JP4964634B2 - Method for producing dried ceramic molded body - Google Patents

Description

  The present invention relates to a method for producing a dried ceramic molded body in which a drying step can be completed in a short time.

  Honeycomb structures are widely used for catalyst carriers, various filters, and the like. Recently, it has attracted attention as a diesel particulate filter (DPF) for capturing particulate matter discharged from a diesel engine.

  In general, the honeycomb structure is mainly composed of ceramic. In order to manufacture such a honeycomb structure, first, a ceramic raw material obtained by adding various additives such as water and binder to the ceramic is made into a clay, and then extruded to form a honeycomb shape. A formed body (honeycomb substrate) is prepared. If the honeycomb substrate is dried and then fired, a honeycomb structure can be manufactured.

  Depending on the size and application of the honeycomb structure to be obtained, a honeycomb structure having an outer wall portion formed on the outer periphery thereof may be used. A honeycomb structure having such an outer wall portion is manufactured, for example, by coating a coating material containing ceramic powder on the outer periphery of the honeycomb substrate in a layered manner to form a coating layer, followed by drying and firing. be able to.

  Conventional techniques relating to such a method for drying a honeycomb substrate include a natural drying method in which the honeycomb substrate is simply left at room temperature, and a method in which a current is passed between electrodes provided above and below the honeycomb substrate. A dielectric drying method for drying using high frequency energy and a hot air drying method for drying by introducing hot air generated by a gas burner or the like are well known. However, recently, instead of these drying methods, or in combination with these drying methods, a drying method using microwaves (microwave drying method) having advantages such as a high drying speed has come to be performed. (For example, see Patent Documents 1 to 3).

  However, the natural drying method requires more time than other drying methods to obtain a sufficiently dry state. In particular, when the honeycomb substrate is large, there is a problem that a considerably long time is required. On the other hand, when a honeycomb substrate having a coating layer formed on the outer periphery of the honeycomb substrate is dried by a hot-air drying method or a microwave drying method, there is an advantage that the drying is completed in a short time compared to a natural drying method. . However, there is a problem that cracks are likely to occur on the surface of the dried coat layer, and the quality and production yield are lowered. In order to avoid the occurrence of such cracks, measures such as drying in an appropriately humidified atmosphere (humidity controlled atmosphere) can be considered, but the drying time is prolonged, so it is insufficient in terms of practicality Met.

JP 2002-283329 A JP 2002-283330 A International Publication No. 2005/023503 Pamphlet

  The present invention has been made in view of such problems of the prior art, and the problem is that even if the ceramic substrate is large, cracks are not generated in the coat layer in a short time. It is an object of the present invention to provide a method for producing a dried ceramic molded body that can be uniformly dried without unevenness and can produce a high-quality dried ceramic molded body with good yield.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved by maintaining the surface temperature of the ceramic molded body at 80 ° C. or higher and performing drying. The present invention has been completed.

  That is, according to this invention, the manufacturing method of the dry ceramic molded object shown below is provided.

[1] A ceramic molded body comprising an unfired or fired ceramic base formed of a ceramic raw material, and a coating layer formed on the outer periphery of the ceramic base and made of a coating material containing ceramic powder. Dry ceramic molding including obtaining a dried ceramic molded body by maintaining the surface temperature at 80 ° C. or higher in an atmosphere of superheated steam of 100 ° C. or higher, where the water vapor partial pressure is 70% or more of the total pressure. Body manufacturing method.

[ 2 ] The method for producing a dried ceramic molded body according to [1 ], wherein the ceramic base is a honeycomb-shaped structure having a plurality of cells serving as fluid flow paths partitioned by partition walls.

[ 3 ] The method for producing a dried ceramic molded body according to [ 1 ] or [ 2 ], wherein the temperature of the superheated steam is 120 to 180 ° C.

[ 4 ] The method for producing a dried ceramic molded body according to any one of [1] to [ 3 ], wherein the coat layer has a thickness of 0.5 mm or more.

  According to the method for producing a dried ceramic molded body of the present invention, a high quality dried ceramic molded body can be obtained by drying uniformly in a short time without causing cracks in the coat layer even if the ceramic substrate is large. It can be manufactured with good yield.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment, and is based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention. It should be understood that modifications and improvements as appropriate to the following embodiments also fall within the scope of the present invention.

