WO2024096102A1 - ジルコニア仮焼体及び組成物並びにこれらの製造方法 - Google Patents

ジルコニア仮焼体及び組成物並びにこれらの製造方法 Download PDF

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Publication number
WO2024096102A1
WO2024096102A1 PCT/JP2023/039628 JP2023039628W WO2024096102A1 WO 2024096102 A1 WO2024096102 A1 WO 2024096102A1 JP 2023039628 W JP2023039628 W JP 2023039628W WO 2024096102 A1 WO2024096102 A1 WO 2024096102A1
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Prior art keywords
zirconia
powder
content
mass
less
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English (en)
French (fr)
Japanese (ja)
Inventor
貴理博 中野
信介 樫木
貴広 丹羽
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Kuraray Noritake Dental Inc
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Kuraray Noritake Dental Inc
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Priority to CN202380076655.4A priority Critical patent/CN120152946A/zh
Priority to KR1020257016320A priority patent/KR20250097859A/ko
Priority to JP2024554589A priority patent/JPWO2024096102A1/ja
Priority to EP23885856.7A priority patent/EP4613722A1/en
Publication of WO2024096102A1 publication Critical patent/WO2024096102A1/ja
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K6/00—Preparations for dentistry
    • A61K6/80—Preparations for artificial teeth, for filling teeth or for capping teeth
    • A61K6/802—Preparations for artificial teeth, for filling teeth or for capping teeth comprising ceramics
    • A61K6/818—Preparations for artificial teeth, for filling teeth or for capping teeth comprising ceramics comprising zirconium oxide
    • 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
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K6/00—Preparations for dentistry
    • A61K6/80—Preparations for artificial teeth, for filling teeth or for capping teeth
    • A61K6/802—Preparations for artificial teeth, for filling teeth or for capping teeth comprising ceramics
    • A61K6/824—Preparations for artificial teeth, for filling teeth or for capping teeth comprising ceramics comprising transition metal oxides
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
    • A61L27/02—Inorganic materials
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    • 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
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    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3224—Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
    • C04B2235/3225—Yttrium oxide or oxide-forming salts thereof
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    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3231—Refractory metal oxides, their mixed metal oxides, or oxide-forming salts thereof
    • C04B2235/3244—Zirconium oxides, zirconates, hafnium oxides, hafnates, or oxide-forming salts thereof
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    • C04B2235/54—Particle size related information
    • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
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Definitions

  • the present invention relates to a zirconia calcined body and composition, and a method for producing the same. More specifically, the present invention relates to a zirconia (zirconium oxide (IV); ZrO 2 ) calcined body and composition having high translucency even when sintered for a short time, and a method for producing the same.
  • a zirconia zirconium oxide (IV); ZrO 2
  • III zirconium oxide
  • ZrO 2 zirconium oxide
  • Oxide ceramics are widely used industrially, and in particular, zirconia sintered bodies containing yttria have been used in recent years as dental materials such as dental prostheses due to their high strength and aesthetic properties.
  • the raw materials for such zirconia sintered bodies are mainly zirconium oxide powder and yttrium oxide powder, either individually or in solid solution. These raw materials are ground, mixed, dried, molded, and heat treated to obtain a calcined body (mill blank), which is then machined into a shape similar to the desired dental prosthesis and further sintered to produce dental materials such as dental prostheses.
  • Patent Document 1 discloses a method for producing a zirconia sintered body that is a mixture of tetragonal crystals in which zirconia and yttria are solid-dissolved, and cubic crystals in which zirconia and yttria are solid-dissolved.
  • Patent Documents 2 and 3 have been proposed to solve the problem of sintering in such a short time.
  • Patent Document 2 discloses that by using zirconium oxide and yttrium oxide individually as raw materials while simultaneously using a tetragonal solid solution of zirconium oxide and yttrium oxide, the difference in translucency between a zirconia sintered body obtained by short-term retention at the maximum sintering temperature of 30 minutes and a zirconia sintered body obtained by long-term retention of said retention time of about 2 hours is small, and further discloses that excellent translucency is achieved with sintering for 15 minutes.
  • Patent Document 3 discloses a zirconia workpiece for dental cutting, which has a porosity of 15 to 30%, and uses Zpex Smile (registered trademark) or the like as the powder material or workpiece used to manufacture the sintered body, and discloses that in a specific embodiment, a sintered body with excellent translucency and strength was obtained by sintering for a short period of time.
  • Zpex Smile registered trademark
  • the shorter the sintering time the more advantageous it is in terms of manufacturing costs.
  • the holding time at the maximum sintering temperature is further shortened from about 30 minutes to, for example, 10 minutes. It has been confirmed that in the invention of Patent Document 1, there is a problem in that the translucency is lower than in a long-term holding time of, for example, about 2 hours, because there is not a sufficient gradient in the concentrations of zirconium and yttrium elements to be able to utilize the mass transfer between the tetragonal and cubic crystals to promote sintering.
  • Patent Document 2 when the holding time at the maximum sintering temperature was shortened to 10 minutes, the proportion of monoclinic crystals remaining in the calcined body without undergoing phase transition was high, and the reaction speed was insufficient for the phase transition from monoclinic crystals to tetragonal crystals or cubic crystals. As a result, there was a problem that the translucency was low when comparing a short holding time at the maximum sintering temperature of, for example, 10 minutes with a long holding time of, for example, 2 hours.
  • Patent Document 3 does not disclose the use of undissolved yttria in short-time sintering with a holding time of 2 minutes at the maximum sintering temperature, but only discloses a zirconia workpiece using yttrium dissolved in zirconia, and discloses in Reference Example 1 that sufficient translucency cannot be obtained unless yttrium dissolved in zirconia is used. Furthermore, even in the case of short-time sintering, there is no mention that the translucency of a zirconia sintered body obtained by short-time sintering with a holding time of 2 minutes is comparable to that of a zirconia sintered body obtained by sintering with a holding time of 2 hours.
  • Patent Document 3 the reason why sintering cannot be performed in a short time using an yttrium compound that is not dissolved in zirconia is that the yttrium compound that is not dissolved in zirconia is not a material that favors substance diffusion. Therefore, in the case where the zirconia calcined body contains a yttrium compound that is not solid-dissolved in zirconia, there was a problem that a zirconia sintered body obtained by short-time retention at the maximum sintering temperature for a retention time of about 10 minutes was lower than a zirconia sintered body obtained by long-time retention at the maximum sintering temperature for the retention time of about 2 hours.
  • the present invention aims to provide a zirconia calcined body and composition, as well as a method for producing the same, for obtaining a zirconia sintered body that can maintain high translucency after a short sintering time of 10 minutes or less at the maximum sintering temperature, equivalent to that of a long-term sintering.
  • the present invention includes the following inventions.
  • a zirconia calcined body in which zirconia particles are solidified to a degree that does not result in sintering A zirconia calcined body containing zirconia and a stabilizer capable of suppressing a phase transition of zirconia, wherein when ⁇ L 1 *(W-B) for a first sintered body produced by sintering the zirconia calcined body at 1550°C for 120 minutes is compared with ⁇ L 2 *(W-B) for a second sintered body produced by sintering the zirconia calcined body at 1550°C for 10 minutes, the calcined body satisfies the following formula (1): ⁇ L 2 *(W ⁇ B)/ ⁇ L 1 *(W ⁇ B) ⁇ 0.85 (1)
  • the zirconia contains monoclinic zirconia and tetragonal zirconia, the monoclinic content is 55% or more, the tetragonal content is 10% or more, and a part of the yttria is not solid-dissolved in the zirconia;
  • the zirconia contains tetragonal zirconia, does not fall under (A-1), has a tetragonal content of 10% or more, and is yttria in which a portion of the yttria is not solid-dissolved in the zirconia;
  • A-3) The zirconia contains monoclinic zirconia and cubic zirconia, and the content of the monoclinic zirconia is 55% or more and the content of the cubic zirconia is 15% or more;
  • the zirconia contains monoclinic zirconia and cubic zirconia, does not fall under (A-3), and the content of the cubic zirconia is 15% or more; (A-5) The
  • the zirconia calcined body according to any one of [1] to [9] having an average primary particle size of 40 to 110 nm.
  • a zirconia composition comprising zirconia and a stabilizer capable of suppressing a phase transition of zirconia, A zirconia composition that satisfies the following formula (1) when ⁇ L 1 *(WB) for a first sintered body produced by sintering the zirconia composition at 1550°C for 120 minutes is compared with ⁇ L 2 *(WB) for a second sintered body produced by sintering the zirconia composition at 1550°C for 10 minutes.
  • the ratio of the total mass of the zirconia powder (T) and the zirconia powder (M) to the mass of the stabilizer powder is 85.0 mass%:15.0 mass% to 99.8 mass%:0.2 mass%.
  • the zirconia composition according to [12] which satisfies the condition (ii), and further wherein a part of the stabilizer is not solid-dissolved in zirconia.
  • a method for producing a zirconia calcined body comprising firing the zirconia composition according to any one of [11] to [23] above to a degree that does not result in sintering of zirconia particles together.
  • a method for producing a zirconia sintered body comprising sintering the zirconia calcined body according to any one of [1] to [10].
  • the zirconia calcined body and composition, and the method for producing the same, of the present invention it is possible to obtain a zirconia sintered body that can maintain high translucency equivalent to that of a sintered body for a long period of time, even after sintering for a short period of time in which the holding time at the maximum sintering temperature is 10 minutes or less.
  • the zirconia calcined body and composition of the present invention, and the manufacturing method thereof it is possible to obtain a zirconia sintered body that can maintain high translucency equivalent to that of a long-term sintered body after a short sintering time in which the maximum sintering temperature is less than 1600° C. (particularly preferably 1560° C. or less) and the holding time at the maximum sintering temperature is 10 minutes or less. Therefore, the manufacturing efficiency is excellent and it is industrially advantageous.
  • the zirconia calcined body of the present invention contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, and when ⁇ L 1 *(W-B) for a first sintered body produced by sintering at 1550°C for 120 minutes is compared with ⁇ L 2 *(W-B) for a second sintered body produced by sintering at 1550°C for 10 minutes, it satisfies the following formula (1). ⁇ L 2 *(W ⁇ B)/ ⁇ L 1 *(W ⁇ B) ⁇ 0.85 (1)
  • the zirconia calcined body can be a precursor (intermediate product) of the zirconia sintered body.
  • the zirconia calcined body refers to a body in which zirconia particles are solidified to a degree that does not result in sintering.
  • "Not completely sintered” means a state in which the zirconia sintered body is not completely sintered (semi-sintered state), and in a completely sintered body, the relative density increases with sintering and densification progresses, so that the relative density of the zirconia sintered body is 95% or more.
  • the relative density can be calculated as the ratio of the actual density measured by the Archimedes method to the theoretical density.
  • the upper and lower limits of numerical ranges can be appropriately combined.
  • the total of the tetragonal crystal fraction f t , cubic crystal fraction f c , monoclinic crystal fraction f m , and undissolved yttria content f y calculated by the following formulas (2-1), (2-2), (2-3), and (2-4) does not exceed 100%.
  • the zirconia calcined body of the present invention contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia (hereinafter, also simply referred to as "stabilizer").
  • the stabilizer examples include oxides such as calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y 2 O 3 hereinafter, also referred to as "yttria"), cerium oxide (CeO 2 ), scandium oxide (Sc 2 O 3 ), niobium oxide (Nb 2 O 5 ), lanthanum oxide (La 2 O 3 ), erbium oxide (Er 2 O 3 ), praseodymium oxide (Pr 2 O 3 , Pr 6 O 11 ), samarium oxide (Sm 2 O 3 ), europium oxide (Eu 2 O 3 ), thulium oxide (Tm 2 O 3 ), gallium oxide (Ga 2 O 3 ), indium oxide (In 2 O 3 ), and ytterbium oxide (Yb 2 O 3 ), with yttria being preferred.
