Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C13/00—Dental prostheses; Making same
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C13/00—Dental prostheses; Making same
  • A61C13/08—Artificial teeth; Making same
  • A61C13/083—Porcelain or ceramic teeth
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C5/00—Filling or capping teeth
  • A61C5/70—Tooth crowns; Making thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D15/00—Separating processes involving the treatment of liquids with solid sorbents; Apparatus therefor
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G25/00—Compounds of zirconium
  • C01G25/02—Oxides
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/48—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on zirconium or hafnium oxides, zirconates, zircon or hafnates
  • C04B35/486—Fine ceramics

Definitions

• the present invention relates to a zirconia calcined body. More specifically, the present invention relates to a zirconia calcined body that reaches a relative density of 99.0% or more when fired at a high rate of temperature increase of 350°C/min, and that has excellent translucency.
• Zirconia sintered bodies are widely used industrially, and in particular in recent years have been used as dental materials such as dental prostheses.
• these dental prostheses are manufactured by pressing zirconia particles or molding them using a composition containing zirconia particles to produce a zirconia molded body having the desired shape, such as a disk or a rectangular column, which is then calcined to produce a calcined body (mill blank), which is then cut (milled) into the shape of the desired dental prosthesis and further fired.
• Zirconia is a compound that undergoes phase transitions between multiple crystal systems. Therefore, partially stabilized zirconia (PSZ) and fully stabilized zirconia (FSZ) are used in various fields , in which a stabilizer such as yttria (yttrium oxide; Y2O3 ) is dissolved in zirconia to suppress the phase transition.
• a stabilizer such as yttria (yttrium oxide; Y2O3 ) is dissolved in zirconia to suppress the phase transition.
• zirconia materials have been used as frame materials because they are strong but have low translucency.
• dental prostheses are often made entirely from zirconia.
• Patent Document 1 discloses that the density of the finally obtained zirconia sintered body can be improved by setting the sintering shrinkage rate ( ⁇ / ⁇ T: g/cm 3 ⁇ ° C.) to 0.0120 or more and 0.0135 or less in the region of relative density from 70% to 90% when sintered at 5° C./min.
• Patent Document 1 makes no mention of the change in density of the sintered body when the temperature is increased at a rate of heating faster than 5° C./min.
• the inventors found that when the invention according to Patent Document 1 is heated at a high rate (350° C./min) and held for a certain period of time, the density of the sintered body does not reach a relative density of 99.0% or more, and light translucency is not achieved when sintered at 5° C./min. Therefore, it was found that there is room for improvement in the invention according to Patent Document 1 in order to further shorten the time.
• the object of the present invention is to provide a zirconia calcined body that reaches a relative density of 99.0% or more when fired at a high rate of temperature increase of 350°C/min, and that has excellent translucency when obtained as a zirconia sintered body.
• the inventors have found that, when the amount of change in density between the calcined body at the upper limit temperature and the lower limit temperature of the nth interval (n is an integer of 1 or more) is taken as ⁇ n and the amount of change in temperature is taken as ⁇ T, in a temperature range of 1200° C.
• a zirconia calcined body having a transition point at which the maximum value of the amount of change (( ⁇ n +1 / ⁇ T) - ( ⁇ n / ⁇ T)) between the density change rate in the nth interval and the density change rate in the n+1th interval is 0.010 or more, is found to have excellent translucency, even when subjected to high-speed sintering with a high temperature rise rate of 350° C./min., and have conducted further research based on this finding, which has led to the completion of the present invention.
• the present invention includes the following inventions.
• [1] Contains zirconia and yttria, Six target temperatures are set at 50°C intervals from 1150°C to 1400°C. Six samples were prepared by heating the sample from a temperature range of 400° C. or less at a heating rate of 350° C./min to six different target temperatures, then holding the sample at each target temperature for 10 minutes and then lowering the temperature to 25° C. A temperature interval of target temperatures from 1150°C to 1400°C is divided into intervals every 50°C, and the six types of samples are used.
• the calcined zirconia body When the amount of change in density between the calcined body at the upper limit temperature and the lower limit temperature of an nth interval (n is an integer of 1 or more) is ⁇ n , and the amount of change in temperature is ⁇ T, the calcined zirconia body has a displacement point in the temperature range of 1200°C or more and 1350°C or less where the maximum value of the amount of change (( ⁇ n + 1 / ⁇ T) - ( ⁇ n / ⁇ T)) between the density change rate in the nth interval and the density change rate in the n+1th interval is 0.010 or more.
• the zirconia calcined body of the present invention a relative density of 99.0% or more can be achieved by rapid sintering with a rapid temperature increase of 350° C./min, and the obtained zirconia sintered body has excellent translucency. Furthermore, according to the present invention, a zirconia calcined body having excellent translucency can be provided, even when the holding time at the maximum sintering temperature is 2 minutes.
• the zirconia calcined body of the present invention contains zirconia and yttria, Six target temperatures are set at 50°C intervals from 1150°C to 1400°C. Six samples were prepared by heating the sample from a temperature range of 400° C. or less at a heating rate of 350° C./min to six different target temperatures, then holding the sample at each target temperature for 10 minutes and then lowering the temperature to 25° C. The temperature interval of the target temperature from 1150°C to 1400°C is divided into intervals of 50°C each, and the six types of samples are used.
• the amount of change in density between the calcined body at the upper limit temperature and the lower limit temperature of the nth interval (n represents an integer of 1 or more) is ⁇ n , and the amount of change in temperature is ⁇ T, in the temperature range of 1200°C or more and 1350°C or less, there is a transition point where the maximum value of the amount of change (( ⁇ n + 1 / ⁇ T) - ( ⁇ n / ⁇ T)) between the density change rate ⁇ n / ⁇ T in the nth interval and the density change rate ⁇ n+1 / ⁇ T in the n+1th interval is 0.010 or more.
