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

Abstract

A method for manufacturing an embossed sheet of substrate, the method being configured to produce a controlled thickness of the embossed sheet of substrate embossed in a congruency nip, and to reduce a content of a second type of clusters initially present in a non-embossed sheet of substrate. The method comprises providing an embossing roller system comprising at least a first and a second embossing roller, comprising first embossing structures protruding from or recessed in a first base surface of the first embossing roller, each of the protruding first embossing structures protruding from the first base surface and comprising rising flanks oriented away from the first base surface towards a summit that tops the protruding first embossing structure, and each of the recessed first embossing structures recessing from the first base surface and comprising recessing flanks oriented from the first base surface inside of the first embossing roller towards a bottom that delimits the recessed first embossing structure, second embossing structures protruding from or recessed in a second base surface of the second embossing roller, congruent according to the congruency nip separating each of the second embossing structures during embossing at least along the rising and recessing flanks from respective corresponding first embossing structures of the first embossing roller, and forming a summit nip between each of the summits of the first embossing structures and a corresponding counter side on the second embossing structures, with a value of the summit nip at least greater than the congruency nip. The method further comprises adjusting the first embossing roller and the second embossing roller for embossing with a base nip between a portion of the first base surface and a corresponding portion of the second base surface, and the congruency nip, whereby the congruency nip has a value smaller than the average starting thickness of the non-embossed substrate; inserting the non-embossed sheet of substrate in a roller nip comprising at least base nip zones of the base nip, congruency nip zones of the congruency nip and summit nip zones of the summit nip; embossing the non-embossed sheet of substrate, thereby producing the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness for parts of the sheet of substrate embossed in the congruency nip zones; compressing in the congruency nip zones at least one of the first type of clusters inside the embossed sheet of substrate; and processing at least one of the second type of clusters by compressing in the congruency nip zones the at least one second type of cluster inside the embossed sheet of substrate and for each one of the at least one second type of cluster either maintaining the at least one second type of cluster inside the embossed sheet of substrate; or causing the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the summit nip zones, and to remain as debris in proximity of the second roller's counter side of the one of the summit nip zones.

Description

[0001] Method and device for manufacturing an embossed sheet of substrate to produce 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 thereby producing a controlled thickness of the embossed sheet of substrate embossed in a congruency nip and reducing a content of a second type of clusters initially present in a nonembossed sheet of substrate.

[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 made from a sheet of substrate, generally made from sustainable substrates (e.g., paper- or cellulose-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] Sheets of substrate of variating thickness may lead - upon their folding and transforming into a filter rod - to filters with variating filling factors, i.e., impact on gas flow and filtering properties.

[0007] The sheet of substrate's grammage allows to have an 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.

[0008] The above-mentioned publication provides a method and an embossing set-up to manufacture from the sheet of 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.

[0009] It has been found that such manufacturing method and embossing set-up may generate debris from the substrate, such as for example originating from clusters contained in the substrate and released from the substrate at the time of embossing. As a result, the manufactured embossed sheet of substrate 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 substrate and any product that makes use of the embossed sheet of substrate.

[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] 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.

[0012] 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.

[0013] 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 forthe manufacturing ofthe 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 and the presence of clusters in the filtering element produced.

[0014] Summary of invention

[0015] In a first aspect the invention provides a method for manufacturing an embossed sheet of substrate, the method being configured to produce a controlled thickness of the embossed sheet of substrate embossed in a congruency nip, and to reduce a content of a second type of clusters initially present in a non-embossed sheet of substrate. The method comprises providing the non-embossed sheet of substrate comprising a first material, afirst type of clusters comprising the first material, and the second type of clusters comprising a second material different from the first material, the non- embossed sheet of substrate having an average starting thickness; providing an embossing roller system comprising at least a first and a second embossing roller, comprising first embossing structures protruding from or recessed in a first base surface of the first embossing roller, each ofthe protruding first embossing structures protruding from the first base surface and comprising rising flanks oriented away from the first base surface towards a summit that tops the protruding first embossing structure, wherein the summit of any one of the protruding first embossing structures comprises either one of the items in a list comprising one convex curved summit with curvature equal or larger than 10 pm, and one summit delimited by at least one edge, wherein each one of the at least one edge has a curvature equal or larger than 10 pm, and each of the recessed first embossing structures recessing from the first base surface and comprising recessing flanks oriented from the first base surface inside of the first embossing roller towards a bottom that delimits the recessed first embossing structure, second embossing structures protruding from or recessed in a second base surface of the second embossing roller, congruent according to the congruency nip separating each of the second embossing structures during embossing at least along the rising and recessing flanks from respective corresponding first embossing structures of the first embossing roller, and forming a summit nip between each of the summits of the first embossing structures and a corresponding counter side on the second embossing structures, with a value of the summit nip at least greater than the congruency nip, the first embossing structures and the second embossing structures being aligned along a plurality of parallel lines on respective surfaces of the first embossing roller and the second embossing roller.

[0016] The method further comprises adjusting the first embossing roller and the second embossing roller for embossing with a base nip between a portion of the first base surface and a corresponding portion of the second base surface, and the congruency nip, whereby the congruency nip has a value smaller than the average starting thickness; inserting the non-embossed sheet of substrate in a roller nip comprising at least base nip zones of the base nip, congruency nip zones of the congruency nip and summit nip zones of the summit nip; embossing the non-embossed sheet of substrate, thereby producing the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness for parts of the sheet of substrate embossed in the congruency nip zones; compressing in the congruency nip zones at least one of the first type of clusters inside the embossed sheet of substrate; and processing at least one of the second type of clusters by compressing in the congruency nip zones the at least one second type of cluster inside the embossed sheet of substrate and for each one of the at least one second type of cluster either: maintaining the at least one second type of cluster inside the embossed sheet of substrate; or causing the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the summit nip zones, and to remain as debris in proximity of the second roller's counter side of the one of the summit nip zones.

[0017] In a preferred embodiment, at least a summit of a second protruding embossing structure of the second embossing roller corresponding to a corresponding one of the bottoms of the recessed first embossing structures, and comprising either one of the items in the list comprising one convex curved summit with curvature equal or larger than 10 pm, and one summit delimited by at least one edge, wherein each one of the at least one edge has a curvature equal or larger than 10 pm, and which during embossing forms a bottom nip between the one of the bottoms of the first embossing structures and the corresponding counter side on the summit of the second protruding embossing structure, with a value of the bottom nip at least greater than that of the congruency nip. The roller nip further comprises bottom nip zones of the bottom nip; and the processing of at least the second type of clusters additionally comprises causing the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the bottom nip zones, and remain as debris in proximity of the first roller's counter side of the one of the bottom nip zones.

[0018] In a further preferred embodiment, along each line of the plurality of parallel lines on the first embossing roller, protruding first embossing structures alternate with recessed first embossing structures.

[0019] In a further preferred embodiment, the first embossing structures and the second embossing structures form anyone of ridges and grooves along each one of the plurality of the parallel lines.

[0020] In a further preferred embodiment, the formed ridges and grooves define on the first and the second embossing roller respectively a first radial profile and a corresponding second radial profile.

[0021] In a further preferred embodiment, the method further comprises detaching the debris from any one of at least the first roller's surface and the second roller's surface with a roller cleaning tool.

[0022] In a further preferred embodiment, the method further comprises removing the detached debris from the embossing roller system with an air-depression cleaning system.

[0023] In a further preferred embodiment the roller cleaning tool comprises at least a scraper for each of the first and second embossing rollers, each scraper comprising an edge configured to be presented towards the roller surface of the corresponding embossing roller, and having a shape fitting in the corresponding first and second radial profile of the embossing roller, and configured in such a way that the debris in proximity to any one of the roller surfaces is detached from the roller surface while the embossing roller rotates.

[0024] In a further preferred embodiment, the roller cleaning tool comprises at least a debris collecting tool for each of the first and second embossing rollers, which may be any one from a list comprising a brush, a gas blower, an ionized air blower, an ultrasonic system, a fluid projection system, each debris collecting tool configured to be directed towards the roller surface of the corresponding embossing roller, and configured in such a way that the debris in proximity to any one of the roller surfaces is detached from the roller surface while the embossing roller rotates.

[0025] 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.

[0026] 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 cassette is removably mounted in a frame.

[0027] 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.

[0028] In a further preferred embodiment, the further embossing roller system is part of a production chain for manufacturing from the sheet of substrate of a filtering element configured for an inhalable drug delivery device, and for filtering a mainstream gas flow passing through the filtering element.

[0029] In a further preferred embodiment, each of the protruding first and second embossing structures and each of the recessed first and second embossing structures comprises at least two contiguous rising flanks for protruding embossing structures or recessing flanks for recessed embossing structures that define an angle between themselves that has a value between 40° and 140°.

[0030] In a further preferred embodiment, each of the protruding first and second embossing structures and each of the recessed first and second embossing structures are described by a summit of a protruding first or second embossing structure to a bottom of a recessed respectively first or second embossing structure height value situated in a range between 0,05 mm and 1 ,5 mm.

