The invention relates to a filter cigarette as well as processes of manufacturing such a filter cigarette.

For cigarettes, low ignition propensity (LIP) has become a regulatory requirement in many countries and in the EU. LIP regulation is generally based on standard test methods (e.g. ASTM E2187-04) . Tests are conducted by positioning a lit cigarette on layers of a special paper and measuring the length of the cigarette that is left after self-extinguishing . If self- extinguishing occurs before a pre-determined residual length of the cigarette has been reached, a single test is passed. The test is repeated for a given number of cigarettes (e.g. 40) , and the product is considered to be LIP-compliant if a certain percentage of cigarettes passes the test.

The current standard technology to obtain LIP properties is the use of a cigarette paper that comprises bands (zones) hav ^¬ ing a lower air permeability than the base paper. These bands of a width of approximately 4 mm to 8 mm are equally spaced on the cigarette paper in a way that a minimum number of two bands is found on each cigarette, as illustrated in Figures 1 to 3. Figure 1 is a schematic longitudinal view showing a conventional LIP filter cigarette having a length l _c , which comprises a tobacco rod wrapped with a cigarette paper 1 and a filter 2, both being connected by a tipping paper 3 having a length 1 _T . The length of the tobacco rod not covered by the tipping paper 3 is l _Rf . The distance d _B between the bands 4 (measured centre/centre or left edge/left edge) is chosen as I _RE /2. The cigarette paper used for manufacturing such ciga- rettes has a regular pattern of bands 4 with a distance of d _B , as shown in Figure 2. Due to the usual, unregistered way of applying the cigarette paper to the cigarettes, the position of the bands 4 on the finished cigarettes is randomly distributed, as shown in Figure 3.

The air permeability of the base cigarette paper and the bands can be described both in terms of porosity (driven by a pressure gradient across the paper or band, respectively) and in terms of diffusivity (driven by a concentration gradient across the paper or band, respectively) . For the base cigarette paper, usually the porosity is given (basic porosity) , as measured according to CORESTA Recommended Method No. 40 and indicated in Coresta units (1 CU = 1 ml/ (cm ² min kPa) . For the banded regions (band-like zones) , the air permeability is often expressed by diffusivity. The diffusivity (diffusion capacity) can be measured as described in CORESTA Recommended Method No. 77 ("Determination of diffusion capacity by measurement of C0 ₂ transfer rate through materials used as cigarette papers and cigarette papers having an oriented zone of reduced diffusion capacity", May 2013) and indicated in cm/s. As a general rule, the lower the diffusivity of the bands is chosen the higher will be the number of cigarettes that pass the LIP test. On the other hand, a low diffusivity of the bands increases the probability that the cigarette extinguishes in free-air burning conditions which is reflecting the nor- mal use of the product by smokers. Free-air self-extinguishing will cause frustration of the smoker as the cigarette either has to be re-lit or discarded before being fully smoked. As a consequence, the general industry practice is to select the diffusivity of the bands in a way that the LIP pass criteria are met reliably but free-air self-extinguishing is minimized.

For a long time, it has been another objective of the industry to provide cigarettes that extinguish reliably once the burning zone has reached the mouth- sided end of the tobacco rod. Such cigarettes do not have to be crushed or pressed but ra- ther extinguish without further action when being left smouldering in an ashtray. This not only results in a more comfortable handling for the smoker but also reduces the smell left on the smoker's fingers caused by the crushing operation. Var- ious solutions for self-extinguishing at the cigarette end have been suggested, such as applying bands of suitable materials to the cigarette paper at the end of an unfiltered cigarette that cause it to extinguish if smoking is discontinued (US 1,555,320 and US 1,996,002).

The object of the invention is to provide a filter cigarette that passes LIP tests and also self-extinguishes once the burning zone reaches the mouth-sided end area of the cigarette .

This object is achieved by a filter cigarette comprising the features of claim 1. Claims 11 and 13 are directed to processes of manufacturing such filter cigarettes. Advantageous embodiments of the invention follow from the dependent claims.

