High heat-resistant clay material and ceramic heat-resistant tableware made from said high heat-resistant clay material

Abstract

It is unclear whether conventional cordierite-based ceramic heat-resistant tableware has the thermal shock resistance required for "ceramic heat-resistant tableware for use over an open flame (high heat resistance)." [Solution] Ceramic raw materials are blended and prepared within the composition ranges expressed in the Segel formula as follows: R2O (R2O = K2O + Na2O) = 0.0337-0.0357, CaO = 0.0217-0.0312, MgO = 0.9167-0.8883, Li2O = 0.0279-0.0449, Al2O3 = 0.7793-0.7807, B2O3 = 0.0173-0.0276, SiO2 = 2.1412-2.1640, and the numerical value of each component is set by converting the sum of the molar ratios of R2O, CaO, MgO, and Li2O to "1." This makes it possible to provide a raw material for cordierite-based ceramic heat-resistant tableware that has appropriate "thermal shock strength" and appropriate "coefficient of thermal expansion."

Description

[Technical Field]

[0001] The present invention relates to a highly heat-resistant clay material and ceramic heat-resistant tableware made using the highly heat-resistant clay material. [Background technology]

[0002] Traditionally, the most well-known ceramic heat-resistant tableware, especially earthenware pots for use over an open flame, is Banko ware, produced mainly in Yokkaichi City, Mie Prefecture. This earthenware pot (hereafter referred to as petalite earthenware pot) is made primarily from petalite (Li2O·Al2O3·8SiO2), a lithia-based (Li2O-Al2O3-SiO2-based) pot with low expansion and high thermal shock resistance. Like regular ceramics, earthenware pots are made through the same processes as regular porcelain ware: mixing the raw materials, dehydrating, kneading, molding, drying, bisque firing, glazing, firing, and finishing. The basic raw material mix for the base is approximately 40% petalite, 45% kibushi clay and gairome clay, and 15% kaolin or roseki.

[0003] Petalite, the main raw material, has been imported steadily from Zimbabwe until now, but due to various circumstances, direct imports are no longer possible. As a result, Banko ware manufacturers are being forced to reduce production of petalite earthenware pots and increase prices due to the shortage of petalite supply and the high price.

[0004] There are also earthenware pots (hereinafter referred to as cordierite earthenware pots) made primarily from cordierite (2MgO·2Al2O3·5SiO2), which has an extremely low coefficient of thermal expansion, excellent thermal shock resistance, and is relatively available (see, for example, Patent Document 1).

[0005] Specifically, the direct-fire porcelain base is made by adding 1 to 10 parts by weight of a flux to 100 parts by weight of the main components, which are 5 to 20% by weight of talc, 5 to 20% by weight of feldspar, 30 to 40% by weight of clay minerals, and the remainder cordierite. The talc contains MgO that converts Al2O3 and SiO2 supplied from the clay minerals and feldspar into cordierite during firing, and the feldspar melts during firing to bond the cordierite particles together. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 63-147852 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the above-mentioned prior art, the thermal shock test involves holding the sample in an incubator preheated to 304±3°C for one hour, then immediately placing it in a water bath at 24±3°C.Once the sample has cooled to the water temperature, it is removed and the presence or absence of defects in the base material is examined.However, since the heating temperature in the incubator is too low to test "ceramic heat-resistant tableware for direct flame use (high heat resistance)," there were issues that needed to be resolved, such as it being unclear whether this cordierite-based base material for direct flame use has the thermal shock strength required for "ceramic heat-resistant tableware for direct flame use (high heat resistance)." [Means for solving the problem]

[0008] In view of the problem based on the above-mentioned prior art that it is unclear whether or not a ceramic heat-resistant tableware for use on an open flame (high heat resistance) has thermal shock resistance, the present invention provides a ceramic heat-resistant tableware having the following characteristics in the Segel formula: R2O (R2O = K2O + Na2O) = 0.0337 to 0.0357, CaO = 0.0217 to 0.0312, MgO = 0.9167 to 0.8883, Li2O = 0.0279 to 0.0449, Al2O3 = 0.7793 to 0.7807, B2O3 = 0.0173 to 0.0276, SiO2 = By blending and preparing ceramic raw materials within the composition range expressed as 2.1412 to 2.1640, and by setting the numerical value of each component by converting the sum of the molar ratios of R2O, CaO, MgO, and Li2O to "1," it is possible to provide raw materials for cordierite-based, high-heat-resistant ceramics for direct fire use that have "thermal shock strength" and an appropriate "coefficient of thermal expansion," thereby resolving the above-mentioned problems. [Effects of the Invention]