• zirconia composition refers to a composition containing zirconia powder and a stabilizer powder.
• molded body refers to a body that has not yet reached a semi-sintered state (calcined state) or a sintered state. In other words, the molded body is distinguished from the calcined body and the sintered body in that the molded body is a body that has been molded and then not sintered.
• the term "calcined zirconia body” refers to a body in a semi-sintered state in which zirconia particles are necked (adhered) to each other and are not completely sintered.
• zirconia sintered body refers to a body in a sintered state in which zirconia particles are completely sintered.
• zirconia particles are solidified by sintering, and the relative density increases and densification progresses with sintering, so that the zirconia sintered body is in a completely sintered state with a relative density of 95% or more.
• zirconia means zirconium (IV) oxide ( ZrO2 ), and ZrO2 particles contain a small amount of HfO2 (0.5 mass% or more and 3 mass% or less) relative to the amount of ZrO2.
• zirconia zirconia particles
• zirconia powder mean those containing ZrO2 and HfO2 .
• particles and powders in which a stabilizer is dissolved in zirconia are also included in “zirconia particles” and “zirconia powder”, respectively.
• normal pressure means standard atmospheric pressure (1 atm).
• the term “theoretical density” refers to a density calculated from the volume of a unit cell of a crystal and the sum of the masses contained in the unit cell.
• a "transition point” refers to a point at which the difference (amount of change) in the rate of density change between adjacent sections in 50° C. intervals in a specific temperature range described separately becomes a value other than 0.
• the temperature at the transition point between the nth section and the n+1th section refers to the upper limit temperature of the nth section at which (( ⁇ n+1 / ⁇ T) - ( ⁇ n / ⁇ T)) becomes a value other than 0.
• the upper and lower limits of numerical ranges can be appropriately combined.
• the amount of change (( ⁇ n+1 / ⁇ T)-( ⁇ n / ⁇ T)) is preferably 0.050 or less, more preferably 0.045 or less, and even more preferably 0.040 or less, since a zirconia sintered body having superior light transmissivity can be obtained in high-speed sintering with a high temperature rise rate of 350° C./min.
• the method for measuring the density of the calcined body and the method for calculating the density change are as described in the Examples below.
• a zirconia sintered body that reaches a relative density of 99.0% or more and has excellent translucency during rapid sintering with a rapid heating rate of 350°C/min is not clear, but is presumed to be as follows.
• rapid sintering including a rapid temperature rise of 350° C./min hereinafter also simply referred to as “rapid sintering”
• a sintered body having a low relative density is expected to have pores inside.
• the inventors have proposed that, in the rapid sintering, by having a transition point where the maximum value of the change (( ⁇ n+1 / ⁇ T) - ( ⁇ n / ⁇ T)) is 0.010 or more in the temperature range of 1200°C or higher and 1350°C or lower, rapid grain growth is suppressed in the temperature range before the transition point, thereby suppressing the incorporation of vacancies in the low temperature range of 1200°C or higher and 1350°C or lower, and that in the high temperature range above 1350°C, when the zirconia raw material undergoes a crystal phase transition (for example, a phase transition from monoclinic to tetragonal or cubic), the density difference between the phases has the effect of promoting the expulsion of voids. It is believed that this makes it possible to obtain a sintered body that has a relative density of 99.0% or more even during high-speed sintering and has excellent light transmittance.
• the density of the calcined body at the temperature (°C) of the transition point is preferably 4.5 g/cm3 or less , more preferably 4.2 g/cm3 or less, and even more preferably 4.1 g/cm3 or less , in order to further promote the expulsion of voids in the high temperature region.
• the density of the calcined body at the transition temperature (°C) is preferably 3.0 g/cm or more, more preferably 3.1 g/cm or more , and even more preferably 3.2 g/cm or more , in order to reach a relative density of 99.0% or more during high-speed sintering.
• the zirconia calcined body contains yttria (Y 2 O 3 ) as a stabilizer capable of suppressing the phase transition of zirconia.
• the yttria content in the zirconia calcined body is preferably 2.5 mol% or more, more preferably 3.0 mol% or more, even more preferably 3.5 mol% or more, and particularly preferably 4.0 mol% or more, based on the total moles of zirconia ( zirconium (IV) oxide; ZrO2) and stabilizer.
• a content of 2.5 mol% or more is preferable in that the crystal system contained in the sintered body contains more cubic crystals, thereby improving translucency.
• the content of the stabilizer is preferably 10 mol % or less, more preferably 9.0 mol % or less, further preferably 8.5 mol % or less, and particularly preferably 8 mol % or less. When it is 10 mol % or less, it is preferable from the viewpoint of preventing a decrease in strength.
• the stabilizer capable of suppressing the phase transition of zirconia may be yttria alone, or may further contain a stabilizer other than yttria capable of suppressing the phase transition of zirconia.
• stabilizers capable of suppressing the phase transition of zirconia other than yttria include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide ( Y2O3 ), cerium oxide ( CeO2 ), scandium oxide (Sc2O3), niobium oxide (Nb2O5 ) , lanthanum oxide ( La2O3 ) , erbium oxide ( Er2O3 ), praseodymium oxide ( Pr2O3 , Pr6O11 ) , samarium oxide ( Sm2O3 ) , europium oxide ( Eu2O3 ), thulium oxide ( Tm2O3 ), gallium oxide ( Ga2O3 ) , indium oxide (In2O3 ) , and ytterbium oxide ( Yb2O3 ) .
• the stabilizers may be used alone or in combination of two or more.
• the zirconia calcined body of the present invention may contain additives other than zirconia and stabilizers, such as colorants (including pigments, composite pigments, and fluorescent agents), alumina ( Al2O3 ), titanium oxide ( TiO2 ), and silica ( SiO2 ), as long as the effects of the present invention are achieved.
