JP7509636B2 - Honeycomb substrate and honeycomb structure - Google Patents

Description

The present invention relates to a honeycomb substrate and a honeycomb structure.

In order to purify harmful substances contained in exhaust gas discharged from an engine, an exhaust gas purification device having a honeycomb substrate carrying a catalyst capable of purifying exhaust gas is provided in the exhaust pipe passage.
In order to improve the efficiency of purifying harmful substances by an exhaust gas purification device, it is necessary to maintain the temperature inside the exhaust gas purification device at a temperature suitable for catalyst activation (hereinafter also referred to as catalyst activation temperature).

However, in vehicles that are not equipped with a means for directly heating the honeycomb substrate that constitutes the exhaust gas purification device, the temperature of the exhaust gas is low immediately after the vehicle begins to drive, so the temperature inside the exhaust gas purification device does not reach the catalyst activation temperature, making it difficult to effectively prevent the emission of harmful substances.
Furthermore, in hybrid vehicles that do not have a means for directly heating the honeycomb substrate, when the motor is running and the engine is stopped, the temperature inside the exhaust gas purification device drops and can become lower than the catalyst activation temperature, making it difficult to effectively prevent the emission of harmful substances.

In order to solve such problems, the honeycomb substrate itself has been made into a heating element that generates heat when electricity is passed through it, and when necessary, the temperature inside the exhaust gas purification device has been raised to a temperature equal to or higher than the catalyst activation temperature.
However, in an actual honeycomb substrate used in an exhaust gas purification device, there may be unevenness in the amount of heat generated at different locations depending on the cross-sectional shape, electrode arrangement, etc., so it is desirable to reduce temperature unevenness in the honeycomb substrate and achieve a uniform temperature distribution.

As an exhaust gas purification device for uniformly heating the temperature of a honeycomb substrate in this manner, Patent Document 1 discloses a honeycomb structure in which the opening ratio in the central portion is reduced so that more current flows in the central portion.
That is, Patent Document 1 discloses a honeycomb structure having a columnar honeycomb structure part including porous partition walls which serve as fluid flow paths and define a plurality of cells extending from a first end face which is one end face to a second end face which is the other end face, and an outer peripheral wall located on the outer periphery, and a pair of electrode parts disposed on side surfaces of the honeycomb structure part, the electrical resistivity of the honeycomb structure part being 1 to 200 Ωcm, each of the pair of electrode parts being formed in a band shape extending in the extension direction of the cells of the honeycomb structure part, and the electrical resistivity of the pair of electrode parts being 1 to 200 Ωcm ... The honeycomb structure disclosed has a honeycomb structure in which one of the electrode parts is disposed on the opposite side of the center of the honeycomb structure part with respect to the other electrode part of the pair of electrode parts, and when a region from the center to a position that is 10% of the length from the center to the periphery toward the periphery is defined as a central region in a cross section of the honeycomb structure part that is perpendicular to the extension direction of the cells, and a region from the periphery to a position that is 10% of the length from the periphery toward the center is defined as a peripheral region, the opening ratio of the central region is 0.70 to 0.95 times the opening ratio of the peripheral region.

Furthermore, Patent Document 2 discloses a catalytic converter device in which catalyst carriers having different volume resistivities are combined so that the amount of heat generated by current flow in each portion approaches uniformity.
That is, Patent Document 2 discloses a catalytic converter device having a catalyst carrier which supports a catalyst for purifying exhaust gas discharged from an internal combustion engine and is heated by passing an electric current through it, a pair of electrodes which are arranged in contact with the catalyst carrier at opposing positions across the catalyst carrier when viewed in an orthogonal cross section perpendicular to the flow direction of the exhaust gas, and a plurality of partitions which partition the catalyst carrier in a direction perpendicular to the center line of the electrodes and each partition has a different volume resistivity so that the amount of heat generated by passing an electric current through each partitioned part of the catalyst carrier becomes nearly uniform.

International Publication No. 2015/151823 JP 2012-188958 A

In such an electrically heated honeycomb structure, the current tends to flow through the shortest path between the electrodes.
In the honeycomb structure described in Patent Document 1, a pair of electrode parts are disposed on opposite sides of the center of a cylindrical honeycomb structure part. Since the honeycomb structure described in Patent Document 1 is cylindrical and the partition walls are arranged in a lattice pattern, the length of the path between the pair of electrodes varies depending on the location. Therefore, the length of the path through which the current flows also varies.
If the length of a path through which a current flows is short, the resistance in that path is low, and therefore, the current can flow easily through that path.
Since the amount of heat generated by a honeycomb structure depends on the current density, the honeycomb structure described in Patent Document 1 has a problem in that the amount of heat generated varies depending on the location.

The catalytic converter device described in Patent Document 2 required many different types of catalyst carriers, which increased manufacturing costs and reduced its practicality.

