Apparatus and method for manufacturing a crimped sheet of filter material

Abstract

The crimping apparatus comprises a first crimping roller (40) and a second crimping roller (42), each being provided with a set of ridges (46) extending circumferentially on an outer surface thereof, each ridge (46) having a root (50), a crest (52) and two flanks (54), the ridges (46) exhibiting a ridge depth (D) and being axially spaced by a defined pitch (P) between the ridges (46). The ridges (46) of one or each of the first crimping roller (40) and the second crimping roller (42) are configured such that the pitch (P) between the ridges (46) is comprises between 0.8 mm and 1.2 mm and the depth-to pitch-ratio (D / P) is comprised between 1.1 and 2.0.

Description

[0001] Apparatus and method for manufacturing a crimped sheet of filter material

[0002] TECHNICAL FIELD

[0003] The invention relates to an apparatus for crimping a sheet of filter material and a method for manufacturing a crimped sheet of filter material, the crimped sheet of filter material being e.g. usable in the production of a filter for an aerosol-generating article.

[0004] BACKGROUND

[0005] An aerosol-generating article generally comprise a plurality of components including an aerosol-generating substrate and a filter.

[0006] An aerosol-generating article filter may comprise a plurality of channels to allow air to flow through the filter.

[0007] The plurality of channels may be provided by crimping a sheet of filter material to form troughs in the sheet of filter material and subsequently gathering the crimped sheet of material to form a rod and cutting the rod into a plurality of segments, each segment defining a respective filter. The trough formed in the crimped sheet of filter material provide airflow channels in the filter.

[0008] It is possible to manufacture a crimped sheet of filter material by feeding the sheet of material between a pair of crimping rollers, one of the crimping rollers or each one of the crimping rollers being provided on its outer surface with ridges extending circumferentially to form parallel troughs in the crimped sheet of filter material. The crimped sheet of filter material is subsequently gathered to form a filter rod and the filter rod is then cut into segments to form a plurality of aerosol-generating article filters.

[0009] Once the filter is added to the aerosol-generating article, it creates resistance to the circulation of an airflow through the aerosol-generating article and in particular the pressure drop (PD) of the airflow or resistance to draw (RTD).

[0010] In particular, for filters essentially made of natural fibers, as opposed to standard cellulose acetate, the sheet of filter material when gathered in the wrapper tends to form larger gaps and holes which also impacts on the visual appearance at the mouth end crosssection. If the filling density of the filter is increased to reduce the voids, the resistance to draw becomes too high and the user experience is negatively impacted.

[0011] SUMMARY

[0012] One of the aims of the invention is to provide an apparatus and a method for crimping a sheet of filter material that allows obtaining an aerosol-generating article component with suitable properties which are related to the crimping, in particular a suitable pressure drop (PD), while maintaining a good visual appearance.

[0013] In this view, the invention proposes a crimping apparatus for crimping a sheet of filter material comprising natural fibres, the apparatus comprising a first crimping roller configured to rotate about a first roller axis and a second crimping roller configured to rotate about a second roller axis, the first crimping roller and the second crimping roller being each provided on an outer surface thereof with a respective set of ridges extending circumferentially, each ridge having a root, a crest and two flanks on either sides of the crest, the ridges exhibiting a depth, the ridges of each set of ridges being spaced by a defined pitch between the ridges, wherein the ridges of at least one or each of the first crimping roller and the second crimping roller being configured with a pitch comprised between 0.8 mm and 1.2 mm and a depth-to-pitch ratio is comprised between 1.1 and 2.0.

[0014] The combination of the range of pitch and the range of depth-to-pitch ratio allows obtaining an aerosol-generating article filter with airflow channels extending therethrough with suitable properties and in particular with a reduced pressure drop, while exhibiting a good visual appearance, in particular with a mouth end cross-sectional surface of the filter which exhibits no hole having an excessive area and a limited “total hole area” which is defined as the sum of the areas of the detectable holes at the cross-section of the filter. The user experience can thus be enhanced.

[0015] The first rotation axis and the second rotation axis are preferably parallel.

[0016] Both the first crimping roller and the second crimping roller are provided with a set of ridges. Preferably, the rollers are designed and arranged in a way that ridges of the first crimping roller interleave with ridges of the second crimping roller.

[0017] As used herein, the term "sheet" denotes a laminar element having a width and length that are substantially greater than the thickness thereof.

[0018] As used herein, the term "crimped sheet" denotes a sheet with a plurality of troughs. The term "crimping" denotes the formation of a plurality of troughs on a sheet of material.

[0019] As used herein, the term "ridge" denotes a protrusion provided on an outer surface of a crimping roller, the protrusion being elongated and forming a crest and two flanks, one on each side of the crest. Each ridge has a root which connects the ridge to the outer surface of the crimping roller.

[0020] As used herein, the term “profile” refers to the shape of a ridge or a set of ridges of a crimping roller in view in section in radial plane passing via the rotation axis of the crimping roller.

[0021] Each ridge of a crimping roller has “ridge profile”. The ridges of each set of ridges provided on a crimping roller define collectively a “crimping roller profile” or “roller profile”.

[0022] As used herein, the term “crest” refers to the highest surface or point of the ridge.