[0031] In a further preferred embodiment, the ridges and grooves are arranged in a periodic manner which is described by a dimensional spacing of at least 0,1 mm between two adjacent ridges and grooves.

[0032] In a further preferred embodiment, the first and the second embossing rollers are driven and selfsynchronized by means of the first and second embossing structures engaged into each other between the rollers.

[0033] 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. 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 0,01 mm and 1 ,5 mm.

[0034] 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.

[0035] In a second aspect, the invention provides a system for manufacturing an embossed sheet of substrate, the system being configured to produce a controlled thickness value of the embossed sheet of substrate embossed in a congruency nip, and to reduce a content of a second type of clusters initially present in a non-embossed sheet of substrate, the non-embossed sheet of substrate comprising a first material, a first type of clusters comprising the first material, and the second type of clusters comprising a second material different from the first material, the non-embossed sheet of substrate having an average starting thickness. The system comprises an embossing roller system comprising at least a first and a second embossing roller, comprising first embossing structures protruding from or recessed in a first base surface of the first embossing roller, each ofthe protruding first embossing structures protruding from the first base surface and comprising rising flanks oriented away from the first base surface towards a summit that tops the protruding first embossing structure, wherein the summit of any one of the protruding first embossing structures comprises either one of the items in a list comprising one convex curved summit with curvature equal or largerthan 10 pm, and one summit delimited by at least one edge, wherein each one of the at least one edge has a curvature equal or larger than 10 pm, and each of the recessed first embossing structures recessing from the first base surface and comprising recessing flanks oriented from the first base surface inside of the first embossing roller towards a bottom that delimits the recessed first embossing structure, and second embossing structures protruding from or recessed in a second base surface of the second embossing roller, congruent according to the congruency nip separating each of the second embossing structures during embossing at least along the rising and recessing flanks from respective corresponding first embossing structures of the first embossing roller, and forming a summit nip between each of the summits of the first embossing structures and a corresponding counter side on the second embossing structures, with a value of the summit nip at least greater than the congruency nip, the first embossing structures and the second embossing structures being aligned along a plurality of parallel lines on respective surfaces of the first embossing roller and the second embossing roller. The system further comprises nip adjustment features for adjusting the first embossing roller and the second embossing roller for embossing with a base nip between a portion of the first base surface and a corresponding portion of the second base surface, and the congruency nip whereby the congruency nip has a value smaller than the average starting thickness, and for forming a roller nip comprising at least base nip zones of the base nip, congruency nip zones of the congruency nip and summit nip zones of the summit nip, for receiving the non-embossed sheet of substrate; whereby an embossing of the non-embossed sheet of substrate enables to produce the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness for parts of the sheet of substrate embossed in the congruency nip zones; compress in the congruency nip zones at least one of the first type of clusters inside the embossed sheet of substrate; process at least one of the second type of clusters by compressing in the congruency nip zones the at least one second type of cluster inside the embossed sheet of substrate and for each one of the at least one second type of cluster either: maintain the at least one second type of cluster inside the embossed sheet of substrate; or cause the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the summit nip zones, and to remain as debris in proximity of the second roller's counter side of the one of the summit nip zones.

[0036] In a further preferred embodiment, the at least first and second embossing roller further comprise at least a summit of a second protruding embossing structure of the second embossing roller corresponding to a corresponding one of the bottoms of the recessed first embossing structures, and comprising either one of the items in the list comprising one convex curved summit with curvature equal or larger than 10 pm, and one summit delimited by at least one edge, wherein each one of the at least one edge has a curvature equal or larger than 10 pm, and which during embossing forms a bottom nip between the one of the bottoms of the first embossing structures and the corresponding counter side on the summit of the second protruding embossing structure, with a value of the bottom nip at least greaterthan that of the congruency nip, the roller nip further comprising bottom nip zones of the bottom nip; and the processing of at least the second type of clusters additionally comprises causing the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the bottom nip zones, and remain as debris in proximity of the first roller's counter side of the one of the bottom nip zones.

[0037] In a further preferred embodiment, wherein along each line of the plurality of parallel lines on the first embossing roller, protruding first embossing structures alternate with recessed first embossing structures.

[0038] In a further preferred embodiment, the first embossing structures and the second embossing structures form anyone of ridges and grooves along each one of the plurality of the parallel lines.

[0039] In a further preferred embodiment, the formed ridges and grooves define on the first and the second embossing roller respectively a first radial profile and a corresponding second radial profile.

[0040] In a further preferred embodiment, the system further comprises a roller cleaning tool for detaching the debris from any one of at least the first roller's surface and the second roller's surface. In a further preferred embodiment, the system further comprises an air-depression cleaning system for removing the detached debris from the embossing roller system.

[0041] In a further preferred embodiment, the roller cleaning tool comprises at least a scraperfor each of the first and second embossing rollers, each scraper comprising an edge configured to be presented towards the roller surface of the corresponding embossing roller, and having a shape fitting in the corresponding radial profile of the embossing roller, and configured in such a way that the debris in proximity to any one of the roller surfaces is removed from the roller surface while the embossing roller rotates.

[0042] In a further preferred embodiment, the roller cleaning tool comprises at least a debris collecting tool for each of the first and second embossing rollers, which may be any one from a list comprising a brush, a gas blower, an ionized air blower, an ultrasonic system, a fluid projection system, each debris collecting tool configured to be directed towards the roller surface of the corresponding embossing roller, and configured in such a way that the debris in proximity to any one of the roller surfaces is removed from the roller surface while the embossing roller rotates.

[0043] In a further preferred embodiment, the first and the second embossing rollers are mounted in a corresponding quick exchange fixture, whereby each of the quick exchange fixtures is removably mounted in a frame.

[0044] In a further preferred embodiment, the first and the second embossing rollers are mounted and adjusted in a quick exchange cassette, whereby the quick exchange cassette is removably mounted in a frame.

[0045] 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 third and the fourth embossing rollers forming a further nip to receive the embossed sheet of substrate for further embossing.

[0046] 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.

[0047] In a further preferred embodiment, each of the protruding first and second embossing structures and each of the recessed first and second embossing structures comprises at least two contiguous rising flanks for protruding embossing structures or recessing flanks for recessed embossing structures that define an angle between themselves that has a value between 40° and 140°.

[0048] In a further preferred embodiment, each of the protruding first and second embossing structures and each of the recessed first and second embossing structures are described by a summit of a protruding first or second embossing structure to a bottom of a recessed respectively first or second embossing structure height value situated in a range between 0,05 mm and 1 ,5 mm.

[0049] In a further preferred embodiment, the ridges and grooves are arranged in aperiodic manner which is described by a dimensional spacing of at least 0,1 mm between two adjacent ridges and grooves.

[0050] In a further preferred embodiment, the first and second embossing structures are configured to engage into each other between the rollers during embossing and drive and self-synchronize the first and the second embossing rollers.

[0051] In a further preferred embodiment, the system further comprises a synchronization mechanism to drive and synchronize the first and the second embossing rollers, which is any one from a list comprising toothed-wheels gears, helicoidal gears, servomotors.

[0052] Brief Description of the Figures

[0053] The invention will be better understood through the description of example embodiments of the invention and in reference to the Figures, wherein

[0054] Figure 1 shows an example of a system for manufacturing an embossed sheet of substrate with a controlled thickness value and a reduced content of clusters according to the invention;

[0055] Figure 2 shows a further example of a system for manufacturing an embossed sheet of substrate with a controlled thickness value and a reduced content of clusters according to the invention;

[0056] Figure 3 shows an example of a piece of a sheet of substrate priorto embossing, and which comprises substrate clusters;

[0057] Figure 4 shows an example of an embossed sheet of substrate obtained with to the invention;

[0058] Figure 5 shows a further example of an embossed sheet of substrate and a cluster detached as debris as obtained with the invention;

[0059] Figure 6 shows a preferred embodiment for a set of embossing rollers driven by toothed wheels;

[0060] Figure 7 contains an example of an embossed sheet of substrate and a magnified cross-section of embossing rollers used for embossing according to the invention;

[0061] Figure 8 contains a further example of an embossed sheet of substrate and a magnified cross-section of embossing rollers used for embossing according to the invention;

[0062] Figure 9 contains yet a further example of an embossed sheet of substrate and magnified crosssections of embossing rollers used for embossing according to the invention;

[0063] Figure 10 contains yet a further example of an embossed sheet of substrate and a magnified crosssection of embossing rollers used for embossing according to the invention; Figure 11 contains yet a further example of an embossed sheet of substrate and a magnified crosssection of embossing rollers used for embossing according to the invention;

[0064] Figure 12 contains yet a further example of an embossed sheet of substrate and a magnified crosssection of embossing rollers used for embossing according to the invention;