The present invention was made to solve the above problems, and aims to provide a honeycomb substrate that can be heated uniformly when electrically heated.

The honeycomb substrate of the present invention is an elliptical or cylindrical honeycomb substrate having partition walls that divide and form a large number of cells, the honeycomb substrate being a resistance heating element, and a cross section perpendicular to the longitudinal direction of the honeycomb substrate has a first region surrounded by two line segments extending from the center of the cross section to the outer periphery and an arc connecting the two line segments, a second region that is a region that is point-symmetric with the first region with the center of the cross section as the center of point symmetry, a third region located between one of the line segments forming the first region and the second region, and a fourth region located between the other line segment forming the first region and the second region, and the cells formed in the first region and the second region The partition walls are formed in a lattice shape along a first direction connecting the center of the cross section and the midpoint of the arc of the first region and a direction perpendicular to the first direction in a cross section perpendicular to the longitudinal direction of the honeycomb substrate, the partition walls of the cells formed in the third region are formed in a lattice shape along a second direction oblique to the first direction and a direction perpendicular to the second direction in a cross section perpendicular to the longitudinal direction of the honeycomb substrate, and the partition walls of the cells formed in the fourth region are formed in a lattice shape along a third direction oblique to the first direction and a direction perpendicular to the third direction in a cross section perpendicular to the longitudinal direction of the honeycomb substrate.

In the honeycomb substrate of the present invention, a pair of electrodes are disposed on the surface of the honeycomb substrate where the arcs forming the first region are located, and on the surface of the honeycomb substrate where the arcs forming the second region are located.
When a current is applied between the pair of electrodes, the honeycomb substrate, which is a resistance heating element, generates heat.
When the honeycomb substrate is heated in this manner, the current flows through the partition walls of the cells.
It is assumed that in all regions of the honeycomb substrate, the partition walls of the cells are formed in a lattice pattern along the first direction and a direction perpendicular to the first direction.
In a cross section perpendicular to the longitudinal direction of such a honeycomb substrate, a line segment connecting the midpoint of the arc of the first region and the midpoint of the arc of the second region is defined as a center line.
Generally, since a current has a property of passing through the path with the least resistance between electrodes, if the resistance is the same, the current passes through the shortest path between the electrodes. Therefore, the current flowing from the arc in the first region flows toward the arc in the second region along the first direction parallel to the center line.
Therefore, on the outer periphery of the cross section of the honeycomb substrate, the further away from the midpoint of the arc of the first region, the shorter the path of the current flowing from that position along the first direction from the first region to the second region becomes.
If the length of the path through which the current flows is short, the resistance in that path is low, and therefore the density of the current flowing through that path increases.
Since the amount of heat generated by a honeycomb substrate is proportional to the density of the current flowing through that portion, the amount of heat generated by the honeycomb substrate increases as the distance from the center line increases. Therefore, such a honeycomb substrate cannot be heated uniformly.
However, in the honeycomb substrate of the present invention, the partition walls of the cells formed in the third region are formed in a lattice shape along a second direction oblique to the first direction and a direction perpendicular to the second direction. In other words, the partition walls of the cells formed in the third region are not parallel to the first direction. Similarly, the partition walls of the cells formed in the fourth region are formed in a lattice shape along a third direction oblique to the first direction and a direction perpendicular to the third direction. In other words, the partition walls of the cells formed in the fourth region are not parallel to the first direction.
Therefore, in the third and fourth regions, the current cannot flow along the first direction, but flows obliquely to the first direction, so that the path of the current flowing through the third and fourth regions becomes longer.
As a result, the difference between the path of the current flowing from the midpoint of the arc of the first region to the midpoint of the arc of the second region and the path of the current flowing from a position away from the midpoint of the arc of the first region to the second region can be reduced.
Therefore, the honeycomb substrate of the present invention can be heated uniformly during electrical heating.

In the honeycomb substrate of the present invention, the acute angle formed between the first direction and the second direction is preferably 30° to 60°. Also, the acute angle formed between the first direction and the third direction is preferably 30° to 60°.
With such an angle, the path of the current flowing through the third region and the path of the current flowing through the fourth region can be appropriately long, so that the honeycomb substrate can be heated more uniformly.

In the honeycomb substrate of the present invention, the thermal conductivity of the honeycomb substrate is preferably 1 to 70 W/mK.
Even in the case of such a honeycomb substrate having a low thermal conductivity, the entire honeycomb substrate can be heated uniformly.

In the honeycomb substrate of the present invention, the electrical resistivity of the honeycomb substrate is preferably 0.1 to 50 Ω·cm.
Within this range, the honeycomb substrate is heated appropriately.
If the electrical resistivity of the honeycomb substrate is less than 0.1 Ω·cm, the amount of heat generated will be small.
If the electrical resistivity of the honeycomb substrate exceeds 50 Ω·cm, the current does not flow easily and the input power becomes too large.

