Patent Publication Number: US-8973589-B2

Title: Embossing techniques

Description:
CLAIM FOR PRIORITY 
     This application is a National Stage Entry entitled to and hereby claims priority under 35 U.S.C. §§365 and 371 to corresponding PCT Application No. PCT/EP2011/055781, filed Apr. 13, 2011, which in turn claims priority to GB Application No. 1006725.4, filed Apr. 22, 2010. The entire contents of the aforementioned applications are herein expressly incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates to improvements in embossing techniques. In particular, the invention relates to embossing techniques for smoking articles. 
     BACKGROUND TO THE INVENTION 
     As used herein, the term “smoking article” includes smokeable products such as cigarettes, cigars and cigarillos whether based on tobacco, tobacco derivatives, expanded tobacco, reconstituted tobacco or tobacco substitutes and also heat-not-burn products. 
     Conventional filtered cigarettes generally comprise a rod of tobacco wrapped in a cigarette paper and a filter plug wrapped in a plug wrap. The filter plug and tobacco rod are connected using a tipping paper. The amount of smoke drawn through the filter depends on various factors, for example the air permeability of the cigarette paper, plug wrap and/or tipping paper. For instance, a cigarette paper of a high air permeability will permit airflow through the cigarette paper and will dilute the smoke more than a cigarette paper of lower air permeability. The air permeability of the cigarette paper used in cigarette manufacture is therefore a factor in controlling, at least, the smoke dilution of the cigarette. 
     One method of modifying the air permeability of paper is through an embossing process, as discussed, for example, in GB 1524211. The embossing process generally comprises exerting pressure at localised areas on the surface of the paper in order to open or stretch the fibrous structure of the paper to create indentations or holes in the paper. This has the effect of modifying the air permeability of the paper. Controlling the embossing process provides a means for controlling the air permeability of the paper. 
     Disadvantageously, the embossing process can cause a reduction in the tensile strength of the paper. This reduction in tensile strength can result in papers such as cigarette papers, plug wraps and tipping papers tearing as the paper is put under stress and/or strain during the cigarette and/or filter manufacturing process. This is undesirable and has the effect of limiting the rate of production. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention there is provided an embossing apparatus for applying an embossing pattern to a wrapper for a smoking article, the embossing apparatus configured so as to act to at least partially minimise the reduction, in at least one direction, in the tensile strength of the wrapper resulting from the application of said embossing pattern. In this sense, partially minimised may be taken to mean that the reduction in tensile strength caused by embossing the wrapper may be offset though configuration of the embossing apparatus for that purpose. 
     Advantageously, minimising the degree to which tensile strength is reduced by the embossing process may avoid or mitigate some of the problems associated with reduced tensile strength. In particular, improving the tensile strength of the wrapper in this manner may mitigate the problem of tearing of the wrapper, which can reduce production. 
     Typically, the embossing pattern is applied so as to increase the diffusivity and/or permeability of said wrapper and wherein the embossing pattern is selected such that for a given increase in diffusivity and/or permeability, the embossing pattern minimises an embossing stress and/or strain placed on the wrapper, during application of the embossing pattern, in at least one direction. 
     Variations in the stress and/or strain on the wrapper can alter the effects of the embossing process. For example, deeper embossing, by applying a greater embossing force, can cause larger holes/indentations which affect the diffusivity and/or permeability of the wrapper. It is a further advantage of the present invention that a desired amount of diffusivity and/or permeability may be better controlled, having better consistency, by selecting an embossing pattern which minimises the embossing stress and/or strain placed on the paper. 
     Preferably, application of the embossing pattern is arranged to result in an embossed wrapper having different strength characteristics in different directions. 
     Preferably, the embossing apparatus comprises an embossing roller for applying the embossing to the wrapper; and means for maintaining the embossing roller at a predetermined distance from said wrapper so as to limit the depth of the embossing. Advantageously, maintaining the predetermined distance is one method for minimising the stress placed on the wrapper as the embossing roller applies the embossing pattern to the wrapper. 
