Patent Publication Number: US-2015082759-A1

Title: Holding sealing material, method for producing holding sealing material, method for manufacturing exhaust gas purifying apparatus, and exhaust gas purifying apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2013-195586, filed Sep. 20, 2013. The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a holding sealing material, a method for producing a holding sealing material, a method for manufacturing an exhaust gas purifying apparatus, and an exhaust gas purifying apparatus. 
     2. Discussion of the Background 
     Particulate matter (hereinafter also referred to as PM) such as soot in exhaust gas discharged from internal combustion engines including diesel engines causes damage to environment and human bodies, and these days people have paid attention to this problem. Since exhaust gas contains toxic gas components such as CO, HC, and NOx, people also worry about the influences of the toxic gas components on the environment and human bodies. 
     These issues have led to the development of various exhaust gas purifying apparatuses for capturing PM in exhaust gas and converting toxic gas components. These exhaust gas purifying apparatuses include: an exhaust gas treating body made of porous ceramics such as silicon carbide or cordierite; a metal container (casing) housing the exhaust gas treating body; and a mat-shaped holding sealing material that includes inorganic fibers, and is disposed between the exhaust gas treating body and the casing. 
     Some main purposes of using a holding sealing material in an exhaust gas purifying apparatus are, for example: to protect the exhaust gas treating body from being damaged by contact between the exhaust gas treating body and the casing surrounding the exhaust gas treating body as a result of vibrations and impacts during travel of an automobile or the like; to hold the exhaust gas treating body tightly to prevent the exhaust gas treating body from slipping out from the exhaust gas purifying apparatus; and to prevent exhaust gas leakage from space between the exhaust gas treating body and the casing. 
     A known method for manufacturing an exhaust gas purifying apparatus is to press-fit an exhaust gas treating body wrapped with a holding sealing material into a casing. In an exhaust gas purifying apparatus manufactured by this method, the holding sealing material is compressed in the casing. Therefore, the holding sealing material is exerting a restoring force that is attributed to the elasticity of inorganic fibers and tends to bring the holding sealing material back toward its original form (that is, holding force for holding the exhaust gas treating body), and thus holds the exhaust gas treating body. 
     However, when an exhaust gas treating body wrapped with a holding sealing material is press-fit into a casing, the holding sealing material experiences a shear force on the main face in contact with the casing and the main face in contact with the exhaust gas treating body respectively in mutually opposite directions. Accordingly, the side faces of the holding sealing material are deformed to be partially oblique to the end faces of the exhaust gas treating body. The deformed parts of the side faces of the holding sealing material are not compressed, and unfortunately, are prone to wind erosion caused by flow of exhaust gas and reduce the holding force. 
     JP 2006-161667 A and German Patent No. DE 10 2004 056 804 B4 disclose holding sealing materials provided with an oblique face projecting forward from the inside to the outside in the press-fitting direction on the side face which is the front face in the press-fitting direction. When either of the holding sealing materials of JP 2006-161667 A and German Patent No. DE 10 2004 056 804 B4 is wrapped around an exhaust gas treating body and press-fit into a casing, the side face of the holding sealing material is deformed. This deformation is compensated by the oblique face, so that the side face of the holding sealing material becomes substantially parallel to the end face of the exhaust gas treating body. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a holding sealing material includes inorganic fibers, a longitudinal direction, a width direction, a thickness direction, a first main face, a second main face, and a structure. The width direction is perpendicular to the longitudinal direction. The thickness direction is perpendicular to the longitudinal direction and the width direction. The first main face is substantially perpendicular to the thickness direction. The second main face is opposite to the first main face in the thickness direction. The holding sealing material is to be wrapped along the longitudinal direction around an exhaust gas treating body housed in a casing of an exhaust gas purifying apparatus and disposed between the exhaust gas treating body and the casing so that the first main face faces an outer circumference face of the exhaust gas treating body and the second main face faces an inner circumference face of the casing. The structure is plastically deformed by applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction. 
     According to another aspect of the present invention, in a method for producing a holding sealing material, a material mat including inorganic fibers is provided. The material mat has a first main face substantially perpendicular to a thickness direction of the material mat, a second main face opposite to the first main face in the thickness direction. The holding sealing material is to be wrapped along a longitudinal direction perpendicular to the thickness direction and a width direction of the material mat around an exhaust gas treating body housed in a casing of an exhaust gas purifying apparatus and disposed between the exhaust gas treating body and the casing so that the first main face faces an outer circumference face of the exhaust gas treating body and the second main face faces an inner circumference face of the casing. The first main face and the second main face of the material mat are immobilized. A shear stress is applied to the first main face and the second main face respectively in mutually opposite directions along the width direction to plastically deform the material mat. 
     According to further aspect of the present invention, in a method for manufacturing an exhaust gas purifying apparatus, a material mat including inorganic fibers is provided. The material mat has a first main face substantially perpendicular to a thickness direction of the material mat, a second main face opposite to the first main face in the thickness direction. The first main face and the second main face of the material mat are immobilized. Shear stress is applied to the first main face in a first shear direction and to the second main face in a second shear direction opposite to the first shear direction to plastically deform the material mat to produce a holding sealing material. The first shear direction and the second shear direction are along a width direction perpendicular to the thickness direction and a longitudinal direction of the material mat. The holding sealing material is wrapped along the longitudinal direction around an exhaust gas treating body so that the first main face of the holding sealing material contacts the exhaust gas treating body to produce a wrapped body. The wrapped body is press-fitted into a casing in a same direction as the first shear direction. 
     According to the other aspect of the present invention, an exhaust gas purifying apparatus includes a casing, an exhaust gas treating body, and a holding sealing material. The exhaust gas treating body is housed in the casing. The holding sealing material is wrapped around the exhaust gas treating body and disposed between the exhaust gas treating body and the casing. The holding sealing material includes inorganic fibers, a longitudinal direction, a width direction, a thickness direction, a first main face, a second main face, and a structure. The width direction is perpendicular to the longitudinal direction. The thickness direction is perpendicular to the longitudinal direction and the width direction. The first main face is provided substantially perpendicular to the thickness direction and faces an outer circumference face of the exhaust gas treating body. The second main face is provided opposite to the first main face in the thickness direction and faces an inner circumference face of the casing. The structure is plastically deformed by applying shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG. 1  is a perspective view schematically illustrating one example of the material mat. 
         FIG. 2  is a perspective cross-sectional view schematically illustrating one example of the needle-punched material mat. 
         FIGS. 3A to 3D  are cross-sectional views schematically illustrating one example of the deformation step. 
         FIG. 4  is a cross-sectional view schematically illustrating one example of the material mat after a cutting step. 
         FIG. 5A  is a perspective view schematically illustrating one example of the holding sealing material of an embodiment of the present invention, and  FIG. 5B  is a plan view of the holding sealing material shown in  FIG. 5A . 
         FIG. 6  is a perspective view schematically illustrating one example of a wrapped body including an exhaust gas treating body wrapped with a holding sealing material. 
         FIG. 7  is a partial perspective cross-sectional view schematically illustrating one example of the press-fitting step. 
         FIG. 8  is a partial perspective cross-sectional view schematically illustrating an exhaust gas purifying apparatus produced by the method for manufacturing an exhaust gas purifying apparatus of an embodiment of the present invention. 
         FIG. 9  is a perspective view schematically illustrating one example of the exhaust gas purifying apparatus of an embodiment of the present invention. 
         FIG. 10  is an A-A line cross-sectional view of the exhaust gas purifying apparatus shown in  FIG. 9 . 
         FIGS. 11A and 11B  are schematic views of an apparatus for measuring the surface pressure of a holding sealing material. 
         FIG. 12  is an illustrative view schematically demonstrating how to measure a deformation quantify of a holding sealing material. 
         FIG. 13A  is a photograph of a holding sealing material of Example 2 taken before firing, and  FIG. 13B  is a photograph of the holding sealing material of Example 2 taken after firing. 
         FIG. 14A  is a photograph of a holding sealing material of Example 3 taken before firing, and  FIG. 14B  is a photograph of the holding sealing material of Example 3 taken after firing. 
         FIG. 15A  is a photograph of a holding sealing material of Comparative Example 1 taken before firing, and  FIG. 15B  is a photograph of the holding sealing material of Comparative Example 1 taken after firing. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. 
     The holding sealing material of the embodiment of the present invention is a holding sealing material for use in an exhaust gas purifying apparatus that includes: a casing; an exhaust gas treating body housed in the casing; and the holding sealing material that is wrapped around the exhaust gas treating body and disposed between the exhaust gas treating body and the casing, 
     the holding sealing material including inorganic fibers and having a mat shape with a first main face, a second main face opposite to the first main face, side faces along a longitudinal direction of the holding sealing material, and end faces along a width direction perpendicular to the longitudinal direction, 
     wherein the holding sealing material is plastically deformed by applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction before being wrapped around an exhaust gas treating body. 
     The holding sealing material of the embodiment of the present invention is plastically deformed by applying a shear stress to the two opposite main faces before being wrapped around an exhaust gas treating body. Therefore, the holding sealing material of the embodiment of the present invention is less likely to be further deformed when the holding sealing material is wrapped around an exhaust gas treating body and press-fit into a casing in the same direction as the direction of the shear stress applied to the inner main face of the holding sealing material (the face in contact with the exhaust gas treating body). In the case where an exhaust gas purifying apparatus including the holding sealing material of the embodiment of the present invention is used in such a manner that exhaust gas flows in the same direction as the press-fitting direction, the holding sealing material is less likely to be deformed. Thus, the holding sealing material of the embodiment of the present invention is designed to be resistant to deformation when used in an exhaust gas purifying apparatus. 
     As described above, the holding sealing material of the embodiment of the present invention is less likely to be deformed around an exhaust gas treating body that is being press-fit into a casing and in an exhaust gas purifying apparatus that is in operation, and therefore can prevent wind erosion and a reduction in the holding force. Additionally, since the holding sealing material of the embodiment of the present invention is thus less likely to be deformed, the surface pressure of the holding sealing material measured before wrapping the holding sealing material around an exhaust gas treating body can be considered as the holding force of the holding sealing material in an exhaust gas purifying apparatus. Thus, it is easy to calculate the holding force of the holding sealing material of the embodiment of the present invention in an exhaust gas purifying apparatus. 
