Wrapping material for smoking articles with directionally dependent diffusion capacity

Abstract

A wrapping material for a smoking article is disclosed, which has a laminar shape that extends further in two mutually orthogonal spatial directions X and Y than in a third spatial direction Z orthogonal to the spatial directions X and Y. The wrapping material has, at least in part of its area, a first and a second diffusion capacity D.sub.1 and D.sub.2 for a diffusion of CO.sub.2 through the wrapping material in the +Z-direction and the Z-direction, respectively, wherein for the first and second diffusion capacity D.sub.1 and D.sub.2, each an average of 10 values, one or both of the following relationships (i) and (ii) hold:
|D.sub.1D.sub.2|0.03 cm/s(i)
at a probability of error of 1% $\begin{array}{cc}2\frac{.Math.D_1-D_2.Math.}{D_1+D_2}0.030.& \left(\mathrm{ii}\right)\end{array}$

Claims

1. Wrapping material for a smoking article, which has a laminar shape that extends further in two mutually orthogonal spatial directions X and Y than in a spatial direction Z orthogonal to the two spatial directions X and Y, whereby the wrapping material has, in at least a part of its area, a first and a second diffusion capacity D.sub.1 and D.sub.2 for the diffusion of CO.sub.2 through the wrapping material in the +Z-direction and the Z-direction respectively, wherein the diffusion capacities D.sub.1 and D.sub.2 are to be determined according to CORESTA Recommended Method No. 77, characterized in that for the diffusion capacity D.sub.1 and D.sub.2, each an average over 10 values, one or both of the following relationships (i) and (ii) holds or hold:
|D.sub.1D.sub.2|0.03 cm/s(i) (ii) with a probability of error of 1% $2\frac{.Math.D_1-D_2.Math.}{D_1+D_2}0.030.$

2. Wrapping material according to claim 1, in which one or both of the following relationships (iii) and (iv) holds or hold for the first and second diffusion capacity D.sub.1 and D.sub.2: $\begin{array}{cc}.Math.D_1-D_2.Math.0.07\mathrm{cm}\text{/}s,& \left(\mathrm{iii}\right)\\ 2\frac{.Math.D_1-D_2.Math.}{D_1+D_2}0.050.& \left(\mathrm{iv}\right)\end{array}$

3. Wrapping material according to claim 1, in which $\frac{D_1+D_2}{2}0.01\mathrm{cm}\text{/}s$ and $\frac{D_1+D_2}{2}5.0\mathrm{cm}\text{/}s.$

4. Wrapping material according to claim 3, in which, in a section of the wrapping material, which is intended for self-extinguishing of a smoking article manufactured from the wrapping material, the following holds $0.005\mathrm{cm}\text{/}s\frac{D_1+D_2}{2}0.5\mathrm{cm}\text{/}s.$

5. Wrapping material according to claim 1, in which said part of the area of the wrapping material with the properties described in claim 1 accounts for at least 25% of the total area of the wrapping material.

6. Wrapping material according to claim 1, in which one or both of the relationships (i) and (ii) holds or hold in such areas of the wrapping material that are intended to obtain self-extinguishing of a smoking article manufactured therefrom, wherein these areas account for 20% to 40% of the total area of the wrapping material.

7. Wrapping material according to claim 1, with a thickness d for which the following holds: d10 m and d100 m.

8. Wrapping material according to claim 1, with a basis weight of at least 10 g/m.sup.2 and at most 100 g/m.sup.2 .

9. Wrapping material according to claim 1, which comprises at least two plies, which are with each other or with an intermediate ply located therebetween in close physical contact, wherein the two plies have different diffusion capacities.

10. Wrapping material according to claim 9, wherein the wrapping material has an upper face and a lower face, wherein one of the two plies is an uppermost ply that borders on the upper face, and one ply is a lowermost ply that borders on the lower face of the material.

11. Wrapping material according to claim 9, in which the absolute difference of the diffusion capacities of the two plies is at least 0.05 cm/s and at most 5.0 cm/s.

12. Wrapping material according to claim 9, in which the lower diffusion capacity of the two plies is at least 1% and at most 95% of the higher diffusion capacity of the two plies.

