Method and device for manufacturing an embossed sheet of substrate with a controlled thickness value and a reduced content of clusters

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

[0001] Method and device for manufacturing an embossed sheet of substrate with a controlled thickness value and a reduced content of clusters

[0002] Technical Field

[0003] The invention is in the field of embossing, and more particularly embossing of a sheet of substrate woven or non-woven and comprising any material from a list comprising paper, woven cellulose-based material, non-woven cellulose-based material, natural fibrous material, synthetic fibrous material, porous material, and mixtures thereof.

[0004] Background Art

[0005] In an International application of the present applicant, having the filing number PCT / IB2023 / 062474, and being unpublished at the time of filing the present application, an invention is described that is in the field of manufacturing for the inhalable drug delivery system industry, including smoking products in which medical drugs or nicotine may be dispensed in a gas to a user in various inhalable ways, comprising for example vapor, heated tobacco, and conventional burned tobacco as known from cigarettes and cigars, more specifically in a field of embossing, and relating to a component of a filtering element, and the filtering element as such. The manufactured component therein is generally made from sustainable substrates (e.g., paper- or cellulosed-based), which is used to produce sustainable cigarette filters, or filters for other various drug delivery devices. Such substrates may undergo a step of accelerated drying, e.g., using forced air drying, which has a direct impact on their thickness stability.

[0006] These sustainable substrates of variating thickness are leading - upon their folding and transforming into a filter rod - to filters with variating filling factors (i.e., impact on gas flow / filtering properties) and also on influences on their mechanical properties, e.g., stiffness.

[0007] A grammage of these sustainable substrates may vary for instance between 25 gsm and 100 gsm and their thicknesses vary - typically and according to their fabrication process - between 50 pm and 500 pm. Therefore, the mass density of such substrates may typically be found in the region between 0.1 g / cm3 and 1.0 g / cm3.

[0008] The sustainable substrate's grammage gives a much better idea as to the actual thickness of a paper. As a general rule, 10-35 gsm is of tissue consistency; 35-70 gsm is lighter textweight, 70-100 gsm is medium textweight, 100-120 gsm is heavy textweight / light cardstock, 120— 150 gsm is regular cardstock weight, 150-200 gsm is heavy cardstock, and greater than 200 gsm is super heavy cardstock.

[0009] The above-mentioned invention provides a method and an embossing set-up to manufacture from the sustainable substrate an embossed sheet of material that has a controlled material thickness. This may allow to compensate for a material that is uneven prior to embossing, i.e., has a variable thickness, and to confer an improved control of draft through a filtering element made using the embossed sheet of material.

[0010] The filtering element of a drug-delivery device has a major influence on the customer experience of the end user of such a device and the common practice consists in designing filter elements with predefined Pressure Drop (PD) values for specific products and market segments. This means that the filter-element manufacturing process targets to produce filter-element with predefined PD values and the lowest possible Coefficient of Variation (CV). The present invention is of importance in achieving the latter goal, namely in reducing the CV value and thus increasing the reproducibility of the aforesaid manufacturing process.

[0011] It has been found that such manufacturing method and embossing set-up may generate debris from the sustainable substrate, such as for example originating from clusters contained in the sustainable substrate and released from the sustainable substrate at the time of embossing. Indeed, this may also happen with a non-sustainable substrate in case this contains for example clusters that release from the non-sustainable substrate at the time of embossing. As a result, the manufactured may vary and be negatively affected by the debris, despite all care taken. For example, the debris may deposit on surfaces of embossing tools and affect embossing behaviour. It is also possible that the debris gets included in the manufactured embossed sheet of material and any product that makes use of the embossed sheet of material.

[0012] The present invention aims to provide a solution to produce an embossed sheet of substrate that offers an improved homogeneity of its thickness value and comprises a reduced content of components susceptible of generating debris.

[0013] The invention is particularly advantageous for example when the embossed sheet of substrate is intended for use in a further manufacturing process that aims at obtaining filtering elements as presented herein above, in which the manufacturing process involves a subsequent embossing of the embossed sheet of substrate.

[0014] More particularly, the invention advantageously alleviates negative effects produced in the prior art embossing process described in the above cited International application, when embossing a substrate for the manufacturing of the component of the filtering element, and the filtering element as such, or any other product made from the substrate, more particularly for a case in which the substrate presents inhomogeneous thickness values and / or contains clusters prior to embossing. The negative effects may comprise an unacceptably large variance of filtering properties. Summary of invention in a first aspect, the invention provides a method for manufacturing an embossed sheet of substrate. The method is configured to produce a controlled thickness value of the embossed sheet of substrate and to reduce a content of clusters present in the non-embossed substrate. The method comprises steps of providing a sheet of substrate comprising a first material, the sheet of substrate having an average starting thickness; providing an embossing roller system comprising at least a first and a second embossing roller, having respectively a first radial profile and a corresponding second radial profile congruent to the first radial profile, the first radial profile comprising embossing structures protruding from or recessed in a base surface of the first embossing roller, and forming radially oriented ridges and grooves respectively; inserting the sheet of substrate in a nip formed between the first and the second embossing roller; adjusting an embossing pressure between the first and the second embossing roller to obtain a determined nip value of the nip, smaller than the average starting thickness; embossing the sheet of substrate; thereby obtaining the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness; compressing in the nip at least a first type of cluster comprising the first material inside the embossed sheet of substrate; processing at least a second type of cluster made of a second material different from the first material in any one of the following manners: compressing and maintaining the at least one second type of cluster in the embossed sheet of substrate; extracting the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure (P), which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to a surface of the embossed sheet of substrate; extracting the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure, which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to any one of the base surfaces and the embossing structures of the first and the second embossing rollers.

[0015] The method further comprises detaching the debris from the base surfaces and the embossing structures by means of a roller cleaning tool; and removing the detached debris from the embossing roller system by means of an air-depression cleaning system.

[0016] In a preferred embodiment, the method further comprises after embossing the sheet of substrate: leading the embossed sheet of substrate through at least an additional debris removal system, thereby deflecting the embossed sheet of substrate on a removal tool of the additional debris removal system, configured to detach debris adhering to the surface of the embossed sheet of substrate; and removing the detached debris from the debris removal system by means of an additional air-depression cleaning system corresponding to the additional debris removal system.

[0017] In a further preferred embodiment, the removal tool to detach debris adhering to the surface of the embossed sheet of substrate comprises any one of the following items of a list comprising: a cylinder comprising a roughened surface configured to be in contact with the embossed sheet of substrate; a curved roughened surface configured to be in contact with the embossed sheet of substrate; a blade comprising an edge configured to be in contact with the embossed sheet of substrate; an ultrasonic wave generator configured to project an ultrasonic beam towards the embossed sheet of substrate.

[0018] In a further preferred embodiment, the roller cleaning tool comprises at least a scrapper for each of the embossing rollers, each scrapper comprising an edge configured to be presented towards the roller surface of the corresponding embossing roller, and having a shape fitting congruently in the corresponding radial profile of the embossing roller, and configured in such a way that the debris adhering to any one of the base surface and the embossing structures of the roller surface is removed from the roller surface while the embossing roller rotates.

[0019] In a further preferred embodiment, the step of providing the embossing roller system comprises mounting each of the first and the second embossing rollers in a corresponding quick exchange fixture, whereby each of the quick exchange fixtures is removably mounted in a frame.

[0020] In a further preferred embodiment, the step of providing the embossing roller system comprises mounting and adjusting the first and the second embossing rollers in a quick exchange cassette, whereby the quick exchange is removably mounted in a frame.

[0021] In a further preferred embodiment, the method further comprises providing a further embossing roller system comprising a third and a fourth embossing roller, with further embossing features configured for embossing at least an aerodynamic profile on the embossed sheet of substrate, the embossed aerodynamic profiles being configured to modify in a determined manner flow properties for a gas flow passing through the embossed aerodynamic profiles by creating a gas flow turbulence; inserting the embossed sheet of substrate in a further nip formed between the third and the fourth embossing rollers; further embossing the embossed sheet of substrate.

[0022] In a further preferred embodiment, the further embossing roller system is part of a production chain for manufacturing from the sheet of substrate a filtering element configured for an inhalable drug delivery device, and for filtering a mainstream gas flow passing through the filtering element.

