JP2012205868A - Earthen pot container and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an earthen pot container that has no metal heating part, is all-in-one design type and excellent in handling property, and can use the induction heating (IH heating); and to provide a method for manufacturing the earthen pot container.SOLUTION: The earthen pot container is flat at a bottom, comprises the electrical conductive ceramics and/or the ceramics centering on the silica alumina that contains the metal and makes the surface a ceramics at least at the bottom part, and can be heated by the induction heating. There is also provided a method for manufacturing the earthen pot container.

Description

The present invention relates to an earthenware pot that can be used in an induction heating method (IH method) and a method for producing the same.

At present, an induction heating (IH) type heat source and a cooking appliance corresponding to the heat source are widely used as an all-electric system for home use. However, although this method of heating is very efficient, due to electromagnetic induction, the target was limited to products made of metal, ferroelectrics, and ferromagnetics. In other words, in the case of a high-frequency induction heating type heating device called an ordinary so-called IH heater, induction heating is performed by electromagnetic waves having a frequency of 10 MHz to 100 MHz, and this heating is effective for heating a metal. This is because induction heating is not caused because it does not have conductivity or magnetism.

On the other hand, recently, there are ceramic cooking utensils with good heat retention, such as traditional earthenware pots, which are essential items for so-called pot dishes. Crystallized glass called Pyroceram or similar ceramics is also widely used, and there is a growing demand for using them.

Several heating techniques have been proposed to use these so-called ceramic pots. These are shown below, but all use metal as a heating source. That is, Japanese Patent Application Laid-Open Nos. 2005-334351 and 2006-116295 have proposed metal plates and metal foils attached to the bottom of a clay pot. As a result, the earthenware pot can be heated for the intended purpose, but the earthenware pot itself is not always handled properly, and when used with a normal heat source, there are cases where problems such as corrosion of metal parts due to flame occur. Furthermore, since metal and ceramics generally have poor consistency, there has been a problem that they may be peeled off depending on handling.

In Japanese Patent Laid-Open No. 10-137130, a net or a plate, which is a heat generating portion, is placed inside a pan, and heat is generated inside the pan during use. This leaves a problem in handling as above.
Japanese Patent Application Laid-Open No. 2005-296761 discloses that a metal sprayed layer is provided on the inner bottom surface of a pan to generate heat. Furthermore, Japanese Patent Application Laid-Open No. 2006-014761 discloses that a sprayed layer of 100 to 300 microns is provided on the bottom surface of a container by a low temperature spraying method, and it is proposed to heat the portion by induction. . In addition to the same problems as described above, the sprayed layer has a problem that its surface is active due to its characteristics and it is easily corroded by an acid or the like.

Furthermore, in Japanese Patent Application Laid-Open No. 2006-061298, the container portion is made of metal to provide the same function, and a heat generating portion is provided at the bottom of the metal pan, and a function similar to that of a bowl is provided by applying a glaze to the metal pan. ing. However, it is clear that so-called clay pots are different in terms of heat retention and others.
As shown in these figures, there are earthenware pots that can be used for induction heating (IH), but the part that becomes the heat generating part is not the earthenware pot body or the ceramic part, but is made of metal. Even though these are fixed as described above, there is a metal-ceramic bond that originally has no good affinity, so the handling becomes complicated and there is a difference in the thermal expansion between the earthenware pot part and the heating part, etc. There was a possibility that peeling occurred in the long term, and it was not always satisfactory.

JP-A-2005-296761 JP 2006-116295 A JP 10-137130 A JP-A-2005-296761 JP 2006-014761 A JP 2006-061298 A

An object of the present invention is to solve the above problems and to provide a clay pot-like container having no metal heat generating portion, excellent in handleability and capable of induction heating, and a method for producing the same. .

