I) chloride As an In source: Indium(III) nitrate trihydrate

[0056] <Example 1> (A) 100 g of NXA100 (manufactured by Sumitomo Chemical Co., Ltd.), 0.5 g of a dispersant (SN Dispersant 5468, manufactured by Sunopco Corporation), and 62 g of pure water were mixed together. This was placed in a polyamide pot and ball-milled at 65 rpm for 6 hours to prepare an alumina slurry. Next, (B) 2 g of magnesium oxide powder (500A, manufactured by Ube Materials Co., Ltd.), 6 g of anhydrous citric acid, and 123 g of pure water were stirred and mixed for 5 hours as a sintering aid, which is a source of Mg, to prepare a magnesium oxide dispersion. Next, 100 g of the alumina slurry, 48 g of pure water, 6.6 g of the magnesium oxide dispersion, 1.2 g of binder (SA-261P, manufactured by Japan Coating Resin Co., Ltd.), 0.6 g of plasticizer (PEG400, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and (C) 0.099 g of holmium chloride hexahydrate as a raw material for red colorants (raw material for red colorants) (holmium oxide: Ho ２ O ３An amount equivalent to 800 ppm of α-alumina powder was weighed and mixed and stirred for 10 minutes to prepare a gingival alumina dispersion slurry. The gingival alumina dispersion slurry was then spray-dried and granulated to prepare gingival alumina granules (aggregated particle size 44 μm). The gingival alumina granules were filled into a mold of a predetermined shape and uniaxially pressurized at a pressure of 200 MPa for 1 minute to produce a gingival alumina molded body. The gingival alumina molded body was heated from 25°C to 600°C at a heating rate of 10°C / min, then left to degrease for 30 minutes, and then heated to 700°C at a heating rate of 10°C / min for 2 hours to produce a gingival alumina pre-sintered body. Next, the temperature was increased from 700°C to 1450°C at a heating rate of 10°C / min, and after a 2-hour quenching period, it was allowed to cool to produce a gingival-colored alumina sintered body. The evaluation results are shown in Table 1.

[0057] <Examples 2-8, Comparative Examples 1-5> Except for appropriately changing the raw materials for the red coloring agent and their proportions to obtain the pre-sintered bodies shown in Tables 1-2, alumina pre-sintered bodies for gingival coloring were prepared in accordance with Example 1. The evaluation results are shown in Tables 1-2.

[0058]

[0059]

[0060] <Example 9> (A) 100 g of NXA100 (manufactured by Sumitomo Chemical Co., Ltd.), 0.5 g of a dispersant (SN Dispersant 5468, manufactured by Sunopco Corporation), and 62 g of pure water were mixed together. This mixture was placed in a polyamide pot and ball-milled at 65 rpm for 6 hours to prepare an alumina slurry. Next, (B) 2 g of magnesium oxide powder (500A, manufactured by Ube Materials Co., Ltd.), 6 g of anhydrous citric acid, and 123 g of pure water were stirred and mixed for 5 hours to prepare a magnesium oxide dispersion as a sintering aid, which is a source of Mg. Next, 100 g of the alumina slurry, 48 g of pure water, 6.6 g of the magnesium oxide dispersion, 1.2 g of binder (SA-261P, manufactured by Japan Coating Resin Co., Ltd.), and 0.6 g of plasticizer (PEG400, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed out and mixed and stirred for 10 minutes to prepare an uncolored alumina dispersion slurry for gingival coloring. Furthermore, the uncolored alumina dispersion slurry for gingival coloring was spray-dried and dried to prepare uncolored alumina granules for gingival coloring. The uncolored alumina granules for gingival coloring were filled into a mold having a predetermined shape and uniaxially pressurized at a pressure of 200 MPa for 1 minute to produce a molded alumina body for gingival coloring. A gingival-colored alumina molded body was heated from 25°C to 600°C at a heating rate of 10°C / min, then degreased for 30 minutes, and then heated to 700°C at a heating rate of 10°C / min for 2 hours of pre-sintering to produce a gingival-colored alumina pre-sintered body (uncolored pre-sintered body). Next, the gingival-colored alumina pre-sintered body (uncolored pre-sintered body) was immersed for 5 minutes in an aqueous solution of 1.725 g of chromium(III) chloride hexahydrate dispersed in 460 g of water, and then dried at 100°C for 30 minutes to produce a gingival-colored alumina pre-sintered body impregnated with a coloring agent. The Cr content (oxide equivalent) relative to the α-alumina powder in the gingival-colored alumina pre-sintered body was 170 ppm. The Cr content was measured by ICP emission spectrometry. Subsequently, the gingival-colored alumina sintered body was heated from 25°C to 1450°C at a heating rate of 10°C / min, and after 2 hours of aging, it was allowed to cool to produce a gingival-colored alumina sintered body. The evaluation results are shown in Table 3.

