JP2019199079A - Method for manufacturing ceramic molding for sintering and method for manufacturing ceramic sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a ceramics compact for sintering capable of producing a dense and excellent ceramic sintered body having extremely small residual voids and no residual stress. A method for producing a ceramics compact for sintering, which comprises hydrostatically pressing a raw material powder containing a ceramics powder and a thermoplastic resin having a Tg higher than room temperature. A raw material powder slurry is prepared by adding the thermoplastic resin to a solvent so as to be 2% by mass or more and 40% by mass or less with respect to the total mass of the ceramic powder and the thermoplastic resin, and wet casting using the raw material powder slurry. To form a cast molded product, which is then dried and subjected to a first-stage hydrostatic pressure molding at a temperature lower than the Tg of the thermoplastic resin to form a first-stage pressure molded product. The one-stage pressure-molded body is heated to Tg or higher of the thermoplastic resin and subjected to WIP molding as the second-stage hydrostatic pressure molding to produce a ceramic molded body. [Selection diagram] None

Description

  The present invention uses a method for producing a sintered ceramic molded body having a small residual void and a reduced amount by achieving both pressure transmission and plastic flow during molding, and a molded body produced by this production method. The present invention relates to a method for producing a sintered ceramic body.

  In general, it is preferable to reduce the residual bubbles inside the sintered body of any ceramic because mechanical strength, thermal conductivity, light transmission, electrical characteristics, long-term reliability, and the like are improved. In addition, as a method for producing thick ceramics with a high yield, conventionally, a method of pressure-forming powder has been widely used. The most classic method is a method of forming a uniaxial press and then cold isostatic pressing (also called cold isostatic press, Cold Isostatic Press (CIP)), or filling a raw material powder into a rubber mold or the like. Thus, there is a method for direct CIP molding, which is still widely used industrially today. In many cases, thermoplastic resin (so-called binder) is mixed in the ceramic powder starting material (raw material powder) for the purpose of improving shape retention during molding and preventing cracks during molding and sintering. Has been.

  When the process of mixing and adding this thermoplastic resin to the raw material powder is used, the crushing strength of the secondary agglomerated raw material powder and granulated raw material when granulated is increased, and the inside of the molded body is pressed when thick ceramics are pressed. It is possible to sufficiently transmit the pressure until the molding density is improved. Furthermore, it is possible to improve the shape retention of the molded body and prevent cracks and deformation in the subsequent process. In this way, a molded body having a relatively high molding density can be molded into a desired shape with a high yield. However, on the other hand, there are problems that the plastic flow of the raw powder and raw granule during uniaxial pressing and CIP molding is hindered, causing large internal residual stress during molding, and bridging of the raw powder and intergranular voids are induced. I am in trouble. Therefore, it is known that when the molded body is densified by sintering or the like, residual stress and residual bubbles exist inside, and various characteristics are deteriorated.

  Therefore, as a method of improving the plastic fluidity of the thermoplastic resin mixed and added to the ceramic powder raw material to promote densification during ceramic molding, warm isostatic pressing (also called warm isostatic pressing. Warm isostatic press. Press (WIP)) molding has been proposed. For example, in Patent Document 1 (Japanese Patent No. 2858972), a ceramic resin is mixed with a thermoplastic resin, and after the primary molding, a rubber coating is applied and then a secondary hydrostatic pressure is applied. A method for producing a ceramic molded body characterized in that, when the mixture is put into a rubber mold or the like and subjected to hydrostatic pressure molding, the temperature is raised to a temperature range in which the thermoplastic resin is thermally softened at the time of hydrostatic pressure. Is disclosed. A hydrostatic pressurizing apparatus capable of adjusting the temperature rise to a temperature range where the thermoplastic resin is thermally softened is referred to as “Warm Isostatic Press (WIP)”.

  Note that a warm isostatic press for heating the entire powder uniformly at a low temperature, a so-called WIP device itself, has been known for a very long time, for example, as in Patent Document 2 (Japanese Patent Publication No. 54-14352). It can be confirmed in the literature. An external circulation heating type WIP apparatus improved to a more practical structure is also disclosed in Patent Document 3 (Japanese Patent Laid-Open No. 61-124503).

  The molding technology for ceramics mixed with a thermoplastic resin using such a WIP device is subsequently applied as a technology for pressure bonding processes of laminated ceramics. For example, Patent Document 4 (International Publication No. 2012/060402) discloses an example in which an isostatic press (WIP) can be used as a method for forming a laminated green sheet of an all-solid battery. A known example of thermocompression bonding with a ton pressure is shown. Or patent document 5 (Unexamined-Japanese-Patent No. 2014-57021) has disclosed the embodiment which performs warm isostatic pressing (WIP) as a press molding method of multilayer ceramic electronic components, such as a multilayer ceramic capacitor, An example is shown in which the laminated sheet is preheated to a predetermined temperature in a vacuum-packed state and then subjected to warm isostatic pressing at a temperature of 70 ° C.

  However, in general, when a thermoplastic resin is pressurized at a temperature higher than the glass transition temperature, plastic deformation and plastic flow occur predominantly, and the force that transmits the applied pressure to the inside of the molded body is very weak. There's a problem. Therefore, even if the raw material powder has improved shape retention and crushing strength by mixing and adding a thermoplastic resin and improving pressure transmission, pressure transmission to the inside of the molded body is rapidly achieved by WIP treatment. There was a fatal defect that attenuated, and in particular left a large amount of voids inside the thick molded body.

  Therefore, although the WIP apparatus itself has been known for a long time, it is only used for producing a thin (thin) sheet molded body as described above, and the above-mentioned Patent Document 1 and later. However, it has been difficult to use WIP as a thick ceramic molding technology.

In addition to dry raw materials, there are known a casting method and an extrusion molding method in which a ceramic raw material is kneaded and slurryed with a thermoplastic resin in a wet manner and then molded in a wet state. The wet molded body molded by these molding methods has a tendency to become a considerably good molded body with few coarse voids already after the above process. Therefore, it has been judged that this is sufficient, and there is no known example in which the molded body is further subjected to after press molding.
However, the ceramic sintered body produced by the conventional method such as the casting method as described above has been required to further improve various properties such as light transmittance.

  Although Patent Document 6 (Japanese Patent No. 5523431) exemplifies an embodiment, as a raw material powder molding method, uniaxial pressure molding press molding or isotropic pressure molding cold isostatic pressing is described. Any one of a pressure forming die (CIP), a warm isostatic pressing die (WIP), a hot isostatic pressing die (HIP), and an isotropic pressing after uniaxial pressing is arbitrarily selected. In addition to this, as another example, it is exemplified that it may be mold forming such as cast molding or extrusion molding. However, there is no special description that combines the former molding process and the latter molding process. In addition, there is no knowledge in the prior literature on how the process affects the properties of a molded body when a wet molded body by a casting method or the like is further subjected to CIP molding or WIP molding.

Japanese Patent No. 2858972 Japanese Patent Publication No.54-14352 JP 61-124503 A International Publication No. 2012/060402 JP 2014-57021 A Japanese Patent No. 5523431

  The present invention has been made in view of the above circumstances, and is capable of producing a ceramic sintered body for sintering capable of producing a dense and excellent ceramic sintered body having extremely small residual voids and no residual stress. It is an object of the present invention to provide a method for producing a ceramic sintered body using the ceramic molded body produced by the method and the method for producing a sintered ceramic molded body.

