JP7594455B2 - Mat material, exhaust gas purification device, and method for manufacturing the mat material - Google Patents

Description

The present invention relates to a mat material, an exhaust gas purification device, and a method for manufacturing the mat material.

Exhaust gas emitted from internal combustion engines such as diesel engines contains particulate matter (hereinafter referred to as PM), and in recent years, the harm that this PM poses to the environment and human body has become a problem. In addition, exhaust gas also contains harmful gas components such as CO, HC, and NOx, and there are concerns about the impact that these harmful gas components have on the environment and human body.

Therefore, various exhaust gas purification devices have been proposed that capture PM in exhaust gas and purify harmful gas components. The exhaust gas purification devices are composed of an exhaust gas treatment body made of porous ceramics such as silicon carbide or cordierite, a metal casing that houses the exhaust gas treatment body, and a retaining seal material (mat material) arranged between the exhaust gas treatment body and the metal casing. The main purpose of this retaining seal material (mat material) is to prevent the exhaust gas treatment body from coming into contact with the metal casing that covers its outer periphery and being damaged by vibrations and impacts caused by the running of the automobile, and to prevent exhaust gas from leaking between the exhaust gas treatment body and the metal casing.

When high-pressure exhaust gas flows into such an exhaust gas purification device, the exhaust gas treatment body is pushed by the exhaust gas and falls off the metal casing, which is a problem.

Patent Document 1 describes how, in order to improve the holding performance of the holding seal material, inorganic particles are attached to the surface of the inorganic fibers that make up the holding seal material, thereby improving the friction coefficient of the holding seal material.

Furthermore, Patent Document 2 describes how, in order to improve the holding performance of the holding seal material, the inorganic fibers that make up the holding seal material are compressed and fixed with an organic binder to form grooves on the surface, thereby improving the friction coefficient of the holding seal material.

JP 2013-213463 A JP 2017-31870 A

The present inventors measured the coefficient of friction between the holding sealer and the metal casing of the holding sealer described in Patent Document 1, and found that the coefficient of friction was smaller than expected.
The present inventors speculate that the reason for this is as follows.

The holding sealer described in Patent Document 1 is used such that its main surface is in contact with the metal casing. It is considered that frictional force is generated between the surface of the holding sealer that is in contact with the metal casing and the surface of the metal casing.
However, when the surface of the holding sealer is viewed microscopically, the inorganic fibers constituting the holding sealer are entangled with one another, and therefore the surface of the holding sealer is not uniform.
When the surface of the holding sealing material is viewed microscopically, the area occupied by the inorganic fibers on the surface of the holding sealing material is smaller than the area of the mat material. Therefore, it is considered that the inorganic fibers are in point contact with the surface of the metal casing.

Furthermore, in Patent Document 1, inorganic particles are placed on the surface of the inorganic fibers. Since the particles make point contact with the surface, it is believed that even if the inorganic particles are placed on the surface of the inorganic fibers, the holding seal material will make point contact with the surface of the metal casing.

When the retaining seal material is in point contact with the surface of the metal casing, the actual contact area between the retaining seal material and the surface of the metal casing is small. In this case, the coefficient of friction between the retaining seal material and the metal casing is smaller than the coefficient of friction when it is assumed that the retaining seal material and the metal casing are in surface contact.

In other words, for the reasons mentioned above, it is believed that when the retaining seal material described in Patent Document 1 is used, the coefficient of friction between the retaining seal material and the metal casing becomes smaller than expected.

In addition, attaching inorganic particles to inorganic fibers complicates the manufacturing process and increases manufacturing costs.

In addition, the inventors measured the coefficient of friction between the retaining seal material described in Patent Document 2 and the metal casing, but were unable to confirm any effect of improving the coefficient of friction.

The present invention was made in consideration of these problems, and aims to provide a mat material that can improve the surface friction coefficient.

In other words, the mat material of the present invention is a mat material made of inorganic fibers, and the mat material has a first main surface and a second main surface located opposite the first main surface, and at least one of the first main surface and the second main surface has been subjected to a surface treatment to change the surface condition.

Since the mat material of the present invention has at least one of the first and second main surfaces subjected to surface treatment to change the surface condition, it is possible to improve the friction coefficient of the surface, particularly the surface to be processed of the first and second main surfaces that have been surface-treated.
In addition, since no additional materials such as inorganic particles are required and the manufacturing process is simple, it is possible to reduce manufacturing costs.

In the mat member of the present invention, it is preferable that the first main surface and the second main surface are subjected to the surface treatment to change the surface state.
Since each of the main surfaces is a processed surface that has been subjected to a surface treatment, the mat material can have a high coefficient of friction on each of the main surfaces.

