WO2003026808A1

WO2003026808A1 - Paper coated with band having thickness gradient

Info

Publication number: WO2003026808A1
Application number: PCT/US2002/029731
Authority: WO
Inventors: Michael Lee Watkins; Jimmy L. Lyons-Hart
Original assignee: Philip Morris Products Inc.
Priority date: 2001-09-21
Filing date: 2002-09-20
Publication date: 2003-04-03

Abstract

A method and apparatus provides a web of material that can be used to wrap the tobacco in the tobacco portion of a cigarette. The web of material has bands of add-on material across the web, with the bands of add-on material having a different permeability to air than the remainder of the web. The bands of add-on material have a gradient in thickness (A), and therefore permeability, across the width of each band. The banded web can be embodied in cigarette paper used to wrap the tobacco in the tobacco rod portion of a cigarette.

Description

PAPER COATED WITH BAND HAVING THICKNESS GRADIENT

Field of the Invention

The present invention relates to methods and apparatus for applying a predetermined pattern of add-on material to a base web, preferably in the form of stripes, and more particularly, to methods and apparatus for producing cigarette papers having banded regions of additional material in a desired pattern to enhance burn characteristics along the length of the cigarette.

Background of the Invention

Techniques have been developed for printing or coating paper webs such as cigarette papers, with patterns of additional material, such as bands of material that create regions having different permeability. These prior techniques have included printing with gravure presses, blade coating, roller coating, silkscreening and stenciling.

In related, commonly assigned U.S. Patent No. 5,997,691, a method and apparatus for the production of a web having uniform banded regions of add-on material is disclosed. The disclosed method includes the steps of establishing a first slurry, and preparing a base web by laying the first slurry into a sheet form while moving the base web sheet along a first path. The method further comprises the steps of preparing a second slurry and repetitively discharging the second slurry so as to establish stripes upon the base web.

Summary of the Invention

A method and apparatus for achieving enhanced burn characteristics along the length of a cigarette according to an embodiment of the invention includes the production of the cigarette paper with banded regions having gradients in permeability across the banded regions effective to improve burn characteristics along the length of the tobacco rod of a cigarette. The gradient in permeability across the banded regions can be configured to alleviate the possibility of self- extinguishment as the burning portion or coal of the cigarette reaches the banded region. According to aspects of another embodiment of the invention, the banded regions along the cigarette paper can be spaced from each other at a frequency effective to improve burn characteristics of the tobacco rod wrapped by the cigarette paper.

Brief Description of the Drawing Figures

Various advantages and characteristics of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings in which like reference characters refer to like parts throughout, and in which:

Fig. 1 illustrates an optical image of a burning cigarette having banded regions of relatively low permeability.

Fig. 2 is a finite element model of a burning cigarette used to analyze characteristics of the cigarette along its length.

Fig. 3 illustrates an arrangement of thermocouples and infrared measurement equipment used in analyzing the combustion of a cigarette.

Fig. 4 illustrates an arrangement of thermocouples relative to banded regions on the cigarette paper of a burning cigarette. Fig. 5 illustrates a thermocouple arrangement on a cigarette having banded regions of different relative permeability.

Fig. 6 illustrates a burning region of a cigarette at different locations along the cigarette relative to a banded region of relatively low permeability.

Fig. 7 illustrates variations in combustion products along a banded cigarette.

Fig. 8 illustrates coal velocity or the velocity of a burning portion of a cigarette relative to position along the cigarette. Fig. 9 illustrates relative coal velocity in a burning cigarette having banded and un-banded regions.

Fig. 10 illustrates the cross-sectional area of a burning portion of a cigarette at different positions along the cigarette. Fig. 11 illustrates the relative radiant flux from a burning portion of a cigarette at different positions along the cigarette.

Fig. 12 illustrates the relative radiated power from a burning portion of cigarette at different positions along the cigarette.

Fig. 13 illustrates 3 examples of bands on a cigarette having different permeability/basis weight profiles.

Fig. 14A illustrates a slotted belt for use in a moving orifice type device for laying bands of add-on material having gradients in permeability across the bands.

