Colored zirconia ceramic and method for manufacturing same

Abstract

Disclosed are a colored zirconia ceramic and a method for manufacturing same. The disclosed colored zirconia ceramic is a ceramic made of zirconia or a zirconia-based solid solution containing aluminum as a solute, has excellent mechanical properties, and does not contain a pigment. The disclosed method for manufacturing the colored zirconia ceramic comprises: a first step for preparing composites; a second step for mixing the composites and producing a granulated mixture; a third step for compacting the granulated mixture to produce a compact; a fourth step for primarily heating the compact at 155-175°C for 30-40 hours and then secondarily heating the compact at 650-850°C for 30-40 hours to degrease and heat-treat the compact; a fifth step for pre-sintering the degreased and heat-treated compact at 1450-1550°C; and a sixth step for sintering the pre-sintered compact at a sintering temperature of 1550-1700°C in a vacuum at a pressure of 10-1 to 10-5 Torr.

Description

Colored zirconia ceramics and their manufacturing method

[0001] The present invention relates to colored zirconia ceramics and a method for producing the same, and more particularly, to colored zirconia ceramics that are expressed without adding pigments and a method for producing the same.

[0002]

[0003] When ceramic materials are subjected to rapid temperature changes, internal stresses and volume changes can cause cracks on the surface, ultimately leading to failure. Therefore, for various heat-resistant or insulating devices and materials, resistance to thermal shock—that is, heat resistance—is paramount.

[0004] Therefore, among ceramic materials, zirconia, with its superior structural properties, is widely utilized. Zirconium dioxide (ZrO2), commonly known as zirconia, is a white crystalline oxide and the ceramic material closest to metal. Zirconia possesses excellent material properties, including high heat resistance, low thermal conductivity, chemical stability, high strength, high hardness, and high fracture toughness, making it a heat-resistant material for applications such as glass melting and steelmaking.

[0005] On the other hand, zirconia's high brittleness as a ceramic material limits its applications. However, since the discovery that it can overcome this inherent weakness, zirconia has been utilized in a variety of fields, including thread guides, various dies, and nozzles. Recently, efforts are actively underway to color zirconia ceramics to apply them to decorative items requiring superior mechanical properties, such as watch bezels, cases, and watch bands, as well as substrates for various mechanical and electronic components.

[0006] Furthermore, with improving living standards, zirconia is increasingly being used in decorative items like jewelry as well as watches, leading to a growing demand for zirconia in various colors. However, when coloring zirconia, it must maintain its color even during high-temperature firing without affecting its excellent physical and chemical properties. The various colored zirconias developed so far have been achieved by adding pigments to zirconia. However, this method has the disadvantage of destroying the stability of zirconia, thereby reducing its mechanical properties.

[0007] Therefore, research is actively being conducted on materials with excellent thermal shock resistance by dissolving aluminum oxide (Al2O3) in zirconia to complement the structural characteristics due to heat while being expressed, without adding pigment to zirconia.

[0008]

[0009] The present invention was created in consideration of the above-mentioned points, and its purpose is to provide colored zirconia ceramics having improved mechanical properties while being colored by employing aluminum oxide based on zirconia, and a method for manufacturing the same.

[0010]

[0011] To achieve the above-mentioned purpose, the colored zirconia ceramics according to the present invention include zirconia.

[0012] The above colored zirconia ceramics contain 60 to 95 wt% of zirconia and 5 to 40 wt% of aluminum oxide.

[0013] The average particle size of the above zirconia and the above aluminum oxide is characterized by being 50 to 80 nm.

[0014] The above colored zirconia ceramics further contain 2.5 mol% to 3.5 mol% of a stabilizer based on the total mol%,

[0015] The above stabilizer is characterized in that it is yttrium oxide.

[0016] The above colored zirconia ceramics are characterized in that they further contain at least one of 1 to 5 wt% of a dispersant, 1 to 5 wt% of a defoaming agent, and 1 to 5 wt% of a binder based on the total wt%.

[0017] The above color is characterized by being black or gray.

[0018] The above color is characterized by being expressed without adding pigment.

[0019] In the above method for manufacturing colored zirconia ceramics, a first step of preparing a composite; a second step of mixing the composite and producing a granulated mixture; a third step of molding the granulated mixture to produce a molded body; a fourth step of degreasing and heat-treating the molded body by first heating it at 155 to 175°C for 30 to 40 hours and then secondarily heating it at 650 to 850°C for 30 to 40 hours; a fifth step of pre-sintering the degreasing and heat-treated molded body at 1450 to 1550°C; and a fifth step of pre-sintering the molded body in a vacuum at an atmospheric pressure of 10 -1 ~ 10 -5 Torr, and the sintering temperature is 1550 to 1700℃, including the sixth step;

[0020] The above composite is characterized by being composed of zirconia alone or comprising 60 to 95 wt% of zirconia and 5 to 40 wt% of aluminum oxide.

[0021] The above complex is characterized in that it further includes at least one of 1 to 5 wt% of a dispersant, 1 to 5 wt% of a defoaming agent, and 1 to 5 wt% of a binder based on the total wt%.

[0022] The complex further comprises 2.5 to 3.5 mol% of a stabilizer based on the total mol%, and the stabilizer is characterized in that it is yttrium oxide.

