JP2018052806A - Zirconia sintered body and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zirconia sintered body which can be widely used as a dental material, especially a zirconia sintered body which can be applied to both of a dental material for back tooth and a dental material for front tooth, and provide a simple manufacturing method therefor.SOLUTION: There is provided a manufacturing method of a zirconia sintered body having a molding process for molding a powder composition containing a first zirconia power with yttria content of 2 mol% to 4 mol% and a second zirconia powder with yttria content of over 4 mol% and 6 mol% or less and having yttria content of over 3 mol% and 5.2 mol% or less to obtain a molded body, and a sintering process for sintering the molded body to obtain a sintered body.SELECTED DRAWING: None

Description

  The present invention relates to a zirconia sintered body having both translucency and high strength and a method for producing the same.

  Since the zirconia sintered body has high mechanical strength and high aesthetics based on translucency, it is used not only as a structural material and a decorative member but also as a dental material (Patent Documents 1 to 4). When a zirconia sintered body is used as a dental material, it is required to have a high translucency of 40% or more of total light transmittance and a high bending strength of 800 MPa or more (Patent Document 1).

  As a zirconia sintered body satisfying such requirements, it is manufactured by a hot isostatic pressing (hereinafter referred to as “HIP”) treatment, and has a total light transmittance of 43% or more at a sample thickness of 0.5 mm, and A zirconia sintered body having a three-point bending strength of 1700 MPa or more and an yttria content of 2 to 4 mol% is disclosed (Patent Document 2). However, since the HIP process requires a large-scale apparatus, the practical use of the zirconia sintered body of Patent Document 2 has been limited.

  On the other hand, a zirconia sintered body having both high mechanical strength and high translucency without requiring HIP treatment and a method for producing the same have been studied.

  Patent Document 1 discloses a method of forming and sintering a zirconia powder having a BET specific surface area and crystallinity controlled and having a yttria content of about 3 mol%. In Patent Document 1, the total light transmittance with respect to D65 light at a sample thickness of 0.5 mm is 41.20% to 44.06% by baking at a maximum temperature of 1450 ° C. for 2 hours, and the bending strength is 860 to 600%. It is disclosed that a zirconia sintered body of 891 MPa can be obtained. However, the total light transmittance of this zirconia sintered body is less than 30% at the maximum when converted to the total light transmittance with respect to D65 light (hereinafter also simply referred to as “total light transmittance”) at a sample thickness of 1 mm. The zirconia sintered body of Patent Document 1 has insufficient translucency for use as a dental material.

  As a zirconia sintered body having mechanical strength and translucency that can be used practically as a dental material, Patent Document 3 controls the sintering shrinkage rate, the BET specific surface area, etc. up to a relative density of 70 to 90%. The zirconia powder obtained by subjecting the zirconia powder having an yttria content of 2 to 4 mol% to atmospheric pressure sintering has a total light transmittance of 35% or more and a three-point bending strength of 1000 MPa or more. It is disclosed that there is.

  In Patent Document 4, a zirconia sintered body having both high mechanical strength and high translucency and having high translucency that can be applied as a dental material for anterior teeth, and without using HIP treatment, Disclosed is a method for producing a zirconia sintered body. The zirconia sintered body disclosed in Patent Document 4 has a yttria content exceeding 4 mol% and not more than 6.5 mol%, and is a zirconia sintered body obtained by atmospheric pressure sintering, and has a total light transmittance of 42. %, And the three-point bending strength was 550 to 870 MPa.

  Since the zirconia sintered body disclosed in Patent Documents 3 and 4 and can be produced by atmospheric pressure sintering has high mechanical strength and high translucency, it is used as a practical dental material.

JP, 2006-108176, A JP 2008-050247 A JP 2010-150063 A Japanese Patent Laying-Open No. 2015-143178

  The zirconia sintered bodies of Patent Documents 3 and 4 satisfy the mechanical strength and translucency required as dental materials. However, in actual use, materials with higher strength are applied as dental materials for back teeth, and materials with higher translucency are applied as dental materials for anterior teeth. Was done. Further, Patent Document 4 discloses only one point of a zirconia sintered body having a total light transmittance of 44%, a three-point bending strength of 870 MPa, and high mechanical strength and translucency. In order to repeatedly produce a knot, it was necessary to control the production conditions in great detail.

  In view of these problems, the present invention provides a zirconia sintered body that can be widely used as a dental material, in particular, a zirconia sintered body that can be applied to both a back tooth dental material and an anterior dental material, and a simple manufacturing method thereof. The purpose is to do.

  The present inventors examined a zirconia sintered body having mechanical properties and translucency that satisfy the properties required for dental materials, in particular, dental materials for anterior teeth and posterior teeth, and a method for producing the same. As a result, it was found that such a zirconia sintered body can be easily produced by controlling the state of the raw material powder, and the present invention has been completed.

  That is, the present invention includes a first zirconia powder having an yttria content of 2 mol% or more and 4 mol% or less, and a second zirconia powder having an yttria content of more than 4 mol% and 6 mol% or less, and the yttria content is It has a molding step of forming a powder composition that exceeds 3 mol% and 5.2 mol% or less to obtain a molded body, and a sintering step that sinters the molded body to obtain a sintered body. It is a manufacturing method of a zirconia sintered compact.

  According to the present invention, the present invention provides a zirconia sintered body that can be widely used as a dental material, in particular, a zirconia sintered body that can be applied to either a back tooth dental material or an anterior tooth dental material, and such a zirconia sintered body. The manufacturing method which can be manufactured can be provided.

The graph which shows the yttria density distribution of Example 1 Graph showing the yttria concentration distribution of Comparative Example 2

  Hereinafter, the manufacturing method of the zirconia sintered compact of this invention is demonstrated.

  The production method of the present invention includes a first zirconia powder having an yttria content of 2 mol% or more and 4 mol% or less, and a second zirconia powder having an yttria content of more than 4 mol% and 6 mol% or less, and containing yttria A molding step of molding a powder composition (hereinafter also simply referred to as “powder composition”) having an amount of more than 3 mol% and not more than 5.2 mol% to obtain a molded body.