     The holding sealing material of the embodiment of the present invention is preferably treated by needle punching. 
     The needle punching entangles inorganic fibers in the holding sealing material with one another to reduce the mobility of the inorganic fibers. This facilitates the plastic deformation of the holding sealing material by applying a shear stress to the two main faces of the holding sealing material. 
     In the case where the holding sealing material of the embodiment of the present invention is treated by needle punching, the shear stress is preferably applied to the first main face and the second main face such that the needle holes made by the needle punching are slanted at least 15° with respect to at least one of directions respectively perpendicular to the first main face and the second main face when viewed in a cross section parallel to the width direction. 
     The inorganic fibers are made less likely to return to their original state by, for example, carrying out the needle punching perpendicularly on the main faces and applying a shear stress to the two main faces such that needle holes are slanted at least 15°. This further facilitates the plastic deformation. 
     The holding sealing material of the embodiment of the present invention preferably includes an organic binder. 
     The organic binder in the holding sealing material fixes entangled inorganic fibers, and prevents the inorganic fibers from returning into the original state, thereby facilitating the plastic deformation. 
     The method for producing a holding sealing material of the embodiment of the present invention is a method for producing a holding sealing material for use in an exhaust gas purifying apparatus that includes: a casing; an exhaust gas treating body housed in the casing; and the holding sealing material that is wrapped around the exhaust gas treating body and disposed between the exhaust gas treating body and the casing, 
     the method including: a material mat preparing step of preparing a material mat that includes inorganic fibers and has a mat shape with a first main face, a second main face opposite to the first main face, side faces along a longitudinal direction of the material mat, and end faces along a width direction perpendicular to the longitudinal direction; and 
     a deformation step of plastically deforming the material mat by immobilizing the first main face and the second main face of the material mat, and applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction. 
     The method for producing a holding sealing material of the embodiment of the present invention allows for the production of the above-described holding sealing material of the embodiment of the present invention, that is, a holding sealing material that is plastically deformed by applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction before being wrapped around an exhaust gas treating body. Therefore, the method allows for the production of a holding sealing material that is less likely to be deformed around an exhaust gas treating body that is being press-fit into a casing and in an exhaust gas purifying apparatus that is in operation, and therefore can prevent wind erosion and a reduction in the holding force, and allows for easy calculation of the holding force in an exhaust gas purifying apparatus. 
     The material mat prepared in the material mat preparing step of the method for producing a holding sealing material of the embodiment of the present invention is preferably a material mat, at least one of the first main face and the second main face of which is treated by needle punching. 
     The needle punching is carried out on the holding sealing material to entangle inorganic fibers with one another and thereby to reduce the mobility of the inorganic fibers. This facilitates the plastic deformation of the holding sealing material by applying a shear stress to the two main faces of the holding sealing material. 
     In the case where a material mat treated by needle punching is prepared, the shear stress is applied to the first main face and the second main face in the deformation step preferably such that needle holes made by the needle punching are slanted at least 15° with respect to at least one of directions respectively perpendicular to the first main face and the second main face when viewed in a cross section parallel to the width direction. 
     In the case where the shear stress is applied to the two main faces such that needle holes are slanted at least 15°, the inorganic fibers are made less likely to return into their original state. This further facilitates the plastic deformation. 
     In the method for producing a holding sealing material of the embodiment of the present invention, the material mat prepared in the material mat preparing step is preferably a material mat impregnated with an organic binder solution, and in the deformation step, the material mat is immobilized and dried while the shear stress is applied to the first main face and the second main face. 
     In this case, the organic binder exerts a fixing force to maintain the shape of the holding sealing material, and therefore facilitates the plastic deformation. 
     The method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention is a method for manufacturing an exhaust gas purifying apparatus that includes: a casing; an exhaust gas treating body housed in the casing; and a holding sealing material that is wrapped around the exhaust gas treating body and disposed between the exhaust gas treating body and the casing, 
     the method including: a wrapped body preparing step of preparing a wrapped body by wrapping the holding sealing material of the embodiment of the present invention or the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention around an exhaust gas treating body such that either the first main face or the second main face of the holding sealing material contacts the exhaust gas treating body; and 
     a press-fitting step of press-fitting the wrapped body into a casing in the same direction as the direction of the shear stress applied to the main face of the holding sealing material which is in contact with the exhaust gas treating body. 
     In the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention, the holding sealing material of the embodiment of the present invention is used, and the press-fitting direction is the same as the direction of the shear stress applied to the inner main face of the holding sealing material. An advantage attributable to these features is that the holding sealing material is less likely to be deformed when the wrapped body is press-fit into the casing. Another advantage is that the holding sealing material is less likely to be deformed when the resulting exhaust gas purifying apparatus is used in such a manner that exhaust gas flows in the same direction as the press-fitting direction. 
     As described above, the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention allows for the manufacture of an exhaust gas purifying apparatus including a holding sealing material that is less likely to be deformed around an exhaust gas treating body that is being press-fit into a casing and in an exhaust gas purifying apparatus that is in operation, and therefore can prevent wind erosion and a reduction in the holding force, and allows for easy calculation of the holding force in an exhaust gas purifying apparatus. 
     The exhaust gas purifying apparatus of the embodiment of the present invention includes: 
     a casing; 
     an exhaust gas treating body housed in the casing; and 
     a holding sealing material that is wrapped around the exhaust gas treating body and disposed between the exhaust gas treating body and the casing, 
     wherein the holding sealing material is the holding sealing material of the embodiment of the present invention or the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention, and is wrapped around the exhaust gas treating body such that either the first main face or the second main face of the holding sealing material contacts the exhaust gas treating body, and 
     the exhaust gas treating body wrapped with the holding sealing material is press-fit into the casing in the same direction as the direction of the shear stress applied to the main face of the holding sealing material which is in contact with the exhaust gas treating body. 
     Since the exhaust gas purifying apparatus of the embodiment of the present invention includes a holding sealing material that is less likely to be deformed around an exhaust gas treating body that is being press-fit into a casing and in the exhaust gas purifying apparatus that is in operation, the exhaust gas purifying apparatus can prevent wind erosion and a reduction in the holding force, and allows for easy calculation of the holding force of the holding sealing material in the exhaust gas purifying apparatus. 
     The term “perpendicular” herein means being somewhat perpendicular enough to ensure the effects of the embodiment of the present invention, and may refer to being completely perpendicular or to being substantially perpendicular. The term “parallel” likewise means being somewhat parallel enough to ensure the effects of the embodiment of the present invention, and may refer to being completely parallel or to being substantially parallel. 
     The following specifically demonstrates the embodiment of the present invention, but is not intended to limit the present invention. Various modifications and alterations can be made without departing from the scope of this invention. 
     The method for producing a holding sealing material of the embodiment of the present invention is described first, and then the holding sealing material of the embodiment of the present invention, the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention, and the exhaust gas purifying apparatus of the embodiment of the present invention are described in this order. 
     [Method for Producing Holding Sealing Material] 
     The method for producing a holding sealing material of the embodiment of the present invention is a method for producing a holding sealing material for use in an exhaust gas purifying apparatus that includes: a casing; an exhaust gas treating body housed in the casing; and a holding sealing material that is wrapped around the exhaust gas treating body and disposed between the exhaust gas treating body and the casing, 
     the method including: a material mat preparing step of preparing a material mat that includes inorganic fibers and has a mat shape with a first main face, a second main face opposite to the first main face, side faces along a longitudinal direction of the material mat, and end faces along a width direction perpendicular to the longitudinal direction; and 
     a deformation step of plastically deforming the material mat by immobilizing the first main face and the second main face of the material mat, and applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction. 
     The method for producing a holding sealing material of the embodiment of the present invention includes a material mat preparing step of preparing a material mat that includes inorganic fibers and has a mat shape with a first main face, a second main face opposite to the first main face, side faces along a longitudinal direction of the material mat, and end faces along a width direction perpendicular to the longitudinal direction. 
       FIG. 1  is a perspective view schematically illustrating one example of the material mat. 
     The material mat  100  shown in  FIG. 1  includes inorganic fibers, and has a mat shape with a first main face  101 , a second main face  102  opposite to the first main face  101 , side faces  103  along the longitudinal direction (the direction indicated by the arrow X in  FIG. 1 ), and end faces  104  along the width direction perpendicular to the longitudinal direction X (the direction indicated by the arrow Y in  FIG. 1 ). The arrow Z in  FIG. 1  indicates the thickness direction. 
     The material mat can be prepared by, for example, punching out from a mat made of inorganic fibers entangled by fiber spinning. 
     The inorganic fibers constituting the material mat are not particularly limited, and may be alumina-silica fibers, alumina fibers, silica fibers, or the like. Alternatively, glass fibers or biosoluble fibers may be used. The inorganic fibers may be changed depending on the desired features of the holding sealing material such as heat resistance and resistance to wind erosion, and fibers with larger diameters and longer lengths, which meet the environmental requirements in various countries, are preferable. 
     Low-crystalline alumina inorganic fibers are preferable among these, and low-crystalline alumina inorganic fibers having a mullite composition are more preferable. Inorganic fibers including a spinel compound are more preferable. High-crystalline alumina materials, which are hard and easy to break, are not suitable for holding sealing materials, which are required to function as a cushioning material. 
     In the case of low-crystalline alumina inorganic fibers including a spinel compound, the crystallization rate is preferably 0.1 to 30%, and more preferably 0.4 to 20%. When inorganic fibers having a crystallization rate within these ranges are used, the holding sealing material has high repulsion and high reconstructed surface pressure as measured after a durability test, and thus has high quality. By contrast, inorganic fibers having a crystallization rate of less than 0.1% or more than 30% remarkably reduce the repulsion and reconstructed surface pressure. The crystallization rate can be calculated from the integrated intensity ratio between a diffraction peak of mullite (2θ=26.4°) and a diffraction peak of γ-alumina (2θ=45.4°). 