     In a preferred embodiment, the embossing apparatus comprises at least two embossing rollers for applying the embossing to the wrapper running in a longitudinal direction between the at least two rollers, wherein the maintaining means maintains a minimum distance between circumferential surfaces of the at least two embossing rollers. 
     According to another aspect of the present invention there is provided an embossed wrapper for a smoking article, wherein the embossing is applied in a pattern selected such that for a given increase in diffusivity and/or permeability resulting from the embossing, the embossed pattern acts to at least partially minimise the reduction, in at least one direction, in the tensile strength of the wrapper resulting from the application of said embossing. 
     Preferably, the embossed pattern is selected to minimise weakness lines running through an embossed region of the wrapper, in a least one direction. Weakness lines are introduced during the embossing process as the fibrous structure of the wrapper material, typically cigarette paper, is opened and stretched. It is an advantage of selecting an appropriate embossed pattern that the extent to which the weakness lines cause a reduction in tensile strength can be minimised. 
     Preferably, the embossed pattern comprises an embossed region and a non-embossed region, and a leading edge between the embossed region and the non-embossed region, the leading edge being arranged to be non-perpendicular to a longitudinal direction of the wrapper. 
     Optionally, the embossed pattern comprises a spiral or helical pattern when the wrapper is wrapped around the smoking article. This arrangement of embossing pattern has further advantages in that the spiral or helical pattern is a mechanism for encouraging the smoking article to self-extinguish in the absence of being drawn. This is a particularly an advantage in relation to Low Ignition Propensity smoking articles. 
     In a preferred embodiment, the embossed pattern of the wrapper comprises indentations which have no substantially perpendicular edges with respect to a longitudinal direction of the wrapper. Optionally, the embossed pattern of the wrapper comprises indentations of rhomboidal shape which have no substantially perpendicular edges with respect to a longitudinal direction of the wrapper. In one optional embodiment, the embossed pattern is formed from an array of indentations in which transversally adjacent indentations are longitudinally offset from each other. 
     According to another aspect of the present invention, there is provided an embossing roller for applying an embossing pattern to a wrapper for a smoking article, wherein the embossing roller comprises a plurality of embossing protrusions arranged such that for a given increase in diffusivity and/or permeability of a wrapper embossed using said roller, the embossed protrusions act to at least partially minimise the reduction, in at least one direction, in the tensile strength of the wrapper resulting from the application of said embossing. 
     Preferably, the embossing protrusions are arranged such that applying the embossing roller to the wrapper results in a wrapper as described above. 
     The above embossing patterns advantageously reduce the strain and/or stress placed on the wrapper when the wrapper and/or smoking article is being manufactured. 
     According to another aspect of the present invention, there is provided a method of embossing a wrapper for a smoking article, the method comprising applying an embossing pattern to the wrapper so as to act to at least partially minimise the reduction, in at least one direction, in the tensile strength of the wrapper resulting from the application of said embossing pattern. 
     In a preferred embodiment the applying step comprises applying an embossing roller to the wrapper, the method further comprising maintaining the embossing roller at a predetermined distance from said wrapper so as to limit the depth of the embossing. 