In the honeycomb substrate of the present invention, the honeycomb substrate is preferably made of a material containing SiC, Si, SiO ₂ , carbon or borosilicate.
These materials are excellent materials for resistive heating elements.

The honeycomb structure of the present invention is a honeycomb structure including the honeycomb base material of the present invention and a pair of electrodes arranged on a surface of the honeycomb base material, characterized in that one electrode is arranged on the surface of the honeycomb base material where an arc forming a first region is located, and the other electrode is arranged on the surface of the honeycomb base material where an arc forming a second region is located.
The honeycomb structure of the present invention includes the honeycomb substrate of the present invention, and therefore the honeycomb substrate can be uniformly heated by applying a current from the electrodes.

In the honeycomb structure of the present invention, it is preferable that the one electrode is arranged so as to cover the entire arc forming the first region, and the other electrode is arranged so as to cover the entire arc forming the second region.
By arranging the electrodes in this manner, the honeycomb substrate can be heated more uniformly.

FIG. 1 is a perspective view that diagrammatically illustrates an example of a honeycomb substrate of the present invention. FIG. 2A is a cross-sectional view taken along line AA in FIG. FIG. 2B is a schematic diagram showing the first region, the second region, the third region, and the fourth region of the honeycomb substrate shown in FIG. 2A. FIG. 3 is a cross-sectional view that diagrammatically illustrates an example of a cross section perpendicular to the longitudinal direction of a conventional honeycomb substrate on which a pair of electrodes are arranged. FIG. 4 is a cross-sectional view that diagrammatically shows an example of a cross section perpendicular to the longitudinal direction of a honeycomb substrate of the present invention. FIG. 5 is a cross-sectional view that typically shows an example of the case where exhaust gas passes through the honeycomb substrate of the honeycomb structure of the present invention. FIG. 6 is a cross-sectional view that diagrammatically shows an example of the honeycomb structure of the present invention.

Detailed Description of the Invention
The honeycomb substrate of the present invention will be described in detail below.
A honeycomb substrate having an elliptical or cylindrical shape and partition walls that define a large number of cells, the honeycomb substrate being a resistance heating element, a cross section perpendicular to the longitudinal direction of the honeycomb substrate has a first region surrounded by two line segments extending from a center of the cross section to an outer periphery and an arc connecting the two line segments, a second region that is a region that is point-symmetric with the first region with the center of the cross section as a center of point symmetry, a third region located between one of the line segments forming the first region and the second region, and a fourth region located between the other line segment forming the first region and the second region, the partition walls of the cells formed in the first region and the second region being arranged such that In a cross section perpendicular to the longitudinal direction of the honeycomb substrate, the honeycomb substrate is formed in a lattice pattern along a first direction connecting the center of the cross section and the midpoint of the arc of the first region, and a direction perpendicular to the first direction, and the partition walls of the cells formed in the third region are formed in a lattice pattern along a second direction oblique to the first direction and a direction perpendicular to the second direction in a cross section perpendicular to the longitudinal direction of the honeycomb substrate, and the partition walls of the cells formed in the fourth region are formed in a lattice pattern along a third direction oblique to the first direction and a direction perpendicular to the third direction in a cross section perpendicular to the longitudinal direction of the honeycomb substrate.
As long as the honeycomb substrate of the present invention has the above-mentioned configuration, it may have any other configuration as long as the effects of the present invention can be exhibited.

FIG. 1 is a perspective view that diagrammatically illustrates an example of a honeycomb substrate of the present invention.
FIG. 2A is a cross-sectional view taken along line AA in FIG.
FIG. 2B is a schematic diagram showing the first region, the second region, the third region, and the fourth region of the honeycomb substrate shown in FIG. 2A.

The honeycomb substrate 10 shown in Figure 1 is a cylindrical resistive heating element having partition walls 12 that define a large number of cells 11.

As shown in Figures 2A and 2B, a cross section perpendicular to the longitudinal direction of the honeycomb substrate 10 has a first region 20 surrounded by a first line segment 21 and a second line segment 22 extending from the center O of the cross section to the outer periphery and an arc 23 connecting the first line segment 21 and the second line segment 22, and a second region 30 which is point-symmetric to the first region 20 with the center O of the cross section as the center of point symmetry.
Furthermore, as shown in Figures 2A and 2B, a cross section perpendicular to the longitudinal direction of the honeycomb substrate 10 has a first line segment 21 forming the first region 20, a third region 40 located between the first line segment 21 and the second region 30, and a fourth region 50 located between the second line segment 22 forming the first region and the second region 30.

As shown in FIG. 2A, the partition walls 12 of the cells 11 formed in the first region 20 and the second region 30 are formed in a lattice shape along a first direction D1 connecting the center O of the cross section and the midpoint 23a of the arc 23 of the first region 20, and a direction perpendicular to the first direction D1, in a cross section perpendicular to the longitudinal direction of the honeycomb substrate 10.

