Manufacturing method of recycled powder

Abstract

To provide at least one of recycled powder obtained by horizontal recycling of dental blank scraps, manufacturing method thereof, manufacturing method of recycled dental blanks, and recycled dental blanks obtained thereby.SOLUTION: A manufacturing method of recycled powder includes: a pulverization step of pulverizing dental blank scraps to obtain a pulverized product; and a recovery step of recovering, from the pulverized product, powder having a color tone of L* of 90 or more and 100 or less, a* of 0 or more and 1 or less, and b* of 0 or more and 5 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for producing recycled powder obtained by recycling dental blanks, and more particularly to a method for producing recycled powder obtained by recycling dental blanks made of green compacts of ceramics.

Background Art

[0002] Sintered bodies (ceramic materials) such as alumina and zirconia with excellent biocompatibility are widely used as dental materials. Among ceramics, sintered bodies of zirconia are frequently used as dental prostheses such as crowns, bridges, inlays, onlays, and abutments because they have both aesthetic properties similar to natural teeth and high mechanical strength.

[0003] In the method for producing dental prostheses made of sintered bodies, first, raw material powder is formed into a formed body (compressed powder), and this is calcined to produce a green compact (dental blank). Next, the green compact is subjected to cutting in a dental laboratory or the like, and a shape of a dental prosthesis considering thermal shrinkage due to sintering is imparted. Thereafter, the green compact is sintered to form a sintered body (dental prosthesis), and fine adjustment is performed, and finally, it is worn by a patient.

[0004] By the way, from the viewpoints of reducing industrial waste and environmental load, the demand for recycling ceramic materials is increasing. As a method for recycling ceramic materials, for example, a technique for recycling an electrolyte sheet for a fuel cell made of a sintered body of zirconia (Patent Document 1) and a technique for recycling a grinding ball made of a sintered body of zirconia (Patent Document 2) are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Green bodies such as dental blanks are considered suitable for recycling (especially horizontal recycling and closed-loop recycling) because they have not been sintered. However, Patent Documents 1 and 2 both relate to the recycling technology of sintered bodies, and are not recycling technologies for dental blanks, especially the end materials of dental blanks generated after cutting.

[0007] In addition to this, multiple types of dental blanks are used according to the characteristics of the intended dental prosthesis. The end materials of dental blanks generated after cutting are difficult to recycle themselves because they are a mixture of different compositions and types. Therefore, at present, there is only the possibility of cascade recycling such as disposal by processing companies such as dental laboratories or diversion to cement raw materials. Even if the end materials of dental blanks could be recovered, in horizontal recycling, it is essential to separate the recovered individual end materials after compositional analysis. For this reason, in reality, horizontal recycling of the end materials of dental blanks has been impossible.

[0008] An object of the present disclosure is to provide at least any one of recycled powder obtained by horizontal recycling of end materials of dental blanks, a method for producing the same, a method for producing recycled dental blanks, and the recycled dental blanks obtained thereby.

Means for Solving the Problems

[0009] In the present disclosure, regarding the possibility of recycling dental blanks, especially horizontal recycling, the color tone of the end materials of dental blanks after cutting was focused on and examined. As a result, it was found that the end materials of dental blanks discharged in the manufacturing process of dental prostheses can be recycled (reprocessed) as raw materials for dental blanks by performing a simple operation, and furthermore, the powder obtained by such recycling can be suitably used as a raw material for dental blanks.

[0010] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] A method for producing recycled powder, comprising: a pulverizing step of pulverizing an end material of a dental blank to obtain a pulverized product; and a recovering step of recovering a powder having a color tone of L being 90 or more and 100 or less, a being 0 or more and 1 or less, and b being 0 or more and 5 or less from the pulverized product. * being 90 or more and 100 or less, a * being 0 or more and 1 or less, b * being 0 or more and 5 or less from the pulverized product. [2] The method for producing recycled powder according to [1] above, further comprising a sorting step of sorting the end material prior to the pulverizing step. [3] The method for producing recycled powder according to [2] above, wherein the sorting method in the sorting step is a method in which the end material is sorted into a color tone unit composed of an end material having a color tone of L being 90 or more and 100 or less, a being 0 or more and 1 or less, and b being 0 or more and 5 or less, and a color tone unit composed of an end material having a color tone different from the color tone. * being 90 or more and 100 or less, a * being 0 or more and 1 or less, b * being 0 or more and 5 or less. [4] The method for producing recycled powder according to any one of [1] to [3] above, wherein the pulverizing step is a pulverizing step including a rough pulverizing step of dry-pulverizing the end material to obtain a roughly pulverized product and a particle size adjusting step of wet-pulverizing the roughly pulverized product. [5] The method for producing recycled powder according to any one of [1] to [4] above, wherein the recovering method in the recovering step is a recovering method of dividing the pulverized product obtained by the pulverizing step into a certain unit and recovering the unit corresponding to the pulverized product having a color tone of L being 90 or more and 100 or less, a being 0 or more and 1 or less, and b being 0 or more and 5 or less. * being 90 or more and 100 or less, a * being 0 or more and 1 or less, b * being 0 or more and 5 or less. [6] A recycling method for a dental blank, comprising: a pulverizing step of pulverizing an end material of the dental blank to obtain a pulverized product; and a recovering step of recovering a powder having a color tone of L being 90 or more and 100 or less, a being 0 or more and 1 or less, and b being 0 or more and 5 or less from the pulverized product. * being 90 or more and 100 or less, a * being 0 or more and 1 or less, b * being 0 or more and 5 or less. [7] A method for manufacturing a recycled dental blank using recycled powder obtained from at least one of the above [1] to [5]. [8] The color tone is L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, b * is a recycled powder that is 0 or more and 5 or less.