  A powder composition is provided for the forming step. In the powder composition, the yttria content is more than 3 mol% and not more than 5.2 mol%. When the yttria content is 3 mol% or less, the obtained zirconia sintered body has a total light transmittance of 42% or less with respect to D65 light at a sample thickness of 1 mm, and the use that can be applied as a dental material is limited. On the other hand, if the yttria content exceeds 5.2 mol%, a zirconia sintered body having a three-point bending strength of 800 MPa or more required as a dental material cannot be obtained even with the production method of the present invention.

  The yttria content of the powder composition is preferably 3.5 mol% to 4.8 mol%, more preferably 3.8 mol% to 4.6 mol%, and even more preferably 3.8 mol% to 4.3 mol%. .

  The powder composition includes a first zirconia powder (hereinafter also referred to as “low yttria powder”) having an yttria content of 2 mol% to 4 mol%, and a second yttria content of more than 4 mol% and 6 mol% or less. Zirconia powder (hereinafter also referred to as “high yttria powder”). By sintering such a powder composition, the resulting zirconia sintered body tends to improve the mechanical strength as the average crystal grain size increases, so even without controlling the detailed production conditions, A zirconia sintered body having mechanical strength and translucency exceeding the characteristics required as a dental material can be obtained.

  The yttria content of the low yttria powder is 2 mol% or more and 4 mol% or less, preferably 2 mol% or more and 3.5 mol% or less, and more preferably 2.3 mol% or more and 3.5 mol% or less. On the other hand, the yttria content of the high yttria powder is more than 4 mol% and 6 mol% or less, preferably 4 mol% or more and 5.7 mol% or less, more preferably 4.5 mol% or more and 5.7 mol% or less.

  In the present invention, the powder composition comprises a zirconia powder having a yttria content of 2.3 mol% to 3.5 mol% as a low yttria powder, and a yttria content of 5.2 mol% to 5.7 mol% as a high yttria powder. It is preferable to contain zirconia powder.

  The content ratio of the low yttria powder and the high yttria powder in the powder composition may be a ratio at which the powder composition has the target yttria content. The content ratio of the low yttria powder and the high yttria powder in the powder composition varies depending on the yttria content of each powder, but the weight ratio of the low yttria powder and the high yttria powder is low yttria powder: high yttria powder = 1. % By weight: 99% by weight to 99% by weight: 1% by weight. More preferable weight ratio is low yttria powder: high yttria powder = 20 wt%: 80 wt% to 80 wt%: 20 wt%, and further 35 wt%: 65 wt% to 65 wt%: 35 wt%. Is mentioned.

  The low yttria powder and the high yttria powder are each a hydrolysis step for obtaining a hydrated zirconia sol by hydrolysis of an aqueous zirconium salt solution, and drying after mixing an yttrium compound with the obtained hydrated zirconia sol. It can be manufactured by a manufacturing method having a process and a calcining process of calcining dried powder to obtain calcined powder. As a preferable method for producing low yttria powder and high yttria powder, for example, hydrated zirconia sol obtained by hydrolyzing at least one member selected from the group consisting of zirconium oxychloride salt, zirconyl nitrate salt, zirconium chloride salt and zirconium sulfate salt In addition, after mixing at least one of yttrium oxide and yttrium chloride, drying in the air at 80 ° C. or higher and 200 ° C. or lower, and then calcining in the air at 1050 ° C. or higher and 1250 ° C. or lower can be given. .

The powder composition may contain alumina (Al ₂ O ₃ ). The alumina content of the powder composition is 0% by weight or more and 0.1% by weight or less, more preferably 0% by weight or more and less than 0.1% by weight, more preferably 0% by weight or more as a weight ratio of alumina to the weight of the powder composition 0.075 wt% or less can be mentioned, and when the powder composition contains alumina, the alumina content is more than 0 wt% and 0.1 wt% or less as a weight ratio of alumina to the weight of the powder composition, Furthermore, it is more than 0% by weight and less than 0.1% by weight, further more than 0% by weight and 0.075% by weight or less, and further 0.01% by weight or more and 0.075% by weight or less.

  The crystallite diameter of the powder composition is from 200 to 400 mm, and more preferably from 300 to 400 mm. The crystallite diameter of the powder composition is determined by XRD peaks (hereinafter referred to as “main XRD peaks”) of tetragonal (111) plane and cubic (111) plane in powder X-ray diffraction (hereinafter referred to as “XRD”) measurement. Can also be obtained from the following equation.

Crystallite diameter = κλ / βcosθ
In the above formula, κ is the Scherrer constant (κ = 1), λ is the wavelength of the measured X-ray (λ is 1.541862Å when using the CuKα ray as a source), β is the half width (°) of the main XRD peak, And θ are the Bragg angles of the main XRD peak.

  The main XRD peak is an XRD peak that appears in the vicinity of 2θ = 30.1 to 30.2 ° in XRD using CuKα rays as a radiation source. The peak is an XRD peak in which a tetragonal (111) plane and a cubic (111) plane overlap. When calculating the crystallite diameter, the main XRD peak is subjected to waveform processing without performing tetragonal and cubic peak separation. The Bragg angle (θ) of the main XRD peak after waveform processing and the half width (β) of the main XRD peak corrected for the mechanical spread width may be obtained.

  In the powder composition, the ratio of tetragonal crystals and cubic crystals (hereinafter also referred to as “T + C phase ratio”) obtained by the following formula is preferably 60% or more, more preferably 65% or more.

T + C phase ratio (%) = 100−fm (%)
In the above formula, fm is a monoclinic phase rate determined from the XRD pattern.

  From the viewpoint of homogenizing the physical properties of the powder composition, it is preferable that the powder composition, the low yttria powder, and the high yttria powder have the same BET specific surface area and average particle diameter.