In the mat member of the present invention, it is preferable that the surface to be processed, of the first main surface and the second main surface, has raised inorganic fibers.
This makes it possible to more suitably exhibit the effect of improving the friction coefficient.
More specifically, when the processed surface has raised inorganic fibers, the fiber orientation is forced to change to a random orientation at the interface where friction occurs. This makes it difficult for the inorganic fibers to move in response to external forces, suppressing stepwise displacement and improving the holding force. As a result, the friction coefficient is effectively improved.
As a result of measurements conducted by the present inventors, it has been confirmed that a mat material having brushed inorganic fibers on its main surface has a frictional force equal to or greater than that of a mat material having inorganic particles attached thereto, such as that described in Patent Document 1.

Note that "gradual displacement" here means that the frictional resistance of the entire mat material decreases as each inorganic fiber at the friction-generating interface gradually displaces (moves).

In the mat material of the present invention, the raised inorganic fibers form fiber agglomerates, and it is preferable that the fiber agglomerates are partially separated from the processed surface.

In the mat material of the present invention, it is preferable that the processed surface has a plurality of the fiber agglomerates, and that ends of the plurality of fiber agglomerates in the same direction are spaced apart from the processed surface.
Such a mat material can be produced using a processing device such as a raising device, and therefore can be made into a mat material that is excellent in mass productivity.

In the mat material of the present invention, the friction coefficient of the surface to be processed, of the first main surface and the second main surface, which has been subjected to the surface processing, is preferably 0.21 to 0.45 when the bulk density of the mat material is 0.3 g/cm ³ and at 25°C.

In the mat material of the present invention, it is preferable that the bulk density of the first main surface and the second main surface near the processed surface on which the surface treatment has been applied is smaller than the bulk density near the center of the thickness direction of the mat material.

In the mat material of the present invention, the bulk density of the first main surface and the second main surface near the processed surface that has been subjected to the surface processing is preferably 0.05 to 0.18 g/ ^cm3 , and the bulk density of the mat material near the center in the thickness direction is preferably 0.11 to 0.20 g/ ^cm3 .

In the mat material of the present invention, the bulk density of the first and second main surfaces near the processed surfaces on which the surface treatment has been applied is preferably 45 to 95% of the bulk density near the center of the thickness direction of the mat material.

The exhaust gas purification device of the present invention is an exhaust gas purification device comprising an exhaust gas treatment body, a metal casing that houses the exhaust gas treatment body, and a mat material that is disposed between the exhaust gas treatment body and the metal casing and holds the exhaust gas treatment body, and is characterized in that the mat material is the mat material of the present invention.

As described above, the mat material of the present invention has the effect of improving the surface friction coefficient. Therefore, it is possible to obtain an exhaust gas purification device in which the exhaust gas treatment body is held with high retention force.

The method for manufacturing the mat material of the present invention is characterized by including a mat preparation step for preparing a mat made of inorganic fibers, and a surface processing step for performing a surface treatment on at least one of a first main surface of the mat and a second main surface of the mat located opposite the first main surface to change the surface condition.

In the method for manufacturing the mat material of the present invention, in the surface processing step, it is preferable to subject at least one of the first main surface and the second main surface to a brushed treatment.

In the method for manufacturing a mat material of the present invention, it is preferable that the mat is manufactured by a needling method in the mat preparation step.

FIG. 1 is a perspective view showing an example of the mat material of the present invention. FIG. 2 is a perspective view showing a schematic state of the mat material shown in FIG. 1 before surface treatment is applied thereto. FIG. 3 is a schematic diagram showing a contact mechanism when a rough surface is pressed against a flat surface with a load W and a lateral force F is applied. FIG. 4 is an enlarged perspective view showing a schematic view of a part of the processed surface of the mat material shown in FIG. FIG. 5 is a cross-sectional view showing a schematic example of a needle mat that has not been surface-treated. FIG. 6 is a cross-sectional view showing a schematic example of the mat material of the present invention. FIG. 7 is a cross-sectional view that illustrates an example of an exhaust gas purification device of the present invention. FIG. 8 is a plan view that illustrates the processed surface of the mat member of the second embodiment. FIG. 9 is a schematic diagram showing an apparatus for measuring the friction coefficient of a mat material. FIG. 10 is a schematic diagram showing an apparatus for measuring the friction coefficient of a mat material. FIG. 11 is a graph showing the measurement results of the friction coefficients of the mat materials in the examples and the comparative examples. FIG. 12 is a photograph of the processed surface of the mat material of Example 2 observed with a microscope.

Detailed Description of the Invention
The mat material of the present invention will be described in detail below.
The mat material of the present invention is a mat material made of inorganic fibers, characterized in that the mat material has a first main surface and a second main surface located opposite the first main surface, and at least one of the first main surface and the second main surface has been subjected to surface treatment to change the surface condition.