• colorants including pigments, composite pigments, and fluorescent agents
• alumina Al2O3
• titanium oxide TiO2
• SiO2 silica
• the pigment examples include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically, NiO, Cr2O3 , etc. ) (excluding Y2O3 and CeO2 ).
• An oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb is preferred, and an oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb is more preferred.
• the zirconia calcined body of the present invention may not contain erbium oxide (Er 2 O 3 ).
• Examples of the composite pigment include (Zr, V) O 2 , Fe (Fe, Cr) 2 O 4 , (Ni, Co, Fe) (Fe, Cr) 2 O 4. ZrSiO 4 , (Co, Zn) Al 2 O 4 , etc.
• Examples of the fluorescent agent include Y 2 SiO 5 : Ce, Y 2 SiO 5 : Tb, (Y, Gd, Eu) BO 3 , Y 2 O 3 : Eu, YAG: Ce, ZnGa 2 O 4 : Zn, BaMgAl 10 O 17 : Eu, etc.
• the zirconia calcined body of the present invention may contain a fluorescent agent.
• the zirconia sintered body has fluorescence.
• the fluorescent agent may contain a metal element. Examples of the metal element include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm.
• the fluorescent agent may contain one of these metal elements alone, or may contain two or more of them. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, and Bi and Eu are more preferred.
• Examples of the fluorescent agent include oxides, hydroxides, acetates, and nitrates of the above-mentioned metal elements.
• the fluorescent agent may also be Y2SiO5 :Ce, Y2SiO5 :Tb, ( Y, Gd ,Eu ) BO3 , Y2O3 :Eu, YAG:Ce, ZnGa2O4 : Zn , BaMgAl10O17 :Eu, etc.
• the content of the fluorescent agent in the zirconia calcined body is not particularly limited and can be adjusted as appropriate depending on the type of fluorescent agent or the application of the zirconia sintered body. From the viewpoint of favorable use as a dental prosthesis, the content of the fluorescent agent, calculated as the oxide of the metal element contained in the fluorescent agent, relative to 100 mass% zirconia contained in the zirconia calcined body is preferably 0.001 mass% or more, more preferably 0.005 mass% or more, and even more preferably 0.01 mass% or more.
• the content of the fluorescent agent is not limited as long as suitable fluorescence is exhibited in terms of oxide of the metal element contained in the fluorescent agent, but may be 1 mass % or less, 0.5 mass % or less, or 0.1 mass % or less.
• the fluorescence is not inferior to that of human natural teeth, and when the content is equal to or less than the upper limit, the decrease in translucency and mechanical strength can be suppressed.
• the bending strength of the zirconia calcined body of the present invention is preferably 15 MPa or more in order to ensure strength that allows mechanical processing in the calcined body state.
• the bending strength of the zirconia calcined body is preferably 70 MPa or less, and more preferably 60 MPa or less, in order to facilitate mechanical processing in the calcined body state.
• the bending strength can be measured in accordance with ISO 6872:2015 (Dentistry-Ceramic materials), but only the size of the test specimen is changed, and measurements are performed using test specimens measuring 5 mm x 10 mm x 50 mm.
• the faces and C-faces of the test specimen (surfaces where the corners of the test specimen are chamfered at a 45° angle) are finished in the longitudinal direction with 600 grit sandpaper.
• the test specimen is positioned so that the widest face faces vertically (load direction).
• the support distance (span) is 30 mm
• the crosshead speed is 0.5 mm/min.
• the density of the zirconia calcined body of the present invention is preferably 2.7 g/cm 3 or more, more preferably 3.0 g/cm 3 or more, and even more preferably 3.2 g/cm 3 or more.
• the density of the zirconia calcined body is preferably 4.0 g/cm3 or less , more preferably 3.8 g/ cm3 or less, and even more preferably 3.6 g/cm3 or less . When the density is within the above range, molding can be easily performed.
• the density of the zirconia calcined body can be calculated by (mass of the zirconia calcined body) / (volume of the zirconia calcined body).
• the method for producing the zirconia calcined body is not particularly limited as long as it is a method that can obtain a desired displacement point.
• a method for producing the zirconia calcined body a zirconia composition is subjected to a pulverization treatment, and a molded body obtained by molding the pulverized zirconia composition is fired (calcined) to an extent that zirconia particles are not sintered together, and the zirconia calcined body of the present invention can be produced by applying excess energy to the pulverization treatment under predetermined conditions compared to the conventional technology.
• the zirconia composition is produced by mixing the raw powders, zirconia powder and yttria powder. There are no particular limitations on the mixing method, and known methods and devices can be used.
• the zirconia particles constituting the zirconia powder and the yttria particles constituting the yttria powder can be prepared, for example, by a breakdown process in which coarse particles are pulverized or crushed into fine powder, or a building-up process in which atoms or ions are synthesized through a nucleation and growth process.
• the zirconia constituting the zirconia powder is not particularly limited, and any of tetragonal zirconia, monoclinic zirconia, and cubic zirconia can be used. In the zirconia powder, these may be used alone or in combination of two or more.
• zirconia powder commercially available zirconia particles may be used, or a commercially available powder may be used after being pulverized in a known pulverizing and mixing device (such as a ball mill).
• a known pulverizing and mixing device such as a ball mill.
• yttria powder commercially available yttria particles may be used, or a commercially available powder may be used after being pulverized in a known pulverizing and mixing device (such as a ball mill).
