GB2130468A

GB2130468A - Improvements in or relating to tobacco smoke filters

Info

Publication number: GB2130468A
Application number: GB08323512A
Authority: GB
Inventors: David Wyn Bassett
Original assignee: Imperial Group PLC
Current assignee: Imperial Group PLC
Priority date: 1982-09-02
Filing date: 1983-09-01
Publication date: 1984-06-06
Also published as: GB2130468B; GB8323512D0

Abstract

A cigarette filter plug (10) made of cellulose acetate comprises a cylindrical section (12) and an abutting tubular section (14) at the mouth end, both sections being enwrapped in porous plugwrap material (16). One section is provided with a circumferential channel (181) which has longitudinal corrugations or striae, and the whole plug is wrapped in tipping paper (20) which is provided with perforations (22) in the region overlying the channel. The corrugated or striated channel is formed by applying a web of porous plugwrap material to a cylindrical filter element of cellulose acetate and pressing a region of the element into the desired corrugated channel shape using a hot knurling tool at a temperature in the range 60-300 DEG C and a pressure in the range 1-70 psi. <IMAGE>

Description

SPECIFICATION Improvements in or relating to tobacco smoke filters This invention relates to improvements in or relating to tobacco smoke filters, in particular a ventilated filter plug for use with a cigarette or similar elongate smoking article.

It is known to provide a cellulose acetate filter plug with a circumferential channel or cavity, as shown for example in Fig. 1 of British Patent 1 602962. It is an object of the present invention to provide a circumferentially channeled filter plug that enables the filter manufacturer to keep a close control on smoking and ventilation characteristics in response to smoker's requirements and types of tobacco used. Cellulose acetate is a resilient fibrous material, and channels or cavities formed in a cellulose acetate filter may become distorted under conditions of storage or use, thereby adversely affecting the performance of the filter. It is a further object of the present invention to provide means whereby such distortion may be minimized without affecting substantially the permeability or porosity of the surface of any such channel or cavity.

According to a first aspect of the present invention there is provided a ventilated filter plug for an elongate smoking article, the plug comprising, (a) first and second cylindrical sections of filter material in axial abutment one with the other, each section having tobacco smoke filtration characteristics different from those of the other, (b) a circumferential channel in the cylindrical surface of one of the sections, (c) a web of porous plugwrap material enwrapping the sections and closely following the contours of said channel, (d) a web of tipping paper enwrapping the sections and plugwrap, an annular cavity being thereby defined between the underside of the tipping paper and the plugwrap material in the channel, and (e) means in the tipping paper to admit ambient air to the annular cavity.

According to a second aspect of the present invention there is provided a method of stabilizing the shape of a concave region in the surface of a tobacco smoke filter element made of a resilient filter material without affecting substantially the permeability or porosity of the region, the method comprising applying a web of porous plugwrap material to the surface of the element and subsequently pressing a region of the element together with the plugwrap material into a desired concave shape using a knurling device.

The invention will now be described by way of example only with reference to the accompanying non-scaled diagrammatic drawings in which, Figures 1 and 2 are longitudinal sections through alternative embodiments of filter plugs according to the invention.

Figure 3 is a perspective view of a filter rod element used in the embodiment of Fig. 2.

Figure 4 is a longitudinal section through the element of Fig. 3.

Figure 5 is a transverse section through the element of Fig. 3 taken at line V-V. And, Figures 6 and 7 are perspective views showing stages in the making of the element of Fig. 3.

Referring to the drawings there is shown in Fig. 1 a cigarette filter plug 10 comprising a cylindrical filter element 1 2 made of cellulose acetate fibre in axially abutting relationship with a second, tubular filter element 1 4 made of cellulose acetate fibre.

The elements 12, 1 4 are together wrapped around with a web of porous plugwrap material 16, which is usually paper. A circumferential channel 181 is formed in the periphery of the element 1 4 together with the enwrapping plugway 1 6 by a hot knurling tool (not shown) in a manner to be described hereinafter to corrugate the surface of the channel 1 81 together with that portion of the plugwrap 1 6 within the channel into longitudinal striae which strengthen the surface of the channel and minimize any distortion which may occur in storage or use. It will be seen that the plugwrap is thus in contact with the contours of the channel at all times.

A tipping paper wrapper 20 is then wrapped round the combination of filter elements 12, 14 and plugwrap 1 6. This forms an annular cavity defined by the underside of the tipping paper and the surface of the plugwrap within the channel. The tipping paper is provided with a circumferential series of vents 22 arranged to admit ambient air into the cavity. Alternatively, the tipping paper may be provided with a region of high porosity instead of the vents 22.

The tubular element 1 4 is normally at the mouth end of the filter and may, for cosmetic reasons, be closed off at its open end by a disc of filter material (not shown).

Fig. 2 is similar to Fig. 1 save that the channel 181 of Fig. 1 is now formed instead as channel 1 82 in the periphery of element 1 2 at a location as close as may be conveniently possible to the join between the solid and tubular elements. All other features of Fig. 1 are given the same numbers in Fig. 2.

In an alternative embodiment, not shown, the tubular element 14 may be replaced by a solid element of filter material, but made of a material or having a structure such that its filtration characteristics are different to those of element 1 2.

