JP5707667B2 - Translucent zirconia sintered body, method for producing the same, and use thereof - Google Patents

Description

  The present invention relates to a zirconia sintered body that is sintered under normal pressure, has a high density and strength, and is excellent in translucency. It is particularly suitable for use as a zirconia sintered body used in dental applications, a mill blank such as a denture material, and an orthodontic bracket.

A zirconia sintered body in which a small amount of Y ₂ O ₃ is dissolved as a stabilizer has high strength and high toughness. Widely used. In the case of dental materials, not only mechanical properties such as high strength and high toughness but also optical properties such as translucency and color tone are required from an aesthetic point of view.

  Zirconia single crystals have translucency, and zirconia single crystals (cubic zirconia) containing about 10 mol% of yttria have been conventionally used for jewelry, but have a problem of low strength. On the other hand, it is known that a normal zirconia sintered body which is a polycrystalline body has no translucency. It is known that the pores existing between and within the grains cause light scattering as a cause of this, and so far, by reducing the pores, that is, by increasing the density of the sintered body, it becomes a polycrystalline zirconia sintered body. Research has been done to give transparency.

For example, Patent Document 1 discloses translucent zirconia containing ₂ mol% or more of Y ₂ O ₃ and ₃ to 20 mol% of TiO ₂ , but contains a large amount of TiO ₂ to provide translucency, There was a problem with strength.

Patent Document 2 discloses a zirconia sintered body having a translucent sintered body density of 99.8% in a composition of ₃ mol% Y ₂ O ₃ and 0.25 wt% Al ₂ O ₃ , and has a total light beam for visible light. A transmittance of 49% (thickness 0.5 mm) has been reported. However, the sintered body is obtained by pressure sintering using a hot isostatic press (HIP), and sufficient translucency has not been obtained so far by normal pressure sintering.

JP-A-62-91467 Japanese Patent Laid-Open No. 20-50247

  The present invention eliminates the above-mentioned drawbacks in the conventional method, provides a sintered body having a high density and strength, and excellent translucency. In particular, such a zirconia sintered body is provided. An object of the present invention is to provide a powder that can be produced by a simple process by atmospheric pressure sintering and a production method using the powder.

  As a result of detailed studies on the relationship between the sinterability of zirconia powder and the total light transmittance of the obtained sintered body, the present inventors have found that a translucent zirconia sintered body using yttria-containing zirconia containing no alumina. In order to obtain the above, it has been found that it is necessary to control the sintering rate in a specific temperature range of the zirconia, and the present invention has been completed.

That is, the present invention
1) It is composed of zirconia containing 2 to 4 mol% of yttria as a stabilizer and not containing alumina, and has a relative density of 99.8% or more and a total light transmittance of 35% or more at a thickness of 1.0 mm. Translucent zirconia sintered body.
2) The translucent zirconia sintered body according to 1) above, wherein the crystal grain size is 0.20 to 0.45 μm.
3) The light transmission according to any one of 1) to 2) above, wherein the monoclinic phase ratio after immersion in hot water at 140 ° C. for 24 hours (generally generally referred to as “hydrothermal treatment”) is 20% or less. Sintered zirconia.
4) The translucent zirconia sintered body according to any one of 1) to 3) above, which has a three-point bending strength of 1000 MPa or more.
5) A translucent zirconia sintered body characterized in that it is sintered at 1350-1450 ° C. under normal pressure after molding zirconia powder containing 2-4 mol% yttria as a stabilizer and not containing alumina. Production method.
6) The production method according to 5) above, wherein the zirconia powder containing 2 to 4 mol% yttria as a stabilizer and not containing alumina is a powder calcined at 1000 ° C or higher and 1150 ° C or lower.
7) The production method according to any one of 5) to 6) above, wherein spray-molded powder granules are used as the zirconia powder.
8) The production method according to 7) above, wherein the zirconia powder is a spray granulated powder further containing an organic binder.
9) From ² to 4 mol% yttria as a stabilizer, BET specific surface area of 10 to 16 m ² / g, relative density from 70% to 90% at normal pressure sintering (in the atmosphere, heating rate of 300 ° C./hour) Sinter shrinkage rate (Δρ / ΔT: g / cm ³ · ° C.) of 0.0120 or more and 0.0135 or less, translucent zirconia sintering powder,
It consists of

  Conventionally, it has been known to use fine alumina (sol etc.) for high-density zirconia sintered body, but its addition amount exceeds 0.2 wt% from the viewpoint of improving the characteristics required of the sintered body. However, a zirconia sintered body containing a large amount of different component alumina has no sufficient translucency even at high density due to the effects of light refraction and scattering. The sintered body of the present invention is a zirconia sintered body containing no alumina, is excellent in basic characteristics required for the sintered body, and is excellent in translucency.

