Filter paper for cigarette filters

Abstract

Disclosed herewith is a filter paper for manufacturing filters for smoking articles, in particular filter cigarettes, with the following properties the filter paper comprises fibers comprising pulp fibers, at least 80% by weight, preferably at least 90% by weight, particularly preferably at least 95% by weight and highly particularly preferably 100% by weight of the filter paper is formed by long-fiber pulp fibers, of the fibers, a proportion with respect to the number of the fibers of between 2% and 10%, preferably between 3% and 9% and particularly preferably between 4% and 8% has a length of less than 0.2 mm, the air permeability of the filter paper, measured in accordance with ISO 2965:2009, is between 500 cm.Math.min.sup.−1.Math.kPa.sup.−1 and 15000 cm.Math.min.sup.−1.Math.kPa.sup.−1 and preferably between 1000 cm.Math.min.sup.−1.Math.kPa.sup.−1 and 9000 cm.Math.min.sup.−1.Math.kPa.sup.−1, the number-averaged length of the fibers in the filter paper is greater than 1 mm and less than 5 mm, preferably greater than 2 mm and less than 4 mm, and the number-averaged width of the fibers in the filter paper is between 10 μm and 50 μm, preferably between 20 μm and 40 μm, and particularly preferably between 25 μm and 35 μm.

Claims

1. Filter paper for manufacturing filters for smoking articles, with the following properties: the filter paper comprises fibers comprising pulp fibers, at least 80% by weight of the filter paper is formed by long-fiber pulp fibers, of the fibers, a proportion with respect to the number of the fibers of between 2% and 10% has a length of less than 0.2 mm, the air permeability of the filter paper, measured in accordance with ISO 2965:2009, is between 500 cm.Math.min.sup.−1.Math.kPa.sup.−1 and 15000 cm.Math.min.sup.−1.Math.kPa.sup.−1, the number-averaged length of the fibers in the filter paper is greater than 1 mm and less than 5 mm, and the number-averaged width of the fibers in the filter paper is between 10 μm and 50 μm, wherein said filter paper is crimped in the machine direction or in the cross direction, and wherein the elongation at break in the direction or the directions in which the filter paper is crimped is at most 25%.

2. Filter paper according to claim 1, in which the pulp fibers are bleached, unbleached or form a mixture of bleached and unbleached pulp fibers.

3. Filter paper according to claim 1, in which the long-fiber pulp is sourced from coniferous wood, or from hemp, flax, sisal, aback cotton, ramie, jute, kenaf, gampie, kozu or matsumata.

4. Filter paper according to claim 1, which comprises at most 5% by weight of short-fiber pulp fibers with respect to the mass of the filter paper, wherein said short-fiber pulp fibers are sourced from birch, beech or eucalyptus wood, or from esparto grass.

5. Filter paper according to claim 1, which comprises at most 5% by weight filler materials with respect to the mass of the filter paper, wherein said filler materials are selected from the group consisting of calcium carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, titanium dioxide, talcum, kaolin or aluminum hydroxide, and mixtures thereof.

6. Filter paper according to claim 1, which contains pigments or colorants.

7. Filter paper according to claim 6, wherein the pigments or colorants are iron oxides or a mixture of iron oxides.

8. Filter paper according to claim 1, which contains alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), a hydrophobic substance or one or more fatty acids or one or more fatty alcohols, starch or wet strength agents.

9. Filter paper according to claim 1, wherein the tensile strength in the machine direction is at least 8 N/15 mm and/or at most 45 N/15 mm.

10. Filter paper according to claim 1, wherein the tensile strength in the cross direction is at least 4 N/15 mm and/or at most 9 N/15 mm.

11. Filter paper according to claim 1, wherein the elongation at break in the machine direction is at least 1% and/or at most 2%.

12. Filter paper according to claim 1, wherein the elongation at break in the cross direction is at least 5% and/or at most 6%.