One embodiment of a method for producing a dried ceramic molded body according to the present invention includes an unfired or fired ceramic base formed of a ceramic raw material, and a coating material containing ceramic powder formed on the outer periphery of the ceramic base. The ceramic molded body provided with a coat layer made of is dried in an atmosphere of superheated steam of 100 ° C. or higher, where the water vapor partial pressure is 70% or more of the total pressure, while maintaining the surface temperature at 80 ° C. or higher, This includes obtaining a dried ceramic molded body. The details will be described below.

  Specific examples of the ceramic molded body to be dried in the method for producing a dried ceramic molded body according to the present invention include a honeycomb molded body 1 as shown in FIGS. The ceramic molded body to be dried is not limited to the honeycomb-shaped structure as shown in FIGS. 1 and 2, and may be any shape such as a columnar shape, a plate shape, an annular shape, and an indefinite shape.

  A honeycomb molded body 1 shown in FIGS. 1 and 2 is a honeycomb-shaped structure (honeycomb substrate 5) having a plurality of cells 3 that serve as fluid flow paths partitioned by partition walls 2. In addition, the honeycomb formed body 1 is generally configured by disposing a coat layer 4 on the outer periphery of the honeycomb substrate 5 so as to surround a plurality of cells 3. In addition, the cross-sectional shape orthogonal to the axial direction (flow channel direction) of the cell 3 is not limited, and a shape such as a quadrangle as well as a circle as shown in FIG. 1 can be arbitrarily selected.

  The honeycomb substrate 5 is formed of, for example, a ceramic raw material obtained by adding various additives such as water and a binder to ceramic. Examples of the ceramic include oxide ceramics such as alumina, mullite, zirconia, and cordierite; non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride. A silicon carbide / metal silicon composite material, a silicon carbide / graphite composite material, or the like can also be used.

  Examples of the binder include polyvinyl alcohol, polyethylene glycol, starch, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, polyethylene oxide, sodium polyacrylate, polyacrylamide, polyvinyl butyral, ethyl cellulose, cellulose acetate, polyethylene, and ethylene-acetic acid. Examples include vinyl copolymers, polypropylene, polystyrene, acrylic resins, polyamide resins, glycerin, polyethylene glycol, and dibutyl phthalate.

  Further, the honeycomb substrate 5 may be unfired (unfired body) or fired (fired body). Here, the “unfired body” refers to a ceramic particle used in a state in which the shape of the particle is maintained while being molded, and the ceramic is not sintered. . On the other hand, the term “fired body” means that the ceramic used is exposed to high temperature, even if it is in a state modified to other compounds or the same substance (ceramic). This means that the particle shape has changed due to grain growth or formation of bonds between grains.

  The coating layer 4 disposed on the outer periphery of the honeycomb substrate 5 can be formed by applying a coating material containing at least ceramic powder as an aggregate and water in layers. Specific examples of the ceramic constituting the ceramic powder contained in the coating material include the same ceramics as described above. In addition to the ceramic powder and water, the coating material may contain, for example, a colloidal oxide (inorganic binder) such as silica sol or alumina sol as a reinforcing material. Moreover, you may contain organic binders, such as methylcellulose and polyvinyl alcohol, as a reinforcing material. Furthermore, it is also preferable that the coating material contains a ceramic fiber made of amorphous mullite, silica-alumina, or the like as an aggregate.

  By including a thermosetting material such as a sol material, a cement material, or a fiber as a reinforcing material in the coating material, it is possible to more effectively suppress the occurrence of cracks in the coating layer. Moreover, containing an organic binder in the coating material is also effective for suppressing cracks. For this reason, more efficient and effective drying can be performed by using together the coating material containing these reinforcing materials, and performing drying using superheated steam. In addition, when the coating material containing these reinforcement | strengthening materials is used, the workability | operativity at the time of a coating may fall, or the characteristic of the product obtained may fall. For this reason, in the conventional method for producing a dried ceramic molded body, it is not always good that the coating material contains a reinforcing material. However, according to the method for producing a dried ceramic molded body of the present invention, a coating material containing a reinforcing material can be positively used.

