HK1185312A - Improvements in embossing techniques - Google Patents

Description

Improvements in embossing techniques

Technical Field

The present invention relates to improvements in imprint technology. In particular, the present invention relates to embossing techniques for smoking articles.

Background

As used herein, the term "smoking article" includes smokeable products-such as cigarettes, cigars and cigarillos (whether tobacco-based or not), tobacco derivatives, tobacco in general, reconstituted tobacco or tobacco substitutes, and heated but non-combustible products.

Conventional filter cigarettes typically include a tobacco rod wrapped in cigarette paper and a filter plug wrapped in plugwrap. Tipping paper was used to join the filter plug and tobacco rod. The amount of smoke drawn through the filter depends on various factors such as the air permeability of the cigarette paper, plugwrap and/or tipping paper. For example, a high air permeability cigarette paper will allow air flow through the cigarette paper and dilute the smoke more than a low air permeability cigarette paper. Thus, the air permeability of the cigarette paper used in cigarette manufacture is a factor in controlling at least the dilution of the smoke of the cigarette.

As discussed for example in GB1524211, one method changes the air permeability of the paper by an embossing process. The embossing process typically involves applying pressure to localized areas on the paper surface to open or stretch the fibrous structure of the paper to form indentations or holes in the paper. This has the effect of changing the air permeability of the paper. Controlling the embossing process can provide a means for controlling the air permeability of the paper.

Disadvantageously, the embossing process may result in a reduction in the tensile strength of the paper. This reduction in tensile strength can cause paper, such as cigarette paper, plugwrap, and tipping paper, to tear under stress and/or strain as the paper is subjected to during the cigarette and/or filter manufacturing process. This is undesirable and can have the effect of limiting productivity.

Disclosure of Invention

According to one aspect of the present invention there is provided an embossing apparatus for applying an embossing pattern to a wrapper of a smoking article, the embossing apparatus being configured to at least partially minimise the reduction in tensile strength of the wrapper in at least one direction resulting from the application of the embossing pattern. In this sense, partial minimization can be used to indicate: the reduction in tensile strength caused by embossing the wrapper can be compensated by configuring the embossing device for embossing.

Advantageously, minimizing the extent of the reduction in tensile strength caused by the coining process may avoid or mitigate certain problems associated with the reduction in tensile strength. In particular, improving the tensile strength of the wrapper in this manner can alleviate the problem of tearing of the wrapper (which can reduce productivity).

Typically, an embossing pattern is applied to increase the diffusivity and/or air permeability of the wrapper, and wherein the embossing pattern is selected such that for a given increment of diffusivity and/or air permeability the embossing pattern minimizes the embossing stress and/or strain distributed to the wrapper in at least one direction during the application of the embossing pattern.

Variations in the stress and/or strain on the wrapper can alter the effect of the embossing process. For example, deeper impressions made by applying greater impression forces may result in larger pores/gaps, thereby affecting the diffusivity and/or air permeability of the wrapper. A further advantage of the present invention is that by selecting the embossing pattern to minimize the embossing stress and/or strain distributed on the paper, the desired amount of diffusivity and/or air permeability can be better controlled and have better consistency.

Preferably, the applied embossing pattern is arranged to cause the embossed wrapper to have different strength characteristics in different directions.

Preferably, the imprinting apparatus comprises: an embossing roller for applying an embossing to the wrapper; and means for retaining the embossing roller at a predetermined distance from said wrapper so as to limit the depth of embossing. Advantageously, maintaining the predetermined distance as the embossing roller applies the embossing pattern to the wrapper is one method for minimizing the stress distributed on the wrapper.

In a preferred embodiment, the embossing means comprises at least two embossing rollers for applying an embossing to a wrapper extending in a longitudinal direction between said at least two embossing rollers, wherein said retaining means maintains a minimum distance between the peripheral surfaces between said 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 to minimise, at least in part, the reduction in tensile strength of the wrapper in at least one direction resulting from the application of the embossing for a given increment of diffusivity and/or air permeability resulting from the embossing.

Preferably, the embossing pattern is selected to minimise a line of weakness extending in at least one direction through the embossed region of the wrapper. Lines of weakness are introduced during the embossing process as the fibrous structure of the wrapper material, typically cigarette paper, is opened and stretched. One advantage of selecting an appropriate embossing pattern is that the extent to which the lines of weakness cause a reduction in tensile strength can be minimised.