     In the case where the material mat is subjected to later-described needle punching which forms an entangled structure, the average fiber length of the inorganic fibers is preferably 4 to 120 mm. Fibers with an average fiber length within this range are entangled with one another at needle-punched sites to increase the strength of the mat. The average fiber diameter of the inorganic fibers is preferably 2 to 12 μm, and more preferably 3 to 10 μm. 
     The weight per unit surface area of the material mat is not particularly limited, but is preferably 400 g/m 2  to 2000 g/m 2 . If the material mat has a weight per unit surface area of less than 400 g/m 2 , the material mat may be processed into a holding sealing material that is not effective enough in protecting an exhaust gas treating body from vibrations in an exhaust gas purifying apparatus that is in operation, and therefore may cause the exhaust gas treating body to be damaged or to be slipped out from the casing. On the other hand, if the weight per unit surface area of the material mat is more than 2000 g/m 2 , the material mat may be processed into a holding sealing material having too strong restoring force which is stronger than the strength of the exhaust gas treating body and may break the exhaust gas treating body. 
     The bulk density of the material mat is not particularly limited, and is preferably 0.10 to 0.30 g/cm 3 . If the bulk density of the material mat is less than 0.10 g/cm 3 , the inorganic fibers may not be sufficiently entangled with one another, and some inorganic fibers may easily drop off. Accordingly, the material mat tends to lose its original shape. On the other hand, if the bulk density of the material mat is more than 0.30 g/cm 3 , the material mat is hard and easy to break. 
     In the material mat preparing step, it is preferable to prepare a material mat, at least one of the main faces of which is treated by needle punching (also referred to as needling treatment). Such a material mat is also referred to as a needle mat. 
     The needle punching refers to pushing and pulling a fiber-interlacing means such as a needle or the like in and out the substrate mat. The material mat is constituted by inorganic fibers which have a predetermined average fiber length and are entangled loosely with one another. By the needle punching, the loosely entangled inorganic fibers in the material mat are entangled more complicatedly, so that the mat has an entangled structure capable of maintaining its shape to some extent without an organic binder. Additionally, the entangled inorganic fibers are less likely to move. Accordingly, the material mat can be processed into a holding sealing material that can be easily plastically deformed by applying a shear stress to the two main faces. 
     The needle punching can be accomplished by using a needle punching apparatus, for example. The needle punching apparatus includes a supporting plate for supporting a material mat, and a needle board that is disposed above the supporting plate and is reciprocally movable in the pushing direction (the thickness direction of the material mat). The needle board is provided with a large number of needles. The material mat is disposed on the supporting plate, and the needle board is moved with respect to the material mat such that a large number of needles are pushed into and pulled from the material mat. This entangles the inorganic fibers of the material mat complicatedly. 
     The number of repetition of the needle punching and the number of needles may be determined based on the desired bulk density, weight per unit surface area, and the like. 
     The material mat treated by the needle punching has a plurality of needle holes made by the needle punching. 
       FIG. 2  is a perspective cross-sectional view schematically illustrating one example of the needle-punched material mat.  FIG. 2  shows a cross section obtained by cutting a material mat along the thickness direction. 
     The material mat  100  shown in  FIG. 2  has a plurality of needle holes  105 . The needle holes  105  are surrounded by entangled inorganic fibers  106  that extend along the thickness direction of the material mat  100 . 
     When the inorganic fibers are oriented in the same direction, the material mat is expected to be processed into a holding sealing material that can exert, when used in an exhaust gas purifying apparatus, larger forces for pushing an exhaust gas treating body and a metal container in the direction of the needle holes, that is, the direction along which the inorganic fibers are oriented. 
     The density of needle holes is preferably 10 to 500 holes per 100 cm 2  of the material mat. If the density of needle holes is less than 10 holes per 100 cm 2  of the material mat, a holding sealing material processed from the material mat may be torn in use. On the other hand, if the density of needle holes is more than 500 holes per 100 cm 2  of the material mat, a holding sealing material processed from the material mat is difficult to bend in use. 
     The direction of the needle punching is not particularly limited, but the needle punching is preferably carried out on at least one of the first main face and the second main face of the material mat perpendicularly, and more preferably on both the first main face and the second main face of the material mat perpendicularly. In other words, the material mat preferably has needle holes that extend perpendicularly in at least one of the first main face and the second main face of the material mat, and more preferably has needle holes that extend perpendicularly in the first main face and the second main face of the material mat. 
     As described above, the term “perpendicular” herein means being somewhat perpendicular enough to ensure the effects of the embodiment of the present invention, and may refer to being completely perpendicular or to being substantially perpendicular. For example, the angle range of approximately 80 to 100° to either main face of the material mat is acceptable. 
     In the material mat preparing step, a material mat with a binder, such as an organic binder, affixed thereto is preferably prepared although the material mat may be or may not be treated by the needle punching. 
     The binder affixed to the material mat further fixes the entangled inorganic fibers, and reduces the bulk of the material mat. Additionally, the organic binder fixes entangled inorganic fibers and prevents the fibers from returning their original state, thereby facilitating the plastic deformation. 
     Examples of methods for affixing the binder to the material mat include a method involving blowing a predetermined amount of a binder solution to the material mat with a spray or the like, and a method involving impregnating the material mat into a binder solution. 
     As the binder solution, an emulsion obtained by dispersing an organic binder such as an acrylic resin in water can be used. The binder solution may optionally contain an inorganic binder such as silica sol or alumina sol. 
     The organic binder preferably contains at least one selected from, but not particularly limited to, acrylic resin, acryl rubber, acrylonitrile-butadiene rubber, and styrene-butadiene rubber. 
     The amount of organic binder affixed is preferably 0.2 to 12.0 g/100 g of inorganic fibers (0.2 to 12.0% by weight), and more preferably 4.0 to 10.0 g/100 g of inorganic fibers (4.0 to 10.0% by weight) on a solids content basis. 
     If the amount of organic binder affixed is less than 0.2 g/100 g of inorganic fibers on a solids Content basis, the amount is too little and is not effective enough to sufficiently fix the entangled inorganic fibers. On the other hand, if the amount of organic binder affixed is more than 12.0 g/100 g of inorganic fibers on a solids content basis, too much organic binder is present and is decomposed to unfavorably produce a large amount of toxic gas when a holding sealing material processed from the material mat is used in an exhaust gas purifying apparatus. 
     The weight loss of the holding sealing material of the embodiment of the present invention by heating at 600° C. for 1 hour is preferably 0.2 to 12.0%, and more preferably 4.0 to 10.0% when the weight of the holding sealing material before the heating is regarded as 100%. The weight loss of the holding sealing material by heating at 600° C. for 1 hour corresponds to the amount of organic binder contained in the holding sealing material. 
     Thereafter, the material mat is dried to remove the water content in the organic binder solution. Optionally, the material mat with the organic binder affixed thereto may be compressed during the drying. For example, the following drying conditions can be applied: 95° C. to 150° C., for 1 to 30 minutes. 
     The drying of the material mat may be carried out before or after a later-described deformation step. How to dry the material mat in the deformation step is demonstrated later. 
     The method for producing a holding sealing material of the embodiment of the present invention includes a deformation step of plastically deforming the prepared material mat by immobilizing the first main face and the second main face of the material mat, and applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction. 
       FIGS. 3A to 3D  are cross-sectional views schematically illustrating one example of the deformation step. 
       FIGS. 3A to 3D  show an example demonstrating how a needle-punched material mat is plastically deformed. In  FIGS. 3A to 3D , an end face of the material mat is aligned at the front. The lateral direction in  FIGS. 3A to 3D  corresponds to the width direction of the material mat. 
     First, as shown in  FIG. 3A , the material mat  100  is sandwiched between an upper base  510  and a lower base  520  at the first main face  101  and the second main face  102 . 
     In  FIG. 3A , needle holes  105  are made perpendicularly to the first main face  101  and the second main face  102  of the material mat  100 . 
     Next, as shown in  FIG. 3B , a pressing force F 1  is applied to the first main face  101  and the second main face  102  of the material mat  100  in the thickness direction of the material mat  100  (the vertical directions in  FIG. 3B ). The pressing forces F 1  compress the material mat  100  to immobilize the first main face  101  and the second main face  102  of the material mat  100 . 
     In the deformation step, the material mat is compressed preferably to 45 to 95% of the original material mat thickness. Considering that the resulting holding sealing material is to be disposed between an exhaust gas treating body and a casing for the exhaust gas purifying apparatus (described later), the thickness of the compressed material mat is preferably 120 to 300% of the space between the exhaust gas treating body and the casing. 
     Subsequently, as shown in  FIG. 3C , a shear stress F 2  is applied to the first main face  101  and the second main face  102  of the material mat  100  respectively in the mutually opposite directions along the width direction of the material mat  100  while the material mat  100  is immobilized. The shear stresses F 2  slant the side faces of the material mat  100  to plastically deform the material mat  100 . The deformation of the material mat  100  is accompanied by slanted needle holes  105 . 
     The extent of the plastic deformation of the material mat is not particularly limited, but the material mat is preferably deformed such that in a cross section parallel to the width direction of the material mat, at least either of a hypothetical line perpendicular to the first main face of the material mat and a hypothetical line perpendicular to the second main face of the material mat moves an angle of at least 15°, more preferably at least 20°, before and after the deformation (this angle is referred to as deformation angle). The deformation angle is preferably at most 40°, and more preferably at most 30°. 
     Specifically, it is preferable to prepare a material mat, one or both of the first main face and the second main face of which is/are treated by the needle punching, and to apply a shear stress to the first main face and the second main face such that needle holes are slanted at least 15° with respect to at least one of directions respectively perpendicular to the first main face and the second main face when viewed in a cross section parallel to the width direction of the material mat. Alternatively, it is preferable to prepare a material mat, at least one of the first main face and the second main face of which is treated by the needle punching perpendicularly, and to apply a shear stress to the first main face and the second main face such that needle holes are slanted at least 15° with respect to at least one of the directions respectively perpendicular to the first main face and the second main face when viewed in a cross section parallel to the width direction of the material mat. In particular, it is preferable to prepare a material mat, both the first main face and the second main face of which are treated by the needle punching perpendicularly, and to apply a shear stress to the first main face and the second main face such that needle holes are slanted at least 15° with respect to the direction perpendicular to both the first main face and the second main face of the material mat when viewed in a cross section parallel to the width direction of the material mat. In these cases, the inorganic fibers are made less likely to return to their original state, thereby further facilitating the plastic deformation. 