  • the stabilizer may be used alone or in combination of two or more kinds.
  • the content of the stabilizer in the zirconia calcined body of the present invention is preferably 2 mol% or more, more preferably 3 mol% or more, even more preferably 3.5 mol% or more, and particularly preferably 4 mol% or more, based on the total moles of zirconia (zirconium (IV) oxide; ZrO2 ) and the stabilizer.
  • a content of 2 mol% or more is preferable because the crystal form contained in the zirconia sintered body contains more cubic crystals, thereby improving translucency.
  • the content of the stabilizer is preferably 9 mol % or less, more preferably 8 mol % or less, even more preferably 7.5 mol % or less, and particularly preferably 7 mol % or less, from the viewpoint of suppressing a decrease in strength of the sintered body.
  • the content of the stabilizer may be within any of these ranges in combination.
  • the content of the stabilizer is preferably 2 to 9 mol%, more preferably 3 to 8 mol%, further preferably 3.5 to 7.5 mol%, and particularly preferably 4 to 7 mol%.
  • the content of the stabilizer in the zirconia calcined body of the present invention can be adjusted by changing the compounding ratio in consideration of the content of the stabilizer dissolved in each crystal system, for example by adjusting the content of the stabilizer that is not dissolved in the zirconia composition described below, or by adjusting the content of cubic zirconia having a high content of the stabilizer dissolved in zirconia.
  • the stabilizer content refers to the total content of stabilizer dissolved in zirconia and stabilizer not dissolved in zirconia.
  • the stabilizer content in the zirconia calcined body of the present invention can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis (XRF), etc.
  • ICP inductively coupled plasma
  • XRF X-ray fluorescence analysis
  • the zirconia calcined body of the present invention satisfies the following formula (1) when comparing ⁇ L 1 *(WB) for a first sintered body produced by sintering at 1550°C for 120 minutes with ⁇ L 2 *(WB) for a second sintered body produced by sintering at 1550°C for 10 minutes. ⁇ L 2 *(W ⁇ B)/ ⁇ L 1 *(W ⁇ B) ⁇ 0.85 (1)
  • Both ⁇ L 1 *(W-B) for the first sintered body and ⁇ L 2 *(W-B) for the second sintered body are values calculated using the L* value of lightness (color space) in the L*a*b* color system (JIS Z 8781-4:2013 Colorimetry-Part 4: CIE 1976 L*a*b* color space).
  • the lightness L* value can be measured under a D65 light source using, for example, a spectrophotometer (product name "Crystal Eye”) manufactured by Olympus Corporation, or a spectrophotometer CM-3610A or CM-36dGV manufactured by Konica Minolta, Inc.
  • the maximum sintering temperature was 1550° C.
  • the holding time (holding time) at the maximum sintering temperature was 120 minutes (hereinafter, sintering with a holding time of 120 minutes at the maximum sintering temperature is also referred to as “120-minute sintering” or “long-term sintering”).
  • the holding time (holding time) at the maximum sintering temperature was 10 minutes (hereinafter, sintering with a holding time of 10 minutes at the maximum sintering temperature is also referred to as “10-minute sintering” or “short-time sintering”).
  • the reason why the zirconia calcined body of the present invention can provide a zirconia sintered body that can maintain high translucency at the same level as that of a zirconia sintered body sintered for a long period of time, even after sintering for a short period of time in which the holding time at the maximum sintering temperature is 10 minutes or less, is as follows.
  • the stabilizer is yttria, but the present invention is not limited to the case in which the stabilizer is yttria.
  • the holding time at the maximum sintering temperature is shortened to 10 minutes, in the case where the concentration gradient of the metal element (preferably yttrium element) of the stabilizer in the zirconia crystal system is small, the transfer of yttrium element or yttrium ions between substances hardly occurs. Therefore, the stabilization of the energy accompanying the substance transfer is insufficient, sintering becomes insufficient, and the light transmittance decreases, which is a difficulty caused by the 10-minute sintering.
  • the concentration gradient of the metal element preferably yttrium element
  • a zirconia powder and a yttria powder of a specific crystal system are selected according to the amount of yttria dissolved in the solid solution, and the calcined body is produced.
  • a source that supplies elemental yttrium or yttrium ions and a destination to which the elemental yttrium or yttrium ions move are both present within the system of the zirconia calcined body, and an appropriate concentration gradient of elemental yttrium or yttrium ions is achieved between the two, and the elemental yttrium or yttrium ions move between crystals in the zirconia crystal system during sintering.
  • a zirconia crystal system or yttrium source as a supplier that supplies yttrium element or yttrium ions
  • a zirconia crystal system as a destination to which yttrium element or yttrium ions can move, present within the system of the zirconia calcined body, the difference in concentration of yttrium element or yttrium ions between substances present in the system during sintering is increased, and material transfer occurs while particles are solidifying during sintering.
  • the movement of yttrium element or yttrium ions progresses sufficiently, and when combined with a raw material powder having a predetermined average particle size, they act together, and the yttrium element is more uniformly distributed in the obtained zirconia sintered body. It is considered that the translucency of the zirconia sintered body satisfies the above formula (1).
  • Patent Document 3 discloses an example in which the holding time at the maximum sintering temperature could be shortened to 2 minutes only when zirconia powder in which zirconia contains 4 mol % or more and 5.5 mol % or less of yttrium dissolved therein was used.
  • the yttrium compound that is not dissolved is not dispersed on the outermost surface of the zirconia particles as in the other examples, but rather, in addition to using only yttrium that dissolves in zirconia, the porosity of the cut body is reduced by performing CIP treatment multiple times (specifically, 5 to 10 times), and further sintering at a high temperature with a maximum sintering temperature of 1600° C.
  • CIP treatment multiple times specifically, 5 to 10 times
  • the difference in concentration of yttrium element or yttrium ion between substances present in the system during sintering is increased to promote the mass transfer that occurs during sintering, thereby providing excellent light transmittance in a short sintering time of 10 minutes or less, even if the maximum sintering temperature is less than 1600° C. Therefore, unlike Patent Document 3, repeated CIP treatment five or more times is not essential during the production of a molded body, and since the maximum sintering temperature is lower and the sintering time is short, both a lower maximum sintering temperature and a shorter sintering time are achieved, which is industrially advantageous.
  • the effects of the present invention can be achieved as long as the migration of yttrium element or yttrium ions can be promoted.
  • a preferred embodiment will be described below taking as an example a case where the stabilizer is yttria.
  • the present invention is not limited to the case where the stabilizer is yttria. Therefore, when another stabilizer is used, the "content of yttria" can be read as the content of the other stabilizer, and the “elemental distribution of yttrium” can be read as the elemental distribution of the other metal element.
  • the standard deviation of the yttrium element distribution is preferably 2 mol% or more, and in order to obtain a more excellent light transmissibility, the standard deviation is more preferably 2.1 mol% or more, even more preferably 2.5 mol% or more, and particularly preferably 3 mol% or more.
  • the standard deviation of the yttrium element distribution is preferably less than 21 mol%, more preferably 20 mol% or less, even more preferably 18 mol% or less, and particularly preferably 15 mol% or less, in view of the fact that in short-time sintering, yttrium element or yttrium ions are likely to move between substances present in the system during sintering and the resulting zirconia sintered body has superior translucency.
  • the standard deviation of the yttrium element distribution may be any combination of these ranges.
  • the standard deviation of the yttrium element distribution is preferably 2 mol% or more and less than 21 mol%, more preferably 2.1 mol% or more and 20 mol% or less, even more preferably 2.5 mol% or more and 18 mol% or less, and particularly preferably 3 mol% or more and 15 mol% or less.
  • the zirconia calcined body has a zirconia content of 2.1 mol % or more and 15 mol % or less.
  • the standard deviation of the yttrium element distribution can be adjusted by the content f y of undissolved yttria, the specified average particle size of the raw material powder used as the yttrium source, the content and blending ratio of the specified raw material powder in the raw material composition, etc., and can be more simply adjusted by the content f y of undissolved yttria and the specified average particle size of the raw material powder used as the yttrium source.
  • the zirconia calcined body of the present invention preferably satisfies either of the following conditions (i) or (ii): (i) the zirconia contains tetragonal zirconia, and a portion of the stabilizer is not solid-dissolved in the zirconia; or (ii) The zirconia includes monoclinic zirconia and cubic zirconia.
  • Examples of embodiments of condition (i) include a zirconia calcined body in which the zirconia contains only tetragonal zirconia, and a part of the stabilizer is not solid-dissolved in the zirconia; a zirconia calcined body in which the zirconia contains monoclinic zirconia and tetragonal zirconia, and a part of the stabilizer is not solid-dissolved in the zirconia; and a zirconia calcined body in which the zirconia contains tetragonal zirconia and cubic zirconia, and a part of the stabilizer is not solid-dissolved in the zirconia.
  • condition (i) specifically, a zirconia calcined body that satisfies any one of the following conditions (A-1), (A-2), (A-5), or (A-6) is preferred.
  • condition (ii) specifically, a zirconia calcined body that satisfies either the following condition (A-3) or (A-4) is preferred.
  • the yttria content, the standard deviation of the yttrium element distribution, and the like can be appropriately selected in combination within the ranges described in this specification.
  • the zirconia contains monoclinic zirconia and tetragonal zirconia, the monoclinic content is 55% or more, the tetragonal content is 10% or more, and a part of the yttria is not solid-dissolved in the zirconia;
  • the zirconia contains tetragonal zirconia, does not fall under (A-1), has a tetragonal content of 10% or more, and is yttria in which a portion of the yttria is not solid-dissolved in the zirconia;
  • A-3) The zirconia contains monoclinic zirconia and cubic zirconia, and the content of the monoclinic zirconia is 55% or more and the content of the cubic zirconia is 15% or more;
  • the zirconia contains monoclinic zirconia and cubic zirconia, does not fall under (A-3), and the content of the cubic zirconia is 15% or more; (A-5) The
  • the tetragonal, cubic, and monoclinic contents in the embodiments (A-1), (A-2), (A-3), (A-4), (A-5), and (A-6) are calculated from the above formulas (2-1), (2-2), and (2-3), respectively.
  • the method for measuring the tetragonal, cubic, and monoclinic contents is as described in the Examples below.
  • the zirconia includes monoclinic zirconia and tetragonal zirconia,
  • the zirconia calcined body has a monoclinic content of 55% or more, a tetragonal content of 10% or more, and a part of the yttria is not solid-dissolved in the zirconia (hereinafter, also referred to as "embodiment (A-1)").
  • the content of monoclinic crystals is preferably 55% or more, more preferably 56% or more, even more preferably 58% or more, and particularly preferably 60% or more.
  • the content of the monoclinic system is preferably 85% or less, more preferably 80% or less, further preferably 75% or less, and particularly preferably 70% or less.
  • the content of the monoclinic system may be within any of these ranges.
  • the content of the monoclinic system is preferably 55% or more and 85% or less, more preferably 56% or more and 80% or less, even more preferably 58% or more and 75% or less, and particularly preferably 60% or more and 70% or less.
  • the difference in concentration of yttrium element or yttrium ion in the system during sintering can be set to a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal elements or their ions constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the difference in concentration is not particularly limited as long as a desired range of standard deviation is obtained in the zirconia sintered body after sintering and the translucency that satisfies formula (1) is obtained.
  • the method for measuring the monoclinic content is as described in the Examples section below.
  • the content of the tetragonal system is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and particularly preferably 25% or more.
