Glaze and heat-resistant ceramic ware

Abstract

To provide a glaze having excellent heat resistance and transparency and a heat-resistant ceramic ware including a glaze layer formed by using the same.SOLUTION: A glaze includes 20-80 mass% of β-spodumene to the total solid content of glaze and includes 10-80 mass% of at least one or more kinds of an addition material selected from clay, dolomite, lime, feldspar, agalmatolite, chamotte, talc, magnesite, alumina, a barium compound, a strontium compound, petalite, cordierite, fused silica, and zinc oxide to the total solid content of the glaze.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a heat-resistant glaze and heat-resistant ceramic having a glaze layer formed using the same. [Background technology]

[0002] Low-expansion ceramic sintered bodies using cordierite (2MgO·2Al2O3·5SiO2) or petalite are used in industrial applications as ceramics characterized by their low expansion and low thermal expansion. They are known to have a small thermal expansion coefficient and excellent thermal shock resistance.

[0003] Conventional heat-resistant materials for direct fire have been used for heat-resistant ceramic tableware such as clay pots. They are also used in products that require low expansion performance such as roofing tiles and bricks. Petalite and cordierite are the mainstream heat-resistant materials for direct fire in Japan. The reason why ceramics and other products break due to thermal shock is because of the change in volume that accompanies heating and cooling. Petalite and cordierite are materials with low thermal expansion, and by mixing them with clay, heat resistance can be improved.

[0004] In this way, petalite, which is a low-expansion raw material, is mixed with clay to form a mixed clay, and sintered versions of this mixed clay are widely used as heat-resistant ceramics. For example, Patent Document 1 proposes a method for producing a heat-resistant material, which comprises kneading 20-80% by weight of clay and 80-20% by weight of petalite of a given mesh size to form a kneaded body, kneading this with a kneaded body of carbon particles and a silicic acid compound, and then firing the kneaded body at a given temperature. Patent Document 2 also describes a glaze-colored tile in which a glaze containing petalite as a main component is applied to a tile base and then fired.

[0005] In ceramics with a glaze layer on a base, if the thermal expansion coefficients of the base and the glaze layer are significantly different, tensile stress is applied to the base when the temperature changes due to heating and cooling, which can cause the base to crack or the glaze layer to peel off from the surface of the base. In such cases, adding a specified amount of petalite to both the base and the glaze can prevent cracking and peeling.

[0006] Since much of the mineral matter, such as petalite, is imported, there is a risk that it may become difficult to obtain due to changes in the resource situation, etc. Therefore, new compositions for heat-resistant ceramics using raw materials that are relatively stably available are being developed.

[0007] For example, Patent Document 3 describes a heat-resistant clay raw material mainly composed of clay and fused quartz. It is described that the heat-resistant clay raw material described in Patent Document 3 can be produced at low cost without relying on petalite, and can be used as a raw material for heat-resistant ceramics that have low expansion and high heat resistance regardless of firing conditions. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2011-57517 A [Patent Document 2] Japanese Patent Application Publication No. 60-90883 [Patent Document 3] JP 2019-137605 A Summary of the Invention [Problem to be solved by the invention]

[0009] When the heat-resistant clay raw material described in Patent Document 3 is used, it is suitable for use as a base material for heat-resistant ceramics. However, the fused quartz that imparts low expansion performance is difficult to melt (dissolve) during firing, and is difficult to make transparent when used in a glaze layer. Therefore, it is considered that it cannot be applied to glaze applications that require transparency.

[0010] The present invention has been made in view of the above background, and has an object to provide a glaze having excellent heat resistance and transparency, and heat-resistant ceramic having a glaze layer formed using the same. [Means for solving the problem]

[0011] The glaze of the present invention is characterized in that it contains β-spodumene in an amount of 20 to 80 mass % based on the total solid content of the glaze.

[0012] The glaze contains at least one additive selected from clay, dolomite, lime, feldspar, pyrolite, chamotte, talc, magnesite, alumina, barium compounds, strontium compounds, petalite, cordierite, fused silica, and zinc oxide in an amount of 10 to 80 mass% relative to the total solid content of the glaze.

[0013] It is characterized by containing clay and dolomite as additives.

