JP2019147700A - Method for producing honeycomb structure - Google Patents

Abstract

To provide a method for producing a honeycomb structure having a low thermal expansion coefficient, a low firing shrinkage, and a sharp pore distribution.SOLUTION: A method for producing a honeycomb structure composed of aluminum titanate, includes the steps of molding a raw material composition containing titania powder and alumina powder to obtain a honeycomb molding, and firing the honeycomb molding. The titania powder contains titania coarse powder, and titania impalpable powder with a smaller average particle size D50 than that of the titania coarse powder, and the titania coarse powder has a higher iron content than that of the titania impalpable powder.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a honeycomb structure.

Conventionally, exhaust gas discharged from an internal combustion engine such as a diesel engine contains particulate matter (hereinafter also referred to as PM). In recent years, it has been a problem that this PM is harmful to the environment and the human body. ing.
Accordingly, various honeycomb filters made of a honeycomb structure using cordierite, silicon carbide, aluminum titanate, or the like have been proposed as filters for collecting PM in the exhaust gas and purifying the exhaust gas.

Among these, the honeycomb structure using aluminum titanate has a higher melting temperature than the honeycomb structure using cordierite, so that it is difficult for melting damage to occur when burning PM as a honeycomb filter, Since the thermal expansion coefficient is lower than that of a honeycomb structure using silicon carbide, it is known that even a large filter is not easily broken by thermal stress applied during PM combustion.

In Patent Document 1, in a method of manufacturing a ceramic honeycomb structure made of aluminum titanate by firing a clay made by mixing a TiO ₂ source powder and an Al ₂ O ₃ source powder, 0.2 to 4 μm The use of a TiO ₂ source powder having relatively small particle size in the range and relatively large particle size in the range of 10-100 μm is described. According to the method described in Patent Document 1, it is said that an aluminum titanate ceramic honeycomb structure having few cracks and a large average pore diameter can be obtained while maintaining the excellent performance of a low thermal expansion coefficient.

International Publication No. 2008/078747

However, in the method described in Patent Document 1, the sinterability may be deteriorated by increasing the particle size of titania or the like. As a result, the strength of the resulting honeycomb structure is reduced and the pore distribution is not uniform. May cause.

The present invention has been made to solve the above problems, and provides a method for producing a honeycomb structure having a low coefficient of thermal expansion, a low firing shrinkage ratio, and a sharp pore distribution. Objective.

A method for manufacturing a honeycomb structure of the present invention includes a step of obtaining a honeycomb formed body by molding a raw material composition containing titania powder and alumina powder, and a step of firing the honeycomb formed body. The titania powder includes a titania coarse powder and a titania fine powder having an average particle diameter D50 smaller than that of the titania coarse powder. The titania coarse powder includes the titania fine powder. It contains more iron than powder.

In the method for manufacturing a honeycomb structure of the present invention, a titania coarse powder having a large average particle diameter and a titania fine powder having a small average particle diameter are used in combination as the titania powder. In other words, titania coarse particles having a large average particle diameter and titania fine particles having a small average particle diameter are used in combination as titania particles. As described above, the sinterability is reduced by using titania coarse particles. However, the inclusion of iron that facilitates sintering in the titania coarse powder results in uniform sintering, so the spacing between the alumina particles and the titania coarse particles is uniform, and uniform pores are formed in the gaps. can do.

Further, the presence of coarse titania particles makes it easier for alumina particles and titania coarse particles having a large particle diameter to maintain their positions during firing, and therefore shrinkage during firing is reduced.

Furthermore, since the titania fine particles are present, the synthesis reaction and sintering of aluminum titanate are facilitated, so that deterioration of the thermal expansion coefficient and strength can be suppressed.

In the method for manufacturing a honeycomb structure of the present invention, the average particle diameter D50 of the titania coarse powder is 5 to 25 μm, and the average particle diameter D50 of the titania fine powder is 0.1 to 1.5 μm. preferable.
In this case, the thermal expansion coefficient can be lowered, the firing shrinkage rate can be reduced, and the pore distribution of the fired aluminum titanate porous body can be sharpened.

In the method for manufacturing a honeycomb structure of the present invention, the average particle size D50 of the titania coarse powder is equal to or smaller than the average particle size D50 of the alumina powder. Is preferred.
In this case, shrinkage during firing can be further suppressed.

In the method for manufacturing a honeycomb structure of the present invention, the iron content of the coarse titania powder is preferably 0.1 to 0.3%. Moreover, it is preferable that the iron content of the titania fine powder is less than 0.1%.
In this case, the synthesis reaction and sintering of aluminum titanate are likely to proceed.

