Laminated sheet, method of producing the sheet, exhaust gas processing device, and method of producing the device

Abstract

A disclosed laminated sheet includes a first mat containing first inorganic fibers and a second mat containing second inorganic fibers, the second mat being laminated on the first mat. The average fiber length of the first inorganic fibers is larger than the average fiber length of the second inorganic fibers. Development of cracks in the outer surface of the laminated sheet can be prevented by winding the laminated sheet around an exhaust gas processing unit such that the first mat faces outward.

1 . A laminated sheet, comprising:
 a first mat containing first inorganic fibers; and   a second mat containing second inorganic fibers, the second mat being laminated on the first mat;   wherein an average fiber length of the first inorganic fibers is larger than an average fiber length of the second inorganic fibers.   
   
   
       2 . The laminated sheet as claimed in  claim 1 , wherein the first inorganic fibers and the second inorganic fibers are composed of a same material. 
   
   
       3 . The laminated sheet as claimed in  claim 1 , wherein the average fiber length of the first inorganic fibers is within a range between about 20 mm and about 120 mm. 
   
   
       4 . The laminated sheet as claimed in  claim 1 , wherein the average fiber length of the second inorganic fibers is within a range between about 0.5 mm and about 10 mm. 
   
   
       5 . The laminated sheet as claimed in  claim 1 , wherein the first mat and/or the second mat further contain a binder. 
   
   
       6 . The laminated sheet as claimed in  claim 1 , further comprising:
 an interface layer at an interface between the first mat and the second mat.   
   
   
       7 . The laminated sheet as claimed in  claim 6 , wherein a thickness of the interface layer is within a range between about 0.05 mm and about 2 mm. 
   
   
       8 . The laminated sheet as claimed in  claim 1 , wherein a thickness of the laminated sheet is within a range between about 6 mm and about 20 mm. 
   
   
       9 . A method of producing a laminated sheet, comprising:
 a first step of preparing a first mat containing first inorganic fibers; and   a second step of laminating a second mat containing second inorganic fibers on the first mat;   wherein an average fiber length of the first inorganic fibers is larger than an average fiber length of the second inorganic fibers.   
   
   
       10 . The method as claimed in  claim 9 , wherein the second step includes a substep of forming the second mat directly on the first mat. 
   
   
       11 . The method as claimed in  claim 9 , wherein the second step includes substeps of separately preparing the second mat and then laminating the first mat and the second mat. 
   
   
       12 . The method as claimed in  claim 11 , wherein the second step further includes a substep of joining the first mat and the second mat by adhesive bonding and/or by sewing. 
   
   
       13 . The method as claimed in  claim 9 , wherein the first mat is prepared by a needling method. 
   
   
       14 . The method as claimed in  claim 9 , wherein the second mat is prepared by a sheet making method. 
   
   
       15 . An exhaust gas processing device, comprising:
 an exhaust gas processing unit; and   a holding sealer wound around at least a portion of an outer surface of the exhaust gas processing unit; wherein   the holding sealer is composed of the laminated sheet as claimed in  claim 1  and wound around the exhaust gas processing unit such that the first mat of the laminated sheet faces outward.   
   
   
       16 . The exhaust gas processing device as claimed in  claim 15 , wherein the exhaust gas processing unit is a catalyst carrier or an exhaust gas filter. 
   
   
       17 . A method of producing an exhaust gas processing device including an exhaust gas processing unit and a holding sealer wound around at least a portion of an outer surface of the exhaust gas processing unit, comprising the steps of:
 preparing the holding sealer with the laminated sheet produced by the method as claimed in  claim 9 ; and   winding the holding sealer around the exhaust gas processing unit such that the first mat of the laminated sheet faces outward.   
   
   
       18 . The method as claimed in  claim 17 , wherein the exhaust gas processing unit is a catalyst carrier or an exhaust gas filter.