Dielectric drying process for ceramic molded bodies and process for the production of ceramic structures

Abstract

A dielectric drying method for ceramic molded bodies, wherein the method comprises drying a plurality of ceramic molded bodies arranged side by side in an arrangement direction Y perpendicular to a conveying direction X on the top of a drying table, by conveying the ceramic molded bodies between electrodes of an upper electrode and a lower electrode, and applying a high frequency between the electrodes, wherein the upper electrode comprises: a central region; and two end regions, between which the central region is located in the arrangement direction Y; wherein the central area has a flat surface section that runs parallel to an upper end face of the ceramic molded body, wherein each of the two end regions has an inclined section which is inclined towards the side of the lower electrode; and where the ratio L2 / L1 is between 0 and 1.70, where L1 is the shortest distance between the central area and the ceramic molded body, and L2 is the shortest distance between each end of the two end areas and the ceramic molded body.

Description

Technical area

[0001] The present invention relates to a dielectric drying process for ceramic moldings and a process for producing ceramic structures. Background of the invention

[0002] Ceramic structures are used in a wide variety of applications. For example, honeycomb-shaped ceramic structures with partition walls defining a plurality of cells, each extending from a first end face to a second end face, are frequently used in catalyst supports, diesel particulate filters (DPFs), gasoline particulate filters (BPFs), and the like.

[0003] The ceramic structure is manufactured by molding a green body containing a ceramic raw material to obtain a ceramic preform, which is then dried and fired. Hereinafter, a stage after extrusion and before drying is referred to as a ceramic preform, and a stage after firing is referred to as a ceramic structure. A dielectric drying method is generally used to dry the ceramic preform. In dielectric drying, the ceramic preform may be placed between a pair of electrodes, a current may be passed through the electrodes to induce molecular movement of a water dipole in the ceramic preform, and the ceramic preform may be dried by frictional heat.The term "dielectric drying" used below means high-frequency dielectric drying (with a frequency of approximately 1 to 100 MHz) in which an object to be dried is placed between the pair of electrodes to carry out the drying, but does not mean microwave drying (with a frequency of approximately 300 MHz to 300 GHz) in which electromagnetic waves are emitted from an oscillator onto the object to be dried to carry out the drying.

[0004] However, in the case of dielectric drying, it is difficult to dry the ceramic formed body uniformly, resulting in problems such as cracking and the like during firing or uneven dimensions of the ceramic structure. Therefore, various measures have been taken for dielectric drying. For example, Patent Literature 1 proposes a method for drying a honeycomb formed body (ceramic formed body) using a drying table in which a specific region is formed as a perforated plate, including a portion in contact with an opened lower end surface of the honeycomb formed body, because when the honeycomb formed body is placed on the drying table and dielectrically dried, a high-humidity region is generated around the upper and lower end surfaces.

[0005] Furthermore, Patent Literature 2 proposes a method for drying honeycomb formed bodies (ceramic formed bodies), in which electrodes provided above the upper end surfaces and below the lower end surfaces of the honeycomb formed bodies are divided into a plurality of electrodes whose positions correspond to the upper and lower end surfaces, respectively, and the honeycomb formed bodies are intermittently moved for each pair of electrode units, so as to suppress fluctuations in drying the honeycomb formed bodies continuously conveyed by a conveyor belt.

[0006] Furthermore, Patent Literature 3 proposes a method for drying a honeycomb formed body in which the honeycomb formed body is rotated about its longitudinal axis between a pair of electrodes in order to dry the honeycomb formed body uniformly.

[0007] Further prior art is also known from patent literature 4. Reference listPatent literature [Patent Literature 1] JP S60-037 382 B2 [Patent Literature 2] JPH05-105 501 A [Patent literature 3] JP H06- 298 563 A [Patent literature 4] DE 11 2020 005 946 T5 Summary of the inventionProblem to be solved by the invention