The present invention is a clay pot-like container that has a flat bottom and is made of conductive ceramics and / or ceramics mainly composed of silica / alumina containing at least a metal whose surface is ceramicized, which can be heated by induction heating. In addition, an ordinary earthenware pot is mainly composed of an alumina-silica composite oxide, and has a good affinity with it and heat generation by induction occurs efficiently. By increasing the affinity with the alumina-silica composite oxide, which is the main component of the earthenware pot, with the surface as an oxide, these conductive oxides and metals are placed in the ceramics, in particular with the bottom surface flat. It became possible to heat efficiently by supporting it at a high concentration.

This will be described in detail below.
In other words, conventional clay pots are molded with moisture by adding a ceramic material such as feldspar to a silica-alumina-based material mainly composed of clay. After drying this molding, it is heated and fired at about 1000 to 1300 ° C. to make an unglazed earthenware pot. This is made into a clay pot-like container having a coating that is vitrified by applying a glaze to the product and further vitrified by vitrification. The role of glaze is inherently porous, so that unglazed porcelain may have liquid permeability, and since it is not necessarily the target color tone, it has the effect of stopping the eye and improving the color and appearance. Yes. In the present invention, the ceramic forming the earthenware container has an affinity for the ceramic, has a large dielectric effect, is excellent in electrical conductivity, and has a thermal expansion coefficient close to that of a ceramic material. It has succeeded in including the above-mentioned metallic material so that it can be stably held as a unit. Further, the induced current is efficiently transmitted by flattening the bottom surface.

In other words, as a substance that generates heat by induction heating, a conductive material or a ferromagnetic material can be raised, but a ferroelectric material that can be expected to have a dielectric effect in a high frequency electromagnetic field is also conceivable.
In general, ferroelectrics are often part of ceramic materials such as metal oxides, but in addition to these properties, the thermal expansion coefficient is not significantly different from ceramic materials. It arrange | positions so that it may be concentrated and contained in the bottom part, and it was made to fulfill this invention. In order to further improve efficiency, the bottom of the pan-like body is flattened to improve the adhesion with the dielectric power source.

Here, as the dielectric material, a titanium oxide compound, particularly TiO, which has a very high affinity with the silica / alumina ceramics, which is the basic material of the pot-shaped container, has a very large electrical conductivity, which is similar to that of a metal, and is very large in ordinary households. Efficient heat generation has been observed under induction heating (IH) conditions. It was also found that tin oxide (SnO 2) having high conductivity is also very effective. Furthermore, it has been found that metal oxides having a spinel structure, such as so-called ferrite, such as ferrites such as nickel ferrite and cobalt ferrite are very effective. Furthermore, perovskite oxides such as barium titanate are also effective from the viewpoint of dielectric properties.

On the other hand, there is no argument that it would be more effective if a metal could be included in the pan-like body, but in that case, the metal surface was previously oxidized or the like because of the affinity between the metal and silica / alumina ceramics. It is made into ceramics and mixed with silica-alumina ceramics in this bulk. In particular, when nickel / iron alloy is used here, nickel ferrite is formed on the surface, which is very effective. Although it can be used when the metal is iron, it is particularly desirable to be magnetic iron oxide (Fe 3 O 4) having a spinel structure, which is a so-called black skin whose surface is a dense oxide. Even if it is a metal, when an oxide having a certain thickness is formed on the surface, the metal with poor affinity between the surface oxide and the metal substrate may cause peeling due to the surface oxide. It is necessary to be careful. It is also effective to cover the surface with titanium oxide or the like having good affinity for both in advance.

These substances to be heating elements (hereinafter referred to as exothermic substances) are added as particles. The size of the particles is not particularly specified, but usually 2 mm or less is preferable from the surface unevenness of the ceramic unglazed surface, and preferably 0.5 mm to 1 mm. However, when using a metal, care should be taken because if the metal is oxidized from the surface, the whole may become an oxide in the case of fine particles. In such a case, it is desirable to perform a pretreatment such as coating the surface with an oxide in advance. In the case of mixing with a bulk material, there is a possibility that the amount may be reduced, and a problem may occur in the burning. However, in mud casting, there is consistency with the ceramic material, and 0.1 to 0.5 mm is appropriate.

