Cigarette paper containing carbon fibers for improved ash charactaristics

Abstract: The present invention is directed to a method for improving the ash characteristics of a paper wrapper for a smoking article and for improving the ash characteristics of the smoking article itself. Specifically, it has been unexpectedly discovered that the ash cohesiveness of a paper wrapper is noticeably improved when carbon fibers having an average length less than about 0.75 inches are incorporated into the paper in an amount up to about 60% by weight. Paper wrappers made with carbon fibers in accordance with the present invention have superior ash characteristics in comparison to paper wrappers incorporating only flax or other cellulosic fibers. Further, the ash cohesiveness of the paper is improved without resulting in the decline in the quality of other ash characteristics.

Description: Field of the Invention The present invention is generally directed to a method for improving the ash characteristics of a paper used to construct smoking articles. More particularly, the present invention is directed to a process for improving the ash cohesiveness of cigarette paper by incorporating carbon fibers into the paper sheet. Background of the Invention 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 calcium carbonate. Besides being used to hold the cigarette together, cigarette wrapping papers and tipping papers also contribute to and control many physical properties and characteristics of the cigarette. For instance, cigarette wrapping paper affects the rate at which the cigarette burns, i.e. the number of puffs per cigarette and the total tar delivery per puff. Another property of the cigarette that is affected by the wrapper is the appearance and cohesiveness of the ash that is formed as the cigarette burns. Ideally, cigarette ash should be cohesive, should not flake off from the cigarette, and should have an aesthetically pleasing appearance. The quality of cigarette ash is generally determined by rating the ash according to four criteria. The first criterion is ash color. In general, a whiter ash has a more aesthetic appearance and is thus more desirable. The second criterion is ash cohesiveness and the ability of the ash to avoid excessive flaking. The ash should not flake off the cigarette unless the cigarette is flicked or tapped on an object. Further, once the cigarette is tapped, the ash should break off in clumps and not disintegrate. The last two criteria used to evaluate cigarette ash are dependant for the most part upon the cigarette wrapping paper and not upon the ash characteristics of the tobacco column. For example, the third criterion for evaluating cigarette ash is the thickness of the char line appearing on the wrapper as a cigarette is burned. Thinner char lines are preferred. Finally, the last criterion is the extent to which the cigarette wrapper stains downstream (towards the filter) from the ash as the cigarette is smoked. A high quality wrapping paper will not stain or discolor throughout the length of the cigarette as the cigarette is puffed. In the past, various methods have been devised in order to improve the ash characteristics of a smoking article. For instance, previous efforts for improving the appearance of ash have included changing the type of cellulosic fiber used to make the cigarette wrapping paper. Also, ash modifiers have been added to the paper or to the tobacco. In particular, it has been proposed in the past to add to the paper starches or salts to improve ash characteristics without adversely affecting the qualities of the paper. Unfortunately, the use of conventional cellulosic fibers and ash modifiers does not provide sufficient ash cohesiveness such that the ash does not flake off too easily. Thus, a need exists for a method of improving cigarette ash characteristics without detrimentally affecting the other properties of the cigarette. In particular, a need exists for a method that improves the ash cohesiveness of a cigarette wrapping paper without adversely affecting the appearance of the ash or the permeability of the paper, the taste, the bum rate, the puff count, or the tar delivery per puff of a cigarette incorporating the paper. US 4,938,238 discloses an improved wrapper for a smoking article having a combustible fuel element encircled by an insulating layer and a physically separate aerosol generating means. The wrapper encircles at least a portion of the insulating layer for the fuel element and comprises a permeable sheet material which during burning of the fuel provides a coherent layer to assist in controlling the amount of peripheral air to the fuel element during smoking. The sheet material comprises a conventional cigarette paper as an inner wrap and a cellulose based outer wrap, which contains about 10 to 30% by weight of high temperature resistant micro fibers consisting of glass, aluminum silicate, silicon carbide, calcium sulfate or carbon. Such a inner wrap/outer wrap combination is, in particular because of its thickness, not suitable for conventional paper wrapped smoking articles such as cigarettes. Summary of the Invention The present invention recognizes and addresses various disadvantages of prior art constructions and methods. Accordingly, it is an object of the present invention to provide a method for improving the ash characteristics of a cigarette paper and of a cigarette incorporating the paper. It is another object of the present invention to provide a method for improving the ash cohesiveness of a cigarette paper without adversely affecting other