Advantages of the Invention

[0011] According to the present disclosure, it is possible to provide at least any one of a recycled powder obtained by horizontal recycling of end materials of a dental blank, a method for manufacturing the same, a method for manufacturing a recycled dental blank, and a recycled dental blank obtained thereby.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0013] Hereinafter, the present disclosure will be described by showing an example of an embodiment. In addition, any combination of the configurations and numerical values in this specification is also included in the present disclosure, and any combination of the upper limit value and the lower limit value of the numerical values disclosed in this specification is also included in the present disclosure. Hereinafter, the main terms in the present disclosure will be shown.

[0014] The "dental prosthesis" is at least any one of a crown, a bridge, an inlay, an onlay, an abutment, other dentures, and dental coatings, and in particular, at least any one of dentures and dental coatings made of a ceramic material (sintered body).

[0015] The "dental blank" is a composition that is a precursor of a dental prosthesis, and in particular, a green body of a ceramic suitable as a precursor of a dental prosthesis. A dental prosthesis is obtained by sintering a dental blank.

[0016] The "edge material of a dental blank (hereinafter also simply referred to as 'edge material')" is a dental blank after cutting out the shape of a dental prosthesis by cutting such as CAD / CAM processing, and is a dental blank having one or more holes (perforations) in the shape of the dental prosthesis, and at least one of its divided parts.

[0017] The "recycled dental blank (hereinafter also referred to as'regenerated blank')" is a dental blank manufactured using recycled powder (described later) as part or all of the raw materials.

[0018] The "sintered body" is a composition composed of crystal particles of ceramics and having a certain shape, and is a composition obtained by molding (and pre-sintering if necessary) and sintering ceramic powder.

[0019] The "pre-sintered body" is a composition composed of fused particles of ceramics and having a certain shape, and is a composition obtained by pre-sintering (preliminary sintering, semi-sintering) a molded body (compacted powder) obtained by molding ceramic powder.

[0020] The "recycled powder" is powder obtained by recycling treatment (recycling) of a sintered body, pre-sintered body or molded body, and mixed powder containing the same. In the present embodiment, in particular, it is powder obtained by recycling treatment of pre-sintering and mixed powder containing the same.

[0021] The "synthetic powder" is powder other than powder obtained by recycling treatment of a sintered body, pre-sintered body or molded body, and in particular, is powder obtained by one or more selected from the group of hydrothermal synthesis method, hydrolysis method and neutralization coprecipitation method, and other liquid phase methods.

[0022] The "color tone" is measured by using a spectrocolorimeter (for example, CM-700d, manufactured by Konica Minolta Inc.) equipped with an illumination-receiving optical system conforming to the geometric condition c of JIS Z 8722, and measured by the SCI method using a black background, and L * a * b* It is a color tone represented by a color system. The color tone of a composition having fluidity such as powder is the color tone measured as a molded body (compacted powder). Note that L * a * b * The color tone represented by the color system is the lightness L * and the hue a * and b * corresponds to the coordinates in the color space determined by three values, and is the color tone corresponding to the coordinates in the color space determined by these three values. [Method for producing recycled powder] This embodiment includes a pulverization step of pulverizing the end material of a dental blank to obtain a pulverized product, and a recovery step of recovering powder having a color tone such that L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, and b * is 0 or more and 5 or less, from the pulverized product. In the production of dental prostheses, a wide variety of dental blanks are used, and these are discharged (discarded) together. Therefore, the discharged end materials (aggregates thereof) differ greatly in their properties, including color tone, chemical composition, and contained elements. In such a situation, in the production method of this embodiment, those having a specific color tone can be recovered as powder from such end materials (aggregates of end materials). The recovered powder can be recycled as recycled powder suitable as a raw material powder for dental blanks.