FIG. 1 is a perspective view showing an example of the mat material of the present invention.
FIG. 1 shows a mat material 1 of the present invention which is rectangular in plan view.
The planar shape of the mat material 1 is not limited to a rectangle, but may be other shapes depending on the place where it is used.
In addition, a convex portion 2a is provided at one longitudinal end 2 of the mat material 1, and a concave portion 3a is provided at the other longitudinal end 3 of the mat material 1 so that the ends fit together when the mat material 1 is wrapped around an object.
The provision of such convex portions 2a and concave portions 3a improves sealing performance when the mat material 1 is disposed in an exhaust gas purification device, which will be described later.
The mat material of the present invention does not necessarily have to have any protrusions or recesses at the ends of the mat material.
In addition, the ends of the mat material may be L-shaped so that the ends fit together when the mat material is wrapped around the object.

The mat material 1 is made of inorganic fibers.
The inorganic fibers are not particularly limited, and examples thereof include alumina fibers, alumina-silica fibers, silica fibers, biosoluble fibers, glass wool, rock wool, etc. Among these, alumina-silica fibers are preferred.
These inorganic fibers have high heat resistance, and a mat material formed from such inorganic fibers is unlikely to change shape due to temperature changes.

Furthermore, when the inorganic fibers are alumina-silica fibers, the composition ratio of alumina to silica, by weight, is preferably alumina (Al ₂ O ₃ ):silica (SiO ₂ )=60:40 to 80:20, and more preferably alumina (Al ₂ O ₃ ):silica (SiO ₂ )=70:30 to 74:26.

The average fiber length of the inorganic fibers is preferably from 1 to 150 mm, and more preferably from 10 to 80 mm.
If the average fiber length of the inorganic fibers is less than 1 mm, the fiber length of the inorganic fibers is too short, resulting in insufficient entanglement of the inorganic fibers with each other, making it difficult to obtain sufficient strength for the mat material, and the shape retention of the mat material is likely to decrease.
Furthermore, when the average fiber length of the inorganic fibers exceeds 150 mm, the fiber length of the inorganic fibers is too long, so that the number of fibers constituting the mat material is reduced, and the density of the mat material is reduced, resulting in a decrease in the shear strength of the mat material.

The average fiber diameter of the inorganic fibers is preferably from 1 to 20 μm, more preferably from 2 to 15 μm, and even more preferably from 3 to 10 μm.
If the average fiber diameter of the inorganic fibers is less than 1 μm, the breaking load is low and the inorganic fibers are easily broken by impact or the like.
If the average fiber diameter of the inorganic fibers exceeds 20 μm, defects are likely to occur inside the fibers, reducing the strength of the inorganic fibers and lowering the surface pressure value as a mat material for holding the exhaust gas treatment body.

The average fiber length and average fiber diameter of inorganic fibers are determined by observing 100 random inorganic fibers within the field of view of the mat material using a SEM (scanning electron microscope).

As shown in FIG. 1, the mat material 1 has a first main surface 4 and a second main surface 5 located opposite the first main surface 4, and the first main surface 4 and the second main surface 5 have been subjected to surface treatment to change the surface condition.
This makes it possible to improve the coefficient of friction of the processed surface 6, which is the surface of the mat material 1 that has been subjected to the surface treatment.
Moreover, the mat member 1 can be produced at low cost through a simple manufacturing process without using additional materials such as inorganic particles.

FIG. 2 is a perspective view showing a schematic state of the mat material shown in FIG. 1 before surface treatment is applied thereto.
As shown in Figs. 1 and 2, the first main surface 4 and the second main surface 5 of the mat material 1 have their surface conditions changed by being subjected to a surface treatment.

The mat material 1 may have only one of the first main surface 4 and the second main surface 5 as a processed surface 6 that has been subjected to surface treatment, but as shown in Figures 1 and 2, it is preferable that the surface condition of the first main surface 4 and the second main surface 5 of the mat material 1 be changed by being subjected to surface treatment.
In other words, it is preferable that each of the main surfaces 4 and 5 is the surface 6 to be processed.
This allows the mat material to have a high coefficient of friction on each of the main surfaces 4 and 5.

When each of the main surfaces 4, 5 is a surface to be processed 6, the first main surface 4 and the second main surface 5 may be subjected to different types of surface treatments, but typically are subjected to the same type of surface treatment (preferably a nap-raising treatment).

As shown in FIG. 1 , the processed surface 6 of the first main surface 4 or the second main surface 5 that has been subjected to surface processing preferably has raised inorganic fibers 10 .
This makes it possible to more suitably exhibit the effect of improving the friction coefficient.
Such a processed surface 6 can be effectively formed by carrying out a nap raising process as the above-mentioned surface treatment.