A preferable BET specific surface area is 5 m ² / g or more and less than 17 m ² / g, and further 5 m ² / g or more and 15 m ² / g or less. Preferred average particle diameters are 0.30 μm or more and 0.60 μm, further 0.35 μm or more and 0.55 μm or less, and further 0.40 μm or more and 0.50 μm or less.

  A powder composition contains a low yttria powder and a high yttria powder, and if the powder composition of the target composition is obtained, the manufacturing method is arbitrary. It is convenient to obtain the powder composition by mixing low yttria powder and high yttria powder. If both become uniform, the mixing method is arbitrary, and at least one of dry mixing and wet mixing, and further wet mixing can be mentioned. As a preferred mixing method, mixing in an aqueous solvent can be mentioned. In order to mix uniformly, it is preferable to use non-granulated powder such as calcined powder as the low yttria powder and the high yttria powder.

  When the powder composition contains alumina, the low yttria powder and the high yttria powder may be mixed and then mixed with alumina to form a powder composition. However, at least one of the low yttria powder and the high yttria powder may be mixed with the alumina. After that, it is preferable to mix the low yttria powder and the high yttria powder to obtain a powder composition.

It is preferable that the powder composition to be subjected to the molding step is a granulated powder. Since the granulated powder composition has high fluidity, it tends to be densified during sintering. As the granulated powder, and the average particle diameter is 30μm or more 80μm or less, the bulk density can be given not more than 1.10 g / cm ³ or more 1.40 g / cm ^3.

  The granulated powder is obtained by mixing a powder composition and an organic binder and spray drying the mixture. The content of the organic binder in the granulated powder can be from 1% by weight to 5% by weight with respect to the weight of the powder composition.

  If a molded body having a desired shape is obtained in the molding process, the molding method is arbitrary. Examples of the molding method include at least one selected from the group consisting of press molding, cold isostatic pressing, sheet molding, and injection molding.

  The shape of the molded body is arbitrary, and can include any one or more of a group consisting of a spherical shape, a substantially spherical shape, an elliptical shape, a disk shape, a cylindrical shape, a cubic shape, a rectangular parallelepiped shape, a polyhedral shape, and a substantially polyhedral shape. .

  The production method of the present invention may have a calcining step of calcining the molded body obtained in the molding step to obtain a calcined body. The calcination process is a process between the forming process and the sintering process. By the calcination step, the yttria content exceeds 3 mol% and is 5.2 mol% or less, more preferably 3.5 mol% or more and 4.8 mol% or less, further 3.8 mol% or more and 4.6 mol% or less, or even 3 A zirconia calcined body of 0.8 mol% or more and 4.3 mol% or less is obtained. The calcined body is a molded body at the initial stage of sintering, and has a structure including necking between powders. In the calcination step, the calcined body can be processed into an arbitrary shape.

  The calcination is preferably performed at a calcination temperature of 600 ° C. to 1400 ° C., more preferably 600 ° C. to 1200 ° C., and even more preferably 800 ° C. to 1100 ° C.

  Examples of the holding time at the calcination temperature include 1 hour to 5 hours, further 1 hour to 3 hours, and further 1 hour to 2 hours.

  The calcining atmosphere may be an atmosphere other than the reducing atmosphere, and is preferably at least one of an oxygen atmosphere and an air atmosphere, and is easily set to an air atmosphere.

  In the sintering process, the molded body obtained in the molding process is sintered to obtain a sintered body. As a result, the yttria content exceeds 3 mol% and is 5.2 mol% or less, more preferably 3.5 mol% or more and 4.8 mol% or less, further 3.8 mol% or more and 4.6 mol% or less, or even 3.8 mol. % To 4.3 mol% of zirconia sintered body is obtained.

  When the production method of the present invention includes a calcining step, the calcined body may be sintered instead of the formed body in the sintering step.

  The sintering temperature in the sintering step is preferably 1400 ° C. or higher and 1600 ° C. or lower, more preferably 1420 ° C. or higher and 1580 ° C. or lower, further 1440 ° C. or higher and 1560 ° C. or lower, and further preferably 1480 ° C. or higher and 1560 ° C. or lower. Other sintering temperatures include 1450 ° C. or higher and 1650 ° C. or lower, 1500 ° C. or higher and 1650 ° C. or lower, 1500 ° C. or higher and 1650 ° C. or lower, and 1550 ° C. or higher and 1650 ° C. or lower.

  The heating rate in the sintering step is 150 ° C./hour or more and 800 ° C./hour or less, further 150 ° C./hour or more and 700 ° C./hour or less, and further 200 ° C./hour or more and 600 ° C./hour or less. it can. Thereby, progress of sintering in a temperature rising process can be suppressed, and a molded object can be sintered under sintering temperature.

  The holding time at the sintering temperature (hereinafter also simply referred to as “holding time”) varies depending on the sintering temperature. Examples of the holding time include 1 hour to 5 hours, further 1 hour to 3 hours, and further 1 hour to 2 hours.

  The sintering atmosphere may be an atmosphere other than the reducing atmosphere, and is preferably at least one of an oxygen atmosphere or an air atmosphere, and it is simple to use an air atmosphere.

  As a particularly preferable sintering step, sintering is performed under atmospheric pressure at a heating rate of 700 ° C./hour or less and a sintering temperature of 1440 ° C. or more and 1560 ° C. or less.

  Any sintering method can be applied in the sintering step. Examples of the sintering method include at least one selected from the group consisting of atmospheric pressure sintering, HIP treatment, PSP, and vacuum sintering. In general, as a means for improving the translucency, after a sintered body is obtained by sintering under normal pressure, a special sintering method such as HIP or other pressure sintering or SPS is used. However, the special sintering method not only complicates the manufacturing process but also increases the manufacturing cost. Therefore, the sintering step in the present invention is preferably atmospheric pressure sintering, and more preferably only atmospheric pressure sintering. Normal pressure sintering is a method of sintering by simply heating without applying an external force to the compact during sintering. A specific example of normal pressure sintering is sintering under atmospheric pressure.