[0023] Hereinafter, each step in the method for producing recycled powder of this embodiment will be described by taking the case where the end material of the dental blank is the end material of a calcined body of zirconia as an example. <Pulverization step> The pulverization step of pulverizing the end material of the dental blank to obtain a pulverized product is a step of pulverizing the end material to obtain a pulverized product. The pulverized product is one in which the end material has become powdery, and this itself can be regarded as recycled powder. However, since the end materials subjected to the pulverization step may contain many materials with different properties, the pulverized product obtained through the subsequent recovery step becomes recycled powder more suitable as a raw material powder for dental blanks.

[0024] The starting material to be used in the grinding process is a calcined body, more specifically a calcined body of ceramics, and even more specifically a calcined body of zirconia (zirconium dioxide, ZrO 2 2) (hereinafter also referred to as "zirconia calcined body"). The calcined body is composed of sintering initial fused particles, and the fused particles are particles in a state where the particles are necked to each other. Compared with a sintered body in which crystal particles are firmly bonded via grain boundaries, the calcined body requires very little energy for grinding and is suitable for recycling treatment by pulverization.

[0025] The zirconia calcined body may be a calcined body made of zirconia, but the main component is zirconia and it may contain metal elements such as stabilizing elements and coloring elements as sub-components.

[0026] One or more selected from the group of yttrium (Y), calcium (Ca), and magnesium (Mg) are listed as stabilizing elements, and one or more selected from the group of titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), praseodymium (Pr), neodymium (Nd), europium (Eu), gadolinium (Gd), terbium (Tb), erbium (Er), and ytterbium (Yb) are listed as coloring elements, respectively. Also, one or more selected from the group of aluminum (Al), silicon (Si), and germanium (Ge) are listed as other metal elements. The existence state of these metal elements is arbitrary, but they may be dissolved in zirconia or may exist as oxides or other compounds.

[0027] The end material may have a structure consisting of one layer, that is, a structure consisting of the overall composition. On the other hand, for dental restorations, harmony in aesthetics with the surrounding dentin (the patient's natural teeth) is required. In order to achieve the same aesthetics as that of natural teeth where the aesthetics changes from the tooth root to the cutting part, the end material may have a structure consisting of two or more layers (for example, two or more and 15 or less layers, further two or more and 10 or less layers, and still further three or more and eight or less layers). In this case, the end material is not limited to a structure laminated so that the boundary of each layer is clear, and may be a structure in which two or more layers are laminated so as to form a gradation. Note that the gradation may be a gradation formed by at least either the color tone or the translucency. When the dental blank has a structure in which two or more layers are laminated If it has, the metal element such as a coloring element may be contained in at least one layer, and it is preferable that at least either the type or the content of the coloring element in each layer is different.

[0028] In the pulverization step, the pulverization may be any pulverization that can obtain a pulverized product to such an extent that the end material can be used as recycled powder. Examples of such pulverization include pulverization in which the average particle size of the pulverized product of the end material is 0.1 μm or more, 0.3 μm or more, or 0.4 μm or more, and is 10 μm or less, 5 μm or less, or 1 μm or less. Pulverization in which the average particle size of the pulverized product of the end material is 0.1 μm or more and 10 μm or less, or 0.4 μm or more and 1 μm or less, is preferable.

[0029] The average particle size of the pulverized product of the end material can be determined by the planimetric method using a SEM observation image. Specifically, draw a circle with a known area on the SEM observation image, measure the number of particles (Nc) of the pulverized product inside the circle and the number of particles (Ni) of the pulverized product on the circumference of the circle, and after making the total number of particles (Nc + Ni) 250 ± 50, the average particle size of the pulverized product may be determined using the following formula (1).

[0030] Average particle size = 2 / {π × (Nc + (1 / 2) × Ni) / (A / M 2 )} 0.5 ··· (1) In formula (1), Nc is the number of particles of the crushed material inside the circle, Ni is the number of particles of the crushed material on the circumference of the circle, A is the area of the circle, and M is the magnification of SEM observation (for example, 5000 to 10000 times). When the number of particles (Nc + Ni) in one SEM observation image is less than 200, (Nc + Ni) may be set to 250 ± 50 using a plurality of SEM observation images.

[0031] The pulverization method may be at least one of dry pulverization and wet pulverization, and may be dry pulverization or wet pulverization. Examples of dry pulverization include pulverization methods using one or more selected from the group consisting of jaw crushers, hammer crushers, shredders, roll crushers, hammer mills, cutting mills, rod mills, roller mills, rotor mills, impact crushers, jet crushers, ball mills, and mortars. Examples of wet pulverization include pulverization methods using one or more selected from the group consisting of ball mills, bead mills, planetary mills, wet jet mills, colloid mills, and homogenizers. A preferred pulverization method is wet pulverization using zirconia spheres (at least one of zirconia balls and zirconia beads) as the pulverization medium. This makes it less likely for impurities to contaminate during pulverization.