Fig. 14B illustrates an individual asymmetrical slot in the belt of Fig. 14A. Fig. 15 illustrates a perspective of a paper making machine constructed in accordance with an embodiment of the invention, many of the details being described in detail in commonly assigned U.S. Patent No. 5,997,691, which is incorporated herein in its entirety by reference.

Fig. 16 illustrates a slotted belt similar to that shown in Fig. 14A, showing the direction of travel of a base web and a band of add-on material.

Fig. 17 illustrates a slotted belt similar to that shown in Fig. 14A, showing another direction of travel of a base web and a band of add-on material.

Detailed Description of the Invention

A cigarette paper used to wrap the tobacco in the tobacco rod of a cigarette can be provided with banded regions having relatively low permeability in order to reduce the thermal energy transmitted to an ignitable substrate material. An example of a method and apparatus for producing such banded cigarette paper is described in a commonly assigned U.S. Patent No. 5,997,691, which is incorporated herein in its entirety by reference.

Steep gradients in permeability along the length of the cigarette rod can contribute to conditions and mechanisms including uneven combustion that can make self-extinguishment of the cigarette more likely. The self-extinguishment can occur when the combustion rate is slowed down such as upon entering a banded region having lower permeability to air. For example, when the coal, or burning portion of a tobacco rod transitions from a non-banded region of cigarette paper, with relatively- high permeability, to the banded region of cigarette paper, with relatively low permeability, the smoldering combustion of the tobacco that occurs between puffs can decrease to the point that the cigarette may self-extinguish.

Referring to Fig. 15, a preferred embodiment of the present invention comprises a cigarette paper making machine 2, which preferably includes a head box 4 operatively located at one end of a Fourdrinier wire 6, a source of feed stock slurry such as a run tank 8 in communication with the head box 4, and a moving orifice applicator 10 in operative communication with another source of slurry such as a day tank 12.

The head box 4 can be one typically utilized in the paper making industry for laying down cellulosic pulp upon the Fourdrinier wire 6. In the usual context, the head box 4 is communicated to the run tank 8 through a plurality of conduits 14. Preferably, the feed stock from the run tank 8 is a refined cellulosic pulp such as a refined flax or wood pulp as is the common practice in the cigarette paper making industry.

The Fourdrinier wire 6 carries the laid slurry pulp from the head box 4 along a path in the general direction of arrow 16 in Fig. 15, whereupon water is allowed to drain from the pulp through the wire 6 by the influence of gravity and at some locations with the assistance of vacuum boxes 18 at various locations along the Fourdrinier wire 6 as is the established practice in the art of cigarette paper making. At some point along the Fourdrinier wire 6, sufficient water is removed from the base web pulp to establish what is commonly referred to as a dry line 20 where the texture of the slurry transforms from one of a glossy, watery appearance to a surface appearance more approximating that of the finished base web (but in a wetted condition). At and about the dry line 20, the moisture content of the pulp material is approximately 85 to 90%, which may vary depending upon operating conditions and the like.

Downstream of the dry line 20, the base web 22 separates from the Fourdrinier wire 6 at a couch roll 24. From there, the Fourdrinier wire 6 continues on the return loop of its endless path. Beyond the couch roll 24, the base web 22 continues on through the remainder of the paper making system which further dries and presses the base web 22 and surface conditions it to a desired final moisture content and texture. Such drying apparatus are well known in the art of paper making and may include drying felts 26 and the like.

