JP7516780B2 - Zirconia sintered body - Google Patents

Description

The present disclosure relates to compositions having zirconia layers laminated therein, and further to zirconia laminates.

Zirconia (ZrO ₂ ) sintered bodies are manufactured by molding and sintering raw material powders that mainly contain zirconia. The raw material powders are thermally shrunk and densified by heat treatments such as sintering and calcination, but the behavior during heat treatment varies depending on the characteristics of the raw material powders, particularly their composition.

Zirconia makes up the majority of the raw material powder. Nevertheless, even raw material powders that differ only in the amount of additives of less than 0.1% by mass have significantly different thermal contraction behaviors. When a molded body made by stacking raw material powders with such slight differences in composition is heat-treated, defects such as partial peeling of the layers or the occurrence of distortion occur. The above-mentioned defects occur even when the same zirconia is used and additives are added. In order to heat-treat the molded body without causing these defects, special adjustments and processing have been required (for example, Patent Documents 1 and 2).

Patent Document 1 discloses that by adjusting the composition and thermal shrinkage behavior of the raw powder by coating it with a dopant and then molding it, a sintered body made of laminated bodies without distortion and with different color tones can be obtained. In addition, Patent Document 2 discloses that by applying vibrations that form a boundary layer where the powders of the upper and lower layers are mixed, and then molding the laminated bodies, a sintered body made of laminated bodies with layers with different colorant contents and with changes in color tone can be obtained.

Special table 2016-527017 publication JP 2014-218389 A

In the laminates disclosed in Patent Documents 1 and 2, the difference in the additive content between layers is at most less than 0.5% by mass, which is only a very small difference in composition. Furthermore, since the zirconia that accounts for the majority of the raw material powder has the same composition, these laminates also have the same texture, which is mainly due to the translucency of zirconia. Therefore, they provide a different texture compared to natural teeth, which have a texture due to changes in translucency.

The present disclosure aims to provide at least one of a laminate having a texture change, particularly a change in translucency, derived from zirconia and suitable as a dental prosthetic component, a precursor thereof, or a method for producing the same.

The inventors focused on the molded body before heat treatment, i.e., the state after molding of the raw material powder. As a result, they confirmed that the state of distortion generated at the time of molding of a molded body in which raw material powders with different contents of zirconia stabilizer are laminated is significantly different from that of a molded body in which raw material powders with only different additive contents are laminated. They also confirmed that such distortion has a significant effect on the state of the calcined body and sintered body after heat treatment. Furthermore, they found that by controlling the state of the molded body, the above-mentioned problems are less likely to occur even if a laminate in which raw material powders with different contents of zirconia stabilizer are laminated is heat treated.

In other words, the gist of the present disclosure is as follows.
[1] A structure in which two or more zirconia layers containing zirconia containing a stabilizer are laminated, and at least
A first zirconia layer containing zirconia having a stabilizer content of 4 mol% or more;
a second zirconia layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first zirconia layer;
A sintered body comprising:
[2] The sintered body according to the above [1], wherein the stabilizer content of the stabilizer-containing zirconia contained in the second zirconia layer is 1.5 mol % or more and 7.0 mol % or less.
[3] The sintered body according to the above [1] or [2], wherein the stabilizer content of the stabilizer-containing zirconia contained in the second zirconia layer is 5.0 mol % or more and 7.0 mol % or less.
[4] The sintered body according to any one of the above [1] to [3], wherein the content of the stabilizer in the stabilizer-containing zirconia contained in the first zirconia layer is 4.0 mol % or more and 6.0 mol % or less.
[5] The sintered body according to any one of the above [1] to [4], wherein the difference between the stabilizer content of the first zirconia layer and the stabilizer content of the second zirconia layer is 0.2 mol % or more.
[6] The sintered body according to any one of the above [1] to [5], wherein the stabilizer is one or more selected from the group consisting of yttria (Y ₂ O ₃ ), calcia (CaO), magnesia (MgO) and ceria (CeO ₂ ).
[7] The sintered body according to any one of the above [1] to [6], wherein at least one of the zirconia layers contains alumina.
[8] The sintered body according to any one of [1] to [7] above, having a warpage of 1.0 mm or less as measured using a thickness gauge in accordance with JIS B 7524:2008.
[9] The sintered body according to any one of the above [1] to [8], having a density of 5.7 g/cm ³ or more and 6.3 g/cm ³ or less, as measured by a method according to JIS R 1634.
[10] The sintered body according to any one of the above [1] to [9], having a zirconia layer having a total light transmittance of 30% or more and 50% or less for light with a wavelength of 600 nm in a sample thickness of 1.0 mm.
[11] The sintered body according to any one of the above [1] to [10], having a three-point bending strength of 500 MPa or more as measured according to a method in accordance with JIS R 1601.
[12] A powder composition layer having a structure in which two or more powder composition layers made of a powder composition containing zirconia containing a stabilizer and a binder are laminated, and at least
A first powder composition layer including zirconia having a stabilizer content of 4 mol% or more and a binder;
A second powder composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first powder composition layer and a binder;
Equipped with
The method for producing a sintered body according to any one of the above [1] to [11], further comprising a step of sintering a molded body having a binder content difference between the first powder composition layer and the second powder composition layer of more than 0.01 mass % at 1200°C or higher and 1600°C or lower.
[13] A powder composition layer having a structure in which two or more powder composition layers made of a powder composition containing zirconia containing a stabilizer and a binder are laminated, and at least
A first powder composition layer including zirconia having a stabilizer content of 4 mol% or more and a binder;
A second powder composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first powder composition layer and a binder;
Equipped with
A step of calcining the molded body having a binder content difference between the first powder composition layer and the second powder composition layer of more than 0.01 mass % at 800 ° C. or more and less than 1200 ° C. to obtain a calcined body; and
The method for producing a sintered body according to any one of the above [1] to [11], further comprising a step of sintering the calcined body at 1200°C or higher and 1600°C or lower.
[14] The manufacturing method according to the above [12] or [13], wherein the warpage of the molded product measured using a thickness gauge conforming to JIS B 7524:2008 is 1.0 mm or less.
[15] The method according to any one of the above [12] to [14], wherein the binder is at least one selected from the group consisting of polyvinyl alcohol, polyvinyl butyrate, wax and acrylic resin.
[16] The method according to any one of the above [12] to [15], wherein the powder composition contained in the powder composition layer is a powder in a granulated state.
[17] The method according to any one of the above [12] to [16], wherein the density of the molded body is 2.4 g/ ^cm3 or more and 3.7 g/ ^cm3 or less.
[18] A dental material comprising the sintered body according to any one of [1] to [11] above.

The present disclosure can provide a laminate, a precursor thereof, or a method for producing the same, which has a texture change, particularly a change in translucency, derived from zirconia and is suitable as a dental prosthetic component.

Schematic diagram showing a cross section of a sintered body having a structure in which two zirconia layers are laminated. Schematic diagram showing a cross section of a sintered body having a structure in which three zirconia layers are laminated. Schematic diagram showing how to measure warpage Schematic diagram showing the method for measuring three-point bending strength Schematic diagram showing zirconia with a necking structure

The sintered body of the present disclosure will be described below with reference to an example embodiment.

The present embodiment has a structure in which two or more zirconia layers containing zirconia containing a stabilizer are laminated, and at least
A first zirconia layer containing zirconia having a stabilizer content of 4 mol% or more;
a second zirconia layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first zirconia layer;
The sintered body is characterized by comprising:

The sintered body of this embodiment is a composition having a multilayer structure, a so-called laminate, and is a laminate made of a sintered structure. In this embodiment, the sintered structure is a structure made of zirconia in the later stage of sintering.

The sintered body of this embodiment has a zirconia layer (hereinafter, simply referred to as "zirconia layer") that contains zirconia containing a stabilizer. The zirconia layer is made of zirconia crystal particles that contain a stabilizer. Therefore, the sintered body of this embodiment can also be considered as a laminate having two or more zirconia-containing layers that are made of zirconia crystal particles that contain a stabilizer.

Figure 1 is a schematic diagram showing an example of the structure of the sintered body of this embodiment, and shows a cross section of a sintered body (100) having a structure in which two zirconia layers containing zirconia containing a stabilizer are stacked. In Figure 1, the direction in which the layers are stacked (hereinafter also referred to as the "stacking direction") is shown in the Y-axis direction, and the direction in which each layer spreads (hereinafter also referred to as the "horizontal direction") is shown in the X-axis direction.

The sintered body (100) is shown as a sintered body having a structure in which the first zirconia layer (hereinafter also referred to as the "first layer") (11) contains zirconia with a stabilizer content of 4 mol% or more, and the second zirconia layer (hereinafter also referred to as the "second layer") (12) contains zirconia with a stabilizer content different from that of the zirconia contained in the first zirconia layer, and the first layer (11) and the second layer (12) are adjacently laminated. By having a structure in which zirconia layers containing zirconia with different stabilizer contents are laminated, the sintered body becomes a laminate in which changes in texture, particularly changes in translucency, can be visually recognized. Note that the sintered body (100) shows a state in which the first layer and the second layer are in contact with each other via an interface. However, the sintered body of this embodiment may be laminated without a visible interface, and the interface between the layers is not limited to being linear.

In the sintered body (100), the first layer and the second layer have approximately the same thickness. However, in the sintered body of this embodiment, the thickness of each layer (hereinafter also referred to as "layer thickness") may be different, and either the first layer or the second layer may be thick. For example, the layer thicknesses of the first layer and the second layer may satisfy the following relationship, and further, the layer thickness of the zirconia layer with a high stabilizer content is thicker than the layer thickness of the zirconia layer with a low stabilizer content. The layer thickness may be 1 mm or more and 20 mm or less, further 2 mm or more and 15 mm or less, or further 3 mm or more and 10 mm or less.

D _high ≧D _low , preferably 2×D _low ≧D _high ≧D _low
Here, D _high is the layer thickness of the zirconia layer having a high stabilizer content, and D _low is the layer thickness of the zirconia layer having a low stabilizer content.

The shape of the sintered body in this embodiment may be any shape, including at least one selected from the group consisting of spherical, elliptical, discoid, cylindrical, cubic, rectangular, and polyhedral shapes, shapes suitable for dental materials, including dental prosthetic materials such as crowns, bridges, onlays, and onlays, and any other shape depending on the intended use. In this embodiment, the spherical shape includes shapes similar to a true sphere other than a true sphere, such as an approximately spherical shape, and the polyhedral shape may include shapes similar to a polyhedron, such as an approximately polyhedral shape, in addition to a polyhedron.

The dimensions of the sintered body of this embodiment are arbitrary, and examples of the dimensions include a length of 10 mm to 120 mm, a width of 12 mm to 120 mm, and a height of 6 mm to 40 mm. The thickness of the sintered body of this embodiment in the stacking direction, i.e., the height of the sintered body, is arbitrary, but examples of the dimensions include a length of 4 mm to 40 mm, and even a length of 5 mm to 30 mm.