In order to achieve the above object, the present invention provides the following method for producing a sintered ceramic molded body and method for producing a ceramic sintered body.
1.
A method for producing a ceramic molded body for sintering, wherein a raw material powder containing a ceramic powder and a thermoplastic resin having a glass transition temperature higher than room temperature is pressed under hydrostatic pressure to form a predetermined shape, the ceramic powder and the thermoplastic A raw material powder slurry is prepared by adding a resin to a solvent so that the thermoplastic resin is 2% by mass or more and 40% by mass or less based on the total mass of the ceramic powder and the thermoplastic resin, and the raw material powder slurry is used. After forming a cast molded body by wet casting into a predetermined shape, it is dried, and this is first-stage hydrostatic pressure-molded at a temperature lower than the glass transition temperature of the thermoplastic resin. Forming a body, and then heating the first-stage pressure-molded body to a temperature equal to or higher than the glass transition temperature of the thermoplastic resin to perform warm isostatic pressing (WIP) molding as second-stage hydrostatic pressure molding. The method for manufacturing a sintered ceramics molded body to manufacture a ceramic molded body.
2.
The method for producing a sintered ceramic body according to 1, wherein the first hydrostatic pressure molding is cold isostatic pressing (CIP) molding.
3.
After forming the first-stage pressure molded body, heating of the first-stage pressure molded body is started while the first-stage hydrostatic pressure is maintained, and then the second-stage hydrostatic pressure is applied. 2. The method for producing a sintered ceramic molded body according to 1, wherein WIP molding is performed as pressure molding.
4).
4. The method for producing a sintered ceramic molded body according to any one of 1 to 3, wherein the pressure medium for WIP molding is water or oil.
5.
The said thermoplastic resin is a manufacturing method of the ceramic molded object for sintering in any one of 1-4 which has a glass transition temperature higher than room temperature and lower than the boiling point of the pressurization medium of WIP shaping | molding.
6).
The thermoplastic resin is a group consisting of polyvinyl alcohol, polyvinyl acetate, a copolymer of polyvinyl alcohol and polyvinyl acetate, methyl cellulose, ethyl cellulose, polyvinyl butyral, vinyl polypropionate, and a copolymer of polyvinyl alcohol and vinyl propionate. The method for producing a sintered ceramic molded body according to any one of 1 to 5, which is at least one selected from:
7.
The method for producing a sintered ceramic molded body according to any one of 1 to 6, wherein the cast molded body is formed by solid-liquid separation of the raw material powder slurry by centrifugal casting.
8).
Using the ceramic molded body produced by the method for producing a sintered ceramic molded body according to any one of 1 to 7, a sintering treatment is performed in an inert atmosphere or vacuum, and hot isostatic pressing ( HIP) A method for producing a ceramic sintered body obtained by processing to obtain a ceramic sintered body.
9.
9. The method for producing a ceramic sintered body according to 8, wherein the ceramic molded body is degreased before the sintering treatment.
10.
The method for producing a ceramic sintered body according to 8 or 9, wherein an annealing treatment is further performed after the HIP treatment.

  According to the present invention, when press-molding a ceramic molded body, particularly a thick ceramic molded body, pressure transmission into the molded body and plastic flow of the thermoplastic resin can be effectively made compatible, and the remaining It is possible to produce a dense ceramic molded body in which the voids are extremely small and the residual stress is eliminated. Further, by sintering this ceramic molded body, a truly high-density ceramic sintered body with extremely few remaining bubbles can be produced. As a result, it is possible to provide a high-quality ceramic sintered body having better characteristics than the conventional ones with improved mechanical strength, thermal conductivity, light transmittance, and the like.

[Method for producing sintered ceramic body]
Below, the preparation methods of the ceramic molding for sintering which concerns on this invention are demonstrated. The room temperature referred to here is the environmental temperature in the molding process of the ceramic molded body for sintering, and is usually 25 ± 5 ° C.
The method for producing a sintered ceramic molded body according to the present invention is a sintering ceramic that is molded into a predetermined shape by hydrostatic pressure using a raw material powder containing ceramic powder and a thermoplastic resin having a glass transition temperature higher than room temperature. A method for producing a molded body, wherein the ceramic powder and the thermoplastic resin are added to a solvent so that the thermoplastic resin is 2% by mass or more and 40% by mass or less based on a total mass of the ceramic powder and the thermoplastic resin. The raw material powder slurry is prepared and wet cast into a predetermined shape using the raw material powder slurry to form a cast molded body, and then dried, and this is dried at a temperature lower than the glass transition temperature of the thermoplastic resin. A first-stage pressure-molded body is formed by hydrostatic pressure molding of the first stage, and then the first-stage pressure molded body is heated to a temperature higher than the glass transition temperature of the thermoplastic resin. It is characterized in making a warm isostatic pressing as pressing (WIP) performing molded ceramic body.
Details of the present invention will be described below.

(Raw material powder slurry)
The raw material powder slurry used in the present invention contains at least ceramic powder, a thermoplastic resin (binder) and a solvent as essential components. The ceramic powder is 60% by mass to 98% by mass and the glass transition temperature is higher than room temperature. It is prepared by adding a plastic resin (binder) to a solvent so as to contain 2% by mass or more and 40% by mass or less.

  Among these, the ceramic powder constitutes a target ceramic sintered body. The composition is selected according to the target characteristics and is not particularly limited in the present invention. That is, the ceramic powder may be an oxide, or may be a nitride or fluoride. Furthermore, the present invention can be suitably used even for a metal material such as an intermetallic compound.

For example, when producing a transparent ceramic sintered body for a Faraday rotator, when a preferable terbium-containing oxide material is selected, the following three types may be mentioned.
That is,
(I) A terbium-containing garnet-type oxide transparent ceramic comprising a sintered body of oxide garnet (TAG-based composite oxide) containing Tb and Al as main components and Sc as another component,
(Ii) a terbium-containing garnet-type oxide transparent ceramic comprising a sintered body of a TGG composite oxide having a composition formula of Tb ₃ Ga ₅ O ₁₂ ,
(Iii) A terbium-containing bixbite type oxide transparent ceramic represented by the following formula (A).
(Tb _x R _1-x ) ₂ O ₃ (A)
(In the formula (A), x is 0.4 ≦ x ≦ 0.7, and R includes at least one element selected from the group consisting of lanthanoid elements other than scandium, yttrium, and terbium.)

The material (i) is further spread.
The transparent ceramic (i) is a terbium-containing oxide containing Tb and Al as main components and Sc as other components, and has a garnet structure as a structure.
In the garnet structure, a high terbium composition ratio is preferable because the Faraday rotation angle (Verde constant) per unit length increases. Further, it is preferable that the composition ratio of aluminum is high because the terbium crystal field is freed and the distortion of terbium ions is reduced. Furthermore, since aluminum has the smallest ionic radius among the trivalent ions that can exist stably in oxides having a garnet structure, the lattice constant of the garnet structure can be reduced while maintaining the composition ratio of terbium ions. Therefore, the Faraday rotation angle (Verde constant) per unit length is increased, which is preferable. Further, it is preferable that the aluminum composition ratio in the garnet-type oxide is high because the thermal conductivity of the entire system is improved.

  If the cation sites of the entire system are occupied only by terbium and aluminum, the perovskite structure becomes more stable, which causes the generation of perovskite heterogeneous phases. Here, scandium (Sc) is a material having an intermediate ionic radius that can be dissolved in both the terbium site constituting the garnet structure and a part of the aluminum site, and a combination of terbium and aluminum. When the ratio deviates from the stoichiometric ratio due to variations in weighing, it is necessary for the terbium site and the aluminum site to match the stoichiometric ratio and thereby minimize the crystallite formation energy. It is also a buffer material that can be dissolved by adjusting the distribution ratio. Therefore, scandium is a preferable element to be added because a garnet composition single-phase sintered body can be stably obtained.

Therefore, for example, in the TAG basic composition formula (Tb ₃ Al ₅ O ₁₂ ), a portion of 0 to less than 0.08 of the total amount of terbium sites 3 and 0 to less than 0.16 of the total amount of sites 5 of aluminum It is preferable to substitute the above part with scandium (Sc) because the garnet structure is more stabilized.

  Furthermore, part of the terbium site may be replaced with yttrium or lutetium. Both yttrium and lutetium have a smaller ionic radius than terbium, and the garnet structure is more stable, so it does not get in the way. Furthermore, since yttrium and lutetium do not have an absorption peak in the oscillation wavelength band of 0.9 μm or more and 1.1 μm or less of a general fiber laser system, even if they are replaced, they do not get in the way.

The garnet-type oxide material composed of Tb ₃ Ga ₅ O ₁₂ (ii) will be described.
This material is a garnet structure material composed of oxides of terbium (Tb) and gallium (Ga). This structure is also preferable because the composition ratio of terbium is high and the Faraday rotation angle (Verde constant) per unit length is large. A high gallium composition ratio is preferable because the melting point is greatly lowered, the production temperature can be lowered, and the cost can be reduced. Further, Tb ₃ Ga ₅ O ₁₂ has been widely used as a Faraday rotator for fiber laser systems, and is preferable because long-term reliability data is accumulated.

The oxide material having a bixbite structure represented by the formula (A) in (iii) will be described.
This material has a sesquioxide type terbium oxide structure as a skeleton, and a large amount of terbium ion sites, that is, in the range of 1-x (0.4 ≦ x ≦ 0.7) in the formula (A), scandium, yttrium, The oxide material has a structure in which terbium ions are substituted with at least one element selected from the group consisting of a group of lanthanoid elements other than terbium.

  The terbium ion concentration in the sesquioxide structure is the highest structure among several terbium oxide structures. Therefore, the composition ratio of terbium is high, and the Faraday rotation angle (Verde constant) per unit length is large, which is preferable.

  Even if a part of the terbium ion is replaced with another ion in the range of 1−x (0.4 ≦ x ≦ 0.7) in the formula (A), the Faraday rotation angle per unit length (Verde (Constant) can be maintained high, and the terbium ion-derived absorption density per unit cell can be reduced by substituting partly with other ions that do not have absorption instead of terbium ions that have absorption.