     Preferably, running a web of wrapper material, in a longitudinal direction, through at least two embossing rollers, and the maintaining step comprises using a coaxial cammed movement limiter and a mechanical stop to prevent radial movement of at least one of the rollers in at least one direction. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Embodiments of the invention will now be described by way of example with reference to accompanying figures, in which: 
         FIG. 1  is a perspective illustration of a smoking article having a paper wrapper with an embossed region and a non-embossed region; 
         FIG. 2  is an enlarged view of a section of a wrapper having an embossed pattern for an example arrangement/formation of embossing protrusions; 
         FIG. 3  is a schematic illustration of an embossing unit for manufacturing an embossed wrapper; 
         FIG. 4  is an illustration of a wrapper having a plurality of embossed and non-embossed regions in a banded formation; 
         FIG. 5   a  is a front elevation of an embossing drive roller and a contrast roller showing a non-embossed region of the embossing drive roller in communication with the contrast roller; 
         FIG. 5   b  is the front elevation of  FIG. 5   a  showing an embossed region of the embossing drive roller in communication with the contrast roller; 
         FIG. 6   a  is a side elevation of an embossing drive roller, of one embodiment of the present invention, having a cammed movement limiter for maintaining a minimum distance between the drive roller and contrast roller; 
         FIG. 6   b  a front elevation of the embossing drive roller of  FIG. 6   a;    
         FIG. 7  is an illustration of a wrapper having an embossed region which is arranged in a spiral formation when wrapped around a smoking article; 
         FIGS. 8   a  and  8   b  are example embossing patterns according to embodiments of the present invention; and 
         FIG. 9  is an illustration of a wrapper showing longitudinal non-embossed strips. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A smoking article  100  is shown in  FIG. 1 . The smoking article  100  is discussed below in the context of a cigarette  100  comprising a substantially cylindrical cellulose acetate filter  200  and an axially aligned substantially cylindrical smokable material rod  300  connected to the filter  200  by a sheet of overlying tipping paper  400 . However, the invention is not confined to cigarettes. It is applicable to other types of smoking article, including those referred to above. 
     Typically, the smokable material rod  300  comprises a substantially cylindrical core of tobacco material  310  wrapped in a wrapper  320 . The wrapper  320  provides a circumferential boundary for the cylindrical core  310 , as is shown in  FIG. 1 , with the end faces of the core  310  being left open in a conventional manner. The wrapper  320  comprises a base paper such as a cigarette paper. 
     The permeability of the wrapper  320  may be inherently low so as to substantially limit the permeation of external air through the wrapper  320  into the burning tobacco core  310 . One reason for restricting the flow of external air to the burning tobacco core may be to cause or encourage the cigarette to self-extinguish if it is not regularly drawn upon by the smoker. Smoking articles displaying this characteristic are often referred to as Low Ignition Propensity (LIP) smoking articles. National regulation often requires that low ignition propensity smoking articles exhibit full length burn percentages of less than a particular threshold, for example 25% of the tobacco rod, when tested in accordance with ASTM E2187-04 or ASTM E2187-09, which are standards against which the ignition propensity properties of smoking articles can be assessed. In one embodiment, the permeability of the wrapper  320  may be less than 30 Coresta and preferably is less than 20 Coresta. This provides the cigarette  100  with a low ignition propensity to meet industry standards defined by ASTM E2187-04 and ASTM E2187-09. 
     The properties of the wrapper  320  can be improved by forming an embossed region  321  in the wrapper  320 , as shown in  FIG. 1 . The remaining area of the wrapper is left non-embossed, and therefore constitutes a non-embossed region  322 . 
     The embossed region  321  of the wrapper  320  has a higher air permeability than the non-embossed region  322 . This allows a greater amount of external air to pass through the embossed region  321  of the wrapper  320  into the tobacco core  310 , thereby increasing smoke dilution during puffing. As such, the permeability of the embossed region  321  will differ from that of the non-embossed region  322 . Selection of the required permeability value of the embossed region may be made in dependence on factors including the permeability of the non-embossed region  322  and the relative area of the embossed region  321 . 
     In addition to having higher air permeability, the embossed region  321  of the wrapper  320  also has significantly higher gas diffusivity than the non-embossed region  322 . For example the gas diffusivity of the embossed region  321  may be at least five, preferably six or seven times greater than the gas diffusivity of the non-embossed region  322 . The higher gas diffusivity of the embossed region  321  of the wrapper  320  allows smoke components such as CO and nitrogen oxide to diffuse out of the burning tobacco rod  300  through the embossed region  321  of the wrapper  320 . As such, smoke components which would otherwise be drawn into the filter  200  during puffing are diffused out of the cigarette before reaching the filter  300  due to the higher gas diffusivity of the embossed region  321 . Furthermore, the additional oxygen diffusing through the cigarette paper toward the burning tobacco due to the higher diffusivity of the embossed region  321  increases the burn rate and, therefore, reduces the puff number of the cigarette  100 . 