The filter cigarette according to the invention comprises a tobacco rod wrapped with a cigarette paper having a basic porosity and a filter attached to an end of the wrapped tobacco rod by means of a tipping. The cigarette paper includes at least one first circumferentially extending band-like zone having a lower porosity than the basic porosity and one second circumferentially extending band-like zone having a lower porosity than the basic porosity. The second band-like zone is longitudinally spaced to the at least one first band-like zone. According to the invention, the second band-like zone has a lower diffusivity than the at least one ^' first band-like zone . Here and in the following, the air permeability of the bandlike zones is expressed as porosity when compared to the porosity (basic porosity) of the cigarette paper in the areas away from the band-like zones, as measured by the well- established CORESTA Recommended Method No. 40. The permeability of the band-like zones as such and when compared to each other is expressed as diffusivity D* (diffusion capacity) , as measured by the recently introduced CORESTA Recommended Method No. 77.

In advantageous embodiments of the invention, the second bandlike zone is closer to the filter than the at least one first band-like zone. Preferably, the distance between the second band-like zone and the rod-sided end of the tipping is less than 5 mm. In particular, the second band-like zone may be adjacent to the rod-sided end of the tipping, i.e. the above distance is almost 0 mm or exactly 0 mm. The latter includes the case that there is some overlap between the second bandlike zone and the tipping; since the tipping usually is imper- vious to air, such overlap would not result in a particular effect. A typical width of the second band-like zone (measured in longitudinal direction of the filter cigarette) is in the range of from 3 mm to 9 mm. Thus, in the filter cigarette according to the invention, band-like zones with two different air permeability levels are applied to the cigarette paper in such a way that a band-like zone having a lower permeability is in close vicinity to the tipping (usually a tipping paper) at the mouth-sided end of the filter cigarette. The permeability of the band-like zones is chosen in a way that the band-like zone(s) distal from the mouth-sided end (i.e. the first band-like zones (s) ) has (have) a diffusivity comparable to standard LIP cigarettes, thus allowing to pass the LIP test but minimizing free-air self- extinguishing during smoking. The second band-like zone, which is positioned closer to or adjacent to the tipping, has a dif- fusivity which is chosen low enough to result in extinguishing once the cigarette burning zone reaches this band-like zone. It has been found that for a reliable extinguishment at the end of smoking, the diffusivity of the second band-like zone has to be lower than 0.05 cm/s, while the diffusivity of the first band- like zone(s) can be chosen to be in the range of from 0.06 cm/s to 0.18 cm/s, as usually applied for LIP ciga- rettes. These values are expressed as diffusivity as measured by the method indicated above. Generally, in the band-like zones, the diffusivity or porosity relates to the composite comprising the cigarette paper plus the material applied to the cigarette paper for providing the band-like zones.

The second band-like zone may be marked, for example by colouring. Such marking can be advantageous, e.g., for detecting the second band-like zone in a manufacturing process (see below) , or may provide a pleasant appearance of the filter ciga- rette. If the marking is just used as a detection aid, a normally invisible marking may be preferred, e.g. by a fluorescent dye which is excited by a UV lamp during the manufacturing process. In principle, all kinds of substances known in the art for that purpose can be used to provide the at least one first band-like zone and/or the second band-like zone on the cigarette paper so that the respective porosity (air permeability, diffusivity) is smaller than the basic porosity of the ciga- rette paper. In advantageous embodiments of the invention, the at least one first band-like zone and/or the second band-like zone comprises, e.g., a starch, an alginate, guar gum, a salt of an organic acid, a burn retardant or mixtures of such substances. The desired porosity can be adjusted, e.g., by the concentration of the respective substance in a solvent or slurry during the manufacturing process, as is generally known in the art and also described in more detail in the embodiments below. Preferably, a filter cigarette according to the invention includes one or two first band-like zones, which are spaced to each other and preferably (but not necessarily) have the same- diffusivity. Other numbers, like three, four or five, are conceivable as well.

