Smoking article wrapper for controlling burn rate and method for making same

Abstract: This invention relates to the control of the burn rate of a cigarette. The burn rate is controlled by the use of a paper wrapper to which regions of cellulosic material are applied and bonded. The cellulosic material is applied during a manufacturing step for the base paper wrapper, either off or on-line of the paper wrapper-forming

Description: The present invention relates to a paper wrapper construction for use in conjunction with a smoking article, such as a cigarette. Specifically the paper wrapper of this invention can be used to effectively control the burn rate of the smoking article. The paper wrapper of the present invention comprises cellulosic material which is applied to regions of a base paper web. It is beneficial to make cigarettes in commercial quantities which will have a reduced burn rate if not drawn on by the smoker but which look, feel, taste and burn like conventional cigarettes when being drawn on by the smoker at normal intervals. It is recognized by those skilled in the art that the wrapper configuration and construction strongly influences these characteristics. Cigarette wrappers, i.e., papers, have known burn characteristics, including burn rates and static burn capabilities. There have been various attempts to modify the burn characteristics of such wrappers. These attempts have employed a variety of wrapper configurations and constructions. For example, it is known that the burn characteristics can be modified by adding fillers, coatings, or additives to the papers. Weinert United States Patent No. 4,489,650 refers to a self-extinguishing cigarette in which the interior surface of the wrapper is coated with clay. In Cohn United States Patent No. 4,044,778, the cigarette wrapper referred to includes rings or areas coated with deposits from an alkali silicate solution which renders the wrapper non-burning in the coated areas. In Adams et al. United States Patent No. 4,889,145, the cigarette wrapper referred to includes an area containing a coating of a porosity reducing composition. The coating is comprised of a non-polymer with a polymer binder. Examples of the non-polymer were given as a fatty alcohol and a fatty acid salt. Durocher United States Patent No. 4,615,345 refers to another attempt to modify the burn characteristics of wrappers. In Durocher the wrapper is made of a cellulose fiber base which normally does not sustain burning when the wrapper is incorporated into a cigarette. This type of wrapper is treated in selected zones with an alkali metal burn promoter such as the potassium salt of citric acid. It is referred to therein that a cigarette made with a wrapper so treated will smolder without being drawn on by the smoker when in the treated zone but when the treated zone is consumed will extinguish itself unless the cigarette is drawn on by the smoker. Baker et al. United States Patent No. 4,077,414 also refers to a wrapper with modified burn characteristics. In Baker, a wrapper with inherently high porosity is modified by treating the paper with what was referred to as a "gel-forming" substance so as to produce bands of low porosity regions. The "gel-forming" substances disclosed in Baker were all soluble in water and thus were solutions, as opposed to slurries, when applied to the cigarette paper wrapper. In addition to modifying wrapper burn characteristics by adding fillers, coatings or burn additives directly to the base paper web, burn characteristics have been shown to be able to be modified by applying to the base paper web a strip or patch of a paper having different characteristics than the base web to be modified. For example, it is shown in our co-pending application no.91309456.1 (EP-A-0483998) 1990, that cigarette paper can be modified by applying strips of a different paper at periodically spaced positions across the width of the paper web, so that cigarettes produced from the paper web have periodically spaced circumferential bands on the inside of the paper for modifying the burning characteristics of the paper and the cigarette. One treated paper material suitable for forming the periodically spaced strips is described in Hampl United States Patent No. 4,739,775. However, the wrappers discussed in Hampl were formed by the adhesion of the treated paper material to the base paper web by a process which would be difficult and costly to use for mass production. US-A-4 739 775 discloses a laminar cigarette wrapper in which strips of paper are glued to the base web. The wrapper exhibits self-extinguishing properties. As discussed above, various types of cigarette wrapper configurations have been proposed for modifying the burn characteristics of cigarettes. However, these wrappers have various problems and disadvantages. Although the wrappers of Weinert and Cohn produce cigarettes with modified burn characteristics, they do not look, feel, taste and burn like conventional cigarettes when being drawn on by the smoker. Although the wrappers of Durocher solve some of the problems exhibited by the Weinert and Cohn wrappers, Durocher did not disclose a process for making such cigarette wrappers in commercial quantities. In addition, although co-pending application 91309456.1 discloses commercially feasible methods that can produce wrappers with both modified burn characteristics and that