13. Wrapping material according to claim 10, in which the diffusion capacity of the uppermost ply is lower than that of the lowermost ply and in which an intermediate ply is located between the uppermost and the lowermost ply the diffusion capacity of which is at most 200% of the diffusion capacity of the lowermost ply and at least 50% of the diffusion capacity of the uppermost ply.

14. Wrapping material according to claim 9, in which the close physical contact can be obtained by mechanical pressure on the plies.

15. Wrapping material according to claim 9, in which both plies are formed by paper, which contains pulp and wherein the plies differ by one or more of the properties pulp type, degree of refining of the pulp, filler, if present, and/or filler content, if present.

16. Wrapping material according to claim 9, in which at least the ply having a higher diffusion capacity is artificially perforated.

17. Wrapping material according to claim 1, with an upper face and a lower face, whereby the coefficient of diffusion of a virtual layer that borders the upper face is lower than the coefficient of diffusion of a virtual layer that borders the lower face.

18. Wrapping material according to claim 1, in which the wrapping material is perforated, wherein the mean cross section of the perforation holes in a virtual layer bordering the upper face of the wrapping material is lower than in a virtual layer bordering the lower face.

19. Wrapping material according to claim 18, in which the mean cross sectional area of the perforation holes on the lower face is at least 30% larger than the mean cross sectional area of the perforation holes on the upper face.

20. Wrapping material according to claim 1, in which the wrapping material or the individual plies of the wrapping material consist of paper, reconstituted tobacco, tobacco leaves or tobacco substitute materials.

21. Wrapping material according to claim 20, in which the paper contains pulp fibers derived from wood, flax, hemp, sisal, abac, cotton, or esparto grass.

22. Wrapping material according to claim 21, in which the paper contains at least one mineral filler.

23. Wrapping material according to claim 22, in which the fraction of the filler relative to the mass of the paper is between 20% and 50% of the total paper mass.

24. Wrapping material according to claim 1, which contains at least one burn additive selected from the group containing tri-sodium citrate, tri-potassium citrate, malates, tartrates, acetates, nitrates, succinates, fumarates, gluconates, glycolates, lactates, oxylates, salicylates, -hydroxy caprylates, bicarbonates, carbonates and phosphates and mixtures thereof.

25. Wrapping material according to claim 24, in which the fraction of burn additive relative to the mass of the wrapping material is less than 3%.

26. Wrapping material according to claim 20, in which the paper has a basis weight of at least 10 g/m.sup.2 and at most 100 g/m.sup.2.

27. Wrapping material according to claim 20, in which the thickness of the paper is at least 10 m and at most 200 m.

28. Smoking article comprising a tobacco column and a wrapping material that surrounds the tobacco column, wherein the wrapping material is formed by a wrapping material according to claim 1.

29. Smoking article according to claim 28, in which the diffusion capacity for CO.sub.2 from the tobacco column through the wrapping material towards the outside is greater than in the opposite direction.

30. Smoking article according to claim 28, at the end of which a filter is provided.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1a shows a perspective view of a wrapping material, which illustrates its geometry.

(2) FIG. 1b shows a sectional view of the wrapping material of FIG. 1a.

(3) FIG. 2 is a diagram, which displays the relationship between the directionality of the diffusion capacity of the wrapping material and the difference in the diffusion capacity of the two plies constituting the two-plied wrapping material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) Firstly, the general structure of a wrapping material according to one embodiment of the invention should be explained referring to FIGS. 1a and 1b.

(5) The wrapping material 101, shown in FIGS. 1a and 1b, is a laminar structure and therefore it extends substantially further in a direction X, tagged 102, and a different direction Y, tagged 103, than in a third direction Z, tagged 104, which is orthogonal to the X-direction 102 and the Y-direction 103. The wrapping material has an upper face 105 and a lower face 106, wherein the designations are arbitrarily selected and in particular do not need to coincide with the term upper side, known from paper production. The Z-direction 104 defines the thickness 107 of the wrapping material is defined at each point by the distance between the upper face 105 and the lower face 106.