[0009] In short, in this invention, the high heat-resistant clay material is as set forth in claim 1 of the claims, and therefore ceramic heat-resistant tableware made using this high heat-resistant clay material is a clay pot with performance that could not be achieved by conventional cordierite earthenware pots, that is, it can withstand thermal shocks of 350°C or more in the thermal shock test of ``JIS S2400 Ceramic Heat-Resistant Tableware'' and can be used as cordierite-based ceramic heat-resistant tableware for direct fire use with an appropriate thermal expansion coefficient, and can also be used as other ceramic heat-resistant tableware that is not ``for direct fire use (high heat resistance)'', such as oven dishes such as gratin dishes, and microwave dishes, and has extremely great practical effects. DETAILED DESCRIPTION OF THE INVENTION

[0010] The high heat-resistant clay material according to the present invention is for cordierite-based ceramic heat-resistant tableware, and this high heat-resistant clay material is adjusted to have a composition expressed by the Segel formula as follows: (1)R2O(R2O=K2O+Na2O)=0.0337~0.0357 (2) CaO = 0.0217 to 0.0312 (3) MgO = 0.9167 to 0.8883 (4) Li2O = 0.0279 to 0.0449 (5) Al2O3 = 0.7793 to 0.7807 (6) B2O3 = 0.0173 to 0.0276 (7) SiO2 = 2.1412 to 2.1640

[0011] Each of the values ​​(1) to (7) above is a molar ratio, and the sum of the molar ratios of the above (1) to (4) contained in the high heat-resistant clay raw material is converted to "1", and the molar ratios of the above (1) to (4) within that "1" are expressed as converted values. Each of the values ​​(5) to (7) above is also the content of each component in the high heat-resistant clay raw material, expressed as a converted value of the molar ratio relative to (1) + (2) + (3) + (4) = 1.

[0012] The high heat-resistant clay raw material may be prepared by appropriately blending ceramic raw materials containing at least one of the above (1) to (7), such as cordierite, mullite, chamotte, magnesite, dolomite, talc, lime, wollastonite, alumina, silica, lithium carbonate, petalite, spodumene, eucryptite, feldspar, ulexite, colemanite, frit, kaolins, sericite, clays, rosestone, pottery stone, bentonite, and colorants, so as to fall within the range of the composition expressed by the Segel formula.

[0013] "Ceramic heat-resistant tableware" in "JIS S2400" specifies ceramic heat-resistant tableware for use on an open flame or baking pan, and is divided into four types: "For open flame (high heat resistance)", "For open flame", "For baking pan (300°C or less)", and "For baking pan (200°C or less)". In this case, the item falls into the "For open flame (high heat resistance)" category, and its "usage classification" is "for use in direct contact with a flame for cooking, etc., and must be able to withstand rapid heating and cooling", and its "thermal shock strength (°C)" must be "350 or more". [Thermal shock test] The sample is kept for one hour in a preheated incubator to achieve the test temperature difference (temperature difference between the heating temperature and the water) appropriate for the sample type, and then immediately placed in a water bath at 24±3°C without overlapping. After the sample has cooled to the water temperature, it is removed and the "thermal shock strength" is judged based on the presence or absence of defects in the base material. However, the water tank must be large enough to cool all the heated samples, with a depth of at least 15 mm from the water surface to the samples, and the amount of water must be set so that the water temperature does not rise above 29°C even when the samples are cooled. Since the present invention relates to ceramic heat-resistant tableware and its raw materials for "direct flame use (high heat resistance)," the test temperature difference is set to 350 to 360°C. [Measurement of thermal expansion coefficient] A 20mm x 5mm sample is measured using a thermal dilatometer under the following conditions: 25°C to 700°C Heating rate: 10°C / min

[0014] This time, eight types of raw materials A to H shown in Table 1 below were prepared. In addition to the above (1) to (7), Fe2O3 and TiO2 contained in raw materials A to H are contained in the ceramic raw materials listed in paragraph

[0012] , and do not affect the "thermal shock strength" or "thermal expansion coefficient." However, if the molar ratio is high, it may affect the "thermal expansion coefficient." Therefore, it is preferable to set the molar ratio to the extent shown in Table 1 below.