In the sintered body of this embodiment, the first layer and the second layer are preferably stacked adjacent to each other. In addition, the first layer and the second layer are preferably located as the lowest layer in the stacking direction (hereinafter also referred to as the "lowest layer") or the highest layer in the stacking direction (hereinafter also referred to as the "top layer"). It is preferable that one of the first layer or the second layer is located as the lowest layer, and the other of the first layer or the second layer is located as the top layer.

The sintered body of this embodiment may have a structure in which two or more zirconia layers containing zirconia containing a stabilizer are laminated, and may have a structure in which three or more, or even four or more zirconia layers are laminated. By increasing the number of layers, the sintered body becomes a laminate in which subtle changes in texture can be visually recognized. In the case of achieving a texture more similar to that of natural teeth, the sintered body of this embodiment may have a structure in which two to ten zirconia layers are laminated, or even two to five zirconia layers are laminated, or even two to four zirconia layers are laminated.

The zirconia layer other than the first layer and the second layer (hereinafter also referred to as the "third layer") may be a zirconia layer containing zirconia containing a stabilizer whose content is equal to or greater than the minimum value and equal to or less than the maximum value of the stabilizer content of the zirconia contained in the first layer and the second layer. The sintered body of this embodiment may include multiple third layers.

The third layers may be stacked in any order, but it is preferable that the third layer is sandwiched between the first and second layers. When multiple third layers (the first third layer is also called the "third layer", and the second or subsequent third layers are also called the "fourth layer", "fifth layer", etc.) are included, it is preferable that the sintered body of this embodiment has a structure in which the zirconia layers are stacked so that the change in the content of the stabilizer in the stacking direction is constant, i.e., increases (or decreases). In this embodiment, the structure in which the third layer is sandwiched between the first and second layers means a structure in which the third layer is located between the first and second layers in the stacking direction, and is not limited to a structure in which the third layer is stacked directly adjacent to both the first and second layers. In this embodiment, the numbers "1", "2", "3", etc." are given for convenience of explanation, and do not mean the order of stacking or the stacking state.

Figure 2 is a schematic diagram showing another example of the structure of the sintered body of this embodiment, and is a schematic diagram showing a cross section of a sintered body (200) having a structure in which three zirconia layers are stacked. The sintered body (200) has a structure in which a third layer (23) is stacked in addition to a first layer (21) and a second layer (22), and has a structure in which the third layer (23) is sandwiched between the first layer (21) and the second layer (22).

When multiple zirconia layers such as a fourth layer, a fifth layer, etc. are included, it is preferable that the zirconia layers are stacked so that the content of the stabilizer changes uniformly in the stacking direction. This allows a gradation of translucency to be formed in the stacking direction.

The sintered body of this embodiment preferably has a warpage (hereinafter simply referred to as "warpage") of 1.0 mm or less, measured using a thickness gauge conforming to JIS B 7524:2008. A sintered body having a structure with two or more zirconia layers will be warped in the stacking direction (or the opposite direction to the stacking direction) by sintering. When such a sintered body is placed on a horizontal plate, a gap is formed between the sintered body and the horizontal plate.

The warpage in this embodiment is a value measured using a thickness gauge (hereinafter, simply referred to as "gauge") conforming to JIS B 7524:2008. The warpage of the sintered body of this embodiment is preferably 0.3 mm or less, more preferably 0.2 mm or less, even more preferably 0.1 mm or less, and even more preferably 0.05 mm or less. It is preferable that the sintered body has no warpage (warpage is 0 mm), but the sintered body of this embodiment may have a warpage that cannot be measured with a gauge (warpage is 0 mm or more). For example, the sintered body of this embodiment has a warpage exceeding 0 mm, and even 0.01 mm or more. It is preferable that the warpage is 0.06 mm or less, even 0.05 mm or less, or even below the measurement limit (less than 0.03 mm).

The warpage can be measured by the maximum thickness of a gauge that can be inserted into the gap formed when the convex part of the sintered body is placed in contact with the horizontal plate. Figure 3 is a schematic diagram showing a method for measuring the warpage. The sintered body (300) shows a cross section of a disk-shaped sample, and shows a sintered body in a state of warping in the stacking direction (Y-axis direction). In Figure 3, the warpage of the sintered body (300) is emphasized for the purpose of explanation. As shown in Figure 3, when measuring the warpage, the convex part of the sintered body (300) with a concave-convex shape is placed in contact with the horizontal plate (31). This forms a gap between the surface where the sintered body (300) and the horizontal plate (31) are in contact (hereinafter also referred to as the "bottom surface") and the horizontal plate (31). The gauge is inserted into the gap, and the warpage can be measured by the maximum thickness of the gauge that can be inserted. In FIG. 3, the gauge (32A) is located at the bottom of the bottom surface of the sintered body (300) and can be inserted into the gap, while the gauge (32B) is not located at the bottom of the bottom surface of the sintered body (300) and cannot be inserted into the gap. The gauges (32A) and (32B) in FIG. 3 are gauges that differ from each other by one step in thickness (e.g., 0.01 mm), and the warpage of the sintered body (300) is the thickness of the gauge (32A). For ease of explanation, FIG. 3 shows both gauges (32A) and (32B) inserted, but the warpage can be measured by inserting the gauges into the gap in order from the thinner gauge (e.g., after measuring using the gauge (32A), remove it and then measure using the thicker gauge (32B), etc.).

The sintered body of this embodiment preferably has a warpage (hereinafter also referred to as "deformation amount") relative to the dimensions of the sintered body of 1.0 or less, more preferably 0.5 or less, even more preferably 0.2 or less, and even more preferably 0.15 or less. The deformation amount can be, for example, 0 or more, even 0.01 or more, or even 0.05 or more.

The amount of deformation can be calculated from the following formula.
Deformation amount = (warpage: mm) / (sintered body size: mm) x 100

The dimensions of the sintered body are the size of the sintered body in the direction perpendicular to the direction of warping. Since the sintered body (300) in FIG. 3 is warped in the stacking direction (Y-axis direction), the dimensions of the sintered body (300) are the size (33) of the sintered body in the horizontal direction (X-axis direction) perpendicular to the stacking direction. The dimensions can be measured by known measuring methods using calipers, micrometers, etc. For example, in the case of a disk-shaped or cylindrical laminate, a caliper is used to measure the diameter of the upper end and the diameter of the lower end at four points each, the average of the diameters of the upper end and the lower end is calculated, and the average of the calculated values is used as the dimension of the laminate.

In this embodiment, the warpage and deformation are preferably values measured using a disk-shaped sample as the measurement sample, and more preferably values measured using a disk-shaped sample with a diameter of 5 mm to 120 mm.

The sintered body of this embodiment is composed of a zirconia layer containing zirconia containing a stabilizer. The zirconia layer is a layer mainly composed of zirconia, and the zirconia is zirconia containing a stabilizer (hereinafter also referred to as "stabilizer-containing zirconia"). The sintered body and zirconia layer of this embodiment may contain not only stabilizer-containing zirconia but also inevitable impurities such as hafnia (HfO ₂ ), but preferably do not contain impurities. Examples of impurities include silica (SiO ₂ ) and titania (TiO ₂ ), and the sintered body of this embodiment may be substantially free of silica or titania.

In the sintered body of this embodiment, the zirconia is preferably zirconia obtained by heat-treating a zirconia sol and sintering the zirconia, more preferably zirconia obtained by heat-treating a zirconia sol obtained by hydrolysis of a zirconium compound and sintering the zirconia, and even more preferably zirconia obtained by heat-treating a zirconia sol obtained by hydrolysis of zirconium oxychloride and sintering the zirconia.

The zirconia contained in the zirconia layer is sintered zirconia, i.e., zirconia crystal particles.

The stabilizer may be any one that has a function of suppressing the phase transition of zirconia. The stabilizer is preferably one or more selected from the group consisting of yttria (Y ₂ O ₃ ), calcia (CaO), magnesia (MgO) and ceria (CeO ₂ ), and more preferably yttria. The stabilizer is in a state of being contained in zirconia and in a state of being solid-dissolved in zirconia. In addition, it is preferable that the sintered body of this embodiment does not contain an undissolved stabilizer, that is, does not contain a stabilizer that is not solid-dissolved in zirconia. In this embodiment, "does not contain an undissolved stabilizer" means that an XRD peak derived from the stabilizer is not confirmed in the XRD measurement and analysis of the XRD pattern described below, and it is acceptable to contain an undissolved stabilizer to the extent that an XRD peak derived from the stabilizer is not confirmed. The content of the stabilizer in the stabilizer-containing zirconia contained in the first layer (hereinafter also referred to as the "stabilizer content of the first layer") is 4 mol% or more, preferably 4.1 mol% or more, and more preferably 4.2 mol% or more. The stabilizer content of the first layer is 6.0 mol% or less, further 5.8 mol% or less, further 5.5 mol% or less, and further 5.0 mol% or less. The stabilizer content of the first layer can be, for example, 4 mol% or more and 6.0 mol% or less, and further 4 mol% or more and less than 5.0 mol%.

The stabilizer content of the stabilizer-containing zirconia contained in the second layer (hereinafter also referred to as the "stabilizer content of the second layer") may be different from the stabilizer content of the first layer, but it is preferable that the stabilizer content of the second layer is higher than that of the first layer. In other words, it is preferable that the sintered body of this embodiment does not include a zirconia layer in which the zirconia stabilizer content is less than 4 mol%. This makes it easier to obtain a sintered body that exhibits a translucent feel closer to that of natural teeth.

The stabilizer content of the second layer may be 1.5 mol% or more, further 2.0 mol% or more, or even 3.0 mol% or more, but is preferably 4.0 mol% or more, more preferably more than 4.0 mol%, even more preferably more than 4.5 mol%, even more preferably more than 5.0 mol%, and even more preferably more than 5.0 mol%. The stabilizer content of the second layer may be 7.0 mol% or less, further 6.5 mol% or less, even 6.0 mol% or less, or even 5.8 mol% or less. The stabilizer content of the first layer and the second layer is different, and the stabilizer content of both layers is within this range, so that the sintered body is more likely to exhibit a texture that can be visually recognized as a texture close to that of natural teeth. The stabilizer content of the second layer can be 1.5 mol% or more and 7.0 mol% or less, further 3.0 mol% or more and 6.5 mol% or less, further 5.0 mol% or more and 6.5 mol% or less, and further more than 5.0 mol% and 6.5 mol% or less.

The sintered body of this embodiment preferably comprises at least a first zirconia layer and a zirconia layer containing zirconia with a stabilizer content of 5 mol% or more, and more preferably comprises a first zirconia layer and a zirconia layer containing zirconia with a stabilizer content of more than 5 mol%. In another embodiment, the sintered body of this embodiment preferably comprises a first layer having a stabilizer content of 4.0 mol% or more and 5.1 mol% or less, and a second layer having a stabilizer content of 4.5 mol% or more and 6.0 mol% or less, and even more preferably a first layer having a stabilizer content of 4.0 mol% or more and 5.0 mol% or less, and a second layer having a stabilizer content of more than 5.0 mol% and 6.0 mol% or less.