• zirconia powders include, for example, zirconia powders (product names "Zpex (registered trademark)” (Y 2 O 3 content: 3 mol%), “Zpex (registered trademark) 4" (Y 2 O 3 content: 4 mol%), “Zpex (registered trademark) Smile (registered trademark)” (Y 2 O 3 content: 5.5 mol%), "TZ-3Y” (Y 2 O 3 content: 3 mol%), “TZ-3YS” (Y 2 O 3 content: 3 mol%), “TZ-4YS” (Y 2 O 3 content: 4 mol%), "TZ-6Y” (Y 2 O 3 content: 6 mol%), “TZ-6YS” (Y 2 O 3 content: 6 mol%), and “TZ-8YS” (Y 2 O 3 content: 5.5 mol%)).
• the zirconia composition is then further pulverized under predetermined conditions to obtain the desired transition point.
• a zirconia composition containing zirconia and yttria is subjected to a grinding treatment under predetermined conditions, the mixing of zirconia particles and yttria particles is promoted, resulting in a uniform composition distribution, thereby limiting the temperature region where a phase transition of zirconia occurs, and the desired transition point not seen in conventional products can be obtained. Rapid grain growth is suppressed in the temperature region before the transition point, thereby suppressing the incorporation of vacancies in the low temperature region of 1200°C or higher and 1350°C or lower.
• the zirconia raw material undergoes a crystal phase transition (for example, a phase transition from monoclinic to tetragonal or cubic), the density difference between the phases promotes the expulsion of voids, and it is presumed that excellent translucency can be exhibited even when the holding time at the maximum sintering temperature is 2 minutes.
• a crystal phase transition for example, a phase transition from monoclinic to tetragonal or cubic
• the following method is preferably used. (i) grinding media with a diameter of less than 1 mm is used and the grinding time is 10 minutes or more, or (ii) grinding media with a diameter of 1 mm or more is used and the grinding time is more than 40 hours.
• the grinding media diameter is preferably 0.1 to 0.5 mm, since the desired displacement point is easily obtained by using grinding media with a fine diameter.
• Commercially available grinding media having a diameter of less than 1 mm may be used.
• An example of a grinding device using grinding media with a diameter of less than 1 mm is a bead mill.
• the grinding time is not particularly limited, but since yttria particles are easily ground to a very small size, it is preferably 10 minutes or more, more preferably 12 minutes or more, even more preferably 15 minutes or more, and particularly preferably 20 minutes or more.
• the grinding time is preferably 20 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and particularly preferably 2 hours or less.
• the grinding time means the residence time of the slurry in the vessel (grinding chamber).
• the grinding media diameter is preferably 1.5 mm or more, and more preferably 2.0 mm or more, since the grinding time is long and the amount of energy required for the grinding process can be increased in combination with the grinding time.
• Commercially available grinding media having a diameter of 1 mm or more may be used.
• An example of a grinding device using grinding media with a diameter of 1 mm or more is a ball mill.
• the grinding time is not particularly limited, but is preferably more than 40 hours, more preferably 55 hours or more, and even more preferably 80 hours or more, particularly preferably 100 hours or more, because the mixing of the zirconia particles and the yttria particles is promoted by applying excess energy compared to conventional techniques when grinding the zirconia composition, resulting in a uniform composition distribution and making it easier to obtain the desired displacement point.
• the grinding process time is preferably 1000 hours or less, more preferably 800 hours or less, even more preferably 500 hours or less, and particularly preferably 300 hours or less.
• the zirconia composition may be in the form of granules, a slurry, and the like.
• the slurry can be produced by mixing the mixed powder obtained by the pulverization treatment with a solvent (preferably water).
• the average particle size of the zirconia composition after the pulverization process is preferably 0.2 ⁇ m or less, since the sintered body has excellent mechanical strength and translucency.
• the average particle size of zirconia particles and yttria particles can be measured by a dynamic light scattering particle size distribution measurement method. For example, using a dynamic light scattering particle size distribution measurement device manufactured by Horiba Ltd. (product name "SZ-100V2”), a slurry diluted with water to about 0.1% by mass is irradiated with ultrasonic waves for 30 minutes, and then the average particle size can be measured on a volume basis while applying ultrasonic waves.
• a dynamic light scattering particle size distribution measurement device manufactured by Horiba Ltd. product name "SZ-100V2”
• the zirconia composition may further contain additives such as a binder, a dispersant, an emulsifier, an antifoaming agent, a pH adjuster, a lubricant, a light transmittance adjuster, etc.
• additives may be used alone or in combination of two or more kinds.
• the binder include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.
• the binder content in the zirconia composition of the present invention is preferably 10 mass% or less, more preferably 7 mass% or less, and even more preferably 5 mass% or less, relative to 100 mass% of zirconia.
• Plasticizers include, for example, polyethylene glycol, glycerin, propylene glycol, dibutyl phthalate, etc.
• Dispersants include, for example, ammonium polycarboxylate (e.g., triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic acid ester copolymer, polyacrylic acid, bentonite, carboxymethylcellulose, anionic surfactants (e.g., polyoxyethylene alkyl ether phosphate esters such as polyoxyethylene lauryl ether phosphate esters), nonionic surfactants, oleic glyceride, amine salt surfactants, oligosaccharide alcohols, and stearic acid.
• ammonium polycarboxylate e.g., triammonium citrate
• ammonium polyacrylate e.g., acrylic copolymer resin
• acrylic acid ester copolymer acrylic acid ester copolymer
• polyacrylic acid bentonite
• carboxymethylcellulose e.g., anionic surfactants (e.g., polyoxyethylene alkyl ether phosphate esters
• Emulsifiers include, for example, alkyl ethers, phenyl ethers, and sorbitan derivatives.
• defoaming agents examples include alcohol, polyether, polyethylene glycol, silicone, wax, etc.
• pH adjusters include ammonia and ammonium salts (including ammonium hydroxide such as tetramethylammonium hydroxide).
• Lubricants include, for example, polyoxyethylene alkyl ethers and waxes.
