Mat Material, Exhaust Gas Purification Apparatus, and Method for Manufacturing Exhaust Gas Purification Apparatus

The present invention relates to a mat material, an exhaust gas conversion apparatus, and a method for producing an exhaust gas conversion apparatus.

Exhaust gas discharged from an internal combustion engine such as a diesel engine contains a particulate matter (hereinafter, also referred to as “PM”). Adverse effects of PM on the environment and human bodies have been problems. The exhaust gas also contains harmful gas components such as CO, HC, and NOx. This causes concerns about the effects of such harmful gas components on the environment and human bodies.

In view of the above, various exhaust gas conversion apparatuses that collect PM in exhaust gas and convert harmful gas components have been proposed. Such an exhaust gas conversion apparatus includes an exhaust gas treatment unit including porous ceramic such as silicon carbide or cordierite, a casing for housing the exhaust gas treatment unit, and a mat material containing inorganic fiber aggregates between the exhaust gas treatment unit and the casing. This type of mat material is disposed mainly, for example, for preventing the exhaust gas treatment unit from being damaged by contact with the casing that covers the periphery of the exhaust gas treatment unit due to vibrations and impacts caused by operation of automobiles or the like, and for preventing exhaust gas leakage from a space between the exhaust gas treatment unit and the casing.

The mat material contains inorganic fibers. The basic shape of the mat material in a plan view is a rectangular shape including long sides extending in the longitudinal direction and short sides substantially perpendicular to the long sides. A recess is formed on one short side of the rectangular shape, and a protrusion having a shape similar to a cut out shape of the recess is formed on the other short side. The mat material is wound around an exhaust gas treatment unit, and the protrusion is fitted with the recess so as to prevent leakage of exhaust gas from the mat material.

The exhaust gas treatment unit having the mat material wound therearound is press-fitted into a casing and installed in an exhaust gas conversion apparatus.

For example, according to the disclosure of Patent literature 1, a first surface uses a sheet material (mat material) having concave parts and convex parts with an average difference h between the concave parts and the convex parts of 0.4 mm≤h≤9 mm in order to decrease the contact area between the sheet material and another member, which makes it possible to easily place the sheet material at a predetermined position without using a surface lubricant.

Patent literature 1 is silent about detailed dimensions of the recess and the protrusion. When a mat material is produced and press-fitted into a casing, a portion of the mat material on the most upstream side of the fitting portion may be deformed, and when an exhaust gas treatment unit is fixed at a predetermined position, a portion of the mat material may stick out from the casing in some cases.

The present invention was made to solve the above problems and aims to provide a mat material that does not easily stick out from a casing during press-fitting.

Specifically, the present invention provides a mat material having a generally rectangular shape in a plan view, the mat material including inorganic fibers, wherein the mat material includes a first main surface and a second main surface opposite to each other in a thickness direction, a first end surface and a second end surface opposite to each other in a longitudinal direction that is a winding direction, and a first side surface and a second side surface opposite to each other in a width direction perpendicular to the thickness direction and the longitudinal direction, the mat material includes, on the first end surface, a protrusion designed to protrude toward the second end surface during winding of the mat material, and non-protruding portions provided at both sides of the protrusion in the width direction and designed not to protrude toward the second end surface during winding of the mat material, the mat material includes, on the second end surface, a recess designed to fit the shape of the protrusion on the first end surface during winding of the mat material, and non-recessed portions provided at both sides of the recess in the width direction and designed to fit the shapes of the non-protruding portions on the first end surface during winding of the mat material, and a ratio [D/C] of a length [D] of the non-recessed portion in the width direction to a length [C] of the non-recessed portion in the longitudinal direction is 1.0 or more.

When a mat material having a protrusion and its corresponding recess as the one shown in Patent literature 1 is wound around an exhaust gas treatment unit, a portion of a first end surface and portions of a second end surface are arranged in a staggered manner at the fitting portion where the end surfaces of the mat material fit each other.

The portion of the first end surface is the protrusion on the first end surface, and the portions of the second end surface are the non-recessed portions on the second end surface. There are two non-recessed portions on the second end surface, with one adjacent to the first side surface and the other one adjacent to the second side surface. During winding of the mat material, the shape of the protrusion on the first end surface fits the shape of the recess on the second end surface, and the shapes of the non-protruding portions on the first end surface fit the shapes of the non-recessed portions on the second end surface.

During press-fitting into the casing, the mat material is easily deformed as it is pulled toward the upstream side in the press-fitting direction due to the shear stress generated between the exhaust gas treatment unit and the casing. This deformation easily occurs particularly at the non-recessed portion with no structure that prevents deformation at further upstream, i.e., the non-recessed portion on the most upstream side.

Presumedly, in the non-recessed portions, portions closer to the main body of the mat material (i.e., portions excluding the protrusion and the non-recessed portions) are less easily deformed by the shear force, and portions further away from the main body of the mat material are more easily deformed by the shear force. In other words, the shorter the lengths of the non-recessed portions, the less easily the non-recessed portions are deformed.

Meanwhile, the larger the width of each non-recessed portion (the distance corresponding to the length from the first or second side surface to the recess), the longer the region where the non-recessed portions are fixed to the main body of the mat material, so that the non-recessed 15 portions are not easily deformed by shear force.