[0014] The glaze contains β-spodumene in an amount of 50 to 80% by mass relative to the total solid content of the glaze, and contains clay and dolomite as the additives in an amount of 10 to 50% by mass relative to the total solid content of the glaze.

[0015] The heat-resistant ceramic of the present invention is a heat-resistant ceramic having a ceramic base and a glaze layer formed on all or part of the base, characterized in that the base is a fired body of a heat-resistant clay raw material containing clay and a low-expansion material as main components, the low-expansion material contains fused quartz, and the glaze used to form the glaze layer contains β-spodumene.

[0016] The heat-resistant clay raw material is characterized in that, out of a total of 100 parts by mass of the clay, which is the main component of the heat-resistant clay raw material, and the low-expansion material, the clay is 10 to 70 parts by mass, and the remainder is the low-expansion material. Effect of the Invention

[0017] The glaze of the present invention contains 20 to 80 mass % of β-spodumene based on the total solid content of the glaze, and therefore can form a glaze layer having excellent heat resistance and transparency without relying on petalite.

[0018] The glaze contains at least one additive selected from clay, dolomite, lime, feldspar, pyrolite, chamotte, talc, magnesite, alumina, barium compounds, strontium compounds, petalite, cordierite, fused silica, and zinc oxide in an amount of 10 to 80 mass% based on the total solid content of the glaze, providing excellent adhesion to the base and preventing the glaze layer from peeling off.

[0019] The addition of clay and dolomite as additives makes it easier for β-spodumene to melt during firing and for bonds to form between the glaze layer and the base material, resulting in superior heat resistance and transparency of the glaze layer.

[0020] The glaze contains 50 to 80 mass% of β-spodumene based on the total solid content of the glaze, and contains 10 to 50 mass% of clay and dolomite as additives based on the total solid content of the glaze, so the glaze layer is less susceptible to thermal expansion and has even better heat resistance.

[0021] The heat-resistant ceramic of the present invention has a base material that is fired from a heat-resistant clay raw material whose main components are clay and a low-expansion material, the low-expansion material contains fused quartz, and the glaze used to form the glaze layer contains β-spodumene, so that both the base material and the glaze layer can have a low thermal expansion coefficient. This reduces the difference in thermal expansion coefficient between the base material and the glaze layer when the heat-resistant ceramic is heated and cooled, resulting in excellent heat resistance. In addition, the glaze layer has excellent transparency, allowing the color of the base material to be transmitted.

[0022] Of the total 100 parts by mass of clay, which is the main component of the heat-resistant clay raw material, and the low-expansion material, the clay is 10 to 70 parts by mass and the remainder is the low-expansion material, so the thermal expansion coefficient of the base material is lower and the heat resistance is even better. [Brief description of the drawings]

[0023] [Figure 1]FIG. 1 is a diagram showing an example of the heat-resistant ceramic of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The heat-resistant ceramics manufactured using the glaze of the present invention will be described with reference to Fig. 1. Fig. 1(a) is a perspective view of an example of the heat-resistant ceramics of the present invention, and Fig. 1(b) is an enlarged cross-sectional view of the bottom in the vertical direction. Note that the figure is a schematic view and does not correspond to the actual dimensional ratio. As shown in FIG. 1(a), the heat-resistant ceramic 1 is a shallow pot (handles and the like are not shown). As shown in FIG. 1(b), the heat-resistant ceramic 1 has a glaze layer 3 on the surface of the base 2. The glaze layer 3 is formed as a glass-like layer by applying (glazing) the glaze of the present invention to a molded body of heat-resistant clay raw material that becomes the base 2, and then heating and firing the body at a temperature of, for example, 900°C or higher. Since the glaze layer 3 has excellent heat resistance as described below, the heat-resistant ceramic 1 is unlikely to crack or peel off during heating and cooling in direct fire cooking, etc. In FIG. 1, the heat-resistant ceramic 1 has the glaze layer 3 only on the upper surface of the base 2, but the glaze layer 3 may also be formed on the lower surface of the base 2.