• Examples of the light transmittance adjusting agent include aluminum oxide (Al 2 O 3 ), titanium oxide (TiO 2 ), silicon dioxide (SiO 2 ), zircon, lithium silicate, and lithium disilicate.
• the BET specific surface area of the particles constituting the zirconia composition is preferably 7.0 m 2 /g or more, more preferably 7.5 m 2 /g or more, and even more preferably 8.0 m 2 /g or more, when measured in accordance with JIS Z 8830:2013. When it is 7.0 m 2 / g or more, it is possible to suppress the sintered body from becoming cloudy when sintered.
• the BET specific surface area is preferably 50 m 2 /g or less, more preferably 45 m 2 /g or less, and even more preferably 40 m 2 /g or less. When it is 50 m 2 /g or less, it is less susceptible to the effect of temperature unevenness in the sintering furnace.
• the BET specific surface area can be measured using a commercially available product such as a fully automatic specific surface area measuring device (product name "Macsorb (registered trademark) HM model-1200", BET flow method (single point method/multiple point method), manufactured by Mountec Co., Ltd.).
• a fully automatic specific surface area measuring device product name "Macsorb (registered trademark) HM model-1200", BET flow method (single point method/multiple point method), manufactured by Mountec Co., Ltd.
• the BET specific surface area can be measured by the BET flow method (single point method) using the fully automatic specific surface area measuring device.
• the "BET specific surface area” referred to here is a specific surface area measured without distinguishing between primary particles and secondary particles.
• a molding process is performed to mold the zirconia composition after the crushing process to produce a molded body.
• the molded body is obtained by applying an external force to the zirconia composition using a known method.
• the molding method is not particularly limited, and for example, the following methods can be used. (a) slip casting a slurry containing the zirconia composition after the pulverization treatment; (b) gel-casting a slurry containing the zirconia composition after the pulverization treatment; (c) press-molding the zirconia composition after the pulverization treatment; (d) forming a zirconia composition containing zirconia particles, yttria particles, and a resin; (e) a step of polymerizing a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer; and (f) a step of layer-by-layer manufacturing of granules containing zirconia particles and yttria particles.
• the specific method of slip casting is not particularly limited.
• a method can be employed in which the slurry is poured into a mold and then dried.
• the content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, because this makes it easy to pour the slurry into a mold, prevents a long drying time from being required, and enables the number of times the mold can be used to be increased.
• the slurry may be poured into the mold under normal pressure, but it is preferable to pour the slurry under pressurized conditions from the viewpoint of production efficiency.
• the specific method of gel casting is not particularly limited.
• a method can be employed in which the slurry is gelled in a mold to obtain a shaped wet body, and then this is dried.
• the content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, because this can prevent drying from taking a long time and can also suppress the occurrence of cracks during drying.
• Gelation may be achieved, for example, by adding a gelling agent, or by adding a polymerizable monomer and then polymerizing it.
• gelling agent there is no limit to the type of gelling agent, and for example, a water-soluble gelling agent can be used. Specifically, agarose, gelatin, etc. can be preferably used. A single type of gelling agent may be used alone, or two or more types may be used in combination.
• the amount of gelling agent used is not particularly limited as long as problems such as cracks do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less based on the mass of the slurry after the gelling agent is mixed.
• the type of polymerizable monomer is not particularly limited, and examples thereof include (meth)acrylate monomers such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; and (meth)acrylamide monomers such as N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N,N-bis(2-hydroxyethyl)(meth)acrylamide.
• (meth)acrylate monomers such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-
• One type of polymerizable monomer may be used alone, or two or more types may be used in combination.
• the amount of the polymerizable monomer used is not particularly limited as long as problems such as cracks do not occur during sintering, but can be 10 mass % or less, 5 mass % or less, or 1 mass % or less, based on the mass of the slurry after the polymerizable monomer is mixed.
• the polymerization is preferably performed using a polymerization initiator.
• a polymerization initiator There are no particular restrictions on the type of polymerization initiator, but photopolymerization initiators are particularly preferred.
• the photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used for dental purposes are particularly preferred.
• photopolymerization initiators include (bis)acylphosphine oxides (including salts), thioxanthones (including salts such as quaternary ammonium salts), ketals, ⁇ -diketones, coumarins, anthraquinones, benzoin alkyl ether compounds, and ⁇ -aminoketone compounds.
• the photopolymerization initiator may be used alone or in combination of two or more.
• polymerization (gelation) to be performed in both the ultraviolet region (including the near ultraviolet region) and the visible light region, and in particular, polymerization (gelation) can be sufficiently performed using any light source, such as lasers such as Ar lasers and He-Cd lasers; halogen lamps, xenon lamps, metal halide lamps, light-emitting diodes (LEDs), mercury lamps, fluorescent lamps, and other lighting.
• lasers such as Ar lasers and He-Cd lasers
• drying method used to dry the shaped wet body there are no particular limitations on the drying method used to dry the shaped wet body, and examples include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. Only one of these may be used, or two or more may be used. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred, as they are able to suppress the occurrence of cracks during drying.
• molds used in slip casting and gel casting there are no particular limitations on the type of mold used in slip casting and gel casting; for example, porous molds made of plaster, resin, ceramics, etc., and non-porous molds made of metal, resin, etc. can be used.
• the specific method of press molding is not particularly limited, and the press molding can be performed using a known press molding machine.
• a specific example of the press molding method is uniaxial pressing.
• multi-stage molding may be performed.
• a CIP (Cold Isostatic Pressing) process may be further performed.
• the shape of the molded body is not particularly limited, and may be a disk shape, a rectangular parallelepiped shape, or a dental product shape (for example, a dental crown shape).
• the molded body may be, for example, a columnar zirconia molded body obtained by filling a die with a zirconia composition (for example, granules) and compacting it with a uniaxial press.