  • the content of the tetragonal system is preferably 44% or less, more preferably 42% or less, further preferably 40% or less, and particularly preferably 38% or less.
  • the content of the tetragonal system may be in any combination of these ranges.
  • the content of the tetragonal system is preferably 10% or more and 44% or less, more preferably 15% or more and 42% or less, even more preferably 20% or more and 40% or less, and particularly preferably 25% or more and 38% or less.
  • the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set to a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the tetragonal content is as described in the Examples section below.
  • Another preferred embodiment is a zirconia calcined body in which the content of the monoclinic system is 55% or more and 75% or less, and the content of the tetragonal system is 25% or more and 45% or less.
  • another preferred embodiment is a zirconia calcined body in which the proportion of yttria not dissolved in the zirconia is 1 to 25%.
  • the proportion of yttria that is not dissolved in zirconia (hereinafter also referred to as the "content of undissolved yttria f y " or "f y ”) can be calculated based on the following formula (2-4).
  • f y (%) I y / (I m + I t + I c + I y ) ⁇ 100 (2-4)
  • the concentration gradient of the yttrium element can be set within a desired range, the yttrium element is likely to move even in a short-time sintering, and the obtained zirconia sintered body has excellent translucency.
  • the content f y of undissolved yttria is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 3.5% or more.
  • the content f y of undissolved yttria is preferably 25% or less in terms of being able to suppress a decrease in the strength of the sintered body, and is more preferably 20% or less, further preferably 18% or less, and particularly preferably 16% or less in terms of being able to reduce the standard deviation of the distribution of yttrium element, being more likely to cause migration of yttrium element in short-time sintering, and having the obtained zirconia sintered body have better translucency.
  • the content f y of undissolved yttria may be any of these ranges in combination.
  • the content f y of undissolved yttria is preferably 1 to 25%, more preferably 2 to 20%, even more preferably 3 to 18%, and particularly preferably 3.5 to 16%.
  • the content f y of undissolved yttria can be adjusted by adjusting the predetermined average particle size of the yttria powder used as the yttrium source, the predetermined content and blending ratio of the yttria powder in the raw material composition, and the like.
  • the zirconia in the zirconia calcined body may contain a cubic crystal system, but it is preferable that it does not contain a cubic crystal system, since this facilitates the movement of yttrium element or yttrium ions. In other words, in embodiment (A-1), it is preferable that the zirconia calcined body does not simultaneously contain a cubic crystal system and a tetragonal crystal system.
  • An example of a preferred embodiment (A-2) is a zirconia calcined body that contains zirconia having a tetragonal crystal system, does not fall under (A-1), has a tetragonal content of 10% or more, and is yttria that is not partly dissolved in zirconia (hereinafter, also referred to as "embodiment (A-2)").
  • the zirconia in the zirconia calcined body contains a tetragonal system.
  • the content of the tetragonal system is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and particularly preferably 25% or more.
  • the content of the tetragonal system is preferably less than 98%, more preferably 97.5% or less, even more preferably 97% or less, and particularly preferably 96.5% or less, in order to suppress a decrease in the strength of the sintered body.
  • the content of the tetragonal system may be in any combination of these ranges.
  • the content of the tetragonal system is preferably 10% or more and 98% or less, more preferably 15% or more and 97.5% or less, even more preferably 20% or more and 97% or less, and particularly preferably 25% or more and 96.5% or less.
  • the zirconia does not contain monoclinic zirconia, and for example, the content of the tetragonal zirconia is preferably more than 45% and less than 98%, more preferably 55% or more and 97.5% or less, even more preferably 70% or more and 97% or less, and particularly preferably 80% or more and 96.5% or less.
  • the difference in concentration of yttrium element or yttrium ions in the system during sintering can be set to a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal elements or ions thereof that constitute the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the tetragonal content is as described in the Examples section below.
  • the content of the monoclinic system is 0% or more and less than 55%.
  • the content of the monoclinic system is preferably 1% or more, more preferably 2% or more, even more preferably 2.5% or more, and particularly preferably 10% or more.
  • the content of the monoclinic system is preferably less than 55%, more preferably 50% or less, even more preferably 40% or less, and particularly preferably 30% or less.
  • the content of the monoclinic system may be within any of these ranges.
  • the content of the monoclinic system is preferably 1% or more and less than 55%, more preferably 2% or more and 50% or less, even more preferably 2.5% or more and 40% or less, and particularly preferably 10% or more and 30% or less.
  • Another preferred embodiment is a zirconia calcined body in which the zirconia contains a tetragonal crystal system, the content of the monoclinic crystal system is 0%, the content of the tetragonal crystal system is 80% or more and 97% or less, and a part of the stabilizer is not dissolved in the zirconia.
  • part of the stabilizer in the yttria contained in the zirconia calcined body is undissolved yttria.
  • the content f y of undissolved yttria can be calculated based on the above formula (2-4).
  • the content f y of undissolved yttria is preferably more than 2%, more preferably 2.5% or more, even more preferably 3% or more, and particularly preferably 3.5% or more, because the concentration gradient of the yttrium element can be set to a desired range when combined with tetragonal zirconia, the movement of the yttrium element is likely to occur even in short-time sintering, and the obtained zirconia sintered body has excellent translucency.
  • the content f y of undissolved yttria is preferably 25% or less in terms of being able to suppress a decrease in the strength of the sintered body, and is more preferably 20% or less, further preferably 18% or less, and particularly preferably 16% or less in terms of being able to reduce the standard deviation of the distribution of yttrium element, being more likely to cause migration of yttrium element in short-time sintering, and having the obtained zirconia sintered body have better translucency.
  • the content f y of undissolved yttria may be any of these ranges in combination.
  • the content f y of undissolved yttria is preferably 1 to 25%, more preferably 2 to 20%, even more preferably 3 to 18%, and particularly preferably 3.5 to 16%.
  • the zirconia in the zirconia calcined body may contain a cubic crystal system, but it is preferable that it does not contain a cubic crystal system, since this facilitates the movement of yttrium element or yttrium ions. In other words, in embodiment (A-2), it is preferable that the zirconia calcined body does not simultaneously contain a cubic crystal system and a tetragonal crystal system.
  • the zirconia includes monoclinic zirconia and cubic zirconia,
  • the zirconia calcined body has a monoclinic content of 55% or more and a cubic content of 15% or more (hereinafter, also referred to as "embodiment (A-3)").
  • the content of monoclinic crystals is preferably 55% or more, more preferably 56% or more, even more preferably 58% or more, and particularly preferably 60% or more.
  • the content of the monoclinic system is preferably 85% or less, more preferably 80% or less, further preferably 75% or less, and particularly preferably 70% or less.
  • the content of the monoclinic system may be within any of these ranges.
  • the content of the monoclinic system is preferably 55% or more and 85% or less, more preferably 56% or more and 80% or less, even more preferably 58% or more and 75% or less, and particularly preferably 60% or more and 70% or less.
  • the difference in concentration of yttrium element or yttrium ions in the system during sintering can be set to a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal elements or ions thereof that constitute the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the monoclinic content is as described in the Examples section below.
  • the content of the cubic crystal system is preferably 15% or more, more preferably 18% or more, even more preferably 20% or more, and particularly preferably 25% or more.
  • the content of the cubic crystal system is preferably 44% or less, more preferably 42% or less, further preferably 40% or less, and particularly preferably 38% or less.
  • the content of the cubic crystal system may be within any of these ranges.
  • the content of the cubic crystal system is preferably 15% to 44%, more preferably 15% to 42%, even more preferably 20% to 40%, and particularly preferably 25% to 38%.
  • the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set to a desired range, and when combined with a raw material powder having a specified average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the cubic crystal content is as described in the Examples section below.
  • Another suitable embodiment of embodiment (A-3) is a zirconia calcined body in which a portion of the yttria is not dissolved in zirconia, and the proportion of the yttria not dissolved in zirconia is 1 to 15%.
  • the content f y of undissolved yttria can be calculated based on the above formula (2-4).
  • the content f y of undissolved yttria is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 3.5% or more, because when cubic zirconia and monoclinic zirconia are combined, the concentration gradient of the yttrium element can be set in a desired range, the movement of the yttrium element is likely to occur even in short-time sintering, and the obtained zirconia sintered body has excellent translucency.
  • the content f y of undissolved yttria is preferably 15% or less from the viewpoint of suppressing a decrease in the strength of the sintered body, and is more preferably 14% or less, further preferably 12% or less, and particularly preferably 11% or less, from the viewpoints that the standard deviation of the distribution of yttrium element can be reduced, the movement of yttrium element is likely to occur during sintering in a short period of time, and the obtained zirconia sintered body has better translucency.
  • the content f y of undissolved yttria may be any of these ranges in combination.
  • the content f y of undissolved yttria is preferably 1 to 15%, more preferably 2 to 14%, even more preferably 3 to 12%, and particularly preferably 3.5 to 11%.
  • the zirconia in the zirconia calcined body may contain a tetragonal crystal system, but it is preferable that it does not contain a tetragonal crystal system, since this facilitates the movement of yttrium element or yttrium ions. In other words, in embodiment (A-3), it is preferable that the zirconia calcined body does not simultaneously contain a cubic crystal system and a tetragonal crystal system.
  • a preferred embodiment (A-4) is a zirconia calcined body that contains cubic zirconia and monoclinic zirconia, does not fall under (A-3), and has a cubic zirconia content of 15% or more (hereinafter, also referred to as "embodiment (A-4)").
  • the zirconia in the zirconia calcined body contains cubic zirconia.
  • the content of the cubic zirconia is preferably 15% or more, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 40% or more.
  • the content of the cubic crystal system is preferably 98% or less, more preferably 97% or less, even more preferably 96.5% or less, and particularly preferably 96% or less.
  • the content of the cubic crystal system may be within any of these ranges.
  • the content of the cubic crystal system is preferably 15% or more and 98% or less, more preferably 20% or more and 97% or less, even more preferably 30% or more and 96.5% or less, and particularly preferably 40% or more and 96% or less.
  • the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set to a desired range, and when combined with a raw material powder having a specified average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the cubic crystal content is as described in the Examples section below.
  • the zirconia in the zirconia calcined body contains monoclinic zirconia.
  • the content of monoclinic zirconia is preferably 1% or more, more preferably 2% or more, even more preferably 2.5% or more, and particularly preferably 3% or more.
  • the content of the monoclinic system is preferably less than 55%, more preferably 50% or less, even more preferably 45% or less, and particularly preferably 40% or less.
  • the content of the monoclinic system may be within any of these ranges.
  • the content of the monoclinic system is preferably 1% or more and less than 55%, more preferably 2% or more and 50% or less, even more preferably 2.5% or more and 45% or less, and particularly preferably 3% or more and 40% or less.
  • the monoclinic content is within the above range, when cubic zirconia, which is a supplier of yttrium element or yttrium ions, is combined with undissolved yttria as necessary, the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set to a desired range, and when combined with a raw material powder having a specified average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the monoclinic content is as described in the Examples section below.
  • another preferred embodiment is a zirconia calcined body that contains cubic zirconia and monoclinic zirconia, in which the cubic content is 40% or more and 90% or less, and the monoclinic content is 10% or more and less than 55%.
  • Another suitable embodiment of embodiment (A-4) is a zirconia calcined body that contains cubic zirconia and monoclinic zirconia, in which the cubic content is 70% or more and 97% or less, and the monoclinic content is 3% or more and 30% or less.
  • Another suitable embodiment of embodiment (A-4) is a zirconia calcined body in which a portion of the yttria is not dissolved in zirconia, and the proportion of the yttria that is not dissolved in zirconia is 1 to 15%.
  • the content f y of undissolved yttria can be calculated based on the above formula (2-4).