  In the formula (A), the range of x is preferably 0.4 ≦ x ≦ 0.7, more preferably 0.4 ≦ x ≦ 0.6. When x is less than 0.4, the Faraday rotation angle (Verde constant) per unit length becomes small, which is not preferable. Further, when x exceeds 0.7, the amount of terbium-derived absorption increases to a level that cannot be ignored, which is not preferable.

  Various transparent ceramic sintered bodies (terbium-containing composite oxide sintered bodies) that are the subject of the present invention contain the composite oxide represented above as a main component. Here, “containing as a main component” means that 90% by mass or more of any of the above complex oxides is contained. The content of any one of the above complex oxides is preferably 99% by mass or more, more preferably 99.9% by mass or more, still more preferably 99.99% by mass or more, and 99.999. It is particularly preferable that the content is at least mass%.

Further, it is preferable to appropriately add a metal oxide serving as a sintering aid as a subsidiary component. Although depending on the material type, typical sintering aids include SiO ₂ , ZrO ₂ , HfO ₂ , CaO, BaO, LiF, MgO and the like, and besides metal oxides, there are carbon (C) and the like. These are preferably added in the range of 0 to 0.5% by mass. It is preferable to add these sintering aids to the terbium-containing oxide sintered body, which is the main component, because it can promote densification, reduce residual bubbles, and suppress heterogeneous precipitation.

  The transparent ceramic sintered body (terbium-containing composite oxide sintered body) which is the subject of the present invention is composed of the above-mentioned main component and subcomponents, but may further contain other elements. Examples of other elements typically include sodium (Na), phosphorus (P), tungsten (W), tantalum (Ta), molybdenum (Mo), and the like.

  The content of other elements is preferably 10 parts by mass or less, more preferably 0.1 parts by mass or less, and 0.001 parts by mass or less (substantially) when the total amount of Tb is 100 parts by mass. It is particularly preferable that it is zero).

Here, the ceramic powder used in the production of the terbium-containing composite oxide sintered body includes terbium, a metal powder of these element groups including all elements for constituting various composite oxide compositions, or An aqueous solution of nitric acid, sulfuric acid, uric acid or the like, or an oxide powder of the above series of elements can be suitably used.
The purity of the powder is preferably 99.9% by mass or more.

  A predetermined amount of these elements are weighed, mixed, and fired to terbium-containing oxide having a desired configuration, specifically, an aluminum garnet type (above (i)), a gallium garnet type (above (ii) )), A calcined raw material mainly composed of a bixbite type (above (iii)) oxide dissolved in an element other than terbium.

  The firing temperature at this time needs to be finely adjusted depending on the composition and cannot be generally mentioned, but is preferably at least 900 ° C. or higher and lower than the sintering temperature performed thereafter, 1000 ° C. or higher, and A temperature lower than the sintering temperature performed later is more preferable. In addition, depending on the raw material, when heated to a certain temperature or more, adhesion aggregation may deteriorate rapidly. When using such a raw material, it is preferable to carefully adjust the upper limit temperature and to calcinate in a temperature range in which adhesion aggregation does not deteriorate. In addition, it is not necessary to pay much attention to the temperature rise rate and temperature drop rate during firing, but attention should be paid to the holding time. If the firing holding time is unnecessarily extended, adhesion aggregation proceeds gradually. For this reason, the upper limit range of the holding time must be selected with some care.

  Here, “main component” means that the main peak obtained from the powder X-ray diffraction result of the fired raw material is a diffraction peak derived from the crystal system of the desired material. When the presence concentration of the heterogeneous phase is less than 1%, the powder X-ray diffraction pattern is substantially clearly detected only from the main phase, and the heterogeneous pattern is often buried in the background level. .

  Next, the obtained fired raw material is pulverized or classified to obtain a ceramic powder whose particle size distribution is controlled within a predetermined range. The particle size of the ceramic powder is not particularly limited, but it is preferable to select a powder having a facet surface as small as possible on the surface of the primary particles because the sinterability is improved. In addition, when the raw materials purchased are not used as they are, pulverization treatment such as wet ball milling, wet bead milling, wet jet milling, dry jet milling, etc. can be applied to suppress the generation of coarse particles and coarse atmospheric pores. Since a molded object can be produced, it is preferable. Further, it is preferable to select a high-purity starting material powder of 3N or higher as the purity because it can promote densification in the sintering process and prevent various characteristic deterioration due to impurities.

  In addition, it does not specifically limit about the powder shape in that case, For example, square, spherical, and plate-shaped powder can be utilized suitably. Moreover, it can use suitably even if it is the powder which carried out secondary aggregation, and it can use suitably also if it is the granular powder granulated by granulation processes, such as a spray-dry process.

  Furthermore, the process for preparing these ceramic powders is not particularly limited. Ceramic powders produced by a coprecipitation method, a pulverization method, a spray pyrolysis method, a sol-gel method, an alkoxide hydrolysis method, or any other synthesis method can be suitably used. Further, the obtained ceramic powder may be appropriately treated by a wet ball mill, a bead mill, a wet jet mill, a dry jet mill, a hammer mill or the like.

  Furthermore, various dispersants may be added during the wet pulverization treatment in order to prevent excessive aggregation of the primary particles. Further, when the primary particles are amorphous and excessively fluffy, or when using a starting material having a large aspect ratio such as a plate shape or a needle shape, a calcination step is further performed after the pulverization treatment. By adding, the shape of the primary particles may be adjusted.

  In order to produce a ceramic sintered body having a composite composition, a plurality of types of ceramic powders may be mixed and molded. In the present invention, such a mixed ceramic powder may be used. However, for the purpose of mixing well before firing, it is preferable to use a wet slurry dispersed in a solvent, and subject to a blending process such as wet ball mill mixing, wet bead mill mixing, or wet jet mill emulsification. Furthermore, after mixing a plurality of types of starting materials, it may be calcined to change the phase to the target compound.

Further, as another transparent ceramic sintered body, for example, a spinel (MgAl ₂ O ₄ ) sintered body can be mentioned. Specifically, this is a highly transparent spinel sintered body that can be used for ultraviolet window materials, high-strength window materials for visible regions, infrared window materials, etc., and has several sintering aids for the purpose of improving transparency. Agents are often added. However, lithium fluoride, which is most easily improved in sinterability, cannot be used because it absorbs in the ultraviolet region. Instead, magnesium oxide is preferably 0.08% by mass to 1% by mass with respect to MgAl ₂ O ₄ . In this range, it is more preferable to add at about 0.1% by mass. Further, it is preferable that the additive is uniformly and finely dispersed in the base material because densification is promoted.

  Further, for example, a calcium fluoride / lithium fluoride sintered body can be mentioned. Specifically, it is a highly transparent calcium fluoride sintered body that can be used in an optical lens or the like, and preferably 0.08% by mass or more and less than 3% by mass with respect to calcium for the purpose of improving transparency. Is 0.08% by mass or more and 1% by mass or less, and particularly preferably about 0.1% by mass of lithium fluoride is added. However, lithium fluoride needs to be uniformly and finely dispersed in calcium fluoride as a base material. In addition, if 3% by mass or more of lithium fluoride is added, even if a blending process is performed, it is no longer possible to perform homogeneous dispersion mixing.

  Examples of the silicon nitride ceramic sintered body include a silicon nitride powder blended with an oxide auxiliary agent (magnesium oxide powder and yttrium oxide powder). Specifically, it is a silicon nitride ceramic sintered body having a high thermal conductivity that can be used for a heat dissipation substrate, and is preferably 0.01% by mass or more and 1% by mass with respect to silicon for the purpose of improving the thermal conductivity. Less than, more preferably 0.05 mass% or more and 0.8 mass% or less of magnesium oxide powder is added. In addition, for the purpose of improving the insulator pressure and bending strength, preferably 0.01% by mass or more and less than 1% by mass, more preferably 0.05% by mass or more and 0.8% by mass or less of yttrium oxide powder with respect to silicon. Added. These oxide additives are preferably dispersed uniformly and finely in the base material because densification is promoted.

  It is preferable to mix these plural types of ceramic powders and prepare them for the raw material powder slurry. In the present invention, such a mixed ceramic powder may be used. However, for the purpose of mixing well, it is preferable to use a wet slurry dispersed in a solvent for the raw material powder slurry, and to perform a blending process such as wet ball mill mixing, wet bead mill mixing, or wet jet mill emulsification.