In a process of manufacturing filter cigarettes according to the invention, a web of cigarette paper including sections which each comprise at least one transversely extending first band-like zone and one transversely extending second band-like zone is unwound from a bobbin and longitudinally wrapped around an endless tobacco rod to provide an endless wrapped tobacco rod. This endless wrapped tobacco rod includes sections each comprising at least one circumferentially extending first band-like zone and one circumferentially extending second band-like zone. In order to attach filter segments, the wrapped tobacco rod has to be cut into pieces. This cutting step is performed in register with each respective second band-like zone to ensure that, in each finished cigarette, the second band-like zone has a well-defined position with respect to the rod-sided end of the tipping. As seen above, the distance between the second band-like zone and the rod- sided end of the tipping is preferably small.

To aid the registering step, the second band- like zones can be marked by a marking (see above) , which is detected by a sensor or detector to enable the wrapped tobacco rod to be cut at the correct positions, preferably close to each respective second band-like zone. In this process, the first and second band-like zones can already be applied to the cigarette paper web during the manufacturing process of the web, e.g. by printing. In another process of manufacturing filter cigarettes according to the invention, a web of cigarette paper, which includes sections each comprising at least one transversely extending first band-like zone, is unwound from a bobbin. In each one of these sections, one transversely extending second band- like zone is applied to the web. Thereafter, the web is longitudinally wrapped around an endless tobacco rod to provide an endless wrapped tobacco rod including sections each comprising at least one circumferentially extending first band-like zone and one circumferentially extending second band-like zone. The wrapped tobacco rod is cut in register with each respective second band-like zone to ensure that, in each finished cigarette, the second band-like zone has a well-defined position with respect to the rod-sided end of the tipping (i.e. preferably a small distance) .

In this process, the cigarette paper web, upon delivery, just includes the first band-like zones, while the second band-like zones are applied to the web during the manufacturing process. This allows to utilize the known spatial and temporal relation between the step of applying a respective second band-like zone to the web and the cutting step (which is essentially determined by the distance between the applying station and the cutting station as well as the speed of the web) to cut the wrapped tobacco rod in register (i.e. synchronized) with each respective second band- like zone. The positions of the first band-like zones on the finished cigarettes are more randomly distributed. Any disadvantageous effect resulting therefrom can be counter-acted by using more than one first band-like zone per cigarette. For applying the second band- like zones to the web, they are preferably printed onto the web on a cigarette machine during cigarette manufacturing using gravure or inkjet printing. For example, the second band- like zones can be printed onto the web with a printing ink, wherein the printing ink comprises an aqueous solution of one or more substances like starches, alginates, guar gum, organic acids, burn retardants. In this context, the term "solution" also encompasses a slurry.

Such applied or printed second band-like zones preferably have a width, measured in longitudinal direction of the tobacco rod, in the range of from 3 mm to 9 mm and a porosity of less than 20 CU.

In the following, the invention is explained in more detail by means of embodiments. The drawings show in

Figure 1 a schematic longitudinal view of a conventional LIP filter cigarette comprising two band-like zones having the same porosity,

Figure 2 a top view of a web of cigarette paper used for wrapping a tobacco rod to provide filter cigarettes like that in Figure 1,

Figure 3 schematic longitudinal views of several filter cigarettes manufactured by using the web of Figure 2, in which the positions of the band-like zones are randomly distributed,

Figure 4 a schematic longitudinal view of a first embodiment of the filter cigarette according to the invention, Figure 5 a top view of a web of cigarette paper used for wrapping a tobacco rod to provide filter cigarettes like that in Figure 4, Figure 6 schematic longitudinal views of several filter cigarettes manufactured by using the web of Figure 5, wherein the positions of the band-like zones are registered during the manufacturing process by means of a sensor or detector,

Figure 7 a schematic longitudinal view of a second embodiment of the filter cigarette according to the invention, and Figure 8 schematic longitudinal views of several filter cigarettes manufactured by using a web like that in Figure 2, wherein an additional band-like zone is printed onto the web in register with the position of the filters.

Figures 1 to 3 relate to a conventional LIP filter cigarette and a process of manufacturing such cigarettes, as explained in detail further above. Figure 4 illustrates a first embodiment of a filter cigarette according to the invention, designated by 10.

