JP5327587B2 - Manufacturing method of ceramics - Google Patents

Description

    The present invention relates to a method for producing ceramics used for a ceramic honeycomb filter or the like for exhaust gas purification.

  From the viewpoint of environmental conservation, ceramic honeycomb filters are used for exhaust system parts such as diesel engines in order to collect particulate matter contained in large amounts in exhaust gas. In this filter, for example, as shown in FIG. 1, the flow path 11c of the ceramic honeycomb structure 11 is alternately plugged with the sealing portions 1a and 1b, so that the exhaust gas is not sealed on the inflow side 2a. It flows in from the channel 11c, passes through the partition wall 11b, and is discharged from the channel 11c that is not sealed on the outflow side 2b. When the exhaust gas passes through the partition wall 11b, particulate matter in the exhaust gas is collected on the partition wall surface and in the pores.

  The ceramic honeycomb structure 11 used as the filter has been manufactured by the following process. A ceramic raw material, for example, cordierite-forming raw material powder, a molding aid, a pore former and water are mixed and kneaded to form a ceramic clay, and this ceramic clay is extruded through a mold, and the outer peripheral wall 11a A ceramic honeycomb formed body having a honeycomb structure in which the partition walls 11b are integrally formed. Next, this molded body is dried and further fired to obtain a ceramic honeycomb structure 11 having fine pores in the partition walls 11b. In order to improve the collection efficiency of particulate matter in the exhaust gas and reduce the pressure loss, a pore former is used to control the pore diameter and porosity of the partition wall, but the porosity is 50% or more. In the case of extruding a ceramic honeycomb molded body that becomes a large ceramic honeycomb structure having such a high porosity and an outer diameter exceeding 150 mm, a foamed foamed resin has been used as a pore former.

By the way, when a ceramic clay is extruded and formed into a ceramic honeycomb molded body, the moldability of the molded body is affected by the rheological properties of the ceramic clay, so the ceramic clay is molded while ensuring fluidity. It is necessary to ensure the shape retention of the body.
Patent Document 1 discloses a method for producing a ceramic structure in which a compact is obtained from a plastic ceramic clay obtained by mixing a cordierite raw material containing an alumina component, a foamed resin, water and a plasticizer. A technique for preventing the foamed resin from being crushed during kneading and the deformation of the molded body during molding by using hydraulic alumina as a part of the components is disclosed. It is described that the ceramic clay preferably has a hardness value of 17 to 30 mm as measured by a hardness meter in which a conical tip and a support portion are connected by a spring material.

Patent Document 2 discloses a clay used as a raw material for extruding a ceramic honeycomb structure, in which a change in strain with time when a constant stress value is applied at a molding temperature is measured ( 1) Value obtained by dividing the stress value by the strain generated at the same time as applying stress: Elasticity 0 (G ₀ : Pa), (2) When the stress value is continuously applied, the strain change over time (shear rate) Value divided by the value when it becomes almost constant: Viscosity 0 (η ₀ : Pa · sec), (3) When the shear rate becomes almost constant, the straight line is extrapolated to the time axis of 0 seconds The value obtained by subtracting the strain obtained in (1) above from the strain at the time of elasticity: elasticity 1 (G ₁ : Pa), (4) the stress value after adding the stress for 4 seconds to the above ( The value obtained by subtracting the strain obtained in 1) and dividing by the average shear rate over 4 seconds: Viscosity 1 (η ₁ : Pa · sec) is η ₀ / G ₀ ≦ 105 (sec), η ₁ / G ₁ ≦ 70 (sec) It is said that by molding with the back clay, the fluidity is good and the shape retention after extrusion molding can be maintained.