look, feel, taste and burn like a conventional cigarette when being drawn on by the smoker, such methods are not the only solutions to the problems discussed. Additionally, the wrappers and coatings referred to in Baker et al. and Adams et al. are not the only types that can potentially modify the burn rate of a cigarette. Johnson United States Patent No. 4,861,427 refers to a fibrous web product with bacterial cellulose as a surface treatment. In Johnson the bacterial cellulose treatment referred to is applied to the entire web. The resulting coating web is used as printing materials which have gloss, smoothness, ink receptivity and surface strength. Johnson does not refer to the application of the cellulose to papers in selected portions of the web, i.e., in bands or other patterns, nor does Johnson refer to burn control properties that such an application of bacterial cellulose will impart to the resulting paper. Johnson does not disclose the use of the coated web for cigarette paper. It would be desirable to provide a paper wrapper for a smoking article that effectively controls the burn rate of the smoking article. It would also be desirable to provide a paper wrapper for a smoking article that looks, feels, tastes and burns like a conventional cigarette when being drawn on by the smoker. EP-A-0 486 213, which forms part of the state of the art by virtue of Article 54(3) EPC discloses a paper cigarette wrapper comprising a cellulosic base web having a plurality of cross directional regions of greater basis weight than the base web. These cross directional regional of cellulosic material, including microcrystalline cellulose and BUCKEYE™, a fibrillated cellulose. In accordance with the present invention, there is provided a paper wrapper for a smoking article comprising a paper base web having one or more regions of microfibrillated fibrous cellulose bonded to the paper base web provided by a microfibrillated fibrous cellulose suspension applied directly to the paper base web, the regions of microfibrillated fibrous cellulose adding between about 0.5 g/m 2 and about 10 g/m 2 (dry weight) on top of the base paper. This paper wrapper can be incorporated into a smoking article comprising a tobacco filler and said paper wrapper. In addition, a method for making the smoking article wrapper is also provided. This method comprises: a) advancing the base paper web along a travel path, and b) applying a stable suspension of microfibrillated cellulosic material in a liquid directly to the base paper web at a position on the path to form one or more regions of microfibrillated fibrous cellulose on the web, the regions of microfibrillated fibrous cellulose adding between about 0.5 g/m 2 and about 10 g/m 2 (dry weight) on top of the base paper. The paper wrapper of this invention may be used for cigarettes of any length or circumference and having different fillers, such as tobacco, expanded tobacco, a variety of tobacco blend types, reconstituted tobacco materials, non-tobacco filler materials and combinations thereof. Paper consists of a web of cellulosic fibers held together by hydrogen bonding. A paper web without an inorganic filler such as calcium carbonate is non-porous and either does not burn or burns very slowly. The calcium carbonate, or other inorganic filler, present in cigarette paper disrupts the fiber bonding and opens the structure of the paper to allow the entry of air to support combustion. The invention disclosed herein consists of the application of additional cellulose microfibrils onto the surface of a base paper web in order to modify and tailor the burn characteristics of the resulting paper web. When such a paper web is incorporated into the wrapper of a smoking article, the burn characteristics of the resulting smoking article are also modified. As used herein, the term "microfibrillated fibrous cellulose" is defined to mean cellulose in the form of microfibrils. "Fibrils" are the threadlike elements of the wall of the cellulose fiber visible with an optical microscope. Upon examination by electron microscopy "fibrils" are found to consist of still finer "microfibrils." The base paper web of the present invention is a conventional cigarette paper onto which is applied a slurry of fibrous cellulose microfibrils. A main advantage of the present invention is that the microfibrillated fibrous cellulose can be applied by means of various conventional coating or printing techniques. Furthermore, the microfibrils can be applied on-line or off-line of the base paper making apparatus beyond the wet end of the paper machine. As a result of the above advantages, smoking articles incorporating the wrappers disclosed herein can be mass produced. A unique aspect of the present invention is that the application of the slurry of microfibrillated fibrous cellulose under the processes disclosed herein results in a dense mat of microfibrils present on the surface of the base paper web as revealed by scanning electron microscopy studies. It is believed that the dense mat of microfibrillated fibrous cellulose which contains no inorganic filler or added burn chemicals, provides a region which slows combustion. The dense mat of microfibrillated fibrous cellulose then can be used to control the burn rate of a cigarette. A smoking article incorporating a wrapper with the dense mat of microfibrillated fibrous cellulose of the present invention