[0023] In a further preferred embodiment, the step of providing the further embossing roller system comprises mounting each of the third and fourth embossing roller in a corresponding quick exchange fixture, whereby each of the quick exchange fixtures is removably mounted in a frame. In a further preferred embodiment, the step of providing the further embossing roller system comprises mounting each of the third and fourth embossing roller mounting and adjusting the first embossing roller and the second embossing roller in a quick exchange cassette, whereby the quick exchange is removably mounted in a frame.

[0024] In a further preferred embodiment, each of the radially oriented ridges and grooves comprises two contiguous radially directed flanks that define an angle between two contiguous flanks of the radially ridges and grooves that has a value between 75° and 140°.

[0025] In a further preferred embodiment, the radially oriented ridges and grooves are described by a top-of-ridge to bottom-of-groove height value situated in a range 0.1 mm and 1 .0 mm.

[0026] In a further preferred embodiment, the radially oriented ridges and grooves are arranged in a parallel, periodic manner which is described by a dimensional spacing of at least 0.5 mm between two adjacent ridges and grooves.

[0027] In a further preferred embodiment, the first and the second embossing rollers are driven and selfsynchronized by means of the radial embossing features engaged into each other by applying an embossing pressure between the rollers.

[0028] In a further preferred embodiment, the first and the second embossing rollers are driven and synchronized by any means from a list of synchronization means comprising toothed-wheels gears, helicoidal gears, servomotors.

[0029] In a further preferred embodiment, the non-embossed sheet of substrate has a grammage in a range between 10 gsm and 150 gsm and a starting average thickness value in a range between 0.02 mm and 1 .0 mm.

[0030] In a further preferred embodiment, the sheet of substrate comprises any material from a list comprising paper, woven cellulose-based material, non-woven cellulose-based material, natural fibrous material, synthetic fibrous material, porous material, and mixtures thereof.

[0031] In a second aspect, the invention provides a system for manufacturing an embossed sheet of substrate. The system is configured to produce a controlled thickness value of the embossed sheet of substrate and to reduce a content of clusters present in the non-embossed substrate. The system comprises an embossing roller system comprising at least a first and a second embossing roller, having respectively a first radial profile and a corresponding second radial profile congruent to the first radial profile, the first radial profile comprising embossing structures protruding from or recessed in a base surface of the first embossing roller, and forming radially oriented ridges and grooves respectively. The embossing roller system further comprises a nip formed between the first and the second embossing roller and configured for inserting therein a sheet of substrate comprising a first material, the sheet of substrate having an average starting thickness; pressure adjusting means configured to adjust an embossing pressure between the first and the second embossing roller and obtain a determined nip value of the nip, smaller than the average starting thickness; whereby an embossing of the sheet of substrate enables to obtain the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness; compress at least a first type of cluster comprising the first material inside the embossed sheet of substrate; process at least a second type of cluster made of a second material different from the first material in any one of the following manners: compress and maintain the at least one second type of cluster in the embossed sheet of substrate; extract the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure, which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to a surface of the embossed sheet of substrate; extract the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure (P), which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to any one of the base surfaces and the embossing structures of the first and second embossing rollers.

[0032] The system further comprises a roller cleaning tool configured to detach the debris from the base surfaces and the embossing structures; and an air-depression cleaning system configured to remove the detached debris from the embossing roller system.

[0033] In a preferred embodiment, the system further comprises at least an additional debris removal system, configured to further lead through the embossed sheet of substrate, a removal tool in the additional debris removal system configured to deflect the embossed sheet of substrate, and configured to detach debris adhering to the surface of the embossed sheet of substrate; and an additional air-depression cleaning system corresponding to the additional debris removal system, configured for removing the detached debris from the debris removal system by means of an additional air-depression cleaning system.

[0034] In a further preferred embodiment, the removal tool to detach debris adhering to the surface of the embossed sheet of substrate comprises any one of the following items of a list comprising: a cylinder comprising a roughened surface configured to be in contact with the embossed sheet of substrate; a curved roughened surface configured to be in contact with the embossed sheet of substrate; a blade comprising an edge configured to be in contact with the embossed sheet of substrate; an ultrasonic wave generator configured to project an ultrasonic beam towards the embossed sheet of substrate.

[0035] In a further preferred embodiment, the roller cleaning tool comprises at least a scrapper for each of the embossing rollers, each scrapper comprising an edge configured to be presented towards the roller surface of the corresponding embossing roller, and having a shape fitting congruently in the corresponding radial profile of the embossing roller, and configured in such a way that the debris (302) adhering to any one of the base surface and the embossing structures of the roller surface is removed from the roller surface while the embossing roller rotates.

[0036] In a further preferred embodiment, the system further comprises at least two quick exchange fixtures, respectively configured to mount each of the first and the second embossing rollers, whereby each of the quick exchange fixtures is removably mounted in a frame.

[0037] In a further preferred embodiment, the system further comprises a quick exchange cassette configured to comprise the first and the second embossing rollers adjusted inside the quick exchange cassette, and the quick exchange cassette is removably mounted in a frame.

[0038] In a further preferred embodiment, the system further comprises a further embossing roller system comprising a third and a fourth embossing roller, with further embossing features configured for embossing at least an aerodynamic profile on the embossed sheet of substrate, the embossed aerodynamic profiles being configured to modify in a determined manner flow properties for a gas flow passing through the embossed aerodynamic profiles by creating a gas flow turbulence. The further embossing roller system further comprises a further nip formed between the third and the fourth embossing rollers, and configured for inserting therein the embossed sheet of substrate.

[0039] In a further preferred embodiment, the further embossing roller system is part of a production chain for manufacturing from the sheet of substrate a filtering element configured for an inhalable drug delivery device, and for filtering a mainstream gas flow passing through the filtering element.

[0040] In a further preferred embodiment, the system further comprises at least two further quick exchange fixtures, respectively configured to mount each one of the third and fourth embossing rollers, whereby each of the further quick exchange fixture is removably mounted in a frame.

[0041] In a further preferred embodiment, the system further comprises a further quick exchange cassette configured to comprise the third embossing roller and the fourth embossing roller adjusted inside the further quick exchange cassette, and the further quick exchange cassette is removably mounted in a frame.

[0042] In a further preferred embodiment, each of the radially oriented ridges and grooves comprises two contiguous radially directed flanks that define an angle between two contiguous flanks of the radially ridges and grooves that has a value between 75° and 140°.

[0043] In a further preferred embodiment, the radially oriented ridges and grooves are described by a top-of-ridge to bottom-of-groove height value situated in a range 0.1 mm and 1 .0 mm. In a further preferred embodiment, the radially oriented ridges and grooves are arranged in a parallel, periodic manner which is described by a dimensional spacing of at least 0.5 mm between two adjacent ridges and grooves.

[0044] In a further preferred embodiment, the first and the second embossing rollers are configured to be driven and self-synchronized by means of the radial embossing features engaged into each other by applying an embossing pressure between the rollers.

[0045] In a further preferred embodiment, the first and the second embossing rollers are driven and synchronized by any means from a list of synchronization means comprising toothed-wheels gears, helicoidal gears, servomotors.

[0046] In a further preferred embodiment, the non-embossed sheet of substrate has a grammage in a range between 10 gsm and 150 gsm and a starting average thickness value in a range between 0.02 mm and 1 .0 mm.

[0047] In a further preferred embodiment, the sheet of substrate comprises any material from a list comprising paper, woven cellulose-based material, non-woven cellulose-based material, natural fibrous material, synthetic fibrous material, porous material, and mixtures thereof.