[0023]

[0024] The colored zirconia ceramics according to the present invention are made of zirconia or zirconia containing aluminum oxide, and are expressed in black or gray without adding a metal pigment, while having the effect of improving mechanical properties such as toughness, tensile strength, and hardness.

[0025] In addition, the method for manufacturing colored zirconia ceramics according to the present invention comprises the following steps: a first step of preparing a composite; a second step of mixing the composite and producing a granulated mixture; a third step of molding the granulated mixture to produce a molded body; a fourth step of performing a de-heating treatment by first heating the molded body at 155 to 175°C for 30 to 40 hours and then secondarily heating it at 650 to 850°C for 30 to 40 hours; a fifth step of pre-sintering the de-heated molded body at 1440 to 1550°C; and a fifth step of pre-sintering the molded body under vacuum at an atmospheric pressure of 10 -1 ~ 10 -5 Torr, and the sintering temperature is 1550 to 1700℃, thereby providing excellent mechanical properties.

[0026]

[0027] Figure 1 is an EDS analysis photograph of zirconia.

[0028] Fig. 2 shows a watch component using colored zirconia ceramics according to an embodiment of the present invention.

[0029]

[0030] All terms described in this specification are currently widely used and have been selected in consideration of the functions of the present invention. However, these terms may vary depending on the intentions of those skilled in the art, customs, or the emergence of new technologies. Furthermore, if the inventor specifies any term in the present invention, its meaning will be described in the description of the invention. Therefore, the terms used in the present invention should not be interpreted simply as names of terms, but rather based on their actual meaning and the overall content described in the description of the present invention.

[0031] Hereinafter, with reference to the attached drawings, a colored zirconia ceramic and a manufacturing method thereof according to an embodiment of the present invention will be described in detail. In the drawings, portions irrelevant to the description have been omitted to clearly explain the present invention, and the same reference numerals will be used throughout the specification for identical or similar components.

[0032] The present invention provides colored zirconia ceramics.

[0033] The colored zirconia ceramics according to an embodiment of the present invention may include zirconia. In addition, the colored zirconia ceramics according to an embodiment of the present invention may include 60 to 95 wt% of zirconia and 5 to 40 wt% of aluminum oxide.

[0034] The above zirconia is included in the colored zirconia ceramics of the present invention.

[0035] Zirconium dioxide (ZrO2), also known as zirconia, is a white crystalline oxide and is the ceramic material closest to metal. It is widely used due to its excellent structural properties. The zirconia has a density of 5.68 g / cm. 3, has excellent material properties such as high heat resistance with a melting point of 2715℃ and a boiling point of 400℃, low thermal conductivity, chemical stability, high strength, high hardness, and high fracture toughness, and is used as a heat-resistant material for glass melting, iron and steel making, etc. Referring to Fig. 1, Table 1 shows the chemical composition of the above zirconia.

[0036] Chemical composition wt% wt% sigma B4.48 0.29 C5.53 0.29 O2 1.29 0.33 Zr 68.70 0.50 total 100.00

[0037] On the other hand, although zirconia has the same chemical composition, its structure can change depending on the temperature, which can change its physical properties. That is, the zirconia can be monoclinic from room temperature to 1170℃, and can change into tetragonal and cubic structures as the temperature increases. Therefore, zirconia that is sintered at 1500℃ or higher into a tetragonal structure undergoes a phase transition to a monoclinic system when naturally cooled to 950℃ or lower. The phase-transformed zirconia is accompanied by a volume change of 3 to 5%, and the resulting stress may exceed the deformation resistance of the zirconia, which may cause cracks. In order to complement the structural characteristics of zirconia, aluminum oxide and / or a stabilizer described below can be included to improve them.

[0038] Accordingly, the colored zirconia ceramics of the present invention may be formed solely or may include 60 to 95 wt% of zirconia and 5 to 40 wt% of aluminum oxide. In another embodiment, the zirconia may include 75 to 85 wt% of zirconia and 15 to 25 wt% of aluminum oxide. If the content of the zirconia is less than 60 wt%, sinterability may be reduced, making it difficult to obtain sufficient strength. In addition, if the content of the zirconia is more than 95 wt%, a decrease in the content of aluminum oxide may occur, resulting in changes in mechanical properties and expressed color.

[0039] The above aluminum oxide (Al2O3) is included in the colored zirconia ceramics of the present invention. Aluminum oxide has the highest strength among oxides due to its strong ionic bonding. Furthermore, aluminum oxide is known to have excellent corrosion resistance and chemical resistance. Therefore, to complement the structural characteristics of zirconia, aluminum oxide (Al2O3) can be dissolved in zirconia to improve thermal shock resistance. In addition to improving thermal shock resistance, adding aluminum oxide to zirconia not only improves physical properties but also minimizes color change upon cooling.

[0040] Therefore, the aluminum oxide may be included in an amount of 5 to 40 wt% based on the total wt% of the colored zirconia ceramics. As another example, the aluminum oxide may be included in an amount of 15 to 25 wt% based on the total wt% of the colored zirconia ceramics. If the content of the aluminum oxide is less than 5 wt%, changes in the physical properties and expressed color of the colored zirconia ceramics of the present invention may occur. In addition, if only the content of the aluminum oxide is increased to exceed 25 wt% while the particle size of the aluminum oxide, the sintering pretreatment conditions, and the vacuum pressure and conditions during sintering are fixed, the physical properties may deteriorate.