Fig. 1 (a) is a perspective view schematically showing an example of a honeycomb structure manufactured by the manufacturing method of the present invention, and Fig. 1 (b) is an A of the honeycomb structure shown in Fig. 1 (a). FIG.

(Detailed description of the invention)
Hereinafter, the manufacturing method of the honeycomb structure of the present invention will be described.
The method for manufacturing a honeycomb structured body of the present invention includes a forming step for obtaining a honeycomb formed body by forming a raw material composition, and a firing step for firing the honeycomb formed body.

(Molding process)
In the forming step, a honeycomb formed body is obtained by forming the raw material composition.

The raw material composition includes titania powder and alumina powder. The raw material composition preferably further contains silica powder and magnesia powder. Moreover, it is preferable that a raw material composition further contains a pore former.

The titania powder includes a titania coarse powder and a fine titania powder having an average particle diameter D50 smaller than that of the titania coarse powder.

In this specification, the average particle diameter D50 of the titania powder is a particle diameter corresponding to 50% cumulative from the smaller diameter side of the volume-based cumulative particle diameter by the laser diffraction / scattering particle size distribution measurement method. The same applies to the average particle diameter D50 of alumina powder or the like.

The average particle diameter D50 of the titania coarse powder is not particularly limited as long as it is larger than the average particle diameter D50 of the titania fine powder, but is equal to the average particle diameter D50 of the alumina powder or from the average particle diameter D50 of the alumina powder. Is preferably small.

The average particle diameter D50 of the titania coarse powder is preferably 5 μm or more, and more preferably 10 μm or more. Further, the average particle diameter D50 of the titania coarse powder is preferably 25 μm or less, and more preferably 20 μm or less.

The average particle diameter D50 of the titania fine powder is preferably 0.1 μm or more, and more preferably 0.4 μm or more. The average particle diameter D50 of the titania fine powder is preferably 1.5 μm or less, and more preferably 1 μm or less.

The titania coarse powder contains more iron than the titania fine powder. The titania fine powder may contain iron or may not contain iron (that is, it may be below the detection limit).

In this specification, the iron content of titania powder is measured by ICP emission spectroscopic analysis.

The iron content of the titania coarse powder is preferably 0.1 to 0.3%. Further, the iron content of the titania fine powder is preferably less than 0.1%, more preferably less than 0.01%.

The mixing ratio of the titania coarse powder and the titania fine powder is preferably a titania coarse powder: titania fine powder = 40: 60-80: 20, and more preferably 45: 55-75: 25, by weight. .

The titania powder is preferably the total of the titania coarse powder and the titania fine powder, and is contained in the raw material composition in an amount of 15 to 40% by weight.

The average particle diameter D50 of the alumina powder is not particularly limited, but it is preferably equal to the average particle diameter D50 of the titania coarse powder or larger than the average particle diameter D50 of the titania coarse powder.

The average particle diameter D50 of the alumina powder is preferably 10 μm or more, and more preferably 15 μm or more. Moreover, the average particle diameter D50 of the alumina powder is preferably 40 μm or less, and more preferably 30 μm or less.

The alumina powder is preferably contained in the raw material composition in an amount of 20 to 45% by weight.

As described above, the raw material composition preferably further includes silica powder and magnesia powder.
When the silicon element derived from silica and the magnesium element derived from magnesia are dissolved in the aluminum titanate, thermal decomposition of the aluminum titanate can be suppressed, and use at a high temperature is possible.

When the raw material composition contains silica powder, the average particle diameter D50 of the silica powder is preferably 0.1 μm or more. The average particle diameter D50 of the silica powder is preferably 10 μm or less, and more preferably 5 μm or less.

When the raw material composition contains silica powder, the silica powder is preferably contained in the raw material composition in an amount of 0.5 to 5% by weight.

When the raw material composition contains magnesia powder, the average particle diameter D50 of the magnesia powder is preferably 1 μm or more, and more preferably 2 μm or more. Moreover, it is preferable that the average particle diameter D50 of a magnesia powder is 10 micrometers or less. The average particle diameter D50 of the magnesia powder is preferably larger than the average particle diameter D50 of the silica powder.

When the raw material composition includes magnesia powder, the magnesia powder is preferably contained in the raw material composition in an amount of 0.5 to 5% by weight.

Moreover, it is preferable that a raw material composition further contains a pore former.

Examples of the pore former include acrylic resin, graphite, and starch.