[0008] The dielectric drying of the ceramic molded body is performed by arranging a plurality of ceramic molded bodies (e.g., 2 to 5) side by side in an arrangement direction Y perpendicular to a conveying direction X on a top surface of the drying table, continuously conveying the drying table between the upper electrode and the lower electrode by a conveying unit (such as a conveyor belt), and applying a high frequency. Although the method described in Patent Literature 1 can suppress fluctuation in the dried state of the upper part and the lower part of each ceramic molded body arranged on the drying table, it is difficult to suppress fluctuation in the dried state along the arrangement direction Y (the width direction of the drying table).Since the ceramic molded body arranged near the central region in the arrangement direction Y is located in an environment where the electric field strength is higher, it has a higher drying rate, and as a result, a drying shrinkage rate tends to increase. On the other hand, since the ceramic molded body arranged near the end in the arrangement direction Y is located in an environment where the electric field strength is lower, it has a lower drying rate, and so the drying shrinkage rate tends to decrease. As a result, the dry state varies depending on the different positions of the ceramic molded bodies arranged adjacently in the arrangement direction Y.

[0009] Furthermore, the method described in Patent Literature 2 is for suppressing variations in the dried state of the ceramic molded bodies arranged on a plurality of drying tables along the conveying direction X, but not for suppressing variations in the dry state of the plurality of ceramic molded bodies along the arrangement direction Y.

[0010] Furthermore, since the method described in Patent Literature 3 is applied to a batch furnace, it is difficult to apply said method to a continuous furnace designed for mass production.

[0011] The present invention was developed to solve the above-mentioned problems. An object of the present invention is to provide a dielectric drying method and apparatus for ceramic molded articles, which can suppress fluctuations in the dried states of a plurality of ceramic molded articles arranged on the drying table in the arrangement direction Y perpendicular to the conveying direction X.

[0012] Another object of the present invention is to provide a method for producing ceramic structures which enables the production of ceramic structures with a uniform shape. Means of solving the problem

[0013] As a result of intensive research on dielectric drying of a plurality of ceramic moldings arranged side by side in the arrangement direction Y perpendicular to the conveying direction X on the top side of the drying table, the inventors concerned have found that the above-mentioned problems can be solved by regulating the shape of the upper electrode so that the distances to the plurality of ceramic moldings meet predetermined conditions.

[0014] Accordingly, the present invention relates to a dielectric drying method for ceramic molded bodies, the method comprising drying a plurality of ceramic molded bodies arranged side by side in an arrangement direction Y perpendicular to a conveying direction X on an upper surface of a drying table by conveying the ceramic molded bodies between electrodes of an upper electrode and a lower electrode, and applying a high frequency between the electrodes, wherein the upper electrode comprises: a central region; and two end regions between which the central region is located in the arrangement direction Y; wherein the central region has a flat surface portion parallel to an upper end surface of the ceramic molded body, each of the two end regions having an inclined portion inclined toward the lower electrode side;and wherein a ratio L2 / L1 is between 0 and 1.70, where L1 is a shortest distance between the central region and the ceramic molded body, and L2 is a shortest distance between a respective end of the two end regions and the ceramic molded body;

[0015] Furthermore, the present invention relates to a method for producing ceramic structures, which comprises the method for dielectric drying of the ceramic moldings. Effects of the invention

[0016] According to the present invention, it is possible to provide a dielectric drying method for ceramic molded bodies, with which fluctuations in the dried states of a plurality of ceramic molded bodies arranged on the drying table in the arrangement direction Y perpendicular to the conveyance direction X can be suppressed.

[0017] Furthermore, according to the present invention, it is possible to provide a method for producing ceramic structures which enables ceramic structures having a uniform shape to be produced. Brief description of the drawings Fig. 1 shows a schematic view of a dielectric drying device along a conveying direction X, which is suitable for use in a dielectric drying method for ceramic molded bodies according to an embodiment of the present invention. Fig. Figure 2 shows a schematic view of the dielectric drying device of Fig. 1 along an arrangement direction Y. Fig. Figure 3 shows a view with depicted density distributions of electric field lines in the schematic view of the dielectric drying device of Fig. 2. Fig.Figure 4 shows a view showing density distributions of electric field lines in the case where an upper electrode in the form of a flat plate is used. Fig. 5 shows a schematic view of a dielectric drying device along an arrangement direction Y, in the case where auxiliary electrodes are arranged on the upper end surfaces of a plurality of ceramic molded bodies. And Fig. 6 is a diagram showing a relationship between a ratio L2 / L1 and a difference in heat quantity for various embodiments. Detailed description of the invention

[0018] Embodiments of the present invention will be described in detail below. It should be noted that the present invention is not limited to the following embodiments, and various modifications and improvements can be made based on the general knowledge of one skilled in the art, which are within the scope of the present invention without departing from the spirit of the present invention.