[0041] The average particle size of the above zirconia and the above aluminum oxide may be 50 to 80 nm, respectively. When the average particle size of the above zirconia and the above aluminum oxide is nanocrystalline, it provides excellent formability and can improve the mechanical properties of the present invention. This is because the particle distribution is more uniform as the present invention is formed with a uniform nanoparticle size, which can prevent crystal grain growth.

[0042] Therefore, if the average particle size is less than 50 nm, shrinkage may occur during sintering. In addition, if the average particle size exceeds 80 nm, sintering may not occur properly, which may affect the mechanical properties and there is a risk of color change.

[0043] The above stabilizer may be further included in the colored zirconia ceramics. The stabilizer may be added to alleviate the problem of cracking occurring during natural cooling after sintering of the zirconia. The stabilizer may be selected from at least one of yttrium oxide (Y2O3), magnesium oxide (MgO), calcium oxide (CaO), and cerium oxide (Ce2O3).

[0044] Therefore, when the stabilizer is yttrium oxide, it may contain 2.5 to 3.5 mol% based on the total mol% of colored zirconia ceramics. In addition, when the stabilizer is magnesium oxide, it may contain 8 to 9 mol% based on the total mol%, and calcium oxide may contain 8 to 9 mol% based on the total mol%. In an embodiment of the present invention, yttrium oxide may be mainly selected as the metal stabilizer. When the content of the stabilizer is less than the range, a volume change due to phase transition may occur during natural cooling after sintering, which may exceed the deformation resistance, thereby causing cracks to occur. When the content of the stabilizer exceeds the range, it may be meaningless in terms of critical significance.

[0045] At least one of the above dispersing agent, antifoaming agent and binder may be further included in the colored zirconia ceramics.

[0046] The above dispersant can evenly disperse each component to make the composition of each sphere uniform. In other words, the dispersant can prevent the generated microparticles from re-agglomerating when converting large particles and aggregated particles into smaller particles. Therefore, the dispersant can use an adsorbent material such as a surfactant or a polymer material. The dispersant can be selected from a polycarboxylic acid ammonium-based, alkylamine-based, or silicone-based surfactant. In the present invention, the polycarboxylic acid ammonium salt-based dispersant can be mainly selected, but is not limited thereto.

[0047] Therefore, the dispersant may be included in an amount of 1 to 5 wt% based on the total wt%. In another embodiment, the dispersant may be included in an amount of 2 to 3 wt% based on the total wt%. In addition, if the dispersant is a polycarboxylic acid ammonium salt-based dispersant, it may not have a negative effect on the molded article because it does not contain a sulfur component.

[0048] The above-mentioned antifoaming agent has an excellent antifoaming effect, as it can remove harmful foam. Therefore, the antifoaming agent can be selected from organic phosphates, alcohols, etc. In embodiments of the present invention, polyether-based antifoaming agents are mainly selected, but are not limited thereto.

[0049] Therefore, the above-mentioned antifoaming agent may be included in an amount of 1 to 5 wt% based on the total wt%. In another embodiment, the above-mentioned antifoaming agent may be included in an amount of 1 to 2 wt% based on the total wt%.

[0050] The above-mentioned binder not only binds each component but also softens the mixture, increasing fluidity and allowing the powder to fill voids, thereby improving density. Therefore, the binder can influence the production of a high-density molded article. Accordingly, the binder can be selected from a polyvinyl alcohol-based material, an acrylic resin, or the like. In the present invention, the binder is primarily selected from a polyvinyl alcohol-based material, but is not limited thereto.

[0051] Therefore, the binder may be included in an amount of 1 to 5 wt% based on the total wt%. In another embodiment, the binder may be included in an amount of 1 to 4 wt% based on the total wt%. The polyvinyl alcohol system is water-soluble and can dissolve in water to bind the zirconia particles.

[0052] Figure 2 shows a watch component using colored zirconia ceramics according to an embodiment of the present invention.

[0053] Referring to Fig. 2, the watch part using the colored zirconia ceramics of the present invention has excellent mechanical properties as well as decorative properties, as it is expressed in black or gray without containing metal pigments, and contains the above components as effective ingredients.

[0054] Therefore, the colored zirconia ceramics of the present invention can be usefully used as a decorative material. That is, they can be used as accessories for jewelry, decorative objects, watches (such as wristwatches), electronic products, and daily necessities such as ceramic knives and scissors. In particular, the colored zirconia ceramics according to an embodiment of the present invention can be used as, for example, a wristwatch component, and can be used as a case body, bezel, dial, front cover, or rear cover of the wristwatch. In addition, the colored zirconia ceramics of the present invention can have various shapes depending on the use, and specifically, can be shaped into a ring, a disk, a polygonal plate, etc.

[0055]

[0056] [Method for Manufacturing Colored Zirconia Ceramics]

[0057] The present invention provides a method for manufacturing colored zirconia ceramics.