Preferably, the embossed pattern comprises embossed and non-embossed regions and a leading edge between the embossed and non-embossed regions, the leading edge being arranged non-perpendicular to the longitudinal direction of the wrapper.

Optionally, the embossed pattern comprises a spiral or screw thread pattern when the wrapper is wrapped around the smoking article. This arrangement of the embossed pattern has the following further advantages: the spiral or thread pattern is a mechanism for causing the smoking article to self-extinguish without being smoked. This is particularly advantageous in relation to the requirements associated with low ignition propensity smoking articles.

In a preferred embodiment, the embossed pattern of the wrapper comprises a notch which is free of substantially perpendicular edges relative to the longitudinal direction of the wrapper. Optionally, the embossed pattern of the wrapper comprises a rhomboidal notch having no substantially perpendicular edges relative to the longitudinal direction of the wrapper. In an alternative embodiment, the embossed pattern is formed by a set of indentations in which laterally adjacent indentations are longitudinally offset from one another.

According to another aspect of the present invention there is provided an embossing roller for applying an embossing pattern to a wrapper of a smoking article, wherein the embossing roller comprises a plurality of embossing protuberances arranged such that for a given increment of diffusivity and/or air permeability of the wrapper embossed using the roller, the embossing protuberances act to at least partially minimise the reduction in tensile strength of the wrapper in at least one direction resulting from the application of said embossing.

Preferably, the embossing protuberances are arranged such that application of the embossing rollers to the wrapper results in the wrapper described above.

The above-described embossed pattern advantageously reduces the strain and/or stress distributed to the wrapper when the wrapper and/or smoking article is manufactured.

According to another aspect of the present invention there is provided a method of embossing a wrapper of a smoking article, the method comprising applying an embossing pattern to the wrapper so as to at least partially minimise the reduction in tensile strength of the wrapper in at least one direction resulting from the application of the embossing pattern.

In a preferred embodiment, the applying step comprises applying an embossing roller to the wrapper, the method further comprising retaining the embossing roller at a predetermined distance from the wrapper so as to limit the depth of embossing.

Preferably, the web material is made to extend in the longitudinal direction through at least two embossing rollers, and said holding step comprises: coaxial cam motion limiters and mechanical stops are used to prevent radial movement of the at least one roller in at least one direction.

Drawings

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

figure 1 is a perspective view of a smoking article having a wrapper with an embossed region and a non-embossed region;

FIG. 2 is an enlarged view of a section of wrapper having an embossing pattern for an exemplary arrangement/formation of embossing protuberances;

figure 3 is a schematic view of an embossing unit for making embossed wrapper paper;

FIG. 4 is a schematic view of a wrapper having a plurality of embossed and non-embossed regions in the form of bands;

FIG. 5a is a front view of the impression driver roller and the counter roller showing a non-impression area of the impression driver roller in communication with the counter roller;

FIG. 5b is a front view of FIG. 5a showing the nip region of the nip drive roller in communication with the opposed roller;

FIG. 6a is a side view of an impression drive roller having a cam motion limiter for maintaining a minimum distance between the drive roller and an opposing roller according to one embodiment of the present invention;

FIG. 6b is a front view of the platen drive roller of FIG. 6 a;

figure 7 is a schematic view of a wrapper having embossed areas arranged in a spiral form when wrapped around a smoking article;

FIGS. 8a and 8b are exemplary imprint patterns according to embodiments of the present invention; and

figure 9 is a schematic view of a wrapper showing a longitudinal non-embossed band.

Detailed Description

Figure 1 shows a smoking article 100. The smoking article 100 is discussed below in the context of a cigarette 100, the cigarette 100 comprising a generally cylindrical cellulose acetate filter 200 and an axially aligned generally cylindrical rod of smokable material 300 attached to the filter 200 by a sheet of lap tipping paper 400. However, the present invention is not limited to cigarettes. The invention is also applicable to other types of smoking articles (including those described above).

Generally, the rod of smokable material 300 comprises a generally cylindrical core of tobacco material 310 wrapped in a wrapper 320. As shown in fig. 1, the wrapper 320 provides a circumferential boundary for a cylindrical core 310, wherein the end faces of the core 310 are held open in a conventional manner. The wrapper 320 comprises a base paper such as cigarette paper.