The binder added to the raw material powder slurry is a thermoplastic resin having a glass transition temperature higher than room temperature, preferably higher than room temperature by 3 ° C. or more, and the kind thereof is not particularly limited, but generally used polyvinyl alcohol ( Glass transition temperature Tg = 55 to 85 ° C .; depends on saponification degree, polymerization degree), polyvinyl acetate (glass transition temperature Tg = 25-40 ° C .; depends on saponification degree, polymerization degree), polyvinyl alcohol and polyvinyl acetate Polymer (glass transition temperature Tg = 30 to 80 ° C .; depends on saponification degree, polymerization degree), methylcellulose (glass transition temperature Tg = −90 to 120 ° C .; depends on hydration degree and substitution degree. In the present invention, glass higher than room temperature Adjusted to be a transition temperature), ethyl cellulose (glass transition temperature Tg = 70 to 160 ° C., depending on the degree of substitution), polyvinyl Tyral (glass transition temperature Tg = 60-110 ° C .; depending on saponification degree, polymerization degree), vinyl polypropionate (glass transition temperature Tg = 10-45 ° C .; depending on saponification degree, polymerization degree. In the present invention, glass higher than room temperature And a copolymer of polyvinyl alcohol and vinyl polypropionate (glass transition temperature Tg = 15 to 75 ° C .; depending on saponification degree and polymerization degree. In the present invention, a glass transition temperature higher than room temperature) It is preferable to select from the above. All of these are moderately tacky and have a glass transition temperature higher than room temperature (or adjusted to be higher than room temperature, preferably adjusted to be 3 ° C. or higher than room temperature), which will be described later. In the range lower than the boiling point of the pressure medium (water or oil) in WIP molding (or adjusted to be lower than the boiling point, preferably adjusted to be 5 ° C. or more lower than the boiling point), It is easy to handle and preferable. Specifically, the glass transition temperature Tg of the thermoplastic resin is preferably 35 to 100 ° C, more preferably 40 to 90 ° C, and still more preferably 45 to 85 ° C.
The glass transition temperature Tg is usually a midpoint glass transition temperature value when a thermoplastic resin is measured by differential scanning calorimetry (DSC). For example, the glass transition temperature Tg is a midpoint glass transition temperature calculated by a method according to JIS K7121: 1987 by measuring a change in calorie under conditions of a heating rate of 10 ° C./min and a measurement temperature of −50 to 250 ° C. . In the case where moisture in the sample affects the glass transition temperature Tg, the measurement may be performed after the sample is heated to 150 ° C. and dried.

  For the addition of the thermoplastic resin, the concentration (mass%) of a solvent (for example, an ethanol solvent) dissolved in advance to an appropriate concentration (mass%) (thermoplastic resin solution) or separated without melting is used. A thermoplastic resin powder prepared so as to have an appropriate numerical value dispersed in a solvent such as ethanol (thermoplastic resin dispersion) may be used, and its concentration is, for example, 5% by mass to 40% by mass. Is preferred.

  Since the addition amount of the thermoplastic resin varies depending on the composition of the objective ceramic sintered body and its final use, it is necessary to determine the optimum ratio in a preliminary experiment. In the present invention, the powder obtained by spray-drying the raw material powder slurry is uniaxially press-molded using a raw material powder slurry obtained by adding the ceramic powder and thermoplastic resin as raw material powder components to a solvent. It is preferable to increase the shape retention during casting by increasing the amount of thermoplastic resin added compared to the case of performing direct CIP molding. For example, when an amount of 2% to 40% by mass, preferably 3.5% to 20% by mass, is added to the total mass of the ceramic powder and the thermoplastic resin when preparing the raw material powder slurry, A compact and a sintered body can be obtained.

  That is, as a raw material powder component contained in the raw material powder slurry, the ceramic powder is contained in an amount of 60% by mass to 98% by mass and the thermoplastic resin (binder) is contained in an amount of 2% by mass to 40% by mass, preferably the ceramic powder. 80 mass% or more and 96.5 mass% or less and the said thermoplastic resin (binder) is 3.5 mass% or more and 20 mass% or less. At this time, the total of the ceramic powder and the thermoplastic resin is 100% by mass.

  In the present invention, the ceramic powder is dispersed in a solvent to form a wet slurry, and the thermoplastic resin is further added to form a raw material powder slurry.

The selection of the solvent for slurrying the ceramic powder is not particularly limited in the present invention. However, in general, one or a mixture of two or more selected from water, ethanol and an organic solvent (alcohol other than ethanol, acetone, etc.) is preferably selected, and among these, ethanol is preferable. In addition, when selecting water as a solvent, it is preferable to mix and add a dispersing agent, an antifoamer, etc. together. In this case, it is necessary to search for an optimum range for each addition amount in a preliminary experiment.
Moreover, although the solvent in which the thermoplastic resin added as a binder melt | dissolves can be used, it is more preferable to select the solvent in which a thermoplastic resin melt | dissolves.

  In preparing the raw material powder slurry, after adding the thermoplastic resin solution or thermoplastic resin dispersion to the wet slurry in which the ceramic powder is dispersed in the solvent, the mixture is further stirred by ball mill mixing, bead mill mixing, wet jet mill mixing, etc. It is preferable to do. However, when the calcination treatment is performed for the purpose of changing the shape, crystallinity, and average primary particle diameter of the ceramic powder, the ceramic powder is used after the calcination treatment in order to prevent thermal decomposition, thermal denaturation, and heat volatilization. Must be dispersed in a solvent to obtain a wet slurry, and a thermoplastic resin solution or a thermoplastic resin dispersion must be added.

  In addition, in the raw material powder slurry used in the present invention, various organic additives (excluding the thermoplastic resin as the binder) are added for the purpose of quality stability and yield improvement in the subsequent ceramic manufacturing process. Also good. In the present invention, these are not particularly limited. That is, various dispersants, lubricants, plasticizers and the like can be suitably used. However, it is preferable to select a high-purity type that does not contain unnecessary metal ions as these organic additives. Furthermore, since certain dispersants have the effect of lowering the glass transition temperature of the thermoplastic resin, attention must be paid to the amount of the dispersant added.

(Molding process)
Then, the shaping | molding procedure of the ceramic molded object for sintering in this invention is demonstrated.
(Casting)
First, a raw material powder slurry prepared as described above is used to obtain a cast molded body obtained by wet casting the raw material powder components into a predetermined shape.

  Here, the cast molding is formed by solid-liquid separation and molding a slurry (raw material powder slurry) obtained by adding the ceramic powder and the thermoplastic resin as a raw material powder component to a solvent. preferable. More specifically, the aggregated precipitate obtained by settling the raw material powder slurry is filled in a centrifuge tube container, and this is subjected to a centrifugal separation process (centrifugal casting), and the solid content of a predetermined shape is obtained by the above casting molding. More preferably, it is obtained as a body.

  The centrifugal casting machine used for such centrifugal casting is the same structure as the centrifugal separator, and is filled with raw material powder slurry in a container to be a mold, and the container is rotated at high speed by the centrifugal force. The raw material powder slurry is formed by solid-liquid separation. At this time, the centrifugal force of the centrifugal separation treatment is preferably 1000 G or more, and more preferably 2000 G or more. Further, the centrifugation time is preferably 20 to 240 minutes, more preferably 30 to 180 minutes.

  Next, the obtained cast molded body is preferably dried at room temperature to 110 ° C. for 1 to 4 days, more preferably 40 to 75 ° C. for 2 to 4 days to obtain a cast dry molded body made of raw material powder components.

  The shape of the cast dry molded body corresponds to the target sintered body shape, and is, for example, a cylindrical shape having a diameter of 10 to 60 mm and a length of 5 to 40 mm. Or it is the cube shape of width 10-85mm, thickness 2-30mm, and length 10-130mm.

(First stage hydrostatic pressure molding)
Next, a glass transition temperature of the thermoplastic resin contained in the raw material powder component in a state where the cast dry molded body obtained as described above is directly inserted into a rubber mold or vacuum-packed with a waterproof film and sealed. The first stage hydrostatic pressure molding is performed at a lower temperature to produce a first stage pressure molded body.

  Here, it is preferable that the first hydrostatic pressure molding is cold isostatic pressing (CIP) molding. That is, it is preferable to perform the first-stage hydrostatic pressure molding by mounting the cast dry molded body directly inserted in a rubber mold or vacuum-packed with a waterproof film and mounting it on a CIP device. The pressure medium in this case is water or oil.

The applied pressure and pressurization holding time at this time vary depending on the ceramic composition selected and the intended use of the final product, and therefore need to be adjusted as appropriate. However, unless the applied pressure is generally increased to 40 MPa or more, the density of the molded body does not increase, and it is difficult to obtain a high-quality sintered body. Although there is no restriction | limiting in particular about the upper limit of an applied pressure, If too much pressure is applied, since a lamination crack will generate | occur | produce, it is not preferable. In most ceramic materials, an applied pressure of 400 MPa or less is often sufficient.
Further, the pressure holding time is preferably, for example, 1 to 10 minutes, and more preferably 1 to 3 minutes.