[0058] Colored zirconia ceramics according to an embodiment of the present invention comprises a first step of preparing a composite; a second step of granulating the composite to produce a granulated mixture; a third step of molding the granulated mixture to produce a molded body; a fourth step of degreasing and heat-treating the molded body by first heating it at 155 to 175°C for 30 to 40 hours and then secondarily heating it at 650 to 850°C for 30 to 40 hours; a fifth step of pre-sintering the degreasing and heat-treated molded body at 1450 to 1550°C; and a fifth step of pre-sintering the molded body in a vacuum at an atmospheric pressure of 10. -1 ~ 10 -5Torr, and the sintering temperature may include a sixth step of sintering at 1550 to 1700°C.

[0059]

[0060] [1] Step 1 (Preparing the complex)

[0061] The first step is to prepare a composite. Specifically, the composite may be composed solely of the zirconia, or may comprise 75 to 85 wt% of zirconia and 15 to 25 wt% of aluminum oxide. Furthermore, the average particle sizes of the zirconia and aluminum oxide are each 50 to 80 nm. When the average particle size is nanocrystalline, it provides excellent formability and can improve the mechanical properties of the present invention. This is because the more uniform the nanoparticle size of the present invention is formed, the more uniform the particle distribution is, which can prevent grain growth.

[0062] The above zirconia is included in the composite. Zirconium dioxide (ZrO2), also known as zirconia, is a white crystalline oxide and is the ceramic material closest to metal. It is widely used due to its excellent structural properties. The above zirconia has a density of 5.68 g / cm. 3 , has excellent material properties such as high heat resistance with a melting point of 2715℃ and a boiling point of 400℃, low thermal conductivity, chemical stability, high strength, high hardness, and high fracture toughness, and can be included in the present invention.

[0063] Therefore, when the zirconia forms a composite with aluminum oxide, the zirconia may be included in an amount of 60 to 95 wt% based on the total wt% of the composite. As another example, the zirconia may be included in an amount of 75 to 85 wt% based on the total wt% of the composite. When the content of the zirconia is less than 60 wt%, sinterability may be reduced, making it difficult to obtain sufficient strength. In addition, when the content of the zirconia exceeds 90 wt%, a decrease in the content of aluminum oxide may occur, which may result in changes in mechanical properties and expressed color.

[0064] The above aluminum oxide (Al2O3) is included in the composite. Aluminum oxide has the highest strength among oxides due to its strong ionic bonding. Furthermore, aluminum oxide is known to have excellent corrosion and chemical resistance. Therefore, to complement the structural characteristics of zirconia, aluminum oxide (Al2O3) can be dissolved in zirconia to improve thermal shock resistance. In addition to improving thermal shock resistance, adding aluminum oxide to zirconia not only improves physical properties but also minimizes color change upon cooling.

[0065] Therefore, the aluminum oxide may be included in an amount of 5 to 40 wt% based on the total wt% of the composite. In another embodiment, the aluminum oxide may be included in an amount of 15 to 25 wt% based on the total wt% of the composite. If the content of the aluminum oxide is less than 5 wt%, changes in the physical properties and expressed color of the colored zirconia ceramics of the present invention may occur. In addition, if only the content of the aluminum oxide is increased to exceed 25 wt% while the particle size of the aluminum oxide, the sintering pretreatment conditions, and the vacuum pressure and conditions during sintering are fixed, the physical properties may deteriorate.

[0066] The above complex may further include a stabilizer. The stabilizer may be added to alleviate the problem of cracking occurring during natural cooling after sintering of zirconia. The metal stabilizer may be selected from at least one of yttrium oxide (Y2O3), magnesium oxide (MgO), calcium oxide (CaO), and cerium oxide (Ce2O3).

[0067] Therefore, when the stabilizer is yttrium oxide, it may contain 2.5 to 3.5 mol% based on the total mol% of the composite. In addition, when the stabilizer is magnesium oxide, it may contain 8 to 9 mol% based on the total mol% of the composite, and calcium oxide may contain 8 to 9 mol% based on the total mol% of the composite. In an embodiment of the present invention, yttrium oxide may be mainly selected as the metal stabilizer. When the content of the stabilizer is less than the range, a volume change due to phase transition may occur during natural cooling after sintering, which may exceed the deformation resistance, thereby causing cracks to occur. When the content of the stabilizer exceeds the range, it may be meaningless in terms of critical significance.

[0068] The above complex may further comprise at least one of a dispersant, an antifoaming agent, and a binder.

[0069] The above dispersant can evenly disperse each component to make the composition of each sphere uniform. In other words, the dispersant can prevent the generated microparticles from re-agglomerating when converting large particles and aggregated particles into smaller particles. Therefore, the dispersant can use an adsorbent material such as a surfactant or a polymer material. The dispersant can be selected from a polycarboxylic acid ammonium-based, alkylamine-based, or silicone-based surfactant. In the present invention, the polycarboxylic acid ammonium salt-based dispersant can be mainly selected, but is not limited thereto.

[0070] Therefore, the dispersant may be included in an amount of 1 to 5 wt% based on the total wt%. In another embodiment, the dispersant may be included in an amount of 2 to 3 wt% based on the total wt%. In addition, if the dispersant is a polycarboxylic acid ammonium salt-based dispersant, it may not have a negative effect on the molded article because it does not contain a sulfur component.