The permeability of the wrapper 320 may itself be low, thereby actually limiting the permeation of outside air through the wrapper 320 into the burning tobacco core 310. One reason for limiting the flow of outside air into the burning tobacco core is: if not regularly smoked by the smoker, this may result in or promote self-extinguishment of the cigarette. Smoking articles having this characteristic are commonly referred to as Low Ignition Propensity (LIP) smoking articles. When tested according to ASTM E2187-04 or ASTM E2187-09, which are standards by which the ignition proclivity characteristics of smoking articles can be assessed, national regulations often specify that low ignition proclivity smoking articles have a percentage of full length burn of less than a particular threshold-for example 25% of a tobacco rod. In one embodiment, the wrapper 320 may have an air permeability of less than 30CU (Coresta) and preferably less than 20 CU. This provides cigarette 100 with a low propensity for flammability that meets industry standards as defined by ASTM E2187-04 and ASTM E2187-09.

As shown in fig. 1, the characteristics of the wrapper 320 may be improved by forming embossed regions 321 in the wrapper 320. The remaining areas of the wrapper are not embossed and therefore constitute non-embossed areas 322.

The embossed areas 321 of the wrapper 320 have a higher air permeability than the non-embossed areas 322. This allows a greater amount of outside air to enter the tobacco core 310 through the embossed area 321 of the wrapper 320, thereby increasing the dilution of the smoke during smoking. Thus, the air permeability of the embossed regions 321 will be different from the air permeability of the non-embossed regions 322. The desired air permeability value of the embossed region may be selected based on factors including the air permeability of the relevant area of the embossed region 321 and the non-embossed region 322.

In addition to having a higher gas permeability, the embossed regions 321 of the wrapper 320 also have a significantly higher gas diffusivity than the non-embossed regions 322. For example, the gas diffusivity of the embossed region 321 may be at least 5 times, preferably 6 or 7 times, the gas diffusivity of the non-embossed region 322. The higher gas diffusivity of the embossed area 321 of the wrapper 320 allows smoke constituents, such as CO and nitrous oxides, to diffuse out of the burning tobacco rod 300 through the embossed area 321 of the wrapper 320. In this way, smoke constituents that will be drawn into the filter 200 during smoking diffuse out of the cigarette before reaching the filter 300 due to the higher gas diffusivity of the embossed region 321. In addition, the higher diffusivity of the embossed area 321 results in additional oxygen diffusing through the cigarette paper toward the burning tobacco to increase the burn rate and, thus, decrease the number of puffs of the cigarette 100.

The combination of the embossed area 321 and the non-embossed area 322 provides a cigarette 100 that can meet the generally accepted LIP criteria described above and also provides a smoking experience that is configured to have a particular number of puffs. While this is one reason for making a cigarette paper having embossed regions 321 and non-embossed regions 322, those skilled in the art will appreciate that there may be other reasons and that the present invention generally relates to embossing processes without regard to the application of the embossing material.

As described above, the embossing process may result in a reduction in the tensile strength of the wrapper paper, as shown in figure 2, due to the formation of nicks or holes resulting in a line of weakness 240 through the embossed region. In the example shown, the line of weakness 240 runs through the centre of the rows of notches, perpendicular to the longitudinal direction of the paper shown by arrow X. These weakening lines 240 are created when the embossed pattern is formed as a result of the paper being stretched in the longitudinal direction X, in particular as a result of the stretching caused by each indentation. These lines of weakness 240 through the paper reduce the tensile strength of the wrapper and this can lead to longitudinal splitting of the wrapper during the cigarette manufacturing process.

Additionally, as noted above, the wrapper 320 may have embossed and non-embossed regions 321 and 322, meaning that the wrapper 320 will change from the non-embossed regions 322 to the embossed regions 321 as at least once the wrapper 320 is embossed. This change corresponds to the leading edge or row 250 of the embossed pattern on the embossing roller 510. As described in more detail below with reference to the embossing apparatus and process, this can result in significant lines of weakness being created at the leading edge/row of the embossed pattern.