The partition walls 12 of the cells 11 formed in the third region 40 are formed in a lattice pattern along a second direction D2 oblique to the first direction D1 and a direction perpendicular to the second direction in a cross section perpendicular to the longitudinal direction of the honeycomb substrate 10.
The acute angle formed by the first direction D1 and the second direction D2 is not particularly limited, but is preferably 30° to 60°.

The partition walls 12 of the cells 11 formed in the fourth region 50 are formed in a lattice pattern along a third direction D3 oblique to the first direction D1 and a direction perpendicular to the third direction D3 in a cross section perpendicular to the longitudinal direction of the honeycomb substrate 10.
The acute angle formed between the first direction D1 and the third direction D3 is not particularly limited, but is preferably 30° to 60°.

As will be described in more detail later, when the acute angle formed between the first direction D1 and the second direction D2 is 30° to 60°, or when the acute angle formed between the first direction D1 and the third direction D3 is 30° to 60°, the path of the current flowing through the third region 40 and the path of the current flowing through the fourth region 50 can be appropriately lengthened. As a result, the honeycomb substrate 10 can be heated more uniformly.

Furthermore, it is preferable that the acute angle formed between the first direction D1 and the second direction D2 is the same as the acute angle formed between the first direction D1 and the third direction D3.

A pair of electrodes is arranged on the honeycomb substrate 10 at the arc 23 that forms the first region 20 and the arc 33 that forms the second region 30, and a current flows through the honeycomb substrate 10.

Here, a conventional honeycomb substrate having electrodes disposed thereon and current flowing therethrough will be described.
FIG. 3 is a cross-sectional view that diagrammatically illustrates an example of a cross section perpendicular to the longitudinal direction of a conventional honeycomb substrate on which a pair of electrodes are arranged.

As shown in FIG. 3, a conventional honeycomb substrate 510 is a heating resistor having a cylindrical shape and partition walls 512 that define a large number of cells 511 .
For ease of explanation, the upper end of the honeycomb substrate 510 in FIG. 3 is referred to as upper end T ₅₁₀ and the lower end is referred to as lower end B ₅₁₀ .

In FIG. 3, partition walls 512 of cells 511 of a honeycomb substrate 510 are formed in a lattice shape along a direction connecting an upper end T ₅₁₀ and a lower end B ₅₁₀ and a direction perpendicular to said direction.

Further, in the honeycomb substrate 510 , a positive electrode 561 is disposed on an upper surface ₅₁₀ a centered on the upper end T 510 , and a negative electrode 562 is disposed on a lower surface 510 b centered on the lower end B ₅₁₀ .

Here, a case where a current flows between the electrodes 561 and 562 will be described.
Since current has the property of passing through the path between electrodes that has the least resistance, if the electrical resistivity is the same, the current will flow in proportion to the length of the path between the electrodes.
In the honeycomb substrate 510, a current flows through the partition walls 512 of the cells 511, and the partition walls 512 of the cells 511 are formed along a direction connecting the upper end T ₅₁₀ and the lower end B _510. Therefore, in the honeycomb substrate 510, the shortest path from the upper end T ₅₁₀ to the lower end B ₅₁₀ is a straight line passing through the center O of the honeycomb substrate 510.
In addition, in FIG. 3, the shortest distance from a point _510a1 , which is a point on the upper surface 510a other than the upper end T ₅₁₀ , to the lower surface 510b is parallel to the direction connecting the upper end T ₅₁₀ and the lower end B ₅₁₀ .
Therefore, the shortest distance of the path from each point on the upper surface 510a to the lower surface 510b becomes shorter the farther away from the upper end _T510 .

If the length of the path through which the current flows is short, the resistance in that path is small, and therefore the density of the current flowing through that path increases.
Since the amount of heat generated by the honeycomb substrate 510 is proportional to the square of the current flowing through that portion, the amount of heat generated by the honeycomb substrate 510 increases as the distance from the line segment connecting the upper end T ₅₁₀ to the lower end B ₅₁₀ increases. Therefore, in such a honeycomb substrate 510, the circumferential end sides of the positive electrode 561 and the negative electrode 562 heat up quickly, and therefore the substrate cannot be heated uniformly.

