Drying method and drying device for green honeycomb molded body

The drying method for a green honeycomb molded body according to the invention is a method for drying a green honeycomb molded body having a plurality of through-holes. The method includes the steps of: mounting a green honeycomb molded body on a gas dispersion plate; and irradiating the molded body with microwaves simultaneously while supplying heated air through the gas dispersion plate into the through-holes of the molded body, in an atmosphere containing water vapor surrounding the molded body; wherein prior to the supply of heated air and the irradiation of microwaves, a sealing member is situated on the outer side of an edge of the molded body on the gas dispersion plate side, to prevent the heated air from the gas dispersion plate from contacting the outer peripheral wall of the molded body.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2012/055724 filed Mar. 6 , 2012, claiming priority based on Japanese Patent Application No. 2011-049267filed Mar. 7, 2011, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a drying method and a drying device for a green honeycomb molded body.

BACKGROUND ART

A ceramic honeycomb structure with numerous through-holes is produced by molding a green honeycomb molded body containing ceramic starting material powder and a solvent, and drying and firing it. Patent Literature 1 below discloses a method using microwaves and heated air, as a method of drying a green honeycomb molded body.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the prior art methods, however, the green honeycomb molded body undergoes deformation or cracking during drying.

In light of this problem, it is an object of the present invention to provide a drying method and a drying device for a green honeycomb molded body, which can minimize deformation and cracking of the green honeycomb molded body during drying.

Solution to Problem

The invention provides a method of drying a green honeycomb molded body having a plurality of through-holes, using microwaves and heated air, the method comprising the steps of: mounting a green honeycomb molded body on a gas dispersion plate capable of releasing heated air; and irradiating the green honeycomb molded body with microwaves simultaneously while supplying heated air through the gas dispersion plate into the through-holes of the green honeycomb molded body, in an atmosphere containing water vapor surrounding the green honeycomb molded body; wherein prior to the supply of heated air and the irradiation of microwaves, a sealing member is situated on the outer side of an edge of the green honeycomb molded body on the gas dispersion plate side, to prevent the heated air from the gas dispersion plate from contacting the outer peripheral wall of the green honeycomb molded body.

The invention also provides a drying device for a green honeycomb molded body having a plurality of through-holes, the device comprising a container; a microwave source that supplies microwaves into the container; a heated air source that supplies heated air into the container; a water vapor supply port that supplies water vapor into the container; a gas dispersion plate in the container, that supplies heated air from the heated air source onto one end face on which the openings of the plurality of through-holes are formed in the green honeycomb molded body; and a sealing member situated on the outer side of an edge on the gas dispersion plate side of the green honeycomb molded body, that prevents heated air from the gas dispersion plate from contacting the outer peripheral wall of the green honeycomb molded body.

When the region of the gas dispersion plate through which heated air is released (the gas-releasing region) is larger than the end face of the green honeycomb molded body, the sections of the gas-releasing region not covered by the end face of the green honeycomb molded body are preferably plugged by the sealing member. The green honeycomb molded body is readily deformed at the initial stage of drying, during which a large amount of solvent remains. By avoiding release of heated air from the sections not covered by the end face of the green honeycomb molded body, as mentioned above, it is possible to effectively inhibit deformation during the initial stage of drying, and to more reliably prevent deformation and cracking of the molded body.

According to the invention, the sealing member is preferably made of a material capable of following the contraction that occurs during drying of the green honeycomb molded body. For example, even if the entire gas-releasing region is covered by the end face of the green honeycomb molded body in the initial stage of drying, the gas-releasing region can sometimes be exposed if the area of the end face of the green honeycomb molded body decreases during drying. By using a sealing member capable of following contraction of the green honeycomb molded body, it is possible to sufficiently prevent leakage of heated air from this region to the outer side of the green honeycomb molded body during drying. This can more reliably prevent excessive drying of the outer peripheral wall of the green honeycomb molded body.

In addition, using a sealing member made of such a material can effectively avoid inconveniences such as the following. Specifically, because the through-holes of the green honeycomb molded body have relatively high pressure loss, exposure of the gas-releasing region with contraction of the green honeycomb molded body tends to result in a large amount of heated air flowing from that region to the outer side of the molded body, and less gas flowing through the through-holes of the molded body. When this condition occurs, drying of the molded body interior becomes insufficient, and problems such as collapse of the cells and cracking of the molded body are produced in the post-drying steps (for example the cutting step).