  Hereinafter, the present invention will be described in more detail.

  The “average particle size” related to the zirconia powder in the present invention is a particle having a median value (median diameter; particle size corresponding to 50% of the cumulative curve) of the cumulative particle size distribution expressed by volume. Is the diameter of a sphere having the same volume as that measured by a particle size distribution measuring apparatus using a laser diffraction method.

“Stabilizer concentration” refers to a value expressed as mole% of the ratio of stabilizer / (ZrO ₂ + stabilizer).

  “Monoclinic phase ratio (fm)” means the (111) and (11-1) planes of the monoclinic phase, the (111) plane of the tetragonal phase, and the cubic crystal by powder X-ray diffraction (XRD) measurement. The diffraction intensity of the (111) plane is obtained, and the value calculated by the following formula 1 is used.

(Where I represents the peak intensity of each diffraction line, and the subscripts m, t, and c represent the monoclinic phase, tetragonal phase, and cubic phase, respectively).

  The “reaction rate” related to the hydrated zirconia sol is obtained by ultrafiltration of a hydrated zirconia sol-containing liquid and determining the amount of zirconium in the unreacted substance present in the filtrate by inductively coupled plasma emission spectrometry. The amount of zirconia sol produced is calculated and the value expressed as the ratio of the amount of hydrated zirconia sol to the amount of raw material charged.

The “relative density” is a ratio (%) of (ρ / ρ ₀ ) × 100 using the measured density ρ actually measured by the Archimedes method and the theoretical density ρ ₀ obtained by the calculation formula of Equation 2 shown below. The value expressed in terms of. Here, the theoretical density of 3 mol% yttria-containing zirconia was set to 6.0956 (g / cm ³ ).

  The translucent zirconia sintered body of the present invention contains 2 to 4 mol% yttria as a stabilizer. If the stabilizer is less than 2 mol%, not only the strength is lowered, but also the crystal phase becomes unstable, making it difficult to produce a sintered body. On the other hand, if it exceeds 4 mol%, the strength decreases. The yttria concentration suitable for high intensity is 2.5 to 3 mol%, and the yttria concentration suitable for total light transmittance is 3 to 4 mol%.

  The translucent zirconia sintered body of the present invention satisfies the above composition, has a relative density of 99.8% or more, and has a total light transmittance of at least 35%, preferably 37 at a thickness of 1.0 mm. % Or more, and further has a high translucency up to 40%.

  The translucent zirconia sintered body of the present invention is obtained by atmospheric pressure sintering without using pressure sintering such as HIP, and the total light transmittance at a thickness of 1.0 mm reaches 40%. Translucency can be achieved.

  The translucent zirconia sintered body of the present invention preferably further has a crystal grain size of 0.20 to 0.45 μm. When the crystal grain size is less than 0.20 μm, since there are many fine pores between and within the grains, the relative density hardly reaches 99.8%. If the crystal grain size exceeds 0.45 μm, hydrothermal degradation of the sintered body is remarkable and the sintered body is destroyed.

  The translucent zirconia sintered body of the present invention preferably has a monoclinic phase ratio of 20% or less after being immersed in hot water at 140 ° C. for 24 hours. When the monoclinic phase ratio exceeds 20%, the sintered body is easily broken due to hydrothermal deterioration of the sintered body. A more preferable monoclinic phase rate is 10% or less.

  The translucent zirconia sintered body of the present invention preferably has a three-point bending strength of 1000 MPa or more. The three-point bending strength is 1100 MPa or more, and more preferably 1200 MPa or more.

  The zirconia powder for a translucent zirconia sintered body of the present invention contains 2 to 4 mol% of yttria as a stabilizer but does not contain alumina as an additive.

The zirconia powder for a translucent zirconia sintered body of the present invention preferably has a BET specific surface area of 10 to 16 m ² / g. When the zirconia powder has a BET specific surface area of less than 10 m ² / g, it becomes a powder that is difficult to sinter at low temperatures, and when it exceeds 16 m ² / g, agglomeration between particles becomes remarkable and the sinterability is adversely affected. . The BET specific surface area is particularly preferably in the range of 12 to 15 m ² / g.