13. Filter paper according to claim 1, wherein the basis weight is between 20 and 60 g.Math.m.sup.−2.

14. Filter paper according to claim 1, wherein the thickness is between 60 μm and 160 μm.

15. Filter paper according to claim 1, wherein at least 95% by weight of the filter paper is formed by long-fiber pulp fibers.

16. Filter paper according to claim 1, wherein of the fibers, a proportion with respect to the number of the fibers of between 4% and 8% has a length of less than 0.2 mm.

17. Filter paper according to claim 1, wherein the air permeability of the filter paper, measured in accordance with ISO 2965:2009, is between 1000 cm.Math.min.sup.−1.Math.kPa.sup.−1 and 9000 cm.Math.min.sup.−1.Math.kPa.sup.−1.

18. Filter paper according to claim 1, wherein the number-averaged length of the fibers in the filter paper is greater than 2 mm and less than 4 mm.

19. Filter paper according to claim 1, wherein the number-averaged width of the fibers in the filter paper is between 25 μm and 35 μm.

20. Process for manufacturing a filter paper for the manufacture of filters for smoking articles, comprising the following steps: (A) Providing an aqueous suspension of unrefined fiber material, wherein the unrefined fiber material comprises unrefined long-fiber pulp fibers and the proportion of unrefined long-fiber pulp fibers is at least 80% by weight of the unrefined fiber material and the aqueous suspension contains between 1% by weight and 5% by weight unrefined fiber material, (B) refining the fiber material in the aqueous suspension from step (A) or the fiber material from a separated part of the aqueous suspension from step (A) in a Papillon refiner with a refining energy between 30 W.Math.h.Math.kg.sup.−1 and 100 W.Math.h.Math.kg.sup.−1 with respect to the mass of the unrefined fiber material and a specific refining edge load of between 0.3 J.Math.m.sup.−1 and 1.0 J.Math.m.sup.−1, and (C) supplying the suspension from step (B) to a paper machine, and forming a filter paper in the paper machine, wherein the number-averaged length of the fibers in the suspension supplied in step (C) is greater than 1 mm and less than 5 mm, and wherein the number-averaged width of the fibers of the suspension supplied in step (C) is between 10 μm and 50 μm, and wherein said filter paper is crimped in the machine direction or in the cross direction, and wherein the elongation at break in the direction or the directions in which the filter paper is crimped is at most 25%.

21. Process according to claim 20, in which between step (B) and (C), a further suspension is added to the suspension which has undergone refining in step (B), and which contains unrefined long-fiber pulp fibers, so that in the mixture of both suspensions, at least 40% by weight of the long-fiber pulp fibers are refined, wherein said further suspension is formed by the separated part of the suspension provided in step (A).

22. Process according to claim 20, in which the step (B) for refining the fiber material is carried out and the suspension supplied in step (C) has a proportion of fibers with a length of less than 0.2 mm of between 2% and 10% with respect to the number of fibers.

23. Process according to claim 22, in which fibers with a length of at most 0.2 mm are added between steps (B) and (C).

24. Process according to claim 22, in which the suspension supplied in step (C) has a proportion of fibers with a length of less than 0.2 mm of between 4% and 8% with respect to the number of fibers.

25. Process according to claim 20, which further comprises a step (D) of crimping the filter paper in the machine direction and/or in the cross direction.

26. Process according to claim 20, in which the proportion of unrefined long-fiber pulp fibers in step (A) is at least 95% by weight of the unrefined fiber material.

27. Process according to claim 20, in which the paper machine of step (C) is an inclined-wire machine.

28. Process according to claim 20, in which the number-averaged length of the fibers in the suspension supplied in step (C) is greater than 2 mm and less than 4 mm.

29. Process according to claim 20, in which the number-averaged width of the fibers of the suspension supplied in step (C) is between 25 μm and 35 μm.