[0015] [Table 1]

[0016] The above raw materials A to H were formed into approximately 15 cm dishes on an electric potter's wheel and fired in an electric furnace under the following [Condition 1] to produce samples A1 to H1, and fired under the following [Condition 2] to produce samples A2 to H2.These samples A1 to H1 and A2 to H2 were subjected to thermal shock tests and thermal expansion coefficient measurements, and the results and evaluations are shown in Tables 2 and 3 below. In the following Tables 2 and 3, the "thermal expansion coefficient" column shows the result of the thermal expansion coefficient measurement, "2.70 (×10 -6 / °C) or less is marked as "○", and anything else is marked as "×". In the "thermal shock strength" column, if the result of the thermal shock test was "cracked", it is marked as "×", and if the result was "no cracked", it is marked as "○". In the evaluation column, if the results of both the thermal shock strength and thermal expansion coefficient measurements were "○", it is marked as "○", and anything else is marked as "×". [Condition 1] Maximum temperature: 1180°C Baking time: 8 hours Heating rate: 2.5°C / min [Condition 2] Maximum temperature: 1210°C Baking time: 8 hours Heating rate: 2.5°C / min

[0017] [Table 2]

[0018] [Table 3]

[0019] Samples A1, B1, and C1 had a thermal expansion coefficient of "×" and a thermal shock strength of "×", samples D1, E1, and F1 had a thermal expansion coefficient of "○" and a thermal shock strength of "○", and samples G1 and H1 had a thermal expansion coefficient of "○" and a thermal shock strength of "×". The results for samples G1 and H1 show that not only the thermal expansion coefficient but also densification is a major factor in cracking, and it is presumed that excessive densification caused the base material to become dense, resulting in cracking. Therefore, samples D1, E1, and F1 were evaluated as "good."

[0020] Samples A2, B2, and C2 had a thermal expansion coefficient of "x" and a thermal shock strength of "x", samples D2, E2, and F2 had a thermal expansion coefficient of "good" and a thermal shock strength of "good", and samples G2 and H2 had a thermal expansion coefficient of "x" and a thermal shock strength of "x". The results for samples G1 and H1 show that the thermal expansion coefficient is relatively low, but it is presumed that the firing temperature was too high and the material was fired too hard, causing the material to become dense and crack. Therefore, samples D2, E2, and F2 were evaluated as "good."

[0021] In other words, since the samples produced from raw materials D, E, and F were evaluated as "good," the raw materials that are evaluated as "good" are those expressed by the above Segel formula.

[0022] Furthermore, the ceramic heat-resistant tableware of the present invention can be used for "direct flame use (high heat resistance)" as specified in "JIS S2400 Ceramic Heat-Resistant Tableware," and there is no problem with using it for "direct flame use," "baking flame use (300°C or less)," or "baking flame use (200°C or less)," which have weaker thermal shock resistance than "direct flame use (high heat resistance)," specifically oven dishes such as gratin dishes and microwave dishes.

Claims

1. In the Segel system, R 2 O (R) 2 O=K 2 O+Na 2 O) = 0.0337 ~ 0.0357 CaO=0.0217~0.0312, MgO=0.9167~0.8883, Li 2 O=0.0279~0.0449、 Al 2 O 3 =0.7793~0.7807、 B 2 O 3 =0.0173~0.0276、 Yes 2 = 2.1412~2.1640, The ceramic raw materials are blended and prepared within the composition range expressed as R 2 O, CaO, MgO and Li 2 A highly heat-resistant clay raw material characterized in that the sum of the molar ratios of O is converted to "1".

2. 2. A ceramic heat-resistant tableware produced by firing the highly heat-resistant clay material according to claim 1.

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