  • the content f y of undissolved yttria is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 3.5% or more, because when cubic zirconia and monoclinic zirconia are combined, the concentration gradient of the yttrium element can be set in a desired range, the movement of the yttrium element is likely to occur even in short-time sintering, and the obtained zirconia sintered body has excellent translucency.
  • the content f y of undissolved yttria is preferably 15% or less from the viewpoint of suppressing a decrease in the strength of the sintered body, and is more preferably 14% or less, further preferably 12% or less, and particularly preferably 11% or less, from the viewpoints that the standard deviation of the distribution of yttrium element can be reduced, the movement of yttrium element is likely to occur during sintering in a short period of time, and the obtained zirconia sintered body has better translucency.
  • the content f y of undissolved yttria may be any of these ranges in combination.
  • the content f y of undissolved yttria is preferably 1 to 15%, more preferably 2 to 14%, even more preferably 3 to 12%, and particularly preferably 3.5 to 11%.
  • the zirconia in the zirconia calcined body may contain a tetragonal crystal system, but it is preferable that it does not contain a tetragonal crystal system because it is easier to promote the movement of yttrium element or yttrium ions. In other words, in embodiment (A-4), it is preferable that the zirconia calcined body does not simultaneously contain a cubic crystal system and a tetragonal crystal system.
  • the zirconia contains tetragonal zirconia and cubic zirconia
  • An example of the zirconia calcined body is one in which the tetragonal content is 5% or more and less than 50%, the cubic content is 50% or more and less than 95%, and a part of the yttria is not solid-dissolved in the zirconia (hereinafter, also referred to as "embodiment (A-5)").
  • the tetragonal content is preferably 6% or more, more preferably 8% or more, even more preferably 9% or more, and particularly preferably 10% or more.
  • the content of the tetragonal system is preferably less than 49%, more preferably less than 48%, even more preferably less than 46%, and particularly preferably less than 40%.
  • the tetragonal content may be in any combination of these ranges.
  • the tetragonal content is preferably 6% or more and less than 49%, more preferably 8% or more and less than 48%, even more preferably 9% or more and less than 46%, and particularly preferably 10% or more and less than 40%.
  • the difference in concentration of yttrium element or yttrium ion in the system during sintering can be set to a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal elements or their ions constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the tetragonal content is as described in the Examples section below.
  • the cubic crystal content is preferably 51% or more, more preferably 52% or more, even more preferably 54% or more, and particularly preferably 60% or more.
  • the content of the cubic crystal system is preferably less than 94%, more preferably less than 92%, even more preferably less than 91%, and particularly preferably less than 90%.
  • the content of the cubic crystal system may be within any of these ranges.
  • the content of the cubic crystal system is preferably 51% or more and less than 94%, more preferably 52% or more and less than 92%, even more preferably 54% or more and less than 91%, and particularly preferably 60% or more and less than 90%.
  • the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set within a desired range, and when combined with a raw material powder having a specified average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the cubic crystal content is as described in the Examples section below.
  • a part of the stabilizer among the yttria contained in the calcined zirconia body is undissolved yttria.
  • the content f y of undissolved yttria can be calculated based on the above formula (2-4).
  • the content f y of undissolved yttria is preferably 0.001% or more, more preferably 0.01% or more, even more preferably 0.02% or more, particularly preferably 0.05% or more, and most preferably 0.1% or more, because when cubic zirconia and tetragonal zirconia are combined, the concentration gradient of the yttrium element can be set in a desired range, the movement of the yttrium element is likely to occur even in short-time sintering, and the obtained zirconia sintered body has excellent translucency.
  • the content f y of undissolved yttria is preferably 12% or less from the viewpoint of suppressing a decrease in the strength of the sintered body, and is more preferably 10% or less, further preferably 9% or less, particularly preferably 8% or less, and most preferably 5% or less, from the viewpoints that the standard deviation of the distribution of yttrium element can be reduced, the movement of yttrium element is likely to occur during sintering in a short period of time, and the obtained zirconia sintered body has better translucency.
  • the content f y of undissolved yttria may be any of these ranges in combination.
  • the content f y of undissolved yttria is preferably 0.001 to 12%, more preferably 0.01 to 10%, even more preferably 0.02 to 9%, particularly preferably 0.05 to 8%, and most preferably 0.1 to 5%.
  • the zirconia in the zirconia calcined body preferably does not contain a monoclinic system, since this facilitates the migration of yttrium element or yttrium ions.
  • the zirconia contains tetragonal zirconia and cubic zirconia,
  • An example of the zirconia calcined body is one that does not fall under (A-5), has a cubic crystal content of 10% or more and less than 50%, and is yttria in which a portion of the yttria is not solid-dissolved in zirconia (hereinafter, also referred to as "embodiment (A-6)").
  • the content of the tetragonal system is 50% or more and less than 90%.
  • the tetragonal content is preferably 51% or more, more preferably 52% or more, even more preferably 54% or more, and particularly preferably 60% or more.
  • the content of the tetragonal system is preferably less than 89%, more preferably less than 88%, even more preferably less than 86%, and particularly preferably less than 85%.
  • the tetragonal content may be within any of these ranges.
  • the tetragonal content is preferably 51% or more and less than 89%, more preferably 52% or more and less than 88%, even more preferably 54% or more and less than 86%, and particularly preferably 60% or more and less than 85%.
  • the difference in concentration of yttrium element or yttrium ion in the system during sintering can be set to a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal elements or their ions constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the tetragonal content is as described in the Examples section below.
  • the cubic crystal content is preferably 11% or more, more preferably 12% or more, even more preferably 14% or more, and particularly preferably 15% or more.
  • the content of the cubic crystal system is preferably less than 49%, more preferably less than 48%, even more preferably less than 46%, and particularly preferably less than 40%.
  • the content of the cubic crystal system may be within any of these ranges.
  • the content of the cubic crystal system is preferably 11% or more and less than 49%, more preferably 12% or more and less than 48%, even more preferably 14% or more and less than 46%, and particularly preferably 15% or more and less than 40%.
  • the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set within a desired range, and when combined with a raw material powder having a specified average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency.
  • the method for measuring the cubic crystal content is as described in the Examples section below.
  • a part of the stabilizer among the yttria contained in the calcined zirconia body is undissolved yttria.
  • the content f y of undissolved yttria can be calculated based on the above formula (2-4).
  • the content f y of undissolved yttria is preferably 0.001% or more, more preferably 0.01% or more, even more preferably 0.02% or more, particularly preferably 0.05% or more, and most preferably 0.1% or more, because when cubic zirconia and tetragonal zirconia are combined, the concentration gradient of the yttrium element can be set in a desired range, the movement of the yttrium element is likely to occur even in short-time sintering, and the obtained zirconia sintered body has excellent translucency.
  • the content f y of undissolved yttria is preferably 12% or less from the viewpoint of suppressing a decrease in the strength of the sintered body, and is more preferably 10% or less, further preferably 9% or less, particularly preferably 8% or less, and most preferably 5% or less, from the viewpoints that the standard deviation of the distribution of yttrium element can be reduced, the movement of yttrium element is likely to occur during sintering in a short period of time, and the obtained zirconia sintered body has better translucency.
  • the content f y of undissolved yttria may be any of these ranges in combination.
  • the content f y of undissolved yttria is preferably 0.001 to 12%, more preferably 0.01 to 10%, even more preferably 0.02 to 9%, particularly preferably 0.05 to 8%, and most preferably 0.1 to 5%.
  • the zirconia in the zirconia calcined body preferably does not contain a monoclinic system, since this facilitates the migration of yttrium element or yttrium ions.
  • the stabilizer is yttria, and the standard deviation of the yttrium element distribution is 2 mol% or more and less than 21 mol%, so that even in a short sintering time of 10 minutes or less, the movement of yttrium elements or yttrium ions between substances in the system during sintering proceeds sufficiently, and the translucency of the resulting zirconia sintered body satisfies the above formula (1).
  • the zirconia calcined body of the present invention preferably does not include, for example, a zirconia calcined body in which the zirconia is only tetragonal zirconia and cubic zirconia and does not contain a stabilizer that is not solid-dissolved in the zirconia; a zirconia calcined body in which the zirconia is only cubic zirconia and a part of the stabilizer is not solid-dissolved in the zirconia; a zirconia calcined body in which the zirconia is only cubic zirconia and does not contain a stabilizer that is not solid-dissolved in the zirconia; a zirconia calcined body in which the zirconia is only monoclinic zirconia and tetragonal zirconia and does not contain a stabilizer that is not solid-dissolved in the zirconia
  • the zirconia calcined body may not include a porosity of 15 to 30%.
  • the pore volume is a value determined by measuring the number of interconnected pores, not including closed pores, having a diameter of about 5 nm to 250 ⁇ m by mercury intrusion porosimetry.
  • the skeletal volume is a value calculated from the true density measured by a gas phase displacement method.
  • the pore volume and skeletal volume can be measured using a fully automatic multifunction mercury porosimeter (POREMASTER, manufactured by Anton Paar Japan K.K.) with a zirconia calcined body machined into a rectangular column (5 mm x 5 mm x 5 mm) as a sample (measurement conditions: mercury surface tension: 480 erg/cm 2 , contact angle: 140°, discharge contact angle: 140°, pressure: 0 to 50,000 psia), and the skeletal volume can be calculated by measuring the true density using an automatic dry density meter (AccuPic II 1340, manufactured by Shimadzu Corporation).
  • POREMASTER fully automatic multifunction mercury porosimeter
  • the density of the zirconia calcined body of the present invention is preferably 3.6 g/cm 3 or less, more preferably 3.5 g/cm 3 or less, and even more preferably 3.4 g/cm 3 or less.
  • the density of the zirconia calcined body of the present invention is preferably 2.5 g/cm 3 or more, more preferably 2.7 g/cm 3 or more, and even more preferably 2.9 g/cm 3 or more.
  • the density of the zirconia calcined body can be calculated by (mass of the zirconia calcined body) / (volume of the zirconia calcined body).
  • the average primary particle size of the particles in the zirconia calcined body of the present invention is preferably 40 nm or more, more preferably 45 nm or more, and even more preferably 50 nm or more.
  • the average primary particle size of the particles in the zirconia calcined body of the present invention is preferably 110 nm or less, more preferably 105 nm or less, and even more preferably 100 nm or less.
  • the average primary particle size of the particles in the zirconia calcined body may be within any combination of these ranges.
  • the average primary particle size is preferably 40 to 110 nm, more preferably 45 to 105 nm, and even more preferably 50 to 100 nm.
  • the method for measuring the average primary particle size of particles in the zirconia calcined body is as described in the Examples below.
  • the zirconia calcined body of the present invention may contain additives other than zirconia and stabilizers, so long as the effects of the present invention are achieved.
  • additives include colorants (including pigments, composite pigments, and fluorescent agents), binders, dispersants, emulsifiers, defoamers, pH adjusters, lubricants, translucency adjusters, etc.
  • colorants including pigments, composite pigments, and fluorescent agents
  • binders include dispersants, emulsifiers, defoamers, pH adjusters, lubricants, translucency adjusters, etc.
  • One type of additive may be used alone, or two or more types may be used in combination.
  • the pigment may be, for example, an oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Er.
  • Examples of the composite pigment include (Zr, V) O2 , Fe(Fe, Cr) 2O4 , (Ni, Co, Fe )(Fe, Cr)2O4.ZrSiO4 , and (Co, Zn ) Al2O4 .
  • 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 preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, calculated as the oxide of the metal element contained in the fluorescent agent. When the content is equal to or more than the lower limit, the fluorescence is not inferior to that of a human natural tooth, and when the content is equal to or less than the upper limit, the decrease in translucency and mechanical strength can be suppressed.