When the raw material composition contains a pore former, the average particle diameter D50 of the pore former is preferably 5 μm or more, and more preferably 10 μm or more. The average particle diameter D50 of the pore former is preferably 50 μm or less, and more preferably 40 μm or less.

When the raw material composition includes a pore former, the pore former is preferably contained in the raw material composition in an amount of 5 to 40% by weight.

The raw material composition may contain a molding aid, an organic binder, and a dispersion medium.
Examples of the molding aid include ethylene glycol, dextrin, fatty acid, fatty acid soap, and polyalcohol. Examples of the organic binder include hydrophilic organic polymers such as carboxymethyl cellulose, polyvinyl alcohol, methyl cellulose, and ethyl cellulose. Examples of the dispersion medium include a dispersion medium composed only of water, or a dispersion medium composed of 50% by volume or more of water and an organic solvent. Examples of the organic solvent include alcohols such as benzene and methanol.

The raw material composition may further contain other materials. Examples of other materials include plasticizers, dispersants, lubricants, and the like.
Examples of the plasticizer include polyoxyalkylene compounds such as polyoxyethylene alkyl ether and polyoxypropylene alkyl ether. Examples of the dispersant include sorbitan fatty acid esters. Examples of the lubricant include glycerin.

In the forming step, the raw material composition is formed to obtain a honeycomb formed body.
For example, the raw material composition put into an extruder is extruded in the mold direction while being mixed and kneaded in a sealed state using a screw having various shapes, etc., to obtain a kneaded state suitable for extrusion molding, Extrusion molding is performed through a mold to produce a continuous body of honeycomb molded bodies in which a large number of through holes are arranged in parallel in the longitudinal direction with a wall portion therebetween.

In the forming step, a formed body corresponding to a part of the shape of the honeycomb structure may be formed. That is, a molded body having the same shape as the honeycomb structure may be manufactured by forming a formed body corresponding to a part of the shape of the honeycomb structure and combining the formed bodies.

Then, if necessary, plug the predetermined through-holes among the many through-holes on both end faces where the through-holes are exposed, microwave dryer, hot air dryer, dielectric dryer, vacuum dryer, vacuum Drying is performed using a dryer, a freeze dryer, or the like, followed by a degreasing process for decomposing and eliminating organic components in the honeycomb formed body.

(Baking process)
In the firing step, the honeycomb formed body obtained in the forming step is fired to obtain a fired body.
In the firing step, the reaction between the alumina particles and the titania particles proceeds to form an aluminum titanate phase.

The firing temperature is preferably 1300 to 1600 ° C.
Firing can be performed using a known single furnace, a so-called batch furnace, or a continuous furnace. Although baking time is not specifically limited, It is preferable to hold | maintain for 1 to 20 hours in said baking temperature. Moreover, it is preferable to perform a baking process in an atmospheric condition. The oxygen concentration may be adjusted by mixing an inert gas such as nitrogen gas or argon gas in the air atmosphere.

Through the above steps, a honeycomb structure made of aluminum titanate can be manufactured.

Fig. 1 (a) is a perspective view schematically showing an example of a honeycomb structure manufactured by the manufacturing method of the present invention, and Fig. 1 (b) is an A of the honeycomb structure shown in Fig. 1 (a). FIG.
The honeycomb structure 10 shown in FIG. 1 (a) has a columnar shape, and the exhaust gas introduction cell 11a and the exhaust gas whose cross-sectional shape perpendicular to the longitudinal direction (the direction indicated by the double arrow a in FIG. 1 (a)) is substantially rectangular. Many discharge cells 11b are formed. The exhaust gas introduction cell 11a and the exhaust gas discharge cell 11b are formed with a cell partition wall 13 therebetween. An outer peripheral wall 16 is formed on the outer periphery of the honeycomb structure 10.

As shown in FIG. 1B, the exhaust gas discharge cell 11b is sealed by the sealing portion 12b on the end surface 14 on the side where the exhaust gas is introduced, and the exhaust gas introduction cell 11a is open. On the other hand, on the end face 15 on the exhaust gas discharge side, the exhaust gas introduction cell 11a is sealed by the sealing portion 12a, and the exhaust gas discharge cell 11b is open.

Since the end surface 15 of the exhaust gas introduction cell 11a is sealed, the exhaust gas G introduced into the exhaust gas introduction cell 11a from the end surface 14 passes through the cell partition wall 13 which is a porous wall, and then passes through the exhaust gas exhaust cell 11b. It is discharged from the end face 15. During this time, PM in the exhaust gas is collected by the cell partition wall 13 and the exhaust gas is purified.