The moving orifice applicator 10 preferably comprises an elongate chamber box 30 for establishing a reservoir of add-on slurry in an oblique relation across the path of the Fourdrinier wire 6. The moving orifice applicator also includes an endless perforated steel belt 200, whose pathway is directed about a drive wheel 34, a guide wheel 36 at the apex of the moving orifice applicator 10 and a follower wheel 38 at the opposite end of the chamber box 30 from the drive wheel 34. The endless belt 200 is directed through a bottom portion of the chamber box 30 and subsequently through a cleaning box 42 as it exits the chamber box 30, moves toward the drive wheel 34 and continues along the remainder of its circumlocution. As each slotted orifice 202 (Fig. 14B) of the belt 200 passes through the bottom portion of the chamber box 30, the orifice 202 is communicated with the reservoir of slurry established in the chamber box 30. At such time, a stream 40 of slurry discharges from the orifice 202 as the orifice 202 traverses the length of the chamber box 30. The discharge stream 40 impinges upon the base web 22 passing beneath the moving orifice 202 so as to create a stripe of additional (add-on) material upon the base web 22. The operational speed of the belt 200 may be varied from one layout to another, but in the preferred embodiment, the belt is driven at 1500 or more feet per minute when the Fourdrinier wire is moving at approximately 800 or more feet per minute (e.g., 1000 to 3000 feet/minute) and the chamber box 30 is oriented at an angle relative to the direction of movement of the base web 22. The spacing of the orifices 202 along the belt 200 and the operational speed of the belt 200 is selected such that a plurality of streams 40, 40' emanate from beneath the chamber box 30 during operation of the moving orifice application, simultaneously. Because of the oblique orientation of the moving orifice applicator relative to the path 16 of the base web 22 and the relative speeds of the Fourdrinier wire 6 and the endless belt 200, each stream 40 of add-on material will create a stripe of add-on material upon the base web 22. By adjusting the speed of the belt and angle of the applicator 10, the moving orifice applicator 10 can repetitively generate stripes of add-on material that are oriented normal to a longitudinal edge of the base web 22. If desired, the angle and/or relative speeds may be altered to produce stripes which are angled obliquely to the edge of the base web 22.

For a particular orifice 202, after it exits from the chamber box 30, the adjacent portions of the belt 200 about the orifice 202 are cleansed of entrained addon slurry at the cleaning station 42 and the orifice then proceeds along the circuit of the endless belt 200 to reenter the chamber box 30 to repeat an application of a stripe upon the base web 22.

Preferably, a vacuum box 19 is located coextensively beneath the chamber box 30 of the moving orifice applicator 10 so as to provide local support for the Fourdrinier wire 6 and facilitate the bonding/integration of the add-on slurry with the base web 22. The chamber box 30 receives add-on slurry from the day tank 12 at spaced locations along the chamber box 30. Uniform pressure can be maintained along the length of the chamber box 30 by the interaction of a flow distribution system 60, a pressure monitoring system 62 and a programmable logic controller 64 such that the pumping action of the belt 22 and other flow disturbances along the length of the chamber box 30 are compensated locally and continuously to achieve the desired uniformity of pressure throughout the chamber box 30. A main circulation pump 15 delivers slurry from the day tank 12 to the flow distribution system 60. Details regarding how the controller initiates and maintains uniform pressure along the chamber box 30 can be found in commonly assigned U.S. Patent No. 5,997,691, the disclosure of which is hereby incorporated by reference.

Fig. 2 represents a finite element model used to simulate the coal behavior in the vicinity of the band. In one aspect of the invention, the oxygen concentration in the vicinity of the coal can be mediated by reducing the permeability gradient at the back end of the band, which is the end of the band toward the filter.

The mechanism by which banded cigarette paper reduces ignition propensity is to inhibit oxygen diffusion to the tobacco rod, and reduce the power available for igniting a substrate during smoldering combustion. Oxygen diffusion through a formed coal or burning portion of a cigarette is low, relative to the cigarette paper. Oxygen diffusion is also low in the banded regions relative to the un-banded regions of the cigarette paper. These relative diffusion rates hold for smolder and puffing. During puffing, air flow from behind the band is enhanced, relative to smolder, due to the increased pressure gradients.