  In the method for producing a dried ceramic molded body according to the present invention, the ceramic molded body including the honeycomb molded body 1 as shown in FIGS. 1 and 2 is dried while maintaining the surface temperature at 80 ° C. or higher. In addition, the surface temperature of the ceramic molded body at the time of drying can be measured by bringing a thermocouple into contact with the surface of the ceramic molded body. When the honeycomb formed body 1 shown in FIGS. 1 and 2 is dried, moisture contained in the coat layer 4 evaporates to form an outer wall portion, and a dry ceramic formed body can be obtained. When the honeycomb substrate 5 is an unfired body containing moisture, this moisture is also evaporated to form a dried honeycomb substrate 5. Thus, when the surface temperature is maintained at 80 ° C. or higher and the ceramic molded body is dried, the drying can be completed in a short time without generating cracks in the coating layer.

  Examples of the method for maintaining the surface temperature of the ceramic molded body at 80 ° C. or higher include a method in which a heating medium such as superheated steam adjusted to an appropriate temperature is brought into contact with the ceramic molded body. In addition to the method using superheated steam, for example, there is a method of heating a ceramic molded body by microwave heating, dielectric heating, or infrared heating in a humidified atmosphere. Furthermore, there is also a method in which an electric current is passed through the ceramic molded body and heated using Joule heat. Among these methods, it is preferable to dry the ceramic compact using superheated steam because the atmosphere can be easily controlled.

Temperature of overheating steam state, and are 100 ° C. or higher, it is good Mashiku is 120 to 180 ° C., and more preferably a 140 to 180 ° C.. When superheated steam at 100 ° C. or higher is used, drying can be completed in a shorter time without generating more cracks in the coat layer. It should be noted that, when the temperature of the superheated steam is less than 100 ℃, the time required for drying intends island a long period of time. On the other hand, drying is possible even when the temperature of the superheated steam is higher than 180 ° C., but the drying rate is remarkably increased, so that cracks may occur in the coating layer.

  The water vapor partial pressure (volume ratio of water vapor) of the superheated water vapor used for drying is 70% or more, preferably 80% or more, more preferably 90 to 100% of the total pressure. By using superheated steam having a steam partial pressure of 70% or more, the coating layer can be further dried without causing cracks. If the water vapor partial pressure of the superheated steam is less than 70%, drying is completed in a short time, but cracks are likely to occur in the coating layer.

  In the case of using superheated steam, drying may be performed by placing the ceramic molded body in a drier having a predetermined condition of superheated steam. Further, it is preferable to irradiate the ceramic molded body with microwaves or irradiate infrared rays because drying can be performed more rapidly. In the case where the honeycomb formed body 1 as shown in FIGS. 1 and 2 is dried, it is also a preferable embodiment that superheated steam is passed through the cells 3. As a method for ventilating superheated steam into the cell 3, for example, (1) A method in which the honeycomb formed body is placed vertically and the superheated steam is forcibly sent from above or below the cell 3 using a blower fan or the like. (2) A method of sucking superheated steam by installing an exhaust fan above or below the cell 3, (3) A method of naturally ventilating using convection (updraft) due to a temperature difference of the superheated steam, etc. Can be mentioned. Further, by using a baffle plate or the like and controlling the flow of superheated steam at the inlet or outlet of the cell 3, it is possible to control the amount of ventilation at each position in the honeycomb formed body 1 and adjust the drying speed. is there. Thus, by allowing superheated steam to flow through the cell, drying can be promoted from both the inner surface and the outer surface of the coat layer, so it is possible to form a crack-free coat layer more quickly. is there.

  The size of the ceramic molded body to be dried in the method for producing a dried ceramic molded body of the present invention is not particularly limited. However, the effect of the method for producing a dried ceramic molded body of the present invention is particularly remarkable when a relatively large ceramic molded body is dried. Specifically, it is effective when the thickness of the coat layer of the ceramic molded body is preferably 0.5 mm or more, more preferably 1.0 mm or more.

  The time required for drying the ceramic molded body varies depending on the dimensions and shape of the ceramic molded body, the thickness and surface area of the coat layer, the moisture content, etc., but is usually 1 to 120 minutes, preferably about 1 to 20 minutes. It is. In general, if drying takes a long time, the number of cracks generated in the coat layer decreases, but it is not effective because of poor productivity.