The filter cigarette 10 comprises a tobacco rod 12, which is wrapped with a cigarette paper 14 having a basic porosity. A filter 16, e.g. containing cellulose acetate, is attached to one end of the tobacco rod 12 by means of a tipping 18 (in the embodiment made of paper) . In the end area of the tobacco rod 12, the tipping 18 somewhat overlaps the cigarette paper 14. The total length of the filter cigarette 10 is designated by l _c , the length of the cigarette paper 14 by l _Cp , the length of the tipping 18 by 1 _T , and the difference between l _c and 1 _T by

The cigarette paper 14 comprises one first band-like zone 20, which extends circumferentially about the tobacco rod 12. Insofar, Figure 4 is not a pure longitudinal section, but schematic. The first band-like zone 20 has a lower porosity than the basic porosity of cigarette paper 14. Closer to the filter 16, the cigarette paper 14 comprises one second band-like zone 22, which extends circumferentially about the tobacco rod 12. The second band-like zone 22 has a lower diffusivity than the first band-like zone 20. In the embodiment, the widths of the first band-like zone 20 and the second band-like zone 22 are the same. The distance d _B T between the rod-sided end of the tipping 18 and the closest edge of the second band-like zone 20 is generally small, preferably between 0 mm and 5 mm. The distance of the first band-like zone 20 and the second band-like zone 22 (measured centre- centre, or in Figure 4 left edge-left edge) is designated by d _B .

The first band- like zone 20 is designed as a conventional band providing LIP properties so that the filter cigarette 10, when lit, self-extinguishes (with a relatively high probability) when put on a support but does not self-extinguish (with a relatively high probability) when held in air. The lower- diffusivity second band-like zone 22, however, reliably results in self-extinguishment of the cigarette when completely smoked and the burning zone has reached the mouth-sided end area of the tobacco rod 12.

In the embodiment, the band-like zones 20 and 22 having different diffusivities are provided to a cigarette paper web at the paper manufacturing process by applying porosity-reducing substances such as alginate, starch, cellulose fibers and/or guar gum, as known to a skilled person. To ensure an advantageous position of the band-like zones 20, 22 on the finished cigarettes 10, the band pattern can be chosen such that d _B is half of l _Rf .

Thus, the cigarette paper web used for manufacturing the cigarettes 10 has a regular pattern of band-like zones 20 and 22, see Figure 5. This regular pattern has to reflect the fact that, in the common way of attaching filters to cigarettes, first a double-length rod (having a length of twice l _Cp ) is cut from an endless rod of tobacco longitudinally wrapped with the web, which is then cut in the middle. The two single- length rods are spaced apart and a double-length filter segment is inserted in between the two single-length rods. The double- length filter segment and the two single-length rods are then combined by wrapping and gluing with a double- length tipping paper. Finally, the resulting double cigarette is cut in the middle to obtain two single cigarettes.

In Figure 5, double sections (each double section with two first ^' band-like zones 20 and two second band-like zones 22) are arranged in a repeating pattern, wherein the length of each double section equals to twice the total length l _Cp of the cigarette paper 14 in one cigarette 10.

To ensure that the lower-diffusivity second band- like zone 22 is always in close vicinity to the tipping 18 of a cigarette 10, the cigarette paper has to be applied in a registered way during cigarette making, as for example described for standard LIP papers in US 2005/0172977 A and WO 2011/057743 A. This results in the same positioning of the band-like zones 20, 22 in all cigarettes 10, as illustrated in Figure 6. As the cigarette paper registration process on a cigarette maker relies on recognition of the band position by a sensor or detector, one of the bands can be marked, e.g. coloured. Preferably the lower-diffusivity second band-like zone 22, proximal to the filter 16, is coloured which also assists the smoker in recognizing the self-extinguishing zone.

