GB2128070A - Improvements in or relating to tobacco smoke filters - Google Patents

Abstract

The shape of a concave region (4) in the surface of a cellulose acetate filter element for a cigarette is stabilized by applying a web of porous plug wrap material (2) to the surface of the element (1) and pressing a region of the element together with the plug wrap material into the desired concave shape using a knurling device at a temperature of at least 60 DEG C and a pressure of at least 700 kg/m<2>. <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 to a ventilated filter plug for use with a cigarette.

It is known to provide a cellulose acetate filter plug with a circumferential channel or cavity, as shown for example in Figure 1 of British Patent 1602962.

Channels or cavities formed in a cellulose acetate filter, the cellulose acetate being a resilient fibrous material, may become distorted under conditions of storage or use, thereby adversely affecting the performance of the filter. It is an object of the present invention to provide means whereby such distortion may be minimised.

According to 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 fibrous material without affecting substantially the permeability or porosity of the region, the method comprising applying a web of porous plug wrap material to the surface of the element and subsequently pressing a region of the element together with the plug wrap material into a desired concave shape using a knurling device.

The fibrous material is preferably cellulose acetate and the knurling is carried out at a temperature in the range 600 - 300"C, preferably in the range 1500 240"C.

The knurling may be done at a pressure in the range 700 - 49000 kg/m2, in the region of contact.

The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which, Figure 1 is a perspective view of a filter rod element prepared according to the invention, Figure 2 is a longitudinal section through the element of Figure 1, Figure 3 is a transverse section through the element of Figure 1 taken at line Ill-Ill, and, Figures 4 and 5 are perspective views showing stages in the making of the element of Figure 1.

Referring first to Figures 4 and 5 there is shown a fibrous cellulose acetate filter rod 1, such as is used in filter-tip cigarettes, and a porous cellulose web 2 of plug wrap material.

Figure 4 shows the rod 1 and web 2 before the web is applied to the surface of the rod. Figure 5 shows the web 2 so applied to the surface of the rod 1 by known methods to form a cylindrical filter element 3.

For the purposes of illustration the thickness of the web 2 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 3 by a hot knurling tool at a temperature in the range 1500 - 240"C and at a pressure of about 35000 kg/m2. The channel so formed is shown as 4 in Figures 1 and 2 but it will be seen that the surface of the channel is corrugated by the knurling process into longitudinal striae 5, as shown in Figures 1 and 3.

It is found that the striae strengthen the surface of the channel 4 and minimize any distortion occurring either in storage or in use.

A filter element produced according to the invention may be 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. The tipping paper may be provided with vents or regions of porosity to admit ambient air to the cavity.

Various temperatures in the range 60 - 3000C and pressures in the range 700 - 49000 kg/m2 may be chosen to produce the knurling, in accordance with individual requirements.

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.

In further embodiments, not illustrated, the filter rod may be hollow either in part or along the entirety of its length.

1. A method of stabilizing the shape of a concave region in the surface of a tobacco smoke filter element made of a resilient fibrous material without affecting substantially the permeability or porosity of the region, the method comprising applying a web of porous plug wrap material to the surface of the element and subsequently pressing a region of the element together with the plug wrap material into a desired concave shape using a knurling device.

2. A method as claimed in claim 1 wherein the fibrous material is cellulose acetate.

3. A method as claimed in claim 2 wherein the knurling is carried out at a temperature in the range 60"-300"C.

4. A method as claimed in claim 3 wherein the knurling is carried at a temperature in the range 1500 - 2400C.

5. A method as claimed in any one of claims 2 to 4 wherein the knurling is carried out at a pressure in the range 700 - 49000 kg/m2, in the region of contact.

6. A method as claimed in claim 5 wherein the knurling is carried out at a pressure of about 35000 kg/m2.

7. 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 the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to tobacco smoke filters This invention relates to improvements in or relating to tobacco smoke filters, in particular to a ventilated filter plug for use with a cigarette. It is known to provide a cellulose acetate filter plug with a circumferential channel or cavity, as shown for example in Figure 1 of British Patent 1602962. Channels or cavities formed in a cellulose acetate filter, the cellulose acetate being a resilient fibrous material, may become distorted under conditions of storage or use, thereby adversely affecting the performance of the filter. It is an object of the present invention to provide means whereby such distortion may be minimised. According to 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 fibrous material without affecting substantially the permeability or porosity of the region, the method comprising applying a web of porous plug wrap material to the surface of the element and subsequently pressing a region of the element together with the plug wrap material into a desired concave shape using a knurling device. The fibrous material is preferably cellulose acetate and the knurling is carried out at a temperature in the range 600 - 300"C, preferably in the range 1500 240"C. The knurling may be done at a pressure in the range 700 - 49000 kg/m2, in the region of contact. The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which, Figure 1 is a perspective view of a filter rod element prepared according to the invention, Figure 2 is a longitudinal section through the element of Figure 1, Figure 3 is a transverse section through the element of Figure 1 taken at line Ill-Ill, and, Figures 4 and 5 are perspective views showing stages in the making of the element of Figure 1. Referring first to Figures 4 and 5 there is shown a fibrous cellulose acetate filter rod 1, such as is used in filter-tip cigarettes, and a porous cellulose web 2 of plug wrap material. Figure 4 shows the rod 1 and web 2 before the web is applied to the surface of the rod. Figure 5 shows the web 2 so applied to the surface of the rod 1 by known methods to form a cylindrical filter element 3. For the purposes of illustration the thickness of the web 2 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 3 by a hot knurling tool at a temperature in the range 1500 - 240"C and at a pressure of about 35000 kg/m2. The channel so formed is shown as 4 in Figures 1 and 2 but it will be seen that the surface of the channel is corrugated by the knurling process into longitudinal striae 5, as shown in Figures 1 and 3. It is found that the striae strengthen the surface of the channel 4 and minimize any distortion occurring either in storage or in use. A filter element produced according to the invention may be 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. The tipping paper may be provided with vents or regions of porosity to admit ambient air to the cavity. Various temperatures in the range 60 - 3000C and pressures in the range 700 - 49000 kg/m2 may be chosen to produce the knurling, in accordance with individual requirements. 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. In further embodiments, not illustrated, the filter rod may be hollow either in part or along the entirety of its length. CLAIMS

1. A method of stabilizing the shape of a concave region in the surface of a tobacco smoke filter element made of a resilient fibrous material without affecting substantially the permeability or porosity of the region, the method comprising applying a web of porous plug wrap material to the surface of the element and subsequently pressing a region of the element together with the plug wrap material into a desired concave shape using a knurling device.

2. A method as claimed in claim 1 wherein the fibrous material is cellulose acetate.

3. A method as claimed in claim 2 wherein the knurling is carried out at a temperature in the range 60"-300"C.

4. A method as claimed in claim 3 wherein the knurling is carried at a temperature in the range 1500 - 2400C.

5. A method as claimed in any one of claims 2 to 4 wherein the knurling is carried out at a pressure in the range 700 - 49000 kg/m2, in the region of contact.

6. A method as claimed in claim 5 wherein the knurling is carried out at a pressure of about 35000 kg/m2.

7. 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 the accompanying drawings.