     The combination of the embossed region  321  and the non-embossed region  322  provides a cigarette  100  which may conform to recognized LIP standards as above, and which provides a smoking experience arranged to have a particular puff number. While this is one reason for manufacturing a cigarette paper having an embossed region  321  and non-embossed region  322 , a person skilled in the art will appreciate that there may be other reasons, and that the present invention relates generally to embossing processes irrespective of the application for the embossed material. 
     As described above, the embossing process can cause a reduction in the tensile strength of the wrapper because creating indentations or holes results in lines of weakness  240  through the embossed region, as shown in  FIG. 2 . The lines of weakness  240 , running through the centre of the rows on indentations are, in the illustrated example, perpendicular to the longitudinal direction of the paper, shown by arrow X. These lines of weakness  240  occur as a result of the stretching of the paper, in the longitudinal direction X, while the embossing pattern is being formed, in particular as a result of the stretching caused by each indentation. These lines of weakness  240 , though the wrapper, reduce the tensile strength and this can cause ripping during the cigarette manufacturing process. 
     In addition, as described above, the wrapper  320  may have embossed and non-embossed regions,  321  and  322 , meaning that at least once as the wrapper  320  is being embossed there will be a change from a non-embossed region  322  to an embossed region  321 . This change corresponds to a leading edge or leading row  250  of the embossing pattern on the embossing roller  510 . As described in greater detail below, in relation to the embossing apparatus and process, a significant line of weakness may be caused at the leading edge/row of the embossing pattern. 
     An example embossing unit  500  is schematically illustrated in  FIG. 3 . The embossing unit  500  comprises an embossing drive roller  510  and one or more embossing contrast rollers  520 , which together emboss a web of base paper  320  as the paper web  320  moves between the embossing drive roller  510  and the embossing contrast roller(s)  520 . In this example, the width of the web of paper is approximately 26.5 mm, which is sufficient to wrap around the circumference of the tobacco rod  300  and provide a lap seam  330  for gluing the wrapper  320  in place around the rod  300 . The embossing rollers  510 ,  520  comprise an embossing pattern on their circumferential surface. The embossing pattern may comprise a plurality of embossing protrusions  260 . In one embodiment the embossing protrusions  260  comprise a plurality of protruding pyramids with a base width B 1  of approximately 0.3 mm and a height B 2  of approximately 0.15 mm, as shown in  FIG. 2 , which are arranged in rows. 
     The circumferential surface of the embossing contrast roller(s)  520  are forced against the circumferential surface of the embossing drive roller  510 . In one embodiment, the force may be applied by a pneumatic system comprising a piston  530 . In an alternative embodiment, the embossing unit  500  may use a set of cams to control the relative positions of the embossing contrast rollers  520 . The force exerted on the paper web  320  between the embossing rollers  510 ,  520  is proportional to the air pressure exerted against the piston  530  in the pneumatic system. The air pressure on the piston  530  can be varied by a control unit  540  which is configured to increase or decrease the air pressure in the pneumatic system according to a set of control parameters, which may be predetermined or may be adaptively determined according to the results of the embossing process. In one embodiment, the diameter of the piston  530  is approximately 2.75 inches. However, in an alternative setup, the diameter of the piston  530  may be reduced to provide greater control over the embossing force applied to the paper  320  by the embossing rollers  510 ,  520 . The use of a smaller diameter piston  530  will result in a smaller increase in embossing force for a given increase in air pressure applied to the piston  530 . A corresponding effect will be provided for decreases in air pressure. A suitable alternative diameter for the piston  530  may be approximately 1 inch. 
     The embossing unit  500  may also comprise one or more drive rollers  550  configured to drive the paper web  320  through the embossing unit  500 , in addition to drive provided to the embossing drive roller  510 . In  FIG. 3 , a pair of such drive rollers  550  is provided in the paper path preceding the embossing rollers  510 ,  520 . In alternative examples, drive rollers  550  may be provided at other points in the paper web path, in addition to or in place of those illustrated in  FIG. 3 . 