[0025] The glaze of the present invention contains β-spodumene in an amount of 20 to 80 mass% based on the total solid content of the glaze. Here, β-spodumene means a tetragonal lithium-based aluminosilicate represented by the composition Li2O·Al2O3·4SiO2. β-spodumene is obtained, for example, by firing (overfiring) lithium ores such as naturally occurring petalite and α-spodumene at a temperature of 900°C or higher, causing an irreversible transition of the crystal structure from monoclinic to tetragonal.

[0026] The glaze of the present invention contains 20 to 80 mass% of β-spodumene with a stabilized crystal structure relative to the total solid content of the glaze, and therefore is less susceptible to the effects of changes in the crystal structure due to firing temperature and time, compared to the glaze containing lithium ore. For example, when a glaze containing α-spodumene and a glaze containing β-spodumene each contain the same amount of spodumene, the glaze containing α-spodumene changes its thermal expansion coefficient (linear expansion coefficient) as the crystal structure of α-spodumene changes depending on the firing conditions. On the other hand, the glaze containing β-spodumene does not change its crystal structure even if the firing conditions change, so its thermal expansion coefficient remains low. Therefore, when using a glaze containing α-spodumene to manufacture ceramics and the like, it is necessary to strictly control the firing conditions in order to manufacture products of a certain quality. In contrast, when producing ceramics and other products using glazes containing β-spodumene, the impact of differences in firing conditions on quality is relatively small (there is a wide margin for firing conditions), and it is thought that this contributes to improving product yields.

[0027] β-spodumene has a lower thermal expansion coefficient than α-spodumene, so that it can reduce the thermal expansion coefficient of the glaze layer after firing, and is suitable as a raw material for glazes that require heat resistance (heat-resistant glazes). In recent years, an increasing number of countries have banned the export of raw ores that have not been processed to a certain extent (for example, fired or refined), and there is a concern that it will become difficult to obtain unprocessed ores such as petalite and α-spodumene in the future. Therefore, from the viewpoint of stable raw material security, it is important to use relatively easily available raw materials as raw materials for glazes and ceramics. β-spodumene can be obtained, for example, by overfiring α-spodumene, and is a processed material that is relatively easily available, making it preferable.

[0028] The glaze of the present invention preferably contains 25 to 75 mass% of β-spodumene, more preferably 30 to 70 mass%, and even more preferably 40 to 70 mass% of β-spodumene, based on the total solid content of the glaze. When the content of β-spodumene is 25 mass% or more, the thermal expansion coefficient of the glaze layer can be reduced and transparency can be easily ensured. In addition, when the content of β-spodumene is 75 mass% or less, raw material costs can be easily reduced.

[0029] The glaze of the present invention preferably contains at least one selected from clay (e.g., frog's eye clay, wood-bush clay, kaolinite, dickite, nacrite, halloysite, kaolin such as New Zealand kaolin, Korean kaolin, and Hadong kaolin), dolomite, lime (e.g., rat lime, white lime, etc.), feldspar, phallospar, chamotte, talc, magnesite, alumina, barium compounds, strontium compounds, petalite, cordierite, fused silica, and zinc oxide (zinc oxide) in an amount of 10 to 80 mass% based on the total solid content of the glaze. These additives can adjust the melting temperature of the glaze during firing or increase the adhesion between the glaze layer and the base material (undercoat) after firing, thereby suppressing peeling of the glaze layer. These additives may be used alone or in combination of two or more. When two or more kinds of additives are used in combination, each kind of additive is preferably contained in an amount of 5 to 25 mass % and more preferably 10 to 15 mass % based on the total amount of solids in the glaze.

[0030] The glaze of the present invention preferably contains 20 to 75 mass % of additives based on the total solid content of the glaze, more preferably 30 to 70 mass %, and even more preferably 40 to 70 mass %. When the content of additives is 20 mass % or more, peeling of the glaze layer is easily suppressed. Also, when the content of additives is 75 mass % or less, the thermal expansion coefficient of the glaze layer is easily reduced.

[0031] The glaze of the present invention preferably contains clay and dolomite as additives. In this case, dolomite acts as a melting agent (a material that promotes melting) to facilitate melting of raw materials such as β-spodumene during firing, while clay contributes to the formation of a bond between the glaze layer and the base. This makes the glaze layer more excellent in heat resistance and transparency. When clay and dolomite are contained as additives, the mass ratio of the additives is preferably (clay:dolomite)=(2:1) to (1:3).