Patent Document 3 discloses a clay used as a raw material for extrusion molding of a honeycomb structure, and the rheological characteristics of the clay are storage elastic moduli of 1.5 × 10 ^{6 to} 5.0 × 10 ⁶ ( Pa), complex viscosity 4.0 × to 9.0 × 10 ⁴ (Pa · s), yield value 5.0 × 10 ^{4 to} 1.5 × 10 ⁵ (Pa) in capillary rheometer test, plastic viscosity 10.0 to 1000.0 (Pa · s) It is disclosed to extrude with some ceramic clay. This ceramic clay is particularly suitable as a raw material for extrusion molding of a thin-walled honeycomb structure having a wall thickness of 100 μm or less, has good extrudability, and is difficult to cause surface breakage and sacrificial formation on the molded body.

JP 2003-89575 A JP-A-6-279090 JP 2000-302525 A

  However, even if the characteristics of the clay are measured by the method described in Patent Document 1, the method described in Patent Document 1 evaluates only the hardness of the clay, and in particular, the porosity. In the case of ceramic clay used for the formation of large ceramics with a high porosity such as 50% or more and an outer diameter exceeding 150 mm, a pore-forming material that is a foamed resin foamed on the clay is used. Since many are included, the characteristic to be measured sometimes tends to vary. Therefore, even if the characteristics of the clay are within the range specified in Patent Document 1, the optimal characteristics of the clay may not be obtained, and the quality of the product has become unstable.

  In addition, the characteristics of ceramic clay are measured by the methods described in Patent Document 2 and Patent Document 3, and the ceramics are large in size with a high porosity such as 50% or more and an outer diameter exceeding 150 mm. In the case of extruding the ceramic molded body, the following problems have occurred. Even if it is measured by the measurement method described in Patent Document 2 and Patent Document 3 and extrusion molding is performed with a ceramic clay having characteristics within the specified range, the fluidity of the ceramic clay during extrusion molding is ensured. In the case where problems such as crushing of the flow path, breakage of the partition wall, waviness of the flow path occur, or conversely, the molded body tends to be deformed by its own weight, so the shape retaining property after extrusion molding is not ensured and due to its own weight. There was a case of deformation. As a result of studies by the present inventors, the characteristic measurement method described in Patent Document 1 and Patent Document 2 is a method for measuring clay characteristics suitable for a ceramic material having a low porosity. In the case of ceramic clay used for the formation of large ceramics with a high porosity such as 50% or more and an outer diameter exceeding 150 mm, the pore making is a foamed resin that is already foamed in the clay. Since many materials are included, the measured characteristics are likely to vary. When the characteristics are measured by the method described in Patent Document 2 or Patent Document 3, and even if the characteristics of the clay are within the range specified by Patent Document 2 or Patent Document 3, the optimal characteristics are not obtained. And the product quality was unstable.

  The present invention solves the above problems, and appropriately evaluates the characteristics of the ceramic clay used for the formation of large ceramics with a high porosity such as 50% or more and an outer diameter exceeding 150 mm. It aims at providing the manufacturing method of ceramics.

That is, in the method for producing a ceramic of the present invention, a molding raw material containing a ceramic material and a foamed resin is mixed and kneaded to form clay, and then the molding clay is filled into a molding machine and molded. A ceramic manufacturing method for obtaining a ceramic having a porosity of 50% or more, an outer diameter of 150 mm or more, and a total length of 150 mm or more by firing the molded body, wherein the shear rate and shear stress of the clay A linear regression line is derived by a least square method with respect to the measured values plotted with the square root of the shear rate as the horizontal axis and the square root of the shear stress as the vertical axis, and the slope a and the linear regression line A value b of an intersection of the linear regression line and the vertical axis is obtained , and molding is performed using a clay with a ² of 60 Pa · s or less and b ² of 50 to 250 kPa .

  In the present invention, the ceramic is preferably a honeycomb structure.

  In the present invention, the ceramic is preferably a honeycomb filter.