30. Process for manufacturing a filter paper according to claim 1, comprising the following steps: (A) Providing an aqueous suspension of unrefined fiber material, wherein the unrefined fiber material comprises unrefined long-fiber pulp fibers and the proportion of unrefined long-fiber pulp fibers is at least 80% by weight of the unrefined fiber material and the aqueous suspension contains between 1% by weight and 5% by weight unrefined fiber material, (B) refining the fiber material in the aqueous suspension from step (A) or the fiber material from a separated part of the aqueous suspension from step (A) in a Papillon refiner with a refining energy between 30 W.Math.h.Math.kg.sup.−1 and 100 W.Math.h.Math.kg.sup.−1 with respect to the mass of the unrefined fiber material and a specific refining edge load of between 0.3 J.Math.m.sup.−1 and 1.0 J.Math.m.sup.−1, and (C) supplying the suspension from step (B) to a paper machine, and forming a filter paper in the paper machine, wherein the number-averaged length of the fibers in the suspension supplied in step (C) is greater than 1 mm and less than 5 mm, wherein the number-averaged width of the fibers of the suspension supplied in step (C) is between 10 μm and 50 μm, and wherein said filter paper is crimped in the machine direction or in the cross direction, and wherein the elongation at break in the direction or the directions in which the filter paper is crimped is at most 25%.

31. Cigarette filter which is manufactured at least in part from a filter paper with the following properties: the filter paper comprises fibers comprising pulp fibers, at least 80% by weight of the filter paper is formed by long-fiber pulp fibers, of the fibers, a proportion with respect to the number of the fibers of between 2% and 10% has a length of less than 0.2 mm, the air permeability of the filter paper, measured in accordance with ISO 2965:2009, is between 500 cm.Math.min.sup.−1.Math.kPa.sup.−1 and 15000 cm.Math.min.sup.−1.Math.kPa.sup.−1, the number-averaged length of the fibers in the filter paper is greater than 1 mm and less than 5 mm, and the number-averaged width of the fibers in the filter paper is between 10 μm and 50 μm, wherein said filter paper from which said cigarette filter is manufactured at least in part is crimped in the machine direction or in the cross direction, and wherein the elongation at break in the direction or the directions in which the filter paper is crimped is at most 25%.

32. Cigarette filter according to claim 31, which is present in one of the following forms: as filter rod with a length of 60 mm to 200 mm, from which filter plugs or filter plug segments can be manufactured, as filter plug with a length of 10 mm to 50 mm, or as filter plug segment with a length of 3 mm to 10 mm.

33. Filter cigarette comprising a tobacco rod and a cigarette filter, wherein the cigarette filter is formed by a filter plug according to claim 32 or contains a filter plug segment according to claim 32.

34. Filter cigarette according to claim 33, of which the cigarette filter has a filtration efficiency for NFDPM of 20% to 80%.

35. Filter cigarette according to claim 33, with a segmented cigarette filter, which comprises a filter plug segment according to claim 32 and a filter plug segment from cellulose acetate, wherein the filter plug segment from cellulose acetate is located at the mouth end of the cigarette.

36. Cigarette filter according to claim 31, with a diameter of 3 mm to 10 mm.

37. Cigarette filter according to claim 31, with a specific draw resistance of 10 Pa.Math.mm.sup.−1 to 40 Pa.Math.mm.sup.−.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a table 1, which contains the fiber properties of 16 different filter papers, the fiber material of which has been refined with different settings of a Papillon refiner.

(2) FIG. 2 shows a table 2, which contains the basis weight, the thickness, the air permeability, the tensile strength and the elongation of the 16 papers of the table from FIG. 1.

(3) FIG. 3 shows a table 3, which contains the filtration efficiency, the draw resistance and the specific draw resistance of the 16 papers of the table from FIG. 1.

(4) FIG. 4 shows the relationship between the air permeability of the filter paper according to the invention and the filtration efficiency for NFDPM of paper filters manufactured from the filter papers.