     The embossing unit  500  further comprises an analysis unit  560  which is configured to analyse the properties of the paper web  320  after it has passed between the embossing rollers  510 ,  520 . The analysis unit  560  comprises one or more sensors  561  for collecting information about the structure of the embossed paper  320 . The collected information may, for example, include one or more of the air permeability of the paper  320  in the embossed  321  and non-embossed regions  322 , the thickness of the paper  320  in the embossed  321  and non-embossed regions  322  and the transmission of the paper  320  in the embossed  321  and non-embossed regions  322 . 
     As shown in  FIG. 3 , the analysis unit  560  is communicatively coupled to the control unit  540  to allow control signals to pass between the analysis unit  560  and the control unit  540 . This communication may take place by any known means, for example via a wireless communication link. In this way, the control unit  540  may receive information from the analysis unit  560  regarding the properties of the embossed paper  320  and may use the information to adjust the force being exerted against the paper  320  by the embossing rollers  510 ,  520 . The feedback mechanism provided by the above-described communication between the analysis unit  560  and the control unit  540  allows the embossing unit  500  to maintain embossing according to the control parameters being used. For example, the feedback mechanism may be used to maintain a particular value of air permeability in the embossed paper  320 . 
     The air permeability and gas diffusivity of the embossed region  321  of the paper  320  can be selected by varying the force applied to the paper  320  during the embossing process. As such, the force applied to the paper web  320  as it passes between the embossing rollers  510 ,  520  can be varied in dependence of the exact properties which are desired for the wrapper  320 . An example embossing force applied to the wrapper  320  by the embossing rollers  510 ,  520  is in the range of between 2 Kgf and 55 Kgf. The precise embossing forces will depend partly on parameters such as the thickness and inherent air permeability of the wrapper  320  being used. 
     In addition, the air permeability and gas diffusivity of the embossed region  321  of the paper  320  can be selected by varying the size and number of the embossing protrusions  260  as well as varying the coverage area of the embossing protrusions  260 . 
     As described above, the embossing process reduces the tensile strength of the paper  320 . Configuring a wrapper  320  to have embossed  321  and non-embossed  322  regions can add to this problem because applying an embossing drive roller  510  having embossed and non-embossed regions to the paper web  320  results in a variation in the pressure which is applied to the paper web  320 . This is particularly a problem for embossing wrappers  320  with bands or other patterns which extend transversally across the wrapper  320 , as shown in  FIG. 4 . 
     As the wrapper is passed longitudinally through the embossing drive roller  510 , a weakness is caused in the paper web  320  transversally at the start of each new embossed region. This is further explained with reference to  FIGS. 5   a  and  5   b , which shows an example arrangement for an embossing unit  500  having an embossing roller  510 , and a single contrast roller  520 , where the paper web  320  runs between these two rollers. As shown in  FIG. 5   a , a non-embossed portion of paper  322  sits between both rollers, at a non-embossed region  600  of the embossing drive roller  510 . In  FIG. 5   b , the rollers have rotated such that a leading edge/row  250  of the embossing protrusions  260 , at an embossed region  620  of the embossing drive roller  510 , is pressed against the paper web  320  to cause embossing of the paper web  320 . The embossing drive roller  510  rotates around its axis, causing a portion of its circumferential surface, containing embossing protrusions  260 , to press against a portion of the circumferential surface of the contrast roller  520 , through the paper web  320 . The embossing rollers  510 ,  520  continue to rotate such that when the embossing protrusions  260  are situated between the contrast roller and the embossing drive roller, as shown in  FIG. 5   b , the distance between the respective circumferential surfaces of the rollers  510 ,  520  expands in order to permit the additional height of the embossing protrusions  260  to pass between the rollers  510 ,  520 . 