  The zirconia powder for a translucent zirconia sintered body of the present invention preferably has an average particle size in the range of 0.4 to 0.7 μm. When the average particle size of the zirconia powder is smaller than 0.4 μm, the number of fine particles that increase the cohesiveness of the powder increases and it becomes difficult to mold, whereas when it exceeds 0.7 μm, there are many coarse particles containing hard agglomerated particles. Therefore, it becomes difficult to mold, and the coarse particles inhibit the densification of the sintering, so that the sinterability is poor. A preferable average particle diameter is 0.5 to 0.6 μm.

  The zirconia powder for a translucent zirconia sintered body of the present invention may be obtained by drying, calcining and pulverizing, for example, a hydrated zirconia sol obtained by hydrolysis of a zirconium salt aqueous solution. A hydrated zirconia sol obtained by adding an alkali metal hydroxide and / or an alkaline earth metal hydroxide to the zirconium salt aqueous solution and then hydrolyzing it until the reaction rate becomes 98% or more, is added with a stabilizer. As a raw material, yttrium may be added and dried.

  Zirconium salts used for the production of the hydrated zirconia sol include zirconium oxychloride, zirconyl nitrate, zirconium chloride, zirconium sulfate and the like. In addition, a mixture of zirconium hydroxide and acid may be used. Examples of the alkali metal hydroxide and / or alkaline earth metal hydroxide added to the zirconium salt aqueous solution include hydroxides such as lithium, sodium, potassium, magnesium, and calcium. The hydroxide is preferably added as an aqueous solution.

  The dried powder of hydrated zirconia sol obtained above is calcined at a temperature of 1000 to 1150 ° C. When the calcining temperature is outside this range, the zirconia fine powder obtained under the following pulverization conditions of the present invention becomes remarkably strong, or the average particle size becomes 0.4 because the number of coarse particles containing hard agglomerated particles increases. It is outside the range of ~ 0.7 μm, and it is difficult to obtain the zirconia powder of the present invention. A more preferable calcining temperature is 1050 to 1150 ° C.

  The calcined powder obtained above is further subjected to sinterability by wet pulverization using, for example, zirconia balls having a diameter of 3 mm or less until the average particle diameter is in the range of 0.4 to 0.7 μm. It is preferable to adjust to.

The zirconia powder for a translucent zirconia sintered body of the present invention has a sintering shrinkage rate (Δρ /) at a relative density of 70% to 90% in atmospheric pressure sintering (in the atmosphere, a heating rate of 300 ° C./hour). ΔT: g / cm ³ · ° C.) is preferably 0.0120 or more and 0.0135 or less, particularly 0.0125 or more and 0.135 or less (relative density in the composition of the present invention is 3 mol% yttria-containing zirconia) The theoretical density was calculated by converting 6.09556 (g / cm ³ ) as 100%).

  The zirconia powder for a translucent zirconia sintered body of the present invention is formed into a molded body having a relative density of about 50 ± 5% by ordinary press molding (hydrostatic pressure pressing (CIP treatment if necessary)). When such a molded body is heated in the atmosphere, sintering shrinkage starts from a temperature equal to or higher than the calcination temperature, particularly around 1100 ° C. The shrinkage rate of sintering is constant in the range from 70% to 90% relative density. The shrinkage rate gradually decreases from the point where the relative density exceeds 90%, and finally the temperature is further increased near 100%. But it will not shrink.

The sintering shrinkage rate (Δρ / ΔT: g / cm ³ · ° C.) from 70% to 90% relative density in atmospheric pressure sintering (in the air, heating rate 300 ° C./hour) is obtained by molding zirconia powder. (After die molding, CIP treatment (pressure 2 t / cm ² )), and then can be measured by a general-purpose thermal dilatometer (DL9700 manufactured by ULVAC-RIKO). Since the sintering shrinkage rate in the present invention is a measured value at a relative density of 70% or more, it is not affected by variations in the initial molding density (relative density around 50%). Furthermore, since the sintering shrinkage rate is constant at a relative density of 70% to 90% and the shrinkage rate is a linear function of temperature and relative density, an accurate sintering shrinkage rate can be obtained without using a special approximate calculation process. It is possible to ask.

The zirconia powder for a translucent zirconia sintered body of the present invention has a sintering shrinkage rate (Δρ /) at a relative density of 70% to 90% in atmospheric pressure sintering (in the atmosphere, a heating rate of 300 ° C./hour). If ΔT: g / cm ³ · ° C.) deviates from the above range, it is difficult to obtain a sintered body having high translucency with a relative density of 99.8% or more.