[0071] The above-mentioned antifoaming agent has an excellent antifoaming effect, as it can remove harmful foam. Therefore, the antifoaming agent can be selected from organic phosphates, alcohols, etc. In embodiments of the present invention, polyether-based antifoaming agents are mainly selected, but are not limited thereto.

[0072] Therefore, the above-mentioned antifoaming agent may be included in an amount of 1 to 5 wt% based on the total wt%. In another embodiment, the above-mentioned antifoaming agent may be included in an amount of 1 to 2 wt% based on the total wt%.

[0073] The above-mentioned binder not only binds each component but also softens the mixture, increasing fluidity and allowing the powder to fill voids, thereby improving density and contributing to the production of a high-density molded article. Therefore, the binder may be selected from the polyvinyl alcohol family, acrylic resin, or the like. In the present invention, the binder is primarily selected from the polyvinyl alcohol family, but is not limited thereto.

[0074] Therefore, the binder may be included in an amount of 1 to 5 wt% based on the total wt%. In another embodiment, the binder may be included in an amount of 1 to 4 wt% based on the total wt%. The polyvinyl alcohol system is water-soluble and can dissolve in water to bind the zirconia particles.

[0075]

[0076] [2] Step 2 (Mixing and Granulation)

[0077] The second step is a step of mixing and granulating the complex to produce a granulated mixture. The mixing of the complex is performed by mixing the complex prepared in the first step with a liquid material. The mixing can be performed by a method widely known in the art. Specifically, the liquid material has a predetermined viscosity and can include a solvent, a lubricant, etc. The liquid material can be removed during a high-temperature sintering process. The solvent can be selected from at least one of water and an organic solvent, and specifically, at least one of water, ether, acetone, and alcohol (ethanol, etc.) can be selected. The lubricant can be selected as long as it is commonly used in the art.

[0078] Accordingly, the liquid material may contain 0.5 to 15 parts by weight of a lubricant per 100 parts by weight of a solvent. By mixing the complex with the liquid material, a mixture having a predetermined viscosity can be prepared. The mixture may be a mixture of the complex and the liquid material in a weight ratio of 1:0.1 to 0.9. The mixture may be placed in a stirrer and stirred to obtain a mixture, which may then be sprayed in the form of droplets using a sprayer, and then dried to prepare a mixture in the form of granules having a uniform size.

[0079] The average particle size of the above granulated mixture may be 50 to 80 nm. If the average particle size of the powder is less than 50 nm, the granules may scatter during molding, making it difficult to control the density, and may cause shrinkage during firing. In addition, if the average particle size exceeds 80 nm, the pores created within the granules may cause many bubbles to exist after molding, which may affect the mechanical properties, and there is a risk of color deterioration.

[0080]

[0081] [3] Stage 3 (shaping)

[0082] The third step is a step of molding the granulated mixture to produce a molded body. Specifically, the molding agent may have any shape. That is, the molded body may have various shapes such as a ring, a disk, a polygonal plate, etc. As another example, the molded body may have a shape such as a finished product (a watch, a watch part, etc.) or a semi-finished product (a base). The molding method for producing the molded body is not particularly limited. That is, the molding method may be selected from sheet molding, extrusion molding, injection molding, press molding, etc. The press molding is a method of manufacturing a molded body by filling a mold with powder and applying pressure. Depending on the method of applying pressure, there are uniaxial pressing molding for one direction, and isostatic pressing molding for multiple multi-axes. The molding method of the present invention is mainly uniaxial pressing molding, in which powder is charged into a mold. Then, molding can be performed by applying a pressure of 700 to 1,500 kgf / cm2 to the mold loaded with powder for 1 to 2 hours. Therefore, in the present invention, a molded body having an arbitrary shape can be manufactured preferably through press forming.

[0083]

[0084] [4] Step 4 (Degreasing / Heat Treatment)

[0085] Step 4 involves degreasing and heat-treating the molded body. Specifically, the physical properties of the colored zirconia ceramics depend on the degree of uniformity of the mixture. Therefore, the degreasing and heat-treating step can minimize foreign substances and create a uniform mixture. Specifically, when mixing the composite and liquid materials to produce the mixture, the organic components of the dispersant, antifoaming agent, and binder can cause pores or cracks during the sintering step described below. Therefore, the degreasing and heat-treating step can remove these organic substances.

[0086] Therefore, the above-mentioned degreasing and heat treatment step may include first heating at 155 to 175°C for 30 to 40 hours, followed by second heating at 650 to 850°C for 30 to 40 hours. During the first heating, moisture within the molded body can be removed, and during the second heating, organic components within the molded body can be removed. This step-by-step heating can suppress thermal stress of the molded body, thereby preventing the banding phenomenon in which the molded body bends.

[0087] Meanwhile, if the temperature and time ranges are exceeded during the degreasing and heat treatment stages, residual organic matter may cause cracks to occur during the sintering stage. Furthermore, if the temperature and time ranges are exceeded during the degreasing and heat treatment stages, warping or breakage of the molded body may occur.