[0032] A preferred pulverization process includes a coarse pulverization process of dry-pulverizing the end material to obtain a coarsely pulverized material, and a particle size adjustment process of wet-pulverizing the coarsely pulverized material. By the coarse pulverization process, the end material is made into a coarsely pulverized material on the order of mm, for example, a coarsely pulverized material of 1 to 10 mm. By going through the coarse pulverization process, the average particle size of the pulverized material of the above-mentioned end material can be made more efficiently, and the pulverization time in the pulverization process can be shortened and the energy required for pulverization can be reduced. <Recovery Process> The manufacturing method of the present embodiment recovers a powder from the pulverized material having a color tone where L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, and b * is 0 or more and 5 or less. The color tone where L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, and b *Powder with a value of 0 or more and 5 or less (hereinafter also referred to as "base powder", and the said color tone as "base color tone") is powder obtained from end materials, and the base powder is composed of the same components as a dental blank which is a precursor of a dental prosthesis. Therefore, the base powder is suitable for horizontal recycling into a dental blank. Furthermore, the base powder has a color tone similar to that of a dental blank from which a dental prosthesis having the lightest color tone in a dental color sample (for example, Vita Classical Shade) can be obtained. has a color tone similar to that of a dental blank.

[0033] The base powder can be used as it is as the raw material powder of a dental blank. In addition, by making it a mixed powder of the base powder and powder having a color tone different from that of the base powder (hereinafter also referred to as "color - adjusting powder"), it can also be used as the raw material powder of a dental blank suitable for a dental prosthesis having a color tone other than the base color tone.

[0034] The color tone of the base powder only needs to have the base color tone, but it is preferably to satisfy the following lightness L * and hue a * and b * Note that the lightness L * and hue a * and b * represent one color tone corresponding to the coordinates indicated by these three values, and each does not independently represent a color tone.

[0035] Lightness L * : 90 or more or 95 or more, and 100 or less or 99 or less, Hue a * : 0 or more or 0.2 or more, and 1 or less or 0.8 or less, Hue b * : 0 or more or 0.2 or more, and 5 or less, 3 or less or 0.8 or less.

[0036] The color tone of the color - adjusting powder is such that L * is less than 90, a * is less than 0 or more than 1, or b *It is a powder with a value less than 0 or greater than 5, and any powder containing the same components as the above-mentioned base powder may be used. It may also be at least one of a powder composed only of zirconia and a zirconia powder containing a stabilizing element. Specific color-adjusting powders include at least one of a pulverized product of the end material having a color tone different from that of the base powder and a synthetic powder.

[0037] Generally, dental blanks contain coloring elements. The recovered end materials have different contents of coloring elements and are aggregates of residues of dental blanks after cutting. Therefore, the color tone of the end material becomes darker compared to the basic color tone. In this case, since the color tone of the pulverized product obtained in the pulverization process also becomes darker than the base color tone, it is preferable to mix a powder with a lighter color tone, such as yttrium-stabilized zirconium powder, as the color-adjusting powder.

[0038] If the base powder can be recovered, the recovery method in the recovery process is arbitrary. For example, there is a recovery method in which the pulverized product obtained by the pulverization process is divided into certain units, and the unit corresponding to the pulverized product having the base color tone is recovered. Also, a similar operation can be performed on the coarsely pulverized product obtained in the coarse pulverization process by unit division, and the unit corresponding to the base powder is subjected to a particle size adjustment process, and then recovered by solid-liquid separation and drying. In addition, the "unit" in these cases may be at least one of a mass unit and a volume unit, or any unit that becomes a lot suitable for the process and equipment of the recycling process.

[0039] The recovered base powder can be recycled as recycled powder and further as a raw material for various ceramic materials. In particular, it can be used as a powder suitable as a raw material for dental blanks. <Separation process> The manufacturing method of the present embodiment preferably includes a sorting step of sorting end materials prior to the grinding step. The end materials are dental blanks after cutting, and are collected from processing businesses such as dental laboratories as aggregates of used dental blanks with different color tones and compositions. By having the sorting step, it becomes easier to predict the attributes of the end materials to be subjected to the grinding step, that is, the color tone of the ground materials generated by the grinding step. As a result, unit separation in the recovery step and the coarse grinding step becomes simple or unnecessary, and more efficient recovery of base tone powder can be expected.

[0040] In the sorting step, the end materials are sorted. The sorting may be any method of dividing the end materials into units based on certain attributes, but it is preferably a method of dividing the units according to at least one of the composition and the color tone, and more preferably a method of dividing the units according to the color tone.