The content of the stabilizer in the stabilizer-containing zirconia contained in the third layer (hereinafter also referred to as the "stabilizer content of the third layer") is equal to or greater than the minimum value and equal to or less than the maximum value of the content of the zirconia stabilizer contained in the first layer and the second layer, and is preferably greater than the minimum value and less than the maximum value of the content of the zirconia stabilizer contained in the first layer and the second layer. The stabilizer content of the third layer can be, for example, 1.5 mol% to 7.0 mol%, further 3.0 mol% to 6.5 mol%, and further 4.0 mol% to 6.0 mol%. When the content of the zirconia stabilizer contained in the first layer is 4.0 mol% and the content of the zirconia stabilizer contained in the second layer is 6.0 mol%, the content of the zirconia stabilizer in the third layer can be 4.0 mol% to 6.0 mol%, preferably greater than 4.0 mol% and less than 6.0 mol%. In addition, if the stabilizer content of the third layer is the same as that of the first or second layer, the zirconia layer that has the same stabilizer content as that of the third layer and is located at the top or bottom can be regarded as the first or second layer.

The difference between the stabilizer content of the first layer and the stabilizer content of the second layer is preferably 0.2 mol% or more, more preferably 0.5 mol% or more, even more preferably 0.7 mol% or more, even more preferably 1.0 mol% or more, and even more preferably 1.2 mol% or more. The greater the difference in stabilizer content, the greater the difference in translucency between the zirconia layers tends to be, but warping may also be greater. If the difference between the stabilizer content of the first layer and the stabilizer content of the second layer is less than 2.5 mol%, or even less than 2.0 mol%, the translucency of the sintered body is likely to be the same as that of natural teeth. It is more preferable that the difference between the stabilizer content of the first layer and the stabilizer content of the second layer is 0.7 mol% or more but less than 2.5 mol%, and the warping is 0.5 mm or less.

The sintered body of this embodiment preferably has a structure in which the difference in stabilizer content between adjacent stacked zirconia layers is 0.5 mol% or more and 3.0 mol% or less, further 1.0 mol% or more and 2.5 mol% or less, and further 1.2 mol% or more and 2.0 mol% or less.

The content of the stabilizer in the sintered body of this embodiment (the content of the stabilizer in the entire sintered body) is arbitrary, but for example, it is preferably more than 1.5 mol% and less than 7.0 mol%, further 2.5 mol% to 6.5 mol%, further 3.0 mol% to 6.0 mol%, further 3.5 mol% to 5.8 mol%, further 4.1 mol% to 5.5 mol%, and more preferably 4.7 mol% to 5.3 mol%. The stabilizer content of the sintered body is calculated from the following formula and varies depending on the thickness of each zirconia layer.
Stabilizer content of sintered body
= (thickness of first layer/height of sintered body) x stabilizer content of first layer
+ (thickness of second layer/height of sintered body) × stabilizer content of second layer
+ ...
+ (thickness of nth layer/height of sintered body) × content of stabilizer in nth layer

Since the stabilizer content of the first layer is 4 mol% or more, for example, if the stabilizer content of the second layer exceeds 4.0 mol%, the stabilizer content of the sintered body having two zirconia layers of equal thickness will exceed 4.0 mol%.

In the sintered body of this embodiment, the stabilizer content of the first layer is preferably 4.0 mol% or more and 5.0 mol% or less, the stabilizer content of the second layer is more than 5.0 mol% and 6.0 mol% or less, and the difference between the stabilizer content of the first layer and the stabilizer content of the second layer is preferably 0.7 mol% or more and 1.8 mol% or less, and more preferably the yttria content of the first layer is 4.0 mol% or more and 5.0 mol% or less, the yttria content of the second layer is more than 5.0 mol% and 6.0 mol% or less, and the difference between the yttria content of the first layer and the yttria content of the second layer is preferably 0.7 mol% or more and 1.8 mol% or less.

In this embodiment, the content of the stabilizer is the molar ratio of the stabilizer to the total of zirconia and the stabilizer, and when the stabilizer is yttria (Y ₂ O ₃ ), it can be calculated as {Y ₂ O ₃ /(ZrO ₂ +Y ₂ O ₃ )}×100 (mol %).

The sintered body of this embodiment may contain alumina, and preferably at least one zirconia layer contains alumina. The alumina content of the sintered body of this embodiment may be 0% by mass or more, as a ratio of the weight of alumina to the weight of the sintered body, and may be 0% by mass or more and 0.15% by mass or less, or even 0% by mass or more and 0.10% by mass or less, or even 0% by mass or more and 0.07% by mass or less. When alumina is contained, the alumina content is more than 0% by mass and 0.15% by mass or less, preferably 0.005% by mass or more and 0.10% by mass or less, and more preferably 0.01% by mass or more and 0.70% by mass or less.

The alumina content of each zirconia layer may be in the same range as above. The alumina content of each zirconia layer may affect the thermal shrinkage behavior in the calcination stage. The alumina content of each zirconia layer is arbitrary, and each zirconia layer may have a different alumina content, but it is preferable that the alumina content is equal. When the alumina content of each zirconia layer is different, the difference in alumina content between adjacent zirconia layers may be more than 0 mass% and 1.0 mass% or less, more than 0 mass% and 0.5 mass% or less, more than 0 mass% and 0.03 mass% or less, and even more than 0.005 mass% and 0.01 mass% or less. For example, in the case of a zirconia layer made of zirconia containing alumina (Al ₂ O ₃ ) and stabilized with yttria (Y ₂ O ₃ ), the alumina content can be calculated as {Al ₂ O ₃ /(ZrO ₂ +Y ₂ O ₃ +Al ₂ O ₃ )}×100 (mass %).

The sintered body and each zirconia layer of this embodiment may not contain a colorant. On the other hand, in order to obtain an arbitrary color, the sintered body of this embodiment may contain an element having a function of coloring zirconia (hereinafter also referred to as a "colorant"). The colorant may be an element having a function of coloring zirconia, and may further be an element having a function of coloring zirconia and a function of suppressing phase transition. Specific examples of colorants include at least one of transition metal elements and lanthanoid rare earth elements, preferably at least one selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), praseodymium (Pr), neodymium (Nd), europium (Eu), gadolinium (Gd), terbium (Tb), erbium (Er) and ytterbium (Yb), more preferably at least one selected from the group consisting of iron, cobalt, manganese, praseodymium, gadolinium, terbium and erbium, and even more preferably at least one selected from the group consisting of iron, cobalt and erbium.

The content of the coloring agent, expressed as the mass ratio of each coloring agent converted to oxide relative to the mass of each zirconia layer, can be, for example, 0 mass% or more and 0.3 mass% or less, preferably 0 mass% or more and 0.2 mass% or less.

The colorant contained in the sintered body of this embodiment may be in any state, including at least one of an oxide state and a state in which the colorant is dissolved in zirconia.

When two or more zirconia layers contain a colorant, the content and type of colorant may differ between the zirconia layers.

The sintered body of this embodiment preferably includes at least a zirconia layer containing zirconia whose crystal phase is at least one of tetragonal (T phase) and cubic (C phase), more preferably includes at least a zirconia layer containing zirconia whose main phase is tetragonal, and even more preferably includes a zirconia layer containing zirconia whose main phase is tetragonal and a zirconia layer containing zirconia whose main phase is cubic. Note that the "main phase" in this embodiment means the crystal phase that has the highest abundance (proportion of integrated intensity of peak) among the crystal phases of zirconia. The abundance can be determined from the XRD pattern of the surface of the sintered body.

The following conditions can be exemplified as conditions for measuring the XRD pattern of the sintered body surface.
Radiation source: CuKα radiation (λ=1.541862Å)
Measurement mode: Step scan Scan condition: 0.000278° per second
Measurement range: 2θ=10-140°
Irradiation width: constant (10mm)

The obtained XRD pattern is subjected to Rietveld analysis to determine the ratio of tetragonal and cubic crystals (ratio of integrated peak intensities), and the crystal phase with the higher ratio is determined as the main phase. The measurement of the XRD pattern and the Rietveld analysis can be performed using a general-purpose powder X-ray diffraction device (e.g., X'pert PRO MPD, manufactured by Spectris) and analysis software (e.g., RIETAN-2000).

The density of the sintered body of this embodiment, as measured by a method conforming to JIS R 1634, can be, for example, 5.7 g/ ^cm3 or more and 6.3 g/ ^cm3 or less, preferably 5.9 g/ ^cm3 or more and 6.1 g/ ^cm3 or less. A density in this range corresponds to a relative density of 99% or more, and is a density that results in a so-called dense sintered body having practical strength.

The sintered body of this embodiment preferably includes at least a zirconia layer having a translucent feel. Furthermore, it is preferable that the zirconia layer has a total light transmittance (hereinafter also simply referred to as "total light transmittance") for light with a wavelength of 600 nm at a sample thickness of 1.0 mm of 30% to 50%, furthermore 32% to 45%, furthermore 35% to 42%.

In the sintered body of this embodiment, the difference in total light transmittance between adjacently stacked zirconia layers is preferably 1% to 10%, and more preferably 1.5% to 5%.

The total light transmittance of the sintered body of this embodiment is preferably 30% to 50%, more preferably 32% to 45%, and even more preferably 35% to 42%. The total light transmittance of the sintered body of this embodiment can be measured by cutting out any part of the sintered body in the horizontal direction and processing it to a sample thickness of 1 mm.

Total light transmittance can be measured according to a method in accordance with JIS K 7361, using light with a wavelength of 600 nm as the incident light, and can be calculated as the transmittance value obtained by adding up the diffuse transmittance and linear transmittance for the incident light. A sample with a thickness of 1 mm and a surface roughness (Ra) of ≦0.02 μm is used as the measurement specimen, and light with a wavelength of 600 nm is irradiated onto the sample using a general spectrophotometer (e.g., V-650, manufactured by JASCO Corporation). The transmitted light is collected using an integrating sphere to measure the transmittance (diffuse transmittance and linear transmittance) of the sample, which can be used as the total light transmittance.

The sintered body of this embodiment preferably has a three-point bending strength of 500 MPa or more, more preferably 550 MPa or more, and even more preferably 600 MPa or more, measured according to a method conforming to JIS R 1601. The three-point bending strength can be, for example, less than 1100 MPa, or even 1000 MPa or less.

Figure 4 is a schematic diagram showing the measurement of the three-point bending strength of a sintered body (400) consisting of two zirconia layers. The sintered body (400) is shown as a sintered body having a structure in which two zirconia layers with different layer thicknesses are laminated. In Figure 4, the X-axis direction indicates the lamination direction, and the Y-axis direction indicates the horizontal direction. The measurement sample used for the measurement of the three-point bending strength is a rectangular sintered body made with the width and thickness in the lamination direction and the length in the horizontal direction. The dimensions of the measurement sample are width 4 mm, thickness 3 mm, and length 45 mm. As shown in Figure 4, the three-point bending strength can be measured by applying a load (41) perpendicular to the length of the measurement sample (400). The measurement sample can be positioned so that the load (41) is applied to the middle of the support distance (42). The support distance is 30 mm.