     In  FIG. 3C , the angle of the needle holes  105  described above is indicated by α. 
     The angle α of the needle holes is preferably at least 15°, and more preferably at least 20°. In addition, the angle α of the needle holes is preferably at most 40°, and more preferably at most 30°. 
     Preferably, in the material mat preparing step of the method for producing a holding sealing material of the embodiment of the present invention, a material mat impregnated with an organic binder solution is prepared, and in the deformation step, the material mat is immobilized and dried while a shear stress is applied to the first main face and the second main face of the material mat. In this case, the organic binder has holding force to maintain the shape of the holding sealing material, thereby facilitating the plastic deformation. The material mat is more preferably a needle mat. 
     In this step, the drying temperature is preferably 95° C. to 150° C., and the drying period is preferably 1 to 30 minutes. The preferable range of the deformation angle and the preferable range of the needle hole angle α are the same as those described above. 
     The immobilization of the material mat shown in  FIG. 3B  and the plastic deformation of the material mat shown in  FIG. 3C  may be carried out at the same time. As long as the material mat is immobilized, the material mat may not be necessarily compressed. 
     Thereafter, the upper base  510  and the lower base  520  are removed as shown in  FIG. 3D . Thus, the plastically deformed material mat  100  is obtained. 
     The method for producing a holding sealing material of the embodiment of the present invention preferably further includes a cutting step of cutting the plastically deformed material mat such that the material mat has side faces perpendicular to at least one of the first main face and the second main face. 
     The method for producing a holding sealing material of the embodiment of the present invention provides a holding sealing material that is less likely to be deformed in an exhaust gas purifying apparatus. Therefore, in the case where the side faces are perpendicular to the main faces of the holding sealing material in the state of not being wrapped around an exhaust gas treating body yet, it is unlikely that the side faces partially become slanted with respect to the end faces of the exhaust gas treating body. 
       FIG. 4  is a cross-sectional view schematically illustrating one example of the material mat after the cutting step. 
     The material mat  110  shown in  FIG. 4  is a piece cut out from the plastically deformed material mat  100  shown in  FIG. 3D . The side face of the material mat  110  shown in  FIG. 4  is perpendicular to both the first main face  111  and the second main face  112 . 
     In the cutting step, the plastically deformed material mat is preferably cut in such a manner to have side faces perpendicular to at least one of the first main face and the second main face of the material mat, and more preferably to have side faces perpendicular to both the first main face and the second main face of the material mat. 
     The cutting of the material mat can be accomplished by punching out a predetermined shape from the material mat. 
     Any method and device for punching the material mat can be used without particular limitation, and conventionally known methods can be used. 
     An example of usable punching blades is a Thomson blade designed to have the same shape as a desired punching pattern of the material mat, and an example of usable punching devices is an oil hydraulic pressing machine. 
     Thus, the method for producing a holding sealing material of the embodiment of the present invention preferably includes the cutting step, but a material mat may be formed into a holding sealing material by the deformation step without performing the cutting step. 
     Through the above-described steps, a holding sealing material can be produced. 
     The holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention can be used for an exhaust gas purifying apparatus. The holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention is also one aspect of the embodiment of the present invention. The holding sealing material and the exhaust gas purifying apparatus are described in detail later. 
     [Holding Sealing Material] 
     The holding sealing material of the embodiment of the present invention is a holding sealing material for use in an exhaust gas purifying apparatus that includes: a casing; an exhaust gas treating body housed in the casing; and the holding sealing material that is wrapped around the exhaust gas treating body and disposed between the exhaust gas treating body and the casing, 
     the holding sealing material including inorganic fibers and having a mat shape with a first main face, a second main face opposite to the first main face, side faces along a longitudinal direction of the holding sealing material, and end faces along a width direction perpendicular to the longitudinal direction, 
     wherein the holding sealing material is plastically deformed by applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction before being wrapped around the exhaust gas treating body. 
       FIG. 5A  is a perspective view schematically illustrating one example of the holding sealing material of the embodiment of the present invention, and  FIG. 5B  is a plan view of the holding sealing material shown in  FIG. 5A . In  FIG. 5B , an end face of the holding sealing material is aligned at the front. The lateral direction in  FIG. 5B  corresponds to the width direction of the holding sealing material. 
     The holding sealing material  10  shown in  FIG. 5A  is a mat having a rectangular shape with a predetermined longitudinal length (indicated by the arrow L in  FIG. 5A ), a predetermined width (indicated by the arrow W in  FIG. 5A ) and a predetermined thickness (indicated by the arrow T in  FIG. 5A ) when viewed in a plan view. 
     The holding sealing material  10  has a first main face  11 , a second main face  12  opposite to the first main face  11 , side faces  13  along the longitudinal direction of the holding sealing material, and end faces  14  along the width direction perpendicular to the longitudinal direction. In the holding sealing material  10 , one of the ends in the longitudinal direction of the mat has a projection  17 , and the other end has a recess  18 . The projection  17  and the recess  18  are designed to be engaged with each other when the holding sealing material  10  is wrapped around an exhaust gas treating body in the process of assembling a later-described exhaust gas purifying apparatus. Namely, the longitudinal direction of the holding sealing material is the same as the wrapping direction. 
     The longitudinal length L of a mat herein refers to the length of the mat excluding the projection and the recess at the ends of the mat. 
     The holding sealing material  10  shown in  FIG. 5B  is plastically deformed by applying a shear stress to the first main face  11  and the second main face  12  respectively in the mutually opposite directions (the directions indicated by the arrows in  FIG. 5B ) along the width direction. In  FIG. 5B , broken lines are drawn on the end face  14  of the holding sealing material  10  for ease of understanding. 
     The longitudinal length L of the mat is preferably within the range of the length of the circumference of the columnar exhaust gas treating body to be wrapped with the mat ±95 mm. In the case where the longitudinal length L of the mat is within the above range, the holding sealing material can be wrapped around the exhaust gas treating body without gap, and therefore is not displaced or twisted. 
     The width W of the mat is preferably shorter by 5 to 15 mm than the longitudinal length of the exhaust gas treating body. 
     The thickness T of the mat is preferably 5 to 15 mm. 
     The holding sealing material of the embodiment of the present invention is a mat including inorganic fibers. 
     The inorganic fibers constituting the holding sealing material are the same as the inorganic fibers constituting the material mat described in [Method for producing holding sealing material], and therefore the description thereof is omitted. The average fiber length and the average fiber diameter of the inorganic fibers are also the same as those described above. 
     At least one of the main faces of the holding sealing material of the embodiment of the present invention is preferably treated by the needle punching. The needle-punched holding sealing material has a plurality of needle holes made by the needle punching. 
     In the needle-punched holding sealing material, the inorganic fibers are entangled with one another, and are less likely to move. Accordingly, the holding sealing material can be plastically deformed easily by applying a shear stress to the two main faces of the holding sealing material. 
     The needle punching is as described in [Method for producing holding sealing material]. 
     The holding sealing material of the embodiment of the present invention preferably contains an organic binder. 
     The organic binder in the holding sealing material fixes entangled inorganic fibers, and prevents the inorganic fibers from returning into the original state, thereby facilitating the plastic deformation. 
     The organic binder used in the holding sealing material is the same as the organic binder affixed to the material mat described in [Method for producing holding sealing material], and the description thereof is omitted. The amount of organic binder used in the holding sealing material is the same as the amount of organic binder affixed to the material mat. 
     The holding sealing material of the embodiment of the present invention is preferably produced by the [Method for producing holding sealing material] described above. 
     Therefore, in the case where the holding sealing material of the embodiment of the present invention is treated by the needle punching, the shear stress is preferably applied to the first main face and the second main face such that the angle of needle holes with respect to at least one of directions respectively perpendicular to the first main face and the second main face is at least 15° in a cross section parallel to the width direction. In particular, the shear stress is preferably applied to the first main face and the second main face such that the angle of needle holes is at least 15° with respect to the direction perpendicular to both the first main face and the second main face in the cross section parallel to the width direction. One or both of the first main face and the second main face of the holding sealing material is/are preferably treated by the needle punching before the application of the shear stress. More preferably, at least one of the first main face and the second main face of the holding sealing material is treated by the needle punching perpendicularly, and further more preferably, both the first main face and the second main face of the holding sealing material are treated by the needle punching perpendicularly. 
     For example, in the case where after the main faces of the holding sealing material are treated by the needle punching perpendicularly, the shear stress is applied to the two main faces such that the angle of needle holes become at least 15°, the inorganic fibers are made less likely to return to their original state, thereby facilitating the plastic deformation of the holding sealing material. 
     The holding sealing material of the embodiment of the present invention can be produced by the method for producing a holding sealing material of the embodiment of the present invention, but is not limited only to those produced by the method for producing a holding sealing material of the embodiment of the present invention, provided that it meets the feature that “the holding sealing material is plastically deformed by applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction of the holding sealing material before being wrapped around an exhaust gas treating body”. 
     The side faces of the holding sealing material of the embodiment of the present invention are preferably perpendicular to at least one of the first main face and the second main face of the holding sealing material, and more preferably perpendicular to both the first main face and the second main face when the holding sealing material is not wrapped around an exhaust gas treating body yet. 
     The holding sealing material of the embodiment of the present invention is less likely to be deformed in an exhaust gas purifying apparatus. Therefore, in the case where the side faces are perpendicular to the main faces of the holding sealing material in the state of not being wrapped around an exhaust gas treating body yet, it is unlikely that the side faces partially become slanted with respect to the end faces of the exhaust gas treating body. 
     The holding sealing material of the embodiment of the present invention is not limited to a structure including a single mat, and may be a laminate of two or more mats. 
     In the case where the holding sealing material of the embodiment of the present invention is a laminate of two or more mats, all the mats are preferably deformed plastically, but the laminate may include mats) which is/are not plastically deformed. In the case where the holding sealing material includes a plurality of plastically deformed mats, all the mats are plastically deformed preferably to the same extent but may be plastically deformed to different extents. 