The relationship of the annular channel (181 or 182) to the junction between the elements 12, 14, in combination with the venting characteristics of the tipping paper and the filtration characteristics of the two sections enables the manufacturer to keep a close control on smoking and ventilation characteristics in response to the requirements of smokers, market trends, and the type of tobacco used.

The presence of the annular channel beneath the tipping paper vents 22 substantially increases the admittance of free ventilation air without the need to increase the size or number of the vents.

There now follows a more detailed description of the manufacture of the channeled filter elements of Figs. 1 and 2.

Referring now to Figs. 6 and 7 there is shown a fibrous cellulose acetate filter rod 51 which corresponds to the filter element 1 2 of Fig. 2 and a porous cellulose web 52 of plugwrap material which corresponds to the plugwrap 1 6 of Fig. 2.

Fig. 6 shows the rod 51 and web 52 before the web is applied to the surface of the rod.

Fig. 7 shows the web 52 so applied to the surface of the rod 51 by known methods to form a cylindrical filter element 53. For the purposes of illustration the thickness of the web 52 relative to the dimensions of the rod 1 has been greatly exaggerated.

An annular concavity, or circumferential channel, is now formed in the cylindrical surface of the filter element 53 by a hot knurling tool at a temperature in the range 150-240GC and at a pressure of about 50 psi. The channel so formed is shown as 54 in Figs. 3 and 4 but it will be seen that the surface of the channel is corrugated by the knurling process into longitudinal striae 55, as shown in Figs. 3 and 5.

It is found that the striae strengthen the surface of the channel 54 and minimize any distortion occurring either in storage or in use.

The filter element so produced is now wrapped in tipping paper so as to form an annular cavity defined by the underside of the tipping wrapper and the surface of the channel.

Various temperatures in the range 60-300"C and pressures in the range 1-70 psi may be chosen to produce the knurling, in accordance with individual requirements.

The method as described is applicable to a hollow tube of cellulose acetate so as to provide the element 14 of Fig. 1.

Additives such as moisture or plasticizer may be added to the porous plug wrap before or during the knurling process so as to enhance the stability of the final product.

Filter materials other than cellulose acetate may be used, such as paper or other cellulosic material.

The metric equivalents of Imperial units used above are as follows: 1-70 psi = 700-49000 kg/m2 50 psi = 35000 kg/m2

Claims

CLAIMS 1. A ventilated filter plug for an elongate smoking article, the plug comprising, (a) first and second cylindrical sections of filter material in axial abutment one with the other, each section having tobacco smoke filtration characteristics different from those of the other, (b) a circumferential channel in the cylindrical surface of one of the sections, (c) a web of porous plugwrap material enwrapping the sections and closely foliowing the contours of said channel, (d) a web tipping paper enwrapping the sections and plugwrap, an annular cavity being thereby defined between the underside of the tipping paper and the plugwrap material in the channel, and (e) means in the tipping paper to admit ambient air to the annular cavity.
2. A filter plug as claimed in claim 1 wherein the channel is provided with means to render the shape of the channel resistant to distortion.
3. A filter plug as claimed in claim 2 wherein said means to render the shape of the channel resistant to distortion is provided by longitudinal corrugations or striae in the surface of the channel.
4. A filter plug as claimed in any preceding claim wherein one section is a solid cylinder and the other section is a hollow cylinder or tube.
5. A filter plug as claimed in claim 4 wherein the hollow section is at the mouth end of the plug.
6. A filter plug as claimed in claim 5 wherein the hollow section is closed off at the mouth end by a plug or disc of filter material.
7. A filter plug as claimed in any preceding claim wherein the means in the tipping paper to admit ambient air is provided by ventilating apertures.
8. A filter plug as claimed in any preceding claim wherein the filter material is cellulose acetate.
9. A method of stabilizing the shape of a concave region in the surface of a tobacco smoke filter element made of a resilient filter material, being an element of a filter plug according to any preceding claim, without affecting substantially the permeability or porosity of the region, the method comprising applying a web of porous plugwrap material to the surface of the element and subsequently pressing a region of the element together with the plugwrap material into a desired concave shape using a knurling tool.
10. A method as claimed in claim 9 including forming longitudinal corrugations or striae in the surface of the desired concave shape by means of the knurling tool.
11. A method as claimed in claim 9 or 10 wherein the filter material is cellulose acetate.
1 2. A method as claimed in any one of claims 9 to 11 wherein the knurling is carried out at a temperature in the range 60-300"C and at a pressure in the range 1-70 psi.
1 3. A method as claimed in claim 1 2 wherein the knurling is carried out at a temperature in the range 150-240"C.
14. A method as claimed in claim 12 or 1 3 wherein the knurling is carried out at a pressure of about 50 psi.

1 5. A ventilated filter plug for an elongate smoking article substantially as hereinbefore described with reference to Fig. 1 or Figs. 2 to 7 of the accompanying drawings.

1 6. A method of stabilizing the shape of a concave region in the surface of a tobacco smoke filter element substantially as hereinbefore described with reference to Figs. 6 and 7 of the accompanying drawings.