[0023] As used herein, the term “root” refers to lowest point of the ridge or the lowest point between two ridges.

[0024] As used herein, the term "pitch" refers to the axial distance between the median point of the crests of two adjacent ridges of a set of ridges of a crimping roller.

[0025] The ridges of each set of ridges have preferably the same ridge profile and are spaced axially with a constant pitch.

[0026] As used herein, the term “ridge depth” refers to the height of a ridge taken between the crest of the ridge and the root of the ridge. A plurality of parallel ridges extending circumferentially on an outer surface of a crimping roller may be formed by separate axially spaced annular ridges. Each annular ridges extends around the corresponding crimping roller.

[0027] Two adjacent ridges defined between them a “roller trough”. Each roller trough has a bottom which is defined by the area of the outer surface of the crimping roller extending between the roots of the two adjacent ridges.

[0028] Each ridge may be symmetrical, so that the flanks on the opposite sides of the crest of the ridge are symmetrical. In this case, the angle between two flanks forming the same ridge is twice any of the two flank angles.

[0029] Alternatively, one or more of the ridges may be asymmetrical. That is, the flank angles of both flanks of a ridge may be different.

[0030] In some embodiments, the ridge depth of the ridges of each crimping roller is comprised between 0.88 mm and 2.0 mm. More preferably, the ridge depth of the ridges of each crimping roller (first crimping roller and second crimping roller) is comprised between about 1.4 mm and about 1.6 mm.

[0031] In some embodiments, each flank angle is comprised between 0° and 3.4°, preferably between 0.5° and 3.4°, preferably about 2°. The inclination of each flank relative to the radial direction eases the operation of crimping the sheet of filter material with limiting the risk of damaging the sheet of filter material, in particular the risk of tearing off the sheet of filter material. The inclination inferior to 3.4° promotes appropriate deformation of the sheet of filter material to form stable troughs in the sheet of filter material.

[0032] In some embodiments, the crest of each ridge has a width comprised between 0.2 mm and 0.5 mm, preferably between 0.3 mm and 0.4 mm, more preferably between 0.3 mm and 0.35 mm. Such crest allows forming troughs that are beneficial to the pressure drop generated by an aerosol-generating article component.

[0033] Preferably, each ridge has a trapezoidal ridge profile.

[0034] In some embodiments, one or each flank of a ridge connects to the crest of the ridge via a crest fillet. The crest fillet is a sharp or rounded junction between the flank and the crest. When rounded, the crest fillet is convex. The provision of a rounded crest fillet avoids damaging the sheet of material, in particular shredding the sheet of material.

[0035] Preferably, each crest fillet has a radius of curvature comprised between 0.0 mm and 0.3 mm, preferably between 0.05 and 0.2 mm, for example 0.1 mm. This range of radius of curvature is appropriate for forming stable troughs in the sheet of material whilst limiting the risk of damaging the sheet of material.

[0036] In some embodiments, each crest fillet has a radius of curvature R of 0.0 mm. In such embodiments, each crest fillet defines a sharp junction between the crest and the flank joining at the crest fillet. Advantageously, the sharp junction between the crest and the flank allows to provide defined troughs or lines in the crimped sheet without damaging it. The crimped sheet prepared by ridges having sharp edges or junctions between the crest and the flank allows to obtain a suitable pressure drop and a good visual appearance of the filter.

[0037] In some embodiments, each flank connects a bottom between the ridge and an adjacent ridge via a root fillet. Preferably, each root fillet has a radius of curvature comprised between 0 mm and 1.3 mm, preferably between 0.05 and 0.3 mm, for example 0.1 mm.

[0038] In some embodiments, the crimp apparatus is configured to crimp the sheet of filter material with a crimping depth comprised between 0.2 mm and 1 .5 mm, preferably between 0.5 mm and 1.2 mm, most preferably between 0.6 mm and 1.0 mm.

[0039] The invention also relates to a method of manufacturing a crimped sheet of filter material for an aerosol-generating article filter, the method comprising feeding a sheet of filter material between the first crimping roller and the second crimping roller of a crimping apparatus as defined above while rotating the first crimping roller and the second crimping roller, such that the ridges of the first crimping roller and the ridges of the second crimping roller form troughs in the sheet of filter material.

[0040] In some embodiments, the method comprises manufacturing a crimped sheet of filter material as per the method of manufacturing a crimped sheet of filter material as defined above, gathering the crimped sheet of filter material to form a filter rod, cutting the filter rod in a rod-shaped filter, each rod-shaped filter having a portion of gathered crimped sheet of filter material formed from a cut segment of the filter rod. In some embodiments, the troughs of the crimped sheet define corrugations in the filter.

[0041] Preferably, the troughs and / or corrugations are formed in the longitudinal direction or conveying direction of the sheet of filter material.

[0042] In some embodiments, the sheet of filter material comprises a non-woven substrate comprising natural fibers and a binder. Such a sheet of filter material is suitable for forming a filter of an aerosol-generating article.

[0043] In some embodiments, the weight content of the natural fibers of the non-woven substrate is comprised between 85% and 95%, preferably between 86.9% and 95%, in particular between 90% and 93%, and the weight content of the binder is comprised between 5% and 15%, preferably between 5% and 13.1%, in particular between 7% and 10%.