• the surface pressure in the press molding when producing the zirconia molded body is preferably 30 to 200 MPa.
• the surface pressure in the press is 30 MPa or more, the shape retention of the zirconia molded body is excellent, and when it is 200 MPa or less, the density of the zirconia molded body does not increase too much, making it easier to prevent hardening.
• the above-mentioned molded body also includes a molded body densified by a high-temperature pressure treatment such as a CIP (Cold Isostatic Pressing) treatment.
• a high-temperature pressure treatment such as a CIP (Cold Isostatic Pressing) treatment.
• the pressure of the CIP is preferably 30 to 200 MPa.
• a zirconia molded body is produced by a method having a step of molding a zirconia composition containing zirconia particles, yttria particles, and a resin
• the specific method for molding the zirconia composition is not particularly limited, and for example, injection molding, cast molding, extrusion molding, etc. can be used.
• a method of molding the composition by a fusion melt molding (FDM), an inkjet method, a powder/binder lamination method, or other additive manufacturing methods (3D printing, etc.) may be used.
• FDM fusion melt molding
• injection molding and cast molding are preferred, and injection molding is more preferred.
• the type of the resin but it is preferable to use the binders described above.
• the stereolithography method (SLA) of (b) is preferred.
• SLA stereolithography method
• a shape corresponding to a desired shape of the finally obtained zirconia sintered body can be imparted to the zirconia molded body at the time of production. Therefore, the stereolithography may be particularly suitable in cases where the zirconia sintered body is used as a dental material such as a dental prosthesis.
• the type of polymerizable monomer is not particularly limited, and may be any of monofunctional polymerizable monomers such as monofunctional (meth)acrylates and monofunctional (meth)acrylamides, and polyfunctional polymerizable monomers such as bifunctional aromatic compounds, bifunctional aliphatic compounds, and trifunctional or higher compounds.
• the polymerizable monomers may be used alone or in combination of two or more. Among these, it is preferable to use a polyfunctional polymerizable monomer, particularly when a stereolithography method is employed.
• the oligomer is not particularly limited as long as it is a compound in which two or more of the above polymerizable monomers are bonded and has polymerizability.
• Examples of monofunctional (meth)acrylates include (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and sec-butyl (meth)acrylate.
• hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)
• Examples of monofunctional (meth)acrylamides include (meth)acrylamide, N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-di-n-propyl(meth)acrylamide, N,N-di-n-butyl(meth)acrylamide, N,N-di-n-hexyl(meth)acrylamide, N,N-di-n-octyl(meth)acrylamide, N,N-di-2-ethylhexyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and N,N-bis(2-hydroxyethyl)(meth)acrylamide.
• (meth)acrylamide is preferred because of its excellent polymerizability, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.
• bifunctional aromatic compounds include 2,2-bis((meth)acryloyloxyphenyl)propane, 2,2-bis[4-(2-hydroxy-3-acryloyloxy-2-hydroxypropoxy)phenyl]propane, 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (commonly known as "Bis-GMA"), 2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane, 2 , 2-bis(4-(meth)acryloyloxy
• Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred due to their excellent polymerizability and the mechanical strength of the resulting zirconia molded body.
• 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average number of moles of ethoxy groups added: 2.6, commonly known as "D-2.6E”) is preferred.
• bifunctional aliphatic compounds include glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate,
• (meth)acrylates include 1,6-hexanediol di(meth)acrylate, 2-ethyl-1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,2-bis(3-methacryloyloxy-2-
• trifunctional or higher compounds examples include (meth)acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacryloyloxy-2,2,6,6-tetra(meth)acryloyloxymethyl-4-oxaheptane.
• (meth)acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth
• N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetramethacrylate and 1,7-diacryloyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxaheptane are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded body.
• the polymerization of the composition is preferably carried out using a polymerization initiator, and the composition preferably further contains a polymerization initiator.
• a polymerization initiator There are no particular limitations on the type of polymerization initiator, but photopolymerization initiators are particularly preferred.
• the photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred. Specific examples of photopolymerization initiators are the same as those mentioned above in the explanation of gel casting.
• stereolithography When manufacturing a zirconia molded body by stereolithography using a zirconia composition, there are no particular limitations on the specific method of stereolithography, and any known method can be appropriately adopted for stereolithography. For example, a method can be adopted in which a stereolithography device is used to photopolymerize a liquid composition with ultraviolet light, a laser, or the like, thereby sequentially forming layers having the desired shape to obtain the desired zirconia molded body.
• the zirconia molded body may be subjected to a humidification treatment and then a CIP treatment.
• a humidification treatment When press molding is performed, the powder containing zirconia particles before press molding may be subjected to a humidification treatment, and then press molding may be performed.
• the humidification treatment may be performed by any known method without any restrictions, and may be performed by spraying water with a sprayer or using a hygrostat or thermo-hygrostat.
• the moisture increase amount due to the humidification treatment depends on the average particle size of the contained zirconia particles, the average particle size of the stabilizer particles, etc., but is preferably more than 2 mass% with respect to the mass of the pre-wet powder (powder before humidification treatment) and the molded body, more preferably more than 3 mass%, even more preferably more than 4 mass%, particularly preferably more than 5 mass%, and is preferably 15 mass% or less, more preferably 13 mass% or less, and even more preferably 11 mass% or less.
• the moisture increase amount due to the humidification treatment can be calculated as a percentage by dividing the value obtained by subtracting the mass of the pre-wet powder and the molded body from the mass of the wet powder (powder after humidification treatment) and the molded body by the mass of the pre-wet powder and the molded body.
• the pressure of the CIP treatment is similar to that described above in the description of press molding.
• Step of Layer-by-Layer Manufacturing of Granules Containing Zirconia Particles and Yttria Particles there is no particular limitation on the specific method.