Here, the function and effect of the raised inorganic fibers 10 will be described in more detail with reference to FIG.
First, in a general elastic body such as a mat material, the mechanism by which a holding force is generated is as follows.
FIG. 3 is a schematic diagram showing a contact mechanism when a rough surface is pressed against a flat surface with a load W and a lateral force F is applied.
F (holding force) is generally expressed as W (surface pressure) × μ (friction coefficient), but in the case of an elastic body such as a mat material, as shown in Figure 3, when each protrusion of the elastic body E is pressed against a plane P with a load W, the tip of the protrusion is deformed by the contact pressure _pn and forms a contact surface with a contact area A _n , so that F (holding force) is the sum of the shear forces τ _n × A _n of the true contact points (each protrusion) where friction occurs, as shown in the following equation (1).
F=τ ₁ ×A ₁ +τ ₂ ×A ₂ +τ ₃ ×A ₃ +...=Στ _n ×A _n (1)
Here, τ _n represents the average shear force of each protrusion, and n represents the number of each protrusion.
Therefore, when the projections are misaligned, the stress of the projections is relaxed and the shear force is reduced or eliminated, resulting in a decrease in F (holding force).

The friction coefficient _μM of the elastic body is expressed by the following formula (2).
μ _M = μ _K +C(μ _S −μ _K )W ^−1/3 (2)
Here, μ _K indicates the dynamic friction coefficient, μ _S indicates the static friction coefficient, W indicates the load, and C indicates the stiffness.

In contrast, when the processed surface of the mat material of the present invention has raised inorganic fibers, the fiber orientation is forcibly changed to a random orientation at the interface where friction occurs. This makes it difficult for the inorganic fibers to move in response to external forces, suppressing stepwise shifting and making it possible to improve the holding force F. As a result, the coefficient of friction is effectively improved.

FIG. 4 is an enlarged perspective view showing a schematic view of a part of the processed surface of the mat material shown in FIG.
As shown in FIG. 4 , the raised inorganic fibers 10 form fiber agglomerates 11 , and it is preferable that the fiber agglomerates 11 are partially separated from the surface 6 to be processed.

The term "fiber aggregate" used herein means a fiber aggregate in which a plurality of inorganic fibers are integrated together.
The fiber mass 11 is formed when inorganic fibers on the work surface 6 are caught by a needle and partially peeled off from the work surface 6.
Therefore, the fiber agglomerations 11 and other inorganic fibers (for example, inorganic fibers at the center in the thickness direction of the mat material) basically differ only in the fiber orientation direction.
However, since fiber agglomeration 11 is formed by being hooked on a needle, there is usually a low-accumulation part 12 of inorganic fibers in its center, as shown in Fig. 4. In other words, the center part of fiber agglomeration 11 may have a lower density of inorganic fibers than the surrounding area.
By having the low-accumulation portion 12 at the center of the fiber agglomerate 11, it is possible to more effectively improve the coefficient of friction. On the other hand, if the fiber agglomerate 11 does not have the low-accumulation portion 12 at the center and the overall accumulation degree (density) is uniform, the fiber agglomerate 11 will become a hard mass, and there is a risk that the effect of improving the coefficient of friction will not be effectively obtained.
In addition, the presence of the low-accumulation portion 12 enables the fiber mass 11 to absorb the shock of pressure when assembling the exhaust gas treatment body and the mat material during the manufacturing process of the exhaust gas purification device, thereby preventing the mat material body from being damaged.
On the other hand, if the fiber agglomeration 11 is a hard agglomeration without the low-pile portion 12 in the center, the fiber agglomeration 11 may press against the main body of the mat material during assembly, destroying the inorganic fibers of the main body of the mat material.

As shown in FIG. 4 , the work surface 6 of the mat material has a plurality of fiber agglomerates 11 , and it is preferable that the ends 13 of the plurality of fiber agglomerates 11 in the same direction D are spaced apart from the work surface 6 .
In other words, it is preferable that one end 13 of the fiber agglomerate 11 in a certain direction D is separated from the work surface 6, and the other end 14 of the fiber agglomerate 11 in the same direction D is integrated with the work surface 6 without being separated from the work surface 6.
Such a mat material can be produced using a processing device such as a raising device, and therefore can be made into a mat material that is excellent in mass productivity.

Note that in FIG. 4, the direction D in which the end 13 away from the work surface 6 is oriented is shown as the longitudinal direction of the mat material, but the direction D is not particularly limited and can be set as appropriate.

In the mat material of the present invention, the friction coefficient of the processed surface of the first main surface or the second main surface that has been subjected to the above-mentioned surface treatment is preferably 0.21 to 0.45, and more preferably 0.23 to 0.45, when the bulk density of the mat material is 0.3 g/cm ³ and the temperature is 25° C.