[0032] From the viewpoint of promoting melting during firing, the glaze of the present invention preferably contains zinc oxide as a melting agent, and more preferably further contains lime. The melting agent promotes melting of the raw materials during firing, thereby making the film quality of the glaze layer uniform and contributing to improving the mechanical strength, and also reduces particulate components that scatter light in the glaze layer, contributing to improving transparency.

[0033] The glaze of the present invention contains clay and dolomite in an amount of, for example, 10 to 50% by mass based on the total solid content of the glaze. Furthermore, it is more preferable that the glaze of the present invention contains 50 to 80% by mass of β-spodumene based on the total solid content of the glaze, and 10 to 50% by mass of clay and dolomite based on the total solid content of the glaze. In this case, the thermal expansion coefficient of the glaze layer is further reduced, and the adhesion to the base material is also excellent, so that the heat resistance is further excellent. Furthermore, it is more preferable that the glaze of the present invention contains 50 to 80% by mass of β-spodumene based on the total solid content of the glaze, and 10 to 50% by mass of clay, dolomite, and zinc oxide based on the total solid content of the glaze.

[0034] When applying the glaze, it is preferable to add a predetermined amount of water and a paste to the above-mentioned various powdered solid raw materials to prepare a slurry. Examples of the paste that can be used include synthetic paste, dextrin, and gum arabic. The amounts of water and paste can be appropriately adjusted so that the viscosity of the slurry glaze exhibits an appropriate level of fluidity.

[0035] The substrate on which the glaze layer is formed will be described. The substrate may be a ceramic base, metal, ceramic (e.g., alumina), carbon, glass, rock, or resin. The thermal expansion coefficient of the glaze layer of the glaze of the present invention can be adjusted by adjusting the content of β-spodumene. Therefore, by reducing the difference in thermal expansion coefficient between the substrate and the glaze layer depending on the type of substrate, a protective layer or decorative layer with excellent adhesion to various substrates can be formed. For example, when the substrate has a relatively large thermal expansion coefficient (e.g., a thermal expansion coefficient of 10×10 -6 In the case of metals and resins with thermal expansion coefficients larger than 10×10, the content of β-spodumene can be made relatively small to approach the thermal expansion coefficient of the base material. -6 In the case of heat-resistant porcelain and ceramics, the β-spodumene content can be made relatively high to approach the thermal expansion coefficient of the base material.

[0036] The glaze of the present invention is easy to form a bond at the interface with ceramics, glass, rock, etc., and is easy to make the most of the appearance of the substrate by allowing the texture and color of the substrate surface to pass through appropriately. Therefore, the substrate is preferably a ceramic base, ceramics, glass, rock, etc.

[0037] When manufacturing heat-resistant ceramic cookware and tableware such as clay pots, appearance (color and texture) is an important quality factor. For example, in the case of Mishima clay pots, a heat-resistant transparent glaze layer with a low thermal expansion coefficient and a specific color is formed on a base made of clay made from heat-resistant clay raw materials, resulting in a gray color with a unique texture that stimulates consumer purchasing desire. Therefore, from the viewpoint of achieving both heat resistance and appearance without relying on petalite, it is particularly preferable that the glaze layer formed by the glaze of the present invention is provided on a heat-resistant ceramic base.

[0038] In addition, the glaze of the present invention becomes a protective layer with high surface hardness after firing, so it can be used to form a glaze layer on a substrate made of carbon or resin, which has a relatively low surface hardness, from the viewpoint of surface protection. In this case, it is more preferable to add a silane coupling agent that forms a bond between an organic material and an inorganic material to improve adhesion.

[0039] When petalite is used as a raw material to provide heat resistance as in the past, the firing temperature needs to be high to change it to β-spodumene. In contrast, when β-spodumene is used as a raw material, it is not necessary to change the crystal system, and heat resistance is exhibited even at a relatively low firing temperature, making it possible to lower the firing temperature. As a result, the glaze of the present invention can be applied to substrates made of materials that deform or change in quality at high temperatures, and can be formed on the surfaces of substrates on which it was previously difficult to form a heat-resistant glaze layer (e.g., low-temperature glass substrates, resin substrates, etc.).