Next, the function and effect of the present invention will be described.
A method for producing a ceramic according to the present invention, wherein a molding raw material containing a ceramic material and a foamed resin is mixed and kneaded to form clay, and then the molding clay is filled into a molding machine and molded to form. A ceramic manufacturing method for obtaining a ceramic having a porosity of 50% or more, an outer diameter of 150 mm or more, and a total length of 150 mm or more by firing the molded body, wherein the shear rate and shear stress of the clay A linear regression line is derived by a least square method with respect to the measured values plotted with the square root of the shear rate as the horizontal axis and the square root of the shear stress as the vertical axis, and the slope a and the linear regression line By obtaining the value b of the intersection of the linear regression line and the vertical axis and performing molding using a clay with a ² of 60 Pa · s or less and b ² of 50 to 250 kPa , the following effects are obtained. . That is, the shear rate and shear stress of the clay are measured and, as shown in FIG. 3, the minimum two values are plotted against the measured values plotted with the square root of the shear rate on the horizontal axis and the square root of the shear stress on the vertical axis. deriving a primary regression line in multiplication, the seeking value b at the intersection of the primary slope of the regression line a and the linear regression line and the longitudinal axis, a ² is 60 Pa · s or less, and, b ² is in 50~250kPa By molding using the above-mentioned clay, the characteristics of the clay can be evaluated properly and the quality of the product can be stabilized even if the evaluation method of the prior art does not produce a difference in evaluation results. Can do it.

Here, when a ² exceeds 60 Pa · s, the fluidity of the kneaded material is remarkably lowered, and the increase in the extrusion speed when the extrusion pressure is increased is very small, and the productivity cannot be improved. In addition, when the clay passes through the mold, in a region where the shear rate near the center of the groove width of the forming groove is very large, a large shear stress is applied, and the shear rate near the mold surface of the forming groove is very high. In a small region, a small shear stress is applied. That is, unevenness of the shear stress occurs in the partition wall thickness direction of the honeycomb structure, and uniform extrusion cannot be performed. In some cases, the partition walls are cracked or distorted. Preferably, it is 1 to 40 Pa · s.

When b ² is less than 50 kPa, the molded body extruded from the honeycomb structure extrusion mold is easily deformed by its own weight, resulting in poor appearance. On the other hand, if it exceeds 250 kPa, a very high extrusion pressure is required to extrude the clay from the mold, and the mold for large honeycomb structures exceeding φ150 mm causes problems such as warpage and breakage. Preferably, it is 80-230 kPa.

  In the present invention, a ceramic having a high porosity such as a porosity of 50% or more can be produced by including a foamed resin in the molding raw material. The foamed resin is preferably a foamed foamed resin.

  In the present invention, since the ceramic is a honeycomb structure, the ceramic structure can be used as a honeycomb structure used in a ceramic honeycomb filter for collecting particulate matter contained in a large amount in exhaust gas.

  In the present invention, since the ceramic is a honeycomb filter, it can be used as a ceramic honeycomb filter for collecting particulate matter contained in a large amount in exhaust gas.

  In the present invention, when the ceramic has an outer diameter of 150 mm or more and a total length of 150 mm or more, it is possible to maintain the collection performance and pressure loss characteristics of the particulate matter in the exhaust gas. When the outer diameter is less than 150 mm and the total length is less than 150 mm, the collection performance of particulate matter in the exhaust gas is deteriorated, which is not preferable.

In the method for manufacturing a ceramic honeycomb structure of the present invention, a forming raw material containing a ceramic material and a foamed resin is mixed and kneaded to form a clay, and the molding clay is filled into a molding machine and molded. A method for producing ceramics, wherein a green body is obtained, and the green body is fired to obtain ceramics having a porosity of 50% or more, an outer diameter of 150 mm or more, and a total length of 150 mm or more. A stress is measured, and a linear regression line is derived by a least square method with respect to the measured values plotted with the square root of the shear rate on the horizontal axis and the square root of the shear stress on the vertical axis, and the slope a of the primary regression line a and the primary regression line and the vertical axis determined Me value b at the intersection of, a ² is out of the range of less than 60 Pa · s, or, when b ² is outside the range of 50～250KPa, mixing of the clay The kneading conditions can be changed. As a result, it is possible to obtain a clay whose characteristics are appropriately evaluated, and to stabilize the quality of the product.