(6) In FIG. 1b a virtual middle face A.sub.1, tagged 108, is also shown, which is separated from the upper face 105 at every point by at least one tenth of the thickness of the wrapping material at this point. A further virtual middle face A.sub.2, tagged 109, is also shown in FIG. 1b, which is separated from the lower face 106 at every point by at least on tenth of the thickness of the wrapping material at this point. The virtual middle faces A.sub.1, 108, and A.sub.2, 109, are themselves separated from each other, again by at least one tenth of the thickness of the wrapping material at every point and are located such that the virtual middle face A.sub.1, 108, is closer to the upper face 105 at every point than the virtual middle face A.sub.2, 109.

(7) The upper face 105 and the middle face A.sub.1, 108 define a virtual upper layer 110 of the wrapping material lying between these two faces. In addition, a virtual lower layer 111 is defined between the lower face 106 and the middle face A.sub.2, 109. In an analogous manner, the virtual middle layer 112 is defined by the part of the wrapping material between the middle face A.sub.1, 108, and the middle face A.sub.2, 109.

(8) The wrapping material in the present exemplary embodiment is characterized in that the diffusion capacity of the virtual upper layer 110 or the coefficient of diffusion of the material, respectively, in this virtual upper layer 110 is lower than that of the virtual lower layer 111, and that the diffusion capacity or the coefficient of diffusion, respectively, of the virtual middle layer 112 does not substantially exceed the diffusion capacity or the coefficient of diffusion, respectively, of the virtual lower layer 111 and does not substantially fall below the diffusion capacity or the coefficient of diffusion, respectively, of the virtual upper layer 110.

(9) Thus, overall, a wrapping material is created with a diffusion capacity that is directional in the Z-direction. In particular, the diffusion capacity for carbon dioxide in nitrogen is higher from the lower face to the upper face than in the opposite direction.

(10) Although the origin of the effect according to the invention is not fully explained, it is in any case certain that it cannot be discerned from the model equation of diffusion obvious to the skilled person, that is, from Fick's law mentioned above.

(11) From this it would follow that by reversing the direction of the concentration gradients, the direction of the mass flow is also reversed, but the absolute mass flow remains the same. Fick's law in this form is only valid for free diffusion. The model equation for diffusion in porous materials, however, is very often based on this equation, but uses a reduced coefficient of diffusion corresponding to the porosity of the material. Thus, according to such a simple model, the absolute mass flow is also invariant with respect to reversing the direction of the concentration gradient in porous materials.

(12) It is only when the porous material is no longer considered to be a continuum and instead, diffusion through individual pores is described using a more complex model, for example a numerical solution of the corresponding equations with pores which narrow in a stepwise or continuous manner under appropriate boundary conditions, can it be seen that a reversal of the direction of the concentration gradients not only causes a reversal in the direction of the mass flow, but also a change in its absolute value. The wrapping materials according to the invention utilize this effect.

(13) All measurements of the diffusion capacity were carried out in accordance with CORESTA Recommended Method No. 77 on a Diffusivity Tester A50 from the company Borgwaldt KC.

(14) Comparison Examples

(15) For comparison, five cigarette and plug wrap papers from the prior art were used and in a first step, it was checked that these conventional papers, designated as A to E, do not exhibit the effect according to the invention.

(16) In Table 1 the thickness of the conventional papers A to E and their basis weight are given. The diffusion capacity of each of the papers A-E was measured at different positions 10 times. Mean values (MW) and standard deviations (STD) are labeled with Measurement 1 and are shown in Table 1. Afterwards the papers were flipped over, so that now the other face of the paper was facing the half-chamber of the measurement instrument containing carbon dioxide. Again, 10 measurements at different positions were carried out and the corresponding mean value (MW) and the respective standard deviation (STD) are given as Measurement 2 in Table 1. A t-test for comparison of the mean values of two samples, whose p-values are given in Table 1, shows that at a probability of error of 5%, no statistical differences exist in the diffusion capacity and therefore no directionality of the diffusion capacity in the Z-direction is detectable.