     The holding sealing material of the embodiment of the present invention is intended to be used in an exhaust gas purifying apparatus. The exhaust gas purifying apparatus is described in detail later. 
     The holding sealing material of the embodiment of the present invention and the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention preferably have a surface pressure reduction rate, as determined in a manner described later in EXAMPLES, of not more than 15% or have a deformation quantity, as determined in a manner described later in EXAMPLES, of not more than 2 mm, and more preferably meets both of these features. 
     [Method for Manufacturing Exhaust Gas Purifying Apparatus] 
     The method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention is a method for manufacturing an exhaust gas purifying apparatus that includes: a casing; an exhaust gas treating body housed in the casing; and a holding sealing material that is wrapped around the exhaust gas treating body and disposed between the exhaust gas treating body and the casing, 
     the method including: 
     a wrapped body preparing step of preparing a wrapped body by wrapping the holding sealing material of the embodiment of the present invention or the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention around an exhaust gas treating body such that either the first main face or the second main face of the holding sealing material contacts the exhaust gas treating body; and 
     a press-fitting step of press-fitting the wrapped body into a casing in the same direction as the direction of the shear stress applied to the main face of the holding sealing material which is in contact with the exhaust gas treating body. 
     In the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention, a holding sealing material preparing step for preparing the holding sealing material of the embodiment of the present invention or the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention is carried out first of all. 
     The holding sealing material of the embodiment of the present invention and the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention are described as above in [Holding sealing material] and [Method for producing holding sealing material]. 
     In the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention, it is preferable to prepare a holding sealing material that has side faces perpendicular to at least one of the first main face and the second main face when the holding sealing material is not wrapped around an exhaust gas treating body yet, and is more preferable to prepare a holding sealing material having side faces perpendicular to both the first main face and the second main face. 
     The holding sealing material of the embodiment of the present invention and the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention are less likely to be deformed when used in an exhaust gas purifying apparatus. Therefore, in the case where the side faces are perpendicular to the main faces of the holding sealing material in the state of not being wrapped around an exhaust gas treating body yet, it is unlikely that the side faces partially become slanted with respect to the end faces of the exhaust gas treating body. 
     Next, in the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention, the wrapped body preparing step is carried out in which a wrapped body is prepared by wrapping the prepared holding sealing material around an exhaust gas treating body such that either the first main face or the second main face of the holding sealing material contacts the exhaust gas treating body. 
       FIG. 6  is a perspective view schematically illustrating one example of a wrapped body including an exhaust gas treating body wrapped with a holding sealing material. 
     The wrapped body  50  shown in  FIG. 6  including an exhaust gas treating body  20  around which the holding sealing material  10  shown in  FIGS. 5A and 5B  is wrapped such that the second main face  12  of the holding sealing material  10  contacts the exhaust gas treating body  20 . The projection  17  and the recess  18  of the holding sealing material are engaged with each other. 
     Subsequently, in the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention, the press-fitting step is carried out in which the prepared wrapped body is press-fit into a casing. 
     In the press-fitting step, the wrapped body is press-fit into the same direction as the direction of the shear stress applied to the main face of the holding sealing material which is in contact with the exhaust gas treating body. 
       FIG. 7  is a partial perspective cross-sectional view schematically illustrating one example of the press-fitting step. 
     In  FIG. 7 , the wrapped body  50  shown in  FIG. 6  is press-fit into the casing  30 . As described above, in the wrapped body  50  shown in  FIG. 6 , the holding sealing material  10  is wrapped around the exhaust gas treating body  20  such that the second main face  12  of the holding sealing material  10  contacts the exhaust gas treating body  20 . 
     Accordingly, the press-fitting direction indicated by the arrow is the same as the direction of the shear stress applied to the main face (i.e. the second main face  12 ) of the holding sealing material  10  which is in contact with the exhaust gas treating body  20 . 
       FIG. 7  shows how to press-fit the wrapped body  50  into the casing  30  using a press-fitting jig  80 . 
     The press-fitting jig  80  entirely has a substantially cylindrical shape, and the inside thereof is tapering from one end to the other end. 
     One of the ends of the press-fitting jig  80  is a smaller-diameter end  81  having an inner diameter slightly smaller than the inner diameter of the casing  30 . The other end of the press-fitting jig  80  is a larger-diameter end  82  having an inner diameter that is equal to or larger than the outer diameter of the wrapped body  50 . 
     The use of the press-fitting jig  80  facilitates press-fitting the wrapped body  50  into the casing  30 . 
     Any method for press-fitting the wrapped body into the casing can be used without particular limitation, and the wrapped body may be press-fit into the casing by hands, for example. 
     In the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention, the casing may be compressed from the outside using a pressing machine or the like to reduce the inner diameter of the casing, and thereby to hold the wrapped body. 
     Through the above steps, an exhaust gas purifying apparatus can be produced. 
       FIG. 8  is a partial perspective cross-sectional view schematically illustrating an exhaust gas purifying apparatus produced by the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention. 
     The holding sealing material  10  used in the exhaust gas purifying apparatus  200  shown in  FIG. 8  is plastically deformed before the press-fitting step, and therefore is less likely to be deformed even after the press-fitting step. Even when the exhaust gas purifying apparatus  200  is used in such a manner that exhaust gas flows in the same direction as the press-fitting direction, the holding sealing material  200  is less likely to be deformed. 
     [Exhaust Gas Purifying Apparatus] 
     The exhaust gas purifying apparatus of the embodiment of the present invention includes: 
     a casing; 
     an exhaust gas treating body housed in the casing; and 
     a holding sealing material that is wrapped around the exhaust gas treating body and disposed between the exhaust gas treating body and the casing, 
     wherein the holding sealing material is the holding sealing material of the embodiment of the present invention or the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention, and is wrapped around the exhaust gas treating body such that either the first main face or the second main face of the holding sealing material contacts the exhaust gas treating body, and 
     the exhaust gas treating body wrapped with the holding sealing material is press-fit into the casing in the same direction as the direction of the shear stress applied to the main face of the holding sealing material which is in contact with the exhaust gas treating body. 
       FIG. 9  is a perspective view schematically illustrating one example of the exhaust gas purifying apparatus of the embodiment of the present invention. 
     The exhaust gas purifying apparatus  200  shown in  FIG. 9  includes an exhaust gas treating body  20 , a casing  30  housing the exhaust gas treating body  20 , and a holding sealing material  10  that is wrapped around the exhaust gas treating body  20 , and disposed between the exhaust gas treating body  20  and the casing  30 . 
     The exhaust gas purifying apparatus  200  is an example including the holding sealing material  10  shown in  FIGS. 5A and 5B . 
     The casing  30  shown in  FIG. 9  is mainly made of a metal such as stainless steel, and has a cylindrical shape. The inner diameter thereof is slightly smaller than the total of the diameter of the end face of the exhaust gas treating body  20  and the thickness of the holding sealing material  10  in the state of being wrapped around the exhaust gas treating body  20 , and the length thereof is substantially the same as the length of the exhaust gas treating body  20  along the longitudinal direction (the direction indicated by the double pointed arrow W 1  in  FIG. 9 ). 
     The structure of the holding sealing material  10  has been already described, and therefore the description thereof is omitted. 
     As shown in  FIG. 9 , the exhaust gas purifying apparatus  200  is provided with a honeycomb filter  20  in which each of cells  21  is sealed at either end with a sealing material  23 , as the exhaust gas treating body  20 . 
     The honeycomb filter  20  is mainly made of porous ceramics, and has a round pillar shape. The honeycomb filter  20  further includes, on the periphery of the honeycomb filter  20 , a sealing material layer  25  for reinforcing the periphery of the honeycomb filter  20 , adjusting the shape of the honeycomb filter  20 , and improving the heat insulation properties of the honeycomb filter  20 . 
     The shape of the exhaust gas treating body in the exhaust gas purifying apparatus of the embodiment of the present invention is not particularly limited, and may not be the substantially round pillar shape. The exhaust gas treating body may have any shape, such as a substantially cylindroid shape or a substantially rectangular columnar shape, and may have any size, provided that it has a columnar shape. 
     The exhaust gas treating body in the exhaust gas purifying apparatus of the embodiment of the present invention may be an integrated honeycomb structured body made of cordierite or the like, or an aggregated honeycomb structured body in which a plurality of pillar-shaped honeycomb fired bodies each of which is made of silicon carbide or the like, and includes cells arranged parallel to one another with a cell wall interposed therebetween are bonded to one another with an adhesive layer mainly made of ceramics. 
     A catalyst may be supported on the exhaust gas treating body in the exhaust gas purifying apparatus of the embodiment of the present invention. 
     Examples of the catalyst include: noble metals such as platinum, palladium, and rhodium; alkali metals such as potassium and sodium; alkaline earth metals such as barium; metal oxides such as cerium oxide; and the like. Any of these catalysts may be used alone, or two or more of these may be used in combination. 
     In the case where the exhaust gas treating body in the exhaust gas purifying apparatus of the embodiment of the present invention is a honeycomb structured body, the cells may not be sealed with the sealing material and may have open ends. In this case, a catalyst such as platinum is supported on the exhaust gas treating body so that the exhaust gas treating body functions as a catalyst carrier for converting toxic gas components such as CO, HC, and NOx in exhaust gas. 
     The exhaust gas purifying apparatus of the embodiment of the present invention can be manufactured by the [Method for manufacturing exhaust gas purifying apparatus] described above. 
     Specifically, in the exhaust gas purifying apparatus  200  shown in  FIG. 9 , the holding sealing material  10  is wrapped around the exhaust gas treating body  20  such that the second main face  12  of the holding sealing material  10  contacts the exhaust gas treating body  20 . The exhaust gas treating body  20  wrapped with the holding sealing material  10  is press-fit into the casing  30  in the same direction as the direction of the shear stress applied to the main face (i.e. the second main face  12 ) of the holding sealing material  10  which is in contact with the exhaust gas treating body  20 . 
     The following demonstrates how exhaust gas flows through the exhaust gas purifying apparatus having the above-described structure based on  FIG. 10 . 
       FIG. 10  is an A-A line cross-sectional view of the exhaust gas purifying apparatus shown in  FIG. 9 . 
     As shown in  FIG. 10 , exhaust gas discharged from an internal combustion engine (exhaust gas is indicated by G and the flow of the exhaust gas is indicated by the arrow in  FIG. 10 ) flows into the exhaust gas purifying apparatus  200 , specifically into a cell  21  that is open at the exhaust gas flow-in end  26   a  of the honeycomb filter  20 , and passes through a cell wall  22  separating cells  21 . At this time, PM in the exhaust gas is captured in the cell wall  22 , and thus the exhaust gas is purified. The purified exhaust gas flows out from another cell  21  that is open at the exhaust gas flow-out end  26   b , and thus is discharged to the outside. 