     The embossing rollers  510 ,  520  rotate at a sufficiently high number of revolutions per minute such that the embossing drive roller  510  pulses against the embossing contrast roller  520 , or vice versa, as the portion of the circumferential surface of the embossing roller which contacts the paper web changes from an embossed region  620  to a non-embossed region  600 . This pulsing movement causes inertia as the circumferential surface of the embossing drive roller  510  moves closer and further away from circumferential surface of the contrast roller(s). This pulsing movement and inertia cause an increase in pressure on the paper web  320  as the leading edge  250  of the embossed region  620  is pressed against the paper web  320 , and this results in a deeper embossing indentation. As described above, this introduces a significant weakness line  240  in the paper web  320 , which can cause tearing of the paper web  320  during the cigarette manufacturing process. In addition, there is the further disadvantage of inconsistent embossing through the wrapper results in inconsistencies in the air permeability and diffusivity of the wrapper  320 . The example arrangement in  FIGS. 5   a  and  5   b  show the contrast roller  520  having no embossing pattern. However, the contrast roller(s)  520  may have thin longitudinal lines (not shown) of emboss pattern in order to assist drive to the paper web  320 . 
     According to embodiments of the invention, the pressure applied to the moving web is controlled by limiting the movement of the embossing drive roller  510  as it moves toward and away from the contrast roller(s)  520  (or vice versa), in order to limit or prevent the pulsing movement described above. This may be achieved by limiting the movement of either the embossing drive roller  510  and/or the contrast rollers  520 . This method stops the circumferential surfaces of the rollers  510 ,  520  from moving together in the non-embossed regions  600  of the embossing pattern which could occur as shown in  FIG. 5   a . In one embodiment, this method may employ the use of one or more cam stops or screw stops, also referred to as a cammed movement limiter. The embossing drive roller  510  is accordingly maintained at a predetermined distance from the paper web  320  so as to limit the depth of the embossing applied to the paper web  320 . 
     An example configuration of a suitable cammed movement limiter is shown in  FIGS. 6   a  and  6   b .  FIG. 6   a  shows a side elevation of an embossing drive roller  510  situated above at least one contrast roller  520 , with a paper web  320  running between the rollers  510 ,  520 .  FIG. 6   b  shows a front elevation of the embossing drive roller  510 . In one embodiment, the embossing drive roller  510  has a co-axial cammed movement limiter  700 , formed integrally with the embossing drive roller  510  or fixed by any suitable means to the embossing drive roller  510 . The embossing drive roller  510  is mounted to a roller drive unit  720  (partially shown in  FIG. 6   a ), which delivers the rotational drive for the embossing drive roller. The cammed movement limiter  700  is arranged to butt against a stop  740 , which is fixed to the roller drive unit or a housing  760  of the embossing drive roller  510 . The embossing drive roller  510  is prevented from moving in direction Y, beyond a predetermined minimum distance from the contrast rollers  520 , by the cammed movement limiter  700  abutting the stop  740 . This means that the non-embossed regions  600  of the circumferential surface of the embossing drive roller  510  are prevented from moving closer than the predetermined minimum distance from the contrast rollers  520 , alleviating the problem of the increase in pressure on the paper web  320  at the leading edge  250  of the embossed region  620 . 
     In addition or alternatively, another solution to the above problem of reduced tensile strength is to determine an embossing pattern which minimises the stress under which the paper web is placed. In one embodiment this is achieved by disrupting or altering the leading edge/row of the embossed pattern on the embossing drive roller  510 . In this sense, disrupting or altering the leading edge means changing the embossed region  620  from having a substantially perpendicular row of embossing protrusions  260  (as shown in  FIG. 2 ) to any other suitable configuration. 