[0065] Figures 13A and 13B contain magnified cross-sectional views from embossing rollers used for embossing a sheet of substrate to obtain a sheet of substrate with a controlled thickness value and a reduced content of clusters according to preferred embodiments of the invention;

[0066] Figures 14A and 14B contain further magnified cross-sectional views from embossing rollers used for embossing a sheet of substrate to obtain a sheet of substrate with a controlled thickness value and a reduced content of clusters according to preferred embodiments of the invention;

[0067] Figures 15A-15C contain views of examples for quick-exchange devices configured for housing a set of embossing rollers according to the invention;

[0068] Figure 16 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 scrapers according to the invention;

[0069] Figure 17 contains two views of example embodiments for any of the embossing rollers according to the invention;

[0070] Figure 18 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;

[0071] Figure 19 contains a further schematic illustration of a set of embossing rollers with ring-shaped shoulders at their extremities;

[0072] Figure 20 contains a further schematic illustration of a set of embossing rollers without ring-shaped shoulders at their extremities;

[0073] Figure 21 contains a schematic illustration of a further embossed sheet of substrate together with a corresponding cross-section of embossing rollers according to the invention;

[0074] Figure 22 contains a schematic illustration of a further embossed sheet of substrate together with a corresponding cross-section of embossing rollers according to the invention;

[0075] Figure 23 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;

[0076] Figure 24 schematically illustrates an obtaining of filtering elements using an embossed sheet of substrate as resulting from the invention;

[0077] Figure 25 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; Figures 26A and 26B schematically illustrate a structure of an inhalable drug delivery device according to prior art;

[0078] Figure 27 contains a flowchart illustrating an example embodiment of a method for manufacturing an embossed sheet of substrate according to the invention.

[0079] Same references will be used to designate same or similar features that appear throughout the Figures.

[0080] Glossary

[0081] - 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;

[0082] - 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;

[0083] - woven substrate: a fibrous substrate (e.g., natural or synthetic fibers), in which the substrate substantially consists of interlaced fibers;

[0084] - 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;

[0085] - 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.

[0086] - online: the embossing roller system is directly integrated the filter-element production line;

[0087] Detailed Description of Example Embodiments of the Invention

[0088] 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 ofthe properties of the filtering elements obtained through folding of the embossed sheet of substrate. Figure 1 shows an example of a system for manufacturing an embossed sheet of substrate with a controlled thickness value and a reduced content of clusters according to the invention. A sheet of substrate 100 is embossed using an embossing roller system 108, in orderto obtain an embossed sheet of substrate 101 with a controlled thickness value and a reduced content of clusters (clusters not illustrated in Figure 1). For simplicity purposes, the embossing roller system 108 is represented as comprising a frame 107, which accommodates two embossing rollers, 104 and 105. According to a feed direction 109, the sheet of substrate 100 to be embossed is guided using optionally at least a deflection roller 112, into a nip 106 between a first embossing roller 104 and a second embossing roller 105, which bear respectively first embossing structures and second embossing structures (not illustrated in Figure 1). More precisely the first embossing structures and the second embossing structures are protruding from or recessed in a base surface of the embossing rollers 104, 105 and they are congruent according to a congruency nip, which is a part of the nip 106, and which will be further detailed in the description of this invention. For subsequent figures and considerations, a zone 102 on the substrate to be embossed 100, a zone 103 on the embossed substrate 101 , a figurative process input interface 110, and a figurative process output interface 111 are also represented in Figure 1.

[0089] Referring now to Figure 2, this shows a further example of a system for manufacturing an embossed sheet of substrate with a controlled thickness value and a reduced content of clusters according to the invention. According to the figurative process input interface 110 and to the feed direction 109, the sheet of substrate to be embossed 100 is guided using optionally at least the deflection roller 112, into the nip 106 between the first embossing roller 104 and the second embossing roller 105, which bear embossing structures (not represented). Figure 2 further illustrates roller cleaning tools 200 and 201 configured to detach debris (debris not illustrated) from a vicinity of the surfaces of the first embossing roller 104 and second embossing roller 105, and which are thus located in front of the rotating embossing rollers 104 and 105's respective surfaces. In this example, the roller cleaning tools 200 and 201 are respectively functionally connected to air-depression cleaning systems 203 and 202, which are configured to remove the detached debris from the embossing roller system 108, for example by exhausting the detached debris. The embossing roller system 108 may comprise means 204 to adjust the nip 106 (e.g., by adjusting an embossing pressure between the embossing rollers 104, 105), means suggested by a set of opposing arrows.

[0090] Referring now to Figure 3, this shows an example of the zone 102 from the sheet of substrate to be embossed 100, fed along the direction 109, prior to embossing, and which comprises substrate clusters. Figure 3 shows a cross-sectional view 307 along a line 300 from the sheet of substrate 100 to be embossed according to the invention (as shown in Figure 1). The cross-sectional view 307 illustrates the sheet of substrate 100 priorto embossing, notably fibers 301 of a first material giving the sheet of substrate 100 its basics structure; the fibers 301 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 100, which are addressed by the invention, comprise substantially different substrate thickness values, illustrated as 304, 305, and 306, and a presence of at least a cluster of the first material 303 and of at least a cluster of a second material 302 that are embedded in and even protruding from a surface of the sheet of substrate 100, as depicted in the cross-sectional view 307.

[0091] Referring now to Figure 4, this shows an example of the zone 103 from the embossed sheet of substrate 101 as obtained with the invention and also indicates the feed direction 109, in which the substrate was fed during the embossing, whereas lines 405 schematically illustrate embossed features embossed by means of the embossing structures present on the embossing rollers (not represented). Figure 4 shows a cross-sectional view 404 along a line 400 from the embossed sheet of substrate 101 (as shown in Figure 1), embossed according to the invention, in which the fibers 301 giving the embossed sheet of substrate 101 its basics structure, and which may be of natural or synthetic origin and present in a woven or non-woven manner are not exhaustively illustrated. The cross-sectional view 404 shows substantially constant thickness values 401 , 402, and 403, and crushed and downsized clusters 302, 303 still embedded in the embossed sheet of substrate 101 , as well as a cluster 406, possibly downsized, and still adhering as debris at a surface of the embossed sheet of substrate 101 , to migrate to a zone of the summit nip in the vicinity of the surfaces of the embossing rollers 104, 105 (not represented).

[0092] Referring now to Figure 5, this shows an example of the zone 103 from the embossed sheet of substrate 101 as obtained with the invention and also indicates the feed direction 109, in which the substrate was fed during the embossing, whereas lines 505 schematically illustrate embossed features embossed by means of the embossing structures present on the embossing rollers (not represented). Figure 5 shows a cross-sectional view 504 along a line 500 from the embossed sheet of substrate 101 (as shown in Figure 1), embossed according to the invention, in which the fibers 301 giving the embossed sheet of substrate 101 its basics structure, and which may be of natural or synthetic origin and present in a woven or non-woven manner are not exhaustively illustrated. The cross-sectional view 504 shows substantially constant thickness values 501 , 502, and 503, and crushed and downsized clusters 302, 303 still embedded in the embossed sheet of substrate 101 , as well as a cluster 506, possibly downsized, and already detached as debris from the sheet of substrate 101 , to migrate to a zone of the summit nip in the vicinity of the surfaces ofthe embossing rollers 104, 105 (not represented).

[0093] Referring now to Figure 6, this shows a preferred embodiment for a set of embossing rollers driven by toothed-wheels, in which the first 104 and the second 105 embossing rollers are mounted on axes 601 and driven by respective toothed-wheels 600 located at their extremities. The first embossing roller 104 comprises, as illustrated by a zone 603, embossing structures protruding from or recessed in a base surface of the first embossing roller (detail not represented in the figure) and the second embossing roller 105 comprises embossing structures protruding from or recessed in a base surface of the second embossing roller congruent according to the congruency nip with those of the first embossing roller, as illustrated by a zone 602. The zone 603 on the first embossing roller 104 and the zone 602 on the second embossing roller 105 are defined in a symbolic schematic manner and their hatching representation will be used throughout the subsequent figures and considerations.

[0094] Referring now to Figure 7, this shows an example of the zone 103 of the embossed sheet of substrate 101 and a magnified cross-section 700 of embossing rollers used for embossing. More precisely, Figure 7 shows a view from above of the zone 103 from the sheet of substrate 101 embossed according to the invention, along a feed direction 109, with a controlled thickness value and with a reduced content of clusters, the embossed sheet of substrate 101 bearing protruding embossed features 701 and recessed embossed features 702, which are represented in a symbolical manner in Figure 7. The protruding embossed features 701 and the recessed embossed features 702 are arranged in a parallel, periodical manner, described by the dimensional period parameters / and p. In the cross-sectional view 700 illustrating a zone of a nip between the embossing rollers 104 and 105 used to obtain the embossed sheet of substrate 101 , and which both correspond to a symbolic line 712 along the embossed sheet of substrate 101, a summit of a protruding first embossing structure 704, a bottom of a recessed first embossing structure 710, and a rising flank 707 of a protruding first embossing structure are illustrated for the first embossing structures present on the first embossing roller 104, whereas a summit of a protruding second embossing structure 711 , a bottom of a recessed second embossing structure 705, and a recessing flank 708 of a second recessed embossing structure are illustrated for the second embossing structures present on the second embossing roller 105. Furthermore, Figure 7 illustrates a summit nip 706, a bottom nip 709, and a congruency nip 703, which is smaller than or at the most equal with the summit nip or the bottom nip. A height value h of the summit to bottom height of the first embossing structures present on the first embossing roller 104 is also depicted in Figure 7.