[0019] (1) Dielectric drying method and dielectric drying device for ceramic molded bodies

[0020] A dielectric drying method for ceramic molded bodies according to an embodiment of the present invention is carried out by drying a plurality of ceramic molded bodies arranged side by side in an arrangement direction Y perpendicular to a conveyance direction X on an upper surface of a drying table by conveying the ceramic molded bodies between an upper electrode and a lower electrode (between the electrodes) and applying a high frequency between the electrodes.

[0021] Fig. 1 shows a schematic view of a dielectric drying device along the conveying direction X, which is suitable for use in the dielectric drying process for ceramic moldings. Fig. 2 further shows a schematic view of the dielectric drying device along the arrangement direction Y.

[0022] As in Fig. 1 and Fig.2, a dielectric drying device 100 comprises: an upper electrode 130; a lower electrode 140; and a conveying unit 120 (e.g., a conveyor belt) capable of conveying a plurality of ceramic molded bodies 10 between the electrodes of the upper electrode 130 and the lower electrode 140, wherein the ceramic molded bodies 10 are arranged side by side in the arrangement direction Y perpendicular to the conveying direction X on an upper surface of a drying table 20. The upper electrode 130 is arranged above a dielectric drying furnace 110, and the lower electrode 140 is arranged below the dielectric drying furnace 110. The dielectric drying device 100 with such a basic structure is known from the prior art. In addition, the dielectric drying device 100 may include other known devices (e.g.,a device for ventilation drying), as long as this does not impair the effect of the present invention.

[0023] The plurality of ceramic molded bodies 10 arranged on the drying table 20 are conveyed by the conveying unit 120 between the electrodes of the upper electrode 130 and the lower electrode 140 into the dielectric drying furnace 110. In this case, the high-frequency energy generated by passing an electric current between the upper electrode 130 and the lower electrode 140 causes molecular movement of the water dipole in the ceramic molded bodies 10, and the ceramic molded bodies 10 can be dried by the resulting frictional heat.

[0024] The number of the plurality of ceramic molded bodies 10 arranged on the drying table 20 can be adjusted accordingly depending on the size of the drying table 20 and the like. The number is preferably 2 to 5, and more preferably 3 to 5.

[0025] The dimensions of the plurality of ceramic molded bodies 10 arranged on the drying table 20 are not limited in principle. Preferably, their dimensions in the vertical direction Z are substantially the same, and more preferably, their dimensions are substantially the same in all directions.

[0026] Both the upper electrode 130 and the lower electrode 140A utilize a known electrode plate design. Furthermore, the upper electrode 130 can be machined to the desired shape using a known method.

[0027] The upper electrode 130 comprises: a central region A; and two end regions B, between which the central region A is located in the arrangement direction Y of the plurality of ceramic molded bodies 10.

[0028] The central region A has a flat surface portion 131 parallel to the upper end surfaces 11a of the plurality of ceramic molded bodies 10. Furthermore, each of the two end regions B has an inclined portion 132 inclined toward the lower electrode 140 side.

[0029] The expression "inclined portion 132 is inclined toward the lower electrode 140 side" used herein means that a portion has an inclination angle toward the lower electrode 140 side in a range of more than 0° and less than 180° with respect to the flat surface portion in the central region A (inclination angle of 0°).

[0030] A ratio L2 / L1 is between 0 and 1.70, and preferably between 0 and 0.70, where L1 is a shortest distance between the central region A of the upper electrode 130 and each of the ceramic molded bodies 10, and L2 is a shortest distance between a respective end of the two end regions B of the upper electrode 130 and each of the ceramic molded bodies 10

[0031] By regulating the ratio L2 / L1 to the above-mentioned value range, density distributions of the electric field lines of the two ceramic molded bodies 10 at the two ends in the arrangement direction Y are substantially equal to those of the electric field lines of the three ceramic molded bodies 10 in the middle with respect to the arrangement direction Y, as shown in Fig.3. Therefore, electric field strengths of the two ceramic molded bodies 10 at both ends with respect to the arrangement direction Y are substantially equal to those of the three ceramic molded bodies 10 in the center with respect to the arrangement direction Y, so that fluctuations in the dried states of the plurality of ceramic molded bodies 10 along the arrangement direction Y can be suppressed.