It is desirable that the content of the exothermic substance is concentrated in the bottom dielectric part. It is desirable that the bottom part of the pan-like body is flat, and 50% or more of the bottom constituent material is a heating element in the flat part. Since there is almost no heat generation at the side wall, it can be made less or not at all. In this manufacturing method, a predetermined amount of the exothermic material is added to a bulk material raw material that is kneaded with clay minerals, porcelain clay, feldspar, etc., which are ordinary ceramic raw materials. This is further kneaded to be uniform and molded. At this time, a kneaded material having a larger exothermic material is used at the bottom.

On the other hand, it can be shaped while changing the content ratio of the exothermic substance in the pan-like container. That is, the raw material of alumina / silica ceramics, which is the raw material, and the exothermic substance are stirred together with the dispersion material to form a mud (slip), which is shaped by a so-called mud casting (slip casting) method. At this time, it is necessary to keep the exothermic material to 0.5 mm or less. If the particles are made larger, the falling speed to the bottom is greater than the mud component, and the pyrogen concentration at the bottom may be too high. Therefore, it is desirable to adjust the particle size in consideration of the specific gravity difference between the exothermic substance and the raw material of alumina / silica ceramics.

In addition, in the case of the mud casting method, the wall thickness is generally the same including the bottom, so that the thickness can be made the same in advance, and then the mud having an increased amount of exothermic material can be added only to the bottom. In this case, a normal method may be used, but it may be molded once and then dried, and a mud containing a large amount of exothermic material is added only to the bottom and laminated inside the pan-like body. Even in such a case, it is necessary to add a certain amount of exothermic material to the bulk body from the beginning, thereby improving adhesion and preventing peeling and breakage due to thermal expansion.

Further, in the case of molding by a normal stamp type or the like, the exothermic substance amount in the material kneaded in advance is 50% or more at the bottom, and it is gradually reduced at other parts to correspond to the wall. By the way, it is possible to control the coefficient of thermal expansion and prevent damage due to the difference in thermal expansion even during heating or cleaning.

Molded by the mud casting method, and when the inner part of the inner surface is filled with excessive pyrogens, or when the kneaded material is added later, it is not dried in advance but is dried before it contains a lot of pyrogens. It is necessary to add mud and a kneaded body, re-dry, and then perform a baking treatment. As a result, the moisture in the mud added later is absorbed into the dried pan-like container more efficiently and integrated. Furthermore, as a result of the mutual diffusion at the contact portion, the component changes more continuously, thermal expansion and contraction occur continuously in the main body, and cracks and the like can be prevented during heating and cooling. The pan-like body, which contains the exothermic material at the bottom, thus produced is dried again, and after correcting the shape as necessary, it is baked by a normal baked process. The condition of the unglazed baking is not particularly specified, but 1000 ° C. to 1300 ° C. is appropriate when clay with a small amount of iron is used. In this way, the unglazed baking is performed, and after cooling, re-correction is performed as necessary, and then the glaze is applied. At this stage, normal glaze may be used.

In this way, an earthenware pot is made, but if it is used in a normal manner, the temperature of the earthenware pot is 100 ° C. or less (the temperature is 200-300 ° C. even in a portion directly exposed to fire, and the difference in coefficient of thermal expansion is noticeable. Cracks will not occur, but the temperature may rise to about 800 ° C if nothing is put in the pan on an open fire, so check the temperature etc. in consideration of that point. However, it is necessary to confirm that no cracks occur.