[0041] For example, when sorting the end materials according to the color tone, if the color tone is such that L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, and b * is 0 or more and 5 or less, the end materials may be sorted into a color tone unit (hereinafter also referred to as a "base tone unit") composed of such end materials and a color tone unit (hereinafter also referred to as a "non-base tone unit") composed of end materials having a color tone different from the base color tone. Also, when sorting the end materials according to the composition, any method may be used as long as they are sorted into a composition unit composed of end materials having a composition that exhibits the base color tone and a composition unit composed of end materials having a composition that exhibits a color tone different from the base color tone. Note that analysis of the composition requires sample collection and instrumental analysis for each end material, whereas analysis of the color tone can be easily performed by non-contact optical analysis (for example, during transportation by a belt conveyor). Therefore, the sorting method is preferably sorting by a unit (color tone unit) based on the color tone rather than sorting by a unit (composition unit) based on the composition.

[0042] The end materials sorted into the non-base tone units can be recycled as raw materials for color-adjusted powders and other ceramic materials in the same manner as the base powders through the above-described grinding treatment and recovery treatment.

[0043] The non-base units may be classified into two or more sub-units. As a result, the color tone and composition of the end materials contained in each sub-unit become more subdivided and uniform, making it more suitable for color tone control by mixing with the base powder and recycling for other uses.

[0044] Since it becomes easier to separate the end materials in the separation process, the end materials are preferably the end materials of a dental blank with an information tag attached that contains at least specific information linked to the material information. "Specific information" is information that can be linked to the material information, and "material information" preferably includes one or more selected from the group of composition information, product information, and manufacturing information (all described later).

[0045] The specific information preferably includes one or more selected from the group of raw material ratio, composition (chemical composition), average composition, contained elements, color tone, color tone code, average color tone, and average color tone code (hereinafter also referred to as "composition information"). The properties of the end materials can be directly confirmed by the composition information. The specific information preferably includes one or more selected from the group of raw material ratio, composition, contained elements, color tone, and color tone code, and preferably includes at least one of the composition and the color tone code. Also, when the end material has a structure composed of two or more layers, the composition information preferably includes one or more selected from the group of average composition, average color tone, and average color tone code in addition to, or instead of, the composition, color tone, and color tone code. The "raw material ratio" is information regarding the type (e.g., product name of the powder) and usage amount of each raw material used in the manufacture of the dental blank, and the color tone is the target color tone of the dental prosthesis obtained by sintering the end material (dental blank). Also, the "color tone code" is a code representing each color tone in the dental color tone sample book, for example, a code indicated by any alphabet and number from A1 to D4 in Vita Classical Shade.

[0046] The specific information preferably includes at least one of the model number and the manufacturer's name of the dental blank (end material) (hereinafter also referred to as "product information"), and preferably includes at least the manufacturer's name. The "model number" is the product name of the dental blank in the manufacturer of the dental blank. By including the product information in the specific information, rough sorting becomes possible after collection. That is, the end materials collected from processing operators such as dental laboratories may contain products of different manufacturers of dental blanks. In this case, first, sorting can be performed for each manufacturer or for each manufacturer and product, and sorting for horizontal recycling can be efficiently and easily carried out.

[0047] The specific information preferably includes one or more selected from the group of the manufacturing lot, manufacturing location, manufacturing year, and recovery deadline of the dental blank (hereinafter also referred to as "manufacturing information"), more preferably includes at least one of the manufacturing year and the recovery deadline, and even more preferably includes the recovery deadline. By including the manufacturing information, not only recycling but also traceability becomes possible. Note that the "manufacturing year" is information that can specify the manufacturing time, and instead of the manufacturing year, it may be the manufacturing month or the manufacturing date.

[0048] The specific information is preferably attached by an information tag composed of a code symbol such as a code tag. The information tag can be read by a means for reading the code symbol, specifically, at least one of a barcode reader and image analysis, etc., so that the end materials can be easily sorted. The information tag may include one or more selected from the group of letters, numbers, and symbols. The type, size, display form, etc. of the code symbol may be appropriately selected according to the amount of information attached to the information tag, the shape of the dental blank, etc. For example, it may be at least one of one-dimensional and two-dimensional code symbols, specifically, at least one of a barcode and a QR code (registered trademark). The information tag may include its own code, etc. Also, it is preferable that the code symbol can read the information even if a part of it is missing. <Washing process> Prior to or after each of the separation process, pulverization process, coarse pulverization process, particle size adjustment process, or recovery process, an impurity reduction process for reducing impurities may be included. Thereby, impurities associated with the recovered end material and impurities mixed before and after each process can be reduced.

[0049] The method for reducing impurities may be any method as long as it reduces the impurities in the end material, pulverized material, or recycled powder (hereinafter also referred to as "end material, etc."). Washing, and more preferably, water washing may be sufficient.

[0050] In cases such as when impurity reduction is performed by water washing, after the impurity reduction process, a drying process for drying the end material, etc. after water washing may be included. The drying method may be any method as long as it reduces the water physically adsorbed on the end material, etc. For example, a method of drying in an air atmosphere at 80°C or higher and 150°C or lower can be mentioned. The drying time may be appropriately adjusted according to the amount of the end material, etc. to be dried and the characteristics of the dryer, and examples include 30 minutes or more and 24 hours or less.