[0032] However, if the ratio L2 / L1 is outside the above range, the density distributions of the electric field lines of the two ceramic molded bodies 10 at both ends in the arrangement direction Y are lower than those of the electric field lines of the three ceramic molded bodies 10 in the middle with respect to the arrangement direction Y, as shown in Fig.4. Therefore, the electric field strengths of the two ceramic molded bodies 10 at both ends with respect to the arrangement direction Y are smaller than those of the three ceramic molded bodies 10 in the middle with respect to the arrangement direction Y, so that the dried states of the plurality of ceramic molded bodies 10 vary along the arrangement direction Y. In particular, the two ceramic molded bodies 10 at the two ends in the arrangement direction Y are harder to dry than the three ceramic molded bodies 10 in the middle with respect to the arrangement direction Y.

[0033] Preferably, in the upper electrode 130, an inclination starting point P of each of the two end portions B with respect to the arrangement direction Y is located at the same position as an outer end Q of the respective ceramic molded bodies 10 at both ends, or is located outside the outer end Q.

[0034] As described above, the regulation of the position of the starting point P enables easy regulation of the density distribution of the electric field lines in the region where the two ceramic molded bodies 10 are located at the two ends with respect to the arrangement direction Y to the same extent as the density distribution of the electric field lines in the region where the three central ceramic molded bodies 10 are located in the middle with respect to the arrangement direction Y. This can stably achieve the effect of suppressing fluctuations in the dried states of the plurality of ceramic molded bodies 10 along the arrangement direction Y.

[0035] Auxiliary electrodes 30 can be attached to the upper end surfaces 11a of the plurality of ceramic molded bodies 10. The attachment of the auxiliary electrodes 30 can result in uniform electric field strengths at the upper end surfaces 11a of the ceramic molded bodies 10, which would otherwise be uneven during dielectric drying. This can contribute to uniform heating of the ceramic molded bodies 10 as a whole, thus reducing uneven drying.

[0036] This shows Fig. 5 is a schematic view of a dielectric drying device along the arrangement direction Y, in the case where the auxiliary electrodes 30 are arranged on the upper end surfaces 11a of the plurality of ceramic molded bodies 10. Fig. The dielectric drying device 200 shown in Figure 5 corresponds to the one shown in Fig.2, except that in the former case, the auxiliary electrodes 30 are arranged on the upper end surfaces 11a of the plurality of ceramic molded bodies 10.

[0037] The material of the individual auxiliary electrodes 30 is not limited to a specific material. Preferably, the material has a conductivity that is higher than that of the ceramic molded body 10. If the material has such conductivity, its practical use as an auxiliary electrode 30 can be sufficiently ensured. Examples of the material of the auxiliary electrode 30 include aluminum, copper, aluminum alloys, copper alloys, graphite, and the like, which can be used alone or in combination with two or more materials.

[0038] For example, a perforated plate can be used as auxiliary electrode 30.

[0039] The term “perforated plate” refers to a plate that has openings.

[0040] The degree of perforation of the perforated plate is preferably between 20 and 90%, particularly preferably between 40 and 80%, although this is not necessarily limited to this. Regulating the degree of perforation within such a range can lead to a uniform electric field strength at the upper end surface 11a of the ceramic molded body 10, which would otherwise be uneven during dielectric drying. This can contribute to uniform heating of the ceramic molded bodies 10 as a whole, thus reducing uneven drying.

[0041] The term “perforation ratio of the perforated plate” refers to the ratio of the perforated areas to the total area of ​​the surface of the perforated plate in contact with the upper end surface 11a of the ceramic molded body 10.

[0042] The openings on the surface of the perforated plate in contact with the upper end surface 11a of the ceramic molded body 10 may have various shapes, including, but not limited to, a circular shape, a square shape, and a slit shape.

[0043] In the case where the auxiliary electrodes 30 are arranged on the upper end surfaces 11a of the plurality of ceramic molded bodies 10, L1 is the shortest distance between the central region A and the auxiliary electrode 30, and L2 is the shortest distance between each end portion of the two end regions B and the auxiliary electrode 30.