[0044] This composition is suitable in combination with the ridges of the first crimping roller and the second crimping roller of the crimping apparatus for performing crimping with obtaining appropriate troughs and properties of the aerosol-generating article component whilst limiting the risk of deterioration of the sheet of filter material, in particular the risk of shredding the sheet of filter material.

[0045] In some embodiments, the natural fibers comprise or consist of wood pulp, the wood pulp preferably being obtained by a kraft process and / or the binder comprises at least one binding agent being a water-based polymer emulsion.

[0046] The binder may be selected from one or more of an aqueous copolymer dispersion of Ethylene Vinyl Acetate (EVA) and a Polyvinyl Acetate (PVAc) a cellulose derivative, such as ethyl / methyl cellulose, hydroxyethylAmethyl cellulose and / or carboxymethyl cellulose and / or a polysaccharide (or a derivative of a polysaccharide) such as dextrin or starch.

[0047] In some embodiments, the binder comprises a combination of ethylene-vinyl acetate (EVA) and PolyVinyl Acetate (PVAc), wherein the weight ratio of EVA to PVAc is preferably between 70:30 and 30:70, more preferably between 60:40 and 40:60 and even more preferably between 55:45 and 45:55. The filter is for example cylindrical in shape. The filter may have a length comprised between 5 and 30 mm. The filter may be approximately about 7 mm in length or 10 mm, but may have a length of between approximately about 5 mm and approximately about 27 mm.

[0048] The aerosol-generating article is for example in the shape of a rod comprising a rodshaped aerosol-generating substrate and a rod-shaped filter arranged in line. The filter and the aerosol-generating substrate are assembled, for example by wrapping an assembly sheet around at least a portion of the filter and at least a portion of the aerosol-generating substrate, the assembly sheet being preferably adhesive, and / or by wrapping an article wrapper around at least a portion of the filter and at least a portion of the aerosol-generating substrate, the article wrapper being for example cigarette paper. A thus obtained aerosolgenerating article such as a cigarette or a heat-no-burn stick.

[0049] The aerosol-generating article may have a total length between approximately 30 mm and approximately about 100 mm. The aerosol-generating article may have an external circumference between approximately about 15 mm and approximately about 30 mm. Preferably, the aerosol-generating article has an external circumference comprised between 16 mm and 25 mm, such as an external circumference of 16.8 (+ / - 0.2) mm or 21.4 (+ / -0.2) mm or 24.2 (+ / - 0.2) mm.

[0050] Alternatively, the filter is for example configured for use in an aerosol-generating article comprising a replaceable and / or replenishable aerosol-generating substrate. The filter is then provided at a downstream end of the aerosol-generating article, e.g. in a mouthpiece of the aerosol-generating article.

[0051] The aerosol-generating substrate comprises for example a vaporizable material.

[0052] As used herein, the term “aerosol” may include a suspension of vaporizable material such as liquid droplets and / or gas. Said suspension may be in a gas including air. Aerosol herein may generally refer to / include a vapour. Aerosol may include one or more components of a vaporizable material.

[0053] As used herein, the term “vaporizable material” or “precursor” may refer to a smokable material which may for example comprise nicotine or tobacco and an aerosol former. Tobacco may take the form of various materials such as shredded tobacco, granulated tobacco, tobacco leaf and / or reconstituted tobacco. Suitable aerosol formers include: a polyol such as sorbitol, glycerol, and glycols like propylene glycol or triethylene glycol; a non-polyol such as monohydric alcohols, acids such as lactic acid, glycerol derivatives, esters such as triacetin, triethylene glycol diacetate, triethyl citrate, glycerin or vegetable glycerin. In some embodiments, the aerosol generating agent may be glycerol, propylene glycol, or a mixture of glycerol and propylene glycol. The substrate may also comprise at least one of a gelling agent, a binding agent, a stabilizing agent, and a humectant.

[0054] The invention also relates to a filter rod, in particular a filter, formed a crimped and gathered sheet of material surrounded by a wrapper, the sheet of material comprising a non-woven substrate comprising natural fibers and a binder, the filter rod comprising cross- sectional surface with holes exhibiting a maximal hole area and a total hole area, the maximal hole area being 0.2 mm2or less, preferably of 0.15 mm2or less and the total hole area being lower than 1.6 mm2, preferably lower than 1.5 mm2.

[0055] As used herein, the term “filter” refers to one individual rod-shaped filter of aerosol generating article and the term “filter rod” refers to a filter rod having the length of one filter, i.e. a filter, or to a filter rod having the length of several filters, i.e. a filter rod that may be sectioned into a plurality of filters.

[0056] The visual aspect of the end cross-sectional surface of a filter of an aerosol generating article can impact the quality perceived by the user (or “perceived quality”). In particular, the presence of visibly detectable large holes and / or a large number of visibly detectable holes and / or a high density of visibly detectable holes on the end cross-sectional surface of the filter can lower the perceived quality.

[0057] Providing filter rods with cross-sectional surfaces exhibiting a maximal hole area of 0.2 mm2less, preferably of 0.15 mm2or less and a total hole area lower than 1.6 mm2, preferably lower than 1.5 mm2allows preserving the perceived quality.