An example imprint unit 500 is schematically illustrated in fig. 3. The embossing unit 500 includes an embossing drive roller 510 and one or more embossing counter-rollers 520, which rollers 510 and 520 together emboss the web of base paper 320 as the paper web 320 moves between the embossing drive roller 510 and the embossing counter-roller 520. In this example, the width of the paper web is about 26.5mm, which is sufficient to wrap around the circumference of the tobacco rod 300 and provide a lap seam 330 to affix the wrapper 320 in place around the rod 300. The embossing rollers 510, 520 include an embossing pattern on their outer peripheral surfaces. The embossing pattern may include a plurality of embossing protrusions 260. In one embodiment, as shown in FIG. 2, the embossing protrusions 260 comprise a plurality of protruding cones arranged in rows having a base width B1 of about 0.3mm and a height B2 of about 0.15 mm.

The outer peripheral surface of the platen opposed roller 520 is pressed against the outer peripheral surface of the platen drive roller 510. In one embodiment, the force may be applied by a pneumatic system including a piston 530. In an alternative embodiment, the embossing unit 500 may use a set of cams to control the relative position of the embossing counter-rollers 520. The force exerted on the web 320 between the impression rollers 510, 520 is proportional to the air pressure exerted on the piston 530 in the pneumatic system. The air pressure on the piston 530 may be varied by a control unit 540, said control unit 540 being configured to increase or decrease the air pressure in the pneumatic system according to a set of control parameters, which may be predetermined or adaptively determined according to the outcome of the embossing process. In one embodiment, the diameter of the piston 530 is about 2.75 inches. However, in an alternative arrangement, the diameter of the piston 530 may be reduced in order to provide better control of the embossing force applied by the embossing rollers 510, 520 to the paper 320. The use of a smaller diameter piston 530 will result in a smaller increment of the coining force (for a given increment of air pressure applied to the piston 530). A corresponding action will be provided to reduce the gas pressure. A suitable alternative diameter for piston 530 may be about 1 inch.

The embossing unit 500 may also include one or more drive rollers 550, which rollers 550 are configured to drive the paper web 320 through the embossing unit 500 in addition to the drive provided to the embossing drive roller 510. In fig. 3, a pair of such drive rollers 550 is provided in the paper path in front of the impression rollers 510, 520. In alternative examples, the drive rollers 550 may be disposed at other points in the web path in addition to or instead of those locations shown in fig. 3.

The imprinting unit 500 further comprises an analyzing unit 560, said analyzing unit 560 being configured to analyze the properties of the web 320 after the web 320 has passed between the imprinting 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 following: the air permeability of the paper 320 in the embossed area 321 and the non-embossed area 322, the thickness of the paper 320 in the embossed area 321 and the non-embossed area 322, and the conveyance of the paper 320 in the embossed area 321 and the non-embossed area 322.

As shown in fig. 3, the analysis unit 560 is communicatively coupled to the control unit 540, allowing control signals to pass between the analysis unit 560 and the control unit 540. Such communication may be made in any known manner, for example, via a wireless communication connection. In this way, the control unit 540 may receive information from the analysis unit 560 about the characteristics of the imprinted paper 320 and may use the information to adjust the force exerted by the imprinting rollers 510, 520 on the paper 320. The feedback mechanism provided by the communication between the analysis unit 560 and the control unit 540 described above allows the stamping unit 500 to maintain the stamping operation according to the control parameters used. For example, the feedback mechanism may be used to maintain a particular value of air permeability in the imprinted paper 320.

The air permeability and gas diffusivity of the embossed region 321 of the paper 320 may be selected by varying the force applied to the paper 320 during the embossing process. As such, as the web 320 passes between the impression rollers 510, 520, the force applied to the web 320 may vary depending on the exact characteristics that the wrapper 320 is desired to have. An exemplary embossing force applied to the paper 320 by the embossing rollers 510, 520 is in a range between 2Kgf and 55 Kgf. The exact embossing force will depend in part on parameters such as the thickness and inherent air permeability of the wrapper 320 used.

In addition, the air permeability and gas diffusivity of the embossed region 321 of the paper 320 may be selected by varying the size and number of embossed protrusions 260 and varying the coverage area of the embossed protrusions 260.

As described above, the embossing process reduces the tensile strength of the paper 320. Configuring the wrapper 320 with embossed and non-embossed areas 321 and 322 may increase this problem because applying the embossing drive roll 510 with embossed and non-embossed areas to the web 320 causes the pressure applied to the web 320 to change. This is particularly a problem for embossed wrappers 320 having bands or other patterns extending transversely across the wrapper 320, as shown in figure 4.