cigarette ash characteristics. Still another object of the present invention is to provide a method for improving the ash cohesiveness of a cigarette paper by incorporating into the paper carbon fibers. Another object of the present invention is to provide a method for improving the ash cohesiveness of a cigarette paper by incorporating into the paper carbon fibers having an average length less than 1,91 cm (0.75 inches). It is another object of the present invention is to provide a method for improving the ash cohesiveness of a cigarette paper by incorporating into the paper carbon fibers having an average length less 1,91 cm (0.75 inches) and added in an amount less than 60% by weight. These and other objects of the present invention are achieved by providing a process for improving the ash characteristics of a paper wrapper for a smoking article. The process includes the step of incorporating carbon fibers into a paper wrapper. The carbon fibers have an average length less than 1,91 cm (0.75 inches), particularly from 0,318 cm (0.125 inches) to 1,27 cm (0.5 inches), and more particularly 0,635 cm (0.25 inches). The carbon fibers can be added to the paper wrapper in an amount from less than 60% by weight, and more particularly from 5% to 20% by weight. According to the present invention, the paper wrapper can have a basis weight from 18 g/m 2 to 60 g/m 2 , but typically is from 45 g/m 2 to to 55 g/m 2 in one embodiment and from 22 g/m 2 to 32 g/m 2 in an alternative embodiment. The paper wrapper can have a permeability of from 5 Coresta units to 2000 Coresta units, particularly from 5 Coresta units to 80 Coresta units. In one embodiment, a filler can be coated onto the paper wrapper or incorporated into the paper wrapper. The filler, for instance, can be a calcium carbonate. For example, calcium carbonate filler can be added in an amount of from 20% by weight to 40% by weight. The paper wrapper can also be coated with a bum control additive. The bum control additive, for instance, can be an alkali metal salt, an acetate, a phosphate salt, or mixtures thereof. For example, the burn control additive can be a citrate and can be added to the paper in an amount from 0.3% to 12% by weight. In still another embodiment, a viscosity modifier can be incorporated into the paper. For instance, the viscosity modifier can be an alginate. This makes it easier to process the carbon fibers in the slurry. A better formation is obtained. Other objects, features and aspects of the present invention are discussed in greater detail below. Detailed Description of Preferred Embodiments It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention which broader aspects are embodied in the exemplary construction. The present invention is generally directed to a method for improving the ash characteristics of a wrapping paper and for improving the ash characteristics of a smoking article incorporating the wrapping paper. Specifically, the characteristic of ash cohesiveness is improved by adding to the paper carbon fibers having an average length less than 1,91 cm (0.75 inches), and more particularly between 0,318 cm (0.125 inches) to 1,27 cm (0.50 inches). The carbon fibers are generally added to the wrapping paper at an amount up to 60% by weight, and more particularly between 5% to 20% by weight. Further, the ash cohesiveness of the paper is improved without significantly harming other ash characteristics or qualities of the wrapping paper. Paper wrappers for smoking articles made in accordance with the present invention exhibit an ash that is significantly more cohesive than many prior art constructions containing only flax or other cellulosic fibers in the paper sheet. When traditional paper wrappers burn, the organic matters, i.e. flax and other cellulosic fibers within the paper, tend to bum and flake off. However, by incorporating carbon fibers into the paper wrapper in accordance with the present invention, a cohesive ash can form. As a paper wrapper incorporated with carbon fibers burns, the carbon fibers form a matrix-like structure that is substantially free from flaking, thus producing a cohesive ash. The construction of a cigarette wrapping paper made in accordance with the present invention will now be discussed in greater detail. In addition to carbon fibers, the wrapping paper can also include cellulosic fibers obtained, for instance, from flax, softwood or hardwood. The flax or other cellulosic fibers are generally added in an amount of 15% to 99% by weight, and more particularly from 50% to 65% by weight. Moreover, the wrapping paper can also include a filler, such as calcium carbonate or other white pigments such as magnesium or titanium oxides, to further enhance the characteristics of the wrapping paper. Depending on the amount of filler added to the wrapping paper, the amount of flax or other cellulosic fibers in the paper can vary substantially. For example, in a preferred embodiment of the present invention, calcium carbonate filler is added to the wrapping paper at a level of from 20% by weight to 40% by weight, and particularly from 25% by weight to 35% by weight. At a filler level of 30% by weight, for instance, the flax or other cellulosic fibers can range from an amount between 15% to 69% by weight, depending on the amount of carbon fibers added to the wrapper. Preferably, when the filler is added in an amount of 30% by weight, the carbon fibers are added in amount between 5% to 20% by weight and the flax fibers are added in an amount between 50% to 65% by weight. The permeability of a paper wrapper made according