Another embodiment of a filter ^' cigarette, designated by 30, is shown in Figure 7. Filter cigarette 30 comprises a tobacco rod 32 wrapped with a standard LIP cigarette paper 34 and a filter 36 attached by means of a tipping 38. In the embodiment, the cigarette paper 34 includes generally two first band-like zones 40 having a lower porosity than the basic porosity of the cigarette paper 34. Moreover, a second band-like zone 42 having an even lower porosity or diffusivity is located in close vicinity to the rod-sided end of the tipping 38, the distance being d _BT - The other distances indicated in Figure 7 are like those in Figure 4. In the embodiment, the filter cigarettes 30 are manufactured by using a cigarette paper web like the web shown in Figure 2, which includes all first band-like zones 40, but on which the second band-like zones 42 are missing initially. On the finished cigarettes, the positions of the first band-like zones 40 can vary, as depicted in Figure 8, in which individual cigarettes are designated by 50, 51, 52, 53 and 54. However, the second band- like zone 42 always has to be applied at the same position on a filter cigarette 30 in order to ensure self- extinguishment of the cigarette only if it has been smoked al- most completely. This is achieved by applying, preferably by printing, a solution of a suitable substance at the cigarette maker after unwinding the cigarette paper web from the bobbin but before rod formation. Suitable methods for printing include but are not limited to gravure printing (see WO 2006/029723 A) and inkjet printing. In a later step of the manufacturing process, the wrapped tobacco rod is cut in register with the respective second band-like zones 42, as also explained further above . Citric acid and other organic acids are suitable means for lowering the burn rate of cigarettes when applied to the cigarette paper. WO 85/04080 A describes that a cigarette paper treated with such substances reduces the ignition propensity of cigarettes. According to WO 85/04080 A, bands created by using such an acid and covering at least 50% of the cigarette paper surface area yield the desired effect.

Surprisingly, it was found that a single citric acid band- like zone 42 of about 5 mm width when applied directly adjacent to the tipping 38 was effective in extinguishing the cigarette at the end of smoking. A possible explanation is that the oxygen supply in this region is further reduced by the low porosity of the second band-like zone 42, which is positioned adjacent to the basically non-porous tipping 38. Carbonates contained in the cigarette paper might be dissolved by the organic acid, resulting in an organic salt finely distributed in the paper pores, thus lowering the porosity.

Generally, suitable printing ink substances for this printing operation include:

- aqueous solutions of solid substances such as a starch, an alginate,

- aqueous solutions of acids like citric, malic, malonic, succinic, glutaric, maleic, lactic, adipic or tartaric acid,

- aqueous solutions of burn retardants like magnesium chloride, as described in EP 2 071 965 A.

In the following, some numerical examples are presented. Example 1 (Conventional cigarette as in Fig. 1 as a reference)

A cigarette rod comprising a standard American Blend tobacco having a length of 63 mm and a weight of 720 mg was combined with a standard cellulose acetate filter having a length of 21 mm using a standard tipping paper with 25 mm width (measured in longitudinal direction of the cigarette rod) . The cigarette paper used for forming the rod had a basic porosity of 75 CU and equally spaced LIP bands of 7 mm width and a distance (as measured form centre to centre) of 29.5 mm. The diffusivity in the band regions was set to 0.12 cm/s. 92% of these cigarettes passed the LIP test according to ASTM 2187-4.

When left in an ashtray, all cigarettes burned until the burn- ing zone reached the tipping paper or even burned into the tipping paper.

Example 2 (Cigarette as in Figure 4)

A cigarette similar to that of Example 1 was produced with a cigarette paper having two different bands (band-like zones) . The diffusivity of the first band (first band-like zone 20) was 0.12 cm/s and that of the second band (second band- like zone 22) was 0.04 cm/s. The width of both bands was 7 mm and the distance between the bands was 29.5 mm. The cigarette paper was applied in registered manner to ensure that the second band starts directly behind the rod- sided end of the tipping. 100% of these cigarettes passed the LIP test according to ASTM 2187-4.

When left in an ashtray, the cigarettes extinguished reliably when the burning zone reached the second band. Example 3 (Cigarette like in Figure 7)

On the cigarettes of Example 1, an aqueous solution of citric acid was applied with a paint brush to create a band (second band- like zone 42) having a width of 5 mm and located on the cigarette paper directly adjacent to the tipping. The amount of citric acid in the band was 3 mg per cigarette. After application of the band, the cigarettes were stored in a controlled atmosphere of 20 °C and 60% relative humidity for one week. 98% of these cigarettes passed the LIP test according to ASTM 2187-4. In the region treated with citric acid, the permeability (porosity) of the cigarette paper was reduced from the initial value of 75 CU to less than 20 CU. When left in an ashtray, all cigarettes immediately extinguished when the burning zone reached the applied band.