[0088]

[0089] [5] Step 5 (Pre-sintering)

[0090] Step 5 is a sintering pretreatment step. Specifically, the sintering pretreatment step can be performed at 1450 to 1550°C for 1 to 4.5 hours on the degreasing and heat-treated molded body. The sintering pretreatment step is a process to remove impurities, moisture, and other foreign substances that were not processed in the degreasing and heat-treatment step before sintering to create a uniform mixture. In addition, the sintering pretreatment step is a process to apply heat at a sufficient temperature to make particles with a large specific surface area, such as powder, into a more dense mass. The sintering pretreatment step can be performed according to a typical ceramic sintering pretreatment process.

[0091] Meanwhile, if the temperature and time, which are the pre-sintering conditions, fall below the range, residual foreign substances may remain, which may cause cracks and color changes during the sintering step. If the temperature and time, which are the pre-sintering conditions, fall outside the range, deformation of the molded body may occur.

[0092]

[0093] [6] Step 6 (Sintering)

[0094] The sixth step is the sintering step. Specifically, the sintering step refers to a process of applying sufficient temperature and pressure to make particles with a large specific surface area, such as powder, into a more dense mass. The sintering method can be classified into vacuum sintering, pressureless sintering, pressure sintering, spark plasma sintering, reaction sintering, etc., depending on the process conditions. In the present invention, the sintering can be performed according to a conventional ceramic sintering method. That is, the sintering is performed using a high vacuum sintering furnace in a vacuum or argon (Ar) gas atmosphere at a pressure of 10 -1 ~ 10 -5 Torr, and the sintering temperature can be 1550 to 1700℃ for 1.0 to 4.5 hours. Upon completion of this sintering, a sintering agent of colored zirconia ceramics having excellent color and mechanical properties can be manufactured.

[0095] Meanwhile, if the firing conditions of pressure, temperature, and time fall below the specified range, sintering will not occur properly, making it impossible to manufacture the dense colored zirconia ceramics of the present invention. Furthermore, if the firing conditions of pressure, temperature, and time exceed the specified range, volume expansion of the zirconia may occur, resulting in a deterioration in mechanical properties.

[0096] Additionally, the colored zirconia ceramics according to the present invention may further include a processing step after the sintering in the sixth step is completed. That is, if the sintered body is a wristwatch component, it may be cut to have an actual shape. The cutting process may be performed using laser processing or the like, and may be shaped to have the shape of components such as the case body, bezel, and / or dial that constitute the wristwatch.

[0097] In this way, the method for manufacturing colored zirconia ceramics according to an embodiment of the present invention provides a process that has excellent decorative properties and excellent mechanical properties by expressing black or gray only according to manufacturing conditions without adding pigment.

[0098]

[0099] Below, manufacturing examples and examples are provided. The following manufacturing examples and examples are provided solely to aid in understanding the present invention.

[0100]

[0101] <Manufacturing of colored zirconia ceramics>

[0102] [Examples 1 to 6] - Colored zirconia ceramics

[0103] In order to manufacture the colored zirconia ceramics of the present invention, a composite was manufactured by including at least one of zirconia and aluminum oxide with the components and contents shown in Table 3 below, and then a dispersant (polycarboxylic acid ammonium salt), an antifoaming agent (polyether), a binder (PVA), and a stabilizer (yttrium oxide) were further included in the contents shown in Table 3 below based on the total wt% of the composite. Next, a liquid material was prepared by mixing 5 parts by weight of a lubricant with 100 parts by weight of a solvent. The composite and the liquid material were mixed in a weight ratio of 100:55, and the mixture was stirred using a ball mill to manufacture a mixture, which was then spray-dried to manufacture a granule form having a uniform size. This is loaded into a press mold to manufacture a plate-shaped molded body, and then the molded body is first heated at 160°C for 35 hours, then secondarily heated at 750°C for 335 hours to undergo degreasing heat treatment, and then the degreasing heat-treated molded body can be subjected to sintering pretreatment at 1500°C for 2 hours. The pre-sintered molded body can be sintered under a vacuum atmosphere in a vacuum sintering furnace for 10 -3 Colored zirconia ceramics (specimens) according to each example were manufactured by sintering at 1600°C for 2 h under atmospheric pressure. Table 2 below shows the components and contents of examples and comparative examples of the present invention.

[0104]

[0105] [Comparative Examples 1 to 4] - Colored zirconia ceramics

[0106] Comparative Examples 1 to 4 were prepared by manufacturing colored zirconia ceramics in the same manner as in Example 1, except that the components and contents of the composites were different from those of Examples 1 to 6. Table 2 below shows the components and contents of the examples and comparative examples of the present invention.

[0107]

[0108] [Comparative Example 5] - Including pigment

[0109] In order to manufacture the colored zirconia ceramics of the present invention, a composite was manufactured including zirconia and aluminum oxide with the components and contents shown in Table 3 below, and then a dispersant (polycarboxylic acid ammonium salt), an antifoaming agent (polyether), a binder (PVA), a stabilizer (yttrium oxide), and a pigment (including nickel oxide, cobalt oxide, and iron oxide) were further added in the contents shown in Table 3 below based on the total wt% of the composite to prepare the composite. Next, a liquid material was prepared by mixing 5 parts by weight of a lubricant with 100 parts by weight of a solvent. The composite and the liquid material were mixed in a weight ratio of 100:55, stirred using a ball mill to manufacture a mixture, and then spray-dried to manufacture a granule form having a uniform size. This was placed in a press mold to produce a plate-shaped molded body, and then the molded body was first heated at 160°C for 35 hours, then secondarily heated at 750°C for 335 hours to undergo degreasing heat treatment, and then the degreasing heat-treated molded body was heated from room temperature to 1600°C, and then sintered at the sintering temperature for 2 hours to obtain colored zirconia ceramics. Table 2 below shows the components and contents of examples and comparative examples of the present invention.