[0048] Brief Description of the Figures

[0049] The invention will be better understood through the description of example embodiments of the invention and in reference to the Figures, wherein

[0050] Figure 1 shows an example of a system for manufacturing an embossed sheet of substrate according to the invention;

[0051] Figure 2 shows an example of a piece of a sheet of substrate prior to embossing, and which comprises clusters;

[0052] Figure 3 shows an example of a piece of an embossed sheet of substrate as obtained with the invention;

[0053] Figure 4 shows a further example of the system for manufacturing an embossed sheet of substrate according to the invention;

[0054] Figure 5(A) shows a preferred embodiment of the system for manufacturing an embossed sheet of substrate with additional debris removal systems according to the invention;

[0055] Figure 5(B) shows a cross section through an embossed sheet of substrate before and after passing through an additional debris removal system;

[0056] Figure 6 shows a preferred embodiment for a set of embossing rollers driven by toothed wheels; Figure 7 contains an example of an embossed sheet of substrate and magnified cross-sections of embossing rollers used for embossing;

[0057] Figure 8 contains a further example of an embossed sheet of substrate and a magnified crosssection of embossing rollers used for embossing;

[0058] Figure 9 contains yet a further example of an embossed sheet of substrate and magnified crosssections of embossing rollers used for embossing;

[0059] Figure 10 contains yet a further example of an embossed sheet of substrate and a magnified cross-section of embossing rollers used for embossing;

[0060] Figures 1 1 (A)-1 1 (C) contain views of examples for quick-exchange devices configured for housing a set of embossing rollers according to the invention;

[0061] Figure 12 contains a view of a system for manufacturing an embossed sheet of substrate with an example embodiment of a roller cleaning tool in form of scrappers according to the invention;

[0062] Figure 13 contains two views of example embodiments for any of the embossing rollers according to the invention;

[0063] Figure 14 contains a view of a system for manufacturing an embossed sheet of substrate with a schematical illustration of two different types of gears for driving and synchronizing the embossing rollers according to the invention;

[0064] Figure 15 contains a view of an embossing roller with ring-shaped zones at its extremities that comprise axially oriented ridges and grooves used to drive and synchronize embossing rollers according to an example of the invention;

[0065] Figure 16 contains a schematic illustration of a set of embossing rollers with ring-shaped shoulders at their extremities;

[0066] Figure 17 contains a further schematic illustration of a set of embossing rollers with ring-shaped shoulders at their extremities;

[0067] Figure 18 illustrates a preferred embodiment of the system for manufacturing an embossed sheet of substrate according to the invention, where it is a part of an online production line for manufacturing a filter element;

[0068] Figure 19 illustrates a further preferred embodiment of the system as in Figure 18 with additional debris removal systems according to the invention;

[0069] Figure 20 illustrates a further example of an embossed sheet of substrate further embossed according to the invention, bearing aerodynamic profiles; Figure 21 schematically illustrates an obtaining of filtering elements using an embossed sheet of substrate as resulting from the invention;

[0070] Figure 22 schematically illustrates how a filtering element, in this case a cigarette filter, may be mounted to a tobacco containing section in order to obtain a cigarette according to prior art;

[0071] Figure 23 schematically illustrates a structure of an inhalable drug delivery device according to prior art;

[0072] Figure 24 contains a flowchart illustrating an example embodiment of a method for manufacturing an embossed sheet of substrate according to the invention.

[0073] Same references will be used to designate same or similar features that appear throughout the Figures.

[0074] Glossary

[0075] With regard to a sheet of substrate

[0076] - cluster: an agglomeration of matter embedded in a sheet of substrate, originating from a substrate manufacturing process and presenting locally different physical properties than the substantial rest of the substrate; the cluster may consist of the same matter as the substantial rest of the substrate (e.g., cluster of fibers) and locally exhibit a higher mass density, or it may consist of a foreign matter (e.g., additives, impurities) and locally exhibit a higher hardness than the substantial rest of the substrate;

[0077] - debris: an agglomeration of matter, initially embedded in the sheet of substrate, which upon embossing according to the invention is ejected / separated from the substrate;

[0078] - woven substrate: a fibrous substrate (e.g., natural or synthetic fibers), in which the substrate substantially consists of interlaced fibers;

[0079] - non-woven substrate: a substrate consisting of non-fibrous material, of short fibers, and of long fibers, which are bonded together by chemical means or by mechanical or heat treatment;

[0080] - average starting thickness: the mean value of all thickness values of the non-embossed sheet of substrate measured at a plurality of spots along the substrate.

[0081] With regard to a filtering element

[0082] - resistance to draw (RTD), or pressure drop (PD): the amount of suction that must be used to pull a gas flow a filter, usually given as the pressure required to force air through the filter at the rate of 17.5 ml / sec; - coefficient of variation (CV): the ratio between the standard deviation and the mean value of the individual PD values measured for the filtering elements of a production batch; as a statistical value, CV provides an indication about the reproducibility of a production method, whereas CV values of 5% or less indicate a stable process.

[0083] With regard to a filter-element production line

[0084] - online: the embossing roller system is directly integrated the filter-element production line;

[0085] - atline: the embossing roller system is integrated into an adjacent production flow, next to the filter-element production line;

[0086] - offline: the embossing roller system is integrated into the substrate production line, whereby the embossed substrate is used to manufacture filter elements on a different production line.

[0087] Detailed Description of Example Embodiments of the Invention

[0088] The inventive system and method for manufacturing an embossed sheet of substrate result from ecology-motivated research which for example aims to replace conventional cellulose acetate cigarette filters, while at least maintaining their well-established filtering properties (e.g., resistance to draw and its coefficient of variation), with other categories of suitable, sustainable sheet substrates, more preferably with filters made of paper-based materials, or any material from a list comprising paper, wool, plant- or animal-based fibrous material. The invention provides a method and a system configured for manufacturing an embossed sheet of substrate, and for producing a controlled thickness value of the embossed sheet of substrate, that may be used as a component of a filtering element and that may further be embossed to comprise further embossed features configured for influencing a flow of a mainstream gas flow traversing the filtering element. The embossing according to the invention also reduces a content of clusters present in the non-embossed substrate, whereas both the constancy of the controlled thickness value of the embossed sheet substrate and the reduced content of clusters have a direct positive impact on the reduction of the statistic variations of the properties of the filtering elements obtained through folding of the embossed sheet of substrate.

[0089] Referring now to Figure 1 , this shows an example of a system for manufacturing an embossed sheet of substrate according to the invention. A sheet of substrate 101 is embossed using an embossing roller system 102, in order to obtain an embossed sheet of substrate 100 with a controlled thickness value and a reduced content of clusters present in the non-embossed substrate 101 (clusters not illustrated in Figure 1). According to a feed direction 112, the sheet of substrate 101 to be embossed is guided using optionally at least a deflection roller 113, into a nip 105 between a first 103 embossing roller and a second 104 embossing roller, which bear congruent radial embossing features (not represented). More precisely the first embossing roller 103 has a first radial profile and the second embossing roller 104 has a corresponding second radial profile congruent to the first radial profile. The first radial profile comprises embossing structures protruding from or recessed in a base surface of the first embossing roller 103 and forming radially oriented ridges and grooves respectively. The embossing roller system 102 may comprise pressure P applying means suggested by a set of opposing arrows. The system for manufacturing an embossed sheet of substrate further comprises roller cleaning tools 106 and 107 configured to detach the debris (debris not illustrated) from the base surfaces and the embossing structures, and thus located in front of the rotating embossing rollers 103 and 104. The system for manufacturing an embossed sheet of substrate further comprises an airdepression cleaning system 108, 109, configured to remove the detached debris from the embossing roller system 102, for example by exhausting the detached debris. For subsequent Figures and considerations, zones 110 and 111 are respectively indicated on the sheet of substrate to be embossed 101 and on the embossed sheet of substrate 100 embossed according to the invention.

[0090] Referring now to Figure 2 this shows an example of a piece of the sheet of substrate prior to embossing, and which comprises substrate clusters. Figure 2 shows a cross-sectional view 201 along a line 204 from a zone 110 of the sheet of substrate 101 (as shown in Figure 1) to be embossed according to the invention. The cross-sectional view 201 illustrates the sheet of substrate 101 prior to embossing, notably fibers 200 giving the sheet of substrate 101 its basics structure; the fibers 200 may be of natural or synthetic origin and they may be present in a woven or non-woven manner (not exhaustively illustrated). Main issues affecting the sheet of substrate 101 , which are addressed by the invention, comprise substantially different substrate thickness values 203 and a presence of clusters 202 that are embedded in and even protruding from a surface of the sheet of substrate 101 , as depicted in the cross-sectional view 201.