(5) FIG. 5 shows the relationship between the draw resistance of a filter and the filtration efficiency for NFDPM for the paper filters according to the invention (circles), conventional paper filters (squares) and conventional filters from cellulose acetate (triangles).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) The following examples are intended to demonstrate the invention and its advantages.

(7) As the fiber material, unrefined long-fiber pulp fibers which had only been bleached were refined in a Papillon refiner at different revolutionary speeds between 600 min.sup.−1 and 1200 min.sup.−1 and power settings between about 60 kW and about 140 kW. 16 different combinations of power settings and revolutionary speeds in total were selected. The specific values are provided in table 1 (“Settings of the Papillon Refiner”), which is shown in FIG. 1. Unrefined long-fiber pulp fibers were added to the refined long-fiber pulp fibers, so that the entire suspension of long-fiber pulp fibers contained about 60% by weight refined and about 40% by weight unrefined long-fiber pulp fibers.

(8) Furthermore, the properties of the fibers in the suspension were determined following ISO 16065 using a L&W Fiber Tester Plus—code 912 Plus, wherein the fine fibers, that is fibers with a length of less than 0.2 mm, were also taken into consideration.

(9) The mean fiber length, the mean fiber width and the proportion of fine fibers as a % with respect to the number of fibers are provided in the corresponding columns of table 1 from FIG. 1. The mean fiber length for the exemplary filter papers according to the invention is between about 2 mm and 2.5 mm, the mean fiber width is between 30.5 μm and 31.5 μm and the proportion of fine fibers is between 5% and 8% with respect to the number of fibers in the fiber material.

(10) The inventors believe that such constant fiber properties can only be achieved with a Papillon refiner despite the variable air permeability of the filter paper, and that these fiber properties essentially contribute to the filtration efficiency of the filters manufactured from these filter papers.

(11) 16 different filter papers were manufactured on an inclined-wire machine from these 16 differently refined long-fiber pulps. The filter papers are numbered from 1 to 16 according to the column “No.” in tables 1 to 3 shown in FIGS. 1 to 3, wherein in all tables, each number designates the same filter paper and the filter manufactured therefrom, respectively.

(12) The basis weight in accordance with ISO 536:2012, the thickness in accordance with ISO 534:2011 and the air permeability in accordance with ISO 2965:2009 were determined for each filter paper and are shown in the corresponding columns in table 2 (FIG. 2). The basis weight is between 34.9 g.Math.m.sup.−2 and 36.6 g.Math.m.sup.−2 and thus is in a very narrow range; also, the thickness only varies between 83 μm and 101 μm. The air permeability of the filter paper on the other hand varies as a function of the degree of refining of the fiber material and is between 1099 cm.Math.min.sup.−1.Math.kPa.sup.−1 and 8364 cm.Math.min.sup.−1.Math.kPa.sup.−1.

(13) In addition, the tensile strength and the elongation at break were determined in accordance with ISO 1924-2:2008 for the non-crimped filter paper respectively in the machine direction (MD) and in the cross direction (CD). Furthermore, these values are provided in the corresponding columns of table 2 (FIG. 2). The values for the tensile strength exceed the minimum technically required to manufacture filters from the filter papers. Similarly, the elongation at break is in a range which is well suited to further processing of the filter paper.

(14) Paper filter rods with a circumference of 24.35 mm and a length of 132 mm were manufactured on a laboratory filter maker from a 240 mm wide reel of each of the 16 filter papers by using an non-porous filter wrapping paper.

(15) The draw resistance of each paper filter rod was determined in accordance with ISO 6565:2011 and is provided in the corresponding columns of table 3 (FIG. 3) calculated for a length of 22 mm and for a specific draw resistance.