to the present invention can generally range from 5 Coresta units to 2000 Coresta units, depending on the type, particle size, and amount of filler present within the paper. In most applications, the permeability of a cigarette paper wrapper is between 15 Coresta units to 55 Coresta units. As carbon fibers are added to a paper wrapper made according to the present invention, the permeability of the paper increases, i.e. the Coresta value increases. As such, a paper wrapper incorporating relatively high amounts of carbon fibers, e.g. above 20% by weight, can have a permeability above the Coresta value normally desired for paper wrappers. To decrease the permeability of a paper wrapper containing such high amounts of carbon fibers, the fiber furnish can simply be refined to a greater extent to decrease the Coresta value to a desired level without having to decrease the level of carbon fibers within the paper wrapper. As stated above, various ratios of flax and carbon fibers can be used in a paper wrapper made according to the present invention. The basis weight of the paper wrapper increases as the amount of flax fibers and carbon fibers increases. Therefore, the basis weight of a paper wrapper made in accordance with the present invention can vary depending on the exact ratio of flax and carbon fibers used. Generally, the basis weight can range from 18 grams per square meter (g/m 2 ) to 80 grams per square meter (g/m 2 ). In particular, the basis weight is between 20 g/m 2 to 55 g/m 2 . The cigarette paper can also be treated with a burn control additive which may have a further effect on the overall basis weight of the paper wrapper. Such bum control additives can include, for instance, alkali metal salts, acetates, phosphate salts, or mixtures thereof. For example, the bum control additive can be a citrate and can be added to the paper in an amount from 0.3% to 12% by weight. As described above, the present invention is directed to incorporating into a paper wrapper carbon fibers to improve the ash characteristics of the paper and to a smoking article constructed with the paper. The carbon fibers added to the paper wrapper can have an average length less than 1,91 cm (0.75 inches). However, because it is possible that relatively long fibers might cause entangling, it is generally preferred that the average length be between 0,318 cm (0.125 inches) to 1,27 cm (0.5 inches). For example, in one embodiment, the carbon fibers have an average length of approximately 0,635 cm (0.25 inches). One particular commercially available carbon fiber that can be used in the present invention is TYPE 3C carbon fiber marketed by Fortafil Fibers, Inc. TYPE 3C carbon fiber has an average length of 0,635 cm (0.25 inches) and a diameter of 7.3 µm (microns). In producing paper wrappers in accordance with the present invention, the paper wrapper can be made by creating a fiber suspension of carbon fibers and flax or other cellulosic fibers. For instance, the fiber suspension can be formed from a fiber furnish that has been cooked in a digester, washed, bleached, and refined. As noted above, the amount of refinement can vary depending on the level of permeability required. Other additives can also be added to the fiber suspension before forming the paper wrapper. For example, a filler slurry formed from water and a particular filler can be combined with the suspension. Furthermore, a viscosity modifier can also be added to the fiber suspension to aid in the processing of the cigarette paper by increasing the viscosity of the fiber suspension mixture. The viscosity modifier can be, for instance, an alginate. To form the paper wrapper, the fiber suspension mixture can be spread out onto a screen or set of screens and dried. It is also believed that a filler can be coated onto the paper after it has been formed. The present invention may be better understood with reference to the following example. EXAMPLE The ash characteristics of paper wrappers incorporating carbon fibers were examined. The carbon fibers were TYPE 3C carbon fibers marketed by Fortafil Fibers, Inc., having an average length of 0,635 cm (0.25 inches) and a median particle diameter of 7.3 µm (microns). The paper wrapper also incorporated ALBACAR 5970 calcium carbonate filler having a median particle size of 1.9 µm (microns). The ALBACAR 5970 filler was obtained from Specialty Minerals, Inc. of Adams, Massachusetts. Cigarette wrappers were made incorporating the following mixtures of TYPE 3C carbon fibers, flax fibers, and ALBACAR 5970 filler: Carbon fiber/flax fiber paper wrappers Carbon Fiber (wt%) Flax Fiber (wt%) ALBACAR 5970 (wt%) Basis wt. (g/m 2 ) CORESTA (cm/min) 0 69 31 49 5 18 52 30 51 18 35 35 30 53 300 54 18 28 54 2000 Cigarettes were hand rolled from sheets comprising various ratios of fibers as listed in the above example. The cigarettes were lit and allowed to bum freely. As the cigarette burned, the formed ash was observed and evaluated. From this example, it was discovered that cigarette ash containing carbon fibers was noticeably more cohesive than cigarette ash containing no carbon fibers. Specifically, as the cigarette burned, the carbon fibers left behind a matrix-like arrangement that was free from flakes or fissures. These and other modifications and variations of the present invention may be practiced by those of ordinary skill in the art, without departing from the scope of the present invention, which is set forth in the appended claims. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the description so further described in such appended claims.