A clay pot-like container with a flat bottom and heat-generating substances concentrated on the bottom is integrated with the heating element.It looks the same as an ordinary clay pot, and can be heated directly by fire and generates heat mainly from the bottom. Since it contains a substance, the bottom is heated by induction heating, and has the same effect as a normal earthenware pan. Furthermore, unlike clay pots with a hot plate attached, handling becomes easy. Moreover, efficient heat generation is also performed by induction heating, and it can be used directly on the induction heating apparatus. In addition, in the case of a clay pot with a heating plate, it is often prohibited to use it from the equipment side with normal household induction heaters, but the mainland pot-shaped container is an integral type, so it can be used freely. ,No problem.

Hereinafter, the manufacturing method will be described. First, the manufacturing process by the mud casting (slip casting) method is shown. First, the so-called porcelain clay, which is a silica / alumina ceramic material that should be the bulk material of the pot, and so-called porcelain containing mainly feldspar, etc. is kneaded with excess water to make mud, and the heat generation is slightly larger than that of porcelain. A substance, such as nickel / iron alloy particles whose surface is oxidized, is added and stirred well, dispersed uniformly, and placed in a gypsum mold. Then, the water in the mud is absorbed by the gypsum, and these mud substances precipitate along the wall of the gypsum body. At this time, the slightly large heat generating material having a large specific gravity is precipitated by gravity so that the concentration is increased downward, that is, on the bottom side. As a result, a pan-like body is formed in which the ratio of the heat-generating substance is increased in the lower part. After a suitable time, the remaining mud is removed and dried to such an extent that the shape does not change, and the mold is removed and dried completely. This is heated and fired by controlling the firing temperature according to the silica / alumina ceramic raw material to make an unglazed baking, and further, coloring, glaze application and firing are performed to complete a pan-like body.
A schematic diagram of a cross-section of the earthenware pot manufactured in this way is shown in FIG. Here, 20 is an exothermic substance, and the initial particles are enlarged, so that the rate of precipitation downward is high, and it can be seen that the concentration increases as going downward.

In addition to the pan-like body, a heat generating material can be further added to the bottom. That is, a mud or a kneaded material composed mainly of a heat-generating substance and a silica / alumina ceramic raw material as a binder is added only to the bottom of the molded body. At this time, the amount of the exothermic substance is not particularly specified as long as it is 50% or more, but is usually 60 to 90% (mass). As a result, the thickness of the bottom increases, but heat can be generated more efficiently. By performing drying, baking, coloring, glaze application, and baking in the same manner as described above, a clay pot-like container that can optimally generate induction heating can be completed.
A schematic cross-sectional view of this is shown in FIG. Here, it can be seen that in addition to FIG. 100, the exothermic substance 21 is further added.

The process after drying is not particularly specified, but the shape after drying is adjusted, necessary corrections / corrections are performed, and firing is performed to make unbaked. The temperature of the unglazing may be determined depending on the bulk body to be used, and is usually 1000 to 1300 ° C. The heating and cooling are gradually performed over time. The unglazed product thus produced is corrected as necessary, and after the glaze is applied, finish firing is performed. The temperature for finish firing is the glaze temperature, which is 1000 ° C. or lower. This is an example of the mud casting method, but normal kneading molding may be used. However, as described above, it is necessary to change the component according to the site and change the component almost continuously to keep the thermal expansion distribution continuous.

Moreover, it can manufacture also by shape | molding a kneaded material instead of a mud casting method. In this case, two or more kinds of kneaded materials having different exothermic substances are prepared, and first, the bottom is molded with the most exothermic substance-containing kneaded material. Laminate and mold in order of increasing amount of kneaded material. Next, it is dried, corrected as necessary, and heated and baked to make unglazed. This is further re-corrected as necessary, and is colored, glazed and fired to make a finished earthenware container. A schematic cross-sectional view of the clay pot produced in this way is shown in FIG. As shown here, the amount of the exothermic material increases toward the bottom. Here, the one with the pyrogen content changed to 3 levels is used. The ratio of the amount of exothermic substance in the bulk having the bottom 31 is the largest, the ratio of the exothermic substance in the lower part 32 of the wall is intermediate, and the ratio of the exothermic substance in the upper part 33 of the wall is minimum.
By changing the quantity ratio stepwise in this way, the thermal expansion coefficient of the bulk body containing the exothermic material is changed stepwise, so that peeling due to the difference in thermal expansion does not occur even during heating.
Hereinafter, the present invention will be described by way of examples, but it goes without saying that the present invention is not limited thereto.