The honeycomb structure manufactured by the method for manufacturing a honeycomb structure of the present invention preferably functions as a honeycomb filter that removes PM in exhaust gas. Moreover, the honeycomb structure manufactured by the method for manufacturing a honeycomb structure of the present invention may be used as a catalyst carrier by supporting various catalysts and the like without sealing.

Hereinafter, examples that further embody the method for manufacturing a honeycomb structure of the present invention will be described.

[Preparation of honeycomb structure]
Example 1
Titanium coarse powder with D50 of 13.6 μm (iron content 0.25%): 11.1 wt%, titania fine powder with D50 of 0.6 μm (iron content less than 0.01%): 11.1 wt% Alumina powder with D50 of 21.5 μm: 30.4% by weight Silica powder with D50 of 1.1 μm: 2.8% by weight, magnesia powder with D50 of 3.8 μm: 1.4% by weight, D50 of 31. 9 μm acrylic resin (pore forming material): 18.5% by weight, methylcellulose (organic binder): 7.1% by weight, molding aid (ester type nonion): 4.7% by weight, ion-exchanged water (dispersion medium) : 12.9 wt% of the composition was mixed with a mixer to prepare a raw material composition.
The compounding ratio of the titania coarse powder and the titania fine powder used in the preparation of the raw material composition is a titania coarse powder: titania fine powder = 50: 50 in weight ratio.

The prepared raw material composition was put into an extruder and subjected to extrusion to produce a honeycomb formed body having the shape shown in FIG. 1A and having no cells sealed.

The cells of the honeycomb formed body were alternately plugged using a sealing material having the same composition as the raw material composition. After drying and degreasing, a cylindrical honeycomb structure was produced by firing at 1450 ° C. for 15 hours in an air atmosphere and firing.

(Example 2)
A honeycomb structure was manufactured in the same manner as in Example 1 except that the titania coarse powder was changed to 15.5 wt% and the titania fine powder was changed to 6.7 wt%.
The compounding ratio of the titania coarse powder and the titania fine powder used for the preparation of the raw material composition is a titania coarse powder: titania fine powder = 70: 30 in weight ratio.

(Comparative Example 1)
The titania coarse powder was 0% by weight, the titania fine powder was 19.6% by weight, the alumina powder was 26.8% by weight, the silica powder was 2.5% by weight, the magnesia powder was 1.3% by weight, and the pore former was 28%. A honeycomb structure was prepared in the same manner as in Example 1 except that the content was changed to 1 wt%, the organic binder 6.3 wt%, the molding aid 4.2 wt%, and the dispersion medium 11.4 wt%. Produced.
The compounding ratio of the titania coarse powder and the titania fine powder used in the preparation of the raw material composition is a titania coarse powder: titania fine powder = 0: 100 in weight ratio.

(Comparative Example 2)
A honeycomb structure was produced in the same manner as in Example 1 except that the titania coarse powder was changed to 22.2 wt% and the titania fine powder was changed to 0 wt%.
The compounding ratio of the titania coarse powder and the titania fine powder used for the preparation of the raw material composition is a titania coarse powder: titania fine powder = 100: 0.

(Comparative Example 3)
A honeycomb structure was fabricated in the same manner as in Example 1 except that a titania coarse powder having an iron content of less than 0.01% was used.
The compounding ratio of the titania coarse powder and the titania fine powder used in the preparation of the raw material composition is a titania coarse powder: titania fine powder = 50: 50 in weight ratio.

[Baking shrinkage]
The total length of the obtained honeycomb structure before and after firing was measured, and the firing shrinkage rate was calculated from the following formula.
Firing shrinkage percentage (%) = [(full length before firing) − (full length after firing)] / (full length before firing)] × 100

[Mechanical strength]
As the mechanical strength of the honeycomb structure, the bending strength was measured by the following method.
First, as a sample for measuring three-point bending strength, a raw material composition mixed and kneaded with the same composition as each example and comparative example was formed into a rectangular parallelepiped, degreased under the same conditions, and processed into 6 mm × 6 mm × 40 mm after firing. Ten members were prepared. A load was applied in a direction perpendicular to the main surface of the three-point bending strength measurement sample (the wider one of the outer peripheral surfaces of the sample), and the breaking load (the load at which the sample broke) was measured. The breaking load was measured for ten three-point bending strength measurement samples, and the average value was taken as the bending strength. The three-point bending strength test was performed using an Instron 5582 with reference to JIS R 1601, a span distance of 30 mm, and a speed of 1 mm / min.