Advantageous Effects of Invention

According to the invention it is possible to provide a drying device and a drying method for a green honeycomb molded body, that can prevent deformation and cracking of the green honeycomb molded body during drying.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the drying device for a green honeycomb molded body according to the invention will now be explained with reference toFIG. 1(a). Throughout the explanation, identical or similarly functioning elements will be referred to by like reference numerals and will be explained only once.

The drying device100of the green honeycomb molded body of this embodiment serves to dry a green honeycomb molded body70, and it mainly comprises a container10, a microwave source20that supplies microwaves into the container10, a mounting stage40situated inside the container10, a heated air source30that supplies heated air to the plurality of through-holes70aof the green honeycomb molded body70through a gas dispersion plate (gas outlet)42of the mounting stage40, and a sealing member80that prevents heated air from the gas dispersion plate42from contacting the outer side of the green honeycomb molded body70.

First, the green honeycomb molded body70that is to be dried will be explained.

The green honeycomb molded body70according to this embodiment is a cylinder with a plurality of through-holes70aeach extending in the Z-axial direction, as shown inFIG. 1. There are no particular restrictions on the outer shape of the green honeycomb molded body70, and for example, it may be circular columnar, elliptic cylindrical, prismatic (for example, regular polygonal columnar such as equilateral triangular columnar, square columnar, regular hexagonal columnar or regular octagonal columnar, or a triangular columnar, square columnar, hexagonal columnar or octagonal columnar shape other than a regular polygonal columnar shape). The cross-sectional shapes of each of the through-holes70aare also not particularly restricted, and for example, they may be circular, elliptical or polygonal such as square, rectangular, triangular or hexagonal. The through-holes70amay also include a combination of different sizes and different cross-sectional shapes.

There are no particular restrictions on the arrangement of the through-holes70aas seen from the end face of the green honeycomb molded body70in the Z-axial direction, and for example, it may be a square arrangement in which the central axes of the through-holes70aare disposed each at the vertices of a square, or a regular triangular arrangement in which the central axes of the through-holes70aare disposed at the vertices of a regular triangle.

The sizes of the through-holes70aare also not particularly restricted, and if the cross-section is square, for example, the sides may be 0.8 to 2.5 mm. The thicknesses of the partitions separating the through-holes70afrom each other may be, for example, 0.15 to 0.76 mm.

There are no particular restrictions on the lengths of the through-holes70aof the green honeycomb molded body70in the direction of their extension (the full lengths in the Z-direction), and they may be 40 to 350 mm, for example. There are also no particular restrictions on the outer diameter of the green honeycomb molded body70, and it may be 100 to 320 mm, for example.

FIG. 2andFIG. 3show concrete examples of the green honeycomb molded body70. The green honeycomb molded body70A shown inFIG. 2has through-holes70awith square cross-sectional shapes. The green honeycomb molded body70B shown inFIG. 3has a plurality of through-holes71a,71bwith different cross-sectional shapes. The plurality of through-holes71a,71bare partitioned by partitions72extending substantially parallel to the central axis of the green honeycomb molded body70B. The through-holes71ahave cross-sectional shapes that are regular hexagonal. The through-holes71b, on the other hand, have cross-sectional shapes that are flattened hexagonal, and they are disposed surrounding the through-holes71a.

The green honeycomb molded body70is a green body (unfired body) that is to become a ceramic by subsequent firing, and it is most preferably a green body for a porous ceramic. Specifically, the green honeycomb molded body70contains a ceramic starting material. The ceramic is not particularly restricted, and examples include oxides such as alumina, silica, mullite, cordierite, glass and aluminum titanate, and silicon carbide, silicon nitride, metals and the like. Aluminum titanate may further include magnesium and/or silicon.

The green honeycomb molded body70preferably includes an inorganic compound source powder as the ceramic starting material, an organic binder such as methyl cellulose, and additives that are added as necessary.

For example, when the ceramic is aluminum titanate, the inorganic compound source powder may include an aluminum source powder such as α-alumina powder, and a titanium source powder such as anatase or rutile titania powder, and/or aluminum titanate powder, and if necessary, also a magnesium source powder such as magnesia powder or magnesia spinel powder, and/or a silicon source powder such as silicon oxide powder or glass frit.