  Further, the temperature of the molded body at the time of pressing is maintained at a temperature lower than the glass transition temperature of the thermoplastic resin contained in the raw material powder component, for example, 10 times higher than the glass transition temperature of the thermoplastic resin contained in the raw material powder component. It is preferable to be maintained at a temperature lower by at least ° C., and it is particularly preferable that the molded body is maintained at room temperature without heating.

  In this CIP treatment, since the temperature is kept below the glass transition temperature of the thermoplastic resin contained in the raw material powder component at the time of pressing, the thermoplastic resin in the raw material powder previously has gaps between the ceramic powders (primary particles). Hardly solidified in a well-filled state, when the raw material powder is pressed, the pressure applied to the surface of the compact is sequentially transmitted between the adjacent hard thermoplastic resin and hard ceramic powder (primary particles). As a result, pressure is firmly applied to the inside of the molded body, which is preferable.

(Second stage hydrostatic pressure molding)
Next, the obtained first-stage press-molded body is heated to a temperature equal to or higher than the glass transition temperature of the thermoplastic resin and subjected to warm isostatic pressurization (WIP) molding as second-stage hydrostatic pressure press-molding. A molded body is produced.

The second-stage hydrostatic pressure molding is preferably performed according to the following procedure.
(S1) First, in a WIP apparatus used for WIP molding, the temperature of the pressure vessel portion for WIP molding and the pressure medium is preheated so as to be equal to or higher than the glass transition temperature of the thermoplastic resin contained in the raw material powder component, and stable. Let me.
(S2) In the heated WIP apparatus, the first-stage pressure molded body is filled in a rubber mold, or the first-stage pressure molded body is vacuum-packed with a waterproof film and sealed. Load it.
(S3) While maintaining the state in which the first-stage pressure molded body is filled, the first-stage pressure molded body is held and heated to the same temperature as the WIP device that heats the first-stage pressure molded body. Then, WIP molding is performed as the second hydrostatic pressure molding.

  In S3, after filling the first-stage pressure molded body, WIP molding is performed as the second-stage hydrostatic pressure molding while heating the first-stage pressure molded body to the same temperature as the WIP device. You may make it do.

  Here, the temperature of the pressure vessel part for WIP molding and the pressure medium, that is, the temperature at which the first-stage pressure molded body is heated is equal to or higher than the glass transition temperature of the thermoplastic resin contained in the raw material powder component. It is preferably 5 ° C. or more higher than the glass transition temperature of the plastic resin. In addition, when the glass transition temperature of the said thermoplastic resin is 50 degrees C or less, it is preferable to make the temperature which heats a 1st step | paragraph press-molded body 10 degreeC or more higher than the glass transition temperature. Moreover, it is preferable that the upper limit of the temperature which heats a 1st step | paragraph press-molded body is 130 degrees C or less.

  The pressure medium used is preferably water or oil, more preferably water or oil having a boiling point of more than 100 ° C. At this time, although it varies depending on the type of the thermoplastic resin selected, if the glass transition temperature of the thermoplastic resin is 91 ° C. or higher, use of water as the pressurizing medium may cause bumping and is dangerous. Therefore, it is preferable to select oil having a boiling point of more than 100 ° C. as the pressure medium. In addition, since there are various types of oil, it is preferable to select an oil that does not have a risk of bumping even when heated to a target temperature.

  The applied pressure and pressurization holding time in WIP molding vary depending on the selected ceramic composition, the type of thermoplastic resin, the addition ratio, and the intended use of the final product, and therefore need to be adjusted as appropriate. However, unless the applied pressure is generally increased to 40 MPa or more, it is difficult for the thermoplastic resin heated above the glass transition temperature to cause plastic flow through the gaps in the packed ceramic molded body. The raw material rearrangement inside the molded body, which is in a state where the internal stress is accumulated by being pressurized in the CIP process, does not occur, and it is difficult to reduce the residual stress and block the coarse cavity to make it denser. The upper limit is not particularly limited, but it is generally known that the maximum ultimate pressure of the WIP device is lower than that of the CIP device. This is a limitation in manufacturing the device for safely operating the device, including thermal expansion of the entire device due to heating. Specifically, the maximum applied pressure of a general WIP device is about 200 MPa, but in the present invention, if such an applied pressure is applied, the effect can be sufficiently exhibited.

  Further, the pressure holding time is preferably, for example, 1 to 10 minutes, and more preferably 1 to 3 minutes.

Instead of the first-stage hydrostatic pressure molding and the second-stage hydrostatic pressure molding described above, the following may be performed.
(First stage hydrostatic pressure molding)
A product obtained by inserting the cast dry molded body into a rubber mold or vacuum-packed and sealed with a waterproof film is mounted on a WIP device and molded under the conditions of the first hydrostatic pressure molding (first Production of a step-pressure molded body).
(Second stage hydrostatic pressure molding)
After producing the first-stage pressure-molded body, the first-stage hydrostatic pressure is maintained (that is, the first-stage pressure-molded body is attached to the WIP apparatus and pressurized), Heating of the first-stage pressure molded body is started, and then WIP molding is performed under the conditions of the second-stage hydrostatic pressure molding.

In the present invention, the first stage pressure molding (hydrostatic pressure molding at a temperature lower than the glass transition temperature of the thermoplastic resin, preferably CIP molding) and the second stage hydrostatic pressure molding (WIP molding). ) It is essential to carry out both steps in this order.
For example, when looking at the distribution of ceramic powder and binder (thermoplastic resin) in the cast and dried cast body after drying, the ceramic powder and binder (thermoplastic resin) are relatively uniformly dispersed. Alternatively, the binder (thermoplastic resin) is present so as to fill the gaps between the ceramic powders, but the density of the compact is relatively low.
Next, in the first stage pressure molding (hydrostatic pressure molding at a temperature lower than the glass transition temperature of the thermoplastic resin, preferably CIP molding) in the first half, an applied pressure is applied to the cast dry molded body. It has a function to transmit even to the inside of a thick molded body. At this time, the binder (thermoplasticity) is formed so that the ceramic powder and the binder (thermoplastic resin) in the cast dry molded body are relatively uniformly dispersed in the first-stage pressure molded body, or the gap between the ceramic powders is filled. While the state where the resin is present is maintained, the density of the first-stage pressure-formed body becomes somewhat higher than the density of the cast dry-formed body.
Next, in the second half hydrostatic pressure molding (WIP molding) process in the latter half, the negative effect generated in the first stage pressure molding process, that is, the internal stress of the molded body with respect to the first stage pressure molded body. It is responsible for removing strain and the occurrence of partial coarse voids by plastic flow and rearrangement. At this time, in the ceramic molded body, the ceramic powder and the binder (thermoplastic resin) in the first-stage pressure molded body are relatively uniformly dispersed, or the binder (thermoplastic The density of the ceramic molded body is still higher than the density of the first-stage pressure molded body while the state where the resin is present is maintained.
As long as a series of actions of the first and second hydrostatic pressure moldings are working correctly, the range of conditions set in the two hydrostatic pressure molding processes is arbitrary.

However, it is necessary to confirm and verify that this series of actions is working correctly. This confirmation and verification is preferably performed by the following method.
That is, as a first confirmation method, a series of actions of the first and second stage hydrostatic pressure molding after the first stage pressure molding process and the second stage pressure molding process worked correctly. Since the density d _{CIP + WIP} of the molded body (ceramic molded body) is always larger than the molded body density d _CIP immediately after the first-stage pressure molding step, the molded body density d _{CIP + WIP} > the molded body. It is to confirm that the density is d _CIP .
Further, as a second confirmation method, for comparison, a sample in which only the second-stage pressure molding (WIP molding) is performed on the cast dry molded body without performing the first-stage pressure molding is tried. density d _WIP of the molded bodies where only WIP molding Toko is, since lower than the green density d _{CIP + WIP,} confirming that compact density d _{CIP + WIP>} a compact density d _WIP It is. In addition, in the molded body in which only the second-stage pressure molding (WIP molding) is performed without performing the first-stage pressure molding as described above, coarse voids are formed therein.

  As described above, when a ceramic molded body, particularly a thick ceramic molded body, is press-molded by the method for producing a sintered ceramic molded body of the present invention, pressure transmission to the inside of the molded body and plasticity of the thermoplastic resin are achieved. It is possible to obtain a dense ceramic molded body that can effectively balance the flow, has a very small residual void, and eliminates residual stress.