[0058] The invention also relates to a plurality of filters or filter rods formed a crimped and gathered sheet of material surrounded by a wrapper, the sheet of material comprising a non-woven substrate comprising natural fibers and a binder, each filter or filter rod comprising a cross-sectional surface exhibiting a hole maximal area and a total hole area, wherein the average hole maximal surface of the filters is 0.2 mm2or less, preferably of 0.15 mm2or less and wherein the average total hole area of the filters is lower than 1.6 mm2, preferably lower than 1.5 mm2.

[0059] Due to productions tolerances, values of the maximal hole area and the total hole area may slightly vary over a population of filters or filters rods, in particular filters produced from a same filter rod or filters produced from a same sheet of material. In such cases, the average values of the ranges are considered. Preferably, the number of filters or filter rods can be respectively 20 or 50 or 100 to determine the average values of the range.

[0060] Providing filters with cross-sectional surfaces exhibiting an average maximal hole area of is 0.2 mm2or less, preferably of 0.15 mm2or less and an average total hole area lower than 1.6 mm2, preferably lower than 1.5 mm2allows preserving the perceived quality.

[0061] The crimping apparatus with crimping rollers exhibiting a particular crimping profile as defined above allows forming a filter rod that can be sectioned into filters having cross- sectional surfaces which satisfy the required average maximum hole area and average total hole area.

[0062] The “total hole area” of the cross-sectional surface of a filter is the sum of the area of the holes detectable in the cross-sectional surface of the filter considered. The “maximum hole area” or “largest hole area” of the cross-sectional surface of a filter is the area of the hole having the maximal area among the holes of the cross-sectional surface of the filter, i.e. the area of the largest hole of the cross-sectional surface of the filter. Preferably the cross-sectional surface of the filter is considered at one cross-sectional end of the filter.

[0063] BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The invention and its advantages will be better understood upon reading the following description, which is given by way of non-limiting examples and which is made with reference to the appended drawings, in which:

[0065] - Figure 1 is a schematic view of an installation for manufacturing aerosol-generating article filters, the installation comprising a crimping apparatus having a pair of crimping rollers for crimping a sheet of filter material; - Figure 2 is a partial sectional view of the pair of crimping rollers taken along II - II on Figure 1 and illustrating a nip delimited between the pair of crimping rollers;

[0066] - Figure 3 is a schematic view of a profile of a set of crimping ridges of a crimping roller; and

[0067] - Figure 4 is a schematic view of a cross-sectional surface of a filter rod.

[0068] DETAILED DESCIRPTION OF PREFERRED EMBODIMENTS

[0069] As illustrated on Figure 1 , an installation 10 for manufacturing aerosol-generating article filters 12 comprises a crimping apparatus 14 for crimping a sheet of filter material 18.

[0070] The sheet of filter material 18 is preferably a web of material. The sheet of filter material 18 is for example unwound from a coil 20. The installation 10 comprises a reel 22 for unwinding the sheet of material 18 from the coil 20. Alternatively, the sheet of filter material 18 is supplied from a festoon of bale or pallet.

[0071] The installation 10 comprises for example a gathering station 24 configured for gathering the crimped sheet of filter material 18 into a rod. The gathering station 24 comprises for example a guide 26 having a wide inlet and a narrow outlet, and is configured to pass the crimped sheet of filter material 18 through the guide 26 from the wide inlet to the narrow outlet such as to gather the crimped sheet of material 18 and form a continuous filter rod 28. The guide 26 is for example a funnel.

[0072] The gathering station 24 is optionally configured for wrapping the gathered sheet of filter material 18 into a wrap 30. The wrap 30 is for example provided as a web unrolled from a wrap coil 32 and passed through the guide 26 along with the crimped sheet of filter material 18 such that at the outlet of the guide 26, the wrap 30 is wrapped around the gathered sheet of filter material 18 to form the continuous filter rod 28. The continuous filter rod 28 thus comprises the wrap 30 wrapped around the gathered sheet of filter material 18. The wrap 30 holds the gathered sheet of filter material 18 in the gathered configuration.

[0073] The installation 10 comprises for example a cutting station 34 configured for cutting the continuous filter rod 28 into discrete filter rods 12. Each filter rod 12 exhibits for example the length of several filters of an aerosol-generating article. In such case, the filter rod 12 is subsequently cut into a plurality of filters of an aerosol-generating article. In an alternative, each filter rod 12 exhibits the length of one filter and is thus a filter.

[0074] The crimping apparatus 14 comprises a first crimping roller 40 and a second crimping roller 42 defining between them a nip 44. The first and second crimping roller are interleaved at the nip. The first crimping roller 40 has a first roller axis A1 and is mounted to rotate about the first roller axis A1 . The second crimping roller 42 has a second roller axis A2 and is mounted to rotate about the second roller axis A2. The first roller axis A1 and the second roller axis A2 are parallel to each other. The first roller axis A1 and the second roller axis A2 extend perpendicularly to the conveying direction of the sheet.