can thus have simplified burn rate control. Burn rate control can be modified or tailored to the extent desired by optimizing the application level of the microfibrillated fibrous cellulose or the width and spacing of the regions or bands of the dense mat of microfibrillated fibrous cellulose. The cigarette with which the paper wrapper of this invention may be used may be of any length or circumference. Preferably, the circumference of the cigarette may be in the range from about 15 millimeters to about 28 millimeters. In addition, the cigarettes with which the paper wrapper of this invention may be used may contain various fillers such as tobacco, expanded tobacco, a variety of tobacco blend types, reconstituted tobacco materials, non-tobacco filler materials and combinations thereof. The paper wrappers of this invention may be made from flax or other cellulosic fibers, such as wood pulp or esparto, and an inorganic filler, typically calcium carbonate, with a loading of between about 20 percent by weight and about 40 percent by weight. Other suitable conventional mineral fillers, or a combination of fillers, may be used such as the various phases of calcium or magnesium carbonates, or the like, along with hydroxides of magnesium or the like. Burn additives such as citrates, phosphates, succinates or the like may also be used in the paper wrappers. Cigarette papers in use cover a wide range in porosity and burn rate. The inherent porosity of the paper varies from about 2 to about 150 Coresta units. Papers with lower values for inherent porosity require less added fibrous cellulose in the banded region to control the burn rate than papers with higher values. Therefore simple experimentation will be required to adjust the level of slurry applied to the base paper based on the type of base paper used and the desired burn characteristics. Preferably, the base paper should have a basis weight of about 25 to about 30 g/m 2 ; the inherent porosity should be in the range from about 20 to about 60 Corresta units; the calcium carbonate concentration should be in the range from about 25 to about 37 percent; and the citrate concentration should in the range from about 0.5 to about 3 percent. A preferred base paper (referred to as "conventional cigarette wrapper") has the following characteristics unless specifically stated otherwise: basis weight of about 25 g/m 2 , inherent porosity in the range from about 25 to about 30 Corresta units, calcium carbonate concentration in the range from about 25 to about 30 percent and citrate concentration in the range from about 0.5 to about 3 percent. The addition of a microfibrillated fibrous cellulose to form regions or bands in the paper wrapper has been found to affect the burn rate of the resulting cigarette. A slurry of the microfibrillated fibrous cellulose is applied to the paper wrapper, in the desired locations and patterns, during or after the initial manufacturing of the base paper wrapper. If the slurry is applied during the initial manufacturing, this step should preferably be performed beyond the wet end of the base paper making apparatus. Any cellulose material capable of forming a suspension in a liquid which is sufficiently stable for coating or printing may be used. Preferably, the cellulose material is suspended in water, thus forming a stable slurry since cellulose is insoluble in water. The ability of the cellulosic material of the present invention to form a stable suspension is a unique feature of this invention. If the cellulosic material is not capable of forming a stable suspension in liquid then the cellulosic material will either "settle out" of solution or "dissolve" into solution. Excessive"settling" of the microfibrillated fibrous cellulose would destroy the potential to print or coat cellulose in the fibrous form onto a base paper web as disclosed in the present invention. It should be noted that the materials disclosed herein generally do require considerable agitation to maintain the suspension and are not permanently stable as is a solution or a true gel, but they are intermediate in character compared to those materials and to totally heterogeneous slurries. If the microfibrillated fibrous cellulose "settles out" of solution, then the microfibrillated fibrous cellulose will collect at the bottom of the mixing apparatus or will plug orifices of spray/application devices and thus would be incapable of being printed or coated onto a base paper web using conventional printing or coating techniques, which is a unique aspect of the present invention. Furthermore, even if this first printing/coating problem were surmounted then a second problem would still exist. This later problem is a result of the fact that adhesion of the microfibrillated fibrous cellulose to the base paper web would be difficult without the addition of a binding material to the fibrous cellulose. This is a result of the fact that a key feature of the present invention is that the microfibrillated fibrous celluloses disclosed herein are capable of bonding, with or without the addition of a binding material, to an underlying base paper web. Such bonding (generally hydrogen bonding) is possible because of the high surface area or the high degree of refining of the microfibrillated fibrous cellulose materials disclosed herein compared to that of conventional paper making fibers. Because of these characteristics