• a method of forming a slurry and then drying it with a spray dryer to form granules can be adopted, and the obtained granules can be used for powder layer-by-layer manufacturing.
• the powder additive manufacturing method is not particularly limited, but examples include a powder bed method, an SLS method (selective laser sintering method), an SLM method (selective laser melting method), an electron beam method, an arc discharge method, a binder jet method, etc.
• it is preferable not to use organic substances even in the granule manufacturing stage For methods in which it is better not to use organic substances during additive manufacturing, it is preferable not to use organic substances even in the granule manufacturing stage.
• the zirconia calcined body of the present invention is obtained by a calcination process in which the molded body is calcined.
• the calcination temperature (maximum calcination temperature) in the calcination step is preferably 800° C. or higher, more preferably 850° C. or higher, even more preferably 900° C. or higher, and particularly preferably 950° C. or higher, in terms of ensuring a semi-sintered state using the above-mentioned specific zirconia composition.
• the calcination temperature is preferably 1200° C. or less, more preferably 1150° C. or less, further preferably 1100° C. or less, and particularly preferably 1050° C. or less. That is, in the method for producing the zirconia calcined body of the present invention, the temperature is preferably 800°C to 1200°C.
• the rate of temperature rise up to the maximum calcination temperature when the zirconia molded body of the present invention is calcined is not particularly limited, but is preferably 0.1° C./min or more, more preferably 0.2° C./min or more, and even more preferably 0.5° C./min or more, and is preferably 50° C./min or less, more preferably 30° C./min or less, and even more preferably 20° C./min or less.
• productivity is improved.
• the density of the zirconia sintered body is preferably 5.80 g/cm 3 or more, more preferably 5.82 g/cm 3 or more, and even more preferably 5.87 g/cm 3 or more, in view of improving the translucency since the higher the density, the fewer the internal voids and the less likely light scattering occurs. It is particularly preferable that the zirconia sintered body does not substantially contain voids.
• the content of zirconia and stabilizer in the zirconia sintered body is the same as the content in the composition before the sintered body is produced and/or in the calcined body.
• the biaxial bending strength is preferably 800 MPa or more, more preferably 820 MPa or more, and even more preferably 840 MPa or more.
• Biaxial bending strength can be measured in accordance with ISO 6872:2015.
• the method for producing the zirconia sintered body of the present invention includes a method for producing a zirconia sintered body, in which the above-mentioned zirconia calcined body is fired.
• a preferred production method includes a step of firing the above-mentioned zirconia calcined body under normal pressure at 1350° C. to 1700° C.
• the manufacturing method of the present invention makes it possible to easily manufacture a zirconia sintered body having excellent translucency even after sintering for a short period of time, in which the holding time at the maximum sintering temperature is 10 minutes or less (for example, 2 minutes).
• the maximum sintering temperature is preferably set at a condition that maximizes the translucency of the zirconia sintered body.
• the maximum sintering temperature is preferably more than 1200° C., more preferably 1250° C. or more, and even more preferably 1300° C. or more.
• the maximum sintering temperature is preferably 1700° C. or less, more preferably 1650° C. or less, and even more preferably 1600° C. or less.
• the sintering can be sufficiently advanced and a dense sintered body can be easily obtained. Also, by setting the maximum sintering temperature to the above upper limit or lower, the deactivation of the fluorescent agent can be suppressed.
• the holding time at the maximum sintering temperature is preferably 10 minutes or less, more preferably 5 minutes or less, even more preferably 3 minutes or less, and particularly preferably 2 minutes or less.
• the retention time is preferably 30 seconds or more, more preferably 45 seconds or more, and even more preferably 1 minute or more.
• the rate at which the temperature is lowered during the firing process is preferably set so as to shorten the time required for the firing process.
• the rate at which the temperature is increased can be set so as to reach the maximum sintering temperature in the shortest time possible, depending on the performance of the firing furnace.
• the rate at which the temperature is lowered from the maximum sintering temperature is preferably set so as to prevent defects such as cracks from occurring in the sintered body. For example, after heating is completed, the sintered body can be allowed to cool at room temperature.
• the calcination and firing in the present invention can be carried out using a firing furnace.
• a firing furnace There is no particular limitation on the type of firing furnace, and for example, an electric furnace or a degreasing furnace generally used in industry can be used.
• a commercially available dental baking oven for example, "Sintra CS" (Shenpaz) may be used.
• the zirconia sintered body of the present invention can be produced without the HIP treatment.
• the HIP treatment can be performed after sintering under normal pressure to further improve the translucency and mechanical strength.
• the sintered body obtained by sintering at the above-mentioned maximum sintering temperature (the sintered body before the HIP treatment) is referred to as the "primary sintered body", and the sintered body after the HIP treatment is referred to as the "HIP-treated sintered body”.
• the HIP treatment can be carried out using a known hot isostatic press (HIP) device.
• HIP hot isostatic press
• the HIP pressure is not particularly limited, and since a dense sintered body with high strength can be obtained, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more.
• the upper limit of the HIP pressure is not particularly limited, but can be, for example, 400 MPa or less, 300 MPa or less, or even 200 MPa or less.
• the heating rate is not particularly limited, and is preferably 0.1°C/min or more, more preferably 0.2°C/min or more, and even more preferably 0.5°C/min or more.
• the heating rate is preferably 50°C/min or less, more preferably 30°C/min or less, and even more preferably 20°C/min or less. Having a heating rate equal to or greater than the above lower limit improves productivity.
• the HIP time (the time during which the maximum pressure and temperature are maintained) is not particularly limited, and since a dense zirconia sintered body with high strength can be obtained, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. In addition, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.
• the pressure medium is not particularly limited, and from the viewpoint of low influence on zirconia, the pressure medium can be at least one selected from the group consisting of oxygen, oxygen containing 3% hydrogen, air, and an inert gas (e.g., nitrogen, argon, etc.).