[Method of manufacturing sintered ceramics (densification of ceramics)]
The method for producing a ceramic sintered body according to the present invention includes a sintering treatment using the ceramic molded body produced by the method for producing a sintered ceramic molded body according to the present invention, and hot isostatic pressing (HIP). ) To further densify and obtain a ceramic sintered body.
At this time, it is preferable to degrease the ceramic molded body before the sintering treatment. Further, it is preferable to perform an annealing process after the HIP process.
Specifically, the following processing is performed.

(Degreasing)
In the production method of the present invention, a normal degreasing step can be suitably used. That is, it is possible to go through a temperature rising degreasing process using a general heating furnace. Also, the kind of the atmospheric gas at this time is not particularly limited, and air, oxygen, oxygen-containing mixed gas, hydrogen, fluorine, hydrofluoric acid gas, nitrogen, ammonia gas, and the like can be suitably used. The degreasing temperature is not particularly limited, but when added thermoplastic resin, dispersant and other organic substances are added, the temperature is raised to and maintained at a temperature at which all these organic components can be completely decomposed and eliminated. It is preferable.

(Sintering)
In the production method of the present invention, a general sintering process can be suitably used. That is, a heating and sintering process such as a resistance heating method or an induction heating method can be suitably used. The atmosphere at this time is not particularly limited, and various atmospheres such as inert gas, oxygen gas, hydrogen gas, fluorine gas, hydrofluoric acid gas, argon gas, nitrogen gas, ammonia gas, or also under reduced pressure (in vacuum) Sintering is also possible. However, since the compatible gas differs depending on the type of ceramic material to be handled, it is preferable to correspond correctly. For example, in the case of oxide ceramics, it is preferable to select from an oxygen-based gas group or a reduced-pressure atmosphere, and in the case of fluoride ceramics, fluorine, hydrofluoric acid-based gas groups, or an inert gas such as argon or nitrogen, or a reduced-pressure atmosphere. In the case of nitride ceramics, it is preferable to select from a nitrogen or ammonia gas group or a reduced pressure atmosphere. In addition, it goes without saying that furnace material selection and airtightness management will be thorough according to the type of gas used.

  The sintering temperature in the sintering step of the present invention needs to be appropriately adjusted depending on the composition and crystal system selected. In general, it is preferable to perform the sintering treatment in a temperature range that is several tens or hundreds of degrees lower than the melting point of the ceramic material having the final composition. In many cases, a sintering holding time of several hours is sufficient in the sintering step. However, if the porous sintered body is not intentionally produced, the relative density of the sintered body needs to be densified to 95% or more. Further, it is more preferable to keep the sintering treatment for 10 hours or longer to densify the relative density of the sintered body to 99% or more because the final transparency of the transparent ceramic sintered body is improved.

  In addition, selection of the temperature increase rate in a sintering process becomes quite important. Although it is preferable to select a temperature increase rate as small as possible, there are limitations due to productivity and cost constraints. Therefore, it is preferable that at least 100 ° C./hr can be secured. It is preferable to make the temperature increase rate small because it can promote densification, improve transparency, and suppress segregation and cracks.

(Hot isostatic pressing (HIP))
In the production method of the present invention, an additional hot isostatic pressing (HIP (Hot Isostatic Pressing)) is performed after the sintering process.

Incidentally, the pressurized gas medium type in this case, argon, an inert gas such as nitrogen or Ar-O ₂ can be used suitably. The pressure applied by the pressurized gas medium is preferably 50 to 300 MPa, and more preferably 100 to 300 MPa. If the pressure is less than 50 MPa, the densification improvement effect may not be obtained. If the pressure exceeds 300 MPa, further densification improvement cannot be obtained even if the pressure is increased, and there is a risk that the load on the device becomes excessive and the device is damaged. . The applied pressure is preferably 196 MPa or less, which can be processed with a commercially available HIP device, for convenience and convenience.

  In addition, when the sintered compact selected is a fluoride, it is preferable to perform what is called a capsule HIP process in which a HIP process is performed after sealing with a soft steel capsule or the like.

  The temperature (predetermined holding temperature) during the HIP process is set in the range of 1000 to 1800 ° C, preferably 1100 to 1700 ° C. If the heat treatment temperature is higher than 1800 ° C., there is an increase in risk that the medium gas enters the sintered body and the sintered body and the HIP furnace are melted and fixed. Further, when the heat treatment temperature is less than 1000 ° C., the effect of improving the densification of the sintered body is hardly obtained. In addition, the holding time of the heat treatment temperature is not particularly limited, but if the holding time is too long, defects inside the sintered body are gradually accumulated, which is not preferable. Typically, it is suitably set in the range of 1 to 3 hours.

  The heater material, the heat insulating material, and the processing container for HIP processing are not particularly limited, but graphite, or molybdenum (Mo), tungsten (W), and platinum (Pt) can be suitably used. Gadolinium, silicon carbide, and tantalum carbide can also be suitably used. In the case of a sintered body group having a relatively low temperature condition of HIP processing temperature of 1500 ° C. or less, platinum (Pt) can be used as a heater material, a heat insulating material, and a processing container, so that the selection of the atmosphere to be selected is free. It is preferable because the degree of point defects in the sintered body obtained can be reduced and the point defect concentration can be reduced. Further, when the treatment temperature is 1500 ° C. or higher, graphite is preferable as the heater material and the heat insulating material.

(Annealing)
In the production method of the present invention, when producing a transparent ceramic sintered body, after completion of the HIP treatment, point defects are generated in the obtained transparent ceramic sintered body, and a light gray or black gray appearance is exhibited. There is a case. In such a case, at a temperature below the HIP treatment temperature, typically 1000 to 1500 ° C., an oxide is an oxygen atmosphere, a fluoride is a fluorine or hydrofluoric acid atmosphere, and a nitride is used. If present, it is preferable to perform an annealing process (defect recovery process) in a nitrogen or ammonia atmosphere. The holding time in this case is preferably 3 hours or more because it is necessary to secure a sufficient time for the point defect to recover. In addition, if the set temperature of the annealing process is excessively increased to over 1500 ° C., or if the holding time is extended to a length of several tens of hours, bubbles are regenerated in the transparent ceramic material, which is called a rebound phenomenon. Since it occurs, it is not preferable.

(Optical evaluation)
In the production method of the present invention, when producing a transparent ceramic sintered body, it is possible to optically polish one surface, which is the minimum, for the purpose of evaluating the optical quality of the sintered body that has undergone the above series of production steps. preferable. The optical surface accuracy at this time is not particularly limited. However, if the optical surface warp is too severe, correct optical evaluation becomes difficult. For example, when the measurement wavelength is λ = 633 nm, λ or less is preferable, λ / 2 or less is more preferable, and λ / 4 or less is particularly preferable. Note that it is possible to further reduce the optical loss by appropriately forming an antireflection film on the optically polished surface.

  As described above, by observing the inside through the optically polished surface with a microscope, it is possible to observe and evaluate residual bubbles, coarse cavities, and the presence or absence of residual strain through a crossed Nicol image.

  As described above, according to the method for producing a ceramic sintered body of the present invention, a truly high-density ceramic sintered body with extremely few remaining bubbles can be produced. As a result, mechanical strength, thermal conductivity, light A high-quality ceramic sintered body with improved characteristics, such as permeability, electrical characteristics, and long-term reliability can be obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the examples.

[Example 1]
Terbium oxide powder, scandium oxide powder manufactured by Shin-Etsu Chemical Co., Ltd., and aluminum oxide powder manufactured by Daimei Chemical Co., Ltd. were obtained. Furthermore, a liquid of tetraethyl orthosilicate (TEOS) manufactured by Kishida Chemical Co., Ltd. was obtained. The purity was 99.9% by mass or more for the powder material and 99.999% by mass for the liquid material.
A garnet type oxide raw material (mixed raw material No. 1) having the final composition shown in Table 1 was prepared by adjusting the mixing ratio using the above raw materials.
That is, a mixed powder weighed so that the number of moles of terbium, aluminum, and scandium each had a molar ratio of the composition shown in Table 1 was prepared. Subsequently, TEOS was weighed and added to the raw material so that the amount added was in mass% (0.01 mass%) in Table 1 in terms of SiO ₂ . Thereafter, dispersion and mixing were performed in an ethanol ball mill apparatus in ethanol. The processing time was 15 hours.
In addition, the above mixed raw material No. 1 is further spray-dried to produce a granular raw material having an average particle diameter of 20 μm. The granular raw material is placed in an yttria crucible and fired at 1200 ° C. in a high-temperature muffle furnace for 3 hours, When the obtained fired raw material was analyzed by a diffraction X-ray diffractometer manufactured by Panalical (XRD analysis), it was found that the fired raw material was a garnet single phase (cubic crystal) from comparison of the reference data and measurement pattern of the X-ray diffraction pattern. ) Only confirmed.