When each main surface is a surface to be processed, the friction coefficients of the first main surface and the second main surface may be different from each other, but from the viewpoint of easy production using the same processing equipment, it is preferable that they are substantially the same.

In the mat material of the present invention, it is preferable that the bulk density near the surface to be processed is smaller than the bulk density near the center of the thickness direction of the mat material.

More specifically, in the mat material of the present invention, the bulk density in the vicinity of the surface to be processed is preferably 0.05 to 0.18 g/ ^cm3 , and the bulk density in the vicinity of the center in the thickness direction of the mat material is preferably 0.11 to 0.20 g/ ^cm3 , and more preferably the bulk density in the vicinity of the surface to be processed is 0.05 to 0.14 g/ ^cm3 , and the bulk density in the vicinity of the center in the thickness direction of the mat material is preferably 0.11 to 0.20 g/ ^cm3 .
More specifically, in the mat material of the present invention, the bulk density in the vicinity of the processed surface is preferably 45 to 95%, and more preferably 60 to 90%, of the bulk density in the vicinity of the center in the thickness direction of the mat material.
Here, the bulk density near the processed surface is the bulk density of the processed portion (the portion including the processed surface) when the mat material is divided into thirds in the thickness direction, and the bulk density near the center of the thickness direction of the mat material is the bulk density in the center portion (the portion not including the processed surface) when the mat material is divided into thirds in the thickness direction.

When each main surface is a surface to be processed, the bulk densities near the first main surface and the second main surface may be different from each other, but from the viewpoint of easy production using the same processing equipment, it is preferable that they are substantially the same.

The mat material of the present invention may be a mat produced by a papermaking method (hereinafter referred to as a papermaking mat) that has been surface-treated, but it is preferable that the mat material is a mat produced by a needling method (hereinafter referred to as a needle mat) that has been surface-treated.
When a needle mat is used, it is possible to obtain a more effective improvement effect on the coefficient of friction than when a paper-formed mat is used.
The reason for this will be described in detail below with reference to FIGS.
FIG. 5 is a cross-sectional view showing a schematic example of a needle mat that has not been surface-treated.
FIG. 6 is a cross-sectional view showing a schematic example of the mat material of the present invention.
5 and 6 show cross sections of a portion that has not been needle punched.
In addition, the upper right corner of FIG. 6 shows a partially enlarged view of the surface of the mat material to be processed.

The needle mat is basically produced by laminating fibers in a cross layer, so that the inorganic fibers 10 oriented in the in-plane direction of the mat are oriented so as to overlap in the thickness direction of the mat, as shown in FIG.
Therefore, it is considered that each inorganic fiber 10 is easily movable, and stepwise misalignment is easily caused at the interface where friction occurs, and the holding force is easily reduced.

However, as shown in Figure 6, in a mat material 1 manufactured by the needling method and having a brushed surface 6, the orientation of the inorganic fibers 10 is forcibly changed to a random orientation at the interface where friction occurs, as shown in the enlarged view of Figure 6. This makes it difficult for the inorganic fibers to move in response to external forces, effectively suppressing stepwise displacement, and significantly improving the holding force F.

In contrast, papermaking mats have less bias in fiber orientation than needle mats, so the inorganic fibers are less likely to move and are less likely to shift in stages. As a result, the effect of raising the nap on improving the coefficient of friction is smaller than with needle mats.

Next, a method for producing the mat material of the present invention will be described.
The manufacturing method of the mat material of the present invention is characterized by including a mat preparation step of preparing a mat made of inorganic fibers, and a surface processing step of applying surface processing to at least one of a first main surface of the mat and a second main surface located opposite the first main surface of the mat to change the surface condition.

The inorganic fiber mat can be obtained by various methods, for example, a papermaking method or a needling method, but it is preferable to produce it by the needling method, which can more effectively improve the friction coefficient as described above, compared to the case where the mat is produced by the papermaking method.
In the case of the papermaking method, the paper can be produced, for example, by the following method.
The inorganic fibers are opened and dispersed in a solvent to obtain a mixture. The mixture is poured into a molding machine having a filtering mesh formed on the bottom surface, and the solvent in the mixture is removed to obtain an inorganic fiber aggregate. The inorganic fiber aggregate is then dried to obtain a mat.
In the case of the needling method, the production can be carried out, for example, by the following method.
A spinning mixture made of a basic aluminum chloride aqueous solution and silica sol or the like is spun by a blowing method to produce an inorganic fiber precursor. The inorganic fiber precursor is then compressed to produce a continuous sheet-like product of a predetermined size, and a mat is obtained by subjecting the product to a firing treatment. A needle punching treatment is performed either before or after the firing treatment to entangle the inorganic fibers.