The sintered body of this embodiment can be used for known zirconia applications, such as structural materials and optical materials, but can also be suitably used as a dental material for dentures, such as crowns and bridges, and can be a dental material that includes the sintered body of this embodiment.

Next, we will explain the manufacturing method of the sintered body of this embodiment.

The manufacturing method of this embodiment is as follows:
The powder composition layer has a structure in which two or more powder composition layers made of a powder composition containing zirconia containing a stabilizer and a binder are laminated, and at least
A first powder composition layer including zirconia having a stabilizer content of 4 mol% or more and a binder;
Zirconia having a stabilizer content different from that of the zirconia contained in the first powder composition layer;
a second powder composition layer comprising a binder; and
Equipped with
and sintering a molded body having a binder content difference between the first powder composition layer and the second powder composition layer of more than 0.01 mass % at 1200°C or higher and 1600°C or lower.

In addition, another manufacturing method of this embodiment is as follows:
The powder composition layer has a structure in which two or more powder composition layers made of a powder composition containing zirconia containing a stabilizer and a binder are laminated, and at least
A first powder composition layer including zirconia having a stabilizer content of 4 mol% or more and a binder;
A second powder composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first powder composition layer and a binder;
Equipped with
A step of calcining the molded body having a binder content difference between the first powder composition layer and the second powder composition layer of more than 0.01% by mass at 800 ° C. or more and less than 1200 ° C. to obtain a calcined body; and
and sintering the calcined body at 1200°C or higher and 1600°C or lower.

Further, another manufacturing method of the present embodiment is as follows:
The zirconia composition layer has a structure in which two or more layers containing a stabilizer and zirconia having a necking structure are laminated, and at least
A first zirconia composition layer containing zirconia having a stabilizer content of 4 mol% or more;
A second zirconia composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first zirconia composition layer;
and sintering the calcined body comprising the above-mentioned component at a temperature of 1200° C. or higher and 1600° C. or lower.

The molded body to be subjected to the manufacturing method of this embodiment is:
The powder composition layer has a structure in which two or more powder composition layers made of a powder composition containing zirconia containing a stabilizer and a binder are laminated, and at least
A first powder composition layer including zirconia having a stabilizer content of 4 mol% or more and a binder;
A second powder composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first powder composition layer and a binder;
Equipped with
The molded article has a binder content difference between the first powder composition layer and the second powder composition layer of more than 0.01 mass %.

It is known that a powder composition containing a binder improves the cohesive strength of zirconia and suppresses the occurrence of defects during molding, such as cracks and chips. In order to make the strength of the resulting molded body uniform, it is usually necessary to make the binder content in the powder composition used to prepare the molded body uniform. In contrast, it is believed that the binder in the molded body of this embodiment not only improves the strength of the molded body, but also has a different function from the conventional one, that is, by making the binder content between layers different, suppresses the occurrence of stress between the stacked layers. As a result, deformation during molding is suppressed, and it is believed that a molded body consisting of a laminate of powder compositions containing zirconia with different stabilizer contents can be heat treated without causing excessive defects.

The following describes the main differences between the molded body used in the manufacturing method of this embodiment and the sintered body described above.

The molded body to be subjected to the manufacturing method of this embodiment is:
The powder composition layer has a structure in which two or more powder composition layers made of a powder composition containing zirconia containing a stabilizer and a binder are laminated, and at least
A first powder composition layer including zirconia having a stabilizer content of 4 mol% or more and a binder;
A second powder composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first powder composition layer and a binder;
Equipped with
The molded article has a binder content difference between the first powder composition layer and the second powder composition layer of more than 0.01 mass %.

The molded body is a composition having a multi-layer structure, a so-called laminate, and is a laminate made of a powder composition. The molded body can be used as a precursor of a calcined body or a sintered body.

Instead of having a zirconia layer, the molded body has a powder composition layer (hereinafter also referred to as a "powder layer") made of a powder composition containing zirconia containing a stabilizer and a binder, and has a structure equivalent to the laminated structure shown in Figure 1 or Figure 2. Therefore, the molded body can also be considered as a laminated body having two or more layers containing zirconia powder containing a stabilizer and a binder.

The molded product preferably has a warpage of 1.0 mm or less, more preferably 0.3 mm or less, even more preferably 0.1 mm or less, and even more preferably 0.05 mm or less. The molded product preferably has no warpage (warpage of 0 mm), but may have a warpage that cannot be measured with a gauge (warpage of 0 mm or more). The molded product may have a warpage of more than 0 mm, or even 0.01 mm or more. The warpage is preferably 0.06 mm or less, more preferably 0.05 mm or less, or even below the measurement limit (less than 0.03 mm).

The deformation amount of the molded body is preferably 1.0 or less, more preferably 0.5 or less, more preferably 0.2 or less, and even more preferably 0.15 or less. The deformation amount can be, for example, 0 or more, 0.01 or more, or even 0.05 or more.

The zirconia contained in the powder layer is preferably zirconia obtained by heat-treating a zirconia sol, more preferably zirconia obtained by hydrolysis of a zirconium compound and heat-treated, and even more preferably zirconia obtained by hydrolysis of zirconium oxychloride and heat-treated.

The zirconia contained in the powder layer is preferably zirconia powder. The zirconia powder preferably has an average particle size of 0.3 μm or more and 0.7 μm or less, and more preferably 0.4 μm or more and 0.5 μm or less.

The binder contained in the powder layer is preferably a binder that vaporizes at 1200°C or less, more preferably an organic binder, and even more preferably an organic binder that has fluidity at room temperature (for example, 10°C to 30°C). The binder may not contain a plasticizer or a release agent. The organic binder is at least one selected from the group consisting of polyvinyl alcohol, polyvinyl butyrate, wax, and acrylic resin, preferably at least one of polyvinyl alcohol and acrylic resin, and more preferably an acrylic resin. In this embodiment, the acrylic resin is a polymer containing at least one of an acrylic acid ester or a methacrylic acid ester. The acrylic resin contained in the powder composition may be any resin that is used as a binder for ceramics. Specific examples of acrylic resins include at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid, acrylic acid copolymers, and methacrylic acid copolymers, and derivatives thereof.

The stabilizer content of the stabilizer-containing zirconia contained in the first powder layer (hereinafter also referred to as the "first powder layer"), the stabilizer content of the stabilizer-containing zirconia contained in the second powder layer (hereinafter also referred to as the "second powder layer"), and the stabilizer content of the stabilizer-containing zirconia contained in the third powder layer (hereinafter also referred to as the "third powder layer") may be the same as the stabilizer content of the first layer, the second layer, and the third layer, respectively.

The amount of stabilizer contained in the compact and each powder layer is arbitrary, as long as it is the same as that of the sintered body of this embodiment described above.

From the viewpoint of suppressing defects during molding, the binder content of each powder layer is preferably 1.5% by mass or more, more preferably 1.5% by mass or more and 8.0% by mass or less, even more preferably 2.0% by mass or more and 6.0% by mass or less, and even more preferably 2.5% by mass or more and 5.5% by mass or less.

In the molded body, the difference in binder content between the first powder layer and the second powder layer (hereinafter also referred to as the "binder amount difference") is preferably greater than 0.01% by mass and greater than 0.03% by mass. In this way, the molded body has different binder contents between the first powder layer and the second powder layer. This suppresses stress generation during molding. From the viewpoint of suppressing stress generation, the binder amount difference can be greater than 0.01% by mass and less than 5% by mass, and even greater than 0.03% by mass and less than 3.5% by mass, preferably greater than 0.04% by mass and less than 3% by mass, more preferably greater than 0.05% by mass and less than 2% by mass, even more preferably greater than 0.06% by mass and less than 1.5% by mass, and even more preferably greater than 0.07% by mass and less than 1% by mass. In another embodiment, the difference in binder amount is more than 0.01% by mass and not more than 3% by mass, further 0.03% by mass or more and not more than 2% by mass, further 0.1% by mass or more and not more than 1.2% by mass, further 0.12% by mass or more and not more than 1% by mass, and further 0.13% by mass or more and not more than 0.5% by mass.

The binder content is the weight ratio of the binder to the weight of the powder composition in the powder layer excluding the binder ({binder/(powder composition-binder)} x 100). In producing the powder composition, the total mass of the components of the powder composition other than the binder (e.g., stabilizer, zirconia, and alumina converted into oxides) is calculated, and then the weight ratio of the desired binder relative to this is calculated to produce the powder composition.

In order to suppress warping of the molded body, it is preferable to adjust the content of the binder in each powder layer according to the content of the stabilizer in the adjacent powder layer. The first powder layer and the second powder layer are such that the second powder layer has a higher content of stabilizer and binder than the first powder layer;
The second powder layer has a smaller content of stabilizer and binder than the first powder layer;
The second powder layer may have a larger stabilizer content and a smaller binder content than the first powder layer, and the second powder layer may have a smaller stabilizer content and a larger binder content than the first powder layer, for example.
It is preferable that the second powder layer has a larger stabilizer content and a smaller binder content than the first powder layer, or that the second powder layer has a smaller stabilizer content and a larger binder content than the first powder layer. The first powder layer and the second powder layer only need to have different stabilizer and binder contents, but it is preferable that the binder amount difference is large because warping of the molded body tends to be suppressed, and it is also preferable that one of the first powder layer and the second powder layer has a smaller stabilizer content and a larger binder content than the other powder layer.

In addition, in adjacently stacked powder layers, it is preferable that one powder layer containing zirconia with a low stabilizer content has a higher binder content than the other powder layer. Furthermore, in the case of adjacently stacked powder layers, and the zirconia contained in one of the powder layers is a mixture of two or more zirconias with different stabilizer contents, it is preferable that one powder layer containing zirconia with a low stabilizer content has a lower binder content than the other powder layer.

From the viewpoint of ease of use, the powder composition contained in the powder layer is preferably a powder in a granulated state of zirconia powder and a binder (hereinafter also referred to as "granulated powder"), and more preferably a granulated powder (hereinafter also referred to as "powder granules") granulated into granules by spray drying or the like.

The particle size of the granulated powder is arbitrary, but examples of the average agglomeration size include 1 μm to 150 μm, preferably 1 μm to 100 μm, more preferably 5 μm to 50 μm, and even more preferably 5 μm to 30 μm. In another embodiment, the average agglomeration size is 20 μm to 50 μm.

In this embodiment, the average aggregate diameter is the diameter corresponding to the cumulative 50% in the volumetric particle size distribution measurement. The volumetric particle size distribution is a value that can be measured using a general-purpose device (e.g., MT3100II, manufactured by Microtrac Bell), and is the volumetric diameter of particles that are approximately spherical.

It is more preferable that the molded body includes at least a powder layer containing zirconia having a tetragonal or cubic crystal as the main phase.