The mixed raw material No. 1 was again dispersed and mixed in ethanol in a nylon ball mill. The processing time was 20 hours. The wet slurry thus obtained was divided into two groups. On one side, 20 mass of a polyvinyl alcohol-polyvinyl acetate copolymer (glass transition temperature 48 ° C.) made by Nippon Vinegar Bipovar Co., Ltd. as a binder in ethanol. % Of the thermoplastic resin solution dissolved so as to be 4% by mass of the copolymer of polyvinyl alcohol and polyvinyl acetate with respect to the mass of the entire raw material powder (mixed raw material No. 1 + binder). After that, the binder added slurry (raw material powder slurry (1)) was stirred and mixed for 3 hours. On the other side, the same thermoplastic resin solution was weighed and added so that the copolymer of polyvinyl alcohol and polyvinyl acetate was 1% by mass with respect to the mass of the entire raw material powder (mixed raw material No. 1 + binder), and then The binder added slurry (raw material powder slurry (2)) was stirred and mixed for 3 hours. In the raw material powder slurries (1) and (2), both binders were dissolved in the slurry.
The raw material powder slurries (1) and (2) divided into these two groups were allowed to stand for 24 hours to be settled and precipitated to form an aggregated precipitate. Each supernatant was removed, the remaining aggregated sediment was filled into a round bottom centrifuge tube with a diameter of 10 mmφ, and set in a centrifuge. These round bottom centrifuge tubes were rotated at a maximum centrifugal force of 3000 G for 1 hour (60 minutes). The aggregated sediment filled in the round bottom centrifuge tube was centrifuged. After completion of the centrifugation, the supernatant was removed again, and the solid molded body (centrifugal cast body) was recovered. The collected solid molded body was oven-dried at 60 ° C. for 48 hours to obtain a cast dry molded body.

The obtained cast dry molded bodies were further divided into five groups (Example 1-1, Comparative Examples 1-1 to 1-4) as shown in Table 2. And the ceramic molded object sample was produced in the molding process (three levels of casting drying-CIP processing-WIP processing, casting drying-CIP processing, casting drying-WIP processing) under the conditions shown in Table 2 A press process is performed, and a minus sign indicates that the press process is not performed (hereinafter the same).
In addition, the room temperature in this shaping | molding process was 20 degreeC. The CIP conditions were: pressurizing medium: water, pressurizing medium temperature: 20 ° C., applied pressure of 196 MPa, pressurizing time: 2 minutes. The WIP conditions were as follows: pressurized medium: water, pressurized medium temperature: 60 ° C., CIP compact heating temperature: 60 ° C., applied pressure of 196 MPa, pressurized time: 2 minutes.

About the obtained ceramic molded object sample, the weight w (g) of each sample is measured, diameter r (mm) and length L (mm) are also measured, and each molded object density is expressed by the following formula. It was obtained by calculation.
Molded body density (g / cm ³ ) = (4000 w) / (πr ² L)
Moreover, the external appearance of the ceramic molded body sample was visually observed.

Next, each ceramic compact was degreased in a muffle furnace at 1000 ° C. for 2 hours. Subsequently, the degreased ceramic formed body was charged into an oxygen atmosphere furnace, and sintered at 1730 ° C. for 3 hours to obtain a sintered body. Further, each of these sintered bodies was charged into a carbon heater HIP furnace and subjected to HIP treatment in an Ar atmosphere under a pressure of 200 MPa, a heating temperature of 1600 ° C., and a holding time of 2 hours. Subsequently, each of the obtained HIP-treated sintered bodies was charged into an oxygen atmosphere furnace, and an annealing treatment was performed at a heating temperature of 1350 ° C. for a holding time of 4 hours to obtain a ceramic sintered body in which oxygen deficiency was recovered.
Each ceramic sintered body thus obtained was ground and polished so as to have a diameter of 5 mm and a length of 15 mm, and the optical end faces of each ceramic sintered body were subjected to optical surface accuracy λ / 2 (measurement wavelength λ = The sample for evaluation was obtained by final optical polishing in the case of 633 nm.

Next, the total light transmittance and the forward scattering rate of each sample were measured as follows. Here, the n number of samples was 3 each, and the average value of the measurement results was the measured value of each sample (hereinafter the same).
(Measurement method of total light transmittance and forward scattering rate)
The total light transmittance at a wavelength of 1064 nm was measured using a spectrophotometer V-670 manufactured by JASCO Corporation. As a measuring method, firstly, the spectrophotometer V-670 was irradiated with light (wavelength 1064 nm light (hereinafter the same)) dispersed with a spectroscope without setting an evaluation sample, and the light was previously set in the apparatus. Received by the integrating sphere, and the collected light is received by the detector. The obtained illuminance is set to I _0, and then an evaluation sample is set in the apparatus. This time, the dispersed light is incident on the evaluation sample, and the transmitted light is collected again by the integrating sphere and received by the detector. To do. The total light transmittance was calculated | required by Formula (1) by using the obtained illumination intensity as I.
Further, the forward scattering rate was continuously measured. In other words, the integration sphere setup is switched to a mode that removes the linearly transmitted light, and the light that is split again with the evaluation sample set is incident on the evaluation sample, and the linearly transmitted light out of the transmitted light is transmitted. Light other than light was collected by an integrating sphere and received by a detector. Using the obtained illuminance as Is, the forward scattering rate was determined by equation (2).
Total light transmittance (% / 15 mm) = I / I ₀ × 100 (1)
Forward scattering rate (% / 15 mm) = Is / I ₀ × 100 (2)
The above results are summarized in Table 2.

  From the above results, Example 1-1 in which the molding step of casting drying-CIP treatment-WIP treatment was performed using the raw material powder slurry to which 4% by mass of a binder (thermoplastic resin) was added had the highest density of the compact. The total light transmittance after sintering was maximized, and the forward scattering rate was minimized. Similarly, even in the case of the raw material powder slurry to which the binder has been added, in Comparative Examples 1-1 and 1-2 in which the molding steps of casting drying-CIP processing and casting drying-WIP processing were performed, it is difficult to increase the density of the molded body. The transmittance was also slightly lower than in Example 1-1, and the forward scattering rate was also deteriorated. In addition, from comparison between Comparative Example 1-1 and Comparative Example 1-2, the molding density of the casting drying-WIP process is higher than the molding condition of the casting drying-CIP process. As a result, it was confirmed that the total light transmittance and forward scattering were inferior. In addition, in the raw material powder slurry (Comparative Examples 1-3 and 1-4) with a binder addition amount of 1% by mass, a certain amount of molding is performed under any molding conditions of casting drying-CIP processing, casting drying-CIP processing-WIP processing. Although the body density was shown, some cracks occurred in the ceramic molded body, and the total light transmittance and the forward scattering rate were not so good. This is presumably because most of the added binder was discharged out of the system during casting and drying, and the net amount of binder remaining in the molded body greatly exceeded 1% by mass.

[Example 2]
Spinel (MgAl ₂ O ₄ ) powder manufactured by Daimei Chemical Industry Co., Ltd. was obtained. The purity was 99.99% by mass or more (denoted as 4N—MgAl ₂ O ₄ ). Furthermore, magnesium oxide powder made by Ube Materials Co., Ltd. was also obtained. The purity was 99.99% by mass or more.
Using the above raw materials, magnesium oxide powder was weighed and mixed so as to be 0.1% by mass in terms of MgO with respect to 4N-MgAl ₂ O ₄ to prepare a starting raw material, and then an alumina ball mill in ethanol Dispersion / mixing processing was performed in the apparatus. The processing time was 15 hours. Thereafter, spray drying treatment was further performed to prepare a granular raw material having an average particle diameter of 20 μm.
The granular raw material was placed in an alumina crucible and fired in a muffle furnace at 650 ° C. for a holding time of 3 hours to obtain a fired raw material (firing raw material No. 1). When the obtained fired raw material was subjected to a diffraction pattern analysis with a powder X-ray diffractometer manufactured by Panalical (XRD analysis), it was found that the sample consisted of only a spinel single phase based on a comparison between the reference data of the X-ray diffraction pattern and the measurement pattern It was confirmed.

  The fired raw material was again dispersed and mixed in ethanol using an alumina ball mill. The processing time was 20 hours. The wet slurry thus obtained was divided into two groups, and on one side, polyvinyl alcohol (glass transition temperature 60 ° C.) manufactured by Nippon Vinegar Bipoval Co., Ltd. as a binder was dissolved in ethanol so as to be 20% by mass. The thermoplastic resin solution was weighed and added so that the polyvinyl alcohol was 4% by mass with respect to the mass of the entire raw material powder (calcined raw material No. 1 + binder), and then the binder added slurry (raw material powder slurry (1)) for 3 hours. ) Was mixed with stirring. On the other hand, the same thermoplastic resin solution was weighed and added so that the polyvinyl alcohol would be 1% by mass with respect to the mass of the whole raw material powder (firing raw material No. 1 + binder), and then the binder added slurry (raw material powder) Slurry (2)) was mixed with stirring. In the raw material powder slurries (1) and (2), both binders were dissolved in the slurry.