  • binders 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% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, relative to 100% by 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, sorbitan derivatives, and ammonium salts.
  • 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 alkylate ether and wax.
  • 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 zirconia calcined body of the present invention can be produced by firing (calcining) a zirconia composition (for example, a molded body) to a degree that does not result in sintering of zirconia particles together.
  • a zirconia composition for example, a molded body
  • the zirconia composition is a composition containing zirconia powder and a powder of a stabilizer capable of suppressing the phase transition of zirconia.
  • the zirconia composition may be, for example, a shaped compact.
  • the molded body is a body obtained by applying an external force to a powder containing zirconia-based particles.
  • the zirconia composition and the zirconia molded body are not necked (adhered) because they are not yet fired.
  • a zirconia composition includes zirconia and a stabilizer capable of inhibiting a phase transformation of zirconia, the stabilizer comprising: When comparing ⁇ L 1 *(W-B) for a first sintered body produced by sintering the zirconia composition at 1550°C for 120 minutes with ⁇ L 2 *(W-B) for a second sintered body produced by sintering the zirconia composition at 1550°C for 10 minutes, a zirconia composition that satisfies the following formula (1) can be mentioned.
  • ⁇ L 1 *(WB) and ⁇ L 2 *(WB) are as explained for the zirconia calcined body.
  • the temperature at which the zirconia composition is fired is preferably 200° C. or higher, more preferably 300° C. or higher, and even more preferably 400° C. or higher, from the viewpoints that excellent translucency can be obtained in a short time in the subsequent sintering step, organic substances can be removed, and there is no adverse effect on the subsequent sintering step.
  • the calcination temperature is preferably 900° C. or lower, more preferably 700° C. or lower, and even more preferably 600° C. or lower.
  • the calcination temperature may be any combination of these ranges.
  • the calcination temperature is, for example, preferably 200 to 900°C, more preferably 300 to 700°C, and further preferably 400 to 600°C.
  • the pressure during calcination is not particularly limited, and may be normal pressure.
  • the time for treatment at the calcination temperature is preferably 30 minutes or more, and more preferably 120 minutes or more. By setting the time to 120 minutes or more, organic substances can be removed and adverse effects in the subsequent sintering step can be easily avoided.
  • the calcination time is preferably 360 minutes or less, more preferably 240 minutes or less. By setting the calcination time to 240 minutes or less, the diffusion distance of the stabilizer can be suppressed and the concentration gradient of the stabilizer can be maintained, which is preferable in that excellent translucency can be obtained in a short time in the subsequent sintering step.
  • the calcination time may be within any of these ranges in combination.
  • the calcination time is, for example, preferably 30 to 360 minutes, and more preferably 120 to 240 minutes.
  • Examples of methods for producing the zirconia composition include a method including the steps of producing a zirconia powder, producing a powder of a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also referred to as a "stabilizer powder"), and mixing the zirconia powder and the stabilizer powder to produce a powder containing zirconia-based particles.
  • a stabilizer powder capable of suppressing the phase transition of zirconia
  • zirconia-based particles particles including zirconia particles and stabilizer particles are referred to as "zirconia-based particles.”
  • zirconia powder and stabilizer powder There is no particular limitation on the method for producing the raw material powders, zirconia powder and yttria powder. For example, a breakdown process in which coarse particles are pulverized or crushed to produce fine powder; a building-up process in which atoms or ions are synthesized through a nucleation and growth process, etc. can be used.
  • the zirconia powder includes tetragonal zirconia powder (T), monoclinic zirconia powder (M), and cubic zirconia powder (C).
  • the average primary particle diameter (r1) of the zirconia powder (hereinafter also referred to as "average particle diameter (r1)") is preferably 40 nm or more, more preferably 45 nm or more, and even more preferably 50 nm or more, in view of excellent light transmissivity of a zirconia calcined body obtained by short-time sintering.
  • the average particle size (r1) of the zirconia powder is preferably 110 nm or less, more preferably 105 nm or less, and even more preferably 100 nm or less, from the viewpoint of excellent light transmittance of a zirconia calcined body obtained by short-time sintering.
  • the average particle size (r1) of the zirconia powder may be any of the above ranges in combination.
  • the average particle size (r1) of the zirconia powders is preferably 40 to 110 nm, more preferably 45 to 105 nm, and even more preferably 50 to 100 nm.
  • the average particle diameters of the tetragonal zirconia powder (T), the monoclinic zirconia powder (M), and the cubic zirconia powder (C) are within the range of the average particle diameter (r1), when a specific crystal system is selected and used, the migration of the metal elements or ions thereof constituting the stabilizer is sufficiently promoted even in a short sintering time of 10 minutes or less, and the obtained zirconia sintered body has excellent translucency.
  • the average primary particle diameter (r2) of the stabilizer powder capable of suppressing the phase transition of zirconia (hereinafter also referred to as "average particle diameter (r2)") is preferably 20 nm or more, more preferably 40 nm or more, even more preferably 45 nm or more, and particularly preferably 50 nm or more, in view of excellent translucency of a zirconia calcined body obtained by short-time sintering.
  • the average particle size (r2) of the stabilizer powder is preferably 350 nm or less, more preferably 300 nm or less, even more preferably 250 nm or less, and particularly preferably 200 nm or less, from the viewpoint of excellent light transmittance of the zirconia calcined body obtained by short-time sintering.
  • the average particle size (r2) of the stabilizer powder may be any of these ranges in combination.
  • the average particle size (r1) of the zirconia powder is preferably 20 to 350 nm, more preferably 40 to 300 nm, even more preferably 45 to 250 nm, particularly preferably 50 to 200 nm, and most preferably 60 to 110 nm.
  • the average particle size (r2) of the stabilizer powder is within the above range, when it is combined with a zirconia powder having a specific crystal system and the above-mentioned predetermined average particle size (r1), the migration of the metal elements or ions constituting the stabilizer is sufficiently promoted even in a short sintering time of 10 minutes or less, and the obtained zirconia sintered body has excellent translucency.
  • the average particle size (r2) of the stabilizer powder may be greater than 60 nm.
  • examples of such embodiments include a zirconia composition in which the average particle size (r2) of the stabilizer powder is greater than 60 nm and is equal to or smaller than 300 nm.
  • the average particle size (r1) and the average particle size (r2) are average primary particle sizes, and can be measured, for example, by using a laser diffraction/scattering type particle size distribution measuring device manufactured by Horiba, Ltd. (product name "Partica LA-950") to irradiate a slurry diluted with water with ultrasonic waves for 30 minutes, and then measuring the size on a volume basis while applying ultrasonic waves.
  • a laser diffraction/scattering type particle size distribution measuring device manufactured by Horiba, Ltd. (product name "Partica LA-950"
  • the following describes an example of a method for preparing zirconia powder.
  • the method for preparing zirconia powder can also be used as a method for preparing stabilizer particles, unless otherwise specified.
  • a preferred embodiment of the present invention is a zirconia composition that satisfies either of the following conditions (i) or (ii).
  • the zirconia powder (T) is a tetragonal zirconia powder, and a part of the stabilizer is not solid-dissolved in the zirconia; or
  • the zirconia powder includes a monoclinic zirconia powder (M) and a cubic zirconia powder (C).
  • suitable embodiments that satisfy the condition (i) include a zirconia composition in which the zirconia contains only tetragonal zirconia powder (T), and a part of the stabilizer is not solid-dissolved in the zirconia; a zirconia composition in which the zirconia contains monoclinic zirconia powder (M) and tetragonal zirconia powder (T), and a part of the stabilizer is not solid-dissolved in the zirconia; and a zirconia composition in which the zirconia contains tetragonal zirconia powder (T) and cubic zirconia powder (C), and a part of the stabilizer is not solid-dissolved in the zirconia.
  • Another preferred embodiment is a zirconia composition that satisfies the above condition (i) and further contains a monoclinic zirconia powder (M).
  • Another preferred embodiment is a zirconia composition that satisfies the above condition (ii) and further includes a zirconia composition in which a portion of the stabilizer is not dissolved in zirconia.
  • zirconia raw material used for producing the zirconia powder tetragonal zirconia, monoclinic zirconia, and cubic zirconia can be used.
  • the zirconia raw material produced by the production method described in Japanese Patent No. 6543926 produced by hydrolysis reaction
  • the zirconia raw material can be a commercially available product.
  • Examples of commercially available products include zirconia powder "TZ-0” (monoclinic 0Y (0 mol % yttria)), zirconia powder with 3 mol % yttria solid solution “TZ-3Y-E” (tetragonal 3Y), zirconia powder with 6 mol % yttria solid solution “TZ-6Y” (cubic 6Y), and zirconia powder with 10 mol % yttria solid solution "TZ-10Y” (cubic 10Y), all of which are manufactured by Tosoh Corporation.
  • the coarse particles of the zirconia raw material are separately pulverized according to the crystal system to produce tetragonal zirconia powder (T), monoclinic zirconia powder (M), and cubic zirconia powder (C), each adjusted to fall within the range of the average particle size (r2).
  • T tetragonal zirconia powder
  • M monoclinic zirconia powder
  • C cubic zirconia powder
  • it is preferable to prepare the zirconia powder by pulverizing the zirconia raw material separately from the raw material of the stabilizer powder (e.g., the yttria raw material).
  • the stabilizer powder can also be adjusted to the average particle size (r2) by grinding the raw material compound (e.g., yttria) using a known method (e.g., ball mill).
  • the average particle size of the raw material compound is not particularly limited as long as it can be adjusted to within the range of the average particle size (r2) by grinding.
  • the average particle diameter of the zirconia powder having the above average particle diameter (r1) and the stabilizer powder having the above average particle diameter (r2) can be adjusted by a known method such as pulverizing the raw material powder.
  • a known method such as pulverizing the raw material powder.
  • fine-sized grinding media for grinding, for example, grinding media of 100 ⁇ m or less.
  • the obtained zirconia powder is preferably classified. For classification, known methods and devices can be used.
  • Known methods include, for example, elutriation using the difference in sedimentation velocity caused by particle-size-dependent dispersibility, and elutriation can be accelerated using a centrifuge.
  • Known devices include, for example, porous membranes (membrane filters having a pore size of 100 nm, etc.), classification devices (wet classification devices, dry classification devices), etc. By performing operations such as pulverization and classification, including changing the pulverization time as necessary, a raw material powder having a desired average particle size can be obtained.
  • the concentration gradient of the yttrium element or yttrium ion is easily within a predetermined range.
  • mass transfer occurs while the particles are solidifying with each other during sintering, the movement of the yttrium element or yttrium ion progresses sufficiently even in a short sintering time of 10 minutes or less, and the yttrium element is more uniformly distributed in the obtained zirconia sintered body, and it is considered that the translucency of the zirconia sintered body satisfies the above formula (1).
  • the stabilizer is yttria
  • the present invention is not limited to the case in which the stabilizer is yttria.
  • the content of yttria dissolved in tetragonal zirconia (hereinafter also referred to as "amount of dissolved yttria”) is preferably 2 mol % or more, more preferably 2.2 mol % or more, and even more preferably 2.5 mol % or more, based on the total moles of zirconia and yttria.
  • the amount of yttria dissolved in the tetragonal zirconia is preferably less than 5 mol%, more preferably 4.8 mol% or less, even more preferably 4.5 mol% or less, particularly preferably 4.0 mol% or less, and most preferably 3.8 mol% or less.
  • the amount of yttria dissolved in the tetragonal zirconia may be within any of these ranges.