Figs. 3-5 illustrate a technique used to obtain thermal data associated with burning cigarettes. Fig. 6 illustrates the behavior of a smoldering coal or burning portion of a tobacco rod in a cigarette as it approaches a band on the cigarette paper wrapping the tobacco rod. The infrared images indicate the total thermal energy being released by the coal. As the coal power output increases so does the area depicted in the images. In image A of Fig. 6, the coal is propagating between two bands. As the coal enters the band, which has a permeability to air that is significantly lower than the un-banded region, as illustrated at image B, the rate of combustion is reduced and the heat generated is rate limited by oxygen diffusions. Data obtained by Magnetic Resonance Imaging (MRI) has shown that during the period of lower temperature such as in image B, there can be a build up of volatile combustion byproducts, in the rod. However, in the middle of the band, as illustrated at image C, the rate of combustion is increased and the coal begins to grow in volume. It has also been observed that during this phase of coal development any build up of volatile byproducts can act as additional sources of fuel for combustion, resulting in flare-up. At the point illustrated by image C in Fig. 6, the diffusion of oxygen is assisted by the convective flow resulting from the thermal gradients in the tobacco rod and the proximity of the coal to the non-banded region of the cigarette paper. Before the coal has left the band, as illustrated at image D in Fig. 6, it has grown back to the size it had between bands. Fig. 7 illustrates the concentration of hydrogen containing species associated with reduced temperatures. Figs. 8-12 also provide quantitative data of the same behavior. The coal velocity, size, flux, and power are all at a minimum as the char line, or edge of burning cigarette paper, enters a band. In some cases, the available oxygen can even fall below a rate necessary to sustain the coal, and the cigarette is extinguished. The minimums in coal velocity, size, flux and power are generally observed to be spatially out of phase with the band by approximately half a band width. Narrower bands result in smaller power reductions, while wider bands can increase the probability of extinguishment. Figs. 8, and 10-12 illustrate comparisons for banded and un-banded cigarette paper having a higher permeability to air - with base paper measured at 85 Coresta Units (CU); and having a lower permeability to air - with base paper measured at 33 CU.

According to aspects of an embodiment of the invention, each of the banded regions on the cigarette paper that wraps a tobacco rod in a cigarette can be provided with a gradient in permeability to reduce the sharp change in permeability that would otherwise occur at a transition between banded and un-banded regions. These gradients in permeability improve the uniformity of combustion along the length of the cigarette rod, and reduce the likelihood of self-extinguishment of the cigarette. As illustrated in Fig. 13, the permeability basis weight can be provided with a higher amount at a leading edge, a trailing edge, or some combination of the two along a band on a cigarette. The control of a gradient in permeability across a banded region can be used to control oxygen diffusion such that it would be possible to tailor the combustion rate and reduce sharp changes in coal dynamics that are associated with self-extinguishment. The banded regions can also at the same time provide a desired reduction in the total thermal input to ignitable substrates.

Band permeability gradients can be created using techniques used to create the banded cigarette paper. These include, but are not limited to, moving orifice devices (MOD) and gravure printing techniques. In the case of a MOD application, the orifices through the belt are provided with an asymmetrical cross section that would result in a higher application of stock along an edge portion (or other selected position) of the band. The details of the flow dynamics would determine the details of the required orifice geometry to achieve the desired permeability gradient. As illustrated in Figs. 14A and 14B, a slotted belt 200 can be provided with a plurality of asymmetrical orifices 202 along its centerline CL. The shape of the orifices results in a greater amount of the add-on material that passes through the belt being provided to one side of the centerline. As a result of this configuration, the bands of add-on material that are formed across the direction of travel of the cigarette paper will have a gradient in thickness across at least a portion of each band, and therefore a gradient in permeability. Although the illustrated orifices have a larger portion above the centerline of the slotted belt, the asymmetry of an orifice can provide a larger portion above the centerline, below the centerline, or even at the centerline. The resultant permeability/basis weight in a direction transverse to the band of addon material is illustrated for each of these possible asymmetries by the lines in Fig. 13. In the case of gravure printing the geometry of the transfer roller would be modified appropriately.