The density of the molded body is, for example, 2.4 g/ ^cm3 or more and 3.7 g/ ^cm3 or less, and preferably 3.1 g/ ^cm3 or more and 3.5 g/ ^cm3 or less. A density in this range corresponds to a relative density of 40% to 60%.

The density of the molded body is determined from the weight, which is determined by gravimetric measurement, and the volume, which is determined by dimensional measurement.

The molded body and each powder layer are opaque and have a total light transmittance of 0%, but when measurement error is taken into account, the total light transmittance can be, for example, between 0% and 0.2%.

The molded body only needs to have a strength sufficient to prevent cracking or chipping when subjected to calcination or sintering.

The molded body is obtained by stacking the powder compositions and molding them. Each powder composition is obtained by mixing zirconia powder and a binder in any desired ratio by a known method. The molding is preferably pressure molding. For example, a powder composition having a composition corresponding to the bottom layer is filled into a mold to form the bottom layer. Then, a powder composition having a composition corresponding to the composition of the layer adjacent to the bottom layer is filled on top of the bottom layer. When a molded body having a structure in which three or more powder layers are stacked is obtained, a similar operation can be repeated to stack the necessary powder compositions. After filling with a powder composition having a composition corresponding to the composition of the top layer, a preform is obtained by uniaxial pressure molding at an arbitrary pressure, and this is subjected to cold isostatic pressing (hereinafter also referred to as "CIP") processing to obtain a molded body. During stacking, it is not necessary to apply vibration to form a mixed layer between the layers, such as vibration using a vibrator. In addition, uniaxial pressure molding is preferably performed after filling with a powder composition having a composition corresponding to the top layer, and it is preferable not to apply pressure before filling with a powder composition having a composition corresponding to the top layer.

The molding pressure for uniaxial pressure molding is preferably 15 MPa or more and 200 MPa or less, and more preferably 18 MPa or more and 100 MPa or less. In uniaxial pressure molding, warping of the molded body tends to be suppressed as the molding pressure increases. The molding pressure for CIP processing can be 98 MPa or more and 392 MPa or less.

The main differences between the calcined body used in the manufacturing method of this embodiment and the sintered body described above are explained below.

The calcined body to be subjected to the manufacturing method of this embodiment is:
The zirconia composition layer has a structure in which two or more layers containing a stabilizer and zirconia having a necking structure are laminated, and at least
A first zirconia composition layer containing zirconia having a stabilizer content of 4 mol% or more;
A second zirconia composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first zirconia composition layer;
The calcined body comprises:

The calcined body is a composition having a multilayer structure, a so-called laminate, and is a laminate consisting of a structure having a necking structure, a so-called calcined grain. The calcined body can be processed as necessary and used as a precursor of a sintered body, and is also called a pre-sintered body or a semi-sintered body.

The necking structure is a structure that zirconia that has been heat-treated below the sintering temperature has, and is a structure in which zirconia particles are chemically adhered to each other. As shown in FIG. 5, the zirconia (51) contained in the zirconia composition layer of the calcined body is a part of the particle shape of zirconia in the powder composition. In this embodiment, the structure having the necking structure is a structure made of zirconia in the early stage of sintering. This is different from the sintered structure, that is, the structure made of zirconia crystal particles in the later stage of sintering. Therefore, the calcined body of this embodiment can also be considered as a laminate having two or more layers containing zirconia made of zirconia particles having a necking structure of zirconia containing a stabilizer.

Instead of having a zirconia layer, the calcined body has a zirconia composition layer (hereinafter also referred to as the "composition layer") that contains a stabilizer and also contains zirconia with a necking structure, and has a structure equivalent to the layered structure shown in Figure 1 or Figure 2.

The calcined body preferably has a warpage of 1.0 mm or less, more preferably 0.3 mm or less, even more preferably 0.2 mm or less, even more preferably 0.1 mm or less, and even more preferably 0.05 mm or less. The calcined body preferably has no warpage (warpage of 0 mm), but may have a warpage that cannot be measured with a gauge (warpage of 0 mm or more). The calcined body may have a warpage of more than 0 mm, or even 0.01 mm or more. The warpage is preferably 0.06 mm or less, even 0.05 mm or less, or even below the measurement limit (less than 0.03 mm).

The calcined body preferably has a deformation amount of 1.0 or less, more preferably 0.5 or less, even more preferably 0.2 or less, and even more preferably 0.15 or less. The deformation amount can be, for example, 0 or more, 0.01 or more, or even 0.05 or more.

The zirconia contained in the calcined body is preferably in a state in which zirconia obtained by heat-treating zirconia sol has been heat-treated at a temperature lower than the sintering temperature, more preferably in a state in which zirconia obtained by heat-treating zirconia sol obtained by hydrolysis of a zirconium compound has been heat-treated at a temperature lower than the sintering temperature, and even more preferably in a state in which zirconia obtained by heat-treating zirconia sol obtained by hydrolysis of zirconium oxychloride has been heat-treated at a temperature lower than the sintering temperature.

The content of the stabilizer in the stabilizer-containing zirconia contained in the first composition layer (hereinafter also referred to as the "first composition layer"), the content of the stabilizer in the stabilizer-containing zirconia contained in the second composition layer (hereinafter also referred to as the "second composition layer"), and the content of the stabilizer in the stabilizer-containing zirconia contained in the third composition layer (hereinafter also referred to as the "third composition layer") may be the same as the stabilizer content in the first layer, second layer, and third layer, respectively.

The amount of stabilizer contained in the calcined body and each composition layer is arbitrary, as long as it is the same as that of the sintered body of the present embodiment described above.

It is more preferable that the calcined body contains at least a zirconia composition layer containing zirconia having a tetragonal or cubic crystal as the main phase.

The calcined body may have a density of 2.4 g/ ^cm3 or more and 3.7 g/ ^cm3 or less, preferably 3.1 g/ ^cm3 or more and 3.5 g/ ^cm3 or less. A density in this range corresponds to a relative density of 40% to 60%. The calcined body may be a laminate having a strength suitable for processing such as CAD/CAM processing.

The density of the calcined body is determined from the weight, which is determined by gravimetric measurement, and the volume, which is determined by dimensional measurement.

The calcined body and each composition layer are opaque and have a total light transmittance of 0%, but when measurement error is taken into account, the total light transmittance can be, for example, 0% or more and 0.2% or less.

The calcined body only needs to have a strength that is unlikely to cause defects during processing such as CAD/CAM or cutting.

By treating the molded body at a temperature below the sintering temperature, the molded body becomes a calcined body. The calcination method and conditions can be publicly known methods.

The holding temperature during calcination (hereinafter also referred to as the "calcination temperature") is 800°C or higher and 1200°C or lower, preferably 900°C or higher and 1150°C or lower, and more preferably 950°C or higher and 1100°C or lower.

The holding time at the calcination temperature (hereinafter also referred to as the "calcination time") is preferably 0.5 hours or more and 5 hours or less, more preferably 0.5 hours or more and 3 hours or less.

The atmosphere in the calcination step (hereinafter also referred to as the "calcination atmosphere") is preferably an atmosphere other than a reducing atmosphere, more preferably at least one of an oxygen atmosphere and an air atmosphere, and even more preferably an air atmosphere.

In the manufacturing method of this embodiment, either the molded body or the calcined body (hereinafter, these are also collectively referred to as "molded body, etc.") is treated at a temperature higher than 1200°C and lower than 1600°C. This causes the molded body, etc. to become a sintered body. Prior to sintering, the molded body, etc. may be processed into any shape.

The sintering method and sintering conditions can be any known method. The sintering method can be at least one selected from the group consisting of atmospheric sintering, HIP treatment, SPS, and vacuum sintering. As it is widely used as an industrial sintering method, the sintering method is preferably atmospheric sintering, and more preferably atmospheric sintering in an air atmosphere. The sintering method is preferably atmospheric sintering only, and more preferably no pressure sintering is performed after atmospheric sintering. This allows the sintered body to be obtained as an atmospheric sintered body. In this embodiment, atmospheric sintering is a method in which the sintered body is sintered by simply heating it without applying an external force to the sintered body during sintering.

The holding temperature during sintering (hereinafter also referred to as "sintering temperature") is 1200°C or higher and 1600°C or lower, preferably 1300°C or higher and 1580°C or lower, more preferably 1400°C or higher and 1560°C or lower, even more preferably 1430°C or higher and 1560°C or lower, and even more preferably 1480°C or higher and 1560°C or lower. In another embodiment, the sintering temperature is 1450°C or higher and 1650°C or lower, preferably 1500°C or higher and 1650°C or lower, and more preferably 1500°C or higher and 1650°C or lower.

The rate of temperature rise to the sintering temperature is 50°C/hour or more and 800°C/hour or less, preferably 100°C/hour or more and 800°C/hour or less, more preferably 150°C/hour or more and 800°C/hour or less, and even more preferably 150°C/hour or more and 700°C/hour or less.

The holding time at the sintering temperature (hereinafter also referred to as "sintering time") varies depending on the sintering temperature, but is preferably from 1 hour to 5 hours, more preferably from 1 hour to 3 hours, and even more preferably from 1 hour to 2 hours.

The sintering atmosphere (hereinafter also referred to as the "sintering atmosphere") is preferably an atmosphere other than a reducing atmosphere, more preferably at least one of an oxygen atmosphere and an air atmosphere, and even more preferably an air atmosphere. An air atmosphere is, for example, composed mainly of nitrogen and oxygen, with an oxygen concentration of about 18 to 23 volume %.

Preferred sintering conditions for the sintering process include atmospheric sintering in an air atmosphere.

The sintered body of the present embodiment will be described below using examples, but the present invention is not limited to these examples.
(Density measurement)
The densities of the compacts and calcined bodies were calculated from the weights measured by gravimetry and the volumes measured by dimensional measurements. For dimensional measurements, disk-shaped samples were used, and the diameters of the upper and lower ends and the thicknesses were measured at four points each using a vernier caliper, and the average thicknesses and the average diameters of the upper and lower ends were measured.
The density of the sintered body was measured by a method according to JIS R 1634.

(Warpage and deformation)
The disk-shaped green body, calcined body, or sintered body was used as a measurement sample, and the amount of deformation of each was calculated according to the following formula.
Deformation amount = (warping: mm) / (dimension: mm) x 100
The measurement of warpage was performed by the measurement method shown in FIG. 3. The measurement sample was placed so that the convex part of the measurement sample was in contact with the horizontal plate. A thickness gauge (product name: 75A19, manufactured by Nagai Gauge Manufacturing Co., Ltd.) conforming to JIS B 7524:2008 was inserted into the gap formed between the horizontal plate and the bottom surface to measure the warpage. The measurement was performed by inserting a gauge arranged parallel to the horizontal plate into the gap formed between the horizontal plate and the bottom surface of the measurement sample, and measuring the gauge thickness that was the maximum thickness of the gauge that could be inserted into the gap, and the gauge thickness was taken as the warpage. The warpage was measured sequentially at 0.01 mm increments from a gauge thickness of 0.03 mm by using a single gauge or a combination of gauges.
The dimensions of the measurement sample were measured by using a vernier caliper to measure the diameter at the upper end and the diameter at the lower end at four points each, and the average value of the diameters at the upper and lower ends was calculated.