  • the amount of yttria dissolved in the tetragonal zirconia is preferably 2 mol% or more and less than 5 mol%, more preferably 2.0 mol% or more and 4.8 mol% or less, even more preferably 2.2 mol% or more and 4.5 mol% or less, particularly preferably 2.2 mol% or more and 4.0 mol% or less, and most preferably 2.5 mol% or more and 3.8 mol% or less.
  • the amount of yttria dissolved in the tetragonal zirconia powder (T) obtained from the zirconia raw material is similar to the amount of yttria dissolved in the zirconia raw material.
  • the amount of yttria dissolved in the monoclinic zirconia used in the present invention is preferably 0 to 1 mol %, more preferably 0 to 0.5 mol %, and even more preferably 0 mol %, based on the total moles of zirconia and yttria.
  • the amount of yttria dissolved in the monoclinic zirconia powder (M) obtained from the zirconia raw material is similar to the amount of yttria dissolved in the zirconia raw material.
  • the amount of yttria dissolved in cubic zirconia is preferably 5 mol % or more, more preferably 5.5 mol % or more, and even more preferably 6 mol % or more, based on the total moles of zirconia and yttria.
  • the amount of yttria dissolved in the cubic zirconia is preferably 15 mol % or less, more preferably 12 mol % or less, and even more preferably 10 mol % or less.
  • the amount of yttria dissolved in the cubic zirconia may be within any of these ranges.
  • the amount of yttria dissolved in the cubic zirconia is preferably more than 5 mol% and not more than 15 mol%, more preferably 5.5 mol% or more and 12 mol% or less, and even more preferably 6 mol% or more and 10 mol% or less.
  • the amount of yttria dissolved in the cubic zirconia powder (C) obtained from the zirconia raw material is the same as the amount of yttria dissolved in the zirconia raw material.
  • the amount of yttria dissolved in tetragonal, monoclinic, and cubic zirconia can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis (XRF), etc.
  • ICP inductively coupled plasma
  • XRF X-ray fluorescence analysis
  • the zirconia composition of the present invention may contain additives other than zirconia and stabilizers as long as the effects of the present invention are achieved.
  • the additives include colorants (including pigments, composite pigments, and fluorescent agents), binders, dispersants, emulsifiers, defoamers, pH adjusters, lubricants, alumina (Al 2 O 3 ), titanium oxide (TiO 2 ), and silica (SiO 2 ).
  • the additives may be used alone or in combination of two or more. Examples of the additives include the same additives as those exemplified for the zirconia calcined body. The additives may be added when the raw materials are mixed or pulverized, or may be added to the powder after pulverization.
  • the zirconia powder and the stabilizer powder may be mixed by dry mixing or wet mixing.
  • the mixing ratio of the zirconia powder and the stabilizer powder can be adjusted appropriately to obtain the desired crystal system content depending on the embodiment (e.g., embodiments (A-1) to (A-6), etc.).
  • the ratio of the total mass of the zirconia powder (T) and the zirconia powder (M) to the mass of the stabilizer powder is preferably 85.0 mass%:15.0 mass% to 99.8 mass%:0.2 mass%.
  • the contents of the zirconia powder (T) and the zirconia powder (M) can be adjusted within the above ranges so as to obtain the tetragonal content and the monoclinic content in the embodiments (A-1) and (A-2).
  • the content of the zirconia powder (M) in the zirconia composition is preferably 0 to 85 mass%, more preferably 0 to 82 mass%, and even more preferably 0 to 80 mass%, of the total mass of the zirconia powder (T) and the zirconia powder (M).
  • the zirconia powder (T) contains a stabilizer capable of suppressing the phase transition of the dissolved zirconia.
  • the content of the stabilizer capable of suppressing the phase transition of dissolved zirconia in the zirconia powder (T) is preferably 2 to 4 mol %, more preferably 2 to 3.5 mol %, and even more preferably 2 to 3 mol %, based on the total moles of zirconia and the stabilizer.
  • the ratio of the total mass of the zirconia powder (M) and the zirconia powder (C) to the mass of the stabilizer powder is preferably 85.0 mass%:15.0 mass% to 100 mass%:0 mass%.
  • the contents of the zirconia powder (M) and the zirconia powder (C) can be adjusted within the above ranges so as to obtain the monoclinic content and the cubic content in the embodiments (A-3) and (A-4).
  • the content of the zirconia powder (C) in the zirconia composition satisfying condition (ii) is preferably 15.0 to 95.0 mass %, more preferably 18.0 to 82.0 mass %, and even more preferably 20.0 to 80.0 mass %, of the total mass of the zirconia powder (M) and the zirconia powder (C).
  • the content of the stabilizer capable of suppressing the phase transition of dissolved zirconia in the zirconia powder (M) is preferably 0 to 1 mol%, more preferably 0 to 0.5 mol%, and even more preferably 0 mol%, relative to the total moles of zirconia and stabilizer.
  • the content of the stabilizer capable of suppressing the phase transition of dissolved zirconia in the zirconia powder (C) is preferably 5 mol% or more and 15 mol% or less, more preferably 5.5 mol% or more and 12 mol% or less, and even more preferably 6 mol% or more and 10 mol% or less, based on the total moles of zirconia and stabilizer.
  • the ratio of the total mass of the zirconia powder (T) and the zirconia powder (C) to the mass of the stabilizer powder is preferably 88.0 mass%:12.0 mass% to 99.999 mass%:0.001 mass%, more preferably 90.0 mass%:10.0 mass% to 99.99 mass%:0.01 mass%, even more preferably 91.0 mass%:9.0 mass% to 99.98 mass%:0.02 mass%, particularly preferably 92.0 mass%:8.0 mass% to 99.95 mass%:0.05 mass%, and most preferably 95.0 mass%:5.0 mass% to 99.9 mass%:0.1 mass%.
  • the respective contents of the zirconia powder (T) and the zirconia powder (C) can be adjusted within the above-mentioned ranges so as to obtain the tetragonal content and the cubic content in the embodiments (A-5) and (A-6).
  • the solvent used in the wet mixing is not particularly limited as long as it contains water, and an organic solvent may be used, a mixed solvent of water and an organic solvent may be used, or only water may be used.
  • the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, 2-methoxyethanol, 2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol, diethylene glycol monobutyl ether, and glycerin; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, diethyl ether, diisopropyl ether, 1,4-dioxane, and dimethoxyethane (including modified ethers such as propylene glycol monomethyl ether acetate (commonly known as "PGMEA”) (preferably ether-modified ethers and/or ester-
  • the zirconia composition of the present invention may be in a dry state, or may contain or be contained in a liquid.
  • the zirconia composition may be in the form of a powder, a paste, a slurry, etc.
  • the method of wet-mixing the raw materials in a solvent containing water is not particularly limited.
  • the raw materials may be wet-pulverized and mixed in a known pulverizing and mixing device (such as a ball mill) to form a slurry containing zirconia-based particles, and then the slurry containing the zirconia-based particles may be dried and granulated to produce a granular zirconia composition.
  • a known pulverizing and mixing device such as a ball mill
  • the mixed powder obtained by mixing the zirconia powder and the stabilizer powder is also referred to below as "powder containing zirconia-based particles.”
  • drying the slurry to form granules there are no particular limitations on the drying method, and for example, spray drying, supercritical drying, freeze drying, hot air drying, reduced pressure drying, etc. can be used. Of these, spray drying, supercritical drying, and freeze drying are preferred, spray drying and supercritical drying are more preferred, and spray drying is even more preferred, since they can suppress the aggregation of particles during drying and produce a denser zirconia sintered body.
  • the slurry containing zirconia-based particles to be dried may be a slurry in which the dispersion medium is water, but it is preferable to use a slurry in which the dispersion medium is other than water, such as an organic solvent, because this can suppress the aggregation of particles during drying and result in a denser zirconia sintered body.
  • the moisture content in the slurry containing zirconia-based particles to be dried is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, because this can suppress the aggregation of particles during drying and result in a denser zirconia sintered body.
  • the moisture content can be measured using a Karl Fischer moisture meter.
  • drying conditions for each drying method there are no particular limitations on the drying conditions for each drying method, and known drying conditions can be used as appropriate.
  • an organic solvent as the dispersion medium, it is preferable to perform drying in the presence of a non-flammable gas, and it is more preferable to perform drying in the presence of nitrogen, in order to reduce the risk of explosion during drying.
  • the supercritical fluid used in supercritical drying for example, water, carbon dioxide, etc. can be used, but it is preferable that the supercritical fluid be carbon dioxide, as this can suppress the aggregation of particles and result in a denser zirconia sintered body.
  • the dispersion medium of the slurry containing zirconia-based particles to be dried contains a liquid having a surface tension of 50 mN/m or less at 25°C, since this can suppress the aggregation of zirconia particles during drying and allows a denser zirconia sintered body to be obtained.
  • the surface tension of the liquid is preferably 40 mN/m or less, and more preferably 30 mN/m or less.
  • the surface tension at 25°C can be measured using values found in, for example, the Handbook of Chemistry and Physics, and for liquids not found therein, the values found in International Publication No. 2014/126034 can be used. For liquids not found in any of these publications, the surface tension can be measured using known measurement methods, such as the hanging ring method or the Wilhelmy method. Surface tension at 25°C is preferably measured using an automatic surface tensiometer "CBVP-Z” made by Kyowa Interface Science Co., Ltd., or a "SIGMA702" made by KSV INSTRUMENTS LTD. (now Biolin Scientific AB, Sweden).
  • an organic solvent having the above surface tension can be used.
  • the organic solvent any of the above-mentioned organic solvents having the above surface tension can be used, but at least one selected from the group consisting of methanol, ethanol, 2-methoxyethanol, 1,4-dioxane, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol is preferred, since it is possible to suppress the aggregation of particles during drying and obtain a denser zirconia sintered body, and at least one selected from the group consisting of methanol, ethanol, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol is more preferred.
  • the content of the above liquid in the dispersion medium is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, because this can suppress the aggregation of particles during drying and result in a denser zirconia sintered body.
  • a slurry with a dispersion medium other than water can be obtained by replacing the dispersion medium of a slurry whose dispersion medium is water.
  • a method can be adopted in which a dispersion medium other than water (such as an organic solvent) is added to a slurry whose dispersion medium is water, and then the water is distilled off. When distilling off the water, a part or all of the dispersion medium other than water may be distilled off together. The addition of the dispersion medium other than water and the distillation off of the water may be repeated multiple times.
  • a method can be adopted in which a dispersion medium other than water is added to a slurry whose dispersion medium is water, and then the dispersoid is precipitated. Furthermore, the dispersion medium of a slurry whose dispersion medium is water may be replaced with a specific organic solvent, and then further replaced with another organic solvent.
  • the fluorescent agent may be added after replacing the dispersion medium, but it is preferable to add it before replacing the dispersion medium, because it is possible to obtain a more uniform zirconia sintered body with excellent physical properties.
  • a colorant and/or a translucency adjuster when contained in the slurry, it may be added after replacing the dispersion medium, but it is preferable to add it before replacing the dispersion medium, because it is possible to obtain a more uniform zirconia sintered body with excellent physical properties.