As the wrapper passes longitudinally through the embossing drive roller 510, a weakening is caused to be distributed transversely in the web 320 at the start of each new embossing area. This will be further elucidated with reference to fig. 5a and 5b, which show an exemplary arrangement of an embossing unit 500 with an embossing roller 510 and a single counter roller 520, wherein the web 320 extends between these two rollers. As shown in fig. 5a, the non-imprinted portion of the paper 322 is located between the two rollers at the non-imprinted region 600 of the imprint drive roller 510. In fig. 5b, the roller has rotated such that the leading edge/row 250 of embossing protuberances 260 is pressed against the web 320 at the embossing region 620 of the embossing drive roller 510 causing the web 320 to be embossed. The impression drive roller 510 rotates about its axis causing a portion of its outer peripheral surface containing the impression protuberances 260 to press against a portion of the outer peripheral surface of the opposed roller 520 and cause the paper web 320 to pass therethrough. As shown in fig. 5b, the embossing rollers 510, 520 continue to rotate so that when the embossing protuberance 260 is positioned between the opposing roller and the embossing drive roller, the distance between the respective peripheral surfaces of the rollers 510, 520 is enlarged to allow additional height of the embossing protuberance 260 to pass between the rollers 510, 520.

As the portion of the outer circumferential surface of the embossing roller that contacts the web changes from the embossing area 620 to the non-embossing area 600, the embossing rollers 510, 520 rotate at a sufficiently high rpm so that the embossing drive roller 510 pulses against the embossing counter roller 520, or vice versa. This pulse motion causes inertia as the outer peripheral surface of the platen drive roller 510 moves closer to and further from the outer peripheral surface of the opposed roller. This pulsating motion and inertia results in an increase in pressure on the web 320 as the leading edge 250 of the nip 620 presses against the web 320, and this results in a deeper nip. As described above, this creates significant lines of weakness 240 in the web 320, which can result in tearing of the web 320 during the cigarette manufacturing process. In addition, there is a disadvantage that the air permeability and diffusivity of the wrapper 320 are not uniform due to non-uniform embossing in the wrapper. The example arrangement in fig. 5a and 5b shows opposing rollers 520 having a non-embossed pattern. However, the opposed rollers 520 may have longitudinal threads (not shown) embossed with a pattern to assist in driving the web 320.

According to an embodiment of the present invention, the pressure applied to the moving web as it moves toward and away from the opposed roller 520 (or vice versa) is controlled by limiting the movement of the impression drive roller 510 so as to limit or prevent the pulsating movement described above. This may be accomplished by limiting the movement of the platen drive roller 510 and/or the opposed roller 520. This approach prevents the peripheral surfaces of the rollers 510, 520 from moving together to the non-embossed areas 600 of the embossed pattern (as can occur as shown in fig. 5). In one embodiment, this method may be implemented using one or more cam stops or screw stops, also referred to as cam motion limiters. The impression drive roller 510 is maintained at a predetermined distance from the web 320, respectively, to limit the depth of the impression applied to the web 320.

Figures 6a and 6b show an example configuration of a suitable cam movement limiter. Fig. 6a shows a side view of an impression drive roller 510 positioned above at least one opposed roller 520, wherein a web 320 extends between the rollers 510, 520. Fig. 6b shows a front view of the platen drive roller 510. In one embodiment, the platen drive roller 510 has a coaxial cam motion limiter 700, the limiter 700 being integrally formed with the platen drive roller 510 or being secured to the platen drive roller 510 by any suitable means. The platen drive roller 510 is mounted to a roller drive unit 720 (partially shown in fig. 6 a), the roller drive unit 720 transmitting a rotational drive force for the platen drive roller. The cam motion limiter 700 is disposed in abutment against a stop 740, the stop 740 being fixed to a roller drive unit or housing 760 of the platen drive roller 510. By the cam motion limiter 700 abutting the stop 740, the platen drive roller 510 can be prevented from moving in the Y-direction beyond a predetermined minimum distance from the opposed roller 520. This means that the non-nip region 600 of the peripheral surface of the nip drive roller 510 is prevented from moving less than the predetermined minimum distance from the counter roller 520, thereby compensating for the problem of increased pressure on the web 320 at the leading edge 250 of the nip region 620.