[0091] Referring now to Figure 3 this shows an example of a piece of the embossed sheet of substrate 100 as obtained with the invention. Figure 3 shows a cross-sectional view 301 along a line 302 from a zone 111 of the embossed sheet of substrate 100 (as shown in Figure 1) embossed according to the invention, with a controlled thickness value and a reduced content of clusters. Lines 300 schematically illustrate ridges and grooves embossed by means of the radial embossing features present on the embossing rollers (not represented) and the cross-sectional view 301 originates from the embossed sheet of substrate 100. The fibers 200 give the embossed sheet of substrate 100 its basics structure. The fibers 200 may be of natural or synthetic origin and they may be present in a woven or non-woven manner (not exhaustively illustrated). The cross-sectional view 301 shows a substantially constant thickness value 303 and crushed and downsized clusters 304 still embedded in the embossed sheet of substrate 100, as well as clusters 305 and 306, possibly downsized, and respectively still adhering as debris at a surface of the embossed sheet of substrate 100, or already detached as debris from the sheet of substrate 100, to adhere to the surfaces or the embossing rollers (not represented).

[0092] Referring now to Figure 4 this shows a further example of the system for manufacturing an embossed sheet of substrate according to the invention similar as in Figure 1 but extended with an additional embossing roller bearing radial embossing structures (structures not illustrated). The sheet of substrate 101 is embossed using a three-rollers embossing system 400, in order to obtain an embossed sheet of substrate 100 with a controlled thickness value and with a reduced content of clusters. According to the feed direction 112, the sheet of substrate to be embossed 101 is guided using the optional deflection roller 113, to the embossing rollers 401 , 402, 403 bearing radial embossing features (not represented). The depicted system for manufacturing an embossed sheet of substrate further comprises roller cleaning tools 106 and 107 configured to detach the debris (debris not illustrated) from the embossing rollers, thus located in front of the rotating embossing rollers 401 and 403. The system for manufacturing an embossed sheet of substrate further comprises an air-depression cleaning system 108, 109, configured to remove the detached debris from the embossing roller system 400, for example by exhausting the detached debris.

[0093] Referring now to Figure 5(A) this shows a preferred embodiment of the system for manufacturing an embossed sheet of substrate with additional debris removal systems according to the invention, while Figure 5(B) shows a cross-sectional view through an embossed sheet of substrate before and after passing through an additional debris removal system. The system for manufacturing an embossed sheet of substrate produces an embossed sheet of substrate 507 with a controlled thickness value and with a substantially reduced content of clusters. As indicated by the feed direction 112, the sheet of substrate 101 to be embossed is fed into the nip (not represented) between the first 103 and the second 104 embossing rollers, which bear radial embossing features (not represented), and which respectively rotate in front of the roller cleaning tools 106 and 107, whereas the detached debris (not represented) are exhausted from the embossing system using the air-depression cleaning system 108, 109. The cross-sectional view from the zone 301 of the embossed sheet of substrate 100, with controlled thickness value and with reduced content of clusters is also depicted in Figure 5(B) and it illustrates the crushed and downsized clusters 304 embedded in the embossed sheet of substrate 100 and the downsized clusters 305 still adhering at a surface of the embossed sheet of substrate 100. In a further process step of this embodiment, the embossed sheet of substrate 100 with controlled thickness value and with reduced content of clusters, passes through at least an additional debris removal system 505, 506, mainly comprising an additional debris removal means 501 , 502 (e.g., a rotating roughened cylinder) and an air-depression cleaning device 503, 504. The additional debris removal means may be embodied by a roughened (preferably with a mean surface roughness value Ra below 1 .0 pm) metallic or ceramic curved surface configured to be in contact with the embossed sheet of substrate cylinder, or by an edge configured to be in contact with the embossed sheet of substrate, or by an ultrasonic wave generator configured to project an ultrasonic beam towards the embossed sheet of substrate, enabling the detachment of substrate clusters 305 from the sheet of substrate 100. A further cross-sectional view 500, from the embossed sheet of substrate 507 with a controlled thickness value and with a substantially reduced content of clusters, shows the remained crushed and downsized clusters 304 still embedded in the embossed sheet of substrate 507 is also depicted in Figure 5(B).

[0094] Figure 6 shows a preferred embodiment for a set of embossing rollers driven by toothed-wheels, in which the first 103 and the second 104 embossing rollers are driven by respective toothed- wheels located at their extremities. The first embossing roller 103 comprises as illustrated by a zone 600 a first radial profile comprising embossing structures protruding from or recessed in a base surface of the first embossing roller, and forming radially oriented ridges and grooves respectively (detail not represented in the figure) and the second embossing roller 104 comprises as illustrated by a zone 601 a second radial profile congruent to the first radial profile. The zone 600 on the first embossing roller 103 and the zone 601 on the second embossing roller 104 are defined in a symbolic schematic manner and their hatching representation will be used throughout the subsequent figures and considerations.

[0095] Figure 7 contains an example of the embossed sheet of substrate 100 and magnified crosssections 709 and 710 of embossing rollers used for embossing. More precisely, Figure 7 shows a view from above of the zone 111 from the sheet of substrate 100 embossed according to the invention, with a controlled thickness value and with a reduced content of clusters, the embossed sheet of substrate bearing recessed axial grooves 701 and protruded axial ridges 700. The embossed protruded ridges 700 and the recessed grooves 701 are arranged in a parallel manner described by the dimensional period parameter I. In the cross-sectional views 709, 710 illustrating two variants of a zone of a nip between the embossing rollers 103 and 104 used to obtain the embossed sheet of substrate 100, and which both correspond to a symbolic line 708 along the embossed sheet of substrate 100, obtuse-angled embossing features 703, 705 corresponding to the embossed ridges 700, obtuse flank-angled embossing features 702, 704 corresponding to the embossed grooves 701 , the top-of-ridge to bottom-of-groove height value h, as well as nip thickness values 706, 707 are illustrated. The obtuse flank-angled embossing features 703, 705 and 702, 704 respectively depicted in 709, 710 may have substantially identical geometrical dimension, whereas the features 704, 705 show sharp edges and the features 702, 703 exhibit slightly rounded (e.g., with a radius between 0.02 and 0.05 mm) edges.

[0096] Figure 8 contains a further example of the embossed sheet of substrate and a magnified crosssection of embossing rollers used for embossing. As such, Figure 8 illustrates a detailed view from above of the zone 111 from the embossed sheet of substrate 100 embossed according to the invention, with controlled thickness value and with reduced content of clusters, which further contains recessed axial grooves 801 and protruded axial ridges 800. The embossed protruded ridges 800 and the recessed grooves 801 are arranged in a periodic parallel manner described by the dimensional period parameter I. In a cross-sectional view 805 from a zone of a nip between the embossing rollers 103 and 104 used to obtain the embossed sheet of substrate 100, which further corresponds to a symbolic line 806 along the embossed sheet of substrate 100, embossing features 803 corresponding to the embossed ridges 800, embossing features 802 corresponding to the embossed grooves 801 , both 802 and 803 with a substantial sinusoidal profile, the top-of-ridge to bottom-of-groove height value h, as well as a nip thickness value 804 are depicted.

[0097] Figure 9 contains yet a further preferred example of the embossed sheet of substrate and magnified cross-sections of embossing rollers used for embossing. Figure 9 illustrates a view from above of the zone 111 from the sheet of substrate 100 embossed according to the invention, with a controlled thickness value and with a reduced content of clusters, which further contains recessed grooves 901 and protruded ridges 900, whereas the embossed ridges are disconnected by zones 906 in which the embossed sheet of substrate 100 maintains the height level of the grooves 901. The embossed protruded ridges 900 are arranged in an array-like manner described by the dimensional period parameters p a nd I. In the cross-sectional views 910, 911 illustrating two variants of a zone of a nip between the embossing rollers 103 and 104 used to obtain the embossed sheet of substrate 100, and which both correspond to a symbolic line 909 along the embossed sheet of substrate, obtuse flank-angled embossing features 902, 903 corresponding to the embossed ridges 900, base roller surfaces 907, 908 corresponding to the discontinuities 906, the top-of-ridge to bottom-of-groove height value h, as well as a nip thickness value 904, 905 are illustrated. The obtuse flank-angled embossing features 902, 903 respectively depicted in 910, 911 may have substantially identical geometrical dimension, whereas the features 903 show sharp top edges and the features 902 exhibit slightly rounded (e.g. with a radius between 0.02 and 0.05 mm) top edges.