[0095] Referring now to Figure 8, this contains an example ofthe embossed sheet of substrate 101 and a magnified cross-section 809 of embossing rollers used for embossing. More precisely, Figure 8 shows a view from above of an example ofthe zone 103 from the sheet of substrate 101 embossed along a feed direction 109 according to the invention, the embossed sheet of substrate bearing recessed axial grooves 801 and protruding axial ridges 800. The embossed protruding ridges 800 and the recessed grooves 801 are arranged in a parallel manner described by a dimensional period parameter / . In the cross-sectional view 809, illustrating a zone of a nip between the embossing rollers 104 and 105 used to obtain the embossed sheet of substrate 101 , and which corresponds to a symbolic line 802 along the embossed sheet of substrate 101, a summit of a ridge 804 formed by a protruding first embossing structure on the first embossing roller 104, a bottom of a groove 805 formed by recessed second embossing structure on the second embossing roller 105, as well as a summit nip 806 are depicted. Furthermore, a rising flank 807, a recessing flank 808, a congruency nip 803, as well as the height value h of the summit of the ridge to bottom of the groove height of the first embossing structures that are present on the first embossing roller 104 are illustrated in the cross-sectional view 809 from Figure 8.

[0096] Referring now to Figure 9, this contains a further example of the embossed sheet of substrate and magnified cross-sections of embossing rollers used for embossing. As such, Figure 9 illustrates a view from above of an example of the zone 103 from the sheet of substrate 101 embossed along a feed direction 109 according to the invention, which further contains recessed axial grooves 901 and protruding axial ridges 900. The embossed protruding ridges 900 and the embossed recessed grooves 901 are arranged in a parallel manner described by the dimensional period parameter / . In the cross-sectional view 913, illustrating a zone of a nip between the embossing rollers 104 and 105 used to obtain the embossed sheet of substrate 101 , and which corresponds to a symbolic line 902 along the embossed sheet of substrate 101, a summit of a ridge 903 formed by a protruding first embossing structure on the first embossing roller 104, a bottom of a groove 904 formed by a recessed second embossing structure on the second embossing roller 105, as well as a base nip 908, a bottom nip 906, a summit nip 905, as well as congruency nip 903 are depicted. As the symbolic line 902 along the embossed sheet of substrate 101 starts from the physical extremity of the embossed sheet of substrate 101 , the cross-section view 913 further contains parts of the base surfaces ofthe rollers 104 and 105, which further define the base nip 908. The height value h of the summit of the ridge to the bottom ofthe groove height ofthe first embossing structures that are present on the first embossing roller 104 are also illustrated in the cross-sectional view 913 from Figure 9, which in further detailed cross-section view 909 shows a detail of the nip between the embossing rollers 104 and 105. In this detail, base nip zone 908, congruency nip zone 910, summit nip zone 912, and bottom nip zone 911 are symbolically delimitated by dotted lines. For this example, the embossing structures that are present on the embossing rollers 104 and 105 have a substantial sinusoidal profile, whereas the bottom nip is equal to the congruency nip, which is smaller than the summit nip.

[0097] The embossed recessed axial grooves and the embossed protruding axial ridges described in the example herein above are arranged in a parallel manner and they are stretching without interruptions over the embossed sheet of substrate, which originates from the fact that the corresponding embossing protruding structures and the corresponding embossing recessed structures are radially distributed in a continuous manner, radially circumventing the embossing rollers 104, 105. However, this shall not be understood as a limitation to the invention: the embossed recessed axial grooves and the embossed protruding axial ridges may also present interruptions, as it will be further exposed in following figures and considerations.

[0098] Referring now to Figure 10, this contains yet a further preferred example of the embossed sheet of substrate and a magnified cross-section of embossing rollers used for embossing. Figure 10 illustrates a view from above of an example of the zone 103 from the sheet of substrate 101 embossed along a feed direction 109 according to the invention, with a controlled thickness value and with a reduced content of clusters, which further contains recessed grooves 1001 and protruding ridges 1000, whereas the embossed ridges are disconnected by zones 1002 in which the embossed sheet of substrate 101 maintains the height level ofthe grooves 1001. The embossed protruding ridges 1000 are arranged in an array-like manner described by the dimensional period parameters p and / . In the cross-sectional view 1011 from Figure 10, a zone of a nip between the embossing rollers 104 and 105, and which corresponds to a symbolic line 1003 along the embossed sheet of substrate 101 , a summit of a ridge 1004 formed by a protruded first embossing structure, a rising flank 1007 of a first embossing structure, and a base surface 1005 of the first embossing roller 104 is shown, together with a summit nip 1010, a base nip 1009, and a congruency nip 1008. The base nip 1009 is equal to the congruency nip 1008, which is smaller than the summit nip 1010.

[0099] Referring to Figure 11, this contains yet a further example of the embossed sheet of substrate and a magnified cross-section of embossing rollers used for embossing. Figure 11 contains a detailed top view from an example of the zone 103 from the embossed sheet of substrate 101 embossed along a feed direction 109 according to the invention, which further contains embossed recessed axial grooves 1101 and embossed protruding axial ridges 1100, whereas the embossed protruding ridges are disconnected by zones 1102 in which the embossed sheet of substrate 101 maintains the height level of the grooves 1101. The embossed protruding ridges 1100 are arranged in an array-like manner, are described by the dimensional period parameters p and / , and they may be inclined, e.g. under of angle in a range between 10° and 40°, with respect to the feed direction 109. In a cross-section view 1100 from a zone of a nip between the embossing rollers 104 and 105 used to obtain the embossed sheet of substrate 101 , which further corresponds to a symbolic line 1103 along the embossed sheet of substrate, a base surface 1105 and a summit 1109 of the first embossing roller 104, and a base surface 1109 and a bottom 1107 of the second embossing roller 105 are illustrated, together with a summit nip 1108, a base nip 1109, and a congruency nip 1106. Forthis example, the embossing structures that are present on the embossing rollers 104 and 105 have a substantial sinusoidal profile, the bottom nip is equal to the congruency nip, which is smaller than the summit nip, and the height value h of the embossing structures that are present on the first embossing roller 104 is also shown in the cross-sectional view 1110 from Figure 11.

[0100] Referring now to Figure 12, this contains a yet further example forthe embossed sheet of substrate and a magnified cross-section of embossing rollers used for embossing. More specific, Figure 12 shows a view from above of an example ofthe zone 103 from the sheet of substrate 101 embossed along a feed direction 109 according to the invention, which further contains recessed embossed features 1201 and protruding embossed features 1200. The protruding embossed features 1200 and the recessed embossing features 1201 are arranged in a parallel manner described by dimensional period parameters p and / . In the cross-sectional view 1212, illustrating a zone of a nip between the embossing rollers 104 and 105 used to obtain the embossed sheet of substrate 101 , and which corresponds to a symbolic line 1202 along the embossed sheet of substrate 101 , a summit 1204, a flank 1207, and a bottom 1210 of the first embossing roller 104, a summit 1211, a flank 1208, and a bottom 1205 of the second embossing roller 105 are shown. The cross-sectional view 1212 from Figure 12 further includes a summit nip 1206, a bottom nip 1209, a congruency nip 1203, and the height value h of the summit to bottom height of the first embossing structures present on the first embossing roller 104. For this example, the embossing structures that are present on the embossing rollers 104 and 105 have a substantial pyramidal shape, whereas the congruency nip is smallerthan the summit nip and then the bottom nip. In addition to the examples depicted in the previous figures, where contiguous flanks represented rising or recessing flanks that converged towards the summit of protruding structures, respectively towards the bottom of a recessed structures, the here depicted example describes contiguous flanks that converge toward an edge of the protruding or embossed feature (i.e. , a pyramid) and the angle between two contiguous flanks will be the angle between two faces oh the pyramid.