  One of the features of the production method of the present invention is that the decrease in mechanical strength accompanying the increase in the average crystal grain size of the zirconia sintered body obtained as the sintering temperature increases, and the average crystal It may be mentioned that the mechanical strength may increase as the particle size increases. Thereby, it becomes easy to obtain a zirconia sintered body having a higher total light transmittance while maintaining a high mechanical strength. Therefore, it is easy to manufacture a zirconia sintered body that has both mechanical properties and translucency that satisfy the properties required for both front and back dental materials without detailed manufacturing condition control. can do.

  As another aspect of the present invention, the present invention provides a first zirconia powder having an yttria content of 2 mol% to 4 mol%, and a second zirconia powder having an yttria content of more than 4 mol% and 6 mol% or less. A molding step of molding a powder composition having a yttria content of more than 3 mol% and not more than 5.2 mol% to obtain a molded body, and a calcination step of calcining the molded body to obtain a calcined body, It can also be set as the manufacturing method of the zirconia calcined body characterized by having.

  The zirconia sintered body obtained by the production method of the present invention has a wider yttria concentration distribution than the conventional sintered body. That is, according to the production method of the present invention, the yttria content exceeds 3 mol% and is 5.2 mol% or less, and the maximum value of the frequency of the yttrium concentration distribution in the quantitative analysis of elements of the energy dispersive X-ray spectrum is 7 A zirconia sintered body characterized by being 5% or less is obtained.

  The zirconia sintered body obtained by the production method of the present invention has an yttria content of 3.5 mol% to 4.8 mol%, more preferably 3.8 mol% to 4.6 mol%, and even more preferably 3.8 mol%. It is preferable that it is 4.3 mol% or less.

  In the present invention, the yttria content of the zirconia sintered body is an average composition of the sintered body determined by composition analysis, and can be measured by ICP measurement.

  In the zirconia sintered body obtained by the production method of the present invention, the maximum value of the frequency of yttrium concentration distribution (hereinafter also simply referred to as “frequency”) in the quantitative analysis of elements in the energy dispersive X-ray spectroscopic spectrum is 7.5. % Or less, preferably 7.0% or less.

  The fact that the maximum value of frequency (hereinafter also referred to as “maximum frequency”) is 7.5% or less indicates that the zirconia sintered body obtained by the production method of the present invention has different yttria concentration regions in the sintered body. Means having more. The fact that the yttrium content is in the above range and that the sintered body has such an yttria distribution is considered to be one of the reasons contributing to the improvement of the mechanical properties of the sintered body. The maximum frequency is 3.0% or more, and further 5.0% or more.

  The quantitative analysis of the elements of the EDS spectrum was carried out by obtaining an EDS spectrum from a scanning electron microscope (hereinafter also referred to as “SEM”) observation of the sintered body, and zirconium (Zr) and yttrium (Y) of the obtained EDS spectrum. The intensity of the characteristic X-ray may be quantified. The quantification of the EDS spectrum can be performed by measuring at 40,000 or more randomly extracted points in the SEM observation chart. The yttrium concentration is preferably determined as a ratio of the strength of yttrium to the strength of zirconium (hereinafter also referred to as “Y / Zr ratio”). The yttrium concentration distribution is preferably an yttrium concentration distribution shown by dividing a certain yttrium concentration as a concentration range, and is an yttrium concentration distribution shown by dividing the Y / Zr ratio into concentration ranges of 0.5%. Is mentioned. The frequency is a ratio (%) of the number of measurement points corresponding to each yttrium concentration with respect to the total number of measurement points in the quantification of the EDS spectrum. Since the sintered body obtained by the manufacturing method of the present invention has a homogeneous composition on the surface and inside, the yttrium concentration distribution of the entire sintered body can be measured by EDS observation of the surface.

The crystal phase of the zirconia sintered body obtained by the production method of the present invention is tetragonal. The tetragonal crystal preferably includes a T phase and a T ^* phase. The ratio of the T ^* phase to the T phase in the crystal phase (hereinafter also referred to as “T ^* / T ratio”) is 62% or more and less than 100%, preferably 65% or more and less than 100%. Since the mechanical strength is increased, the T ^* / T ratio is more preferably 76% or more and less than 100%, and further preferably 76% or more and 90% or less.

The zirconia sintered body obtained by the production method of the present invention may contain alumina (Al ₂ O ₃ ). The alumina content of the zirconia sintered body obtained by the production method of the present invention is 0% by weight or more and 0.1% by weight or less as a weight ratio of alumina to the weight of the zirconia sintered body obtained by the production method of the present invention. Is 0% by weight or more and less than 0.1% by weight, and further 0% by weight or more and 0.075% by weight or less. When the zirconia sintered body obtained by the production method of the present invention contains alumina, alumina can be used. The content is more than 0 wt% and 0.1 wt% or less, more than 0 wt% and less than 0.1 wt% as the weight ratio of alumina to the weight of the zirconia sintered body obtained by the production method of the present invention, Further, it may be greater than 0% by weight and 0.075% by weight or less, and further 0.01% by weight or more and 0.075% by weight or less.

  The mechanical strength and translucency of the zirconia sintered body are affected by the average crystal grain size, and both are in a trade-off relationship. That is, the mechanical strength increases as the average crystal grain size decreases, but the translucency decreases. On the contrary, as the average crystal grain size increases, the mechanical strength decreases, but the translucency increases. In order to achieve both the mechanical strength and the translucency required for dental materials, the translucency is increased by making the yttria content exceed 3 mol%, and the average crystal grain size is set to about 0.41 μm. The strength was high.

  On the other hand, in the production method of the present invention, even when the average crystal grain size exceeds 0.41 μm, further 0.42 μm or more, and even 0.45 μm or more, it is required for dental materials. A zirconia sintered body having a mechanical strength equal to or higher than the mechanical strength can be manufactured. Examples of the average crystal grain size of the zirconia sintered body obtained by the production method of the present invention include 1.5 μm or less, and further 1.0 μm or less. The average grain size is preferably 0.55 μm or more and 1.5 μm or less, more preferably 0.6 μm or more and 1.0 μm or less.