[0098] Figure 10 contains yet a further example of the embossed sheet of substrate and a magnified cross-section of embossing rollers used for embossing. Figure 10 contains a detailed top view from the zone 111 from the embossed sheet of substrate 100 embossed according to the invention, with the controlled thickness value and with the reduced content of clusters, which further contains recessed axial grooves 1001 and protruded axial ridges 1000, whereas the embossed ridges are disconnected by zones 1002 in which the embossed sheet of substrate 100 maintains the height level of the grooves 1001 . The embossed protruded ridges 1000 arranged in an array-like manner are described by the dimensional period parameters p and I. In a crosssection view 1007 from a zone of a nip between the embossing rollers 103 and 104 used to obtain the embossed sheet of substrate 100, which further corresponds to a symbolic line 1006 along the embossed sheet of substrate, embossing features 1003 with a substantially sinusoidal profile and corresponding to the embossed ridges 1000, base roller surfaces 1004 corresponding to the discontinuities 1002, the top-of-ridge to bottom-of-groove height value h, as well as a nip thickness value 1005 are illustrated.

[0099] Flank angles of ridges and grooves

[0100] The ridges and grooves defined by the embossing profiles contained by the first 103 and the second 104 embossing rollers have manyfold purposes, namely (i) to homogenize the substrate thickness of the sheet of substrate (i.e., to flatten it), (ii) to induce a certain gradient of the applied embossing pressure, and (iii) to create zones (i.e., the bottom of roller grooves) to temporarily accommodate the debris ejected from the embossed substrate. Whereas a rather flat roller surface would mainly fulfil the former aim, the latter would imply the opposite, namely a high density of grooves. Considerations related to the high penetrating effect of ridges with very acute flank angles and the lack of effects related to ridges of with very obtuse flank angles, further corroborated with embossing trials on woven and non-woven substrates lead to a range between 75° and 140° forthe flank angles, most preferably between 80° and 120°, this combined with a profile heights in a range between 0,1 mm and 1 .0 mm. The necessity of a large number of grooves to temporarily accommodate the debris, together with the combination between the aforementioned flank angle and profile height values give a lateral spacing between two adjacent ridges or grooves larger than 0,5 mm, most preferably between 0,5 mm and 20 mm.

[0101] Figures 11 (A)-11(C) contain views of examples for quick-exchange devices configured for housing a set of embossing rollers according to the invention. The embossing rollers 103 and 104 may be removably housed in a quick-exchange device, generically illustrated under reference 1100 in Figure 11 (A). In a preferred embodiment 1106 of such a quick-exchange device, an axle of at least one of the rollers 103, 104 is movable in all three coordinate directions (not illustrated) in order to allow a self-synchronization of the embossing rollers. As shown in Figure 11(B), the quick-exchange device comprises a frame 1101 having two seats intended to receive respective roller fixtures 1102 and 1103, whereas the roller fixture 1103 serves for mounting the roller 104, which is driven by a here non-represented external drive, and roller fixture 1102 serves for mounting the roller 103. In a further preferred embodiment 1107 shown in Figure 11(C) of the quick-exchange device, the rollers 103 and 104 are mounted in a cassette 1104, which contains means (not represented) for adjusting and correcting the positions and the rotation axes of the rollers 103 and 104, and which is removably mounted in a frame 1105. In preferred embodiments, the roller 103 is driven by the externally driven roller 104 via gearwheels (not represented) located at one end of the rollers. However, other synchronizing means, e.g. electric servomotors, may also be used.

[0102] Figure 12 contains a view of a system for manufacturing an embossed sheet of substrate with an example embodiment of a roller cleaning tool in form of scrappers according to the invention. In this example embodiment of the invention, the detachment of debris from the surfaces of rollers 103, 104 is carried out by means of metallic (e.g. brass) or ceramic (e.g. oxides, nitrides, carbides) adapted-shape scrappers 1202 and 1203. The rollers 103, 104 and the scrappers 1202, 1203 are respectively mounted on the roller fixtures 1102 and 1103, which are themselves part of a quick-exchange device (not represented). However, the quick-exchange device is optional, and the scrappers may be attached to any form of roller supports. To obtain an optimal debris removal from the roller surfaces, the specific edge shape geometries 1204, 1205 of the scrappers 1202, 1203 respectively shall be congruent to the embossing structures (i.e., ridges and recesses, not represented) present on the surfaces of rollers 103, 104. In a further embodiment, optional means 1201 of lateral displacement are provided for the roller fixture 1102, in order to allow a self-synchronization of the embossing rollers, by maintaining the matching scrapper positions.

[0103] Figure 13 contains two views of example embodiments for any of the embossing rollers according to the invention. More precisely, Figure 13 illustrates an example embodiment for any one of embossing rollers 103 or 104, which comprises a rotation axis 1303, a roller surface 1300 and a toothed wheel 1301 at one extremity of the one embossing roller, enabling the one embossing roller 103 or 104 to be driven by a motor assembly having a corresponding toothed wheel (not represented) and to be synchronized with the other one of the embossing rollers 103 or 104 (other one not represented in Figure 13). The embossing features present on the roller surface 1300 are not represented explicitly. Figure 13 also shows a further example embodiment for any one of embossing rollers 103 or 104, in which the embossing roller does not comprise any toothed wheel. In this example any one of embossing rollers 103 or 104 is typically driven and synchronized with the other one of the rollers 103 and 104 (not illustrated in the Figure 13) by a servo motor mechanism (not represented) that directly rotates the rotation axis 1303. Embossing features present on a roller surface 1302 are not represented explicitly.

[0104] Figure 14 contains a view of a system for manufacturing an embossed sheet of substrate with a schematical illustration of two different types of gears for driving and synchronizing the embossing rollers according to the invention. Figure 14 illustrates preferred embodiments for driving and synchronizing the embossing rollers 103 and 104, belonging to an embossing roller system 1402, according to the invention. The feed direction of the sheet of substrate 101 and of the embossed sheet of substrate 100 is given by the arrows 112, whereas Figure 14 also illustrates the adapted-shape scrappers 1202 and 1203, the air-depression cleaning systems 108 and 109, as well as the at least one optional deflection roller 113. In a preferred embodiment, toothed wheels 1301 may be used to drive and synchronize the embossing rollers 103 and 104, whereas in a further preferred embodiment depicted in the view 1400 helicoidal gears 1401 are used to drive and synchronize the embossing rollers instead of the toothed wheels 1301 . Figure 15 contains a view of an embossing roller with ring-shaped zones at its extremities that comprise axially oriented ridges and grooves used to drive and synchronize embossing rollers according to an example of the invention. Figure 15 illustrates a variation of a first embossing roller 1500 (the designation here is similar to the first embossing roller 103), part of a preferred embodiment of an embossing roller system according to the invention (not illustrated), the variation of the first embossing roller 1500 containing a zone 1501 , which extends all around the roller 1500 and substantially occupying a majority of its lateral surface, and two zones 1502, all around the roller 1500 and substantially located at its extremities. The zone 1501 contains radially orientated ridges and grooves, to obtain an embossed sheet of substrate with controlled thickness and with reduced content of clusters, the zones 1502 contain substantially similar ridges and grooves, except that they are axially orientated, that may be used to drive the variation of the first embossing roller 1500 and synchronize it with a second embossing roller of the used embossing roller system (not represented).

[0105] Figure 16 contains a schematic illustration of a set of embossing rollers with ring-shaped shoulders at their extremities. More precisely Figure 16 represents a set of embossing rollers 1601 , 1602, bearing protrusion and recess embossing features (not represented), each comprising at a corresponding extremity a toothed wheel 1603, 1604, the teeth of which intertwine to synchronously drive the embossing rollers 1601 , 1602, to rotate about respective rotation axes 1605, 1606. The embossing rollers 1601 , 1602, further each comprise two ringshaped shoulders 1607, 1608, one towards each extremity of the respective embossing roller 1601 , 1602, and configured such that a ring-shaped shoulder on one embossing roller faces a corresponding ring-shaped shoulder of the opposite embossing roller. The ring-shaped shoulders 1607, 1608, are generally designed to form a ring which centered on the rotation axis of the embossing roller, whose circumference protrudes from a base surface of the embossing roller where it is located. This level of detail is not illustrated in Figure 16 to maintain a better readability. Figure 16 further represents two magnified views 1609, 1610, of areas where the ring-shaped shoulders 1607 and 1608 are resting on each other as may be the case during embossing. This is substantiated by distance 1611 between the ring-shaped shoulders 1607 and 1608 being 0, while a nip 1612 is maintained between the embossing rollers 1601 and 1602 with a determined nip width value n separating a base surface 1614 of the embossing roller 1601 from an opposite base surface 1613 of the embossing roller 1602. The base surfaces are schematically represented and in the views 1609 and 1610 do not comprise any embossing features in the example of Figure 16. The determined nip width value n of the nip 1612 enables to insert a sheet of substrate in it (sheet of substrate not represented) for embossing, in order to obtain a sheet of substrate with a controlled thickness and a reduced content of surface clusters.