[0040] Next, the heat-resistant ceramic of the present invention will be described below. The heat-resistant ceramic of the present invention has a ceramic base and a glaze layer formed on a part or all of the base. The base is a fired body of a heat-resistant clay raw material whose main components are clay and a low-expansion material containing molten quartz, and the glaze layer is a glassy layer formed by firing a glaze containing β-spodumene.

[0041] The heat-resistant ceramic of the present invention has the above-mentioned structure, and the thermal expansion coefficients of both the base and glaze layer of the heat-resistant ceramic can be reduced, and the difference between these values ​​can be freely adjusted to be small. This makes it possible to suppress cracks and peeling of the glaze layer when the heat-resistant ceramic is heated or cooled.

[0042] Examples of the clay used in the present invention include clays containing kaolin minerals (kaolins such as frogeye clay, kibushi clay, kaolinite, dickite, nacrite, halloysite, New Zealand kaolin, Korean kaolin, and Hadong kaolin), sericite, and the like.

[0043] The low expansion material may contain at least one selected from petalite, cordierite, α-spodumene, β-spodumene, β-eucryptite (Li2O·Al2O3·2SiO2), lithium-based minerals such as mullite (3Al2O3·2SiO2), zircon (ZrO2·SiO2), borosilicate glass (Na2O-B2O3-SiO2), etc., in addition to fused quartz. As a result, at least a part of the petalite in the conventional heat-resistant clay raw material is replaced with other low expansion materials including fused quartz, so that the petalite content in the heat-resistant clay raw material can be reduced. From the viewpoint of stable raw material security, it is preferable that the low expansion material does not contain lithium-based minerals or their processed products, and it is particularly preferable that it is only fused quartz.

[0044] The total content of the main components, clay and low expansion material, in the entire heat-resistant clay raw material is 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The content of each component in the entire heat-resistant clay raw material is, for example, 20% by mass or more and less than 70% by mass of fused quartz, 30% by mass or more and less than 80% by mass of clay, and several mass % to about 40% by mass of additives.

[0045] The clay is preferably 10 to 70 parts by mass in a total of 100 parts by mass of the clay and the low expansion material, which are the main components of the heat-resistant clay raw material. The proportion of the clay in the total of 100 parts by mass of the clay and the low expansion material, which are the main components, is preferably 30 to 70 parts by mass, more preferably 40 to 60 parts by mass. If the clay in the main component is less than 10 parts by mass, it may be difficult to mold it into a product shape, and if it exceeds 70 parts by mass, there is a risk that sufficient heat resistance cannot be obtained due to the high thermal expansion coefficient of the clay. When the clay in the main component is 40 to 60 parts by mass, the low expansion material, which is the remainder excluding the clay, is 40 to 60 parts by mass, and both moldability and low thermal expansion of the base material are excellent.

[0046] The thermal expansion coefficient of the glaze layer and base of heat-resistant ceramics from room temperature to 700°C is 0.1 to 5.0 × 10 -6 / K, more preferably 0.1 to 3.0 × 10 -6 / K, and more preferably 0.1 to 2.0 × 10 -6 / K. The difference in thermal expansion coefficient between the glaze layer and the base is -1.0 to 1.0 × 10 -6 / K, more preferably from -0.5 to 0.5 × 10 -6 / K. The difference in thermal expansion coefficient is ±1.0×10 -6 By setting the content within the range of 1 / K, good heat resistance can be obtained.

[0047] The heat-resistant ceramics of the present invention are produced by the following steps: (A) molding a china clay made from a heat-resistant clay raw material; (B) applying a glaze to the surface of the molded china clay body; and (C) firing it in a firing furnace and then cooling it in the furnace.

[0048] In the molding process (A), the minerals that make up the heat-resistant clay raw material are mixed in predetermined amounts. This mixing can be done using either the well-known wet or dry method. When mixing using the wet method, the mixture (sludge) is dehydrated and turned into a cake to produce the clay for molding. The material is molded after being kneaded. Methods that can be used include roller machine molding, press molding, pressure casting (compression) molding, slip molding, water trowel molding, hand mixing, and tatara molding, and the material is molded into the desired shape, such as a clay pot or dish. The heat-resistant clay raw material can be either red clay or white clay.