[0044] By regulating the ratio L2 / L1 within the above-mentioned value range, the density distributions of the electric field lines of the two ceramic molded bodies 10 at the two ends in the arrangement direction Y are substantially equal to those of the electric field lines of the three ceramic molded bodies 10 in the center with respect to the arrangement direction Y. Therefore, electric field intensities of the two ceramic molded bodies 10 at both ends with respect to the arrangement direction Y are substantially equal to those of the three ceramic molded bodies 10 in the center with respect to the arrangement direction Y, so that fluctuations in the dried states of the plurality of ceramic molded bodies 10 along the arrangement direction Y can be suppressed.

[0045] In the case where the auxiliary electrodes 30 are arranged on the upper end surfaces 11a of the plurality of ceramic molded bodies 10, in the upper electrode 130, an inclination starting point P of each of the two end portions B with respect to the arrangement direction Y is preferably located at the same position as an outer end Q of the respective ceramic molded bodies 10 at both ends, or is located outside the outer end Q.

[0046] As described above, adjusting the position of the starting point P makes it possible to easily adjust the density distribution of the electric field lines in the region where the two ceramic molded bodies 10 are located at both ends with respect to the arrangement direction Y to the same extent as the density distribution of the electric field lines in the region where the three central ceramic molded bodies 10 are located in the middle with respect to the arrangement direction Y. This can stably achieve the effect of suppressing fluctuations in the dried states of the plurality of ceramic molded bodies 10 along the arrangement direction Y.

[0047] An inclination angle θ of each of the two end regions B of the upper electrode 130 with respect to a flat portion of the central region A is preferably between 30 and 90°, and more preferably between 45 and 90°.

[0048] As described above, the regulation of the inclination angle θ makes it possible to easily regulate the density distribution of the electric field lines in the region where the two ceramic molded bodies 10 are located at both ends with respect to the arrangement direction Y to the same extent as the density distribution of the electric field lines in the region where the three central ceramic molded bodies 10 are located in the middle with respect to the arrangement direction Y. This can stably achieve the effect of suppressing fluctuations in the dried states of the plurality of ceramic molded bodies 10 along the arrangement direction Y.

[0049] In a vertical direction Z, a shortest distance L3 between the respective end portion of the two end regions B and the ceramic molded body 10 or the auxiliary electrode 30, if the auxiliary electrodes 30 are arranged, is preferably between -50 and 50 mm and more preferably between -30 and 30 mm.

[0050] As described above, the regulation of L3 makes it possible to easily regulate the density distribution of the electric field lines in the region where the two ceramic molded bodies 10 are located at both ends with respect to the arrangement direction Y to the same extent as the density distribution of the electric field lines in the region where the three central ceramic molded bodies 10 are located in the middle with respect to the arrangement direction Y. This can stably achieve the effect of suppressing fluctuations in the dried states of the plurality of ceramic molded bodies 10 along the arrangement direction Y.

[0051] The drying table 20 on which the ceramic molded bodies 10 are placed is not limited to any particular configuration. Preferably, perforated plates are arranged at portions in contact with the lower end surfaces 11b of the plurality of ceramic molded bodies 10. Such an arrangement can allow water vapor to be easily discharged from the lower end surfaces 11b of the ceramic molded bodies 10 during dielectric drying, so that the ceramic molded bodies 10 can be easily and uniformly dried.

[0052] Non-limiting examples of the material of the perforated plate are aluminum, copper, aluminum alloys, copper alloys and graphite. These can be used alone or in combination of two or more materials.

[0053] The degree of perforation and the shape of the openings of the perforated plates used for the drying table 20 are not limited to a particular design and may also correspond to those of the perforated plate used for the auxiliary electrode 30.

[0054] Various conditions (frequency, power, heating time, etc.) during dielectric drying can be adjusted accordingly depending on the objects to be dried (ceramic molded bodies 10), the design of the dielectric drying devices 100, 200, etc. For example, the frequency during dielectric drying is preferably between 10 MHz and 100 MHz.

[0055] The ceramic molded bodies 10 to be subjected to dielectric drying preferably have a water content between 1 and 60%, more preferably between 5 and 55%, and even more preferably between 10 and 50%, although the water content is not limited thereto. Ceramic molded bodies 10 with a water content within such a range tend to fluctuate with respect to their dried states during dielectric drying. For this reason, the effect of the present invention can be achieved particularly easily in the case where the ceramic molded bodies 10 used have a water content within the aforementioned range.

