A filter for a cigarette comprises a porous material sheet wrapped around the filter rod and a cellulose acetate thread formed tram substantially uncrimped cellulose acetate filaments. The cellulose acetate thread is positioned within the filter rod and extends along the central axis of the filter rod.
1. A filter for a cigarette or other smoking article comprising:
a porous filter rod having a substantially cylindrical shape, and
a cellulose acetate thread formed from cellulose acetate filaments, the cellulose acetate thread extending along the filter substantially parallel to the central cylindrical axis of the filter rod and configured to prevent staining and discoloration of the filter,
wherein the porous filter rod has a bulk density in the range 50-150 kg/m 3 and the cellulose acetate thread has a bulk density in the range 400-800 kg/m 3 .
2. The filter according to claim 1 , wherein the cellulose acetate thread extends along substantially the whole length of the filter rod.
3. The filter according to claim 1 , wherein the porous filter rod comprises a cellulose acetate tow.
4. The filter according to claim 3 , wherein the cellulose acetate tow comprises a disordered overlapping arrangement of cellulose acetate filaments and the cellulose acetate thread comprises an ordered arrangement of cellulose acetate filaments extending substantially parallel to the central cylindrical axis of the filter rod, such that the cellulose acetate thread is structurally distinct from the cellulose acetate tow.
5. The filter according to claim 1 , wherein the cellulose acetate filaments of the cellulose acetate thread include a pigment.
6. The filter according to claim 5 , wherein the cellulose acetate thread has a different color from the porous filter rod.
7. The filter according to claim 1 , wherein the cellulose acetate thread incorporates a plasticizer.
8. The filter according to claim 1 , wherein the cellulose acetate filaments in the thread have a twist rate in the range 100-200 turns per meter.
9. The filter according to claim 1 , wherein the cellulose acetate thread extends along the central cylindrical axis of the filter rod.
10. The filter according to claim 1 , wherein multiple cellulose acetate threads extend along the filter parallel to the central cylindrical axis of the filter rod, and wherein said multiple cellulose acetate threads are arranged in a symmetric pattern about the central cylindrical axis of the filter rod.
11. The filter according to claim 1 , wherein the cellulose acetate thread is formed from substantially uncrimped cellulose acetate filaments.
12. The filter according to claim 1 , wherein the filter is a component within a smoking article comprising a tobacco rod.
13. A smoking article comprising a tobacco rod and the filter according to claim 1 .
14. A method of making a filter for a cigarette or other smoking article comprising:
forming a cellulose acetate thread from cellulose acetate filaments; and
inserting the cellulose acetate thread into a porous filter rod having a substantially cylindrical shape, such that the cellulose acetate thread extends along the filter substantially parallel to the central cylindrical axis of the filter rod,
wherein the porous filter rod has a bulk density in the range 50-150 kg/m 3 and wherein the cellulose acetate thread has a bulk density in the range 400-800 kg/m 3 and is configured to prevent staining and discoloration of the filter.
15. The method according to claim 14 , wherein the cellulose acetate filaments include a pigment.