The zirconia powder of the present invention is a powder that can obtain a highly translucent sintered body in normal pressure sintering without using pressure sintering such as HIP treatment. The higher the shrinkage rate (Δρ / ΔT: g / cm ³ · ° C.), the better. Even if the sintering shrinkage rate is larger than the range of the present invention, it is difficult to obtain a sintered body having high translucency in atmospheric pressure sintering.

  The sintering shrinkage rate used in the present invention is different when the heating rate changes, but has a constant value when the heating rate is determined, and is a value inherent to the powder.

In the powder of the present invention, the sintering shrinkage rate (Δρ / ΔT: g / cm ³ · ° C.) is 0.0120 or more and 0.0135 or less, and if it is out of this range, atmospheric pressure sintering, particularly 1450 ° C. or less, Furthermore, a zirconia sintered body having high translucency cannot be obtained in atmospheric pressure sintering at 1400 ° C. or lower.

  The zirconia powder for a translucent zirconia sintered body of the present invention is preferably a spray-molded powder granule, and in particular, a spray granulated powder containing an organic binder in addition to yttria as a stabilizer and alumina sol as an additive. Is preferably used.

When zirconia granules are formed by spray drying with zirconia powder as a slurry, the flowability when forming a molded body is high, and bubbles are hardly generated in the sintered body. It is preferable that the granule has a particle size of 30 to 80 μm and a light bulk density of 1.10 to 1.40 g / cm ³ .

  In the case of using a binder for the granule, examples of the binder include commonly used binders such as polyvinyl alcohol, polyvinyl butyrate, wax, and acrylic. Among them, carboxyl groups or derivatives thereof (for example, salts, Acrylic materials having an ammonium salt are particularly preferred. Examples of the acrylic binder include polyacrylic acid, polymethacrylic acid, acrylic acid copolymer, methacrylic acid copolymer, and derivatives thereof. The amount of the binder added is preferably 0.5 to 10% by weight, particularly 1 to 5% by weight, based on the ceramic powder in the ceramic powder slurry.

  The translucent zirconia sintered body of the present invention is formed at a temperature of 1350 to 1450 ° C., particularly 1400 ° C. or less and 100 ° C./hour or less under normal pressure after molding a zirconia powder containing 2 to 4 mol% of yttria as a stabilizer. It is preferable to manufacture by sintering.

  When the sintering temperature is less than 1350 ° C., the relative density does not reach 99.8%, and when it exceeds 1450 ° C., the hydrothermal degradation of the sintered body proceeds remarkably, and the sintered body tends to break.

  The translucent zirconia sintered body of the present invention is obtained by atmospheric pressure sintering, but the sintering atmosphere is not particularly limited as long as it is not a reducing atmosphere, and may be an oxygen atmosphere or in-air sintering. It is particularly preferable to sinter in the atmosphere.

  Since the translucent zirconia sintered body of the present invention has high density, high strength and excellent translucency, the zirconia sintered body used in dental applications, specifically, a mill blank such as a denture material, It is excellent as a sintered body used as an orthodontic bracket, and the powder for a translucent zirconia sintered body of the present invention can be sintered under normal pressure without using a large pressure sintering apparatus such as HIP. A translucent zirconia sintered body can be manufactured.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples at all.

  In the examples, the average particle diameter of the zirconia powder was measured using a Microtrac particle size distribution meter (manufactured by Honeywell, model: 9320-HRA). As sample pretreatment conditions, the powder was suspended in distilled water and dispersed for 3 minutes using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho, model: US-150T). The monoclinic phase ratio determined by XRD measurement was calculated from Equation 1 (in all examples, cubic crystals were not included). Moreover, the average particle diameter of the zirconia granule was calculated | required with the screening test method.

The raw material powder was molded by a mold press at a pressure of 700 kgf / cm ² , and the preform was subjected to cold isostatic pressing (CIP) treatment at a pressure of 2 t / cm ² using a rubber mold to obtain a molded body. The obtained molded body was sintered at a predetermined temperature (holding time 2 hours). The average particle diameter of the crystal grains of the zirconia sintered body is determined by subjecting the mirror-polished sintered body to a thermal etching treatment and using a field emission scanning electron microscope (FESEM) (manufactured by JEOL Ltd., model: JSM-T220). Calculated by the planimetric method. The sintered body density was measured by Archimedes method.