[0056] The term “water content” of the ceramic molded bodies 10 used here refers to a water content that is measured using a moisture meter of the infrared radiator type.

[0057] The ceramic molded body 10 is preferably, but not limited to, a honeycomb molded body having partition walls defining a plurality of cells extending from a first end surface to a second end surface.

[0058] In particular, the cell shape of the honeycomb shaped body (cell shape in a cross-section orthogonal to an extension direction of the cells) is not limited. Examples of the cell shape include a triangle, a square, a hexagon, an octagon, a circle or a combination thereof.

[0059] Non-limiting examples of a shape of the honeycomb molded body include, but are not limited to, a cylindrical shape, an elliptical columnar shape, and a polygonal columnar shape having square, rectangular, triangular, pentagonal, hexagonal, and octagonal end surfaces.

[0060] The ceramic molded body 10 can be obtained by molding a green body obtained by kneading a raw material composition containing a ceramic raw material and water.

[0061] The usable ceramic raw material specifically includes cordierite-forming raw materials, cordierite, silicon carbide, silicon-silicon carbide composite materials, mullite, aluminum titanate, and the like. These can be used alone or in combination with two or more raw materials. The cordierite-forming raw material is a ceramic raw material defined as having a chemical composition in which silicon dioxide is in the range of 42 to 56 mass percent, alumina is in the range of 30 to 45 mass percent, and magnesia is in the range of 12 to 16 mass percent. To form cordierite, the cordierite-forming raw material is calcined.

[0062] In addition to the ceramic raw material and water, the raw material composition may contain a dispersant, a binder (e.g., an organic binder, an inorganic binder, or the like), a pore former, a surfactant, or the like. The mixing ratio of the individual raw materials preferably depends on the structures, materials, etc. of the ceramic molded bodies 10 to be produced, but this should not be limited thereto.

[0063] A method for kneading the raw material composition for forming the green body may include, for example, the use of a kneader, a vacuum-based kneader, or the like. Furthermore, a method for forming the ceramic molded body 10 may employ, for example, a known molding method such as extrusion and injection molding. Particularly in the case of a honeycomb molded body to be produced as the ceramic molded body 10, the extrusion may be performed using a die having the desired cell shape, partition wall thickness (cell wall), and cell density. For example, low-wear cemented carbide alloys may be used as the material for the die.

[0064] In the case of the dielectric drying methods and the dielectric drying apparatuses 100, 200 for the ceramic molded bodies 10 according to the embodiment of the present invention, the shape of the upper electrode 130 is regulated such that the ratio L2 / L1 is within a predefined range, so that the density distributions (i.e., the electric field strengths) of the electric field lines are equal at both ends and in the center with respect to the arrangement direction Y. Thus, it is possible to suppress fluctuations in the dried states of the plurality of ceramic molded bodies 10 along the arrangement direction Y. (2) Processes for the production of ceramic structures

[0065] The method for producing ceramic structures according to an embodiment of the present invention comprises the above-described dielectric drying method for the ceramic molded bodies 10.

[0066] In particular, the method for producing ceramic structures according to the embodiment of the present invention is not limited to steps performed in addition to the dielectric drying method described above; steps known from the prior art may well be used. In particular, the method for producing ceramic structures according to the embodiment of the present invention may further comprise a heating step for drying the ceramic molded bodies 10 using the dielectric drying method described above, and firing the ceramic dry bodies to produce ceramic structures.

[0067] In particular, a method for firing the ceramic dry bodies is not limited to a specific design. For example, the ceramic dry bodies can be fired in a kiln. Furthermore, known settings for the kiln and for the firing process can be selected accordingly, depending on the external shapes, materials, and the like of the honeycomb structures to be produced. Before firing, organic substances, such as a binder, can be removed by calcination.

