Retaining material for pollution control element, method for manufacturing the same, and pollution control device

Abstract

A retaining material that can sufficiently maintain the function of retaining a pollution control element in a pollution control device at high temperature. In one aspect, the retaining material has a mat shape and contains inorganic fiber material, with the retaining material containing: a surface layer containing inorganic colloid particles; and an internal region positioned further to the inside than the surface layer, impregnated with inorganic colloid particles and organic binder; wherein the surface layer contains inorganic colloid particles at a higher concentration than the internal region; and the amount of inorganic colloid particles in the internal region is 1 mass % to 10 mass % based on the total mass of the retaining material.

What is claimed is: 
     
         1 . A method for manufacturing a retaining material, comprising:
 a step of impregnating a first liquid containing inorganic colloid particles and an organic binder into a sheet including an inorganic fiber material so that inorganic colloid particles are essentially uniformly dispersed in the thickness direction of the sheet and organic binder is essentially uniformly dispersed in the thickness direction of the sheet;   a step of drying the sheet impregnated with the first liquid; and   a step of forming a surface layer by coating a surface of the sheet with a second liquid containing inorganic colloid particles.   
     
     
         2 . The method according to  claim 1 , wherein the second liquid is coated respectively onto opposite surfaces of the sheet. 
     
     
         3 . The method according to  claim 1 , wherein the composition of the first liquid is adjusted such that the amount of inorganic colloid particles in an internal region of the sheet positioned further to the inside than the surface layer is 1 mass % to 10 mass % based on the total mass of the internal region. 
     
     
         4 . The method according to  claim 1 , wherein the composition of the second liquid and the amount of coating of the second liquid are adjusted such that the amount of inorganic colloid particles per unit area of the surface layer is 1 g/m 2  to 20 g/m 2 . 
     
     
         5 . The method according to  claim 1 , wherein the composition of the first and second liquids and the amount of coating of the second liquid are adjusted such that the amount of organic binder is 3 mass % or less based on the total mass of the retaining material.