[0051] The manufacturing method of the present embodiment preferably has an impurity reduction process as the first process, and preferably has an impurity reduction process prior to the pulverization process (or the separation process if it has a separation process). Further, the impurity reduction process may be an independent process, or may be performed when transferring the end material, etc. to each process. [Recycling method for end material of dental blank] The manufacturing method of the recycled powder of the present embodiment includes a pulverization process of pulverizing the end material of the dental blank to obtain a pulverized material, and a recovery process of recovering a powder having an L * of 90 or more and 100 or less, an a * of 0 or more and 1 or less, and a b * of 0 or more and 5 or less from the pulverized material. It can also be regarded as a recycling method for the end material of the dental blank (hereinafter also referred to as "the recycling method of the present embodiment"). As described above, the recycled powder can be used as a raw material powder for dental blanks, and it is possible to horizontally recycle the end material.

[0052] The recycling method of this embodiment is the same as the pulverization step and the recovery step in the above-described method for producing recycled powder, and may also include at least one of the classification step and the impurity reduction step in the above-described method for producing recycled powder. [Recycled powder] The recycled powder obtained by the production method of this embodiment may be any powder that can be used as a raw material for a recycled blank. Preferred recycled powders include, for example, L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, b * is 0 or more and 5 or less (hereinafter also referred to as "this recycled powder").

[0053] This recycled powder has L * is 90 or more and 100 or less, a * is 0 or more and 1 or less, b * is 0 or more and 5 or less, and further L * a * b * Lightness L in the color system * , Hue a * and hue b * preferably satisfy the following.

[0054] Lightness L * : 90 or more or 95 or more, and 100 or less or 99 or less, Hue a * : 0 or more or 0.2 or more, and 1 or less or 0.8 or less, Hue b * : 0 or more or 0.2 or more, and 5 or less, 3 or less or 0.8 or less Since this recycled powder exhibits such a color tone, it can be used as a base powder. That is, this recycled powder can be directly used in the method for manufacturing a green body (dental blank). In addition to this, the recycled powder containing a coloring element can be used as a base powder. That is, conventionally, a powder mixing system uses a powder not containing a coloring element as a base powder, and a powder containing a coloring element is mixed with the base powder to produce a green body (dental blank) suitable for dental prostheses. In contrast, by using this recycled powder, in addition to enabling horizontal recycling of the green body (dental blank), a powder mixing system based on a powder containing a coloring element, which has never existed before, can be realized. By such a powder mixing system, a green body (dental blank) suitable for dental prostheses can be produced, and in addition to or instead of a powder not containing a coloring element, a dental prosthesis having an arbitrary color tone can be obtained using this recycled powder as a base powder.

[0055] The color tone of the recycled powder can be measured by filling 3.0 g of the powder into a mold with a diameter of 25 mm, performing uniaxial pressure molding at a pressure of 19.6 MPa, then subjecting it to CIP treatment at a pressure of 196 MPa to form a disk with a thickness of 3.0 ± 0.5 mm, and polishing the measurement surface by 0.1 mm using #800 waterproof abrasive paper and then measuring it.

[0056] Since this recycled powder is a powder made from dental blanks as raw materials, it can be mentioned that the main component is zirconia and it is a powder containing metal elements such as a stabilizing element and a coloring element as secondary components.

[0057] Examples of the stabilizing element contained in the recycled powder include one or more selected from the group consisting of yttrium, calcium, and magnesium. Further, examples of the coloring element contained in the recycled powder include one or more selected from the group consisting of titanium, iron, cobalt, nickel, manganese, praseodymium, neodymium, europium, gadolinium, terbium, erbium, and ytterbium, and preferably include one or more transition metal elements selected from the group consisting of titanium, iron, cobalt, nickel, and manganese, and one or more rare earth elements selected from the group consisting of praseodymium, neodymium, europium, gadolinium, terbium, erbium, and ytterbium.

[0058] The recycled powder is a powder obtained by pulverizing a calcined body that has undergone molding and calcination. To undergo these steps, it is considered that the recycled powder also contains the coloring elements contained by immersion in the coloring solution and the coloring elements contained by solid-phase mixing, in different states from those of the coloring elements contained in zirconia. Therefore, it is preferable that at least a part of the coloring elements in the recycled powder is contained in solid solution in zirconia, and it is more preferable that at least a part of the transition metal elements is contained in solid solution in zirconia. On the other hand, the coloring elements may be contained as other compounds (for example, oxides). [Method for manufacturing a recycled blank] The method for manufacturing a dental blank according to this embodiment may be a method for manufacturing a recycled dental blank (recycled blank) using the recycled powder obtained by the manufacturing method according to this embodiment (hereinafter also referred to as "this recycled powder"), and in a method similar to the known method for manufacturing a dental blank, this recycled powder may be used as a raw material powder. Further, in the method for manufacturing a recycled dental blank using this recycled powder, a powder containing this recycled powder may be used as a raw material powder, and a mixed powder containing this recycled powder, for example, a mixed powder of this recycled powder and a synthetic powder, may be used as a raw material powder.