they are inherently capable of hydrating extensively and thus are able to form more stable suspensions in water than are conventional paper making fibers. The ability of the cellulose materials contemplated by this invention to hydrate extensively is believed to be related to the increase in surface area of cellulose when cellulose fibers undergo refining or other processes. Refinement creates a high degree of fibrillation and/or exposes microfibrils along the cellulose fiber and thus results in an increase in surface area. It is believed that this increase in surface area creates more sites for hydration of the fibers in the slurry or suspension and thus increases the swelling of the fibers which augments the stabilization of the slurry or suspension and thus allows the fibrous cellulose to adhere to an underlying base paper web. The adhesion of the refined fibrous cellulose to an underlying base paper web allows regions of burn rate altering material to be formed on a smoking article wrapper. A desirable feature of this burn altering region is that it does not include any material that is foreign to the base paper web: it only includes fibrous cellulose with or without binder. If the microfibrillated fibrous cellulose material does form a sufficiently stable suspension in liquid (i.e., does not "settle out" rapidly) then the suspension will be able to be coated or printed on to a base paper web and form regions of microfibrillated fibrous cellulose capable of altering and tailoring the burn rate of a smoking article. Because of the increase in surface area of refined cellulose materials there are more sites for hydrogen bonding to take place, and thus more sites for adhesion to occur to an underlying base paper web without or with minimal need for a binder. In summary, any new or novel microfibrillated fibrous cellulosic material that exhibits the properties discussed herein is capable of being incorporated into the smoking article of this invention. Homogenization of the cellulosic material prior to slurry make-up has been found to enhance the rheological properties of the slurry and therefore allows for a greater flexibility in slurry application techniques. Binders which may be used with the cellulosic material are carboxymethyl cellulose (CMC), hydroxypropyl cellulose, starch, guar, or various other polysaccharide hinders or the like. Preferably, the binder is CMC or hydroxypropyl cellulose. A slurry of the cellulosic material is made by first mixing the cellulose with water. The concentration of solid added to the water is between about 0.5 wt.% and about 10 wt.%, depending upon the specific type of cellulosic material. The desired concentration of solid cellulosic material which should be added to the water is also dependant upon the particular slurry application process used, as would be expected to one of ordinary skill in the art. The addition of a binder material to the slurry causes the slurry to exhibit improved rheological properties and therefore allows for a greater range of application techniques to be employed, such as conventional paper coating or printing techniques, i.e., gravure or flexigraphic coating, or other suitable coating or printing techniques. If the cellulosic material was not coprocessed with a binder during its manufacturing process, then binder can be added to the slurry. If the cellulosic material was co-processed with a binder during manufacture adding binder to the slurry may not be necessary to achieve the desired rheological properties for application of the slurry to the base paper web. The total amount of binder present in the slurry should be in the range from about 0.1 % to about 10 %, by weight. Preferably, the amount of binder present should be in the range from about 0.5 % to about 2 %, by weight. The binder may be omitted from the slurry for some cellulosic materials, if desired, and the cellulosic slurry can then be applied to the paper by techniques such as a spraying operation or extrusion-type process such as those used in the application of hot melt materials. Although the application options are more limited when the binder is omitted from the cellulosic slurry, the advantages to omitting it are that the taste of the smoking article may be improved and that one less processing step is required for fabrication of the smoking article wrapper. After the cellulosic slurry is formed, either with or without binder, it is then applied to the base paper web by the processes discusses herein. After the slurry is applied to the base paper web, the slurry can be dried using a drum dryer or infrared heater, or the like, as in conventional paper manufacturing. Typically between about 10 g/m 2 and about 200 g/m 2 wet weight of the cellulosic slurry is applied to the paper to result in dry weight of cellulosic material of between about 0.5 g/m 2 and about 10 g/m 2 . The preferred wet weight is dependant upon the particular type and concentration of cellulosic slurry employed. The cellulosic slurry may be applied to form bands at any desired interval and width depending on the particular desired burn control rate. Preferably, bands are applied at intervals of about 10 mm to about 25 mm. The width of the band may be varied depending on the type of cigarette and paper used in addition to the type and level of slurry applied. Preferably the width of the band is about 5 mm to about 10 mm.