On the other hand, in the honeycomb substrate 10, the partition walls 12 of the cells 11 formed in the third region 40 are formed in a lattice shape along a second direction D2 oblique to the first direction D1 and a direction perpendicular to the second direction D2. In other words, the partition walls 12 of the cells 11 formed in the third region 40 are not parallel to the first direction D1. Similarly, the partition walls 12 of the cells 11 formed in the fourth region 50 are formed in a lattice shape along a third direction D3 oblique to the first direction D1 and a direction perpendicular to the third direction D3. In other words, the partition walls 12 of the cells 11 formed in the fourth region 50 are not parallel to the first direction D1.
Therefore, in the third region 40, the current cannot flow along the first direction D1, but flows obliquely to the first direction D1. That is, in the third region 40, the partition walls 12 of the cells 11 are formed along the second direction D2 and a direction perpendicular to the second direction D2, so that the current flows in a zigzag pattern. Therefore, the path of the current flowing in the third region 40 is longer than the path of the current flowing linearly along the first direction D1.
Similarly, in the fourth region 50, the current cannot flow along the first direction D1, but flows obliquely to the first direction D1. That is, in the fourth region 50, the partition walls 12 of the cells 11 are formed along the third direction D3 and a direction perpendicular to the third direction D3, so that the current flows in a zigzag pattern. Therefore, the path of the current flowing in the fourth region 50 is longer than the path of the current flowing linearly along the first direction D1.
As a result, the difference between the length of the current path flowing from the midpoint 23a of the arc 23 in the first region 20 to the midpoint 33a of the arc 33 in the second region 30 and the length of the current path flowing from a position away from the midpoint 23a of the arc 23 in the first region 20 to the second region 30 can be reduced.
Therefore, the honeycomb substrate 10 can be heated uniformly during electrical heating.

The above content will now be explained in more detail.
FIG. 4 is a cross-sectional view that diagrammatically shows an example of a cross section perpendicular to the longitudinal direction of a honeycomb substrate of the present invention.
The honeycomb substrate 10 shown in Figure 4 is a honeycomb substrate in which the angle formed by the first line segment 21 and the second line segment 22 is 90°, the acute angle formed by the first direction D1 and the second direction D2 is 45°, and the acute angle formed by the first direction D1 and the third direction D3 is 45°.

Here, the shortest path of the resistor from the midpoint 23a of the arc 23 in the first region 20 to the midpoint 33a of the arc 33 in the second region 30 is a straight line passing through the center O.

On the other hand, the shortest distance of the path of the resistor from point _23a1 on arc 23 of first region 20, which is away from midpoint 23a of arc 23 of first region 20 toward first line segment 21, to arc 33 of second region 30, is linear along first direction D1 in first region 20 and second region 30, as shown in FIG. 4, and is zigzag along partition 12 formed along second direction D2 and a direction perpendicular to second direction D2 in third region 40 (the arrows in FIG. 4 indicate the direction of current flow).
Since the acute angle formed by the first direction D1 and the second direction D2 is 45°, in the third region 40, the path is longer by √2 times compared to the straight path from the point _23a1 along the first direction D1.

Similarly, the shortest distance of the path of the resistor from point 23a2 on arc 23 of first region 20, which is away from midpoint _23a of arc 23 of first region 20 toward second line segment 22, to arc 33 of second region 30, is, as shown in FIG. 4 , linear along first direction D1 in first region 20 and second region 30, while in fourth region 40, is zigzag along partition 12 formed along third direction D3 and a direction perpendicular to third direction D3 (arrows in FIG. 4 indicate the direction of current flow).
Since the acute angle formed by the first direction D1 and the third direction D3 is 45°, in the fourth region 50, the path is longer by √2 times compared to the straight path from the point _23a2 along the first direction D1.

Moreover, as the current flows from the arc 23 of the first region 20 toward the first line segment 21 from the midpoint 23a of the arc 23 of the first region 20, the proportion of the distance through which the current flows through the first region 20 and the second region 30 decreases, and the proportion of the distance through which the current flows through the third region 40 increases. The same is true when the current flows through the fourth region 50.
Therefore, the difference between the shortest distance from the midpoint 23a of the arc 23 in the first region 20 to the midpoint 33a of the arc 33 in the second region 30 and the shortest distance from one point of another arc 23 in the first region 20 to one point of the arc 33 in the second region 30 can be reduced.
Therefore, the honeycomb substrate 10 can be heated evenly.

Next, the mechanism by which exhaust gas is purified by the honeycomb substrate 10 will be described with reference to the drawings.
FIG. 5 is a cross-sectional view that typically shows an example of the case where exhaust gas passes through the honeycomb substrate of the honeycomb structure of the present invention.
FIG. 5 is also a cross-sectional view of the honeycomb substrate 10 in a direction perpendicular to the longitudinal direction.
When exhaust gas discharged from an internal combustion engine (the flow of exhaust gas is indicated by arrows G in FIG. 5 ) reaches the honeycomb substrate 10, the exhaust gas flows into cells 11 that open into the end face of the honeycomb substrate 10 on the exhaust gas inlet side. Furthermore, the exhaust gas passes through the cells 11 while coming into contact with catalysts 13 supported on partition walls 12. At this time, harmful gas components in the exhaust gas, such as CO, HC, and _NOx , are purified by the catalysts 13 supported on the partition walls 12. Then, the exhaust gas flows out of the cells that open into the end face of the honeycomb substrate 10 on the exhaust gas outlet side.