The thickness of the mat is not particularly limited, but is preferably from 2 to 40 mm, and more preferably from 5 to 20 mm.
If the thickness of the mat is less than 2 mm, the retaining force of the mat material is insufficient, and the exhaust gas treatment body is likely to fall off.
If the thickness of the mat exceeds 40 mm, the mat loses its flexibility, making it difficult to handle when wrapping the mat material around the exhaust gas treatment body, and the mat material is prone to wrinkles and cracks when wrapped.

Then, a surface treatment process is carried out to change the surface condition by applying surface treatment to at least one of the first main surface of the mat and the second main surface located on the opposite side of the mat to the first main surface.

In the method for producing a mat material of the present invention, it is preferable that in the surface processing step, at least one of the first main surface and the second main surface is subjected to a nap raising treatment.
This makes it possible to generate raised inorganic fibers on the first main surface and/or the second main surface, so that the effect of improving the friction coefficient as described above is more suitably exhibited.
The specific means for performing the nap raising treatment is not particularly limited, and examples thereof include a treatment device such as a nap raising device, sandpaper, etc. The nap raising treatment may also be performed manually with a needle.
From the viewpoint of mass productivity, it is preferable to carry out the raising treatment using a treatment device such as a raising device.
The raising device, for example, has one or more rollers wrapped with cardboard clothing having a large number of needles, and the mat is run over the rollers while rotating, thereby scraping out the inorganic fibers from the main surface of the mat.

The exhaust gas purification device of the present invention will be described below.
The exhaust gas purification device of the present invention is an exhaust gas purification device comprising an exhaust gas treatment body, a metal casing that houses the exhaust gas treatment body, and a mat material that is arranged between the exhaust gas treatment body and the metal casing and holds the exhaust gas treatment body, wherein the mat material is the mat material of the present invention.

As described above, the mat material of the present invention has the effect of improving the surface friction coefficient. Therefore, the exhaust gas treatment device of the present invention can be an exhaust gas purification device in which the exhaust gas treatment body is held with high retention force.

FIG. 7 is a cross-sectional view that illustrates an example of an exhaust gas purification device of the present invention.
As shown in Figure 7, the exhaust gas purification device 100 of the present invention comprises a metal casing 50, an exhaust gas treatment body 40 housed in the metal casing 50, and a mat material 1 arranged between the exhaust gas treatment body 40 and the metal casing 50 and holding the exhaust gas treatment body 40.

The exhaust gas treatment body 40 has a columnar shape in which a large number of cells 41 are arranged in parallel in the longitudinal direction with cell walls 42 separating them.
In addition, if necessary, an inlet pipe for introducing exhaust gas discharged from the internal combustion engine and an exhaust pipe for discharging exhaust gas that has passed through the exhaust gas purification device to the outside will be connected to the end of the metal casing 50.

A case where exhaust gas passes through the exhaust gas purification device 100 having the above-mentioned configuration will be described below with reference to FIG.
As shown in Fig. 7, exhaust gas discharged from an internal combustion engine and flowing into the exhaust gas purification device 100 (in Fig. 7, the exhaust gas is indicated by G, and the flow of the exhaust gas is indicated by arrows) flows into one cell 41 opening at the exhaust gas inlet end face of the exhaust gas treatment body (honeycomb filter) 40, and passes through a cell wall 42 separating the cells 41. At this time, PM in the exhaust gas is captured by the cell wall 42, and the exhaust gas is purified. The purified exhaust gas flows out from the other cell 41 opening at the exhaust gas outlet end face, and is discharged to the outside.

In the exhaust gas purification device 100 shown in Figure 7, the mat material 1 is the mat material of the present invention, and it is preferable that both the first and second main surfaces of the mat material 1 are processed surfaces whose surface condition has been changed by surface treatment (preferably brushing treatment).

The material of the metal casing that constitutes the exhaust gas purification device of the present invention is not particularly limited as long as it is a heat-resistant metal, and specific examples include metals such as stainless steel, aluminum, and iron.

In addition to a generally cylindrical shape, the casing can be suitably shaped in a clamshell shape, or in a generally elliptical or polygonal shape in cross section.

The exhaust gas treatment body 40 shown in FIG. 7 is a filter in which one end of the cell 41 is sealed with a sealing material 43, but the exhaust gas treatment body constituting the exhaust gas purification device of the present invention does not have to have the ends of the cells sealed. Such an exhaust gas treatment body can be suitably used as a catalyst carrier.

The exhaust gas treatment body 40 may be made of a non-oxide porous ceramic such as silicon carbide or silicon nitride, or may be made of an oxide porous ceramic such as alumina, cordierite, or mullite. Of these, silicon carbide is preferred.

The cell density in the cross section of the exhaust gas treatment body 40 is not particularly limited, but a preferred lower limit is 31.0 cells/ ^cm2 (200 cells/ ^inch2 ), a preferred upper limit is 93.0 cells/ ^cm2 (600 cells/ ^inch2 ), a more preferred lower limit is 38.8 cells/ ^cm2 (250 cells/ ^inch2 ), and a more preferred upper limit is 77.5 cells/ ^cm2 (500 cells/ ^inch2 ).