     The exhaust gas purifying apparatus of the embodiment of the present invention is used in such a manner that exhaust gas flows into the apparatus in the same direction as the press-fitting direction (e.g. the direction of the shear stress applied to the main face of the holding sealing material which is in contact with the exhaust gas treating body). As described above, since the holding sealing material is already plastically deformed, the holding sealing material is less likely to be deformed even through exhaust gas flows in the same direction as the press-fitting direction. 
     The following describes the effects of the holding sealing material, the method for producing a holding sealing material, a method for manufacturing an exhaust gas purifying apparatus, and the exhaust gas purifying apparatus of the embodiment of the present invention. 
     (1) The holding sealing material of the embodiment of the present invention is plastically deformed by applying a shear stress to the two opposite main faces before being wrapped around an exhaust gas treating body. Therefore, the holding sealing material of the embodiment of the present invention is less likely to be further deformed when the holding sealing material is wrapped around an exhaust gas treating body and press-fit into a casing in the same direction as the direction of the shear stress applied to the inner main face of the holding sealing material (the face in contact with the exhaust gas treating body). In the case where an exhaust gas purifying apparatus including the holding sealing material of the embodiment of the present invention is used in such a manner that exhaust gas flows in the same direction as the press-fitting direction, the holding sealing material is less likely to be deformed. Thus, the holding sealing material of the embodiment of the present invention is designed to be resistant to deformation when used in an exhaust gas purifying apparatus. 
     (2) The holding sealing material of the embodiment of the present invention is less likely to be deformed around an exhaust gas treating body that is being press-fit into a casing and in an exhaust gas purifying apparatus that is in operation, and therefore can prevent wind erosion and a reduction in the holding force. Additionally, since the holding sealing material of the embodiment of the present invention is thus less likely to be deformed, the surface pressure of the holding sealing material measured before wrapping the holding sealing material around an exhaust gas treating body can be considered as the holding force of the holding sealing material in an exhaust gas purifying apparatus. Thus, it is easy to calculate the holding force of the holding sealing material of the embodiment of the present invention in an exhaust gas purifying apparatus. 
     (3) The method for producing a holding sealing material of the embodiment of the present invention allows for the production of the above-described holding sealing material of the embodiment of the present invention, that is, a holding sealing material that is plastically deformed by applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction before being wrapped around an exhaust gas treating body. Therefore, the method allows for the production of a holding sealing material that is less likely to be deformed around an exhaust gas treating body that is being press-fit into a casing and in an exhaust gas purifying apparatus that is in operation, and therefore can prevent wind erosion and a reduction in the holding force, and allows for easy calculation of the holding force in an exhaust gas purifying apparatus. 
     (4) In the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention, the holding sealing material of the embodiment of the present invention is used, and the press-fitting direction is the same as the direction of the shear stress applied to the inner main face of the holding sealing material. An advantage attributable to these features is that the holding sealing material is less likely to be deformed when the wrapped body is press-fit into the casing. Another advantage is that the holding sealing material is less likely to be deformed when the resulting exhaust gas purifying apparatus is used in such a manner that exhaust gas flows in the same direction as the press-fitting direction. 
     (5) The method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention allows for the manufacture of an exhaust gas purifying apparatus including a holding sealing material that is less likely to be deformed around an exhaust gas treating body that is being press-fit into a casing and in an exhaust gas purifying apparatus that is in operation, and therefore can prevent wind erosion and a reduction in the holding force, and allows for easy calculation of the holding force in an exhaust gas purifying apparatus. 
     (6) Since the exhaust gas purifying apparatus of the embodiment of the present invention includes a holding sealing material that is less likely to be deformed around an exhaust gas treating body that is being press-fit into a casing and in the exhaust gas purifying apparatus that is in operation, the exhaust gas purifying apparatus can avoid wind erosion and a reduction in the holding force, and allows for easy calculation of the holding force of the holding sealing material in the exhaust gas purifying apparatus. 
     EXAMPLES 
     The following shows examples specifically illustrating the embodiment of the present invention. It should be noted that the present invention is not limited only to these examples. 
     Production of Holding Sealing Material 
     Example 1 
     A base mat made of alumina fibers having an alumina-silica composition was prepared. The base mat had a composition rate Al 2 O 3 :SiO 2  of 72:28. The base mat was subjected to needle punching into a needle mat (material mat) having thickness of 9.7 mm, a bulk density of 0.18 g/cm 3 , and a weight per unit surface area of 1740 g/m 2 . 
     Next, the needle mat was cut into dimensions as viewed in a plan view of 150 mm (total length)×70 mm (width). 
     The cutting of the needle mat was carried out with a Thomson blade and an oil hydraulic pressing machine. 
     The cut-out needle mat was impregnated with a binder solution to a binder content of 10% by weight relative to the amount of alumina fibers in the needle mat. 
     The binder solution used was an acrylic latex emulsion obtained by sufficiently dispersing an acrylic resin in water. 
     The needle mat impregnated with the binder solution was plastically deformed by applying a shear stress to the first main face and the second main face respectively in the mutually opposite directions along the width direction. 
     Specifically, lines perpendicular to the first main face and the second main face of the needle mat were drawn on the end faces of the needle mat, and the needle mat was deformed by applying a shear stress such that the angle formed by each line before and after the deformation (deformation angle) was 40°, and then the deformed mat was immobilized. At this time, the deformed mat was compressed to 80% of the original thickness. 
     Thereafter, through drying at an atmospheric temperature of 140° C. for 10 minutes, a deformed needle mat was prepared. 
     Finally, the deformed needle mat was cut into dimensions as viewed in a plan view of 50 mm (total length)×50 mm (width) such that the side faces of the needle mat were perpendicular to the first main face and the second main face. In this manner, a holding sealing material of Example 1 was prepared. 
     Example 2 
     A needle mat (material mat) was prepared and cut into dimensions as viewed in a plan view of 150 mm (total length)×70 mm (width) in the same manner as in Example 1. The cut needle mat was impregnated with a binder solution. 
     The needle mat was plastically deformed in the same manner as in Example 1 except that the deformation angle was changed to 30°. 
     Finally, the deformed needle mat was cut into dimensions as viewed in a plan view of 50 mm (total length)×50 mm (width) in the same manner as in Example 1 such that the side faces of the needle mat were perpendicular to the first main face and the second main face. In this manner, a holding sealing material of Example 2 was prepared. 
     Example 3 
     A needle mat (material mat) was prepared and cut into dimensions as viewed in a plan view of 150 mm (total length)×70 mm (width) in the same manner as in Example 1. The cut needle mat was impregnated with a binder solution. 
     The needle mat was plastically deformed in the same manner as in Example 1 except that the deformation angle was changed to 15°. 
     Finally, the deformed needle mat was cut into dimensions as viewed in a plan view of 50 mm (total length)×50 mm (width) in the same manner as in Example 1 such that the side faces of the needle mat were perpendicular to the first main face and the second main face. In this manner, a holding sealing material of Example 3 was prepared. 
     Example 4 
     A needle mat (material mat) was prepared and cut into dimensions as viewed in a plan view of 150 mm (total length)×70 mm (width) in the same manner as in Example 1. The cut needle mat was impregnated with a binder solution. 
     The needle mat was plastically deformed in the same manner as in Example 1 except that the deformation angle was changed to 1°. 
     Finally, the deformed needle mat was cut into dimensions as viewed in a plan view of 50 mm (total length)×50 mm (width) in the same manner as in Example 1 such that the side faces of the needle mat were perpendicular to the first main face and the second main face. In this manner, a holding sealing material of Example 4 was prepared. 
     Comparative Example 1 
     A needle mat (material mat) was prepared and cut into dimensions as viewed in a plan view of 150 mm (total length)×70 mm (width) in the same manner as in Example 1. The cut needle mat was impregnated with a binder solution. 
     No shear stress was applied to the needle mat in Comparative Example 1. Namely, the needle mat of Comparative Example 1 was not deformed. 
     Specifically, lines perpendicular to the first main face and the second main face of the needle mat were drawn on the end faces of the needle mat, and the needle mat was compressed to 80% of the original thickness, and immobilized. The deformation angle of Comparative Example 1 was regarded as 0° for ease of comparison. 
     Thereafter, the mat was dried at an atmospheric temperature of 140° C. for 10 minutes. Thus, an undeformed needle mat was prepared. 
     Finally, the undeformed needle mat was cut into dimensions as viewed in a plan view of 50 mm (total length)×50 mm (width) such that the side faces of the needle mat were perpendicular to the first main face and the second main face. In this manner, a holding sealing material of Comparative Example 1 was prepared. 
     Evaluation of Holding Sealing Material 
     (1) Surface Pressure Reduction Rate of Holding Sealing Material 
     The holding sealing materials of Examples 1 to 4 and Comparative Example 1 were calculated for the surface pressure reduction rate in the manner described below, and thus were each evaluated by a simulation for a change in the surface pressure caused when an exhaust gas treating body wrapped with the holding sealing material was press-fit into a casing. 
       FIGS. 11A and 11B  are schematic views of an apparatus for measuring the surface pressure of a holding sealing material. 
     A surface pressure measuring apparatus  600  is provided with facing stainless steel plates (upper plate  610  and lower plate  620 ) disposed one above the other. The upper plate  610  is a load cell that can measure the load applied to the lower face of the upper plate  610  (which is a face to be in contact with the holding sealing material). 
     First, two holding sealing materials  10   a  and  10   b  and a stainless steel plate (a middle plate  630 ) were disposed such that the upper plate  610 , the holding sealing material  10   a , the middle plate  630 , the holding sealing material  10   b , and the lower plate  620  are arranged in the stated order. The holding sealing material  10   a  was sandwiched between the upper plate  610  and the middle plate  630 , and the holding sealing material  10   b  was sandwiched between the middle plate  630  and the lower plate  620 . The middle plate  630  is a load cell that can measure the load (static friction) applied to the middle plate. 
     The holding sealing materials were compressed into 50% of the original thickness, and then left (maintained) for 1 hour in the compressed state. 
     The holding sealing materials were measured for the surface pressure in this state and the measured values were treated as the initial surface pressures P 0  (kPa) of the holding sealing materials. 
     Next, the middle plate  630  was moved at room temperature in the direction indicated by the arrow in  FIG. 11A  (substantially horizontally) at 1.0 mm/min to apply a shear stress to the main faces of the holding sealing materials. 
     In  FIG. 11B , the middle plate is in a moved position. 
     The middle plate was pulled in the same direction as the direction of the shear stress applied to the main faces of the holding sealing materials which were in contact with the middle plate. 
     The surface pressure and friction were measured while the middle plate was moved, and the load measured when the dynamic friction became stable was recorded as the final surface pressure P 1  (kPa). 
     The surface pressure reduction rate (%) of the holding sealing materials was calculated from the obtained data. 
       Surface pressure reduction rate(%)={( P   0   −P   1 )/( P   0 )}×100
 