[0061] <Examples 10-15> Except for appropriately changing the raw materials for the red coloring agent and their proportions to obtain the pre-sintered bodies shown in Table 3, and further changing the coloring agent solvent as shown in Table 3, gingival-colored alumina sintered bodies were prepared in accordance with Example 9. The evaluation results for each are shown in Table 3.

[0062]

[0063] From the results in Tables 1 and 3, the sintered bodies obtained by firing the gingival color alumina temporary sintered bodies of each example containing the predetermined components (A) to (C) are a ＊ The value is +4 to +30, b ＊ The values ​​were in the range of -5 to +10, indicating good reproduction of gingival color, and also showing high flexural strength. As shown in Table 2, the sintered bodies made from the provisional sintered bodies of each comparative example that did not contain at least one of components (A) to (C) either did not reproduce gingival color or had low flexural strength values, failing to achieve both gingival color reproduction and strength.

Claims

1. (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher, (B) Mg as an element contained in the sintering aid, (C) containing at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder, and the sintered body of the 3.0 mm thick gingival alumina powder is fired under atmospheric pressure (1013 hPa) and 1450°C, and a black background is used to measure the alumina powder. ＊ The value is +4 to +30, b ＊ A gingival alumina pre-sintered body having a value of -5 to +10, wherein the sintered body obtained by firing the gingival alumina pre-sintered body under atmospheric pressure (1013 hPa) and 1450°C has a bending strength of 800 MPa or more.

2. A method for producing a pre-sintered alumina body for gingival coloring, characterized by pre-sintering at 500 to 1000°C an alumina molded body for gingival coloring, comprising: (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder.

3. A method for producing a gingival color alumina molded body, comprising press-molding the gingival color alumina granules at 10 to 400 MPa, wherein the granules include: (A) α-alumina powder with an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or higher; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder, and the aggregated particle diameter is 5 to 100 μm.

4. A method for producing alumina granules for gingival coloring, comprising: (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or higher; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder; and spray-drying the alumina dispersion slurry.

5. A method for producing a gingival color alumina pre-sintered body for gingival color according to claim 1, characterized in that (A) α-alumina powder with an average primary particle size of 30 to 300 nm and a purity of 99.5% or more, (B) a pre-sintered body containing Mg as an element in the sintering aid, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder, and (C) at least one element selected from Ho, Er, Cr, Mn, Cu, and Eu is supported on the pre-sintered body as a red coloring agent.

6. A method for producing a pre-sintered alumina body for gingival coloring according to claim 1, comprising: (A) α-alumina powder with an average primary particle diameter of 30 to 300 nm and a purity of 99.5% or more; (B) Mg as an element contained in a sintering aid; and (C) at least one element selected from the group consisting of Ho, Er, Cr, Mn, Cu, and Eu as a red coloring agent, wherein the content of (B) Mg is 100 to 5000 ppm by mass as metallic magnesium relative to the (A) α-alumina powder; spray drying the alumina dispersion slurry to obtain alumina granules for gingival coloring with an aggregated particle diameter of 5 to 100 μm; press-molding the alumina granules for gingival coloring at 10 to 400 MPa to obtain a pre-sintered alumina body for gingival coloring; and further pre-sintering the pre-sintered alumina body for gingival coloring at 500 to 1000°C.

Images