  Preferably, according to the production method of the present invention, a zirconia sintered body having an yttria content of more than 3 mol% and 5.2 mol% or less and an average crystal grain size of 0.42 μm or more is obtained. The zirconia sintered body is a so-called translucent zirconia sintered body having higher mechanical strength and translucency than mechanical strength and translucency required for dental materials.

  The zirconia sintered body obtained by the production method of the present invention is obtained by atmospheric pressure sintering, and has high mechanical strength while having such a large average crystal grain size. As the mechanical strength of the zirconia sintered body obtained by the production method of the present invention, the three-point bending strength obtained by a measuring method according to JIS R 1601 is 810 MPa or more, more preferably more than 870 MPa, preferably It is mentioned that it is 900 MPa or more. In particular, the zirconia sintered body obtained by the production method of the present invention has an yttria content of 3.8 mol% or more and 4.2 mol% or less, more preferably 3.8 mol% or more and 4.15 mol% or less, but 900 MPa or more. It can have a high three-point bending strength of 1300 MPa or less, more preferably 900 MPa or more and 1200 MPa or less.

  The zirconia sintered body obtained by the production method of the present invention has the above-mentioned mechanical strength, and has a total light transmittance of 43% or more, more than 44%, or even 44.5% or more. is there. When the yttria content exceeds 3 mol% and is 5.2 mol% or less, the total light transmittance is 49% or less. In the present invention, the total light transmittance can be measured by a method based on JIS K 7361 for a sintered body having a sample thickness of 1 mm using a D65 light source.

  Such a zirconia sintered body does not impair the translucency of the conventional zirconia sintered body for dental materials, and further has a translucency higher than that of the conventional zirconia sintered body for dental materials. And a zirconia sintered body having mechanical strength required as a dental material. As described above, the zirconia sintered body obtained by the production method of the present invention can be used as a dental material, and further can be used as any dental material of a back dental material and an anterior dental material.

  Hereinafter, the present invention will be described specifically by way of examples. However, the present invention is not limited to these examples.

  A method for measuring the characteristics of the sintered body and powder of the present invention will be described below.

(Total light transmittance)
The total light transmittance was measured by a method based on JIS K 7361 using a turbidimeter (device name: NDH2000, manufactured by Nippon Denshoku) and using a D65 light source.

  As a measurement sample, a disk-shaped sintered body having a thickness of 1 mm and polished on both sides was used.

(3-point bending strength)
The bending test was measured by a three-point bending test based on JIS R 1601 “Fine ceramic bending strength test method”. The measurement was performed 10 times, and the average value was taken as the 3-point bending strength. The measurement was carried out using a columnar sintered body sample having a width of 4 mm and a thickness of 3 mm, and a distance between supporting points of 30 mm.

(Sintered body density)
The actual density of the sintered body was measured by a measurement method based on JIS R 1634 (Method for measuring sintered ceramic density / open porosity of fine ceramics). The relative density was determined from the ratio of the actually measured density to the theoretical density.

The theoretical density (ρ ₀ ) was determined by the following equation (1).

ρ ₀ = 100 / [(A / ρ _A ) + (100−A) / ρ _X ]
In the above formula, [rho ₀ is the theoretical density (g / ^cm 3), A is the content of _Al 2 _{O 3} (wt%), ρ _A is the theoretical density of the ^{_{Al 2 O 3 (3.99g / cm}} 3), Ρ _X is the theoretical density (g / cm ³ ) of the Xmol% yttria-containing zirconia sintered body.

Ρ _X in the above formula shows a different value depending on the crystal phase of the zirconia sintered body. In this specification, the theoretical density ρ _X is J. Am. Ceram. Soc. 69 [4] 325-32 (1986) (hereinafter also referred to as “reference document”).

(Average crystal grain size)
The average crystal grain size of the sintered body sample was determined by a planimetric method from an SEM photograph obtained by a field emission scanning electron microscope (FESEM). That is, the mirror-polished sintered body sample was thermally etched, and this was observed using a field emission scanning electron microscope (device name: JSM-T220, manufactured by JEOL Ltd.). The average crystal grain size was calculated from the obtained SEM photograph by the planimetric method.

(Yttria concentration distribution)
The maximum frequency was measured using FE-SEM / EDS (device name: JSM-7600F, manufactured by JEOL Ltd.) as follows. The surface of the sintered body was observed with SEM at 24,000 times to obtain an SEM observation drawing. The EDS spectrum at 40000 points in the obtained SEM observation chart was measured, and the intensity of characteristic X-rays of zirconium and yttrium was quantitatively analyzed to determine the yttrium concentration (Y / Zr ratio) relative to the zirconium concentration. The yttrium concentration distribution was divided into 0.5% ranges in the range where the Y / Zr ratio exceeded 0.25%, and the frequency in each yttrium concentration range was plotted.

  Prior to the measurement, the sintered body sample was subjected to Ag sputter coating as a pretreatment.

(Crystal phase)
A general X-ray diffractometer (device name: X′Pert PRO MPD, manufactured by Spectris Co., Ltd.) was used to perform XRD measurement of the sintered body sample. The XRD measurement conditions are shown below. The obtained XRD pattern was subjected to Rietveld analysis using Rietan-2000, and the crystal phase of the sintered body sample was identified.
Radiation source: CuKα ray (λ = 0.1541862 nm)
Measurement mode: Continuous scan
Scanning speed: 1 ° / min
Step width: 0.02 °
Divergence slit: 0.5 deg
Scattering slit: 0.5 deg
Light receiving slit: 0.3 mm
Measurement range: 2θ = 10 ° to 140 °

(Average particle diameter of powder)
The average particle size of the zirconia powder was measured using a Microtrac particle size distribution meter (device name: 9320-HRA, manufactured by Honeywell).