[0075] As visible on Figure 2, each of the first crimping roller 40 and the second crimping roller 42 is provided on an outer surface thereof with a set of ridges 46, the ridges 46 of each set of ridges 46 extending circumferentially on the outer surface of the first crimping roller 40 or the second crimping roller 42 for forming parallel troughs in the sheet of filter material 18 passing in the nip 44 delimited between the first crimping roller 40 and the second crimping roller 42.

[0076] Each ridge 56 is an elongated protrusion extending circumferentially on the outer surface of the corresponding crimping roller (first crimping roller 40 or second crimping roller 42).

[0077] The ridges 46 of each set extend circumferentially parallel to each other on the outer surface of the corresponding crimping roller.

[0078] Each ridge 46 is for example an annular protrusion extending around the corresponding crimping roller.

[0079] Each ridge 56 exhibits a ridge profile.

[0080] Each ridge 46 comprises a root 50, a crest 52 and two flanks 54 located on each side of the crest 52. The flanks 54 extend from the root 50 to the crest 52. The ridges 46 each set of ridges 46 extend substantially parallel to each other. Each flank 54 defines a flank angle with a radial direction that is radial with respect to the roller axis (first roller axis A1 or second roller axis A2) of the corresponding crimping roller (first crimping roller 40 or second crimping roller 42).

[0081] The two flanks 54 of each ridge 46 are for example symmetrical with respect to the crest 52 of the ridge 46.

[0082] Each flank 54 defines a flank angle a with a radial direction that is perpendicular to the roller axis (first roller axis A1 or second roller axis A2) of the corresponding crimping roller (first crimping roller 40 or second crimping roller 42).

[0083] The two flanks 54 of each ridge 46 have for example a rectilinear profile in a cross section of the ridge 46 in an axial plane including the roller axis (first roller axis A1 or second roller axis A2) of the corresponding crimping roller (first crimping roller 40 or second crimping roller 42).

[0084] The ridges 46 of each set of ridges 46 are separated by roller troughs 56. Each roller trough 56 is delimited between two adjacent ridges 46 of the set of ridges 46. Each roller trough 56 has a bottom 58 extending between the roots 50 of the adjacent ridges 46 delimiting the roller trough 56.

[0085] The first crimping roller 40 and the second crimping roller 42 each comprise a respective set of ridges 46.

[0086] The ridges 46 of the first crimping roller 40 preferably interleave with the ridges 46 of the second crimping roller 42.

[0087] As used herein, “interleave” means that ridges 46 of first crimping roller 40 are inserted between ridges 46 of the second crimping roller 42 and vice-versa. In other words, ridges 46 of the first crimping roller 40 are engaged into troughs 56 delimited between the ridges 46 of the second crimping roller 42 and vice-versa.

[0088] The distance between the first roller axis A1 and the second roller axis A2 is strictly inferior to the sum of the radial distance between the first roller axis A1 and the crests 52 of the ridges 46 of the first crimping roller 40 and the distance between the second roller axis A2 and the crests 52 of the ridges 46 of the second crimping roller 42. In some embodiments, the crimping apparatus 40 is configured to crimp the sheet of filter material 18 with a crimping depth CD comprises between 0.2 mm and 1.5 mm, preferably between 0.5 mm and 1.2 mm, most preferably between 0.6 and 1.2 mm.

[0089] The crimping depth CD is advantageous to accommodate a sheet of filer material having a sheet width comprised between 120 and 180 mm, preferably between 130 and 150 mm. By selecting the crimping depth CD and / or the sheet width appropriately, the resistance-to-draw can be maintained low while the visual of the filter is not negatively impacted.

[0090] When ridges 46 of the first crimping roller 40 and ridges 46 of the second crimping roller 42 are interleaved, the crimping depth CD corresponds to the depth of penetration of the ridges 46 of one of the first crimping roller 40 and the second crimping roller 42 between the ridges 46 of the other among the first crimping roller 40 and the second crimping roller 42.

[0091] The crimping depth CD corresponds to the difference between the sum of the radial distance between the first roller axis A1 and the crests 52 of the ridges 46 of the first crimping roller 40 and the distance between the second roller axis A2 and the crests 52 of the ridges 46 of the second crimping roller 42 and the distance between the first roller axis A1 and the second roller axis A2.

[0092] The ridges 46 of the first crimping roller 40 and the ridges 46 of the second crimping roller 46 preferably have similar or identical ridge profile and define similar or identical roller profiles.

[0093] The geometry of the ridges 46 of one set is described in detail with reference to Figure 3.

[0094] As stated before, each ridge 46 has a root 50, a crest 52 and two flanks 54 on either side of the crest 52. A trough 56 is delimited between the facing flanks 54 of two adjacent ridges 46. The trough 56 has a bottom 58 extending between the roots 50 of the two adjacent ridges 46.

[0095] The ridges 46 preferably have the same ridge profile. Each ridge 46 exhibits a ridge depth D.

[0096] The ridges 46 are spaced axially uniformly, i.e., with a constant pitch. The pitch P is the axial distance between the crests 52 of two adjacent ridges 46 of the set. The crest point is defined as the highest point of the ridge 46 and, if the crest 52 is flat, the pitch P is determined from the median point of the crest 52.