  • examples of build-up processes include the gas-phase pyrolysis method, in which an oxide is precipitated by thermally decomposing an oxyacid salt of a metal ion with high vapor pressure or an organometallic compound while vaporizing it; the gas-phase reaction method, in which synthesis is carried out by a gas-phase chemical reaction between a gaseous metal compound with high vapor pressure and a reactive gas; the evaporation concentration method, in which the raw material is heated and vaporized, and then rapidly cooled in an inert gas at a specified pressure to condense the vapor into fine particles; the melt method, in which the molten liquid is cooled into small droplets and solidified into a powder; the solvent evaporation method, in which the solvent is evaporated to increase the concentration in the liquid and precipitate in a supersaturated state; and the precipitation method, in which the solute concentration is made supersaturated by reaction with a precipitant or hydrolysis, and sparingly soluble compounds such as oxides and hydrolysis, and spar
  • Precipitation methods are further classified into homogeneous precipitation methods, in which a precipitant is produced in a solution by a chemical reaction, eliminating local non-uniformity in the precipitant concentration; coprecipitation methods, in which a plurality of metal ions coexisting in a solution are precipitated simultaneously by adding a precipitant; hydrolysis methods, in which an oxide or hydroxide is obtained by hydrolysis from a metal salt solution or an alcohol solution of a metal alkoxide or the like; and solvothermal synthesis methods, in which an oxide or hydroxide is obtained from a high-temperature, high-pressure fluid.
  • the solvothermal synthesis methods are further classified into hydrothermal synthesis methods, in which water is used as a solvent, and supercritical synthesis methods, in which a supercritical fluid such as water or carbon dioxide is used as a solvent.
  • hydrothermal synthesis methods in which water is used as a solvent
  • supercritical synthesis methods in which a supercritical fluid such as water or carbon dioxide is used as a solvent.
  • the zirconium source for the building-up process may be, for example, a nitrate, acetate, chloride, or alkoxide.
  • Specific examples of the zirconium source include zirconium oxychloride, zirconium acetate, and zirconyl nitrate.
  • the zirconia powder When the zirconia powder is produced by a method such as a building-up process, so long as the average particle size of the zirconia particles is within the desired range, the zirconia powder may be used in the process of mixing the zirconia powder with a stabilizer powder in the form of a slurry containing zirconia particles without drying. There are no particular limitations on the method for preparing the slurry containing zirconia particles, and it may be obtained, for example, via the breakdown process or building-up process described above.
  • the zirconia composition of the present invention When the zirconia composition of the present invention is in a dry state, it can be obtained by drying a slurry containing zirconia particles.
  • the zirconia composition of the present invention may be subjected to a molding process to form a molded body.
  • molded body refers to a body that has not yet reached a semi-sintered state (calcined state) or a sintered state.
  • the molded body is distinguished from the calcined body and the sintered body in that the molded body is a body that has not yet been sintered after being molded.
  • the type of the molding step is not particularly limited, but since the zirconia molded body of the present invention, and further the zirconia calcined body and zirconia sintered body of the present invention can be easily obtained, the molding step is preferably (i) slip casting a slurry containing zirconia-based particles; (ii) gel casting a slurry containing zirconia-based particles; (iii) press-molding the powder containing zirconia-based particles; (iv) forming a composition comprising zirconia-based particles and a resin;
  • the method is preferably at least one of (v) a step of polymerizing a composition containing zirconia-based particles and a polymerizable monomer or oligomer; and (vi) a step of layer-by-layer manufacturing of granules containing zirconia-based particles, and more preferably a method having a molding step of molding zirconia-based particles, a polyol, and
  • the content of the dispersion medium in the slurry containing the zirconia-based particles 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 excessive time required for drying, and allows the mold to be used more frequently.
  • the slurry may be poured into the mold under normal pressure, but from the viewpoint of production efficiency, it is preferable to pour the slurry into the mold under pressurized conditions.
  • the type of mold used for slip casting and for example, porous molds made of plaster, resin, ceramics, etc. can be used. Porous molds made of resin or ceramics are excellent in terms of durability.
  • the slurry containing the zirconia-based particles used in slip casting may further contain one or more of the other components, such as the binder, plasticizer, dispersant, emulsifier, defoamer, pH adjuster, and lubricant, as described above.
  • the content of the dispersion medium in the slurry containing the zirconia-based particles is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, since this can prevent drying from taking a long time and also suppresses the occurrence of cracks during drying.
  • the gelation may be performed, for example, by adding a gelling agent, or by adding a polymerizable monomer and then polymerizing it.
  • a gelling agent for example, a polymerizable monomer and then polymerizing it.
  • a porous mold made of gypsum, resin, ceramics, etc., or a non-porous mold made of metal, resin, etc., can be used.
  • 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 no problems such as cracks occur during sintering, but it 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.
  • the polymerizable monomers may be used alone or in combination of two or more kinds.
  • the amount of polymerizable monomer used is not particularly limited as long as it does not cause problems such as cracks during sintering, but it 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 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
  • examples of the acylphosphine oxides include 2,4,6-trimethylbenzoyldiphenylphosphine oxide (commonly known as "TPO"), 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide, 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide, 2,3,5,6-tetramethylbenzoyldiphenylphosphine oxide, benzoyldi(2,6-dimethylphenyl)phosphonate, sodium salt of 2,4,6-trimethylbenzoylphenylphosphine oxide, potassium salt of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and ammonium salt of 2,4,6-trimethylbenzoyldiphenylphos
  • examples of the bisacylphosphine oxides include bis(2,6-dichlorobenzoyl)phenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, bis(2,6-dimethoxybenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and bis(2,3,6-trimethylbenz
  • ⁇ -diketones examples include diacetyl, benzyl, camphorquinone, 2,3-pentadione, 2,3-octadione, 9,10-phenanthrenequinone, 4,4'-oxybenzyl, and acenaphthenequinone.
  • camphorquinone is preferred, particularly when using a light source in the visible light range.
  • Slurries containing the above-mentioned zirconia-based particles used in gel casting may also contain one or more of the other components described above, such as binders, plasticizers, dispersants, emulsifiers, antifoaming agents, pH adjusters, and lubricants, just like slurries used in slip casting.
  • 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.
  • 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.
  • the pressing pressure in the press molding is appropriately set to an optimum value depending on the size, open porosity, biaxial bending strength, and particle size of the raw material powder of the target molded body, and is usually 5 MPa to 1000 MPa.
  • a cold isostatic pressing (CIP) treatment may be further performed after uniaxial pressing.
  • the powder containing the zirconia-based particles used in press molding may further contain one or more of the other components, such as the binder, plasticizer, dispersant, emulsifier, defoamer, pH adjuster, lubricant, and translucency adjuster, as described above. These components may be blended when preparing the powder.
  • resins that function as binders can be preferably used.
  • resins include paraffin wax, polyvinyl alcohol, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, atactic polypropylene, methacrylic resin, and fatty acids such as stearic acid. These resins may be used alone or in combination of two or more types.
  • composition containing the zirconia-based particles and resin may further contain one or more of the other components, such as the plasticizer, dispersant, emulsifier, defoamer, pH adjuster, and lubricant, as described above.
  • the specific method is not particularly limited, and for example, (a) a method of polymerizing a composition containing zirconia-based particles and a polymerizable monomer or oligomer in a mold, (b) a stereolithography (SLA) method using a composition containing zirconia-based particles and a polymerizable monomer or oligomer, etc.
  • the stereolithography method (b) is preferred.
  • the stereolithography a shape corresponding to a desired shape of the finally obtained zirconia sintered body can be imparted at the time of manufacturing the zirconia molded body, and therefore, the stereolithography may be preferable in some cases, particularly when the zirconia sintered body of the present invention is used as a dental material for dental prostheses and the like.
  • the type of polymerizable monomer in the composition containing the zirconia-based particles and the polymerizable monomer or oligomer 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, trifunctional or higher compounds, etc.
  • the polymerizable monomers may be used alone or in combination of two or more kinds.
  • 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. Among these, it is preferable to use a polyfunctional polymerizable monomer, particularly when a stereolithography method is employed.
  • 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)
  • acrylates examples include alkyl (meth)acrylates such as t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate; alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic group-containing (meth)acrylates such as benzyl (meth)acrylate and phenyl (meth)acrylate; and (meth)acrylates having functional groups such as 2,3-dibromopropyl (meth)acrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, and 11-(meth)acryloyloxyundecyltrimethoxysilane.
  • alkyl (meth)acrylates such as t-butyl
  • 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-acryloyloxypropoxy)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)acryloyloxypentaethoxy
  • Examples of (meth)acrylates include bis(4-(meth)acryloyloxydipropoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, and 1,4-bis(2-(meth)acryloyloxyethyl)pyromellitate.
  • 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-
  • triethylene glycol dimethacrylate (commonly known as "TEGDMA") and 2,2,4-trimethylhexamethylene bis(2-carbamoyloxyethyl)dimethacrylate are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded body.
  • TEGDMA triethylene glycol dimethacrylate
  • 2,2,4-trimethylhexamethylene bis(2-carbamoyloxyethyl)dimethacrylate are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded body.
  • 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 carried out using a polymerization initiator, and it is preferable that the composition further contains a polymerization initiator.
  • a polymerization initiator There are no particular limitations on the type of polymerization initiator, but a photopolymerization initiator is particularly preferable.
  • the photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and among them, photopolymerization initiators used for dental applications are preferable. Specific examples of photopolymerization initiators are the same as those mentioned above in the explanation of gel casting, and a duplicate explanation will be omitted here.
  • composition containing the zirconia-based particles and the polymerizable monomer may further contain one or more of the other components, such as the plasticizer, dispersant, emulsifier, defoamer, pH adjuster, and lubricant, as described above.
  • stereolithography When manufacturing a zirconia molded body by stereolithography using a composition containing zirconia-based particles and a polymerizable monomer, 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 content of zirconia-based particles in a composition containing zirconia-based particles and a polymerizable monomer is preferably as high as possible from the viewpoint of subsequent sintering properties.
  • the content of zirconia particles in the composition is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more.
  • the viscosity of the composition is within a certain range.
  • the content of zirconia-based particles in the above composition is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less. Adjusting the viscosity of the composition can be particularly important when implementing the controlled liquid level method, in which light is irradiated from below through the bottom surface of a container to harden layers and sequentially form zirconia molded bodies one layer at a time, in order to raise the hardened layer by one layer and allow the composition for forming the next layer to smoothly flow between the underside of the hardened layer and the bottom surface of the container.
  • the specific viscosity of the composition at 25°C is preferably 20,000 mPa ⁇ s or less, more preferably 10,000 mPa ⁇ s or less, and even more preferably 5,000 mPa ⁇ s or less.
  • the viscosity is preferably 100 mPa ⁇ s or more. Since the viscosity of the composition tends to increase as the content of zirconia particles increases, it is preferable to appropriately adjust the balance between the content of zirconia particles and the viscosity of the composition in accordance with the performance of the optical modeling device used, taking into account the balance between the speed of optical modeling and the precision of the resulting zirconia molded body.
  • the viscosity can be measured using an E-type viscometer.
  • the zirconia molded body in order to further increase the density of the zirconia molded body, the zirconia molded body may be subjected to a humidification treatment and then a CIP treatment.
  • a humidification treatment When performing press molding, 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 particle size of the contained zirconia particles, the 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.
  • a method can be adopted in which a slurry is obtained and then dried with a spray dryer to form granules, and the obtained granules can be used for powder layered 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 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 sintered body of the present invention can be produced by using a zirconia calcined body. Specifically, the zirconia sintered body of the present invention can be obtained, for example, by sintering the above-mentioned zirconia calcined body. In the zirconia sintered body, zirconia particles are solidified together by sintering, and the relative density increases as the sintering proceeds, and densification progresses, resulting in a completely sintered state in which the relative density is 95% or more.
  • the stabilizer content in the zirconia sintered body of the present invention is the same as the stabilizer content in the zirconia calcined body.
  • the zirconia sintered body of the present invention satisfies the above formula (1) when the first translucency ⁇ L 1 *(WB) of a zirconia sintered body produced by sintering at 1550° C. for 120 minutes is compared with the second translucency ⁇ L 2 *(WB) of a zirconia sintered body produced by sintering at 1550° C. for 10 minutes. Therefore, the zirconia sintered body of the present invention can maintain high 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, at the same level as that of sintering for a long period of time.