[0106] In a further example represented in Figure 17 the ring-shaped shoulders of Figure 16 may be replaced by radial recesses 1701 and 1702, which each form recesses in the embossing rollers 1601 and 1602 respectively as compared to the base surfaces 1613 and 1614. Hence, as represented in the two magnified views 1706 and 1707, when the embossing rollers 1601 and 1602 are pressured one towards the other, as is depicted by arrows 1705 in the radial recesses 1701 and 1702, their base surfaces 1613 and 1614 may be coming into contact such that a distance 1703 tends to become similar to that of a sheet of substrate inserted therein for embossing (not represented), and a distance 1704 between radial recesses 1701 and 1702 facing each other from one embossing roller to the other is greater than 0. The pressure depicted by the arrows 1705 may be exerted by pressuring means comprised in the embossing set-up (not represented), well known in the prior art, for example by hydraulic or pneumatic pressuring means.

[0107] The embodiments illustrated in the foregoing Figures are applicable to any one of the following manners to integrate an embossing system to emboss a sheet of substrate with a controlled thickness value and a reduced content of clusters in a filtering-element production line: online, atline, offline. The following two Figures are detailing preferred embodiments of online integration.

[0108] Figure 18 illustrates a preferred embodiment of the system for manufacturing an embossed sheet of substrate according to the invention, where it is a part of an online production line for manufacturing a filter element. More precisely, Figure 18 illustrates a preferred embodiment of the system for manufacturing an embossed sheet of substrate 1801 according to the invention, as a part of an online production line for manufacturing a filter element of length L (filter element and length not represented). The online production line further comprises for example a compacting device 1809 comprising a funnel 1807 into which a further embossed sheet of substrate 1805 is fed, folded, and formed into a filter rod 1808 output by the compacting device 1809. Hence the further embossed sheet of substrate 1805 is compacted with the funnel 1807. The filter rod 1808 may be pulled by means of a pulling jig 1810 to a further process step 1811 of cutting. The production line contains the embossing system 1801 , according to the invention, to produce the embossed sheet of substrate 100 with controlled thickness value and with reduced content of cluster, whereas the first embossing roller 103, the second embossing roller 104, the adapted-shape scrappers 1202 and 1203, the air-depression cleaning systems 108 and 109, as well as the removed debris 306 are showed in Figure 18. A magnified view from a zone 110 of the sheet of substrate 101 prior to embossing using the embossing system 1801 schematically depicts inhomogeneities of substrate thickness values and substrate clusters, while a further magnified view of a zone 111 from the embossed sheet of substrate 100 schematically shows the embossed sheet substrate with the controlled thickness value and with the reduced content of cluster. In a further preferred embodiment, the embossed sheet of substrate 100 with controlled thickness and with reduced content of clusters is fed into a second embossing system 1802 that contains a third 1803 and a fourth 1804 embossing roller, configured to further emboss at least an aerodynamic profile to obtain the embossed sheet of substrate 1805, the embossed aerodynamic profiles being configured to modify in a determined manner flow properties for a gas flow passing through the embossed aerodynamic profiles by creating a gas flow turbulence. A further magnified view from a zone 1806 of the further embossed sheet of substrate 1805 illustrates an example embossing obtained with the embossing set-up 1802 configured to emboss at least an aerodynamic profile, according to a preferred embodiment of the invention. As an option, the production line may comprise a bobbin dispensing device 1800 configured to carry a bobbin with a web of sheet of substrate 101 and unwind it out towards the embossing setup 1801.

[0109] Figure 19 illustrates a further preferred embodiment of the system as in Figure 18 with additional debris removal systems according to the invention. Figure 19 illustrates a further preferred embodiment of the embossing set-up 1801 according to the invention as a part of an online production process, wherein the embossing set-up 1801 is part of an online production line for manufacturing a filter element of length L (filter element and length not represented). The online production line further comprises for example a compacting device 1809 comprising a funnel 1807 into which the embossed sheet of substrate 1902 is fed, folded and formed into a filter rod 1904 output by the compacting device 1809. Hence the embossed sheet of substrate 1902 is compacted with the funnel 1807. The filter rod 1904 may be pulled by means of a pulling jig 1810 to a further process step 1811 of cutting. The production line contains the embossing system 1801 , according to the invention, to produce an embossed sheet of substrate with controlled thickness value and reduced content of clusters, whereas the first embossing roller 103, the second embossing roller 104, the adapted-shape scrappers 1202 and 1203, the airdepression cleaning systems 108 and 109, as well as the removed debris 306 are illustrated in Figure 19. In a preferred embodiment, the embossed sheet of substrate 100 with controlled thickness value and with reduced content of clusters passes through at least one of the additional debris removal systems 1900 and 1901 , whereas the air-depression cleaning systems 503 and 504, as well as the additional removed debris 305 are equally illustrated in Figure 19. The so-conditioned embossed sheet of substrate 507 with controlled thickness value and with substantially reduced content of clusters is fed into the second embossing system 1802 that contains the third 1803 and the fourth 1804 embossing rollers, configured to emboss at least an aerodynamic profile on the embossed sheet of substrate 1902, the embossed aerodynamic profiles being configured to modify in a determined manner flow properties for a gas flow passing through the embossed aerodynamic profiles by creating a gas flow turbulence. As an option, the production line may comprise the bobbin dispensing device 1800 configured to carry the bobbin with the web of sheet of substrate 101 and unwind it out towards the embossing set-up 1801 .

[0110] Figure 20 illustrates a further example of an embossed sheet of substrate further embossed according to the invention, bearing aerodynamic profiles. More precisely, Figure 20 contains a detailed top view from a zone 1903 (as in Figure 19) of a sheet of substrate embossed according to the invention, with controlled thickness value and with substantially reduced content of clusters, which shows recessed 2001 and protruded 2002 embossed radial features 2003, substantially parallel and separated by a distance I, whereas each embossed radial feature 2003 defines a plurality of enclosures 2006, which are longitudinally distributed along the corresponding embossed radial feature and separated by a distance p. Figure 20 further includes a cross-sectional view 2007 from a zone of a nip between the embossing rollers 1803 and 1804 used to obtain the embossed the sheet of substrate 1903, which corresponds to a symbolic line 2004 along the embossed sheet of substrate, and which also illustrates a height hi of an embossed protrusion feature, as well as a nip thickness value 2105.

[0111] Figure 21 schematically illustrates an obtaining of filtering elements using an embossed sheet of substrate as resulting from the invention. Starting from the process step of cutting 1811 , Figure 21 illustrates under reference 2100 a cutting process that involves cutting the filter rod 1808 into individual pieces of filter elements 2101 each having the length L, and as an example, cut as two twin-filter elements by means of a cutting device 2102. Figure 21 further illustrates a magnified photograph view 2103 at an extremity of one of the filter elements 2101 , in which the embossed sheet of substrate 1805 is folded and compacted to fit in a cylindrical wrapper 2104, represented as a section of the cylindrical wrapper 2104. A detailed view 2105 of a part of the section 2103, in which the view is slightly from an angle, schematically illustrates how the embossed sheet of substrate 1805 is folded and packed in a manner of an accordion. In the view 2105 a substrate thickness 2106 is represented to be the same all over, and while this may be desired to be in this manner, there may also be embossed features (not represented) in which the substrate thickness may vary according to the embossed features.

[0112] Figure 22 schematically illustrates how a filtering element, in this case a cigarette filter, may be mounted to a tobacco containing section in order to obtain a cigarette according to prior art. More precisely, Figure 22 schematically illustrates how a cigarette filter - type filtering element 2101 , in a preferred embodiment initially obtained as two twin-filters, may be mounted to a tobacco containing section 2201 in order to obtain a cigarette 2202 according to prior art. Part (A) shows two twin-filter elements 2101 , part (B) shows the two twin-filter elements 2101 positioned between tobacco containing sections 2201 , and a filter paper 2200 being wound and glued around the two filter elements 2101 and partly over a part of each tobacco containing section 2201 , resulting in two twin-cigarettes 2202 shown in part (C). Part (D) shows one of cigarettes 2202 obtained after cutting the two twin-cigarettes in a middle 2203 thereof.