(16) Each paper filter rod was divided into six paper filter plugs of equal length of 22 mm and cigarettes were manufactured therefrom with a length of 83 mm, a circumference of 24.5 mm, a length of the tobacco rod of 61 mm and a tobacco weight of 600 mg. The tobacco was formed into a tobacco rod with a conventional cigarette paper with an air permeability of 50 cm.Math.min.sup.−1.Math.kPa.sup.−1. The paper filters were wrapped with a 27 mm long tipping paper, so that the tipping paper overlaps the tobacco rod by 5 mm and thereby connects the paper filter to the tobacco rod.

(17) The tobacco blend and all geometrical data of the cigarettes were identical, so that they only differed with respect to the paper filter. With these cigarettes, the filtration efficiency was determined according to the procedure described above.

(18) The filtration efficiency for nicotine-free dry particulate matter (NFDPM) is provided for each of the 16 filter plugs (22 mm) in table 3 (FIG. 3). The filtration efficiency for NFPDM was between 36.2% and 55.2%. By modification of the length of the filter plug or by using a different reel width to manufacture the paper filter rod, filtration efficiencies below or above this interval can be achieved without any problems, so that the filter paper according to the invention can cover an interval of filtration efficiencies that is normal for filters from cellulose acetate.

(19) FIG. 4 shows the relationship between the filtration efficiency for NFDPM of the paper filter according to the invention and the air permeability of the filter paper. It can be seen that the air permeability is an essential parameter for adjusting the filtration efficiency over a wide range, because all other parameters, such as, for example, basis weight, thickness or fiber properties, were kept almost constant.

(20) The essential advantage of the invention can be demonstrated in FIG. 5. The figure shows the relationship between the draw resistance of a filter and the filtration efficiency for NFDPM for the paper filters according to the invention (circles), conventional paper filters (squares) and conventional filters from cellulose acetate (triangles). All filters had a length of 22 mm.

(21) One of the disadvantages of conventional paper filters can clearly be seen. For example, if a filtration efficiency for NFDPM of 45% is desired, then a conventional paper filter has a draw resistance of about 300 Pa, while a conventional cellulose acetate filter has a draw resistance of about 600 Pa. The draw resistance of an unventilated filter cigarette is essentially determined by the draw resistance of the filter and of the tobacco rod. For a king-size cigarette with a circumference of 24 mm to 25 mm, the smoker expects a draw resistance of about 1000 Pa. Thus, if the conventional cellulose acetate filter with a draw resistance of 600 Pa is exchanged for a conventional paper filter with 300 Pa in an existing cigarette design, the draw resistance of the filter cigarette drops to 700 Pa, that is by 30%. This difference is clearly noticeable for the smoker and is not wanted.

(22) With the filter paper according to the invention, however, at a filtration efficiency for NFDPM of 45%, a paper filter with a draw resistance of about 400 Pa can be manufactured, see example 6, so that the draw resistance of the cigarettes drops to 800 Pa. Thus, in comparison to a conventional filter paper, much less effort is required to adjust the cigarette design to the modified draw resistance.

(23) Similarly, with a conventional filter formed from cellulose acetate at a draw resistance of 700 Pa, a filtration efficiency for NFDPM slightly below 50% can be achieved, while at this draw resistance a conventional paper filter has a filtration efficiency of 70%. With the filter paper according to the invention, for example that of example 3, a paper filter can be manufactured which has a filtration efficiency of slightly above 50% at a similar draw resistance, and is thus closer to a filter from cellulose acetate than a conventional paper filter. This means that the paper filter according to the invention also offers advantages over a conventional paper filter, when the draw resistance of the filter is to be kept constant.

(24) Overall, FIG. 5 shows that with respect to filtration efficiency and draw resistance the paper filters according to the invention are always between conventional paper filters and conventional cellulose acetate filters and additionally at higher draw resistances, the difference between the paper filters according to the invention and the filters from cellulose acetate becomes smaller.

(25) With the filter papers and the paper filters according to the invention, the advantages of paper filters can be utilized better and the change from cellulose acetate filters to the paper filters according to the invention requires fewer adjustments of the cigarette design than for conventional paper filters.