Examples of organic binders include celluloses such as methyl cellulose, carboxylmethyl cellulose, hydroxyalkylmethyl cellulose and sodium carboxylmethyl cellulose; alcohols such as polyvinyl alcohol; and ligninsulfonic acid salts. The amount of organic binder is preferably no greater than 20 parts by weight, more preferably no greater than 15 parts by weight and even more preferably no greater than 6 parts by weight, with respect to 100 parts by weight of the inorganic compound source powder. The lower limit for the organic binder is preferably 0.1 part by weight and more preferably 3 parts by weight.

Examples of additives include pore-forming agents, lubricants, plasticizers, dispersing agents and solvents.

Pore-forming agents include carbon materials such as graphite; resins such as polyethylene, polypropylene and polymethyl methacrylate; plant materials such as starch, nut shells, walnut shells and corn; ice; and dry ice. The amount of pore-forming agent to be added is preferably 0 to 40 parts by weight and more preferably 0 to 25 parts by weight, with respect to 100 parts by weight of the inorganic compound source powder.

Lubricants include alcohols such as glycerin; higher fatty acids such as caprylic acid, lauric acid, palmitic acid, arachidic acid, oleic acid and stearic acid; and stearic acid metal salts such as aluminum stearate. The amount of lubricant addition is preferably 0 to 10 parts by weight and more preferably 1 to 5 parts by weight, with respect to 100 parts by weight of the inorganic compound source powder.

The plasticizer may be a polyoxyalkylenealkyl ether, for example. The amount of plasticizer is preferably 0.1 to 20 parts by weight, more preferably 0.1 to 10 parts by weight and even more preferably 0.1 to 6 parts by weight with respect to 100 parts by weight of the inorganic compound source powder.

Examples of dispersing agents include inorganic acids such as nitric acid, hydrochloric acid and sulfuric acid; organic acids such as oxalic acid, citric acid, acetic acid, malic acid and lactic acid; alcohols such as methanol, ethanol and propanol; and surfactants such as ammonium polycarboxylate. The amount of dispersing agent to be added is preferably 0 to 20 parts by weight and more preferably 2 to 8 parts by weight, with respect to 100 parts by weight of the inorganic compound source powder.

Examples of solvents to be used include alcohols such as methanol, ethanol, butanol and propanol; glycols such as propylene glycol, polypropylene glycol and ethylene glycol; and water. Water is preferred among these, and more preferably ion-exchanged water is used for a low impurity content. The amount of solvent used is preferably 10 to 100 parts by weight and more preferably 20 to 80 parts by weight, with respect to 100 parts by weight of the inorganic compound source powder.

The weight of the solvent with respect to the weight of the entire molded body is not particularly restricted, but it is preferably 10 to 30 wt % and more preferably 15 to 20 wt %.

Such a green honeycomb molded body70can be produced in the following manner, for example.

First, the inorganic compound source powder, organic binder, solvent and if necessary additives to be added, are prepared. These are mixed with a kneader or the like to obtain a starting mixture, and the obtained starting mixture may be extruded from an extruder having an outlet opening corresponding to the cross-sectional shape of the green honeycomb molded body, and then cut to a prescribed length to obtain a green honeycomb molded body70.

The container10is able to house the green honeycomb molded body70, the mounting stage40and the outlet section36aof a pipe line36. The container10is preferably made of metal from the viewpoint of blocking microwaves. An exhaust port10bis provided in the container10, whereby gas in the container10is discharged to the exterior. The container10also has a waveguide10athat receives microwaves supplied from the microwave source20.

The microwave source20generates microwaves to heat the green honeycomb molded body70. The wavelength of the microwaves is not particularly restricted so long as it can heat the green honeycomb molded body70. The preferred wavelength range is 895-940 MHz or 2400-2500 MHz. The microwave source20is preferably one that allows the output of the microwaves to be lowered as drying proceeds. The microwave output is not particularly restricted, and may be 1 to 10 kW, for example, for each green honeycomb molded body. More specifically, the microwave output per unit weight of the green honeycomb molded body70is preferably 0.02 to 10 kW/kg, more preferably 0.2 to 4 kW/kg and even more preferably 1 to 3 kW/kg. If the microwave output per unit weight of the green honeycomb molded body70is less than 0.02 kW/kg a long time will be required for drying of the green honeycomb molded body70, and if it exceeds 10 kW/kg, abnormal heat release may take place in the organic material in the green honeycomb molded body70, and the green honeycomb molded body70will tend to undergo combustion, resulting in lower yield.