[0113] Figure 23 schematically illustrates a structure of an inhalable drug delivery device 2300 in parts (A) and (B), according to the prior art. Part (A) depicts a delivery system comprising a drugcontaining component 2301 and a filtering element 2302 fabricated using a sheet of substrate embossed according to the invention. Part (B) depicts an inhalable drug delivery system comprising the drug-containing component 2301 , a cooling component 2303, and of the filtering element 2302 fabricated using a sheet of substrate embossed according to the invention. Figure 24 contains a flowchart illustrating an example embodiment of a method for manufacturing an embossed sheet of substrate 2409 according to the invention. The method is configured to produce a controlled thickness value of the embossed sheet of substrate and to reduce a content of dusters present in the substrate prior to embossing. The method comprises steps of

[0114] • providing a sheet of substrate 2400 comprising the first material 200, the sheet of substrate having an average starting thickness;

[0115] • providing an embossing roller system 2401 comprising at least the first and the second embossing roller, having respectively the first radial profile and the corresponding second radial profile congruent to the first radial profile, the first radial profile comprising embossing structures protruding from or recessed in a base surface of the first embossing roller, and forming radially oriented ridges and grooves respectively;

[0116] • inserting the sheet of substrate in the nip 2402 formed between the first and the second embossing rollers;

[0117] • adjusting an embossing pressure 2403 between the first and the second embossing roller to obtain the determined nip value of the nip, smaller than the average starting thickness;

[0118] • embossing the sheet of substrate 2404, thereby obtaining the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness;

[0119] • compressing 2405 in the nip at least the first type of cluster comprising the first material inside the embossed sheet of substrate;

[0120] • processing 2406 at least the second type of cluster made of a second material different from the first material in any one of the following manners: o compressing and maintaining the at least one second type of cluster in the embossed sheet of substrate; o extracting the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure, which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to a surface of the embossed sheet of substrate; o extracting the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure, which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to any one of the base surfaces and the embossing structures of the first and second embossing rollers;

[0121] • detaching the debris from the base surfaces and the embossing structures 2407 by means of a roller cleaning tool; and

[0122] • removing the detached debris from the embossing roller system 2408 by means of an airdepression cleaning system 108, 109. Nip value, controlled thickness and cluster size

[0123] In one example of embodiment, a sheet of substrate used to produce a cigarette filter, having a grammage of 62 gsm, exhibits thickness values between 360 pm and 480 pm (i.e., a variation range of 120 pm) and an average thickness value of 410 pm was treated. For this substrate, clusters of lateral expansions in a range between 0.5 mm and 5.0 mm were evidenced, whereas the substrate thickness values measured at the cluster spots reached values up to 580 pm. In this example, embossing to obtain the controlled thickness and a reduced content of clusters was carried out with nip values of 100 pm and a linear force of 13,6 kN / m. As a result of the embossing, a variation range of 20 pm (instead of initially 120 pm) was found for the measured substrate thickness values and no protruding clusters were observed.

[0124] Integration of the embossing roller system

[0125] While carrying out the embossing process according to the invention care should be taken that both the non-embossed sheet of substrate 101 and the embossed sheet of substrate 100 shall be strained and stay under a certain substrate tension. This is common practice in the field of embossing. In one example of realisation of the invention, embossing trials carried out according to the invention on different types of sheets of substrates, both woven and non-woven, showed a range between 1 N and 10 N for an optimal substrate tension for both substrates 100, 101 . The aforementioned trials also pointed out that, in a preferred embodiment, the substrate tensions for the sheets of substrate 100 and 101 shall be varied independently, as for instance a thinner sheet of substrate requires a lower substrate tension after 100 than before 101 the embossing roller system. Furthermore, under too low substrate tensions (e.g., <1 N) in the non-embossed sheet of substrate 101 , this may become loose and form crinkles in the nip between the embossing rollers, which will have a negative effect on the controlled thickness supposed to be obtained through embossing, whereas too high substrate tensions (e.g. >10 N) in the embossed sheet of substrate 100 might generate its rupture and interrupt the embossing process.

Claims

Claims1 . Method for manufacturing an embossed sheet of substrate (100), the method being configured to produce a controlled thickness value of the embossed sheet of substrate and to reduce a content of clusters present in the non-embossed substrate (101), the method comprising steps of providing a sheet of substrate (101) comprising a first material (200), the sheet of substrate having an average starting thickness; providing an embossing roller system (102) comprising at least a first and a second embossing roller (103, 104), having respectively a first radial profile and a corresponding second radial profile congruent to the first radial profile, the first radial profile comprising embossing structures protruding from or recessed in a base surface of the first embossing roller, and forming radially oriented ridges and grooves respectively; inserting the sheet of substrate in a nip (105) formed between the first and the second embossing roller; adjusting an embossing pressure (P) between the first and the second embossing roller to obtain a determined nip value of the nip, smaller than the average starting thickness; embossing the sheet of substrate; thereby obtaining the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness; compressing in the nip at least a first type of cluster comprising the first material inside the embossed sheet of substrate; processing at least a second type of cluster made of a second material different from the first material in any one of the following manners: compressing and maintaining the at least one second type of cluster in the embossed sheet of substrate; extracting the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure (P), which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to a surface of the embossed sheet of substrate;extracting the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure (P), which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to any one of the base surfaces and the embossing structures of the first and the second embossing rollers; the method further comprising: detaching the debris from the base surfaces and the embossing structures by means of a roller cleaning tool (106, 107); and removing the detached debris from the embossing roller system (102) by means of an air-depression cleaning system (108, 109).

2. The method according to claim 1 , further comprising after embossing the sheet of substrate: leading the embossed sheet of substrate through at least an additional debris removal system (505, 506), thereby deflecting the embossed sheet of substrate on a removal tool (501 , 502) of the additional debris removal system, configured to detach debris (305) adhering to the surface of the embossed sheet of substrate (100); and removing the detached debris (305) from the debris removal system by means of an additional air-depression cleaning system (503, 504) corresponding to the additional debris removal system.

3. The method according to claim 2, wherein the removal tool to detach debris (305) adhering to the surface of the embossed sheet of substrate (100) comprises any one of the following items of a list comprising: a cylinder comprising a roughened surface configured to be in contact with the embossed sheet of substrate; a curved roughened surface configured to be in contact with the embossed sheet of substrate; a blade comprising an edge configured to be in contact with the embossed sheet of substrate;an ultrasonic wave generator configured to project an ultrasonic beam towards the embossed sheet of substrate.

4. The method according to any one of claims 1 to 3, wherein the roller cleaning tool comprises at least a scrapper (1202, 1203) for each of the embossing rollers, each scrapper comprising an edge configured to be presented towards the roller surface of the corresponding embossing roller, and having a shape fitting congruently in the corresponding radial profile of the embossing roller, and configured in such a way that the debris (306) adhering to any one of the base surface and the embossing structures of the roller surface is removed from the roller surface while the embossing roller rotates.

5. The method according to any one of claims 1 to 4, wherein the step of providing the embossing roller system comprises mounting each of the first and the second embossing rollers in a corresponding quick exchange fixture (1102, 1103), whereby each of the quick exchange fixtures is removably mounted in a frame (1 101).

6. The method according to any one of claims 1 to 4, wherein the step of providing the embossing roller system comprises mounting and adjusting the first and the second embossing rollers in a quick exchange cassette (1104), whereby the quick exchange is removably mounted in a frame (1105).

7. The method according to any one of the claims 1 to 6, further comprising providing a further embossing roller system comprising a third (1803) and a fourth (1804) embossing roller, with further embossing features configured for embossing at least an aerodynamic profile on the embossed sheet of substrate, the embossed aerodynamic profiles being configured to modify in a determined manner flow properties for a gas flow passing through the embossed aerodynamic profiles by creating a gas flow turbulence; inserting the embossed sheet of substrate in a further nip formed between the third and the fourth embossing rollers; further embossing the embossed sheet of substrate.