     Table 1 shows the surface pressure reduction rates of the holding sealing materials of Examples 1 to 4 and Comparative Example 1. 
     The calculated surface pressure reduction rates were used to evaluate how much the surface pressure of each holding sealing material was reduced when the exhaust gas treating body wrapped with the holding sealing material was press-fit into a casing. 
     (2) Deformation Quantity of Holding Sealing Material 
     The holding sealing materials of Examples 1 to 4 and Comparative Example 1 were measured for deformation quantity in the manner described below, and thus were each evaluated by a simulation for the deformation quantity caused when an exhaust gas treating body wrapped with the holding sealing material was press-fit into a casing. 
       FIG. 12  is an illustrative view schematically demonstrating how to measure the deformation quantify of a holding sealing material. 
     As shown in  FIG. 12 , the holding sealing material  10   a  was measured for the deformation quantity (the length t shown in  FIG. 12 ) in a cross section parallel to the width direction after the measurement of the final surface pressure P 1 , and the obtained length was regarded as the deformation quantity (mm) of the holding sealing material. 
     Table 1 shows the deformation quantities of the holding sealing materials of Examples 1 to 4 and Comparative Example 1. 
     The obtained deformation quantities were used to evaluate how much each holding sealing material was deformed upon press-fitting an exhaust gas treating body wrapped with the holding sealing material into a casing. 
     (3) Recovery Rate of Deformation Angle 
     Holding sealing materials which were prepared separately from the samples tested above under the same conditions as in Examples 1 to 4 and Comparative Example 1 were determined for a recovery rate of the deformation angle after firing at a high temperature. 
     The holding sealing materials were measured for the deformation angle before and after firing at an atmospheric temperature of 600° C. for 1 hour, and the following equation was used to calculate the recovery rate (%) of the deformation angle. 
       Recovery rate(%) of deformation angle={(deformation angle before firing−deformation angle after firing)/(deformation angle before firing)}×100
 