(Total light transmittance)
The total light transmittance was measured using a spectrophotometer (device name: V-650, manufactured by JASCO Corporation) according to a method conforming to JIS K 7361. A disk-shaped sample was used for the measurement. Prior to the measurement, both sides of the sample were polished to a sample thickness of 1 mm and a surface roughness (Ra) of 0.02 μm or less. Light with wavelengths of 220 to 850 nm was transmitted through the sample and collected with an integrating sphere to measure the transmittance at each wavelength, and the transmittance at a wavelength of 600 nm was taken as the total light transmittance.

(Three-point bending strength)
The three-point bending strength was measured by a method conforming to JIS R 1601. The measurement sample was a columnar shape with a length in the lamination direction, a width of 4 mm, a thickness of 3 mm, and a length of 45 mm. The measurement was performed with a support distance of 30 mm and a load applied in the horizontal direction of the measurement sample.
(Average aggregate diameter)
The average agglomeration diameter was measured by putting a powdered granule sample into a Microtrac particle size distribution analyzer (device name: MT3100II, manufactured by Microtrac Bell Co., Ltd.).
The particle size at which the cumulative volume reached 50% was taken as the average agglomerated size.

(Crystalline Phase)
The crystal phase of the laminate sample was measured by XRD measurement under the following conditions: A general XRD device (device name: X'pert PRO MPD, manufactured by Spectris) was used as the measuring device.
Radiation source: CuKα radiation (λ=1.541862Å)
Measurement mode: Step scan Scan condition: 0.000278° per second
Measurement range: 2θ=10-140°
Irradiation width: constant (10mm)
The obtained XRD pattern was subjected to Rietveld analysis using analysis software (RIETAN-2000) to determine the ratio of tetragonal and cubic crystals (ratio of integrated peak intensities), and the crystal phase with the highest ratio was determined as the main phase.

Synthesis Example 1 (Synthesis of Zirconia Powder)
(Zirconia powder A1)
A hydrated zirconia sol was obtained by hydrolysis of an aqueous solution of zirconium oxychloride. Yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration became 5.5 mol%, and then the sol was dried at 180°C. The dried zirconia sol was fired at 1160°C for 2 hours, washed with distilled water, and dried in air at 110°C. α-alumina was mixed with the dried powder to obtain a mixed powder, and distilled water was added to the mixed powder to obtain a slurry, which was then processed in a ball mill for 22 hours.
After the ball milling, an acrylic acid-based binder (acrylic resin) was added to the slurry as a binding agent so that the weight ratio of the binder to the mixed powder weight in the slurry was 3.13 mass%. The mixed slurry was spray-dried at 180°C to obtain powder granules containing 3.13 mass% of the acrylic acid-based binder (acrylic resin) and 0.05 mass% of alumina, with the remainder being 5.5 mol% yttria-containing zirconia, and having an average agglomeration diameter of 45 μm.

(Zirconia powder A2)
Powder granules containing 3.5 mass% of an acrylic acid-based binder, 0.05 mass% of alumina, and the remainder being 5.5 mol% yttria-containing zirconia and having an average agglomeration diameter of 44 μm were obtained in the same manner as for zirconia powder A1, except that an acrylic acid-based binder was added to and mixed with the slurry so that the weight ratio of the binder to the slurry weight was 3.5% by mass.
(Zirconia powder A3)
Powder granules containing 4.0 mass% of an acrylic acid-based binder, 0.05 mass% of alumina, with the remainder being 5.5 mol% yttria-containing zirconia, and having an average agglomeration diameter of 46 μm were obtained in the same manner as for zirconia powder A1, except that an acrylic acid-based binder was added to and mixed with the slurry so that the weight ratio of the binder to the slurry weight was 4.0 mass%.
(Zirconia powder A4)
Powder granules containing 5.0 mass% of an acrylic acid-based binder, 0.05 mass% of alumina, with the remainder being 5.5 mol% yttria-containing zirconia, and having an average agglomeration diameter of 46 μm were obtained in the same manner as for zirconia powder A1, except that an acrylic acid-based binder was added to and mixed with the slurry so that the weight ratio of the binder to the slurry weight was 5.0 mass%.
(Zirconia powder A5)
Powder granules containing 6.0 mass% of an acrylic acid-based binder, 0.05 mass% of alumina, with the remainder being 5.5 mol% yttria-containing zirconia, and having an average agglomeration diameter of 45 μm were obtained in the same manner as for zirconia powder A1, except that an acrylic acid-based binder was added to and mixed with the slurry so that the weight ratio of the binder to the slurry weight was 6.0 mass%.
(Zirconia powder A6)
Powder granules containing 3.05 mass% of an acrylic acid-based binder and 0.05 mass% of alumina, with the remainder being 5.2 mol% yttria-containing zirconia, and having an average agglomeration diameter of 43 μm, were obtained in the same manner as for zirconia powder A1, except that yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration was 5.2 mol%, and an acrylic acid-based binder was added to the slurry and mixed so that the weight ratio of the binder to the slurry weight was 3.05 mass%.
(Zirconia powder A7)
Powder granules containing 3.08 mass% of an acrylic acid-based binder, 0.05 mass% of alumina, and the remainder being 5.8 mol% yttria-containing zirconia, and having an average agglomeration diameter of 44 μm were obtained in the same manner as for zirconia powder A1, except that yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration was 5.80 mol%, and an acrylic acid-based binder was added to the slurry and mixed so that the weight ratio of the binder to the slurry weight was 3.08 mass%.

(Zirconia powder B1)
A dried powder was obtained in the same manner as for zirconia powder A1, and α-alumina and distilled water were mixed with this to form a slurry. This was then treated in a ball mill for 22 hours to obtain a slurry containing a powder containing 0.05 mass% alumina and the remainder being 5.5 mol% yttria-containing zirconia.
In addition, a dried powder was obtained in the same manner as for zirconia powder A1, except that yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration was 3.0 mol%, and α-alumina and distilled water were mixed with this to form a slurry, which was then treated in a ball mill for 22 hours to obtain a slurry containing a powder containing 0.05 mass% alumina and the remainder being 3.0 mol% yttria-containing zirconia.
The two slurries obtained were mixed to obtain a slurry containing 0.05% by mass of alumina and 4.0 mol% yttria-containing zirconia powder, and then an acrylic acid-based binder was added to the slurry so that the weight ratio of the binder to the slurry weight was 3.05% by mass, and mixed. The mixed slurry was spray-dried at 180° C. to obtain powder granules containing 3.05% by mass of the acrylic acid-based binder and 0.05% by mass of alumina, with the remainder being 4.0 mol% yttria-containing zirconia, and having an average agglomeration diameter of 43 μm.

(Zirconia powder B2)
A slurry containing a powder containing 0.05 mass% alumina and the balance being 5.5 mol% yttria-containing zirconia, and a slurry containing a powder containing 0.05 mass% alumina and the balance being 2.5 mol% yttria-containing zirconia were mixed, and an acrylic acid-based binder was added to the slurry and mixed so that the weight ratio of the binder to the slurry weight was 3.08 mass%, and powder granules containing 3.08 mass% acrylic acid-based binder and 0.05 mass% alumina, the balance being 4.0 mol% yttria-containing zirconia, and having an average agglomeration diameter of 46 μm were obtained in a manner similar to that for zirconia powder B1, except that the slurry was mixed with a slurry containing 0.05 mass% alumina and the balance being 2.5 mol% yttria-containing zirconia, and an acrylic acid-based binder was added to the slurry and mixed such that the weight ratio of the binder to the slurry weight was 3.08 mass%.
(Zirconia powder B3)
A slurry containing a powder containing 0.05 mass% alumina and the balance being 5.5 mol% yttria-containing zirconia, and a slurry containing a powder containing 0.05 mass% alumina and the balance being 2.5 mol% yttria-containing zirconia were mixed, and an acrylic acid-based binder was added to the slurry and mixed so that the weight ratio of the binder to the slurry weight was 2.0 mass%, and powder granules containing 2.0 mass% acrylic acid-based binder and 0.05 mass% alumina, the balance being 4.15 mol% yttria-containing zirconia, and having an average agglomeration diameter of 45 μm were obtained in a manner similar to that for zirconia powder B1, except that the slurry was mixed with a slurry containing 0.05 mass% alumina and the balance being 2.5 mol% yttria-containing zirconia, and an acrylic acid-based binder was added to the slurry and mixed such that the weight ratio of the binder to the slurry weight was 2.0 mass%.
(Zirconia powder B4)
Powder granules containing 3.06 mass% of an acrylic acid-based binder and 0.05 mass% of alumina, with the remainder being 4.5 mol% yttria-containing zirconia, and having an average agglomeration diameter of 45 μm, were obtained in the same manner as for zirconia powder B1, except that the mixing ratio of the two slurries was changed so that the yttria content was 4.5 mol% and that an acrylic acid-based binder was added to and mixed with the slurry so that the weight ratio of the binder to the slurry weight was 3.06 mass%.

(Zirconia powder C1)
A hydrated zirconia sol was obtained by hydrolysis of an aqueous solution of zirconium oxychloride. Yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration became 4.05 mol%, and then the sol was dried at 180°C. The dried zirconia sol was fired at 1160°C for 2 hours, washed with distilled water, and dried in air at 110°C. The dried powder was mixed with α-alumina to obtain a mixed powder, and distilled water was added to the mixed powder to obtain a slurry, which was then processed in a ball mill for 22 hours.
After the ball milling, an acrylic acid-based binder was added to the slurry so that the weight ratio of the binder to the weight of the mixed powder in the slurry was 3.30 mass%. The mixed slurry was spray-dried at 180° C. to obtain powder granules containing 3.30 mass% of the acrylic acid-based binder, 0.05 mass% of alumina, and the remainder being 4.05 mol% yttria-containing zirconia, with an average agglomeration diameter of 43 μm.
(Zirconia powder C2)
Powder granules containing 3.20 mass% of an acrylic acid-based binder and 0.05 mass% of alumina, with the remainder being 4.10 mol% yttria-containing zirconia, and having an average agglomeration diameter of 46 μm, were obtained in the same manner as for zirconia powder C1, except that yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration was 4.10 mol%, and an acrylic acid-based binder was added to the slurry and mixed so that the weight ratio of the binder to the slurry weight was 3.20 mass%.
(Zirconia powder C3)
Powder granules containing 3.29 mass% of an acrylic acid-based binder and 0.05 mass% of alumina, with the remainder being 4.25 mol% yttria-containing zirconia, and having an average agglomeration diameter of 44 μm, were obtained in the same manner as for zirconia powder C1, except that yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration was 4.25 mol%, and an acrylic acid-based binder was added to the slurry and mixed so that the weight ratio of the binder to the slurry weight was 3.29 mass%.
(Zirconia powder C4)
A powder granule was obtained in the same manner as for zirconia powder C1, except that yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration was 4.00 mol%, that α-alumina was not used, and that an acrylic acid-based binder was added to the slurry and mixed so that the weight ratio of the binder to the slurry weight was 3.50 mass%. The powder granule was composed of 3.50 mass% of the acrylic acid-based binder and the remainder was 4.00 mol% yttria-containing zirconia, and had an average agglomeration diameter of 44 μm.
(Zirconia powder C5)
Powder granules containing 3.50 mass% of an acrylic acid-based binder, 0.05 mass% of alumina, and the remainder being 4.00 mol% yttria-containing zirconia, and having an average agglomeration diameter of 46 μm were obtained in the same manner as for zirconia powder C1, except that yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration was 4.00 mol%, and an acrylic acid-based binder was added to the slurry and mixed so that the weight ratio of the binder to the slurry weight was 3.50 mass%.
(Zirconia powder C6)
Powder granules containing 3.50 mass% of an acrylic acid-based binder and 0.10 mass% of alumina, with the remainder being 4.00 mol% yttria-containing zirconia, and having an average agglomeration diameter of 45 μm, were obtained in the same manner as for zirconia powder C1, except that yttrium chloride was added to the hydrated zirconia sol so that the yttria concentration was 4.00 mol%, α-alumina was mixed in so that the alumina content was 0.10 mass%, and an acrylic acid-based binder was added to the slurry and mixed so that the weight ratio of the binder to the slurry weight was 3.50 mass%.