Claims: A paper wrapper for a smoking article comprising a paper base web having one or more regions of microfibrillated fibrous cellulose bonded to the paper base web, the said regions being provided by a microfibrillated fibrous cellulose suspension applied directly to the paper base web, the regions of fibrous cellulose adding between about 0.5 g/m 2 and about 10 g/m 2 dry weight on top of the base paper. A wrapper according to claim 1 wherein the regions of microfibrillated fibrous cellulose include a binder. A wrapper according to claim 2 wherein the binder is carboxymethyl cellulose, hydroxypropyl cellulose, starch or guar. A method for making a smoking article paper wrapper according to any preceding claim characterised by: a) advancing the base paper web along a travel path, and b) applying a stable suspension of microfibrillated cellulosic material in a liquid directly to the base paper web at a position on the path to form one or more regions of microfibrillated fibrous cellulose on the web, the regions of microfibrillated fibrous cellulose adding between about 0.5 g/m 2 and about 10 g/m 2 dry weight on top of the base paper. A method according to claim 4 wherein the stable suspension is a slurry of microfibrillated cellulosic material and water. A method according to claim 5 wherein the suspension contains from about 0.5 wt.% to about 10 wt.% microfibrillated cellulosic material. A method according to claim 5 or 6 wherein step b) comprises applying to the base paper web a suspension of microfibrillated cellulosic material, water and a binder. A method according to claim 7 wherein the binder is carboxymethyl cellulose, hydroxypropyl cellulose, starch or guar. A method according to claim 7 or 8 wherein the suspension contains from 0.1 wt.% to 10 wt.%, preferably from 0.5 wt.% to 2 wt.%, binder. A method according to any of claims 4 to 9 wherein the suspension is applied by coating, by printing, by a gravure roll, or by a rubber-covered grooved roll. A method according to any of claims 4 to 10 further comprising a preliminary step prior to step a) of manufacturing the base paper web with a paper making apparatus having a wet end, wherein the microfibrillated fibrous cellulose-applying position is located on-line and beyond the wet end of the paper making apparatus. A method according to any of claims 4 to 10 wherein the base paper web is manufactured by a paper making apparatus and the microfibrillated cellulosic material of step b) is applied off-line of the paper making apparatus. A smoking article comprising a tobacco filler and a paper wrapper according to any of claims 1 to 3.

Inventors: BALDWIN SHERYL D, GAUTAM NAVIN, HOUGHTON KENNETH S, ROGERS ROBERT M, RYDER JUDITH L, BALDWIN, SHERYL D., GAUTAM, NAVIN, HOUGHTON, KENNETH S., ROGERS, ROBERT M., RYDER, JUDITH L.
Applicants: PHILIP MORRIS PROD, PHILIP MORRIS PRODUCTS INC.
Application year: 1992
Main classification: A24D1
IPC codes: A24D1, A24B15, D21H27, D21H11