[0110]

[0111] [Comparative Examples 6 and 7] - Colored zirconia ceramics

[0112] Comparative Examples 6 and 7 were produced by manufacturing colored zirconia ceramics in the same manner as in Example 3, except that the sintering temperature was set to 1500°C and 1700°C, respectively. Table 3 below shows the components and contents of Example 3 and Comparative Examples 6 and 7 of the present invention.

[0113]

[0114] Ingredients and contentsZirconia (wt%)Aluminum oxide (wt%)Dispersant (wt%)Antifoaming agent (wt%)Binder (wt%)Stabilizer (mol%)Pigment (wt%)Example 1100021.5230Example 2604021.5230Example 3802021.5230Example 495521.5230Example 5802021.5200Example 6802000030Comparative example 1554521.5230Comparative example 297321.5230Comparative example 3554500030Comparative example 4554521.5200Comparative example 5554521.5230.05wt%

[0115] Ingredients and contentsZirconia (wt%)Aluminum oxide (wt%)Dispersant (wt%)Antifoaming agent (wt%)Binder (wt%)Stabilizer (wt%)Sintering temperature (℃)Example 3802021.5231600Comparative example 6802021.5231500Comparative example 7802021.5231700

[0116]

[0117] <Example of an exam>

[0118] [Test Example 1] - Density of sintered body

[0119] The density of colored zirconia ceramics specimens manufactured according to the examples and comparative examples of the present invention was measured by the “Archimedes method.”

[0120]

[0121] [Test Example 2] - Breaking Strength

[0122] The fracture strength of each colored zirconia ceramics specimen manufactured according to the examples and comparative examples of the present invention was measured through a three-point bending strength test using a UTM (Universal Testing Machine, Model No. 4206, Instron, USA) with a crosshead speed of 0.5 mm / min and a span distance of 30 mm.

[0123]

[0124] [Test Example 3] - Fracture Toughness and Hardness

[0125] According to the examples and comparative examples of the present invention, the fracture toughness of each colored zirconia ceramic specimen was measured by the Vickers indentation method using a Vickers hardness tester (AVK-C2, Mitutoyo, Japan) with a load of 10 kg. In addition, the hardness was measured using a micro Vickers hardness tester with a load of 500 g.

[0126]

[0127] Table 4 shows the results of property analysis according to examples and comparative examples of the present invention.

[0128] Density of sintered body (g / cm) of examples and comparative examples 3 )Fracture strength (MPa)Fracture toughness (MPa·m 1 / 2 )Hardness (MPa)Example 16.0515307.61480Example 25.4916078.01523Example 35.6516928.51591Example 45.7816708.21545Example 55.574311.3305Example 65.5216818.31570Comparative Example 15.5114807.21405Comparative Example 25.9716158.11520Comparative Example 35.2714707.11391Comparative Example 45.213951.2315Comparative Example 55.207583.9987Comparative Example 65.517988.6998Comparative Example 75.497888.4987

[0129] Referring to Table 4, it was confirmed that the examples of the present invention had overall superior sintered body density, fracture strength, fracture toughness, and hardness compared to the comparative examples. That is, except for Example 5, the density of the sintered body in most examples was 5.45 g / cm. 3 Above, the fracture strength is 1500 MPa or more, and the fracture toughness is 7.5 MPa·m. 1 / 2 Above, it was confirmed that the hardness was over 1450 MPa.

[0130] Specifically, it was found that the density of the sintered body was improved in Example 1, which consisted solely of zirconia, compared to Examples 2 to 6, which mixed zirconia with aluminum oxide, and that the density of the sintered body increased as the amount of zirconia increased. However, excluding the density of the sintered body, it was found that the fracture strength and fracture toughness were improved in Examples 2 to 6 (except Example 5), which mixed zirconia and aluminum oxide, compared to Example 1, which consisted solely of zirconia. This confirms that the examples with added aluminum oxide improved the mechanical properties by complementing the structural characteristics of zirconia, compared to those composed solely of zirconia. On the other hand, it was found that Example 5, which did not include a stabilizer, had lower mechanical properties compared to the other examples. In addition, when comparing Examples 3 and 6, which have the same content of zirconia and aluminum oxide, it was confirmed that the mechanical properties of the colored zirconia ceramics of the present invention were affected depending on the presence or absence of the additives, such as a dispersant, an antifoaming agent, and a binder.

[0131] On the other hand, it was found that most of the comparative examples had lower mechanical properties than the examples. That is, except for comparative example 2 with a high zirconia content, it was found that the density of the sintered body decreased in comparative examples 1 and 3 to 5 when the zirconia and aluminum oxide contents were outside the range of the examples, additives (dispersants, antifoaming agents, binders) were not included, stabilizers were not included, or pigments were included. In addition, it was found that comparative examples 6 and 7, which had the same zirconia and aluminum oxide contents as example 3 but different only in sintering temperature, had lower sintered body densities.