The mounting stage40is situated inside the container10, and it is a stage for placement of the green honeycomb molded body70on its top side. The mounting stage40comprises a gas dispersion plate42, and a non-air-permeable ring member44surrounding the sides of the gas dispersion plate42. The green honeycomb molded body70is mounted on the gas dispersion plate42in such a manner that one end face on which the openings of the plurality of through-holes70aare provided (the bottom side)70dis facing the top side of the gas dispersion plate42. For this embodiment the size of the top side of the gas dispersion plate42(the gas-releasing region) is the same size as the end face70dof the green honeycomb molded body70, but it may be slightly larger than the end face70d.

The gas dispersion plate42is a plate with a plurality of holes running from the front to back sides, and it evens out the gas flow in the in-plane direction when gas supplied from below passes through it upward. The gas dispersion plate42may be a perforated plate having formed therein a plurality of holes running in straight lines from the front to back sides (for example, the same honeycomb structure as the green honeycomb molded body), but so long as it is constructed so as to allow gas to be released upward, it may be a porous board having numerous curved pores running from the front to back sides, for example.

There are also no particular restrictions on the material of the gas dispersion plate42, which may be a ceramic such as alumina or cordierite. The thickness of the gas dispersion plate42may be 10 to 100 mm, for example.

When the gas dispersion plate42is a perforated plate, the two-dimensional configuration of the holes is not limited, and for example, it may be square, circular, hexagonal or octagonal. The sizes of the holes, with square shapes for example, may be 0.7 to 10 mm as the lengths on one of the sides. The thickness of the walls between holes may be 0.03 to 3.0 mm, for example.

When the gas dispersion plate42is a porous board, on the other hand, the mean pore size is not particularly restricted but is preferably 0.1 to 100 μm. The mean pore size can be measured by mercury porosimetry. The porosity is preferably 10% to 90%. It may also be a perforated plate composed of porous boards.

The ring member44surrounds the sides of the gas dispersion plate42and prevents leakage of gas from the sides.

The heated air source30comprises a blower32situated outside the container10, a pipe line36that directs gas from the blower32to the bottom side of the gas dispersion plate42, and a heater34provided in the pipe line36, that heats the gas flowing through the pipe line36. The gas heating temperature is not particularly restricted, but the minimum temperature is preferably 30° C., more preferably 40° C., even more preferably 50° C. and most preferably 70° C., and the maximum temperature is preferably 200° C., more preferably 120° C. and even more preferably 100° C. The gas is also not particularly restricted, but air is preferred from the viewpoint of economy. There are no particular restrictions on the gas flow rate, but the gas speed averaged over the area of the gas dispersion plate directly above the gas dispersion plate42is preferably 0.1 to 10 m/s and more preferably 0.5 to 5 m/s.

The outlet section36aof the pipe line36has a diameter that enlarges with the area of the bottom side of the gas dispersion plate42, and it contacts the bottom side of the ring member44.

A water vapor supply port10cis formed on the wall of the container10. A water vapor source is connected to the water vapor supply port10cvia a water vapor supply line L1, and water vapor is supplied into the container10, allowing the surroundings of each green honeycomb molded body to be kept in an atmosphere in which water vapor is present. Preferably, an amount of water vapor that saturates the inside of the container10is supplied from the line L1. By creating a high humidity environment inside the container10, it is possible to minimize deformation of the green honeycomb molded body70, and especially deformation during the initial stage of drying. The water vapor supply conditions are not particularly restricted, and for example, preferably the temperature is 100° C. to 200° C. and the supply rate is 0.1 to 5.0 kg/min. More specifically, it is preferably 0.1 to 30 kg/hr per unit weight of the green honeycomb molded body70.

The sealing member80is a member serving to prevent the heated air from the gas dispersion plate42from contacting the outer peripheral wall of the green honeycomb molded body70. The sealing member80is disposed in such a manner as to cover the outer side of the bottom end of the green honeycomb molded body70, and the perimeter of the gas dispersion plate42.

The sealing member80is preferably made of a material that can follow the contraction that occurs during drying of the green honeycomb molded body70. Such a material may be silicone rubber, fluorine rubber, or the like. When the sealing member80is made of such a material in tubular form, and situated as shown inFIG. 1(a), there are formed a section80aextending along the axial direction (Z-direction) and a section80bspreading out in the direction perpendicular to the Z-direction (the XY plane). Alternatively, the tubular sealing member80may be machined beforehand, forming a section80aextending along the Z-direction and a section80bspreading out in the direction horizontal to the axial direction.