  Even when the honeycomb formed body 1 as shown in FIGS. 1 and 2 is dried, the cell density, partition wall thickness, cell shape, dimensions, and the like of the honeycomb formed body 1 are not particularly limited.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

Example 1
A cylindrical fired body made of ceramic having a honeycomb structure (outer diameter × channel length: 200 mm × 200 mm, cell density: 45 cells / cm ² , partition wall thickness: 0.3 mm) was prepared. A slurry-like coating material containing ceramic powder and silica sol (reinforcing material) was applied to the outer periphery of the fired body to obtain a honeycomb formed body on which a coating layer having a thickness of about 1.5 mm was formed. A thermocouple is placed in contact with the surface of the obtained honeycomb formed body, and is in a superheated steam atmosphere at 100 ° C. (partial pressure of superheated steam: 100% (superheated steam / hot air (volume ratio) = 100/0)), batch type Using a drier, drying was performed while measuring the surface temperature of the honeycomb formed body to obtain a dried honeycomb formed body. The time required for drying was 20 min. The “time required for drying” means “the ratio of the mass reduced by the actual drying to the reduced mass when the honeycomb formed body is completely dried (water content: 0%) is 95% or more. Means "time required for". Hereinafter, it has the same meaning. When the crack generation state on the outer wall portion (coat layer) surface of the obtained dried honeycomb molded body was visually observed, generation of cracks was not recognized.

(Examples 2-13, Comparative Examples 1-8)
Other than using a coating material containing the type of reinforcing material shown in Table 1 (however, Examples 10 and 11 do not contain a reinforcing material) and drying in a dry atmosphere shown in Table 1 Produced a dried honeycomb molded body in the same manner as in Example 1 described above. Table 1 shows the results of visual observation of the occurrence of cracks on the outer wall (coat layer) surface of the obtained dried honeycomb molded body. FIG. 3 shows a graph in which the surface temperature (° C.) of the honeycomb formed body is plotted with respect to the drying time (min) for Examples 11 and 13 and Comparative Example 8.

  As shown in Table 1, in Examples 1 to 13, it can be dried in a shorter time than Comparative Examples 1 to 8, and it is clear that cracks are hardly generated on the surface of the outer wall portion to be formed. is there. In addition, it became clear that drying was completed in a shorter time as the temperature of superheated steam was raised (Examples 1-4). Further, it is clear that cracks occur when the partial pressure of superheated steam is less than 70% (Comparative Examples 4 and 5). From the graph shown in FIG. 3, even when the temperature of the drying atmosphere is set to 80 ° C. (Comparative Example 8), the surface temperature of the honeycomb formed body in which drying is progressing does not rise to 80 ° C. It is clear. In addition, as in Examples 11 and 13, when the temperature of the drying atmosphere is set to be higher than 80 ° C., the honeycomb molded body can be dried with the surface temperature maintained at 80 ° C. or higher. It is clear that drying can be completed in a short time without cracks.

  According to the method for producing a dried ceramic molded body of the present invention, a high-quality honeycomb structure widely used for a catalyst carrier, various filters including DPF, and the like can be easily produced.

It is a front view which shows an example of the ceramic molded object (honeycomb molded object) used with the manufacturing method of the dry ceramic molded object of this invention. It is AA sectional drawing of FIG. 6 is a graph plotting the surface temperature (° C.) of the honeycomb formed body with respect to the drying time (min) for Examples 11 and 13 and Comparative Example 8. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Honeycomb molded object 2 Partition 3 Cell 4 Coat layer 5 Honeycomb base | substrate

Claims (4)

A ceramic molded body comprising an unfired or fired ceramic base formed of a ceramic raw material, and a coating layer formed on the outer periphery of the ceramic base and made of a coating material containing ceramic powder,
A dried ceramic molded body comprising obtaining a dried ceramic molded body by drying by holding the surface temperature at 80 ° C. or higher in an atmosphere of superheated steam of 100 ° C. or higher, where the water vapor partial pressure is 70% or more of the total pressure. Manufacturing method. 2. The method for producing a dried ceramic molded body according to claim 1, wherein the ceramic substrate is a honeycomb-shaped structure having a plurality of cells serving as fluid flow paths partitioned by partition walls. The method for producing a dried ceramic molded body according to claim 1 or 2 , wherein the temperature of the superheated steam is 120 to 180 ° C. The method for producing a dry ceramic molded body according to any one of claims 1 to 3 , wherein the coat layer has a thickness of 0.5 mm or more.

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