[0059] As a specific manufacturing method, there is a method for manufacturing a recycled dental blank, which includes a molding step of molding the recycled powder to obtain a molded body, and a calcination step of calcining the molded body.

[0060] For the recycled powder used in the molding step, recycled powder with appropriately adjusted color tone and composition may be used according to the color tone of the intended dental prosthesis. For example, when manufacturing a dental blank (calcined body) for producing a dental prosthesis having a color tone corresponding to A1 of Vita Classical Shade, recycled powder may be used as the base powder. On the other hand, when manufacturing a dental blank (calcined body) for producing a dental prosthesis having a color tone darker than A1 of Vita Classical Shade, recycled powder may be used in the mixed powder of the base powder and the color adjusting powder. In the mixed powder, the base powder functions as a diluting component for the color adjusting powder, while the color adjusting powder functions as a coloring element for the base powder. Therefore, when aiming for a dental prosthesis with a darker color tone, the content ratio of the color adjusting powder in the mixed powder may be increased.

[0061] The molding method in the molding step may be any method that can form the recycled powder into a molded body (compressed powder body). For example, one or more selected from the group of press molding, injection molding, sheet molding, extrusion molding, and casting molding may be mentioned. The molding method may be a molding method suitable for the production of dental blanks, and press molding is preferred.

[0062] The calcination step may be a calcination (heat treatment) in which the particles constituting the recycled powder become fused particles, and may be the same as the calcination in the production of known dental blanks. Examples of the calcination conditions include treatment at 800 °C or higher and lower than 1200 °C in an air atmosphere.

[0063] The obtained recycled blank can be made into a sintered body (dental prosthesis) by a known sintering method. Examples of the sintering method include sintering treatment at a temperature of 1200 °C or higher and 1600 °C or lower in an air atmosphere.

Examples

[0064] Hereinafter, the present disclosure will be described by way of examples. However, the present disclosure is not limited to the examples. <Composition analysis> The composition of the composition was measured by ICP analysis. As a pretreatment for the analysis, the sample powder was heat-treated in an air atmosphere at 1000 °C for 1 hour. <Average particle size> The average particle size of the powder sample was determined by the planimetric method using SEM observation images. That is, a circle with a known area was drawn on the SEM observation image obtained under the following conditions, and the number of particles of the pulverized material (Nc) inside the circle and the number of particles of the pulverized material (Ni) on the circumference of the circle were measured. After ensuring that the total number of particles (Nc + Ni) was 250 ± 50, the average particle size of the pulverized material was determined using the above formula (1).

[0065] Acceleration magnification: 15V Observation magnification: 5000 times <Green body density> The mass of the green body was determined by measuring with an electronic balance, and the volume was determined from the dimensions measured with calipers. The measured density was obtained from the obtained mass and volume and used as the green body density. <Sintered body density> The mass of the green body was determined by measuring with an electronic balance, and the volume was determined by the Archimedes method according to JIS R 1634. The measured density was obtained from the obtained mass and volume and used as the green body density. For the Archimedes method, ion-exchanged water was used as the solvent, and the pretreatment was performed by the boiling method. <Color tone> The color tone was measured by a spectrophotometer (device name: CM-700d, manufactured by Konica Minolta Inc.) equipped with an illumination and light-receiving optical system conforming to the geometric condition c of JIS Z 8722, using the method of placing a black calibration box as the background of the measurement sample (black background measurement). The measurement conditions are as follows.

[0066] Light source: D65 light source Field of view angle: 10° Measurement method: SCI The color tone of the powder sample was measured after filling 3.0 g of the powder into a mold with a diameter of 25 mm, performing uniaxial pressure molding at a pressure of 19.6 MPa, then subjecting it to CIP treatment at a pressure of 196 MPa to form a disk with a thickness of 3.0 ± 0.5 mm, and polishing the measurement surface with #800 waterproof abrasive paper by 0.1 mm.

[0067] The color tone of the calcined body sample could be measured after polishing the measurement surface with #800 waterproof abrasive paper by 0.1 mm.

[0068] The sintered body sample was measured after mirror-polishing both sides of the sintered body to a thickness of 1.0 ± 0.1 mm and a surface roughness (Ra) of 0.02 μm or less. <Total light transmittance> The total light transmittance was measured using a haze meter (device name: NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) with a D65 light source in accordance with the method specified in JIS K 7361-1. The measurement sample used was a disk-shaped sintered body with a thickness of 1.0 ± 0.1 mm that had been polished on both sides so that the surface roughness Ra ≤ 0.02 μm.