In other words, presumedly, the non-recessed portions can be made less susceptible to deformation by adjusting the length and the width of each non-recessed portion.

The above effect can be achieved even when there are multiple protrusions on the first end surface and multiple recesses on the second end surface.

In the mat material of the present invention, the ratio [D/C] of the length [D] of the non-recessed portion in the width direction to the length [C] of the non-recessed portion in the longitudinal direction is 1.0 or more.

The structure described above is one in which the length [C] of the non-recessed portion in the longitudinal direction is relatively short, and the length [D] of the non-recessed portion in the width direction is relatively long, compared to the structure disclosed in Patent literature 1.

Thus, when the shape of the mat material satisfies the above conditions, the non-recessed portions are not easily deformed by the shear force during press-fitting, and the mat material does not easily stick out from the casing.

Preferably, the mat material of the present invention is a needle-punched mat.

Preferably, the mat material of the present invention is a mat material including multiple entanglement points formed by needling, wherein at least one of a 4 mm×4 mm first region without the entanglement points or a 3 mm×8 mm second region without the entanglement points is arranged in a 25 mm×25 mm region.

When the first region and/or the second region is arranged in the 25 mm×25 mm region, the surface pressure of the mat material can be increased.

In the mat material of the present invention, preferably, the inorganic fibers have an average fiber length of 1 to 150 mm.

Preferably, the mat material of the present invention is a papermaking mat.

In the mat material of the present invention, preferably, the inorganic fibers have an average fiber length of 200 to 20000 μm.

In the mat material of the present invention, preferably, an inorganic binder is attached to a surface of each inorganic fiber.

When an inorganic binder is attached to the surface of each inorganic fiber, the inorganic binder attached to the surface of each inorganic fiber increases the frictional resistance between the inorganic fibers, so that the holding power can be increased.

In the mat material of the present invention, preferably an organic binder is attached to the surface of each inorganic fiber.

When an organic binder is attached to the surface of each inorganic fiber, the adhesion between the inorganic fibers can be increased to prevent inorganic fiber scattering during handling of the mat material.

In the mat material of the present invention, preferably, an inorganic binder and an organic binder are attached to the surface of each inorganic fiber.

An inorganic binder, when attached to the surface of each inorganic fiber, increases the frictional resistance between the inorganic fibers and thus can increase the holding power.

An organic binder, when attached to the surface of each inorganic fiber, can improve the adhesion between the inorganic fibers and prevent inorganic fiber scattering during handling of the mat material.

Preferably, the mat material of the present invention further contains a polymeric dispersant.

When the mat material further contains a polymeric dispersant, the organic binder and the inorganic binder can be easily attached in a dispersed state to the surface of each inorganic fiber.

Preferably, in the mat material of the present invention, the inorganic binder and the organic binder are attached in an individually dispersed state to the surface of each inorganic fiber.

When the inorganic binder and the organic binder are attached in an individually dispersed state to the surface of each inorganic fiber, the inorganic binder is in a dispersed state in a coating formed from the organic binder. The coating in such a state has excellent mechanical strength and thus can prevent the inorganic fibers from slipping on each other and increase the holding power.

In the mat material of the present invention, preferably, aggregates of the inorganic binder and the organic binder are attached to the surface of each inorganic fiber.

Aggregates of the inorganic binder and the organic binder, when attached to the surface of each inorganic fiber, can increase the friction between the inorganic fibers and improve the holding power.

In the mat material of the present invention, preferably, the surface of each inorganic fiber is at least partially covered with a coating layer containing a mixture of the inorganic binder and the organic binder.

The coating layer containing a mixture of the inorganic binder and the organic binder has a higher mechanical strength than a coating layer containing only the organic binder. Thus, the coating layer does not easily peel off, making it possible to increase the frictional resistance between the inorganic fibers.

In the mat material of the present invention, preferably, the coating layer is formed from a continuous flaky mixture of the inorganic binder and the organic binder.

When the coating layer is formed from the flaky mixture, the surface roughness of the coating layer increases due to the flaky mixture, which can further increase the frictional resistance between the inorganic fibers.

In the mat material of the present invention, preferably, the coating layer has a stepped shape.

When the coating layer has a stepped shape, the frictional resistance between the inorganic fibers can be further increased.

In the mat material of the present invention, preferably, a particulate mixture of the inorganic binder and the organic binder is attached to a surface of the coating layer.

When the particulate mixture of the inorganic binder and the organic binder is attached to the surface of the coating layer, the frictional resistance between the inorganic fibers can be further increased than when no such particulate mixture is attached to the coating layer.

In the mat material of the present invention, preferably, a ratio [A/C] of a length [A] of the mat material in the longitudinal direction to the length [C] of the non-recessed portion in the longitudinal direction is 10 or more.

When the ratio [A/C] of the length [A] of the mat material in the longitudinal direction to the length [C] of the non-recessed portion in the longitudinal direction is in the above range, the non-recessed portions each have a shape that is not easily deformed during press-fitting.

An exhaust gas conversion apparatus of the present invention is an exhaust gas conversion apparatus including: a casing; an exhaust gas treatment unit; and a mat material between the casing and the exhaust gas treatment unit, wherein the mat material is the mat material of the present invention.