A commercially available Shigaraki porcelain clay (mainly kaolin and feldspar) was kneaded with water to form a slurry, and a nickel / iron (4/2) alloy whose surface with an average particle size of 100 μm was heated and oxidized was mixed.
The mixing ratio was porcelain 80: alloy 20 (mass ratio). After thoroughly mixing this, a neutral detergent was added as a surfactant, and water was added to make a mud. A two-piece gypsum earthenware mold was assembled, and a well-stirred mud was added to the mold. After standing for 15 minutes, the remaining mud was discharged and air-dried. After 30 minutes, the mold was removed and further dried for 3 days. Furthermore, a mud made of porcelain clay 20: alloy 80 (mass ratio) was prepared in the same manner, and poured into the inside of the dried earthen pot so that the thickness of the bottom became about 6 mm.
Residual mud was removed after another 15 minutes. This was dried again for 3 days, then placed in a heating furnace, heated to 1000 ° C. over 3 hours, held at 1000 ° C. for 3 hours, and then gradually cooled. When it was taken out, the slips from the back were also integrated, and no cracks were seen.
This product was glazed under normal conditions. The glaze was spread on the inside of the pan, and the glaze was applied so as to be uniform except for the bottom of the outside. After drying, it was heated at 800 ° C.
When taken out after heating and slow cooling, the appearance was the same as a normal clay pot. The wall thickness was 8 mm at the wall and 15 mm at the bottom. Moreover, when water was added and it switched to the induction heater (IH heater) and the switch was turned on, it was heated and it was able to be made boiling water.

In the same manner as in Example 1, mud was put in a gypsum mold to produce a clay pot. However, titanium oxide (TiO) powder was put in place of the nickel / iron alloy. The mixing ratio to the clay was the same as in Example 1. Using this slip, it was put into a plaster mold to make a clay pot shape and dried. An apparent thickness of about 8 mm is formed on the bottom of the earthen pot in which the gum-like kneaded material kneaded so as to be TiO: ceramic clay = 90: 10 (mass ratio) is preliminarily damped with water. Filled and dried. After drying, cracks were observed in the portion where the kneaded material was slightly packed, so that mud mixed with porcelain clay and water was put in the cracked portion, and the surface was corrected and further drying was performed. About this thing, the unglazed baking was made like Example 1, and it further applied the glaze to make a clay pot. The distribution of the titanium pan in the height direction was measured from the outside along the wall of the pan with a portable X-ray fluorescence analyzer, NITON (Rigaku Denki). It was found that there was a distribution in titanium oxide (TiO), which is a heat generating material. When heating by induction heating was performed in the same manner as in Example 1, it was possible to boil water by heating without problems.

Commercially available Seto porcelain is used as a bulk material, and barium titanate particles with an average particle size of 200 μm are used as exothermic materials, and kneaded materials of three kinds of combinations of porcelain clay: barium titanate = 20: 80, 60:40, 80:20. Created. The kneaded material was a material using water as a medium, and was adjusted to a hardness enough to enable the potter's wheel work. About this, first, a bottom part is formed with a 20:80 kneaded body (plate shape with a diameter of 200 mm and a thickness of 10 mm), and a rise is formed on the bottom so that a wall with a height of 30 mm and a thickness of about 8 mm is formed. Further, a wall of 80:20 kneaded body having a height of 30 mm and a thickness of about 7 mm was stacked thereon. On the other hand, using a clay from Seto porcelain, it was smoothed by a potter's wheel and processed into a clay pot with a smooth bottom and dried. Since it has become a clay pot with a uniform shape after drying for 3 days, file it so that the bottom is flatter and make the curved surface between the wall and bottom so that there is no protrusion on the bottom. Finishing, this thing was put into the kiln and calcined at 1200 degreeC. As a result, high-density unglazed baking was achieved. There were no cracks. About this, the glaze was applied like Example 1 and it baked and it was set as the earthenware pot. With respect to this, since the joining portion was sufficiently joined by the potter's wheel work at the time of molding, peeling or cracking did not occur even when heating / cooling was repeated. In addition, although the heat processing by IH was performed on the conditions similar to Example 1, it was able to heat easily.

