Smoking articles such as cigarettes are conventionally made by wrapping a column of tobacco in a white wrapping paper. At one end, the smoking article usually includes a filter through which the article is smoked. Filters are attached to smoking articles using a tipping paper which is glued to the white wrapping paper. The wrapping papers and tipping papers used to construct smoking articles are typically made from flax or other cellulosic fibers and contain a filler, such as a calcium or magnesium compound.
Besides being used to hold the cigarette together and to provide the cigarette with an aesthetic appearance, cigarette wrapping papers also contribute to or control many physical properties or characteristics of the cigarette. For instance, cigarette wrapping paper can be used to control the rate at which the cigarette burns, the number of puffs per cigarette, and the tar delivery per puff. Cigarette paper can also be used to limit the amount of smoke that emanates from the lit end of the cigarette when it is left burning. Further, cigarette paper is even used to reduce the tendency of cigarettes to ignite surfaces which come into contact with the cigarette and to cause the cigarette to self extinguish when left unattended.
One of the more important properties of cigarette wrapping paper that is used to control the above-described characteristics of a cigarette is the permeability of the paper. Increasing or decreasing the permeability of a wrapping paper, for instance, varies the burn rate, tar delivery, and puff count of a cigarette made with the paper. Problems have been experienced in the past, however, in the ability to widely vary the permeability of a wrapping paper without adversely effecting other properties of the paper or the overall taste of the cigarette.
One method that is used for controlling the permeability of a wrapping paper is to vary the fiber furnish that is used to make the paper. In general, it is known that if longer fibers are used to construct the wrapping paper, the paper will have a higher permeability.
Another method for controlling the permeability of a wrapping paper is to either increase or decrease the refining of the fiber furnish. Generally speaking, refining the fiber furnish to a greater extent causes a reduction in permeability. More particularly, refining the cellulosic material that is used to make the paper down into smaller sizes creates more surface area, which reduces permeability and leads to better formation.
Another method for altering the permeability of a wrapping paper is to change the amount of filler added to the paper. Increasing or decreasing the filler loading of the paper causes an increase or decrease in permeability respectively. As more filler is added to the paper, the filler tends to interfere with the hydrogen bonding between fibers creating the increase in permeability. Unfortunately, however, altering filler levels in cigarette paper also affects the burn rate of the cigarette independently of permeability, which may be an undesired result.
Other problems are also experienced when filler levels are altered. For instance, as filler content is increased, the strength of the paper is compromised. Conversely, when not enough filler is incorporated into the paper, the opacity of the paper significantly decreases, adversely affecting the appearance of the cigarette. As such, there is increasing pressure to keep filler levels in cigarette paper constant or at least within a preset range.
In some applications, it is desirable to create a wrapping paper that has a high natural permeability. For instance, high permeable wrapping papers are needed in some applications to produce cigarettes that have a fast burn rate and/or a low tar delivery. Some of the methods and processes described above for varying the permeability of a wrapping paper can be used, under some circumstances, to produce papers with high natural permeability characteristics.
In order to increase the permeability of wrapping papers, it is more common, however, to perforate the papers by using a laser or by using an electrostatic charge. Unfortunately, perforating the wrapping paper requires an additional step and thus increases the cost of producing the papers.
Thus, a need exists for a method of naturally adjusting the permeability of a cigarette paper without adversely affecting other characteristics of the paper. A need also exists for a method of altering the permeability of a wrapping paper without having to significantly alter the amount of filler contained within the paper. A need further exists for a method of producing wrapping papers with a high permeability that do not have to be perforated.