[0068] Since the method for manufacturing ceramic structures according to the embodiment of the present invention includes the dielectric drying method, which makes it possible to suppress variations in the dried states of the plurality of ceramic molded bodies 10 in the arrangement direction Y, ceramic structures having a uniform shape can be manufactured. Examples of implementation

[0069] In the following, the present invention will be described in more detail with reference to embodiments, whereby the present invention is in no way limited to these embodiments (Production of ceramic molded bodies)

[0070] Honeycomb bodies were prepared as ceramic bodies. First, a cordierite-forming raw material obtained by blending alumina, kaolin, and talc as the ceramic raw material was mixed with a binder containing an organic binder, a water-absorbent resin as a pore-forming agent, and water (42 mass%) as a dispersion medium to form a raw material composition, which was then kneaded to produce green bodies. Each of the prepared green bodies was extruded to obtain a honeycomb body with cells each having a square cross-sectional shape orthogonal to the extrusion direction of the cells. The honeycomb body had an outer diameter of 144 mm, a length (length in the direction of extension of the cells) of 260 mm, and an outer cylindrical shape. Furthermore, the honeycomb bodies had a water content of 42% and a weight of 1320 g.The water content and weight of the honeycomb moldings are to be understood as average values ​​of all honeycomb moldings produced. (Dielectric drying of ceramic moldings)

[0071] Dielectric drying of the ceramic moldings prepared above was carried out, using the following procedure in detail: Five ceramic molded bodies were arranged side by side in the arrangement direction Y on the top of the drying table and auxiliary electrodes of the same thickness were placed on the upper end surfaces of the five ceramic molded bodies (see Fig. 5). In this way, a total of nine drying tables were prepared, each of which held five ceramic molds.

[0072] For the dielectric drying device, upper electrodes with different shapes (an inclination angle θ was between 0 and 90°) were used, and the distances (L1 to L3) between the respective upper electrode and the respective ceramic molded bodies were set to a predetermined value. The said settings are listed in Table 1.

[0073] Dielectric drying was carried out by placing nine drying tables, each containing five honeycomb molded bodies, on the conveyor belt of the dielectric drying device. The drying tables were then transported to the dielectric drying oven and dried at a frequency of 40.68 MHz (ISM band), a power of 85.0 kW, and a heating time of 12 minutes. (Calculating the difference in heat quantity)

[0074] First, each of the ceramic molded bodies arranged next to each other in the arrangement direction Y was analyzed by a simulation based on the finite difference method in the time domain (FDTD method). During the simulation, the electric field strength E was determined at each grid point in the ceramic molded body.

[0075] Subsequently, based on the determined electric field strength E, the heat quantity H at each grid point was calculated according to the following equation (1): [Equation 1] H=12ωεtanδ|E|2

[0076] In equation (1), ω is an angular frequency (2π × 40 MHz), ε is a dielectric constant of the ceramic molded body, and tan δ is the tangent of a dielectric loss of the ceramic molded body.

[0077] The heat quantities H at the grid points of the respective ceramic moldings were summed to calculate the total heat quantity of the respective ceramic moldings.

[0078] With regard to the difference in heat quantity, the total heat quantities of the five ceramic molded bodies arranged side by side in the arrangement direction Y were defined as H1 to H5 (in Fig. 5, the total heat quantities of the ceramic molded bodies were defined sequentially as H1 to H5 from the left end to the right end) and the difference in heat quantity was calculated based on the following equation (2): [Equation 2] Difference in heat quantity=(H3H1+H2+H3+H4+H5−H1H1+H2+H3+H4+H5)×100

[0079] The results of the difference in heat quantity are shown in Table 1. Furthermore, Fig. 6 is a diagram showing a relationship between the ratio L2 / L1 and the difference in heat quantity. In Fig. 6, the area surrounded by the dashed frame corresponds to the scope of application of the present invention. Table 1 Sample No. L1 (mm) L2 (mm) L3 (mm) L2 / L1 Angle of inclination Θ (°) Difference in heat quantity (%) Classification A 100 0 0 0,00 90 -1,3 Example B 100 25 0 0,25 90 -0,3 Example C 100 40 0 0,40 90 0,6 Example D 100 90 0 0,90 90 2,8 Example E 100 125 0 1,25 90 3,7 Example F 100 175 0 1,75 90 5,7 Comparison example G 100 172 0 1,72 0 5,0 Comparison example H 100 136 0 1,36 30 4,4 Example I 100 115 0 1,15 45 3,9 Example J 100 91 0 0,91 60 3,3 Example K 100 74 0 0,74 70 2,8 Example L 100 64 50 0,64 90 4,8 Example M 100 64 -50 0,64 90 -3,2 Example

[0080] As Table 1 and Fig. 6, it was found that in the embodiments of the present invention in which the ratio L2 / L1 was in the range of 0 to 1.70, the difference in the amount of heat was less than 5.0%, so that fluctuations in the dried states of the ceramic molded bodies along the arrangement direction Y could be suppressed.