In recent years, induction heating (IH) heaters have also been used for tabletop stoves, and there has been a problem that it is virtually impossible to cook pots using earthen pots. In order to improve these, methods such as putting a heating element in the earthenware pot or laying the heating element under the earthenware pot have been devised. There are many cases. Therefore, it is expected that the technology of the present invention that can directly use the earthenware pot as an induction heating (IH) heater will be widely and generally put into practical use.

  It is a model figure of the section of the earthenware pot container concerning the present invention.

100 Schematic cross-sectional view by mud casting 200 Schematic cross-sectional view by adding bottom sediment to mud casting 300 Schematic cross-sectional view by molding kneaded body 11 Pyrogen 21 Bottom kneaded substance 31 Kneaded body with a large amount of pyrogen 32 Kneading of intermediate amount of pyrogen Body 33 Kneaded body with less heat generation material

Claims (11)

A clay pot-like container that has a flat bottom and is made of conductive ceramics and / or ceramics mainly composed of silica / alumina containing at least a metal whose surface is ceramicized at the bottom, and that can be heated by induction heating. The earthenware pot according to claim 1, wherein the content of the conductive ceramics and / or the metal whose surface has been ceramicized is 50% or more at the bottom of the earthenware pot. The earthenware pot is thick at the bottom and thin in the wall, and has a high content of conductive ceramics at the bottom and / or metal that has been ceramicized on the surface, and the wall extends from a portion close to the bottom to the top. The earthenware pot according to claim 1 or 2, wherein the container is lowered as it goes. The earthenware pot according to any one of claims 1 to 3, wherein the conductive ceramic is conductive titanium oxide. The earthenware pot according to any one of claims 1 to 4, wherein the conductive ceramic is titanium monoxide (TiO). The earthenware pot according to any one of claims 1 to 3, wherein the conductive ceramic is a perovskite oxide. The earthenware pot according to any one of claims 1 to 3, wherein the conductive ceramic is a spinel oxide. The earthenware pot according to any one of claims 1 to 3, wherein the metal whose surface is ceramicized is iron or an iron alloy having a particle diameter of 0.1 to 2 mm, and the surface is a so-called blackened particle. 9. The metal according to claim 1, wherein the metal ceramicized on the surface is a nickel / iron alloy having a particle diameter of 0.1 to 2 mm, and the surface is converted to an oxide by firing. Earthenware container. An earthenware pot container that has a flat bottom and is composed of conductive ceramics and / or ceramics mainly composed of silica / alumina containing at least a metal whose surface is ceramicized, that can be heated by induction heating. Conductive ceramics with a slightly larger diameter and / or a slurry made of a metal with a ceramic surface and silica / alumina based material with a small particle size are prepared in advance, molded by the slurry casting method, and manufactured by heating and firing. A method for producing an earthenware pot characterized by the following. Conductive earthenware pots that have a flat bottom and are made of conductive ceramics and / or ceramics mainly composed of silica / alumina containing at least the bottom metallized metal that can be heated by induction heating. By changing the composition of the ceramic and / or the metalized silica-alumina-based material kneaded material with the surface ceramicized, and forming the bottom part and the wall part or this connected part with the kneaded substance with different composition, A method for producing an earthenware pot characterized in that the composition is continuously changed.

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