     Table 1 shows the recovery rates of the deformation angle of the holding sealing materials of Examples 1 to 4 and Comparative Example 1. 
       FIGS. 13A and 13B  are photographs of the holding sealing material of Example 2 taken before and after firing,  FIGS. 14A and 14B  are photographs of the holding sealing material of Example 3 taken before and after firing, and  FIGS. 15A and 15B  are photographs of the holding sealing material of Comparative Example 1 taken before and after firing. 
     In Table 1, holding sealing materials that met the following two requirements are shown as “+”: the surface pressure reduction rate is not more than 15%; and the deformation quantity is not more than 2 mm, holding sealing materials that met either of the requirements are shown as “±”, and holding sealing materials that met neither of the requirements are shown as “−”. Among the holding sealing materials evaluated as “+”, the holding sealing material that showed the best performance is shown as “++”. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Surface 
                   
                   
                   
               
               
                   
                 Defor- 
                 pressure 
                 Defor- 
               
               
                   
                 mation 
                 reduction 
                 mation 
                 Recovery 
                 Evalu- 
               
               
                   
                 angle 
                 rate 
                 quantity 
                 rate 
                 ation 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Example 1 
                 40° 
                 14.8% 
                 3.3 
                 mm 
                     0% 
                 ± 
               
               
                 Example 2 
                 30° 
                 0.5% 
                 0 
                 mm 
                 6.7% 
                 ++ 
               
               
                 Example 3 
                 15° 
                 7.2% 
                 1.8 
                 mm 
                  40% 
                 + 
               
               
                 Example 4 
                  1° 
                 14.3% 
                 3.2 
                 mm 
                 100%  
                 ± 
               
               
                 Comparative 
                  0° 
                 18.9% 
                 4.1 
                 mm 
                 Not 
                 − 
               
               
                 Example 1 
                   
                   
                   
                   
                 measured 
               
               
                   
               
            
           
         
       
     
     The results revealed that the holding sealing materials of Examples 1 to 4 that were plastically deformed in advance by applying a shear stress to the main faces had a surface pressure reduction rate of not more than 15%, and that these holding sealing materials are less likely to show a reduction in the surface pressure when a shear stress is further applied thereto. In particular, the holding sealing material of Example 2, which had a deformation angle of 30°, and the holding sealing material of Example 3, which had a deformation angle of 15°, were found to have a small deformation quantity (not more than 2 mm) as well as a small surface pressure reduction rate (not more than 15%). 
     The results also revealed that the holding sealing material of Comparative Example 1 that was not plastically deformed by applying a shear stress to the main faces showed a reduction in the surface pressure, and was deformed when a shear stress was applied thereto. 
     From these results, the holding sealing material of the embodiment of the present invention that is plastically deformed by applying a shear stress to the main faces is less likely to be deformed around an exhaust gas treating body that is being press-fit into a casing and in an exhaust gas purifying apparatus that is in operation, and therefore can prevent wind erosion and a reduction in the holding force. 
     An essential feature of the holding sealing material of the embodiment of the present invention is that the holding sealing material of the embodiment of the present invention is plastically deformed by applying a shear stress to the first main face and the second main face respectively in mutually opposite directions along the width direction before being wrapped around an exhaust gas treating body. An essential feature of the method for producing a holding sealing material of the embodiment of the present invention is that a material mat is plastically deformed by applying a shear stress to the first main face and the second main face of the material mat in the mutually opposite directions along the width direction. Essential features of the method for manufacturing an exhaust gas purifying apparatus of the embodiment of the present invention are that the holding sealing material of the embodiment of the present invention or the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention is used, and that the wrapped body is press-fit into the same direction as the direction of the shear stress applied to the main face of the holding sealing material which is in contact with the exhaust gas treating body. Essential features of the exhaust gas purifying apparatus of the embodiment of the present invention are that the exhaust gas purifying apparatus includes the holding sealing material of the embodiment of the present invention or the holding sealing material produced by the method for producing a holding sealing material of the embodiment of the present invention, and that an exhaust gas treating body wrapped with the holding sealing material is press-fit into a casing in the same direction as the direction of the shear stress applied to the main face of the holding sealing material which is in contact with the exhaust gas treating body. 
     These essential features can be combined with the other features described in the detailed description of the embodiment of the invention (e.g. the structure of the holding sealing material, the conditions for the production of a holding sealing material, the structure of the exhaust gas purifying apparatus, the conditions for the manufacture of an exhaust gas purifying apparatus) to produce desired effects. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.