The exhaust gas treatment body 40 may support a catalyst for purifying the exhaust gas. The catalyst to be supported is preferably a precious metal such as platinum, palladium, or rhodium, and among these, platinum is more preferable. In addition, other catalysts such as alkali metals such as potassium or sodium, or alkaline earth metals such as barium may also be used. These catalysts may be used alone or in combination of two or more kinds.
When these catalysts are supported, PM can be easily burned and removed, and toxic exhaust gas can also be purified.

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

Example 1
A mat made of inorganic fibers (mullite fibers) was prepared by a needling method.
This mat was punched out into a square with each side measuring 50 mm.
The mat had a thickness of 8.5 mm, and the inorganic fibers constituting the mat had a fiber length of 1 to 150 mm, an average fiber length of 10 mm, and an average fiber diameter of 5.5 μm.

Next, one of the main surfaces of the mat punched into a square shape was evenly processed with sandpaper (grit 150) and the nap-raising process was repeated three times to produce the mat material of Example 1.

Example 2
FIG. 8 is a plan view that illustrates the processed surface of the mat member of the second embodiment.
The mat used in Example 1 was punched out into a square with each side measuring 50 mm.
Next, one main surface of the mat punched into a square was subjected to a nap raising treatment using a needle having a diameter of 1 mm, thereby producing a mat material of Example 2.
In detail, a needle was manually inserted obliquely into the main surface to a depth of about 2 mm and then pulled up to scratch out the inorganic fibers of the main surface, and this process was carried out at intervals of about 3 mm across the entire main surface, as shown in FIG.

(Comparative Example 1)
The mat used in Example 1 was punched out into a square having sides of 50 mm and used as is.

(Measurement of coefficient of friction)
The friction coefficients of the mat materials of the examples and comparative examples were measured by the following method.
9 and 10 are schematic diagrams showing an apparatus for measuring the friction coefficient of a mat material.
In the friction coefficient measuring device 200, stainless steel flat plates (a left plate 210 and a right plate 220) are arranged on the left and right sides of the device so as to face each other.

First, the two mat materials 1a and 1b and the middle plate 230 were arranged in the following order: left plate 210, mat material 1a, a stainless steel flat plate (middle plate 230), mat material 1b, and right plate 220.
Protruding members 240 are provided on the surfaces of the left plate 210 and the right plate 220 to prevent slippage between the left plate 210 and the mat material 1a, and between the right plate 220 and the mat material 1b (between the plates and the mat materials).
In the mat material of the embodiment, the surface that was subjected to the nap-raising process was placed on the side of the middle plate 230 .
The mat material 1 a is sandwiched between the left plate 210 and the middle plate 230 , and the mat material 1 b is sandwiched between the middle plate 230 and the right plate 220 .
Furthermore, the middle plate 230 is a load cell, and the load applied to the middle plate can be measured.

First, pressure was applied to the left plate 210 and the right plate 220 in the direction of the middle plate 230, and the mat material was compressed until its bulk density (GBD) became 0.3 g/cm ³ .
The compressed state was maintained (relaxed) for 10 minutes.

Next, with the temperature between the mat material and the middle plate being 25°C, 100°C, 200°C or 300°C, the middle plate 230 was moved in the direction indicated by the arrow in Figure 10 (upward) at a speed of 25 mm/min to apply shear stress to the main surface of the mat material.
FIG. 10 shows the state in which the middle plate has been moved.
The direction in which the mid-plate is moved is the same as the direction in which the shear stress is applied to the main surface of the mat material on the side in contact with the mid-plate.
The load value of the load cell during movement and the static friction force acting on the middle plate were measured, and the coefficient of friction when the static friction force was at a maximum (static friction coefficient) was measured.

(Measurement of bulk density)
First, a mat material was punched out into a square having sides of 50 mm, and then cut into three equal parts in the thickness direction.
Next, the weight and thickness of each of the three cut mat pieces were measured using a dial gauge (measurement probe φ20 mm, load 4.9 kPa).
Then, the bulk density near the processed surface (processed portion) and the bulk density near the center of the thickness of the mat material (central portion) were calculated from the surface specific gravity (weight/area) calculated from the weight, as shown in the formula below.
(weight/area)/thickness=bulk density [g/cm ³ ]

FIG. 11 and Table 1 show the measurement results of the friction coefficients of the mat materials in the examples and comparative examples.
Table 2 also shows the ratio of the friction coefficient of the mat material of the embodiment to the friction coefficient of the mat material of the comparative example.