     In one example, the embossing drive roller  510  has embossing protrusions  260  in a spiral or helical pattern. An embossing drive roller  510  with such a spiral or helical pattern would result in a cigarette wrapper  320 , as shown in  FIG. 7 . When such a cigarette wrapper  320  is wrapped around a smokable material rod, a band of embossing  321  is formed in the wrapper  320  which spirals around the circumference of the smokable material rod  300 . The spiral band  321  may extend along all or part of the length of the rod  300 . Selection of the length and width of the spiral band  321  may be made in dependence of the total length of the rod  300  and the properties of the wrapper  320  and smokable material  310 . This configuration means that there is no laterally or perpendicularly extending leading edge to the embossing  321 , and therefore the increase in pressure on the paper web  320  as the leading edge  250  of the embossed region  620  can be avoided. The configuration of the embossed region  321  of the wrapper  320  also means that when the cigarette rests against a surface, for example if a cigarette is dropped, a portion of the embossed region  321  of the wrapper  320  will rest against the surface. This limits the airflow through those blocked portions, which further reduces the air permeability of the cigarette wrapper  320  and further encourages the cigarette to self-extinguish. 
     A person skilled in the art will appreciate other formations for embossing protrusions  260  which may help mitigate the problems of reduced tensile strength of the paper web  320 . For example, any pattern which interrupts the leading edge  250  may provide improvements in relation to tensile strength. In particular, staggering the leading edge  250  of the embossing protrusions  260  can give the desired result. 
     In addition or alternatively, the formation of embossing protrusions may also be altered to minimise the strain exerted on the paper web  320  during the embossing process. As an alternative to the embossing formation shown in  FIG. 2 , embossing formations similar to  FIGS. 8   a  and  8   b  may be used. 
     In one embodiment, the embossing formation is a rhomboid pattern shown in  FIG. 8   a . Configuring dimension ‘C 1 ’ to be equal to or greater than dimension ‘B 1 ’ used in the embossing pattern of  FIG. 2 , having the same number, size and distribution of embossing protrusions, has the effect of reducing the strain on the paper web in the longitudinal dimension, when compared to the embossing pattern of  FIG. 2 . The reason that the strain on the paper web is reduced in this direction is that the protrusion is effective over a greater distance of paper web in this direction, and therefore strain (defined as the extension of the paper web divided by its original length) and/or stress (the force applied to the paper per unit area) is reduced in this direction. 
     In another embodiment, adjacent embossing protrusions  260  are offset from each other in the longitudinal direction A, as shown in  FIG. 8   b . This pattern reduces the longitudinal weakness at lines ‘C’ and ‘D’ because the weakness lines  240  run through fewer indentations in the paper web  320 . 
     In addition, or as an alternative, to changing the embossed pattern and/or formation, it is possible to minimise the depth of the embossing in order to improve the tensile strength of the paper, without reducing the desired effects on the permeability or diffusivity of the wrapper  320 . As described above, the air permeability and gas diffusivity of the embossed region  321  of the paper  320  can be selected by varying the size and number of the embossing protrusions  260  as well as varying the coverage area of the embossing protrusions  260 . In order to minimise the depth of the embossing to improve the tensile strength of the paper, the embossing drive roller  510  is provided with a higher number of protrusions of a smaller dimension than those shown and discussed in relation to  FIG. 2 . The applied pressure is spread over a greater surface area, meaning that the depth of embossing is reduced. By reducing the depth of embossing the stress/strain on the paper web  320  is reduced, such that the above problem of reduced tensile weakness may be avoided or diminished. For instance, the protrusions can have a base width of less than 0.3 mm, for instance approximately 0.2 mm, 0.1 mm or less, and a height of less than 0.15 mm, for instance approximately 0.1, 0.09, 0.08 mm, 0.07 mm, 0.06 mm or less. 
     In addition, or as an alternative to the above solutions, a further method for preventing or diminishing the problem of reduced tensile strength may be achieved by having non-embossed strips which run longitudinally along the length of the wrapper, as shown in  FIG. 9 . By not embossing the paper web  320  transversally across the whole width of the paper web, disrupts the weakness lines  240  shown in  FIG. 9 . This improves the tensile strength of the paper web in comparison to an embossed paper web which does not have longitudinal non-embossed strips. 
     A person skilled in the art will appreciate that the above solutions any be utilised in any combination to produce desired results. 
     Although the invention has been described above in relation to a cigarette paper, the invention is also applicable to other smoking article wrapping materials, such as tipping paper, plug wrap and cigar papers, as would be appreciated by those skilled in the art.