In order to prevent bearing of load from the sealing member80on the green honeycomb molded body70and resulting deformation, the inner diameter D1of the section80aextending in the Z-direction, when not mounted, is preferably slightly smaller than the outer diameter D2of the green honeycomb molded body70when dry, and the difference (D2-D1) may be about 1 to 20 mm. For example, when the diameter of the green honeycomb molded body70is 150 mm, the inner diameter of the sealing member80is preferably about 140 to 130 mm. There are no particular restrictions on the length L80bof the sealing member80in the Z-direction, and it may be 1 to 100 mm. The thickness of the sealing member80may be 0.5 to 5 mm, for example.

A method of drying the green honeycomb molded body according to this embodiment will now be explained.

First, as shown inFIG. 1(a), the base side (section80a) of the sealing member80is mounted on the outer side of one edge of the green honeycomb molded body70, and the green honeycomb molded body70is mounted on the top side of the gas dispersion plate42of the container10, with the end face70dfacing. Thus, the tip end of the sealing member80(section80b) spreads out to cover the perimeter of the gas dispersion plate42.

Next, the blower32is activated, together with the heater34. Also, microwaves are supplied into the container10from a microwave source20. In addition, water vapor is continuously supplied into the container from the water vapor supply port10b, creating an atmosphere in which water vapor is present, surrounding each green honeycomb molded body70.

This causes a water vapor-containing atmosphere to surround the green honeycomb molded body70, and heated gas is supplied to the bottom side of the gas dispersion plate42through the pipe line36, passes through the gas dispersion plate42, passes through each of the through-holes70aof the green honeycomb molded body70, is discharged from the top side70uof the green honeycomb molded body70, and is then discharged from the exhaust port10bof the container10. Also, microwaves are irradiated onto the green honeycomb molded body70. There may be a time period during which both heated air and microwaves are simultaneously supplied, and the timing for their initial or final supply does not necessarily need to be simultaneous.

Supplying heat and gas in this manner removes the solvent component of the green honeycomb molded body70, and allows drying to proceed. As drying proceeds, the output of microwaves supplied from the microwave source20is preferably lowered. This has the effect of inhibiting runaway (ignition) due to local temperature increase resulting from excessive drying. There are no particular restrictions on the final extent of drying of the molded body that is reached as a result of the drying by heated air and microwaves in a water vapor atmosphere, but the dryness factor of the molded body at the point when the microwave and water vapor supply is terminated, i.e. the ratio of the solvent mass removed by drying with respect to the solvent mass before drying the molded body, is preferably at least 80%, more preferably at least 90% and even more preferably at least 95%. After terminating supply of the microwaves and water vapor, heated air alone is preferably blown to promote further drying.

According to this embodiment, creating a water vapor atmosphere around the green honeycomb molded body during the heated gas supply and microwave irradiation inhibits excessive drying of the outer sides of the green honeycomb molded body before the center section.

Also, by using a sealing member80capable of following contraction of the green honeycomb molded body70, it is possible to sufficiently prevent leakage of heated air to the outer side of the green honeycomb molded body70during drying (seeFIG. 6), and to more reliably prevent excessive drying of the outer peripheral wall of the green honeycomb molded body70. In addition, using the sealing member80can effectively avoid inconveniences such as the following. Specifically, when the open area of the through-holes70aof the green honeycomb molded body70is relatively small, exposure of the gas-releasing region of the gas dispersion plate42with contraction of the green honeycomb molded body70results in a large amount of heated air flowing from that region to the outer side of the molded body70, and less gas flowing through the through-holes70a. When this condition occurs, drying of the molded body70interior becomes insufficient, and problems such as collapse of the cells and cracking of the molded body are produced in the post-drying steps (for example the cutting step). According to this embodiment, such inconveniences can be adequately reduced, allowing yield to be increased.

The edges of the through-holes70aof the green honeycomb molded body70dried in this manner are sealed if necessary, and subsequently fired, to obtain a ceramic honeycomb structure. The ceramic honeycomb structure can be used as a diesel particulate filter or a catalyst support in a flue gas treatment device.