The catalyst 13 is not particularly limited as long as it can treat exhaust gas, but examples include three-way catalysts made of precious metals such as platinum, palladium, and rhodium. These catalysts may be used alone or in combination of two or more types.

When a three-way catalyst made of a precious metal is supported, the amount of the precious metal supported on the entire honeycomb substrate is preferably 0.1 to 15 g/L, and more preferably 0.5 to 10 g/L.
In this specification, the amount of precious metal supported refers to the weight of precious metal per apparent volume of the honeycomb substrate. Note that the apparent volume of the honeycomb substrate includes the volume of voids, and includes the volume of the adhesive layer if an adhesive layer is included.
When these catalysts are supported, toxic exhaust gases such as CO, HC, and _NOx can be effectively purified.

The honeycomb substrate 10 is not particularly limited as long as it is a resistance heating element, but is preferably made of a material containing SiC, Si, SiO ₂ , carbon, or borosilicate.
These materials are excellent materials for resistive heating elements.
Also, it is preferable that the heating element is a resistive heating element having a positive temperature coefficient (PTC material).
Such PTC materials include impurity-doped silicon, _MoSi2 , and the like.

The thermal conductivity of the honeycomb substrate 10 is preferably 1 to 70 W/mK, and more preferably 1 to 10 W/mK.
Even in the case of a honeycomb substrate having such a low thermal conductivity, the entire honeycomb substrate can be heated uniformly.

The electrical resistivity of the honeycomb substrate 10 is preferably 0.1 to 50 Ω·cm, and more preferably 1 to 30 Ω·cm.
Within this range, the honeycomb substrate is heated appropriately.
If the electrical resistivity of the honeycomb substrate is less than 0.1 Ω·cm, the amount of heat generated will be small.
If the electrical resistivity of the honeycomb substrate exceeds 50 Ω·cm, the current does not flow easily and the input power becomes too large.

In FIG. 1, the honeycomb substrate 10 has a cylindrical shape, but the honeycomb substrate of the present invention may have an elliptical cylindrical shape.

The thickness of the cell partition walls of the honeycomb substrate is preferably uniform. Specifically, the thickness of the cell partition walls is preferably less than 0.30 mm. Also, it is preferably 0.05 mm or more.

Next, a honeycomb structure using the honeycomb substrate of the present invention will be described.
A honeycomb structure using the honeycomb substrate of the present invention is also one aspect of the present invention.

FIG. 6 is a cross-sectional view that diagrammatically shows an example of the honeycomb structure of the present invention.
The honeycomb structure 1 shown in Figure 6 comprises the above-mentioned honeycomb substrate 10, a positive electrode 61 arranged in an arc 23 of the first region 20 of the honeycomb substrate 10, and a negative electrode 62 arranged in an arc 33 of the second region of the honeycomb substrate 10.
In the honeycomb structure 1 , the honeycomb substrate 10 can be uniformly heated by passing a current from the positive electrode 61 to the negative electrode 62 .
In the honeycomb structure of the present invention, a negative electrode may be disposed on an arc in the first region of the honeycomb substrate, and a positive electrode may be disposed on an arc in the second region of the honeycomb substrate.

In addition, in the honeycomb structure 1, the positive electrode 61 may be arranged so as to cover the entire arc 23 forming the first region 20, and the negative electrode 62 may be arranged so as to cover the entire arc 33 forming the second region 30.
By arranging the electrodes in this manner, the honeycomb substrate 10 can be heated more uniformly.

When mounting the honeycomb structure 1 on a vehicle, a retaining material is placed around the honeycomb structure 1, which is then housed in a casing and connected to the exhaust pipe.

The retaining material is preferably made of inorganic fibers. Examples of inorganic fibers include alumina fibers and alumina-silica fibers.

The casing is not particularly limited as long as it is made of a heat-resistant metal, and examples of the metal include stainless steel, aluminum, iron, etc.

In addition, holes will be formed in the holding material and casing to pass the wiring for each electrode.

Next, we will explain the manufacturing method of the honeycomb structure 1.

(1) Preparation of honeycomb substrate (1-1) Ceramic raw material preparation process First, the ceramic raw material to be used as the raw material for the honeycomb substrate is prepared. The ceramic raw material can be prepared by mixing a ceramic mixture such as SiC, Si, _SiO2 , or boric acid, an organic binder, a plasticizer, a lubricant, and water.
If necessary, a pore-forming agent such as spherical acrylic particles or graphite may be added to the above ceramic raw material.

