Filter For A Smoking Article

Abstract

The present invention relates to smoking articles incorporating an improved filter in which the amount of smoke filtration varies with increased strength of draw. In particular, the filter comprises a plurality of passageways, at least one primary passageway I comprising a section of material which extends from the rod of smokable material to the mouth end of the smoking article and which has a high capacity to filter smoke and a high capacity to resist the passage of smoke. Via a series of small holes in an otherwise non-porous interface between the different passageways, smoke may be drawn between the primary passageway I and one or more secondary passageways II which have a low capacity to filter and resist the passage of smoke. At lower strengths of draw, smoke may become drawn through the small holes between the primary and secondary passageways. At higher strengths of draw, however, the rate at which smoke may pass through the small holes is limited by the restricted orifice effect and in this way the level of filtration of the smoke at different strengths of draw may be controlled.

1 . A smoking article filter that provides an increased level of smoke filtration with increasing strength of draw, the filter comprising:
 first and second filter passageways, the first passageway having a higher smoke filtration capacity than the second passageway,
 wherein smoke from the first passageway is directed to the second passageway by means of one or more perforations, and 
 wherein as the strength of draw is increased, the amount of smoke passing through the perforations is limited by the restricted orifice effect. 
   
     
     
         2 . The smoking article filter as claimed in  claim 1 , wherein the diameter of the perforations is sufficiently small so that with increased draw the proportion of smoke passing through the perforations is increasingly restricted. 
     
     
         3 . The smoking article filter as claimed in  claim 1 , wherein the perforations are between 0.01 mm and 2 mm in diameter. 
     
     
         4 . The smoking article filter as claimed in  claim 1 , wherein one of the passageways comprises a void. 
     
     
         5 . The smoking article filter as claimed in  claim 1 , wherein the first and second passageways comprise smoke filtration material, the filtration capacity of the smoke filtration material of the first passageway being higher than that of the second passageway. 
     
     
         6 . The smoking article filter as claimed in  claim 1 , wherein the filter is ventilated. 
     
     
         7 . The smoking article filter as claimed in  claim 6 , wherein the ventilation is facilitated by deep vents. 
     
     
         8 . The smoking article filter as claimed in  claim 1 , wherein the filter is not ventilated. 
     
     
         9 . The smoking article filter as claimed in  claim 1 , wherein the filter comprises a plurality of longitudinally abutted filter sections. 
     
     
         10 . The smoking article filter as claimed in  claim 9 , wherein at least one of the filter sections is an annular filter section. 
     
     
         11 . The smoking article filter as claimed in  claim 1 , wherein the smoking article is a cigarette. 
     
     
         12 . A smoke filtration method correlated with draw strength, the method comprising:
 configuring a smoking article with a filter comprising first and second filter passageways, the first passageway having a higher smoke filtration capacity than the second passageway,
 wherein smoke from the first passageway is directed to the second passageway by means of one or more small perforations, wherein at lower strengths of draw, smoke passes through the perforations, and as the strength of draw is increased, the amount of smoke that passes through the perforations is limited by the restricted orifice effect. 
   
     
     
         13 . The method as claimed in  claim 12 , wherein the diameter of the perforations is sufficiently small so that with increased draw the amount of smoke passing through the perforations is increasingly restricted. 
     
     
         14 . The method as claimed in  claim 12 , wherein as the strength of draw is increased, the amount of smoke that is drawn via the first passageway is limited by the restricted orifice effect and excess smoke is drawn via the second passageway. 
     
     
         15 . The smoking article filter as claimed in  claim 1 , wherein the perforations are between 0.1 mm and 1 mm in diameter. 
     
     
         16 . A smoking article filter, comprising:
 first and second longitudinally abutting filter sections;   a first passageway disposed in the second filter section and a second passageway circumscribing the first passageway;   an annular section separating the first filter section from the second passageway; and   a plurality of perforations disposed on the annular ring member.   
     
     
         17 . The smoking article filter of  claim 16 , wherein the first passageway is a high resistance passageway and the second passageway is a low resistance passageway. 
     
     
         18 . The smoking article filter of  claim 17 , wherein smoke drawn through the smoking article passes from the first filter section through the high resistance first passageway in the second filter section for a higher amount of smoke filtration. 
     
     
         19 . The smoking article of  claim 17 , wherein smoke drawn through the smoking article passes from the first filter section to the second passageway through the plurality of perforations disposed on the annular section. 
     
     
         20 . The smoking article filter of  claim 19 , wherein smoke passing through the low resistance second passageway undergoes a reduced amount of smoke filtration.