A drying device200according to a second embodiment will now be explained with reference toFIG. 4andFIG. 5. For this embodiment, only the aspects different from the first embodiment will be explained, while avoiding redundant explanation. The drying device200according to this embodiment accomplishes simultaneous drying of two green honeycomb molded bodies70.

According to this embodiment, as shown inFIG. 4, the mounting stage40comprises two gas dispersion plates (gas outlets)42and non-air-permeable ring members44surrounding the sides of the two gas dispersion plates42, and the outer shape is discoid. The two green honeycomb molded bodies70are mounted on the gas dispersion plates42in such a manner that one end face (the bottom side)70don which the openings of the plurality of through-holes70aare provided is each facing the top side of the respective gas dispersion plate42, and each sealing member80covers the outer side of the bottom end of the green honeycomb molded body70and the perimeter of the gas dispersion plate42. Each gas dispersion plate42and sealing member80is the same as for the first embodiment. The two gas dispersion plates42are disposed so that the distance D between the green honeycomb molded bodies70mounted on the gas dispersion plates42is greater than ½λ, where λ is wavelength of the microwaves supplied by the microwave source20.

A vertical shaft52is provided at the center bottom side of the mounting stage40, and the vertical shaft52is rotatable by a motor50. This allows the mounting stage40to be rotated around the vertical shaft inside the container10. The rotational speed is not particularly restricted and may be 1 to 60 rpm.

As shown inFIG. 4andFIG. 5, an opening36abis provided on the outlet section36aof the pipe line36, facing upward and appearing as a ring shape as viewed from above. The tip36aeof the outlet section36acontacts with the bottom side of the ring member44, as shown inFIG. 4. If the outlet section36ahas a ring-shaped opening36abfacing upward in this manner, the heated air can be supplied to each of the through-holes70aof each green honeycomb molded body70through the gas dispersion plate42serving as the gas outlet, regardless of the rotational position of the rotating mounting stage40. The tip36aeof the outlet section36ais set so as to be in sliding contact with the bottom side of the ring member44, and it can be gas-sealed.

According to this embodiment, the same function and effect are exhibited as by the first embodiment. In addition, since the spacing D between the green honeycomb molded bodies70is greater than ½ of the wavelength λ of the microwaves, the microwaves can sufficiently surround the area between the green honeycomb molded bodies70, and uniform drying of the two molded bodies is facilitated.

Furthermore, since microwaves can be efficiently utilized when multiple green honeycomb molded bodies70are to be dried at one time in this type of drying device200, having the same microwave output and heated gas supply volume per green honeycomb molded body70allows the drying time to be shortened compared to drying each alone.

A fastener85may be provided to anchor the green honeycomb molded body70to the mounting stage40.

The present invention is not limited to the embodiments described above, and various modified modes are possible. For example, the aforementioned embodiment has the surface of the gas dispersion plate42disposed horizontally, with the green honeycomb molded body70being placed on the top side of the gas dispersion plate42so that the green honeycomb molded body70is held, but this is not limitative. For example, the surface of the gas dispersion plate42may be disposed perpendicularly, and the green honeycomb molded body70held by another holding member in such a manner that the end face70dof the green honeycomb molded body70contacts with the perpendicular surface.

Also, according to the second embodiment, two gas dispersion plates42are provided on the mounting stage40, two green honeycomb molded bodies70are mounted on the gas dispersion plates42and the molded bodies are dried at one time, but three or more gas dispersion plates may instead be provided for drying of three or more green honeycomb molded bodies70at one time.

Also, the use of a flexible sealing member80was mentioned as a particularly preferred example for this embodiment, but so long as deformation of the green honeycomb molded body can be prevented during the initial stage of drying, an annular plate covering the exposed portion of the gas-releasing region may be used as the sealing member.

In addition, the second embodiment can be carried out even if the spacing between the two green honeycomb molded bodies70is ½ or less of the microwave wavelength λ.

Also, a firing base with the same composition as the green honeycomb molded body70and having a through-hole structure, known as a “stilt”, may be provided instead of the gas dispersion plate42, or on the gas dispersion plate42, and the green honeycomb molded body70placed thereover. In this case, as shown inFIG. 6(a), the stilt42aand the green honeycomb molded body70may be integrated with the sealing member80beforehand, and the integrated body mounted on the gas dispersion plate42. By using a sealing member80made of a material capable of following contraction of the green honeycomb molded body, it is possible to keep the perimeter of the stilt42a(the exposed gas-releasing region) covered by the sealing member80, as shown inFIG. 6(b).