Claims: A process for improving the ash characteristics of a paper wrapper for a smoking article comprising the step of: incorporating into a paper wrapper carbon fibers, said carbon fibers having an average length less than 1,91 cm (0.75 inches). A process as defined in claim 1, wherein said carbon fibers have an average length between 0,318 cm (0.125 inches) to 1,27 cm (0.5 inches). A process as defined in claim 1, wherein said carbon fibers have an average length between 0,635 cm (0.25 inches) to 0,889 cm (0.35 inches). A process as defined in claim 1, wherein said carbon fibers are incorporated into said paper wrapper in an amount less than 60% by weight. A process as defined in claim 1, wherein said carbon fibers are incorporated into said paper wrapper in an amount from 5% to 20% by weight. A process as defined in claim 1, further comprising the step of incorporating into said paper wrapper a filler. A process as defined in claim 6, wherein said filler comprises calcium carbonate. A process as defined in claim 6, wherein said filler is incorporated into said paper wrapper in an amount between 20% to 40% by weight. A process as defined in claim 6, wherein said filler comprises calcium carbonate and is incorporated into said paper wrapper in an amount between 28% to 32%. A process as defined in claim 1, wherein said paper wrapper has a basis weight from 45 g/m 2 to 60 g/m 2 . A process as defined in claim 1, wherein said paper wrapper has a permeability from 5 Coresta units to 2000 Coresta units. A process as defined in claim 1, further comprising the step of coating said paper with a burn control additive, said bum control additive being a material selected from the group consisting of alkali metal salts, acetates, phosphate salts, and mixtures thereof. A process as defined in claim 12, wherein said burn control additive comprises a citrate, said citrate being added to said paper wrapper in an amount from 0.3% to 12% by weight. A process as defined in claim 1, wherein said paper wrapper comprises cellulosic fibers, said cellulosic fibers being incorporated into said paper wrapper in an amount from 30% to 95% by weight; and said carbon fibers are incorporated into said paper wrapper in an amount less than 30% by weight. A process as defined in claim 14, wherein said carbon fibers are incorporated into said paper wrapper in an amount from 5% to 20% by weight. A process as defined in claim 14, further comprising the step of adding a filler to said paper wrapper in amount from 20% to 40% by weight. A process as defined in claim 14, wherein said cellulosic fibers comprising flax fibers, said flax fibers being incorporated into said paper wrapper in an amount from 50% to 65% by weight. A process as defined in claim 14, wherein said paper wrapper has a basis weight from 45 g/m 2 to 60 g/m 2 . A process as defined in claim 14, wherein said paper wrapper has a permeability from 15 Coresta units to 80 Coresta units. A paper wrapper for a smoking article having improved ash characteristics comprising: a paper web comprising cellusoic fibers and a filler, said filler being present in said web in an amount from 20% to 40% by weight; carbon fibers incorporated into said paper web, said carbon fibers having an average length of from 0,318 cm (0.125 inches) to 1,27 cm (0.50 inches), said carbon fibers being incorporated into said paper web in an amount from 5% to 30% by weight; and wherein said paper wrapper has a basis weight of from 18 g/m 2 to 60g/m 2 , and a permeability of from 5 Coresta units to 80 Coresta units. A paper wrapper as defined in claim 20, wherein said carbon fibers are incorporated into said paper web in an amount from 5% to 20% by weight. A paper wrapper as defined in claim 20, wherein said paper wrapper has a permeability of from 15 Coresta units to 55 Coresta units. A paper wrapper as defined in claim 20, wherein said paper wrapper has a basis weight of from 45 g/m 2 to 60 g/m 2 . A paper wrapper as defined in claim 20, wherein said carbon fibers have a diameter of less than 10 µm (microns).

Inventors: HAMPL VLADIMIR JR, HAMPL, VLADIMIR, JR.
Applicants: SCHWEITZER MAUDUIT INT INC, SCHWEITZER-MAUDUIT INTERNATIONAL, INC.
Application year: 2000
Main classification: A24D1
IPC codes: D21H27, D21H13, A24D1