  As a pretreatment, the sample powder was suspended in distilled water to form a slurry, which was then subjected to a dispersion treatment for 3 minutes using an ultrasonic homogenizer (device name: US-150T, manufactured by Nippon Seiki Seisakusho).

  Here, the average particle diameter of the zirconia powder is the same as the median diameter that is the median value of the cumulative curve of the particle size distribution expressed on a volume basis, that is, the particle diameter corresponding to 50% of the cumulative curve. The diameter of the volume sphere. The said average particle diameter is the value measured with the particle size distribution measuring apparatus by a laser diffraction method.

(Crystallite diameter of powder composition)
The crystallite size of the powder composition was determined from the main XRD peak using the following formula.

Crystallite diameter = κλ / βcosθ
In the above formula, κ is the Scherrer constant (κ = 1), λ is the wavelength of the measured X-ray (λ is 1.541862Å when using the CuKα ray as a source), β is the half width (°) of the main XRD peak, And θ are the Bragg angles of the main XRD peak.

(Crystal phase of powder composition)
The T + C phase ratio was calculated from the following formula from the XRD pattern of the crystal phase of the powder composition.

T + C phase ratio (%) = 100−fm (%)
In the above formula, fm is a monoclinic phase rate.

(Average particle size of granulated powder)
The average particle size of the granulated powder was determined by a screening test method.

Example 1
(Low yttria powder)
A hydrous zirconia sol was obtained by hydrolyzing the zirconium oxychloride aqueous solution. Yttria was added to the hydrated zirconia sol so that the yttria concentration was 2.5 mol%, and then dried and calcined to obtain a yttria-containing zirconia calcined powder. The calcination conditions were 2 hours at 1160 ° C. in the air. The obtained calcined powder was washed with distilled water and then dried to obtain 2.5 mol% yttria-containing zirconia powder.

After mixing α-alumina having an average particle size of 0.3 μm with 2.5 mol% yttria-containing zirconia powder so as to be 0.05 wt% as Al ₂ O _{3 with} respect to the weight of the powder, distilled water was added. This was pulverized and mixed to obtain a slurry containing the low yttria powder of this example. The pulverization and mixing were performed in a water solvent in a ball mill using zirconia balls having a diameter of 2 mm as the pulverization medium, and the mixing time was 24 hours.

The obtained low yttria powder had an yttria content of 2.5 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 11.2 m ² / g, and an average particle size of 0.42 μm.
(High yttria powder)
Except that yttria was added to the hydrated zirconia sol so that the yttria concentration was 5.5 mol%, a 5.5 mol% yttria-containing zirconia powder containing 0.05 wt% alumina was obtained. It was set as the high yttria powder of the Example.
The obtained high yttria powder had an yttria content of 5.5 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 10.1 m ² / g, and an average particle size of 0.40 μm.

(Powder composition)
After the pulverization and mixing, the slurry of low yttria powder and the slurry of high yttria powder were mixed at a ratio of 50% by weight: 50% by weight and sufficiently stirred to obtain a slurry containing the powder composition of this example. After adding 3% by weight of an organic binder to the slurry containing the powder composition, this was spray dried to obtain a granulated powder. The granulated powder had an average particle size of 44 μm and a light bulk density of 1.28 g / cm ³ . The evaluation results of the powder composition of this example are shown in Table 1.

(Sintered body)
The obtained powder granules were molded by a uniaxial press of 19.6 MPa, and then molded by a cold isostatic press (hereinafter also referred to as “CIP”) treatment of 196 MPa to obtain a molded body. The obtained compact is sintered at normal pressure in an air atmosphere at a sintering temperature of 1450 ° C., a heating rate of 600 ° C./hr, and a holding time of 2 hours, so that the yttria content is 4.0 mol%. An example zirconia sintered body was obtained.

The crystal phase of the zirconia sintered body of this example consisted only of tetragonal crystals, and the tetragonal crystals included T phase and T ^* phase, and the T ^* / T ratio was 69.5%.

  The evaluation results of the zirconia sintered body of this example are shown in Table 2.

Example 2
The powder composition obtained in Example 1 was used, and the zirconia sintering of this example having an yttria content of 4.0 mol% was performed in the same manner as in Example 1 except that the sintering temperature was 1500 ° C. Got the body. The evaluation results of the zirconia sintered body of this example are shown in Table 2.

Example 3
The powder composition obtained in Example 1 was used, and the yttria content was 4.0 mol% in the same manner as in Example 1 except that the sintering temperature was 1550 ° C. Got the body.

The crystal phase of the zirconia sintered body of this example consisted only of tetragonal crystals, and the tetragonal crystals included T phase and T ^* phase, and the T ^* / T ratio was 81.8%. The maximum frequency of the zirconia sintered body of this example was 6.9%. The yttria concentration distribution is shown in FIG.

  The evaluation results of the zirconia sintered body of this example are shown in Table 2.

Example 4
Using the powder composition obtained in Example 1, a molded body was obtained in the same manner as in Example 1, and calcined at a calcining temperature of 1000 ° C. to obtain a calcined body.

  Sintered in the same manner as in Example 1 except that the calcined body obtained instead of the molded body was used and the sintering temperature was 1600 ° C., and the yttria content was 4.0 mol%. A zirconia sintered body of a certain example was obtained.

The crystal phase of the zirconia sintered body of this example consisted only of tetragonal crystals, and the tetragonal crystals contained a T phase and a T ^* phase. The maximum frequency of the zirconia sintered body of this example was 6.9%.

  The evaluation results of the zirconia sintered body of this example are shown in Table 2.

  From the above table, according to the production method of the present invention, as the sintering temperature is increased, the obtained sintered body has a translucency of 44% or more, and the strength becomes 900 MPa or more, further 1000 MPa or more. It could be confirmed.