EXAMPLES

Example

(Method for Producing Honeycomb Molded Body)

The following powder was used as the inorganic compound source powder to obtain a green honeycomb molded body. The charging composition for the inorganic compound source powder was [Al2O3]/[TiO2]/[MgO]/[SiO2]=35.1%/51.3%/9.6%/4.0%, as the molar percentages based on alumina [Al2O3], titania [TiO2], magnesia [MgO] and silica [SiO2]. The content of the silicon source powder was 4.0 wt % with respect to the total of the aluminum source powder, titanium source powder, magnesium source powder and silicon source powder.(1) Aluminum Source Powderα-Alumina Powder with Mean Particle Size Listed in Table 1

24.6 parts by weight(2) Titanium Source PowderRutile Titania Powder with Mean Particle Size Listed in Table 1

42.0 parts by weight(3) Magnesium Source PowderMagnesia Spinel Powder with Mean Particle Size Listed in Table 1

15.7 parts by weight(4) Silicon Source PowderGlass frit with mean particle size listed in Table 1 (CK0832 by Takara Standard)

3.4 Parts by Weight

To a mixture comprising aluminum source powder, titanium source powder, magnesium source powder and silicon source powder there were added 14.3 parts by weight of corn starch having the mean particle size listed in Table 1, as a pore-forming agent, 5.5 parts by weight of methyl cellulose (trade name: METOLOSE 90SH-30000) as an organic binder, 4.6 parts by weight of polyoxyethylene polyoxypropylene butyl ether (trade name: UNILUBE 50 MB-72, viscosity at 20° C.: 1020 mPa·s) as a plasticizer, and 0.3 part by weight of glycerin as a lubricant, and after further adding 27 parts by weight of water as a dispersing medium (solvent), a kneader was used for kneading at 25° C. to prepare a green body (starting mixture for molding). Next, the green body was extrusion molded to produce a plurality of green honeycomb molded bodies. The green honeycomb molded bodies were circular columnar (length: 220 mm) with numerous through-holes, the numerous through-holes being arranged in a matrix-shaped square (seeFIG. 2). The cross-sectional shapes of the through-holes were square with 1.43 mm sides, and the partition thickness was 0.32 mm.

The green honeycomb molded bodies were dried with a drying device such as shown inFIG. 1. Specifically, drying treatment was carried out with a sealing member having an inner diameter slightly smaller than the diameter of the green honeycomb molded body (thickness: 1 mm, length: 10 mm, material: silicone rubber) mounted on each green honeycomb molded body, as shown inFIG. 1.

The drying conditions were as follows.

Specifications of Gas Dispersion Plate:

Two-dimensional configuration of holes: square with 5.2 mm sides; and

The microwave frequency was 2.45 GHz, and the microwave output was 24 kW up to a drying time of 0 to 5.5 minutes and 14.4 kW from 5.5 to 11 minutes.

The supply gas was air, and the supply gas heating temperature was 70° C. The gas supply rate was set so that the gas speed averaged over the area of the gas dispersion plate directly above the gas dispersion plate was 1 m/s. The temperature of the water vapor was 120° C., and the supply rate was 1.4 kg/min. The microwave exposure time was from time 0 to 11 minutes, the water vapor supply was from time 0 to 5.5 minutes, and the heated air supply was from time 0 to 11 minutes.

No deformation or cracking was seen in the green honeycomb molded bodies of the examples. The dryness factor of the green honeycomb molded body was 91.9%. The dryness factor is the value calculated by the following formula, based on the values of the weight of the green honeycomb molded body before drying and the weight after drying.
Dryness factor(%)=(Weight before drying−weight after drying)/(weight before drying×water content)×100

Drying treatment of a green honeycomb molded body was carried out in the same manner as the examples except that no sealing member was used. The dried molded body had a smaller outer diameter at the lower end than the other sections, and numerous creases were observed in the peripheral surface of the lower section of the molded body. The dryness factor of the green honeycomb molded body was 73.8%.

INDUSTRIAL APPLICABILITY

According to the invention it is possible to provide a drying device and a drying method for a green honeycomb molded body, that can prevent deformation and cracking of the green honeycomb molded body during drying.

REFERENCE SIGNS LIST