GB2136669A

GB2136669A - Cigarette filter

Info

Publication number: GB2136669A
Application number: GB08307353A
Authority: GB
Inventors: Ernest Brian Hayes
Original assignee: Filtrona PLC
Current assignee: Essentra PLC
Priority date: 1983-03-17
Filing date: 1983-03-17
Publication date: 1984-09-26
Also published as: GB8307353D0

Abstract

A cigarette filter comprises a filtering core 4, wrapped with inherently smoke-permeable material. The filter has longitudinal corrugations which provide externally of the wrapper passages 3 which are open at one end of the filter and extend longitudinally therefrom only partially towards its other end. The wrapper carries means 6 which render it smoke-impermeable over a region which extends only partially the length of the passages and separates from the said one end of the filter a corrugated portion 7 of the wrapper which is smoke-permeable. <IMAGE>

Description

SPECIFICATION Cigarette filter The present invention relates to cigarette filters and provides a cigarette filter comprising a filtering core, around the core a wrapper of inherently smokepermeable material having longitudinal corrugations which provide externally of the wrapper passages which are open at one end of the filter and extend longitudinally therefrom only partially towards its other end, and means carried by said wrapper which renders it smoke-impermeable over a region which extends only partially the length of the passages and separates from the said one end of the filter a corrugated portion of the wrapper which is smoke-permeable.

Such a filter may be provided with an outer wrap which may be air-impermeable or air-permeable; in the latter case the outer wrap may be of inherently air-permeable material and/or provided with ventilating perforations. The outer wrap may be a tipping overwrap by which the filter is incorporated in a filter cigarette.

In use the filter will preferably be incorporated in a filter cigarette with the channels open at their upstream end, i.e. against the tobacco rod, though it would be possible to employ the filter in the reverse orientation - i.e. with the passages open at the buccal end and terminating short of the tobacco rod end.

The means rendering the inherently permeable wrapper material impermeable over part of its corrugated length will usually extend around the whole periphery of the filter, though is not essential and partially circumferentially extending smokepermeable regions may be provided. The said means may take a variety of forms; thus it may be material with which the wrapper is impregnated, a coating applied to the one or both faces of the wrapper, a layer laminated to one or both faces of the wrapper, or a combination of any of the above; in one instance the corrugated wrapper comprises two layers of smoke-permeable sheet (e.g. porous paper plugwrap) adhered together by an intervening layer of impermeable adhesive which constitutes the said means and extends only partially the length of the passages (i.e. the corrugated wrapper portion).

In general, the wrapper may be corrugated before or after application of the means rendering it impermeable. Where the said means appears on only one face of the wrapper, this face may be either the inner or outer face of the wrapper in the finished filter, the current preference being for said means to be on the inner wrapper face.

The smoke-permeable region of the corrugated wrapper may be at the end where the corrugations terminate, or may be an intermediate region with the wrapper rendered impermeable on either side thereof. The means rendering the wrapper material impermeable may be applied so as to leave a plurality of longitudinally spaced smoke-permeable regions.

The inherently smoke-permeable material of the corrugated wrapper may be such that it becomes blocked by the passage of tobacco smoke therethrough; in this case smoke may inherently pass to the smokers mouth along the passages provided externally of the corrugated wrapper, with the permeable portions thereof becoming blocked during smoking so that the smoke is subsequently constrained to travel the full length of the filtering core.

The filtering core of filters according to the invention may be a unitary body or a composite of two or more plugs which may abut or be longitudinally spaced; the core, whether unitary or composite, may extend to the full filter length or may stop short of one or both ends to leave a terminal recess or recesses.

The filtering cores offilters according to the invention may conform to the inner surface of the corrugated wrapper, or the corrugations may define channels between the core and the inner face of the corrugated wrapper.

The invention is illustrated, by way of example only, in the accompanying drawings in which like reference numerals indicate like parts and in which: Figure l is a schematic longitudinal sectional view through one filter according to the invention; Figures 2 and 3 are like views of two other filters according to the invention; and Figure 4 is an end elevation view of the right-hand end of the Figure 1 filter.

The filter illustrated in Figure 1 comprises a filtering core 4 e.g. of bonded cellulose acetate filamentary tow, surrounded by a wrapper 2 which is corrugated over part of its length to provide externally thereof longitudinal channels 3 extending from one end of the filter only partially towards the other; wrapper 2 is of inherently smoke-permeable paper, but has a coating 6 which renders it smokeimpermeable over a length extending from the said one end of the filter only partially towards the other end of the corrugations where they terminate at plain end 5 of the wrapper. A region 7 of the wrapper is thus left smoke-permeable. In this embodiment the wrapper 2 is in turn surrounded by a plain plugwrap 1 which defines the passages 3 in combination with the corrugated portion of wrapper 2.

The core 4 conforms to the inner surface of wrapper 2 and coating 6. The illustrated embodiment could be attached to a tobacco rod by ring tipping or by a full tipping overwrap. The filter would normally be used with channels 3 open to the tobacco rod.

Figure 2 shows a slightly different filter in which the outer wrap 1 is a tipping overwrap by which the filter is attached tp a wrapped tobacco rod 8, and in which the coating 6 extends the full length (plain and corrugated) of wrapper 2 apart from circumferential region 7 which is upstream of the closed end of passages 3.

Figure 3 shows another embodiment in which the corrugations and passages 3 terminate at a plain wrapper portion 5 midway along the filter, further corrugations defining with the wrapper 1 further passages 9 which extend from plain wrapper portion 5 to the other end of the filter.

The layer 6 may in each case be a coating of sealant material (e.g. of hot melt or other adhesive or PVA) applied (e.g. printed) to the surface of wrapper 2 before or after corrugation and before the wrapper is applied around core 4. It might instead be a patch of impermeable material applied to the wrapper 2 before or after corrugation and before wrapping of the core 4; and it might instead be a layer of impermeable adhesive bonding two layers of porous plugwraptogether before or after the laminate is corrugated.

For the production of filters according to the invention the sealant coating, impregnant or patch material is preferably applied to a continuous length of wrapper material 2 at lingitudinally spaced regions leaving smoke-permeable regions 7 therebetween, this being effected before or after embossing of the wrapper to produce the corrugations separated by plain uncorrugated portions 5. The resulting composite wrapper may then be continuously wrapped around a continuously produced filter core 4, which may conform to the inner profile of the wrapper. The resulting continuous wrapped rod may be further enwrapped in outer wrapper 1, though the latter might instead be omitted and applied only as a tipping overwrap when the filter is incorporated in a filter cigarette. The initially produced continuous filter, with or without an outer wrapper 1, is then cut into convenient finite lengths, which will usually be an even multiple (e.g. sextuple) of the eventual individual lengths. These multiple lengths may be cut into double lengths for the production of filter cigarettes in conventional manner. The invention resides not only in the individual filters with or without a plain outer wrapper, but also in such double and multiple length rods with or without a plain outer wrapper, and in filter cigarettes incorporating the filters.

Claims

1. A cigarette filter comprising a filtering core, around the core a wrapper of inherently smokepermeable material having longitudinal corrugations which provide externally of the wrapper passages which are open at one end of the filter and extend longitudinally therefrom only partially towards its other end, and means carried by said wrapper which renders it smoke-permeable over a region which extends only partially the length of the passages and separates from the said one end of the filter a corrugated portion of the wrapper which is smoke-permeable.