[0097] The pitch P is comprised between 0.8 mm and 1.2 mm and the depth-to-pitch ratio D / P is comprised between 1.1 and 2.0.

[0098] The depth D is for example comprised between 0.88 m and 2.0 mm. In a preferred example, the depth D is comprised between 1.4 mm and about 1.6 mm.

[0099] Each flank 54 defines a flank angle a which is comprised between 0° and 3.4°, preferably between 0.5° and 3.4°, for example about 2°.

[0100] The two flanks 54 of each ridge 46 are preferably symmetrical with respect to the crest 52 of the ridge 46. The flank angles a of the two flanks 54 of each ridge 46 are preferably equal.

[0101] The two flanks 54 of each ridge 46 have preferably a rectilinear profile.

[0102] In some embodiments, each ridge 46 exhibits a trapezoidal ridge profile, the crest 52 of the ridge 46 being flat. The crest 52 has preferably a width W comprises between 0.2 mm and 0.5 mm, preferably between 0.3 mm and 0.4 mm, more preferably between 0.3 mm and 0.35 mm.

[0103] In some embodiments, each flank 54 of each ridge 46 connects to the crest 52 of the ridge 46 via a crest fillet 60. The crest fillet 60 is a rounded junction between the flank 54 and the crest 52. The crest fillet 60 is convex. The provision of a crest fillet avoids damaging the sheet of filter material 18. Preferably, each crest fillet 60 has a radius of curvature R comprised between 0.0 mm and 0.3 mm, preferably about 0.1 mm. This range of radius of curvature is appropriate for forming stable troughs in the sheet of material whilst limiting the risk of damaging the sheet of material.

[0104] In some embodiments, each crest fillet 60 has a radius of curvature R of 0.0 mm. In such embodiments, each crest fillet 60 defines a sharp edge between the crest 52 and the flank 54 joining at the crest fillet 60.

[0105] In some embodiments, each flank 54 connects to a bottom 58 between adjacent ridges 46 via a root fillet 62. Preferably, each root fillet 62 has a radius of curvature r comprised between 0 mm and 1.3 mm, preferably between 0.05 and 0.3 mm, for example 0.1 mm.

[0106] The bottoms 58 extending the adjacent ridges 46 have a bottom width B. The bottom width B is for example comprises between 0.3 mm and 1.1 mm, preferably about 0.7 mm.

[0107] With referring to Figure 1 , a method of manufacturing a crimped sheet of filter material 18 for an aerosol-generating article component, the method comprising feeding the sheet of filter material 18 between the first crimping roller 40 and the second crimping roller 42 of the crimping apparatus 14 while rotating the first crimping roller 40 and the second crimping roller 42, such that the ridges 46 form troughs in the sheet of filter material 18.

[0108] Besides, a method of manufacturing an aerosol-generating article component comprises manufacturing the crimped sheet of filter material 18, gathering the crimped sheet of filter material 18 to form a continuous filter rod 28 and cutting the continuous filter rod 28 in filter rods 12, each filter rod 12 including a segment of gathered crimped sheet 18.

[0109] The gathering of the crimped sheet of filter material 18 is performed in the gathering station 24, in particular by passing the crimped sheet of filter material 18 through the guide 26, optionally together with a wrap 30 from a roll 32 such that the gathered sheet of filter material 18 is wrapped into the wrap 30 which holds the gathered sheet of filter material 18 in the gathered configuration.

[0110] The cutting of the continuous filter rod 28 is performed in a cutting station 34. Preferably, the troughs provided in the crimped sheet of filter material 18 define channels in the filter rod 12 including the gathered sheet of filter material 18.

[0111] Preferably, the filter rod 12 has a density comprised between 100 mg / cm3and 200 mg / cm3, preferably between 120 mg / cm3and 160 mg / cm3, for example 150 mg / cm3.

[0112] The pressure drop through the filter rod 12 is for example comprised between 1.3 mmWC / mm and 4.5 mmWC / mm, preferably between 1.6 mmWC / mm and 3 mmWC / mm, as determined according to the conditions described in ISO 6565:2015

[0113] The sheet of filter material 18 comprises for example a non-woven substrate comprising natural fibers and a binder. Such a sheet of material is suitable for forming a filter of an aerosol-generating article.

[0114] In some embodiments, the weight content of natural fibers is comprised between 85% and 95%, preferably between 86.9% and 95%, in particular between 90% and 93%, and the weight content of the binder is comprised between 5% and 15%, preferably between 5% and 13.1 %, in particular between 7% and 10%.

[0115] Such composition is suitable in combination with the ridges 46 of the crimping apparatus 14 for performing crimping with appropriate troughs and properties of the filter rod 12 whilst limiting the risk of deterioration of the sheet of material 18, in particular the risk of shredding the sheet of material 18 during crimping thereof.

[0116] In some embodiments, the natural fibers comprise or consist of wood pulp, the wood pulp preferably being obtained by a kraft process and / or the comprises at least one binding agent, the binding agent being for example a water-based polymer emulsion.