Example 1
(Molded body)
A mold with an inner diameter of 48 mm was filled with 25 g of zirconia powder A1, and then the mold was tapped to form a first powder layer. The same amount of zirconia powder B1 was filled on the first powder layer, and the mold was tapped to form a second powder layer, and then uniaxial press molding was performed at a pressure of 49 MPa. Then, a CIP treatment was performed at a pressure of 196 MPa to obtain a laminate consisting of two layers, which was used as the molded body of this example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.0 mol%, the difference in yttria content between the layers was 1.50 mol%, and the difference in binder content (binder amount difference) was 0.08 mass%.
The warpage of the molded product was 0.06 mm, and the amount of deformation was 0.12.

(Calcined body)
The molded body was calcined at a temperature increase rate of 20° C./hour at a calcination temperature of 1000° C. for a calcination time of 2 hours to obtain a laminate, which was used as the calcined body of this example.
The calcined body had a warp of 0.06 mm and a deformation amount of 0.12.

(Sintered body)
The calcined body was sintered at a heating rate of 100° C./hour, a sintering temperature of 1500° C., and a sintering time of 2 hours to obtain a laminate, which was used as the sintered body of this example.

The warp of the sintered body was 0.06 mm, and the deformation amount was 0.15. The stabilizer content of the sintered body was 4.75 mol%.

Example 2
A laminate was obtained in the same manner as in Example 1, except that zirconia powder A2 and zirconia powder B2 were used instead of zirconia powder A1 and zirconia powder B1, and this was used as the molded body of this Example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.0 mol%, the difference in yttria content between the layers was 1.50 mol%, and the difference in binder content was 0.42 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage was 0.04 mm for the molded body, 0.05 mm for the calcined body, and 0.04 mm for the sintered body, and the deformation was 0.08 for the molded body, 0.10 for the calcined body, and 0.10 for the sintered body.

Example 3
A laminate was obtained in the same manner as in Example 1, except that zirconia powder A4 and zirconia powder B2 were used instead of zirconia powder A1 and zirconia powder B1, respectively, and this was used as the molded body of this Example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.0 mol%, the difference in yttria content between the layers was 1.50 mol%, and the difference in binder content was 1.92 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage of the molded body was below the measurement limit (less than 0.03 mm), the calcined body was 0.04 mm, and the sintered body was below the measurement limit (less than 0.03 mm). The deformation amount of the calcined body was 0.09.

Example 4
A laminate was obtained in the same manner as in Example 1, except that zirconia powder A5 and zirconia powder B2 were used instead of zirconia powder A1 and zirconia powder B1, respectively, and this was used as the molded body of this Example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.0 mol%, the difference in yttria content between the layers was 1.50 mol%, and the difference in binder content was 2.92 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage was 0.04 mm for the molded body, 0.03 mm for the calcined body, and less than the measurement limit (less than 0.03 mm) for the sintered body, and the deformation amount was 0.08 for the molded body and 0.06 for the calcined body.

From Examples 1 to 4, it was confirmed that when the yttria content difference is 1.50 mol%, warping of the calcined body tends to be suppressed as the binder amount difference increases, and that when the binder amount difference is 0.5 mass% or more, warping in the sintered body state is below the measurement limit.

Example 5
A laminate was obtained in the same manner as in Example 1, except that zirconia powder B3 was used instead of zirconia powder B1, and this was used as the molded body of this Example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.15 mol%, the difference in yttria content between the layers was 1.35 mol%, and the difference in binder content was 1.13 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage was 0.04 mm for the molded body, 0.03 mm for the calcined body, and 0.03 mm for the sintered body, and the deformation was 0.08 for the molded body, 0.06 for the calcined body, and 0.08 for the sintered body.

Example 6
A laminate was obtained in the same manner as in Example 1, except that zirconia powder B4 was used instead of zirconia powder B1, and this was used as the molded body of this Example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.5 mol%, the difference in yttria content between the layers was 1.0 mol%, and the difference in binder content was 0.07 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage was 0.05 mm for the molded body, 0.05 mm for the calcined body, and 0.05 mm for the sintered body, and the deformation amount was 0.10 for the molded body, 0.10 for the calcined body, and 0.13 for the sintered body. The stabilizer content of the sintered body was 5.0 mol%.

Example 7
A laminate was obtained in the same manner as in Example 1, except that zirconia powder A3 and zirconia powder B4 were used instead of zirconia powder A1 and zirconia powder B1, respectively, and this was used as the molded body of this example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.5 mol%, the difference in yttria content between the layers was 1.0 mol%, and the difference in binder content was 0.94 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage was 0.04 mm for the molded body, 0.04 mm for the calcined body, and 0.03 mm for the sintered body, and the deformation was 0.08 for the molded body, 0.08 for the calcined body, and 0.08 for the sintered body.

Example 8
A laminate was obtained in the same manner as in Example 1, except that zirconia powder C1 was used instead of zirconia powder B1, and this was used as the molded body of this Example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.05 mol%, the difference in yttria content between the layers was 1.45 mol%, and the difference in binder content was 0.2 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage of the molded body, calcined body and sintered body was below the measurement limit (less than 0.03 mm).

Example 9
A laminate was obtained in the same manner as in Example 1, except that zirconia powder C2 was used instead of zirconia powder B1, and this was used as the molded body of this Example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.1 mol%, the difference in yttria content between the layers was 1.4 mol%, and the difference in binder content was 0.1 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used. The stabilizer content of the sintered body was 4.8 mol%.

The warpage was 0.03 mm for the molded body, 0.03 mm for the calcined body, and 0.04 mm for the sintered body, and the deformation was 0.06 for the molded body, 0.06 for the calcined body, and 0.10 for the sintered body.

Example 10
A laminate was obtained in the same manner as in Example 1, except that zirconia powder C3 was used instead of zirconia powder B1, and this was used as the molded body of this Example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.25 mol%, the difference in yttria content between the layers was 1.25 mol%, and the difference in binder content was 0.19 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage of the molded body was below the measurement limit (less than 0.03 mm), the calcined body was 0.03 mm, and the sintered body was 0.03 mm. The deformation amount was 0.06 for the calcined body and 0.08 for the sintered body.

The density of the green body was 3.28 g/ ^cm3 , the density of the calcined body was 3.22 g/ ^cm3 , and the density of the sintered body was 6.06 g/ ^cm3 .

Example 11
A laminate was obtained in the same manner as in Example 10 except that the pressure in the uniaxial press molding was 19.6 MPa, and this was used as the molded body of this example.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage of the molded body was below the measurement limit (less than 0.03 mm), the calcined body was 0.03 mm, and the sintered body was 0.05 mm. The deformation amount was 0.07 for the calcined body and 0.14 for the sintered body.

The density of the green body was 3.25 g/ ^cm3 , the density of the calcined body was 3.19 g/ ^cm3 , and the density of the sintered body was 6.06 g/ ^cm3 .

Example 12
A laminate was obtained in the same manner as in Example 10 except that the pressure in the uniaxial press molding was 98 MPa, and this was used as the molded body of this example.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage of the molded body, calcined body and sintered body was below the measurement limit (less than 0.03 mm).

The density of the green body was 3.35 g/ ^cm3 , the density of the calcined body was 3.29 g/ ^cm3 , and the density of the sintered body was 6.06 g/ ^cm3 .

From Examples 10 to 12, it can be seen that increasing the pressure of the uniaxial press molding tends to improve the density of the molded body and the calcined body. At the same time, it can be seen that warping tends to be suppressed when the calcined body and the sintered body are formed.

Example 13
A laminate was obtained in the same manner as in Example 10, except that a mold having an inner diameter of 110 mm was used and the pressure of the uniaxial press molding was 98 MPa, and this was used as the molded body of this example.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The warpage of the molded body, calcined body and sintered body was below the measurement limit (less than 0.03 mm).

From Examples 12 and 13, it can be seen that there is no difference (or more accurately, no change) in the warping of the compact, calcined body, and sintered body due to differences in the dimensions of the laminate.

The sintered bodies obtained in all examples had a change in translucency between the top and bottom layers, and had a texture similar to that of natural teeth.

Example 14
A laminate was obtained in the same manner as in Example 1, except that a die with an inner diameter of 110 mm was used, the pressure of the uniaxial press molding was 19.6 MPa, and zirconia powder C4 was used instead of zirconia powder B1, and this was used as the molded body of this example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.0 mol%, the difference in yttria content between the layers was 1.5 mol%, and the difference in binder content was 0.4 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used. The stabilizer content of the sintered body was 4.75 mol%.

The warpage was 0.05 mm for the molded body, 0.11 mm for the calcined body, and less than the measurement limit (less than 0.03 mm) for the sintered body, and the deformation amount was 0.05 for the molded body and 0.11 for the calcined body.

Example 15
A laminate was obtained in the same manner as in Example 1, except that a die with an inner diameter of 110 mm was used, the pressure of the uniaxial press molding was 19.6 MPa, and zirconia powder C5 was used instead of zirconia powder B1, and this was used as the molded body of this example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.0 mol%, the difference in yttria content between the layers was 1.5 mol%, and the difference in binder content was 0.37 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used. The stabilizer content of the sintered body was 4.75 mol%.

The warpage was 0.05 mm for the molded body, 0.14 mm for the calcined body, and below the measurement limit (less than 0.03 mm) for the sintered body, while the deformation was 0.05 for the molded body and 0.11 for the calcined body.

Example 16
A laminate was obtained in the same manner as in Example 1, except that a mold with an inner diameter of 110 mm was used, the pressure of the uniaxial press molding was 19.6 MPa, and zirconia powder C6 was used instead of zirconia powder B1, and this was used as the molded body of this example. The stabilizer content of the first powder layer was 5.5 mol% and the stabilizer content of the second powder layer was 4.0 mol%, the difference in yttria content between the layers was 1.5 mol%, and the difference in binder content was 0.4 mass%. A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used. The stabilizer content of the sintered body was 4.75 mol%.