[AT conversion rate]
X-ray diffraction measurement was performed using a powder having a particle size of 0.5 mm or less produced by pulverizing a part of the obtained honeycomb structure, and the integrated intensity I _{AT (101)} of the (101) plane of aluminum titanate from the integrated intensity _{I TiO2} of TiO ₂ (110) plane ₍₁₁₁₎ was determined AT conversion ratio from the following equation.
AT conversion rate (%) = [I _{AT (101)} / (I _{AT (101)} + I _{TiO2 (111)} )] × 100

[Thermal expansion coefficient]
A sample having a cross-sectional shape of 4.8 mm × 4.8 mm × total length 20 mm was cut out from the obtained honeycomb structure so that the direction of the total length substantially coincided with the flow path direction, and a thermomechanical analyzer (NETZSCH DIL402C) was used. The average coefficient of thermal expansion between 50 and 1000 ° C. is measured by measuring the increase in length in the full length direction when heated from room temperature to 1000 ° C. at a heating rate of 10 ° C./min while applying a constant load of 20 g. Asked.

[Porosity distribution]
The obtained honeycomb structure was cut out to 10 mm × 10 mm × 10 mm to prepare a sample for pore distribution measurement. The pore distribution was measured with a porosimeter (manufactured by Shimadzu Corporation, Autopore III 9420) using a sample for pore distribution measurement. The contact angle was 130 ° and the surface tension was 485 mN / m by mercury porosimetry. A pore distribution was measured in the range of pore diameters of 1 to 100 μm, and a pore distribution curve was drawn with the pore diameter (μm) on the X axis and the log differential pore volume (mL / g) on the Y axis.

The values of d10, d50, and d90 were calculated from each pore distribution curve.
In addition, as an index of whether the shape of the pore distribution curve is sharp, a value represented by the equation (d90−d10) / d50 was calculated and defined as the pore sharpness. It can be said that the smaller the value, the sharper the shape of the pore distribution curve.
d10, d50, and d90 are pore diameters corresponding to cumulative 10%, cumulative 50%, and cumulative 90% from the small diameter side of the cumulative pore volume in the pore distribution curve.

The measurement results are summarized in Table 1.

From Table 1, in Example 1 and Example 2, a baking shrinkage rate is small and bending strength is high. Further, the AT conversion rate is 100%, and the thermal expansion coefficient is low. Furthermore, it has a sharp pore distribution.

On the other hand, in Comparative Example 1 where no titania coarse powder is used, the firing shrinkage rate is large. In Comparative Example 2 where no titania fine powder is used, the AT conversion rate is low, the bending strength is low, and the thermal expansion coefficient is high. In Comparative Example 3 where the iron content of the titania coarse powder is low, the AT conversion rate is low, the thermal expansion coefficient is high, and the pore sharpness is large.

From the above results, a honeycomb having a low coefficient of thermal expansion, a low firing shrinkage ratio, and a sharp pore distribution by using both titania coarse powder and titania fine powder in combination and containing iron in the titania coarse powder. It is thought that a structure is obtained.

DESCRIPTION OF SYMBOLS 10 Honeycomb structure 11a Exhaust gas introduction cell 11b Exhaust gas discharge cell 12a, 12b Sealing part 13 Cell partition wall 14 End surface 15 in which exhaust gas is introduced End surface 16 in which exhaust gas is exhausted Outer wall G

Claims (5)

A step of obtaining a honeycomb formed body by forming a raw material composition containing titania powder and alumina powder;
A method of manufacturing a honeycomb structure made of aluminum titanate, including a step of firing the honeycomb formed body,
The titania powder includes a titania coarse powder and a fine titania powder having an average particle diameter D50 smaller than that of the titania coarse powder.
The method for manufacturing a honeycomb structure, wherein the coarse titania powder contains more iron than the fine titania powder. The titania coarse powder has an average particle diameter D50 of 5 to 25 μm,
The method for manufacturing a honeycomb structured body according to claim 1, wherein an average particle diameter D50 of the titania fine powder is 0.1 to 1.5 µm. 3. The honeycomb structure according to claim 1, wherein an average particle diameter D50 of the titania coarse powder is equal to or smaller than an average particle diameter D50 of the alumina powder. Production method. The method for manufacturing a honeycomb structured body according to any one of claims 1 to 3, wherein the iron content of the titania coarse powder is 0.1 to 0.3%. The method for manufacturing a honeycomb structured body according to claim 4, wherein the titania fine powder has an iron content of less than 0.1%.

Images