[0069] Synthesis example <Preparation of calcined body> As a simulated sample of the end material of a dental blank, a calcined body having the same composition and properties as the dental blank was prepared by the following method. Commercially available zirconia powder (synthetic powder; Zpex, Zpex - Yellow, Zpex - Gray, and Zpex - Pink for calcined bodies 1 to 4. Zpex4, Zpex4 - Yellow, Zpex - Gray, and Zpex - Pink for calcined bodies 5 to 8. Zpex - Smile, Zpex - SmileYellow, Zpex - Smile - Gray, and Zpex - Pink for calcined bodies 9 to 12. All are manufactured by Tosoh Corporation) was filled into a 200 mL polypropylene container at the blending ratio [mass%] of the powders shown in Tables 1 to 3, and this was dry - mixed by stirring the container. 26 g of the obtained powder was filled into a mold of 57 mm × 34 mm, uniaxial pressure molding was performed at a pressure of 19.6 MPa, and then a compact was obtained by CIP treatment at a pressure of 196 MPa. The obtained compact was fired under the following conditions to obtain a calcined body.

[0070] Calcination temperature: 1000 °C Temporary firing time: 1 hour Heating rate: 50 °C / hour Temporary firing atmosphere: atmospheric atmosphere Cooling rate: 300 °C / hour The same operation was repeated to produce four each of the temporary fired bodies 1 to 12 shown in Tables 1 to 3. Note that the remainder in the temporary fired body composition in the following table is zirconia.

[0071]

Table 1

[0072]

Table 2

[0073]

Table 3

[0074] The evaluation results of the obtained recycled powder are shown in the following table.

[0075]

Table 4

[0076] Examples 13 to 25 <Manufacture of recycled blanks> 3 g of the recycled powders of Examples 1 to 12 were each filled into a mold with a diameter of 25 mm, uniaxially pressed at a pressure of 19.6 MPa, and then subjected to CIP treatment at a pressure of 196 MPa to obtain a molded body. The obtained molded body was fired under the following conditions to obtain the recycled blanks of Examples 13 to 25.

[0077] Temporary firing temperature: 1000 °C Temporary firing time: 1 hour Heating rate: 50 °C / hour Temporary firing atmosphere: air atmosphere Cooling rate: 300 °C / hour The evaluation results of the obtained recycled blanks are shown in the following table.

[0078]

Table 5

[0079] Furthermore, the obtained temporarily fired body was sintered under the following conditions to obtain a sintered body.

[0080] Sintering method: atmospheric pressure sintering Sintering atmosphere: air atmosphere Holding temperature: 1450 °C (Examples 13 to 16, 21 to 24) 1500 °C (Examples 17 to 20) Holding time: 2 hours The evaluation results of the obtained sintered body are shown in the following table together with the evaluation results of the sintered body obtained by sintering the main calcined bodies obtained in the synthesis examples under the same conditions. The color tone names indicate colors in accordance with the index of Vita Classical Shade.

[0081]

Table 6

[0082] Example 25 <Manufacture of Recycled Blank with Mixed Powder> A mixed powder was obtained in the same manner as in Synthesis Example 1, except that the recycled powders obtained in Examples 5 to 8 and synthetic powders (product names: Zpex4 - Yellow, Zpex - Gray, and Zpex - Pink, all manufactured by Tosoh Corporation) as color - adjusting powders were used, and the mixing ratios shown in the following table were used.

[0083]

Table 7

[0084]

Table 8

[0085] The results are shown in the following table.

[0086]

Table 9

Claims

1. A separating step of separating the scraps, a crushing step of crushing the scraps of dental blanks to obtain a crushed product, and a crushing step of crushing the crushed product to obtain a product having a color tone of L. ＊ is 90 or more and 100 or less, a ＊ is 0 to 1, b ＊ a recovery step of recovering powder having a color tone of 0 or more and 5 or less, ＊ is 90 or more and 100 or less, a ＊ is 0 to 1, b ＊ A method for producing recycled powder, in which scraps are separated into a color tone unit consisting of scraps having a base color tone of 0 to 5 inclusive, and a color tone unit consisting of scraps having a color tone different from the base color tone.

2. 3. The method for producing recycled powder according to claim 1, wherein the pulverization step includes a coarse pulverization step of dry-pulverizing scraps to obtain a coarsely pulverized product, and a particle size adjustment step of wet-pulverizing the coarsely pulverized product.

3. The method for producing recycled powder according to claim 1 or 2, wherein the dental blank scraps are calcined ceramic bodies.

4. The method for producing recycled powder according to claim 1 or 2, wherein the scraps have a structure consisting of one layer.

5. The method for producing recycled powder according to claim 1 or 2, wherein the mill ends have a structure consisting of two or more layers.

6. A method for producing recycled dental blanks using the recycled powder obtained according to claim 1 or 2.

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