[0117] The nonwoven sheet is preferably obtained by short fiber airlaid technology. The average length of the natural fibers, according to some embodiments, is at most 3.5 mm, preferably at most 3.0 mm and most preferably at most 2.8 mm, and / or the average length of the natural fibers is at least 2.0 mm, preferably at least 2.3 mm and most preferably at least 2.5 mm. The binder may be selected from one or more of an aqueous copolymer dispersion of Ethylene Vinyl Acetate, EVA, and a Polyvinyl Acetate, PVAc, a cellulose derivative, such as ethyl / methyl cellulose, hydroxyethylAmethyl cellulose and / or carboxymethyl cellulose and / or a polysaccharide (or a derivative of a polysaccharide) such as dextrin or starch.

[0118] In some embodiments, the binder comprises a combination of ethylene-vinyl acetate (EVA) and PolyVinyl Acetate (PVAc), wherein the weight ratio of EVA to PVAc is preferably comprised between 70:30 and 30:70, more preferably between 60:40 and 40:60 and even more preferably between 55:45 and 45:55.

[0119] The sheet of material 18 has preferably a thickness between 0.3 mm and 1.3 mm and / or a basis weight between 40 g / m2and 60g / m2and / or a width comprises between 50 mm and 240 mm.

[0120] The sheet of filter material 18 has also preferably a volume density of at least 50 mg / cm3, preferably of at least 55 mg / cm3and most preferably of at least 60 mg / cm3, or at least 62 mg / cm3, and / or a volume density of at most 110 mg / cm3, preferably of at most 100 mg / cm3and most preferably of at most 90 mg / cm3.

[0121] The particular profile of the ridges 46 of the first crimping roller 40 and the second crimping roller 42 allows obtaining a crimped sheet of filter material 18 having troughs that allow forming a filter with appropriate properties, in particular with a low range of pressure drop through the filter.

[0122] Examples have been carried out using a sheet of filter material 18 comprising a nonwoven substrate comprising natural fibers and a binder, with a content of natural fibers of 93% and content of binder of 7%. The natural fibers are made of 100% Southern bleached softwood kraft (SBSK). The binder comprises EVA and PVAc with a mass ratio of 50:50. The sheet of filter material 18 has a thickness of 5 mm, a basis weight of 50 g / m2 and a width of 120 mm.

[0123] Filter rods have been produced using crimping rollers with three different profiles and the pressure drop through the filter rods have been measured.

[0124] In each case, the two crimping rollers have identical roller profiles.

[0125] It was possible to manufacture 108-mm filter rods with pressure drops comprised between 175 and 220 mmH20 with no holes of significant size at the end sectional surfaces of the filter rods. This could not be achieved with roller profile 1 or roller profiled 2. When trying to achieve filter rods with lower pressure drop with using roller profile 1 or roller profile 2, the filter rods then occurred to have visible holes at their end surfaces. Visible holes on the filter cross-section negatively affects the visual aspect of the aerosolgenerating article including the filter.

[0126] The examples show that the crimping rollers with the roller profile 3 having the pitch (P) and the depth to pitch ratio (D / P) as per the invention allow obtaining filters with a pressure drop through the filter which is lower than that of the filters obtained with the other roller profiles, whilst keeping a good visual aspect, in particular with no holes of significant size in the filter.

[0127] The visual aspect of the end cross-sectional surface of a filter of an aerosol generating article can impact the perceived quality. In particular, the presence of visibly detectable large holes and / or a large number of visibly detectable holes and / or the density of visibly detectable holes on the end cross-sectional surface of the filter can lower the perceived quality.

[0128] Figure 4 illustrates the end cross-sectional surface of a filter rod 12 made a crimped and gathered sheet of material 18 surrounded by a wrapper 30. The end cross-section surface of the filter rod 12 exhibits holes 64 of various sizes. The holes 64 result from the crimping and gathering of the sheet of material 18. Holes 64 may vary in shape even though holes 64 are illustrated as circular on Figure 4 for sake of illustration only.

[0129] The size of the holes 64 and the total area of holes 64 of the end cross-sectional area of a filter rod 12 is for example measured by capturing an image of the end cross- sectional area of the filter or filter rod (as illustrated e.g., on Figure 4) and performing image analysis the captured image to detect and measure the holes 64 end cross-sectional area of the filter or filter rod.

[0130] The crimping profile of the crimping rollers 40, 42 and the crimping parameters, in particular the crimping depth CD, influence the number of holes 64 and area of the holes 64 of the end cross-sectional surface of the filter rod 12.

[0131] Examples were prepared with using a same crimping profile similar to the crimping profile 3 but with different crimping depths. For each example, a hundred of filter rods were prepared by forming a continuous rod by crimping and gathering a sheet of material comprising a non-woven substrate including natural fibers and a binder and sectioning the continuous rod into the plurality of filter rods. Measures of maximum hole area and total hole area were performed of the filters of each example. The examples and tests were performed using filter rods having a length of 108 mm for ease of manipulation of the filter rods as compared to shorter filters but the results are applicable to filters.

[0132] As seen from these results, varying the crimping depth influences the dimensions of the holes of the end cross-sectional surface of the filter rods. It also influences the pressure drop of the filter.

[0133] Providing filter rods comprising individually and / or in average a cross-sectional surface having no hole having a surface area of 0.2 mm2or more, preferably of 0.15 mm2or more and the total hole area is lower than 1 .6 mm2, preferably lower than 1.5 mm2allows preserving the perceived quality, with appropriate pressure drop across the filter.