[0101] Referring now to Figure 13, this contains magnified cross-sectional views from embossing rollers used for embossing a sheet of substrate to obtain a sheet of substrate with a controlled thickness value and a reduced content of clusters, according to the invention. More specifically, Figure 13A shows a detail from embossing structures having substantially curved summits and bottoms, which are present on the first embossing roller 104 and on the second embossing roller 105, whereas the embossed substrate 101 is represented between the two embossing rollers, as well as its basics structure, and which may be of natural or synthetic origin and present in a woven or non-woven manner (not exhaustively illustrated). Figure 13A shows a bottom nip 1300, a summit nip 1302, a congruency nip 1301, whereby the bottom nip 1300 is equal to the congruency nip 1301, which is smaller than the summit nip 1302. Crushed and downsized clusters 302, 303 are still embedded in the embossed sheet of substrate 101, and clusters 506, possibly downsized, migrated to a zone of the summit nip 1302 in the vicinity of the surfaces of the embossing roller 105. Figure 13B, shows a detail from embossing structures, which are present on the first embossing roller 104 and on the second embossing roller 105, having substantially flattop summits and bottoms delimitated by edges characterized by radii R larger than 10 pm. The embossed substrate 101 is represented between the two embossing rollers, as well as its basics structure, and which may be of natural or synthetic origin and present in a woven or non-woven manner (not exhaustively illustrated). Figure 13B shows a bottom nip 1303, a summit nip 1305, a congruency nip 1304, whereby the bottom nip 1303 is equal to the congruency nip 1304, which is smaller than the summit nip 1305. Crushed and downsized clusters 302, 303 are still embedded in the embossed sheet of substrate 101 , and clusters 506, possibly downsized, migrated to a zone of the summit nip 1305 in the vicinity of the surfaces of the embossing rollers 105. For both exposed examples, i.e., substantially rounded A or flattop B summit, the thickness of the embossed substrate 101 remain inferior to the summit nip and this facilitates the accumulation of the detached debris 506 in the zone of the summit nip, in the vicinity of the second embossing roller 105. Referring now to Figure 14, this contains magnified cross-sectional views from embossing rollers used for embossing a sheet of substrate to obtain a sheet of substrate with a controlled thickness value and a reduced content of clusters, according to the invention. More specifically, Figure 14A shows a detail from embossing structures having substantially curved summits and bottoms, which are present on the first embossing roller 104 and on the second embossing roller 105, whereas the embossed sheet of substrate 101 is represented between the two embossing rollers, as well as its basics structure, and which may be of natural or synthetic origin and present in a woven or non-woven manner (not exhaustively illustrated). Figure 14A shows a bottom nip 1400, a summit nip 1402, a congruency nip 1401, whereby the congruency nip 1401 is smaller than the summit nip 1402 and also than the bottom nip 1400. Crushed and downsized clusters 302, 303 are still embedded in the embossed sheet of substrate 101, while clusters 506, possibly downsized, migrated to a zone of the summit nip 1402 and to a zone of the bottom nip 1400, in the vicinity of the surfaces ofthe embossing rollers 105 and 104, respectively. Figure 14B as such, shows a detail from embossing structures, which are present on the first embossing roller 104 and on the second embossing roller 105, having substantially flattop summits and bottoms delimitated by edges characterized by radii R largerthan 10 pm. The embossed substrate 101 is represented between the two embossing rollers, as well as its basics structure, and which may be of natural or synthetic origin and present in a woven or non-woven manner (not exhaustively illustrated). Figure 14B shows a bottom nip 1403, a summit nip 1405, a congruency nip 1404, whereby the congruency nip 1404 is smaller than the summit nip 1405 and also smaller than the bottom nip 1403. Crushed and downsized clusters 302, 303 are still embedded in the embossed sheet of substrate 101, while clusters 506, possibly downsized, migrated to a zone of the summit nip 1405 and to a zone of the bottom nip 1403 in the vicinity of the surfaces of the embossing rollers 105 and 104, respectively. For both exposed examples, i.e., substantially rounded A orflattop B summit, the thickness ofthe embossed substrate 101 remains inferior to the summit nip and this facilitates the accumulation of the detached debris 506 in a zone of the summit nip and in a zone of the bottom nip, respectively in the vicinity of the second embossing roller 105 and of the first embossing roller 104.

[0102] For a better understanding of the correlations and relations between the average starting thickness, the congruency nip, the summit nip and the bottom nip, several examples of embodiments will be further illustrated.

[0103] In a preferred embodiment, a non-woven substrate having a starting average thickness of 400 pm was embossed according to the invention, in order to obtain a controlled thickness and to reduce a content of clusters. In this case the congruency nip was adjusted to 200 pm, whereas the summit nip and the bottom nip were set in a range between 230 pm to 250 pm. The summits were of substantially of convex curved shape with a radius of 140 pm. The embossing step was part of online manufacturing process of filtering elements, and the filtering elements fabricated in this manner exhibited a coefficient of variation (CV) of their pressure drop (PD) of approximately 4,5%. In a further preferred embodiment example, a woven substrate having a starting average thickness of 110 pm was embossed according to the invention, in order to reduce a content of clusters and to obtain a controlled thickness. In this case the congruency nip was set at 110 pm, whereas the summit nip and the bottom nip were set in a range between 115 pm and 120 pm. The summits were substantially of convex curved shape with a radius of 190 pm. The embossing step was part of online manufacturing process of filtering elements, and the filtering elements fabricated in this manner exhibited a coefficient of variation (CV) of their pressure drop (PD) of approximately 1 ,8%.

[0104] Referring to Figures 15A-15C, these contain views of examples for quick-exchange devices configured for housing a set of embossing rollers according to the invention. The embossing rollers 104 and 105 may be removably housed in a quick-exchange device, generically illustrated under reference 1500 in Figure 15A. In a preferred embodiment 1506 of such a quick-exchange device, an axle of at least one of the rollers 104, 105 is movable in all three coordinate directions (not illustrated) in order to allow a self-synchronization of the embossing rollers. As shown in Figure 15B, the quickexchange device comprises a frame 1501 having two seats intended to receive respective roller fixtures 1502 and 1503, whereas the roller fixture 1503 serves for mounting the roller 105, which is driven by a here non-represented external drive, and roller fixture 1502 serves for mounting the roller 104. In a further preferred embodiment 1507 shown in Figure 15C of the quick-exchange device, the rollers 104 and 105 are mounted in a cassette 1504, which contains means (not represented) for adjusting and correcting the positions and the rotation axes of the rollers 104 and 105, and which is removably mounted in a frame 1505. In preferred embodiments, the roller 104 is driven by the externally driven roller 105 via gearwheels (not represented) located at one end of the rollers. However, other synchronizing means, e.g. electric servomotors, may also be used.

[0105] Referring to Figure 16, this 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 profiled scrapers according to the invention. In this example embodiment of the invention, the detachment of debris from the surfaces of rollers 104, 105 is carried out by means of metallic (e.g., brass) or ceramic (e.g., oxides, nitrides, carbides) adapted-shape scrapers 1601 and 1602. The rollers 104, 105 and the scrapers 1601 , 1602 are respectively mounted on the roller fixtures 1603 and 1604, which are themselves part of a quick-exchange device (not represented). However, the quick-exchange device is optional, and the scrapers may be attached to any form of roller supports. As illustrated in the detailed view 1605, in order to obtain an optimal debris removal from the roller surfaces, the specific scraper edge shape geometries 1608 of the scrapers 1602 shall penetrate into the recessed embossing structures 1606 and glide over the protruding embossing structures 1607 that are present on a first embossing roller 104. For clarity reasons, the profiled scraper forthe second embossing roller 105 is not illustrated in Figure 16, but this shall be understood in an identical manner. In a further embodiment, optional means 1600 of lateral displacement are provided for the roller fixture 1603, in order to allow a selfsynchronization of the embossing rollers, by maintaining the matching scraper positions. Referring to Figure 17, this contains two views of example embodiments for any of the embossing rollers according to the invention. More precisely, Figure 17 illustrates an example embodiment for any one of embossing rollers 104 or 105, which comprises a rotation axis 1703, a roller surface 1700 and a toothed wheel 1701 at one extremity of the one embossing roller, enabling the one embossing roller 104 or 105 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 104 or 105 (other one not represented in Figure 17). The embossing features present on the roller surface 1700 are not represented explicitly. Figure 17 also shows a further example embodiment for any one of embossing rollers 104 or 105, in which the embossing roller does not comprise any toothed wheel. In this example any one of embossing rollers 104 or 105 is typically driven and synchronized with the other one of the rollers 104 and 105 (not illustrated in the Figure 17) by a servo motor mechanism (not represented) that directly rotates the rotation axis 1703. Embossing features present on a roller surface 1702 are not represented explicitly.

[0106] Referring now to Figure 18, this 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 18 illustrates preferred embodiments for driving and synchronizing the embossing rollers 104 and 105, belonging to an embossing roller system 1802, according to the invention. The feed direction of the sheet of substrate 100 and of the embossed sheet of substrate 101 is given by the arrows 109, whereas Figure 18 also illustrates the figurative process input interface 110 and the figurative process output interface 111 , the roller cleaning tools 200 and 201 , the air-depression cleaning systems 202 and 203, as well as the at least one optional deflection roller 112. In a preferred embodiment, toothed wheels 1701 may be used to drive and synchronize the embossing rollers 104 and 105, whereas in a further preferred embodiment depicted in the view 1800 helicoidal gears 1801 are used to drive and synchronize the embossing rollers instead of the toothed wheels 1701.