Additionally or alternatively, another solution to the above-described problem of reducing tensile strength is to determine an embossed pattern that minimizes the stress to which the web is subjected. In one embodiment, this is accomplished by interrupting or changing the leading edge/row of the embossing pattern on the embossing drive roller 510. In this sense, interrupting or altering the leading edge means changing the coined region 620 from having a generally vertical arrangement of coined projections 260 (as shown in FIG. 2) to any other suitable configuration.

In one example, the embossing drive roller 510 has embossing protuberances 260 in a spiral or threaded pattern. An embossing drive roller 510 having such a spiral or thread pattern will form a cigarette wrapper 320 as shown in fig. 7. When such a cigarette wrapper 320 is wrapped around the rod of smokeable material, an embossed band 321 is formed in the wrapper 320 which spirals around the circumference of the rod of smokeable material 300. The helical band 321 may extend along all or part of the length of the rod 300. The length and width of the spiral band 321 may be selected based on the overall length of the rod 300 and the characteristics of the wrapper 320 and smokable material 310. This configuration means that the nip 321 does not have a transversely or vertically extending leading edge and therefore an increase in pressure on the web 320 due to the leading edge 250 of the nip region 620 can be avoided. The configuration of the embossed area 321 of the wrapper 320 also means that when a cigarette is placed on a surface-for example if the cigarette falls, a portion of the embossed area 321 of the wrapper 320 will abut against the surface. This restricts the flow of air through those obstructed portions, further reducing the air permeability of the cigarette wrapper 320 and further promoting self-extinguishment of the cigarette.

Those skilled in the art will appreciate other forms of embossing protrusions 260 that may help alleviate the problem of reduced tensile strength of the web 320. For example, any pattern of interrupted leading edge 250 may provide an improvement with respect to tensile strength. In particular, the leading edges 250 of the embossing protrusions 260 in a staggered arrangement may achieve the desired results.

Additionally or alternatively, the form of the embossing protrusions may also be varied to minimize the strain imparted to the web 320 during the embossing process. As an alternative to the embossing form shown in fig. 2, an embossing form similar to that of fig. 8a and 8b may be used.

In one embodiment, the embossed form is a rhomboid pattern as shown in FIG. 8 a. The dimension 'C1' is configured to be equal to or greater than the dimension 'B1' used in the embossing pattern of fig. 2 having the same number, size and distribution, the pattern so configured having the effect of reducing strain on the web along the longitudinal dimension when compared to the embossing pattern of fig. 2. The reason why the strain on the web decreases in this direction is: the projections act over a greater distance of the web in this direction and thus the strain (defined as the extension of the 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, as shown in FIG. 8b, adjacent embossing protrusions 260 are offset from each other in the longitudinal direction A. This pattern reduces the degree of longitudinal weakening at lines 'C' and 'D' because the lines of weakness 240 extend through fewer gaps in the web 320.

Additionally, or as an alternative to changing the pattern and/or form of the embossing, the depth of the embossing can be minimized to increase the tensile strength of the paper without reducing the desired effect of the air 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 may be selected by varying the size and number of the embossing protrusions 260 and varying the coverage area of the embossing protrusions 260. To minimize the embossing depth in order to increase the tensile strength of the paper, the embossing drive roller 510 is provided with a greater number of projections, but smaller size, than those shown in fig. 2 and discussed in connection with fig. 2. The applied pressure is distributed over a larger surface area, which means that the depth of the imprint is reduced. The aforementioned weakness in tensile capacity can be avoided or reduced by reducing the stress/strain on the web 320 by reducing the impression depth. For example, the projections may have a base width of less than 0.3mm, e.g., about 0.2mm, 0.1mm, or less, and a height of less than 0.15mm, e.g., about 0.1, 0.09, 0.08mm, 0.07mm, 0.06mm, or less.

In addition, or as an alternative to the above solution, another approach may be to prevent or mitigate the problem of reduced tensile strength by having non-embossed bands (as shown in figure 9) extending longitudinally along the length of the wrapper. The line of weakness 240 is interrupted as shown in fig. 9 by embossing the web 320 not transversely across its entire width. This increases the tensile strength of the web compared to an embossed web without a longitudinal non-embossed band.