  The total light transmittance of the sintered body was measured with a light source D65 in accordance with JIS K7361 using a turbidimeter (Nippon Denshoku Industries Co., Ltd., model: NDH2000). The sample used was a disc-shaped one having a thickness of 1 mm obtained by polishing the sintered body on both sides. The strength of the sintered body was evaluated by a three-point bending measurement method.

  The hydrothermal durability test was evaluated by immersing the sintered body in 140 ° C. hot water for 24 hours and determining the ratio of the monoclinic phase to be formed (monoclinic phase ratio). The monoclinic phase ratio was obtained by the above-described Equation 1 by the same calculation method as that of the monoclinic phase ratio of the zirconia fine powder by performing XRD measurement on the sintered body subjected to the immersion treatment.

Examples and Comparative Examples To the hydrated zirconia sol obtained by the hydrolysis reaction of zirconium oxychloride, yttrium chloride was added to a yttria concentration of 3 mol% and dried, and the calcining temperature of 1000 to 1150 ° C. was 1 It was calcined for 10 hours, and distilled water was added to make a slurry having a zirconia concentration of 45% by weight. This slurry was pulverized for 24 hours with a vibration mill using zirconia balls having a diameter of 3 mm to obtain zirconia powder.

The obtained powder was press-molded with CIP (pressure 2 t / cm ² ) and sintered under the condition of 1400 ° C. Similarly, a CIP-molded compact was subjected to a sintering shrinkage rate (Δρ) from a relative density of 70% to 90% at a temperature rising rate of 300 ° C./hour in the air using a heat shrinkage meter (DL9700, ULVAC-RIKO). / ΔT: g / cm ³ · ° C.).

Sintering shrinkage rate (Δρ / ΔT: g / cm ³ · ° C.) of BET specific surface area and relative density of 70% to 90% of zirconia powder, atmospheric pressure 1400 ° C. and heating rate 100 ° C./hour Table 1 shows the sintered relative density, the average crystal grain size, the total light transmittance, the bending strength, and the monoclinic phase ratio after hydrothermal deterioration when sintered.

When the BET specific surface area and the sintering shrinkage rate (Δρ / ΔT: g / cm ³ · ° C.) were changed depending on the calcining conditions, the light transmission having a relative density of 99.8% or more at 0.0120 or more and 0.0140 or less. A sintered zirconia sintered body was obtained.

The relationship between the sintering shrinkage rate (Δρ / ΔT: g / cm ³ · ° C.) and the sintering density is shown in FIG.

  Only in a sintered body having a relative density of 99.8% or more, a translucency with a total light transmittance of 35% or more is obtained. It is.

Relationship between sintering shrinkage rate (Δρ / ΔT: g / cm ³ · ° C.) and sintered body relative density Thermal shrinkage curve (No. 7) in atmospheric pressure sintering of zirconia powder (heating rate 300 ° C./hour)

Claims (9)

It is made of zirconia containing 2 to 4 mol% yttria as a stabilizer and not containing alumina, the relative density is 99.8% or more, the total light transmittance at a thickness of 1.0 mm is 35% or more, and the crystal grain size is A translucent zirconia sintered body characterized by 0.20 to 0.45 μm and a three-point bending strength of 1060 to 1230 MPa. The translucent zirconia sintered body according to claim 1, wherein the monoclinic phase ratio after being immersed in hot water at 140 ° C for 24 hours is 20% or less. The zirconia powder containing 2 to 4 mol% yttria as a stabilizer and not containing alumina is sintered at 1350 to 1450 ° C under normal pressure and not HIP sintered. The manufacturing method of translucent zirconia sintered compact of this. The method according to claim 3, wherein the zirconia powder containing 2 to 4 mol% yttria as a stabilizer and not containing alumina is a powder calcined at 1000 ° C or higher and 1150 ° C or lower. The method according to any one of claims 3 to 4, wherein the stabilizer is a spray-molded powder granule of zirconia powder containing 2 to 4 mol% of yttria and not containing alumina. The production method according to claim 5, wherein the spray-molded powder granules of zirconia powder containing 2 to 4 mol% yttria as a stabilizer and not containing alumina are spray granulated powders further containing an organic binder. A dental material comprising the sintered body according to claim 1. The dental material according to claim 7, wherein the dental material is an orthodontic bracket. The dental material according to claim 7, wherein the dental material is a denture and / or a denture mill blank.

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