[0107] Referring to Figure 19, this contains a schematic illustration of a set of embossing rollers with ringshaped shoulders at their extremities. More precisely Figure 19 represents a set of embossing rollers 1901 , 1902, which shall be seen as preferred embodiments of the first 104 and second 105 embossing rollers, bearing protruding and recessed embossing features (not represented), each comprising at a corresponding extremity a toothed wheel 1903, 1904, the teeth of which intertwine to synchronously drive the embossing rollers 1901 , 1902, to rotate about respective rotation axes 1905, 1906. The embossing rollers 1901 , 1902, further each comprise two ring-shaped shoulders 1907, 1908, one towards each extremity ofthe respective embossing roller 1901 , 1902, 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 1907, 1908, are generally designed to form a ring which is 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 19 to maintain a better readability. Figure 19 further represents two magnified views 1909, 1910, of areas where the ring-shaped shoulders 1907 and 1908 are resting on each other as may be the case during embossing. This is substantiated by distance 1911 between the ring-shaped shoulders 1907 and 1908 being 0, while a base nip 1912 is maintained between the embossing rollers 1901 and 1902 with a determined base nip width value n separating a base surface 1914 ofthe embossing roller 1901 from an opposite base surface 1913 of the embossing roller 1902. The base surfaces are schematically represented and the views 1909 and 1910 do not comprise any embossing features in the example of Figure 19. The determined nip width value n of the nip 1912 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.

[0108] Referring to Figure 20, this contains a further example, in which the ring-shaped shoulders of Figure 19 may be replaced by radial recesses 2001 and 2002, which each form recesses in the embossing rollers 2001 and 2002 respectively as compared to the base surfaces 2013 and 2014. Hence, as represented in the two magnified views 2006 and 2007, when the embossing rollers 2001 and 2002 are pressured one towards the other, as is depicted by arrows 2005 in the radial recesses 2001 and 2002, their base surfaces 2013 and 2014 may be coming into contact such that a distance 2003 tends to become similar to that of a sheet of substrate inserted therein for embossing (not represented), and a distance 2004 between radial recesses 2001 and 2002 facing each other from one embossing roller to the other is greater than 0. The pressure depicted by the arrows 2005 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.

[0109] Referring to Figure 21 , this illustrates a further example of an embossed sheet of substrate further embossed according to the invention. More precisely, Figure 21 contains a detailed top view from an example of the zone 103 (as in Figure 1) of a sheet of substrate 101 embossed according to the invention, with controlled thickness value and with substantially reduced content of clusters, which shows recessed 2102 and protruding 2103 embossed radial features, which are substantially parallel. Figure 21 further includes a cross-sectional view 2104 from a zone of a nip between the embossing rollers 104 and 105 used to obtain the embossed the sheet of substrate 101 , which corresponds to a symbolic line 2101 along the embossed sheet of substrate. In a further detailed view 2100 of a part of the base nip zone between the embossing rollers 104 and 105, the ring-shaped shoulders 1907 and 1908 are resting on each other as may be the case during embossing. This is substantiated by distance 1911 between the ring-shaped shoulders 1907 and 1908 being 0, while a base nip 1912 is maintained between the embossing rollers 104 and 105 with a determined base nip width value n separating a base surface 1914 of the embossing roller 1041 from an opposite base surface 1913 of the embossing roller 105. The determined base nip width value n of the nip 1912 enables to insert a sheet of substrate in it (sheet of substrate not represented) for embossing, in orderto obtain a sheet of substrate with a controlled thickness and a reduced content of surface clusters. In this example, the protruding and the recessed embossing structures present on the embossing rollers 104, 105 have substantially flattop summits and bottoms.

[0110] Referring to Figure 22, this illustrates a further example of an embossed sheet of substrate further embossed according to the invention. More precisely, Figure 22 contains a detailed top view from an example of the zone 103 (as in Figure 1) of a sheet of substrate 101 embossed according to the invention, with controlled thickness value and with substantially reduced content of clusters, which shows recessed 2202 and protruding 2203 embossed radial features, which are substantially parallel. Figure 22 further includes a cross-sectional view 2204 from a zone of a nip between the embossing rollers 104 and 105 used to obtain the embossed the sheet of substrate 101 , which corresponds to a symbolic line 2201 along the embossed sheet of substrate. In a further detailed view 2200 of a part of the base nip zone between the embossing rollers 104 and 105, when the embossing rollers 104 and 105 are pressured one towards the other, as is depicted by arrows 2005 in the radial recesses 2001 and 2002, their base surfaces 2013 and 2014 may give a nip such that a base nip 2003 tends to become similar to that of a sheet of substrate inserted therein for embossing (not represented), and a distance 2004 between radial recesses 2001 and 2002 facing each other from one embossing roller to the other is greater than 0. The pressure depicted by the arrows 2005 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. In this example, the protruding and the recessed embossing structures present on the embossing rollers 104, 105 have substantially flattop summits and bottoms.

[0111] 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 Figure is detailing a preferred embodiment of online integration.

[0112] Referring to Figure 23, this 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 23 illustrates a preferred embodiment of the system for manufacturing an embossed sheet of substrate 101 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 2309 comprising a funnel 2307 into which a further embossed sheet of substrate 2305 is fed, folded, and formed into a filter rod 2308 output by the compacting device 2309. Hence the further embossed sheet of substrate 2305 is compacted with the funnel 2307. The filter rod 2308 may be pulled by means of a pulling jig 2310 to a further process step 2311 of cutting. The production line contains the embossing system 2301, according to the invention, to produce the embossed sheet of substrate 101 with controlled thickness value and with reduced content of cluster, whereas the first embossing roller 104, the second embossing roller 105, the roller cleaning tools 200 and 201 , the air-depression cleaning systems 202 and 203, as well as the removed debris 506 are showed in Figure 23. A magnified view from a zone 102 of the sheet of substrate 100 prior to embossing using the embossing system 2301 schematically depicts inhomogeneities of substrate thickness values and substrate clusters, while a further magnified view of a zone 103 from the embossed sheet of substrate 101 schematically shows the embossed sheet substrate with the controlled thickness value and with the reduced content of clusters. In a further preferred embodiment, the embossed sheet of substrate 101 with controlled thickness and with reduced content of clusters is fed into a second embossing system 2302 that contains a third 2303 and a fourth 2304 embossing roller, configured to further emboss at least an aerodynamic profile to obtain the embossed sheet of substrate 2305, 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 2306 of the further embossed sheet of substrate 2305 illustrates an example embossing obtained with the embossing set-up 2302 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 2300 configured to carry a bobbin with a web of sheet of substrate 100 and unwind it out towards the embossing set-up 2301.

[0113] Referring to Figure 24, this 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 2311 , Figure 24 illustrates under reference 2400 a cutting process that involves cutting the filter rod 2308 into individual pieces of filter elements 2401 each having the length L, and as an example, cut as two twin-filter elements by means of a cutting device 2402. Figure 24 further illustrates a magnified photograph view 2403 at an extremity of one of the filter elements 2401 , in which the embossed sheet of substrate 2305 is folded and compacted to fit in a cylindrical wrapper 2404, represented as a section of the cylindrical wrapper 2404. A detailed view 2405 of a part of the section 2403, in which the view is slightly from an angle, schematically illustrates how the embossed sheet of substrate 2305 is folded and packed in a manner of an accordion to form the rod. In the view 2405 a substrate thickness 2406 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.

[0114] Referring to Figure 25, this 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 25 schematically illustrates how a cigarette filter - type filtering element 2401 , in a preferred embodiment initially obtained as two twin-filters, may be mounted to a tobacco containing section 2501 in order to obtain a cigarette 2502 according to prior art. Part A shows two twin-filter elements 2401 , part B shows the two twin-filter elements 2401 positioned between tobacco containing sections 2501 , and a filter paper 2500 being wound and glued around the two filter elements 2401 and partly over a part of each tobacco containing section 2501 , resulting in two twincigarettes 2502 shown in part C. Part D shows one of cigarettes 2502 obtained after cutting the two twin-cigarettes in a middle 2503 thereof.

[0115] Referring to Figure 26, this schematically illustrates a structure of an inhalable drug delivery device 2600 in parts A and B, according to the prior art. Part A depicts a delivery system comprising a drugcontaining component 2601 and a filtering element 2602 fabricated using a sheet of substrate embossed according to the invention. Part B depicts an inhalable drug delivery system comprising the drug-containing component 2601 , a cooling component 2603, and of the filtering element 2602 fabricated using a sheet of substrate embossed according to the invention.