Referring again to Figs. 6 and 10, the coal is smallest in volume at the edge of a banded region that is first approached by the coal ("the first-approach edge"). Accordingly, the first-approach edge of a uniform banded region presents a region of greater chance for self extinguishment. To counteract such tendencies, in a practice of the present invention, it is preferred to apply a lesser amount of add-on material along the first-approached edge portion so that minimization of the coal is lessened. Accordingly a permeability gradient such as line A in Fig. 13 is preferred in alleviating self extinguishment. In order to maintain effectiveness of the band in reducing ignition propensity, the paper may be further modified to increase the overall band width so as to maintain sufficiently low heat transfer to an ignitable substrate to achieve desired reduced ignition properties.

The band permeability/add-on weight gradient can be utilized to help reach a desired balance between cigarette design attributes that contribute to reduction in ignition propensity and those that exacerbate self-extinguishment. The gradient can be configured to adjust other or additional burn rate parameters such as puff count, coal retention, side stream smoke output and static burn rate, for example.

According to aspects of another embodiment of the invention, the spatial frequency of the bands can be increased and the band width can be decreased, with the result that the heat output from the coal will be reduced while observed sharp changes in combustion rates etc. would be reduced, thereby reducing the likelihood of self-extinguishment. Various combinations of spatial frequencies or band spacings can be used to achieve the desired reduction in the permeability gradient at the edge of each band. Referring to Figure 16, the asymmetric portion 203 of the orifice 202 may be oriented relative to the CL of the band (which moves left to right in the Figure) and the direction 16 of the base web such that an edge portion 41 of the band 40, has a lesser add-on rate than the remainder of the band 40. In another orientation, shown in Figure 17, an asymmetric portion 203 of the orifice 202 may be aligned with the cross-direction of the bands 40 so as to create a central region 42 having a greater add-on rate than edge portions 41'.

While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modification can be made, and equivalents employed, without departing from the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method of manufacturing a web having an applied pattern of add-on material, comprising the steps of: moving a base web along a first path; preparing a slurry of add-on material; repetitively discharging the add-on slurry upon the moving sheet of base web by establishing a reservoir of the add-on slurry across the first path and moving a belt having at least one asymmetric orifice along an endless path, said belt moving step including the step of moving said belt along a first portion of said endless path where said at least one asymmetric orifice is communicated with said reservoir so as to discharge said add-on slurry from said reservoir through said at least one asymmetric orifice onto said base web as said at least one asymmetric orifice traverses said first path portion to form at least one band of add-on material having a gradient in thickness across a width of the at least one band.

2. The method according to claim 1, wherein the base web is cigarette paper, and said at least one band of add-on material has a lower permeability to air than unhanded portions of said cigarette paper, said step of discharging the add-on slurry through said at least one asymmetric orifice resulting in a greater thickness of said add-on material being deposited on said base web over a first portion of each of said at least one bands, and a lesser thickness of said add-on material being deposited on said base web over a second portion of each of said at least one bands.

3. The method according to claim 2, wherein said first portions of each of said at least one bands are located along a trailing edge of each of said at least one bands in the direction of movement of said base web, and said second portions of each of said at least one bands are located along a leading edge of each of said at least one bands in the direction of movement of said base web.

4. The method according to claim 2, wherein said first portions of each of said at least one bands are located along a leading edge of each of said at least one bands in the direction of movement of said base web, and said second portions of each of said at least one bands are located along a trailing edge of each of said at least one bands in the direction of movement of said base web.

5. The method according to claim 2, wherein said first portions of each of said at least one bands are located between a trailing edge of each of said at least one bands in the direction of movement of said base web and a leading edge of each of said at least one bands in the direction of movement of said base web, and said second portions of each of said at least one bands are located at the trailing edge and the leading edge of each of said at least one bands.

6. The method according to claim 2, wherein said second portions of each of said at least one bands are located between a trailing edge of each of said at least one bands in the direction of movement of said base web and a leading edge of each of said at least one bands in the direction of movement of said base web, and said first portions of each of said at least one bands are located at the trailing edge and the leading edge of each of said at least one bands.

7. The method according to claim 2, wherein the base web has a permeability to air measured at approximately 85 Coresta Units.

8. The method according to claim 2, wherein the base web has a permeability to air measured at approximately 33 Coresta Units.