(1-2) Extrusion Molding Step Next, the ceramic raw material prepared in the above ceramic raw material preparation step is extruded using a predetermined die, and cut to a predetermined length to produce a honeycomb formed body having a predetermined shape.
The shape of the honeycomb formed body, the shape of the cells, the arrangement of the cells, the thickness of the cell partition walls, the thickness of the outer peripheral wall, etc. can be adjusted by adjusting the shape of the die. In particular, the direction of the partition walls of the cells formed in the first region, the second region, the third region, and the fourth region can be adjusted by adjusting the shape of the die.

(1-3) Drying step Next, the honeycomb molded body obtained in the above extrusion molding step is dried using a microwave dryer, a hot air dryer, a dielectric dryer, a reduced pressure dryer, a vacuum dryer, a freeze dryer, etc. In drying the honeycomb molded body, a microwave dryer and a hot air dryer may be used in combination, or the honeycomb molded body may be dried using a microwave dryer until the moisture content is reduced to a certain level, and then the moisture in the honeycomb molded body may be completely removed using a hot air dryer.

(1-4) Degreasing Step Next, the honeycomb formed body after the drying step is heated at 300 to 650° C. for 0.5 to 3 hours to remove organic matter from the honeycomb formed body, thereby producing a honeycomb degreased body.

(1-5) Firing Step The honeycomb degreased body obtained in the above degreasing step is fired in an inert gas atmosphere such as a nitrogen atmosphere or an argon atmosphere at 1200 to 1500° C. for 0.5 to 4 hours.
Through the above steps, a honeycomb substrate can be produced.

(2) Electrode Arrangement Step Next, a pair of electrodes are arranged on the arc of the first region and the arc of the second region. The electrodes are preferably arranged by a thermal spraying method, a dipping method, or the like.

Through the above steps, the honeycomb structure of the present invention can be manufactured.

(Example)
EXAMPLES Hereinafter, examples that more specifically disclose the present invention will be described, however, the present invention is not limited to only the following examples.

Example 1
[Manufacturing of honeycomb substrate]

Si powder, boric acid powder, and silica powder were mixed in a mass ratio of 16:6:78, and the resulting mixed powder (74.4 wt%) was mixed with 6.7 wt% organic binder (methylcellulose), 4.5 wt% lubricant (UNILUBE, manufactured by NOF Corp.), and 14.4 wt% water, and kneaded to prepare a raw material composition.

The obtained raw material composition was molded using an extrusion molding machine to obtain a cylindrical honeycomb molded body in which the cross section of each cell was a square. At this time, the molded body was molded so that the angle formed by the first line segment 21 and the second line segment 22 in Fig. 1 was 90°, the acute angle formed by the first direction D1 and the second direction D2 was 45°, and the acute angle formed by the first direction D1 and the third direction D3 was 45°.
The honeycomb molded body was dried by high-frequency dielectric heating, and then dried at 120° C. for 2 hours using a hot air dryer, and both end faces were cut off by a predetermined amount to obtain a dried honeycomb body.
The dried honeycomb body was degreased (calcined) at 600° C. for 10 hours, and then fired at 1325° C. for 3 hours in an inert atmosphere to produce a honeycomb substrate. The electrical resistivity of the honeycomb substrate was 1.5 Ωcm.

Next, Si powder, boric acid powder, and silica powder were mixed in a mass ratio of 80:10:10, and methyl cellulose as a binder, lubricant (UNILUB manufactured by NOF Corp.), water, and ethanol were added and mixed to prepare an electrode paste. This electrode paste was printed on the entire surface of the arcs in the first and second regions so that the thickness after firing would be 0.35 mm.

Next, the electrode paste printed on the outer peripheral wall of the honeycomb substrate was dried at 870°C, degreased at 600°C for 10 hours, fired at 1325°C for 3 hours in an inert atmosphere, and further oxidized to obtain a honeycomb structure having electrodes. The end face of the obtained honeycomb structure was a circle with a diameter of 130 mm, and the length in the longitudinal direction of the honeycomb structure was 60 mm.
The partition wall thickness of the honeycomb structure was 0.15 mm in all regions, and the cell density was 85.3 cells/cm ² in all regions.

The electrical resistivity of the electrode portion was 0.05 Ω·cm. The thermal conductivity of the honeycomb substrate was 1.6 W/mK.

Example 2
A honeycomb structure was obtained in the same manner as in Example 1, except that in the molding of the honeycomb molded body, the angle formed by the first line segment 21 and the second line segment 22 in Figure 1 was 90°, the acute angle formed by the first direction D1 and the second direction D2 was 30°, and the acute angle formed by the first direction D1 and the third direction D3 was 30°.

Example 3
A honeycomb structure was obtained in the same manner as in Example 1, except that the honeycomb molded body was molded so that the angle formed by the first line segment 21 and the second line segment 22 in Figure 1 was 90°, the acute angle formed by the first direction D1 and the second direction D2 was 60°, and the acute angle formed by the first direction D1 and the third direction D3 was 60°.