[0116] Figure 27 contains a flowchart illustrating an example embodiment of a method for manufacturing an embossed sheet of substrate 2700 according to the invention. The method is configured to produce a controlled thickness value of the embossed sheet of substrate 2700 in a congruency nip and to reduce a content of a second type of clusters initially present in a non-embossed sheet of substrate 2701 . The method comprises steps of

[0117] • providing 2702 the non-embossed sheet of substrate 2701 comprising a first material, a first type of clusters comprising the first material, and the second type of clusters comprising a second material different from the first material, the non-embossed sheet of substrate having an average starting thickness;

[0118] • providing 2703 an embossing roller system comprising at least a first and a second embossing roller, comprising first embossing structures protruding from or recessed in a first base surface of the first embossing roller, each ofthe protruding first embossing structures protruding from the first base surface and comprising rising flanks oriented away from the first base surface towards a summit that tops the protruding first embossing structure, wherein the summit of any one of the protruding first embossing structures comprises either one of the items in a list comprising one convex curved summit with curvature equal or largerthan 10 pm, and one summit delimited by at least one edge, wherein each one of the at least one edge has a curvature equal or larger than 10 pm, and each of the recessed first embossing structures recessing from the first base surface and comprising recessing flanks oriented from the first base surface inside of the first embossing roller towards a bottom that delimits the recessed first embossing structure, further comprising second embossing structures protruding from or recessed in a second base surface of the second embossing roller, congruent according to the congruency nip separating each of the second embossing structures during embossing at least along the rising and recessing flanks from respective corresponding first embossing structures of the first embossing roller, and forming a summit nip between each of the summits of the first embossing structures and a corresponding counter side on the second embossing structures, with a value of the summit nip at least greater than the congruency nip, the first embossing structures and the second embossing structures being aligned along a plurality of parallel lines on respective surfaces of the first embossing roller and the second embossing roller;

[0119] • adjusting 2704 the first embossing roller and the second embossing roller for embossing with a base nip between a portion of the first base surface and a corresponding portion of the second base surface, and the congruency nip, whereby the congruency nip has a value smaller than the average starting thickness;

[0120] • inserting 2705 the non-embossed sheet of substrate 2701 in a roller nip comprising at least base nip zones of the base nip, congruency nip zones of the congruency nip and summit nip zones of the summit nip;

[0121] • embossing 2706 the non-embossed sheet of substrate; thereby producing the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness for parts of the sheet of substrate embossed in the congruency nip zones;

[0122] • compressing 2707 in the congruency nip zones at least one of the first type of clusters inside the embossed sheet of substrate;

[0123] • processing 2708 at least one of the second type of clusters by compressing in the congruency nip zones the at least one second type of cluster inside the embossed sheet of substrate and for each one of the at least one second type of cluster either: maintaining the at least one second type of cluster inside the embossed sheet of substrate; or causing the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the summit nip zones, and to remain as debris in proximity of the second roller's counter side of the one of the summit nip zones.

Claims

Claims1 . Method for manufacturing an embossed sheet of substrate, the method being configured to produce a controlled thickness of the embossed sheet of substrate embossed in a congruency nip, and to reduce a content of a second type of clusters initially present in a non-embossed sheet of substrate, the method comprising providing the non-embossed sheet of substrate comprising a first material, a first type of clusters comprising the first material, and the second type of clusters comprising a second material different from the first material, the non-embossed sheet of substrate having an average starting thickness; providing an embossing roller system comprising at least a first and a second embossing roller, comprising first embossing structures protruding from or recessed in a first base surface of the first embossing roller, each ofthe protruding first embossing structures protruding from the first base surface and comprising rising flanks oriented away from the first base surface towards a summit that tops the protruding first embossing structure, wherein the summit of any one of the protruding first embossing structures comprises either one of the items in a list comprising one convex curved summit with curvature equal or larger than 10 pm, and one summit delimited by at least one edge, wherein each one of the at least one edge has a curvature equal or larger than 10 pm, and each of the recessed first embossing structures recessing from the first base surface and comprising recessing flanks oriented from the first base surface inside of the first embossing roller towards a bottom that delimits the recessed first embossing structure, further comprising second embossing structures protruding from or recessed in a second base surface of the second embossing roller, congruent according to the congruency nip separating each of the second embossing structures during embossing at least along the rising and recessing flanks from respective corresponding first embossing structures of the first embossing roller, and forming a summit nip between each of the summits of the first embossing structures and a corresponding counter side on the second embossing structures, with a value of the summit nip at least greater than the congruency nip, the first embossing structures and the second embossing structures being aligned along a plurality of parallel lines on respective surfaces of the first embossing roller and the second embossing roller,adjusting the first embossing roller and the second embossing roller for embossing with a base nip between a portion of the first base surface and a corresponding portion of the second base surface, and the congruency nip, whereby the congruency nip has a value smaller than the average starting thickness; inserting the non-embossed sheet of substrate in a roller nip comprising at least base nip zones of the base nip, congruency nip zones of the congruency nip and summit nip zones of the summit nip; embossing the non-embossed sheet of substrate; thereby producing the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness for parts of the sheet of substrate embossed in the congruency nip zones; compressing in the congruency nip zones at least one of the first type of clusters inside the embossed sheet of substrate; processing at least one of the second type of clusters by compressing in the congruency nip zones the at least one second type of cluster inside the embossed sheet of substrate and for each one of the at least one second type of cluster either: maintaining the at least one second type of cluster inside the embossed sheet of substrate; or causing the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the summit nip zones, and to remain as debris in proximity of the second roller's counter side of the one of the summit nip zones.

2. The method of manufacturing the embossed sheet of substrate according to claim 1 , further wherein at least a summit of a second protruding embossing structure of the second embossing roller corresponding to a corresponding one of the bottoms of the recessed first embossing structures, and comprising either one of the items in the list comprising one convex curved summit with curvature equal or larger than 10 pm, and one summit delimited by at least one edge, wherein each one of the at least one edge has a curvature equal or larger than 10 pm, and which during embossing forms a bottom nip between the one of the bottoms of the first embossing structures and the corresponding counter side on the summit of the second protruding embossing structure, with a value of the bottom nip at least greater than that of the congruency nip, the roller nip further comprising bottom nip zones of the bottom nip; andthe processing of at least the second type of clusters additionally comprises causing the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the bottom nip zones, and remain as debris in proximity of the first roller's counter side of the one of the bottom nip zones.

3. The method of manufacturing the embossed sheet of substrate according to any one of claims 1 and 2, further wherein along each line of the plurality of parallel lines on the first embossing roller, protruding first embossing structures alternate with recessed first embossing structures.

4. The method of manufacturing the embossed sheet of substrate according to any one of claims 1 and 2, further wherein the first embossing structures and the second embossing structures form anyone of ridges and grooves along each one of the plurality of the parallel lines.

5. The method of manufacturing the embossed sheet of substrate according to claim 4, further wherein the formed ridges and grooves define on the first and the second embossing roller respectively a first radial profile and a corresponding second radial profile.

6. The method of manufacturing the embossed sheet of substrate according to any one of claims 1 to 5, further comprising detaching the debris from any one of at least the first roller's surface and the second roller's surface with a roller cleaning tool in vicinity of at least the first roller's surface and the second roller's surface.

7. The method of manufacturing the embossed sheet of substrate according to claim 6, further comprising removing the detached debris from the embossing roller system with an air-depression cleaning system.

8. The method of manufacturing the embossed sheet of substrate according to claim 6 dependent from claim 5, wherein the roller cleaning tool comprises at least a scraper for each of the first and second embossing rollers, each scraper comprising an edge configured to be presented towards the roller surface of the corresponding embossing roller, and having a shape fitting in the corresponding first and second radial profile of the embossing roller, and configured in such a way that the debris in proximity to any one of the roller surfaces is detached from the roller surface while the embossing roller rotates.

9. The method of manufacturing the embossed sheet of substrate according to claim 6, wherein the roller cleaning tool comprises at least a debris collecting tool for each of the first and second embossing rollers, which may be any one from a list comprising a brush, a gas blower, an ionized air blower, an ultrasonic system, a fluid projection system, each debris collecting tool configured to be directed towards the roller surface of the corresponding embossing roller, and configured in such a way that the debris in proximity to any one of the roller surfaces is detached from the roller surface while the embossing roller rotates.

10. The method of manufacturing the embossed sheet of substrate according to any one of claims 1 to 9, 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, whereby each of the quick exchange fixtures is removably mounted in a frame.11 . The method of manufacturing the embossed sheet of substrate according to any one of claims 1 to 9, 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, whereby the quick exchange cassette is removably mounted in a frame.

12. The method of manufacturing the embossed sheet of substrate according to any one of claims 1 to 11 , further comprising 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.

13. The method of manufacturing the embossed sheet of substrate according to claim 12, wherein the further embossing roller system is part of a production chain for manufacturing from the sheet of substrate of a filtering element configured for an inhalable drug delivery device, and for filtering a mainstream gas flow passing through the filtering element.

14. The method of manufacturing the embossed sheet of substrate according to any one of claims 1 to 13, wherein each of the protruding first and second embossing structures and each of the recessed first and second embossing structures comprises at least two contiguous rising flanks for protruding embossing structures or recessing flanks for recessed embossing structures that define an angle between themselves that has a value between 40° and 140°.

