Filter mouthpiece for a smoking article

DETAILED DESCRIPTION It is now surprisingly found that if a ventilated filter mouthpiece, that is one in which ambient air is admitted to the filter by means of, for example, perforate tipping, is provided with a perforate tube open at both ends, extending from the tobacco rod end of the filter toward but not so far as the mouth end of the filter, a cigarette may be made which, when smoked, displays a substantially constant DPM (dry particulate matter) delivery.
If desired, the mouthpiece can be configured to provide an initially high DPM delivery, which rapidly drops to a lower level and maintains that lower level substantially throughout the smoking of the cigarette.
In one embodiment, ambient air is admitted to the filter through two separate places on the mouthpiece surface, one adjacent the tobacco rod end of the filter and one toward the mouth end, preferably adjacent the mouth end of the hollow tube.
A preferred arrangement is to provide a rod end filter portion abutting a mouth end filter portion, the first portion having a hollow tube extending therethrough, the walls of which are perforate.
The two filter portions are overwrapped and are attached to a wrapped tobacco rod by a tipping, the tipping being air permeable in one or more discrete areas as described above.
It is particularly preferred that the lengths of the rod end and the mouth end filter portions be in the ratio of approximately 3:1.
Preferred lengths are in the range of from 17 mm to 21 mm, particularly preferably 19 mm, for the rod end portion, and from 4 mm to 8 mm, particularly preferably 6 mm, for the mouth end portion.
The filter portions may be of cellulose acetate, crepe paper or other suitable materials, and the tube may be of cellulose acetate, poly propylene or other suitable material.
Alternatively, the tube may be formed by a bore through the first filter portion, the walls of which are partially sealed, for example by heating, or completely sealed and subsequently perforated.
It is preferred that the hollow tube has about 6 or 7 pairs of holes along its length