Example 5
(Low yttria powder)
A low yttria powder was obtained in the same manner as in Example 1. The obtained low yttria powder had an yttria content of 2.5 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 11.2 m ² / g, and an average particle size of 0.41 μm.
(High yttria powder)
A high yttria powder was obtained in the same manner as in Example 1. The obtained high yttria powder had an yttria content of 5.5 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 10.1 m ² / g, and an average particle size of 0.42 μm.
(Powder composition)
After the pulverization and mixing, the slurry of low yttria powder and the slurry of high yttria powder were mixed at a ratio of 55% by weight: 45% by weight and sufficiently stirred to obtain a slurry containing the powder composition of this example. After adding 3% by weight of an organic binder to the slurry containing the powder composition, this was spray dried to obtain a granulated powder. The granulated powder had an average particle size of 46 μm and a light bulk density of 1.29 g / cm ³ . The evaluation results of the powder composition of this example are shown in Table 3.

(Sintered body)
A molded body and a sintered body were obtained in the same manner as in Example 1. Table 4 shows the evaluation results of the zirconia sintered body of this example having an yttria content of 3.85 mol%.

Example 6
The zirconia sintered body of this example having an yttria content of 3.85 mol% in the same manner as in Example 4 except that the powder composition obtained in Example 5 was used and the sintering temperature was 1500 ° C. Got. Table 4 shows the evaluation results of the zirconia sintered body of this example.

Example 7
The zirconia sintered body of this example having an yttria content of 3.85 mol% in the same manner as in Example 4 except that the powder composition obtained in Example 5 was used and the sintering temperature was 1550 ° C. Got. Table 4 shows the evaluation results of the zirconia sintered body of this example.

Example 8
(Low yttria powder)
Example 1 except that yttria was added to the hydrated zirconia sol so that the yttria concentration was 3.0 mol%, the calcining temperature was 1100 ° C., and the mixing time of the ball mill was 16 hours. A low yttria powder was obtained in the same manner. The obtained low yttria powder had an yttria content of 3.0 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 13.1 m ² / g, and an average particle size of 0.40 μm.
(High yttria powder)
High yttria powder was obtained in the same manner as in Example 1. The obtained high yttria powder had an yttria content of 5.5 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 10.1 m ² / g, and an average particle size of 0.41 μm.
(Powder composition)
The slurry of the low yttria powder and the slurry of the high yttria powder after pulverization and mixing were mixed at a ratio of 60% by weight: 40% by weight and sufficiently stirred to obtain a slurry containing the powder composition of this example. After adding 3% by weight of an organic binder to the slurry containing the powder composition, this was spray dried to obtain a granulated powder. The granulated powder had an average particle size of 43 μm and a light bulk density of 1.27 g / cm ³ . The evaluation results of the powder composition of this example are shown in Table 5.

(Sintered body)
A compact and a sintered body having an yttria content of 4.0 mol% were obtained in the same manner as in Example 1. The evaluation results of the zirconia sintered body of this example are shown in Table 6.

Example 9
The powder composition obtained in Example 8 was used, and the zirconia sintering of this example having an yttria content of 4.0 mol% was performed in the same manner as in Example 7 except that the sintering temperature was 1500 ° C. Got the body. The evaluation results of the zirconia sintered body of this example are shown in Table 6.

Example 10
The powder composition obtained in Example 8 was used, and the zirconia firing of this example having an yttria content of 4.0 mol% was performed in the same manner as in Example 8 except that the sintering temperature was 1550 ° C. A ligature was obtained. The evaluation results of the zirconia sintered body of this example are shown in Table 6.

Example 11
(Low yttria powder)
A low yttria powder was obtained in the same manner as in Example 1. The obtained low yttria powder had an yttria content of 2.5 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 11.2 m ² / g, and an average particle size of 0.39 μm.
(High yttria powder)
A high yttria powder was obtained in the same manner as in Example 1. The obtained high yttria powder had an yttria content of 5.5 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 10.1 m ² / g, and an average particle size of 0.40 μm.
(Powder composition)
The slurry containing the powder composition of this example was obtained by mixing the slurry of the low yttria powder and the slurry of the high yttria powder after the pulverization and mixing at a ratio of 45 wt%: 55 wt% and stirring sufficiently. After adding 3% by weight of an organic binder to the slurry containing the powder composition, this was spray dried to obtain a granulated powder. The granulated powder had an average particle size of 42 μm and light bulk density of 1.27 g / cm ³ . The evaluation results of the powder composition of this example are shown in Table 7.

(Sintered body)
A molded body and a sintered body having an yttria content of 4.15 mol% were obtained in the same manner as in Example 1. Table 8 shows the evaluation results of the zirconia sintered body of this example.

Example 12
The zirconia sintered body of this example having an yttria content of 4.15 mol% in the same manner as in Example 11 except that the powder composition obtained in Example 11 was used and the sintering temperature was 1500 ° C. Got. Table 8 shows the evaluation results of the zirconia sintered body of this example.

Example 13
The zirconia sintered body of this example having an yttria content of 4.15 mol% in the same manner as in Example 11 except that the powder composition obtained in Example 11 was used and the sintering temperature was 1550 ° C. Got. Table 8 shows the evaluation results of the zirconia sintered body of this example.

  From the above table, even if the sintered body has a yttria content exceeding 4.0 mol%, the strength should be improved to 870 MPa or more, further 900 MPa or more, or even 1000 MPa or more as the sintering temperature increases. It has been shown.

Example 14
(Low yttria powder)
A low yttria powder was obtained in the same manner as in Example 8. The obtained low yttria powder had an yttria content of 3.0 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 13.0 m ² / g and an average particle size of 0.40 μm.
(High yttria powder)
A high yttria powder was obtained in the same manner as in Example 1. The obtained high yttria powder had an yttria content of 5.5 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 10.0 m ² / g, and an average particle size of 0.41 μm.
(Powder composition)
After the pulverization and mixing, the slurry of low yttria powder and the slurry of high yttria powder were mixed at a ratio of 40% by weight: 60% by weight and sufficiently stirred to obtain a slurry containing the powder composition of this example. After adding 3% by weight of an organic binder to the slurry containing the powder composition, this was spray dried to obtain a granulated powder. The granulated powder had an average particle size of 45 μm and a light bulk density of 1.29 g / cm ³ . The evaluation results of the powder composition of this example are shown in Table 9.