(17) TABLE-US-00001 TABLE 1 Data for materials and comparison examples Measure- Measure- ment 1 ment 2 Material Diffusion Diffusion Basis Capacity Capacity Weight Thickness MW STD STD t-Test Code g/m.sup.2 m cm/s cm/s MW cm/s cm/s p-Value A 22.0 38 1.16 0.04 1.18 0.03 0.224 B 25.0 44 2.24 0.03 2.23 0.03 0.466 C 26.0 58 2.26 0.04 2.22 0.05 0.065 D 24.5 72 4.04 0.08 3.98 0.07 0.092 E 21.0 69 5.43 0.09 5.51 0.09 0.062
Exemplary Embodiments

(18) The papers A-E were now bonded together in all possible combinations of two papers by pressure between two rollers with a line load of 5 N/mm, wherein the rollers were heated to a temperature of 90 C. This resulted in 15 possible two-plied wrapping materials.

(19) Of each of these 15 wrapping materials, the diffusion capacity was measured again. In a first measurement series, 10 measurements were carried out at different positions for each wrapping material, whereby the ply with the higher diffusion capacity was facing the half-chamber, into which carbon dioxide was passed. This measurement series was labeled Measurement 3 and the corresponding mean values (MW) and standard deviations (STD) were calculated and are shown in Table 2.

(20) After that, the wrapping materials were flipped over, so that now the ply with the lower diffusion capacity was facing the half-chamber into which carbon monoxide was passed. Again, 10 measurements at different positions were carried out for each wrapping material. The measurement series was labeled Measurement 4 and the corresponding mean values (MW) and standard deviations (STD) were calculated and entered into Table 2.

(21) For the wrapping materials, consisting of two plies of the same paper, that is AA, BB, CC, DD and EE, there is no difference between the diffusion capacities of the two plies. Consequently, in measurement series 3, an arbitrarily chosen first side and in measurement series 4 the second side of the wrapping material was facing the half-chamber into which carbon dioxide was passed.

(22) As a technically relevant effect may be expected starting from a difference of 0.03 cm/s, a t-test was carried out to test whether the absolute difference of the mean values is greater than 0.03 cm/s with a probability of error of 1%. The t-test was carried out in the usual manner as follows:

(23) Let d.sub.1,i and d.sub.2,i, with i=1, 2, 3, . . . , 10 be the N=10 measured individual values of the diffusion capacity. The mean values D.sub.1 and D.sub.2 of the diffusion capacities are then estimated by

(24) $D_1=\frac{1}{N}\underset{i=1}{\overset{N}{.Math.}}{d}_{1,i}$$\mathrm{and}$$D_2=\frac{1}{N}\underset{i=1}{\overset{N}{.Math.}}{d}_{2,i}$

(25) The standard deviations s.sub.1 and s.sub.2 of the individual values are estimated by

(26) $s_1=\sqrt{\frac{1}{N-1}\underset{i=1}{\overset{N}{.Math.}}{\left(d_{1,i}-D_1\right)}^2}$$\mathrm{and}$$s_2=\sqrt{\frac{1}{N-1}\underset{i=1}{\overset{N}{.Math.}}{\left(d_{2,i}-D_2\right)}^2}$

(27) The absolute difference in the mean values, D, is calculated by
D=|D.sub.1D.sub.2|

(28) The difference of the mean values is approximately normally distributed with a standard deviation s, given by

(29) $s=\sqrt{\frac{1}{N}\left(s_1^2+s_2^2\right)}$

(30) The test statistic t is determined by

(31) $t=\frac{D-0.03}{s}$
whereby D and s have to be given in cm/s.

(32) If t>2.82, the null hypothesis H.sub.0:D<0.03 cm/s is to be rejected with an error probability of less than 1%, and the mean diffusion capacities D.sub.1 and D.sub.2 differ by more than 0.03 cm/s. The probability of an error is given in Table 2 as p-value.

(33) The results show that for all combinations of two different materials with the exception of the combination BC, the mean values for the diffusion capacity of measurement series 3 and 4 differ statistically by at least 0.03 cm/s with a probability of error of 1%. Hence, all these materials show a directional diffusion capacity with respect to the Z-direction.

(34) For the material combination BC, the difference in the diffusion capacity of the plies B and C is only 0.02 cm/s, which is obviously not sufficient to statistically detect the effect according to the invention.