• the oxygen concentration is not particularly limited, but can be, for example, more than 0% and 20% or less.
• at least one inert gas such as nitrogen, argon, etc.
• the HIP treatment is performed in a reducing atmosphere, such as by using an inert gas, blackening may occur due to oxygen defects.
• a step of heat treatment at 1650° C. or less in air or in an oxygen-rich atmosphere (hereinafter also referred to as "tempering treatment") after the HIP treatment step, and it is more preferable to perform the heat treatment in an oxygen-rich atmosphere from the viewpoint of efficient heat treatment.
• An oxygen-rich atmosphere means that the oxygen concentration is greater than the oxygen concentration in air.
• the oxygen-rich atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and not more than 100%, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%.
• the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, blackening may occur due to oxygen defects.
• a step of heat treatment in air or in an oxygen-rich atmosphere at 1650° C. or less after the HIP treatment step (hereinafter also referred to as "tempering treatment").
• the heat treatment in an oxygen-rich atmosphere.
• the oxygen-rich atmosphere means that the oxygen concentration is higher than that of air.
• the oxygen-rich atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and not more than 100%, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%.
• the zirconia sintered body of the present invention is not particularly limited as long as it exhibits the effects of the present invention, and may be a primary sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment.
• the temperature of the heat treatment in air or in an oxygen-rich atmosphere can be appropriately changed.
• the temperature of the heat treatment in the air or in an oxygen-rich atmosphere is preferably 1650° C. or less, more preferably 1600° C. or less, and even more preferably 1550° C. or less, from the viewpoint of the aesthetics of the zirconia sintered body.
• the temperature of the heat treatment in the air or in an oxygen-excessive atmosphere is preferably 1400° C. or less, more preferably 1300° C. or less, and even more preferably 1200° C.
• the temperature of the heat treatment is preferably 500° C. or higher, more preferably 600° C. or higher, and even more preferably 700° C. or higher.
• a general dental zirconia firing furnace can be used for the tempering process.
• Commercially available dental zirconia firing furnaces may be used. Examples of commercially available products include Noritake Katana (registered trademark) F-1, F-1N, and F-2 (all manufactured by SK Medical Electronics Co., Ltd.).
• a zirconia sintered body obtained by firing the zirconia calcined body of the present invention can be suitably used for dental products.
• dental products include copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, orthodontic wires, laminate veneers, and the like.
• the zirconia calcined body of the present invention for parts such as implant screws and implant fixtures, discoloration of the gums that would occur if metal materials were used can be suppressed, resulting in excellent aesthetics.
• dental products can be obtained by cutting the calcined zirconia body of the present invention and then firing it.
• CAD/CAM system is not particularly limited, and any known device can be used. Examples of known devices include a CAD/CAM system ("Katana (registered trademark) CAD/CAM system” manufactured by Kuraray Noritake Dental Co., Ltd.).
• the present invention includes embodiments that combine all or part of the above configurations in various ways within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved.
• Example 1 A commercially available zirconia powder ( Y2O3 : 0 mol %) and a commercially available yttria powder were put into water, and these were placed in a ball mill container together with zirconia grinding media (diameter: 2 mm) and ground in the ball mill for 96 hours to obtain a slurry (average particle size: 0.2 ⁇ m or less).
• an organic binder was added to the obtained slurry, which was then mixed and stirred.
• the stirred slurry was dried and granulated using a spray dryer to obtain a powder.
• This powder was poured into a cylindrical mold and uniaxially pressed at a pressure of 200 MPa to obtain a molded body.
• the obtained molded body was placed in an electric furnace, heated from room temperature at a rate of 10°C/min, and held at 500°C for 2 hours to degrease the organic components, then heated at a rate of 10°C/min and held at 955°C for 2 hours, and slowly cooled at a rate of -10°C/min to obtain a zirconia calcined body.
• Example 2 and Comparative Examples 1-2 A zirconia calcined body was produced in the same manner as in Example 1, except that the conditions were changed as shown in Table 1. In Example 2 and Comparative Examples 1 and 2, the same yttria raw material as in Example 1 was used.
• the content of yttria means the ratio (mol %) of the number of moles of yttria to the total number of moles of zirconia and yttria.
• “-" means that no grinding treatment was performed.
• the yttria content refers to the value in the slurry, the green body, the calcined body, and the sintered body.
• the commercially available product in Comparative Example 1 was a product manufactured by Tosoh Corporation (product name "Zpex").
• the zirconia calcined bodies of Examples 1 and 2 and Comparative Examples 1 and 2 were pulverized under the conditions shown in Table 1 and formed into disk shapes with a diameter of about 18 mm and a thickness of about 1.2 mm to obtain compacts.
• the compacts were held at a maximum calcination temperature of 1000° C. for 2 hours and slowly cooled at a rate of ⁇ 0.4° C./min to obtain calcined zirconia bodies.
• the unit of density is g/cm 3 .
• the translucency of the sample was measured using a spectrophotometer (product name "Crystal Eye”) manufactured by Olympus Corporation in a measurement mode with a 7-band LED light source.
• a spectrophotometer product name "Crystal Eye” manufactured by Olympus Corporation in a measurement mode with a 7-band LED light source.
• the translucency of the zirconia sintered body which is a flat sample
• LB* lightness
• the L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013).
• the light transmittance ⁇ L*(W ⁇ B) of the sintered body was rated as acceptable when it was 13 or more. The results are shown in Table 1.
• a zirconia sintered body having a relative density of 99.0% or more and excellent translucency was obtained by rapid sintering with a rapid temperature increase of 350° C./min.
• the zirconia calcined body of the present invention is useful for producing dental products for treatment in dental clinics.

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