(Sintered body)
A compact and a sintered body having an yttria content of 4.5 mol% were obtained in the same manner as in Example 1. Table 10 shows the evaluation results of the zirconia sintered body of this example.

Example 15
The powder composition obtained in Example 14 was used, and the zirconia sintering of this example having an yttria content of 4.5 mol% was performed in the same manner as in Example 14 except that the sintering temperature was 1500 ° C. Got the body. Table 10 shows the evaluation results of the zirconia sintered body of this example.

Example 16
The powder composition obtained in Example 11 was used, and the zirconia sintering of this example having an yttria content of 4.5 mol% was performed in the same manner as in Example 14 except that the sintering temperature was 1550 ° C. Got the body. Table 10 shows the evaluation results of the zirconia sintered body of this example.

  From the above table, the sintered body having a yttria content of 4.5 mol% has lower strength than the sintered body having a yttria content of 4.0 mol%, but both exceed 800 MPa and are practical as dental materials. It was shown to show strength.

Comparative Example 1
(Low yttria powder)
A low yttria powder was obtained in the same manner as in Example 8. The obtained low yttria powder had an yttria content of 3.0 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 12.9 m ² / g and an average particle size of 0.42 μm.
(High yttria powder)
High yttria powder was obtained in the same manner as in Example 1. The obtained high yttria powder had an yttria content of 5.5 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 9.9 m ² / g and an average particle size of 0.43 μm.
(Powder composition)
After the pulverization and mixing, the slurry of low yttria powder and the slurry of high yttria powder were mixed at a ratio of 10% by weight: 90% by weight and sufficiently stirred to obtain a slurry containing the powder composition of this example. After adding 3% by weight of an organic binder to the slurry containing the powder composition, this was spray dried to obtain a granulated powder. The granulated powder had an average particle size of 43 μm and a light bulk density of 1.28 g / cm ³ . The evaluation results of the powder composition of this comparative example are shown in Table 11.

(Sintered body)
A molded body and a sintered body having an yttria content of 5.25 mol% were obtained in the same manner as in Example 1. The three-point bending strength of the sintered body of this comparative example is 613 MPa, does not have the bending strength required for dental use, and the zirconia sintered body whose yttria content exceeds 5.2 mol% It was confirmed that the mechanical strength was lowered.

Comparative Example 2
A hydrous zirconia sol was obtained by hydrolyzing the zirconium oxychloride aqueous solution. A zirconia powder was obtained in the same manner as the low yttria powder of Example 1 except that yttria was added to the hydrated zirconia sol so that the yttria concentration was 4.0 mol%, and this was used as the zirconia powder of this comparative example. .

The obtained low yttria powder had an yttria content of 4.0 mol%, an alumina content of 0.05 wt%, a BET specific surface area of 11.2 m ² / g, and an average particle size of 0.41 μm.

  A compact and a sintered body having an yttria content of 4.0 mol% are obtained in the same manner as in Example 1 except that the zirconia powder of this example is used and the sintering temperature is 1550 ° C. It was.

The crystal phase of the zirconia sintered body of this comparative example was composed only of tetragonal crystals, and the tetragonal crystals included T phase and T ^* phase, and the T ^* / T ratio was 75.4%. The maximum frequency of the zirconia sintered body of this comparative example was 8.0%. The yttria concentration distribution is shown in FIG.

The sintered body of this comparative example had a total light transmittance of 45.3% and a three-point bending strength of 870 MPa. This was obtained at the same sintering temperature and was lower in strength than the sintered body of Example 11 having an yttria content of 4.1 mol%. Furthermore, the minimum value of the bending strength of this comparative example was as large as 703 MPa. From this, it has been confirmed that the production method of the present invention can obtain a sintered body having higher strength than the conventional one. Further, the sintered body of this comparative example had a high T ^* / T ratio, and it was shown that yttria was uniformly distributed as compared with the sintered body of the example.

  The method for producing a zirconia sintered body of the present invention is a method for producing a zirconia sintered body having high translucency and high mechanical strength with good reproducibility, and is used as a dental material for both front teeth and back teeth. it can.

Claims (9)

  A first zirconia powder having an yttria content of 2 mol% to 4 mol% and a second zirconia powder having an yttria content of more than 4 mol% and not more than 6 mol%, and the yttria content of more than 3 mol% A zirconia sintered body comprising: a molding step of molding a powder composition of 2 mol% or less to obtain a molded body; and a sintering step of sintering the molded body to obtain a sintered body. Production method.   The production method according to claim 1, wherein the powder composition contains alumina. The method according to claim 1 or 2, wherein the powder composition has a BET specific surface area of 5 m ² / g or more and less than 17 m ² / g. The weight ratio of said 1st zirconia powder and 2nd zirconia powder is 35 weight%: 65
The production method according to any one of claims 1 to 3, wherein the weight% is from 65% to 35% by weight.   The yttria content of the first zirconia powder is 2 mol% or more and 3.5 mol% or less, and the yttria content of the second zirconia powder is 4.5 mol% or more and 5.7 mol% or less. The manufacturing method as described in any one of thru | or 4.   The manufacturing method according to any one of claims 1 to 5, wherein a sintering temperature in the sintering step is 1400 ° C or higher and 1600 ° C or lower.   The yttria content is more than 3 mol% and not more than 5.2 mol%, and the maximum value of the frequency of yttrium concentration distribution in the quantitative analysis of elements of the energy dispersive X-ray spectroscopic spectrum is 7.5% or less. Zirconia sintered body. The zirconia sintered body according to claim 7, wherein the crystal phase is a tetragonal crystal including a T phase and a T ^* phase.   9. The zirconia sintered body according to claim 7, wherein the average crystal grain size is more than 0.41 μm and 1.5 μm or less.

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