(35) In this test, all five material combinations from the same material do not show a sufficiently large absolute difference in the mean diffusion capacity, which confirms that the directionality of the diffusion capacity is caused by the selection of the materials and not by the mechanical treatment during bonding of the plies.

(36) TABLE-US-00002 TABLE 2 Data for exemplary embodiments Difference of Measure- Measure- mean values ment 3 ment 4 Meas- Diffusion Diffusion ure- t-Test Capacity Capacity ments of the D > 0.03 MW STD MW STD 3 and 4 plies t- p- Code cm/s cm/s cm/s cm/s cm/s cm/s statistic Value AA 0.623 0.014 0.627 0.015 0.005 0.00 3.937 0.998 AB 0.780 0.021 0.698 0.012 0.082 1.08 6.735 <10.sup.3 AC 0.776 0.018 0.688 0.013 0.088 1.10 8.318 <10.sup.3 AD 0.850 0.031 0.688 0.012 0.162 2.88 12.593 <10.sup.3 AE 0.970 0.016 0.811 0.020 0.159 4.27 15.976 <10.sup.3 BB 1.114 0.034 1.091 0.025 0.023 0.00 0.502 0.686 BC 1.133 0.023 1.120 0.020 0.012 0.02 1.828 0.950 BD 1.401 0.025 1.263 0.025 0.138 1.80 9.724 <10.sup.3 BE 1.577 0.033 1.440 0.029 0.137 3.19 7.707 <10.sup.3 CC 1.163 0.025 1.180 0.020 0.018 0.00 1.200 0.870 CD 1.401 0.036 1.270 0.019 0.131 1.78 7.838 <10.sup.3 CE 1.636 0.029 1.484 0.023 0.153 3.17 10.524 <10.sup.3 DD 2.013 0.046 2.000 0.047 0.013 0.00 0.823 0.784 DE 2.277 0.047 2.165 0.046 0.111 1.39 3.901 0.002 EE 2.716 0.068 2.724 0.042 0.009 0.00 0.843 0.790

(37) A further analysis of the data shows a relationship between the difference in the diffusion capacity of the two plies the extent of the directionality of the diffusion capacity, characterized by the difference in the diffusion capacity of measurement series 3 and 4

(38) In FIG. 2, the data for all wrapping materials of Table 2 is shown, as well as a quadratic regression line, for which a coefficient of determination of 0.9122 results. This shows a rather good statistical relationship between these two parameters and coincides with the expectation that larger differences in the diffusion capacity between the plies also results in a larger directionality of the diffusion capacity of the wrapping material. Hence, this diagram suggests that the invention can also be employed for materials extending beyond these ranges.

(39) To demonstrate the effect of appropriate perforation, a paper with a thickness of 70 m and a basis weight of 78 g/m.sup.2 was selected. This paper has an unperforated diffusion capacity of less than 0.01 cm/s, for which reason the directionality was not investigated further. The paper was then perforated in 6 tracks with an appropriately set-up laser. Between the tracks, running in parallel, there was a distance of 0.5 mm and on each track, 50 holes per cm were perforated. The laser was focused conically so that on one face of the paper, the holes had a diameter of about 0.1 mm, while on the other face, the diameter was typically 0.07 mm.

(40) The diffusion capacity was measurement with a measuring head with an opening of 320 mm so that all 6 tracks were positioned parallel to the longer side of the measuring head under the opening of the measuring head. The measurement was carried out at 10 different positions. In a first series of measurements, the face with the larger hole diameter was facing the half-chamber containing carbon dioxide and a mean diffusion capacity of 0.163 cm/s at a standard deviation of 0.012 cm/s resulted. Afterwards, the paper was flipped over so that now the face with the smaller hole diameter was facing the half-chamber containing carbon dioxide. Again, the diffusion capacity was determined at 10 different positions and this resulted in a mean value of 0.103 cm/s with a standard deviation of 0.011 cm/s. A t-test to check if the absolute difference of the mean values exceeded a value of 0.03 cm/s showed a p-value of less than 10.sup.3 and thereby a directional diffusion capacity in the Z-direction at a probability of error of 1%.