Smoking filter and smoking article

Abstract

A smoking filter contains a hydrotalcite compound exhibiting a lamellar structure in which a large number of octahedral layers of a metal hydroxide are laminated one upon the other. The smoking filter permits selectively removing formaldehyde contained in mainstream smoke.

What is claimed is:  
     
         1 . A smoking filter containing a hydrotalcite compound exhibiting a lamellar structure in which a large number of octahedral layers of a metal hydroxide are laminated one upon the other.  
     
     
         2 . The smoking filter according to  claim 1 , wherein the hydrotalcite compound is represented by a general formula:  
       M 2+   1-x M 3+   x (OH) 2 (A n− ) x/n .mH 2 O  
       where M 2+  represents a divalent metal ion selected from the group consisting of a Mg ion, a Zn ion, a Ni ion and a Ca ion, M 3+  represents an Al ion, A n−  represents an anion having a valency of n, which is selected from the group consisting of CO 3 , SO 4 , OOC—COO, Cl, Br, F, NO 3 , Fe(CN) 6   3− , Fe(CN) 6   4− , phthalic acid, isophthalic acid, terephthalic acid, maleic acid, alkenyl acid and its derivative, malic acid, salicylic acid, acrylic acid, adipic acid, succinic acid, citric acid and sulfonic acid, 0.1<x<0.4, and 0<m<2.  
     
     
         3 . The smoking filter according to  claim 1 , wherein a hydrotalcite compound having an average particle diameter falling within a range of between 200 μm and 800 μm is dispersed in fiber tow or an unwoven fabric sheet.  
     
     
         4 . The smoking filter according to  claim 3 , wherein the fiber is formed of cellulose acetate.  
     
     
         5 . The smoking filter according to  claim 1 , wherein the filter is prepared by forming a paper sheet added with a hydrotalcite compound having an average particle diameter not larger than 10 μm.  
     
     
         6 . The smoking filter according to  claim 1 , comprising filter segments, at least one filter segment containing a hydrotalcite compound.  
     
     
         7 . The smoking filter according to  claim 6 , comprising a charcoal filter segment in addition to the filter segment containing the hydrotalcite compound.  
     
     
         8 . The smoking filter according to  claim 1 , comprising filter segments and hydrotalcite particles filled in the space present between the adjacent filter segments.  
     
     
         9 . A smoking article including the smoking filter according to  claim 1 , and a tobacco rod connected to the smoking filter.