Example 4
A honeycomb structure was obtained in the same manner as in Example 1, except that the honeycomb molded body was molded so that the angle formed by the first line segment 21 and the second line segment 22 in Figure 1 was 120°, the acute angle formed by the first direction D1 and the second direction D2 was 45°, and the acute angle formed by the first direction D1 and the third direction D3 was 45°.

Example 5
A honeycomb structure was obtained in the same manner as in Example 1, except that the honeycomb molded body was molded so that the angle formed by the first line segment 21 and the second line segment in Figure 1 was 90°, the acute angle formed by the first direction D1 and the second direction was 15°, and the acute angle formed by the first direction D1 and the third direction D3 was 15°.

(Comparative Example 1)
A honeycomb structure was obtained in the same manner as in Example 1, except that in the molding of the honeycomb formed body, the first to fourth regions were not provided and the shape was formed as shown in FIG.

(Electrical test)
For the honeycomb structures manufactured in Examples 1 to 5 and Comparative Example 1, electrical terminals were formed on each electrode and a voltage of 200 V was applied for 20 seconds. The surface temperature of the honeycomb structure was measured using a thermal camera, and the difference between the maximum and minimum temperatures was confirmed.
As the thermo camera, an infrared thermography camera (R300SR-H: manufactured by Nippon Avionics Co., Ltd.) was used, and the software InfReC Analyzer NS9500 Standard Version 2.5 was used to measure the maximum and minimum temperatures in the image of the honeycomb structure. In the honeycomb structure of Comparative Example 1, the difference between the maximum and minimum temperatures was 115°C, whereas in the honeycomb structures of Examples 1 to 5, the differences between the maximum and minimum temperatures were 70°C, 85°C, 88°C, 90°C, and 103°C, respectively, which was smaller, and it was confirmed that the honeycomb structures were heated more uniformly.

1 Honeycomb structure 10, 510 Honeycomb substrate 11, 511 Cell 12, 512 Partition wall 13 Catalyst 20 First region 21 First line segment 22 Second line segment 23 Arc 23a of first region Midpoint of arc 30 of first region Second region 33 Arc 33a of second region Midpoint of arc 40 of second region Third region 50 Fourth region 61, 561 Positive electrode 62, 562 Negative electrode D1 First direction D2 Second direction D3 Third direction

Claims (8)

An elliptical or cylindrical honeycomb substrate having partition walls that define a large number of cells,
The honeycomb substrate is a resistance heating element,
The cross section perpendicular to the longitudinal direction of the honeycomb substrate is
a first region surrounded by two line segments extending from the center of the cross section to the outer periphery and an arc connecting the two line segments;
A second region that is a region that is point-symmetric to the first region with respect to the center of the cross section;
a third region located between one of the line segments forming the first region and the second region;
a fourth region located between the second region and another line segment forming the first region,
The partition walls of the cells formed in the first region and the second region are formed in a lattice shape along a first direction connecting a center of the cross section and a midpoint of an arc of the first region and a direction perpendicular to the first direction in a cross section perpendicular to the longitudinal direction of the honeycomb substrate,
The partition walls of the cells formed in the third region are formed in a lattice shape along a second direction oblique to the first direction and a direction perpendicular to the second direction in a cross section perpendicular to the longitudinal direction of the honeycomb substrate,
A honeycomb substrate characterized in that the partition walls of the cells formed in the fourth region are formed in a lattice pattern along a third direction oblique to the first direction and a direction perpendicular to the third direction in a cross section perpendicular to the longitudinal direction of the honeycomb substrate. The honeycomb substrate according to claim 1, wherein the acute angle formed between the first direction and the second direction is between 30° and 60°. The honeycomb substrate according to claim 1 or 2, wherein the acute angle formed between the first direction and the third direction is between 30° and 60°. The honeycomb substrate according to any one of claims 1 to 3, wherein the thermal conductivity of the honeycomb substrate is 1 to 70 W/mK. The honeycomb substrate according to any one of claims 1 to 4, wherein the electrical resistivity of the honeycomb substrate is 0.1 to 50 Ω·cm. The honeycomb substrate according to any one of claims 1 to 5, wherein the honeycomb substrate is made of a material containing SiC, Si, SiO ₂ , carbon or borosilicate. A honeycomb substrate according to any one of claims 1 to 6,
A honeycomb structure including a pair of electrodes disposed on a surface of the honeycomb substrate,
One electrode is disposed on a surface of the honeycomb substrate where the arc forming the first region is located;
A honeycomb structure, characterized in that the other electrode is disposed on the surface of the honeycomb substrate where the arc forming the second region is located. the one electrode is disposed so as to cover the entire arc forming the first region,
The honeycomb structure according to claim 7 , wherein the other electrode is disposed so as to cover the entire arc forming the second region.

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