Those skilled in the art will appreciate that the above-described solutions can be employed in any combination to produce desired results.

Although the invention has been described above in connection with cigarette paper, the invention is also applicable to other smoking article wrappers, such as tipping paper, plugwrap and cigar paper, as will be appreciated by those skilled in the art.

Claims (20)

1. An embossing apparatus for applying an imprint to a wrapper of a smoking article, the embossing apparatus being configured to apply an imprint pattern to the wrapper for at least partially minimising a reduction in tensile strength of the wrapper in at least one direction resulting from the application of the imprint.

2. An embossing apparatus as claimed in claim 1, wherein the application of the embossing pattern is intended to increase the diffusivity and/or air permeability of the wrapper, and wherein the embossing pattern is selected such that for a given diffusivity and/or air permeability increase, the embossing pattern minimises the embossing stress and/or strain distributed on the wrapper in at least one direction during application of the embossing pattern.

3. An embossing apparatus as claimed in claim 2, wherein the application of the embossing pattern is arranged to cause the embossed paper to have different strength characteristics in different directions.

4. The embossing apparatus of any one of the preceding claims, further comprising:

an embossing roller for applying an embossing to said wrapper; and

means for maintaining said embossing roller at a predetermined distance from said wrapper so as to limit the depth of embossing.

5. An embossing apparatus as claimed in claim 4, further comprising at least two embossing rollers for applying an embossing to a wrapper travelling between the at least two rollers in the longitudinal direction, wherein the retaining means maintains a minimum distance between the peripheral surfaces of the at least two embossing rollers.

6. 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 air permeability resulting from the embossing, the embossing pattern acts to at least partially minimise the reduction in tensile strength of the wrapper in at least one direction resulting from the application of the embossing.

7. An embossed wrapper according to claim 6, wherein the embossing pattern is selected to minimise a line of weakness extending in at least one direction through the embossed region of the wrapper.

8. An embossed wrapper according to claim 6 or 7, wherein the embossed pattern comprises embossed and non-embossed regions and a leading edge between the embossed and non-embossed regions, the leading edge being arranged non-perpendicular to the longitudinal direction of the wrapper.

9. An embossed wrapper according to any of claims 6 to 8, wherein the embossed pattern comprises a spiral or screw thread pattern when the wrapper is wrapped around a smoking article.

10. An embossed wrapper according to any one of claims 6 to 9, wherein the embossed pattern of the wrapper comprises a notch having no substantially perpendicular edges relative to the longitudinal direction of the wrapper.

11. An embossed wrapper according to any one of claims 6 to 10, wherein the embossed pattern of the wrapper comprises rhomboidal notches having no substantially perpendicular edges relative to the longitudinal direction of the wrapper.

12. An embossed wrapper according to any one of claims 6 to 9, wherein the embossed pattern is formed by a series of notches in which laterally adjacent notches are longitudinally offset from one another.

13. An embossing roller for applying an embossing pattern onto a wrapper of a smoking article, wherein the embossing roller comprises a plurality of embossing protuberances arranged such that for a given increment of diffusivity and/or air permeability of the wrapper embossed using the roller, the embossing protuberances act to at least partially minimise the reduction in tensile strength of the wrapper in at least one direction resulting from the application of the embossing.

14. An embossing roll according to claim 13, wherein the embossing protuberances are arranged such that application of the embossing roll to the wrapper results in a wrapper according to any of claims 6 to 12.

15. A method of embossing a wrapper of a smoking article, the method comprising:

applying an embossing pattern to the wrapper so as to at least partially minimize a reduction in the tensile strength of the wrapper in at least one direction resulting from the application of said embossing.

16. A method according to claim 15, wherein said applying step comprises applying an embossing roller to said wrapper, said method further comprising:

the embossing rollers are held at a predetermined distance from the wrapper to limit the depth of embossing.

17. The method of claim 15 or 16, wherein the applying step comprises:

extending the web material in a longitudinal direction through at least two embossing rollers, and the holding step comprises:

coaxial cam motion limiters and mechanical stops are used to prevent radial movement of the at least one roller in at least one direction.

18. A smoking article comprising a rod of smokable material and a wrapper according to any one of claims 6 to 12.

19. A smoking article substantially as herein described with reference to the accompanying drawings.

20. An embossing apparatus substantially as herein described with reference to the accompanying drawings.