The warpage was 0.05 mm for the molded body, 0.15 mm for the calcined body, and less than the measurement limit (less than 0.03 mm) for the sintered body, while the deformation amount was 0.05 for the molded body and 0.15 for the calcined body.

From Examples 14 to 16, as the alumina content in the layer with a low stabilizer content decreased, the warping of the calcined body decreased, but there was no change in the magnitude of warping of the compacted body and sintered body.

Example 17
A laminate was obtained in the same manner as in Example 1, except that a die with an inner diameter of 110 mm was used, the pressure of the uniaxial press molding was 98 MPa, and zirconia powders A7 and C5 were used instead of zirconia powders A1 and B1, and this was used as the molded body of this example. The stabilizer content of the first powder layer was 5.8 mol%, the stabilizer content of the second powder layer was 4.0 mol%, the difference in yttria content between the layers was 1.8 mol%, and the difference in binder content was 0.42 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used. The stabilizer content of the sintered body was 4.9 mol%.

The warpage of the calcined body was 0.04 mm, while the compact and sintered bodies were below the measurement limit (less than 0.03 mm), and the deformation amount of the calcined body was 0.03.

Example 18
A laminate was obtained in the same manner as in Example 1, except that a die with an inner diameter of 110 mm was used, the pressure of the uniaxial press molding was 98 MPa, and zirconia powders A6 and C5 were used instead of zirconia powders A1 and B1, and this was used as the molded body of this example. The stabilizer content of the first powder layer was 5.2 mol% and the stabilizer content of the second powder layer was 4.0 mol%, the difference in yttria content between the layers was 1.2 mol%, and the difference in binder content was 0.45 mass%.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used. The stabilizer content of the sintered body was 4.6 mol%.

The warpage of the molded body, calcined body and sintered body was below the measurement limit (less than 0.03 mm).

Comparative Example 1
A mold having an inner diameter of 110 mm was filled with 25 g of zirconia powder containing 4.25 mol% yttria, and then the mold was tapped to form a first powder layer. The same amount of zirconia powder containing 4.25 mol% yttria was filled on the first powder layer, and the mold was tapped to form a second powder layer, after which uniaxial press molding was performed at a pressure of 98 MPa. Then, a CIP process was performed at a pressure of 196 MPa to obtain a laminate consisting of two layers, which was used as the molded body of this comparative example. The difference in yttria content between the layers was 0 mol%, and the difference in binder amount was 0 mass%.

A calcined body and a sintered body were produced in the same manner as in Example 1, except that the molded body was used. In both cases, the warpage was below the measurement limit (<0.03 mm).

In the calcined body of this comparative example, in which the first and second layers had the same yttria content, no warping occurred. In addition, the obtained sintered body had no change in translucency.

Comparative Example 2
A zirconia powder containing 0.094 mass% iron oxide and 0.0045 mass% cobalt oxide, with the remainder being 4 mol% yttria-containing zirconia, was filled into a mold with an inner diameter of 110 mm, and then the mold was tapped to form a first powder layer. The same amount of zirconia powder containing 4 mol% yttria was filled on the first powder layer, and the mold was tapped to form a second powder layer, after which uniaxial press molding was performed at a pressure of 98 MPa. Then, a CIP process was performed at a pressure of 196 MPa to obtain a laminate consisting of two layers, which was used as the molded body of this comparative example. The difference in yttria content between the layers was 0 mol%, and the difference in binder amount was 0.02 mass%.

A calcined body was produced in the same manner as in Example 1, except that this molded body was used, and the warpage was 0.67 mm.

In the calcined body of this comparative example, in which the first and second layers had the same yttria content but differed in colorant content by 0.139 mass%, the calcined body exhibited significant warping.

Reference Example 1
The zirconia powder A1 was filled into a mold having an inner diameter of 48 mm, and the mold was tapped and then subjected to uniaxial press molding at a pressure of 49 MPa. Then, a CIP process was performed at a pressure of 196 MPa to obtain a molded body.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The obtained sintered body contained 0.05% by mass of alumina, with the remainder being 5.5 mol% yttria-containing zirconia, and its crystal phase consisted of tetragonal and cubic crystals, with the main phase being cubic. The total light transmittance of the sintered body was 37.5%, and the three-point bending strength was 600 MPa.

Reference Example 2
The zirconia powder B1 was filled into a mold having an inner diameter of 48 mm, and the mold was tapped and then uniaxial press molding was performed at a pressure of 49 MPa. Then, CIP processing was performed at a pressure of 196 MPa to obtain a molded body.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The obtained sintered body contained 0.05% by mass of alumina, with the remainder being 4.0 mol% yttria-containing zirconia, and its crystal phase was composed of tetragonal and cubic crystals, with the main phase being tetragonal. The total light transmittance of the sintered body was 36%, and the three-point bending strength was 1100 MPa.

Reference Example 3
Zirconia powder B4 was filled into a mold having an inner diameter of 48 mm, and the mold was tapped and then uniaxial press molding was performed at a pressure of 49 MPa. Then, CIP processing was performed at a pressure of 196 MPa to obtain a molded body.

A calcined body and a sintered body were obtained in the same manner as in Example 1, except that the molded body was used.

The resulting sintered body contained 0.05% by mass of alumina, with the remainder being 4.5 mol% yttria-containing zirconia, and had a total light transmittance of 37%.

100, 200, 300, 400: Zirconia sintered body 11, 21: First layer 12, 22: Second layer 23: Third layer 32A, 32B: Thickness gauge 33: Size of sintered body 41: Load 42: Support distance 51: Zirconia having a necking structure

Claims (18)

The powder composition layer has a structure in which two or more powder composition layers made of a powder composition containing zirconia containing a stabilizer and a binder are laminated, and at least
A first powder composition layer including zirconia having a stabilizer content of 4 mol% or more and a binder;
A second powder composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first powder composition layer and a binder;
Equipped with
The molded body has a difference in binder content between the first powder composition layer and the second powder composition layer of more than 0.01% by mass, and the molded body is sintered at 1200° C. or more and 1600° C. or less. The molded body has a structure in which two or more zirconia layers containing zirconia containing a stabilizer are laminated, and at least
A first zirconia layer containing zirconia having a stabilizer content of 4 mol% or more;
a second zirconia layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first zirconia layer;
A method for producing a sintered body, comprising: The powder composition layer has a structure in which two or more powder composition layers made of a powder composition containing zirconia containing a stabilizer and a binder are laminated, and at least
A first powder composition layer including zirconia having a stabilizer content of 4 mol% or more and a binder;
A second powder composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first powder composition layer and a binder;
Equipped with
A step of calcining the molded body having a binder content difference between the first powder composition layer and the second powder composition layer of more than 0.01 mass % at 800 ° C. or more and less than 1200 ° C. to obtain a calcined body; and
The method has a structure in which two or more zirconia layers containing zirconia containing a stabilizer are laminated, and further comprises a step of sintering the calcined body at 1200 ° C. or more and 1600 ° C. or less.
A first zirconia layer containing zirconia having a stabilizer content of 4 mol% or more;
a second zirconia layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first zirconia layer;
A method for producing a sintered body, comprising: The manufacturing method according to claim 1 or 2, wherein the warpage of the molded product measured using a thickness gauge conforming to JIS B 7524:2008 is 1.0 mm or less. The manufacturing method according to any one of claims 1 to 3, wherein the binder is one or more selected from the group consisting of polyvinyl alcohol, polyvinyl butyrate, wax, and acrylic resin. The method according to claim 1 , wherein the powder composition contained in the powder composition layer is a powder in a granulated state. The method according to any one of claims 1 to 5, wherein the density of the molded body is 2.4 g/ ^cm3 or more and 3.7 g/ ^cm3 or less. The manufacturing method according to any one of claims 1 to 6, wherein the stabilizer content of the stabilizer-containing zirconia contained in the second zirconia layer is 1.5 mol% or more and 7.0 mol% or less. The manufacturing method according to any one of claims 1 to 6, wherein the stabilizer content of the stabilizer-containing zirconia contained in the second zirconia layer is 5.0 mol% or more and 7.0 mol% or less. The manufacturing method according to any one of claims 1 to 8, wherein the stabilizer content of the stabilizer-containing zirconia contained in the first zirconia layer is 4.0 mol% or more and 6.0 mol% or less. The manufacturing method according to any one of claims 1 to 9, wherein the difference between the stabilizer content of the first zirconia layer and the stabilizer content of the second zirconia layer is 0.2 mol% or more. The method according to any one of claims 1 to 10, wherein the stabilizer _{is at least one selected from the group consisting of yttria (Y2O3 )} , calcia (CaO), magnesia (MgO) and ceria ( _CeO2 ). The manufacturing method according to any one of claims 1 to 11, wherein at least one of the zirconia layers contains alumina. The manufacturing method according to any one of claims 1 to 12, wherein the warpage of the sintered body measured using a thickness gauge conforming to JIS B 7524:2008 is 1.0 mm or less. The method according to any one of claims 1 to 13, wherein the sintered body has a density of 5.7 g/ ^cm3 or more and 6.3 g/ ^cm3 or less, as measured by a method in accordance with JIS R 1634. The manufacturing method according to any one of claims 1 to 14, wherein the sintered body has a zirconia layer with a total light transmittance of 30% to 50% for light with a wavelength of 600 nm when the sample is 1.0 mm thick. The calcined body,
The zirconia composition layer has a structure in which two or more layers containing a stabilizer and zirconia having a necking structure are laminated, and at least
A first zirconia composition layer containing zirconia having a stabilizer content of 4 mol% or more;
A second zirconia composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first zirconia composition layer;
The method according to claim 2 , wherein the calcined body comprises: The zirconia composition layer has a structure in which two or more layers containing a stabilizer and zirconia having a necking structure are laminated, and at least
A first zirconia composition layer containing zirconia having a stabilizer content of 4 mol% or more;
A second zirconia composition layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first zirconia composition layer;
The present invention has a structure in which two or more zirconia layers containing zirconia containing a stabilizer are laminated, the structure being characterized by having a step of sintering a calcined body having a warpage of 1.0 mm or less as measured using a thickness gauge in accordance with JIS B 7524:2008 at 1200 ° C. or more and 1600 ° C. or less, and at least
A first zirconia layer containing zirconia having a stabilizer content of 4 mol% or more;
a second zirconia layer containing zirconia having a stabilizer content different from that of the zirconia contained in the first zirconia layer;
A method for producing a sintered body, comprising: The method according to claim 17, wherein the calcined body contains one or more elements selected from the group consisting of europium (Eu), gadolinium (Gd), terbium (Tb), erbium (Er) and ytterbium (Yb), more preferably one or more elements selected from the group consisting of iron, cobalt, manganese, praseodymium, gadolinium, terbium and erbium.