15. The method of manufacturing the embossed sheet of substrate according to any one of claims 1 to 14, wherein each of the protruding first and second embossing structures and each of the recessed first and second embossing structures are described by a summit of a protruding first or second embossing structure to a bottom of a recessed respectively first or second embossing structure height value situated in a range between 0,05 mm and 1 ,5 mm.

16. The method of manufacturing the embossed sheet of substrate according to any one of claims 4 to 5, wherein the ridges and grooves are arranged in a periodic manner which is described by a dimensional spacing of at least 0,1 mm between two adjacent ridges and grooves.

17. The method of manufacturing the embossed sheet of substrate according to any one of claims 1 to 16, wherein the first and the second embossing rollers are driven and self-synchronized by means ofthe first and second embossing structures engaged into each other between the rollers.

18. The method of manufacturing the embossed sheet of substrate according to any one of claims 1 to 16, 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.

19. The method of manufacturing the embossed sheet of substrate 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 0,01 mm and 1 ,5 mm.

20. The method of manufacturing the embossed sheet of substrate 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.21 . A system for manufacturing an embossed sheet of substrate, the system being configured to produce a controlled thickness value of the embossed sheet of substrate embossed in a congruency nip, and to reduce a content of a second type of clusters initially present in a nonembossed sheet of substrate, the non-embossed sheet of substrate comprising a first material, a first type of clusters comprising the first material, and the second type of clusters comprising a second material different from the first material, the non-embossed sheet of substrate having an average starting thickness, the system comprising an embossing roller system comprising at least a first and a second embossing roller, comprising first embossing structures protruding from or recessed in a first base surface of the first embossing roller, each ofthe protruding first embossing structures protruding from the first base surface and comprising rising flanks oriented away from the first base surface towards a summit that tops the protruding first embossing structure, wherein the summit of any one of the protruding first embossing structures comprises either one of the items in a list comprising one convex curved summit with curvature equal or largerthan 10 pm, and one summit delimited by at least one edge, wherein each one of the at least one edge has a curvature equal or larger than 10 pm, and each of the recessed first embossing structures recessing from the first base surface and comprising recessing flanks oriented from the first base surface inside of the first embossing roller towards a bottom that delimits the recessed first embossing structure, further comprising second embossing structures protruding from or recessed in a second base surface of the second embossing roller, congruent according to the congruency nipseparating each of the second embossing structures during embossing at least along the rising and recessing flanks from respective corresponding first embossing structures of the first embossing roller, and forming a summit nip between each of the summits of the first embossing structures and a corresponding counter side on the second embossing structures, with a value of the summit nip at least greater than the congruency nip, the first embossing structures and the second embossing structures being aligned along a plurality of parallel lines on respective surfaces of the first embossing roller and the second embossing roller, nip adjustment features for adjusting the first embossing roller and the second embossing roller for embossing with a base nip between a portion of the first base surface and a corresponding portion of the second base surface, and the congruency nip whereby the congruency nip has a value smaller than the average starting thickness, and for forming a roller nip comprising at least base nip zones of the base nip, congruency nip zones of the congruency nip and summit nip zones of the summit nip, for receiving the non-embossed sheet of substrate; whereby an embossing of the non-embossed sheet of substrate enables to produce the controlled thickness value of the embossed sheet of substrate smaller than the average starting thickness for parts of the sheet of substrate embossed in the congruency nip zones; compress in the congruency nip zones at least one of the first type of clusters inside the embossed sheet of substrate; process at least one of the second type of clusters by compressing in the congruency nip zones the at least one second type of cluster inside the embossed sheet of substrate and for each one of the at least one second type of cluster either: maintain the at least one second type of cluster inside the embossed sheet of substrate; or cause the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the summit nip zones, and to remain as debris in proximity of the second roller's counter side of the one of the summit nip zones.

22. The system for manufacturing the embossed sheet of substrate according to claim 21 , further wherein the at least first and second embossing roller further compriseat least a summit of a second protruding embossing structure of the second embossing roller corresponding to a corresponding one of the bottoms of the recessed first embossing structures, and comprising either one of the items in the list comprising one convex curved summit with curvature equal or larger than 10 pm, and one summit delimited by at least one edge, wherein each one of the at least one edge has a curvature equal or larger than 10 pm, and which during embossing forms a bottom nip between the one of the bottoms of the first embossing structures and the corresponding counter side on the summit of the second protruding embossing structure, with a value of the bottom nip at least greater than that of the congruency nip, the roller nip further comprising bottom nip zones of the bottom nip; and and the processing of at least the second type of clusters additionally comprises causing the at least one second type of cluster to emerge from the embossed sheet of substrate, by migrating it from the congruency nip zones to one of the bottom nip zones, and remain as debris in proximity of the first roller's counter side of the one of the bottom nip zones.

23. The system for manufacturing the embossed sheet of substrate according to any one of claims 21 and 22, further wherein along each line of the plurality of parallel lines on the first embossing roller, protruding first embossing structures alternate with recessed first embossing structures.

24. The system for manufacturing the embossed sheet of substrate according to any one of claims 21 and 22, further wherein the first embossing structures and the second embossing structures form anyone of ridges and grooves along each one of the plurality of the parallel lines.

25. The system for manufacturing the embossed sheet of substrate according to claim 24, further wherein the formed ridges and grooves define on the first and the second embossing roller respectively a first radial profile and a corresponding second radial profile.

26. The system for manufacturing the embossed sheet of substrate according to any one of claim 21 to 25, further comprisinga roller cleaning tool in vicinity of at least the first roller's surface and the second roller's surface for detaching the debris from any one of at least the first roller's surface and the second roller's surface.

27. The system for manufacturing the embossed sheet of substrate according to claim 26, further comprising an air-depression cleaning system for removing the detached debris from the embossing roller system.

28. The system for manufacturing the embossed sheet of substrate according to claim 26 dependent from claim 25, wherein the roller cleaning tool comprises at least a scraper for each of the first and second embossing rollers, each scraper comprising an edge configured to be presented towards the roller surface of the corresponding embossing roller, and having a shape fitting in the corresponding radial profile of the embossing roller, and configured in such a way that the debris in proximity to any one of the roller surfaces is removed from the roller surface while the embossing roller rotates.

29. The system for manufacturing the embossed sheet of substrate according to claim 26, wherein the roller cleaning tool comprises at least a debris collecting tool for each of the first and second embossing rollers, which may be any one from a list comprising a brush, a gas blower, an ionized air blower, an ultrasonic system, a fluid projection system, each debris collecting tool configured to be directed towards the roller surface of the corresponding embossing roller, and configured in such a way that the debris in proximity to any one of the roller surfaces is removed from the roller surface while the embossing roller rotates.

30. The system for manufacturing the embossed sheet of substrate according to any one of claims 21 to 29, wherein the first and the second embossing rollers are mounted in a corresponding quick exchange fixture, whereby each of the quick exchange fixtures is removably mounted in a frame.31 . The system for manufacturing the embossed sheet of substrate according to any one of claims 21 to 29, wherein the first and the second embossing rollers are mounted and adjusted in aquick exchange cassette, whereby the quick exchange cassette is removably mounted in a frame.

32. The system for manufacturing the embossed sheet of substrate according to any one of claims 21 to 31 , further comprising 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 third and the fourth embossing rollers forming a further nip to receive the embossed sheet of substrate for further embossing.

33. The system for manufacturing the embossed sheet of substrate according to claim 32, 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.

34. The system for manufacturing the embossed sheet of substrate according to any one of claims 21 to 33, wherein each of the protruding first and second embossing structures and each of the recessed first and second embossing structures comprises at least two contiguous rising flanks for protruding embossing structures or recessing flanks for recessed embossing structures that define an angle between themselves that has a value between 40° and 140°.

35. The system for manufacturing the embossed sheet of substrate according to any one of claims 21 to 34, wherein each of the protruding first and second embossing structures and each of the recessed first and second embossing structures are described by a summit of a protruding first or second embossing structure to a bottom of a recessed respectively first or second embossing structure height value situated in a range between 0,05 mm and 1 ,5 mm.

36. The system for manufacturing the embossed sheet of substrate according to any one of claims 24 to 25, wherein the ridges and grooves are arranged in aperiodic manner which is described by a dimensional spacing of at least 0,1 mm between two adjacent ridges and grooves.

37. The system for manufacturing the embossed sheet of substrate according to any one of claims 21 to 33, wherein the first and second embossing structures are configured to engage into each other between the rollers during embossing and drive and self-synchronize the first and the second embossing rollers.

38. The system for manufacturing the embossed sheet of substrate according to any one of claims 21 to 33, further comprising a synchronization mechanism to drive and synchronize the first and the second embossing rollers, which is any one from a list comprising toothed-wheels gears, helicoidal gears, servomotors.

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