[0134] The user experience can thus be enhanced, namely with a lower resistance to draw (RTD) while maintaining a consumer-acceptable visual appearance. It is also possible to achieve higher resistance to draw by increasing the crimping depth without sheet breakage during crimping. The resistance to draw is indeed correlated to the pressure drop the components of the aerosol-generating article.

[0135] The invention is not limited to the examples described above and illustrated on the drawings. Other examples may be contemplated.

Claims

CLAIMS1. Crimping apparatus for crimping a sheet of filter material comprising natural fibres, the crimping apparatus comprising a first crimping roller (40) configured to rotate about a first roller axis (A1) and a second crimping roller (42) configured to rotate about a second roller axis (A2), each of the first crimping roller (40) and the second crimping roller (42) being provided with a set of ridges (46) extending circumferentially on an outer surface thereof, each ridge (46) having a root (50), a crest (52) and two flanks (54), the ridges (46) exhibiting a ridge depth (D) and being axially spaced by a defined pitch (P) between the ridges (46), wherein the ridges (46) of one or each of the first crimping roller (40) and the second crimping roller (42) are configured such that the pitch (P) between the ridges (46) is comprises between 0.8 mm and 1.2 mm and the depth-to pitch-ratio (D / P) is comprised between 1.1 and 2.0.

2. Crimping apparatus according to claim 1 , wherein the ridge depth (D) is comprised between 0.88 m and 2.0 mm, preferably between 1.4 mm and 1.6 mm.

3. Crimping apparatus according to claim 1 or 2, wherein each flank (54) defines a flank angle (a) with a radial direction of the crimping roller (40, 42), the flank angle (a) being lower than 3.4° and preferably comprised between 0.5° and 3.4°.

4. Crimping apparatus according to any one of the preceding claims, wherein the crest (52) of each ridge (46) has a width comprised between 0.2 mm and 0.5 mm and optionally wherein each ridge (46) has a trapezoidal ridge profile.

5. Crimping apparatus according to any one of the preceding claims, wherein each flank (54) of each ridge (46) connects to the crest (52) of the ridge (46) via a crest fillet (60) and optionally wherein each crest fillet (60) has a radius of curvature (R) comprised between 0 mm and 0.3 mm.

6. Crimping apparatus according to any one of the preceding claims, wherein each flank (54) of each ridge (46) connects to the outer surface via a root fillet (62) and optionally wherein each root fillet (62) has a radius of curvature (r) comprised between 0 mm and 1.3 mm.

7. Crimping apparatus according to any one of the preceding claims, configured to crimp the sheet of filter material (18) with a crimping depth (CD) comprised between 0.2 mm and 1.5 mm, preferably between 0.5 mm and 1.2 mm, most preferably 0.6 mm and 1.0 mm.

8. Crimping apparatus according to any one of the preceding claims, wherein the ridges (46) of the first crimping roller (40) and the ridges (46) of the second crimping roller (42) define identical roller profiles, in particular with a same pitch (P) and a same depth to pitch ratio (D / P).

9. A method of manufacturing a crimped sheet of filter material for an aerosolgenerating article filter, the method comprising feeding a sheet of filter material (18) between the first crimping roller (40) and the second crimping roller (42) of a crimping apparatus (14) as in any one of the preceding claims while rotating the first crimping roller (40) and the second crimping roller (42) such that the ridges (46) of each set of ridges (46) form troughs in the sheet of filter material (18).

10. A method of manufacturing an aerosol-generating article filter, the method comprising manufacturing a crimped sheet of filter material as per the method of manufacturing a crimped sheet of claim 9, gathering the crimped sheet of filter material to form a rod, cutting the rod in a rod-shaped filter, each filter having a portion of a gathered crimped sheet formed from a cut segment of the crimped sheet of filter material.

11. A method of manufacturing an aerosol-generating article component as in claim 10, wherein the trough of the crimped sheet of filter material defines corrugations in the filter.

12. A method of manufacturing an aerosol-generating article component as in claim 10 or 11 , wherein the sheet of filter material comprises a non-woven substrate comprising natural fibers and a binder.

13. An aerosol-generating article comprising a filter obtained by the method of any one of claims 10 to 12.

14. Filter rod, in particular filter, formed of a crimped and gathered sheet of material surrounded by a wrapper, the sheet of material comprising a non-woven substrate comprising natural fibers and a binder, the filter comprising a cross-sectional surface exhibiting a maximum hole area and a total hole area, wherein the largest hole areais 0.2 mm2or less, preferably of 0.15 mm2or less and the total hole area is lower than 1.6 mm2, preferably lower than 1.5 mm2.

15. A plurality of filter rods, in particular filters, formed a crimped and gathered sheet of material surrounded by a wrapper, the sheet of material comprising a non-woven substrate comprising natural fibers and a binder, each filter comprising a cross-sectional surface exhibiting a maximum hole area and a total hole area, wherein the average maximal hole area of the filters is 0.2 mm2or less, preferably of 0.15 mm2or less and wherein the average total hole area of the filters is lower than 1.6 mm2, preferably lower than 1.5 mm2.

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