[0049] In the glazing step (B), the surface of the molded body formed in the step (A) is glazed. The glaze can be any of the above-mentioned glazes, which are applied after being made into a slurry. The method of glazing can be dipping, spraying, or the like, and the glaze is applied to the surface of the molded body.

[0050] In the firing step (C), the molded body obtained above is placed in a gas kiln or an electric kiln and fired at a temperature of, for example, 1000 to 1400°C. The firing time is about 1 to 24 hours. By firing at 1000°C or higher, the β-spodumene in the glaze can be melted to make the glaze layer transparent. Also, by firing at 1400°C or lower, the fused quartz in the ceramic can be sintered without being completely melted. This allows production of ceramics that maintain the performance of low-expansion crystals such as petalite. The firing temperature is preferably 1200 to 1300°C from the viewpoint of both heat resistance and transparency. The molded body may be fired by heating under pressure. Here, there are two firing conditions: oxidation firing and reduction firing, and either condition may be used. Oxidation firing is a method in which a large amount of air (oxygen) is supplied into the kiln and firing is performed under conditions in which sufficient oxygen is present. Reduction firing is a method of firing in which wood, coal, gas, etc. are put into a kiln in such an amount that incomplete combustion occurs.

[0051] The heat-resistant ceramic of the present invention can be manufactured so as to satisfy the standard of a temperature difference of 350° C. or more, specified in JIS S 2400 based on the Industrial Standardization Act for factories certified by the Ministry of Economy, Trade and Industry, when exposed to direct flame. [Industrial Applicability]

[0052] The glaze of the present invention can form a glaze layer having excellent heat resistance and transparency by using β-spodumene, which is stably available, and can be widely used for forming surface protective layers and decorative layers of various substrates, and can be particularly used for heat-resistant ceramics such as direct-fire cookers, fireproof bricks, and fireproof tiles.

[0053] Petalite, which was the main raw material for heat-resistant ceramics, has become difficult to import into Japan due to the development of processing technology for lithium-ion batteries. This technological development is also necessary to protect Japan's heat-resistant ceramics industry. As petalite is a natural raw material that has not been processed, there is a possibility that it will be banned under the guidelines of the Republic of Zimbabwe and the People's Republic of China. It has also become increasingly rare domestically, and is no longer affordable enough to be consumed in large quantities. There is a possibility that domestic technology will develop and the industry will be protected if Japanese companies take the lead in developing new raw materials. [Explanation of symbols]

[0054] 1. Heat-resistant ceramics 2. Base 3 Glaze layer

Claims

1. A glaze containing 20 to 80 mass % of β-spodumene based on the total solid content of the glaze.

2. The glaze according to claim 1, characterized in that it contains at least one additive selected from the group consisting of clay, dolomite, lime, feldspar, pyrophyllite, chamotte, talc, magnesite, alumina, barium compounds, strontium compounds, petalite, cordierite, fused silica, and zinc oxide in an amount of 10 to 80 mass % based on the total solid content of the glaze.

3. 2. The glaze according to claim 1, further comprising as additives clay and dolomite.

4. The glaze contains 50 to 80 mass% of the β-spodumene based on the total solid content of the glaze, 3. The glaze according to claim 1, wherein the additives include clay and dolomite in an amount of 10 to 50 mass % based on the total solid content of the glaze.

5. A heat-resistant ceramic having a ceramic base and a glaze layer formed on a part or all of the base, The base material is a fired body of a heat-resistant clay raw material mainly composed of clay and a low-expansion material, the low expansion material includes fused silica; The heat-resistant ceramic ware is characterized in that the glaze used to form the glaze layer contains β-spodumene.

6. The heat-resistant ceramic according to claim 5, characterized in that, in a total of 100 parts by mass of the clay, which is the main component of the heat-resistant clay raw material, and the low-expansion material, the clay is 10 to 70 parts by mass, and the remainder is the low-expansion material.

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