  • the zirconia sintered body of the present invention may contain a fluorescent agent.
  • the fluorescent agent is the same as the fluorescent agent in the zirconia calcined body.
  • the zirconia sintered body of the present invention may contain one type of these alone or two or more types in combination.
  • "based on 100 mass % of zirconia contained in the zirconia calcined body" can be read as "based on 100 mass % of zirconia contained in the zirconia sintered body.”
  • the zirconia sintered body of the present invention may contain a colorant.
  • the colorant include the same colorants as those in the zirconia calcined body.
  • the content of the colorant in the zirconia sintered body is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more.
  • the content of the colorant is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, and may be 0.1% by mass or less, or even 0.05% by mass or less.
  • the zirconia sintered body of the present invention may contain a translucency adjuster.
  • the translucency adjuster include the same ones as those in the zirconia calcined body.
  • the content of the translucency adjuster in the zirconia sintered body there is no particular restriction on the content of the translucency adjuster in the zirconia sintered body, and it can be adjusted as appropriate depending on the type of translucency adjuster and the application of the zirconia sintered body, but from the viewpoint of favorable use as a dental prosthesis, it is preferable that the content be 0.1 mass% or less relative to 100 mass% of zirconia contained in the zirconia sintered body.
  • the method for producing the zirconia sintered body of the present invention includes a method for producing a zirconia sintered body by sintering the above-mentioned zirconia calcined body.
  • a production method including a step of sintering the above-mentioned zirconia calcined body at a temperature higher than 900°C and not higher than 1700°C under normal pressure is preferable.
  • the zirconia sintered body of the present invention that can maintain high translucency equivalent to that of long-term sintering after sintering in a short time in which the holding time at the maximum sintering temperature is 10 minutes or less.
  • the zirconia sintered body of the present invention can also be produced by sintering the zirconia calcined body of the present invention under normal pressure.
  • the sinterable temperature (for example, the maximum sintering temperature) is preferably set at a condition that maximizes the translucency of the zirconia sintered body.
  • the sintering temperature is preferably more than 900°C, more preferably 1000°C or more, and even more preferably 1050°C or more, and is preferably 1700°C or less, more preferably 1650°C or less, and even more preferably less than 1600°C.
  • a method for producing a zirconia sintered body includes sintering a zirconia calcined body at more than 900° C. and not more than 1560° C. under normal pressure, from the viewpoint of excellent light transmissibility in short-time sintering even at a lower sinterable temperature.
  • this method is industrially advantageous because it has excellent light transmissibility in short-time sintering at a lower sinterable temperature.
  • the sinterable temperature By setting the sinterable temperature to the above lower limit or higher and the above upper limit or lower, the sintering can be sufficiently advanced and a dense sintered body can be easily obtained.
  • the deactivation of the fluorescent agent can be suppressed.
  • the holding time at the sinterable temperature is preferably 10 minutes or less, more preferably 9 minutes or less, even more preferably 8 minutes or less, even more preferably 7 minutes or less, particularly preferably 6 minutes or less, and most preferably 5 minutes or less.
  • the holding time is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 3 minutes or more.
  • the sintering time required to produce the sintered body can be shortened without decreasing the translucency of the zirconia sintered body produced.
  • the holding time at the maximum sintering temperature required to produce the sintered body can be shortened to 10 minutes or less. This improves production efficiency, and when the zirconia calcined body of the present invention is applied to a dental product, the time required from determining the dimensions of the dental product to be used in treatment and cutting to making the dental product ready for treatment can be shortened, thereby reducing the time burden on patients. Also, energy costs can be reduced.
  • the heating rate and temperature drop rate in the sintering process are preferably set so as to shorten the time required for the sintering process.
  • the heating rate can be set so as to reach the maximum sintering temperature in the shortest time depending on the performance of the sintering furnace.
  • the heating rate up to the maximum sintering temperature can be, for example, 10°C/min or more, 50°C/min or more, 100°C/min or more, 120°C/min or more, 150°C/min or more, or 200°C/min or more.
  • the temperature drop rate is preferably set so as not to cause defects such as cracks in the sintered body. For example, after heating is completed, the sintered body can be allowed to cool at room temperature.
  • the sintering in the present invention can be carried out using a sintering furnace.
  • a sintering furnace There are no particular limitations on the type of sintering furnace, and for example, electric furnaces and degreasing furnaces used in general industry can be used.
  • electric furnaces and degreasing furnaces used in general industry can be used.
  • dental porcelain furnaces which have a relatively low sintering temperature (for example, the maximum sintering temperature), can also be used.
  • the zirconia sintered body of the present invention can be easily manufactured without HIP treatment, but by carrying out HIP treatment after sintering under normal pressure as described above, it is possible to further improve the translucency and mechanical strength.
  • the zirconia sintered body of the present invention has excellent translucency and excellent linear light transmittance, and is therefore particularly suitable as a dental material for dental prostheses and the like. In particular, it is extremely useful not only as a dental prosthesis used in the cervical region, but also as a dental prosthesis used on the occlusal surfaces of molars and the incisal ends of front teeth.
  • the zirconia sintered body of the present invention is extremely useful as a dental prosthesis, particularly for use on the incisal ends of front teeth.
  • the present invention includes embodiments that combine 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.
  • Examples 1 to 15 and Comparative Examples 1 to 6 [Preparation of zirconia compositions of Examples 1 to 15 and Comparative Examples 1 to 3]
  • the above raw material powders were mixed to have the compositions shown in Table 1, water was added, and the mixture was wet-pulverized and mixed in a ball mill for 20 hours.
  • a binder was then added to the pulverized slurry, which was then dried with a spray dryer to obtain a granular zirconia composition.
  • total yttria content represents the content of yttria relative to the total moles of zirconia and yttria.
  • a pellet-shaped calcined body was prepared as follows so as to obtain a zirconia sintered body sample for evaluating translucency. First, a cylindrical mold having a diameter of 19 mm was used, and the raw material composition was placed in the mold so that the thickness of the processable zirconia composite sintered body after sintering was 1.2 mm. Next, the raw material composition was press-molded with a uniaxial press molding machine at a surface pressure of 200 MPa to produce a pellet-shaped molded body.
  • the obtained pellet-shaped molded body was heated to 1000°C at a rate of 10°C/min using a sintering furnace "Noritake Katana (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd., and then was held for 2 hours and cooled to obtain a zirconia calcined body.
  • the properties of the zirconia sintered bodies produced in each example and comparative example were measured using the following methods.
  • ⁇ Method for measuring average primary particle size of particles in zirconia composition Regarding each particle (zirconia particle, yttria particle) in the zirconia composition, the average primary particle diameter of the primary particles constituting the granules obtained by the above-mentioned method of producing the zirconia composition using each raw material powder alone was measured by the following method.
  • the surface of the obtained granular powder was imaged (SEM image) using a scanning electron microscope (product name "VE-9800", manufactured by Keyence Corporation). After the grain boundaries of each particle were noted in the obtained image, the average primary particle size was calculated by image analysis. For the measurement of particle diameter, image analysis software (product name "Image-Pro Plus ver.
  • the particle size obtained by Image-Pro Plus is the diameter passing through the center of gravity of the particle, and the diameter passing through the center of gravity of the particle is obtained by measuring the length of a line segment connecting the outlines passing through the center of gravity, which is determined from the outline of the particle, at two-degree intervals around the center of gravity, and averaging the measured values (180 particles). In the measurement of particle size, particles that were not on the edge of the image were the subject of measurement.
  • Particles that were not on the edge of the image refers to particles excluding particles whose outlines did not fit within the screen of the SEM photograph image (particles whose outlines are interrupted on the top, bottom, left, and right boundaries).
  • the particle sizes of all particles that were not on the edge of the image were measured by selecting the option to exclude all particles on the boundary lines in Image-Pro Plus. For one sample of each Example and Comparative Example, the particle size of each granule in three fields of view was obtained, and the average primary particle size was calculated.
  • XRF X-ray fluorescence analysis
  • the tetragonal crystal fraction f t , cubic crystal fraction f c , and monoclinic crystal fraction f m of the calcined zirconia body were determined by analyzing the crystal phase in the calcined zirconia body. Specifically, the X-ray diffraction measurement was performed using a fully automatic horizontal multipurpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and X-ray analysis integrated software (SmartLab Studio II, manufactured by Rigaku Corporation) under the following conditions, and the area intensity of each peak (area intensity I of peak) was determined.
  • the crystalline phase ratio was calculated from the following formulas (2-1), (2-2), and (2-3), respectively, by assigning each peak to a crystalline phase.
  • Tetragonal crystal ratio f t (%) I t /(I m +I t +I c +I y ) ⁇ 100 (2-1)
  • Cubic crystal fraction f c (%) I c /(I m +I t +I c +I y ) ⁇ 100
  • Monoclinic ratio f m (%) I m /(I m +I t +I c +I y ) ⁇ 100 (2-3) (In the formula, fm represents the monoclinic rate (%), ft represents the tetragonal rate (%), and fc represents the cubic rate (%).
  • f y (%) I y / (I m + I t + I c + I y ) ⁇ 100 (2-4)
  • ⁇ Measurement of standard deviation of yttrium element distribution in zirconia calcined body The yttrium element distribution in the zirconia calcined body was measured under the following conditions using a field emission scanning electron microscope (FE-SEM Regulus 8220, manufactured by Hitachi High-Tech Corporation) and an energy dispersive X-ray analyzer (Aztec Energy X-Max 50, manufactured by Oxford Instruments), and the yttrium element was observed at 1.923 keV. The standard deviation (mol %) of yttrium element originating from the stabilizer in 10 particles was determined. Measurement magnification: 20,000 times Analysis mode: Point analysis Acceleration voltage: 5 kV Working distance: 15mm ⁇ 1mm X-ray take-off angle: 30 degrees Dead time: 7% Measurement time: 100 seconds
  • the particle size obtained by Image-Pro Plus is the diameter passing through the center of gravity of the particle, and the diameter passing through the center of gravity of the particle is the length of a line segment connecting the outlines passing through the center of gravity determined from the outlines of the particles, measured at 2 degree intervals around the center of gravity, and the average of the measured values (180 particles).
  • particles that were not on the edge of the image were the subject of measurement.
  • particles that were not on the edge of the image refers to particles excluding particles whose outlines did not fit within the screen of the SEM photograph image (particles whose outlines are interrupted on the top, bottom, left, and right boundaries).
  • the particle sizes of all particles that were not on the edge of the image were measured by selecting the option to exclude all particles on the boundary lines in Image-Pro Plus.
  • the particle sizes of the crystal particles in three fields of view were obtained, and the average primary particle size was calculated.
  • the temperature increase and decrease rates were set to be the same for 10-minute sintering and 120-minute sintering.
  • the two types of zirconia sintered bodies obtained were each polished into a flat plate sample having a thickness of 1.20 mm to be used as a sample for measuring the translucency.
  • 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.
  • the translucency of a zirconia sintered body which is a flat sample
  • the L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013).
  • a first translucency ⁇ L 1 *(W-B) for the first sintered body produced by sintering at 1550°C for 120 minutes and a second translucency ⁇ L 2 *(W-B) for the second sintered body produced by sintering at 1550°C for 10 minutes were determined, and the ratio of ⁇ L 2 *(W-B) to ⁇ L 1 *(W-B) ( ⁇ L 2 *(W-B)/ ⁇ L 1 * (W-B)) was calculated as the rate of change in translucency.
  • a rate of change in light transmittance of 0.85 or more (85% or more) was deemed acceptable.
  • the zirconia calcined body and composition of the present invention, as well as the method for producing them, are useful for use as dental materials such as dental prostheses.

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