  According to the present invention, a ceramic manufacturing method for appropriately evaluating the state of a ceramic clay used for forming a large ceramic having a high porosity such as a porosity of 50% or more and an outer diameter exceeding 150 mm Can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
Ceramic raw materials prepared by adjusting each powder of kaolin, talc, silica, alumina, and aluminum hydroxide to a weight ratio of SiO ₂ : 50%, Al ₂ O ₃ : 35%, MgO: 15%, and molding aid As the methylcellulose, hydroxypropylmethylcellulose, lubricant, microcapsule as the pore former, and water kneaded into the kneader, the amount of water added, kneading time was changed, the ceramic clay of Examples 1-6 Produced. Next, the shear rate and shear stress of these ceramic clays are measured with a flow tester (die size φ1.0 × L10.0 mm, stroke 1.0 to 2.0 mm, load 55, 65, 75 kg). Measurements were taken on the clay of each sample with three types of loads (P1, P2, P3) to measure the shear rate and shear stress, and to calculate the square root of each value of the shear rate and shear stress. The slope a and intercept b of the linear regression equation derived by the least square method when the square root of the shear rate and the square root of the shear stress are plotted on the vertical axis are calculated, the square a ² of the slope a and ^{2 of} the intercept b. The power b ² was calculated. At the same time, the hardness of the clay was measured by the method described in Citation 1. The results are shown in Table 1. Then, the obtained kneaded material was extruded using an extrusion die so that a formed body having a honeycomb structure was obtained. And the generation | occurrence | production state of the crack of a honeycomb molded object after extrusion molding and cell deformation | transformation was evaluated. The evaluation was that the rate of occurrence of the honeycomb molded body in which sharpness and cell deformation occurred was less than 1% with respect to the number of the formed honeycomb molded bodies (A), and 1% or more and less than 3% (◯), those that were 3% or more and less than 5% were indicated by (Δ), and those that were 5% or more were indicated by (×).

From the results of Table 1, when the hardness of the clay is measured by the method described in the cited document 1 which is the prior art, even if the value is the same (Examples 2 and 3, Examples 4 and 5), It can be seen that there is a large difference in the rate of occurrence of cracks and cell deformation in the honeycomb molded body. On the other hand, by evaluating the clay with the method of the present invention, the values measured for the hardness of the clay with the method described in the cited document 1 as the prior art are the same (Examples 2 and 3, Example 4 and 5) Even if the calculated values of a ² and b ² are evaluated, the occurrence of cracks and cell deformation of the honeycomb formed body can be evaluated, the occurrence rate of cracks and cell deformation is small, and the quality It can be seen that this is a production method capable of obtaining a stable honeycomb formed body.

Front view of ceramic honeycomb filter Schematic cross-sectional schematic diagram of the main part showing an example of use of a ceramic honeycomb filter The figure which showed the evaluation method of the clay of this invention

Explanation of symbols

1a, 1b: plugging material 2a, 2b: exhaust gas flow 11: ceramic honeycomb filter 11a: outer peripheral wall 11b: partition wall 11c: flow path 12: storage containers 13a, 13b, 14: support member

Claims (3)

After mixing and kneading a molding material containing a ceramic material and a foamed resin to form clay, the molding clay is filled into a molding machine to obtain a molded body, and the molded body is fired. A ceramic manufacturing method for obtaining a ceramic having a porosity of 50% or more, an outer diameter of 150 mm or more, and a total length of 150 mm or more, wherein the shear rate and shear stress of the clay are measured, and the square root of the shear rate is measured. A linear regression line is derived by a least-squares method with respect to the measured values plotted with the square root of the shear stress as the vertical axis, and the slope a of the primary regression line and the value of the intersection of the primary regression line and the vertical axis A method for producing ceramics, characterized in that b is obtained and molding is performed using a clay with a ² of 60 Pa · s or less and b ² of 50 to 250 kPa . The method for producing a ceramic according to claim 1 , wherein the ceramic is a honeycomb structure. Method of manufacturing a ceramic according to claim 1 or claim 2, wherein said ceramic is a honeycomb filter.

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