[0081] On the other hand, it was found that in comparative examples where the ratio L2 / L1 was outside the range of 0 to 1.70, the difference in heat amount was 5.0% or more, so that larger fluctuations occurred in the dried states of the ceramic molded bodies along the arrangement direction Y.

[0082] As is apparent from the above results, according to the present invention, it is possible to provide a dielectric drying method and a dielectric drying apparatus for ceramic molded bodies that suppress fluctuations in the dried states of a plurality of ceramic molded bodies arranged on the drying table in the arrangement direction Y perpendicular to the conveyance direction X. Furthermore, according to the present invention, it is possible to provide a method for manufacturing ceramic structures that enables the production of ceramic structures with a uniform shape. List of reference symbols 10 ceramic molded bodies 11a upper end face 11b lower end face 20 drying table 30 Auxiliary electrode 100, 200 dielectric drying device 110 dielectric drying oven 120 conveyor unit 130 upper electrode 131 flat surface section 132 sloping section 140 lower electrode

Claims

[1] A dielectric drying method for ceramic moldings, the method comprising drying a plurality of ceramic moldings arranged side by side in an arrangement direction Y perpendicular to a conveying direction X on an upper surface of a drying table by conveying the ceramic moldings between electrodes of an upper electrode and a lower electrode, and applying a high frequency between the electrodes, wherein the upper electrode comprises: a central region; and two end regions between which the central region is located in the arrangement direction Y; wherein the central region has a flat surface portion which runs parallel to an upper end surface of the ceramic molded body, wherein each of the two end portions has an inclined portion inclined toward the lower electrode side; and wherein a ratio L2 / L1 is between 0 and 1.70, where L1 is a shortest distance between the central region and the ceramic molded body, and L2 is a shortest distance between a respective end of the two end regions and the ceramic molded body [2] The dielectric drying method for ceramic molded bodies according to claim 1, wherein an inclination starting point of each of the two end portions with respect to the arrangement direction Y is located at the same position as an outer end of the respective ceramic molded bodies at both ends, or is located outside the outer end. [3] The dielectric drying method for ceramic molded bodies according to claim 1, wherein auxiliary electrodes are arranged on upper end surfaces of the ceramic molded bodies, and wherein L1 is the shortest distance between the central portion and the auxiliary electrode, and L2 is the shortest distance between each end of the two end portions and the auxiliary electrode [4] The dielectric drying method for ceramic molded bodies according to claim 3, wherein the inclination starting point of each of the two end portions with respect to the arrangement direction Y is located at the same position as an outer end of the respective auxiliary electrodes at both ends, or is located outside the outer end [5] The dielectric drying method for ceramic molded bodies according to any one of claims 1 to 4, wherein the ratio L2 / L1 is between 0 and 0.

70. [6] The dielectric drying method for ceramic molded bodies according to any one of claims 1 to 5, wherein an inclination angle of each of the two end portions with respect to a flat portion of the central portion is between 30 and 90°. [7] The dielectric drying method for ceramic molded bodies according to any one of claims 1 to 6, wherein in a vertical direction Z a shortest distance L3 between the respective end of the two end regions and the upper end surface of the ceramic molded body or the auxiliary electrode, if the auxiliary electrodes are arranged, is between -50 and 50 mm, wherein a positive value for the distance L3 describes the case that the respective end region is located vertically above the upper end surface of the ceramic molded body or the auxiliary electrode, and a negative value for the distance L3 describes the case that the respective end region is located vertically below the upper end surface of the ceramic molded body or the auxiliary electrode. [8] The dielectric drying method for ceramic molded bodies according to any one of claims 1 to 7, wherein each of the ceramic molded bodies has a water content between 1 and 60%. [9] The dielectric drying method for ceramic molded bodies according to any one of claims 1 to 8, wherein the ceramic molded bodies are honeycomb-shaped bodies, each of the honeycomb-shaped bodies comprising partition walls defining a plurality of cells each extending from a first end face to a second end face. [10] A method for producing ceramic structures, comprising the dielectric drying method for ceramic molded bodies according to any one of claims 1 to 9.

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