| 摘要 |
A smoke filter for a smoking article (e.g. a cigarette) comprises a filter plug having an airflow duct whose floor extends along the filter plug from the mouth end of the plug such that the end of the duct remote from the mouth end is deeper than the end of the duct at the mouth end, with a region of progressively decreasing depth from the deep end towards the shallow end. The at least one duct may comprise a plurality of grooves equiangularly spaced around the periphery of the filter plug, in which case it is possible for the grooves to extend helically and to be divided into sets of opposite hand such that each groove of one set intersects several grooves of the other set. Alternatively, the airflow duct may comprise a single annular groove extending around the filter plug with a shallower side at the mouth end of the plug and a deeper side remote from the mouth end, in which case a relatively stiff tipping is required. In all cases the tipping includes ventilation perforations communicating with the deeper end of the air duct.
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