8. The method according to claim 7, wherein the further embossing roller system is part of a production chain for manufacturing from the sheet of substrate a filtering element configured for an inhalable drug delivery device, and for filtering a mainstream gas flow passing through the filtering element.

9. The method according to any one of claims 7 to 8, wherein the step of providing the further embossing roller system comprises mounting each of the third and fourth embossing roller in a corresponding quick exchange fixture, whereby each of the quick exchange fixtures is removably mounted in a frame.

10. The method according to any one of claims 7 to 8, wherein the step of providing the further embossing roller system comprises mounting each of the third and fourth embossing roller mounting and adjusting the first embossing roller and the second embossing roller in a quick exchange cassette, whereby the quick exchange is removably mounted in a frame.1 1 . The method according to any one of claims 1 to 6, wherein each of the radially oriented ridges and grooves comprises two contiguous radially directed flanks that define an angle between two contiguous flanks of the radially ridges and grooves that has a value between 75° and 140°.

12. The method according to any one of claims 1 to 6, wherein the radially oriented ridges and grooves are described by a top-of-ridge to bottom-of-groove height value situated in a range 0.1 mm and 1 .0 mm.

13. The method according to any one of claims 1 to 6, wherein the radially oriented ridges and grooves are arranged in a parallel, periodic manner which is described by a dimensional spacing of at least 0.5 mm between two adjacent ridges and grooves.

14. The method according to any one of claims 1 to 6, wherein the first and the second embossing rollers are driven and self-synchronized by means of the radial embossingfeatures engaged into each other by applying an embossing pressure (P) between the rollers.

15. The method according to any one of claims 1 to 6, wherein the first and the second embossing rollers are driven and synchronized by any means from a list of synchronization means comprising toothed-wheels gears, helicoidal gears, servomotors.

16. The method according to any one of the preceding claims, wherein the non-embossed sheet of substrate has a grammage in a range between 10 gsm and 150 gsm and a starting average thickness value in a range between 0.02 mm and 1 .0 mm.

17. The method according to any one of the preceding claims, wherein the sheet of substrate comprises any material from a list comprising paper, woven cellulose-based material, non-woven cellulose-based material, natural fibrous material, synthetic fibrous material, porous material, and mixtures thereof.

18. A system for manufacturing an embossed sheet of substrate (100), the system being configured to produce a controlled thickness value of the embossed sheet of substrate and to reduce a content of clusters present in the non-embossed substrate (101), the system comprising an embossing roller system (102) comprising at least a first and a second embossing roller (103, 104), having respectively a first radial profile and a corresponding second radial profile congruent to the first radial profile, the first radial profile comprising embossing structures protruding from or recessed in a base surface of the first embossing roller, and forming radially oriented ridges and grooves respectively; the embossing roller system further comprising a nip (105) formed between the first and the second embossing roller and configured for inserting therein a sheet of substrate (101) comprising a first material (200), the sheet of substrate having an average starting thickness; pressure adjusting means configured to adjust an embossing pressure (P) between the first and the second embossing roller and obtain a determined nip value of the nip, smaller than the average starting thickness;whereby an embossing of the sheet of substrate enables to obtain the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness; compress at least a first type of cluster comprising the first material inside the embossed sheet of substrate; process at least a second type of cluster made of a second material different from the first material in any one of the following manners: compress and maintain the at least one second type of cluster in the embossed sheet of substrate; extract the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure (P), which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to a surface of the embossed sheet of substrate; extract the at least one second type of cluster as debris from the sheet of substrate by means of the embossing pressure (P), which causes the at least one second type of cluster to emerge from the embossed sheet of substrate and adhere as debris to any one of the base surfaces and the embossing structures of the first and second embossing rollers; the system further comprising: a roller cleaning tool (106, 107) configured to detach the debris from the base surfaces and the embossing structures; and an air-depression cleaning system (108, 109) configured to remove the detached debris from the embossing roller system (102).

19. The system according to claim 18, further comprising at least an additional debris removal system (505, 506), configured to further lead through the embossed sheet of substrate, a removal tool in the additional debris removal system configured to deflect the embossed sheet of substrate, and configured to detach debris (305) adhering to the surface of the embossed sheet of substrate (100); andan additional air-depression cleaning system (503, 504) corresponding to the additional debris removal system, configured for removing the detached debris (305) from the debris removal system by means of an additional air-depression cleaning system (503, 504).

20. The system according to claim 19, wherein the removal tool to detach debris (305) adhering to the surface of the embossed sheet of substrate (100) comprises any one of the following items of a list comprising: a cylinder comprising a roughened surface configured to be in contact with the embossed sheet of substrate; a curved roughened surface configured to be in contact with the embossed sheet of substrate; a blade comprising an edge configured to be in contact with the embossed sheet of substrate; an ultrasonic wave generator configured to project an ultrasonic beam towards the embossed sheet of substrate.21 . The system according to any one of claims 18 to 20, wherein the roller cleaning tool comprises at least a scrapper (1202, 1203) for each of the embossing rollers, each scrapper comprising an edge configured to be presented towards the roller surface of the corresponding embossing roller, and having a shape fitting congruently in the corresponding radial profile of the embossing roller, and configured in such a way that the debris (302) adhering to any one of the base surface and the embossing structures of the roller surface is removed from the roller surface while the embossing roller rotates.

22. The system according to any one of claims 18 to 21 , further comprising at least two quick exchange fixtures (1102,1 103), respectively configured to mount each of the first and the second embossing rollers, whereby each of the quick exchange fixtures is removably mounted in a frame (1101).

23. The system according to any one of claims 18 to 21 , further comprising a quick exchange cassette (1104) configured to comprise the first and the second embossing rollersadjusted inside the quick exchange cassette, and the quick exchange cassette is removably mounted in a frame (1105).

24. The system according to any one of the claims 18 to 23, further comprising a further embossing roller system comprising a third (1803) and a fourth (1804) embossing roller, with further embossing features configured for embossing at least an aerodynamic profile on the embossed sheet of substrate, the embossed aerodynamic profiles being configured to modify in a determined manner flow properties for a gas flow passing through the embossed aerodynamic profiles by creating a gas flow turbulence; the further embossing roller system further comprising a further nip formed between the third and the fourth embossing rollers, and configured for inserting therein the embossed sheet of substrate.

25. The system according to claim 24, wherein the further embossing roller system is part of a production chain for manufacturing from the sheet of substrate a filtering element configured for an inhalable drug delivery device, and for filtering a mainstream gas flow passing through the filtering element.

26. The system according to any one of claims 24 to 25, further comprising at least two further quick exchange fixtures, respectively configured to mount each one of the third and fourth embossing rollers, whereby each of the further quick exchange fixture is removably mounted in a frame.

27. The system according any one of claims 24 to 25, further comprising a further quick exchange cassette configured to comprise the third embossing roller and the fourth embossing roller adjusted inside the further quick exchange cassette, and the further quick exchange cassette is removably mounted in a frame.

28. The system according to any one of claims 18 to 23, wherein each of the radially oriented ridges and grooves comprises two contiguous radially directed flanks that define an anglebetween two contiguous flanks of the radially ridges and grooves that has a value between 75° and 140°.

29. The system according to any one of claims 18 to 23, wherein the radially oriented ridges and grooves are described by a top-of-ridge to bottom-of-groove height value situated in a range 0.1 mm and 1 .0 mm.

30. The system according to any one of claims 18 to 23, wherein the radially oriented ridges and grooves are arranged in a parallel, periodic manner which is described by a dimensional spacing of at least 0.5 mm between two adjacent ridges and grooves.31 . The system according to any one of claims 18 to 23, wherein the first and the second embossing rollers are configured to be driven and self-synchronized by means of the radial embossing features engaged into each other by applying an embossing pressure (P) between the rollers.

32. The system according to any one of claims 18 to 23, wherein the first and the second embossing rollers are driven and synchronized by any means from a list of synchronization means comprising toothed-wheels gears, helicoidal gears, servomotors.

33. The system according to any one of the claims 18 to 32, wherein the non-embossed sheet of substrate has a grammage in a range between 10 gsm and 150 gsm and a starting average thickness value in a range between 0.02 mm and 1 .0 mm.

34. The system according to any one of the claims 18 to 33, wherein the sheet of substrate comprises any material from a list comprising paper, woven cellulose-based material, non-woven cellulose-based material, natural fibrous material, synthetic fibrous material, porous material, and mixtures thereof.