As shown in FIG. 11 and Tables 1 and 2, the mat material of the embodiment having a raised surface has a higher friction coefficient than the mat material of the comparative example having no surface treatment, and it was confirmed that the friction coefficient was improved by 5% or more.
Furthermore, the mat member of the embodiment does not require any additional materials and the manufacturing process is simple, so that it can be manufactured at low cost.

Table 3 shows the measurement results of the bulk density of the mat material in the examples and comparative examples. Table 3 also shows the results of calculating the ratio of the bulk density of the processed part (the upper part in Comparative Example 1) to the bulk density of the center part in each example and comparative example.

As shown in Table 3, the untreated mat material of the comparative example had similar bulk density at the top and center, and the entire mat material had a uniform bulk density, whereas the mat material of the example with a brushed surface had a lower bulk density in the processed area compared to the center, and it was confirmed that the bulk density decreased near the brushed processed surface.

(Surface Observation)
Fig. 12 is a photograph of the processed surface of the mat material of Example 2 observed with a microscope. In Fig. 12, the state before the surface processing by the nap raising treatment is shown on the left side, and the state after the surface processing by the nap raising treatment is shown on the right side.
As shown in Figure 12, the mat material of the embodiment having a brushed surface has inorganic fibers 10 brushed on the work surface 6, and it was confirmed that these brushed inorganic fibers 10 form fiber agglomerates 11 partially separated from the work surface 6.
Furthermore, many of the fiber agglomerates 11 had low-density portions 12 in their centers where the density of inorganic fibers was lower than that of the surrounding areas.

1 Mat material 1a Mat material 1b Mat material 2 One end 2a Convex portion 3 Other end 3a Concave portion 4 First main surface 5 Second main surface 6 Work surface 10 Inorganic fiber 11 Fiber agglomerate 12 Low accumulation portion 13 One end of fiber agglomerate 14 Other end of fiber agglomerate 40 Exhaust gas treatment body 41 Cell 42 Cell wall 43 Sealing material 50 Metal casing 100 Exhaust gas purification device 200 Friction coefficient measuring device 210 Left plate 220 Right plate 230 Middle plate 240 Projecting member G Exhaust gas

Claims (11)

A mat material made of inorganic fibers,
The mat material has a first main surface and a second main surface located opposite to the first main surface,
At least one of the first main surface and the second main surface is surface-treated to have inorganic fibers raised on the surface to be treated;
The raised inorganic fibers form a fiber mass, and a low-density portion of the inorganic fibers is present in the center of the fiber mass. The mat material according to claim 1, wherein the first main surface and the second main surface have a surface condition changed by the surface treatment. The mat material according to claim 1, wherein the fiber mass is partially separated from the work surface. The processed surface has a plurality of the fiber agglomerates,
The mat material according to claim 3 , wherein ends of the plurality of fiber agglomerates in the same direction are spaced apart from the surface to be processed. The mat material according to any one of claims 1 to 4, wherein the friction coefficient of the processed surface of the first main surface or the second main surface that has been subjected to the surface treatment is 0.21 to 0.45 when the bulk density of the mat material is 0.3 g/cm ³ and at 25°C. A mat material according to any one of claims 1 to 5, wherein the bulk density of the first main surface and the second main surface near the processed surface on which the surface treatment has been applied is smaller than the bulk density near the center in the thickness direction of the mat material. The bulk density of the first main surface and the second main surface in the vicinity of the processed surface on which the surface processing has been performed is 0.05 to 0.18 g/cm ³ ;
The mat material according to any one of claims 1 to 6, wherein the bulk density of the mat material in the vicinity of the center in the thickness direction is 0.11 to 0.20 g/ ^cm3 . A mat material according to any one of claims 1 to 7, wherein the bulk density of the first main surface and the second main surface near the processed surface on which the surface treatment has been performed is 45 to 95% of the bulk density near the center in the thickness direction of the mat material. An exhaust gas treatment body;
A metal casing that houses the exhaust gas treatment body;
An exhaust gas purification apparatus comprising: a mat material disposed between the exhaust gas treatment body and the metal casing and holding the exhaust gas treatment body,
9. An exhaust gas purification device, comprising the mat material according to claim 1. A mat preparation step of preparing a mat made of inorganic fibers;
a surface treatment step of performing a surface treatment on at least one of a first main surface of the mat and a second main surface of the mat located opposite to the first main surface to change a surface state;
A method for producing a mat material, comprising:
In the surface processing step, a needle is inserted obliquely into at least one of the first and second main surfaces and then pulled up to scrape out the inorganic fibers , so that the raised inorganic fibers form a fiber mass and a low-density portion of the inorganic fibers is present in the center of the fiber mass . This is a method for manufacturing a mat material. The method for producing a mat material according to claim 10, wherein in the mat preparation step, the mat is produced by a needling method.

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