[0132] Therefore, it was found that the density of the sintered body depends on the presence or absence of stabilizer, pigment, dispersant, etc., the content of zirconia and aluminum oxide, sintering temperature, etc. In addition, although omitted from the drawing, it was found that while the density of the sintered body improved as the content of zirconia and aluminum increased within a certain range, the particle size decreased, so the sinterability was affected by the tetragonal / monoclinic ratio, which is a structural characteristic of zirconia.

[0133] It was found that the fracture strength and fracture toughness of Examples 2 to 6 (except Example 5), which were a mixture of zirconia and aluminum oxide, were superior to Example 1, which was composed of only zirconia, unlike the density of the sintered body. This confirmed that aluminum oxide improved the mechanical properties by complementing the structural characteristics of zirconia. On the other hand, as shown in the comparative examples, it was found that the fracture strength and fracture toughness of Comparative Examples 1, 3 to 7 decreased compared to the examples, except for Comparative Example 2. Therefore, it was found that the fracture strength and fracture toughness depend on the presence or absence of a stabilizer, the presence or absence of a pigment, the presence or absence of a dispersant, etc., and the contents of zirconia and aluminum oxide.

[0134] Hardness also showed a similar trend to fracture strength and fracture toughness, and it was found that Examples 2 to 6 (except Example 5), which were composed of zirconia and aluminum oxide, were improved by about 130 MPa or more compared to Example 1, which was composed of only zirconia. However, as the zirconia content increased, the composition ratio of zirconia, which has lower hardness than aluminum oxide, increased, which caused microcracks to form in the material due to excessive grain growth, and thus the hardness of Example 4 was found to decrease. On the other hand, it was found that the hardness of Comparative Examples 1 and 3 to 7, excluding Comparative Example 2, was decreased compared to the Examples. In addition, it was found that the hardness of Comparative Example 2 was decreased as the zirconia content increased further compared to Example 4.

[0135]

[0136] In this way, the colored zirconia ceramics according to the embodiment of the present invention do not contain a pigment, and include at least one of aluminum oxide, a stabilizer, a dispersant, an antifoaming agent, and a binder based on zirconia, thereby providing colored zirconia ceramics that are expressed in black or gray under predetermined sintering conditions and have excellent mechanical properties.

[0137] The embodiments described above are merely illustrative, and those skilled in the art will readily appreciate various modifications and equivalent alternative embodiments. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the invention as set forth in the claims.

Claims

1. In colored zirconia ceramics, The above colored zirconia ceramics are colored zirconia ceramics containing zirconia.

2. In paragraph 1, The above colored zirconia ceramics are, 60 to 95 wt% zirconia; and Colored zirconia ceramics containing 5 to 40 wt% of aluminum oxide.

3. In paragraph 2, Colored zirconia ceramics characterized in that the average particle sizes of the zirconia and the aluminum oxide are each 50 to 80 nm.

4. In paragraph 1 or 2, The above colored zirconia ceramics further contain 2.5 mol% to 3.5 mol% of a stabilizer based on the total mol%, Colored zirconia ceramics characterized in that the above stabilizer is yttrium oxide.

5. In paragraph 4 The colored zirconia ceramics are characterized in that the colored zirconia ceramics further contain at least one of 1 to 5 wt% of a dispersing agent, 1 to 5 wt% of a defoaming agent, and 1 to 5 wt% of a binder based on the total wt%.

6. In paragraph 5, Colored zirconia ceramics characterized in that the color is black or gray.

7. In paragraph 6, Colored zirconia ceramics characterized in that the above color is expressed without adding pigment.

8. In the method for manufacturing colored zirconia ceramics, Step 1: Preparing the complex; A second step of mixing the above complex and producing a granulated mixture; A third step of manufacturing a molded body by molding the above granulated mixture; The fourth step is to degrease and heat-treat the above-mentioned molded body by first heating it at 155 to 175°C for 30 to 40 hours and then second heating it at 650 to 850°C for 30 to 40 hours; A fifth step of pre-sintering the above-mentioned molded body, which has been degreased and heat-treated, at 1450 to 1550°C; and The above pre-sintered molded body is placed in a vacuum at a pressure of 10 -1 ~ 10 -5 A method for manufacturing colored zirconia ceramics, comprising a sixth step of sintering at a sintering temperature of 1550 to 1700°C and a sintering pressure of 1 Torr.

9. In paragraph 8, In the above first step, The above complex is composed of zirconia alone, or A method for manufacturing colored zirconia ceramics, characterized in that the above composite comprises 60 to 95 wt% of zirconia and 5 to 40 wt% of aluminum oxide.

10. In paragraph 8, In the above first step, A method for manufacturing colored zirconia ceramics, characterized in that the above complex further includes at least one of 1 to 5 wt% of a dispersant, 1 to 5 wt% of a defoaming agent, and 1 to 5 wt% of a binder based on the total wt%.

11. In paragraph 8, In the above first step, A method for manufacturing colored zirconia ceramics, characterized in that the complex further comprises 2.5 to 3.5 mol% of a stabilizer based on the total mol%, and the stabilizer is yttrium oxide.

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