  The raw material powder slurries (1) and (2) divided into these two groups were allowed to stand for 24 hours to be settled and precipitated to form an aggregated precipitate. Each supernatant was removed, and the remaining aggregated precipitate was filled into a round bottom centrifuge tube having a diameter of 10 mmφ and set in a centrifuge. These round bottom centrifuge tubes were rotated at a maximum centrifugal force of 2000 G for 3 hours (180 minutes). The aggregated sediment filled in the round bottom centrifuge tube was centrifuged. After completion of the centrifugation, the supernatant was removed again, and the solid molded body (centrifugal cast body) was recovered. The collected solid molded body was oven-dried at 60 ° C. for 48 hours to obtain a cast dry molded body.

The obtained cast dry molded bodies were further divided into five groups (Example 2-1 and Comparative Examples 2-1 to 2-4) as shown in Table 3. And the ceramic molded object sample was produced in the shaping | molding process (3 levels of casting dry-CIP process-WIP process, casting dry-CIP process, casting dry-WIP process) of the conditions shown in Table 3.
In addition, the room temperature in this shaping | molding process was 20 degreeC. CIP conditions were as follows: pressurized medium: water, pressurized medium temperature: 20 ° C., applied pressure of 196 MPa, pressurized time: 2 minutes. The WIP conditions were as follows: pressurized medium: water, pressurized medium temperature: 70 ° C., CIP compact heating temperature: 70 ° C., applied pressure of 196 MPa, pressurized time: 2 minutes.

About the obtained ceramic molded object sample, the weight w (g) of each sample is measured, diameter r (mm) and length L (mm) are also measured, and each molded object density is expressed by the following formula. It was obtained by calculation.
Molded body density (g / cm ³ ) = (4000 w) / (πr ² L)
Moreover, the external appearance of the ceramic molded body sample was visually observed.

Next, each ceramic compact was degreased in a muffle furnace at 800 ° C. for 3 hours. Subsequently, the degreased ceramic molded body was charged into an oxygen atmosphere furnace, and sintered at 1450 ° C. for 3 hours to obtain a sintered body. Further, each of these sintered bodies was charged into a carbon heater HIP furnace and subjected to HIP treatment in an Ar atmosphere under a pressure of 200 MPa, a heating temperature of 1550 ° C., and a holding time of 2 hours. Subsequently, each of the obtained HIP-treated sintered bodies was charged into an oxygen atmosphere furnace, and annealed at a heating temperature of 1100 ° C. for a holding time of 4 hours to recover oxygen deficiency (spinel sintering) Body).
Each ceramic sintered body thus obtained was ground and polished so as to have a diameter of 5 mm and a length of 15 mm, and the optical end faces of each ceramic sintered body were subjected to optical surface accuracy λ / 2 (measurement wavelength λ = The sample for evaluation was obtained by final optical polishing in the case of 633 nm.
With respect to each sample thus obtained, the total light transmittance and the forward scattering rate were measured under the same measurement conditions as in Example 1. The results obtained are summarized in Table 3.

  From the above results, Example 2-1 in which the molding step of casting drying-CIP treatment-WIP treatment was performed using the raw material powder slurry to which 4% by mass of a binder (thermoplastic resin) was added had the highest density of the compact. The total light transmittance after sintering was maximized, and the forward scattering rate was minimized. Similarly, even in the raw material powder slurry to which the binder is added, in Comparative Examples 2-1 and 2-2 in which the molding process of casting drying-CIP processing and casting drying-WIP processing is performed, the density of the molded body is difficult to increase, The transmittance was also slightly lower than in Example 2-1, and the forward scattering rate was also deteriorated. From comparison between Comparative Example 2-1 and Comparative Example 2-2, the molding density of the casting drying-WIP process is higher than the molding condition of the casting drying-CIP process. As a result, it was confirmed that the total light transmittance and forward scattering were inferior. Moreover, in the raw material powder slurry (Comparative Examples 2-3 and 2-4) having a binder addition amount of 1% by mass, a ceramic molded body under any molding conditions of casting drying-CIP processing and casting drying-CIP processing-WIP processing. Cracks occurred in the film, and total light transmittance and forward scattering rate could not be measured. That is, it is considered that when the added amount of the binder is 1% by mass, the shape retention of the ceramic molded body is insufficient as discussed in Example 1.

  As described above, in forming the ceramic powder as shown in this example, a raw material powder slurry is prepared by adding 2% by mass to 40% by mass of a thermoplastic resin in advance as a raw material powder component, and using the raw material powder slurry. After wet casting to produce a cast molded body and drying, the cast dry molded body is subjected to cold isostatic pressing (CIP) molding at room temperature below the glass transition temperature of the thermoplastic resin, and thereafter The CIP compact is warm and isostatically pressed (WIP) while being heated above the glass transition temperature of the thermoplastic resin, so that the residual voids are extremely small and the residual stress is eliminated. A good ceramic molded body can be produced. Moreover, by carrying out a sintering treatment using this ceramic molded body, a truly high-density ceramic sintered body with extremely few remaining bubbles can be produced. As a result, it is possible to provide a high-quality ceramic sintered body having improved light transmittance, mechanical strength, and thermal conductivity and better characteristics than conventional ones.

  Although the present invention has been described with the above embodiment, the present invention is not limited to this embodiment, and those skilled in the art can conceive other embodiments, additions, changes, deletions, and the like. It can be changed within the range, and any embodiment is included in the scope of the present invention as long as the effects of the present invention are exhibited.

Claims (10)

  A method for producing a ceramic molded body for sintering, wherein a raw material powder containing a ceramic powder and a thermoplastic resin having a glass transition temperature higher than room temperature is pressed under hydrostatic pressure to form a predetermined shape, the ceramic powder and the thermoplastic A raw material powder slurry is prepared by adding a resin to a solvent so that the thermoplastic resin is 2% by mass or more and 40% by mass or less based on the total mass of the ceramic powder and the thermoplastic resin, and the raw material powder slurry is used. After forming a cast molded body by wet casting into a predetermined shape, it is dried, and this is subjected to first-stage hydrostatic pressure molding at a temperature lower than the glass transition temperature of the thermoplastic resin. Forming a body, and then heating the first-stage pressure-molded body to a temperature equal to or higher than the glass transition temperature of the thermoplastic resin to perform warm isostatic pressing (WIP) molding as second-stage hydrostatic pressure molding. The method for manufacturing a sintered ceramics molded body to manufacture a ceramic molded body.   The method for producing a sintered ceramic body according to claim 1, wherein the first hydrostatic pressure molding is cold isostatic pressing (CIP) molding.   After forming the first-stage pressure-formed body, heating of the first-stage pressure-molded body is started while maintaining the first-stage hydrostatic pressure state, and then the second-stage hydrostatic pressure is applied. The method for producing a sintered ceramic molded body according to claim 1, wherein WIP molding is performed as pressure molding.   The method for producing a sintered ceramic molded body according to any one of claims 1 to 3, wherein the pressure medium for the WIP molding is water or oil.   The method for producing a sintered ceramic molded body according to any one of claims 1 to 4, wherein the thermoplastic resin has a glass transition temperature that is higher than room temperature and lower than a boiling point of a pressure medium for WIP molding. .   The thermoplastic resin is a group consisting of polyvinyl alcohol, polyvinyl acetate, a copolymer of polyvinyl alcohol and polyvinyl acetate, methyl cellulose, ethyl cellulose, polyvinyl butyral, vinyl polypropionate, and a copolymer of polyvinyl alcohol and vinyl propionate. The method for producing a sintered ceramic molded body according to any one of claims 1 to 5, wherein at least one selected from the group consisting of:   The method for producing a sintered ceramic molded body according to any one of claims 1 to 6, wherein the cast molded body is formed by solid-liquid separation of the raw material powder slurry by centrifugal casting.   A ceramic molded body produced by the method for producing a sintered ceramic molded body according to any one of claims 1 to 7, and subjected to a sintering treatment in an inert atmosphere or in a vacuum, and further hot isotropy A method for producing a ceramic sintered body obtained by pressure (HIP) treatment to obtain a ceramic sintered body.   The method for producing a ceramic sintered body according to claim 8, wherein the ceramic molded body is degreased before the sintering treatment.   The method for producing a ceramic sintered body according to claim 8 or 9, wherein an annealing treatment is further performed after the HIP treatment.